Gains and losses in zinc-ion batteries by proton- and water-assisted reactions

Research on aqueous zinc-ion batteries (AZIBs) has expanded significantly over the last decade due to their promising performance, cost, and safety as well as environmentally friendly features. The use of aqueous electrolytes enables promising AZIB properties while simultaneously introducing undesired reactions and processes. This review focuses on fundamental and critical considerations of water-related equilibria and reactions in zinc-ion batteries. First, we examine Zn²⁺/water ionic equilibria and their consequences for the chemistry of electrodes. Then, we focus on the mechanisms and kinetics of proton and Zn²⁺ insertion in host frameworks. Next, special attention is given to the water-related dissolution, deposition, and amorphization phenomena of transition-metal-based cathode materials. Finally, we highlight the role of water- and proton-assisted reactions through a systematic comparison of aqueous and nonaqueous zinc-ion batteries.