Diaphragm for vanadium redox flow battery and preparation method of diaphragm

Abstract

The invention discloses a diaphragm for a vanadium redox flow battery and a preparation method of the diaphragm, and belongs to the technical field of battery diaphragms.The preparation method comprises the steps that (1) a sulfonated polymer is dissolved in an organic solvent to prepare pouring liquid A, and the sulfonated polymer is sulfonated polyether-ether-ketone or sulfonated polyether sulfone; (2) pouring liquid B containing sulfonated polymer and alkaline filler is prepared, the alkaline filler is polyimide or a metal organic framework, and an organic ligand structure of the metal organic framework contains amino; the mass ratio of the sulfonated polymer to the alkaline filler is 1: (0.05-0.3); and (3) enabling the pouring liquid A and the pouring liquid B to form films on the two sides of a polytetrafluoroethylene film respectively to prepare the diaphragm with the asymmetric structure for the vanadium redox flow battery. Through the asymmetric design of the coatings on the two sides of the diaphragm, the obtained diaphragm for the vanadium redox flow battery is good in stability, high in oxidation resistance, low in vanadium ion permeability, high in proton conductivity, high in ion selectivity and low in preparation cost, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly relates to a separator for a vanadium redox flow battery and a preparation method thereof. Background Art

[0002] To meet the growing energy demand, it is crucial to develop efficient energy storage technologies. Flow batteries have attracted much attention in large-scale energy storage due to their high energy efficiency, environmental friendliness, fast response, and potential economic benefits, especially showing broad application potential in hydropower, power grid dispatching, and supply-demand regulation. The ion exchange membrane is a key component of the flow battery, and developing a separator with low cost and high ion selectivity is a necessary condition for promoting the development of flow batteries.

[0003] Currently, the commonly used ion exchange membrane in the market is the DuPont Nafion commercial membrane, which has excellent chemical stability and high proton conductivity. However, its vanadium-blocking performance needs to be further improved, and the price of the Nafion membrane is expensive, which limits its application in vanadium redox flow batteries.

[0004] Polyether ether ketone (PEEK) is a high-performance semi-crystalline thermoplastic polymer with excellent thermal stability, mechanical strength and electrochemical stability. It has a high degree of commercialization and low cost. Unsulfonated PEEK is almost insoluble in organic solvents. After sulfonation, its crystallinity decreases and solubility increases, making it more suitable for the preparation and modification of proton exchange membranes. Sulfonated polyether ether ketone (SPEEK) is considered to be a material with the most potential to replace Nafion membranes due to its low cost, high proton conductivity and relatively low vanadium ion selectivity. However, the sulfonated polyether ether ketone has poor swelling resistance, and the stability of the SPEEK ion exchange membrane prepared by the direct casting method becomes poor. Side reactions such as chain segment degradation will occur at higher temperatures. Moreover, the rigid benzene ring structure contained in the SPEEK main chain has weak electron-withdrawing ability, and the degree of hydrophilic-hydrophobic phase separation is small. The formed hydrophilic channels have small diameters, many bifurcations and poor connectivity, which cannot meet the actual large-scale long-term cyclic use. In the prior art, this problem is usually solved by preparing a sulfonated polyether ether ketone-based composite diaphragm. For example, the Chinese patent document with the publication number CN102532575A discloses a preparation method of a perfluorosulfonic acid resin / sulfonated polyether ether ketone composite diaphragm. The invention uses perfluorosulfonic acid resin and polyether ether ketone as raw materials to prepare a mixed solution, and uses this mixed solution to treat a polypropylene diaphragm to obtain a double-sided perfluorosulfonic acid resin / sulfonated polyether ether ketone composite diaphragm, which can be widely used in the field of all-vanadium redox flow batteries; the Chinese patent document with the publication number CN108649244A discloses a preparation method of a SPEEK / lignin composite diaphragm. The invention uses low-cost sulfonated polyether ether ketone (SPEEK) as the matrix, and uses lignin as a proton selective conduction channel, and adopts film-forming methods such as step-by-step dispersion and solution casting to prepare a SPEEK / lignin composite diaphragm for all-vanadium redox flow batteries.

