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Metal–Organic Framework-Derived Magnesium Oxide@Carbon Interlayer for Stable Lithium–Sulfur Batteries
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  • Hyeonmuk Kang
    Hyeonmuk Kang
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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    Orcidhttps://orcid.org/0000-0003-0174-555X
  • Jaewook Shin
    Jaewook Shin
    Advanced Battery Center, KAIST Institute for NanoCentury, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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    Orcidhttps://orcid.org/0000-0002-7431-9255
  • Tae-Hee Kim
    Tae-Hee Kim
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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  • Yongju Lee
    Yongju Lee
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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  • Daehee Lee
    Daehee Lee
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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  • Junho Lee
    Junho Lee
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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  • Gyungtae Kim
    Gyungtae Kim
    Department of Measurement & Analysis, National NanoFab Center, Daejeon 34141, Republic of Korea
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  • EunAe Cho*
    EunAe Cho
    Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
    *Phone: +82-42-350-3317. Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-2871-6903
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ACS Sustainable Chemistry & Engineering

Cite this: ACS Sustainable Chem. Eng. 2023, 11, 4, 1344–1354
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https://doi.org/10.1021/acssuschemeng.2c05064
Published January 19, 2023

Copyright © 2023 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Lithium sulfur (Li–S) batteries represent a promising future battery technology. However, the low electrical conductivity of solid-state sulfur species (S, Li2S2, and Li2S) and the polysulfide shuttle effect deteriorate their practical capacity and cycling retention. Herein, we present an interlayer composed of magnesium oxide (MgO) nanoparticles and carbon matrix for the Li–S batteries. In the composite, MgO can capture dissolved polysulfides that diffuse to the carbon matrix along the oxide surface for further reduction reactions. As a novel precursor to produce the composite structure, a Mg metal–organic-framework, Mg-MOF-74, is adopted and synthesized on a free-standing carbon paper (MOF/C-paper). Through pyrolysis, Mg-MOF-74 is converted into highly porous carbon containing uniformly distributed MgO nanoparticles (MgO@C/C-paper). The Li–S cells assembled with MgO@C/C-paper and C-paper interlayer show significantly higher initial capacities (980 and 898 mAh g–1, respectively) than the interlayer-free cell (729 mAh g–1) owing to the conductive interlayers. After 200 cycles at 0.2 C, the MgO@C/C-paper cell presents a cycle retention (78.3%) superior to that of the C-paper cell (76.5%). With a higher sulfur loading of 3.3 mg cm–2, the MgO@C/C-paper cell exhibits an even higher capacity retention (80.1%) than the C-paper cell (54.6%) after 100 cycles. The excellent cycle stability of the MgO@C/C-paper cell over the C-paper cell demonstrates that the unique structure of the MOF-derived MgO@C is highly effective in anchoring and reutilizing dissolved polysulfides.

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Synopsis

MOF-derived MgO@C interlayer increases utilization of polysulfides and reversibility of the Li−S cell for sustainable energy storage.

Introduction

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Since the conception of the lithium ion battery (LIB), LIBs have played a key role in the revolution of mobile electronic devices owing to their high gravimetric energy density (260 Wh kg–1). However, the advancement of portable devices and large-scale applications such as electric vehicles (EVs) and energy storage systems (ESSs) requires higher energy density than an LIB can supply. Among post-LIB candidates, lithium–sulfur (Li–S) batteries have a better chance of reaching commercialization owing to their high theoretical energy density (2500 Wh kg–1), low cost, and the environmental friendliness of the sulfur cathode material. (1,2) Compared to conventional transition-metal oxide cathodes (275 mAh g–1), which involve a maximum of one electron per transition-metal atom, the sulfur cathode has a higher theoretical capacity (1675 mAh g–1), as it is a lightweight element and incorporates two electrons per sulfur atom to form lithium sulfide (Li2S). (3)
Despite these advantages, sulfur cathodes have several challenges that must be overcome. In particular, low electrical conductivity of solid-state sulfur species (S, Li2S2, and Li2S) and the dissolution of lithium polysulfides (Li2Sn, 4 ≤ n ≤ 8) hinder the full utilization of the theoretical capacity and result in poor cyclic retention. (4,5) Low electrical conductivity of sulfur leads to large overpotential and low practical capacity, limiting the sulfur loading mass as well. The dissolved polysulfides lose electric contact with the cathode and subsequently become inactive. In addition, they can move to the lithium anode and react to form S or Li2S2/Li2S, which passivates the anode surface and increases the cell overpotential due to the ensuing poor electrical conductivity.
In an effort to address the aforementioned issues, conductive host materials such as graphene, (6) graphene oxide, (7) and highly porous carbon (8−10) have been added into the sulfur cathodes to enhance the electrical conductivity. (11,12) However, addition of a host material to the cathode includes the extra step of a melt diffusion process (13) and reduces the sulfur content of the cathode. To increase sulfur loading mass and to use simple synthesis processes, free-standing interlayers have been widely developed. Starting with a multiwall carbon nanotube (MWCNT) interlayer, a variety of carbon-based interlayers have been explored. (14−18) Although those interlayers can enhance both the specific capacity and cycle stability of sulfur cathodes by providing electrical conductivity to the sulfur cathode, the nonpolar surface of carbon materials cannot effectively suppress polysulfide shuttling due to having a low affinity for polar polysulfide and limitations in improving the cycle stability. (19)
For efficient polysulfide capture, inorganic compounds such as transition-metal oxides, (11,20−23) sulfides, (24,25) and carbides (26,27) have been incorporated into carbon materials. Among them, metal oxides are known to have the highest affinity to polysulfides. (20) However, the anchored polysulfide on a metal oxide surface cannot react further due to low electrical conductivity of the metal oxides. To utilize the dissolved polysulfides, the anchored polysulfides should diffuse to neighboring conducting carbon. Thus, in addition to the chemical affinity with polysulfides, diffusion of anchored polysulfides on metal oxide is a crucial factor to be considered in designing an interlayer. A recent study showed that MgO is a promising material among different metal oxides considering strong binding and a low surface diffusion barrier through density functional theory (DFT) calculation and experimental results. (28)
In this study, we present a commercial carbon paper coated with porous carbon and magnesium oxide (MgO). As a novel precursor for the MgO and carbon composite, an Mg metal–organic framework, Mg-MOF-74, was synthesized on a free-standing carbon paper (MOF/C-paper). Through pyrolysis, Mg-MOF-74 is converted into highly porous carbon containing uniformly distributed MgO nanoparticles (MgO@C/C-paper). The unique structure of the MOF-derived MgO@C provides uniformly abundant anchoring sites and short diffusion pathways for dissolved polysulfides, thereby improving cycle retention of the Li–S cell. The roles of MgO@C/C-paper interlayer in capturing and reutilizing dissolved polysulfides are investigated using scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), and X-ray photoelectron spectroscopy (XPS).

Results and Discussions

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Figure 1a,b shows SEM images of a pristine carbon paper (C-paper) composed of carbon fibers with a diameter of approximately 5 μm and a smooth surface. The C-paper has a porous structure with a thickness of approximately 110 μm. An X-ray diffraction (XRD) pattern (Figure 2) reveals that the C-paper consists of graphitic carbon. (29) To produce a metal–organic framework (MOF) on the carbon fibers, the C-paper was soaked in a solution containing magnesium acetate tetrahydrate (Mg(CH3COO)2·4H2O) as a metal precursor and 2,5-dihydroxyterephthalic acid (H4DHTP) as an organic ligand and kept at 125 °C for 6 h (denoted as “MOF/C-paper”). As illustrated in Figure 1c,d, most of the carbon fibers are covered with the reaction products throughout the C-paper. The XRD pattern of MOF/C-paper displays distinct peaks at 6.7° and 11.7° (Figure 2) that correspond to (110) and (300) of space group R3, respectively, (30) in addition to the graphitic carbon peaks. These outcomes imply that crystalline Mg-MOF-74 was formed on graphitic carbon fibers throughout the C-paper. Then, the MOF/C-paper was heat-treated at 900 °C under an Ar gas condition for 1 h. (31) The XRD pattern of the heat-treated MOF/C-paper (Figure 2) exhibits only graphitic carbon peaks without the Mg-MOF-74 peaks observed from the MOF/C-paper, indicating that the organic ligands in Mg-MOF-74 were pyrolyzed into carbon. Similar to the MOF/C-paper, most of the carbon fibers in the heat-treated MOF/C-paper (Figure 1e,f) are covered with pyrolyzed MOF throughout the C-paper. The thicknesses of the MOF/C-paper and heat-treated MOF/C-paper were similar (∼110 μm) to that of the pristine C-paper.

Figure 1

Figure 1. Top-view and cross-sectional SEM images of (a, b) C-paper, (c, d) MOF/C-paper, and (e, f) heat-treated MOF/C-paper.

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Figure 2

Figure 2. XRD patterns of C-paper, MOF/C-paper, and heat-treated MOF/C-paper.

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Since the boiling point of Mg is 1091 °C, (32) Mg in Mg-MOF-74 would survive the heat treatment and be oxidized when the heat-treated MOF/C-paper was exposed to air. A strand of the heat-treated MOF/C-paper was carefully collected by cutting a fiber (Figure 3a) for elemental mapping. Unavoidably, pyrolyzed MOF was partially removed from the fiber during the cutting process. The elemental mapping image (Figure 3b) shows that Mg is uniformly distributed in the pyrolyzed MOF. Transmission electron microscopy (TEM) images of the pyrolyzed MOF (Figure 3c) demonstrate nanosized (approximately 2 nm) particles in an amorphous matrix. The fast Fourier transformed (FFT) images for a nanoparticle (Figure 3d) and for a carbon matrix (Figure 3e) illustrate the rock salt phase (Fm3̅m) with a lattice parameter of 0.21 nm, which correspond to Mg-oxide (MgO) (33) and amorphous carbon, respectively. These results demonstrate that pyrolyzed MOF is composed of MgO nanoparticles in an amorphous carbon matrix (MgO@C). The absence of MgO peaks from the XRD pattern (Figure 2) of the heat-treated MOF/C-paper (denoted as “MgO@C/C-paper”) is related to the small crystallite size of MgO and strong intensity of graphitic carbon peaks from the C-paper.

Figure 3

Figure 3. (a) SEM and (b) EDS elemental Mg mapping images of a fiber collected from the heat-treated MOF/C-paper. (c) TEM image of pyrolyzed MOF and FFT images for (d) the nanoparticle marked with a red square and (e) carbon matrix marked with a blue square in (c).

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To support that the MOF/C-paper was pyrolyzed into MgO@C/C-paper, Mg-MOF-74 was prepared in powder form (denoted as “MOF powder”, Figure S1a) and heat-treated in the same manner as MOF/C-paper (denoted as “heat-treated MOF powder”, Figure S1b). While the MOF powder exhibits the XRD peaks of Mg-MOF-74 peak distinctively at 6.7° and 11.7° (Figure S2), the heat-treated MOF powder presents only MgO-related XRD peaks at 43° and 62°, without Mg-MOF-74 peaks or carbon peaks. These results confirm that the heat-treated MOF powder is composed of crystalline MgO and amorphous carbon (denoted as “MgO@C powder”).
To estimate the composition of MgO, MOF-derived amorphous carbon, and graphitic C-paper in the MgO@C/C-paper, thermogravimetric analysis (TGA) was conducted for MgO@C powder and MgO@C/C-paper in an air condition to 900 °C. The MgO@C powder sample lost approximately 53.4% of its original weight at temperature around ∼300 °C (Figure S3a), confirming the MOF-derived carbon has an amorphous structure, (34) and retained 46.6% of its original weight up to 900 °C. Thus, the weight ratio of MgO to MOF-derived amorphous carbon in MgO@C is 46.6 to 53.4. The MgO@C/C-paper lost its weight slightly at a temperature around ∼300 °C and mostly at temperatures above ∼600 °C, where approximately 97.5% of graphitic carbon oxidized from its original weight (Figure S3b). (35) Accordingly, MgO@C/C-paper is composed of 2.5 wt % MgO, 2.9 wt % MOF-derived amorphous carbon, and 94.6 wt % of graphitic C-paper. The free-standing C-paper and MgO@C/C-paper have a weight of 14.1 and 14.4 mg, respectively. A simple calculation shows that MgO@C/C-paper only has 0.16 mg of extra MgO added from the original C-paper.
The electrical conductivity of MgO@C/C-paper was measured to be 0.71 S cm–2, which was slightly lower than that of the C-paper (0.94 S cm–2) due to the presence of insulating MgO. The Barrett–Joyner–Halenda (BJH) measurement (Figure S4) exhibits that MOF-derived carbon has mesopores with an average pore size of 5.2 nm. Owing to the highly porous MOF-derived carbon, the MgO@C/C-paper has a substantially larger Brunauer–Emmett–Teller (BET) surface area (0.70 m2/g) than that of the C-paper (0.29 m2/g).
With a cathode sulfur loading of 1.7 mg cm–2, three types of Li–S coin cells were assembled: a standard cell without an interlayer and also C-paper and MgO@C/C-paper that employ C-paper and MgO@C/C-paper interlayer, respectively, between the cathode and the separator. The ratio between electrolyte and sulfur (E/S) was 20 μL/g. The cycle test was performed at the current density 0.2 C, with cutoff voltages of 1.7 and 2.8 V (Figure 4a). The standard cell has an initial capacity of 729 and 543 mAh g–1 after 200 cycles with retention of 74.5%. On the other hand, the interlayer-containing cells, C-paper and MgO@C/C-paper, deliver substantially enhanced initial capacities of 898 and 980 mAh g–1, respectively. After 200 cycles, C-paper had a capacity of 687 mAh g–1 with retention 76.5%, and MgO@C/C-paper had a capacity of 767 mAh g–1 with retention 78.3%. In addition, the Coulombic efficiency of standard, C-paper, and MgO@C/C-paper after 200 cycles is 98.3, 98.7, and 99.0%, respectively. The high electrical conductivity and the large surface of the interlayers provide plenty of reaction sites for polysulfides, enhancing the polysulfide utilization. However, it is expected that the formation of Li2S2 and Li2S eventually passivates the surface of the C-paper, (36) whereas the MgO@C layer prevents the passivation.

Figure 4

Figure 4. Electrochemical performance of the Li–S cells without an interlayer (denoted as “standard”) and with C-paper and MgO@C/C-paper interlayer at 0.2 C. (a) Cycling performances with a sulfur loading mass of 1.7 mg cm–2. Charge–Discharge curves of (b) standard, (c) C-paper, and (d) MgO@C/C-paper.

