CN113067100A - Water-based PVDF (polyvinylidene fluoride) coated lithium ion battery diaphragm and preparation method thereof - Google Patents
Water-based PVDF (polyvinylidene fluoride) coated lithium ion battery diaphragm and preparation method thereof Download PDFInfo
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- 239000002033 PVDF binder Substances 0.000 title claims abstract description 106
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 54
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 54
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 30
- 238000002360 preparation method Methods 0.000 title abstract description 12
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims abstract description 103
- 239000000839 emulsion Substances 0.000 claims abstract description 96
- 238000000576 coating method Methods 0.000 claims abstract description 80
- 239000011248 coating agent Substances 0.000 claims abstract description 71
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- MHWAJHABMBTNHS-UHFFFAOYSA-N 1,1-difluoroethene;1,1,2,2-tetrafluoroethene Chemical group FC(F)=C.FC(F)=C(F)F MHWAJHABMBTNHS-UHFFFAOYSA-N 0.000 claims description 2
- OQMIRQSWHKCKNJ-UHFFFAOYSA-N 1,1-difluoroethene;1,1,2,3,3,3-hexafluoroprop-1-ene Chemical group FC(F)=C.FC(F)=C(F)C(F)(F)F OQMIRQSWHKCKNJ-UHFFFAOYSA-N 0.000 claims description 2
- XLOFNXVVMRAGLZ-UHFFFAOYSA-N 1,1-difluoroethene;1,1,2-trifluoroethene Chemical group FC(F)=C.FC=C(F)F XLOFNXVVMRAGLZ-UHFFFAOYSA-N 0.000 claims description 2
- COVXBJIKNGVTNV-UHFFFAOYSA-N 1-chloro-1,2,2-trifluoroethene;1,1-difluoroethene Chemical group FC(F)=C.FC(F)=C(F)Cl COVXBJIKNGVTNV-UHFFFAOYSA-N 0.000 claims description 2
- 239000004642 Polyimide Substances 0.000 claims description 2
- 239000004745 nonwoven fabric Substances 0.000 claims description 2
- 229920003229 poly(methyl methacrylate) Polymers 0.000 claims description 2
- 229920000120 polyethyl acrylate Polymers 0.000 claims description 2
- 229920001721 polyimide Polymers 0.000 claims description 2
- 239000004926 polymethyl methacrylate Substances 0.000 claims description 2
- 239000012798 spherical particle Substances 0.000 claims description 2
- 238000005507 spraying Methods 0.000 claims description 2
- 239000000843 powder Substances 0.000 description 10
- 239000002002 slurry Substances 0.000 description 9
- 239000011347 resin Substances 0.000 description 8
- 229920005989 resin Polymers 0.000 description 8
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 7
- 229910052744 lithium Inorganic materials 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 229920000098 polyolefin Polymers 0.000 description 6
- 239000007788 liquid Substances 0.000 description 4
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- 230000007547 defect Effects 0.000 description 3
- 239000008367 deionised water Substances 0.000 description 3
- 229910021641 deionized water Inorganic materials 0.000 description 3
- 239000002270 dispersing agent Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000004094 surface-active agent Substances 0.000 description 3
- 239000002174 Styrene-butadiene Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 239000002518 antifoaming agent Substances 0.000 description 2
- MTAZNLWOLGHBHU-UHFFFAOYSA-N butadiene-styrene rubber Chemical compound C=CC=C.C=CC1=CC=CC=C1 MTAZNLWOLGHBHU-UHFFFAOYSA-N 0.000 description 2
- 238000011161 development Methods 0.000 description 2
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- 229920000642 polymer Polymers 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000011115 styrene butadiene Substances 0.000 description 2
- 229920003048 styrene butadiene rubber Polymers 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- DQWPFSLDHJDLRL-UHFFFAOYSA-N triethyl phosphate Chemical compound CCOP(=O)(OCC)OCC DQWPFSLDHJDLRL-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 230000001112 coagulating effect Effects 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 239000011245 gel electrolyte Substances 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
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- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 1
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- 231100000167 toxic agent Toxicity 0.000 description 1
- 239000003440 toxic substance Substances 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- 239000000080 wetting agent Substances 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Cell Separators (AREA)
Abstract
The invention provides a water-based PVDF coated lithium ion battery diaphragm, which comprises a base film and a PVDF coating coated on one side or two sides of the base film, wherein the coating is prepared from a mixed emulsion, the mixed emulsion comprises a PVDF emulsion and a binder emulsion, the weight proportion of the PVDF emulsion in the mixed emulsion is 70-98%, and the weight proportion of the binder emulsion in the mixed emulsion is 2-30%. The invention also provides a preparation method of the aqueous PVDF coating lithium ion battery diaphragm. The aqueous PVDF coating lithium ion battery diaphragm provided by the invention has excellent comprehensive performance, and the preparation method has the advantages of simple production process and no pollution.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a water-based PVDF-coated lithium ion battery diaphragm and a preparation method thereof.