[0005] Polytetrafluoroethylene (PTFE), known as the "king of plastics", has the characteristics of being acid and alkali resistant and resistant to organic solvents. It is insoluble in most solvents. The pores of the PTFE membrane are large and the ion conductivity is very low. Direct use cannot meet the application conditions of the battery diaphragm. If PTFE and SPEEK are combined, it is beneficial to prepare a high-performance vanadium redox flow battery diaphragm. Summary of the Invention

[0006] In order to solve the deficiencies existing in the above-mentioned prior art, the present invention provides a preparation method of a diaphragm for a vanadium redox flow battery. Through the asymmetric design of the coatings on both sides of the diaphragm, the obtained diaphragm for a vanadium redox flow battery has good stability, strong antioxidant property, low vanadium ion permeability, high proton conductivity, strong ion selectivity and low preparation cost, which is beneficial to the preparation of a high-performance vanadium redox flow battery.

[0007] The specific technical solutions adopted are as follows:

[0008] A preparation method of a separator for a vanadium redox flow battery, comprising the following steps:

[0009] (1) Dissolve a sulfonated polymer in an organic solvent to prepare a casting solution A, wherein the sulfonated polymer is sulfonated polyether ether ketone or sulfonated polyarylether sulfone;

[0010] (2) Prepare a casting solution B containing a sulfonated polymer and a basic filler, wherein the basic filler is polyimide or a metal-organic framework, and the organic ligand structure of the metal-organic framework contains an amino group; the mass ratio of the sulfonated polymer to the basic filler is 1:0.05 - 0.3;

[0011] (3) Form films of the casting solution A and the casting solution B on both sides of a polytetrafluoroethylene membrane respectively to prepare a separator for a vanadium redox flow battery with an asymmetric structure.

[0012] The method of the present invention can prepare a separator for a vanadium redox flow battery with an asymmetric structure. The separator for a vanadium redox flow battery uses a PTFE membrane as a support body, has good structural stability. On the one hand, the casting solution A fills the pores of the PTFE membrane. On the other hand, the sulfonated polymer in the casting solution A can improve the hydrophilicity of the PTFE membrane, can provide a transport channel for the movement of protons and water molecules, improve the ion transport ability. The sulfonic acid groups in the sulfonated polymer of the casting solution B can form acid-base ion pairs with the basic groups in the basic filler, further improve the proton conductivity and reduce the ion penetration of the electrolyte, and enhance the performance of the separator.

[0013] Preferably, in step (1), the organic solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, etc.

[0014] More preferably, the solid content in the casting solution A is 5wt% - 30wt%.

[0015] Preferably, the metal-organic framework is metal-organic framework UiO-66-NH 2 , MOF-801, MOF808 or MIL-101; the solvent of the casting solution B is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

[0016] More preferably, the mass ratio of the sulfonated polymer to the basic filler is 1:0.05 - 0.15.

[0017] Preferably, the solid content in the casting solution B is 5wt% - 30wt%, and more preferably 5wt% - 15wt%.

[0018] Preferably, the thickness of the polytetrafluoroethylene membrane is 30 - 50μm, the average pore diameter is 0.2 - 0.45μm, and further is 0.2μm.

[0019] Specifically, the casting solution A is flowed on one side surface of the polytetrafluoroethylene membrane and dried at 10 - 30°C for 12 - 36 hours. Then, the casting solution B is flowed on the other side surface of the polytetrafluoroethylene membrane and dried at 10 - 30°C for 12 - 36 hours to obtain the diaphragm for vanadium redox flow battery.

[0020] The present invention also provides a diaphragm for vanadium redox flow battery prepared by the preparation method of the diaphragm for vanadium redox flow battery.

