polymer lithium battery separator technology development route and industry development trends

　　polymer lithium battery separator technology development route and industry development trends. polymer lithium battery separator technology is currently a pain point in my country's power battery industry. As one of the four main materials of lithium batteries, the separator directly affects the safety of the battery. Its porosity, thickness, liquid absorption, and electrostatic value directly affect the electrical performance of the battery. The separator is a high value-added material with the highest technical barriers among current polymer lithium battery materials, accounting for about 15% of the cost of lithium batteries.

　　polymer lithium battery separator technology development route

　　There are currently four main industrialized polymer lithium battery separator manufacturing technologies: wet method, dry method, semi-dry method and non-woven method. polymer lithium battery separator technology routes are mainly divided into two types: dry process and wet process separator. The dry process has lower cost but is not suitable for high specific energy batteries. The wet process is thinner and can meet the requirements of high specific energy of power batteries, but the cost is more expensive.

　　High-end polymer lithium battery separator technology has a very high threshold. It not only requires a huge investment, but also requires a strong R&D and production team, skilled process technology and high-level production lines, and it will not be possible to break through in a short time. However, the YYW-US trade war and the ZTE and Huawei incidents have sounded the alarm for my country's manufacturing industry. For the entire power battery industry, it is urgent to break through high-end separator technology for lithium batteries as soon as possible.

　　Dry technology (Dry) is mainly used in the manufacture of polypropylene (PP) separators. Dry technology mainly includes three process technologies: blown film + uniaxial stretching, cast sheet + uniaxial stretching and biaxial stretching. Relatively speaking, dry technology has simpler processes, lower equipment costs, and lower production efficiency than wet technology.

　　Coated (or composite) separators are the focus of today's separator application development. Using a coating layer on the surface of the separator can bring obvious benefits. First, it improves the thermal stability of the separator; second, it improves the wettability of the separator to the electrolyte. , which is conducive to reducing the internal resistance of lithium batteries and increasing the discharge power; in addition, it can prevent or reduce the oxidation of the separator, which is beneficial to the operation of high-voltage positive electrodes and extending the battery cycle life. Coating materials mainly include: alumina, boehmite, PVDF, PVDF+HFP, nanocomposites, aramid, etc.

　　Future development: thin diaphragm. As the specific energy of power lithium batteries increases rapidly, 16-micron, 12-micron or even 8-micron separators are beginning to be used, and separators made by wet processes can meet the requirements. With the reduction of subsidies for new energy vehicles and the gradual improvement of dry separator technology, the proportion of dry separators in ternary batteries has gradually increased.

　　Development Trend of polymer lithium battery Separator Technology

　　The development of power batteries has clarified the direction and put forward specific requirements for the development of separators. The development of power batteries focuses on three aspects: increasing energy density, ensuring safety, and reducing costs. The specific energy of the single unit reaches more than 300Wh/kg, the specific energy of the system strives to reach 260Wh/kg, and the cost is reduced to less than 1 yuan/Wh. Correspondingly, the requirements for separators are from two aspects: higher safety, and more conducive to battery performance.

　　One is ceramic coating based on PE and PP separators. The safe use temperature of ceramic-coated PE composite separators can be increased to 150~160℃, and the safe use temperature of ceramic-coated PP composite separators can be increased to 180~200℃. Ceramic coating improves the safety of the separator, but the main adverse effects are increased weight, increased cost, and increased internal resistance of the battery.

　　The second is polymer coating based on PE and PP separators or asymmetric coating of ceramics and polymers on both sides. Different types of polymers will affect the performance of the composite membrane, and the effects cannot be generalized.

　　The third is a composite membrane of non-woven fabrics and ceramic particles. If PET non-woven fabric is used, the safe use temperature of the composite membrane can reach about 250°C.

　　The fourth is to use high-temperature-resistant polymer materials and new film-making processes to manufacture high-security separators, such as polyimide (PI) films. The safe use temperature of PI film can reach 300℃.

　　Development trends of polymer lithium battery separator industry

　　As the third largest application field of lithium batteries, polymer lithium battery energy storage is limited by practical difficulties such as technology, cost and policy uncertainty, and its current application scale is limited. Based on the demand in the three major fields, it is expected that the polymer lithium battery separator industry will continue to maintain a compound growth rate of about 30% by 2020.

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