CN114927831A - Composite diaphragm, preparation method thereof and lithium ion battery - Google Patents
Composite diaphragm, preparation method thereof and lithium ion battery Download PDFInfo
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- CN114927831A CN114927831A CN202210514831.5A CN202210514831A CN114927831A CN 114927831 A CN114927831 A CN 114927831A CN 202210514831 A CN202210514831 A CN 202210514831A CN 114927831 A CN114927831 A CN 114927831A
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- 239000002131 composite material Substances 0.000 title claims abstract description 74
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 17
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 17
- 238000002360 preparation method Methods 0.000 title abstract description 10
- 239000011248 coating agent Substances 0.000 claims abstract description 97
- 238000000576 coating method Methods 0.000 claims abstract description 97
- 229920000642 polymer Polymers 0.000 claims abstract description 82
- 238000002844 melting Methods 0.000 claims abstract description 55
- 239000011247 coating layer Substances 0.000 claims abstract description 49
- 230000008018 melting Effects 0.000 claims abstract description 48
- 239000000919 ceramic Substances 0.000 claims abstract description 32
- 229920000098 polyolefin Polymers 0.000 claims abstract description 31
- 239000002245 particle Substances 0.000 claims abstract description 27
- 239000012528 membrane Substances 0.000 claims abstract description 12
- 239000006255 coating slurry Substances 0.000 claims description 40
- 239000002562 thickening agent Substances 0.000 claims description 39
- 239000000080 wetting agent Substances 0.000 claims description 39
- 239000011230 binding agent Substances 0.000 claims description 37
- 239000002270 dispersing agent Substances 0.000 claims description 31
- -1 polyethylene Polymers 0.000 claims description 22
- 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 claims description 19
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- 239000004642 Polyimide Substances 0.000 claims description 8
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 8
- 229940113115 polyethylene glycol 200 Drugs 0.000 claims description 8
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- 239000004698 Polyethylene Substances 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 6
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- 235000010482 polyoxyethylene sorbitan monooleate Nutrition 0.000 claims description 5
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- 229920003171 Poly (ethylene oxide) Polymers 0.000 claims description 3
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- HDSBZMRLPLPFLQ-UHFFFAOYSA-N Propylene glycol alginate Chemical compound OC1C(O)C(OC)OC(C(O)=O)C1OC1C(O)C(O)C(C)C(C(=O)OCC(C)O)O1 HDSBZMRLPLPFLQ-UHFFFAOYSA-N 0.000 claims description 3
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- XECAHXYUAAWDEL-UHFFFAOYSA-N acrylonitrile butadiene styrene Chemical compound C=CC=C.C=CC#N.C=CC1=CC=CC=C1 XECAHXYUAAWDEL-UHFFFAOYSA-N 0.000 claims description 3
- 239000004676 acrylonitrile butadiene styrene Substances 0.000 claims description 3
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- 235000014113 dietary fatty acids Nutrition 0.000 claims description 3
- 239000000194 fatty acid Substances 0.000 claims description 3
- 229930195729 fatty acid Natural products 0.000 claims description 3
- 150000004665 fatty acids Chemical class 0.000 claims description 3
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 claims description 3
- 229920000747 poly(lactic acid) Polymers 0.000 claims description 3
- 229920001495 poly(sodium acrylate) polymer Polymers 0.000 claims description 3
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- 239000000770 propane-1,2-diol alginate Substances 0.000 claims description 3
- 235000010409 propane-1,2-diol alginate Nutrition 0.000 claims description 3
- 239000000377 silicon dioxide Substances 0.000 claims description 3
- 235000019982 sodium hexametaphosphate Nutrition 0.000 claims description 3
- GCLGEJMYGQKIIW-UHFFFAOYSA-H sodium hexametaphosphate Chemical compound [Na]OP1(=O)OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])O1 GCLGEJMYGQKIIW-UHFFFAOYSA-H 0.000 claims description 3
- NNMHYFLPFNGQFZ-UHFFFAOYSA-M sodium polyacrylate Chemical compound [Na+].[O-]C(=O)C=C NNMHYFLPFNGQFZ-UHFFFAOYSA-M 0.000 claims description 3
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 claims description 3
- 239000004925 Acrylic resin Substances 0.000 claims description 2
- 229920000178 Acrylic resin Polymers 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
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- 239000004094 surface-active agent Substances 0.000 description 28
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- 239000000853 adhesive Substances 0.000 description 5
- 230000001070 adhesive effect Effects 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 5
- 238000004804 winding Methods 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 239000002033 PVDF binder Substances 0.000 description 4
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 4
- 238000004080 punching Methods 0.000 description 4
- 238000007789 sealing Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 3
- 229920006231 aramid fiber Polymers 0.000 description 3
- 210000004027 cell Anatomy 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 238000009966 trimming Methods 0.000 description 3
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 239000006230 acetylene black Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
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- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 238000003760 magnetic stirring Methods 0.000 description 2
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- 239000000126 substance Substances 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910010710 LiFePO Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
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- 125000003636 chemical group Chemical group 0.000 description 1
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- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011267 electrode slurry Substances 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
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- 229920006015 heat resistant resin Polymers 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
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- 238000009413 insulation Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000009191 jumping Effects 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
-
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- 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
Abstract
The invention provides a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite separator comprises a polyolefin base film, a first coating layer coated on one side of the polyolefin base film and a second coating layer coated on the other side of the polyolefin base film; the first coating comprises a low melting point polymer and/or a high melting point polymer; the second coating comprises high melting point polymer and/or ceramic particles; the melting point of the low-melting-point polymer is 90-120 ℃; the melting point of the high-melting-point polymer is 160-300 ℃. According to the composite diaphragm provided by the invention, the low-closed-cell melting point polymer and the high-rupture-membrane melting point polymer are coated on the surface of the polyolefin base membrane, so that the purpose of greatly increasing the difference value between the closed-cell temperature and the rupture temperature is achieved, and the high-safety diaphragm is obtained, so that the safety performance of the battery is enhanced; meanwhile, the composite diaphragm has better ductility and tensile mechanical property, and the puncture resistance of the composite diaphragm is favorably improved.
Description
Technical Field
The invention belongs to the technical field of diaphragm materials, and particularly relates to a composite diaphragm, a preparation method of the composite diaphragm and a lithium ion battery.
