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Combined Effects of Anion Substitution and Nanoconfinement on the Ionic Conductivity of Li-Based Complex Hydrides
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  • Roman Zettl
    Roman Zettl
    Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria
    Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
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  • Laura de Kort
    Laura de Kort
    Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
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  • Maria Gombotz
    Maria Gombotz
    Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria
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  • H. Martin R. Wilkening
    H. Martin R. Wilkening
    Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria
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    Orcidhttp://orcid.org/0000-0001-9706-4892
  • Petra E. de Jongh*
    Petra E. de Jongh
    Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
    *E-mail: [email protected]
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    Orcidhttp://orcid.org/0000-0002-2216-2620
  • Peter Ngene*
    Peter Ngene
    Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
    *E-mail: [email protected]
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    Orcidhttp://orcid.org/0000-0003-3691-0623
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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2020, 124, 5, 2806–2816
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https://doi.org/10.1021/acs.jpcc.9b10607
Published January 21, 2020

Copyright © 2020 American Chemical Society. This publication is licensed under CC-BY-NC-ND.

Abstract

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Solid-state electrolytes are crucial for the realization of safe and high capacity all-solid-state batteries. Lithium-containing complex hydrides represent a promising class of solid-state electrolytes, but they exhibit low ionic conductivities at room temperature. Ion substitution and nanoconfinement are the main strategies to overcome this challenge. Here, we report on the synthesis of nanoconfined anion-substituted complex hydrides in which the two strategies are effectively combined to achieve a profound increase in the ionic conductivities at ambient temperature. We show that the nanoconfinement of anion substituted LiBH4 (LiBH4–LiI and LiBH4–LiNH2) leads to an enhancement of the room temperature conductivity by a factor of 4 to 10 compared to nanoconfined LiBH4 and nonconfined LiBH4–LiI and LiBH4-LiNH2, concomitant with a lowered activation energy of 0.44 eV for Li-ion transport. Our work demonstrates that a combination of partial ion substitution and nanoconfinement is an effective strategy to boost the ionic conductivity of complex hydrides. The strategy could be applicable to other classes of solid-state electrolytes.

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1. Introduction

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Solid-state electrolytes are indispensable for the realization of safe batteries offering high energy densities (1,2) crucial for the development of both mobile applications and large-scale stationary systems that can effectively store electricity from renewable but intermittent energy sources such as solar, wind, or tidal. Current battery systems, especially those designed for electric vehicles, may suffer from flammable and volatile organic based liquid electrolytes. In many cases, this narrow electrochemical stability window of conventional aprotic electrolytes prevents the use of anode materials providing high energy densities like metallic lithium. These disadvantages have led to a renewed interest in inorganic solid-state electrolytes, because they are potentially safer than liquid electrolytes and chemically compatible with Li metal. In addition, if sulfur-based cathode materials are considered, they prevent the dissolution and shuttling of polysulfides, which is one of the most serious hurdles that needs to be overcome in these type of batteries that promise high energy densities. (3)
Various classes of materials have been investigated as solid-state ion conductors for all-solid-state batteries. (4−8) These materials include garnets, (9) perovskites, (10) and polymers (11) as well as glass type electrolytes. (12) The complex metal hydrides, particularly those containing Li and Na, such as LiBH4, Li2B12H10, NaB10H10, and NaCB11H12 constitute a relatively new class of solid electrolytes. (13−17) Due to their lightweight and high hydrogen content, these materials have been intensively investigated over the last 20 years for reversible hydrogen storage. The hydrogen could be used for fuel cells with polymer electrolyte membranes. (18−21) Over a decade ago, it was shown that they also exhibit fast ionic conductivity and some also show good electrochemical stability windows up to 3 V versus Li/Li+. (22−24)
The main challenge for solid-state electrolytes in general has been the inherently low room temperature ionic conductivity, compared to liquid electrolytes. Therefore, most research effort has been focused on enhancing the ionic conductivities by structural modifications. For instance, the high ionic conductivity in complex hydrides is often a result of structural phase transition at high temperatures. A typical example is LiBH4, which exhibits an ionic conductivity of 1 × 10–3 S cm–1 above 110 °C, (14,23) due to the formation of the hexagonal phase, whereas at room temperature, the compound crystallizes into the orthorhombic structure, which shows poor ion conductivity. (25−27)
Two main approaches, which have separately been introduced in literature, have proved to be successful in boosting the room temperature ionic conductivity of solid electrolytes, especially complex hydrides. The first approach takes advantage of the partial substitution of the complex anion (e.g., BH4– in LiBH4) by halides such as Cl– and I– or by amides. (28−30) Iso- or aliovalent replacement of the Li+ cations by Na+, Ca2+ or Ce3+ has been reported as well. (31−33) Partial ion substitution is generally achieved by high-energy ball milling (34) or by heating a physical mixture of the compounds at temperatures of 200 to 300 °C; note that the melting point of LiBH4 is 278 °C. (35) For instance, solid solutions of LiBH4–LiX (X = Cl, Br, I) and LiBH4–Li3N or new compounds like in LiBH4–LiNH2 with room temperature ionic conductivities that are much higher than the individual compounds have been reported. Several studies have been conducted to investigate the effect of heat treatment, (36) the influence of LiX contents, (35) and the influence of the kind of the substituting anion. (37)
It is generally believed that anion substitution leads to an increase in distance between neighboring BH4– units which is associated with weaker Coulomb interactions in LiBH4 and hence a decrease of the transition temperature at which the compound changes from orthorhombic to hexagonal symmetry. (38) Indeed, substitution with larger halide anions leads to stabilization of the hexagonal phase of LiBH4 at near ambient temperatures as clearly seen in the most investigated anion substituted complex hydride LiBH4–LiI. (14) Alternatively, treatment at elevated temperatures (150 °C) of LiBH4 together with LiNH2 leads to the formation of a new phase, Li2(BH4)(NH2). The formation of a new phase causes a conductivity enhancement and a relatively low phase transition temperature of approximately 50 °C. (30,39) A main disadvantage of this method is, however, that the resulting compounds suffer from poor electrochemical and thermal cycling stability because of phase segregation.
The second approach, which has led to a large increase in the ionic conductivity in several classes of solid electrolytes, is interface engineering by forming nanocomposites with oxides such as SiO2 and Al2O3. (40−43) This approach, especially when using carbon scaffolds, was originally proposed to enhance the hydrogen sorption properties of complex hydrides, (44−48) but it was additionally shown to influence the ion mobility in the materials as well. The increase in ionic conductivity is currently believed to be caused by interactions of the hydride with the scaffold surface leading to either interfacial space charge zones (49) or to the formation of highly conducting compounds at this interface (50) due to changes in structure or defect density. The exact nature of the hydride/oxide interface is still a subject of intensive investigation. Alternatively, it has been shown that nanocrystalline LiBH4 has an enhanced ionic conductivity compared to the microcrystalline form. (51) Interface engineering of LiBH4 is normally achieved by nanoconfinement, e.g., via melt infiltration (52) of LiBH4 in the nanopores of the oxides (40,42) or by ball milling (41−43) a mixture of LiBH4 and the metal oxide. The two preparation methods have been reported to lead to comparable effects. Results from testing all-solid-state Li–S batteries using LiBH4/SiO2 nanocomposites as electrolytes showed that this approach enhances the ionic conductivity of LiBH4 and leads to better electrochemical and cycling stability. (53−55)
It has been shown that in these so-called dispersed ionic conductors, only the conductor or electrolyte (e.g., LiBH4) near the interface with the oxide (within 1–2 nm) exhibits very high ion mobility at room temperature. (48,55) Nevertheless, the volume fraction far from the interface is crucial to achieve interconnected LiBH4 particles as the silica or alumina particles do not contribute to the ionic conductivity. Only a percolating network of fast Li+ diffusion pathways will guarantee facile Li ion transport over long distances. We hypothesize that the overall long-range ionic conductivity of the nanocomposite can be further improved if the conductive regions are interconnected via highly conductive Li+ diffusion pathways rather than just bulk LiBH4.
For this purpose, we prepared nanoconfined anion substituted LiBH4. In these nanocomposites, the combined effects of partial anion substitution, either with I– or NH2–, and nanoconfinement in metal oxides (SiO2 and Al2O3) indeed leads to high room temperature Li-ion conductivities. In agreement with this observed enhancement, the activation energy for Li ion transport is lower than those probed for nanoconfined LiBH4 and the unconfined anion-substituted (LiBH4–LiI, LiBH4–LiNH2) systems. By using different preparation methods, we show that the enhancement seen for nanoconfined LiBH4–LiI and LiBH4–LiNH2 is indeed due to the combined effects of interfacial interactions with the metal oxide surface groups and the presence of highly conducting anion-substituted LiBH4 located further away from the SiO2 or Al2O3 surfaces. LiBH4 was used as an excellent model system to demonstrate the effect of combining anion substitution and nanoconfinement, and we believe that this approach and outcome are applicable to a wide variety of solid-state electrolytes.

2. Experimental Section

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Synthesis of Silica Supports

MCM-41 was synthesized using the procedure described by Cheng et al. (56) In brief, hexadecyltrimethylammonium bromide (Sigma-Aldrich, ≥96.0%) and tetramethylammonium hydroxide solution (Sigma-Aldrich, 25 wt % in H2O) were mixed with deionized water. After the addition of the silica source (Aerosil 380), the white suspension was stirred for 2 h at 30 °C and kept at this temperature for another 24 h unstirred in a closed polypropylene bottle. The composition of the mixture was 1.00 SiO2: 0.19 (TMA)OH: 0.27 (CTA)Br: 40 H2O. The jelly like product was heated to 140 °C in stainless steel autoclaves and kept there for 48 h. After being naturally cooled to room temperature, the mixture was thoroughly washed, filtered, and dried at 120 °C for approximately 12 h. The final calcination step (550 °C, 12 h) was carried out after heating the sample first to 100 °C for 1 h as an additional drying step.
SBA-15 was prepared according to Zhao et al. (57) Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Sigma-Aldrich, PEG–PPG-PEG, Pluronic, P-123), hydrochloric acid fuming 37% (Merck, for analysis), and deionized water were stirred at 35 °C. Tetraethyl orthosilicate (Sigma-Aldrich, ≥99.0% GC, TEOS) was added dropwise to the solution, and the solution was then stirred for 24 h at 40 °C resulting in a composition of 0.015 P123:5.2 HCl: 129 H2O: 1 TEOS. This mixture was kept at 100 °C in a closed polypropylene bottle for 48 h, followed by extensive washing and filtration. Subsequently, the product was predried (60 °C, 24 h, air), dried (120 °C, 8 h, air), and calcined (1.2 °C min–1, 550 °C, 6 h, air).

Electrolyte Preparation

Alumina (Al2O3) was purchased from Sasol (product brand Puralox SCCa-5/200), while lithium amide (95% pure), lithium iodide (98% pure), and lithium borohydride (95% pure) were purchased from Sigma-Aldrich. The metal oxide supports (MCM-41, SBA-15 and Al2O3) were first dried under a vacuum at 220 °C overnight; then we stored them in an Ar purified glovebox (MBraunLabmaster, typically H2O and O2 < 1 ppm). All subsequent sample handling and transfer were carried out in the glovebox to avoid contamination with air or traces of moisture. The LiBH4–LiI/oxide nanocomposites were prepared using two different methods. In the first method, LiBH4 and LiI were physically mixed in molar ratios of 10, 20, 30, and 40 mol % LiI with respect to LiBH4. Subsequently, the materials were mixed with the desired amount of the oxide and placed in a quartz reactor which was then inserted inside a stainless-steel high-pressure autoclave (Parr). The amounts were calculated in order to fill the oxide pores by 130%, meaning that all pores were filled and voids between particles and space between grains were filled additionally. Melt infiltration was carried out at 50 bar H2 pressure and a temperature of 295 °C for 30 min; the heating rate was approximately 3 °C min–1. (48) During this process, LiI-LiBH4 forms a solid solution ((1–x)LiBH4-xLiI with x = 0.1, 0.2, 0.3, 0.4) which melts and infiltrates the pores of the oxide. Upon cooling, the molten solid solution solidifies in the pores of the support material, and the excess amount remains at the external surface of the support.
In the second approach, the samples were prepared by combing solution impregnation and melt infiltration. A solution of LiI and water or ethanol was prepared. The desired amount of the solution was added dropwise, using a syringe and a septum, to the metal oxide support contained in a round-bottom flask. This was done outside the glovebox but by using a Schlenk line to avoid contamination. The impregnated oxide was kept at room temperature for 3 h, after which the solvent was removed. Subsequently, the mixture was dried at 250 °C overnight under a dynamic vacuum. In order to reach the desired amount of LiI in the pores, the procedure was repeated twice. The LiI/metal oxide nanocomposite was mixed with LiBH4 to reach a molar ratio LiI/LiBH4 of 20:80 with the volume of LiBH4–LiI corresponding to 130% of the total pore volume of the silica (or alumina). The mixture was then inserted into a sample holder placed inside a stainless-steel high-pressure autoclave, pressurized to 50 bar H2 and heated at 3 °C min–1 to 295 °C. The dwell time was 30 min. The molten LiBH4 infiltrates the oxide pores and reacts with the nanoconfined LiI to form LiBH4–LiI.
Reference samples of LiBH4–LiI solid solutions and nanoconfined LiBH4 were prepared under the same autoclave conditions as outlined above. Solid solutions were synthesized by heating mixtures of LiBH4 and LiI without adding the metal oxide support; nanoconfined LiBH4 was obtained without adding LiI to the mixture. A third reference sample was bulk LiBH4, which was ground and melted under the same autoclave conditions and recrystallized.
LiBH4–LiNH2/oxide nanocomposites were prepared using a two-step preparation method. First, LiBH4 and LiNH2 were physically mixed in a molar ratio of 50% LiNH2 with respect to LiBH4. Afterward, the physical mixture was placed in a stainless-steel reactor which was then inserted into a stainless-steel high-pressure autoclave. The solid-state reaction was carried out at 50 bar H2 pressure and at 150 °C (heating rate 2.5 °C min–1) for 30 min to form a solid solution with the composition 0.5LiBH4-0.5LiNH2. Subsequently, the solid solution was mixed with the desired amount of oxide in order to fill the pores by 130%. Melt infiltration was carried out at 50 bar H2 pressure at 120 °C (2.5 °C min–1) for 30 min. Upon cooling, the molten solid solution recrystallized in the pores of the support material to form nanoconfined LiBH4–LiNH2.

Characterization of Pristine Materials and Composites

X-ray diffraction was performed with a Bruker-AXS D-8 Advance X-ray diffractometer with Co Kα1,2 radiation (λ = 1.79026 Å). The samples were placed in an airtight sample holder, and diffractograms were recorded at room temperature covering a 2θ range of 10° to 100° for alumina-based samples and of 20 to 80° 2θ for the silica containing samples as well as the crystalline samples. The increment and scan duration per point was 0.12° 2θ and 4 s, respectively, for the alumina samples; 0.06° 2θ and 2 s, respectively, for the silica samples; and 0.03° 2θ and 1 s, respectively, for the crystalline samples. Rietveld refinement was carried out using the software X’PertHighScore Plus. A Le-Bail fit was applied to analyze the pattern; literature patterns of hexagonal LiBH4 taken from the Inorganic Crystal Structure Database served as reference. To refine the patterns, we used the lattice parameters of hexagonal LiBH4 as starting values (a = 4.28 Å, b = 4.28 Å, c = 6.98 Å).
Diffuse reflectance infrared Fourier transform spectra (DRIFTS) were obtained by a PerkinElmer 2000 spectrometer and a MCT detector. Sixteen scans were accumulated with a resolution of 4 cm–1 in the range of 500 to 4500 cm–1. An airtight sample holder (KBr background) guaranteed no air contamination during the measurements. Data acquisition was realized by recording absorbance versus wavenumber. The absorbance is directly converted to K-M units, introduced by Kubleka and Munk, which includes a scattering component and is, therefore, typically used for the analysis of powder samples.

Conductivity Measurement

Alternating current (AC) impedance spectroscopy measurements were performed using a Princeton Applied Research Parstat 2273. Lithium foil (Sigma-Aldrich, 99.9%, 0.38 mm thick and 12 mm in diameter leading to a surface of 1.33 cm2) was firmly placed on top of two 13 mm stainless steel dies. A 100–300 mg portion of the electrolyte was placed between the two lithium foils in a standard pellet die set. The sample was pressed using a pressure of 2 tons, resulting in a final electrolyte thickness of 1 to 2 mm, excluding the Li foil. With the weight of the samples, we calculated that the void fraction of the pellets is below 20%. The pressed sample pellet, which is tightly connected to the Li foils and stainless-steel dies, was placed in a custom-made impedance cell housed in a Büchi B-585 glass oven that was placed in an Ar-filled glovebox. The voltage amplitude of the AC signal was 1 V; we measured complex impedances over a frequency range from 1 MHz to 1 Hz. Generally, the pellets were heated from room temperature to 50 or 130 °C (depending on the sample), and then the samples were cooled down to room temperature. During this temperature cycle, impedance scans were acquired in steps of 5 or 10 °C. Before the acquisition of each scan, the measurement cell was allowed to equilibrate at the desired temperature for 45 min (while heating), 90 min (while cooling), and 150 min (for measurements at room temperature). The entire sequence was repeated for 2 to 3 cycles to investigate any hysteresis behavior and to detect any changes of the samples. Matlab and ZView software were used to fit the raw data by using Nyquist plots. A constant phase element (CPE) and a resistor connected in parallel were used as appropriate equivalent circuit to parametrize the data. Capacitances, C, were calculated according to C = R(1–n)/n × Q1/n. R is the resistance in Ω, i.e., it denotes the real part of the complex impedance; Q has the numerical value of the admittance at ω = 1 rad s–1. n is a dimensionless variable characterizing the deviation of the CPE from the behavior of an ideal RC unit, which would yield n = 1.

NMR Line Shape Measurement

To underpin the findings by conductivity spectroscopy, we recorded 7Li (spin-3/2) nuclear magnetic resonance (NMR) spectra at a magnetic field of 7 T, corresponding to a Larmor frequency of 116 MHz, by employing a Bruker Advance III solid-state spectrometer. We used a standard broadband probe to acquire variable-temperature NMR spectra with a one pulse sequence under static, i.e., nonrotating conditions. The π/2 pulse length slightly depended on temperature and ranged from 2.1 to 2.3 μs. Such short pulse lengths ensured nonselective excitation of the whole spectra. Up to 16 scans were accumulated to form an average free induction decay, which, after Fourier transformation, yield the 7Li NMR spectra. The temperature in the sample chamber was monitored by a Eurotherm controller. Temperature adjustment was achieved, with an accuracy of ±2K, with a heater that was constantly flushed with a stream of dry nitrogen gas.

3. Results and Discussion

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Structure of ((1–x)LiBH4-xLiI and Its Nanoconfined Counterpart As Seen by XRD and DRIFTS

First, we discuss the structural properties of (i) the LiBH4–LiI solid solutions ((1–x)LiBH4-xLiI) containing 10 to 40 mol % I (x = 0.1, 0.2, 0.3 and 0.4) and (ii) the nanocomposites with different oxides viz. γ-Al2O3, SBA-15, and MCM-41. The compositions of the samples in wt % are given in Table S1. Structural details of the hydrides, oxides, and nanocomposite materials are shown in Figure 1 as well as in Table S2 and Figures S1 to S6. Figure 1 shows the XRD powder pattern of a 20 mol % LiI-LiBH4 solid solution and the patterns of the nanocomposites prepared using two different routes, i.e., comelt infiltration and impregnation with LiI followed by melt infiltration with LiBH4. For comparison, the XRD pattern of LiI and the patterns of orthorhombic and hexagonal LiBH4 are also included. The influence of LiI on the on XRD patterns of the solid solutions and the composites is illustrated in Figures S7 and S8. The patterns shown here are normalized to the highest intensities; hkl values are added to distinct reflections of LiBH4 (58,59) and LiI, (60−62) respectively. The XRD patterns of the LiBH4–LiI samples with 10 and 20 mol % LiI (Figure S7) clearly differ from those of orthorhombic LiBH4 and LiI. Instead they resemble the pattern of hexagonal LiBH4 being the stable phase at elevated temperatures. The reflections in the range from 27° to 32° 2θ are shifted toward lower 2θ values by approximately 1° 2θ. This shift reveals successful incorporation of LiI and is caused by lattice expansion because I– is larger than BH4–. (35) A similar shift has been reported in literature. (14) Rietveld refinement of the diffraction data for the 0.8LiBH4-0.2LiI solid solution yielded an hcp unit cell with the following lattice parameters a = 4.44 Å, b = 4.44 Å, and c = 7.19 Å. Simultaneously with lattice expansion, the density increased from 0.67 g/cm3 for bulk LiBH4 to 1.20 g/cm3 for 0.8LiBH4-0.2LiI. Samples with more than 20 mol % LiI revealed reflections of pure LiI indicating a solubility limit for the LiBH4–LiI system (Figure S7).

Figure 1

Figure 1. XRD powder patterns of the various LiBH4–LiI/oxide nanocomposites investigated. For comparison, the positions of the reflection of LiBH4 in its hexagonal form are included as well. In addition, the pattern of LiBH4–LiI (20 mol % of LiI) and LiI are also shown. Values in brackets refer to hkl indices. The shift of the reflections toward lower diffraction angles indicates successful incorporation of LiI that stabilizes the hexagonal form of LiBH4.

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Confinement of the LiBH4–LiI solid solutions in the oxide nanopores led to both broadening and a decrease in intensity of the diffraction peaks (see Figures 1 and S8). Peak broadening is expected because of size effects and lattice strain, whereas the decrease in intensity suggests a decrease in the long-range order. Note, however, that the composites shown here contain 30 vol % more LiBH4–LiI than is required to fill all the pores of the scaffold. This is essential for interconnectivity between the LiBH4 particles. For the nanocomposites with LiBH4–LiI ≤ 100% of the total pore volume of the scaffold, no crystalline phase was observed. Thus, we conclude that nanoconfinement led to a significant decrease in crystallinity of the samples. The similarity in the diffraction patterns of the nanocomposites prepared using the different methods (Figure 1) suggests that both methods are useful for the preparation of LiBH4–LiI/metal oxide solutions. Moreover, the use of different oxide supports did not lead to major differences in the XRD patterns of the nanocomposites.
Further evidence for successful incorporation of the solid solutions into the oxide pores is provided by nitrogen physisorption measurements. The measurements showed that only a negligible amount of nitrogen was adsorbed by the nanocomposites. This finding proved that the pores were occupied by the electrolyte LiBH4–LiI.
DRIFTS was used to investigate the nature of chemical bonding in the different samples prepared. In Figure 2 the spectrum of the LiBH4–LiI/Al2O3 nanocomposite is compared to spectra of bulk LiBH4, LiBH4–LiI, and pristine Al2O3. The spectra are presented in arbitrary K-M units (for further explanation see the Experimental Section). Macrocrystalline, that is, bulk LiBH4, shows characteristic bands between 1000 and 1500 cm–1 which correspond to [BH4]− bending vibrations; bands appearing in the range from 2000 to 2800 cm–1 can be associated with stretching vibrations in [BH4]−. (63,64) The most preeminent bands of LiBH4 are marked with dashed lines in gray color; the corresponding wavenumbers are indicated. The spectrum of the LiBH4–LiI solution resembles that of LiBH4, the band characterizing the stretching vibrations (2379 cm–1) is, however, slightly shifted toward a lower wavenumber. Most likely, this shift is due to the effect of negative chemical pressure resulting from an increased unit cell by addition of I, as previously observed for halide-substituted BH4. (65) Also, a stronger electronic interaction between iodine and Li, because of the higher electronegativity of the halides compared to BH4–, can lead to such a change in vibration frequencies. (66) For LiBH4–LiI/Al2O3, the bands are clearly broadened due to nanoconfinement. A similar broadening effect is also observed for LiBH4/Al2O3. It suggests that the structure of the confined materials is different from the bulk compound. This observation is in line with previous studies on nanoconfined LiBH4. (67−69)

Figure 2

Figure 2. DRIFT spectra of Al2O3, nanoconfined LiBH4–LiI/Al2O3, nanoconfined LiBH4/Al2O3, and LiBH4–LiI (20 mol % of LiI). For comparison, the spectrum of LiBH4 is also shown. Main peaks are marked by vertically drawn dashed lines with the wavenumbers indicated. K-M intensities (see the ordinate axis) are in arbitrary units. See text for further explanation.

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Interestingly, the bands of Al2O3 in the region from 3400 to 3800 cm–1, representing OH surface groups, (70) almost disappear after the pores are filled with electrolyte; see the vertical arrows in Figure 2. The same behavior is found for the characteristic vibrations of the surface OH-silanol groups of silica (71,72) in the samples LiBH4/SiO2, LiI/SiO2, and LiBH4–LiI/SiO2 (see Figures S9 and S10). Interaction of LiBH4 with the surface is the origin of the high ionic conductivity of LiBH4/oxide nanocomposites.

Ionic Conductivity of Nanoconfined LiBH4–LiI

To evaluate the effects of different LiI concentrations on ionic conductivity, we recorded complex impedance data at different temperatures and analyzed the results in the Nyquist representation; see Figure 3. An overview of results from impedance spectroscopy of the LiBH4–LiI solid solutions and the nanocomposites is given in Table S3 and Figure S11. The overall ionic conductivity of the confined and pure solid solutions increased with increasing amounts of added LiI. At LiI contents higher than 20 mol %, the conductivity started to decrease (Figure S12). This is in line with results from XRD pointing to crystalline (unreacted) LiI above this compositional limit. Hence, the sample LiI-LiBH4 with 20 mol % LiI was chosen for a more detailed study.

Figure 3

Figure 3. (a) Nyquist plots, that is, the imaginary part, – Z″, of the complex impedance plotted versus the real part Z′, of nanoconfined LiBH4–LiI/Al2O3 and LiBH4/Al2O3. The LiBH4–LiI sample (20 mol % LiI) is also shown. Values in pF show the capacitances obtained after parametrizing the main (nondepressed) semicircles with the equivalent circuit shown; see also Experimental section. The line approximating the second semicircle of the curve belonging to LiBH4/Al2O3, which shows up at higher frequencies, is drawn to guide the eye. (b) Arrhenius plot (half-logarithmic plot of σ′ vs 1000/T) to illustrate the change of conductivity with increasing temperature. Dashed and solid lines represent linear fits to determine activation energies EA, which range from 0.44(1) eV to 0.59(1) eV. Nanoconfined LiBH4–LiI/Al2O3 shows the highest conductivities. At room temperature (25 °C), its ion conductivity is slightly larger than 10–4 S cm–1; a conductivity of 10–3 S cm–1, needed to realize Li-ion batteries, is reached at 66 °C.

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Figure 3a shows the corresponding Nyquist plot recorded at 25 °C; in Figure 3b, the temperature dependence of the ionic conductivity is displayed using an Arrhenius plot. For comparison, the Nyquist plots and conductivity data referring to LiBH4–LiI and nanoconfined LiBH4 are also shown. Capacitances C ranged from 147 to 210 pF; values larger than 100 pF typically indicate electrical relaxation processes influenced by interfacial regions. (73) For nanoconfined composites, it is widely believed that ion transport mainly occurs along the heterogeneous solid–solid interphase, that is, at the interface between the insulating oxide and the electrolyte. (41−43) The exponents n turned out to take values close to 1 meaning that the corresponding CPEs (constant phase elements) of all three samples behaved almost like an ideal RC unit. This observation is in line with the interpretation that the semicircle seen in the complex plane plot is governed by a response strongly influenced by grain boundary effects.
For LiBH4/Al2O3, a second semicircle is seen at lower frequencies, which is either too small to be detected or is absent in LiBH4–LiI and LiBH4–LiI/Al2O3. The presence of the second semicircle suggests two different conducting phases. We attribute the main semicircle with the higher electrical relaxation rate to LiBH4 interacting with the oxide surface and the semicircle appearing at lower frequencies to LiBH4, which is farther away from the interface. This feature is also seen in 7Li NMR spectroscopy; see Figure 4. We suppose that the addition of LiI led to both an increase of the high conducting regions and an enhancement of interfacial conductivity. Thus, for LiBH4–LiI/Al2O3, the two contributions could not be resolved any longer when data recorded at 25 °C were analyzed.

