Lithium insertion into the raw multi-walled carbon nanotubes pre-doped with lithium - an electrochemical impedance study

The raw carbon nanotubes were synthesized by electric arc method and doped with lithium. Electrochemical impedance spectroscopy was applied for the raw carbon nanotubes pre-doped with lithium during Li-ion insertion in the electrolyte of I M LiClO4/EC + DMC. After treated with lithium compounds the reversible capacity was increased than that of raw carbon nanotubes. The impedance spectra measured consist of a depressed semicircle in the high frequency range and a straight line at low frequency. Obtained spectroscopies were analyzed with an equivalent circuit model. Kinetic parameters such as the charge transfer resistance and the chemical diffusion coefficient of Li-ion in the carbon nanotubes were evaluated. It showed that the D, increased as the Li concentration increased. The possible reasons that can explain the variations in the diffusion coefficient with the open circuit voltage are controlled by the effective cross-section of the diffusion. (C) 2003 Elsevier B.V. All rights reserved.