A heat-resistant ceramic-coated separator and a method of manufacturing the same

Abstract

This invention relates to the technical field of battery separators, and discloses a heat-resistant ceramic-coated separator and its preparation method. The separator includes a base film and a coating layer disposed on at least one surface of the base film. The raw materials of the coating layer include ceramic particles, composite modified PAM particles, a binder, and water. The composite modified PAM particles are obtained by polymerizing acrylamide, a modified monomer, a crosslinking agent, and nanofillers. The modified monomer is a mixture of styrene and vinylpyrrolidone, the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine, and the nanofillers include silane coupling agent-modified nanoclay and CNTs. This invention, by adding composite modified PAM particles to the separator coating layer, can improve the particle mixing degree within the coating slurry and prevent ceramic particles from detaching at high temperatures, forming a continuous and stable interface and improving the heat resistance of the battery separator.

Description

Technical Field

[0001] This invention relates to the technical field of battery separators, and in particular to a heat-resistant ceramic-coated separator and its preparation method. Background Technology

[0002] The separator in a lithium-ion battery acts between the positive and negative electrodes to prevent short circuits caused by contact between them. During battery operation, the entire battery generates heat, placing high demands on the separator's heat resistance. Due to the thermal shrinkage effect, the separator deforms and shrinks as the temperature rises. This shortening in both the lateral and longitudinal directions increases the possibility of contact between the positive and negative electrodes, significantly increasing the probability of a short circuit. Therefore, the separator needs higher heat resistance. Besides enhancing the separator's inherent heat resistance, a coating slurry containing heat-insulating materials can be applied to the separator to further improve its overall heat resistance.

[0003] Patent CN110776863B discloses a modified adhesive for lithium-ion battery ceramic separators and its preparation method, which introduces amino resin and / or phenolic resin structures into the molecular chain structure of acrylic adhesives. Utilizing the principle that acrylamide and its derivatives containing amide groups and phenolic substances can react with aldehydes under weakly alkaline conditions, specific groups of amino resin and / or phenolic resin are introduced into the molecular chain structure of aqueous acrylic adhesives through copolymerization or post-reaction processes, thereby improving the adhesive's performance. However, the introduction of amino resin and / or phenolic resin structures in the aforementioned patent leads to a sharp increase in viscosity, thus affecting the coating process. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a heat-resistant ceramic-coated diaphragm and its preparation method. By modifying monomers and nanofillers to obtain composite modified PAM particles, these polyacrylamide particles are then used as crosslinking agents to encapsulate the attached ceramic particles for diaphragm coating. This not only improves the particle mixing degree in the coating slurry but also enhances the melting temperature and heat resistance of the diaphragm.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a heat-resistant ceramic-coated diaphragm, the diaphragm comprising a base membrane and a coating layer disposed on at least one surface of the base membrane; the raw materials of the coating layer comprising ceramic particles, composite modified PAM particles, a binder and water; the composite modified PAM particles are prepared by polymerization reaction of acrylamide, modified monomer, crosslinking agent and nanofiller; wherein the modified monomer is a mixture of styrene and vinylpyrrolidone in a mass percentage of 60-70%:30-40%, the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​in a mass percentage of 50-60%:40-50%, and the nanofiller comprises silane coupling agent modified nanoclay and CNTs.

[0007] The raw materials for the separator coating in this invention include composite modified PAM particles, ceramic particles, and a binder. The composite modified PAM particles can improve the particle mixing degree in the coating slurry and prevent ceramic particles from falling off at high temperatures, forming a continuous and stable interface and improving the heat resistance and melting temperature of the battery separator. Specifically, the composite modified PAM particles use styrene and vinylpyrrolidone as modifying monomers and are synergistically compounded with binary nanofillers, which not only improves the heat resistance of the separator but also ensures its mechanical properties, thus meeting the application requirements of the separator in batteries.

