Ionic liquid / polymer composite membranes, their manufacturing methods, and applications

Abstract

The present invention discloses a method for producing ionic liquid / polymer composite membranes. A substrate containing at least one of polybenzimidazole and polybenzimidazole derivatives and an ionic liquid monomer containing an unsaturated double bond are uniformly mixed in a good solvent to obtain a casting solution. The casting solution is spread on a substrate and dried to remove the solvent, yielding a solid membrane. The solid membrane is then irradiated with ionizing radiation to induce polymerization / crosslinking of the ionic liquid, generating entanglement between the polyionic liquid molecular chains and the polymer molecular chains of the substrate, thereby immobilizing the ionic liquid within the substrate to form a composite membrane. The present invention also discloses ionic liquid / polymer composite membranes and their uses. This invention is the first to propose irradiating a solid membrane based on polybenzimidazole or a polybenzimidazole derivative with ionizing radiation to immobilize the ionic liquid component within the substrate. The resulting composite membrane exhibits excellent performance, is simple and safe to operate, and is suitable for industrial mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and more specifically, relates to an ionic liquid / polymer composite membrane, and a manufacturing method and use thereof.

Background Art

[0002] In batteries and electrochemical devices, the membrane is an important component that separates electrolytes and functions as a conductive discharge carrier to complete the internal circuit. The properties of the ion exchange membrane affect the performance and cost of the battery system. An ion exchange membrane that is inexpensive, durable, highly conductive, and low in permeability can significantly improve the performance of the battery and reduce the cost of the battery.

[0003] Compared with commercially available Nafion membranes (Nafion, registered trademark), polybenzimidazole (PBI)-based membranes not only have extremely low vanadium permeability after acidification due to their structural characteristics, but also have excellent chemical stability and mechanical strength. However, due to its dense structure and the donation effect after acidification, the proton transport efficiency is extremely low. Therefore, the modification of polybenzimidazole membranes mainly aims to improve their proton transport ability. Ionic liquids are room temperature molten salts, and due to their excellent electrochemical properties, their applications in the field of separators for fuel cells and vanadium flow batteries have attracted extensive attention in recent years. Some researchers have used ionic liquids to construct proton transport paths and can improve the conductivity of ion exchange membranes through the Grotthuss mechanism and vehicle transfer mechanism. However, in current research, it has been found that the binding force between ionic liquid monomers and PBI is weak, and leakage of ionic liquids is likely to occur during use, which affects the practical life and application efficiency of ion exchange membranes.

[0004] CN106558717B discloses a high-temperature composite proton exchange membrane for fuel cells and a method for producing it. In this method, polybenzimidazole and an ionic liquid are directly dissolved in an organic solvent to obtain a mixed solution, which is then cast to form a film to obtain a high-temperature composite proton exchange membrane for fuel cells. However, the formed ionic liquid / polymer membrane system is unstable, and the ionic liquid is prone to leakage.

[0005] CN107248583A discloses a crosslinked polybenzimidazole-polyionic liquid high-temperature proton exchange membrane and a method for producing it. In this membrane, a crosslinking agent is added to a mixed solution of polybenzimidazole and an imidazole-based polyionic liquid derived from polybenzimidazole, and then a crosslinking reaction is induced at high temperature to introduce a polyionic liquid structure into the polymer matrix of fluorine-containing polybenzimidazole. The polyionic liquid is then bonded to the polymer by covalent crosslinking, thereby preventing the leakage of the ionic liquid.

[0006] Unlike substrates such as PVDF, polybenzimidazole (PBI) and its derivatives exhibit high radiation stability and are less likely to generate free radicals. Therefore, those skilled in the art typically cannot immobilize polyionic liquids onto PBI using radiation grafting techniques. To date, there have been no reports of successful covalent bonding of ionic liquids containing unsaturated double bonds to PBI via graft polymerization using ionizing radiation technology. Existing technologies have various limitations, and there is a need to develop structurally stable ionic liquid / PBI polymer composite ion exchange membranes that are easy to manufacture, low-cost, perform well, and have high retention rates for ionic liquids. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In consideration of the above-mentioned shortcomings or the need for improvement of the prior art, the present invention provides an ionic liquid / polymer composite membrane, a method for producing the same, and its applications, with the objective of providing a polyionic liquid / polymer composite membrane and a method for producing the same that is easy to operate, suitable for industrial production, and has excellent performance. [Means for solving the problem]

