Classification and Analysis of Halide Mixtures in Li10P3S12M (M = Cl, Br, I) Solid Electrolytes for Superionic Conductors

The lithium thiophosphate group of solid electrolytes (SEs) is considered one of the best lithium-ion conductors that could be compatible with liquid electrolytes. However, the interface stability of lithium thiophosphate SEs against the lithium anode and oxide cathode could be a challenge due to severe degradation over charge–discharge cycles. In this study, we aim to analyze and introduce the addition of halides into lithium thiophosphate SEs with a molar ratio of 3Li₃PS₄ to 1LiM (M = Cl, Br, I) in order not only to improve ion conductivity but also to increase the interface stability of the SEs. Li₁₀P₃S₁₂Br (LPSBr) and Li₁₀P₃S₁₂I (LPSI) results in high ionic conductivity at 1.7 and 2.9 mS cm^–1, respectively, at room temperature. Although LPSBr has lower ion conductivity, it shows better electrochemical stability compared to LPSI. By combining the advantages of both LiI and LiBr to form Li₁₀P₃S₁₂Br_1–xI_x, we have observed improvements not only in high ionic conductivity but also in the interface stability of SEs, which is important for extending the lifetime cycle of all-solid-state lithium batteries (ASSLBs).