Diaphragm of all-vanadium redox flow battery, preparation method of diaphragm, all-vanadium redox flow battery and energy storage device

Abstract

The invention relates to a diaphragm of an all-vanadium redox flow battery, a preparation method of the diaphragm, the all-vanadium redox flow battery and an energy storage device. The diaphragm of the all-vanadium redox flow battery comprises perfluorinated sulfonic acid resin and a porous material loaded with ionic liquid, the porous material loaded with the ionic liquid comprises a porous material and the ionic liquid loaded on the porous material, the porous material comprises ZIF-8, and the ionic liquid comprises 1-butyl-3-methylimidazolium tetrafluoroborate. The diaphragm of the all-vanadium redox flow battery comprises the ionic liquid, and the performance stability of the diaphragm can effectively solve the problem of rapid loss of the ionic liquid.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, and in particular to a separator for a vanadium redox flow battery and its preparation method, a vanadium redox flow battery, and an energy storage device. Background Technology

[0002] Ionic liquids, as unique organic salts, are composed of specific organic cations and inorganic or organic anions, and exist in a liquid state at or near room temperature. These substances possess numerous characteristics such as low volatility, high thermal stability, a wide electrochemical window, and tunable physicochemical properties, leading to their widespread application in many fields. In vanadium redox flow battery systems, ionic liquids have been introduced into the membrane application research. Ionic liquids can optimize the ion conduction performance of the membrane and enhance its barrier performance against vanadium ions (suppressing vanadium ion permeation through the Donnan effect, thereby improving membrane performance), which is of great significance for improving the overall performance of vanadium redox flow batteries. However, the loss of ionic liquids has become a critical issue in the application of ionic liquids to vanadium redox flow battery membranes. During long-term battery operation, ionic liquids may gradually leak from the membrane, which not only affects the original function of the membrane and leads to a decline in battery performance, but also poses a serious threat to the long-term stable operation of the battery. Therefore, effectively solving the problem of ionic liquid loss is a critical challenge that urgently needs to be overcome in the application of ionic liquids in vanadium redox flow battery separators, and it is of vital importance to promoting the further development of vanadium redox flow battery technology. Summary of the Invention

[0003] Therefore, it is necessary to provide a separator for a vanadium redox flow battery that includes an ionic liquid and whose performance stability can effectively solve the problem of rapid loss of the ionic liquid.

[0004] The present invention provides a separator for a vanadium redox flow battery, comprising a perfluorosulfonic acid resin and a porous material loaded with an ionic liquid; The porous material loaded with ionic liquid includes a porous material and an ionic liquid loaded on the porous material. The porous material includes ZIF-8, and the ionic liquid includes 1-butyl-3-methylimidazolium tetrafluoroborate.

[0005] In one embodiment, in the separator of the vanadium redox flow battery, the mass percentage of the porous material loaded with ionic liquid is 1-10%; and / or In the porous material loaded with ionic liquid, the mass percentage of the ionic liquid is 23.4%.

[0006] This invention also provides a method for preparing a separator for an all-vanadium redox flow battery, comprising the following steps: By loading 1-butyl-3-methylimidazolium tetrafluoroborate onto ZIF-8, a porous material loaded with ionic liquid was obtained. Preparation of film-forming materials comprising perfluorosulfonic acid resin, solvent, and porous material supported on ionic liquid; and The film-forming material is used to prepare the separator for an all-vanadium redox flow battery.

[0007] In one embodiment, the method further includes a step of preparing ZIF-8, which includes the following steps: Zn(NO3)2·6H2O was added to deionized water to prepare the first solution; 2-Methylimidazole was added to deionized water to prepare the second solution; The first solution and the second solution are mixed to obtain the reaction solution; Place the reaction solution in a reaction vessel and hydrothermally react at 140-160℃ for 2-4 hours; The reaction liquid in the reactor was removed, allowed to stand and cool, and then centrifuged to obtain the precipitate; and The precipitate was washed with water and dried to obtain ZIF-8.

