Crown ether grafted polymer, its preparation method and application

Abstract

The application discloses a crown ether grafted polymer and a preparation method and application thereof, which takes a polybenzimidazole (PBI) polymer as a matrix and a crown ether group as a grafting group. The crown ether group is grafted on a molecular chain of the polybenzimidazole (PBI) polymer, the crown ether itself has a large size structure, and can reduce the accumulation of the molecular chain of the polybenzimidazole (PBI) polymer. Meanwhile, the crown ether is a hydrophilic group and has the ability of transferring protons. The crown ether group is introduced into the molecular chain of the polybenzimidazole (PBI) polymer, and the ionic conductivity of a polybenzimidazole ion conductive membrane can be improved.

Description

Technical Field

[0001] This invention belongs to the field of ion-conducting membrane technology, specifically relating to a crown ether-grafted polymer, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow batteries (VRFBs) have garnered widespread attention due to their energy-power decoupling, long lifespan, and excellent safety. The ion-conducting membrane (ICM) is one of the core components of a VRFB. It not only blocks the active materials of the positive and negative electrodes to prevent cross-contamination and self-discharge, but also transports balancing ions to maintain charge balance between the electrodes. The performance of the ICM significantly impacts battery performance. The selectivity of the ICM affects the coulombic efficiency and capacity retention, while its ionic conductivity affects the voltage efficiency. Therefore, an ideal ICM should possess both high ionic conductivity and high selectivity. Furthermore, the ICM needs sufficient mechanical strength and chemical stability to withstand the impact of the electrolyte during operation and the strong acidity of the electrolyte and the presence of the active material VO2. + It has strong oxidizing properties.

[0003] Polybenzimidazole (PBI) polymers are currently the most commonly used polymer materials for ion-conducting membranes in VRFBs due to their excellent stability and ability to protonate and inhibit vanadium ion penetration in strongly acidic environments. However, the strong interactions between PBI molecular chains result in dense chain packing, severely hindering proton transfer and thus affecting the electrochemical performance of VRFBs. Therefore, further improving the performance of PBI polymers is of great significance for enhancing the overall performance of VRFBs. Summary of the Invention

[0004] The purpose of this invention is to provide a crown ether-grafted polymer, its preparation method, and its application. This invention, by introducing crown ether groups into the polymer chain of polybenzimidazole (PBI) polymers, can effectively improve the ionic conductivity of polybenzimidazole (PBI) ion-conducting membranes, thereby enhancing the electrochemical performance of vanadium redox flow batteries.

[0005] In a first aspect, the present invention provides a crown ether-grafted polymer, employing the following technical solution:

[0006] A crown ether-grafted polymer, using a polybenzimidazole (PBI)-based polymer as the matrix and a crown ether group as the grafting group; its structural formula is one of formulas I to VI:

[0007]

[0008] Wherein: R represents a crown ether group, and the crown ether group is one of formulas VII to XI:

[0009] .

[0010] Secondly, the present invention provides a method for preparing a crown ether-grafted polymer, comprising the following steps:

[0011] Polybenzimidazole (PBI) polymers were dissolved in a solvent to obtain a polymer solution; chlorinated crown ethers and catalysts were added to the polymer solution, and the reaction was carried out under an inert atmosphere. After the reaction was completed, the crown ether-grafted polymer was obtained.

[0012] Among them, the structural formula of polybenzimidazole (PBI) polymers is one of formulas 1 to 6:

[0013]

[0014] Chlorinated crown ethers have one of the structural formulas from formula 7 to 11:

[0015] .

[0016] Preferably, the solvent is one or both of dimethyl sulfoxide and N,N-dimethylacetamide, and the mass fraction of polybenzimidazole (PBI) polymer in the solvent is 2.5 to 3.5 wt%.

[0017] Preferably, the molar ratio of repeating units of the polybenzimidazole (PBI) polymer to chlorinated crown ether is 1:(0.7~0.9).

[0018] The repeating unit of polybenzimidazole (PBI) polymers is the structural formula shown in parentheses, that is, the structural formula of polybenzimidazole (PBI) polymers is: Its repeating unit is .

[0019] Preferably, the catalyst is one or two of lithium carbonate and lithium hydroxide; the mass of the catalyst is 18-20% of the mass of the polybenzimidazole (PBI) polymer.

[0020] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0021] Preferably, the reflux reaction temperature is 90~110℃ and the reflux reaction time is 36~72h.