[0008] To achieve the above objective, according to one aspect of the present invention, a method for manufacturing an ionic liquid / polymer composite membrane is provided. The method for manufacturing the ionic liquid / polymer composite membrane is as follows: A polymer substrate containing at least one of polybenzimidazole or a derivative of polybenzimidazole is homogeneously mixed with an ionic liquid monomer containing an unsaturated double bond in a good solvent to obtain a cast solution. The steps include spreading the aforementioned casting solution onto a substrate, drying it to remove the solvent, and obtaining a solid film, The steps include: irradiating the solid film with ionizing radiation to induce the ionic liquid monomers by the ionizing radiation, forming a polyionic liquid and its crosslinked products inside the substrate, generating physical entanglement between the molecular chains of the polyionic liquid and the molecular chains of the substrate, thereby fixing the ionic liquid components in the polymer substrate and forming a composite film; Includes.

[0009] In one embodiment, the irradiated solid film is further washed and protonated to form an ionic liquid / polymer composite ion exchange film.

[0010] In one embodiment, the derivative of polybenzimidazole is at least one of diphenyl ether polybenzimidazole, diphenyl sulfonyl polybenzimidazole, poly[2,5-benzimidazole], and fluorine-containing polybenzimidazole.

[0011] In one embodiment, the anion of the ionic liquid monomer is at least one of tetrafluoroborate ions, bromide ions, chloride ions, or nitrate ions, and the cation is vinylimidazolium or alliimidazolium containing a double bond.

[0012] In one embodiment, the mass of the ionic liquid monomer is 10 to 200% of the mass of the base material, preferably 50% to 100%.

[0013] In one embodiment, the good solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0014] In one embodiment, the substrate is further mixed with inorganic nanoparticles, the inorganic nanoparticles comprising at least one of graphene, mesoporous carbon, functionalized carbon nanotubes, and two-dimensional transition metal carbon / nitrogen compounds.

[0015] In one embodiment, the ionizing radiation is gamma-ray radiation, electron beam radiation, or X-ray radiation, and the irradiation dose of the ionizing radiation is in the range of 10 kGy to 300 kGy, preferably in the range of 80 kGy to 200 kGy.

[0016] According to another aspect of the present invention, an ionic liquid / polymer composite film is provided, comprising a polymer substrate and a polyionic liquid fixed to the substrate by entanglement with the molecular chains of the substrate, wherein the polymer substrate comprises at least one of polybenzimidazole and a derivative of polybenzimidazole, and the polyionic liquid is formed by polymerizing an ionic liquid monomer containing an unsaturated double bond.

[0017] Another aspect of the present invention provides an application for the ionic liquid / polymer composite membrane, characterized in that the ionic liquid / polymer composite membrane is used as an electrolyte separator in an all-vanadium flow battery or fuel cell. [Effects of the Invention]

[0018] Compared to conventional technologies, the above-described technical means of the present invention can achieve the following beneficial effects.

[0019] Because polybenzimidazole (PBI) and its derivatives have high radiation stability, those skilled in the art would not normally conceive of using ionizing radiation techniques to immobilize ionic liquids containing unsaturated double bonds on a PBI matrix. In this invention, a PBI substrate and an ionic liquid monomer containing unsaturated double bonds are uniformly mixed with a solvent to prepare a cast solution, which is then spread and the solvent is evaporated to form a solid film. At this time, the ionic liquid monomer is uniformly dispersed in the substrate. Next, the solid film is irradiated with ionizing radiation, and experimental results show that during irradiation, the ionic liquid monomer dispersed in the substrate polymerizes to form a crosslinked structure, and because the ionic liquid is uniformly dispersed in the substrate, physical entanglement occurs between the molecular chains of the polyionic liquid and the molecular chains of the polymer in the substrate, forming a composite film. In the technical means of this invention, as the molecular weight of the polyionic liquid increases, chemical bonds are more easily formed between the contained ionic liquid units and the polymer, or molecular entanglement occurs more directly, and the structural properties become more stable. Furthermore, experiments confirmed that the polyionic liquid in the resulting composite film is strongly bonded to the substrate, making leakage of the ionic liquid difficult. Breaking away from conventional thinking, this invention solves the problem that ionic liquid monomers and PBI substrates cannot be directly introduced by graft polymerization using ionizing radiation technology. First, the ionic liquid monomer and substrate are uniformly dispersed in a cosolvent to form a film. Next, radiation is irradiated into the solid film to achieve polymerization / crosslinking of the ionic liquid, and finally, the polymer molecular chains in the substrate become physically intertwined, forming a composite film. Achieving the production of composite films in a solid state using ionizing radiation technology is easier and safer to control compared to solid-liquid graft reactions or liquid-liquid graft reactions in the liquid phase, making it suitable for industrial mass production and offering promising industrial applications. [Brief explanation of the drawing]

