Modified sulfonated polyethersulfone membrane as well as preparation method and application thereof

Abstract

The invention discloses a modified sulfonated polyethersulfone membrane as well as a preparation method and application thereof, and the preparation method of the membrane comprises the following steps: preparing a membrane from a sulfonated polyethersulfone solution by adopting a tape casting method, drying, immersing the formed membrane into an acrylic acid solution, initiating a grafting reaction by ultraviolet light, and then washing and drying to obtain the modified sulfonated polyethersulfone membrane. The carboxyl is grafted to the surface of the membrane through ultraviolet initiation, so that the physical and chemical properties such as hydrophilicity and hydroxyl conductivity of the membrane are remarkably improved, and efficient transmembrane transportation of carriers is realized.

Description

Technical Field

[0001] This invention relates to a modified sulfonated polyethersulfone membrane, its preparation method and application, belonging to the field of alkaline zinc-iron redox flow battery technology. Background Technology

[0002] With the development of green energy, the demand for large-scale energy storage technology is becoming increasingly urgent, and flow batteries have received widespread attention from researchers in recent years. Flow batteries have advantages such as long service life, high safety, and power-capacity separation design, and have great application prospects in the field of large-scale energy storage. They mainly utilize the change of redox state of active materials in the solution on both sides of the positive and negative electrodes to achieve charging and discharging. The core device consists of a stack, an electrolyte tank, and a circulation system, among which the core components of the stack include the separator, electrodes, and bipolar plates.

[0003] Between the positive and negative electrodes of a flow battery lies a separator, which selectively allows ions to pass through to form a complete battery pathway, while simultaneously isolating the positive and negative electrolytes to prevent cross-contamination and short circuits. In alkaline zinc-iron flow batteries, an ideal separator should possess the following characteristics: ① stability under alkaline conditions and resistance to alkali corrosion; ② high ionic conductivity and selectivity; ③ high mechanical strength to resist dendrite penetration and support long-term stable operation. Currently, the most commonly used separator in the flow battery field is the perfluorosulfonic acid ion exchange membrane (Nafion) manufactured by DuPont. TM However, high cost, complex processes, and poor ion selectivity leading to poor long-term stability are limiting factors for Nafion. TM The large-scale application of membranes in the field of flow batteries.

[0004] From an economic perspective, sulfonated polyethersulfone (SPES), prepared using the cheaper polyethersulfone (PES) material, shows promising development prospects in zinc-iron flow batteries. PES exhibits excellent thermal stability and superior chemical stability in highly corrosive environments. Most importantly, the excellent mechanical properties of PES membranes effectively resist zinc dendrite puncture of the separator, improving the long-term stability of the battery. While PES materials possess excellent physicochemical properties, the lack of ion-exchange groups limits its application in flow batteries. Sulfonation is a commonly used polymer modification method that, while imbuing the material with ion-exchange groups, can significantly improve membrane properties such as hydrophilicity, water flux, ion permeability, and ion conductivity. Therefore, researchers often use sulfonated PES as the base membrane material. However, SPES membranes still suffer from low conductivity, making further modification of SPES membranes to improve their performance in alkaline zinc-iron flow batteries crucial. Summary of the Invention

[0005] The purpose of this invention is to provide a modified sulfonated polyethersulfone membrane, its preparation method, and its applications. By grafting carboxyl groups onto the membrane surface through UV initiation, the physicochemical properties of the membrane, such as hydrophilicity and hydroxide conductivity, are significantly improved, achieving efficient transmembrane transport of charge carriers. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0006] A modified sulfonated polyethersulfone membrane includes: a sulfonated polyethersulfone matrix membrane; and a carboxyl-containing functional layer located on at least one side surface of the sulfonated polyethersulfone matrix membrane, wherein the carboxyl-containing functional layer is covalently grafted to the surface of the matrix membrane, thereby enabling the membrane to simultaneously possess both sulfonic acid groups and carboxyl groups, both types of anionic functional groups.

[0007] The carboxyl-containing functional layer is a graft copolymer layer formed by graft polymerization of vinyl unsaturated carboxylic acid monomers under ultraviolet light.

