An aqueous binder for secondary batteries and a method for preparing the same

Abstract

The application relates to the technical field of water-based adhesives, and particularly provides a water-based adhesive for secondary batteries and a preparation method thereof. The water-based adhesive for secondary batteries comprises a first acrylate polymer and a second acrylate polymer in a weight ratio of 1:9-9:1. The first acrylate polymer can provide good dispersion capacity of positive and / or negative active particles and final slurry stability, and the second acrylate polymer can improve the flexibility of the pole piece while not losing the adhesion and cohesion, simultaneously improve the compatibility with electrolyte, further reduce the interface impedance, and finally benefit the low internal resistance performance of the battery cell. Therefore, the water-based adhesive of the application can realize good dispersion capacity of positive and / or negative active particles, improve the flexibility of the pole piece, and further reduce the interface impedance while maintaining good adhesion and cohesion.

Description

Technical Field

[0001] This application relates to the field of water-based adhesives, specifically to a water-based adhesive for secondary batteries and its preparation method. Background Technology

[0002] Aqueous binders are indispensable components of secondary batteries, such as lithium-ion batteries, for both the positive and negative electrode materials, playing a role in dispersing and bonding them. Therefore, aqueous binders are one of the key auxiliary materials for lithium-ion batteries, significantly impacting their performance. Aqueous acrylic binders are commonly used in lithium-ion battery negative electrode materials, characterized by good dispersibility and high cohesive strength; however, they suffer from excessive hardness, leading to some application problems. Therefore, further research on aqueous acrylic binders is necessary to address their insufficient flexibility while improving their dispersibility and dispersion stability for positive and / or negative electrode materials, effectively reducing resistance and improving cycle performance. Summary of the Invention

[0003] However, existing acrylate-based water-based adhesives cannot simultaneously achieve high dispersibility and good flexibility for negative electrode materials. To address these issues, the inventors have conducted extensive research, experimentation, and analysis, and based on this, hereby submit this application.

[0004] This application provides an aqueous adhesive for secondary batteries and a method for preparing the same.

[0005] The technical solution adopted in this application is as follows:

[0006] A water-based adhesive for a secondary battery comprises a first acrylate polymer and a second acrylate polymer in a weight ratio of 1:9 to 9:1; the concentration of the water-based adhesive is 3-60 wt%.

[0007] The preparation method of the first acrylate polymer is as follows: a first monomer combination composed of a first hydrophilic monomer and a first hydrophobic monomer is polymerized in water for the first time, and then a second monomer combination composed of a second hydrophilic monomer and a second hydrophobic monomer is added for the second polymerization, thus obtaining the polymer.

[0008] The preparation method of the second acrylate polymer is as follows: a surfactant and / or protective colloid are added to water, and then a mixed monomer composed of a third monomer, a fourth monomer and a fifth monomer are added to carry out a polymerization reaction to obtain the polymer.

[0009] The general formula of the third monomer is CH2=C(R 1 )COOM, where R 1 Selected from H or C1-C4 alkyl groups, M is selected from H, Na + Li+ and K + At least one of them;

[0010] The fourth monomer contains at least one of the soft monomers;

[0011] The general formula of the fifth monomer is R 2 CH=CHR 3 CN, where R 2 Selected from H or methyl, R 3 It is either absent or selected from at least one of the C1-C4 alkylene groups.

[0012] Preferably, the first hydrophilic monomer accounts for 60-100% of the weight of the first monomer combination, and the second hydrophilic monomer accounts for 0-60% of the weight of the second monomer combination.

[0013] Preferably, the first hydrophilic monomer and the second hydrophilic monomer are individually selected from the general formula CH2=CR 4 R 5 The monomer, of which R 4 Selected from H or C1-C4 alkyl, R 5 Selected from -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) a H and -COO(CH2) b One or more of PO3H, and / or one or more of organic structures containing the functional groups -COOM, -(C6H5)COOM, -SO3M and -(C6H5)SO3M, wherein a = 1-40, b = 1-12, and M is selected from H, Li + Na + and K + One or more of them.

