Preparation method of an aqueous binder for a lithium-ion battery and the aqueous binder for a lithium-ion battery

Abstract

This application relates to the technical field of aqueous adhesives, and specifically provides a preparation method of an aqueous adhesive for lithium-ion batteries and an aqueous adhesive for lithium-ion batteries. The VAE polymer and acrylic monomers in the VAE emulsion are prepared according to a weight ratio of 1:4 - 4:1; add the VAE emulsion and water into a container, mix evenly, add a part of the weight of the acrylic monomers, heat up to a certain temperature, dropwise add the first initiator solution, then dropwise add the remaining acrylic monomers, and then dropwise add the second initiator solution, and cool down to obtain the aqueous adhesive; alternatively, add the VAE emulsion and water into a container, mix evenly, add the acrylic monomers, heat up to a certain temperature, dropwise add the third initiator solution, continue to react for 0 - 6 hours, and cool down to obtain the aqueous adhesive. The aqueous adhesive of this application can provide good peel strength and softness for the positive electrode material of lithium-ion batteries.

Description

Technical Field

[0001] This application relates to the technical field of aqueous adhesives, and specifically, to a preparation method of an aqueous adhesive for lithium-ion batteries and an aqueous adhesive for lithium-ion batteries. Background Art

[0002] The aqueous adhesive for lithium-ion battery cathode materials is usually a polyacrylic acid (PAA) aqueous adhesive. However, it is difficult for PAA-based aqueous adhesives to balance the peel strength between the electrode sheet and the aluminum foil and the softness of the electrode sheet. Too low peel strength will cause the electrode sheet to fall off, and too low softness will make the electrode sheet too brittle and prone to cracking after rolling. Therefore, there is an urgent need to improve the softness of PAA-based aqueous adhesives while ensuring sufficient peel strength. Summary of the Invention

[0003] To solve the technical problems in the prior art that it is difficult for PAA-based aqueous adhesives to simultaneously obtain good peel strength and softness, etc., this application provides a preparation method of an aqueous adhesive for lithium-ion batteries and an aqueous adhesive for lithium-ion batteries.

[0004] This application adopts the following technical solutions:

[0005] A preparation method of an aqueous adhesive for lithium-ion batteries, comprising the following steps:

[0006] Prepare VAE polymer and acrylic monomer in the VAE emulsion according to a weight ratio of 1:4 - 4:1;

[0007] Add the VAE emulsion and water into a container, mix evenly, add a part of the weight of the acrylic monomer, heat to a certain temperature, dropwise add the first initiator solution, then dropwise add the remaining acrylic monomer, and then dropwise add the second initiator solution, and cool down to obtain the aqueous adhesive;

[0008] Or, add the VAE emulsion and water into a container, mix evenly, add the acrylic monomer, heat to a certain temperature, dropwise add the third initiator solution, continue to react for 0 - 6 hours, and cool down to obtain the aqueous adhesive.

[0009] Preferably, the weight ratio of VAE polymer to acrylic monomer in the VAE emulsion is 1:2 - 2:1.

[0010] Preferably, the acrylic monomer is composed of a hydrophilic monomer and a hydrophobic monomer, and the hydrophilic monomer accounts for 40 - 90% of the weight of the acrylic monomer.

[0011] More preferably, the chemical general formula of the hydrophilic monomer is CH2=CR 1 R 2 wherein, R 1 is selected from H or C1 - C4 alkyl, R2 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 functional groups of -COOH, -COOM, -(C6H5)COOM, -SO3M and -(C6H5)SO3M, a = 1 - 40, b = 1 - 12, M is selected from Li + , Na + and K + One or more of them.

[0012] More preferably, the chemical general formula of the hydrophobic monomer is CH2 = CR 3 R 4 , wherein, R 3 is selected from H or C1 - C4 alkyl, R 4 is selected from -COOC n H 2n+1 and -C m H 2m CN, one or more of them, n = 1 - 40, m = 0 - 6.

[0013] Preferably, the partial weight is 10 - 90% by weight.

