An aqueous binder for hard carbon anode materials of sodium-ion batteries

Abstract

The present invention relates to the technical field of aqueous adhesives, and provides an aqueous adhesive for a hard carbon negative electrode material of a sodium-ion battery, which is composed of an aqueous acrylic adhesive and a styrene-butadiene rubber latex adhesive in a weight ratio of 9:1 - 3:7; the preparation method of the aqueous acrylic adhesive includes: mixing a first hydrophilic monomer with the chemical formula CH2=CR 1 R 2 and a first hydrophobic monomer with the chemical formula CH2=CR 3 R 4 , adding them into water, heating to a preset reaction temperature, dropping a first water-soluble initiator solution, continuing the reaction for 0 - 8 hours after dropping, and then dropping a second hydrophilic monomer with the chemical formula CH2=CR 5 R 6 and a second hydrophobic monomer with the chemical formula CH2=CR 7 R 8 , after the dropping is completed, continuing the heat preservation reaction for 0 - 6 hours, and then cooling to obtain the product. The aqueous adhesive of the present application combines the characteristics of the aqueous acrylic adhesive and the styrene-butadiene rubber latex adhesive, has a good dispersion effect on the hard carbon material, and has a good adhesion to the electrode sheet, and can improve the electrical performance of the sodium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous adhesives, and relates to an aqueous adhesive for hard carbon anode materials of sodium-ion batteries. Background Art

[0002] Although the capacity of sodium-ion batteries is lower than that of lithium-ion batteries, they have high safety and low cost, and can meet the application scenarios of energy storage power stations, low-speed electric vehicles, electric tricycles, etc. Amorphous materials, especially hard carbon materials that are difficult to graphitize, are widely used as anode materials in sodium-ion batteries because of their higher sodium storage capacity. Compared with graphite particles, hard carbon particles have a lower particle size and a higher specific surface area, and are more difficult to stably disperse and bond to the current collector. When using the traditional graphene anode binder SBR (styrene-butadiene rubber) latex, due to the point bonding method of SBR, it is difficult to firmly bond finer hard carbon particles together, and the phenomenon of "powder falling off" is very likely to occur. Moreover, SBR does not have the ability to disperse hard carbon particles, and only relies on CMC (cellulose) in the formula for dispersion, and the dispersion ability is limited. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide an aqueous adhesive for hard carbon anode materials of sodium-ion batteries.

[0004] The technical solution of the present invention is as follows:

[0005] An aqueous adhesive for hard carbon anode materials of sodium-ion batteries is composed of an aqueous acrylic adhesive and a styrene-butadiene rubber emulsion adhesive in a weight ratio of 9:1 - 3:7;

[0006] The preparation method of the aqueous acrylic adhesive includes: mixing a first hydrophilic monomer with the chemical formula CH2=CR 1 R 2 and a first hydrophobic monomer with the chemical formula CH2=CR 3 R 4 , adding them to water, heating to a preset reaction temperature, dropping a first water-soluble initiator solution, continuing to react for 0 - 8 hours after dropping, and then dropping a second hydrophilic monomer with the chemical formula CH2=CR 5 R 6 and a second hydrophobic monomer with the chemical formula CH2=CR 7 R 8 , after dropping, continuing to keep the temperature and react for 0 - 6 hours, and then cooling to obtain it;

[0007] The proportion of the first hydrophobic monomer in the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is 10 - 70%;

[0008] R 1 、R 3 、R5 and R 7 independently selected from H or C1-C4 alkyl;

[0009] R 2 and R 6 independently selected from C1-C18 carboxylates, C1-C18 sulfonates, C1-C18 sulfates, C1-C18 phosphates, hydroxy-containing C1-C4 substituted alkyls, amine-containing C1-C4 substituted alkyls, carboxyl-containing C1-C8 substituted alkyls, amide groups of the formula CONR 9 R 10 or polyether-modified esters of the formula COO(CH2CH2O) m R 11 wherein R 9 and R 10 are independently selected from H, methyl or ethyl, and R 11 is selected from H, C1-C4 alkyl or C1-C4 substituted alkyl, and m = 1-30;

[0010] R 4 and R 8 are independently selected from ester groups of the formula COOR 12 phenyl, substituted phenyl or nitrile groups, wherein R 12 is a C1-C22 alkyl.

