Binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of secondary batteries, and discloses a binder as well as a preparation method and application thereof. The adhesive comprises a polymer, and the raw material of the polymer comprises the following monomer components in percentage by mass: 40-60% of an ethylenic bond type unsaturated nitrile monomer; 30%-50% of an ethylenically unsaturated carboxylic acid monomer and / or an ethylenically unsaturated carboxylic anhydride monomer; 5%-20% of an ethylenic bond type unsaturated hydrophilic monomer which does not contain carboxyl; 0.5%-5% of a (methyl) acrylic acid long-chain alkyl ester monomer; 0.5%-5% of a fatty alcohol-polyoxyethylene ether (methyl) acrylate monomer; and 0.5%-3% of (methyl) acrylic acid ethylidene urea ethyoxyl ester. The adhesive has good adhesive property and processability, and can assist in improving the electrical property of the battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a binder, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are among the most promising rechargeable batteries, boasting advantages such as environmental friendliness, high energy density, and long cycle life. A lithium-ion battery consists of components including a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode, as the carrier of lithium ions, requires superior stability to extend battery life. The negative electrode comprises a negative active material, a conductive agent, a binder, and a current collector, and may also include a dispersant. Currently, styrene-butadiene latex and polyacrylic acid binders are widely used. However, styrene-butadiene latex binders have poor dispersibility and suspension properties, necessitating the addition of carboxymethyl cellulose (CMC) as a thickener and dispersant. However, CMC requires high dosages and is inherently brittle, leading to problems such as thick coating cracking during electrode processing and electrode cracking during charge and discharge. Furthermore, this type of binder has low peel strength, resulting in rapid capacity decay during battery cycling and reduced battery life. Polyacrylic acid binders have high bonding strength, which gives batteries excellent cycle performance. However, polyacrylic acid has a high glass transition temperature, which can cause the electrode to crack, decarburize at the edges, and shed powder at the bending points during processing, making the application conditions harsh. Summary of the Invention

[0003] This invention provides an adhesive, its preparation method, and its application to solve the problems in the prior art where adhesives for negative electrode sheets cannot simultaneously meet the requirements of good bonding performance and processing performance.

[0004] In a first aspect, the present invention provides an adhesive comprising a polymer, wherein the polymer raw materials, by mass percentage, comprise the following monomer components: Alkenyl-bonded unsaturated nitrile monomers, 40%~60%; Alkene-bonded unsaturated carboxylic acid monomers and / or alkene-bonded unsaturated carboxylic acid anhydrides, 30%~50%; Carboxyl-free olefinic unsaturated hydrophilic monomers, 5%~20%; (Meth)acrylate long-chain alkyl ester monomer, 0.5%~5%; wherein the carbon chain length of the long-chain alkyl group in the (meth)acrylate long-chain alkyl ester monomer is C12~C22; The fatty alcohol polyoxyethylene ether (meth) acrylate monomer is 0.5% to 5%; in the fatty alcohol polyoxyethylene ether (meth) acrylate monomer, the carbon chain length of the fatty alcohol is C12 to C22. Ethylene urea methacrylate and / or ethylene urea acrylate, 0.5%~3%.

[0005] In one optional embodiment, the raw materials for the polymer, by mass percentage, comprise the following components: Alkenyl-bonded unsaturated nitrile monomers, 45%~55%; Alkene-bonded unsaturated carboxylic acid monomers and / or alkene-bonded unsaturated carboxylic acid anhydrides, 35%~45%; Carboxyl-free olefinic unsaturated hydrophilic monomers, 8%~18%; (Meth)acrylate long-chain alkyl ester monomers, 1%~4%; Fatty alcohol polyoxyethylene ether (meth)acrylate monomer, 1%~4%; Ethylene urea methacrylate and / or ethylene urea acrylate, 1%~2%.

[0006] In one optional embodiment, the number-average molecular weight of the polymer is 100,000 to 200,000; in a further optional embodiment, the number-average molecular weight of the polymer is 120,000 to 180,000.

[0007] In one optional embodiment, the polymer has a weight-average molecular weight of 400,000 to 800,000; in a further optional embodiment, the polymer has a weight-average molecular weight of 500,000 to 700,000.

[0008] In one alternative embodiment, the pH of the adhesive is 5 to 9.

[0009] In one optional embodiment, the adhesive has a solid content of 4% to 10%; in a further optional embodiment, the adhesive has a solid content of 5% to 8%.

[0010] In one optional embodiment, the olefinically unsaturated nitrile monomer includes at least one of acrylonitrile, α-haloacrylonitrile, and α-alkylacrylonitrile; in a further optional embodiment, the olefinically unsaturated nitrile monomer includes at least one of acrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, α-methylacrylonitrile, and α-ethylacrylonitrile.