Figure 4

Figure 4. 7Li NMR spectra of (a) LiBH4–LiI, (b) nanoconfined LiBH4/Al2O3 without LiI, and (c) nanoconfined LiBH4–LiI/Al2O3. Spectra were recorded at a Larmor frequency of 116 MHz at the temperatures indicated. Dashed lines in parts a and b show the deconvolution of the entire line with appropriate Gaussian and Lorentzian functions to estimate the number fraction of mobile Li ions in these compounds. For LiBH4–LiI/Al2O3, the spectrum has almost adopted its final form at temperatures as low as 30 °C. While the sharp line represents fast Li ions, the broader foot comprises both the central line of a fraction of slower Li ions and quadrupole intensities. The latter become visible as a sharp powder pattern at elevated temperature where dipole–dipole interactions are effectively averaged out due to rapid Li+ exchange. See text for further information.

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The Arrhenius plot shown in Figure 3b shows that ion transport at temperatures lower than 100 °C is clearly faster in the nanocomposites LiBH4–LiI/Al2O3 and LiBH4–LiI/SiO2 than in LiBH4–LiI and the nanoconfined samples LiBH4/Al2O3 and LiBH4/SiO2. For instance, at room temperature (25 °C), the ionic conductivity of LiBH4–LiI/Al2O3 (0.1 mS cm–1) was four times higher than that of LiBH4/Al2O3 and eight times higher than that of LiBH4–LiI. In agreement with the trend for the increase in ionic conductivity, the activation energy for long-range ion transport decreased from 0.52(1) eV for LiBH4/oxide to 0.44(1) eV for LiBH4–LiI/oxide. LiBH4–LiI showed a rather high activation energy of 0.59 eV. These values are similar to those reported in literature for LiBH4/Al2O3 and LiI-LiBH4 systems. (35,41)
7Li NMR line shapes of these samples, which have been recorded at room temperature and above, clearly revealed that Li+ acts as mobile charge carrier. (74) Selected lines are shown in Figure 4. For the LiBH4–LiI solid solution (see Figure 4a), the line at room temperature is composed of two contributions. The narrow line on top of the broader signal reflects the mobile Li spins whose jump rates exceed the line widths of this line in the rigid lattice, which turns out to be approximately 13 kHz. Narrow NMR lines are caused by sufficiently fast Li+ exchange processes able to average local dipole–dipole interactions that lead to line broadening at low temperatures. In the case of LiBH4–LiI, the line shape did not change much when going to 30 °C; however, a significant change was seen at 90 °C where a fully narrowed central line appeared, that is, on top of a quadrupole powder pattern. This distinct pattern, showing sharp 90° singularities separated by Δ = 15.6 kHz, is characteristic for hexagonal LiBH4(-LiI). A similar situation is seen for nanoconfined LiBH4/Al2O3 (see Figure 4b). However, the number fraction of rapid Li+ ions was higher at 22 and 30 °C (24%) compared to that seen for nonconfined LiBH4–LiI. This difference is in line with the slightly higher conductivity seen for LiBH4/Al2O3. It is worth noting that the motionally narrowed spectra recorded at 90 °C and at 120 °C were governed by electric quadrupole intensities being different than those of bulk LiBH4 and bulk LiBH4–LiI. The spectra of nonconfined LiBH4 and nonconfined LiBH4–LiI reveal patterns produced by a symmetric electric field gradient (EFG) the ions were subjected to. They agree with those of similar systems studied earlier. (40)
In contrast to the nonconfined samples, the NMR line of nanoconfined LiBH4/Al2O3 recorded at 90 °C shows a nonsymmetric EFG. Its shape points to structural disorder and strain which the Li spins sense. Δ reduces from 15.6 to 11.5 kHz. Careful inspection of the powder pattern shows that another set of singularities is present (see inset of Figure 4b), which is characterized by Δ = 18.3 kHz. Assuming axial symmetry for this pattern, we obtained a quadrupole coupling constant δq of ca. 36.6 kHz which was identical to that of bulk LiBH4 (δq = 37 kHz). (75) The two quadrupole patterns represent the Li ions near the insulator surface (Δ = 11.5 kHz) and the ions farther away, that is, located in the bulk regions (Δ = 18.3 kHz). NMR revealed that these two species are exposed to different electric interactions. Two sources of electrical relaxation have also been seen in the corresponding Nyquist plot, vide supra.
For nanoconfined LiBH4–LiI/Al2O3 (Figure 4c), we also observed a quadrupole powder pattern that is characterized by a lower Δ (= 9.5 kHz) than that expected for bulk LiBH4(-LiI). However, a pronounced pattern attributable to Li ions in bulk LiBH4–LiI, as seen for LiBH4/Al2O3 ,was missing. Instead, already at temperatures as low as 30 °C, an almost fully narrowed 7Li NMR line was observed which clearly points to very fast ion dynamics in this nanocomposite. (74) We conclude that the majority of ions in this nanocomposite take part in rapid Li+ exchange, which perfectly agrees with the conductivity trend seen in Figure 3b. From a structural point of view, the single EFG pattern observed points to a homogeneous sample as compared to nanoconfined LiBH4/Al2O3. Presumably, if the ions reside in areas farther away from the surface of the oxide, they are subjected to a structurally stressed LiBH4–LiI phase with high ionic conductivity. This modified region, e.g., influenced by space charge zones, regions with higher defect density or increased structural disorder, may extend over almost the whole LiBH4–LiI phase leading to the enhancement in conductivity observed.
Note that all our samples were prepared under the same conditions and, therefore, the remarkable increase in ionic conduction for LiBH4–LiI/Al2O3 seen by impedance spectroscopy and 7Li NMR is mainly attributed to the combined effects of anion substitution and interface engineering by nanoconfinement. Table 1 compares conductivities, activation energies, and Arrhenius prefactors of the samples investigated. The slight differences in ionic conductivity of the nanocomposites prepared with different oxides (SBA-15, MCM-41, or Al2O3) are most likely due to differences in properties of these materials (see Figures S1 to S6 and Table S2). For example, the oxides differ in morphology, pore size, and pore size distribution, surface area, surface/interface energy, density of the surface groups, and the nature of the pores (e.g., pore corrugations). Detailed elucidation of the exact influence of these properties on ionic conductivity is, however, beyond the scope of the present work.
Table 1. Room Temperature Conductivities (σ) of the Samples Studied by Impedance Spectroscopyd
sampleσ(25 °C) (S cm–1)EA(eV)log10(A) (S cm−1K)
LiBH4/MCM-412.29 × 10–50.49(2)6.0(3)
LiBH4–LiI/MCM-41 comelt infiltration3.86 × 10–50.43(1)5.3(1)
LiBH4–LiI/MCM-41 impregnation (H2O)1.63 × 10–50.52(2)6.5(3)
LiBH4–LiI/MCM-41 impregnation (EtOH)4.57 × 10–60.47(0)5.2(1)
LiBH4–LiI/SBA-15 comelt infiltration1.29 × 10–40.44(1)6.0(2)
LiBH4–LiI/Al2O3 comelt infiltration1.27 × 10–40.44(1)6.1(1)
LiBH4–LiI1.54 × 10–50.59(2)7.8(3)
LiBH4–LiNH22.92 × 10–61.03(1)a 0.19(1)b1.8(1)a 13(1)b
LiBH4–LiNH2/ MCM-411.16 × 10–40.43(1)c5.5(2)
a

EA determined in the temperature range from 30 to 50 °C.

b

EA determined in the temperature range from 60 to 85 °C.

c

EA determined in the temperature range from 30 to 85 °C.

d

The table also includes activation energies (EA) and pre-factors (log10(A)) of the Arrhenius laws used to approximate the temperature dependence of the ionic conductivity. If not stated otherwise, EA has been determined in the temperature range from 25 to 130°C.

Importance of LiBH4(-LiI)/Oxide Interface

To further demonstrate that both the interaction of LiBH4 with the oxide interface and partial anion substitution are important for the enhancement in ionic conductivity, we employed a preparation technique that is supposed to hinder the interaction of LiBH4 with the oxide interface but still form LiBH4–LiI in the pores. This comparison showed that the nanocomposites prepared by coinfiltration of a physical mixture of LiBH4 and LiI exhibited much higher conductivities than those which were prepared via solution impregnation (Table 1). If we first add LiI to fill the pores via impregnation with LiI/H2O or LiI/C2H5OH solution and then add LiBH4 by melt infiltration as a second step, we see that the resulting ionic conductivity is significantly lower. At first glance, this difference is surprising as results from XRD and IR (DRIFTS) suggest that both samples have similar structures (cf. Figure 1 and Figure S9). We attribute the marked change seen in conductivity to the fact that if LiI is added first, we do not have the original SiOH groups present at the interface anymore (see Figure S9 for the loss of silanol groups in LiI/SiO2). This changed the properties of the interface with the LiBH4, and as a result, the conductivity is not as high as that with the other preparation technique.

LiBH4–LiNH2 System

To demonstrate the general applicability of the strategy outlined above, we measured also the conductivity of another nanoconfined electrolyte containing two complex anions, i.e., nanoconfined LiBH4–LiNH2. XRD revealed the formation of two new phases,namel, Li2(BH4)(NH2) and Li4(BH4)(NH2)3 (see Figure 5a). This is unlike the LiBH4–LiX systems where the high temperature phase of LiBH4 was stabilized through the replacement of BH4– by halides causing lattice strain but no change in crystal structure. For nanoconfined LiBH4–LiNH2/MCM-41, XRD points to a loss of crystallinity, that is, long-range order. As mentioned above, the same feature was observed for the LiBH4–LiI solid solutions. In addition, results from DRIFTS measurements (see Figure 5b) revealed that the characteristic vibrations related to LiBH4–LiNH2, (1000 to 1500 cm–1 and 2000 to 2800 cm–1 (BH4–), 1500 to 1600 cm–1 and 3200 to 3300 cm–1 (NH2–), shifted toward lower wavenumbers and became significantly broader upon nanoconfinement. The bands related to the surface silanol groups (3700 cm–1) were absent, as seen for nanoconfined LiBH4–LiI. Hence, we conclude that the LiBH4–LiNH2 composite was successfully infiltrated into the nanopores of MCM-41 leading to profound changes of its structure. (66)

Figure 5

Figure 5. (a) X-ray powder diffraction patterns of nanoconfined and nonconfined LiBH4–LiNH2. For comparison, the expected patterns of orthorhombic LiBH4 and LiNH2 are also shown. The pattern at the top represents that of the oxide substrate, SiO2. (b) DRIFT spectra of the samples shown in part a; the spectra reveal broadening of the signals, which shift toward lower wavenumbers upon nanoconfinement. Those bands which results from silanol OH groups are absent for LiBH4–LiNH2/SiO2 indicating surface reactions between the electrolyte and the surface of the oxide. See text for further explanation.

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In Figure 6, the ionic conductivities of selected LiBH4–LiNH2 samples are shown. First, when compared to LiBH4, it is clear that the addition of LiNH2 to LiBH4 increases the room temperature ionic conductivity by approximately 2 orders of magnitude. This increase is ascribed to the formation of Li2(BH4)(NH2). (39) The sudden increase in conductivity of Li2(BH4)(NH2) at approximately 35 °C originates from a structural phase change leading to a highly conducting phase at temperature higher than 40 °C. Nanoconfined LiBH4–LiNH2/MCM-41 showed an even better ionic conductivity at this temperature; remarkably, this high ionic conductivity was also preserved at lower temperatures. When compared to LiBH4 and LiBH4–LiNH2, the room temperature ionic conductivity of nanoconfined LiBH4–LiNH2/MCM-41 was higher by 4 and 2 orders of magnitude, respectively. It also exceeded that of nanoconfined LiBH4/MCM-41 by a factor of 2 if conductivities at T = 30 °C were considered (cf. Figure 6). At approximately 50 °C, LiBH4–LiNH2/MCM-41 reached a conductivity of 1 mS cm–1. Below 45 °C, the overall activation energy governing ion transport in LiBH4–LiNH2/MCM-41 (0.43 eV) is comparable to that of bulk LiBH4 and significantly lower than that of LiBH4–LiNH2 at room temperature. For LiBH4/MCM-41 and LiBH4–LiNH2 at higher temperatures, we see that EA is somewhat lower, 0.26 and 0.19 eV, respectively; see Figure 6 and Table 1. On the basis of the results from the DRIFTS measurements, the remarkable increase in ionic conductivity is again attributed to the combined effect of anion substitution and interface effects, as observed for nanoconfined LiBH4–LiI. These results illustrate that the synergistic effects of nanoconfinement, that is, interface engineering, and partial ion substitution is applicable to different Li-based electrolytes in various nonconducting nanoporous scaffolds.

Figure 6

Figure 6. Ionic conductivity of nanoconfined LiBH4–LiNH2/SiO2 as a function of the inverse temperature. For comparison, data on LiBH4/SiO2, nonconfined LiBH4–LiNH2 and bulk LiBH4 are also included. The lines are to guide the eye.

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4. Conclusion

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We have shown how two routes, namely, ion substitution and interface engineering, can be effectively combined to enhance the ionic conductivity of solid-state electrolytes. Using complex hydrides as model systems, we developed an approach where anion substituted LiBH4 (Li2(BH4)xI1–x and Li2(BH4)x(NH2)1–x) are confined in nanoporous SiO2 or Al2O3 in order to exploit both the effect of ion substitution and nanoconfinement or interface engineering to boost the Li-ion conductivities of LiBH4 at ambient conditions. Indeed, the ionic conductivity of the nanocomposites of LiBH4–LiI/Al2O3 reached 0.1 mS cm–1 at room temperature. The room temperature conductivities of nonsubstituted LiBH4/Al2O3 and LiBH4–LiI without nanoconfinement were 1 order of magnitude lower. Activation energies are in line with this trend, with 0.44, 0.52, and 0.59 eV for the LiBH4–LiI/Al2O3, LiBH4/Al2O3, and LiBH4–LiI, respectively. Detailed structural investigations and 7Li NMR line shape measurements show that the combined effects of interaction with the interface of the oxides and phase stabilization due to partial anion substitution (by the iodide anion) produces faster Li+ diffusion pathways in LiBH4–LiI/oxide than those in the case of LiBH4/oxide and LiBH4–LiI. Results on LiBH4–LiNH2 confined in mesoporous silica (MCM-41) show that this concept is also applicable to other Li-bearing hydrides. The enhancement effect depends also on the type and property of the scaffold. Our study clearly shows that combining partial anion substitution and nanoconfinement is a very promising approach to achieve high room temperature ionic conductivities in solid-state ion conductors.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.9b10607.

  • Calculation of the amount of material needed for melt infiltration to reach the desired pore filling; physisorption data; high-resolution scanning electron microscopy images; additional XRD patterns and DRIFTS data; further conductivity Arrhenius plot comparing different supports; comparison of room temperature conductivity values of samples with varying LiI content (0 to 40 mol %) (PDF)

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Author Information

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  • Corresponding Authors
  • Authors
    • Roman Zettl - Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria;  Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
    • Laura de Kort - Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands
    • Maria Gombotz - Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria
    • H. Martin R. Wilkening - Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology (NAWI Graz), Stremayrgasse 9, 8010 Graz, Austria;  Orcidhttp://orcid.org/0000-0001-9706-4892
  • Author Contributions

    R.Z. and L.d.K. contributed equally to this work.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We greatly appreciate funding from the NWO materials for sustainability (Mat4Sus-739.017.009) and NWO-ECHO (712.015.005) grants. P.N. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC-2014-CoG No 648991). R.Z. and H.M.R.W. thank the Austrian Federal Ministry for Science, Research and Economy as well as the Christian-Doppler Forschungsgesellschaft for financial support; further support by the FFG (The Austrian Research Promotion Agency) in the frame of the project Safe Battery is also acknowledged. R.Z. thanks the project SOLABAT (project no. 853627) funded by the Klima- und Energiefonds of FFG for additional support. Furthermore, we thank Sander Lambregts and Hans Meeldijk for physisorption and SEM measurements as well as Oscar Brandt Corstius for the synthesis of MCM-41.

