Impedance studies of copper foil and graphite-coated copper foil electrodes in lithium-ion battery electrolyte

The electrochemical impedance spectroscopy of battery grade copper foil and graphite-coated copper foil electrodes in 1 M LiPF6 in a ternary organic carbonate electrolyte has been obtained. Detailed studies showed that both electrodes gave similar impedance spectra of two successive semicircular arcs. When overpotential was increased for both electrodes, the high frequency semicircles remained the same on each electrode, but the second semicircle increased for both electrodes. Based on the impedance spectra results of the electrodes, it appeared that the high frequency response represented a surface oxidation 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 then proposed.