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

Low cost, safety, and environmental benignity make rechargeable aqueous Zn/MnO 2 batteries promising candidates for large-scale energy storage. However, the synthesis of MnO 2 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 Mn 3 O 4 nanoparticles in large quantity. As the cathode material of aqueous zinc ion battery, Mn 3 O 4 gradually transforms to ε-MnO 2 in 1 M ZnSO 4 + 1 M MnSO 4 aqueous electrolyte with increasing cycles. Benefiting from the unexpected phase transition from Mn 3 O 4 to ε-MnO 2, 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/MnO 2 battery in large-scale energy storage.