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In Figure 4b–d, the prepared coin cells demonstrate discharge voltage plateaus at approximately 2.3 and 2.1 V, corresponding to the reduction of elemental sulfur to high-order polysulfides (Li2Sx, 6 ≤ x ≤ 8) and a further reduction of these polysulfides to lower-order polysulfides (Li2Sx, 4 ≤ x ≤ 6) and lithium sulfide (Li2S), respectively. Comparing standard, C-paper, and MgO@C/C-paper cells, at the first cycle, the capacity coming from the first plateau is 318, 346, and 359 mAh g–1, respectively. The standard cell, without an interlayer, has the smallest capacity due to a lack of electrical conductivity. A conductive interlayer on the top of the sulfur cathode surface, where the electrochemical reaction predominantly occurs, enhances the utilization of nonconductive sulfur (S8) and lithium sulfides (Li2S2 and Li2S). (15,21,37) The effect of the MgO@C/C-paper interlayer is emphasized at the second plateau where higher capacity is extracted by reduction of polysulfides (Standard: 411 mAh g–1, C-paper: 552 mAh g–1, and MgO@C/C-paper: 621 mAh g–1). The voltage plateau at 2.1 V was extended for the MgO@C/C-paper over the C-paper implying that the MgO@C layer promotes the reduction of low-order polysulfides (at 2.1 V) more than the reduction of elemental sulfur to high-order polysulfides (at 2.3 V), resulting in the higher specific capacity compared to the C-paper.
After 20 cycles, the first plateau for the standard cell dramatically decreased having 192 mAh g–1 and moderately decreased capacity of 347 mAh g–1 for the second plateau. Repeated polysulfide dissolution and S/Li2S2/Li2S deposition result in the separation of sulfur and carbon in the cathode. Insulating sulfur species at the interface between the electrolyte and cathode passivates the cathode. It has been reported that the low electrical conductivity of the sulfur species and the loss of the active material related to polysulfide dissolution decreases the sulfur utilization. (25,38,39) For C-paper and MgO@C/C-paper, the change in the first plateau is relatively moderate (C-paper: 271 mAh g–1, MgO@C/C-paper: 285 mAh g–1). However, an abrupt voltage decay decreased the capacity derived from the second plateau of the C-paper 437 mAh g–1, whereas MgO@C/C-paper maintains the capacity of 529 mAh g–1. The difference in the second plateau capacity after 20 cycles is expected to come from the passivation of active sites of the C-paper interlayer.
In order to separate the role of MgO, MgO particles are removed by using 2 M HCl acid leaching (Figure S5). TEM high-angle annular dark-field (HAADF) images and energy-dispersive X-ray spectroscopy (EDS) mapping of heat-treated MOF powder show MgO nanoparticles and clear Mg peaks, whereas the acid-leached heat-treated MOF powder only demonstrates clear amorphous carbon matrix without any Mg peaks. MgO@C/C-paper after acid leaching, denoted as “C/C-paper”, is assembled in a Li–S full cell to compare the electrochemical performance (Figure S6). C/C-paper has an initial capacity of 891 mAh g–1, which is very similar to that of the C-paper (898 mAh g–1). Also, it retained its capacity of 680 mAh g–1 at 50 cycles showing a similar decay curve when compared to the C-paper. Such a result confirms that the presence of MgO nanoparticles can increase the capacity of the Li–S cell.
One of the crucial challenges in the commercialization of Li–S batteries is the limitation of sulfur loading. With an increased sulfur loading of 3.3 mg cm–2 (Figure 5), the initial specific capacity of sulfur dramatically drops to approximately 300 mAh g–1 at the first cycle at 0.05 C, whereas the interlayer-containing cells retain the cathode-specific capacities of approximately 1000 mAh g–1. During 100 cycles at 0.2 C, the capacity only retained at approximately 200 mAh g–1 without an interlayer (Figure 5b). The C-paper cell that initially had a high capacity (1st cycle: 987 mAh g–1) underwent a rapid capacity fading, delivering the specific capacity of 414 mAh g–1 at the 100th cycle (54.6% of the second cycle capacity, 759 mAh g–1). On the other hand, the MgO@C/C-paper cell shows an excellent cycle retention, presenting a cathode capacity of 584 mAh g–1 at the 100th cycle (80.1% of the second cycle capacity, 729 mAh g–1). Compared to the MgO@C/C-paper cell, the rapid capacity fading of the C-paper cell is related to the decay of the voltage plateau at 2.1 V (Figure 5a). These outcomes reflect that, with the higher sulfur loading, a greater amount of polysulfides is dissolved, accelerating passivation of the C-paper and capacity fading. In contrast, with the MgO@C/C-paper, passivation of the C-paper is effectively suppressed, thereby enabling reduction of polysulfides.

Figure 5

Figure 5. (a) Charge–Discharge curves and (b) electrochemical performance of the Li–S cells without an interlayer (denoted as “standard”) and with C-paper and MgO@C/C-paper interlayer at 0.2 C with sulfur loading of 3.3 mg cm–2.

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There are different MOF and MOF-derived materials used in Li–S battery studies. For example, the HKUST-1 based MOF@GO separator shows an initial capacity of 1207 mAh g–1 and retains 870 mAh g–1 at the 100th cycle at 0.5 C, (40) and Y-FTZB-coated separator shows an initial capacity of 1101 mAh g–1 and retains its capacity of 557 mAh g–1 after 300 cycles at 0.25 C. (41) Although the overall capacity of this work is slightly lower than the previous results, considering the loading mass (0.6–1.0 mg cm–2) of previous results, this result is comparable.
The charge–discharge curves and rate performance of the three Li–S batteries are shown in Figure S7. As C-rate increases, the voltage gap between charge and discharge plateaus increases due to the limited conductivity of the standard sulfur cathode. However, the cell with MgO@C/C-paper has flatter plateaus and reduced overpotential. MgO@C-paper has a capacity of 1237 mAh g–1 at 0.05 C and 651 mAh g–1 at 1 C having higher rate capability compared to other cells. Also, it recovers up to 1011 mAh g–1 when the C-rate returns to 0.05 C, suggesting superior rate performance of MgO@C/C-paper.
To achieve high sulfur utilization and cycle stability, dissolved polysulfides should be anchored and reduced to Li2S2/Li2S. To estimate polysulfide-anchoring capacity, coin cells were disassembled after the first discharge (Figure S8). While the standard cell displays a yellowish electrolyte, the interlayer-containing cells show colorless electrolytes, implying yellow-colored polysulfides were captured by the interlayers. (42) Compared to the pristine states (Figure 6a,b), the pores in the C-paper and MgO@C/C-paper were severely clogged throughout the interlayers (Figure 5c,d). Elemental mapping images display sulfur signals uniformly distributed throughout the interlayers. These outcomes reflect that a considerable amount of polysulfide was captured by the interlayers in the first discharge (Figure 6e,f). In addition, the MgO@C/C-paper has stronger S signals than the C-paper. To estimate polysulfide capturing ability, pristine C-paper and MgO@C/C-paper were soaked in a 5 mM polysulfide (Li2S6) solution for an hour and washed with 1,2-dimethoxymethane (DME) solution (Figure S9). The sulfur contents measured using elemental analysis (EA) were found to be 278 and 408 ppm in the C-paper and MgO@C/C-paper, respectively. These results demonstrate that MgO@C enhance the polysulfide capturing capability, possibly due to the highly porous carbon and polar MgO nanoparticles. (28)

Figure 6

Figure 6. Top view SEM images of the interlayers (a), (b) before and (c, d) after the first discharge. Cross-section images and elemental EDS mapping images of (e) C-paper and (f) MgO@C/C-paper.

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To evaluate the capabilities of reducing the anchored polysulfides, coin cells were prepared using the C-paper and MgO@C/C-paper as blank cathodes. Polysulfide (Li2S8) was dissolved in the electrolyte as an active material instead of sulfur cathode. Voltage–Time curves were measured at a constant current of 27 μA (Figure S10), displaying sloping discharge profiles above 2.1 V and voltage plateaus at 2.1 V, corresponding to the reduction of dissolved Li2S8 to Li2S6 and the reduction of Li2S6 to Li2S2 or Li2S, respectively. (43) Whereas the capacities from the reaction of Li2S8 to Li2S6 are similar for both blank cathodes, the MgO@C/C-paper cathode produces a longer voltage plateau and approximately 1.5 times higher capacity than the C-paper cathode. These results demonstrate that MgO@C promotes reduction of the anchored polysulfides to Li2S2 or Li2S.
To determine the state of the sulfur species on the blank cathodes, the discharged blank cathodes were disassembled, washed in DME solution, and dried in a vacuum chamber. The washed blank cathodes are transferred using a vacuum transfer vessel to collect X-ray photoelectron spectroscopy (XPS) S 2p spectra (Figure 7). R-SO2-R/SO42–, S2O32–/SO32–, ST–1, and S2– peaks are observed at binding energies of 169.0, 167.2, 162.0, and 160.4 eV, respectively. (44) Since the soluble polysulfides were removed by DME, R-SO2-R/SO42– and S2O32–/SO32– signals reflect the oxidation of sulfur species during the sample transfer or due to the residual bis(trifluoromethyl sulfonyl)imide (LiTFSI). Compared to the C-paper, MgO@C/C-paper exhibits the higher relative intensity of R-SO2-R/SO42– and S2O32–/SO32–, indicating a greater amount of polysulfides anchored in accordance with the EA results (Figure S9). The ST–1 and S2– species correspond to Li2S2 and Li2S, respectively. The peak areal ratios of S2– to ST–1 (S2–/ST–1) were calculated to be 5.9 and 1.8 for the MgO@C/C-paper and C-paper, respectively, implying that lithium persulfide (Li2S2) was further reduced to lithium sulfide (Li2S) in the MgO@C/C-paper. At a given state of discharge, Li2S2 would be more thinly formed in the MgO@C/C-paper than in the C-paper owing to the larger surface area of MgO@C layer, allowing further reduction to Li2S.

Figure 7

Figure 7. XPS spectra of S 2p of (a) C-paper and (b) MgO@C/C-paper cathode after the first discharge in the Li2S8 solution.

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For stable Li–S battery cycling, the solid-state Li2S2/Li2S should be oxidized back to polysulfides to retain the cycle stability. In this regard, the C-paper and MgO@C/C-paper blank cathodes were observed at the discharged and charged states. The C-paper and MgO@C/C-paper cathodes were charged up to 2.27 V in order to oxidize solid-state Li2S2/Li2S to soluble polysulfides. Compared to the pristine state (Figure 8a,b), discharged C-paper and MgO@C/C-paper cathodes show different morphologies (Figure 8c,d), being covered with solid-state Li2S2 and/or Li2S, as identified by the XPS results. The S contents in the C-paper and MgO@C/C-paper were measured using EDS and found to be 25.2 and 22.2 atom %, respectively (Table S1). When charged, the C-paper cathode is still covered with Li2S2/Li2S, but the MgO@C/C-paper cathode seems similar to its pristine state (Figure 8e,f). In fact, the S contents were lowered to 13.5 and 3.1 atom % in the C-paper and MgO@C/C-paper after charging to 2.27 V. In other words, approximately 46% and 86% of the solid-state sulfur species (Li2S2/Li2S) were oxidized back to polysulfide, in the C-paper and MgO@C/C-paper, respectively. These results imply that the C-paper is passivated by the formation of Li2S2/Li2S where MgO@C/C-paper is capable of reutilizing the solid-state sulfur species.

Figure 8

Figure 8. SEM images of the blank cathodes. (a) Pristine C-paper, (b) pristine MgO@C/C-paper, (c) discharged C-paper, (d) discharged MgO@C/C-paper, (e) charged C-paper, and (f) charged MgO@C/C-paper.

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The Nyquist plots of the standard, C-paper, and MgO@C/C-paper cells are shown in Figure S11. The first semicircle shown at the high-frequency region represents charge transfer resistance (Rct) at the interface between the cathode and the electrolyte. The next semicircle represents the interfacial contact resistance (Rint) due to the formation of an insulating layer (Li2S2/Li2S). (45) Before cycling, C-paper and MgO@C/C-paper show a very similar plot in the high-frequency region and have very small Rct compared to the standard cell. This result is due to the presence of a conductive interlayer at the cathode surface. All the cells have a small semicircle corresponding to Rint in the medium-frequency region due to self-discharge. After 10 cycles, MgO@C/C-paper cell has the smallest Rct and Rint among other cells. Such a low resistance confirms that the MgO@C layer prevents C-paper from passivation by high reutilization of the solid-state sulfur species.
Figure 9 presents the high-angle annular dark-field (HAADF) cross-sectional images and EDS mapping images of C-paper and MgO@C/C-paper. In the C-paper, as observed in SEM images, Li2S2/Li2S is observed on carbon fiber both at charged and discharged states. Inactive Li2S2/Li2S residue could not be oxidized back to polysulfides and passivates carbon surface. In the MgO@C/C-paper cathode, Mg and S signals are overlapped both at charged and discharged states. Theses outcomes reflect that polysulfides diffuse through the MgO@C layer and reduce to Li2S2/Li2S. In addition, compared to the discharged state (Figure 9c), sulfur signals are substantially weaker in the charged MgO@/C-paper (Figure 9d), implying oxidation of Li2S2/Li2S to the polysulfide.

Figure 9

Figure 9. STEM HAADF images and EDS mapping of (a) discharged and (b) charged C-paper and (c) discharged and (d) charged MgO@C/C-paper.

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The unique structure of the MOF-derived MgO@C, which consists of highly porous carbon with MgO nanoparticles, efficiently improves the utilization and cycle retention of sulfur. Figure 10 schematically illustrates roles of the MgO@C layer in promoting the redox reactions of sulfur species on C-paper interlayer. The highly porous MOF-derived carbon and polar MgO provide abundant polysulfide capturing sites. The uniformly distributed nanosized MgO with low surface diffusion barrier provides the anchored polysulfides with fast and short diffusion pathways to carbon for the reduction to Li2S2/Li2S. Owing to the large surface area, the solid-state Li2S2/Li2S are deposited thinly on the MOF-derived carbon, thereby providing a short electron pathway from the carbon fiber to the Li2S2/Li2S surface. Thus, Li2S2 can be further reduced to Li2S during discharge, and Li2S/Li2S2 can be efficiently oxidized back to polysulfide.

Figure 10

Figure 10. Schematic diagram of redox reaction of polysulfide on C-paper and MgO@C/C-paper; MgO nanoparticle anchors dissolved polysulfides and diffused to carbon composite for reduction.

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Conclusion

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MgO@C was synthesized on a free-standing carbon paper (MgO@C/C-paper) and presented as an interlayer between the cathode and the separator of a Li–S cell. By pyrolyzing a novel precursor for the MgO@C, highly porous carbon was obtained with uniformly distributed MgO nanoparticles. The Li–S cells assembled with C-paper and MgO@C/C-paper demonstrated initial discharge capacities (898 and 980 mAh g–1, respectively) much higher than that of the interlayer-free cell (729 mAh g–1), owing to the high electrical conductivity of the interlayers. The MgO@C/C-paper cell exhibited superior cycle stability of the C-paper cell; at the 200th cycle, capacity retention of MgO@C/C-paper and C-paper cell was 78.3% and 76.5%, respectively, with a sulfur loading of 1.7 mg cm–2. In the MgO@C, MgO nanoparticle anchors dissolved polysulfides that diffuse to carbon matrix for electrochemical reactions. The unique structure of MOF-derived MgO@C provides polysulfides with numerous anchoring sites and short diffusion pathways from MgO to carbon, enabling efficient utilization of dissolved polysulfides. In addition, passivation of the carbon substrate is prevented since the solid-state sulfur species (Li2S2/Li2S) deposited on MgO@C is efficiently oxidized to polysulfide during charging, increasing the utilization and the reversibility of the Li–S cell.

Experimental Section

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Material Preparation

Synthesis of Mg-MOF-74 and MgO@C/C-paper

Mg-MOF-74 was synthesized on carbon paper (denoted as “MOF/C-paper”) through a solvothermal method using magnesium acetate tetrahydrate (Mg(CH3COO)2·4H2O) as a metal precursor and 2,5-dihydroxyterephthalic acid (H4DHTP) as an organic ligand. (30) The magnesium acetate tetrahydrate was dissolved in a mixture of 1 mL of deionized (DI) water, 1 mL of ethanol, and 8 mL of N,N-dimethylformamide (DMF). H4DHTP was dissolved in 10 mL of DMF and stirred for 1 h. The fully dissolved H4DHTP solution was added dropwise to the magnesium acetate solution. The prepared solution was transferred into a Teflon-lined autoclave, and commercial carbon paper (t: 0.10 ± 0.01 mm, density: 0.78 g/cm3) was soaked in the solution. The C-paper was composed of carbon fibers with a diameter of approximately 5 μm with a highly porous structure (Figure 1a–c), allowing penetration of the solution. The autoclave was placed in a convection oven and kept at 125 °C for 6 h for the solvothermal reaction. The soaked carbon paper was washed with DMF and dried in a vacuum oven overnight to obtain MOF/C-paper. To convert Mg-MOF-74 to MgO and carbon, the prepared MOF/C-paper was heat-treated at 900 °C under an Ar gas condition for 1 h (denoted as “MgO@C/C-paper”).

