A microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery and its preparation method and application

Abstract

The present invention relates to a microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium liquid flow batteries, and its preparation method and application, belonging to the field of energy storage. First, a sulfonated polybenzimidazole polymer is obtained by sulfonation treatment, and then a film casting solvent and a metal ion pore-forming agent are added and stirred evenly to form a film casting liquid and cast into a membrane, and finally a microporous membrane is formed by acid etching. In order to solve the problems of insufficient proton conduction capacity of polybenzimidazole membranes in all-vanadium liquid flow batteries and low battery energy conversion efficiency, the present invention selects a variety of metal ion pore-forming agents that can form coordination effects with sulfonated polybenzimidazole polymers, forms pores by acid etching, constructs a fast proton transmission channel in the polymer membrane, improves the proton conduction capacity of the polybenzimidazole membrane, and thus improves the energy efficiency of the battery.

Description

Technical Field

[0001] The invention relates to a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery, a preparation method thereof and an application thereof, and belongs to the field of energy storage. Background Art

[0002] The large-scale, high-quality development of renewable energy is key to my country's future energy structure. my country's new energy sector is developing rapidly, maintaining an average double-digit annual growth rate. By the end of 2024, my country's installed wind power capacity will be approximately 510 million kilowatts and its installed photovoltaic capacity will be approximately 840 million kilowatts. However, due to the intermittent and seasonal characteristics of renewable energy sources such as wind and solar power, they cannot be directly integrated into the power grid. To ensure the stable and reliable operation of the power grid system, it is urgently needed to equip it with matching energy storage technologies. Among them, all-vanadium liquid flow batteries are considered the preferred technology for the development of energy storage technology due to their inherent safety, simple expansion, and high flexibility. However, the large-scale commercial application of all-vanadium liquid flow batteries is constrained by their high cost, of which the cost of the proton exchange membrane accounts for 30% of the total cost.

[0003] Currently, the proton exchange membrane commonly used in all-vanadium redox flow batteries is primarily Nafion membrane, due to its excellent chemical stability and high proton conductivity. However, its poor vanadium resistance results in low coulombic efficiency, rapid capacity decay, and increased maintenance costs. Furthermore, because Nafion membranes are perfluorinated, their production is expensive, leading to increased battery costs. Furthermore, the production process produces fluorine-containing waste, which can cause significant damage to the ecological environment. Summary of the Invention

[0004] In response to the problems of insufficient proton conductivity of polybenzimidazole membranes in all-vanadium redox flow batteries and low battery energy conversion efficiency, the purpose of the present invention is to provide a microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow batteries and its preparation method and application, so as to solve the problem of low proton conductivity in related technologies.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery, wherein the main chain structure of the proton exchange membrane is shown in formula (I);

[0007] ;

[0008] First, a sulfonated polybenzimidazole polymer is obtained by sulfonation, followed by adding a casting solvent and a metal ion pore-forming agent and stirring evenly to form a casting solution, which is then cast into a membrane. Finally, a microporous sulfonated polybenzimidazole proton exchange membrane is formed by acid etching. The microporous structure of the proton exchange membrane is formed by acid washing with the metal ion pore-forming agent, which is a metal chloride from the fourth period of the periodic table.

[0009] The casting solvent is dimethyl sulfoxide, the metal ion pore-forming agent is one of CrCl3, MnCl2, FeCl3, CoCl3, NiCl2, CuCl2, and ZnCl2, and the molar concentration of the metal ion pore-forming agent is 0.01 to 0.1 M. The micropore diameter of the microporous sulfonated polybenzimidazole proton exchange membrane is 1.2 to 1.8 Å, and the micropores are formed in situ by acid etching after coordination of metal ions with imidazole groups of the sulfonated polybenzimidazole polymer. The surface resistance of the microporous sulfonated polybenzimidazole proton exchange membrane is 0.130 to 0.154 Ω·cm. 2 .

