High-performance ion exchange membrane for flow battery and application of high-performance ion exchange membrane

Abstract

The invention discloses a high-performance ion exchange membrane for a flow battery and application of the high-performance ion exchange membrane. The preparation method of the ion exchange membrane comprises the following steps: S1, dissolving a polymer a, a polymer b and a polymer c in an organic solvent to form a mixed solution; s2, adding a template agent into the mixed solution to obtain a membrane casting solution; s3, coating the surface of a substrate with the membrane casting solution, and drying to obtain an initial membrane; s4, immersing the initial membrane in water or an organic solvent, and removing the template agent to form a porous structure membrane; s5, soaking the porous structure membrane in an acid solution to obtain an ion exchange membrane; the polymer a is selected from at least one of polysulfone, polyether sulfone, polyvinylidene fluoride and polybenzimidazole; the polymer b is a polymer containing a sulfonic acid group; and the polymer c is selected from at least one of polypyrrole, polyvinylpyrrolidone and polybenzimidazole. The ion exchanger prepared by the invention can be applied to a flow battery and has good battery performance.

Description

Technical Field

[0001] The present invention relates to the research field of flow batteries, and particularly to a high-performance ion exchange membrane for flow batteries and its applications. Background Art

[0002] As an emerging technology in the field of electrochemical energy storage, flow batteries exhibit many remarkable advantages compared with other energy storage methods. Their system design has high flexibility, enabling free site selection for construction; the storage capacity is quite considerable, allowing for deep discharge; the energy conversion efficiency is relatively high, and the operation process is safe, environmentally friendly, and has low maintenance costs. With these advantages, flow batteries have broad application prospects in many aspects such as energy storage for renewable energy power generation such as wind energy and solar energy, emergency power supply systems, standby power stations, and peak shaving and valley filling of power systems.

[0003] In the flow battery system, the battery separator plays a crucial role. Its core function is to effectively isolate the positive and negative electrolyte solutions and establish a proton transport channel. The proton conductivity, chemical stability, and ion selectivity of the membrane will significantly affect the electrochemical performance and overall service life of the battery. Therefore, an ideal membrane should have high ion selectivity, low surface resistance, and thus high ion conduction efficiency; in addition, good chemical stability and low cost are also essential elements. Currently, the Nafion membrane developed by DuPont is still the main source for flow batteries. The Nafion membrane indeed exhibits excellent characteristics in key aspects such as electrochemical performance indicators and service life. However, defects such as high price and poor ion selectivity are further highlighted, and these factors severely restrict the wide application of the Nafion membrane in large-scale industrial production. In view of this, it is particularly crucial and urgent to develop a battery separator with the advantages of high selectivity, high stability, and low cost.

[0004] Currently, many scholars have made many contributions in the field of ion exchange membranes. For example, sulfonic acid groups are grafted onto the polymer main chain or side chain through sulfonation. This method has simple technology and cheap raw materials, but the conductivity of the prepared membrane is proportional to the sulfonation degree. The higher the sulfonation degree, the higher the swelling rate of the membrane, resulting in a decrease in ion selectivity. Secondly, the higher the sulfonation degree, the worse the stability of the membrane. Some scholars have also proposed the pore size sieving effect to achieve selective separation and conduction of ions. Such porous membranes are an effective approach. However, when preparing porous membranes by the phase inversion method, when the pore size is reduced to a certain extent, it becomes difficult to further reduce the pore size. Therefore, the selectivity can only be improved by increasing the thickness of the skin layer, but the increase in the skin layer thickness will hinder the conduction of hydrogen ions. Therefore, how to maintain the balance between proton conductivity and ion selectivity has become an important issue for such membranes.