Material Characterizations

The surface and cross-section of each sample were observed using a scanning electron microscope (SEM, Phillips, XL30S). An elemental analysis was conducted using energy-dispersive X-ray spectroscopy (EDS) attached to the SEM. Morphological and elemental analysis of the samples were conducted using a scanning transmission electron microscope (S/TEM, FEI Titan cubed G2 60-300). The S/TEM specimens were prepared via ion-beam milling using the focused ion beam (FIB, FEI Helios G4 UX) method. The structural phase was classified with a high-resolution powder X-ray diffractometer (XRD, RIGAKU, SmartLab) using Cu K-α-1 (λ = 1.5418 Å) radiation at a scanning speed of 0.5°/min in the 2θ range of 5–80°. The surface elemental information and corresponding valence states were confirmed by X-ray photoelectron spectrometry (XPS, ThermoFisher Scientific, K-Alpha+, MXP10). The conductivity of the carbon interlayer was measured using a manual probe station (SUMMIT11862B) with a Keithley instrument (4200-SCS/F). The surface area and pore size distribution of the interlayers were measured by a surface area and pore size analyzer (3Flex) using the Brunauer–Emmett–Teller (BET) method. The thermal stability and volatile components of the interlayer were monitored via a high-resolution thermogravimetric analysis (TGA, TG209 F1 Libra) in the temperature range of 30–900 °C with a step of 5 °C/min in air. The electrical conductivity of the interlayers was measured with a manual probe station (SUMMIT11862B) integrated with a Keithley instrument (4200-SCS/F).

Electrochemical Measurements

Li–S full cells were prepared without an interlayer and using the carbon paper and MgO@C/C as an interlayer. A Li metal disk (D: 15.6 mm, w: 0.45 mm, MTI Korea) was used as an anode, and a polyethylene separator (Tonen Chemical Corporation) was used as a separator. To fabricate the cathode, a slurry was prepared by mixing 70 wt % sulfur powder (325 mesh S8, Alfa Aesar), 20 wt % carbon black (Super-P), and 10 wt % poly(vinylidene fluoride) (PVDF, Sigma-Aldrich) in N-methyl-1,2-pyrrolidone (NMP, Sigma-Aldrich). The slurry was cast using the doctor-blade method onto an aluminum (Al) foil current collector and dried in a vacuum oven at 80 °C overnight. The cathode cast on Al foil had a loading mass of the active material of 1.7 mg cm–2. As an electrolyte, 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a mixture of 1,3-dioxolane/1,2-dimethoxyethane (DOL/DME, 1:1 v/v) was used with 0.2 M LiNO3 as an additive. CR2032-type coin cells were assembled in an argon-filled glovebox (MOTech Co., Ltd.). Electrochemical tests were performed in a cutoff voltage range of 1.7–2.8 V (vs Li+/Li) using a battery cycler (WonATech) at room temperature (25 °C). The cells were cycled at 0.05 C in the first cycle for the activation step, and the remaining cycles were cycled at 0.2 C. To investigate the interaction between the dissolved polysulfide and the interlayers, the cells were assembled using carbon and MgO@C/C interlayers as a cathode and 50 μL of a 0.125 M Li2S8 solution in DOL/DME as an active material. The cell was discharged and charged at 0.027 mA. The electrochemical impedance spectroscopy (EIS) result was obtained using a VersaSTAT 4 Potentiostat Galvanostat with VersaStudio software. The measurement was taken at the open-circuit voltage with the frequency range from 1 MHz to 0.01 Hz with amplitude of 10 mV.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.2c05064.

  • SEM images of the MOF powder and the heat-treated MOF powder, XRD patterns of the MOF powder and heat-treated MOF powder, Thermogravimetric analysis (TGA) curve of (a) MgO@C powder and (b) MgO@C/C-paper, BJH pore size distribution of the MOF powder and MgO@C powder, TEM HAADF images, EDS mapping images, and EDS spectrum of heat-treated MOF powder and after acid etching, electrochemical performance of the Li–S cells without an interlayer and with C-paper, C/C-paper, and MgO@C/C-paper at 0.2C, charge–discharge curves of standard, C-paper, and MgO@C/C-paper at different C-rates, rate performance of cells with different interlayers, photo images of the coin cells without and with interlayers after the first discharge, schematic diagram of the interlayer interacting with a polysulfide solution, and elemental analysis of sulfur with C-paper and MgO@C/C-paper after soaking in 5 mM polysulfide solution, charge and discharge curve of the coin cells assembled with C-paper and MgO@C/C-paper as a blank cathode and polysulfide (Li2S8) dissolved in the electrolyte as an active material, electrochemical impedance spectroscopy (EIS) spectra of the standard coin cell, C-paper cell, and MgO@C/C-paper cell before cycling and after 10 cycles, and quantitative elemental composition of cycled interlayer obtained from the EDS spectra (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Hyeonmuk Kang - Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea;  Orcidhttps://orcid.org/0000-0003-0174-555X
    • Jaewook Shin - Advanced Battery Center, KAIST Institute for NanoCentury, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea;  Orcidhttps://orcid.org/0000-0002-7431-9255
    • Tae-Hee Kim - Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
    • Yongju Lee - Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
    • Daehee Lee - Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
    • Junho Lee - Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-Ro, Yuseong-gu, Daejeon 34141, Republic of Korea
    • Gyungtae Kim - Department of Measurement & Analysis, National NanoFab Center, Daejeon 34141, Republic of Korea
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Thanks go to the KAIST Analysis Center for Research Advancement (KARA) and to the National NanoFab Center for granting access to their equipment. This research was supported by the KAIST-funded Global Singularity Research Program for 2022 and by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE), (P0017120, The Competency Development Program for Industry Specialist).

