A method for preparing a zinc-bromine flow battery separator

Abstract

This invention discloses a method for preparing a separator for a zinc-bromine flow battery, belonging to the field of composite material technology. This method involves preparing a precisely controlled porous base membrane, combined with a modified functional coating, and then employing an innovative gradient hot-pressing process after cross-linking. Through three-stage temperature-pressure synergistic control, the porous structure of the base membrane is maintained while the density of the coating is improved. This overcomes the contradiction of traditional separators that "block bromine but not dendrites, and resist dendrites but block ions," providing key technical support for the long cycle life and high energy efficiency of zinc-bromine flow batteries.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and specifically relates to a method for preparing a zinc-bromine flow battery separator. Background Technology

[0002] Zinc-bromine flow batteries have shown great promise for large-scale energy storage due to their high energy density, low cost, and environmental friendliness. However, the performance bottleneck of their core component, the separator, has long constrained their commercialization. The separator must simultaneously meet the dual requirements of suppressing the diffusion of bromine and polybrominates and maintaining strong mechanical stability (resistance to zinc dendrite penetration).

[0003] Currently, the separators for zinc-bromine flow batteries are mainly perfluorosulfonic acid membranes or porous polyolefin membranes. However, although perfluorosulfonic acid membranes have excellent proton conductivity, their wide pore size distribution (>1 μm) results in high bromide ion permeability (≥3×10⁻⁶). -7 The rate is cm² / s, and the cost is high (accounting for more than 30% of the total battery cost); porous polyolefin membranes have good mechanical strength and chemical stability, but their surface hydrophobicity leads to low ion transport efficiency, and they lack bromine barrier function, making them prone to self-discharge due to bromine diffusion.

[0004] Existing technologies mainly modify porous polyolefin membranes through sulfonation polymer modification or crosslinking and coating. However, while sulfonated polyether ether ketones can repel bromide ions due to the negative charge of sulfonic acid groups, excessive swelling reduces mechanical strength, and they cannot effectively disperse current density during zinc deposition, allowing zinc dendrites to easily penetrate. Conventional crosslinking agents (such as glutaraldehyde) can improve membrane stability, but the uncontrollable crosslinking reaction easily leads to pore blockage, sacrificing ionic conductivity (<50 mS / cm). Although single-stage hot pressing can enhance density, high temperature and high pressure can easily damage the porous structure, causing a sharp drop in porosity.

[0005] Chinese patent document CN119133948A discloses a zinc-bromine flow battery separator with bromine fixation function, its preparation method, and its application. This method involves setting a hydrophilic coating on a porous separator, which can effectively adsorb and fix elemental bromine and polybrominates, reducing battery self-discharge and improving the coulombic efficiency of the battery stack. However, the separator prepared by this method physically adsorbs bromine molecules through the polar groups (such as sulfonic acid groups) of the hydrophilic coating, but does not construct a negative charge repulsion layer, resulting in limited blocking efficiency for bromide ions and polybrominates. Furthermore, the use of micron-sized inorganic particles as stabilizers leads to stress concentration due to excessively large particle size, making it difficult to resist zinc dendrite penetration. Summary of the Invention

[0006] The purpose of this invention is to provide a zinc-bromine flow battery separator and its preparation method. The zinc-bromine flow battery separator prepared by this method can improve the density of the coating while maintaining the porous structure of the base film, overcoming the contradiction of traditional separators that "block bromine but not dendrites, and block ions while resisting dendrites". This provides key technical support for the long cycle life and high energy efficiency of zinc-bromine flow batteries.

[0007] To achieve this objective, the present invention provides a method for preparing a zinc-bromine flow battery separator, comprising the following steps:

[0008] (1) Mix olefin polymer particles with a small molecule organic solvent, add polyethylene glycol to the mixture, heat and stir to react, and obtain a casting solution; coat the casting solution on a smooth planar substrate to obtain a wet film, immerse the wet film in deionized water, take out the obtained membrane material, wash, and perform vacuum three-stage step heating drying to obtain a porous base membrane;

[0009] (2) Disperse nano-titanium dioxide particles in anhydrous ethanol, add 3-aminopropyltriethoxysilane, sonicate, centrifuge, wash and dry to obtain modified titanium dioxide;

[0010] (3) Dissolve sulfonated polyether ether ketone in dimethylacetamide and stir until completely dissolved to obtain a sulfonated polyether ether ketone solution;

[0011] (4) The modified titanium dioxide obtained in step (2), the sulfonated polyether ether ketone solution obtained in step (3), and the carbon nanotubes are placed in a high-speed shear emulsifier and sheared to obtain a composite coating.

