Non-fluorine binder and application thereof in field of secondary battery

Abstract

The invention relates to a non-fluorine binder and application thereof in the field of secondary batteries, and belongs to the technical field of battery binders. The technical problem to be solved by the invention is to provide the non-fluorine binder which has good solubility in NMP (N-Methyl Pyrrolidone). The binder comprises modified resin, and the modified resin is formed by polymerizing thermoplastic resin, a functional monomer and a nitrile group-containing unsaturated monomer. The binder has normal-temperature solubility in an NMP solvent, can improve the high-temperature tolerance of a material in a carbonic ester electrolyte and the binding force to a metal foil, can be applied to the fields of lithium ion battery edge coating protection glue, conductive dispersion glue and positive and negative electrode binders, can be independently used, can also be used in cooperation with other binders, and can be applied to the fields of lithium ion battery edge coating protection glue, conductive dispersion glue and positive and negative electrode binders. The fluorine resin has outstanding price and environmental advantages, and can replace traditional fluorine resin to be applied to lithium ion batteries.

Description

Technical Field

[0001] The present invention relates to a non-fluorine binder and its application in the field of secondary batteries, belonging to the technical field of battery binders. Background Art

[0002] A lithium battery binder is a polymer material that bonds powder materials such as positive and negative active materials and conductive agents to a current collector (copper or aluminum foil). Its functions are to bond several materials, stabilize the structure of the electrode sheet, 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 process. Usually, the dosage of the binder accounts for 2% - 5% of the positive and negative active materials.

[0003] With the in-depth understanding of lithium batteries, in terms of current technologies, the basic requirements for adhesives can be met. Currently, the main problem to be solved is the contradiction between the requirements of the slurry and electrode sheet processing, electrolyte resistance, and battery performance. For example, PVDF is a relatively traditional and classic positive electrode binder material with good comprehensive 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 binders. When PVDF is used as a binder in high-nickel positive electrode materials, problems such as slurry gelation in the production process and the elimination reaction of PVDF molecules due to the presence of alkali will occur.

[0004] To address the above problems, thermoplastic elastomers, rubbers, and polyesters have become alternative materials for positive electrode binders. However, currently, these three major types of materials have disadvantages such as insolubility in NMP, poor resistance to electrolyte swelling, or poor electrochemical stability.

[0005] Thermoplastic elastomers have high flexibility and initial adhesion, can improve the flexibility of coatings and electrode sheets, and solve the gel problem in the pulping process, meeting the requirements of electrode sheet processing. However, they have problems such as insolubility in NMP, poor resistance to electrolytes, or poor resistance to electrochemical oxidation. Therefore, there is little research on adhesives. Only the research team of Dominic Rochefort in Canada uses a commercial copolymer of ethylene, acrylate, and maleic anhydride (Lotader 5500) as the binder for lithium iron phosphate positive electrodes, and this material shows good electrode sheet processing performance, battery capacity, and cycling performance. However, products such as the Lotader series are composed of high-content low-polarity components such as ethylene (thermoplastic resins), and the polymer resin itself has a low polarity, so it can only be used in low-polarity solvents such as toluene. Currently, all supporting systems in the lithium battery industry use N-methyl-2-pyrrolidone (NMP) as a solvent. Therefore, the adhesives used need to 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 binders that dissolve well at room temperature in NMP. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a non-fluorinated binder with good solubility in NMP.

[0007] The non-fluorinated binder of the present invention includes a modified resin, which is polymerized from a thermoplastic resin, a functional monomer, and a nitrile group-containing unsaturated monomer. By weight percentage, the thermoplastic resin accounts for 20-50%, the functional monomer accounts for 2-20%, and the rest is the nitrile group-containing unsaturated monomer; and the concentration of the modified resin after being dissolved at room temperature in NMP is ≥2 wt%; 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.

[0008] The present invention graft-modifies the thermoplastic resin to make it have room-temperature solubility in NMP solvent, while improving the high-temperature tolerance of the material in carbonate electrolytes and the adhesion to metal foils, so that it can be applied to the fields of side coating protective adhesives, conductive dispersion adhesives, and positive and negative electrode binders for lithium-ion batteries, and can be used alone or in combination with other binders.

[0009] The thermoplastic resins commonly used in the art that can be used as battery adhesives are all applicable to the present invention. In one embodiment of the present invention, the thermoplastic resin includes at least one of an ethylene-acrylic acid copolymer with an acrylic acid monomer content <18%, an ethylene-vinyl acetate copolymer with a vinyl acetate monomer content <33%, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-maleic anhydride copolymer.

