An aqueous soft glue for improving the softness and processability of a hard carbon negative electrode sheet, a hard carbon negative electrode sheet and a preparation method thereof

Abstract

This application relates to the technical field of preparing hard carbon anode sheets for sodium-ion batteries, specifically disclosing an aqueous soft adhesive for improving the flexibility and processing performance of hard carbon anode sheets, the hard carbon anode sheet itself, and a method for preparing the same. The aqueous soft adhesive for improving the flexibility and processing performance of hard carbon anode sheets is obtained by a mixed polymerization reaction of a first monomer and a second monomer. The first monomer is acrylamide, and the second monomer is butyl acrylate. The aqueous soft adhesive is obtained as follows: materials are taken in parts by mass, 1 part surfactant and 1 part protective colloid are added to 100 parts water, then 30 parts of the first monomer and 50 parts of the second monomer are added, followed by 0.1 parts initiator. The mixture is heated to 70°C for a polymerization reaction for 10 hours to obtain the aqueous soft adhesive. Using the aqueous soft adhesive in combination with a polyacrylic acid-based aqueous binder to prepare hard carbon anode sheets can significantly improve the stability and processing performance of the sheets.

Description

Technical Field

[0001] This application relates to the field of preparation technology of hard carbon negative electrode sheets for sodium-ion batteries, specifically to an aqueous soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets, hard carbon negative electrode sheets and their preparation methods. Background Technology

[0002] Hard carbon is a type of carbon that does not graphitize after high-temperature treatment. Its internal crystals are arranged in a disordered manner with large interlayer spacing, which allows hard carbon anodes to store more charge in the same volume, thus improving the energy density and range of the battery.

[0003] Hard carbon materials are widely used as anode materials in sodium-ion batteries due to their high capacity and good rate performance. However, ensuring the stability and processing performance of hard carbon anode sheets is crucial in the fabrication process. Currently, the CMC (carboxymethyl cellulose) + SBR (styrene-butadiene rubber) system is a commonly used binder, but it has limitations in terms of the dispersibility and adhesion of hard carbon particles.

[0004] PAA (polyacrylic acid) waterborne adhesives, due to their abundant functional groups such as ester and cyano groups, have good affinity for hard carbon particles, effectively dispersing them and providing good adhesion. However, because PAA waterborne adhesives have a high Tg (glass transition temperature), the hard carbon negative electrode sheets produced are often hard and brittle, leading to problems such as cracking and material shedding during processing.

[0005] Currently, there is no effective solution that can simultaneously balance the stability and processing performance of hard carbon anode sheets. Summary of the Invention

[0006] In view of the above problems, this application proposes the following technical solution.

[0007] In the first aspect, this application proposes an aqueous soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets, and adopts the following technical solution.

[0008] A water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets, wherein the water-based soft adhesive is obtained by a mixed polymerization reaction of several first monomers and several second monomers.

[0009] The first monomer has the general formula CH2=CR1R2, where R1 is one of H or a C1-C4 alkyl group, and R2 is -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, or -COO(CH2CH2O). a H、-COO(CH2) bOne of the functional groups PO3H, -COOM, -(C6H5)COOM, -SO3M and -(C6H5)SO3M, wherein a = 1 to 40, b = 1 to 12, and M is selected from H, Li+, Na+ and K+.

[0010] The second monomer has the general formula CH2=CHCOOR3, wherein R3 is selected from C2-C18 alkyl groups or C2-C18 alkyl groups substituted with hydroxyl groups.

[0011] In the synthesis of all monomers of the water-based software, the molar percentage of all second monomers is greater than 50%.

[0012] By adopting the above technical solution, combining the above-mentioned water-based soft adhesive with PAA (polyacrylic acid) water-based adhesive to prepare hard carbon negative electrode sheets, the stability and processing performance of the electrode sheets can be significantly improved.

[0013] A preferred embodiment of the water-based soft adhesive for improving the flexibility and processability of hard carbon negative electrode sheets is that the water-based soft adhesive is obtained by a mixed polymerization reaction of a first monomer and a second monomer. The first monomer is acrylamide.

[0014] The second monomer is selected as follows: the homopolymer of the second monomer is a flexible adhesive with a glass transition temperature below -15°C. The second monomer is butyl acrylate or hydroxyethyl acrylate.

[0015] By adopting the above technical solution, the water-based soft adhesive prepared by this technology can significantly improve the softness and processing performance of hard carbon negative electrode sheets.

[0016] A preferred embodiment of the water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets is that the water-based latex is obtained by adding a surfactant and a protective colloid to water, then adding all the first monomer and all the second monomer, followed by adding an initiator, and heating to 60-80°C for a polymerization reaction for 6-24 hours to obtain the water-based soft adhesive.

