Understanding Electrochemical Reaction Mechanisms of Sulfur in All‐Solid‐State Batteries through Operando and Theoretical Studies **

Abstract

AbstractDue to its outstanding safety and high energy density, all‐solid‐state lithium‐sulfur batteries (ASLSBs) are considered as a potential future energy storage technology. The electrochemical reaction pathway in ASLSBs with inorganic solid‐state electrolytes is different from Li‐S batteries with liquid electrolytes, but the mechanism remains unclear. By combining operando Raman spectroscopy and ex situ X‐ray absorption spectroscopy, we investigated the reaction mechanism of sulfur (S8) in ASLSBs. Our results revealed that no Li2S8, Li2S6, and Li2S4 were formed, yet Li2S2 was detected. Furthermore, first‐principles structural calculations were employed to disclose the formation energy of solid state Li2Sn (1≤n≤8), in which Li2S2 was a metastable phase, consistent with experimental observations. Meanwhile, partial S8 and Li2S2 remained at the full lithiation stage, suggesting incomplete reaction due to sluggish reaction kinetics in ASLSBs.