Background
Since the first commercialized lithium ion battery in the world invented by the company sony of japan in 1991, the lithium ion battery has been developed rapidly due to its characteristics of high energy density, long cycle life, high specific power, low self-discharge rate, no memory effect, safety, reliability, environmental friendliness, etc., and is widely used in portable electronic (3C) products such as notebook computers, smart phones, tablet computers, digital cameras, etc., and in the field of new energy automobiles, and has become an indispensable product in daily life.
In the internal structure of the lithium ion battery, the anode, the cathode, the diaphragm and the electrolyte are four most central materials, and play a role in directly determining and comprehensively influencing key performance indexes of the lithium ion battery, such as energy density, cycle performance, rate performance, internal resistance and the like, and safety performances of high temperature resistance, flame retardance, self-turn-off, electrochemical stability and the like. The diaphragm is used as one of the key inner layer components and mainly has the main function of isolating the positive electrode and the negative electrode so as to prevent the two electrodes from contacting and being short-circuited; meanwhile, the lithium ion battery is used as a migration channel of lithium ions, the lithium ions in the electrolyte can freely pass through the micropores during charging and discharging so as to ensure the normal operation of the battery, and the lithium ion battery is a key inner layer component with the most technical barrier in the lithium ion battery industry chain.
With the development of new energy automobiles and high-energy density batteries, the lithium battery market meets the opportunity of rapid development, and simultaneously puts higher requirements on the comprehensive performance of the lithium battery, such as large current and high-rate discharge, long-time stable and uniform output, higher heat resistance and dimensional stability, good electrolyte wettability and liquid retention and the like. However, the traditional PP/PE polyolefin separator cannot meet the application in the fields of power batteries and the like due to poor high temperature resistance, electrolyte wettability, puncture resistance and oxidation resistance. On the other hand, a thinner polyolefin diaphragm is required to be used in the high-energy density power battery, and the use of the diaphragm with the thinner thickness enables the diaphragm to be more easily subjected to thermal contraction deformation at high temperature to cause the contact of a positive pole piece and a negative pole piece, and internal short circuit causes local rapid heat release, so that safety problems such as ignition, explosion and the like are caused, and huge potential safety hazards exist.
Therefore, the traditional polyolefin diaphragm can not meet the use requirements of the current high-end 3C products and power batteries, and becomes a difficult problem to be overcome urgently in the high-performance process of the lithium battery, and the diaphragm coating technology is an effective means for solving the defects of the traditional polyolefin diaphragm, improving the comprehensive performance of the diaphragm and reducing the safety risk.
Polyvinylidene fluoride (PVDF) is widely applied to the field of lithium battery diaphragm coating due to excellent physical and chemical properties, and the PVDF coating increases the wettability of the diaphragm and electrolyte and the adhesion property of a pole piece to a certain extent, and effectively combines the characteristics of good lyophilicity, high ionic conductivity and strong chemical corrosion resistance of gel electrolyte and the characteristics of high rigid structure and mechanical property of a traditional base film.
The existing PVDF coating technology of the lithium ion battery comprises an oil coating process and a water coating process. The oil coating process disclosed in chinese patent CN108258169A is to coat PVDF resin, additives and organic solvent slurry on the surface of polyolefin, and then immerse the polyolefin in a coagulating bath to cure and dry the coating to form a composite membrane. The method must use an organic solvent, which not only pollutes the environment, but also has the problems of difficult recycling and high cost, in particular to the common organic solvent acetone which is a flammable, explosive and easy-to-prepare toxic compound, belongs to a restrictive raw material, and has unsafe factors in the production process.
