A functional coating binder, its preparation method and lithium ion battery

Abstract

The present application relates to the technical field of lithium battery, especially to a functional coating binder, a preparation method thereof and a lithium ion battery, according to weight parts, effective components of raw materials of the functional coating binder include the following components: 10-60.0 parts of unsaturated monomer containing double hydroxyl and double ester group; 5-50.0 parts of ethylenic unsaturated carboxylic acid or anhydride; 15-60.0 parts of strong polar unsaturated monomer; 1-40.0 parts of high molecular auxiliary agent; 0.1-20.0 parts of initiator; 1-60.0 parts of pH regulator. The functional coating binder provided by the present application has excellent compatibility and universality, meanwhile, the functional coating binder has excellent electrochemical stability and conductivity, when applied to electrochemical energy storage devices, can give the devices excellent service life and lower internal resistance.

Description

TECHNICAL FIELD

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

[0002] With the rapid development and application of lithium batteries, the requirement for energy density of lithium batteries is higher and higher. Increasing the active material loading and the compaction density has become the core path to improve the energy density of lithium batteries. However, the problem of insufficient peeling strength is increasingly prominent. When the interface adhesion between the positive active material and the current collector is weak and the peeling strength is insufficient, the active material is easily peeled off during the processes such as electrode sheet processing and winding, which 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 pure process defect to a core technical challenge affecting industrial iteration, and it is urgent to seek a breakthrough through material innovation and process optimization.

[0003] Therefore, how to improve the interface adhesion of the binder is a technical problem to be solved at present. SUMMARY

[0004] In order to solve the problem of insufficient interface adhesion of the binder in the prior art, the present application provides a functional coating binder. Through the synergistic effect of the components, the peeling strength of the functional coating and the active material is significantly improved under the premise of meeting the requirements of electrochemical stability and electrolyte resistance, thereby solving the problem of insufficient interface adhesion of the binder in the prior art.

[0005] The technical scheme adopted by the present application to solve the technical problem is:

[0006] A functional coating binder, the effective components of the raw materials include the following components in terms of weight fraction:

[0007] unsaturated monomer containing double hydroxyl and double ester group 10-60.0 parts;

[0008] ethylenically unsaturated carboxylic acid or anhydride 5-50.0 parts;

[0009] strongly polar unsaturated monomer 15-60.0 parts;

[0010] high molecular auxiliary agent 1-40.0 parts;

[0011] initiator 0.1-20.0 parts;

[0012] pH regulator 1-60.0 parts.

[0013] Optionally, the unsaturated monomer containing double hydroxyl and double ester group is prepared by the following method:

[0014] S01: acyl chlorination of beta-carboxyethyl acrylate by dichloro sulfoxide to obtain an acyl chlorination monomer;

[0015] S02: acylation of glycerol with the acyl chlorination monomer at 0-5℃ to obtain an unsaturated monomer containing double hydroxyl and double ester groups.

[0016] Optionally, the mass ratio of the beta-carboxyethyl acrylate to the dichloro sulfoxide in step S01 is 1: (0.4-0.6).

[0017] Optionally, the molar ratio of the glycerol to the acyl chlorination monomer in step S02 is 1:1.

[0018] Optionally, the ethylenically unsaturated carboxylic acid or anhydride is selected from at least one of acrylic acid, beta-carboxyethyl acrylate, itaconic acid, methacrylic acid, fumaric acid, maleic acid, and acrylic anhydride, itaconic anhydride, methacrylic anhydride, fumaric anhydride, maleic anhydride.

[0019] Optionally, the strong polar unsaturated monomer is selected from at least one of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-hydroxyethyl acrylamide, N-vinyl pyrrolidone, 2-acrylamido-2-methylpropane sulfonic acid, sodium vinyl sulfonate, sodium p-styrene sulfonate, sodium styryl sulfonate, 2-acrylamido-2-methylpropyl phosphonic acid, vinyl phosphonic acid, allyl polyoxyethylene ether phosphate, 2-hydroxyethyl methacrylate phosphate.

[0020] Optionally, the high molecular auxiliary is selected from at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxymethyl cellulose.

[0021] Optionally, the initiator is selected from at least one of persulfate initiator, hydroperoxide initiator, organic peroxide initiator, diacyl peroxide initiator, azo initiator, and oxidation-reduction initiator.

[0022] Another object of the present application is to provide a preparation method of the functional coating binder as described above, comprising the following steps:

[0023] S1: according to the formula amount, adding the unsaturated monomer containing double hydroxyl and double ester groups, the ethylenically unsaturated carboxylic acid or anhydride, the strong polar unsaturated monomer, and the high molecular auxiliary into water to obtain a liquid component, and then adding part of the liquid component into a reaction kettle and the other part into a premix kettle;

[0024] S2: preparing an initiator solution by using the initiator;

[0025] S3: After deoxidation, open the stirring, and heat the liquid components in the reaction kettle to 40-100 DEG C, then the initiator solution and the liquid components in the premix kettle are added into the reaction kettle respectively, constant temperature reaction and heat preservation treatment, then the aqueous acrylic copolymer glue liquid is obtained;

[0026] S4: The pH regulator is added into the aqueous acrylic copolymer glue liquid, the pH is adjusted to 4-9, and the functional coating adhesive is obtained.

