ADHESIVE MATERIAL AND SECONDARY BATTERY

Abstract

The invention relates to a flexible adhesive and a secondary battery. The adhesive consists of a modified resin formed by the polymerization of a thermoplastic resin and a modified monomer. The modified monomer consists of a functional monomer and a dispersion monomer. By mass fraction, the flexible adhesive consists of 20 to 50 parts thermoplastic resin, 5 to 25 parts functional monomer, and 40 to 60 parts dispersion monomer. The modified resin has a concentration of at least 2% by mass after dissolution in N-methyl-2-pyrrolidone (NMP) at room temperature. The functional monomer consists of at least one of the unsaturated monomers with a carboxyl (anhydride), sulfonic acid, amino, or hydroxyl group. The dispersion monomer consists of an acrylate monomer. The thermoplastic resin dissolves in NMP at 100°C or less. The adhesive is fluorine-free and dissolves well in NMP.The adhesive is soluble at room temperature in NMP solvent, possesses excellent toughness, electrolyte resistance, and adhesion to metal materials, and can be used as an adhesive in lithium-ion batteries.

Description

A flexible adhesive and its application in secondary batteries

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to Chinese patent application CN2023117004954, filed on December 12, 2023, and is incorporated herein by reference in its entirety for all other purposes. Technical Field

[0003] The invention relates to a flexible adhesive and application thereof in a secondary battery, belonging to the technical field of battery adhesives. Background Art

[0004] Lithium battery binders are polymer materials that bond powders of positive and negative electrode active materials, conductive agents, and other materials to the current collector (copper or aluminum foil). Their function is to bond the materials together, stabilize the electrode structure, and ensure electronic contact between the electrode active material and the conductive agent, as well as between the active material and the current collector, during the battery reaction. Typically, binder usage accounts for 2% to 5% of the total positive and negative electrode active materials.

[0005] As our understanding of lithium batteries deepens, the basic requirements for adhesives can be met with current technology. Currently, the main issue that needs to be resolved is the conflicting requirements between slurry and electrode processing, electrolyte resistance, and battery performance. For example, PVDF is a relatively traditional and classic positive electrode adhesive material with excellent overall performance. However, with the continuous development of positive electrode materials and the continuous improvement of battery performance requirements, higher requirements are also placed on positive electrode adhesives. When PVDF is used as an adhesive in high-nickel positive electrode materials, the presence of slurry gel and alkali in the production process will cause PVDF molecules to undergo elimination reactions.

[0006] To address these issues, thermoplastic elastomers, rubber, and polyester have become candidates for positive electrode binder materials. However, these three types of materials currently have disadvantages such as insolubility in NMP, poor resistance to electrolyte swelling, or poor electrochemical stability.

[0007] Thermoplastic elastomers offer high flexibility and initial adhesion, improving the flexibility of coatings and electrodes and preventing gelation during the pulping process, thus meeting electrode processing requirements. However, they are often insoluble in NMP and resistant to electrolytes or electrochemical oxidation. Consequently, little research has been conducted on adhesives. Chinese Patent Publication No. CN1437623A discloses a polyurethane hot-melt adhesive containing an acrylic copolymer and a thermoplastic resin, while Chinese Patent Publication No. CN114846107A discloses a polyurethane hot-melt adhesive composition and its preparation method. Both utilize thermoplastic materials as hot-melt adhesives.

[0008] At present, all supporting systems in the lithium battery industry use N-methyl-2-pyrrolidone (NMP) as a solvent. Therefore, the adhesives used must have good solubility and fluidity under NMP solvent conditions to meet the application requirements of the industry. Therefore, there is an urgent need to study adhesives that dissolve well in NMP at room temperature.

[0009] Summary of the Invention

[0010] The technical problem solved by the present invention is to provide a flexible binder with good solubility in NMP.

[0011] The flexible adhesive of the present invention comprises a modified resin, wherein the modified resin is polymerized from a thermoplastic resin and a modified monomer, wherein the modified monomer comprises a functional monomer and a dispersing monomer, and the modified monomer comprises 20 to 50 parts by weight of the thermoplastic resin, 5 to 25 parts by weight of the functional monomer, and 40 to 60 parts by weight of the dispersing monomer;

[0012] The modified resin has a concentration of ≥2 wt% after being dissolved in NMP at room temperature;

[0013] The functional monomer includes at least one of an unsaturated monomer having a carboxyl group (anhydride), an unsaturated monomer having a sulfonic acid group, an unsaturated monomer having an amino group, and an unsaturated monomer having a hydroxyl group; the dispersing monomer includes an acrylate monomer;

[0014] The thermoplastic resin is a resin that dissolves in NMP at a temperature of ≤100°C.

