Composite diaphragm for high-performance lithium ion battery and preparation method of composite diaphragm

Abstract

The invention discloses a composite diaphragm for a high-performance lithium ion battery and a preparation method of the composite diaphragm, and belongs to the technical field of battery diaphragms. The composite diaphragm for the high-performance lithium ion battery comprises a diaphragm base membrane and ceramic slurry coated on the surface of the diaphragm base membrane, the ceramic slurry is prepared from the following raw material components: aluminum oxide composite aerogel, deionized water, a dispersing agent, a defoaming agent, a surfactant, a binder, a plasticizer and a flame retardant, and the composite diaphragm for the high-performance lithium ion battery is prepared by the following steps: aging aluminum oxide sol in a tetraethoxysilane alcoholic solution by adopting a sol-gel method; then, triethoxy-2-pyridine silane is adopted for surface modification, and acetylation is carried out, so that the catalyst is obtained; lithium polyacrylate is adopted as the dispersing agent, n-caprylic acid is adopted as the defoaming agent, fatty alcohol-polyoxyethylene ether is adopted as the surfactant, polyvinyl alcohol is adopted as the binder, polyethylene glycol is adopted as the plasticizer, and hexa-p-formylphenoxy cyclotriphosphazene is adopted as the flame retardant.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a high-performance composite separator for lithium-ion batteries and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and portable electronic devices, higher requirements are being placed on the energy density, cycle life, and safety performance of lithium-ion batteries. As a key component of lithium-ion batteries, the separator plays a crucial role in isolating the positive and negative electrodes and preventing short circuits within the battery. It also needs to possess good electrolyte wettability, excellent ion transport capabilities, and structural stability under high temperatures or abnormal operating conditions. While traditional polyolefin separators offer advantages such as low cost, good mechanical strength, and controllable pore structure, their inherent drawbacks are becoming increasingly apparent: Firstly, polyolefin materials have a low melting point, making them prone to thermal shrinkage or even melting and closure at high temperatures, leading to internal short circuits and thermal runaway. Secondly, their strong hydrophobicity results in poor wettability to polar electrolytes, limiting the rapid migration of lithium ions and affecting battery rate performance. Furthermore, polyolefins themselves lack flame-retardant properties, making it difficult to effectively suppress fire risks under conditions of battery abuse.

[0003] To overcome the aforementioned problems, researchers have recently adopted a strategy of coating the base membrane surface with inorganic ceramic particles to form a composite membrane. The ceramic layer not only significantly improves the thermal dimensional stability of the membrane and suppresses the shrinkage and deformation of the base membrane at high temperatures, but also enhances its affinity for the electrolyte through its abundant surface hydroxyl groups, thereby improving ionic conductivity. Simultaneously, some functional ceramic materials also possess intrinsic flame-retardant or endothermic decomposition properties, which can absorb heat, release non-flammable gases, or form a dense protective layer in the early stages of thermal runaway, effectively delaying or preventing flame spread.

[0004] However, existing ceramic-coated membranes still face many challenges: for example, severe particle agglomeration in ceramic slurry can reduce coating uniformity and affect the continuity of ion transport channels; in addition, relying solely on physical coating makes it difficult to balance high porosity, high thermal stability and high ionic conductivity.

[0005] Therefore, there is an urgent need to develop a high-performance composite separator for lithium-ion batteries and its efficient and controllable preparation method to comprehensively improve the safety and electrochemical performance of lithium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance composite separator for lithium-ion batteries and its preparation method, so as to solve the technical problems mentioned in the background art.

[0007] The technical solution to achieve the objective of this invention is: In a first aspect, the present invention provides a high-performance composite separator for lithium-ion batteries, comprising a base membrane and a ceramic layer on the surface of the base membrane; the ceramic layer is obtained by coating a ceramic slurry on the surface of the base membrane; the raw material components of the ceramic slurry include alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant.

[0008] Furthermore, the base membrane is a polyolefin membrane with a thickness of 7 μm.

[0009] Furthermore, the mass ratio of the alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant is (80~100): (100~120): (2~4): (1.2~1.8): (0.2~2): (30~50): (8~12): (5~15).

[0010] Furthermore, the alumina composite aerogel is obtained by aging alumina sol in an ethyl silicate alcohol solution using the sol-gel method, followed by surface modification with triethoxy-2-pyridinesilane and acetylation.

