Thermal Runaway Behavior of Sulfide-Based Solid Electrolytes for All-Solid-State Batteries

Lithium-ion batteries, which contain flammable liquid electrolytes, are susceptible to explosions when subjected to mechanical and thermal stress. Consequently, all-solid-state batteries (ASSBs), featuring solid electrolytes in place of liquid counterparts, have gained increasing attention as a promising alternative to current Li-ion batteries due to their potentially superior safety profile. Among these, thiophosphate-based solid electrolytes are considered particularly promising due to their high Li⁺ ion conductivity and suitable mechanical flexibility, resulting in improved electrochemical performance for ASSBs. However, regrettably, the safety of sulfide-based ASSBs remains uncertain, as their thermal stability has primarily been assessed under specific, mild conditions, such as low state-of-charge (SOC) levels. In this presentation, we demonstrate the safety concerns associated with various solid electrolytes used in all-solid-state batteries with Ni-rich layered oxide cathode materials, particularly in the context of thermal and mechanical stress. Additionally, we propose not only the mechanisms responsible for the thermal degradation of solid electrolytes in the presence of Ni-rich layered oxide cathode materials but also the key factors that determine the thermal runaway of solid electrolytes. This discovery provides a deeper insight into the failure modes of all-solid-state batteries, shedding light on the broader understanding of their potential challenges and safety considerations.