[0008] In one embodiment, the step of loading 1-butyl-3-methylimidazolium tetrafluoroborate onto ZIF-8 includes the following steps: 1-Butyl-3-methylimidazolium tetrafluoroborate was dispersed in dimethyl sulfoxide to obtain a dispersion; ZIF-8 was added to the dispersion to obtain a mixture; The mixture is placed in a vacuum environment and treated at 70-90℃ for 8-16 hours to obtain a porous material loaded with ionic liquid.

[0009] In one embodiment, the method further includes a step of milling the porous material loaded with the ionic liquid; and / or In the dispersion, the content of 1-butyl-3-methylimidazolium tetrafluoroborate is 3-8 wt%, and in the porous material loaded with ionic liquid, the mass percentage of the ionic liquid is 23.4%; and / or In the separator of the vanadium redox flow battery, the mass percentage of the porous material loaded with ionic liquid is 1-10%.

[0010] In one embodiment, the step of preparing the film-forming material into a separator for an all-vanadium redox flow battery includes the following steps: The film-forming material is coated onto a glass plate using a coating apparatus to obtain a pre-film. The prepared membrane is dried to remove the solvent; and The pre-drying membrane is then heat-treated to obtain the separator for the vanadium redox flow battery. The heat treatment temperature is higher than the drying temperature.

[0011] In one embodiment, in the step of drying the prepared membrane to remove the solvent, the drying temperature is 70-90°C and the drying time is 8-16 hours; and / or In the step of heat-treating the prepared film after drying to obtain the separator for the all-vanadium redox flow battery, the heat treatment temperature is 110-130℃ and the heat treatment time is 18-30h; and / or The step of preparing the film-forming material comprising a perfluorosulfonic acid resin, a solvent, and a porous material loaded with an ionic liquid includes the following steps: A perfluorosulfonic acid resin solution is prepared by dissolving the perfluorosulfonic acid resin in a solvent, wherein the solvent is dimethyl sulfoxide; A porous material loaded with an ionic liquid is added to a perfluorosulfonic acid resin solution to obtain a solution to be treated; and After sequentially stirring, sonicating, and vacuum degassing the solution to be treated, a film-forming material is obtained.

[0012] The present invention also provides an all-vanadium redox flow battery, comprising the vanadium redox flow battery separator described above or the vanadium redox flow battery separator prepared by the preparation method described above.

[0013] The present invention also provides an energy storage device, including the above-described vanadium redox flow battery.

[0014] Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions or metal clusters with multidentate organic ligands through coordination bonds. They possess significant characteristics such as high specific surface area, tunable pore size, structural diversity, and functional designability, showing broad application prospects in gas adsorption and separation, catalysis, sensing, and drug delivery. Utilizing the porous adsorption characteristics of MOFs to adsorb loaded ionic liquids and incorporate them into the membrane of an all-vanadium redox flow battery can effectively solve the problem of rapid ionic liquid loss and maintain the membrane's performance stability.

[0015] Among them, ZIF-8, as a typical representative of MOFs, is composed of Zn 2+Ions and 2-methylimidazolium ligands construct a three-dimensional microporous network with an SOD topology through tetrahedral coordination, exhibiting high specific surface area and excellent thermal and chemical stability, especially good hydrolysis resistance in aqueous systems. This further contributes to the high performance and low ionic liquid loss rate of the aforementioned vanadium redox flow battery separator. 1-Butyl-3-methylimidazolium tetrafluoroborate, like ZIF-8, possesses a methylimidazolium structure, allowing for more stable loading of the ionic liquid onto ZIF-8. This again contributes to the high performance and low ionic liquid loss rate of the aforementioned vanadium redox flow battery separator. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a flowchart illustrating a method for preparing the separator of an all-vanadium redox flow battery according to an embodiment of the present invention. Figure 2 for Figure 1 The flowchart of step S110 of the method for preparing the separator of the all-vanadium redox flow battery is shown. Figure 3 for Figure 1 The flowchart shows step S120 of the method for preparing the separator of the all-vanadium redox flow battery. Figure 4 for Figure 1 The flowchart shows step S130 of the method for preparing the separator of the all-vanadium redox flow battery. Figure 5 for Figure 1 The flowchart shows step S140 of the method for preparing the separator of the all-vanadium redox flow battery. Detailed Implementation

