The solid state diffusion of lithium into graphite during electrochemical intercalation processes was investigated using potentiostatic intermittent titration and impedance spectroscopy. The diffusion coefficient (D) as a function of the intercalation level (X) and the electrode potential (E) was calculated on the basis of both methods and gave similar results. The D versus X or E plots were found to be non-monotonic, with three pronounced minima at the same potentials in which the cyclic voltammetry of these systems showed the peaks related to the phase transition between the lithium - graphite intercalation stages. It was found that the critical diffusion length for these electrodes related to the graphite particles' dimensions along their basal planes and not to the electrode thickness. The reason for the peak-like dependence of the D on X and E was discussed in light of the nature of the intercalation processes.

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. Levi, M.D., Aurbach, D.: Journal of Physical Chemistry B, 1997, 101[23], 4641-7