Structural Engineering Developments in Sulfide Solid-State Electrolytes for Lithium and Sodium Solid-State Batteries

Solid-state batteries (SSBs), especially those derived from lithium and sodium, show great promise as the next generation of energy storage devices due to their remarkable energy density, compact electrode architecture, nonflammability, and the use of metallic anodes. The solid-state electrolytes (SSEs), a significant part of SSBs, are essential to their functionality. A family of SSEs known as sulfide-based has been extensively studied for many years as a potential SSE for sodium and lithium SSBs. It offers excellent ionic conductivity, favorable mechanical properties, and ease of manufacturing. Notwithstanding its advantages, it also presents several problems, which require careful consideration for it to be successfully commercialized. This review summarizes the recent advancements in SSEs for lithium and sodium SSBs. It explores how structural engineering strategies impact the electrochemical properties of argyrodites SSEs for lithium SSBs and Na₃PS₄-based SSEs for sodium SSBs. The review provides comprehensive information on successful structural engineering approaches, such as introducing vacancies, mobile ions stuffing, and doping, for both lithium and sodium SSEs. It also discusses the air stability and electrochemical stability against electrodes, offering insights for designing and synthesizing next-generation SSEs that can lead to more durable and efficient energy storage systems.