Essential Electronic Properties of Stage-1 Li/Li⁺-Graphite-Intercalation Compounds for Different Concentrations

We use first-principles calculations within the density functional theory (DFT) to explore the electronic properties of stage-1 Li-and Li⁺-graphite-intercalation compounds (GIC) for different concentrations of LiC_x/Li⁺C_x, with x = 6, 12, 18, 24, 32 and 36. The essential properties, e.g., geometric structures, band structures and spatial charge distributions are determined by the hybridization of the orbitals, the main focus of our work. The band structures/density of states/spatial charge distributions display that Li-GIC shows a blue shift of Fermi energy just like metals, but Li⁺-GIC still remains as in the original graphite or exhibits so-called semi-metallic properties, possessing the same densities of free electrons and holes. According to these properties, we find that there exist weak but significant van der Waals interactions between interlayers of graphite, and 2s-2p_z hybridization between Li and C. There scarcely exist strong interactions between Li⁺-C. The dominant interaction between the Li and C is 2s-2p_z orbital-orbital coupling; the orbital-orbital coupling is not significant in the Li⁺ and C cases, but dipole-diploe coupling is.