Enhanced proton exchange membrane, preparation method thereof and flow battery containing enhanced proton exchange membrane

Abstract

The invention provides an enhanced proton exchange membrane, a preparation method thereof and a flow battery containing the enhanced proton exchange membrane. The preparation method of the enhanced proton exchange membrane comprises the following steps: (1) coating a base material layer with a coating solution to prepare a perfluorinated sulfonic acid resin / N, N-dimethylformamide wet membrane, the coating solution being a solution formed by dissolving perfluorinated sulfonic acid resin in N, N-dimethylformamide; (2) covering the perfluorinated sulfonic acid resin / N, N-dimethylformamide wet film with an expanded polytetrafluoroethylene film, and removing N, N-dimethylformamide to obtain a first composite film; and (3) coating the surface of the expanded polytetrafluoroethylene membrane of the first composite membrane with a membrane coating solution, removing N, N-dimethylformamide, and performing high-temperature annealing treatment to obtain the enhanced proton exchange membrane. The proton exchange membrane prepared by the method is low in thickness, excellent in vanadium resistance, high in mechanical strength and low in swelling rate.

Description

Technical Field

[0001] The present invention relates to the field of membrane materials and their preparation methods, and particularly to an enhanced proton exchange membrane, a preparation method thereof, and a flow battery containing the same. Background Art

[0002] With the popularization of new energy power generation, energy storage technology has become a bottleneck restricting the development of new energy. Flow batteries have the characteristics of intrinsic safety and long life, can meet the needs of large-scale energy storage, and have become an important choice in the field of new energy power generation.

[0003] However, due to the two major problems of excessively high cost and serious self-discharge that need to be faced in the commercialization of flow batteries, the development of flow batteries has been severely restricted. Among them, the most important determining factor is the high-cost proton exchange membrane material in the flow battery system, which is also the key step restricting the commercial development of flow batteries. A good proton exchange membrane for flow batteries should have good ion selectivity, good mechanical and chemical stability, a low swelling rate, and excellent vanadium ion barrier performance, etc.

[0004] Currently, in the existing technology, the proton exchange membranes of flow batteries still mostly use imported Nafion NR212 perfluorosulfonic acid homogeneous membranes, but this membrane has defects such as a relatively thick thickness, a high price, poor vanadium resistance, low mechanical strength, and an excessive swelling rate. Therefore, there is an urgent need in the art for a proton exchange membrane with a low thickness, good vanadium resistance, high mechanical strength, and a low swelling rate. Summary of the Invention

[0005] In order to overcome the technical defects such as high cost, excessive swelling rate, poor vanadium resistance, and low mechanical strength of the proton exchange membrane materials of flow batteries in the prior art, the present invention provides an enhanced proton exchange membrane, a preparation method thereof, and a flow battery containing the same. The present invention selects a solution formed by dissolving a perfluorosulfonic acid resin in a specific solvent as the film-forming solution, and cooperates with a specific high-temperature annealing treatment to achieve that the prepared enhanced proton exchange membrane has a low thickness while being able to reduce the swelling rate of the material and improve the vanadium resistance and mechanical strength.

[0006] Specifically, one aspect of the present invention provides a preparation method of an enhanced proton exchange membrane, which includes the following steps:

[0007] (1) Coating a coating solution on a substrate layer to obtain a perfluorosulfonic acid resin / N,N-dimethylformamide wet film, wherein the coating solution is a solution formed by dissolving a perfluorosulfonic acid resin in N,N-dimethylformamide;

[0008] (2) Covering an expanded polytetrafluoroethylene membrane on the perfluorosulfonic acid resin / N,N-dimethylformamide wet film and removing N,N-dimethylformamide to obtain a first composite membrane;

[0009] (3) Coating the coating solution on the surface of the expanded polytetrafluoroethylene membrane of the first composite membrane, removing N,N-dimethylformamide, and then performing high-temperature annealing treatment to obtain the enhanced proton exchange membrane; the temperature of the high-temperature annealing treatment is 180-220 °C; the time of the high-temperature annealing treatment is 20-30 min.

