Ceramic coating diaphragm based on polydopamine gradient modification as well as preparation method and application of ceramic coating diaphragm

Abstract

The invention discloses a ceramic coating diaphragm based on polydopamine gradient modification and a preparation method and application thereof, and belongs to the technical field of partition plates / diaphragms. The ceramic coated separator of the present application comprises: a base film; the surface of the base membrane is coated with the n coatings, the coatings comprise polydopamine modified ceramic particles, the surfaces of the ceramic particles are coated with polydopamine, and n is larger than or equal to 2; wherein the content of the polydopamine is sequentially decreased from the first coating to the nth coating, and the particle size of the ceramic particles is sequentially increased from the first coating to the nth coating, the gradient structure design is adopted, so that the binding force of the polycoatings and the base membrane is effectively improved, and meanwhile, the mechanical strength and the thermal stability of the diaphragm are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of separator / membrane technology, and more specifically, relates to a ceramic-coated separator based on polydopamine gradient modification, its preparation method and application. Background Technology

[0002] The separator is a crucial component of liquid lithium-ion batteries, serving to both isolate the positive and negative electrodes and facilitate lithium-ion transport. It is a decisive factor in battery capacity, cycle performance, and safety. Currently, the most widely used battery separator materials are polyethylene (PE) and polypropylene (PP) microporous membranes. With the rapid development of battery technology, higher demands are placed on lithium battery separators, requiring excellent electrical insulation, chemical corrosion resistance, electrochemical stability, heat resistance, and mechanical properties. Simultaneously, separators must possess good liquid absorption and retention capabilities, and low internal resistance. Due to their inherent melting point characteristics, PE and PP are prone to thermal shrinkage in high-temperature environments, affecting their insulating function between the positive and negative electrodes and potentially leading to dangerous accidents. Therefore, improving the high-temperature resistance of lithium battery separators is imperative.

[0003] Coating one or both sides of a PE microporous membrane with ceramic particles is the easiest technical means to improve the heat resistance of lithium battery separators. Pure ceramic coatings are brittle and prone to cracking at high temperatures, and a single coating is difficult to balance adhesion and heat resistance. Ceramic-coated separators, formed by mixing ceramic particles, binders, and other additives in water into a uniform slurry and coating it onto a polymer base membrane, can improve the heat resistance and electrolyte wettability of the separator to a certain extent.

[0004] However, existing ceramic-coated separators still suffer from insufficient adhesion between the coating and the base membrane. This is because the base membrane has a low surface energy, and the binder used in ceramic coating is mainly polyacrylate emulsion. Polyacrylate emulsion binder has poor wettability to the base membrane, resulting in poor adhesion between the separator and ceramic particles, which can lead to severe detachment during battery cycling. Summary of the Invention

[0005] 1. The problem to be solved To address the problem that existing ceramic-coated diaphragms struggle to balance adhesion and heat resistance, the primary objective of this invention is to provide a ceramic-coated diaphragm based on polydopamine gradient modification. A second objective of this invention is to provide a method for preparing the above-mentioned ceramic-coated diaphragm; A third objective of the present invention is to provide a lithium battery comprising the above-described ceramic-coated separator.

[0006] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a ceramic-coated separator based on polydopamine gradient modification, comprising: Base film; And n layers of coating: coated on the surface of the base film, the coating comprising polydopamine-modified ceramic particles, the polydopamine being coated on the surface of the ceramic particles, n≥2; The polydopamine content satisfies the following condition: decreasing sequentially from the first coating to the nth coating; The particle size of the ceramic particles satisfies the following condition: it increases sequentially from the first coating to the nth coating.

[0007] A ceramic-coated separator based on polydopamine gradient modification according to any embodiment of the first aspect of the present invention comprises: Base film; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Second coating: Located outside the first coating, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; ... The nth coating: located outside the (n-1)th coating, comprises polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; The polydopamine content satisfies the following conditions: it decreases sequentially from the first coating to the nth coating, and the particle size of the ceramic particles increases sequentially from the first coating to the nth coating, where n ≥ 2.

[0008] The number of coating layers can be increased or decreased according to the requirements of the membrane properties. For example, three, four, or five coating layers can be applied to the base membrane surface. The number of coating layers affects the thickness and performance of the membrane. However, since the ceramic particles are modified by polydopamine, the bonding force between the coating layers is effectively improved, so a high bonding force can still be maintained.

[0009] The polydopamine gradient-modified ceramic-coated separator enhances the adhesion between the base film and the ceramic in the bottom coating, improves the heat resistance of the surface coating and its affinity with the electrolyte, and achieves good adhesion between the base film and the ceramic, thereby improving the electrical performance of lithium-ion batteries.

[0010] A ceramic-coated diaphragm based on polydopamine gradient modification according to any embodiment of the first aspect of the present invention comprises: a base film; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Second coating: Located outside the first coating and in contact with the electrolyte, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Wherein, the polydopamine content satisfies the following condition: first coating > second coating; The particle size of the ceramic particles satisfies the condition that the first coating layer is smaller than the second coating layer.

[0011] According to any embodiment of the first aspect of the present invention, the polydopamine-modified ceramic-coated diaphragm has a polydopamine content of 5wt%-10wt% in the first coating, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, and a polydopamine content of 1wt%-3wt% in the second coating, for example, 1wt%, 2wt%, or 3wt%.

[0012] As described herein, the polydopamine content in different coatings enables functional grading of the coatings. The first coating, which is in contact with the base film, has a higher polydopamine content and is a high-adhesion layer, improving the adhesion between the coating layer and the base film. The second coating, which covers the surface of the first coating and is in contact with the electrolyte, is a high-heat-resistant layer. Its polydopamine content is lower than that of the first coating, resulting in a higher content of ceramic particles and a higher proportion of ceramic particles to enhance thermal stability.

