Aqueous polymeric binder, preparation method therefor and use thereof

Abstract

The present application relates to the technical field of lithium battery materials and binders, and discloses an aqueous polymeric binder, a preparation method therefor and a use thereof. The aqueous polymeric binder is obtained by copolymerizing a polymerization unit comprising an acrylic monomer, an acrylate monomer, an oil-soluble monomer, a water-soluble monomer, and an amphiphilic water-soluble monomer in an aqueous solvent; and the mass percentages of the monomers are as follows: acrylic monomer: 5%-15%; acrylate monomer: 45%-60%; oil-soluble monomer: 10%-40%; water-soluble monomer: 5%-20%; and amphiphilic water-soluble monomer: 5%-10%. The aqueous polymeric binder of the present application is mainly used for bonding of an edge coating of a negative electrode sheet of a lithium-ion battery; on the basis of the specific copolymerization monomer components and proportions, the obtained binder has excellent PP base film bonding performance and electrolyte swelling resistance; in addition, the binder avoids material mixing with a negative electrode, and has good prospects of application.

Description

A water-based polymer binder and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 29, 2023, with application number 202311607350.X and invention name “A water-based polymer binder, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium battery materials and binders, and specifically relates to a water-based polymer binder and a preparation method and application thereof. Background Art

[0003] During multiple cycles of lithium-ion batteries, lithium crystals may appear, which may pierce the diaphragm and cause direct contact between the positive and negative electrodes, thereby causing a short circuit. At the same time, during the cutting process, the equipment needs to identify and cut the edges of the electrode. Traditional processes that use direct cutting may cause cutting dislocation or damage the negative electrode material area. Therefore, a side coating is required to protect it and ensure its normal cutting process. At the same time, the bonding between the side coating and the diaphragm can ensure that the electrode and the diaphragm are firmly bonded to avoid the risk of dislocation. The process of edge coating glue is mainly to mix it with boehmite, then coat it into a film, and then use the diaphragm for hot pressing to ensure that it is effectively bonded to the diaphragm.

[0004] Water-based acrylic pressure-sensitive adhesives (PSAs) are light-resistant and aging-resistant, non-toxic, pollution-free, and low-cost. They also possess excellent pressure sensitivity and adhesion, resulting in stable performance, making them widely used in many fields. However, when conventional acrylic adhesives are used for edge coating and protection of lithium-ion battery negative electrodes, they present the following problems: 1. Poor wettability with polypropylene (PP) separators and a large surface energy difference result in weak adhesion; 2. Severe crosstalk with the negative electrode slurry occurs (crosstalk refers to the phenomenon in which the edge coating adhesive slurry and the negative electrode slurry come into contact simultaneously, resulting in interpenetration due to differences in surface tension and properties, rather than distinct streams. This can also lead to coating anomalies, necessitating high crosstalk performance requirements for the edge coating adhesive slurry, which must be avoided during processing); and 3. Electrolyte resistance is generally low. Furthermore, existing acrylic PSAs are typically synthesized using emulsions in the presence of emulsifiers, and the addition of emulsifiers affects their performance in lithium-ion battery negative electrode edge coating and protection.

[0005] Therefore, the development of a water-based polyacrylate binder suitable for coating and protecting the edge of the negative electrode of lithium-ion batteries, having good adhesion and solvent resistance, and improving the anti-channeling performance of the negative electrode slurry has broad market prospects. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the above-mentioned prior art, the primary purpose of this application is to provide a water-based polymer binder.

[0007] Another object of the present application is to provide a method for preparing the above-mentioned aqueous polymer binder.

[0008] Another object of the present application is to provide an application of the above-mentioned aqueous polymer binder in bonding the negative electrode sheet and the separator of a lithium-ion battery.

[0009] The purpose of this application is achieved through the following technical solutions:

[0010] The first aspect of the present application provides an aqueous polymer binder, which is obtained by copolymerizing polymerization units including acrylic monomers, acrylic ester monomers, oil-soluble monomers, water-soluble monomers and amphiphilic water-soluble monomers in an aqueous solvent; the mass percentage ratio of each monomer is: acrylic monomer 5% to 15%, acrylic ester monomer 45% to 60%, oil-soluble monomer 10% to 40%, water-soluble monomer 5% to 20%, and amphiphilic water-soluble monomer 5% to 10%.

