Organic symmetric flow battery based on nitrogen-containing heterocyclic ring-containing bipolar electrode active materials

Abstract

The application discloses an organic symmetric flow battery based on nitrogen-containing hetero-fused ring bipolar electrode active material, and in particular relates to an electrode active material of a non-aqueous symmetric flow battery taking nitrogen-containing hetero-fused ring organic small molecule N,N'-dimethyl-5,7,12,14-tetraazapentacene (DMTAPs) as bipolar electrode active material. The material has good electrochemical cycle stability, and can be used as positive and negative electrode active materials of the flow battery in combination with a non-aqueous electrolyte, thereby reducing the probability of occurrence of side reactions in the battery, and effectively relieving the cross-pollution effect in the battery. In summary, when the DMTAPs material is used as bipolar electrode active material of the flow battery, the non-aqueous symmetric flow battery constructed has the advantages of prolonged battery cycle life and the like, and is helpful to realize low-cost, high-performance large-scale electrochemical energy storage.

Description

Technical Field

[0001] This invention relates to the field of organic electrode materials, and in particular to a preparation scheme for a bipolar electrode active material based on a nitrogen-containing heterocyclic ring and its application method in flow batteries. Background Technology

[0002] Redox flow batteries possess advantages such as rapid current response, adjustable scale, independent output power and battery energy, and long cycle life, making them one of the ideal technologies for large-scale energy storage. Currently, the most commonly used electrolyte solvent in flow batteries deployed on a large scale is water. Active materials include inorganic materials such as vanadium, zinc-bromine, iron-chromium, and zinc, as well as various types of organic electrode active materials. Functional organic electrode materials are generally composed of abundant elements such as C, H, O, N, and S, and can often be synthesized through low-energy, pollution-free organic chemical reactions, offering advantages such as low toxicity, abundant resources, and low cost. In recent years, various types of organic electrode materials have been reported, such as organic nitrogen-containing fused heterocyclic materials, quinone electrode materials, and organic free radical materials. These materials can be used as active materials in aqueous flow batteries by modifying water-soluble functional groups (sulfonic acid groups, hydroxyl groups, carboxylic acid groups, amino groups, etc.) or preparing corresponding salts (usually sodium salts). However, considering the solubility, redox potential, and electrochemical stability of active materials, organic redox active molecules have higher compatibility with non-aqueous electrolyte systems. Compared to the narrow electrochemical window of aqueous solutions, the wide variety of non-aqueous electrolytes offers a wider electrochemical window, providing flexibility for the design of functionalized organic redox active materials in battery systems. Therefore, non-aqueous flow batteries based on organic redox active materials exhibit unique advantages in energy storage systems. In recent years, numerous studies on non-aqueous flow batteries have been reported. In 2015, Wei et al. reported an all-organic flow battery with 2,5-di-tert-butyl-1-methoxy-4-[2'-methoxyethoxy]benzene (DBMMB) as the positive electrode and 9-fluorenone (FL) as the negative electrode. Based on the potential difference between the positive and negative electrode materials, the battery could achieve an operating voltage of 2.37 V. In 2021, Romadina et al. synthesized a novel phenazine derivative containing polyethylene glycol ether substituents. Using this material as the negative electrode active material and a triphenylamine derivative as the positive electrode material, they assembled a flow battery with a voltage of 2.3 V. After 50 charge-discharge cycles, the capacity retention was approximately 65%, demonstrating good cycle stability. The above research focuses on the screening and optimization of electrode active materials, which has promoted the research progress of non-aqueous organic flow batteries. However, non-aqueous organic flow batteries still face challenges such as low output voltage, poor cycle stability and electrolyte cross-contamination.