[0013] According to any embodiment of the first aspect of the present invention, the ceramic-coated diaphragm based on polydopamine gradient modification has the following particle size: the first coating layer < the second coating layer. Preferably, the particle size of the ceramic particles in the first coating layer is 50-300 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm. Preferably, the particle size of the ceramic particles in the second coating layer is 0.5-5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm.

[0014] Preferably, the sum of the particle size of the ceramic particles in the first coating and the particle size of the ceramic particles in the second coating is 600~1300nm, for example, it can be 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, or 1300nm; when the sum of the particle size of the ceramic particles in the first coating and the particle size of the ceramic particles in the second coating is 600~1300nm, the diaphragm has high peel strength, low thermal shrinkage rate, low electrolyte contact angle, and high ionic conductivity.

[0015] The selection of ceramic particle size, as described herein, is based on the principle that the bottom layer uses small-sized ceramic particles, which can tightly and firmly bond with the base film, providing a dense bottom layer structure that effectively blocks lithium dendrite penetration and improves heat resistance. The surface layer uses small-sized ceramic particles to construct a porous, high-specific-surface-area rough structure, which can homogenize the lithium-ion flow and inhibit dendrite concentrated growth from the source. The gradient structure of the coating surface creates a gradient distribution of small pores to large pores from the bottom layer to the surface layer. The large pores on the surface layer facilitate rapid absorption and transport of electrolyte, while the small pores on the bottom layer can lock in the electrolyte through capillary action, which is beneficial for electrolyte retention during long-term cycling and alleviates capacity decay caused by electrolyte drying.

[0016] As described herein, the content of polydopamine and the particle size of ceramic particles have a synergistic effect. This effect manifests in the following ways: small-diameter ceramic particles and high-content dopamine achieve a strong bond with the base film and form a dense underlayer. The strong bond is characterized by: high-content dopamine fully coating the surface of the ceramic particles, forming a network between ceramic particles and between the ceramic particles and the base film, enhancing the cohesiveness of the underlayer coating; small-diameter ceramic particles have a high specific surface area, allowing for sufficient contact with dopamine to strengthen the bond with the base film, achieving high-strength adhesion between the coating and the base film, and improving the heat resistance of the base film; the dense layer is characterized by: small ceramic particles directly contacting the base film, forming a complete, dense, and low-porosity underlayer on the base film surface. The combination of high-content dopamine and small-diameter ceramic particles significantly reduces the risk of ceramic coating peeling off the base film, improving battery safety and lifespan; the dense underlayer effectively prevents significant shrinkage of the base film at high temperatures, maintaining the integrity of the separator and preventing short circuits between the positive and negative electrodes.

[0017] The combination of a relatively low polydopamine content with large-particle ceramics, compared to the first coating, achieves affinity for the electrolyte and rapid lithium-ion transport, while simultaneously improving the mechanical strength and thermal stability of the separator. Specifically, the relatively low polydopamine content maximizes the exposure of hydrophilic sites on ceramic particles such as alumina, enabling them to quickly and fully adsorb and hold the electrolyte. Meanwhile, the hydroxyl and amino functional groups of the surface polydopamine enhance surface hydrophilicity, promoting electrolyte wetting and facilitating rapid lithium-ion transport. The high porosity of the coating formed by the accumulation of large ceramic particles helps maintain the coating's pore structure, which is beneficial for lithium-ion migration, increases lithium-ion conductivity, and improves the battery's high-rate charge-discharge performance. Furthermore, the catechol and amino functional groups in the polydopamine molecules undergo oxidative cross-linking during battery use and heat generation, forming a denser network structure and enhancing the surface's mechanical strength and thermal stability. According to any embodiment of the first aspect of the present invention, a ceramic-coated diaphragm based on polydopamine gradient modification is provided, wherein the ceramic particles in the first coating are one or more of alumina, boehmite, calcium carbonate, magnesium oxide, magnesium hydroxide, barium titanate, silicon dioxide, titanium dioxide, silicon carbide, silicon nitride, and zirconium oxide, and dopamine is coated on the particle surface by in-situ polymerization to form a strong adhesion interface; the ceramic particles in the second coating are one or more of alumina, boehmite, calcium carbonate, magnesium oxide, magnesium hydroxide, barium titanate, silicon dioxide, titanium dioxide, silicon carbide, silicon nitride, and zirconium oxide.

[0018] According to any embodiment of the first aspect of the present invention, the ceramic-coated diaphragm based on polydopamine gradient modification has a coating thickness of 1-3 μm, for example, 1 μm, 2 μm, or 3 μm; and a coating thickness of 1-5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0019] The thickness of the first coating and the second coating as described herein satisfies that the thickness of the first coating is less than or equal to that of the second coating. This is because the main function of the first coating is adhesion, and a thin and dense coating is sufficient to provide excellent adhesion. If the coating is too thick, the small particles and large amount of polydopamine will lead to excessively low porosity, small pores, low air permeability, and excessively high tortuosity, which will increase the resistance to ion transport. The porous structure formed by the large particles of the second coating requires a certain thickness to form continuous and interconnected channels in order to achieve uniform ion flow and construct efficient ion channels.

[0020] According to any embodiment of the first aspect of the present invention, the ceramic-coated diaphragm based on polydopamine gradient modification is wherein the base membrane is a porous base membrane of polyethylene (PE) or polypropylene (PP) and the thickness of the porous base membrane is 3-20 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, or 20 μm.

[0021] The gradient transition between the first and second coatings involves a gradient change in the ceramic particle size and polydopamine concentration between them. The polydopamine content in the bottom layer is 5wt%-10wt%, while that in the top layer is 1wt%-3wt%. On one hand, the high polydopamine content in the bottom layer enhances the adhesion between the coating and the base film, while the low polydopamine content in the top layer, combined with the high-temperature resistant ceramics, improves thermal stability and surface hydrophilicity. On the other hand, the gradient transition between the first and second coatings is achieved through the spontaneous diffusion of polydopamine from high to low concentrations, resulting in a more uniform polydopamine concentration at the junction. This leads to a tighter connection between the first and second coatings, improving the adhesion between the membrane and the coatings, as well as between the coatings themselves.

