Functional coating binder, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to a functional coating binder, a preparation method thereof and a lithium ion battery, and the functional coating binder comprises the following active ingredients in parts by weight: 10-60.0 parts of unsaturated monomer containing dihydroxyl and diester group; 5 to 50.0 parts of ethylenically unsaturated carboxylic acid or anhydride; 15 to 60.0 parts of a strong polar unsaturated monomer; 1 to 40.0 parts of a polymer additive; 0.1 to 20.0 parts of an initiator; and 1 to 60.0 parts of a pH regulator. The functional coating binder provided by the invention has excellent compatibility and universality, meanwhile, the functional coating binder has excellent electrochemical stability and conductivity, and when the functional coating binder is applied to an electrochemical energy storage device, the device can be endowed with excellent service life and lower internal resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a functional coating binder, a preparation method thereof, and a lithium ion battery. Background Art

[0002] With the rapid development and application of lithium batteries, the demand for lithium battery energy density is becoming increasingly higher. Among them, increasing the active material loading and compaction density has become the core path to improving the energy density of lithium batteries. However, the resulting problem of insufficient peel strength has become increasingly prominent. When the interface adhesion between the positive electrode active material and the current collector is weak and the peel strength is insufficient, it is very easy to cause serious active material shedding during the electrode processing and winding process. This not only leads to a decrease in process yield, but also becomes a key bottleneck restricting the mass production of high-energy-density batteries. This interface bonding failure problem has evolved from a simple process defect to a core technical challenge affecting industry iteration, and it is urgent to seek breakthroughs through material innovation and process optimization.

[0003] In view of this, how to improve the interfacial adhesion of adhesives is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] In order to solve the problem of insufficient interfacial adhesion of binders in the prior art, the present invention provides a functional coating binder. Through the synergistic effect of various components, the binder significantly improves the peel strength between the functional coating and the active material while meeting the requirements of electrochemical stability and electrolyte resistance, thereby solving the problem of insufficient interfacial adhesion of binders in the prior art.

[0005] The technical solution adopted by the present invention to solve its technical problem is: A functional coating binder, wherein the active ingredients of the raw materials include the following components in parts by weight: 10-60.0 parts of unsaturated monomers containing dihydroxyl and diester groups; 5-50.0 parts of ethylenically unsaturated carboxylic acid or anhydride; 15-60.0 parts of strongly polar unsaturated monomer; 1 to 40.0 parts of polymer additives; 0.1 to 20.0 parts of initiator; 1 to 60.0 parts of pH adjuster

[0006] Alternatively, the unsaturated monomer containing dihydroxyl and diester groups is prepared according to the following method: S01: β-carboxyethyl acrylate is chlorinated with thionyl chloride to obtain a chlorinated monomer; S02: subjecting glycerol to an acylation reaction with the acyl chloride monomer at 0-5° C. to obtain an unsaturated monomer containing a dihydroxyl group and a diester group.

[0007] Optionally, in step S01, the mass ratio of the β-carboxyethyl acrylate to the thionyl chloride is 1:(0.4-0.6).

[0008] Optionally, in step S02, the molar ratio of the glycerol to the acyl chloride monomer is 1:1.

[0009] Optionally, the ethylenically unsaturated carboxylic acid or anhydride is selected from at least one of acrylic acid, β-carboxyethyl acrylate, itaconic acid, methacrylic acid, fumaric acid, maleic acid, acrylic anhydride, itaconic anhydride, methacrylic anhydride, fumaric anhydride, and maleic anhydride.

[0010] Optionally, the strongly polar unsaturated monomer is selected from at least one of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-hydroxyethyl acrylamide, N-vinyl pyrrolidone, 2-acrylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate, sodium p-styrenesulfonate, sodium phenyl sulfonate, 2-acrylamido-2-methylpropylphosphonic acid, vinylphosphonic acid, allyl polyoxyethylene ether phosphate, and 2-hydroxyethyl methacrylate phosphate.

[0011] Optionally, the polymer auxiliary agent is selected from at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and hydroxymethyl cellulose.

[0012] Optionally, the initiator is selected from at least one of persulfate initiators, hydroperoxide initiators, organic peroxide initiators, diacyl peroxide initiators, azo initiators and redox initiators.

[0013] Another object of the present invention is to provide a method for preparing the functional coating binder as described above, comprising the following steps: S1: adding an unsaturated monomer containing a dihydroxyl group and a diester group, an ethylenically unsaturated carboxylic acid or anhydride, a strongly polar unsaturated monomer, and a polymer additive to water according to the formula to obtain a liquid component, adding a portion of the liquid component to a reactor, and adding another portion of the liquid component to a premixing kettle; S2: preparing the initiator into an initiator solution; S3: After deoxygenation, stirring is started, and the liquid components in the reactor are heated to 40-100° C., and then the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction is carried out at a constant temperature and heat preservation treatment to obtain a water-based acrylic copolymer glue; S4: adding a pH adjuster to the aqueous acrylic copolymer glue solution to adjust the pH to 4-9 to obtain a functional coating binder.

