Water-based binder for lithium battery and preparation method of water-based binder

Abstract

The invention relates to the field of lithium battery materials, in particular to a water-based binder for a lithium battery and a preparation method of the water-based binder. The aqueous binder for the lithium battery at least comprises the following raw materials in parts by mass: 55-75 parts of acrylic acid / acrylate, 15-25 parts of acrylonitrile, 3-8 parts of a crosslinking monomer, 2-4 parts of a reaction aid and 80-120 parts of deionized water. The water-based binder prepared by the invention not only can replace the existing PVDF binder product, but also can balance the performance contradiction of the existing water-based binder, considers good electrochemical stability and mechanical property requirements, has better cycle performance and low impedance, and meets various performance requirements of the existing lithium battery material.

Description

Technical Field

[0001] The present application relates to the field of lithium battery materials, and more specifically to an aqueous binder for lithium batteries and a preparation method thereof. Background Art

[0002] With the growing global demand for renewable energy storage and the rapid development of the electric vehicle industry, the demand for high-performance lithium-ion batteries is increasing. In lithium-ion batteries, binders are an important component of electrode materials. They must not only ensure good bonding between active material particles, but also ensure sufficient adhesion between these particles and the current collector. Traditional organic solvent-based binders such as polyvinylidene fluoride (PVDF) have been widely used in lithium battery production due to their excellent chemical and electrochemical stability. However, with increasing environmental protection requirements and concerns about production process safety, water-based binders have gradually become a research hotspot due to their environmental friendliness and safety.

[0003] Traditional binders generally use oil-soluble polymers such as polyvinylidene fluoride (PVDF), requiring the use of organic solvents such as N-methylpyrrolidone (NMP). With increasing environmental protection requirements and rising solvent recovery costs, water-based binders are gradually gaining prominence. For example, patent CN118240510A proposes a water-based binder for lithium battery electrodes. By introducing maleic anhydride-modified polybutadiene into an acrylic polymer and applying it to lithium batteries, this improves polymer stability while enhancing lithium ion conductivity, while also maintaining a balanced battery life and performance.

[0004] At the same time, existing water-based binders still face some technical bottlenecks, such as the contradiction between adhesion and flexibility, which makes it difficult to take into account the mechanical requirements of high-energy-density electrodes; poor electrical and electrochemical stability, the residual hydrophilic groups in the aqueous system promote the dissolution of metal ions and catalyze the decomposition of the electrolyte, and the problem of cycle performance is more obvious; in addition, some water-based binders coat active substances, resulting in obstruction of the ion / electron conduction path and high interface impedance. Summary of the Invention

[0005] In summary, how to further solve the aforementioned performance issues of water-based binders has become an important research topic facing researchers in the field of lithium battery technology. Through continuous research in this field, the present applicant has finally proposed a water-based binder for lithium batteries and a preparation method thereof. The resulting water-based binder can not only replace existing PVDF-based binder products, but also balance the performance contradictions of existing water-based binders, taking into account both good electrochemical stability and mechanical performance requirements, with better cycle performance and low impedance, thus meeting the various performance requirements of existing lithium battery materials.

[0006] A water-based binder for lithium batteries, whose raw materials include at least 55-75 parts by mass of acrylic acid / acrylate, 15-25 parts by mass of acrylonitrile, 3-8 parts by mass of a cross-linking monomer, 2-4 parts by mass of a reaction aid and 80-120 parts by mass of deionized water.

[0007] In a preferred embodiment, the acrylic acid / acrylic acid ester is at least one of acrylic acid, methacrylic acid, hydroxypropyl acrylate, butyl acrylate, isobutyl acrylate, isobornyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and 2-ethylhexyl acrylate.

[0008] In a preferred embodiment, the acrylic acid / acrylic acid esters are a combination of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate.

[0009] In a preferred embodiment, the mass ratio of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate is (25-35): (20-25): (8-15).

[0010] In a preferred embodiment, the mass ratio of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate is (28-33): (22-25): (9-12).

[0011] In a preferred embodiment, the cross-linking monomer is a combination of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate.

[0012] In a preferred embodiment, the mass ratio of the N,N'-methylenebisacrylamide to polyethylene glycol di(meth)acrylate is (2-4):(0.5-1.2).

[0013] In a preferred embodiment, the mass ratio of the N,N'-methylenebisacrylamide to polyethylene glycol di(meth)acrylate is (3-3.5):(0.8-1).

[0014] In a preferred embodiment, the reaction aid includes an initiator, an emulsifier and a pH adjuster.

