Composite coating separator, method for manufacturing the same, and secondary battery

Abstract

The application discloses a composite coating diaphragm and a preparation method thereof and a secondary battery, and relates to the technical field of secondary batteries.The application provides a composite coating diaphragm with a base film, a hydrophilic support layer of a bottom layer and an electrophilic functional layer of a surface layer, the electrophilic functional layer of the surface layer takes amino-functionalized porous aluminum oxide as a core, is compounded with quaternary ammonium polyether amine and polyethylene glycol dimethyl ether, actively adsorbs electrolyte anions through amino groups and quaternary ammonium groups, and reduces an ion transmission energy barrier; the hydrophilic support layer of the bottom layer is composed of gradient particle size ceramic particles grafted with acrylic acid and sodium carboxymethyl cellulose and polyethylene glycol dimethyl ether, realizes fast spreading and stable storage of electrolyte through hydrophilic groups; the two layers are tightly combined through hydrogen bond action of amino groups and carboxyl groups, form a synergistic system of 'adsorption-spreading-storage', realize synchronous improvement of electrolyte infiltration rate, liquid storage stability, ion conduction efficiency and coating binding force, and adapt to the demand of high-voltage and long cycle life batteries.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to a composite coated separator, its preparation method, and a secondary battery. Background Technology

[0002] The separator is a core component of a secondary battery, its main function being to isolate the positive and negative electrodes and ensure smooth lithium-ion transport. Its electrolyte wettability and electrolyte retention capacity directly affect the battery's internal resistance, cycle life, and rate performance. Existing commercially available polyolefin-based separators suffer from slow electrolyte wetting and insufficient electrolyte retention due to their low surface energy and weak polarity. To improve this, the industry often employs coating modification technologies, mainly including the following two types of solutions: (1) Modification with a single inorganic coating: thermal stability is improved by coating ceramic particles (such as alumina and silicon dioxide). However, the surface polarity of inorganic particles is uniform, the electrolyte wetting rate is slow, and the coating has weak adhesion to the base film and is easy to fall off.

[0003] (2) Organic-inorganic composite coating modification: organic polymers (such as PVDF, PEO) are combined with inorganic particles for coating, taking into account both wettability and thermal stability. However, most existing schemes are single-layer designs that rely on single polarity (hydrophilic or electrophilic) modification, which have defects such as difficulty in balancing wettability and liquid retention stability, and poor ion conduction selectivity.

[0004] In addition, existing coating processes used to prepare modified coatings (such as blade coating and spot coating) are prone to causing poor coating uniformity and blockage of base film pores, which further limits ion transport efficiency.

[0005] In summary, existing coating modification methods have not solved the problem of synergistic optimization of "rapid wetting, stable liquid retention, and efficient ion conduction". There is an urgent need to develop a coating diaphragm technology based on a novel structural design and process route to simultaneously improve electrolyte wetting rate, liquid retention stability, ion conduction efficiency, and coating adhesion.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a composite coated separator, its preparation method, and a secondary battery, aiming to simultaneously improve electrolyte wetting rate, electrolyte retention stability, ion conduction efficiency, and coating adhesion.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a composite coated membrane, comprising a base membrane, a bottom hydrophilic support layer, and a surface electrophilic functional layer arranged sequentially. The bottom hydrophilic support layer contains ceramic particles grafted with acrylic acid, sodium carboxymethyl cellulose, and silane coupling agent. The surface electrophilic functional layer contains aminated porous alumina, quaternized polyetheramine, and polyethylene glycol dimethyl ether.

[0009] In an optional embodiment, the mass ratio of the acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent in the raw materials for preparing the bottom hydrophilic support layer is 100:(0.5-1.0):(0.05-0.1). And / or, the silane coupling agent is an aminosilane; And / or, in the raw materials for preparing the surface electrophilic functional layer, the mass ratio of aminated porous alumina, quaternized polyetheramine and polyethylene glycol dimethyl ether is 100:(3.0-8.0):(0.8-2.0).

[0010] In an optional embodiment, the acrylic-grafted ceramic particles include nano-sized particles and micro-sized particles, wherein the particle size of the nano-sized particles is 80nm-200nm, the particle size of the micro-sized particles is 1.5μm-3.0μm, and the mass ratio of nano-sized particles to micro-sized particles is 1:(0.3-0.7). And / or, the grafting rate of acrylic acid in the grafted acrylic acid ceramic particles is 5%-20%.

[0011] In an optional embodiment, the amino loading in the amination-treated porous alumina is 0.8 mmol / g-1.5 mmol / g, the pore size is 10 nm-99 nm, and the specific surface area is ≥900 m² / g. 2 / g; And / or, the degree of quaternization of the quaternized polyetheramine is 60%-80% and the average molecular weight is 1000Da-2000Da.

[0012] In an optional embodiment, the thickness of the bottom hydrophilic support layer is 1μm-2μm, and the thickness of the surface electrophilic functional layer is 0.2μm-0.5μm; And / or, the total coating weight of the bottom hydrophilic support layer and the top electrophilic functional layer is 1.5 g / m². 2 -3.5g / m 2 ; And / or, the thickness of the base film is 6μm-12μm, and the porosity of the base film is 38%-52%; And / or, the base film is made of polyolefin.

[0013] In a second aspect, the present invention provides a method for preparing a composite coated membrane according to any of the foregoing embodiments, comprising: forming a bottom hydrophilic support layer and a surface electrophilic functional layer on a base membrane.

[0014] In an optional implementation, the method includes: employing a two-layer synchronous coating process, first coating a bottom layer of hydrophilic paste and drying it, then simultaneously coating a top layer of electrophilic paste, and finally performing ultraviolet irradiation crosslinking after drying.

