Method for preparing membrane material for flow battery by soft template method, obtained membrane material and application of membrane material

Abstract

The invention discloses a method for preparing a membrane material for a flow battery by a soft template method, the obtained membrane material and application thereof, and belongs to the field of membrane materials. The method comprises the following steps: (1) mixing a polyvinylidene fluoride material, sulfonated polyetheretherketone, polyethylene glycol and an organic solvent to form a homogeneous solution; (2) coating a matrix with the homogeneous solution obtained in the step (1), and drying to form a film to obtain a composite material of the film and the matrix; and (3) immersing the composite material in water for treatment to obtain the membrane material. The prepared membrane material transmits charge balance ions through the action mechanisms of pore size screening conduction in a nanoscale pore structure and an ion transmission channel formed in the membrane, and the ionic conductivity of the membrane is greatly improved through the synergistic effect of the two, so that the voltage efficiency of a battery is remarkably improved.

Description

Technical Field

[0001] The present application relates to a method for preparing a membrane material for a liquid flow battery by a soft template method, and the obtained membrane material and application thereof, and belongs to the field of membrane materials. Background Art

[0002] At present, actively promoting the transformation of energy structure and seizing the new round of technological and economic commanding heights has become a consensus among countries around the world, and the development and utilization model of the "distributed energy + energy storage" system has received widespread attention. my country attaches great importance to the development of distributed energy. In recent years, driven by relevant national policies and plans, the development of distributed energy has continued to accelerate. The state has approved 108 pilot demonstration projects, which have become a new feature of distributed energy development. Distributed energy will play a more important role in my country's energy production in the future, effectively improving resource utilization efficiency and alleviating environmental problems. It is estimated that by 2030, the scale of distributed energy development in my country will reach 350-570GWh, accounting for 11.5%-19.1% of the national installed power capacity. Therefore, distributed energy storage technology will have broad application prospects in the future. In addition, the development of distributed energy storage technology can reserve mature technology for the large-scale entry of photovoltaic power generation into thousands of households in the future, increase the penetration rate of new energy from 15% to 40%, effectively alleviate the capacity expansion of distribution networks, and save users' electricity bills.

[0003] At present, the more mature electrochemical energy storage technologies mainly include liquid flow batteries, lithium-ion batteries, lead-acid batteries, etc. Compared with other energy storage technologies, liquid flow battery technology has the advantages of safety, reliability, long life, and environmental friendliness. Liquid flow battery energy storage has unique advantages such as high energy conversion efficiency, large storage capacity, free site selection, deep discharge, long battery life, safety and environmental protection. It is considered to be one of the most commercially promising energy storage batteries, especially suitable for application scenarios with long-term energy storage requirements. At present, liquid flow battery energy storage technology represented by all-vanadium liquid flow batteries is developing rapidly and is currently in the stage of industrial promotion.

[0004] In liquid flow batteries, membrane materials are an important component of the battery, play a vital role in the performance of the battery, and account for a high proportion of the battery cost. Therefore, developing low-cost, high-performance, high-stability battery separators is an important step in the development of all-vanadium liquid flow batteries.

[0005] Polyvinylidene fluoride has attracted more attention due to its advantages such as good oxidation stability, good acid resistance, high mechanical properties and low price. Summary of the invention

[0006] According to one aspect of the present application, a method for preparing a membrane material for a flow battery by a soft template method is provided. The method is simple in process and easy to mass produce. During the deionized water treatment process of the membrane, part of the polyethylene glycol will dissolve in the deionized water to form a nanoscale pore structure, thereby promoting the conduction of ions; in addition, part of the polyethylene glycol is wrapped by an organic polymer resin that is insoluble in deionized water and preserved in the membrane material, which significantly improves the ion conductivity of the membrane material in the all-vanadium flow battery system. The prepared membrane material transmits charge-balancing ions through the mechanism of pore size screening conduction in the nanoscale pore structure and the ion transmission channel formed in the membrane. The synergistic effect of the two greatly improves the ion conductivity of the membrane, thereby significantly improving the voltage efficiency of the battery. The prepared membrane material has excellent acid resistance and stability, and its performance can be effectively regulated according to the content of each substance in the casting solution, and has good battery performance in the all-vanadium flow battery.

