Preparation of conductive Cu_1.5Mn_1.5O₄ and Mn₃O₄ spinel mixture powders as positive active materials in rechargeable Mg batteries operative at room temperature

We prepared conductive mixtures of Cu_1.5Mn_1.5O₄ and Mn₃O₄ spinels (CMO–MOs) as positive electrode active materials in rechargeable Mg batteries (RMBs) using a sol–gel complex polymerization method. The CMO–MO spinel mixtures with high specific surface areas above 100 m² g⁻¹ were obtained with mild calcination in Ar at 300 °C. The conductivity of CMO–MOs was estimated to be approximately 1000 times higher than that of a conventional MgMn₂O₄ (MMO) spinel powder. The discharge capacities evaluated using 2032-type coin-cell battery with a Mg-alloy negative electrode at room temperature increase with an increase in the specific surface area of the spinel powders. The specific surface area for providing the theoretical capacity of the conductive CMO–MOs was about one-third that of the insulative MMO. High specific surface area and high conductivity are key parameters for the positive active material to realize practical room-temperature operation of RMBs.