[0011] Furthermore, the dispersant includes lithium polyacrylate; the defoamer includes octanoic acid; the surfactant includes fatty alcohol polyoxyethylene ether; the binder includes polyvinyl alcohol; and the plasticizer includes polyethylene glycol.

[0012] Furthermore, the flame retardant is a hexa-p-aldehyde phenoxycyclotriphosphazene.

[0013] In a second aspect, the present invention provides a method for preparing a high-performance composite separator for lithium-ion batteries as described in the first aspect, the preparation steps including: (1) Disperse the alumina composite aerogel in anhydrous ethanol, then add flame retardant and sodium hydroxide, stir at room temperature for 4-6 hours, then add concentrated ammonia, reflux for 11-13 hours, cool to room temperature, filter, wash and dry to obtain the premix; (2) Mix the premix, water, dispersant, 2 / 3 of the defoamer and surfactant and ball mill for 11-13 hours. Then add the binder, plasticizer and remaining defoamer and continue ball milling for 11-13 hours. After ball milling, degas under vacuum to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer.

[0014] Furthermore, the mass ratio of the alumina composite aerogel, anhydrous ethanol, sodium hydroxide, and concentrated ammonia is (18~21):(80~100):(4.5~5.5):(53~55).

[0015] Furthermore, the preparation steps of the alumina composite aerogel are as follows: A1. Mix aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol, and stir at room temperature for 4-6 hours to form a sol; then add formamide and propylene oxide sequentially and continue stirring for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol. A2. Pour the ethanol solution of tetraethyl orthosilicate into a centrifuge tube containing aluminum sol, until the liquid level reaches 2 / 3 of the tube height. Then, let it stand at 43~47℃ for 23~25 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours to obtain a wet gel. A3. Dissolve triethoxy-2-pyridinesilane in anhydrous ethanol, then add it to the wet gel and react at 55~65℃ for 23~24h. Then wash with anhydrous ethanol, dry, grind and sieve to obtain composite aerogel preform. A4. Disperse the composite aerogel preform in acetonitrile, then add triacetaldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol, heat under reflux for 3-5 hours, then cool to room temperature, filter, wash, and dry to obtain alumina composite aerogel.

[0016] Further, in step A1, the molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide is 1:20:(7~9):(0.7~0.9):(7~9); in step A3, the molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate is (1.5~1.6):(15~16):3; the molar ratio of triethoxy-2-pyridinesilane, paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol is 127:(610~630):(2.1~2.2):(120~140):(250~254); and the mass ratio of the composite aerogel preform to acetonitrile is 1:(8~10).

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The present invention provides a high-performance composite separator for lithium-ion batteries. The separator includes a base film and a ceramic layer coated on the surface of the base film. The ceramic layer is formed by coating a ceramic slurry on the surface of the base film. The raw material components of the ceramic slurry mainly include alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer and flame retardant. Through the synergistic effect of the above components, the composite separator exhibits excellent comprehensive performance in terms of flame retardancy, thermal stability and ionic conductivity.

[0018] (2) This invention uses alumina composite aerogel as an inorganic filler in the ceramic slurry of the ceramic layer of a composite separator for high-performance lithium-ion batteries. The alumina composite aerogel is obtained by aging alumina sol in an alcoholic solution of tetraethyl orthosilicate using a sol-gel method, followed by surface modification with triethoxy-2-pyridinesilane and acetylation. First, alumina sol is introduced into an alcoholic solution of tetraethyl orthosilicate, and an alumina-silica hybrid network is formed through hydrolysis-condensation reaction. After aging, a three-dimensional framework structure with high porosity and large specific surface area is constructed. Subsequently, the ethoxysilane groups in triethoxy-2-pyridinesilane undergo a condensation reaction with the hydroxyl groups on the gel surface to achieve effective surface modification of the aerogel. Further acetylation treatment yields a silica-alumina composite aerogel containing ortho-acetylpyridine functional groups. This composite aerogel possesses excellent high-temperature resistance, effectively supporting the ceramic layer structure and inhibiting thermal shrinkage of the polyolefin-based membrane at high temperatures, significantly improving the thermal stability of the separator. Secondly, its high specific surface area and abundant mesoporous structure facilitate rapid penetration and uniform distribution of the electrolyte, enhancing the membrane's hydrophilicity and liquid retention capacity, thereby improving lithium-ion migration efficiency and increasing ionic conductivity. Thirdly, the surface-grafted acetylpyridine groups not only enhance the interfacial compatibility between the inorganic filler and the organic binder, ensuring the density and adhesion of the coating, but their polar structure also further promotes electrolyte wetting.

