A high conductivity water-based binder and a method for preparing the same

Abstract

The application relates to a high-conductivity water-based binder and a preparation method thereof. The water-based binder is a copolymer which is copolymerized by the following monomers and comprises, in percentage by mass, 30-55% of a first monomer, 15-30% of a second monomer, 2-15% of a third monomer, 20-35% of a fourth monomer and 0-16% of a fifth monomer. The binder has excellent bonding strength, ion conductivity, dispersibility and processing stability, is suitable for a lithium ion battery negative electrode slurry, shows low pole piece resistance, high rate performance and long cycle life, and has a good application prospect.

Description

Technical Field

[0001] This application relates to the field of electrode material technology, and in particular to a high conductivity water-based binder and its preparation method. Background Technology

[0002] Currently, the technical requirements and product planning of lithium-ion batteries are rising rapidly with the development of the electric vehicle market and the electrochemical energy storage market. Lithium-ion batteries that combine high energy density and high rate performance have become the industry's central pursuit. As one of the most important components in lithium-ion battery electrodes, the binder plays a crucial role in maintaining the adhesion between the current collector and the coating, constructing a conductive network, and maintaining the forces between materials during charge-discharge cycles. It also plays a role in battery performance, ensuring the uniform dispersion of conductive agents and active materials in the solvent, and in the cutting and bending of the electrodes. Simultaneously, to achieve higher energy density, it is necessary to obtain a higher proportion of active materials with as little binder as possible. This places high demands on the binder's wettability, dispersibility, adhesion, ionic conductivity, and electronic conductivity after dispersing the conductive agent.

[0003] Waterborne binders offer inherent advantages in terms of environmental friendliness and cost compared to traditional polyvinylidene fluoride (PVDF) binders. Currently, the most widely used waterborne binder is the sodium carboxycellulose-styrene-butadiene rubber (CMC-SBR) system. CMC provides thickening, wetting, and dispersing functions, while SBR provides strong adhesion and electrode flexibility. The binder is distributed on the surface of the active material, exhibiting some coating properties. However, its electronic conductivity primarily relies on the electronic pathways formed by the dispersed conductive agents, and it itself lacks ionic conductivity. Ionic conductivity pathways mainly exist in areas less coated by the binder, with ion migration occurring through direct contact between the active material and the electrolyte via the SEI film. The processing of lithium-ion battery slurries requires the binder system to have good wetting and dispersibility for both the conductive agents and active materials. With the development of lithium-ion battery anode materials, the low particle size, wide particle size distribution, and high specific surface area of ​​high-rate materials necessitate binders with even better wetting and dispersing properties. For traditional systems, a larger proportion of binder is required to maintain the processability of the slurry. The reduction in the proportion of active material will inevitably affect the specific capacity of the electrode, making it impossible to achieve both rate capability and energy density. Summary of the Invention

[0004] This invention proposes an aqueous binder with high ionic conductivity, which can achieve significantly high lithium-ion conductivity.

[0005] In a first aspect of this application, a high-conductivity waterborne adhesive is provided. The waterborne adhesive is a copolymer composed of the following monomers, comprising, by mass percentage: 30%-55% of a first monomer, 15%-30% of a second monomer, 2%-15% of a third monomer, 20%-35% of a fourth monomer, and 0%-16% of a fifth monomer; wherein the first monomer is selected from at least one of acrylonitrile and methacrylonitrile; the second monomer is selected from at least one of acrylic acid, methacrylic acid, lithium acrylate, and lithium methacrylate; the third monomer is selected from one or more of acrylamide and its N-substituted derivatives; the fourth monomer is selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrene sulfonate, and olefinic unsaturated monomers containing sulfonic acid groups or sulfonates; and the fifth monomer is selected from one or more of olefinic unsaturated functional monomers containing nitrogen, ether bonds, or ester groups.

[0006] By employing the above technical solution, this application provides a waterborne binder with high electrical conductivity. Based on the high lithium loading of lithiated acrylic monomers and the high lithium-ion mobility of sulfonic acid monomers, and optionally introducing some ethoxy, amino, and imide monomers, the dissociation degree of lithium acrylate and the lithium-ion migration ability are improved to achieve significantly high lithium-ion conductivity. Furthermore, utilizing the water solubility of acrylamide monomers, which is between that of acrylonitrile monomers and other hydrophilic monomers, effective copolymerization of hydrophilic and hydrophobic monomers is achieved. After polymerization, a Hoffmann degradation reaction is used to degrade some amide groups into primary amino groups, while the acrylamide monomers are partially converted into more hydrophilic and ionizable ethyleneamine monomers, thereby further enhancing the overall hydrophilicity of the polymer and its lithium-ion retention capacity.

[0007] Furthermore, based on the total mass percentage of the monomers: the first monomer is 40-50%, the second monomer is 15-20%, the third monomer is 5-15%, and the fourth monomer is 20-30%.

[0008] Optionally, the copolymer comprises an ethyleneamine monomer, wherein the ethyleneamine monomer is obtained from an acrylamide monomer via a Hoffmann degradation reaction.

[0009] Optionally, the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is (0.66-4):1.