[0017] By employing the above technical solution, monomers form small droplets dispersed in water to form an emulsion. A surfactant stabilizes the emulsion, maintaining the orderly progress of the polymerization reaction and forming latex particles. Protective colloids adsorb onto the surface of the generated latex particles, preventing particle aggregation. The initiator forms free radicals upon heating, initiating the polymerization reaction. The initiator can be persulfate, peroxide, etc.

[0018] A preferred embodiment of the water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets is that the protective colloid is selected from at least one of polyvinyl alcohol, carboxymethyl cellulose ether, hydroxymethyl cellulose ether, hydroxypropyl cellulose ether, and polyvinylpyrrolidone.

[0019] By adopting the above technical solution, the protective colloid is adsorbed onto the surface of the generated latex particles, preventing the latex particles from agglomerating and promoting the continuous reaction.

[0020] A preferred embodiment of the water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets is that the surfactant is selected from one or more of nonionic and anionic surfactants.

[0021] By employing the above technical solutions, nonionic surfactants adsorb a large amount of water through hydrogen bonding, thereby stabilizing the emulsion. Anionic surfactants adsorb the oil phase liquid at their lipophilic end, while their hydrophilic end carries a negative charge, causing the oil phase droplets to repel each other and preventing droplet aggregation, thus stabilizing the emulsion.

[0022] Secondly, this application proposes a method for preparing a hard carbon negative electrode sheet, and adopts the following technical solution.

[0023] A method for preparing a hard carbon negative electrode sheet includes: mixing a polyacrylic acid-based water-based binder with water and dispersing it evenly; adding conductive carbon black and dispersing it evenly; then adding hard carbon negative electrode material and dispersing it evenly to obtain a primary slurry; adjusting the viscosity of the primary slurry at 25°C to between 3000 and 4000 mPa·s; then adding the aforementioned water-based soft adhesive and dispersing it evenly to obtain a secondary slurry; coating the secondary slurry onto copper foil, drying it, and cutting it to obtain the hard carbon negative electrode sheet.

[0024] In the above methods, by mass, the ratio of polyacrylic acid water-based adhesive: conductive carbon black: hard carbon negative electrode material: water-based soft adhesive is (2-3):(0.5-1.5):(94-97):1.

[0025] By adopting the above technical solution, the combination of polyacrylic acid water-based adhesive and water-based soft adhesive has significantly improved the flexibility and processing performance of hard carbon negative electrode sheets.

[0026] A preferred embodiment of the preparation method of the hard carbon negative electrode sheet is that the total amount of the polyacrylic water-based binder, the conductive carbon black, the hard carbon negative electrode material and the water-based soft adhesive, and the mass ratio of water is 100:(100-150).

[0027] By adopting the above technical solution, the slurry after mixing the above materials has a suitable viscosity, is not prone to sedimentation, and has a suitable density after drying, thus significantly improving the softness and processing performance of the hard carbon negative electrode sheet. The viscosity of the primary slurry can be achieved by adjusting its water content.

[0028] A preferred embodiment of the preparation method for the hard carbon negative electrode sheet is as follows: A polyacrylic acid-based water-based binder and half the amount of water are mixed in a mixer and dispersed at 250-350 rpm for 10-20 minutes. Conductive carbon black is then added, and the mixture is stirred at 100-200 rpm for 5-15 minutes, followed by high-speed stirring at 600-1000 rpm for 100-140 minutes. The stirring speed is then reduced to 250-300 rpm, half of the hard carbon negative electrode material is added, and the mixture is dispersed for 5-15 minutes. The remaining half of the hard carbon negative electrode material and the remaining half of the water are then added and dispersed for 5-15 minutes. Finally, the mixture is stirred at 600-1000 rpm for 100-140 minutes to obtain a primary slurry. The viscosity of the primary slurry at 25°C is adjusted to between 3000 and 4000 mPa·s by controlling the water content. Add the water-based soft adhesive to the primary slurry, disperse at 450-550 rpm for 20-40 minutes, and then filter through a 100-200 mesh screen to obtain the secondary slurry. Place copper foil on a coating machine, coat it evenly with the secondary slurry, dry it, and finally cut it to obtain a hard carbon negative electrode sheet.

[0029] By adopting the above technical solution, the components are fully dispersed, and the flexibility and processing performance of the electrode sheet are significantly improved.

[0030] Thirdly, this application also proposes a hard carbon negative electrode sheet and adopts the following technical solution.

[0031] A hard carbon negative electrode sheet is prepared according to the above-described preparation method.

[0032] By adopting the above technical solution, the electrode's flexibility and processing performance are significantly improved, providing a new solution for the preparation of hard carbon negative electrode sheets for sodium-ion batteries.