Background
The diaphragm is used as an important component of the lithium ion battery, mainly plays a role in isolating the positive electrode and the negative electrode, has ion insulation property and only transmits electrons. In order to further improve the high-temperature cycle performance of the battery, many researchers have applied a high-temperature resistant coating on the surface of the separator to improve the thermal stability of the separator.
The invention discloses a safety diaphragm and a battery, and relates to the field of battery diaphragms, in particular to a high-safety diaphragm and a battery, which comprise a porous base material, a heat-resistant coating coated on at least one side of the porous base material, and a low-closed pore temperature coating coated on the porous base material or the heat-resistant coating; the heat-resistant coating comprises a heat-resistant resin; the low closed cell temperature coating comprises a self-closing cell material; the self-closing pore material comprises an adhesive self-closing resin with a low melting temperature or a low viscous flow temperature. The heat-resistant coating is arranged to improve the rupture temperature and the heat-resistant shrinkage performance of the diaphragm, and meanwhile, the low-closed-pore-temperature coating is introduced, wherein the cohesive self-closing resin with low melting temperature or low viscous flow temperature can be rapidly melted or softened at a certain temperature to close pores of the porous base membrane, so that the purpose of reducing the closed pore temperature is achieved, the difference between the closed pore temperature and the rupture temperature is improved, the high-safety diaphragm is obtained, and the safety of the battery is enhanced.
However, the current thermal-shutdown coating diaphragm still has the problems of thicker thickness, poor thermal stability and poor mechanical property, and is easy to be pierced by lithium dendrites, which is not beneficial to further improving the safety performance and electrochemical performance of the lithium ion battery, so that a high-temperature-resistant and piercing-resistant composite diaphragm needs to be developed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite diaphragm, a preparation method thereof and a lithium ion battery. According to the composite diaphragm provided by the invention, the low-closed-cell melting point polymer and the high-rupture-membrane melting point polymer are coated on the surface of the polyolefin base membrane, so that the purpose of greatly increasing the difference value between the closed-cell temperature and the rupture temperature is achieved, and the high-safety diaphragm is obtained, so that the safety performance of the battery is enhanced; meanwhile, the composite diaphragm has better ductility and tensile mechanical property, the puncture resistance strength of the composite diaphragm is favorably improved, the deformation of the diaphragm is further prevented, the failure of the battery is avoided, the deformation resistance of the battery is improved, and the bad burr result caused by the winding and trimming of the battery can be prevented; in addition, the invention adopts a unique coating mode of point coating, which is beneficial to improving the air permeability of the diaphragm, realizes the purpose of developing the low-air permeability high-porosity composite diaphragm, reduces the internal resistance of the battery and further improves the electrochemical performance of the battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a composite separator including a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film;
the first coating comprises a low melting point polymer and/or a high melting point polymer;
the second coating comprises high melting point polymer and/or ceramic particles;
the melting point of the low-melting-point polymer is 90-120 ℃;
the melting point of the high-melting-point polymer is 160-300 ℃.
In the present invention, the melting point of the low-melting polymer may be, for example, 90 ℃, 92 ℃, 95 ℃, 97 ℃, 100 ℃, 102 ℃, 105 ℃, 107 ℃, 110 ℃, 112 ℃, 115 ℃, 117 ℃ or 120 ℃.
In the present invention, the melting point of the high-melting polymer may be, for example, 160 ℃, 165 ℃, 170 ℃, 175 ℃, 180 ℃, 185 ℃, 190 ℃, 195 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃.
In the invention, the composite diaphragm has lower closed pore temperature by controlling the melting point of the low-melting-point polymer, thereby being beneficial to blocking lithium ion transmission and cell reaction and further preventing thermal runaway; by controlling the melting point of the high-melting-point polymer, the difference between the pore closing temperature and the film breaking temperature of the composite diaphragm is greatly improved, and the high-safety diaphragm is obtained, so that the safety performance of the battery is enhanced.
Preferably, the second coating surface is further coated with a high melting point polymer coating.
Preferably, the low melting point polymer comprises any one or a combination of two of polyethylene, polymethyl methacrylate, acrylonitrile-butadiene-styrene, polylactic acid, polyvinyl chloride or polyvinyl butyral, for example, polyethylene and polymethyl methacrylate, acrylonitrile-butadiene-styrene, polylactic acid or polyvinyl chloride.
Preferably, the high melting point polymer comprises any one or a combination of two of polypropylene, polyimide or aramid, for example, polypropylene and aramid, polyimide or aramid.
Preferably, the ceramic particles comprise any one or combination of two of alumina, boehmite, titania or silica, and may be, for example, alumina and boehmite, titania or silica.
Preferably, the ceramic particles have an average particle size of 0.8 μm to 0.9. mu.m, and may be, for example, 0.8 μm, 0.82 μm, 0.85 μm, 0.88 μm, or 0.9. mu.m.
Preferably, the first and second coating layers further comprise any one or a combination of at least two of a thickener, a dispersant, a wetting agent, or a binder.
Preferably, the thickener comprises one or two of acacia, sodium carboxymethylcellulose, propylene glycol alginate, sodium polyacrylate, polyoxyethylene, polyvinyl methyl ether-decadiene copolymer, methyl acrylate-decadiene copolymer or polyurethane, preferably one or two of sodium carboxymethylcellulose, polyvinyl methyl ether-decadiene copolymer or methyl acrylate-decadiene copolymer, such as acacia and sodium carboxymethylcellulose, propylene glycol alginate, sodium polyacrylate, polyoxyethylene or polyvinyl methyl ether-decadiene copolymer.
Preferably, the dispersant comprises any one or a combination of two of sodium tripolyphosphate, sodium hexametaphosphate, polyacrylamide or fatty acid polyglycol ester, preferably polyacrylamide, and for example, can be sodium tripolyphosphate and sodium hexametaphosphate, polyacrylamide or fatty acid polyglycol ester.
Preferably, the wetting agent comprises polyethylene glycol 200 or tween-80, preferably polyethylene glycol 200.
Preferably, the binder comprises any one or a combination of two of polypropylene alcohol, carboxymethyl cellulose, polyurethane, polystyrene, polyacrylate, vinyl acetate resin, acrylic resin or chlorinated rubber, preferably polypropylene alcohol or chlorinated rubber, for example, polypropylene alcohol and carboxymethyl cellulose, polyurethane, polystyrene, polyacrylate, vinyl acetate resin.