[0022] As described herein, gradient concentration coatings can achieve: (1) Functional integration: Gradient concentration can integrate multiple functions within a single coating, and can simultaneously possess the ultra-high adhesion and dense underlayer of the inner layer as well as the high heat resistance and high wettability of the outer layer; (2) Interface bonding strength: Gradient transition can enhance the bonding force between the coating and the substrate and reduce the risk of peeling; (3) Thermal stress matching: The use of polydopamine modified ceramic particles can effectively improve the interface between the base film and the ceramic particles, making the base film and ceramic particles more firmly bonded. The rigid and heat-resistant ceramic layer network fixes the molecular chain of the base film, greatly restricting its free movement and shrinkage. At the same time, the gradient design can alleviate the thermal stress caused by the difference in thermal expansion coefficient between the coating and the substrate material, effectively preventing the base film from shrinking significantly at high temperatures, maintaining the integrity of the diaphragm, and improving the stability of the coating in temperature change environments.

[0023] A ceramic-coated separator based on a polydopamine gradient modification according to any embodiment of the first aspect of the present invention, the ceramic-coated separator comprising: Base film: thickness 3-20 μm, porosity 35%-60%; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Second coating: Located outside the first coating, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; ... The nth coating: located outside the (n-1)th coating, in contact with the electrolyte, and comprises polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; n≥2; The ceramic-coated diaphragm satisfies: Heat shrinkage rate at 180℃ for 1 hour <5%, for example, it can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%; peel strength ≥78N / m (for example, it can be 80N / m, 84N / m, 88N / m, 90N / m, 94N / m, 98N / m, 100N / m, 104N / m, 108N / m, 110N / m, 114N / m, 118N / m, 120N / m, 124N / m, 128N / m, 130N / m, 134N / m). m, 138N / m, 140N / m, 144N / m, 148N / m, 150N / m, needle penetration strength >500gf, electrolyte contact angle <28°, for example, can be 10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, conductivity >0.56mS / cm, for example, can be 0.6mS / cm, 0.8mS / cm, 1mS / cm, 1.2mS / cm, 1.4mS / cm, 1.6mS / cm.

[0024] According to any embodiment of the first aspect of the present invention, a polydopamine gradient-modified ceramic-coated separator comprises: Base film: thickness 3-20 μm, porosity 35%-60%; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, with a polydopamine content of 5wt%-10wt%; Second coating: Located outside the first coating and in contact with the electrolyte, it consists of polydopamine-modified ceramic particles with a polydopamine content of 1wt%-3wt%. The ceramic-coated diaphragm satisfies: Heat shrinkage rate at 180℃ <5%, peel strength ≥78N / m, needle penetration strength >500gf, electrolyte contact angle <28°, conductivity >0.56mS / cm.

[0025] Preferably, the heat shrinkage rate at 180℃ for 1 hour is <5%, the peel strength is ≥78N / m, the needle penetration strength is >510gf, the electrolyte contact angle is <28°, and the conductivity is >0.7mS / cm.

[0026] [Testing Method] Heat shrinkage: Tested according to GB / T36363-2018. Cut a 10cm × 10cm sample, mark the transverse (TD) and longitudinal (MD) widths on the sample, and measure the transverse and longitudinal widths using a fully automatic image measuring projector (Kunshan Gaopin Precision Instrument Co., Ltd., GP-300C). Clamp the sample between two sealed A4 sheets of paper, place the sample in a 150℃ oven for 1 hour, and after the sample returns to room temperature, measure the transverse and longitudinal widths again using the fully automatic image measuring projector. Take three measurements and average the results. MD heat shrinkage rate (%) = (MD length before heating - MD length after heating) ÷ MD length before heating × 100; TD heat shrinkage rate (%) = (TD length before heating - TD length after heating) ÷ TD length before heating × 100; Peel strength: The test was conducted according to the requirements of GB / T 2792-2014. A 2.5cm×20cm sample was cut. The peel strength test plate was confirmed to be 100mm long. The sample was manually peeled 10mm to a fixed position. The peel strength double-sided adhesive tape (3M adhesive model 4910) was attached to the test plate and the surface sticker was removed, leaving about 20mm of sticker (at the tape position mark). The sample peel length was 70mm. The sample was rolled back and forth three times with a pressure roller (1.7kg pressure roller). The prepared sample was manually peeled 10mm to a fixed position and fixed between the upper and lower clamps of the tensile testing machine (High-speed Rail Testing Instruments (Dongguan) Co., Ltd., AI-3000-SU) (the distance between the clamps was (100±5)mm). The sample was ensured to be flat and wrinkle-free, and vertical and not skewed. The tensile speed was 50mm / min. The peel strength value was measured based on the width and thickness of the sample by clicking the program.

[0027] Puncture strength: The test was conducted according to the method specified in GB / T 36363-2018. A 50*100 mm diaphragm was cut along the TD direction and fixed on the sample holder of the puncture testing machine (model: KES-GNDG5, KNC Technology Co., Ltd.). A steel needle with a diameter of 1.0 mm was used to puncture the diaphragm at a speed of 0.1 cm / sec. The maximum load of the steel needle penetrating the diaphragm was read. The test was performed more than 5 times and the arithmetic mean was taken.

[0028] Electrolyte Contact Angle: Cut a 2.5cm*20cm sample and fix it flat on the sample stage, ensuring the test surface is facing upwards and horizontal. Double-sided tape or sample clips can be used for fixation to prevent wrinkling of the diaphragm. Turn on the contact angle measuring instrument (Dongguan Shengding Precision Instruments Co., Ltd., SDC-200SE model), including the main unit, light source, and computer software. Adjust the sample stage to a horizontal position, and adjust the camera focus and light source intensity to ensure a clear field of view and good contrast, capable of clearly capturing the droplet outline. Clean the syringe and draw up the test liquid (2uL electrolyte, electrolyte composition: LiPF6 1M, EC: EMC=3 / 7, VC=2%). After the droplet contacts the sample surface, immediately (usually within 1-2 seconds) capture an image using the high-speed camera. On the acquired clear image, use the analysis software to manually or automatically fit the droplet outline. The software will automatically calculate the left and right contact angles and the average contact angle; record the average value.

