Anion exchange membrane and manufacturing method thereof

Abstract

The invention discloses an anion exchange membrane and a preparation method thereof, and belongs to the field of functional polymer membrane materials. The membrane mainly solves the problems of high swelling degree and poor barrier property of an electrode active material caused by complete quaternization of the existing polyaryl piperidinium anion exchange membrane, and the quaternization reaction degree (preferably 85%) of a piperidine ring is accurately controlled, so that a polymer network simultaneously contains a quaternary ammonium ion conduction group and a tertiary amine hydrogen bond supply group, and the membrane has the advantages of simple preparation process, low cost and the like. Therefore, efficient formation of the ion channel is maintained. The swelling degree and the permeability of an electrode active material of the prepared membrane are obviously lower than those of a completely quaternized membrane on the premise of keeping relatively high ionic conductivity. The membrane is simple and controllable in preparation process, and is suitable for electrochemical energy storage devices such as alkaline flow batteries and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer membrane materials, specifically relating to an anion exchange membrane for use in electrochemical energy storage devices, and more particularly to a polyarylpiperidine-onium anion exchange membrane with low swelling and low permeation of active substances and its preparation method. Background Technology

[0002] Against the backdrop of the global energy structure accelerating its transformation towards cleaner and lower-carbon energy sources, the large-scale grid connection of renewable energy sources, represented by wind power and photovoltaics, has created an increasingly urgent demand for efficient and long-duration energy storage technologies. Flow batteries, with their significant advantages such as independently designable power and capacity, high intrinsic safety, and long cycle life, have become one of the key technological routes in the field of large-scale stationary energy storage.

[0003] As a core component of flow batteries, the performance of ion exchange membranes directly determines the battery's energy efficiency, capacity retention, and long-term operational reliability. This component primarily performs the following functions: firstly, it blocks active materials in the positive and negative electrode electrolytes to prevent cross-contamination and capacity decay; secondly, it allows specific ions that support charge transfer to pass through, forming a complete current loop. Therefore, an ideal ion exchange membrane must simultaneously possess high ion selectivity, high ion conductivity, excellent chemical and dimensional stability, and sufficient mechanical strength.

[0004] Currently, research on high-performance anion exchange membranes largely focuses on polyarylpiperidine polymers, such as the anion exchange membrane disclosed in CN115521445A. These materials, with aromatic and piperidine rings forming the main chain structure, exhibit good mechanical strength, thermal stability, and alkali-resistant chemical stability. Referring to a preparation method disclosed in CN118374037A, to improve the ion conductivity of the membrane, conventional techniques typically involve fully quaternizing the nitrogen atoms on the piperidine rings of the polymer to maximize the introduction of positively charged quaternary ammonium groups, thereby increasing the ion exchange capacity. However, complete quaternization leads to an excessively high density of ionic groups within the membrane, causing strong volume swelling in the electrolyte environment. This swelling phenomenon can lead to a series of adverse effects: First, the membrane size changes significantly, which may damage the sealing structure of the fuel cell stack, causing electrolyte leakage or even internal short circuits; second, the intermolecular forces of the polymer weaken after swelling, resulting in a decrease in the mechanical strength and durability of the membrane; third, swelling makes the internal structure of the membrane loose, which may exacerbate the penetration of electrode active materials, leading to a decrease in the coulombic efficiency of the battery.

[0005] Controlling the content of ionic groups in anion exchange membranes using copolymerization can lead to excessive nonpolarity, hindering the formation of well-developed and continuous ion transport channels. Controlling the swelling degree of anion exchange membranes through crosslinking results in decreased membrane flexibility, which is detrimental to membrane formation. Methods disclosed in CN121238166A and CN121082133A show that coating or ion modification methods can be used to control swelling. However, partial quaternization can control the content of ion exchange membranes while retaining a large number of polar tertiary amine groups for constructing ion transport channels, thus effectively solving the problem of the mutual constraint between anti-swelling, active material barrier properties, and ion conduction properties.