[0014] Preferably, the first hydrophobic monomer and the second hydrophobic monomer are individually selected from the general formula CH2=CR 6 R 7 The monomer, of which R 6 Selected from H or C1-C4 alkyl, R 7 Selected from -COOC n H 2n+1 and -C m H 2m One or more of CN, n = 1-40, m = 0-6.

[0015] Preferably, the weight ratio of the first monomer combination to the second monomer combination is 1:9-9:1.

[0016] Preferably, after the first polymerization, the conversion rate of the first monomer combination is not less than 70%.

[0017] Preferably, the general formula of the soft monomer is CH2=CHCOOR 8 , where R 8 It is selected from C2-C36 alkyl, C2-C36 substituted alkyl or substituted amino.

[0018] Preferably, the mixed monomers consist of 5-50% of the third monomer, 5-50% of the fourth monomer, and 20-90% of the fifth monomer by weight, at 100% weight.

[0019] The method for preparing the aqueous adhesive for the secondary battery according to any of the above embodiments is composed of mixing a first aqueous solution containing the first acrylate polymer and a second aqueous solution containing the second acrylate polymer.

[0020] In summary, this application has the following beneficial effects:

[0021] 1. The first acrylate polymer of this application provides excellent dispersion of positive and / or negative electrode active particles and final slurry stability. The second acrylate polymer improves electrode flexibility without sacrificing adhesion and cohesion, while simultaneously enhancing compatibility with the electrolyte, further reducing interfacial impedance, and ultimately contributing to the low internal resistance performance of the battery cell. Therefore, the aqueous binder of this application achieves excellent dispersion of positive and / or negative electrode active particles, improves electrode flexibility, and further reduces interfacial impedance while maintaining good adhesion and cohesion.

[0022] 2. This application has prepared two acrylate polymers with different characteristics and functions by selecting monomers, designing structures, and optimizing preparation processes. Furthermore, by blending these two acrylate polymers, the effects of both polymers are brought into full play, achieving a synergistic effect. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below.

[0024] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0025] This application provides an aqueous binder for secondary batteries, comprising a first acrylate polymer and a second acrylate polymer in a weight ratio of 1:9 to 9:1; the concentration of the aqueous binder is 3-60 wt%.

[0026] Specifically, the weight ratio of the first acrylate polymer and the second acrylate polymer can be 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc., and further, the weight ratio can be 6:1 to 1:6. The concentration of the water-based adhesive refers to the sum of the weight concentrations of the first acrylate polymer and the second acrylate polymer in the water-based adhesive. It can be tested using the volatile matter test method. Specifically, a fixed amount (e.g., 2g or 5g) of the water-based adhesive is placed in an open glass container (e.g., a glass dish) and heated in an oven at 105°C for 2 hours. The weight change of the water-based adhesive before and after heating is measured, and the volatile matter is calculated. For example, the concentration of water-based adhesives can be 3wt%, 5wt%, 10wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, etc.

[0027] The preparation method of the above-mentioned first acrylate polymer is as follows: the first monomer combination composed of the first hydrophilic monomer and the first hydrophobic monomer is polymerized in water for the first time, and then the second monomer combination composed of the second hydrophilic monomer and the second hydrophobic monomer is added for the second polymerization, thus obtaining the polymer.

[0028] In the preparation of the first acrylate polymer mentioned above, the first acrylate polymer obtained by the first polymerization of the first monomer combination and the second polymerization of the second monomer has a good hydrophilic and hydrophobic structural composition and distribution, and achieves good dispersion performance for positive and / or negative electrode active particles, especially for negative electrode active particles, such as carbon black, carbon microspheres, graphite, etc., with good dispersibility and dispersion stability.

[0029] The preparation method of the above-mentioned second acrylate polymer is as follows: a surfactant and / or protective colloid are added to water, and then a mixed monomer composed of a third monomer, a fourth monomer and a fifth monomer are added, and a polymerization reaction is carried out to obtain the polymer.

[0030] The general formula for the third monomer is CH2=C(R 1)COOM, where R 1 Selected from H or C1-C4 alkyl groups, M is selected from H, Na + Li + and K + At least one of the following; the third monomer has good hydrophilicity and can provide a certain degree of hydrophilicity to the second acrylate polymer. For example, the third monomer can be acrylic acid, methacrylic acid, sodium acrylate, sodium methacrylate, etc.

