Viologen electrolyte with multi-electron transfer capability, preparation method and application of viologen electrolyte in aqueous organic flow battery

Abstract

The invention belongs to the field of new energy materials, and particularly relates to a viologen electrolyte with multi-electron transfer capability, a preparation method and application of the viologen electrolyte in an aqueous organic flow battery. The preparation method comprises the following steps: reacting triethanolamine with phosphorus tribromide to generate a tris (2-bromoethyl) amine intermediate, condensing the tris (2-bromoethyl) amine intermediate with 4, 4 '-dipyridyl to generate a trinuclear viologen precursor, and finally performing quaternization and anion exchange to obtain a target product. The solubility of the prepared viologen electrolyte in an aqueous solution reaches up to 1.82 M, the theoretical charge capacity is 103 Ah L <-1 >, and the viologen electrolyte can perform highly reversible multi-electron redox reaction and shows excellent electrochemical performance. When the material is applied to the aqueous organic flow battery as a negative electrode active material, the battery shows the outstanding advantages of high coulombic efficiency, high energy density, long cycle life and the like.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials, specifically relating to a viologen electrolyte with multi-electron transfer capability, its preparation method, and its application in aqueous organic flow batteries. Background Technology

[0002] With the rapid development and large-scale grid connection of renewable energy, the development of efficient and low-cost large-scale energy storage technologies has become an urgent need in the energy sector. Aqueous organic flow batteries, with their outstanding advantages such as high safety, independent power and energy control, and environmental friendliness, are considered one of the most promising energy storage technologies. While commercially available vanadium redox flow batteries are technologically mature, their development is constrained by resource, cost, and environmental factors. The scarcity and price volatility of vanadium resources, as well as the potential environmental risks of electrolytes, have prompted academia and industry to actively seek new organic electrolyte materials with superior performance and sustainable supply.

[0003] Among numerous organic electroactive materials, viologen compounds are considered ideal anode candidates due to their reversible redox properties, tunable structure, and high water solubility. However, traditional viologen molecules, such as methyl viologen, still have significant limitations in practical applications: their relatively negative operating potential easily triggers hydrogen evolution side reactions, limiting the potential window; limited electron transfer restricts theoretical capacity; and their solubility and long-term cycling stability still have room for improvement.

[0004] These inherent defects severely limit the performance of traditional viologen materials in practical battery systems. Therefore, developing novel viologen electrolytes with multi-electron transfer capabilities, high solubility, and excellent electrochemical stability has become a key breakthrough in advancing aqueous organic flow battery technology. The design of next-generation viologen electrolytes requires achieving synergistic operation of multiple redox centers at the molecular level, while simultaneously balancing their solubility, redox potential, and structural stability. This is not only a current research focus but also the core of realizing the commercial application of high-performance aqueous organic flow batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a viologen electrolyte material with multi-electron transfer capability for aqueous organic flow batteries. This viologen electrolyte is a compound having the following general formula. , R is derived from one of methyl, methanesulfonyloxy, carboxymethyl, hydroxyethyl, cyanomethyl, trifluoroethyl, nitromethyl, methoxymethyl, aminomethyl, or tert-butyl.

[0006] The three-armed viologen compound provided by this invention possesses a molecular structure design that combines local π-π conjugation stability with overall charge isolation effectiveness. Specifically, each viologen functional unit contains a strong π-π conjugation system composed of a bipyridine structure. This conjugation system ensures that the charge and free radicals generated by a single redox center during electron transfer can be effectively delocalized, thereby endowing it with excellent electrochemical reversibility and high reaction kinetics. More importantly, these independent conjugated units are connected to the central bridging atom via saturated alkyl chains. This 'conjugation interruption' design cleverly prevents excessive delocalization of electrons throughout the macromolecule, thus ensuring that the three viologen units can independently perform their respective electron transfers, collectively contributing to the molecule's multi-electron transfer capability, without leading to the merging or failure of redox potentials.