[0014] Another object of the present invention is to provide a lithium ion battery comprising the functional coating binder as described above.

[0015] The beneficial effects of the present invention are: The functional coating adhesive provided by the present invention is a water-based product that is green, environmentally friendly, and economical. It also has excellent compatibility and universality, and can exhibit excellent comprehensive properties such as high peel strength and low resistance for active materials such as lithium iron phosphate with smaller particle sizes and lithium manganese iron phosphate with different surface structures. At the same time, the functional coating adhesive has excellent electrochemical stability and conductivity. When applied to electrochemical energy storage devices, it can give the devices excellent service life and lower internal resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and examples.

[0017] Figure 1 Schematic diagram of the functional coating binder forming molecular chains interlaced at the interface of the present invention; Figure 2 Schematic diagram of the preparation process of the unsaturated monomer containing dihydroxyl and diester groups in the present invention; Figure 3 This is a photograph of the functional carbon-coated aluminum foil prepared in Example 1 of the present invention; Figure 4 This is a photo of the functional carbon-coated aluminum foil prepared in Example 2 of the present invention after testing; Figure 5 This is a diagram of the positive electrode peeling force on the carbon-coated aluminum foil prepared in Example 1 of the present invention; Figure 6 This is a diagram of the positive electrode peeling force on the carbon-coated aluminum foil prepared in Example 3 of the present invention; Figure 7 This is a diagram of the positive electrode peeling force on the carbon-coated aluminum foil prepared in Comparative Example 1 of the present invention; Figure 8 This is a diagram of the positive electrode peeling force on the carbon-coated aluminum foil prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0018] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0019] In order to increase the active material loading and compaction density, with the iteration of lithium battery positive electrode materials, current lithium battery positive electrode materials mostly use lithium iron phosphate or lithium iron manganese phosphate with smaller particle size as active materials; as the particle size of the active material decreases, higher requirements are placed on the bonding performance of the binder. When existing binders are used for lithium battery positive electrodes that use smaller particle size active materials, there are problems with bonding difficulties, serious powder loss, and too low peel strength, which has become a key problem restricting the further iteration of lithium batteries.

[0020] To solve the problem of powder shedding of small-particle active materials, some studies have attempted to use temporary solutions such as oily coating and multiple coatings to partially meet the needs of the current lithium battery industry. However, these solutions still have defects in terms of energy conservation and environmental protection, processing yield, and compatibility. In general, in the field of lithium battery functional coatings, low peel strength has become a key problem that restricts the further iteration of lithium batteries. There is an urgent need for a functional coating solution with qualified comprehensive performance. The fundamental requirement is an excellent adhesive product that can significantly improve the peel strength between the functional coating and the active material while meeting the requirements of electrochemical stability and electrolyte resistance, and improve the problem of active material shedding during the electrode processing process, laying a solid foundation for further improving the energy density of lithium batteries, thereby driving the industry towards a more efficient and safer direction.

[0021] In order to solve the problem of insufficient interfacial bonding strength of adhesives in the prior art, the present invention provides a functional coating adhesive. The active ingredients of the adhesive raw materials include the following components in parts by weight: 10-60.0 parts of unsaturated monomers containing dihydroxyl and diester groups; 5-50.0 parts of ethylenically unsaturated carboxylic acid or anhydride; 15-60.0 parts of strongly polar unsaturated monomer; 1 to 40.0 parts of polymer additives; 0.1 to 20.0 parts of initiator; 1 to 60.0 parts of pH adjuster

[0022] Among them, the unsaturated monomer containing dihydroxyl and diester groups refers to an unsaturated monomer containing both dihydroxyl and diester groups. The present invention uses the unsaturated monomer containing dihydroxyl and diester groups to exhibit outstanding interfacial interaction after being matched with other monomers in the system. For details, see Figure 1As shown, on the one hand, in the unsaturated monomer containing dihydroxy and diester groups, the presence of diester groups can greatly improve the binder's affinity for N-methylpyrrolidone (NMP). When wet-coating the positive electrode active material layer, NMP can penetrate into the functional coating structure together with the polyvinylidene fluoride (PVDF) dissolved therein, so that PVDF and the functional coating binder reach a closer relative distance. At the same time, its dihydroxy groups combined with the strongly polar unsaturated groups can form a strong electrostatic interaction force with PVDF, thereby improving the peel strength. On the other hand, the NMP affinity enables the binder of the functional coating to penetrate into the positive electrode active material layer, while PVDF penetrates into the functional coating in reverse, solving the problem of weak conventional interface bonding and exponentially improving the interface peel strength. The synergistic effect can effectively improve the problem of active material shedding during the electrode processing process. The presence of dihydroxy and strong polar groups can avoid the problem of the binder being destroyed by the electrolyte when used in lithium batteries, thereby avoiding a significant attenuation of the peel strength.