As one of the preferable technical solutions of the present invention, the present invention provides a composite separator, which includes a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film, and is composed of:
the first coating comprises the following components in percentage by mass: 49 to 60 percent of low-melting-point polymer, 40 to 50 percent of high-melting-point polymer, 2 to 5.5 percent of binder, 0.5 to 2.5 percent of dispersant, 0.5 to 2 percent of thickener and 0.1 to 1 percent of wetting agent;
the second coating comprises the following components in percentage by mass: 86-98% of ceramic particles, 2-5% of binder, 0.5-3% of thickening agent and 0.1-0.7% of wetting agent.
In the present invention, the content of the low melting point polymer in the first coating layer is 49% to 60% by mass, and may be, for example, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%.
In the invention, the coating film can realize the low-temperature thermal response hole sealing function and has better comprehensive performance by adjusting the mass percentage content of the low-melting-point polymer; an excessively low content results in an excessively high closing temperature of the composite separator, and conversely results in too poor air permeability of the coated film.
In the present invention, the content of the high melting point polymer in the first coating layer may be 40% to 50% by mass, for example, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%.
In the invention, the mass percentage of the high-melting-point polymer is adjusted, so that the coating film has high temperature resistance and better comprehensive performance, and if the mass percentage is too low, the heat resistance of the composite diaphragm is reduced, otherwise, the air permeability of the coating film is poor.
In the present invention, the mass percentage of the binder in the first coating layer is 2% to 5.5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.5%; the mass percentage content of the dispersant is 0.5% to 2.5%, and may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%; the mass percentage of the thickener is 0.5 to 2 percent, for example, 0.5 percent, 0.8 percent, 1 percent, 1.2 percent, 1.5 percent, 1.8 percent and 2 percent; the content of the wetting agent may be, for example, 0.1% to 1% by mass, or 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, or 1%.
In the present invention, the mass percentage content of the ceramic particles in the second coating layer is 86% to 98%, for example, 86%, 88%, 90%, 92%, 94%, 96%, 98%; the mass percentage of the binder is 2% to 5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%; the content of the thickener by mass is 0.5% to 3%, for example, may be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%, and the content of the wetting agent by mass is 0.1% to 0.7%, for example, may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%.
In the invention, the mass percentage of the ceramic particles in the second coating is adjusted to ensure that the air permeability of the coating film is better and the puncture resistance is higher, and if the mass percentage is too low, the puncture resistance of the composite diaphragm is reduced, otherwise, the air permeability of the coating film is too poor.
In the invention, the contents of the binder, the dispersant, the thickener and the wetting agent in the first coating and the second coating are adjusted, so that the composite diaphragm has better ductility and tensile mechanical property, the puncture resistance of the composite diaphragm is favorably improved, the deformation of the diaphragm is further prevented, the failure of a battery is avoided, the deformation resistance of the battery is improved, and the bad burr result caused by the winding and trimming of the battery can be prevented.
As a second preferred embodiment of the present invention, the present invention provides a composite separator, which includes a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film, and comprises the following components:
the first coating comprises the following components in percentage by mass: 85 to 98 percent of low-melting-point polymer, 2 to 5.5 percent of binder, 0.5 to 2.5 percent of dispersant, 0.5 to 2 percent of thickener and 0.1 to 1 percent of wetting agent;
the second coating comprises the following components in percentage by mass: 60 to 65 percent of ceramic particles, 30 to 35 percent of high-melting-point polymer, 0.5 to 2.5 percent of dispersant, 2 to 5.5 percent of binder, 0.5 to 2 percent of thickener and 0.1 to 1 percent of wetting agent.
In the present invention, the mass percentage content of the low melting point polymer in the first coating layer is 85% to 98%, and for example, may be 85%, 87%, 89%, 90%, 92%, 94%, 96%, 98%.
In the invention, the mass percentage content of the low-melting-point polymer is adjusted, so that the coating film can realize a low-temperature thermal response hole sealing function and improve the comprehensive performance of the coating film, and if the content is too low, the hole sealing temperature of the composite diaphragm is too high, otherwise, the air permeability of the coating film is too poor.
In the present invention, the mass percentage content of the binder in the first coating layer is 2% to 5.5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.5%; the mass percentage content of the dispersant is 0.5% to 2.5%, and may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%; the content of the thickener by mass% may be 0.5% to 2%, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, and the content of the wetting agent by mass% may be 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 1%.
In the present invention, the mass percentage content of the ceramic particles in the second coating layer is 60% to 65%, and may be, for example, 60%, 61%, 62%, 63%, 64%, 65%.
In the invention, the mass percentage content of the ceramic particles in the second coating is adjusted, so that the air permeability of the coating film is better and the puncture resistance is higher, and if the content is too low, the puncture resistance of the composite diaphragm is reduced, otherwise, the air permeability of the coating film is reduced.
In the present invention, the content of the high melting point polymer in the second coating layer may be 30% to 35% by mass, for example, 30%, 31%, 32%, 33%, 34%, 35%.
In the invention, the mass percentage of the high-melting-point polymer in the second coating is adjusted, so that the coating film has both high temperature resistance and better comprehensive performance, and if the mass percentage is too low, the heat resistance of the composite diaphragm is reduced, otherwise, the air permeability of the coating film is too poor.
In the present invention, the content of the dispersant in the second coating layer may be 0.5% to 2.5% by mass, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%; the mass percentage content of the binder is 2% to 5.5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.5%; the mass percentage of the thickener is 0.5 to 2 percent, for example, 0.5 percent, 0.8 percent, 1 percent, 1.2 percent, 1.5 percent, 1.8 percent and 2 percent; the content of the wetting agent may be, for example, 0.1% to 1% by mass, or 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 1%.
In the invention, the contents of the binder, the dispersant, the thickener and the wetting agent in the first coating and the second coating are adjusted, so that the composite diaphragm has better ductility and tensile mechanical property, the puncture resistance of the composite diaphragm is favorably improved, the deformation of the diaphragm is further prevented, the failure of a battery is avoided, the deformation resistance of the battery is improved, and the bad burr result caused by the winding and trimming of the battery can be prevented.