[0012] (5) After plasma treatment, the porous base membrane obtained in step (1) is coated with the composite coating obtained in step (4) and dried to obtain a porous base membrane coated with the composite coating.

[0013] (6) The porous base membrane coated with the composite coating is immersed in the crosslinking agent solution, heated and reacted, rinsed with deionized water, vacuum dried, and subjected to gradient hot pressing to obtain the zinc-bromine flow battery separator.

[0014] Preferably, in step (1), the olefin polymer particles are polyethylene or polypropylene, and the small molecule organic solvent is xylene, paraffin oil, tetrahydronaphthalene, or decahydronaphthalene; the mass ratio of the olefin polymer particles to the small molecule organic solvent is 1:4~6.

[0015] Preferably, in step (1), the mass ratio of olefin polymer particles to polyethylene glycol is 100:5~10; the heating and stirring reaction temperature is 80~120℃, the time is 6~12h; and the coating thickness is 200~400μm.

[0016] Preferably, in step (1), the vacuum three-stage stepped heating and drying conditions are to perform three equal temperature difference heating and drying operations within the range of 40~80℃, with a temperature difference range of 10~15℃ and a drying time of 6~8h, with the drying time being the same each time.

[0017] Preferably, in step (2), the mass ratio of nano-titanium dioxide particles to 3-aminopropyltriethoxysilane is 5~15:1; the ultrasonic time is 20~40 min; the drying temperature is 50~70℃; and the time is 10~14 h.

[0018] Preferably, in step (3), the degree of sulfonation of sulfonated polyether ether ketone is 60%~80%; the mass ratio of dimethylacetamide to sulfonated polyether ether ketone is 100:5~10.

[0019] Preferably, in step (4), the mass ratio of sulfonated polyether ether ketone solution, modified titanium dioxide, and carbon nanotubes is 105~110:0.25~1:0.1~1; the shearing treatment controls the speed of the high-speed shear emulsifier to be 10000~15000 rpm and the time to be 0.5~1.5h.

[0020] Preferably, in step (5), the plasma is oxygen plasma, the plasma treatment time is 1~5 min, the power is 50~200 W, the cavity pressure is 5~15 Pa; the drying temperature is 50~70℃, the drying time is 5~15 min; and the thickness of the composite coating is 10~50 μm.

[0021] Preferably, in step (6), the crosslinking agent solution is an ethanol solution of epichlorohydrin and triethylamine, with a mass ratio of ethanol, epichlorohydrin, and triethylamine of 100:1~3:0.1~0.2; the drying temperature is 40~60℃, and the time is 10~14h; the gradient hot pressing conditions are as follows: first stage: temperature 80~100℃, pressure 5~10 MPa, duration 10~20 minutes; second stage: temperature 120~140℃, pressure 15~20 MPa, duration 15~30 minutes; third stage: temperature 60~80℃, pressure 2~5 MPa, cooling and shaping for 10~15 minutes.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The technical solution provided by the present invention introduces modified nano-titanium dioxide particles. TiO2 nanoparticles modified with 3-aminopropyltriethoxysilane coupling agent are uniformly dispersed in the SPEEK matrix to form rigid physical cross-linking points, which hinder the permeation path of water molecules. At the same time, the hydroxyl groups (-OH) on the surface of TiO2 form hydrogen bonds with the sulfonic acid groups of SPEEK, which further inhibits swelling. Furthermore, the three-dimensional network formed by cross-linking restricts the movement of molecular chains through covalent bonds, effectively reducing the swelling phenomenon of sulfonated polyether ether ketone. Compared with traditional polyethylene film, the volume swelling rate can be reduced by 14.1%, and the bromine corrosion resistance and impermeability can be improved by 75.8%.

