Aqueous binder for lithium batteries and method for its preparation

Abstract

The application relates to the field of lithium battery materials, and more particularly to a water-based binder for a lithium battery and a preparation method thereof. The water-based binder for the lithium battery comprises, in mass parts, at least: 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 application can not only replace existing PVDF-based binder products, but also balance the performance contradictions of existing water-based binders, and can meet the requirements of good electrochemical stability and mechanical properties, has better cycle performance and low impedance, and can meet the various performance requirements of existing lithium battery materials.

Description

Technical Field

[0001] This application relates to the field of lithium battery materials, and more specifically mentions an aqueous binder for lithium batteries and its preparation method. Background Technology

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

[0003] Traditional binders generally use oil-soluble polymers such as polyvinylidene fluoride (PVDF), requiring organic solvents such as N-methylpyrrolidone (NMP). With increasing environmental requirements and rising solvent recycling costs, water-based binders are gradually emerging. For example, patent CN118240510A proposes a water-based binder for lithium-ion battery electrodes. This binder introduces maleic anhydride-modified polybutadiene into acrylate polymers and applies it to lithium-ion batteries. This improves polymer stability, enhances lithium-ion conductivity, and simultaneously ensures battery life and performance.

[0004] However, existing waterborne binders still face some technical bottlenecks, such as the contradiction between adhesion and flexibility, making it difficult to meet the mechanical requirements of high-energy-density electrodes; poor electrochemical stability, with residual hydrophilic groups in the waterborne system promoting the dissolution of metal ions and catalyzing electrolyte decomposition, and the cycle performance problem is more obvious; in addition, the coating of active substances in some waterborne binders leads to the obstruction of ion / electron conduction pathways and high interfacial impedance. Summary of the Invention

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

[0006] A water-based binder for lithium batteries, comprising, by weight, at least the following raw materials: 55-75 parts of acrylic acid / acrylate, 15-25 parts of acrylonitrile, 3-8 parts of crosslinking monomer, 2-4 parts of reaction aid, and 80-120 parts of deionized water.

[0007] In a preferred embodiment, the acrylic / acrylate is at least one selected from 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 / acrylate is a composition 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 crosslinking monomer is a composition of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate.

[0012] In a preferred embodiment, the mass ratio of 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 N,N'-methylenebisacrylamide to polyethylene glycol di(meth)acrylate is (3~3.5):(0.8~1).

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

[0015] In a preferred embodiment, the initiator is at least one selected from 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 selected from sodium allyl hydroxypropanesulfonate, sodium dodecyl diphenyl ether disulfonate, acrylonitrile phenol polyoxyethylene ether, and alkylphenol polyoxyethylene ether ammonium sulfate.

[0018] In a preferred embodiment, the emulsifier is sodium allyl hydroxypropanesulfonate 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 the acrylic acid / acrylate, acrylonitrile, and crosslinking monomer is (60~70):(16~23):(5~8).

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

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

[0024] In a preferred embodiment, the mass ratio of the acrylic / 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 / acrylate, auxiliary monomer and functional additive is (65~70):(11~12):(4~4.5).

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

[0027] In a preferred embodiment, the mass ratio of 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 additive is a composition of nano-zirconia and propylenetrimethoxysilane.

[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-zirconia to propylenetrimethoxysilane is (1~3):(1~2).

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

[0033] The preparation method of the aqueous binder for lithium batteries described in this application specifically includes the following steps: S1: Add acrylic acid / acrylate, acrylonitrile, crosslinking monomer and auxiliary monomer to deionized water, heat to 50~55℃, stir at 300~400 rpm for 30~40 min until uniform, to obtain a reaction mixture; S2: Add emulsifier and pH adjuster to the reaction mixture and mix and stir, then mix initiator with deionized water to obtain initiation solution, then add 10~20wt% of initiation solution to the reaction mixture, heat to 75~80℃, keep warm for 30~35 min, then heat to 85~88℃, add the remaining initiation solution dropwise, and stir at 100~120 rpm for 2~2.5 h, finally heat to 90~93℃, stir at 60~80 rpm for 1.5~2 h; S3: After the reaction is complete, add functional additives, stir at 300~400 rpm for 20~30 min, filter through 200~300 mesh, to obtain the final product.

[0034] The application has practical and beneficial effects:

[0035] 1. The aqueous binder proposed in this application can not only replace existing PVDF binder products, but also balance the performance contradictions of existing aqueous binders, take into account good electrochemical stability and mechanical performance requirements, have better cycle performance and low impedance, and meet the various performance requirements of existing lithium battery materials.

