Electrodeposition of copper from spent Li-ion batteries by electrochemical quartz crystal microbalance and impedance spectroscopy techniques

Information about the copper electrodeposition mechanism at different pH values was obtained using an electrochemical quartz crystal microbalance (EQCM) technique, as well as potentiodynamic, potentiostatic, and electrochemical impedance spectroscopy (EIS) techniques. In agreement with the measurements obtained from the EQCM and potentiostatic experiments, an intermediate Cu+ species and a CuO layer are formed. Simultaneous mechanism of direct reduction of Cu2+ and copper oxide (CuO) reduction at pH 2.0 and 4.5 occur. The EIS experiment shows a diffusion-controlled process by the presence of a Warburg element, a CPE related to the irregular metallic copper electrodeposition, and a resistance of the electrodeposit.