[0007] The viologen electrolyte of the present invention, which has the ability to transfer multiple electrons, can be one of the following compounds: , , , , , , , , or .

[0008] The preparation method of the viologen electrolyte with multi-electron transfer capability of the present invention includes the following steps: Step 1: Weigh phosphorus tribromide and add it to 1,4-dioxane. While stirring, slowly add a solution formed by dissolving triethanolamine in 1,4-dioxane. Then, heat the reaction mixture in a water bath at 70-80°C and stir for 3-5 hours until the gas is completely released. After the reaction is complete, cool the mixture to room temperature and filter it. Wash the resulting white solid residue with cold 1,4-dioxane. Then, mix this white solid with dichloromethane and sodium hydroxide aqueous solution and extract by vigorous stirring at room temperature for 12 hours. After that, separate the organic phase, dry it with anhydrous sodium sulfate, filter it and concentrate it under vacuum to finally obtain the colorless oily product tris(2-bromoethyl)amine.

[0009] The molar ratio of phosphorus tribromide to triethanolamine is 3:1-4:1.

[0010] Step 2: Under argon protection, 4,4'-bipyridine and the colorless oily product tris(2-bromoethyl)amine obtained above were mixed in acetonitrile, and the reaction mixture was heated to 70-80°C and refluxed for 6-10 hours. After the reaction was completed, the mixture was cooled to room temperature, and the resulting yellow precipitate was collected by filtration. The solid was then thoroughly washed with N,N-dimethylformamide, acetonitrile, and ethyl acetate in sequence to obtain the yellow solid product.

[0011] The molar ratio of 4,4'-bipyridine to tris(2-bromoethyl)amine is 4:1-5:1.

[0012] Step 3: The yellow solid obtained in step (2) is mixed with the alkylating agent in dimethyl sulfoxide to carry out a quaternization reaction; after the reaction is completed, acetonitrile is added to the mixture to induce precipitation, the precipitate is collected by filtration, and the solid is washed with acetonitrile; finally, the obtained solid product is treated by using an anion exchange column to exchange the anion from bromide ions to chloride ions, thereby obtaining viologen electrolyte with multiple electron transfer.

[0013] The alkylating agent is one of iodomethane, iodomethylmethanesulfonate, iodoacetic acid, 2-iodoethanol, iodoacetonitrile, 2-iodo-1,1,1-trifluoroethane, iodonitromethane, iodomethylmethyl ether, N-Boc-aminomethyliodide, or tert-butyliodide.

[0014] The molar ratio of the trinuclear viologen precursor salt to the alkylating agent is 1:4-1:5; the quaternization reaction is carried out at room temperature or low temperature for 20-48 hours; anion exchange is achieved by passing the quaternization product solution through a chloride-type anion exchange resin column.

[0015] The viologen compound obtained by the above method is used to prepare the negative electrode electrolyte for aqueous organic flow batteries.

[0016] The negative electrode electrolyte of the aqueous organic flow battery includes viologen electrolyte and supporting electrolyte; the supporting electrolyte is at least one of sodium chloride and tetraethylammonium chloride; the concentration of viologen electrolyte in the negative electrode electrolyte is from 0.01 M to its upper limit of solubility.

[0017] The aforementioned aqueous organic flow battery uses anion exchange membrane as the separator and carbon felt as the electrode material for both the positive and negative electrodes.

[0018] The beneficial effects of this invention are: This invention successfully achieved multi-electron transfer characteristics within a single molecule by constructing a polynuclear viologen molecular structure, significantly improving the theoretical specific capacity of the material. Simultaneously, the electrolyte exhibits excellent solubility in water, laying the foundation for high-energy-density battery design. Its moderate redox potential effectively suppresses hydrogen evolution side reactions, demonstrating good electrochemical reversibility and rapid reaction kinetics. Furthermore, the material exhibits excellent cycle stability, high capacity retention during long-term charge-discharge testing, and its synthesis route is simple and the raw materials are readily available, providing an ideal negative electrode material for the practical application of high-performance aqueous organic flow batteries. Attached Figure Description

[0019] Figure 1 The reaction route diagram is for the compound in Example 1.

