Preparation method of aramid nanofiber microsphere and ceramic hybrid coating slurry and separator

Abstract

The present invention relates to the technical field of battery materials, and specifically relates to a preparation method of aramid nanofibrous microspheres and ceramic mixed coating slurry and separator. The preparation method of the coating slurry is as follows: during the polymerization reaction of meta-aramid in an organic solvent, a methylene group or an ether bond is introduced into the meta-aramid main chain to obtain a modified meta-aramid stock solution; the modified meta-aramid stock solution and a precipitation solvent are introduced into a precipitation device, and after being subjected to high-speed shearing treatment by the precipitation device, they are washed after cooling to obtain modified aramid nanofibrous microspheres; the aramid nanofibrous microspheres, ceramic particles, thickening agent, binder and wetting agent are uniformly dispersed in water to obtain the coating slurry. The coating slurry is uniformly coated on a base film, and then the separator is obtained after drying treatment. The separator of the present invention has the characteristics of good wettability, high membrane-breaking temperature, high puncture strength, excellent heat resistance, and easy control of coating thickness.

Description

Technical Field

[0001] The present invention relates to a preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry and a separator, belonging to the technical field of battery materials. Background Art

[0002] Lithium-ion batteries have played an increasingly important role in fields such as electronic products and electric vehicles due to their advantages of high working voltage, high energy density, long cycle life, etc. However, with the increasing applications of lithium-ion batteries, some safety issues have become increasingly prominent. One of the most important components to ensure battery safety is the separator, which is located between the positive and negative electrodes, can prevent physical contact between the electrodes, and at the same time enable the transmission of free ions and isolate the electron flow.

[0003] Currently, most commercial lithium-ion battery separators are usually made of polyolefin materials such as polyethylene (PE), polypropylene (PP), and their mixtures. However, these materials often have poor liquid absorption rate, thermal stability, and mechanical strength, thus seriously affecting battery safety and restricting the applications of PP and PE. Therefore, to improve the performance of the separator through modification, conventional methods include surface coating, surface grafting, blending, etc. Among these modification methods, surface coating has received the most attention as a strategy to improve the performance of the separator. Currently, it is common in the market to coat a layer of inorganic aluminum oxide (Al2O3) powder or silicon dioxide (SiO2) on a PE-based film or a PP-based film to improve the puncture resistance and thermal shrinkage rate of the separator. For example, Chinese Patent Application CN110444714A provides a ceramic aramid-coated separator for lithium-ion batteries and its preparation method. In this method, N,N-dimethylacetamide (DMAC)-lithium chloride (LiCl) solution is used to dissolve aramid fibers, and nano-Al2O3 particles and inorganic ceramic particles are coated on the separator to form a separator coating material with a 3D three-dimensional pore structure. However, the wettability and breakdown temperature need to be improved, and the heat resistance performance at higher temperatures cannot be satisfied. The heat resistance performance of other aramid-coated separators also does not reach a higher level. Aramid has excellent mechanical properties, flame retardancy, heat resistance, and electrical insulation properties, but the oil-based aramid-coated separator has high costs, a relatively thick thickness, and is difficult to control. Summary of the Invention

[0004] Aiming at the deficiencies existing in the prior art, the present invention provides a preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry and a separator. The addition of methylene or ether bonds increases the flexibility of the molecular chain, causing the molecular chain to curl into aramid nanofiber microspheres with low molecular weight. By combining the aramid nanofiber microspheres with ceramic particles, a coating slurry is obtained, which can more precisely control the coating thickness. The separator has the characteristics of good wettability, high breakdown temperature, excellent heat resistance, and easy control of coating thickness.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry, and the preparation method is as follows:

[0006] S1. Prepare a modified meta-aramid stock solution:

[0007] During the polymerization reaction of meta-aramid in an organic solvent, a methylene group or an ether bond is introduced into the main chain of meta-aramid to obtain a modified meta-aramid stock solution;

[0008] S2. Prepare aramid nanofiber microspheres:

[0009] The modified meta-aramid stock solution and a precipitation solvent are introduced into a precipitation device, and after being subjected to high-speed shearing treatment by the precipitation device and then washed after cooling, modified aramid nanofiber microspheres are obtained;

[0010] S3. Prepare the coating slurry:

[0011] The aramid nanofiber microspheres, ceramic particles, thickener, binder and wetting agent are uniformly dispersed in water to obtain the coating slurry.

[0012] Further, in step S1, the preparation process of introducing a methylene group into the main chain of meta-aramid to prepare a modified meta-aramid stock solution is as follows:

[0013] Dissolve m-phenylenediamine, isophthaloyl chloride and 4,4'-diaminodiphenylmethane in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove unreacted raw materials to obtain a methylene-substituted modified meta-aramid stock solution;

[0014] The preparation process of introducing an ether bond into the main chain of meta-aramid to prepare a modified meta-aramid stock solution is as follows:

[0015] Dissolve m-phenylenediamine, isophthaloyl chloride and 4,4'-diaminodiphenyl ether in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a modified meta-aramid stock solution with an ether bond.

