The Electrochemical Intercalation of Li into Graphite in Li/Polymer Electrolyte/Graphite Cells

Abstract

The electrochemical intercalation of Li into graphite has been studied in Li/polymer electrolyte/graphite cells using anin situ x‐ray diffraction (XRD) technique. In cells containing an electrolyte of , a minor irreversible reduction of the electrolyte is observed only during the first discharge. In these cells, Li is reversibly intercalated into graphite to form , principally at potentials between 0.2 and 0.0 V vs. Li⁺/Li. No evidence for the cointercalation of EC was obtained. In cells containing electrolyte, a massive reduction of electrolyte occurs during the first discharge at ∼0.8 V vs. Li⁺/Li, which precludes Li intercalation into graphite. In situ XRD data are consistent with the absence of the intercalation of PC or solvates into the graphite lattice, either prior to or during the solvent reduction process. The latter appears to be a surface‐catalyzed process, the extent of which is determined by a combination of thermodynamic and kinetic factors including the reduction potential of the electrolyte, and the passivating films which form on the graphite surface as a result of electrolyte reduction.