[0010] In one or more embodiments, in the coating solution, the mass fraction of the perfluorosulfonic acid resin is 5%-30%, preferably 10%-20%.

[0011] In one or more embodiments, in step (1), the material of the substrate layer is polyimide or polyethylene terephthalate.

[0012] In one or more embodiments, in step (1), the coating method is solution casting coating.

[0013] In one or more embodiments, in step (1), the coating gap is 100-400 μm.

[0014] In one or more embodiments, in step (1), the coating speed is 8-15 mm / s.

[0015] In one or more embodiments, in step (2), the thickness of the expanded polytetrafluoroethylene membrane is 5-20 μm.

[0016] In one or more embodiments, in step (2), the method for removing N,N-dimethylformamide is drying. The drying temperature is preferably 120-160 °C; the drying time is preferably 3-10 min.

[0017] In one or more embodiments, in step (2), the thickness of the first composite membrane is 10-40 μm.

[0018] In one or more embodiments, in step (3), the coating method is solution casting coating.

[0019] In one or more embodiments, in step (3), the coating gap is 100-400 μm.

[0020] In one or more embodiments, in step (3), the coating speed is 8-15 mm / s.

[0021] In one or more embodiments, in step (3), the method for removing N,N-dimethylformamide is drying, and the drying temperature is preferably 120-160 °C; the drying time is preferably 5-20 min.

[0022] In one or more embodiments, in step (3), the high-temperature annealing treatment is carried out in an oven.

[0023] In one or more embodiments, the thickness of the enhanced proton exchange membrane is 16 - 70 μm.

[0024] The second aspect of the present invention provides an enhanced proton exchange membrane, which is prepared by using the preparation method of the enhanced proton exchange membrane described in any one of the embodiments herein.

[0025] In one or more embodiments, the longitudinal tensile strength of the enhanced proton exchange membrane is 46 - 65 MPa.

[0026] In one or more embodiments, the transverse tensile strength of the enhanced proton exchange membrane is 42 - 63 MPa.

[0027] In one or more embodiments, the longitudinal swelling rate of the enhanced proton exchange membrane is 0.3% - 0.5%.

[0028] In one or more embodiments, the transverse swelling rate of the enhanced proton exchange membrane is 0.1% - 0.3%.

[0029] In one or more embodiments, the puncture resistance of the enhanced proton exchange membrane is 160 - 240 N / mm.

[0030] The third aspect of the present invention provides a flow battery, which includes an enhanced proton exchange membrane prepared by using the preparation method of the enhanced proton exchange membrane described in any one of the embodiments herein or the enhanced proton exchange membrane described in any one of the embodiments herein. Detailed Description

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned herein. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0033] In this text, terms such as "comprising", "including", "containing" and similar terms encompass the meanings of "consisting essentially of" and "consisting of". For example, when this text discloses that "A comprises B and C", it should be considered that "A consists essentially of B and C" and "A consists of B and C" have been disclosed in this text.

[0034] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0035] In this text, unless otherwise specified, percentages refer to mass percentages and ratios refer to mass ratios.

[0036] In this text, when describing embodiments or examples, it should be understood that it is not used to limit the present invention to these embodiments or examples. On the contrary, all alternatives, improvements and equivalents of the methods and materials described in the present invention can be covered within the scope defined by the claims.

[0037] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0038] In the present invention, perfluorosulfonic acid resin is also called Nafion resin. N,N-dimethylformamide is also called DMF. Dimethyl sulfoxide is also called DMSO.

[0039] In some preferred embodiments, the mass fraction of the solution formed by dissolving perfluorosulfonic acid resin in N,N-dimethylformamide is 5-30%, preferably 10%-20%, such as 20%. Using N,N-dimethylformamide as a high-boiling solvent can be beneficial to improving the crystallinity of perfluorosulfonic acid resin, thereby improving the mechanical strength of the prepared proton exchange membrane and reducing the swelling rate.

