DIFFUSION-COEFFICIENTS OF LITHIUM IONS DURING INTERCALATION INTO GRAPHITE DERIVED FROM THE SIMULTANEOUS MEASUREMENTS AND MODELING OF ELECTROCHEMICAL IMPEDANCE AND POTENTIOSTATIC INTERMITTENT TITRATION CHARACTERISTICS OF THIN GRAPHITE-ELECTRODES

The solid state diffusion of Lithium into graphite during electrochemi cal intercalation processes was investigated using potentiostatic inte rmittent titration (PITT) and impedance spectroscopy (EIS). The diffus ion coefficient (D) as a function of the intercalation level (X) and t he electrode potential (E) was calculated on the basis of both methods and gave similar results. The D vs X or E plots were found to be nonm onotonous, with three pronounced minima at the same potentials in whic h the cyclic voltammetry of these systems shows the peaks related to t he phase transition between the Lithium-graphite intercalation stages. It was found that the critical diffusion length for these electrodes relates to the graphite particles' dimensions along their basal planes and not to the electrode thickness. The reason for the peaklike depen dence of the D on X and E is discussed in light of the nature of the i ntercalation processes.