Bi Doping-Enhanced Reversible-Phase Transition of α-MnO2 Raising the Cycle Capability of Aqueous Zn-Mn Batteries.

Rechargeable aqueous zinc-manganese oxide batteries have attracted extensive attention in energy-storage systems owing to their high safety and low cost but still suffer from the lack of advanced cathode materials with both high capacity and a long cycle life. Here, the bismuth-doped α-MnO2 was synthesized by a hydrothermal method. The preintercalation of Bi3+ effectively enlarges the lattice spacing and boosts the electrochemical performance of Zn/MnO2 batteries. The systematical studies suggest that Bi doping significantly optimized the electrochemical behavior and especially enhanced the reversibility of dissolution-deposition and phase transition processes. As a result, the Bi-doped α-MnO2 cathode achieves a superior performance: high reversible specific capacity (325 mA h g-1 at 300 mA g-1) and long cycling stability (90.9% capacity retention after 2000 cycles at 1000 mA g-1). By comparison with the α-MnO2 electrode, the Bi-doped α-MnO2 electrode exhibits a longer and stabler discharge plateau. It is different from most anionic doping methods, which attribute the performance improvement to superior ion diffusion kinetics and enhanced structural stability. Therefore, this work offers a new viewpoint and approach to improve the electrochemical property of Zn/MnO2 batteries.