[0016] Further, in the preparation process of introducing a methylene group into the main chain of meta-aramid to prepare a modified meta-aramid stock solution, the mass fraction of 4,4'-diaminodiphenylmethane in the modified meta-aramid polymer is 2%-30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:(0.95-1.05);

[0017] In the process of preparing a modified meta-aramid spinning solution by introducing an ether bond into the main chain of meta-aramid, the mass fraction of 4,4'-diaminodiphenyl ether in the modified meta-aramid polymer is 2%-30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:(0.95-1.05).

[0018] Further, the low-temperature polymerization reaction temperature is 5-10 °C, and the reaction time is 1-2 h.

[0019] Further, the precipitation solvent includes water, DMAC and calcium chloride; the mass ratio of water, DMAC and calcium chloride is 100:(30-40):(2-4); the temperature of the precipitation solvent is 30-40 °C.

[0020] Further, the solid content of the modified meta-aramid spinning solution is 12-18%; the mass ratio of the modified meta-aramid spinning solution to the precipitation solvent is 1:(5-20);

[0021] In step S2, the stirring speed of the high-speed shearing treatment is 1500-3000 r / min.

[0022] Further, in step S3, the mass ratio of water, aramid nanofibers, ceramic particles, thickener, binder and wetting agent is (22-25):1:(6-8):(0.05-0.07):(0.5-0.7):(0.05-0.07).

[0023] Further, the ceramic particles are at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite.

[0024] Further, the thickener is at least one of cellulose thickeners, inorganic salt thickeners, and amine oxide thickeners;

[0025] The binder is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate;

[0026] The wetting agent is at least one of siloxanes, fatty alcohol ethers, and polyoxyethylene ethers.

[0027] The present invention also discloses a method for preparing an aramid nanofiber and ceramic hybrid-coated separator. The method for preparing the separator is: uniformly coating a coating slurry on a base film, and then obtaining the separator after drying; the coating slurry is prepared according to the preparation method described in the present invention.

[0028] The beneficial effects of the present invention are:

[0029] In the preparation method of the aramid nanofiber microsphere and ceramic hybrid coating slurry of the present invention, methylene or ether bonds are introduced into the main chain of poly(m-phenylene isophthalamide) to increase the flexibility of the molecular chain. Under the state of high-speed shear stirring, fine precipitated fibers are formed. Due to the addition of methylene or ether bonds, the flexibility of the meta-aramid molecular chain is increased, causing the molecular chain to curl into low-molecular-weight nanofibers. By controlling the introduced groups and the high-speed shear treatment conditions, the particle size of the aramid nanofibers can be controlled, and by combining ceramic particles of different particle sizes, the coating thickness can be controlled more precisely.

[0030] The separator prepared by the preparation method of the present invention has the characteristics of good wettability, high film-breaking temperature, high puncture strength, excellent heat resistance, and easy control of coating thickness. Moreover, in the present invention, aramid nanofibers, ceramics, a binder, a thickener, and a wetting agent are formulated into a coating slurry and coated on one or both sides of a polyolefin separator, and a stable coating structure is formed after drying, finally obtaining a high-performance aramid nanofiber and ceramic coated separator. Compared with aramid oil coating, the cost of the hybrid aqueous coating of aramid nanofibers and ceramic particles is lower, the coating method is simpler, and it is convenient for large-scale continuous production. In addition, compared with ceramic separators, due to the good affinity between aramid nanofibers and the electrolyte, the coated separator has better wettability with the electrolyte, which can further extend the cycle life of the battery. The hybrid coating of aramid nanofibers and ceramics optimizes the lithium ion transport path, and the battery assembled with the separator of the present invention has better ionic conductivity. Description of the Drawings

[0031] Figure 1 SEM image of the aramid nanofibers prepared in Example 1;

[0032] Figure 2 SEM image of the aramid nanofibers prepared in Example 2;

[0033] Figure 3 SEM cross-sectional image of the hybrid coating of aramid nanofibers and ceramics prepared in Example 4. Detailed Description of the Invention

[0034] The following provides a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the essence of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0036] A preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry, the preparation method comprising:

[0037] S1. Prepare a modified meta-aramid stock solution:

[0038] During the meta-aramid polymerization reaction in an organic solvent, introduce a methylene group or an ether bond onto the meta-aramid main chain to obtain a modified meta-aramid stock solution;

[0039] S2. Prepare aramid nanofiber microspheres:

[0040] Feed the modified meta-aramid stock solution and a precipitation solvent into a precipitation device, subject them to high-speed shearing treatment in the precipitation device, wash after cooling to obtain modified aramid nanofiber microspheres;

[0041] S3. Prepare the coating slurry:

[0042] Disperse aramid nanofiber microspheres, ceramic particles, a thickening agent, a binder, and a wetting agent evenly in water to obtain the coating slurry.