As a third preferred technical solution, the present invention provides a composite separator, including a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film, wherein the second coating layer has a high melting point polymer coating layer coated on the surface thereof, and the composition of the composite separator is as follows:
the first coating comprises the following components in percentage by mass: the mass percentage content of the low-melting polymer is 85% to 98%, and may be, for example, 85%, 87%, 89%, 90%, 92%, 94%, 96%, 98%; the mass percentage of the binder is 2% to 5.5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.5%; the mass percentage content of the dispersant is 0.5% to 2.5%, and may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%; the mass percentage content of the thickening agent is 0.5-2%, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%; the content of the wetting agent may be, for example, 0.1% to 1% by mass, or 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 1%.
The second coating comprises the following components in percentage by mass: the mass percentage of the ceramic particles is 86-98%, for example, 86%, 88%, 90%, 92%, 94%, 96%, 98%; the mass percentage content of the binder is 2% to 5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%; the mass percentage of the thickener is 0.5% to 3%, and may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%; the content of the wetting agent may be, for example, 0.1% to 0.7% by mass, or may be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%.
The high-melting-point polymer coating comprises the following components in percentage by mass: the mass percentage of the high-melting polymer is 85% to 98%, and may be, for example, 85%, 87%, 89%, 90%, 92%, 94%, 96%, 98%; the mass percentage content of the binder is 2% to 5.5%, and may be, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.5%; the mass percentage content of the dispersant is 0.5% to 2.5%, and may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%; the mass percentage content of the thickening agent is 0.5-2%, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%; the content of the wetting agent may be 0.1% to 1% by mass, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 1%.
In the invention, the composite diaphragm has the advantages of low closed-pore thermal response function, high-rupture high-temperature resistance and puncture resistance.
Preferably, the thickness of the composite separator is 7 μm to 16 μm, and may be, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm.
According to the invention, the composite diaphragm has good air permeability and low impedance by adjusting the thickness of the composite diaphragm.
In a second aspect, the present invention provides a method of making the composite separator of the first aspect, the method comprising the steps of:
and coating the first coating slurry on one side of the base film, then coating the second coating slurry on the other side of the base film, optionally coating a high-melting-point polymer on the surface of the second coating, and drying to obtain the composite diaphragm.
As one of the preferable technical schemes of the invention, the preparation method of the composite diaphragm comprises the following steps:
(1) mixing 50-60% of low-melting-point polymer, 40-50% of high-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, adding deionized water, stirring by adopting high-speed magnetic force of 400-1000rpm for 0.01-7h, and stirring by adopting magnetic force for 0.01-10 h; then ultrasonically dispersing for 0.1-4h, mixing 0.01-5g of surfactant and stirring for 0.1-3h at the rotating speed of 300-1000rpm, further mixing 0.01-8g of surfactant and stirring for 0.1-6h at the rotating speed of 100-600 rpm, and filtering to obtain first coating slurry with the mixing viscosity of 0.5-100 cP;
(2) mixing 86-98% of ceramic particles, 2-5% of binder, 0.5-3% of thickener and 0.1-0.7% of wetting agent, adding deionized water, and stirring for 0.01-8h by adopting high-speed magnetic stirring at 500 plus materials and 1000rpm, and stirring for 0.01-12h by adding magnetic force to obtain ceramic slurry; ultrasonically dispersing the treated ceramic slurry for 0.1-5h, heating at 10-55 ℃ for dissolving and dispersing for 0.1-4h, mixing 0.01-5g of surfactant, stirring at the rotating speed of 300-1000rpm for 0.1-3h, heating at 10-55 ℃ for dissolving and dispersing for 0.1-1.6h, further mixing 0.01-8g of surfactant, stirring at the rotating speed of 100-600 rpm for 0.1-6h, and filtering to obtain a second coating slurry with the mixing viscosity of 20-150 cP;
(3) and coating the first coating slurry on one side of the base film, then coating the second coating slurry on the other side of the base film, and drying to obtain the composite diaphragm.
As a second preferred embodiment of the present invention, a method for preparing the composite separator comprises:
(1) mixing 85-98% of low-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, adding deionized water, stirring for 0.01-8h by adopting high-speed magnetic force of 500-1000rpm, and stirring for 0.01-12h by adding magnetic force; then ultrasonically dispersing for 0.1-5h, mixing 0.01-5g of surfactant and stirring for 0.1-3h at the rotating speed of 300-1000rpm, further mixing 0.01-8g of surfactant and stirring for 0.1-6h at the rotating speed of 100-600 rpm, and filtering to obtain first coating slurry with the mixing viscosity of 0.5-100 cP;
(2) mixing 60-65% of ceramic particles, 30-35% of high-melting-point polymer, 0.5-2.5% of dispersing agent, 2-5.5% of binding agent, 0.5-2.5% of thickening agent and 0.1-1% of wetting agent, adding deionized water, stirring for 0.01-6.6h by adopting high-speed magnetic force of 300-1200rpm, stirring for 0.01-13h by adding magnetic force, then ultrasonically dispersing for 0.1-8h, heating, dissolving and dispersing for 0.1-4h at 10-55 ℃, mixing 0.01-5g of surfactant, stirring for 0.1-3h at the rotating speed of 300-1000rpm, heating, dissolving and dispersing for 0.1-1.6h at 10-55 ℃, further mixing 0.01-8g of surfactant, stirring for 0.1-6h at the rotating speed of 100-600 rpm, and filtering to obtain second coating slurry with the mixing viscosity of 20-150 cP;
(3) and coating the first coating slurry on one side of the base film, coating the second coating slurry on the other side of the base film, and drying to obtain the composite diaphragm.
