Atmospheric pressure hydrothermal synthesis and characterization of hollandite-type α-Mn<sub>1−</sub><i><sub>x</sub></i>Ti<i><sub>x</sub></i>O<sub>2</sub> for rechargeable magnes

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-Mn1−xTixO2 was x ≃ 0.2, and average particle size decreased with an increase in x. Despite the high surface area, α-Mn1−xTixO2 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.