[0005] The composite membrane prepared by solution casting of sulfonated polyether ether ketone and polyvinylidene fluoride mentioned in Chinese invention patent CN111718505A has a single ion transport channel and only sulfonic acid groups as effective functional groups, resulting in an insignificant effect in the actual application of liquid flow batteries. The highest Coulomb efficiency is only 87.35%. Chinese invention patent CN114276572A proposes to introduce amino groups and sulfonic acid groups into polyether ether ketone polymers to prepare a bifunctional composite membrane, which has a better energy efficiency of 82.42% in battery applications. However, this method has more synthesis steps and higher costs. Chinese invention patent CN108075091A mentions the preparation of porous polyvinylidene fluoride membranes by removing additives. Although this method has a simple process, the single ion transport channel lacks functional groups for ion transport, resulting in the inability to balance ion selectivity and conductivity. He et al. (Polymers 2019, 11, 676) mixed polyether ether ketone with different sulfonation degrees and polyvinylidene fluoride to prepare a composite membrane. This method uses the sulfonic acid groups in sulfonated polyether ether ketone and the hydrophobicity of polyvinylidene fluoride to form microphase separation regions to increase the conductivity of the composite membrane. However, the ion selectivity of the composite membrane prepared by this method is not high. Wang Feiran et al. (Acta Chim. Sinica 2021, 79, 1123—1128) used polyvinylidene fluoride as the membrane material and polyethylene glycol and polyvinylpyrrolidone as the template and stabilizer respectively to prepare a porous composite membrane, which has better performance in battery applications. Summary of the Invention

[0006] The object of the present invention is to provide a high-performance ion exchange membrane for liquid flow batteries. The ion exchange membrane provided by the present invention is composed of three polymer materials, and two of the polymers carry sulfonate functional groups and tertiary amine functional groups respectively. The purpose is to enhance the proton transport rate by using the hydrogen bond network formed by sulfonic acid groups and tertiary amine groups. At the same time, the easy protonation property of tertiary amine groups in acidic solutions makes the N atom carry a positive charge to form N + , and use the Donnan exclusion effect to improve the ion selectivity of the membrane. In addition, by regulating the template agent, porous channels are formed inside the composite membrane, which helps the electrolyte diffuse in the membrane and improves the conductivity of the ion exchange membrane. The preparation method has a simple process, low production cost, and excellent battery performance of the membrane.

[0007] The present invention directly uses three relatively mature polymer raw materials in the market. By regulating the components, pore size and functional groups, the preparation of a ternary component, multi-channel and multi-functional composite membrane is realized. In the actual application of all-vanadium flow batteries, the Coulomb efficiency is as high as 98.88%, and the energy efficiency is as high as 88.37%.

[0008] The present invention provides a method for preparing a high-performance ion exchange membrane for a flow battery. By blending different polymers and regulating processes such as membrane ion channels and acid doping, a high-performance ion exchange membrane for a flow battery can be prepared. The specific steps are as follows:

[0009] S1. Dissolve polymer a, polymer b, and polymer c in an organic solvent to form a mixed solution;

[0010] S2. Add a templating agent to the mixed solution to obtain a casting solution;

[0011] S3. Coat the casting solution on the surface of a substrate and dry it to obtain an initial membrane;

[0012] S4. Immerse the initial membrane in water or an organic solvent to remove the templating agent and form a porous structure membrane;

[0013] S5. Immerse the porous structure membrane in an acidic solution for soaking treatment to obtain the ion exchange membrane;

[0014] The polymer a is selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, or polybenzimidazole;

[0015] The polymer b is a polymer containing a sulfonic acid group;

[0016] The polymer c is selected from at least one of polypyrrole, polyvinylpyrrolidone, or polybenzimidazole.

[0017] Preferably, the polymer b is selected from at least one of perfluorosulfonic acid resin, sulfonated polyarylene ether ketone, sulfonated polyether ether ketone, sulfonated polytetramethyldiphenyl ether ketone, sulfonated polystyrene, sulfonated polyphenylene sulfide, sulfonated polyphenylene ether, sulfonated copolyimide, sulfonated polyethersulfone, and is preferably sulfonated polyether ether ketone, perfluorosulfonic acid resin, sulfonated polyethersulfone;

[0018] The present invention only sulfonates each polymer by the post-sulfonation method: for the pretreated polymer, sulfonating agents such as concentrated sulfuric acid and chlorosulfonic acid are used to introduce sulfonic acid groups into the polymer under certain reaction conditions. Taking sulfonated polyether ether ketone as an example: the dried polyether ether ketone is added to concentrated sulfuric acid under stirring to control the reaction temperature and time for sulfonation reaction. After the reaction is completed, the mixed solution is poured into deionized water to terminate the reaction, and the obtained solid precipitate is sulfonated polyether ether ketone, which is dried for standby. The sulfonation degree of the polymer can be controlled by regulating the reaction temperature and time.