[0024] (2) The technical solution provided by the present invention uses epichlorohydrin as a crosslinking agent to react with the hydroxyl (-OH) and sulfonic acid (-SO3H) groups of sulfonated polyether ether ketone (SPEEK) to form a stable ether bond (COC) covalent crosslinking network. By adjusting the concentration of the crosslinking agent and the reaction time, the crosslinking density is precisely controlled. Through gradient hot pressing, the synergistic effect of the crosslinking network and gradient hot pressing achieves the effect of controllable crosslinking reaction and uniform pore distribution that is not easy to block. Compared with the material without gradient hot pressing and the material with a higher concentration of crosslinking agent, the tensile strength can be increased by 28.0% and 14.8%, and the puncture strength can be increased by 37.5% and 57.1%. The volume swelling rate is also significantly reduced by 4.4% and 3.3%, that is, the resistance to bromine corrosion and the resistance to permeation can be increased by 49.4% and 42.3%, respectively. At the same time, the peel strength is significantly improved by 27.8% and 130%, respectively. Moreover, the pore size distribution is significantly narrower than that of the material without gradient hot pressing, changing from 70~250nm to 50~150nm.

[0025] (3) The technical solution provided by the present invention controls the degree of sulfonation of sulfonated polyether ether ketone, so that the sulfonic acid group (-SO3H) of SPEEK dissociates into -SO3 in the electrolyte. - A fixed negative charge layer is formed, and by introducing nano-titanium dioxide, the average pore size of the TiO2 and SPEEK composite coating is 80~120 nm, which is smaller than the diameter of hydrated ions of polybrominates. The barrier effect is enhanced by size sieving. TiO2 carries a positive charge on its surface in acidic electrolyte, forming a dipole synergy with the negative charge of SPEEK. Through this synergistic effect, a negative charge repulsion layer is constructed, which changes the problem that the traditional sulfonic acid groups only adsorb bromine molecules through polar interaction, rather than repelling bromine ions and polybrominates through the Donnan effect. This reduces the volume swelling ratio of the membrane by 14.1% compared to conventional polyethylene membranes, which is a 75.8% improvement in performance. Compared to materials with sulfonation degrees outside the range, it is 4.1% lower, which is a 47.7% improvement in bromine corrosion resistance and impermeability.

[0026] (4) The technical solution provided by the present invention modifies titanium dioxide with carbon nanotubes by 3-aminopropyltriethoxysilane coupling agent to construct a conductive network, so that the zinc deposition current density is evenly distributed, which can effectively inhibit the growth of zinc dendrite tips. The puncture strength can be increased by 96.4% compared with conventional polyethylene film, which solves the problem that traditional membranes "block bromine but do not resist dendrites, and resist dendrites but block ions".

[0027] (5) The technical solution provided by the present invention softens the polymer chain and initially compresses the macropores through gradient hot pressing in the first stage, activates the cross-linking reaction in the second stage to enhance the network density while retaining the micropores, and cools and shapes in the third stage to avoid the distortion of the pore structure caused by internal stress. The three-dimensional network structure formed by the cross-linking of epichlorohydrin makes the pore size distribution of the diaphragm narrower while significantly improving the mechanical properties of the material, and the tensile strength can be increased by 78.6%.

[0028] (6) The technical solution provided by the present invention avoids the collapse of the pore structure of the base film by vacuum three-stage stepped heating drying (40-80℃), and combined with gradient hot pressing process (maximum temperature 140℃), the energy consumption is reduced by 40% compared with the freeze drying process. It significantly reduces costs and is suitable for continuous production.

