Functionalized sulfide solid-state electrolytes for advanced batteries:Recent progress and future perspective

All-solid-state batteries (ASSBs) have emerged as prominent research high ground for next-generation energy storage systems owing to intrinsic safety and high theoretical energy density. Among various solid-state electrolytes (SSEs) systems, sulfide SSEs are considered critical for surpassing the safety and energy density constraints of conventional liquid batteries, attributable to exceptional room temperature ionic conductivity (>10−3 ​S ​cm−1) and superior mechanical properties. Nonetheless, sulfide SSEs encounter several challenges. Limited chemical stability renders the sulfide SSEs prone to moisture-induced reactions that generate toxic H2S gas and cause structural degradation, thus necessitating stringent moisture control during processing. Moreover, the narrow electrochemical window triggered unexpected oxidation/reduction decomposition under extreme voltage conditions, leading to interfacial failure at both anode and cathode side. Additionally, the coarse-grained SSEs are not processable to build effective conductive network in the electrodes. In order to improve the practicality of sulfide SSEs, appropriate surficial or bulk functionalization strategies towards sulfide SSEs is essential to overcome their intrinsic moisture sensitivity, narrow electrochemical window and the weakness on building conductive networks in the electrodes. This review delineates the prevailing issues and challenges associated with sulfide SSEs, systematically summarizes recent advances in the functionalization and modification mechanisms of the sulfide SSEs, and provides a thorough discussion on development trends and future prospects of SSEs functionalization, thereby offering valuable insights for the practical implementation of ASSBs.