[0031] The fourth monomer contains at least one of the soft monomers. For example, the fourth monomer can be a soft monomer or a combination of soft monomers and other monomers in a weight ratio of 1-20:1. The other monomers can be hard monomers and / or acrylamide monomers. Soft monomers can impart better flexibility to the second acrylate polymer. In this application, a soft monomer refers to a homopolymer obtained by homopolymerization of the monomer with a glass transition temperature (Tg) below 0°C, or further, not exceeding -10°C. Conversely, a hard monomer refers to a homopolymer obtained by homopolymerization of the monomer with a glass transition temperature (Tg) above 0°C, or further, not below 10°C. In this application, the general formula of the soft monomer can be CH2=CHCOOR. 8 , where R 8 The monomers are selected from C2-C36 alkyl, C2-C36 substituted alkyl, amino, or substituted amino groups. For example, soft monomers may be butyl acrylate, octyl acrylate, hexyl acrylate, lauryl acrylate, stearate acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl acrylate, etc., while hard monomers may be methyl methacrylate, ethyl methacrylate, etc. Acrylamide monomers may be N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-diethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, etc.

[0032] The general formula for the fifth monomer is R. 2 CH=CHR 3 CN, where R 2 Selected from H or methyl, R 3 The fifth monomer is either absent or selected from at least one of the C1-C4 alkylene groups. The fifth monomer has high polarity and, in combination with the fourth monomer, can impart good hydrophilic and hydrophobic properties to the second acrylate polymer. For example, the fifth monomer can be acrylonitrile, methacrylonitrile, 3-butenonitrile, etc.

[0033] In the preparation of the aforementioned second acrylate polymer, the addition of surfactants and / or protective colloids, such as a single protective colloid or a combination of protective colloid and surfactant in a weight ratio of 1:1 to 20:1, can improve the dispersion uniformity of the third, fourth, and fifth monomers in water, thereby enhancing the polymerization effect. These surfactants can also participate in the polymerization reaction, introduce branched structures into the second acrylate polymer, improve its flexibility, and enhance the entanglement between the second and first acrylate polymers, thus improving the synergistic effect. Specifically, the amount of surfactant used can be 0-5% of the weight of the mixed monomers, and can be AEO-3, AEO-9, AEO-15, Span 20, Span 40, Span 60, Span 80, Tween 20, Tween 40, Tween 60, Tween 80, etc., without particular limitations. Specifically, the amount of protective colloid used can be 0-50% of the weight of the mixed monomers. The protective colloid can be polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), carboxymethyl cellulose ether, hydroxymethyl cellulose ether, hydroxypropyl cellulose ether, etc. Taking PVA as an example, the degree of hydrolysis can be 70-99%, or further, 80-95%. Further, the amount of protective colloid used can be 0.5-30% of the weight of the mixed monomers, or even further, 1-20% of the weight of the mixed monomers.

[0034] The second acrylate polymer prepared according to the above-mentioned preparation method has good flexibility and hydrophilic and hydrophobic properties. While improving the flexibility of the electrode, it does not lose the adhesion and cohesion of the electrode, and at the same time improves the compatibility with the electrolyte, which can further reduce the interfacial impedance and ultimately achieve the low internal resistance performance of the battery cell.

[0035] In a preferred embodiment of this application, the first hydrophilic monomer accounts for 60-100% by weight in the first monomer combination, and the second hydrophilic monomer accounts for 0-60% by weight in the second monomer combination. Through the above-described configuration of the first and second hydrophilic monomers, the hydrophilicity and hydrophobicity of the first acrylate polymer are relatively balanced, and the polymer chain structure layout is relatively reasonable, resulting in good dispersibility for the positive electrode active particles and / or negative electrode materials. For example, the weight percentage of the first hydrophilic monomer in the first monomer combination can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc., and further, the weight percentage of the first hydrophilic monomer in the first monomer combination is 65-90%. The weight percentage of the second hydrophilic monomer in the second monomer combination can be 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc., and further, the weight percentage of the second hydrophilic monomer in the second monomer combination can be 10-50%.

