Impact of Moisture Exposure on Thermal Stability and Safety of Solid‐State Batteries

ABSTRACT Sulfide‐based solid‐state batteries (SSBs) hold significant potential for next‐generation energy storage, yet their practical deployment is hindered by the moisture sensitivity of sulfide solid electrolytes. Even small amounts of water vapor, such as those found in dry rooms, can cause harmful reactions in materials like Li 3 PS 4 (LPS), producing toxic H 2 S gas and unstable interfaces that affect thermal stability. This study examines how moisture exposure influences the thermo‐electrochemical stability of LPS at the material and cell‐level. Using a controlled glove‐bag setup, we evaluated various relative humidity levels (0%, 0.5%, 1.5%, and 5%) to reflect realistic manufacturing environments. Exposure to 5% relative humidity led to significant thermal instability, driven by the accumulation of H 2 S and other reactive byproducts, which causes higher self‐heating rates and an earlier thermal runaway onset. These findings underscore the crucial role of moisture control in enhancing the safety and performance of sulfide‐based SSBs.