[0015] In a preferred embodiment, the initiator is at least one of potassium persulfate, ammonium persulfate, tert-butyl hydroperoxide and benzoyl peroxide.

[0016] In a preferred embodiment, the initiator is potassium persulfate or ammonium persulfate.

[0017] In a preferred embodiment, the emulsifier is at least one of sodium allyloxyhydroxypropane sulfonate, sodium dodecyl diphenyl ether disulfonate, acrylonitrile phenol polyoxyethylene ether and alkylphenol polyoxyethylene ether ammonium sulfate.

[0018] In a preferred embodiment, the emulsifier is sodium allyloxyhydroxypropane sulfonate or sodium dodecyl diphenyl ether disulfonate.

[0019] In a preferred embodiment, the pH adjuster is at least one of sodium dihydrogen phosphate, sodium dihydrogen citrate, disodium dihydrogen pyrophosphate and p-toluenesulfonic acid.

[0020] In a preferred embodiment, the pH adjuster is sodium dihydrogen phosphate or sodium dihydrogen citrate.

[0021] In a preferred embodiment, the mass ratio of acrylic acid / acrylates, acrylonitrile and cross-linking monomer is (60-70): (16-23): (5-8).

[0022] In a preferred embodiment, the mass ratio of acrylic acid / acrylates, acrylonitrile and cross-linking monomer is (65-70): (18-22): (6-7).

[0023] In a preferred embodiment, the aqueous binder for lithium batteries further comprises, by weight, 9 to 15 parts of auxiliary monomers and 3 to 6 parts of functional additives.

[0024] In a preferred embodiment, the mass ratio of the acrylic acid / acrylate, auxiliary monomer and functional additive is (60-70): (10-14): (3.5-5).

[0025] In a preferred embodiment, the mass ratio of the acrylic acid / acrylate, auxiliary monomer and functional additive is (65-70): (11-12): (4-4.5).

[0026] In a preferred embodiment, the auxiliary monomer is a combination of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate.

[0027] In a preferred embodiment, the mass ratio of the 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate is (5-8): (0.5-1.5): (4-6).

[0028] In a preferred embodiment, the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate is (6-7): (0.6-1.2): (4.5-5.5).

[0029] In a preferred embodiment, the functional auxiliary agent is a composition of nano-zirconium oxide and propenyltrimethoxysilane.

[0030] In a preferred embodiment, the average particle size of the nano-zirconia is 20-40 nm.

[0031] In a preferred embodiment, the mass ratio of the nano-zirconium oxide to acryltrimethoxysilane is (1-3): (1-2).

[0032] In a preferred embodiment, the mass ratio of the nano-zirconium oxide to acryltrimethoxysilane is (2-3): (1-1.5).

[0033] The preparation method of the aqueous binder for the lithium battery mentioned above in the present application specifically includes the following steps: S1: adding acrylic acid / acrylic esters, acrylonitrile, a cross-linking monomer and an auxiliary monomer to deionized water, heating to 50-55°C, and stirring at 300-400 rpm for 30-40 minutes until uniform to obtain a reaction mixture; S2: adding an emulsifier and a pH adjuster to the reaction mixture and mixing and stirring, and mixing an initiator with deionized water to obtain an initiating solution, then adding 10-20 wt% of the initiating solution to the reaction mixture, heating to 75-80°C, keeping warm for 30-35 minutes, then heating to 85-88°C, adding the remaining initiating solution dropwise, stirring and keeping warm at 100-120 rpm for 2-2.5 hours, and finally heating to 90-93°C, stirring and keeping warm at 60-80 rpm for 1.5-2 hours; S3: after the reaction is completed, adding a functional additive, stirring at 300-400 rpm for 20-30 minutes, and filtering through 200-300 mesh to obtain.

[0034] This application has practical beneficial effects: 1. The water-based binder proposed in this application can not only replace existing PVDF binder products, but also balance the performance contradictions of existing water-based binders, taking into account good electrochemical stability and mechanical performance requirements, with better cycle performance and low impedance, and meet the various performance requirements of existing lithium battery materials.

[0035] 2. The present application adds a compound combination of specific cross-linking monomers and auxiliary monomers to the water-based adhesive, which can effectively improve the overall comprehensive performance of the water-based adhesive. The combined effect of these monomers can greatly increase the number of three-dimensional cross-linking points inside the water-based adhesive, forming a controllable three-dimensional network structure. By stabilizing the covalent cross-linking points, the molecular chain slip is suppressed, and the adhesive maintains structural integrity during electrolyte immersion and long-term circulation. Compared with existing PVDF adhesives, it avoids the introduction of fluorine elements and avoids the gelation of the slurry caused by the removal of hydrogen fluoride. Compared with existing water-based adhesives, it balances the contradictions between performances.