[0036] 2. This application incorporates a specific combination of crosslinking monomers and auxiliary monomers into the waterborne adhesive, which can effectively improve the overall performance of the waterborne adhesive. The combined effect of these monomers can significantly increase the number of three-dimensional crosslinking points within the waterborne adhesive, forming a controllable three-dimensional network structure. By stabilizing the covalent crosslinking points and inhibiting molecular chain slippage, the adhesive maintains structural integrity during electrolyte immersion and long-term cycling. Compared with existing PVDF adhesives, this avoids the introduction of fluorine and the gelation phenomenon of slurry caused by hydrogen fluoride removal. Furthermore, it balances the performance contradictions compared with existing waterborne adhesives.

[0037] 3. On the other hand, the added functional additives can help accelerate Li⁺ hopping migration, increase interfacial Li⁺ flux, and assist in the formation of a rigid dot network, inhibiting the displacement of active materials, hindering microcrack propagation, and preferentially reacting with electrolyte byproduct HF, reducing erosion of the positive electrode active material. Furthermore, the addition of functional additives can also participate in copolymer free radical polymerization, becoming part of the polymer network, forming a 1-2 nm thick hydrophobic layer on the binder surface, blocking H₂O / O₂ penetration, thereby helping to improve overall performance and compensate for cycle performance deficiencies. Attached Figure Description

[0038] Figure 1 This is a photograph of the water-based adhesive prepared according to Example 1 of this application.

[0039] Figure 2 and Figure 3 This is a schematic diagram showing the molecular weight test results of the water-based adhesive prepared in Example 1 of this application. Detailed Implementation Example 1

[0040] A water-based binder for lithium batteries, comprising, by weight, the following raw materials: 68.5 parts acrylic acid / acrylate, 21.4 parts acrylonitrile, 6 parts crosslinking monomer, 11.8 parts auxiliary monomer, 3 parts reaction aid (0.8 parts initiator, 1.5 parts emulsifier and 0.7 parts pH adjuster), 4.1 parts functional aid, and 95 parts deionized water.

[0041] The acrylic / acrylate composition is a combination of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate in a mass ratio of 33:25:10.5.

[0042] The crosslinking monomers are N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate in a mass ratio of 3:1.

[0043] The polyethylene glycol di(meth)acrylate is of national standard industrial grade and comes from Shandong Xuchen Chemical Technology Co., Ltd.

[0044] The initiator is potassium persulfate; the emulsifier is sodium allyl hydroxypropanesulfonate; and the pH adjuster is sodium dihydrogen phosphate.

[0045] The auxiliary monomers are a composition of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide and phenoxyethyl acrylate in a mass ratio of 6:0.8:5.

[0046] The functional additive is a composition of nano-zirconia and propylenetrimethoxysilane in a mass ratio of 2.5:1.

[0047] The average particle size of the nano-zirconia is 25 nm.

[0048] In this embodiment, the preparation method of the aqueous binder for lithium batteries specifically includes the following steps: S1: Add acrylic acid / acrylate, acrylonitrile, crosslinking monomer and auxiliary monomer to deionized water, heat to 50°C, and stir at 320 rpm for 35 min until homogeneous to obtain a reaction mixture; S2: Add emulsifier and pH adjuster to the reaction mixture, mix and stir, and mix initiator with deionized water to obtain initiation solution, then add 15 wt% of initiation solution to the reaction mixture, heat to 78°C, keep warm for 30 min, then heat to 86°C, add the remaining initiation solution dropwise, and stir at 120 rpm for 2 h, and finally heat to 92°C, stir at 80 rpm for 2 h; S3: After the reaction is completed, add functional additives, stir at 300 rpm for 25 min, and filter through 300 mesh to obtain the final product.

[0049] The actual product image of the water-based adhesive prepared in this embodiment is shown below. Figure 1 As shown.

[0050] The molecular weight test results of the water-based adhesive prepared in this embodiment are shown in the schematic diagram below. Figure 2 and Figure 3 As shown. Example 2

[0051] The only difference between this embodiment and Example 1 is as follows: The water-based binder for lithium batteries, by weight, comprises the following raw materials: 68.5 parts acrylic acid / acrylate, 18.5 parts acrylonitrile, 7 parts crosslinking monomer, 11.8 parts auxiliary monomer, 3 parts reaction aid (0.8 parts initiator, 1.5 parts emulsifier and 0.7 parts pH adjuster), 4.1 parts functional aid, and 95 parts deionized water.