[0020] [Figure 1] This flowchart shows the steps for a method of producing an ionic liquid / polymer composite film in one embodiment. [Figure 2] This is a schematic diagram showing the entanglement of the polyionic liquid and the substrate after irradiation in one embodiment. [Figure 3] It is a schematic diagram of the structure of the composite membrane after adding nanoparticles in one embodiment. [Figure 4] It shows the change in the absorption peak in the range of 2000 - 1400 cm-1 of the PIL / PBI composite membrane of Example 1 before and after irradiation. [Figure 5] SEM images of the microstructure of the composite membranes obtained under different conditions. (a) SEM image of the microstructure of PBI without adding PIL. (b) SEM image of the microstructure of the unirradiated PIL / PBI composite membrane. (c) SEM image of the microstructure of the irradiated PIL / PBI composite membrane of Example 1. [Figure 6] It is a comparison diagram of the vanadium permeability of the irradiated PIL / PBI composite membrane of Example 1 and the commercially available Nafion 115 membrane. [Figure 7] It is a comparison diagram of the cell efficiency at different current densities of the cell assembled using the irradiated PIL / PBI composite membrane of Example 1 and the commercially available Nafion 115 membrane. (a) Coulomb efficiency curve at different current densities. (b) Voltage efficiency curve at different current densities. (c) Energy efficiency curve at different current densities.

Embodiments for Carrying out the Invention

[0021] To make the objectives, technical means and advantages of the present invention clearer, the present invention will be described in more detail below by referring to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used for explaining the present invention and are not intended to limit the present invention. Also, the technical features related to the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] As shown in FIG. 1, the method for manufacturing an ionic liquid / polymer composite membrane according to an embodiment of the present invention mainly includes the following steps.

[0023] In step S100, a polymer substrate and an ionic liquid monomer containing an unsaturated double bond are homogeneously mixed in a good solvent to obtain a cast solution. The polymer substrate contains at least one of polybenzimidazole or a derivative of polybenzimidazole.

[0024] Both the base material and the ionic liquid monomer are solids, and they are dissolved in a good solvent and mixed uniformly. The amount of ionic liquid used is 1% to 200% of the mass of the base material, preferably 50% to 100%.

[0025] The base material may contain polybenzimidazole (PBI) or its derivatives. Specifically, the derivative of polybenzimidazole can be selected from at least one of diphenyl ether polybenzimidazole (OPBI), diphenyl sulfonyl polybenzimidazole, poly[2,5-benzimidazole] (ABPBI), fluorine-containing polybenzimidazole (6FPBI), or from composites of the above PBI and its derivatives with other polymer materials. Polybenzimidazole (PBI) is preferred as the base material.

[0026] Ionic liquid monomers are doping substances that need to be immobilized in composite films. They often consist of ionic liquids that have inorganic anions and organic cations, are hydrophilic, and contain unsaturated double bonds. When irradiated with ionizing radiation, they can cleave and undergo polymerization reactions. Specifically, examples of anions in ionic liquid monomers include tetrafluoroborate ions, bromide ions, chloride ions, or nitrate ions, while examples of cations in ionic liquid monomers include vinylimidazolium or alliimidazolium, which contain double bonds.

[0027] A good solvent is one that can dissolve the substrate and the ionic liquid monomer and can be removed during curing and film formation. Specifically, it can be selected from organic solvents such as N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylformamide. When dissolved in a good solvent, the ionic liquid monomer does not undergo polymerization reactions, but subsequently polymerizes over a wide area to form a polyionic liquid when irradiated with ionizing radiation.

[0028] In step S200, the casting solution is spread onto the substrate, dried to remove the solvent, and a solid film is obtained.

