Polyolefin microporous film preparation method for lithium ion battery and microporous film

Abstract

The invention discloses a polyolefin microporous film preparation method for a lithium ion battery and a microporous film. A mode of twice bidirectional drawing is adopted, and the overall rate of the twice drawing is 16 to 100 times. The preparation method comprises the following steps of (a) extruding a casting piece; (b) performing primary bidirectional drawing at a bidirectional drawing rate which is controlled to be 4 to 10 times to obtain an oily thin film; (c) performing extraction to obtain a microporous film A; (d) performing secondary bidirectional drawing at a bidirectional drawing rate which is controlled to be 4 to 10 times to obtain a thinner microporous film B; (e) performing heat setting to obtain a polyolefin microporous film. The polyolefin microporous film microcosmically has a completely drawn fiber structure, is uniform in aperture and high in performance consistency, and has higher mechanical performance, higher air permeability and enhanced ionic conductivity; the yield can be greatly improved; the lithium ion battery adopting the microporous film has high assembling performance, and the performance and the stability of the battery are enhanced.

Description

technical field [0001] The invention relates to the technical field of polymer microporous membrane materials, in particular to a preparation method of polyolefin microporous membranes for lithium ion batteries. Background technique [0002] With the gradual promotion of lithium-ion batteries in electric vehicles and new energy industries, the global demand for lithium-ion batteries continues to grow. Due to its high porosity, tear strength, low electrical resistance, good acid and alkali resistance and elasticity, polyolefin microporous membranes are the first choice for lithium-ion battery separators. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. A separator with excellent performance plays an important role in improving the overall performance of the battery. [0003] At present, the polyolefin microporous membrane prepared by t...

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Problems solved by technology

[0005] 1. Stretching to form a film with a single high-magnification after casting is prone to clipping, edge tearing, uneven film thickness, thin middle and thick sides, etc. If the width is too large; if the film width is too large, it will easily lead to unstable stretching temperature field and uneven temperature control, which will directly affect the consistency of film thickness and microstructure;

[0006] 2. If the width of the film is too large, it is easy to cause uneven tension during extraction, resulting in poor consistency in film thickness;

[0007] 3. If the width of the film is too large, it is difficult to control the tension of the sheet during heat setting, and the temperature field is unstable, which may easily cause uneven product performance;

[0008] 4. The width of the film is too large, and the uniformity of the product in the transverse direction is poor, resulting in poor uniformity of film performance, which affects the use and performance of downstream batteries;

[0009] 5. Due to the limited stretching ratio of single stretching at large ratios, the porosity of the film is low, the air permeability is poor, and the mechanical properties are not good

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