[0014] Preferably, the dropping times of the dropping of the first initiator solution, the dropping of the second initiator solution and the dropping of the third initiator solution are 30 minutes - 6 hours respectively.

[0015] Preferably, each of the first initiator, the second initiator and the third initiator is independently selected from one or more of water-soluble azo initiators, water-soluble peroxide initiators, water-soluble persulfide initiators or water-soluble redox initiators.

[0016] Preferably, the dropping time of the dropping of the remaining acrylic monomer is 1 - 8 hours.

[0017] A lithium-ion battery aqueous adhesive is obtained by the preparation method of the lithium-ion battery aqueous adhesive described in any one of the above embodiments.

[0018] In summary, the present application has the following beneficial effects:

[0019] 1. The water-based adhesive for lithium-ion batteries of the present application is formed by the reaction of vinyl acetate-ethylene copolymer (VAE) and acrylic monomers, having a structure with VAE as the core (soft core) and acrylic polymer (PAA) grafted on the surface. VAE and PAA cooperate to provide good adhesion to the current collector aluminum foil. VAE has good flexibility, and the hydrogen bond between the ester bond of VAE and PAA improves the flexibility of the electrode sheet. Therefore, the water-based adhesive of the present application can achieve good peel strength and softness simultaneously.

[0020] 2. The inventors found that the hydrogen bond between the protective colloid - polyvinyl alcohol (PVA) in the VAE emulsion and PAA also helps to improve the flexibility of the electrode sheet.

[0021] 3. The present application uses VAE as the soft core, which is more likely to undergo a hydrogen abstraction reaction with free radicals, generating new free radicals on the VAE polymer molecular chain and initiating the polymerization reaction of acrylic monomers to form a structure with PAA polymer chains grafted on the surface of the VAE soft core. The hydrophilic PAA polymer chains can provide good stability for the water-based binder.

[0022] 4. The inventors further found that the combination of the hydrophilic-hydrophobic structure of VAE and the hydrophilic-hydrophobic structure of PAA polymer chains works synergistically, enabling the entire water-based adhesive to have a good hydrophilic-hydrophobic structure, which plays a good dispersing role for the active particles of the positive electrode material and has a relatively high peel strength at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the interaction among VAE, PVA, and PAA in the water-based adhesive of the present application.

[0024] 1 - VAE soft core, 2 - PAA, 3 - PVA. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below.

[0026] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. In case of any contradiction, this specification shall prevail.

[0027] On the one hand, the present application provides a preparation method for a water-based adhesive for lithium-ion batteries, including the following steps: preparing VAE polymer and acrylic monomers in the VAE emulsion according to a weight ratio of 1:4 - 4:1;

[0028] Add VAE emulsion and water into a container, mix evenly, add a part of the weight of acrylic monomers, heat up to a certain temperature, dropwise add the first initiator solution, then dropwise add the remaining acrylic monomers, and then dropwise add the second initiator solution, and cool down to obtain an aqueous adhesive.

[0029] Alternatively, add VAE emulsion and water into a container, mix evenly, add acrylic monomers, heat up to a certain temperature, dropwise add the third initiator solution, continue to react for 0 - 6 hours, and cool down to obtain an aqueous adhesive.

[0030] The solid content of the VAE emulsion is usually 40 - 70 wt%, and the weight of the VAE polymer in the above VAE emulsion is calculated based on the solid content in the VAE emulsion. The weight of the VAE polymer = the weight of the VAE emulsion × the solid content.

[0031] The VAE emulsion is obtained by free radical emulsion polymerization of vinyl acetate and ethylene in water under a surfactant (or also polyvinyl alcohol). In addition to vinyl acetate and ethylene as the main monomers, other monomers can be added, such as methacrylic acid, acrylic acid, 2 - hydroxyethyl methacrylate, 2 - hydroxyethyl acrylate, 2 - hydroxypropyl methacrylate, 2 - hydroxypropyl acrylate, acrylamide, N - methylacrylamide, methyl methacrylate, butyl methacrylate, isooctyl methacrylate, etc. The addition amount of other monomers can be 0 - 10% of the total weight of all monomers. The weight ratio of the above vinyl acetate and ethylene is 9:1 - 6:4, a further choice is 9:1 - 7:3, and a further choice is 85:15 - 75:25.