[0029] After obtaining a mixed casting solution, the casting solution is directly deposited into a film. Specifically, the film is formed by casting using a casting method, and after removing the solvent by ultrasonic degassing and heat drying, a solid film is obtained. At this time, all materials are solid, no liquid substances are present, and the ionic liquid monomer is dispersed in the substrate. Specifically, the thickness of the solid film can be controlled to 10 to 200 μm, preferably 10 to 50 μm.

[0030] In step S300, the solid film is irradiated with ionizing radiation to induce ionic liquid monomers, which in turn form a polyionic liquid and its crosslinked counterparts within the substrate. This creates a physical entanglement between the molecular chains of the polyionic liquid and the molecular chains of the substrate, fixing the ionic liquid components within the polymer substrate and forming a composite film.

[0031] Polybenzimidazole (PBI) and its derivatives are generally known to have high radiation stability, and those skilled in the art would not typically conceive of using ionizing radiation techniques to immobilize ionic liquids containing unsaturated double bonds on a PBI matrix. In this invention, it has been found that ionic liquid monomers within a solid film undergo polymerization reactions during ionizing radiation irradiation. Therefore, in this invention, step S300 is performed, irradiating a cured solid film with ionizing radiation to polymerize the ionic liquid monomers dispersed in the substrate, forming a polyionic liquid (PIL) and its crosslinked structure. The immobilization of the ionic liquid is achieved by utilizing the entanglement between the polyionic liquid and the polymer molecular chains in the substrate, and the crosslinked structure of the polyionic liquid.

[0032] Specifically, as shown in Figure 2, after film formation in step S200, the solidified film contains PBI polymer molecular chains and ionic liquid monomer VEImBr dispersed within the PBI polymer molecular chains. After irradiation with ionizing radiation EB, the ionic liquid monomer VEImBr polymerizes to form polyionic liquid PVEImBr. Because the PVEImBr chains and PBI chains are intertwined, the polyionic liquid is fixed in the substrate, preventing leakage from the composite film.

[0033] In one embodiment, the ionizing radiation can be selected from gamma-ray radiation, electron beam radiation, or X-ray radiation. The irradiation dose of the ionizing radiation can be 10 kGy to 300 kGy, preferably 80 kGy to 200 kGy. If the irradiation dose is too high, the structure of the material will be destroyed and its performance will be affected, and if the irradiation dose is too low, polymerization of the ionic liquid monomer will be difficult.

[0034] In one embodiment, in step S100, inorganic nanoparticles can be added to the casting solution, i.e., the substrate, ionic liquid monomer, and inorganic nanoparticles are dissolved in a good solvent. By adding nanoparticles, the ionic liquid forms crosslinks and entanglements during irradiation, encapsulating and fixing the added conductive nanoparticles, further improving the electrochemical properties of the composite film. As shown in Figure 3, after film formation in step S200, the solid film contains molecular chains of PBI polymer, ionic liquid monomer VEImBr dispersed within the molecular chains of PBI polymer, and nanoparticles MXene. After irradiation with ionizing radiation EB, the ionic liquid monomer VEImBr polymerizes to ultimately produce a PBI / PIL composite film based on the PBI / PIL composite film, doped and modified with MXene. This further reduces leakage of the ionic liquid while improving the electrochemical properties of the composite film through the properties of the nanomaterial itself. Specifically, the nanoparticles can be selected from materials such as graphene, mesoporous carbon, functionalized carbon nanotubes, and two-dimensional transition metal carbon / nitrogen compounds.

[0035] In the above method for manufacturing an ionic liquid / polymer composite film, the raw materials are first uniformly mixed with a solvent, then spread and cured to disperse the ionic liquid monomer in the substrate, and finally, the ionic liquid monomer is polymerized by irradiation with ionizing radiation, creating entanglement between the molecular chains of the polyionic liquid and the molecular chains of the substrate, thereby achieving fixation of the ionic liquid. Each step of the above method is interrelated and acts synergistically, resulting in a composite film with stable performance that effectively prevents leakage of the ionic liquid. Furthermore, the production of composite films in a solid state using the ionizing radiation technology proposed in this invention is easier to control and suitable for industrial mass production.