[0023] The present invention introduces a polymer additive into the system, so that the functional coating binder has excellent dispersing and wetting ability on the carbon material. The introduction of the polymer additive not only stabilizes the reaction process, but also eliminates the use of additional dispersing and wetting additives. The carbon slurry that meets the requirements can be prepared using the existing homogenization process.

[0024] The functional coating adhesive provided by the present invention is a water-based product that is green, environmentally friendly, and economical. It also has excellent compatibility and universality, and can exhibit excellent comprehensive properties such as high peel strength and low resistance for active materials such as lithium iron phosphate with smaller particle sizes and lithium manganese iron phosphate with different surface structures. At the same time, the functional coating adhesive has excellent electrochemical stability and conductivity. When applied to electrochemical energy storage devices, it can give the devices excellent service life and lower internal resistance.

[0025] The unsaturated monomer preferably containing dihydroxyl and diester groups is prepared according to the following method: S01: β-carboxyethyl acrylate (A) is chlorinated with thionyl chloride to obtain chlorinated monomer (B); Preferably, DMF is used as a catalyst in this step, the reaction temperature is 0-25°C, and the reaction time is 4-6 hours; the mass ratio of DMF to β-carboxyethyl acrylate is (0.02-0.08):1; S02: acylation reaction of glycerol with acyl chloride monomer (B) at 0-5°C to obtain an unsaturated monomer containing dihydroxyl and diester groups; The reaction temperature was strictly controlled at 0-5°C in this step.

[0026] The preparation process of the unsaturated monomer containing dihydroxyl and diester groups is as follows: Figure 2As shown, there are two types of unsaturated monomer structures containing dihydroxyl and diester groups, of which the main product is Figure 2 The product C in the Figure 2 Product D in.

[0027] The unsaturated monomer containing dihydroxyl and diester groups prepared by the present invention enables the functional coating binder to exert excellent active material interface peel strength. The fundamental reason is that the affinity for NMP is improved, the highly polar unsaturated monomer exerts excellent electrostatic interaction force, and the synergistic effect exerts high peel strength. Unlike conventional functional coating binders, the binder of the present invention has good affinity with NMP. When the positive electrode active material layer is wet-coated, NMP can penetrate into the functional coating structure together with the PVDF dissolved therein, so that the strong polar groups of PVDF and the functional coating binder reach a closer relative distance, thereby forming a stronger electrostatic interaction force. At the same time, the NMP affinity can enable the binder of the functional coating to penetrate into the positive electrode active material layer, while PVDF reversely penetrates into the functional coating, that is, the NMP affinity shortens the relative distance between the strong polar functional groups and PVDF, exerts a strong electrostatic interaction, and at the same time enables the binder to form molecular chains at the interface, eliminating the problem of weak conventional interface bonding force, and exponentially improving the interface peeling strength, thereby effectively improving the problem of active material shedding in the electrode processing process, and providing effective assistance for further improving the energy density of lithium batteries.

[0028] Existing binders typically enhance the peel strength with the active layer through the interaction of monomers with different polarities. However, this approach has limited effect on enhancing interfacial adhesion and is insufficient to meet the bonding requirements of small-particle active materials. Therefore, the present invention creatively introduces unsaturated monomers containing dihydroxy and diester groups into the system, allowing the binder to form interlaced molecular chains at the interface, eliminating the problem of weak conventional interfacial bonding and exponentially enhancing interfacial peel strength.

[0029] Specifically, in the present invention, the mass ratio of β-carboxyethyl acrylate to thionyl chloride in step S01 is preferably 1:(0.4-0.6), and the molar ratio of glycerol to acyl chloride monomer in step S02 is preferably 1:1.

[0030] The present invention preferably uses at least one of an ethylenically unsaturated carboxylic acid or anhydride selected from acrylic acid, β-carboxyethyl acrylate, itaconic acid, methacrylic acid, fumaric acid, maleic acid, and acrylic anhydride, itaconic anhydride, methacrylic anhydride, fumaric anhydride, and maleic anhydride; and preferably uses a strongly polar unsaturated monomer selected from acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-hydroxyethyl acrylamide, N-vinyl pyrrolidone, 2-acrylamido-2-methylpropanesulfonic acid, sodium vinylsulfonate, sodium p-styrenesulfonate, sodium phenylsulfonate, 2-acrylamido-2-methylpropylphosphonic acid, vinylphosphonic acid, allyl polyoxyethylene ether phosphate, and 2-hydroxyethyl methacrylate phosphate. At least one of; preferably, the polymer auxiliary agent is selected from at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and hydroxymethyl cellulose; preferably, the initiator is selected from at least one of persulfate initiators, hydroperoxide initiators, organic peroxide initiators, diacyl peroxide initiators, azo initiators, and redox initiators; preferably, the pH regulator is selected from at least one of an inorganic base and an organic base; specifically, the inorganic base is preferably selected from at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water, and the organic base is preferably selected from at least one of ethanolamine, diethanolamine, and triethanolamine.

