A method for preparing a VMT modified polymer composite membrane

Abstract

This invention belongs to the field of flow battery membrane technology and relates to a method for preparing a VMT-modified polymer composite membrane, comprising: preparing sodium-ion sulfonated polyether ether ketone; preparing dealuated vermiculite powder; preparing zeolite VMT; dispersing sodium-ion sulfonated polyether ether ketone in an organic solvent, and adding 0.5~1.5% (by mass) of zeolite VMT to prepare a SPEEK / VMT composite membrane. This invention solves the technical problems in the prior art where excessive swelling of polymer chains causes disordered expansion of ion channels, and insufficient rigidity of the membrane leads to easy creep in alkaline electrolytes, resulting in poor overall membrane performance.

Description

Technical Field

[0001] This invention belongs to the field of flow battery separator technology, and specifically relates to a method for preparing a VMT modified polymer composite membrane. Background Technology

[0002] With the large-scale use of fossil fuels, global carbon emissions continue to rise. Renewable energy sources such as solar and wind power suffer from inherent intermittency and volatility, resulting in unstable power generation quality and difficulty in directly connecting to the grid to meet load demands. Therefore, there is an urgent need to develop efficient and safe large-scale energy storage technologies to optimize the energy structure. Flow batteries, with their advantages of power-capacity decoupling, long cycle life (>15,000 cycles), high safety, and environmental friendliness, have become one of the preferred technologies for grid-scale energy storage.

[0003] As a core component of flow batteries, the separator plays a crucial role in separating the positive and negative electrolytes, preventing cross-contamination, and conducting charge carriers to maintain charge balance. An ideal separator should possess characteristics such as high ionic conductivity, high ion selectivity, excellent chemical / mechanical stability, and low cost. Currently, commercially available perfluorosulfonic acid membranes (Nafion) have high proton conductivity, but they suffer from the following technical bottlenecks: (1) poor ion selectivity, leading to capacity decay caused by the permeation of active materials; (2) high manufacturing cost (>$500 / m³). 2 (3) Perfluorinated skeletons pose environmental persistence risks. In contrast, sulfonated polyether ether ketone (SPEEK), as a non-fluorinated hydrocarbon-based membrane material, can achieve a balance between ion conductivity and selectivity through sulfonation degree control, and has advantages such as low cost and easy processing, and is regarded as the most commercially promising alternative. However, SPEEK faces severe challenges at high sulfonation degree (>60%): (1) mechanical properties deteriorate sharply, swelling rate exceeds 30%, and it is difficult to withstand the stack clamping force; (2) excessive swelling of polymer chains leads to disordered expansion of ion channels and a significant increase in the permeation rate of active materials; (3) insufficient rigid skeleton makes the membrane prone to creep in alkaline electrolyte. Therefore, developing a composite membrane with low cost, long service life, excellent comprehensive performance and applicability to various electrolyte systems is a key issue that needs to be solved to promote the large-scale application of flow batteries. Summary of the Invention

[0004] This invention provides a method for preparing a VMT-modified polymer composite membrane to solve the technical problems in existing flow battery membranes, such as disordered expansion of ion channels caused by excessive swelling of polymer chains and insufficient rigidity of the membrane leading to easy creep in alkaline electrolytes, resulting in poor overall membrane performance and difficulty in being applicable to various battery systems.

[0005] The technical solution adopted in this invention is a method for preparing a VMT-modified polymer composite film, which is carried out according to the following steps:

[0006] S1: Preparation of sodium ion-type sulfonated polyether ether ketone;

[0007] S2: Preparation of dealuminized vermiculite powder;

[0008] S3: Preparation of VMT (Vacuole zeolite);

[0009] S4: Disperse sodium ion-type sulfonated polyether ether ketone in an organic solvent, and add 0.5~1.5% (by mass) of zeolite VMT to prepare a SPEEK / VMT composite membrane.

[0010] Furthermore, the specific steps of S1 are as follows:

[0011] S1.1: Mix dry polyether ether ketone powder with 98% sulfuric acid at a mass-volume ratio of 1g:(4-8)mL, stir at room temperature for 3-8 minutes and let stand for 3-8 minutes to form a paste-like mixture;

[0012] S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath, heat it to 60~80℃, and stir it at a speed of 100~300 rpm for 10min~20min;

[0013] S1.3: Add 98% sulfuric acid to the product obtained in S1.2 according to the same mass-volume ratio as in S1.1, and stir at 500-700 rpm for 20-30 min at 60-80℃.

[0014] S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone;

[0015] S1.5: Immerse sulfonated polyether ether ketone in a 0.5~2.0M sodium hydroxide solution and react at 40~60℃ for 2~4 hours. Wash the product until neutral and dry it to obtain sodium ion type sulfonated polyether ether ketone.