[0008] The vinyl unsaturated carboxylic acid monomers are selected from at least one of the following: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and any combination of two or more thereof.

[0009] The carboxyl groups in the carboxyl-containing functional layer are -COOH and / or -COO. - It exists in form.

[0010] The carboxyl-containing functional layer is located on at least one of the two surfaces of the substrate membrane, preferably on both surfaces.

[0011] The sulfonated polyethersulfone matrix film is obtained by introducing sulfonic acid groups into polyethersulfone through a sulfonation reaction.

[0012] The sulfonation reaction is carried out in a sulfonation system containing chlorosulfonic acid and / or sulfuric acid.

[0013] The membrane is an ion-conducting membrane suitable for alkaline systems, preferably a hydroxide ion-conducting membrane.

[0014] The carboxyl-containing functional layer makes the film surface negatively charged, thereby generating an electrostatic repulsion effect on negatively charged ions in the alkaline system and inhibiting the formation tendency of zinc deposit dendrites.

[0015] The membrane prepared by the method described above.

[0016] A method for preparing the modified sulfonated polyethersulfone film includes the following steps:

[0017] (1) Prepare a sulfonated polyethersulfone casting solution and form a film to obtain a sulfonated polyethersulfone matrix film;

[0018] (2) The substrate membrane is brought into contact with a grafting solution containing vinyl unsaturated carboxylic acid monomers, so that the monomers wet the surface of the substrate membrane;

[0019] (3) The substrate film after impregnation is subjected to ultraviolet irradiation to initiate a grafting reaction, and a carboxyl-containing functional layer is formed on the surface of the substrate film;

[0020] (4) The grafted membrane is washed and dried to obtain a modified sulfonated polyethersulfone membrane.

[0021] The sulfonated polyether sulfone described in step (1) is obtained by sulfonating polyether sulfone in a sulfonation system containing chlorosulfonic acid and / or sulfuric acid.

[0022] The ratio of polyethersulfone to chlorosulfonic acid and sulfuric acid is: 1 g : (1-3) mL : (5-20) mL.

[0023] The sulfonation reaction temperature is 40-80℃, preferably 40-60℃; the reaction time is 3-10 h, preferably about 6 h.

[0024] The solvent of the casting solution in step (1) is selected from at least one of amide-based polar aprotic solvents and sulfoxide-based solvents.

[0025] The solvent is selected from N,N-dimethylacetamide and / or dimethyl sulfoxide.

[0026] The concentration of sulfonated polyethersulfone in the casting solution is 0.15-0.35 g / mL, preferably 0.18-0.30 g / mL, and more preferably 0.20-0.25 g / mL.

[0027] In step (1), the casting solution is dispersed before film formation. The dispersion treatment includes ultrasonic treatment for 0.5-3 h and / or ball milling for 24-96 h, preferably ball milling for no less than 48 h.

[0028] In step (1), a film is formed by casting, with a doctor blade gap of 50-500 μm, preferably 100-300 μm, and more preferably about 200 μm.

[0029] The drying process after film formation in step (1) includes:

[0030] First, pre-dry at 50-90℃ for 2-12 hours to set the shape; then dry under vacuum at 100-150℃ to remove residual solvent.

[0031] The grafting solution mentioned in step (2) is a solution of vinyl unsaturated carboxylic acid monomers in a polar solvent, preferably containing water.

[0032] The volume fraction of vinyl unsaturated carboxylic acid monomers in the grafting solution is 5%-40%, preferably 10%-30%, and more preferably 15%-25%.

[0033] The wavelength of ultraviolet irradiation in step (3) is 300-400 nm, preferably about 365 nm.

[0034] The ultraviolet irradiation time in step (3) is 5-120 min, preferably 10-90 min, and more preferably 30-60 min.

[0035] Step (3) is carried out under the protection of an inert gas, which is selected from nitrogen and / or argon.

[0036] In step (4), water is used for washing until the pH of the washing solution is neutral or close to neutral.

[0037] In step (4), the drying temperature is 50-90℃, preferably 60-80℃; the drying time is 6-24 h, preferably about 12 h.