[0010] By employing the above technical solution and controlling the amounts of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate according to the aforementioned mass ratio, when the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is (0.66-4):1, the copolymerization of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate increases the density of sulfonic acid groups, forming more ion channels and facilitating the rapid migration of lithium ions. This synergistic effect can significantly improve the ionic conductivity of the binder.

[0011] Optionally, the third monomer is selected from at least one of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, and N-isopropylacrylamide.

[0012] Optionally, the fourth monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, vinyl sulfonic acid, lithium vinyl sulfonate, allyl sulfonic acid, lithium allyl sulfonate, methpropylene sulfonic acid, lithium methpropylene sulfonate, sodium methpropylene sulfonate, p-styrene sulfonic acid, lithium p-styrene sulfonate, 3-(allyloxy)propane sulfonic acid, 3-(allyloxy)propane sulfonate, 3-(allyloxy)propane sulfonate, etc. Sodium p-(methallyloxy)propanesulfonate, p-(methallyloxy)benzenesulfonic acid, lithium p-(methallyloxy)benzenesulfonate, sodium p-(methallyloxy)benzenesulfonate, 2-ethanesulfonate of methacrylate, lithium 2-ethanesulfonate of methacrylate, sodium 2-ethanesulfonate of methacrylate, lithium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, sulfonylenolpyruvate, lithium sulfonylenolpyruvate, and sodium sulfonylenolpyruvate.

[0013] Optionally, the fifth monomer is selected from at least one of dimethylaminoethyl methacrylate, ethoxyethoxyethyl acrylate, N-vinylpyrrolidone, butyl acrylate, maleimide, N,N-dimethylaminomethyl acrylate, and N,N-dimethylaminomethyl methacrylate.

[0014] In a second aspect, this application provides a method for preparing the high-conductivity aqueous adhesive described in the first aspect, comprising the following preparation steps: a1: Add the fourth monomer to the water and stir to dissolve; a2: Then add the first monomer, the second monomer, and the third monomer in sequence; a3: Dissolve the initiator in water and add it dropwise to step a2 for 3-5 hours to initiate the reaction. After the reaction, heat the solution to 60-100℃ and keep it at that temperature for 0.5-2.5 hours to obtain the first water-based adhesive mother liquor. a4: Adjust the pH and solid content of the first aqueous binder mother liquor prepared in step a3 using lithium hydroxide and water to obtain the aqueous binder.

[0015] Optionally, the initiator described in step a3 is ammonium persulfate.

[0016] Optionally, the pH in step a4 is 7.5-8.5 and the solid content is 6%.

[0017] Optionally, step a4 further includes the following preparation steps: a41: Take a portion of the first aqueous adhesive mother liquor prepared in step a3, cool it to 30-50℃, add lithium hydroxide to adjust the pH, add sodium hypobromide, keep warm and stir for 0.5-1.5h, and obtain the second aqueous adhesive mother liquor through Hoffmann degradation reaction; a42: Add the remaining first aqueous adhesive mother liquor prepared in step a3, and add lithium hydroxide and water to adjust the pH and solid content of the second aqueous adhesive mother liquor to obtain the aqueous adhesive.

[0018] Optionally, the pH in step a41 is 11.0-13.0, and the pH in step a42 is 7.5-8.5.

[0019] In a third aspect of this application, this application provides the application of the high conductivity aqueous binder described in the first aspect of this application in the preparation of a negative electrode slurry for lithium-ion batteries.

[0020] In summary, the present invention has at least one of the following beneficial technical effects: 1. This application provides a high-conductivity waterborne binder, based on the high lithium loading of lithiated acrylic monomers and the high lithium-ion mobility of sulfonic acid monomers. Optionally, some ethoxy, amino, and imide monomers are introduced to improve the dissociation degree of lithium acrylate and the migration ability of lithium ions, thereby achieving significantly high lithium-ion conductivity. Furthermore, the water solubility of acrylamide monomers, which is between that of acrylonitrile monomers and other hydrophilic monomers, is utilized to achieve effective copolymerization of hydrophilic and hydrophobic monomers. After polymerization, a Hoffmann degradation reaction is used to degrade some amide groups into primary amino groups, while the acrylamide monomers are partially converted into more hydrophilic and ionizable ethyleneamine monomers, thereby further enhancing the overall hydrophilicity of the polymer and its lithium-ion retention capacity.

[0021] 2. This application provides the application of a high-conductivity aqueous binder in the preparation of a negative electrode slurry for lithium-ion batteries, wherein the battery has a charge DCR > 34mΩ, discharge performance > 85%, and cycle capacity retention > 92%. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] CMC was purchased from Daicel Corporation of Japan, SBR from Zeon Corporation of Japan, lithium iron phosphate from Hunan Yuneng New Energy Battery Materials Co., Ltd. (Y7), polyvinylidene fluoride binder from Solvay (Shanghai) Co., Ltd. (5130), and conductive agent SP from Shenzhen Kejing Zhida Technology Co., Ltd.

[0024] Example 1

[0025] Example 1 provides a high-conductivity water-based adhesive, wherein the water-based adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 45% of the first monomer, 20% of the second monomer, 5% of the third monomer, and 30% of the fourth monomer; The first monomer is acrylonitrile; the second monomer is methacrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid.