[0010] The method for preparing the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery comprises the following steps:

[0011] S1) polymerizing 1,4-naphthalenedicarboxylic acid and 3,3'-diaminobenzidine under polyphosphoric acid catalysis to obtain a polymer backbone;

[0012] S2) dissolving the polymer backbone obtained in step S1 in concentrated sulfuric acid for sulfonation, washing with deionized water and drying to obtain a sulfonated polybenzimidazole polymer;

[0013] S3) dissolving the sulfonated polybenzimidazole polymer obtained in step S2 in a film casting solvent, adding a metal ion pore-forming agent, stirring evenly, and drying to form a film, thereby obtaining a sulfonated polybenzimidazole membrane containing metal ions;

[0014] S4) soaking the proton exchange membrane obtained in step S3 in a hydrochloric acid solution, removing excess metal ions by acid etching, washing with deionized water and drying to obtain a microporous sulfonated polybenzimidazole proton exchange membrane.

[0015] In the method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery, in step S1, the mass ratio of 1,4-naphthalenedicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid is 1:1:40-80.

[0016] In the method for preparing the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery, in step S1, the polymerization reaction temperature is 140-200° C., and the polymerization reaction time is 8-24 hours.

[0017] In the method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery, in step S2, the mass ratio of the polymer main chain to concentrated sulfuric acid is 1:5-20, the sulfonation treatment temperature is 60-120° C., and the sulfonation treatment time is 4-12 hours.

[0018] The application of the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery is used as the proton exchange membrane of the all-vanadium redox flow battery.

[0019] The application of the microporous sulfonated polybenzimidazole proton exchange membrane for the all-vanadium redox flow battery is that the positive and negative electrolytes of the all-vanadium redox flow battery are both solutions of vanadium ions with a molar concentration of 1.65M and a valence of 3.5, the supporting electrolyte is a sulfuric acid solution with a molar concentration of 3M, the volume of the positive electrolyte and the negative electrolyte are both 20mL; the bipolar plates of the all-vanadium redox flow battery are graphite bipolar plates, and the current collector of the all-vanadium redox flow battery is graphite carbon felt.

[0020] The application of the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow batteries has the following technical indicators: thickness of 40±5μm, micropore diameter of 1.2-1.8Å, sulfonation degree of 50%-70%, and ion exchange capacity of 1.9-3.4meq / g.

[0021] The design concept of the present invention is:

[0022] The present invention designs and prepares a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery. The proton exchange membrane is based on a sulfonated polybenzimidazole polymer. The imidazole groups on the sulfonated polybenzimidazole polymer coordinate with metal ions. A metal ion pore-forming agent is added during the membrane casting process. The metal ions are subsequently washed away by acid etching, thereby forming a microporous structure with the size of the metal ions in situ on the membrane. Through the size screening effect, rapid proton transmission is achieved while preventing vanadium ion transmission, thereby improving the ion selectivity of the membrane.

[0023] The present invention has a unique method for constructing a microporous structure, which uses a metal ion pore-forming agent to coordinate with the imidazole group of a sulfonated polybenzimidazole polymer, and forms a microporous structure by acid etching after film casting. This method of using a metal ion pore-forming agent to construct micropores in situ within the membrane has not been reported in the prior art. In particular, by selecting a specific metal chloride in the fourth period of the periodic table as a pore-forming agent, the present application can accurately control the size and distribution of micropores, providing a size screening channel for proton transport, effectively preventing the penetration of impurity ions such as vanadium ions, and thus significantly improving the ion selectivity and proton conductivity of the proton exchange membrane.

[0024] The advantages and beneficial effects brought about by the technical solution provided by the present invention are as follows:

[0025] 1. This invention provides a method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow batteries. Based on the original sulfonated polybenzimidazole proton exchange membrane, a microporous structure tailored to the size of metal ions is constructed, simultaneously improving the proton conductivity and ion selectivity of the proton exchange membrane, thereby increasing the energy efficiency of the all-vanadium redox flow battery. Furthermore, this invention uses inexpensive polybenzimidazole as a raw material, resulting in simple preparation, high mechanical strength, stable chemical properties, and high cyclic stability, offering significant cost advantages over commercial Nafion membrane materials.

