CN116031577A - Lithium battery composite diaphragm and preparation method thereof - Google Patents
Lithium battery composite diaphragm and preparation method thereof Download PDFInfo
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- CN116031577A CN116031577A CN202310027232.5A CN202310027232A CN116031577A CN 116031577 A CN116031577 A CN 116031577A CN 202310027232 A CN202310027232 A CN 202310027232A CN 116031577 A CN116031577 A CN 116031577A
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- lithium battery
- microsphere
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- 239000002131 composite material Substances 0.000 title claims abstract description 56
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 36
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 229920000642 polymer Polymers 0.000 claims abstract description 82
- 239000004005 microsphere Substances 0.000 claims abstract description 75
- 239000011258 core-shell material Substances 0.000 claims abstract description 44
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 41
- 239000010410 layer Substances 0.000 claims abstract description 27
- 239000004094 surface-active agent Substances 0.000 claims abstract description 25
- 239000006087 Silane Coupling Agent Substances 0.000 claims abstract description 23
- 239000006255 coating slurry Substances 0.000 claims abstract description 23
- 150000002148 esters Chemical class 0.000 claims abstract description 23
- 239000011148 porous material Substances 0.000 claims abstract description 21
- 239000011247 coating layer Substances 0.000 claims abstract description 18
- 239000000126 substance Substances 0.000 claims abstract description 17
- 239000011248 coating agent Substances 0.000 claims abstract description 13
- 238000000576 coating method Methods 0.000 claims abstract description 13
- 239000000463 material Substances 0.000 claims abstract description 13
- 230000003301 hydrolyzing effect Effects 0.000 claims abstract description 4
- 238000003756 stirring Methods 0.000 claims description 31
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 30
- -1 polyethylene Polymers 0.000 claims description 29
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 28
- 239000012528 membrane Substances 0.000 claims description 27
- 239000004698 Polyethylene Substances 0.000 claims description 21
- 229920000573 polyethylene Polymers 0.000 claims description 21
- 239000011257 shell material Substances 0.000 claims description 20
- 239000011162 core material Substances 0.000 claims description 17
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 16
- ZXEKIIBDNHEJCQ-UHFFFAOYSA-N isobutanol Chemical compound CC(C)CO ZXEKIIBDNHEJCQ-UHFFFAOYSA-N 0.000 claims description 16
- 239000002244 precipitate Substances 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- 229920003235 aromatic polyamide Polymers 0.000 claims description 13
- WYTZZXDRDKSJID-UHFFFAOYSA-N (3-aminopropyl)triethoxysilane Chemical compound CCO[Si](OCC)(OCC)CCCN WYTZZXDRDKSJID-UHFFFAOYSA-N 0.000 claims description 12
- LZZYPRNAOMGNLH-UHFFFAOYSA-M Cetrimonium bromide Chemical compound [Br-].CCCCCCCCCCCCCCCC[N+](C)(C)C LZZYPRNAOMGNLH-UHFFFAOYSA-M 0.000 claims description 12
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 claims description 12
- 238000001035 drying Methods 0.000 claims description 12
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 11
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 11
- 238000002844 melting Methods 0.000 claims description 11
- 239000002002 slurry Substances 0.000 claims description 11
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 claims description 10
- 239000006184 cosolvent Substances 0.000 claims description 10
- 239000002904 solvent Substances 0.000 claims description 10
- 229920006231 aramid fiber Polymers 0.000 claims description 9
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 claims description 8
- IMNFDUFMRHMDMM-UHFFFAOYSA-N N-Heptane Chemical compound CCCCCCC IMNFDUFMRHMDMM-UHFFFAOYSA-N 0.000 claims description 8
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 8
- 238000001914 filtration Methods 0.000 claims description 8
- 230000008018 melting Effects 0.000 claims description 8
- KPSSIOMAKSHJJG-UHFFFAOYSA-N neopentyl alcohol Chemical compound CC(C)(C)CO KPSSIOMAKSHJJG-UHFFFAOYSA-N 0.000 claims description 8
- 238000000614 phase inversion technique Methods 0.000 claims description 8
- 230000015572 biosynthetic process Effects 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 7
- 239000002245 particle Substances 0.000 claims description 7
- 239000004743 Polypropylene Substances 0.000 claims description 6
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 claims description 6
- 238000009835 boiling Methods 0.000 claims description 6
- 238000004140 cleaning Methods 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 6
- 229920001155 polypropylene Polymers 0.000 claims description 6
- 238000007493 shaping process Methods 0.000 claims description 6
- MTEZSDOQASFMDI-UHFFFAOYSA-N 1-trimethoxysilylpropan-1-ol Chemical compound CCC(O)[Si](OC)(OC)OC MTEZSDOQASFMDI-UHFFFAOYSA-N 0.000 claims description 4
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 claims description 4
- KKUKTXOBAWVSHC-UHFFFAOYSA-N Dimethylphosphate Chemical compound COP(O)(=O)OC KKUKTXOBAWVSHC-UHFFFAOYSA-N 0.000 claims description 4
- NHTMVDHEPJAVLT-UHFFFAOYSA-N Isooctane Chemical compound CC(C)CC(C)(C)C NHTMVDHEPJAVLT-UHFFFAOYSA-N 0.000 claims description 4
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 claims description 4
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 claims description 4
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 4
- 239000004793 Polystyrene Substances 0.000 claims description 4
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 4
- LMWDXGDQPKBWPQ-UHFFFAOYSA-M [Cl-].C(C)[N+](CC1=CC=CC=C1)(CC)CC.C(CCCCCCCCCCCCCCCCC)[NH-].C(C)[N+](CC)(CC)CC1=CC=CC=C1 Chemical compound [Cl-].C(C)[N+](CC1=CC=CC=C1)(CC)CC.C(CCCCCCCCCCCCCCCCC)[NH-].C(C)[N+](CC)(CC)CC1=CC=CC=C1 LMWDXGDQPKBWPQ-UHFFFAOYSA-M 0.000 claims description 4
- JVSWJIKNEAIKJW-UHFFFAOYSA-N dimethyl-hexane Natural products CCCCCC(C)C JVSWJIKNEAIKJW-UHFFFAOYSA-N 0.000 claims description 4
- XJWSAJYUBXQQDR-UHFFFAOYSA-M dodecyltrimethylammonium bromide Chemical compound [Br-].CCCCCCCCCCCC[N+](C)(C)C XJWSAJYUBXQQDR-UHFFFAOYSA-M 0.000 claims description 4
- IIEWJVIFRVWJOD-UHFFFAOYSA-N ethyl cyclohexane Natural products CCC1CCCCC1 IIEWJVIFRVWJOD-UHFFFAOYSA-N 0.000 claims description 4
- 239000005038 ethylene vinyl acetate Substances 0.000 claims description 4