[0026] Preparation method: 210 parts by weight of deionized water and 30 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid were added to a glass reactor. High-purity nitrogen was introduced and the mixture was stirred at 300 rpm for 30 min to dissolve the acid. Then, 45 parts by weight of acrylonitrile, 20 parts by weight of methacrylic acid, and 5 parts by weight of acrylamide were added sequentially, and the temperature was raised to 70°C. 0.1 parts by weight of ammonium persulfate was dissolved in 25 parts by weight of deionized water and then added dropwise to the reactor over a period of 4 h. The temperature was then raised to 80°C and maintained for 2 h to obtain the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content of 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0027] Example 2

[0028] Example 2 provides a high-conductivity water-based adhesive, wherein the water-based adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 43% of the first monomer, 26% of the second monomer, 7% of the third monomer, and 24% of the fourth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0029] Preparation method: 235 parts by weight of deionized water, 12 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and 12 parts by weight of sodium p-styrenesulfonate were added to a glass reactor. High-purity nitrogen was introduced, and the mixture was stirred at 300 rpm for 30 min. Then, 43 parts by weight of acrylonitrile, 26 parts by weight of acrylic acid, and 7 parts by weight of acrylamide were added sequentially. The temperature was raised to 70°C and maintained. 0.05 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 4 h to initiate the reaction. After 6 h of reaction, the temperature was raised to 80°C and maintained for 1 h to complete the reaction and obtain the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content of 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0030] Example 3

[0031] Example 3 provides a high-conductivity water-based adhesive, wherein the water-based adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 46% of the first monomer, 25% of the second monomer, 4% of the third monomer, and 25% of the fourth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid and sodium allyl sulfonate.

[0032] Preparation method: 257 parts by weight of deionized water, 15 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and 10 parts by weight of sodium allyl sulfonate were added to a glass reactor. High-purity nitrogen gas was introduced, and the mixture was stirred at 300 rpm for 30 min to dissolve the substances. Then, 46 parts by weight of acrylonitrile, 25 parts by weight of acrylic acid, and 4 parts by weight of acrylamide were added sequentially. The temperature was raised to 68°C and maintained at that temperature. 0.06 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 4 h to initiate the reaction. After 6 h of reaction, the temperature was raised to 80°C and maintained at that temperature for 1 h to complete the reaction and obtain the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0033] Example 4

[0034] Example 4 provides a high-conductivity water-based adhesive, wherein the water-based adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 40% of the first monomer, 20% of the second monomer, 12% of the third monomer, 12% of the fourth monomer, and 16% of the fifth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; the fourth monomer is sodium p-styrene sulfonate; and the fifth monomer is dimethylaminoethyl methacrylate and ethoxyethoxyethyl acrylate.

[0035] Preparation method: 257 parts by weight of deionized water, 12 parts by weight of sodium p-styrene sulfonate, 8 parts by weight of dimethylaminoethyl methacrylate, and 8 parts by weight of ethoxyethoxyethyl acrylate were added to a glass reactor. High-purity nitrogen gas was introduced and the mixture was stirred at 300 rpm for 30 min to dissolve the substances. Then, 40 parts by weight of acrylonitrile, 20 parts by weight of acrylic acid, and 12 parts by weight of acrylamide were added sequentially. The temperature was raised to 72℃ and maintained at a constant temperature. 0.1 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 3 h to initiate the reaction. After 6 h of reaction, the temperature was raised to 80℃ and maintained at this temperature for 1 h to complete the reaction and obtain the water-based adhesive mother liquor. The water-based adhesive mother liquor was adjusted to pH 8.0 and solid content of 6% using lithium hydroxide and deionized water to obtain the water-based adhesive.

[0036] Example 5

[0037] Example 5 provides a high-conductivity water-based adhesive, wherein the water-based adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 52.6% of the first monomer, 21.05% of the second monomer, 5.3% of the third monomer, and 21.05% of the fourth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0038] Preparation method: 186 parts by weight of deionized water, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and 10 parts by weight of sodium p-styrenesulfonate were added to a glass reactor. High-purity nitrogen gas was introduced, and the mixture was stirred at 300 rpm for 30 min to dissolve the substances. Then, 45 parts by weight of acrylonitrile, 20 parts by weight of acrylic acid, and 5 parts by weight of acrylamide were added sequentially. The temperature was raised to 65℃ and maintained at a constant temperature. 0.1 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 3 h to initiate the reaction. After 1 h of initiation, 5 parts by weight of acrylonitrile were added dropwise to the reactor over a period of 1 h. After a cumulative reaction of 6 h, the temperature was raised to 80℃ and maintained at this temperature for 1 h to complete the reaction and obtain the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content of 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0039] Example 6