[0026] 2. The proton exchange membrane prepared in this invention is made from polybenzimidazole polymer, which exhibits high chemical stability, excellent mechanical strength, and low production cost. Crucially, the imidazole groups on the polybenzimidazole membrane readily bind protons under acidic conditions, thereby hindering the permeation of vanadium ions through Donnan repulsion, resulting in excellent ion selectivity. Therefore, polybenzimidazole membranes are the most promising membrane material for future all-vanadium redox flow batteries.

[0027] 3. The present invention brings about a significant improvement in comprehensive performance. The prepared microporous sulfonated polybenzimidazole proton exchange membrane has been optimized in terms of key technical indicators such as thickness, micropore diameter, sulfonation degree and ion exchange capacity. While ensuring that the membrane has high mechanical strength and chemical stability, it achieves a combination of low surface resistance and high ion selectivity. Compared with the original sulfonated polybenzimidazole proton exchange membrane without the addition of pore-forming agent and the commercial Nafion membrane, the proton exchange membrane of the present invention exhibits lower surface resistance and higher coulombic efficiency, voltage efficiency, energy efficiency and capacity retention rate, indicating that its application performance in all-vanadium liquid flow batteries has been significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the surface resistance test device. In the figure, 1, U-shaped test cell, 2, sulfuric acid solution, 3, microporous sulfonated polybenzimidazole proton exchange membrane, 4, electrode.

[0029] Figure 2 Schematic diagram of the all-vanadium redox flow battery structure. Figure 3: Microporous sulfonated polybenzimidazole proton exchange membrane, 5: Positive electrode, 6: Positive electrolyte reservoir, 7: Positive peristaltic pump, 8: Negative peristaltic pump, 9: Negative electrolyte reservoir, 10: Negative electrode.

[0030] Figure 3 This is the performance diagram of the 200-cycle all-vanadium redox flow battery of Example 6.

[0031] Figure 4 This is the performance diagram of the 200-cycle all-vanadium liquid flow battery of Comparative Example 1.

[0032] Figure 5This is the performance diagram of the 200-cycle all-vanadium liquid flow battery of Comparative Example 2. DETAILED DESCRIPTION

[0033] In practice, the present invention first produces a sulfonated polybenzimidazole polymer through sulfonation. A casting solvent and a metal ion pore-forming agent are then added and stirred to form a casting solution, which is then cast into a membrane. Finally, a microporous membrane is formed through acid etching. To address the issues of insufficient proton conductivity and low energy conversion efficiency of polybenzimidazole membranes in all-vanadium redox flow batteries, the present invention selects a variety of metal ion pore-forming agents that can form coordination interactions with the sulfonated polybenzimidazole polymer. Through acid etching, pores are formed in the polymer membrane to create rapid proton transport channels, thereby enhancing the proton conductivity of the polybenzimidazole membrane and, consequently, the battery's energy efficiency.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0035] In the embodiment of the present invention, the prepared microporous proton exchange membrane was subjected to a surface resistance test and an all-vanadium redox flow battery test. The test parameters and equipment were based on the contents described in "NB / T 42080-2023 General Technical Requirements and Test Methods for Ion Conducting Membranes for All-vanadium Redox Flow Batteries" and "NB / T 42081-2016 All-vanadium Redox Flow Battery Single Cell Performance Test Method". The test environment and steps are as follows:

[0036] 1) Surface resistance test

[0037] Test environment:

[0038] ——Ambient temperature: 25±5℃;

[0039] ——Air humidity: 50±5%;

[0040] Test steps:

[0041] a) Prepare a 3 M sulfuric acid solution as the supporting electrolyte;

[0042] b) placing a microporous sulfonated polybenzimidazole proton exchange membrane in a test device, and adding 10 mL of supporting electrolyte on both sides of the microporous sulfonated polybenzimidazole proton exchange membrane;

[0043] c) Connect the test device to the electrochemical workstation to perform surface resistance testing.

[0044] d) Record the test data and take the average value after repeating each test three times.

