The Mg-V2O5 Intercalation Phase Diagram First Principles

Multi-valent (MV) ion intercalation batteries that replace the Li⁺ with a MV cation such as Mg²⁺, provide a realistic and compelling approach to meet the high energy density demanded by the next generation of electronics and vehicles. One of the challenges in achieving high energy density MV-ion systems is to develop a suitable cathode with a high enough voltage and diffusivity of the MV cation. Mg intercalation into V₂O₅ is one of the very few that has been shown to function reversibly at reasonable efficiency. In this study, we gain insight into the thermodynamics of Mg insertion into V₂O₅ from first-principles calculations.  We have calculated the 0 K phase diagram, the equilibrium voltage curves and the migration barriers for Mg diffusion in both the α and δ-V₂O₅ polymorphs. Our calculations indicate that Mg in V₂O₅ is a “phase separating” system at room temperature and benchmarking our calculations with experiments leads to the conclusion that Mg cycles on a metastable α-V₂O₅ host. We believe that this study can be further used to improve the performance of V₂O₅ as a cathode material for Mg-batteries.