Solid Electrolyte with Oxidation Tolerance Provides a High‐Capacity Li2S‐Based Positive Electrode for All‐Solid‐State Li/S Batteries

Abstract The electrochemical window of solid electrolytes (SEs) plays a crucial role in designing active material–SE interfaces in high‐energy‐density all‐solid‐state batteries (ASSBs). However, the suitable electrochemical window for individual active materials is not yet investigated, as the electrochemical window of SEs is overestimated. In this study, the oxidation onset voltages (OOVs) of several SEs, namely those compatible with Li 2 S as a high‐capacity positive electrode material are determined. Results reveal that SEs with low OOVs decrease the capacity and increase the interfacial resistance of the corresponding ASSBs. The OOVs of SEs must exceed that of Li 2 S by more than 0.2 V to achieve high capacity, which in turn depends on SE ionic conductivity. Therefore, an Li 2 S positive electrode is combined with pseudobinary Li‐oxyacid salts as SEs, exhibiting high OOVs and ionic conductivities, to afford a high‐capacity (500 Wh kg −1 ) ASSB with high Li 2 S content.