[0008] By using a blend of styrene and vinylpyrrolidone as modifying monomers, styrene, due to its rigid benzene ring, can improve the heat resistance of PAM when copolymerized with acrylamide. However, when used alone, its copolymerization rate is slow, which is not conducive to forming a superior copolymer chain structure with acrylamide and can affect the mechanical properties of the membrane. Vinylpyrrolidone, on the other hand, has high reactivity and good compatibility with PAM molecular chains. Using it in combination with styrene as a modifying monomer can balance reactivity and heat resistance of the molecular chain while ensuring certain mechanical properties.

[0009] By employing a binary composite of nanoclay and CNTs as nanofillers, the layered structure of the nanoclay blocks heat conduction pathways, while the high aspect ratio of carbon nanotubes (CNTs) further inhibits heat transfer, thus synergistically modifying the PAM molecular chains to enhance heat resistance. The nanofillers form a physical support framework in the coating layer, filling pores and enhancing mechanical properties. Furthermore, the nanoclay is modified with a silane coupling agent, which not only reduces particle aggregation but also improves its compatibility with the PAM molecular chains, further ensuring the uniform dispersion of the nanofillers within the PAM molecular chains.

[0010] After mixing the coating raw materials, the composite modified PAM particles are dissolved in water. The coating slurry ultimately exists as a water-based composite gel suspension system, with water as the continuous phase and the gel particles formed by the swelling of the composite modified PAM as the core of the dispersed phase. Ceramic particles, binders, and nanofillers are dispersed in it through chemical bonding and physical adsorption, which makes the coating slurry have fluidity, stability, and density. It can be uniformly coated on the surface of the base membrane. After drying, a dense coating layer is obtained, which can ensure the heat resistance and structural stability of the diaphragm.

[0011] Preferably, the mass ratio of the ceramic particles, composite modified PAM particles, binder and water is 100:20-25:7-10:2.5-5.0.

[0012] Preferably, the ceramic particles include one or more of alumina, boehmite, and barium sulfate; the particle size of the ceramic particles is 0.1-3 μm.

[0013] Preferably, the adhesive is polyimide.

[0014] Preferably, the base film is a single PP base film, a single PE base film, or a PP / PE co-extruded base film.

[0015] Preferably, the mass ratio of acrylamide, modified monomer, crosslinking agent and nanofiller is 85-105:20-40:7-13:2-6; the mass ratio of silane coupling agent modified nanoclay and CNT is 2-2.4:1.

[0016] Preferably, the nano-clay includes one or more of montmorillonite, bentonite, and kaolinite; the particle size of the nano-clay is 50-80 nm.

[0017] Preferably, the CNT has a diameter of 10-15 nm and a length of 1-3 μm.

[0018] Preferably, the silane coupling agent modified nano-clay is prepared by dispersing nano-clay in a silane coupling agent hydrolysate and reacting it, and the silane coupling agent used is an epoxy-containing silane coupling agent.

[0019] Preferably, the preparation of the silane coupling agent modified nano-clay includes the following steps: by mass, take 300-500 parts of anhydrous ethanol and 10-20 parts of water, mix them, add 0.5-1 parts of glacial acetic acid and 3-8 parts of silane coupling agent, stir evenly to obtain a silane coupling agent hydrolysate; take 100 parts of nano-clay (particle size 50-80nm) and add it to the silane coupling agent hydrolysate, disperse it ultrasonically, and then stir and react at 60-65℃ for 2.5-3h; after the reaction is completed, cool and dry.

[0020] Secondly, the present invention also provides a method for preparing a heat-resistant ceramic-coated diaphragm, comprising the following steps:

[0021] (1) Add silane coupling agent modified nano-clay and CNT to water and disperse ultrasonically, then add acrylamide, modified monomer and crosslinking agent to obtain a mixed solution; heat the mixed solution to 60-70℃, introduce nitrogen to remove oxygen, add initiator and accelerator to react, then heat to 80-86℃ to continue the reaction; the reaction product is dried and crushed to obtain composite modified PAM particles;

[0022] (2) Add composite modified PAM particles to water, then add ceramic particles and binder, stir to obtain coating slurry; apply coating slurry to one or both sides of base film to obtain diaphragm.

