A high dispersibility nano-alumina slurry for diaphragm coating and a preparation method thereof

Abstract

The application provides a high-dispersibility nano-alumina slurry for diaphragm coating and a preparation method thereof, and belongs to the technical field of alumina slurry. An anchoring agent is introduced to stably disperse alumina in an aqueous phase and provide sites for subsequent formation of borate ester bonds; when the anchoring agent is used, the phosphoric acid group thereof preferentially forms a strong interface with the surface of alumina to construct a stable adsorption layer, and the catechol group thereof is distributed outside the adsorption layer to reduce site competition; a flexible ion-conducting agent containing boron is introduced, which can reversibly complex with the catechol site of the anchoring agent to form a borate ester bond, so as to regulate the thixotropy and anti-settling of the slurry, and improve the solubility in water and the preparation stability by adjusting the ionization degree of the phenylboronic acid group to improve the solubility in water and the preparation stability; when the slurry is prepared, the soft agglomerates are sheared and dispersed to form an adsorption layer, and then the flexible ion-conducting agent containing boron is added dropwise to construct a loose three-dimensional dynamic network, so that the settling is slowed down during standing, the viscosity is reduced by shearing to facilitate leveling, and the thixotropy is recovered after shearing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alumina slurry, and relates to a high-dispersity nano-alumina slurry for diaphragm coating and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in consumer electronics, electric vehicles and energy storage systems due to their high energy density and long cycle life. With the continuous improvement of battery energy density, safety problems have become increasingly prominent. In order to improve the heat resistance and safety of the battery, coating a layer of inorganic ceramic coating on the surface of the polyolefin diaphragm has become an industry standard configuration. The ceramic coating not only significantly improves the heat shrinkage resistance of the diaphragm, but also improves the electrolyte wettability to some extent. Ceramic diaphragm coating slurry is mainly divided into solvent type and water-based system, and at present, water-based ceramic slurry has become the mainstream development direction. Traditional water-based ceramic slurry is usually physically mixed by inorganic particles, water-based binder and dispersant. However, the existing water-based slurry technology still has some deficiencies in practical application.

[0003] Traditional alumina coating technology usually adopts a physical mixing method to mix alumina nanoparticles with ordinary binders to prepare a slurry. First, the surface energy of alumina nanoparticles is high, and it is easy to agglomerate in the slurry, resulting in uneven coating, holes or defects, affecting the denseness and protection effect of the coating; second, the bonding force between the coating and the diaphragm substrate mainly depends on the physical adhesion of the binder, and the bonding force is weak, the coating is easy to fall off during battery manufacturing and cycling, affecting the long-term stability and reliability of the battery.

[0004] Secondly, this simple inorganic coating improves safety while not having ion conduction capability itself, often blocking some pores of the diaphragm, increasing the transmission path and resistance of lithium ions, leading to an increase in the internal resistance of the battery, and a decrease in the rate performance and power density. This limits the performance of the battery in application scenarios requiring fast charging and discharging. SUMMARY

[0005] To address the aforementioned problems, the present invention aims to provide a highly dispersible nano-alumina slurry for diaphragm coating and its preparation method. This application prepares an anchoring agent containing phosphate and catechol groups, which stably disperses alumina in the aqueous phase and provides sites for subsequent formation of borate ester bonds. During use, the phosphate groups preferentially form a strong interfacial interaction with the alumina surface to construct a stable adsorption layer, while the catechol groups are distributed on the outer side of the adsorption layer to reduce site competition. A boron-containing flexible ion-conducting agent is introduced, which reversibly complexes with the catechol sites of the anchoring agent to form borate ester bonds, regulating the thixotropy and anti-settling properties of the slurry. Adjusting the pH increases the ionization degree of the phenylboronic acid groups to improve water solubility and formulation stability. During slurry preparation, high-speed shearing breaks up soft aggregates and forms an adsorption layer. Subsequently, the boron-containing flexible ion-conducting agent is added dropwise to construct a loose three-dimensional dynamic network, achieving reduced sedimentation during static settling, reduced viscosity during coating to facilitate leveling, and thixotropic recovery after shear reduction. Stirring and vacuum degassing reduce defects and improve uniformity.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a highly dispersible nano-alumina slurry for diaphragm coating, the method comprising:

[0008] S1: Prepare a ethylene glycol phosphate methacrylate solution. Add sodium hydroxide solution to adjust the pH under ice bath stirring to obtain a pre-neutralized monomer solution. Add 3-methacrylamide and acrylamide to obtain a mixed monomer solution. Add disodium ethylenediaminetetraacetate under nitrogen atmosphere to obtain pre-reaction solution A. Adjust the pH with hydrochloric acid solution and add VA-044 initiator to obtain reaction solution A. React in the dark and dialyze to obtain anchoring agent solution.

[0009] S2: Poly(ethylene glycol) methacrylate is passed through a chromatography column packed with alkaline alumina to remove the polymerization inhibitor, resulting in de-inhibited poly(ethylene glycol) methacrylate. The de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid are added to a mixed solvent to obtain solution B, wherein the mixed solvent is a mixture of ethanol, deionized water, and N,N-dimethylformamide. After heating under a nitrogen atmosphere, azobisisobutyronitrile is added to obtain reaction solution C. The reaction is carried out, and the product is purified by repeated precipitation with cold diethyl ether and vacuum dried to obtain the initial product. The initial product is added to deionized water and the pH is adjusted with sodium hydroxide to obtain a boron-containing flexible ion-conducting agent solution.

[0010] S3: Add alumina powder to the anchoring agent solution, add deionized water and shear to obtain a pre-dispersed liquid. Adjust the pH with ammonia water and stir to add boron-containing flexible ion-conducting agent solution. After the addition is completed, continue stirring to obtain a pretreated slurry. Vacuum degassing is used to obtain a highly dispersible nano alumina slurry for membrane coating.

[0011] As a preferred technical solution of the present application, in step S1, the concentration of the ethylene glycol methacrylate phosphate solution is 30-50%, for example, it can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, but not limited to the listed values, other values not listed in this range are also applicable.

[0012] In some optional embodiments, the concentration of the sodium hydroxide solution is 2-3M, for example, it can be 2.0M, 2.1M, 2.2M, 2.3M, 2.4M, 2.5M, 2.6M, 2.7M, 2.8M, 2.9M or 3.0M, but not limited to the listed values, other values not listed in this range are also applicable.

