Edge Effects on the Characteristics of Li Diffusion in Graphene

We study the adsorption and diffusion or Li atoms on the surface of planar graphenes by means of density functional theory. When the dimensionality of graphene is reduced to a quasi-one-dimension, armchair and zigzag edges appear. We show that the presence of these edges affects not only the reactivity of the carbon material toward the adsorption of Li adatoms but also their diffusion properties. These properties strongly depend on the specific morphology of the edges. Our results indicate that Li adatoms will diffuse toward the edges while Li diffusion channels appear along the ribbon axis. For most of the diffusion paths studied here, energy barriers are lower than those in graphene. This effect is significantly more pronounced toward the edges, where energy barriers can be up to 0.15 eV smaller than those in in graphene, producing an increase of up to 2 orders of magnitude in the diffusion coefficient at room temperature. Our results indicate that electrodes fabricated with these materials should increase the power of Li-ion batteries.