A first-principles study of the lithium insertion behaviors in graphene/Si composites anodes

Abstract

C/Si composites is one of the most commercially promising alternatives for anodes of lithium-ion batteries, which can retain high capacity, mechanical robustness and conductivity. However, the fundamental understanding about lithiation behaviors of Li atom in C/Si composites is insufficient. In this paper, Li insertion and diffusion properties at the monolayer and bilayer graphene/Si (Gr/Si) interfaces with different Si surface orientations are investigated by first-principles calculations. It is shown that in the Gr/Si composites, the presence of graphene on Si surface alter the energetics of Li intercalation significantly, and the interaction between Li and the host becomes much stronger. The binding energy at a surface site is larger than that at an intermediate site and an inner site. The neighboring atom arrangement for Li dopant and the distance between Li and neighboring Si atoms, the charge transfer and charge density difference are also analyzed. Furthermore, the diffusion in Gr/Si composites is also studied. The results show that surface to surface diffusion is much easier than the surface to intermediate or intermediate to inner diffusion. And a large barrier should be overcome cross the surface to intermediate region to diffuse to the inner of the Si substrate.