[0017] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0018] In the description of this application, it should be understood that, where they appear, the terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0019] Furthermore, where applicable, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0020] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., shall be interpreted broadly. For example, they may refer to a fixed connection, a detachable connection, or an integral part; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; they may refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0022] It should be noted that, if an element is described as "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is described as "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] An embodiment of the present invention discloses a separator for a vanadium redox flow battery. The separator comprises a perfluorosulfonic acid resin and a porous material loaded with an ionic liquid. The porous material loaded with the ionic liquid comprises a porous material and an ionic liquid loaded on the porous material. The porous material comprises ZIF-8. The ionic liquid comprises 1-butyl-3-methylimidazolium tetrafluoroborate.

[0024] Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions or metal clusters with multidentate organic ligands through coordination bonds. They possess significant characteristics such as high specific surface area, tunable pore size, structural diversity, and functional designability, showing broad application prospects in gas adsorption and separation, catalysis, sensing, and drug delivery. Utilizing the porous adsorption characteristics of MOFs to adsorb loaded ionic liquids and incorporate them into the membrane of an all-vanadium redox flow battery can effectively solve the problem of rapid ionic liquid loss and maintain the membrane's performance stability.

[0025] Among them, ZIF-8, as a typical representative of MOFs, is composed of Zn 2+ Ions and 2-methylimidazolium ligands construct a three-dimensional microporous network with an SOD topology through tetrahedral coordination, exhibiting high specific surface area and excellent thermal and chemical stability, especially good hydrolysis resistance in aqueous systems. This further contributes to the high performance and low ionic liquid loss rate of the aforementioned vanadium redox flow battery separator. 1-Butyl-3-methylimidazolium tetrafluoroborate, like ZIF-8, possesses a methylimidazolium structure, allowing for more stable loading of the ionic liquid onto ZIF-8. This again contributes to the high performance and low ionic liquid loss rate of the aforementioned vanadium redox flow battery separator.

[0026] In this embodiment, the mass percentage of the porous material loaded with ionic liquid in the separator of the vanadium redox flow battery is 1-10%. Once the mass percentage of ionic liquid in the porous material is determined, a higher mass percentage results in a higher mass percentage of ionic liquid in the separator. If the mass percentage of the porous material loaded with ionic liquid is too low, the ionic liquid content will be too small, limiting its performance-enhancing effect on the separator. Conversely, if the mass percentage of the porous material loaded with ionic liquid is too high, the mass percentage of perfluorosulfonic acid resin will be significantly reduced, affecting the separator's function. Considering these factors, the mass percentage of the porous material loaded with ionic liquid in the separator of the vanadium redox flow battery is set to 1-10%.

[0027] In this embodiment, the mass percentage of the ionic liquid in the porous material loaded with ionic liquid is 23.4%. Once the mass percentage of the porous material loaded with ionic liquid in the membrane is determined, if the mass percentage of ionic liquid in the porous material is too small, the content of ionic liquid will be too low, resulting in limited performance improvement of the membrane. Conversely, if the pore size of the porous material for loading ionic liquid is limited, if the mass percentage of ionic liquid in the porous material loaded with ionic liquid is too large, a large amount of ionic liquid will accumulate on the surface of the porous material and cannot be well protected by the porous material, leading to ionic liquid loss after application in the membrane. Considering the above factors, the mass percentage of ionic liquid in the porous material loaded with ionic liquid is set to 23.4%.

[0028] like Figure 1 As shown, the present invention also provides a method for preparing a separator for an all-vanadium redox flow battery, comprising the following steps: Step S110: Prepare ZIF-8.