[0022] Thirdly, the present invention provides an ion-conducting membrane prepared using the aforementioned crown ether-grafted polymer.

[0023] Fourthly, a method for preparing an ion-conducting membrane includes the following steps:

[0024] S1: Casting a casting solution containing a crown ether-grafted polymer and polyethyleneimine into a film to obtain a base film;

[0025] S2: The base film will be processed sequentially as follows:

[0026] Soak in hot water;

[0027] Soak in an acidic solution;

[0028] Wash until neutral;

[0029] The treated base film is obtained;

[0030] S3: Immerse the treated base membrane in an acid solution to absorb the acid and obtain an ion-conducting membrane.

[0031] Preferably, in step S1, the mass ratio of the crown ether grafted polymer to the polyethyleneimine is 1:0.7~0.9; and the casting temperature is 70~90℃.

[0032] Preferably, in step S1, the method for preparing the casting solution containing the crown ether-grafted polymer and polyethyleneimine is as follows: dissolve the crown ether-grafted polymer in a solvent, then add polyethyleneimine under an inert atmosphere, stir to dissolve, and obtain the casting solution.

[0033] More preferably, the solvent is one or two of dimethyl sulfoxide and N,N-dimethylacetamide; the mass fraction of the crown ether-grafted polymer in the solvent is 0.8~1.2wt%; and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0034] Preferably, in step S2, the temperature of the hot water is 70~90℃; the soaking time of the base membrane in the hot water is 3~5h; the acid solution is a sulfuric acid solution with a concentration of 0.4~0.6mol / L, and the soaking time of the base membrane in the acid solution is 3~5h.

[0035] Preferably, in step S2, before obtaining the treated base film after washing to neutrality, the step further includes: soaking in alkaline solution and washing to neutrality.

[0036] More preferably, the alkaline solution is one of sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium carbonate, sodium carbonate, and lithium carbonate solutions, and the concentration of the alkaline solution is 1.5~3 mol / mL; the base film is immersed in the alkaline solution for 36~72 h.

[0037] Preferably, in step S3, the acid solution is a sulfuric acid solution with a concentration of 2-4 mol / L and an acid absorption time of 18-36 h.

[0038] The above-described one or more technical solutions of the present invention can achieve at least one of the following beneficial effects:

[0039] This invention grafts crown ether groups onto the molecular chains of polybenzimidazole (PBI) polymers. The crown ethers themselves have a large-size structure, which can reduce the stacking of the polybenzimidazole (PBI) polymer molecular chains. At the same time, the crown ether is a hydrophilic group with the ability to transfer protons. Introducing crown ether groups into the polybenzimidazole (PBI) polymer molecular chains can improve the ionic conductivity of polybenzimidazole ion-conducting membranes. Attached Figure Description

[0040] Figure 1 Infrared spectra of the ion-conducting membranes prepared in Examples 1 and 3.

[0041] Figure 2 The XRD patterns are of the ion-conducting membranes prepared in Examples 1, 3 and Comparative Example 1.

[0042] Figure 3 The images show scanning electron microscope (SEM) images of the cross-section and surface of the ion-conducting membranes prepared in Examples 1 and 2, respectively; (a) and (b) are cross-sectional SEM images and surface SEM images of the ion-conducting membrane prepared in Example 1, respectively; (c) and (d) are cross-sectional SEM images and surface SEM images of the ion-conducting membrane prepared in Example 2, respectively.

[0043] Figure 4 The ion-conducting membranes prepared for Example 1 and Comparative Example 1 were used in an all-vanadium redox flow battery. The coulombic efficiency of the battery at different current densities was ( Figure 4 a) Voltage efficiency ( Figure 4 b) and energy efficiency ( Figure 4 c) Data chart. Detailed Implementation

[0044] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] As mentioned above, in the first aspect, the present invention provides a crown ether-grafted polymer, employing the following technical solution:

[0048] A crown ether-grafted polymer, using a polybenzimidazole (PBI)-based polymer as the matrix and a crown ether group as the grafting group; its structural formula is one of formulas I to VI:

[0049]

[0050] Wherein: R represents a crown ether group, and the crown ether group is one of formulas VII to XI:

[0051] .