[0036] 3. On the other hand, the added functional additives can help accelerate Li + Jump migration, improve interface Li +Flux, and help form a rigid point network, inhibiting the displacement of active materials, hindering the expansion of microcracks, and preferentially reacting with the electrolyte byproduct HF, reducing the erosion of the positive electrode active material. In addition, the addition of functional additives can also participate in the free radical polymerization of the copolymer, becoming part of the polymer network, forming a hydrophobic layer with a thickness of 1-2nm on the binder surface, blocking H2O / O2 penetration, thereby helping to improve the overall comprehensive performance and make up for the shortcomings of cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a physical picture of the water-based adhesive product prepared in Example 1 of this application.

[0038] Figure 2 and Figure 3 Schematic diagram of the molecular weight test results of the water-based adhesive prepared in Example 1 of the present application. DETAILED DESCRIPTION Example 1

[0039] A water-based binder for lithium batteries, comprising, by parts by mass, 68.5 parts of acrylic acid / acrylates, 21.4 parts of acrylonitrile, 6 parts of a cross-linking monomer, 11.8 parts of an auxiliary monomer, 3 parts of a reaction aid (0.8 parts of an initiator, 1.5 parts of an emulsifier, and 0.7 parts of a pH adjuster), 4.1 parts of a functional additive, and 95 parts of deionized water.

[0040] The acrylic acid / acrylic acid esters are a composition of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate, with a mass ratio of 33:25:10.5.

[0041] The cross-linking monomer is a composition of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate, with a mass ratio of 3:1.

[0042] Polyethylene glycol di(meth)acrylate is national standard industrial grade and comes from Shandong Xuchen Chemical Technology Co., Ltd.

[0043] The initiator is potassium persulfate; the emulsifier is sodium allyloxyhydroxypropane sulfonate; and the pH regulator is sodium dihydrogen phosphate.

[0044] The auxiliary monomer is a composition of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate, with a mass ratio of 6:0.8:5.

[0045] The functional additive is a composition of nano zirconium oxide and propylene trimethoxysilane, with a mass ratio of 2.5:1.

[0046] The average particle size of nano-zirconia is 25 nm.

[0047] In this embodiment, the preparation method of the aqueous binder for lithium batteries specifically includes the following steps: S1: adding acrylic acid / acrylic esters, acrylonitrile, a cross-linking monomer and an auxiliary monomer to deionized water, heating to 50°C, and stirring at 320 rpm for 35 minutes until uniform to obtain a reaction mixture; S2: adding an emulsifier and a pH adjuster to the reaction mixture and mixing and stirring, and mixing an initiator with deionized water to obtain an initiating solution, then adding 15 wt% of the initiating solution to the reaction mixture, heating to 78°C, keeping warm for 30 minutes, then heating to 86°C, adding the remaining initiating solution dropwise, stirring and keeping warm at 120 rpm for 2 hours, and finally heating to 92°C, stirring and keeping warm at 80 rpm for 2 hours; S3: after the reaction is completed, adding a functional additive, stirring at 300 rpm for 25 minutes, and filtering through 300 mesh to obtain.

[0048] The actual product picture of the water-based adhesive prepared in this embodiment is as follows Figure 1 shown.

[0049] The molecular weight test results of the water-based binder prepared in this embodiment are shown in FIG. Figure 2 and Figure 3 shown. Example 2

[0050] The only difference between this embodiment and Example 1 is that the raw materials of the aqueous binder for lithium batteries, calculated by mass, include: 68.5 parts of acrylic acid / acrylates, 18.5 parts of acrylonitrile, 7 parts of cross-linking monomers, 11.8 parts of auxiliary monomers, 3 parts of reaction aids (0.8 parts of initiator, 1.5 parts of emulsifier and 0.7 parts of pH adjuster), 4.1 parts of functional additives, and 95 parts of deionized water.

[0051] The other embodiments are the same. Example 3

[0052] The only difference between this embodiment and Example 1 is that the raw materials of the aqueous binder for lithium batteries, calculated by mass, include: 68.5 parts of acrylic acid / acrylates, 21.4 parts of acrylonitrile, 6 parts of a cross-linking monomer, 10 parts of an auxiliary monomer, 3 parts of a reaction aid (0.8 parts of an initiator, 1.5 parts of an emulsifier, and 0.7 parts of a pH adjuster), 3.5 parts of a functional additive, and 95 parts of deionized water.

[0053] The other embodiments are the same.