[0021] Preferably, in the diaphragm for vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane is 30 - 50 μm, the thickness of the sulfonated polymer coating film is 20 - 40 μm, and the thickness of the sulfonated polymer and alkaline filler coating film is 20 - 40 μm.

[0022] The present invention also provides a vanadium redox flow battery including the diaphragm for vanadium redox flow battery.

[0023] Preferably, the side of the sulfonated polymer coating film of the diaphragm for vanadium redox flow battery faces the positive electrode of the vanadium redox flow battery, and the side of the sulfonated polymer and alkaline filler coating film faces the negative electrode of the vanadium redox flow battery. Such a corresponding setting can not only ensure proton conduction but also be beneficial to the chemical stability of the diaphragm itself.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) By adding an alkaline filler to the casting solution B, the present invention forms acid-base ion pairs in the composite membrane by using the sulfonic acid groups in the sulfonated polymer and the alkaline groups in the alkaline filler to improve the proton conductivity and reduce the electrolyte ion penetration. The alkaline groups, as proton acceptors in the proton transport channel, can transfer protons from one sulfonic acid group to another. The formation of acid-base pairs can also effectively inhibit the passage of large-sized ions in the electrolyte, effectively inhibit the penetration of the electrolyte, effectively improve the performance of the battery diaphragm, and achieve ultra-high ion selectivity (3.27×10 3 S min cm -3 ) and low vanadium permeability (1.09×10 -8 cm 2 min -1 ). At the same time, it shows excellent CE value (95.92%), VE value (75.06%), and EE value (69.66%), as well as a longer self-discharge time (nearly 141 h). Using the diaphragm for vanadium redox flow battery of the present invention can improve the battery performance by about 30% or more.

[0026] (2) The present invention selects low-cost sulfonated polymer and alkaline filler. Through -NH in the alkaline filler 2 and -SO in the sulfonated polymer 3The acid-base interaction and unique asymmetric casting enhance the PTFE structure design, achieving low expansion rate, high proton conductivity, and excellent vanadium ion barrier performance. It not only optimizes the battery performance but also significantly reduces the cost, promoting the large-scale commercial application of all-vanadium redox flow batteries (VRFB). Description of the Drawings

[0027] Figure 1 Schematic diagram for the preparation of the separator for the asymmetric vanadium flow battery.

[0028] Figure 2 Schematic diagram for the assembly of a single cell.

[0029] Figure 3 For the products of Example 1 and Comparative Examples 1 - 3 of the present invention used as separators for all-vanadium flow batteries, the comparison chart of VRFB performance of the membrane at 80 mA cm -2 is shown. Detailed Description of the Invention

[0030] To make the objectives, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description through specific embodiments. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined correspondingly without conflict.

[0031] The operating methods without specific conditions noted in the following examples are generally according to conventional conditions or according to the conditions recommended by the manufacturers. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following examples can be obtained from conventional biochemical reagent companies without special instructions.

[0032] In the following examples, the polytetrafluoroethylene membrane is provided by Longjin Membrane Technology Co., Ltd., with a thickness of 40 μm and an average pore size of 0.2 μm. The metal-organic framework UiO-66-NH 2 According to the literature of UIO-66-NH 2 -derived mesoporous carbon used as a high-performance anode for the potassium-ion battery was synthesized; the schematic diagram for the preparation of the representative asymmetric separator for the vanadium flow battery is as Figure 1 shown.

[0033] Example 1

[0034] Using polyetheretherketone (PEEK) and concentrated sulfuric acid (98% H 2 SO 4 ), a sulfonation reaction (60 °C, 6 h) was carried out. After the reaction was cooled, the sulfonation product was poured into deionized water for phase inversion, and the precipitate was separated. Subsequently, the precipitate was washed and dried to finally obtain dry sulfonated polyetheretherketone SPEEK.