As a third preferred technical solution of the present invention, a method for preparing the composite separator comprises:
(1) mixing 85-98% of low-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, adding deionized water, stirring for 0.01-8h by adopting high-speed magnetic force of 500-1000rpm, and stirring for 0.01-12h by adding magnetic force; then ultrasonically dispersing for 0.1-5h, mixing 0.01-5g of surfactant, stirring for 0.1-3h at the rotating speed of 300-1000rpm, further mixing 0.01-8g of surfactant, stirring for 0.1-6h at the rotating speed of 100-600 rpm, and filtering to obtain first coating slurry with the mixing viscosity of 0.5-100 cP;
(2) mixing 86-98% of ceramic particles, 2-5% of binder, 0.5-3% of thickener and 0.1-0.7% of wetting agent, adding deionized water, and stirring for 0.01-8h by adopting high-speed magnetic stirring at 500 plus materials and 1000rpm, and stirring for 0.01-12h by adding magnetic force to obtain ceramic slurry; ultrasonically dispersing the treated ceramic slurry for 0.1-5h, heating at 10-55 ℃ for dissolving and dispersing for 0.1-4h, mixing 0.01-5g of surfactant, stirring at the rotating speed of 300-1000rpm for 0.1-3h, heating at 10-55 ℃ for dissolving and dispersing for 0.1-1.6h, further mixing 0.01-8g of surfactant, stirring at the rotating speed of 100-600 rpm for 0.1-6h, and filtering to obtain a second coating slurry with the mixing viscosity of 20-150 cP;
(3) mixing 85-98% of high-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, adding deionized water, stirring for 0.01-8h by adopting high-speed magnetic force of 500-1000rpm, and stirring for 0.01-12h by adding magnetic force; then ultrasonically dispersing for 0.1-5h, mixing 0.01-5g of surfactant and stirring for 0.1-3h at the rotating speed of 300-1000rpm, further mixing 0.01-8g of surfactant and stirring for 0.1-6h at the rotating speed of 100-600 rpm, and filtering to obtain high-melting-point polymer coating slurry with the mixing viscosity of 0.5-100 cP;
(4) and coating the first coating slurry on one side of the base film, coating the second coating slurry on the other side of the base film, coating the high-melting-point polymer coating slurry on the surface of the second coating, and drying to obtain the composite diaphragm.
Preferably, the solids content of the first coating slip is 25% to 30%, for example 25%, 26%, 27%, 28%, 29%, 30% may be possible.
Preferably, the viscosity of the first coating slurry is 0.5cp to 250cp, for example, 0.5cp, 1cp, 5cp, 10cp, 20cp, 50cp, 80cp, 100cp, 120cp, 150cp, 180cp, 200cp, 220cp, 250 cp.
Preferably, the solids content of the second coating slip is 25% to 30%, for example 25%, 26%, 27%, 28%, 29%, 30% may be possible.
Preferably, the viscosity of the second coating slurry is 20cp to 250cp, for example, 20cp, 30cp, 40cp, 50cp, 80cp, 100cp, 120cp, 150cp, 180cp, 200cp, 220cp, 250 cp.
According to the invention, the heat resistance of the coating film is better by adjusting the solid contents of the first coating slurry and the second coating slurry; in addition, the viscosity of the coating film is controlled, so that the mechanical property and the adhesive force of the coating film are better.
Preferably, the coating mode is dot coating.
According to the invention, the dot coating mode is adopted to enable the coating to be more uniform, and meanwhile, the coating diaphragm has the advantages of better thickness and air permeability consistency, the wettability of the electrolyte on the isolating diaphragm can be effectively improved, the liquid retention amount of the electrolyte is improved, the performance of the battery is further improved, in addition, the water jumping phenomenon at the later cycle stage of the battery can be effectively prevented, the aging standing time of liquid injection is shortened, and the yield and the quality of a battery product are improved.
In a third aspect, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, wherein the diaphragm is the composite diaphragm according to the first aspect.
The composite diaphragm provided by the invention can realize high-rate charge and discharge of a lithium ion battery, and can improve the rate performance, cycle life, heat-resistant stability and safety of the battery.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a composite diaphragm, which improves the following properties:
(1) the low-melting-point polymer is used for effectively reducing the closed pore temperature of the diaphragm, so that the lithium ion transmission and the battery reaction can be blocked, and the thermal runaway can be prevented; meanwhile, the high-melting-point polymer has a higher melting point, so that the heat-resistant shrinkage rate of the diaphragm can be reduced, the thermal runaway phenomenon of the battery can be prevented, and the effect of improving the safety of the battery can be achieved;
(2) the diaphragm provided by the invention has better ductility and tensile mechanical property by further preferably selecting the doping proportion of the binder, the dispersant, the wetting agent and the thickener, is favorable for improving the puncture resistance of the diaphragm, further prevents the diaphragm from deforming, prevents the battery from losing efficacy, improves the deformation resistance of the battery, and can improve the safety performance of the battery;
(3) the invention adopts a dot-coating mode, is beneficial to improving the air permeability of the diaphragm, achieves the aim of developing the low-air-permeability high-porosity composite diaphragm, reduces the internal resistance of the battery, and further improves the rate capability and the cycle performance of the battery.
Drawings
FIG. 1 is a schematic structural view of a composite separator provided in examples 1-2, wherein 1 is a polyolefin-based film, 2 is a first coating layer, and 3 is a second coating layer;
fig. 2 is a schematic structural diagram of the composite separator provided in example 3, in which 1 is a polyolefin-based film, 2 is a first coating layer, 3 is a second coating layer, and 4 is a high-melting-point polymer coating layer.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the detailed description. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
This embodiment provides a composite separator, as shown in fig. 1, including a polyolefin-based film (PE or PP, supplier: enigie or star source), a first coating layer coated on one side of the polyolefin-based film, and a second coating layer coated on the other side of the polyolefin-based film.