[0016] Furthermore, the specific steps of S2 include:

[0017] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:(10-20) mL, react for 0.5-2 h, and then wash the vermiculite with deionized water;

[0018] S2.2: Mix the product of S2.1 with 1.0~3.0 M sulfuric acid solution at a mass-volume ratio of 1g:(15-30)mL, and stir at 30~50℃ for 2-4 hours;

[0019] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0020] Furthermore, the specific steps of S3 include:

[0021] S3.1: Grind the dealuminolite powder and mix it with 0.5~2.0 M sodium hydroxide solution at a mass-volume ratio of 1g:(50-100)mL, and react at 60~80℃ for 24~60 hours;

[0022] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

[0023] Furthermore, the specific steps of S4 are as follows:

[0024] S4.1: Disperse sodium ion-type sulfonated polyether ether ketone in a high-boiling-point organic solvent at a solid-liquid mass ratio of 1:20 to 1:30, stir at 40 to 80°C for 4 to 6 hours, then add 0.5 to 1.5% of the mass of sodium ion-type sulfonated polyether ether ketone, add zeolite VMT, continue stirring for 2 to 4 hours, and degas by ultrasonication for 10 to 20 minutes to obtain the casting solution;

[0025] S4.2: Pour the casting solution onto a glass plate, dry it at 70~90℃ for 10~14h, and then heat it to 90~110℃ and continue drying for 1~3h to obtain the SPEEK / VMT composite membrane.

[0026] Furthermore, the high-boiling-point organic solvent mentioned in S4.1 is any one of commercially available analytical grade dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0027] The beneficial effects of this invention are:

[0028] (1) This invention utilizes the high viscosity of concentrated sulfuric acid at low temperature and high concentration to form a "wet sand-like" acid paste with PEEK powder. The acid molecules are driven to undergo a self-diffusion reaction in the PEEK lattice through programmed temperature variation. With appropriate shearing, controllable sulfonation is achieved. Compared with the traditional one-time preparation of sulfonated polyether ether ketone long chains, this method "locks" sulfuric acid in the pores of PEEK under non-flow conditions, forming a confined reaction micro-region. The method of this invention does not have free acid in the reaction, making the number and distance of sulfonic acid groups more uniform. Therefore, the degree of SPEEK sulfonation obtained will be more uniform.

[0029] (2) The present invention adopts an oxidation-then-acid etching method. First, hydrogen peroxide treatment is used to achieve expansion modification and exposure of catalytic sites to improve reaction efficiency. Then, acid treatment is used to efficiently leach the exposed Al. 3+ Compared to traditional single acid treatment, this method significantly improves the aluminum removal process, which is beneficial for the interlayer intercalation of transported ions in the later stages.

[0030] (3) This invention utilizes the oxidation-acid etching-alkali etching method for the first time. After completing the oxidation and expansion of the interlayer domain, the aluminum is further removed by acid. Finally, the required cubic sodium aluminum silicate VMT is reconstructed by controlling the alkali treatment temperature and time. The original vermiculite is etched into tetrahedral silicon after alkali treatment. Cubic zeolite is generated through the dissolution-recrystallization mechanism. Uniform cubic crystals can be observed by SEM, instead of the original scaly pseudomorph of vermiculite. The formed zeolite can not only increase hydrophilicity, but also promote ion sieving.

[0031] (4) In this invention, zeolite VMT is combined with homogenized SPEEK matrix. The introduction of zeolite VMT can alleviate the mechanical property decay caused by high sulfonation degree and reduce permeability by utilizing its nanopores to sieve macromolecules. It is a membrane preparation strategy that combines low cost and high stability. In addition, the hydroxyl groups on the surface of SPEEK are easily ionized and become electronegative after ion exchange pretreatment. The alkali-treated VMT surface is also enriched with negatively charged hydroxyl groups. The two promote the rapid transition and transport of sodium ions through electrostatic synergy, which effectively improves the ion conductivity of the composite membrane.

[0032] (5) The raw materials of this composite separator are cheap, readily available, green and environmentally friendly. Its preparation process is mainly based on solution casting, and the equipment is simple to operate and the process is concise and efficient. This method has good scalability, is easy to scale up production, has industrial application prospects, and is expected to promote the commercialization of flow battery composite separator materials and help the flow battery industry develop on a large scale.

[0033] In summary, this invention prepares a SPEEK / VMT composite separator by incorporating a novel zeolite VMT into SPEEK using a solution casting method. This separator maintains high ionic conductivity while significantly suppressing active ion permeation, improving ion selectivity and chemical and mechanical stability. When applied to flow batteries, it exhibits excellent performance with high capacity retention, high operating efficiency, low self-discharge rate, and low polarization. Furthermore, the separator uses inexpensive raw materials, is compatible with various electrolyte systems, and its superior cycle stability provides broad prospects for its industrial application in various types of flow batteries. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1SEM images of raw vermiculite and cubic zeolite VMT prepared in Example 1; wherein: (a) is raw vermiculite, and (b) is SEM image of cubic zeolite VMT prepared in Example 1.