[0023] The composite modified PAM particles are obtained through a segmented heating process. Pre-reaction at relatively low temperatures allows for the polymerization of some vinylpyrrolidone, forming a prepolymer backbone and preventing explosive polymerization caused by the simultaneous reaction of a large number of monomers at relatively high temperatures. The main polymerization reaction, occurring at relatively high temperatures, ensures the complete polymerization of vinylpyrrolidone, styrene, and acrylamide, guaranteeing the heat resistance and crosslinking density of the final product.

[0024] Preferably, in step (1), the mass ratio of acrylamide, modified monomer, crosslinking agent, nanofiller and water is 85-105:20-40:7-13:2-6:1000.

[0025] As a preferred option, in step (1), the temperature is first raised to 60-70℃ and reacted for 30-60 minutes, and then the temperature is raised to 80-86℃ and the reaction continues for 2-3 hours.

[0026] Preferably, in step (1), the initiator is ammonium persulfate; the accelerator is N,N,N',N'-tetramethylethylenediamine; and the mass ratio of acrylamide, initiator and accelerator is 85-105:0.03-0.11:0.03-0.11.

[0027] Preferably, in step (2), the coating thickness of the coating slurry is 4-6 μm.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Adding composite modified PAM particles to the separator coating layer can improve the particle mixing degree in the coating slurry and prevent ceramic particles from falling off at high temperature, forming a continuous and stable interface, and improving the heat resistance and melting temperature of the battery separator.

[0030] (2) The composite modified PAM particles use styrene and vinylpyrrolidone as modified monomers and are compounded with binary nanofillers, which can not only improve the heat resistance of the separator, but also ensure its mechanical properties, thus meeting the application requirements of the separator in the battery. Detailed Implementation

[0031] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] The preparation of the heat-resistant ceramic-coated diaphragm in this invention includes the following steps:

[0033] (1) Preparation of composite modified PAM particles:

[0034] a. Add silane coupling agent modified nano-clay and CNT to water at a mass ratio of 2-2.4:1. Use silane coupling agent modified nano-clay and CNT as nanofillers. Disperse the nanofiller using ultrasonication for 30-60 minutes to obtain a nanofiller dispersion.

[0035] b. Add acrylamide, modified monomer, and crosslinking agent to the nanofiller dispersion. The mass ratio of acrylamide, modified monomer, crosslinking agent, nanofiller, and water is 85-105:20-40:7-13:2-6:1000. The modified monomer is a mixture of styrene and vinylpyrrolidone at a mass percentage of 60-70%:30-40%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​at a mass percentage of 50-60%:40-50%, to obtain a mixed solution.

[0036] c. First, heat the mixed solution to 60-70℃, then purge with nitrogen to completely remove oxygen. Add the initiator and accelerator and react for 30-60 minutes. The mass ratio of acrylamide, initiator, and accelerator is 85-105:0.03-0.11:0.03-0.11. Then, heat to 80-86℃ and continue the reaction for 2-3 hours. The reaction product is dried to constant weight, crushed, and sieved to obtain composite modified PAM particles.

[0037] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles and binder, stir at 70-80℃ for 1-3h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, binder and water in the coating slurry is 100:20-25:7-10:2.5-5.0. Coat the coating slurry on one or both sides of the base film. The wet film coating thickness is 4-6μm. Dry and cool to obtain diaphragm.

[0038] In a specific embodiment of the present invention, in step (1), the nanoclay includes one or more of montmorillonite, bentonite, and kaolinite, and the particle size of the nanoclay is 50-80 nm. The carbon nanotubes (CNTs) have a diameter of 10-15 nm and a length of 1-3 μm.

