First-Principles Approach to Assess the Viability of MoOPO4 as an Electrode Material for Mg-Ion Batteries

Searching for novel high-performance magnesium battery cathodes is an attractive subject in the development of energy storage devices. In this work, density functional theory calculations are employed to predict the theoretical feasibility of bulk MoOPO₄ (B-MoOPO₄) and monolayer MoOPO₄ (M-MoOPO₄) as magnesium battery electrodes. The structural and electronic properties of both MoOPO₄ are investigated, with a particular emphasis on the magnesium storage and diffusion behaviors within the structures. The results reveal that both B-MoOPO₄ and M-MoOPO₄ exhibit favorable electronic conductivity and low magnesium ion diffusion barriers, suggesting their potential for high rate performance. Furthermore, both B-MoOPO₄ and M-MoVOPO₄ possess a substantial number of active sites available for magnesium storage, with theoretical capacities of 259 mAh/g and 130 mAh/g, respectively, and theoretical energy densities reaching 417 and 73 Wh/kg, respectively. Open-circuit voltage calculations indicate a magnesiation voltage window of 1.95 to 1.01 V for B-MoOPO₄ and a voltage window of 0.67 to 0.44 V for M-MoOPO₄. In conclusion, both B-MoOPO₄ and M-MoOPO₄ demonstrate the feasibility of serving as magnesium battery electrodes. B-MoOPO₄ is better suited as a cathode due to its higher intercalation potential, while M-MoOPO₄, with its lower magnesium intercalation potential, is more inclined to serve as an anode.