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    Review-The Importance of Chemical Interactions between Sulfur Host Materials and Lithium Polysulfides for Advanced Lithium-Sulfur Batteries
    Pang, Quan; Liang, Xiao; Kwok, C. Y.; Nazar, Linda F.
    Journal of the Electrochemical Society (2015), 162 (14), A2567-A2576CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
    A review. This overview details the recently recognized importance of strong chem. interactions between sulfur host materials and lithium polysulfides/sulfide to improve the performance of Li-S batteries, esp. with respect to cycle life. Sulfur hosts consisting of functionally modified surfaces, metal oxides, and carbides that rely on either polar interactions or the thiosulfate mechanism for sulfide binding, metal-org. frameworks that exhibit Lewis-acid behavior, and functional polymers are reviewed. Variety of studies are summarized that explore the nature and strength of the interaction of these materials with polysulfides and its effect on cycle life, showing that capacity fading is reduced to as low as 0.03% per cycle with effective functional cathode host surfaces.
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  13. 13
    Lv, D.; Zheng, J.; Li, Q.; Xie, X.; Ferrara, S.; Nie, Z.; Mehdi, L. B.; Browning, N. D.; Zhang, J.-G.; Graff, G. L.; Liu, J.; Xiao, J. High Energy Density Lithium-Sulfur Batteries: Challenges of Thick Sulfur Cathodes. Adv. Energy Mater. 2015, 5 (16), 1402290,  DOI: 10.1002/aenm.201402290
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  14. 14
    Chen, L.; Yu, H.; Li, W.; Dirican, M.; Liu, Y.; Zhang, X. Interlayer design based on carbon materials for lithium–sulfur batteries: a review. Journal of Materials Chemistry A 2020, 8 (21), 10709– 10735,  DOI: 10.1039/D0TA03028G
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    14
    Interlayer design based on carbon materials for lithium-sulfur batteries
    Chen, Lei; Yu, Hui; Li, Wenxiao; Dirican, Mahmut; Liu, Yong; Zhang, Xiangwu
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (21), 10709-10735CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A review. Lithium-sulfur batteries were extensively investigated during the past two decades for their extremely high theor. specific energy (2600 W h kg-1) and volumetric energy d. (2800 W h L-1). However, their industrialization has been restrained due to the insulating nature of sulfur, vol. expansion of sulfur cathodes, formation of lithium dendrites, and terrible shuttle effect of sol. lithium polysulfides (Li2Sx, 3 ≤ x ≤ 8). Many researchers have been struggling with the design of interlayers having remarkable cond. and polysulfide-trapping capability so that these persistent drawbacks can be overcome. This review summarizes recently developed Li-S batteries with novel interlayers based on carbon materials, such as graphene, carbon nanotubes, carbon fibers, and nanofibers. The electrochem. properties of Li-S batteries with various interlayers are systematically compared. In particular, the enhancing mechanisms of Li-S batteries after the insertion of these interlayers are highlighted. Existing challenges and future development strategies with regard to high-energy Li-S batteries having carbon interlayers have also been summarized, and a prospective has been provided.
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  15. 15
    Jeong, Y. C.; Kim, J. H.; Nam, S.; Park, C. R.; Yang, S. J. Rational Design of Nanostructured Functional Interlayer/Separator for Advanced Li-S Batteries. Adv. Funct. Mater. 2018, 28 (38), 1707411,  DOI: 10.1002/adfm.201707411
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    Huang, J.-Q.; Xu, Z.-L.; Abouali, S.; Akbari Garakani, M.; Kim, J.-K. Porous graphene oxide/carbon nanotube hybrid films as interlayer for lithium-sulfur batteries. Carbon 2016, 99, 624– 632,  DOI: 10.1016/j.carbon.2015.12.081
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    16
    Porous graphene oxide/carbon nanotube hybrid films as interlayer for lithium-sulfur batteries
    Huang, Jian-Qiu; Xu, Zheng-Long; Abouali, Sara; Akbari Garakani, Mohammad; Kim, Jang-Kyo
    Carbon (2016), 99 (), 624-632CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Highly porous, conductive graphene oxide (GO)/carbon nanotube (CNT) composite films are synthesized via facile vacuum filtration of hybrid dispersion. The flexible film is used as interlayer between separator and sulfur cathode to entrap active materials and prevent polysulfide shuttle. The lithium-sulfur (Li-S) battery furnished with an optimal GO/CNT interlayer delivers an excellent reversible capacity of 671 mA h/g after 300 cycles with a low degrdn. rate of 0.33 mA h/g or 0.043% per cycle at 0.2C. The encouraging outcome arises from synergistic effects of interlayer characteristics: namely, (i) the porous structure facilitates easy ion transport and electrolyte penetration; (ii) the GO layers with oxygenated functional groups entrap active materials, preventing polysulfide shuttle and enhancing their recycling; and (iii) the highly conductive CNTs offer fast pathways for electron/ion transfer.
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  17. 17
    Singhal, R.; Chung, S.-H.; Manthiram, A.; Kalra, V. A free-standing carbon nanofiber interlayer for high-performance lithium–sulfur batteries. Journal of Materials Chemistry A 2015, 3 (8), 4530– 4538,  DOI: 10.1039/C4TA06511E
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    17
    A free-standing carbon nanofiber interlayer for high-performance lithium-sulfur batteries
    Singhal, Richa; Chung, Sheng-Heng; Manthiram, Arumugam; Kalra, Vibha
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (8), 4530-4538CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Free-standing porous carbon nanofibers with tunable surface area and pore structure have been investigated as an interlayer between the sulfur cathode and the separator to inhibit the shuttling of the intermediate polysulfides in lithium-sulfur batteries. Specifically, the effects of thickness, surface area, and pore size distribution of carbon nanofiber interlayers on the performance of lithium-sulfur batteries have been studied. The carbon nanofiber interlayer not only reduces the electrochem. resistance but also localizes the migrating polysulfides and traps them, thereby improving the discharge capacity as well as cyclability. It was found that the optimum thickness of the interlayer is a crit. factor to achieve good cell performance, in addn. to the surface area and pore structure. A high initial discharge capacity of 1549 mA-h/g at C/5 rate, which is 92% of the theor. capacity of sulfur, with 98% av. coulombic efficiency and 83% capacity retention after 100 cycles was obtained with a meso-microporous carbon nanofiber interlayer.
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  18. 18
    Su, Y. S.; Manthiram, A. A new approach to improve cycle performance of rechargeable lithium-sulfur batteries by inserting a free-standing MWCNT interlayer. Chem. Commun. (Camb) 2012, 48 (70), 8817– 9,  DOI: 10.1039/c2cc33945e
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    18
    A new approach to improve cycle performance of rechargeable lithium-sulfur batteries by inserting a free-standing MWCNT interlayer
    Su, Yu-Sheng; Manthiram, Arumugam
    Chemical Communications (Cambridge, United Kingdom) (2012), 48 (70), 8817-8819CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A conductive multiwalled carbon nanotube (MWCNT) interlayer acting as a pseudo-upper current collector not only reduces the charge transfer resistance of sulfur cathodes significantly, but also localizes and retains the dissolved active material during cycling.
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    Huang, J.-Q.; Zhang, Q.; Wei, F. Multi-functional separator/interlayer system for high-stable lithium-sulfur batteries: Progress and prospects. Energy Storage Materials 2015, 1, 127– 145,  DOI: 10.1016/j.ensm.2015.09.008
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    Liu, X.; Huang, J. Q.; Zhang, Q.; Mai, L. Nanostructured Metal Oxides and Sulfides for Lithium-Sulfur Batteries. Adv. Mater. 2017, 29 (20), 1601759,  DOI: 10.1002/adma.201601759
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    Zhuang, R.; Yao, S.; Shen, X.; Li, T. A freestanding MoO2-decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery. International Journal of Energy Research 2019, 43 (3), 1111– 1120,  DOI: 10.1002/er.4334
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    A freestanding MoO2-decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery
    Zhuang, Ruiyuan; Yao, Shanshan; Shen, Xiangqian; Li, Tianbao
    International Journal of Energy Research (2019), 43 (3), 1111-1120CODEN: IJERDN; ISSN:0363-907X. (John Wiley & Sons Ltd.)
    Summary : Lithium-sulfur (Li-S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge-discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO2 nanoparticles (MoO2-CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li-S battery. The S/MoO2-CNFs/Li battery showed a discharge capacity of 6.93 mAh cm-2 (1366 mAh g-1) in the first cycle at a c.d. of 0.42 mA cm-2 and 1006 mAh g-1 over 150 cycles. Moreover, even at the highest c.d. (8.4 mA cm-2), the battery achieved 865 mAh g-1. The stable electrochem. behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO2-CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO2-CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.
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  22. 22
    Xiao, Z.; Yang, Z.; Wang, L.; Nie, H.; Zhong, M.; Lai, Q.; Xu, X.; Zhang, L.; Huang, S. A Lightweight TiO(2)/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long-Life Lithium-Sulfur Batteries. Adv. Mater. 2015, 27 (18), 2891– 8,  DOI: 10.1002/adma.201405637
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    22
    A Lightweight TiO2/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long-Life Lithium-Sulfur Batteries
    Xiao, Zhubing; Yang, Zhi; Wang, Lu; Nie, Huagui; Zhong, Mei-e; Lai, Qianqian; Xu, Xiangju; Zhang, Lijie; Huang, Shaoming
    Advanced Materials (Weinheim, Germany) (2015), 27 (18), 2891-2898CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    An integrated selective interlayer was obtained by coating the surface of a C-S battery cathode with a com. graphene-TiO2 film, which accounted for 7.8 wt.% of the entire cathode. The porous graphene afforded an addnl. elec. conductive network and phys. trapped sulfide and polysulfides. The TiO2 in the barrier film further chem. suppressed the dissoln. of polysulfides and alleviated the undesirable shuttle effect. The porous CNT-S cathode coated with the graphene-TiO2 film delivered a reversible specific capacity of 1040 mA-h/g over 300 cycles at 0.5 C, with ultralow capacity degrdn. rates of 0.01% and 0.018% per cycle at 2 and 3 C, resp., over 1000 cycles.
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  23. 23
    Hwang, J.-Y.; Kim, H. M.; Lee, S.-K.; Lee, J.-H.; Abouimrane, A.; Khaleel, M. A.; Belharouak, I.; Manthiram, A.; Sun, Y.-K. High-Energy, High-Rate, Lithium-Sulfur Batteries: Synergetic Effect of Hollow TiO2-Webbed Carbon Nanotubes and a Dual Functional Carbon-Paper Interlayer. Adv. Energy Mater. 2016, 6 (1), 1501480,  DOI: 10.1002/aenm.201501480
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    Park, J.; Yu, B.-C.; Park, J. S.; Choi, J. W.; Kim, C.; Sung, Y.-E.; Goodenough, J. B. Tungsten Disulfide Catalysts Supported on a Carbon Cloth Interlayer for High Performance Li-S Battery. Adv. Energy Mater. 2017, 7 (11), 1602567,  DOI: 10.1002/aenm.201602567
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    Tan, L.; Li, X.; Wang, Z.; Guo, H.; Wang, J. Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2018, 10 (4), 3707– 3713,  DOI: 10.1021/acsami.7b18645
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    25
    Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries
    Tan, Lei; Li, Xinhai; Wang, Zhixing; Guo, Huajun; Wang, Jiexi
    ACS Applied Materials & Interfaces (2018), 10 (4), 3707-3713CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The further development of Li-S batteries is limited by the fact that the sol. polysulfide leads to the shuttle effect, thereby reducing the cycle stability and cycle life of the batteries. To address this issue, here a thin and lightwt. (8 μm and 0.24 mg/cm2) reduced graphene oxide@MoS2 (rGO@MoS2) interlayer between the cathode and the com. separator is developed as a polysulfide barrier. The rGO plays the roles of both a polysulfide phys. barrier and an addnl. current collector, while MoS2 has a high chem. adsorption for polysulfides. The expts. demonstrate that the Li-S cell constructed with an rGO@MoS2-coated separator shows a high reversible capacity of 1122 mAh/g at 0.2 C, a low capacity fading rate of 0.116% for 500 cycles at 1 C, and an outstanding rate performance (615 mAh/g at 2 C). Such an interlayer is expected to be ideal for lithium-sulfur battery applications because of its excellent electrochem. performance and simple synthesis process.
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    Pourali, Z.; Yaftian, M. R.; Sovizi, M. R. Li2S/transition metal carbide composite as cathode material for high performance lithium-sulfur batteries. Mater. Chem. Phys. 2018, 217, 117– 124,  DOI: 10.1016/j.matchemphys.2018.06.074
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    Li2S/transition metal carbide composite as cathode material for high performance lithium-sulfur batteries
    Pourali, Zeinab; Yaftian, Mohammad Reza; Sovizi, Mohammad Reza
    Materials Chemistry and Physics (2018), 217 (), 117-124CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)
    Lithium sulfide (Li2S) with high capacity (1166 mAh g-1) is a promising cathode material for lithium/sulfur (Li/S) batteries which can be paired with non-lithium anodes for avoiding safety issues. Nonetheless, the application of Li2S in Li/S cells is limited because their low electronic and ionic conductivities, on one hand, and the polysulfides dissoln. problems, on the other hand. In this study, Li2S/Ti3C2TX composite has been prepd. by a soln.-based method followed by high energy ball milling process. XRD and SEM techniques revealed the presence of nano-size Li2S particles in the prepd. composite. The as-prepd. electrode exhibited an initial capacity of 708 mAh g-1 with a capacity retention of ∼74.5% after 100 cycles (528 mAh g-1), which was higher than that of the microsize com. Li2S at 0.1 C. This superior performance was attributed to the high elec. cond. and two dimensional structure of Ti3C2TX. These advantages result in the redn. of energy barrier for the transport of Li ions through nano-size Li2S particles. Consequently, a homogeneous distribution of Li2S particles in the composite inhibited the lithium polysulfide dissoln. The results confirmed the Li2S/Ti3C2TX composite based electrode as a potential candidate for applying in metal-free anodes of rechargeable Li/S batteries.
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    Zhou, F.; Li, Z.; Luo, X.; Wu, T.; Jiang, B.; Lu, L. L.; Yao, H. B.; Antonietti, M.; Yu, S. H. Low Cost Metal Carbide Nanocrystals as Binding and Electrocatalytic Sites for High Performance Li-S Batteries. Nano Lett. 2018, 18 (2), 1035– 1043,  DOI: 10.1021/acs.nanolett.7b04505
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    27
    Low Cost Metal Carbide Nanocrystals as Binding and Electrocatalytic Sites for High Performance Li-S Batteries
    Zhou, Fei; Li, Zheng; Luo, Xuan; Wu, Tong; Jiang, Bin; Lu, Lei-Lei; Yao, Hong-Bin; Antonietti, Markus; Yu, Shu-Hong
    Nano Letters (2018), 18 (2), 1035-1043CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Lithium sulfur (Li-S) batteries are considered as promising energy storage systems for the next generation of batteries due to their high theor. energy densities and low cost. Much effort has been made to improve the practical energy densities and cycling stability of Li-S batteries via diverse designs of materials nanostructure. However, achieving simultaneously good rate capabilities and stable cycling of Li-S batteries is still challenging. Herein, we propose a strategy to utilize a dual effect of metal carbide nanoparticles decorated on carbon nanofibers (MC NPs-CNFs) to realize high rate performance, low hysteresis, and long cycling stability of Li-S batteries in one system. The adsorption expts. of lithium polysulfides (LiPS) to MC NPs and corresponding theor. calcns. demonstrate that LiPS are likely to be adsorbed and diffused on the surface of MC NPs because of their moderate chem. bonding. MC NPs turn out to have also an electrocatalytic role and accelerate electrochem. redox reactions of LiPS, as proven by cyclic voltammetry anal. The fabricated Li-S batteries based on the W2C NPs-CNFs hybrid electrodes display not only high specific capacity of 1200 mAh/g at 0.2C but also excellent rate performance and cycling stability, for example, a model setup can be operated at 1C for 500 cycles maintaining a final specific capacity of 605 mAh/g with a degrdn. rate as low as 0.06%/cycle.
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    Tao, X.; Wang, J.; Liu, C.; Wang, H.; Yao, H.; Zheng, G.; Seh, Z. W.; Cai, Q.; Li, W.; Zhou, G.; Zu, C.; Cui, Y. Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design. Nat. Commun. 2016, 7, 11203,  DOI: 10.1038/ncomms11203
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    Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design
    Tao, Xinyong; Wang, Jianguo; Liu, Chong; Wang, Haotian; Yao, Hongbin; Zheng, Guangyuan; Seh, Zhi Wei; Cai, Qiuxia; Li, Weiyang; Zhou, Guangmin; Zu, Chenxi; Cui, Yi
    Nature Communications (2016), 7 (), 11203CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Lithium-sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissoln. of lithium polysulfides, vol. expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technol. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption expts. and theor. calcns. reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.
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    Li, Z. Q.; Lu, C. J.; Xia, Z. P.; Zhou, Y.; Luo, Z. X-ray diffraction patterns of graphite and turbostratic carbon. Carbon 2007, 45 (8), 1686– 1695,  DOI: 10.1016/j.carbon.2007.03.038
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    X-ray diffraction patterns of graphite and turbostratic carbon
    Li, Z. Q.; Lu, C. J.; Xia, Z. P.; Zhou, Y.; Luo, Z.
    Carbon (2007), 45 (8), 1686-1695CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    To identify the influence of microstructural variation on the x-ray diffraction intensities, x-ray diffraction patterns of hexagonal graphite (h-graphite) and turbostratic C (t-C) were simulated by the general Debye equation. The numeric d. of interat. distance (NDID) is sensitive to the size and microstructure of a crystallite, so that it is used to characterize the structures of h-graphite and t-C. The dependence of the diffraction angles and full width at half max. (FWHMs) of diffraction lines on the crystallite size and distortion factors was examd. by computer simulation. The distortion factors for t-C, including rotation, translation, curvature, local pos. fluctuation of interlayer spacing of graphene layers and fluctuation of at. positions, have different influence on the NDIDs, hence on the x-ray diffraction patterns. The simulation results indicate that the diffraction angles and FWHMs of diffraction lines cannot be simply used to characterize the lattice parameters and crystallite sizes of t-C.
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    Campbell, J.; Tokay, B. Controlling the size and shape of Mg-MOF-74 crystals to optimize film synthesis on alumina substrates. Microporous Mesoporous Mater. 2017, 251, 190– 199,  DOI: 10.1016/j.micromeso.2017.05.058
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    Controlling the size and shape of Mg-MOF-74 crystals to optimize film synthesis on alumina substrates
    Campbell, James; Tokay, Begum
    Microporous and Mesoporous Materials (2017), 251 (), 190-199CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
    Mg-MOF-74 is a metal org. framework with the highest CO2 adsorption capacity of any porous material. Therefore, it has been suggested for CO2 sepns. as both an adsorbent and incorporated into membranes. Design of the Mg-MOF-74 crystal morphol. is important to expand the applicability of the material. In this paper one step synthesis of Mg-MOF-74 films has been achieved by controlling the Mg-MOF-74 crystal morphol. Results show that increasing the fraction of ethanol and water in the reaction soln. relative to DMF (DMF) increases the size of the crystals produced, while resulting in a subsequent drop in yield. By using solvent compn. to control the Mg-MOF-74 crystal size and shape the synthesis of Mg-MOF-74 thin films was achieved in one step, without the need for seeding. Films could be produced as thin as 1 μm, ten times thinner than any other previous membranes in the M-MOF-74 series, in a fraction of the time (only 2.5 h). Thicker films (up to 14 μm) could also be produced by increasing the fraction of ethanol and water in reaction soln., offering a methodol. by which the thickness of Mg-MOF-74 membranes can be controlled. Films were produced on porous tubular alumina supports, and single gas measurements were conducted resulting in a CO2 permeance of 7.4 × 10-7 mol m-2 s-1 Pa-1 and an ideal CO2/CH4 selectivity of 0.5.
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    Carrasco, J. A.; Romero, J.; Abellan, G.; Hernandez-Saz, J.; Molina, S. I.; Marti-Gastaldo, C.; Coronado, E. Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures. Chem. Commun. (Camb) 2016, 52 (58), 9141– 4,  DOI: 10.1039/C6CC02252A
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    Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures
    Carrasco, J. A.; Romero, J.; Abellan, G.; Hernandez-Saz, J.; Molina, S. I.; Marti-Gastaldo, C.; Coronado, E.
    Chemical Communications (Cambridge, United Kingdom) (2016), 52 (58), 9141-9144CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A hierarchical porous carbon prepd. via direct carbonization of Ni-MOF-74 loaded with furfuryl alc. at 450 °C displays high specific capacitance in comparison with other MOF-derived carbons as a result of the formation of micropores smaller than 1 nm.
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    Liu, S. H.; Liu, X. J.; Liu, B.; Liu, L. M.; Jin, W. Z.; Hu, X. J. Effect of some alloying elements on boiling point of magnesium. Mater. Sci. Technol. 2005, 21 (6), 735– 738,  DOI: 10.1179/174328405X43126
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    Effect of some alloying elements on boiling point of magnesium
    Liu, S. H.; Liu, X. J.; Liu, B.; Liu, L. M.; Jin, W. Z.; Hu, X. J.
    Materials Science and Technology (2005), 21 (6), 735-738CODEN: MSCTEP; ISSN:0267-0836. (Maney Publishing)
    The evapn. capacity of alloys differs with temp., and this is the basis of a new exptl. method to measure the b.ps. of various kinds of alloys. In the present work, the effects of Al, Zn, Mn and La addns. on the b.p. of magnesium were studied. Various elemental addns. and their varying contents in magnesium alloys have different influences on the b.p. of the alloys. Among these addns., Zn affected the b.p. of magnesium alloys most obviously, followed by Mn, Al and La. The b.p. of Mg-6 wt.% Zn alloy was the highest in the present study, up to 1715 K.
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    Sun, Y.; Wang, J.; Guo, J.; Zu, Q.; Huang, J.; Peng, Q. Atomic-scale oxidation mechanisms of single-crystal magnesium. Nanoscale 2019, 11 (48), 23346– 23356,  DOI: 10.1039/C9NR07265A
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    Atomic-scale oxidation mechanisms of single-crystal magnesium
    Sun, Yong; Wang, Jinming; Guo, Jianxin; Zu, Qun; Huang, Jianyu; Peng, Qiuming
    Nanoscale (2019), 11 (48), 23346-23356CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Understanding the oxidn. process of active metals plays a crucial role in improving their mech./oxidn. properties. Using in situ environmental transmission electron microscopy and d.-functional theory, we firstly clarify the oxidn. process of single-crystal Mg at the at. scale by using a new double-hole technique. A unique incipient interval-layered oxidn. mechanism of single-crystal Mg has been confirmed, in which O atoms intercalate through the clean (2‾1‾10) surface into the alternate-layered tetrahedral sites, forming a metastable HCP-type MgO0.5 structure. Upon the increased incorporation of oxygen at the neighboring interstitial sites, the HCP-type Mg-O tetrahedron structure sharply transforms into the FCC-type MgO oxide. In addn., a typical anisotropic growth mechanism of oxides has been identified, wherein it involves two routes: the epitaxial growth of the MgO layer and the inward migration of the MgO/Mg interface. The whole oxidn. rate of single-crystal Mg is mostly detd. by the inward migration rate of the MgO/Mg interface, which is about six times higher than that of the epitaxial growth rate of the MgO layer along the same orientation planes. Moreover, the inward migration rate of the (020)MgO(0110)Mg interface is about twice as large as that of the (200)MgO→ (0002)Mg interface. This continuous oxide growth is mainly related to the deffects in the MgO layer, which builds effective channels for the diffusion of O and Mg atoms. The in situ double-hole observations together with theor. calcns. provide a potential trajectory to probe the oxidn. fundamentals of other active metals.
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    Chen, S.; Xin, Y.; Zhou, Y.; Zhang, F.; Ma, Y.; Zhou, H.; Qi, L. Branched CNT@SnO2 nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability. J. Mater. Chem. A 2014, 2 (37), 15582– 15589,  DOI: 10.1039/C4TA03218G
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    Branched CNT@SnO2 nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability
    Chen, Shuai; Xin, Yuelong; Zhou, Yiyang; Zhang, Feng; Ma, Yurong; Zhou, Henghui; Qi, Limin
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (37), 15582-15589CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A novel hierarchical heterostructure consisting of carbon-coated SnO2 mesocryst. nanorods radially aligned on carbon nanotubes (CNTs) was designed and fabricated by a two-step growth process. SnO2 nanorods were first grown directly on CNTs by a facile solvothermal reaction, which were subsequently coated with a thin layer of carbon to form a branched CNT@SnO2@carbon sandwich-type heterostructure. When used as an anode material in lithium-ion batteries, the branched CNT@SnO2@C heterostructures exhibited highly reversible lithium storage behavior and excellent rate capability. The reversible capacity of the CNT@SnO2@C heterostructure reached 984 mA-h/g at a c.d. of 720 mA/g, and retained 590 mA-h/g at 3.6 A/g and 420 mA-h/g at 7.2 A/g. This superior performance might be ascribed to the improved mech. capability and high loading content of SnO2 of the branched architecture, the good elec. cond. of the CNT backbones and the carbon layer, and the high electrochem. reactivity of the one-dimensional mesocryst. SnO2 nanorods.
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    Xu, Z.; Chen, Y.; Li, W.; Li, J.; Yu, H.; Liu, L.; Wu, G.; Yang, T.; Luo, L. Preparation of boron nitride nanosheet-coated carbon fibres and their enhanced antioxidant and microwave-absorbing properties. RSC Adv. 2018, 8 (32), 17944– 17949,  DOI: 10.1039/C8RA02017E
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    Preparation of boron nitride nanosheet-coated carbon fibres and their enhanced antioxidant and microwave-absorbing properties
    Xu, Zhichao; Chen, Yongjun; Li, Wei; Li, Jianbao; Yu, Hui; Liu, Longyang; Wu, Gaolong; Yang, Tao; Luo, Lijie
    RSC Advances (2018), 8 (32), 17944-17949CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    In this study, annealing carbon fibers with boron and FeCl3·6H2O at elevated temps. was demonstrated as a novel route to coat carbon fibers with boron nitride (BN) nanosheets. The effect of annealing temp. on the thickness and microstructure of BN coating was investigated. Results showed that BN coating hardly formed at 1000°C, and uniform BN coating was achieved at 1100°C and 1200°C. However, further increasing the temp. to 1250°C triggered the formation of discretely distributed BN particles on the surface of the BN coating in addn. to the formation of a uniform BN coating. The BN coating and particles were constructed by numerous BN nanosheets with a bending and crumpling morphol. The thickness of the BN coating increased with increasing annealing temp. The oxidn. resistance of the carbon fibers dramatically enhanced after BN nanosheets were coated onto the carbon fiber surface. Moreover, given the low dielec. loss tangent of BN, the BN coating can improve the impedance matching of carbon fibers and enhance the microwave-absorbing property of carbon fibers significantly.
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    Lin, Y.; Chen, D.; Wang, S.; Han, D.; Xiao, M.; Meng, Y. Addressing Passivation of a Sulfur Electrode in Li-S Pouch Cells for Dramatically Improving Their Cyclic Stability. ACS Appl. Mater. Interfaces 2020, 12 (26), 29296– 29301,  DOI: 10.1021/acsami.0c05385
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    Addressing Passivation of a Sulfur Electrode in Li-S Pouch Cells for Dramatically Improving Their Cyclic Stability
    Lin, Yilong; Chen, Dongdong; Wang, Shuanjin; Han, Dongmei; Xiao, Min; Meng, Yuezhong
    ACS Applied Materials & Interfaces (2020), 12 (26), 29296-29301CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The effective passivation of a sulfur electrode in Li-S pouch cells is addressed by increasing the discharging cutoff voltage from 1.6 to 2.0 V. This simple method can effectively suppress the generation of solid and insulated Li2S deposition while reserves the majority of capacity and improves the cyclic stability of Li-S pouch cells. Upon increasing the discharging cutoff voltage from 1.6 to 2.0 V, the Li-S pouch cell loses only 8% of the initial discharge capacity and remarkably promotes the capacity retention rate from 62.4 to 91.6% within 40 cycles at 0.05C. The anal. of electrochem. and physics of a sulfur cathode demonstrates that the less Li2S deposition under the discharging cutoff voltage of 2.0 V can ensure fast reaction kinetics in Li-S pouch cells with high areal sulfur loadings and lean electrolyte. The mechanism of the passivation of a sulfur electrode is studied and discussed in detail. This brand new methodol. may provide an effective approach to enhance the cyclic stability of a Li-S battery.
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    Yu, F.; Zhou, H.; Shen, Q. Modification of cobalt-containing MOF-derived mesoporous carbon as an effective sulfur-loading host for rechargeable lithium-sulfur batteries. J. Alloys Compd. 2019, 772, 843– 851,  DOI: 10.1016/j.jallcom.2018.09.103
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    Modification of cobalt-containing MOF-derived mesoporous carbon as an effective sulfur-loading host for rechargeable lithium-sulfur batteries
    Yu, Faqi; Zhou, He; Shen, Qiang
    Journal of Alloys and Compounds (2019), 772 (), 843-851CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    Cobalt-contg. metal-org. frameworks (MOF) are synthesized, then carbonized and then acid etched to obtain mesoporous carbon for its potential application as lithium-sulfur (Li-S) battery cathode scaffolds. Before etching the resulting mesoporous carbon acquires a sp. surface area of 206.5 m2 g-1 and a pore vol. of 0.29 cm3 g-1, and in its sulfur-loading composite-1 the S-content is ∼45.2%. After etching the modified mesoporous carbon exhibits a great improvement in porosity (Surface area ∼650.2 m2 g-1 and pore vol. ∼ 0.77 cm3 g-1) and/or in sulfur-loading amt. (i.e., the S-content of composite-2 ∼ 50.0%). At 0.5 C (1 C = 1675 mA g-1), a composite-2 cathode delivers a high discharge capacity of 925.1 mAh g-1 in 2nd cycle and maintains a specific value of 781.1 mAh g-1 in the 140th cycle, much higher than those of composite-1 cathode. Both of the two composite electrodes display a slight increase of electrolyte-soln. resistance and surface-film resistance and an obvious decrease of charge-transfer resistance. By comparison, these resistances of composite-2 are smaller than those of composite-1. This, together with the acid-modified structural parameters reasonably account for the enhanced electrochem. properties of composite-2.
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    Yan, Y.; Wei, L.; Su, X.; Deng, S.; Feng, J.; Yang, J.; Chi, M.; Lei, H.; Li, Z.; Wu, M. The Crystallinity of Metal Oxide in Carbonized Metal Organic Frameworks and the Effect on Restricting Polysulfides. ChemNanoMat 2020, 6 (2), 274– 279,  DOI: 10.1002/cnma.201900642
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    The Crystallinity of Metal Oxide in Carbonized Metal Organic Frameworks and the Effect on Restricting Polysulfides
    Yan, Yingchun; Wei, Liangqin; Su, Xin; Deng, Shenzhen; Feng, Jianze; Yang, Jun; Chi, Mingna; Lei, Hu; Li, Zhongtao; Wu, Mingbo
    ChemNanoMat (2020), 6 (2), 274-279CODEN: CHEMSB; ISSN:2199-692X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Metal/carbon nanohybrids show promise for alleviating polysulfides shuttling in lithium-sulfur batteries. However, the synergetic effect between amorphous metal and carbon to restrict the migration of polysulfides is still far from fully understood. Herein, two porous metal/carbon nanohybrids with different crystallinity metal oxides components (amorphous Al2O3 and crystal Fe3O4) have been prepd. through pyrolysis of the MOF precursors, which are adopted as a sulfur support to impede the polysulfides shuttling. As expected, the amorphous Al2O3 with nitrogen-doped porous carbon exhibits an attractive durability at 1 C over 1000 cycles, meanwhile, the coulombic efficiency could maintain at 97.5%. Compared to it, crystal Fe3O4 shows an inferior electrochem. performance, which is attributed to the amorphous structure that can accelerate ions diffusion and charge transfer to improve the rate performance and capacity. The distinguished discharge performance of the design will be potentially used to develop applicable Li-S batteries.
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    Li, G.; Wang, S.; Zhang, Y.; Li, M.; Chen, Z.; Lu, J. Revisiting the Role of Polysulfides in Lithium-Sulfur Batteries. Adv. Mater. 2018, 30 (22), 1705590,  DOI: 10.1002/adma.201705590
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    Bai, S.; Liu, X.; Zhu, K.; Wu, S.; Zhou, H. Metal–organic framework-based separator for lithium–sulfur batteries Nature Energy 2016, 1 (7),  DOI: 10.1038/nenergy.2016.94 .
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    Li, M.; Wan, Y.; Huang, J.-K.; Assen, A. H.; Hsiung, C.-E.; Jiang, H.; Han, Y.; Eddaoudi, M.; Lai, Z.; Ming, J.; Li, L.-J. Metal–Organic Framework-Based Separators for Enhancing Li–S Battery Stability: Mechanism of Mitigating Polysulfide Diffusion. ACS Energy Letters 2017, 2 (10), 2362– 2367,  DOI: 10.1021/acsenergylett.7b00692
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    Metal-Organic Framework-Based Separators for Enhancing Li-S Battery Stability: Mechanism of Mitigating Polysulfide Diffusion
    Li, Mengliu; Wan, Yi; Huang, Jing-Kai; Assen, Ayalew H.; Hsiung, Chia-En; Jiang, Hao; Han, Yu; Eddaoudi, Mohamed; Lai, Zhiping; Ming, Jun; Li, Lain-Jong
    ACS Energy Letters (2017), 2 (10), 2362-2367CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    The shuttling effect of polysulfides severely hinders the cycle performance and commercialization of Li-S batteries, and significant efforts have been devoted to searching for feasible solns. to mitigate the effect in the past two decades. Recently, metal-org. frameworks (MOFs) with rich porosity, nanometer cavity sizes, and high surface areas have been claimed to be effective in suppressing polysulfide migration. However, the formation of large-scale and grain boundary-free MOFs is still very challenging, where a large no. of grain boundaries of MOF particles may also allow the diffusion of polysulfides. Hence, it is still controversial whether the pores in MOFs or the grain boundaries play the crit. role. In this study, we perform a comparative study for several commonly used MOFs, and our exptl. results and anal. prove that a layer of MOFs on a separator did enhance the capacity stability. Our results suggest that the chem. stability and the aggregation (packing) morphol. of MOF particles play more important roles than the internal cavity size in MOFs.
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    Ponraj, R.; Kannan, A. G.; Ahn, J. H.; Kim, D. W. Improvement of Cycling Performance of Lithium-Sulfur Batteries by Using Magnesium Oxide as a Functional Additive for Trapping Lithium Polysulfide. ACS Appl. Mater. Interfaces 2016, 8 (6), 4000– 6,  DOI: 10.1021/acsami.5b11327
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    Improvement of Cycling Performance of Lithium-Sulfur Batteries by Using Magnesium Oxide as a Functional Additive for Trapping Lithium Polysulfide
    Ponraj, Rubha; Kannan, Aravindaraj G.; Ahn, Jun Hwan; Kim, Dong-Won
    ACS Applied Materials & Interfaces (2016), 8 (6), 4000-4006CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Trapping lithium polysulfides formed in the sulfur pos. electrode of lithium-sulfur batteries is one of the promising approaches to overcome the issues related to polysulfide dissoln. In this work, we demonstrate that intrinsically hydrophilic magnesium oxide (MgO) nanoparticles having surface hydroxyl groups can be used as effective additives to trap lithium polysulfides in the pos. electrode. MgO nanoparticles were uniformly distributed on the surface of the active sulfur, and the addn. of MgO into the sulfur electrode resulted in an increase in capacity retention of the lithium-sulfur cell compared to a cell with pristine sulfur electrode. The improvement in cycling stability was attributed to the strong chem. interactions between MgO and lithium polysulfide species, which suppressed the shuttling effect of lithium polysulfides and enhanced the utilization of the sulfur active material. To the best of our knowledge, this report is the first demonstration of MgO as an effective functional additive to trap lithium polysulfides in lithium-sulfur cells.
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    Fan, F. Y.; Carter, W. C.; Chiang, Y. M. Mechanism and Kinetics of Li2S Precipitation in Lithium-Sulfur Batteries. Adv. Mater. 2015, 27 (35), 5203– 9,  DOI: 10.1002/adma.201501559
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    Mechanism and Kinetics of Li2S Precipitation in Lithium-Sulfur Batteries
    Fan, Frank Y.; Carter, W. Craig; Chiang, Yet-Ming
    Advanced Materials (Weinheim, Germany) (2015), 27 (35), 5203-5209CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In this paper, we characterize the kinetics and morphol. of Li2S electrodeposited from nonaq. (glyme-based) polysulfide solns. onto carbon fibers and multiwalled carbon nanotubes (MWCNT). Deposition is studied under potentiostatic conditions as a function of overpotential, and galvanostatic conditions as a function of current rate. The deposition mechanism is detd. from a combination of kinetic analyses and direct observations of Li2S morphol. at various stages of deposition by electron microscopy. It is shown that the morphol. of electrodeposited Li2S depends on the nucleation d. and relative rates of nucleation vs. growth, each of which can be manipulated by controlling the overpotential, the characteristics of the substrate, and the choice of solvent. Guidelines for optimizing storage capacity through substrate choice and electrokinetic control are presented.
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    Yang, X.; Gao, X.; Sun, Q.; Jand, S. P.; Yu, Y.; Zhao, Y.; Li, X.; Adair, K.; Kuo, L. Y.; Rohrer, J.; Liang, J.; Lin, X.; Banis, M. N.; Hu, Y.; Zhang, H.; Li, X.; Li, R.; Zhang, H.; Kaghazchi, P.; Sham, T. K.; Sun, X. Promoting the Transformation of Li2 S2 to Li2 S: Significantly Increasing Utilization of Active Materials for High-Sulfur-Loading Li-S Batteries. Adv. Mater. 2019, 31 (25), 1901220,  DOI: 10.1002/adma.201901220
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    Deng, Z.; Zhang, Z.; Lai, Y.; Liu, J.; Li, J.; Liu, Y. Electrochemical Impedance Spectroscopy Study of a Lithium/Sulfur Battery: Modeling and Analysis of Capacity Fading. J. Electrochem. Soc. 2013, 160 (4), A553– A558,  DOI: 10.1149/2.026304jes
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    Electrochemical impedance spectroscopy study of a lithium/sulfur battery: modeling and analysis of capacity fading
    Deng, Zhaofeng; Zhang, Zhian; Lai, Yanqing; Liu, Jin; Li, Jie; Liu, Yexiang
    Journal of the Electrochemical Society (2013), 160 (4), A553-A558CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
    The electrochem. behavior of a lithium/sulfur battery was studied by electrochem. impedance spectroscopy. An impedance model based on the anal. of electrochem. impedance spectra as a function of temp. and depth of discharge was developed. Then, by monitoring the evolution of impedance during the cycling process, the capacity fading mechanism of lithium/sulfur battery was investigated. The results show that the semicircle at the middle frequency of the electrochem. impedance spectra is ascribed to the charge-transfer process and the semicircle at high frequency is related to the interphase contact resistance. Furthermore, electrolyte resistance, interphase contact resistance, and charge-transfer resistance vary with cycle no. in different manners, and the charge-transfer resistance is the key factor contributing to the capacity fading of lithium/sulfur battery.
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  2. Shuaiqiang Feng, Jiongfan Wang, Jianfeng Wen, Xinyu Li, Zhiyong Wang, Yaping Zeng, Jianrong Xiao. Improvement of Redox Kinetics of Dendrite-Free Lithium–Sulfur Battery by Bidirectional Catalysis of Cationic Dual-Active Sites. ACS Sustainable Chemistry & Engineering 2023, 11 (23) , 8544-8555. https://doi.org/10.1021/acssuschemeng.3c01158
  3. Xu Zhang, Fengrui Liu, Chengjie Li, Da Lei, Qiang Zhang, Qingfeng Song, Xinlei Ma, Xingchen Jin, Fengxiang Zhang. Synergistic chemisorption and electrocatalysis of MoO2 nanoparticles/carbon nanosheets with strong catalyst-support interactions for high performance lithium–sulfur batteries. Carbon 2025, 235 , 120060. https://doi.org/10.1016/j.carbon.2025.120060
  4. Qiancheng Zhu, Weize Sun, Hua Zhou, Deyu Mao. A Review of Lithium–Sulfur Batteries Based on Metal–Organic Frameworks: Progress and Prospects. Batteries 2025, 11 (3) , 89. https://doi.org/10.3390/batteries11030089
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  • Abstract

