Atmospheric pressure hydrothermal synthesis and characterization of hollandite-type α-Mn_1−xTi_xO₂ for rechargeable magnesium battery cathodes

Abstract

Hollandite-type α-MnO₂ and its solid solutions with TiO₂ for the cathode active materials of rechargeable magnesium batteries were synthesized with a hydrothermal method under atmospheric pressure through the oxidation of Mn²⁺ ions with ammonium persulfate [(NH₄)₂S₂O₈] within 2 h. The solubility limit of Ti in α-Mn_1−xTi_xO₂ was x ≃ 0.2, and average particle size decreased with an increase in x. Despite the high surface area, α-Mn_1−xTi_xO₂ exhibited lower catalytic activity for oxidative electrolyte decomposition and better discharge capacity retention than α-MnO₂. Capacity retention was the highest and the increment of charge overpotential during cycles was the smallest at x = 0.2.