At present, in addition to the local standard DB44/T 1152-2013 "Polyethylene Separator for Lithium-ion Batteries " in CHINA, there are relevant regulations on the test methods, inspection rules, packaging, transportation and storage of polyethylene separators, and the regulations on lithium-ion battery separators The national standard "General Polyolefin Separator for Li-ion Batteries" is still being drafted.
The performance requirements of lithium-ion battery separators mainly include: ①electronic insulation ; ②appropriate pore size and porosity; ③good electrochemical stability, corrosion resistance to electrolyte; ④good thermal stability, low closed cell temperature and high fusing temperature; ⑤ good affinity with electrolyte, with a certain liquid absorption rate; ⑥ sufficient mechanical properties and small thickness; ⑦ good spatial stability and flatness.
Test Standards and Methods
Referring to the regulations of the United States Professional Battery Consortium (USABC) on the performance parameters of lithium-ion battery separators, the performance of battery separators can be divided into physical and chemical properties, mechanical properties, thermal properties, and electrochemical properties [33].
Physical and chemical properties
Physical and chemical properties include thickness, porosity, average pore size and distribution, air permeability, tortuosity, wettability, liquid absorption rate, and chemical stability.
As the most basic parameter of the battery separator, the thickness is inversely proportional to the permeability of lithium ions . Therefore, the thickness should be as small as possible when the mechanical properties meet the actual needs ; porosity refers to the volume to the total material. The percentage of volume is closely related to the gas permeability, liquid absorption rate and electrochemical resistance of the battery separator . The porosity can be obtained by liquid absorption method, calculation method and instrument measurement method; the pore size and distribution are generally observed by SEM electron microscope The measurement can also be measured by using an instrument combined with the Laplace equation; the wettability and liquid absorption rate are the ability of the separator to retain the electrolyte, so as to reduce the internal resistance of the battery and improve battery performance. The specific testing standards and methods are shown in Table 1.
mechanical properties
Mechanical properties mainly include puncture strength, mixed puncture strength and tensile strength. The separator material must not only withstand the puncture force of the electrode mixture during the battery operation, but also meet the physical impact, puncture, wear,
Compression and tension external forces play an important role . The specific test methods are shown in Table 2.
thermal properties
Thermal properties mainly include thermal closure temperature, fusing temperature and thermal shrinkage rate. The closed cell temperature is set by the special protection mechanism of the separator for the battery , that is, when the temperature exceeds the closed cell temperature, the micropores in the separator are closed , preventing the passage of lithium ions, and reducing the short circuit to a certain extent.
The melting temperature refers to the temperature at which the diaphragm ruptures and short-circuits . The higher the temperature, the smaller the risk of short-circuiting. The specific test methods are shown in Table 3.
Electrochemical properties
Electrochemical properties mainly include linear voltammetry scanning test (LSV), electrochemical impedance spectroscopy (EIS), cycle performance (CP), ionic conductivity and resistance (Mac-Mullin) values, specific test methods
