Polyvinyl composite microporous membrane with thermocompression bonding characteristic

Abstract

The present invention relates to polyvinyl composite microporous membrane with thermocompression bonding characteristics. High-crystallinity and high-density polyethylene is modified by using ethylene-propylene methylene copolymer of the middle molecular weight and polyisobutylene rubber. The membrane with thermocompression bonding characteristics is obtained by using aliphatic dibasic acid ester with a flash point above 210 DEG C as a craft solvent and a pore forming agent. The membrane is hot pressed to bond integrally with a positive electrode sheet. The thermal shrinkage of the membrane is suppressed. The composite membrane has the characteristics of high strength and high temperature resistence, and can be used for lithium-ion batteries with high security and long cycle life.

Description

technical field [0001] The present invention relates to a polyolefin microporous diaphragm for lithium-ion batteries and a manufacturing method thereof, in particular to a polyethylene-based composite microporous diaphragm with thermocompression bonding properties by controlling the amorphous content, which is suitable for high safety and long cycle life Lithium battery field such as lithium ion power battery or energy storage battery. Background technique [0002] Polyolefin microporous membrane has a penetrating three-dimensional network of nanoscale pores, is resistant to high-voltage oxidation, and is stable to the organic electrolyte of lithium-ion batteries. As a diaphragm material, it has been widely used in lithium-ion batteries for mobile phones and notebook computers. Typical The commercialized polyolefin microporous diaphragm is "dry method" PP / PE / PP three-layer composite diaphragm and single layer "wet method" high molecular weight PE diaphragm. In addition to th...

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Problems solved by technology

[0004] 1. The strength and toughness of the diaphragm is insufficient, and it is easy to tear in the transverse direction; the transverse elongation at break is less than 20%;

[0005] 2. Although the middle microporous layer is made of PE that is shut down at a high temperature of 135-145°C, the PP microporous layer with a limited melting point and thermal stretching strengthening still has large thermal shrinkage and high temperature resistance at high temperatures above 130°C The disadvantage of insufficient membrane rupture;

[0006] 3. Compared with PVDF-HFP physical gel separator or coating separator, there is a lack of thermal pressure bonding ability between the dry separator and the pole piece

[0009] 1. During manufacture, high-molecular-weight powdery high-density polyethylene is mixed with liquid paraffin oil high-temperature compatibilizer and then heated and kneaded. Due to the difference in density between the two, the solid content of the slurry is prone to fluctuations, and the feeding stability and The consistency of the melt composition is not good; the product stability and consistency are affected;

[0010] 2. Due to the thermal stretching strengthening process, the thermal shrinkage is too large at high temperatures above 120 °C; the battery safety is insufficient;

[0011] 3. Compared with the PVDF-HFP physical gel diaphragm or coating diaphragm, the existing "wet" PE diaphragm and the pole piece also lack thermal pressure bonding ability; the thickness direction also lacks elasticity and stress absorption capacity, which is in safety The high-end requirements of power batteries cannot be met in terms of performance and battery cycle life.

[0018] 1. Since the existing polyolefin diaphragm is basically an inert material, the adhesion between the coating and the coating is not enough, the coating is thick and easy to peel off, and the thermal shrinkage of the polyolefin diaphragm is not obvious if it is too thin;

[0019] 2. After corona treatment, the micropores of the polyolefin diaphragm have capillary action. When the above coating scheme is implemented, the colloid in the slurry easily enters the micropores of the polyolefin diaphragm, which may affect the diaphragm after the solvent evaporates and dries to form a film. The pore size distribution and air permeability of the coating method are difficult to control in batch production, and the manufacturing cost of the coating composite diaphragm is high

[0020] In order to improve the bonding strength between the separator and the positive pole piece and improve the safety of the potassium battery in terms of overcharge resistance, the Chinese invention patent application 01112218.8 proposes to mix and add monomer polymers that can be thermally cross-linked to form a gel in the electrolyte, using The gel improves the bonding strength between the separator and the positive electrode sheet. The same gel will also form a gel in the micropores of the separator during the thermal crosslinking formation process, thereby affecting the permeability of the separator. In addition, the reaction is not complete The monomers may also oxidize and produce gas on the positive side, which may even affect the cycle performance of the battery

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