What are the basic manufacturing processes for lithium battery separators?

The dry diaphragm process is the most commonly used method in the diaphragm preparation process. The process is to mix high molecular polymers, additives and other raw materials to form a uniform melt. During extrusion, the lamella structure is formed under tensile stress, and the lamella structure is heat treated. A hard and elastic polymer film is obtained, then stretched at a certain temperature to form slit-like micropores, and then heat-set to prepare a microporous film. The current dry process mainly includes two processes: dry uniaxial stretching and biaxial stretching. Dry single drawing Dry single drawing uses polyethylene (PE) or polypropylene (PP) polymers with good fluidity and low molecular weight, and uses the manufacturing principle of hard elastic fibers to first prepare high-orientation and low-crystallinity polymers. After the olefin cast sheet is stretched at low temperature to form micro-defects such as silver streaks, high-temperature annealing is used to pull the defects apart, thereby obtaining a microporous film with uniform pore size and uniaxial orientation. The dry single drawing process is as follows: 1. Feeding: raw materials such as PE or PP and additives are pretreated according to the formula and then transported to the extrusion system. 2. Casting: The pretreated raw material is melted and plasticized in the extrusion system, and then the melt is extruded from the die, and the melt is cast to form a base film with a specific crystalline structure. 3. Heat treatment: the base film is heat treated to obtain a hard elastic film. 4. Stretching: Cold stretch and hot stretch the hard elastic film to form a nanoporous film. 5. Slitting: Cut the nano-microporous membrane into finished membranes according to customer specifications. It is known that the dry double drawing process is a process with independent intellectual property rights developed by the Institute of Chemistry, Chinese Academy of Sciences, and is also a unique diaphragm manufacturing process in my country. Because the β crystal form of PP is a hexagonal crystal system, single crystal nucleation and loose wafer arrangement. It has a lamellar structure that grows in a divergent beam shape along the radial direction and does not have a complete spherulite structure. Under heat and stress applications It will be transformed into a denser and more stable α crystal, and holes will appear in the material after absorbing a large amount of impact energy. In this process, a β crystal modifier with nucleation purpose is added to PP, and the difference in density between different phases of PP is used to transform the crystal form to form micropores during the stretching process. The dry double drawing process is as follows: 1. Feeding: The raw materials such as PP and pore former are pretreated according to the formula and then transported to the extrusion system. 2. Casting: A PP cast sheet with high β crystal content and good β crystal morphology uniformity is obtained. 3. Longitudinal stretching: Longitudinal stretching is performed on the cast sheet at a certain temperature, and the β crystal is easy to form pores under tensile stress to cause pores. 4. Transverse stretch: the sample is stretched transversely at a higher temperature to expand the pores and at the same time improve the uniformity of the pore size distribution. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: 18650 lithium battery charging process and charging principle analysis