The mechanism of lithium intercalation in graphite film electrodes in aprotic media. Part 2. Potentiostatic intermittent titration and in situ XRD studies of the solid-state ionic diffusion

The potentiostatic intermittent titration technique (PITT) and in situ XRD have been used to measure the dependence of the diffusion coefficient D_o of lithium ions in graphite on the intercalation level X. Thin graphite electrodes provide an excellent opportunity to obtain highly-resolved data (with respect to X). A non-monotonic peak-shape dependence of log D_o vs. X has been observed, which correlates well with the corresponding dependence of the XRD peak intensity and the cyclic voltammetric peaks. The results thus obtained have been explained tentatively within a framework similar to the Daumas and Herold cluster model for the staged phase transition. Problems connected with the determination of the true values of D_o for porous electrodes are also discussed.