[0027] Still another purpose of the present application is to provide a lithium ion battery comprising the functional coating adhesive as described above.

[0028] The present application has the following beneficial effects:

[0029] The functional coating adhesive provided by the present application is aqueous product, green and environmentally friendly, and has good economy; and has excellent compatibility and universality, and can exhibit excellent high peeling strength, low resistance and other comprehensive performance for the current smaller particle size of lithium iron phosphate and different surface structure of active materials such as manganese iron phosphate; at the same time, the functional coating adhesive has excellent electrochemical stability and conductivity, and when applied to electrochemical energy storage devices, can give the device excellent service life and lower internal resistance. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application is further illustrated below in combination with the drawings and examples.

[0031] Figure 1 is a schematic diagram of the functional coating adhesive in the present application forming molecular chain interpenetration at the interface;

[0032] Figure 2 is a schematic diagram of the preparation process of the unsaturated monomer containing double hydroxyl and double ester group in the present application;

[0033] Figure 3 is a photo of the functional coated carbon aluminum foil prepared in Example 1 of the present application;

[0034] Figure 4 is a photo of the functional coated carbon aluminum foil prepared in Example 2 of the present application after testing;

[0035] Figure 5 is a positive electrode peeling force diagram of the coated carbon aluminum foil prepared in Example 1 of the present application;

[0036] Figure 6 is a positive electrode peeling force diagram of the coated carbon aluminum foil prepared in Example 3 of the present application;

[0037] Figure 7 is a positive electrode peeling force diagram of the coated carbon aluminum foil prepared in Comparative Example 1 of the present application;

[0038] Figure 8Figure 3 is a positive electrode peel force diagram on a carbon-coated aluminum foil prepared by Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0039] The present application will now be further described in detail. The examples described below are exemplary and are intended to serve to explain the present application and cannot be understood as limiting the present application, all other examples obtained by a person of ordinary skill in the art without making creative efforts based on the examples of the present application fall within the scope of protection of the present application.

[0040] To improve the active material load and the compaction density, with the iteration of lithium battery positive electrode materials, the current lithium battery positive electrode materials mostly use smaller particle size lithium iron phosphate or lithium manganese iron phosphate as the active material; with the decrease of the particle size of the active material, higher requirements are put forward for the bonding performance of the binder, and the existing binder has the problem of difficult bonding when used in the lithium battery positive electrode using smaller particle size active material, the powder dropping phenomenon is serious, and the peel strength is too low, which has become a key problem restricting the further iteration of lithium batteries.

[0041] To solve the problem of powder dropping of small particle size active material, some temporary solutions such as oily coating and multiple coating are currently tried to partially meet the needs of the current lithium battery industry, but these solutions still have defects in energy saving and environmental protection, processing yield and compatibility. In general, in the field of lithium battery functional coating subdivision, the peel strength is too low, which has become a key problem restricting the further iteration of lithium batteries, and at present, an excellent functional coating solution is urgently needed, which fundamentally needs an excellent binder product to significantly improve the peel strength of the functional coating and the active material under the premise of meeting the demand of electrochemical stability and electrolyte resistance, to improve the problem of active material falling off in the processing of the electrode sheet, to lay a solid foundation for further improving the energy density of lithium batteries, and to promote the industry to a more efficient and safer direction.

[0042] To solve the problem of insufficient interface adhesion of the binder in the prior art, the present application provides a functional coating binder, the effective components of the raw materials of the binder include the following components according to weight fraction:

[0043] Unsaturated monomer containing double hydroxyl and double ester group 10-60.0 parts;

[0044] Ethylenically unsaturated carboxylic acid or anhydride 5-50.0 parts;

[0045] Strongly polar unsaturated monomer 15-60.0 parts;

[0046] High molecular weight additive 1-40.0 parts;

[0047] Initiator 0.1-20.0 parts;

[0048] pH adjuster 1-60.0 parts.

[0049] The unsaturated monomer containing double hydroxyl and double ester groups refers to an unsaturated monomer containing double hydroxyl and double ester groups; the unsaturated monomer containing double hydroxyl and double ester groups in the application shows outstanding interface interaction after being matched with other monomers in the system; for details, see Figure 1 As shown in the figure, on the one hand, the double ester group in the unsaturated monomer containing double hydroxyl and double ester groups can well improve the N-methyl pyrrolidone (NMP) affinity of the binder, and when the positive active material layer is coated by wet method, NMP can penetrate into the functional coating structure together with polyvinylidene fluoride (PVDF) dissolved therein, so that the PVDF and the functional coating binder can be closer to each other, and the double hydroxyl groups can form strong electrostatic interaction with the PVDF, thereby improving the peeling strength; on the other hand, the NMP affinity enables the binder of the functional coating to penetrate into the positive active material layer, and the PVDF penetrates into the functional coating in the opposite direction, thereby solving the problem of weak interface combination in the conventional technology, doubling the interface peeling strength, and effectively improving the problem of active material falling during the processing of the pole piece; the presence of the double hydroxyl groups and the strong polar groups can avoid the problem that the binder is damaged by the electrolyte when applied to the lithium battery, thereby avoiding significant attenuation of the peeling strength.