[0003] During operation, the different chemical potentials of the electrode materials on both sides of a flow battery cause active molecules to easily cross the separator and shuttle between the electrodes, leading to electrolyte cross-contamination and unpredictable side reactions. This phenomenon inevitably reduces the utilization rate of active materials and the coulombic efficiency of the flow battery, ultimately causing battery failure. One effective strategy to solve this scientific problem is to use bipolar electrode active materials to construct symmetrical flow batteries, replacing the traditional asymmetric battery structure. Currently, the construction and modification strategies of bipolar electrode materials mainly include designing and preparing novel free radical active materials, physically mixing different types of electrode materials to form eutectic crystals, or connecting different active molecular fragments through covalent bonds. However, the currently prepared bipolar electrode materials have relatively large molecular weights and limited variety, and their performance still cannot meet the performance requirements of practical applications of flow batteries (specifically, the constructed battery voltage and energy density are still relatively low). In particular, the positive and negative active portions of existing bipolar electrode materials are still composed of two distinct active centers or functional groups. If cross-contamination occurs during charging and discharging, side reactions may occur in the electrode active molecules, leading to battery capacity degradation and decreased cycle performance. Furthermore, it should be noted that, unlike the application of organic electrode materials in solid-state electrode-based battery systems (such as organic lithium-ion batteries), non-aqueous flow batteries require organic electrode active materials to have good solubility in the non-aqueous electrolyte used. Solid-state electrode-based battery systems, on the other hand, require organic electrode materials to be insoluble or extremely difficult to dissolve in the non-aqueous electrolyte. Therefore, the organic electrode materials designed for non-aqueous flow batteries should have good solubility in the non-aqueous electrolyte. Summary of the Invention

[0004] To overcome the above technical difficulties, the purpose of this invention is to provide a bipolar electrode active material based on a nitrogen-containing heterocyclic ring, which has high solubility in non-aqueous electrolytes and allows for interconversion between the positive and negative electrode active centers, and is used in a non-aqueous symmetric flow battery. The organic symmetric flow battery consists of a positive electrode, a negative electrode, and a separator. Both the positive and negative electrode electrolytes are composed of an organic mixed solution based on N,N'-dimethyl-5,7,12,14-tetraazapentabenzene small molecules and a supporting electrolyte salt. The method of this invention effectively suppresses cross-contamination effects within the flow battery, reduces the probability of side reactions of active molecules, effectively improves battery stability, and extends battery life.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] Both the positive and negative electrolytes of the organic symmetric flow battery contain nitrogen-containing heterocyclic organic small molecule active materials.

[0007] The structural formula of the nitrogen-containing heterofused ring organic small molecule is as follows:

[0008]

[0009] X1~X 10 Each is independently selected from H, alkyl, or alkoxy; R a -R b Each is independently selected from alkyl or alkoxy groups; the alkyl group is methyl, ethyl, or tert-butyl; the alkoxy group is methoxy or ether.

[0010] Among them, X1~X 10 and R a -R b They are the same or different from each other.

[0011] Based on the principle of "like dissolves like," the selected functional groups in the "grafting" process help increase the solubility of the target molecule in non-aqueous electrolytes, thereby improving the energy density of the flow battery. a -R b The groups are independently selected from alkyl chains such as methyl, ethyl, and tert-butyl, alkoxy chains such as methoxy and ether chains, or other polar functional groups. The selected groups enhance the solubility of the target molecule in non-aqueous electrolytes, regulate the redox potential, and improve structural stability. It is important to note that R... a -R b H should be avoided because when R a or R b When the concentration is H, the resulting organic active molecules generally exhibit defects such as poor conductivity in non-aqueous electrolytes and instability in electrochemical processes. X1~X 10 and R a -R b Modification of water-soluble functional groups (sulfonic acid groups, hydroxyl groups, carboxylic acid groups, amino groups, etc.) or their preparation as corresponding salts (usually sodium salts) is avoided, as these functional groups reduce the solubility of the target structure in non-aqueous electrolytes. The structures and their derivatives are used as bipolar electrode active materials in non-aqueous flow batteries.

[0012] Preferably, this invention provides a highly electrochemically active bipolar electrode material, N,N'-dimethyl-5,7,12,14-tetraazapentabenzene (DMTAPs), and its preparation method. Specifically, the structural formulas of the two isomers of the bipolar material are as follows:

[0013]

[0014] 5,14-dihydro-5,7,12,14-tetraazapentabenzene was prepared by condensation of 2,5-dihydroxy-1,4-benzoquinone and 1,2-phenylenediamine under solvent-free and acidic catalyst-free conditions. This product was then deprotonated using an organolithium reagent and treated with iodomethane to obtain the target product.

