Chiral viologen derivative for improving solubility of electrolyte, synthetic method of chiral viologen derivative and application of chiral viologen derivative in flow battery

Abstract

The invention discloses a chiral viologen derivative for improving the solubility of an electrolyte, a synthesis method of the chiral viologen derivative and application of the chiral viologen derivative in a flow battery, and belongs to the technical field of flow energy storage. An optical isomer and a racemate are prepared through a chiral resolution strategy, and the solubility of viologen molecules can be improved. Meanwhile, the number of hydrogen bonds between molecules and water is increased due to introduction of dihydroxyl groups, the water solubility of the molecules is remarkably improved, the theoretical capacity and the volume energy density of the electrolyte are improved, and the electrolyte can be used for a neutral aqueous organic flow battery with high capacity, high power and long service life and is very suitable for large-scale energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow energy storage, and in particular relates to a chiral viologen derivative for improving electrolyte solubility, a synthesis method thereof, and an application in a liquid flow battery. Background Art

[0002] Energy and environment are two major problems facing the world today. With the continuous development of science and technology, the rapid increase in population, the demand for energy is increasing, and electric energy has gradually become an indispensable secondary energy source in people's production and life. The development of new energy is an inevitable trend. The development and utilization of clean and renewable energy requires advanced energy storage technology as a necessary support. As a large-capacity electrochemical energy storage device, flow battery is the preferred technology for large-scale application of renewable energy. Traditional flow batteries are based on transition metal active materials, such as all-vanadium flow batteries. The electrolyte materials of this flow battery are relatively expensive, highly corrosive, and the electrolyte will cross-contaminate, which is not conducive to its sustainable development. Compared with inorganic systems, the organic redox molecules in neutral aqueous organic flow batteries (AORFBs) are composed of (C, H, O, N), with low raw material cost and sustainable use, and the organic molecular structure is highly adjustable, which can improve the electrode potential and solubility of the molecules, and has a broader application prospect.

[0003] As the core component of flow batteries, electrolyte materials play a vital 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 lack of conjugation of viologen molecules leads to the instability of their double electron transfer performance. To address this problem, researchers have tried to enhance the conjugation effect of viologen molecules by introducing conjugated groups such as thiazolylthiazole, phenyl and five-membered heterocycles into the pyridine structure. However, it is worth noting that the introduction of these electron-donating groups will reduce the molecular polarity and increase the molecular weight of the compound, so this type of modification strategy often significantly reduces the solubility of viologen molecules.

[0004] Therefore, improving the water solubility of molecules through chiral resolution strategy is of great significance for the development of viologen-based AORFBs. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a class of chiral viologen derivatives that improve electrolyte solubility, a synthesis method thereof, and an application in liquid flow batteries, so as to solve the technical problem that the prior art expands the molecular structure of viologen and introduces electron-donating groups, resulting in a significant decrease in its solubility. At the same time, the provided viologen derivatives can be effectively used in neutral aqueous liquid flow batteries.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention discloses a class of chiral viologen derivatives for improving electrolyte solubility, and the structural formula is as follows:

[0008]

[0009] Wherein, X represents the counterparticle, which is 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 of:

[0012]

[0013] n is 1 to 10;

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

[0015] R3, R4 and R8, R9 are connected via S, Se, Te or a double bond.

[0016] Preferably, the structural formula is as shown below:

[0017]

[0018] More preferably, the structure R a -R e The structure is as follows by chiral resolution:

[0019]

[0020] n is 1 to 10.

[0021] The invention also discloses the application of the viologen derivative in preparing the negative electrode electrolyte material of a neutral aqueous organic redox flow battery.

[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 the DSVN / AMVN membrane is used as the anion exchange membrane to prepare a single cell or a battery stack composed of multiple cells; wherein the single cell or battery stack uses carbon felt as the positive and negative electrodes, and copper sheets and graphite plates as current collectors to form a neutral aqueous liquid 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 for improving electrolyte solubility, comprising: dissolving precursors A and XR in water, reacting at 120° C. for 12 to 24 hours to obtain a reaction solution, cooling the reaction solution to room temperature and fully stirring it, then adding water, and then slowly dropping ethanol and acetone, precipitating the product by the difference in solvent polarity, and then filtering and drying to obtain the target viologen derivative;

[0025] The structural formula of precursor A is as follows:

[0026]

[0027] R2, R5, R7 and R 10 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 a counter particle, which is Cl or Br.

[0031] Preferably, the structural formula of the specifically selected isomer of 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] The present invention discloses a method for improving electrolyte solubility through a chiral splitting strategy and its application in a liquid flow battery. The viologen molecules reported in the prior art have poor solubility, which seriously limits the large-scale development of aqueous organic liquid flow batteries. The present invention prepares optical isomers and racemates through a chiral splitting strategy, which can improve the solubility of viologen molecules. At the same time, the introduction of dihydroxyl groups increases the number of hydrogen bonds between the molecules and water. This solution significantly improves the water solubility of the molecules and improves the theoretical capacity and volume energy density of the electrolyte. Such derivatives are used as negative electrode electrolytes of neutral aqueous organic liquid flow batteries, and are matched with TEMPO derivatives or ferrocene and applied in neutral aqueous liquid flow batteries to show extremely high electrochemical stability, high energy efficiency, and capacity utilization.