[0052] Some crown ether groups were grafted onto the molecular chains of polybenzimidazole (PBI) polymers. The crown ethers themselves have a large-size structure, which can reduce the stacking of the polybenzimidazole (PBI) polymer molecular chains. At the same time, the crown ether is a hydrophilic group with the ability to transfer protons. Introducing crown ether groups into the molecular chains of polybenzimidazole (PBI) polymers can improve the ionic conductivity of polybenzimidazole ion-conducting membranes.

[0053] Secondly, the present invention provides a method for preparing a crown ether-grafted polymer, comprising the following steps:

[0054] Polybenzimidazole (PBI) polymers were dissolved in a solvent to obtain a polymer solution; chlorinated crown ethers and catalysts were added to the polymer solution, and the reaction was carried out under an inert atmosphere. After the reaction was completed, the crown ether-grafted polymer was obtained.

[0055] Among them, the structural formula of polybenzimidazole (PBI) polymers is one of formulas 1 to 6:

[0056]

[0057] Chlorinated crown ethers have one of the structural formulas from formula 7 to 11:

[0058] .

[0059] Preferably, the solvent is one or both of dimethyl sulfoxide and N,N-dimethylacetamide, and the mass fraction of polybenzimidazole (PBI) polymer in the solvent is 2.5~3.5 wt%.

[0060] Preferably, the molar ratio of repeating units of the polybenzimidazole (PBI) polymer to chlorinated crown ether is 1:(0.7~0.9).

[0061] Preferably, the catalyst is one or two of lithium carbonate and lithium hydroxide; the mass of the catalyst is 18-20% of the mass of the polybenzimidazole (PBI) polymer.

[0062] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0063] Preferably, the reflux reaction temperature is 90~110℃ and the reflux reaction time is 36~72h.

[0064] Thirdly, the present invention provides an ion-conducting membrane prepared using the aforementioned crown ether-grafted polymer.

[0065] Fourthly, a method for preparing an ion-conducting membrane includes the following steps:

[0066] S1: Casting a casting solution containing a crown ether-grafted polymer and polyethyleneimine into a film to obtain a base film;

[0067] S2: The base film will be processed sequentially as follows:

[0068] Soak in hot water;

[0069] Soak in an acidic solution;

[0070] Wash until neutral; obtain the treated base film;

[0071] S3: Immerse the treated base membrane in an acid solution to absorb the acid and obtain an ion-conducting membrane.

[0072] Preferably, in step S1, the mass ratio of the crown ether grafted polymer to the polyethyleneimine is 1:0.7~0.9; and the casting temperature is 70~90℃.

[0073] Preferably, in step S1, the method for preparing the casting solution containing the crown ether-grafted polymer and polyethyleneimine is as follows: dissolve the crown ether-grafted polymer in a solvent, then add polyethyleneimine under an inert atmosphere, stir to dissolve, and obtain the casting solution.

[0074] More preferably, the solvent is one or two of dimethyl sulfoxide and N,N-dimethylacetamide; the mass fraction of the crown ether-grafted polymer in the solvent is 0.8~1.2 wt%; and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0075] Preferably, in step S2, before obtaining the treated base film after washing to neutrality, the step further includes: soaking in alkaline solution and washing to neutrality.

[0076] More preferably, the alkaline solution is one of sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium carbonate, sodium carbonate, and lithium carbonate solutions, and the concentration of the alkaline solution is 1.5~3 mol / mL; the base film is immersed in the alkaline solution for 36~72 h.

[0077] In the preparation process of the ion-conducting membrane, this invention employs an alkaline immersion treatment; the OH- in the alkaline solution... -The grafting process removes hydrogen atoms from the imidazole rings of polybenzimidazole polymers, forming negatively charged nitrogen atoms. The interaction between these negatively charged nitrogen atoms and alkali metal ions (such as sodium and lithium ions) in the solution reduces the spacing between the polybenzimidazole membrane molecular chains, significantly improving the membrane's ion selectivity. Simultaneously, the grafting of crown ethers onto the polybenzimidazole polymers, with their large-scale structure, keeps the reduction in molecular chain spacing within a certain range. Furthermore, the crown ethers, as hydrophilic groups, possess proton-transferring capabilities, ensuring that the ion conductivity of the ion-conducting membrane remains high. Therefore, through the synergistic effect of crown ether grafting and alkali treatment, the ion-conducting membrane can simultaneously possess both high ion conductivity and high selectivity, thereby significantly improving the electrochemical performance of the flow battery.