[0011] Furthermore, the acrylic monomer is one or more of acrylic acid or methacrylic acid; the acrylate monomer is one or more of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C13-C16 (meth)acrylate, octadecyl (meth)acrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0012] More preferably, the acrylic monomer is a partially neutralized acrylic monomer, with a neutralization degree of 10% to 100%; more preferably, a neutralization degree of 40% to 100%. The inventors discovered that selecting a partially neutralized acrylic monomer can further improve the electrolyte resistance of the waterborne polymer binder.

[0013] Furthermore, the oil-soluble monomer is one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and styrene.

[0014] Furthermore, the water-soluble monomer is one or more of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

[0015] Furthermore, the amphiphilic water-soluble monomer is methoxy polyethylene glycol (meth) acrylate, methoxy polypropylene glycol (meth) acrylate, sodium p-styrene sulfonate, C2-C18 One or more of alkyl acrylamides.

[0016] Furthermore, the polymerization unit also includes a cross-linking monomer accounting for 0 to 1% of the total mass of the polymerization monomer; the cross-linking monomer is one or more of divinylbenzene, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, N,N-methylenebisacrylamide, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, trimethylolpropane tri(3-aziridinyl propionate), polyurethane acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated bisphenol A diacrylate.

[0017] In the present application, the polymerizable monomers are composed of acrylic monomers, acrylic ester monomers, oil-soluble monomers, water-soluble monomers and amphiphilic water-soluble monomers.

[0018] The second aspect of the present application provides a method for preparing the aqueous polymer binder described in the first aspect of the present application, comprising the following preparation steps:

[0019] (1) adding acrylic acid monomer, acrylic acid ester monomer, oil-soluble monomer, water-soluble monomer, amphiphilic water-soluble monomer and cross-linking monomer into water and stirring and mixing to obtain phase A;

[0020] (2) adding the initiator to water and stirring to mix evenly, then heating to the initiation temperature to obtain phase B;

[0021] (3) Phase A and a reducing agent are added dropwise to phase B to react at room temperature. After the reaction is completed, the temperature is lowered, the mixture is neutralized, and the mixture is cooled and filtered to obtain a water-based polymer binder.

[0022] Furthermore, the initiator in step (2) is one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptylnitrile; the amount of the initiator added is 0.1% to 2% of the total mass of the polymerization monomer; and the initiation temperature is 30 to 100°C.

[0023] Furthermore, the reducing agent in step (3) is one or more of sodium bisulfite and tert-butyl hydroperoxide.

[0024] Furthermore, the insulation reaction time in step (3) is 2 to 24 hours.

[0025] Furthermore, the total amount of water added in step (1) and step (2) is 0.5 to 5 times the total mass of the polymerization monomers.

[0026] Furthermore, step (3) is: adding phase A and a reducing agent dropwise to phase B for heat-insulating reaction, heating to 60-100° C., adding an initiator, and continuing the reaction for 1-3 hours. After the reaction is completed, cooling, neutralizing, cooling, and filtering are performed to obtain a water-based polymer binder.

[0027] The third aspect of the present application provides the use of the aqueous polymer binder described in the first aspect of the present application in bonding the negative electrode sheet and the separator of a lithium-ion battery.

[0028] Furthermore, the application method is: mixing and homogenizing the aqueous polymer binder and boehmite to obtain a side-coating slurry; coating the side-coating slurry and the lithium-ion battery negative electrode slurry on the surface of the negative electrode collector, drying it to form a film, and then hot-pressing and bonding it with the separator.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) The aqueous polymer binder of this application is primarily used for bonding the edge coating of negative electrode plates. By adding acrylic monomers, the binder's electrolyte resistance is improved. By controlling the ratio of oil-soluble monomers to water-soluble monomers, it has good bonding strength and anti-channeling performance, while maintaining a high level of electrolyte resistance. The aqueous polymer binder of this application has excellent PP-based film bonding performance and electrolyte swelling resistance, and can significantly improve the anti-channeling performance with the negative electrode slurry.

[0031] (2) The polymer monomers of the present application ensure the stability of the water-based polymer binder during processing through the emulsification effect of acrylic acid and amphiphilic water-soluble monomers, without the need to add additional emulsifiers, thereby ensuring that the binder has good bonding strength; and by controlling the addition ratio of the amphiphilic water-soluble monomers, the water-based polymer binder's resistance to material leakage and electrolyte resistance are maintained at a high level. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0033] FIG1 is an appearance diagram of the aqueous polymer binder emulsion obtained in Examples 1-5.

