Preparation method of waterborne PVDF (Polyvinylidene Fluoride)- PVDF copolymer composite coating membrane

Abstract

The invention provides a preparation method of a waterborne PVDF (Polyvinylidene Fluoride)-PVDF copolymer composite coating membrane. The method comprises the following steps: 1) preparation of PVDF-PVDF copolymer-ceramic mixed slurry: mixing and stirring deionized water, PVDF and a PVDF copolymer to obtain a uniform solution, adding a dispersing agent, mixing with mixed ceramic powder, uniformly stirring at the temperature of 30 to 50 DEG C, and performing ball milling for 0.5 to 2 hours to obtain the PVDF-PVDF copolymer-ceramic mixed slurry; (2) coating: coating one side or two sides of a base membrane with the PVDF-PVDF copolymer-ceramic mixed slurry prepared in the step 1) to form a waterborne coating, and drying in a three-stage drying oven at the temperature of 40 to 90 DEG C to obtain the waterborne PVDF-PVDF copolymer composite coating membrane. The preparation method has the beneficial effects that the swelling ratio of the membrane in electrolyte is increased, the electric conductivity of a lithium battery is increased, the internal resistance of the lithium battery is lowered, and the rate discharge performance and cycle performance of the lithium battery are improved.

Description

technical field [0001] The invention relates to the technical field of lithium battery diaphragm preparation, in particular to a preparation method of water-based PVDF and its copolymer composite coating diaphragm. Background technique [0002] With the high-capacity, high-power, and high-efficiency charge and discharge performance requirements of 3C products in the market, the performance requirements for lithium battery separators are getting higher and higher. Under the premise of ensuring safety, the thickness of the separator needs to be thinner and thinner, but the thickness of the separator The thinner the mechanical strength, the greater the possibility of fracture or puncture. The two are actually contradictory, and a trade-off needs to be made between the two to obtain an ideal product. [0003] In the prior art, the battery diaphragm is generally coated with a ceramic layer on the surface of the diaphragm substrate, and then coated with a water-based PVDF adhesive...

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Problems solved by technology

The invention patent with application number CN 201210000157.5 discloses a diaphragm, which is composed of a ceramic material layer coated on the surface of the base film and a polymer bonding layer coated on the outer surface of the ceramic layer, which improves the heat resistance of the diaphragm Performance and mechanical strength, but compared with the original film, the gas permeability loss of the coated diaphragm is larger, which hinders the conduction of lithium ions and increases the internal resistance of the lithium battery; the coating process is complicated, resulting in a decrease in product production efficiency, and an increase in thickness and weight. Not conducive to the lightweight of the product

The application number is CN201510057002.9, a composite modified diaphragm and its preparation method. After mixing polyvinylidene fluoride-hexafluoropropylene and ceramics in a certain proportion, it is coated on the film substrate to obtain good permeability and air permeability. Composite modified diaphragm with low value, but polyvinylidene fluoride or polyvinylidene fluoride copolymer is a crystalline polymer, especially the crystallinity of polyvinylidene fluoride (PVDF) is about 50%, and the conduction of lithium ions is mainly In the amorphous region, the crystalline region limits the conduction of lithium ions

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