[0078] Preferably, in step S2, the temperature of the hot water is 70~90℃; the soaking time of the base membrane in the hot water is 3~5h; the acid solution is a sulfuric acid solution with a concentration of 0.4~0.6mol / L, and the soaking time of the base membrane in the acid solution is 3~5h.

[0079] Preferably, in step S3, the acid solution is a sulfuric acid solution with a concentration of 2-4 mol / L; and the acid absorption time is 18-36 h.

[0080] The polyethyleneimine used in this embodiment of the invention has a molecular weight of 600 Da and the following structural formula:

[0081] .

[0082] Example 1

[0083] The synthetic route of the crown ether-grafted polymer in this embodiment is as follows:

[0084]

[0085] The specific preparation method is as follows:

[0086] 1g of polybenzimidazole polymer (as shown in Formula 5, with a molecular weight of 4.72 × 10⁻⁶) was added. 5 Da (repeating unit 1180) was dissolved in 30 mL of DMSO to obtain a clear solution. 0.646 g of 4'-chloromethylbenzo15-crown-5 ether (as shown in Formula 7) and 0.19 g of lithium carbonate were added to the clear solution. The mixture was then refluxed at 100 °C for 48 h under a nitrogen atmosphere. After the reaction was complete, the reaction solution was poured into deionized water. After complete precipitation, the mixture was filtered. The filter cake was washed and dried to obtain the crown ether-grafted polybenzimidazole polymer (as shown in Formula V-1). The molar ratio of the repeating unit of the polybenzimidazole polymer to 4'-chloromethylbenzo15-crown-5 ether was 1:0.8.

[0087] The preparation method of the ion-conducting membrane is as follows:

[0088] (1) At 80°C, 0.2 g of crown ether-grafted polybenzimidazole polymer (shown in Formula V-1) was dissolved in 20 mL of DMSO to obtain a homogeneous and transparent solution. Under nitrogen protection, 0.177 g of polyethyleneimine was added to the homogeneous and transparent solution, and then stirred at 500 rpm for 48 h to obtain a casting solution; the casting solution was cast into a film at 80°C to obtain a base film.

[0089] (2) The base membrane was soaked in deionized water at 80°C for 4 hours, and then soaked in sulfuric acid solution with a concentration of 0.5 mol / L for 4 hours. After soaking, the base membrane was washed with deionized water until the washing water was neutral, and the acid-treated base membrane was obtained.

[0090] (3) The acid-treated base film was immersed in a sodium hydroxide solution with a concentration of 2 mol / L for 48 h. After immersion, the base film was washed with deionized water until the washing water was neutral, thus obtaining the alkali-treated base film.

[0091] (4) The base membrane after alkali treatment was immersed in a sulfuric acid solution with a concentration of 3 mol / L for 24 h to obtain the ion-conducting membrane S1.

[0092] Example 2

[0093] The method is basically the same as Example 1, except that in step (3) of the ion-conducting membrane preparation method, a 2 mol / L lithium hydroxide solution is used to replace the 2 mol / L sodium hydroxide solution; the ion-conducting membrane S2 is prepared accordingly.

[0094] Comparative Example 1

[0095] Without crown ether grafting, the ion-conducting membrane DS1 was prepared directly using a polybenzimidazole polymer (as shown in Formula 5) according to the preparation method of the ion-conducting membrane in Example 1.

[0096] Example 3

[0097] The method is basically the same as in Example 1, except that step (3) is omitted in the preparation method of the ion-conducting membrane, that is, no alkali treatment is performed, and the corresponding ion-conducting membrane S3 is prepared.

[0098] Example 4

[0099] The synthetic route of the crown ether-grafted polymer in this embodiment is as follows:

[0100]

[0101] The specific preparation method is as follows:

[0102] 1g of polybenzimidazole polymer (as shown in Formula 4, with a molecular weight of 4.72 × 10⁻⁶) was added. 5 Da (repeating unit 1200) was dissolved in 30 mL of DMF to obtain a homogeneous and transparent solution. 0.643 g of 4'-chloromethylbenzo18-crown-6 ether (as shown in Formula 9) and 0.2 g of lithium carbonate were added to the homogeneous and transparent solution. The mixture was then refluxed at 110 °C for 36 h under a nitrogen atmosphere. After the reaction was complete, the reaction solution was poured into deionized water. After complete precipitation, the mixture was filtered. The filter cake was washed and dried to obtain the crown ether-grafted polybenzimidazole polymer (as shown in Formula IV-1). The molar ratio of the repeating unit of the polybenzimidazole polymer to 4'-chloromethylbenzo18-crown-6 ether was 1:0.7.