[0020] Figure 2 The image shows the 1H NMR spectrum of the compound in Example 1.

[0021] Figure 3 This is a cyclic voltammogram of the compound from Example 1 in different supporting electrolytes.

[0022] Figure 4 This is a cyclic voltammogram of the compound from Example 1, with scan rates of 5, 10, 25, 50, 100, and 200 mV s. -1 .

[0023] Figure 5 This is a rate curve for the aqueous flow battery corresponding to the compound in Example 1.

[0024] Figure 6 This is a long-cycle diagram of the aqueous flow battery corresponding to the compound in Example 1.

[0025] Figure 7 This is a rate capability diagram for the aqueous flow battery corresponding to the compound in Example 2.

[0026] Figure 8 This is a long-cycle diagram of the aqueous flow battery corresponding to the compound in Example 2.

[0027] Figure 9 This is a rate capability diagram for the aqueous flow battery corresponding to the control example compound.

[0028] Figure 10 This is a long-cycle diagram of the aqueous flow battery corresponding to the example compound. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features described in the various embodiments of the invention below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1

[0031] The preparation route for 1',1''',1''''-(azatriyltri(ethane-2,1-diyl))tri(1-methyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride is shown in the attached instructions. Figure 1 As shown.

[0032] Step 1: Under stirring, 34.1 g (126 mmol) of phosphorus tribromide was weighed and dissolved in 80 mL of 1,4-dioxane to prepare a solution. Then, 6.0 g (40 mmol) of triethanolamine was dissolved in 20 mL of 1,4-dioxane and slowly added dropwise to the phosphorus tribromide solution at a rate of 1 mL / min, while stirring continuously until no more gas was produced. The reaction mixture was reacted at 70 °C for 4 hours. After the reaction was complete, the mixture was cooled to room temperature and filtered. The resulting white residue was collected and washed three times with 25 mL of ice-cold 1,4-dioxane. The white solid was then extracted with a mixture of 100 mL of dichloromethane and 100 mL of sodium hydroxide aqueous solution (1 M). The two-phase mixture was stirred vigorously at room temperature for 12 hours. After separation, the organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to give a colorless oily product, tris(2-bromoethyl)amine, in 90% yield.

[0033] Step 2: Weigh 21.1 g of 4,4'-bipyridine (135 mmol) and 10.1 g of tris(2-bromoethyl)amine (30 mmol) and mix them in 100 mL of acetonitrile. Reflux at 120 °C for 8 hours under argon protection. After cooling to room temperature, filter and collect the precipitate. Wash three times successively with 50 mL of DMF, 50 mL of acetonitrile, and 50 mL of ethyl acetate to obtain a yellow solid 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide, with a yield of 85%.

[0034] Step 3: 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1,1'-diyl))tribromide (10 mmol) was mixed with 6.4 g of iodomethane (45 mmol) in 25 mL of dimethyl sulfoxide and reacted at room temperature for 24 hours. After the reaction was complete, 75 mL of acetonitrile was added to the reaction mixture. The mixture was then filtered and washed three times with 50 mL of acetonitrile. Finally, the product was subjected to column chromatography anion exchange using Amberlite IRA-900 resin (chloride ion form) to give a grayish-white solid (1',1''',1'''''-(azatriyltris(ethane-2,1-diyl))tris(1-methyl-[4,4'-bipyridine]-1,1'-diyl))hexachloride in 80% yield.

[0035] Figure 2 This is the 1H NMR spectrum of (1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-methyl-[4,4'-bipyridine]-1,1'-dionium))hexachloride prepared in Example 1. It can be seen that corresponding 1H NMR peaks exist at 3.41, 4.37, 4.71, 8.41, 8.47, 8.92, and 9.09.

