ZnO Additive Boosts Charging Speed and Cycling Stability of Electrolytic Zn–Mn Batteries

Electrolytic aqueous zinc-manganese (Zn-Mn) batteries have the advantage of high discharge voltage and high capacity due to two-electron reactions. However, the pitfall of electrolytic Zn-Mn batteries is the sluggish deposition reaction kinetics of manganese oxide during the charge process and short cycle life. We show that, incorporating ZnO electrolyte additive can form a neutral and highly viscous gel-like electrolyte and render a new form of electrolytic Zn-Mn batteries with significantly improved charging capabilities. Specifically, the ZnO gel-like electrolyte activates the zinc sulfate hydroxide hydrate assisted Mn²⁺ deposition reaction and induces phase and structure change of the deposited manganese oxide (Zn₂Mn₃O₈·H₂O nanorods array), resulting in a significant enhancement of the charge capability and discharge efficiency. The charge capacity increases to 2.5 mAh cm^-2 after 1 h constant-voltage charging at 2.0 V vs. Zn/Zn²⁺, and the capacity can retain for up to 2000 cycles with negligible attenuation. This research lays the foundation for the advancement of electrolytic Zn-Mn batteries with enhanced charging capability.