[0040] In the present invention, a solution formed by dissolving perfluorosulfonic acid resin in N,N-dimethylformamide can be obtained by mixing perfluorosulfonic acid resin and the solvent N,N-dimethylformamide evenly. In some specific embodiments, perfluorosulfonic acid resin is dissolved in N,N-dimethylformamide and stirred. The dissolution temperature can be 20-80°C, such as 20°C, 50°C, 80°C. The stirring time can be 2-6h, such as 3h, 4h, 5h.

[0041] In the present invention, a dry perfluorosulfonic acid resin can be obtained by evaporating a perfluorosulfonic acid resin dispersion. The evaporation temperature can be 60 - 120 °C, such as 75 °C, 80 °C, 85 °C. The evaporation time can be 8 - 12 h, such as 9 h, 10 h, 11 h. The perfluorosulfonic acid dispersion can be selected from Nafion D520 or Nafion D2020.

[0042] In the present invention, the solution formed by dissolving the perfluorosulfonic acid resin in N,N-dimethylformamide is also called the perfluorosulfonic acid resin / N,N-dimethylformamide film-forming solution.

[0043] In step S1, the material of the substrate layer is not particularly limited as long as the substrate layer can play a supporting role during the film-forming process and the obtained proton exchange membrane can be easily peeled off from under the substrate layer. For example, it can be polyimide.

[0044] In step S1, the coating method is preferably the solution casting coating method. The coating gap is preferably set to 100 - 400 μm, such as 120 μm, 140 μm, 160 μm, 200 μm, 270 μm, 300 μm, 350 μm, 400 μm. The coating speed is preferably set to 8 - 15 mm / s, such as 8 mm / s, 10 mm / s, 12 mm / s.

[0045] In step S2, the expanded polytetrafluoroethylene membrane serves as the reinforcing layer in the proton exchange membrane. The covering method can be to unfold the expanded polytetrafluoroethylene membrane and lay it flat on the wet perfluorosulfonic acid resin / N,N-dimethylformamide membrane. The thickness of the expanded polytetrafluoroethylene membrane is preferably 5 - 20 μm, such as 5 μm, 8 μm, 10 μm, 15 μm, 20 μm.

[0046] In step S2, the method of removing N,N-dimethylformamide can be carried out in an oven. The drying temperature can be 120 - 160 °C, such as 130 °C, 140 °C, 150 °C. The drying time can be 3 - 10 min, such as 4 min, 6 min, 8 min, 10 min. The thickness of the first composite membrane obtained after drying is preferably 10 - 40 μm, such as 14 μm, 25 μm, 36 μm.

[0047] In step S3, after the solution formed by dissolving the perfluorosulfonic acid resin in N,N-dimethylformamide is coated on the surface of the expanded polytetrafluoroethylene membrane, a structure of perfluorosulfonic acid resin membrane-expanded polytetrafluoroethylene membrane-perfluorosulfonic acid resin / N,N-dimethylformamide membrane is formed. The coating method can be the same as or different from the coating method set in step S1.

[0048] In step S3, the N,N-dimethylformamide can be removed in an oven. The drying temperature can be 120-160°C, such as 130°C, 140°C, 150°C. The drying time can be 5-20 min, such as 5 min, 10 min, 15 min, 20 min.

[0049] In step S3, the high-temperature annealing treatment can be carried out in an oven. The temperature of the high-temperature annealing treatment is 180-220°C, such as 190°C, 200°C, 210°C. The time of the high-temperature annealing treatment is 20-30 min, such as 22 min, 25 min, 28 min. Performing the high-temperature annealing treatment on the composite membrane can ensure the mechanical properties of the membrane and reduce the swelling rate.

[0050] In step S3, after the high-temperature annealing treatment, the thickness of the prepared enhanced proton exchange membrane is preferably 16-70 μm, such as 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm.

[0051] In some preferred embodiments, the proportion of the thickness of the reinforcing layer (the thickness of the expanded polytetrafluoroethylene membrane) of the enhanced proton exchange membrane in the total thickness is 20%-32%, such as 20%, 26%, 32%.

[0052] In some preferred embodiments, the thickness of the reinforcing layer of the enhanced proton exchange membrane is 5-20 μm, and the total thickness is 16-70 μm.