[0040] Example 6 provides a high-conductivity waterborne adhesive, wherein the waterborne adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 50% of the first monomer, 22.22% of the second monomer, 5.56% of the third monomer, and 22.22% of the fourth monomer; The first monomer is methacrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0041] Preparation method: In a glass reactor, 186 parts by weight of deionized water, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts by weight of sodium p-styrenesulfonate, and 2.5 parts by weight of lithium hydroxide were added. High-purity nitrogen gas was introduced, and the mixture was stirred at 300 rpm for 30 minutes to dissolve the compounds. Then, 45 parts by weight of methacrylonitrile, 20 parts by weight of acrylic acid, 5 parts by weight of acrylamide, and 0.6 parts by weight of sodium bisulfite were added sequentially. The temperature was raised to 60°C and maintained at that temperature. 0.1 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 3 hours to initiate the reaction. After 6 hours of reaction, the temperature was raised to 80°C and maintained at that temperature for 1 hour to complete the reaction and obtain the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0042] Example 7

[0043] Example 7 provides a high-conductivity waterborne adhesive, wherein the waterborne adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 35% of the first monomer, 14% of the second monomer, 17% of the third monomer, 26% of the fourth monomer, and 8% of the fifth monomer; The first monomer is methacrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide and N-isopropylacrylamide; the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate and sodium methpropylenesulfonate; and the fifth monomer is N-vinylpyrrolidone.

[0044] Preparation method: 186 parts by weight of deionized water, 12 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 8 parts by weight of sodium p-styrenesulfonate, and 6 parts by weight of sodium methpropylenesulfonate were added to a glass reactor. High-purity nitrogen gas was introduced, and the mixture was stirred at 300 rpm for 30 minutes to dissolve the substances. Then, 35 parts by weight of methacrylonitrile, 14 parts by weight of acrylic acid, 5 parts by weight of acrylamide, 12 parts by weight of N-isopropylacrylamide, and 8 parts by weight of N-vinylpyrrolidone were added sequentially. The temperature was raised to 72℃ and maintained at this temperature. 0.08 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 4 hours to initiate the reaction. After 6 hours of reaction, the temperature was raised to 80℃ and maintained for 1 hour to complete the reaction, yielding the first aqueous adhesive mother liquor. The aqueous adhesive mother liquor was adjusted to pH 8.0 and solid content 6% using lithium hydroxide and deionized water to obtain the aqueous adhesive.

[0045] Example 8

[0046] Example 8 provides a high-conductivity waterborne adhesive, wherein the waterborne adhesive is a copolymer, and the copolymer is copolymerized from the following monomers, comprising, by mass percentage: 45% first monomer, 20% second monomer, 10% third monomer, 25% fourth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fourth monomer is 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0047] Preparation method: a1: Add 257 parts by weight of deionized water to a glass reactor, then add 15 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid and 10 parts by weight of sodium p-styrenesulfonate, purge with high-purity nitrogen, and stir at 300 rpm for 30 min to dissolve. a2: Then add 45 parts by weight of acrylonitrile, 20 parts by weight of acrylic acid, and 10 parts by weight of acrylamide in sequence, and heat to 68°C and keep the temperature constant. a3: Dissolve 0.1 parts by weight of ammonium persulfate in 50 parts by weight of deionized water, and then add it dropwise to the reaction vessel for 4 hours to initiate the reaction. After 6 hours of reaction, raise the temperature to 80°C and keep it at that temperature for 1 hour to end the reaction and obtain the first water-based adhesive mother liquor. a4: Take 326 parts by weight of the first aqueous adhesive mother liquor prepared in step a3, cool it to 40°C, add lithium hydroxide to adjust the pH to 12.0, add 13.0 parts by weight of sodium hypobromite, keep warm and stir for 1 hour to obtain the second aqueous adhesive mother liquor, wherein the acrylamide monomer is obtained as ethyleneamine monomer through Hoffmann degradation reaction. a5: Add 81 parts by weight of the first aqueous adhesive mother liquor prepared in step a3 to step a4, and add lithium hydroxide and deionized water to adjust the second aqueous adhesive mother liquor to pH=8.0 and solid content of 6% to obtain the aqueous adhesive.

[0048] The weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is 1.5:1.

[0049] Example 9

[0050] Example 9 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that the total weight of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate remains unchanged, and the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is 2:3.

[0051] Specifically, the preparation step a1 is different, specifically: 257 parts by weight of deionized water are added to a glass reactor, followed by 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid and 15 parts by weight of sodium p-styrenesulfonate. High-purity nitrogen gas is introduced and the mixture is stirred at 300 rpm for 30 min to dissolve.

[0052] Example 10

[0053] Example 10 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that the total weight of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate remains unchanged, and the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is 4:1.

[0054] Specifically, the preparation step a1 is different, specifically: 257 parts by weight of deionized water are added to a glass reactor, followed by 20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid and 5 parts by weight of sodium p-styrenesulfonate. High-purity nitrogen gas is introduced and the mixture is stirred at 300 rpm for 30 min to dissolve.

[0055] Comparative Example 1 Comparative Example 1 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that the preparation method is different.

[0056] Specifically, the preparation step a4 is different, specifically: take 326 parts of the first aqueous adhesive mother liquor prepared by step a3, cool it to 40°C, add lithium hydroxide to adjust the pH to 12.0, keep it warm and stir for 1 hour to obtain the second aqueous adhesive mother liquor.