[0032] In this application, the VAE emulsion is further preferably a VAE emulsion containing polyvinyl alcohol as a protective colloid. As a protective colloid, the dosage of polyvinyl alcohol in the VAE emulsion is generally between 1 - 6% of the weight of the VAE emulsion. In this application, the degree of hydrolysis of polyvinyl alcohol is selected to be between 70 - 99%, and further, the degree of hydrolysis of polyvinyl alcohol is selected to be between 80 - 90%. The inventors unexpectedly found that the presence of polyvinyl alcohol in the VAE emulsion can further improve the flexibility of the aqueous adhesive film formed on the electrode sheet.

[0033] In this application, further, the weight ratio of the VAE polymer to the acrylic monomers in the VAE emulsion is 1:2 - 2:1.

[0034] In this application, further, the acrylic monomers are composed of hydrophilic monomers and hydrophobic monomers, and the hydrophilic monomers account for 40 - 90% of the weight of the acrylic monomers. Further, the hydrophilic monomers account for 50 - 90% of the weight of the acrylic monomers. Further still, the hydrophilic monomers account for 70 - 85% of the weight of the acrylic monomers. By adjusting the ratio of hydrophilic monomers and hydrophobic monomers, aqueous adhesives with different hydrophilic - hydrophobic properties can be obtained.

[0035] A hydrophilic monomer refers to a compound containing at least one carbon-carbon unsaturated double bond in the molecule that can undergo free radical polymerization, and the molecular structure of the compound has at least one hydrophilic group, such as a hydroxyl group, a carboxyl group, a carboxylate, a phosphate group, a sulfonate group, an amino group, a substituted amino group, an amide group, a substituted amide group, etc., or a polyethylene glycol group containing at least two ethylene glycol units. A hydrophobic monomer refers to a compound containing at least one carbon-carbon unsaturated double bond in the molecule that can undergo free radical polymerization, and the molecular structure of the compound does not contain a hydrophilic group.

[0036] In the present application, further, the general chemical formula of the hydrophilic monomer is CH2=CR 1 R 2 , where R 1 is selected from H or a C1-C4 alkyl group, and R 2 is selected from one or more of -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) a H and -COO(CH2) b PO3H, and / or one or more of organic structures containing functional groups of -COOH, -COOM, -(C6H5)COOM, -SO3M, and -(C6H5)SO3M, a = 1-40, b = 1-12, and M is selected from one or more of Li + , Na + and K + . For example, the hydrophilic monomer can be acrylic acid, methacrylic acid, acrylamide, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, acrylamide, N,N-dimethylacrylamide, etc.

[0037] In the present application, further, the general chemical formula of the hydrophobic monomer is CH2=CR 3 R 4 , where R 3 is selected from H or a C1-C4 alkyl group, and R 4 is selected from one or more of -COOC n H 2n+1 and -C m H 2m CN, n = 1-40, and m = 0-6. For example, the hydrophobic monomer can be methyl methacrylate, ethyl methacrylate, butyl methacrylate, isooctyl methacrylate, lauryl methacrylate, stearyl methacrylate, acrylonitrile, etc.

[0038] In the present application, further, the partial weight is 10 - 90% by weight. Adding acrylic monomers step by step into the reaction system for free radical polymerization can better control the reaction process and adjust the copolymerization of monomers with different polymerization reaction rates. Of course, in the present application, the acrylic monomers can also be added into the reaction system all at once, and the performance difference between the obtained aqueous adhesive and the aqueous adhesive obtained by adding the acrylic monomers step by step is very small.

[0039] In the present application, further, the dropping times for dropping the first initiator solution, the second initiator solution, and the third initiator solution are 30 minutes - 6 hours respectively. Further, the dropping time of the first initiator solution is 30 minutes - 2 hours; further, the dropping time of the second initiator solution is 30 minutes - 4 hours, and further, the dropping time of the second initiator solution is 30 minutes - 2 hours; further, the dropping time of the third initiator solution is 30 minutes - 4 hours.

