Facet-dependent magnesiation behavior of α-Sn as an anode for magnesium ion batteries

Abstract

The adsorption and magnesiation behavior of Mg onto α-Sn and Mg₂Sn through (100), (110) and (111) surfaces were investigated by using first-principles calculations. It was found that the Mg atom prefers to be adsorbed on the surface rather than diffuse into the sub-surface of Sn. The diffusion energy barrier is higher for Mg diffusing from the surface to the subsurface compared with the internal diffusion. Mg diffuses much faster along the <100> direction than along the <110> and <111> directions. The diffusion process from the surface to the subsurface is a rate-limiting step for Mg intercalation into Sn. The surface magnesiation is also a rate-limiting step for Mg intercalation into Mg₂Sn though (100) and (110) surfaces, whereas the surface magnesiation of the Mg₂Sn (111) surface is easier than the (100) and (110) surfaces. Surface modification is necessary to improve the magnesiation behavior of Sn as an anode for MIBs, especially when the anode materials are reduced to the nanoscale.