Water-based binder and preparation method therefor, and carbon-coated aluminum foil

Abstract

The present application relates to the technical field of secondary batteries, and in particular relates to a water-based binder and a preparation method therefor, and a carbon-coated aluminum foil. The water-based adhesive is mainly prepared from the following components in parts by weight: 60-80 parts of an acrylamide monomer, 10-20 parts of an unsaturated acid monomer, 10-20 parts of an acrylate monomer, 0.1-3 parts of a chain transfer agent, 100-400 parts of water, and a pH regulator. The amount of the pH regulator is regulated such that the pH value of a mixed system of the components is 1-6. In the present application, a water-based binder having narrow molecular weight distribution and high end group fidelity can be obtained by means of acid-initiated polymerization under a set pH value; and the binder has excellent dispersing performance and binding performance, can be used for preparing a slurry of a lithium-ion battery active material, and is particularly suitable for preparing a carbon-coated aluminum foil.

Description

Aqueous binder, its preparation method and carbon-coated aluminum foil TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to an aqueous binder, its preparation method and carbon-coated aluminum foil. BACKGROUND

[0002] The aluminum substrate as a traditional cathode current collector has a very high reduction potential value. Aluminum will be rapidly oxidized in the presence of oxygen to form a very thin aluminum oxide layer (2 nm). The oxide layer forms a chemical bond with the surface and acts as a protective layer to prevent further oxidation, thereby providing corrosion resistance. However, when exposed to extreme pH environments, the protective layer will break, and aluminum will directly contact the cathode slurry, forming soluble aluminum species, which will corrode the cathode active material, especially at high temperatures. In addition, the solid products produced during the corrosion process can increase the contact resistance between the active material and the current collector, and the soluble products can contaminate the electrolyte. So far, solving the problem of aluminum corrosion during the operation of lithium-ion batteries at high potentials has become the key to ensuring the efficient and stable operation of the battery.

[0003] In the prior art, a layer of active material is usually coated on the surface of the current collector to improve the performance of the electrode. The commonly used carbon-coated aluminum foil can effectively solve the corrosion problem of the aluminum foil when it contacts the electrode slurry and operates at high potentials. In the carbon-coated current collector, the high molecular binder provides functional groups to connect the electrode coating, the carbon coating and the bottom aluminum foil. The high molecular binder plays a key role in improving the adhesion between the electrode and the current collector and its capacity retention.

[0004] In the industrialized controllable synthesis of existing binders, exogenous thermal free radical initiators are usually used to initiate polymerization, but the use of exogenous initiators also has some limitations. First, the use of free radical initiators will cause the heterogeneity of the terminal groups and the termination of the chain, resulting in higher dispersity and impure copolymers. Moreover, the storage and use of exogenous initiators pose certain safety hazards in industrial production.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0007] One object of the present application is to provide an aqueous binder that does not require an exogenous initiator, has a narrow molecular weight distribution and high terminal group fidelity, and has excellent dispersion performance and bonding performance.

[0008] Another object of the present application is to provide a preparation method of the aqueous binder.

[0009] It is still another object of the present application to provide a carbon-coated aluminum foil.

[0010] To achieve the above object, the present application provides, in one aspect, a water-based adhesive prepared mainly from the following components in parts by weight:

[0011] acrylamide monomers 60-80 parts, unsaturated acid monomers 10-20 parts, acrylic ester monomers 10-20 parts, chain transfer agent 0.1-3 parts, water 100-400 parts, and pH adjuster; the amount of the pH adjuster is adjusted so that the pH of the mixed system of the components is 1-6.

[0012] In the detailed embodiment of the present application, the amount of the pH adjuster is adjusted so that the pH of the mixed system of the components is 2-5.

[0013] In the detailed embodiment of the present application, the acrylamide monomers include at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, diacetone acrylamide, N,N-dimethyl acrylamide, t-butyl acrylamide, N-methoxymethyl acrylamide, N-hydroxyethyl acrylamide, and acryloyl morpholine.

[0014] In the detailed embodiment of the present application, the acrylamide monomers include N,N-dimethyl acrylamide and acrylamide. Further, the mass ratio of the N,N-dimethyl acrylamide to the acrylamide in the acrylamide monomers is (1-2):1.

[0015] In the detailed embodiment of the present application, the acrylamide monomers account for ≥70% of the mass percentage of all monomers.

