Computational Investigation of Chalcogenide Spinel Conductors for All-Solid-State Mg Batteries

Abstract

We report seven new MgLn2X4 (Ln = lanthanoid, X = S, Se) spinels that have low barriers for Mg migration (< 380 meV) and are stable or nearly stable (within 50 meV/atom of stability with respect to competing structures and compositions) as calculated with density functional theory. As the size of the Ln increases, Mg mobility is found to increase, but stability in the spinel structure is found to decrease. Main textMagnesium batteries are an interesting alternative to Li-ion technology because of the potential for improved safety and higher energy density. 1-3 The ability to use Mg metal as an anode is beneficial because of its high volumetric energy density (3830 mAh/mL) relative to that of graphite (700 mAh/mL), which is generally employed as an anode in Li-ion batteries using liquid or polymer gel electrolytes. 4 Only a few good liquid electrolytes exist for Mg batteries as Mg metal cannot be deposited reversibly in electrolytes that react with the metal. For this reason, we recently explored whether solid electrolytes with sufficient Mg-ion conductivity exist. 5 Unlike for Li and Na, for which a large number of solids with very high ionic conductivity have been reported, 6,7