[0045] 2) All-vanadium redox flow battery testing

[0046] Test environment:

[0047] ——Ambient temperature: 25±5℃;

[0048] ——Air humidity: 50±5%;

[0049] ——Electrolyte temperature: 35±5℃.

[0050] Test steps:

[0051] a) Assembling a microporous sulfonated polybenzimidazole proton exchange membrane into a battery test system and adding positive and negative electrolytes;

[0052] b) Turn on the peristaltic pump and leave the battery system for 1 hour;

[0053] c) Battery system at 200mA / cm 2 Charging is performed at a current density up to the charge cut-off voltage;

[0054] d) Battery system at 200mA / cm 2 Discharge at a current density up to the discharge cut-off voltage;

[0055] e) Repeat steps c) to d);

[0056] f) Record various parameters of each charge and discharge cycle.

[0057] Example 1: (Metal ion pore-forming agent is CrCl3)

[0058] In this embodiment, a method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery comprises the following steps:

[0059] 1) Film making process

[0060] S1. Dissolve 1,4-naphthalene dicarboxylic acid and 3,3'-diaminobenzidine in polyphosphoric acid and polymerize at 180°C for 8 hours to produce a black, viscous polymer backbone. The mass ratio of 1,4-naphthalene dicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid is 1:1:60.

[0061] S2. Dissolve the polymer backbone obtained in step S1 in concentrated sulfuric acid for sulfonation, stir at 120°C for 6 hours, rinse with deionized water, and dry to obtain a sulfonated polybenzimidazole polymer. The mass ratio of the polymer backbone to concentrated sulfuric acid (98 wt%) is 1:15.

[0062] S3. Dissolve 0.1 g of the sulfonated polybenzimidazole polymer obtained in step S2 in 10 mL of dimethyl sulfoxide (DMSO), and add CrCl3 metal ion pore-forming agent to a molar concentration of 0.05 M of the CrCl3 metal ion pore-forming agent. After stirring evenly, dry the mixture to form a film to obtain a sulfonated polybenzimidazole membrane containing metal ions.

[0063] S4. The sulfonated polybenzimidazole membrane containing metal ions obtained in step S3 is immersed in a hydrochloric acid solution with a molar concentration of 3M to wash away excess metal ions, and then washed with deionized water and dried to obtain a microporous sulfonated polybenzimidazole proton exchange membrane.

[0064] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.23 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0065] 2) Surface resistance test

[0066] like Figure 1 As shown, the surface resistance test device mainly includes a U-shaped test cell 1, a sulfuric acid solution 2, a microporous sulfonated polybenzimidazole proton exchange membrane 3, and an electrode 4. The membrane tested is the microporous sulfonated polybenzimidazole proton exchange membrane prepared in this embodiment. The microporous sulfonated polybenzimidazole proton exchange membrane 3 is placed in the middle sample area at the bottom of the inner cavity of the U-shaped test cell 1. The test solution is 10mL of a 3M sulfuric acid solution 2 placed on both sides of the microporous sulfonated polybenzimidazole proton exchange membrane 3 in the inner cavity of the U-shaped test cell 1. The sulfuric acid solution 2 is connected to the electrochemical workstation via the electrode 4. After standing for 10 minutes before the test, the surface resistance test is performed using the electrochemical workstation.

[0067] 3) All-vanadium redox flow battery testing

[0068] like Figure 2 As shown, the all-vanadium redox flow battery mainly includes a microporous sulfonated polybenzimidazole proton exchange membrane 3, a positive electrode 5, a positive electrode electrolyte storage tank 6, a positive electrode peristaltic pump 7, a negative electrode peristaltic pump 8, a negative electrode electrolyte storage tank 9, and a negative electrode 10. The specific structure is as follows:

[0069] The bottom of the negative electrolyte reservoir tank 9 is connected to the bottom of the negative electrode 10 via a pipeline (with a negative electrode peristaltic pump 8 installed on it), and the top of the negative electrolyte reservoir tank 9 is connected to the top of the negative electrode 10 via a pipeline, forming the negative electrode portion of the all-vanadium redox flow battery. The bottom of the positive electrolyte reservoir tank 6 is connected to the bottom of the positive electrode 5 via a pipeline (with a positive electrode peristaltic pump 7 installed on it), and the top of the positive electrolyte reservoir tank 6 is connected to the top of the positive electrode 5 via a pipeline, forming the positive electrode portion of the redox flow battery. The negative electrode 10 and the positive electrode 5 are arranged vertically parallel to each other, separated by a microporous sulfonated polybenzimidazole proton exchange membrane 3. The two sides of the microporous sulfonated polybenzimidazole proton exchange membrane 3 are in contact with the electrolyte in the negative electrode 10 and the positive electrode 5, respectively.