[0036] Figure 2 SEM image of the SPEEK / VMT-1 composite membrane prepared in Example 1;

[0037] Figure 3 The graph shows a comparison of the capacity and voltage of the SPEEK / VMT-1 composite membrane prepared in Example 1 and Nafion used in zinc-iron flow batteries.

[0038] Figure 4 This is a comparison chart of the discharge capacity of the SPEEK / VMT-1 composite film prepared in Example 1 and Nafion used in zinc-iron flow batteries.

[0039] Figure 5 This is a comparison chart of the coulombic efficiency of the SPEEK / VMT-1 composite membrane prepared in Example 1 and that of Nafion used in zinc-iron flow batteries.

[0040] Figure 6 SEM image of cubic zeolite VMT prepared in Example 2;

[0041] Figure 7 The image shows a SEM image of the SPEEK / VMT-0.5 composite membrane prepared in Example 2.

[0042] Figure 8 A comparison of the discharge capacity of the SPEEK / VMT-0.5 composite film prepared in Example 2 and Nafion 212 used in zinc-iron flow batteries;

[0043] Figure 9 SEM image of cubic zeolite VMT prepared in Example 3;

[0044] Figure 10 The image shows a SEM image of the SPEEK / VMT-1.5 composite membrane prepared in Example 3.

[0045] Figure 11 A comparison of the discharge capacity of SPEEK / VMT-1.5 composite membrane and Nafion212 in zinc-iron flow batteries;

[0046] Figure 12 The images show a morphological comparison of the SPEEK prepared in Example 1 and the SPEEK prepared by the conventional method, where: (a) is the SPEEK (sulfonated polyether ether ketone) prepared in Example 1, and (b) is the SPEEK prepared by the conventional method.

[0047] Figure 13This is a schematic diagram showing the discharge capacity retention rate of the SPEEK / VMT-1 composite film prepared in Example 1 and the VMT-1 composite film prepared in Comparative Example 1 in a zinc-iron flow battery.

[0048] Figure 14 SEM image of vermiculite powder prepared in Comparative Example 2;

[0049] Figure 15 SEM image of vermiculite powder prepared in Comparative Example 3;

[0050] Figure 16 SEM image of the flaky vermiculite powder prepared in Comparative Example 4;

[0051] Figure 17 SEM image of VMT prepared in Comparative Example 5.

[0052] Figure 18 SEM image of VMT prepared in Comparative Example 6;

[0053] Figure 19 The image shows the SEM image of the zeolite VMT prepared in Comparative Example 7. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0055] This invention provides a method for preparing a VMT-modified polymer composite film, comprising the following steps:

[0056] S1: Preparation of sodium ion-type sulfonated polyether ether ketone;

[0057] S1.1: Mix dry polyetheretherketone powder with 98% sulfuric acid at a mass-volume ratio of 1g:(4-8)mL, stir at room temperature for 3-8 minutes and let stand for 3-8 minutes to form a paste mixture;

[0058] The polyetheretherketone powder used in this application is derived from commercially available products. The purpose of letting it stand for 3-8 minutes is to allow concentrated sulfuric acid to penetrate into the polyetheretherketone particles through capillary action.

[0059] S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath, heat it to 60~80℃, and stir it at a speed of 100~300 rpm for 10min~20min;

[0060] During the stirring process, the shear force generated by the blades causes the polyetheretherketone particles to rub and collide with each other, thereby continuously exposing new reaction surfaces and achieving the effect of micro-grinding.

[0061] S1.3: Add 98% sulfuric acid to the product obtained in S1.2 according to the same mass-volume ratio as in S1.1, and stir at 500-700 rpm for 20-30 min at 60-80℃.

[0062] In the specific embodiments of this application, the sulfonation reaction in S1.3 is gradually advanced from the surface of the material to the interior under the synergistic effect of heat and mechanical shear force, thereby effectively avoiding the problem of excessive sulfonation of the surface due to excessively fast reaction. At the same time, the slower rotation speed is used in S1.2 because the mixture is in the form of paste, and too fast a speed is not conducive to uniform mixing. In S1.3, the rotation speed is increased because after the second addition of concentrated sulfuric acid, the mixture gradually dissolves from the paste and transforms into a liquid state. Increasing the rotation speed helps to promote the full integration of the two.

[0063] S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone;

[0064] In the specific embodiments of this application, the degree of sulfonation of sulfonated polyether ether ketone is 55-65%. In practical applications, a higher degree of sulfonation is not necessarily better; the appropriate degree of sulfonation needs to be selected according to actual needs.

[0065] S1.5: Immerse sulfonated polyether ether ketone in a 0.5~2.0M sodium hydroxide solution and react at 40~60℃ for 2~4 hours. Wash the product until neutral and dry it to obtain sodium ion type sulfonated polyether ether ketone.

