CN114883750A - 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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- CN114883750A CN114883750A CN202210345177.XA CN202210345177A CN114883750A CN 114883750 A CN114883750 A CN 114883750A CN 202210345177 A CN202210345177 A CN 202210345177A CN 114883750 A CN114883750 A CN 114883750A
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- 239000002131 composite material Substances 0.000 title claims abstract description 75
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 32
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 32
- 238000002360 preparation method Methods 0.000 title abstract description 16
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- 238000000576 coating method Methods 0.000 claims abstract description 136
- 229920000642 polymer Polymers 0.000 claims abstract description 101
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- 229920006231 aramid fiber Polymers 0.000 claims abstract description 83
- 239000002002 slurry Substances 0.000 claims abstract description 71
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- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 claims abstract description 6
- BAPJBEWLBFYGME-UHFFFAOYSA-N Methyl acrylate Chemical compound COC(=O)C=C BAPJBEWLBFYGME-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000000178 monomer Substances 0.000 claims abstract description 6
- 229920000573 polyethylene Polymers 0.000 claims abstract description 4
- JIGUQPWFLRLWPJ-UHFFFAOYSA-N Ethyl acrylate Chemical compound CCOC(=O)C=C JIGUQPWFLRLWPJ-UHFFFAOYSA-N 0.000 claims abstract description 3
- GYCMBHHDWRMZGG-UHFFFAOYSA-N Methylacrylonitrile Chemical compound CC(=C)C#N GYCMBHHDWRMZGG-UHFFFAOYSA-N 0.000 claims abstract description 3
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- 238000012360 testing method Methods 0.000 description 23
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 20
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 3
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
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- XQUPVDVFXZDTLT-UHFFFAOYSA-N 1-[4-[[4-(2,5-dioxopyrrol-1-yl)phenyl]methyl]phenyl]pyrrole-2,5-dione Chemical compound O=C1C=CC(=O)N1C(C=C1)=CC=C1CC1=CC=C(N2C(C=CC2=O)=O)C=C1 XQUPVDVFXZDTLT-UHFFFAOYSA-N 0.000 description 1
- OZAIFHULBGXAKX-UHFFFAOYSA-N 2-(2-cyanopropan-2-yldiazenyl)-2-methylpropanenitrile Chemical compound N#CC(C)(C)N=NC(C)(C)C#N OZAIFHULBGXAKX-UHFFFAOYSA-N 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 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
- 230000009471 action Effects 0.000 description 1
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- 238000007792 addition Methods 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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- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
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- 238000001523 electrospinning Methods 0.000 description 1
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- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
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- 238000012986 modification Methods 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
- H01M50/411—Organic 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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
-
- 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
-
- 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
- H01M50/491—Porosity
-
- 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
- H01M50/494—Tensile strength
-
- 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
- H01M50/497—Ionic conductivity
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
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- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Cell Separators (AREA)
Abstract
The invention provides a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite diaphragm comprises a base film, a thermal response polymer coating coated on one side of the base film and an aramid fiber coating coated on the other side of the base film; the thermal response polymer in the thermal response polymer coating is a homopolymer of any one monomer of methyl acrylate, methacrylonitrile, polyethylene microspheres, polystyrene, butadiene, butenenitrile or ethyl acrylate or a copolymer of any two or three of the monomers. According to the invention, the thermal response polymer slurry and the aramid fiber slurry are coated on the two sides of the base film to prepare the lightweight thermal response composite diaphragm, the adopted thermal response polymer can be heated, melted and collapsed at 120 ℃ to generate a thermal response effect, so that the transmission of lithium ions is cut off, the thermal runaway and short circuit of the battery are avoided, and the effects of protecting the battery and avoiding accidents are achieved.
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
At present, commercial polyolefin diaphragms and coated diaphragms have the problems of poor heat resistance, easy shrinkage under heating and easy generation of lithium dendrites and thermal runaway caused by piercing of the diaphragms, so that the direct contact of positive and negative electrodes with the pierced diaphragms causes short circuit of batteries, and further the safety performance and the service life of the lithium ion batteries are influenced. In addition, as high-performance lithium ion battery separators are largely applied to the fields of electronic devices and electric vehicles, they are gradually becoming one of the hot spots being studied. The performance of the diaphragm directly influences the internal resistance, discharge capacity, cycle service life and quality of the battery, so that a thermal response diaphragm with low melting point, small coating surface density and better air permeability needs to be developed, namely the melting point is lower than the thermal closed pore temperature (130 ℃) of a wet-process polyethylene diaphragm, the safety service life of the lithium ion battery is favorably improved, thermal runaway and short circuit accidents of the lithium ion battery are prevented, and the rapid development of future power batteries is favorably promoted.
