ABSTRACT
It is well known that graphite is one of the most investigated materials both theoretically and experimentally. Up to now, it has served as the best anode in the Li+-band battery. This layered system is purely composed of the hexagonal-symmetry carbon layers, in which the weak but significant van der Walls interactions would greatly modify the low-lying π-electronic structure and thus dominate the essential physical properties. Monolayer graphene is identified to be a zero-gap semiconductor, while a 3D graphite belongs to a semimetal. The electronic properties strongly depend on the way the graphitic planes are stacked on each other. In general, there are three kinds of stacking configurations: AAA (simple hexagonal), ABAB (Bernal), and ABCABC (rhombohedral). The total free carrier density is predicted to be 3.5 × 1020 e/cm3 in simple hexagonal graphite and ∼1019 in Bernal graphite at room temperature. When various atoms and molecules are further intercalated into the AB-stacked graphite, many graphite-intercalation compounds are formed. When many free conductions (holes) are induced after the intercalation, such systems exhibit the donor-type (acceptor-type) behaviors. Among these compounds, only the stage n lithium intercalation systems display the AAA stacking configuration, as confirmed from the X-ray diffraction patterns. Here, n clearly indicates the number of graphitic sheets between two periodical guest-atom layers, in which n = 1, 2, 3, and 4 (Figure 3.8c–f), being 38arranged from the highest concentration to the lower one, will be studied thoroughly in terms of the essential properties. It is also noticed that the other alkali intercalation compounds present the MC8 structure in the stage-1 configuration (M = K, Rb; Cs). Obviously, both LiC6 and MC8 should have very different band structures and fundamental properties.