[0036] The active material provided in this embodiment can be used as the negative electrode electrolyte in an aqueous flow battery. Specific examples are given below: A three-electrode system was used, with a glassy carbon electrode as the working electrode, a platinum sheet electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. Cyclic voltammetry tests were performed on this substance in electrolytes containing different supporting electrolytes (1M Et4NCl, 1M NaCl, and 1M NH4Cl) in deionized water as the solvent. The scan rate was 25 mV / s. -1 .like Figure 3 As shown, in the 1M Et4NCl system, the peak shape is more symmetrical, indicating better reversibility in this electrolyte. In contrast, in the NaCl and NH4Cl system, the peak potential difference increases, indicating that the electrode process is more significantly controlled by diffusion. These results highlight the important influence of electrolyte cations on the electrochemical behavior of this material, suggesting that Et4NCl is preferred as a supporting electrolyte to achieve better electrochemical performance.

[0037] A three-electrode system was used, with a glassy carbon electrode as the working electrode, a platinum sheet electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, to measure the following: Figure 4The figure shows the cyclic voltammetry curves of 2 mmol of this material at different scan rates in 1 M Et4NCl. The redox peaks are well maintained, and a pair of distinct redox peaks can be seen. The equilibrium potential is -0.28 V. With the increase of scan rate, the current density of the oxidation and reduction peaks increases significantly. This is because the increase of scan rate accelerates the reaction rate at the electrode surface, while the equilibrium potential does not change significantly, indicating that the chemical reaction kinetics are fast and the charge transfer process at the electrode surface is highly efficient.

[0038] A flow battery was assembled using this active material. The negative electrode electrolyte was a 15 mL aqueous solution containing 0.05 M of this active material and 1 M Et4NCl. The positive electrode electrolyte was a 15 mL aqueous solution containing 0.3 M TEMPTMA and 1 M Et4NCl. Anion exchange membranes were used as separators, and carbon felt was used as the positive and negative electrodes. The electrolyte was circulated between the battery and the storage tank using a peristaltic pump. Rate testing and long-cycle testing were performed, such as... Figure 5 The battery shown ranges from 20 to 110 mA cm⁻¹ -2 It can operate stably under different current densities, and its coulombic efficiency remains above 99.5%. Figure 6 As shown at 50 mA cm -2 Long-cycle testing was conducted at a current density of approximately 95%. After 200 charge-discharge cycles, the battery maintained a capacity of approximately 95% and showed no decay in coulombic efficiency, demonstrating that the Et4NCl electrolyte system can effectively ensure the efficient and stable operation of this active material.

[0039] Example 2

[0040] Step 1: Change the molar ratio of phosphorus tribromide and triethanolamine to 4:1, and keep the other conditions the same as in Example 1 to obtain the colorless oily product tris(2-bromoethyl)amine with a yield of 88%.

[0041] Step 2: The molar ratio of 4,4'-bipyridine to tris(2-bromoethyl)amine was changed to 4:1, and the other conditions were the same as in Example 1, to obtain 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-onium))tribromide in a yield of 42%.

[0042] Step 3: Change the molar ratio of 1,1'',1''''-(azatriyltri(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-onium))tribromide and iodomethane to 1:4, and keep the other conditions the same as in Example 1 to obtain the final grayish-white solid product 1',1''',1''''-(azatriyltri(ethane-2,1-diyl))tri(1-methyl-[4,4'-bipyridine]-1,1'-dionium))hexachloride with a yield of 70%.

[0043] A flow battery was assembled using this active material. The negative electrode electrolyte was a 15 mL aqueous solution containing 0.05 M of the active material and 1 M NaCl. The positive electrode electrolyte was a 15 mL aqueous solution containing 0.3 M TEMPTMA and 1 M NaCl. Anion exchange membranes were used as the separator, and carbon felt was used as the positive and negative electrodes. The electrolyte was circulated between the battery and the storage tank using a peristaltic pump. This material also showed good application potential in a lower-cost sodium chloride-supported electrolyte system. Figure 7 As shown, in the range of 20 to 110 mA cm -2 Rate testing was conducted within the specified current density range, and the battery exhibited stable charge and discharge capabilities. For example... Figure 8 As shown at 50 mA cm -2 Long-term cycling tests were conducted, and after 200 cycles, the battery capacity retention exceeded 90%, and the coulombic efficiency stabilized at around 99.5%. These results demonstrate that even in a simple NaCl electrolyte, this material exhibits excellent electrochemical reversibility and cycle life, providing important evidence for its low-cost, large-scale energy storage applications.