[0039] In a specific embodiment of the present invention, step (1) of preparing silane coupling agent modified nano-clay includes the following steps: by mass, 400 parts of anhydrous ethanol and 15 parts of deionized water are mixed evenly, 0.8 parts of glacial acetic acid are added dropwise, and after stirring for 5 min, 5 parts of silane coupling agent KH560 are slowly added and stirred continuously to form a transparent and uniform silane coupling agent hydrolysate; 100 parts of nano-clay (particle size 50-80 nm) are added to the silane coupling agent hydrolysate, ultrasonically dispersed for 40 min, and then transferred to a 60℃ constant temperature water bath and stirred for 3 h; after the reaction is completed, it is cooled and dried.

[0040] In a specific embodiment of the present invention, in step (1), the initiator is ammonium persulfate. The accelerator is N,N,N',N'-tetramethylethylenediamine.

[0041] In a specific embodiment of the present invention, in step (2), the ceramic particles include one or more of alumina, boehmite, and barium sulfate, with a particle size of 0.1-3 μm. The binder is polyimide. The diaphragm base membrane is a single PP base membrane, a single PE base membrane, or a PP / PE co-extruded base membrane.

[0042] Example 1

[0043] (1) Preparation of composite modified PAM particles:

[0044] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0045] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0046] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0047] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0048] Example 2

[0049] (1) Preparation of composite modified PAM particles:

[0050] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.4:1 (total of 4.5g nanofillers), and ultrasonically disperse for 55min to obtain nanofiller dispersion;

[0051] b. Add 100g acrylamide, 25g modified monomer, and 12g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0052] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.08g initiator and 0.08g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; the reaction product is dried to constant weight, crushed and passed through an 8000-mesh sieve to obtain composite modified PAM particles.

[0053] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0054] Example 3

[0055] (1) Preparation of composite modified PAM particles:

[0056] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0057] b. Add 95g acrylamide, 35g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 60%:40%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 55%:45%, to obtain a mixed solution.

[0058] c. Heat the mixed solution to 65°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 50 minutes, then heat to 85°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0059] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0060] Example 4

[0061] (1) Preparation of composite modified PAM particles:

[0062] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0063] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0064] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0065] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (alumina, average particle size of 2μm) and polyimide. Stir at 80℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:25:7:5. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0066] Comparative Example 1

[0067] (1) Preparation of modified adhesive: According to the existing technical formula, by mass parts, 50 parts of methyl acrylate, 20 parts of acrylamide and 15 parts of amino resin are mixed, 0.03 parts of potassium persulfate and 100 parts of deionized water are added, and the mixture is reacted at 75°C for 3 hours to obtain amino resin modified acrylic copolymer adhesive.

[0068] (2) Preparation of coating slurry and diaphragm: 100 parts of ceramic particles (alumina, average particle size of 2μm), 20 parts of amino resin modified acrylic copolymer adhesive, 5 parts of polyvinyl alcohol (adhesive) and 4 parts of deionized water were mixed and stirred for 2h to obtain coating slurry; the coating slurry was coated on one side of a single PE base film (wet film thickness of 6μm), dried at 80℃ for 5min, and cooled to obtain diaphragm.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that only styrene is used as the modified monomer.

[0071] (1) Preparation of composite modified PAM particles:

[0072] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0073] b. Add 95g acrylamide, 30g modified monomer (styrene), and 10g crosslinking agent to the nanofiller dispersion. The crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40% to obtain a mixed solution.

[0074] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0075] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that the proportion of vinylpyrrolidone in the modified monomer is too high.

[0078] (1) Preparation of composite modified PAM particles:

[0079] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0080] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 30%:70%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0081] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0082] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0083] Comparative Example 4

[0084] The difference from Example 1 is that the proportion of silane coupling agent modified nano-clay in the nanofiller is too high.