[0040] In the present application, based on the weight of the first initiator in the first initiator solution, it is 0.2 - 0.8% of the weight of the acrylic monomers. Based on the weight of the second initiator in the second initiator solution, it is 0.2 - 0.8% of the weight of the acrylic monomers. Based on the weight of the third initiator in the third initiator solution, it is 0.3 - 1.5% of the weight of the acrylic monomers. The concentrations of the first initiator solution, the second initiator solution, and the third initiator solution can be 1 - 20 wt%.

[0041] In the present application, further, the first initiator, the second initiator, and the third initiator are each independently selected from one or more of water-soluble azo initiators, water-soluble peroxide initiators, water-soluble persulfide initiators, or water-soluble redox initiators. There is no particular limitation on the water-soluble azo initiator, which can be azobis(isobutyramidine) hydrochloride (AIBA), azobis(2-methylpropionamidine) dihydrochloride (AIBI), etc.; there is no particular limitation on the water-soluble peroxide initiator, which can be hydrogen peroxide, sodium peroxide, ammonium peroxide, etc.; there is no particular limitation on the water-soluble persulfide initiator, which can be ammonium persulfate, potassium persulfate, sodium persulfate, etc.; there is no particular limitation on the water-soluble redox initiator, which can be ammonium persulfate / sodium bisulfite, potassium persulfate / sodium bisulfite, hydrogen peroxide / tartaric acid, hydrogen peroxide / sodium formaldehyde sulfoxylate, ammonium persulfate / ferrous sulfate, hydrogen peroxide / ferrous sulfate, etc. Different water-soluble initiators correspond to different reaction temperatures. For example, when the water-soluble initiator is AIBA, a certain temperature can be 50 - 60 °C, when the water-soluble initiator is ammonium persulfate, a certain temperature can be 60 - 80 °C, and when the water-soluble initiator is ammonium persulfate / sodium bisulfite, a certain temperature can be 40 - 45 °C.

[0042] In the present application, further, the dropping time of the remaining acrylic monomers is 1 - 8 hours. Further still, the dropping time of the remaining acrylic monomers is 2 - 6 hours.

[0043] In the present application, the solid content of the aqueous adhesive is 5 - 60 wt%, further, the solid content is 10 - 40 wt%, and the viscosity (25 °C) is 500 - 20000 mPa·s.

[0044] On the other hand, the present application provides an aqueous adhesive for lithium-ion batteries, which is obtained by the preparation method of the aqueous adhesive for lithium-ion batteries described in any of the above embodiments. The application of the aqueous adhesive of the present application in the positive electrode material of a lithium-ion battery to prepare a positive electrode paste can be carried out according to a conventional method.

[0045] Hereinafter, the technical solutions of the present application will be described in detail with reference to examples, comparative examples and experimental data.

[0046] Preparation Example 1

[0047] Add 2 parts of sodium dodecylbenzenesulfonate, 0.7 part of Triton X-100 and 37.3 g into a reaction kettle, add 28 parts of vinyl acetate, heat up to 67 °C, introduce ethylene gas, when the pressure in the reaction kettle reaches 4 MPa, dropwise add 0.2 part of ammonium persulfate aqueous solution (concentration 10 wt%), control the polymerization temperature at 75 ± 2 °C, increase the pressure of ethylene gas introduction to 5.7 MPa, and dropwise add 20 parts of vinyl acetate. After dropping vinyl acetate, stop introducing ethylene gas, continue to react for 6 hours, cool down, exhaust gas, defoam, and discharge to obtain a VAE emulsion, and the measured solid content is 59.8%.

[0048] Preparation Example 2

[0049] In Preparation Example 1, replace 2 parts of sodium dodecylbenzenesulfonate and 0.7 part of Triton X-100 with 2.7 parts of polyvinyl alcohol 17-88 (17 represents the degree of polymerization of polyvinyl alcohol is 1700, 88 represents the degree of alcoholysis is 88%), and keep the remaining steps unchanged to obtain a VAE emulsion, and the measured solid content is 59.5%.