[0054] Comparative Example 1 The only difference between this comparative example and Example 1 is that the raw materials of the aqueous binder for lithium batteries, calculated by mass, include: 68.5 parts of acrylic acid / acrylates, 21.4 parts of acrylonitrile, 2.5 parts of a cross-linking monomer, 20 parts of an auxiliary monomer, 3 parts of a reaction aid (0.8 parts of an initiator, 1.5 parts of an emulsifier, and 0.7 parts of a pH adjuster), 4.1 parts of a functional additive, and 90 parts of deionized water.

[0055] The other embodiments are the same.

[0056] Comparative Example 2 The only difference between this comparative example and Example 1 is that the raw materials of the aqueous binder for lithium batteries, calculated by mass, include: 68.5 parts of acrylic acid / acrylates, 10.4 parts of acrylonitrile, 6 parts of cross-linking monomers, 6.8 parts of auxiliary monomers, 3 parts of reaction aids (0.8 parts of initiator, 1.5 parts of emulsifier and 0.7 parts of pH adjuster), 1.2 parts of functional additives, and 85 parts of deionized water.

[0057] The other embodiments are the same.

[0058] Comparative Example 3 The only difference between this comparative example and Example 1 is that the crosslinking monomer is a combination of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate, with a mass ratio of 6:0.5.

[0059] The other embodiments are the same.

[0060] Comparative Example 4 The only difference between this comparative example and Example 1 is that the acrylic acid / acrylic acid ester is a composition of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate, with a mass ratio of 40.5:25:3.

[0061] The other embodiments are the same.

[0062] Comparative Example 5 The only difference between this comparative example and Example 1 is that the acrylic acid / acrylic acid ester is a composition of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate, with a mass ratio of 33:25:10.5.

[0063] The other embodiments are the same.

[0064] Comparative Example 6 The only difference between this comparative example and Example 1 is that the auxiliary monomer is a combination of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate in a mass ratio of 10:0.2:1.

[0065] The other embodiments are the same.

[0066] Performance Testing Preparation of positive electrode sheet: The positive electrode active material NCM811, conductive carbon black and the binder prepared in the embodiment and the comparative example are prepared into a slurry in a mass ratio of 95:3:2, coated on a 15μm aluminum foil current collector, and then vacuum dried to prepare a positive electrode sheet.

[0067] Preparation of the negative electrode sheet: SiOx / C (Si content 15wt%), conductive carbon black and the binder prepared in the embodiment and comparative example are prepared into a slurry in a mass ratio of 94:3:3, coated on an 8μm copper foil current collector, and then vacuum dried to prepare the negative electrode sheet.

[0068] Lithium-ion battery preparation: The above-prepared positive electrode sheet, negative electrode sheet, separator and electrolyte were assembled into a lithium-ion battery. The electrolyte was 1.2M LiPF6 in EC:EMC:DEC (3:5:2, containing 2% FEC), and the separator was 12μm ceramic-coated PP (Al2O3@PP).

[0069] 1. Peel strength: The test reference standard GB 2792-2014 is used. The electrode is peeled from the current collector and the peel force is measured at an angle of 180° and a rate of 50 mm / min. The test is aged at 85°C for 48 hours and then retested. The average of 10 positive electrode test results is recorded in Table 1.

[0070] 2. Interface impedance: The test reference standard GB / T 33827-2017, three-electrode system (Li / electrolyte / electrode), frequency 0.01 Hz to 100 kHz, amplitude 10 mV, test impedance after 200 cycles at 45°C. The results are the average of 10 tests and recorded in Table 1.

[0071] 3. Flexibility: Using a cylindrical bending tester, the positive electrode sheet prepared above was cut into 5 cm rectangular strips, then wound onto a metal cylinder with a diameter of 2 cm, pulled at a constant speed of 180° and cycled 5 times. The electrode sheet was observed for clear visible cracks, and the active material shedding rate was detected before and after the test. The results are recorded in Table 1.

[0072] 4. Cycle performance: The test reference standard is to charge the lithium-ion battery at a constant current of 0.5C to a voltage of 4.2V at 25°C, then charge at a constant voltage with a cut-off current value of 0.05C, and then discharge at a constant current of 0.5C to 3V. This is considered one cycle. After repeating 1000 cycles, the capacity retention rate after 1000 cycles is calculated. The results are the average of 10 tests and recorded in Table 1.