[0015] In one embodiment of the present invention, the thermoplastic resin includes at least one of ethylene-acrylic acid copolymer with an acrylic acid monomer content of ≥18%, ethylene-vinyl acetate copolymer with a vinyl acetate monomer content of ≥33%, ethylene-vinyl acetate-carbonate copolymer and ethylene-vinyl alcohol copolymer.

[0016] In some embodiments of the present invention, the unsaturated monomer having a carboxyl (anhydride) group includes at least one of (meth)acrylic acid, undecylenic acid, octadecylenic acid, crotonic acid, itaconic acid, fumaric acid, maleic anhydride, 2-ethylacrylic acid, isoctonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0017] In some embodiments of the present invention, the unsaturated monomer having a sulfonic acid group includes at least one of 2-acrylamido-2-methylpropanesulfonic acid, allyloxyhydroxypropylsulfonic acid or allyloxyhydroxypropylsulfonic acid, vinylsulfonic acid, vinylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, propylenesulfonic acid and methpropylenesulfonic acid.

[0018] In some embodiments of the present invention, the unsaturated monomer having an amino group includes at least one of dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, 2-(dimethylamino)ethyl methacrylate, and N-(2-aminoethyl)acrylamide.

[0019] In some embodiments of the present invention, the unsaturated monomer having a hydroxyl group includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxyethyl caprolactone acrylate.

[0020] In some embodiments of the present invention, the dispersing monomer includes at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, glycidyl (meth)acrylate, lauryl acrylate, octadecyl acrylate, phenoxyethyl (meth)acrylate, caprolactone acrylate, tetrahydrofuran (meth)acrylate, ethoxylated tetrahydrofuran acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl acrylate, glycidyl methacrylate and allyl glycidyl ether.

[0021] In a preferred embodiment of the present invention, the thermoplastic resin is 25 to 45 parts.

[0022] In a specific embodiment of the present invention, the molecular weight of the thermoplastic resin is 50,000 to 400,000.

[0023] In one embodiment of the present invention, the modifying monomer further includes a cross-linking monomer.

[0024] Preferably, the cross-linking monomer accounts for no more than 1.5% of the total weight of the modified resin.

[0025] In a specific embodiment of the present invention, the cross-linking monomer includes at least one of ethylene glycol dimethacrylate, ethylene glycol acrylate, allyl methacrylate, allyl methacrylate, N,N-methylenebisacrylamide, and divinylbenzene.

[0026] In a preferred embodiment of the present invention, the modifying monomer consists of a functional monomer, a dispersing monomer and a cross-linking monomer.

[0027] In a specific embodiment of the present invention, by weight, the thermoplastic resin comprises 20 to 50 parts, the functional monomer comprises 5 to 25 parts, the dispersing monomer comprises 40 to 60 parts, and the cross-linking monomer comprises 0.01 to 1.5 parts.

[0028] The present invention also provides use of the flexible adhesive of the present invention in a secondary battery.

[0029] The flexible adhesive of the present invention can form a homogeneous solution in an NMP solvent and has excellent flexibility and electrolyte resistance as well as adhesion to metal materials.

[0030] The normal temperature described in the present invention is 25°C.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention obtains a modified resin by a specific graft copolymerization modification of a thermoplastic resin, which can be well dissolved in NMP at room temperature, thereby improving the binder's tolerance to carbonate electrolytes and improving the material's adhesion to foil. The binder has room-temperature solubility in NMP solvent and can form a homogeneous solution in NMP solvent. It has excellent flexibility and electrolyte resistance as well as adhesion to metal materials. It can be applied to the fields of lithium-ion battery edge coating protective glue, conductive dispersion glue, and positive and negative electrode binders. It can be used alone or in combination with other binders. The combined binders include, but are not limited to, ethylene-vinylidene fluoride resin, ethylene-propylene fluoride resin, polyacrylonitrile and its derivatives.