[0053] The present invention includes an enhanced proton exchange membrane prepared by using the preparation method of the enhanced proton exchange membrane described in any one of the embodiments herein.

[0054] Among them, the longitudinal tensile strength of the enhanced proton exchange membrane is preferably 46-65 MPa, more preferably 46-58 MPa. The transverse tensile strength is preferably 42-63 MPa, more preferably 42-55 MPa. The longitudinal swelling rate is preferably 0.3%-0.5%. The transverse swelling rate is preferably 0.1%-0.3%. The puncture resistance is preferably 160-240 N / mm, more preferably 160-224 N / mm.

[0055] Advantages of the present invention:

[0056] By selecting a specific solvent and a dispersion of perfluorosulfonic acid resin as the membrane-forming solution and cooperating with a high-temperature annealing treatment under specific conditions, the prepared enhanced proton exchange membrane has a low thickness, a low swelling rate, excellent vanadium resistance performance, and high mechanical strength. The preparation method of the present invention has a simple process, low cost, and can be adapted to industrial scale-up production.

[0057] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art unless otherwise specified. The raw material compounds in the embodiments can all be obtained through commercial channels.

[0058] Example 1

[0059] S0. The perfluorosulfonic acid resin dispersion Nafion D520 (Chemours Company, USA) was evaporated at 80 °C for 10 h to obtain a dry Nafion resin; the Nafion resin was dissolved in the solvent DMF (N,N-dimethylformamide), and stirred at 80 °C for 4 h. After the Nafion resin was dissolved, a Nafion / DMF film-forming solution with a solid content (i.e., mass fraction) of 20 wt% (i.e., a solution formed by dissolving perfluorosulfonic acid resin in N,N-dimethylformamide) was obtained.

[0060] S1. The Nafion / DMF film-forming solution prepared in step S1 was coated on the substrate layer polyimide base film. The coating gap was set to 200 μm and the coating speed was set to 10 mm / s by a casting coater to obtain a Nafion / DMF wet film (i.e., a perfluorosulfonic acid resin / N,N-dimethylformamide wet film).

[0061] S2. An 8-μm-thick ePTFE membrane (expanded polytetrafluoroethylene membrane) (an expanded polytetrafluoroethylene membrane that has been commercially produced) was unfolded and laid flat on the obtained Nafion / DMF wet film; then it was placed in an oven at 140 °C and dried for 5 min to remove the solvent, obtaining a first composite membrane with a thickness of about 16 μm.

[0062] S3. The first composite membrane prepared in step S2 was laid flat on a coater, and then the Nafion / DMF film-forming solution prepared in step S1 was coated on the surface of the ePTFE of the first composite membrane. The coating gap was set to 200 μm and the coating speed was set to 10 mm / s by a casting coater to prepare another layer of Nafion / DMF wet film; then the composite membrane was placed in an oven at 140 °C and dried for 10 min to remove the solvent, and then placed in an oven at 200 °C for high-temperature annealing treatment for 25 min, obtaining a reinforced proton exchange membrane with a thickness of about 30 μm.

[0063] Description: Since the ePTFE membrane has a porosity of 80%, when preparing the first composite membrane in step S2, the ePTFE membrane will absorb a part of the Nafion / DMF membrane-forming solution; when coating the Nafion / DMF membrane-forming solution on the other surface of the ePTFE membrane in step S3, the unfilled pores in the ePTFE membrane will also absorb a part of the Nafion / DMF membrane-forming solution until the pores are filled. Therefore, although the coating gap settings and coating speeds in step S2 and step S3 are the same, the thicknesses of the two layers of Nafion / DMF wet membranes relative to the ePTFE membrane surface are not the same. The total thickness of the finally prepared enhanced proton membrane is 30 microns.

[0064] Example 2

[0065] The difference between Example 2 and Example 1 is only that in step S0, a Nafion / DMF membrane-forming solution with a solid content of 15% is prepared. In step S1, the coating gap is set to 270 μm. In step S2, the thickness of the first composite membrane is about 16 μm. In step S3, the coating gap is set to 270 μm; the thickness of the enhanced proton exchange membrane is about 30 μm. The remaining operating conditions and steps are the same as those in Example 1.