[0038] The vinyl unsaturated carboxylic acid monomer is acrylic acid, and the grafting solution is a mixed solution of acrylic acid and water.

[0039] Application of the modified sulfonated polyethersulfone membrane in electrochemical energy storage devices;

[0040] Preferably, the application is as a separator in an alkaline zinc-iron flow battery;

[0041] The modified sulfonated polyethersulfone membrane is used to conduct hydroxide ions and inhibit zinc dendrite growth.

[0042] The beneficial effects of this invention are:

[0043] By introducing carboxyl groups onto the membrane surface via UV grafting after membrane formation, the physicochemical properties such as membrane hydrophilicity and hydroxide conductivity are significantly improved, enabling efficient transmembrane ion transport and developing a new generation of high-performance ion-conducting membranes for alkaline zinc-iron flow batteries.

[0044] The surface of the obtained ultraviolet grafted membrane carries a certain negative charge due to the presence of carboxyl groups, which can affect the zinc deposition process during the operation of the alkaline zinc-iron flow battery. This causes the negatively charged zincate ions to gather away from the membrane due to charge repulsion, thereby regulating the zinc deposition process, promoting uniform zinc deposition, inhibiting dendrite formation, and extending the service life of the membrane in the alkaline zinc-iron flow battery.

[0045] The grafting reaction is initiated by ultraviolet light without the need for an additional initiator. The carboxyl groups grafted onto the film surface are derived from low-cost acrylic acid monomers. Based on the photosensitivity of sulfonated polyethersulfone itself, the experiment reflects that this ultraviolet grafting reaction has a certain degree of universality. Compared with other conventional modification methods, it provides a simpler, more effective, and lower-cost polymer modification method. Attached Figure Description

[0046] Figure 1 For SPES H 1 NMR spectrum;

[0047] Figure 2 The images are scanning electron microscope (SEM) images of the SPES film: (a) surface view, (b) cross-sectional view.

[0048] Figure 3 FT-IR spectra of SPES film and SPES-X film (X=50);

[0049] Figure 4 Scanning electron microscope images of SPES-X film (X=50): (a) surface view, (b) cross-sectional view;

[0050] Figure 5 Tensile strength of SPES, sulfonated polyether ether ketone (SPEEK), and SPES-X film (X=0, 30, 50, 60);

[0051] Figure 6 Water absorption and swelling of SPES, SPEEK and SPES-X membranes (X=0,30,50,60), (a) water absorption rate, (b) swelling rate;

[0052] Figure 7 Thermogravimetric analysis curves of SPES, SPEEK, and SPES-X membranes (X=0, 30, 50, 60);

[0053] Figure 8 The grafting degree of SPES and SPES-X films (X=0,30,50,60);

[0054] Figure 9 The water contact angles for SPES and SPES-X membranes (X=0, 30, 50, 60°).

[0055] Figure 10 Hydroxide conductivity and sheet resistance of SPES, SPEEK and SPES-X films (X=0,30,50,60), (a) hydroxyl conductivity, (b) sheet resistance.

[0056] Figure 11 SPES, SPEEK, and SPES-X membranes (X=0, 30, 50, 60) at 40-200 mA cm⁻¹ -2 Performance of alkaline zinc-iron flow batteries at current densities: (a) coulombic efficiency (CE), (b) voltage efficiency (VE), (c) energy efficiency (EE);

[0057] Figure 12 SPES, SPEEK, and SPES-X membranes (X=50) at 80 mA cm⁻¹ -2 Long-term stability under certain conditions. Detailed Implementation

[0058] Example 1

[0059] Preparation of sulfonated polyether sulfone (SPES)

[0060] 100 mL of concentrated sulfuric acid (98%) was added to a three-necked flask. Using a top stirrer, the mixture was heated to 60 °C in an oil bath at 800 rpm, maintaining this stirring speed and temperature throughout the reaction. 10 g of polyethersulfone (PES) powder was added and stirred for 2 hours to ensure complete dissolution. Then, 20 mL of chlorosulfonic acid was added dropwise, and the reaction was maintained for 4 hours. After the reaction was complete, the solution was poured into cold water to precipitate, yielding a pale yellow SPES product. The SPES product was then washed in an ultrasonic cleaner, with the pure water continuously replaced until the pH of the washing solution approached neutral. Finally, the obtained product was dried in an 80 °C oven for 24 hours.

