CN116904147A - Modified binder and preparation method and application thereof - Google Patents
Modified binder and preparation method and application thereof Download PDFInfo
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- CN116904147A CN116904147A CN202310841966.7A CN202310841966A CN116904147A CN 116904147 A CN116904147 A CN 116904147A CN 202310841966 A CN202310841966 A CN 202310841966A CN 116904147 A CN116904147 A CN 116904147A
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- 239000011230 binding agent Substances 0.000 title claims abstract description 55
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 239000000178 monomer Substances 0.000 claims abstract description 96
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical compound C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 claims abstract description 88
- 239000003999 initiator Substances 0.000 claims abstract description 37
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 claims abstract description 36
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 claims abstract description 36
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 claims abstract description 27
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 claims abstract description 27
- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 claims abstract description 26
- 238000006243 chemical reaction Methods 0.000 claims abstract description 24
- XSAOIFHNXYIRGG-UHFFFAOYSA-M lithium;prop-2-enoate Chemical compound [Li+].[O-]C(=O)C=C XSAOIFHNXYIRGG-UHFFFAOYSA-M 0.000 claims abstract description 22
- 239000003995 emulsifying agent Substances 0.000 claims abstract description 21
- 239000007795 chemical reaction product Substances 0.000 claims abstract description 19
- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical compound FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 claims abstract description 18
- 238000007334 copolymerization reaction Methods 0.000 claims abstract description 13
- 238000000034 method Methods 0.000 claims abstract description 10
- 239000006185 dispersion Substances 0.000 claims abstract description 9
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 5
- 239000000344 soap Substances 0.000 claims description 18
- LCPVQAHEFVXVKT-UHFFFAOYSA-N 2-(2,4-difluorophenoxy)pyridin-3-amine Chemical group NC1=CC=CN=C1OC1=CC=C(F)C=C1F LCPVQAHEFVXVKT-UHFFFAOYSA-N 0.000 claims description 15
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 15
- 229910001416 lithium ion Inorganic materials 0.000 claims description 15
- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims description 15
- 230000001070 adhesive effect Effects 0.000 claims description 11
- 239000000853 adhesive Substances 0.000 claims description 10
- 235000014113 dietary fatty acids Nutrition 0.000 claims description 9
- 229930195729 fatty acid Natural products 0.000 claims description 9
- 239000000194 fatty acid Substances 0.000 claims description 9
- 150000004665 fatty acids Chemical class 0.000 claims description 9
- NVJCKICOBXMJIJ-UHFFFAOYSA-M potassium;1,4a-dimethyl-7-propan-2-yl-2,3,4,4b,5,6,10,10a-octahydrophenanthrene-1-carboxylate Chemical compound [K+].C12CCC(C(C)C)=CC2=CCC2C1(C)CCCC2(C)C([O-])=O NVJCKICOBXMJIJ-UHFFFAOYSA-M 0.000 claims description 9
- 230000035484 reaction time Effects 0.000 claims description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 8
- 229910052744 lithium Inorganic materials 0.000 abstract description 8
- 230000000052 comparative effect Effects 0.000 description 12
- 229920001577 copolymer Polymers 0.000 description 9
- 229920003048 styrene butadiene rubber Polymers 0.000 description 8
- 229920002125 Sokalan® Polymers 0.000 description 7
- 239000002174 Styrene-butadiene Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 239000002390 adhesive tape Substances 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000006258 conductive agent Substances 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 150000002500 ions Chemical class 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
- 230000014759 maintenance of location Effects 0.000 description 2
- 239000004584 polyacrylic acid Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 125000003011 styrenyl group Chemical group [H]\C(*)=C(/[H])C1=C([H])C([H])=C([H])C([H])=C1[H] 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F285/00—Macromolecular compounds obtained by polymerising monomers on to preformed graft polymers
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J151/00—Adhesives based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers
- C09J151/003—Adhesives based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers grafted on to macromolecular compounds obtained by reactions only involving unsaturated carbon-to-carbon bonds
-
- 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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
-
- 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 discloses a modified binder which is formed by stepwise copolymerization of a monomer 1, a monomer 2 and a monomer 3, wherein the monomer 1 is styrene, the monomer 2 is any one of propylene, butadiene and vinylidene fluoride, and the monomer 3 is acrylic acid or lithium acrylate. The preparation method comprises the steps of (1) adding a monomer 1, a monomer 2, an emulsifying agent and an initiator into a reaction kettle for polymerization reaction; (2) Adding the monomer 3 and the initiator into the reaction product of the step (1) through a booster pump, and continuing to react for 1-3 hours after uniform dispersion; (3) repeating the procedure of the step (2) 2 times; (4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder. The modified binder provided by the invention can exert the advantages of SBR and PAA, and meanwhile avoids the disadvantages of SBR and PAA, namely, the modified binder has good processability and excellent binding capacity, and can also greatly improve the low-temperature performance, the rate performance and the cycle performance of a lithium battery.