[0085] (1) Preparation of composite modified PAM particles:

[0086] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 3.0:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0087] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0088] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0089] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0090] Comparative Example 5

[0091] The difference from Example 1 is that the proportion of N,N'-bis(acryloyl)cysteine ​​in the crosslinking agent is too high.

[0092] (1) Preparation of composite modified PAM particles:

[0093] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0094] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 40%:60%, to obtain a mixed solution.

[0095] c. Heat the mixed solution to 60°C, purge with nitrogen to completely remove oxygen, add 0.07g initiator and 0.07g accelerator and react for 40 minutes, then heat to 83°C and continue the reaction for 3 hours; dry the reaction product to constant weight, crush it and pass it through an 8000-mesh sieve to obtain composite modified PAM particles.

[0096] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0097] Comparative Example 6

[0098] The difference from Example 1 is that a one-step polymerization reaction is used.

[0099] (1) Preparation of composite modified PAM particles:

[0100] a. Add silane coupling agent modified nano-clay (montmorillonite, average particle size of 60nm) and CNT (average diameter of 12nm, length of 1-3μm) to 1000g of water at a mass ratio of 2.2:1 (total of 3.2g of nanofiller), and ultrasonically disperse for 45min to obtain nanofiller dispersion;

[0101] b. Add 95g acrylamide, 30g modified monomer, and 10g crosslinking agent to the nanofiller dispersion. The modified monomer is a mixture of styrene and vinylpyrrolidone with a mass percentage of 70%:30%, and the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​with a mass percentage of 60%:40%, to obtain a mixed solution.

[0102] c. Heat the mixed solution to 83°C, purge with nitrogen to completely remove oxygen, then add 0.07g initiator and 0.07g accelerator and react for 3 hours; the reaction product is dried to constant weight, crushed and passed through an 8000-mesh sieve to obtain composite modified PAM particles.

[0103] (2) Preparation of coating slurry and diaphragm: Add composite modified PAM particles to water, then add ceramic particles (barium sulfate, average particle size of 2μm) and polyimide. Stir at 76℃ for 2h to obtain coating slurry. The mass ratio of ceramic particles, composite modified PAM particles, polyimide and water in the coating slurry is 100:23:8:4. Coat the coating slurry on one side of a single PE base film. The wet film coating thickness is 6μm. Dry at 76℃ for 2min and cool to obtain diaphragm.

[0104] Table 1 Performance test results of the diaphragm

[0105]

[0106] As shown in Table 1, the diaphragm prepared by the present invention has a lower thermal shrinkage rate and a higher peel strength compared with the diaphragm obtained by conventional technology in Comparative Example 1.

[0107] Comparative Example 2, by using only styrene as the modifying monomer, may result in insufficient crosslinking density in some areas. Furthermore, the amide groups of vinylpyrrolidone can form multiple hydrogen bonds with ceramic particles and polyimide groups, strengthening interfacial bonding. The lack of this component will lead to weakened bonding strength and reduced peel strength. In contrast, Comparative Example 3, with its excessively high proportion of vinylpyrrolidone in the modifying monomer, will result in an increase in flexible segments and insufficient rigidity of the crosslinked network, amplifying the thermal shrinkage effect.

[0108] In Comparative Example 4, the excessively high proportion of clay in the nanofiller led to the layering of the clay, resulting in decreased uniformity of thermal barrier properties in the coating. In some areas, there was no montmorillonite to block heat conduction, and the insufficient proportion of CNTs prevented them from effectively assisting montmorillonite in suppressing heat conduction, causing shrinkage at high temperatures. Furthermore, the imbalance between the clay and CNT ratio prevented the effective synergistic filling of coating pores, thus affecting peel strength.