Based on the above problems, CN103208604A discloses an electrospun composite membrane with a thermal pore-closing function and a lithium ion battery. The electrospinning composite diaphragm with the thermal pore-closing function is of a non-woven fabric structure and comprises polyimide nanofibers and low-melting-point polymer nanofibers containing bismaleimide and azodiisobutyronitrile, wherein the polyimide nanofibers and the low-melting-point polymer nanofibers are staggered in a mixed sequence. The melting point of the low-melting-point polymer nanofiber is 90-110 ℃, the secondary hot hole-closing function can be realized, the direct contact of the positive electrode and the negative electrode of the lithium ion battery caused by the action of thermal inertia is avoided, and the safety performance of the lithium ion battery is remarkably improved. Secondly, CN107359300A discloses a lithium ion battery diaphragm coated with aramid fiber in a composite mode and a preparation method thereof, the diaphragm comprises a lithium ion battery base film and a coating coated on one side or two sides of the base film, the coating is obtained by aramid fiber composite slurry after coating, water vapor preheating and hot air drying, the coating has good mechanical performance and high temperature resistance, and meanwhile, the diaphragm is provided with an open pore structure, and the wettability of electrolyte is greatly improved. In addition, the method has the characteristics of environmental friendliness, low cost, simple process, convenience for continuous production and the like. Finally, CN104485437A discloses a composite nanofiber membrane with a thermal pore-closing function, a preparation method and an energy storage device, wherein the composite nanofiber membrane with the thermal pore-closing function is a non-woven fabric structure and is formed by mutually crosslinking and compounding fibrillated cellulose nanofibers and at least one low-melting-point polymer nanofiber; the low-melting-point polymer nanofiber is a nanofiber containing polyolefin and polyester. The pore closing temperature of the diaphragm is 130-170 ℃, the fiber film does not shrink after pore closing, the thermal shrinkage rate is less than 2% after heating for 30min at the high temperature of 200 ℃, and the safety of the energy storage device is obviously improved.
However, the current thermal pore-closing coating diaphragm still has the problems of too thick thickness, relatively low air permeability, liquid retention capacity and heat shrinkage resistance, and is not beneficial to improving the manufacturing of a light-weight lithium ion battery and optimizing the electrochemical performance. Therefore, it is necessary to develop a composite separator having a thermal response function with light weight.
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. The invention provides a thermal response composite diaphragm aiming at improving the heat-resistant stability and the safety of a lithium ion battery diaphragm and the physical and chemical properties of the lithium ion battery diaphragm, such as improving the air permeability, the tensile strength, the ionic conductivity and the like of the diaphragm, and the thermal response composite diaphragm can realize the high-rate charge and discharge of the battery and improve the rate performance, the cycle life, the heat-resistant stability and the safety 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 comprising a base film, a thermally responsive polymer coating coated on one side of the base film, and an aramid coating coated on the other side of the base film;
the thermal response polymer in the thermal response polymer coating is a homopolymer of any one monomer of methyl acrylate, methacrylonitrile, polyethylene microspheres, polystyrene, butadiene, butenenitrile or ethyl acrylate or a copolymer of any two or three of the monomers.
In the present invention, the thermal response refers to the behavior of a polymer capable of melting by heat at 120 ℃.
According to the invention, the thermal response polymer slurry and the aramid fiber slurry are coated on the two sides of the base film to prepare the lightweight thermal response composite diaphragm, the adopted thermal response polymer can be heated, melted and collapsed at 120 ℃ to generate a thermal response effect, so that the transmission of lithium ions is cut off, the thermal runaway and short circuit of the battery are avoided, and the effects of protecting the battery and avoiding accidents are achieved. In addition, the composite diaphragm has the advantages of lower surface density, thinner thickness, better air permeability, good tensile strength, higher ionic conductivity, excellent heat-resistant stability, needling resistance and no fire, and further improves the rate capability and the cycle safety life of the lithium ion battery.
Preferably, the thickness of the composite separator is 9.5 μm to 13 μm, and may be, for example, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm.
Preferably, the thickness of the thermo-responsive polymer coating is 1.5 μm to 5 μm, and may be, for example, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm.
In the invention, the composite diaphragm has better comprehensive performance by adjusting the thickness of the thermal response polymer coating, and the thermal response effect of the composite diaphragm is too poor if the thickness is too thin, otherwise, the air permeability of the composite diaphragm is poor, and the performance of the battery is further influenced.
Preferably, the aramid coating has a thickness of 1 μm to 3 μm, and may be, for example, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm.
In the invention, the composite diaphragm has better comprehensiveness by adjusting the thickness of the aramid coating, the heat-resistant shrinkage of the composite diaphragm is not obviously improved if the thickness is too thin, otherwise, the surface density and the thickness of the composite diaphragm are increased, the improvement of the air permeability is not facilitated, and the battery performance is further influenced.
Preferably, the glass transition temperature of the aramid fiber in the aramid fiber coating is 100 ℃ to 450 ℃, and may be, for example, 100 ℃, 120 ℃, 150 ℃, 200 ℃, 220 ℃, 250 ℃, 280 ℃, 300 ℃, 320 ℃, 350 ℃, 370 ℃, 400 ℃ and 450 ℃.
