Formation of Lithium‐Graphite Intercalation Compounds in Nonaqueous Electrolytes and Their Application as a Negative Electrode for a Lithium Ion (Shuttlecock) Cell

Abstract

Electrochemical reduction of natural graphite was carried out in 1M ethylene carbonate (EC)/1,2‐dimethoxyethane (DME) (1:1 by volume) solution at 30°C. Natural graphite was reduced stepwise to (golden yellow in color). The staging phenomenon was observed by x‐ray diffraction (XRD). The first stage (; ) and the second stage (; ) compounds were identified as a commensurate structure in which lithium atoms form a close‐packed two‐dimensional array. A second‐stage compound with a different in‐plane lithium ordering based on a two‐dimensional packing in lithium intercalated sheets also was observed; also third (; ), fourth‐(; ), and eighth‐(; ) stage compounds were identified. The electrochemical oxidation of the first‐stage compound was examined and shown to be reversible over the entire range, i.e., . 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 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, and fabricated in discharged states, are demonstrated.