[0029] Electrical conductivity: The test was conducted according to the method specified in NB / T10827-2021. A φ19mm sample (φ19mm represents the diameter of a circular sample) was cut and assembled with the positive and negative electrode shells of a CR2016 button cell to form a button cell. The electrolyte was LiPF6 1mol / L, EC:EMC = 3:7, and VC = 2.0wt%. The button cell was assembled in the following order: negative electrode shell, separator, gasket (φ15.8*0.5mm, i.e., the diameter of the gasket is 15.8mm and the thickness is 0.5mm), corrugated spring, and positive electrode shell. Four drops of electrolyte were added using a 1mL dropper to fully wet the separator. The battery was sealed with a sealing machine, and the electrolyte on the surface of the button cell was wiped clean with alcohol. The battery was then left to stand for 3 hours. The electrochemical workstation (Metrohm, PGSTAT204) was turned on, and the "Impedance Test" was selected for testing. The lower frequency limit was 10000Hz, the upper frequency limit was 100000Hz, and the current was 100mA. The resistance of batteries composed of one, two, three, and four separator layers was tested, with three sets of parallel data for each sample. A curve was plotted with the number of separator layers on the x-axis and the corresponding battery resistance on the y-axis. The slope of the curve with a goodness of fit ≥0.99 is the separator resistance R (Ω). The separator ionic conductivity is calculated as d / (R*A) (S / cm), where d is the separator thickness in cm and A is the effective area of ​​the gasket in cm². 2 .

[0030] The second aspect of the present invention provides a method for preparing the above-mentioned ceramic-coated diaphragm based on polydopamine gradient modification, which includes raw materials: slurry A, which is coated on a base film to form a first coating; and slurry B, which is coated on the first coating to form a second coating.

[0031] The slurry A comprises polydopamine-modified ceramic particles, a dispersant, a thickener, a binder, and water. The polydopamine-modified ceramic particles, dispersant, thickener, and binder are mixed in a mass ratio of (50~90):(0.01~1):(0.1~3):(3~8). The solid content of slurry A is 10%-40%, and the particle size of the polydopamine-modified ceramic particles in slurry A is 50-300 nm.

[0032] According to the preparation method of any embodiment of the second aspect of the present invention, the dispersant is one or more selected from polyvinylpyrrolidone, polyacrylamide, polyvinyl alcohol, sodium polyacrylate, and ammonium polyacrylate; The thickener is one or more of sodium alginate, cellulose polymers, natural gums, and starch. The adhesive is one or more of the following: styrene-butadiene rubber, acrylate, sodium polyacrylate, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide, and polytetrafluoroethylene.

[0033] According to any embodiment of the second aspect of the present invention, ceramic particles are dispersed in Tris-HCl buffer solution with pH=7-10, dopamine hydrochloride is added, stirred and polymerized, and centrifuged and dried to obtain polydopamine modified ceramic particles. Preferably, the method for preparing the polydopamine-modified ceramic particles in the first coating includes the following steps: Ceramic particles were dispersed in Tris-HCl buffer solution with pH 7-10, and dopamine hydrochloride (0.5-2 mg / mL) was added. The mixture was stirred and polymerized for 6-12 h, and then centrifuged and dried to obtain polydopamine-modified ceramic particles.

[0034] According to any embodiment of the second aspect of the present invention, the preparation steps of the slurry A include: a. Mix polydopamine-modified ceramic particles, dispersant and water, stir and disperse evenly to obtain ceramic dispersion; b. Dissolve the thickener in deionized water to obtain a thickening solution; mix the ceramic dispersion with the thickening solution to obtain a thickened slurry; c. The thickened slurry is ground to obtain a semi-finished slurry; d. After the semi-finished slurry cools to room temperature, add the binder and mix evenly to obtain slurry A containing polydopamine-modified ceramic particles; According to any embodiment of the second aspect of the present invention, the slurry B comprises polydopamine-modified ceramic particles, a dispersant, a thickener, a binder, and water, wherein the polydopamine-modified ceramic particles, dispersant, thickener, and binder are mixed in a mass ratio of (50~90):(0.01~1):(0.1~3):(3~8); the solid content of slurry B is 10%-40%; and the particle size of the polydopamine-modified ceramic particles in slurry B is 0.5-5 μm.

[0035] According to the preparation method of any embodiment of the second aspect of the present invention, the adhesive is one or more selected from styrene-butadiene rubber, acrylate, sodium polyacrylate, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide, and polytetrafluoroethylene.

[0036] The dispersant is one or more of polyvinylpyrrolidone, polyacrylamide, polyvinyl alcohol, sodium polyacrylate, and ammonium polyacrylate; The thickener is one or more of sodium alginate, cellulose polymers, natural gums, and starch.

[0037] According to any embodiment of the second aspect of the present invention, the method for preparing the polydopamine-modified ceramic particles in the second coating includes the steps of: Ceramic particles were dispersed in Tris-HCl buffer solution with pH 7-10, and dopamine hydrochloride (0.2-0.5 g / mL) was added. The mixture was stirred and polymerized for 2-4 hours, and then centrifuged and dried to obtain polydopamine-modified ceramic particles.

[0038] According to any embodiment of the second aspect of the present invention, in the preparation method of the polydopamine-modified ceramic particles in the first coating, the mixing time of dopamine hydrochloride and ceramic particles is 6-12 hours, which is higher than the mixing time of dopamine hydrochloride and ceramic particles in the preparation method of the polydopamine-modified ceramic particles in the second coating, which is 2-4 hours. The content of polydopamine in the first coating and the second coating is controlled by controlling the polymerization time. Since a higher content of polydopamine is required in the first coating, the required polymerization time is also longer.

