Lithium intercalation into a plasma-enhanced-chemical-vapour-deposited carbon film electrode

Electrochemical lithium intercalation into a PECVD (plasma enhanced chemical vapour deposited) carbon film electrode was investigated in 1 M $LiPF_6-EC$ (ethylene carbonate) and DEC (diethyl carbonate) solution during lithium intercalation and deintercalation, by using cyclic voltammetry supplemented with ac-impedance spectroscopy. The size of the graphitic crystallite in the a- and c-axis directions obtained from the carbon film electrode was much smaller than those of the graphite one, indicating less-developed crystalline structure with hydrogen bonded to carbon, from the results of AES (Auger electron spectroscopy), powder XRD (X-ray diffraction) method, and FTIR(Fourier transform infra-red) spectroscopy. It was shown from the cyclic voltammograms and ac-impedance spectra of carbon film electrode that a threshold overpotential was needed to overcome an activation barrier to entrance of lithium into the carbon film electrode, such as the poor crystalline structure of the carbon film electrode showing disordered carbon and the presence of residual hydrogen in its structure. The experimental results were discussed in terms of the effect of host carbon structure on the lithium intercalation capability.