- 239000000835 fiber Substances 0.000 claims description 4
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 4
- INJVFBCDVXYHGQ-UHFFFAOYSA-N n'-(3-triethoxysilylpropyl)ethane-1,2-diamine Chemical compound CCO[Si](OCC)(OCC)CCCNCCN INJVFBCDVXYHGQ-UHFFFAOYSA-N 0.000 claims description 4
- 239000003208 petroleum Substances 0.000 claims description 4
- 229920001200 poly(ethylene-vinyl acetate) Polymers 0.000 claims description 4
- 229920000747 poly(lactic acid) Polymers 0.000 claims description 4
- 229920003229 poly(methyl methacrylate) Polymers 0.000 claims description 4
- 229920002037 poly(vinyl butyral) polymer Polymers 0.000 claims description 4
- 239000004626 polylactic acid Substances 0.000 claims description 4
- 239000004926 polymethyl methacrylate Substances 0.000 claims description 4
- 229920002223 polystyrene Polymers 0.000 claims description 4
- 239000004800 polyvinyl chloride Substances 0.000 claims description 4
- 229920000915 polyvinyl chloride Polymers 0.000 claims description 4
- JMXKSZRRTHPKDL-UHFFFAOYSA-N titanium ethoxide Chemical compound [Ti+4].CC[O-].CC[O-].CC[O-].CC[O-] JMXKSZRRTHPKDL-UHFFFAOYSA-N 0.000 claims description 4
- 238000006555 catalytic reaction Methods 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 claims description 3
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 claims description 2
- 150000004645 aluminates Chemical class 0.000 claims description 2
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical compound [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 claims description 2
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 claims description 2
- 229910001626 barium chloride Inorganic materials 0.000 claims description 2
- FPCJKVGGYOAWIZ-UHFFFAOYSA-N butan-1-ol;titanium Chemical compound [Ti].CCCCO.CCCCO.CCCCO.CCCCO FPCJKVGGYOAWIZ-UHFFFAOYSA-N 0.000 claims description 2
- 239000001110 calcium chloride Substances 0.000 claims description 2
- 229910001628 calcium chloride Inorganic materials 0.000 claims description 2
- 229910001629 magnesium chloride Inorganic materials 0.000 claims description 2
- 239000004745 nonwoven fabric Substances 0.000 claims description 2
- 239000003960 organic solvent Substances 0.000 claims description 2
- 229920001721 polyimide Polymers 0.000 claims description 2
- 230000000379 polymerizing effect Effects 0.000 claims description 2
- 239000001103 potassium chloride Substances 0.000 claims description 2
- 235000011164 potassium chloride Nutrition 0.000 claims description 2
- 229910001631 strontium chloride Inorganic materials 0.000 claims description 2
- AHBGXTDRMVNFER-UHFFFAOYSA-L strontium dichloride Chemical compound [Cl-].[Cl-].[Sr+2] AHBGXTDRMVNFER-UHFFFAOYSA-L 0.000 claims description 2
- 230000008961 swelling Effects 0.000 abstract description 3
- 238000009833 condensation Methods 0.000 abstract 1
- 230000005494 condensation Effects 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 34
- 230000000052 comparative effect Effects 0.000 description 13
- 238000012360 testing method Methods 0.000 description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 7
- 235000019441 ethanol Nutrition 0.000 description 7
- 229910001416 lithium ion Inorganic materials 0.000 description 7
- 239000004760 aramid Substances 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 5
- 229920000098 polyolefin Polymers 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000001453 impedance spectrum Methods 0.000 description 4
- 238000003828 vacuum filtration Methods 0.000 description 4
- 239000000839 emulsion Substances 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 238000007789 sealing Methods 0.000 description 3
- 239000011149 active material Substances 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000004067 bulking agent Substances 0.000 description 2
- 238000005524 ceramic coating Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000001804 emulsifying effect Effects 0.000 description 2
- 238000003475 lamination Methods 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 229910052809 inorganic oxide Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical group [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000006068 polycondensation reaction Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- 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
Landscapes
- Cell Separators (AREA)
Abstract
The invention discloses a high-safety lithium battery composite diaphragm and a preparation method thereof, wherein the high-safety lithium battery composite diaphragm comprises a base film and a coating layer, the coating layer is obtained by coating a coating slurry comprising a heat-resistant high polymer solution, core-shell structure microspheres, a pore-forming agent and a silane coupling agent on the base film, and the heat-resistant high polymer content in the heat-resistant high polymer solution is 0.5-15wt%; the microsphere with the core-shell structure comprises a shell layer and a core: the material forming the shell layer material comprises hydrolytic condensation ester substances; the core-forming material comprises polymer microsphere, surfactant and swelling agent. The core-shell structure microspheres are added into the coating slurry, so that the prepared diaphragm has lower closed pore temperature and higher rupture temperature, further the safety of the diaphragm can be obviously improved, and double protection is provided for a battery. Meanwhile, the polymer microsphere is coated in the core by the microsphere with the core-shell structure, so that the influence of the chemically inert polymer microsphere on the battery performance can be avoided.
Description
Technical Field
The invention relates to a lithium ion battery, in particular to a high-safety lithium battery composite diaphragm and a preparation method thereof.
Background
The diaphragm is a barrier which plays a safety function in the lithium ion battery, the diaphragm which is commonly used at present is made of polyolefin materials, the melting point of the diaphragm is lower, the temperature is generally lower than 150 ℃, the high-temperature heat resistance is poor, when the internal temperature of the battery is close to the thermal deformation temperature of the diaphragm, the diaphragm can shrink and deform, and then the positive electrode and the negative electrode can be in direct contact to cause internal thermal runaway. As the energy density of the battery increases, the separator used in the battery is also gradually thinned, but this greatly increases the risk and hazard of short circuits occurring in the battery.
