The lamination interface generated by a power outage during the electrorefining of copper using a wax-less permanent-cathode was investigated to elucidate the formation mechanism of the interface. X-ray diffraction, X-ray photoelectron spectroscopic measurements and electrochemical quartz crystal microbalance measurements revealed that the interface is composed mostly of CuCl (s) . Based on the thermodynamics of aqueous solution containing copper ions and chloride anions, it is considered that Cu+ ions are spontaneously generated through the reaction Cu + Cu2+ → 2Cu+ at the surface of the copper cathode, resulting in the deposition of insoluble CuCl (s) . Circulation of electrolyte during the power outage could suppress the accumulation of Cu+ ions in the vicinity of the cathode and minimize the formation of CuCl (s) layer, which makes the lamination interface after recovery from the power outage.