[0103] The preparation method of the ion-conducting membrane is as follows:

[0104] (1) At 80°C, 0.2 g of crown ether-grafted polybenzimidazole polymer (as shown in Formula IV-1) was dissolved in 20 mL of DMF to obtain a homogeneous and transparent solution. Under nitrogen protection, 0.170 g of polyethyleneimine was added to the homogeneous and transparent solution, and then stirred at 500 rpm for 48 h to obtain a casting solution; the casting solution was cast into a film at 90°C to obtain a base film.

[0105] (2) The base membrane was soaked in deionized water at 90°C for 4 hours, and then soaked in sulfuric acid solution with a concentration of 0.6 mol / L for 3 hours. After soaking, the base membrane was washed with deionized water until the washing water was neutral, and the acid-treated base membrane was obtained.

[0106] (3) The acid-treated base film was immersed in a 3 mol / L sodium hydroxide solution for 36 h. After immersion, the base film was washed with deionized water until the washing water was neutral, thus obtaining the alkali-treated base film.

[0107] (4) The base membrane after alkali treatment was immersed in a sulfuric acid solution with a concentration of 3 mol / L for 24 h to absorb acid and obtain ion conduction membrane S4.

[0108] Example 5

[0109] The synthetic route of the crown ether-grafted polymer in this embodiment is as follows:

[0110]

[0111] The specific preparation method is as follows:

[0112] 1g of polybenzimidazole polymer (as shown in Formula 2, with a molecular weight of 4.46 × 10⁻⁶) was added. 5Da (repeating unit 1320) was dissolved in 30 mL of DMSO to obtain a homogeneous and transparent solution. 0.729 g of 4'-chloromethylbenzo12-crown-4-ether (as shown in Formula 8) and 0.20 g of lithium carbonate were added to the homogeneous and transparent solution. The mixture was then refluxed at 90 °C for 60 h under a nitrogen atmosphere. After the reaction was complete, the reaction solution was poured into deionized water. After complete precipitation, the mixture was filtered. The filter cake was washed and dried to obtain the crown ether-grafted polybenzimidazole polymer (as shown in Formula II-1). The molar ratio of the repeating unit of the polybenzimidazole polymer to 4'-chloromethylbenzo12-crown-4-ether was 1:0.9.

[0113] The preparation method of the ion-conducting membrane is as follows:

[0114] (1) At 80°C, 0.2 g of crown ether-grafted polybenzimidazole polymer (shown in Formula II-1) was dissolved in 20 mL of DMSO to obtain a homogeneous and transparent solution. Under nitrogen protection, 0.180 g of polyethyleneimine was added to the homogeneous and transparent solution, and then stirred at 500 rpm for 48 h to obtain a casting solution; the casting solution was cast into a film at 70°C to obtain a base film.

[0115] (2) The base membrane was soaked in deionized water at 70°C for 5 hours, and then soaked in sulfuric acid solution with a concentration of 0.4 mol / L for 5 hours. After soaking, the base membrane was washed with deionized water until the washing water was neutral, and the acid-treated base membrane was obtained.

[0116] (3) The acid-treated base film was immersed in a 1.5 mol / L potassium hydroxide solution for 36 h. After immersion, the base film was washed with deionized water until the washing water was neutral, thus obtaining the alkali-treated base film.

[0117] (4) The base membrane after alkali treatment was immersed in a sulfuric acid solution with a concentration of 3 mol / L for 24 h to absorb acid and obtain the ion-conducting membrane S5.

[0118] Example 6

[0119] The synthetic route of the crown ether-grafted polymer in this embodiment is as follows:

[0120]

[0121] The specific preparation method is as follows:

[0122] 1g of polybenzimidazole polymer (as shown in Formula 6, with a molecular weight of 5.97 × 10⁻⁶) was added. 5Da (repeating unit 1180) was dissolved in 30 mL of DMSO to obtain a homogeneous and transparent solution. 0.723 g of 4'-chloromethylbenzo24-crown-8 ether (as shown in Formula 11) and 0.2 g of lithium carbonate were added to the solution. The mixture was then refluxed at 90 °C for 60 h under a nitrogen atmosphere. After the reaction was complete, the reaction solution was poured into deionized water. After complete precipitation, the mixture was filtered. The filter cake was washed and dried to obtain the crown ether-grafted polybenzimidazole polymer (as shown in Formula VI-1). The molar ratio of the repeating unit of the polybenzimidazole polymer to 4'-chloromethylbenzo24-crown-8 ether was 1:0.9.