[0019] The mass ratio of the polymer a, the polymer b, and the polymer c is 0.2 - 2:0.2 - 2:0.2 - 2, preferably 0.6 - 0.9:0.2 - 0.4:0.4.

[0020] In the present invention, the polymer a has strong hydrophobicity. Blending it with the polymers b and c with strong hydrophilicity can not only play a role in restricting its swelling, but also achieve microphase separation by the different hydrophilic and hydrophobic properties between different polymers, which is helpful for the establishment of ion transport channels. Secondly, the polymer a has good chemical stability and mechanical properties by itself, which is helpful for improving the mechanical properties, acid and alkali resistance, and antioxidant properties of the composite membrane as a whole.

[0021] In the present invention, the polymer b contains abundant sulfonic acid groups, and its sulfonic acid groups are helpful for the transport of hydrogen ions. The polymer c contains tertiary amine groups, which can accept protons under acidic conditions to achieve proton transport. At the same time, the basic tertiary amine groups will undergo acid-base interaction with the acidic sulfonic acid groups to form a hydrogen bond network to enhance the proton transport rate. And the easy protonation property of the tertiary amine groups makes the N atom carry a positive charge to form N+, and the Donnan exclusion effect is used to improve the ion selectivity of the membrane.

[0022] In step S1, the organic solvent is selected from at least one of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, or N,N-dimethylformamide, and preferably dimethyl sulfoxide and N,N-dimethylformamide.

[0023] In step S2, the template agent is selected from at least one of imidazole, phenolphthalein, and polyethylene glycol, and its addition amount is 5-30% of the total mass of the polymer a, the polymer b, and the polymer c;

[0024] The mass concentration of the template agent in the casting solution is 7-30%.

[0025] In step S3, the drying conditions are: the temperature is 60-120 °C and the time is 8-24 hours.

[0026] In step S4, the organic solvent is ethanol, methanol, dichloromethane, or acetonitrile.

[0027] The temperature for removing the template agent is 40 °C - 80 °C, the time is 1-24 hours, and it is carried out under the conditions of a shaker or static state.

[0028] Using a template agent to create pores is a relatively controllable and simple method. Immerse the dried membrane in water or an organic solvent to remove the soluble template agent in the membrane, and the remaining "cavities" are connected to each other to form nano-scale pore diameters, which is beneficial to better block the migration of active substances by improving the ion transport path in the membrane, improve the selectivity of the membrane, and at the same time the rich transport paths are also helpful for improving the conductivity of the membrane.

[0029] In step S5, the acidic solution is a sulfuric acid solution or a hydrochloric acid solution, the hydrogen ion concentration is 1-3 mol / L, and the soaking time is 8-24 hours.

[0030] After the ion exchange membrane prepared by the present invention is treated by acid soaking, the protonation property of the tertiary amine group in polymer c causes the N atom to carry a positive charge to form N + . The positively charged N will form a hydrogen bond network with the sulfonic acid group to facilitate proton transport. At the same time, the N in the ion exchange membrane + will improve the ion selectivity of the membrane due to the Donnan exclusion effect.

[0031] The high-performance ion exchange membrane provided by the present invention can be used as a separator for a flow battery. Among them, the flow battery includes a vanadium redox flow battery, a zinc / bromine flow battery, a polysulfide / sodium bromide flow battery, an iron / chromium flow battery, and a vanadium / bromine flow battery, but is not limited to these several flow batteries, and preferably is a vanadium redox flow battery.

[0032] The present invention has the following beneficial effects:

[0033] (1) The present invention realizes rapid ion transport by blending three polymers. Its principle is to utilize the acid-base interaction between the sulfonic acid group and the tertiary amine group to form a hydrogen bond network, and the proton transport rate in the hydrogen bond network is greatly enhanced;

[0034] (2) The present invention utilizes the protonation property of the tertiary amine group to make the inside of the membrane carry a positive charge, and hinders the transport of active substances in the electrolyte through the Donnan exclusion effect, thereby improving the ion selectivity of the membrane;

[0035] (3) The present invention can adjust the pore size and quantity of the ion exchange membrane by adjusting the type and dosage of the template agent, thereby enriching the proton transport path and improving the proton conductivity;

[0036] (4) The ion exchange membrane prepared by the present invention has the advantages of low cost and excellent chemical stability, and the preparation process of the membrane material is simple and easy to realize mass production;

[0037] (5) The ion exchange prepared by the present invention is applicable to a flow battery and has good battery performance. Description of the Drawings

[0038] Figure 1 is the surface morphology diagram of the membrane provided in Example 1.