[0057] Comparative Example 2 Comparative Example 2 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that it does not contain acrylonitrile.

[0058] Specifically, the preparation step a2 is different, which is as follows: then add 20 parts by weight of acrylic acid and 10 parts by weight of acrylamide in sequence, heat to 68°C and keep the temperature constant.

[0059] Comparative Example 3 Comparative Example 3 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium p-styrenesulfonate by mass.

[0060] Comparative Example 4 Comparative Example 4 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that sodium styrene sulfonate is replaced by 2-acrylamido-2-methylpropanesulfonic acid.

[0061] Comparative Example 5 Comparative Example 5 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that the mass of p-2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate is replaced with acrylic acid.

[0062] Comparative Example 6 Comparative Example 6 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that an equal mass of acrylic acid is replaced with 2-acrylamido-2-methylpropanesulfonic acid.

[0063] Comparative Example 7 Comparative Example 7 provides a high-conductivity water-based adhesive, which differs from Example 8 in that an equal amount of acrylic acid is replaced with sodium p-styrene sulfonate.

[0064] Comparative Example 8 Comparative Example 8 provides a high-conductivity waterborne adhesive, which differs from Example 8 in that 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium vinyl sulfonate by mass.

[0065] Comparative Example 9 Comparative Example 9 provides a high-conductivity waterborne adhesive, wherein the waterborne adhesive is a copolymer, the copolymer being copolymerized from the following monomers, comprising, by mass percentage: 48% first monomer, 30% second monomer, 7% third monomer, 15% fifth monomer; The first monomer is acrylonitrile; the second monomer is acrylic acid; the third monomer is acrylamide; and the fifth monomer is N-vinylpyrrolidone and butyl acrylate.

[0066] Preparation method: 257 parts by weight of deionized water were added to a glass reactor, followed by 48 parts by weight of acrylonitrile, 30 parts by weight of acrylic acid, 7 parts by weight of acrylamide, 10 parts by weight of N-vinylpyrrolidone, and 5 parts by weight of butyl acrylate. The temperature was raised to 72°C and maintained at that temperature. 0.08 parts by weight of ammonium persulfate was dissolved in 50 parts by weight of deionized water and then added dropwise to the reactor over a period of 4 hours to initiate the reaction. Heating was stopped after 9 hours of reaction to obtain a water-based adhesive mother liquor. The water-based adhesive mother liquor was adjusted to pH 8.0 and solid content of 6% using lithium hydroxide and deionized water to obtain the water-based adhesive.

[0067] Comparative Example 10 Comparative Example 10 provides a commercially available adhesive in which CMC and SBR are used in a mass ratio of 4:6.

[0068] Comparative Example 11 Comparative Example 11 provides an acrylic resin adhesive (PAA), which is a pale blue, transparent, high-viscosity solution adhesive. This adhesive is a commercially available water-based acrylic resin adhesive with a glass transition temperature (Tg) of approximately -25°C to 0°C, a viscosity (25°C, Brookfield) of 5000-15000 mPa·s, a pH value of approximately 6.5-8.5, and a solid content of 40-60%.

[0069] Performance testing and evaluation 1. Battery slurry dispersibility, wettability, and stability testing A slurry formulation was designed with a weight ratio of 96.5:2.5:1 for artificial graphite (QCG-X from Shanshan Technology), water-based binder (Examples 1-10, Comparative Examples 1-11), and conductive agent SP. The slurry preparation process was as follows: the water-based binder was first dissolved in deionized water and dispersed at high speed to prepare a colloid solution with a solid content of 8-11%. Then, all of the conductive agent SP was added to the colloid solution and dispersed to prepare a conductive adhesive. Finally, all of the artificial graphite was added to the conductive adhesive and dispersed to prepare a negative electrode slurry. Deionized water was added to ensure the slurry output viscosity was between 3500-4500 mPa∙s, with a solid content of 48-52%. The fineness of each slurry was measured using a scraper fineness meter. The viscosity change within 24 hours of standing and the change in solid content between the upper and lower layers of the slurry after 48 hours of standing were also measured to evaluate the dispersibility, wettability, and overall stability of the slurry for the conductive carbon black and graphite by the binder. Specific results are shown in Table 1.

[0070] 2. Peel strength test of negative electrode sheet The above slurry was prepared at 100g / m 2 The areal density of the coating was applied to the copper foil of the negative current collector to form the negative electrode sheet, and the electrode sheet was rolled at a compaction density of 1.60 g / mm. The rolled electrode sheet was cut into strips of 20 cm × 5 cm, and the strips were adhered to a 1 mm thick steel plate with double-sided adhesive on the current collector foil side. Transparent tape was pasted on the coating layer side. The coating layer was peeled off in a 180° direction at a speed of 100 mm / min using a tensile testing machine, and the peel stress was measured. The specific results are shown in Table 1.

[0071] 3. Negative electrode resistance test Take the rolled electrode sheet and cut it into strips of 20cm × 5cm. Place them in an electrode resistance tester. Take six evenly spaced points from one end of the electrode sheet to the other to test the electrode resistance under a pressure of 400kg. Calculate the average value of the results. See Table 1 for specific results.