[0066] Example 3

[0067] The difference between Example 3 and Example 1 is only that in step S0, a Nafion / DMF membrane-forming solution with a solid content of 10% is prepared. In step S1, the coating gap is set to 400 μm. In step S2, the thickness of the first composite membrane is about 16 μm. In step S3, the coating gap is set to 400 μm; the thickness of the enhanced proton exchange membrane is about 30 μm. The remaining operating conditions and steps are the same as those in Example 1.

[0068] Example 4

[0069] The difference between Example 4 and Example 1 is only that in step S1, the coating gap is set to 160 μm. In step S2, the thickness of the first composite membrane is about 14 μm. In step S3, the coating gap is set to 160 μm; the thickness of the enhanced proton exchange membrane is about 25 μm. The remaining operating conditions and steps are the same as those in Example 1.

[0070] Example 5

[0071] The difference between Example 5 and Example 1 is only that in step S1, the coating gap is set to 180 μm. In step S2, the thickness of the ePTFE membrane is 5 μm, and the thickness of the first composite membrane is about 13 μm. In step S3, the coating gap is set to 180 μm; the thickness of the enhanced proton exchange membrane is about 25 μm. The remaining operating conditions and steps are the same as those in Example 1.

[0072] Comparative Example 1

[0073] The difference between Comparative Example 1 and Example 1 is only that in step S0, Nafion resin is dissolved in a mixed solution of water and n-propanol (mass ratio 1:1), stirred at 80 °C for 4 h, and after the Nafion resin is dissolved, a Nafion / water-alcohol film-forming solution with a solid content of 20 wt% is obtained. The remaining operating conditions and steps are the same as those in Example 1.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is only that in step S0, Nafion resin is dissolved in a mixed solution of DMSO, stirred at 80 °C for 4 h, and after the Nafion resin is dissolved, a Nafion / DMSO film-forming solution with a solid content of 20 wt% is obtained. The remaining operating conditions and steps are the same as those in Example 1. After high-temperature annealing at 200 °C, it was found that the composite membrane turned gray.

[0076] Comparative Example 3

[0077] The difference between Comparative Example 3 and Example 4 is only that in step S3, the obtained composite membrane was not subjected to high-temperature annealing treatment. The remaining operating conditions and steps are the same as those in Example 4.

[0078] Since high-temperature annealing treatment was not used in Comparative Example 3, the enhanced proton exchange membrane could barely be peeled off from the polyimide base membrane.

[0079] Comparative Example 4

[0080] The difference between Comparative Example 4 and Example 4 is only that in step S3, the obtained composite membrane was subjected to high-temperature annealing treatment for a longer time (160 °C, 2 h). The remaining operating conditions and steps are the same as those in Example 4.

[0081] Test Example 1

[0082] The thickness, tensile strength, swelling ratio, and puncture strength of the enhanced proton exchange membranes of Test Examples 1-5 and Comparative Examples 1-4, as well as the Nafion NR212 membrane (Chemours Company) in the prior art, were measured, and the performance of the flow battery prepared using them was tested. The test methods are as follows:

[0083] 1. Thickness: A 10 cm × 10 cm sample was intercepted, and the thicknesses of 9 points at the four corners and the middle of the sample were measured, and the average value was taken.

[0084] 2. Tensile strength: 15 cm × 1 cm samples in the MD (longitudinal) and TD (transverse) directions were intercepted, and they were stretched at a speed of 50 mm / min in the tensile mode using a universal material testing machine, and the load value at the moment of specimen fracture was recorded. There were 5 effective specimens, and the average value of the test results was taken.

[0085] 3. Swelling ratio: Cut 3 samples, measure the initial length M1 in the MD direction and the initial length T1 in the TD direction; after soaking in deionized water (25 ± 2 °C) for 2 h, measure the length M2 in the MD direction and the length T2 in the TD direction; swelling ratio in the MD direction = (M2 - M1) / M1 * 100%; swelling ratio in the TD direction = (T2 - T1) / T1 * 100%, and take the average value of the test results.

