Design and applications of transition metal sulfides in room-temperature Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have attracted considerable research interests in the past years, due to their advantages in natural resources, materials cost, specific capacity, and energy density etc.; however, they are suffering from various threats from S cathodes, encompassing shuttle effect, low electronic conductivity, volume change, and sluggish kinetics etc. Transition metal sulfides are demonstrated as promising redox regulators to help tackle these key issues as a result of their excellent chemical affinity and/or catalytic ability and improve the overall performance of RT Na-S batteries. Herein, the recent advances in rational design of the mainstream transition metal sulfides for RT Na-S batteries are comprehensively reviewed, including cobalt sulfides, iron sulfides, nickel/zinc sulfides, molybdenum sulfides, and their heterostructures. The emphasis is on fundamental properties of these sulfides, interactions between metal sulfides and polysulfides, materials design strategies and electrochemical performance. Potential developmental directions are also put forward to promote the further progress on RT Na-S batteries.