[0050] Preparation Example 3

[0051] In Preparation Example 1, replace 2 parts of sodium dodecylbenzenesulfonate and 0.7 part of Triton X-100 with 5 parts of polyvinyl alcohol 17-88, and keep the remaining steps unchanged to obtain a VAE emulsion, and the measured solid content is 60.3%.

[0052] Preparation Example 4

[0053] In Preparation Example 1, 2 parts of sodium dodecylbenzenesulfonate and 0.7 part of Triton X-100 were replaced with 2.7 parts of hydroxypropyl methylcellulose, and the remaining steps remained unchanged to obtain a VAE emulsion with a measured solid content of 59.4%.

[0054] Preparation Example 5

[0055] In Preparation Example 1, 2 parts of sodium dodecylbenzenesulfonate and 0.7 part of Triton X-100 were replaced with 5 parts of hydroxypropyl methylcellulose, and the remaining steps remained unchanged to obtain a VAE emulsion with a measured solid content of 59.7%.

[0056] Example 1

[0057] The acrylic monomers consisted of methacrylic acid, 2-hydroxyethyl methacrylate, and methacrylonitrile in a weight ratio of 4:4:2.

[0058] 16.7 parts of the VAE emulsion of Preparation Example 1 and 65 parts of water were added to a reactor, mixed evenly, 7 parts of the above acrylic monomers and 0.05 part of sodium bisulfite were added, the temperature was raised to 45°C, and 0.5 part of an aqueous solution of ammonium persulfate with a concentration of 10 wt% was added dropwise within 2 hours. Then, 3 parts of the above acrylic monomers were added dropwise within 4 hours, and then 0.3 part of an aqueous solution of ammonium persulfate with a concentration of 10 wt% was added dropwise within 1.5 hours. The temperature was lowered to below 30°C, the pH was adjusted to 7.5 - 8, and water was added to adjust the solid content to 19.9 wt% to obtain an aqueous adhesive.

[0059] Example 2

[0060] In Example 1, the VAE emulsion of Preparation Example 1 was replaced with an equal weight of the VAE emulsion of Preparation Example 2, and the remaining steps remained unchanged.

[0061] Example 3

[0062] In Example 1, the VAE emulsion of Preparation Example 1 was replaced with an equal weight of the VAE emulsion of Preparation Example 3, and the remaining steps remained unchanged.

[0063] Example 4

[0064] In Example 1, the VAE emulsion of Preparation Example 1 was replaced with an equal weight of the VAE emulsion of Preparation Example 4, and the remaining steps remained unchanged.

[0065] Example 5

[0066] In Example 1, the VAE emulsion of Preparation Example 1 was replaced with an equal weight of the VAE emulsion of Preparation Example 5, and the remaining steps remained unchanged.

[0067] Example 6

[0068] The acrylic monomer is composed of methacrylic acid, hydroxypropyl methacrylate, methacrylonitrile and butyl methacrylate in a weight ratio of 4:3:2:1.

[0069] Add 20 parts of the VAE emulsion prepared in Preparation Example 2 and 65 parts of water to the reactor, mix evenly, add 5 parts of the above acrylic monomer, heat up to 73°C, and dropwise add 0.6 part of an aqueous ammonium persulfate solution with a concentration of 10 wt% within 3 hours. Then, dropwise add 3 parts of the above acrylic monomer within 4 hours, and then dropwise add 0.4 part of an aqueous ammonium persulfate solution with a concentration of 10 wt% within 2 hours. Cool down to below 30°C, adjust the pH to 7.5 - 8, and add water to adjust the solid content to 20.2 wt% to obtain an aqueous adhesive.

[0070] Example 7

[0071] The acrylic monomer is composed of methacrylic acid, hydroxypropyl methacrylate and methacrylonitrile in a weight ratio of 4:3:3.