[0013] In some optional embodiments, the pH of the ethylene glycol methacrylate phosphate solution is adjusted to 4.5-5.5 using a sodium hydroxide solution, for example, it can be adjusted to 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4 or 5.5, but not limited to the listed values, other values not listed in this range are also applicable.

[0014] In some optional embodiments, the molar ratio of ethylene glycol methacrylate phosphate to 3-methacryloyl dopamine is (1-2):(1-3), for example, it can be (1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0):(1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8 or 3.0), but not limited to the listed values, other values not listed in this range are also applicable.

[0015] In some optional embodiments, the molar ratio of ethylene glycol methacrylate phosphate to acrylamide is (1-2):(10-15), for example, it can be (1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0):(10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5 or 15.0), but not limited to the listed values, other values not listed in this range are also applicable.

[0016] In some optional embodiments, the total solid content of the mixed monomer solution is 10-15%, for example, it can be 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.5%, 14.0%, 14.5% or 15.0%, but not limited to the listed values, other values not listed in the range are also applicable.

[0017] In some optional embodiments, the amount of the disodium ethylenediaminetetraacetate is 0.01-0.05% of the total mass of the ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, for example, it can be 0.010%, 0.014%, 0.018%, 0.022%, 0.026%, 0.030%, 0.034%, 0.038%, 0.042%, 0.046% or 0.050%, but not limited to the listed values, other values not listed in the range are also applicable.

[0018] In some optional embodiments, the concentration of the hydrochloric acid solution is 1-2M, for example, it can be 1.0M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M or 2.0M, but not limited to the listed values, other values not listed in the range are also applicable.

[0019] In some optional embodiments, the pH of the pre-reaction solution A is adjusted to 4-5 using a hydrochloric acid solution, for example, it can be adjusted to 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but not limited to the listed values, other values not listed in the range are also applicable.

[0020] In some optional embodiments, the amount of the VA-044 initiator (azo-diisobutylimidazoline hydrochloride) is 0.5-1% of the total mass of the ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but not limited to the listed values, other values not listed in the range are also applicable.

[0021] In some optional embodiments, the temperature of the light-protected reaction of the reaction solution A is 50-60℃, for example, it can be 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃ or 60℃, but not limited to the listed values, other values not listed in the range are also applicable.

[0022] In some optional embodiments, the reaction solution A is reacted in the dark for 8-12 hours, for example, it can be 8.0 hours, 8.4 hours, 8.8 hours, 9.2 hours, 9.6 hours, 10.0 hours, 10.4 hours, 10.8 hours, 11.2 hours, 11.6 hours or 12.0 hours, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0023] In some optional embodiments, the solid content of the anchoring agent solution is 8-12%, for example, it can be 8.0%, 8.4%, 8.8%, 9.2%, 9.6%, 10.0%, 10.4%, 10.8%, 11.2%, 11.6% or 12.0%, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0024] As a preferred technical solution of the present application, in step S2, the volume ratio of ethanol to deionized water in the mixed solvent is (8-9):(2-1), for example, it can be (8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0):(2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1 or 1.0), but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0025] In some optional embodiments, the volume fraction of N,N-dimethylformamide in the mixed solvent is 2-6%, for example, it can be 2.0%, 2.4%, 2.8%, 3.2%, 3.6%, 4.0%, 4.4%, 4.8%, 5.2%, 5.6% or 6.0%, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0026] In some optional embodiments, the molar ratio of deprotection (ethylene glycol) methacrylate and 3-acrylamidobenzenesulfonic acid is (10-15):(1-3), for example, it can be (10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5 or 15.0):(1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8 or 3.0), but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0027] In some optional embodiments, the solid content of the solution B is 15-20%, for example, it can be 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5% or 20.0%, but not limited to the listed values, and other values not listed in the range are also applicable.

[0028] In some optional embodiments, the solution B is heated to 65-70°C under a nitrogen atmosphere, for example, it can be heated to 65.0°C, 65.5°C, 66.0°C, 66.5°C, 67.0°C, 67.5°C, 68.0°C, 68.5°C, 69.0°C, 69.5°C or 70.0°C, but not limited to the listed values, and other values not listed in the range are also applicable.

[0029] In some optional embodiments, the amount of azobisisobutyronitrile is 0.5-1.5% of the total mass of the de-polymerization (ethylene glycol) methacrylate and 3-acrylamidobenzenboronic acid, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, but not limited to the listed values, and other values not listed in the range are also applicable.

[0030] In some optional embodiments, the reaction time of the reaction solution C is 12-16h, for example, it can be 12.0h, 12.4h, 12.8h, 13.2h, 13.6h, 14.0h, 14.4h, 14.8h, 15.2h, 15.6h or 16.0h, but not limited to the listed values, and other values not listed in the range are also applicable.

[0031] In some optional embodiments, the number of times of repeated precipitation purification of the product with cold diethyl ether is 2-3 times, for example, it can be 2.0 times or 3.0 times, but not limited to the listed values, and other values not listed in the range are also applicable.

[0032] In some optional embodiments, the initial product is added to deionized water and the pH is adjusted to 8-8.5 with sodium hydroxide, for example, it can be adjusted to 8.00, 8.05, 8.10, 8.15, 8.20, 8.25, 8.30, 8.35, 8.40, 8.45 or 8.50, but not limited to the listed values, and other values not listed in the range are also applicable.

