Ionic liquid / polymer composite membrane and its manufacturing method and application

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 relates to the technical field of battery separators, and more particularly to ionic liquid / polymer composite membranes, and their preparation methods and applications. [Background technology]

[0002] In batteries and electrochemical devices, membranes are important components that separate electrolytes and function as conductive discharge carriers to complete the internal circuit. The properties of ion exchange membranes affect the performance and cost of battery systems. Inexpensive, durable ion exchange membranes with high conductivity and low permeability can significantly improve battery performance and reduce battery costs.

[0003] Compared to commercially available Nafion® membranes, polybenzimidazole (PBI)-based membranes not only exhibit extremely low vanadium permeability after acidification due to their structural characteristics, but also have excellent chemical stability and mechanical strength. However, their dense structure and the Donnan effect after acidification result in extremely low proton transport efficiency. Therefore, the primary purpose of modifying PBI membranes is to improve their proton transport capacity. Ionic liquids are room-temperature molten salts, and their excellent electrochemical properties have recently attracted widespread attention for their application in fuel cells and vanadium flow battery separators. Some researchers have used ionic liquids to construct proton transport pathways and improve the conductivity of ion-exchange membranes through the Grotthuss mechanism and the vehicle transmission mechanism. However, current research has revealed that the binding strength between ionic liquid monomers and PBI is weak, which makes ionic liquids prone to leakage during use, affecting the service 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 its preparation. Polybenzimidazole and an ionic liquid are directly dissolved in an organic solvent to obtain a mixed solution, which is then cast into a membrane to obtain a high-temperature composite proton exchange membrane for fuel cells. However, the resulting ionic liquid / polymer membrane system is unstable, and the ionic liquid is prone to leak.

[0005] CN107248583A discloses a high-temperature proton exchange membrane made of crosslinked polybenzimidazole and polyionic liquid, and a method for preparing the same. A crosslinking agent is added to a mixed solution of polybenzimidazole and an imidazole-based polyionic liquid derived from polybenzimidazole, followed by a crosslinking reaction at high temperature to introduce a polyionic liquid structure into the fluorine-containing polybenzimidazole polymer matrix, and the polyionic liquid is covalently crosslinked to the polymer, thereby preventing the ionic liquid from leaking out.

[0006] Unlike substrates such as PVDF, polybenzimidazole (PBI) and its derivatives are highly radiation stable and less susceptible to free radical generation. Therefore, practitioners generally have difficulty immobilizing polyionic liquids onto PBI using radiation grafting techniques. To date, there have been no reports of successful covalent grafting of ionic liquids containing unsaturated double bonds onto PBI using ionizing radiation techniques. Existing techniques have various limitations, making it necessary to develop structurally stable ionic liquid / PBI polymer composite ion exchange membranes that are simple to fabricate, inexpensive, have excellent performance, and offer high ionic liquid retention. Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above-mentioned shortcomings or needs for improvement in the prior art, the present invention provides an ionic liquid / polymer composite membrane and its manufacturing method and use. The objective of the present invention is to provide a polyionic liquid / polymer composite membrane and its manufacturing method that is simple to operate, suitable for industrial production, and has excellent performance. [Means for solving the problem]

[0008] In order to achieve the above object, according to one aspect of the present invention, there is provided a method for producing an ionic liquid / polymer composite membrane, the method comprising the steps of: a step of uniformly mixing a polymer substrate containing at least one of polybenzimidazole and a polybenzimidazole derivative with an ionic liquid monomer containing an unsaturated double bond in a good solvent to obtain a casting solution; spreading the casting solution onto a substrate and drying it to remove the solvent and obtain a solid film; irradiating the solid film with ionizing radiation, inducing the ionic liquid monomers by the ionizing radiation to form polyionic liquid and its crosslinked products within the substrate, and causing physical entanglement between the molecular chains of the polyionic liquid and the molecular chains of the substrate, thereby immobilizing the ionic liquid components in the polymer substrate and forming a composite film; Includes:

[0009] In one embodiment, the method further comprises washing and protonating the irradiated solid membrane to form an ionic liquid / polymer composite ion exchange membrane.

