The intercalation phase diagram of Mg in V${}_2$O${}_5$ from first principles

Abstract

We have investigated Mg intercalation into orthorhombic V${}_2$O${}_5$, one of only three cathodes known to reversibly intercalate Mg ions. By calculating the ground state Mg${}_x$V${}_2$O${}_5$ configurations and by developing a cluster expansion for the configurational disorder in $\delta$-V${}_2$O${}_5$, a full temperature-composition phase diagram is derived. Our calculations indicate an equilibrium phase separating behavior between fully demagnesiated $\alpha$-V${}_2$O${}_5$ and fully magnesiated $\delta$-V${}_2$O${}_5$, 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.

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