In the invention, the heat-resistant shrinkage rate of the composite diaphragm is greatly reduced by adjusting the glass transition temperature of the aramid fiber.
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:
(1) mixing a thermal response polymer with a solvent, adding a surfactant, stirring, and filtering to obtain thermal response polymer slurry;
(2) mixing aramid fiber, a surfactant and a solvent, and filtering to obtain aramid fiber slurry;
(3) and coating the thermal response polymer slurry on one side of the base film, coating the aramid fiber slurry on the other side of the base film, and drying to obtain the composite diaphragm.
The invention adopts a separate coating mode, which has the advantage of improving the quality of finished products.
Preferably, D of the thermo-responsive polymer in step (1) 50 The particle diameter is 0.3 μm to 2 μm, and may be, for example, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm.
In the present invention, D is adjusted by the thermoresponsive polymer 50 The composite diaphragm has better air permeability due to the particle size.
Preferably, the melting point of the thermo-responsive polymer in step (1) is 105 ℃ to 115 ℃, and may be, for example, 105 ℃, 107 ℃, 109 ℃, 110 ℃, 112 ℃, 115 ℃.
In the invention, the melting point of the thermal response polymer is adjusted, so that the thermal response temperature of the composite diaphragm is added with utilization space and value, if the melting point is too low, the battery is not favorable to work at too high temperature, and if the melting point is too high, the melting point is close to the melting point of the base film of 135 ℃, so that the exertion of thermal response is influenced.
Preferably, the content of the thermally responsive polymer in the step (1) is 88 to 99% by mass, for example, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% by mass based on 100% by mass of the total dry material in the thermally responsive polymer slurry.
In the invention, the composite diaphragm has better air permeability and lower ionic conductivity by adjusting the mass percentage of the thermal response polymer.
Preferably, the surfactant in step (1) is any two or three of sodium alginate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinyl alcohol, polyacrylate or ethylene polyoxyethylene alkylphenol ether.
Preferably, the surfactant in step (1) is contained in an amount of 1% to 12% by mass, for example, 1%, 2%, 5%, 8%, 10%, 11%, 12% by mass, based on 100% by mass of the total dry matter in the thermally responsive polymer slurry.
Preferably, the solvent in step (1) is deionized water.
Preferably, the mixing in step (1) is carried out under ultrasound and stirring.
Preferably, the time of the ultrasound is 0.1min to 30min, for example, 0.1min, 0.5min, 1min, 5min, 10min, 20min, 30 min.
Preferably, the stirring time is 0.01h to 1h, and may be, for example, 0.01h, 0.05h, 0.1h, 0.3h, 0.5h, 0.8h, 1 h.
Preferably, the solids content of the thermally responsive polymer slurry in step (1) is 30% to 35%, and may be, for example, 30%, 31%, 32%, 33%, 34%, 35%.
In the invention, the solid content of the thermal response polymer slurry is adjusted, so that the thickness and the surface density of the composite diaphragm are higher in consistency, and the battery performance is better.
Preferably, D of the aramid fiber in the step (2) 50 The particle diameter is 0.1 μm to 0.5. mu.m, and may be, for example, 0.1. mu.m, 0.2. mu.m, 0.3. mu.m, 0.4. mu.m, or 0.5. mu.m.
Preferably, the mass percentage of the aramid fiber in the step (2) is 40-66% based on 100% of the total mass of dry materials in the aramid fiber slurry, and for example, may be 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 66%.
In the invention, the cost of the composite diaphragm is greatly reduced and the air permeability is better by adjusting the mass percentage of the aramid fiber.
Preferably, the surfactant in step (2) is any two or three of polyacrylate, sulfate, ethylene-vinyl acetate copolymer, alkyl polyoxyethylene ether or polyvinyl alcohol.
Preferably, the mass percentage of the surfactant in the step (2) is 34-60% based on 100% of the total mass of dry materials in the aramid pulp, and may be 34%, 36%, 38%, 40%, 45%, 50%, 55%, 60%, for example.
Preferably, the solvent in step (2) is dimethylacetamide.
Preferably, the mixing in step (2) is carried out under milling and stirring.
Preferably, the rate of milling is 500rpm to 1500rpm, and may be, for example, 500rpm, 800rpm, 1000rpm, 1200rpm, 1500 rpm.
Preferably, the stirring time is 0.5h to 6h, for example, 0.5h, 1h, 2h, 4h, 6 h.
Preferably, the solid content of the aramid pulp in the step (2) is 10% to 30%, for example, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30% can be achieved.
According to the invention, the solid content of the aramid fiber slurry is adjusted, so that the composite diaphragm has better consistency of thickness and surface density and better battery performance.
Preferably, the thermally responsive polymer paste is applied in step (3) by casting or gravure roll coating.
Preferably, the aramid pulp is coated in the step (3) by casting.
Preferably, the thickness of the slurry of the thermally responsive polymer coated in step (3) is 2 μm to 4 μm, and may be, for example, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm.