Description
Technical Field
The invention belongs to the field of adhesives, and particularly relates to a modified binder, a preparation method thereof and application thereof in lithium ion batteries.
Background
The lithium ion battery is a new generation green high-energy battery with excellent performance, has become one of the key points of the development of high and new technology, has the advantages of high voltage, high capacity, low consumption, no memory effect, no pollution, small volume, small internal resistance, less self discharge, good cycle stability and the like, and is widely applied to the fields of digital products such as mobile phones, notebook computers, video cameras, digital cameras and the like, new energy automobiles and the like. Along with the wider and wider application of lithium ion batteries, the requirements on the lithium ion batteries are also higher and higher, such as the requirements on the performances of energy density, cycle stability, safety and the like of the lithium ion batteries.
The binder for the lithium ion battery also has a certain influence on the performance of the lithium ion battery. The water-based binder used in the lithium ion battery at present mainly comprises a styrene butadiene rubber system (SBR system) and a polyacrylic acid system (PAA system), wherein the SBR system has excellent processing performance, good binding performance and pole piece softness, but has higher impedance due to the lack of polar groups in the synthesis process, so that the low-temperature performance and the rate capability of the lithium battery are affected; while the PAA system has excellent ionic conductivity, the PAA binder has hard and brittle pole pieces due to the defects of the self structure, so that the processing performance of the pole pieces in the production process of the lithium battery is seriously affected, for example: the edge is easy to fall powder in die cutting, the pole piece is hard enough to influence the winding, stress cannot be released in the circulating process, uneven stress is caused, uneven interface appears, local lithium precipitation is caused, and finally the safety and the circulating performance of the lithium battery can be influenced.
Disclosure of Invention
The invention aims to solve the technical problems, overcome the defects and the shortcomings in the background art, and provide a modified binder, a preparation method and application thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a modified adhesive is formed by stepwise copolymerization of a monomer 1, a monomer 2 and a monomer 3, wherein the monomer 1 is styrene, the monomer 2 is any one of propylene, butadiene and vinylidene fluoride, and the monomer 3 is acrylic acid or lithium acrylate.
In the modified binder, it is further preferable that the monomer 3 is lithium acrylate. The addition of the lithium acrylate can solve the problem that the pole piece is relatively brittle, and meanwhile, the bonding performance and the ion conductivity of the adhesive can be greatly improved.
The modified binder is preferably one having a weight average molecular weight of 15 to 50 ten thousand.
In the modified binder, when the monomer 2 is selected from propylene or butadiene, the mass ratio of the monomer 1 to the monomer 2 is preferably (20 to 30): (70-80), wherein the addition amount of the monomer 3 accounts for 0.9-12% of the total mass of the monomer 1 and the monomer 2.
In the modified binder, when the monomer 2 is selected from vinylidene fluoride, the mass ratio of the monomer 1 to the monomer 2 is preferably (10 to 25): (75-90), wherein the addition amount of the monomer 3 accounts for 0.9-12% of the total mass of the monomer 1 and the monomer 2.