[0011] In one alternative embodiment, the olefinic unsaturated carboxylic acid monomer includes at least one of acrylic acid and methacrylic acid.

[0012] In one optional embodiment, the olefinically unsaturated carboxylic anhydride monomer includes at least one of maleic anhydride and fumaric anhydride.

[0013] In one optional embodiment, the carboxyl-free olefinic unsaturated hydrophilic monomer includes at least one of acrylamide, methacrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxyethyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate.

[0014] In one optional embodiment, the (meth)acrylate long-chain alkyl ester monomer includes at least one of dodecyl acrylate, dodecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, eicosyl acrylate, eicosyl methacrylate, docosyl acrylate, and docosyl methacrylate; in a further optional embodiment, the (meth)acrylate long-chain alkyl ester monomer includes at least one of dodecyl acrylate, dodecyl methacrylate, tetradecyl acrylate, and tetradecyl methacrylate.

[0015] In one optional embodiment, the number of ethylene oxide units in the fatty alcohol polyoxyethylene ether (meth) acrylate monomer is 5 to 25; in a further optional embodiment, the number of ethylene oxide units is 10 to 15.

[0016] In one optional embodiment, the fatty alcohol polyoxyethylene ether (meth) acrylate monomer includes at least one of dodecyl alcohol polyoxyethylene ether methacrylate, dodecyl alcohol polyoxyethylene ether acrylate, tridecyl alcohol polyoxyethylene ether methacrylate, tetradecyl alcohol polyoxyethylene ether methacrylate, tetradecyl alcohol polyoxyethylene ether methacrylate, hexadecyl alcohol polyoxyethylene ether methacrylate, hexadecyl alcohol polyoxyethylene ether methacrylate, heptadecanol polyoxyethylene ether methacrylate, and octadecyl alcohol polyoxyethylene ether methacrylate.

[0017] In a second aspect, the present invention provides a method for preparing the above-mentioned adhesive, comprising the following steps: S1: heating a protective adhesive aqueous solution; S2: Under a protective gas atmosphere, add olefinic unsaturated nitrile monomers, olefinic unsaturated carboxylic acid monomers and / or olefinic unsaturated carboxylic anhydride monomers, carboxyl-free olefinic unsaturated hydrophilic monomers, (meth)acrylate long-chain alkyl ester monomers, fatty alcohol polyoxyethylene ether (meth)acrylate monomers, ethylidene urea ethoxylate methacrylate and / or ethylidene urea ethoxylate acrylate, and an initiator to the protective adhesive aqueous solution to carry out a polymerization reaction; S3: Heat preservation, removal of residual monomers, to obtain the adhesive.

[0018] In the above-mentioned method for preparing the adhesive provided by the present invention, the method for removing residual monomers in S3 can be any conventional method in the art, typically, but not limited to, vacuum distillation to remove residual monomers.

[0019] In one alternative embodiment, after S3, the step further includes using a neutralizing agent to adjust the pH of the adhesive to 5-9; typically, without limitation, the temperature at which this step is performed is 70-85°C.

[0020] In one alternative embodiment, the initiator includes an oxidizing agent and a reducing agent.

[0021] In the above-mentioned method for preparing the adhesive provided by the present invention, typically and without limitation, the concentration of the protective adhesive aqueous solution can be a conventional concentration in the art, such as 0.10wt% to 2.00wt%; the reducing agent and the oxidizing agent are both added in the form of aqueous solution, with the concentration of the reducing agent aqueous solution being 0.10wt% to 2.00wt% and the concentration of the oxidizing agent aqueous solution being 0.10wt% to 2.00wt%.

[0022] In one optional embodiment, the mass of the oxidant is 0.1% to 1% of the sum of the masses of the monomer components; in a further optional embodiment, it is 0.2% to 0.8%.

[0023] In one optional embodiment, the mass of the reducing agent is 0.1% to 1% of the sum of the masses of the monomer components; in a further optional embodiment, it is 0.2% to 0.8%.

[0024] In one optional embodiment, the mass ratio of the oxidant to the reducing agent is 1:2 to 2:1; in a further optional embodiment, it is 1:1 to 2:1.

[0025] In one optional embodiment, the mass concentration of the neutralizing agent is 5% to 15%.

[0026] In one optional embodiment, the oxidant includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide; in a further optional embodiment, the oxidant is sodium persulfate.

[0027] In one optional embodiment, the reducing agent includes at least one of sodium dithionite, isoascorbic acid, sodium metabisulfite, and sodium bisulfite; in a further optional embodiment, the reducing agent is sodium bisulfite.

[0028] In one optional embodiment, the neutralizing agent includes at least one of an aqueous solution of sodium hydroxide, an aqueous solution of sodium bicarbonate, and an aqueous solution of lithium hydroxide.

[0029] In one optional embodiment, the mass of the protective adhesive in the aqueous solution is 0.1% to 2% of the sum of the masses of the monomer components; in a further optional embodiment, it is 0.2% to 1.5%.