[0015] The two structures of bipolar flow battery active molecules exhibit a redox potential difference exceeding 2.3V between the positive and negative electrodes, indicating a relatively high voltage level. Simultaneously, the introduced methyl functional group effectively increases the electrochemical stability of the target molecule, thus achieving a bipolar flow battery active material with high stability and high voltage.

[0016] The novel symmetric flow battery system based on DMTAPs molecules of this invention is illustrated in the following diagram of the symmetric flow battery mold structure. Figure 1 As shown.

[0017] The battery system includes a porous diaphragm (1), a current collector (2), a liquid storage tank (3), a bipolar end plate (4), a metal support frame (5), a circulation pump (6), and a liquid storage tank (7), with gaskets used to seal between the components.

[0018] Furthermore, the metal support frame is made of common hard metals or alloys such as copper, stainless steel, and aluminum alloy; the bipolar end plate is a high-density graphite plate; the current collector is graphite carbon felt or carbon fiber felt; the diaphragm is a porous diaphragm with high ion conductivity (preferably Daramic AA-800); and the storage tank and reservoir are made of metal or non-metal materials resistant to organic solvents. The storage tank and reservoir are filled with electrolyte.

[0019] The electrolyte is an organic mixture of the electrode material of this invention and supporting electrolyte salts and organic solvents.

[0020] Furthermore, the supporting electrolyte salt includes, but is not limited to, tetrabutylammonium tetrafluoroborate, tetrabutylammonium perchlorate, tetrabutylammonium trifluoromethanesulfonate, and tetrabutylammonium bis(trifluoromethanesulfonyl)imide, which are soluble in organic solvents. The preferred supporting electrolyte salt is tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-TFSl).

[0021] Furthermore, the organic solvents are all non-aqueous organic solvents, specifically including one or more of acetonitrile, dimethyl sulfoxide, diethylene glycol dimethyl ether, dichloromethane, dichloroethane, 1,3-dioxolane, ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate, with acetonitrile being the preferred organic solvent.

[0022] Furthermore, the concentration of the active materials in the positive and negative electrode electrolytes is 0.01–1.0 mol·L⁻¹. -1The preferred concentration is 0.05 mol·L⁻¹ -1 , with 0.05~1.0mol·L -1 The preferred concentration of TBA-TFSl is 0.5 mol·L⁻¹. -1 A mixed solution. The concentrations of active materials, supporting electrolyte salts, and solution volumes are the same on both sides of the battery.

[0023] like Figure 2 As shown, DMTAPs are dissolved in acetonitrile solvent and stored in a storage tank as a bipolar electrolyte. During battery charging and discharging, the positive and negative electrolytes in the storage tank are pumped from the storage tank to the positive and negative electrode reservoirs via a circulation pump, where redox reactions occur in the current collector regions of the positive and negative electrodes, respectively. The electrolyte then flows back to the storage tank until the charging and discharging process is complete. During battery charging, DMTAPs in the electrolyte lose electrons at the negative electrode, and simultaneously gain electrons at the negative electrode. Inside the battery, TFSI... - Electrons migrate across the separator from the negative electrode to the positive electrode to balance the charges on both sides. Electrons flow from the negative electrode to the positive electrode through the external circuit. During battery discharge, electrons flow from the positive electrode to the negative electrode through the external circuit, and the direction of ion flow and electrode reactions inside the battery are reversed compared to charging.