[0007] The method for preparing a membrane material for a flow battery by a soft template method described in the present application comprises the following steps:

[0008] (1) mixing polyvinylidene fluoride, sulfonated polyetheretherketone, polyethylene glycol, and an organic solvent to form a homogeneous solution;

[0009] (2) applying the homogeneous solution of step (1) on a substrate, drying to form a film, and obtaining a composite material of the film and the substrate;

[0010] (3) The composite material is immersed in water for treatment to obtain the membrane material.

[0011] Optionally, the average molecular weight of the polyethylene glycol is 200-600; preferably, the average molecular weight of the polyethylene glycol is 400.

[0012] Optionally, the content of the polyvinylidene fluoride in the homogeneous solution is 5 to 30 wt %, preferably 10 wt % to 25 wt %, and more preferably 15 wt % to 18 wt %.

[0013] Optionally, the content of the polyvinylidene fluoride in the homogeneous solution is independently selected from any value of 5wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 25wt%, 30wt% or a range between any two of the above.

[0014] Optionally, the content of the sulfonated polyetheretherketone in the homogeneous solution is 0.5 to 8 wt %, preferably 0.8 to 6 wt %, and more preferably 2 to 4 wt %.

[0015] Optionally, the content of the sulfonated polyether ether ketone in the homogeneous solution is independently selected from any value of 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 3.5 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt% or a range value between any two of the above.

[0016] Optionally, the content of the polyethylene glycol in the homogeneous solution is 1-10 wt%, preferably 2-7 wt%, more preferably 3-5 wt%.

[0017] Optionally, the content of the polyethylene glycol in the homogeneous solution is independently selected from any value of 1 wt%, 2 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt% or a range value between any two of the above.

[0018] Optionally, the mass ratio of the polyvinylidene fluoride to the sulfonated polyether ether ketone is 5:1 to 2:1.

[0019] Optionally, the mass ratio of the polyvinylidene fluoride to the sulfonated polyether ether ketone is independently selected from any value of 2:1, 3:1, 4:1, 5:1 or a range value between any two of the above.

[0020] Optionally, in the step (2), the temperature for drying and forming the film is 30-80 °C. Preferably, in the step (2), the temperature for drying and forming the film is 40-60 °C.

[0021] Specifically, in the step (2), the temperature for drying and forming the film is 50 °C.

[0022] Optionally, in the step (2), the time for drying and forming the film is 10-6 min; preferably, in the step (2), the time for drying and forming the film is 30-50 min.

[0023] Specifically, in the step (2), the time for drying and forming the film is 40 min.

[0024] Optionally, in the step (3), the treatment time is 1-10 h; preferably, in the step (3), the treatment time is 4-6 h.

[0025] Specifically, in the step (3), the treatment time is 5 h.

[0026] Optionally, the organic solvent is selected from any one or more of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0027] Optionally, the water is deionized water.

[0028] The present application selects a hydrophobic and flexible polyvinylidene fluoride material with chemical stability, thermal stability and high mechanical properties as the membrane matrix, selects a hydrophilic and rigid negatively charged sulfonated polyetheretherketone to adjust the conductivity and morphological characteristics of the membrane, and further selects a flexible and water-soluble polyethylene glycol as a soft template. The three are mixed and dissolved in a solvent to obtain the required casting solution. By designing and optimizing the addition amount of various materials, the solvent evaporation method is used to obtain porous polyvinylidene fluoride membrane materials of different forms, thereby optimizing battery performance.

[0029] In another aspect, the present application provides a membrane material prepared by the method for preparing a membrane material for a liquid flow battery using the soft template method.

[0030] In another aspect, the present application provides an application of the membrane material in an all-vanadium liquid flow battery.

[0031] The beneficial effects of this application include:

[0032] (1) The casting solution formed by directly mixing the flexible, highly hydrophobic PVDF and the rigid, hydrophilic SPEEK will have the problem of phase separation, which affects the quality of the film. When the flexible, highly hydrophilic PEG is added to the mixed solution of PVDF and SPEEK, PEG can serve as a bridge connecting the hydrophilic SPEEK and the flexible, hydrophobic PVDF through its hydrophilicity and flexible skeleton, thereby forming a homogeneous casting solution. In addition, the dissolution of PEG in the casting solution is conducive to the formation of pores, and the morphology of the membrane material can be further optimized by optimizing the content of PEG in the casting solution.

[0033] (2) During the deionized water treatment process of this type of membrane, part of the polyethylene glycol will dissolve in the deionized water to form a nanoscale pore structure, thereby promoting the conduction of ions; in addition, part of the polyethylene glycol is preserved in the membrane material because it is wrapped by an organic polymer resin that is insoluble in deionized water, which significantly improves the ion conductivity of the membrane material in the all-vanadium liquid flow battery system.