[0034] FIG2A is a diagram showing the hot-pressed bonding state of the aqueous polymer binder obtained in Examples 1-5 mixed with boehmite.

[0035] FIG2B shows the hot-pressed bonding state of the aqueous polymer binder obtained in Example 2-9 mixed with boehmite.

[0036] FIG3 shows the test results of the negative electrode slurry resistance performance of the aqueous polymer binder obtained in Examples 1-5 at room temperature within 5 minutes, wherein the left side is the edge-coated slurry and the right side is the negative electrode slurry. DETAILED DESCRIPTION

[0037] The present application is described in further detail below with reference to examples and drawings, but the implementation manner of the present application is not limited thereto.

[0038] The product performance testing methods in the following examples are as follows:

[0039] (1) Peel strength test:

[0040] A water-based polymer binder and boehmite were mixed in a mass ratio of 1:5 to obtain a uniform slurry. The resulting slurry was coated and dried to form a film (50-60 μm). The film was then hot-pressed onto a PP separator (13-20 μm) at 3 MPa, 90°C, and 8 minutes. The film was then allowed to cool to room temperature before testing. The sample was 2 cm wide and 10 cm long, stretched at a speed of 50 cm / min, and peeled upward at 180 degrees. The peel strength was tested using a universal mechanical tensile tester.

[0041] (2) Resistance to negative electrode slurry leakage:

[0042] A water-based polymer binder and boehmite were mixed in a mass ratio of 1:5 to obtain a uniform slurry, which was then filtered to obtain the negative electrode side coating slurry. Carboxymethyl cellulose (CMC) was added to the water to dissolve uniformly, and then conductive carbon was added and dispersed for 2 hours. Graphite negative electrode material was added and dispersed at high speed for 2 hours. The speed was reduced and styrene-butadiene rubber (SBR) was added. The negative electrode slurry was filtered to obtain the negative electrode slurry. The mass ratio of water, CMC, conductive carbon, graphite negative electrode material, and SBR was 50:0.5:0.5:48:1. Approximately 0.2 mL of the negative electrode side coating slurry and the negative electrode slurry were pipetted separately, allowing the two slurries to contact each other. The cross-contamination phenomenon was observed, and the time required for significant cross-contamination of the two materials was observed.

[0043] (3) Electrolyte resistance:

[0044] A water-based polymer binder and boehmite were mixed in a mass ratio of 1:5 to obtain a uniform slurry, which was then filtered to obtain a negative electrode edge coating slurry. The negative electrode edge coating slurry was applied to copper foil, dried to form a film (50-60 μm), and then hot-pressed with a PP separator (13-20 μm). The hot pressing conditions were 3 MPa, 90°C, and 8 minutes. After hot pressing, the negative electrode was allowed to stand at room temperature to obtain a negative electrode plate. The negative electrode plate was immersed in the electrolyte and its mass swelling rate (mass swelling rate = (mass of the film after swelling - initial mass of the film) / initial mass of the film × 100%) and the appearance of the plate were tested after immersion in the electrolyte at 60°C for 7 days. The film and separator were observed to see if there was any cracking or detachment on the plate.

[0045] Example 1-1 to Example 1-5

[0046] The aqueous polymer binders of Examples 1-1 to 1-5 were prepared by the following method:

[0047] (1) 5 g of acrylic acid (neutralization degree 85%), 20 g of the oil-soluble monomer shown in Table 1, 10 g of methyl methacrylate, 40 g of isooctyl acrylate, 10 g of acrylamide, 5 g of hydroxyethyl acrylate, 5 g of sodium p-styrenesulfonate, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0048] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0049] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0050] Different oil-soluble monomers were selected according to Table 1, and the product properties were tested. The results are shown below:

[0051] Table 1 Properties of waterborne polymer binders obtained from different oil-soluble monomers

[0052] It can be seen from the results in Table 1 that the water-based polymer binders obtained using different oil-soluble monomers in this application all have good hot pressing bonding performance, anti-channeling performance and electrolyte resistance. The electrolyte resistance is reflected by the mass swelling rate and the performance of the electrode appearance. If the mass swelling rate is low and the electrode appearance is normal without shedding, the electrolyte resistance of the water-based polymer binder is better.

