Polyethylene based composite material microporous diaphragm with hot-pressing adhesive characteristic

Abstract

The invention relates to a polyethylene based composite material microporous diaphragm with a hot-pressing adhesive characteristic. According to the polyethylene based composite material microporous diaphragm, ethylene propylene monomer and polyisobutene rubbers with medium molecular weights are adopted to modify high-crystallinity high-density polyethylene, and fatty series dibasic acid ester of which the flashing point is more than 210DEG C is adopted as a process solvent and a pore forming agent of a diaphragm to obtain the diaphragm with the hot-pressing adhesive characteristic. The diaphragm with the hot-pressing adhesive characteristic and a positive pole piece are adhered into a whole body after hot-pressing lamination, so that the thermal contraction of the diaphragm is inhibited. The composite material diaphragm has high strength and high-temperature resistance, and can be applied to lithium ion power batteries with high safety and long cycle lives.

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...

AI Technical Summary

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 thereby improve the safety of the lithium 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. 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 be oxidized and gas-produced on the positive side, which may even affect the cycle performance of the battery

Images