[0029] Step S120: 1-Butyl-3-methylimidazolium tetrafluoroborate is loaded onto ZIF-8 to obtain a porous material loaded with ionic liquid.

[0030] Step S130: Prepare a film-forming material comprising a perfluorosulfonic acid resin, a solvent, and a porous material loaded with an ionic liquid.

[0031] Step S140: Prepare the film-forming material into a separator for a vanadium redox flow battery.

[0032] In this embodiment, the method for preparing the separator of the vanadium redox flow battery further includes a step of preparing ZIF-8. It is understood that in other embodiments, commercially available ZIF-8 can be directly purchased, in which case step S110 can be omitted.

[0033] In the above-mentioned method for preparing the separator of the vanadium redox flow battery, 1-butyl-3-methylimidazolium tetrafluoroborate is first loaded onto ZIF-8 to obtain a porous material loaded with ionic liquid. Then, a film-forming material including perfluorosulfonic acid resin, solvent and porous material loaded with ionic liquid is prepared, and the film-forming material is used to prepare the separator of the vanadium redox flow battery. This not only allows the ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) to be applied to the separator of the vanadium redox flow battery to improve the performance of the separator, but also reduces the ionic liquid loss rate and improves the stability of the separator.

[0034] like Figure 2 As shown, in this embodiment, the step of preparing ZIF-8, namely step S110, includes the following steps: Step S111: Add Zn(NO3)2·6H2O to deionized water to prepare the first solution.

[0035] Step S112: Add 2-methylimidazole to deionized water to prepare the second solution.

[0036] Step S113: Mix the first solution and the second solution to obtain the reaction solution.

[0037] Step S114: Place the reaction solution in a reaction vessel and hydrothermally react at 140-160℃ for 2-4 hours.

[0038] Step S115: Remove the reaction liquid from the reactor, let it stand and cool down, and then centrifuge it to obtain the precipitate.

[0039] Step S116: The precipitate is washed with water and dried to obtain ZIF-8.

[0040] In the above steps for preparing ZIF-8, a first solution and a second solution are prepared first, and then the first and second solutions are mixed. This ensures that Zn(NO3)2·6H2O and 2-methylimidazole in the reaction solution are thoroughly and uniformly mixed. The reaction solution is then placed in a reaction vessel and subjected to hydrothermal reaction at 140-160℃ for 2-4 hours. After removal and cooling, the solution is centrifuged to obtain the precipitate. The precipitate is washed with water and dried to obtain ZIF-8. This method is very convenient for preparing ZIF-8.

[0041] like Figure 3 As shown, in this embodiment, the step of loading 1-butyl-3-methylimidazolium tetrafluoroborate onto ZIF-8, i.e., step S120, includes the following steps: Step S122: 1-Butyl-3-methylimidazolium tetrafluoroborate is dispersed in dimethyl sulfoxide to obtain a dispersion.

[0042] Step S124: Add ZIF-8 to the dispersion to obtain a mixture.

[0043] Step S126: Place the mixture in a vacuum environment and treat it at 70-90℃ for 8-16 hours to obtain a porous material loaded with ionic liquid.

[0044] In step S120 above, 1-butyl-3-methylimidazolium tetrafluoroborate is first dispersed in dimethyl sulfoxide to obtain a dispersion. Then, ZIF-8 is added to the dispersion. Finally, the mixture is placed under vacuum and treated at 70-90°C for 8-16 hours to obtain a porous material loaded with ionic liquid. This method facilitates the loading of 1-butyl-3-methylimidazolium tetrafluoroborate onto ZIF-8.

[0045] In this embodiment, the step of loading 1-butyl-3-methylimidazolium tetrafluoroborate onto ZIF-8, i.e., step S120, further includes the following steps: Step S128 involves grinding the porous material loaded with ionic liquid. This refines the particles of the porous material, reduces agglomeration, and ensures more uniform dispersion during subsequent film formation.