[0033] The flexible adhesive of the present invention has excellent adhesion and stable electrochemical properties, does not contain fluorine, has outstanding price and environmental advantages, and can replace traditional fluorine resins for use in lithium-ion batteries. DETAILED DESCRIPTION

[0034] The flexible adhesive of the present invention comprises a modified resin, wherein the modified resin is polymerized from a thermoplastic resin and a modified monomer, wherein the modified monomer comprises a functional monomer and a dispersing monomer, and the modified monomer comprises 20 to 50 parts by weight of the thermoplastic resin, 5 to 25 parts by weight of the functional monomer, and 40 to 60 parts by weight of the dispersing monomer;

[0035] The modified resin has a concentration of ≥2 wt% after being dissolved in NMP at room temperature;

[0036] The functional monomer includes at least one of an unsaturated monomer having a carboxyl group (anhydride), an unsaturated monomer having a sulfonic acid group, an unsaturated monomer having an amino group, and an unsaturated monomer having a hydroxyl group; the dispersing monomer includes an acrylate monomer;

[0037] The thermoplastic resin is a resin that dissolves in NMP at a temperature of ≤100°C.

[0038] This invention graft-modifies thermoplastic resins, enabling room-temperature solubility in NMP solvents. This also improves the material's high-temperature tolerance in carbonate electrolytes and its adhesion to metal foils. This makes it suitable for applications in lithium-ion battery edge coatings, conductive dispersions, and as positive and negative electrode binders, either alone or in combination with other binders.

[0039] Commonly used thermoplastic resins for battery adhesives that are heat-soluble in NMP are suitable for use in the present invention. In one embodiment of the present invention, the thermoplastic resin includes at least one of an ethylene-acrylic acid copolymer having an acrylic acid monomer content of ≥18%, an ethylene-vinyl acetate copolymer having a vinyl acetate monomer content of ≥33%, an ethylene-vinyl acetate-carbonate copolymer, and an ethylene-vinyl alcohol copolymer.

[0040] Functional monomers can improve the adhesion of the resin to the metal foil and the electrolyte resistance of the resin. In some embodiments of the present invention, the unsaturated monomer having a carboxyl group (anhydride) includes at least one of (meth) acrylic acid, undecylenic acid, octadecylenic acid, crotonic acid, itaconic acid, fumaric acid, maleic anhydride, 2-ethyl acrylic acid, isocrotonic acid, α-acetoxy acrylic acid, β-trans-aryloxy acrylic acid, α-chloro-β-E-methoxy acrylic acid, and β-diamino acrylic acid, maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0041] In some embodiments of the present invention, the unsaturated monomer having a sulfonic acid group includes at least one of 2-acrylamido-2-methylpropanesulfonic acid, allyloxyhydroxypropylsulfonic acid or allyloxyhydroxypropylsulfonic acid, vinylsulfonic acid, vinylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, propylenesulfonic acid, and methpropylenesulfonic acid.

[0042] In some embodiments of the present invention, the unsaturated monomer having an amino group includes at least one of dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, 2-(dimethylamino)ethyl methacrylate, and N-(2-aminoethyl)acrylamide.

[0043] In some embodiments of the present invention, the unsaturated monomer having a hydroxyl group includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxyethyl caprolactone acrylate.

[0044] Dispersing monomers can improve the solubility and dispersibility of the resin in NMP. In some embodiments of the present invention, the dispersing monomers include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, glycidyl (meth)acrylate, lauryl acrylate, octadecyl acrylate, phenoxyethyl (meth)acrylate, caprolactone acrylate, tetrahydrofuran (meth)acrylate, ethoxylated tetrahydrofuran acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl acrylate, glycidyl methacrylate, and allyl glycidyl ether.

[0045] In a preferred embodiment of the present invention, the thermoplastic resin is 25 to 45 parts.

[0046] In a specific embodiment of the present invention, the molecular weight of the thermoplastic resin is 50,000 to 400,000.

[0047] In one embodiment of the present invention, the modifying monomer further includes a cross-linking monomer.

[0048] Preferably, the cross-linking monomer accounts for no more than 1.5% of the total weight of the modified resin.

[0049] The crosslinking monomer can enhance intermolecular cohesion and polymer molecular weight through intermolecular crosslinking, thereby increasing sustained adhesion. In a specific embodiment of the present invention, the crosslinking monomer includes at least one of hydroxyacrylamide, ethylene glycol dimethacrylate, ethylene glycol acrylate, allyl methacrylate, allyl methacrylate, N,N-methylenebisacrylamide, and divinylbenzene.