[0066] S2: Preparation of dealuminized vermiculite powder;

[0067] Vermiculite (VMT) is a natural two-dimensional layered silicate mineral. Its 2:1 layered structure has unique advantages: (1) intralayer isomorphic substitution generates a large number of negative charges, which can repel anions and exhibit intrinsic ion sieving ability; (2) interlayer cations are easy to control, providing channels for rapid transport of sodium ions; (3) the high aspect ratio nanosheet structure can effectively enhance the mechanical strength of the polymer matrix. However, if natural vermiculite is used directly as a filler, due to its severe interlayer stacking and poor compatibility with polymers, it is easy to cause phase separation and structural defects, which may lead to a decline in membrane performance. Therefore, achieving synergistic effects between vermiculite and SPEEK through surface chemical modification, interface engineering and structural regulation has become an important innovative approach to constructing high-performance composite membranes.

[0068] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:(10-20) mL, react for 0.5-2 hours, and then wash the vermiculite with deionized water;

[0069] In a specific embodiment of this application, hydrogen peroxide (H2O2) molecules first penetrate into the interlayer domain of vermiculite, and then decompose under the catalytic action of interlayer iron ions. The oxygen produced forms internal pressure, which in turn causes the vermiculite structure to dissociate and expand.

[0070] S2.2: Mix the product of S2.1 with 1.0~3.0 M sulfuric acid solution at a mass-volume ratio of 1g:(15-30)mL, and stir at 30~50℃ for 2-4 hours;

[0071] In a specific embodiment of this application, the reaction mechanism of S2.2 is as follows: hydrogen ions (H+) in hydrogen peroxide... + First, the interlayer cations of vermiculite are replaced, then the Al-O bonds in its octahedral structure are broken, and finally aluminum ions are dissolved in the form of Al2(SO4)3.

[0072] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0073] S3: Preparation of VMT (Vacuole zeolite);

[0074] S3.1: Grind the dealuminolite powder and mix it with 0.5~2.0 M sodium hydroxide solution at a mass-volume ratio of 1g:(50-100)mL, and react at 60~80℃ for 24~60 hours;

[0075] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT;

[0076] VMT (Vacuoleite) is a sodium aluminum silicate with a cubic structure.

[0077] S4: Preparation of SPEEK / VMT composite membrane;

[0078] S4.1: Disperse sodium ion-type sulfonated polyether ether ketone in a high-boiling-point organic solvent at a solid-liquid mass ratio of 1:20 to 1:30, stir at 40 to 80°C for 4 to 6 hours, then add 0.5 to 1.5% of the mass of sodium ion-type sulfonated polyether ether ketone, add zeolite VMT, continue stirring for 2 to 4 hours, and degas by ultrasonication for 10 to 20 minutes to obtain a uniform casting solution.

[0079] The high-boiling-point organic solvent is any one of commercially available analytical grade dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

[0080] S4.2: Pour the casting solution onto a glass plate, dry it at 70~90℃ for 10~14h, and then heat it to 90~110℃ and continue drying for 1~3h to obtain the SPEEK / VMT composite membrane.

[0081] The SPEEK / VMT composite membrane prepared in this application has high ionic conductivity, excellent ion selectivity, superior mechanical properties, and high chemical stability at high current densities. In flow battery applications, this membrane exhibits high capacity retention, high efficiency, low self-discharge rate, low polarization, and low preparation cost, and is suitable for various flow battery systems.

[0082] Example 1

[0083] S1: Preparation of sodium ion-type sulfonated polyether ether ketone;

[0084] S1.1: Mix dry polyetheretherketone powder with 98% sulfuric acid at a mass-volume ratio of 1g:6mL, stir at room temperature for 5 min, and let stand for 5 min to form a paste-like mixture.

[0085] S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath and heat it to 70°C. Stir it at a speed of 200 rpm for 10 minutes.

[0086] S1.3: Add 6 mL of 98% sulfuric acid to the product obtained in S1.2 and stir at 600 rpm for 25 min at 70 °C.

[0087] S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone;

[0088] S1.5: The sulfonated polyether ether ketone is immersed in a 1.25M sodium hydroxide solution and reacted at 50°C for 3 hours. The product is washed until neutral and dried to obtain sodium ion type sulfonated polyether ether ketone.

[0089] S2: Preparation of dealuminized vermiculite powder

[0090] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:15mL, react for 1 hour, and then wash the vermiculite with deionized water.

[0091] S2.2: Mix the product of S2.1 with 2.0M sulfuric acid solution at a mass-volume ratio of 1g:20mL and stir at 40℃ for 3 hours;

[0092] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0093] S3: Preparation of VMT (Vacuole zeolite);

[0094] S3.1: Grind the dealuminolite powder and mix it with 1.5 M sodium hydroxide solution at a mass-volume ratio of 1 g: 70 mL, and react at 70 °C for 48 hours;

[0095] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

[0096] Figure 1 (a) is a SEM image of the original vermiculite. Figure 1 (b) is a SEM image of the cubic zeolite VMT prepared in Example 1. Figure 1 (b) It can be seen that the anticolaite prepared in Example 1 exhibits a regular cubic structure.

