Modeling interfaces between solids: Application to Li battery materials

We present a general scheme to model an energy for analyzing interfaces between crystalline solids, quantitatively including the effects of varying configurations and lattice strain. This scheme is successfully applied to the modeling of likely interface geometries of several solid state battery materials including Li metal, ${\mathrm{Li}}_{3}{\mathrm{PO}}_{4}, {\mathrm{Li}}_{3}{\mathrm{PS}}_{4}, {\mathrm{Li}}_{2}\mathrm{O}$, and ${\mathrm{Li}}_{2}\mathrm{S}$. Our formalism, together with a partial density of states analysis, allows us to characterize the thickness, stability, and transport properties of these interfaces. We find that all of the interfaces in this study are stable with the exception of ${\mathrm{Li}}_{3}{\mathrm{PS}}_{4}/\mathrm{Li}$. For this chemically unstable interface, the partial density of states helps to identify mechanisms associated with the interface reactions. Our energetic measure of interfaces and our analysis of the band alignment between interface materials indicate multiple factors, which may be predictors of interface stability, an important property of solid electrolyte systems.