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

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 Li2S 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 Li2S by more than 0.2 V to achieve high capacity, which in turn depends on SE ionic conductivity. Therefore, an Li2S 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 Li2S content. The oxidation onset voltages (OOVs) of several solid electrolytes (SEs) are determined for all‐solid‐state Li/S batteries with Li2S as a high‐capacity active material. The OOVs of SEs must exceed that of Li2S by more than 0.2 V to achieve high capacity. The developed electrodes using Li2S and pseudobinary Li‐oxyacid salts achieve high areal capacities in the all‐solid‐state battery.