[0033] In some optional embodiments, the solid content of the boron-containing flexible ionic agent solution is 5-10%, for example, it can be 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, or 10.0%, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0034] As a preferred technical solution of the present application, in step S3, the particle size of the alumina powder is 300-500 nm, for example, it can be 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, or 500 nm, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0035] In some optional embodiments, the mass fraction of the alumina powder in the pre-dispersion solution is 68-78 wt.%, for example, it can be 68 wt.%, 69 wt.%, 70 wt.%, 71 wt.%, 72 wt.%, 73 wt.%, 74 wt.%, 75 wt.%, 76 wt.%, 77 wt.%, or 78 wt.%, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0036] In some optional embodiments, the linear velocity of the shear after the alumina powder is added to the anchor agent solution is 8-12 m / s, for example, it can be 8.0 m / s, 8.4 m / s, 8.8 m / s, 9.2 m / s, 9.6 m / s, 10.0 m / s, 10.4 m / s, 10.8 m / s, 11.2 m / s, 11.6 m / s, or 12.0 m / s, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0037] In some optional embodiments, the time of shear after the alumina powder is added to the anchor agent solution is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min, or 60 min, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0038] In some optional embodiments, the mass ratio of the anchoring agent to the alumina powder is (0.5-2.5):100, for example, it can be 0.5:100, 0.7:100, 0.9:100, 1.1:100, 1.3:100, 1.5:100, 1.7:100, 1.9:100, 2.1:100, 2.3:100, or 2.5:100, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0039] In some optional embodiments, the concentration of the ammonia water is 2-5%, for example, it can be 2.0%, 2.3%, 2.6%, 2.9%, 3.2%, 3.5%, 3.8%, 4.1%, 4.4%, 4.7%, or 5.0%, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0040] In some optional embodiments, the pH of the pre-dispersion is adjusted to 7.2-8.2 using ammonia water, for example, it can be adjusted to 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, or 8.2, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0041] In some optional embodiments, the linear velocity of stirring after adjusting the pH of the pre-dispersion using ammonia water is 2-5m / s, for example, it can be 2.0m / s, 2.3m / s, 2.6m / s, 2.9m / s, 3.2m / s, 3.5m / s, 3.8m / s, 4.1m / s, 4.4m / s, 4.7m / s, or 5.0m / s, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0042] In some optional embodiments, the mass ratio of the boron-containing flexible ionophore to the alumina powder is (1-3):100, for example, it can be 1.0:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100, 2.0:100, 2.2:100, 2.4:100, 2.6:100, 2.8:100, or 3.0:100, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0043] In some optional embodiments, the time for dropping the boron-containing flexible ionophore solution is 10-30min, for example, it can be 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min, or 30min, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0044] In some optional embodiments, the time for the continued stirring is 20-30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0045] In a second aspect, the present application provides a high-dispersibility nano-alumina slurry for diaphragm coating.

[0046] The present application prepares an anchoring agent which can stably disperse alumina in an aqueous phase and provide a site for forming a borate ester bond with a boron-containing component. The glycol methacrylate phosphate is pre-neutralized with a sodium hydroxide solution in an ice bath to partially ionize the phosphate groups, reduce polymerization instability caused by the strong acidity of the monomer, and avoid local strong alkaline conditions to initiate oxidation side reactions of the catechol structure. Subsequently, the mixed monomer system is composed of 3-methacryloyl dopamine (providing catechol sites) and acrylamide (providing a hydrophilic backbone and segment flexibility), nitrogen deoxygenation is used to reduce the inhibition of dissolved oxygen on free radical polymerization and the oxidation of catechol. Ethylenediaminetetraacetic acid disodium salt is added to complex trace metal ions, further inhibiting metal ion-catalyzed oxidation of catechol. The system pH is adjusted, and a water-soluble azo initiator VA-044 is used to initiate free radical polymerization under light-proof conditions to obtain a copolymer containing phosphate groups and catechol groups. Dialysis is used to remove unreacted monomers, oligomers, and inorganic salts to obtain an anchoring agent solution with more stable composition and more controllable ionic strength. When the anchoring agent is used subsequently, the phosphate groups preferentially form strong interfacial interactions with the alumina surface hydroxyl / metal sites to construct a relatively stable adsorption layer on the particle surface; while the catechol groups do not undertake the main anchoring task and are more distributed on the outside of the adsorption layer to provide space conditions for dynamic bonding with the boron-containing component, thereby reducing the site competition between the same functional groups in anchoring and crosslinking.

[0047] The present application introduces a boron-containing flexible ionophore, which can form a reversible boronate ester bond with the catechol site of the anchoring agent in the aqueous phase, and uses the reversible bond to regulate the thixotropy and anti-settling of the slurry. The poly(ethylene glycol) methacrylate monomer is first passed through an alkaline alumina column to remove the polymerization inhibitor, avoiding the consumption of free radicals by the polymerization inhibitor, which leads to a decrease in polymerization conversion rate or abnormal molecular weight distribution; the de-inhibited poly(ethylene glycol) methacrylate is dissolved in an ethanol / water mixed solvent with 3-acrylamidophenylboronic acid, and N,N-dimethylformamide is added as a cosolvent to improve the solubility of the aromatic boronic acid monomer in the system and maintain homogeneity as much as possible, reducing the composition drift of copolymerization. After nitrogen is passed, azobisisobutyronitrile is added to perform free radical copolymerization, obtaining a copolymer containing polyethylene glycol segments and phenylboronic acid side groups; the product is repeatedly precipitated with cold diethyl ether and vacuum dried to remove residual monomers, oligomers and solvents, reducing the influence of impurities and residual solvents during subsequent slurry preparation. The polymer is dissolved in deionized water and the pH is adjusted with sodium hydroxide, which on the one hand improves the ionization degree of the phenylboronic acid group (forms borate form), thereby improving the solubility of the boron-containing polymer in water and the preparation stability; on the other hand, it provides a more suitable reaction environment for subsequent complexation with catechol to form a bond, making it easier for the boronic acid / borate site to participate in dynamic boronate ester bonding during slurry preparation.

[0048] The present application uses anchoring adsorption and dynamic boronate ester network to achieve high dispersion and anti-settling of alumina particles, and obtains rheological properties suitable for diaphragm coating. Alumina is added to the anchoring agent solution and dispersed by high-speed shearing, mainly relying on two types of action to complete the pre-dispersion: first, shearing provides enough mechanical energy to break up soft agglomerates; second, the phosphate groups in the anchoring agent molecules form strong interfacial interactions with the alumina surface hydroxyl / metal sites, allowing the polymer to form a relatively stable adsorption layer on the particle surface; the hydrophilic skeleton and the extended catechol site of the adsorption layer improve the hydration stability of the particles and reduce the tendency of re-agglomeration. Then the pH of the pre-dispersion is adjusted with dilute ammonia water, and the boron-containing flexible ionophore solution is added dropwise under relatively mild shearing conditions. The phenylboronic acid / borate site of the boron-containing polymer will reversibly complex with the extended catechol site of the anchoring agent to form a boronate ester bond, thereby forming a loose three-dimensional dynamic network between the particles: this network provides some structural support to the particles when at rest, helping to slow down the settling; during the coating shearing process, some of the dynamic bonds can be broken, causing the system viscosity to decrease, which is beneficial for leveling; after the shearing decreases, the bonds can reorganize to some extent, giving the slurry some thixotropic recovery ability, which is beneficial for the stability of the coating formation. Subsequent stirring is to avoid the formation of microgel / flocculation caused by excessive local concentration, and vacuum defoaming removes the air bubbles introduced during dispersion and stirring, reducing coating defects and improving coating uniformity. The present application establishes a dispersion foundation through strong anchoring on the particle surface, and then regulates the rheology and stability of the slurry through dynamic boronate ester bonds under weak alkaline conditions, to obtain a high-dispersion alumina inorganic slurry suitable for diaphragm coating.