[0019] (3) The present invention can effectively enhance the flame retardancy of the composite separator by adding flame retardant to the ceramic slurry of the ceramic layer of the composite separator for high-performance lithium-ion batteries.

[0020] (4) In the preparation of the ceramic slurry of the ceramic layer of the high-performance lithium-ion battery composite separator of the present invention, the alumina composite aerogel and the flame retardant containing benzaldehyde functional group are first introduced into the concentrated ammonia water system for pre-reaction. The acetylpyridine group loaded on the surface of the alumina composite aerogel and the benzaldehyde structure in the flame retardant undergo a condensation reaction under ammonia catalysis to construct a terpyridine structure with a rigid conjugated structure in situ. The nitrogen-rich heterocyclic characteristics of the premix further enhance the flame retardancy of the material, that is, at high temperature, the combustion process is effectively suppressed by endothermic decomposition, release of inert gases such as ammonia and nitrogen, and promotion of char formation. At the same time, the terpyridine structure has strong polarity and abundant coordination sites, which can significantly improve the affinity of the ceramic layer for polar electrolyte, improve the interface wettability, and provide more transport channels and migration sites for lithium ions, thereby synergistically improving the ionic conductivity. Detailed Implementation

[0021] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0022] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0023] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0024] The base film is a 7μm thick PE film.

[0025] The dispersant is lithium polyacrylate; the defoamer is octanoic acid; the surfactant is fatty alcohol polyoxyethylene ether; the binder is polyvinyl alcohol; and the plasticizer is polyethylene glycol.

[0026] Example A method for preparing a high-performance composite separator for lithium-ion batteries, comprising the following steps: (1) Disperse the alumina composite aerogel in anhydrous ethanol, then add flame retardant and sodium hydroxide, stir at room temperature for 4-6 h, then add concentrated ammonia, reflux for 11-13 h, cool to room temperature, filter, wash and dry to obtain a premix; the mass ratio of alumina composite aerogel, anhydrous ethanol, sodium hydroxide and concentrated ammonia is (18-21): (80-100): (4.5-5.5): (53-55); (2) Mix the premix, water, dispersant, 2 / 3 of the defoamer and surfactant and ball mill for 11-13 hours. Then add the binder, plasticizer and remaining defoamer and continue ball milling for 11-13 hours. After ball milling, degas under vacuum to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer.

[0027] The mass ratio of the alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant is (80~100): (100~120): (2~4): (1.2~1.8): (0.2~2): (30~50): (8~12): (5~15).

[0028] The preparation steps of the alumina composite aerogel are as follows: A1. Mix aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol, and stir at room temperature for 4-6 hours to form a sol; then add formamide and propylene oxide sequentially and continue stirring for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol; wherein, the molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide is 1:20:(7-9):(0.7-0.9):(7-9); A2. Pour the ethanol solution of tetraethyl orthosilicate into a centrifuge tube containing aluminum sol, until the liquid level reaches 2 / 3 of the tube height. Then, let it stand at 43~47℃ for 23~25 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours to obtain a wet gel. A3. Dissolve triethoxy-2-pyridinesilane in anhydrous ethanol, then add it to a wet gel and react at 55-65℃ for 23-24 h. Then wash with anhydrous ethanol, dry, grind and sieve to obtain a composite aerogel preform; wherein the molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate is (1.5-1.6):(15-16):3; A4. The composite aerogel preform is dispersed in acetonitrile, then triacetaldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol are added and heated under reflux for 3-5 hours. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain alumina composite aerogel. The molar ratio of triethoxy-2-pyridinesilane, triacetaldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol is 127:(610-630):(2.1-2.2):(120-140):(250-254). The mass ratio of the composite aerogel preform to acetonitrile is 1:(8-10).

