Grain boundary(GB),an intrinsic topological defect of polycrystalline materials.[1,2] To understand the effect of topological defects on the Li adsorption on graphene,we have performed the first-principles calculations to study the adsorption and diffusion of lithium adatom on graphene with(5,0)|(3,3),(2,1)|(2,1)and(2,0)|(2,0)GBs.Our results show GBs would enhance the Li adsorption on graphene significantly.In three cases of GBs,the energy barrier for the diffusion of Li adatom along the boundary is lower than that perpendicular to boundary,leading to Li adatom tends to diffuse along the boundary and to migrate from non-boundary sites toward the boundary zone(Fig.2).The difference charge density and the Bader charge analysis both show there is a significant charge transfer from Li adatom to its nearest neighboring carbon atoms.These results suggest that not only the edge,point defect and dopant,[3-5] but also the grain boundary can enhance the lithium adsorption of graphene,which would be very helpful to design the graphene-based anode materials of Li-ion batteries.