[0086] 4. Puncture strength: Cut 3 samples of 10 cm × 10 cm, use the puncture mode of a universal material testing machine to apply force at a speed of 50 mm / min until the film is pierced, record the force value at this time, calculate its puncture resistance strength, and take the average value of the test results.

[0087] 5. All-vanadium redox flow battery test: Use a hard graphite plate with an electrode area of 48 cm 2 , and a thickness of 2.0 mm; 70 mL of vanadium electrolyte for each of the positive and negative electrodes (total vanadium concentration 1.7 mol / L, average valence state of vanadium ions 3.5, sulfate ion concentration 4.3 mol / L). Set the charge-discharge interval to 1.00 - 1.55 V; perform constant-current charge and discharge, with current densities of 80 mA / cm 2 , 120 mA / cm 2 , 160 mA / cm 2 , and use a charge-discharge instrument to measure the Coulomb, voltage, and energy efficiency of the battery at each current density.

[0088] The thickness, tensile strength, swelling ratio, and puncture strength results of the enhanced proton exchange membranes prepared in Examples 1 - 5 and Comparative Examples 1 - 4 are shown in Table 1.

[0089] Table 1: Test results of thickness, tensile strength, swelling ratio, and puncture strength

[0090]

[0091] As can be seen from Table 1, the only difference between Comparative Examples 1 and 2 and Example 1 is that in step S1, the solvent of the film-forming solution used in Comparative Example 1 is a water-alcohol solution, and that used in Comparative Example 2 is DMSO, while that used in Example 1 is DMF. However, from the results of the tensile strength, swelling ratio, and puncture resistance strength of the prepared enhanced proton exchange membranes, the results of Example 1 are much higher than those of Comparative Examples 1 and 2, which indicates that using DMF as a solvent is beneficial to improving the crystallinity of perfluorosulfonic acid resin, thereby improving the mechanical strength of the proton exchange membrane and reducing its swelling ratio.

[0092] The differences between Comparative Examples 3 and 4 and Example 4 are only that in step S3, high-temperature annealing was not used in Comparative Example 3, Comparative Example 4 used high-temperature annealing treatment at 140 °C for 2 h, while Example 4 used annealing at 200 °C for 25 min. However, from the results of the tensile strength, swelling rate, and puncture resistance strength of the prepared enhanced proton exchange membrane, the results of Example 4 are far higher than those of Comparative Example 3 and Comparative Example 4. This shows that high-temperature annealing at a reasonable time and reasonable temperature is beneficial to improving the mechanical strength of the proton exchange membrane and reducing its swelling rate.

[0093] Moreover, from the comparison of the effects of the enhanced proton exchange membranes of Examples 1-5 and Nafion's NR212 membrane, it can be seen that for the enhanced proton exchange membranes prepared in Examples 1-5, whether in the MD or TD direction, their swelling rates are much lower than those of Nafion's NR212 membrane, and they have higher tensile strength. At the same time, their thickness is thinner compared to Nafion's NR212, and they have higher puncture resistance strength.

[0094] The results of the coulombic efficiency, voltage efficiency, and energy efficiency of the flow batteries prepared with Nafion NR212, the enhanced proton exchange membranes of Examples 1-5, and Comparative Examples 1 and 4 are shown in Table 2. The battery prepared with the enhanced membrane of Comparative Example 2 leaked liquid, and no battery data was obtained.

[0095] Table 2: Results of coulombic efficiency, voltage efficiency, and energy efficiency of flow batteries

[0096]

[0097]

[0098] As can be seen from Table 2, the difference between Comparative Example 1 and Example 1 is only that in step S1, the solvent used in Comparative Example 1 is an aqueous alcohol solution, while the solvent used in Example 1 is DMF. However, the coulombic efficiency, voltage efficiency, and energy efficiency performance of the flow battery prepared with the enhanced proton exchange membrane of Example 1 are all higher than those of Comparative Example 1. This shows that using DMF as a high-boiling solvent is beneficial to improving the crystallinity of perfluorosulfonic acid resin, thereby improving the vanadium resistance performance of the composite membrane, and its flow battery has higher voltage efficiency and energy efficiency.

