Lithium-Ion Transport and Exchange between Phases in a Concentrated Liquid Electrolyte Containing Lithium-Ion-Conducting Inorganic Particles

Understanding Li+ transport in organic–inorganic hybrid electrolytes, where Li+ has to lose its organic solvation shell to enter and transport through the inorganic phase, is crucial to the design of high-performance batteries. As a model system, we investigate a range of Li+-conducting particles suspended in a concentrated electrolyte. We show that large Li1.3Al0.3Ti1.7P3O12 and Li6PS5Cl particles can enhance the overall conductivity of the electrolyte. When studying impedance using a cell with a large cell constant, the Nyquist plot shows two semicircles: a high-frequency semicircle related to ion transport in the bulk of both phases and a medium-frequency semicircle attributed to Li+ transporting through the particle/liquid interfaces. Contrary to the high-frequency resistance, the medium-frequency resistance increases with particle content and shows a higher activation energy. Furthermore, we show that small particles, requiring Li+ to overcome particle/liquid interfaces more frequently, are less effective in facilitating Li+ transport. Overall, this study provides a straightforward approach to study the Li+ transport behavior in hybrid electrolytes.

When measuring EIS at low temperatures (e.g. 10 °C), a 300 mV AC amplitude is necessary in order to obtain smooth Nyquist plots due to the large resistance of the samples at this temperature.Although a 300 mV AC amplitude seems very high compared to common EIS measurements (10 mV), the large distance between Pd electrodes ensures a weak electric field strength.The applied frequency range for all the measurements is 1 MHz − 0.1 Hz, with 20 data points for each decade.8][9] EIS data fit was conducted using the BioLogic EC-Lab ® V11.43 software.The overall resistance, which is determined from the intersection of the lowfrequency straight line and the semicircle in the Nyquist plots, are used to calculate the conductivity of suspension samples according to equation (1).The overall resistance agrees very well with the sum of R1 and R2 obtained from EIS fitting.
Diffusion coefficients are measured using pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) on a Bruker AvanceNEO 400 MHz spectrometer coupled with a diffBB probe at 25 °C using the pulsedgradient double stimulated-echo sequence (PGDSTE) in a similar way as previously reported. 10The diffusion time (Δ) was set to 100 ms, and the maximum gradient was set to ≤ 1450 gauss cm -1 .Diffusion coefficients of EC at Δ = 20 ms and 500 ms were also measured, and the results shows negligible change (< 5 %).When measuring the electrophoretic mobility of Li + in the high concentration liquid electrolyte EC/LiTFSI=2/1, 0.5 wt% poly(ethylene oxide) (Mw 600k) is added to the liquid electrolyte to suppress convection. For the Li + /Na + exchange experiment, a 10 wt% NaClO4 in EC solution was first prepared in a glovebox.
Then 134 mg LATP particles and 560 mg NaClO4/EC solution (0.4 mL) was quickly mixed and stirred at 30 °C on a hot plate.After a certain mixing time, the mixture was filtered using a 0.2 μm PTFE solution was filled into a 5 mm NMR tube.A 3 mm NMR tube filled with an external standard, an acetone solution containing 0.5 M NaClO4 and 0.5 M LiTFSI, was inserted into the 5 mm NMR tube.The height of the sample and standard solution were over 3 cm, sufficient to cover the whole NMR coil region.The 23 Na and 7 Li NMR spectra was recorded using a Bruker Ascend TM 500 MHz spectrometer at ambient temperature with a 90° pulse.The recycle delay (d1) was set to > 5 × T1.The concentration of Na + and Li + in the sample can be calculated by measuring the geometry of the 3 mm and 5 mm tubes.The molar ratio between Na + and Li + , which is irrelevant to the NMR tube geometries, can be further calculated, or obtained directly from the NMR peak integrals.
Table S1.Fitting parameters for the Nyquist plots shown in Figure 1c and the characteristic frequencies for R1 and R2 processes.

Figure S4 .
Figure S4.Stability test of the impedance measurements.The suspension containing 36.3 vol% LPSCl-

Figure S8 .
Figure S8.A comparison of the one-dimentional diffusion length (√2) and migration length (μEt) of