Diaphragm for lithium ion battery and preparation method thereof

Abstract

The present invention relates to a microporous membrane material, particularly relates to diaphragm for lithium ion batteries and a preparation method thereof, and belongs to the technical field of membrane. The diaphragm is a composite microporous membrane prepared from a polyolefin intermediate layer and fluorine-containing polymer outer layers of the same thickness on both sides by melt extrusion, biaxial stretching and heat setting processes, wherein the polyolefin layer is a polyvinyl layer, a polypropylene layer or a composite layer of polyethylene and polypropylene, the fluorine-containing polymer outer layer is a melt-processable modified vinyl fluorine resin layer which is copolymerized by vinyl fluoride, ethylene and fluorine-containing functional monomer, the thickness of the composite microporous membrane is 5-30 microns, the fluorine-containing polymer outer layer at one side is 1-10 microns, the pore diameter is of 0.01-0.1 microns, and the porosity is of 50-80%. The diaphragm prepared by the invention is uniform in thickness and pore size, stable in dimension, excellent in mechanical property and chemical stability, good in electrolyte wettability and electrode adhesion, simple in preparation process and easy to implement.

Description

technical field [0001] The invention relates to a microporous membrane material, in particular to a separator suitable for lithium ion batteries and a preparation method thereof, belonging to the technical field of membranes. Background technique [0002] The battery is mainly composed of electrode materials, electrolyte and separator. The function of the battery separator is to ensure the passage of ions in the electrolyte, and when reducing the distance between the positive and negative electrodes of the battery, it can isolate the positive and negative plates of the battery in a small space of the battery to prevent the two plates of the battery from contacting each other. cause a short circuit. [0003] In practical applications, the diaphragm material is mainly porous polyolefin, and the first used is porous polypropylene diaphragm, which is represented by Celgard Company. The preparation methods of separator mainly include phase separation method and stretching poros...

AI Technical Summary

Problems solved by technology

The weather resistance of polypropylene microporous membrane is poor, and the performance of polypropylene particles will deteriorate rapidly after being placed indoors for 4 months

The mechanical properties and mechanical properties of polyethylene microporous film and polypropylene microporous film are not perfect, and the ductility is poor, and if they are negligent and easy to tear in the battery winding that blocks the positive and negative plates, resulting in positive and negative electrodes. The plates are in contact with each other, so it will cause an internal short circuit of the battery during use and may cause an explosion

[0006] Polyethylene microporous membrane and polypropylene microporous membrane are flammable. Although polypropylene microporous membrane is more flammable than polyethylene microporous membrane, the oxygen limit index is only 0.18. Polyethylene microporous membrane melts at about 130°C , and the polypropylene microporous membrane melts at about 150 ° C, so the thermal stability is relatively poor

All in all, the comprehensive performance of polyethylene microporous membrane and polypropylene microporous membrane as a lithium battery separator is not perfect, and there are certain safety hazards, so it is necessary to find materials with better performance to replace them.