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 EC-DMC Li salt solutions was studied using simultaneously slow scan rate 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 the electroanalytical response of these electrodes during intercalation with lithium. At slow enough scan rates, the CV of these electrodes probe mostly the accumulation - consumption of lithium and phase transition between intercalation stages, perturbed by slow kinetics and solid state diffusion. Impedance spectra of these electrodes reflect clearly a separation among different time constants which relate to migration of Li through surface films, charge transfer, solid state diffusion, and finally - accumulation of Li in the bulk. The diffusion coefficient of Li in graphite was found to be a peak shaped function of the potential and the intercalation level. The peaks of - log D vs E, X (X Li in Li_xC₆) correspond to the CV peaks (which reflect phase transitions). The particle size and the solution composition influence very strongly the resolution of all the above electroanalytical tools in the separation of the various processes which occur during intercalation of lithium into graphite. The effect of the particle size and the solution composition on the electroanalytical response of these electrodes is discussed.