The present invention also provides a method for preparing the modified binder, comprising the following steps:
(1) Adding the monomer 1, the monomer 2, the emulsifier and the initiator into a reaction kettle for polymerization reaction;
(2) Adding the monomer 3 and the initiator into the reaction product of the step (1) through a booster pump, and continuing to react for 1-3 hours after uniform dispersion;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder.
In the above preparation method, preferably, in the step (1), the polymerization reaction temperature is 60-70 ℃, the pressure is 1-3MPa, and the reaction time is 1-5 hours.
In the preparation method, preferably, in the step (1), the emulsifier is disproportionated potassium abietate soap and fatty acid soap with a mass ratio of 1:1, and the addition amount of the emulsifier is 4% -6% of the total mass of the monomer 1, the monomer 2 and the monomer 3.
In the above preparation method, preferably, in the step (1), the initiator is sodium persulfate, and the addition amount of the initiator is 0.04-0.06% of the total mass of the monomer 1, the monomer 2 and the monomer 3.
In the above preparation method, preferably, in the step (2), the addition amount of the monomer 3 is one third of the total addition amount of the monomer 3; the addition amount of the initiator is 0.04-0.08% of the total mass of the monomer 1, the monomer 2 and the monomer 3.
The invention also provides an application of the modified binder or the modified binder prepared by the preparation method in a lithium ion battery as a general inventive concept.
Compared with the prior art, the invention has the advantages that:
(1) The modified binder provided by the invention can exert the advantages of SBR and PAA, and meanwhile avoids the disadvantages of SBR and PAA, namely, the modified binder has good processability and excellent binding capacity, and can also greatly improve the low-temperature performance, the rate performance and the cycle performance of a lithium battery.
(2) The modified binder is prepared by step-by-step copolymerization of styrene, propylene (or butadiene or vinylidene fluoride) and acrylic acid (or lithium acrylate), wherein a-CH-n group is a flexible group of the binder, so that the flexibility of a pole piece can be improved, a styrene group is a polar group, the cohesiveness and a framework structure can be provided for copolymerization, and a-COO-H/Li group in the acrylic acid or the lithium acrylate is a strong polar group, so that the cohesiveness of a copolymer can be improved.
(3) When the monomer 2 in the modified adhesive is vinylidene fluoride, the addition amount of the monomer 2 is required to be increased appropriately to form a long-chain group of vinylidene fluoride, the characteristic that the traditional SBR pole piece is relatively brittle can be improved by utilizing the flexible group of the long-chain vinylidene fluoride, and meanwhile, a better adhesive effect is achieved by utilizing the strong polarity of fluorocarbon bonds, so that the adhesive force between the adhesive and the foil is enhanced.
(4) The modified adhesive adopts multistage copolymerization, styrene and propylene (or butadiene or vinylidene fluoride) are copolymerized in the first step, the main molecular structure is ensured to be a structure of styrene and propylene (or butadiene or vinylidene fluoride), then acrylic acid or lithium acrylate is copolymerized in multiple steps, and the copolymer containing the strong polar group can be formed by copolymerizing the acrylic acid or the lithium acrylate with the tail end of the copolymer, so that the copolymer and the foil material are ensured to have better adhesion effect, and better bonding effect is achieved.
Detailed Description
The invention will be described more fully hereinafter with reference to the preferred embodiments for the purpose of facilitating an understanding of the invention, but the scope of the invention is not limited to the specific embodiments described below.
Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.
Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.
Example 1:
the modified binder is prepared by stepwise copolymerization of styrene, propylene and acrylic acid, and has a weight average molecular weight of about 20 ten thousand, wherein the mass ratio of the styrene to the propylene is 25:75, and the addition amount of the acrylic acid accounts for 3% of the total mass of the styrene and the propylene.
The preparation method of the modified binder in the embodiment comprises the following steps:
(1) Adding styrene, propylene, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 2 hours at a reaction temperature of 65 ℃ and a pressure of 2MPa to obtain a copolymer with a molecular weight of 3 ten thousand; wherein, the emulsifier accounts for 5% of the total mass of styrene, propylene and acrylic acid in the whole reaction process, and the initiator accounts for 0.06%;
(2) Adding acrylic acid and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 2 hours after uniform dispersion, wherein the addition amount of the acrylic acid in the step is 1% of the total mass of styrene and propylene, and the addition amount of the initiator is 0.06% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder with the weight average molecular weight of about 20 ten thousand.
