In search of high performance anode materials for Mg batteries: Computational studies of Mg in Ge, Si, and Sn

We present ab initio studies of structures, energetics, and diffusion properties of Mg in bulk Si, Ge, and Sn diamond structures to evaluate their potential as insertion type anode materials for Mg batteries. We show that Si could provide the highest specific capacity (3817 mAh g−1) and the lowest average insertion voltage (∼0.15 eV vs. Mg) for Mg storage. Nevertheless, due to its significant percent lattice expansion (∼216%) and slow Mg diffusion, Sn and Ge are more attractive; both anodes have lower lattice expansions (∼120% and ∼178%, respectively) and diffusion barriers (∼0.50 and ∼0.70 eV, respectively, for single-Mg diffusion) than Si. We show that Mg–Mg interactions at different stages of charging can decrease significantly the diffusion barrier compared to the single atom diffusion, by up to 0.55 eV.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Prospective anode materials for Mg batteries studied ab initio. ► Mg diffusion, voltages, volume expansion studied in Si, Ge, Sn. ► Mg–Mg interactions decrease diffusion barrier. ► Highest Mg capacity, largest volume expansion in Si. ► Lower volume expansion, lower diffusion barriers in Ge, Sn.