The aqueous coating process disclosed in chinese patent CN108832063A is to prepare PVDF resin powder, an aqueous binder, a surfactant and a dispersant into a base material, mix the base material and water into a slurry, and coat the slurry on one side or both sides of a base film to obtain a battery separator. In the preparation process of the base material, the preparation process has multiple and complicated steps, the PVDF resin powder, the water-based adhesive, the surfactant and the dispersant need to be mixed, milled, stirred, dispersed and the like, and sometimes, in order to improve the stability of the slurry, multiple compounding procedures need to be carried out. According to the method, the PVDF resin powder and other components are mixed to prepare the base material, and the PVDF resin powder is difficult to be uniformly distributed in the base material due to the characteristics of the PVDF resin powder, so that the PVDF resin powder in the obtained base material is not uniformly distributed, and the thickness of the coated coating is improved and is not uniformly distributed, so that the performance of the lithium ion battery is influenced.
Therefore, there is a need for further technical improvements in PVDF coated lithium ion battery separator slurry for making coatings.
Disclosure of Invention
Aiming at the defects of the PVDF coating technology in the prior art, the invention provides the water-based PVDF coated lithium ion battery diaphragm which comprises the base film and the PVDF coating coated on one side or two sides of the base film, and the water-based PVDF coated lithium ion battery diaphragm has the characteristics of simple production process, no pollution and excellent comprehensive performance of the prepared battery diaphragm.
The invention provides the following technical scheme:
the water-based PVDF coated lithium ion battery diaphragm comprises a base film and a PVDF coating coated on one side or two sides of the base film, wherein the coating is prepared from a mixed emulsion, the mixed emulsion comprises a PVDF emulsion and a binder emulsion, the weight proportion of the PVDF emulsion in the mixed emulsion is 70-98%, and the weight proportion of the binder emulsion in the mixed emulsion is 2-30%.
The coating used by the water-based PVDF coated lithium ion battery diaphragm provided by the invention is prepared from mixed emulsion, and the mixed emulsion comprises PVDF emulsion and binder emulsion. The PVDF emulsion is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-trifluoroethylene, vinylidene fluoride-tetrafluoroethylene, vinylidene fluoride-chlorotrifluoroethylene and vinylidene fluoride-perfluorobutene copolymer emulsion.
As a preferred embodiment, the PVDF emulsion is selected from at least one of polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer emulsion.
The PVDF emulsion used in the invention has no special requirements on the solid content of the emulsion. As a preferred embodiment, the emulsion solid content of the PVDF emulsion is 10-40%.
The coating used by the water-based PVDF coated lithium ion battery diaphragm provided by the invention is prepared from mixed emulsion, and the mixed emulsion comprises PVDF emulsion and binder emulsion. In the mixed emulsion, the weight ratio of the PVDF emulsion meets the requirement of preparing the battery diaphragm with required performance.
In a preferred embodiment, the weight ratio of the PVDF emulsion in the mixed emulsion is 70-98%.
In another preferred embodiment, the PVDF emulsion is 85 to 97% by weight.
In another preferred embodiment, the PVDF emulsion is used in an amount of 90 to 96% by weight.
The coating used by the water-based PVDF coated lithium ion battery diaphragm provided by the invention is prepared from mixed emulsion, and the mixed emulsion comprises PVDF emulsion and binder emulsion. The binder emulsion used is preferably at least one selected from the group consisting of polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate and polyethyl acrylate.
The coating used by the water-based PVDF coated lithium ion battery diaphragm provided by the invention is prepared from mixed emulsion, and the mixed emulsion comprises PVDF emulsion and binder emulsion. In the mixed emulsion, the weight ratio of the adhesive emulsion is satisfied to prepare the battery diaphragm with required performance.
In a preferred embodiment, the weight ratio of the binder emulsion in the mixed emulsion is 2 to 30%.
In another preferred embodiment, the binder emulsion is 3 to 15% by weight.
In another preferred embodiment, the binder emulsion is 4 to 10% by weight.
The thickness of the PVDF coating is preferably 0.1-0.3 mu m.
In a preferred embodiment, the water-based PVDF in the coating is uniformly arranged in the form of spherical particles, and the particle size of the spherical PVDF particles is 100-300 nm.
The base film used by the aqueous PVDF coated lithium ion battery diaphragm provided by the invention can be a base film commonly used in the field.
In a preferred embodiment, the base film is selected from any one of a polyethylene separator, a polypropylene separator, a polyethylene/polypropylene composite separator, a polyimide separator, and a nonwoven fabric separator.
In another preferred embodiment, the base film is selected from polyethylene separators, and has a thickness of 5 to 25 μmm, a porosity of 30 to 60%, and an air permeability of 100 to 200sec/100 cc.
