Acidity Modulation of Electrolyte Enables High Reversible Mn²⁺/MnO₂ Electrode Reaction of Electrolytic Zn-MnO₂ Battery

An electrolytic Zn-MnO₂ battery based on a deposition/dissolution mechanism has shown great prospects in energy storage applications, due to its low cost and high energy density. However, the multi-electron electrochemical reaction of the manganese-based cathode in this battery depends on the electrolyte acidity. Here, the reaction mechanism at the cathode side is investigated when electrolytes with different acidities are used. The results show that the Mn²⁺/MnO₂ deposition/dissolution and the cation intercalation coexist in the cathode of the electrolytic Zn-MnO₂ battery when the electrolyte has a pH > 0.4. The battery exhibits an unstable variation of coulombic efficiency. Upon the increase of the proton concentration in the electrolyte, the manganese-based cathode demonstrated a one-step deposition/dissolution mechanism, which benefits a high discharge voltage up to 2 V of the battery and a stable coulombic efficiency of above 90%. This work provides a useful electrolyte design for electrolytic Zn-MnO₂ batteries.