[0072] Table 1

[0073]

[0074] Based on Examples 1-7, Comparative Examples 10-11, and Table 1, it can be seen that the water-based binder implemented according to the proportion of each monomer in this invention, when applied to the fast-charging graphite system, has lower slurry fineness, significantly lower viscosity change after 24 hours of standing, and a solid content difference of no more than 1% between the upper and lower layers after 48 hours compared to commercially available CMC / SBR system binders or PAA. The negative electrode sheet prepared with the water-based binder has stronger peel strength and lower electrode resistance. This indicates that the combination of strongly ionic monomers and hydrophobic monomers used in the water-based binder of this invention has significant advantages for the wettability, stability, mechanical properties, and dispersibility of conductive agents in the fast-charging graphite system.

[0075] Based on Examples 8, 9-10, and Table 1, it can be seen that adjusting the ratio of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate in the water-based binder can affect the wettability and stability of the water-based binder in the fast-charging graphite system. When the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is 1.5:1, the water-based binder exhibits optimal wettability, stability, mechanical properties, and dispersibility with conductive agents in the fast-charging graphite system.

[0076] Based on Example 8, Comparative Example 1, and Table 1, it can be seen that in Example 8, acrylamide was converted into ethyleneamine through the Hoffmann degradation reaction. The water-based binder showed the best wettability, stability, mechanical properties, and dispersibility of the conductive agent in the fast-charging graphite system.

[0077] Based on Example 8, Comparative Example 2, and Table 1, it can be seen that when the first monomer is missing in the water-based binder, the combined effect of ethyleneamine and acrylonitrile converted from acrylamide through the Hoffmann degradation reaction is disrupted. As a result, the water-based binder has poorer wettability, stability, mechanical properties, and dispersibility of conductive agents in the fast-charging graphite system than in Example 8.

[0078] Based on Example 8, Comparative Examples 3-4 and Table 1, it can be seen that 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate in the water-based binder have a synergistic effect. The absence of either monomer will reduce the wettability, stability, mechanical properties of the water-based binder in the fast-charging graphite system, as well as the dispersibility of the conductive agent.

[0079] As can be seen from Example 8, Comparative Examples 5-7 and Table 1, when either the second monomer or the fourth monomer is missing from the water-based binder, the synergistic effect of the carboxylic acid group and the sulfonic acid group is broken, and consequently the wettability, stability, mechanical properties, and dispersibility of the conductive agent in the water-based binder for the fast-charging graphite system all decrease.

[0080] As can be seen from Example 8, Comparative Example 8 and Table 1, when 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium vinyl sulfonate in equal mass, the wettability, stability, mechanical properties and dispersibility of the waterborne binder in the fast-charging graphite system also decrease. This may be because the side groups and amide hydrogen bonding of 2-acrylamido-2-methylpropanesulfonic acid are replaced by simple vinyl sulfonate groups, the steric hindrance of the side groups is reduced, and the conformation of the polymer molecular chain tends to be coiled, making it difficult for the benzene ring of sodium styrene sulfonate to be fully exposed at the interface, thereby reducing the wettability, stability, mechanical properties and dispersibility of the waterborne binder.

[0081] As can be seen from Example 8, Comparative Example 9 and Table 1, when the fourth monomer is missing in the water-based binder, even if the fifth monomer is introduced, the wettability, stability, mechanical properties and dispersibility of the water-based binder for the fast-charging graphite system are reduced.

[0082] 4. Battery fabrication and performance testing (1) Preparation of positive electrode sheet The active material lithium iron phosphate, the conductive agent sp, and PVDF were dissolved in 75 parts by weight of N-methylpyrrolidone (NMP) at a weight ratio of 97:1:2. After being mixed evenly, a positive electrode slurry was prepared. The slurry was evenly coated on the positive electrode current collector aluminum foil, and then dried, rolled, and slit to obtain the positive electrode sheet.

[0083] (2) Preparation of negative electrode sheet The negative electrode sheet was prepared according to the above-mentioned negative electrode sheet processing parameters. A negative electrode slurry was prepared by uniformly mixing artificial graphite (QCG-X from Shanshan Technology), water-based binder (Examples 1-10, Comparative Examples 1-11), conductive agent sp, and deionized water in a weight ratio of 96.5:2.5:1:100. The slurry was then uniformly coated onto the negative electrode current collector copper foil, and after drying, rolling, and slitting, the negative electrode sheet was obtained.

[0084] (3) Preparation of the diaphragm PE porous polymer film is used as the separator.

[0085] (4) Preparation of electrolyte A 1 mol / L electrolyte was prepared by dissolving lithium hexafluorophosphate in a carbonate solvent (ethylene carbonate, propylene carbonate, and methyl ethyl carbonate in a volume ratio of 2:2:2).

[0086] (5) Battery manufacturing The positive electrode, separator, and negative electrode are wound in sequence to obtain the battery cell. The battery cell is encapsulated with aluminum-plastic film, baked at 85°C for 24 hours, and after water removal, electrolyte is injected. After vacuum sealing, resting, formation, secondary sealing, and shaping, a lithium-ion battery is obtained.

