Facile Surface Modification of MgMn₂O₄ Positive-Electrode Material for Improving Cycle Performance of Magnesium Rechargeable Batteries

Abstract

MgMn 2 O 4 with a tetragonal spinel structure shows promise as a positiveelectrode 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 MgMn 2 O 4 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 MgMn 2 O 4 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 MgMn 2 O 4 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 Zrsurface 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.

Phase Transition Mechanism of ZnMn2O4 Spinel Oxide with Electrochemical Magnesium-Ion Insertion

“…Rietveld analysis showed that all of the Bragg peaks in the XRD pattern were attributed to the tetragonal spinel phase with a space group of I 4 1 / amd with lattice constants of a = 5.718(9) and c = 9.068(15) (Table S1). This structure is similar to the structure of ZnMn 2 O 4 and MgMn 2 O 4 ,,, reported in previous reports. The Zn:Mn ratio was 0.50, which was confirmed by ICP-OES measurements.…”

“…Among the 3d transition metal oxides, spinel oxides are the most promising because of their relatively high potential and capacity. − In spinel oxides, it has been reported that Mg 2+ insertion/extraction reactions using Me 3+ /Me 4+ redox (Me: the transition metal in spinel oxide) and Me 2+ /Me 3+ redox are possible . However, electrolyte decomposition occurs due to the relatively high potential of Me 3+ /Me 4+ redox; , the use of Me 2+ /Me 3+ redox has attracted much attention.…”

“…In terms of relatively high voltage and capacity, 3d transition metal oxides are attractive as cathode materials for magnesium rechargeable batteries. The 3d transition metal oxide materials such as V 2 O 5 , − MnO 2 , , polyanions, − layered rocksalt, , and spinels − have been developed, achieving higher charge–discharge potentials and capacities than those of sulfide-based cathode materials.…”