Example 2:
the modified binder is prepared by stepwise copolymerization of styrene, butadiene and acrylic acid, and has a weight average molecular weight of about 48 ten thousand, wherein the mass ratio of the styrene to the butadiene is 25:75, and the addition amount of the acrylic acid accounts for 4.5% of the total mass of the styrene and the propylene.
The preparation method of the modified binder in the embodiment comprises the following steps:
(1) Adding styrene, butadiene, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 4 hours at a reaction temperature of 70 ℃ and a pressure of 2.5MPa to obtain a copolymer with a molecular weight of about 10 ten thousand; wherein, the emulsifier accounts for 6% of the total mass of the styrene, the butadiene and the acrylic acid in the whole reaction process, and the initiator accounts for 0.05%;
(2) Adding acrylic acid and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 3 hours after uniform dispersion, wherein the addition amount of the acrylic acid in the step is 1.5% of the total mass of styrene and butadiene, and the addition amount of the initiator is 0.06% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder with the molecular weight of about 48 ten thousand.
Example 3:
the modified binder is prepared by stepwise copolymerization of styrene, propylene and lithium acrylate, and has a weight average molecular weight of about 18 ten thousand, wherein the mass ratio of the styrene to the propylene is 25:75, and the addition amount of the lithium acrylate accounts for 3% of the total mass of the styrene and the propylene.
The preparation method of the modified binder in the embodiment comprises the following steps:
(1) Adding styrene, propylene, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 2 hours at a reaction temperature of 70 ℃ and a pressure of 2MPa to obtain a copolymer with a molecular weight of about 3 ten thousand; wherein, the emulsifier accounts for 5% of the total mass of the styrene, the propylene and the lithium acrylate in the whole reaction process, and the initiator accounts for 0.06%;
(2) Adding lithium acrylate and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 2 hours after uniform dispersion, wherein in the step, the addition amount of the lithium acrylate is 1% of the total mass of styrene and propylene, and the addition amount of the initiator is 0.06% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder with the weight average molecular weight of about 18 ten thousand.
Example 4:
the modified binder is prepared by stepwise copolymerization of styrene, vinylidene fluoride and lithium acrylate, and has a weight average molecular weight of about 40 ten thousand, wherein the mass ratio of the styrene to the propylene is 15:85, and the addition amount of the lithium acrylate accounts for 9% of the total mass of the styrene and the propylene.
The preparation method of the modified binder in the embodiment comprises the following steps:
(1) Adding styrene, vinylidene fluoride, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 4 hours at a reaction temperature of 70 ℃ and a pressure of 2MPa to obtain a copolymer with a molecular weight of about 10 ten thousand; wherein, the emulsifier accounts for 5% of the total mass of the styrene, the vinylidene fluoride and the lithium acrylate in the whole reaction process, and the initiator accounts for 0.06%;
(2) Adding lithium acrylate and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 2 hours after uniform dispersion, wherein in the step, the addition amount of the lithium acrylate is 3% of the total mass of styrene and propylene, and the addition amount of the initiator is 0.06% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder with the weight average molecular weight of about 40 ten thousand.
Example 5:
the modified binder is prepared by stepwise copolymerization of styrene, vinylidene fluoride and acrylic acid, and has a weight average molecular weight of about 40 ten thousand, wherein the mass ratio of the styrene to the propylene is 15:85, and the addition amount of the acrylic acid accounts for 12% of the total mass of the styrene and the propylene.
