A class of chiral viologen derivatives that enhance electrolyte solubility, their synthesis methods, and their applications in flow batteries.

Abstract

This invention discloses a class of chiral viologen derivatives for improving electrolyte solubility, their synthesis method, and their application in flow batteries, belonging to the field of flow energy storage technology. This invention prepares optical isomers and racemates through a chiral resolution strategy, which can improve the solubility of viologen molecules. Simultaneously, the introduction of dihydroxyl groups increases the number of hydrogen bonds between the molecule and water. This approach significantly improves the water solubility of the molecule and enhances the theoretical capacity and volumetric energy density of the electrolyte. It can be used in high-capacity, high-power, long-life neutral aqueous organic flow batteries, making it highly suitable for large-scale energy storage.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to a class of chiral viologen derivatives that improve electrolyte solubility, their synthesis method, and their application in flow batteries. Background Technology

[0002] Energy and the environment are two major challenges facing the world today. With the continuous development of science and technology and the rapid increase in population, the demand for energy is growing, and electricity is gradually becoming an indispensable secondary energy source in people's production and daily life. Developing new energy sources is an inevitable trend. The development and utilization of clean and renewable energy requires advanced energy storage technology as a necessary support. Flow batteries, as a large-capacity electrochemical energy storage device, are the preferred technology for the large-scale application of renewable energy. Traditional flow batteries are based on transition metal active materials, such as vanadium redox flow batteries. The electrolyte materials of such flow batteries are relatively expensive, highly corrosive, and prone to cross-contamination, which is not conducive to their sustainable development. Compared with inorganic systems, the organic redox molecules in neutral aqueous organic flow batteries (AORFB) are composed of (C, H, O, N), which have low raw material costs and are sustainable. Furthermore, the organic molecular structure is highly tunable, which can improve the electrode potential and solubility of the molecules, and has a broader application prospect.

[0003] Electrolyte materials, as a core component of flow batteries, play a crucial role in optimizing battery performance. Pyridine compounds, especially viologen, have been widely used in the negative electrolyte system of aqueous redox flow batteries due to their excellent electron acceptor properties. However, the inherent insufficient conjugation of viologen molecules leads to unstable two-electron transfer performance. To address this issue, researchers have attempted to enhance the conjugation effect of viologen molecules by introducing conjugated groups, such as thiazothiazoles, phenyl groups, and five-membered heterocycles, into the pyridine structure. However, it is worth noting that the introduction of these electron-donating groups reduces molecular polarity and increases the molecular weight of the compound; therefore, such modification strategies often significantly reduce the solubility of viologen molecules.

[0004] Therefore, improving molecular water solubility through chiral resolution strategies is of great significance for the development of vigorin-based AORFB. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a class of chiral viologen derivatives that improve the solubility of electrolytes, their synthesis method and their application in flow batteries, so as to solve the technical problem that the introduction of electron-donating groups into the viologen molecule structure leads to a significant decrease in its solubility. At the same time, the viologen derivatives provided can be effectively applied in neutral aqueous flow batteries.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a class of chiral viologen derivatives that enhance the solubility of electrolytes, with the following structural formula:

[0008]

[0009] Where X represents the counterparticle, which is either Cl or Br;

[0010] R1 and R6 are hydrophilic groups;

[0011] Preferably, R1 and R6 are hydrophilic groups capable of chiral separation, including the following structure R a -R e Any one of them:

[0012]

[0013] n is 1 to 10;

[0014] R2, R5, R7 and R 10 It is any one of -Me, -OMe, -OEt, -COOH, and -COONH4;

[0015] R3, R4, R8, and R9 are connected by S, Se, Te, or double bonds.

[0016] Preferably, the structural formula is as follows:

[0017]

[0018] More preferably, the structure R a -R e The structure is split using chirality as follows:

[0019]

[0020] n is 1 to 10.

[0021] This invention also discloses the application of the above-mentioned viologen derivatives in the preparation of negative electrode electrolyte materials for neutral aqueous organic redox flow batteries.

