What are the process technologies for lithium battery separator industry? The production process of lithium battery separators is complex and the technical barriers are high. Lithium battery separator is the key inner component in lithium batteries. Key properties such as battery capacity, cycle performance, and charge and discharge current density are directly related to the separator. The improvement of separator performance plays an important role in improving the overall performance of lithium batteries.

　　What are the process technologies for lithium battery separator industry?

　　There are currently four main industrialized lithium battery separator manufacturing technologies: wet method, dry method, semi-dry method and non-woven method. There are further classifications of wet and dry methods.

　　1. Wet technology

　　Lithium battery separator wet process technology is mainly used in the manufacture of polyethylene (PE) separators. Since the process requires the use of paraffin oil mixed with PE to occupy the space and create holes, and it needs to be removed by solvent extraction after the stretching process, so the process is called a wet method. Wet technology involves stretching the film in 2 directions and is therefore divided into simultaneous stretching and step-by-step stretching.

　　There is an ongoing debate as to whether synchronized stretching or split stretching is more advanced. The dispute is reflected in aspects such as product quality, efficiency, and process adaptability. Comparing the microscopic morphology of the product, the separator manufactured by the simultaneous stretching process has higher porosity, more uniform pore distribution, and better thickness uniformity;

　　At the same time, the products produced by simultaneous stretching have uniform strength, higher yield, and theoretically better overall performance. If compared in terms of production efficiency, lithium battery process adaptability, etc., it is not possible to judge the advantages and disadvantages for the time being. The only difference is the difference in equipment levels and process maturity of different companies. Judging from user feedback, the difference in performance between the two products is not obvious.

　　2. Dry technology

　　Dry technology 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.

　　3. Semi-dry technology

　　The semi-dry method is used in the manufacture of polyethylene (PE) separators and is a newly introduced method in recent years. It also uses a pore-forming agent to occupy the space and then removes it using evaporation. The non-woven method (Non-Woven) is currently mainly used in the manufacture of polyester (PET) non-woven fabrics and ceramic particle composite separators. The inevitable large pores in non-woven fabrics bring a high risk of short circuit to the composite separator. This defect restricts the application of non-woven separators and requires breakthrough improvements in process technology.

　　4. Non-woven fabric method

　　Non-woven separator substrates are usually made of polyethylene terephthalate (PET, with a melting point of up to 225°C) and polyimide (PI, with a melting point of over 500°C), which have obvious advantages in heat resistance. At the same time, due to its three-dimensional hole structure, it can effectively avoid short circuits caused by acupuncture and improve the liquid retention rate.

　　At present, domestic and foreign companies have achieved a lot of results in the research, application and performance optimization of non-woven separators, but there are no successful cases of large-scale commercial application in lithium-ion batteries.

　　Development trends of 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 lithium battery separators are from two aspects: higher safety, and more conducive to battery performance. From the perspective of benefiting the performance of lithium batteries, it is necessary to further optimize the structural characteristic parameters and consistency of the separator. For example, thickness, reasonable value of porosity, optimized pore size, optimized pore size distribution, etc. In addition, the consistency of the diaphragm is always a core issue in large-scale production.

　　Lithium battery separators mainly include polyolefin separators and non-woven separators. Polyolefin materials have excellent mechanical properties, chemical stability and relatively cheap characteristics. Therefore, polyolefin microporous membranes such as PE and PP have been widely used in the early stages of lithium battery research and development, and have become the mainstream direction of lithium battery separators.

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