Impact of Sulfide-based Solid Electrolyte Particle Size Distribution on the Electrochemistry of ASSB via Impedance Study

Sulfide based solid electrolytes (SE) offer high ionic conductivity and can be processed at a low temperature (cold pressing) and hence have been used extensively by the battery community in their quest for the development of all-solid-state batteries (ASSB). In this study, we try to investigate the impact of Argyrodite (Li 6 PS 5 Cl) particle size and its distribution, on the solid electrolyte (SE), cathode composite and in turn on the overall performance of the battery. Electrochemical Impedance Spectroscopy (EIS) provides key insights in the understanding of the behaviour of different SE. EIS in this particular study has been used to extract (i) the ionic conductivity of solid electrolytes ( $\sigma_{SE}$ ) with small ( $< 20\mu\mathrm{m}$ ) and large particle size ( $50-150\mu\mathrm{m}$ ) distribution, (ii) the effective ionic conductivity ( $\sigma_{cathode.comp}$ ) in their respective cathode composites, (iii) the tortuosity based on ionic conductivity ( $\tau_{cond}$ ). The following are the highlights of this study: 1) On Solid Electrolyte itself: Given the same amount and same pressure, the ionic conductivity of large particle size distribution is higher. Consequently, the saturation pressure (Pressure to reach the highest ionic conductivity) is lower for large particle size. 2) On Cathode composite and its cycling: the composites with large particle size show the highest compacity values among all and also is the best performing cell. 3) Ionic conductivity-based tortuosity calculated which varied in the range 1.9-2.5. 1.9 being the lowest for large particles.