[0015] In an optional embodiment, the preparation process of the bottom hydrophilic slurry includes: mixing acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, a silane coupling agent, and a first solvent, stirring at 500 r / min-800 r / min for 30 min-45 min, and then ultrasonically treating for 15 min-25 min; preferably, the first solvent is a mixed solvent formed by mixing N,N-dimethylformamide and water, the volume ratio of N,N-dimethylformamide to water is (0.3-0.6):1, and the mass ratio of the first solvent to the acrylic acid-grafted ceramic particles is (2.0-4.0):1; And / or, the preparation process of the surface electrophilic paste includes: mixing aminated porous alumina, quaternized polyetheramine, polyethylene glycol dimethyl ether and a second solvent, ultrasonically dispersing for 20 min-30 min, and then stirring at a high speed of 2000 r / min-3000 r / min for 40 min-60 min; preferably, the second solvent is a mixed solvent formed by mixing ethanol and water, and the volume ratio of ethanol to water is (0.5-0.7):1, and the mass ratio of the second solvent to aminated porous alumina is (2.0-4.0):1.

[0016] In an optional embodiment, the coating roller speed of the bottom hydrophilic paste is lower than that of the coating roller speed of the top electrophilic paste, and the coating roller speed ratio is controlled to be 1:(1.2-1.5), with a coating gap of 20μm-50μm. And / or, after applying the bottom hydrophilic paste, dry it at 50℃-60℃ for 5min-10min, then simultaneously apply the top electrophilic paste, and then dry it at 70℃-90℃ for 20min-30min. And / or, at wavelengths of 254nm-365nm and doses of 50mJ / cm 2 -80mJ / cm 2 Under the conditions of ultraviolet irradiation crosslinking, the irradiation time is 3min-8min.

[0017] Thirdly, the present invention provides a secondary battery, comprising any of the composite coated separators in the foregoing embodiments or composite coated separators prepared by any of the preparation methods in the foregoing embodiments.

[0018] This invention has the following beneficial effects: This invention provides a composite coated membrane having a base film, a bottom hydrophilic support layer, and a surface electrophilic functional layer. The surface electrophilic functional layer uses aminated porous alumina as its core, compounded with quaternized polyetheramine and polyethylene glycol dimethyl ether, through the interaction of amino (-NH2) and quaternary ammonium groups (-N)... +R3) Actively adsorbs electrolyte anions, reducing the ion transport energy barrier; the bottom hydrophilic support layer is composed of gradient-size ceramic particles grafted with acrylic acid, sodium carboxymethyl cellulose, and polyethylene glycol dimethyl ether, which enables rapid electrolyte spreading and stable storage through hydrophilic groups (-COOH, -OH); the two layers are tightly bonded by hydrogen bonding between amino and carboxyl groups, forming a synergistic "adsorption-spreading-storage" system, achieving simultaneous improvement in electrolyte wetting rate, electrolyte retention stability, ion conduction efficiency, and coating adhesion, adapting to the requirements of high-voltage, long-cycle-life batteries. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the composite coating membrane provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] Addressing the technical pain points of existing coated separators—namely, the difficulty in simultaneously achieving electrolyte wetting rate and electrolyte retention stability, low ion conduction efficiency, and poor adaptability to high-voltage scenarios—this paper innovatively proposes a core approach of "gradient functional zoning + synergistic molecular modification + specialized molding process." By designing a gradient coating structure of "electrophilic surface layer + hydrophilic bottom layer," the surface layer enables directional adsorption of electrolyte anions, while the bottom layer facilitates rapid electrolyte spreading and storage. Combined with directional molecular modification of key components and a dual-layer synchronous coating-UV crosslinking process, a synergistic system of "adsorption-spreading-transport-stabilization" is constructed. Ultimately, this achieves simultaneous breakthroughs in wettability, electrolyte retention, ion conduction efficiency, and structural stability, making the separator suitable for high-voltage, long-cycle secondary batteries.

[0023] like Figure 1As shown, this embodiment of the invention provides a composite coated membrane, comprising a base membrane, a bottom hydrophilic support layer (hydrophilic layer), and a surface electrophilic functional layer (electrophilic layer) arranged sequentially, forming a large liquid storage space. The coating is a two-layer structure of "surface electrophilic functional layer + bottom hydrophilic support layer", with each layer having a clear functional division and synergistic effect, forming a synergistic system of "adsorption-spreading-storage".

[0024] [Base membrane] The type of base membrane is not limited; it can be a polyolefin membrane, specifically polypropylene (PP), polyethylene (PE), etc.

[0025] In some embodiments, the thickness of the base film is 6μm-12μm, such as 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc. The porosity of the base film is 38%-52%, such as 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, etc.

[0026] [Bottom Hydrophilic Support Layer] The bottom hydrophilic support layer contains acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent. The hydrophilic groups (-COOH, -OH) enable rapid spread and stable storage of the electrolyte, while providing structural support for the surface layer.

[0027] In some embodiments, the mass ratio of acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent in the raw materials for preparing the bottom hydrophilic support layer is 100:(0.5-1.0):(0.05-0.1), such as 100:0.5:0.05, 100:0.6:0.06, 100:0.7:0.07, 100:0.8:0.08, 100:0.9:0.09, 100:1.0:0.10, etc. The electrolyte wetting rate and electrolyte stability can be further improved by adjusting the content of each component. The silane coupling agent can be an aminosilane, specifically KH-550 (3-aminopropyltriethoxysilane), KH792 (N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane), etc.

[0028] Acrylic acid-grafted ceramic particles are composite particles formed by "growing" organic acrylic polymer chains onto the surface of inorganic ceramic particles. The inorganic ceramic particles can be alumina, boehmite, etc.; the acrylic polymer chains can be acrylic monomers such as acrylic acid, methyl methacrylate, butyl acrylate, etc., which can be used alone or in combination. The monomer dosage is 20-100% of the ceramic particle mass. An initiator initiates the polymerization; initiator types can include ammonium persulfate, azobisisobutyronitrile, etc., with the initiator dosage being 0.5-2% of the monomer mass.

[0029] The core of ceramic particles is typically alumina (Al₂O₃) or boehmite (AlOOH). These provide essential properties such as high temperature resistance, high thermal conductivity, and mechanical strength. The ceramic particle core is encased in an acrylic polymer shell. Through a chemical reaction (such as free radical polymerization), polyacrylic acid (PAA) or its copolymer chains are grafted onto the surface of the ceramic particles. This polymer shell imparts new surface properties to the particles. Acrylic acid-grafted ceramic particles can be synthesized in-house or commercially available. The grafting rate of acrylic acid in these particles ranges from 5% to 20%, such as 5%, 10%, 15%, 20%, etc.

