At present, the production process of lithium-ion battery separator can be divided into two categories: dry method and wet method. Dry method can be subdivided into uniaxial stretching process and biaxial stretching process.
The production process and characteristics of lithium-ion battery separator The dry uniaxial stretching process first uses the method of producing hard elastic fibers to prepare low-crystallinity, high-oriented PP or PE films, and then anneals to obtain high-crystallinity oriented films. This film is first stretched at low temperature to form micro-defects such as silver streaks, and then the defects are pulled apart at high temperature to form micropores. Very representative companies using this method include Celgard Corporation of the United States and UBE Corporation of Japan, whose main products are PE and PP films. Founded in 1981, Celgard holds a patent for the dry uniaxial stretching manufacturing process.
Wet method is also called phase separation method or thermal phase separation method. Add small molecules with high boiling point as porogens to polyolefin, heat and melt to form a homogeneous system, then cool down to cause phase separation, and extract small molecules with organic solvents to prepare interpenetrating microporous membrane materials . From a theoretical analysis, the separator produced by the dry biaxial stretching process is biaxially stretched, and the transverse tensile strength is significantly higher than the separator 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 biaxial stretching process has more advantages. However, the wet-process separator can obtain higher porosity and better air permeability, which can meet the requirements of high-current charging and discharging of power batteries. However, because the wet method uses PE material , the melting point is only 140°C, so the thermal stability is poor. Representative companies using this method include Japan's Asahi (Asahi Kasei), Toray Tonen (Tonen Chemical), and American Entek.
