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 Mg_0.5VPO₄O 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. [ABSTRACT FROM AUTHOR]