[0022] Preferably, the viologen derivative is used as the negative electrode electrolyte material, the TEMPO derivative is used as the positive electrode electrolyte material, NaCl or KCl is used as the supporting electrolyte, and a DSVN / AMVN membrane is used as the anion exchange membrane to prepare a single cell or a stack of multiple cells; wherein, the single cell or the stack uses carbon felt as the positive and negative electrodes, and copper sheet and graphite plate as current collectors to form a neutral aqueous flow battery.

[0023] Preferably, the concentration of the negative electrode electrolyte prepared by using the viologen derivative as the negative electrode electrolyte material is 0.1-3 mol / L; and the concentration of the supporting electrolyte is 0.5-2 mol / L.

[0024] The present invention also discloses a method for synthesizing the chiral viologen derivative with improved electrolyte solubility, comprising: dissolving precursor A and XR in water, reacting at 120°C for 12-24 h to obtain a reaction solution, cooling the reaction solution to room temperature and stirring thoroughly, then adding water, and then slowly adding ethanol and acetone dropwise to precipitate the product by means of the difference in solvent polarity, and then filtering and drying to obtain the target viologen derivative;

[0025] The structural formula of precursor A is shown below:

[0026]

[0027] R2, R5, R7 and R 10 It is any one of -Me, -OMe, -OEt, -COOH and -COONH4; R3, R4 and R8, R9 are connected by S, Se, Te or double bonds;

[0028] The structural formula of XR is shown in any of the following structures:

[0029]

[0030] X represents the counterparticle, which is either Cl or Br.

[0031] Preferably, the structural formula of the isomer selected for XR is as follows:

[0032]

[0033] Preferably, the molar ratio of precursor A to XR is 1:2 to 2.5.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] This invention discloses a method for improving electrolyte solubility through a chiral resolution strategy and its application in flow batteries. Existing technologies report poor solubility of viologen molecules, severely limiting the large-scale development of aqueous organic flow batteries. This invention prepares optical isomers and racemates through a chiral resolution strategy, which can improve the solubility of viologen molecules. Simultaneously, the introduction of dihydroxyl groups increases the number of hydrogen bonds between the molecule and water. This approach significantly improves the molecule's water solubility and enhances the theoretical capacity and volumetric energy density of the electrolyte. Using these derivatives as the negative electrode electrolyte in neutral aqueous organic flow batteries, and matching them with TEMPO derivatives or ferrocene in neutral aqueous flow batteries, demonstrates extremely high electrochemical stability, high energy efficiency, and high capacity utilization.

[0036] The present invention discloses a method for synthesizing viologen derivatives. Precursor A and XR are dissolved in a solvent and reacted at 120°C to generate viologen-based derivatives. The terminal N atom is ionized to introduce a hydrophilic group, improving the water solubility of the molecule. This synthesis method effectively avoids the use of organic solvents such as N,N-dimethylformamide, tetrahydrofuran, and acetonitrile. The solvents used in the reaction are inexpensive, the method is simple, the yield is high, it can be synthesized in large quantities, and the synthesis speed is fast.

[0037] This invention utilizes a chiral resolution strategy to prepare optical isomers and racemates, thereby improving the solubility of viologen molecules. Simultaneously, the introduction of dihydroxyl groups increases the number of hydrogen bonds between the molecule and water. This approach significantly improves the water solubility of the molecule and enhances the theoretical capacity and volumetric energy density of the electrolyte. It can be used in high-capacity, high-power, long-life neutral aqueous organic flow batteries, making it highly suitable for large-scale energy storage. Attached Figure Description

[0038] Figure 1 These are measured solubility graphs of three types of diol-Vi in embodiments of the present invention;

[0039] Figure 2 These are the UV solubility test charts for three types of diol-Vi in embodiments of the present invention;

[0040] Figure 3 These are conductivity test graphs for three different concentrations of diol-Vi in embodiments of the present invention;

[0041] Figure 4 This is a test diagram of a 1.5M R-diol-Vi / 0.8M MiAcNH-TEMPO battery from Embodiment 1 of the present invention. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0044] The present invention will now be described in further detail with reference to the accompanying drawings:

[0045] This invention discloses a method for preparing chiral viologen derivatives that enhance electrolyte solubility. The chemical reaction formula for synthesizing this type of compound is as follows:

[0046]

[0047] R1 and R6 are hydrophilic dihydroxy groups, including the following structures R a -R e Any one of them:

[0048]

[0049] n = 1 - 10.

