First-principles study of VPO₄O as a cathode material for rechargeable Mg batteries

The electrochemical properties of VPO4O as a cathode for Mg batteries were studied by performing first principles calculations. Mg insertion features a plateau at about 2.8 V up to Mg0.5VPO4O and then another plateau at around 2.2 V up to MgVPO4O, with a theoretical capacity of about 154 mA h g-1 and 144 mA h g-1, respectively. MgVPO4O is found to be dynamically stable with the absence of negative frequencies in the phonon density of states. The insertion of one Mg reduced two VO6 units instead of reducing only one VO6 unit. In addition, MgVPO4O shows an energy barrier of about 0.58 eV for Mg-ion vacancy migration along the [111] direction, which is comparable to that of many other cathode materials. Our results indicated that MgVPO4O has the potential to be a promising candidate as a cathode material for Mg batteries.