[0039] According to any embodiment of the second aspect of the present invention, the preparation steps of the slurry B include: a. Mix polydopamine-modified ceramic particles, dispersant and water, stir and disperse evenly to obtain ceramic dispersion; b. Dissolve the thickener in deionized water to obtain a thickening solution; mix the ceramic dispersion with the thickening solution to obtain a thickened slurry; c. The thickened slurry is ground to obtain a semi-finished slurry; d. After the semi-finished slurry cools to room temperature, a polymer binder is added and mixed evenly to obtain slurry B containing polydopamine-modified ceramic particles.

[0040] According to any embodiment of the second aspect of the present invention, the method for preparing the ceramic-coated diaphragm includes the step of: coating slurry A onto a base film by roller coating to form a first coating layer; The slurry B is coated onto the first coating layer by roller coating to form the second coating layer, thus obtaining a ceramic composite diaphragm.

[0041] According to the preparation method of any embodiment of the second aspect of the present invention, after the first coating is applied, it is dried at 50-80°C and then a second coating is applied, and the second coating is dried at 50-80°C to obtain a ceramic composite diaphragm.

[0042] According to the preparation method of any embodiment of the second aspect of the present invention, the coating thickness of the first coating is 1-3 μm, the first coating is dried at 50-80°C after coating, the coating thickness of the second coating is 1-5 μm, and the gradient-coated ceramic composite diaphragm is obtained after drying at 50-80°C.

[0043] A third aspect of the present invention provides a lithium battery comprising a separator; The diaphragm is the ceramic-coated diaphragm described in any embodiment of the first aspect of the present invention; The diaphragm is a ceramic-coated diaphragm obtained by the preparation method described in any embodiment of the second aspect of the present invention.

[0044] The modified ceramic particles designed in this invention contain polar functional groups, amine groups and phenolic hydroxyl groups, on which the polydopamine contains polar functional groups. The polar oxygen on the alumina ceramic particles forms hydrogen bonds with the hydrogen on the amino group of the polydopamine, which stabilizes the ceramic slurry and improves the uniformity of the coating. The biomimetic adhesion of polydopamine enhances the bonding force with the base film. The presence of catechol and amine functional groups in the polydopamine molecules in the surface coating can improve the wettability of the electrolyte. As the internal temperature of the battery rises during use, the catechol and amine groups in the polydopamine molecules in the separator undergo oxidative cross-linking at high temperatures (120-180℃), forming a denser network structure, which further improves the mechanical strength and thermal stability of the separator.

[0045] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses a gradient structure design to coat at least two coatings on the surface of the base film, wherein the polydopamine content decreases sequentially from the first coating to the nth coating, that is, it decreases outward along the base film. The bottom coating, which is in direct contact with the base film, has a high polydopamine content to enhance the bonding force between the coating and the base film, while the outer coating, which is in contact with the electrolyte, has a low polydopamine content to combine with high-temperature resistant ceramics to improve the thermal stability of the diaphragm. The gradient transition effectively enhances the bonding force between the coating and the substrate, reduces the risk of peeling, and alleviates the thermal stress caused by the difference in thermal expansion coefficients between the coating and the substrate materials, thereby improving the stability of the coating in temperature-changing environments. (2) The particle size of the ceramic particles in the coating material of the separator of this application satisfies the following: the size increases sequentially from the first coating to the nth coating, that is, it increases outward along the base film. The first coating forms a tight and firm bond with the base film through small particles that are in direct contact with the base film, effectively blocking the penetration of lithium dendrites. The nth coating uses large particles to construct a porous, high specific surface area rough structure, which can homogenize the lithium ion flow and inhibit the concentrated growth of dendrites from the source. The gradient structure of particle pore size constructs a gradient distribution from small pores to large pores from the bottom layer to the surface layer. The large pores on the surface layer facilitate the rapid absorption and transport of electrolyte, while the small pores on the bottom layer can lock the electrolyte through capillary action, which is beneficial to the electrolyte retention capacity during long-term cycling and alleviates the capacity decay caused by electrolyte induction. (3) In this application, polydopamine-modified ceramic particles are used as the material for the membrane coating. The hydroxyl and amino functional groups of polydopamine improve the surface hydrophilicity (contact angle ≤30°), while the porous structure of ceramic promotes electrolyte wetting. The catechol and amino functional groups in the polydopamine molecules in the surface coating undergo oxidative cross-linking at high temperature (120-180℃) to form a denser network structure, which significantly improves the mechanical strength and thermal stability of the surface layer. Attached Figure Description The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless specifically indicated, these drawings are intended only to conceptually illustrate the structural construction described herein and are not necessarily drawn to scale.

[0046] Figure 1 This is a schematic diagram of the diaphragm structure of this application, from top to bottom: base membrane, first coating, second coating, and nth coating; Detailed Implementation The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0047] Example 1 (1) The diaphragm provided in this embodiment includes: Base membrane: 9μm PE base membrane, porosity 38%; First coating: in contact with the base film, comprising 5wt% polydopamine-modified Al2O3 particles (average particle size of 300nm), i.e., the polydopamine loading is 5wt%, and the coating thickness of the first coating is 1μm; The second coating is located outside the first coating and is in contact with the electrolyte. It consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size 1 μm), i.e., the polydopamine loading is 3 wt%, and the coating thickness of the second coating is 2 μm. (2) The raw materials and proportions for preparing the diaphragm provided in this embodiment are as follows: Slurry A: By dry weight ratio, it comprises: 5wt% polydopamine-modified Al2O3 particles (average particle size 300nm): sodium polyacrylate (dispersant): sodium carboxymethyl cellulose (thickener): acrylate (binder) = 90:0.4:2.0:7.6, and the solid content of slurry A is 30%. The preparation method of 5wt% polydopamine-modified Al2O3 particles (average particle size 300nm) includes the following steps: The ceramic particles were dispersed in Tris-HCl buffer at pH 8.5, and dopamine hydrochloride (2 mg / mL) was added. The mixture was stirred and polymerized for 10 h, and then centrifuged and dried to obtain 5 wt% polydopamine-modified Al2O3 particles.