[0010] The functional monomer can improve the adhesion of the resin to the metal foil. In some embodiments of the present invention, the unsaturated monomer having a carboxyl group (anhydride) includes at least one of (meth)acrylic acid, undecenoic acid, octadecenoic 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, and β-diaminoacrylic acid, maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluorinated alkyl maleate.

[0011] The unsaturated monomer having a sulfonic acid group includes at least one of 2-acrylamido-2-methylpropanesulfonic acid, allyloxypropylsulfonic acid or allyloxypropylsulfonic acid, vinylsulfonic acid, vinylsulfonate, 2-acrylamide-2-methylpropanesulfonic acid, propenesulfonic acid, and methacrylic acid.

[0012] The unsaturated monomers having an amino group include at least one of dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, ethyl 2-(dimethylamino)methacrylate, and N-(2-aminoethyl)acrylamide.

[0013] The unsaturated monomers having a hydroxyl group include at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxyethylcaprolactone acrylate.

[0014] In one embodiment of the present invention, the nitrile group-containing unsaturated monomers include at least one of acrylonitrile, 3-butenenitrile, 3-pentenenitrile, 4-pentenenitrile, and methacrylonitrile.

[0015] In a preferred embodiment of the present invention, the proportion of the thermoplastic resin is 30-50%.

[0016] In a specific embodiment of the present invention, the molecular weight of the thermoplastic resin is 50,000-400,000.

[0017] The present invention also provides the application of the non-fluorine binder described in the present invention in the field of secondary batteries.

[0018] The non-fluorine binder of the present invention has performance equivalent to that of PVDF and can replace PVDF and be used in lithium-ion batteries, including but not limited to being used as a binder for active materials, a ceramic binder for edge coating of electrode sheets (tab glue), etc.

[0019] The normal temperature described in the present invention is 25°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention obtains a modified resin by graft copolymerization modification of a specific thermoplastic resin, enabling it to dissolve well in NMP, improving the tolerance of the binder to carbonate electrolytes, and enhancing the adhesion of the material to foil.

[0022] The binder of the present invention has normal temperature solubility in NMP solvent, can improve the high-temperature tolerance of the material in carbonate electrolytes and the adhesion to metal foils, and can be applied to the fields of edge coating protection glue, conductive dispersion glue, and positive and negative electrode binders in lithium-ion batteries, and can be used alone or in combination with other binders.

[0023] The non-fluorine binder of the present invention has excellent adhesion and stable electrochemistry, does not contain fluorine, has prominent price and environmental advantages, and can replace traditional fluorine-containing resins and be applied in lithium-ion batteries. Detailed implementation manners

[0024] The non-fluorine binder of the present invention comprises a modified resin, which is polymerized from a thermoplastic resin, a functional monomer and a nitrile group-containing unsaturated monomer. By weight percentage, the thermoplastic resin accounts for 20-50%, the functional monomer accounts for 2-20%, and the rest is the nitrile group-containing unsaturated monomer; and the concentration of the modified resin after being dissolved at room temperature in NMP is ≥2 wt%; 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.

[0025] The present invention graft-modifies the thermoplastic resin to make it soluble at room temperature in an NMP solvent, and at the same time improves the high-temperature tolerance of the material in a carbonate-based electrolyte and the adhesion to a metal foil, so that it can be applied to the fields of side coating protective glue, conductive dispersion glue and positive and negative electrode binders of lithium-ion batteries, and can be used alone or in combination with other binders.

[0026] The thermoplastic resins commonly used in the art and applicable to battery adhesives are all applicable to the present invention. In one embodiment of the present invention, the thermoplastic resin includes at least one of an ethylene-acrylic acid copolymer with an acrylic acid monomer content <18%, an ethylene-vinyl acetate copolymer with a vinyl acetate monomer content <33%, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-maleic anhydride copolymer.

[0027] The functional monomer can improve the adhesion of the resin to the metal foil. In some embodiments of the present invention, the unsaturated monomer having a carboxyl group (anhydride) includes at least one of (meth)acrylic acid, undecenoic acid, octadecenoic 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, and β-diaminoacrylic acid, maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloro maleic acid, dichloro maleic acid, fluoro maleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate.