[0036] Accordingly, the present invention also relates to an ionic liquid / polymer composite membrane obtained by the above method. The composite membrane comprises a substrate and a polyionic liquid and its crosslinked structure fixed to the substrate by entanglement with the molecular chains of polymers in the substrate. The polyionic liquid is formed by polymerization of ionic liquid monomers, and the selection of the substrate and ionic liquid monomer has been described above and will not be repeated here. In one embodiment, the polyionic liquid / polymer composite membrane further comprises nanoparticles that can be fixed within the polyionic liquid / polymer composite membrane after irradiation to improve the conductivity of the membrane.

[0037] Accordingly, the present invention also relates to the application of the above-mentioned ionic liquid / polymer composite membrane, after protonation treatment, to an ionic liquid / polymer composite membrane used as an electrolyte separator in a total vanadium flow battery or fuel cell. In an ionic liquid / polymer composite ion exchange membrane, the ionic liquid is strongly bonded to the substrate by entanglement, making it less likely to leak into the electrolyte, and thus significantly improving the performance of the battery.

[0038] The present invention will be described below with reference to specific examples.

[0039] Example 1 (1) 0.5 g of polybenzimidazole (PBI) and 0.5 g of 1-vinyl-3-ethylimidazolium bromide were placed in a 25 mL beaker, then 9 g of N,N-dimethylacetamide was added, and the mixture was stirred at 60°C for 24 hours to form a 5% mass fraction cast solution. After removing air bubbles by sonication for 1 hour, the solution was placed upside down on a clean glass plate and left for 5-10 minutes, then dried at 60°C for 24 hours to form a film.

[0040] (2) The solid film from step (1) was placed in a polyethylene bag, spread flat, and vacuum-sealed. Then, it was irradiated with an electron beam with an absorbed dose of 80 kGy to obtain a composite film. The irradiated composite film was immersed in deionized water for 3 days to obtain a composite ion exchange film.

[0041] (3) Performance testing of composite ion exchange membranes To study the crosslinking mechanism of polymerizable ionic liquids under irradiation conditions, infrared tests were performed on a simple PBI film, a composite VImBr / PBI film obtained after irradiation in step (2), and an unirradiated VImBr / PBI solid film in step (2). As shown in Figure 4, after irradiation, at 1600 cm², -1 The amplitude of the characteristic absorption peak at -C=C- was significantly reduced, indicating that the ionic liquid containing unsaturated double bonds was cross-linked after irradiation.

[0042] To compare the leakage of ionic liquid before and after irradiation, the composite membrane was immersed in a 3M sulfuric acid solution for 3 days, and the ionic liquid retention rate of the composite membrane at two different ratios before and after irradiation was measured. The results are shown in Table 1 below.

[0043] Table 1. Ionic liquid retention rates of composite films with different ratios before and after irradiation. JPEG0007884302000001.jpg20168

[0044] Ionic liquid retention rate = The image is JPEG0007884302000002.jpg935, where m1 is the mass of the film before immersion and m2 is the mass of the dried film after immersion. As shown in Table 1, when the ionic liquid content is 50% of the substrate, the ionic liquid retention rate of the unirradiated composite film is 26.85%, and when the absorbed dose is 160 kGy, the ionic liquid retention rate is 64.93%. When the ionic liquid content is 100% of the substrate, the ionic liquid retention rate of the unirradiated composite film is 41.86%, and when the absorbed dose is 160 kGy, the ionic liquid retention rate is 81.97%. It has been shown that the manufacturing method proposed in this invention can effectively improve the retention rate of the ionic liquid and reduce ionic liquid leakage.

[0045] As shown in Figure 5, an SEM image of the microstructure of the composite film produced in Example 1 is shown. The figure shows that the composite film is a homogeneous phase film, indicating good compatibility between the ionic liquid and PBI, and that no phase separation occurs.

[0046] The conductivity of the composite film produced in Example 1 was measured. A 3cm × 1cm composite film was immersed in a 1M H2SO4 solution and left to stand for 24 hours. After wiping off the surface moisture, it was placed on two copper plates 1cm apart and sandwiched between them. The AC impedance curve was then measured using an electrochemical workstation, and the calculated conductivity was 77.57 mS / cm, indicating that the composite film produced in this invention has good conductivity.