[0016] In the detailed embodiment of the present application, the unsaturated acid monomers include at least one of unsaturated carboxylic acid monomers or inorganic salts thereof, and unsaturated sulfonic acid monomers or inorganic salts thereof. Further, the unsaturated carboxylic acid monomers include at least one of (meth)acrylic acid, maleic anhydride, itaconic acid, and fumaric acid; and the unsaturated sulfonic acid monomers include at least one of styrene sulfonic acid, allyl sulfonic acid, and methacrylic acid sulfonic acid.

[0017] In the detailed embodiment of the present application, the acrylic ester monomers include at least one of alkyl (meth)acrylate, alkylhydroxy (meth)acrylate, polyethylene glycol methyl ether acrylate, di(hydroxyethyl acrylate) phosphoric acid ester, 2-methyl-2-propenoic acid-2-hydroxyethyl ester phosphoric acid ester, and di[2-(methacryloyloxy)ethyl] phosphoric acid ester.

[0018] In the detailed description of the present application, the pH regulator comprises at least one of sulfuric acid, sulfonic acid, phosphoric acid, hydrochloric acid, acetic acid, citric acid, lactic acid, oxalic acid and malic acid.

[0019] In the detailed description of the present application, the chain transfer agent comprises a mercaptan chain transfer agent.

[0020] Another aspect of the present application provides a preparation method of the water-based adhesive, comprising the following steps: mixing the components in proportion under a protective atmosphere, uniformly, and then discharging after reaction at 25-90℃, and performing neutralization treatment.

[0021] Another aspect of the present application provides a carbon-coated aluminum foil, comprising an aluminum foil substrate and a carbon coating layer arranged on the surface of the aluminum foil substrate, wherein the carbon coating layer is prepared from a slurry containing the water-based adhesive.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The present application can obtain a water-based adhesive with narrow molecular weight distribution and high end group fidelity by using monomers in a certain ratio, without photoinitiator or thermal free radical initiator, and by acid-induced polymerization at a set pH value. The improvement of end group fidelity can improve the interaction between the adhesive and the surface of a specific material, thereby improving the bonding strength, and also helps the adhesive to maintain high chemical stability.

[0024] (2) The water-based adhesive of the present application has excellent dispersing performance and adhesive performance, and can be used for the preparation of slurry of lithium ion battery active materials, and is especially suitable for the preparation of carbon-coated aluminum foil.

[0025] Other aspects can be apparent after reading and understanding the detailed description. DETAILED DESCRIPTION

[0026] The technical solutions of the present application will be described clearly and completely in combination with the specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0027] One aspect of the present application provides a water-based adhesive, which is mainly prepared from the following components in parts by weight:

[0028] 60-80 parts of acrylamide monomer, 10-20 parts of unsaturated acid monomer, 10-20 parts of acrylic ester monomer, 0.1-3 parts of chain transfer agent, 100-400 parts of water, and a pH adjusting agent; the amount of the pH adjusting agent is adjusted so that the pH value of the mixed system of the components is 1-6.

[0029] The water-based adhesive can be obtained by using monomers in a certain ratio, without using a light or thermal free radical initiator, and by acid-initiated polymerization at a set pH value. The terminal group fidelity is improved, which can improve the interaction between the adhesive and the surface of a specific material, thereby improving the bonding strength, and also helps the adhesive to maintain high chemical stability. The water-based adhesive does not include a light or thermal free radical initiator.

[0030] The water-based adhesive of the present application starts the polymerization reaction under the action of acid, and the acid can also accelerate the reaction rate, so that high molecular weight homopolymers or high molecular weight block copolymers with less termination can be obtained. The water-based adhesive has a long chain length, and when mixed with the remaining components to prepare a slurry, it is adsorbed on the surface of the particles in the slurry, which increases the repulsive force between the particles, thereby reducing the particle packing in the slurry, which is beneficial to improving the dispersibility and reducing the viscosity of the slurry. At the same time, by selecting the types of monomers, relatively high molecular weight polymers can be obtained while ensuring solubility and adhesive properties.