[0061] Preparation of SPES membrane

[0062] Weigh 2 g of dried SPES powder into a centrifuge tube, add 10 mL of N,N-dimethylacetamide (DMAc), mix thoroughly with a shaker, sonicate for 1 h, add spherical ink beads to the mixture, and then ball mill on a shaker for more than 48 h to obtain a uniformly dispersed SPES casting solution.

[0063] The casting solution is then poured onto a glass plate placed on a coating machine. A 200-micron doctor blade is used to smooth the casting solution. The glass plate coated with the casting solution is placed in a 60°C oven and dried for 8 hours for setting. Then, the glass plate is placed in a 120°C vacuum oven to thoroughly dry and remove the solvent. Finally, after the glass plate cools to room temperature, it is placed in deionized water to obtain the SPES membrane.

[0064] Preparation of UV-grafted membranes

[0065] First, take 5 mL of 99.9% acrylic acid in a beaker, add 20 mL of deionized water, and prepare a 20% (v / v) acrylic acid solution. Then, immerse the SPES membrane prepared in the previous step into the acrylic acid solution and transfer it into a UV reaction chamber. Nitrogen protection is provided during the reaction, and a 365 nm UV lamp is turned on for 50 min. After the reaction, the grafted membrane is repeatedly washed with pure water until the pH of the washing solution is close to neutral. Then, it is dried in a 60℃ vacuum oven for 12 h. The resulting membrane is designated SPES-50.

[0066] Examples 2-4

[0067] The process is basically the same as in Example 1, except that in Example 1, the illumination time of the ultraviolet grafting reaction was set to 50 min, while in Examples 2-4, the illumination time of the ultraviolet grafting reaction was set to 0 min, 30 min, and 60 min, respectively. All other conditions remained the same, and the prepared films were designated as SPES-0, SPES-30, and SPES-60, respectively.

[0068] Comparative Example 1

[0069] Weigh 2 g of dried SPEEK powder into a centrifuge tube, add 10 mL of N,N-dimethylacetamide (DMAc), mix thoroughly with a shaker, sonicate for 1 hour, add spherical ink beads to the mixture, and ball mill on a shaker for at least 48 hours to obtain a uniformly dispersed SPEEK casting solution. Then, pour the casting solution onto a glass plate placed on a coating machine, and smooth the solution with a 200-micron doctor blade. Place the coated glass plate in a 60°C oven to dry for 8 hours for setting, then place it in a 120°C vacuum oven to thoroughly dry and remove the solvent. Finally, after the glass plate cools to room temperature, place it in deionized water to obtain the SPEEK membrane.

[0070] Test methods

[0071] SPES H 1 NMR characterization: SPES powder was subjected to H2S analysis. 1 NMR characterization was used to determine whether the PES was successfully grafted with sulfonic acid groups. Figure 1 The characterization results showed that a new peak appeared at a low field position of 8.3 after the sulfonation reaction, which reflects that the chemical shift of the ortho hydrogen to the low field of 8.3 due to the presence of the sulfonic acid group, proving that the sulfonic acid group was successfully grafted onto the PES backbone, and SPES was successfully synthesized.

[0072] Morphological characterization of SPES films: The surface and cross-sectional morphology of SPES films were characterized using scanning electron microscopy. Figure 2 The results showed that the membrane surface was smooth and without obvious defects, and the membrane interior had good uniformity.

[0073] FT-IR characterization of SPES and SPES-X films (X=50): FT-IR characterization of SPES and SPES-50 films was performed to determine whether the UV grafting reaction was successful. Figure 3 The results showed that at 1700cm -1 The characteristic peak of C=O stretching vibration appeared at 3500 cm⁻¹. -1 The significantly enhanced -OH characteristic peaks on the left and right indicate the presence of -COOH on the membrane after the reaction, proving the successful occurrence of the UV grafting reaction.

