Lithium battery separator coating technical methods and methods. In recent years, as the power lithium battery market has heated up, wet-coated separators have become more and more popular in China. Even some people in the industry believe that wet-coated separators will dominate the future power battery separator market. "Wet method + coating" for lithium batteries has been a recognized development direction of separators in the industry. Today, the editor has compiled relevant content about coating slurry formulas and coating processes. Everyone is welcome to read and leave comments for additional information.

　　Lithium battery separator coating technology

　　Depending on the downstream requirements for specific performance and the positioning of lithium battery separator products, different coating technologies need to be used. As for coating, the core of the technology lies in the formulation of the slurry. At the same time, the slurry accounts for a large proportion of the cost in separator coating. Generally, the slurry accounts for 65% of the total coating cost. The development direction of power lithium batteries is high output, high capacity, and fast charging. The requirements for separator coating technology and processes will become more diversified. The continuous innovation of formulas will also become the core competitiveness of coating.

　　Separator ceramic coating slurry mainly includes four main components: ceramic particles, binders, solvents and additives. Different slurry ratios need to be used for different application scenarios. The rigid supporting effect of ceramics makes the ceramic modified diaphragm have excellent thermal stability and dimensional integrity at high temperatures, and supports the maintenance of the diaphragm structure at high temperatures. At high temperatures, the diaphragm base is closed-pored and transparent, and the diaphragm is not coated. The shrinkage is serious, and the coated lithium battery separator has greatly improved shrinkage resistance due to the existence of the ceramic layer, and has better mechanical properties and safety.

　　Lithium battery separator coating method, flexible and diverse

　　Separator coating is not technically difficult. Gravure roller coating, dip coating, narrow coating or spray coating can be used. Mainstream domestic base film manufacturers and a large number of OEMs can achieve it.

　　Gravure roller coating

　　The gravure roller coating process is currently a commonly used coating method. The micro-gravure roller brings the slurry out of the slurry box, and the excess paint is scraped off by a fixed-thickness scraper, and then applied to the diaphragm under pressure. The principle of this method is relatively simple, the groove capacity of the gravure roller is easy to control, and the product accuracy is better. The disadvantage is that due to the action of high-hardness alumina ceramic particles, the anilox roller is easy to wear, which will cause the coating to gradually become thinner during the continuous coating process, and a new roller needs to be replaced; when the coating target thickness changes, the roller needs to be replaced and cannot be adjusted flexibly. .

　　narrow gap extrusion coating

　　Narrow slit extrusion coating, referred to as narrow coating, is a process in which the slurry is extruded from the extrusion nozzle and applied to the diaphragm through a certain pressure. The thickness of the coating is controlled by the slit width of the extrusion nozzle and the metering pump. This process is suitable for a wide viscosity range, has good product accuracy, can coat thin layers, and has high coating speed, but the maintenance of the extrusion nozzle is relatively difficult.

　　dip coating

　　The basic principle of dip coating is to soak the lithium battery separator in a slurry of a certain concentration for a certain period of time, then take it out and dry it to obtain a coating of a certain thickness on the surface of the separator. The principle and operation of this method are simple, but thickness control is relatively difficult.

　　Electrospinning

　　The electrospinning method is a process in which slurry is sprayed onto the separator through electric field force, which charges the slurry. Under the action of the electric field force, the slurry breaks through the surface tension and forms nanofilaments that are sprayed towards the separator. This process has the advantages of a wide range of applicable materials, easy operation, large specific surface area, high porosity, good fiber uniformity, and high yield. However, it has the disadvantages of small crystallinity and orientation, poor mechanical properties, and poor mechanical properties. Optimized through modification methods such as heat treatment and blending.

　　Equipment for coating and processing of lithium battery separators currently basically needs to be imported. The supply is stable and the equipment is compact and complete. A production line requires an investment of 1.5-2 million yuan and an output of about 4 million square meters per year. For those who have both base film production and coating processing capabilities For enterprises, generally each base film production line needs to be equipped with 10 coating production lines. Most lithium battery separator coating manufacturers use the gravure roller coating method. The reason is that the processing speed and precision of gravure roller coating are high, and the process is mature. At the same time, the processing and maintenance of the roller are relatively simple and the cost is relatively low. Narrow coating is often chosen as the preferred solution because the process has high precision, fast processing speed, and great viscosity flexibility. However, the narrow coating extrusion nozzle is relatively difficult to process and maintain, and the cost is relatively high.

　　Comparison of wet coating and dry double pull coating

　　1. Basement membrane

　　Dry: If the wet PE base film is used directly into the battery, it cannot be used or is difficult to use because the thermal temperature of the base film is too low. In order to improve thermal stability, the surface of the base film must be coated to make up for the 50% defects. But will there be improvement through different coating techniques? Being born disabled and physically weak, it doesn't matter how much armor you wear outside.

　　Wet: In the field of power lithium batteries, many manufacturers are switching to wet coating, and wet single layers are also used. The pore sizes of wet separators are uniform, but the dry separators are incomparable. The pore sizes of dry base membranes are uneven, so what’s the use of coating?

　　2. Breathability

　　Dry: As long as the pore size of the dry double pull-based membrane is uniform enough, the battery will have no problem charging and discharging, there will be no short circuit, and the overall safety is good, so it does not need to be as uniform as the wet membrane. Although the pore size of the wet-laid membrane is more uniform, the pore size itself is too small. Coupled with the coating, how to ensure high air permeability.

　　Wet: Wet lithium battery separators can have high or low air permeability according to battery requirements.

　　3. Melting point

　　The materials of dry process lithium battery separators and wet process separators are quite different, with a melting point difference of more than 40 degrees. At 120 degrees, 70%-80% of the wet separators will close up; at 150 degrees, the dry separators can still maintain a relatively good condition.

　　The lower melting point is the biggest difference between the two separators, which is determined by the characteristics of the material itself, but as long as it meets the requirements for lithium battery use, it is sufficient.

　　High-performance lithium batteries require separators with uniform thickness and excellent mechanical properties, breathability, and physical and chemical properties. The excellence of the separator directly affects the capacity, cycle capacity, safety performance and other characteristics of lithium batteries. Excellent separators play an important role in improving the overall performance of the battery.

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