[0050] The application introduces a high molecular additive into the system, so that the binder of the functional coating has excellent dispersion and wetting capacity for carbon materials; the introduction of the high molecular additive can not only stabilize the reaction process, but also can save the use of additional dispersion and wetting additives, and the required carbon slurry can be prepared by using the existing homogenizing process.

[0051] The binder of the functional coating provided by the application is a water-based product, which is green, environmentally friendly and economical; and has excellent compatibility and universality; the binder can exhibit excellent high peeling strength, low resistance and other comprehensive properties for the current smaller particle size lithium iron phosphate and different surface structure lithium iron manganese phosphate and other active materials; at the same time, the binder of the functional coating has excellent electrochemical stability and conductivity, and when applied to an electrochemical energy storage device, the binder can give the device excellent service life and lower internal resistance.

[0052] The unsaturated monomer containing double hydroxyl and double ester groups is preferably prepared by the following method:

[0053] S01: acyl chlorination of β-carboxyethyl acrylate (A) by dichlorosulfide to obtain acyl chlorination monomer (B);

[0054] In the step, DMF is preferably used as the catalyst, the reaction temperature is 0-25℃, the reaction time is 4-6h, and the mass ratio of DMF to β-carboxyethyl acrylate is (0.02-0.08):1.

[0055] S02: acylating reaction of glycerol and acyl chloride monomer (B) at 0-5℃ to obtain an unsaturated monomer containing double hydroxyl and double ester groups;

[0056] The reaction temperature is strictly controlled at 0-5℃ in this step.

[0057] The preparation process of the unsaturated monomer containing double hydroxyl and double ester groups is shown in the following scheme: Figure 2 The generated unsaturated monomer containing double hydroxyl and double ester groups has two structural forms, wherein the main product is product C in the following scheme: Figure 2 The by-product is product D in the following scheme. Figure 2

[0058] The unsaturated monomer containing double hydroxyl and double ester groups prepared by the present application can make the functional coating binder have excellent interfacial peeling strength of active material, and the fundamental reason is that the NMP affinity is improved, the strong polar unsaturated monomer has excellent electrostatic interaction force, and the synergistic effect has high peeling strength. Unlike conventional functional coating binders, the binder of the present application has good affinity with NMP, and when the positive active material layer is coated by wet method, NMP can penetrate into the functional coating structure together with PVDF dissolved therein, so that the strong polar groups of PVDF and the functional coating binder can have a closer relative distance, thereby forming a stronger electrostatic interaction force. At the same time, the NMP affinity can make the binder of the functional coating penetrate into the positive active material layer, and the PVDF penetrates into the functional coating in the opposite direction, that is, the NMP affinity makes the relative distance between the strong polar functional groups and the PVDF shorter, and the strong electrostatic interaction is exerted, and at the same time, the binder forms molecular chain penetration at the interface, which eliminates the problem of weak interfacial bonding force of conventional binders, and the interfacial peeling strength is doubled, thereby effectively improving the problem of active material falling off in the process of pole piece processing, and providing effective assistance for further improving the energy density of lithium batteries.

[0059] The existing binder usually improves the peeling strength with the active layer by different polar monomer interaction, but this scheme has limited effect on the improvement of interfacial adhesion, which is insufficient to meet the bonding needs of small particle size active material; based on this, the present application creatively introduces the unsaturated monomer containing double hydroxyl and double ester groups into the system, so that the binder forms molecular chain penetration at the interface, which eliminates the problem of weak interfacial bonding force of conventional binders, and the interfacial peeling strength is doubled.

[0060] Specifically, the mass ratio of β-carboxyethyl acrylate to dichlorosulfoxide in step S01 is 1:(0.4-0.6), and the molar ratio of glycerol to acyl chloride monomer in step S02 is 1:1.

[0061] ​The preferred ethylenically unsaturated carboxylic acid or anhydride is at least one selected from acrylic acid, beta-carboxyethyl acrylate, itaconic acid, methacrylic acid, fumaric acid, maleic acid, and acrylic anhydride, itaconic anhydride, methacrylic anhydride, fumaric anhydride, and maleic anhydride; the preferred strongly polar unsaturated monomer is at least one selected from acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-hydroxyethyl acrylamide, N-vinyl pyrrolidone, 2-acrylamido-2-methylpropane sulfonic acid, sodium vinyl sulfonate, sodium p-styrene sulfonate, sodium allyl sulfonate, 2-acrylamido-2-methylpropyl phosphonic acid, vinyl phosphonic acid, allyl polyoxyethylene ether phosphonate, and 2-hydroxyethyl methacrylate phosphate; the preferred high molecular weight additive is at least one selected from polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and hydroxymethyl cellulose; the preferred initiator is at least one selected from persulfate initiators, hydroperoxide initiators, organic peroxide initiators, diacyl peroxide initiators, azo initiators, and oxidation-reduction initiators; and the preferred pH adjuster is at least one selected from inorganic bases and organic bases; specifically, the preferred inorganic base is at least one selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, and aqueous ammonia, and the preferred organic base is at least one selected from ethanolamine, diethanolamine, and triethanolamine.