[0039] Figure 2 is the charge-discharge cycle curve of the vanadium redox flow battery provided in Example 1. Detailed Embodiments

[0040] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0041] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0042] Example 1: Preparation of a High-Performance Ion Exchange Membrane for a Flow Battery

[0043] (1) Dissolve 0.9 g of polyvinylidene fluoride, 0.2 g of sulfonated polyether ether ketone, and 0.4 g of polyvinylpyrrolidone in 7.86 g of N,N-dimethylformamide, and stir well at 50 °C for 12 h to form a homogeneous solution;

[0044] (2) Add 0.225 g of polyethylene glycol template agent to the homogeneous solution in step (1), and continue to stir well at 50 °C for 12 h to form a homogeneous casting solution with a casting solution concentration of 18 wt%;

[0045] (3) Pour the casting solution in step (2) onto a glass plate by casting, and place it in an oven at 100 °C for 24 h to obtain an initial membrane;

[0046] (4) Peel off the initial membrane in step (3), put it into deionized water, and place it in a shaker at 60 °C for 12 h to remove the polyethylene glycol template agent, obtaining a porous structure ion exchange membrane;

[0047] (5) Immerse the porous structure ion exchange membrane in step (4) in a 3 mol / L sulfuric acid aqueous solution for 12 h to finally obtain an ion exchange membrane.

[0048] Figure 1 Figure 19 shows the surface morphology of the membrane provided in Example 1. It can be seen that there are a large number of holes on the membrane surface, which are the "voids" left after removing the template agent. The formation of a large number of holes helps ion transport and improves the conductivity of the membrane.

[0049] The ion exchange membrane was subjected to performance testing. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane (testing instrument: Chenhua Electrochemical Workstation, the same electrochemical workstation was used in the following examples and comparative examples) is shown in Table 1 as 0.165 Ω·cm 2 , and the excellent surface resistance is mainly due to the rich hydrogen bond network and rich ion transport channels in the ion exchange membrane; the mechanical properties of the ion exchange membrane (testing instrument: Shanghai Hengyu Thin Film Mechanical Property Testing and Analysis Instrument, the same instrument was used in the following examples and comparative examples) are shown in Table 1 as 35.13 Mpa.

[0050] A vanadium redox flow battery was assembled using the ion exchange membrane (Blue Electric Tester, the same testing instrument was used in the following examples and comparative examples), where the electrode was activated carbon felt, the bipolar plate was graphite plate, the effective area of the membrane was 16 cm 2 , the current density was 80 mA / cm -2 , and the electrolyte composition was: 1.5 mol / L V 3+ +1.5 mol / L V 4++3 mol / L H2SO4. The charge-discharge process adopts a constant current charge-discharge mode, and the charge / discharge process adopts a voltage cut-off mode, with the cut-off voltages being 1.65 V and 0.8 V respectively. The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane is 98.53%, the voltage efficiency is 89.68%; the energy efficiency is 88.37% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect among various polymers and the abundant ion transport channels.

[0051] Figure 2 It is the charge-discharge cycle curve of the all-vanadium redox flow battery provided in Example 1.

[0052] Example 2. Preparation of a high-performance ion exchange membrane

[0053] Except that the content of polyethylene glycol in step (2) is reduced to 0.075 g, the rest are the same as in Example 1.

[0054] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.217 Ω·cm as shown in Table 1 2 , and the increase in surface resistance is mainly due to the reduction in the content of the template agent, resulting in a decrease in ion channels; the mechanical properties of the ion exchange membrane are 35.43 Mpa as shown in Table 1.

[0055] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane in this example is 98.76%, the voltage efficiency is 88.31%; the energy efficiency is 87.21% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect among various polymers and the abundant ion transport channels.

[0056] Example 3. Preparation of a high-performance ion exchange membrane

[0057] Except that polyethylene glycol is replaced with phenolphthalein in step (2), the rest are the same as in Example 1.

[0058] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.183 Ω·cm as shown in Table 1 2 , and the excellent surface resistance is mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 35.07 Mpa as shown in Table 1.