[0050] R3 and R4 are connected by S, Se, Te, or a double bond, and R8 and R9 can be connected by S, Se, Te, or a double bond as shown below:

[0051]

[0052] The synthesis method of this chiral viologen derivative is as follows: Precursor A and XR are dissolved in a solvent and reacted at 120℃ for 24 h to obtain a reaction solution. The reaction solution is cooled to room temperature, and the reaction mixture is poured into a beaker and stirred vigorously. Deionized water is added, followed by the slow addition of ethanol and acetone. The mixture is filtered, and the product is precipitated by the difference in polarity. The product is then dried in an oven at 60℃ for 12 h. X is either Cl or Br.

[0053] R2, R5, R7, R 10 R 11 R 12 It can be any one of -Me, -OMe, -OEt, -COOH, and -COONH4.

[0054] R is R a To R e Any one of them.

[0055] Preferred values ​​are R2, R5, R7, and R. 10 R 11 R 12 =0

[0056] Preferably, n=1.

[0057] Preferably, R1 = R6 = R c .

[0058] Example

[0059] Let n = 1, R2 = 0, R5 = 0, R7 = 0, R 10 =0, R 11 =0, R 12 =0, R=R c If X = Cl, and the electrolyte is NaCl with a concentration of 1 M, then the structural formula of the precursor is:

[0060]

[0061] Precursor A0 22.2g and 30mL Cl-R a Cl-R aR and Cl-R aS The reaction mixture was reacted in 20 mL of water at 120 °C for 24 h to obtain a reaction solution. The reaction mixture was cooled to room temperature, poured into a beaker, and stirred vigorously. 20 mL of deionized water was added, followed by the slow addition of 300 mL of ethanol and 50 mL of acetone. The mixture was filtered and dried in an oven at 60 °C for 12 h. The equivalent ratio of precursor A0 to Cl-R was 1:2.5. The obtained products were named R-diol-Vi, S-diol-Vi, and RS-diol-Vi, respectively. The yields of the products were similar, with an average of 50.94 g and a yield of 95%. The structural formulas of the three diol-Vi products are shown below:

[0062]

[0063] The 1H NMR spectra of the three diol-Vi samples prepared in this embodiment are as follows.

[0064] R-diol-Vi: 1 H NMR(400MHz,D2O)δ9.09(d,J=6.7Hz,4H),8.55(d,J=6.5

[0065] Hz, 4H), 4.93 (dd, J=13.5, 2.8Hz, 2H), 4.65 (dd, J=13.5, 9.0Hz, 2H), 4.20 (td, J=8.3, 5.0Hz, 2H), 3.71 (d, J=5.2Hz, 4H).

[0066] S-diol-Vi: 1 H NMR(400MHz,D2O)δ9.10(d,J=6.7Hz,4H),8.57(d,J=6.6

[0067] Hz, 4H), 4.95 (dd, J = 13.5, 2.6 Hz, 2H), 4.67 ( dd, J = 13.5, 9.0 Hz, 2H), 4.22 ( dd, J = 8.7, 3.2 Hz, 2H), 3.73 ( d, J = 5.1 Hz, 4H).

[0068] RS-diol-Vi: 1 H NMR (400MHz, D2O) δ9.13 (d, J=6.6Hz, 4H), 8.60 (d, J=

[0069] 6.2Hz, 4H), 4.97 (dd, J=13.5, 2.8Hz, 2H), 4.70 (dd, J=13.5, 9.0Hz, 2H), 4.29–4.20 (m, 2H), 3.75 (d, J=5.2Hz, 4H).

