Proton exchange membrane for all-vanadium redox flow battery and preparation method of proton exchange membrane

Abstract

The invention provides a proton exchange membrane for an all-vanadium redox flow battery and a preparation method of the proton exchange membrane. The preparation method of the proton exchange membrane for the all-vanadium redox flow battery comprises the following steps: (1) mixing a perfluorosulfonic acid resin solution, a bismuth salt catalyst, a phosphine coordination compound and N, N '-carbonyldiimidazole to obtain a membrane preparation solution; (2) coating a substrate with the film preparation liquid prepared in the step (1) to obtain a wet film attached to the substrate; and (3) drying and annealing the base material and the wet membrane on the base material, and peeling off the formed membrane from the base material to obtain the proton exchange membrane for the all-vanadium redox flow battery. According to the proton exchange membrane for the all-vanadium redox flow battery prepared by the method, the activation overpotential of chemical conversion of an electroactive substance can be reduced, so that the voltage efficiency and coulombic efficiency of the battery are improved, and the purpose of improving the energy efficiency is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of liquid flow battery energy storage, and in particular relates to a proton exchange membrane for an all-vanadium liquid flow battery and a preparation method thereof. Background Art

[0002] With the efficient use of renewable energy such as wind and solar energy, the demand for large and medium-sized energy storage is increasing. Vanadium redox flow battery (VRFB) has attracted much attention due to its advantages such as fast response to changes in energy demand, small impact on the environment, long life cycle and flexible operation. Compared with other flow batteries, VRFB uses VO 2+ / VO2 and V 3+ / V 2+ The redox pair serves as the positive and negative electrolytes, avoiding cross-contamination of the positive and negative electrolyte active substances during the long-term operation of the battery system, thereby significantly reducing costs.

[0003] The proton exchange membrane is a key component of a VRFB, determining the efficiency, lifespan, and cost of the VRFB system. The membrane separates the positive and negative half-cells and provides proton conduction. An ideal VRFB membrane should possess high proton conductivity and excellent stability. The current mainstream technology for perfluorosulfonic acid proton exchange membranes aims to achieve an optimal balance between coulombic efficiency and voltage efficiency. However, when the membrane thickness is increased, the internal resistance increases, resulting in a lower voltage efficiency. When the membrane thickness is too low, vanadium ions can more easily pass through the membrane, reducing the coulombic efficiency. This technical approach significantly limits the membrane's performance and restricts its use in all-vanadium redox flow batteries.

[0004] Adding a catalyst to the system can reduce the electrochemical overpotential. CN106972186A mentioned that a catalyst such as BiCl3 / Bi(NO3)3 can be coated on the surface of the proton exchange membrane to reduce the electrochemical overpotential. 3+ / V 2+ However, the BiCl3 / Bi(NO3)3 catalyst is easily soluble in the electrolyte and has a weak interaction with the proton exchange membrane, so it cannot fully play a catalytic role. Summary of the Invention

[0005] To address the existing problems of BiCl3 / Bi(NO3)3 catalysts being easily soluble in the electrolyte, having a weak interaction with the proton exchange membrane, and being unable to fully exert their catalytic effect, the present invention provides a proton exchange membrane for an all-vanadium redox flow battery and a preparation method thereof. The present invention combines a bismuth catalyst, a ligand, and N,N'-carbonyldiimidazole into a perfluorosulfonic acid membrane solution. The coordination effect of the phosphine coordination compound enhances the interaction between the proton membrane and the bismuth ions. The large number of anionic groups in the ligand also helps attract vanadium ions to the surface, resulting in a better catalytic effect and further improving the voltage efficiency of the battery. N,N'-carbonyldiimidazole can activate the sulfonic acid groups. The two substances work synergistically to reduce the activation overpotential of the chemical conversion of the electroactive substance, thereby improving the voltage efficiency and coulombic efficiency of the battery, achieving the goal of improving energy efficiency.

[0006] Specifically, the first aspect of the present invention provides a method for preparing a proton exchange membrane for an all-vanadium redox flow battery, the method comprising the following steps: (1) mixing a perfluorosulfonic acid resin solution, a bismuth salt catalyst, a phosphine coordination compound, and N,N'-carbonyldiimidazole to obtain a membrane-forming solution; (2) coating the film-forming solution obtained in step (1) on a substrate to obtain a wet film attached to the substrate; (3) Drying and annealing the substrate and the wet film thereon, and peeling the formed film off the substrate to obtain the proton exchange membrane for the all-vanadium redox flow battery.