[0049] Compared with the prior art, the application has the following beneficial effects:

[0050] The application prepares an anchoring agent, which can stably disperse alumina in an aqueous phase and provide a site for forming a borate ester bond with a boron-containing component; the anchoring agent is used to inhibit oxidation and initiate free radical polymerization through pre-neutralization, deoxidation and complexation, so as to obtain a copolymer containing a phosphoric acid group and a catechol group in a side chain; when the anchoring agent is used, the phosphoric acid group preferentially forms a strong interface with the surface of alumina to construct a stable adsorption layer, and the catechol group is distributed outside the adsorption layer to provide space conditions for dynamic bonding, thereby reducing site competition.

[0051] The application introduces a boron-containing flexible ionophore, which can form a reversible borate ester bond with a catechol site of the anchoring agent in an aqueous phase, and uses the reversible bond to regulate thixotropy and anti-settling of the slurry; the boron-containing flexible ionophore is removed from an inhibitor, free radical copolymerization is performed to obtain a copolymer containing a polyethylene glycol segment and a phenylboronic acid side group, and the copolymer is subjected to repeated precipitation and vacuum drying to remove residual monomers, oligomers and solvents; the copolymer is dissolved in deionized water and the pH is adjusted to improve ionization of the phenylboronic acid group, improve solubility in water and preparation stability, and provide a more suitable reaction environment for subsequent complexation with catechol to form a bond, so that the boronic acid / borate site is more likely to participate in dynamic borate ester bonding.

[0052] The application uses anchoring adsorption and a dynamic borate ester network to achieve high dispersion and anti-settling of alumina particles, and obtain rheological properties suitable for coating of a diaphragm; high-speed shearing is used to disperse soft agglomerates and make the anchoring agent form a relatively stable adsorption layer on the surface of the particles, so as to improve hydration stability and reduce the tendency of re-agglomeration; after the pH of the pre-dispersion liquid is adjusted, the boron-containing flexible ionophore is added dropwise, so that the boron-containing flexible ionophore reversibly complexes with the extended catechol site to form a borate ester bond, and a loose three-dimensional dynamic network is formed between the particles, so as to slow down the settling when at rest, reduce the viscosity when coating shearing to facilitate leveling, and realize a certain thixotropy recovery after shearing is reduced; subsequent stirring avoids local concentration being too high to cause microgel / flocculation, and vacuum defoaming is used to remove bubbles to reduce coating defects and improve coating uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The infrared spectrum of the anchoring agent prepared by the preparation method described in Example 1 of the application;

[0054] Figure 2 The infrared spectrum of the boron-containing flexible ionophore prepared by the preparation method described in Example 1 of the application;

[0055] Figure 3 The actual picture of the nano-alumina slurry prepared by the preparation method described in Example 1 of the application. DETAILED DESCRIPTION

[0056] The technical solutions of the present application will be described in detail below with reference to specific examples and their accompanying drawings. The examples described herein are specific embodiments of the present application, which are used to illustrate the concept of the present application; these descriptions are all explanatory and exemplary, and should not be understood as limiting the embodiments of the present application and the protection scope of the present application. In addition to the examples described herein, those skilled in the art can also employ other technical solutions that are obvious based on the content disclosed in the claims and the specification of the present application, which include technical solutions that employ any obvious substitutions and modifications to the examples described herein.

[0057] The chemical reagents used in the examples and comparative examples of the present application are all commercially available products, which are not further purified or treated.

[0058] Example 1

[0059] The present example provides a high-dispersibility nano-alumina slurry for diaphragm coating and a preparation method thereof, and the preparation method of the high-dispersibility nano-alumina slurry for diaphragm coating specifically comprises the following steps:

[0060] S1: A glycol methacrylate phosphate solution with a concentration of 45% is prepared, and a sodium hydroxide solution with a concentration of 2.8M is added under ice-bath stirring to adjust the pH to 5.2 to obtain a pre-neutralized monomer solution, and 3-methacryloyl dopamine and acrylamide are mixed to obtain a mixed monomer solution, wherein the molar ratio of glycol methacrylate phosphate to 3-methacryloyl dopamine is 1.8:2.5, the molar ratio of glycol methacrylate phosphate to acrylamide is 1.8:14, and the total solid content of the mixed monomer solution is 14%, and disodium ethylenediaminetetraacetate is added under a nitrogen atmosphere to obtain a pre-reaction liquid A, wherein the amount of disodium ethylenediaminetetraacetate is 0.04% of the total mass of glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, and after adjusting the pH to 4.8 using a hydrochloric acid solution with a concentration of 1.8M, VA-044 initiator is added to obtain a reaction liquid A, wherein the amount of VA-044 initiator is 0.8% of the total mass of glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, and the reaction liquid A is reacted at 58°C for 11h in the dark, and after dialysis, an anchoring agent solution with a solid content of 11% is obtained; Figure 1 The infrared spectrum of the anchoring agent is shown in the figure, and the wide peak at 3600-3200cm -1 corresponds to the O-H / N-H stretching vibration of the catechol hydroxyl group and the amide group in the anchoring agent, accompanied by hydrogen bonding, indicating that the system has obvious hydrophilic characteristics; the absorption at about 2930cm -1 is the stretching vibration of aliphatic C-H, indicating that the acrylic ester / acrylamide copolymer skeleton has been formed; the absorption at about 1660cm -1 and about 1540cm -1absorptions can be attributed to the amide I band (C=O stretching) and the amide II band (N-H bending and C-N stretching coupling), respectively, indicating that the hydrophilic amide segment was introduced and remained; the absorptions in the range of 1600-1500 cm -1 can be attributed to the aromatic ring skeleton vibration, indicating the presence of the catechol aromatic structure; the absorption peaks in the range of about 1250 cm -1 and 1100-900 cm -1 can be attributed to the P=O and P-O (including P-O-C) stretching vibration related to the phosphate group, indicating that the phosphate group-containing side chain has been introduced into the copolymer, providing a structural basis for the subsequent formation of a strong interface with the surface sites of alumina.