[0070] The positive electrolyte reservoir 6 is filled with positive electrolyte, and the negative electrolyte reservoir 9 is filled with negative electrolyte. Both contain a 1.65M solution of vanadium ions with a valence of 3.5. The supporting electrolyte in the electrolyte is a 3M sulfuric acid solution. The volume of both the positive and negative electrolytes is 20 mL. The bipolar plates used in the all-vanadium redox flow battery are graphite bipolar plates, the current collector used is graphite carbon felt, and the membrane used is the microporous sulfonated polybenzimidazole proton exchange membrane prepared in this example.

[0071] Example 2: (Metal ion pore-forming agent is MnCl2)

[0072] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent used in the membrane formation process is MnCl2, and the molar concentration of the MnCl2 metal ion pore-forming agent is 0.02M. The preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the liquid flow battery and the test parameters are the same as those in Example 1.

[0073] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.66 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0074] Example 3: (Metal ion pore-forming agent is FeCl3)

[0075] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent used in the membrane formation process is FeCl3, and the molar concentration of the FeCl3 metal ion pore-forming agent is 0.03M. The rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the flow battery and the test parameters are the same as in Example 1.

[0076] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.29 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0077] Example 4: (Metal ion pore-forming agent is CoCl2)

[0078] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent in the membrane formation process is CoCl2, and the molar concentration of the CoCl2 metal ion pore-forming agent is 0.04M. The rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the liquid flow battery and the test parameters are the same as in Example 1.

[0079] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.49 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0080] Example 5: (Metal ion pore-forming agent is NiCl2)

[0081] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent used in the membrane formation process is NiCl2, and the molar concentration of the NiCl2 metal ion pore-forming agent is 0.06M. The rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the flow battery, and the test parameters are the same as in Example 1.

[0082] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.38 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0083] Example 6: (Metal ion pore-forming agent is CuCl2)

[0084] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent used in the membrane formation process is CuCl2, and the molar concentration of the CuCl2 metal ion pore-forming agent is 0.07M. The rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the liquid flow battery and the test parameters are the same as in Example 1.

[0085] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.46 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0086] Example 7: (Metal ion pore-forming agent is ZnCl2)

[0087] In this embodiment, the difference from Example 1 is that the metal ion pore-forming agent in the membrane formation process is ZnCl2, and the molar concentration of the ZnCl2 metal ion pore-forming agent is 0.08M. The rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the liquid flow battery and the test parameters are the same as in Example 1.

[0088] In this embodiment, the technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness of 40±5 μm, micropore diameter of 1.48 Å, sulfonation degree of 60%, and ion exchange capacity of 2.79 meq / g.

[0089] Comparative Example 1:

[0090] The difference from Example 1 is that in Comparative Example 1, the original sulfonated polybenzimidazole proton exchange membrane was not added with a pore-forming agent during the membrane preparation process, and the rest, such as the preparation of the sulfonated polybenzimidazole polymer, the test of the membrane surface resistance, the electrolyte of the liquid flow battery and the test parameters, were the same as in Example 1.

[0091] In this comparative example, the technical indicators of the original sulfonated polybenzimidazole proton exchange membrane without the addition of a pore-forming agent are as follows: thickness of 40±5 μm, degree of sulfonation of 60%, and ion exchange capacity of 2.79 meq / g.

[0092] Comparative Example 2:

[0093] The difference from Example 1 is that in Comparative Example 2, the commercial membrane selected is Nafion212 membrane, and the test of membrane surface resistance, the electrolyte of the flow battery and the test parameters are the same as those in Example 1.

