Critical Factors Contributing to the Thermal Runaway of Thiophosphate Solid Electrolytes for All-Solid-State Batteries

Although all-solid-state batteries are suggested as a means to tackle the safety concerns associated with current Li-ion batteries, there is presently a lack of comprehensive understanding regarding their thermal safety. In this context, critical factors contributing to the thermal runaway of thiophosphate solid electrolytes with charged Li_1-xNi_0.8Co_0.1Mn_0.1O₂ (NCM) under thermal and mechanical abuse conditions are demonstrated, considering parameters such as heating rate under thermal abuse conditions and the hybridization of S atom in structure. In particular, the thermal behavior of various solid electrolytes, including thiophosphates, thioantimonates, and halides, is investigated to clarify critical elements in Li₆PS₅Cl (LPSCl) contributing to its thermal instability when combined with charged NCM. Various ex situ analyses, along with density functional theory calculations, reveal a correlation between the hybridization of S atoms and the thermal instability of solid electrolytes, suggesting that sulfur acts as a key element triggering the thermal runaway of sulfide-based solid electrolytes.