Highly Reversible Aqueous Zn‐MnO ₂ Battery by Supplementing Mn ²⁺ ‐Mediated MnO ₂ Deposition and Dissolution

Rechargeable Zn‐MnO 2 batteries are boosted by the reversible intercalation reactions in mild aqueous electrolytes, but they still suffer from cathode degradation. Herein, Zn‐MnO 2 batteries with high durability and high energy density are achieved by supplementing MnO 2 deposition and dissolution in a mild aqueous electrolyte. The main finding is that adjusting Mn 2+ concentration to a critical range enables a reversible MnO 2 /Mn 2+ redox conversion without the involvement of oxygen evolution. This can recycle the by‐products from MnOOH disproportionation (MnOOH → MnO 2 + Mn 2+ ), 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 MnO 2 deposition/dissolution and provide paths for efficient charge and mass transport. This work provides a feasible way to push the development of Zn‐MnO 2 batteries in mild aqueous electrolytes.