[0099] Moreover, when comparing the enhanced proton exchange membranes of Examples 1-5 with Nafion's NR212 membrane, while the membrane thickness of Examples 1-5 is thinner, they have higher battery performance than Nafion's NR212 membrane. This shows that the proton exchange membrane prepared by the preparation method of Examples 1-5 has higher vanadium resistance performance, and through a lower thickness, it achieves higher proton conduction and maintains a relatively high voltage efficiency.

Claims

1. A method for preparing an enhanced proton exchange membrane, characterized in that, It includes the following steps: (1) Coating a coating solution on a substrate layer to obtain a perfluorosulfonic acid resin / N,N-dimethylformamide wet film, wherein the coating solution is a solution formed by dissolving perfluorosulfonic acid resin in N,N-dimethylformamide; (2) Covering an expanded polytetrafluoroethylene film on the perfluorosulfonic acid resin / N,N-dimethylformamide wet film, and removing N,N-dimethylformamide to obtain a first composite film; (3) Coating the coating solution on the surface of the expanded polytetrafluoroethylene film of the first composite film, removing N,N-dimethylformamide, and then performing high-temperature annealing treatment to obtain the enhanced proton exchange membrane; the temperature of the high-temperature annealing treatment is 180-220°C; the time of the high-temperature annealing treatment is 20-30 min.

2. The preparation method of the enhanced proton exchange membrane according to claim 1, characterized in that In the coating solution, the mass fraction of the perfluorosulfonic acid resin is 5%-30%, preferably 10%-20%.

3. The preparation method of the enhanced proton exchange membrane according to claim 1, wherein, The method has one or more of the following characteristics: In step (1), the material of the substrate layer is polyimide or polyethylene terephthalate; In step (1), the coating method is solution casting; In step (1), the coating gap is 100-400 μm; In step (1), the coating speed is 8-15 mm / s.

4. The preparation method of the enhanced proton exchange membrane according to claim 1, wherein, The method has one or more of the following characteristics: In step (2), the thickness of the expanded polytetrafluoroethylene film is 5-20 μm; In step (2), the method for removing N,N-dimethylformamide is drying, and the drying temperature is preferably 120-160°C; the drying time is preferably 3-10 min; In step (2), the thickness of the first composite film is 10-40 μm.

5. The preparation method of the enhanced proton exchange membrane according to claim 1, characterized in that, The method has one or more of the following characteristics: In step (3), the coating method is solution casting; In step (3), the coating gap is 100-400 μm; In step (3), the coating speed is 8-15 mm / s.

6. The preparation method of the enhanced proton exchange membrane according to claim 1, characterized in that, The method has one or more of the following characteristics: In step (3), the method for removing N,N-dimethylformamide is drying, and the drying temperature is preferably 120-160°C; the drying time is preferably 5-20 min; In step (3), the high-temperature annealing treatment is carried out in an oven.

7. The preparation method of the enhanced proton exchange membrane according to claim 1, characterized in that, The thickness of the enhanced proton exchange membrane is 16-70 μm.

8. An enhanced proton exchange membrane, characterized in that, It is prepared by using the preparation method of the enhanced proton exchange membrane according to any one of claims 1-7.

9. The enhanced proton exchange membrane according to claim 8, characterized in that, The enhanced proton exchange membrane has one or more of the following characteristics: The longitudinal tensile strength of the enhanced proton exchange membrane is 46-65 MPa; The transverse tensile strength of the enhanced proton exchange membrane is 42-63 MPa; The longitudinal swelling rate of the enhanced proton exchange membrane is 0.3%-0.5%; The transverse swelling rate of the enhanced proton exchange membrane is 0.1%-0.3%; The puncture resistance of the enhanced proton exchange membrane is 160-240 N / mm.

10. A flow battery, characterized in that, It includes an enhanced proton exchange membrane prepared by using the preparation method of the enhanced proton exchange membrane described in any one of claims 1-7 or the enhanced proton exchange membrane described in any one of claims 8-9.

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