[0031] In the water-based adhesive of the present application, the amount of each component can be as follows:

[0032] The amount of acrylamide monomer can be 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, or a range formed by any two of them;

[0033] The amount of unsaturated acid monomer can be 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or a range formed by any two of them;

[0034] The amount of acrylic ester monomer can be 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or a range formed by any two of them;

[0035] The amount of chain transfer agent can be 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, 3 parts, or a range formed by any two of them;

[0036] The amount of water can be 100 parts, 150 parts, 200 parts, 250 parts, 300 parts, 350 parts, 400 parts, or a range formed by any two of them;

[0037] The amount of the pH adjuster needs to satisfy the following condition: adjusting the pH value of the mixed system after mixing of each component for preparing the aqueous binder to 1-6, for example, the pH value can be 1, 2, 3, 4, 5, 6 or a range formed by any two of them.

[0038] In the detailed description of the present application, the amount of the pH adjuster is adjusted to make the pH value of the mixed system of each component 1-5 or 2-5 or 1-3. The present application further regulates the pH value of the mixed system in the above range, which helps to improve the conversion rate of the polymerization reaction and obtain the aqueous binder with excellent dispersibility and bonding performance.

[0039] In the detailed description of the present application, the acrylamide monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, diacetone acrylamide, N,N-dimethyl acrylamide, t-butyl acrylamide, N-methoxymethyl acrylamide, N-hydroxyethyl acrylamide and acryloyl morpholine. Further, the acrylamide monomer includes at least one of acrylamide, methacrylamide, N,N-dimethyl acrylamide and acryloyl morpholine.

[0040] In the detailed description of the present application, the acrylamide monomer includes N,N-dimethyl acrylamide and acrylamide. Further, in the acrylamide monomer, the mass ratio of N,N-dimethyl acrylamide and acrylamide is (1-2):1.

[0041] As in different embodiments, in the acrylamide monomer, the mass ratio of N,N-dimethyl acrylamide and acrylamide can be 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1 or a range formed by any two of them. The acrylamide monomer composition as above can further improve the initiation conversion rate under acidic conditions.

[0042] In the detailed description of the present application, the mass percentage of the acrylamide monomer in all monomers is ≥70%. Wherein, all monomers refer to the acrylamide monomer, the unsaturated acid monomer and the acrylate monomer. As in different embodiments, the mass percentage of the acrylamide monomer in all monomers can be 70%, 72%, 75%, 78%, 80% or a range formed by any two of them. On the one hand, the amount of the acrylamide monomer in the above range helps to achieve acid-initiated polymerization at a set pH value and improve the conversion rate; on the other hand, the appropriate amount of the acrylamide monomer is more helpful to improve the dispersibility of the aqueous binder and also take into account the bonding performance.

[0043] In the detailed description of the present application, the unsaturated acid monomer includes unsaturated carboxylic acid monomer or its inorganic salt, unsaturated sulfonic acid monomer or its inorganic salt. Further, the unsaturated carboxylic acid monomer includes at least one of (meth)acrylic acid, maleic anhydride, itaconic acid and fumaric acid; the unsaturated sulfonic acid monomer includes at least one of styrene sulfonic acid, allyl sulfonic acid and methacrylic acid sulfonic acid. The corresponding inorganic salt can be sodium salt, etc.

[0044] By introducing a certain amount of unsaturated carboxylic acid monomer or its inorganic salt and / or unsaturated sulfonic acid monomer or its inorganic salt, the water-based adhesive can have a certain charge, and the molecular chains of the water-based adhesive can be prevented from being excessively entangled by the charge force, thereby improving the dispersibility and providing additional active sites to improve the bonding performance.

[0045] In the detailed description of the present application, the acrylate monomer includes at least one of (meth)acrylic alkyl ester, (meth)acrylic alkyl hydroxy ester, polyethylene glycol methyl ether acrylate, di(hydroxyethyl acrylate) phosphate, 2-methyl-2-acrylic acid-2-hydroxyethyl ester phosphate and di[2-(methacryloyloxy)ethyl] phosphate.

[0046] Among them, the (meth)acrylic alkyl ester can include but is not limited to dodecyl methacrylate; the (meth)acrylic alkyl hydroxy ester includes but is not limited to 3-hydroxy-1-adamantyl methacrylate.

[0047] The water-based adhesive prepared by matching various monomers in the present application can form an effective three-dimensional cross-linked structure during the preparation of the slurry blend and the coating process, while taking into account the high dispersibility, the bonding performance is improved.