[0052] All other implementation schemes are the same. Example 3

[0053] The only difference between this embodiment and Example 1 is as follows: The water-based binder for lithium batteries, by weight, comprises the following raw materials: 68.5 parts acrylic acid / acrylate, 21.4 parts acrylonitrile, 6 parts crosslinking monomer, 10 parts auxiliary monomer, 3 parts reaction aid (0.8 parts initiator, 1.5 parts emulsifier and 0.7 parts pH adjuster), 3.5 parts functional aid, and 95 parts deionized water.

[0054] All other implementation schemes are the same.

[0055] Comparative Example 1

[0056] The only difference between this comparative example and Example 1 is as follows: the water-based binder for lithium batteries, by weight, comprises: 68.5 parts acrylic acid / acrylate, 21.4 parts acrylonitrile, 2.5 parts crosslinking monomer, 20 parts auxiliary monomer, 3 parts reaction aid (0.8 parts initiator, 1.5 parts emulsifier and 0.7 parts pH adjuster), 4.1 parts functional aid, and 90 parts deionized water.

[0057] All other implementation schemes are the same.

[0058] Comparative Example 2

[0059] The only difference between this comparative example and Example 1 is as follows: the water-based binder for lithium batteries, by weight, comprises: 68.5 parts acrylic acid / acrylate, 10.4 parts acrylonitrile, 6 parts crosslinking monomer, 6.8 parts auxiliary monomer, 3 parts reaction aid (0.8 parts initiator, 1.5 parts emulsifier and 0.7 parts pH adjuster), 1.2 parts functional aid, and 85 parts deionized water.

[0060] All other implementation schemes are the same.

[0061] Comparative Example 3

[0062] The only difference between this comparative example and Example 1 is that the crosslinking monomer is a composition of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate in a mass ratio of 6:0.5.

[0063] All other implementation schemes are the same.

[0064] Comparative Example 4

[0065] The only difference between this comparative example and Example 1 is that the acrylic / acrylate composition is a combination of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate in a mass ratio of 40.5:25:3.

[0066] All other implementation schemes are the same.

[0067] Comparative Example 6

[0068] The only difference between this comparative example and Example 1 is that the auxiliary monomer is a composition of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide, and phenoxyethyl acrylate in a mass ratio of 10:0.2:1.

[0069] All other implementation schemes are the same.

[0070] Performance testing

[0071] Preparation of positive electrode sheet: The positive electrode active material NCM811, conductive carbon black and the binder prepared in the examples and comparative examples were prepared into a slurry in a mass ratio of 95:3:2 and coated on a 15μm aluminum foil current collector. Then, the slurry was vacuum dried to prepare the positive electrode sheet.

[0072] Preparation of negative electrode sheet: SiOx / C (Si content 15wt%), conductive carbon black and binder prepared in the examples and comparative examples are prepared into a slurry in a mass ratio of 94:3:3 and coated on an 8μm copper foil current collector. Then, the slurry is vacuum dried to prepare the negative electrode sheet.

[0073] Lithium-ion battery preparation: The positive electrode, negative electrode, separator, and electrolyte prepared above are assembled into a lithium-ion battery. The electrolyte is 1.2M LiPF6 in EC:EMC:DEC (3:5:2, containing 2% FEC), and the separator is 12μm ceramic-coated PP (Al2O3@PP).

[0074] 1. Peel strength: The test reference standard GB 2792-2014. The electrode and current collector were peeled off at a 180° angle and a rate of 50 mm / min. The peel force was measured. The aging test conditions were 85°C high temperature storage for 48 hours and then retested. The average value of 10 positive electrode test results was recorded in Table 1.

[0075] 2. Interface impedance: The test reference standard GB / T 33827-2017, three-electrode system (Li / electrolyte / electrode), frequency 0.01Hz~100kHz, amplitude 10mV, the impedance after 200 cycles at 45℃, and the result is the average of 10 tests recorded in Table 1.

[0076] 3. Flexibility: Using a cylindrical bending tester, the positive electrode sheet prepared above was cut into a 5cm rectangular strip, then wound onto a 2cm diameter metal cylinder, pulled at a constant speed of 180° and cyclically 5 times. The electrode sheet was observed to see if there were any obvious cracks. The active material shedding rate was measured before and after the test, and the results were recorded in Table 1.