[0050] In a preferred embodiment of the present invention, the modifying monomer consists of a functional monomer, a dispersing monomer and a cross-linking monomer.

[0051] In a specific embodiment of the present invention, by weight, the thermoplastic resin comprises 20 to 50 parts, the functional monomer comprises 5 to 25 parts, the dispersing monomer comprises 40 to 60 parts, and the cross-linking monomer comprises 0.01 to 1.5 parts.

[0052] The modified resin of the present invention can be obtained by polymerization using conventional graft copolymerization methods in the art.

[0053] In one embodiment of the present invention, a solution polymerization method is used. A thermoplastic resin is dissolved in an NMP solvent at high temperature, and polymer modification is performed by solution grafting under certain reaction conditions to obtain an NMP solution, which is applied in the field of lithium battery-related binders.

[0054] The present invention also provides the use of the flexible binder of the present invention in a secondary battery. The flexible binder of the present invention can form a homogeneous solution in NMP solvent, and has excellent flexibility and electrolyte resistance as well as adhesion to metal materials.

[0055] In a specific embodiment, the secondary battery is a lithium-ion battery.

[0056] The normal temperature described in the present invention is 25°C.

[0057] The following examples further describe the specific embodiments of the present invention, but the present invention is not limited to the scope of the embodiments. The performance test of the products in the examples is carried out using the following method:

[0058] (1) Dissolution test

[0059] The sample to be tested was placed in a beaker with magnetic stirring, NMP was added to dissolve (concentration ≥ 2%), and the mixture was stirred and dispersed at 25° C. for 24 hours. The dissolution state of the sample to be tested in the NMP solvent was observed.

[0060] (2) Electrolyte swelling test (70℃ / 24h)

[0061] In the present invention, the electrolyte swelling degree refers to the swelling degree of the part that is insoluble in the electrolyte when the modified rubber film is immersed in a carbonate electrolyte salt solution at 70°C / 24h. Here, the electrolyte swelling degree of the modified rubber can be specifically calculated by the following method: prepare an NMP solution containing a modified resin, and completely dry the dispersion in a blast oven at 110°C to form a film with a thickness of 0.2 to 0.5 mm. Cut the film into 2.5 mm squares and accurately weigh about 1 g. The mass of the diaphragm obtained by cutting is set to W0. The obtained diaphragm is immersed in 100 g of electrolyte (Shanshan 12663) at 70°C for 24 hours. Then, the diaphragm is removed from the electrolyte, the excess electrolyte components on the surface are wiped off with a dust-free cloth, and the mass of the diaphragm is weighed W1. The mass change is calculated according to the following formula and is used as the electrolyte swelling degree.

[0062] Swelling % = {(W1-W0) / W0}*100

[0063] (3) DMC solvent dissolution test (70℃ / 24h)

[0064] The sample preparation method is the same as above. The modified rubber diaphragm is dried and weighed as M0, then immersed in DMC solvent, sealed, and stored at 70℃ for 24h. After being taken out, the excess solvent on the surface is wiped off with a dust-free cloth, and placed in a 110℃ forced air oven for 5h. The weight of the diaphragm is weighed as M1.

[0065] Dissolution % = {(M0-M1) / M0}*100

[0066] (4) Prepare lithium cobalt oxide positive electrode and test the peeling force between the coating and aluminum foil

[0067] The positive electrode slurry was prepared according to the formula and process in the table below. The slurry formula is shown in Table 1, and the stirring process is shown in Table 2.

[0068] Table 1

[0069] Table 2

[0070] Pole sheet preparation: The positive electrode slurry is coated on the aluminum foil to make a single-sided surface density of 240g / m 2 , 40mm width pole piece, test 180° coating peeling force.

[0071] Example 1

[0072] In a 500mL four-necked flask, add NMP solvent, add 20 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 25 parts of acrylic acid, 55 parts of lauryl acrylate and 0.2 parts of allyl methacrylate at one time, add peroxide or azo initiator every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0073] Example 2

[0074] In a 500mL four-necked flask, add NMP solvent, add 30 parts of ethylene vinyl acetate (Taiwan Polymer UE3330) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 12 parts of methacrylic acid, 58 parts of isooctyl acrylate and 0.5 parts of ethylene glycol dimethacrylate at one time, add peroxide or azo initiator every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0075] Example 3

