In the lithium-ion battery, the positive and negative active materials are coated onto a substrate to form electrodes, which are then wound or laminated to form a core. The substrates used are mainly copper foil and aluminum foil. The current lithium batteries have aluminum foils as the positive electrode and copper foils as the negative electrode. This is because copper is easily oxidized at the higher potential positive electrode, and the surface of the aluminum foils has a dense oxide layer, it has a protective effect on the internal aluminum at high potential. In this article, we will talk about copper foil commonly used in negative electrode. Copper has high mechanical strength and excellent conductivity. The content of copper in the Earth's crust is about 0.01% . Copper foil can be divided into electrolytic copper and calendered copper according to the different manufacturing methods, calendered copper has good ductility, production has higher technical difficulties, its preparation requires more procedures, higher costs, less domestic enterprises use this method to produce, some of the better international players are American based companies like Olin brass and Japanese mining company Nippon Nippon Co. . At present, most copper foils used in power cell factories are produced by electrolysis. In 1922, Edison invented and applied for a patent for the continuous electrolysis of copper foil, using a rotating metal roller immersed in a copper sulfate electrolyte as the cathode and an insoluble metal as the anode. In 1937, ANACONDE copper plant in the United States Applied Edison's patent to produce electrolytic copper foil. Throughout the history of electrolytic copper foil, it has always followed the trend of printed circuit boards. With the large-scale application of lithium-ion battery in consumer electronics, electrolytic copper foil has been brought into a brand-new field, as a negative current collector, its good conductivity, resistance to rolling and low-cost characteristics, so that its rapid and large-scale application. Now with new energy vehicles, 5g and large-scale application of energy storage, electrolytic copper foil demand presents a new explosion.

In order to increase the volume energy density of the core as much as possible, the designers of the core have to load more active materials into the limited shell in order to guarantee the safety, circulation and other performance. I want to use copper foil as the current collector of the negative electrode, the future may be in the following directions: 1 extremely thin copper foil: This trend is now obvious, from 8um down to 6um, and now some manufacturers in a small batch of imports of 4.5 um, perhaps in the future there will be a push for mass production of copper foil below 4um. This effect is also obvious, that is, to increase the volume and mass energy density of the cell as much as possible, but this puts forward higher requirements for both the manufacture of copper foil and the coating control of the cell, after all, the thinner the copper foil, the greater the risk of tape breakage during the coating process. 2 perforating copper foil: by means of Chemical Etching, micropores are formed on the surface of copper foil, the weight of the substrate is reduced, the mass energy density of the core is increased, the control of Pore size and the type of etchant are needed to be optimized, the other is to evaluate the influence of residual etchant on the performance of the cell, such as circulation, gas production and so on. 3 Spray Copper Foil: This is the equivalent of double sided copper plating on a plastic substrate, which retains the ability to collect current and conduct electrons, while also reducing the weight of the substrate and increasing the mass and energy density of the cell, but in the manufacturing process, it may face the challenge of cold pressing, pole-ear welding and other processes. With the continuous improvement of new energy vehicle penetration, the existing copper foil production capacity is also increasingly insufficient, there is a certain gap between supply and demand, it is expected that the copper foil industry will gradually expand production in the future to meet the market demand for power cells.

The preparation of electrolytic copper foil can be divided into three steps: dissolving copper, raw copper foil and surface treatment. In the copper dissolving process, the copper material and sulfuric acid are mixed in a copper dissolving tank to form a copper sulfate solution, which is chemical equation as follows: Cu + o 2→ CuOCuO + H2SO4→ Cuso 4 + H2o copper dissolving process needs to pay attention to the dust in the controlled environment, the foreign matter in the raw material solution, to prevent subsequent contact with the copper foil surface, resulting in bump, this situation may be in the coating, hanging to the die head, resulting in a broken band. So in this step to increase the filtration process, thoroughly will be impurities in the solution filtered. The CuSO4 solution obtained in the copper dissolving process is used as the electrolyte, the titanium roller with large diameter is used as the cathode, and the arc-shaped lead alloy plate is used as the anode, to form a continuous layer of copper. Through the continuous rotation of the Cathode Roll, the deposited copper foil will continue to peel off into a roll, to get raw foil, schematic as follows:

Copper foil is divided into rough surface and smooth surface, with the cathode roll contact with the smooth surface, and with the electrolyte in direct contact with the rough surface, the SEM picture is as follows:

Because copper is easy to oxidize, it is necessary to coarsening, plating barrier layer and anti-oxidation layer to store and transport. The process is illustrated as follows:

Because of the different models and production processes of different manufacturers, such as winding, lamination and so on, it is difficult for the copper and aluminum foil base material to have a width that can be used by different manufacturers. Therefore, it is necessary to have a cutting process, the specific width required to slice into the enterprise. 

Source: Battery Ark