[0059] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane in this example is 98.88%, the voltage efficiency is 88.14%; the energy efficiency is 87.15% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect among various polymers and the abundant ion transport channels.

[0060] Example 4: Preparation of High-performance Ion Exchange Membrane

[0061] Except that the sulfuric acid aqueous solution in step (6) is replaced with hydrochloric acid aqueous solution, the rest are the same as in Example 1.

[0062] The ion exchange membrane was subjected to performance testing. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.166 Ω·cm as shown in Table 1 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 35.11 Mpa as shown in Table 1.

[0063] The coulombic efficiency of the vanadium redox flow battery assembled with the ion exchange membrane was 98.54%, the voltage efficiency was 89.64%; the energy efficiency was 88.33% (Table 2), indicating that the ion exchange membrane had good vanadium redox flow battery performance. This was attributed to the synergistic effect between various polymers and abundant ion transport channels.

[0064] Example 5: Preparation of High-performance Ion Exchange Membrane

[0065] Except that the acid leaching time of the ion exchange membrane in step (6) was reduced to 8 h, the rest were the same as in Example 1.

[0066] The ion exchange membrane was subjected to performance testing. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.182 Ω·cm as shown in Table 1 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 35.67 Mpa as shown in Table 1.

[0067] The coulombic efficiency of the vanadium redox flow battery assembled with the ion exchange membrane was 98.55%, the voltage efficiency was 88.31%; the energy efficiency was 87.03% (Table 2), indicating that the ion exchange membrane had good vanadium redox flow battery performance. This was attributed to the synergistic effect between various polymers and abundant ion transport channels.

[0068] Example 6: Preparation of High-performance Ion Exchange Membrane

[0069] Except that polyvinylidene fluoride in step (1) was replaced with polybenzimidazole, the rest were the same as in Example 1.

[0070] The ion exchange membrane was subjected to performance testing. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.167 Ω·cm as shown in Table 1 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 38.24 Mpa as shown in Table 1.

[0071] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane in this example is 98.53%, the voltage efficiency is 89.66%, and the energy efficiency is 88.34% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect between various polymers and the abundant ion transport channels.

[0072] Example 7. Preparation of a high-performance ion exchange membrane

[0073] Except that in step (1), sulfonated polyether ether ketone is replaced with perfluorosulfonic acid resin, the rest are the same as in Example 1.

[0074] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.162 Ω·cm as shown in Table 1 2 , and the excellent surface resistance is mainly due to the abundant hydrogen bond network and ion transport channels in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 35.32 Mpa as shown in Table 1.

[0075] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane in this example is 98.51%, the voltage efficiency is 89.69%, and the energy efficiency is 88.32% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect between various polymers and the abundant ion transport channels.

[0076] Example 8. Preparation of a high-performance ion exchange membrane

[0077] Except that in step (1), polyvinylpyrrolidone is replaced with polybenzimidazole, the rest are the same as in Example 1.

[0078] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.171 Ω·cm as shown in Table 1 2 , and the excellent surface resistance is mainly due to the abundant hydrogen bond network and ion transport channels in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 39.14 Mpa as shown in Table 1.

[0079] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane is 98.62%, the voltage efficiency is 89.58%, and the energy efficiency is 88.25% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect between various polymers and the abundant ion transport channels.

[0080] Example 9. Preparation of a high-performance ion exchange membrane

[0081] Except that in step (1), the content of polyvinylidene fluoride is reduced to 0.6 g, the rest are the same as in Example 1.

[0082] The performance of the ion exchange membrane was tested. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.162 Ω·cm as shown in Table 1. 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 33.14 Mpa as shown in Table 1.

[0083] The coulombic efficiency of the vanadium redox flow battery assembled with the ion exchange membrane was 97.76%, the voltage efficiency was 89.65%; the energy efficiency was 87.65% (Table 2), indicating that the ion exchange membrane had good vanadium redox flow battery performance. This was attributed to the synergistic effect among various polymers and abundant ion transport channels.

[0084] Example 10: Preparation of a high-performance ion exchange membrane

[0085] Except that in step (1), the sulfonated polyether ether ketone was replaced with perfluorosulfonic acid resin and the dosage was increased to 0.4 g, the rest were the same as in Example 1.

[0086] The performance of the ion exchange membrane was tested. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.159 Ω·cm as shown in Table 1. 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 34.69 Mpa as shown in Table 1.