[0043] Specifically, in step S1, the preparation process of introducing a methylene group onto the meta-aramid main chain to prepare a modified meta-aramid stock solution is as follows:

[0044] Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove unreacted raw materials to obtain a methylene-substituted modified meta-aramid stock solution;

[0045] The preparation process of introducing an ether bond onto the meta-aramid main chain to prepare a modified meta-aramid stock solution is as follows:

[0046] Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain an ether-bond modified meta-aramid stock solution.

[0047] Specifically, in the preparation process of introducing a methylene group onto the meta-aramid main chain to prepare a modified meta-aramid stock solution, the mass fraction of 4,4'-diaminodiphenylmethane in the modified meta-aramid polymer is 2% - 30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:(0.95 - 1.05);

[0048] In the preparation process of introducing an ether bond onto the meta-aramid main chain to prepare a modified meta-aramid stock solution, the mass fraction of 4,4'-diaminodiphenyl ether in the modified meta-aramid polymer is 2% - 30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:(0.95 - 1.05).

[0049] Specifically, the low-temperature polymerization reaction temperature is 5-10 °C, and the reaction time is 1-2 h.

[0050] Specifically, the precipitation solvent includes water, DMAC, and calcium chloride; the mass ratio of water, DMAC, and calcium chloride is 100: (30-40): (2-4); the temperature of the precipitation solvent is 30-40 °C.

[0051] Specifically, the solid content of the modified meta-aramid stock solution is 12-18%; the mass ratio of the modified meta-aramid stock solution to the precipitation solvent is 1: (5-20);

[0052] In step S2, the stirring speed of the high-speed shearing treatment is 1500-3000 r / min.

[0053] Specifically, in step S3, the mass ratio of water, aramid nanofibers, ceramic particles, thickener, binder, and wetting agent is (22-25): 1: (6-8): (0.05-0.07): (0.5-0.7): (0.05-0.07).

[0054] Specifically, the ceramic particles are at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite.

[0055] Specifically, the thickener is at least one of cellulose thickeners, inorganic salt thickeners, and amine oxide thickeners;

[0056] Specifically, the binder is a polyacrylate emulsion-type binder; more specifically, the binder is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate;

[0057] The wetting agent is at least one of siloxanes, fatty alcohol ethers, and polyoxyethylene ethers.

[0058] More specifically, in step S3, pure water, aramid nanofibers, ceramic particles, thickener, binder, and wetting agent are sequentially added to a planetary mixer and stirred and dispersed to obtain a coating slurry, where the stirring time is 30-40 min and the stirring speed is 30-40 r / min.

[0059] A method for preparing an aramid nanofiber and ceramic hybrid-coated separator, the method for preparing the separator is: using a micro gravure coater to uniformly coat the coating slurry on a base film, and then performing a drying treatment, and winding to obtain an aramid nanofiber and ceramic hybrid-coated separator.

[0060] Specifically, during the preparation of the separator, the drying temperature is 145-155 °C.

[0061] More specifically, in the embodiment of the present invention, the base film is a 7-μm polyethylene diaphragm, but this is not a limitation to the present invention.

[0062] Example 1

[0063] (1) Preparation of methylene-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5°C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a methylene-substituted modified meta-aramid stock solution with a solid content of 15%.

[0064] (2) Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30°C.

[0065] (3) Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and introduce them into a precipitation device. Stir at a speed of 1500 r / min, and high-speed shear through the precipitation device to form precipitation fibers. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0066] (4) Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 700-900 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (methyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) to a planetary stirrer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 rpm to obtain a coating slurry.

[0067] (5) Preparation of diaphragm: Use a micro gravure coater to evenly coat the slurry on a 7-μm polyethylene diaphragm, and then dry the diaphragm at a drying temperature of 145°C. After winding, obtain a mixed-coated diaphragm with a coating thickness of 2 μm on both sides of aramid nanofibers and ceramics.

[0068] Example 2

[0069] (1)Preparation of ether bond-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5 °C, carry out low-temperature polycondensation reaction, with a stirring speed of 800 r / min and a reaction time of 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain an ether bond-substituted modified meta-aramid stock solution with a solid content of 18%.

[0070] (2)Formulation of precipitation solvent: Mix and compound water, DMAC, and calcium chloride, and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30 °C.

[0071] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and introduce them into a precipitation device. Stir at a speed of 1500 r / min, and high-speed shear through the precipitation device to form precipitated fibers. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain ether bond-substituted aramid nanofibers.