In order to improve the defects of the polyolefin membrane and improve the endurance mileage and the heat resistance, ceramic modification is usually carried out on the polyolefin membrane, and the ceramic coating is used for improving the wettability and the heat resistance of the membrane and the electrolyte. However, this method can only improve the heat resistance of the separator to a certain extent because the base film is polyolefin, and cannot raise the rupture temperature of the separator to 200 ℃.
When thermal runaway occurs in the battery, a large amount of heat is generated, at the moment, if the diaphragm is closed rapidly in time at the initial stage of the thermal runaway, then continuous transmission of ions is blocked to form open circuit, the effect of protecting the battery can be achieved, and the temperature at which the micropores are closed is the closed-pore temperature. For lithium batteries, it is desirable that the closed cell temperature is somewhat lower, and that the cells are closed when the temperature increases, preventing the occurrence of short circuits, thereby improving the safety of the battery. If the battery triggers further thermal runaway, if the used diaphragm has higher rupture temperature, the diaphragm can have better integrity in a certain temperature range, and the contact of the positive electrode plate and the negative electrode plate can not be caused by thermal shrinkage at high temperature or deformation at lower rupture temperature so as to cause further battery runaway.
In general, the polyolefin material has a closed cell temperature of 130-140 ℃, the closed cell temperature is not greatly changed after the heat-resistant inorganic ceramic coating is coated, and the rupture (thermal shrinkage deformation) temperature is 150-170 ℃. The safe use of the diaphragm has a small closed pore-rupture temperature interval, and the safety performance of the battery is not greatly ensured only at about 40 ℃.
The Chinese patent publication No. CN 113013547A discloses a lithium battery composite diaphragm and a preparation method thereof, and the safety of the lithium battery composite diaphragm needs to be further improved.
Therefore, there is a need to develop a composite membrane and a preparation method thereof that can greatly increase the membrane rupture temperature and reduce the closed cell temperature, and double-improve the safety performance of the battery.
Disclosure of Invention
The invention aims to solve the defects of the background technology, and provides a composite diaphragm capable of greatly improving the diaphragm rupture temperature and reducing the closed pore temperature and a preparation method thereof, and the composite diaphragm is double in improvement of the safety performance of a battery.
The technical scheme of the invention is as follows: a lithium battery composite diaphragm, the diaphragm is baked at 250 ℃ for 1h, the heat shrinkage rate in MD direction and TD direction is less than 1.5%, the closed pore temperature of the diaphragm is less than or equal to 125 ℃, and the rupture temperature is more than or equal to 300 ℃.
Preferably, the membrane ion conductivity is greater than 0.7mS/cm;
the membrane comprises a base membrane and a coating layer, wherein the coating layer comprises a core-shell structure microsphere, and the core-shell structure microsphere comprises a shell layer and a core: the material forming the shell layer material comprises a hydrolytically polymerizable ester substance; the material forming the core comprises polymer microspheres and an expanding agent, wherein the melting point of the polymer microspheres is 90-120 ℃, and the expanding agent is an organic solvent with the boiling point lower than 120 ℃.
Further, the coating layer further comprises at least one of a heat-resistant polymer solution, a pore-forming agent and a silane coupling agent;
and/or the core-forming material further comprises a surfactant;
the ester substance is at least one selected from tetraethoxysilane, tetrabutyl orthotitanate, tetraethyl orthotitanate, triisopropyl aluminate and trimethyl aluminate;
and/or the content of the heat-resistant high polymer in the heat-resistant high polymer solution is 0.5-15 wt%; the heat-resistant high polymer is at least one of para-aramid fiber and meta-aramid fiber;
and/or the mass ratio of the core-shell structure microsphere, the heat-resistant polymer, the pore-forming agent and the silane coupling agent is 1 (0.3-2.5) (0.04-0.2) (0.02-0.35).
Further, the polymer microsphere is at least one selected from polystyrene, polyethylene, polymethyl methacrylate, polypropylene, polyacrylic acid-butadiene-styrene, polylactic acid, polyvinyl chloride, ethylene-vinyl acetate copolymer and polyvinyl butyral;
the surfactant is at least one selected from octadecyl amide ethyl diethyl benzyl ammonium chloride, octadecyl amide ethyl trimethyl ammonium sulfate, dodecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide;
the expanding agent is at least one selected from n-butanol, isobutanol, neopentyl alcohol, heptane, isooctane and petroleum ether;
the mass ratio of the polymer microsphere to the surfactant to the expanding agent is 1 (0.5-1) (0.08-0.2);
the mass ratio of the surfactant in the core material to the ester substance in the shell material is 1 (0.25-2);
the particle diameter D50 of the core-shell structure microsphere is 200-600nm, and the thickness of the shell layer is 10-40nm.
Still further, the pore-forming agent is selected from at least one of dimethyl carbonate, ethyl acetate, cyclohexane or dimethyl phosphate;
the silane coupling agent is at least one selected from gamma-aminopropyl triethoxysilane, gamma-glycidol ether oxypropyl trimethoxysilane, gamma- (methylpropanoyloxy) propyl trimethoxysilane, gamma-aminopropyl triethoxysilane, gamma- (methacryloyloxy) propyl trimethoxysilane, N- (beta-aminoethyl) -gamma-aminopropyl triethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyl methyl dimethoxy silane.
Preferably, the thickness of the coating layer is 0.5-4 mu m, the closed pore temperature of the lithium battery composite membrane is 100-125 ℃, and the membrane rupture temperature is 300-600 ℃.
The heat shrinkage rates of the composite diaphragm prepared by the invention in the MD direction and the TD direction after baking at 250 ℃ for 1h are less than 1.5%, the closed pore temperature of the diaphragm is less than or equal to 125 ℃, and the rupture temperature is more than or equal to 300 ℃. Therefore, the composite membrane prepared by the invention has lower closed pore temperature and higher membrane breaking temperature, and simultaneously has lower heat shrinkage in the MD direction and the TD direction, and achieves good balance in the closed pore temperature, the membrane breaking temperature and the heat shrinkage, thereby obviously improving the safety of the membrane and finally providing better double protection for the battery.
