Thermal Failure Mechanism of Sulfide‐Based All‐Solid‐State Battery with Si‐Based Anode

ABSTRACT Sulfide‐based all‐solid‐state batteries (ASSBs) with high‐capacity cathodes/anodes are currently the most promising candidates among next‐generation power batteries. However, the intrinsic risk of thermal runaway remains a significant safety concern for ASSBs, urging a thorough exploration of their thermal failure mechanisms. Notably, the thermal stability and underlying failure mechanisms between the Si‐based anode and sulfide solid‐state electrolytes (SSEs) remain unexplored. Herein, we systematically investigate the exothermic behavior of four representative sulfide SSEs with a Si/C anode. Although the sulfide SSEs exhibit superior thermal stability towards Si/C anode compared to liquid electrolytes, with few significant exothermic reactions below 350°C, they do undergo intense exothermic reactions at higher temperatures. In‐depth characterizations identify Li ₂ S, P ₂ S _x , and PO _x species as the key reaction products, along with a significant amount of heat generation. Furthermore, by integrating reaction mechanisms from both composite anode and cathode, we propose a three‐stage thermal failure mechanism of LiNi _x Co _y Mn _z O ₂ | sulfide SSE | Si/C ASSB. The thermal failure of ASSB is initiated by the release of oxygen from the cathode, followed by solid–solid reactions between the cathode and sulfide SSEs. The final stage involves the Si/C anode, which participates in a complex chain of exothermic reactions, culminating in catastrophic thermal failure of ASSB.