Preparation method of binaphthalene-biphenyl vanadium redox flow battery proton exchange membrane material

Abstract

The invention provides a preparation method of a binaphthalene-biphenyl vanadium redox flow battery proton exchange membrane material, and belongs to the field of vanadium redox flow battery diaphragm materials. Sulfonated binaphthol and biphenyl in different proportions are used as comonomers, the comonomers and 5-fluoroisatin are subjected to an acid catalysis condensation polymerization reaction, and the structural formula is shown in (I). Trifluoroacetic acid and trifluoromethanesulfonic acid are adopted as heterogeneous solvents and catalysts of polymerization reaction, polycondensation and introduction of sulfonic acid groups are completed in one step, reaction conditions are mild, subsequent sulfonation treatment is not needed, the yield is high, and the cost is low. The ion exchange membrane prepared from the copolymer has excellent proton conduction channel and efficient vanadium ion screening capability. And in an all-vanadium redox flow battery performance test, high proton conductivity, low vanadium ion permeability and relatively high coulombic efficiency and energy efficiency of the battery are shown, and the application prospect is relatively wide.

Description

Technical Field

[0001] This invention relates to the fields of polymer materials and vanadium redox flow batteries, and particularly to a method for preparing a proton exchange membrane material for a biphenylnaphthalene-biphenyl vanadium redox flow battery. Background Technology

[0002] Large-scale energy storage technology plays a crucial role in the global energy structure transformation as a key component in addressing the grid connection stability of intermittent renewable energy sources. Vanadium redox flow batteries (VRFBs), with their advantages of power-capacity decoupling, deep discharge capability, long lifespan, and high safety, have demonstrated enormous potential in large-scale grid energy storage and peak-shaving applications, and are one of the key technologies for solving the grid connection stability issues of intermittent renewable energy sources such as solar and wind power. Among the core components of VRFBs, the ion exchange membrane plays an irreplaceable role. It is not only an ion conduction channel forming a conductive circuit within the battery, but also a critical barrier preventing the cross-mixing of vanadium ions in the positive and negative electrode electrolytes. Its performance directly determines the battery's efficiency, lifespan, and cost.

[0003] Currently, the most commonly used membrane in VRFB (Vibration Reduction Fusion Battery) is the perfluorosulfonic acid membrane (such as the Nafion series), which possesses high ionic conductivity and excellent chemical stability. However, its inherent high vanadium ion permeability and high price pose significant challenges to the further commercialization of VRFB. The ion cluster channels (approximately 3-5 nanometers) formed by the unique hydrophilic-hydrophobic microphase separation structure inside the perfluorosulfonic acid membrane are much larger than the size of hydrated vanadium ions (approximately 0.6-0.8 nanometers), resulting in poor sieving effect for vanadium ions of different valence states. Driven by concentration gradients and electric fields, vanadium ions migrate across the membrane, causing cross-contamination of the positive and negative electrode electrolytes, which in turn leads to a series of problems such as battery self-discharge, capacity decay, and increased side reactions. In addition, the complex perfluorination production process of perfluorosulfonic acid membranes results in high manufacturing costs, with market prices reaching hundreds to thousands of US dollars per square meter, accounting for more than 25% of the total cost of the VRFB system, severely restricting its promotion in the field of large-scale energy storage.

[0004] To overcome the inherent defects of perfluorosulfonic acid membranes, researchers have focused on developing non-fluorinated hydrocarbon polymer membranes, such as sulfonated polyether ether ketone (SPEEK) and sulfonated polyarylether sulfone (SPAES). These materials, with their wide availability, low cost, and high structural designability, have become ideal alternatives to VRFB ion exchange membranes. However, these membrane materials face a key challenge: the trade-off between proton conductivity and vanadium ion permeability. These two parameters are typically positively correlated; increasing proton conductivity often increases vanadium ion permeability, and vice versa. Compared to perfluorosulfonic acid membranes, hydrocarbon polymer membranes exhibit relatively weaker chemical stability against the strongly acidic and oxidizing electrolytes in VRFBs. During long-term operation, the polymer backbone may degrade, and functional groups may become ineffective due to oxidation, significantly shortening the lifespan of VRFBs. Therefore, developing novel ion exchange membranes with strong ion conductivity, low vanadium ion permeability, high ion selectivity, excellent chemical and mechanical stability, and low cost is of great significance for promoting the development and application of all-vanadium redox flow battery technology. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention introduces a proton-conducting sulfonic acid group into binaphthol, using sulfonated binaphthol and biphenyl as the central core structure. By polymerizing with 5-F indigo in different ratios with biphenyl to form a polyaryl skeleton structure, ion channels of different sizes are constructed to achieve microscopic control of vanadium ion permeability. This results in the preparation of a high-efficiency, high-vanadium-ion-selectivity proton exchange membrane material for application in the field of vanadium-ion flow batteries.