Preferably, the aramid pulp is coated in step (3) to a thickness of 0.5 μm to 2 μm, and may be, for example, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm.
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 thermal response 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, wherein aramid fiber slurry and thermal response polymer slurry are coated on the two surfaces of a base film, the coated thermal response polymer has a thermal response function of 105-115 ℃, the base film can be subjected to a thermal sealing hole effect at the temperature, the transmission of lithium ions is cut off, the thermal runaway and short circuit of a battery are prevented, the occurrence of accidents such as fire and the like is further avoided, and the safety performance and the service life of the battery are greatly improved; in addition, the aramid fiber coating has a high-temperature heat-resistant shrinkage function, and the composite diaphragm hardly shrinks thermally at a high temperature of 150 ℃; meanwhile, the membrane has lower surface density, greatly improves the wettability, the liquid retention capacity, the air permeability, the ionic conductivity and the tensile strength of the membrane to electrolyte, and has the advantages of needle-prick prevention and no fire;
according to the invention, the wetting property, the caking property, the peeling strength, the heat-resistant stability and the ductility of the coating diaphragm can be effectively improved by further optimizing the high-performance surfactant;
compared with other commodity coated membranes, the membrane has the advantages of lower surface density, better air permeability, simple preparation process and low cost, and can improve the rate capability, the cycle performance, the safety performance and the heat-resistant stability of the battery.
Drawings
Fig. 1 is a schematic structural diagram of a composite separator provided in example 1, wherein 1 is a base film, 2 is an aramid coating layer, and 3 is a thermal response polymer coating layer;
FIG. 2 is a SEM surface topography map of a thermally responsive polymer coating before and after heating the composite membrane provided in example 1 to 110 ℃;
fig. 3 is a flow chart of a preparation process of the lithium ion battery provided in example 1.
Detailed Description
The technical solution of the present 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
The present embodiment provides a composite separator, as shown in fig. 1, including a PP-based film, a thermo-responsive polymer coating layer coated on one side of the PP-based film, and an aramid coating layer coated on the other side of the PP-based film. The thickness of the composite diaphragm is 9.5 mu m, the thickness of the thermal response polymer coating is 1.5 mu m, the thickness of the aramid fiber coating is 1 mu m, and the D of the thermal response polymer 50 The particle size is 0.8 mu m, the melting point is 110 ℃, and the glass transition temperature of the aramid fiber in the aramid fiber coating is 450 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 10min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of a surfactant polyacrylate and an ethylene glycol alkylphenol ether (the mass ratio of the polyacrylate to the ethylene glycol alkylphenol ether is 9:1) for multiple times, adopting a high-speed cutting stirring mode, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry, stirring for 0.6h, and filtering to obtain thermal response polymer slurry with the solid content of 35%, wherein the thermal response polymer slurry in the step (1) comprises 95% by mass and the surfactant is 5% by mass based on 100% by mass of dry materials in the thermal response polymer slurry;
(2) will D 50 Mixing aramid fiber with the particle size of 0.05 mu m, polyvinyl alcohol and a barium sulfate surfactant (the mass ratio of polyvinyl alcohol to barium sulfate is 2:8) and a solvent, wherein the grinding speed is 600rpm, the stirring time is 4h, and filtering is carried out to obtain aramid fiber slurry with the solid content of 18%, wherein the aramid fiber content in the step (2) is 15% by mass and the surfactant content is 85% by mass based on 100% by mass of the total dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of a PP (polypropylene) base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PP base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the winding and unwinding tension is 5N, the rewinding temperature is 50 ℃, the rewinding speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24h to obtain the composite diaphragm.
Fig. 2 is a SEM surface morphology change diagram of the thermally responsive polymer coating before and after the composite membrane provided in example 1 is heated to 110 ℃, and it can be seen from fig. 2 that the thermally responsive polymer collapses when being heated to block the transmission of lithium ions.
Example 2
The embodiment provides a composite diaphragm, which comprises a PP (polypropylene) base film, a thermal response polymer coating coated on one side of the PP base film and an aramid fiber coating coated on the other side of the PP base film. The thickness of the composite diaphragm is 11 micrometers, the thickness of the thermal response polymer coating is 2.5 micrometers, the thickness of the aramid fiber coating is 2 micrometers, and the thickness of the thermal response polymer D is 50 The grain diameter is 1.2 mu m, the melting point is 110 ℃, and the glass transition of aramid fiber in the aramid fiber coating is realizedThe temperature was 350 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 15min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of a surfactant polyacrylate and an ethylene glycol alkylphenol ether (the mass ratio of the polyacrylate to the ethylene glycol alkylphenol ether is 9:1) for multiple times, adopting a high-speed cutting stirring mode, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry, stirring for 0.6h, and filtering to obtain a thermal response polymer slurry with the solid content of 32%, wherein the thermal response polymer in the step (1) accounts for 94% by weight and the surfactant accounts for 6% by weight based on 100% by weight of dry materials in the thermal response polymer slurry;
(2) will D 50 Aramid fiber with the particle size of 0.3 mu m, polyvinyl alcohol and barium sulfate surfactant (the mass ratio of polyvinyl alcohol to barium sulfate is 2:8) and a solvent are mixed, wherein the grinding speed is 1000rpm, the stirring time is 4 hours, and aramid fiber slurry with the solid content of 20% is obtained after filtering, wherein the aramid fiber content in the step (2) is 53% by mass and the surfactant content is 47% by mass based on 100% by mass of dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of a PP (polypropylene) base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PP base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the winding and unwinding tension is 5N, the rewinding temperature is 50 ℃, the rewinding speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24h to obtain the composite diaphragm.