[0062] The carbon-coated aluminum foil prepared from the functional coating binder provided by the present application can exhibit excellent interfacial peeling force, is particularly suitable for the preparation of current lithium battery wet electrodes, can effectively solve the problem of peeling strength decay caused by the increase in active material loading and compaction density, and helps the technical iteration of the lithium battery industry.

[0063] Another object of the present application is to provide a preparation method of the functional coating binder as described above, which comprises the following steps:

[0064] S1: According to the formula amount, the unsaturated monomer containing double hydroxyl and double ester group, the ethylenically unsaturated carboxylic acid or anhydride, the strongly polar unsaturated monomer, and the high molecular weight additive are added to water, preferably pure water, and the mixture of the above components and water is mixed into a uniform liquid component by stirring or homogenization, and then a part of the liquid component is added to a reaction kettle and the rest is added to a premix kettle; preferably, 5-30% of the total mass of the liquid component is added to the reaction kettle, and the rest is added to the premix kettle;

[0065] S2: The initiator is prepared into an initiator solution;

[0066] The initiator is dissolved in pure water according to the formula amount, and preferably an initiator solution with a concentration of 0.1-20.0 wt.% is prepared;

[0067] S3: After deoxidation, open the stirring, and warm the liquid components in the reactor to 40-100℃, then add the initiator solution and the liquid components in the premixing reactor into the reactor respectively, and keep the temperature constant, and after the treatment, the aqueous acrylic copolymer glue liquid is obtained;

[0068] Preferably, in this step, the oxygen is removed by passing nitrogen into the reactor, the stirring is opened, the liquid components in the reactor are slowly warmed to 40-100℃, then the initiator solution and the liquid components in the premixing reactor are added into the reactor respectively at a preset rate, the reaction temperature is kept within the preset range, after all the components are added into the reactor, the temperature is kept for 30-600 minutes, and the aqueous acrylic copolymer glue liquid is obtained;

[0069] S4: The pH regulator is added into the aqueous acrylic copolymer glue liquid, and the pH is adjusted to 4-9, and the functional coating adhesive is obtained.

[0070] According to the formula amount, the pH regulator is added into the aqueous acrylic copolymer glue liquid, and the pH is adjusted to 4-9, and the functional coating adhesive with a solid content of 5-40.0 wt.% and high bonding capacity is obtained.

[0071] The preparation method of the functional coating adhesive provided by the application is simple, the prepared functional coating adhesive is an aqueous product, is green and environmentally friendly, is economical, has excellent compatibility and universality, can exhibit excellent high peeling strength, low resistance and other comprehensive performances on active materials such as lithium iron phosphate with smaller particle size and lithium manganese iron phosphate with different surface structures, and has excellent electrochemical stability and conductivity, and when applied to an electrochemical energy storage device, can endow the device with excellent service life and lower internal resistance.

[0072] Another purpose of the application is to provide a lithium ion battery comprising the functional coating adhesive as described above.

[0073] The lithium ion battery provided by the application adopts the functional coating adhesive which is an aqueous product, is green and environmentally friendly, is economical, has excellent compatibility and universality, can exhibit excellent high peeling strength, low resistance and other comprehensive performances on active materials such as lithium iron phosphate with smaller particle size and lithium manganese iron phosphate with different surface structures, and has excellent electrochemical stability and conductivity, and when applied to a lithium ion battery, can endow the lithium ion battery with excellent service life and lower internal resistance.

[0074] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the drawings.

[0075] The unsaturated monomer containing double hydroxyl and double ester groups in each embodiment of the present application and the comparative example is prepared according to the following method unless otherwise specified:

[0076] S01: Under a nitrogen atmosphere, acyl chloride of β-carboxyethyl acrylate is carried out by dichloro sulfoxide, to obtain acyl chloride monomer, the mass ratio of dichloro sulfoxide to β-carboxyethyl acrylate is 0.5:1; DMF is used as a reaction catalyst, the mass ratio of DMF to β-carboxyethyl acrylate is 0.06:1; the reaction temperature is 15℃, and the reaction time is 4 hours.

[0077] S02: Under ice bath (0-5℃) stirring, acylation reaction of acyl chloride monomer is carried out by slowly adding to glycerol, to obtain unsaturated monomer containing double hydroxyl and double ester groups; the molar ratio of acyl chloride 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.

[0078] Example 1

[0079] The present embodiment provides a preparation method of a functional coating adhesive, comprising the following steps:

[0080] S1: According to the weight fraction, 25.0 parts of unsaturated monomer containing double hydroxyl and double ester 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, and the mixture of raw materials and water is uniformly dispersed by a stirring machine to form a liquid component, 30% of the total mass of the liquid component is added to a reaction kettle, and 70% is added to a premix kettle.

[0081] S2: 2.0 parts of initiator ammonium persulfate is dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0082] S3: After removing oxygen in the reaction kettle by nitrogen, the stirring is started, the liquid component in the reaction kettle is slowly heated to 72℃, then the initiator solution and the liquid component in the premix kettle are added to the reaction kettle respectively, the reaction temperature is kept at 72℃, after all the components are added to the reaction kettle, the temperature is kept for 90 minutes, to obtain an aqueous acrylic copolymer glue.

