Detailed explanation of the production process flow of Nickel Metal Hydride No. 5 battery coating technology

　　Detailed explanation of the production process of Nickel Metal Hydride No. 5 battery coating technology. Pole piece coating is of great significance to the capacity, consistency, and safety of lithium batteries. According to incomplete statistics: battery failure caused by the pole piece coating process accounts for more than 10% of all Nickel Metal Hydride No. 5 battery failures, and it is also one of the hot topics in the industry. Pole piece coating generally refers to a process in which a uniformly stirred slurry is evenly coated on the current collector and the organic solvent in the slurry is dried.

　　Detailed explanation of the production process flow of Nickel Metal Hydride No. 5 battery coating technology

　　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 pole pieces. Some domestic units with strong economic strength, in order to ensure reliable manufacturing performance For lithium-ion batteries, a large amount of money has been spent to introduce expensive pole plate coating machines from abroad.

　　The general process flow of coating: the coated substrate is fed into the coating machine from the unwinding device. The first and last ends of the substrate are connected into a continuous belt on the splicing table and sent to the tension adjustment device and the automatic correction device by the puller device. After adjusting the film path tension and the film path position, they enter the coating device. The pole piece slurry is coated in sections according to the predetermined coating amount and blank length in the coating device.

　　During double-sided coating, the front coating and blank length are automatically tracked for coating. The coated wet electrode sheet is sent to the drying tunnel for drying. The drying temperature is set according to the coating speed and coating thickness. The dried pole pieces are rolled up after tension adjustment and automatic deviation correction for the next step of processing.

　　The pole piece slurry coating is relatively thick, the coating volume is large, and the drying load is large. Currently, hot air impact drying technology is commonly used. The positive electrode substrate is aluminum foil. The chemical properties of aluminum foil are very active and are easily oxidized. During the manufacturing process of aluminum foil, a dense oxide film will be formed to prevent further oxidation of the aluminum foil. Because the oxide film is thin, porous, soft, and has good adsorption properties, high temperature and high humidity can destroy this oxide film. Speed up the oxidation reaction.

　　Currently, single-sided coating is used. When the first side is coated, the other side is completely exposed to the hot air. However, the dry hot air for coating (oil-based) should be around 130°C, such as the moisture content in the hot air. If it 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 falling off.

　　The selection of coating methods and control parameters have an important impact on the performance of lithium-ion batteries, mainly as follows:

　　1) Coating drying temperature control: If the drying temperature is too low during coating, the pole piece cannot be guaranteed to be completely dry. If the temperature is too high, the organic solvent inside the pole piece may evaporate too quickly, causing turtles to appear on the surface coating of the pole piece. cracking, falling off, etc.;

　　2) Coating surface density: If the coating surface density is too small, the battery capacity may not reach the nominal capacity. If the coating surface density is too high, it will easily cause a waste of ingredients. In severe cases, if there is excessive positive electrode capacity, due to lithium The precipitation forms lithium dendrites that pierce the battery separator and cause a short circuit, causing safety hazards;

　　3) Coating size: If the coating size is too small or too large, the positive electrode inside the battery may not be completely covered by the negative electrode. During the charging process, lithium ions are embedded from the positive electrode and move to the electrolyte that is not completely covered by the negative electrode. Medium, the actual capacity of the positive electrode cannot be used efficiently. In severe cases, lithium dendrites will form inside the battery, which can easily pierce the separator and cause the internal circuit of the battery;

　　4) Coating thickness: Coating thickness that is too thin or too thick will have an impact on the subsequent pole piece rolling process and cannot guarantee the performance consistency of the battery pole pieces.

　　In addition, pole piece coating is of great significance to the safety of lithium batteries. Before coating, 5S work must be done to ensure that no particles, debris, dust, etc. are mixed into the pole pieces during the coating process. If debris is mixed in, it will cause a micro short circuit inside the battery, and in severe cases, the battery may catch fire and explode.

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