[0072] (4)Preparation of aramid nanofiber and ceramic mixed slurry: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 700-900 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (ethyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence for stirring and dispersion. Stir for 30 min, and control the stirring speed at 30 rpm to obtain a coating slurry.

[0073] (5)Preparation of separator: Use a micro gravure coater to evenly coat the slurry on a polyethylene separator with a thickness of 7 μm, and then dry the separator at a drying temperature of 145 °C. After winding, obtain an aramid nanofiber and ceramic mixed-coated separator with a coating thickness of 1.7 μm on both sides.

[0074] Example 3

[0075] (1)Preparation of methylene-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5°C, carry out low-temperature polycondensation reaction, with a stirring speed of 800 r / min and a reaction time of 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a methylene-substituted modified meta-aramid stock solution with a solid content of 15%.

[0076] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30°C.

[0077] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device, with a stirring speed of 2500 r / min. The precipitation fibers are formed by high-speed shearing in the precipitation device. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0078] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 700 - 900 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (butyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 30 min, with the stirring speed controlled at 30 rpm to obtain a coating slurry.

[0079] (5)Preparation of separator: Uniformly coat the slurry on a polyethylene separator with a thickness of 7 μm by micro gravure coating, and then dry the separator at a drying temperature of 145°C. After winding, a mixed coating separator of aramid nanofibers and ceramics with a coating thickness of 1.8 μm on both sides is obtained.

[0080] Example 4

[0081] (1)Preparation of ether bond-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5°C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain the ether bond-substituted modified meta-aramid stock solution with a solid content of 18%.

[0082] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir well after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30°C.

[0083] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device. Stir at a speed of 2500 r / min, and high-speed shear through the precipitation device to form precipitation fibers. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain ether bond-substituted aramid nanofibers.

[0084] (4)Preparation of aramid nanofiber and ceramic mixed slurry: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 700 - 900 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (isooctyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 r / min to obtain the coating slurry.

[0085] (5)Preparation of separator: Uniformly coat the slurry on a polyethylene separator with a thickness of 7 μm by micro gravure coating, and then dry the separator at a drying temperature of 145°C. After winding, obtain an aramid nanofiber and ceramic mixed-coated separator with a coating thickness of 1.5 μm on both sides.

[0086] Example 5

[0087] (1)Preparation of methylene-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a methylene-substituted modified meta-aramid stock solution with a solid content of 15%.

[0088] (2)Formulation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir well after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30 °C.

[0089] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device. Stir at a speed of 2500 r / min, and form precipitated fibers through high-speed shearing in the precipitation device. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0090] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 300 - 500 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (methyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 rpm to obtain a coating slurry.

[0091] (5)Preparation of separator: Uniformly coat the slurry on a polyethylene separator with a thickness of 7 μm by micro gravure coating, and then dry the separator at a drying temperature of 145 °C. After winding, obtain a mixed-coated separator with a coating thickness of 1.3 μm on both sides of aramid nanofibers and ceramics.

[0092] Example 6

[0093] (1)Preparation of ether bond-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain the ether bond-substituted modified meta-aramid stock solution with a solid content of 18%.

[0094] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30 °C.

[0095] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device, with a stirring speed of 2500 r / min. The precipitation fibers are formed by high-speed shearing in the precipitation device. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain the ether bond-substituted aramid nanofibers.

[0096] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 300 - 500 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (methyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 rpm to obtain the coating slurry.

[0097] (5)Preparation of separator: Use a micro gravure coater to evenly coat the slurry on a polyethylene separator with a thickness of 7 μm, and then dry the separator at a drying temperature of 145 °C. After winding, obtain a mixed-coated separator with a coating thickness of 1 μm on both sides of aramid nanofibers and ceramics.

[0098] Example 7

[0099] (1)Preparation of methylene-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in 82 kg of DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a methylene-substituted modified meta-aramid stock solution with a solid content of 15%.

[0100] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30 °C.

[0101] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device, with a stirring speed of 3000 r / min. Through high-speed shearing in the precipitation device, precipitation fibers are formed. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0102] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 22 kg of pure water, 1 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 300 - 500 nm, 0.07 kg of thickener sodium carboxymethylcellulose, 0.5 kg of polyacrylate binder (methyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary stirrer in sequence and stir for dispersion for 30 min with a stirring speed controlled at 30 rpm to obtain a coating slurry.

[0103] (5)Preparation of separator: Use a micro gravure coater to evenly coat the slurry on a polyethylene separator with a thickness of 7 μm, and then dry the separator at a drying temperature of 145 °C. After winding, a mixed-coated separator of aramid nanofibers and ceramics with a coating thickness of 0.9 μm on each side is obtained.