[0029] (7) The technical solution provided by the present invention replaces perfluorosulfonic acid resin with sulfonated polyether ether ketone to avoid pollution from fluorine-containing waste; plasma pretreatment and silane-modified titanium dioxide can improve the coating interface bonding and peel strength by 91.7%, which can ensure the stable operation of the diaphragm in a strong acid electrolyte and has excellent environmental stability and long-term stability. Detailed Implementation

[0030] In the description of this invention, it should be noted that unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. The plasma equipment used in this invention is the Femto-3 low-pressure oxygen plasma equipment manufactured by Diener Electronic, Germany, with a radio frequency power of 0~300 W, a vacuum degree of 1~100 Pa, and a gas flow rate of 0~100 sccm; the microgravure roller coater is the STAR-200 microgravure roller coater manufactured by Shenzhen Kejing Materials Technology Co., Ltd., with a coating speed of 5~15 m / min (adjustable, accuracy ±0.2 m / min) and a coating gap of 10~100 μm (digitally fine-tuned, accuracy ±1 μm); the gradient hot press is the Carver 3851 gradient hot press manufactured by Carver, Inc., USA, with a temperature range of room temperature to 300℃ (accuracy ±1℃) and a pressure range of 0~20 MPa. Other reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] The technical solutions provided by the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0032] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0033] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0034] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0035] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0036] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Example 2

[0037] 50g of polyethylene granules were mixed with 200g of paraffin oil, and 2.5g of polyethylene glycol was added. The mixture was stirred at 80℃ for 12h to obtain a uniform casting solution. The casting solution was coated onto a silicon wafer to obtain a wet film with a thickness of 200μm. The wet film was then immediately immersed in deionized water at 25℃ for 30min. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 40℃, 50℃, and 60℃ for 8h each to obtain a porous base membrane.

[0038] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 2g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 40min, the mixture was refluxed at 70°C for 5h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 70°C for 10h to obtain modified titanium dioxide. 10g of sulfonated polyether ether ketone with a sulfonation degree of 60% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 110g of sulfonated polyether ether ketone solution. 0.25g of modified titanium dioxide, 110g of sulfonated polyether ether ketone solution, and 0.1g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 15000rpm, and the mixture was treated for 0.5h to obtain a composite coating.

[0039] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 200W, the cavity pressure to 15Pa, and the gas flow rate to 50sccm for 1 minute. Then, it was placed on a microgravure roller coater with the coating speed set to 10m / min and the gap to 10μm to coat with a composite coating. After removal, it was placed in a 50℃ forced-air drying oven for 15 minutes to obtain a porous base membrane coated with a composite coating.

[0040] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:3:0.2. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 80°C for 2 hours. After removal, the membrane was rinsed with deionized water and then vacuum dried in a vacuum drying oven at 60°C for 10 hours to obtain the composite membrane.

[0041] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 80℃, pressure 10 MPa, duration 15 minutes; second stage: temperature 120℃, pressure 20 MPa, duration 22.5 minutes; third stage: temperature 60℃, pressure 5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Example 3

[0042] 50g of polyethylene granules and 300g of decahydronaphthalene were mixed, and 5g of polyethylene glycol was added. The mixture was stirred at 120℃ for 6 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 400μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 60℃, 70℃, and 80℃ for 6 hours each to obtain a porous base membrane.

[0043] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 0.667g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 20min, the mixture was refluxed at 50°C for 7h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 50°C for 14h to obtain modified titanium dioxide. 5g of sulfonated polyether ether ketone with a sulfonation degree of 80% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 105g of sulfonated polyether ether ketone solution. 1g of modified titanium dioxide, 105g of sulfonated polyether ether ketone solution, and 1g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 10000rpm, and the mixture was treated for 1.5h to obtain a composite coating.

[0044] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 50W, the cavity pressure to 5Pa, and the gas flow rate to 30sccm for 5 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 5 m / min and the gap to 50 μm to coat with a composite coating. After removal, it was placed in a 70℃ forced-air drying oven for 5 minutes to obtain a porous base membrane coated with a composite coating.

[0045] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:1:0.1. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 60°C for 6 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 40°C for 14 hours to obtain the composite membrane.

[0046] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 100℃, pressure 5 MPa, for 15 minutes; second stage: temperature 140℃, pressure 15 MPa, for 22.5 minutes; third stage: temperature 80℃, pressure 2 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Example 4

[0047] 50g of polyethylene granules and 250g of tetrahydronaphthalene were mixed, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 40℃, 55℃, and 70℃ for 7 hours each to obtain a porous base membrane.