[0076] In a 500mL four-necked flask, add NMP solvent, add 40 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles (molecular weight 200,000) under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 20 parts of N-(2-aminoethyl) acrylamide and 40 parts of isobornyl acrylate and 1.0 part of allyl methacrylate at one time, add peroxide or azo initiator once every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0077] Example 4

[0078] In a 500 mL four-necked flask, add NMP solvent, add 40 parts of ethylene-acrylic acid (Dow SK 1420) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 15 parts of acrylic acid, 5 parts of allyl sulfonic acid, 40 parts of glycidyl acrylate and 0.05 parts of allyl methacrylate at one time, add peroxide or azo initiator every 3 hours, and keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0079] Example 5

[0080] In a 500 mL four-necked flask, add NMP solvent, add 40 parts of ethylene-acrylic acid (Dow SK 1420) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 5 parts of methacrylic acid, 55 parts of tetrahydrofuran acrylate and 0.1 part of N,N-methylenebisacrylamide at one time, add peroxide or azo initiator every 3 hours, and keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0081] Example 6

[0082] In a 500 mL four-necked flask, add NMP solvent, add 30 parts of ethylene-acrylic acid (Dow SK 1420) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 10 parts of itaconic acid, 60 parts of allyl glycidyl ether and 0.2 parts of allyl methacrylate at one time, add peroxide or azo initiator every 3 hours, and keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0083] Example 7

[0084] In a 500 mL four-necked flask, add NMP solvent and, while stirring, add 35 parts of ethylene-acrylic acid (Dow SK 1420) resin particles, dissolve at 70°C to form a colorless transparent solution. Then, cool to the reaction temperature of 60-70°C and add a peroxide or azo initiator. Add 20 parts of methacrylic acid, 45 parts of isooctyl acrylate, and 0.1 part of divinylbenzene at one time. Add the peroxide or azo initiator every 3 hours. Keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0085] Example 8

[0086] In a 500 mL four-necked flask, add NMP solvent, add 25 parts of ethylene-acrylic acid (Dow SK 1420) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 25 parts of allyloxyhydroxypropyl sulfonic acid, 50 parts of tetrahydrofuran methacrylate and 0.1 part of hydroxyacrylamide at one time, add peroxide or azo initiator once every 3 hours, and keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0087] Comparative Example 1

[0088] In a 500mL four-necked flask, add NMP solvent, add 18 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 25 parts of acrylic acid, 57 parts of lauryl acrylate and 0.2 parts of allyl methacrylate at one time, add peroxide or azo initiator every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0089] Comparative Example 2

[0090] In a 500 mL four-necked flask, add NMP solvent, add 52 parts of ethylene-acrylic acid (Dow SK 1420) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 15 parts of methacrylic acid, 23 parts of lauryl acrylate and 0.1 part of allyl methacrylate at one time, add peroxide or azo initiator every 3 hours, and keep the reaction at 70°C for 15 hours to obtain a flexible adhesive.

[0091] Comparative Example 3

[0092] In a 500mL four-necked flask, add NMP solvent, add 40 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 60 parts of isobornyl acrylate and 1.0 part of allyl methacrylate at one time, add peroxide or azo initiator once every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0093] Comparative Example 4

[0094] In a 500mL four-necked flask, add NMP solvent, add 40 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 60 parts of N-(2-aminoethyl) acrylamide and 1.0 part of allyl methacrylate at one time, add peroxide or azo initiator once every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0095] Comparative Example 5

[0096] In a 500mL four-necked flask, add NMP solvent, add 40 parts of ethylene vinyl acetate (Japan Mitsui 40W) resin particles under stirring, dissolve at 70°C to form a colorless transparent solution, then cool to the reaction temperature of 60-70°C, add peroxide or azo initiator, add 20 parts of N-(2-aminoethyl) acrylamide and 40 parts of isobornyl acrylate at one time, add peroxide or azo initiator every 3 hours, keep the reaction at 70°C for 15 hours, and obtain a flexible adhesive.

[0097] Comparative Example 6

[0098] Unmodified EVA resin (Japan Mitsui 40W).

[0099] Comparative Example 7

[0100] Unmodified resin EAA (Dow SK 1420).