[0072] Add 10 parts of the VAE emulsion prepared in Preparation Example 3 and 60 parts of water to the reactor, mix evenly, add 8 parts of the above acrylic monomer, heat up to 73°C, and dropwise add 0.5 part of an aqueous ammonium persulfate solution with a concentration of 10 wt% within 3 hours. Then, dropwise add 4 parts of the above acrylic monomer within 4 hours, and then dropwise add 0.4 part of an aqueous ammonium persulfate solution with a concentration of 10 wt% within 2.5 hours. Cool down to below 30°C, adjust the pH to 7.5 - 8, and add water to adjust the solid content to 20 wt% to obtain an aqueous adhesive.

[0073] Example 8

[0074] In Example 2, the acrylic monomer was adjusted to be composed of methacrylic acid, hydroxyethyl methacrylate and methacrylonitrile in a weight ratio of 3:2:5, and the remaining steps remained unchanged.

[0075] Comparative Example 1

[0076] Dilute the VAE emulsion prepared in Preparation Example 2 with water to a concentration of 20 wt%.

[0077] Comparative Example 2

[0078] Add 75 parts of water, 12 parts of methacrylic acid, 4 parts of acrylamide, 3 parts of methacrylonitrile and 1 part of laurate to the reaction kettle, and stir and blend at a rotation speed of 400 rpm. Heat up to 75°C, dropwise add 1 part of an aqueous ammonium persulfate solution with a concentration of 40 wt% within 2 hours, keep the temperature for 3 hours after dropping, cool down to below 30°C, adjust the pH to 7.5 - 8, and the solid content is 20.1 wt% to obtain an aqueous adhesive.

[0079] Comparative Example 3

[0080] Mix the VAE emulsion of Preparation Example 2 and the water-based adhesive of Comparative Example 2 evenly at a weight ratio of 1:1.

[0081] Comparative Example 4

[0082] Mix the VAE emulsion of Preparation Example 2 and the water-based adhesive of Comparative Example 2 evenly at a weight ratio of 1:2.

[0083] Comparative Example 5

[0084] In Example 2, the acrylic monomer was adjusted to be composed of methacrylic acid, 2-hydroxyethyl methacrylate, and methacrylonitrile at a weight ratio of 2:1:7, and the remaining steps remained unchanged.

[0085] Performance Test

[0086] Two cathode materials, lithium manganate and lithium iron phosphate, were used for testing, and the formulations were as follows:

[0087] Lithium manganate: water-based adhesive: super P carbon black: lithium manganate = 2.2:2.0:95.8.

[0088] Lithium iron phosphate: water-based adhesive: super P carbon black: lithium iron phosphate = 3.0:2.0:95.0.

[0089] The dispersion process is shown in Table 1 below.

[0090] Table 1

[0091]

[0092] The test method for the pole piece peel strength is as follows:

[0093] Flat coating machine (MSK-AFA-SC300, manufacturer: Shenzhen Kejing Zhida Technology Co., Ltd.)

[0094] Standard tape: the surface material coated with standard pressure-sensitive adhesive (40 mm wide, single-sided tape, manufacturer: 3M)

[0095] Double-sided tape (50 mm wide, double-sided tape, manufacturer: Yiwu Yongda Adhesive Products Factory)

[0096] Test plate (length 125 mm ± 1 mm, width 50 mm ± 1 mm, thickness 1.5 - 2.0 mm, the test plate material is OCr18Ni9 or 1Cr18Ni9Ti specified in GB / T3280-2015)

[0097] Aluminum foil (single-sided shiny aluminum foil, thickness 12 μm, manufacturer: Xiamen Xiashun Aluminum Foil Co., Ltd.)

[0098] Operation steps:

[0099] S1. Use a coater to form a film. After forming, place it in an oven and bake at 105°C for 10 minutes. The areal density requirements for the dried electrode sheets are 280 ± 5 g / ㎡ for lithium manganate and 200 ± 5 g / ㎡ for lithium iron phosphate.

[0100] S2. Cut the electrode sheets, with the requirements: 50 mm × 125 mm, and the number of electrode sheets: 5.

[0101] S3. Place the cut electrode sheets in an oven for secondary drying, bake at 100°C for 30 minutes. After baking, place them in a desiccator and cool to room temperature.

[0102] S4. Label the 5 electrode sheets, measure the weight and thickness of each numbered electrode sheet, record the data, and then place the electrode sheets in a self-sealing bag and seal it.

