Thermal Runaway Mechanism of Composite Cathodes for All‐Solid‐State Batteries

Sulfide‐based all‐solid‐state batteries (ASSBs) are widely recognized as one of the most promising next‐generation energy storage technologies. High‐mass‐loaded composite cathode is crucial for the electrochemical performance of ASSBs. However, the safety characteristics of practical composite cathodes have not been reported. Herein, the thermal runaway mechanisms of composite cathodes under different pressures are systematically revealed by employing pellet pressing of the LiNi0.8Co0.1Mn0.1O2 (NCM811) and Li6PS5Cl (LPSC). Completely different from conventional safety perceptions of powder, as the compaction density of the composite cathode increases, an inert P2Sx protective layer is generated in situ via the intensified the redox reactions at the interface, which inhibited exothermic reactions between the oxygen released from the NCM811 and LPSC. This work sheds light on the thermal runaway mechanisms of practical composite cathodes in sulfide‐based ASSBs, which can effectively build a bridge between academic and industrial research for the safety design of ASSBs.