[0097] S4: Preparation of SPEEK / VMT composite membrane;

[0098] S4.1: Disperse sodium ion sulfonated polyether ether ketone in dimethyl sulfoxide at a solid-liquid ratio of 1:25, stir at 60°C for 5 hours, then add zeolite VMT accounting for 1% of the mass of sodium ion sulfonated polyether ether ketone, continue stirring for 3 hours, and ultrasonically degas for 15 minutes to obtain casting solution.

[0099] S4.2: Pour the casting solution onto a clean glass plate, dry it at 80°C for 12 hours, then raise the temperature to 100°C and continue drying for 2 hours to remove the solvent and obtain the SPEEK / VMT composite membrane.

[0100] Figure 2 The image shown is a SEM image of the SPEEK / VMT-1 composite membrane prepared in Example 1. "VMT-1" is a sample designation, meaning that the modified composite membrane prepared in this application has an analcime VMT content of 1.0% of the SPEEK mass. Figure 2 It can be seen that the zeolite VMT is uniformly dispersed in the SPEEK matrix, and the surface of the composite membrane is smooth and dense, without obvious pores and impurities, which ensures the homogeneity and mechanical stability of the membrane.

[0101] Figure 3 The graph shows a comparison of the capacity and voltage of the SPEEK / VMT-1 composite film prepared in Example 1 and Nafion used in zinc-iron flow batteries. Figure 3 As shown, the zinc-iron flow battery equipped with the SPEEK / VMT-1 composite membrane exhibits less polarization than the zinc-iron flow battery equipped with Nafion212.

[0102] Figure 4 This is a comparison chart of the discharge capacity of the SPEEK / VMT-1 composite film prepared in Example 1 and Nafion used in zinc-iron flow batteries. Figure 4 As shown, the zinc-iron flow battery equipped with Nafion212 exhibits rapid capacity decay due to the poor ion selectivity of the separator and the self-discharge caused by ion cross-contamination, resulting in rapid capacity decay. In contrast, the SPEEK / VMT-1 composite membrane has a better capacity retention rate.

[0103] Figure 5 The graph shows a comparison of the coulombic efficiency of the SPEEK / VMT-1 composite film prepared in Example 1 and that of Nafion used in zinc-iron flow batteries. Figure 5 As shown, in this embodiment, the coulombic efficiency of the zinc-iron flow battery assembled with the SPEEK / VMT-1 composite membrane remained consistently close to 100%, indicating that the introduction of analcime VMT effectively enhanced the ion selectivity and chemical stability of the separator while improving ionic conductivity. Given that the cost of this composite membrane is significantly lower than that of Nafion 212, these results fully demonstrate the promising application prospects of the SPEEK / VMT-1 composite membrane in zinc-iron flow batteries.

[0104] This invention uses SPEEK as a matrix, adds zeolite VMT, and prepares a composite membrane by solution casting. In specific implementation, this invention first precisely controls the degree of sulfonation of SPEEK through acid paste phase change-shear activation method to optimize its molecular chain structure, and then completes ion exchange through alkali pretreatment to introduce sodium ion sulfonic acid groups.

[0105] For vermiculite, a porous structure is constructed by etching with hydrogen peroxide and sulfuric acid, and the surface is reconstructed and functionalized using an alkaline solution. After uniformly combining the two, the resulting SPEEK / VMT composite film has both good chemical stability and significantly improved ion conduction performance, and exhibits excellent electrochemical performance when applied to flow batteries.

[0106] Example 2

[0107] S1: Preparation of sodium ion-type sulfonated polyether ether ketone;

[0108] S1.1: Mix dry polyetheretherketone powder with 98% concentrated sulfuric acid at a mass-volume ratio of 1g:4mL, stir at room temperature for 8min, and let stand for 8min to form a paste-like mixture.

[0109] S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath and heat it to 80°C. Stir it at 300 rpm for 10 minutes.

[0110] S1.3: Add 8 mL of 98% sulfuric acid to the product obtained in S1.2 and stir at 700 rpm for 30 min at 80 °C.

[0111] S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone;

[0112] S1.5: The sulfonated polyether ether ketone is immersed in a 2M sodium hydroxide solution and reacted at 60°C for 4 hours. The product is washed until neutral and dried to obtain sodium ion type sulfonated polyether ether ketone.

[0113] S2: Preparation of dealuminized vermiculite powder

[0114] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:10mL, react for 2 hours, and then wash the vermiculite with deionized water.

[0115] S2.2: Mix the product of S2.1 with 3.0M sulfuric acid solution at a mass-volume ratio of 1g:15mL and stir at 50°C for 4 hours;

[0116] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0117] S3: Preparation of VMT (Vacuole zeolite);

[0118] S3.1: Grind the dealuminolite powder and mix it with 2 M sodium hydroxide solution at a mass-volume ratio of 1g:50mL, and react at 80℃ for 60 hours;

[0119] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

[0120] S4: Preparation of SPEEK / VMT composite membrane;

[0121] S4.1: Disperse sodium ion sulfonated polyether ether ketone in dimethylformamide at a solid-liquid ratio of 1:20, stir at 80°C for 6 hours, then add 0.5% of the mass of sodium ion sulfonated polyether ether ketone in zeolite VMT, continue stirring for 4 hours, and ultrasonically degas for 20 minutes to obtain casting solution.

