Inverse-spinel Mg2MnO4 material as cathode for high-performance aqueous magnesium-ion battery

Aqueous magnesium ion batteries (AMIBs) are promising energy storage systems due to their low cost and environmentally friendly. However, the strong electrostatic attraction of Mg2+ limits the selection of cathode materials for AMIBs. Here, an inverse-spinel Mg2MnO4 material is reported as high-performance cathode for AMIBs. Mn-salt additive is used to construct a reversible manganese oxide (MnO1.44) on the surface of Mg2MnO4 electrode, which not only suppresses the dissolution of Mn element of Mg2MnO4 material but also promotes the transfer of Mg2+. The battery is fabricated by Mg2MnO4 cathode, polyimide (PI) anode and 1 M MgSO4 + 0.1 M MnSO4 electrolyte. Benefiting from the addition of Mn salt, the Mg2MnO4//PI system delivers a discharge capacity of 70.7 mA h g−1 at 100 C and capacity retention of 89% over 10,000 cycles. An impressive energy density of 60.1 Wh kg−1 is obtained at a power density of 15,300 W kg−1, which benefits from the pseudocapacitance character of Mg2MnO4 cathode and PI anode. This work pushes the AMIBs a brand-new stage.