Interfacial Challenges of Halide‐Based All‐Solid‐State Batteries

Abstract As the demand for high energy density and battery safety grows, all‐solid‐state batteries (ASSBs) have garnered considerable attention as promising energy storage systems by removing flammable liquid electrolytes (LEs). Cutting‐edge sulfide inorganic solid electrolytes (ISEs) such as Li 10 GeP 2 S 12 and Li 6 PS 5 Cl have shown high Li + conductivity comparable to those of LEs. However, the narrow electrochemical stability windows of sulfide ISEs hinder the development of high‐energy density ASSBs with severe interfacial challenges. Recently, halide ISEs such as Li 3 YCl 6 and Li 3 InCl 6 are attracting increasing attention because of their high Li + ion conductivity, excellent thermal stability, and high oxidative stability above 4 V. These properties are crucial to developing ASSBs with high energy density, and exceptional cycle and rate performances when employing high‐voltage cathode materials. Nevertheless, recent studies have identified severe interfacial challenges in ASSBs utilizing halide ISEs. Moreover, the safety of ASSBs is assumed to be better than conventional LE batteries but studies find the opposite conclusion when certain types of ISEs are employed, which can be attributed to products from side reactions at the interfaces. The objective here is to summarize the interfacial challenges associated with halide ISEs‐based ASSBs that will guide the development of high‐performance and safe ASSBs.