[0074] Morphological characterization of SPES-X film (X=50): The surface and cross-sectional morphology of SPES-50 film were characterized using scanning electron microscopy. Figure 4 The results showed that the membrane surface was smooth with no obvious defects, and the membrane interior had good uniformity and no obvious pores, which was not much different from the SPES membrane.

[0075] Tensile strength of SPES, SPEEK, and SPES-X membranes (X=0, 30, 50, 60): The tensile strength of the membranes was tested using a universal testing machine to reflect their mechanical strength properties. Figure 5 The results showed that the UV grafting reaction slightly reduced the tensile strength of the modified film compared to the pure SPES film, but the overall impact was not significant, and both were higher than those of the SPEEK film, indicating that the UV grafting reaction did not significantly affect the mechanical properties of the film.

[0076] Water absorption and swelling of SPES, SPEEK, and SPES-X membranes (X=0,30,50,60): The water absorption rate is calculated from the mass difference between the dry and wet membranes, and the swelling rate comes from the difference in side length between the dry and wet membranes, which reflects the dimensional stability of the membrane. Figure 6 The results showed that with the increase of hydrophilic carboxyl groups on the UV-grafted membrane, the high-grafted membrane exhibited a higher water absorption rate. The increase in water absorption rate inevitably led to an increase in swelling rate, indicating that the UV grafting reaction partially affected the dimensional stability of the membrane.

[0077] Thermogravimetric analysis curves of SPES, SPEEK, and SPES-X membranes (X=0, 30, 50, 60): The chemical stability of the membrane is reflected by thermogravimetric (TG) testing. Figure 7 The results showed that the membrane experienced rapid weight loss at 400-600℃, which was due to the large-scale decomposition of the sulfonic acid groups and the PES backbone. However, the thermal stability of the membranes with different grafting degrees was not significantly different and was close to that of the pure membrane, and was superior to that of the SPEEK membrane. This indicates that the UV grafting reaction has little effect on the thermal stability of the membrane.

[0078] Grafting degree of SPES and SPES-X membranes (X=0,30,50,60): The grafting degree of the membrane surface is reflected by IEC testing. Figure 8 The results showed that as the irradiation time increased, the IEC value of the membrane gradually increased. After 50 minutes, the trend of change was no longer obvious. This is because before 50 minutes, the main reaction was the grafting reaction of acrylic acid. As the reaction time increased, the degree of grafting gradually increased. However, after 50 minutes, the main reaction was the self-polymerization reaction of acrylic acid monomers, which copolymerized into polyacrylic acid rather than grafting onto the membrane surface. This indicates that before 50 minutes, extending the irradiation time can increase the degree of grafting, but after 50 minutes, continuing to extend the irradiation time can hardly promote the growth of the degree of grafting.

[0079] Water contact angles of SPES and SPES-X membranes (X=0,30,50,60): Water contact angles were tested using the seat drop method to reflect changes in the hydrophilicity of the membrane surface. Figure 9 The results showed that the water contact angle of the UV-grafted membrane was significantly reduced due to the presence of carboxyl groups on the membrane surface, and this reduction trend was more pronounced as the reaction time was extended. This indicates that the UV grafting reaction can improve the hydrophilicity of the membrane surface, and the improvement effect is related to the light exposure time.

[0080] Hydroxide conductivity and sheet resistance of SPES, SPEEK, and SPES-X films (X=0, 30, 50, 60): The film samples were immersed in 3M NaOH solution for 48 hours, then sandwiched between two circular titanium sheets and connected to an electrochemical workstation (model: CHI760E). Hydroxide conductivity and sheet resistance were measured and calculated using the AC impedance method. The test frequency was 10 Hz. 3 -10 6 Hz, AC amplitude is 5 mV. Figure 10 The results showed that the hydroxide conductivity of the grafted membrane was higher than that of the pure SPES membrane and the SPEEK membrane. According to Donnan equilibrium, a high density of fixed negative charges usually repels mobile ions of the same charge, such as hydroxide ions. However, in this patent, the hydroxide conductivity was significantly improved by grafting acrylic acid groups onto the surface of the SPES membrane using ultraviolet light. This is likely due to the extremely high hydrophilicity and water retention capacity of the PAA layer, which constructs a continuous hydrogen bond network on the membrane surface and greatly promotes OH- ions through the Grotthuss mechanism. - The transport of ions is facilitated by the carboxyl groups on the membrane surface, which in turn promotes the transport of charge carriers rather than hinders it through electrostatic repulsion. Furthermore, the surface resistivity of the membrane is lower than that of pure SPES and SPEEK membranes during testing, and this change becomes more pronounced with prolonged illumination time. This trend aligns with the variation of the water contact angle, indicating that the carboxyl groups on the membrane surface improve the transmembrane transport capacity of charge carriers, enabling rapid ion transport.

