Conductivity Enhancement of MgMxOy (M=Co, Ni) Oxide Cathodes for Mg Battery Applications

Mg batteries have received a lot of interest due to its improved safety of handling, abundance and low cost of magnesium. Furthermore, Mg is more stable in air than Li and may provide capacity as high as 2200 mAh/g or 3830 mAh cm⁻³. Thus, Mg battery is known to have great potential for many practical applications and becomes one of post LIB technologies. Unfortunately, divalent Mg ions are expected to exhibit slow diffusion in Mg compounds. Thus, to find appropriate cathode materials for Mg battery has been difficult. Recently, MgCo₂O₄ Spinel Oxide and Mg_0.67Ni_1.33O₂ were found to be potential high voltage (~3V) cathode for Mg batteries based on the work of Tetsu Ichitsubo’s group. The conductivity of MgCo₂O₄ is in the order of 10^-1S/cm. On the other hand, the conductivity of Mg-doped NiO is much lower than that of MgCo₂O₄ spinel. The electronic conduction of semi-conducting oxides is highly dependent on the hole jumping in between those cations occupying the tetrahedral and/or octahedral sites of oxygen sublattice. Thus, the conductivity of these oxide cathodes may be enhanced by proper substitution of aliovalent cations. Therefore, the objective of this work is to enhance the electrical conductivity of Mg-containing transition metal oxides with either spinel or rock salt structure by the substitution of aliovalent cations with proper valence and ionic radius in the cation sublattice. After the electrical conductivity of cathode materials is improved, the electrochemical property such as capacity, charge/discharge cycles of Mg batteries is expected to be enhanced as well. The conductivity and crystal structure of prepared samples will be examined by using AC-impedance spectroscopy and XRD. The electrochemical properties including CV and cell testing will be conducted after cell assembly using the obtained cathode and Mg anode.