Enhancing Mg2+ and Mg2+/Li+ Storage by Introducing Active Defect Sites and Edge Surfaces in MoSe2

Recently, Mg-ion batteries (MIBs) and Mg-Li hybrid ion batteries (MLIBs) are deemed as potential energy-storage devices. However, due to the insufficient storage sites of Mg2 + in the cathode, MIBs show a low reversible capacity. For MLIBs, the property is also seriously restricted due to the main Li+ intercalation reaction and less Mg2+ intercalation reaction. Herein, ultrathin MoSe2 nanosheets with enriched atomic defects and exposed edge surfaces are prepared by the hydrothermal method and subsequent hydrogen treatment. It is found that the Mg2+ storage performance is markedly enhanced, and Mg2+/Li+ co-intercalation can be achieved. Density functional theory (DFT) calculation shows that, by introducing a large number of atomic defects and edge exposed surfaces in the ultrathin MoSe2 nanosheets, the Mg2+ storage sites are increased, and the diffusion and migration ability of Mg2+ and Li+ are improved, resulting in a significant property improvement. Further, the Mg2+ intercalation in MIBs and Mg2+/Li+ co-intercalation in MLIBs are confirmed. The discharge-charge mechanisms only based on the intercalation reactions for both MIBs and MLIBs are also revealed.