[0029] Example 1 A method for preparing a high-performance composite separator for lithium-ion batteries, comprising the following steps: (1) Disperse 80 parts by weight of alumina composite aerogel in 356 parts by weight of anhydrous ethanol, then add 5 parts by weight of flame retardant and 20 parts by weight of sodium hydroxide, stir at room temperature for 4 hours, then add 236 parts by weight of 25wt% ammonia water, reflux for 11 hours, cool to room temperature, filter, wash 3 times with anhydrous ethanol, and dry to obtain premix. (2) Mix the premix, 100 parts by weight of water, 2 parts by weight of dispersant, 0.8 parts by weight of defoamer, and 0.2 parts by weight of surfactant and ball mill for 11 hours. Then add 30 parts by weight of binder, 8 parts by weight of plasticizer, and 0.4 parts by weight of defoamer and continue ball milling for 11 hours. After ball milling, degas under vacuum until all bubbles are removed to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer with a thickness of 4μm.

[0030] The preparation steps of alumina composite aerogel are as follows: A1. Aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol were mixed and stirred at room temperature for 4 hours to form a sol. Then, formamide and propylene oxide were added sequentially and stirred for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol. The molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide was 1:20:7:0.7:7. A2. Pour a 10% volume concentration of tetraethyl orthosilicate ethanol solution into a centrifuge tube containing aluminum sol, with the liquid level reaching 2 / 3 of the tube height. Then, let it stand at 43°C for 23 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours. Each time, pour off the supernatant and add anhydrous ethanol back to the centrifuge tube to 2 / 3 of the tube height to obtain a wet gel. A3. Triethoxy-2-pyridinesilane was dissolved in anhydrous ethanol, then added to a wet gel and reacted at 55°C for 23 h. The mixture was then washed three times with anhydrous ethanol, dried at 30°C for 24 h, and then dried again at 60°C for 48 h. The mixture was then ground and passed through a 2000-mesh sieve to obtain a composite aerogel preform. The molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate was 1.5:15:3. A4. The composite aerogel preform was dispersed in acetonitrile in 8 times its mass, and then paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol were added. The mixture was heated under reflux for 3 hours, then cooled to room temperature, filtered, washed, and dried to obtain alumina composite aerogel. The molar ratio of triethoxy-2-pyridinesilane, paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol was 127:610:2.1:120:250.

[0031] Example 2 A method for preparing a high-performance composite separator for lithium-ion batteries, comprising the following steps: (1) 90 parts by weight of alumina composite aerogel were dispersed in 400 parts by weight of anhydrous ethanol, then 10 parts by weight of flame retardant and 22 parts by weight of sodium hydroxide were added. The mixture was stirred at room temperature for 5 hours, then 240 parts by weight of 25 wt% ammonia water was added and refluxed for 12 hours. After cooling to room temperature, the mixture was filtered, washed three times with anhydrous ethanol, and dried to obtain the premix. (2) Mix the premix, 110 parts by weight of water, 3 parts by weight of dispersant, 1 part by weight of defoamer, and 1.1 parts by weight of surfactant and ball mill for 12 hours. Then add 40 parts by weight of binder, 10 parts by weight of plasticizer, and 0.5 parts by weight of defoamer and continue ball milling for 12 hours. After ball milling, degas under vacuum until all bubbles are removed to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer with a thickness of 4μm.

[0032] The preparation steps of alumina composite aerogel are as follows: A1. Aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol were mixed and stirred at room temperature for 5 hours to form a sol. Then, formamide and propylene oxide were added sequentially and stirred for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol. The molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide was 1:20:8:0.8:8. A2. Pour a 10% volume concentration of tetraethyl orthosilicate ethanol solution into a centrifuge tube containing aluminum sol, with the liquid level reaching 2 / 3 of the tube height. Then, let it stand at 45°C for 24 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours. Each time, pour off the supernatant and add anhydrous ethanol back to the centrifuge tube to 2 / 3 of the tube height to obtain a wet gel. A3. Triethoxy-2-pyridinesilane was dissolved in anhydrous ethanol, then added to a wet gel and reacted at 60°C for 24 h. The mixture was then washed three times with anhydrous ethanol, dried at 30°C for 24 h, and then dried again at 60°C for 48 h. The mixture was then ground and passed through a 2000-mesh sieve to obtain a composite aerogel preform. The molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate was 1.55:15.5:3. A4. The composite aerogel preform was dispersed in acetonitrile in 9 times its mass, and then paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol were added. The mixture was heated under reflux for 4 hours, then cooled to room temperature, filtered, washed, and dried to obtain alumina composite aerogel. The molar ratio of triethoxy-2-pyridinesilane, paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol was 127:620:2.26:130:252.