The preparation method comprises the following steps:
(1) polymethyl methacrylate (melting point 105 ℃ C., density 1.2 g/cm) 3 The glass transition temperature is 105 ℃; the supplier: wanhua chemical group Ltd) 50%, polyimide (melting point 230 ℃, thickness 6 μm, porosity 60%, melting point 300 ℃, supplier: changchun gchoqi polyimide materials ltd) 43%, polypropylene alcohol (supplier: guangzhou city new dilute metallurgy chemical company limited) 4.7% of binder, 1.1% of polyacrylamide dispersant and 1.65g/cm of sodium carboxymethyl cellulose thickener (density is 1.65 g/cm) 3 (ii) a The supplier: zhengzhou hua crystallography chemical company, ltd) 1% and polyethylene glycol 200 (molecular weight: 200 of a carrier; density 1.125g/cm 3 (ii) a The supplier: jinan Xiangfeng Wei industrialisation chemical Co., Ltd.) 0.2% of the wetting agent, adding deionized water, stirring for 3.5h by adopting high-speed magnetic force of 700rpm, and stirring for 5h by adding magnetic force; then ultrasonically dispersing for 2 hours, mixing 2.5g of surfactant, stirring for 3 hours at the rotating speed of 600rpm, further mixing 4g of surfactant, stirring for 3 hours at the rotating speed of 400rpm, and filtering to obtain first coating slurry with the mixing viscosity of 50cP, wherein the solid content of the slurry is 25%;
(2) mixing 96.2% of alumina (with average particle size of 0.85 μm), 2.5% of a polyvinyl alcohol binder, 1.2% of a sodium carboxymethylcellulose thickening agent and 0.1% of a polyethylene glycol 200 wetting agent, adding deionized water, stirring for 4 hours by adopting high-speed magnetic force of 700rpm, and stirring for 6 hours by adding magnetic force to obtain ceramic slurry; ultrasonically dispersing the treated ceramic slurry for 5 hours, heating at 55 ℃, dissolving and dispersing for 4 hours, mixing 5g of surfactant, stirring for 3 hours at the rotating speed of 1000rpm, heating at 55 ℃, dissolving and dispersing for 1.6 hours, further mixing 0.01g of surfactant, stirring for 3 hours at the rotating speed of 600rpm, and filtering to obtain second coating slurry with the mixed viscosity of 135cP, wherein the solid content of the slurry is 30%;
(3) and coating the first coating slurry on one side of the base film, then coating the second coating slurry on the other side of the base film, and drying to obtain the composite diaphragm.
Example 2
The present embodiment provides a composite separator, as shown in fig. 1, including a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film.
The preparation method comprises the following steps:
(1) mixing 92.9% of low-melting-point polymer polyethylene microsphere emulsion, 4% of adhesive polypropylene glycol, 1% of dispersant polyacrylamide, 2% of thickener carboxymethylcellulose sodium and 0.1% of wetting agent polyethylene glycol 200; adding deionized water, stirring for 4h by adopting high-speed magnetic force of 1000rpm, and stirring for 6h by adding magnetic force; then ultrasonically dispersing for 5h, mixing 3g of surfactant sodium carboxymethylcellulose, stirring for 3h at the rotating speed of 1000rpm, further mixing 2g of surfactant polyacrylamide, stirring for 6h at the rotating speed of 500rpm, and filtering to obtain first coating slurry with the mixing viscosity of 50cP, wherein the solid content of the slurry is 25%;
(2) mixing 60% of ceramic alumina particles, 35% of high-melting-point polymer aramid, 1% of dispersant sodium tripolyphosphate, 2.7% of binder polyacrylate, 1% of thickener carboxymethylcellulose sodium and 0.3% of wetting agent Tween-80, adding deionized water, stirring for 5.6h by adopting high-speed magnetic force of 700rpm, stirring for 13h by adding magnetic force, then ultrasonically dispersing for 8h, heating, dissolving and dispersing for 4h at 45 ℃, mixing 3g of surfactant polyacrylate, stirring for 3h at 1000rpm, heating, dissolving and dispersing for 1.6h at 45 ℃, further mixing 1g of surfactant carboxymethylcellulose sodium, stirring for 6h at 600rpm, filtering to obtain second coating slurry with the mixing viscosity of 120cP, wherein the solid content of the slurry is 30%;
(3) and coating the first coating slurry on one side of the base film, then coating the second coating slurry on the other side of the base film, and drying to obtain the composite diaphragm.
Example 3
The present embodiment provides a composite separator, as shown in fig. 2, including a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film.
The preparation method comprises the following steps:
(1) mixing 92.9% of low-melting-point polymer polyethylene microsphere emulsion, 4% of binder polypropylene glycol, 1% of dispersant polyacrylamide, 2% of thickener carboxymethylcellulose sodium and 0.1% of wetting agent polyethylene glycol 200, adding deionized water, stirring for 4 hours by adopting high-speed magnetic force of 1000rpm, and stirring for 6 hours by adding magnetic force; then ultrasonically dispersing for 5h, mixing 3g of surfactant sodium carboxymethyl cellulose, stirring for 3h at the rotating speed of 1000rpm, further mixing 2g of surfactant polyacrylamide, stirring for 6h at the rotating speed of 500rpm, and filtering to obtain first coating slurry with the mixing viscosity of 50cP, wherein the solid content of the slurry is 25%;
(2) mixing 96.2% of ceramic alumina particles, 2.5% of adhesive polyacrylate, 1.2% of thickening agent carboxymethylcellulose sodium and 0.1% of wetting agent Tween-80, adding deionized water, stirring for 8 hours by adopting high-speed magnetic force of 1000rpm, and stirring for 12 hours by adopting magnetic force to obtain ceramic slurry; ultrasonically dispersing the treated ceramic slurry for 5h, heating at 55 ℃ for dissolving and dispersing for 4h, mixing 5g of surfactant polyacrylate and stirring at 1000rpm for 3h, heating at 55 ℃ for dissolving and dispersing for 1.6h, further mixing 8g of surfactant carboxymethylcellulose sodium and stirring at 600rpm for 6h, and filtering to obtain a second coating slurry with the mixed viscosity of 150 cP;
(3) mixing 94.6% of high-melting-point polymer aramid fiber, 3% of adhesive polyacrylate, 1% of dispersing agent carboxymethylcellulose sodium, 1.2% of thickening agent methylcellulose sodium and 0.2% of wetting agent Tween-80, adding deionized water, stirring for 1h by adopting high-speed magnetic force of 500 plus material of 1000rpm, and stirring for 5h by adding magnetic force; then ultrasonically dispersing for 0.5h, mixing 5g of surfactant polyacrylate and stirring for 2h at the rotating speed of 500rpm, further mixing 2g of surfactant carboxymethylcellulose sodium and stirring for 2h at the rotating speed of 600rpm, and filtering to obtain high-melting-point polymer coating slurry with the mixing viscosity of 50cP, wherein the solid content of the slurry is 30%;
(4) and coating the first coating slurry on one side of the base film, coating the second coating slurry on the other side of the base film, drying, coating the high-melting-point polymer coating slurry on the surface of the second coating, and drying to obtain the composite diaphragm.