[0036] In a preferred embodiment of this application, the first hydrophilic monomer and the second hydrophilic monomer are each selected from the general formula CH2=CR 4 R 5 The monomer, of which R 4 Selected from H or C1-C4 alkyl, R 5 Selected from -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) a H and -COO(CH2) b One or more of PO3H, and / or one or more of organic structures containing the functional groups -COOM, -(C6H5)COOM, -SO3M and -(C6H5)SO3M, wherein a = 1-40, b = 1-12, and M is selected from H, Li + Na + and K + One or more of these. For example, the first and second hydrophilic monomers can be individually selected from acrylic acid, methacrylic acid, sodium acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, acrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, polyethylene glycol acrylate, etc.

[0037] In a preferred embodiment of this application, the first hydrophobic monomer and the second hydrophobic monomer are each selected from the general formula CH2=CR. 6 R 7 The monomer, of which R 6 Selected from H or C1-C4 alkyl, R 7 Selected from -COOC n H 2n+1 and -C m H 2m One or more of CN, n = 1-18, m = 0-6. For example, the first hydrophobic monomer and the second hydrophobic monomer can be individually selected from acrylonitrile, butyl acrylate, butyl methacrylate, ethyl acrylate, isooctyl acrylate, isooctyl methacrylate, etc.

[0038] In a preferred embodiment of this application, the weight ratio of the first monomer combination and the second monomer combination is 1:9 to 9:1. For example, the total weight ratio of the first monomer combination and the second monomer combination can be 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc. Further, the weight ratio of the first monomer combination and the second monomer combination can be 7:1 to 1:7.

[0039] In a preferred embodiment of this application, after the first polymerization, the conversion rate of the first monomer combination is not less than 70%. After the first polymerization, the conversion rate of the first monomer combination is not less than 70%, resulting in a small amount of the first monomer combination remaining in the reaction system, which will not affect the ratio of the second hydrophilic monomer and the second hydrophobic monomer in the added second monomer combination. Further, after the first polymerization, the conversion rate of the first monomer combination is not less than 75%, or even further, not less than 80%.

[0040] In a preferred embodiment of this application, the mixed monomers, by weight, consist of 5-50% of a third monomer, 5-50% of a fourth monomer, and 20-90% of a fifth monomer. Further, by weight, the mixed monomers may consist of 10-40% of a third monomer, 10-40% of a fourth monomer, and 20-80% of a fifth monomer. For example, the mixed monomers may consist of 10% of a third monomer, 10% of a fourth monomer, and 80% of a fifth monomer; or 10% of a third monomer, 30% of a fourth monomer, and 60% of a fifth monomer; or 20% of a third monomer, 20% of a fourth monomer, and 60% of a fifth monomer; or 20% of a third monomer, 15% of a fourth monomer, and 65% of a fifth monomer; or 15% of a third monomer, 25% of a fourth monomer, and 60% of a fifth monomer; or 25% of a third monomer, 20% of a fourth monomer, and 55% of a fifth monomer, etc., but are not limited to the examples described above.

[0041] In another aspect, this application provides a method for preparing an aqueous adhesive for a secondary battery according to any of the above embodiments, which is composed of a first aqueous solution containing a first acrylate polymer and a second aqueous solution containing a second acrylate polymer.

[0042] For example, the first aqueous solution can be prepared as follows: A measured amount of water is added to a container and the temperature is raised to the polymerization reaction temperature. Simultaneously, the first monomer combination and a water-soluble initiator solution (such as ammonium persulfate solution, potassium persulfate solution, etc.) are added dropwise over 0.5-5 hours. After the addition is complete, the reaction is continued at a constant temperature for 0-8 hours. Then, the second monomer combination and the water-soluble initiator solution are added dropwise simultaneously over 0.5-4 hours. After the addition is complete, the reaction continues for 0-6 hours to obtain the final solution. Alternatively, the preparation method can be as follows: The first monomer combination and a measured amount of water are added to a container and the temperature is raised to the polymerization reaction temperature. A water-soluble initiator solution (such as ammonium persulfate solution, potassium persulfate solution, etc.) is added dropwise over 0.5-5 hours. After the addition is complete, the reaction is continued at a constant temperature for 0-8 hours. Then, the second monomer combination is added, and the water-soluble initiator solution is added dropwise or gradually over 0.5-4 hours. After the addition is complete, the reaction continues for 0-6 hours to obtain the final solution.