[0033] Example 3 A method for preparing a high-performance composite separator for lithium-ion batteries, comprising the following steps: (1) 100 parts by weight of alumina composite aerogel were dispersed in 444 parts by weight of anhydrous ethanol, then 15 parts by weight of flame retardant and 24 parts by weight of sodium hydroxide were added. The mixture was stirred at room temperature for 6 hours, then 244 parts by weight of 25 wt% ammonia water were added and refluxed for 13 hours. After cooling to room temperature, the mixture was filtered, washed three times with anhydrous ethanol, and dried to obtain the premix. (2) Mix the premix, 120 parts by weight of water, 4 parts by weight of dispersant, 1.2 parts by weight of defoamer and 2 parts by weight of surfactant and ball mill for 13 hours. Then add 50 parts by weight of binder, 12 parts by weight of plasticizer and 0.6 parts by weight of defoamer and continue ball milling for 13 hours. After ball milling, degas under vacuum until all bubbles are removed to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer with a thickness of 4μm.

[0034] The preparation steps of alumina composite aerogel are as follows: A1. Aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol were mixed and stirred at room temperature for 6 hours to form a sol. Then, formamide and propylene oxide were added sequentially and stirred for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol. The molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide was 1:20:9:0.9:9. A2. Pour a 10% volume concentration of tetraethyl orthosilicate ethanol solution into a centrifuge tube containing aluminum sol, with the liquid level reaching 2 / 3 of the tube height. Then, let it stand at 47°C for 25 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours. Each time, pour off the supernatant and add anhydrous ethanol back to the centrifuge tube to 2 / 3 of the tube height to obtain a wet gel. A3. Triethoxy-2-pyridinesilane was dissolved in anhydrous ethanol, then added to a wet gel and reacted at 65°C for 24 h. The mixture was then washed three times with anhydrous ethanol, dried at 30°C for 24 h, and then dried again at 60°C for 48 h. The mixture was then ground and passed through a 2000-mesh sieve to obtain a composite aerogel preform. The molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate was 1.6:16:3. A4. The composite aerogel preform was dispersed in acetonitrile at 10 times its mass, and then paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol were added. The mixture was heated under reflux for 5 hours, then cooled to room temperature, filtered, washed, and dried to obtain alumina composite aerogel. The molar ratio of triethoxy-2-pyridinesilane, paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol was 127:630:2.2:140:254.

[0035] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that the alumina composite aerogel is obtained by aging alumina sol in an ethyl silicate alcohol solution using the sol-gel method. The specific preparation steps are as follows: A1. Mix aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol, and stir at room temperature for 5 hours to form a sol; then add formamide and propylene oxide sequentially and continue stirring for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol; wherein, the molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide is 1:20:8:0.8:8; A2. Pour a 10% (v / v) tetraethyl orthosilicate ethanol solution into a centrifuge tube containing aluminum sol, filling the tube to 2 / 3 of its height. Then, allow it to age at 45°C for 24 hours. Next, replace the solution with anhydrous ethanol four times within 48 hours. Each time, discard the supernatant and refill the centrifuge tube with anhydrous ethanol to 2 / 3 of its height. Then, dry the tube at 30°C for 24 hours and then at 60°C for 48 hours. Grind the solution and pass it through a 2000-mesh sieve to obtain an alumina composite aerogel. The remaining components and steps are the same as in Example 2.

[0036] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the ceramic slurry raw material components include ultrafine alumina with a particle size of 100~200nm, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant, while the remaining components and steps are the same as in Example 2.

[0037] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that the ceramic slurry raw material components include alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, and plasticizer, while the remaining components and steps are the same as in Example 2.