[0030] Specifically, the preparation process of acrylic acid-grafted ceramic particles is as follows: 1. Pretreatment: Cleaning and activation of ceramic particle surface Take ceramic particles (such as alumina or boehmite), ultrasonically clean them with anhydrous ethanol or deionized water for 15-30 minutes to remove surface oil, dust and other impurities, filter them and dry them at 100-120℃ for 2-4 hours to ensure that there is no moisture on the surface (to avoid affecting the subsequent coupling reaction).

[0031] 2. Introduction of reaction sites: Surface grafting of silane coupling agents (1) Prepare an ethanol-water mixed solution (volume ratio of about 7:3), add a silane coupling agent (such as KH-570, which contains double bonds and can copolymerize with acrylic acid monomers), the amount of coupling agent is 0.5%-2% of the mass of ceramic particles, and adjust the pH to 4-5 (to promote the hydrolysis of coupling agent).

[0032] (2) Add the dried ceramic particles to the above solution and stir at 60-80℃ for 2-4 hours to allow the coupling agent to hydrolyze and combine with the hydroxyl groups on the surface of the ceramic particles through Si-O- bonds, forming unsaturated double bonds (reaction sites) on the surface.

[0033] (3) After the reaction is complete, filter and wash with ethanol three times to remove the ungrafted free coupling agent. Dry at 80-100℃ for 1-2 hours to obtain "ceramic particles with double bonds on the surface".

[0034] 3. Graft polymerization: Acrylic acid monomers "grow" on the surface of particles. (1) Set up a polymerization reaction apparatus (a three-necked flask with a stirrer and a nitrogen port), add the above modified ceramic particles and solvent (such as deionized water, ethanol or dimethyl sulfoxide, depending on the solubility of the monomer), and ultrasonically disperse for 30 minutes to make the particles uniformly suspended.

[0035] (2) Add acrylic monomers (such as acrylic acid, methyl methacrylate, butyl acrylate, etc., which can be used alone or in combination). The amount of monomer is 20%-100% of the mass of ceramic particles (to determine the thickness of the grafted chain). Then add initiators (such as ammonium persulfate, azobisisobutyronitrile, the amount of which is 0.5%-2% of the mass of monomers).

[0036] (3) Purge with nitrogen for 30 minutes to remove air (to prevent free radicals from being oxidized), raise the temperature to 60-85℃ (corresponding to the decomposition temperature of the initiator), stir the reaction for 4-8 hours, and the monomers initiate free radical polymerization at the double bonds on the surface of the ceramic particles to form composite particles with acrylic polymer linkages.

[0037] 4. Post-processing: purification and drying (1) After the reaction is complete, cool the reaction solution to room temperature, centrifuge (8000-10000r / min, 10-15 minutes), and collect the precipitate.

[0038] (2) Wash the precipitate repeatedly with solvents (such as ethanol or deionized water) 3-5 times to remove unpolymerized free monomers and homopolymers (non-grafted polymers).

[0039] (3) The washed composite particles are vacuum dried at 60-80℃ for 4-6 hours to obtain the final acrylic polymer grafted ceramic composite particles.

[0040] Sodium carboxymethyl cellulose is a commercially available raw material, such as that from Daicel Co., Ltd. The degree of substitution of sodium carboxymethyl cellulose is 0.6-0.9. "Degree of substitution" refers to the average percentage of carboxymethyl (-CH2-COO) groups on each of the three hydroxyl groups (-OH) on the cellulose glucose unit. - The number of items replaced.

[0041] Silane coupling agents are also commercially available materials. There are no restrictions on the type of silane coupling agent, such as KH-550, KH-792, etc., which can be purchased from Shanghai Maclean.

[0042] In some embodiments, the acrylic acid-grafted ceramic particles include nano-sized particles and micro-sized particles, forming a gradient particle size ceramic particle structure. The nano-sized particles have a diameter of 80 nm-200 nm, such as 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, etc.; the micro-sized particles have a diameter of 1.5 μm-3.0 μm, such as 1.5 μm, 1.8 μm, 2.0 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.0 μm, etc. The mass ratio of nano-sized particles to micro-sized particles is 1:(0.3-0.7), such as 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, etc. This embodiment of the invention uses a gradient of nano-sized and micro-sized particles, which can effectively improve the wettability of the electrolyte and enhance the liquid absorption and retention capacity of the diaphragm.

[0043] In some embodiments, the thickness of the bottom hydrophilic support layer is 1μm-2μm, such as 1.0μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2.0μm, etc. Within this thickness range, the electrolyte wetting rate and electrolyte retention stability can be further improved.

[0044] [Surface Electrophilic Functional Layer] The surface electrophilic functional layer contains aminated porous alumina, quaternized polyetheramine, and polyethylene glycol dimethyl ether. Aminated ordered porous alumina with a large specific surface area serves as the core carrier, combined with quaternized polyetheramine and polyethylene glycol dimethyl ether. This is achieved through the interaction of amino groups (-NH2) and quaternary ammonium groups (-N). + R3) actively adsorbs electrolyte anions (such as PF6) - This reduces the ion transport energy barrier and improves conduction selectivity.

[0045] Aminated porous alumina is a functional material produced by introducing amino (-NH2) functional groups onto a porous alumina framework through surface chemical modification. Aminated porous alumina can be prepared in-house using existing methods or commercially available, such as from Shandong Guoci Functional Materials Co., Ltd. The amino loading in aminated porous alumina ranges from 0.8 mmol / g to 1.5 mmol / g, such as 0.8 mmol / g, 0.9 mmol / g, 1.0 mmol / g, 1.1 mmol / g, 1.2 mmol / g, 1.3 mmol / g, 1.4 mmol / g, and 1.5 mmol / g. The pore size ranges from 10 nm to 99 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 99 nm. The specific surface area is ≥900 m². 2 / g, such as 900m 2 / g、930m 2 / g、950m 2 / g、980m 2 / g, 1000m 2 / g、1100m 2 / g etc.