[0083] S4: 20.0 parts of ammonia water pH adjuster is added to the aqueous acrylic copolymer glue, to adjust the pH to 6.7, to obtain a functional coating adhesive with high bonding capacity with a solid content of 20.0 wt.%.

[0084] The 30.0 parts of the above binder (dry weight 6.0 parts) is 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 80°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 1.1 microns is obtained.

[0085] The functional coated carbon aluminum foil prepared in this example is shown in Figure 3

[0086] Example 2

[0087] This example provides a method for preparing a functional coating binder, comprising the following steps:

[0088] S1: According to the weight fraction, 25.0 parts of unsaturated monomer containing dihydroxy and diester group, 10.0 parts of acrylic acid, 20.0 parts of acrylamide, 40.0 parts of 2-acrylamido-2-methylpropane sulfonic acid, and 5.0 parts of polyethylene glycol are mixed with 450 parts of pure water. The mixture of raw materials and water is uniformly dispersed by a blender to form a liquid component. 25% of the total mass of the liquid component is added to a reaction kettle, and 75% is added to a premix kettle.

[0089] S2: Dissolve 3.0 parts of initiator sodium persulfate in pure water to prepare a 1.5 wt.% initiator solution.

[0090] S3: After removing oxygen in the reaction kettle by nitrogen gas, start stirring, slowly heat the liquid component in the reaction kettle to 80°C, then add the initiator solution and the liquid component in the premix kettle to the reaction kettle, keep the reaction temperature at 80°C, after all components are added to the reaction kettle, keep the temperature for 120 minutes, to obtain an aqueous acrylic acid copolymer glue.

[0091] S4: Add 12.0 parts of sodium hydroxide to the aqueous acrylic acid copolymer glue to adjust the pH to 5.8, to obtain a functional coating binder with high bonding capacity with a solid content of 16.0 wt.%.

[0092] The 30.0 parts of the above binder (dry weight 6.0 parts) is 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 80°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 1.1 microns is obtained.

[0093] Example 3

[0094] This example provides a method for preparing a functional coating binder, comprising the following steps: ​

[0095] S1: 60.0 parts of unsaturated monomers containing dihydroxyl and diester groups, 20.0 parts of acrylic acid, 10.0 parts of acrylonitrile, 5.0 parts of acrylamide, 5.0 parts of sodium carboxymethyl cellulose, all mixed with 350 parts of pure water, the mixture of raw materials and water is dispersed into a uniform liquid component by a blender, 20% of the total mass of the liquid component is added to the reaction kettle, and 80% is added to the premix kettle.

[0096] S2: 3.2 parts of initiator potassium persulfate is dissolved in pure water to prepare a 1.6 wt.% initiator solution.

[0097] S3: After removing oxygen in the reaction kettle by nitrogen purging, the stirring is started, the liquid component in the reaction kettle is slowly heated to 70°C, then the initiator solution and the liquid in the premix kettle are added to the reaction kettle respectively, the reaction temperature is maintained at 70°C, after all components are added to the reaction kettle, the temperature is maintained for 150 minutes, and an aqueous acrylic copolymer glue is obtained.

[0098] S4: 25.0 parts of lithium hydroxide is added to the aqueous acrylic copolymer glue to adjust the pH to 7.1, and a functional coating binder for high adhesion is obtained with a solid content of 20.0 wt.%.

[0099] The above 35.0 parts of binder (dry weight 7.0 parts) is 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 microns, and a functional coating slurry with high adhesion is obtained after adjusting the solid content. Coating it on a smooth battery-grade aluminum foil, drying at 80°C, a functional carbon-coated aluminum foil with a dense appearance, good consistency and a coating thickness of 1.0 microns is obtained.

[0100] Example 4

[0101] The present embodiment provides a method for preparing a functional coating binder, comprising the following steps:

[0102] S1: 20.0 parts of unsaturated monomers containing dihydroxyl and diester groups, 25.0 parts of acrylic acid, 20.0 parts of acrylonitrile, 15.0 parts of acrylamide, 20.0 parts of polyvinyl alcohol, all mixed with 400 parts of pure water, the mixture of raw materials and water is dispersed into a uniform liquid component by a blender, 15% of the total mass of the liquid component is added to the reaction kettle, and 85% is added to the premix kettle.

[0103] S2: 4.0 parts of initiator (mass ratio of ammonium persulfate and sodium sulfite 2:1) is dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0104] S3: After removing oxygen in the reaction kettle by nitrogen, the stirring was started, and the liquid components in the reaction kettle were slowly warmed to 75°C. Then the initiator solution and the liquid components in the premix kettle were added to the reaction kettle, respectively. The reaction temperature was maintained at 75°C. After all the components were added to the reaction kettle, the temperature was maintained for 120 minutes. The aqueous acrylic copolymer glue was obtained.

[0105] S4: 13.5 parts of sodium hydroxide was added to the aqueous acrylic copolymer glue, and the pH was adjusted to 6.5. The functional coating binder for high bonding capacity with a solid content of 20.0 wt.% was obtained.

