The Intercalation Phase Diagram of Mg in V2O5 from First-Principles

We have investigated Mg intercalation into orthorhombic V2O5, one of only three cathodes known to reversibly intercalate Mg ions. By calculating the ground-state MgxV2O5 configurations and by developing a cluster expansion for the configurational disorder in delta-V2O5, a full temperature-composition phase diagram is derived. Our calculations indicate an equilibrium phase-separating behavior between fully demagnesiated alpha-V2O5 and fully magnesiated delta-V2O5, but also motivate the existence of potentially metastable solid solution transformation paths in both phases. We find significantly better mobility for Mg in the delta polymorph, suggesting that better performance can be achieved by cycling Mg in the delta phase.