[0035] SPEEK was dissolved in N,N-dimethylformamide to prepare casting solution A, and the solid content in casting solution A was 7.5 wt%; SPEEK and metal-organic framework UiO-66-NH with a mass ratio of 1:0.1 2 were dissolved in N,N-dimethylformamide solvent to prepare casting solution B, and the solid content in casting solution B was 7.5 wt%;

[0036] Using the solution casting method, the polytetrafluoroethylene PTFE membrane was fixed with a clamp and placed on a smooth-surfaced support mold. Casting solution A was evenly cast and flowed on one side surface of the flat PTFE membrane and left to dry at 20 °C for 24 hours; subsequently, casting solution B was evenly cast and flowed on the other side surface of the PTFE membrane, and after drying at 20 °C for 24 hours, a separator for vanadium redox flow battery with an asymmetric structure was obtained.

[0037] In this separator for vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane is 40 μm, the thickness of the sulfonated polymer coating is 25 μm, and the thickness of the sulfonated polymer and alkaline filler coating is 25 μm.

[0038] Example 2

[0039] Using polyarylethersulfone (PAES) and concentrated sulfuric acid (98% H 2 SO 4 ), a sulfonation reaction (60 °C, 6 h) was carried out. After the reaction was cooled, the sulfonation product was poured into deionized water for phase inversion, and the precipitate was separated. Subsequently, the precipitate was washed and dried to finally obtain dry sulfonated polyarylethersulfone SPAES.

[0040] SPAES was dissolved in N,N-dimethylformamide to prepare casting solution A, and the solid content in casting solution A was 7.5 wt%; SPAES and metal-organic framework UiO-66-NH with a mass ratio of 1:0.1 2 were dissolved in N,N-dimethylformamide solvent to prepare casting solution B, and the solid content in casting solution B was 7.5 wt%;

[0041] Using the solution casting method, fix the polytetrafluoroethylene (PTFE) membrane with a fixture, place it on a smooth-surfaced support mold, evenly pour and spread casting solution A on one smooth surface of the PTFE membrane, and let it stand and dry at 20°C for 24 hours; then evenly pour and spread casting solution B on the other surface of the PTFE membrane, and after drying at 20°C for 24 hours, a separator for a vanadium redox flow battery with an asymmetric structure is obtained.

[0042] In this separator for the vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane is 40 μm, the thickness of the sulfonated polymer coating is 25 μm, and the thickness of the sulfonated polymer and alkaline filler coating is 25 μm.

[0043] Example 3

[0044] Use polyether ether ketone (PEEK) and concentrated sulfuric acid (98% H 2 SO 4 ) to carry out a sulfonation reaction (60°C, 6 h). After the reaction cools down, pour the sulfonation product into deionized water for phase inversion, separate the precipitate, and then wash and dry the precipitate to finally obtain dry sulfonated polyether ether ketone (SPEEK).

[0045] Dissolve SPEEK in N,N-dimethylformamide to prepare casting solution A, and the solid content in casting solution A is 7.5 wt%; dissolve SPEEK and polyimide with a mass ratio of 1:0.1 in N,N-dimethylformamide solvent to prepare casting solution B, and the solid content in casting solution B is 7.5 wt%;

[0046] Using the solution casting method, fix the polytetrafluoroethylene (PTFE) membrane with a fixture, place it on a smooth-surfaced support mold, evenly pour and spread casting solution A on one smooth surface of the PTFE membrane, and let it stand and dry at 20°C for 24 hours; then evenly pour and spread casting solution B on the other surface of the PTFE membrane, and after drying at 20°C for 24 hours, a separator for a vanadium redox flow battery with an asymmetric structure is obtained.

[0047] In this separator for the vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane is 40 μm, the thickness of the sulfonated polymer coating is 25 μm, and the thickness of the sulfonated polymer and alkaline filler coating is 25 μm.

[0048] Example 4

[0049] Use polyarylether sulfone (PAES) and concentrated sulfuric acid (98% H 2 SO 4 ) to carry out a sulfonation reaction (60°C, 6 h). After the reaction cools down, pour the sulfonation product into deionized water for phase inversion, separate the precipitate, and then wash and dry the precipitate to finally obtain dry sulfonated polyarylether sulfone (SPAES).

