Advances in sulfide solid-state electrolytes for lithium batteries

All-solid-state lithium batteries (ASSLBs), where solid-state electrolytes (SSEs) take the place of liquid electrolytes, are considered as the next generation of energy storage devices. They are anticipated to overcome the current bottlenecks of high-temperature thermal runaway and difficulties in energy density enhancement faced by traditional liquid lithium batteries. Among the common types of SSEs, sulfide SSEs show high ionic conductivity comparable to that of liquid electrolytes, good mechanical properties, and thermal stability. According to chemical composition, sulfide SSEs can be classified into binary, ternary, and multi-component ones. They are a category that is of great commercial value at present. However, sulfide SSEs still have many issues that need to be resolved, such as instability in air, mismatch with electrodes, a narrow electrochemical window, and lithium dendrite growth. Currently, the overall performance of sulfide SSEs is mainly enhanced by doping, constructing artificial interface layers, optimizing the synthesis process, and applying protective coatings. This article comprehensively elaborates on the types of sulfide SSEs, structural properties, ionic conduction mechanisms, preparation methods, current modification methods, and some landmark achievements in recent years. The future development direction of sulfide SSEs is envisioned to provide a theoretical foundation and technical support for the development of high-performance solid-state batteries (SSBs).