References

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    The ionic cond. and electrochem. intercalation properties of La2/3-xLi3xTiO3 solid solns. (for 0.07≤x≤0.13) were studied. These compds. present a perovskite-type structure (ABO3) with cation deficiency at the A-sites. The purely ionic cond. was confirmed and the mechanism of ionic conduction studied using impedance spectroscopy techniques. The temp. dependence of cond. can be modelized by a Vogel-Tamman-Fulcher (VTF)-type relation. In these materials, where the high ionic cond. may originate from the presence of vacancies in the A-sites of the perovskite structure, the VTF behavior would suggest a mechanism of conduction involving the tilting of the TiO6 octahedra. The Li intercalation was also studied in LiClO4(M)-PC electrolyte using galvanostatic discharge and charge at very low rates (one Li/250 and /1500 h) to approach the equil. The Li intercalation leads to the presence of a plateau around 1.5 V/Li in the discharge curve; it is partly reversible and the capacity of the electrode is not very high. A max. Li uptake of 0.15 was found. The diffusion coeff. of Li in the intercalated material was detd. by impedance spectroscopy at room temp. and found to range from 10-8 cm2s-1 to 10-9 cm2s-1 as intercalation proceeds. Since the exptl. impedance spectroscopy data performed at room temp. follow a Warburg behavior at low frequency, the intercalation seems to proceed in a single-phase process although a plateau is observable in the discharge curve.
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    Li, J.; Lin, Y.; Yao, H. H.; Yuan, C. F.; Liu, J. Tuning thin-film electrolyte for lithium battery by grafting cyclic carbonate and combed poly(ethylene oxide) on polysiloxane. ChemSusChem 2014, 7 (7), 1901– 1908,  DOI: 10.1002/cssc.201400113
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    Tuning Thin-Film Electrolyte for Lithium Battery by Grafting Cyclic Carbonate and Combed Poly(ethylene oxide) on Polysiloxane
    Li, Jie; Lin, Yue; Yao, Hehua; Yuan, Changfu; Liu, Jin
    ChemSusChem (2014), 7 (7), 1901-1908CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A tunable polysiloxane thin-film electrolyte for all-solid-state lithium-ion batteries was developed. The polysiloxane was synthesized by hydrosilylation of polymethylhydrosiloxane with cyclic [(allyloxy)methyl]ethylene ester carbonic acid and vinyl tris(2-methoxyethoxy)silane. 1H NMR spectroscopy and gel-permeation chromatog. demonstrated that the bifunctional groups of the cyclic propylene carbonate (PC) and combed poly(ethylene oxide) (PEO) were well grafted on the polysiloxane. At PC/PEO = 6:4, the polysiloxane-based electrolyte had an ionic cond. of 1.55×10-4 and 1.50×10-3 S cm-1 at 25 and 100°, resp. The LiFePO4/Li batteries fabricated with the thin-film electrolyte presented excellent cycling performance in the temp. range from 25-100° with an initial discharge capacity at a rate of 1 C of 88.2 and 140 mA h g-1 at 25 and 100°, resp.
  12. 12
    Hayashi, A.; Sakuda, A.; Tatsumisago, M. Development of sulfide solid electrolytes and interface formation processes for bulk-type all-solid-state Li and Na batteries. Front. Energy Res. 2016, 4, 25,  DOI: 10.3389/fenrg.2016.00025
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    de Jongh, P. E.; Blanchard, D.; Matsuo, M.; Udovic, T. J.; Orimo, S. Complex hydrides as room-temperature solid electrolytes for rechargeable batteries. Appl. Phys. A: Mater. Sci. Process. 2016, 122, 251,  DOI: 10.1007/s00339-016-9807-2
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    Matsuo, M.; Orimo, S. Lithium fast-ionic conduction in complex hydrides: review and prospects. Adv. Energy Mater. 2011, 1 (2), 161– 172,  DOI: 10.1002/aenm.201000012
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    Lithium fast-ionic conduction in complex hydrides: review and prospects
    Matsuo, Motoaki; Orimo, Shin-ichi
    Advanced Energy Materials (2011), 1 (2), 161-172CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
    A review. Complex hydrides exhibit various energy-related functions such as hydrogen storage, microwave absorption, and neutron shielding. Furthermore, another novel energy-related function was recently reported by the authors; lithium fast-ionic conduction, which suggests that complex hydrides may be a potential candidate for solid electrolytes in lithium-ion batteries. This review presents the recent progress in the development of lithium fast-ionic conductors of complex hydrides. First, the fast-ionic conduction in LiBH4 as a result of clarifying the mechanism of microwave absorption is presented, and then the conceptual development of complex hydrides as a new type of solid-state lithium fast-ionic conductors in LiBH4-, LiNH2-, and LiAlH4-based complex hydrides is discussed. Finally, the future prospects of this study from both application and fundamental viewpoints are described: possible use as solid electrolytes for batteries, formation of ionic liqs. in complex hydrides, and similarity between complex hydrides and Laves-phase metal hydrides.
  15. 15
    Lu, Z. H.; Ciucci, F. Metal borohydrides as electrolytes for solid-state Li, Na, Mg, and Ca batteries: A first-principles study. Chem. Mater. 2017, 29 (21), 9308– 9319,  DOI: 10.1021/acs.chemmater.7b03284
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    Metal Borohydrides as Electrolytes for Solid-State Li, Na, Mg, and Ca Batteries: A First-Principles Study
    Lu, Ziheng; Ciucci, Francesco
    Chemistry of Materials (2017), 29 (21), 9308-9319CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Metal borohydrides are a family of materials that were recently discovered to have extraordinary ionic conductivities, making them promising candidates as electrolytes for solid-state batteries (SSBs). In fact, various groups have measured the ionic conductivities and assembled batteries using specific borohydrides. However, there are no comprehensive studies assessing the thermodn. properties or discussing the suitability of metal borohydrides as electrolytes in SSBs, esp. for beyond-lithium applications. In this work, we investigate the electrochem. stability, interfacial characteristics, mech. properties, and ionic conductivities of Li, Na, Ca, and Mg borohydrides using first-principles calcns. Our results suggest that Li and Na borohydrides are unstable at high voltages. However, the corresponding decompn. products, i.e., B12H122--contg. phases, have wide electrochem. windows which protect the electrolyte, leading to large electrochem. windows as wide as 5 V. In addn., our simulations indicate that metal borohydrides are ductile, suggesting facile processing. However, their low shear moduli may result in metal dendrite formation. For Ca and Mg borohydrides, while they possess reasonably good electrochem. stability, the low cationic diffusivity may impede their practical use. Finally, the anion rotation barrier was shown to correlate with the superionic phase transition temp., suggesting that anion mixing may be a potential approach to achieve room-temp. superionic cond.
  16. 16
    Møller, K.; Sheppard, D.; Ravnsbæk, D.; Buckley, C.; Akiba, E.; Li, H.-W.; Jensen, T. Complex metal hydrides for hydrogen, thermal and electrochemical energy storage. Energies 2017, 10 (10), 1645,  DOI: 10.3390/en10101645
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    Yoshida, K.; Sato, T.; Unemoto, A.; Matsuo, M.; Ikeshoji, T.; Udovic, T. J.; Orimo, S. Fast sodium ionic conduction in Na2B10H10-Na2B12H12 pseudo-binary complex hydride and application to a bulk-type all-solid-state battery. Appl. Phys. Lett. 2017, 110 (10), 103901,  DOI: 10.1063/1.4977885
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    17
    Fast sodium ionic conduction in Na2B10H10-Na2B12H12 pseudo-binary complex hydride and application to a bulk-type all-solid-state battery
    Yoshida, Koji; Sato, Toyoto; Unemoto, Atsushi; Matsuo, Motoaki; Ikeshoji, Tamio; Udovic, Terrence J.; Orimo, Shin-ichi
    Applied Physics Letters (2017), 110 (10), 103901/1-103901/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    We developed highly Na-ion conductive Na2B10H10-Na2B12H12 pseudo-binary complex hydride via mech. ball-milling admixts. of the pure Na2B10H10 and Na2B12H12 components. Both of these components show a monoclinic phase at room temp., but ball-milled mixts. partially stabilized highly ion-conductive, disordered cubic phases, whose fraction and favored structural symmetry (body-centered cubic or face-centered cubic) depended on the conditions of mech. ball-milling and molar ratio of the component compds. First-principles mol.-dynamics simulations demonstrated that the total energy of the closo-borane mixts. and pure materials is quite close, helping to explain the obsd. stabilization of the mixed compds. The ionic cond. of the closo-borane mixts. appeared to be correlated with the fraction of the body-centered-cubic phase, exhibiting a max. at a molar ratio of Na2B10H10:Na2B12H12 =1:3. A cond. as high as log(σ/S/cm) = -3.5 was obsd. for the above ratio at 303 K, being approx. 2-3 orders of magnitude higher than that of either pure material. A bulk-type all-solid-state Na-ion battery with a closo-borane-mixt. electrolyte, Na-metal neg.-electrode, and TiS2 pos.-electrode demonstrated a high specific capacity, close to the theor. value of NaTiS2 formation and a stable discharge/charge cycling for at least eleven cycles, with a high discharge capacity retention ratio >91% from the second cycle. (c) 2017 American Institute of Physics.
  18. 18
    Sakintuna, B.; Lamari-Darkrim, F.; Hirscher, M. Metal hydride materials for solid hydrogen storage: A review. Int. J. Hydrogen Energy 2007, 32 (9), 1121– 1140,  DOI: 10.1016/j.ijhydene.2006.11.022
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    Metal hydride materials for solid hydrogen storage: A review
    Sakintuna, Billur; Lamari-Darkrim, Farida; Hirscher, Michael
    International Journal of Hydrogen Energy (2007), 32 (9), 1121-1140CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
    A review. Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gas or liq. cannot fulfill future storage goals. Chem. or phys. combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. The present paper reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 wt.% for on-board applications. Efforts have been devoted to these materials to decrease their desorption temp., enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as well as by ball milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kinetics and lower decompn. temps., however, the state-of-the-art materials are still far from meeting the aimed target for their transport applications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides.
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    Zuttel, A.; Wenger, P.; Rentsch, S.; Sudan, P.; Mauron, P.; Emmenegger, C. LiBH4 a new hydrogen storage material. J. Power Sources 2003, 118 (1–2), 1– 7,  DOI: 10.1016/S0378-7753(03)00054-5
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    LiBH4 a new hydrogen storage material
    Zuttel, A.; Wenger, P.; Rentsch, S.; Sudan, P.; Mauron, Ph.; Emmenegger, Ch.
    Journal of Power Sources (2003), 118 (1-2), 1-7CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
    The challenge for H storage materials is to pack H atoms or mols. as close as possible. Light wt. group 3 metals, e.g. Al and B, are able to bind 4 H atoms and form, together with an alkali metal, an ionic or at least partially covalent compd. These compds. are rather stable and often desorb the H only above their m.ps. Complex hydrides like NaAlH4, when catalyzed, decomp. already at room temp. LiBH4, a complex hydride which consists 18% of H, was studied. H desorption from LiBH4 was catalyzed by SiO2 and 13.5% of the H was liberated at 200°.
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    Umegaki, T.; Yan, J. M.; Zhang, X. B.; Shioyama, H.; Kuriyama, N.; Xu, Q. Boron- and nitrogen-based chemical hydrogen storage materials. Int. J. Hydrogen Energy 2009, 34 (5), 2303– 2311,  DOI: 10.1016/j.ijhydene.2009.01.002
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    Boron- and nitrogen-based chemical hydrogen storage materials
    Umegaki, Tetsuo; Yan, Jun-Min; Zhang, Xin-Bo; Shioyama, Hiroshi; Kuriyama, Nobuhiro; Xu, Qiang
    International Journal of Hydrogen Energy (2009), 34 (5), 2303-2311CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
    A review. Boron- and nitrogen-based chem. hydrides are expected to be potential hydrogen carriers for PEM fuel cells because of their high hydrogen contents. Significant efforts have been devoted to decrease their dehydrogenation and hydrogenation temps. and enhance the reaction kinetics. This article presents an overview of the boron- and nitrogen-based compds. as hydrogen storage materials.
  21. 21
    Schuth, F.; Bogdanovic, B.; Felderhoff, M. Light metal hydrides and complex hydrides for hydrogen storage. Chem. Commun. 2004, 20, 2249– 2258,  DOI: 10.1039/B406522K
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    Duchene, L.; Kuhnel, R.-S.; Stilp, E.; Cuervo Reyes, E.; Remhof, A.; Hagemann, H.; Battaglia, C. A stable 3 V all-solid-state sodium-ion battery based on a closo-borate electrolyte. Energy Environ. Sci. 2017, 10 (12), 2609– 2615,  DOI: 10.1039/C7EE02420G
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    A stable 3 V all-solid-state sodium-ion battery based on a closo-borate electrolyte
    Duchene, L.; Kuhnel, R.-S.; Stilp, E.; Cuervo Reyes, E.; Remhof, A.; Hagemann, H.; Battaglia, C.
    Energy & Environmental Science (2017), 10 (12), 2609-2615CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    We report on a particularly stable 3 V all-solid-state sodium-ion battery built using a closo-borate based electrolyte, namely Na2(B12H12)0.5(B10H10)0.5. Battery performance is enhanced through the creation of an intimate cathode-electrolyte interface resulting in reversible and stable cycling with a capacity of 85 mA h g-1 at C/20 and 80 mA h g-1 at C/5 with more than 90% capacity retention after 20 cycles at C/20 and 85% after 250 cycles at C/5. We also discuss the effect of cycling outside the electrochem. stability window and show that electrolyte decompn. leads to faster though not crit. capacity fading. Our results demonstrate that owing to their high stability and cond. closo-borate based electrolytes could play a significant role in the development of a competitive all-solid-state sodium-ion battery technol.
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    Asakura, R.; Duchene, L.; Kuhnel, R. S.; Remhof, A.; Hagemann, H.; Battaglia, C. Electrochemical oxidative stability of hydroborate-based solid state electrolytes. ACS Appl. Energy Mater. 2019, 2 (9), 6924– 6930,  DOI: 10.1021/acsaem.9b01487
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    Electrochemical Oxidative Stability of Hydroborate-Based Solid-State Electrolytes
    Asakura, Ryo; Duchene, Leo; Kuhnel, Ruben-Simon; Remhof, Arndt; Hagemann, Hans; Battaglia, Corsin
    ACS Applied Energy Materials (2019), 2 (9), 6924-6930CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)
    A robust methodol. is reported based on linear sweep voltammetry to det. exptl. the electrochem. oxidative stability of hydroborate-based solid-state electrolytes for all-solid-state batteries. To accelerate kinetics and improve the sensitivity to decompn., different solid-state electrolyte/carbon composites are explored and a low scan rate of 10μV s-1 is employed. Using LiBH4 as a model system, it is shown that proper selection of the conductive carbon and its ratio in the composite are important for an accurate detn. of the intrinsic oxidative stability. This method is robust with respect to the choice of the current collector material and the ionic cond. of the solid-state electrolyte. The measured oxidative stability of LiBH4 of 2.0 V vs. Li+/Li is in good agreement with the value predicted by first-principles calcns. The irreversible electrochem. decompn. of LiBH4 outside the oxidative stability limit is independently confirmed by galvanostatic cycling. This method is applied to reassess the electrochem. oxidative stability of selected, highly conductive hydroborate-based solid-state electrolytes, including Li2(CB9H10)(CB11H12), Na3(BH4)(B12H12), Na4(B12H12)(B10H10), and Na4(CB11H12)2(B12H12), and the necessity of selecting cathode materials is emphasized for all-solid-state batteries based on the accurate understanding of the oxidative stability of the solid-state electrolytes.
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    Kim, S.; Oguchi, H.; Toyama, N.; Sato, T.; Takagi, S.; Otomo, T.; Arunkumar, D.; Kuwata, N.; Kawamura, J.; Orimo, S. A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries. Nat. Commun. 2019, 10, 1081,  DOI: 10.1038/s41467-019-09061-9
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    A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries
    Kim Sangryun; Toyama Naoki; Sato Toyoto; Takagi Shigeyuki; Orimo Shin-Ichi; Oguchi Hiroyuki; Orimo Shin-Ichi; Otomo Toshiya; Arunkumar Dorai; Kuwata Naoaki; Kawamura Junichi
    Nature communications (2019), 10 (1), 1081 ISSN:.
    All-solid-state batteries incorporating lithium metal anode have the potential to address the energy density issues of conventional lithium-ion batteries that use flammable organic liquid electrolytes and low-capacity carbonaceous anodes. However, they suffer from high lithium ion transfer resistance, mainly due to the instability of the solid electrolytes against lithium metal, limiting their use in practical cells. Here, we report a complex hydride lithium superionic conductor, 0.7Li(CB9H10)-0.3Li(CB11H12), with excellent stability against lithium metal and a high conductivity of 6.7 × 10(-3) S cm(-1) at 25 °C. This complex hydride exhibits stable lithium plating/stripping reaction with negligible interfacial resistance (<1 Ω cm(2)) at 0.2 mA cm(-2), enabling all-solid-state lithium-sulfur batteries with high energy density (>2500 Wh kg(-1)) at a high current density of 5016 mA g(-1). The present study opens up an unexplored research area in the field of solid electrolyte materials, contributing to the development of high-energy-density batteries.
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    Matsuo, M.; Nakamori, Y.; Orimo, S.; Maekawa, H.; Takamura, H. Lithium superionic conduction in lithium borohydride accompanied by structural transition. Appl. Phys. Lett. 2007, 91 (22), 224103,  DOI: 10.1063/1.2817934
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    Lithium superionic conduction in lithium borohydride accompanied by structural transition
    Matsuo, Motoaki; Nakamori, Yuko; Orimo, Shin-ichi; Maekawa, Hideki; Takamura, Hitoshi
    Applied Physics Letters (2007), 91 (22), 224103/1-224103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The elec. cond. of LiBH4 measured by a.c. complex impedance increased by 3 orders of magnitude due to structural transition from orthorhombic to hexagonal at ∼390 K. The hexagonal phase exhibited a high elec. cond. of about 10-3 S/cm. The cond. calcd. from the Nernst-Einstein equation using the correlation time obtained from 7Li NMR agreed with the measured elec. cond. The elec. cond. in the hexagonal phase is due to Li superionic conduction.
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    Soulié, J. P.; Renaudin, G.; Černý, R.; Yvon, K. Lithium boro-hydride LiBH4: I. Crystal structure. J. Alloys Compd. 2002, 346 (1), 200– 205,  DOI: 10.1016/S0925-8388(02)00521-2
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    Lithium boro-hydride LiBH4. I. Crystal structure
    Soulie, J-Ph.; Renaudin, G.; Cerny, R.; Yvon, K.
    Journal of Alloys and Compounds (2002), 346 (1-2), 200-205CODEN: JALCEU; ISSN:0925-8388. (Elsevier Science B.V.)
    The crystal structure of LiBH4 was studied by synchrotron x-ray powder diffraction at room temp. and at 408 K. At room temp. it has orthorhombic symmetry [space group Pnma, a 7.17858(4), b 4.43686(2), c 6.80321(4) Å]. The tetrahedral (BH4)- anions (point symmetry m) are aligned along two orthogonal directions and are strongly distorted with respect to bond lengths [B-H 1.04(2)-1.28(1) Å] and bond angles [H-B-H 85.1(9)-120.1(9)°]. As the temp. is increased the structure undergoes a 1st-order transition and becomes hexagonal (space group P63mc, a 4.27631(5), c 6.94844(8) Å at T = 408 K). The (BH4)- tetrahedra align along c, become more sym. [point symmetry 3m, B-H 1.27(2)-1.29(2) Å, H-B-H 106.4(2)-112.4(9)°] and show displacement amplitudes that are consistent with dynamical disorder about their trigonal axis.
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    Aeberhard, P. C.; Refson, K.; David, W. I. F. Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4. Phys. Chem. Chem. Phys. 2013, 15 (21), 8081– 8087,  DOI: 10.1039/c3cp44520h
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    Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4
    Aeberhard, Philippe C.; Refson, Keith; David, William I. F.
    Physical Chemistry Chemical Physics (2013), 15 (21), 8081-8087CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The crystal structure of the hexagonal phase of solid lithium borohydride (LiBH4) is studied by ab initio mol. dynamics simulations of both the low and high-temp. phases. A temp. range of 200-535 K is simulated with the aim of characterizing the disorder in the high-temp. structure in detail. The mechanism and kinetics of the reorientational motion of the borohydride units (BH4-) are detd. and are consistent with published neutron scattering expts.; it is found that rotational diffusivity increases by an order of magnitude at the phase transition temp. The av. equil. orientation is characterized by a broad distribution of orientations, and reorientational jumps do not occur between sharply defined orientations. In addn., split positions with partial occupancy for the lithium and boron atoms are found (in agreement with previous theor. studies), which, together with the disordered BH4- orientational distribution in equil., lead to the conclusion that the correct crystallog. space group of the high-temp. phase is P63/mmc rather than P63mc.
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    Matsuo, M.; Takamura, H.; Maekawa, H.; Li, H. W.; Orimo, S. Stabilization of lithium superionic conduction phase and enhancement of conductivity of LiBH4 by LiCl addition. Appl. Phys. Lett. 2009, 94 (8), 084103,  DOI: 10.1063/1.3088857
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    Stabilization of lithium superionic conduction phase and enhancement of conductivity of LiBH4 by LiCl addition
    Matsuo, Motoaki; Takamura, Hitoshi; Maekawa, Hideki; Li, Hai-Wen; Orimo, Shin-Ichi
    Applied Physics Letters (2009), 94 (8), 084103/1-084103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    LiBH4 exhibits lithium superionic conduction accompanied by structural transition at around 390 K. Addn. of LiCl to LiBH4 drastically affects both the transition and elec. cond.: Transition from low-temp. (LT) to high-temp. (HT) phases in LiBH4 is obsd. at 370 K upon heating and the HT phase can be retained at 350-330 K upon cooling. Further, the cond. in the LT phase is more than one or two orders of magnitude higher than that of pure LiBH4. These properties could be attributed to the dissoln. of LiCl into LiBH4, suggested by in situ x-ray diffraction measurement. (c) 2009 American Institute of Physics.
  29. 29
    Oguchi, H.; Matsuo, M.; Hummelshoj, J. S.; Vegge, T.; Norskov, J. K.; Sato, T.; Miura, Y.; Takamura, H.; Maekawa, H.; Orimo, S. Experimental and computational studies on structural transitions in the LiBH4-LiI pseudobinary system. Appl. Phys. Lett. 2009, 94 (14), 141912,  DOI: 10.1063/1.3117227
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    Experimental and computational studies on structural transitions in the LiBH4-LiI pseudobinary system
    Oguchi, H.; Matsuo, M.; Hummelshoj, J. S.; Vegge, T.; Norskov, J. K.; Sato, T.; Miura, Y.; Takamura, H.; Maekawa, H.; Orimo, S.
    Applied Physics Letters (2009), 94 (14), 141912/1-141912/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Structural transition properties of the LiBH4+xLiI (x = 0-1.00)pseudobinary system were examd. by powder x-ray diffraction and DSC combined with periodic d. functional theory calcns. The authors exptl. and computationally confirmed the stabilization of the high-temp. hexagonal, Li super(fast-)ionic conduction phase of LiBH4 with x = 0.33 and 1.00, and the results also imply the existence of intermediate phases with x = 0.07-0.20. The studies are of importance for further development of LiBH4 and the derived hydrides as solid-state electrolytes. (c) 2009 American Institute of Physics.
  30. 30
    Matsuo, M.; Remhof, A.; Martelli, P.; Caputo, R.; Ernst, M.; Miura, Y.; Sato, T.; Oguchi, H.; Maekawa, H.; Takamura Complex hydrides with (BH4)− and (NH2)− anions as new lithium fast-ion conductors. J. Am. Chem. Soc. 2009, 131 (45), 16389,  DOI: 10.1021/ja907249p
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    Complex Hydrides with (BH4)- and (NH2)- Anions as New Lithium Fast-Ion Conductors
    Matsuo, Motoaki; Remhof, Arndt; Martelli, Pascal; Caputo, Riccarda; Ernst, Matthias; Miura, Yohei; Sato, Toyoto; Oguchi, Hiroyuki; Maekawa, Hideki; Takamura, Hitoshi; Borgschulte, Andreas; Zuttel, Andreas; Orimo, Shin-Ichi
    Journal of the American Chemical Society (2009), 131 (45), 16389-16391CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Some of the authors have reported that a complex hydride, Li(BH4), with the (BH4)- anion exhibits lithium fast-ion conduction (more than 1 × 10-3 S/cm) accompanied by the structural transition at ∼390 K for the first time in 30 years since the conduction in Li2(NH) was reported in 1979. Here we report another conceptual study and remarkable results of Li2(BH4)(NH2) and Li4(BH4)(NH2)3 combined with the (BH4)- and (NH2)- anions showing ion conductivities 4 orders of magnitude higher than that for Li(BH4) at RT, due to being provided with new occupation sites for Li+ ions. Both Li2(BH4)(NH2) and Li4(BH4)(NH2)3 exhibit a lithium fast-ion cond. of 2 × 10-4 S/cm at RT, and the activation energy for conduction in Li4(BH4)(NH2)3 is evaluated to be 0.26 eV, less than half those in Li2(BH4)(NH2) and Li(BH4). This study not only demonstrates an important direction in which to search for higher ion cond. in complex hydrides but also greatly increases the material variations of solid electrolytes.
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    Yao, Z. P.; Kim, S.; Michel, K.; Zhang, Y. S.; Aykol, M.; Wolverton, C. Stability and conductivity of cation- and anion-substituted LiBH4-based solid-state electrolytes. Phys. Rev. Mater. 2018, 2 (6), 065402,  DOI: 10.1103/PhysRevMaterials.2.065402
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    Stability and conductivity of cation- and anion-substituted LiBH4-based solid-state electrolytes
    Yao, Zhenpeng; Kim, Soo; Michel, Kyle; Zhang, Yongsheng; Aykol, Muratahan; Wolverton, Chris
    Physical Review Materials (2018), 2 (6), 065402CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
    The high-temp. phase of LiBH4 (HT-LiBH4) exhibits a promisingly high lithium ion cond. but is unstable at room temp. We use d. functional theory (DFT) calcns. to investigate the stabilization effect of halogen and alkali cation/anion substitutions on HT-LiBH4 as well the underlying mechanism for the high lithium ion cond. We find that increasing the substituent concn. enhances the stabilization of HT-LiBH4 (i.e., the DFT energy difference between the low- and high-temp. forms of substituted LiBH4 is reduced). Cation/anion substitution also leads to a higher Li defect (vacancy, interstitial, and Frenkel) formation energy, thereby reducing the Li defect (vacancy, interstitial, and Frenkel) concns. Using DFT migration barriers input into kinetic Monte Carlo simulations and the Materials INTerface (MINT) framework, we calc. the room-temp. lithium ion conductivities for Li(BH4)1-xIx (x=0.25 and 0.5) and Li1-yKyBH4 (y=0.25). Our calcns. suggest that the lower I concn. leads to a higher lithium ion cond. of 5.7×10-3 S/cm compared with that of Li(BH4)0.5I0.5 (4.2×10-5 S/cm) because of the formation of more Li-related defects. Based on our findings, we suggest that the stabilization of HT-LiBH4-based lithium ion conductors can be controlled by carefully tuning the cation/anion substituent concns. to maximize the lithium ionic conductivities of the specific system.
  32. 32
    Mezaki, T.; Kuronuma, Y.; Oikawa, I.; Kamegawa, A.; Takamura, H. Li-ion conductivity and phase stability of Ca-doped LiBH4 under high pressure. Inorg. Chem. 2016, 55 (20), 10484– 10489,  DOI: 10.1021/acs.inorgchem.6b01678
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    Li-Ion Conductivity and Phase Stability of Ca-Doped LiBH4 under High Pressure
    Mezaki, Takeya; Kuronuma, Yota; Oikawa, Itaru; Kamegawa, Atsunori; Takamura, Hitoshi
    Inorganic Chemistry (2016), 55 (20), 10484-10489CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The effect of Ca doping on the Li-ion cond. and phase stability of the rock-salt-type LiBH4 phase emerging under high pressures in the range of gigapascals has been investigated. Insitu electrochem. measurements under high pressure were performed using a cubic-anvil-type app. Ca doping drastically enhanced the ionic cond. of the rock-salt-type phase: the ionic cond. of undoped and 5 mol %Ca-doped LiBH4 was 2.2 × 10-4 and 1.4 × 10-2 S·cm-1 under 4.0 GPa at 220 °C, resp. The activation vol. of LiBH4-5 mol %Ca(BH4)2, at 3.2 cm3/mol, was comparable to that of other fast ionic conductors, such as lithium titanate and NASICONs. Moreover, Ca-doped LiBH4 showed lithium plating-stripping behavior in a cyclic voltammogram. These results indicate that the cond. enhancement by Ca doping can be attributed to the formation of a LiBH4-Ca(BH4)2 solid soln.; however, the solid soln. decompd. into the orthorhombic LiBH4 phase and the orthorhombic Ca(BH4)2 phase after unloading the high pressure.
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    Ley, M. B.; Jorgensen, M.; Cerny, R.; Filinchuk, Y.; Jensen, T. R. From M(BH4)3 (M = La, Ce) Borohydride frameworks to controllable synthesis of porous hydrides and ion conductors. Inorg. Chem. 2016, 55 (19), 9748– 9756,  DOI: 10.1021/acs.inorgchem.6b01526
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    From M(BH4)3 (M = La, Ce) Borohydride Frameworks to Controllable Synthesis of Porous Hydrides and Ion Conductors
    Ley, Morten Brix; Joergensen, Mathias; Cerny, Radovan; Filinchuk, Yaroslav; Jensen, Torben R.
    Inorganic Chemistry (2016), 55 (19), 9748-9756CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Rare earth metal borohydrides show a no. of interesting properties, e.g., Li ion cond. and luminescence, and the materials is well explored. However, previous attempts to obtain M(BH4)3 (M = La, Ce) by reacting MCl3 and LiBH4 yielded LiM(BH4)3Cl. Here, a synthetic approach is presented, which gave M(BH4)3 (M = La, Ce) via formation of intermediate complexes with di-Me sulfide. The cubic c-Ce(BH4)3 (Fm‾3c) is isostructural to high-temp. polymorphs of A(BH4)3 (A = Y, Sm, Er, Yb) borohydrides. The larger size of the Ce3+ ion makes the empty void in the open ReO3-type framework structure potentially accessible to small guest mols. like H2. Another new rhombohedral polymorph, r-M(BH4)3 (M = La, Ce), is a closed form of the framework, prone to stacking faults. The new compds. M(BH4)3 (M = La, Ce) can be combined with LiCl by an addn. reaction to form LiM(BH4)3Cl also known as Li4[M4(BH4)12Cl4]; the latter contains the unique tetranuclear cluster [M4(BH4)12Cl4]4- and shows high Li-ion cond. This reaction pathway opens a way to synthesize A4[M4(BH4)12X4] (M = La, Ce) compds. with different anions (X) and metal ions (A) and potentially high ion cond.
  34. 34
    Rude, L. H.; Groppo, E.; Arnbjerg, L. M.; Ravnsbaek, D. B.; Malmkjaer, R. A.; Filinchuk, Y.; Baricco, M.; Besenbacher, F.; Jensen, T. R. Iodide substitution in lithium borohydride, LiBH4-LiI. J. Alloys Compd. 2011, 509 (33), 8299– 8305,  DOI: 10.1016/j.jallcom.2011.05.031
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    Iodide substitution in lithium borohydride, LiBH4-LiI
    Rude, Line H.; Groppo, Elena; Arnbjerg, Lene M.; Ravnsbaek, Dorthe B.; Malmkjaer, Regitze A.; Filinchuk, Yaroslav; Baricco, Marcello; Besenbacher, Flemming; Jensen, Torben R.
    Journal of Alloys and Compounds (2011), 509 (33), 8299-8305CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH4-LiI. The structural chem. and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance IR spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is obsd. as formation of two solid solns. of Li(BH4)1-xIx, which merge into one upon heating. The solid solns. have hexagonal structures (space group P63 mc) similar to the structures of h-LiBH4 and β-LiI. The solid solns. have iodide contents in the range ∼0-62 mol% and are stable from below room temp. to the m.p. at 330 °C. Thus the stability of the solid solns. is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH4 and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid soln. Li(BH4)1-xIx, measured by the Sieverts method, are improved as compared to those of LiBH4. After four cycles of hydrogen release and uptake the Li(BH4)1-xIx solid soln. maintains 68% of the calcd. hydrogen storage capacity in contrast to LiBH4, which maintains only 25% of the storage capacity after two cycles under identical conditions.
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    Miyazaki, R.; Karahashi, T.; Kumatani, N.; Noda, Y.; Ando, M.; Takamura, H.; Matsuo, M.; Orimo, S.; Maekawa, H. Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH4. Solid State Ionics 2011, 192 (1), 143– 147,  DOI: 10.1016/j.ssi.2010.05.017
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    Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH4
    Miyazaki, R.; Karahashi, T.; Kumatani, N.; Noda, Y.; Ando, M.; Takamura, H.; Matsuo, M.; Orimo, S.; Maekawa, H.
    Solid State Ionics (2011), 192 (1), 143-147CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
    In the present work, we focus attention on the effect of LiI addn. to newly discovered pure lithium ion conductor, LiBH4. Solid soln. of the compn. LiBH4-LiI (LiI: 6.25-33.3 mol%) was synthesized by solid state reaction. Elec. cond. was measured from room temp. to 140 °C by ac impedance method, which revealed the fast-ion conduction phase of LiBH4 can be stabilized to lower temp., below the room temp. Solid soln. with LiI showed higher conductivities and lower activation energies in comparison with LiBH4. Powder XRD measurement was carried out at 120 °C (just above the transition temp. of LiBH4). The lattice consts. of the solid soln. were detd. DSC measurement showed a systematic compositional dependence on the transition temp. The stabilization mechanism was discussed.
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    Sveinbjornsson, D.; Myrdal, J. S. G.; Blanchard, D.; Bentzen, J. J.; Hirata, T.; Mogensen, M. B.; Norby, P.; Orimo, S. I.; Vegge, T. Effect of heat treatment on the lithium ion conduction of the LiBH4-Lil solid solution. J. Phys. Chem. C 2013, 117 (7), 3249– 3257,  DOI: 10.1021/jp310050g
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    Effect of Heat Treatment on the Lithium Ion Conduction of the LiBH4-LiI Solid Solution
    Sveinbjornsson, Dadi; Myrdal, Jon Steinar Gardarsson; Blanchard, Didier; Bentzen, Janet Jonna; Hirata, Takumi; Mogensen, Mogens Bjerg; Norby, Poul; Orimo, Shin-ichi; Vegge, Tejs
    Journal of Physical Chemistry C (2013), 117 (7), 3249-3257CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The LiBH4-LiI solid soln. is a good Li+ conductor and a promising cryst. electrolyte for all-solid-state lithium based batteries. The focus of the present work is on the effect of heat treatment on the Li+ conduction. Solid solns. with a LiI content of 6.25-50% were synthesized by high-energy ball milling and annealed at 140°. Powder x-ray diffraction and SEM were used for characterizing the samples and for comparing their crystallite sizes and the d. of defects before and after the annealing. The Li+ cond. was measured using impedance spectroscopy, resulting in conductivities exceeding 0.1 mS/cm at 30° and 10 mS/cm at 140°. It was found that the formation of defect-rich microstructures during ball milling increased the specific conductivities of these compds. significantly. The phase transition temps. between the orthorhombic and hexagonal structures of LiBH4 were measured using differential scanning calorimetry. The measured transition temps. range from 100 to -70° and show a linear decrease of 70° for every 10% of LiI addn. up to a LiI content of 25%. The relative stability of the two structures was calcd. using d. functional theory, and together with the differential scanning calorimetry measurements, the calcns. were used to evaluate the change in entropic difference between the structures with LiI content.
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    Maekawa, H.; Matsuo, M.; Takamura, H.; Ando, M.; Noda, Y.; Karahashi, T.; Orimo, S. I. Halide-stabilized LiBH4, a room-temperature lithium fast-ion conductor. J. Am. Chem. Soc. 2009, 131 (3), 894,  DOI: 10.1021/ja807392k
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    Halide-Stabilized LiBH4, a Room-Temperature Lithium Fast-Ion Conductor
    Maekawa, Hideki; Matsuo, Motoaki; Takamura, Hitoshi; Ando, Mariko; Noda, Yasuto; Karahashi, Taiki; Orimo, Shin-ichi
    Journal of the American Chemical Society (2009), 131 (3), 894-895CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review on development of lithium superionic conductors based on LiBH4 and lithium halides. Using these compds., room-temp. high lithium ion cond. was imparted to a hydride system that had not been considered a lithium ion electrolyte. The electrochem. measurements showed a great advantage of this material as an extremely lightwt. lithium electrolyte for high energy d. batteries. Versatile properties of these materials make them suitable for use in all-solid-state batteries.
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    Stephenson, C. C.; Rice, D. W.; Stockmayer, W. H. Order-disorder transitions in the alkali borohydrides. J. Chem. Phys. 1955, 23 (10), 1960– 1960,  DOI: 10.1063/1.1740617
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    Order-disorder transitions in the alkali borohydrides
    Stephenson, C. C.; Rice, D. W.; Stockmayer, W. H.
    Journal of Chemical Physics (1955), 23 (), 1960CODEN: JCPSA6; ISSN:0021-9606.
    Order-disorder transitions were obsd. at 76°K. for KBH4, 44°K. for RbBH4, and 27°K. for CsBH4. A plot of the log of the transition temp. vs. the corresponding values of the distance between the centers of neighboring borohydride ions yielded a straight line. This straight line is to be expected if the higher energy of the disordered phase is due principally to increased overlap energy.
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    Yan, Y. G.; Kuhnel, R. S.; Remhof, A.; Duchene, L.; Reyes, E. C.; Rentsch, D.; Lodziana, Z.; Battaglia, C. A lithium amide-borohydride solid-state electrolyte with lithium-ion conductivities comparable to liquid electrolytes. Adv. Energy Mater. 2017, 7 (19), 1700294,  DOI: 10.1002/aenm.201700294
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    Blanchard, D.; Nale, A.; Sveinbjornsson, D.; Eggenhuisen, T. M.; Verkuijlen, M. H. W.; Suwarno; Vegge, T.; Kentgens, A. P. M.; de Jongh, P. E. Nanoconfined LiBH4 as a fast lithium ion conductor. Adv. Funct. Mater. 2015, 25 (2), 184– 192,  DOI: 10.1002/adfm.201402538
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    Nanoconfined LiBH4 as a Fast Lithium Ion Conductor
    Blanchard, Didier; Nale, Angeloclaudio; Sveinbjoernsson, Dadi; Eggenhuisen, Tamara M.; Verkuijlen, Margriet H. W.; Suwarno; Vegge, Tejs; Kentgens, Arno P. M.; de Jongh, Petra E.
    Advanced Functional Materials (2015), 25 (2), 184-192CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid-state batteries. LiBH4 is a promising solid electrolyte for Li-ion batteries. It displays high lithium mobility, although only above 110° at which a transition to a high temp. hexagonal structure occurs. Herein, it is shown that confining LiBH4 in the pores of ordered mesoporous silica scaffolds leads to high Li+ cond. (0.1 mS cm-1) at room temp. This is a surprisingly high value, esp. given that the nanocomposites comprise 42 vol% of SiO2. Solid state 7Li NMR confirmed that the high cond. can be attributed to a very high Li+ mobility in the solid phase at room temp. Confinement of LiBH4 in the pores leads also to a lower solid-solid phase transition temp. than for bulk LiBH4. However, the high ionic mobility is assocd. with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO2 pore walls. These results point to a new strategy to design low-temp. ion conducting solids for application in all solid-state lithium ion batteries, which could enable safe use of Li-metal anodes.
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    Epp, V.; Wilkening, M. Motion of Li+ in nanoengineered LiBH4 and LiBH4:Al2O3 comparison with the microcrystalline form. ChemPhysChem 2013, 14 (16), 3706– 3713,  DOI: 10.1002/cphc.201300743
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    Motion of Li+ in Nanoengineered LiBH4 and LiBH4:Al2O3 Comparison with the Microcrystalline Form
    Epp, Viktor; Wilkening, Martin
    ChemPhysChem (2013), 14 (16), 3706-3713CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Nanocryst. LiBH4 and the two-phase analog LiBH4:Al2O3 have been prepd. by ball milling and used as model systems to track the changes in NMR relaxation rates with respect to coarse-grained, thermodynamically stable LiBH4. This revealed that interface (nano)engineering influences the hexagonal-to-orthorhombic phase transition and thus alters the ion-transport properties of Li in one- and two-phase LiBH4 towards higher diffusivities at lower temps.
