Effect of heat treatment on positive electrode properties and crystal structures of Mo-modified MgMn2O4

To improve electrode properties of MgMn2O4 (MMO), which has attracted attention as a positive electrode material for magnesium rechargeable batteries, we performed modification of MMO with a Mo compound and investigated particularly effects of heat-treatment temperature (600-800 °C) in the modification process on the electrode properties and crystal structures. The Mo-modified MMO were successfully synthesized by immersing MMO in an aqueous solution containing Mo ion, followed by the heat treatment. Discharge/charge cycle tests revealed that Mo-modified MMO heat-treated at 700 °C exhibited the highest discharge capacity and cycle characteristics. Crystal-structure analyses using synchrotron X-ray diffraction data showed that the heat treatment at higher temperature could relax the distortion of the crystal structure although it increased an amount of Mg and Mn cation mixing. The crystal-structure change and surface modification with a Mo compound are considered to be the factors for improved positive-electrode properties of MMO.