[0046] In this embodiment, the content of 1-butyl-3-methylimidazolium tetrafluoroborate in the dispersion is 3-8 wt%. This makes it very easy to control the amount of 1-butyl-3-methylimidazolium tetrafluoroborate used. It is understood that in other embodiments, the content of 1-butyl-3-methylimidazolium tetrafluoroborate can also be set according to actual needs.

[0047] like Figure 4 As shown, in this embodiment, the step of preparing a film-forming material comprising a perfluorosulfonic acid resin, a solvent, and a porous material loaded with an ionic liquid, namely step S130, includes the following steps: Step S132: Dissolve the perfluorosulfonic acid resin in a solvent to prepare a perfluorosulfonic acid resin solution. The solvent is dimethyl sulfoxide.

[0048] Step S134: Add a porous material loaded with ionic liquid to a perfluorosulfonic acid resin solution to obtain a solution to be treated.

[0049] Step S136: After sequentially stirring, sonicating and vacuum degassing the solution to be treated, a film-forming material is obtained.

[0050] The above steps for preparing a film-forming material comprising a perfluorosulfonic acid resin, a solvent, and a porous material loaded with an ionic liquid are very convenient for preparing the film-forming material.

[0051] like Figure 5 As shown, in this embodiment, the step of preparing the film-forming material into a separator for an all-vanadium redox flow battery, namely step S140, includes the following steps: Step S142: Apply the film-forming material to the glass plate using a coating device to obtain a pre-film.

[0052] Step S144: Dry the prepared membrane to remove the solvent.

[0053] Step S146: Heat-treat the prepared membrane after drying to obtain the separator for the vanadium redox flow battery. The temperature of the heat treatment is higher than that of the drying treatment.

[0054] In the steps described above for preparing the membrane of a vanadium redox flow battery from the film-forming material, heat treatment at a temperature higher than the drying temperature can improve the toughness of the membrane.

[0055] In this embodiment, in the step of drying the prepared film to remove the solvent, that is, in step S144, the drying temperature is 70-90°C and the drying time is 8-16 hours.

[0056] In this embodiment, in the step of heat-treating the pre-drying membrane to obtain the separator of the all-vanadium redox flow battery, that is, in step S146, the heat treatment temperature is 110-130°C and the heat treatment time is 18-30h.

[0057] The present invention also provides an all-vanadium redox flow battery, comprising the vanadium redox flow battery separator described above or the vanadium redox flow battery separator prepared by the preparation method described above.

[0058] The present invention also provides an energy storage device. This energy storage device includes the aforementioned vanadium redox flow battery.

[0059] The present invention will be further described below with reference to embodiments. Example 1 I. Preparation of porous material ZIF-8: Weigh 2.04 g of Zn(NO3)2·6H2O and add it to 15 mL of deionized water. Stir continuously until Zn(NO3)2·6H2O is completely dissolved. Then weigh 6.98 g of 2-methylimidazole (2-MI) and dissolve it in 60 mL of deionized water. Add the above Zn(NO3)2·6H2O solution and mix. The mixture is then subjected to hydrothermal reaction at 150 °C for 3 h in a reaction vessel. After standing for 24 h and cooling, the precipitate is obtained by centrifugation and washed repeatedly with water 5 times to remove unreacted residues. After drying at 80 °C for 8 h, a white granular product ZIF-8 is obtained.

[0060] II. Vacuum Loading of Ionic Liquids: The ionic liquid used in this embodiment is 1-butyl-3-methylimidazolium tetrafluoroborate. A 5wt% dispersion of 1-butyl-3-methylimidazolium tetrafluoroborate was prepared by dispersing it in dimethyl sulfoxide (DMSO). 5500 mg of the 5wt% 1-butyl-3-methylimidazolium tetrafluoroborate dispersion was weighed and mixed with 900 mg of ZIF-8, and then treated at 80°C under vacuum for 12 h. Subsequently, the mixture was removed and ground to obtain ZIF-8 material loaded with the ionic liquid, named ZIF-8 / IL. The mass percentage of the ionic liquid was 23.4wt%, calculated as 5500 mg * 5wt% / (900 mg + 5500 mg * 5wt%).