[0033] In summary, the aqueous soft adhesive, hard carbon anode electrode, and preparation method thereof for improving the softness and processing performance of hard carbon anode electrodes of this application have the following beneficial effects: This application provides an aqueous soft adhesive that, when used in combination with PAA-based aqueous adhesives, can improve the softness and processing performance of hard carbon anode electrodes, solving the problems of electrode brittleness, easy cracking, and material shedding. This technology is applicable to the preparation process of hard carbon anode electrodes for sodium-ion batteries, and has significant application effects, especially in scenarios where improved electrode softness and processing performance are required.

[0034] This application introduces a specific proportion of soft monomers with a Tg below -15℃, resulting in an aqueous soft adhesive that significantly improves the softness and processing performance of hard carbon negative electrode sheets. Compared with soft adhesives such as SBR (styrene-butadiene rubber), PVAC (polyvinyl acetate), and VAE (ethylene-vinyl acetate copolymer), the hard carbon electrode sheets prepared in this application exhibit superior performance in both softness and needle winding tests, while maintaining high electrode adhesion and cohesion. Detailed Implementation

[0035] Example 1

[0036] This embodiment prepares a water-based soft gel.

[0037] The first monomer has the general formula CH2=CR1R2. In this embodiment, the first monomer used is acrylamide, that is, R1 is H and R2 is -CONH2.

[0038] The general formula of the second monomer is CH2=CHCOOR3. The second monomer used in this embodiment is butyl acrylate, that is, R3 is a C4 alkyl group.

[0039] The preparation method of water-based latex is as follows.

[0040] Take the materials according to the mass fractions, add 1 part surfactant and 1 part protective colloid to 100 parts water, then add 30 parts first monomer and 50 parts second monomer, then add 0.1 parts initiator, heat to 70℃ and carry out polymerization reaction for 10 hours to obtain water-based soft glue.

[0041] In the above preparation method, the surfactant is alkylphenol polyoxyethylene ether, the protective colloid is polyvinyl alcohol, and the initiator is ammonium persulfate.

[0042] Example 2

[0043] The method for preparing hard carbon negative electrode sheets is as follows.

[0044] According to the mass fraction, take 2 parts of polyacrylic acid water-based adhesive and 60 parts of water and mix them in a mixer. Disperse at 300 rpm for 15 minutes, then add 1 part of SP conductive carbon black and stir at 150 rpm for 10 minutes. Then stir at 800 rpm for 120 minutes. Reduce the speed to 300 rpm, add 48 parts of hard carbon anode material and disperse for 10 minutes. Then add 48 parts of hard carbon anode material and 60 parts of water and disperse for 10 minutes. Then stir at 800 rpm for 120 minutes to obtain the primary slurry. Adjust the viscosity of the primary slurry to 3587 mPa·s at 25°C by adjusting the water content. Add 1 part of the water-based soft adhesive prepared in Example 1 to the primary slurry, disperse at 500 rpm for 30 minutes, and then filter with a 150-mesh filter to obtain the secondary slurry.

[0045] The copper foil is placed on a coating machine, and a secondary slurry is evenly coated on it. It is then placed in a 100℃ environment and baked until dry. The foil is then cut into 12.5cm × 5cm pieces with a single-sided surface density of 100-110 g / m³. 2 Hard carbon negative electrode sheet.

[0046] Experimental Example 1

[0047] Electrode peel strength test method: Place the cut electrode sheets in a 35% RH constant temperature chamber for 30 minutes. With the coated side facing outwards and the copper foil side facing inwards, bond two electrode sheets together and feed them into an electric roller press to compress the electrode sheets until the compaction density is 0.95 g / cm³. 3 After rolling, let it sit for 30 minutes. During this time, select five 12.5cm×5cm stainless steel plates, apply double-sided tape of the corresponding size to the stainless steel plates, and then attach the electrode sheet to the double-sided tape with the coating facing down. Then, attach a 2.5cm wide masking tape to the copper foil. Roll the electrode sheet steel plate back and forth once with a certain pressure (1kgf) using an electric rolling roller. Then, use an electronic peeler to test the adhesion of the electrode sheet. The same method is used, but the electrode sheet is attached to the double-sided tape with the coating facing up, and the cohesion of the electrode sheet can be tested.

[0048] The softness was tested using an IMT-RRD01*1 softness tester.

[0049] Needle winding test: A cylindrical bending tester of model BEVS1603 was used to simulate the requirements of the winding process in cell manufacturing on the flexibility of the electrode sheet. The test result is the minimum diameter of the cylinder that can prevent the electrode sheet from cracking during the needle winding test.

[0050] The test results for the following items are shown in Table 1 below.

[0051] Table 1. Performance tests of electrodes prepared with four different binder combinations.