[0024] The DMTAPs used in this invention are small organic molecules based on nitrogen-containing heterofused rings that are bipolar electrode active materials. In previous studies, these nitrogen-containing heterofused rings were generally only used as one electrode in a battery (typically the negative electrode in aqueous flow batteries). However, the tetraazapyrapentabenzene derivatives proposed in this invention can be used as both the positive and negative electrodes in non-aqueous flow batteries. This molecule contains two isomers, both of which can be used independently as bipolar electrode active materials in non-aqueous flow batteries. Both structures contain multiple nitrogen-containing electrochemical active centers, and only nitrogen-containing electrochemical active centers. These multiple nitrogen-containing redox active centers can undergo two different types of redox reactions, and there is a high redox potential difference between the two reactions. Therefore, this material can be used as both the positive and negative electrodes in a flow battery. Furthermore, it should be noted that the two nitrogen-containing redox active centers can interconvert and exhibit good electrochemical cycling stability, thus reducing the probability of side reactions within the battery. Even if cross-contamination occurs inside the battery during charging and discharging, the electrochemically active molecules within the battery can recover to their initial state through self-discharge, thereby extending the lifespan of the flow battery and reducing operating and maintenance costs. Furthermore, these molecules are small organic molecules, which have the advantages of simple preparation processes and small molecular weights. With proper structural modification, their solubility in non-aqueous electrolytes can be improved, thus increasing the battery's energy density.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention discloses a novel symmetric flow battery based on DMTAPs molecules. This battery can effectively solve the problems of active material side reactions and poor cycle stability caused by electrolyte cross-contamination in flow batteries, while also helping to simplify the battery structure and extend the battery life.

[0027] 2. Preferably, the active material DMTAPs designed and applied in flow batteries according to the present invention can provide an average battery voltage of more than 2.3V while maintaining good cycle stability. Attached Figure Description

[0028] Figure 1 This is a structural diagram of a symmetrical flow battery mold.

[0029] Figure 2 This is a schematic diagram of an exemplary novel symmetric flow battery based on DMTAPs molecules.

[0030] Figure 3 Yes, Q-DMTAP MRI. 1 H spectrum.

[0031] Figure 4 This is a cyclic voltammetry diagram of Q-DMTAP in a preferred electrolyte.

[0032] Figure 5 This is a schematic diagram of the electron transfer reaction of Q-DMTAP.

[0033] Figure 6 It is a B-DMTAP nuclear magnetic resonance image. 1 H spectrum.

[0034] Figure 7 This is a cyclic voltammetry diagram of B-DMTAP in a preferred electrolyte.

[0035] Figure 8 This is a schematic diagram of the electron transfer reaction of B-DMTAP.

[0036] Figure 9 This is the selected charge / discharge capacity-voltage curve for a symmetric flow battery based on Q-DMTAP during long-cycle operation.

[0037] Figure 10 The corresponding charge / discharge capacity and coulombic efficiency of the bipolar symmetric flow battery based on Q-DMTAP are shown.

[0038] Figure 11 The corresponding energy efficiency and voltage efficiency of the bipolar symmetric flow battery based on Q-DMTAP are shown.

[0039] Figure 12This is a selected battery charge / discharge time-voltage curve based on Q-DMTAP bipolar symmetric flow during long-cycle operation.

[0040] Figure 13 This is a selected battery charge / discharge time-voltage curve based on B-DMTAP bipolar symmetric flow during long-cycle operation.

[0041] Figure 14 The corresponding charge / discharge capacity, coulombic efficiency, and energy efficiency of the bipolar symmetric flow battery based on B-DMTAP are shown.

[0042] Figure 15 This is an image of DMTAPs being insoluble in an aqueous electrolyte.

[0043] Figure 16 This is a cyclic voltammetry graph of DMTAPs in an aqueous electrolyte.

[0044] Figure 17 This is a cyclic voltammetry diagram of 5,14-dihydro-5,7,12,14-tetraazapentabenzene in a non-aqueous electrolyte. Detailed Implementation

[0045] The present invention will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting, and in these embodiments, the same reference numerals denote the same structures.

[0046] The following description is intended to enable those skilled in the art to make and use the invention, and is provided in the context of a specific application and its requirements. It will be apparent to those skilled in the art that various modifications can be made to the disclosed embodiments. Furthermore, the general principles defined in this invention can be applied to other embodiments and applications without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the disclosed embodiments, but should be given the broadest scope consistent with the scope of the invention.