[0061] S2: removing the polymerization inhibitor of poly(ethylene glycol) methacrylate by a chromatographic column filled with basic alumina to obtain a de-inhibited poly(ethylene glycol) methacrylate, and adding the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid into a mixed solvent to obtain solution B, wherein the mixed solvent is obtained by compounding ethanol, deionized water and N,N-dimethylformamide; the volume ratio of ethanol to deionized water in the mixed solvent is 8.5:1.5, the volume fraction of N,N-dimethylformamide in the mixed solvent is 5%, the molar ratio of the de-inhibited poly(ethylene glycol) methacrylate to 3-acrylamidophenylboronic acid is 14:2.5, and the solid content of solution B is 19%; after being heated to 69°C under a nitrogen atmosphere, adding azobisisobutyronitrile to obtain reaction liquid C, wherein the amount of azobisisobutyronitrile is 1.2% of the total mass of the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid, and reacting for 15 h; the product is purified by repeatedly precipitating in cold ether for 3 times and vacuum drying to obtain a primary product, which is added into deionized water and adjusted to a pH of 8.4 by sodium hydroxide to obtain a boron-containing flexible ionophore solution with a solid content of 9%; Figure 2 is an infrared spectrum of the boron-containing flexible ionophore. The wide peak appearing in the range of 3600-3200 cm -1 can be attributed to the O-H / N-H stretching vibration, which is derived from the hydrogen bonding of the amide group, the boron-containing site and the polyether segment; the absorptions in the range of 2950-2870 cm -1 can be attributed to the aliphatic CH stretching vibration, indicating that the hydrocarbon backbone of the copolymer main chain and the polyether side chain has been formed; the absorption peaks in the range of 1730-1710 cm -1 can be attributed to the ester carbonyl (C=O) stretching vibration, indicating that the polyethylene glycol methacrylate segment has been introduced into the copolymer; the absorptions appearing in the range of 1660-1540 cm -1 can be attributed to the amide I band / amide II band, indicating that the 3-acrylamidophenylboronic acid monomer has been introduced and remained in the form of an amide structure; the absorption peaks in the range of 1600-1500 cm -1 can be attributed to the aromatic ring skeleton vibration, which is consistent with the aromatic ring structure of the phenylboronic acid side group; the absorptions in the range of 1150-1050 cm-1 absorptions in the range of 1400-1300 cm -1 near 1400-1300 cm

[0062] S3: alumina powder with particle size of 450 nm was added into the anchor agent solution, deionized water was added to the solution, and the pre-dispersion was obtained by shearing at a linear speed of 11 m / s for 50 min, wherein the mass ratio of the anchor agent to the alumina powder was 2.0:100, and the mass fraction of the alumina powder in the pre-dispersion was 72 wt.%. After adjusting the pH to 8.0 by using ammonia water with a concentration of 4%, the solution was stirred at a linear speed of 4 m / s, and a solution containing a boron-containing flexible ion-conducting agent was added, wherein the mass ratio of the boron-containing flexible ion-conducting agent to the alumina powder was 2.5:100. The solution was added dropwise for 25 min, and the stirring was continued for 28 min after the dropwise addition was completed to obtain a pretreatment slurry. Vacuum degassing was performed to obtain a high-dispersity nano-alumina slurry for diaphragm coating. Figure 3 The high-dispersity nano-alumina slurry for diaphragm coating obtained in the embodiment was a milky white uniform slurry, and the overall appearance had no obvious particle feeling, no visible coarse agglomerates or flocculent precipitates, and no obvious foam layer.

[0063] Example 2

[0064] The embodiment provides a high-dispersity nano-alumina slurry for diaphragm coating and a preparation method thereof. The preparation method of the high-dispersity nano-alumina slurry for diaphragm coating specifically comprises the following steps.

[0065] S1: a solution of ethylene glycol methacrylate phosphate with a concentration of 30% was prepared, and a sodium hydroxide solution with a concentration of 2M was added under ice-bath stirring to adjust the pH to 4.5 to obtain a pre-neutralization monomer solution. 3-methacryloyl dopamine and acrylamide were mixed to obtain a mixed monomer solution, wherein the molar ratio of ethylene glycol methacrylate phosphate to 3-methacryloyl dopamine was 1:1, and the molar ratio of ethylene glycol methacrylate phosphate to acrylamide was 1:10. The total solid content of the mixed monomer solution was 10%. Ethylenediaminetetraacetic acid disodium salt was added to the pre-reaction liquid A under a nitrogen atmosphere, wherein the amount of ethylenediaminetetraacetic acid disodium salt was 0.01% of the total mass of ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide. After adjusting the pH to 4 by using a hydrochloric acid solution with a concentration of 1M, VA-044 initiator was added to obtain reaction liquid A, wherein the amount of VA-044 initiator was 0.5% of the total mass of ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide. The reaction was carried out at 50°C for 8h in the dark. After dialysis, an anchor agent solution with a solid content of 8% was obtained.

[0066] S2: removing the polymerization inhibitor of poly(ethylene glycol) methacrylate by a chromatographic column filled with basic alumina to obtain a de-inhibited poly(ethylene glycol) methacrylate, adding the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid into a mixed solvent to obtain solution B, wherein the mixed solvent is a mixture of ethanol, deionized water and N,N-dimethylformamide; the volume ratio of ethanol to deionized water in the mixed solvent is 9:1, the volume fraction of N,N-dimethylformamide in the mixed solvent is 2%, the molar ratio of the de-inhibited poly(ethylene glycol) methacrylate to the 3-acrylamidophenylboronic acid is 10:1, the solid content of the solution B is 15%, and then adding azobisisobutyronitrile into the solution B under a nitrogen atmosphere after heating to 65°C to obtain reaction liquid C, wherein the amount of the azobisisobutyronitrile is 0.5% of the total mass of the de-inhibited poly(ethylene glycol) methacrylate and the 3-acrylamidophenylboronic acid, the reaction is carried out for 12 hours, the product is purified by repeated precipitation with cold ether for 2 times and vacuum drying to obtain a primary product, and then adding deionized water and adjusting the pH to 8 with sodium hydroxide to obtain a boron-containing flexible ionophore solution with a solid content of 5%;