The invention also provides a preparation method of the aqueous PVDF coating lithium ion battery diaphragm, which comprises the following steps:
(1) weighing the PVDF emulsion and the binder emulsion according to a ratio, stirring at room temperature for 5-15 minutes, and uniformly mixing to obtain a mixed emulsion;
(2) coating the PVDF mixed emulsion on one side or two sides of a base film to form a water-based coating;
(3) and drying in an oven at 50-90 ℃ to obtain the water-based PVDF coating lithium ion battery diaphragm.
In the preparation method provided by the invention, the coating mode can be a coating mode commonly used in the field.
As a preferred embodiment, the coating means is selected from at least one of gravure coating, slot coating, dip coating, and spray coating.
The water-based PVDF coating lithium ion battery diaphragm provided by the invention is suitable for being applied to the field of high-energy-density power lithium ion batteries.
Compared with the prior art, the water-based PVDF coating lithium ion battery diaphragm provided by the invention has the following advantages:
(1) organic solvents such as acetone and the like in the traditional oily coating process are not used, so that the defect that the production efficiency of the product is reduced due to the complex coating process is avoided;
(2) the ultrathin aqueous PVDF coating lithium ion battery diaphragm with excellent comprehensive performance can be prepared only by adding the binder, and other wetting agents, surfactants, defoaming agents, dispersing agents and the like are not required to be added;
(3) adopting stable water-based PVDF (polyvinylidene fluoride) original emulsion and matching with proper binder emulsion, and obtaining an ultrathin coating with PVDF particles closely and uniformly arranged after coating, wherein the thickness of the coating is only 0.1-0.3 mu m;
(4) the ultrathin coating can effectively improve the binding power of the diaphragm and the pole piece, and the uniform distribution of PVDF particles can reduce the air permeability loss caused by the thickness of the coating, improve the swelling rate of the diaphragm in electrolyte, improve the conductivity of the lithium battery, and reduce the internal resistance of the lithium battery, thereby improving the rate discharge performance and the cycle performance of the lithium battery;
(5) the invention adopts water as the solvent of PVDF resin, has environment-friendly production process, high safety and low production cost, and is beneficial to industrial popularization.
Drawings
Fig. 1 is an SEM image of the surface of the aqueous PVDF-coated lithium ion battery separator prepared in example 1.
Detailed Description
The present invention is further illustrated by the following examples, which are not intended to limit the invention to these embodiments. It will be appreciated by those skilled in the art that the present invention encompasses all alternatives, modifications and equivalents as may be included within the scope of the claims.
Example 1
Weighing 95 parts of vinylidene fluoride-hexafluoropropylene copolymer emulsion with the solid content of 20 percent and 5 parts of polyethyl methacrylate emulsion with the solid content of 58 percent according to the mass fraction, uniformly mixing, stirring at room temperature for 10 minutes to obtain mixed emulsion, and coating the PVDF mixed emulsion on the two sides of a polyethylene base film with the thickness of 15 mu m and the porosity of 40 percent by adopting a gravure coating mode, wherein the coating speed is 20 m/min; and drying by using a three-stage oven, wherein the temperature of each stage of oven is 55 ℃, 70 ℃ and 60 ℃, and the water-based PVDF coating lithium ion battery diaphragm is prepared after drying, the thickness of the composite diaphragm is 15.2 mu m, and the thickness of each side coating is 0.1 mu m.
Example 2
Weighing 90 parts of polyvinylidene fluoride emulsion with the solid content of 30 percent and 10 parts of polymethyl acrylate emulsion with the solid content of 40 percent according to the mass fraction, uniformly mixing, stirring at room temperature for 15 minutes to obtain mixed emulsion, and coating the PVDF mixed emulsion on one side of a polyethylene base film with the thickness of 20 mu m and the porosity of 38 percent by adopting a narrow slit type coating mode, wherein the coating speed is 25 m/min; and drying by using three-stage drying ovens, wherein the temperatures of all stages of drying ovens are respectively 50 ℃, 60 ℃ and 55 ℃, and the water-based PVDF coating lithium ion battery diaphragm is prepared after drying, wherein the thickness of the composite diaphragm is 20.2 mu m, and the thickness of the coating is 0.2 mu m.
Example 3
Weighing 92 parts of vinylidene fluoride-hexafluoropropylene copolymer emulsion with the solid content of 35 percent and 8 parts of polybutylmethacrylate emulsion with the solid content of 48 percent according to the mass fraction, uniformly mixing the two parts, stirring the mixture at room temperature for 8 minutes to obtain mixed emulsion, and coating the PVDF mixed emulsion on the two sides of a polyethylene base film with the thickness of 25 mu m and the porosity of 45 percent in a dip-coating type coating mode at the coating speed of 30 m/min; and drying by using a three-stage drying oven, wherein the temperature of each stage of drying oven is 60 ℃, 80 ℃ and 70 ℃, and the water-based PVDF coating lithium ion battery diaphragm is prepared after drying, the thickness of the composite diaphragm is 25.6 mu m, and the thickness of each side coating is 0.3 mu m.