[0081] Rate performance of SPES, SPEEK, and SPES-X films (X=0, 30, 50, 60) in alkaline zinc-iron flow batteries: The results were obtained using a flow battery testing system with an effective area of ​​4 cm². 2 The system consists of a membrane sample, two carbon felt electrodes, a pair of electrode frames, two conductive graphite plates, several seals, and two PTFE shells. The membrane sample is fixed to the electrode frames and sandwiched between the two electrodes to separate the anolyte (20 mL 0.4 M Fe(CN)6). 4- 3M NaOH solution) and cathode electrolyte (10 mL 0.4M Zn(OH)4) 2- (3M NaOH solution). Rate performance testing range is 40-200 mA cm⁻¹. -2The test used constant current charging and discharging, with a charging cutoff time set and a discharging cutoff voltage set to 0.1V. Figure 11 The results showed that at various current densities, the occurrence of ultraviolet grafting reaction improved the EE and VE of the battery, which was consistent with the test results of hydroxide conductivity. However, the membrane with excessively long illumination time would reduce the CE of the membrane. Taking all factors into consideration, SPES-50 had the best battery performance, which was significantly higher than that of SPES pure membrane and SPEEK membrane.

[0082] SPES, SPEEK, and SPES-X membranes (X=50) at 80 mA cm⁻¹ -2 Long-term cycle stability: SPES-50, which exhibited the best battery performance in the previous step, was selected and tested under the same conditions at 80 mA cm⁻¹. -2 Long-term cycling tests were conducted to verify its long-term stability. Figure 12 The results showed that the SPES-50 membrane was at 80 mA cm⁻¹ -2 The membrane operated stably for over 1900 cycles (1700 h) with an energy efficiency of over 86%, while the pure SPES membrane could only operate for 900 cycles with an energy efficiency of only 80%. The results show that UV grafting modification of the SPES membrane can significantly improve the membrane's performance in the battery, while also ensuring its long-term stable operation due to the regulatory effect of the negative charge on the membrane surface on zinc dendrites.

[0083] Matters not covered in this invention are common knowledge.

[0084] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A modified sulfonated polyethersulfone membrane, characterized in that, include: Sulfonated polyethersulfone matrix film; And a carboxyl-containing functional layer located on at least one side of the sulfonated polyethersulfone matrix membrane, wherein the carboxyl-containing functional layer is covalently grafted to the surface of the matrix membrane, thereby enabling the membrane to simultaneously possess both sulfonic acid groups and carboxyl groups, two types of anionic functional groups.

2. The modified sulfonated polyethersulfone film according to claim 1, characterized in that, The carboxyl-containing functional layer is a graft copolymer layer formed by graft polymerization of vinyl unsaturated carboxylic acid monomers under ultraviolet light; the vinyl unsaturated carboxylic acid monomers are selected from at least one of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and any combination thereof; the carboxyl groups in the carboxyl-containing functional layer are -COOH and / or -COO. - The form exists; and the carboxyl-containing functional layer is located on at least one of the two surfaces of the substrate membrane, preferably on both surfaces.

3. The modified sulfonated polyethersulfone film according to claim 1 or 2, characterized in that, The sulfonated polyethersulfone matrix membrane is obtained by introducing sulfonic acid groups into polyethersulfone through a sulfonation reaction, wherein the sulfonation reaction is carried out in a sulfonation system containing chlorosulfonic acid and / or sulfuric acid; the membrane is an ion-conducting membrane suitable for alkaline systems, preferably a hydroxide ion-conducting membrane, and the carboxyl-containing functional layer makes the membrane surface negatively charged, so as to generate electrostatic repulsion against negatively charged ions in the alkaline system, thereby inhibiting the formation tendency of zinc deposit dendrites.