[0044] Example 3

[0045] In this embodiment, iodomethyl methanesulfonate is used as the alkylating agent.

[0046] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in step 2 was reacted with 11.7 g of iodomethylmethanesulfonate (45 mmol) under the same conditions as in Example 1, yielding the final grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-methanesulfonyloxymethyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride, in 88% yield.

[0047] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 98% after 200 cycles, and the coulombic efficiency remained stable at around 99.8%.

[0048] Example 4

[0049] In this embodiment, iodoacetic acid is used as the alkylating agent.

[0050] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 was dissolved in 9.3 g of iodoacetic acid (50 mmol) in 25 mL of dimethyl sulfoxide and reacted at room temperature for 24 hours. To ensure the reaction proceeds smoothly, the system must be kept dry to avoid hydrolysis of iodoacetic acid. After the reaction was complete, 75 mL of acetonitrile was added to precipitate the product. The product was filtered, and the solid was washed with acetonitrile. After treatment with a chloride-type anion exchange resin, a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-carboxymethyl-[4,4'-bipyridine]-1,1'-dionium) hexachloride was obtained, with a yield of 78%.

[0051] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 96% after 500 cycles, and the coulombic efficiency remained stable at around 99.4%.

[0052] Example 5

[0053] In this embodiment, 2-iodoethanol is used as the alkylating agent.

[0054] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 was dissolved in 7.0 g of 2-iodoethanol (45 mmol) in 25 mL of dimethyl sulfoxide and reacted at room temperature for 24 hours. The reaction was carried out under neutral conditions to protect the hydroxyl groups and maintain the stability of the reagents. Subsequent precipitation, filtration, washing, and anion exchange procedures were the same as in Example 1, yielding a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-hydroxyethyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride, in 70% yield.

[0055] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 97% after 500 cycles, and the coulombic efficiency remained stable at around 99.5%.

[0056] Example 6

[0057] In this embodiment, iodoacetonitrile is used as the alkylating agent.

[0058] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-diamium))tribromide (10 mmol) obtained in Step 2 was dissolved in 25 mL of dimethyl sulfoxide with 6.7 g of iodoacetonitrile (45 mmol) and reacted at room temperature for 24 hours. Subsequent processing was the same as in Example 1, yielding a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-cyanomethyl-[4,4'-bipyridine]-1,1'-diamium)hexachloride, with a yield of 75%.

[0059] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 98% after 1000 cycles, and the coulombic efficiency remained stable at around 99.8%.

[0060] Example 7

[0061] In this embodiment, 1-iodo-2,2,2-trifluoroethane was used as the alkylating agent.

[0062] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 was dissolved in 25 mL of dimethyl sulfoxide with 10.0 g of 1-iodide-2,2,2-trifluoroethane (45 mmol) and reacted at room temperature for 36 hours. Subsequent processing was the same as in Example 1, yielding a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tri(1-trifluoroethyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride, with a yield of 75%.

[0063] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 92% after 1000 cycles, and the coulombic efficiency remained stable at around 98.3%.

[0064] Example 8

[0065] In this embodiment, nitrobomethyl iodide is used as the alkylating agent.

[0066] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-diamium))tribromide (10 mmol) obtained in Step 2 was dissolved in 25 mL of dimethyl sulfoxide with 8.3 g of nitromethane (45 mmol) and reacted at room temperature in the dark for 24 hours. Subsequent processing was the same as in Example 1, yielding a pale yellow solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tri(1-nitromethyl-[4,4'-bipyridine]-1,1'-diamium)hexachloride, with a yield of 80%.