[0053] The appearance of the aqueous polymer binder emulsions (the oil-soluble monomer is styrene) obtained in Examples 1-5 is shown in FIG1 .

[0054] FIG2A shows the state of the aqueous polymer binder (the oil-soluble monomer is styrene) mixed with boehmite obtained in Examples 1-5, coated and dried to form a film, and then hot-pressed bonded to the PP separator. The coating is firmly bonded to the copper foil without cracking or falling off.

[0055] The test results of the negative electrode slurry resistance performance of the aqueous polymer binder (the oil-soluble monomer is styrene) obtained in Examples 1-5 at room temperature within 5 minutes are shown in Figure 3 (the left side of the figure is the edge coating slurry, and the right side is the negative electrode slurry).

[0056] Example 2-1 to Example 2-9

[0057] The aqueous polymer binders of Examples 2-1 to 2-9 were prepared by the following method:

[0058] (1) 5 g of acrylic acid (neutralization degree 85%), 20 g of styrene, 10 g of methyl methacrylate, 40 g of isooctyl acrylate, 15 g of the water-soluble monomer shown in Table 2, 5 g of methoxypolyethylene glycol monomethacrylate, 0.45 g of polyethylene glycol diacrylate, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0059] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0060] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0061] Different water-soluble monomers were selected according to Table 2 to test the product performance. The results are shown below:

[0062] Table 2 Properties of water-based polymer binders obtained from different water-soluble monomers

[0063] It can be seen from the results in Table 2 that the water-based polymer binders obtained by using different water-soluble monomers in the present application all have good hot pressing bonding performance, anti-channeling performance and electrolyte resistance performance.

[0064] FIG2B shows the state of hot pressing bonding of the aqueous polymer binder (water-soluble monomers are acrylamide and hydroxyethyl acrylate) obtained in Example 2-9 mixed with boehmite, dried and coated to form a film, and then bonded to the PP diaphragm. After hot pressing, the diaphragm is firmly bonded to the copper foil.

[0065] Example 3-1 to Example 3-4

[0066] The aqueous polymer binders of Examples 3-1 and 3-4 were prepared by the following method:

[0067] (1) 5 g of acrylic acid (neutralization degree 75%), 20 g of styrene, 10 g of methyl methacrylate, 40 g of isooctyl acrylate, 10 g of acrylamide, 5 g of isobornyl methacrylate, 5 g of the amphiphilic water-soluble monomer shown in Table 3, 0.45 g of N,N-methylenebisacrylamide, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0068] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0069] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0070] Different amphiphilic water-soluble monomers were selected according to Table 3, and the product properties were tested. The results are shown below:

[0071] Table 3 Properties of water-based polymer binders obtained from different amphiphilic water-soluble monomers

[0072] It can be seen from the results in Table 3 that the water-based polymer binders obtained by using different amphiphilic water-soluble monomers in the present application all have good hot pressing bonding performance, anti-channeling performance and electrolyte resistance performance.

[0073] Example 4-1 to Example 4-8

[0074] The aqueous polymer binders of Examples 4-1 to 4-8 were prepared by the following method:

[0075] (1) 5 g of acrylic acid with different neutralization degrees shown in Table 4, 20 g of styrene, 10 g of methyl methacrylate, 25 g of isooctyl acrylate, 10 g of lauryl methacrylate, 5 g of acrylamide, 5 g of isobornyl methacrylate, 5 g of sodium p-styrenesulfonate, 0.45 g of N,N-methylenebisacrylamide, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0076] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0077] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0078] According to Table 4, acrylic acid with different neutralization degrees was selected and the product performance was tested. The results are shown below:

[0079] Table 4 Properties of waterborne polymer binders obtained from acrylic acid with different neutralization degrees

[0080] From the results in Table 4, it can be seen that with the increase of the neutralization degree of acrylic acid, the bonding performance and anti-channeling performance of the obtained water-based polymer binder first increase and then decrease, and the electrolyte resistance performance shows an increasing trend. When the neutralization degree is within the range of 40% to 100%, better hot pressing bonding performance, anti-channeling performance and electrolyte resistance can be achieved.

