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.