[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, bromide, chloride, or nitrate, and the cation is a vinylimidazolium or allylimidazolium containing a double bond.

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

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

[0014] In one embodiment, the substrate is further admixed 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 any one of gamma ray radiation, electron beam radiation, or X-ray radiation, and the exposure 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] Another aspect of the present invention provides an ionic liquid / polymer composite membrane comprising a polymer substrate, and a polyionic liquid and its crosslinked structure immobilized on the substrate by entanglement with molecular chains of the substrate, wherein the polymer substrate comprises at least one of polybenzimidazole and polybenzimidazole derivatives, and the polyionic liquid is formed by polymerizing an ionic liquid monomer containing an unsaturated double bond.

[0017] According to yet another aspect of the present invention, there is provided a use of the ionic liquid / polymer composite membrane, wherein 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 with the prior art, the above 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 consider using ionizing radiation techniques to immobilize ionic liquids containing unsaturated double bonds onto PBI matrices. In the present invention, a PBI substrate and an ionic liquid monomer containing unsaturated double bonds are homogeneously mixed in a solvent to prepare a casting solution. The casting solution is then spread to evaporate the solvent, forming a solid film. At this stage, the ionic liquid monomer is uniformly dispersed throughout the substrate. The solid film is then irradiated with ionizing radiation. Experiments have shown that during irradiation, the ionic liquid monomer dispersed in the substrate polymerizes to form a crosslinked structure. Furthermore, because the ionic liquid is uniformly dispersed throughout the substrate, physical entanglement occurs between the molecular chains of the polyionic liquid and the molecular chains of the polymer in the substrate, resulting in the formation of a composite film. With the technical solution of the present invention, as the molecular weight of the polyionic liquid increases, chemical bonds are more likely to form between the ionic liquid units and the polymer, or molecular entanglement occurs more easily, resulting in more stable structural properties. Experiments also confirmed that the polyionic liquid in the resulting composite membrane was tightly bound to the substrate, preventing leakage. This invention overcomes the conventional wisdom, addressing the inability to directly introduce ionic liquid monomers and PBI substrates via ionizing radiation graft polymerization. Instead, the ionic liquid monomer and substrate are uniformly dispersed in a cosolvent to form a membrane. The solid membrane is then irradiated with radiation to polymerize and crosslink the ionic liquid, which ultimately physically entangles with the polymer chains in the substrate to form a composite membrane. Compared to liquid-phase solid-liquid and liquid-liquid grafting reactions, the use of ionizing radiation to produce composite membranes in the solid state offers a simpler and safer process, making it suitable for industrial mass production and promising for industrial applications. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a flowchart illustrating steps in a method for making an ionic liquid / polymer composite membrane in one embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating entanglement of a polyionic liquid with a substrate after irradiation in one embodiment. [Figure 3] FIG. 1 is a structural schematic diagram of a composite membrane after adding nanoparticles in one embodiment. [Figure 4] 1 shows the change in the absorption peak in the range of 2000 to 1400 cm −1 of the PIL / PBI composite film of Example 1 before and after irradiation. [Figure 5] SEM images of the microstructure of composite membranes obtained under different conditions: (a) SEM image of the microstructure of PBI without PIL addition; (b) SEM image of the microstructure of an unirradiated PIL / PBI composite membrane; and (c) SEM image of the microstructure of the PIL / PBI composite membrane after irradiation in Example 1. [Figure 6] FIG. 1 is a comparison diagram of vanadium permeability between the PIL / PBI composite membrane after irradiation in Example 1 and a commercially available Nafion 115 membrane. [Figure 7] FIG. 10 is a comparison of the cell efficiency at different current densities of a battery assembled using the irradiated PIL / PBI composite membrane of Example 1 and a commercially available Nafion 115 membrane: (a) Coulombic efficiency curves at different current densities; (b) voltage efficiency curves at different current densities; and (c) energy efficiency curves at different current densities. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to clarify the objectives, technical means and advantages of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features according to various embodiments of the present invention described below can be combined with each other unless they are mutually inconsistent.