[0028] 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, vinyl sulfonate, 2-acrylamide-2-methylpropanesulfonic acid, propenesulfonic acid, and methallylsulfonic acid.

[0029] The unsaturated monomers having an amino group include at least one of dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, ethyl 2-(dimethylamino)methacrylate, and N-(2-aminoethyl)acrylamide.

[0030] The unsaturated monomers having a hydroxyl group include at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxyethyl caprolactone acrylate.

[0031] The nitrile group-containing unsaturated monomer can improve the solubility of the resin in NMP and the adhesion to metal materials. All the commonly used nitrile group-containing unsaturated monomers in the art are applicable to the present invention. In one embodiment of the present invention, the nitrile group-containing unsaturated monomer includes at least one of acrylonitrile, 3-butenenitrile, 3-pentenenitrile, 4-pentenenitrile, and methacrylonitrile.

[0032] In a preferred embodiment of the present invention, the proportion of the thermoplastic resin is 30-50%.

[0033] In a specific embodiment of the present invention, the molecular weight of the thermoplastic resin is 50,000-400,000. The molecular weights described in the present invention are all weight-average molecular weights.

[0034] The modified resin of the present invention can be polymerized by the conventional graft copolymerization method in the art.

[0035] In one embodiment of the present invention, solution polymerization is used for polymerization. The thermoplastic resin is dissolved in a weakly polar solvent, and under certain reaction conditions, polymer modification is carried out by solution grafting. After drying, it can be dissolved in NMP solvent at room temperature and applied to the field of binders related to lithium batteries.

[0036] In a specific embodiment, the reaction medium for solution polymerization includes, but is not limited to, weakly polar solvents such as benzene, toluene, xylene, ethyl acetate, and butyl acetate.

[0037] The present invention also provides the application of the non-fluorine binder described in the present invention in the field of secondary batteries. In a specific embodiment, the secondary battery is a lithium-ion battery.

[0038] The non-fluorine binder of the present invention has performance equivalent to that of PVDF and can replace PVDF and be used in lithium-ion batteries, including but not limited to being used as an active material binder, a ceramic binder for edge coating of the electrode sheet (tab glue), etc. In a specific embodiment, the secondary battery is a lithium-ion battery.

[0039] The room temperature described in the present invention is 25°C.

[0040] The following further describes the specific embodiments of the present invention in conjunction with the examples, and the present invention is not limited to the scope of the examples described herein. The performance tests of the products in the examples are carried out by the following methods:

[0041] (1) Dissolution Test

[0042] Place the sample to be tested into a beaker with magnetic stirring, add NMP for dissolution (concentration ≥ 2%), stir and disperse at 25°C for 24 hours, and observe the dissolution state of the sample to be tested in the NMP solvent.

[0043] (2) Electrolyte Swelling Degree Test (70°C / 24h)

[0044] In the present invention, the electrolyte swelling degree refers to the swelling degree of the part insoluble in the electrolyte when the modified rubber film is immersed in the carbonate electrolyte salt solution at 70°C for 24 hours. Here, the electrolyte swelling degree of the modified rubber can be specifically calculated by the following method. Prepare an NMP solution containing the modified resin, dry the dispersion completely in a forced-air oven at 110°C to form a film with a thickness of 0.2 - 0.5 mm. Cut the film into squares with a side length of 2.5 mm, and accurately weigh about 1 g. Let the mass of the film piece obtained by cutting be W0. Immerse the obtained film piece in 100 g of electrolyte (Shanshan 12663) at 70°C for 24 hours. Then, take out the film piece from the electrolyte, wipe off the excess electrolyte components on the surface with a dust-free cloth, and weigh the mass of the film piece W1. Calculate the mass change according to the following formula and take it as the electrolyte swelling degree.

[0045] Swelling degree % = {(W1 - W0) / W0} * 100

[0046] (3) DMC Solvent Elution Test (70°C / 24h)

[0047] The sample preparation method is the same as above. Dry and weigh the modified rubber film piece and record it as M0. Subsequently, immerse it in the DMC solvent, seal it, store it in an environment at 70°C for 24 hours, take it out, wipe off the excess solvent on the surface with a dust-free cloth, and place it in a forced-air oven at 110°C for baking for 5 hours, and weigh the mass of the film piece M1.

[0048] Elution % = {(M0 - M1) / M0} * 100

[0049] (4) Prepare a lithium cobaltate positive electrode plate and test the peeling force between the coating and the aluminum foil

[0050] Prepare the slurry according to the following formula and process. Among them, the slurry formula is shown in Table 1, and the stirring process is shown in Table 2.

