THE MECHANISM OF LITHIUM INTERCALATION IN GRAPHITE FILM ELECTRODES INAPROTIC MEDIA .1. HIGH-RESOLUTION SLOW-SCAN RATE CYCLIC VOLTAMMETRIC STUDIES AND MODELING

Using slow scan rate (4 to 80 mu V s(-1)) cyclic voltammetry for thin graphite electrodes (8 to 10 mu m thick), two limiting cases for the i ntercalation mechanism of Li ion in graphite in aprotic solvents have been observed: (i) quasi-equilibrium, capacitive-like step at very slo w potential scan rates and (ii) semi-infinite diffusion of Li+ ions in side the graphite matrix at higher scan rates. Each of these two limit ing types of behavior has been appropriately modeled, and from the com parison of experimental and simulated voltammetric curves quantitative information has been extracted, including (a) the effective heterogen eous rate constants for Li+ ion transfer through the graphite\solution interface; (b) the lateral attraction parameter for the intercalated species; (c) half-peak width and peak potential separation; and (d) di ffusion coefficients of the intercalated ions. The features of the exp erimental CV curves are in qualitative agreement with the island model of the staging process proposed in the literature. The diffusion coef ficients of Li+ ions in graphite evaluated from the voltammetric data were found to be close to those obtained from a potentiostatic intermi ttent titration technique applied to the same electrodes.