Sulfonated polyetheretherketone-based diaphragm as well as preparation method and application thereof

Abstract

The invention provides a sulfonated polyetheretherketone-based diaphragm as well as a preparation method and application thereof, and belongs to the technical field of flow battery diaphragms. The preparation method comprises the following steps: firstly, sulfonating polyether-ether-ketone to obtain sulfonated polyether-ether-ketone; and then preparing an electrostatic spinning solution from sulfonated polyether-ether-ketone and MXene powder, and carrying out electrostatic spinning on the electrostatic spinning solution to obtain the sulfonated polyether-ether-ketone-based diaphragm. Sulfonated polyether-ether-ketone and MXene materials are used as raw materials to prepare the nanofiber diaphragm through electrostatic spinning, on one hand, a hydrogen bond formed between MXene and sulfonated polyether-ether-ketone can increase the mechanical stability of the nanofiber diaphragm, and on the other hand, the water absorption rate, the swelling degree and the pore distribution of the nanofiber diaphragm are improved by adding MXene; and the practical performance of the diaphragm is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow battery diaphragms, and particularly relates to a sulfonated polyether ether ketone-based diaphragm, a preparation method thereof, and an application thereof. Background Art

[0002] Liquid flow batteries have advantages such as high safety, long cycle life, recyclable electrolytes, and high cost performance in the life cycle, and are considered to be one of the preferred technologies for large-scale energy storage technologies. Among them, iron-chromium liquid flow batteries use iron ions and chromium ions with rich raw materials and low prices as active substances, which can greatly reduce the manufacturing cost of the battery and have higher safety. In addition, iron-chromium liquid flow batteries also have good environmental adaptability and show good industrialization and market promotion application prospects.

[0003] The diaphragm is an important part of a liquid flow battery. It not only blocks the intermixing of active substances in the positive and negative electrolytes to avoid self-discharge, but also provides a channel for proton transfer in the electrolyte to balance charges. An ideal liquid flow battery diaphragm should have characteristics such as high proton conduction ability, high ion selectivity, high electrochemical stability, and low cost. However, at present, liquid flow battery diaphragms are mainly perfluorosulfonic acid proton exchange membranes represented by the Nafion series membranes produced by DuPont Company. Their high price limits the large-scale commercialization of liquid flow batteries to a certain extent. In order to reduce costs, non-perfluorinated proton exchange membranes have become a research hotspot. Long et al. used crown ethers with appropriate cavity sizes as cross-linking agents to construct a series of selectively cross-linked sulfonated polyimide membranes, which have excellent chemical structure and mechanical stability during the cycling of liquid flow batteries.

[0004] Polyether ether ketone (PEEK) is a commercial high-performance engineering plastic with good thermal stability, compressive resistance, and high mechanical strength. In particular, its polymer main chain has a phenylene oxide structure, which makes the benzene ring hydrogen have a relatively high electron cloud density, contributing to the performance of blocking electrolytes, conducting protons, and insulating electrons, and has attracted the attention of diaphragm researchers. The currently used Nafion membrane costs 100 yuan per milligram, while the purchased PEEK costs 300 yuan per kilogram. Therefore, selecting PEEK as the material to prepare a non-perfluorinated proton exchange membrane can greatly reduce the cost of the membrane. Compared with traditional manufacturing processes such as solution casting method, melt stretching method, and chemical vapor deposition method, the nanofiber membrane prepared by electrospinning method has advantages such as high porosity, large specific surface area, and high axial strength, and has become an emerging battery diaphragm preparation technology. Ye et al. dissolved PEEK in dichloroacetic acid at 180 °C, and then used a coaxial electrospinning process to coat the PEEK spinning solution inside the nanofiber shell of the spinable polymer polybutylene succinate to obtain nanofibers with a core-shell structure, and then removed the outer shell by low-temperature treatment to obtain PEEK nanofibers.