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    Choi, Y. S.; Lee, Y. S.; Oh, K. H.; Cho, Y. W. Interface-enhanced Li ion conduction in a LiBH4-SiO2 solid electrolyte. Phys. Chem. Chem. Phys. 2016, 18 (32), 22540– 22547,  DOI: 10.1039/C6CP03563A
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    Interface-enhanced Li ion conduction in a LiBH4-SiO2 solid electrolyte
    Choi, Yong Seok; Lee, Young-Su; Oh, Kyu Hwan; Cho, Young Whan
    Physical Chemistry Chemical Physics (2016), 18 (32), 22540-22547CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    A fast solid state Li ion conductor composed of LiBH4 and SiO2 is developed by means of interface engineering. A composite of LiBH4-SiO2 was simply synthesized by high energy ball-milling, and two types of SiO2 (MCM-41 and fumed silica) having different sp. surface areas were used to evaluate the effect of the LiBH4/SiO2 interface on the ionic cond. enhancement. The ionic cond. of the ball-milled LiBH4-MCM-41 and LiBH4-fumed silica mixt. is as high as 10-5 S cm-1 and 10-4 S cm-1 at room temp., resp. In particular, the cond. of the latter is comparable to the LiBH4 melt-infiltrated into MCM-41. The conductivities of the LiBH4-fumed silica mixts. at different mixing ratios were analyzed employing a continuum percolation model, and the cond. of the LiBH4/SiO2 interface layer is estd. to be 105 times higher than that of pure bulk LiBH4. The result highlights the importance of the interface and indicates that significant enhancement in ionic cond. can be achieved via interface engineering.
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    Choi, Y. S.; Lee, Y. S.; Choi, D. J.; Chae, K. H.; Oh, K. H.; Cho, Y. W. Enhanced Li ion conductivity in LiBH4-Al2O3 mixture via interface engineering. J. Phys. Chem. C 2017, 121 (47), 26209– 26215,  DOI: 10.1021/acs.jpcc.7b08862
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    Gutowska, A.; Li, L. Y.; Shin, Y. S.; Wang, C. M. M.; Li, X. H. S.; Linehan, J. C.; Smith, R. S.; Kay, B. D.; Schmid, B.; Shaw, W. Nanoscaffold mediates hydrogen release and the reactivity of ammonia borane. Angew. Chem., Int. Ed. 2005, 44 (23), 3578– 3582,  DOI: 10.1002/anie.200462602
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    Nanoscaffold mediates hydrogen release and the reactivity of ammonia borane
    Gutowska, Anna; Li, Liyu; Shin, Yongsoon; Wang, Chongmin M.; Li, Xiaohong S.; Linehan, John C.; Smith, R. Scott; Kay, Bruce D.; Schmid, Benjamin; Shaw, Wendy; Gutowski, Maciej; Autrey, Tom
    Angewandte Chemie, International Edition (2005), 44 (23), 3578-3582CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    H-rich materials infused in nanoscaffolds offer a promising approach to on-board H storage. A mesoporous scaffold decreases the temp. for H release from NH3 borane (AB), a conventional H-storage material, to <80° and increases the purity of the H released.
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    Berube, V.; Radtke, G.; Dresselhaus, M.; Chen, G. Size effects on the hydrogen storage properties of nanostructured metal hydrides: A review. Int. J. Energy Res. 2007, 31 (6–7), 637– 663,  DOI: 10.1002/er.1284
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    Size effects on the hydrogen storage properties of nanostructured metal hydrides: a review
    Berube, Vincent; Radtke, Gregg; Dresselhaus, Mildred; Chen, Gang
    International Journal of Energy Research (2007), 31 (6-7), 637-663CODEN: IJERDN; ISSN:0363-907X. (John Wiley & Sons Ltd.)
    This review summarizes the effects that nanotechnol. can have on the main properties of metal hydrides and highlights the main competing behaviors between the system requirements, the necessary trade-offs, and the research priorities necessary to obtain hydride storage materials for practical automotive applications. Metal hydrides are often preferred over pressurized gas and other hydrogen storage methods because of their gravimetric and volumetric storage capacities and safe operating pressures. In addn. to the hydrogen storage capacity, other properties that have often been disregarded must now be addressed before hydrogen storage in metal hydrides becomes feasible. The slow hydriding/dehydriding kinetics, high release temp., low storage efficiency due to the high enthalpy of formation, and thermal management during the hydriding reaction remain important difficulties in meeting the objectives set by the Department of Energy for hydrogen storage systems. Nanotechnol. offers new ways of addressing those issues by taking advantage of the distinctive chem. and phys. properties obsd. in nanostructures. Nanostructured materials significantly improve the reaction kinetics, reduce the enthalpy of formation, and lower the hydrogen absorption and release temps. through destabilization of the metal hydride and multiple catalytic effects in the system. However, nanostructures can also lead to poor cyclability, degrdn. of the sorption properties, and a significant redn. of the thermal cond. that could make metal hydrides impractical for hydrogen storage.
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    de Jongh, P. E.; Adelhelm, P. Nanosizing and nanoconfinement: new strategies towards meeting hydrogen storage goals. ChemSusChem 2010, 3 (12), 1332– 1348,  DOI: 10.1002/cssc.201000248
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    Nanosizing and Nanoconfinement: new Strategies Towards Meeting Hydrogen Storage Goals
    de Jongh, Petra E.; Adelhelm, Philipp
    ChemSusChem (2010), 3 (12), 1332-1348CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. H is expected to play an important role as an energy carrier in a future, more sustainable society. However, its compact, efficient, and safe storage is an unresolved issue. One of the main options is solid-state storage in hydrides. Unfortunately, no binary metal hydride satisfies all requirements regarding storage d. and H release and uptake. Increasingly complex hydride systems are studied, but high thermodn. stabilities as well as slow kinetics and poor reversibility are important barriers for practical application. Nanostructuring by ball-milling is an established method to reduce crystallite sizes and increase reaction rates. Since 5 years attention has also turned to alternative prepn. techniques that enable particle sizes <10 nm and are often used in conjunction with porous supports or scaffolds. The impact of nano-sizing and -confinement on the H sorption properties of metal hydrides is discussed. The authors illustrate possible prepn. strategies, provide insight into the reasons for changes in kinetics, reversibility and thermodn., and highlight important progress in this field. All in all the authors provide the reader with a clear view of how nano-sizing and -confinement can beneficially affect the H sorption properties of the most prominent materials that are currently considered for solid-state H storage.
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    Ngene, P.; van Zwienen, M.; de Jongh, P. E. Reversibility of the hydrogen desorption from LiBH4: a synergetic effect of nanoconfinement and Ni addition. Chem. Commun. 2009, 46 (43), 8201– 8203,  DOI: 10.1039/c0cc03218b
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    Suwarno; Ngene, P.; Nale, A.; Eggenhuisen, T. M.; Oschatz, M.; Embs, J. P.; Remhof, A.; de Jongh, P. E. Confinement effects for lithium borohydride: comparing silica and carbon scaffolds. J. Phys. Chem. C 2017, 121 (8), 4197– 4205,  DOI: 10.1021/acs.jpcc.6b13094
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    Confinement Effects for Lithium Borohydride: Comparing Silica and Carbon Scaffolds
    Suwarno; Ngene, Peter; Nale, Angeloclaudio; Eggenhuisen, Tamara M.; Oschatz, Martin; Embs, Jan Peter; Remhof, Arndt; de Jongh, Petra E.
    Journal of Physical Chemistry C (2017), 121 (8), 4197-4205CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    LiBH4 is a promising material for hydrogen storage and as a solid-state electrolyte for Li ion batteries. Confining LiBH4 in porous scaffolds improves its hydrogen desorption kinetics, reversibility, and Li+ cond., but little is known about the influence of the chem. nature of the scaffold. Here, quasielastic neutron scattering and calorimetric measurements were used to study support effects for LiBH4 confined in nanoporous silica and carbon scaffolds. Pore radii were varied from 8 Å to 20 nm, with increasing confinement effects obsd. with decreasing pore size. For similar pore sizes, the confinement effects were more pronounced for silica than for carbon scaffolds. The shift in the solid-solid phase transition temp. is much larger in silica than in carbon scaffolds with similar pore sizes. A LiBH4 layer near the pore walls shows profoundly different phase behavior than cryst. LiBH4. This layer thickness was 1.94 ± 0.13 nm for the silica and 1.41 ± 0.16 nm for the carbon scaffolds. Quasi-elastic neutron scattering confirmed that the fraction of LiBH4 with high hydrogen mobility is larger for the silica than for the carbon nanoscaffold. These results clearly show that in addn. to the pore size the chem. nature of the scaffold also plays a significant role in detg. the hydrogen mobility and interfacial layer thickness in nanoconfined metal hydrides.
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    Ionic conduction in space charge regions
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    Verdal, N.; Udovic, T. J.; Rush, J. J.; Liu, X. F.; Majzoub, E. H.; Vajo, J. J.; Gross, A. F. Dynamical perturbations of tetrahydroborate anions in LiBH4 due to nanoconfinement in controlled-pore carbon scaffolds. J. Phys. Chem. C 2013, 117 (35), 17983– 17995,  DOI: 10.1021/jp4063737
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    Dynamical Perturbations of Tetrahydroborate Anions in LiBH4 due to Nanoconfinement in Controlled-Pore Carbon Scaffolds
    Verdal, Nina; Udovic, Terrence J.; Rush, John J.; Liu, Xiangfeng; Majzoub, Eric H.; Vajo, John J.; Gross, Adam F.
    Journal of Physical Chemistry C (2013), 117 (35), 17983-17995CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Neutron vibrational spectroscopy and quasielastic neutron scattering (QENS) were used to probe the dynamical properties of BH4- anions in both bulk LiBH4 and LiBH4 confined in nanoporous carbons (NPCs) having ≤4-nm-diam., hexagonally arranged, cylindrical pores. The BH4- torsional band of the confined LiBH4 is significantly broadened relative to that of bulk LiBH4, reflecting a disruption of the bulk crystal lattice and thus a broader distribution of BH4- rotational potentials. QENS measurements of bulk orthorhombic LiBH4 indicate a single quasielastic component yielding an activation energy for localized BH4- jump reorientation of 19.2 ± 0.8 kJ/mol, consistent with previous QENS and NMR results. At room temp., the measurements are in good agreement with BH4- reorientational jumps about a single C2 or C3 tetrahedral symmetry axis, with evidence for multiaxis rotations emerging as the temp. increases. In contrast, the QENS spectra of the NPC-confined LiBH4 exhibit two quasielastic components, one an order of magnitude broader than the other. The narrower component is presumably assocd. with more slowly reorienting BH4- anions in the interior of the pores and the broader component with much more rapidly reorienting BH4- anions in the vicinity of the pore surfaces. For 4-nm pores, these components yield two corresponding activation energies for reorientation: 16 ± 1 and 10.6 ± 0.7 kJ/mol. Probably both components undergo single C2- or C3-axis reorientational jumps <330 K, albeit with one an order of magnitude faster than the other. By 400 K (which is above the bulk phase transition temp.), both reorient more diffusively around multiple axes. These results are qual. consistent with comparative dynamical measurements of LiBH4 confined in a 13-nm-av.-pore-size carbon aerogel, which exhibited a much broader pore size distribution.
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    Breuer, S.; Uitz, M.; Wilkening, H. M. R. Rapid Li ion dynamics in the interfacial regions of nanocrystalline solids. J. Phys. Chem. Lett. 2018, 9 (8), 2093– 2097,  DOI: 10.1021/acs.jpclett.8b00418
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    Rapid Li ion dynamics in interfacial regions of nanocrystalline solids
    Breuer, S.; Uitz, M.; Wilkening, H. M. R.
    Journal of Physical Chemistry Letters (2018), 9 (8), 2093-2097CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Diffusive processes are ubiquitous in nature. In solid state physics, metallurgy and materials science the diffusivity of ions govern the functionality of many devices such as sensors or batteries. Motional processes on surfaces, across interfaces or through membranes can be quite different to that in the bulk. A direct, quant. description of such local diffusion processes is, however, rare. Here, we took advantage of 7Li longitudinal nuclear magnetic relaxation to study, on the at. length scale, the diffusive motion of lithium spins in the interfacial regions of nanocryst., orthorhombic LiBH4. Magnetization transients and free induction decays revealed a fast subset of Li ions having access to surface pathways that offer activation barriers (0.18 eV) much lower than those in the cryst. bulk regions (0.55 eV). These observations make orthorhombic borohydride a new nanostructured model system to study disorder-induced enhancements in interfacial diffusion processes.
  52. 52
    de Jongh, P. E.; Eggenhuisen, T. M. Melt infiltration: an emerging technique for the preparation of novel functional nanostructured materials. Adv. Mater. 2013, 25 (46), 6672– 6690,  DOI: 10.1002/adma.201301912
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    Melt Infiltration: an Emerging Technique for the Preparation of Novel Functional Nanostructured Materials
    de Jongh, Petra E.; Eggenhuisen, Tamara M.
    Advanced Materials (Weinheim, Germany) (2013), 25 (46), 6672-6690CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The rapidly expanding toolbox for design and prepn. is a major driving force for the advances in nanomaterials science and technol. Melt infiltration originates from the field of ceramic nanomaterials and is based on the infiltration of porous matrixes with the melt of an active phase or precursor. In recent years, it has become a technique for the prepn. of advanced materials: nanocomposites, pore-confined nanoparticles, ordered mesoporous and nanostructured materials. Although certain restrictions apply, mostly related to the melting behavior of the infiltrate and its interaction with the matrix, this review illustrates that it is applicable to a wide range of materials, including metals, polymers, ceramics, and metal hydrides and oxides. Melt infiltration provides an alternative to classical gas-phase and soln.-based prepn. methods, facilitating in several cases extended control over the nanostructure of the materials. This review starts with a concise discussion on the phys. and chem. principles for melt infiltration, and the practical aspects. In the second part of this contribution, specific examples are discussed of nanostructured functional materials with applications in energy storage and conversion, catalysis, and as optical and structural materials and emerging materials with interesting new phys. and chem. properties. Melt infiltration is a useful prepn. route for material scientists from different fields, and we hope this review may inspire the search and discovery of novel nanostructured materials.
  53. 53
    Unemoto, A.; Yasaku, S.; Nogami, G.; Tazawa, M.; Taniguchi, M.; Matsuo, M.; Ikeshoji, T.; Orimo, S. Development of bulk-type all-solid-state lithium-sulfur battery using LiBH4 electrolyte. Appl. Phys. Lett. 2014, 105 (8), 083901,  DOI: 10.1063/1.4893666
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    Development of bulk-type all-solid-state lithium-sulfur battery using LiBH4 electrolyte
    Unemoto, Atsushi; Yasaku, Syun; Nogami, Genki; Tazawa, Masaru; Taniguchi, Mitsugu; Matsuo, Motoaki; Ikeshoji, Tamio; Orimo, Shin-ichi
    Applied Physics Letters (2014), 105 (8), 083901/1-083901/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Stable battery operation of a bulk-type all-solid-state Li-S battery was demonstrated by using a LiBH4 electrolyte. The electrochem. activity of insulating elemental S as the pos. electrode was enhanced by the mutual dispersion of elemental S and C in the composite powders. Subsequently, a tight interface between the S-C composite and the LiBH4 powders was manifested only by cold-pressing owing to the highly deformable nature of the LiBH4 electrolyte. The high reducing ability of LiBH4 allows using the use of a Li neg. electrode that enhances the energy d. The results demonstrate the interface modification of insulating S and the architecture of an all-solid-state Li-S battery configuration with high energy d. (c) 2014 American Institute of Physics.
  54. 54
    Das, S.; Ngene, P.; Norby, P.; Vegge, T.; de Jongh, P. E.; Blanchard, D. All-solid-state lithium-sulfur battery based on a nanoconfined LiBH4 electrolyte. J. Electrochem. Soc. 2016, 163 (9), A2029– A2034,  DOI: 10.1149/2.0771609jes
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    All-Solid-State Lithium-Sulfur Battery Based on a Nanoconfined LiBH4 Electrolyte
    Das, Supti; Ngene, Peter; Norby, Poul; Vegge, Tejs; de Jongh, Petra E.; Blanchard, Didier
    Journal of the Electrochemical Society (2016), 163 (9), A2029-A2034CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
    In this work we characterize all-solid-state lithium-sulfur batteries based on nano-confined LiBH4 in mesoporous silica as solid electrolytes. The nano-confined LiBH4 has fast ionic lithium cond. at room temp., 0.1 mScm-1, negligible electronic cond. and its cationic transport no. (t+ = 0.96), close to unity, demonstrates a purely cationic conductor. The electrolyte has an excellent stability against lithium metal. The behavior of the batteries is studied by cyclic voltammetry and repeated charge/discharge cycles in galvanostatic conditions. The batteries show good performance, delivering high capacities vs. sulfur mass, typically 1220 mAhg-1 after 40 cycles at moderate temp. (55°), 0.03 C rates and working voltage of 2 V.
  55. 55
    Lefevr, J.; Cervini, L.; Griffin, J. M.; Blanchard, D. Lithium conductivity and ions dynamics in LiBH4/SiO2 solid electrolytes studied by solid-state NMR and quasi-elastic neutron scattering and applied in lithium sulfur batteries. J. Phys. Chem. C 2018, 122 (27), 15264– 15275,  DOI: 10.1021/acs.jpcc.8b01507
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    Lithium Conductivity and Ions Dynamics in LiBH4/SiO2 Solid Electrolytes Studied by Solid-State NMR and Quasi-Elastic Neutron Scattering and Applied in Lithium-Sulfur Batteries
    Lefevr, Jessica; Cervini, Luca; Griffin, John M.; Blanchard, Didier
    Journal of Physical Chemistry C (2018), 122 (27), 15264-15275CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Composite solid-state electrolytes based on ball-milled LiBH4/SiO2 aerogel exhibit high lithium conductivities, and we have found an optimal wt. ratio of 30/70 wt % LiBH4/SiO2 with a cond. of 0.1 mS cm-1 at room temp. We have studied the Li+ and BH4- dynamics using quasi-elastic neutron scattering and solid-state NMR and found that only a small fraction (∼10%) of the ions have high mobilities, whereas most of the LiBH4 shows behavior similar to macrocryst. material. The modified LiBH4 is formed from interaction with the SiO2 surface and most probably from reaction with the surface silanol groups. We successfully applied these composite electrolytes in lithium-sulfur solid-state batteries. The batteries show reasonable capacity retention (794 mAh g-1 sulfur after 10 discharge-charge cycles, Coulombic efficiency of 88.8 ± 2.7%, and av. capacity loss of 7.2% during the first 10 cycles).
  56. 56
    Cheng, C.-F.; Zhou, W.; Ho Park, D.; Klinowski, J.; Hargreaves, M.; Gladden, L. F. Controlling the channel diameter of the mesoporous molecular sieve MCM-41. J. Chem. Soc., Faraday Trans. 1997, 93 (2), 359– 363,  DOI: 10.1039/a605136g
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    Controlling the channel diameter of the mesoporous molecular sieve MCM-41
    Cheng, Chi-Feng; Zhou, Wuzong; Park, Dong Ho; Klinowski, Jacek; Hargreaves, Mark; Gladden, Lynn F.
    Journal of the Chemical Society, Faraday Transactions (1997), 93 (2), 359-363CODEN: JCFTEV; ISSN:0956-5000. (Royal Society of Chemistry)
    The authors describe a simple method of controlling the channel diam. of the mesoporous mol. sieve MCM-41 in the 26.1-36.5 Å range and the wall thickness in the 13.4-26.8 Å range while using the same gel mixt. This is achieved by varying the synthesis temp. in the 70-200° range and/or reaction times in the 0.5-96 h range. The unit cell parameter, channel diam., thickness of the channel wall, surface area, d.p. and grain morphol. were monitored by x-ray diffraction, N2 adsorption, 29Si magic-angle-spinning NMR and TEM. MCM-41 with wider and thicker-walled channels and higher d.p. was prepd. at higher temps. and at longer reaction times. Thick-wall MCM-41 has higher thermal stability but lower surface area. The material with the thickest channel wall ever reported (26.8 Å) can withstand calcination at nearly 1000° with little structural damage. The authors suggest a mechanism for the increase of wall thickness and channel diam. Fascinating morphol. features involving sealed silicate tubes and vesicles up to 1200 Å in diam. are obsd.
  57. 57
    Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279 (5350), 548– 552,  DOI: 10.1126/science.279.5350.548
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    Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores
    Zhao, Dongyuan; Feng, Jianglin; Huo, Qisheng; Melosh, Nicholas; Frederickson, Glenn H.; Chmelka, Bradley F.; Stucky, Galen D.
    Science (Washington, D. C.) (1998), 279 (5350), 548-552CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Use of amphiphilic triblock copolymers to direct the organization of polymg. silica species has resulted in the prepn. of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approx. 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500°C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore vol. fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepd. over a wide range of uniform pore sizes and pore wall thicknesses at low temp. (35° to 80°C), using a variety of poly(alkylene oxide) triblock copolymers and by the addn. of cosolvent org. mols. The block copolymer species can be recovered for reuse by solvent extn. with ethanol or removed by heating at 140°C for 3 h, in both cases, yielding a product that is thermally stable in boiling water.
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    Hartman, M. R.; Rush, J. J.; Udovic, T. J.; Bowman, R. C.; Hwang, S. J. Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy. J. Solid State Chem. 2007, 180 (4), 1298– 1305,  DOI: 10.1016/j.jssc.2007.01.031
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    Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy
    Hartman, Michael R.; Rush, John J.; Udovic, Terrence J.; Bowman, Robert C., Jr.; Hwang, Son-Jong
    Journal of Solid State Chemistry (2007), 180 (4), 1298-1305CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)
    The cryst. structure of 7Li11BH4 was studied using neutron powder diffraction at 3.5, 360, and 400 K. The B-H bond lengths and H-B-H angles for the [BH4]- tetrahedra indicated that the tetrahedra maintained a nearly ideal configuration throughout the temp. range studied. The at. displacement parameters at 360 K suggest that the [BH4]- tetrahedra become increasingly disordered of large amplitude librational and reorientational motions as the orthorhombic to hexagonal phase transition (T = 384 K) is approached. In the high-temp. hexagonal phase, the [BH4]- tetrahedra displayed extreme disorder about the trigonal axis along which they are aligned. Neutron vibrational spectroscopy data were collected at 5 K over an energy range of 10-170 meV, and are in agreement with prior Raman and low-resoln. neutron spectroscopy studies.
  59. 59
    Filinchuk, Y.; Chernyshov, D.; Cerny, R. Lightest borohydride probed by synchrotron X-ray diffraction: Experiment calls for a new theoretical revision. J. Phys. Chem. C 2008, 112 (28), 10579– 10584,  DOI: 10.1021/jp8025623
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    Lightest borohydride probed by synchrotron x-ray diffraction: experiment calls for a new theoretical revision
    Filinchuk, Yaroslav; Chernyshov, Dmitry; Cerny, Radovan
    Journal of Physical Chemistry C (2008), 112 (28), 10579-10584CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    A combination of synchrotron x-ray diffraction techniques were applied to resolve ambiguities between exptl. and theor. studies of LiBH4 and to reveal its complex structural evolution as a function of temp. Crystal structures of the low- and high-temp. polymorphs of LiBH4 were detd. from diffraction on single-crystals. Crystallog. data are given. In contrast to recent theor. conjectures, the high-temp. structure is hexagonal, space group P63mc. Exptl. data suggest a nearly isotropic disorder of the rigid tetrahedral BH4 groups as one of the factors stabilizing the hexagonal structure. Tetrahedral BH4 anions are undistorted and geometrically very similar in both polymorphs. The first order phase transition at 381 K is preceded by highly anisotropic lattice expansion and is accompanied by a neg. vol. change. Disorder phenomena and strong lattice anharmonicity, being ignored, lead to the failure of theor. predictions of the structural stability of LiBH4 published so far.
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    Hanawalt, J. D.; Rinn, H. W.; Frevel, L. K. Chemical analysis by X-ray diffraction - Classification and use of X-ray diffraction patterns. Ind. Eng. Chem., Anal. Ed. 1938, 10, 0457– 0512,  DOI: 10.1021/ac50125a001
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    Chemical analysis by x-ray diffraction. Classification and use of x-ray diffraction patterns
    Hanawalt, J. D.; Rinn, H. W.; Frevel, L. K.
    Industrial and Engineering Chemistry, Analytical Edition (1938), 10 (), 457-512CODEN: IENAAD; ISSN:0096-4484.
    This paper gives tabulated data on the diffraction patterns of 1000 chem. compds. which makes it possible to carry out routine testing by the Hull method (C. A. 13, 1980). The scheme of analysis will be readily understood by any one familiar with x-ray diffraction. Every cryst. substance has a characteristic diffraction pattern which is obtained from a small quantity of a mixt. as well as from the pure substance, so that the photograph obtained from a mixt. is the sum of the photographs that would be obtained from the superposed photographs of each individual constituent. The intensity of the lines gives good information with respect to quantity. The thousands of patterns which have been found can be classified in such a way that they can easily be used for the identification of an unknown constituent of a mixt. From the data of the patterns, the position of the 3 strongest lines are read off in the order of decreasing intensity. The first no. represents the group, the second no. the subgroup and the third no. the location within the subgroup. In the entire index book there are only 27 subgroups which contain more than 3 patterns and only one which contains more than 5 patterns. The necessary app. and manipulative technic are described. Wherever it is necessary to maintain an analytical lab., an invaluable supplementary technic will be found in x-ray diffraction. The substances present are shown in their true state of combination. The analysis is conclusive although only minute amts. of material are necessary; the samples are tested in the state received; different cryst. phases, states of oxidation or hydration, or phys. state are recognized; and a permanent record is always on file.
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    Posnjak, E. W. R. Crystal structure of alkali halogenides. J. Wash. Acad. Sci. 1922, 12, 248– 251
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    The crystal structures of the alkali halides. II
    Posnjak, Eugen; Wyckoff, R. W. G.
    Journal of the Washington Academy of Sciences (1922), 12 (), 248-51CODEN: JWASA3; ISSN:0043-0439.
    cf. C. A. 16, 526. The following salts have the "sodium chloride arrangement" of their atoms: LiCl, d100 = 5.17 Å.; LiBr, d100 = 5.48 Å.; LiI, d100 = 6.06 Å.; NaF, d100 = 4.61 Å.; KF, d100 = 5.36 Å.; CsF, d100 = 6.03 Å. By d100 is meant the length of the side of the unit cube. The diffraction data obtained from RbF were such as to indicate that additional work was necessary to obtain its structure in a satisfactory fashion. A tabulation of the structures of all of the alkali halides is appended.
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    Royer, L. Sur les accolements reguliers de cristaux d′especes differentes. C. R. Hebd. Seances Acad. Sci. 1925, 180, 2050
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    Harvey, K. B.; Mcquaker, N. R. Low temperature infrared and raman spectra of lithium borohydride. Can. J. Chem. 1971, 49 (20), 3282,  DOI: 10.1139/v71-546
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    Low temperature infrared and Raman spectra of lithium borohydride
    Harvey, K. B.; McQuaker, N. R.
    Canadian Journal of Chemistry (1971), 49 (20), 3282-6CODEN: CJCHAG; ISSN:0008-4042.
    The ir spectra of polycryst. LiBH4 and LiBD4 were recorded in the region 4000-50 cm-1 at 80°K. Raman spectra of polycryst. samples were also recorded at this temp. The spectra of the BH4- and BD4- lattice vibrations are consistent with sym. equiv. borohydride ions which lie on either general positions, 2-fold axes, or mirror-planes. Six lattice vibrations of translatory origin appear in the ir spectrum of LiBH4 and a mode of libratory origin is inferred from an absorption tentatively assigned as a 2nd overtone of a librational mode. Similar spectral results are obtained for LiBD4. The inferred librational frequencies are 418 cm-1 for the BH4- ions and 319 cm-1 for the BD4- ions.
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    D’Anna, V.; Spyratou, A.; Sharma, M.; Hagemann, H. FT-IR spectra of inorganic borohydrides. Spectrochim. Acta, Part A 2014, 128, 902– 906,  DOI: 10.1016/j.saa.2014.02.130
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    FT-IR spectra of inorganic borohydrides
    D'Anna, Vincenza; Spyratou, Alexandra; Sharma, Manish; Hagemann, Hans
    Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (2014), 128 (), 902-906CODEN: SAMCAS; ISSN:1386-1425. (Elsevier B.V.)
    Inorg. compds. with BH-4 ions are the subject of many recent studies in the context of potential H storage materials. Attenuated total reflectance FTIR (ATR-FTIR) spectra of ref. and research compds. (including deuterated samples) are collected and made available to the research community.
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    D’Anna, V.; Daku, L. M. L.; Hagemann, H. Quantitative spectra-structure relations for borohydrides. J. Phys. Chem. C 2015, 119 (38), 21868– 21874,  DOI: 10.1021/acs.jpcc.5b06045
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    Quantitative Spectra-Structure Relations for Borohydrides
    D'Anna, Vincenza; Lawson Daku, Latevi Max; Hagemann, Hans
    Journal of Physical Chemistry C (2015), 119 (38), 21868-21874CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Among the different potential hydrogen storage materials, borohydrides have been largely investigated because of their high gravimetric and volumetric hydrogen content. In the anal. of borohydrides, vibrational spectroscopy plays an important role since it gives information on the local structure of the BH4- ion inside the solid. Here the GF method, developed by Wilson, is used in order to det. the local symmetry of BH4- in solid borohydrides starting from their vibrational spectra. Two different cases of deformations of BH4- are considered. In the first case, the effects of small angular variations on the vibrational spectra of borohydrides will be taken into account; starting from the splitting of the bands corresponding to the deformation modes, the angular deformations will be estd. In the second one, the BH4- under chem. pressure (in different cubic alkali halides) is considered; in this case, the symmetry of the BH4- remains Td, while the bond lengths change according to the pressure experienced. Different practical examples will be illustrated.
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    Coates, J. Interpretation of infrared spectra, a practical approach. Encycl. Anal. Chem. 2006, 1, 10815– 10837,  DOI: 10.1002/9780470027318.a5606
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    Sun, T.; Liu, J.; Jia, Y.; Wang, H.; Sun, D. L.; Zhu, M.; Yao, X. D. Confined LiBH4: Enabling fast hydrogen release at similar to 100 degrees C. Int. J. Hydrogen Energy 2012, 37 (24), 18920– 18926,  DOI: 10.1016/j.ijhydene.2012.09.119
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    Confined LiBH4: Enabling fast hydrogen release at ∼100 °C
    Sun, Tai; Liu, Jian; Jia, Yi; Wang, Hui; Sun, Dalin; Zhu, Min; Yao, Xiangdong
    International Journal of Hydrogen Energy (2012), 37 (24), 18920-18926CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
    LiBH4 has been attracted tremendous research interest as a hydrogen storage material for mobile applications due to its very high gravimetric hydrogen capacity of 18.6 wt%. However, its real use is heavily hindered by the high operational temp. that is required above 350 °C to release hydrogen with various recent improvements. This is obviously much higher than the ambient temp. of about 100 °C. In this paper, we report the synthesis of LiBH4 confined by SBA-15 template, which achieves fast hydrogen release of LiBH4 at ∼100 °C. The confined LiBH4 system starts to release hydrogen at only 45 °C and can release 8.5 wt% hydrogen (on the basis of LiBH4 itself) within 10 min at 105 °C, which opens a new window and overcome the most challenging barrier to realize practical hydrogen storage of LiBH4.
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    Plerdsranoy, P.; Utke, R. Confined LiBH4-LiAlH4 in nanopores of activated carbon nanofibers. Int. J. Hydrogen Energy 2015, 40 (22), 7083– 7092,  DOI: 10.1016/j.ijhydene.2015.04.021
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    Confined LiBH4-LiAlH4 in nanopores of activated carbon nanofibers
    Plerdsranoy, Praphadsorn; Utke, Rapee
    International Journal of Hydrogen Energy (2015), 40 (22), 7083-7092CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
    Polyacrylonitrile (PAN)-based polymer fiber prepd. from electrospinning technique is carbonized and activated (with concd. KOH soln.) to obtain activated carbon nanofiber (ACNF). ACNF is used in this work as a host material for nanoconfinement of LiBH4-LiAlH4 composite via soln. impregnation. Successful nanoconfinement and homogeneous distribution of hydride composite on ACNF are confirmed by N2 adsorption-desorption and SEM-EDS-mapping techniques, resp. Nanoconfined LiBH4-LiAlH4 in ACNF performs almost single-step decompn. whereas that of milled sample is clearly two-step reaction. Onset dehydrogenation temp. of LiAlH4 from nanoconfined and milled samples is comparable at 100 °C, while that of LiBH4 obtained from nanoconfined sample is up to 80 °C lower than that of milled sample. In addn., significant redn. in main dehydrogenation temp., esp. of LiBH4 in nanoconfined LiBH4-LiAlH4 as compared with milled LiBH4-LiAlH4 (ΔT = up to 94 °C) and with pristine LiBH4 (ΔT = up to 149 °C) is achieved. Hydrogen contents released and reproduced in the 1st and 2nd dehydrogenations of nanoconfined LiBH4-LiAlH4 are 30 and 63% superior to those of milled sample. Reversibility of LiBH4, LiAlH4, and/or Li3AlH6 was accomplished from nanoconfined LiBH4-LiAlH4 under mild temp. and pressure condition (T = 320 °C and P(H2) = 80 bar) as compared with other LiBH4-LiAlH4 (or Al) systems.
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    Javadian, P.; Sheppard, D. A.; Buckley, C. E.; Jensen, T. R. Hydrogen storage properties of nanoconfined LiBH4-NaBH4. Int. J. Hydrogen Energy 2015, 40 (43), 14916– 14924,  DOI: 10.1016/j.ijhydene.2015.08.075
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    Hydrogen storage properties of nanoconfined LiBH4-NaBH4
    Javadian, Payam; Sheppard, Drew A.; Buckley, Craig E.; Jensen, Torben R.
    International Journal of Hydrogen Energy (2015), 40 (43), 14916-14924CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
    In this study a eutectic melting composite of 0.62LiBH4-0.38NaBH4 has been infiltrated in two nanoporous resorcinol formaldehyde carbon aerogel scaffolds with similar pore sizes (37 and 38 nm) but different BET surface areas (690 and 2358 m2/g) and pore vols. (1.03 and 2.64 mL/g). This investigation clearly shows decreased temp. of hydrogen desorption, and improved cycling stability during hydrogen release and uptake of bulk 0.62LiBH4-0.38NaBH4 when nanoconfined into carbon nanopores. The hydrogen desorption temp. of bulk 0.62LiBH4-0.38NaBH4 is reduced by ∼107 °C with the presence of carbon, although a minor kinetic variation is obsd. between the two carbon scaffolds. This corresponds to apparent activation energies, EA, of 139 kJ/mol (bulk) and 116-118 kJ/mol (with carbon aerogel). Bulk 0.62LiBH4-0.38NaBH4 has poor reversibility during continuous hydrogen release and uptake cycling, maintaining 22% H2 capacity after four hydrogen desorptions (1.6 wt.% H2). In contrast, nanoconfinement into the high surface area carbon aerogel scaffold significantly stabilizes the hydrogen storage capacity, maintaining ∼70% of the initial capacity after four cycles (4.3 wt.% H2).
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    Laiti, E.; Persson, P.; Ohman, L. O. Balance between surface complexation and surface phase transformation at the alumina/water interface. Langmuir 1998, 14 (4), 825– 831,  DOI: 10.1021/la970383n
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    Balance between Surface Complexation and Surface Phase Transformation at the Alumina/Water Interface
    Laiti, Erkki; Persson, Per; Oehman, Lars-Olof
    Langmuir (1998), 14 (4), 825-831CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    This paper synthesizes and expands on the results of a recent series of investigations aimed at characterizing the interactions of orthophosphate, phenylphosphonate, and clodronate ions with hydrous alumina surfaces. The paper shows that γ-Al2O3 is a thermodynamically unstable substance in water, which undergoes a (surface) phase transformation into bayerite, β-Al(OH)3. Furthermore, it also shows that while phenylphosphonate ions are exclusively adsorbed via surface complexation to the alumina surfaces, clodronate ions dissolve the alumina phase and ppt. as an aluminum clodronate phase. Orthophosphate ions show a transient behavior in this respect, and the limits for, and consequences of, AlPO4(s) formation are detd. via a series of chem. modeling calcns. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macroscopically derived stoichiometric compns. are used to assign microscopic surface complex structures.
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    Hiyoshi, N.; Yogo, K.; Yashima, T. Adsorption characteristics of carbon dioxide on organically functionalized SBA-15. Microporous Mesoporous Mater. 2005, 84 (1–3), 357– 365,  DOI: 10.1016/j.micromeso.2005.06.010
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    Adsorption characteristics of carbon dioxide on organically functionalized SBA-15
    Hiyoshi, Norihito; Yogo, Katsunori; Yashima, Tatsuaki
    Microporous and Mesoporous Materials (2005), 84 (1-3), 357-365CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
    Aminosilane-modified SBA-15 was prepd. by grafting various aminosilanes on mesoporous SiO2 SBA-15, and its adsorption characteristics towards CO2 were examd. The amt. of CO2 adsorbed was almost the same for both in the presence and in the absence of water vapor. The efficiency of adsorption, defined as the no. of adsorbed CO2 mols. per N atom of aminosilane-modified SBA-15, increased with increasing the surface d. of amine. IR spectroscopy revealed that CO2 was adsorbed on aminosilane-modified SBA-15 through the formation of alkylammonium carbamate in the presence and in the absence of water vapor. Amine pairs, on which CO2 was adsorbed through formation of alkylammonium carbamate, increased with increasing surface d. of amine. In addn., influence of amine structure on the adsorption capacity was also discussed.
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    Zhao, X. S.; Lu, G. Q. Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study. J. Phys. Chem. B 1998, 102 (9), 1556– 1561,  DOI: 10.1021/jp972788m
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    Modification of MCM-41 by Surface Silylation with Trimethylchlorosilane and Adsorption Study
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    Fast Li diffusion in crystalline LiBH4 due to reduced dimensionality: Frequency-dependent NMR spectroscopy
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    The hexagonal and orthorhombic form of lithium borohydride, LiBH4, are investigated by temp. and frequency-dependent NMR spectroscopy. The local electronic structure and microscopic diffusion parameters are detd. by recording both 6,7Li NMR spectra and spin-lattice relaxation (SLR) rates. The rates of the high-temp. flank of the SLR-NMR peaks of hexagonal LiBH4 clearly depend on resonance frequency which unequivocally reveals a low-dimensional diffusion process. Due to the very limited no. of suitable model substances this makes lithium borohydride an extremely attractive material to study the effect of reduced dimensionality on Li dynamics. Most likely, the spatial confinement of Li hopping is also responsible for the very high ionic cond. found for the hexagonal polymorph, recently.