[0106] The above 40.0 parts of binder (dry weight 8.0 parts) was 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity was obtained, which was coated on a smooth battery-grade aluminum foil. After drying at 85°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 0.9 microns was obtained.

[0107] Example 5

[0108] The present embodiment provides a method for preparing a functional coating binder, comprising the following steps:

[0109] S1: According to the weight fraction, 10.0 parts of unsaturated monomer containing dihydroxy and diester group, 50.0 parts of β-carboxyethyl acrylate, 25.0 parts of acrylonitrile, 14.0 parts of 2-acrylamido-2-methylpropane sulfonic acid, 1.0 parts of hydroxymethyl cellulose, and 500 parts of pure water were mixed. The mixture of raw materials and water was uniformly dispersed by a blender to form a liquid component. 10% of the total mass of the liquid component was added to the reaction kettle, and 90% was added to the premix kettle.

[0110] S2: 2.4 parts of initiator (mass ratio of sodium persulfate and sodium bisulfite 2:1) was dissolved in pure water to prepare an initiator solution with a concentration of 1.2 wt.%.

[0111] S3: After removing oxygen in the reaction kettle by nitrogen, the stirring was started, and the liquid components in the reaction kettle were slowly warmed to 70°C. Then the initiator solution and the liquid components in the premix kettle were added to the reaction kettle, respectively. The reaction temperature was maintained at 70°C. After all the components were added to the reaction kettle, the temperature was maintained for 120 minutes. The aqueous acrylic copolymer glue was obtained.

[0112] S4: 7.0 parts of sodium hydroxide was added to the aqueous acrylic copolymer glue, and the pH was adjusted to 5.3. The functional coating binder for high bonding capacity with a solid content of 15.0 wt.% was obtained.

[0113] The 60.0 parts of the above binder (dry weight 9.0 parts) is 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 85°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 1.0 microns is obtained.

[0114] Example 6

[0115] The present embodiment provides a method for preparing a functional coating binder, comprising the following steps:

[0116] S1: According to the weight fraction, 25.0 parts of unsaturated monomer containing dihydroxy and diester group, 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, 10.0 parts of polyvinyl pyrrolidone, are mixed with 450 parts of pure water. The mixture of raw materials and water is uniformly dispersed by a blender to form a liquid component. 5% of the total mass of the liquid component is added to the reaction kettle, and 95% is added to the premix kettle.

[0117] S2: Dissolve 3.6 parts of initiator (mass ratio of ammonium persulfate and ascorbic acid 2:1) in pure water to prepare a 1.8 wt.% initiator solution.

[0118] S3: After removing oxygen in the reaction kettle by nitrogen, start stirring, slowly warm the liquid component in the reaction kettle to 80°C, then add the initiator solution and the liquid component in the premix kettle to the reaction kettle, keep the reaction temperature at 80°C, after all components are added to the reaction kettle, keep warm for 90 minutes, to obtain an aqueous acrylic acid copolymer glue.

[0119] S4: Add 18.0 parts of calcium hydroxide to the aqueous acrylic acid copolymer glue to adjust the pH to 6.9 to obtain a functional coating binder with high bonding capacity with a solid content of 18.0 wt.%.

[0120] The 50.0 parts of the above binder (dry weight 9.0 parts) is 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 80°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 0.8 microns is obtained.

[0121] Comparative Example 1

[0122] The present comparative example provides a method for preparing a functional coating binder, comprising the following steps:

[0123] S1: 55.0 parts of methacrylic acid, 15.0 parts of acrylonitrile, 20.0 parts of acrylamide, 10.0 parts of polyvinylpyrrolidone, all mixed with 400 parts of pure water, and the mixture of raw materials and water was dispersed by a blender into a uniform liquid component. 30% of the total mass of the liquid component was added to the reaction kettle, and 70% was added to the premix kettle.

[0124] S2: 2.0 parts of initiator ammonium persulfate was dissolved in pure water to prepare a 2.0 wt.% initiator solution.

[0125] S3: After removing oxygen in the reaction kettle by purging with nitrogen, the stirring was started, and the liquid component in the reaction kettle was slowly heated to 72°C. Then the initiator solution and the liquid component in the premix kettle were added to the reaction kettle, and the reaction temperature was maintained at 72°C. After all the components were added to the reaction kettle, the temperature was maintained for 90 minutes to obtain an aqueous acrylic copolymer sizing solution.

[0126] S4: 20.0 parts of ammonia water pH adjuster was added to the aqueous acrylic copolymer sizing solution to adjust the pH to 6.7 to obtain a functional coating binder for high adhesion with a solid content of 20.0 wt.%.

[0127] The above 30.0 parts of binder (dry weight 6.0 parts) was 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 microns. After adjusting the solid content, a functional coating slurry with high adhesion 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.

[0128] Comparative Example 2

[0129] This comparative example provides a method for preparing a functional coating binder, comprising the following steps:

[0130] S1: 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 were mixed with 450 parts of pure water, and the mixture of raw materials and water was dispersed by a blender into a uniform liquid component. 25% of the total mass of the liquid component was added to the reaction kettle, and 75% was added to the premix kettle.

[0131] S2: 3.0 parts of initiator sodium persulfate was dissolved in pure water to prepare a 1.5 wt.% initiator solution.