[0087] The coulombic efficiency of the vanadium redox flow battery assembled with the ion exchange membrane in this example was 97.61%, the voltage efficiency was 90.43%; the energy efficiency was 88.27% (Table 2), indicating that the ion exchange membrane had good vanadium redox flow battery performance. This was attributed to the synergistic effect among various polymers and abundant ion transport channels.

[0088] Example 11: Preparation of a high-performance ion exchange membrane

[0089] Except that in step (1), the content of polyvinylpyrrolidone was reduced to 0.2 g, the rest were the same as in Example 1.

[0090] The performance of the ion exchange membrane was tested. In this invention, a vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 0.174 Ω·cm as shown in Table 1. 2 , and the excellent surface resistance was mainly due to the abundant hydrogen bond network and abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane was 34.97 Mpa as shown in Table 1.

[0091] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane is 98.21%, the voltage efficiency is 88.85%; the energy efficiency is 87.26% (Table 2), indicating that the ion exchange membrane has good all-vanadium redox flow battery performance. This is attributed to the synergistic effect between various polymers and the abundant ion transport channels.

[0092] Comparative Example 1,

[0093] Except that only 1.5 g of polyvinylidene fluoride is used as the polymer in step (1), the rest are the same as in Example 1.

[0094] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 5.43 Ω·cm as shown in Table 1 2 , and the relatively high surface resistance is mainly due to the lack of functional groups available for proton transport in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 45.12 Mpa as shown in Table 1.

[0095] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example is 94.23%, the voltage efficiency is 69.26%; the energy efficiency is 65.27% (Table 2).

[0096] Comparative Example 2,

[0097] Except that only 1.5 g of sulfonated polyether ether ketone is used as the polymer in step (1), the rest are the same as in Example 1.

[0098] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 1.78 Ω·cm as shown in Table 1 2 , and the relatively high surface resistance is mainly due to the absence of a hydrogen bond network between the polymers in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 28.76 Mpa as shown in Table 1, and the lower tensile strength is attributed to the inherent properties of the polymer.

[0099] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example is 94.56%, the voltage efficiency is 79.71%; the energy efficiency is 75.38% (Table 2).

[0100] Comparative Example 3,

[0101] Except that only 0.9 g of polyvinylidene fluoride and 0.2 g of sulfonated polyether ether ketone are used as the polymers in step (1), the rest are the same as in Example 1.

[0102] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 2.34 Ω·cm as shown in Table 1 2 , and the relatively high surface resistance is mainly due to the absence of a hydrogen bond network between the polymers in the ion exchange membrane; the mechanical properties of the ion exchange membrane are 32.46 Mpa as shown in Table 1.

[0103] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example was 93.74%, the voltage efficiency was 75.86%, and the energy efficiency was 71.12% (Table 2).

[0104] Comparative Example 4

[0105] Except that only 0.9 g of polyvinylidene fluoride and 0.4 g of polyvinylpyrrolidone were used for the polymer in step (1), the rest were the same as in Example 1.

[0106] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 1.95 Ω·cm as shown in Table 1 2 . The relatively high surface resistance was mainly due to the absence of a hydrogen bond network between the polymers in the ion exchange membrane; the mechanical properties of the ion exchange membrane were 32.74 Mpa as shown in Table 1.

[0107] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example was 96.59%, the voltage efficiency was 76.04%, and the energy efficiency was 73.45% (Table 2).

[0108] Comparative Example 5

[0109] Except that only 0.2 g of sulfonated polyether ether ketone and 0.4 g of polyvinylpyrrolidone were used for the polymer in step (1), the rest were the same as in Example 1.

[0110] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 1.27 Ω·cm as shown in Table 1 2 . The relatively high surface resistance was mainly due to the absence of a hydrogen bond network between the polymers in the ion exchange membrane; the mechanical properties of the ion exchange membrane were 29.77 Mpa as shown in Table 1.

[0111] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example was 96.78%, the voltage efficiency was 81.23%, and the energy efficiency was 78.62% (Table 2).

[0112] Comparative Example 6

[0113] Except that the template agent was not included in step (2), the rest were the same as in Example 1.

