Highly Reversible Aqueous Zn‐MnO2 Battery by Supplementing Mn2+‐Mediated MnO2 Deposition and Dissolution

Rechargeable Zn‐MnO2 batteries are boosted by the reversible intercalation reactions in mild aqueous electrolytes, but they still suffer from cathode degradation. Herein, Zn‐MnO2 batteries with high durability and high energy density are achieved by supplementing MnO2 deposition and dissolution in a mild aqueous electrolyte. The main finding is that adjusting Mn2+ concentration to a critical range enables a reversible MnO2/Mn2+ redox conversion without the involvement of oxygen evolution. This can recycle the by‐products from MnOOH disproportionation (MnOOH → MnO2 + Mn2+), resulting in a battery with extremely high durability (16 000 cycles without obvious capacity fading), high energy density (602 Wh kg−1 based on the active mass of the cathode), and high‐rate capacity (430 mAh g−1 at 19.5 A g−1). The utilization of a 3D carbon nanotube foam skeleton can accommodate the volume change during MnO2 deposition/dissolution and provide paths for efficient charge and mass transport. This work provides a feasible way to push the development of Zn‐MnO2 batteries in mild aqueous electrolytes. Aqueous Zn‐MnO2 batteries with high energy density, high stability, and high rate capacity are achieved by constructing a highly reversible cyclic cathode chemistry conversion in a mild electrolyte, and the conversion is enabled by building an Mn(II)‐mediated MnO2/Mn2+ redox to recycle the by‐products from cathode disproportionation.