Li absorption and intercalation in single layer graphene and few layer graphene by first principles.

We present an exhaustive first-principles investigation of Li absorption and intercalation in single layer graphene and few layer graphene, as compared to bulk graphite. For single layer graphene, the cluster expansion method is used to systemically search for the lowest energy ionic configuration as a function of absorbed Li content. It is predicted that there exists no Li arrangement that stabilizes Li absorption on the surface of single layer graphene unless that surface includes defects. From this result follows that defect-poor single layer graphene exhibits significantly inferior capacity compared to bulk graphite. For few layer graphene, we calibrate a semiempirical potential to include the effect of van der Waals interactions, which is essential to account for the contribution of empty (no Li) gallery to the total energy. We identify and analyze the Li intercalation mechanisms in few layer graphene and map out the sequence in stable phases as we move from single layer graphene, through few layer, to bulk graphite.