[0104] Example 8

[0105] (1)Preparation of ether bond-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 2%. After complete dissolution, keep the temperature at 5 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain the ether bond-substituted modified meta-aramid stock solution with a solid content of 18%.

[0106] (2)Formulation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:30:2, and the temperature of the precipitation solvent is 30 °C.

[0107] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:5 and feed them into a precipitation device, with a stirring speed of 3000 r / min. The precipitation fibers are formed by high-speed shearing in the precipitation device. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain the ether bond-substituted aramid nanofibers.

[0108] (4)Preparation of aramid nanofiber and ceramic mixed slurry: Add 22 kg of pure water, 6 kg of aramid nanofibers, 6 kg of aluminum oxide particles with a particle size of 300 - 500 nm, 0.07 kg of thickener sodium carboxymethyl cellulose, 0.5 kg of polyacrylate binder (methyl acrylate), and 0.05 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 rpm to obtain the coating slurry.

[0109] (5)Preparation of separator: Uniformly coat the slurry on a 7-μm-thick polyethylene separator by micro gravure coating, and then dry the separator at a drying temperature of 145 °C. After winding, obtain an aramid nanofiber and ceramic mixed-coated separator with a coating thickness of 0.8 μm on both sides.

[0110] Example 9

[0111] (1)Preparation of modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride and 4,4'-diaminodiphenyl ether in 82 kg of DMAC. Among them, the molar ratio of the total molar amount of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 30%. After complete dissolution, keep the temperature at 10 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 2 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents and catalysts to obtain a modified meta-aramid stock solution substituted with ether bonds.

[0112] (2)Preparation of precipitation solvent: Mix water, DMAC and calcium chloride and stir evenly after mixing. Among them, the content of DMAC is 40% by mass fraction, the content of calcium chloride is 4% by mass fraction, and the temperature of the precipitation solvent is 40 °C.

[0113] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:20 and introduce them into a precipitation device. Stir at a speed of 1500 r / min, and high-speed shear through the precipitation device to form precipitation fibers. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0114] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 25 kg of pure water, 1 kg of aramid nanofibers, 8 kg of aluminum oxide particles with a particle size of 700 - 900 nm, 0.05 kg of thickener sodium carboxymethyl cellulose, 0.7 kg of polyacrylate binder (methyl acrylate) and 0.07 kg of polyoxyethylene ether wetting agent (fatty alcohol polyoxyethylene ether) into a planetary mixer in sequence and stir and disperse for 40 min with the stirring speed controlled at 40 rpm to obtain a coating slurry.

[0115] (5)Preparation of separator: Use a micro gravure coater to evenly coat the slurry on a polyethylene separator with a thickness of 7 μm, and then dry the separator at a drying temperature of 155 °C. After winding, obtain a mixed coated separator of aramid nanofibers and ceramics with a coating thickness of 2 μm on both sides.

[0116] Example 10

[0117] (1)Preparation of methylene-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:0.95, and the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer is 30%. After complete dissolution, keep the temperature at 10 °C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 2 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain a methylene-substituted modified meta-aramid stock solution with a solid content of 12%.

[0118] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:40:4, and the temperature of the precipitation solvent is 40 °C.

[0119] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:20 and feed them into a precipitation device, with a stirring speed of 2000 r / min. The precipitation fibers are formed by high-speed shearing in the precipitation device. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain methylated modified aramid nanofibers.

[0120] (4)Preparation of a mixed slurry of aramid nanofibers and ceramics: Add 25 kg of pure water, 1 kg of aramid nanofibers, 8 kg of silica with a particle size of 700 - 900 nm, 0.05 kg of amine oxide thickener (lauramidopropylamine oxide), 0.7 kg of polyacrylate binder (methyl acrylate), and 0.07 kg of siloxane wetting agent (organic gemini polyether modified siloxane) into a planetary mixer in sequence and stir for dispersion for 40 min with a stirring speed controlled at 40 rpm to obtain a coating slurry.

[0121] (5)Preparation of separator: Uniformly coat the slurry on a polyethylene separator with a thickness of 7 μm by micro gravure coating, and then dry the separator at a drying temperature of 145 °C. After winding, a mixed-coated separator with a coating thickness of 2 μm on both sides of aramid nanofibers and ceramics is obtained.

[0122] Example 11

[0123] (1)Preparation of ether bond-substituted modified meta-aramid: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. Among them, the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:1.05, and the mass fraction of 4,4'-diaminodiphenyl ether in the meta-aramid polymer is 15%. After complete dissolution, keep the temperature at 5°C and carry out low-temperature polycondensation reaction with a stirring speed of 800 r / min for 1 h. After the reaction is completed, neutralize and filter the product to remove unreacted reagents to obtain the ether bond-substituted modified meta-aramid stock solution with a solid content of 15%.