[0081] Example 5-1 to Example 5-4, Comparative Example 1 to Comparative Example 4

[0082] The aqueous polymer binders of Examples 5-1 to 5-4 and Comparative Examples 1 to 4 were prepared by the following method:

[0083] (1) Different masses of acrylic acid (neutralization degree 75%) shown in Table 5, 20 g of styrene, 10 g of methyl methacrylate, 20 g of isooctyl acrylate, 20 g of lauryl methacrylate, 5 g of acrylamide, 5 g of isobornyl methacrylate, 5 g of methoxypolyethylene glycol acrylate, 0.45 g of polyethylene glycol diacrylate, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0084] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0085] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0086] According to Table 5, acrylic acid of different qualities was selected and the product performance was tested. The results are shown below:

[0087] Table 5 Properties of waterborne polymer binders obtained with different acrylic acid addition amounts

[0088] The results in Table 5 show that without the addition of acrylic acid monomer, the resulting waterborne polymer adhesive exhibits significantly reduced bonding performance, resistance to cross-contamination, and electrolyte resistance, failing to meet application requirements. With increasing levels of acrylic acid monomer, the peel strength, resistance to cross-contamination, and electrolyte resistance of the resulting waterborne polymer adhesive initially improve and then decrease. Acrylic acid monomer additions in the 5% to 15% range exhibit superior hot press adhesion, resistance to cross-contamination, and electrolyte resistance.

[0089] Example 6-1 to Example 6-4, Comparative Example 5 to Comparative Example 9

[0090] The aqueous polymer binders of Examples 6-1 to 6-4 and Comparative Examples 5 to 9 were prepared by the following method:

[0091] (1) 7 g of acrylic acid (neutralization degree 75%), different amounts of oil-soluble monomers as shown in Table 6, 10 g of methyl methacrylate, 20 g of isooctyl acrylate, 20 g of butyl acrylate, 15 g of acrylamide, 5 g of isobornyl methacrylate, 7 g of methoxypolyethylene glycol acrylate, 0.45 g of N,N-methylenebisacrylamide, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0092] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0093] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0094] According to Table 6, different addition amounts of oil-soluble monomers were selected and the product properties were tested. The results are shown below:

[0095] Table 6 Properties of waterborne polymer binders obtained with different addition amounts of oil-soluble monomers

[0096] The results in Table 6 show that without the addition of oil-soluble monomer, the adhesive properties of the resulting water-based polymer binder significantly deteriorate. With increasing amounts of oil-soluble monomer, the peel strength, resistance to cross-contamination, and electrolyte resistance of the resulting water-based polymer binder initially improve and then decrease. The addition of oil-soluble monomer in an amount ranging from 10% to 40% exhibits superior hot press adhesion, resistance to cross-contamination, and electrolyte resistance.

[0097] Example 7-1 to Example 7-2, Comparative Example 10 to Comparative Example 13

[0098] The aqueous polymer binders of Examples 7-1 to 7-2 and Comparative Examples 10 to 13 were prepared by the following method:

[0099] (1) 5 g of acrylic acid (neutralization degree 75%), 10 g of styrene, 10 g of acrylonitrile, 10 g of methyl methacrylate, 20 g of isooctyl acrylate, 20 g of butyl acrylate, 5 g of isobornyl methacrylate, different amounts of water-soluble monomers as shown in Table 7, 5 g of methoxypolyethylene glycol acrylate, 0.45 g of N,N-methylenebisacrylamide, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0100] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0101] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0102] The performance of the products was tested by selecting different amounts of water-soluble monomers according to Table 7. The results are shown below:

[0103] Table 7 Properties of water-based polymer binders obtained with different addition amounts of water-soluble monomers

[0104] As can be seen from the results in Table 7, when no water-soluble monomer is added, the bonding performance, anti-diffusion performance, and electrolyte resistance of the resulting water-based polymer adhesive are significantly reduced, which does not meet the requirements for use. As the amount of water-soluble monomer added increases, the peel strength and electrolyte resistance of the resulting water-based polymer adhesive show a trend of first increasing and then decreasing, while the anti-diffusion performance shows an improving trend. Acrylamide has a thermal cross-linking effect, which can strengthen the network structure of the polymer and improve the material's resistance to electrolyte swelling; and acrylamide has strong polar bonds, which can improve its bonding performance; but too much acrylamide will cause the cohesion of the film to be too large and the film to become hard due to its high glass transition temperature (Tg), which in turn leads to a decrease in bonding performance. Water-soluble monomers have better hot pressing adhesion, anti-diffusion performance, and electrolyte resistance when added in an amount ranging from 5% to 20%.