[0006] Because polyarylpiperidine has a relatively rigid backbone, when the content of charged functional groups in the polymer is insufficient, the polymer has poor solubility in the solvent. This leads to the presence of incompletely dissolved gels or particles in the casting solution, which can easily cause defects or agglomeration during film formation, thus affecting the membrane performance. Therefore, preparing partially quaternized polyarylpiperidine onium anion exchangers with uniform structure and good film-forming properties is also a challenge. Summary of the Invention

[0007] The purpose of this invention is to develop a method for manufacturing a polyarylpiperidium anion exchange membrane, which possesses low swelling, low electrode active material permeability, and good ion conduction performance, mechanical and chemical stability.

[0008] Specifically, the technical solution of this invention includes: using a polyarylpiperidine copolymer as the backbone, controlling the proportion of oniumized piperidine salt by adjusting the feeding ratio of the quaternizing reagent and the reaction conditions to obtain a polyarylpiperidine onium polymer that retains a portion of tertiary amine piperidine. Subsequently, anion exchange membranes are prepared using a solution casting method, and their water absorption and swelling, active material permeation, ion conductivity, and film-forming properties are tested. The parameters during the preparation process are optimized based on the balance requirements of various performance aspects.

[0009] The specific steps adopted in the technical solution of the present invention are as follows:

[0010] (1) Synthesis of neutral polyarylepiperidine polymers

[0011] Biphenyl, N-methyl-4-piperidinone, and 2,2,2-trifluoroacetophenone were dissolved in dichloromethane at a concentration of 32 wt%, wherein the molar ratio of the ketone monomer (the sum of N-methyl-4-piperidinone and 2,2,2-trifluoroacetophenone) to biphenyl was 1-1.15:1, and the molar ratio of N-methyl-4-piperidinone to 2,2,2-trifluoroacetophenone was 3:2. Under nitrogen protection, the system temperature was lowered to 0 °C using an ice-water bath. Then, trifluoroacetic acid and trifluoromethanesulfonic acid were slowly added dropwise, with the molar ratio of the ketone monomer to trifluoroacetic acid being 1.3-1.6:1 and the molar ratio to trifluoromethanesulfonic acid being 1:7-9. After the addition was complete, the reaction was continued at 0 °C for 4-8 h. The resulting viscous reaction solution was poured into an excess of a 1:1 ethanol-water mixture to precipitate the polymer. The sample was collected by filtration and soaked in a 1 M potassium carbonate aqueous solution at 60 °C for 12 h. It was then washed with deionized water until neutral and dried under vacuum at 60 °C to obtain a neutral polyarylpiperidine polymer with an intrinsic viscosity range of 0.4–0.55 dL·g. -1 .

[0012] (2) Partial quaternization reaction

[0013] Quaternization treatment: A neutral polyarylepiperidine polymer of a certain molecular weight is suspended in N-methylpyrrolidone, dimethyl sulfoxide or N,N-dimethylformamide, the concentration of the polymer in the solvent is 5-10 wt%, a certain amount of quaternization reagent iodomethane is added, and the reaction is carried out at 15-60 ℃ in the dark for 12-48 h.

[0014] Post-processing: Pour the reaction solution from step one into one of dichloromethane, dichloroethane, and diethyl ether to precipitate the polymer. The volume of the precipitate used should be 3-10 times the volume of the reaction solution. After filtration and collection, wash with ethanol, 0.5 M sodium thiosulfate or NaOH solution, or water for a period of time. After vacuum drying at 30-60 °C for 3-12 h, a partially quaternized polyarylpiperidineonium polymer is obtained.

[0015] (3) Casting to form a film

[0016] The polymer obtained in step (2) was dissolved in a film-forming solvent at 5-10 wt%, stirred at 25-60 °C for 3-12 h, and then degassed under vacuum for 3-10 min to obtain a clear casting solution. The casting solution was cast onto a horizontal glass plate, evaporated at 80-120 °C for 3-12 h, and then solidified. The solidified solution was then immersed in deionized water to allow the membrane to detach, and subsequently dried under vacuum at 30-60 °C for 3-12 h to obtain a partially quaternized polyarylpiperidineonium anion exchange membrane.