[0005] However, PEEK has extremely high chemical stability and is difficult to dissolve in common organic solvents at room temperature for electrospinning. Therefore, the development of PEEK nanofiber membranes faces great difficulties. Sulfonation modification of PEEK by controlling the reaction temperature and time is the main method to improve its spinnability at room temperature. Xiong et al. prepared an ion gel filled with ionic liquid in halloysite nanotubes and constructed a halloysite ion gel / sulfonated polyether ether ketone composite proton exchange membrane by electrospinning technology, showing single cell performance comparable to that of Nafion 212 membrane. Currently, the fiber membranes prepared from sulfonated polyether ether ketone as raw materials have problems of high swelling degree and water absorption rate, which easily damage the dimensional stability of the membrane, resulting in increased ion permeability and reduced battery performance. Therefore, it is of great significance to study a sulfonated polyether ether ketone-based separator and its preparation method for use in iron-chromium flow batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide a sulfonated polyether ether ketone-based separator, its preparation method and application, so as to solve the problem of high swelling degree and water absorption rate of fiber membranes prepared from sulfonated polyether ether ketone as raw materials in the prior art.

[0007] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a sulfonated polyether ether ketone-based separator, comprising the following steps:

[0009] (1) Sulfonate polyether ether ketone to obtain sulfonated polyether ether ketone;

[0010] (2) Prepare an electrospinning solution from sulfonated polyether ether ketone and MXene powder, and perform electrospinning on the electrospinning solution to obtain a sulfonated polyether ether ketone-based separator.

[0011] Preferably, the specific steps of the sulfonation in step (1) are: mix polyether ether ketone and concentrated sulfuric acid and carry out a sulfonation reaction, then cool, filter, and dry to obtain sulfonated polyether ether ketone.

[0012] Preferably, the mass-volume ratio of the polyether ether ketone to the concentrated sulfuric acid is 2-8 g:80-120 mL.

[0013] Preferably, the temperature of the sulfonation reaction is 50-70 °C, and the time of the sulfonation reaction is 6-10 h.

[0014] Preferably, the preparation steps of the electrospinning solution in step (2) are: disperse MXene powder and sulfonated polyether ether ketone in an organic solvent to prepare an electrospinning solution; the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and N-methylpyrrolidone.

[0015] Preferably, the mass of the MXene powder accounts for 10-20% of the mass of the sulfonated polyether ether ketone.

[0016] Preferably, the mass of the sulfonated polyether ether ketone accounts for 10-25% of the total mass of the sulfonated polyether ether ketone and the organic solvent.

[0017] Preferably, the process parameters of the electrospinning in step (2) are as follows: the spinning voltage is 16-24 kV, the feeding speed is 0.5-4.0 mL / h, the collection distance is 10-15 cm, and the spinning time is 1-3 h.

[0018] The present invention also provides a sulfonated polyether ether ketone-based separator prepared by the preparation method of the sulfonated polyether ether ketone-based separator described above.

[0019] The present invention also provides an application of the sulfonated polyether ether ketone-based separator described above in an iron-chromium flow battery.

[0020] Advantages of the present invention:

[0021] (1) The present invention uses sulfonated polyether ether ketone and MXene materials as raw materials to prepare nanofiber separators by electrospinning. On the one hand, the hydrogen bonds formed between MXene and sulfonated polyether ether ketone can increase the mechanical stability of the nanofiber separator. On the other hand, the addition of MXene improves the water absorption rate, swelling degree and pore distribution of the nanofiber separator, and enhances the practical performance of the separator.

[0022] (2) By introducing MXene, the present invention significantly reduces the pores of the nanofiber separator, ensures the penetration of the electrolyte and the rapid transmission of ions during charge and discharge, and thus improves the reaction reversibility and electrochemical performance of the battery. Description of the drawings

[0023] Figure 1 It is a comparison chart of the water absorption rate, swelling degree, tensile properties and water contact angle of the sulfonated polyether ether ketone-based separators prepared in Examples 1-3 and Comparative Example 1, wherein a is the comparison chart of the water absorption rate and swelling degree, b is the comparison chart of the tensile properties, and c is the comparison chart of the water contact angle;

[0024] Figure 2 It is the N2 isothermal adsorption curve of the sulfonated polyether ether ketone-based separators prepared in Example 2 and Comparative Example 1;

[0025] Figure 3 It is the pore size distribution curve of the sulfonated polyether ether ketone-based separators prepared in Example 2 and Comparative Example 1;

[0026] Figure 4 It is the Coulomb efficiency chart of the sulfonated polyether ether ketone-based separator prepared in Example 2;

[0027] Figure 5Voltage efficiency graph of the sulfonated polyether ether ketone-based separator prepared in Example 2;

[0028] Figure 6 Energy efficiency graph of the sulfonated polyether ether ketone-based separator prepared in Example 2;

[0029] Figure 7 Process flow chart for preparing the sulfonated polyether ether ketone-based separator of the present invention. Detailed implementation manners

[0030] The present invention provides a method for preparing a sulfonated polyether ether ketone-based separator, which includes the following steps:

[0031] (1) Sulfonate polyether ether ketone to obtain sulfonated polyether ether ketone;

[0032] (2) Prepare an electrospinning solution from the sulfonated polyether ether ketone and MXene powder, and perform electrospinning on the electrospinning solution to obtain a sulfonated polyether ether ketone-based separator.