[0030] In one optional embodiment, the heating temperature in S1 is 30~85°C; in a further optional embodiment, the heating temperature is 35~80°C.

[0031] In one optional embodiment, in step S2, the polymerization reaction temperature is 30~85°C and the time is 3~6h; in a further optional embodiment, the polymerization reaction temperature is 35~80°C and the time is 4~5h.

[0032] In one optional embodiment, the heat preservation time in step S3 is 1 to 3 hours; in a further optional embodiment, the heat preservation time is 1.5 to 2 hours.

[0033] In one alternative embodiment, the protective adhesive includes at least one of polyvinyl alcohol and carboxymethyl cellulose.

[0034] In one alternative embodiment, the protective gas includes at least one of nitrogen and rare gases.

[0035] In a second aspect, the present invention provides a negative electrode sheet, comprising a negative electrode active material, and further comprising the above-mentioned binder or the binder prepared by the above-mentioned preparation method; typically, without limitation, the negative electrode active material comprises at least one of artificial graphite, natural graphite, hard carbon, and silicon carbide.

[0036] The technical solution of this invention has the following advantages: 1. The adhesive provided by the present invention comprises a polymer, wherein the raw materials of the polymer, by mass percentage, comprise the following monomer components: 40%~60% olefinically unsaturated nitrile monomers; 30%~50% olefinically unsaturated carboxylic acid monomers and / or olefinically unsaturated carboxylic anhydride monomers; 5%~20% olefinically unsaturated hydrophilic monomers without carboxyl groups; 0.5%~5% (meth)acrylate long-chain alkyl ester monomers; wherein the carbon chain length of the long-chain alkyl group in the (meth)acrylate long-chain alkyl ester monomers is C12~C22; 0.5%~5% fatty alcohol polyoxyethylene ether (meth)acrylate monomers; wherein the carbon chain length of the fatty alcohol in the fatty alcohol polyoxyethylene ether (meth)acrylate monomers is C12~C22; and 0.5%~3% ethylidene urea ethoxylate and / or ethylidene urea ethoxylate. This binder is a solution-based binder suitable for coating battery negative electrode sheets with a thickness of 120~140μm. Using this binder imparts excellent dispersibility and stability to the negative electrode slurry, improves the adhesion and flexibility of the negative electrode sheet, enhances its processing performance, and extends its lifespan. Specifically, the use of long-chain alkyl (meth)acrylate monomers improves the wetting, dispersibility, and flexibility of the binder. Fatty alcohol polyoxyethylene ether (meth)acrylate monomers improve the suspension stability of slurries using this binder. The monomers of the polymer in this binder include long-chain alkyl (meth)acrylate long-chain alkyl ester monomers with carbon chain lengths of C12~C22, fatty alcohol polyoxyethylene ether (meth)acrylate monomers with carbon chain lengths of C12~C22, and other olefinic monomers. The long alkyl chains on different polymer molecular chains can effectively reduce the migration of polymer from the bottom to the top of the electrode during baking through association, ensuring the uniformity of polymer binder distribution in the electrode and improving the dispersibility and processability of the corresponding slurry using this binder. However, the long-chain alkyl ester monomers of (meth)acrylate, with their larger side groups, increase the distance between different polymer chains and reduce the cohesive strength between them. Introducing highly polar ethylidene methacrylate and / or ethylidene acrylate can utilize the flexibility of the ethoxy group and the strong polarity of the ethylidene to build hydrogen bonds between the ethylidene and nitrile / carboxyl groups between different polymer chains. When using monomers containing amide groups, these hydrogen bonds also include the amide groups. This enhances the cohesive strength between polymer chains, thereby significantly improving the adhesion of the product and effectively reducing electrode rebound while satisfying the requirements for electrode dispersion and processability. Furthermore, ethylidene methacrylate and / or ethylidene acrylate can also enhance the interaction between the binder, the electrode active material, and the current collector.

[0037] 2. This invention provides a method for preparing the above-mentioned adhesive, comprising the following steps: S1: heating a protective adhesive aqueous solution; S2: under a protective gas atmosphere, adding an olefinically unsaturated nitrile monomer, an olefinically unsaturated carboxylic acid monomer and / or an olefinically unsaturated carboxylic anhydride monomer, a carboxyl-free olefinically unsaturated hydrophilic monomer, a (meth)acrylate long-chain alkyl ester monomer, a fatty alcohol polyoxyethylene ether (meth)acrylate monomer, an ethylidene urea ethoxylate methacrylate and / or an ethylidene urea ethoxylate acrylate, and an initiator to the protective adhesive aqueous solution to carry out a polymerization reaction; S3: maintaining the temperature to remove residual monomers, thereby obtaining the adhesive. This preparation method is simple, and all monomers can be polymerized in a single step to prepare the corresponding polymer, facilitating the large-scale production of the adhesive. Detailed Implementation