[0070] Applications of the viologen derivatives prepared above as negative electrode electrolyte materials:

[0071] The preparation of neutral aqueous organic flow battery electrode materials using the three diol-Vi viologen derivatives obtained in the examples can be achieved through the following steps:

[0072] Step 1: Assemble the core fixture;

[0073] In the neutral aqueous organic redox flow battery system used in the test, the battery was designed as a single cell. The assembly process was rigorous and meticulous, with the following components being securely fastened in sequence using bolts: positive electrode plate, positive electrode insulating plate, positive electrode conductive plate, positive electrode flow frame, positive electrode graphite felt, positive electrode gasket, anion exchange membrane, negative electrode gasket, negative electrode graphite felt, negative electrode flow frame, negative electrode conductive plate, negative electrode insulating plate, and so on, up to the negative electrode plate. After assembly, all bolt connections must be carefully checked for stability, and any looseness should be promptly tightened to ensure the overall structural tightness.

[0074] Before formal testing, a dual test of sealing performance and pressure resistance is required. This involves connecting two additional liquid reservoirs to the assembled fixture system and configuring a peristaltic pump for circulation for two hours. During this process, close monitoring is necessary for any liquid leaks, and the liquid volume must be checked to ensure it remains constant before and after circulation. If the system successfully passes both tests, confirming no leaks and constant volume, it is considered ready for subsequent use. Conversely, if any leaks or volume changes are detected, the test must be stopped immediately, and the positions and tightness of all components must be readjusted until all problems are resolved and the system passes the test again.

[0075] Step 2: Electrode material preparation.

[0076] Prepare a sufficient amount of 1M NaCl solution in a volumetric flask. The cathode electrolyte is a methylimidazolium-functionalized (2,2,6,6-tetramethylpiperidin-1-yl)oxy solution with the chemical formula C0. 15 H 26 N4O2, abbreviated as MiAcNH-TEMPO.

[0077] Preparation of a 1.5M diol-Vi / 0.8M MiAcNH-TEMPO neutral aqueous organic flow battery

[0078] 2.83 g of each of the three diol-Vi derivatives and 3.46 g of MiAcNH-TEMPO were dissolved in 5 mL and 13 mL of 1M NaCl solution, respectively, and stirred or sonicated until completely dissolved. The concentrations of the two derivatives in the NaCl solution were 1.5 M and 0.8 M, respectively. The volume ratio of the resulting mixtures was 1:2.6 to ensure complete charge and discharge of diol-Vi. Argon gas was bubbled through the mixture for 10 minutes. The derivatives diol-Vi and MiAcNH-TEMPO were used as the anolyte and catholyte of the battery, respectively, and are referred to as 1.5 M diol-Vi / 0.8 M MiAcNH-TEMPO.

[0079] Step 3: Assemble a neutral aqueous organic redox flow battery and conduct performance tests;

[0080] Place the fixture prepared in step one and the solution from step two into a glove box. Use the prepared diol-Vi solution as the anolyte and the MiAcNH-TEMPO solution as the catholyte. Connect the external power supply, peristaltic pump, and Xinwei tester, set the program, and the charge-discharge test can be performed.

[0081] Following the above steps, the basic test data for the prepared 1.5M diol-Vi / 0.8M MiAcNH-TEMPO system are as follows: two-electron storage, voltage range 0.3–1.5V (single-electron test), 0.1V–2.1V (two-electron test), current density 60mA / cm². 2 After 200 cycles, the capacity retention rate was 96.67%, and the capacity decay rate per cycle was 0.0167%.

[0082] Therefore, the battery tests mentioned above show that this type of molecule has excellent stability. The chirally separated R-diol-Vi and S-diol-Vi have greater molecular water solubility, up to 2.76 M, and their theoretical capacity is greater. Higher concentration batteries can be tested. These chirally separated viologen derivatives can be used as the anolyte in neutral aqueous organic flow batteries.

[0083] In electrochemical tests, the neutral aqueous organic redox battery based on 1.5M diol-Vi / 0.8M MiAcNH-TEMPO exhibited extremely strong stability. Furthermore, other hydrophilic groups, such as:

[0084]

[0085] (where n takes the value of 1-10) can also be modified, and chiral separation can improve solubility to obtain better anolyte materials.