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    Figure 1

    Figure 1. Top-view and cross-sectional SEM images of (a, b) C-paper, (c, d) MOF/C-paper, and (e, f) heat-treated MOF/C-paper.

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    Figure 2

    Figure 2. XRD patterns of C-paper, MOF/C-paper, and heat-treated MOF/C-paper.

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    Figure 3

    Figure 3. (a) SEM and (b) EDS elemental Mg mapping images of a fiber collected from the heat-treated MOF/C-paper. (c) TEM image of pyrolyzed MOF and FFT images for (d) the nanoparticle marked with a red square and (e) carbon matrix marked with a blue square in (c).

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    Figure 4

    Figure 4. Electrochemical performance of the Li–S cells without an interlayer (denoted as “standard”) and with C-paper and MgO@C/C-paper interlayer at 0.2 C. (a) Cycling performances with a sulfur loading mass of 1.7 mg cm–2. Charge–Discharge curves of (b) standard, (c) C-paper, and (d) MgO@C/C-paper.

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    Figure 5

    Figure 5. (a) Charge–Discharge curves and (b) electrochemical performance of the Li–S cells without an interlayer (denoted as “standard”) and with C-paper and MgO@C/C-paper interlayer at 0.2 C with sulfur loading of 3.3 mg cm–2.

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    Figure 6

    Figure 6. Top view SEM images of the interlayers (a), (b) before and (c, d) after the first discharge. Cross-section images and elemental EDS mapping images of (e) C-paper and (f) MgO@C/C-paper.

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    Figure 7

    Figure 7. XPS spectra of S 2p of (a) C-paper and (b) MgO@C/C-paper cathode after the first discharge in the Li2S8 solution.

