The mechanism of lithium intercalation in graphite film electrodes in aprotic media. Part 1. High resolution slow scan rate cyclic voltammetric studies and modeling

Using slow scan rate (4 to 80 μVs^-1) cyclic voltammetry for thin graphite electrodes (8 to 10 μm thick), two limiting cases for the intercalation mechanism of Li ion in graphite in aprotic solvents have been observed: (i) quasi-equilibrium, capacitive-like step at very slow potential scan rates and (ii) semi-infinite diffusion of Li⁺ ions inside the graphite matrix at higher scan rates. Each of these two limiting types of behavior has been appropriately modeled, and from the comparison of experimental and simulated voltammetric curves quantitative information has been extracted, including (a) the effective heterogeneous rate constants for Li⁺ ion transfer through the graphitelsolution interface; (b) the lateral attraction parameter for the intercalated species; (c) half-peak width and peak potential separation; and (d) diffusion coefficients of the intercalated ions. The features of the experimental CV curves are in qualitative agreement with the island model of the staging process proposed in the literature. The diffusion coefficients of Li⁺ ions in graphite evaluated from the voltammetric data were found to be close to those obtained from a potentiostatic intermittent titration technique applied to the same electrodes.