[0011] Preferably, the weight ratio of the aqueous acrylic adhesive to the styrene-butadiene rubber latex adhesive is 8:2 - 4:6.

[0012] Preferably, the weight concentrations of the aqueous acrylic adhesive and the styrene-butadiene rubber are 10-50% respectively.

[0013] Preferably, the proportion of the first hydrophobic monomer in the total weight of the first hydrophilic monomer and the first hydrophobic monomer is 20-60%.

[0014] Preferably, the ratio of the total weight of the second hydrophilic monomer and the second hydrophobic monomer to the total weight of the first hydrophilic monomer and the first hydrophobic monomer is 0 or 1:9 - 9:1.

[0015] More preferably, the ratio of the total weight of the second hydrophilic monomer and the second hydrophobic monomer to the total weight of the first hydrophilic monomer and the first hydrophobic monomer is 3:7 - 7:3.

[0016] Preferably, the proportion of the second hydrophobic monomer in the total weight of the second hydrophilic monomer and the second hydrophobic monomer does not exceed the proportion of the first hydrophobic monomer in the total weight of the first hydrophilic monomer and the first hydrophobic monomer.

[0017] More preferably, the proportion of the second hydrophobic monomer in the total weight of the second hydrophilic monomer and the second hydrophobic monomer does not exceed 70% of the proportion of the first hydrophobic monomer in the total weight of the first hydrophilic monomer and the first hydrophobic monomer.

[0018] Preferably, while adding dropwise the second hydrophilic monomer with the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer with the chemical formula CH2=CR 7 R 8 dropwise add a second water-soluble initiator solution.

[0019] More preferably, the dropping time for adding dropwise the second water-soluble initiator solution is 2 h - 6 h.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The water-based adhesive of the present application combines the advantages of acrylate adhesives and styrene-butadiene rubber adhesives. The acrylate adhesive provides a high coating effect on hard carbon particles and a high bonding strength to the electrode sheet, while the styrene-butadiene rubber adhesive provides flexibility and filling properties. Therefore, the water-based adhesive of the present application has good coating and dispersibility for the hard carbon negative electrode material, high adhesion to the electrode sheet, and good flexibility.

[0022] 2. By controlling the polymerization process, the acrylate polymer chains in the acrylate emulsion prepared in the present application have good hydrophilic-hydrophobic properties. The hydrophobic chain segments achieve the coating of the surface of hard carbon particles, and the hydrophilic chain segments extend in the aqueous phase and entangle with each other. The hard carbon particles are completely coated by the acrylate polymer chains, thereby achieving the bulk bonding of the entire electrode sheet, increasing the interaction force between hard carbon particles, improving stability, and reducing the "powder dropping" phenomenon. In addition, a certain proportion of SBR emulsion with a low Tg is compounded in the water-based adhesive of the present application. On the one hand, it can effectively reduce the overall hardness of the electrode sheet. On the other hand, the increase in the flexibility of the adhesive can also promote the contact tightness between hard carbon particles and the current collector, and to a certain extent, increase the adhesion between the electrode sheet and the current collector. Specific Embodiments

[0023] The technical solutions of the present invention are further described and illustrated below through specific embodiments.

