Manufacture of Copper Foils for the Current Collector of Lithium-Ion Batteries By Electrochemical Deposition

Abstract

Manufacture of copper foils by electrochemical deposition is a mature and indispensable technique in the modern industry, and one of the important products is the copper clad laminate for printed circuit board industry. In recent years, as the rapid increase in electric cars industry, the demand for Cu foils acting as the current collector of negative electrodes for lithium-ion batteries (LIBs) surges strikingly. Nonetheless, the method to produce Cu foils for LIBs could not be conducted by electrochemical deposition but by rolling, since the rolled copper foils provides a double side smooth surface, which is crucial to achieve good capacity retention rate of LIBs. Moreover, rolled copper foils possess excellent mechanical properties such as tensile strength to ensure the foils pass through the following roll-to-roll coating process without fracture. Unfortunately, rolled Cu foils are much costly in comparison with the electroplating, especially for thin foils since it require more times of rolling and annealing the copper ingot. Meanwhile, the surface roughness of electrodeposited Cu foils on both sides is distinctively different by the conventional electrolyte composition, which is known to deteriorate the capacity retention rate of LIBs. Consequently, we introduced several organic additives that had been applied in copper damascene plating into copper foils plating, and attempted to manufacture Cu foils with optimal quality that can meet the requirements to be adopted into LIBs. Unlike damascene process, the target of using additives is not to change the deposition rate of copper, but to modify the surface morphology and strengthen the structure of the deposited copper. In addition, the applied current density of Cu foil plating usually ranges from 500 to 1000 mA·cm-2, which is 20 times more than damascene plating. Correspondingly, the convection rate in the plating bath ought to be extremely high to make sure the limiting current density higher than the applied current density. Therefore, the electrochemical behavior of each additives has yet to be studied under such high current densities and strong flow-rate environments. Last but not least, the degradation rate of the organic additives may be much faster since the current density is much higher. To produce Cu foils with consistent quality, understanding the bath aging problem and the proper method to maintain the bath is very important. In this research, the effects of the selected additives on the structure and surface morphology of deposited copper, the electrochemical behavior of additives under high current density, and the full consideration to solve the bath aging issue will be presented. Ultimately, a proper solution to manufacture Cu foils for LIBs by electrochemical deposition will be proposed.