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  • Abstract

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    Figure 1

    Figure 1. XRD powder patterns of the various LiBH4–LiI/oxide nanocomposites investigated. For comparison, the positions of the reflection of LiBH4 in its hexagonal form are included as well. In addition, the pattern of LiBH4–LiI (20 mol % of LiI) and LiI are also shown. Values in brackets refer to hkl indices. The shift of the reflections toward lower diffraction angles indicates successful incorporation of LiI that stabilizes the hexagonal form of LiBH4.

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    Figure 2

    Figure 2. DRIFT spectra of Al2O3, nanoconfined LiBH4–LiI/Al2O3, nanoconfined LiBH4/Al2O3, and LiBH4–LiI (20 mol % of LiI). For comparison, the spectrum of LiBH4 is also shown. Main peaks are marked by vertically drawn dashed lines with the wavenumbers indicated. K-M intensities (see the ordinate axis) are in arbitrary units. See text for further explanation.

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    Figure 3

    Figure 3. (a) Nyquist plots, that is, the imaginary part, – Z″, of the complex impedance plotted versus the real part Z′, of nanoconfined LiBH4–LiI/Al2O3 and LiBH4/Al2O3. The LiBH4–LiI sample (20 mol % LiI) is also shown. Values in pF show the capacitances obtained after parametrizing the main (nondepressed) semicircles with the equivalent circuit shown; see also Experimental section. The line approximating the second semicircle of the curve belonging to LiBH4/Al2O3, which shows up at higher frequencies, is drawn to guide the eye. (b) Arrhenius plot (half-logarithmic plot of σ′ vs 1000/T) to illustrate the change of conductivity with increasing temperature. Dashed and solid lines represent linear fits to determine activation energies EA, which range from 0.44(1) eV to 0.59(1) eV. Nanoconfined LiBH4–LiI/Al2O3 shows the highest conductivities. At room temperature (25 °C), its ion conductivity is slightly larger than 10–4 S cm–1; a conductivity of 10–3 S cm–1, needed to realize Li-ion batteries, is reached at 66 °C.

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    Figure 4

    Figure 4. 7Li NMR spectra of (a) LiBH4–LiI, (b) nanoconfined LiBH4/Al2O3 without LiI, and (c) nanoconfined LiBH4–LiI/Al2O3. Spectra were recorded at a Larmor frequency of 116 MHz at the temperatures indicated. Dashed lines in parts a and b show the deconvolution of the entire line with appropriate Gaussian and Lorentzian functions to estimate the number fraction of mobile Li ions in these compounds. For LiBH4–LiI/Al2O3, the spectrum has almost adopted its final form at temperatures as low as 30 °C. While the sharp line represents fast Li ions, the broader foot comprises both the central line of a fraction of slower Li ions and quadrupole intensities. The latter become visible as a sharp powder pattern at elevated temperature where dipole–dipole interactions are effectively averaged out due to rapid Li+ exchange. See text for further information.

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    Figure 5

    Figure 5. (a) X-ray powder diffraction patterns of nanoconfined and nonconfined LiBH4–LiNH2. For comparison, the expected patterns of orthorhombic LiBH4 and LiNH2 are also shown. The pattern at the top represents that of the oxide substrate, SiO2. (b) DRIFT spectra of the samples shown in part a; the spectra reveal broadening of the signals, which shift toward lower wavenumbers upon nanoconfinement. Those bands which results from silanol OH groups are absent for LiBH4–LiNH2/SiO2 indicating surface reactions between the electrolyte and the surface of the oxide. See text for further explanation.

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    Figure 6

    Figure 6. Ionic conductivity of nanoconfined LiBH4–LiNH2/SiO2 as a function of the inverse temperature. For comparison, data on LiBH4/SiO2, nonconfined LiBH4–LiNH2 and bulk LiBH4 are also included. The lines are to guide the eye.

