Alkali‐Metal Sulfide as Cathodes toward Safe and High‐Capacity Metal (M = Li, Na, K) Sulfur Batteries

Abstract Rechargeable alkali‐metal–sulfur (M–S) batteries, because of their high energy density and low cost, have been recognized as one of the most promising next‐generation energy storage technologies. Nevertheless, the dissolution of metal polysulfides in organic liquid electrolytes and safety issues related to the metal anodes are greatly hindering the development of the M–S batteries. Alkali‐metal sulfides (M 2 S x ) are emerging as cathode materials, which can pair with various safe nonalkali‐metal anodes, such as silicon and tin. As a result, the combined M 2 S x cathode‐based M–S batteries can achieve high capacity as well as safety, thereby providing a more feasible battery technology for practical applications. In this review, recent progress in developing M 2 S x cathode‐based M–S batteries is systematically summarized, including the activation methods for M 2 S x cathodes, M 2 S x cathode optimization, and the improvement of electrolytes and anode materials. Furthermore, perspectives and future research directions of M 2 S x cathode‐based M–S batteries are proposed.