[0048] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0049] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0050] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0051] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, for 20 minutes; second stage: temperature 130℃, pressure 17.5 MPa, for 15 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 10 minutes, to obtain the zinc-bromine flow battery separator. Example 5

[0052] 50g of polypropylene granules were mixed with 250g of xylene, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 62℃, and 74℃ for 8 hours each to obtain a porous base membrane.

[0053] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0054] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0055] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0056] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, for 10 minutes; second stage: temperature 130℃, pressure 17.5 MPa, for 30 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 15 minutes, to obtain the zinc-bromine flow battery separator. Comparative Example 1

[0057] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0058] The porous base membrane was placed in a low-pressure oxygen plasma device, with the power adjusted to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm. After treatment for 3 minutes, it was then placed in a 60℃ forced-air drying oven and dried for 10 minutes to obtain the modified porous base membrane.

[0059] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The modified porous membrane was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the diaphragm.

[0060] The membrane was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery membrane. Comparative Example 2

[0061] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0062] Dissolve 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% in 100g of dimethylacetamide and stir until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution.

[0063] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with sulfonated polyether ether ketone solution. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with sulfonated polyether ether ketone solution.

[0064] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The base film coated with sulfonated polyether ether ketone solution was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the film surface. The reaction was carried out at 70°C for 4 hours. After removal, the film was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain a composite membrane.

[0065] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Comparative Example 3

[0066] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0067] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0068] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0069] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0070] The composite separator was placed in a hot press, and the hot press conditions were set to 110℃ and 12.5 MPa for 37.5 minutes; then it was allowed to cool and set naturally for 12.5 minutes. The hot pressing process yielded the zinc-bromine flow battery separator. Comparative Example 4

[0071] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0072] 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution; 0.6g of titanium dioxide, 107.5g of sulfonated polyether ether ketone solution and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and after treatment for 1h, a composite coating was obtained.

[0073] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0074] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0075] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Comparative Example 5

[0076] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0077] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 30% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0078] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0079] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0080] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Comparative Example 6

[0081] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven and dried at 60℃ for 24 hours to obtain a porous base membrane.

[0082] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0083] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0084] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:2:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0085] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator. Comparative Example 7

[0086] 50g of polyethylene granules were mixed with 250g of paraffin oil, and 4g of polyethylene glycol was added. The mixture was stirred at 100℃ for 8 hours to obtain a uniform casting solution. The casting solution was coated onto a glass substrate to obtain a wet film with a thickness of 300μm. The wet film was then immediately immersed in deionized water at 25℃ for 30 minutes. After removal, the membrane material was obtained. The membrane material was washed three times with a 1:1 ethanol-water solution and then placed in a vacuum drying oven. It was dried at 50℃, 60℃, and 70℃ for 8 hours each to obtain a porous base membrane.

[0087] 10g of nano-titanium dioxide particles were dispersed in 200ml of ethanol, and 1g of 3-aminopropyltriethoxysilane was added. After ultrasonic treatment for 30min, the mixture was refluxed at 60°C for 6h, centrifuged and washed for 10min, and then dried in a vacuum drying oven at 60°C for 12h to obtain modified titanium dioxide. 7.5g of sulfonated polyether ether ketone with a sulfonation degree of 70% was dissolved in 100g of dimethylacetamide and stirred until completely dissolved to obtain 107.5g of sulfonated polyether ether ketone solution. 0.6g of modified titanium dioxide, 107.5g of sulfonated polyether ether ketone solution, and 0.5g of carbon nanotubes were placed in a high-speed shear emulsifier, the speed was adjusted to 12000rpm, and the mixture was treated for 1h to obtain a composite coating.

[0088] The porous base membrane was placed in a low-pressure oxygen plasma device with the power set to 100W, the cavity pressure to 10Pa, and the gas flow rate to 40sccm for 3 minutes. Then, it was placed on a microgravure roller coater with the coating speed set to 7.5 m / min and the gap to 30 μm to coat with a composite coating. After removal, it was placed in a 60℃ forced-air drying oven for 10 minutes to obtain a porous base membrane coated with a composite coating.

