Multivalent metal–sulfur batteries for green and cost-effective energy storage: Current status and challenges

Multivalent metal–sulfur (M-S, where M = Mg, Al, Ca, Zn, Fe, etc.) batteries offer unique opportunities to achieve high specific capacity, elemental abundancy and cost-effectiveness beyond lithium-ion batteries (LIBs). However, the slow diffusion of multivalent-metal ions and the shuttle of soluble polysulfide result in impoverished reversible capacity and limited cycle performance of M−S (Mg–S, Al–S, Ca–S, Zn–S, Fe–S, etc.) batteries. It is a necessity to optimize the electrochemical performance, while deepening the understanding of the unique electrochemical reaction mechanism, such as the intrinsic multi-electron reaction process, polysulfides dissolution and the instability of metal anodes. To solve these problems, we have summarized the state-of-the-art progress of current M−S batteries, and sorted out the existing challenges for different multivalent M−S batteries according to sulfur cathode, electrolytes, metallic anode and current collectors/separators, respectively. In this literature, we have surveyed and exemplified the strategies developed for better M−S batteries to strengthen the application of green, cost-effective and high energy density M−S batteries.