[0007] In one or more embodiments, the mass fraction of the perfluorosulfonic acid resin in the perfluorosulfonic acid resin solution is 5%-30%, preferably 10%-20%.

[0008] In one or more embodiments, the solvent in the perfluorosulfonic acid resin solution is N,N-dimethylformamide.

[0009] In one or more embodiments, the perfluorosulfonic acid resin is dissolved in N,N-dimethylformamide to form the perfluorosulfonic acid resin solution.

[0010] In one or more embodiments, the bismuth salt catalyst is selected from one or more of bismuth chloride, bismuth nitrate, bismuth sulfate, and bismuth citrate.

[0011] In one or more embodiments, the phosphine coordination compound is a phosphine coordination compound containing a hydroxyl group, preferably one or more selected from hydroxyethylidene diphosphonic acid, bishydroxyethylphosphonic acid and hydroxyethylphosphonic acid.

[0012] In one or more embodiments, the mass ratio of the perfluorosulfonic acid resin to the bismuth salt catalyst is 1:(0.01-0.05).

[0013] In one or more embodiments, the mass ratio of the bismuth salt catalyst to the phosphine coordination compound is 1:(0.01-0.06).

[0014] In one or more embodiments, the molar ratio of the phosphine coordination compound to N,N'-carbonyldiimidazole is 1:(0.8-1.2).

[0015] In one or more embodiments, the material of the substrate layer is selected from one or more of PEN, PI and PET.

[0016] In one or more embodiments, the coating is performed by solution casting.

[0017] In one or more embodiments, the coating speed is 8-15 mm / s.

[0018] In one or more embodiments, the drying method is oven drying, the oven drying temperature is preferably 120-160° C., and the oven drying time is preferably 8-12 minutes.

[0019] In one or more embodiments, the annealing temperature is 180-220° C., and the annealing time is 18-22 minutes.

[0020] In one or more embodiments, the proton exchange membrane for all-vanadium redox flow battery has a thickness of 30-50 μm.

[0021] A second aspect of the present invention provides a proton exchange membrane for an all-vanadium redox flow battery, which is prepared using the method for preparing a proton exchange membrane for an all-vanadium redox flow battery as described in any embodiment herein.

[0022] A third aspect of the present invention provides an all-vanadium redox flow battery, which includes a proton exchange membrane for an all-vanadium redox flow battery as described in any embodiment herein.

[0023] A fourth aspect of the present invention provides the use of a proton exchange membrane for an all-vanadium redox flow battery as described in any embodiment herein in improving the energy efficiency of the all-vanadium redox flow battery.

[0024] A fifth aspect of the present invention provides the use of a phosphine coordination compound and N,N'-carbonyldiimidazole in the preparation of a proton exchange membrane for an all-vanadium redox flow battery.

[0025] The sixth aspect of the present invention provides the use of phosphine coordination compounds and N,N'-carbonyldiimidazole in reducing the dissolution of bismuth salt catalyst in proton exchange membrane for all-vanadium redox flow battery in electrolyte and increasing the interaction force between bismuth salt catalyst and proton exchange membrane. DETAILED DESCRIPTION

[0026] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used herein. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art with respect to the present invention. In the event of conflict, the definitions herein shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0028] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0029] Throughout this document, all features, such as values, amounts, contents, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0030] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0031] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0032] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0033] The present invention provides a method for preparing a proton exchange membrane for an all-vanadium redox flow battery, the method comprising the following steps: (1) mixing a perfluorosulfonic acid resin solution, a bismuth salt catalyst, a phosphine coordination compound, and N,N'-carbonyldiimidazole to obtain a membrane-forming solution; (2) coating the film-forming solution obtained in step (1) on a substrate to obtain a wet film attached to the substrate; (3) Drying and annealing the substrate and the wet film thereon, and peeling the formed film off the substrate to obtain the proton exchange membrane for the all-vanadium redox flow battery.

[0034] In the perfluorosulfonic acid resin solution of the present invention, the mass fraction of the perfluorosulfonic acid resin may be 5%-30%, preferably 10%-20%. In some embodiments, the solvent is N,N-dimethylformamide.

[0035] In some embodiments, a perfluorosulfonic acid resin is dissolved in a solvent such as N,N-dimethylformamide to form a perfluorosulfonic acid resin solution. In some specific embodiments, the perfluorosulfonic acid resin is dissolved in N,N-dimethylformamide and stirred until completely dissolved. The dissolution temperature may be 20-80°C or 60-80°C. The stirring time may be 3-5 hours.