[0077] 4. Cyclic performance: The test reference standard is to charge the lithium-ion battery at 0.5C constant current to 4.2V at 25℃, then charge at constant voltage with a cutoff current of 0.05C, and then discharge at 0.5C constant current to 3V. This is one cycle. After repeating 1000 cycles, the capacity retention rate after 1000 cycles is calculated, and the average value of 10 tests is recorded in Table 1.

[0078] Table 1 Performance Test Results

[0079] Example Peel strength (N / cm) Peel strength (N / cm) after 85℃ / 48h Interfacial impedance (Ω·cm²) Flexibility (cracks, rate of loss of active material %) Cyclic capacity retention rate (%) Example 1 3.24 2.97 5.24 No obvious cracks, 0.23 91.1 Example 2 3.17 2.91 5.31 No obvious cracks, 0.24 90.6 Example 3 3.22 2.93 5.27 No obvious cracks, 0.21 90.8 Comparative Example 1 2.84 2.52 6.14 No obvious cracks, 0.41 86.5 Comparative Example 2 2.93 2.54 5.87 No obvious cracks, 0.36 88.6 Comparative Example 3 2.89 2.61 5.91 No obvious cracks, 0.37 87.8 Comparative Example 4 3.01 2.72 5.77 No obvious cracks, 0.40 88.2 Comparative Example 6 2.99 2.68 5.69 No obvious cracks, 0.35 88.4

[0080] From the final performance test results of the examples and comparative examples, it can be seen that Comparative Examples 1 and 2, because they did not adopt the specific ratio of raw materials specified in this application, were significantly inferior to the examples in the overall performance test of the batteries made with the binder. Comparative Examples 3 to 6, on the other hand, did not further follow the specific raw material selection and ratio specified in this application, resulting in a significant decrease in their performance test results compared to Examples 1 to 3. This is because the crosslinking monomers and auxiliary monomers, etc., added without following the specified ratio, had significantly reduced synergistic effects, failing to form more stable covalent crosslinking points as in Examples 1 to 3, thus hindering the inhibition of molecular chain slippage and the formation of a stable crosslinking network. Consequently, the structural integrity could not be optimal, leading to a significant decrease in the performance balance of the aqueous binder.

Claims

1. An aqueous binder for lithium batteries, characterized in that: By weight, its raw materials include at least: 55-75 parts of acrylic acid / acrylate, 15-25 parts of acrylonitrile, 3-8 parts of crosslinking monomer, 2-4 parts of reaction aid, 80-120 parts of deionized water, 9-15 parts of auxiliary monomer and 3-6 parts of functional aid. The crosslinking monomer is a composition of N,N'-methylenebisacrylamide and polyethylene glycol di(meth)acrylate in a mass ratio of (2~4):(0.5~1.2). The reaction aids include initiators, emulsifiers, and pH adjusters; The mass ratio of auxiliary monomers to functional additives in the acrylic / acrylate compounds is (60~70):(10~14):(3.5~5). The auxiliary monomer is a composition of 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide, and phenoxyethyl acrylate in a mass ratio of (5~8):(0.5~1.5):(4~6). The functional additive is a composition of nano-zirconia and propylenetrimethoxysilane in a mass ratio of (1~3):(1~2). The acrylic / acrylate is a composition of methacrylic acid, hydroxyethyl acrylate and isobornyl acrylate, in a mass ratio of (25~35):(20~25):(8~15). The acrylic / acrylate composition has an acrylonitrile to crosslinking monomer mass ratio of (60~70):(16~23):(5~8).

2. The aqueous binder for lithium batteries according to claim 1, characterized in that: The average particle size of the nano-zirconia is 20~40 nm.

3. A method for preparing an aqueous binder for lithium batteries according to any one of claims 1 to 2, characterized in that: Specifically, the following steps are included: S1: Add acrylic acid / acrylate, acrylonitrile, crosslinking monomer, and auxiliary monomer to deionized water, heat to 50-55℃, and stir at 300-400 rpm for 30-40 min until homogeneous to obtain a reaction mixture; S2: Add emulsifier and pH adjuster to the reaction mixture, mix and stir, and mix initiator with deionized water to obtain initiation solution. Then add 10-20 wt% of the initiation solution to the reaction mixture, heat to 75-80℃, maintain the temperature for 30-35 min, then heat to 85-88℃, add the remaining initiation solution dropwise, and stir at 100-120 rpm for 2-2.5 h, and finally heat to 90-93℃, stir at 60-80 rpm for 1.5-2 h; S3: After the reaction is complete, add functional additives, stir at 300-400 rpm for 20-30 min, and filter through a 200-300 mesh filter to obtain the final product.

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