[0087] (6) Battery DCR test The battery DCR was tested according to GB / T31484-2015.

[0088] Charging DCR Test: The lithium-ion battery was discharged to 2.5V at a constant current of 0.33C, then charged to 3.65V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage of 3.65V. It was then discharged to 2.5V at a constant current of 0.33C and allowed to stand for 30 minutes. Next, it was charged at a constant current of 0.1C for 60 minutes to adjust the state of charge (SOC) to 10%. After resting for 60 minutes, it was discharged at a constant current of 1C for 30 seconds, then rested for 40 seconds before being charged at a constant current of 1C for 30 seconds. This cycle of SOC adjustment and subsequent testing steps was repeated until the battery was fully charged. The charging DCR for each SOC state was calculated using the following formula: DCR = (V1 - V2) / I In the formula, V1 represents the voltage after being left idle in the SOC state, and V2 represents the voltage during 1 second of charging.

[0089] Discharge DCR test: The lithium-ion battery was discharged to 2.5V at a constant current of 0.33C, then charged to 3.65V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage of 3.65V. It was then left to stand for 30 minutes; discharged at a constant current of 0.1C for 60 minutes to adjust the state of charge (SOC) to 90%; left to rest for 60 minutes; discharged at a constant current of 1C for 30 seconds; left to rest for 40 seconds; and then charged at a constant current of 1C for 30 seconds. This cycle of SOC adjustment and subsequent testing steps was repeated until the battery was fully charged. The discharge DCR for each SOC state was calculated using the same formula as the charging DCR. The charging DCR at 50% SOC was used as a reference. Specific results are shown in Table 2.

[0090] (7) Battery rate discharge test Battery discharge rate was tested according to GB / T31484-2015.

[0091] The lithium-ion battery was charged at 0.33C constant current to 3.65V at 25 degrees Celsius, then charged at 3.65V constant voltage to the cutoff current of 0.05C, and then discharged at constant current to 2.5V. The average capacity of the three discharges was taken as the standard capacity value C1. Then, it was fully charged at constant current and constant voltage at a rate of 0.33C. After that, it was discharged at a rate of 3C to 2.5V to obtain the capacity value C2 at the 3C rate. The battery 3C rate retention rate was calculated as C2 / C1×100%. The specific results are shown in Table 2.

[0092] (8) Battery room temperature cycle test The battery was tested for room temperature cycling according to GB / T31484-2015.

[0093] The lithium-ion battery was charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to a cutoff current of 0.05C, and allowed to rest for 30 minutes. It was then discharged at a constant current of 1C to 2.5V and allowed to rest for 30 minutes. The initial discharge capacity was measured. This cycle was repeated for 500 charge / discharge cycles. The discharge capacity after the 500th cycle was measured, and the capacity retention after the 500th cycle was calculated using the following formula: Capacity retention rate after 500 cycles (%) = (Discharge capacity after 500 cycles / Discharge capacity after the first cycle) × 100%. See Table 2 for specific capacity retention rate results.

[0094] Table 2

[0095]

[0096] Based on Examples 1-7, Comparative Examples 10-11, and Table 2, it can be seen that the lithium concentration inside the binder after lithiation and neutralization by carboxylic acid groups and sulfonic acid groups in Examples 1-7, as well as the lithium ion migration ability introduced by heteroatoms such as sulfonic acid groups, ethoxy groups, and amino groups, is significantly reduced, resulting in a significant reduction in the overall ion migration impedance of the electrode. Therefore, compared with Comparative Examples 10-11, the battery prepared by the aqueous binder of Examples 1-7 has a significant advantage in rate performance, and based on the advantages of slurry processing performance and electrode performance, its cycle performance is also better than that of the battery prepared by the binder of Comparative Examples 10-11.

[0097] As shown in Examples 8-10 and Table 2, adjusting the ratio of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate in the aqueous binder can affect the rate performance and cycle performance of the batteries prepared based on the aqueous binder prepared in Examples 8-10. The aqueous binder prepared with a weight ratio of 1.5:1 yields the best rate performance and cycle performance for the subsequently prepared batteries.

[0098] Based on Example 8, Comparative Example 1, and Table 2, it can be seen that the water-based binder prepared by converting acrylamide into ethyleneamine through the Hoffmann degradation reaction in Example 8 produces batteries with the best rate performance and cycle performance.

[0099] As can be seen from Example 8, Comparative Example 2 and Table 2, when the first monomer is missing in the aqueous binder, the combined effect of ethyleneamine and acrylonitrile converted from acrylamide through the Hoffmann degradation reaction is disrupted, and the rate performance and cycle performance of the battery prepared afterward are significantly reduced.

[0100] Based on Example 8, Comparative Examples 3-4 and Table 2, it can be seen that 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate in the aqueous binder have a synergistic effect. The aqueous binder prepared by lacking either monomer will result in a significant decrease in the rate performance and cycle performance of the subsequently prepared battery.

[0101] As can be seen from Example 8, Comparative Examples 5-7 and Table 2, when either the second or fourth monomer is missing from the aqueous binder, the synergistic effect of the carboxylic acid group and the sulfonic acid group is broken. Consequently, the rate performance of the battery prepared with the aqueous binder decreases significantly, and the cycle performance also shows a downward trend.