[0047] Example 1

[0048] A bipolar electrode active material with a high potential difference, Q-DMTAP, has the following structural formula:

[0049]

[0050] The specific steps are as follows:

[0051] Preparation of 1,5,14-dihydro-5,7,12,14-tetraazapentabenzene

[0052] Weigh 0.420 g (3.00 mmol) of 2,5-dihydroxy-1,4-benzoquinone and 1.622 g (15.0 mmol) of 1,2-phenylenediamine, grind them separately in a mortar until they are powdery and mix thoroughly. Transfer the mixture to a 100 mL reaction flask and use a vacuum pump to remove air from the reaction system. After 20 minutes, introduce nitrogen gas to ensure the reaction proceeds under nitrogen atmosphere. Heat the reaction apparatus in an oil bath at 180 °C for 4 hours. After the reaction is complete, cool the reaction system to room temperature, scrape off the crude product and transfer it to a glass mortar. Add a small amount of acetone and grind vigorously until no obvious particulate solids remain, resulting in a slurry suspension. The slurry suspension was filtered through a funnel to remove the residue. After washing with acetone solvent several times, the residue was transferred to a drying oven and vacuum dried for 10 hours to obtain a blue-purple solid powder, namely relatively pure 5,14-dihydro-5,7,12,14-tetraazapentabenzene, with a yield of 88.5%.

[0053] Preparation of 2,5,12-dimethyl-5,12-dihydro-5,7,12,14-tetraazapentabenzene (Q-DMTAP)

[0054] Weigh 0.711 g (2.50 mmol) of 5,14-dihydro-5,7,12,14-tetraazapentabenzene and add it to a reaction flask. Then add 120 mL of anhydrous tetrahydrofuran and stir to form a suspension. Use a vacuum pump to purge air from the reaction system to completely remove air. After 20 minutes, introduce nitrogen gas to ensure the reaction proceeds under nitrogen atmosphere. Under nitrogen atmosphere, measure 2.6 mL of n-butyllithium solution (6.50 mmol, 2.5 M in hexanes) and add it dropwise to the reaction flask. Stir the reaction at room temperature for 2 hours. After 2 hours, measure 3.903 g of iodomethane (27.5 mmol) and add it dropwise to the reaction flask. Continue stirring at room temperature for 10 hours, then terminate the reaction. After the reaction is complete, measure 50 mL of ultrapure water and add it dropwise to the reaction flask. Stir thoroughly to quench excess reactants. Then use a rotary evaporator to remove tetrahydrofuran from the reaction solution to obtain the crude product. The crude product was separated and purified by silica gel chromatography to obtain 0.253 g (0.810 mmol) of 5,12-dimethyl-5,12-dihydro-5,7,12,14-tetraazapentabenzene (Q-DMTAP), which was dark green needle-like crystals with a yield of 27.8%.

[0055] The obtained Q-DMTAP was characterized by NMR, and the results are as follows: Figure 3 As shown.

[0056] Q-DMTAP nuclear magnetic resonance 1 H spectrum. 1HNMR (400MHz, Chloroform-d) δ = 7.29 (d, J = 7.8Hz, 2H), 7.08 (d, J = 7.7Hz, 2H), 7.00 (t, J = 7.5Hz, 2H), 6.92 (d, J = 8.2Hz, 2H), 5.98 (s, 2H), 3.36 (s, 6H).

[0057] The redox properties of Q-DMTAP were tested using cyclic voltammetry (CV). TBA-TFSI was used as the supporting electrolyte salt, and acetonitrile was used as the solvent. Figure 4 As shown, within the potential scan range of -1.9 to 1.2 V (vs. Ag / AgCl), Q-DMTAP exhibits four distinct redox plateaus, representing four single-electron transfer reactions, corresponding to... Figure 5 The four redox reaction processes shown have redox potentials of approximately -1.67V (vs. Ag / AgCl), -1.60V (vs. Ag / AgCl), 0.52V (vs. Ag / AgCl), and 0.94V (vs. Ag / AgCl) for peaks 1 / 1', 2 / 2', 3 / 3', and 4 / 4', respectively. Therefore, the theoretical voltage of the battery assembled using this material as the sole electrode active material is close to 2.37V. The redox peaks exhibit good reversibility, and the volt-ampere characteristic curves from multiple CV tests show good overlap, indicating that the material has certain cycle stability.

