Electrochemical impedance study of Li-ion insertion into the raw acid-oxidized carbon nanotubes

Electrochemical impedance spectroscopy (EIS) was applied for the raw acid-oxidized multiwall carbon nanotubes during Li-ion insertion with the electrolyte of 1M LiPF6 in EC and DMC. Impedance spectroscopy consists of two separated arcs in the high and intermediate range frequency. The high frequency arc is attributed to Li migration within the surface films and the medium frequency arc is associated with the charge transfer. Obtained spectra were analyzed with an equivalent circuit model. Kinetic parameters such as the charge transfer resistance, film resistance, diffusion coefficient and exchange current were evaluated. The contribution of the film to the measured impedance response is discussed.