The preparation method of the modified binder in the embodiment comprises the following steps:
(1) Adding styrene, vinylidene fluoride, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 4 hours at a reaction temperature of 70 ℃ and a pressure of 2MPa to obtain a copolymer with a molecular weight of about 10 ten thousand; wherein, the emulsifier accounts for 4% of the total mass of the styrene, the vinylidene fluoride and the lithium acrylate in the whole reaction process, and the initiator accounts for 0.056%;
(2) Adding propylene and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 2 hours after uniform dispersion, wherein the addition amount of acrylic acid in the step is 4% of the total mass of styrene and propylene, and the addition amount of the initiator is 0.05% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder with the weight average molecular weight of about 40 ten thousand.
Comparative example 1:
the comparative example uses styrene butadiene rubber as a comparison, and directly purchases lithium-battery-grade SBR of Henan Jinbang power supply S2919 model.
Comparative example 2:
the comparative example uses polyacrylic acid as a comparison, and directly purchases the Duyindele LA133 model lithium battery level water-based adhesive.
Comparative example 3:
the preparation method of the modified binder in the comparative example comprises the following steps:
(1) Adding styrene, propylene, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 2 hours at a reaction temperature of 65 ℃ and a pressure of 2MPa, wherein the emulsifier accounts for 5% of the total mass of the styrene, the propylene and the acrylic acid in the whole reaction process, and the initiator accounts for 0.06%; the mass ratio of the styrene to the propylene is 25:75;
(2) Adding acrylic acid and an initiator sodium persulfate into the reaction product obtained in the step (1) through a booster pump, and continuously reacting for 2 hours after uniform dispersion, wherein in the step, the addition amount of the acrylic acid is 3% of the total mass of styrene and propylene, and the addition amount of the initiator is 0.18% of the total mass of a monomer 1, a monomer 2 and a monomer 3;
(3) Rectifying the reaction product obtained in the step (2) to obtain the modified binder.
Comparative example 4:
the preparation method of the modified binder in the comparative example comprises the following steps:
adding styrene, propylene, acrylic acid, an emulsifier (disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1) and an initiator (sodium persulfate) into a reaction kettle, and reacting for 8 hours at a reaction temperature of 65 ℃ and a pressure of 2MPa to obtain a modified binder; wherein the mass ratio of the styrene to the propylene is 25:75, the addition amount of the acrylic acid is 3% of the total mass of the styrene and the propylene, the emulsifier accounts for 5% of the total mass of the styrene, the propylene and the acrylic acid in the whole reaction process, and the initiator accounts for 0.06%; and rectifying the reaction product to obtain the modified binder.
The modified binders of examples 1-5 and comparative examples 1-4 were tested for adhesion, flexibility, and performance in lithium ion batteries, and the results are shown in table 1, and the specific test methods are:
uniformly dispersing negative active graphite, a conductive agent, a binder and the like into deionized water in a double-planetary stirring mode, uniformly coating the mixture on a copper foil through coating equipment, drying the water through a drying process, and finally preparing a negative electrode plate, wherein the binder in the negative electrode plate adopts the binders in the embodiment and the comparative example.
The preparation of the positive electrode sheet adopts the commercial lithium iron phosphate positive electrode sheet in the current market, namely, the positive electrode active material lithium iron phosphate, the conductive agent, the PVDF binder and the like are uniformly dispersed into NMP in a double-planetary stirring mode, then the NMP is uniformly coated on a copper foil through coating equipment, and finally the NMP is dried through a drying procedure, so that the positive electrode sheet is prepared.
Negative plate adhesion detection: and (3) attaching 10cm 1cm transparent adhesive tape to the surface of the prepared negative electrode plate, rolling the transparent adhesive tape back and forth for 5 times by using a roller to ensure that the transparent adhesive tape is firmly attached, and uniformly stripping by using a tensile tester to obtain the adhesive force of the negative electrode plate.
And (3) detecting the flexibility of the pole piece: folding the obtained negative plate back and forth 180 degrees for 5 times, and observing whether a pole piece is stripped at the folding position: if the pole piece at the folded position is peeled off, the pole piece is judged to be brittle, and if the pole piece at the folded position is not peeled off, the pole piece is judged to be soft.
