According to different physical and chemical characteristics, lithium battery diaphragm materials can be divided into woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, diaphragm paper, rolled membrane, etc.

　　At present, the market oriented membrane materials are mainly polyolefin membranes, mainly composed of polyethylene (PE) and polypropylene (PP). PE products are mainly made by wet process and PP products are mainly made by dry process. The following are the characteristics of PE and PP, generally speaking:

　　(1) PP is relatively more resistant to high temperature, while PE is relatively resistant to low temperature;

　　(2) PP density is smaller than PE;

　　(3) PP has higher melting point and closed cell temperature than PE;

　　(4) PP products are more brittle than PE products;

　　(5) PE is more sensitive to environmental stress.

　　The main diaphragm materials include single-layer PP, single-layer PE, PP+ceramic coating, PE+ceramic coating, double-layer PP/PE, double-layer PP/PP and three-layer PP/PE/PP, among which the first two types of products are mainly used in the field of 3C small batteries, and the latter are mainly used in the field of power lithium batteries.

　　Among the diaphragm materials used for power lithium batteries, double-layer PP/PP diaphragm materials are mainly produced by Chinese enterprises and used in Chinese Mainland, mainly because there is no technology and ability of Chinese enterprises to make double-layer composite films from PP and PE. However, the membranes used in the global automotive power lithium batteries are mainly composed of three layers of PP/PE/PP, double layers of PP/PE, PP+ceramic coating, PE+ceramic coating and other membrane materials.

　　In the structure of lithium battery, the diaphragm is one of the key inner components. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety of the battery. The separator with excellent performance plays an important role in improving the overall performance of the battery.

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