[0006] Based on the above technical concept, one of the objectives of this invention is to provide a biphenyl-biphenyl polymer proton exchange membrane material and its preparation method; A second objective of this invention is to provide the use of the above-mentioned biphenyl-biphenyl polymer proton exchange membrane material.

[0007] The technical solution of this invention is: A binatyl-biphenyl polymer proton exchange membrane material has the following general structural formula:

[0008] Wherein, R1 is selected from hydrogen, fluorine, chlorine, bromine or C1~C5 alkyl; R2 is selected from hydrogen, C1~C5 alkyl, acetyl, propionyl or benzoyl; p represents 1 to 5 CH2 groups.

[0009] In a preferred embodiment of the present invention, R1 is hydrogen and R2 is hydrogen.

[0010] The preparation method of the biphenyl-diphenyl polymer proton exchange membrane material of the present invention includes the following steps: (a) Reaction of binaphthol (BINOL) with 1,3-propanesulfonyl lactone to generate sulfonic acid-modified binaphthol (BINSH); the specific reaction equation is as follows:

[0011] (b) The reaction of BINSH, biphenyl, and 5-fluoroindigo to produce compound BPNSA is carried out by polymerization; the specific reaction equation is as follows:

[0012] Specifically, the key synthetic steps of the binatyl-biphenyl polymer proton exchange membrane material are: The specific synthetic route for step (a) is as follows: 2,2'-Bidinaphthol (2000 mg, 7 mmol) and sodium hydride (1700 mg, 14 mmol) were added to a 100 ml two-necked flask, and the mixture was purged with nitrogen three times under nitrogen protection. Under nitrogen protection, 20 ml of tetrahydrofuran was added and stirred until homogeneous. 1,3-Propanesulfonyl lactone (2560 mg, 21 mmol) was dissolved in 2 ml of tetrahydrofuran and stirred until homogeneous. This solution was then added to the two-necked flask and reacted at room temperature for 24 h. The mixture was poured into ethanol, precipitating a white solid. The solid was repeatedly stirred, washed, filtered, and dried with ethanol to obtain a white powder, BINSH.

[0013] The specific synthetic route for step (b) is as follows: BINSH and biphenyl were polymerized with 5-F indigo at different molar ratios (1:0 / 2:8 / 4:6 / 1:1 / 0:1). Taking BINSH:BP = 1:1 as an example, BINSH (530 mg, 1 mmol), biphenyl (163.5 mg, 1 mmol), and 5-F indigo (363 mg, 2.2 mmol) were placed in a 100 ml single-necked flask, and 2 ml of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 5 ml of trifluoroacetic acid was added to the system, and stirring continued for 15 min until the raw materials were completely dissolved. Maintaining the ice-water bath conditions, 4.5 ml of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually increased to room temperature. Stirring continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the mixture was repeatedly stirred, washed, and dried with ethyl acetate to obtain the brownish-gray polymer BPNSA-a~e.

[0014] The above-mentioned application of the biphenyl-diphenyl polymer proton exchange membrane material in vanadium-ion flow batteries.

[0015] Based on the above applications, the biphenyl-diphenyl polymer proton exchange membrane material of the present invention can be used as a proton exchange membrane material for vanadium-ion flow batteries. The preparation method of the proton exchange membrane in the above applications involves the following steps: Accurately weigh 250 mg of BPNSA and add 5 ml of DMAc as a solvent to obtain a casting solution with a mass fraction of 5 wt%. Stir the casting solution for 24 h, then centrifuge, filter, sonicate, and allow to stand to obtain a homogeneous solution. Pour the obtained casting solution into a PTFE mold and place it in a vacuum oven at 60℃ for 24 h and then at 80℃ for 12 h to obtain a dense ion exchange membrane.