[0114] The ion exchange membrane was subjected to performance testing. In this invention, the all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane was 1.15 Ω·cm as shown in Table 1 2 . The relatively high surface resistance was mainly due to the lack of abundant ion transport channels in the ion exchange membrane; the mechanical properties of the ion exchange membrane were 35.22 Mpa as shown in Table 1.

[0115] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example is 98.24%, the voltage efficiency is 85.03%; the energy efficiency is 83.54% (Table 2).

[0116] Comparative example 7,

[0117] Except that the content of polyethylene glycol in step (2) is increased to 0.6 g, the rest are the same as in Example 1.

[0118] The ion exchange membrane was subjected to performance testing. In this invention, an all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.083 Ω·cm as shown in Table 1 2 , and the relatively low surface resistance is mainly due to the abundant ion transport channels in the ion exchange membrane; the mechanical property of the ion exchange membrane is 34.47 Mpa as shown in Table 1.

[0119] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example is 75.43%, the voltage efficiency is 95.23%; the energy efficiency is 71.83% (Table 2).

[0120] Comparative example 8,

[0121] Except that the acid leaching treatment was not carried out in step (6), the rest are the same as in Example 1.

[0122] The ion exchange membrane was subjected to performance testing. In this invention, an all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.82 Ω·cm as shown in Table 1 2 , and the relatively high surface resistance is mainly due to the failure of the polymer in the ion exchange membrane to construct a stable hydrogen bond network; the mechanical property of the ion exchange membrane is 36.79 Mpa as shown in Table 1.

[0123] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane of this comparative example is 95.27%, the voltage efficiency is 84.19%; the energy efficiency is 80.21% (Table 2).

[0124] Comparative example 9,

[0125] Except that the concentration of the acid solution in step (6) is increased to 8 mol / L, the rest are the same as in Example 1.

[0126] The ion exchange membrane was subjected to performance testing. In this invention, an all-vanadium redox flow battery was taken as an example. The surface resistance of the ion exchange membrane is 0.138 Ω·cm as shown in Table 1 2 , and the relatively high surface resistance is mainly due to the construction of a stable hydrogen bond network in the ion exchange membrane; the mechanical property of the ion exchange membrane is 28.43 Mpa as shown in Table 1, and the relatively low tensile strength is attributed to excessive acid doping in the polymer.

[0127] The coulombic efficiency of the all-vanadium redox flow battery assembled with the ion exchange membrane is 96.78%, the voltage efficiency is 86.44%, and the energy efficiency is 83.65% (Table 2).

[0128] Table 1 Preparation conditions and membrane properties of the examples

[0129]

[0130]

[0131] Table 2 Preparation conditions and membrane properties of the comparative examples

[0132]

[0133]

[0134] Table 3 Battery performance of the examples and comparative examples

[0135]

[0136]

[0137] Comparing Example 1 with Examples 2 and 3, it can be seen that by selecting the amount and type of the template agent, the proton transport channels of the ion exchange membrane can be regulated, thereby optimizing the membrane surface resistance and contributing to the proton conduction of the ion exchange membrane.

[0138] Comparing Example 1 with Examples 4, 5, it can be seen that by selecting the acid leaching time and the type of acid, it helps the protonation of the ion exchange membrane containing tertiary amine groups, thereby increasing the formation of hydrogen bond networks, increasing the proton transport rate, and improving the ion selectivity of the membrane.

[0139] Comparing Example 1 with Examples 6, 7, 8, it can be seen that the reasonable selection of the polymer type is beneficial to improving the mechanical properties of the ion exchange membrane. Utilizing the characteristics of different polymers, the ion exchange membrane has stronger mechanical properties and stability.

[0140] Comparing Example 1 with Examples 9, 10, 11, it can be seen that by adjusting the content between different polymers, the size of the membrane surface resistance of the ion exchange membrane can be changed. The higher the content of sulfonic acid groups and tertiary amine groups, the richer the hydrogen bond network formed and the smaller the surface resistance.

[0141] Comparing Example 1 with Comparative Examples 1, 2, 3, 4, 5, it can be seen that between a single polymer or a combination of two polymers, the former has a higher membrane surface resistance due to the lack of a hydrogen bond network, which is not conducive to proton transport, and the battery performance is mainly manifested as a decrease in voltage efficiency; the latter has lower mechanical properties of the ion exchange membrane due to the lack of sufficient polymers as the support layer.