[0124] (2)Preparation of precipitation solvent: Mix water, DMAC, and calcium chloride and stir evenly after mixing. Among them, the mass ratio of water, DMAC, and calcium chloride is 100:35:3, and the temperature of the precipitation solvent is 35°C.

[0125] (3)Preparation of aramid nanofibers: Mix the modified meta-aramid stock solution and the precipitation solvent in a mass ratio of 1:10 and introduce them into a precipitation device. Stir at a speed of 2500 r / min, and high-speed shear through the precipitation device to form precipitation fibers. Due to the increased flexibility of the molecular chain, the molecular chain curls into nanofibers. After cooling, wash to obtain ether bond-substituted aramid nanofibers.

[0126] (4)Preparation of aramid nanofiber and ceramic mixed slurry: Add 23 kg of pure water, 1 kg of aramid nanofibers, 7 kg of zirconia particles with a particle size of 700 - 900 nm, 0.06 kg of inorganic salt thickener (sodium tripolyphosphate), 0.6 kg of polyacrylate binder (methyl acrylate), and 0.06 kg of fatty alcohol polyoxyethylene ether wetting agent into a planetary mixer in sequence and stir and disperse for 30 min with a stirring speed controlled at 30 rpm to obtain a coating slurry.

[0127] (5)Preparation of separator: Use a micro gravure coater to evenly coat the slurry on a polyethylene separator with a thickness of 7 μm, and then dry the separator at a drying temperature of 150°C. After winding, obtain an aramid nanofiber and ceramic mixed-coated separator with a coating thickness of 2 μm on both sides.

[0128] Comparative Example 1

[0129] Commercially available ceramic separator with a total separator thickness of 11 μm and a coating thickness of 4 μm.

[0130] Comparative Example 2

[0131] Prepare a coated separator using the same method as in Example 1, except that: reduce the stirring speed in step (3), and the stirring speed in this Comparative Example 2 is 1000 r / min.

[0132] Comparative Example 3

[0133] The coated separator was prepared by the same method as in Example 1, except that: the stirring speed in step (3) was increased, and the stirring speed in this Comparative Example 3 was 4000 r / min.

[0134] Comparative Example 4

[0135] The coated separator was prepared by the same method as in Example 1, except that: in step (1) of this Comparative Example 4, 4,4'-diaminodiphenylmethane was not added, that is, the meta-aramid was not modified.

[0136] Comparative Example 5

[0137] The coated separator was prepared by the same method as in Example 1, except that: in step (1) of this Comparative Example 5, the addition ratio of 4,4'-diaminodiphenylmethane was increased. In this Comparative Example 5, the mass fraction of 4,4'-diaminodiphenylmethane in the meta-aramid polymer was 40%.

[0138] Comparative Example 6

[0139] The coated separator was prepared by the same method as in Example 1, except that: in step (4) of this Comparative Example 6, the addition amount of aramid nanofibers was increased. In step (4) of this Comparative Example 6, 3 kg of aramid nanofibers was added.

[0140] Comparative Example 7

[0141] The coated separator was prepared by the same method as in Example 1, except that: no aramid nanofibers were added to the coating slurry in this Comparative Example 7.

[0142] Comparative Example 8

[0143] The coated separator was prepared by the same method as in Example 1, except that: the addition amount of the wetting agent was increased in this Comparative Example 8. In step (4) of this Comparative Example 8, 0.15 kg of a polyoxyethylene ether wetting agent was added.

[0144] Comparative Example 9

[0145] The coated separator was prepared by the same method as in Example 1, except that: the addition amount of the wetting agent was reduced in this Comparative Example 9. In step (4) of this Comparative Example 9, 0.02 kg of a polyoxyethylene ether wetting agent was added.

[0146] The separators prepared in the above examples and comparative examples were subjected to performance tests, and the test results are shown in Table 1 and Table 2 below. The test methods involved were:

[0147] Thickness detection standard: GB / T 36363-2018;

[0148] Tensile strength test standard: GB / T 36363-2018;

[0149] Air permeability value test standard: GB / T 36363-2018;

[0150] Puncture strength test standard: GB / T 36363-2018;

[0151] Thermal shrinkage rate test standard: GB / T 36363-2018;

[0152] Liquid absorption rate test standard: GB / T 13542.2-2009;

[0153] Film rupture temperature test standard: GB / T 36800.1-2018;

[0154] Ionic conductivity test standard: GB / T 36363-2018.

[0155] The ionic conductivity test needs to be assembled into a soft-pack battery. The positive electrode is made of NCM811 material, the negative electrode is made of graphite material, and the electrolyte is lithium hexafluorophosphate, model: LBED8-240421. Specifically, it is assembled by using a Kejing semi-automatic laminator through steps such as laminating, hot pressing, tab welding, top and side sealing, liquid injection, formation, and final sealing.