[0046] The degree of quaternization of quaternized polyetheramines is 60%-80%, such as 60%, 65%, 70%, 75%, 80%, etc. The degree of quaternization refers to the percentage of amine groups (-NH- or -NH2) actually converted into quaternary ammonium salts in the polyetheramine molecular chain. The average molecular weight of quaternized polyetheramines is 1000Da-2000Da, such as 1000Da, 1100Da, 1200Da, 1300Da, 1400Da, 1500Da, 1600Da, 1700Da, 1800Da, 1900Da, 2000Da, etc. Specifically, quaternized polyetheramines are commercially available raw materials, such as those purchased from Wanhua Chemical.

[0047] Polyethylene glycol dimethyl ether is a commercially available raw material, such as that from Hubei Rishengchang New Material Technology Co., Ltd. Its weight-average molecular weight is 250-270, corresponding to a degree of polymerization n=3-8. Adding polyethylene glycol dimethyl ether can effectively disperse the ceramic material.

[0048] In some embodiments, the mass ratio of aminated porous alumina, quaternized polyetheramine, and polyethylene glycol dimethyl ether in the raw materials for preparing the surface electrophilic functional layer is 100:(3.0-8.0):(0.8-2.0), such as 100:3.0:0.8, 100:4.0:1.0, 100:5.0:1.3, 100:6.0:1.5, 100:7.0:1.8, 100:8.0:2.0, etc., and the ion conduction efficiency can be further improved by adjusting the content of each component.

[0049] In some embodiments, the thickness of the surface electrophilic functional layer is 0.2μm-0.5μm, such as 0.2μm, 0.3μm, 0.4μm, 0.5μm, etc.

[0050] The total coating weight of the bottom hydrophilic support layer and the top electrophilic functional layer is 1.5 g / m². 2 -3.5g / m 2 For example, it can be 1.5g / m 2 1.8g / m 2 2.0g / m 2 2.3g / m 2 2.5g / m 2 2.8g / m 2 3.0g / m 2 3.3g / m 2 3.5g / m2 The two layers are tightly bonded together by hydrogen bonds between amino and carboxyl groups, with the total coating weight controlled at 1.5 g / m². 2 -3.5g / m 2 This ensures the compatibility between the coating and the base film (thickness 6-12μm, porosity 38%-52%).

[0051] It should be noted that in this embodiment of the invention, the core component is improved from a general unmodified material to a directional molecularly modified system. Because the improved aminated ordered porous alumina enhances the anion adsorption capacity, the quaternized polyetheramine strengthens the ion conduction selectivity, and the acrylic-grafted ceramic particles improve the organic-inorganic compatibility, the specific interaction between the components and the electrolyte is stronger, which better solves the problems of poor dispersion and weak interfacial bonding of traditional components. Therefore, it produces a structurally stable effect with a coating peel strength ≥30N / m, puncture resistance ≥356gf, and thermal shrinkage rate ≤3% at 180℃.

[0052] This invention also provides a method for preparing a composite coated membrane, wherein a bottom hydrophilic support layer and a surface electrophilic functional layer are formed on a base membrane, and the compositions of the bottom hydrophilic support layer and the surface electrophilic functional layer meet the requirements described above. The preparation method employs a dedicated process route of "slurry customization - gradient coating - synergistic curing" to ensure that the structure and performance meet the design requirements. The steps are as follows: S1, Slurry Preparation Based on the composition of the bottom hydrophilic support layer and the surface electrophilic functional layer, prepare the bottom hydrophilic slurry and the surface electrophilic slurry for later use.

[0053] In some embodiments, the preparation process of the underlying hydrophilic slurry includes: uniformly mixing acrylic-grafted ceramic particles, sodium carboxymethyl cellulose, a silane coupling agent, and a first solvent to obtain the underlying hydrophilic slurry. Specific raw material descriptions for the acrylic-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent are provided above in the specification. To ensure uniform mixing of the raw materials, after mixing, the mixture is stirred at 500-800 rpm for 30-45 minutes, followed by ultrasonic treatment for 15-25 minutes, and then filtered for later use. Specifically, the stirring speed can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc., and the stirring time can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, etc.; the ultrasonic treatment time can be 15 minutes, 20 minutes, 25 minutes, etc.

[0054] Further, the first solvent is a mixed solvent formed by mixing N,N-dimethylformamide and deionized water, but is not limited to this. The volume ratio of N,N-dimethylformamide to water is (0.3-0.6):1, such as 0.3:1, 0.4:1, 0.5:1, 0.6:1, etc.; the mass ratio of the first solvent to the grafted acrylic acid ceramic particles is (2.0-4.0):1, such as 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, etc.

[0055] In some embodiments, the preparation process of the surface electrophilic paste includes: uniformly mixing aminated porous alumina, quaternized polyetheramine, polyethylene glycol dimethyl ether, and a second solvent to obtain the surface electrophilic paste. Specific raw material descriptions for aminated porous alumina, quaternized polyetheramine, and polyethylene glycol dimethyl ether are provided above in the specification. To ensure uniform mixing of the raw materials, the mixture is ultrasonically dispersed for 20-30 minutes after mixing, followed by high-speed stirring at 2000-3000 rpm for 40-60 minutes, and then filtered for later use. Specifically, the ultrasonic treatment time can be 20 minutes, 25 minutes, 30 minutes, etc.; the stirring speed can be 2000 rpm, 2300 rpm, 2500 rpm, 2800 rpm, 3000 rpm, etc.; and the stirring time can be 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc.

[0056] Furthermore, the second solvent is a mixed solvent formed by mixing ethanol and deionized water, but is not limited to this. The volume ratio of ethanol to water is (0.5-0.7):1, such as 0.5:1, 0.6:1, 0.7:1, etc.; the mass ratio of the second solvent to aminated porous alumina is (2.0-4.0):1, such as 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, etc.