4. The modified sulfonated polyethersulfone film according to any one of claims 1-3, characterized in that, The membrane is prepared by the method described in any one of claims 5-9.

5. A method for preparing the modified sulfonated polyethersulfone film according to claim 1, characterized in that, The process includes the following steps: (1) preparing a sulfonated polyethersulfone casting solution and forming a film to obtain a sulfonated polyethersulfone matrix film; (2) contacting the matrix film with a grafting solution containing vinyl unsaturated carboxylic acid monomers to wet the surface of the matrix film; (3) subjecting the wetted matrix film to ultraviolet irradiation to initiate a grafting reaction and forming a carboxyl-containing functional layer on the surface of the matrix film; (4) washing and drying the grafted film to obtain a modified sulfonated polyethersulfone film.

6. The method according to claim 5, characterized in that, The sulfonated polyethersulfone in step (1) is obtained by sulfonating polyethersulfone in a sulfonation system containing chlorosulfonic acid and / or sulfuric acid; the ratio of polyethersulfone to chlorosulfonic acid and sulfuric acid is 1 g : (1-3) mL : (5-20) mL; the sulfonation reaction temperature is 40-80℃, preferably 40-60℃; the reaction time is 3-10 h, preferably about 6 h.

7. The method according to claim 5 or 6, characterized in that, The solvent of the casting solution in step (1) is selected from at least one of amide polar aprotic solvents and sulfoxide solvents, preferably N,N-dimethylacetamide and / or dimethyl sulfoxide; the concentration of sulfonated polyethersulfone in the casting solution is 0.15-0.35 g / mL, preferably 0.18-0.30 g / mL, more preferably 0.20-0.25 g / mL; and the casting solution is dispersed before film formation, the dispersion treatment including ultrasonic treatment for 0.5-3 h and / or ball milling for 24-96 h, preferably ball milling for not less than 48 h.

8. The method according to any one of claims 5-7, characterized in that, In step (1), a film is formed by casting, and the gap between the doctor blades is 50-500 μm, preferably 100-300 μm, and more preferably about 200 μm; The drying process after film formation includes: pre-drying at 50-90℃ for 2-12 h for shaping, and then drying under vacuum at 100-150℃ to remove residual solvent.

9. The method according to any one of claims 5-8, characterized in that, The grafting solution in step (2) is a solution of vinyl unsaturated carboxylic acid monomers in a polar solvent, preferably containing water; the volume fraction of vinyl unsaturated carboxylic acid monomers in the grafting solution is 5%-40%, preferably 10%-30%, more preferably 15%-25%; the wavelength of ultraviolet irradiation in step (3) is 300-400 nm, preferably about 365 nm, the ultraviolet irradiation time is 5-120 min, preferably 10-90 min, more preferably 30-60 min, and the ultraviolet irradiation is carried out under the protection of an inert gas, the inert gas being selected from nitrogen and / or argon; in step (4), water washing is used until the pH of the washing solution is neutral or close to neutral, the drying temperature is 50-90℃, preferably 60-80℃, and the drying time is 6-24 h, preferably about 12 h; wherein the vinyl unsaturated carboxylic acid monomers are preferably acrylic acid, and the grafting solution is preferably a mixed solution of acrylic acid and water.

10. The application of the modified sulfonated polyethersulfone membrane according to any one of claims 1-4 in an alkaline zinc-iron flow battery, characterized in that, The modified sulfonated polyethersulfone membrane is used as an ion-conducting separator / isolation membrane between the positive and negative electrodes; preferably, it is used to improve battery voltage efficiency and energy efficiency and improve cycle stability under operating conditions with a current density of 40-200 mA·cm⁻². Preferably, the application is as a separator in an alkaline zinc-iron flow battery; The modified sulfonated polyethersulfone membrane is used to conduct hydroxide ions and inhibit zinc dendrite growth.

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