[0024] The present invention provides a water-based adhesive for a hard carbon negative electrode material of a sodium-ion battery, which is composed of a water-based acrylic adhesive and a styrene-butadiene rubber emulsion adhesive in a weight ratio of 9:1 - 3:7;

[0025] The preparation method of the water-based acrylic adhesive includes: mixing the first hydrophilic monomer with the chemical formula CH2=CR1R2 and the chemical formula CH2=CR 3 R 4Mix with the first hydrophobic monomer, add it to water, heat up to the preset reaction temperature, dropwise add the first water-soluble initiator solution, continue the reaction for 0 - 8 hours after the dropping is completed, then dropwise add the second hydrophilic monomer with the chemical formula CH2=CR5R6 and the second hydrophobic monomer with the chemical formula CH2=CR7R8. After the dropping is completed, continue the heat preservation reaction for 0 - 6 hours, and then cool down to obtain the product;

[0026] Let the weight of the first hydrophilic monomer be A, the weight of the first hydrophobic monomer be B, the weight of the second hydrophilic monomer be C, and the weight of the second hydrophobic monomer be D.

[0027] The proportion of the first hydrophobic monomer in the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is 10 - 70%, that is, 10% ≤ B / (A + B) ≤ 70%; R1, R3, R5, and R7 are each independently selected from H or C1 - C4 alkyl;

[0028] R2 and R6 are each independently selected from C1 - C18 carboxylates, C1 - C18 sulfonates, C1 - C18 sulfates, C1 - C18 phosphates, C1 - C4 substituted alkyl groups containing hydroxyl groups, C1 - C4 substituted alkyl groups containing amino groups, C1 - C8 substituted alkyl groups containing carboxyl groups, amide groups with the chemical formula CONR9R10, or polyether-modified esters with the chemical formula COO(CH2CH2O)mR11, where R9 and R10 are each independently selected from H, methyl, or ethyl, R11 is selected from H, C1 - C4 alkyl, or C1 - C4 substituted alkyl, and m = 1 - 30;

[0029] R 4 and R 8 are each independently selected from ester groups with the chemical formula COOR 12 , phenyl, substituted phenyl, or nitrile groups, where R 12 is C1 - C22 alkyl.

[0030] In this application, for example, the first hydrophilic monomer and the second hydrophilic monomer can be selected from acrylic acid (AA), methacrylic acid (MAA), sodium acrylate (AANa), lithium acrylate (AALi), sodium methacrylate (MAANa), lithium methacrylate (MAALi), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl methacrylate (HPMA), 2-hydroxypropyl acrylate (HPA), acrylamide (AM), N,N-dimethylacrylamide (DMAA), monomethoxy polyether (meth)acrylate, etc.

[0031] In the present application, for example, the first hydrophobic monomer and the second hydrophobic monomer may be selected from acrylonitrile (AN), methyl methacrylate (MMA), methyl acrylate (MA), ethyl methacrylate (EMA), ethyl acrylate (EA), lauryl methacrylate (LMA), lauryl acrylate (LA), stearyl methacrylate (SMA), stearyl acrylate (SA), isooctyl methacrylate (2-EHA), isooctyl acrylate (2-EHMA), n-butyl methacrylate (BMA), n-butyl acrylate (BA), styrene (St), p-methylstyrene, etc.

[0032] In a preferred embodiment of the present application, the weight ratio of the aqueous acrylic adhesive to the styrene-butadiene rubber latex adhesive is 8:2 - 4:6. More preferably, the weight ratio of the aqueous acrylic adhesive to the styrene-butadiene rubber latex adhesive is 7:3 - 4:6. For example, the weight ratio may be 7:3, 6.5:3.5, 6:4, 5.5:4.5, 5:5, 4.5:5.5, or 4:6.

[0033] In a preferred embodiment of the present application, the weight concentrations of the aqueous acrylic adhesive and the styrene-butadiene rubber are 10 - 50% respectively.