[0047] The vanadium permeability of the composite film produced in Example 1 was measured. The film was sandwiched between two electrolytic cells; the left electrolytic cell contained a 2M sulfuric acid solution of 1.5M vanadyl sulfate, and the right electrolytic cell contained a 2M sulfuric acid solution of 1.5M magnesium sulfate. The vanadium ion concentration in the right electrolytic cell was recorded over 7 days, and the vanadium ion permeability was measured to 3.70 × 10⁻⁶. -3 The value was calculated as mg / (L·min). On the other hand, when comparing the composite film PVE ImBr / PBI film of the present invention with the currently commercially available Nafion 115 film, as shown in Figure 6, the vanadium permeability of the composite film produced in Example 1 after 7 days was approximately 1 / 48 of that of the Nafion 115 film, demonstrating that lower vanadium permeability was achieved in the present invention.

[0048] The composite film obtained in Example 1 was protonated to obtain a PIL / PBI composite film with a swelling degree of 19%. This PIL / PBI composite film was incorporated into a battery, and the 100 mA·cm² of this PIL / PBI composite film and the currently commercially available Nafion 115 film was measured. -2 The Coulomb efficiency, energy efficiency, and voltage efficiency of the battery were measured. As shown in Figure 7, the PIL / PBI composite film obtained in this embodiment had a yield of 100 mA·cm². -2 The battery exhibited a Coulomb efficiency of 98.24%, an energy efficiency of 80.27%, and a voltage efficiency of 82.23%, and its electrochemical properties were superior to those of commercially available Nafion 115 films.

[0049] Example 2 A PIL / PBI composite film was obtained using the same manufacturing method as in Example 1, except that the ionic liquid monomer was changed to 1-allyl-3-ethylimidazolium chloride. The performance of the obtained PIL / PBI composite film was equivalent to that of Example 1.

[0050] Example 3 A PIL / PBI composite film was obtained using the same manufacturing method as in Example 1, except that the polymer was changed to diphenyl ether polybenzimidazole (OPBI). The performance of the obtained PIL / PBI composite film was equivalent to that of Example 1.

[0051] Example 4 A PIL / PBI composite film was obtained using the same manufacturing method as in Example 1, except that the solvent was changed from DMAc to NMP. The performance of the obtained PIL / PBI composite film was equivalent to that of Example 1.

[0052] Comparative Example 1 Polybenzimidazole (PBI) solid powder was mixed with an imidazolium-based ionic liquid solution containing 20-100% unsaturated double bonds (for example, the hydrophilic ionic liquid was selected from 1-vinyl-3-ethylimidazolium bromide or 1-allyl-3-ethylimidazolium chloride, and the hydrophobic ionic liquid was selected from 1-vinyl-3-butylimidazole tetrafluoroborate or 1-vinyl-3-octylimidazole tetrafluoroborate), and co-irradiated with an electron beam under irradiation doses of 10 kGy to 300 kGy. After completion, the ionic liquid monomer and the homopolymers produced under the irradiation conditions were washed away with ethanol and water. Comparison of the mass of the polybenzimidazole substrate showed no change in mass, indicating that the ionic liquid containing unsaturated double bonds cannot be grafted onto polybenzimidazole. Furthermore, thermogravimetric analysis of the PBI substrate surface before and after irradiation grafting revealed that the ionic liquid component was not properly introduced onto the PBI substrate.

[0053] Comparative Example 2 Polybenzimidazole (PBI) solid powder was irradiated with an electron beam in a nitrogen atmosphere at -20°C, with an irradiation dose of 10 kGy to 300 kGy. After irradiation, the PBI powder monomer was added to a pre-deoxygenated imidazolium-based ionic liquid solution containing 20-100% unsaturated double bonds (for example, the hydrophilic ionic liquid was selected from 1-vinyl-3-ethylimidazolium bromide or 1-allyl-3-ethylimidazolium chloride, and the hydrophobic ionic liquid was selected from 1-vinyl-3-butylimidazole tetrafluoroborate or 1-vinyl-3-octylimidazole tetrafluoroborate), and reacted at 40-60°C for 24 hours. The ionic liquid monomer and the homopolymer produced under the irradiation conditions were washed away using ethanol and water. A comparison of the masses of the polybenzimidazole substrates revealed that the mass did not change, indicating that ionic liquids containing unsaturated double bonds cannot be grafted onto polybenzimidazole. Furthermore, thermogravimetric analysis of the PBI substrate surface before and after irradiation grafting revealed that the ionic liquid components were not successfully introduced onto the PBI substrate.