[0067] S3: adding alumina powder with a particle size of 300 nm into an anchoring agent solution, adding deionized water, and then shearing at a linear velocity of 8 m / s for 30 min to obtain a pre-dispersion, wherein the mass ratio of the anchoring agent to the alumina powder is 0.5:100, and the mass fraction of the alumina powder in the pre-dispersion is 75 wt.%, adjusting the pH to 7.2 with 2% ammonia water, and then adding the boron-containing flexible ionophore solution at a linear velocity of 2 m / s, wherein the mass ratio of the boron-containing flexible ionophore to the alumina powder is 1:100, the dropping time is 10 min, and the stirring is continued for 20 min after the dropping to obtain a pretreatment slurry, and then vacuum defoaming to obtain a high-dispersity nano-alumina slurry for diaphragm coating.

[0068] Example 3

[0069] The embodiment provides a high-dispersity nano-alumina slurry for diaphragm coating and a preparation method thereof, and the preparation method of the high-dispersity nano-alumina slurry for diaphragm coating specifically comprises the following steps:

[0070] S1: a 40% ethylene glycol methacrylate phosphate solution was prepared, a 2.2M sodium hydroxide solution was added under ice-bath stirring to adjust the pH to 4.8 to obtain a pre-neutralized monomer solution, 3-methacryloyl dopamine and acrylamide were mixed to obtain a mixed monomer solution, wherein the molar ratio of ethylene glycol methacrylate phosphate to 3-methacryloyl dopamine was 1.2:1.5, the molar ratio of ethylene glycol methacrylate phosphate to acrylamide was 1.2:11, the total solid content of the mixed monomer solution was 11%, disodium ethylenediaminetetraacetate was added under a nitrogen atmosphere to obtain a pre-reaction solution A, wherein the amount of disodium ethylenediaminetetraacetate was 0.02% of the total mass of ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, a 1.2M hydrochloric acid solution was used to adjust the pH to 4.2, and then VA-044 initiator was added to obtain reaction solution A, the amount of VA-044 initiator was 0.6% of the total mass of ethylene glycol methacrylate phosphate, 3-methacryloyl dopamine and acrylamide, and the reaction was carried out at 52°C for 9h in the dark, and after dialysis, an anchoring agent solution with a solid content of 9% was obtained;

[0071] S2: the polymerization inhibitor of poly(ethylene glycol) methacrylate was removed by a chromatographic column packed with basic alumina to obtain a de-inhibited poly(ethylene glycol) methacrylate, the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid were added to a mixed solvent to obtain solution B, wherein the mixed solvent was obtained by compounding ethanol, deionized water and N,N-dimethylformamide; wherein the volume ratio of ethanol to deionized water in the mixed solvent was 8:2, the volume fraction of N,N-dimethylformamide in the mixed solvent was 3%, the molar ratio of de-inhibited poly(ethylene glycol) methacrylate to 3-acrylamidophenylboronic acid was 11:1.5, and the solid content of solution B was 16%, and azobisisobutyronitrile was added after the temperature was raised to 66°C under a nitrogen atmosphere to obtain reaction solution C, wherein the amount of azobisisobutyronitrile was 0.8% of the total mass of de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid, and the reaction was carried out for 13h, the product was purified by repeated precipitation with cold diethyl ether twice and vacuum drying to obtain a primary product, which was added to deionized water and adjusted to a pH of 8.1 with sodium hydroxide to obtain a boron-containing flexible ionophore solution with a solid content of 6%;

[0072] S3: alumina powder with particle size of 350 nm was added into the anchor agent solution, deionized water was added to the solution, and the pre-dispersion was obtained by shearing at a linear velocity of 9 m / s for 40 min, wherein the mass ratio of the anchor agent to the alumina powder was 1.0:100, and the mass fraction of the alumina powder in the pre-dispersion was 68 wt.%. After adjusting the pH to 7.5 by using ammonia water with a concentration of 3%, the solution was stirred at a linear velocity of 3 m / s, and the solution containing the boron-containing flexible ionophore was added into the solution, wherein the mass ratio of the boron-containing flexible ionophore to the alumina powder was 1.5:100, the dropping time was 15 min, and the pre-treatment slurry was obtained by continuing to stir for 22 min after the dropping was completed. The high-dispersibility nano-alumina slurry for diaphragm coating was obtained by vacuum degassing.

[0073] Example 4

[0074] The embodiment provides a high-dispersibility nano-alumina slurry for diaphragm coating and a preparation method thereof. The preparation method of the high-dispersibility nano-alumina slurry for diaphragm coating specifically comprises the following steps:

[0075] S1: a glycol methacrylate phosphate solution with a concentration of 50% was prepared, and a sodium hydroxide solution with a concentration of 3 M was added into the solution under ice-bath stirring to adjust the pH to 5.5 to obtain a pre-neutralization monomer solution. 3-methacryloyl dopamine and acrylamide were mixed to obtain a mixed monomer solution, wherein the molar ratio of the glycol methacrylate phosphate to the 3-methacryloyl dopamine was 2:3, the molar ratio of the glycol methacrylate phosphate to the acrylamide was 2:15, and the total solid content of the mixed monomer solution was 15%. Ethylenediaminetetraacetic acid disodium salt was added into the pre-reaction liquid A under a nitrogen atmosphere, wherein the amount of the ethylenediaminetetraacetic acid disodium salt was 0.05% of the total mass of the glycol methacrylate phosphate, the 3-methacryloyl dopamine and the acrylamide. After the pH was adjusted to 5 by using a hydrochloric acid solution with a concentration of 2 M, a VA-044 initiator was added to obtain the reaction liquid A, wherein the amount of the VA-044 initiator was 1% of the total mass of the glycol methacrylate phosphate, the 3-methacryloyl dopamine and the acrylamide. The reaction was carried out at 60°C for 12 h in the dark, and the anchor agent solution with a solid content of 12% was obtained after dialysis.