[0038] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0039] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0040] Experimental materials Acrylic acid (AA): Produced by Wanhua Chemical; Methacrylic acid (MAA): Produced by Wanhua Chemical; Acrylamide (AM): Produced by Shanghai Zhongcheng Chemical Co., Ltd. Acrylonitrile (AN): Produced by Wanhua Chemical; Dodecyl acrylate: Produced by Wanhua Chemical; Octadecyl acrylate: Produced by Wanhua Chemical; Methacrylate (25 ethoxy) C16-C18 fatty alcohol: produced by Evonik Chemical, C18PEG1105MAW; carbon chain length C16~C18, number of ethylene oxide units is 25; Alkoxy polyethylene glycol methacrylate: Produced by Shanghai Zhongcheng Chemical, BOM 30, carbon chain length C12~C14, number of ethylene oxide units is 10~15; Ethylene urea methacrylate: Produced by Evonik Chemicals, MEEU50W; Ammonium persulfate (APS): Produced by Jinan Jinhao Chemical Co., Ltd. Sodium bisulfite (NaHSO3): Produced by Wanhua Chemical; Polyvinyl alcohol 2488 (PVA2488): Produced by Sinopec Sichuan Chemical Industry Co., Ltd. Sodium carboxymethyl cellulose (CMC): Produced by Sinopharm Chemicals; Conductive carbon black (Super-P): Produced by Yirui Group.

[0041] Example 1 This embodiment provides an adhesive and its preparation method, including the following steps: (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 55℃.

[0042] (2) Mix 35g acrylic acid, 8g acrylamide, 1g dodecyl acrylate, 1g methacrylate (25 ethoxy) C16-C18 fatty alcohol, 52g acrylonitrile, and 3g ethyl urea methacrylate to obtain mixed monomers.

[0043] (3) Dissolve 0.5g APS in 50g water to prepare an oxidizing agent aqueous solution, and dissolve 0.3g NaHSO3 in 50g water to prepare a reducing agent aqueous solution.

[0044] (4) Simultaneously add the mixed monomers from step (2) and the aqueous solutions of oxidant and reducing agent from step (3) to the reaction vessel from step (1) for 3 hours. After the addition is complete, keep warm for 2 hours and then perform vacuum distillation to remove the residual monomers.

[0045] (5) Heat to 80°C, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 8.0, adjust the solid content to 5wt%, and obtain the binder.

[0046] The number-average molecular weight of the polymer in the adhesive is 128,000; the weight-average molecular weight is 602,000; both were tested in accordance with GB / T36214.4-2018.

[0047] Example 2 This embodiment provides an adhesive and its preparation method. Compared with Example 1, the difference is that in step (2), the mixed monomers are 35g acrylic acid, 8g acrylamide, 1g octadecyl acrylate, 1g alkoxy polyethylene glycol methacrylate, 52g acrylonitrile, and 3g ethylidene urea methacrylate; in step (3), 0.1g APS is dissolved in 50g water to prepare an oxidant aqueous solution, and 0.1g NaHSO3 is dissolved in 50g water to prepare a reducing agent aqueous solution.

[0048] Example 3 This embodiment provides an adhesive and its preparation method. Compared with Example 1, the difference is that in step (2), the mixed monomers are 40g acrylic acid, 8g acrylamide, 1g dodecyl acrylate, 1g alkoxy polyethylene glycol methacrylate, 48g acrylonitrile, and 2g ethylidene urea methacrylate.

[0049] Example 4 This embodiment provides an adhesive and its preparation method. Compared with Example 1, the difference is that in step (2), the mixed monomers are 43g acrylic acid, 8g acrylamide, 2.5g dodecyl acrylate, 2.5g alkoxy polyethylene glycol methacrylate, 42g acrylonitrile, and 2g ethylidene urea methacrylate.

[0050] Example 5 This embodiment provides an adhesive and its preparation method. Compared with Example 1, the difference is that in step (2), 35g of acrylic acid, 18g of acrylamide, 2.5g of dodecyl acrylate, 2.5g of alkoxy polyethylene glycol methacrylate, 41g of acrylonitrile, and 1g of ethylidene urea methacrylate are used; in step (3), 0.5g of APS is dissolved in 50g of water to prepare an oxidizing agent aqueous solution, and 1g of NaHSO3 is dissolved in 50g of water to prepare a reducing agent aqueous solution.

[0051] Example 6 This embodiment provides an adhesive and its preparation method. Compared with Example 1, the difference is that in step (2), the mixed monomers are 35g acrylic acid, 15g acrylamide, 4g dodecyl acrylate, 4g alkoxy polyethylene glycol methacrylate, 41g acrylonitrile, and 1g ethylidene urea methacrylate; in step (3), 1g APS is dissolved in 50g water to prepare an oxidant aqueous solution, and 0.5g NaHSO3 is dissolved in 50g water to prepare a reducing agent aqueous solution.

