What is a lithium battery diaphragm

The diaphragm of the lithium battery is the film between the positive and negative stages of the lithium battery. When the lithium battery carries out the electrolytic reaction, it can separate the positive and negative stages to avoid short-circuit fault. In addition, it can make the positive ions of the electrolyte solution freely. The cost of diaphragm accounts for about 10% of the cost of lithium battery. The indoor space of the sales market is not large, and the profit margin at this stage is in the middle of 50%-60%, which is the largest part of the four key raw materials.

The diaphragm belongs to the field of heavy assets. Among the four major raw materials of lithium batteries, the project investment enterprise has a large production capacity and must invest a lot of assets. Therefore, there is not only a technical fortress, but also the purchase, adjustment and installation of machinery and equipment usually take 2-3 years. Only after a long-term upward slope can we ensure that there is a fortress like a good commodity rate. In addition, the depreciation cost in the field is too high, the processing technology is out of date, and the production capacity is out of date. It is very easy to be replaced by the sales market, and small and medium-sized enterprises and new enterprises cannot survive. Companies that have the advantage of preemptive games in long-term infrastructure construction will also accumulate the same advantages in the verification of customers in the middle and lower reaches. Because the diaphragm is very harmful to the characteristics and safety index values of rechargeable batteries, the verification cycle time of rechargeable battery manufacturers generally must be 2-3 years. From entering the diaphragm industry to mass supply, it must be about 4-6 years. In addition, the accumulated capital distribution and iterative updating of processing technology make the advantages of leading enterprises become more and more obvious and difficult to distort.

The diaphragm of lithium battery can be divided into dry-type preparation according to its microporous plate preparation process (a large number of lithium iron phosphate battery rechargeable batteries). Wet preparation and processing technology (a large number of ternary lithium batteries)

The overall wet processing process has a high degree of difficulty and accuracy. It can obtain high porosity and good air permeability. It can produce a diaphragm with light weight, high toughness and high efficiency energy relative density. It is easier to consider the requirements of the middle and lower reaches of lithium batteries for light weight, large space and high efficiency energy relative density. Therefore, with the development trend of increasing requirements for the middle and lower reaches of ternary material power lithium batteries and 3C applications, the demand for wet test diaphragms has gradually exceeded that of dry test diaphragms, increasing from 40% in 16 years to more than 70% now. In addition, due to the use of high-pressure polyethylene in wet manufacturing, the melting point is low, so the heat resistance is weak, which is also a common problem of ternary batteries.