Preparation process of power lithium iron battery separator: dry method and wet method. Anyone who is familiar with the structural principles of power iron lithium batteries knows that the separator in the lithium battery plays a vital role in the performance. However, there are many and very complex production processes for lithium battery separators, including dry and wet manufacturing. , which process is more mature? The editor of this article will talk about it in detail.

　　Preparation process of power lithium iron battery separator: dry method and wet method

　　The production process of power lithium iron battery separators is divided into two categories: dry production process and wet production process. The dry production process is further subdivided into one-way stretching process and two-way stretching process. The many characteristics that lithium-ion battery separators need to possess put forward special requirements for its production process, which includes raw material formula and rapid formula adjustment, micropore preparation technology, and independent design of complete sets of equipment.

　　Lithium iron battery separator dry process

　　The dry method can be subdivided into one-way stretching process and two-way stretching process. The dry uniaxial stretching process is a method of producing hard elastic fibers to prepare highly oriented polypropylene or polyethylene films with low crystallinity. During the high-temperature annealing process, a film with high crystallinity is obtained. This film is first stretched at low temperatures to form micro-defects, and then at high temperatures the defects are pulled apart to form micropores.

　　The dry biaxial stretching process adds a beta crystal modifier with a nucleating effect to polypropylene and utilizes the density difference between different phases of polypropylene to transform the polypropylene from its crystal form into micro-forms during the stretching process. hole. At present, more than one-third of China's production capacity uses the dry double drawing process, and its products occupy a large proportion of the mid- to low-end market. Application scope: large lithium-ion power batteries (electric vehicles, electric motorcycles, power tools, large energy storage equipment, special large batteries)

　　Wet production process of lithium iron battery separator

　　Wet production process, also known as phase separation method or thermal phase separation method, wet process mixes liquid hydrocarbons or some small molecular substances with polyolefin resin. After heating and melting, a uniform mixture is formed, and then the temperature is cooled for phase separation and pressing. The membrane is obtained, and then the membrane is heated 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. The residual solvent is eluted with volatile substances to prepare interconnected microporous membrane materials.

　　The wet production process can not only prepare interconnected microporous membrane materials, but also produce power lithium iron 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 scope: high-performance lithium-ion batteries, etc.

　　In terms of physical and mechanical properties, the separator produced by the dry uniaxial stretching process has more advantages. However, lithium battery separators produced by wet production processes have high porosity and good air permeability, which can meet the high current charging and discharging requirements of power batteries. On the contrary, since the wet production process uses polyethylene material, the melting point of the polyethylene material is only 140°C. Therefore, compared with the lithium battery separator produced by the dry production process, the lithium battery separator produced by the wet production process is Thermal stability is poor.

　　Can the wet process of lithium battery separators replace the dry process?

　　As one of the four core components of lithium batteries, separators account for 10%-14% of the cost of lithium batteries, with gross profit margins as high as 50%-60%. The performance of the separator greatly affects the interface structure and internal resistance of lithium batteries, which in turn affects key characteristics such as battery capacity, charge and discharge current density, and cycle performance.

　　At present, the separator production process can be divided into dry method and wet method according to the difference in micropore formation mechanism, and the two have different characteristics. The dry stretching process is simple, environmentally friendly, and highly productive but has low capacity retention, safety and reliability. The wet process produces small and uniform micropores with better mechanical properties and product uniformity. It is suitable for high-capacity batteries, but it is not environmentally friendly. The output of wet process separators is growing rapidly, and industry experts believe that dry processes will coexist with wet processes for a long time.

　　Judging from the progress of process technology, currently, my country's lithium-ion battery separators have made major breakthroughs in the dry process and have achieved world-class manufacturing levels. The wet separator process technology has also been continuously improved, and production capacity and output have increased steadily in recent years. With the continuous development of wet process technology, the competitive landscape of my country's lithium battery separator industry has also undergone some changes.

　　Judging from the current market applications and the choices of global lithium battery companies, dry separators and wet separators coexist. Lithium-iron battery separator technology is now mature, and battery separators manufactured by either dry or wet methods can well meet the needs of products in different fields.

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