[0052] Example 7 This embodiment provides an adhesive and its preparation method, including the following steps: (1) Add 10g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 35°C.

[0053] (2) Mix 31.5g methacrylic acid, 5g hydroxyethyl acrylate, 0.5g dodecyl acrylate, 2.5g methacrylate (25 ethoxy) C16-C18 fatty alcohol, 60g α-chloroacrylonitrile, and 0.5g ethylidene methacrylate ethoxylate to obtain mixed monomers.

[0054] (3) Dissolve 0.4g APS in 50g water to prepare an oxidizing agent aqueous solution, and dissolve 0.8g NaHSO3 in 50g water to prepare a reducing agent aqueous solution.

[0055] (4) Simultaneously add the mixed monomers from step (2) and the aqueous solutions of oxidant and reducing agent from step (3) to the reaction vessel of step (1) for 5 hours. After the addition is complete, keep warm for 3 hours and then perform vacuum distillation to remove the residual monomers.

[0056] (5) Heat to 80°C, add 5% sodium hydroxide aqueous solution to adjust the pH of the solution to 5.0, and obtain the adhesive.

[0057] Example 8 This embodiment provides an adhesive and its preparation method, including the following steps: (1) Add 7.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 80℃.

[0058] (2) Mix 50g maleic anhydride, 5g sodium vinyl sulfonate, 4g dodecyl acrylate, 0.5g methacrylate (25 ethoxy) C16-C18 fatty alcohol, 40g α-ethyl acrylonitrile, and 0.5g ethylidene methacrylate ethoxylate to obtain mixed monomers.

[0059] (3) Dissolve 0.8g APS in 50g water to prepare an oxidizing agent aqueous solution, and dissolve 0.4g NaHSO3 in 50g water to prepare a reducing agent aqueous solution.

[0060] (4) Simultaneously add the mixed monomers from step (2) and the aqueous solutions of oxidant and reducing agent from step (3) to the reaction vessel from step (1). The addition time is 4 hours. After the addition is completed, keep warm for 1.5 hours and then perform vacuum distillation to remove the residual monomers.

[0061] (5) Add 15% sodium hydroxide aqueous solution to adjust the pH of the solution to 9.0 to obtain the adhesive.

[0062] Example 9 This embodiment provides an adhesive and its preparation method, including the following steps: (1) Add 7.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 85℃.

[0063] (2) Mix 30g methacrylic acid, 17g methacrylamide, 5g octadecyl acrylate, 5g methacrylate (25 ethoxy) C16-C18 fatty alcohol, 40g acrylonitrile, and 3g ethylidene methacrylate ethoxylate to obtain mixed monomers.

[0064] (3) Dissolve 0.2g APS in 50g water to prepare an oxidizing agent aqueous solution, and dissolve 0.2g NaHSO3 in 50g water to prepare a reducing agent aqueous solution.

[0065] (4) Simultaneously add the mixed monomers from step (2) and the aqueous solutions of oxidant and reducing agent from step (3) to the reaction vessel of step (1) for 3 hours. After the addition is complete, keep warm for 1 hour and then perform vacuum distillation to remove the residual monomers.

[0066] (5) Add 15% sodium hydroxide aqueous solution to adjust the pH of the solution to 9.0 to obtain the adhesive.

[0067] Comparative Example 1 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 43g acrylic acid, 8g acrylamide, 2.5g alkoxy polyethylene glycol methacrylate, 43.5g acrylonitrile, and 3g ethylidene urea methacrylate.

[0068] Comparative Example 2 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 43g acrylic acid, 8g acrylamide, 2.5g dodecyl acrylate, 43.5g acrylonitrile, and 3g ethylidene methacrylate.

[0069] Comparative Example 3 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 43g acrylic acid, 8g acrylamide, 46g acrylonitrile, and 3g ethylidene methacrylate ethoxylate.

[0070] Comparative Example 4 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 45g acrylic acid, 8g acrylamide, 2.5g dodecyl acrylate, 2.5g alkoxy polyethylene glycol methacrylate, and 42g acrylonitrile.

[0071] Comparative Example 5 Commercially available SBR 3001A / BCQ15-2CMC adhesive was used as the adhesive in this comparative example.

[0072] Comparative Example 6 Commercially available Indira LA136D PAA adhesive was used as the adhesive in this comparative example.

[0073] Comparative Example 7 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 55g acrylic acid, 4g acrylamide, 0.3g dodecyl acrylate, 7g alkoxy polyethylene glycol methacrylate, 30g acrylonitrile, and 3.7g ethylidene urea methacrylate.