[0034] In a preferred embodiment of the present application, the proportion of the first hydrophobic monomer in the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is 20 - 60%, that is, 20% ≤ B / (A + B) ≤ 60%. More preferably, 30% ≤ B / (A + B) ≤ 60%. For example, B / (A + B) = 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0035] In a preferred embodiment of the present application, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is 0 or 1:9 - 9:1, that is, (C + D) / (A + B) = 0 or (C + D) / (A + B) = 1:9 - 9:1. When (C + D) / (A + B) = 0, those skilled in the art know that the first hydrophilic monomer and the first hydrophobic monomer represent all the monomers, and no second hydrophilic monomer and second hydrophobic monomer are added dropwise in the above preparation method.

[0036] In a more preferred embodiment of the present application, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is 3:7 - 7:3, that is, (C + D) / (A + B) = 3:7 - 7:3. For example, (C + D) / (A + B) may be 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.5:3.5, or 7:3.

[0037] In a preferred embodiment of the present application, the proportion of the second hydrophobic monomer in the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer does not exceed the proportion of the first hydrophobic monomer in the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer, that is, D / (C + D) ≤ B / (A + B). For example, if B / (A + B) = 50%, then D / (C + D) ≤ 50%, and it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0038] In a more preferred embodiment of the present application, the proportion of the second hydrophobic monomer in the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer does not exceed 70% of the proportion of the first hydrophobic monomer in the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer, that is, D / (C + D) ≤ 0.7B / (A + B). For example, if B / (A + B) = 50%, then D / (C + D) ≤ 35%, and it can be 5%, 10%, 15%, 20%, 25%, 30% or 35%.

[0039] In the present application, the first water-soluble initiator can be selected from one or a combination of persulfide initiators, peroxide initiators, azo initiators and redox initiators, and the dosage of the first water-soluble initiator is 0.05 - 1.0% of the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer. Preferably, the dosage of the first water-soluble initiator is 0.2 - 1.0% of the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer. More preferably, the dosage of the first water-soluble initiator is 0.3 - 0.8% of the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer, and specifically, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%.

[0040] In the present application, the second hydrophilic monomer with the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer with the chemical formula CH2=CR 7 R 8 are added dropwise over a period of 30 min - 300 min.

[0041] In a preferred embodiment of the present application, while adding dropwise the second hydrophilic monomer with the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer with the chemical formula CH2=CR 7 R 8 a second water-soluble initiator solution is added dropwise.

[0042] In a more preferred embodiment of the present application, the dropping time of the second water-soluble initiator solution is 2 h - 6 h. In the present application, the second water-soluble initiator can be selected from one or a combination of several of persulfide initiators, peroxide initiators, azo initiators, and redox initiators. The amount of the second water-soluble initiator is 0.05 - 1.0% of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer. Preferably, the amount of the second water-soluble initiator is 0.2 - 1.0% of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer. More preferably, the amount of the second water-soluble initiator is 0.3 - 0.8% of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer. Specifically, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%.

[0043] In the present application, the first water-soluble initiator and the second water-soluble initiator can be respectively selected from persulfide initiators. For example, it can be ammonium persulfate, potassium persulfate, sodium persulfate, etc.; the first water-soluble initiator and the second water-soluble initiator can also be respectively selected from peroxide initiators. For example, it can be selected from hydrogen peroxide; the first water-soluble initiator and the second water-soluble initiator can also be respectively selected from azo initiators. For example, it can be selected from azodiisobutyramidine hydrochloride (AIBA), azodiisobimidazoline hydrochloride (AIBI), etc.; the first water-soluble initiator and the second water-soluble initiator can also be respectively selected from redox initiators. For example, it can be selected from 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.

[0044] In the present application, after cooling, an acid or a base is added to adjust the pH of the aqueous binder to 6.5 - 7.5.

[0045] The technical solutions of the present invention are further described and illustrated below according to each embodiment. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0046] Preparation Example 1

[0047] 400 parts of water was added to a reaction flask, 40 parts of AA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 10 parts of AM monomer and 50 parts of AN monomer were added, and stirring was carried out at a rotation speed of 200 rpm. The temperature was raised to 70 °C, and 40 parts of an aqueous solution of ammonium persulfate with a concentration of 2 wt% was added dropwise over 300 min. After the dropwise addition of the ammonium persulfate aqueous solution was completed, the reaction temperature was maintained at 70 °C for 2 hours. After the heat preservation was completed, a small amount of water was added to adjust the solid content and an appropriate amount of sodium bicarbonate was added to adjust the pH to neutral to obtain an aqueous acrylic binder with a solid content of 16.1 wt% and a viscosity (25 °C) of 4100 mPa·s.

