Mg ion pre-intercalated MnO₂ nanospheres as high-performance cathode materials for aqueous Zn-ion batteries

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.