[0048] The preparation steps of slurry A include: a. Mix polydopamine-modified Al2O3 particles (average particle size of 300nm), dispersant and water, and disperse them by stirring at 1200rpm for 30min in a dispersion pan to obtain a ceramic dispersion. b. Dissolve the thickener in deionized water to obtain a thickening solution, and mix the ceramic dispersion with the thickening solution to obtain a thickened slurry; c. The thickening slurry is conveyed to the grinding mill by a feed pump and ground to obtain a semi-finished slurry; the feed pump speed is 800 rpm, the grinding mill speed is 500 rpm, the grinding media is preferably zirconium beads with a diameter of 0.2 mm, the ratio of the speed of the feed pump to that of the grinding mill is 1.2, and the grinding is carried out twice. d. After the semi-finished slurry is brought back to room temperature, a binder is added and the mixture is stirred evenly to obtain slurry A containing polydopamine-modified Al2O3 particles (average particle size of 300 nm).

[0049] Slurry B: By dry weight ratio, it comprises: 3wt% polydopamine-modified Al2O3 particles (average particle size 1μm): sodium polyacrylate (dispersant): sodium carboxymethyl cellulose (thickener): acrylate (binder) = 90:0.8:2.0:7.2, and the solid content of slurry B is 30%. The preparation method of 3wt% polydopamine-modified Al2O3 particles (average particle size of 1μm) includes the following steps: Al2O3 particles with an average particle size of 1 μm were dispersed in Tris-HCl buffer solution at pH 8.5, and dopamine hydrochloride (0.5 g / mL) was added. The mixture was stirred and polymerized for 4 h, and then centrifuged and dried to obtain polydopamine-modified Al2O3 ceramic particles.

[0050] The preparation steps of the slurry B include: a. Mix polydopamine-modified Al2O3 particles (average particle size 1μm), dispersant and water, and disperse them by stirring at 1000 rpm for 30 min using a dispersion disc to obtain a ceramic dispersion. b. Dissolve the thickener in deionized water to obtain a thickening solution, and mix the ceramic dispersion with the thickening solution to obtain a thickened slurry; c. The thickening slurry is conveyed to the grinding mill by a feed pump and ground to obtain a semi-finished slurry; the feed pump speed is 800 rpm, the grinding mill speed is 5000 rpm, the grinding media is preferably zirconium beads with a diameter of 0.5 mm, the ratio of the speed of the feed pump to that of the grinding mill is 1.2, and the grinding is done once. d. After the semi-finished slurry has returned to room temperature, a binder is added and the mixture is stirred evenly to obtain slurry B containing polydopamine-modified Al2O3 particles (average particle size 1μm).

[0051] (3) Based on the raw materials and proportions provided in (2), this embodiment also provides a coating process for the diaphragm, the specific steps of which include: Slurry A is coated onto the base film using a roller coating machine to form the first coating. The thickness of the first coating is 1 μm. After the first coating is coated, it is dried at 60°C. Slurry B is coated onto the first coating layer by roller coating to form a second coating layer with a thickness of 2 μm. After drying at 65°C, a gradient-coated ceramic composite diaphragm is obtained.

[0052] Based on the coating process described in (3) above, the diaphragm finally obtained in this embodiment is shown in Table 1, which satisfies: Peel strength is 90 N / cm, thermal shrinkage in the MD direction at 180℃ is 4.5%, needle penetration strength is 526 gf, electrolyte contact angle is 15°, and ionic conductivity is 1.4 mS·cm. -1 .

[0053] Example 2 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the polydopamine content in the first coating is 7 wt%; specifically, it includes: First coating: consists of 7 wt% polydopamine-modified Al2O3 particles (average particle size 300 nm), i.e., the polydopamine loading is 7 wt%. The second coating consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size of 1 μm), meaning the polydopamine loading is 3 wt%. The diaphragm finally obtained in this embodiment is shown in Table 1 and satisfies the following: Peel strength is 130 N / cm, thermal shrinkage in the MD direction at 180℃ is 3.8%, needle penetration strength is 550 gf, contact angle is 10.6°, and ionic conductivity is 0.97 mS·cm. -1 ; The increased polydopamine content in the first coating increases the number of polar groups on the surface of the first coating, strengthens the adhesion between the coating and the base film, reduces the thermal deformation rate of the diaphragm, improves thermal stability, and enhances surface hydrophilicity. However, it also lengthens the ion transport path and reduces the electrical conductivity.

[0054] Example 3 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the polydopamine content in the second coating is 1 wt%; specifically, it includes: First coating: consists of 5 wt% polydopamine-modified Al2O3 particles (average particle size 300 nm), i.e., the polydopamine loading is 5 wt%. The second coating consists of 1 wt% polydopamine-modified Al2O3 particles (average particle size of 1 μm), meaning the polydopamine loading is 1 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0055] The polydopamine content in the second coating is reduced, and the total dopamine content in the first and second coatings is less than 8 wt%. The number of polar groups on the membrane surface is reduced, the hydrophilicity of the membrane surface is slightly reduced, and the conductivity is reduced.

[0056] Example 4 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the polydopamine content in the first coating is 10 wt%; specifically, it includes: First coating: consists of 10 wt% polydopamine-modified Al2O3 particles (average particle size 300 nm), i.e., the polydopamine loading is 10 wt%. The second coating consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size of 1 μm), meaning the polydopamine loading is 3 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0057] The increased polydopamine content in the first coating enhances the adhesion between the coating and the base film, reduces the thermal deformation rate of the diaphragm, decreases its surface hydrophilicity, but lengthens the ion transport path and reduces its conductivity.

