Comparison of Tetragonal and Cubic Tin as Anode for Mg Ion Batteries

Using first-principles calculation based on density functional theory, diffusion of Mg atom into α- and β-Sn was investigated. The diffusion barriers are 0.395 and 0.435 eV for an isolated Mg atom in the α- and β-Sn, respectively. However, the diffusion barriers of the Mg atom decrease in the α-Sn, whereas they increase in the β-Sn, when an additional Mg atom was inserted near the original diffusing Mg atom, which is mainly due to strong binding of Mg-Mg atoms in the β-Sn. Therefore, it is better to use the α-Sn, rather than the β-Sn, as an anode material for Mg ion batteries.