What are the advantages and disadvantages of the lithium battery separator manufacturing process?

What are the advantages and disadvantages of the lithium battery separator manufacturing process? Polyolefin is the basic material for lithium battery separators. Polyolefin has excellent mechanical properties, chemical stability and low cost. The main material of the diaphragm base includes polypropylene, polyethylene and additives. The matrix material in the diaphragm is directly related to the mechanical properties of the diaphragm and the degree of wetting of the electrolyte. Although in recent years there have been studies using polyvinylidene fluoride (PVDF), cellulose composite membranes and other materials to prepare lithium battery membranes, the current commercial battery membrane materials still mainly use polyethylene and polypropylene microporous membranes. Lithium battery separator manufacturing technology The engineering technology of lithium battery membrane perforation mainly includes wet process and dry process, and dry process includes uniaxial stretching process and biaxial stretching process. 1. Wet processing of lithium battery diaphragm The wet method is also called phase separation method or thermally induced phase separation method. The small molecules with high boiling points are added as porogens into polyolefins, and after heating, they are melted into a homogeneous system, and then phase separation is carried out at a lower temperature. After stretching, small molecules are extracted with organic solvents to obtain interpenetrating microporous membrane materials. Representative companies adopting this approach include Asahi Chemical, Dongjiao Gas, Entec, etc. At present, it is mainly used for single-layer PE diaphragms. Although the porosity and permeability can be controlled within a wide range, the wet process requires a large amount of organic solvents. On the one hand, it is necessary to consider the recycling of solvents, which increases the complexity and cost of the process, and on the other hand, it also pollutes the environment. 2. The dry biaxial drawing process is used for the processing of lithium battery diaphragm. The dry biaxial drawing process is a process with independent intellectual property rights developed by the Institute of Chemistry of the Chinese Academy of Sciences in the early 1990s. By adding polypropylene to form a nucleus, a crystalline modifier is used, and the density difference between different phases of polypropylene during the drawing process is used to change the crystalline form and form micropores. 3. The unidirectional dry drawing process used to process lithium battery separators uses a unidirectional dry drawing process to process high-oriented polypropylene or polyethylene film with low crystallinity by processing hard elastic fibers, and obtain polypropylene with high crystallinity through high-temperature annealing. Or polyethylene film. The film is stretched at low temperature to form micro-defects, and then pulled open at high temperature to form micro-pores. After decades of development, this process has been very mature in the United States and Japan. At present, Celgard company in the United States and UBE company in Japan use this process to process single-layer PP, PE and three-layer PP/PE/PP composite films. Due to foreign patent protection and intellectual property restrictions, the industrialization of my country's uniaxial stretching film production is progressing slowly. The membrane prepared by this method has a long and flat microporous structure. Since it is only stretched in one direction, the transverse strength is poor, while it is not stretched in the other direction, and there is almost no transverse heat shrinkage. From the perspective of the dry method and the wet method, the film prepared by the dry biaxial stretching method has more advantages in physical and mechanical properties, and can meet the requirements of high-current charging and discharging of high-power batteries. Therefore, the diaphragm processed by the dry biaxial stretching process is more suitable for electric vehicle power lithium-ion batteries. The composite membrane diaphragm has two layers (PP/PE) and three layers (PP/PE/PP). When the temperature of the three-layer film increases, the PE in the middle melts and shrinks at 130 degrees, resulting in heat sealing. But because the melting point of the outer PP is 160 degrees, the film can still maintain a certain degree of safety, so the three-layer film is also more suitable for power lithium-ion batteries. Celgard and UBE have technology and patent rights. 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: What kind of battery is important for my country's new energy vehicles?