[0016] In this invention, the battery device structure includes a fastening end plate, a current collector, bipolar plates, a flow frame, electrodes, and a separator (proton exchange membrane), forming a sandwich-symmetric structure centered on the separator. Furthermore, the electrolyte is connected to the battery's inlet and outlet ports via a storage tank, conduit, and pump. The effective proton conduction area of ​​the proton exchange membrane in this battery is 4 cm². 2 The battery testing uses the Arbin battery testing system. The vanadium redox flow battery testing involved in this invention refers to single-cell testing, and the voltage range for charge and discharge testing is 0.8-1.65 V.

[0017] Based on the above-described applications, the present invention provides a flow battery comprising a positive electrode electrolyte, a negative electrode electrolyte, and a proton exchange membrane disposed therebetween, wherein the proton exchange membrane is made of the binaphthol-biphenyl polymer proton exchange membrane material described in the present invention.

[0018] The beneficial effects of this invention are as follows: 1. The biphenyl-diphenyl polymer proton exchange membrane material provided by the present invention consists of alternating arrangements of ether-free aromatic compounds and large-volume, torsion-resistant indigo fragments, which improves the glass transition temperature and mechanical properties of the polymer membrane.

[0019] 2. The binatyl-biphenyl polymer proton exchange membrane material provided by this invention utilizes the binatyl group, a relatively rigid group, which on the one hand gives the material excellent thermal stability, and on the other hand strengthens the π-π interactions between molecules, promoting intermolecular charge transport. Introducing a long chain with a sulfonic acid group as a flexible side chain onto the binatyl group effectively improves its proton conductivity.

[0020] 3. The binaphthyl-biphenyl polymer proton exchange membrane material of the present invention uses inexpensive binaphthylphenol and biphenyl as raw materials, and adopts a superacid-catalyzed polymerization reaction. The preparation process is simple, the yield is high, the reaction conditions are mild, and the total cost is low, which is conducive to commercial production and application.

[0021] 4. The application of the biphenyl-diphenyl polymer proton exchange membrane material provided by this invention in vanadium-ion flow batteries, at 50 mA·cm-2 At current density, its battery capacity can reach 1.05Ah, which is close to the battery capacity of commercially available Nafion membranes. Its coulombic efficiency can reach 99%, and its energy efficiency and voltage efficiency are both above 90%, exceeding those of commercially available Nafion membranes, demonstrating excellent battery performance. Attached Figure Description

[0022] Figure 1 The diagram shows the structure of the binatyl-biphenyl polymer proton exchange membrane material prepared in Examples 2-5 used in vanadium-ion flow batteries.

[0023] Figure 2 Cyclic voltammetry curves of the binatyl-biphenyl polymer proton exchange membrane materials prepared in Examples 2-5 for use in vanadium-ion flow batteries.

[0024] Figure 3 The biphenyl-diphenyl polymer proton exchange membrane materials prepared in Examples 2-5 were used to measure the coulombic efficiency, voltage efficiency, and energy efficiency of vanadium-ion flow batteries. Detailed Implementation

[0025] The present invention will be further illustrated below through examples, the purpose of which is to provide a better understanding of the invention. Therefore, the examples given do not limit the scope of protection of the present invention.

[0026] I. Preparation of Polymer Monomers Example 1: Preparation of 1,1'-binaphthyl-2,2'-dimethylbis(3-sulfonate propyl) ether

[0027] 2,2'-Bidinaphthol (2000 mg, 7 mmol) and sodium hydride (1700 mg, 14 mmol) were added to a 100 mL two-necked flask, and the mixture was purged with nitrogen three times under vacuum. Under nitrogen protection, 20 mL of tetrahydrofuran was added and stirred until homogeneous. 1,3-Propanesulfonyl lactone (2560 mg, 21 mmol) was dissolved in 2 mL of tetrahydrofuran and stirred until homogeneous. This solution was then added to the two-necked flask and reacted at room temperature for 24 h. The mixture was poured into ethanol, precipitating a white solid. The solid was repeatedly stirred, washed, filtered, and dried with ethanol to obtain a white powder, BINSH, yielding 1800 mg of the final product (90% yield).