[0036] In some embodiments, a perfluorosulfonic acid resin dispersion is evaporated to obtain a dried perfluorosulfonic acid resin. Commercially available perfluorosulfonic acid resin dispersions, such as Nafion D520 dispersion and Nafion D2020 dispersion, can be used. The temperature and time for evaporating the perfluorosulfonic acid resin dispersion can be determined based on the properties of the resin dispersion, such as the type of solvent, to obtain the perfluorosulfonic acid resin. The evaporation temperature can be 60-120°C or 70-90°C. The evaporation time can be 8-12 hours.

[0037] In the present invention, the bismuth salt catalyst is selected from one or more of bismuth chloride, bismuth nitrate, bismuth sulfate, and bismuth citrate. The mass ratio of the perfluorosulfonic acid resin to the bismuth salt catalyst can be 1:(0.01-0.05), such as 1:(0.03-0.05).

[0038] In the present invention, the phosphine coordination compound is selected from one or more of hydroxyethylidene diphosphonic acid, bis(hydroxyethyl)phosphonic acid, and hydroxyethylphosphonic acid. The mass ratio of the bismuth salt catalyst to the phosphine coordination compound can be 1:(0.01-0.06), such as 1:(0.04-0.06). The inventors have discovered through experiments that, among various ligands, phosphine coordination compounds that react with bismuth ions are more effective. This coordination enhances the interaction between the proton membrane and the bismuth ion. Furthermore, the numerous anionic groups in the ligand also help attract vanadium ions to the surface, resulting in a better catalytic effect and further improving the battery's voltage efficiency. Furthermore, the inventors have discovered that selecting a phosphine coordination compound containing a hydroxyl group facilitates the reaction between the ligand and the sulfonate group.

[0039] In the present invention, the molar ratio of the phosphine coordination compound to N,N'-carbonyldiimidazole can be 1:(0.8-1.2), such as 1:0.9, 1:1, 1:1.1, or any range within the aforementioned two ratios. N,N'-carbonyldiimidazole can activate the sulfonic acid group and further promote its reaction with the hydroxyl group.

[0040] In step (1), a perfluorosulfonic acid resin solution, a bismuth salt catalyst, a phosphine coordination compound, and N,N'-carbonyldiimidazole are mixed and then dispersed to obtain a film-forming solution. The dispersion can be performed using a homogenizer. The dispersion time and speed are not particularly limited, and the dispersion can be performed until uniform dispersion is achieved. Exemplary dispersion times can be 10 min to 30 min, and dispersion speeds can be 10,000 to 20,000 rpm.

[0041] The material of the substrate suitable for the present invention can be selected from one or more of PEN (polyethylene naphthalate), PI (polyimide) and PET (ethylene terephthalate).

[0042] In some embodiments, in step (2), the film-forming liquid can be poured onto the substrate and coated using a cast coater. The coating gap can be 350-450 μm, such as 400-420 μm. The coating speed can be 8-15 mm / s, such as 9-12 mm / s. The coating thickness of the film-forming liquid on the substrate surface can be adjusted according to the target film thickness.

[0043] In some embodiments, in step (3), the obtained wet film can be placed in an oven, such as a forced air oven, to dry the film to evaporate the solvent. The drying temperature can be 120-160° C., such as 135-145° C. The drying time can be 8-12 minutes.

[0044] After drying, the dry membrane is obtained and then annealed. In some embodiments, the dry membrane can be placed in an oven, such as a forced-air oven, for annealing. The annealing conditions can be annealing temperature of 180-220°C and annealing time of 18-22 minutes. The membrane is then peeled off from the substrate to obtain the final proton exchange membrane.

[0045] The present invention also includes an all-vanadium redox flow battery, which comprises a positive electrode, a negative electrode, a proton exchange membrane of the present invention, and an electrolyte. The positive and negative electrodes of the battery are separated by the proton exchange membrane of the present invention.

[0046] In the present invention, the structure of the all-vanadium redox flow battery, the positive and negative electrolytes, and the method for making the all-vanadium redox flow battery are conventional in the art. The positive and negative electrolytes can be vanadium ion solutions of different valence states. For example, the positive electrolyte can be VOSO4 +A solution of sulfuric acid, wherein the concentration of VOSO4 is 1.6-1.8 mol / L, such as 1.7±0.05 mol / L, and the concentration of sulfuric acid is 2-4 mol / L. The negative electrode electrolyte can be VSO4 + A solution of sulfuric acid, wherein the concentration of VSO4 can be 1.4-1.6 mol / L, such as 1.5±0.05 mol / L, and the concentration of sulfuric acid can be 2-4 mol / L.