[0123] The preparation method of the ion-conducting membrane is as follows:

[0124] (1) At 80°C, 0.2 g of crown ether-grafted polybenzimidazole polymer (shown in Formula VI-1) was dissolved in 20 mL of DMSO to obtain a homogeneous and transparent solution. Under nitrogen protection, 0.165 g of polyethyleneimine was added to the homogeneous and transparent solution, and then stirred at 500 rpm for 48 h to obtain a casting solution; the casting solution was cast into a film at 80°C to obtain a base film.

[0125] (2) The base membrane was soaked in deionized water at 80°C for 4 hours, and then soaked in sulfuric acid solution with a concentration of 0.5 mol / L for 4 hours. After soaking, the base membrane was washed with deionized water until the washing water was neutral, and the acid-treated base membrane was obtained.

[0126] (3) The acid-treated base film was soaked in a 2 mol / L potassium hydroxide solution for 18 hours. After soaking, the base film was washed with deionized water until the washing water was neutral, thus obtaining the alkali-treated base film.

[0127] (4) The base membrane after alkali treatment was soaked in a sulfuric acid solution with a concentration of 3 mol / L for 24 h to obtain the ion-conducting membrane S6.

[0128] Infrared spectroscopy was performed on the ion-conducting membranes prepared in Examples 1 and 3, and the results are shown below. Figure 1 There was no substantial difference in the infrared spectra of the two examples, indicating that the chemical structures of the ion-conducting membranes in Example 1 and Example 3 are the same, and alkaline treatment will not cause any changes in the chemical structure of the membrane.

[0129] The XRD patterns of the ion-conducting membranes prepared in Examples 1, 3, and Comparative Example 1 are shown below. Figure 2As shown, there is a difference in the 2θ angle in the XRD patterns of the ion-conducting membranes prepared in Example 1 and Example 3, indicating that alkaline treatment alters the crystal structure of the ion-conducting membrane. The XRD patterns of the ion-conducting membranes prepared in Example 1 and Comparative Example 1 differ significantly, indicating that the crystal structure of polybenzimidazole also changes after crown ether grafting.

[0130] Scanning electron microscope (SEM) images of the cross-sections and surfaces of the ion-conducting membranes prepared in Examples 1 and 2 are shown below. Figure 3 As shown, the ion-conducting membranes prepared in Examples 1 and 2 have relatively uniform and dense structures. Due to the strong interaction between nitrogen atoms in the imidazole groups, the polybenzimidazole molecular chains stack. If pure PBI is used for casting, the membrane density will be very high, and the ion conductivity of the pure PBI membrane will be poor. To improve the ion conductivity of the PBI membrane, polyethyleneimine (PEI) is generally added to the casting solution. PEI can form hydrogen bonds with the nitrogen atoms on the polybenzimidazole imidazole, breaking the original stacking pattern of the PBI molecular chains and increasing the interchain spacing, thus expanding ion transport access. Therefore, adding PEI can improve the ion transport channels of PBI, but the structure of the ion-conducting membrane remains relatively dense.

[0131] Performance testing:

[0132] The ion-conducting membranes prepared in Examples 1-6 and Comparative Example 1 were assembled in an all-vanadium redox flow battery, and the battery performance was tested. The specific assembly method was as follows: a graphite plate was used as the current collector, activated carbon felt as the electrode, epoxy resin as the end plates, and a polytetrafluoroethylene (PTFE) plate was used to fix the ion-conducting membrane between the two end plates to form a flow battery; a PTFE tube was used to connect the single cell, electrolyte storage tank, and peristaltic pump to form a complete flow battery device.

[0133] The specific test method is as follows: using deionized water as solvent, 3 mol / L sulfuric acid solution as supporting electrolyte, and 1.5 mol / L VO2+... 2+ / VO2 + and 1.5 mol / L V 2+ / V 3+ These are the positive and negative redox active pairs, constituting the electrolyte. Battery performance was monitored using a blue electrode tester, with the charge / discharge cutoff voltage set at 0.8~1.65 V and the current density at 200 mA / cm². 2 During the test, the electrolyte was protected with nitrogen gas.