[0058] Example 2

[0059] A bipolar electrode active material with a high potential difference, B-DMTAP, has the following structural formula:

[0060]

[0061] The specific steps are as follows:

[0062] Preparation of 1,5,14-dihydro-5,7,12,14-tetraazapentabenzene

[0063] Weigh 0.420 g (3.00 mmol) of 2,5-dihydroxy-1,4-benzoquinone and 1.622 g (15.0 mmol) of 1,2-phenylenediamine, grind them separately in a mortar until they are powdery and mix thoroughly. Transfer the mixture to a 100 mL reaction flask and use a vacuum pump to remove air from the reaction system. After 20 minutes, introduce nitrogen gas to ensure the reaction proceeds under nitrogen atmosphere. Heat the reaction apparatus in an oil bath at 180 °C for 4 hours. After the reaction is complete, cool the reaction system to room temperature, scrape off the crude product and transfer it to a glass mortar. Add a small amount of acetone and grind vigorously until no obvious particulate solids remain, resulting in a slurry suspension. The slurry suspension was filtered through a funnel to remove the residue. After washing with acetone solvent several times, the residue was transferred to a drying oven and vacuum dried for 10 hours to obtain a blue-purple solid powder, namely relatively pure 5,14-dihydro-5,7,12,14-tetraazapentabenzene, with a yield of 88.5%.

[0064] Preparation of 2,5,14-dimethyl-5,14-dihydro-5,7,12,14-tetraazapentabenzene (B-DMTAP)

[0065] Weigh 0.711 g (2.50 mmol) of 5,14-dihydro-5,7,12,14-tetraazapentabenzene and add it to a reaction flask. Then add 120 mL of anhydrous tetrahydrofuran and stir to form a suspension. Use a vacuum pump to purge air from the reaction system to completely remove air. After 20 minutes, introduce nitrogen gas to ensure the reaction proceeds under nitrogen atmosphere. Under nitrogen atmosphere, measure 2.6 mL of n-butyllithium solution (6.50 mmol, 2.5 M in hexanes) and add it dropwise to the reaction flask. Stir the reaction at room temperature for 2 hours. After 2 hours, measure 3.903 g of iodomethane (27.5 mmol) and add it dropwise to the reaction flask. Continue stirring at room temperature for 10 hours, then terminate the reaction. After the reaction is complete, measure 50 mL of ultrapure water and add it dropwise to the reaction flask. Stir thoroughly to quench excess reactants. Then use a rotary evaporator to remove tetrahydrofuran from the reaction solution to obtain the crude product. The crude product was separated and purified by silica gel chromatography to obtain 0.253 g (0.810 mmol) of 5,14-dimethyl-5,14-dihydro-5,7,12,14-tetraazapentabenzene (B-DMTAP), which was dark red needle-like crystals with a yield of 40.4%.

[0066] The obtained B-MTAP was characterized by NMR, and the results are as follows: Figure 6 As shown.

[0067] B-DMTAP NMR 1 H spectrum. 1H NMR (400 MHz, Chloroform-d) δ = 7.91 (dd, J = 6.4, 3.5 Hz, 2H), 7.56 (dd, J = 6.5, 3.4 Hz, 2H), 6.91 (dd, J = 6.0, 3.4 Hz, 2H), 6.78-6.71 (m, 4H), 3.36 (s, 6H).

[0068] The redox properties of B-DMTAP were tested using cyclic voltammetry (CV). TBA-TFSI was used as the supporting electrolyte salt, and acetonitrile was used as the solvent. Figure 7 As shown, the redox behavior of B-DMTAP is similar to that of Q-DMTAP. Within the potential scan range of -2.2–1.6 V (vs. Ag / AgCl), B-DMTAP exhibits four distinct redox plateaus, representing four single-electron transfer reactions. Figure 8 The four redox reaction processes shown have redox potentials of approximately -1.85V (vs. Ag / AgCl), -1.43V (vs. Ag / AgCl), 0.71V (vs. Ag / AgCl), and 1.29V (vs. Ag / AgCl) for peaks 1 / 1', 2 / 2', 3 / 3', and 4 / 4', respectively. Therefore, the theoretical voltage of the battery assembled using this material as the sole electrode active material is close to 2.64V, slightly higher than Q-DMTAP. The redox peaks exhibit good reversibility, and multiple CV tests show good overlap of the volt-ampere characteristic curves, indicating high cycle stability of this material.