[0017] Furthermore, the prepared quaternized polyarylpiperidine anion exchange membrane was used for water absorption and swelling, ion conduction, and electrode active material permeation performance testing. The specific testing steps for water absorption and swelling performance are as follows: In a dry state, a membrane of approximately 1*4 cm was cut, and its length, width, thickness, and weight were measured. The membrane was then immersed in deionized water at 30-90 ℃ for 2 h, and its length, width, thickness, and weight were measured again. The percentage increase in weight and volume was recorded as the membrane's water absorption rate and volume swelling degree. The specific testing steps for ion conduction performance are as follows: A dry membrane of approximately 1*2 cm was cut, and its width and thickness were measured. The membrane was immersed in 1 M NaCl aqueous solution for 12 h to replace the chloride ion form. It was then placed in a conductivity testing fixture with an electrode spacing of 1 cm, and its ion conduction was measured by electrochemical impedance spectroscopy in liquid water at 30-90 ℃. The testing steps for electrode active material permeation performance are as follows: A representative organic active material, 2,6-dihydroxyanthraquinone (2,6-DHAQ), was selected for diffusion permeation testing. This substance is commonly used as a negative electrode active material in alkaline flow battery systems, and its permeation behavior significantly affects the coulombic efficiency and cycle stability of the battery. A circular sample with an effective area of ​​1.0 cm² was cut and immersed in 1 M KOH solution for 24 h to displace the hydroxide ion. It was then placed between the two chambers of a dual-chamber diffusion cell. The left chamber (donor chamber) was injected with a 1 M KOH solution containing 0.1 M 2,6-DHAQ, and the right chamber (acceptor chamber) was injected with an equal volume of blank 1 M KOH solution. Both chambers were magnetically stirred to avoid concentration polarization. The entire apparatus was placed in a 25 °C constant-temperature water bath. Samples were taken from the acceptor chamber every 0.5, 1, 2, 3, and 4 h, and the concentration of 2,6-DHAQ was measured at 414 nm using a UV-Vis spectrophotometer. According to Fick's first law, the permeation flux and permeability coefficient were calculated from the slope of the initial linear segment of the concentration-time curve.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: it controls the ion exchange capacity of polyarylpiperidine-onium anion exchange membrane while retaining a considerable proportion of polar tertiary amine piperidine groups, achieving a balance between low water absorption and swelling rate, low active material permeability, and high ion conductivity. Simultaneously, through extensive quaternization and optimization of preparation parameters, it solves the film-forming problem of low-quaternized polyarylpiperidine-onium polymers. Attached Figure Description

[0019] Figure 1 Liquid NMR of neutral polyarylpiperidine polymers 1 H-NMR, solvent: d-CDCl3.

[0020] Figure 2 Liquid NMR of the 50% quaternized polyarylpiperidineonium anion exchange membrane in Example 1 1¹H-NMR, solvent d-DMSO, actual 52.6%.

[0021] Figure 3 Liquid NMR of the 70% quaternized polyarylpiperidineonium anion exchange membrane in Example 2 1 ¹H-NMR, solvent d-DMSO, actual 73.2%.

[0022] Figure 4 Liquid NMR of the 85% quaternized polyarylpiperidineonium anion exchange membrane in Example 3 1 H-NMR, solvent d-DMSO, actual 87.7%.

[0023] Figure 5 Liquid NMR of the fully quaternized polyarylpiperidineonium anion exchange membrane in Comparative Example 1 1 H-NMR, solvent d-DMSO, actual 99.8%.

[0024] Figure 6 The ionic conductivity of polyarylpiperidine-onium anion exchange membranes with different degrees of quaternization is compared.

[0025] Figure 7 The comparison of water absorption rates of polyarylpiperidine anion exchange membranes with different degrees of quaternization is shown.

[0026] Figure 8 The volume swelling ratio of polyarylpiperidine-onium anion exchange membranes with different degrees of quaternization is compared.

