High-wettability water-based acrylic adhesive as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery diaphragms, in particular to a high-wettability water-based acrylic adhesive as well as a preparation method and application thereof. Multiple polar functional groups are directionally introduced into a molecular structure through a solution polymerization process, so that the surface tension is remarkably reduced, and the interfacial adsorption capacity is synergistically improved. The binder has self-wettability and self-dispersibility, ceramic slurry can rapidly permeate a base material without addition of an auxiliary agent when the binder is applied to a polyolefin base membrane, the wetting speed of 30 microliters of electrolyte reaches 14.5 cm / 30 s or above, the permeability increment of a ceramic coating is 20 s / 100 mL or below, the peel strength is improved to 132 N / m or above, and the service life of the ceramic coating is prolonged. The problems of non-uniform electrolyte distribution, battery internal resistance increase and thermal runaway risk caused by insufficient wettability of a traditional binder are effectively solved, and the safety and rate capability of the lithium battery in a high-temperature environment are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and more specifically, to a highly wettable water-based acrylic binder, its preparation method, and its application. Background Technology

[0002] The lithium-ion battery separator is a crucial component between the positive and negative electrodes, its core function being to prevent short circuits and ensure efficient ion transport. This role requires the separator to possess high porosity and the ability to be uniformly and fully wetted by the electrolyte. Traditional aqueous binders for lithium-ion battery ceramic separators are primarily emulsion-type products synthesized from acrylate monomers. While the manufacturing processes for these products are mature and widely used, they are inherently thermodynamically unstable systems, exhibiting relatively poor mechanical stability, electrolyte stability, and storage stability. Therefore, the market has a clear demand for more stable solution-based aqueous binders.

[0003] On the other hand, when using existing water-based binders to formulate ceramic separator slurries, water generally has insufficient dispersibility for ceramic powder and insufficient wettability for polyolefin-based membranes. Therefore, additional additives such as dispersants, thickeners, and wetting agents are typically required. Although these additives are used in small quantities, they can have unpredictable adverse effects on the key properties of the slurry (such as heat resistance, water absorption, and coatability) and even the overall performance of the final lithium battery. More seriously, if the separator's wettability is insufficient, the electrolyte will not be able to fully fill its pores, leading to impaired ion transport and a significant increase in the battery's internal resistance (including interfacial impedance). This not only reduces the battery's charge / discharge efficiency and rate performance but may also trigger serious safety hazards such as thermal runaway.

[0004] Therefore, there is an urgent need to develop a new type of waterborne binder that can improve its own stability, significantly enhance its dispersion ability in ceramic slurries and its wetting ability in polyolefin-based films, thereby reducing or even eliminating the need for additional additives. Summary of the Invention

[0005] The purpose of this invention is to provide a highly wettable waterborne acrylic adhesive to solve the technical problem of poor wettability of existing waterborne acrylic adhesives on polyolefin-based films.

[0006] To achieve the above objectives, the present invention is implemented through the following solutions; A highly wettable waterborne acrylic adhesive is prepared from the following raw materials in parts by weight: 1-50 parts of protective colloid, 5-50 parts of acrylamide monomer, 2-15 parts of inorganic alkali, 0.5-8 parts of organic solvent, 350-550 parts of deionized water, 2-50 parts of functional monomer, 5-30 parts of organic acid, and 0.02-2.0 parts of initiator; the highly wettable waterborne acrylic adhesive is synthesized by solution polymerization, and its glass transition temperature is 120-220℃, and its solid content is 15.0-25.0%.

[0007] Optionally, the protective colloid is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, and polyethylene glycol.

[0008] Optionally, the acrylamide monomer is selected from at least one of acrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N,N-dimethylacrylamide, N,N-methylenebisacrylamide, and methacrylamide.

[0009] Optionally, the functional monomer is selected from at least one of acrylonitrile, methacrylonitrile, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0010] Optionally, the organic acid is at least one of acrylic acid, methacrylic acid, cis-butenedioic acid, trans-butenedioic acid, 2-methylenesuccinic acid, 2-acrylamido-2-methylpropanesulfonic acid, or a homopolymer or copolymer synthesized from the monomer.

[0011] Optionally, the initiator is selected from at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

[0012] Optionally, the organic solvent is selected from at least one of methanol, ethanol, isopropanol, and dodecyl mercaptan.