[0074] Comparative Example 8 This comparative example provides an adhesive and its preparation method. Compared with Example 4, the difference is that in step (2), the mixed monomers are 5g acrylic acid, 24g acrylamide, 5.5g dodecyl acrylate, 0.25g alkoxy polyethylene glycol methacrylate, 65g acrylonitrile, and 0.25g ethylidene urea methacrylate.

[0075] Experimental Example 1 Take the adhesives provided in the examples and comparative examples, and observe whether their appearance is an aqueous solution or an emulsion. Record the observation results in Table 1.

[0076] Experiment Example 2 The binders obtained in the examples and comparative examples were prepared into negative electrode slurries, and their dispersibility and stability were tested. The test results are shown in Table 1.

[0077] In the examples and comparative examples 1 to 4, the corresponding negative electrode slurries of the binder contain, by mass percentage, 96.5 wt% graphite negative electrode material (BTR SFC-R), 1.0 wt% conductive carbon black, and 2.5 wt% binder (by solid content). The solvent of the slurry is water, and the solid content is 45%.

[0078] The corresponding negative electrode slurries for the binders given in Comparative Examples 5 and 6 contain, by mass percentage, 96.5 wt% graphite negative electrode material (BTR SFC-R), 1.0 wt% conductive carbon black, 0.5 wt% CMC dispersant, and 2.0 wt% binder (by solids content). The solvent of the slurry is water, and the solids content is 45%.

[0079] Evaluation method for the dispersibility of negative electrode slurry: The prepared negative electrode slurry is coated onto a copper foil current collector using a wet film preparation device. The wet film coating thickness is controlled at 120±5μm, and the copper foil size is 7cm×15cm. The dispersion level is judged based on the number of particles on the electrode surface. <10 particles are grade 1, 11~20 particles are grade 2, 21~30 particles are grade 3, 31~40 particles are grade 4, and >40 particles are grade 5.

[0080] The method for evaluating the stability of negative electrode slurry is as follows: The negative electrode slurry is allowed to stand for 48 hours. The upper and lower layers of slurry are weighed separately (the upper layer is measured as m1 and the lower layer as m2). Then, they are placed in an oven at 150℃ for 30 minutes. The corresponding dry weights of the upper and lower layers of slurry are weighed again (the upper layer is measured as m1' and the lower layer as m2'). The solid content of the upper and lower layers of the negative electrode slurry is calculated (the solid content of the upper layer is m1' / m1×100% and the solid content of the lower layer is m2' / m2×100%). The stability of the slurry is determined by comparing the difference in solid content between the upper and lower layers.

[0081] Experimental Example 3 The negative electrode slurry obtained in Experiment 2 was used to prepare a negative electrode sheet. Its peel strength was tested, and the test results are shown in Table 1. Its flexibility was also tested, and the test results are shown in Table 2.

[0082] The negative electrode slurry was passed through a 100-mesh sieve and coated on one side of a 10μm thick copper foil used as the current collector, with a coating thickness of 130μm. After drying at 120℃ for 5 minutes in a drying oven, it was allowed to cool naturally to room temperature. Then, it was dried at 10×10⁻⁶ mm. 4 The negative electrode sheet is obtained by rolling under a unit length load of N / m, and the thickness of the negative electrode sheet is measured as D1.

[0083] The test method for the peel strength of the negative electrode sheet is as follows: cut the negative electrode sheet into strips of 20cm×2.5cm, attach a 1mm thick steel plate to the current collector side with double-sided tape, and attach transparent tape to the coating layer side. Use a tensile testing machine to peel the sheet in a 180° direction at a speed of 100mm / min, and measure the peel strength.

[0084] The test method for the flexibility of the negative electrode sheet is as follows: place a mandrel with a diameter of Φ = 1.0 mm on the current collector side of the negative electrode sheet and conduct a bending test. Observe the state of the electrode sheet at this time through an optical microscope. If the electrode sheet is intact, it is marked as ○. If it falls off or cracks, it is marked as ×.

[0085] Experiment Example 4 The negative electrode sheet prepared in Experiment Example 3 was used to prepare a lithium-ion battery; its 50-cycle capacity retention rate and 50-cycle electrode sheet expansion rate were tested, and the results are shown in Table 2.

[0086] A lithium-ion battery comprises an assembled positive electrode, a negative electrode, a separator, and an electrolyte. In the positive electrode, the positive active material used is NCM811 (LG Chem). The positive active material, conductive carbon black, hydrogenated nitrile rubber dispersant, and polyvinylidene fluoride binder are mixed in a mass ratio of 97.2:1:0.1:1.8, and NMP (N-methylpyrrolidone) solvent is added to prepare a positive electrode slurry with a solid content of 65%. This slurry is coated on one side onto an aluminum foil serving as a current collector, dried, and rolled to obtain the positive electrode sheet with a compaction density of 2.55 g / cm³. 3The diaphragm uses Liyou New Energy P25 diaphragm, and the electrolyte uses Wanhua WT325.

