The Thermal Stability of Lithium Solid Electrolytes with Metallic Lithium

All-solid-state lithium-metal batteries are regarded as promising next-generation battery systems. While thermal runaway in conventional Li-ion batteries is known to cause safety hazards, the thermal issues posed by highly reactive metallic lithium (Li) with non-flammable ceramic solid electrolytes (SEs) have been less studied but are critical for the safety of all-solid-state Li-metal batteries. Here, we quantify the thermal stability of four prevalent oxide SEs with metallic Li using the accelerating rate calorimeter (ARC). Thermal runaway is observed during ARC tests for four widely used SEs when contacting with Li, while no obvious heat releases from garnet with Li. The oxygen generation from SEs at elevated temperatures is found to be responsible for the thermal runaway with Li. Our results indicate potential safety issues in all solid-state batteries (ASSBs) brought by highly reactive metallic Li and oxygen from SEs at increased temperatures, emphasizing the need for investigating thermal safety issues in ASSBs.