The invention also provides a preparation method of the lithium battery composite diaphragm, which comprises the following steps:
s1, dissolving a cosolvent in a first solvent to obtain a first solution, adding a heat-resistant polymer into the first solution, and completely dissolving to obtain a heat-resistant polymer solution with the heat-resistant polymer content of 0.5-15 wt%, wherein the heat-resistant polymer is at least one of para-aramid fiber and meta-aramid fiber;
s2, ultrasonically dispersing the polymer microsphere, the surfactant and the expanding agent in an absolute ethyl alcohol medium to form a core, adding the ester substances, uniformly stirring, then adding ammonia water for catalysis, keeping stirring until the reaction is complete, hydrolyzing and polymerizing the ester substances to form a shell layer on the surface of the core, filtering, and cleaning, filtering and drying the obtained precipitate to obtain the microsphere with a core-shell structure;
s3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent and a silane coupling agent, uniformly stirring, and then adjusting the viscosity of the slurry to 20-600 mPa.S to obtain coating slurry;
s4, coating the coating slurry obtained in the step S3 on a base film, immersing the base film in water for film formation by a phase inversion method, and drying, cooling and shaping to obtain the lithium battery composite diaphragm.
Preferably, in the step S1, the cosolvent is at least one selected from calcium chloride, lithium chloride, potassium chloride, magnesium chloride, strontium chloride and barium chloride, the first solvent is at least one selected from N-methylpyrrolidone NMP, N-dimethylacetamide DMAc, N-dimethylformamide DMF or dimethyl sulfoxide DMSO, and the mass ratio of the cosolvent to the first solvent is (1-4): 100;
in step S2, the polymer microsphere is at least one selected from polystyrene, polyethylene, polymethyl methacrylate, polypropylene, polyacrylic acid-butadiene-styrene, polylactic acid, polyvinyl chloride, ethylene-vinyl acetate copolymer, and polyvinyl butyral;
the surfactant is at least one selected from octadecyl amide ethyl diethyl benzyl ammonium chloride, octadecyl amide ethyl trimethyl ammonium sulfate, dodecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide;
the expanding agent comprises at least one of n-butanol, isobutanol, neopentyl alcohol, heptane, isooctane and petroleum ether;
the mass ratio of the polymer microsphere to the surfactant to the expanding agent is 1 (0.5-1) (0.08-0.2);
the mass ratio of the surfactant in the core material to the ester substance in the shell material is 1 (0.25-2), the mass concentration of the ammonia water is 23-28%, and the mass ratio of the ester substance to the ammonia water is 1 (2-4).
Preferably, in the step S3, the mass ratio of the core-shell structure microsphere, the heat-resistant polymer, the pore-forming agent and the silane coupling agent is 1 (0.3-2.5) (0.04-0.2) (0.02-0.35);
the pore-forming agent is at least one selected from dimethyl carbonate, ethyl acetate, cyclohexane or dimethyl phosphate;
the silane coupling agent is at least one selected from gamma-aminopropyl triethoxysilane, gamma-glycidol ether oxypropyl trimethoxysilane, gamma- (methylpropanoyloxy) propyl trimethoxysilane, gamma- (methacryloyloxy) propyl trimethoxysilane, N- (beta-aminoethyl) -gamma-aminopropyl triethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyl methyl dimethoxy silane.
Preferably, in step S4, the thickness of the base film is 4-20 μm, and the base film is one of a polyethylene microporous film, a polypropylene microporous film, a polyethylene-polypropylene-polyethylene three-layer composite porous film, a polyimide film or a non-woven fabric film;
the thickness of a coating layer on the surface of a base film in the prepared high-safety lithium battery composite diaphragm is 0.5-4 mu m, the closed pore temperature of the prepared high-safety lithium battery composite diaphragm is 100-125 ℃, and the rupture temperature is 300-600 ℃.
Preferably, in the step S1, the heat-resistant polymer is heated in a water bath at 70-80 ℃ when being added into the first dissolving solution for dissolution.
Preferably, in the step S2, the D50 particle size of the obtained microsphere with the core-shell structure is 200-600nm, and the shell thickness is 10-40nm.
Preferably, in step S2, polymer microspheres, a surfactant and an expanding agent are ultrasonically dispersed in an absolute ethanol medium to form a core, an ester substance is added after stirring for 1-2 hours at 60-70 ℃, ammonia water is added for catalysis after uniform stirring at a temperature of 60-70 ℃, the stirring at a temperature of continuous stirring is carried out until the reaction is completed, the ester substance is hydrolyzed and polymerized on the surface of the core to form a shell layer, and the obtained precipitate is filtered, washed, filtered and dried to obtain the microsphere with a core-shell structure.
Preferably, in step S3, the solid content of the coating slurry is 5% -40%.
In the step S2, when the polymer microsphere is dispersed in the ethanol containing the surfactant, the surfactant forms an emulsifying layer to cover the surface of the polymer microsphere, and the expanding agent is wrapped in the emulsifying layer to form a stable polymer microsphere/ethanol emulsion. In step S2, when the ester is added to the polymer microsphere/ethanol emulsion, the ester is captured by the surfactant layer due to the amphiphilicity of the ester, and the ester exists on the surface of the polymer microsphere. When ammonia is added to an emulsion containing polymeric microspheres and an ester, the ammonia catalyzes the hydrolytic polycondensation of the ester to form an inorganic oxide coating.
The invention has the following beneficial effects:
(1) According to the invention, the core-shell structure microspheres are added in the coating slurry, when the internal temperature of the battery exceeds 90 ℃, the expanding agent in the core of the core-shell structure microspheres rapidly expands, so that the shell layer is cracked, the low-melting polymer microspheres in the core are released, and the low-melting polymer melts to block micropores of the base film, so that the diaphragm has low closed pore temperature, and the safety performance of the diaphragm is improved.
(2) The silane coupling agent in the coating slurry contains polar and nonpolar groups at the same time, so that the silane coupling agent can be combined with the microsphere with the core-shell structure and the heat-resistant polymer and can be combined with the base film, the combination firmness of the coating and the base film is improved, the cohesive force of the coating is enhanced, the rupture temperature of the diaphragm is improved, and the thermal stability of the diaphragm is improved. Therefore, the membrane prepared by the invention has lower closed pore temperature and higher membrane rupture temperature, thereby obviously improving the safety of the membrane and providing double protection for the battery.
