Ab initio study on the lithiation mechanism of Mg2Si electrode

The lithiation mechanism of Mg₂Si electrode has been investigated using the first-principles calculations within the density functional theory. The detailed reaction paths of lithium insertion into Mg₂Si were analyzed, and the calculated results indicate that Li₁Mg₂Si is just the critical phase, which the substitution of Li and extrusion of Mg begin to happen. The relative volume changes for the electrode were also discussed along with the reaction paths. It is found that the host material first expands then shrinks largely during the whole process of lithium insertion into electrode, it could be one of the important reasons that the pure Mg₂Si deliver a large initial capacity, but the capacity decreases rapidly with cycling.