Revealing the Thermal Stability of the Li/Sulfide Solid Electrolyte Interface at Atomic Scale via Cryogenic Electron Microscopy

Abstract Understanding the interfacial reaction mechanism between sulfide solid‐state electrolytes (SSEs) and metallic lithium (Li) under thermal runaway is of great significance in improving the safety of all‐solid‐state Li metal batteries (ASLMBs). Herein, multiscale methods including in situ optical microscopy‐thermal infrared imaging combination technique, cryogenic electron microscopy, thermodynamic simulation, and ab initio molecular dynamics methods are utilized to investigate the thermal chemical stability of sulfide SSEs Li 10 GeP 2 S 12 (LGPS) and Li 6 PS 5 Cl (LPSCl) against metallic Li under high temperatures. The results indicate that drastic thermal runaway happened between LGPS and metallic Li at 300 °C due to the continuous Li‐Germanium alloying reaction. In contrast, LPSCl maintains stability against metallic Li up to 400 °C, which is attributed to the formation of Li 2 S‐LiP‐Li 3 P‐LiCl stable interphases in the interfacial reaction between LPSCl and metallic Li. The electrical insulation interphase prevents the further reaction between LPSCl and metallic Li via kinetically decreasing the chemical potential of metallic Li to be within the electrochemical window of LPSCl. This work demonstrates the critical role of stable electrically insulated interphases between metallic Li anode and SSEs in improving the safety of ASLMBs.