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      A quant. anal. of the elec. charge shuttle phenomenon in high-energy Li/S rechargeable batteries encompasses theor. models of the charge process, charge and discharge capacity, overcharge protection, thermal effects, self-discharge, and a comparison of simulated and exptl. data. The models focus on polysulfide chem. and polysulfide interactions with the Li anode. Different battery electrolytes demonstrated different charge shuttling rate consts. Specifically, different electrolyte salt concns. (e.g., LiN(CF3SO2)2) showed lower Li corrosion with polysulfides and a lower shuttle const. This possibly was attributed to such influences as salt concn. effects at the Li-electrolyte interface, rate of heterogeneous reactions of polysulfides with the Li surface, and salt concn. effects on polysulfide soly. and equil., polysulfide mobility, and electrolyte viscosity.
    4. 4
      Kim, J. G.; Son, B.; Mukherjee, S.; Schuppert, N.; Bates, A.; Kwon, O.; Choi, M. J.; Chung, H. Y.; Park, S. A review of lithium and non-lithium based solid state batteries. J. Power Sources 2015, 282, 299– 322,  DOI: 10.1016/j.jpowsour.2015.02.054
      4
      A review of lithium and non-lithium based solid state batteries
      Kim, Joo Gon; Son, Byungrak; Mukherjee, Santanu; Schuppert, Nicholas; Bates, Alex; Kwon, Osung; Choi, Moon Jong; Chung, Hyun Yeol; Park, Sam
      Journal of Power Sources (2015), 282 (), 299-322CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)
      A review. Conventional lithium-ion liq.-electrolyte batteries are widely used in portable electronic equipment such as lap top computers, cell phones, and elec. vehicles; however, they have several drawbacks, including expensive sealing agents and inherent hazards of fire and leakages. All solid state batteries utilize solid state electrolytes to overcome the safety issues of liq. electrolytes. Drawbacks for all-solid state lithium-ion batteries include high resistance at ambient temps. and design intricacies. This paper is a comprehensive review of all aspects of solid state batteries: their design, the materials used, and a detailed literature review of various important advances made in research. The paper exhaustively studies lithium based solid state batteries, as they are the most prevalent, but also considers non-lithium based systems. Non-lithium based solid state batteries are attaining widespread com. applications, as are also lithium based polymeric solid state electrolytes. Tabular representations and schematic diagrams are provided to underscore the unique characteristics of solid state batteries and their capacity to occupy a niche in the alternative energy sector.
    5. 5
      Sun, C. W.; Liu, J.; Gong, Y. D.; Wilkinson, D. P.; Zhang, J. J. Recent advances in all-solid-state rechargeable lithium batteries. Nano Energy 2017, 33, 363– 386,  DOI: 10.1016/j.nanoen.2017.01.028
      5
      Recent advances in all-solid-state rechargeable lithium batteries
      Sun, Chunwen; Liu, Jin; Gong, Yudong; Wilkinson, David P.; Zhang, Jiujun
      Nano Energy (2017), 33 (), 363-386CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
      The all-solid-state lithium batteries using solid electrolytes are considered to be the new generation of devices for energy storage. Recent advances in this kind of rechargeable batteries have brought them much closer to a com. reality. However, several challenges such as insufficient room temp. ionic cond. (10-5∼10-3 S cm-1) when compared to those of conventional org. liq. electrolytes (10-2 S cm-1), the difficulty in informing an effective electrode-electrolyte interface and insufficient fundamental understanding of the interfacial process after charge/discharge, hindering the reality of such devices. To accelerate the research and development, the overall picture about the current state of all solid-state lithium batteries was reviewed in this article with major focus on the material aspects, including inorg. ceramic and org. solid polymer electrolyte materials. In particular, the importance of the electrolytes and their assocd. interfaces with electrodes as well as their effects on the battery performance are emphasized by in-depth discussion and data anal. To overcome the challenges, several possible research directions are also suggested for facilitating further improvement on the battery performance.
    6. 6
      Knauth, P. Inorganic solid Li ion conductors: An overview. Solid State Ionics 2009, 180 (14–16), 911– 916,  DOI: 10.1016/j.ssi.2009.03.022
      6
      Inorganic solid Li ion conductors: An overview
      Knauth, Philippe
      Solid State Ionics (2009), 180 (14-16), 911-916CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
      This short review presents the state-of-the-art knowledge on cryst., composite and amorphous inorg. solid lithium ion conductors, which are of interest as potential solid electrolytes in lithium batteries and might replace the currently used polymeric lithium ion conductors. The discussion of cryst. Li ion conductors includes perovskite-type Lithium Lanthanum Titanates, NASICON-type, LiSICON- and Thio-LiSICON-type Li ion conductors, as well as garnet-type Li ion conducting oxides. The part on composite Li ion conductors discusses materials contg. oxides and mesoporous oxides. In the amorphous Li ion conductor part, mech. attrition of Li compds., oxide and sulfide-based glasses as well as LIPON and related systems are presented.
    7. 7
      Takada, K. Progress and prospective of solid-state lithium batteries. Acta Mater. 2013, 61 (3), 759– 770,  DOI: 10.1016/j.actamat.2012.10.034
      7
      Progress and prospective of solid-state lithium batteries
      Takada, Kazunori
      Acta Materialia (2013), 61 (3), 759-770CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)
      A review. The development of lithium-ion batteries has energized studies of solid-state batteries, because the non-flammability of their solid electrolytes offers a fundamental soln. to safety concerns. Since poor ionic conduction in solid electrolytes is a major drawback in solid-state batteries, such studies were focused on the enhancement of ionic cond. The studies have identified some high performance solid electrolytes; however, some disadvantages have remained hidden until their use in batteries. This paper reviews the development of solid electrolytes and their application to solid-state lithium batteries.
    8. 8
      Li, J. C.; Ma, C.; Chi, M. F.; Liang, C. D.; Dudney, N. J. Solid electrolyte: the key for high-voltage lithium batteries. Adv. Energy Mater. 2015, 5 (4), 1401408,  DOI: 10.1002/aenm.201401408
      There is no corresponding record for this reference.
    9. 9
      Thangadurai, V.; Narayanan, S.; Pinzaru, D. Garnet-type solid-state fast Li ion conductors for Li batteries: Critical review. Chem. Soc. Rev. 2014, 43 (13), 4714– 4727,  DOI: 10.1039/c4cs00020j
      9
      Garnet-type solid-state fast Li ion conductors for Li batteries: critical review
      Thangadurai, Venkataraman; Narayanan, Sumaletha; Pinzaru, Dana
      Chemical Society Reviews (2014), 43 (13), 4714-4727CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Batteries are electrochem. devices that store elec. energy in the form of chem. energy. Among known batteries, Li ion batteries (LiBs) provide the highest gravimetric and volumetric energy densities, making them ideal candidates for use in portable electronics and plug-in hybrid and elec. vehicles. Conventional LiBs use an org. polymer electrolyte, which exhibits several safety issues including leakage, poor chem. stability and flammability. The use of a solid-state (ceramic) electrolyte to produce all-solid-state LiBs can overcome all of the above issues. Also, solid-state Li batteries can operate at high voltage, thus, producing high power d. Various types of solid Li-ion electrolytes have been reported; this review is focused on the most promising solid Li-ion electrolytes based on garnet-type metal oxides. The first studied Li-stuffed garnet-type compds. are Li5La3M2O12 (M = Nb, Ta), which show a Li-ion cond. of ∼10-6 at 25 °C. La and M sites can be substituted by various metal ions leading to Li-rich garnet-type electrolytes, such as Li6ALa2M2O12, (A = Mg, Ca, Sr, Ba, Sr0.5Ba0.5) and Li7La3C2O12 (C = Zr, Sn). Among the known Li-stuffed garnets, Li6.4La3Zr1.4Ta0.6O12 exhibits the highest bulk Li-ion cond. of 10-3 S cm-1 at 25 °C with an activation energy of 0.35 eV, which is an order of magnitude lower than that of the currently used polymer, but is chem. stable at higher temps. and voltages compared to polymer electrolytes. Here, we discuss the chem. compn.-structure-ionic cond. relationship of the Li-stuffed garnet-type oxides, as well as the Li ion conduction mechanism.
    10. 10
      Bohnke, O.; Bohnke, C.; Fourquet, J. L. Mechanism of ionic conduction and electrochemical intercalation of lithium into the perovskite lanthanum lithium titanate. Solid State Ionics 1996, 91, 21– 31,  DOI: 10.1016/S0167-2738(96)00434-1
      10
      Mechanism of ionic conduction and electrochemical intercalation of lithium into the perovskite lanthanum lithium titanate
      Bohnke, O.; Bohnke, C.; Fourquet, J. L.
      Solid State Ionics (1996), 91 (1,2), 21-31CODEN: SSIOD3; ISSN:0167-2738. (Elsevier)
      The ionic cond. and electrochem. intercalation properties of La2/3-xLi3xTiO3 solid solns. (for 0.07≤x≤0.13) were studied. These compds. present a perovskite-type structure (ABO3) with cation deficiency at the A-sites. The purely ionic cond. was confirmed and the mechanism of ionic conduction studied using impedance spectroscopy techniques. The temp. dependence of cond. can be modelized by a Vogel-Tamman-Fulcher (VTF)-type relation. In these materials, where the high ionic cond. may originate from the presence of vacancies in the A-sites of the perovskite structure, the VTF behavior would suggest a mechanism of conduction involving the tilting of the TiO6 octahedra. The Li intercalation was also studied in LiClO4(M)-PC electrolyte using galvanostatic discharge and charge at very low rates (one Li/250 and /1500 h) to approach the equil. The Li intercalation leads to the presence of a plateau around 1.5 V/Li in the discharge curve; it is partly reversible and the capacity of the electrode is not very high. A max. Li uptake of 0.15 was found. The diffusion coeff. of Li in the intercalated material was detd. by impedance spectroscopy at room temp. and found to range from 10-8 cm2s-1 to 10-9 cm2s-1 as intercalation proceeds. Since the exptl. impedance spectroscopy data performed at room temp. follow a Warburg behavior at low frequency, the intercalation seems to proceed in a single-phase process although a plateau is observable in the discharge curve.
    11. 11
      Li, J.; Lin, Y.; Yao, H. H.; Yuan, C. F.; Liu, J. Tuning thin-film electrolyte for lithium battery by grafting cyclic carbonate and combed poly(ethylene oxide) on polysiloxane. ChemSusChem 2014, 7 (7), 1901– 1908,  DOI: 10.1002/cssc.201400113
      11
      Tuning Thin-Film Electrolyte for Lithium Battery by Grafting Cyclic Carbonate and Combed Poly(ethylene oxide) on Polysiloxane
      Li, Jie; Lin, Yue; Yao, Hehua; Yuan, Changfu; Liu, Jin
      ChemSusChem (2014), 7 (7), 1901-1908CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A tunable polysiloxane thin-film electrolyte for all-solid-state lithium-ion batteries was developed. The polysiloxane was synthesized by hydrosilylation of polymethylhydrosiloxane with cyclic [(allyloxy)methyl]ethylene ester carbonic acid and vinyl tris(2-methoxyethoxy)silane. 1H NMR spectroscopy and gel-permeation chromatog. demonstrated that the bifunctional groups of the cyclic propylene carbonate (PC) and combed poly(ethylene oxide) (PEO) were well grafted on the polysiloxane. At PC/PEO = 6:4, the polysiloxane-based electrolyte had an ionic cond. of 1.55×10-4 and 1.50×10-3 S cm-1 at 25 and 100°, resp. The LiFePO4/Li batteries fabricated with the thin-film electrolyte presented excellent cycling performance in the temp. range from 25-100° with an initial discharge capacity at a rate of 1 C of 88.2 and 140 mA h g-1 at 25 and 100°, resp.
    12. 12
      Hayashi, A.; Sakuda, A.; Tatsumisago, M. Development of sulfide solid electrolytes and interface formation processes for bulk-type all-solid-state Li and Na batteries. Front. Energy Res. 2016, 4, 25,  DOI: 10.3389/fenrg.2016.00025
      There is no corresponding record for this reference.
    13. 13
      de Jongh, P. E.; Blanchard, D.; Matsuo, M.; Udovic, T. J.; Orimo, S. Complex hydrides as room-temperature solid electrolytes for rechargeable batteries. Appl. Phys. A: Mater. Sci. Process. 2016, 122, 251,  DOI: 10.1007/s00339-016-9807-2
      There is no corresponding record for this reference.
    14. 14
      Matsuo, M.; Orimo, S. Lithium fast-ionic conduction in complex hydrides: review and prospects. Adv. Energy Mater. 2011, 1 (2), 161– 172,  DOI: 10.1002/aenm.201000012
      14
      Lithium fast-ionic conduction in complex hydrides: review and prospects
      Matsuo, Motoaki; Orimo, Shin-ichi
      Advanced Energy Materials (2011), 1 (2), 161-172CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
      A review. Complex hydrides exhibit various energy-related functions such as hydrogen storage, microwave absorption, and neutron shielding. Furthermore, another novel energy-related function was recently reported by the authors; lithium fast-ionic conduction, which suggests that complex hydrides may be a potential candidate for solid electrolytes in lithium-ion batteries. This review presents the recent progress in the development of lithium fast-ionic conductors of complex hydrides. First, the fast-ionic conduction in LiBH4 as a result of clarifying the mechanism of microwave absorption is presented, and then the conceptual development of complex hydrides as a new type of solid-state lithium fast-ionic conductors in LiBH4-, LiNH2-, and LiAlH4-based complex hydrides is discussed. Finally, the future prospects of this study from both application and fundamental viewpoints are described: possible use as solid electrolytes for batteries, formation of ionic liqs. in complex hydrides, and similarity between complex hydrides and Laves-phase metal hydrides.
    15. 15
      Lu, Z. H.; Ciucci, F. Metal borohydrides as electrolytes for solid-state Li, Na, Mg, and Ca batteries: A first-principles study. Chem. Mater. 2017, 29 (21), 9308– 9319,  DOI: 10.1021/acs.chemmater.7b03284
      15
      Metal Borohydrides as Electrolytes for Solid-State Li, Na, Mg, and Ca Batteries: A First-Principles Study
      Lu, Ziheng; Ciucci, Francesco
      Chemistry of Materials (2017), 29 (21), 9308-9319CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Metal borohydrides are a family of materials that were recently discovered to have extraordinary ionic conductivities, making them promising candidates as electrolytes for solid-state batteries (SSBs). In fact, various groups have measured the ionic conductivities and assembled batteries using specific borohydrides. However, there are no comprehensive studies assessing the thermodn. properties or discussing the suitability of metal borohydrides as electrolytes in SSBs, esp. for beyond-lithium applications. In this work, we investigate the electrochem. stability, interfacial characteristics, mech. properties, and ionic conductivities of Li, Na, Ca, and Mg borohydrides using first-principles calcns. Our results suggest that Li and Na borohydrides are unstable at high voltages. However, the corresponding decompn. products, i.e., B12H122--contg. phases, have wide electrochem. windows which protect the electrolyte, leading to large electrochem. windows as wide as 5 V. In addn., our simulations indicate that metal borohydrides are ductile, suggesting facile processing. However, their low shear moduli may result in metal dendrite formation. For Ca and Mg borohydrides, while they possess reasonably good electrochem. stability, the low cationic diffusivity may impede their practical use. Finally, the anion rotation barrier was shown to correlate with the superionic phase transition temp., suggesting that anion mixing may be a potential approach to achieve room-temp. superionic cond.
    16. 16
      Møller, K.; Sheppard, D.; Ravnsbæk, D.; Buckley, C.; Akiba, E.; Li, H.-W.; Jensen, T. Complex metal hydrides for hydrogen, thermal and electrochemical energy storage. Energies 2017, 10 (10), 1645,  DOI: 10.3390/en10101645
      There is no corresponding record for this reference.
    17. 17
      Yoshida, K.; Sato, T.; Unemoto, A.; Matsuo, M.; Ikeshoji, T.; Udovic, T. J.; Orimo, S. Fast sodium ionic conduction in Na2B10H10-Na2B12H12 pseudo-binary complex hydride and application to a bulk-type all-solid-state battery. Appl. Phys. Lett. 2017, 110 (10), 103901,  DOI: 10.1063/1.4977885
      17
      Fast sodium ionic conduction in Na2B10H10-Na2B12H12 pseudo-binary complex hydride and application to a bulk-type all-solid-state battery
      Yoshida, Koji; Sato, Toyoto; Unemoto, Atsushi; Matsuo, Motoaki; Ikeshoji, Tamio; Udovic, Terrence J.; Orimo, Shin-ichi
      Applied Physics Letters (2017), 110 (10), 103901/1-103901/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      We developed highly Na-ion conductive Na2B10H10-Na2B12H12 pseudo-binary complex hydride via mech. ball-milling admixts. of the pure Na2B10H10 and Na2B12H12 components. Both of these components show a monoclinic phase at room temp., but ball-milled mixts. partially stabilized highly ion-conductive, disordered cubic phases, whose fraction and favored structural symmetry (body-centered cubic or face-centered cubic) depended on the conditions of mech. ball-milling and molar ratio of the component compds. First-principles mol.-dynamics simulations demonstrated that the total energy of the closo-borane mixts. and pure materials is quite close, helping to explain the obsd. stabilization of the mixed compds. The ionic cond. of the closo-borane mixts. appeared to be correlated with the fraction of the body-centered-cubic phase, exhibiting a max. at a molar ratio of Na2B10H10:Na2B12H12 =1:3. A cond. as high as log(σ/S/cm) = -3.5 was obsd. for the above ratio at 303 K, being approx. 2-3 orders of magnitude higher than that of either pure material. A bulk-type all-solid-state Na-ion battery with a closo-borane-mixt. electrolyte, Na-metal neg.-electrode, and TiS2 pos.-electrode demonstrated a high specific capacity, close to the theor. value of NaTiS2 formation and a stable discharge/charge cycling for at least eleven cycles, with a high discharge capacity retention ratio >91% from the second cycle. (c) 2017 American Institute of Physics.
    18. 18
      Sakintuna, B.; Lamari-Darkrim, F.; Hirscher, M. Metal hydride materials for solid hydrogen storage: A review. Int. J. Hydrogen Energy 2007, 32 (9), 1121– 1140,  DOI: 10.1016/j.ijhydene.2006.11.022
      18
      Metal hydride materials for solid hydrogen storage: A review
      Sakintuna, Billur; Lamari-Darkrim, Farida; Hirscher, Michael
      International Journal of Hydrogen Energy (2007), 32 (9), 1121-1140CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
      A review. Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gas or liq. cannot fulfill future storage goals. Chem. or phys. combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. The present paper reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 wt.% for on-board applications. Efforts have been devoted to these materials to decrease their desorption temp., enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as well as by ball milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kinetics and lower decompn. temps., however, the state-of-the-art materials are still far from meeting the aimed target for their transport applications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides.
    19. 19
      Zuttel, A.; Wenger, P.; Rentsch, S.; Sudan, P.; Mauron, P.; Emmenegger, C. LiBH4 a new hydrogen storage material. J. Power Sources 2003, 118 (1–2), 1– 7,  DOI: 10.1016/S0378-7753(03)00054-5
      19
      LiBH4 a new hydrogen storage material
      Zuttel, A.; Wenger, P.; Rentsch, S.; Sudan, P.; Mauron, Ph.; Emmenegger, Ch.
      Journal of Power Sources (2003), 118 (1-2), 1-7CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
      The challenge for H storage materials is to pack H atoms or mols. as close as possible. Light wt. group 3 metals, e.g. Al and B, are able to bind 4 H atoms and form, together with an alkali metal, an ionic or at least partially covalent compd. These compds. are rather stable and often desorb the H only above their m.ps. Complex hydrides like NaAlH4, when catalyzed, decomp. already at room temp. LiBH4, a complex hydride which consists 18% of H, was studied. H desorption from LiBH4 was catalyzed by SiO2 and 13.5% of the H was liberated at 200°.
    20. 20
      Umegaki, T.; Yan, J. M.; Zhang, X. B.; Shioyama, H.; Kuriyama, N.; Xu, Q. Boron- and nitrogen-based chemical hydrogen storage materials. Int. J. Hydrogen Energy 2009, 34 (5), 2303– 2311,  DOI: 10.1016/j.ijhydene.2009.01.002
      20
      Boron- and nitrogen-based chemical hydrogen storage materials
      Umegaki, Tetsuo; Yan, Jun-Min; Zhang, Xin-Bo; Shioyama, Hiroshi; Kuriyama, Nobuhiro; Xu, Qiang
      International Journal of Hydrogen Energy (2009), 34 (5), 2303-2311CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
      A review. Boron- and nitrogen-based chem. hydrides are expected to be potential hydrogen carriers for PEM fuel cells because of their high hydrogen contents. Significant efforts have been devoted to decrease their dehydrogenation and hydrogenation temps. and enhance the reaction kinetics. This article presents an overview of the boron- and nitrogen-based compds. as hydrogen storage materials.
    21. 21
      Schuth, F.; Bogdanovic, B.; Felderhoff, M. Light metal hydrides and complex hydrides for hydrogen storage. Chem. Commun. 2004, 20, 2249– 2258,  DOI: 10.1039/B406522K
      There is no corresponding record for this reference.
    22. 22
      Duchene, L.; Kuhnel, R.-S.; Stilp, E.; Cuervo Reyes, E.; Remhof, A.; Hagemann, H.; Battaglia, C. A stable 3 V all-solid-state sodium-ion battery based on a closo-borate electrolyte. Energy Environ. Sci. 2017, 10 (12), 2609– 2615,  DOI: 10.1039/C7EE02420G
      22
      A stable 3 V all-solid-state sodium-ion battery based on a closo-borate electrolyte
      Duchene, L.; Kuhnel, R.-S.; Stilp, E.; Cuervo Reyes, E.; Remhof, A.; Hagemann, H.; Battaglia, C.
      Energy & Environmental Science (2017), 10 (12), 2609-2615CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      We report on a particularly stable 3 V all-solid-state sodium-ion battery built using a closo-borate based electrolyte, namely Na2(B12H12)0.5(B10H10)0.5. Battery performance is enhanced through the creation of an intimate cathode-electrolyte interface resulting in reversible and stable cycling with a capacity of 85 mA h g-1 at C/20 and 80 mA h g-1 at C/5 with more than 90% capacity retention after 20 cycles at C/20 and 85% after 250 cycles at C/5. We also discuss the effect of cycling outside the electrochem. stability window and show that electrolyte decompn. leads to faster though not crit. capacity fading. Our results demonstrate that owing to their high stability and cond. closo-borate based electrolytes could play a significant role in the development of a competitive all-solid-state sodium-ion battery technol.
    23. 23
      Asakura, R.; Duchene, L.; Kuhnel, R. S.; Remhof, A.; Hagemann, H.; Battaglia, C. Electrochemical oxidative stability of hydroborate-based solid state electrolytes. ACS Appl. Energy Mater. 2019, 2 (9), 6924– 6930,  DOI: 10.1021/acsaem.9b01487
      23
      Electrochemical Oxidative Stability of Hydroborate-Based Solid-State Electrolytes
      Asakura, Ryo; Duchene, Leo; Kuhnel, Ruben-Simon; Remhof, Arndt; Hagemann, Hans; Battaglia, Corsin
      ACS Applied Energy Materials (2019), 2 (9), 6924-6930CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)
      A robust methodol. is reported based on linear sweep voltammetry to det. exptl. the electrochem. oxidative stability of hydroborate-based solid-state electrolytes for all-solid-state batteries. To accelerate kinetics and improve the sensitivity to decompn., different solid-state electrolyte/carbon composites are explored and a low scan rate of 10μV s-1 is employed. Using LiBH4 as a model system, it is shown that proper selection of the conductive carbon and its ratio in the composite are important for an accurate detn. of the intrinsic oxidative stability. This method is robust with respect to the choice of the current collector material and the ionic cond. of the solid-state electrolyte. The measured oxidative stability of LiBH4 of 2.0 V vs. Li+/Li is in good agreement with the value predicted by first-principles calcns. The irreversible electrochem. decompn. of LiBH4 outside the oxidative stability limit is independently confirmed by galvanostatic cycling. This method is applied to reassess the electrochem. oxidative stability of selected, highly conductive hydroborate-based solid-state electrolytes, including Li2(CB9H10)(CB11H12), Na3(BH4)(B12H12), Na4(B12H12)(B10H10), and Na4(CB11H12)2(B12H12), and the necessity of selecting cathode materials is emphasized for all-solid-state batteries based on the accurate understanding of the oxidative stability of the solid-state electrolytes.
    24. 24
      Kim, S.; Oguchi, H.; Toyama, N.; Sato, T.; Takagi, S.; Otomo, T.; Arunkumar, D.; Kuwata, N.; Kawamura, J.; Orimo, S. A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries. Nat. Commun. 2019, 10, 1081,  DOI: 10.1038/s41467-019-09061-9
      24
      A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries
      Kim Sangryun; Toyama Naoki; Sato Toyoto; Takagi Shigeyuki; Orimo Shin-Ichi; Oguchi Hiroyuki; Orimo Shin-Ichi; Otomo Toshiya; Arunkumar Dorai; Kuwata Naoaki; Kawamura Junichi
      Nature communications (2019), 10 (1), 1081 ISSN:.
      All-solid-state batteries incorporating lithium metal anode have the potential to address the energy density issues of conventional lithium-ion batteries that use flammable organic liquid electrolytes and low-capacity carbonaceous anodes. However, they suffer from high lithium ion transfer resistance, mainly due to the instability of the solid electrolytes against lithium metal, limiting their use in practical cells. Here, we report a complex hydride lithium superionic conductor, 0.7Li(CB9H10)-0.3Li(CB11H12), with excellent stability against lithium metal and a high conductivity of 6.7 × 10(-3) S cm(-1) at 25 °C. This complex hydride exhibits stable lithium plating/stripping reaction with negligible interfacial resistance (<1 Ω cm(2)) at 0.2 mA cm(-2), enabling all-solid-state lithium-sulfur batteries with high energy density (>2500 Wh kg(-1)) at a high current density of 5016 mA g(-1). The present study opens up an unexplored research area in the field of solid electrolyte materials, contributing to the development of high-energy-density batteries.
    25. 25
      Matsuo, M.; Nakamori, Y.; Orimo, S.; Maekawa, H.; Takamura, H. Lithium superionic conduction in lithium borohydride accompanied by structural transition. Appl. Phys. Lett. 2007, 91 (22), 224103,  DOI: 10.1063/1.2817934
      25
      Lithium superionic conduction in lithium borohydride accompanied by structural transition
      Matsuo, Motoaki; Nakamori, Yuko; Orimo, Shin-ichi; Maekawa, Hideki; Takamura, Hitoshi
      Applied Physics Letters (2007), 91 (22), 224103/1-224103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The elec. cond. of LiBH4 measured by a.c. complex impedance increased by 3 orders of magnitude due to structural transition from orthorhombic to hexagonal at ∼390 K. The hexagonal phase exhibited a high elec. cond. of about 10-3 S/cm. The cond. calcd. from the Nernst-Einstein equation using the correlation time obtained from 7Li NMR agreed with the measured elec. cond. The elec. cond. in the hexagonal phase is due to Li superionic conduction.
    26. 26
      Soulié, J. P.; Renaudin, G.; Černý, R.; Yvon, K. Lithium boro-hydride LiBH4: I. Crystal structure. J. Alloys Compd. 2002, 346 (1), 200– 205,  DOI: 10.1016/S0925-8388(02)00521-2
      26
      Lithium boro-hydride LiBH4. I. Crystal structure
      Soulie, J-Ph.; Renaudin, G.; Cerny, R.; Yvon, K.
      Journal of Alloys and Compounds (2002), 346 (1-2), 200-205CODEN: JALCEU; ISSN:0925-8388. (Elsevier Science B.V.)
      The crystal structure of LiBH4 was studied by synchrotron x-ray powder diffraction at room temp. and at 408 K. At room temp. it has orthorhombic symmetry [space group Pnma, a 7.17858(4), b 4.43686(2), c 6.80321(4) Å]. The tetrahedral (BH4)- anions (point symmetry m) are aligned along two orthogonal directions and are strongly distorted with respect to bond lengths [B-H 1.04(2)-1.28(1) Å] and bond angles [H-B-H 85.1(9)-120.1(9)°]. As the temp. is increased the structure undergoes a 1st-order transition and becomes hexagonal (space group P63mc, a 4.27631(5), c 6.94844(8) Å at T = 408 K). The (BH4)- tetrahedra align along c, become more sym. [point symmetry 3m, B-H 1.27(2)-1.29(2) Å, H-B-H 106.4(2)-112.4(9)°] and show displacement amplitudes that are consistent with dynamical disorder about their trigonal axis.
    27. 27
      Aeberhard, P. C.; Refson, K.; David, W. I. F. Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4. Phys. Chem. Chem. Phys. 2013, 15 (21), 8081– 8087,  DOI: 10.1039/c3cp44520h
      27
      Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4
      Aeberhard, Philippe C.; Refson, Keith; David, William I. F.
      Physical Chemistry Chemical Physics (2013), 15 (21), 8081-8087CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The crystal structure of the hexagonal phase of solid lithium borohydride (LiBH4) is studied by ab initio mol. dynamics simulations of both the low and high-temp. phases. A temp. range of 200-535 K is simulated with the aim of characterizing the disorder in the high-temp. structure in detail. The mechanism and kinetics of the reorientational motion of the borohydride units (BH4-) are detd. and are consistent with published neutron scattering expts.; it is found that rotational diffusivity increases by an order of magnitude at the phase transition temp. The av. equil. orientation is characterized by a broad distribution of orientations, and reorientational jumps do not occur between sharply defined orientations. In addn., split positions with partial occupancy for the lithium and boron atoms are found (in agreement with previous theor. studies), which, together with the disordered BH4- orientational distribution in equil., lead to the conclusion that the correct crystallog. space group of the high-temp. phase is P63/mmc rather than P63mc.
    28. 28
      Matsuo, M.; Takamura, H.; Maekawa, H.; Li, H. W.; Orimo, S. Stabilization of lithium superionic conduction phase and enhancement of conductivity of LiBH4 by LiCl addition. Appl. Phys. Lett. 2009, 94 (8), 084103,  DOI: 10.1063/1.3088857
      28
      Stabilization of lithium superionic conduction phase and enhancement of conductivity of LiBH4 by LiCl addition
      Matsuo, Motoaki; Takamura, Hitoshi; Maekawa, Hideki; Li, Hai-Wen; Orimo, Shin-Ichi
      Applied Physics Letters (2009), 94 (8), 084103/1-084103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      LiBH4 exhibits lithium superionic conduction accompanied by structural transition at around 390 K. Addn. of LiCl to LiBH4 drastically affects both the transition and elec. cond.: Transition from low-temp. (LT) to high-temp. (HT) phases in LiBH4 is obsd. at 370 K upon heating and the HT phase can be retained at 350-330 K upon cooling. Further, the cond. in the LT phase is more than one or two orders of magnitude higher than that of pure LiBH4. These properties could be attributed to the dissoln. of LiCl into LiBH4, suggested by in situ x-ray diffraction measurement. (c) 2009 American Institute of Physics.
    29. 29