[0057] S2, gradient coating A dual-layer synchronous interface self-assembly coating process is employed. First, a hydrophilic base coat is applied and dried, followed by a simultaneous coating of an electrophilic top coat. The coating roller speed for the hydrophilic base coat is lower than that for the electrophilic top coat, and the roller speed ratio is controlled to be 1:(1.2-1.5), such as 1:1.2, 1:1.3, 1:1.4, or 1:1.5. The coating gap is 20μm-50μm, such as 20μm, 30μm, 40μm, or 50μm. By adjusting the roller speed ratio and coating gap, pore blockage of the base film is avoided.

[0058] Specifically, the equipment for dual-layer synchronous interface self-assembly coating is existing equipment, specifically the Guangdong Ouge Precision Machinery OG600-TB2A. The coating roller speed ratio refers to the ratio of the coating roller speed for coating the bottom hydrophilic slurry to the coating roller speed for coating the top electrophilic slurry. The coating gap refers to the gap between key components of the coating equipment; in this case, it is the distance between the slit die and the diaphragm substrate.

[0059] Furthermore, after applying the bottom layer of hydrophilic paste, it is dried at 50℃-60℃ for 5-10 minutes to achieve pre-drying, and then the top layer of electrophilic paste is applied simultaneously. Specifically, the pre-drying temperature can be 50℃, 53℃, 55℃, 58℃, 60℃, etc.; the drying time can be 5 minutes, 8 minutes, 10 minutes, etc.

[0060] S3, Curing and Molding After coating the surface with electrophilic paste, the coating is first dried and then subjected to ultraviolet irradiation crosslinking to enhance the structural stability and mechanical properties of the coating.

[0061] In some embodiments, drying can be carried out under vacuum drying conditions, with the drying temperature controlled at 70℃-90℃, such as 70℃, 75℃, 80℃, 85℃, 90℃, etc.; and the drying time at 20min-30min, such as 20min, 25min, 30min, etc.

[0062] In some embodiments, at wavelengths of 254 nm-365 nm and doses of 50 mJ / cm 2 -80mJ / cm 2 Under specific conditions, ultraviolet (UV) irradiation crosslinking was performed for 3-8 minutes. The process parameters for UV irradiation crosslinking were optimized to further improve the structural stability and mechanical properties of the coating. Specifically, the irradiation wavelengths could be 254 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, and 365 nm; the irradiation dose could be 50 mJ / cm². 2 55mJ / cm 2 60mJ / cm 2 65mJ / cm 2 70mJ / cm 2 75mJ / cm 2 80mJ / cm 2 Irradiation time can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, etc.

[0063] It should be noted that the present invention improves the preparation process from step-by-step independent coating to a synergistic process of "double-layer synchronous interface self-assembly coating + ultraviolet irradiation crosslinking". Because the improved process avoids the blockage of the base film pores by precisely controlling the coating roller speed ratio and gap, and the ultraviolet irradiation further strengthens the coating crosslinking structure, the forming accuracy and structural durability of the gradient coating are greatly improved, and the coating uniformity and ion transport channel unobstructedness are better balanced. Therefore, the process adaptability effect of base film pore blockage rate ≤5% and performance degradation ≤3% under high and low temperature conditions (-20℃ to 60℃) is achieved.

[0064] It should be noted that the present invention has the following synergistic effects by introducing a bottom hydrophilic support layer and a surface electrophilic functional layer in the diaphragm: (1) Component synergy: The modified electrophilic / hydrophilic components solve the problems of "slow ion transport" and "poor wetting and liquid retention" respectively through the action of modified groups, achieving the effect of 1+1>2; (2) Structural synergy: The functional division and interface combination between gradient layers avoid the performance shortcomings of a single coating; (3) Process synergy: The matching of double-layer synchronous coating and ultraviolet crosslinking ensures the precise molding of the gradient structure, while improving the bonding force between the coating and the base film.

[0065] Because the improved surface layer achieves directional adsorption of electrolyte anions through amino and quaternary ammonium groups, while the bottom layer achieves rapid electrolyte spreading and storage through hydrophilic groups, and the two layers are tightly bonded by hydrogen bonds to form a functional synergy, the energy barrier for electrolyte wetting and ion transport is significantly reduced, better balancing wetting rate and liquid retention stability. Therefore, the core effects of electrolyte wetting time ≤0.2s, ionic conductivity ≥1.8mS / cm, and liquid retention rate ≥95% after 500 cycles are achieved.

[0066] This invention also provides a secondary battery, including the composite coated separator provided in this invention, and may further include a positive electrode, a negative electrode, an electrolyte, etc., to form a complete battery structure. Improvements to the separator are beneficial for enhancing the battery's electrochemical performance and lifespan.

[0067] This invention improves the application adaptability of the separator from ordinary voltage scenarios to high-voltage long-cycle scenarios of ≥4.5V. Because the improved electrophilic-hydrophilic synergistic system reduces the side reactions of electrolyte decomposition under high voltage, the stable coating structure inhibits the performance degradation of the separator during cycling, and significantly slows down the rate of increase in battery internal resistance. This better meets the stringent requirements of high-voltage batteries for the separator, resulting in a battery performance upgrade effect of ≥90% capacity retention and ≥30% reduction in initial internal resistance after 1000 cycles for 4.5V lithium batteries.

[0068] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0069] The preparation process of the acrylic acid-grafted ceramic particles used in the following examples is as follows: 1. Pretreatment: Cleaning and activation of ceramic particle surface Take ceramic particles (alumina, with particle size meeting the requirements of nano- and micron-sized particles; nano-Al2O3 purchased from Shandong Guoci, SAO-FC050E-JL particles with a particle size of 100nm; micron-sized Al2O3 purchased from Shandong Guoci, HMO-070E, with a particle size Dv50 of 2.0μm), ultrasonically clean them with anhydrous ethanol or deionized water for 20 minutes to remove surface oil, dust and other impurities, filter them and dry them at 110℃ for 3 hours.

[0070] 2. Introduction of reaction sites: Surface grafting of silane coupling agents (1) Prepare an ethanol-water mixed solution (volume ratio of about 7:3), add a silane coupling agent (such as KH-570), the amount of coupling agent is 1% of the mass of ceramic particles, and adjust the pH to 4.5.

