Transformed Akhtenskite MnO2 from Mn3O4 as Cathode for a Rechargeable Aqueous Zinc Ion Battery

Low cost, safety, and environmental benignity make rechargeable aqueous Zn/MnO2 batteries promising candidates for large-scale energy storage. However, the synthesis of MnO2 with excellent electrochemical performance is limited to the traditional hydrothermal method, which is difficult to scale up for mass production. Herein, a ball-milling approach is developed to rapidly obtain Mn3O4 nanoparticles in large quantity. As the cathode material of aqueous zinc ion battery, Mn3O4 gradually transforms to ε-MnO2 in 1 M ZnSO4 + 1 M MnSO4 aqueous electrolyte with increasing cycles. Benefiting from the unexpected phase transition from Mn3O4 to ε-MnO2, the cathode delivers a specific capacity of 221 mAh g–1 at a current density of 100 mA g–1 and a good long-term cyclic stability over 500 cycles with 92% capacity retention at a high rate of 500 mA g–1. The excellent battery performance combined with the cost-effective preparation procedure, the good safety of aqueous mild electrolyte, and the easy cell assembly are believed to promote the practical use of the Zn/MnO2 battery in large-scale energy storage.