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Rechargeable Zn-MnO2 batteries with mild and nearly neutral aqueous electrolytes have shown great potential for large-scale energy storage because of their high safety, low cost, environmental friendliness and high energy density. However, MnO2 cathode materials usually have disadvantages such as low capacity and poor cycling stability, which limit the development of Zn-MnO2 batteries. In this study, mesoporous MnO2 nanospheres were prepared by in situ Mg ion pre-intercalation via a simple chemical method. The prepared MnO2 shows a high reversible capacity (247 mA h g−1 at 0.3 A g−1), excellent cycling stability (a capacity retention of 93% over 800 cycles at 0.8 A g−1) and good rate performance. The GITT, in situ EIS, ex situ XRD, ex situ XPS and ex situ SEM show that the zinc storage mechanism of MnO2 should be H+/Zn2+ co-intercalation/de-intercalation. This research could provide specific inspiration and promotion for the development and mechanism research of high-performance rechargeable Zn-MnO2 batteries. [ABSTRACT FROM AUTHOR]