  We have studied the adsorption of Li atoms at the hollow sites of graphene
nanoribbons (zigzag and armchair), graphene, and fullerenes by means of density
functional theory calculations including local and semilocal functionals. The
binding energy of a Li atom on armchair nanoribbons (of about 1.70 eV for LSDA
and 1.20 eV for PBE) is comparable to the corresponding value in graphene (1.55
and 1.04 eV for LSDA and PBE, respectively). Notably, the interaction between
Li and zigzag nanoribbons is much stronger. The binding energy of Li at the
edges of zigzag nanoribbons is about 50% stronger than in graphene for the
functionals studied here. While the charge transfer between the Li adatom and
the zigzag nanoribbon significantly affects the magnetic properties of the
latter providing an additional interaction mechanism that is not present in
two-dimensional graphene or armchair nanoribbons, we find that the morphology
of the edges, rather than magnetism, is responsible for the enhanced
Li-nanoribbon interaction.