[0043] For example, the second aqueous solution can be prepared as follows: Add a surfactant and / or protective colloid to water, stir to dissolve evenly, heat to the polymerization reaction temperature, and dropwise add a mixed monomer consisting of a third, fourth, and fifth monomer, simultaneously adding a water-soluble initiator solution over 1-6 hours. After the addition is complete, continue the reaction at a constant temperature for 0-8 hours to obtain the final solution. Alternatively, the preparation method can be: Add a surfactant and / or protective colloid to water, stir to dissolve evenly, then add a mixed monomer consisting of a third, fourth, and fifth monomer, heat to the polymerization reaction temperature, and dropwise add a water-soluble initiator solution over 0.5-6 hours. After the addition is complete, continue the reaction at a constant temperature for 0-8 hours to obtain the final solution.

[0044] The technical solution of this application will be described in detail below with reference to preparation examples, embodiments, and comparative examples. Unless otherwise specified, the parts in each preparation example, embodiment, and comparative example below are parts by weight.

[0045] Preparation Examples 1-4: Preparation of the First Aqueous Solution

[0046] Preparation Example 1

[0047] Add 400 parts of water to the reactor, and while stirring at 180 rpm, add a first monomer combination consisting of 45 parts of methacrylic acid, 15 parts of acrylamide, 5 parts of hydroxypropyl acrylate, and 35 parts of acrylonitrile, along with 5 parts of sodium bicarbonate. Mix well, raise the temperature to 75°C, and add 10 parts of an aqueous solution containing 0.2 parts of ammonium persulfate dropwise over 30 minutes. After the addition is complete, maintain the temperature for 90 minutes, and the monomer conversion rate is measured to be 72%. Add a second monomer combination consisting of 5 parts of methacrylic acid and 30 parts of acrylonitrile, along with 20 parts of water, and increase the stirring speed to 250 rpm. Mix well, raise the temperature to 72°C, and add 10 parts of an aqueous solution containing 0.3 parts of ammonium persulfate. Maintain the temperature for 180 minutes, lower the temperature to below 45°C, add a certain amount of sodium bicarbonate and water, and adjust the pH of the binder to 7.5-8.0 with a solid content of 8 wt%, to obtain the first aqueous solution.

[0048] Preparation Example 2

[0049] The difference between Preparation Example 2 and Preparation Example 1 is that the second monomer combination was changed from 5 parts methacrylic acid and 30 parts acrylonitrile to 15 parts methacrylic acid and 90 parts acrylonitrile, the water was changed from 20 parts to 100 parts, and the 10 parts aqueous solution containing 0.3 parts ammonium persulfate was changed to 10 parts aqueous solution containing 0.9 parts ammonium persulfate. The remaining steps remained unchanged.

[0050] Preparation Example 3

[0051] Add 400 parts of water to the reactor, and while stirring at 180 rpm, add a first monomer combination consisting of 50 parts of methacrylic acid, 15 parts of acrylamide, 25 parts of hydroxypropyl acrylate, and 10 parts of acrylonitrile, along with 7 parts of sodium bicarbonate. Mix well, raise the temperature to 75°C, and add 10 parts of an aqueous solution containing 0.2 parts of ammonium persulfate dropwise over 30 minutes. After the addition is complete, maintain the temperature and react for 120 minutes. The monomer conversion rate is measured to be 81%. Add a second monomer combination consisting of 10 parts of methacrylic acid and 40 parts of acrylonitrile, along with 30 parts of water, and increase the stirring speed to 250 rpm. Mix well, raise the temperature to 72°C, and add 10 parts of an aqueous solution containing 0.4 parts of ammonium persulfate. Maintain the temperature and react for 180 minutes. Cool down to below 45°C, add a certain amount of sodium bicarbonate and water, and adjust the pH of the binder to 7.5-8.0 with a solid content of 8 wt%, to obtain the first aqueous solution.