(3) The shell layer of the microsphere with the core-shell structure is made of inorganic materials, has the property of being compatible with electrolyte, can reduce direct contact between a core which is not infiltrated and not compatible with the electrolyte and the electrolyte, reduces the internal resistance of a battery, improves the safety of the battery, and ensures the exertion of the battery capacity.
(4) The heat shrinkage rates of the composite diaphragm prepared by the invention in the MD direction and the TD direction after baking at 250 ℃ for 1h are less than 1.5%, the closed pore temperature of the diaphragm is less than or equal to 125 ℃, and the rupture temperature is more than or equal to 300 ℃. Therefore, the composite membrane prepared by the invention has lower closed pore temperature and higher membrane breaking temperature, and simultaneously has lower heat shrinkage in the MD direction and the TD direction, and achieves good balance in the closed pore temperature, the membrane breaking temperature and the heat shrinkage, thereby obviously improving the safety of the membrane and finally providing better double protection for the battery.
Detailed Description
The invention is illustrated in further detail by the following specific examples. The drugs used in the examples are commercially available products unless otherwise specified, and the methods used are conventional in the art.
Example 1
The invention provides a preparation method of a high-safety lithium battery composite diaphragm, which comprises the following steps:
s1, preparing a heat-resistant high polymer solution: cosolvent CaCl 2 Dissolving in a first solvent NMP to obtain a first solution, caCl 2 The mass ratio of the N-methyl pyrrolidone to NMP is 1:100, adding heat-resistant high polymer (meta-aramid) into the first solution, wherein the mass ratio of the meta-aramid to the first solution5.5:100 Heating and stirring in 70 ℃ water bath for 3 hours until meta-aramid fiber is completely dissolved, isolating air, and standing to room temperature to obtain a heat-resistant high polymer solution;
s2, preparing core-shell structure microspheres: polymer microspheres (powdered polyethylene, 2g, melting point 100 ℃), surfactant (cetyltrimethylammonium bromide, CTAB,1.5 g) and bulking agent (isobutanol, density 0.803g/cm3,0.4mL, boiling point 105 ℃) were mixed with 100mL of absolute ethanol and dispersed sonically in a 250mL three-necked flask;
stirring at 60deg.C for 60 min, dripping 1.4g (1.5 mL, density 0.94 g/cm) of ethyl orthosilicate 3 ) Then keeping the temperature at 60 ℃, stirring for 30 minutes, then dripping 4.5g of 25% ammonia water by mass concentration, continuously stirring at 60 ℃ for 2 hours to react completely, filtering to obtain precipitate, fully cleaning the precipitate with ethanol, collecting the precipitate through vacuum filtration, and finally drying at 50 ℃ for 12 hours to obtain the microsphere with the core-shell structure, wherein the particle diameter D50 of the microsphere with the core-shell structure is 428nm, and the thickness of the shell layer is 25nm.
S3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent (dimethyl carbonate) and a silane coupling agent (gamma-aminopropyl triethoxysilane (APTES)), wherein the respective dosages of the core-shell structure microsphere, the heat-resistant high polymer, the pore-forming agent and the silane coupling agent are 200g, 300g, 30g and 40g, uniformly stirring, and then adjusting the viscosity of the slurry to obtain a coating slurry with the solid content of 18.9% and the viscosity of 103 mPa.S;
s4, coating the coating slurry obtained in the step S3 on a base film (a polyethylene film with the thickness of 7 mu m), immersing the base film in water for film formation by a phase inversion method, drying, cooling and shaping to obtain the high-safety lithium battery composite diaphragm, wherein the thickness of the coating layer formed by the coating slurry is measured to be 2.98 mu m.
Example 2
The invention provides a preparation method of a high-safety lithium battery composite diaphragm, which comprises the following steps:
s1, preparing a heat-resistant high polymer solution: cosolvent CaCl 2 Dissolving in a first solvent NMP to obtain a first solution, caCl 2 The mass ratio of the N-methyl pyrrolidone to NMP is 1:100, adding heat-resistant high polymer (meta-aramid) into the first solutionThe mass ratio of meta-aramid to the first dissolving solution is 5.5:100 Heating and stirring in 70 ℃ water bath for 3 hours until meta-aramid fiber is completely dissolved, isolating air, and standing to room temperature to obtain a heat-resistant high polymer solution;
s2, preparing core-shell structure microspheres: polymer microspheres (powdered polyethylene, 2g, melting point 100 ℃ C.), surfactant (cetyltrimethylammonium bromide CTAB,1.5 g) and swelling agent (isobutanol, 0.803 g/cm) 3 0.4mL of absolute ethyl alcohol with the boiling point of 105 ℃ and 100mL of absolute ethyl alcohol are mixed, and the mixture is dispersed in a three-neck flask with 250mL by ultrasonic;
stirring at 60deg.C for 60 min, dripping 1.4g (1.5 mL, density 0.94 g/cm) of ethyl orthosilicate 3 ) Then keeping the temperature at 60 ℃, stirring for 30 minutes, then dripping 4.5g of 25% ammonia water by mass concentration, continuously stirring at 60 ℃ for 2 hours to react completely, filtering to obtain precipitate, fully cleaning the precipitate with ethanol, collecting the precipitate through vacuum filtration, and finally drying at 50 ℃ for 12 hours to obtain the microsphere with the core-shell structure, wherein the particle diameter D50 of the microsphere with the core-shell structure is 428nm, and the thickness of the shell layer is 25nm.
S3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent (dimethyl carbonate) and a silane coupling agent (gamma-aminopropyl triethoxysilane), wherein the dosages of the core-shell structure microsphere, the heat-resistant high polymer, the pore-forming agent and the silane coupling agent are respectively 200g, 67g, 30g and 40g, uniformly stirring, and then adjusting the viscosity of the slurry to obtain a coating slurry with the solid content of 19.1% and the viscosity of 152 mPa.S;
s4, coating the coating slurry obtained in the step S3 on a base film (a polyethylene film with the thickness of 7 mu m), immersing the base film in water for film formation by a phase inversion method, drying, cooling and shaping to obtain the high-safety lithium battery composite diaphragm, wherein the thickness of the coating layer formed by the coating slurry is 3.02 mu m.
