The kinetic and thermodynamic analysis of Li ion in multi-walled carbon nanotubes

In this article, multi-walled carbon nanotubes (MWNTs) produced by CVD were used in electrochemical intercalation reaction with Li+. The characteristics of Li+ intercalation of the MWNTs were determined by using the techniques of galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and the chronoamperometry. The results of the first several charge–discharge cycles showed that the reversible capacity of the MWNTs is larger than the theoretical capacity of graphitized carbon. The equivalent circuit of the Li+ intercalated into the MWNTs was simulated and the parameters of the elements were obtained. The diffusion coefficient calculated based on the results of the impedance was in the range between 1 × 10−10 and 4 × 10−10 cm2 s−1. The diffusion coefficient calculated based on the technique of the chronoamperometery was 3.5 × 10−10 cm2 s−1. The diffusion coefficients of the Li+ reaction with MWNTs were in the range of that of the most carbon materials. By analyzing the results measured above the conclusion is obtained which was Li+ diffusing or intercalating mainly the graphite layers, and Li+ corresponding to the irreversible capacity or the capacity larger than the theoretical capacity may be diffusion into the hollow core of the MWNTs or the caves formed by the entangles nanotubes.