[0061] III. Preparation of Composite Membranes: Perfluorosulfonic acid resin (PFSA) was dissolved in dimethyl sulfoxide (DMSO) to obtain a 15 wt% solution. Then, 5 g of the 15 wt% PFSA / DMSO solution and 0.0076 g of ZIF-8 / IL were weighed out, and the ZIF-8 / IL solution was added and stirred for 12 h. The mixture was then sonicated for 30 min, and vacuum-sealed to remove air bubbles. The solution was coated onto a glass plate using a coating apparatus and dried at 80 °C for 12 h, followed by heat treatment at 120 °C for 24 h. After cooling, the film was peeled off to obtain the PFSA-ZIF-8 / IL-1 membrane, where 1 represents the mass fraction of ZIF-8 / IL in PFSA, 0.0076 g / (5 g * 15 wt% + 0.0076), which is 1.0 wt%.

[0062] Example 2 In Example 2, the mass of ZIF-8 / IL was 0.0232 g, resulting in a PFSA-ZIF-8 / IL-3 membrane, where 3 represents the mass fraction of ZIF-8 / IL in PFSA, specifically 0.0232 g / (5 g * 15 wt% + 0.0232), or 3.0 wt%. Everything else was the same as in Example 1.

[0063] Example 3 In Example 3, the mass of ZIF-8 / IL was 0.0395 g, resulting in a PFSA-ZIF-8 / IL-5 membrane, where 5 represents the mass fraction of ZIF-8 / IL in PFSA, specifically 0.0395 g / (5 g * 15 wt% + 0.0395), or 5.0 wt%. Everything else was the same as in Example 1.

[0064] Example 4 In Example 4, the mass of ZIF-8 / IL was 0.0652g, which yielded a PFSA-ZIF-8 / IL-8 membrane. The 8 represents the mass fraction of ZIF-8 / IL in PFSA, specifically 0.0652g / (5g*15wt%+0.0652), or 8.0wt%.

[0065] Everything else is the same as in Example 1.

[0066] Example 5 In Example 5, the mass of ZIF-8 / IL was 0.0833g, which is to obtain the PFSA-ZIF-8 / IL-10 membrane, where 10 represents the mass fraction of ZIF-8 / IL in PFSA, specifically 0.0833g / (5g*15wt%+0.0833), or 10.0wt%.

[0067] Everything else is the same as in Example 1.

[0068] Comparative Example 1 Perfluorosulfonic acid resin (PFSA) was dissolved in dimethyl sulfoxide (DMSO) to obtain a 15 wt% solution. Then, 5 g of the 15 wt% PFSA / DMSO solution was weighed, stirred for 12 h, sonicated for 30 min, and vacuumed to remove air bubbles. The solution was then coated onto a glass plate using a coating applicator, dried at 80 °C for 12 h, and then heat-treated at 120 °C for 24 h. After cooling, the pure PFSA film was peeled off.

[0069] Comparative Example 2 Perfluorosulfonic acid resin (PFSA) was dissolved in dimethyl sulfoxide (DMSO) to obtain a 15 wt% solution. Then, 5 g of the 15 wt% PFSA / DMSO solution and 184.86 mg of the 5 wt% 1-butyl-3-methylimidazolium tetrafluoroborate dispersion were weighed out, mixed, stirred for 12 h, sonicated for 30 min, and vacuum-sealed to remove air bubbles. The mixture was then coated onto a glass plate using a coating applicator, dried at 80°C for 12 h, and subsequently heat-treated at 120°C for 24 h. After cooling, the membrane was peeled off to obtain the PFSA-IL membrane. The mass of the ionic liquid in the PFSA-IL membrane was the same as that in the PFSA-ZIF-8 / IL-5 membrane in Example 3, both being 9.243 mg. The mass of the ionic liquid in the PFSA-ZIF-8 / IL-5 membrane in Example 3 was 0.0395 g * 23.4 wt%, which is 9.243 mg. The mass of the ionic liquid in the PFSA-IL membrane is 184.86 mg * 5 wt%, which is 9.243 mg.

