First lithiation and charge/discharge cycles of graphite materials, investigated by electrochemical impedance spectroscopy
Résumé
In this study graphite has been characterised by electrochemical impedance spectroscopy (EIS) using a three electrode coin cell. The initial lithiation shows that lithium insertion can be modelled using the Langmuir insertion isotherm as well as the Frumkin insertion isotherm for very low insertion levels. A description of the equivalent circuits used to fit the high frequency (HF) part of the impedance spectra is presented based on chi-square values and the uncertainties in the values of parameters. The HF signature, that appears at the beginning of lithiation does not show behaviour associated solely with the formation of a passivation film but indicates that contact problems related to the electrode volume must be considered too. The study describes the first charge/discharge cycles and shows that the observed phenomena are mostly reversible.