Example 3
The embodiment provides a composite separator, which comprises a PP (polypropylene) base filmThe heat-responsive polymer coating is coated on one side of the PP basal membrane, and the aramid fiber coating is coated on the other side of the PP basal membrane. The thickness of the composite diaphragm is 10 micrometers, the thickness of the thermal response polymer coating is 3 micrometers, the thickness of the aramid fiber coating is 1.5 micrometers, and the thickness of the thermal response polymer D is 50 The particle size is 0.5 mu m, the melting point is 108 ℃, and the glass transition temperature of the aramid fiber in the aramid fiber coating is 250 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 10min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of a surfactant polyacrylate and an ethylene glycol alkylphenol ether (the mass ratio of the polyacrylate to the ethylene glycol alkylphenol ether is 9:1) for multiple times, adopting a high-speed cutting stirring mode, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry, stirring for 0.6h, and filtering to obtain a thermal response polymer slurry with a solid content of 31%, wherein the thermal response polymer slurry in the step (1) comprises 91% by weight and 9% by weight based on 100% by weight of dry materials in the thermal response polymer slurry;
(2) will D 50 Aramid fiber with the particle size of 0.12 mu m, polyvinyl alcohol and barium sulfate surfactant (the mass ratio of polyvinyl alcohol to barium sulfate is 2:8) and a solvent are mixed, wherein the grinding speed is 600rpm, the stirring time is 4 hours, and aramid fiber slurry with the solid content of 15% is obtained after filtering, wherein the aramid fiber content in the step (2) is 47% by mass and the surfactant content is 53% by mass based on 100% by mass of the total dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of a PP (polypropylene) base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PP base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the winding and unwinding tension is 5N, the rewinding temperature is 50 ℃, the rewinding speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24h to obtain the composite diaphragm.
Example 4
The embodiment provides a composite diaphragm, which comprises a PP (polypropylene) base film, a thermal response polymer coating coated on one side of the PP base film and an aramid fiber coating coated on the other side of the PP base film. The thickness of the composite diaphragm is 12 micrometers, the thickness of the thermal response polymer coating is 4 micrometers, the thickness of the aramid fiber coating is 2.5 micrometers, and the thickness of the thermal response polymer D is 50 The particle size is 1.5 mu m, the melting point is 112 ℃, and the glass transition temperature of the aramid fiber in the aramid fiber coating is 200 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 10min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of a surfactant polyacrylate and an ethylene polyoxyethylene alkylphenol ether (the mass ratio of the polyacrylate to the ethylene polyoxyethylene alkylphenol ether is 9:1) for multiple times, adopting a high-speed cutting and stirring mode, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry, stirring for 0.6h, and filtering to obtain a thermal response polymer slurry with the solid content of 34%, wherein the thermal response polymer in the step (1) accounts for 96% by weight and the surfactant is 4% by weight based on 100% by weight of dry materials in the thermal response polymer slurry;
(2) will D 50 Mixing aramid fiber with the particle size of 0.4 mu m, polyvinyl alcohol and barium sulfate surfactant (the mass ratio of polyvinyl alcohol to barium sulfate is 2:8) and a solvent, wherein the grinding speed is 600rpm, the stirring time is 4h, and filtering is carried out to obtain aramid fiber slurry with the solid content of 25%, wherein the aramid fiber content in the step (2) is 60% by mass and the surfactant content is 40% by mass based on 100% by mass of the total dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of a PP (polypropylene) base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PP base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the winding and unwinding tension is 5N, the rewinding temperature is 50 ℃, the rewinding speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24h to obtain the composite diaphragm.