[0047] Beneficial effects of the present invention: The present invention prepares a proton exchange membrane for an all-vanadium redox flow battery by blending a bismuth salt catalyst, a phosphine coordination compound, and N,N'-carbonyldiimidazole into a perfluorosulfonic acid resin solution. This membrane reduces the activation overpotential for chemical conversion of electroactive substances, thereby improving the battery's voltage and coulombic efficiencies, ultimately boosting energy efficiency. The preparation method is simple, exhibits excellent electrochemical performance, and is low-cost, making it amenable to large-scale production.

[0048] The present invention will be described below by way of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the examples are, unless otherwise stated, conventional methods, reagents, and materials in the art. The starting compounds in the examples can all be purchased from commercial sources.

[0049] The Nafion D520 resin dispersion used in the examples and comparative examples was purchased from Thermo Fisher Scientific.

[0050] Example 1 Step (1): Pour the purchased Nafion 520 dispersion into an evaporating dish, adjust the oven temperature to 80°C, and place the evaporating dish in the oven for 10 hours to obtain Nafion resin. Add 20g of the obtained Nafion resin and 80g of DMF solvent into a reactor and stir at 80°C for 4 hours at a stirring speed of 300 rpm. Stop stirring after observing that the Nafion resin is completely dissolved to obtain a perfluorosulfonic acid resin solution with a mass fraction of 20wt%.

[0051] 100 g of the prepared perfluorosulfonic acid resin solution was taken, and 0.62 g of bismuth chloride solid, 0.031 g of hydroxyethylidene diphosphonic acid solid, and 0.024 g of N,N'-carbonyldiimidazole were added to the solution. The mixture was dispersed evenly in a homogenizer at 15,000 rpm for 30 minutes to obtain a film-forming solution.

[0052] Step (2): Pour the film-making solution obtained in the previous step onto the PEN substrate, set the gap of the casting coater to 400 μm, and set the running speed to 10 mm / s to obtain a wet film attached to the substrate.

[0053] Step (3): Place the wet film obtained in the previous step in a 140°C forced air oven and remove the solvent for 10 minutes to obtain a dry film; then place the dry film in a 200°C forced air oven and anneal for 20 minutes, peel off the film from the substrate, and obtain a 40-μm-thick proton exchange membrane for all-vanadium liquid flow batteries.

[0054] Example 2 The only difference between Example 2 and Example 1 is that in step (1), the amount of bismuth chloride solid added in Example 1 is 1 g; the amount of hydroxyethylidene diphosphonic acid solid added is 0.05 g. In step (2), the applicator gap is 410 μm. The remaining operating conditions and steps are the same as in Example 1.

[0055] Example 3 The only difference between Example 3 and Example 1 is that the bismuth chloride solid in Example 1 is replaced with bismuth nitrate solid. The remaining operating conditions and steps are the same as those in Example 1.

[0056] Example 4 The only difference between Example 4 and Example 1 is that the hydroxyethylidene diphosphonic acid solid in Example 1 is replaced with bis(hydroxyethyl)phosphonic acid solid. The remaining operating conditions and steps are the same as those in Example 1.

[0057] Comparative Example 1 Step (1): Pour the purchased Nafion 520 dispersion into an evaporating dish, adjust the oven temperature to 80°C, and place the evaporating dish in the oven for 10 hours to obtain Nafion resin. Add 20g of the obtained Nafion resin and 80g of DMF solvent into a reactor and stir at 80°C for 4 hours at a stirring speed of 300 rpm. Stop stirring after observing that the Nafion resin is completely dissolved to obtain a perfluorosulfonic acid resin solution with a mass fraction of 20wt%.

[0058] 100 g of the prepared perfluorosulfonic acid resin solution was taken, and 0.62 g of bismuth chloride solid was added to the solution. The mixture was dispersed evenly using a homogenizer at 15,000 rpm for 30 minutes to obtain a membrane-forming solution.

[0059] Step (2): Pour the film-making solution obtained in the previous step onto the PEN substrate, set the gap of the casting coater to 400 μm, and set the running speed to 10 mm / s to obtain a wet film attached to the substrate.

[0060] Step (3): Place the wet membrane obtained in the previous step in a 140°C forced air oven and remove the solvent for 10 minutes to obtain a dry membrane; then place the dry membrane in a 200°C forced air oven and anneal for 20 minutes to obtain a 40 μm thick proton exchange membrane for all-vanadium redox flow batteries.

[0061] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no hydroxyethylidene diphosphonic acid solid is added.

[0062] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that N,N'-carbonyldiimidazole is not added.