And (3) assembling a lithium battery: the positive electrode plate and the negative electrode plate are subjected to cold pressing and roller pair working procedures and then are separated into required sizes, then the electrode lugs are welded, the electrode lugs and the diaphragm are wound into a bare cell, and then the bare cell is packaged by an aluminum plastic film, baked for moisture, filled with electrolyte, formed, pumped and sealed to obtain the lithium ion battery full cell.
And (3) cycle performance detection: and (3) carrying out cycle detection on the prepared full battery of the lithium ion battery by using 1C charge/1C discharge on a charge-discharge cabinet, and testing the retention rate of the battery capacity after 2000 cycles.
Multiplying power test: the prepared lithium ion battery full cells were subjected to discharge test with 0.5C/1C/2C, respectively.
And (3) low-temperature performance detection: and (3) fully charging the prepared lithium ion battery, standing for 4 hours at the low temperature of-30 ℃ and then performing discharge test on the retention rate of the battery capacity at 0.5 ℃.
Table 1 properties of the modified binders in each of examples and comparative examples
From the comparison of the above examples and comparative examples, it can be seen that the present invention has a certain improvement in improving the flexibility of the electrode sheet by the staged copolymerization and the addition of acrylic acid/lithium acrylate as a modifying group while improving the rate capability and low temperature capability of the battery, and that the introduction of monomer VDF for the staged copolymerization is optimal in the flexibility, adhesion, and rate and low temperature of the electrode sheet after the addition of the ion conductive monomer lithium acrylate as well as from the experimental data of example 4.
Claims (10)
1. The modified adhesive is characterized by being formed by step-by-step copolymerization of a monomer 1, a monomer 2 and a monomer 3, wherein the monomer 1 is styrene, the monomer 2 is selected from any one of propylene, butadiene and vinylidene fluoride, and the monomer 3 is acrylic acid or lithium acrylate.
2. The modified binder of claim 1 wherein said modified binder has a weight average molecular weight of 15 to 50 ten thousand.
3. The modified binder of claim 1 wherein when said monomer 2 is selected from propylene or butadiene, the mass ratio of said monomer 1 to said monomer 2 is (20-30): (70-80), wherein the addition amount of the monomer 3 accounts for 0.9-12% of the total mass of the monomer 1 and the monomer 2.
4. The modified binder of claim 1 wherein when said monomer 2 is selected from vinylidene fluoride, the mass ratio of said monomer 1 to said monomer 2 is (10-25): (75-90), wherein the addition amount of the monomer 3 accounts for 0.9-12% of the total mass of the monomer 1 and the monomer 2.
5. A method of preparing a modified binder as claimed in any one of claims 1 to 4, comprising the steps of:
(1) Adding the monomer 1, the monomer 2, the emulsifier and the initiator into a reaction kettle for polymerization reaction;
(2) Adding the monomer 3 and the initiator into the reaction product of the step (1) through a booster pump, and continuing to react for 1-3 hours after uniform dispersion;
(3) Repeating the step (2) 2 times;
(4) Rectifying the reaction product obtained in the step (3) to obtain the modified binder.
6. The process according to claim 5, wherein in the step (1), the polymerization is carried out at a temperature of 60 to 70℃and a pressure of 1 to 3MPa for a reaction time of 1 to 5 hours.
7. The preparation method according to claim 5, wherein in the step (1), the emulsifier is disproportionated potassium abietate soap and fatty acid soap in a mass ratio of 1:1, and the addition amount of the emulsifier is 4% -6% of the total mass of the monomer 1, the monomer 2 and the monomer 3.
8. The process according to claim 5, wherein in the step (1), the initiator is sodium persulfate and the addition amount thereof is 0.04 to 0.06% by mass of the total mass of the monomer 1, the monomer 2 and the monomer 3.
9. The method according to claim 5, wherein in the step (2), the amount of the monomer 3 added is one third of the total amount of the monomer 3 added; the addition amount of the initiator is 0.04-0.08% of the total mass of the monomer 1, the monomer 2 and the monomer 3.
10. Use of the modified binder according to any one of claims 1 to 4 or obtained by the preparation method according to any one of claims 5 to 9 in lithium ion batteries.
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