Facile Surface Modification of MgMn₂O₄Positive-Electrode Material for Improving Cycle Performance of Magnesium Rechargeable Batteries

MgMn2O4 with a tetragonal spinel structure shows promise as a positive-electrode material in magnesium rechargeable batteries (MRBs), which have drawn considerable attention as post lithium-ion batteries. However, the material currently suffers from poor cycle performance. In this study, we attempt to improve the cycle performance of MgMn2O4 via the Zr modification of its particle surface. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy demonstrate that the surface modification is successfully performed by immersing MgMn2O4 powder into a Zr-containing aqueous solution, followed by heat treatment. However, Zr segregation is observed at high Zr concentration. Furthermore, structural analyses using synchrotron X-rays indicate that the Zr modification has an influence on the bulk structure of the MgMn2O4 powder. The positive-electrode properties of the powders are investigated using discharge/charge cycle tests, which show that Zr modification can drastically improve the cycle performance and coulombic efficiency. These improvements are supposed to be due to suppression of an unexpected reaction by the Zr-surface modification and lower structural distortion after the modification. These findings clearly demonstrate the significant potential of surface modification as a method for obtaining high-performance MRBs.