[0013] Another object of the present invention is to provide a method for preparing the aforementioned highly wettable waterborne acrylic adhesive, comprising the following steps: (1) Add deionized water, organic solvent and protective colloid to the reaction vessel, heat and stir until the protective colloid is completely dissolved; (2) Cool down to below 40℃, add inorganic alkaline aqueous solution, heat up and stir until uniform; (3) Add organic acid dropwise to neutralize and adjust the pH of the system to 5.0-8.0; (4) Add acrylamide monomers, functional monomers and initiators, and heat to 60-85℃ for 1-4 hours; (5) Cool down to below 45℃, neutralize, and filter out the material.

[0014] Optionally, the reaction temperature in step (4) is 75℃±5℃ and the reaction time is 1.5-2 hours.

[0015] Optionally, the glass transition temperature of the prepared highly wettable waterborne acrylic adhesive (waterborne acrylic emulsion) is 120-220℃, and the overall solid content of the waterborne acrylic emulsion is 15.0-25.0%.

[0016] Another object of the present invention is to provide a lithium battery separator, which is formed by coating a PE base film with the aforementioned highly wettable water-based acrylic adhesive to form a ceramic coating, the ceramic coating having a thickness of 2.0-3.0 μm.

[0017] This application has the following beneficial effects: The present invention introduces multiple polar groups such as hydroxyl, carboxyl, amide, and sulfonic acid groups into the adhesive molecular chain through solution polymerization (constructed by acrylamide monomers, functional monomers, and organic acids), which significantly reduces the surface tension of the adhesive solution and enhances the interfacial adsorption capacity, thereby endowing the adhesive with excellent self-wetting and self-dispersing properties. On the one hand, the polar groups effectively reduce the solid-liquid interfacial energy through directional arrangement, reducing the contact angle of the adhesive solution with the polyolefin-based membrane, and achieving rapid spreading and penetration without wetting agents (wetting speed of 30μL electrolyte reaches more than 14.5 cm² / 30s); on the other hand, the hydrophilic groups stabilize and disperse ceramic particles through steric hindrance and electrostatic repulsion, reducing the amount of dispersant required, and ultimately synergistically reducing the membrane permeability increment to less than 20s / 100mL and increasing the peel strength to more than 132 N / m, fundamentally solving the risk of increased battery internal resistance and thermal runaway caused by insufficient wetting. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments. Example 1

[0019] A method for preparing a highly wettable waterborne acrylic adhesive includes the following steps: 10g of polyvinyl alcohol (PVA) and 1g of methanol are added to a reaction vessel, and deionized water is added to bring the total mass to 400g. The mixture is stirred in a 95°C water bath until the PVA is completely dissolved. After cooling the PVA solution to below 40°C, 5g of sodium hydroxide solution (5wt%) is added, and a measured amount of acrylic acid is added dropwise to adjust the pH of the system to 5.5±0.2. Subsequently, 100g of N-hydroxymethylacrylamide (NMA), 20g of acrylamide (AM), 1g of acrylonitrile, and 0.1g of ammonium persulfate are added to the solution. After stirring and dissolving, the temperature is raised to 75°C, and stirring is maintained. The reaction is carried out for 1.5-2 hours. After cooling to below 45°C, sodium hydroxide solution (5wt%) is added to adjust the pH to 6.0±0.2. The product obtained after filtration is a colorless, transparent, homogeneous aqueous solution, which is the finished product. Example 2

[0020] A method for preparing a highly wettable waterborne acrylic adhesive includes the following steps: 6g of polyvinyl alcohol (PVA) and 0.5g of dodecyl mercaptan are added to a reaction vessel, and deionized water is added to a total mass of 400g. The mixture is stirred in a 95°C water bath until the PVA is completely dissolved. After cooling the PVA solution to below 40°C, 3g of sodium hydroxide solution (5wt%) is added, and a measured amount of methacrylic acid is added dropwise to adjust the pH of the system to 6.5±0.2. Subsequently, 20g of N-hydroxymethylacrylamide (NMA), 80g of acrylamide (AM), 1g of acrylonitrile, and 0.08g of ammonium persulfate are added to the solution. After stirring and dissolving, the temperature is raised to 75°C, and stirring is maintained. The reaction is carried out for 1.5-2 hours. After cooling to below 45°C, sodium hydroxide solution (5wt%) is added to adjust the pH to 7.0±0.2. The product obtained after filtration is a colorless, transparent, homogeneous aqueous solution, which is the finished product. Example 3