[0051] Table 1

[0052] <![CDATA[LiCoO 2 > SP Conductive Agent Binder 1 - PVDF Binder 2 - Modified Resin Solid Content 97％ 1％ 2.0％ 2.0％ 75～85％

[0053] Table 2

[0054] Step Step 1 Step 2 Step 3 Operation Dissolve Binder 1 for 3 hours Add dry powder for blending and knead for 5 hours Slowly stir and cool down for 2 hours for standby

[0055] Preparation of the electrode sheet: Coating the positive electrode slurry on the aluminum foil to make an electrode sheet with a single-sided surface density of 240 g / m 2 , a width of 40 mm, and testing the 180° coating peel strength.

[0056] Example 1

[0057] In a 500 mL four-necked flask, add xylene. Under stirring, add 19 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles and dissolve them into a colorless transparent solution at 65 °C. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 5 g of 2-acrylamido-2-methylpropanesulfonic acid at one time, and simultaneously add 76 g of acrylonitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. After the 70 °C heat preservation reaction for 15 hours, dry the solution at 60 °C by blowing air for standby.

[0058] Example 2

[0059] In a 500 mL four-necked flask, add xylene. Under stirring, add 22.5 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles and dissolve them into a colorless transparent solution at 65 °C. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 10 g of allyl sulfonic acid at one time, and simultaneously add 67.5 g of acrylonitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. After the 70 °C heat preservation reaction for 15 hours, dry the solution at 60 °C by blowing air for standby.

[0060] Example 3

[0061] In a 500 mL four-necked flask, add xylene. Under stirring, add 30 g of ethylene-vinyl acetate ((LG of South Korea, EA28400)) resin particles and dissolve them into a colorless transparent solution at 65 °C. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 20 g of acrylic acid at one time, and simultaneously add 50 g of acrylonitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. After the 70 °C heat preservation reaction for 15 hours, dry the solution at 60 °C by blowing air for standby.

[0062] Example 4

[0063] In a 500 mL four-necked flask, add xylene. Under stirring, add 28.3 g of ethylene-ethyl acrylate (EEA) (DuPont EEA2116 from the United States) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 15 g of methacrylic acid all at once. At the same time, dropwise add 56.7 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours during the process. Keep the reaction at 70 °C for 15 hours to complete. Dry the solution at 60 °C with forced air for standby.

[0064] Example 5

[0065] In a 500 mL four-necked flask, add xylene. Under stirring, add 47.5 g of ethylene-acrylic acid ((LG from South Korea, EAA5080)) resin particles (molecular weight 200,000). Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 5 g of N-(2-aminoethyl)acrylamide all at once. At the same time, dropwise add 47.5 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours during the process. Keep the reaction at 70 °C for 15 hours to complete. Dry the solution at 60 °C with forced air for standby.

[0066] Example 6

[0067] In a 500 mL four-necked flask, add xylene. Under stirring, add 26 g of ethylene-maleic anhydride (EMAH) resin particles (DuPont 21E533 from the United States). Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 20 g of 2-hydroxyethyl acrylate all at once. At the same time, dropwise add 54 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours during the process. Keep the reaction at 70 °C for 15 hours to complete. Dry the solution at 60 °C with forced air for standby.

[0068] Example 7

[0069] In a 500 mL four-necked flask, add xylene. Under stirring, add 30 g of ethylene-butyl acrylate (EBA) resin particles (DuPont AC 34035 from the United States). Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 8 g of maleic anhydride all at once. At the same time, dropwise add 62 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours during the process. Keep the reaction at 70 °C for 15 hours to complete. Dry the solution at 60 °C with forced air for standby.

[0070] Example 8

[0071] In a 500 mL four-necked flask, add xylene. Under stirring, add 30 g of ethylene-vinyl acetate EVA (LG of South Korea, EA28400) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 10 g of undecenoic acid at one time. Meanwhile, add 60 g of 3-butenenitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. Keep the reaction at 70 °C for 15 hours to end. Dry the solution at 60 °C by blowing air for standby.

[0072] Comparative Example 1

[0073] Unmodified EVA resin (LG of South Korea, EA28400)

[0074] Comparative Example 2

[0075] Unmodified EAA resin (LG of South Korea, EAA5080)

[0076] Comparative Example 3

[0077] In a 500 mL four-necked flask, add xylene. Under stirring, add 17 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 6 g of acrylic acid at one time. Meanwhile, add 77 g of acrylonitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. Keep the reaction at 70 °C for 15 hours to end. Dry the solution at 60 °C by blowing air for standby.