[0101] Comparative Example 8

[0102] In a 500 mL four-necked flask, NMP solvent was added, and under stirring, a peroxide or azo initiator was added at a reaction temperature of 60-70°C. 20 parts of N-(2-aminoethyl) acrylamide, 39 parts of isobornyl acrylate and 1.0 part of allyl methacrylate were added at one time. The peroxide or azo initiator was added every 3 hours. The reaction was kept at 70°C for 15 hours to obtain a copolymer. Then, 40 parts of ethylene vinyl acetate (Mitsui 40W, Japan) resin particles were added at 70°C, dissolved and blended, and cooled to room temperature to obtain a composite adhesive.

[0103] Table 1

[0104] It can be seen that the flexible adhesive of the present invention can form a homogeneous solution in NMP solvent, and has excellent flexibility and electrolyte resistance as well as adhesion to metal materials.

Claims

1. A flexible adhesive, characterized in that: The binder comprises a modified resin, wherein the modified resin is polymerized from a thermoplastic resin and a modified monomer, wherein the modified monomer comprises a functional monomer and a dispersing monomer, and by weight, the thermoplastic resin comprises 20 to 50 parts, the functional monomer comprises 5 to 25 parts, and the dispersing monomer comprises 40 to 60 parts; The concentration of the modified resin after being dissolved in NMP at room temperature is ≥ 2wt%; The functional monomer includes at least one of an unsaturated monomer having a carboxyl group (anhydride), an unsaturated monomer having a sulfonic acid group, an unsaturated monomer having an amino group, and an unsaturated monomer having a hydroxyl group; the dispersing monomer includes an acrylate monomer; The thermoplastic resin is a resin that is soluble in NMP at a temperature of ≤100°C.

2. The flexible adhesive according to claim 1, characterized in that: The thermoplastic resin includes at least one of an ethylene-acrylic acid copolymer having an acrylic acid monomer content of ≥18%, an ethylene-vinyl acetate copolymer having a vinyl acetate monomer content of ≥33%, an ethylene-vinyl acetate-carbonate copolymer, and an ethylene-vinyl alcohol copolymer; The unsaturated monomer having a carboxyl group (anhydride) includes at least one of (meth)acrylic acid, undecylenic acid, octadecylenic acid, crotonic acid, itaconic acid, fumaric acid, maleic anhydride, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate; The unsaturated monomer having a sulfonic acid group includes at least one of 2-acrylamide-2-methylpropanesulfonic acid, allyloxyhydroxypropylsulfonic acid or allyloxyhydroxypropylsulfonic acid, vinylsulfonic acid, vinylsulfonic acid salt, 2-acrylamide-2-methylpropanesulfonic acid, propylenesulfonic acid and methpropylenesulfonic acid; The unsaturated monomer having an amino group includes at least one of dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, 2-(dimethylamino)ethyl methacrylate and N-(2-aminoethyl)acrylamide; The unsaturated monomer having a hydroxyl group includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate and hydroxyethyl caprolactone acrylate; Dispersing monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, glycidyl (meth)acrylate, lauryl acrylate, octadecyl acrylate, phenoxyethyl (meth)acrylate, caprolactone acrylate, tetrahydrofuran (meth)acrylate, ethoxylated propylene At least one of tetrahydrofuranyl acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl acrylate, glycidyl methacrylate and allyl glycidyl ether.

3. The flexible adhesive according to claim 1, characterized in that: The thermoplastic resin is 25 to 45 parts.

4. The flexible adhesive according to claim 1, characterized in that: The molecular weight of the thermoplastic resin is 50,000 to 400,000.

5. The flexible adhesive according to claim 1, characterized in that: Modifying monomers also include crosslinking monomers.

6. The flexible adhesive according to claim 1, characterized in that: The cross-linking monomer accounts for no more than 1.5% of the total weight of the modified resin.

7. The flexible adhesive according to claim 5, characterized in that: The cross-linking monomer includes at least one of ethylene glycol dimethacrylate, ethylene glycol acrylate, allyl alcohol methacrylate, allyl methacrylate, N,N-methylenebisacrylamide, and divinylbenzene.

8. The flexible adhesive according to claim 1, characterized in that: The modified monomers are composed of functional monomers, dispersing monomers and cross-linking monomers.

9. The flexible adhesive according to claim 8, characterized in that: 20 to 50 parts of thermoplastic resin, 5 to 25 parts of functional monomer, 40 to 60 parts of dispersing monomer, and 0.01 to 1.5 parts of cross-linking monomer.

10. Use of the flexible adhesive according to any one of claims 1 to 9 in a secondary battery.