[0031] The carbon-coated aluminum foil prepared with the functional coating adhesive provided by the present invention can exert excellent interfacial peeling force, and is particularly suitable for the preparation of current lithium battery wet-process electrodes. It can effectively solve the problem of peeling strength attenuation caused by increased active material loading and compaction density, and help the lithium battery industry to iterate technology.

[0032] Another object of the present invention is to provide a method for preparing the functional coating binder as described above, the preparation method comprising the following steps: S1: According to the formula, an unsaturated monomer containing a dihydroxyl group and a diester group, an ethylenically unsaturated carboxylic acid or anhydride, a strongly polar unsaturated monomer, and a polymer additive are added to water, preferably pure water, and the mixture of the above components and water is mixed by stirring or homogenizing to form a uniform liquid component, and then a portion of the liquid component is added to a reactor, and the other portion of the liquid component is added to a premixing kettle; preferably, 5-30% of the total mass of the liquid component is added to the reactor, and the remaining liquid component is added to the premixing kettle; S2: preparing the initiator into an initiator solution; Dissolve the initiator in pure water according to the formula, preferably to prepare a 0.1 to 20.0 wt.% initiator solution; S3: After deoxygenation, stirring is started, and the liquid components in the reactor are heated to 40-100° C., and then the initiator solution and the liquid components in the premixed reactor are added to the reactor respectively, and the reaction is carried out at a constant temperature and heat preservation treatment to obtain a water-based acrylic copolymer glue; Preferably, in this step, nitrogen is introduced into the reactor to remove oxygen, stirring is started, and the liquid components in the reactor are slowly heated to 40-100° C., and then the initiator solution and the liquid components in the premixed reactor are added to the reactor at a preset rate, respectively. The reaction temperature is maintained within a preset range. After all components are added to the reactor, the reaction is heat-treated for 30-600 minutes to obtain an aqueous acrylic copolymer adhesive solution. S4: adding a pH adjuster to the aqueous acrylic copolymer adhesive to adjust the pH to 4 to 9 to obtain a functional coating binder; According to the formula, a pH regulator is added to the aqueous acrylic copolymer adhesive to adjust the pH to 4-9, thereby obtaining a functional coating adhesive with a high bonding ability and a solid content of 5-40.0 wt.%.

[0033] The preparation method of the functional coating adhesive provided by the present invention has a simple process; the prepared functional coating adhesive is a water-based product, which is green, environmentally friendly and economical; and has excellent compatibility and universality. It can exhibit excellent comprehensive properties such as high peel strength and low resistance for active materials such as lithium iron phosphate with smaller particle size and lithium manganese iron phosphate with different surface structures; at the same time, the functional coating adhesive has excellent electrochemical stability and conductivity, and when applied to electrochemical energy storage devices, it can give the devices excellent service life and lower internal resistance.

[0034] Another object of the present invention is to provide a lithium ion battery comprising the functional coating binder as described above.

[0035] The lithium-ion battery provided by the present invention uses a functional coating binder that is a water-based product, is green, environmentally friendly, and economical; and has excellent compatibility and universality. It can exhibit excellent comprehensive properties such as high peel strength and low resistance for active materials such as lithium iron phosphate with smaller particle sizes and lithium manganese iron phosphate with different surface structures. At the same time, the functional coating binder has excellent electrochemical stability and conductivity. When applied to lithium-ion batteries, it can give lithium-ion batteries an excellent service life and lower internal resistance.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0037] Unless otherwise specified, the unsaturated monomers containing dihydroxyl groups and diester groups in the embodiments and comparative examples of the present invention were prepared as follows: S01: Under a nitrogen atmosphere, β-carboxyethyl acrylate was chlorinated with thionyl chloride to obtain a chlorinated monomer, with the mass ratio of thionyl chloride to β-carboxyethyl acrylate being 0.5:1; DMF was used as a reaction catalyst, with the mass ratio of DMF to β-carboxyethyl acrylate being 0.06:1; the reaction temperature was 15°C, and the reaction time was 4 hours; S02: Slowly add the acylation monomer to glycerol while stirring in an ice bath (0-5°C) to carry out an acylation reaction to obtain an unsaturated monomer containing dihydroxyl and diester groups; the molar ratio of the acylation monomer to glycerol is strictly controlled to be 1:1, and sodium carbonate is added as an acid-binding agent; the reaction is carried out for 5 hours.