[0156] Table 1 Comparison of diaphragm performance data between examples and comparative examples

[0157]

[0158] Table 2 Ionic conductivity data of diaphragms in examples and comparative examples

[0159]

[0160] It can be seen from the data in Table 1 and Table 2 above that: The diaphragms prepared by the preparation method described in the present invention in Examples 1 - 11 have the characteristics of good wettability, high film-breaking temperature, high puncture strength, excellent heat resistance, easy control of coating thickness, and high ionic conductivity. By introducing methylene or ether bonds into the main chain, the flexibility of the molecular chain is increased. Coupled with different stirring speeds, aramid nanofibers with controllable particle sizes can be synthesized, which helps to more precisely control the coating thickness. Aramid microspheres with different particle sizes are combined with ceramic particles with different particle sizes, and the prepared slurry is coated on the surface of the polyethylene diaphragm, which can meet more coating requirements. The results of the examples show that the film-breaking temperature of the diaphragm is significantly increased, and the wettability to the electrolyte is also significantly improved, which helps to improve the cycle life and safety of lithium batteries. At 180 °C, the aramid nanofiber and ceramic hybrid-coated diaphragm still maintains a good morphology, and the transverse and longitudinal thermal shrinkage can be controlled within 3%. In addition, compared with the ceramic diaphragm, the aramid nanofiber and ceramic hybrid-coated diaphragm has a higher ionic conductivity, which is significantly better than the commercially available ceramic diaphragm in Comparative Example 1. Moreover, the production process of the aramid nanofiber and ceramic hybrid-coated diaphragm of the present invention is simple. It not only has excellent wettability and heat resistance, but also the coating thickness of the diaphragm can be precisely regulated, which is convenient for matching the actual working scenario requirements of battery diaphragms and industrial scale-up production, and can be widely used as high-performance lithium-ion battery diaphragms.

[0161] Figure 1 SEM image of the aramid nanofibers prepared in Example 1; Figure 2 SEM image of the aramid nanofibers prepared in Example 2; From Figure 1 and Figure 2 it can be seen that the diameter of the aramid nanofibers prepared in Example 1 is between 500 nm and 3.5 μm, and the diameter of the aramid nanofibers prepared in Example 2 is between 50 nm and 250 nm. Figure 3 SEM cross-sectional image of the aramid nanofiber and ceramic hybrid-coated diaphragm prepared in Example 4, from Figure 3 which it can be seen that the coating thickness is about 1.5 μm.

[0162] It can be seen from the data comparison between Comparative Example 2 and Example 1 that: If the stirring speed in step (3) is too low, it will cause the particle size of the aramid nanofibers to be too large, making it impossible to precisely control the coating thickness, and the coating thickness is too large. Because the stirring speed is too low, the fibers cannot be fully extended and refined in the coagulation bath, forming thicker fibers, which ultimately affects the air permeability of the diaphragm.

[0163] It can be seen from the data comparison between Comparative Example 3 and Example 1 that: if the stirring speed in step (3) is too high, it will cause the destruction of the aramid nanofiber microsphere structure and the decline of the performance of the coating film. Because too high shear rate may lead to excessive mechanical stress on the fibers during the formation process, thus destroying the structural integrity of the fibers, resulting in the decline of the mechanical properties, air permeability and heat resistance of the separator.

[0164] It can be seen from the data comparison between Comparative Example 4 and Example 1 that: if the meta-aramid is not modified in step (1), it will cause the inability to form aramid nanofiber microspheres, the coating thickness cannot be precisely controlled, and the coating thickness is too large. Because no methylene is introduced for modification, the flexibility of the aramid molecular chain is not increased, and the molecular chain cannot curl into low molecular weight nanofiber microspheres, resulting in a significant decline in the air permeability of the separator.

[0165] It can be seen from the data comparison between Comparative Example 5 and Example 1 that: if the addition amount of the modifying monomer 4,4'-diaminodiphenylmethane in step (1) is too much, it will cause the particle size of the aramid nanofiber microspheres to be too small, the coating thickness cannot be precisely controlled, and the coating thickness is too large. Because the particle size of the aramid nanofiber microspheres is too small, they are prone to agglomeration, forming agglomerates of different sizes, resulting in the decline of the air permeability of the separator.

[0166] It can be seen from the data comparison between Comparative Example 6 and Example 1 that: if the addition amount of the aramid nanofiber microspheres is increased, it will cause the thermal shrinkage performance of the separator to deteriorate, affecting the safety performance of the battery. Because the improvement of the thermal shrinkage performance of the separator by ceramics is dominant.

[0167] It can be seen from the data comparison between Comparative Example 7 and Example 1 that: if aramid nanofiber microspheres are not added to the coating slurry, it will cause the decline of the tensile strength, elongation at break, liquid absorption rate and membrane breakage temperature of the separator. Because aramid nanofiber microspheres can increase the mechanical properties and liquid absorption rate of the separator and improve the membrane breakage temperature of the separator.