[0034] (3) The membrane material prepared in the present application transmits charge-balancing ions through the mechanism of pore size screening conduction in the nanoscale pore structure and ion transport channels formed in the membrane. The synergistic effect of the two greatly improves the ion conductivity of the membrane, thereby significantly improving the voltage efficiency of the battery.

[0035] (4) The membrane material prepared in the present application has excellent acid resistance and stability, and its performance can be effectively controlled according to the content of each substance in the casting solution, and has good battery performance in all-vanadium liquid flow batteries.

[0036] (5) The process for preparing the membrane material of the present application is simple and easy to mass produce, thus broadening the preparation method of the membrane material for all-vanadium liquid flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The all-vanadium redox flow battery assembled with Nafion115 membrane in Comparative Example 1 was tested at 80 mA cm -2 Battery performance diagram under working current density conditions;

[0038] Figure 2 The all-vanadium redox flow battery assembled with the membrane material prepared in Comparative Example 3 was -2 Performance diagram under working current density conditions;

[0039] Figure 3 The vanadium redox flow battery assembled with the membrane material prepared in Example 1 was -2 Performance diagram under working current density conditions;

[0040] Figure 4 This is a graph showing the acid resistance stability test of the membrane material prepared in Example 1. DETAILED DESCRIPTION

[0041] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0042] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0043] The performance test conditions of the all-vanadium redox flow battery used in the following examples are as follows: carbon felt is used as the positive and negative electrodes; the positive and negative electrolytes are both 1.5 mol L -1 3.5 valent vanadium + 3 mol L -1 Sulfuric acid solution; the volume of positive and negative electrolytes is 60 mL each; the battery adopts constant current charge and discharge mode at 80 mA cm -2 The battery was charged and discharged under the condition of current density of 1.0-1.55 V. The test instrument was an Arbin charge and discharge instrument of BT2000 model.

[0044] Comparative Example 1

[0045] Comparative Example 1 is a perfluorosulfonic acid ion exchange membrane. A vanadium redox flow battery is assembled using a 125 μm thick Nafion 115 membrane. -2 Under the working current density condition, the electrochemical performance was tested. The test results are as follows Figure 1As shown. It can be seen that the perfluorosulfonic acid ion exchange membrane has excellent ion conductivity in the all-vanadium liquid flow battery, and its voltage efficiency is as high as 88.6%, while the coulombic efficiency of the battery is low, only 90.5%. This is mainly because the side chain sulfonic acid group of the perfluorosulfonic acid ion exchange membrane has excellent proton conductivity, but its barrier ability to vanadium ions is relatively poor, resulting in cross-contamination of vanadium ions at the positive and negative electrodes, making the perfluorosulfonic acid ion exchange membrane have low ion selectivity in the all-vanadium liquid flow battery system, resulting in low coulombic efficiency of the battery.

[0046] Comparative Example 2

[0047] Polyvinylidene fluoride was used as the substrate, and the mass fraction of polyvinylidene fluoride was 18wt%. It was dissolved in DMAc solvent to form a homogeneous solution. The above solution was evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup was transferred to deionized water and soaked for 5 hours. The membrane material prepared above was used to assemble an all-vanadium redox flow battery. -2 The battery was charged and discharged under working current density conditions. Due to the large resistance of the membrane material, the battery could not undergo normal charge and discharge cycles.

[0048] Comparative Example 3

[0049] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution. The above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under the working current density condition. Due to the large resistance of the membrane material, the voltage efficiency of the battery was relatively low, less than 60% ( Figure 2 ).

[0050] Example 1

[0051] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 3% of polyethylene glycol 400 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm-2 The battery is charged and discharged under the working current density condition. The battery performance is as follows Figure 3 As shown, the coulombic efficiency of the battery is 94% and the voltage efficiency is 85%.

[0052] To verify the stability of the designed and prepared membrane material, the membrane of Example 1 was placed in a 40°C pentavalent vanadium (concentration: 1.5 mol L -1 ), sulfuric acid (concentration: 3 mol L -1 ) solution for 7 days, and then assembled the all-vanadium liquid flow battery single cell and carried out cycle performance test. The test results are as follows Figure 4 The battery operated continuously and stably for more than 200 cycles, and its performance remained stable, indicating that this membrane material has excellent stability and has good application prospects in all-vanadium liquid flow battery systems.