[0103] S5. Use double-sided tape to bond the coated side of the electrode sheet to the smooth side of the test plate.

[0104] S6. Use the pressure roller of the adhesive tape rolling machine (YGJ-02) to roll back and forth on the electrode sheet at a speed of about 300 mm / min under its own weight, and let it stand for 5 minutes.

[0105] S7. Fold the free end of the specimen 180 degrees and continuously peel it off at a descending speed of 300 mm / min ± 10 mm / min.

[0106] S8. Stop when 25 mm of the template remains peeled off, and use an electronic peeling test machine (BLD-200N) to read the peeling force. Take the average value of the test results of 5 electrode sheets with the same water-based adhesive.

[0107] Test method for the flexibility of the electrode sheet: Use a softness tester of model IMT-RRD01*1 for testing. Take 5 different positions on the middle line of the same electrode sheet for testing and take the average value.

[0108] The results are shown in Table 2.

[0109] Table 2

[0110]

[0111] From the results in Table 2, it can be seen that the water-based adhesive of the present application can make the comprehensive performance of the peeling force and softness of the positive electrode material of the lithium-ion battery excellent.

[0112] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A preparation method of an aqueous binder for a lithium-ion battery, characterized in that: It includes the following steps: The VAE polymer and acrylic monomers in the VAE emulsion are prepared at a weight ratio of 1:4 - 4:1; the solid content of the VAE emulsion is 40 - 70 wt%. Add the VAE emulsion and water into a container, mix evenly, add a part of the weight of the acrylic monomers, heat up to a certain temperature, dropwise add the first initiator solution, then dropwise add the remaining acrylic monomers, and then dropwise add the second initiator solution, and cool down to obtain the aqueous adhesive. Alternatively, add the VAE emulsion and water into a container, mix evenly, add the acrylic monomers, heat up to a certain temperature, dropwise add the third initiator solution, continue to react for 0 - 6 hours, and cool down to obtain the aqueous adhesive. The acrylic monomers are composed of hydrophilic monomers and hydrophobic monomers, and the hydrophilic monomers account for 40 - 90% of the weight of the acrylic monomers.

2. The preparation method of the aqueous binder for lithium-ion batteries according to claim 1, wherein: The chemical general formula of the hydrophilic monomer is CH2=CR1R2, where R1 is selected from H or C1 - C4 alkyl, and R2 is selected from one or more of -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O)aH, and -COO(CH2)bPO3H, and / or one or more of the organic structures containing -COOH, -COOM, -(C6H5)COOM, -SO3M, and -(C6H5)SO3M functional groups, a = 1 - 40, b = 1 - 12, and M is selected from one or more of Li+, Na+, and K+.

3. The preparation method of the aqueous binder for lithium-ion batteries according to claim 2, characterized in that: The chemical general formula of the hydrophobic monomer is CH2=CR3R4, where R3 is selected from H or C1 - C4 alkyl, and R4 is selected from one or more of -COOCnH2n+1 and -CmH2mCN, n = 1 - 40, m = 0 - 6.

4. The preparation method of the aqueous binder for lithium-ion batteries according to claim 1, characterized in that: The part of the weight is 10 - 90% by weight.

5. The preparation method of the aqueous binder for lithium-ion batteries according to claim 1, characterized in that: The dropping times of the dropwise addition of the first initiator solution, the second initiator solution, and the third initiator solution are 30 minutes - 6 hours respectively.

6. The preparation method of the aqueous binder for lithium-ion batteries according to claim 1, wherein: The first initiator, the second initiator, and the third initiator are each independently selected from one or more of water-soluble azo initiators, water-soluble peroxide initiators, water-soluble persulfide initiators, or water-soluble redox initiators.

7. The preparation method of the aqueous binder for lithium-ion batteries according to claim 1, characterized in that: The dropping time of the dropwise addition of the remaining acrylic monomers is 1 - 8 hours.

8. An aqueous binder for lithium-ion batteries, characterized in that: It is obtained by the preparation method of the aqueous adhesive for lithium-ion batteries according to any one of claims 1 - 7.

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