[0027] Figure 9 The permeability of 2,6-DHAQ molecules in polyarylpiperidine anion exchange membranes with different degrees of quaternization is shown. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described herein represent only some examples, not all examples. Other embodiments obtained by those skilled in the art without inventive effort based on the embodiments of the present invention are protected by the present invention.

[0029] Example 1

[0030] Preparation method of anion exchange membrane with 50% quaternization

[0031] Synthesis of neutral polyarylpiperidine polymers:

[0032] Under nitrogen protection, biphenyl (3.379 g, 21.92 mmol) was added to a 100 mL three-necked flask containing 15 mL of anhydrous dichloromethane and stirred until dissolved. Then, N-methyl-4-piperidinone (1.488 g, 13.152 mmol) and 2,2,2-trifluoroacetophenone (1.526 g, 8.768 mmol) were added sequentially. The reaction system was cooled to 0 °C in an ice bath, and then trifluoroacetic acid (1 mL, 13.46 mmol) and trifluoromethanesulfonic acid (15 mL, 170.7 mmol) were slowly added dropwise with stirring, controlling the addition temperature to not exceed 5 °C. After the addition was complete, the reaction was maintained at 0 °C for 5 h. After the reaction was complete, the reaction solution was slowly poured into 200 mL of a 1 mol·L⁻¹ ethanol / water mixture to precipitate the polymer. The precipitate was collected by filtration and transferred to 200 mL of a 1 mol·L⁻¹ solution. -1 The polymer was neutralized by stirring in a potassium carbonate solution at 60 °C for 6 h. Subsequently, the polymer was washed with a large amount of deionized water until the eluent was neutral. Finally, it was vacuum dried at 60 °C to obtain a white solid neutral polyarylpiperidine polymer with an intrinsic viscosity of 0.529 dL·g. -1 .

[0033] Partial quaternization reaction:

[0034] Weigh 0.50 g of the dried neutral polyarylpiperidine polymer (estimated molar amount of piperidine ring nitrogen atoms based on its structure to be approximately 1.128 mmol) and add it to 10 mL of anhydrous N-methylpyrrolidone, stirring to disperse it. Then, add 0.08 g (0.564 mmol) of iodomethane, corresponding to 50% of the molar amount of piperidine ring nitrogen in the neutral polyarylpiperidine polymer. Under light-protected conditions, stir the reaction at 60 °C for 12 h to obtain a clear solution. Add the reaction solution dropwise to 100 mL of dichloromethane to allow the product to redefine and precipitate. Collect the solid product by filtration and wash with dichloromethane or diethyl ether, preferably dichloromethane. Finally, dry under vacuum at 50 °C to obtain a polymer powder with a quaternization degree of 50%. Dissolve the obtained polymer powder with a quaternization degree of 50% in N-methylpyrrolidone to prepare a homogeneous solution with a solid content of 5 wt%. The solution was cast onto a clean glass substrate and dried in a 60 °C oven for 24 h to form a flat, self-supporting anion exchange membrane.

[0035] Example 2

[0036] Preparation method of anion exchange membrane with 70% quaternization degree

[0037] The synthesis steps of the neutral polyarylpiperidine polymer were exactly the same as in Example 1. During the partial quaternization reaction, the same mass (0.50 g) of dried neutral polyarylpiperidine polymer was weighed and dispersed in 10 mL of anhydrous N-methylpyrrolidone. Subsequently, iodomethane (0.112 g, 0.79 mmol) was added, corresponding to 70% of the molar amount of piperidine ring nitrogen in the precursor. The reaction was stirred at 45 °C for 8 h under light-protected conditions to obtain a clear solution. The reaction solution was added dropwise to 100 mL of dichloromethane, allowing the product to redefine and precipitate. The solid product was collected by filtration and washed with dichloromethane or diethyl ether, preferably dichloromethane. Finally, it was vacuum dried at 50 °C to obtain a polymer powder with a quaternization degree of 70%. The obtained polymer powder with a quaternization degree of 70% was dissolved in N-methylpyrrolidone to prepare a homogeneous solution with a solid content of 5 wt%. The solution was cast onto a clean glass substrate and dried in an 80 ℃ oven for 12 h to form a flat, self-supporting anion exchange membrane.

