Currently, the commercially available membrane materials are mainly polyolefin membranes, primarily made of polyethylene (PE) and polypropylene (PP). PE products are mainly produced using wet processes, while PP products are mainly produced using dry processes. Below are the characteristics of these two materials, in general:
(1) PP is relatively more resistant to high temperatures, while PE is relatively more resistant to low temperatures;
(2) PP has a lower density than PE;
(3) PP has a 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 membrane materials include single-layer PP, single-layer PE, PP+ceramic coating, PE+ceramic coating, double-layer PP/PE, double-layer PP/PP and triple-layer PP/PE/PP, etc. The first two types of products are mainly used in the field of 3C small batteries, while the latter types are mainly used in the field of power lithium batteries.
In the field of lithium-ion battery separator materials, double-layer PP/PP separators are mainly produced by Chinese companies and used in mainland China. This is primarily because no Chinese company yet possesses the technology and capability to fabricate a double-layer composite membrane from PP and PE. Globally, the separators used in automotive lithium-ion batteries mainly consist of triple-layer PP/PE/PP, double-layer PP/PE, and PP+ceramic coating, PE+ceramic coating, and other separator materials.
In the structure of lithium batteries, the separator is one of the key internal components. The performance of the separator determines the battery's interface structure, internal resistance, and other characteristics, directly affecting the battery's capacity, cycle life, and safety performance. A high-performance separator plays an important role in improving the overall performance of the battery.