Example 4
The difference between the embodiment and the embodiment 1 is that the first coating comprises the following components in percentage by mass: the same procedure as in example 1 was repeated except that 40% of the low melting point polymethyl methacrylate polymer and 51% of the high melting point polyimide polymer were used.
Example 5
The difference between the embodiment and the embodiment 2 is that the second coating comprises the following components in percentage by mass: 50% of ceramic alumina particles and 45% of high-melting-point polymer aramid fibers, and the rest were the same as in example 2.
Example 6
The difference between this example and example 3 is that the aramid fiber coated with the high melting point polymer is not coated, and the other steps are the same as those of example 3.
Example 7
This example is different from example 1 in that the melting point of the polymethyl methacrylate is 80 ℃, and the rest is the same as example 1.
Example 8
This example is different from example 1 in that the melting point of the polyimide is 350 ℃, and the rest is the same as example 1.
Comparative example 1
This comparative example is different from example 1 in that the first coating layer and the second coating layer are both polymethyl methacrylate low-melting polymer coating layers, and the others are the same as example 1.
Comparative example 2
This comparative example is different from example 1 in that the first coating layer and the second coating layer are polyimide high melting point polymer coating layers, and the others are the same as example 1.
Comparative example 3
This comparative example is different from example 1 in that the first coating layer and the second coating layer are both alumina coating layers, and the others are the same as example 1.
Application examples 1-8 and comparative application examples 1-3
The lithium ion batteries were prepared by using the composite separators provided in examples 1 to 8 and comparative examples 1 to 3, and the preparation method was as follows:
preparing a positive plate: lithium iron phosphate (LiFePO) with the particle size of 8 mu m 4 ) Acetylene black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 86:7: 7. Specifically, 0.05g of PVDF as a binder is accurately weighed in a weighing bottle, 10 drops of N-methylpyrrolidone (NMP) as a dispersant are dropwise added into the bottle, the mixture is stirred for 1 hour in a heat collection type constant temperature heating magnetic stirrer (without heating), then 0.05g of acetylene black as a conductive agent is added, the stirring is continued for 1 hour, then adding 0.6g of active material lithium iron phosphate, simultaneously adding 15 drops of polyvinylidene fluoride (NMP) solution, uniformly mixing, stirring for 12h on a magnetic stirrer to obtain a positive electrode material with certain viscosity and uniform stirring, adjusting the thickness of an automatic coating machine, controlling the total thickness after coating to be about 30 μm, uniformly coating the slurry on a flat aluminum foil by using a coating machine, drying for 7h at 80 ℃ in a common drying oven, taking out, cutting into circular pole pieces with certain diameter by using a punching machine, weighing, drying at 80 deg.C in a vacuum oven, and transferring to a glove box for use after 12 hr;
preparing a negative plate: mixing graphite, sodium carboxymethylcellulose and styrene butadiene rubber according to the mass ratio of 84:8: 8. Pouring the graphite mixed purified water into a vacuum stirrer, adding sodium carboxymethylcellulose, stirring, and completely dissolving; adding styrene butadiene rubber and deionized water, stirring for 60 minutes, uniformly adding the negative dry materials into a stirrer in four times, stirring for 3-5 hours in high-speed vacuum, and discharging to prepare coating;
electrolyte: drying the lithium hexafluorophosphate LiPF 6 Dissolving in mixed solvent (ethylene carbonate) with volume ratio of 1:1:1Ester/dimethyl carbonate/ethyl methyl carbonate), LiPF 6 The concentration of (2) is 1 mol/L.
Preparing a lithium ion battery: coating the prepared positive and negative electrode slurry on positive and negative current collectors, drying and welding tabs to obtain positive and negative electrode plates, then shearing the positive and negative electrode plates into positive and negative minimum electrode plates with a certain shape, isolating the positive and negative minimum electrode plates by cutting a composite diaphragm with a certain size in a winding or laminating mode, and winding the positive and negative minimum electrode plates into an electric core body; then, performing short circuit evaluation on the electric core body, and screening high-quality electric cores; then the materials are put into a battery shell, a battery cover is covered, and the opening is sealed by welding; and injecting electrolyte into the battery case, forming, sealing secondarily, baking by using a clamp and grading to obtain the finished product soft package battery.
Test conditions
The composite separators provided in examples 1 to 8 and comparative examples 1 to 3 were subjected to a performance test by the following method:
(1) heat shrinkage ratio: the test sample dimensions were 10CM long and 10CM wide; heating by using an oven, wherein the test temperature is 200 ℃, and the test time is 1 hour;
(2) air permeability value: the test sample size was 5CM long and 5CM wide; testing the second time required for 100mL of gas to permeate the diaphragm by adopting a gas permeation tester;
(3) ionic conductivity: the test sample size was 18mm in diameter; punching sheets for later use; adopting an electrochemical workstation to test EIS;
(4) tensile strength: the size of a test sample is 10CM in length and 2CM in width, a universal testing machine is adopted, and the test speed is 100 m/min; the tensile force is 1 KN.
The lithium ion batteries provided in application examples 1 to 8 and comparative application examples 1 to 3 were subjected to electrochemical performance tests, the test methods were as follows:
(1) and (3) needle punching test: after the single battery is fully charged, penetrating through the battery plate at a speed of 25 +/-5 mm/s in a direction perpendicular to the battery plate by using a phi 3mm high-temperature-resistant steel needle (the conical angle of a needle point is 45-60 degrees, and the surface of the needle is smooth and has no rust, an oxide layer and oil stains), wherein the penetrating position is close to the geometric center of a punctured surface, the steel needle stays in the battery, and then observation is carried out for 1 h;
(2) cycle performance: the test is carried out on a battery test system of an electrochemical workstation under the condition of 25 ℃, the tested current density is 0.1C and 1C, and the charging and discharging voltage window is 2.75-4.2V.
(3) Rate capability: the current density is 0.1C/0.5C/1C/2C/3C and the charging and discharging voltage window is 2.75-4.2V when the electrochemical workstation battery is tested on a battery testing system at the temperature of 25 ℃.
