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

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 (M2Sx) 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.