THEORETICAL-STUDY OF LITHIUM-DOPED POLYCYCLIC AROMATIC-HYDROCARBONS

The interactions between carbon layers and lithium atoms are described with a semiempirical molecular orbital method in order to clarify the Li storage mechanism in amorphous carbon (a-C) materials used in Li i on rechargeable batteries. The general electronic and geometric struct ures of Li-doped a-C materials are investigated using ovalene (C32H14) as a model carbon structure. The following results are obtained. (i) The intercalation of Li atoms proceeds preferentially up to the C6Li c onfiguration, followed by the absorption of Li atoms on the surface of the carbon layer. (ii) The adsorption of Li atoms can occur even on t he nearest neighbor site and can form Li cation clusters commensurate with the carbon lattice. (iii) Li atoms located at the acene-edge site s are more stable than those at the phenanthrene-edge sites. This resu lt suggests that the acene-edge structure is favorable for carbon anod e materials. (iv) Substitution of the carbon skeleton by heteroatoms s uch as boron and nitrogen is not effective for Li storage.