[0071] (2) Add the dried ceramic particles to the above solution and stir at 70°C for 3 hours to allow the coupling agent to hydrolyze and combine with the hydroxyl groups on the surface of the ceramic particles through Si-O- bonds, forming unsaturated double bonds (reaction sites) on the surface.

[0072] (3) After the reaction is complete, filter and wash with ethanol three times to remove ungrafted free coupling agent. Dry at 90°C for 1.5 hours to obtain "ceramic particles with double bonds on the surface".

[0073] 3. Graft polymerization: Acrylic acid monomers "grow" on the surface of particles. (1) Set up a polymerization reaction apparatus (a three-necked flask with a stirrer and a nitrogen port), add the above modified ceramic particles and solvent (deionized water), and ultrasonically disperse for 30 minutes to make the particles uniformly suspended.

[0074] (2) Add acrylic monomer (acrylic acid), the amount of monomer is 40% of the mass of ceramic particles (to determine the thickness of the grafted chain), and then add initiator (ammonium persulfate, the amount is 1% of the mass of monomer).

[0075] (3) Purge with nitrogen for 30 minutes to remove air, raise the temperature to 70°C, stir and react for 6 hours. The monomers initiate free radical polymerization at the double bonds on the surface of the ceramic particles to form composite particles with acrylic polymer linkages.

[0076] 4. Post-processing: purification and drying (1) After the reaction is complete, cool the reaction solution to room temperature, centrifuge (9000r / min, 12 minutes) and collect the precipitate.

[0077] (2) Wash the precipitate repeatedly with solvent (ethanol) 4 times.

[0078] (3) The washed composite particles were vacuum dried at 70°C for 5 hours to obtain the final acrylic polymer grafted ceramic composite particles.

[0079] Example 1 This embodiment provides a method for preparing a composite coated membrane, which involves forming a bottom hydrophilic support layer and a surface electrophilic functional layer on a base membrane. The steps are as follows: (1) Slurry preparation Electrophilic surface paste: Aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether were added to a mixed solvent of ethanol and deionized water. The mixture was ultrasonically dispersed for 25 min, followed by high-speed stirring at 2500 rpm for 50 min. After filtration, the paste was ready for use. The aminated ordered porous alumina with a large specific surface area had an amino loading of 1.0 mmol / g, an average pore size of 50 nm, and a specific surface area of ​​1000 m². 2 / g. The degree of quaternization of the quaternized polyetheramine is 70%, and the average molecular weight is 1500 Da. The weight-average molecular weight of polyethylene glycol dimethyl ether is 260. The mass ratio of aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether is 100:5.5:1.4, the volume ratio of ethanol to water is 0.6:1, and the mass ratio of the mixed solvent to the aminated porous alumina is 3.0:1.

[0080] Bottom hydrophilic slurry: Acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent (KH-550) are added to a mixed solvent formed by N,N-dimethylformamide and deionized water. The mixture is stirred at 600 rpm for 40 min, followed by ultrasonic treatment for 20 min, and then filtered for later use. The acrylic acid-grafted ceramic particles include nano-sized and micro-sized particles. The nano-sized particles have a particle size of 100 nm, and the micro-sized particles have a particle size of 2.0 μm. The mass ratio of nano-sized particles to micro-sized particles is 1:0.5, and the grafting rate of acrylic acid in both nano-sized and micro-sized particles is 10%. The mass ratio of acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:0.75:0.075, the volume ratio of N,N-dimethylformamide to water is 0.6:1, and the mass ratio of the mixed solvent to the acrylic acid-grafted ceramic particles is 3.0:1.

[0081] (2) Gradient coating A dual-layer synchronous interface self-assembly coating process was adopted. First, a hydrophilic slurry (1.5μm ± 0.5μm thickness) was coated onto a base film (PP, 10μm thickness, 40% porosity), and pre-dried at 55℃ for 8 min. Then, a surface electrophilic slurry (0.3μm thickness) was simultaneously coated. The coating roller speed ratio was controlled at 1:1.3, the coating gap at 35μm, and the total coating weight was 2.5g / m³. 2 .

[0082] (3) Curing and molding After vacuum drying at 80℃ for 25 min, it was subjected to a wavelength of 365 nm and a dose of 70 mJ / cm. 2 Crosslinked by ultraviolet irradiation for 5 minutes.

[0083] Example 2 This embodiment provides a method for preparing a composite coated membrane, which involves forming a bottom hydrophilic support layer and a surface electrophilic functional layer on a base membrane. The steps are as follows: (1) Slurry preparation Electrophilic surface paste: Aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether were added to a mixed solvent of ethanol and deionized water. The mixture was ultrasonically dispersed for 20 min, followed by high-speed stirring at 2000 rpm for 60 min. After filtration, the paste was ready for use. The aminated ordered porous alumina with a large specific surface area had an amino loading of 0.8 mmol / g, an average pore size of 10 nm, and a specific surface area of ​​1000 m² / g. 2 / g. The degree of quaternization of the quaternized polyetheramine is 60%, and the average molecular weight is 1000 Da. The weight-average molecular weight of polyethylene glycol dimethyl ether is 250. The mass ratio of aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether is 100:3.0:0.8, the volume ratio of ethanol to water is 0.5:1, and the mass ratio of the mixed solvent to the aminated porous alumina is 2.0:1.

[0084] Bottom hydrophilic slurry: Acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent (KH-550) are added to a mixed solvent formed by N,N-dimethylformamide and deionized water. The mixture is stirred at 500 rpm for 45 min, followed by ultrasonic treatment for 15 min, and then filtered for later use. The acrylic acid-grafted ceramic particles include nano-sized particles and micro-sized particles. The nano-sized particles have a particle size of 80 nm, and the micro-sized particles have a particle size of 1.5 μm. The mass ratio of nano-sized particles to micro-sized particles is 1:0.3, and the grafting rate of acrylic acid in both nano-sized and micro-sized particles is 5%. The mass ratio of acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:0.5:0.05, the volume ratio of N,N-dimethylformamide to water is 0.3:1, and the mass ratio of the mixed solvent to the acrylic acid-grafted ceramic particles is 2.0:1.