[0022] As shown in FIG. 1, the method for preparing an ionic liquid / polymer composite membrane according to one 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 mixed uniformly in a good solvent to obtain a casting solution. The polymer substrate contains at least one of polybenzimidazole and a polybenzimidazole derivative.

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

[0025] The substrate may contain polybenzimidazole (PBI) or a derivative thereof. Specifically, the polybenzimidazole derivative may be selected from at least one of diphenylether polybenzimidazole (OPBI), diphenylsulfonyl polybenzimidazole, poly[2,5-benzimidazole] (ABPBI), fluorine-containing polybenzimidazole (6FPBI), etc., or a composite of the above PBI or its derivative with other polymer materials. Polybenzimidazole (PBI) is preferred as the substrate.

[0026] The ionic liquid monomer is a doping substance that needs to be fixed in the composite membrane. It has an inorganic anion and an organic cation, and is often a hydrophilic ionic liquid containing an unsaturated double bond. When irradiated with ionizing radiation, the ionic liquid monomer cleaves and undergoes polymerization. Specifically, the anion of the ionic liquid monomer can be a tetrafluoroborate ion, a bromide ion, a chloride ion, or a nitrate ion, and the cation of the ionic liquid monomer can be a vinylimidazolium or allylimidazolium ion containing a double bond.

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

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

[0029] After obtaining the mixed casting solution, the casting solution is directly formed into a film, specifically, by casting to form a film, and after ultrasonic degassing and heat drying to remove the solvent, 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, which induces the ionic liquid monomer to form a polyionic liquid and its crosslinked product within the substrate, thereby physically entangling the molecular chains of the polyionic liquid with the molecular chains of the substrate, thereby immobilizing the ionic liquid components in 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 normally consider using ionizing radiation techniques to immobilize ionic liquids containing unsaturated double bonds onto a PBI matrix. In the present invention, we discovered that the ionic liquid monomers within the solid film undergo polymerization during ionizing radiation exposure. Therefore, in the present invention, step S300 is performed, in which the cured solid film is irradiated with ionizing radiation to polymerize the ionic liquid monomers dispersed within the substrate, forming a polyionic liquid (PIL) and its crosslinked structure. The immobilization of the ionic liquid is achieved by utilizing the entanglement of the polyionic liquid with the molecular chains of the polymer within the substrate and the crosslinked structure of the polyionic liquid.

[0032] Specifically, as shown in Figure 2, after the film formation in step S200, the solidified film contains PBI polymer molecular chains and the 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 the polyionic liquid PVEImBr. The PVEImBr and PBI chains are entangled with each other, immobilizing the polyionic liquid within the substrate and preventing leakage from the composite film.

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

[0034] In one embodiment, inorganic nanoparticles can be added to the casting solution in step S100, 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 immobilizing 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 PBI polymer molecular chains, ionic liquid monomer VEImBr dispersed in the PBI polymer molecular chains, and nanoparticle MXene. After irradiation with ionizing radiation EB, the ionic liquid monomer VEImBr polymerizes, ultimately producing a PBI / PIL composite film based on the PBI / PIL composite film, doped and modified with MXene. While further reducing ionic liquid leakage, the electrochemical properties of the composite film are improved through the properties of the nanomaterials themselves. 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] The above-described ionic liquid / polymer composite membrane fabrication method involves first homogenously mixing the raw materials in a solvent, then spreading and curing the resulting membrane to disperse the ionic liquid monomer into the substrate. Finally, the ionic liquid monomer is polymerized by exposure to ionizing radiation, which induces entanglement between the polyionic liquid molecular chains and the substrate molecular chains, thereby immobilizing the ionic liquid. The above-described process steps are interrelated and work synergistically to ultimately yield a composite membrane with stable performance and effectively prevent ionic liquid leakage. Furthermore, the solid-state composite membrane fabrication using 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-described method. The composite membrane comprises a substrate and a polyionic liquid and its crosslinked structure immobilized on the substrate by entanglement with the molecular chains of a polymer within the substrate. The polyionic liquid is formed by polymerization of an ionic liquid monomer. The selection of the substrate and the 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 immobilized within the polyionic liquid / polymer composite membrane after irradiation to improve the membrane's conductivity.