[0058] Example 5 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the particle size of the Al2O3 particles in the second coating is 0.5 μm; specifically, it includes: First coating: consists of 5 wt% polydopamine-modified Al2O3 particles (average particle size 300 nm), i.e., the polydopamine loading is 5 wt%. The second coating consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size of 0.5 μm), meaning the polydopamine loading is 3 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0059] The ceramic particle size of the first and second coatings is reduced, the heat resistance of the coatings is improved, the bonding force between the coatings and the base film is increased, the thermal deformation rate of the diaphragm is reduced, the thermal stability is improved, the dopamine is modified more uniformly on the ceramic surface, the hydrophilicity of the diaphragm surface is improved, and the electrical conductivity is improved.

[0060] Example 6 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the particle size of the Al2O3 particles in the first coating is 100 nm; specifically, it includes: First coating: consists of 5 wt% polydopamine-modified Al2O3 particles (average particle size 100 nm), i.e., the polydopamine loading is 5 wt%. The second coating consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size of 1 μm), meaning the polydopamine loading is 3 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0061] The ceramic particles in the first coating have a smaller particle size, improved heat resistance, increased adhesion to the base film, reduced thermal deformation rate of the diaphragm, and consistent surface hydrophilicity and electrical conductivity.

[0062] Example 7 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the particle size of Al2O3 particles in the first coating is 200 nm, and the particle size of Al2O3 particles in the second coating is 0.5 μm; specifically, it includes: First coating: consists of 5 wt% polydopamine-modified Al2O3 particles (average particle size of 200 nm), i.e., the polydopamine loading is 5 wt%. The second coating consists of 3 wt% polydopamine-modified Al2O3 particles (average particle size of 0.5 μm), meaning the polydopamine loading is 3 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0063] The ceramic particle size of the first and second coatings is reduced, the bonding force between the coating and the base film is improved, the thermal deformation rate of the diaphragm is reduced, the thermal stability is reduced, the surface hydrophilicity is improved, and the electrical conductivity is reduced.

[0064] Example 8 The difference between the diaphragm provided in this embodiment and that in Embodiment 1 is that the ceramic particles in the first coating are SiO2 particles with a particle size of 300 nm, and the ceramic particles in the second coating are Si3N4 particles with a particle size of 1 μm; specifically, it includes: First coating: consists of 5 wt% polydopamine-modified SiO2 particles (average particle size 300 nm), i.e., the polydopamine loading is 5 wt%. The second coating consists of 3 wt% polydopamine-modified Si3N4 particles (average particle size of 1 μm), meaning the polydopamine loading is 3 wt%. The diaphragm obtained in this embodiment is shown in Table 1.

[0065] Replacing Al2O3 ceramic particles with SiO2 and Si3N4 particles improves the adhesion between the coating and the base film, reduces the thermal deformation rate of the diaphragm, improves thermal stability, and increases electrical conductivity. However, due to the insufficient wettability of SiO2 and Si3N4 compared to Al2O3, the hydrophilicity of the diaphragm surface is reduced.

[0066] Comparative Example 1 (1) The difference between the diaphragm provided in this comparative example and that in Example 1 is that it uses unmodified Al2O3 (average particle size of 1000nm) as the coating material and the coating thickness is 3μm. (2) The raw materials and proportions for preparing the diaphragm provided in this comparative example are as follows: Slurry: By dry weight ratio, it includes: Al2O3 particles (average particle size 900nm), sodium polyacrylate (dispersant), sodium carboxymethyl cellulose (thickener), acrylate (binder) = 90:0.4:2.0:7.6, and the slurry solid content is 30%; The preparation steps of slurry A include: a. Mix Al2O3 particles (average particle size of 1000 nm), dispersant and water, and disperse them by stirring at 1000 rpm for 30 min using a dispersion disc to obtain a ceramic dispersion. b. Dissolve the thickener in deionized water to obtain a thickening solution; mix the ceramic dispersion with the thickening solution solvent to obtain a thickened slurry; c. The thickened slurry is conveyed to the grinding mill by a feed pump, and a semi-finished slurry is obtained by grinding. d. After the semi-finished slurry has returned to room temperature, a polymer binder is added and the mixture is stirred evenly to obtain a ceramic coating slurry.

[0067] (3) Based on the raw materials and proportions provided in (2), this comparative example also provides a coating process for the diaphragm, the specific steps of which include: The ceramic coating slurry is coated onto the base film using a roller coating machine to a thickness of 3 μm, and then dried at 65°C to obtain a ceramic composite diaphragm.

[0068] Based on the coating process described in (3) above, the diaphragm finally obtained in this comparative example is shown in Table 1, which satisfies: Peel strength is 78 N / cm, heat shrinkage at 150℃ is 40%, needle penetration strength is 503 gf, electrolyte contact angle is 33°, and ionic conductivity is 0.56 mS·cm. -1 .

[0069] This comparative example uses unmodified polydopamine ceramic particles as the coating material. The resulting coating has poor adhesion to the base film, poor thermal stability, poor hydrophilicity, low electrical conductivity, and the base film is easily deformed by heat.

[0070] Comparative Example 2 The diaphragm provided in this comparative example differs from that in Example 1 in that the polydopamine content in the first coating is 1 wt%, and the polydopamine content in the second coating is 10 wt%; specifically, it includes: First coating: consists of 1 wt% polydopamine-modified Al2O3 particles (average particle size 300 nm), i.e., the polydopamine loading is 1 wt%. The second coating consists of 10 wt% polydopamine-modified Al2O3 particles (average particle size of 1 μm), meaning the polydopamine loading is 10 wt%. The diaphragms obtained in this comparative example are shown in Table 1.

[0071] The first coating contains too much polydopamine, while the second coating contains too little. The polydopamine content increases progressively from the base film outwards. As a result, the coating has poor adhesion to the base film, poor thermal stability, poor hydrophilicity, low electrical conductivity, and the base film is easily deformed by heat.

[0072] Table 1. Diaphragm performance parameters of the embodiments and comparative examples of this application.