[0073] Table 1 Performance test results Example Peel strength (N / cm) Peel strength after 85℃ / 48h (N / cm) Interface impedance (Ω·cm²) Flexibility (cracks, active material loss rate%) Cycle capacity retention rate (%) Example 1 3.24 2.97 5.24 No clear cracks, 0.23 91.1 Example 2 3.17 2.91 5.31 No clear cracks, 0.24 90.6 Example 3 3.22 2.93 5.27 No clear cracks, 0.21 90.8 Comparative Example 1 2.84 2.52 6.14 No clear cracks, 0.41 86.5 Comparative Example 2 2.93 2.54 5.87 No clear cracks, 0.36 88.6 Comparative Example 3 2.89 2.61 5.91 No clear cracks, 0.37 87.8 Comparative Example 4 3.01 2.72 5.77 No clear cracks, 0.40 88.2 Comparative Example 5 3.04 2.74 5.82 No clear cracks, 0.33 87.9 Comparative Example 6 2.99 2.68 5.69 No clear cracks, 0.35 88.4 Judging from the final performance test results of the Examples and Comparative Examples, Comparative Examples 1-2 were significantly inferior to the overall performance tests of the batteries made with the binders because they did not adopt the specific raw material ratios specified in this application. Comparative Examples 3-6 did not further follow the specific raw material selection and ratios specified in this application, which resulted in a significant decrease in their performance test results compared to Examples 1-3. This is because the cross-linking monomers and auxiliary monomers added without following the specified ratios significantly reduced their interaction, failing to form more stable covalent cross-linking points like in Examples 1-3, thereby inhibiting molecular chain slippage and forming a stable cross-linked network. The structural integrity could not be optimized, resulting in a significant decrease in the performance balance of the water-based binder.

Claims

1. A water-based binder for lithium batteries, characterized in that: The raw materials include at least 55-75 parts by mass of acrylic acid / acrylate, 15-25 parts by mass of acrylonitrile, 3-8 parts by mass of crosslinking monomer, 2-4 parts by mass of reaction aid and 80-120 parts by mass of deionized water; The cross-linking monomer is a composition of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate, with a mass ratio of (2-4): (0.5-1.2); The reaction aids include initiators, emulsifiers and pH regulators.

2. The aqueous binder for lithium batteries according to claim 1, wherein: The acrylic acid / acrylic acid ester is at least one of acrylic acid, methacrylic acid, hydroxypropyl acrylate, butyl acrylate, isobutyl acrylate, isobornyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and 2-ethylhexyl acrylate.

3. The aqueous binder for lithium batteries according to claim 2, wherein: The acrylic acid / acrylate is a composition of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate, with a mass ratio of (25-35): (20-25): (8-15).

4. The aqueous binder for lithium batteries according to claim 3, wherein: The mass ratio of the acrylic acid / acrylate, acrylonitrile and cross-linking monomer is (60-70): (16-23): (5-8).

5. The aqueous binder for lithium batteries according to claim 1, wherein: The aqueous binder for lithium batteries further comprises, by weight, 9 to 15 parts of auxiliary monomers and 3 to 6 parts of functional additives.

6. The aqueous binder for lithium batteries according to claim 5, wherein: The mass ratio of the acrylic acid / acrylate, auxiliary monomer and functional additive is (60-70): (10-14): (3.5-5).

7. The aqueous binder for lithium batteries according to claim 6, wherein: The auxiliary monomer is a composition of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate, with a mass ratio of (5-8): (0.5-1.5): (4-6).

8. The aqueous binder for lithium batteries according to claim 7, wherein: The functional auxiliary agent is a composition of nano zirconium oxide and acryltrimethoxysilane, with a mass ratio of (1-3): (1-2).

9. The aqueous binder for lithium batteries according to claim 8, wherein: The average particle size of the nano zirconium oxide is 20-40 nm.

10. A method for preparing an aqueous binder for lithium batteries according to any one of claims 5 to 9, characterized in that: The specific steps include: S1: Add acrylic acid / acrylic esters, acrylonitrile, a cross-linking monomer and an auxiliary monomer to deionized water, heat to 50-55°C, and stir at 300-400 rpm for 30-40 minutes until uniform to obtain a reaction mixture; S2: Add an emulsifier and a pH adjuster to the reaction mixture and mix and stir, and mix an initiator with deionized water to obtain an initiating solution, then add 10-20 wt% of the initiating solution to the reaction mixture, heat to 75-80°C, keep warm for 30-35 minutes, then heat to 85-88°C, add the remaining initiating solution dropwise, stir and keep warm at 100-120 rpm for 2-2.5 hours, finally heat to 90-93°C, stir and keep warm at 60-80 rpm for 1.5-2 hours; S3: After the reaction is completed, add a functional additive, stir at 300-400 rpm for 20-30 minutes, and filter through 200-300 mesh to obtain.

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