[0048] In the detailed description of the present application, the pH adjuster includes at least one of sulfuric acid, sulfonic acid, phosphoric acid, hydrochloric acid, acetic acid, citric acid, lactic acid, oxalic acid and malic acid. Further, the pH adjuster includes at least one of sulfuric acid, sulfonic acid, phosphoric acid, hydrochloric acid, acetic acid and oxalic acid.

[0049] In actual operation, the pH adjuster can be added in the form of an aqueous solution to avoid excessive acidity leading to poor stability of the mixed system. For example, taking sulfuric acid as an example, the mass fraction thereof can be 0.1% to 5%, but is not limited thereto, and can be adjusted according to the actual situation.

[0050] In the detailed description of the present application, the chain transfer agent includes a mercaptan chain transfer agent. The mercaptan chain transfer agent includes an aliphatic mercaptan, such as n-dodecyl mercaptan, and the like. The chain transfer agent is not limited to this, and can also include at least one of 2-(((butylthio)carbonylthio)thio)propanoic acid, 3-((((1-carboxyethyl)thio)carbonylthio)thio)propanoic acid, methyl 2-[methyl(4-pyridyl)aminomethylthio]propanoate, 2-cyanopropan-2-yl N-methyl-N-(4-pyridyl)amino dithioate, 2-cyano-2-propyl benzenedithioate, isopropyl alcohol, inorganic phosphate, octanol, 3-chloro-2-hydroxypropyltriethylammonium chloride (CTA), 2,4-diphenyl-4-methyl-1-pentene (TPMS), and an alpha-methyl styrene linear dimer (AMSD).

[0051] In the detailed description of the present application, the chain transfer agent is used in an amount of 0.5wt% to 3wt% of all monomers, and further optionally 1.5wt% to 2.5wt%.

[0052] In the detailed description of the present application, the number average molecular weight of the aqueous binder is 40000 to 70000; and the molecular weight distribution width index of the aqueous binder is 1.1 to 2.1.

[0053] As in different embodiments, the number average molecular weight of the aqueous binder can be 40000, 45000, 50000, 55000, 60000, 65000, 70000, or a range consisting of any two of them; and the molecular weight distribution width index Mw / Mn of the aqueous binder can be 1.1, 1.2, 1.5, 1.6, 1.8, 2, 2.1, or a range consisting of any two of them.

[0054] In some embodiments of the present application, the number average molecular weight of the aqueous binder is 60000 to 65000; and the molecular weight distribution width index of the aqueous binder is 1.1 to 1.35.

[0055] Another aspect of the present application provides a preparation method of any one of the above aqueous binders, comprising the following steps: mixing the components in proportion under a protective atmosphere, uniformly, and then discharging after reaction at 25 to 90°C, and performing neutralization treatment.

[0056] In actual operation, nitrogen can be introduced into the reaction system to remove oxygen, so that the reaction is carried out under a protective atmosphere. During the reaction, stirring operation is accompanied, and the reaction temperature is controlled within a limited range.

[0057] The neutralization treatment can include adding an alkali solution to the material to adjust the pH to 7-8, such as 7. The alkali solution can include ammonia water, sodium hydroxide aqueous solution, calcium hydroxide aqueous solution, magnesium hydroxide aqueous solution, etc., such as ammonia water with a mass fraction of 1%-15%, sodium hydroxide aqueous solution with a mass fraction of 0.1%-10%, calcium hydroxide aqueous solution can be saturated calcium hydroxide aqueous solution, etc.

[0058] In the specific embodiments of the present application, after the reaction, the product is vacuumed to remove residual monomers, and then cooled and discharged.

[0059] In the specific embodiments of the present application, the uniform mixing includes adding the acrylamide monomer, the unsaturated acid monomer, the acrylic ester monomer, and the chain transfer agent into water, and then adding a pH adjuster to adjust the pH of the mixed system to 1-6.

[0060] In the specific embodiments of the present application, the reaction time is 1-96h, such as 12-72h. In different embodiments, the reaction time can be 1h, 5h, 12h, 18h, 24h, 48h, 60h, 72h, etc.

[0061] The present application provides an application of any one of the above-mentioned water-based binders in the preparation of carbon-coated aluminum foil.

[0062] Another aspect of the present application provides a carbon-coated aluminum foil, which includes an aluminum foil substrate and a carbon coating layer arranged on the surface of the aluminum foil substrate, and the carbon coating layer is prepared from a slurry containing any one of the above-mentioned water-based binders.