[0033] In the present invention, the specific steps of the sulfonation in step (1) are: mix polyether ether ketone and concentrated sulfuric acid and then carry out a sulfonation reaction, and then cool, filter, and dry to obtain sulfonated polyether ether ketone.

[0034] In the present invention, it is preferred to dry the polyether ether ketone before mixing it with concentrated sulfuric acid. The drying temperature is 120 °C and the drying time is 5 h.

[0035] In the present invention, the mass-volume ratio of the polyether ether ketone to the concentrated sulfuric acid is 2 - 8 g:80 - 120 mL, preferably 4 - 6 g:90 - 110 mL, and further preferably 5 g:100 mL.

[0036] In the present invention, the mixing method is shaking at room temperature, and the shaking time is 5 - 15 min, preferably 8 - 12 min, and further preferably 10 min.

[0037] In the present invention, the temperature of the sulfonation reaction is 50 - 70 °C, preferably 55 - 65 °C, and further preferably 60 °C. The sulfonation reaction time is 6 - 10 h, preferably 8 - 10 h, and further preferably 10 h.

[0038] In the present invention, the preparation method of the MXene powder is preferably: mix hydrochloric acid solution, lithium fluoride and Ti3AlC2 and then carry out a reaction. After the reaction ends, wash with dilute hydrochloric acid, perform centrifugal separation, wash with deionized water, and freeze-dry the obtained precipitate to obtain MXene powder.

[0039] In the present invention, the mass-volume ratio of lithium fluoride to hydrochloric acid solution is 1-5 g: 40 mL; the mass-volume ratio of Ti3AlC2 to hydrochloric acid solution is 1-3 g: 40 mL; the reaction temperature is 30-50 °C, and the reaction time is 68-74 h; the concentration of the hydrochloric acid solution is 8-10 mol / L.

[0040] In the present invention, the MXene has a relatively large interlayer spacing and a negatively charged surface, and its stacked structure effectively avoids the formation of large pores. In addition, through MXene co-blended electrospinning, the hydrogen bonds formed between MXene and SPEEK further increase the mechanical stability of the nanofiber separator. As the doping amount of MXene increases, the water absorption rate gradually decreases, while the swelling degree first decreases and then slightly increases.

[0041] In the present invention, the preparation steps of the electrospinning solution in step (2) are as follows: dispersing MXene powder and sulfonated polyether ether ketone in an organic solvent to obtain an electrospinning solution; the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and N-methylpyrrolidone.

[0042] In the present invention, the mass of the MXene powder accounts for 10-20% of the mass of the sulfonated polyether ether ketone, preferably 15%.

[0043] In the present invention, the mass of the sulfonated polyether ether ketone accounts for 10-25% of the total mass of the sulfonated polyether ether ketone and the organic solvent, preferably 15-20%.

[0044] In the present invention, the process parameters of the electrospinning in step (2) are as follows: the spinning voltage is 16-24 kV, preferably 18-22 kV, more preferably 20 kV; the feeding speed is 0.5-4.0 mL / h, preferably 1-3 mL / h, more preferably 2 mL / h; the collection distance is 10-15 cm, preferably 11-14 cm, more preferably 12-13 cm; the spinning time is 1-3 h, preferably 2 h.

[0045] The present invention also provides a sulfonated polyether ether ketone-based separator prepared by the preparation method of the sulfonated polyether ether ketone-based separator described above.

[0046] The present invention also provides an application of the sulfonated polyether ether ketone-based separator described above in an iron-chromium flow battery.