[0028] 1 H NMR (400 MHz, DMSO- d 6) δ 8.02 (d, J = 9.0 Hz, 2H), 7.95 – 7.88 (m,2H), 7.56 (d, J= 9.1 Hz, 2H), 7.30 (ddd, J = 8.1, 6.7, 1.2 Hz, 2H), 7.20 (ddd, J =8.2, 6.7, 1.4 Hz, 2H), 6.90 (dd, J = 8.4, 1.1 Hz, 2H), 4.15 – 4.00 (m, 4H), 2.25 (dd, J = 8.1, 6.9 Hz, 4H). II. Polymer Preparation Example 2: Preparation of polymer BPNSA-a

[0029] 1,1'-binaphthyl-2,2'-dimethylbis(3-sulfopropyl) ether BINSH (1060 mg, 2 mmol) and 5F-indigo (363 mg, 2.2 mmol) were placed in a 100 mL single-necked flask, and 2 mL of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 3 mL of trifluoroacetic acid was added to the system, and stirring was continued for 15 min until the starting materials were completely dissolved. While maintaining the ice-water bath conditions, 2 mL of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually raised to room temperature. Stirring was continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the precipitate was repeatedly stirred, washed, and dried with ethyl acetate to obtain 600 mg of the brownish-gray polymer BPNSA-a, with a yield of 67%.

[0030] Example 3: Preparation of polymer BPNSA-b

[0031] 1,1'-binaphthyl-2,2'-dimethylbis(3-sulfopropyl) ether BINSH (530 mg, 1 mmol), biphenyl (163.5 mg, 1 mmol), and 5F-indigo (363 mg, 2.2 mmol) were placed in a 100 mL single-necked flask, and 2 mL of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 5 mL of trifluoroacetic acid was added to the system, and stirring was continued for 15 min until the starting materials were completely dissolved. While maintaining the ice-water bath conditions, 4.5 mL of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually raised to room temperature. Stirring was continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the precipitate was repeatedly stirred, washed, and dried with ethyl acetate to obtain 550 mg of the brownish-gray polymer BPNSA-b, with a yield of 61%.

[0032] Example 4: Preparation of polymer BPNSA-c

[0033] 1,1'-binaphthyl-2,2'-dimethylbis(3-sulfopropyl) ether BINSH (424 mg, 0.8 mmol), biphenyl (184.9 mg, 1.2 mmol), and 5F-indigo (363 mg, 2.2 mmol) were placed in a 100 mL single-necked flask, and 2 mL of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 2.5 mL of trifluoroacetic acid was added to the system, and stirring was continued for 15 min until the starting materials were completely dissolved. While maintaining the ice-water bath conditions, 5 mL of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually raised to room temperature. Stirring was continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the precipitate was repeatedly stirred, washed, and dried with ethyl acetate to obtain 605 mg of the brownish-gray polymer BPNSA-c, with a yield of 62%.

[0034] Example 5: Preparation of polymer BPNSA-d

[0035] 1,1'-binaphthyl-2,2'-dimethylbis(3-sulfopropyl) ether BINSH (212 mg, 0.4 mmol), biphenyl (246.5 mg, 1.6 mmol), and 5F-indigo (363 mg, 2.2 mmol) were placed in a 100 mL single-necked flask, and 2 mL of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 4 mL of trifluoroacetic acid was added to the system, and stirring was continued for 15 min until the starting materials were completely dissolved. While maintaining ice-water bath conditions, 4 mL of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually raised to room temperature. Stirring was continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the precipitate was repeatedly stirred, washed, and dried with ethyl acetate to obtain 530 mg of the brownish-gray polymer BPNSA-d, with a yield of 65%.

[0036] Example 6: Preparation of polymer BPNSA-e

[0037] Biphenyl (327 mg, 2.2 mmol) and 5F-indigo (363 mg, 2.2 mmol) were placed in a 100 mL single-necked flask, and 2 mL of dichloromethane was added. The mixture was stirred for 10 min. Under ice-water bath conditions, 5 mL of trifluoroacetic acid was added to the system, and stirring was continued for 15 min until the starting materials were completely dissolved. While maintaining the ice-water bath conditions, 4.5 mL of trifluoromethanesulfonic acid was added to the single-necked flask, and the temperature was gradually raised to room temperature. Stirring was continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate, and the precipitate was repeatedly stirred, washed, and dried with ethyl acetate to obtain 620 mg of the pale yellow polymer BPNSA-e, with a yield of 90%. Example 7

