Oxalate-assisted Fe2O3 surface functionalization of nanosized MgMn2O4 and α-MnO2 cathodes for rechargeable magnesium batteries†

Mn-based transition metal oxide nanoparticles are promising candidates as cathode active materials for rechargeable magnesium batteries, but their high catalytic activity for oxidative electrolyte decomposition and large surface area deteriorate their cycle performance. A recent study [Yagi et al., J. Mater. Chem. A, 2021, 9, 26401–26409] demonstrated that the catalytic activity was less prominent in Fe-based oxides than in other transition metal oxides, containing Mn. Fe-based oxides show low catalytic activity for oxidative electrolyte decomposition compared with Mn-based congeners. The strong capability of oxalate ions for bridging transition metal ions was utilised to form thin, uniform Fe₂O₃ layers on nanoparticles of MgMn₂O₄ and α-MnO₂. The resulting Fe₂O₃ layers effectively suppressed side reactions during insertion and extraction of the Mg²⁺ ions and improved the capacity retention and cycle performance.