[0050] The casting solution A was prepared by dissolving SPAES in N,N-dimethylformamide, and the solid content in the casting solution A was 7.5 wt%. The casting solution B was prepared by dissolving SPAES and polyimide with a mass ratio of 1:0.1 in the N,N-dimethylformamide solvent, and the solid content in the casting solution B was 7.5 wt%.

[0051] Using the solution casting method, the polytetrafluoroethylene PTFE membrane was fixed with a fixture and placed on a smooth surface support mold. The casting solution A was evenly cast and flowed on one smooth surface of the PTFE membrane, and left to dry statically at 20 °C for 24 hours. Subsequently, the casting solution B was evenly cast and flowed on the other surface of the PTFE membrane, and after drying at 20 °C for 24 hours, a separator for vanadium redox flow battery with an asymmetric structure was obtained.

[0052] In this separator for vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane was 40 μm, the thickness of the sulfonated polymer coating was 25 μm, and the thickness of the sulfonated polymer and alkaline filler coating was 25 μm.

[0053] Comparative Example 1

[0054] Nafion 212 commercial membrane purchased from DuPont Company in the United States.

[0055] Comparative Example 2

[0056] Sulfonation reaction (60 °C, 6 h) was carried out using polyether ether ketone (PEEK) and concentrated sulfuric acid (98% H 2 SO 4 ). After the reaction cooled down, the sulfonation product was poured into deionized water for phase inversion, and the precipitate was separated. Subsequently, the precipitate was washed and dried to finally obtain the dried sulfonated polyether ether ketone SPEEK.

[0057] The casting solution A was prepared by dissolving SPEEK in N,N-dimethylformamide, and the solid content in the casting solution A was 7.5 wt%.

[0058] Using the solution casting method, the polytetrafluoroethylene PTFE membrane was fixed with a fixture and placed on a smooth surface support mold. The casting solution A was evenly cast and flowed on one smooth surface of the PTFE membrane, and left to dry statically at 20 °C for 24 hours. Subsequently, the casting solution A was continuously evenly cast and flowed on the other surface of the PTFE membrane, and after drying at 20 °C for 24 hours, a separator for vanadium redox flow battery with a symmetric structure was obtained.

[0059] In this separator for vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane was 40 μm, and the thickness of the sulfonated polymer coatings on both sides was 25 μm.

[0060] Comparative Example 3

[0061] Using polyether ether ketone (PEEK) and concentrated sulfuric acid (98% H 2 SO 4 ), a sulfonation reaction was carried out at 60 °C for 6 h. After the reaction cooled down, the sulfonation product was poured into deionized water for phase inversion, and the precipitate was separated. Subsequently, the precipitate was washed and dried to finally obtain dry sulfonated polyether ether ketone SPEEK.

[0062] SPEEK and metal-organic framework UiO-66-NH with a mass ratio of 1:0.1 2 were dissolved in N,N-dimethylformamide solvent to prepare casting solution B, and the solid content in casting solution B was 7.5 wt%.

[0063] Using the solution casting method, the polytetrafluoroethylene PTFE membrane was fixed with a clamp and placed on a smooth surface support mold. Casting solution B was evenly cast and flowed on one smooth surface of the PTFE membrane and left to dry at 20 °C for 24 hours; subsequently, casting solution B was again evenly cast and flowed on the other surface of the PTFE membrane, and after drying at 20 °C for 24 hours, a separator for vanadium redox flow battery with a symmetric structure was obtained.

[0064] In this separator for vanadium redox flow battery, the thickness of the polytetrafluoroethylene membrane is 40 μm, and the thickness of the sulfonated polymer and alkaline filler coating films on both sides is 25 μm.