[0142] It can be seen from the comparison between Comparative Examples 1-3 and Comparative Example 6 that in the absence of a templating agent, the membrane surface resistance increases due to the reduction of the proton transport channels in the ion exchange membrane, thereby reducing the battery voltage efficiency and affecting the battery energy efficiency.

[0143] It can be seen from the comparison between Comparative Examples 1-3 and Comparative Example 7 that although an excessive amount of templating agent helps to increase the proton transport channels and reduce the membrane surface resistance of the ion exchange membrane, too many proton transport channels lead to a decrease in the ion selectivity of the membrane and a decrease in the Coulomb efficiency of the battery.

[0144] It can be seen from the comparison between Comparative Examples 1, 4, 5 and Comparative Example 8 that the surface resistance of the ion exchange membrane without acid leaching treatment increases. This is mainly because in the membrane without acid leaching, an effective hydrogen bond network cannot be formed between the polymers in the membrane, which affects the proton transport rate.

[0145] It can be seen from the comparison between Comparative Examples 1, 5, 6 and Comparative Example 9 that the concentration of the acid solution in the acid treatment process has a great influence on the mechanical properties of the ion exchange membrane. The higher the acid concentration, the lower the mechanical properties of the membrane, and thus the worse the stability of the membrane. The doping of a high concentration of acid weakens the interaction between the polymers.

[0146] In summary, by assembling a flow battery with the ion exchange membrane prepared by the method of the present invention, the battery simultaneously has high Coulomb efficiency, voltage efficiency and energy efficiency.

Claims

1. A method for preparing a high-performance ion exchange membrane for a flow battery, comprising the following steps: S1. Dissolve polymer a, polymer b, and polymer c in an organic solvent to form a mixed solution; S2. Add a templating agent to the mixed solution to obtain a casting solution; S3. Coat the casting solution on the surface of a substrate and dry to obtain an initial membrane; S4. Immerse the initial membrane in water or an organic solvent to remove the templating agent and form a porous structure membrane; S5. Immerse the porous structure membrane in an acidic solution for soaking treatment to obtain the ion exchange membrane; The polymer a is selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, and polybenzimidazole; The polymer b is a polymer containing a sulfonic acid group; The polymer c is selected from at least one of polypyrrole, polyvinylpyrrolidone, and polybenzimidazole.

2. The preparation method according to claim 1, characterized in that: The polymer b is selected from at least one of perfluorosulfonic acid resin, sulfonated polyarylene ether ketone, sulfonated polyether ether ketone, sulfonated polytetramethyldiphenyl ether ketone, sulfonated polystyrene, sulfonated polyphenylene sulfide, sulfonated polyphenylene ether, sulfonated copolyimide, and sulfonated polyethersulfone; The mass ratio of the polymer a, the polymer b, and the polymer c is 0.2 - 2:0.2 - 2:0.2 - 2.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the organic solvent is selected from at least one of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, or N,N-dimethylformamide.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S2, the templating agent is selected from at least one of imidazole, phenolphthalein, and polyethylene glycol, and its addition amount is 5 - 30% of the total mass of the polymer a, the polymer b, and the polymer c; The mass concentration of the templating agent in the casting solution is 7 - 30%.

5. The preparation method according to any one of claims 1-4, characterized in that: In step S3, the drying conditions are: temperature is 60 - 120 °C, and time is 8 - 24 hours.

6. The preparation method according to any one of claims 1-5, characterized in that: In step S4, the organic solvent is ethanol, methanol, dichloromethane, or acetonitrile; The temperature for removing the templating agent is 40 °C - 80 °C, and the time is 1 - 24 hours, which is carried out under the conditions of a shaker or static state.

7. The preparation method according to any one of claims 1-6, characterized in that: In step S5, the acidic solution is a sulfuric acid solution or a hydrochloric acid solution, the hydrogen ion concentration is 1 - 3 mol / L, and the soaking time is 8 - 24 hours.

8. An ion exchange membrane prepared by the method according to any one of claims 1 - 7.

9. Application of the ion exchange membrane according to claim 8 as a separator in a flow battery; The coulombic efficiency of the flow battery is ≥97%, and the energy efficiency is ≥87%.

10. The application according to claim 9, characterized in that: The flow battery includes any one of a vanadium redox flow battery, a zinc / bromine flow battery, and an iron / chromium flow battery.

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