[0021] A method for preparing a highly wettable waterborne acrylic adhesive includes the following steps: 15g of polyvinyl alcohol (PVA) and 1.5g of isopropanol are added to a reaction vessel, and deionized water is added to bring the total mass to 400g. The mixture is stirred in a 95°C water bath until the PVA is completely dissolved. After cooling the PVA solution to below 40°C, 7g of sodium hydroxide solution (5wt%) is added, and a measured amount of cis-butenedioic acid is added dropwise to adjust the pH of the system to 6.0±0.2. Subsequently, 80g of N-hydroxymethylacrylamide (NMA), 70g of acrylamide (AM), 2g of methacrylonitrile, and 0.15g of ammonium persulfate are added to the solution. After stirring and dissolving, the temperature is raised to 75°C, and stirring is maintained. The reaction is carried out for 1.5-2 hours. After cooling to below 45°C, sodium hydroxide solution (5wt%) is added to adjust the pH to 6.5±0.2. The product obtained after filtration is a colorless, transparent, homogeneous aqueous solution, which is the finished product.

[0022] Comparative Example 1 Compared with Example 1, the difference is that a measured amount of hydrochloric acid (5wt%) was added instead of acrylic acid to make the pH value of the system reach 5.5±0.2.

[0023] Comparative Example 2 Compared with Example 1, the difference is that 25g of N-hydroxymethylacrylamide (NMA), 5g of acrylamide (AM), 1g of acrylonitrile and 0.1g of ammonium persulfate were added to the solution.

[0024] Comparative Example 3 Compared to Example 1, the difference is that an equal amount of deionized water was used instead of acrylonitrile.

[0025] Comparative Example 4 Commercially available waterborne acrylic ester copolymer adhesive, model SCBA-1, was purchased from Lanting New Energy Technology (Zhejiang) Co., Ltd.

[0026] To test the performance of the binders obtained in Examples 1-3 and Comparative Examples 1-4, they were applied to the lithium battery separator preparation process to prepare the corresponding lithium battery separators. The lithium battery separator preparation process is as follows: calcined alumina with a D50 of 0.8±0.1μm was mixed with pure water and CMC at a weight ratio of 4:6:0.051 and dispersed in a disperser at 1500r / min-2000r / min to prepare a dispersion; 4.0% of the binder by weight of the dispersion was added, and the mixture was dispersed in a disperser at 300-500r / min to prepare a coating slurry, which was then coated on the surface of a PE separator with a coating thickness of 2-3μm and cured at 60-80℃ to obtain the lithium battery separator.

[0027] The binders obtained in Examples 1-3 and Comparative Examples 1-4 were used as binders in the above-described lithium battery separator preparation process, and then coated separators were prepared according to the above-described lithium battery separator preparation process. The air permeability, wettability, and peel strength of the prepared coated separators were compared using conventional methods, and the results are shown in Table 1.

[0028] Table 1. Diaphragm Test Data

[0029] As can be seen from Table 1, the adhesive-coated diaphragm prepared in Example 1 achieves an air permeability increment of 20s / 100mL, a wetting area of ​​14.5cm² in 30s, and a peel strength of 132N / m, meeting the requirements of low air permeability increment, high wettability, and high peel strength. This indicates that acrylic acid, acrylamide, and acrylonitrile, through the triple synergistic effect of carboxyl ionization, amide hydrogen bonding, and cyano polarity, successfully reduce the surface tension to a critical value, achieving a high wetting effect without the need for wetting aids.

[0030] Example 2 (methacrylic acid + high acrylamide ratio) further optimized performance, reducing the air permeability increment to 18s / 100mL, increasing the wetting area to 15.2cm², and enhancing the peel strength to 141.5N / m. Example 3 (maleic acid + methacrylonitrile) performed even better, with a wetting area of ​​18.6cm² and a peel strength of 148N / m. The comprehensive improvement of both examples compared to Example 1 demonstrates the scalability of the present invention: the high dissociation degree of methacrylic acid enhances interfacial adsorption, while the dicarboxyl structure of maleic acid strengthens the ceramic dispersion stability through steric hindrance.