The results of the tests are shown in tables 1 and 2:
TABLE 1
TABLE 2
As can be seen from the data in Table 1, the composite separators provided in examples 1 to 3 of the present invention have a heat shrinkage of not more than 5%, a gas permeation value of not more than 220s/100ml, an ionic conductivity of not less than 3.5mS/cm, a tensile strength of not less than 190MPa and all passed the needle punching test. The composite membranes provided in examples 1 to 3 have high air permeability because the coating contains a high content of low-melting-point polymer, which melts and closes pores when heated at 110 ℃; when the low-melting-point polymer is not added in the coating or the content of the low-melting-point polymer is low, the air permeability value of the prepared composite membrane is not large when the composite membrane is heated at the temperature of about 110 ℃.
Compared with example 1, example 4 has the low content of the low-melting polymer and the high content of the high-melting polymer, and the combination property is inferior to that of example 1; example 5 is the case where the ceramic content in the second coating layer is too low and the high melting point polymer content is too high, affecting the tensile strength of the separator; the overall performance of the separators of examples 6 to 8 was inferior to that of example 1.
Comparative examples 1 to 3 are single-layer coated separators, which are inferior to the composite separator provided in example 1, compared to example 1.
As can be seen from the data in table 2, the capacity retention rate of the lithium ion batteries provided in application examples 1 to 5 is not less than 98.3% after being cycled 1000 times at 0.1C, and is not less than 97% after being cycled 1000 times at 1C.
Compared to example 1, the single layer species coated separators of comparative application examples 1 to 3 had much lower capacity retention at 0.1C and 1C than the lithium ion battery provided in application example 1.
The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.
Claims (10)
1. A composite separator comprising a polyolefin base film, a first coating layer coated on one side of the polyolefin base film, and a second coating layer coated on the other side of the polyolefin base film;
the first coating comprises a low melting point polymer and/or a high melting point polymer;
the second coating comprises high melting point polymer and/or ceramic particles;
the melting point of the low-melting-point polymer is 90-120 ℃;
the melting point of the high-melting-point polymer is 160-300 ℃.
2. The composite separator of claim 1, wherein the second coating surface is further coated with a high melting polymer coating;
preferably, the low melting point polymer comprises any one or two of polyethylene, polymethyl methacrylate, acrylonitrile-butadiene-styrene, polylactic acid, polyvinyl chloride or polyvinyl butyral;
preferably, the high melting point polymer comprises any one of polypropylene, polyimide or aramid or a combination of two;
preferably, the ceramic particles comprise any one or a combination of two of alumina, boehmite, titania, or silica;
preferably, the ceramic particles have an average particle size of 0.8 μm to 0.9 μm.
3. The composite separator of claim 1 or 2, wherein the first and second coating layers further comprise any one or a combination of at least two of a thickener, dispersant, wetting agent, or binder;
preferably, the thickener comprises any one or a combination of two of acacia, sodium carboxymethylcellulose, propylene glycol alginate, sodium polyacrylate, polyoxyethylene, polyvinyl methyl ether-decadiene copolymer, methyl acrylate-decadiene copolymer or polyurethane, preferably any one or a combination of at least two of sodium carboxymethylcellulose, polyvinyl methyl ether-decadiene copolymer or methyl acrylate-decadiene copolymer;
preferably, the dispersant comprises any one or a combination of two of sodium tripolyphosphate, sodium hexametaphosphate, polyacrylamide or fatty acid polyglycol ester, preferably polyacrylamide;
preferably, the wetting agent comprises polyethylene glycol 200 or tween-80, preferably polyethylene glycol 200;
preferably, the binder comprises any one or a combination of two of polypropylene alcohol, carboxymethyl cellulose, polyurethane, polystyrene, polyacrylate, vinyl acetate resin, acrylic resin or chlorinated rubber, preferably polypropylene alcohol or chlorinated rubber.
4. The composite membrane according to any one of claims 1 to 3, wherein the first coating layer comprises the following components in mass percent: 49-60% of low-melting-point polymer, 40-50% of high-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, wherein the second coating comprises the following components in percentage by mass: 86-98% of ceramic particles, 2-5% of binder, 0.5-3% of thickening agent and 0.1-0.7% of wetting agent.
5. The composite membrane according to any one of claims 1 to 3, wherein the first coating layer comprises the following components in mass percent: 85-98% of low-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, wherein the second coating comprises the following components in percentage by mass: 60 to 65 percent of ceramic particles, 30 to 35 percent of high-melting-point polymer, 0.5 to 2.5 percent of dispersant, 2 to 5.5 percent of binder, 0.5 to 2 percent of thickener and 0.1 to 1 percent of wetting agent.
6. The composite membrane according to any one of claims 2 to 3, wherein the first coating layer comprises the following components in mass percent: 85-98% of low-melting-point polymer, 2-5.5% of binder, 0.5-2.5% of dispersant, 0.5-2% of thickener and 0.1-1% of wetting agent, wherein the second coating comprises the following components in percentage by mass: 86-98% of ceramic particles, 2-5% of binder, 0.5-3% of thickening agent and 0.1-0.7% of wetting agent, wherein the high-melting-point polymer coating comprises the following components in percentage by mass: 85 to 98 percent of high melting point polymer, 2 to 5.5 percent of binder, 0.5 to 2.5 percent of dispersant, 0.5 to 2 percent of thickening agent and 0.1 to 1 percent of wetting agent;
preferably, the thickness of the composite separator is 7 μm to 16 μm.
7. A method of making the composite separator of any one of claims 1-6, comprising the steps of:
and coating the first coating slurry on one side of the base film, then coating the second coating slurry on the other side of the base film, optionally coating a high-melting-point polymer on the surface of the second coating, and drying to obtain the composite membrane.
8. The method of claim 7, wherein the first coating slurry has a solids content of 25% to 30%;
preferably, the viscosity of the first coating slurry is 0.5cp to 250 cp;
preferably, the solid content of the second coating slurry is 25 to 30 percent;
preferably, the viscosity of the second coating slurry is 20cp to 250 cp.
9. The method according to claim 7 or 8, characterized in that the coating is applied in a spot-like manner.
10. A lithium ion battery, which is characterized by comprising a positive pole piece, a negative pole piece, an electrolyte and a diaphragm, wherein the diaphragm is the composite diaphragm according to any one of claims 1 to 6.
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| CN115473006A (en) * | 2022-09-26 | 2022-12-13 | 惠州亿纬锂能股份有限公司 | Polyimide composite diaphragm, preparation method thereof and sodium-ion battery |
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