[0094] In this comparative example, the technical specifications of the commercial Nafion 212 membrane are as follows: thickness is 50 μm.

[0095] Table 1 Physicochemical properties of proton exchange membrane

[0096] Thickness (μm) <![CDATA[Sheet Resistance (Ω·cm 2 ).]]> Example 1 40±5 0.136 Example 2 40±5 0.144 Example 3 40±5 0.137 Example 4 40±5 0.154 Example 5 40±5 0.135 Example 6 40±5 0.130 Example 7 40±5 0.151 Comparative Example 1 40±5 0.172 Comparative Example 2 50 0.182

[0097] As shown in Table 1, the thickness of the membranes prepared in each Example and Comparative Example 1 was 40±5 μm. The membrane used in Comparative Example 2 was a commercial Nafion 212 membrane with a thickness of 50 μm. The sheet resistance results showed that the sulfonated polybenzimidazole proton exchange membranes with the addition of pore-forming agents in each Example had lower sheet resistance than the original sulfonated polybenzimidazole proton exchange membrane in Comparative Example 1. The addition of metal ion pore-forming agents in the present invention can effectively increase the proton conductivity of the membrane, and its sheet resistance can reach 0.130 to 0.154 Ω·cm. 2 .

[0098] like Figure 3As shown in the figures, the membrane-assembled all-vanadium liquid flow battery prepared by adding a CuCl2 pore-forming agent with a molar concentration of 0.05 M in Example 6 can maintain a coulombic efficiency of 99.62%, a voltage efficiency of 82.82%, an energy efficiency of 82.51%, and a capacity retention rate of 80.62%, and has good energy efficiency and capacity retention rate.

[0099] Table 2 Flow battery test performance

[0100] Coulombic efficiency% Voltage efficiency% Energy efficiency % Capacity retention rate% Example 1 99.77 82.69 82.50 78.69 Example 2 99.69 82.81 82.56 79.84 Example 3 99.56 82.78 82.42 80.25 Example 4 99.71 81.78 81.54 81.32 Example 5 99.80 82.75 82.58 79.58 Example 6 99.62 82.82 82.51 80.62 Example 7 99.48 81.74 81.32 80.88 Comparative Example 1 99.86 73.32 73.22 80.13 Comparative Example 2 96.18 76.95 74.02 55.82

[0101] As shown in Table 2, the experimental results of Examples 1 to 7 are similar to Figure 3 , coulombic efficiency 99.48-99.80%, voltage efficiency 81.74-82.82%, energy efficiency 81.32-82.58%, capacity retention 78.69-81.32%. Figure 4 ) has higher energy efficiency and is relatively better than the commercial Nafion membrane in Comparative Example 2 ( Figure 5 ) has better energy efficiency and capacity retention.

[0102] The above experimental results show that the microporous sulfonated polybenzimidazole proton exchange membrane provided by the present invention has low surface resistance, and the assembled battery has a high conductivity at 200 mA / cm 2 It has higher coulombic efficiency, voltage efficiency, and energy efficiency under high electrical density, and also has a higher capacity retention rate.

[0103] Experimental results show that the present invention designs and prepares a microporous sulfonated polybenzimidazole proton exchange membrane for use in all-vanadium redox flow batteries. By sulfonation treatment and the addition of an appropriate amount of metal ion pore-forming agent, proton transmission channels are constructed, the proton conductivity of the polybenzimidazole membrane is improved, and the problems of capacity decay and low energy efficiency in all-vanadium redox flow batteries are improved. Compared with the currently commercially available Nafion membrane, the membrane has significant performance and price advantages.

[0104] The above description of the present invention merely provides some specific embodiments for those skilled in the art to understand and implement. A variety of obvious modifications may be made to these embodiments by those skilled in the art, and the basic principles defined in the present invention may be applied to other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention should not be limited to the embodiments shown in this document, and further changes and modifications to the present invention without departing from the spirit and scope of the present invention should be covered by the claims of the present invention.