Example 3
The invention provides a preparation method of a high-safety lithium battery composite diaphragm, which comprises the following steps:
s1, preparing a heat-resistant high polymer solution: cosolvent CaCl 2 Dissolving in a first solvent NMP to obtain a first solution, caCl 2 The mass ratio of the N-methyl pyrrolidone to NMP is 1:100, heat-resistant high polymer is preparedPara-aramid) is added into the first dissolving solution, and the mass ratio of the para-aramid to the first dissolving solution is 5.5:100 Heating and stirring in 70 ℃ water bath for 3 hours until meta-aramid fiber is completely dissolved, isolating air, and standing to room temperature to obtain a heat-resistant high polymer solution;
s2, preparing core-shell structure microspheres: polymer microspheres (powdered polyethylene, 2g, melting point 100 ℃ C.), surfactant (cetyltrimethylammonium bromide CTAB,1.5 g) and swelling agent (isobutanol, 0.803 g/cm) 3 0.4mL of absolute ethyl alcohol with the boiling point of 105 ℃ and 100mL of absolute ethyl alcohol are mixed, and the mixture is dispersed in a three-neck flask with 250mL by ultrasonic;
stirring at 60deg.C for 60 min, dripping 1.4g (1.5 mL, density 0.94 g/cm) of ethyl orthosilicate 3 ) Then keeping the temperature at 60 ℃, stirring for 30 minutes, then dripping 4.5g of 25% ammonia water by mass concentration, continuously stirring at 60 ℃ for 2 hours to react completely, filtering to obtain precipitate, fully cleaning the precipitate with ethanol, collecting the precipitate through vacuum filtration, and finally drying at 50 ℃ for 12 hours to obtain the microsphere with the core-shell structure, wherein the particle diameter D50 of the microsphere with the core-shell structure is 428nm, and the thickness of the shell layer is 25nm.
S3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent (dimethyl carbonate) and a silane coupling agent (gamma-aminopropyl triethoxysilane (APTES)), wherein the respective dosages of the core-shell structure microsphere, the heat-resistant high polymer, the pore-forming agent and the silane coupling agent are 200g, 300g, 30g and 40g, uniformly stirring, and then adjusting the viscosity of the slurry to obtain a coating slurry with the solid content of 18.3% and the viscosity of 114 mPa.S;
s4, coating the coating slurry obtained in the step S3 on a base film (a polyethylene film with the thickness of 7 mu m), immersing the base film in water for film formation by a phase inversion method, drying, cooling and shaping to obtain the high-safety lithium battery composite diaphragm, wherein the thickness of the coating layer formed by the coating slurry is 3.01 mu m.
Example 4
The invention provides a preparation method of a high-safety lithium battery composite diaphragm, which comprises the following steps:
s1, preparing a heat-resistant high polymer solution: cosolvent CaCl 2 Dissolving in a first solvent NMP to obtain a first solution, caCl 2 The mass ratio of the N-methyl pyrrolidone to NMP is 1:100, adding a heat-resistant high polymer (para-aramid) into the first solution, wherein the mass ratio of the para-aramid to the first solution is 5.5:100 Heating and stirring in 70 ℃ water bath for 3 hours until meta-aramid fiber is completely dissolved, isolating air, and standing to room temperature to obtain a heat-resistant high polymer solution;
s2, preparing core-shell structure microspheres: polymer microspheres (powdered polyethylene, 2g, melting point 100 ℃), surfactant (cetyltrimethylammonium bromide CTAB,1.5 g) and bulking agent (isobutanol, 0.4mL, boiling point 105 ℃) were mixed with 100mL of absolute ethanol and dispersed ultrasonically in a 250mL three-necked flask;
stirring at 60deg.C for 60 min, dripping 1.4g (1.5 mL, density 0.94 g/cm) of ethyl orthosilicate 3 ) Then keeping the temperature at 60 ℃, stirring for 30 minutes, then dripping 4.5g of 25% ammonia water by mass concentration, continuously stirring at 60 ℃ for 2 hours to react completely, filtering to obtain precipitate, fully cleaning the precipitate with ethanol, collecting the precipitate through vacuum filtration, and finally drying at 50 ℃ for 12 hours to obtain the microsphere with the core-shell structure, wherein the particle diameter D50 of the microsphere with the core-shell structure is 428nm, and the thickness of the shell layer is 25nm.
S3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent (dimethyl carbonate) and a silane coupling agent (gamma-aminopropyl triethoxysilane), wherein the dosages of the core-shell structure microsphere, the heat-resistant high polymer, the pore-forming agent and the silane coupling agent are respectively 200g, 67g, 30g and 40g, and uniformly stirring, and then adjusting the viscosity of the slurry to obtain a coating slurry with the solid content of 19.5% and the viscosity of 126 mPa.S;
s4, coating the coating slurry obtained in the step S3 on a base film (a polyethylene film with the thickness of 7 mu m), immersing the base film in water for film formation by a phase inversion method, drying, cooling and shaping to obtain the high-safety lithium battery composite diaphragm, wherein the thickness of the coating layer formed by the coating slurry is measured to be 2.97 mu m.
Comparative example 1
The specific preparation method of the composite diaphragm of the comparative example is as follows:
1) Preparing a heat-resistant high polymer solution: the same as in example 1
2) Preparation of the slurry: polyethylene microspheres (melting point 100 ℃) were dissolved in 250ml NMP and mixed with the heat resistant polymer solution obtained in step 1) and alumina (d50=0.8 μm), wherein the polyethylene microspheres: aramid fiber: the mass ratio of the alumina is 2:6:4, and the obtained mixed solution is uniformly stirred to obtain slurry;
3) Preparation of the coating: the coating slurry was coated on a 7 μm polyethylene-based film, immersed in water to form a film by a phase inversion method, and then dried and cooled to fix the film, thereby obtaining a composite separator of comparative example 1, wherein the thickness of the formed coating layer was 3. Mu.m.
