With the promotion of new energy vehicles, the demand for power lithium batteries in the market has begun to expand. As the core material of lithium-ion batteries, the performance of the separator directly affects the capacity, cycling performance, and safety performance of the battery. In industrial production, the main performance requirements for lithium-ion battery separators are as follows:

　　1. Thickness uniformity

　　The thickness uniformity of the separator in lithium-ion batteries directly affects the appearance quality and internal performance of the separator roll. The thickness uniformity of the separator includes longitudinal thickness uniformity and transverse thickness uniformity. The uniformity of lateral thickness is particularly important. Generally, it is required to control within ± 1 micrometer.

　　2. Mechanical properties

　　Tensile strength generally refers to the longitudinal strength reaching over 100mP, and the transverse strength should not be too large, as excessive strength can lead to an increase in the transverse shrinkage rate. The puncture resistance strength is due to the fact that the diaphragm is sandwiched between uneven positive and negative electrodes, which requires a lot of pressure to withstand. To prevent short circuits, the diaphragm must have a certain puncture resistance. In experience, the puncture resistance strength value is between 300-500 grams.

　　3. Penetration performance

　　The size of the permeability of the diaphragm is the result of a combination of factors affecting the internal pore structure of the diaphragm, such as porosity, pore size, pore shape, and pore tortuosity. The lithium battery separator itself has a microporous structure, and the distribution of micropores in the entire separator material should be uniform. The aperture is generally 0.03 μ M~0.12 μ m. If the aperture is too small, it will increase the resistance, while if it is too large, it can easily cause contact between the positive and negative poles or be short circuited by dendrites.

　　4. Physical and chemical properties

　　Good wettability and wetting speed are beneficial for improving the charging and discharging performance and capacity of batteries. Chemical stability: The membrane should maintain long-term stability in the electrolyte and not react with the electrolyte and electrode materials. Thermal stability: When the temperature rises, the diaphragm should maintain its original integrity and certain mechanical properties. The safety protection performance of lithium-ion batteries has become the most important aspect for lithium-ion battery manufacturers.

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