[0065] Sample analysis

[0066] According to Figure 2 a single cell was prepared, and its structure includes a graphite plate, a graphite felt electrode, and the membrane prepared in the above-mentioned example or comparative example (effective area: 4 cm 2 ). During battery assembly, the sulfonated polymer coating film side of the separator for vanadium redox flow battery prepared in the example faces the positive electrode of the vanadium redox flow battery, and the sulfonated polymer and alkaline filler coating film side faces the negative electrode of the vanadium redox flow battery. Using 1.7 mol L -1 V 3.5+ / 4.7 mol L -1 H 2 SO 4 solution as the electrolyte, the charge-discharge test was carried out by a CT3002K-5V1A (Wuhan Blue Electronic Co., Ltd.) battery analyzer. The product membranes of Example 1 and Comparative Examples 1-3 were subjected to 100-cycle performance tests at 80 mA cm -2 , and the results are as Figure 3 shown. Due to the -NH 2 in UIO-66-NH 2 and the -SO 3Regarding the acid-base interaction and co-ion screening ability, both the VE (75.06%) and EE (69.66%) of Example 1 are higher than those of Comparative Example 1, Comparative Example 2, and Comparative Example 3, which are VE (65.48%, 64.40%, and 59.89%) and EE (61.14%, 61.21%, and 56.39%). That is, the performance of the all-vanadium redox flow battery assembled with the asymmetric structure composite membrane of the present invention is superior to that of Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0067] The above-described embodiments have elaborated on the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a diaphragm for a vanadium redox flow battery, characterized in that: The following steps are involved: (1) dissolving a sulfonated polymer in an organic solvent to prepare a casting liquid A, wherein the sulfonated polymer is a sulfonated polyetheretherketone or a sulfonated polyarylethersulfone; (2) preparing a casting solution B comprising a sulfonated polymer and an alkaline filler, wherein the alkaline filler is a polyimide or a metal organic framework, and the organic ligand structure of the metal organic framework contains an amino group; the mass ratio of the sulfonated polymer to the alkaline filler is 1:0.05-0.3; (3) Casting liquid A and casting liquid B are formed on both sides of a polytetrafluoroethylene membrane to prepare a vanadium redox flow battery separator having an asymmetric structure.

2. The method for preparing a diaphragm for a vanadium redox flow battery according to claim 1, characterized in that: In step (1), the organic solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

3. The method for preparing a diaphragm for a vanadium redox flow battery according to claim 1, characterized in that: The solid content of the casting liquid A is 5wt%-30wt%.

4. The method for preparing a diaphragm for a vanadium redox flow battery according to claim 1, characterized in that: The metal organic framework is metal organic framework UiO-66-NH2, MOF-801, MOF808 or MIL-101; the solvent of casting liquid B is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

5. The method for preparing a diaphragm for a vanadium redox flow battery according to claim 1, characterized in that: The solid content of the casting liquid B is 5wt%-30wt%.

6. The method for preparing a diaphragm for a vanadium redox flow battery according to claim 1, characterized in that: The thickness of the polytetrafluoroethylene membrane is 30-50 μm, and the average pore size is 0.2-0.45 μm. 7 . A diaphragm for vanadium redox flow battery produced according to the method for producing a diaphragm for vanadium redox flow battery according to claim 1 .

8. The vanadium redox flow battery separator according to claim 7, characterized in that: In the diaphragm for vanadium liquid flow battery, the thickness of the polytetrafluoroethylene film is 30-50 μm, the thickness of the sulfonated polymer coating is 20-40 μm, and the thickness of the sulfonated polymer and alkaline filler coating is 20-40 μm.

9. A vanadium redox flow battery, characterized in that: A vanadium redox flow battery separator according to claim 7 or 8.

10. The vanadium redox flow battery according to claim 9, characterized in that: The sulfonated polymer coating side of the vanadium flow battery separator faces the positive electrode of the vanadium flow battery, and the sulfonated polymer and alkaline filler coating side faces the negative electrode of the vanadium flow battery.

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