[0031] Comparative Example 1 showed a complete collapse in performance after replacing organic acid with hydrochloric acid. The increase in air permeability soared to 35s / 100mL, the wetting area plummeted to 10.2cm², and the peel strength was only 105N / m. This indicates that the carboxyl group of organic acid is the core group for reducing surface tension. Hydrochloric acid cannot provide stable hydrophilic polar groups, which leads to an increase in solution interfacial energy and loss of wettability and adhesion.

[0032] After adjusting the monomer ratio (5 parts acrylamide and 25 parts N-hydroxymethylacrylamide) in Comparative Example 2, the air permeability increment increased to 28 s / 100 mL, the wetting area decreased to 11.1 cm², and the peel strength decreased to 122 N / m. This indicates that a low acrylamide ratio weakens the density of the hydrogen bond network, while a high N-hydroxymethylacrylamide ratio causes excessive cross-linking, and the decrease in molecular chain flexibility leads to a deterioration in wetting and penetration capabilities.

[0033] When the functional monomer (acrylonitrile) was removed in Comparative Example 3, the air permeability increase reached 42s / 100mL, the wetting area was only 9.8cm², and the peel strength was 98N / m. This indicates that the strong polarity of the cyano group can be directionally adsorbed onto the polyolefin-based membrane. After its removal, the interfacial binding energy decreases, and the ceramic dispersion stability is lost simultaneously.

[0034] Comparative Example 4 (commercially available emulsion-type competitor) showed an air permeability increase of 48s / 100mL, a wetting area of ​​12.5cm², and a peel strength of 110.4N / m; this demonstrates the innovation of the solution polymerization system and the directional introduction of polar groups in this invention, and that competitors cannot achieve self-wetting and self-dispersing functions.

[0035] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A high wet-strength waterborne acrylic binder, characterized by: Prepared from the following raw materials by mass fraction: protective colloid 1-50 parts, acrylamide monomer 5-50 parts, inorganic base 2-15 parts, organic solvent 0.5-8 parts, deionized water 350-550 parts, functional monomer 2-50 parts, organic acid 5-30 parts, initiator 0.02-2.0 parts.

2. The high wet-strength waterborne acrylic binder of claim 1, wherein: The protective colloid is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, and polyethylene glycol.

3. The high wet-strength waterborne acrylic binder of claim 1, wherein: The acrylamide monomer is selected from at least one of acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N,N-dimethyl acrylamide, N,N-methylene bisacrylamide, and methacrylamide.

4. The high absorbency water-based acrylic binder of claim 1, wherein: The functional monomer is selected from at least one of acrylonitrile, methacrylonitrile, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

5. The high absorbency water-based acrylic binder of claim 1, wherein: The organic acid is at least one of acrylic acid, methacrylic acid, cis-butenedioic acid, trans-butenedioic acid, 2-methylenebutanedioic acid, and 2-acrylamido-2-methylpropanesulfonic acid, or a homopolymer or copolymer synthesized from the monomer.

6. The high absorbency water-based acrylic binder of claim 1, wherein: The initiator is selected from at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

7. The high absorbency water-based acrylic binder of claim 1, wherein: The organic solvent is selected from at least one of methanol, ethanol, isopropanol, and dodecyl mercaptan.

8. A method of preparing the high wet-strength waterbome acrylic binder according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: (1) adding deionized water, organic solvent, and protective colloid to a reaction kettle, and stirring to dissolve the protective colloid; (2) cooling to below 40°C, adding an aqueous inorganic base solution, and stirring to homogenize; (3) adding the organic acid dropwise and adjusting the pH of the system to 5.0-8.0; (4) adding the acrylamide monomer, functional monomer, and initiator, and heating to 60-85°C for 1-4 hours; (5) cooling to below 45°C, neutralizing, and filtering the product.

9. The method of claim 8, wherein: The reaction temperature in step (4) is 75°C±5°C, and the reaction time is 1.5-2 hours.

10. A lithium battery separator, characterized by: The high-wettability water-based acrylic adhesive of any one of claims 1-7 is coated on the surface of a PE-based film to form a ceramic coating, and the ceramic coating has a thickness of 2.0-3.0 μm.

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