First-Principles Studies of Lithium Adsorption and Diffusion on Graphene with Grain Boundaries

To understand the effect of topological defects on the Li adsorption on graphene, we have performed first-principles calculations to study the adsorption and diffusion of a lithium adatom on graphene with (5, 0)vertical bar(3, 3), (2, 1)vertical bar(2, 1), and (2, 0)vertical bar(2, 0) grain boundaries (GBs). Our results show that the adsorption of a Li adatom on defect-free graphene is endothermic with respect to the bulk Li and the adsorption of a Li adatom on the GBs of graphene is exothermic. In particular, the presence of a (2, 0)vertical bar(2, 0) GB leads to a decrease of about 0.92 eV in the adsorption energy of a Li adatom on graphene. This suggests that GBs would significantly enhance the Li adsorption on graphene. In three cases of GBs, the energy barrier for the diffusion of a Li adatom along the boundary is lower than that perpendicular to the boundary, indicating that a Li adatom tends to diffuse along the boundary and to migrate from nonboundary sites toward the boundary zone. The difference charge density and the Bader charge analysis both show there is a significant charge transfer from the Li adatom to its nearest neighboring carbon atoms.