[0087] The prepared lithium-ion battery was connected to a testing system, and its initial coulombic efficiency and the coulombic efficiency after 50 cycles were tested using the constant current method. Its capacity retention was calculated. The specific test temperature was room temperature, with cycling at 1C discharge / 0.5C charge and a cutoff voltage of 3.0~4.2V. After 50 charge-discharge cycles, the negative electrode was disassembled in the lithium-intercalated state, and its thickness was measured to be D2. The electrode expansion rate after 50 cycles was (D2 / D1-1)×100%.

[0088] Table 1

[0089] Table 2

[0090] As can be seen from the data in Tables 1 and 2, the binder in the examples that meets the monomer selection and dosage requirements of this invention is an aqueous solution-type binder. This binder enables the slurry containing the binder to have excellent dispersibility and stability; enables the electrode sheet containing the binder to have excellent peel strength and flexibility; and enables the lithium-ion battery containing the binder to have a high cycle capacity retention rate and a low electrode expansion rate after charge-discharge cycles. In Comparative Example 1, the mixed monomers do not contain (meth)acrylate long-chain alkyl ester monomers, and in Comparative Example 2, the mixed monomers do not contain fatty alcohol polyoxyethylene ether (meth)acrylate monomers. The slurries using the binders in Comparative Examples 1 and 2 exhibit poor dispersibility and stability, which in turn leads to poor peel strength of the corresponding electrodes, a reduced cycle capacity retention rate of the corresponding lithium-ion batteries, and an increased electrode expansion rate after charge-discharge cycles. In Comparative Example 3, since it does not contain either (meth)acrylate long-chain alkyl ester monomers or fatty alcohol polyoxyethylene ether (meth)acrylate monomers, the electrode sheet using the binder in Comparative Example 3 exhibits the same defects as those in Comparative Examples 1 and 2, resulting in a × rating for flexibility and the appearance of cracking. In Comparative Example 4, since it does not contain ethylidene urea ethoxylate, the slurry exhibits poor dispersibility and stability, resulting in poor peel strength and flexibility of the corresponding electrode sheet, reduced cycle capacity retention of the lithium-ion battery, and increased electrode sheet expansion rate after charge-discharge cycles. In Comparative Examples 7 and 8, the amounts of each monomer are outside the limits specified in this invention, failing to simultaneously address the product's processing characteristics, adhesion, dispersibility, and the corresponding electrode sheet's anti-expansion performance.

[0091] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An adhesive, characterized in that, The adhesive comprises a polymer, the raw materials of which, by mass percentage, include the following monomer components: Alkenyl-bonded unsaturated nitrile monomers, 40%~60%; Alkene-bonded unsaturated carboxylic acid monomers and / or alkene-bonded unsaturated carboxylic acid anhydrides, 30%~50%; Carboxyl-free olefinic unsaturated hydrophilic monomers, 5%~20%; (Meth)acrylate long-chain alkyl ester monomer, 0.5%~5%; wherein the carbon chain length of the long-chain alkyl group in the (meth)acrylate long-chain alkyl ester monomer is C12~C22; The fatty alcohol polyoxyethylene ether (meth) acrylate monomer is 0.5% to 5%; in the fatty alcohol polyoxyethylene ether (meth) acrylate monomer, the carbon chain length of the fatty alcohol is C12 to C22. Ethylene urea methacrylate and / or ethylene urea acrylate, 0.5%~3%.

2. The adhesive according to claim 1, characterized in that, The raw materials for the polymer, by mass percentage, include the following components: Alkenyl-bonded unsaturated nitrile monomers, 45%~55%; Alkene-bonded unsaturated carboxylic acid monomers and / or alkene-bonded unsaturated carboxylic acid anhydrides, 35%~45%; Carboxyl-free olefinic unsaturated hydrophilic monomers, 8%~18%; (Meth)acrylate long-chain alkyl ester monomers, 1%~4%; Fatty alcohol polyoxyethylene ether (meth)acrylate monomer, 1%~4%; Ethylene urea methacrylate and / or ethylene urea acrylate, 1%~2%.

3. The adhesive according to claim 1 or 2, characterized in that, The number-average molecular weight of the polymer is 100,000 to 200,000; optionally, the number-average molecular weight of the polymer is 120,000 to 180,000. And / or, the weight-average molecular weight of the polymer is 400,000 to 800,000; optionally, the weight-average molecular weight of the polymer is 500,000 to 700,000. And / or, the pH of the adhesive is 5-9; And / or, the solid content of the adhesive is 4% to 10%; optionally, the solid content of the adhesive is 5% to 8%.