Comparative example 2
The specific preparation method of the composite diaphragm of the comparative example is as follows:
1) Preparing a heat-resistant high polymer solution: the same as in example 1
2) Preparation of the slurry: mixing the heat-resistant polymer solution obtained in step 1) with alumina (d50=0.8 μm), wherein the aramid: the mass ratio of the alumina is 6:4, and the obtained mixed solution is uniformly stirred to obtain slurry;
3) Preparation of the coating: the coating slurry was coated on a 7 μm polyethylene-based film, immersed in water to form a film by a phase inversion method, and then dried and cooled to fix the film, thereby obtaining a composite separator of comparative example 1, wherein the thickness of the formed coating layer was 3. Mu.m.
Performance detection
The composite separators of examples 1 to 4 and comparative examples 1 to 2 were assembled together with positive and negative electrode sheets, respectively, to obtain lithium ion batteries of examples 1 to 4 and comparative examples 1 to 2.
The preparation method comprises the following steps: stirring, coating, rolling, slitting and the like the positive plate and the negative plate are prepared by the positive plate slurry, wherein the active material of the positive plate is lithium iron phosphate, and the active material of the negative plate is artificial graphite. The positive plate, the composite diaphragm and the negative plate are placed in a lamination way and are subjected to lamination and top sealing to prepare a soft package lithium ion battery, and then the soft package lithium ion battery is placed in a vacuum oven at 80 ℃ to be baked for 12-24 hours; when the mixed water content of the bare cell negative electrode sheet is less than 150ppm, the soft package lithium ion battery is finally obtained by performing the procedures of automatic liquid injection, high-temperature standing, negative pressure formation, sealing welding, capacity division, detection and the like. The following data were collected and tested for the composite separators and lithium ion batteries of examples 1-4 and comparative examples 1-2:
1. diaphragm closed cell temperature
And recording the resistance values at different temperatures by adopting a temperature rise internal resistance method, wherein the temperature corresponding to the maximum point of the resistance values is the closed pore temperature.
2. Diaphragm rupture temperature
Adopting a TMA instrument to test, and recording a change curve of the diaphragm length along with the temperature until the diaphragm is broken; the temperature when the diaphragm length is instantaneously increased is the diaphragm rupture temperature according to the temperature change curve of the diaphragm length.
3. Ion conductivity of separator
And placing the diaphragm into electrolyte with the temperature of 23+/-2 ℃, keeping sealing, and soaking for 2 hours. And injecting electrolyte into the resistance test die, connecting the resistance test die with an electrochemical workstation, and setting test parameters. Sequentially placing 1 layer of membrane, testing its impedance spectrum, placing one layer, testing its impedance spectrum until it is placed in 4 layers, measuring four impedance spectra, and respectively reading the resistance R of 1-4 layers from the impedance spectra 1 、R 2 、R 3 And R is 4 . Where σ=d/(r×s). Sigma: ion conductivity; d: the thickness of the single layer separator; r: a resistance value; s: the membrane area was tested.
4.250 ℃ and 1h heat shrinkage rate
The composite separator was sandwiched with printing paper, put in an oven at 250 ℃ for baking for 1 hour, and the dimensions of the separator in MD direction and TD direction before and after baking were recorded, heat shrinkage=1-post baking dimension/pre baking dimension.
5. Battery cycle capacity retention rate
The testing method comprises the following steps: at 25 ℃, the battery after capacity division is charged to 3.65V according to a constant current and a constant voltage of 1.0C, the cut-off current is 0.05C, then the battery is discharged to 2.5V according to a constant current of 1.0C, the cycle is carried out, the 2500 th cycle of charge and discharge is followed by calculating the 2500 th cycle capacity retention rate, and the calculation formula is as follows: the 2500 th cycle capacity retention (%) = (2500 th cycle discharge capacity/first cycle discharge capacity) ×100%.
The test results of the above properties are shown in Table 1.
TABLE 1
As can be seen from table 1 above, the functional separators with safety performance prepared in examples 1 to 4 of the present invention have higher heat resistance, the heat shrinkage at 250 ℃ is less than 1.5% for 1h, and the heat shrinkage at 250 ℃ is more than 5% for 1h for the composite separators prepared in comparative examples 1 to 2; in addition, as can be seen from the above table 1, the closed pore temperatures of the functional diaphragms with safety performance prepared in examples 1 to 4 of the present invention are all less than 125 ℃, and the rupture temperatures are all more than 300 ℃. Although the closed pore temperature of the composite membrane prepared in the comparative example 1 is also less than 125 ℃, the ion transmission performance of the membrane is affected due to the direct contact of the electrolyte-inert polyethylene and the electrolyte; in comparative example 2, only the heat-resistant high polymer porous layer is provided, no low-melting polymer is added, the diaphragm has no closed pore temperature, and the diaphragm can directly break after reaching a certain temperature.
In summary, the safety windows of the composite diaphragms prepared in comparative examples 1-2 are significantly smaller than the functional diaphragms with safety performance prepared in examples 1-4 of the present invention, and the composite diaphragms prepared in examples 1-4 do not affect the electrical performance of the battery.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (10)
1. A lithium battery composite diaphragm is characterized in that the heat shrinkage rates of the diaphragm in the MD direction and the TD direction after being baked at 250 ℃ for 1h are less than 1.5%, the closed pore temperature of the diaphragm is less than or equal to 125 ℃, and the rupture temperature of the diaphragm is more than or equal to 300 ℃.
2. The lithium battery composite separator of claim 1, wherein the separator ionic conductivity is greater than 0.7mS/cm;
the membrane comprises a base membrane and a coating layer, wherein the coating layer comprises a core-shell structure microsphere, and the core-shell structure microsphere comprises a shell layer and a core: the material forming the shell layer material comprises a hydrolytically polymerizable ester substance; the material forming the core comprises polymer microspheres and an expanding agent, wherein the melting point of the polymer microspheres is 90-120 ℃, and the expanding agent is an organic solvent with the boiling point lower than 120 ℃.
3. The lithium battery composite separator according to claim 2, wherein the coating layer further comprises at least one of a heat-resistant polymer solution, a pore-forming agent, and a silane coupling agent;
and/or the core-forming material further comprises a surfactant;
the ester substance is at least one selected from tetraethoxysilane, tetrabutyl orthotitanate, tetraethyl orthotitanate, triisopropyl aluminate and trimethyl aluminate;
and/or the content of the heat-resistant high polymer in the heat-resistant high polymer solution is 0.5-15 wt%; the heat-resistant high polymer is at least one of para-aramid fiber and meta-aramid fiber;
and/or the mass ratio of the core-shell structure microsphere, the heat-resistant polymer, the pore-forming agent and the silane coupling agent is 1 (0.3-2.5) (0.04-0.2) (0.02-0.35).