[0038] Example 1 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 25.0 parts of unsaturated monomer containing dihydroxy and diester groups, 30.0 parts of methacrylic acid, 15.0 parts of acrylonitrile, 20.0 parts of acrylamide, and 10.0 parts of polyvinyl pyrrolidone are mixed with 400 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 30% of the total mass of the liquid component is added to the reactor and 70% is added to the premixing kettle.

[0039] S2: 2.0 parts of initiator ammonium persulfate was dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0040] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 72°C. Then, the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 72°C. After all components are added to the reactor, the reaction is kept warm for 90 minutes to obtain a water-based acrylic copolymer glue solution.

[0041] S4: 20.0 parts of ammonia pH regulator was added to the aqueous acrylic copolymer adhesive to adjust the pH to 6.7, thereby obtaining a functional coating adhesive with a solid content of 20.0 wt.% for high bonding ability.

[0042] The above 30.0 parts of binder (6.0 parts by dry weight) were fully dispersed and ground with 3.0 parts of conductive carbon black and 5.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 micron. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.1 microns was obtained.

[0043] The functional carbon-coated aluminum foil prepared in this example is shown in FIG. Figure 3 shown.

[0044] Example 2 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 25.0 parts of unsaturated monomer containing dihydroxy and diester groups, 10.0 parts of acrylic acid, 20.0 parts of acrylamide, 40.0 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 5.0 parts of polyethylene glycol are mixed with 450 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 25% of the total mass of the liquid component is added to the reactor and 75% is added to the premixing kettle.

[0045] S2: 3.0 parts of initiator sodium persulfate was dissolved in pure water to prepare a 1.5 wt.% initiator solution.

[0046] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 80°C. Then, the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 80°C. After all components are added to the reactor, the reaction mixture is kept warm for 120 minutes to obtain a water-based acrylic copolymer glue solution.

[0047] S4: 12.0 parts of sodium hydroxide were added to the aqueous acrylic copolymer adhesive to adjust the pH to 5.8, thereby obtaining a functional coating adhesive with a solid content of 16.0 wt.% for high bonding ability.

[0048] The above 50.0 parts of binder (8.0 parts by dry weight) were fully dispersed and ground with 4.0 parts of conductive carbon black and 4.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 μm. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 75°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 μm was obtained.

[0049] Example 3 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 60.0 parts of unsaturated monomer containing dihydroxy and diester groups, 20.0 parts of acrylic acid, 10.0 parts of acrylonitrile, 5.0 parts of acrylamide, and 5.0 parts of sodium carboxymethyl cellulose are mixed with 350 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 20% of the total mass of the liquid component is added to the reactor and 80% is added to the premixing kettle.

[0050] S2: 3.2 parts of initiator potassium persulfate was dissolved in pure water to prepare a 1.6 wt.% initiator solution.

[0051] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 70°C. Then, the initiator solution and the liquid in the premix kettle are added to the reactor respectively, and the reaction temperature is maintained at 70°C. After all components are added to the reactor, the reaction mixture is kept warm for 150 minutes to obtain a water-based acrylic copolymer glue solution.

[0052] S4: adding 25.0 parts of lithium hydroxide to the aqueous acrylic copolymer adhesive and adjusting the pH to 7.1 to obtain a functional coating adhesive with a solid content of 20.0 wt.% for high bonding ability.

[0053] The above 35.0 parts of binder (7.0 parts by dry weight) were fully dispersed and ground with 5.0 parts of conductive carbon black and 3.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 μm. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 μm was obtained.

[0054] Example 4 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 20.0 parts of unsaturated monomer containing dihydroxy and diester groups, 25.0 parts of acrylic acid, 20.0 parts of acrylonitrile, 15.0 parts of acrylamide, and 20.0 parts of polyvinyl alcohol are mixed with 400 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 15% of the total mass of the liquid component is added to the reactor and 85% is added to the premixing kettle.

[0055] S2: 4.0 parts of initiator (ammonium persulfate and sodium sulfite in a mass ratio of 2:1) were dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0056] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 75°C. Then, the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 75°C. After all components are added to the reactor, the reaction is kept warm for 120 minutes to obtain a water-based acrylic copolymer glue solution.

[0057] S4: 13.5 parts of sodium hydroxide were added to the aqueous acrylic copolymer adhesive to adjust the pH to 6.5, thereby obtaining a functional coating adhesive with a solid content of 20.0 wt.% for high bonding ability.

[0058] The above 40.0 parts of binder (8.0 parts by dry weight) were fully dispersed and ground with 6.0 parts of conductive carbon black and 2.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 micron. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 85°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 0.9 micron was obtained.

[0059] Example 5 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 10.0 parts of unsaturated monomer containing dihydroxy and diester groups, 50.0 parts of β-carboxyethyl acrylate, 25.0 parts of acrylonitrile, 14.0 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 1.0 part of hydroxymethyl cellulose are mixed with 500 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 10% of the total mass of the liquid component is added to the reactor and 90% is added to the premixing kettle.

