Investigation of Rare-Earth Chalcogenide Spinel for Mg Solid State Conductors

Magnesium batteries hold potential for overcoming the safety and energy density limitations faced by Li-ion batteries. However, the development of Mg battery technology is plagued by the poor kinetics of Mg transport in solid state materials. Recently, the chalcogenide spinel structure was found to be suitable for rapid Mg2+ diffusion.[1] Based on this result we engaged in a more elaborate study of chalcogenide spinels. Seven stable MgLn2X4 (Ln = lanthanoid, X = S, Se) spinels were evaluated with density functional theory to have low barriers for Mg migration (<380 meV) and reasonable stability. Two of these materials have been synthesized and studied experimentally. We will show how the conductivity can be systematically improved by judicious choice of metal ions. In particular, the effect of large rare-earth cations on expanding the triangular anion bottleneck to reduce the migration barrier and the structure disorder phenomenon will be discussed. Reference: [1] Canepa, P., Bo, S., Sai Gautam, G. et al. High magnesium mobility in ternary spinel chalcogenides. Nat. Commun. 8, 1759 (2017).