[0038] BPNSA-b, a proton exchange membrane material made of biphenyl-naphthyl-biphenyl polymer, was used as the proton exchange membrane in a vanadium-ion flow battery. The structure of the resulting flow battery is shown in the attached figure. Figure 1 The diagram shows a fastening end plate, current collector, bipolar plate, flow frame, electrodes, and a diaphragm (proton exchange membrane). The specific method is as follows: 250 mg of BPNSA was accurately weighed and added to 5 ml of DMAc as a solvent to obtain a casting solution with a mass fraction of 5 wt%. The casting solution was stirred for 24 h, then centrifuged, filtered, sonicated, and allowed to stand to obtain a homogeneous solution. The resulting casting solution was poured into a PTFE mold and placed in a vacuum oven at 60°C for 24 h and then at 80°C for 12 h to obtain a dense ion exchange membrane, as described in the [Summary of the Invention] section. The membrane was placed in a fixture to form a flow battery, and its battery performance was tested as a single cell. At 50 mA·cm⁻¹... -2 80mA·cm -2 100mA·cm -2 Charge-discharge tests were conducted at current densities ranging from 0.8 to 1.65 V, with a voltage range of 50 mA·cm⁻¹. -2 At the given current density, its battery capacity can reach 1.05 Ah, and the charge / discharge curves are shown in the attached figure. Figure 2 As shown in the attached figure. Its coulombic efficiency can reach 99%, and its energy efficiency and voltage efficiency are both above 90%. Figure 3 As shown, the battery's CE / EE / VE values ​​under 50mA cm⁻² charge-discharge cycles far exceed those of commercially available Nafion membranes, demonstrating superior battery performance.

[0039] The above embodiments provide examples of biphenyl, while the biphenyl compounds of the present invention can be selected from biphenyl, parabenzyl, or tetrabenzyl, wherein the effects of parabenzyl or tetrabenzyl are the same as those of biphenyl. It should be further noted that the above embodiments are merely for understanding the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Any obvious adjustments and modifications made to the above embodiments should fall within the scope of protection of the present invention.

Claims

1. A binaphthol-biphenyl polymer proton exchange membrane material, characterized in that, It has the chemical structure shown in formula (I): Wherein, R1 is selected from hydrogen, fluorine, chlorine, bromine or C1~C5 alkyl; R2 is selected from hydrogen, C1~C5 alkyl, acetyl, propionyl or benzoyl; p represents 1 to 5 CH2 groups.

2. The binaphthol-biphenyl polymer proton exchange membrane material as described in claim 1, characterized in that, R1 is hydrogen, and R2 is hydrogen.

3. The method for preparing the binaphthol-biphenyl polymer proton exchange membrane material according to claim 1 or 2, characterized in that, Includes the following steps: Sulfonic acid-modified binaphthalene, biphenyl compounds, and 5-F indigo were placed in a reaction vessel, and dichloromethane was added. The mixture was stirred for 10 minutes. An acid solvent was added to the system under ice-water bath conditions, and stirring continued for 15 minutes until the reactants were completely dissolved. While maintaining the ice-water bath conditions, the acid solvent was added to the reaction system, and then the temperature was gradually raised to room temperature. Stirring continued until the reaction solution became viscous. The reaction solution was poured into ethyl acetate to precipitate the polymer. After repeated stirring, washing, and drying with ethyl acetate, a brownish-gray polymer, BPNSA, was obtained. 。 4. The preparation method according to claim 3, characterized in that, The molar ratio of BINSH to biphenyl compounds is 1:0, 1:1, 4:6, 2:8, or 0:

1.

5. The preparation method according to claim 3, characterized in that, The acids used are trifluoromethanesulfonic acid, trifluoroacetic acid, sulfuric acid, phosphoric acid, or p-toluenesulfonic acid.

6. The preparation method according to claim 3, characterized in that, The biphenyl compound is bidiphenyl.

7. The application of the binaphthol-biphenyl polymer proton exchange membrane material according to claim 1 or 2 in flow batteries.

8. A polymerization monomer for synthesizing the membrane material as described in claim 1 or 2, characterized in that, The monomer is a binaphthalene monomer modified with a sulfonic acid group.

9. The polymerization monomer as described in claim 8, characterized in that, The monomer is sulfonic acid-modified binaphthalene (BINSH), obtained by the following method: The reaction of binaphthol (BINOL) with 1,3-propanesulfonyl lactone produces sulfonic acid-modified binaphthol (BINSH). The specific reaction equation is as follows: 。 10. A flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, and a proton exchange membrane disposed therebetween, characterized in that, The proton exchange membrane is made of the binaphthol-biphenyl polymer proton exchange membrane material as described in claim 1 or 2.

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