[0078] Comparative Example 4

[0079] In a 500 mL four-necked flask, add xylene. Under stirring, add 52 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 5 g of acrylic acid at one time. Meanwhile, add 43 g of acrylonitrile monomer dropwise within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. Keep the reaction at 70 °C for 15 hours to end. The synthesis and preparation process is the same as that of Example 2, by weight ratio.

[0080] Comparative Example 5

[0081] In a 500 mL four-necked flask, add xylene. Under stirring, add 30 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 1 g of acrylic acid at one time. Meanwhile, dropwise add 69 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. Keep the reaction at 70 °C for 15 hours to end. Dry the solution at 60 °C by blowing air for standby.

[0082] Comparative Example 6

[0083] In a 500 mL four-necked flask, add xylene. Under stirring, add 30 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles. Dissolve them at 65 °C into a colorless transparent solution. Then cool down to the reaction temperature of 60 - 70 °C and add a peroxide or azo initiator. Add 21 g of acrylic acid at one time. Meanwhile, dropwise add 49 g of acrylonitrile monomer within 2 hours. As the reaction proceeds, the emulsion balance becomes worse, and gel particles gradually precipitate out, and the reaction is terminated passively.

[0084] Comparative Example 7

[0085] In a 500 mL four-necked flask, add xylene. Under stirring, add a peroxide or azo initiator at the reaction temperature of 60 - 70 °C. Add 20 g of acrylic acid at one time. Meanwhile, dropwise add 50 g of acrylonitrile monomer within 2 hours. Add the peroxide or azo initiator again every 3 hours in the middle. Keep the reaction at 70 °C for 15 hours to end. Dry the solution at 60 °C by blowing air.

[0086] Mix the above dried substance with 30 g of ethylene-vinyl acetate (LG of South Korea, EA28400) resin particles evenly, dissolve them at high temperature in NMP solvent, and cool to room temperature to present a gel state, and it is impossible to make a positive electrode paste.

[0087] The performance test is shown in Table 3.

[0088] Table 3

[0089]

[0090] It can be seen that the modified resin of the present invention can be well dissolved in NMP, improving the tolerance of the binder to carbonate electrolytes and improving the adhesion of the material to the foil.

Claims

1. Non-fluorine binder, Characterized in that: The binder comprises a modified resin, which is polymerized from a thermoplastic resin, a functional monomer and a nitrile group-containing unsaturated monomer. By weight percentage, the thermoplastic resin accounts for 20-50%, the functional monomer accounts for 2-20%, and the rest is the nitrile group-containing unsaturated monomer; and the concentration of the modified resin after being dissolved at room temperature in NMP is ≥ 2 wt%; 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.

2. The non-fluorine binder according to claim 1, Characterized in that: The thermoplastic resin includes at least one of an ethylene-acrylic acid copolymer with an acrylic acid monomer content < 18%, an ethylene-vinyl acetate copolymer with a vinyl acetate monomer content < 33%, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-maleic anhydride copolymer.

3. The non-fluorine binder according to claim 1, Characterized in that: The unsaturated monomer having a carboxyl group (anhydride) includes at least one of (meth)acrylic acid, undecenoic acid, octadecenoic 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 fluorinated alkyl maleate; The unsaturated monomer having a sulfonic acid group includes at least one of 2-acrylamido-2-methylpropanesulfonic acid, allyloxyhydroxypropyl sulfonic acid or allyloxyhydroxypropyl sulfonic acid, vinyl sulfonic acid, vinyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, propene sulfonic acid, and methacrylic acid sulfonic 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 hydroxyethylcaprolactone acrylate.

4. The non-fluorine binder according to claim 1, Characterized in that: The nitrile group-containing unsaturated monomer includes at least one of acrylonitrile, 3-butenenitrile, 3-pentenenitrile, 4-pentenenitrile, and methacrylonitrile.

5. The non-fluorine binder according to claim 1, Characterized in that: The proportion of the thermoplastic resin is 30-50%.

6. The non-fluorine binder according to claim 1, Characterized in that: The molecular weight of the thermoplastic resin is 50,000-400,000.

7. Application of the non-fluorine binder according to any one of claims 1-6 in the field of secondary batteries.

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