[0038] Example 3

[0039] Preparation method of anion exchange membrane with 85% quaternization degree

[0040] The synthesis steps of the neutral polyarylpiperidine polymer were exactly the same as in Example 1. During the partial quaternization reaction, the same mass (0.50 g) of the dried precursor polymer was weighed and dispersed in 10 mL of anhydrous dimethyl sulfoxide. Subsequently, iodomethane (0.136 g, 0.96 mmol) was added, corresponding to 85% of the molar amount of piperidine ring nitrogen in the neutral polyarylpiperidine polymer. The reaction was stirred at 30 °C for 6 h under light-protected conditions to obtain a clear solution. The reaction solution was added dropwise to 100 mL of diethyl ether, allowing the product to redefine and precipitate. The solid product was collected by filtration and washed with dichloromethane or diethyl ether, preferably dichloromethane. Finally, it was vacuum dried at 50 °C to obtain a polymer powder with a quaternization degree of 85%. The obtained polymer powder with a quaternization degree of 85% was dissolved in anhydrous dimethyl sulfoxide to prepare a homogeneous solution with a solid content of 5 wt%. The solution was cast onto a clean glass substrate and dried in an oven at 100 °C for 10 hours to form a flat, self-supporting anion exchange membrane.

[0041] Comparative Example 1

[0042] Comparative Example 1 provides a fully quaternized anion exchange membrane to illustrate the advantages of the partially quaternized technology of this invention. Its preparation method is as follows:

[0043] The synthesis steps of the neutral polyarylpiperidine polymer were exactly the same as in Example 1. During the quaternization reaction, the same mass (0.50 g) of dried neutral polyarylpiperidine polymer was weighed and dispersed in 10 mL of anhydrous dimethyl sulfoxide. Subsequently, excess iodomethane (0.64 g, 4.5 mmol, approximately twice the amount theoretically required for complete quaternization) was added, and the mixture was stirred at 30 °C for 3 h under light-protected conditions to obtain a clear solution. The reaction solution was added dropwise to 100 mL of diethyl ether, allowing the product to redefine and precipitate. The solid product was collected by filtration and washed with dichloromethane or diethyl ether, preferably diethyl ether. Finally, it was vacuum dried at 50 °C to obtain a fully quaternized polymer powder. The obtained fully quaternized polymer powder was dissolved in anhydrous dimethyl sulfoxide to prepare a homogeneous solution with a solid content of 5 wt%. This solution was cast onto a clean glass substrate and dried in an oven at 100 °C for 3 h, ultimately forming a flat, self-supporting anion exchange membrane.