Example 5
The embodiment provides a composite diaphragm, which comprises a PE base film, a thermal response polymer coating coated on one side of the PE base film and an aramid fiber coating coated on the other side of the PE base film. The thickness of the composite diaphragm is 9.5 mu m, the thickness of the thermal response polymer coating is 1.5 mu m, the thickness of the aramid fiber coating is 1 mu m, and the D of the thermal response polymer 50 The particle size is 0.3 mu m, the melting point is 105 ℃, and the glass transition temperature of the aramid fiber in the aramid fiber coating is 150 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 10min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of sodium alginate and sodium carboxymethylcellulose (the mass ratio of the sodium alginate to the sodium carboxymethylcellulose is 9:1) as surfactants for multiple times, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry in a high-speed cutting and stirring manner, stirring for 0.6h, and filtering to obtain thermal response polymer slurry with the solid content of 30%, wherein the thermal response polymer slurry in the step (1) comprises 88% by mass and the surfactant 12% by mass based on 100% by mass of dry materials in the thermal response polymer slurry;
(2) will D 50 Aramid fiber with particle size of 0.1 mu m, ethylene-vinyl acetate copolymer and polyvinyl alcohol surfactant (mass ratio of ethylene-vinyl acetate copolymer to polyvinyl alcohol is 2:8)) Mixing the aramid fiber slurry with a solvent, wherein the grinding speed is 600rpm, the stirring time is 4 hours, and filtering to obtain aramid fiber slurry with the solid content of 10%, wherein the aramid fiber slurry contains 40% by mass and 60% by mass of the surfactant in the step (2) based on 100% by mass of the dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of the PE base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PE base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the reeling and unreeling tension is 5N, the reeling temperature is 50 ℃, the reeling speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24h to obtain the composite diaphragm.
Example 6
The embodiment provides a composite diaphragm, which comprises a PE base film, a thermal response polymer coating coated on one side of the PE base film and an aramid fiber coating coated on the other side of the PE base film. The thickness of the composite diaphragm is 13 micrometers, the thickness of the thermal response polymer coating is 5 micrometers, the thickness of the aramid fiber coating is 3 micrometers, and the thickness of the thermal response polymer D is 50 The particle size is 2 mu m, the melting point is 115 ℃, and the glass transition temperature of the aramid fiber in the aramid fiber coating is 100 ℃.
The preparation method comprises the following steps:
(1) mixing a thermal response polymer and deionized water, performing ultrasonic dispersion for 10min, then performing low-speed dispersion stirring and mixing for 0.5h, uniformly adding a proper amount of a surfactant polyacrylate and an ethylene glycol alkylphenol ether (the mass ratio of the polyacrylate to the ethylene glycol alkylphenol ether is 9:1) for multiple times, adopting a high-speed cutting stirring mode, adjusting the stirring speed of a stirrer to be 500rpm by using mixed slurry, stirring for 0.6h, and filtering to obtain thermal response polymer slurry with the solid content of 35%, wherein the thermal response polymer slurry in the step (1) comprises 99% by weight and the surfactant of 1% by weight based on 100% by weight of dry materials in the thermal response polymer slurry;
(2) will D 50 Aramid fiber with the particle size of 0.5 mu m, polyvinyl alcohol and barium sulfate surfactant (the mass ratio of polyvinyl alcohol to barium sulfate is 2:8) and a solvent are mixed, wherein the grinding speed is 600rpm, the stirring time is 4 hours, and aramid fiber slurry with the solid content of 30% is obtained after filtering, wherein the aramid fiber content in the step (2) is 66% and the surfactant content is 34% by mass based on 100% of the total mass of dry materials in the aramid fiber slurry;
(3) coating the thermal response polymer slurry on one side of the PE base film in a gravure roll coating mode, and coating the aramid fiber slurry on the other side of the PE base film in a flow casting mode, wherein the coating temperature of a coating machine is 50 ℃, and the drying temperature after coating is 50 ℃; the difference of the winding and unwinding stretching speeds is 0.01; the winding and unwinding tension is 5N, the rewinding temperature is 50 ℃, the rewinding speed is 10m/min, and the contact pressure is 0.05N; the coating thickness is 1 μm; adjusting the technological parameters of the tape casting coating: the temperature of a plurality of drying ovens of the coating machine is set to be 60 ℃, and the speed ratio of casting is 0.12 m/min; the contact pressure of the wire rod is 2N; the total thickness of the finished coating film is 9.5 mu m; and drying the obtained coating film at 65 ℃ for 24 hours to obtain the composite diaphragm.
Example 7
This example is different from example 1 in that the melting point of the thermo-responsive polymer was 95 ℃, and the others were the same as example 1.
Example 8
This example is different from example 1 in that the melting point of the thermo-responsive polymer was 125 ℃, and the others were the same as example 1.
Example 9
This example differs from example 1 in that D of the thermally responsive polymer 50 The particle size was 50nm, and the other examples were the same as in example 1.
Example 10
This example and implementationExample 1 is different in that D of the thermo-responsive polymer 50 The particle size was 4 μm, and the other examples were the same as in example 1.
Example 11
This example differs from example 1 in that the solids content of the thermally responsive polymer syrup was 25%, all other things being equal to example 1.
Example 12
This example differs from example 1 in that the solids content of the thermally responsive polymer syrup was 40%, all other things being equal to example 1.
Example 13
This example differs from example 1 in that the aramid fiber D 50 The particle size was 50nm, and the other examples were the same as in example 1.
Example 14
This example differs from example 1 in that the aramid fiber D 50 The particle size was 1 μm, and the other examples were the same as in example 1.
Example 15
The difference between this example and example 1 is that the solid content of the aramid pulp is 5%, and the rest is the same as example 1.