      Oguchi, H.; Matsuo, M.; Hummelshoj, J. S.; Vegge, T.; Norskov, J. K.; Sato, T.; Miura, Y.; Takamura, H.; Maekawa, H.; Orimo, S. Experimental and computational studies on structural transitions in the LiBH4-LiI pseudobinary system. Appl. Phys. Lett. 2009, 94 (14), 141912,  DOI: 10.1063/1.3117227
      29
      Experimental and computational studies on structural transitions in the LiBH4-LiI pseudobinary system
      Oguchi, H.; Matsuo, M.; Hummelshoj, J. S.; Vegge, T.; Norskov, J. K.; Sato, T.; Miura, Y.; Takamura, H.; Maekawa, H.; Orimo, S.
      Applied Physics Letters (2009), 94 (14), 141912/1-141912/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Structural transition properties of the LiBH4+xLiI (x = 0-1.00)pseudobinary system were examd. by powder x-ray diffraction and DSC combined with periodic d. functional theory calcns. The authors exptl. and computationally confirmed the stabilization of the high-temp. hexagonal, Li super(fast-)ionic conduction phase of LiBH4 with x = 0.33 and 1.00, and the results also imply the existence of intermediate phases with x = 0.07-0.20. The studies are of importance for further development of LiBH4 and the derived hydrides as solid-state electrolytes. (c) 2009 American Institute of Physics.
    30. 30
      Matsuo, M.; Remhof, A.; Martelli, P.; Caputo, R.; Ernst, M.; Miura, Y.; Sato, T.; Oguchi, H.; Maekawa, H.; Takamura Complex hydrides with (BH4)− and (NH2)− anions as new lithium fast-ion conductors. J. Am. Chem. Soc. 2009, 131 (45), 16389,  DOI: 10.1021/ja907249p
      30
      Complex Hydrides with (BH4)- and (NH2)- Anions as New Lithium Fast-Ion Conductors
      Matsuo, Motoaki; Remhof, Arndt; Martelli, Pascal; Caputo, Riccarda; Ernst, Matthias; Miura, Yohei; Sato, Toyoto; Oguchi, Hiroyuki; Maekawa, Hideki; Takamura, Hitoshi; Borgschulte, Andreas; Zuttel, Andreas; Orimo, Shin-Ichi
      Journal of the American Chemical Society (2009), 131 (45), 16389-16391CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Some of the authors have reported that a complex hydride, Li(BH4), with the (BH4)- anion exhibits lithium fast-ion conduction (more than 1 × 10-3 S/cm) accompanied by the structural transition at ∼390 K for the first time in 30 years since the conduction in Li2(NH) was reported in 1979. Here we report another conceptual study and remarkable results of Li2(BH4)(NH2) and Li4(BH4)(NH2)3 combined with the (BH4)- and (NH2)- anions showing ion conductivities 4 orders of magnitude higher than that for Li(BH4) at RT, due to being provided with new occupation sites for Li+ ions. Both Li2(BH4)(NH2) and Li4(BH4)(NH2)3 exhibit a lithium fast-ion cond. of 2 × 10-4 S/cm at RT, and the activation energy for conduction in Li4(BH4)(NH2)3 is evaluated to be 0.26 eV, less than half those in Li2(BH4)(NH2) and Li(BH4). This study not only demonstrates an important direction in which to search for higher ion cond. in complex hydrides but also greatly increases the material variations of solid electrolytes.
    31. 31
      Yao, Z. P.; Kim, S.; Michel, K.; Zhang, Y. S.; Aykol, M.; Wolverton, C. Stability and conductivity of cation- and anion-substituted LiBH4-based solid-state electrolytes. Phys. Rev. Mater. 2018, 2 (6), 065402,  DOI: 10.1103/PhysRevMaterials.2.065402
      31
      Stability and conductivity of cation- and anion-substituted LiBH4-based solid-state electrolytes
      Yao, Zhenpeng; Kim, Soo; Michel, Kyle; Zhang, Yongsheng; Aykol, Muratahan; Wolverton, Chris
      Physical Review Materials (2018), 2 (6), 065402CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
      The high-temp. phase of LiBH4 (HT-LiBH4) exhibits a promisingly high lithium ion cond. but is unstable at room temp. We use d. functional theory (DFT) calcns. to investigate the stabilization effect of halogen and alkali cation/anion substitutions on HT-LiBH4 as well the underlying mechanism for the high lithium ion cond. We find that increasing the substituent concn. enhances the stabilization of HT-LiBH4 (i.e., the DFT energy difference between the low- and high-temp. forms of substituted LiBH4 is reduced). Cation/anion substitution also leads to a higher Li defect (vacancy, interstitial, and Frenkel) formation energy, thereby reducing the Li defect (vacancy, interstitial, and Frenkel) concns. Using DFT migration barriers input into kinetic Monte Carlo simulations and the Materials INTerface (MINT) framework, we calc. the room-temp. lithium ion conductivities for Li(BH4)1-xIx (x=0.25 and 0.5) and Li1-yKyBH4 (y=0.25). Our calcns. suggest that the lower I concn. leads to a higher lithium ion cond. of 5.7×10-3 S/cm compared with that of Li(BH4)0.5I0.5 (4.2×10-5 S/cm) because of the formation of more Li-related defects. Based on our findings, we suggest that the stabilization of HT-LiBH4-based lithium ion conductors can be controlled by carefully tuning the cation/anion substituent concns. to maximize the lithium ionic conductivities of the specific system.
    32. 32
      Mezaki, T.; Kuronuma, Y.; Oikawa, I.; Kamegawa, A.; Takamura, H. Li-ion conductivity and phase stability of Ca-doped LiBH4 under high pressure. Inorg. Chem. 2016, 55 (20), 10484– 10489,  DOI: 10.1021/acs.inorgchem.6b01678
      32
      Li-Ion Conductivity and Phase Stability of Ca-Doped LiBH4 under High Pressure
      Mezaki, Takeya; Kuronuma, Yota; Oikawa, Itaru; Kamegawa, Atsunori; Takamura, Hitoshi
      Inorganic Chemistry (2016), 55 (20), 10484-10489CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The effect of Ca doping on the Li-ion cond. and phase stability of the rock-salt-type LiBH4 phase emerging under high pressures in the range of gigapascals has been investigated. Insitu electrochem. measurements under high pressure were performed using a cubic-anvil-type app. Ca doping drastically enhanced the ionic cond. of the rock-salt-type phase: the ionic cond. of undoped and 5 mol %Ca-doped LiBH4 was 2.2 × 10-4 and 1.4 × 10-2 S·cm-1 under 4.0 GPa at 220 °C, resp. The activation vol. of LiBH4-5 mol %Ca(BH4)2, at 3.2 cm3/mol, was comparable to that of other fast ionic conductors, such as lithium titanate and NASICONs. Moreover, Ca-doped LiBH4 showed lithium plating-stripping behavior in a cyclic voltammogram. These results indicate that the cond. enhancement by Ca doping can be attributed to the formation of a LiBH4-Ca(BH4)2 solid soln.; however, the solid soln. decompd. into the orthorhombic LiBH4 phase and the orthorhombic Ca(BH4)2 phase after unloading the high pressure.
    33. 33
      Ley, M. B.; Jorgensen, M.; Cerny, R.; Filinchuk, Y.; Jensen, T. R. From M(BH4)3 (M = La, Ce) Borohydride frameworks to controllable synthesis of porous hydrides and ion conductors. Inorg. Chem. 2016, 55 (19), 9748– 9756,  DOI: 10.1021/acs.inorgchem.6b01526
      33
      From M(BH4)3 (M = La, Ce) Borohydride Frameworks to Controllable Synthesis of Porous Hydrides and Ion Conductors
      Ley, Morten Brix; Joergensen, Mathias; Cerny, Radovan; Filinchuk, Yaroslav; Jensen, Torben R.
      Inorganic Chemistry (2016), 55 (19), 9748-9756CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Rare earth metal borohydrides show a no. of interesting properties, e.g., Li ion cond. and luminescence, and the materials is well explored. However, previous attempts to obtain M(BH4)3 (M = La, Ce) by reacting MCl3 and LiBH4 yielded LiM(BH4)3Cl. Here, a synthetic approach is presented, which gave M(BH4)3 (M = La, Ce) via formation of intermediate complexes with di-Me sulfide. The cubic c-Ce(BH4)3 (Fm‾3c) is isostructural to high-temp. polymorphs of A(BH4)3 (A = Y, Sm, Er, Yb) borohydrides. The larger size of the Ce3+ ion makes the empty void in the open ReO3-type framework structure potentially accessible to small guest mols. like H2. Another new rhombohedral polymorph, r-M(BH4)3 (M = La, Ce), is a closed form of the framework, prone to stacking faults. The new compds. M(BH4)3 (M = La, Ce) can be combined with LiCl by an addn. reaction to form LiM(BH4)3Cl also known as Li4[M4(BH4)12Cl4]; the latter contains the unique tetranuclear cluster [M4(BH4)12Cl4]4- and shows high Li-ion cond. This reaction pathway opens a way to synthesize A4[M4(BH4)12X4] (M = La, Ce) compds. with different anions (X) and metal ions (A) and potentially high ion cond.
    34. 34
      Rude, L. H.; Groppo, E.; Arnbjerg, L. M.; Ravnsbaek, D. B.; Malmkjaer, R. A.; Filinchuk, Y.; Baricco, M.; Besenbacher, F.; Jensen, T. R. Iodide substitution in lithium borohydride, LiBH4-LiI. J. Alloys Compd. 2011, 509 (33), 8299– 8305,  DOI: 10.1016/j.jallcom.2011.05.031
      34
      Iodide substitution in lithium borohydride, LiBH4-LiI
      Rude, Line H.; Groppo, Elena; Arnbjerg, Lene M.; Ravnsbaek, Dorthe B.; Malmkjaer, Regitze A.; Filinchuk, Yaroslav; Baricco, Marcello; Besenbacher, Flemming; Jensen, Torben R.
      Journal of Alloys and Compounds (2011), 509 (33), 8299-8305CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH4-LiI. The structural chem. and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance IR spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is obsd. as formation of two solid solns. of Li(BH4)1-xIx, which merge into one upon heating. The solid solns. have hexagonal structures (space group P63 mc) similar to the structures of h-LiBH4 and β-LiI. The solid solns. have iodide contents in the range ∼0-62 mol% and are stable from below room temp. to the m.p. at 330 °C. Thus the stability of the solid solns. is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH4 and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid soln. Li(BH4)1-xIx, measured by the Sieverts method, are improved as compared to those of LiBH4. After four cycles of hydrogen release and uptake the Li(BH4)1-xIx solid soln. maintains 68% of the calcd. hydrogen storage capacity in contrast to LiBH4, which maintains only 25% of the storage capacity after two cycles under identical conditions.
    35. 35
      Miyazaki, R.; Karahashi, T.; Kumatani, N.; Noda, Y.; Ando, M.; Takamura, H.; Matsuo, M.; Orimo, S.; Maekawa, H. Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH4. Solid State Ionics 2011, 192 (1), 143– 147,  DOI: 10.1016/j.ssi.2010.05.017
      35
      Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH4
      Miyazaki, R.; Karahashi, T.; Kumatani, N.; Noda, Y.; Ando, M.; Takamura, H.; Matsuo, M.; Orimo, S.; Maekawa, H.
      Solid State Ionics (2011), 192 (1), 143-147CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
      In the present work, we focus attention on the effect of LiI addn. to newly discovered pure lithium ion conductor, LiBH4. Solid soln. of the compn. LiBH4-LiI (LiI: 6.25-33.3 mol%) was synthesized by solid state reaction. Elec. cond. was measured from room temp. to 140 °C by ac impedance method, which revealed the fast-ion conduction phase of LiBH4 can be stabilized to lower temp., below the room temp. Solid soln. with LiI showed higher conductivities and lower activation energies in comparison with LiBH4. Powder XRD measurement was carried out at 120 °C (just above the transition temp. of LiBH4). The lattice consts. of the solid soln. were detd. DSC measurement showed a systematic compositional dependence on the transition temp. The stabilization mechanism was discussed.
    36. 36
      Sveinbjornsson, D.; Myrdal, J. S. G.; Blanchard, D.; Bentzen, J. J.; Hirata, T.; Mogensen, M. B.; Norby, P.; Orimo, S. I.; Vegge, T. Effect of heat treatment on the lithium ion conduction of the LiBH4-Lil solid solution. J. Phys. Chem. C 2013, 117 (7), 3249– 3257,  DOI: 10.1021/jp310050g
      36
      Effect of Heat Treatment on the Lithium Ion Conduction of the LiBH4-LiI Solid Solution
      Sveinbjornsson, Dadi; Myrdal, Jon Steinar Gardarsson; Blanchard, Didier; Bentzen, Janet Jonna; Hirata, Takumi; Mogensen, Mogens Bjerg; Norby, Poul; Orimo, Shin-ichi; Vegge, Tejs
      Journal of Physical Chemistry C (2013), 117 (7), 3249-3257CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The LiBH4-LiI solid soln. is a good Li+ conductor and a promising cryst. electrolyte for all-solid-state lithium based batteries. The focus of the present work is on the effect of heat treatment on the Li+ conduction. Solid solns. with a LiI content of 6.25-50% were synthesized by high-energy ball milling and annealed at 140°. Powder x-ray diffraction and SEM were used for characterizing the samples and for comparing their crystallite sizes and the d. of defects before and after the annealing. The Li+ cond. was measured using impedance spectroscopy, resulting in conductivities exceeding 0.1 mS/cm at 30° and 10 mS/cm at 140°. It was found that the formation of defect-rich microstructures during ball milling increased the specific conductivities of these compds. significantly. The phase transition temps. between the orthorhombic and hexagonal structures of LiBH4 were measured using differential scanning calorimetry. The measured transition temps. range from 100 to -70° and show a linear decrease of 70° for every 10% of LiI addn. up to a LiI content of 25%. The relative stability of the two structures was calcd. using d. functional theory, and together with the differential scanning calorimetry measurements, the calcns. were used to evaluate the change in entropic difference between the structures with LiI content.
    37. 37
      Maekawa, H.; Matsuo, M.; Takamura, H.; Ando, M.; Noda, Y.; Karahashi, T.; Orimo, S. I. Halide-stabilized LiBH4, a room-temperature lithium fast-ion conductor. J. Am. Chem. Soc. 2009, 131 (3), 894,  DOI: 10.1021/ja807392k
      37
      Halide-Stabilized LiBH4, a Room-Temperature Lithium Fast-Ion Conductor
      Maekawa, Hideki; Matsuo, Motoaki; Takamura, Hitoshi; Ando, Mariko; Noda, Yasuto; Karahashi, Taiki; Orimo, Shin-ichi
      Journal of the American Chemical Society (2009), 131 (3), 894-895CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A review on development of lithium superionic conductors based on LiBH4 and lithium halides. Using these compds., room-temp. high lithium ion cond. was imparted to a hydride system that had not been considered a lithium ion electrolyte. The electrochem. measurements showed a great advantage of this material as an extremely lightwt. lithium electrolyte for high energy d. batteries. Versatile properties of these materials make them suitable for use in all-solid-state batteries.
    38. 38
      Stephenson, C. C.; Rice, D. W.; Stockmayer, W. H. Order-disorder transitions in the alkali borohydrides. J. Chem. Phys. 1955, 23 (10), 1960– 1960,  DOI: 10.1063/1.1740617
      38
      Order-disorder transitions in the alkali borohydrides
      Stephenson, C. C.; Rice, D. W.; Stockmayer, W. H.
      Journal of Chemical Physics (1955), 23 (), 1960CODEN: JCPSA6; ISSN:0021-9606.
      Order-disorder transitions were obsd. at 76°K. for KBH4, 44°K. for RbBH4, and 27°K. for CsBH4. A plot of the log of the transition temp. vs. the corresponding values of the distance between the centers of neighboring borohydride ions yielded a straight line. This straight line is to be expected if the higher energy of the disordered phase is due principally to increased overlap energy.
    39. 39
      Yan, Y. G.; Kuhnel, R. S.; Remhof, A.; Duchene, L.; Reyes, E. C.; Rentsch, D.; Lodziana, Z.; Battaglia, C. A lithium amide-borohydride solid-state electrolyte with lithium-ion conductivities comparable to liquid electrolytes. Adv. Energy Mater. 2017, 7 (19), 1700294,  DOI: 10.1002/aenm.201700294
      There is no corresponding record for this reference.
    40. 40
      Blanchard, D.; Nale, A.; Sveinbjornsson, D.; Eggenhuisen, T. M.; Verkuijlen, M. H. W.; Suwarno; Vegge, T.; Kentgens, A. P. M.; de Jongh, P. E. Nanoconfined LiBH4 as a fast lithium ion conductor. Adv. Funct. Mater. 2015, 25 (2), 184– 192,  DOI: 10.1002/adfm.201402538
      40
      Nanoconfined LiBH4 as a Fast Lithium Ion Conductor
      Blanchard, Didier; Nale, Angeloclaudio; Sveinbjoernsson, Dadi; Eggenhuisen, Tamara M.; Verkuijlen, Margriet H. W.; Suwarno; Vegge, Tejs; Kentgens, Arno P. M.; de Jongh, Petra E.
      Advanced Functional Materials (2015), 25 (2), 184-192CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid-state batteries. LiBH4 is a promising solid electrolyte for Li-ion batteries. It displays high lithium mobility, although only above 110° at which a transition to a high temp. hexagonal structure occurs. Herein, it is shown that confining LiBH4 in the pores of ordered mesoporous silica scaffolds leads to high Li+ cond. (0.1 mS cm-1) at room temp. This is a surprisingly high value, esp. given that the nanocomposites comprise 42 vol% of SiO2. Solid state 7Li NMR confirmed that the high cond. can be attributed to a very high Li+ mobility in the solid phase at room temp. Confinement of LiBH4 in the pores leads also to a lower solid-solid phase transition temp. than for bulk LiBH4. However, the high ionic mobility is assocd. with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO2 pore walls. These results point to a new strategy to design low-temp. ion conducting solids for application in all solid-state lithium ion batteries, which could enable safe use of Li-metal anodes.
    41. 41
      Epp, V.; Wilkening, M. Motion of Li+ in nanoengineered LiBH4 and LiBH4:Al2O3 comparison with the microcrystalline form. ChemPhysChem 2013, 14 (16), 3706– 3713,  DOI: 10.1002/cphc.201300743
      41
      Motion of Li+ in Nanoengineered LiBH4 and LiBH4:Al2O3 Comparison with the Microcrystalline Form
      Epp, Viktor; Wilkening, Martin
      ChemPhysChem (2013), 14 (16), 3706-3713CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Nanocryst. LiBH4 and the two-phase analog LiBH4:Al2O3 have been prepd. by ball milling and used as model systems to track the changes in NMR relaxation rates with respect to coarse-grained, thermodynamically stable LiBH4. This revealed that interface (nano)engineering influences the hexagonal-to-orthorhombic phase transition and thus alters the ion-transport properties of Li in one- and two-phase LiBH4 towards higher diffusivities at lower temps.
    42. 42
      Choi, Y. S.; Lee, Y. S.; Oh, K. H.; Cho, Y. W. Interface-enhanced Li ion conduction in a LiBH4-SiO2 solid electrolyte. Phys. Chem. Chem. Phys. 2016, 18 (32), 22540– 22547,  DOI: 10.1039/C6CP03563A
      42
      Interface-enhanced Li ion conduction in a LiBH4-SiO2 solid electrolyte
      Choi, Yong Seok; Lee, Young-Su; Oh, Kyu Hwan; Cho, Young Whan
      Physical Chemistry Chemical Physics (2016), 18 (32), 22540-22547CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      A fast solid state Li ion conductor composed of LiBH4 and SiO2 is developed by means of interface engineering. A composite of LiBH4-SiO2 was simply synthesized by high energy ball-milling, and two types of SiO2 (MCM-41 and fumed silica) having different sp. surface areas were used to evaluate the effect of the LiBH4/SiO2 interface on the ionic cond. enhancement. The ionic cond. of the ball-milled LiBH4-MCM-41 and LiBH4-fumed silica mixt. is as high as 10-5 S cm-1 and 10-4 S cm-1 at room temp., resp. In particular, the cond. of the latter is comparable to the LiBH4 melt-infiltrated into MCM-41. The conductivities of the LiBH4-fumed silica mixts. at different mixing ratios were analyzed employing a continuum percolation model, and the cond. of the LiBH4/SiO2 interface layer is estd. to be 105 times higher than that of pure bulk LiBH4. The result highlights the importance of the interface and indicates that significant enhancement in ionic cond. can be achieved via interface engineering.
    43. 43
      Choi, Y. S.; Lee, Y. S.; Choi, D. J.; Chae, K. H.; Oh, K. H.; Cho, Y. W. Enhanced Li ion conductivity in LiBH4-Al2O3 mixture via interface engineering. J. Phys. Chem. C 2017, 121 (47), 26209– 26215,  DOI: 10.1021/acs.jpcc.7b08862
      There is no corresponding record for this reference.
    44. 44
      Gutowska, A.; Li, L. Y.; Shin, Y. S.; Wang, C. M. M.; Li, X. H. S.; Linehan, J. C.; Smith, R. S.; Kay, B. D.; Schmid, B.; Shaw, W. Nanoscaffold mediates hydrogen release and the reactivity of ammonia borane. Angew. Chem., Int. Ed. 2005, 44 (23), 3578– 3582,  DOI: 10.1002/anie.200462602
      44
      Nanoscaffold mediates hydrogen release and the reactivity of ammonia borane
      Gutowska, Anna; Li, Liyu; Shin, Yongsoon; Wang, Chongmin M.; Li, Xiaohong S.; Linehan, John C.; Smith, R. Scott; Kay, Bruce D.; Schmid, Benjamin; Shaw, Wendy; Gutowski, Maciej; Autrey, Tom
      Angewandte Chemie, International Edition (2005), 44 (23), 3578-3582CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      H-rich materials infused in nanoscaffolds offer a promising approach to on-board H storage. A mesoporous scaffold decreases the temp. for H release from NH3 borane (AB), a conventional H-storage material, to <80° and increases the purity of the H released.
    45. 45
      Berube, V.; Radtke, G.; Dresselhaus, M.; Chen, G. Size effects on the hydrogen storage properties of nanostructured metal hydrides: A review. Int. J. Energy Res. 2007, 31 (6–7), 637– 663,  DOI: 10.1002/er.1284
      45
      Size effects on the hydrogen storage properties of nanostructured metal hydrides: a review
      Berube, Vincent; Radtke, Gregg; Dresselhaus, Mildred; Chen, Gang
      International Journal of Energy Research (2007), 31 (6-7), 637-663CODEN: IJERDN; ISSN:0363-907X. (John Wiley & Sons Ltd.)
      This review summarizes the effects that nanotechnol. can have on the main properties of metal hydrides and highlights the main competing behaviors between the system requirements, the necessary trade-offs, and the research priorities necessary to obtain hydride storage materials for practical automotive applications. Metal hydrides are often preferred over pressurized gas and other hydrogen storage methods because of their gravimetric and volumetric storage capacities and safe operating pressures. In addn. to the hydrogen storage capacity, other properties that have often been disregarded must now be addressed before hydrogen storage in metal hydrides becomes feasible. The slow hydriding/dehydriding kinetics, high release temp., low storage efficiency due to the high enthalpy of formation, and thermal management during the hydriding reaction remain important difficulties in meeting the objectives set by the Department of Energy for hydrogen storage systems. Nanotechnol. offers new ways of addressing those issues by taking advantage of the distinctive chem. and phys. properties obsd. in nanostructures. Nanostructured materials significantly improve the reaction kinetics, reduce the enthalpy of formation, and lower the hydrogen absorption and release temps. through destabilization of the metal hydride and multiple catalytic effects in the system. However, nanostructures can also lead to poor cyclability, degrdn. of the sorption properties, and a significant redn. of the thermal cond. that could make metal hydrides impractical for hydrogen storage.
    46. 46
      de Jongh, P. E.; Adelhelm, P. Nanosizing and nanoconfinement: new strategies towards meeting hydrogen storage goals. ChemSusChem 2010, 3 (12), 1332– 1348,  DOI: 10.1002/cssc.201000248
      46
      Nanosizing and Nanoconfinement: new Strategies Towards Meeting Hydrogen Storage Goals
      de Jongh, Petra E.; Adelhelm, Philipp
      ChemSusChem (2010), 3 (12), 1332-1348CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. H is expected to play an important role as an energy carrier in a future, more sustainable society. However, its compact, efficient, and safe storage is an unresolved issue. One of the main options is solid-state storage in hydrides. Unfortunately, no binary metal hydride satisfies all requirements regarding storage d. and H release and uptake. Increasingly complex hydride systems are studied, but high thermodn. stabilities as well as slow kinetics and poor reversibility are important barriers for practical application. Nanostructuring by ball-milling is an established method to reduce crystallite sizes and increase reaction rates. Since 5 years attention has also turned to alternative prepn. techniques that enable particle sizes <10 nm and are often used in conjunction with porous supports or scaffolds. The impact of nano-sizing and -confinement on the H sorption properties of metal hydrides is discussed. The authors illustrate possible prepn. strategies, provide insight into the reasons for changes in kinetics, reversibility and thermodn., and highlight important progress in this field. All in all the authors provide the reader with a clear view of how nano-sizing and -confinement can beneficially affect the H sorption properties of the most prominent materials that are currently considered for solid-state H storage.
    47. 47
      Ngene, P.; van Zwienen, M.; de Jongh, P. E. Reversibility of the hydrogen desorption from LiBH4: a synergetic effect of nanoconfinement and Ni addition. Chem. Commun. 2009, 46 (43), 8201– 8203,  DOI: 10.1039/c0cc03218b
      There is no corresponding record for this reference.
    48. 48
      Suwarno; Ngene, P.; Nale, A.; Eggenhuisen, T. M.; Oschatz, M.; Embs, J. P.; Remhof, A.; de Jongh, P. E. Confinement effects for lithium borohydride: comparing silica and carbon scaffolds. J. Phys. Chem. C 2017, 121 (8), 4197– 4205,  DOI: 10.1021/acs.jpcc.6b13094
      48
      Confinement Effects for Lithium Borohydride: Comparing Silica and Carbon Scaffolds
      Suwarno; Ngene, Peter; Nale, Angeloclaudio; Eggenhuisen, Tamara M.; Oschatz, Martin; Embs, Jan Peter; Remhof, Arndt; de Jongh, Petra E.
      Journal of Physical Chemistry C (2017), 121 (8), 4197-4205CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      LiBH4 is a promising material for hydrogen storage and as a solid-state electrolyte for Li ion batteries. Confining LiBH4 in porous scaffolds improves its hydrogen desorption kinetics, reversibility, and Li+ cond., but little is known about the influence of the chem. nature of the scaffold. Here, quasielastic neutron scattering and calorimetric measurements were used to study support effects for LiBH4 confined in nanoporous silica and carbon scaffolds. Pore radii were varied from 8 Å to 20 nm, with increasing confinement effects obsd. with decreasing pore size. For similar pore sizes, the confinement effects were more pronounced for silica than for carbon scaffolds. The shift in the solid-solid phase transition temp. is much larger in silica than in carbon scaffolds with similar pore sizes. A LiBH4 layer near the pore walls shows profoundly different phase behavior than cryst. LiBH4. This layer thickness was 1.94 ± 0.13 nm for the silica and 1.41 ± 0.16 nm for the carbon scaffolds. Quasi-elastic neutron scattering confirmed that the fraction of LiBH4 with high hydrogen mobility is larger for the silica than for the carbon nanoscaffold. These results clearly show that in addn. to the pore size the chem. nature of the scaffold also plays a significant role in detg. the hydrogen mobility and interfacial layer thickness in nanoconfined metal hydrides.
    49. 49
      Maier, J. Ionic-conduction in space charge regions. Prog. Solid State Chem. 1995, 23 (3), 171– 263,  DOI: 10.1016/0079-6786(95)00004-E
      49
      Ionic conduction in space charge regions
      Maier, Joachim
      Progress in Solid State Chemistry (1995), 23 (3), 171-263CODEN: PSSTAW; ISSN:0079-6786. (Elsevier)
      A review, with 140 refs., summarizing exptl. and theor. data with emphasis on defect chem. in space charges.
    50. 50
      Verdal, N.; Udovic, T. J.; Rush, J. J.; Liu, X. F.; Majzoub, E. H.; Vajo, J. J.; Gross, A. F. Dynamical perturbations of tetrahydroborate anions in LiBH4 due to nanoconfinement in controlled-pore carbon scaffolds. J. Phys. Chem. C 2013, 117 (35), 17983– 17995,  DOI: 10.1021/jp4063737
      50
      Dynamical Perturbations of Tetrahydroborate Anions in LiBH4 due to Nanoconfinement in Controlled-Pore Carbon Scaffolds
      Verdal, Nina; Udovic, Terrence J.; Rush, John J.; Liu, Xiangfeng; Majzoub, Eric H.; Vajo, John J.; Gross, Adam F.
      Journal of Physical Chemistry C (2013), 117 (35), 17983-17995CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Neutron vibrational spectroscopy and quasielastic neutron scattering (QENS) were used to probe the dynamical properties of BH4- anions in both bulk LiBH4 and LiBH4 confined in nanoporous carbons (NPCs) having ≤4-nm-diam., hexagonally arranged, cylindrical pores. The BH4- torsional band of the confined LiBH4 is significantly broadened relative to that of bulk LiBH4, reflecting a disruption of the bulk crystal lattice and thus a broader distribution of BH4- rotational potentials. QENS measurements of bulk orthorhombic LiBH4 indicate a single quasielastic component yielding an activation energy for localized BH4- jump reorientation of 19.2 ± 0.8 kJ/mol, consistent with previous QENS and NMR results. At room temp., the measurements are in good agreement with BH4- reorientational jumps about a single C2 or C3 tetrahedral symmetry axis, with evidence for multiaxis rotations emerging as the temp. increases. In contrast, the QENS spectra of the NPC-confined LiBH4 exhibit two quasielastic components, one an order of magnitude broader than the other. The narrower component is presumably assocd. with more slowly reorienting BH4- anions in the interior of the pores and the broader component with much more rapidly reorienting BH4- anions in the vicinity of the pore surfaces. For 4-nm pores, these components yield two corresponding activation energies for reorientation: 16 ± 1 and 10.6 ± 0.7 kJ/mol. Probably both components undergo single C2- or C3-axis reorientational jumps <330 K, albeit with one an order of magnitude faster than the other. By 400 K (which is above the bulk phase transition temp.), both reorient more diffusively around multiple axes. These results are qual. consistent with comparative dynamical measurements of LiBH4 confined in a 13-nm-av.-pore-size carbon aerogel, which exhibited a much broader pore size distribution.
    51. 51
      Breuer, S.; Uitz, M.; Wilkening, H. M. R. Rapid Li ion dynamics in the interfacial regions of nanocrystalline solids. J. Phys. Chem. Lett. 2018, 9 (8), 2093– 2097,  DOI: 10.1021/acs.jpclett.8b00418
      51
      Rapid Li ion dynamics in interfacial regions of nanocrystalline solids
      Breuer, S.; Uitz, M.; Wilkening, H. M. R.
      Journal of Physical Chemistry Letters (2018), 9 (8), 2093-2097CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Diffusive processes are ubiquitous in nature. In solid state physics, metallurgy and materials science the diffusivity of ions govern the functionality of many devices such as sensors or batteries. Motional processes on surfaces, across interfaces or through membranes can be quite different to that in the bulk. A direct, quant. description of such local diffusion processes is, however, rare. Here, we took advantage of 7Li longitudinal nuclear magnetic relaxation to study, on the at. length scale, the diffusive motion of lithium spins in the interfacial regions of nanocryst., orthorhombic LiBH4. Magnetization transients and free induction decays revealed a fast subset of Li ions having access to surface pathways that offer activation barriers (0.18 eV) much lower than those in the cryst. bulk regions (0.55 eV). These observations make orthorhombic borohydride a new nanostructured model system to study disorder-induced enhancements in interfacial diffusion processes.
    52. 52
      de Jongh, P. E.; Eggenhuisen, T. M. Melt infiltration: an emerging technique for the preparation of novel functional nanostructured materials. Adv. Mater. 2013, 25 (46), 6672– 6690,  DOI: 10.1002/adma.201301912
      52
      Melt Infiltration: an Emerging Technique for the Preparation of Novel Functional Nanostructured Materials
      de Jongh, Petra E.; Eggenhuisen, Tamara M.
