Lithium battery separator manufacturing process -Lithium - Ion Battery Equipment

Lithium battery separator manufacturing process -Lithium - Ion Battery Equipment

Polyolefins are the basic materials for lithium-ion battery separators. Polyolefins have excellent mechanical properties, chemical stability and low cost. Diaphragm matrix materials mainly include polypropylene, polyethylene materials 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 polyvinylidene fluoride (PVDF), cellulose composite membrane and other materials have been used to prepare lithium ion battery membranes in recent years, polyethylene and polypropylene microporous membranes are still mainly used in commercial battery membrane materials.(Lithium - Ion Battery Equipment)

Lithium-ion battery separator manufacturing technology

The engineering technology of lithium ion battery film perforation mainly includes wet process and dry process, and dry process includes uniaxial stretching process and biaxial stretching process.

1. Wet production of lithium-ion battery separators

The wet method is also called the phase separation method or the thermally induced phase separation method. Add high-boiling small molecules as pore-conducting agents to polyolefins, and after heating, they are fused into a homogeneous system, and then phase-separated at a lower temperature. After stretching, the small molecules are extracted with an organic solvent, and the interpenetrating microporous membrane material can be obtained.

Representative companies using this method include Asahi Chemical, Dongjiao Gas, and Entec. It is currently mainly used for single-layer PE separators.

Although the porosity and permeability can be controlled within a wide range, the wet process requires a large amount of organic solvent. On the one hand, the recycling of the solvent must be considered, which increases the complexity and cost of the process, and on the other hand pollutes the environment.

2. Dry biaxial stretching process for the production of lithium-ion battery separators

The dry biaxial drawing process is a process with independent intellectual property rights developed by the Institute of Chemistry, Chinese Academy of Sciences in the early 1990s. Nucleation by adding polypropylene

The crystal type modifier is used to change the crystal type and form micropores by using the density difference between different phases of polypropylene in the drawing process.

3. Unidirectional dry drawing process for the production of lithium-ion battery separators

The unidirectional dry drawing process is adopted to produce high-oriented polypropylene or polyethylene films with low crystallinity by producing hard elastic fibers, and high-crystallinity polypropylene or polyethylene films are obtained by high temperature annealing. The film is stretched at low temperature to form micro-defects and then opened at high temperature to form micro-pores.

After decades of development, this process is very mature in the United States and Japan. At present, Celgard Company of the United States and UBE Company of Japan use this process to produce single-layer PP, PE and three-layer PP/PE/PP composite films. Due to the limitations of foreign patent protection and intellectual property rights, the industrialization of uniaxial stretching film production in my country has been slow.

The separator prepared by this method has a long and flat microporous structure. Since it is only stretched in one direction, the transverse strength is poor, but it is not stretched in the other direction and has almost no transverse thermal shrinkage.

From 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 separator produced by the dry biaxial stretching process is more suitable for electric vehicle power lithium batteries.

composite membrane

The separators are available in 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. However, 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 batteries. Celgard and UBE own technology and patent rights.



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