[0063] In actual operation, the slurry can be adjusted according to the actual composition of the carbon coating layer. For example, the slurry can include the following components by mass percentage: 6% of the water-based binder (calculated by solid content), 6% of conductive carbon black, and 88% of water. When the water-based binder of the present application is used, the solid content of the water-based binder is adjusted to 15%-25% using water.

[0064] Example 1

[0065] The present embodiment provides a preparation method of a water-based binder, which includes the following steps:

[0066] (1) The acrylamide monomer 75 parts, the unsaturated acid monomer 10 parts, the acrylic ester monomer 15 parts, the chain transfer agent 2 parts, deionized water 300 parts, and an appropriate amount of pH adjuster are weighed by weight fraction, respectively; wherein the acrylamide monomer is N,N-dimethyl acrylamide and acrylamide with a mass ratio of 1.5:1, the unsaturated acid monomer is acrylic acid, the acrylic ester monomer is polyethylene glycol (480) methyl ether acrylate (CAS: 32171-39-4), the chain transfer agent is dodecyl mercaptan, and the pH adjuster is a 1wt% sulfuric acid aqueous solution.

[0067] (2) Under the atmosphere of nitrogen, deionized water was added into the reaction kettle and stirred to remove oxygen completely; then acrylamide monomer, unsaturated acid monomer, acrylic ester monomer and chain transfer agent were added into the reaction kettle, followed by adding pH regulator to adjust the pH of the mixture in the reaction kettle to 3.0; under the atmosphere of nitrogen, the temperature was increased to 70℃, and the reaction was stirred at a speed of 350 rpm for 30 h, then the temperature was decreased, and partial residual monomer was removed by vacuumization, calcium hydroxide solution was added to adjust the pH to 7, thereby obtaining the aqueous binder.

[0068] Example 2

[0069] This example refers to the preparation method of Example 1, the only difference being that in step (2), the amount of pH regulator is different.

[0070] In step (2) of this example, the pH regulator was added to adjust the pH of the mixture in the reaction kettle to 1.0.

[0071] Example 3

[0072] This example refers to the preparation method of Example 1, the only difference being that in step (2), the amount of pH regulator is different.

[0073] In step (2) of this example, the pH regulator was added to adjust the pH of the mixture in the reaction kettle to 2.0.

[0074] Example 4

[0075] This example refers to the preparation method of Example 1, the only difference being that in step (2), the amount of pH regulator is different.

[0076] In step (2) of this example, the pH regulator was added to adjust the pH of the mixture in the reaction kettle to 5.0.

[0077] Example 5

[0078] This example refers to the preparation method of Example 1, the only difference being that in step (1), the composition of acrylamide monomer is different.

[0079] In step (1) of this example, the acrylamide monomer was N,N-dimethyl acrylamide and acrylamide with a mass ratio of 1:1.

[0080] Example 6

[0081] This example refers to the preparation method of Example 1, the only difference being that in step (1), the composition of acrylamide monomer is different.

[0082] In step (1) of this example, the acrylamide monomer was N,N-dimethylacrylamide and acrylamide in a mass ratio of 2:1.

[0083] Example 7

[0084] This example refers to the preparation method of Example 1, except that in step (1) the composition of the acrylamide monomer is different.

[0085] In step (1) of this example, the acrylamide monomer was N,N-dimethylacrylamide.

[0086] Example 8

[0087] This example refers to the preparation method of Example 1, except that in step (1) the composition of the acrylamide monomer is different.

[0088] In step (1) of this example, the acrylamide monomer was acrylamide.

[0089] Example 9

[0090] This example refers to the preparation method of Example 1, except that in step (1) the amounts of the monomers are different.

[0091] In step (1) of this example, the monomers included 65 parts of an acrylamide monomer, 14 parts of an unsaturated acid monomer, and 21 parts of an acrylate monomer.

[0092] Example 10

[0093] This example refers to the preparation method of Example 1, except that in step (1) the amount of chain transfer agent is different.

[0094] In step (1) of this example, the amount of chain transfer agent was 0.5 parts.

[0095] Example 11

[0096] This example refers to the preparation method of Example 1, except that in step (1) the amount of chain transfer agent is different.

[0097] In step (1) of this example, the amount of chain transfer agent was 3 parts.