[0052] Preparation Example 4

[0053] Add 400 parts of water to the reactor, and while stirring at 180 rpm, add a first monomer combination consisting of 20 parts of methacrylic acid, 20 parts of hydroxyethyl acrylate, and 10 parts of acrylonitrile, along with 3 parts of sodium bicarbonate. Mix well, raise the temperature to 73°C, and add 10 parts of an aqueous solution containing 0.1 parts of ammonium persulfate dropwise over 30 minutes. After the addition is complete, maintain the temperature and react for 120 minutes. The monomer conversion rate is measured to be 78%. Add a second monomer combination consisting of 20 parts of methacrylic acid, 10 parts of acrylamide, and 70 parts of acrylonitrile, along with 50 parts of water and 4 parts of sodium bicarbonate. Increase the stirring speed to 250 rpm and mix well. Raise the temperature to 75°C, add 10 parts of an aqueous solution containing 0.8 parts of ammonium persulfate, and maintain the temperature and react for 180 minutes. Cool down to below 45°C, add a certain amount of sodium bicarbonate and water, and adjust the pH of the binder to 7.5-8.0 with a solid content of 8 wt%, to obtain the first aqueous solution.

[0054] Preparation Examples 5-8: Preparation of a Second Aqueous Solution

[0055] Preparation Example 5

[0056] Add 10 parts PVABP-17 and 350 parts water to the reaction vessel, heat to 90°C, stir until BP-17 is completely dissolved, lower the temperature to below 40°C, and add 20 parts acrylic acid, 30 parts isooctyl acrylate, 5 parts methyl acrylate and 45 parts acrylonitrile in sequence. Raise the temperature to 75°C, and add 50 parts of an aqueous solution containing 0.3 parts ammonium persulfate dropwise over 120 min. After the addition is complete, keep the reaction at this temperature for 100 min, lower the temperature to below 40°C, add sodium bicarbonate and water to adjust the pH to 7.0-7.5, and the solid content to 16 wt%, to obtain the second aqueous solution.

[0057] Preparation Example 6

[0058] Add 10 parts PVABP-17 and 350 parts water to the reaction vessel, heat to 90°C, stir until BP-17 is completely dissolved, lower the temperature to below 40°C, and add 10 parts acrylic acid, 20 parts isooctyl acrylate, 10 parts N,N-dimethylacrylamide and 60 parts acrylonitrile in sequence. Raise the temperature to 75°C, and add 50 parts of an aqueous solution containing 0.3 parts ammonium persulfate dropwise over 120 min. After the addition is complete, keep the reaction at this temperature for 100 min, lower the temperature to below 40°C, add sodium bicarbonate and water to adjust the pH to 7.0-7.5, and the solid content to 16 wt%, to obtain the second aqueous solution.

[0059] Preparation Example 7

[0060] The difference between Preparation Example 7 and Preparation Example 6 is that in Preparation Example 6, the amount of isooctyl acrylate was adjusted from 20 parts to 15 parts, and the amount of acrylonitrile was adjusted from 60 parts to 65 parts. The remaining steps remained unchanged.

[0061] Preparation Example 8

[0062] The difference between Preparation Example 8 and Preparation Example 6 is that in Preparation Example 6, BP-17 was changed from 10 parts to 6 parts, isooctyl acrylate was changed from 20 parts to 30 parts, and acrylamide was changed from 10 parts to 0 parts. The remaining steps remained unchanged.

[0063] Example 1

[0064] Preparation Example 1 and the first aqueous solution and the second aqueous solution of Preparation Example 5 were mixed at a weight ratio of 10:1 to obtain an aqueous adhesive.

[0065] Example 2

[0066] Preparation Example 1 and the first aqueous solution and the second aqueous solution of Preparation Example 5 were mixed at a weight ratio of 1:1 to obtain an aqueous adhesive.

[0067] Example 3

[0068] Preparation Example 1 and the first aqueous solution and the second aqueous solution of Preparation Example 5 were mixed at a weight ratio of 1:3 to obtain an aqueous adhesive.

[0069] Example 4

[0070] Preparation Example 2 and the first aqueous solution and the second aqueous solution of Preparation Example 6 were mixed at a weight ratio of 1:1 to obtain an aqueous adhesive.