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    Figure 8

    Figure 8. SEM images of the blank cathodes. (a) Pristine C-paper, (b) pristine MgO@C/C-paper, (c) discharged C-paper, (d) discharged MgO@C/C-paper, (e) charged C-paper, and (f) charged MgO@C/C-paper.

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    Figure 9

    Figure 9. STEM HAADF images and EDS mapping of (a) discharged and (b) charged C-paper and (c) discharged and (d) charged MgO@C/C-paper.

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    Figure 10

    Figure 10. Schematic diagram of redox reaction of polysulfide on C-paper and MgO@C/C-paper; MgO nanoparticle anchors dissolved polysulfides and diffused to carbon composite for reduction.

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  • References

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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1antbbF&md5=83e26c1001891292ed203a540ccf7508
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      The synthesis is reported of a graphene-sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating vol. expansion of the coated sulfur particles during discharge, trapping sol. polysulfide intermediates, and rendering the sulfur particles elec. conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ∼600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy d.
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      Electronic structure and chemical bonding of a graphene oxide-sulfur nanocomposite for use in superior performance lithium-sulfur cells
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      We have investigated the chem. bonding and electronic structure of a graphene oxide-sulfur nanocomposite by XPS, near-edge x-ray absorption fine structure, and x-ray emission spectroscopy. The nanocomposite, synthesized by a chem. reaction-deposition approach followed by low temp. thermal treatment, is composed of a thin and uniform sulfur film anchored on a graphene oxide sheet. The graphene oxide is partially reduced during the chem. synthesis process, resulting in the appearance of a C-H bond and an increase in the ordering of graphene oxide sheets. The moderate chem. interactions between sulfur and graphene oxide can preserve the intrinsic electronic structure of graphene oxide, and on the other hand, immobilize the sulfur on the graphene oxide sheets, which should be responsible for the excellent electrochem. performance of the lithium-sulfur cells by using the graphene oxide-sulfur nanocomposite as the cathode material.
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      Carbon with hierarchical pores from carbonized metal-organic frameworks for lithium sulphur batteries
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      This paper presents a novel method and rationale for using carbonized MOFs for S loading to fabricate cathode structures for Li-S batteries. Unique C materials with differing hierarchical pore structures were synthesized from 4 types of Zn-contg. metal-org. frameworks (MOFs). Cathode materials made from MOFs-derived carbons with higher mesopore (2-50 nm) vols. exhibit increased initial discharge capacities, whereas carbons with higher micropore (<2 nm) vols. lead to cathode materials with better cycle stability.
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    9. 9
      Li, G.; Sun, J.; Hou, W.; Jiang, S.; Huang, Y.; Geng, J. Three-dimensional porous carbon composites containing high sulfur nanoparticle content for high-performance lithium-sulfur batteries. Nat. Commun. 2016, 7, 10601,  DOI: 10.1038/ncomms10601
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      Three-dimensional porous carbon composites containing high sulfur nanoparticle content for high-performance lithium-sulfur batteries
      Li, Guoxing; Sun, Jinhua; Hou, Wenpeng; Jiang, Shidong; Huang, Yong; Geng, Jianxin
      Nature Communications (2016), 7 (), 10601CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Sulfur is a promising cathode material for lithium-sulfur batteries because of its high theor. capacity (1,675 mA h g-1); however, its low elec. cond. and the instability of sulfur-based electrodes limit its practical application. Here we report a facile in situ method for prepg. three-dimensional porous graphitic carbon composites contg. sulfur nanoparticles (3D S@PGC). With this strategy, the sulfur content of the composites can be tuned to a high level (up to 90 wt%). Because of the high sulfur content, the nanoscale distribution of the sulfur particles, and the covalent bonding between the sulfur and the PGC, the developed 3D S@PGC cathodes exhibit excellent performance, with a high sulfur utilization, high specific capacity (1,382, 1,242 and 1,115 mA h g-1 at 0.5, 1 and 2 C, resp.), long cycling life (small capacity decay of 0.039% per cycle over 1,000 cycles at 2 C) and excellent rate capability at a high charge/discharge current.
      >> More from SciFinder ®
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      Qian, X.; Jin, L.; Wang, S.; Yao, S.; Rao, D.; Shen, X.; Xi, X.; Xiang, J. Zn-MOF derived micro/meso porous carbon nanorod for high performance lithium–sulfur battery. RSC Adv. 2016, 6 (97), 94629– 94635,  DOI: 10.1039/C6RA19356K
      10
      Zn-MOF derived micro/meso porous carbon nanorod for high performance lithium-sulfur battery
      Qian, Xinye; Jin, Lina; Wang, Shanwen; Yao, Shanshan; Rao, Dewei; Shen, Xiangqian; Xi, Xiaoming; Xiang, Jun
      RSC Advances (2016), 6 (97), 94629-94635CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      In order to solve the problems of poor cycling stability and low coulombic efficiency in lithium-sulfur battery, induced by the low cond. of sulfur and the shuttle effect of sol. polysulfides, a unique micro/meso porous carbon nanorod (MPCN) was fabricated by carbonizing a zinc metal-org. framework (Zn-MOF) precursor, which was prepd. by a facile aq. soln. method at room temp. The mesopores in the MPCN are beneficial for the infiltration of electrolyte and the transportation of Li ions, and the micropores are sufficient to encapsulate sulfur and adsorb the sol. polysulfides. The MPCN-S cathode displays a discharge capacity of about 1000 mA h g-1 at the current rate of 0.5C and retains 740 mA h g-1 after 200 cycles with the coulombic efficiency up to 95%. Moreover, it still has a discharge capacity as high as 850 mA h g-1 when the current rate increased to 2C, which demonstrates a nice rate capability.
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    11. 11
      Kong, W.; Yan, L.; Luo, Y.; Wang, D.; Jiang, K.; Li, Q.; Fan, S.; Wang, J. Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide-Trapping Shield for High-Performance Li-S Batteries. Adv. Funct. Mater. 2017, 27 (18), 1606663,  DOI: 10.1002/adfm.201606663
      There is no corresponding record for this reference.
    12. 12
      Pang, Q.; Liang, X.; Kwok, C. Y.; Nazar, L. F. Review─The Importance of Chemical Interactions between Sulfur Host Materials and Lithium Polysulfides for Advanced Lithium-Sulfur Batteries. J. Electrochem. Soc. 2015, 162 (14), A2567– A2576,  DOI: 10.1149/2.0171514jes
      12
      Review-The Importance of Chemical Interactions between Sulfur Host Materials and Lithium Polysulfides for Advanced Lithium-Sulfur Batteries
      Pang, Quan; Liang, Xiao; Kwok, C. Y.; Nazar, Linda F.
      Journal of the Electrochemical Society (2015), 162 (14), A2567-A2576CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      A review. This overview details the recently recognized importance of strong chem. interactions between sulfur host materials and lithium polysulfides/sulfide to improve the performance of Li-S batteries, esp. with respect to cycle life. Sulfur hosts consisting of functionally modified surfaces, metal oxides, and carbides that rely on either polar interactions or the thiosulfate mechanism for sulfide binding, metal-org. frameworks that exhibit Lewis-acid behavior, and functional polymers are reviewed. Variety of studies are summarized that explore the nature and strength of the interaction of these materials with polysulfides and its effect on cycle life, showing that capacity fading is reduced to as low as 0.03% per cycle with effective functional cathode host surfaces.
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    13. 13
      Lv, D.; Zheng, J.; Li, Q.; Xie, X.; Ferrara, S.; Nie, Z.; Mehdi, L. B.; Browning, N. D.; Zhang, J.-G.; Graff, G. L.; Liu, J.; Xiao, J. High Energy Density Lithium-Sulfur Batteries: Challenges of Thick Sulfur Cathodes. Adv. Energy Mater. 2015, 5 (16), 1402290,  DOI: 10.1002/aenm.201402290
      There is no corresponding record for this reference.
    14. 14
      Chen, L.; Yu, H.; Li, W.; Dirican, M.; Liu, Y.; Zhang, X. Interlayer design based on carbon materials for lithium–sulfur batteries: a review. Journal of Materials Chemistry A 2020, 8 (21), 10709– 10735,  DOI: 10.1039/D0TA03028G
      14
      Interlayer design based on carbon materials for lithium-sulfur batteries
      Chen, Lei; Yu, Hui; Li, Wenxiao; Dirican, Mahmut; Liu, Yong; Zhang, Xiangwu
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (21), 10709-10735CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A review. Lithium-sulfur batteries were extensively investigated during the past two decades for their extremely high theor. specific energy (2600 W h kg-1) and volumetric energy d. (2800 W h L-1). However, their industrialization has been restrained due to the insulating nature of sulfur, vol. expansion of sulfur cathodes, formation of lithium dendrites, and terrible shuttle effect of sol. lithium polysulfides (Li2Sx, 3 ≤ x ≤ 8). Many researchers have been struggling with the design of interlayers having remarkable cond. and polysulfide-trapping capability so that these persistent drawbacks can be overcome. This review summarizes recently developed Li-S batteries with novel interlayers based on carbon materials, such as graphene, carbon nanotubes, carbon fibers, and nanofibers. The electrochem. properties of Li-S batteries with various interlayers are systematically compared. In particular, the enhancing mechanisms of Li-S batteries after the insertion of these interlayers are highlighted. Existing challenges and future development strategies with regard to high-energy Li-S batteries having carbon interlayers have also been summarized, and a prospective has been provided.
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    15. 15
      Jeong, Y. C.; Kim, J. H.; Nam, S.; Park, C. R.; Yang, S. J. Rational Design of Nanostructured Functional Interlayer/Separator for Advanced Li-S Batteries. Adv. Funct. Mater. 2018, 28 (38), 1707411,  DOI: 10.1002/adfm.201707411
      There is no corresponding record for this reference.
    16. 16
      Huang, J.-Q.; Xu, Z.-L.; Abouali, S.; Akbari Garakani, M.; Kim, J.-K. Porous graphene oxide/carbon nanotube hybrid films as interlayer for lithium-sulfur batteries. Carbon 2016, 99, 624– 632,  DOI: 10.1016/j.carbon.2015.12.081
      16
      Porous graphene oxide/carbon nanotube hybrid films as interlayer for lithium-sulfur batteries
      Huang, Jian-Qiu; Xu, Zheng-Long; Abouali, Sara; Akbari Garakani, Mohammad; Kim, Jang-Kyo
      Carbon (2016), 99 (), 624-632CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Highly porous, conductive graphene oxide (GO)/carbon nanotube (CNT) composite films are synthesized via facile vacuum filtration of hybrid dispersion. The flexible film is used as interlayer between separator and sulfur cathode to entrap active materials and prevent polysulfide shuttle. The lithium-sulfur (Li-S) battery furnished with an optimal GO/CNT interlayer delivers an excellent reversible capacity of 671 mA h/g after 300 cycles with a low degrdn. rate of 0.33 mA h/g or 0.043% per cycle at 0.2C. The encouraging outcome arises from synergistic effects of interlayer characteristics: namely, (i) the porous structure facilitates easy ion transport and electrolyte penetration; (ii) the GO layers with oxygenated functional groups entrap active materials, preventing polysulfide shuttle and enhancing their recycling; and (iii) the highly conductive CNTs offer fast pathways for electron/ion transfer.
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    17. 17
      Singhal, R.; Chung, S.-H.; Manthiram, A.; Kalra, V. A free-standing carbon nanofiber interlayer for high-performance lithium–sulfur batteries. Journal of Materials Chemistry A 2015, 3 (8), 4530– 4538,  DOI: 10.1039/C4TA06511E
      17
      A free-standing carbon nanofiber interlayer for high-performance lithium-sulfur batteries
      Singhal, Richa; Chung, Sheng-Heng; Manthiram, Arumugam; Kalra, Vibha
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (8), 4530-4538CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Free-standing porous carbon nanofibers with tunable surface area and pore structure have been investigated as an interlayer between the sulfur cathode and the separator to inhibit the shuttling of the intermediate polysulfides in lithium-sulfur batteries. Specifically, the effects of thickness, surface area, and pore size distribution of carbon nanofiber interlayers on the performance of lithium-sulfur batteries have been studied. The carbon nanofiber interlayer not only reduces the electrochem. resistance but also localizes the migrating polysulfides and traps them, thereby improving the discharge capacity as well as cyclability. It was found that the optimum thickness of the interlayer is a crit. factor to achieve good cell performance, in addn. to the surface area and pore structure. A high initial discharge capacity of 1549 mA-h/g at C/5 rate, which is 92% of the theor. capacity of sulfur, with 98% av. coulombic efficiency and 83% capacity retention after 100 cycles was obtained with a meso-microporous carbon nanofiber interlayer.
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      Su, Y. S.; Manthiram, A. A new approach to improve cycle performance of rechargeable lithium-sulfur batteries by inserting a free-standing MWCNT interlayer. Chem. Commun. (Camb) 2012, 48 (70), 8817– 9,  DOI: 10.1039/c2cc33945e
      18
      A new approach to improve cycle performance of rechargeable lithium-sulfur batteries by inserting a free-standing MWCNT interlayer
      Su, Yu-Sheng; Manthiram, Arumugam
      Chemical Communications (Cambridge, United Kingdom) (2012), 48 (70), 8817-8819CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A conductive multiwalled carbon nanotube (MWCNT) interlayer acting as a pseudo-upper current collector not only reduces the charge transfer resistance of sulfur cathodes significantly, but also localizes and retains the dissolved active material during cycling.
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    19. 19
      Huang, J.-Q.; Zhang, Q.; Wei, F. Multi-functional separator/interlayer system for high-stable lithium-sulfur batteries: Progress and prospects. Energy Storage Materials 2015, 1, 127– 145,  DOI: 10.1016/j.ensm.2015.09.008
      There is no corresponding record for this reference.
    20. 20
      Liu, X.; Huang, J. Q.; Zhang, Q.; Mai, L. Nanostructured Metal Oxides and Sulfides for Lithium-Sulfur Batteries. Adv. Mater. 2017, 29 (20), 1601759,  DOI: 10.1002/adma.201601759
      There is no corresponding record for this reference.
    21. 21
      Zhuang, R.; Yao, S.; Shen, X.; Li, T. A freestanding MoO2-decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery. International Journal of Energy Research 2019, 43 (3), 1111– 1120,  DOI: 10.1002/er.4334
      21
      A freestanding MoO2-decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery
      Zhuang, Ruiyuan; Yao, Shanshan; Shen, Xiangqian; Li, Tianbao
      International Journal of Energy Research (2019), 43 (3), 1111-1120CODEN: IJERDN; ISSN:0363-907X. (John Wiley & Sons Ltd.)
      Summary : Lithium-sulfur (Li-S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge-discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO2 nanoparticles (MoO2-CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li-S battery. The S/MoO2-CNFs/Li battery showed a discharge capacity of 6.93 mAh cm-2 (1366 mAh g-1) in the first cycle at a c.d. of 0.42 mA cm-2 and 1006 mAh g-1 over 150 cycles. Moreover, even at the highest c.d. (8.4 mA cm-2), the battery achieved 865 mAh g-1. The stable electrochem. behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO2-CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO2-CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.
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    22. 22
      Xiao, Z.; Yang, Z.; Wang, L.; Nie, H.; Zhong, M.; Lai, Q.; Xu, X.; Zhang, L.; Huang, S. A Lightweight TiO(2)/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long-Life Lithium-Sulfur Batteries. Adv. Mater. 2015, 27 (18), 2891– 8,  DOI: 10.1002/adma.201405637
      22
      A Lightweight TiO2/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long-Life Lithium-Sulfur Batteries
      Xiao, Zhubing; Yang, Zhi; Wang, Lu; Nie, Huagui; Zhong, Mei-e; Lai, Qianqian; Xu, Xiangju; Zhang, Lijie; Huang, Shaoming
      Advanced Materials (Weinheim, Germany) (2015), 27 (18), 2891-2898CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      An integrated selective interlayer was obtained by coating the surface of a C-S battery cathode with a com. graphene-TiO2 film, which accounted for 7.8 wt.% of the entire cathode. The porous graphene afforded an addnl. elec. conductive network and phys. trapped sulfide and polysulfides. The TiO2 in the barrier film further chem. suppressed the dissoln. of polysulfides and alleviated the undesirable shuttle effect. The porous CNT-S cathode coated with the graphene-TiO2 film delivered a reversible specific capacity of 1040 mA-h/g over 300 cycles at 0.5 C, with ultralow capacity degrdn. rates of 0.01% and 0.018% per cycle at 2 and 3 C, resp., over 1000 cycles.
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    23. 23
      Hwang, J.-Y.; Kim, H. M.; Lee, S.-K.; Lee, J.-H.; Abouimrane, A.; Khaleel, M. A.; Belharouak, I.; Manthiram, A.; Sun, Y.-K. High-Energy, High-Rate, Lithium-Sulfur Batteries: Synergetic Effect of Hollow TiO2-Webbed Carbon Nanotubes and a Dual Functional Carbon-Paper Interlayer. Adv. Energy Mater. 2016, 6 (1), 1501480,  DOI: 10.1002/aenm.201501480
      There is no corresponding record for this reference.
    24. 24
      Park, J.; Yu, B.-C.; Park, J. S.; Choi, J. W.; Kim, C.; Sung, Y.-E.; Goodenough, J. B. Tungsten Disulfide Catalysts Supported on a Carbon Cloth Interlayer for High Performance Li-S Battery. Adv. Energy Mater. 2017, 7 (11), 1602567,  DOI: 10.1002/aenm.201602567
      There is no corresponding record for this reference.
    25. 25
      Tan, L.; Li, X.; Wang, Z.; Guo, H.; Wang, J. Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2018, 10 (4), 3707– 3713,  DOI: 10.1021/acsami.7b18645
      25
      Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries
      Tan, Lei; Li, Xinhai; Wang, Zhixing; Guo, Huajun; Wang, Jiexi
      ACS Applied Materials & Interfaces (2018), 10 (4), 3707-3713CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The further development of Li-S batteries is limited by the fact that the sol. polysulfide leads to the shuttle effect, thereby reducing the cycle stability and cycle life of the batteries. To address this issue, here a thin and lightwt. (8 μm and 0.24 mg/cm2) reduced graphene oxide@MoS2 (rGO@MoS2) interlayer between the cathode and the com. separator is developed as a polysulfide barrier. The rGO plays the roles of both a polysulfide phys. barrier and an addnl. current collector, while MoS2 has a high chem. adsorption for polysulfides. The expts. demonstrate that the Li-S cell constructed with an rGO@MoS2-coated separator shows a high reversible capacity of 1122 mAh/g at 0.2 C, a low capacity fading rate of 0.116% for 500 cycles at 1 C, and an outstanding rate performance (615 mAh/g at 2 C). Such an interlayer is expected to be ideal for lithium-sulfur battery applications because of its excellent electrochem. performance and simple synthesis process.
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    26. 26
      Pourali, Z.; Yaftian, M. R.; Sovizi, M. R. Li2S/transition metal carbide composite as cathode material for high performance lithium-sulfur batteries. Mater. Chem. Phys. 2018, 217, 117– 124,  DOI: 10.1016/j.matchemphys.2018.06.074
      26
      Li2S/transition metal carbide composite as cathode material for high performance lithium-sulfur batteries
      Pourali, Zeinab; Yaftian, Mohammad Reza; Sovizi, Mohammad Reza
      Materials Chemistry and Physics (2018), 217 (), 117-124CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)
      Lithium sulfide (Li2S) with high capacity (1166 mAh g-1) is a promising cathode material for lithium/sulfur (Li/S) batteries which can be paired with non-lithium anodes for avoiding safety issues. Nonetheless, the application of Li2S in Li/S cells is limited because their low electronic and ionic conductivities, on one hand, and the polysulfides dissoln. problems, on the other hand. In this study, Li2S/Ti3C2TX composite has been prepd. by a soln.-based method followed by high energy ball milling process. XRD and SEM techniques revealed the presence of nano-size Li2S particles in the prepd. composite. The as-prepd. electrode exhibited an initial capacity of 708 mAh g-1 with a capacity retention of ∼74.5% after 100 cycles (528 mAh g-1), which was higher than that of the microsize com. Li2S at 0.1 C. This superior performance was attributed to the high elec. cond. and two dimensional structure of Ti3C2TX. These advantages result in the redn. of energy barrier for the transport of Li ions through nano-size Li2S particles. Consequently, a homogeneous distribution of Li2S particles in the composite inhibited the lithium polysulfide dissoln. The results confirmed the Li2S/Ti3C2TX composite based electrode as a potential candidate for applying in metal-free anodes of rechargeable Li/S batteries.
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    27. 27
      Zhou, F.; Li, Z.; Luo, X.; Wu, T.; Jiang, B.; Lu, L. L.; Yao, H. B.; Antonietti, M.; Yu, S. H. Low Cost Metal Carbide Nanocrystals as Binding and Electrocatalytic Sites for High Performance Li-S Batteries. Nano Lett. 2018, 18 (2), 1035– 1043,  DOI: 10.1021/acs.nanolett.7b04505
      27
      Low Cost Metal Carbide Nanocrystals as Binding and Electrocatalytic Sites for High Performance Li-S Batteries
      Zhou, Fei; Li, Zheng; Luo, Xuan; Wu, Tong; Jiang, Bin; Lu, Lei-Lei; Yao, Hong-Bin; Antonietti, Markus; Yu, Shu-Hong
      Nano Letters (2018), 18 (2), 1035-1043CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Lithium sulfur (Li-S) batteries are considered as promising energy storage systems for the next generation of batteries due to their high theor. energy densities and low cost. Much effort has been made to improve the practical energy densities and cycling stability of Li-S batteries via diverse designs of materials nanostructure. However, achieving simultaneously good rate capabilities and stable cycling of Li-S batteries is still challenging. Herein, we propose a strategy to utilize a dual effect of metal carbide nanoparticles decorated on carbon nanofibers (MC NPs-CNFs) to realize high rate performance, low hysteresis, and long cycling stability of Li-S batteries in one system. The adsorption expts. of lithium polysulfides (LiPS) to MC NPs and corresponding theor. calcns. demonstrate that LiPS are likely to be adsorbed and diffused on the surface of MC NPs because of their moderate chem. bonding. MC NPs turn out to have also an electrocatalytic role and accelerate electrochem. redox reactions of LiPS, as proven by cyclic voltammetry anal. The fabricated Li-S batteries based on the W2C NPs-CNFs hybrid electrodes display not only high specific capacity of 1200 mAh/g at 0.2C but also excellent rate performance and cycling stability, for example, a model setup can be operated at 1C for 500 cycles maintaining a final specific capacity of 605 mAh/g with a degrdn. rate as low as 0.06%/cycle.
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    28. 28
      Tao, X.; Wang, J.; Liu, C.; Wang, H.; Yao, H.; Zheng, G.; Seh, Z. W.; Cai, Q.; Li, W.; Zhou, G.; Zu, C.; Cui, Y. Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design. Nat. Commun. 2016, 7, 11203,  DOI: 10.1038/ncomms11203
      28
      Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design