[0098] Example 12

[0099] This example refers to the preparation method of Example 1, except that in step (1) the type of acrylate monomer is different.

[0100] In step (1) of this example, the acrylate monomer was 2-methyl-2-hydroxyethyl acrylate phosphate ester.

[0101] Comparative Example 1

[0102] Comparative Example 1 refers to the preparation method of Example 1, the difference is that in step (2), the type of unsaturated acid monomer is different, and the amount of pH regulator is different.

[0103] In Comparative Example 1, equal weight of sodium acrylate is used to replace the acrylate in Example 1; in step (2) of Comparative Example 1, a pH regulator is added to adjust the pH of the mixture in the reaction kettle to 6.5.

[0104] Comparative Example 2

[0105] Comparative Example 2 refers to the preparation method of Example 1, the difference is that in step (2), the type and amount of pH regulator are different.

[0106] In step (2) of Comparative Example 2, a pH regulator is added to adjust the pH of the mixture in the reaction kettle to 7.0; the pH regulator is a 0.1% sodium hydroxide aqueous solution.

[0107] Comparative Example 3

[0108] Comparative Example 3 refers to the preparation method of Example 1, the difference is that in step (2), the type and amount of pH regulator are different.

[0109] In step (2) of Comparative Example 3, a pH regulator is added to adjust the pH of the mixture in the reaction kettle to 9.0; the pH regulator is a 0.1% sodium hydroxide aqueous solution.

[0110] Comparative Example 4

[0111] Comparative Example 4 refers to the preparation method of Example 1, the difference is that in step (1), the amount of each monomer is different.

[0112] In step (1) of Comparative Example 4, the monomers include 40 parts of acrylamide monomer, 30 parts of unsaturated acid monomer, and 30 parts of acrylate monomer.

[0113] Comparative Example 5

[0114] Comparative Example 5 provides a preparation method of a water-based adhesive, comprising the following steps:

[0115] (1) 75 parts of acrylamide monomer, 10 parts of unsaturated acid monomer, 15 parts of acrylate monomer, 2 parts of chain transfer agent, 300 parts of deionized water, and 1 part of ammonium persulfate are weighed according to the weight fraction; wherein the acrylamide monomer is N,N-dimethyl acrylamide and acrylamide with a mass ratio of 1.5:1, the unsaturated acid monomer is acrylate, the acrylate monomer is polyethylene glycol (480) acrylate, and the chain transfer agent is dodecyl mercaptan.

[0116] (2) Under the nitrogen atmosphere, deionized water was added into the reaction kettle and stirred to remove oxygen; then acrylamide monomer, unsaturated acid monomer, acrylic ester monomer and chain transfer agent were added into the reaction kettle, and a proper amount of 0.1% sodium hydroxide was added to adjust the pH to neutral, followed by adding ammonium persulfate, heating to 80°C, and stirring at 350 rpm for 30 h. After cooling, the water-based adhesive was obtained.

[0117] Experimental Example 1

[0118] The monomer conversion rate of the preparation of the water-based adhesive prepared in different examples and comparative examples, the molecular weight of the water-based adhesive, and the molecular weight distribution were tested, and the test results are shown in Table 1.

[0119] Table 1 Molecular weight and molecular weight distribution of different water-based adhesives

[0120] Experimental Example 2

[0121] The water-based adhesives prepared in different examples and comparative examples were used to prepare carbon-coated aluminum foil, and the prepared carbon-coated aluminum foil was tested, and the test results are shown in Table 2.

[0122] The preparation of the carbon-coated aluminum foil includes:

[0123] (a) The water-based adhesives of Examples 1-12 and Comparative Examples 1-5 were blended with conductive carbon black in a certain proportion, and ground to a fineness of <1 μm using a grinder to prepare a slurry of carbon coating; wherein the mass ratio of water-based adhesive: conductive carbon black SP: deionized water was 6:6:88, and the amount of water-based adhesive was calculated based on its solid content; before preparing the slurry, the solid content of the water-based adhesive was adjusted to 20% using water.

[0124] (b) The prepared carbon-coated aluminum foil slurry was input into the feeding system of the coating machine, and a 12 μm smooth aluminum foil was selected as the substrate, the coating speed was 70 m / min, and the drying temperature was 90-120°C to obtain a carbon-coated aluminum foil with a coating thickness of 1.5 μm.

