Highly Reversible Aqueous Zn-MnO₂ Battery by Supplementing Mn<SUP>2+</SUP>-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.