[0038] Comparative Example 4 The difference between Comparative Example 4 and Example 2 lies in the preparation method of the composite separator for high-performance lithium-ion batteries. The preparation steps include: (1) Mix 90 parts by weight of alumina composite aerogel, 110 parts by weight of water, 3 parts by weight of dispersant, 1 part by weight of defoamer and 1.1 parts by weight of surfactant and ball mill for 12 hours. Then add 40 parts by weight of binder, 10 parts by weight of plasticizer and 0.5 parts by weight of defoamer and continue ball milling for 12 hours. After ball milling, degas under vacuum until all bubbles are removed to obtain ceramic slurry. (2) The ceramic slurry is uniformly coated on the surface of the base film using a coating machine to form a ceramic layer with a thickness of 9 μm; the remaining components and steps are the same as in Example 2.

[0039] Example of effect Thermal stability: The high-performance lithium-ion battery composite separators prepared in the examples and comparative examples were placed in an environment of 150°C for 30 min and then removed. The dimensional changes of the separators before and after heat treatment were observed and the thermal shrinkage rate (%) was calculated. The thermal shrinkage rate (%) = (area of ​​separator before heat treatment - area of ​​separator after heat treatment) 100% / area of ​​the diaphragm before heat treatment.

[0040] Ion conductivity: The high-performance lithium-ion batteries prepared in the examples and comparative examples were immersed in electrolyte using a composite separator sandwiched between stainless steel sheets. SS / Separator / SS batteries were assembled, and the separator impedance was measured. The measurement frequency range was 1×10⁶ Hz-10 Hz, with an AC amplitude of 10 mV. The intercept of the Nyquist plot obtained by electrochemical impedance spectroscopy on the X-axis represents the impedance of the separator after immersion in electrolyte. The ionic conductivity of the separator = separator thickness / (area of ​​stainless steel sheet) (Diaphragm impedance).

[0041] Liquid absorption rate: determined by differential gravimetric method. The high-performance lithium-ion batteries of Examples 1-3 and Comparative Examples 1-4 were immersed in the electrolyte for 30 min (until saturation). The weights of the membranes before and after immersion were recorded as Wa and Wb, respectively. The liquid absorption rate was calculated using the formula: Liquid uptake (%) = (Wb-Wa) / Wa×100%.

[0042] Flame retardant performance test: Using a slitting machine, the high-performance lithium-ion batteries prepared in the examples and comparative examples were cut into circular pieces with a diameter of 16.5 mm using composite separators. The separators were then burned over an alcohol lamp flame, and the flame area was removed after the flame was applied. The burning phenomenon was recorded using a digital camera.

[0043] Table 1 below shows the performance data of the high-performance composite separators for lithium-ion batteries in Examples 1-3 and Comparative Examples 1-5: Table 1

[0044] As can be seen from the performance data comparison in Table 1 above, the high-performance composite separators for lithium-ion batteries prepared in Examples 1-3 have better thermal stability, ionic conductivity, wettability, and flame retardancy.

[0045] The difference between Comparative Example 1 and Example 2 is that the alumina composite aerogel is obtained by aging alumina sol in an orthosilicate alcohol solution using the sol-gel method, that is, a silica and alumina composite gel without the introduction of pyridine modification. The resulting high-performance lithium-ion battery composite separator has weaker thermal stability, ionic conductivity and wettability.

[0046] The difference between Comparative Example 2 and Example 2 is that the inorganic filler in the ceramic slurry is ultrafine alumina with a particle size of 100~200nm; the resulting high-performance composite separator for lithium-ion batteries has weaker thermal stability, ionic conductivity, and wettability.

[0047] The difference between Comparative Example 3 and Example 2 is that no flame retardant was added to the ceramic slurry raw material, resulting in a composite separator for high-performance lithium-ion batteries with weaker thermal stability, ionic conductivity, wettability, and flame retardancy.

[0048] The difference between Comparative Example 4 and Example 2 is that the raw material components are directly mixed during the preparation of the ceramic slurry, resulting in a high-performance composite separator for lithium-ion batteries with weaker thermal stability, ionic conductivity, wettability, and flame retardancy.

[0049] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance composite separator for lithium-ion batteries, comprising a base film and a ceramic layer on the surface of the base film; characterized in that, The ceramic layer is obtained by coating a ceramic slurry onto the surface of a base film; the raw material components of the ceramic slurry include alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant.