[0089] A 1L crosslinking agent solution was prepared by mixing ethanol, epichlorohydrin, and triethylamine in a mass ratio of 100:10:0.15. The porous base membrane coated with the composite coating was immersed in the crosslinking agent solution, ensuring that the liquid level completely covered the membrane surface. The reaction was carried out at 70°C for 4 hours. After removal, the membrane was rinsed with deionized water and then placed in a vacuum drying oven at 50°C for 12 hours to obtain the composite membrane.

[0090] The composite separator was placed in a gradient hot press, and the gradient hot press conditions were set as follows: first stage: temperature 90℃, pressure 7.5 MPa, lasting 15 minutes; second stage: temperature 130℃, pressure 17.5 MPa, lasting 22.5 minutes; third stage: temperature 70℃, pressure 3.5 MPa, cooling and shaping for 12.5 minutes, to obtain the zinc-bromine flow battery separator.

[0091] Experimental Example 1

[0092] Peel strength test: The bonding strength between the composite coating and the base film was tested using a 90° peel tester with a peel rate of 100 mm / min, in accordance with ASTM D903 standard.

[0093] Experimental Example 2

[0094] Tensile strength and puncture strength tests: Tensile strength and puncture strength were tested on an Instron 5967 universal testing machine in accordance with ASTM D412 and ASTM D3763 standards.

[0095] Experimental Example 3

[0096] Volume swelling rate test: Cut the material into 25×25×2 mm³ specimens, with at least 3 parallel samples per group; use the water displacement method (ASTM D471) to measure the volume swelling rate. Immerse the sample in deionized water and calculate the initial volume V0 based on the volume of water displaced; hang the sample vertically on a corrosion-resistant support, ensuring it is completely submerged in the electrolyte (0.5L deionized water + 225.19g ZnBr2 solid + 65.6g liquid Br2), avoiding contact with the container wall or bottom. Place the container in a constant temperature water bath (60°C±1°C) for 30 days. Remove the sample using PTFE tweezers and immediately immerse it in deionized water to rinse 3 times (5 minutes each time) to remove residual electrolyte. Blot the surface moisture with filter paper and place it in a desiccator (humidity <30%) for equilibration for 24 hours. Remeasure the volume V1 using the water displacement method. Volume swelling rate (%) = V1 - V0 / V0*100.

[0097] Test Example 4

[0098] Pore ​​size distribution test: The pore size distribution was tested on a Porometer CFP 1300PMI pore size analyzer in accordance with ASTM F316-03 standard.

[0099] Table 1 is a performance comparison table of Examples 1-5 and each comparative example.

[0100]

[0101] As shown in Table 1, the membrane materials prepared in Examples 1-5 show that, compared to the pure polyethylene membrane in Comparative Example 1, the tensile strength of Example 1 is increased by 78.6%, the puncture strength is increased by 96.4%, and the volume swelling rate is reduced by 14.1%, meaning that the resistance to bromine corrosion and impermeability are improved by 75.8%. Furthermore, the pore size distribution is significantly narrowed, changing from 100-500 nm to 50-150 nm. This is because the technical solution of this invention introduces modified nano-titanium dioxide particles, and the TiO2 nanoparticles modified with 3-aminopropyltriethoxysilane coupling agent are uniformly distributed... Dispersed within the SPEEK matrix, it forms rigid physical cross-linking points, hindering the permeation path of water molecules. Simultaneously, the hydroxyl groups (-OH) on the TiO2 surface form hydrogen bonds with the sulfonic acid groups of SPEEK, further inhibiting swelling. Moreover, the three-dimensional network formed by cross-linking restricts molecular chain movement through covalent bonds, effectively reducing the swelling phenomenon of sulfonated polyether ether ketone. Furthermore, the conductive network constructed by modifying titanium dioxide with 3-aminopropyltriethoxysilane coupling agent and carbon nanotubes ensures a uniform distribution of zinc deposition current density, effectively inhibiting the growth of zinc dendrite tips and solving the problem of traditional membranes that "block bromine but not dendrites, and block ions while resisting dendrites."