[0063] Test Example 1 The battery preparation conditions are: the active substances in the positive and negative electrolytes are 1.7 mol / LV 4+ / V 5+ and 1.5 mol / L 2+ / V 3+ The supporting electrolyte is 3 mol / L sulfuric acid, the volume of the positive and negative electrolytes is 70 mL, the electrode is a carbon felt electrode, and the effective area of ​​the carbon felt electrode is 48 cm 2 , the compression ratio is 40%.

[0064] The performance of the all-vanadium redox flow battery prepared by using the proton exchange membrane for all-vanadium redox flow battery of Examples 1-4 and Comparative Examples 1-3 was tested. The test conditions were as follows: at a current density of 80 mA / cm 2 -200mA / cm 2 The charge and discharge experiments were carried out under the following conditions: charging to 1.55V, discharging to 1.00V, and the battery operating temperature was 30℃.

[0065] The coulombic efficiency, voltage efficiency and energy efficiency of the all-vanadium redox flow batteries prepared using the proton exchange membranes of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0066] Table 1: Performance test of proton membrane vanadium redox flow battery at different current densities

[0067] As can be seen from the table, compared with comparative examples 1-3, examples 1-4 have higher efficiency performance. This is because the phosphonic acid group in the ligand and N,N'-carbonyldiimidazole are used in combination to better retain the bismuth element in the catalyst, allowing it to better exert its catalytic performance, improve the voltage efficiency of the battery, and achieve the purpose of improving energy efficiency.

[0068] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a proton exchange membrane for an all-vanadium redox flow battery, characterized in that: The method comprises the following steps: (1) mixing a perfluorosulfonic acid resin solution, a bismuth salt catalyst, a phosphine coordination compound and N,N'-carbonyldiimidazole to obtain a membrane-forming solution; wherein the mass fraction of the perfluorosulfonic acid resin in the perfluorosulfonic acid resin solution is 5%-30%; and the phosphine coordination compound is a phosphine coordination compound containing a hydroxyl group; (2) applying the film-forming solution obtained in step (1) on a substrate to obtain a wet film attached to the substrate; (3) Drying and annealing the substrate and the wet film thereon, and peeling off the formed film from the substrate to obtain the proton exchange membrane for the all-vanadium redox flow battery.

2. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: In the perfluorosulfonic acid resin solution, the mass fraction of the perfluorosulfonic acid resin is 10%-20%; and / or In the perfluorosulfonic acid resin solution, the solvent is N,N-dimethylformamide.

3. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The bismuth salt catalyst is selected from one or more of bismuth chloride, bismuth nitrate, bismuth sulfate and bismuth citrate; and / or The phosphine coordination compound is selected from one or more of hydroxyethylidene diphosphonic acid, bishydroxyethylphosphonic acid and hydroxyethylphosphonic acid.

4. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The mass ratio of the perfluorosulfonic acid resin to the bismuth salt catalyst is 1:(0.01-0.05); and / or The mass ratio of the bismuth salt catalyst to the phosphine coordination compound is 1:(0.01-0.06); and / or The molar ratio of the phosphine coordination compound to N,N'-carbonyldiimidazole is 1:(0.8-1.2).

5. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The material of the substrate layer is selected from one or more of PEN, PI and PET; and / or The coating method is solution casting coating; the coating speed is 8-15 mm / s.

6. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The drying method is drying, the drying temperature is 120-160° C., and the drying time is 8-12 minutes; and / or The annealing temperature is 180-220° C., and the annealing time is 18-22 minutes.

7. The method for preparing a proton exchange membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The thickness of the proton exchange membrane for the all-vanadium liquid flow battery is 30-50 μm.

8. A proton exchange membrane for an all-vanadium liquid flow battery, characterized in that: The membrane is prepared by the method for preparing a proton exchange membrane for an all-vanadium liquid flow battery as described in any one of claims 1 to 7.

9. An all-vanadium liquid flow battery, characterized in that: It comprises the proton exchange membrane for all-vanadium liquid flow battery as claimed in claim 8. 10.Selected from the following applications: (1) Use of the proton exchange membrane for all-vanadium redox flow battery as claimed in claim 8 in improving the energy efficiency of all-vanadium redox flow battery; (2) Application of phosphine coordination compounds and N,N'-carbonyldiimidazole in the preparation of proton exchange membranes for all-vanadium redox flow batteries; (3) Application of phosphine coordination compounds and N,N'-carbonyldiimidazole in reducing the dissolution of bismuth salt catalysts in proton exchange membranes used in all-vanadium redox flow batteries into electrolytes and enhancing the interaction between bismuth salt catalysts and proton exchange membranes.

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