[0073] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0074] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

[0075] Any embodiment of any aspect of the present invention can be combined with other embodiments without contradiction. Furthermore, in any embodiment of any aspect of the present invention, any technical feature can be applied to the same technical feature in other embodiments without contradiction.

[0076] Without causing contradictions, any technical feature of any aspect or embodiment of the present invention is equally applicable to any other embodiment or embodiment of any other aspect. Of course, when applicable to each other, appropriate modifications may be made to the corresponding features as necessary. The various aspects and features of the present invention are further described below.

Claims

1. A ceramic-coated diaphragm based on polydopamine gradient modification, characterized in that, include: Base film; And n layers of coating: coated on the surface of the base film, the coating comprising polydopamine-modified ceramic particles, the polydopamine being coated on the surface of the ceramic particles, n≥2; The polydopamine content satisfies the following condition: decreasing sequentially from the first coating to the nth coating; The particle size of the ceramic particles satisfies the following condition: it increases sequentially from the first coating to the nth coating.

2. The ceramic-coated diaphragm based on polydopamine gradient modification according to claim 1, characterized in that, include: Base film; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Second coating: Located outside the first coating and in contact with the electrolyte, comprising polydopamine-modified ceramic particles, wherein the polydopamine is coated on the surface of the ceramic particles; Wherein, the polydopamine content satisfies the following condition: first coating > second coating; The particle size of the ceramic particles satisfies the condition that the first coating layer is smaller than the second coating layer.

3. The ceramic-coated diaphragm based on polydopamine gradient modification according to claim 2, characterized in that, The first coating contains 5wt%-10wt% polydopamine; and / or, The polydopamine content in the second coating is 1wt%-3wt%.

4. The ceramic-coated diaphragm based on polydopamine gradient modification according to claim 2, characterized in that, The ceramic particles in the first coating have a particle size of 50-300 nm; and / or, The ceramic particles in the second coating have a particle size of 0.5-5 μm.

5. The ceramic-coated diaphragm based on polydopamine gradient modification according to claim 1, characterized in that, The base membrane is a porous polyethylene or polypropylene base membrane; and / or... The ceramic particles in the first coating are one or more of the following: alumina, boehmite, calcium carbonate, magnesium oxide, magnesium hydroxide, barium titanate, silicon dioxide, titanium dioxide, silicon carbide, silicon nitride, and zirconium oxide; and / or, The ceramic particles in the second coating are one or more of the following: alumina, boehmite, calcium carbonate, magnesium oxide, magnesium hydroxide, barium titanate, silicon dioxide, titanium dioxide, silicon carbide, silicon nitride, and zirconium oxide; and / or, The coating thickness of the first coating is 1-3 μm, and the coating thickness of the second coating is 1-5 μm.

6. The ceramic-coated diaphragm based on polydopamine gradient modification according to claim 1, characterized in that, The polydopamine-modified ceramic particles are obtained by dispersing ceramic particles in Tris-HCl buffer solution with pH=7-10, adding dopamine hydrochloride, stirring and polymerizing, and then centrifuging and drying.

7. The polydopamine gradient-modified ceramic-coated diaphragm according to claims 1-6, characterized in that, The ceramic-coated diaphragm includes: Base film: thickness 3-20 μm, porosity 35%-60%; First coating: in contact with the base film, comprising polydopamine-modified ceramic particles, with a polydopamine content of 5wt%-10wt%; Second coating: Located outside the first coating and in contact with the electrolyte, it consists of polydopamine-modified ceramic particles with a polydopamine content of 1wt%-3wt%. The ceramic-coated diaphragm satisfies: Heat shrinkage rate at 180℃ <5%, peel strength ≥78N / m, needle penetration strength >500gf, electrolyte contact angle <28°, conductivity >0.56mS / cm.

8. The method for preparing the polydopamine gradient-modified ceramic-coated diaphragm according to any one of claims 1-7, characterized in that, Including raw materials: Slurry A: comprises polydopamine-modified ceramic particles, dispersant, thickener, and binder in a mass ratio of (50~90):(0.01~1):(0.1~3):(3~8), wherein the polydopamine-modified ceramic particles in slurry A have a particle size of 50-300 nm, a polydopamine content of 5wt%-10wt%, and a solid content of 10%~40%. Slurry B: comprises polydopamine-modified ceramic particles, dispersant, thickener, and binder in a mass ratio of (50~90):(0.01~1):(0.1~3):(3~8), wherein the polydopamine-modified ceramic particles in slurry B have a particle size of 0.5-5μm, a polydopamine content of 1wt%-3wt%, and a solid content of 10%~40%. The steps include: applying slurry A onto the base film by roller coating to form a first coating layer; The slurry B is coated onto the first coating layer by roller coating to form the second coating layer, thus obtaining a ceramic composite diaphragm.

9. The method for preparing the polydopamine gradient-modified ceramic-coated diaphragm according to claim 8, characterized in that, The dispersant in slurry A is one or more of polyvinylpyrrolidone, polyacrylamide, polyvinyl alcohol, sodium polyacrylate, and ammonium polyacrylate; and / or, The dispersant in slurry B is one or more of polyvinylpyrrolidone, polyacrylamide, polyvinyl alcohol, sodium polyacrylate, and ammonium polyacrylate; and / or, The thickener in slurry A is one or more of sodium alginate, cellulose polymers, natural gums, and starch; and / or, The thickener in slurry B is one or more of sodium alginate, cellulose polymers, natural gums, and starch; and / or, The binder in slurry A is one or more of the following: styrene-butadiene rubber, acrylate, sodium polyacrylate, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide, and polytetrafluoroethylene; and / or, The binder in slurry B is one or more of the following: styrene-butadiene rubber, acrylate, sodium polyacrylate, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide, and polytetrafluoroethylene.

10. A lithium battery, said lithium battery comprising a separator, characterized in that, The diaphragm is the ceramic composite diaphragm according to any one of claims 1 to 7; The diaphragm is a ceramic composite diaphragm prepared by any one of the methods described in claims 8 to 9.

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