ED copper foil is broadly used in Li-ion battery and printed circuit boards in electronics industry. However, nodules are commonly observed on the surface of ED copper foil made through a conventional electro-deposition method. Patent of US 9,562.298 B2 teaches a new way to reduce the number of the nodules on the surface.
Decreasing of deposition current density can reduce the effects of point discharge, and reduce the size and density of nodules. However it is achieved through reducing production yield.
In the invention of US 9,562,298 B2, a special additive, thiourea, is added into the electrolyte with the concentration from 0.1 to 2.5 ppm. The formulation of the electrolyte system includes copper sulfate , sulfuric acid and additives. The additives include a low molecular weight gel (such as gelatin), hydroxy methyl cellulose (HEC) or polyethylene glycol (PEG) or a sulfur containing compound (for example, Sodium 3-mercaptopropanesulphonate(MPS), bis-(3-soldiumsulfo propyldisulfide)(SPS)), and a complexing agent (for example, chlorine ions). The chemical structure of the materials are shown in the following figure.
A titanium plate overlaid with an iridium element or an oxide as a dimensionally stable anode (DSA), a titanium-made roller as a cathodic drum. A DC is applied between the two poles to electrically deposit the copper ions on the titanium-made roller, and then the deposited ED copper is peeled off from the surface of the titanium-made roller and continuously rolled up for producing the ED copper foil. The surface in contact with the surface of the titanium-made roller is smooth and shiny (called S surface), and the reversed side is matte (called M surface). Usually,the roughness of the S surface of the ED copper foil is more constant and determined by the roughness of titanium drum. The roughness of the M surface is determined by deposition conditions, e.g. copper sulfate electrolyte. The nodules are on the surface of the M surface. By the invented method, the nodules can be significantly reduced.