[0053] Example 2

[0054] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 7% of polyethylene glycol 400 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a CE of 92.6%.

[0055] Example 3

[0056] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 1% polyethylene glycol 400 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a VE of 75.3%.

[0057] Example 4

[0058] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 4:2. They are dissolved in DMAc solvent to form a homogeneous solution, and then 3% of polyethylene glycol 400 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a CE of 93.7%.

[0059] Example 5

[0060] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride: sulfonated polyetheretherketone is 5:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 3% of polyethylene glycol 400 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a VE of 81.7%.

[0061] Example 6

[0062] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride to sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 3% of polyethylene glycol 200 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a CE of 90.1%.

[0063] Example 7

[0064] With polyvinylidene fluoride as the substrate, hydrophilic rigid negatively charged sulfonated polyetheretherketone is used to adjust the conductivity and morphological properties of the membrane. The total mass fraction of polyvinylidene fluoride and sulfonated polyetheretherketone is 18wt%, and the mass ratio of polyvinylidene fluoride to sulfonated polyetheretherketone is 4:1. They are dissolved in DMAc solvent to form a homogeneous solution, and then 3% of polyethylene glycol 600 is added to the solution. After it is fully dissolved, the above solution is evenly coated on a clean glass plate, dried at 50°C for 40 minutes, and then the glass cup is transferred to deionized water and immersed for 5 hours. The membrane material prepared above is used to assemble an all-vanadium redox flow battery. At 80mA cm -2 The battery was charged and discharged under working current density conditions, and the battery performance showed a VE of 80.3%.

[0065] In summary, the present application provides a soft template method for preparing membrane materials for liquid flow batteries. By adjusting the ratio of polyvinylidene fluoride, sulfonated polyetheretherketone and polyethylene glycol with different molecular weights, an all-vanadium liquid flow battery membrane material with excellent performance can be obtained.

[0066] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing membrane materials for flow batteries using a soft template method, It is characterized in that The following steps are included: (1) mixing polyvinylidene fluoride, sulfonated polyetheretherketone, polyethylene glycol, and an organic solvent to form a homogeneous solution; (2) applying the homogeneous solution of step (1) on a substrate, drying to form a film, and obtaining a composite material of the film and the substrate; (3) The composite material is immersed in water for treatment to obtain the membrane material.

2. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that The average molecular weight of the polyethylene glycol is 200-600; Preferably, the average molecular weight of the polyethylene glycol is 400; Preferably, the content of polyethylene glycol in the homogeneous solution is 1 to 10 wt %; Preferably, the content of polyethylene glycol in the homogeneous solution is 2 to 7 wt %; Preferably, the content of polyethylene glycol in the homogeneous solution is 3-5 wt %.

3. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that The content of the polyvinylidene fluoride in the homogeneous solution is 5 to 30 wt %; Preferably, the content of the polyvinylidene fluoride in the homogeneous solution is 10wt% to 25wt%; Preferably, the content of the polyvinylidene fluoride in the homogeneous solution is 15 wt % to 18 wt %.

4. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that The content of the sulfonated polyetheretherketone in the homogeneous solution is 0.5-8wt%; Preferably, the content of the sulfonated polyetheretherketone in the homogeneous solution is 0.8 to 6 wt %; Preferably, the content of the sulfonated polyetheretherketone in the homogeneous solution is 2-4 wt%.

5. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that The mass ratio of the polyvinylidene fluoride to the sulfonated polyetheretherketone is 5:1 to 2:

1.

6. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that The organic solvent is selected from any one or more of N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide; Preferably, the water is deionized water.

7. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that In the step (2), the temperature for drying the film is 30-80°C; Preferably, in step (2), the temperature for drying the film is 40-60°C; Preferably, in step (2), the drying time for film formation is 10-6 min; Preferably, in step (2), the drying time for film formation is 30-50 minutes.

8. The method for preparing a membrane material for a flow battery by a soft template method according to claim 1, It is characterized in that In the step (3), the treatment time is 1-10 hours; Preferably, in step (3), the treatment time is 4-6 hours.

9. A membrane material prepared according to the method for preparing a membrane material for a liquid flow battery using a soft template method according to any one of claims 1 to 8.

10. Use of the membrane material according to claim 9 in an all-vanadium liquid flow battery.

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