[0048] Preparation Example 2

[0049] Add 200 parts of water into a reaction flask, add 30 parts of AA monomer, add sodium bicarbonate to adjust the pH to neutral, add 10 parts of AM monomer and 40 parts of AN monomer, stir at a speed of 200 rpm, heat up to 70 °C, dropwise add 40 parts of an aqueous ammonium persulfate solution with a concentration of 2 wt%, and the dropping time is 300 min; 60 min after the start of the dropwise addition of the aqueous ammonium persulfate solution, start to dropwise add 150 parts of water and 20 parts of AA monomer, and the dropping time is 100 min. After the dropwise addition of the aqueous ammonium persulfate solution is completed, keep the reaction temperature at 70 °C and react for 2 hours. After the heat preservation is completed, add a small amount of water to adjust the solid content and an appropriate amount of sodium bicarbonate to adjust the pH to neutral to obtain an aqueous acrylic adhesive with a solid content of 16.5% and a viscosity (25 °C) of 4200 mPa·s.

[0050] Preparation Example 3

[0051] Add 250 parts of water into a reaction flask, add 50 parts of MAA monomer, add sodium bicarbonate to adjust the pH to neutral, add 15 parts of AM monomer, 30 parts of EA monomer and 5 parts of BA monomer, stir at a speed of 200 rpm, heat up to 70 °C, dropwise add 40 parts of an aqueous ammonium persulfate solution with a concentration of 2 wt%, and the dropping time is 480 min; 10 min after the start of the dropwise addition of the aqueous ammonium persulfate solution, start to dropwise add 150 parts of water, and the dropping time is 150 min. After the dropwise addition of the aqueous ammonium persulfate solution is completed, keep the reaction temperature at 70 °C and react for 2 hours. After the heat preservation is completed, add a small amount of water to adjust the solid content and an appropriate amount of sodium bicarbonate to adjust the pH to neutral to obtain an aqueous acrylic adhesive with a solid content of 16.0% and a viscosity (25 °C) of 4100 mPa·s.

[0052] Preparation Example 4

[0053] Add 200 parts of water into a reaction flask, add 30 parts of MAA monomer, add sodium bicarbonate to adjust the pH to neutral, add 15 parts of AM monomer, 20 parts of EA monomer and 5 parts of BA monomer, stir at a speed of 200 rpm, heat up to 70 °C, dropwise add 10 parts of an aqueous ammonium persulfate solution with a concentration of 3.5 wt%, and the dropping time is 480 min. After the dropwise addition is completed, keep the reaction temperature at 70 °C and react for 2 hours. Then start to dropwise add 9 parts of EA monomer and 21 parts of MAA monomer, and the dropping time is 240 min. While dropping EA monomer and MAA monomer, dropwise add 5 parts of an aqueous ammonium persulfate solution with a concentration of 3 wt%, and the dropping time is 180 minutes. After all the dropping is completed, keep the reaction temperature at 70 °C and react for 2 hours. After the heat preservation is completed, add water to adjust the solid content and sodium bicarbonate to adjust the pH to neutral to obtain an aqueous acrylic adhesive with a solid content of 16.3% and a viscosity (25 °C) of 4000 mPa·s.

[0054] Example 1

[0055] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 1 and an SBR binder (Zeon BM-430B) at a weight ratio of 3:1.

[0056] Example 2

[0057] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 2 and an SBR binder (Zeon BM-430B) at a weight ratio of 1:1.