2. The high-performance composite separator for lithium-ion batteries according to claim 1, characterized in that, The base membrane is a polyolefin membrane with a thickness of 7 μm.

3. The high-performance composite separator for lithium-ion batteries according to claim 1, characterized in that, The mass ratio of the alumina composite aerogel, deionized water, dispersant, defoamer, surfactant, binder, plasticizer, and flame retardant is (80~100): (100~120): (2~4): (1.2~1.8): (0.2~2): (30~50): (8~12): (5~15).

4. The high-performance composite separator for lithium-ion batteries according to claim 1, characterized in that, The alumina composite aerogel is obtained by aging alumina sol in an ethyl silicate alcohol solution using the sol-gel method, followed by surface modification with triethoxy-2-pyridinesilane and acetylation.

5. The high-performance composite separator for lithium-ion batteries according to claim 1, characterized in that, The dispersant includes lithium polyacrylate; the defoamer includes octanoic acid; the surfactant includes fatty alcohol polyoxyethylene ether; the binder includes polyvinyl alcohol; and the plasticizer includes polyethylene glycol.

6. The high-performance composite separator for lithium-ion batteries according to claim 1, characterized in that, The flame retardant is a hexa-p-aldehyde phenoxycyclotriphosphazene.

7. A method for preparing a high-performance composite separator for lithium-ion batteries as described in any one of claims 1 to 6, characterized in that, The preparation steps include: (1) Disperse the alumina composite aerogel in anhydrous ethanol, then add flame retardant and sodium hydroxide, stir at room temperature for 4-6 hours, then add concentrated ammonia, reflux for 11-13 hours, cool to room temperature, filter, wash and dry to obtain the premix; (2) Mix the premix, water, dispersant, 2 / 3 of the defoamer and surfactant and ball mill for 11-13 hours. Then add the binder, plasticizer and remaining defoamer and continue ball milling for 11-13 hours. After ball milling, degas under vacuum to obtain ceramic slurry. (3) A ceramic slurry is uniformly coated onto the surface of the base film using a coating machine to form a ceramic layer.

8. The method for preparing a high-performance composite separator for lithium-ion batteries according to claim 7, characterized in that, The mass ratio of the alumina composite aerogel, anhydrous ethanol, sodium hydroxide, and concentrated ammonia is (18~21):(80~100):(4.5~5.5):(53~55).

9. The method for preparing a high-performance composite separator for lithium-ion batteries according to claim 7, characterized in that, The preparation steps of the alumina composite aerogel are as follows: A1. Mix aluminum trichloride hexahydrate, deionized water, and anhydrous ethanol, and stir at room temperature for 4-6 hours to form a sol; then add formamide and propylene oxide sequentially and continue stirring for 10 minutes to accelerate the sol-gel conversion and obtain aluminum sol. A2. Pour the ethanol solution of tetraethyl orthosilicate into a centrifuge tube containing aluminum sol, until the liquid level reaches 2 / 3 of the tube height. Then, let it stand at 43~47℃ for 23~25 hours to age. Then, replace it with anhydrous ethanol 4 times within 48 hours to obtain a wet gel. A3. Dissolve triethoxy-2-pyridinesilane in anhydrous ethanol, then add it to the wet gel and react at 55~65℃ for 23~24h. Then wash with anhydrous ethanol, dry, grind and sieve to obtain composite aerogel preform. A4. Disperse the composite aerogel preform in acetonitrile, then add triacetaldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol, heat under reflux for 3-5 hours, then cool to room temperature, filter, wash, and dry to obtain alumina composite aerogel.

10. The method for preparing a high-performance composite separator for lithium-ion batteries according to claim 9, characterized in that, In step A1, the molar ratio of aluminum trichloride hexahydrate, deionized water, anhydrous ethanol, formamide, and propylene oxide is 1:20:(7~9):(0.7~0.9):(7~9); in step A3, the molar ratio of triethoxy-2-pyridinesilane to anhydrous ethanol and aluminum trichloride hexahydrate is (1.5~1.6):(15~16):3; the molar ratio of triethoxy-2-pyridinesilane, paraldehyde, ferrous sulfate heptahydrate, trifluoroacetic acid, and peroxytert-butanol is 127:(610~630):(2.1~2.2):(120~140):(250~254); and the mass ratio of the composite aerogel preform to acetonitrile is 1:(8~10).

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