Example 16
The difference between this example and example 1 is that the solid content of the aramid pulp is 35%, and the rest is the same as example 1.
Comparative example 1
This comparative example is different from example 1 in that the thermo-responsive polymer was replaced with polyvinylidene fluoride, and the others were the same as example 1.
Comparative example 2
The present comparative example is different from example 1 in that only the thermo-responsive polymer coating layer is coated on the surface of the base film, and the aramid coating layer is not coated, and the others are the same as example 1.
Comparative example 3
The present comparative example is different from example 1 in that only the aramid coating layer is coated on the surface of the base film, and the thermo-responsive polymer coating layer is not coated, and the others are the same as example 1.
Application examples 1-16 and comparative application examples 1-3
The lithium ion batteries were prepared by using the composite separators provided in examples 1 to 16 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 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 added dropwise, 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, and 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 graphite mixed with 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 for coating;
electrolyte solution: drying the lithium hexafluorophosphate LiPF 6 Dissolving in mixed solvent (ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate) with volume ratio of 1:1:1, and LiPF 6 The concentration of (A) is 1 mol/L;
preparing a lithium ion battery: as shown in fig. 3, the prepared positive and negative electrode slurry is coated on positive and negative current collectors, and the positive and negative electrode plates are obtained by drying and welding tabs, and then the positive and negative electrode plates are cut into positive and negative minimum electrode plates with a certain shape, and the thermal response diaphragm cut to a certain size is wound to isolate the positive and negative electrode plates and to be wound into an electric core body; then, performing short circuit evaluation on the electric core body, and screening high-quality electric cores; then the mixture is put into a battery shell, and a battery cover is covered; and injecting electrolyte into the battery shell, welding and sealing the battery shell to form the battery shell, sealing the battery shell for the second time, baking the clamp and grading the battery shell to obtain a finished product battery core.
Test conditions
The composite separators provided in examples 1 to 16 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;
testing the air permeability values of the thermal response composite membranes with different coating thicknesses before and after being heated to 110 ℃: 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 standby; adopting an electrochemical workstation to test EIS;
testing the ion conductivity of the thermal response composite membrane with different coating thicknesses before and after being heated to 110 ℃: the test sample size was 18mm in diameter; punching sheets for standby; 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 16 and comparative application examples 1 to 3 were subjected to electrochemical performance tests, the test methods were as follows:
(1) cycle performance: the test is carried out on a battery test system of an electrochemical workstation at the temperature of 25 ℃, the tested current density is 0.1C/1C, and the charging and discharging voltage window is 2.75-4.2V.
(2) Rate capability: the current density of the test is 0.1/0.5/1/2/3/C, and the charging and discharging voltage window is 2.75-4.2V when the test is carried out on the electrochemical workstation battery test system under the condition 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 of tables 1 and 2, the polyimide composite separators according to examples 1 to 6 of the present invention have a heat shrinkage of not more than 45%, a gas permeation value of not more than 300s/100ml, an ionic conductivity of not more than 3mS/cm and a tensile strength of not less than 80Kgf/cm 2 。
Compared with the example 1, the melting points of the thermal response polymers in the examples 7 and 8 are beyond the range, which shows that the battery is not favorable to work at an excessively high temperature when the melting point is too low, and the melting point is close to the melting point of the base film of 135 ℃ when the melting point is too high, so that the thermal response is exerted; in examples 9 and 10, when the particle size of the thermally responsive polymer is out of the range, the aggregation phenomenon occurs when the particle size is too small, which affects the air permeability of the separator, and the short circuit easily occurs when the particles with too large particle size are loose.
Comparative example 1 is a polyvinylidene fluoride coated separator, which is inferior in overall performance to example 1, and comparative examples 2 and 3 are single-layer coated separators, which are inferior in thermal shrinkage or tensile strength to the composite separator provided in example 1, as 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 6 is not less than 80% after being cycled 500 times at 0.1C, and the capacity retention rate of the lithium ion batteries is not less than 70% after being cycled 500 times at 1C.
Compared with example 1, the capacity retention rates at 0.1C and 1C of the separator coated with other polymers of comparative application example 1, the separator coated with other polymers of comparative application example 2 and the separator coated with a single layer of comparative application example are much lower than that of the lithium ion battery provided by application example 1, which shows that the composite separator provided by the invention can improve the rate performance, cycle performance, safety performance and heat resistance stability of the battery.
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. The composite diaphragm is characterized by comprising a base film, a thermal response polymer coating coated on one side of the base film and an aramid fiber coating coated on the other side of the base film;
the thermal response polymer in the thermal response polymer coating is a homopolymer of any one monomer of methyl acrylate, methacrylonitrile, polyethylene microspheres, polystyrene, butadiene, butenenitrile or ethyl acrylate or a copolymer of any two or three of the monomers.