[0058] Example 3

[0059] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 3 and an SBR binder (Zeon BM-430B) at a weight ratio of 5:1.

[0060] Example 4

[0061] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 4 and an SBR binder (Ailon AL-1002) at a weight ratio of 3:1.

[0062] Example 5

[0063] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 2 and an SBR binder (Ailon AL-1002) at a weight ratio of 1:1.

[0064] Example 6

[0065] The aqueous adhesive is composed of the aqueous acrylic adhesive prepared in Preparation Example 3 and an SBR binder (Ailon AL-1002) at a weight ratio of 2:3.

[0066] Comparative Example 1

[0067] 250 parts of water was added to a reaction flask, 80 parts of AA monomer was added, the pH was adjusted to neutral with sodium bicarbonate, 12 parts of AM monomer and 8 parts of AN monomer were added, and the mixture was stirred at 200 rpm to fully mix the monomers. The temperature was raised to 70 °C, and 40 parts of an aqueous ammonium persulfate solution with a concentration of 2 wt% was added dropwise over 300 min. 10 min after the start of the dropwise addition of the aqueous ammonium persulfate solution, 150 parts of water was added dropwise over 150 min. After the dropwise addition of the aqueous ammonium persulfate solution was completed, the reaction temperature was maintained at 70 °C for 2 hours. After the heat preservation was completed, water was added to adjust the solid content and sodium bicarbonate was added to adjust the pH to neutral, obtaining an aqueous acrylic adhesive with a solid content of 16.2% and a viscosity (25 °C) of 4100 mPa·s.

[0068] The aqueous adhesive is composed of the above aqueous acrylic adhesive and an SBR binder (Zeon BM-430B) at a weight ratio of 3:1.

[0069] Comparative Example 2

[0070] Add 250 parts of water to the reaction flask, add 20 parts of AA monomer, adjust the pH to neutral with sodium bicarbonate, add 8 parts of AM monomer and 72 parts of AN monomer, stir at 200 rpm to fully mix the monomers, heat up to 70 °C, and dropwise add 40 parts of an aqueous ammonium persulfate solution with a concentration of 2 wt% over 300 min; 10 min after the start of the dropwise addition of the aqueous ammonium persulfate solution, start dropping 150 parts of water over 150 min. After the dropwise addition of the aqueous ammonium persulfate solution is completed, maintain the reaction temperature at 70 °C and react for 2 hours. After the heat preservation is completed, add water to adjust the solid content and sodium bicarbonate to adjust the pH to neutral to obtain an aqueous acrylic binder with a solid content of 16.2% and a viscosity (25 °C) of 3800 mPa·s. During the reaction process, it was found that after the dropwise addition of ammonium persulfate for 30 minutes, a large amount of insoluble filter residue appeared in the reaction system, and a homogeneous aqueous acrylic binder could not be obtained.

[0071] Comparative Example 3

[0072] The SBR binder (Zeon BM-430B) and sodium carboxymethylcellulose are composed in a weight ratio of 1:1.

[0073] Performance Test

[0074] The formulation ratio of the hard carbon formula slurry is binder: SP: hard carbon anode material = 3.5:1:95.5.

[0075] Calculate the amount of water added based on the solid content of the anode slurry before adjusting the viscosity at 45%. Mix the aqueous adhesives to be tested in Examples 1-6 and Comparative Examples 1-3 with 50% water, disperse at 300 rpm for 10-20 minutes, then add 1 part of SP conductive carbon black, stir at 150 rpm for 10 minutes, and then stir at 800 rpm at high speed for 120 minutes; lower the rotation speed to 300 rpm, add 50% of the hard carbon anode material, disperse for 20 minutes, then add the remaining 50% of the hard carbon anode material and the remaining 50% of the water and disperse for 30 minutes, and then stir at 800 rpm at high speed for 120 minutes. After the high-speed stirring is completed, adjust the viscosity (25 °C) to be between 3000 and 4000 mPa·s, and filter through a 150-mesh filter screen to complete the discharging.

