The previous article mainly introduces the related preparation method of lithium ion battery electrolyte. As the other major material of lithium ion battery, the diaphragm is responsible for preventing the short circuit of the battery from being insulated from the positive and negative electrodes, and forming ions by lithium ions. The role of the pathway. This article starts with the preparation method of lithium ion battery separator, and takes everyone to understand the production process of lithium ion battery separator.
1, dry method:
The dry process means that the high molecular polymer and the additive are uniformly mixed, melt extruded, and a crystal structure is formed under tensile stress, and a film is obtained after heat treatment, and then the slit-like micropores are pulled down at a certain temperature to heat-set After the formation of a dry diaphragm, the current main processes include dry single pull and dry double pull.
Dry single pull:
Production process description:
Firstly, the raw materials such as polymers and additives are pretreated and sent to an extrusion system, and then the pretreated raw materials are melt-plasticized in an extrusion system, and then the melt is extruded from a die, and cast to form a specific crystal. The base film of the structure; the base film is heat-treated to obtain a hard elastic film, and then subjected to cold stretching and hot stretching to form a nano microporous film, and finally cut into a finished film according to the customer's demand, the whole process is relatively simple, and the cost is relatively simple. Also lower.
Dry double pull:
Since the β crystal form of PP is a hexagonal crystal system, single crystal nucleation and loose wafer arrangement have a platelet crystal structure which grows into a divergent beam shape in the radial direction without a complete spherulitic structure under heat and stress. It will transform into a denser and more stable alpha crystal, which will create holes inside the material after absorbing a large amount of impact energy. The process involves the addition of a β-crystal modifier with nucleation in PP, utilizing the difference in density between different phases of PP, and undergoing crystal transformation during the stretching process to form micropores. The process flow and dry single pull Similar to the same, the intermediate stretching process is divided into transverse stretching and longitudinal stretching, and the performance is better than that of the uniaxially stretched diaphragm.
2, wet method:
Using the principle of thermally induced phase separation, the plasticizer is mixed with the polyolefin resin, and the solid-liquid phase or liquid-liquid phase separation occurs during the cooling process of the molten mixture, and the film is pressed and heated to a temperature close to the melting point and then stretched. The molecular chains are aligned uniformly, and after a certain period of time, the plasticizer is extracted from the film by a volatile solvent, thereby obtaining interpenetrating submicron-sized microporous membrane materials. The wet process is suitable for the production of a thin single-layer PE separator, which is a preparation process in which the thickness of the separator product is better and the mechanical properties are better. According to whether the orientation is at the same time during stretching, the wet process can also be divided into two methods: a wet two-way asynchronous stretching process and a two-way synchronous stretching process.
The wet asynchronous drawing process is: feeding, casting, longitudinal stretching, transverse stretching, extraction, shaping, and slitting.
The wet synchronous stretching technology process is basically the same as the asynchronous stretching technology, except that the stretching can be simultaneously oriented in both the horizontal and vertical directions, eliminating the need for longitudinal stretching alone, and enhancing the thickness uniformity of the separator.
The membranes prepared by the dry and wet methods have different characteristics. The method and means for detecting the diaphragm have been explained in detail in the previous article. It is not detailed here, only the basic performance is compared.
3, ceramic diaphragm:
With the increase of the energy density of lithium-ion batteries, the requirements for separators are getting higher and higher. Ceramic diaphragms have emerged. A series of methods are used to laminate a layer of ceramics on the surface of the base film to improve the mechanical properties and heat of the separator. Shrinkage performance.
The types of ceramics are alumina and boehmite. The coating method is mainly gravure coating. In addition, spraying, immersing, slit coating and other techniques are applied. The thickness of the coating is also thinner and thinner, depending on the type of battery. A variety of ceramic diaphragms. It should be noted that although the final ceramic diaphragm seems to be a very simple product, the choice of ceramics, the choice of binder, the processing of ceramic paste, the consistency of coating, etc. are all processes that need to be accumulated. It also has a certain technical content, and it is not easy to do well.
4, non-woven membrane:
Generally, it is made by electrospinning. The principle is to electrostatically atomize the polymer fluid. The atomized and split material is not a tiny droplet, but a polymer microjet, which can run a long distance and finally solidify into fiber.
However, its high cost and current instability of electrical properties have limited the application of non-woven membranes, which needs further development and research.
summary:
This paper mainly introduces the industrial production method of lithium ion battery separator. With the increase of the energy density of the power battery, the diaphragm is also thinner and thinner, and the performance requirements are also higher and higher, which is forced by the diaphragm company. Technological innovation can not be eliminated by the new energy industry. I believe that with the development of science and technology, more and more new diaphragms will enter people's field of vision.
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