[0070] Comparative Example 3 Perfluorosulfonic acid resin (PFSA) was dissolved in dimethyl sulfoxide (DMSO) to obtain a 15 wt% solution. Then, 5 g of the 15 wt% PFSA / DMSO solution and 0.0395 g of ZIF-8 (the pure porous material prepared in Example 1, without ionic liquid) were weighed out, stirred for 12 h, sonicated for 30 min, and vacuumed to remove bubbles. The mixture was then coated onto a glass plate using a coating applicator, dried at 80 °C for 12 h, and then heat-treated at 120 °C for 24 h. After cooling, the membrane was peeled off to obtain the PFSA-ZIF-8-5 membrane, where 5 represents the mass fraction of ZIF-8 in PFSA, specifically 0.0395 g / (5 g * 15 wt% + 0.0395), which is 5.0 wt%.

[0071] test I. Test methods for the loss of ionic liquids: The concentration of boron ions in the diaphragm soaking solution was determined using an Agilent 720 inductively coupled plasma optical emission spectrometer. Diaphragms of the same mass from Example 3 and Comparative Example 2 were soaked in the same volume of deionized water at 25°C for 10 days. The soaking solutions were analyzed by MS-OES to determine the immobilization effect of ZIF-8 on 1-butyl-3-methylimidazolium tetrafluoroborate by analyzing the boron ion concentration. The specific test results are shown in Table 1.

[0072] Table 1 Comparison of B element concentration in leachate

[0073] II. Electrical Performance Testing The membranes prepared in Examples 1-5 and the membranes prepared in Comparative Examples 1-3 were assembled into a reactor with an effective reaction area of ​​16 cm². 2 Electrical performance tests were conducted on an all-vanadium redox flow cell. The test conditions were as follows: charge / discharge cutoff voltages of 1.55 V and 1.0 V, respectively; positive and negative electrolyte volumes of 200 mL each; vanadium ion concentration of 1.65 mol / L and sulfate concentration of 3.5 mol / L in the electrolyte; constant current charge / discharge with a current density of 80 mA / cm². 2 Multiple iterations of the test were performed. The test results are shown in Table 2.

[0074] Table 2 Electrical performance test results

[0075] As shown in Table 1, the concentration of element B in the leachate of the membrane prepared in Example 3 is very small and much smaller than that in the leachate of the membrane in Comparative Example 2. The lower the concentration of element B in the leachate of the membrane, the less ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) is lost. This proves that the porous material (ZIF-8) has a fixing effect on ionic liquid, and the PFSA-ZIF-8 / IL membrane has a low ionic liquid loss rate.

[0076] As shown in Table 2, the initial coulombic efficiency and energy efficiency of Examples 1-5, Comparative Example 1 and Comparative Example 2 are all better than those of Comparative Example 1. This indicates that the composite membrane including porous material (ZIF-8) and / or ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) has better performance than the pure PFSA membrane.

[0077] As shown in Table 2, compared to Example 3, the coulombic efficiency of the diaphragm in Comparative Example 2 decreased rapidly in the first 50 cycles, indicating severe ionic liquid loss from the diaphragm in Comparative Example 2. This demonstrates that the porous material (ZIF-8) has a ionic liquid immobilization effect, and the PFSA-ZIF-8 / IL membrane exhibits a low ionic liquid loss rate.