[0047] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0048] Example 1

[0049] The polyether ether ketone (PEEK) particles were vacuum dried at 120 °C for 5 h. Then, 5 g of the dried PEEK particles were weighed and placed in a flask, and 100 mL of concentrated sulfuric acid was added. The mixture was shaken at room temperature for 10 min to make the PEEK particles and concentrated sulfuric acid mix evenly. Then, the flask was placed in an oil bath at 60 °C and magnetically stirred for 10 h for the sulfonation reaction. After the reaction, the reaction solution was slowly added to a large amount of ice water, and the white precipitate was washed repeatedly with deionized water until the solution was close to neutral. Finally, the precipitate was dried at 60 °C for 48 h to obtain sulfonated polyether ether ketone, denoted as SPEEK, which was placed in a desiccator for standby.

[0050] First, 40 mL of hydrochloric acid solution (concentration 9 mol / L) and 4 g of LiF were added to a polytetrafluoroethylene container. After stirring at room temperature for 30 min, 2 g of Ti3AlC2 was added to the container, and then it was stirred at a speed of 400 rpm and reacted at 40 °C for 72 h. After the reaction, it was washed 3 times with dilute hydrochloric acid, centrifuged at a speed of 3500 rpm for 5 min, and washed 5 times with deionized water. The collected lower-layer precipitate was freeze-dried for 48 h to obtain MXene powder.

[0051] 0.3 g of MXene powder was dispersed in N,N-dimethylformamide (DMF), and ultrasonicated in an ultrasonic crusher for 30 min. Then, it was stirred with a magnetic stirrer for 1 h, and 3 g of SPEEK was added, and stirring was continued until it was dissolved until a uniform electrospinning solution was obtained. In the electrospinning solution, the mass of SPEEK accounted for 20% of the total mass of DMF and SPEEK, and the mass of MXene powder accounted for 10% of the mass of SPEEK.

[0052] Using release paper as the substrate, electrospinning was carried out on the above electrospinning solution. The process parameters were: the spinning voltage was set at 20 kV, the advancing speed of the spinning solution was 2 mL / h, the collection distance was 12 cm, and the spinning time was 2 h, to obtain a sulfonated polyether ether ketone-based separator, denoted as MXene / SPEEK-10%.

[0053] Example 2

[0054] The difference from Example 1 was that the addition amount of MXene powder was 0.45 g, and the mass of MXene powder accounted for 15% of the mass of SPEEK. Other conditions were the same, and a sulfonated polyether ether ketone-based separator was obtained, denoted as MXene / SPEEK-15%.

[0055] Example 3

[0056] The difference from Example 1 was that the addition amount of MXene powder was 0.6 g, and the mass of MXene powder accounted for 20% of the mass of SPEEK. Other conditions were the same, and a sulfonated polyether ether ketone-based separator was obtained, denoted as MXene / SPEEK-20%.

[0057] Comparative Example 1

[0058] The polyetheretherketone (PEEK) particles were vacuum dried at 120 °C for 5 h, then 5 g of the dried PEEK particles were weighed and placed in a flask, 100 mL of concentrated sulfuric acid was added, and the mixture was shaken at room temperature for 10 min to mix the PEEK particles and the concentrated sulfuric acid evenly. Then the flask was placed in an oil bath at 60 °C and magnetically stirred for 10 h for sulfonation reaction; after the reaction was completed, the reaction solution was slowly added to a large amount of ice water, and the white precipitate was washed repeatedly with deionized water until the solution was close to neutral; finally, the precipitate was dried at 60 °C for 48 h and placed in a desiccator for standby to obtain sulfonated polyetheretherketone, denoted as SPEEK.

[0059] 3 g of SPEEK was dispersed in N,N-dimethylformamide (DMF), and stirred until completely dissolved to obtain a uniform electrospinning solution, wherein the mass of SPEEK in the electrospinning solution accounted for 20% of the total mass of DMF and SPEEK.

[0060] Using release paper as the substrate, electrospinning was carried out on the above electrospinning solution, and the process parameters were: the spinning voltage was set at 20 kV, the advancing speed of the spinning solution was 2 mL / h, the collecting distance was 12 cm, and the spinning time was 2 h to obtain a sulfonated polyetheretherketone-based separator, denoted as SPEEK.