[0105] Example 8-1 to Example 8-5, Comparative Example 14 to Comparative Example 19

[0106] The aqueous polymer binders of Examples 8-1 to 8-5 and Comparative Examples 14 to 19 were prepared by the following method:

[0107] (1) 6 g of acrylic acid (neutralization degree 75%), 20 g of styrene, 20 g of methyl methacrylate, 40 g of isooctyl acrylate, 10 g of acrylamide, 5 g of hydroxyethyl acrylate, different amounts of amphiphilic water-soluble monomers shown in Table 8, 0.45 g of trimethylolpropane triacrylate, and 100 g of water were added to a flask and stirred at high speed to obtain a uniform phase A.

[0108] (2) Add 200 g of water and 0.5 g of ammonium persulfate to a beaker, stir well, and heat to 60°C to obtain phase B;

[0109] (3) Phase A and 0.2 g of reducing agent sodium bisulfite were simultaneously added dropwise to phase B for 2 h. After the addition was completed, the temperature was kept warm for 4 h. The temperature was then raised to 80 ° C. 0.1 g of initiator ammonium persulfate was added and the reaction was continued for 2 h. After the reaction was completed, the temperature was lowered to room temperature and neutralized with sodium hydroxide to a pH of 7. The mixture was cooled and filtered to obtain a water-based polymer binder.

[0110] According to Table 8, different amounts of amphiphilic water-soluble monomers were added and the product properties were tested. The results are shown below:

[0111] Table 8 Properties of water-based polymer binders obtained with different addition amounts of amphiphilic water-soluble monomers

[0112] The results in Table 8 show that either too low or too high an amount of the amphiphilic water-soluble monomer significantly reduces the waterborne polymer binder's resistance to material crosstalk and electrolyte. An amphiphilic water-soluble monomer addition in the range of 5% to 10% exhibits superior hot press adhesion, resistance to material crosstalk, and electrolyte resistance.

[0113] Example 9-1 to Example 9-7

[0114] Except that "0.45 g of polyethylene glycol diacrylate" in Example 2-9 is replaced by "cross-linking monomer shown in Table 9", the rest is the same as Example 2-9.

[0115] Table 9 Properties of waterborne polymer binders obtained with different cross-linking monomers

[0116] As can be seen from Table 9, the present application adds a cross-linking agent and limits the content of the cross-linking agent to the range of the present application, so that the obtained water-based polymer binder has better hot pressing adhesion, material resistance and electrolyte resistance.

[0117] Example 10-1 to Example 10-4

[0118] Except that "0.5 g of ammonium persulfate" in Example 2-9 is replaced by "the initiator shown in Table 10", the rest is the same as Example 2-9.

[0119] Table 10 Properties of waterborne polymer binders obtained with different initiators

[0120] It can be seen from Table 10 that the initiator is within the scope of this application, and the obtained water-based polymer binder has better hot pressing adhesion performance, material resistance and electrolyte resistance.

[0121] Example 11-1

[0122] The same procedures as in Example 2-9 are except that step (3) in Example 2-9 is replaced by “simultaneously adding phase A and 0.2 g of reducing agent sodium bisulfite to phase B for 2 h, and continuing to keep the temperature to react for 12 h after the addition is completed; then raising the temperature to 80° C., adding 0.1 g of initiator ammonium persulfate, and continuing the reaction for 2 h, and after the reaction is completed, cooling, neutralizing with alkali, cooling and filtering to obtain an aqueous polymer binder”.

[0123] Example 11-2

[0124] The same procedures as in Example 2-9 are except that step (3) in Example 2-9 is replaced by “simultaneously adding phase A and 0.2 g of reducing agent sodium bisulfite to phase B for 2 h, and continuing to keep the temperature for reaction for 24 h after the addition is completed; then raising the temperature to 80° C., adding 0.1 g of initiator ammonium persulfate, and continuing the reaction for 2 h, and after the reaction is completed, cooling, neutralizing with alkali, cooling and filtering to obtain an aqueous polymer binder”.

[0125] Example 11-3

[0126] The same procedures as in Example 2-9 are except that step (3) in Example 2-9 is replaced by “simultaneously adding phase A and 0.2 g of reducing agent sodium bisulfite to phase B for 2 h, and continuing to keep the temperature for reaction for 2 h after the addition is completed; then raising the temperature to 80° C., adding 0.1 g of initiator ammonium persulfate, and continuing the reaction for 2 h, and after the reaction is completed, cooling, neutralizing with alkali, cooling and filtering to obtain an aqueous polymer binder”.

