FORMATION OF LITHIUM-GRAPHITE INTERCALATION COMPOUNDS IN NONAQUEOUS ELECTROLYTES AND THEIR APPLICATION AS A NEGATIVE ELECTRODE FOR A LITHIUM ION (SHUTTLECOCK) CELL

Electrochemical reduction of natural graphite was carried out in 1M LiClO4 ethylene carbonate (EC)/1,2-dimethoxyethane (DME) (1:1 by volume) solution at 30-degrees-C. Natural graphite was reduced stepwise to LiC6 (golden yellow in color). The staging phenomenon was observed by x-ray diffraction (XRD). The first stage (LiC6; C(L) = 3.703 angstrom) and the second stage (LiC12; d2 = 7.06 angstrom) compounds were identified as a commensurate structure in which lithium atoms form a close-packed two-dimensional array A second-stage compound (LiC18) with a different in-plane lithium ordering based on a LiC9 two-dimensional packing in lithium intercalated sheets also was observed; also third (LiC27; d3 = 10.4 angstrom),, fourth (LiC36; d4 = 13.8 angstrom), and eighth-(LiC72; d8 = 27.2 angstrom) stage compounds were identified. The electrochemical oxidation of the first-stage compound (LiC6) was examined and shown to be reversible over the entire range, i.e., square C6 + xLi reversible LixC6. The reaction mechanism for the reduction of graphite and the oxidation of the first-stage compound are discussed in relation to the staging phenomenon from the detailed open-circuit voltage and XRD data. The chemical potential of LiC6 was estimated to be -3.6 kcal . mol-1 from the observed reversible potential. The feasibility of using a lithium-graphite intercalation compound in lithium ion (shuttlecock) cells is described, and the innovative secondary systems, square C6/LiCoO2 and square C6/LiNiO2 fabricated in discharged states, are demonstrated.