[0076] S2: removing the polymerization inhibitor of poly(ethylene glycol) methacrylate by a chromatographic column filled with basic alumina to obtain a de-inhibited poly(ethylene glycol) methacrylate, adding the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid into a mixed solvent to obtain solution B, wherein the mixed solvent is a mixture of ethanol, deionized water and N,N-dimethylformamide; the volume ratio of ethanol to deionized water in the mixed solvent is 8.8:1.2, the volume fraction of N,N-dimethylformamide in the mixed solvent is 6%, the molar ratio of the de-inhibited poly(ethylene glycol) methacrylate to 3-acrylamidophenylboronic acid is 15:3, and the solid content of solution B is 20%; after being heated to 70°C under a nitrogen atmosphere, adding azobisisobutyronitrile to obtain reaction liquid C, wherein the amount of azobisisobutyronitrile is 1.5% of the total mass of the de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid, and the reaction is carried out for 16 h; the product is purified by repeated precipitation with cold ether for 3 times and vacuum drying to obtain a primary product, which is added into deionized water and adjusted to a pH of 8.5 with sodium hydroxide to obtain a boron-containing flexible ionophore solution with a solid content of 10%;

[0077] S3: adding alumina powder with a particle size of 500 nm into the anchoring agent solution, adding deionized water, and shearing at a linear speed of 12 m / s for 60 min to obtain a pre-dispersion, wherein the mass ratio of the anchoring agent to the alumina powder is 2.5:100, and the mass fraction of the alumina powder in the pre-dispersion is 78 wt.%; adjusting the pH to 8.2 using ammonia water with a concentration of 5% and then stirring at a linear speed of 5 m / s to add the boron-containing flexible ionophore solution, wherein the mass ratio of the boron-containing flexible ionophore to the alumina powder is 3:100, the dropping time is 30 min, and the stirring is continued for 30 min after the dropping is completed to obtain a pretreated slurry; vacuum degassing to obtain a high-dispersity nano-alumina slurry for diaphragm coating.

[0078] Comparative Example 1

[0079] This comparative example provides a high-dispersity nano-alumina slurry for diaphragm coating, which is different from Example 1 in that, in S1, no ethylene glycol methacrylate phosphate is added, and the other operation steps and process parameters are exactly the same as those of Example 1.

[0080] Comparative Example 2

[0081] This comparative example provides a high-dispersity nano-alumina slurry for diaphragm coating, which is different from Example 1 in that, in S1, no 3-methacrylamidodopamine is added, and the other operation steps and process parameters are exactly the same as those of Example 1.

[0082] Comparative Example 3

[0083] The comparative example provides a high dispersibility nano-alumina slurry for diaphragm coating, which is different from example 1 in that no boron-containing flexible ion-conducting agent solution is added in S3, and other operation steps and process parameters are completely same as example 1.

[0084] Comparative example 4

[0085] The comparative example provides a high dispersibility nano-alumina slurry for diaphragm coating, which is different from example 1 in that no anchoring agent solution is added in S3, and other operation steps and process parameters are completely same as example 1.

[0086] The high dispersibility nano-alumina slurry for diaphragm coating of examples 1-4 and comparative examples 1-4 above is used to prepare ceramic diaphragms and test the performance, and the specific process is as follows:

[0087] The peel strength is tested according to GB / T 2792-2014;

[0088] The air permeability is tested by using a Gurley 4110 type air permeability tester to test the air permeability of the diaphragm;

[0089] The tensile strength (transverse direction) is tested according to GB / T1040.3-2006;

[0090] The heat shrinkage of the sample is tested according to ASTM D1204 (transverse direction);

[0091] The puncture strength of the sample is tested according to ASTM D3763;

[0092] The test results are shown in Table 1.

[0093] Table 1 Performance test results of high dispersibility nano-alumina slurry for diaphragm coating of examples 1-4 and comparative examples 1-4

[0094] ;

[0095] From the test results of Example 1 and Comparative Example 1 in Table 1, in S1, without adding ethylene glycol methacrylate phosphate, the lack of phosphonic groups in the anchoring agent affects the interface of the alumina surface hydroxyl / metal sites, and the stable adsorption layer on the particle surface is difficult to establish fully, and after slurry, it is more prone to re-agglomeration and local flocculation, and the micro-uniformity of the coating film decreases during coating. Due to the lack of effective anchoring of particles and substrate interface, the coating is more prone to interface cracking and particle shedding under drying shrinkage and peeling load, so the peeling strength decreases. Due to the agglomeration and local accumulation, the pore is more easily blocked or forms an uneven resistance channel, and the gas passage becomes tortuous, so the air permeability resistance rises, and thus the air permeability decreases. Because the coating is uneven and the interface is defective, the stress transfer and overall load-bearing capacity of the membrane are weakened, and during stretching, stress concentration is more likely to occur at the defect and break early, so the tensile strength decreases. Because the distribution of ceramic support phase is discontinuous, the high-temperature constraint effect on the polyolefin substrate is weakened, and the dimensional stability decreases after heating, so the thermal shrinkage rate increases. Because the agglomeration defect and the lack of interface bonding will reduce the local damage resistance, under the puncture load, local peeling and rapid crack propagation are more likely to occur, so the puncture strength decreases.

[0096] From the test results of Example 1 and Comparative Example 2 in Table 1, in S1, without adding 3-methacryloyl dopamine, the lack of catechol sites in the anchoring agent, and the lack of sites for forming reversible borate ester bonds with boron-containing flexible ionophores, the particles are difficult to build an effective dynamic network and network locking structure during the film forming stage, and the thixotropic recovery of the slurry and the contribution of the coating cohesion are weakened. Due to the lack of dynamic bonding and network locking, the connection between particles and the cohesion of the coating decrease after drying and film forming, and the interface is more prone to interlayer slip and micro-crack propagation under peeling load, so the peeling strength decreases. Because of the lack of dynamic network constraint on particle distribution, micro-migration and local densification differences are more likely to occur during the coating process, resulting in more uneven pore structure and local resistance increase, so the air permeability decreases. Because the coating cohesion and interface synergy are weakened, the coating is more likely to become a defect source and induce local premature failure of the substrate during stretching, so the tensile strength decreases. Because of the lack of network structure to constrain the synergy of particles / polymer phases at high temperatures, the thermal shrinkage inhibition effect of the ceramic layer on the substrate is weakened, so the thermal shrinkage rate increases. Because the lack of particle connection and cohesion makes the crack more likely to expand along the particle interface under the puncture load, so the puncture strength decreases.