[0037] Accordingly, the present invention also relates to the use of the ionic liquid / polymer composite membrane described above as a protonation-treated membrane for use as an electrolyte separator in an all-vanadium flow battery or fuel cell. In the ionic liquid / polymer composite ion-exchange membrane, the ionic liquid is firmly bound to the substrate through entanglement, making it less likely to leak into the electrolyte, significantly improving battery performance.

[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, followed by the addition of 9 g of N,N-dimethylacetamide and stirring at 60 °C for 24 hours to form a casting solution with a mass fraction of 5%. After ultrasonic treatment for 1 hour to remove air bubbles, the solution was placed upside down on a clean glass plate and left for 5 to 10 minutes, after which it was dried at 60 °C for 24 hours to form a film.

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

[0041] (3) Performance test of composite ion exchange membrane To investigate the crosslinking mechanism of the polymerizable ionic liquid under irradiation conditions, infrared tests were carried out on the simple PBI film, the composite VImBr / PBI film obtained after irradiation in step (2), and the unirradiated VImBr / PBI solid film in step (2). As shown in Figure 4, after irradiation, the peaks at 1600 cm -1 The amplitude of the characteristic absorption peak of -C=C- at 1000 nm was significantly reduced, indicating that the ionic liquid containing unsaturated double bonds was crosslinked after irradiation.

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

[0043] Table 1. Ionic liquid retention rates of composite membranes with different ratios before and after irradiation. JPEG2025528939000002.jpg20168

[0044] Ionic liquid retention rate = JPEG2025528939000003.jpg935, where m1 is the mass of the membrane before immersion and m2 is the mass of the dried membrane after immersion. As shown in Table 1, when the ionic liquid content was 50% of the substrate, the ionic liquid retention rate of the unirradiated composite membrane was 26.85%. When the absorbed dose was 160 kGy, the ionic liquid retention rate was 64.93%. When the ionic liquid content was 100% of the substrate, the ionic liquid retention rate of the unirradiated composite membrane was 41.86%. When the absorbed dose was 160 kGy, the ionic liquid retention rate was 81.97%. It was demonstrated that the manufacturing method proposed in this invention can effectively improve ionic liquid retention and reduce ionic liquid leakage.

[0045] As shown in Figure 5, an SEM image of the microstructure of the composite membrane prepared in Example 1 is shown. The composite membrane is a homogeneous phase membrane, and the compatibility between the ionic liquid and PBI is good, so no phase separation occurs.

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

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

[0048] The composite membrane obtained in Example 1 was subjected to protonation treatment to obtain a PIL / PBI composite membrane with a swelling degree of 19%. This PIL / PBI composite membrane was incorporated into a battery, and the current capacity of this PIL / PBI composite membrane and the currently commercially available Nafion 115 membrane were compared to 100 mA cm. -2 The coulombic efficiency, energy efficiency, and voltage efficiency of the battery were measured at 100 mA cm. As shown in Figure 7, the PIL / PBI composite membrane obtained in this example had a current of 100 mA cm. -2 The coulombic efficiency of the battery was 98.24%, the energy efficiency was 80.27%, and the voltage efficiency was 82.23%, and its electrochemical properties were superior to those of the commercially available Nafion 115 membrane.

[0049] Example 2 A PIL / PBI composite membrane 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 membrane was equivalent to that of Example 1.

[0050] Example 3 A PIL / PBI composite membrane 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 membrane was equivalent to that of Example 1.

[0051] Example 4 A PIL / PBI composite membrane was obtained by the same production method as in Example 1, except that the solvent was changed from DMAc to NMP. The performance of the obtained PIL / PBI composite membrane 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 (e.g., 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). The mixture was then co-irradiated with an electron beam at doses of 10 kGy to 300 kGy. After irradiation, the ionic liquid monomer and the homopolymer formed under the irradiation conditions were washed away using ethanol and water. The mass of the polybenzimidazole substrate was compared, showing no change in mass, 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.