[0067] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 98% after 800 cycles, and the coulombic efficiency remained stable at around 99.8%.

[0068] Example 9

[0069] In this embodiment, methoxyiodomethane is used as the alkylating agent.

[0070] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 was dissolved in 7.7 g of methoxyiodomethane (45 mmol) in 25 mL of dimethyl sulfoxide and reacted at room temperature for 24 hours. The reaction system was kept strictly dry, and subsequent treatment was the same as in Example 1, yielding a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-methoxymethyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride, with a yield of 83%.

[0071] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 97% after 800 cycles, and the coulombic efficiency remained stable at around 99.5%.

[0072] Example 10

[0073] In this embodiment, N-Boc-aminomethyliodide is used as the alkylating agent.

[0074] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 and 9.2 g of N-Boc-aminomethyl iodide (45 mmol) were dissolved in 25 mL of dimethyl sulfoxide and reacted at room temperature for 24 hours. After the reaction and anion exchange were completed, the resulting solid was dissolved in a trifluoroacetic acid / dichloromethane (1:1, v / v) mixed solution and stirred at room temperature for 2 hours to remove the Boc protecting group. The solvent was removed by rotary evaporation, and the resulting solid was washed with acetonitrile to give a grayish-white solid product 1',1''',1''''-(azatriyltri(ethane-2,1-diyl))tri(1-aminomethyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride in 88% yield.

[0075] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 95% after 1000 cycles, and the coulombic efficiency remained stable at around 99.1%.

[0076] Example 11

[0077] In this embodiment, tert-butyl iodine is used as the alkylating agent.

[0078] Steps 1 and 2 are the same as in Example 1. 8.1 g of 1,1'',1''''-(azatriyltris(ethane-2,1-diyl))tris(([4,4'-bipyridine]-1-onium))tribromide (10 mmol) obtained in Step 2 was dissolved in 25 mL of dimethyl sulfoxide with 9.9 g of tert-butyl iodide (45 mmol) and reacted at room temperature for 48 hours. Subsequent processing was the same as in Example 1, yielding a grayish-white solid product 1',1''',1''''-(azatriyltris(ethane-2,1-diyl))tris(1-tert-butyl-[4,4'-bipyridine]-1,1'-dionium)hexachloride, with a yield of 85%.

[0079] A flow battery was assembled using this active material, with the assembly process and conditions the same as in Example 1. The resulting battery was tested at 50 mA cm⁻¹. -2 After undergoing long-cycle testing, the battery capacity retention rate exceeded 92% after 1000 cycles, and the coulombic efficiency remained stable at around 98.6%.

[0080] Comparison Example

[0081] The two-arm viologen compound (1',1''-(propane-1,3-diyl)bis(1-methyl-[4,4'-bipyridine]-1,1'-dionyl)tetrachloride) with the previously reported structural formula (G. Tang, et al. Angewandte Chemie International Edition, 2025, 64, 22: e202501458) is shown below.

[0082] As a control, the properties of 1',1''',1''''-(azatriyltri(ethane-2,1-diyl))tri(1-methyl-[4,4'-bipyridine]-1,1'-dionium))hexachloride were studied.

[0083] A flow battery was assembled using this active material as a control. The concentration of the control sample was appropriately increased to match the positive electrode capacity and ensure the battery operated within a similar voltage window. The negative electrode electrolyte was 15 mL of an aqueous solution containing 0.15 M of the active material and 1 M NaCl. The positive electrode electrolyte was 15 mL of an aqueous solution containing 0.6 M TEMPTMA and 1 M NaCl. Anion exchange membranes were used as the separator, and carbon felt was used as the positive and negative electrodes. The electrolyte was circulated between the battery and the reservoir using a peristaltic pump. In the same low-cost sodium chloride-supported electrolyte system, the control battery performed as follows: from 20 to 110 mA cm⁻¹. -2 Rate testing within the current density range, such as Figure 9 At 50 mA cm -2 Perform long-loop tests, such as Figure 10 Compared with Embodiments 1 and 4 of the present invention, the control battery has a lower capacity and faster capacity decay, demonstrating that the tri-core viridinium structure has advantages over the dual-core structure in terms of capacity and improved cycle life.