[0102] As can be seen from Example 8, Comparative Example 8 and Table 2, when 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium vinyl sulfonate in equal mass, the rate performance and cycle performance of the battery prepared by the aqueous binder are significantly reduced.

[0103] Based on Example 8, Comparative Example 9, and Table 2, it can be seen that when the fourth type of monomer is missing in the aqueous binder, even if the fifth monomer is introduced, the rate performance of the battery prepared with the aqueous binder will decrease significantly, and the cycle performance will also decrease.

[0104] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the products, methods and principles of this application should be covered within the scope of protection of this application.

Claims

1. A high-conductivity water-based adhesive, characterized in that, The water-based adhesive is a copolymer, which is copolymerized from the following monomers, comprising, by mass percentage: 30%-55% of the first monomer, 15%-30% of the second monomer, 2%-15% of the third monomer, 20%-35% of the fourth monomer, and 0%-16% of the fifth monomer; The first monomer is selected from at least one of acrylonitrile and methacrylonitrile; The second monomer is selected from at least one of acrylic acid, methacrylic acid, lithium acrylate, and lithium methacrylate; The third monomer is selected from one or more of acrylamide and its N-substituted derivatives; The fourth monomer is selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, and alkene unsaturated monomers containing sulfonic acid groups or sulfonates. The fifth monomer is selected from one or more olefinic unsaturated functional monomers containing nitrogen, ether bonds, or ester groups.

2. The high conductivity water-based adhesive according to claim 1, characterized in that, The copolymer contains an ethyleneamine monomer, wherein the ethyleneamine monomer is obtained from an acrylamide monomer via a Hoffmann degradation reaction.

3. The high conductivity water-based adhesive according to claim 1, characterized in that, The weight ratio of 2-acrylamido-2-methylpropanesulfonic acid to sodium p-styrenesulfonate is (0.66-4):

1.

4. The high conductivity water-based adhesive according to claim 1, characterized in that, The third monomer is selected from at least one of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, and N-isopropylacrylamide.

5. The high conductivity water-based adhesive according to claim 1, characterized in that, The fourth monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, vinyl sulfonic acid, lithium vinyl sulfonate, allyl sulfonic acid, lithium allyl sulfonate, methpropylene sulfonic acid, lithium methpropylene sulfonate, sodium methpropylene sulfonate, p-styrene sulfonic acid, lithium p-styrene sulfonate, 3-(allyloxy)propane sulfonic acid, lithium 3-(allyloxy)propane sulfonate, 3-(allyloxy)propane sulfonate, etc. At least one of the following: p-(methallyloxy)propanesulfonate, p-(methallyloxy)benzenesulfonic acid, lithium p-(methallyloxy)benzenesulfonate, p-(methallyloxy)benzenesulfonate, 2-ethanesulfonate of methacrylate, lithium 2-ethanesulfonate of methacrylate, sodium 2-ethanesulfonate of methacrylate, lithium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, sulfonylenolpyruvate, lithium sulfonylenolpyruvate, and sodium sulfonylenolpyruvate.

6. The high conductivity water-based adhesive according to claim 1, characterized in that, The fifth monomer is selected from at least one of dimethylaminoethyl methacrylate, ethoxyethoxyethyl acrylate, N-vinylpyrrolidone, butyl acrylate, maleimide, N,N-dimethylaminomethyl acrylate, and N,N-dimethylaminomethyl methacrylate.

7. A method for preparing the high conductivity water-based adhesive according to claims 1-6, characterized in that, The preparation steps include the following: a1: Add the fourth monomer to the water and stir to dissolve; a2: Then add the first monomer, the second monomer, and the third monomer in sequence; a3: Dissolve the initiator in water and add it dropwise to step a2 for 3-5 hours to initiate the reaction. After the reaction, heat the solution to 60-100℃ and keep it at that temperature for 0.5-2.5 hours to obtain the first water-based adhesive mother liquor. a4: Adjust the pH and solid content of the first aqueous binder mother liquor prepared in step a3 using lithium hydroxide and water to obtain the aqueous binder.

8. The method for preparing the high conductivity water-based adhesive according to claim 7, characterized in that, Step a4 further includes the following preparation steps: a41: Take a portion of the first aqueous adhesive mother liquor prepared in step a3, cool it to 30-50℃, add lithium hydroxide to adjust the pH, add sodium hypobromide, keep warm and stir for 0.5-1.5h, and obtain the second aqueous adhesive mother liquor through Hoffmann degradation reaction; a42: Add the remaining first aqueous adhesive mother liquor prepared in step a3, and add lithium hydroxide and water to adjust the pH and solid content of the second aqueous adhesive mother liquor to obtain the aqueous adhesive.

9. The method for preparing the high conductivity water-based adhesive according to claim 7 or 8, characterized in that, The initiator mentioned in step a3 is ammonium persulfate.

10. The application of the high conductivity aqueous binder according to claims 1-6 in the preparation of anode slurry for lithium-ion batteries.

Images