[0060] S2: Dissolve 2.4 parts of initiator (sodium persulfate and sodium bisulfite in a mass ratio of 2:1) in pure water to prepare a 1.2 wt.% initiator solution.

[0061] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 70°C. Then, the initiator and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 70°C. After all the components are added to the reactor, the reaction is kept warm for 120 minutes to obtain a water-based acrylic copolymer glue solution.

[0062] S4: 7.0 parts of sodium hydroxide was added to the aqueous acrylic copolymer adhesive to adjust the pH to 5.3, thereby obtaining a functional coating adhesive with a solid content of 15.0 wt.% for high bonding ability.

[0063] The above 60.0 parts of binder (9.0 parts by dry weight) were fully dispersed and ground with 7.0 parts of conductive carbon black and 2.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 μm. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 85°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 μm was obtained.

[0064] Example 6 This embodiment provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 25.0 parts of unsaturated monomer containing dihydroxy and diester groups, 20.0 parts of acrylic acid, 15.0 parts of methacrylic acid, 25.0 parts of N-hydroxyethyl acrylamide, 5.0 parts of N-vinyl pyrrolidone, and 10.0 parts of polyvinyl pyrrolidone are mixed with 450 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 5% of the total mass of the liquid component is added to the reactor and 95% is added to the premixing kettle.

[0065] S2: 3.6 parts of initiator (ammonium persulfate and ascorbic acid in a mass ratio of 2:1) were dissolved in pure water to prepare a 1.8 wt.% initiator solution.

[0066] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 80°C. Then, the initiator solution and the liquid components in the premixed kettle are respectively added to the reactor, and the reaction temperature is maintained at 80°C. After all components are added to the reactor, the reaction mixture is kept warm for 90 minutes to obtain a water-based acrylic copolymer glue solution.

[0067] S4: 18.0 parts of calcium hydroxide was added to the aqueous acrylic copolymer adhesive solution, and the pH was adjusted to 6.9 to obtain a functional coating adhesive with a solid content of 18.0 wt.% for high bonding ability.

[0068] The above 50.0 parts of binder (9.0 parts by dry weight) were fully dispersed and ground with 6.0 parts of conductive carbon black and 4.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 micron. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 0.8 micron was obtained.

[0069] Comparative Example 1 This comparative example provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 55.0 parts of methacrylic acid, 15.0 parts of acrylonitrile, 20.0 parts of acrylamide, and 10.0 parts of polyvinyl pyrrolidone are mixed with 400 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 30% of the total mass of the liquid component is added to the reactor and 70% is added to the premixing kettle.

[0070] S2: 2.0 parts of initiator ammonium persulfate was dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0071] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 72°C. Then, the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 72°C. After all components are added to the reactor, the reaction is kept warm for 90 minutes to obtain a water-based acrylic copolymer glue solution.

[0072] S4: 20.0 parts of ammonia pH regulator was added to the aqueous acrylic copolymer adhesive to adjust the pH to 6.7, thereby obtaining a functional coating adhesive with a solid content of 20.0 wt.% for high bonding ability.

[0073] The above 30.0 parts of binder (6.0 parts by dry weight) were fully dispersed and ground with 3.0 parts of conductive carbon black and 5.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 micron. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.1 microns was obtained.

[0074] Comparative Example 2 This comparative example provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 10.0 parts of acrylic acid, 20.0 parts of acrylamide, 40.0 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 5.0 parts of polyethylene glycol are mixed with 450 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 25% of the total mass of the liquid component is added to the reactor and 75% is added to the premixing kettle.

[0075] S2: 3.0 parts of initiator sodium persulfate was dissolved in pure water to prepare a 1.5 wt.% initiator solution.

[0076] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 80°C. Then, the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction temperature is maintained at 80°C. After all components are added to the reactor, the reaction mixture is kept warm for 120 minutes to obtain a water-based acrylic copolymer glue solution.

[0077] S4: 12.0 parts of sodium hydroxide were added to the aqueous acrylic copolymer adhesive to adjust the pH to 5.8, thereby obtaining a functional coating adhesive with a solid content of 16.0 wt.% for high bonding ability.

[0078] The above 50.0 parts of binder (8.0 parts by dry weight) were fully dispersed and ground with 4.0 parts of conductive carbon black and 4.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 μm. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 75°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 μm was obtained.

[0079] Comparative Example 3 This comparative example provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 10.0 parts of unsaturated monomer containing dihydroxy and diester groups, 89.0 parts of β-carboxyethyl acrylate, and 1.0 part of hydroxymethyl cellulose are mixed with 500 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 10% of the total mass of the liquid component is added to the reactor and 90% is added to the premixing kettle.

[0080] S2: Dissolve 2.4 parts of initiator (sodium persulfate and sodium bisulfite in a mass ratio of 2:1) in pure water to prepare a 1.2 wt.% initiator solution.