[0122] S4.2: Pour the casting solution onto a clean glass plate, dry it at 90°C for 14 hours, then raise the temperature to 110°C and continue drying for 14 hours to remove the solvent and obtain the SPEEK / VMT composite membrane.

[0123] Figure 6 The image shows a SEM image of the zeolite VMT prepared in Example 2. The zeolite VMT prepared in Example 2 exhibits a regular cubic structure.

[0124] Figure 7 The image shown is a SEM image of the SPEEK / VMT-0.5 composite membrane prepared in Example 2. Figure 7As can be seen, the analcime prepared in Example 2 is evenly distributed in the SPEEK matrix, and the prepared diaphragm has a relatively smooth surface, dense structure, and no obvious pores or impurities.

[0125] Figure 8 A comparison of the discharge capacity of the SPEEK / VMT-0.5 composite membrane prepared in Example 2 and Nafion 212 used in zinc-iron flow batteries shows that the zinc-iron flow battery with Nafion 212 experiences faster capacity decay. This is because the membrane has poor ion selectivity, and self-discharge caused by ion cross-contamination leads to rapid capacity decay. In contrast, the battery using the SPEEK / VMT-0.5 composite membrane has a better capacity retention rate.

[0126] Example 3

[0127] S1: Preparation of sodium ion-type sulfonated polyether ether ketone;

[0128] S1.1: Mix dry polyetheretherketone powder with 98% concentrated sulfuric acid at a mass-volume ratio of 1g:8mL, stir at room temperature for 3min and let stand for 3min to form a paste-like mixture;

[0129] S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath and heat it to 60°C. Stir it at 100 rpm for 10 minutes.

[0130] S1.3: Add 4 mL of 98% sulfuric acid to the product obtained in S1.2 and stir at 500 rpm for 20 min at 60°C.

[0131] S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone;

[0132] S1.5: The sulfonated polyether ether ketone is immersed in a 0.5M sodium hydroxide solution and reacted at 40°C for 2 hours. The product is washed until neutral and dried to obtain sodium ion type sulfonated polyether ether ketone.

[0133] S2: Preparation of dealuminized vermiculite powder;

[0134] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:20mL, react for 0.5 h, and then wash the vermiculite with deionized water;

[0135] S2.2: Mix the product of S2.1 with 1.0M sulfuric acid solution at a mass-volume ratio of 1g:30mL and stir at 40℃ for 2 hours;

[0136] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0137] S3: Preparation of VMT (Vacuole zeolite);

[0138] S3.1: Mix dealuminized vermiculite powder with 0.5M sodium hydroxide solution at a mass-volume ratio of 1g:100mL and react at 60℃ for 24 hours;

[0139] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

[0140] S4: Preparation of SPEEK / VMT composite membrane;

[0141] S4.1: Disperse sodium ion sulfonated polyether ether ketone in dimethylacetamide at a solid-liquid mass ratio of 1:30, stir at 40°C for 4 hours, then add 1.5% of sodium ion sulfonated polyether ether ketone by mass of zeolite VMT, continue stirring for 2 hours, and finally degas by ultrasonication for 10 minutes to obtain a uniform casting solution.

[0142] S4.2: Pour the casting solution onto a clean glass plate, dry it at 70°C for 10 hours, then raise the temperature to 90°C and continue drying for 1 hour to remove the solvent and obtain the SPEEK / VMT composite membrane.

[0143] Figure 9 Here is a SEM image of the zeolite VMT prepared in Example 3; Figure 10 This is a SEM image of the SPEEK / VMT-1.5 composite membrane prepared in Example 3. Figure 10 It can be seen that the analcime prepared in Example 3 is evenly distributed in the SPEEK matrix, and the prepared diaphragm has a relatively smooth surface, dense structure, and no obvious pores or impurities.

[0144] Figure 11 A comparison of the discharge capacity of SPEEK / VMT-1.5 composite membrane and Nafion 212 in zinc-iron flow batteries, such as... Figure 11 As shown, the zinc-iron flow battery equipped with Nafion212 exhibits rapid capacity decay. This is because the separator has poor ion selectivity, and self-discharge caused by ion cross-contamination leads to rapid capacity decay. In contrast, the battery using the SPEEK / VMT-1.5 composite membrane has a better capacity retention rate.

[0145] Comparative Example 1

[0146] S1: Preparation of sulfonated polyether ether ketone;

[0147] S1.1: Dry the polyetheretherketone powder thoroughly at 80°C and preheat the sulfuric acid (98% by mass) to 60°C;

[0148] S1.2: Mix the dry polyetheretherketone powder with preheated sulfuric acid at a mass-volume ratio of 1g:12mL, and stir at 700 r / min for 2 hours.