4. The adhesive according to any one of claims 1 to 3, characterized in that, The olefinic unsaturated nitrile monomer includes at least one of acrylonitrile, α-haloacrylonitrile, and α-alkylacrylonitrile; optionally, the olefinic unsaturated nitrile monomer includes at least one of acrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, α-methylacrylonitrile, and α-ethylacrylonitrile. And / or, the olefinic unsaturated carboxylic acid monomer includes at least one of acrylic acid and methacrylic acid; And / or, the olefinic unsaturated carboxylic anhydride monomer includes at least one of maleic anhydride and fumaric anhydride; And / or, the carboxyl-free olefinic unsaturated hydrophilic monomer includes at least one of acrylamide, methacrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxyethyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate. And / or, the (meth)acrylate long-chain alkyl ester monomer includes at least one of dodecyl acrylate, dodecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, eicosyl acrylate, eicosyl methacrylate, docosyl acrylate, and docosyl methacrylate; optionally, the (meth)acrylate long-chain alkyl ester monomer includes at least one of dodecyl acrylate, dodecyl methacrylate, tetradecyl acrylate, and tetradecyl methacrylate. And / or, in the fatty alcohol polyoxyethylene ether (meth) acrylate monomer, the number of ethylene oxide units is 5 to 25; optionally, the number of ethylene oxide units is 10 to 15; And / or, the fatty alcohol polyoxyethylene ether (meth) acrylate monomer includes at least one of dodecyl alcohol polyoxyethylene ether methacrylate, dodecyl alcohol polyoxyethylene ether acrylate, tridecyl alcohol polyoxyethylene ether methacrylate, tetradecyl alcohol polyoxyethylene ether methacrylate, tetradecyl alcohol polyoxyethylene ether methacrylate, hexadecyl alcohol polyoxyethylene ether methacrylate, hexadecyl alcohol polyoxyethylene ether methacrylate, heptadecanol polyoxyethylene ether methacrylate, and octadecyl alcohol polyoxyethylene ether methacrylate.

5. A method for preparing an adhesive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Aqueous solution of heat-protective adhesive; S2: Under a protective gas atmosphere, add olefinic unsaturated nitrile monomers, olefinic unsaturated carboxylic acid monomers and / or olefinic unsaturated carboxylic anhydride monomers, carboxyl-free olefinic unsaturated hydrophilic monomers, (meth)acrylate long-chain alkyl ester monomers, fatty alcohol polyoxyethylene ether (meth)acrylate monomers, ethylidene urea ethoxylate methacrylate and / or ethylidene urea ethoxylate acrylate, and an initiator to the protective adhesive aqueous solution to carry out a polymerization reaction; S3: Heat preservation, removal of residual monomers, to obtain the adhesive.

6. The preparation method according to claim 5, characterized in that, Following S3, the process further includes using a neutralizing agent to adjust the pH of the adhesive to 5-9. And / or, the initiator includes an oxidizing agent and a reducing agent.

7. The preparation method according to claim 6, characterized in that, The mass of the oxidant is 0.1% to 1% of the sum of the masses of the monomer components; optionally, it is 0.2% to 0.8%. And / or, the mass of the reducing agent is 0.1% to 1% of the sum of the masses of the monomer components; optionally, it is 0.2% to 0.8%. And / or, the mass ratio of the oxidant to the reducing agent is 1:2 to 2:1; optionally, it is 1:1 to 2:1; And / or, the mass concentration of the neutralizing agent is 5% to 15%.

8. The preparation method according to claim 6, characterized in that, The oxidant includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide; optionally, the oxidant is sodium persulfate. And / or, the reducing agent includes at least one of sodium dithionite, isoascorbic acid, sodium metabisulfite, and sodium bisulfite; optionally, the reducing agent is sodium bisulfite; And / or, the neutralizing agent includes at least one of an aqueous solution of sodium hydroxide, an aqueous solution of sodium bicarbonate, and an aqueous solution of lithium hydroxide.

9. The preparation method according to any one of claims 5 to 8, characterized in that, In the aqueous solution of the protective colloid, the mass of the protective colloid is 0.1% to 2% of the sum of the masses of the monomer components; optionally, it is 0.2% to 1.5%. And / or, in S1, the heating temperature is 30~85℃; optionally, the heating temperature is 35~80℃; And / or, in S2, the polymerization reaction temperature is 30~85℃ and the time is 3~6h; optionally, the polymerization reaction temperature is 35~80℃ and the time is 4~5h. And / or, in S3, the heat preservation time is 1~3h; optionally, the heat preservation time is 1.5~2h; And / or, the protective adhesive includes at least one of polyvinyl alcohol and carboxymethyl cellulose; And / or, the protective gas includes at least one of nitrogen and rare gases.

10. A negative electrode sheet, characterized in that, It includes a negative electrode active material, and also includes the binder as described in any one of claims 1 to 4 or the binder prepared by the preparation method as described in any one of claims 5 to 9.

Images