Chloride ion and polyethylene glycol: Improving the microstructure and enhancing the mechanics of electrolytic copper foil

This study examines the effects of chloride ions (Cl⁻) and polyethylene glycol (PEG) on the properties of ultra-thin electrolytic copper foils. By varying the concentrations of Cl⁻ and PEG, we investigated changes in surface morphology, mechanical properties, and microstructure using scanning electron microscopy (SEM), nanoindentation tests, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Our findings show that increasing Cl⁻ concentration generally leads to smoother and more uniform surface morphologies. An optimal combination of 30 mg/L Cl⁻ and 5 mg/L PEG resulted in a notably smooth and flat copper surface. Mechanical testing demonstrated significant enhancements in both Young's modulus and hardness at these additive concentrations. XRD and EBSD analyses indicated a favorable shift in the crystallographic orientation of the copper grains, promoting more uniform grain growth. TEM analysis underscored the role of nano-twins and dislocations in strengthening the material. These results suggest that a precise balance of Cl⁻ and PEG in the electrolyte can improve the quality and performance of ultra-thin copper foils, providing a basis for further optimization in industrial applications.