[0132] S3: After removing oxygen in the reaction kettle by nitrogen, the stirring was started, and the liquid components in the reaction kettle were slowly warmed to 80°C. Then the initiator solution and the liquid components in the premix kettle were added to the reaction kettle, respectively. The reaction temperature was maintained at 80°C. After all the components were added to the reaction kettle, the temperature was maintained for 120 minutes. The aqueous acrylic copolymer glue was obtained.

[0133] S4: 12.0 parts of sodium hydroxide was added to the aqueous acrylic copolymer glue to adjust the pH to 5.8. The functional coating binder for high bonding capacity with a solid content of 16.0 wt.% was obtained.

[0134] The above 50.0 parts of binder (dry weight 8.0 parts) was 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity 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 microns was obtained.

[0135] Comparative Example 3

[0136] This comparative example provides a method for preparing a functional coating binder, comprising the following steps:

[0137] S1: According to the weight fraction, 10.0 parts of unsaturated monomer containing dihydroxy and diester group, 89.0 parts of β-carboxyethyl acrylate, and 1.0 parts of hydroxymethyl cellulose were mixed with 500 parts of pure water. The mixture of raw materials and water was uniformly dispersed by a blender to form a liquid component. 10% of the total mass of the liquid component was added to the reaction kettle, and 90% was added to the premix kettle.

[0138] S2: 2.4 parts of initiator (mass ratio of sodium persulfate and sodium bisulfite 2:1) was dissolved in pure water to prepare an initiator solution with a concentration of 1.2 wt.%.

[0139] S3: After removing oxygen in the reaction kettle by nitrogen, the stirring was started, and the liquid components in the reaction kettle were slowly warmed to 70°C. Then the initiator solution and the liquid components in the premix kettle were added to the reaction kettle, respectively. The reaction temperature was maintained at 70°C. After all the components were added to the reaction kettle, the temperature was maintained for 120 minutes. The aqueous acrylic copolymer glue was obtained.

[0140] S4: 7.0 parts of sodium hydroxide was added to the aqueous acrylic copolymer glue to adjust the pH to 5.3. The functional coating binder for high bonding capacity with a solid content of 15.0 wt.% was obtained.

[0141] The above 60.0 parts of binder (dry weight 9.0 parts) are 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 85°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 1.0 microns is obtained.

[0142] Comparative Example 4

[0143] This comparative example provides a method for preparing a functional coating binder, comprising the following steps:

[0144] S1: According to the weight fraction, 25.0 parts of unsaturated monomer containing dihydroxy and diester group, 20.0 parts of acrylic acid, 15.0 parts of methacrylic acid, 10.0 parts of polyvinylpyrrolidone, and 450 parts of pure water are mixed. The mixture of raw materials and water is uniformly dispersed by a blender to form a liquid component. 5% of the total mass of the liquid component is added to the reaction kettle, and 95% is added to the premix kettle.

[0145] S2: Dissolve 3.6 parts of initiator (mass ratio of ammonium persulfate and ascorbic acid 2:1) in pure water to prepare a 1.8 wt.% initiator solution.

[0146] S3: After removing oxygen in the reaction kettle by nitrogen purging, start stirring, slowly heat the liquid component in the reaction kettle to 80°C, then add the initiator solution and the liquid component in the premix kettle to the reaction kettle, keep the reaction temperature at 80°C, after all components are added to the reaction kettle, keep the temperature for 90 minutes, get the aqueous acrylic acid copolymer glue.

[0147] S4: Add 18.0 parts of calcium hydroxide to the aqueous acrylic acid copolymer glue, adjust the pH to 6.9, get the functional coating binder for high bonding capacity with solid content of 18.0 wt.%.

[0148] The above 50.0 parts of binder (dry weight 9.0 parts) are 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 microns. After adjusting the solid content, a functional coating slurry with high bonding capacity is obtained. It is coated on a smooth battery-grade aluminum foil, and after drying at 80°C, a functional coated carbon aluminum foil with a dense appearance, good consistency, and a coating thickness of 0.8 microns is obtained.

[0149] Comparative Example 5

[0150] This comparative example uses a mature functional carbon coating binder (Lubrizol K702) according to the conventional carbon coating scheme for evaluation; the carbon coating method is as follows:

[0151] The binder is diluted with a proper amount of deionized water and isopropyl alcohol, stirred uniformly, and then 1:1 of conductive carbon material is added according to the dry weight of the carbon paste, high-speed stirring, grinding, so that the fineness is less than 10 microns; defoaming, filtering to obtain a carbon coating slurry; the carbon coating slurry is coated on the surface of the aluminum foil, and the dry film thickness is controlled to be about 1 micrometer, to obtain a carbon-coated aluminum foil.