[0149] S1.3: The product obtained in S1.2 is sonicated for 15 minutes, and then ice water is poured in while stirring to obtain the product;

[0150] S1.4: The product was repeatedly washed with deionized water until neutral, air-dried at room temperature, and then dried at 80°C for 24 hours to obtain dried sulfonated polyether ether ketone.

[0151] S2: Preparation of dealuminized vermiculite powder

[0152] S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:15mL, react for 1 hour, and then wash the vermiculite with deionized water.

[0153] S2.2: Mix the product of S2.1 with 2.0M sulfuric acid solution at a mass-volume ratio of 1g:20mL and stir at 40℃ for 3 hours;

[0154] S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

[0155] S3: Preparation of VMT (Vacuole zeolite);

[0156] S3.1: Grind the dealuminolite powder and mix it with 1.5 M sodium hydroxide solution at a mass-volume ratio of 1 g: 70 mL, and react at 70 °C for 48 hours;

[0157] S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

[0158] S4: Preparation of SPEEK / VMT composite membrane;

[0159] S4.1: Disperse sulfonated polyether ether ketone in dimethyl sulfoxide at a solid-liquid ratio of 1:25, stir at 60°C for 5 hours, then add zeolite VMT accounting for 1% of the mass of sulfonated polyether ether ketone, continue stirring for 3 hours, and ultrasonically degas for 15 minutes to obtain casting solution.

[0160] S4.2: Pour the casting solution onto a clean glass plate and form a film using a solution casting method. First, dry the film at 80°C for 12 hours, then raise the temperature to 100°C and continue drying for 2 hours to remove the solvent, thus obtaining a VMT composite film.

[0161] Figure 12 (a) is the sulfonated polyether ether ketone (SPEEK) and prepared in Example 1. Figure 12(b) is a morphological comparison diagram of sulfonated polyether ether ketone (SPEEK) prepared by the conventional method (Comparative Example 1). The SPEEK prepared by Comparative Example 1 has a heterogeneous structure, and its degree of sulfonation is about 60% as determined by the ion exchange method. In addition, compared with the SPEEK prepared in Example 1, the morphology of this sulfonated polyether ether ketone (SPEEK) is uneven, and due to the uneven distribution of sulfonation, the sulfonation degree data measured multiple times fluctuates to a certain extent.

[0162] Figure 13 The diagram illustrates the discharge capacity retention of the SPEEK / VMT-1 composite membrane prepared in Example 1 and the VMT-1 composite membrane prepared in Comparative Example 1 in a zinc-iron flow battery. Due to the presence of excessively high or low local sulfonation in the membrane, cross-contamination of active materials is aggravated, which in turn leads to accelerated capacity decay and shortened battery life.

[0163] Comparative Example 2

[0164] The difference from Example 1 is as follows:

[0165] S2.1: Mix vermiculite powder and hydrogen peroxide solution at a mass-volume ratio of 1g: 15mL and treat at room temperature for 1 hour;

[0166] S2.2: The product after S2.1 treatment is thoroughly washed with deionized water and then dried to obtain pre-expanded vermiculite powder;

[0167] Figure 14 The image shows a SEM image of the vermiculite powder prepared in Comparative Example 2. This process only increased the interlayer spacing of the vermiculite and could not create pores through Al removal, resulting in the inability to generate stable anticolater after subsequent alkali treatment.

[0168] Comparative Example 3

[0169] The difference from Example 1 is as follows:

[0170] S2.1: Mix vermiculite powder and H2SO4 solution at a mass-volume ratio of 1g: 20mL and stir at 40℃ for 3 h;

[0171] S2.2: Wash with deionized water until neutral, then dry to obtain vermiculite powder.

[0172] Figure 15 The image shows a SEM image of the vermiculite powder prepared in Comparative Example 3. The etching of Al was incomplete in this process, which resulted in the inability to generate stable anticline after subsequent alkali treatment.

[0173] Comparative Example 4

[0174] The difference from Example 1 is as follows:

[0175] S3.1: Mix dealuminized vermiculite powder with 0.5M sodium hydroxide solution at a mass-volume ratio of 1g:50mL and react at 50℃ for 24 hours;

[0176] Figure 16 The image shows a SEM image of the flake-shaped vermiculite powder prepared in Comparative Example 4. Because the alkaline etching temperature in Comparative Example 4 was insufficient, the original tightly packed layered structure could not be completely destroyed, so the vermiculite still maintained its flake-shaped structure.

[0177] Comparative Example 5

[0178] The difference from Example 1 is as follows:

[0179] S3.1: Mix dealuminized vermiculite powder with 0.5 M sodium hydroxide solution at a mass-volume ratio of 1 g: 50 mL and react at 90 °C for 24 hours;

[0180] Figure 17 The image shows the SEM image of the zeolite VMT prepared in Comparative Example 5. Due to the excessively high alkali etching temperature in Comparative Example 5, some of the cubic zeolite fragments were broken into flakes again after being formed.