[0168] It can be seen from the data comparison between Comparative Example 8 and Example 1 that: if the addition amount of the wetting agent in the coating slurry is too much, it will cause the air permeability of the separator to be too large. Because when the wetting agent is used in excess, a relatively dense film will be formed on the surface of the separator, which will reduce the channels for gas to pass through the separator, resulting in the decline of air permeability.

[0169] It can be seen from the data comparison between Comparative Example 9 and Example 1 that: if the addition amount of the wetting agent in the coating slurry is too little, it will cause the separator to have missed coating. Because if the addition amount of the wetting agent is insufficient, the surface tension may not be reduced to a sufficient degree, resulting in limited spreading ability of the liquid on the surface of the separator. Therefore, using the addition amount of the wetting agent defined in the present invention is more conducive to obtaining a separator with excellent performance.

[0170] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the various technical features in the above embodiments are not exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0171] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry, characterized in that The preparation method is as follows: S1. Prepare the modified meta-aramid stock solution: During the meta-aramid polymerization reaction in an organic solvent, introduce a methylene group or an ether bond onto the main chain of the meta-aramid to obtain the modified meta-aramid stock solution; S2. Prepare aramid nanofibrous microspheres: Introduce the modified meta-aramid stock solution and the precipitation solvent into a precipitation device, and after high-speed shearing treatment by the precipitation device, wash after cooling to obtain the modified aramid nanofibrous microspheres; the stirring speed of the high-speed shearing treatment is 1500 - 3000 r / min; S3. Prepare the coating slurry: Disperse the aramid nanofibrous microspheres, ceramic particles, thickener, binder, and wetting agent evenly in water to obtain the coating slurry; In step S3, the mass ratio of water, aramid nanofibrous microspheres, ceramic particles, thickener, binder, and wetting agent is (22 - 25):1:(6 - 8):(0.05 - 0.07):(0.5 - 0.7):(0.05 - 0.07); In step S1, the preparation process of introducing a methylene group onto the main chain of the meta-aramid to prepare the modified meta-aramid stock solution is as follows: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenylmethane in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove the unreacted raw materials to obtain the methylene-substituted modified meta-aramid stock solution; In the preparation process of introducing an ether bond onto the main chain of the meta-aramid to prepare the modified meta-aramid stock solution: Dissolve m-phenylenediamine, isophthaloyl chloride, and 4,4'-diaminodiphenyl ether in DMAC. After complete dissolution, carry out a low-temperature polycondensation reaction. After the reaction is completed, neutralize and filter the product to remove the unreacted reagents to obtain the modified meta-aramid stock solution with an ether bond; In the preparation process of introducing a methylene group onto the main chain of the meta-aramid to prepare the modified meta-aramid stock solution, the mass fraction of 4,4'-diaminodiphenylmethane in the modified meta-aramid polymer is 2% - 30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenylmethane to isophthaloyl chloride is 1:(0.95 - 1.05); In the preparation process of introducing an ether bond onto the main chain of the meta-aramid to prepare the modified meta-aramid stock solution, the mass fraction of 4,4'-diaminodiphenyl ether in the modified meta-aramid polymer is 2% - 30%; the total molar ratio of m-phenylenediamine and 4,4'-diaminodiphenyl ether to isophthaloyl chloride is 1:(0.95 - 1.05).

2. The preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry according to claim 1, characterized in that The temperature of the low-temperature polymerization reaction is 5 - 10°C, and the reaction time is 1 - 2 h.

3. The preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry according to claim 1, wherein The precipitation solvent includes water, DMAC, and calcium chloride; the mass ratio of water, DMAC, and calcium chloride is 100:(30 - 40):(2 - 4); the temperature of the precipitation solvent is 30 - 40°C.

4. The preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry according to claim 1, characterized in that, The solid content of the modified meta-aramid stock solution is 12 - 18%; the mass ratio of the modified meta-aramid stock solution and the precipitation solvent is 1:(5 - 20).

5. The preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry according to claim 1, characterized in that, The ceramic particles are at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite; 6. The preparation method of an aramid nanofiber microsphere and ceramic hybrid coating slurry according to claim 1, characterized in that, The thickener is at least one of cellulose thickeners, inorganic salt thickeners, and amine oxide thickeners; The binder is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate; The wetting agent is at least one of siloxanes, fatty alcohol ethers, and polyoxyethylene ethers.

7. A preparation method of an aramid nanofiber microsphere and ceramic hybrid-coated separator, characterized in that, The method for preparing the separator is as follows: uniformly coating the coating slurry on the base film, and then obtaining the separator after drying; the coating slurry is prepared according to the preparation method described in any one of claims 1-6.

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