Claims

1. A microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery, characterized in that: The main chain of the proton exchange membrane is polymerized from 1,4-naphthalene dicarboxylic acid and 3,3'-diaminobenzidine, and its structure is shown in formula (I); First, a sulfonated polybenzimidazole polymer is obtained through sulfonation. A casting solvent and a metal ion pore-forming agent are then added and stirred evenly to form a casting solution, which is then cast into a membrane. Finally, a microporous sulfonated polybenzimidazole proton exchange membrane is formed through acid etching. The microporous structure of the proton exchange membrane is formed after acid washing with the metal ion pore-forming agent. The metal ion pore-forming agent is a metal chloride from the fourth period of the periodic table. It can precisely control the size and distribution of micropores, forming a microporous structure with the size of metal ions in situ, providing a size screening channel for proton transport and effectively preventing the penetration of impurity ions. The casting solvent is dimethyl sulfoxide, the metal ion pore-forming agent is one of CrCl3, MnCl2, FeCl3, CoCl3, NiCl2, CuCl2, and ZnCl2, and the molar concentration of the metal ion pore-forming agent is 0.01 to 0.1 M; the micropore diameter of the microporous sulfonated polybenzimidazole proton exchange membrane is The micropores are formed in situ by acid etching after coordination of metal ions with imidazole groups of sulfonated polybenzimidazole polymers. The surface resistance of the microporous sulfonated polybenzimidazole proton exchange membrane is 0.130-0.154Ω·cm 2 .

2. A method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The following steps are involved: S1) polymerizing 1,4-naphthalene dicarboxylic acid and 3,3'-diaminobenzidine under polyphosphoric acid catalysis to obtain a polymer backbone; S2) dissolving the polymer backbone obtained in step S1 in concentrated sulfuric acid for sulfonation, washing with deionized water and drying to obtain a sulfonated polybenzimidazole polymer; S3) dissolving the sulfonated polybenzimidazole polymer obtained in step S2 in a film casting solvent, adding a metal ion pore-forming agent, stirring evenly, and drying to form a film to obtain a sulfonated polybenzimidazole film containing metal ions; S4) soaking the proton exchange membrane obtained in step S3 in a hydrochloric acid solution, removing excess metal ions by acid etching, washing with deionized water and drying to obtain a microporous sulfonated polybenzimidazole proton exchange membrane.

3. The method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery according to claim 2, characterized in that: In step S1, the mass ratio of 1,4-naphthalene dicarboxylic acid, 3,3'-diaminobenzidine and polyphosphoric acid is 1:1:40-80.

4. The method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery according to claim 2, characterized in that: In step S1, the polymerization reaction temperature is 140-200° C., and the polymerization reaction time is 8-24 hours.

5. The method for preparing a microporous sulfonated polybenzimidazole proton exchange membrane for an all-vanadium redox flow battery according to claim 2, characterized in that: In step S2, the mass ratio of the polymer main chain to concentrated sulfuric acid is 1:5-20, the temperature of the sulfonation treatment is 60-120° C., and the time of the sulfonation treatment is 4-12 hours.

6. A use of the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery according to claim 1, characterized in that: The proton exchange membrane is used as the proton exchange membrane of the all-vanadium redox flow battery.

7. The use of the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery according to claim 6, characterized in that: The positive and negative electrolytes of the all-vanadium liquid flow battery are both solutions with a molar concentration of 1.65M and a valence of vanadium ions of 3.

5. The supporting electrolyte is a sulfuric acid solution with a molar concentration of 3M. The volume of the positive and negative electrolytes is 20mL. The bipolar plates of the all-vanadium liquid flow battery are graphite bipolar plates, and the current collector of the all-vanadium liquid flow battery is graphite carbon felt.

8. The use of the microporous sulfonated polybenzimidazole proton exchange membrane for all-vanadium redox flow battery according to claim 6, characterized in that: The technical specifications of the microporous sulfonated polybenzimidazole proton exchange membrane are as follows: thickness 40±5μm, micropore diameter The sulfonation degree is 50% to 70%, and the ion exchange capacity is 1.9 to 3.4 meq / g.

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