[0086] The present invention conducted relevant tests on the three diol-Vi anode electrolyte materials prepared in the above embodiments, and the test results are shown in [reference needed]. Figures 1-4 And Table 1:

[0087] from Figure 1 As can be seen from the examples, the RS-diol-Vi molecules are turbid solutions at concentrations of 2M and 2.5M. From... Figure 2 As can be seen from the examples, the theoretical solubility of R-diol-Vi is 2.76 M, and the theoretical capacity is 147.9 Ah L. -1 The theoretical solubility of S-diol-Vi is 2.75 M, and the theoretical capacity is 147.4 Ah L. -1 The theoretical solubility of RS-diol-Vi is 1.66 M, and the theoretical capacity is 89.98 Ah L. -1 .from Figure 3It can be seen that the conductivity of diol-Vi first increases and then decreases with concentration, reaching a peak at around 1 M. From... Figure 4 It can be seen that the 1.5MR-diol-Vi / 1M MiAcNH-TEMPO battery retains 96.67% of its capacity after 200 cycles, with a single-cycle capacity decay rate of 0.0167%.

[0088] This invention discloses a method for improving electrolyte solubility through a chiral resolution strategy. Viologen molecules are resolved, increasing their solubility, and used as the anolyte. TEMPO derivatives or ferrocene are used as the cathode electrolyte. All electrolyte materials are dissolved in 1M NaCl to increase the solution's conductivity. A DSVN membrane is used as the anion exchange membrane to construct a neutral aqueous organic flow battery with single-electron or double-electron storage. The configuration is Ar = Ar0, n = 1, R = R... a Taking X = Cl as an example, denoted as diol-Vi, when the current density is 60 mA / cm² 2 At a concentration of 1.5 M, the neutral aqueous organic flow battery based on R-diol-Vi / MiAcNH-TEMPO exhibited good cycle stability after 200 cycles. After 200 cycles, the capacity retention was 96.67%, and the capacity decay rate per cycle was 0.0167%.

[0089] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A class of chiral viologen derivatives that enhance the solubility of electrolytes, characterized in that, The structural formula of the chiral viologen derivative is shown below: 。 2. The application of the chiral viologen derivative for improving electrolyte solubility as described in claim 1 in the preparation of negative electrode electrolyte materials for neutral aqueous organic redox flow batteries.

3. The application as described in claim 2, characterized in that, Using the chiral viologen derivative as the negative electrode electrolyte material, the TEMPO derivative as the positive electrode electrolyte material, NaCl or KCl as the supporting electrolyte, and a DSVN / AMVN membrane as the anion exchange membrane, a single cell or a stack of multiple cells is prepared; wherein, the single cell or stack uses carbon felt as the positive and negative electrodes, and copper sheet and graphite plate as current collectors to form a neutral aqueous flow battery.

4. The application as described in claim 3, characterized in that, The concentration of the negative electrode electrolyte prepared by using the chiral viologen derivative as the negative electrode electrolyte material is 0.1~3 mol / L.

5. The application as described in claim 3, characterized in that, The concentration of the supporting electrolyte is 0.5~2 mol / L.

6. The method for synthesizing the chiral viologen derivative for improving electrolyte solubility as described in claim 1, characterized in that, include: Precursor A and XR were dissolved in water and reacted at 120 °C for 12-24 h to obtain a reaction solution. The reaction solution was cooled to room temperature and stirred thoroughly. Then water was added, followed by the slow addition of ethanol and acetone. The product was precipitated by the difference in solvent polarity. The product was then filtered and dried to obtain the target viologen derivative. The structural formula of precursor A is shown below: ； XR refers to XR a XR aR and XR aS X represents the counterparticle, which is Cl; XR a XR aR and XR aS The specific isomer structural formulas selected are shown below: ； n=1。 7. The method for synthesizing viologen derivatives according to claim 6, characterized in that, The molar ratio of precursor A to XR is 1:2.5.

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