Comparative example 1
The PVDF coating membrane prepared according to the conventional oily coating process is taken as a comparative example, namely 10 parts of vinylidene fluoride-hexafluoropropylene copolymer powder, 8 parts of absolute ethyl alcohol and 90 parts of acetone are weighed according to the mass fraction and stirred for 4 hours at the temperature of 40 ℃ until a uniform polymer solution is formed. The polymer solution was filtered through a screen to remove solid impurities, and then allowed to stand for defoaming to obtain a coating solution. Coating the PVDF coating liquid on two sides of a polyethylene base film with the thickness of 15 mu m and the porosity of 40% by adopting a gravure coating mode, wherein the coating speed is 20 m/min; and (3) drying in a vacuum oven at 50 ℃ for 12h to obtain the oily PVDF coated lithium ion battery diaphragm, wherein the thickness of the composite diaphragm is 23 μm, and the thickness of each side coating is 4 μm.
Comparative example 2
Referring to the preparation process of example 1 in patent CN108832063A, 10 parts of vinylidene fluoride-hexafluoropropylene copolymer powder, 4 parts of sodium carboxymethylcellulose, 5 parts of diglyceride, 1 part of BYK-1785 defoaming agent, 5 parts of polyacrylate emulsion with the solid content of 58% and 250 parts of deionized water are weighed according to mass fraction.
The preparation method comprises the steps of mixing the raw materials, grinding for 1 hour to prepare PVDF dispersed slurry, coating the PVDF dispersed slurry on two sides of a polyethylene base film with the thickness of 15 mu m and the porosity of 40% in a gravure coating mode, and drying at a constant temperature of 80 ℃ for 2min to prepare the water-based PVDF-coated lithium ion battery diaphragm, wherein the thickness of the composite diaphragm is 17 mu m, and the thickness of each side coating is 1 mu m.
Comparative example 3
Referring to the preparation process of example 1 in patent CN105552277B, 6.5 parts of vinylidene fluoride-hexafluoropropylene copolymer powder, 0.3 parts of styrene-butadiene latex, 1 part of triethyl phosphate, 0.2 part of fluoroalkyl methoxy ether alcohol and 792 parts of deionized water are weighed by mass fraction.
Mixing triethyl phosphate with deionized water, stirring for 10 minutes, and heating to 50 ℃ to prepare a first mixture; adding vinylidene fluoride-hexafluoropropylene copolymer powder into the mixture I, and grinding for 1 hour to obtain a mixture II; adding styrene-butadiene latex and fluoroalkyl methoxy ether alcohol into the mixture II, uniformly stirring, and filtering by using a 400-mesh stainless steel screen to obtain PVDF slurry; coating the PVDF slurry on two sides of a polyethylene base film with the thickness of 15 mu m and the porosity of 40% by adopting a gravure coating mode, wherein the coating speed is 20 m/min; and (3) drying by using three-stage drying ovens, wherein the temperatures of all stages of drying ovens are respectively 55 ℃, 70 ℃ and 60 ℃, and the PVDF-coated lithium ion battery diaphragm is prepared after drying, the thickness of the diaphragm is 16 mu m, and the thickness of each side coating is 0.5 mu m.
Example 4
The separators prepared in examples 1 to 3 and comparative examples 1 to 3 were subjected to performance tests, respectively, and the obtained data are recorded in table 1.
TABLE 1
As can be seen from table 1 above, the composite separator prepared by the method of examples 1 to 3 of the present invention has better air permeability and liquid absorption rate than those of comparative examples 1 to 3, because the PVDF particles, which are densely and uniformly arranged on the surface of the ultrathin composite separator prepared by the simple coating process of the present invention, can effectively reduce the air permeability loss caused by the introduction of the coating layer, and further improve the liquid absorption rate of the electrolyte.
Example 5
For the diaphragms prepared by the methods of examples 1-3 and comparative examples 1-3, a button cell is prepared by using a lithium iron phosphate positive plate and a graphite negative plate respectively, and the internal resistance of the cell and the binding force between the diaphragm and the plates are examined. The cycle performance of the battery, namely the capacity retention rate of the battery after the battery is circularly charged and discharged for 400 times under the constant current condition of 1C, is further examined, and the obtained data are recorded in Table 2.