[0052]

[0053] In Table 1, the mass ratio of each adhesive combination is 2:1. The first group, PAA + Example 1, is the electrode prepared in Example 2. The other three adhesive combinations are prepared using the same method as in Example 2, that is, using equal masses of SBR-Ryon, VAE, and PVAC to replace the water-based soft adhesive prepared in Example 1, and finally obtaining the electrode.

[0054] In Table 1, PAA is a water-based adhesive of polyacrylic acid, Example 1 refers to the water-based soft adhesive prepared in Example 1, SBR-Zeon is styrene-butadiene rubber prepared by Zeon Corporation of Japan, VAE is a polymer emulsion copolymerized from vinyl acetate and ethylene, and PVAC is a polyvinyl acetate emulsion adhesive.

[0055] As shown in Table 1, compared with soft adhesives such as SBR-Ryon, PVAC, and VAE, the hard carbon electrode sheets prepared from the water-based soft adhesive obtained in this application exhibit superior performance in both flexibility and needle winding tests, while maintaining high electrode adhesion and cohesion. This provides a new solution for the preparation of hard carbon anode sheets for sodium-ion batteries. By introducing a specific proportion of soft monomers with a Tg below -15℃, the water-based soft adhesive prepared in this application significantly improves the flexibility and processing performance of hard carbon anode sheets.

[0056] The above are merely some embodiments of this application. The scope of protection of this application is not limited to the above embodiments. For those skilled in the art, any improvements and modifications made without departing from the inventive design of this application should also fall within the scope of protection of this application.

Claims

1. A water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets, characterized in that, The water-based soft adhesive is obtained by a mixed polymerization reaction of a first monomer and a second monomer; the first monomer is acrylamide; the second monomer is butyl acrylate. The water-based soft adhesive is obtained by taking materials according to the mass fraction, adding 1 part surfactant and 1 part protective colloid to 100 parts water, then adding 30 parts of the first monomer and 50 parts of the second monomer, followed by adding 0.1 parts initiator, heating to 70°C for polymerization reaction for 10 hours to obtain the water-based soft adhesive.

2. The water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets according to claim 1, characterized in that, The protective colloid is selected from at least one of polyvinyl alcohol, carboxymethyl cellulose ether, hydroxymethyl cellulose ether, hydroxypropyl cellulose ether, and polyvinylpyrrolidone.

3. The water-based soft adhesive for improving the softness and processing performance of hard carbon negative electrode sheets according to claim 1, characterized in that, The surfactant is selected from one or more of nonionic and anionic surfactants.

4. A method for preparing a hard carbon negative electrode sheet, characterized in that, The preparation method includes: A water-based polyacrylic acid adhesive is mixed with water and dispersed evenly. Then, conductive carbon black is added and dispersed evenly. Next, hard carbon anode material is added and dispersed evenly to obtain a primary slurry. The viscosity of the primary slurry at 25°C is adjusted to be between 3000 and 4000 mPa·s. Then, the water-based soft adhesive according to any one of claims 1-3 is added and dispersed evenly to obtain a secondary slurry. The secondary slurry is coated on copper foil, dried, and cut to obtain the hard carbon anode sheet. In the above methods, by mass, the ratio of polyacrylic acid water-based adhesive: conductive carbon black: hard carbon negative electrode material: water-based soft adhesive is (2~3): (0.5~1.5): (94~97):

1.

5. The method for preparing the hard carbon negative electrode sheet according to claim 4, characterized in that, The total amount of the polyacrylic water-based adhesive, the conductive carbon black, the hard carbon anode material, and the water-based soft adhesive, in a mass ratio of water to 100:(100~150).

6. The method for preparing the hard carbon negative electrode sheet according to claim 4 or 5, characterized in that, The preparation method is specifically as follows: Mix polyacrylic acid water-based adhesive and half the water in a mixer and disperse at 250-350 rpm for 10-20 minutes. Then add conductive carbon black and stir at 100-200 rpm for 5-15 minutes, followed by high-speed stirring at 600-1000 rpm for 100-140 minutes. Reduce the speed to 250-300 rpm, add half of the hard carbon anode material, and disperse for 5-15 minutes. Then add the remaining half of the hard carbon anode material and the remaining half of the water and disperse for 5-15 minutes. Finally, stir at high-speed stirring at 600-1000 rpm for 100-140 minutes to obtain the primary slurry. Adjust the viscosity of the primary slurry to between 3000 and 4000 mPa·s at 25°C by adjusting the water content. Add the water-based soft adhesive to the primary slurry, disperse at 450-550 rpm for 20-40 minutes, and then filter through a 100-200 mesh screen to obtain the secondary slurry. The copper foil is placed on a coating machine, the secondary slurry is evenly coated, dried, and finally cut to obtain a hard carbon negative electrode sheet.

7. A hard carbon negative electrode sheet, characterized in that, It is prepared according to any one of claims 4-6.

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