[0053] Comparative Example 2 Polybenzimidazole (PBI) solid powder was irradiated with an electron beam at -20°C in a nitrogen atmosphere, with an irradiation dose of 10 to 300 kGy. After irradiation, the PBI powder monomer was added to a pre-deoxidized imidazolium ionic liquid solution containing 20 to 100% unsaturated double bonds (e.g., 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 the reaction was carried out at 40 to 60°C for 24 hours. The ionic liquid monomer and the homopolymer produced under the irradiation conditions were washed away using 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 could not be grafted onto the polybenzimidazole. Furthermore, thermogravimetric analysis of the PBI substrate surface before and after irradiation grafting revealed that the ionic liquid component was not successfully incorporated onto the PBI substrate.

[0054] As can be seen from Comparative Examples 1 and 2, polybenzimidazole (PBI) is difficult to modify with radiation, i.e., ionizing radiation-induced grafting of ionic liquids to polybenzimidazole (PBI) is difficult. This is also the reason why ionizing radiation is not used to fabricate ionic liquid / polymer composite membranes based on polybenzimidazole (PBI). This invention breaks through conventional thinking and solves the problem of the inability to directly introduce ionic liquid monomers and PBI substrates via ionizing radiation-induced graft polymerization. First, the ionic liquid monomer and substrate are uniformly dispersed in a cosolvent to form a coating film. Then, the solid film is irradiated with radiation to polymerize and crosslink the ionic liquid, which ultimately physically entangles with the polymer chains in the substrate to form a composite membrane. Using ionizing radiation to fabricate composite membranes in the solid state offers a simpler and safer process than liquid-phase solid-liquid or liquid-liquid grafting reactions, making it suitable for industrial mass production and demonstrating promise for industrial applications.

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

[0056] It is easily understood by those skilled in the art that the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. 1. A method for producing an ionic liquid / polymer composite membrane, comprising: a step of uniformly mixing a polymer substrate containing at least one of polybenzimidazole and a polybenzimidazole derivative with an ionic liquid monomer containing an unsaturated double bond in a good solvent to obtain a casting solution; spreading the casting solution onto a substrate and drying it to remove the solvent and obtain a solid film; irradiating the solid film with ionizing radiation, inducing the ionic liquid monomers by the ionizing radiation to form polyionic liquid and its crosslinked products within the substrate, and causing physical entanglement between the molecular chains of the polyionic liquid and the molecular chains of the substrate, thereby immobilizing the ionic liquid components in the polymer substrate and forming a composite film; A method for producing an ionic liquid / polymer composite membrane, comprising:

2. 10. The method for preparing an ionic liquid / polymer composite membrane according to claim 1, further comprising washing and protonating the irradiated solid membrane to form an ionic liquid / polymer composite ion exchange membrane.

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

4. 2. The method for producing an ionic liquid / polymer composite membrane according to claim 1, wherein the anion of the ionic liquid monomer is at least one of a tetrafluoroborate ion, a bromide ion, a chloride ion, and a nitrate ion, and the cation is a vinylimidazolium or allylimidazolium ion containing a double bond.

5. The method for producing an ionic liquid / polymer composite membrane according to claim 1, characterized in that the mass of the ionic liquid monomer is 10-200% of the mass of the substrate, preferably 50-100%.

6. 2. The method for producing an ionic liquid / polymer composite membrane according to claim 1, wherein the good solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

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

8. 2. The method for producing an ionic liquid / polymer composite membrane according to claim 1, wherein the ionizing radiation is any one of gamma ray radiation, electron beam radiation, and X-ray radiation, and the exposure dose of the ionizing radiation is in the range of 10 kGy to 300 kGy, preferably 80 kGy to 200 kGy.

9. The polymer substrate includes a polyionic liquid and a crosslinked structure thereof fixed to the substrate by entanglement with molecular chains of the substrate, 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. 10. Use of the ionic liquid / polymer composite membrane according to claim 9, wherein the ionic liquid / polymer composite membrane is used as an electrolyte separator in an all-vanadium flow battery or fuel cell.

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