[0097] From the test results of Example 1 and Comparative Example 3 in Table 1, it can be seen that, without adding the solution of the flexible ionophore containing boron in S3, the system lacks the process of forming reversible borate ester bonds between the phenylboronic acid / borate sites and the catechol sites, and cannot establish a loose three-dimensional dynamic network between the particles to regulate the thixotropy and anti-settling, so that the structure support is insufficient when the slurry is at rest, the structure recovery ability after coating is reduced, and the coating uniformity and film-forming stability are deteriorated. Due to the lack of the contribution of the dynamic network to the connection between the particles and the dry film locking, the cohesive strength of the coating and the interface stability are reduced, and the peeling strength is reduced because the particles are more likely to fall off or the interlayer is damaged during peeling. Due to the more likely local accumulation or particle-poor area of the particle distribution, the pore resistance and the continuity of the channel are deteriorated, resulting in the increase of the overall air permeation resistance, and thus the air permeability is reduced. Due to the reduction of stress transfer efficiency caused by coating defects and insufficient cohesion, stress concentration is more likely to occur in the weak area of the coating during stretching and breakage, thus the tensile strength is reduced. Due to the insufficient uniformity of the ceramic layer structure and the reduction of the restraint, the inhibitory shrinkage effect on the base film at high temperature is weakened, thus the thermal shrinkage rate is increased. Due to the lack of the effect of the dynamic connection between the particles, the crack is more likely to penetrate the particle interface under the puncture load, thus the puncture strength is reduced.

[0098] From the test results of Example 1 and Comparative Example 4 in Table 1, it can be seen that, without adding the solution of the anchoring agent in S3, the surface of the alumina particles lacks a stable adsorption layer and hydration stability support, and the dispersion is more dependent on mechanical shearing, and is more likely to agglomerate, flocculate and settle after shearing is stopped, and is more likely to form particle defects and local pore blocking during film formation, and the particle and base film interface lacks effective anchoring and fixing. Due to the insufficient interface adhesion and the increase of the powder dropping tendency, the interface failure and coating peeling are more likely to occur under the peeling load, thus the peeling strength is reduced. Due to the strong blockage of the gas channel and the more tortuous path caused by the agglomerates and local pore blocking, the air permeation resistance is significantly increased, thus the air permeability is reduced. Due to the more serious stress concentration caused by the coating defects and weak interface bonding, the local damage is more likely to occur during stretching, thus the tensile strength is reduced. Due to the poor continuity of the ceramic support and the insufficient high-temperature restraint on the base film, the dimensional stability at high temperature is significantly reduced, thus the thermal shrinkage rate is increased. Due to the agglomeration defects and interface debonding, local collapse and rapid crack propagation are more likely to occur under the puncture load, thus the puncture strength is reduced.

[0099] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a highly dispersible nano-alumina slurry for diaphragm coating, characterized in that, The preparation method includes: S1: Prepare a ethylene glycol phosphate methacrylate solution. Add sodium hydroxide solution to adjust the pH under ice bath stirring to obtain a pre-neutralized monomer solution. Add 3-methacrylamide and acrylamide to obtain a mixed monomer solution. Add disodium ethylenediaminetetraacetate under nitrogen atmosphere to obtain pre-reaction solution A. Adjust the pH with hydrochloric acid solution and add VA-044 initiator to obtain reaction solution A. React in the dark and dialyze to obtain anchoring agent solution. S2: Poly(ethylene glycol) methacrylate is passed through a chromatography column packed with alkaline alumina to remove the polymerization inhibitor, resulting in de-inhibited poly(ethylene glycol) methacrylate. The de-inhibited poly(ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid are added to a mixed solvent to obtain solution B, wherein the mixed solvent is a mixture of ethanol, deionized water, and N,N-dimethylformamide. After heating under a nitrogen atmosphere, azobisisobutyronitrile is added to obtain reaction solution C. The reaction is carried out, and the product is purified by repeated precipitation with cold diethyl ether and vacuum dried to obtain the initial product. The initial product is added to deionized water and the pH is adjusted with sodium hydroxide to obtain a boron-containing flexible ion-conducting agent solution. S3: Add alumina powder to the anchoring agent solution, add deionized water and shear to obtain a pre-dispersed liquid. Adjust the pH with ammonia water and stir to add boron-containing flexible ion-conducting agent solution. After the addition is completed, continue stirring to obtain a pretreated slurry. Vacuum degassing is used to obtain a highly dispersible nano alumina slurry for membrane coating.

2. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S1: The molar ratio of ethylene glycol methacrylate to 3-methacryloyldopamine is (1-2):(1-3); The molar ratio of ethylene glycol methacrylate to acrylamide is (1-2):(10-15); The total solids content of the mixed monomer solution is 10-15%.

3. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S1: The amount of disodium ethylenediaminetetraacetate added is 0.01-0.05% of the total mass of ethylene glycol methacrylate, 3-methacrylamide, and acrylamide. The amount of VA-044 initiator added is 0.5-1% of the total mass of ethylene glycol methacrylate, 3-methacrylamide, and acrylamide. The solid content of the anchoring agent solution is 8-12%.

4. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S2: The volume ratio of ethanol to deionized water in the mixed solvent is (8-9):(2-1); The volume fraction of N,N-dimethylformamide in the mixed solvent is 2-6%.

5. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S2: The molar ratio of the de-inhibited poly(ethylene glycol) methacrylate to 3-acrylamidophenylboronic acid is (10-15):(1-3); The solid content of solution B is 15-20%.

6. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S2: The amount of azobisisobutyronitrile added is 0.5-1.5% of the total mass of de-inhibited (ethylene glycol) methacrylate and 3-acrylamidophenylboronic acid; The solid content of the boron-containing flexible ion-conducting agent solution is 5-10%.

7. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S3: The alumina powder has a particle size of 300-500 nm.

8. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S3: The mass ratio of the anchoring agent to the alumina powder is (0.5-2.5):

100.

9. The method for preparing a highly dispersible nano-alumina slurry for diaphragm coating according to claim 1, characterized in that, In S3: The mass ratio of the boron-containing flexible ion-conducting agent to the alumina powder is (1-3):

100.

10. A highly dispersible nano-alumina slurry for diaphragm coating prepared by the preparation method according to any one of claims 1-9.

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