4. The lithium battery composite separator according to claim 3, wherein the polymer microspheres are selected from at least one of polystyrene, polyethylene, polymethyl methacrylate, polypropylene, polyacrylic acid-butadiene-styrene, polylactic acid, polyvinyl chloride, ethylene-vinyl acetate copolymer, and polyvinyl butyral;
the surfactant is at least one selected from octadecyl amide ethyl diethyl benzyl ammonium chloride, octadecyl amide ethyl trimethyl ammonium sulfate, dodecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide;
the expanding agent is at least one selected from n-butanol, isobutanol, neopentyl alcohol, heptane, isooctane and petroleum ether;
the mass ratio of the polymer microsphere to the surfactant to the expanding agent is 1 (0.5-1) (0.08-0.2);
the mass ratio of the surfactant in the core material to the ester substance in the shell material is 1 (0.25-2);
the particle diameter D50 of the core-shell structure microsphere is 200-600nm, and the thickness of the shell layer is 10-40nm.
5. The lithium battery composite separator according to claim 3, wherein the pore-forming agent is selected from at least one of dimethyl carbonate, ethyl acetate, cyclohexane, or dimethyl phosphate;
the silane coupling agent is at least one selected from gamma-aminopropyl triethoxysilane, gamma-glycidol ether oxypropyl trimethoxysilane, gamma- (methylpropanoyloxy) propyl trimethoxysilane, gamma-aminopropyl triethoxysilane, gamma- (methacryloyloxy) propyl trimethoxysilane, N- (beta-aminoethyl) -gamma-aminopropyl triethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyl methyl dimethoxy silane.
6. The lithium battery composite separator according to claim 2, wherein the thickness of the coating layer is 0.5-4 μm, the closed pore temperature of the lithium battery composite separator is 100-125 ℃, and the rupture temperature is 300-600 ℃.
7. A method for preparing the lithium battery composite separator according to any one of claims 1 to 6, comprising the steps of:
s1, dissolving a cosolvent in a first solvent to obtain a first solution, adding a heat-resistant polymer into the first solution, and completely dissolving to obtain a heat-resistant polymer solution with the heat-resistant polymer content of 0.5-15 wt%, wherein the heat-resistant polymer is at least one of para-aramid fiber and meta-aramid fiber;
s2, ultrasonically dispersing the polymer microsphere, the surfactant and the expanding agent in an absolute ethyl alcohol medium to form a core, adding the ester substances, uniformly stirring, then adding ammonia water for catalysis, keeping stirring until the reaction is complete, hydrolyzing and polymerizing the ester substances to form a shell layer on the surface of the core, filtering, and cleaning, filtering and drying the obtained precipitate to obtain the microsphere with a core-shell structure;
s3, mixing the heat-resistant high polymer solution obtained in the step S1 and the core-shell structure microsphere obtained in the step S2, adding a pore-forming agent and a silane coupling agent, uniformly stirring, and then adjusting the viscosity of the slurry to 20-600 mPa.S to obtain coating slurry;
s4, coating the coating slurry obtained in the step S3 on a base film, immersing the base film in water for film formation by a phase inversion method, and drying, cooling and shaping to obtain the lithium battery composite diaphragm.
8. The method for preparing a lithium battery composite separator according to claim 7, wherein in the step S1, the cosolvent is at least one selected from calcium chloride, lithium chloride, potassium chloride, magnesium chloride, strontium chloride and barium chloride, the first solvent is at least one selected from N-methylpyrrolidone NMP, N-dimethylacetamide DMAc, N-dimethylformamide DMF and dimethylsulfoxide DMSO, and the mass ratio of the cosolvent to the first solvent is (1-4): 100;
in step S2, the polymer microsphere is at least one selected from polystyrene, polyethylene, polymethyl methacrylate, polypropylene, polyacrylic acid-butadiene-styrene, polylactic acid, polyvinyl chloride, ethylene-vinyl acetate copolymer, and polyvinyl butyral;
the surfactant is at least one selected from octadecyl amide ethyl diethyl benzyl ammonium chloride, octadecyl amide ethyl trimethyl ammonium sulfate, dodecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide;
the expanding agent comprises at least one of n-butanol, isobutanol, neopentyl alcohol, heptane, isooctane and petroleum ether;
the mass ratio of the polymer microsphere to the surfactant to the expanding agent is 1 (0.5-1) (0.08-0.2);
the mass ratio of the surfactant in the core material to the ester substance in the shell material is 1 (0.25-2), the mass concentration of the ammonia water is 23-28%, and the mass ratio of the ester substance to the ammonia water is 1 (2-4).
9. The preparation method of the lithium battery composite diaphragm according to claim 7, wherein in the step S3, the mass ratio of the core-shell structure microsphere to the heat-resistant polymer to the pore-forming agent to the silane coupling agent is 1 (0.3-2.5) (0.04-0.2) (0.02-0.35);
the pore-forming agent is at least one selected from dimethyl carbonate, ethyl acetate, cyclohexane or dimethyl phosphate;
the silane coupling agent is at least one selected from gamma-aminopropyl triethoxysilane, gamma-glycidol ether oxypropyl trimethoxysilane, gamma- (methylpropanoyloxy) propyl trimethoxysilane, gamma- (methacryloyloxy) propyl trimethoxysilane, N- (beta-aminoethyl) -gamma-aminopropyl triethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyl methyl dimethoxy silane.
10. The method for preparing a composite separator for a lithium battery according to claim 7, wherein in the step S4, the thickness of the base film is 4-20 μm, and the base film is one of a polyethylene microporous film, a polypropylene microporous film, a polyethylene-polypropylene-polyethylene three-layer composite porous film, a polyimide film or a non-woven fabric film;
the thickness of a coating layer on the surface of a base film in the prepared lithium battery composite diaphragm is 0.5-4 mu m, the closed pore temperature of the prepared lithium battery composite diaphragm is 100-125 ℃, and the rupture temperature is 300-600 ℃.
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