[0054] As can be seen from Comparative Examples 1 and 2, polybenzimidazole (PBI) is difficult to modify with radiation, meaning that grafting of ionic liquids with polybenzimidazole (PBI) using ionizing radiation is difficult. This is also why ionizing radiation is not used in the production of ionic liquid / polymer composite films based on polybenzimidazole (PBI). In this invention, breaking away from conventional thinking, the problem that ionic liquid monomers and PBI substrates cannot be directly introduced by graft polymerization using ionizing radiation technology is solved. First, the ionic liquid monomer and substrate are uniformly dispersed in a cosolvent to form a coating film. Next, radiation is irradiated in the state of a solid film to achieve polymerization / crosslinking of the ionic liquid, and finally, the polymer molecular chains in the substrate become physically intertwined with the ionic liquid to form a composite film. Achieving the production of composite films in a solid state using ionizing radiation technology is easier and safer to control compared to solid-liquid graft reactions or liquid-liquid graft reactions in the liquid phase, making it suitable for industrial mass production and offering promising industrial applications.

[0055] The above examples confirm that the composite film obtained by the present invention has excellent performance, that the control of radiation reactions in the solid film state proposed in the present invention is simpler, and that it is advantageous for industrial mass production.

[0056] It will be readily apparent to those skilled in the art that the above describes only preferred embodiments of the present invention and does not limit it. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for producing an ionic liquid / polymer composite membrane, A polymer substrate containing at least one of polybenzimidazole or a derivative of polybenzimidazole and an ionic liquid monomer containing an unsaturated double bond are uniformly mixed in a good solvent to obtain a cast solution. The steps include spreading the aforementioned casting solution onto a substrate, drying it to remove the solvent, and obtaining a solid film, The steps include: irradiating the solid film with ionizing radiation to induce the ionic liquid monomers by the ionizing radiation, forming a polyionic liquid and its crosslinked products inside the polymer substrate, generating physical entanglement between the molecular chains of the polyionic liquid and the molecular chains of the polymer substrate, thereby fixing the ionic liquid components in the polymer substrate and forming a composite film; A method for producing an ionic liquid / polymer composite membrane, characterized by containing the following:

2. A method for producing an ionic liquid / polymer composite membrane according to claim 1, further comprising the step of washing and protonating the irradiated solid membrane to form an ionic liquid / polymer composite ion exchange membrane.

3. The method for producing an ionic liquid / polymer composite film according to claim 1, characterized in that the derivative of polybenzimidazole is at least one of diphenyl ether polybenzimidazole, diphenyl sulfonyl polybenzimidazole, poly[2,5-benzimidazole], and fluorine-containing polybenzimidazole.

4. The method for producing an ionic liquid / polymer composite film according to claim 1, characterized in that the anion of the ionic liquid monomer is at least one of tetrafluoroborate ions, bromide ions, chloride ions, or nitrate ions, and the cation is vinylimidazolium or alliimidazolium containing a double bond.

5. A method for producing an ionic liquid / polymer composite film according to claim 1, characterized in that the mass of the ionic liquid monomer is 10 to 200% of the mass of the substrate.

6. The method for producing an ionic liquid / polymer composite film according to claim 1, characterized in that the good solvent contains at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

7. The method for producing an ionic liquid / polymer composite film according to claim 1, wherein the substrate is further mixed with inorganic nanoparticles, and the inorganic nanoparticles include at least one of graphene, mesoporous carbon, functionalized carbon nanotubes, and two-dimensional transition metal carbon / nitrogen compounds.

8. The method for producing an ionic liquid / polymer composite film according to claim 1, characterized in that the ionizing radiation is gamma-ray radiation, electron beam radiation, or X-ray radiation, and the irradiation dose of the ionizing radiation is in the range of 10 kGy to 300 kGy.

9. The material comprises a polymer substrate, a polyionic liquid fixed to the polymer substrate by physical entanglement with the molecular chains of the polymer substrate, and a crosslinked structure of the polyionic liquid. The ionic liquid / polymer composite membrane is characterized in that the polymer substrate comprises at least one of polybenzimidazole and a derivative of polybenzimidazole, and the polyionic liquid is formed by polymerizing an ionic liquid monomer containing an unsaturated double bond.

10. An application of the ionic liquid / polymer composite membrane, characterized in that the ionic liquid / polymer composite membrane described in claim 9 is used as an electrolyte separator in an all-vanadium flow battery or fuel cell.

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