During double-sided coating, the coating process automatically tracks the front coating and blank length. The coated wet electrode sheet is then fed into a drying tunnel for drying, with the drying temperature set according to the coating speed and coating thickness. After drying, the electrode sheet undergoes tension adjustment and automatic alignment before being wound up for further processing.
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 of the aluminum foil. 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, single-sided coating is used. When the first side is coated, the other side is completely exposed to hot air. However, the hot air for drying the coating (oil-based) 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 and affect the adhesion between the positive electrode material and the aluminum foil. In severe cases, it may even cause the foil to fall off.
The choice of coating method and control parameters have a significant impact on the performance of lithium-ion batteries, mainly in the following aspects:
1) Coating drying temperature control: If the drying temperature is too low during coating, the electrode cannot be guaranteed to be completely dry. If the temperature is too high, the organic solvent inside the electrode may evaporate too quickly, causing the coating on the electrode surface to crack or peel off.
2) Coating density: If the coating density is too low, the battery capacity may not reach the nominal capacity. If the coating density is too high, it will easily lead to material waste. In severe cases, if the positive electrode capacity is excessive, lithium dendrites formed due to lithium precipitation will pierce the battery separator and cause a short circuit, resulting in a safety hazard.