[0109] In Comparative Example 5, different proportions of crosslinking agents were used. BMI (bismaleimide) contains a biaromatic ring structure and has excellent thermal stability, while BAC (N,N'-bis(acryloyl)cysteine) has high crosslinking efficiency but weak thermal stability. Excessive BAC leads to insufficient rigidity of the crosslinking network, resulting in increased thermal shrinkage. Excessive BAC also leads to over-crosslinking, resulting in higher viscosity of the coating slurry, which is not conducive to uniform coating. Similarly, Comparative Example 6 uses a one-step polymerization reaction, which will reduce the uniformity of the crosslinking network and cause uneven interfacial bonding between the composite modified PAM, ceramic, and binder. Some areas may not bond effectively, thus affecting the thermal shrinkage rate and peel strength.

[0110] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A heat-resistant ceramic-coated diaphragm, characterized in that, The diaphragm includes a base membrane and a coating layer disposed on at least one surface of the base membrane; the raw materials of the coating layer include ceramic particles, composite modified PAM particles, binder and water; the composite modified PAM particles are prepared by polymerization reaction of acrylamide, modified monomer, crosslinking agent and nanofiller; wherein, the modified monomer is a mixture of styrene and vinylpyrrolidone at a mass percentage of 60-70%:30-40%, the crosslinking agent is a mixture of bismaleimide and N,N'-bis(acryloyl)cysteine ​​at a mass percentage of 50-60%:40-50%, and the nanofiller includes silane coupling agent modified nanoclay and CNT; the nanoclay includes one or more of montmorillonite, bentonite and kaolin.

2. The heat-resistant ceramic-coated diaphragm according to claim 1, characterized in that, The mass ratio of the ceramic particles, composite modified PAM particles, binder and water is 100:20-25:7-10:2.5-5.

0.

3. The heat-resistant ceramic-coated diaphragm according to claim 1 or 2, characterized in that, The ceramic particles include one or more of alumina, boehmite, and barium sulfate; the particle size of the ceramic particles is 0.1-3 μm.

4. The heat-resistant ceramic-coated diaphragm according to claim 1, characterized in that, The mass ratio of acrylamide, modified monomer, crosslinking agent and nanofiller is 85-105:20-40:7-13:2-6; the mass ratio of silane coupling agent modified nanoclay and CNT is 2-2.4:

1.

5. The heat-resistant ceramic-coated diaphragm according to claim 1 or 4, characterized in that, The particle size of the nano-clay is 50-80 nm.

6. The heat-resistant ceramic-coated diaphragm according to claim 1 or 4, characterized in that, The CNT has a diameter of 10-15 nm and a length of 1-3 μm.

7. A method for preparing a heat-resistant ceramic-coated diaphragm as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Add silane coupling agent modified nano-clay and CNT to water and disperse ultrasonically, then add acrylamide, modified monomer and crosslinking agent to obtain a mixed solution; heat the mixed solution to 60-70℃, introduce nitrogen to remove oxygen, add initiator and accelerator to react, then heat to 80-86℃ to continue the reaction; the reaction product is dried and crushed to obtain composite modified PAM particles; (2) Add composite modified PAM particles to water, then add ceramic particles and binder, stir to obtain coating slurry; apply coating slurry to one or both sides of base film to obtain diaphragm.

8. The method for preparing the heat-resistant ceramic-coated diaphragm according to claim 7, characterized in that, In step (1), the mass ratio of acrylamide to water is 85-105:1000; the temperature is first raised to 60-70℃ and reacted for 30-60 minutes, and then the temperature is raised to 80-86℃ and the reaction continues for 2-3 hours.

9. The method for preparing the heat-resistant ceramic-coated diaphragm according to claim 7, characterized in that, In step (1), the initiator is ammonium persulfate; the accelerator is N,N,N',N'-tetramethylethylenediamine; and the mass ratio of acrylamide, initiator and accelerator is 85-105:0.03-0.11:0.03-0.

11.

10. The method for preparing the heat-resistant ceramic-coated diaphragm according to claim 7, characterized in that, In step (2), the coating thickness of the coating slurry is 4-6 μm.

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