[0127] Table 11 Properties of waterborne polymer binders obtained at different heat preservation reaction times

[0128] As can be seen from Table 11, the insulation reaction time is within the range of this application, and the obtained water-based polymer binder has better hot pressing adhesion, material resistance and electrolyte resistance.

[0129] The above embodiments are preferred implementation modes of the present application, but the implementation modes of the present application are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present application should be considered as equivalent replacement methods and are included in the scope of protection of the present application.

Claims

1. A water-based polymer binder, characterized in that: The invention is obtained by copolymerizing polymerization units including acrylic acid monomers, acrylic acid ester monomers, oil-soluble monomers, water-soluble monomers and amphiphilic water-soluble monomers in an aqueous solvent; the mass percentage ratio of each monomer is: acrylic acid monomer 5% to 15%, acrylic acid ester monomer 45% to 60%, oil-soluble monomer 10% to 40%, water-soluble monomer 5% to 20%, and amphiphilic water-soluble monomer 5% to 10%.

2. The aqueous polymer binder according to claim 1, characterized in that The acrylic monomer is one or more of acrylic acid or methacrylic acid; the acrylic ester monomer is methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C (meth)acrylate 13 -C 16 One or more of ester, octadecyl (meth)acrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

3. The aqueous polymer binder according to claim 2, characterized in that: The acrylic monomer is a partially neutralized acrylic monomer, and the neutralization degree of the partially neutralized acrylic monomer is 10% to 100%.

4. The aqueous polymer binder according to claim 3, characterized in that The neutralization degree of the partially neutralized acrylic monomer is 40% to 100%.

5. The aqueous polymer binder according to claim 1, characterized in that The oil-soluble monomer is one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and styrene.

6. The aqueous polymer binder according to claim 1, characterized in that The water-soluble monomer is one or more of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

7. The aqueous polymer binder according to claim 1, characterized in that: The amphiphilic water-soluble monomer is methoxy polyethylene glycol (meth) acrylate, methoxy polypropylene glycol (meth) acrylate, sodium p-styrene sulfonate, C2-C 18 One or more of alkyl acrylamides.

8. The aqueous polymer binder according to any one of claims 1 to 7, characterized in that The polymerization unit also includes a cross-linking monomer accounting for 0 to 1% of the total mass of the polymerization monomer; the cross-linking monomer is one or more of divinylbenzene, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, N,N-methylenebisacrylamide, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, trimethylolpropane tri(3-aziridinyl propionate), polyurethane acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated bisphenol A diacrylate.

9. A method for preparing the aqueous polymer binder according to claim 8, characterized in that: The method comprises the following preparation steps: (1) adding acrylic monomers, acrylic ester monomers, oil-soluble monomers, water-soluble monomers, amphiphilic water-soluble monomers and cross-linking monomers into water and stirring and mixing them uniformly to obtain phase A; (2) adding the initiator to water and stirring to mix evenly, and then heating to the initiation temperature to obtain phase B; (3) adding phase A and a reducing agent dropwise to phase B and maintaining the temperature for reaction; cooling after the reaction is completed, neutralizing, cooling and filtering to obtain a water-based polymer binder.

10. The preparation method according to claim 9, characterized in that: The initiator in step (2) is one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptylnitrile; the amount of the initiator added is 0.1% to 2% of the total mass of the polymerization monomer; and the initiation temperature is 30 to 100°C.

11. The preparation method according to claim 9, characterized in that: The reducing agent in step (3) is one or more of sodium bisulfite and tert-butyl hydroperoxide; and the insulation reaction time is 2 to 24 hours.

12. The preparation method according to claim 9, characterized in that: The total amount of water added in step (1) and step (2) is 0.5 to 5 times the total mass of the polymerization monomers.

13. Use of an aqueous polymer binder according to any one of claims 1 to 8 in bonding a negative electrode plate and a separator of a lithium ion battery.

14. The use according to claim 13, characterized in that The application method comprises: mixing and homogenizing an aqueous polymer binder and boehmite to obtain an edge coating slurry; coating the edge coating slurry and the negative electrode slurry on the surface of the negative electrode current collector of the lithium ion battery, drying the film, and then hot pressing and bonding the film with the separator.

Images