[0081] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 70°C. Then, the initiator solution and the liquid components in the premixed kettle are respectively added to the reactor, and the reaction temperature is maintained at 70°C. After all components are added to the reactor, the reaction mixture is kept warm for 120 minutes to obtain a water-based acrylic copolymer glue solution.

[0082] S4: 7.0 parts of sodium hydroxide was added to the aqueous acrylic copolymer adhesive to adjust the pH to 5.3, thereby obtaining a functional coating adhesive with a solid content of 15.0 wt.% for high bonding ability.

[0083] The above 60.0 parts of binder (9.0 parts by dry weight) were fully dispersed and ground with 7.0 parts of conductive carbon black and 2.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 μm. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 85°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 μm was obtained.

[0084] Comparative Example 4 This comparative example provides a method for preparing a functional coating binder, comprising the following steps: S1: According to the weight parts, 25.0 parts of unsaturated monomer containing dihydroxy and diester groups, 20.0 parts of acrylic acid, 15.0 parts of methacrylic acid, and 10.0 parts of polyvinyl pyrrolidone are mixed with 450 parts of pure water. The raw materials and water are dispersed in a blender to form a uniform liquid component. 5% of the total mass of the liquid component is added to the reactor and 95% is added to the premixing kettle.

[0085] S2: 3.6 parts of initiator (ammonium persulfate and ascorbic acid in a mass ratio of 2:1) were dissolved in pure water to prepare a 1.8 wt.% initiator solution.

[0086] S3: After nitrogen is introduced to remove oxygen in the reactor, stirring is started, and the liquid components in the reactor are slowly heated to 80°C. Then, the initiator solution and the liquid components in the premixed kettle are respectively added to the reactor, and the reaction temperature is maintained at 80°C. After all components are added to the reactor, the reaction mixture is kept warm for 90 minutes to obtain a water-based acrylic copolymer glue solution.

[0087] S4: 18.0 parts of calcium hydroxide was added to the aqueous acrylic copolymer adhesive solution, and the pH was adjusted to 6.9 to obtain a functional coating adhesive with a solid content of 18.0 wt.% for high bonding ability.

[0088] The above 50.0 parts of binder (9.0 parts by dry weight) were fully dispersed and ground with 6.0 parts of conductive carbon black and 4.0 parts of graphite to obtain a uniform carbon slurry with a D50 particle size of less than 1.0 micron. After adjusting the solid content, a functional coating slurry with high bonding ability was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 0.8 micron was obtained.

[0089] Comparative Example 5 This comparative example uses a mature functional carbon coating binder (Lubrizol K702) in the market and is evaluated according to the conventional carbon coating scheme. The carbon coating method is as follows: The adhesive is diluted with an appropriate amount of a premix of deionized water and isopropyl alcohol, stirred evenly, and then the conductive carbon material is added at a dry weight ratio of 1:1 to the carbon material. The conductive carbon material is stirred and ground at high speed to a fineness of less than 10 microns. After degassing and filtering, a carbon-coated slurry is obtained. The carbon-coated slurry is applied to the surface of the aluminum foil, and the dry film thickness is controlled to be about 1 micron to obtain a carbon-coated aluminum foil.

[0090] After the carbon-coated aluminum foils were prepared in the same manner as in the above examples and comparative examples, their performance was tested as follows: The bonding strength between the carbon coating and the aluminum foil was tested by sticking 3M tape on the coating and then peeling it off. If the coating did not fall off at all, it was considered excellent. The coating's resistance to NMP wiping is tested by wiping back and forth with a medical cotton swab dipped in NMP, and the number of times the aluminum foil is exposed is recorded or the test ends when 200 times are reached; Electrolyte swelling was measured by immersing the dried film in an electrolyte solvent with a ratio of ED:DEC:DMC = 1:1:1 and measuring the weight gain of the film after 72 hours at 60°C. The positive electrode layer peel strength was tested by coating a 6% PVDF positive electrode slurry on the carbon coating layer and drying it, then peeling it off at 90 degrees using a 20mm tape. The positive electrode sheet resistance was tested using the two-probe method.

[0091] The high-peelable carbon-coated aluminum foil prepared by the functional coating adhesive prepared in Example 2 was subjected to bonding strength test, NMP wiping resistance test, and electrolyte wiping resistance test. Figure 4 As shown; the positive electrode peeling force on the carbon-coated aluminum foil prepared by Example 1, Example 3, Comparative Example 1 and Comparative Example 3 of the present invention is as follows Figure 5-Figure 8 shown.

[0092] The test results are shown in Table 1: .

[0093] As can be seen from the data in the above table, when the water-soluble functional coating binder of the present invention is used in the current lithium battery wet electrode system, it can be directly prepared together with the carbon material into a carbon slurry with good compatibility. After the surface of the metal current collector (including the composite current collector) is functionalized and carbon-coated, the active material can be firmly combined with the current collector, thereby improving the interface adhesion and effectively reducing the interface resistance.