[0069] Application Example 1

[0070] Bipolar symmetric flow battery based on the Q-DMTAP material described in Embodiment 1 of this invention

[0071] The 0.01 mol·L⁻¹ prepared in Example 1 -1 A mixed solution of Q-DMTAP and 0.5M TBA-TFSI (bis(trifluoromethanesulfonyl)imide tetrabutylammonium salt) in acetonitrile was used as the sole electrolyte in the flow battery. Equal volumes were injected into the positive and negative electrode reservoirs, respectively. The electrode active material in both the positive and negative electrode electrolytes was Q-DMTAP, an organic electrode active small molecule. The electrolyte also contained the supporting electrolyte salt TBA-TFSI and the organic solvent acetonitrile. The battery system included a porous membrane (1), a current collector (2), a reservoir (3), a bipolar end plate (4), a metal support frame (5), a circulation pump (6), and a reservoir (7). All components were sealed with gaskets. The membrane was a porous membrane with high ion conductivity, Daramic AA-800.

[0072] The charging current density is 2 mA cm⁻¹ -1The discharge current density is 2 mA cm⁻¹ -1 .

[0073] Figure 9 It is a bipolar symmetric flow cell based on Q-DMTAP at 2mA cm -2 Charge / discharge capacity-voltage curves at current density. The battery exhibits a clear charge / discharge plateau across different test cycles, with the voltage plateau remaining almost constant throughout the test cycle, and the discharge voltage approaching 2.3V. The Q-DMTAP shows an initial active material utilization rate of 86.1%, corresponding to a coulombic efficiency of 86.3%.

[0074] Figure 10 Based on Q-DMTAP, the corresponding charge / discharge capacity and coulombic efficiency of the bipolar symmetric flow battery are as follows: after 50 charge / discharge cycles, the battery capacity retention rate is approximately 63.4%, and the coulombic efficiency remains stable at over 85% throughout the process.

[0075] Figure 11 The corresponding energy efficiency and voltage efficiency of the bipolar symmetric flow battery based on Q-DMTAP are as follows: the energy efficiency during the charge and discharge process is stable at over 70%, and the voltage efficiency is stable at over 80%.

[0076] Figure 12 The charge-discharge time-voltage curve of the bipolar symmetric flow battery based on Q-DMTAP shows that the battery voltage changes periodically with time, exhibiting good cycle stability.

[0077] Compared to other types of symmetric flow batteries using bipolar electrode materials or asymmetric flow batteries using traditional organic molecules as active materials, this material exhibits superior battery performance.

[0078] Application Example 2

[0079] Bipolar symmetric flow battery based on the B-DMTAP material described in Embodiment 2 of the present invention

[0080] The 0.001 mol·L⁻¹ prepared in Example 1 -1 A mixed solution of acetonitrile (B-DMTAP) and 0.5M TBA-TFSI was used as the sole electrolyte in the flow battery. Equal volumes were injected into the positive and negative electrode reservoirs of the battery, respectively. A porous membrane was used as the separator to assemble the bipolar flow battery and conduct charge-discharge cycle tests.

[0081] The charging current density is 1 mA cm⁻¹ -1 The discharge current density is 1 mA cm⁻¹ -1 .

[0082] Figure 13It is a bipolar symmetric flow cell based on B-DMTAP at 1 mA cm⁻¹ -2 Charge / discharge time-voltage curves at current density. The battery charge / discharge voltage exhibits periodic changes over time, demonstrating good cycle stability. The battery shows a clear charge / discharge plateau at different test cycle numbers, with the voltage plateau remaining almost constant throughout the test cycle, and the discharge voltage approaching 2.7V.

[0083] Figure 14 This data represents the charge / discharge capacity, coulombic efficiency, and energy efficiency of a bipolar symmetric flow battery based on B-DMTAP. After 200 charge / discharge cycles, the battery retains approximately 50.2% of its discharge capacity, with a degradation rate of approximately 0.25% per cycle. After 20 charge / discharge cycles, the battery's coulombic efficiency stabilizes above 70%, and its energy efficiency stabilizes above 65%. Overall, this battery exhibits high charge / discharge voltage, energy efficiency, and coulombic efficiency, while also demonstrating relatively stable cycle performance.

