Abstract:Deposition behavior of Li atoms or aggregates Li_n(n＜10) on graphene negative electrodes for lithium-ion batteries was investigated by the first principles calculations based on density functional theory, including the lowest energy configuration, adsorption energy, charge density difference and density of states. The results show that Li atom preferentially deposits above the center of the carbon six-membered ring of graphene in a dispersed form when n≤2. As the number of Li atoms increases, Li atoms preferentially aggregate to reunite and deposit on graphene when n≥3. It is possible to form Li₄, Li₇ and Li₉ stable agglomerates in the charging process of the lithium ion battery, which indicates that the maximum lithium storage capacity of graphene may exceed that of graphite. However, the lithium dendrites will form easily. The electronic structure analysis shows that the electrons of Li atom or Li_n aggregates transfer to the anti-bonded π orbital of graphene, and the 2s orbital of Li atom and the 2p orbital of C atom are obviously hybridized. The Fermi level of the system moves to the graphene anti-bond π orbital as the number of Li atoms n increases, which leads to the result that the metallicity and electronic conductivity increase. The Li—Li bond at the bottom of the Li_n agglomerate is usually an ionic bond and the outermost Li—Li bond is usually a covalent bond. The Li—C bond between the Li_n agglomerate and graphene is an ionic bond with partial covalent bond property and the strength of the Li—C bond gradually decreases as the number of Li atoms n increases.

Key words: lithium ion battery; graphene; Li_n agglomerates; first-principles; deposition behavior