[0085] (2) Gradient coating A dual-layer synchronous interface self-assembly coating process was adopted. First, a 1μm thick hydrophilic slurry was coated onto a base film (PP, 6μm thick, 38% porosity), and pre-dried at 50℃ for 10 min. Then, a 0.2μm thick electrophilic slurry was simultaneously coated onto the surface. The coating roller speed ratio was controlled at 1:1.2, the coating gap at 20μm, and the total coating weight was 1.5g / m³. 2 .

[0086] (3) Curing and molding After vacuum drying at 70℃ for 20 min, it was subjected to a wavelength of 365 nm and a dose of 50 mJ / cm. 2 Crosslinking under ultraviolet radiation for 8 minutes.

[0087] Example 3 This embodiment provides a method for preparing a composite coated membrane, which involves forming a bottom hydrophilic support layer and a surface electrophilic functional layer on a base membrane. The steps are as follows: (1) Slurry preparation Electrophilic surface paste: Aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether were added to a mixed solvent of ethanol and deionized water. The mixture was ultrasonically dispersed for 30 min, followed by high-speed stirring at 3000 rpm for 40 min. After filtration, the paste was ready for use. The aminated ordered porous alumina with a large specific surface area had an amino loading of 1.5 mmol / g, an average pore size of 99 nm, and a specific surface area of ​​1000 m² / g. 2 / g. The degree of quaternization of the quaternized polyetheramine is 80%, and the average molecular weight is 2000 Da. The weight-average molecular weight of polyethylene glycol dimethyl ether is 270. The mass ratio of aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether is 100:8.0:2.0, the volume ratio of ethanol to water is 0.7:1, and the mass ratio of the mixed solvent to the aminated porous alumina is 4.0:1.

[0088] Bottom hydrophilic slurry: Acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent (KH-550) are added to a mixed solvent formed by N,N-dimethylformamide and deionized water. The mixture is stirred at 800 rpm for 30 min, followed by ultrasonic treatment for 25 min, and then filtered for later use. The acrylic acid-grafted ceramic particles include nano-sized and micro-sized particles. The nano-sized particles have a particle size of 200 nm, and the micro-sized particles have a particle size of 3.0 μm. The mass ratio of nano-sized particles to micro-sized particles is 1:0.7, and the grafting rate of acrylic acid in both nano-sized and micro-sized particles is 20%. The mass ratio of acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:1.0:0.1, the volume ratio of N,N-dimethylformamide to water is 0.6:1, and the mass ratio of the mixed solvent to the acrylic acid-grafted ceramic particles is 4.0:1.

[0089] (2) Gradient coating A dual-layer synchronous interface self-assembly coating process was adopted. First, a 2μm thick hydrophilic slurry was coated onto a base film (PP, 12μm thick, 52% porosity), and pre-dried at 60℃ for 5 minutes. Then, a 0.5μm thick electrophilic slurry was simultaneously coated onto the base film. The coating roller speed ratio was controlled at 1:1.5, the coating gap at 50μm, and the total coating weight was 3.5g / m³. 2 .

[0090] (3) Curing and molding After vacuum drying at 90℃ for 20 min, it was subjected to a wavelength of 365 nm and a dose of 80 mJ / cm. 2 Crosslinked by ultraviolet irradiation for 3 minutes.

[0091] Example 4 The only difference from Example 1 is that, in the preparation of the surface electrophilic paste, the mass ratio of aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether is 100:9.0:2.2.

[0092] Example 5 The only difference from Example 1 is that, in the preparation of the surface electrophilic paste, the mass ratio of aminated ordered porous alumina with a large specific surface area, quaternized polyetheramine, and polyethylene glycol dimethyl ether is 100:2.0:0.7.

[0093] Example 6 The only difference from Example 1 is that, in the preparation of the bottom hydrophilic slurry, the mass ratio of the acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:1.2:0.12.

[0094] Example 7 The only difference from Example 1 is that, in the preparation of the bottom hydrophilic slurry, the mass ratio of the acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:0.4:0.04.

[0095] Example 8 The only difference from Example 1 is that the thickness of the bottom hydrophilic paste coating is 0.5 μm, and the thickness of the top electrophilic paste coating is 0.1 μm.

[0096] Example 9 The only difference from Example 1 is that the thickness of the bottom hydrophilic paste coating is 3 μm, and the thickness of the top electrophilic paste coating is 1 μm.

[0097] Comparative Example 1 The only difference from Example 1 is that only the bottom layer of hydrophilic slurry is coated, and the coating thickness remains the same.

[0098] Comparative Example 2 The only difference from Example 1 is that only the surface electrophilic paste is coated, and the coating thickness remains the same.

[0099] Comparative Example 3 This comparative example provides a base film (the same as in Example 1) for comparison.

[0100] Comparative Example 4 The only difference from Example 1 is that no silane coupling agent (KH-550) is added to the bottom hydrophilic slurry.

[0101] Comparative Example 5 The only difference from Example 1 is that sodium carboxymethyl cellulose in the bottom hydrophilic slurry is replaced with an equal amount of styrene-butadiene rubber.

[0102] Comparative Example 6 The only difference from Example 1 is that quaternized polyetheramine is not added to the surface electrophilic paste.

[0103] Comparative Example 7 The only difference from Example 1 is that the quaternized polyetheramine in the surface electrophilic paste is replaced with an equal amount of polyisobutyleneamine.

[0104] Experimental Example 1 The performance of the composite coated membranes prepared in the test examples and comparative examples is shown in Table 1.

[0105] Test method: (1) Diaphragm heat shrinkage test: Refer to GB / T 36363-2018; (2) Membrane air permeability test: Refer to GB / T 36363-2018; (3) Diaphragm peel strength test: Refer to GB / T 2792-2014; (4) Diaphragm puncture strength test: Refer to GB / T 36363-2018; (5) Membrane ionic conductivity test: Refer to GB / T 36363-2018; (6) Battery testing: Graphite was selected as the negative electrode and lithium nickel manganese oxide (811) was selected as the positive electrode. A 5Ah soft-pack battery was assembled and electrochemical tests were conducted. The electrolyte selected was EC:PC:DEC = 1:1:1 and LiPF6 1Mol / L.

