aaa alkaline battery.Comparison of dry and wet production processes for lithium iron battery separators

　　Comparison of dry and wet production processes for lithium iron battery separators. The many characteristics that lithium iron battery separators need to possess put forward special requirements for their production process. The production process of lithium iron battery separators is divided into two categories: dry production process and wet production process. The dry production process is further subdivided into uniaxial stretching process and biaxial stretching process. Which process is more advantageous? Please see below.

　　Comparison of dry and wet production processes for lithium iron battery separators

　　The production process of lithium iron battery separators includes: raw material formula, independent design of complete sets of equipment, microporous preparation technology, etc. Among them, the core of the lithium battery separator preparation process is micropore preparation technology. According to the difference in micropore formation mechanism, the separator production process can be divided into two types: dry method and wet method.

　　1. Dry production process of lithium iron battery separator

　　The dry method of lithium iron battery separator can be subdivided into uniaxial stretching process and biaxial 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 is a process with independent intellectual property rights developed by the Institute of Chemistry, Chinese Academy of Sciences in the early 1990s. 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.

　　2. Wet production process

　　Also known as phase separation method or thermally induced phase separation method, the 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 lowered for phase separation, and the film is obtained by pressing. The membrane is heated to a temperature close to the melting point, stretched in two directions 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 an interconnected microporous membrane material.

　　The wet production process can not only produce interconnected microporous membrane materials, but also produce 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.

　　From a theoretical analysis, the separator produced by the dry biaxial stretching process has been biaxially stretched. While the longitudinal tensile strength is not much different, the transverse tensile strength is significantly higher than that of the separator produced by the dry uniaxial stretching process. In terms of physical and mechanical properties, the separator produced by the dry uniaxial stretching process has more advantages. However, the lithium iron battery separator produced by the wet production process has 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 iron battery separator produced by the dry production process, the lithium battery separator produced by the wet production process is Thermal stability is poor.

　　The difference between wet production process and dry production process of lithium battery separator

　　The advantages of the dry uniaxial stretching process are that the process is relatively simple, the added value is high, and there is no environmental pollution. However, low-temperature stretching can easily cause perforation of the separator, and the product cannot be made very thin.

　　The wet process produces small and uniform micropores but is not environmentally friendly. The wet process molding process is easy to control, and the produced separator has high biaxial tensile strength and high puncture strength. Normal process flow will not cause perforation, and the micropore size is relatively small and evenly distributed. This product can be made very thin, has better mechanical properties and product uniformity, and is suitable for high-capacity batteries. It is mainly used in high-end mobile phones, notebook computers, 3C electronic products and other fields.

　　The high porosity and air permeability of this kind of separator enable the battery to have higher energy density and better charge and discharge performance, which can meet the high current charge and discharge of power batteries. In the power battery market, it is mainly used by well-known domestic lithium battery manufacturers. However, the wet process requires a large amount of solvent and can easily cause environmental pollution; compared with the dry process, the equipment is complex, the investment is large, the cycle is long, the cost is high, and the energy consumption is large.

　　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%. 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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