[0102] Compared to Comparative Example 2, which directly coated sulfonated polyether ether ketone (without modified titanium dioxide and carbon nanotubes), Example 1 showed a 43.8% increase in tensile strength, a 57.1% increase in puncture strength, and a 7.7% decrease in volume swelling. This means that the resistance to bromine corrosion and impermeability were improved by 63.1%, while the peel strength was increased by 91.7%. Furthermore, the pore size distribution was significantly narrowed, changing from 80-300 nm to 50-150 nm. This is because the SPEEK coating alone lacked rigidity, and while it was partially cross-linked, it was not fully densified. The 3-aminopropyltriethoxysilane coupling agent-modified titanium dioxide and carbon nanotubes formed a cross-linked network, which effectively suppressed tip puncture. The uniform dispersion of nano-titanium dioxide formed a secondary sieving network, synergistically inhibiting the diffusion of polybrominates.

[0103] Compared to Comparative Example 3, which did not use gradient hot pressing treatment, Example 1 showed a 28.0% increase in tensile strength, a 37.5% increase in puncture strength, and a 4.4% decrease in volume swelling rate. This means that the resistance to bromine corrosion and the resistance to permeation were improved by 49.4%, while the peel strength was increased by 27.8%. Furthermore, the pore size distribution was significantly narrowed, changing from 70-250 nm to 50-150 nm. This is because the densification effect of single-stage hot pressing is limited, and uniform compression is not possible, resulting in a wider pore size distribution and a decrease in performance.

[0104] Compared to Comparative Example 4 (unmodified titanium dioxide), Example 1 showed a 33.2% increase in tensile strength, a 44.7% increase in puncture strength, and a 6.4% decrease in volume swelling. This translates to a 58.7% improvement in bromine corrosion resistance and impermeability, along with a 53.3% increase in peel strength. Furthermore, the pore size distribution was significantly narrowed, changing from 80-300 nm to 50-150 nm. This is because the unmodified TiO2 particles lacked the amine functional groups of the silane coupling agent, preventing them from forming chemical bonds with the sulfonic acid groups of SPEEK. This resulted in weak interfacial bonding and poor dispersion, leading to stress concentration and crack propagation in the coating. The larger TiO2 particles resulted in a wider pore size distribution, weakening the size sieving effect and increasing the bromide ion diffusion path.

[0105] Compared to Comparative Example 5, which has a lower degree of sulfonation, Example 1 shows a 24.0% increase in tensile strength, a 37.5% increase in puncture strength, and a 4.1% decrease in volume swelling. This means that the resistance to bromine corrosion and the resistance to penetration are improved by 47.7%, while the peel strength is increased by 35.3%. Furthermore, the pore size distribution is significantly narrowed, changing from 80-300 nm to 50-150 nm. This is due to the introduction of a sulfonated polyether ether ketone composite coating. The sulfonic acid groups of the sulfonated polyether ether ketone provide a strong negative charge field, which actively repels bromide ions through the Donnan effect. The density of sulfonic acid groups (-SO3H) is too low to form an effective Donnan repulsion layer. At the same time, the low degree of sulfonation results in a sparse cross-linking network, making it easier for water molecules to penetrate.

[0106] Compared to Comparative Example 6, which did not undergo vacuum three-stage gradient temperature drying, Example 1 showed a 57.0% increase in tensile strength, a 71.8% increase in puncture strength, and a 10.3% decrease in volume swelling rate. This means that the resistance to bromine corrosion and impermeability was improved by 69.6%, while the peel strength was increased by 109.1%. Furthermore, the pore size distribution was significantly narrowed, changing from 70-250 nm to 50-150 nm. This is because vacuum three-stage gradient temperature drying avoids the collapse of the base film pore structure, while single-stage drying leads to the collapse of the base film pore structure and the formation of stress cracks. The non-uniform pore structure accelerates electrolyte penetration, and the coating swelling intensifies.

[0107] Compared to Comparative Example 7, which had a higher concentration of crosslinking agent, Example 1 showed a 14.8% increase in tensile strength, a 57.1% increase in puncture strength, and a 3.3% decrease in volume swelling. This meant that its resistance to bromine corrosion and its impermeability were improved by 42.3%. At the same time, its peel strength was significantly improved by 130.0%, and its pore size distribution was significantly narrowed from 100-400 nm to 50-150 nm. This is because a higher concentration of epichlorohydrin crosslinking agent would lead to excessive crosslinking, resulting in a sharp drop in porosity and a decrease in ionic conductivity. In addition, a high crosslinking density would cause the coating to become brittle and sacrifice its toughness.

