3.2v 25ah lifepo4 battery cell.　Revealing the secret of international giant Celgard's “pressure box bottom” diaphragm technology

　　Due to the characteristics of the materials themselves, wet separators and dry separators have their own advantages and disadvantages:

　　Wet separators are light, thin and not easy to tear, but the melting point of PE is 135°C and are less safe than dry separators. In addition, the raw materials and production processes are different, and the overall cost is higher than that of dry separators; dry separators have a high melting point, heat resistance, It has better high pressure resistance and oxidation resistance, but is thicker than the wet separator and is easy to tear longitudinally, which requires higher process requirements for battery companies.

　　With the rapid expansion of ternary power batteries, especially high-nickel power batteries, there is an urgent need for separators that combine the advantages of high safety, strong functionality, and low cost, and have become the direction for domestic separator companies to work together. The "three-layer composite membrane" developed by the international separator giant Celgard may be able to give some inspiration to domestic counterparts.

　　The middle layer of Celgard's "three-layer composite film" is polyethylene, with a melting point of around 132°C. When the battery gets out of control and heats up, the polyethylene will melt, closing the pores and cutting off the circuit, which can form a safety protection for the battery; the outer two layers are polypropylene , has antioxidant properties and a melting point above 165°C. Even if the battery temperature rises slightly, the physical shape of the membrane will not be affected, providing a second layer of safety protection for the battery.

　　In addition to high safety, Celgard President Shi Lie publicly stated that the dry process of the company's "three-layer composite membrane" product is more green and environmentally friendly than the wet separator.

　　The wet process requires chemical solvents and solutions. Although manufacturers strive to recycle them, some will eventually evaporate into the air, which is harmful to people and the environment.

　　Faced with the view of some people in China that wet separators have broader application prospects in the field of power batteries, Shi Lie disagrees. In his view, at the beginning of the rise of new energy vehicles, dry-process separators dominated the market because wet-process products have poor oxygen resistance and large lateral shrinkage; they melt when the temperature reaches 130°C, which has great limitations; in terms of strength, , the wet-laid separator has dropped by more than 50% after being used for a period of time, while the three-layer composite membrane has almost no change, and its life span is longer than that of the wet-laid polyethylene separator.

　　Objectively speaking, after the wet separator is coated, it will effectively avoid the "defects" in the inherent characteristics of the material, but this will increase the cost.

　　At present, most domestic ternary power battery systems use "wet method + coating". Due to cost considerations, dry process separators with gradually improved performance are widely used in lithium iron phosphate systems and have also begun to be used in ternary systems, and even some ternary systems. The leading companies in the Yuan system also use dry separators.

　　At present, the proportion of high-nickel power batteries in the world is not high. Whether "wet method + coating" can simultaneously meet the requirements for high safety, strong functionality, and low cost separators remains to be further verified.

　　Shi Lie said that the three-layer composite film is the only separator that can be used in high-energy batteries without coating, and directly using the base film will be more competitive than the polyethylene ceramic separator.

　　"Different customers or different battery designs sometimes require us to apply another layer of ceramic, which will make the price more expensive." Shi Lie added that Celgard has many successful cases in Japan, South Korea and some Chinese battery manufacturers. Over the past many years, the market's feedback on CELGARD's "three-layer composite film" has been very good. Especially in electric vehicles and energy storage batteries, there has never been a safety accident, and its reliability is very guaranteed. We welcome more battery manufacturers to join us for more attempts and cooperation.

　　Gaogong Lithium Battery learned that Celgard is the "originator" of the global dry separator process. It has a history of thirty or forty years in the separator industry and is now a subsidiary of Asahi Kasei. Most dry-process separator companies in China have followed Celgard's dry-process process, but what Chinese manufacturers have not yet been able to copy is the "three-layer composite membrane" developed and introduced by Celgard.

　　“We started researching three-layer membranes a few years ago, but we did not have matching production equipment at that time, and one of the raw materials needed to be imported from abroad.” A senior executive of a domestic dry-process separator company said that most domestically produced double-layer membranes. Because 'it's not thin'.

　　However, with the continuous improvement of raw materials, production equipment and process technology, some domestic dry process separator companies are trying to develop and launch three-layer composite membranes. Please pay attention to the follow-up reports of Gaogong Lithium Battery.

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