      Tao, Xinyong; Wang, Jianguo; Liu, Chong; Wang, Haotian; Yao, Hongbin; Zheng, Guangyuan; Seh, Zhi Wei; Cai, Qiuxia; Li, Weiyang; Zhou, Guangmin; Zu, Chenxi; Cui, Yi
      Nature Communications (2016), 7 (), 11203CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Lithium-sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissoln. of lithium polysulfides, vol. expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technol. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption expts. and theor. calcns. reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.
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    29. 29
      Li, Z. Q.; Lu, C. J.; Xia, Z. P.; Zhou, Y.; Luo, Z. X-ray diffraction patterns of graphite and turbostratic carbon. Carbon 2007, 45 (8), 1686– 1695,  DOI: 10.1016/j.carbon.2007.03.038
      29
      X-ray diffraction patterns of graphite and turbostratic carbon
      Li, Z. Q.; Lu, C. J.; Xia, Z. P.; Zhou, Y.; Luo, Z.
      Carbon (2007), 45 (8), 1686-1695CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      To identify the influence of microstructural variation on the x-ray diffraction intensities, x-ray diffraction patterns of hexagonal graphite (h-graphite) and turbostratic C (t-C) were simulated by the general Debye equation. The numeric d. of interat. distance (NDID) is sensitive to the size and microstructure of a crystallite, so that it is used to characterize the structures of h-graphite and t-C. The dependence of the diffraction angles and full width at half max. (FWHMs) of diffraction lines on the crystallite size and distortion factors was examd. by computer simulation. The distortion factors for t-C, including rotation, translation, curvature, local pos. fluctuation of interlayer spacing of graphene layers and fluctuation of at. positions, have different influence on the NDIDs, hence on the x-ray diffraction patterns. The simulation results indicate that the diffraction angles and FWHMs of diffraction lines cannot be simply used to characterize the lattice parameters and crystallite sizes of t-C.
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    30. 30
      Campbell, J.; Tokay, B. Controlling the size and shape of Mg-MOF-74 crystals to optimize film synthesis on alumina substrates. Microporous Mesoporous Mater. 2017, 251, 190– 199,  DOI: 10.1016/j.micromeso.2017.05.058
      30
      Controlling the size and shape of Mg-MOF-74 crystals to optimize film synthesis on alumina substrates
      Campbell, James; Tokay, Begum
      Microporous and Mesoporous Materials (2017), 251 (), 190-199CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
      Mg-MOF-74 is a metal org. framework with the highest CO2 adsorption capacity of any porous material. Therefore, it has been suggested for CO2 sepns. as both an adsorbent and incorporated into membranes. Design of the Mg-MOF-74 crystal morphol. is important to expand the applicability of the material. In this paper one step synthesis of Mg-MOF-74 films has been achieved by controlling the Mg-MOF-74 crystal morphol. Results show that increasing the fraction of ethanol and water in the reaction soln. relative to DMF (DMF) increases the size of the crystals produced, while resulting in a subsequent drop in yield. By using solvent compn. to control the Mg-MOF-74 crystal size and shape the synthesis of Mg-MOF-74 thin films was achieved in one step, without the need for seeding. Films could be produced as thin as 1 μm, ten times thinner than any other previous membranes in the M-MOF-74 series, in a fraction of the time (only 2.5 h). Thicker films (up to 14 μm) could also be produced by increasing the fraction of ethanol and water in reaction soln., offering a methodol. by which the thickness of Mg-MOF-74 membranes can be controlled. Films were produced on porous tubular alumina supports, and single gas measurements were conducted resulting in a CO2 permeance of 7.4 × 10-7 mol m-2 s-1 Pa-1 and an ideal CO2/CH4 selectivity of 0.5.
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    31. 31
      Carrasco, J. A.; Romero, J.; Abellan, G.; Hernandez-Saz, J.; Molina, S. I.; Marti-Gastaldo, C.; Coronado, E. Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures. Chem. Commun. (Camb) 2016, 52 (58), 9141– 4,  DOI: 10.1039/C6CC02252A
      31
      Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures
      Carrasco, J. A.; Romero, J.; Abellan, G.; Hernandez-Saz, J.; Molina, S. I.; Marti-Gastaldo, C.; Coronado, E.
      Chemical Communications (Cambridge, United Kingdom) (2016), 52 (58), 9141-9144CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A hierarchical porous carbon prepd. via direct carbonization of Ni-MOF-74 loaded with furfuryl alc. at 450 °C displays high specific capacitance in comparison with other MOF-derived carbons as a result of the formation of micropores smaller than 1 nm.
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    32. 32
      Liu, S. H.; Liu, X. J.; Liu, B.; Liu, L. M.; Jin, W. Z.; Hu, X. J. Effect of some alloying elements on boiling point of magnesium. Mater. Sci. Technol. 2005, 21 (6), 735– 738,  DOI: 10.1179/174328405X43126
      32
      Effect of some alloying elements on boiling point of magnesium
      Liu, S. H.; Liu, X. J.; Liu, B.; Liu, L. M.; Jin, W. Z.; Hu, X. J.
      Materials Science and Technology (2005), 21 (6), 735-738CODEN: MSCTEP; ISSN:0267-0836. (Maney Publishing)
      The evapn. capacity of alloys differs with temp., and this is the basis of a new exptl. method to measure the b.ps. of various kinds of alloys. In the present work, the effects of Al, Zn, Mn and La addns. on the b.p. of magnesium were studied. Various elemental addns. and their varying contents in magnesium alloys have different influences on the b.p. of the alloys. Among these addns., Zn affected the b.p. of magnesium alloys most obviously, followed by Mn, Al and La. The b.p. of Mg-6 wt.% Zn alloy was the highest in the present study, up to 1715 K.
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    33. 33
      Sun, Y.; Wang, J.; Guo, J.; Zu, Q.; Huang, J.; Peng, Q. Atomic-scale oxidation mechanisms of single-crystal magnesium. Nanoscale 2019, 11 (48), 23346– 23356,  DOI: 10.1039/C9NR07265A
      33
      Atomic-scale oxidation mechanisms of single-crystal magnesium
      Sun, Yong; Wang, Jinming; Guo, Jianxin; Zu, Qun; Huang, Jianyu; Peng, Qiuming
      Nanoscale (2019), 11 (48), 23346-23356CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Understanding the oxidn. process of active metals plays a crucial role in improving their mech./oxidn. properties. Using in situ environmental transmission electron microscopy and d.-functional theory, we firstly clarify the oxidn. process of single-crystal Mg at the at. scale by using a new double-hole technique. A unique incipient interval-layered oxidn. mechanism of single-crystal Mg has been confirmed, in which O atoms intercalate through the clean (2‾1‾10) surface into the alternate-layered tetrahedral sites, forming a metastable HCP-type MgO0.5 structure. Upon the increased incorporation of oxygen at the neighboring interstitial sites, the HCP-type Mg-O tetrahedron structure sharply transforms into the FCC-type MgO oxide. In addn., a typical anisotropic growth mechanism of oxides has been identified, wherein it involves two routes: the epitaxial growth of the MgO layer and the inward migration of the MgO/Mg interface. The whole oxidn. rate of single-crystal Mg is mostly detd. by the inward migration rate of the MgO/Mg interface, which is about six times higher than that of the epitaxial growth rate of the MgO layer along the same orientation planes. Moreover, the inward migration rate of the (020)MgO(0110)Mg interface is about twice as large as that of the (200)MgO→ (0002)Mg interface. This continuous oxide growth is mainly related to the deffects in the MgO layer, which builds effective channels for the diffusion of O and Mg atoms. The in situ double-hole observations together with theor. calcns. provide a potential trajectory to probe the oxidn. fundamentals of other active metals.
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    34. 34
      Chen, S.; Xin, Y.; Zhou, Y.; Zhang, F.; Ma, Y.; Zhou, H.; Qi, L. Branched CNT@SnO2 nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability. J. Mater. Chem. A 2014, 2 (37), 15582– 15589,  DOI: 10.1039/C4TA03218G
      34
      Branched CNT@SnO2 nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability
      Chen, Shuai; Xin, Yuelong; Zhou, Yiyang; Zhang, Feng; Ma, Yurong; Zhou, Henghui; Qi, Limin
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (37), 15582-15589CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A novel hierarchical heterostructure consisting of carbon-coated SnO2 mesocryst. nanorods radially aligned on carbon nanotubes (CNTs) was designed and fabricated by a two-step growth process. SnO2 nanorods were first grown directly on CNTs by a facile solvothermal reaction, which were subsequently coated with a thin layer of carbon to form a branched CNT@SnO2@carbon sandwich-type heterostructure. When used as an anode material in lithium-ion batteries, the branched CNT@SnO2@C heterostructures exhibited highly reversible lithium storage behavior and excellent rate capability. The reversible capacity of the CNT@SnO2@C heterostructure reached 984 mA-h/g at a c.d. of 720 mA/g, and retained 590 mA-h/g at 3.6 A/g and 420 mA-h/g at 7.2 A/g. This superior performance might be ascribed to the improved mech. capability and high loading content of SnO2 of the branched architecture, the good elec. cond. of the CNT backbones and the carbon layer, and the high electrochem. reactivity of the one-dimensional mesocryst. SnO2 nanorods.
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    35. 35
      Xu, Z.; Chen, Y.; Li, W.; Li, J.; Yu, H.; Liu, L.; Wu, G.; Yang, T.; Luo, L. Preparation of boron nitride nanosheet-coated carbon fibres and their enhanced antioxidant and microwave-absorbing properties. RSC Adv. 2018, 8 (32), 17944– 17949,  DOI: 10.1039/C8RA02017E
      35
      Preparation of boron nitride nanosheet-coated carbon fibres and their enhanced antioxidant and microwave-absorbing properties
      Xu, Zhichao; Chen, Yongjun; Li, Wei; Li, Jianbao; Yu, Hui; Liu, Longyang; Wu, Gaolong; Yang, Tao; Luo, Lijie
      RSC Advances (2018), 8 (32), 17944-17949CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      In this study, annealing carbon fibers with boron and FeCl3·6H2O at elevated temps. was demonstrated as a novel route to coat carbon fibers with boron nitride (BN) nanosheets. The effect of annealing temp. on the thickness and microstructure of BN coating was investigated. Results showed that BN coating hardly formed at 1000°C, and uniform BN coating was achieved at 1100°C and 1200°C. However, further increasing the temp. to 1250°C triggered the formation of discretely distributed BN particles on the surface of the BN coating in addn. to the formation of a uniform BN coating. The BN coating and particles were constructed by numerous BN nanosheets with a bending and crumpling morphol. The thickness of the BN coating increased with increasing annealing temp. The oxidn. resistance of the carbon fibers dramatically enhanced after BN nanosheets were coated onto the carbon fiber surface. Moreover, given the low dielec. loss tangent of BN, the BN coating can improve the impedance matching of carbon fibers and enhance the microwave-absorbing property of carbon fibers significantly.
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    36. 36
      Lin, Y.; Chen, D.; Wang, S.; Han, D.; Xiao, M.; Meng, Y. Addressing Passivation of a Sulfur Electrode in Li-S Pouch Cells for Dramatically Improving Their Cyclic Stability. ACS Appl. Mater. Interfaces 2020, 12 (26), 29296– 29301,  DOI: 10.1021/acsami.0c05385
      36
      Addressing Passivation of a Sulfur Electrode in Li-S Pouch Cells for Dramatically Improving Their Cyclic Stability
      Lin, Yilong; Chen, Dongdong; Wang, Shuanjin; Han, Dongmei; Xiao, Min; Meng, Yuezhong
      ACS Applied Materials & Interfaces (2020), 12 (26), 29296-29301CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The effective passivation of a sulfur electrode in Li-S pouch cells is addressed by increasing the discharging cutoff voltage from 1.6 to 2.0 V. This simple method can effectively suppress the generation of solid and insulated Li2S deposition while reserves the majority of capacity and improves the cyclic stability of Li-S pouch cells. Upon increasing the discharging cutoff voltage from 1.6 to 2.0 V, the Li-S pouch cell loses only 8% of the initial discharge capacity and remarkably promotes the capacity retention rate from 62.4 to 91.6% within 40 cycles at 0.05C. The anal. of electrochem. and physics of a sulfur cathode demonstrates that the less Li2S deposition under the discharging cutoff voltage of 2.0 V can ensure fast reaction kinetics in Li-S pouch cells with high areal sulfur loadings and lean electrolyte. The mechanism of the passivation of a sulfur electrode is studied and discussed in detail. This brand new methodol. may provide an effective approach to enhance the cyclic stability of a Li-S battery.
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    37. 37
      Yu, F.; Zhou, H.; Shen, Q. Modification of cobalt-containing MOF-derived mesoporous carbon as an effective sulfur-loading host for rechargeable lithium-sulfur batteries. J. Alloys Compd. 2019, 772, 843– 851,  DOI: 10.1016/j.jallcom.2018.09.103
      37
      Modification of cobalt-containing MOF-derived mesoporous carbon as an effective sulfur-loading host for rechargeable lithium-sulfur batteries
      Yu, Faqi; Zhou, He; Shen, Qiang
      Journal of Alloys and Compounds (2019), 772 (), 843-851CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      Cobalt-contg. metal-org. frameworks (MOF) are synthesized, then carbonized and then acid etched to obtain mesoporous carbon for its potential application as lithium-sulfur (Li-S) battery cathode scaffolds. Before etching the resulting mesoporous carbon acquires a sp. surface area of 206.5 m2 g-1 and a pore vol. of 0.29 cm3 g-1, and in its sulfur-loading composite-1 the S-content is ∼45.2%. After etching the modified mesoporous carbon exhibits a great improvement in porosity (Surface area ∼650.2 m2 g-1 and pore vol. ∼ 0.77 cm3 g-1) and/or in sulfur-loading amt. (i.e., the S-content of composite-2 ∼ 50.0%). At 0.5 C (1 C = 1675 mA g-1), a composite-2 cathode delivers a high discharge capacity of 925.1 mAh g-1 in 2nd cycle and maintains a specific value of 781.1 mAh g-1 in the 140th cycle, much higher than those of composite-1 cathode. Both of the two composite electrodes display a slight increase of electrolyte-soln. resistance and surface-film resistance and an obvious decrease of charge-transfer resistance. By comparison, these resistances of composite-2 are smaller than those of composite-1. This, together with the acid-modified structural parameters reasonably account for the enhanced electrochem. properties of composite-2.
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    38. 38
      Yan, Y.; Wei, L.; Su, X.; Deng, S.; Feng, J.; Yang, J.; Chi, M.; Lei, H.; Li, Z.; Wu, M. The Crystallinity of Metal Oxide in Carbonized Metal Organic Frameworks and the Effect on Restricting Polysulfides. ChemNanoMat 2020, 6 (2), 274– 279,  DOI: 10.1002/cnma.201900642
      38
      The Crystallinity of Metal Oxide in Carbonized Metal Organic Frameworks and the Effect on Restricting Polysulfides
      Yan, Yingchun; Wei, Liangqin; Su, Xin; Deng, Shenzhen; Feng, Jianze; Yang, Jun; Chi, Mingna; Lei, Hu; Li, Zhongtao; Wu, Mingbo
      ChemNanoMat (2020), 6 (2), 274-279CODEN: CHEMSB; ISSN:2199-692X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Metal/carbon nanohybrids show promise for alleviating polysulfides shuttling in lithium-sulfur batteries. However, the synergetic effect between amorphous metal and carbon to restrict the migration of polysulfides is still far from fully understood. Herein, two porous metal/carbon nanohybrids with different crystallinity metal oxides components (amorphous Al2O3 and crystal Fe3O4) have been prepd. through pyrolysis of the MOF precursors, which are adopted as a sulfur support to impede the polysulfides shuttling. As expected, the amorphous Al2O3 with nitrogen-doped porous carbon exhibits an attractive durability at 1 C over 1000 cycles, meanwhile, the coulombic efficiency could maintain at 97.5%. Compared to it, crystal Fe3O4 shows an inferior electrochem. performance, which is attributed to the amorphous structure that can accelerate ions diffusion and charge transfer to improve the rate performance and capacity. The distinguished discharge performance of the design will be potentially used to develop applicable Li-S batteries.
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    39. 39
      Li, G.; Wang, S.; Zhang, Y.; Li, M.; Chen, Z.; Lu, J. Revisiting the Role of Polysulfides in Lithium-Sulfur Batteries. Adv. Mater. 2018, 30 (22), 1705590,  DOI: 10.1002/adma.201705590
      There is no corresponding record for this reference.
    40. 40
      Bai, S.; Liu, X.; Zhu, K.; Wu, S.; Zhou, H. Metal–organic framework-based separator for lithium–sulfur batteries Nature Energy 2016, 1 (7),  DOI: 10.1038/nenergy.2016.94 .
      There is no corresponding record for this reference.
    41. 41
      Li, M.; Wan, Y.; Huang, J.-K.; Assen, A. H.; Hsiung, C.-E.; Jiang, H.; Han, Y.; Eddaoudi, M.; Lai, Z.; Ming, J.; Li, L.-J. Metal–Organic Framework-Based Separators for Enhancing Li–S Battery Stability: Mechanism of Mitigating Polysulfide Diffusion. ACS Energy Letters 2017, 2 (10), 2362– 2367,  DOI: 10.1021/acsenergylett.7b00692
      41
      Metal-Organic Framework-Based Separators for Enhancing Li-S Battery Stability: Mechanism of Mitigating Polysulfide Diffusion
      Li, Mengliu; Wan, Yi; Huang, Jing-Kai; Assen, Ayalew H.; Hsiung, Chia-En; Jiang, Hao; Han, Yu; Eddaoudi, Mohamed; Lai, Zhiping; Ming, Jun; Li, Lain-Jong
      ACS Energy Letters (2017), 2 (10), 2362-2367CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      The shuttling effect of polysulfides severely hinders the cycle performance and commercialization of Li-S batteries, and significant efforts have been devoted to searching for feasible solns. to mitigate the effect in the past two decades. Recently, metal-org. frameworks (MOFs) with rich porosity, nanometer cavity sizes, and high surface areas have been claimed to be effective in suppressing polysulfide migration. However, the formation of large-scale and grain boundary-free MOFs is still very challenging, where a large no. of grain boundaries of MOF particles may also allow the diffusion of polysulfides. Hence, it is still controversial whether the pores in MOFs or the grain boundaries play the crit. role. In this study, we perform a comparative study for several commonly used MOFs, and our exptl. results and anal. prove that a layer of MOFs on a separator did enhance the capacity stability. Our results suggest that the chem. stability and the aggregation (packing) morphol. of MOF particles play more important roles than the internal cavity size in MOFs.
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    42. 42
      Ponraj, R.; Kannan, A. G.; Ahn, J. H.; Kim, D. W. Improvement of Cycling Performance of Lithium-Sulfur Batteries by Using Magnesium Oxide as a Functional Additive for Trapping Lithium Polysulfide. ACS Appl. Mater. Interfaces 2016, 8 (6), 4000– 6,  DOI: 10.1021/acsami.5b11327
      42
      Improvement of Cycling Performance of Lithium-Sulfur Batteries by Using Magnesium Oxide as a Functional Additive for Trapping Lithium Polysulfide
      Ponraj, Rubha; Kannan, Aravindaraj G.; Ahn, Jun Hwan; Kim, Dong-Won
      ACS Applied Materials & Interfaces (2016), 8 (6), 4000-4006CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Trapping lithium polysulfides formed in the sulfur pos. electrode of lithium-sulfur batteries is one of the promising approaches to overcome the issues related to polysulfide dissoln. In this work, we demonstrate that intrinsically hydrophilic magnesium oxide (MgO) nanoparticles having surface hydroxyl groups can be used as effective additives to trap lithium polysulfides in the pos. electrode. MgO nanoparticles were uniformly distributed on the surface of the active sulfur, and the addn. of MgO into the sulfur electrode resulted in an increase in capacity retention of the lithium-sulfur cell compared to a cell with pristine sulfur electrode. The improvement in cycling stability was attributed to the strong chem. interactions between MgO and lithium polysulfide species, which suppressed the shuttling effect of lithium polysulfides and enhanced the utilization of the sulfur active material. To the best of our knowledge, this report is the first demonstration of MgO as an effective functional additive to trap lithium polysulfides in lithium-sulfur cells.
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    43. 43
      Fan, F. Y.; Carter, W. C.; Chiang, Y. M. Mechanism and Kinetics of Li2S Precipitation in Lithium-Sulfur Batteries. Adv. Mater. 2015, 27 (35), 5203– 9,  DOI: 10.1002/adma.201501559
      43
      Mechanism and Kinetics of Li2S Precipitation in Lithium-Sulfur Batteries
      Fan, Frank Y.; Carter, W. Craig; Chiang, Yet-Ming
      Advanced Materials (Weinheim, Germany) (2015), 27 (35), 5203-5209CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In this paper, we characterize the kinetics and morphol. of Li2S electrodeposited from nonaq. (glyme-based) polysulfide solns. onto carbon fibers and multiwalled carbon nanotubes (MWCNT). Deposition is studied under potentiostatic conditions as a function of overpotential, and galvanostatic conditions as a function of current rate. The deposition mechanism is detd. from a combination of kinetic analyses and direct observations of Li2S morphol. at various stages of deposition by electron microscopy. It is shown that the morphol. of electrodeposited Li2S depends on the nucleation d. and relative rates of nucleation vs. growth, each of which can be manipulated by controlling the overpotential, the characteristics of the substrate, and the choice of solvent. Guidelines for optimizing storage capacity through substrate choice and electrokinetic control are presented.
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    44. 44
      Yang, X.; Gao, X.; Sun, Q.; Jand, S. P.; Yu, Y.; Zhao, Y.; Li, X.; Adair, K.; Kuo, L. Y.; Rohrer, J.; Liang, J.; Lin, X.; Banis, M. N.; Hu, Y.; Zhang, H.; Li, X.; Li, R.; Zhang, H.; Kaghazchi, P.; Sham, T. K.; Sun, X. Promoting the Transformation of Li2 S2 to Li2 S: Significantly Increasing Utilization of Active Materials for High-Sulfur-Loading Li-S Batteries. Adv. Mater. 2019, 31 (25), 1901220,  DOI: 10.1002/adma.201901220
      There is no corresponding record for this reference.
    45. 45
      Deng, Z.; Zhang, Z.; Lai, Y.; Liu, J.; Li, J.; Liu, Y. Electrochemical Impedance Spectroscopy Study of a Lithium/Sulfur Battery: Modeling and Analysis of Capacity Fading. J. Electrochem. Soc. 2013, 160 (4), A553– A558,  DOI: 10.1149/2.026304jes
      45
      Electrochemical impedance spectroscopy study of a lithium/sulfur battery: modeling and analysis of capacity fading
      Deng, Zhaofeng; Zhang, Zhian; Lai, Yanqing; Liu, Jin; Li, Jie; Liu, Yexiang
      Journal of the Electrochemical Society (2013), 160 (4), A553-A558CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      The electrochem. behavior of a lithium/sulfur battery was studied by electrochem. impedance spectroscopy. An impedance model based on the anal. of electrochem. impedance spectra as a function of temp. and depth of discharge was developed. Then, by monitoring the evolution of impedance during the cycling process, the capacity fading mechanism of lithium/sulfur battery was investigated. The results show that the semicircle at the middle frequency of the electrochem. impedance spectra is ascribed to the charge-transfer process and the semicircle at high frequency is related to the interphase contact resistance. Furthermore, electrolyte resistance, interphase contact resistance, and charge-transfer resistance vary with cycle no. in different manners, and the charge-transfer resistance is the key factor contributing to the capacity fading of lithium/sulfur battery.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.2c05064.

