As is well known, the positive electrode substrate of a lithium-ion battery is aluminum foil, and the negative electrode substrate is copper foil. After coating, they are made into positive and negative electrode rolls for further processing. The quality of the electrode sheets largely determines certain battery performance characteristics, and the coating of the substrate is a crucial step in the entire battery manufacturing process!
The coating methods have evolved from the original dip coating and extrusion to the most advanced double-sided simultaneous coating, all in order to improve the coating quality and performance of the electrode sheets. Some economically strong domestic companies have spent a lot of money to import expensive electrode coating machines from abroad in order to manufacture reliable lithium-ion batteries.
The general coating process is as follows: The substrate (metal foil) is unwound from the unwinding device and fed into the coating machine. The ends of the substrate are joined together at the splicing table to form a continuous strip, which is then fed into the tension adjustment device and automatic alignment device by the sheet pulling device. After adjusting the sheet tension and position, it enters the coating unit. The electrode paste is coated in segments according to the predetermined coating amount and blank length in the coating unit. In double-sided coating, the coating process automatically tracks the front side coating and blank length. The coated wet electrode is then sent to the drying tunnel for drying; the drying temperature is set according to the coating speed and coating thickness. After drying, the electrode is tension adjusted and automatically aligned before being wound up for the next processing step.
The electrode slurry coating is relatively thick, with a large coating amount and a high drying load. Currently, hot air impact drying technology is commonly used. The positive electrode substrate is aluminum foil, which is chemically very reactive and easily oxidized. During the manufacturing process of aluminum foil, a dense oxide film is formed, preventing further oxidation. Because the oxide film is thin, porous, and soft, it has good adsorption properties. However, high temperature and high humidity can damage this oxide film and accelerate the oxidation reaction. Currently, most methods use single-sided coating. When the first side is coated, the other side is completely exposed to hot air. The hot air for coating (oil-based) drying needs to be around 130°C. If the moisture content in the hot air is not effectively controlled, it will intensify the oxidation of the aluminum foil, affecting the adhesion between the positive electrode material and the aluminum foil, and in severe cases, even causing it to detach.
American and Japanese coating machine manufacturers have developed double-sided simultaneous coating technology to address the energy efficiency and aluminum foil oxidation issues of single-layer coating machines. This technology completely solves the problem of aluminum foil oxidation during coating. However, the exorbitant price of double-sided simultaneous coating machines is beyond the reach of most battery manufacturers.