[0071] Example 5

[0072] Preparation Example 2 and the first aqueous solution and the second aqueous solution of Preparation Example 7 were mixed at a weight ratio of 1:1 to obtain an aqueous adhesive.

[0073] Example 6

[0074] Preparation Example 2 and the first aqueous solution and the second aqueous solution of Preparation Example 8 were mixed at a weight ratio of 1:1 to obtain an aqueous adhesive.

[0075] Example 7

[0076] Preparation Example 3 and the first aqueous solution and the second aqueous solution of Preparation Example 8 were mixed at a weight ratio of 1:2 to obtain an aqueous adhesive.

[0077] Example 8

[0078] Preparation Example 4 and the first aqueous solution and the second aqueous solution of Preparation Example 7 were mixed at a weight ratio of 14:1 to obtain an aqueous adhesive.

[0079] Example 9

[0080] Preparation Example 1 and the first aqueous solution and the second aqueous solution of Preparation Example 6 were mixed at a weight ratio of 6:1 to obtain an aqueous adhesive.

[0081] Example 10

[0082] Preparation Example 2 and the first aqueous solution and the second aqueous solution of Preparation Example 6 were mixed at a weight ratio of 6:1 to obtain an aqueous adhesive.

[0083] Comparative Example 1

[0084] Prepare the first aqueous solution of Example 1.

[0085] Comparative Example 2

[0086] Prepare the second aqueous solution of Example 5.

[0087] Comparative Example 3

[0088] Add 350 parts of water to the reaction vessel, then add 20 parts of acrylic acid, 30 parts of isooctyl acrylate, 10 parts of methyl acrylate and 40 parts of acrylonitrile in sequence. Raise the temperature to 75°C, and add 50 parts of an aqueous solution containing 0.3 parts of ammonium persulfate dropwise over 120 min. After the addition is complete, keep the reaction at this temperature for 100 min, then cool it down to below 40°C. Add sodium bicarbonate and water to adjust the pH to 7.0-7.5, and the solid content to 16 wt%, to obtain an aqueous adhesive.

[0089] Performance testing

[0090] The preparation process of the graphite negative electrode sheet is as follows: The water-based binder to be tested and 50% water are dispersed at 1000 rpm for 15 minutes, then conductive agent SP conductive carbon black is added and wetted for 12 minutes, followed by high-speed stirring at 1600 rpm for 120 minutes; then the negative electrode material S360-L2-H and the remaining 50% water are added, and high-speed stirring at 1600 rpm is continued for 120 minutes. After dispersion, the viscosity (23℃) is adjusted to between 2500-2700 mPa·s, and the material is filtered through a 150-mesh filter to complete the discharge. Copper foil is placed on a coating machine, the scraper scale of the wet film preparation device is adjusted, the filtered slurry is poured evenly, and the film is placed in a 100℃ environment and baked until dry. The film is then cut into 12.5cm × 5cm pieces with a single-sided surface density of 100-110 g / m³. 2 The electrode film.

[0091] The electrode peel strength test method is as follows: Place the cut electrode sheets in a 35% RH constant temperature chamber for 30 minutes, with the coated side facing outwards and the copper foil side facing inwards. Lay the two electrode sheets together and feed them into an electric roller press to press the electrode sheets to 1.6 g / cm². 3After rolling, let it sit for 30 minutes. During this time, select five 12.5×5cm stainless steel plates, apply double-sided tape of the corresponding size to the steel plates, and then attach the electrode sheet to the double-sided tape with the coating facing down. Then, attach a 2.5cm wide masking tape to the copper foil. Roll the electrode sheet steel plate back and forth with a certain pressure for one revolution using an electric rolling roller, and then use an electronic peeling machine to test the adhesion of the electrode sheet. The same method is used, but the electrode sheet is attached to the double-sided tape with the coating facing up, and the cohesion of the electrode sheet can be tested.

[0092] Electrode flexibility test: A softness tester, model ITM-RRD01, was used.

[0093] Test method for swelling rate of adhesive film electrolyte: Take an adhesive film without air bubbles, trim the edges first, then cut it to a size of about 1×4cm, put it in a 105℃ forced-air drying oven to dry for 4 hours, take it out and weigh it, record it as M1, put it into a small bottle containing electrolyte (1M LiPF6 in EC:DMC:EMC=1:1:1) and soak it at a constant temperature for 48 hours, take it out and wipe the surface electrolyte with filter paper. The wiping and weighing process should be controlled within 1 minute, weigh it as M2, and the swelling rate of the adhesive film is (M2-M1) / M1×100%.