[0134] The ion-conducting membranes prepared in Example 1 and Comparative Example 1 were applied to an all-vanadium redox flow battery, and the battery performance diagrams are shown below. Figure 4 The specific test data for Examples 1-6 and Comparative Example 1 can be found in Table 1.

[0135] Table 1: Performance parameters of ion-conducting membranes prepared in examples and comparative examples applied to flow batteries.

[0136]

[0137] from Figure 4 As shown in Table 1, the energy efficiency of the flow battery prepared by the ion-conducting membrane S1 in Example 1 is significantly higher than that of Comparative Example 1; this indicates that using crown ether-grafted polybenzimidazole can improve the energy efficiency of the flow battery. In Example 2, lithium hydroxide solution was used instead of sodium hydroxide in Example 1 during the alkaline treatment process, which shows that its energy efficiency decreased to some extent, but still maintained a good energy efficiency.

[0138] As can be seen from the data in Table 1, in Example 3, the ion-conducting membrane was not treated with alkali, and the energy efficiency was somewhat lower than that in Example 1, but it was somewhat higher than that in Comparative Example 1.

[0139] As can be seen from the data in Table 1, Examples 4 to 6 mainly used different types of crown ether-grafted polybenzimidazole polymers and changed the process parameters of the ion conduction membrane preparation process. The energy efficiency of the corresponding flow batteries varied to a certain extent, but was still above 80%.

[0140] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A crown ether-grafted polymer, characterized in that, It uses polybenzimidazole polymers as the matrix and crown ether groups as grafting groups; its structural formula is one of formulas I to VI: Wherein: R represents a crown ether group, and the crown ether group is one of formulas VII to XI: 。 2. A method for preparing the crown ether-grafted polymer according to claim 1, characterized in that, Includes the following steps: Polybenzimidazole polymers were dissolved in a solvent to obtain a polymer solution; chlorinated crown ethers and a catalyst were added to the polymer solution, and the reaction was carried out under an inert atmosphere. After the reaction was completed, the crown ether-grafted polymer was obtained. Among them: the structural formula of polybenzimidazole polymers is one of formulas 1 to 6: ； Chlorinated crown ethers have one of the structural formulas from formula 7 to 11: 。 3. The method for preparing the crown ether-grafted polymer according to claim 2, characterized in that, The molar ratio of repeating units to chlorinated crown ethers in the polybenzimidazole polymer is 1:(0.7~0.9); The catalyst is one or both of lithium carbonate and lithium hydroxide; The mass of the catalyst is 18-20% of the mass of the polybenzimidazole polymer.

4. The method for preparing the crown ether-grafted polymer according to claim 2, characterized in that, The inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the reflux reaction temperature is 90~110℃; the reflux reaction time is 36~72h.

5. An ion-conducting membrane, characterized in that, It is prepared using the crown ether grafted polymer as described in claim 1.

6. A method for preparing an ion-conducting membrane according to claim 5, characterized in that, Includes the following steps: S1: Casting a casting solution containing a crown ether-grafted polymer and polyethyleneimine into a film to obtain a base film; S2: The base film will be processed sequentially as follows: Soak in hot water; Soak in an acidic solution; Wash until neutral; The treated base film is obtained; S3: Immerse the treated base membrane in an acid solution to absorb the acid and obtain an ion-conducting membrane.

7. The method for preparing the ion-conducting membrane according to claim 6, characterized in that, In step S1, the mass ratio of the crown ether-grafted polymer to polyethyleneimine is 1:0.7~0.9; the casting temperature is 70~90℃.

8. The method for preparing the ion-conducting membrane according to claim 6, characterized in that, In step S2, the temperature of the hot water is 70~90℃; the base membrane is soaked in the hot water for 3~5 hours; the acid solution is a sulfuric acid solution with a concentration of 0.4~0.6 mol / L, and the base membrane is soaked in the acid solution for 3~5 hours.

9. The method for preparing the ion-conducting membrane according to claim 6 or 8, characterized in that, In step S2, before obtaining the treated base film after washing to neutrality, the step further includes: soaking and washing in an alkaline solution until neutral; wherein: the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium carbonate, sodium carbonate, and lithium carbonate solutions, and the concentration of the alkaline solution is 1.5~3 mol / mL; the base film is soaked in the alkaline solution for 36~72 hours.

10. The method for preparing the ion-conducting membrane according to claim 6, characterized in that, In step S3, the acid solution is a sulfuric acid solution with a concentration of 2-4 mol / L and an acid absorption time of 18-36 h.

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