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A separator for a vanadium redox flow battery, characterised in that, The porous material loaded with ionic liquid comprises a porous material and an ionic liquid loaded on the porous material, the porous material comprises ZIF-8, and the ionic liquid comprises 1-butyl-3-methylimidazolium tetrafluoroborate. In the membrane of the all-vanadium redox flow battery, the mass ratio of the porous material loaded with ionic liquid is 1-10%; and / or 2. The separator for a vanadium redox flow battery of claim 1, wherein, In the porous material loaded with ionic liquid, the mass ratio of the ionic liquid is 23.4%. The method comprises the following steps:

3. A method of making a separator for a vanadium redox flow battery, characterized in that, loading 1-butyl-3-methylimidazolium tetrafluoroborate on ZIF-8 to obtain a porous material loaded with ionic liquid; preparing a film-forming material comprising a perfluorosulfonic acid resin, a solvent and the porous material loaded with ionic liquid; and preparing the film-forming material into a membrane of an all-vanadium redox flow battery. The method further comprises a step of preparing ZIF-8, which comprises the following steps:

4. The method for producing a separator for an all-vanadium redox flow battery according to claim 3, characterized by, adding Zn(NO3)2·6H2O into deionized water to prepare a first solution; adding 2-methylimidazole into deionized water to prepare a second solution; mixing the first solution and the second solution to obtain a reaction solution; placing the reaction solution in a reaction kettle for hydrothermal reaction at 140-160°C for 2-4h; taking out the reaction solution in the reaction kettle, standing and cooling, and then performing centrifugation to obtain precipitate therein; and performing water washing and drying treatment on the precipitate to obtain ZIF-8. The step of loading 1-butyl-3-methylimidazolium tetrafluoroborate on ZIF-8 comprises the following steps:

5. The method of producing a separator for a vanadium redox flow battery according to claim 3, wherein dispersing 1-butyl-3-methylimidazolium tetrafluoroborate in dimethyl sulfoxide to obtain a dispersion liquid; adding ZIF-8 into the dispersion liquid to obtain a mixture liquid; placing the mixture liquid in a vacuum environment, and treating at 70-90°C for 8-16h to obtain a porous material loaded with ionic liquid. The method further comprises a step of grinding the porous material loaded with ionic liquid; and / or 6. The method of producing a separator for a vanadium redox flow battery according to claim 5, wherein In the dispersion liquid, the content of 1-butyl-3-methylimidazolium tetrafluoroborate is 3-8wt%, and in the porous material loaded with ionic liquid, the mass ratio of the ionic liquid is 23.4%; and / or In the membrane of the all-vanadium redox flow battery, the mass ratio of the porous material loaded with ionic liquid is 1-10%. The step of preparing the film-forming material into a membrane of an all-vanadium redox flow battery comprises the following steps:

7. The method of producing a separator for a vanadium redox flow battery as claimed in claim 3, characterized by, coating the film-forming material on a glass plate by using a film coater to obtain a preliminary film; performing drying treatment on the preliminary film to remove the solvent; and performing heat treatment on the preliminary film after the drying treatment to obtain a membrane of an all-vanadium redox flow battery, and the temperature of the heat treatment is higher than that of the drying treatment.

8. The method for preparing a membrane of an all-vanadium redox flow battery according to claim 7, wherein in the step of performing drying treatment on the preliminary film to remove the solvent, the temperature of the drying treatment is 70-90°C, and the time of the drying treatment is 8-16h; and / or ​ In the step of performing heat treatment on the prepared membrane after the drying treatment to obtain the separator of the all-vanadium redox flow battery, the temperature of the heat treatment is 110-130°C, and the time of the heat treatment is 18-30h; and / or The step of preparing the film-forming material including the perfluorosulfonic acid resin, the solvent, and the porous material loaded with the ionic liquid includes the following steps: The perfluorosulfonic acid resin is dissolved in the solvent to configure a perfluorosulfonic acid resin solution, and the solvent is dimethyl sulfoxide; The porous material loaded with the ionic liquid is added to the perfluorosulfonic acid resin solution to obtain a to-be-treated solution; and After the to-be-treated solution is sequentially subjected to stirring, ultrasonic treatment, and vacuum bubble removal treatment, the film-forming material is obtained.

9. An all-vanadium redox flow battery characterised in that, The separator of the vanadium redox flow battery as claimed in claim 1 or 2 or prepared by the preparation method as claimed in any one of claims 3-8.

10. An energy storage device, characterized by, The all-vanadium redox flow battery as claimed in claim 9.

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