[0181] Comparative Example 6

[0182] The difference from Example 1 is as follows:

[0183] S3.1: Mix dealuminized vermiculite powder with 2.0M sodium hydroxide solution at a mass-volume ratio of 1g:50mL and react at 60℃ for 12 hours;

[0184] Figure 18 The SEM image of VMT prepared in Comparative Example 6 is shown below. Figure 18 As shown, due to insufficient alkali etching time in Comparative Example 6, the original tightly packed layered structure could not be completely destroyed, so the vermiculite still maintained its flaky structure.

[0185] Comparative Example 7:

[0186] The difference from Example 1 is as follows:

[0187] S3.1: Mix dealuminized vermiculite powder with 2.0M sodium hydroxide solution at a mass-volume ratio of 1g:50mL and react at 60℃ for 72 hours;

[0188] Figure 19 The SEM image of the zeolite VMT prepared in Comparative Example 7 is shown below. Figure 19 As shown, due to the excessively long alkali etching time in Comparative Example 7, some of the cubic zeolite fragments broke into flakes again after being formed.

[0189] All embodiments are described in a related manner, and the same or similar parts between the embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple, and the relevant parts can be referred to the description of the method embodiments.

[0190] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a VMT-modified polymer composite film, characterized in that, Includes the following steps: S1: Preparation of sodium ion-type sulfonated polyether ether ketone; S2: Preparation of dealuminized vermiculite powder; S3: Preparation of VMT (Vacuole zeolite); S4: Disperse sodium ion-type sulfonated polyether ether ketone in an organic solvent, and add 0.5~1.5% (by mass) of zeolite VMT to prepare a SPEEK / VMT composite membrane.

2. The method for preparing a VMT-modified polymer composite film according to claim 1, characterized in that, The specific steps for S1 are as follows: S1.1: Mix dry polyether ether ketone powder with 98% sulfuric acid at a mass-volume ratio of 1g:(4-8)mL, stir at room temperature for 3-8 minutes and let stand for 3-8 minutes to form a paste-like mixture; S1.2: Place the paste mixture obtained in S1.1 into a constant temperature oil bath, heat it to 60~80℃, and stir it at a speed of 100~300 rpm for 10min~20min; S1.3: Add 98% sulfuric acid to the product obtained in S1.2 according to the same mass-to-volume ratio as in S1.1, and stir at 500-700 rpm for 20-30 min at 60-80℃; S1.4: After the reaction is complete, the reaction product is washed with deionized water until neutral, and dried to obtain sulfonated polyether ether ketone; S1.5: Immerse sulfonated polyether ether ketone in a 0.5~2.0M sodium hydroxide solution and react at 40~60℃ for 2~4 hours. Wash the product until neutral and dry it to obtain sodium ion type sulfonated polyether ether ketone.

3. The method for preparing a VMT-modified polymer composite film according to claim 1, characterized in that, The specific steps of S2 include: S2.1: Mix vermiculite with a 10% hydrogen peroxide solution at a mass-volume ratio of 1g:(10-20) mL, react for 0.5-2 h, and then wash the vermiculite with deionized water; S2.2: Mix the product of S2.1 with 1.0~3.0 M sulfuric acid solution at a mass-volume ratio of 1g:(15-30)mL, and stir at 30~50℃ for 2-4 hours; S2.3: Wash the product of S2.2 until neutral, and dry it to obtain dealuminated vermiculite powder.

4. The method for preparing a VMT-modified polymer composite film according to claim 1, characterized in that, The specific steps of S3 include: S3.1: Grind the dealuminolite powder and mix it with 0.5~2.0 M sodium hydroxide solution at a mass-volume ratio of 1g:(50-100)mL, and react at 60~80℃ for 24~60 hours; S3.2: Wash the reaction product until neutral, centrifuge and dry to obtain zeolite VMT.

5. The method for preparing a VMT-modified polymer composite film according to claim 1, characterized in that, The specific steps for S4 are as follows: S4.1: Disperse sodium ion-type sulfonated polyether ether ketone in a high-boiling-point organic solvent at a solid-liquid mass ratio of 1:20 to 1:30, stir at 40 to 80°C for 4 to 6 hours, then add 0.5 to 1.5% of the mass of sodium ion-type sulfonated polyether ether ketone, add zeolite VMT, continue stirring for 2 to 4 hours, and degas by ultrasonication for 10 to 20 minutes to obtain the casting solution; S4.2: Pour the casting solution onto a glass plate, dry it at 70~90℃ for 10~14h, and then heat it to 90~110℃ and continue drying for 1~3h to obtain the SPEEK / VMT composite membrane.

6. The method for preparing a VMT-modified polymer composite film according to claim 1, characterized in that, The high-boiling-point organic solvent mentioned in S4.1 is any one of commercially available analytical grade dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

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