[0108] The specific embodiments described above provide a further detailed explanation of the present invention; however, these descriptions should not be construed as limiting the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a zinc-bromine flow battery separator, characterized in that, Includes the following steps: (1) Mix olefin polymer particles with a small molecule organic solvent, add polyethylene glycol to the mixture, heat and stir to react, and obtain a casting solution; coat the casting solution on a smooth planar substrate to obtain a wet film, immerse the wet film in deionized water, take out the obtained membrane material, wash, and perform vacuum three-stage step heating drying to obtain a porous base membrane. (2) Disperse nano-titanium dioxide particles in anhydrous ethanol, add 3-aminopropyltriethoxysilane, sonicate, centrifuge, wash and dry to obtain modified titanium dioxide; (3) Dissolve sulfonated polyether ether ketone in dimethylacetamide and stir until completely dissolved to obtain a sulfonated polyether ether ketone solution; (4) The modified titanium dioxide obtained in step (2), the sulfonated polyether ether ketone solution obtained in step (3), and the carbon nanotubes are placed in a high-speed shear emulsifier and sheared to obtain a composite coating. (5) After plasma treatment, the porous base membrane obtained in step (1) is coated with the composite coating obtained in step (4) and dried to obtain a porous base membrane coated with the composite coating. (6) The porous base membrane coated with the composite coating is immersed in the crosslinking agent solution, heated and reacted, rinsed with deionized water, vacuum dried, and subjected to gradient hot pressing to obtain the zinc-bromine flow battery separator.

2. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (1), the olefin polymer particles are polyethylene or polypropylene, and the small molecule organic solvent is xylene, paraffin oil, tetrahydronaphthalene, or decahydronaphthalene; the mass ratio of the olefin polymer particles to the small molecule organic solvent is 1:4~6.

3. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (1), the mass ratio of olefin polymer particles to polyethylene glycol is 100:5~10; the heating and stirring reaction temperature is 80~120℃, and the time is 6~12h; the coating thickness is 200~400μm.

4. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (1), the vacuum three-stage stepped heating and drying conditions are as follows: three equal temperature difference heating and drying processes are carried out in the range of 40~80℃, with a temperature difference range of 10~15℃ and a drying time of 6~8h, with the same drying time each time.

5. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (2), the mass ratio of nano-titanium dioxide particles to 3-aminopropyltriethoxysilane is 5~15:1; the ultrasonic time is 20~40 min; the drying temperature is 50~70℃ and the time is 10~14 h.

6. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (3), the degree of sulfonation of sulfonated polyether ether ketone is 60%~80%; the mass ratio of dimethylacetamide to sulfonated polyether ether ketone is 100:5~10.

7. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (4), the mass ratio of sulfonated polyether ether ketone solution, modified titanium dioxide, and carbon nanotubes is 105~110:0.25~1:0.1~1; the shearing treatment controls the speed of the high-speed shear emulsifier to be 10000~15000 rpm and the time to be 0.5~1.5h.

8. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (5), the plasma is oxygen plasma, the gas flow rate is 30~50 sccm, the plasma treatment time is 1~5 min, the power is 50~200W, the cavity pressure is 5~15 Pa; the drying temperature is 50~70℃, the drying time is 5~15 min; and the thickness of the composite coating is 10~50 μm.

9. The method for preparing the zinc-bromine flow battery separator according to claim 1, characterized in that, In step (6), the crosslinking agent solution is an ethanol solution of epichlorohydrin and triethylamine, with a mass ratio of ethanol, epichlorohydrin, and triethylamine of 100:1~3:0.1~0.2; the drying temperature is 40~60℃ and the time is 10~14h; the gradient hot pressing conditions are as follows: first stage: temperature 80~100℃, pressure 5~10 MPa, duration 10~20 minutes; second stage: temperature 120~140℃, pressure 15~20 MPa, duration 15~30 minutes; third stage: temperature 60~80℃, pressure 2~5 MPa, cooling and shaping for 10~15 minutes.

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