High‐Performance Se–S Composite Cathode Rich in Defects for Wide‐Temperature Solid‐State Lithium Batteries

All‐solid‐state lithium batteries (ASSLBs) are a research hotspot for their superior safety. The solid electrolytes (SEs) are key components in ASSLBs, and the emerging rare‐earth halide SEs (RE‐HSEs) are valued for their comprehensive performances of good ionic conductivity, electrochemical stability, and deformability. In addition, cathode materials can influence the properties of ASSLBs, and sulfur (S) attracts much attention due to the lower toxicity and much higher energy density compared with commercial oxide cathodes. However, the S possesses poor electronic conductivity, which can be improved by the introduction of selenium (Se) with much higher electronic conductivity. In this work, a series of SexS1–x composites is synthesized by a melting method. Due to the introduction of Se and the enriched defects from the melting process, the electronic and ionic conductivities of SexS1–x are improved. After application in ASSLBs based on RE‐HSE Li3YBr6, the SexS1–x materials exhibit good performances with low polarizations, good cycling stabilities, and excellent rate properties at room temperature. Moreover, the assembled solid batteries can realize stable cycling performance (100 cycles) at low temperature (−30 °C) and a normal discharge–charge process at high temperature (120 °C). A series of selenium and sulfur composites (SexS1–x) with improved electronic/ionic conductivities is prepared. The all‐solid‐state lithium battery with the SexS1–x cathode exhibits good cycling stability (250 cycles), large reversible capacity, excellent rate performance (0.1–10C), and wide operating temperature range (−30–120 °C).