| The kinetic processes at the interface of uncoated copper foil or graphite-coated copper (Cu-C) foil anodes and lithium ion battery electrolyte were studied in this dissertation through different electrochemical approaches.; First, as part of an intrinsic stability study of copper foil in Li ion battery electrolyte solutions, the effect of trace amounts of HF in the electrolyte was studied. The open circuit voltage (OCV) results of HF doped electrolyte, along with other OCV results from previous studies, indicate that the adsorption of HF on the graphite coating protected the Cu foil beneath the coating from corrosion.; Controlled-potential electrolysis of copper foil and graphite-coated copper foil electrodes in a typical lithium ion battery electrolyte was then performed in order to construct Tafel plots to obtain values of the exchange current, i0, and charge transfer coefficient, alpha. The charge transfer coefficients of both electrodes were found to be small (alpha = ∼0.25), which was consistent with an assumption of a dominant anodic process in the cell. At 25 °C the graphite-coated copper foil was found to have a higher exchange current than the copper foil. This can be explained by the intercalation of lithium ions into the graphite coating which increases the electron transfer rate. In the range of 0 °C to 50 °C, the exchange currents of both electrodes increased with temperature, but at different rates, while the charge transfer coefficients were not significantly affected by temperature.; Finally, the electrochemical impedance spectroscopy (EIS) of copper foil and graphite-coated copper foil electrodes was studied. It was found that both electrodes gave similar impedance spectra of two successive semicircular arcs. Detailed studies of the effects of different cell parameters including overpotential (eta), temperature and graphite-coating saturation time were then performed. Based on the impedance spectra results of the electrodes, it appeared that the high frequency response represented a surface oxide layer. At low frequency further oxidation occurs at both electrodes, but is kinetically controlled for bare copper, while the graphite-coated copper undergoes diffusional blocking through the porous carbon layer. An equivalent circuit of the impedance spectrum was also proposed. |