[0094] The assembly sequence of the button cell, from bottom to top, is: negative electrode shell - spring contact - gasket - lithium sheet - electrolyte - separator - electrolyte - electrode - positive electrode shell; the initial coulombic efficiency and impedance tests are as follows:

[0095] First-efficiency test: 0.1C, 0.005-1.5V charge / discharge; impedance scan from 100kHz to 0.1Hz.

[0096] The results are shown in Table 1 below.

[0097] Table 1 Performance Test Results

[0098]

[0099]

[0100] As shown in Table 1, the combination of two acrylate polymers used in this application can achieve good dispersion of positive and / or negative electrode active particles, improve the flexibility of the electrode sheet, and further reduce interfacial resistance while maintaining good adhesion and cohesion.

[0101] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An aqueous adhesive for secondary batteries, characterized in that, It comprises a first acrylate polymer and a second acrylate polymer in a weight ratio of 1:9 to 9:1; the concentration of the aqueous adhesive is 3-60 wt%. The preparation method of the first acrylate polymer is as follows: a first monomer combination composed of a first hydrophilic monomer and a first hydrophobic monomer is polymerized in water for the first time, and then a second monomer combination composed of a second hydrophilic monomer and a second hydrophobic monomer is added for the second polymerization, thus obtaining the polymer. The preparation method of the second acrylate polymer is as follows: a surfactant and / or protective colloid are added to water, and then a mixed monomer composed of a third monomer, a fourth monomer and a fifth monomer are added to carry out a polymerization reaction to obtain the polymer. The general formula of the third monomer is CH2=C(R 1 )COOM, where R 1 Selected from H or C1-C4 alkyl groups, M is selected from H, Na + Li + and K + At least one of them; The fourth monomer contains at least one of the soft monomers; The general formula of the fifth monomer is R 2 CH=CHR 3 CN, where R 2 Selected from H or methyl, R 3 It is either absent or selected from at least one of the C1-C4 alkylene groups; The first hydrophilic monomer accounts for 60-100% of the weight of the first monomer combination, and the second hydrophilic monomer accounts for 10-60% of the weight of the second monomer combination; The first hydrophilic monomer and the second hydrophilic monomer are each selected from the general formula CH2=CR 4 R 5 The monomer, of which R 4 Selected from H or C1-C4 alkyl; R 5 Selected from -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) a H and -COO(CH2) b One or more of PO3H, and / or R 5 An organic structure containing one or more of the functional groups -COOM, -(C6H5)COOM, -SO3M, and -(C6H5)SO3M, wherein a = 1-40, b = 1-12, and M is selected from H, Li + Na + and K + One or more of them; The first hydrophobic monomer and the second hydrophobic monomer are each selected from the general formula CH2=CR 6 R 7 The monomer, of which R 6 Selected from H or C1-C4 alkyl, R 7 Selected from -COOC n H 2n+1 and -C m H 2m One or more of CN, n=1-40, m=0-6.

2. The aqueous adhesive for secondary batteries according to claim 1, characterized in that, The weight ratio of the first monomer combination to the second monomer combination is 1:9 to 9:

1.

3. The aqueous adhesive for secondary batteries according to claim 1, characterized in that, After the first polymerization, the conversion rate of the first monomer combination is not less than 70%.

4. The aqueous adhesive for secondary batteries according to claim 1, characterized in that, The general formula of the soft monomer is CH2=CHCOOR 8 , where R 8 Selected from C2-C36 alkyl groups.

5. The aqueous adhesive for secondary batteries according to claim 1, characterized in that, The mixed monomers, by weight, consist of 5-50% of the third monomer, 5-50% of the fourth monomer, and 20-90% of the fifth monomer.

6. A method for preparing the aqueous adhesive for a secondary battery according to any one of claims 1-5, characterized in that, It is composed of a first aqueous solution containing the first acrylate polymer and a second aqueous solution containing the second acrylate polymer.

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