2. The composite separator according to claim 1, wherein the thickness of the composite separator is 9.5 μ ι η to 13 μ ι η;
preferably, the thickness of the thermo-responsive polymer coating is 1.5 μm to 5 μm;
preferably, the aramid coating has a thickness of 1 μm to 3 μm.
3. The composite separator of claim 1 or 2, wherein the aramid in the aramid coating has a glass transition temperature of 100 ℃ to 450 ℃.
4. A method of making the composite separator of any one of claims 1-3, comprising the steps of:
(1) mixing a thermal response polymer with a solvent, adding a surfactant, stirring, and filtering to obtain thermal response polymer slurry;
(2) mixing aramid fiber, a surfactant and a solvent, and filtering to obtain aramid fiber slurry;
(3) and coating the thermal response polymer slurry on one side of the base film, coating the aramid fiber slurry on the other side of the base film, and drying to obtain the composite diaphragm.
5. The method of claim 4, wherein the D of the thermo-responsive polymer in step (1) 50 The grain diameter is 0.3-2 μm;
preferably, the melting point of the thermo-responsive polymer in step (1) is 105 ℃ to 115 ℃;
preferably, the mass percentage of the thermal response polymer in the step (1) is 88-99% based on 100% of the total mass of dry materials in the thermal response polymer slurry.
6. The method according to claim 4 or 5, wherein the surfactant in step (1) is any two or three of sodium alginate, sodium carboxymethylcellulose, polyvinyl acetate, polyvinyl alcohol, polyacrylate or ethylene polyoxyethylene alkylphenol ether;
preferably, the mass percentage of the surfactant in the step (1) is 1-12% based on 100% of the total mass of dry materials in the thermal response polymer slurry;
preferably, the solvent in step (1) is deionized water;
preferably, the mixing in step (1) is carried out under ultrasound and stirring;
preferably, the time of the ultrasonic treatment is 0.1min-30 min;
preferably, the stirring time is 0.01h-1 h;
preferably, the solids content of the thermally responsive polymer slurry in step (1) is 30% to 35%.
7. The method of any one of claims 4-6, wherein D of the aramid fiber in step (2) 50 The grain diameter is 0.1-0.5 μm;
preferably, the mass percentage of the aramid fiber in the step (2) is 40-66% based on 100% of the total mass of dry materials in the aramid fiber slurry.
8. The method according to any one of claims 4 to 7, wherein the surfactant in step (2) is any two or three of polyacrylate, sulfate, ethylene-vinyl acetate copolymer, alkyl polyoxyethylene ether, or polyvinyl alcohol;
preferably, the mass percentage of the surfactant in the step (2) is 34-60% based on 100% of the total mass of dry materials in the aramid fiber slurry;
preferably, the solvent in step (2) is dimethylacetamide;
preferably, the mixing in step (2) is carried out under milling and stirring;
preferably, the rate of milling is 500rpm to 1500 rpm;
preferably, the stirring time is 0.5h-6 h;
preferably, the solid content of the aramid fiber slurry in the step (2) is 10-30%.
9. The method according to any one of claims 4 to 8, wherein the thermally responsive polymer paste is applied in step (3) by casting or gravure roll coating;
preferably, the aramid pulp in the step (3) is coated by casting;
preferably, the thickness of the thermal response polymer paste coating in the step (3) is 2 μm to 4 μm;
preferably, the aramid pulp is coated in step (3) to a thickness of 0.5 μm to 2 μm.
10. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is the composite separator according to any one of claims 1 to 3.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104993089A (en) * | 2015-07-29 | 2015-10-21 | 沧州明珠隔膜科技有限公司 | Aramid coated lithium ion battery diaphragm and preparation method thereof |
| CN105552284A (en) * | 2015-12-22 | 2016-05-04 | 沧州明珠隔膜科技有限公司 | Composite coating lithium-ion battery separator and preparation method thereof |
| CN106252565A (en) * | 2016-09-23 | 2016-12-21 | 佛山市金辉高科光电材料有限公司 | Lithium ion battery separator that a kind of composite coated processes and preparation method thereof |
| CN114039168A (en) * | 2021-11-30 | 2022-02-11 | 惠州亿纬锂能股份有限公司 | Thermal closed-pore diaphragm and preparation method and application thereof |
-
2022
- 2022-03-31 CN CN202210345177.XA patent/CN114883750A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104993089A (en) * | 2015-07-29 | 2015-10-21 | 沧州明珠隔膜科技有限公司 | Aramid coated lithium ion battery diaphragm and preparation method thereof |
| CN105552284A (en) * | 2015-12-22 | 2016-05-04 | 沧州明珠隔膜科技有限公司 | Composite coating lithium-ion battery separator and preparation method thereof |
| CN106252565A (en) * | 2016-09-23 | 2016-12-21 | 佛山市金辉高科光电材料有限公司 | Lithium ion battery separator that a kind of composite coated processes and preparation method thereof |
| CN114039168A (en) * | 2021-11-30 | 2022-02-11 | 惠州亿纬锂能股份有限公司 | Thermal closed-pore diaphragm and preparation method and application thereof |
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