[0106] (7) Wetting rate: The wettability rate is characterized by the rate at which the electrolyte wets the entire 19mm diameter disc of the separator. The specific test method is as follows: the separator is placed in the 2025 coin cell positive electrode case, and 50μL of electrolyte is added, in which the lithium salt concentration is 1mol / L LiTFSI, the solvent is a mixture of DOL and DME, and 1wt% LiNO3 is added. The time it takes for the electrolyte to completely wet the separator is compared.

[0107] Table 1. Performance comparison of composite coated membranes prepared in the examples and comparative examples.

[0108] As can be seen from Table 1, the composite coating membrane with a base film, a bottom hydrophilic support layer, and a surface electrophilic functional layer provided by the present invention achieves simultaneous improvement in electrolyte wetting rate, electrolyte retention stability, ion conduction efficiency, and coating adhesion, thus meeting the requirements of high-voltage and long-cycle-life batteries.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite coated diaphragm, characterized in that, It includes a base film, a bottom hydrophilic support layer, and a surface electrophilic functional layer arranged in sequence; The bottom hydrophilic support layer contains acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and a silane coupling agent. The surface electrophilic functional layer contains aminated porous alumina, quaternized polyetheramine, and polyethylene glycol dimethyl ether.

2. The composite coated diaphragm according to claim 1, characterized in that, In the raw materials used to prepare the underlying hydrophilic support layer, the mass ratio of acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, and silane coupling agent is 100:(0.5-1.0):(0.05-0.1). And / or, the silane coupling agent is an aminosilane; And / or, in the raw materials for preparing the surface electrophilic functional layer, the mass ratio of aminated porous alumina, quaternized polyetheramine and polyethylene glycol dimethyl ether is 100:(3.0-8.0):(0.8-2.0).

3. The composite coated diaphragm according to claim 1, characterized in that, The grafted acrylic acid ceramic particles include nano-sized particles and micro-sized particles. The nano-sized particles have a particle size of 80nm-200nm, and the micro-sized particles have a particle size of 1.5μm-3.0μm. The mass ratio of the nano-sized particles to the micro-sized particles is 1:(0.3-0.7). And / or, the grafting rate of acrylic acid in the grafted acrylic acid ceramic particles is 5%-20%.

4. The composite coated diaphragm according to claim 1, characterized in that, The aminated porous alumina has an amino loading of 0.8 mmol / g-1.5 mmol / g, a pore size of 10 nm-99 nm, and a specific surface area ≥900 m² / g. 2 / g; And / or, the degree of quaternization of the quaternized polyetheramine is 60%-80% and the average molecular weight is 1000Da-2000Da.

5. The composite coated diaphragm according to any one of claims 1-4, characterized in that, The thickness of the bottom hydrophilic support layer is 1μm-2μm, and the thickness of the surface electrophilic functional layer is 0.2μm-0.5μm; And / or, the total coating amount of the bottom hydrophilic support layer and the top electrophilic functional layer is 1.5 g / m². 2 -3.5g / m 2 ; And / or, the thickness of the base film is 6μm-12μm, and the porosity of the base film is 38%-52%; And / or, the base film is made of polyolefin.

6. A method for preparing the composite coated diaphragm according to any one of claims 1-5, characterized in that, include: The underlying hydrophilic support layer and the surface electrophilic functional layer are formed on the base film.

7. The preparation method according to claim 6, characterized in that, include: A dual-layer synchronous coating process is adopted. First, a hydrophilic slurry is coated on the bottom layer and dried. Then, an electrophilic slurry is coated on the top layer simultaneously. After drying, ultraviolet irradiation crosslinking is performed.

8. The preparation method according to claim 7, characterized in that, The preparation process of the underlying hydrophilic slurry includes: mixing acrylic acid-grafted ceramic particles, sodium carboxymethyl cellulose, silane coupling agent and a first solvent, stirring at 500r / min-800r / min for 30min-45min, and then ultrasonically treating for 15min-25min.

9. The preparation method according to claim 8, characterized in that, The first solvent is a mixed solvent formed by mixing N,N-dimethylformamide and water, with a volume ratio of N,N-dimethylformamide to water of (0.3-0.6):1, and a mass ratio of the first solvent to the grafted acrylic acid ceramic particles of (2.0-4.0):

1.

10. The preparation method according to claim 7, characterized in that, The preparation process of the surface electrophilic paste includes: mixing aminated porous alumina, quaternized polyetheramine, polyethylene glycol dimethyl ether and a second solvent, ultrasonically dispersing for 20-30 minutes, and then stirring at a high speed of 2000-3000 r / min for 40-60 minutes.

11. The preparation method according to claim 10, characterized in that, The second solvent is a mixed solvent formed by mixing ethanol and water, and the volume ratio of ethanol to water is (0.5-0.7):1, and the mass ratio of the second solvent to the aminated porous alumina is (2.0-4.0):

1.

12. The preparation method according to claim 7, characterized in that, The coating roller speed of the bottom hydrophilic paste is lower than that of the coating roller speed of the top electrophilic paste, and the coating roller speed ratio is controlled to be 1:(1.2-1.5), with a coating gap of 20μm-50μm; And / or, after coating the underlying hydrophilic slurry, dry it at 50℃-60℃ for 5min-10min, then simultaneously coat the surface electrophilic slurry, and then dry it at 70℃-90℃ for 20min-30min. And / or, at wavelengths of 254nm-365nm and doses of 50mJ / cm 2 -80mJ / cm 2 Under the conditions of ultraviolet irradiation crosslinking, the irradiation time is 3min-8min.

13. A secondary battery, characterized in that, This includes the composite coated diaphragm according to any one of claims 1-5 or the composite coated diaphragm prepared by the preparation method according to any one of claims 6-12.

Images