[0076] Place the copper foil on the coater, adjust the scraper scale of the wet film former, pour the filtered slurry evenly, and send it into an environment of 100 °C for air drying until dry, and cut out a pole piece with a specification of 12.5 cm × 5 cm and a single-sided surface density of 100-110 g / m 2 of the pole piece.

[0077] Test method for bulk density: Select five points in the middle and at the four corners of the pole piece, measure the thickness of the pole piece with a micrometer and record it. After removing one maximum value and one minimum value, calculate the average thickness of the pole piece. Bulk density = pole piece surface density / (pole piece average thickness - copper foil average thickness).

[0078] Method for testing the resistance of the electrode sheet: Select a clean glass sheet with a size of 20 cm × 15 cm, weigh it as m1. Pour the filter material evenly at the short end, and use a 250-μm wet film applicator to evenly coat a 20 cm × 8 cm coating. Send the glass sheet into an environment at 100 °C for air drying for 30 min. Adjust the multimeter to an appropriate range, take out the dried glass sheet, place two current collectors at the short ends, measure and record the coating resistance value, and then weigh the coated glass sheet and record it as m2. Electrode sheet resistance = Coating resistance × (m2 - m1).

[0079] Method for testing the peel strength of the electrode sheet: Send the cut electrode sheet into a constant temperature room at 35% RH and place it for 30 minutes. With the coated surface facing outwards and the copper foil surface facing inwards, laminate two electrode sheets together, and send them into an electric roll press to roll the electrode sheet to 0.95 g / cm 3 , and then place it for another 30 minutes. During this period, select five stainless steel plates with a size of 12.5 cm × 5 cm, stick the corresponding double-sided tape on the stainless steel plates, and then laminate the electrode sheet on the double-sided tape with the coating facing downwards. Then stick a 2.5-cm-wide masking tape on the copper foil. After the electrode sheet and the steel plate are rolled back and forth once by the electric rolling roller under a certain pressure (1 kg), use an electronic peeling machine to test the adhesion of the electrode sheet; in the same way, just change the way of laminating the electrode sheet on the double-sided tape with the coating facing upwards to test the cohesion of the electrode sheet.

[0080] The softness is tested using a softness tester IMT-RRD01*1.

[0081] The results are shown in Table 1 below.

[0082] Table 1

[0083]

[0084] As can be seen from the data in Table 1, the water-based adhesive of this application combines the characteristics of acrylic emulsion adhesive and styrene-butadiene rubber latex adhesive, has a good dispersing effect on hard carbon active materials, has good softness, and has high adhesion to the electrode sheet.

[0085] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments are only preferred embodiments of the present invention, and the scope of implementation of the present invention cannot be limited thereby. That is, equivalent changes and modifications made according to the scope of the present invention patent and the content of the specification should still fall within the scope covered by the present invention. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. An aqueous binder for a hard carbon anode material of a sodium-ion battery, characterized in that, It is composed of an aqueous acrylic adhesive and a styrene-butadiene rubber latex adhesive in a weight ratio of 3:1; The preparation method of the aqueous acrylic adhesive: Add 400 parts of water into a reaction flask, add 40 parts of acrylic monomers, add sodium bicarbonate to adjust the pH to neutral, add 10 parts of acrylamide monomers and 50 parts of acrylonitrile monomers, stir at a speed of 200 rpm, heat up to 70 °C, and dropwise add 40 parts of an aqueous ammonium persulfate solution with a concentration of 2 wt% over 300 min; after the dropwise addition of the aqueous ammonium persulfate solution is completed, maintain the reaction temperature at 70 °C and react for 2 hours. After the heat preservation is completed, add water to adjust the solid content and an appropriate amount of sodium bicarbonate to adjust the pH to neutral to obtain the aqueous acrylic adhesive. The solid content is 16.1 wt%, and the viscosity at 25 °C is 4100 mPa•s.

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