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

We have investigated Mg intercalation into orthorhombic V$_2$O$_5$, one of\nonly three cathodes known to reversibly intercalate Mg ions. By calculating the\nground state Mg$_x$V$_2$O$_5$ configurations and by developing a cluster\nexpansion for the configurational disorder in $\\delta$-V$_2$O$_5$, a full\ntemperature-composition phase diagram is derived. Our calculations indicate an\nequilibrium phase separating behavior between fully demagnesiated\n$\\alpha$-V$_2$O$_5$ and fully magnesiated $\\delta$-V$_2$O$_5$, but also\nmotivate the existence of potentially metastable solid solution transformation\npaths in both phases. We find significantly better mobility for Mg in the\n$\\delta$ polymorph suggesting that better performance can be achieved by\ncycling Mg in the $\\delta$ phase.\n