[0084] Application Example 3

[0085] Bipolar symmetric flow battery based on the Q-DMTAP material described in Embodiment 1 of this invention

[0086] The performance parameters of bipolar symmetric flow batteries based on Q-DMTAP material with different concentrations of active material are compared. The specific data are as follows:

[0087]

[0088] In summary, the preferred concentration of the active materials for both positive and negative electrode electrolytes is 0.05 mol·L⁻¹. -1 .

[0089] Comparative Example 1

[0090] The redox properties of DMTAP in an aqueous electrolyte were tested by cyclic voltammetry (CV). TBA-TFSI was used as the supporting electrolyte salt, and water as the solvent. 10 mg of a mixture of Q-DMTAP and B-DMTAP was weighed and placed in ultrapure water. Figure 15 As shown, DMTAP-based materials are almost insoluble in aqueous electrolytes (with a large amount of solid precipitate). Within the potential scan range of -2.2–1.6 V (vs. Ag / AgCl), DMTAP-based materials do not exhibit stable redox reactions. Figure 16 Compared to acetonitrile in a non-aqueous solvent, its redox potential exceeds the electrochemical window of water. Therefore, using this material as the sole electrode active material is not feasible for aqueous flow batteries.

[0091] Comparative Example 2

[0092] The redox properties of 5,14-dihydro-5,7,12,14-tetraazapentabenzene in a non-aqueous electrolyte were tested by cyclic voltammetry (CV). TBA-TFSI was used as the supporting electrolyte salt, and acetonitrile was used as the solvent. Figure 17 As shown, within the potential scan range of -2.2 to 1.6 V (vs. Ag / AgCl), the redox reversibility of 5,14-dihydro-5,7,12,14-tetraazapentabenzene is poor. The voltammetric characteristic curves after several CV tests almost do not overlap with the initial curves, and the redox peak of this material in the range of 0 to 0.5 V (vs. Ag / AgCl) changes significantly. Therefore, 5,14-dihydro-5,7,12,14-tetraazapentabenzene cannot be directly used as the sole electrode active material for non-aqueous symmetric flow batteries.

Claims

1. An organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material, characterized in that: Both the positive and negative electrolytes of the organic symmetric flow battery contain nitrogen-containing heterocyclic organic small molecule active materials. The structural formula of the nitrogen-containing heterofused ring organic small molecule is as follows: or ; X1~X 10 Each is independently selected from H, alkyl, or alkoxy; R a -R b Each is independently selected from alkyl or alkoxy groups; the alkyl group is methyl, ethyl, or tert-butyl; the alkoxy group is methoxy.

2. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 1, characterized in that: The structural formula of the nitrogen-containing heterofused ring organic small molecule is as follows: or .

3. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 1, characterized in that: Both the positive and negative electrolytes contain nitrogen-containing heterocyclic organic small molecule active materials, supporting electrolyte salts, and organic solvents.

4. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 3, characterized in that: The supporting electrolyte is one or more of tetrabutylammonium tetrafluoroborate, tetrabutylammonium perchlorate, tetrabutylammonium trifluoromethanesulfonate, and bis(trifluoromethanesulfonyl)imide tetrabutylammonium salt.

5. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 3, characterized in that: The organic solvent is one or a combination of two or more of the following: acetonitrile, dimethyl sulfoxide, diethylene glycol dimethyl ether, dichloromethane, dichloroethane, 1,3-dioxolane, ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate.

6. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 3, characterized in that: The supporting electrolyte is bis(trifluoromethanesulfonyl)imide tetrabutylammonium salt; the organic solvent is acetonitrile.

7. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 3, characterized in that: The concentration of active material in the positive and negative electrode electrolytes is 0.01~1.0 mol·L⁻¹ -1 The concentration of the supporting electrolyte in both the positive and negative electrode electrolytes is 0.05~1.0 mol·L⁻¹. -1 The concentrations of active materials, supporting electrolyte salts, and solution volumes used in the electrolytes on both sides of the battery are the same.

8. The organic symmetric flow battery based on a nitrogen-containing heterocyclic bipolar electrode active material according to claim 3, characterized in that: The organic symmetric flow battery system also includes a metal support frame, bipolar end plates, current collectors, a porous diaphragm, a liquid reservoir, a liquid tank, a gasket, and a circulation pump.

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