Alkali-Ion-Assisted Activation of ε-VOPO₄ as a Cathode Material for Mg-Ion Batteries

Rechargeable multivalent-ion batteries are attractive alternatives to Li-ion batteries to mitigate their issues with metal resources and metal anodes. However, many challenges remain before they can be practically used due to the low solid-state mobility of multivalent ions. In this study, a promising material identified by high-throughput computational screening is investigated, ε-VOPO₄, as a Mg cathode. The experimental and computational evaluation of ε-VOPO₄ suggests that it may provide an energy density of >200 Wh kg^-1 based on the average voltage of a complete cycle, significantly more than that of well-known Chevrel compounds. Furthermore, this study finds that Mg-ion diffusion can be enhanced by co-intercalation of Li or Na, pointing at interesting correlation dynamics of slow and fast ions.