    • SEM images of the MOF powder and the heat-treated MOF powder, XRD patterns of the MOF powder and heat-treated MOF powder, Thermogravimetric analysis (TGA) curve of (a) MgO@C powder and (b) MgO@C/C-paper, BJH pore size distribution of the MOF powder and MgO@C powder, TEM HAADF images, EDS mapping images, and EDS spectrum of heat-treated MOF powder and after acid etching, electrochemical performance of the Li–S cells without an interlayer and with C-paper, C/C-paper, and MgO@C/C-paper at 0.2C, charge–discharge curves of standard, C-paper, and MgO@C/C-paper at different C-rates, rate performance of cells with different interlayers, photo images of the coin cells without and with interlayers after the first discharge, schematic diagram of the interlayer interacting with a polysulfide solution, and elemental analysis of sulfur with C-paper and MgO@C/C-paper after soaking in 5 mM polysulfide solution, charge and discharge curve of the coin cells assembled with C-paper and MgO@C/C-paper as a blank cathode and polysulfide (Li2S8) dissolved in the electrolyte as an active material, electrochemical impedance spectroscopy (EIS) spectra of the standard coin cell, C-paper cell, and MgO@C/C-paper cell before cycling and after 10 cycles, and quantitative elemental composition of cycled interlayer obtained from the EDS spectra (PDF)


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