[0084] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A viologen electrolyte with multi-electron transfer capability, characterized in that: The viologen electrolyte is a compound having the following general formula: ， R is derived from one of methyl, methanesulfonyloxy, carboxymethyl, hydroxyethyl, cyanomethyl, trifluoroethyl, nitromethyl, methoxymethyl, aminomethyl, or tert-butyl.

2. The viologen electrolyte with multi-electron transfer capability according to claim 1, characterized in that, The viologen electrolyte is one of the following compounds: 、 、 、 、 、 、 、 、 、 。 3. A method for preparing viologen electrolyte with multi-electron transfer capability according to claim 1, characterized in that, The preparation method steps are as follows: Step 1: Triethanolamine is reacted with phosphorus tribromide in an organic solvent to generate the intermediate tris(2-bromoethyl)amine; Step 2: The tri(2-bromoethyl)amine obtained in Step 1 reacts with 4,4'-bipyridine in an organic solvent and under an inert atmosphere to generate a trinuclear viologen precursor salt, namely 1,1'',1''''-(azatriyltri(ethane-2,1-diyl))tri(([4,4'-bipyridine]-1-onium))tribromide; Step 3: The trinuclear viologen precursor salt obtained in Step 2 is subjected to a quaternization reaction with an alkylating agent in an organic solvent. Subsequently, the anion is replaced with chloride ions through anion exchange to obtain the final product, viologen electrolyte with multi-electron transfer capability.

4. The method for preparing viologen electrolyte with multi-electron transfer capability according to claim 3, characterized in that, In step 1, the molar ratio of phosphorus tribromide to triethanolamine is 3:1-4:1; the organic solvent is 1,4-dioxane; the reaction temperature is 70-80℃; and the reaction time is 3-5 hours.

5. The method for preparing viologen electrolyte with multi-electron transfer capability according to claim 3, characterized in that, In step 2, the molar ratio of 4,4'-bipyridine to tris(2-bromoethyl)amine is 4:1-5:1; the organic solvent is acetonitrile; and the reaction is carried out under reflux at 120°C for 6-10 hours.

6. The method for preparing viologen electrolyte with multi-electron transfer capability according to claim 3, characterized in that, In step 3, the alkylating agent is one of iodomethane, iodomethylmethanesulfonate, iodoacetic acid, 2-iodoethanol, iodoacetonitrile, 2-iodo-1,1,1-trifluoroethane, iodonitromethane, iodomethylmethyl ether, N-Boc-aminomethyliodide, and tert-butyliodide.

7. The method for preparing viologen electrolyte with multi-electron transfer capability according to claim 3, characterized in that, In step 3, the molar ratio of the trinuclear viologen precursor salt to the alkylating agent is 1:4-1:5; the quaternization reaction is carried out at room temperature or low temperature for 20-48 hours; and the anion exchange is achieved by passing the quaternization product solution through a chloride-type anion exchange resin column.

8. An application of the viologen electrolyte with multi-electron transfer capability according to claim 1, characterized in that, The viologen electrolyte is used to prepare the negative electrode electrolyte for aqueous organic flow batteries.

9. The application of the viologen electrolyte with multi-electron transfer capability according to claim 8, characterized in that, The negative electrode electrolyte of the aqueous organic flow battery comprises the viologen electrolyte and the supporting electrolyte as described in claim 1; the supporting electrolyte is at least one of sodium chloride and tetraethylammonium chloride; in the negative electrode electrolyte, the concentration of viologen electrolyte is from 0.01 M to its upper limit of solubility.

10. The application of the viologen electrolyte with multi-electron transfer capability according to claim 8, characterized in that, The aqueous organic flow battery uses an anion exchange membrane as the separator and carbon felt as the electrode material for both the positive and negative electrodes.

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