THE BASIC ELECTROANALYTICAL BEHAVIOR OF PRACTICAL GRAPHITE-LITHIUM INTERCALATION ELECTRODES

The electrochemical behavior of practical carbon electrodes comprising artificial graphite particles of different sizes and PVDF binder in E C-DMC Li salt solutions was studied using simultaneously slow scan rat e cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS ) and potentiostatic intermittent titration (PITT). The theme of this work was to study the effect of the particle size of the graphite on t he electroanalytical response of these electrodes during intercalation with lithium. At slow enough scan rates, the CV of these electrodes p robe mostly the accumulation - consumption of lithium and phase transi tion between intercalation stages, perturbed by slow kinetics and soli d state diffusion. Impedance spectra of these electrodes reflect clear ly a separation among different time constants which relate to migrati on of Li through surface films, charge transfer, solid state diffusion , and finally - accumulation of Li in the bulk. The diffusion coeffici ent of Li in graphite was found to be a peak shaped function of the po tential and the intercalation level. The peaks of -log D vs E, X (X Li in LiXC6) correspond to the CV peaks (which reflect phase transitions ). The particle size and the solution composition influence very stron gly the resolution of all the above electroanalytical tools in the sep aration of the various processes which occur during intercalation of l ithium into graphite. The effect of the particle size and the solution composition on the electroanalytical response of these electrodes is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.