[0094] The difference between Comparative Example 1 and Example 1 is that the unsaturated monomer containing dihydroxy and diester groups is replaced with methacrylic acid. The difference between Comparative Example 2 and Example 2 is that the unsaturated monomer containing dihydroxy and diester groups is not added. Since molecular chains cannot be interlaced at the interface, the peeling strength of the positive electrode layer drops sharply.

[0095] The difference between Comparative Example 3 and Example 5 is that the strongly polar unsaturated monomer is replaced with β-carboxyethyl acrylate, and the difference between Comparative Example 4 and Example 6 is that no strongly polar unsaturated monomer is added. Although there are unsaturated monomers containing dihydroxy and diester groups in the system, due to the absence of strongly polar unsaturated monomers, there are no functional groups that can form strong interactions with PVDF, and only weak interactions are formed. The peeling strength of the positive electrode layer drops sharply, and the resistivity of the positive electrode sheet and the swelling of the electrode liquid both increase significantly.

[0096] Comparative Example 5 uses an existing functional coating binder to prepare a carbon-coated aluminum foil. Although the carbon coating layer has good bonding strength with the aluminum foil, the peeling strength of the positive electrode layer is significantly reduced compared with the embodiments.

[0097] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A functional coating adhesive, characterized in that: The active ingredients of the raw materials include the following components in parts by weight: 10-60.0 parts of unsaturated monomers containing dihydroxyl and diester groups; 5-50.0 parts of ethylenically unsaturated carboxylic acid or anhydride; 15-60.0 parts of strongly polar unsaturated monomer; 1 to 40.0 parts of polymer additives; 0.1 to 20.0 parts of initiator; 1 to 60.0 parts of pH adjuster 2. The functional coating adhesive according to claim 1, wherein The unsaturated monomer containing dihydroxyl and diester groups is prepared as follows: S01: β-carboxyethyl acrylate is chlorinated with thionyl chloride to obtain a chlorinated monomer; S02: subjecting glycerol to an acylation reaction with the acyl chloride monomer at 0-5° C. to obtain an unsaturated monomer containing a dihydroxyl group and a diester group.

3. The functional coating adhesive according to claim 2, wherein In step S01, the mass ratio of the β-carboxyethyl acrylate to the thionyl chloride is 1:(0.4-0.6).

4. The functional coating adhesive according to claim 2, wherein In step S02, the molar ratio of the glycerol to the acyl chloride monomer is 1:

1.

5. The functional coating binder according to any one of claims 1 to 4, characterized in that: The ethylenically unsaturated carboxylic acid or anhydride is selected from at least one of acrylic acid, β-carboxyethyl acrylate, itaconic acid, methacrylic acid, fumaric acid, maleic acid, and acrylic anhydride, itaconic anhydride, methacrylic anhydride, fumaric anhydride, and maleic anhydride.

6. The functional coating binder according to any one of claims 1 to 4, characterized in that: The strongly polar unsaturated monomer is selected from at least one of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-hydroxyethyl acrylamide, N-vinyl pyrrolidone, 2-acrylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate, sodium p-styrenesulfonate, sodium phenyl sulfonate, 2-acrylamido-2-methylpropylphosphonic acid, vinylphosphonic acid, allyl polyoxyethylene ether phosphate, and 2-hydroxyethyl methacrylate phosphate.

7. The functional coating binder according to any one of claims 1 to 4, characterized in that: The polymer auxiliary agent is selected from at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and hydroxymethyl cellulose.

8. The functional coating binder according to any one of claims 1 to 4, characterized in that: The initiator is selected from at least one of persulfate initiators, hydroperoxide initiators, organic peroxide initiators, diacyl peroxide initiators, azo initiators and redox initiators.

9. A method for preparing the functional coating binder according to any one of claims 1 to 8, characterized in that: The steps include: S1: adding an unsaturated monomer containing a dihydroxyl group and a diester group, an ethylenically unsaturated carboxylic acid or anhydride, a strongly polar unsaturated monomer, and a polymer additive to water according to the formula to obtain a liquid component, adding a portion of the liquid component to a reactor, and adding another portion of the liquid component to a premixing kettle; S2: preparing the initiator into an initiator solution; S3: After deoxygenation, stirring is started, and the liquid components in the reactor are heated to 40-100° C., and then the initiator solution and the liquid components in the premixed kettle are added to the reactor respectively, and the reaction is carried out at a constant temperature and heat preservation treatment to obtain a water-based acrylic copolymer glue; S4: adding a pH adjuster to the aqueous acrylic copolymer glue solution to adjust the pH to 4-9 to obtain a functional coating binder.

10. A lithium ion battery, characterized in that: The functional coating adhesive comprises the functional coating adhesive according to any one of claims 1 to 8.

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