Challenges and Prospects of Alkali Metal Sulfide Cathodes Toward Advanced Solid‐State Metal‐Sulfur Batteries

Abstract Rechargeable solid‐state metal‐sulfur batteries (SSMSBs) have attracted extensive attention due to their high energy density, improved safety, and low cost. The development of SSMSBs, however, is hindered by challenges of inferior interface contact, electrode structure deformation, and safety concerns from metal anodes. Alkali metal sulfides (M 2 S x ) are promising candidates for cathode in SSMSBs, as they exhibit minimal volume change and are compatible with non‐alkali metal anodes. Therefore, SSMSBs can achieve high stability and safety, providing a more feasible choice for practical applications. This review comprehensively summarizes recent advancements in M 2 S x ‐based cathodes for SSMSBs, along with state‐of‐the‐art strategies to optimize cathodes, electrolytes, and interfaces to achieve desirable performance. Advanced characterization techniques to understand the reaction mechanisms are discussed in detail. Furthermore, the development perspectives and future research directions for solid‐state batteries (SSBs) with M 2 S x are also elucidated.