      Advanced Materials (Weinheim, Germany) (2013), 25 (46), 6672-6690CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The rapidly expanding toolbox for design and prepn. is a major driving force for the advances in nanomaterials science and technol. Melt infiltration originates from the field of ceramic nanomaterials and is based on the infiltration of porous matrixes with the melt of an active phase or precursor. In recent years, it has become a technique for the prepn. of advanced materials: nanocomposites, pore-confined nanoparticles, ordered mesoporous and nanostructured materials. Although certain restrictions apply, mostly related to the melting behavior of the infiltrate and its interaction with the matrix, this review illustrates that it is applicable to a wide range of materials, including metals, polymers, ceramics, and metal hydrides and oxides. Melt infiltration provides an alternative to classical gas-phase and soln.-based prepn. methods, facilitating in several cases extended control over the nanostructure of the materials. This review starts with a concise discussion on the phys. and chem. principles for melt infiltration, and the practical aspects. In the second part of this contribution, specific examples are discussed of nanostructured functional materials with applications in energy storage and conversion, catalysis, and as optical and structural materials and emerging materials with interesting new phys. and chem. properties. Melt infiltration is a useful prepn. route for material scientists from different fields, and we hope this review may inspire the search and discovery of novel nanostructured materials.
    53. 53
      Unemoto, A.; Yasaku, S.; Nogami, G.; Tazawa, M.; Taniguchi, M.; Matsuo, M.; Ikeshoji, T.; Orimo, S. Development of bulk-type all-solid-state lithium-sulfur battery using LiBH4 electrolyte. Appl. Phys. Lett. 2014, 105 (8), 083901,  DOI: 10.1063/1.4893666
      53
      Development of bulk-type all-solid-state lithium-sulfur battery using LiBH4 electrolyte
      Unemoto, Atsushi; Yasaku, Syun; Nogami, Genki; Tazawa, Masaru; Taniguchi, Mitsugu; Matsuo, Motoaki; Ikeshoji, Tamio; Orimo, Shin-ichi
      Applied Physics Letters (2014), 105 (8), 083901/1-083901/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Stable battery operation of a bulk-type all-solid-state Li-S battery was demonstrated by using a LiBH4 electrolyte. The electrochem. activity of insulating elemental S as the pos. electrode was enhanced by the mutual dispersion of elemental S and C in the composite powders. Subsequently, a tight interface between the S-C composite and the LiBH4 powders was manifested only by cold-pressing owing to the highly deformable nature of the LiBH4 electrolyte. The high reducing ability of LiBH4 allows using the use of a Li neg. electrode that enhances the energy d. The results demonstrate the interface modification of insulating S and the architecture of an all-solid-state Li-S battery configuration with high energy d. (c) 2014 American Institute of Physics.
    54. 54
      Das, S.; Ngene, P.; Norby, P.; Vegge, T.; de Jongh, P. E.; Blanchard, D. All-solid-state lithium-sulfur battery based on a nanoconfined LiBH4 electrolyte. J. Electrochem. Soc. 2016, 163 (9), A2029– A2034,  DOI: 10.1149/2.0771609jes
      54
      All-Solid-State Lithium-Sulfur Battery Based on a Nanoconfined LiBH4 Electrolyte
      Das, Supti; Ngene, Peter; Norby, Poul; Vegge, Tejs; de Jongh, Petra E.; Blanchard, Didier
      Journal of the Electrochemical Society (2016), 163 (9), A2029-A2034CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      In this work we characterize all-solid-state lithium-sulfur batteries based on nano-confined LiBH4 in mesoporous silica as solid electrolytes. The nano-confined LiBH4 has fast ionic lithium cond. at room temp., 0.1 mScm-1, negligible electronic cond. and its cationic transport no. (t+ = 0.96), close to unity, demonstrates a purely cationic conductor. The electrolyte has an excellent stability against lithium metal. The behavior of the batteries is studied by cyclic voltammetry and repeated charge/discharge cycles in galvanostatic conditions. The batteries show good performance, delivering high capacities vs. sulfur mass, typically 1220 mAhg-1 after 40 cycles at moderate temp. (55°), 0.03 C rates and working voltage of 2 V.
    55. 55
      Lefevr, J.; Cervini, L.; Griffin, J. M.; Blanchard, D. Lithium conductivity and ions dynamics in LiBH4/SiO2 solid electrolytes studied by solid-state NMR and quasi-elastic neutron scattering and applied in lithium sulfur batteries. J. Phys. Chem. C 2018, 122 (27), 15264– 15275,  DOI: 10.1021/acs.jpcc.8b01507
      55
      Lithium Conductivity and Ions Dynamics in LiBH4/SiO2 Solid Electrolytes Studied by Solid-State NMR and Quasi-Elastic Neutron Scattering and Applied in Lithium-Sulfur Batteries
      Lefevr, Jessica; Cervini, Luca; Griffin, John M.; Blanchard, Didier
      Journal of Physical Chemistry C (2018), 122 (27), 15264-15275CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Composite solid-state electrolytes based on ball-milled LiBH4/SiO2 aerogel exhibit high lithium conductivities, and we have found an optimal wt. ratio of 30/70 wt % LiBH4/SiO2 with a cond. of 0.1 mS cm-1 at room temp. We have studied the Li+ and BH4- dynamics using quasi-elastic neutron scattering and solid-state NMR and found that only a small fraction (∼10%) of the ions have high mobilities, whereas most of the LiBH4 shows behavior similar to macrocryst. material. The modified LiBH4 is formed from interaction with the SiO2 surface and most probably from reaction with the surface silanol groups. We successfully applied these composite electrolytes in lithium-sulfur solid-state batteries. The batteries show reasonable capacity retention (794 mAh g-1 sulfur after 10 discharge-charge cycles, Coulombic efficiency of 88.8 ± 2.7%, and av. capacity loss of 7.2% during the first 10 cycles).
    56. 56
      Cheng, C.-F.; Zhou, W.; Ho Park, D.; Klinowski, J.; Hargreaves, M.; Gladden, L. F. Controlling the channel diameter of the mesoporous molecular sieve MCM-41. J. Chem. Soc., Faraday Trans. 1997, 93 (2), 359– 363,  DOI: 10.1039/a605136g
      56
      Controlling the channel diameter of the mesoporous molecular sieve MCM-41
      Cheng, Chi-Feng; Zhou, Wuzong; Park, Dong Ho; Klinowski, Jacek; Hargreaves, Mark; Gladden, Lynn F.
      Journal of the Chemical Society, Faraday Transactions (1997), 93 (2), 359-363CODEN: JCFTEV; ISSN:0956-5000. (Royal Society of Chemistry)
      The authors describe a simple method of controlling the channel diam. of the mesoporous mol. sieve MCM-41 in the 26.1-36.5 Å range and the wall thickness in the 13.4-26.8 Å range while using the same gel mixt. This is achieved by varying the synthesis temp. in the 70-200° range and/or reaction times in the 0.5-96 h range. The unit cell parameter, channel diam., thickness of the channel wall, surface area, d.p. and grain morphol. were monitored by x-ray diffraction, N2 adsorption, 29Si magic-angle-spinning NMR and TEM. MCM-41 with wider and thicker-walled channels and higher d.p. was prepd. at higher temps. and at longer reaction times. Thick-wall MCM-41 has higher thermal stability but lower surface area. The material with the thickest channel wall ever reported (26.8 Å) can withstand calcination at nearly 1000° with little structural damage. The authors suggest a mechanism for the increase of wall thickness and channel diam. Fascinating morphol. features involving sealed silicate tubes and vesicles up to 1200 Å in diam. are obsd.
    57. 57
      Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279 (5350), 548– 552,  DOI: 10.1126/science.279.5350.548
      57
      Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores
      Zhao, Dongyuan; Feng, Jianglin; Huo, Qisheng; Melosh, Nicholas; Frederickson, Glenn H.; Chmelka, Bradley F.; Stucky, Galen D.
      Science (Washington, D. C.) (1998), 279 (5350), 548-552CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Use of amphiphilic triblock copolymers to direct the organization of polymg. silica species has resulted in the prepn. of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approx. 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500°C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore vol. fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepd. over a wide range of uniform pore sizes and pore wall thicknesses at low temp. (35° to 80°C), using a variety of poly(alkylene oxide) triblock copolymers and by the addn. of cosolvent org. mols. The block copolymer species can be recovered for reuse by solvent extn. with ethanol or removed by heating at 140°C for 3 h, in both cases, yielding a product that is thermally stable in boiling water.
    58. 58
      Hartman, M. R.; Rush, J. J.; Udovic, T. J.; Bowman, R. C.; Hwang, S. J. Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy. J. Solid State Chem. 2007, 180 (4), 1298– 1305,  DOI: 10.1016/j.jssc.2007.01.031
      58
      Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy
      Hartman, Michael R.; Rush, John J.; Udovic, Terrence J.; Bowman, Robert C., Jr.; Hwang, Son-Jong
      Journal of Solid State Chemistry (2007), 180 (4), 1298-1305CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)
      The cryst. structure of 7Li11BH4 was studied using neutron powder diffraction at 3.5, 360, and 400 K. The B-H bond lengths and H-B-H angles for the [BH4]- tetrahedra indicated that the tetrahedra maintained a nearly ideal configuration throughout the temp. range studied. The at. displacement parameters at 360 K suggest that the [BH4]- tetrahedra become increasingly disordered of large amplitude librational and reorientational motions as the orthorhombic to hexagonal phase transition (T = 384 K) is approached. In the high-temp. hexagonal phase, the [BH4]- tetrahedra displayed extreme disorder about the trigonal axis along which they are aligned. Neutron vibrational spectroscopy data were collected at 5 K over an energy range of 10-170 meV, and are in agreement with prior Raman and low-resoln. neutron spectroscopy studies.
    59. 59
      Filinchuk, Y.; Chernyshov, D.; Cerny, R. Lightest borohydride probed by synchrotron X-ray diffraction: Experiment calls for a new theoretical revision. J. Phys. Chem. C 2008, 112 (28), 10579– 10584,  DOI: 10.1021/jp8025623
      59
      Lightest borohydride probed by synchrotron x-ray diffraction: experiment calls for a new theoretical revision
      Filinchuk, Yaroslav; Chernyshov, Dmitry; Cerny, Radovan
      Journal of Physical Chemistry C (2008), 112 (28), 10579-10584CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A combination of synchrotron x-ray diffraction techniques were applied to resolve ambiguities between exptl. and theor. studies of LiBH4 and to reveal its complex structural evolution as a function of temp. Crystal structures of the low- and high-temp. polymorphs of LiBH4 were detd. from diffraction on single-crystals. Crystallog. data are given. In contrast to recent theor. conjectures, the high-temp. structure is hexagonal, space group P63mc. Exptl. data suggest a nearly isotropic disorder of the rigid tetrahedral BH4 groups as one of the factors stabilizing the hexagonal structure. Tetrahedral BH4 anions are undistorted and geometrically very similar in both polymorphs. The first order phase transition at 381 K is preceded by highly anisotropic lattice expansion and is accompanied by a neg. vol. change. Disorder phenomena and strong lattice anharmonicity, being ignored, lead to the failure of theor. predictions of the structural stability of LiBH4 published so far.
    60. 60
      Hanawalt, J. D.; Rinn, H. W.; Frevel, L. K. Chemical analysis by X-ray diffraction - Classification and use of X-ray diffraction patterns. Ind. Eng. Chem., Anal. Ed. 1938, 10, 0457– 0512,  DOI: 10.1021/ac50125a001
      60
      Chemical analysis by x-ray diffraction. Classification and use of x-ray diffraction patterns
      Hanawalt, J. D.; Rinn, H. W.; Frevel, L. K.
      Industrial and Engineering Chemistry, Analytical Edition (1938), 10 (), 457-512CODEN: IENAAD; ISSN:0096-4484.
      This paper gives tabulated data on the diffraction patterns of 1000 chem. compds. which makes it possible to carry out routine testing by the Hull method (C. A. 13, 1980). The scheme of analysis will be readily understood by any one familiar with x-ray diffraction. Every cryst. substance has a characteristic diffraction pattern which is obtained from a small quantity of a mixt. as well as from the pure substance, so that the photograph obtained from a mixt. is the sum of the photographs that would be obtained from the superposed photographs of each individual constituent. The intensity of the lines gives good information with respect to quantity. The thousands of patterns which have been found can be classified in such a way that they can easily be used for the identification of an unknown constituent of a mixt. From the data of the patterns, the position of the 3 strongest lines are read off in the order of decreasing intensity. The first no. represents the group, the second no. the subgroup and the third no. the location within the subgroup. In the entire index book there are only 27 subgroups which contain more than 3 patterns and only one which contains more than 5 patterns. The necessary app. and manipulative technic are described. Wherever it is necessary to maintain an analytical lab., an invaluable supplementary technic will be found in x-ray diffraction. The substances present are shown in their true state of combination. The analysis is conclusive although only minute amts. of material are necessary; the samples are tested in the state received; different cryst. phases, states of oxidation or hydration, or phys. state are recognized; and a permanent record is always on file.
    61. 61
      Posnjak, E. W. R. Crystal structure of alkali halogenides. J. Wash. Acad. Sci. 1922, 12, 248– 251
      61
      The crystal structures of the alkali halides. II
      Posnjak, Eugen; Wyckoff, R. W. G.
      Journal of the Washington Academy of Sciences (1922), 12 (), 248-51CODEN: JWASA3; ISSN:0043-0439.
      cf. C. A. 16, 526. The following salts have the "sodium chloride arrangement" of their atoms: LiCl, d100 = 5.17 Å.; LiBr, d100 = 5.48 Å.; LiI, d100 = 6.06 Å.; NaF, d100 = 4.61 Å.; KF, d100 = 5.36 Å.; CsF, d100 = 6.03 Å. By d100 is meant the length of the side of the unit cube. The diffraction data obtained from RbF were such as to indicate that additional work was necessary to obtain its structure in a satisfactory fashion. A tabulation of the structures of all of the alkali halides is appended.
    62. 62
      Royer, L. Sur les accolements reguliers de cristaux d′especes differentes. C. R. Hebd. Seances Acad. Sci. 1925, 180, 2050
      There is no corresponding record for this reference.
    63. 63
      Harvey, K. B.; Mcquaker, N. R. Low temperature infrared and raman spectra of lithium borohydride. Can. J. Chem. 1971, 49 (20), 3282,  DOI: 10.1139/v71-546
      63
      Low temperature infrared and Raman spectra of lithium borohydride
      Harvey, K. B.; McQuaker, N. R.
      Canadian Journal of Chemistry (1971), 49 (20), 3282-6CODEN: CJCHAG; ISSN:0008-4042.
      The ir spectra of polycryst. LiBH4 and LiBD4 were recorded in the region 4000-50 cm-1 at 80°K. Raman spectra of polycryst. samples were also recorded at this temp. The spectra of the BH4- and BD4- lattice vibrations are consistent with sym. equiv. borohydride ions which lie on either general positions, 2-fold axes, or mirror-planes. Six lattice vibrations of translatory origin appear in the ir spectrum of LiBH4 and a mode of libratory origin is inferred from an absorption tentatively assigned as a 2nd overtone of a librational mode. Similar spectral results are obtained for LiBD4. The inferred librational frequencies are 418 cm-1 for the BH4- ions and 319 cm-1 for the BD4- ions.
    64. 64
      D’Anna, V.; Spyratou, A.; Sharma, M.; Hagemann, H. FT-IR spectra of inorganic borohydrides. Spectrochim. Acta, Part A 2014, 128, 902– 906,  DOI: 10.1016/j.saa.2014.02.130
      64
      FT-IR spectra of inorganic borohydrides
      D'Anna, Vincenza; Spyratou, Alexandra; Sharma, Manish; Hagemann, Hans
      Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (2014), 128 (), 902-906CODEN: SAMCAS; ISSN:1386-1425. (Elsevier B.V.)
      Inorg. compds. with BH-4 ions are the subject of many recent studies in the context of potential H storage materials. Attenuated total reflectance FTIR (ATR-FTIR) spectra of ref. and research compds. (including deuterated samples) are collected and made available to the research community.
    65. 65
      D’Anna, V.; Daku, L. M. L.; Hagemann, H. Quantitative spectra-structure relations for borohydrides. J. Phys. Chem. C 2015, 119 (38), 21868– 21874,  DOI: 10.1021/acs.jpcc.5b06045
      65
      Quantitative Spectra-Structure Relations for Borohydrides
      D'Anna, Vincenza; Lawson Daku, Latevi Max; Hagemann, Hans
      Journal of Physical Chemistry C (2015), 119 (38), 21868-21874CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Among the different potential hydrogen storage materials, borohydrides have been largely investigated because of their high gravimetric and volumetric hydrogen content. In the anal. of borohydrides, vibrational spectroscopy plays an important role since it gives information on the local structure of the BH4- ion inside the solid. Here the GF method, developed by Wilson, is used in order to det. the local symmetry of BH4- in solid borohydrides starting from their vibrational spectra. Two different cases of deformations of BH4- are considered. In the first case, the effects of small angular variations on the vibrational spectra of borohydrides will be taken into account; starting from the splitting of the bands corresponding to the deformation modes, the angular deformations will be estd. In the second one, the BH4- under chem. pressure (in different cubic alkali halides) is considered; in this case, the symmetry of the BH4- remains Td, while the bond lengths change according to the pressure experienced. Different practical examples will be illustrated.
    66. 66
      Coates, J. Interpretation of infrared spectra, a practical approach. Encycl. Anal. Chem. 2006, 1, 10815– 10837,  DOI: 10.1002/9780470027318.a5606
      There is no corresponding record for this reference.
    67. 67
      Sun, T.; Liu, J.; Jia, Y.; Wang, H.; Sun, D. L.; Zhu, M.; Yao, X. D. Confined LiBH4: Enabling fast hydrogen release at similar to 100 degrees C. Int. J. Hydrogen Energy 2012, 37 (24), 18920– 18926,  DOI: 10.1016/j.ijhydene.2012.09.119
      67
      Confined LiBH4: Enabling fast hydrogen release at ∼100 °C
      Sun, Tai; Liu, Jian; Jia, Yi; Wang, Hui; Sun, Dalin; Zhu, Min; Yao, Xiangdong
      International Journal of Hydrogen Energy (2012), 37 (24), 18920-18926CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
      LiBH4 has been attracted tremendous research interest as a hydrogen storage material for mobile applications due to its very high gravimetric hydrogen capacity of 18.6 wt%. However, its real use is heavily hindered by the high operational temp. that is required above 350 °C to release hydrogen with various recent improvements. This is obviously much higher than the ambient temp. of about 100 °C. In this paper, we report the synthesis of LiBH4 confined by SBA-15 template, which achieves fast hydrogen release of LiBH4 at ∼100 °C. The confined LiBH4 system starts to release hydrogen at only 45 °C and can release 8.5 wt% hydrogen (on the basis of LiBH4 itself) within 10 min at 105 °C, which opens a new window and overcome the most challenging barrier to realize practical hydrogen storage of LiBH4.
    68. 68
      Plerdsranoy, P.; Utke, R. Confined LiBH4-LiAlH4 in nanopores of activated carbon nanofibers. Int. J. Hydrogen Energy 2015, 40 (22), 7083– 7092,  DOI: 10.1016/j.ijhydene.2015.04.021
      68
      Confined LiBH4-LiAlH4 in nanopores of activated carbon nanofibers
      Plerdsranoy, Praphadsorn; Utke, Rapee
      International Journal of Hydrogen Energy (2015), 40 (22), 7083-7092CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
      Polyacrylonitrile (PAN)-based polymer fiber prepd. from electrospinning technique is carbonized and activated (with concd. KOH soln.) to obtain activated carbon nanofiber (ACNF). ACNF is used in this work as a host material for nanoconfinement of LiBH4-LiAlH4 composite via soln. impregnation. Successful nanoconfinement and homogeneous distribution of hydride composite on ACNF are confirmed by N2 adsorption-desorption and SEM-EDS-mapping techniques, resp. Nanoconfined LiBH4-LiAlH4 in ACNF performs almost single-step decompn. whereas that of milled sample is clearly two-step reaction. Onset dehydrogenation temp. of LiAlH4 from nanoconfined and milled samples is comparable at 100 °C, while that of LiBH4 obtained from nanoconfined sample is up to 80 °C lower than that of milled sample. In addn., significant redn. in main dehydrogenation temp., esp. of LiBH4 in nanoconfined LiBH4-LiAlH4 as compared with milled LiBH4-LiAlH4 (ΔT = up to 94 °C) and with pristine LiBH4 (ΔT = up to 149 °C) is achieved. Hydrogen contents released and reproduced in the 1st and 2nd dehydrogenations of nanoconfined LiBH4-LiAlH4 are 30 and 63% superior to those of milled sample. Reversibility of LiBH4, LiAlH4, and/or Li3AlH6 was accomplished from nanoconfined LiBH4-LiAlH4 under mild temp. and pressure condition (T = 320 °C and P(H2) = 80 bar) as compared with other LiBH4-LiAlH4 (or Al) systems.
    69. 69
      Javadian, P.; Sheppard, D. A.; Buckley, C. E.; Jensen, T. R. Hydrogen storage properties of nanoconfined LiBH4-NaBH4. Int. J. Hydrogen Energy 2015, 40 (43), 14916– 14924,  DOI: 10.1016/j.ijhydene.2015.08.075
      69
      Hydrogen storage properties of nanoconfined LiBH4-NaBH4
      Javadian, Payam; Sheppard, Drew A.; Buckley, Craig E.; Jensen, Torben R.
      International Journal of Hydrogen Energy (2015), 40 (43), 14916-14924CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)
      In this study a eutectic melting composite of 0.62LiBH4-0.38NaBH4 has been infiltrated in two nanoporous resorcinol formaldehyde carbon aerogel scaffolds with similar pore sizes (37 and 38 nm) but different BET surface areas (690 and 2358 m2/g) and pore vols. (1.03 and 2.64 mL/g). This investigation clearly shows decreased temp. of hydrogen desorption, and improved cycling stability during hydrogen release and uptake of bulk 0.62LiBH4-0.38NaBH4 when nanoconfined into carbon nanopores. The hydrogen desorption temp. of bulk 0.62LiBH4-0.38NaBH4 is reduced by ∼107 °C with the presence of carbon, although a minor kinetic variation is obsd. between the two carbon scaffolds. This corresponds to apparent activation energies, EA, of 139 kJ/mol (bulk) and 116-118 kJ/mol (with carbon aerogel). Bulk 0.62LiBH4-0.38NaBH4 has poor reversibility during continuous hydrogen release and uptake cycling, maintaining 22% H2 capacity after four hydrogen desorptions (1.6 wt.% H2). In contrast, nanoconfinement into the high surface area carbon aerogel scaffold significantly stabilizes the hydrogen storage capacity, maintaining ∼70% of the initial capacity after four cycles (4.3 wt.% H2).
    70. 70
      Laiti, E.; Persson, P.; Ohman, L. O. Balance between surface complexation and surface phase transformation at the alumina/water interface. Langmuir 1998, 14 (4), 825– 831,  DOI: 10.1021/la970383n
      70
      Balance between Surface Complexation and Surface Phase Transformation at the Alumina/Water Interface
      Laiti, Erkki; Persson, Per; Oehman, Lars-Olof
      Langmuir (1998), 14 (4), 825-831CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      This paper synthesizes and expands on the results of a recent series of investigations aimed at characterizing the interactions of orthophosphate, phenylphosphonate, and clodronate ions with hydrous alumina surfaces. The paper shows that γ-Al2O3 is a thermodynamically unstable substance in water, which undergoes a (surface) phase transformation into bayerite, β-Al(OH)3. Furthermore, it also shows that while phenylphosphonate ions are exclusively adsorbed via surface complexation to the alumina surfaces, clodronate ions dissolve the alumina phase and ppt. as an aluminum clodronate phase. Orthophosphate ions show a transient behavior in this respect, and the limits for, and consequences of, AlPO4(s) formation are detd. via a series of chem. modeling calcns. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macroscopically derived stoichiometric compns. are used to assign microscopic surface complex structures.
    71. 71
      Hiyoshi, N.; Yogo, K.; Yashima, T. Adsorption characteristics of carbon dioxide on organically functionalized SBA-15. Microporous Mesoporous Mater. 2005, 84 (1–3), 357– 365,  DOI: 10.1016/j.micromeso.2005.06.010
      71
      Adsorption characteristics of carbon dioxide on organically functionalized SBA-15
      Hiyoshi, Norihito; Yogo, Katsunori; Yashima, Tatsuaki
      Microporous and Mesoporous Materials (2005), 84 (1-3), 357-365CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
      Aminosilane-modified SBA-15 was prepd. by grafting various aminosilanes on mesoporous SiO2 SBA-15, and its adsorption characteristics towards CO2 were examd. The amt. of CO2 adsorbed was almost the same for both in the presence and in the absence of water vapor. The efficiency of adsorption, defined as the no. of adsorbed CO2 mols. per N atom of aminosilane-modified SBA-15, increased with increasing the surface d. of amine. IR spectroscopy revealed that CO2 was adsorbed on aminosilane-modified SBA-15 through the formation of alkylammonium carbamate in the presence and in the absence of water vapor. Amine pairs, on which CO2 was adsorbed through formation of alkylammonium carbamate, increased with increasing surface d. of amine. In addn., influence of amine structure on the adsorption capacity was also discussed.
    72. 72
      Zhao, X. S.; Lu, G. Q. Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study. J. Phys. Chem. B 1998, 102 (9), 1556– 1561,  DOI: 10.1021/jp972788m
      72
      Modification of MCM-41 by Surface Silylation with Trimethylchlorosilane and Adsorption Study
      Zhao, X. S.; Lu, G. Q.
      Journal of Physical Chemistry B (1998), 102 (9), 1556-1561CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      Siliceous MCM-41 samples were modified by silylation using trimethylchlorosilane (TMCS). The surface coverage of functional groups was studied systematically in this work. The role of surface silanol groups during modification was evaluated using techniques of FTIR and 29Si CP/MAS NMR. Adsorption of water and benzene on samples of various hydrophobicities was measured and compared. It was found that the max. degree of surface attachments of trimethylsilyl (TMS) groups was about 85%, corresponding to the d. of TMS groups of 1.9 per nm2. The degree of silylation is found to linearly increase with increasing pre-outgassing temp. prior to silylation. A few types of silanol groups exist on MCM-41 surfaces, among which both free and geminal ones are responsible for active silylation. Results of water adsorption show that aluminosilicate MCM-41 materials are more or less hydrophilic, giving a type IV isotherm, similar to that of nitrogen adsorption, whereas siliceous MCM-41 are hydrophobic, exhibiting a type V adsorption isotherm. The fully silylated Si-MCM-41 samples are more hydrophobic, giving a type III adsorption isotherm. Benzene adsorption on all MCM-41 samples shows type IV isotherms regardless of the surface chem. Capillary condensation occurs at a higher relative pressure for the silylated MCM-41 than that for the unsilylated sample, though the pore diam. was found reduced markedly by silylation. This is thought attributed to the diffusion constriction posed by the attached TMS groups. The results show that the surface chem. plays an important role in water adsorption, whereas benzene adsorption is predominantly detd. by the pore geometry of MCM-41.
    73. 73
      Irvine, J. T. S.; Sinclair, D. C.; West, A. R. Electroceramics: Characterization by impedance spectros-copy. Adv. Mater. 1990, 2, 132– 138,  DOI: 10.1002/adma.19900020304
      73
      Electroceramics: characterization by impedance spectroscopy
      Irvine, John T. S.; Sinclair, Derek C.; West, Anthony R.
      Advanced Materials (Weinheim, Germany) (1990), 2 (3), 132-8CODEN: ADVMEW; ISSN:0935-9648.
      A review with 13 refs. Various examples are chosen which illustrate the power and usefulness of impedance spectroscopy for characterizing a wide variety of electroceramic materials and phenomena.
    74. 74
      Verkuijlen, M. H. W.; Ngene, P.; de Kort, D. W.; Barre, C.; Nale, A.; van Eck, E. R. H.; van Bentum, P. J. M.; de Jongh, P. E.; Kentgens, A. P. M. Nanoconfined LiBH4 and enhanced mobility of Li+ and BH4– studied by solid-state NMR. J. Phys. Chem. C 2012, 116 (42), 22169– 22178,  DOI: 10.1021/jp306175b
      74
      Nanoconfined LiBH4 and Enhanced Mobility of Li+ and BH4- Studied by Solid-State NMR
      Verkuijlen, Margriet H. W.; Ngene, Peter; de Kort, Daan W.; Barre, Charlotte; Nale, Angeloclaudio; van Eck, Ernst R. H.; van Bentum, P. Jan M.; de Jongh, Petra E.; Kentgens, Arno P. M.
      Journal of Physical Chemistry C (2012), 116 (42), 22169-22178CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The structural and dynamical properties of LiBH4 confined in porous carbon and ordered porous silica were studied using 1H, 7Li, and 11B solid-state NMR. The 11B and 7Li NMR resonances of LiBH4 confined in porous carbon (broad pore size distribution up to <60 nm) are strongly broadened compared to bulk LiBH4. This line broadening is dominated by anisotropic susceptibility effects induced by the nanostructured carbon host. Because of the lack of resoln. caused by the anisotropic susceptibility broadening, the authors studied confined LiBH4 in ordered porous silica (MCM-41 pore size: 1.9 nm). In the 7Li and 11B spectra, a bulk-like LiBH4 resonance is obsd. together with an addnl., more narrow component. Above T = 313 K, this component showed a typical J-coupling pattern in both 11B and 1H spectra corresponding to highly mobile BH4- species. Static 11B solid-state NMR measurements compared with 2nd moment calcns. show that these BH4- species not only rotate as in the bulk material but also experience translations through the crystal lattice. Static 7Li measurements show that Li+ is also highly mobile. Therefore, nanoconfinement of LiBH4 strongly enhances diffusional mobility of borohydride anions and lithium in this material.
    75. 75
      Epp, V.; Wilkening, M. Fast Li diffusion in crystalline LiBH4 due to reduced dimensionality: Frequency-dependent NMR spectroscopy. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82 (2), 020301,  DOI: 10.1103/PhysRevB.82.020301
      75
      Fast Li diffusion in crystalline LiBH4 due to reduced dimensionality: Frequency-dependent NMR spectroscopy
      Epp, V.; Wilkening, M.
      Physical Review B: Condensed Matter and Materials Physics (2010), 82 (2), 020301/1-020301/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The hexagonal and orthorhombic form of lithium borohydride, LiBH4, are investigated by temp. and frequency-dependent NMR spectroscopy. The local electronic structure and microscopic diffusion parameters are detd. by recording both 6,7Li NMR spectra and spin-lattice relaxation (SLR) rates. The rates of the high-temp. flank of the SLR-NMR peaks of hexagonal LiBH4 clearly depend on resonance frequency which unequivocally reveals a low-dimensional diffusion process. Due to the very limited no. of suitable model substances this makes lithium borohydride an extremely attractive material to study the effect of reduced dimensionality on Li dynamics. Most likely, the spatial confinement of Li hopping is also responsible for the very high ionic cond. found for the hexagonal polymorph, recently.

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    • Calculation of the amount of material needed for melt infiltration to reach the desired pore filling; physisorption data; high-resolution scanning electron microscopy images; additional XRD patterns and DRIFTS data; further conductivity Arrhenius plot comparing different supports; comparison of room temperature conductivity values of samples with varying LiI content (0 to 40 mol %) (PDF)


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