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Production process of lithium battery separator

by:dcfpower     2021-03-20

The lithium battery separator is one of the key internal components of the battery. The performance of the diaphragm determines the interface structure and internal resistance of the lithium battery pack, which directly affects the battery's capacity, cycle and safety performance. A diaphragm with excellent performance plays an important role in improving the overall performance of the battery. The popular description is a porous plastic film, which is a kind of high value-added material with the highest technical barrier among lithium battery materials, accounting for about 20%-30% of the cost of lithium batteries, and the gross profit rate can be as high as 60% to 70%. The main reason for the high prices of diaphragms is that some key technologies for diaphragm production are monopolized by Japan and the United States. The indicators of domestic diaphragms, especially high-end diaphragms, have not yet reached the level of foreign products. The difficulty of diaphragm technology lies in the engineering technology of making the hole and the matrix material. The engineering technology of pore-making includes diaphragm pore-making process, production equipment and product stability. The base material includes polypropylene, polyethylene materials and additives.

separator production process has two kinds of dry method and wet method.

The dry production process of lithium battery separator is divided into unidirectional stretching and bidirectional stretching:

Unidirectional stretching adopts the process principle of wafer separation, and its equipment is complicated and the precision is required. High, large investment, complex process, high control difficulty, and environmentally friendly. In terms of the quality of the diaphragm, the micropore size and distribution are uniform, the micropore conductivity is good, and products of different thicknesses can be produced. PP, PE products and three-layer composite products can be produced, but the lateral toughness is slightly worse.

The United States Celgard company has a series of patents for the dry uniaxial stretching process, and the Japanese company JBE has purchased Celgard's related patent use rights.

Biaxial stretching adopts the principle of crystal form conversion. Its equipment is complicated and the investment is large. Generally, additives such as pore formers are needed to assist in pore formation. In terms of the quality of the diaphragm, the micropore size and distribution are uniform, and the stability is poor. Currently, only thicker specifications of PP film can be produced. But the physical and mechanical properties are better than uniaxial stretching.

This is a process (CN1062357) with independent intellectual property rights developed by the Institute of Chemistry, Chinese Academy of Sciences in the early 1990s.

Wet production process of lithium battery diaphragm

The equipment is complicated, the investment is large, the cycle is long, the process is complicated, the cost is high, and the energy consumption is large. However, the micropore size and distribution are uniform, which is suitable for the production of thinner products, and can only produce single-layer PE film. In terms of product quality, it has a higher nipple rate and better air permeability, which can meet the requirements of high current charging and discharging.

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