[0061] Performance test:

[0062] (1) For the sulfonated polyetheretherketone-based separators prepared in Examples 1-3 and Comparative Example 1, the swelling degree and water absorption rate were tested. The determination of the water absorption rate of the separator can be carried out according to the ASTM D570 standard. The specific steps are as follows: The membrane to be tested was cut into small membrane pieces of 5 cm × 5 cm, placed in a DZF-6050 type vacuum oven (Beijing Luxi Technology Co., Ltd.) at 80 °C and dried to constant weight, and the weight of the dry membrane was weighed and denoted as W dry , then placed in a beaker and added with deionized water to completely immerse it, and the membrane was allowed to reach water absorption equilibrium at room temperature. The membrane was taken out, the water on the surface of the membrane was quickly sucked with filter paper and then its mass was accurately weighed and denoted as W wet , and the area S of the wet membrane was recorded wet . The water absorption rate of the separator was calculated by Equation (1-1). Then the wet membrane was placed in a vacuum oven at 80 °C and dried to constant weight, taken out, measured and the area S of the dry membrane was recorded dry . The swelling degree of the separator was calculated according to Equation (1-2).

[0063]

[0064] The test results are as Figure 1As shown in Figure a, it can be seen from the figure that the swelling degree and water absorption rate of SPEEK in Comparative Example 1 are 26.2% and 36.6% respectively. This is because the separator prepared from sulfonated polyether ether ketone contains sulfonic acid groups, and the separator has good hydrophilicity. However, too many water molecules cause the water channels to become larger, increasing the swelling degree and water absorption rate of the separator. An appropriate water absorption rate can ensure efficient ion conduction, and ions are transported in the membrane through the carrier mechanism and the hopping mechanism. However, when the swelling degree increases after excessive water absorption, the dimensional stability of the separator will be damaged, which will lead to an increase in ion permeability and a decrease in battery performance. In Examples 1-3, the swelling degree and water absorption rate of the sulfonated polyether ether ketone-based separator were reduced by adding a certain amount of MXene powder. This is because the MXene material has a relatively large interlayer spacing and a negatively charged surface. Adding MXene powder effectively avoids the formation of large pores in the separator. In addition, after blending MXene powder and SPEEK and then electrospinning, hydrogen bonds are formed between MXene and SPEEK, thereby increasing the mechanical stability of the nanofiber separator. As the doping amount of MXene powder increases, the water absorption rate and swelling degree gradually decrease. When the MXene doping amount is 15%, the water absorption rate and swelling degree of MXene / SPEEK-15% are 12.7% and 14.3% respectively.

[0065] (2) The tensile properties of the sulfonated polyether ether ketone-based separators prepared in Examples 1-3 were tested. The specific test method was to use an XLW-B type electronic tensile testing machine (Jinan Saichen Electronic Technology Co., Ltd.) and a CHY-CB type film thickness gauge (Languang Company, Jinan, China) to measure the thickness of the nanofiber separator. The width of the nanofiber separator sample was cut to 2 cm and the length was 10 cm. The sample strip was placed on the electronic tensile testing machine, and the tensile speed was adjusted to 25 mm / min. The sample strip was stretched until it broke. The test results are as Figure 1 shown in Figure b. Since the fiber separator was prepared by blending and electrospinning MXene and SPEEK, some MXene was directly exposed on the fiber surface, which was more likely to agglomerate, reducing the contact area between the fibers. As a result, the nanofiber separator was prone to slip during the stretching process, thereby reducing the fracture strain of the nanofiber separator. However, as the MXene doping amount increased, the fracture stress gradually increased, and the mechanical properties of the nanofiber separator were enhanced to a certain extent.

[0066] (3) The water contact angles of the sulfonated polyether ether ketone-based separators prepared in Examples 1-3 and Comparative Example 1 were tested. The results are as Figure 1 shown in Figure c: The water contact angle of the MXene / SPEEK-20% separator in Example 3 was 4.7°. This is because MXene itself has a certain hydrophilicity, and the hydrophilic property of the SPEEK nanofiber separator doped with MXene was further improved.

[0067] (4) Test the adsorption performance of the sulfonated polyether ether ketone-based membranes prepared in Test Example 2 and Comparative Example 1. The specific surface area and porosity analysis (BET) test process is as follows: Take 0.1 g of the sample for isothermal N2 adsorption and desorption tests. The specific surface area and pore size distribution of the sample can be calculated and analyzed through the relative pressure and adsorption amount. The test results are as Figures 2 - 3 shown. It can be seen that the nitrogen adsorption amount curve shows an obvious Type IV curve, indicating that it has micropores (1.8 nm) and mesoporous structures (≈6 nm); the specific surface area of the MXene / SPEEK-15% nanofiber membrane in Example 2 (8.2722 m 2 / g) is higher than that of the SPEEK nanofiber membrane (5.9941 m 2 / g), and the pore volume (0.014198 cm 3 / g) is higher than that of the SPEEK nanofiber membrane (0.010606 cm 3 / g). This is because the introduction of MXene significantly reduces the pores of the nanofiber membrane, which improves the reaction reversibility and electrochemical performance of the battery while ensuring electrolyte penetration and rapid ion transport during charge and discharge. Figure 3 shows that the MXene / SPEEK-15% nanofiber membrane mainly exhibits mesoporous characteristics, with pore diameters in the range of 6 - 10 nm, optimizing the ion transport channels and improving its diffusion kinetics.