[0125] The test items include the following contents:

[0126] The prepared carbon-coated aluminum foil was cut into a test sample (200 mm x 25 mm in length and width), the metal side was pasted on a stainless steel plate, and 3M tape (Scotch 600 / 25 mm wide) was pasted on the surface of the coating layer, and a 1 kg roller was rolled back and forth three times. According to the test conditions of national standard GB / T 2792-2014, the size of the cohesion between the carbon-coated layer and the aluminum foil current collector was tested using a universal testing machine.

[0127] 300 times electrolyte wiping: using a cotton swab to dip electrolyte (1 mol / L LiPF6, solvent is EC and DMC in a volume ratio of 1:1), back and forth wiping at the same position of the carbon-coated aluminum foil, wiping distance is about 6 cm, round trip is recorded as 1 time, record and observe whether the aluminum foil substrate leaks after 300 times of wiping experiment.

[0128] Table 2 Test results of carbon-coated aluminum foils prepared by different water-based binders

[0129] Note: Comparative Example 2 and Comparative Example 3 did not react to obtain a water-based binder, and this test was not performed.

[0130] From the above test results, it can be seen that the water-based binder of the present application has a narrow molecular weight distribution, excellent dispersion performance and bonding performance, and can be used for the preparation of slurry of lithium ion battery active material, especially for the preparation of carbon-coated aluminum foil.

[0131] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An aqueous binder prepared mainly from the following components in parts by weight: 60-80 parts of an acrylamide-based monomer, 10-20 parts of an unsaturated acid-based monomer, 10-20 parts of an acrylic ester-based monomer, 0.1-3 parts of a chain transfer agent, 100-400 parts of water, and a pH adjusting agent; the amount of the pH adjusting agent is adjusted so that the pH of the mixed system of the components is 1-6. The amount of the pH adjusting agent is adjusted so that the pH of the mixed system of the components is 2-5.

2. The aqueous binder of claim 1, wherein, The acrylamide-based monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, diacetone acrylamide, N,N-dimethyl acrylamide, t-butyl acrylamide, N-methoxymethyl acrylamide, N-hydroxyethyl acrylamide, and acryloyl morpholine.

3. The aqueous binder of claim 1, wherein, The acrylamide-based monomer includes N,N-dimethyl acrylamide and acrylamide.

4. The aqueous binder of claim 1, wherein, The mass ratio of the N,N-dimethyl acrylamide to the acrylamide is (1-2):

1. The acrylamide-based monomer accounts for ≥70% of the mass percentage of all monomers.

5. The aqueous binder of claim 1, wherein, The unsaturated acid-based monomer includes at least one of an unsaturated carboxylic acid-based monomer or an inorganic salt thereof, and an unsaturated sulfonic acid-based monomer or an inorganic salt thereof.

6. The aqueous binder of claim 1, wherein, The unsaturated carboxylic acid-based monomer includes at least one of (meth)acrylic acid, maleic anhydride, itaconic acid, and fumaric acid. The unsaturated sulfonic acid-based monomer includes at least one of styrene sulfonic acid, allyl sulfonic acid, and methacrylic acid sulfonic acid. The acrylic ester-based monomer includes at least one of an alkyl (meth)acrylate, an alkylhydroxy (meth)acrylate, a polyethylene glycol methyl ether acrylate, di(hydroxyethyl acrylate) phosphoric acid, 2-methyl-2-hydroxyethyl acrylate phosphoric acid ester, and di[2-(methacryloyloxy)ethyl] phosphoric acid ester.

7. The aqueous binder of claim 1, wherein, The pH adjusting agent includes at least one of sulfuric acid, sulfonic acid, phosphoric acid, hydrochloric acid, acetic acid, citric acid, lactic acid, oxalic acid, and malic acid.

8. The aqueous binder of claim 1, wherein, The chain transfer agent includes a thiol-based chain transfer agent.

9. A method for preparing the aqueous binder according to any one of claims 1-8, comprising the following steps: mixing the components in proportion under a protective atmosphere, and then discharging after reaction at 25-90°C, and performing neutralization treatment. The carbon coating layer is prepared from a slurry containing the aqueous binder according to any one of claims 1-8.

10. A carbon-coated aluminum foil comprising an aluminum foil substrate and a carbon coating disposed on a surface of the aluminum foil substrate, wherein, ​

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