Effect of vanadium doping on α-KxMnO2 as a positive electrode active material for rechargeable magnesium batteries

Abstract

α-MnO₂ has recently attracted attention as a promising candidate for positive electrode active materials for rechargeable magnesium batteries (RMBs) due to its ability to accommodate Mg²⁺ ions without phase changes at limited concentrations. However, the stability of this phase and the kinetic barriers to Mg²⁺ insertion remain significant challenges. This study purposes doping of potassium stabilized hollandite MnO₂ (α-K_xMnO₂) with vanadium ions as a method to improve the stability and cyclability of the α-K_xMnO₂ phase. RMBs with V-doped α-K_xMnO₂ positive electrode active materials exhibit discharge potentials over 0.2 V greater than that of undoped α-K_xMnO₂, and improved magnesiation and demagnesiation upon discharge and charge, respectively. V-doped α-K_xMnO₂ also exhibits greater preference for reduction via Mg²⁺ insertion, compared to conversion to disparate phase oxides, enhancing the stability of the α-K_xMnO₂ phase, and increasing capacity retention upon battery cycling.