[0068] (5) Test the battery performance of the sulfonated polyether ether ketone-based membrane in Example 2: Use a CT-4008-5V6A-DB-F type single-cell test system (Shenzhen Neware Battery Technology Co., Ltd.) to conduct charge and discharge cycle tests on the membrane. The effective size of the membrane is 10 cm × 10 cm. Under the condition of a current density of 140 mA / cm 2 , a constant current charge and discharge cycle test is carried out to detect the stability of the membrane. The positive and negative electrode electrolytes are composed of 80 mL of 1.2 mol / L FeCl2·4H2O, 1.4 mol / L CrCl3·3H2O, and 2.5 mol / L HCl. A peristaltic pump with a flow rate of 20 mL / min is used to transport the electrolyte. The electrolyte is circulated at a fixed flow rate of 20 mL / min. Under the condition of a current density of 140 mA / cm 2 , a constant current charge and discharge cycle test is carried out to detect the stability of the membrane. The test results are as Figures 4 - 6As shown, the Coulombic efficiency of MXene / SPEEK-15% can reach over 96%, and the energy efficiency can reach over 70%. The MXene / SPEEK-15% nanofiber separator shows excellent Coulombic efficiency among the tested separators, and its efficiency does not show obvious attenuation after 22 cycles. The MXene / SPEEK-15% nanofiber separator basically meets the performance requirements of the iron-chromium flow battery. This is because through the method of MXene blending electrospinning, an ion interpenetrating cross-linked network is constructed between MXene and SPEEK, reducing swelling and decreasing the fiber pore size. The synergistic effect of the two makes the Coulombic efficiency of the MXene / SPEEK nanofiber separator superior to that of the pure SPEEK nanofiber separator.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a sulfonated polyetheretherketone-based diaphragm, characterized in that: The steps include: (1) sulfonating polyetheretherketone to obtain sulfonated polyetheretherketone; (2) Sulfonated polyetheretherketone and MXene powder are made into an electrospinning solution, and the electrospinning solution is electrospun to obtain a sulfonated polyetheretherketone-based membrane.

2. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 1, characterized in that: The specific steps of sulfonation in step (1) are: mixing polyetheretherketone and concentrated sulfuric acid, carrying out sulfonation reaction, and then cooling, filtering and drying to obtain sulfonated polyetheretherketone.

3. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 2, characterized in that: The mass volume ratio of the polyetheretherketone and concentrated sulfuric acid is 2-8 g:80-120 mL.

4. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 2 or 3, characterized in that: The temperature of the sulfonation reaction is 50-70° C., and the time of the sulfonation reaction is 6-10 hours.

5. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 4, characterized in that: The preparation step of the electrospinning solution in step (2) is: dispersing MXene powder and sulfonated polyetheretherketone in an organic solvent to obtain an electrospinning solution; the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran and N-methylpyrrolidone.

6. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 1, 2 or 5, characterized in that: The mass of the MXene powder accounts for 10-20% of the mass of the sulfonated polyetheretherketone.

7. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 5, characterized in that: The mass of the sulfonated polyetheretherketone accounts for 10-25% of the total mass of the sulfonated polyetheretherketone and the organic solvent.

8. The method for preparing a sulfonated polyetheretherketone-based diaphragm according to claim 3, 5 or 7, characterized in that: The process parameters of the electrospinning in step (2) are: spinning voltage of 16 to 24 kV, propulsion speed of 0.5 to 4.0 mL / h, collection distance of 10 to 15 cm, and spinning time of 1 to 3 h.

9. A sulfonated polyetheretherketone-based diaphragm obtained by the method for preparing a sulfonated polyetheretherketone-based diaphragm according to any one of claims 1 to 8.

10. Use of the sulfonated polyetheretherketone-based diaphragm according to claim 9 in an iron-chromium liquid flow battery.

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