STRUCTURE AND LITHIUM INTERCALATION PROPERTIES OF SYNTHETIC AND NATURAL GRAPHITE

The crystal structure and lithium intercalation properties of commerci ally available synthetic and natural graphites were investigated using x-ray diffraction and electrochemical voltage spectroscopy techniques . It has been found that most graphites are a mixture of hexagonal and rhombohedral phases. A specific x-ray refinement program has been dev eloped to extract the structural parameters of each of the two phases, such as their relative concentrations, structural disorders, layer si zes, and interlayer spacing, etc. The rhombohedral phase content may e xceed 30% in some graphites. It was also observed that as the particle size of the graphite is reduced, the rhombohedral content is increase d. The Lithium intercalation reactions in various graphites were inves tigated by using electrochemical voltage spectroscopy and the correlat ion between lithium intercalation reversibility, phase content, and st ructural disorder of the graphites is discussed in detail. A modified correlation model is developed to facilitate the understanding of the relation between the structures of graphite and the lithium intercalat ion properties. It was found that the total reversible lithium capacit y is related to both the hexagonal and rhombohedral phase contents, an d that the lithium intercalation mechanism in the two structures are s imilar.