The production process of Fe-Li-ion battery separator includes: raw material formulation, independent design of complete sets of equipment, micropore preparation technology, etc. Among them, the core of the lithium-ion battery separator preparation process is the micropore preparation technology. According to the difference in the pore-forming mechanism of the micropores, the separator production process can be divided into two types: dry method and wet method.
1. Dry production process of Fe-Li-ion battery separator
The dry process of Fe-Li-ion 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 high-oriented polypropylene or polyethylene films with low crystallinity, and high crystallinity films are obtained during high temperature annealing. The film is first stretched at low temperature to form micro-defects, and then at high temperature, the defects are pulled apart to form micro-pores.
The dry biaxial stretching process is a process with independent intellectual property rights developed by the Institute of Chemistry of the Chinese Academy of Sciences in the early 1990s. In the dry biaxial stretching process, by adding a beta crystal modifier with nucleation to polypropylene, the difference in density between different phases of polypropylene is used to transform polypropylene from crystal form during the stretching process. Microporous.
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, and after heating and melting, a uniform mixture is formed, and then the temperature is lowered for phase separation, and the film is pressed. The membrane is heated to a temperature close to the melting point, biaxially stretched to orient the molecular chain, and finally kept for a period of time, and the residual solvent is eluted with volatile substances to prepare the interconnected microporous membrane material.
The wet production process can not only prepare interconnected microporous membrane materials, but also produce iron-lithium-ion battery separators with high vertical and horizontal strengths. At present, wet production processes are mainly used to produce single-layer lithium-ion battery separators.
Theoretically, the transverse tensile strength of the diaphragm produced by the dry biaxial stretching process is significantly higher than that of the diaphragm produced by the dry uniaxial stretching process under the condition that the longitudinal tensile strength is not much different. In terms of physical properties and mechanical properties, the separator produced by the dry uniaxial stretching process has more advantages. However, the Fe-Li-ion battery separator produced by the wet production process has high porosity and good air permeability, which can meet the requirements of high-current charging and discharging of power lithium batteries.
On the contrary, since the wet production process uses polyethylene base material, the melting point of the polyethylene base material is only 140 ° C, so, compared with the iron lithium ion battery separator produced by the dry production process, the lithium ion produced by the wet production process The thermal stability of the battery separator is poor.
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, when stretching at low temperature, it is easy to cause perforation of the diaphragm, and the product cannot be made very thin.
The micropore size obtained by the wet process is small and uniform but not environmentally friendly. The wet process molding process is easy to control, and the obtained diaphragm has high bidirectional tensile strength and high puncture strength. The normal process will not cause perforation, and the size of the micropores is relatively small and evenly distributed. The product can be made very thin, with better mechanical properties and product uniformity, suitable for high-capacity batteries, and 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 make the battery have higher energy density and better charging and discharging performance, which can meet the high current charging and discharging of power lithium battery. use. However, the wet process requires a large amount of solvent, which is easy to 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.