Recent progress in zinc sulfur batteries: Mechanism, challenges, and perspectives

•The fundamental mechanism of sulfur redox reaction is reviewed.•Challenges on sluggish sulfur redox kinetics and side reaction are discussed.•Perspectives for catalyst design and hybrid sulfur cathode are emphasized.•Perspectives and opportunities of aqueous zinc sulfur batteries are highlighted. In recent years, safety, non-flammability and low cost of zinc metal and aqueous electrolytes has led to extensive exploration of rechargeable aqueous zinc-ion batteries (ZIBs). However, due to 1) cathode materials limiting the capacities and, 2) water decomposition limiting the safe battery operating voltage window, energy densities of ZIBs are limited. Sulfur as a cathode material is a low-cost option along with showing an exceptional specific capacity; hence aqueous zinc-sulfur batteries (AZSBs) are investigated in recent years. This review begins with a comprehensive understanding of the fundamental sulfur redox reaction mechanism in AZSBs. Furthermore, we identify critical challenges individually of the anode, cathode and the electrolyte component. The challenges range from the sluggish kinetics of sulfur cathodes and side reactions with the aqueous electrolyte to the dendrite growth observed on Zn anodes. Thereafter, various strategies are emphasized to mitigate these challenges, including the development of hybrid sulfur cathodes, the utilization of single-atom-based catalysts, and the incorporation of effective additives for hybrid electrolytes. This work will provide insightful perspectives outlining potential avenues for future research in the domain of AZSBs.