[0152] After the carbon-coated aluminum foil prepared by the above examples and comparative examples is prepared by the same method, its performance is tested, and the test method is as follows:

[0153] The adhesion of the carbon coating layer to the aluminum foil is tested by peeling off the coating after sticking the coating with 3M tape, and the coating is not completely peeled off, which is excellent;

[0154] The NMP wiping resistance of the coating is tested by wiping back and forth with a medical cotton swab dipped with NMP, and the number of times the aluminum foil is exposed or the number of 200 times is recorded;

[0155] The electrolyte swelling is tested by immersing the dried adhesive film in an electrolyte solvent of ED:DEC:DMC=1:1:1, and the weight gain rate of the adhesive film is tested after 60°C for 72 hours;

[0156] The positive electrode layer peeling strength is tested by coating 6% PVDF positive electrode slurry on the carbon coating layer and drying, and using a 20mm tape and 90 degree peeling;

[0157] The positive electrode sheet resistance is tested by the two-probe method.

[0158] The photos of the high-peeling-type carbon-coated aluminum foil prepared by the functional coating binder prepared by Example 2 after adhesion testing, NMP wiping resistance and electrolyte wiping resistance are shown in Figure 4 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 application is shown in Figures 5-8 .

[0159] The test results are shown in Table 1:

[0160] .

[0161] From the above table data, when the water-soluble functional coating binder of the present application is used in the current lithium battery wet electrode system, it can be directly prepared together with carbon material to prepare carbon paste with good compatibility. After the functional carbon coating treatment on the surface of the metal current collector (including the composite current collector), the active material can be firmly combined with the current collector, which can improve the interface adhesion and effectively reduce the interface resistance.

[0162] The difference between Comparative Example 1 and Example 1 is that the unsaturated monomer containing double hydroxyl and double ester groups is replaced by methacrylic acid, and the difference between Comparative Example 2 and Example 2 is that the unsaturated monomer containing double hydroxyl and double ester groups is not added, so that the molecular chain interpenetration cannot be formed at the interface, and the positive electrode layer peeling strength sharply decreases.

[0163] The difference between Comparative Example 3 and Example 5 is that the strong polar unsaturated monomer is replaced by β-carboxyethyl acrylate, and the difference between Comparative Example 4 and Example 6 is that the strong polar unsaturated monomer is not added, and although the unsaturated monomer containing double hydroxyl and double ester groups exists in the system, the strong polar unsaturated monomer is absent, and the functional groups for forming strong interaction with PVDF are also absent, so that only weak interaction exists, the positive electrode layer peeling strength sharply decreases, and the positive electrode sheet resistivity and the electrode liquid swelling both significantly increase.

[0164] Comparative Example 5 uses the existing functional coating binder to prepare the carbon-coated aluminum foil, although the carbon-coated layer has good adhesion with the aluminum foil, but the positive electrode layer peeling strength is significantly decreased compared with each of the examples.

[0165] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content in the specification, and must be determined according to the scope of the claims.

Claims

1. A functional coating binder, characterized in that, The effective components of the raw materials include the following components by weight: unsaturated monomer containing double hydroxyl and double ester group 10-60.0 parts; ethylenically unsaturated carboxylic acid or anhydride 5-50.0 parts; polar unsaturated monomer 15-60.0 parts; polymer auxiliary agent 1-40.0 parts; initiator 0.1-20.0 parts; pH regulator 1-60.0 parts; The unsaturated monomer containing double hydroxyl and double ester group is prepared by the following method: S01: β-carboxyethyl acrylate is acylchlorinated by dichloro sulfoxide to obtain acylchlorinated monomer; S02: glycerol is acylated with the acylchlorinated monomer at 0-5℃ to obtain unsaturated monomer containing double hydroxyl and double ester group; The mass ratio of the β-carboxyethyl acrylate to the dichloro sulfoxide in step S01 is 1:(0.4-0.6); The molar ratio of the glycerol to the acylchlorinated monomer in step S02 is 1:

1.

2. The functional coating binder of claim 1, wherein, 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.

3. The functional coating binder of claim 1, wherein, The 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-styrene sulfonate, 2-acrylamido-2-methylpropyl phosphonic acid, vinyl phosphonic acid, allyl polyoxyethylene ether phosphate, and 2-hydroxyethyl methacrylate phosphate.

4. The functional coating binder of claim 1, wherein, 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.

5. The functional coating binder of claim 1, wherein, The initiator is selected from at least one of persulfate initiator, hydroperoxide initiator, organic peroxide initiator, azo initiator, and oxidation-reduction initiator.

6. A method of producing a functional coating binder as claimed in any one of claims 1 to 5, characterized in that The method comprises the following steps: S1: unsaturated monomer containing double hydroxyl and double ester group, ethylenically unsaturated carboxylic acid or anhydride, strong polar unsaturated monomer, and polymer auxiliary agent are added into water according to the formula amount to obtain liquid component, and then part of the liquid component is added into a reaction kettle and the other part is added into a premix kettle; S2: initiator is prepared into initiator solution; S3: after oxygen removal, the liquid component in the reaction kettle is heated to 40-100℃ under stirring, and then the initiator solution and the liquid component in the premix kettle are added into the reaction kettle, constant temperature reaction and constant temperature treatment are carried out, and then aqueous acrylic copolymer glue liquid is obtained; S4: pH regulator is added into the aqueous acrylic copolymer glue liquid to adjust the pH to 4-9, and then functional coating adhesive is obtained.

7. A lithium-ion battery, characterized by The method comprises the functional coating adhesive according to any one of claims 1-5.

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