[0044] Table 1. Performance parameters of the anion exchange membranes prepared in the examples and comparative examples: membrane samples Theoretical degree of quaternization Actual degree of quaternization <![CDATA[Ionic conductivity (mS·cm -1 )]]> Water absorption rate (%) Volume swelling ratio (%) <![CDATA[Permeability coefficient of 2,6-DHAQ (cm 2 ·s -1 )]]> Example 1 50% 52.6% 48.2 15.0 16.9 — Example 2 70% 73.2% 60.1 17.5 18.3 <![CDATA[6.43*10 -10 ]]> Example 3 85% 87.7% 84.6 18.8 21.7 <![CDATA[8.77*10 -10 ]]> Comparative Example 1 100% 99.8% 100 31.7 42.4 <![CDATA[1.41*10 -9 ]]> Based on the comparative analysis of the data in Table 1, it can be seen that the fully quaternized membrane, after equilibrium in deionized water at 90 ℃, exhibits the highest ionic conductivity (100 mS·cm). -1 However, its water absorption rate (31.7%), volume swelling rate (42.4 vol%), and permeability coefficient to the active ingredient 2,6-dihydroxyanthraquinone (2,6-DHAQ) (1.4×10⁻⁶) are relatively low. -12 cm 2 ·s -1 The swelling ratios are all significantly higher than normal. Excessive swelling can easily lead to membrane dimensional instability, decreased mechanical properties, and sealing failure, severely affecting its long-term operational reliability in electrochemical devices. This invention, by controlling the degree of quaternization to 85%, significantly improves the dimensional stability and barrier properties of the membrane while maintaining excellent ion conductivity. The partially quaternized membrane prepared in Example 3 achieves an ion conductivity of 84.4% of that of a fully quaternized membrane, while its volume swelling ratio is only 51% of the latter, achieving an optimal balance between high ion conductivity and low swelling characteristics. Furthermore, the permeation coefficient of this partially quaternized membrane for 2,6-DHAQ is significantly lower than that of the fully quaternized membrane, demonstrating excellent active material barrier capabilities. This characteristic plays a crucial role in suppressing cross-contamination in flow batteries, improving coulombic efficiency, and cycle stability, indicating that the membrane material of this invention has good application potential in energy storage systems such as alkaline organic flow batteries.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An anion exchange membrane and its manufacturing method, characterized in that... It includes the following steps: Step 1, Partial Quaternization Reaction: A neutral polyarylene piperidine polymer of a certain molecular weight is suspended in a specific solvent at a certain concentration, a certain amount of quaternization reagent iodomethane is added, and the reaction is carried out at a certain temperature in the dark for a period of time. Step 2, Post-processing of the polymer: Pour the reaction solution from Step 1 into a certain amount of precipitation solvent to precipitate the polymer. After filtration and collection, wash with ethanol, a specific cleaning solvent, and water for a period of time. After vacuum drying at a certain temperature for a period of time, a partially quaternized polyarylpiperidineonium polymer is obtained. Step 3: Preparation of the anion exchange membrane: The polymer obtained in Step 2 is dissolved in a film-forming solvent at a certain concentration. The solution is stirred at a certain temperature for a period of time, and then vacuum degassed for a period of time to obtain a clear casting solution. The casting solution is cast onto a horizontal glass plate, evaporated at a certain temperature and humidity for a period of time, and then solidified. It is then immersed in deionized water to allow the membrane to detach, and subsequently vacuum dried at a certain temperature for a period of time to obtain a partially quaternized polyarylpiperidine anion exchange membrane.

2. The anion exchange membrane and its manufacturing method according to claim 1, characterized in that: The intrinsic viscosity of the neutral polyarylpiperidine polymer in step one is 0.4-0.55 dL·g -1 .

3. The anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step one, the solvent for the quaternization reaction is one of N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylformamide, and the polymer concentration in the solvent is 5-10 wt%.

4. The anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step one, the amount of iodomethane added is 50-100% relative to the molar ratio of piperidine units in the neutral polyarylene piperidine polymer.

5. The anion exchange membrane and its manufacturing method according to claim 1, characterized in that: The temperature of the partial quaternization reaction in step one is 15-60 ℃, and the reaction time is 3-12 h.

6. The anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step two, the solvent used for precipitation is dichloromethane, 1,2-dichloroethane, or diethyl ether, and its volume is 3-10 times the volume of the reaction liquid.

7. An anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step two, the specific cleaning solvent is 0.5 M sodium thiosulfate solution, sodium hydroxide solution, or potassium hydroxide solution, the cleaning time is 3-12 h, the drying temperature is 30-60 ℃, and the drying time is 3-12 h.

8. An anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step three, the film-forming solvent is selected from N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylformamide. The stirring and dissolving temperature is 25-60 °C, the stirring time is 3-12 h, and the vacuum degassing time is 3-10 min.

9. An anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step three, the mass fraction of the quaternized polyarylepiperidine polymer in the polymer is 5-10 wt%.

10. An anion exchange membrane and its manufacturing method according to claim 1, characterized in that: In step three, the film-forming temperature is 60-100 ℃, the humidity is 30-80% RH, the time is 6-24 h, the drying temperature is 30-60 ℃, and the drying time is 3-12 h.

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