18650 lithium ion battery cell

Preparation process of 18650 lithium ion battery cell diaphragm

People who are familiar with the structural principle of 18650 lithium ion battery cell know that the diaphragm in lithium battery plays a vital role in the performance of lithium battery, but there are many and very complicated production processes for lithium battery diaphragm. Which process is more mature, dry process or wet process? Let's talk about it in detail. Preparation process of 18650 lithium ion battery cell diaphragm: dry process and wet process The production process of 18650 lithium ion battery cell diaphragm is divided into two categories: dry production process and wet production process. The dry production process is further divided into unidirectional stretching process and bidirectional stretching process. The many characteristics that lithium-ion battery diaphragm needs to have put forward special requirements for its production process, and the production process includes raw material formula and rapid formula adjustment, micropore preparation technology, and complete set of equipment independent design. Dry process of 18650 lithium ion battery cell diaphragm dry process can be divided into unidirectional stretching process and bidirectional stretching process. The dry unidirectional stretching process is to prepare a low-crystallinity, high-oriented polypropylene or polyethylene film by producing hard elastic fibers, and obtain a high-crystallinity film during high-temperature annealing. This film is first stretched at low temperature to form micro defects, and then the defects are pulled apart at high temperature to form micropores. The dry biaxial stretching process, by adding a β-crystal modifier with a nucleating effect to polypropylene, utilizes the density difference between different phases of polypropylene, and transforms polypropylene from a crystal form to form micropores during the stretching process. At present, more than one-third of China's production capacity uses the dry biaxial stretching process, and the products occupy a large proportion in the low-end and mid-end markets. Application scope: Large lithium-ion power batteries (electric vehicles, electric motorcycles, electric tools, large energy storage equipment, special large batteries) iron lithium battery separator wet production process wet production process, also known as phase separation method or thermal phase separation method, wet process liquid hydrocarbons or some small molecular substances are mixed with polyolefin resin, heated and melted to form a uniform mixture, and then cooled to separate the phases, pressed to obtain a membrane, and then heated the membrane to a temperature close to the melting point, biaxially stretched to orient the molecular chains, and finally kept warm for a certain period of time, and the residual solvent was eluted with volatile substances to prepare a microporous membrane material that is interconnected. The wet production process can not only prepare microporous membrane materials that are interconnected, but also produce power iron lithium battery separators with high longitudinal and transverse strength. At present, the wet production process is mainly used to produce single-layer lithium battery separators. Application range: high-performance lithium-ion batteries, etc. In terms of physical properties and mechanical properties, the separator produced by the dry unidirectional stretching process has more advantages. However, the lithium battery separator produced by the wet production process has a higher porosity and good air permeability, which can meet the requirements of high current charging and discharging of power batteries. On the contrary, since the wet production process uses a polyethylene substrate, the melting point of the polyethylene substrate is only 140°C, so compared with the lithium battery separator produced by the dry production process, the lithium battery separator produced by the wet production process has poor thermal stability. Can the wet process of lithium battery separator replace the dry process? As one of the four core components of lithium batteries, the separator accounts for 10%-14% of the cost of lithium batteries, and the gross profit margin is as high as 50%-60%. The performance of the separator greatly affects the interface structure and internal resistance of the lithium battery, which in turn affects the key characteristics of the battery such as capacity, charge and discharge current density, and cycle performance. At present, the separator production process can be divided into dry and wet processes according to the difference in micropore formation mechanism, and the two have different characteristics. The dry stretching process is simple, environmentally friendly, and has high productivity, but the capacity retention and safety reliability are low. The wet process produces small and uniform micropores, with better mechanical properties and product uniformity, which is suitable for high-capacity batteries, but not environmentally friendly. The output of wet process diaphragms has increased rapidly, and industry experts believe that the dry process will coexist with the wet process for a long time. From the perspective of process technology progress, at present, my country's lithium-ion battery diaphragms have made major breakthroughs in the dry process, with world-class manufacturing level, and the wet diaphragm process technology has been continuously improved. In recent years, the production capacity and output have both grown steadily. With the continuous development of wet process technology, the competitive landscape of my country's lithium battery diaphragm industry has also undergone some changes. From the current market application and the choice of global lithium battery companies, dry diaphragms and wet diaphragms coexist. Iron-lithium battery diaphragm technology is now mature, and both dry and wet battery diaphragms can well meet the needs of products in different fields.

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