TABLE 2
From the above table 2, the lithium ion battery assembled by the aqueous PVDF-coated diaphragm has smaller internal resistance, stronger binding force between the diaphragm and a pole piece, more stable cycle performance and excellent comprehensive battery performance.
Claims (12)
1. The utility model provides a waterborne PVDF coating lithium ion battery diaphragm, includes the base film and coats in the PVDF coating of base film unilateral or both sides which characterized in that: the coating is prepared from mixed emulsion, the mixed emulsion comprises PVDF emulsion and binder emulsion, the weight proportion of the PVDF emulsion in the mixed emulsion is 70-98%, and the weight proportion of the binder emulsion in the mixed emulsion is 2-30%.
2. The aqueous PVDF-coated lithium ion battery separator of claim 1, wherein: in the mixed emulsion, the weight ratio of the PVDF emulsion is 85-97%, and the weight ratio of the binder emulsion is 3-15%.
3. The aqueous PVDF-coated lithium ion battery separator of claim 2, wherein: in the mixed emulsion, the weight ratio of the PVDF emulsion is 90-96%, and the weight ratio of the binder emulsion is 4-10%.
4. The aqueous PVDF-coated lithium ion battery separator of claim 1, wherein: the binder emulsion is selected from at least one of polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate and polyethyl acrylate.
5. The aqueous PVDF-coated lithium ion battery separator of claim 1, wherein: the PVDF emulsion is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-trifluoroethylene, vinylidene fluoride-tetrafluoroethylene, vinylidene fluoride-chlorotrifluoroethylene and vinylidene fluoride-perfluorobutene copolymer emulsion.
6. The aqueous PVDF-coated lithium ion battery separator as defined in claim 5, wherein: the PVDF emulsion is selected from at least one of polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer emulsion, and the solid content of the emulsion is 10-40%.
7. The aqueous PVDF-coated lithium ion battery separator of claim 1, wherein: the thickness of the coating is 0.1-0.3 μm, and the waterborne PVDF in the coating is uniformly arranged in spherical particles, and the particle size of the spherical PVDF particles is 100-300 nm.
8. The aqueous PVDF-coated lithium ion battery separator of claim 1, wherein: the base membrane is selected from any one of a polyethylene diaphragm, a polypropylene diaphragm, a polyethylene/polypropylene composite diaphragm, a polyimide diaphragm and a non-woven fabric diaphragm.
9. The aqueous PVDF-coated lithium ion battery separator of claim 8, wherein: the base film is selected from a polyethylene diaphragm, and the thickness of the base film is 5-25 mu mm, the porosity is 30-60%, and the air permeability is 100-200 sec/100 cc.
10. A method of making the aqueous PVDF-coated lithium ion battery separator membrane of any of claims 1-9, characterized in that the method comprises:
(1) weighing the PVDF emulsion and the binder emulsion according to a ratio, stirring at room temperature for 5-15 minutes, and uniformly mixing to obtain a mixed emulsion;
(2) coating the PVDF mixed emulsion on one side or two sides of a base film to form a water-based coating;
(3) and drying in an oven at 50-90 ℃ to obtain the water-based PVDF coating lithium ion battery diaphragm.
11. The method of manufacturing according to claim 10, wherein: the coating manner is selected from at least one of gravure coating, slot coating, dip coating and spray coating.
12. Use of the aqueous PVDF coated lithium ion battery separator of claim 1, wherein: the battery diaphragm is applied to the field of high-energy-density power lithium ion batteries.
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Effective date of registration: 20210927 Address after: 312369 No. 5, Weiqi Road, Shangyu economic and Technological Development Zone, Hangzhou Bay, Shaoxing City, Zhejiang Province Applicant after: SINOCHEM LANTIAN FLUORINE MATERIAL Co.,Ltd. Applicant after: ZHEJIANG RESEARCH INSTITUTE OF CHEMICAL INDUSTRY Ltd. Applicant after: SINOCHEM LANTIAN Co.,Ltd. Address before: 310018 No.27, No.5 Street, Hangzhou Economic and Technological Development Zone, Zhejiang Province Applicant before: ZHEJIANG LANTIAN ENVIRONMENTAL PROTECTION HI-TECH Co.,Ltd. Applicant before: ZHEJIANG RESEARCH INSTITUTE OF CHEMICAL INDUSTRY Ltd. Applicant before: SINOCHEM LANTIAN Co.,Ltd. |
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