[0036] The synthesis method of the viologen derivative disclosed in the present invention is to dissolve the precursor A and XR in a solvent and react at 120°C to generate a viologen-based derivative, ionize and modify the terminal N atom, introduce a hydrophilic group, and improve the water solubility of the molecule. The synthesis method of the present invention can effectively avoid the use of organic solvents such as N,N-dimethylformamide, tetrahydrofuran and acetonitrile, the solvent used in the reaction is low in price, the method is simple, the yield is high, it can be synthesized in large quantities, and the synthesis speed is fast.

[0037] The present invention prepares optical isomers and racemates through a chiral resolution strategy, thereby improving the solubility of viologen molecules. At the same time, the introduction of dihydroxyl groups increases the number of hydrogen bonds between the molecule and water. This solution significantly improves the water solubility of the molecule and increases the theoretical capacity and volume energy density of the electrolyte. It can be used in high-capacity, high-power, long-life neutral aqueous organic flow batteries, and is very suitable for large-scale energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the measured solubility graph of three diol-Vi in the embodiment of the present invention;

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

[0040] Figure 3 : is a test graph of conductivity of three diol-Vi with different concentrations in the embodiment of the present invention;

[0041] Figure 4 This is a test diagram of a 1.5M R-diol-Vi / 0.8M MiAcNH-TEMPO battery according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0045] The present invention discloses a method for preparing a chiral viologen derivative for improving electrolyte solubility. The chemical reaction formula for synthesizing the compound is:

[0046]

[0047] R1, R6 are hydrophilic dihydroxyl groups, including the following structure R a -R e Any of:

[0048]

[0049] n=1-10.

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

[0051]

[0052] The synthesis method of the chiral viologen derivative is specifically as follows: the precursor A and XR are dissolved in a solvent and reacted at 120°C for 24 hours to obtain a reaction solution, the reaction is cooled to room temperature, the reaction mixture is poured into a beaker, vigorously stirred, deionized water is added, ethanol and acetone are slowly added dropwise, filtered, and the product is precipitated by the difference in polarity. Dry in an oven at 60°C for 12 hours. Wherein X is one of Cl and Br;

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

[0054] R for R a to R e Any one of .

[0055] Preferably, R2, R5, R7, R 10 , R 11 , R 12 =0

[0056] Preferably, n=1.

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

[0058] Example

[0059] Take n = 1, R2 = 0, R5 = 0, R7 = 0, R 10 =0, R 11 =0, R 12 =0, R = R c , X=Cl, the supporting electrolyte is NaCl, the concentration is 1M, 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 React in 20mL water at 120℃ for 24h to obtain a reaction solution. Cool the reaction mixture to room temperature, pour the reaction mixture into a beaker, stir vigorously, add 20mL deionized water, slowly drop 300mL ethanol, 50mL acetone, filter, and dry in an oven at 60℃ for 12h. The equivalent ratio of precursor A0 and Cl-R is 1:2.5. The products obtained are named R-diol-Vi, S-diol-Vi and RS-diol-Vi, and the yields of the obtained products are similar, with an average of 50.94g and a yield of 95%. The structural formulas of the three diol-Vi are as follows:

[0062]

[0063] The H-NMR spectrum data of the three diol-Vi prepared in this example 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] Application of the prepared viologen derivative as negative electrode electrolyte material:

[0071] The three diol-Vi viologen derivatives prepared in the examples are used to prepare neutral aqueous organic flow battery electrode materials, which can be prepared by 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 is designed as a single cell structure. The assembly process is rigorous and meticulous. The following components are tightly fixed by bolts in sequence: positive terminal plate, positive insulating plate, positive conductive plate, positive liquid flow frame, positive graphite felt, positive gasket, anion exchange membrane, negative gasket, negative graphite felt, negative liquid flow frame, negative conductive plate, negative insulating plate, until the negative terminal plate. After the assembly is completed, all bolt connections need to be carefully checked for stability. Any looseness should be reinforced in time to ensure the tightness of the overall structure.

[0074] Before the formal test, a double inspection of sealing performance and pressure bearing capacity is required. To this end, two additional liquid storage bottles are connected to the assembled fixture system and a peristaltic pump is configured for circulation operation for two hours. During this process, it is necessary to pay close attention to whether there is any liquid leakage in the system, and check whether the liquid volume remains unchanged before and after the cycle. If the system successfully passes these two tests, that is, it is confirmed that there is no leakage and the volume is constant, it can be considered ready for subsequent use. On the contrary, if any leakage or volume change problem is found, the test must be stopped immediately, and the position and tightness of each component must be readjusted until all problems are resolved and passed the inspection again.

[0075] Step 2: Preparation of electrode materials,

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

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

[0078] Take 2.83g of three diol-Vi and 3.46g of MiAcNH-TEMPO and dissolve them in 5mL and 13mL of 1M NaCl solution respectively, stir or ultrasonicate to make them completely dissolved, the concentration of the two in the NaCl solution is 1.5M and 0.8M. The volume ratio between the mixed solution formed by the two is 1:2.6 to ensure that diol-Vi is fully charged and discharged. Bubble argon for 10 minutes, and the derivatives diol-Vi and MiAcNH-TEMPO are used as the battery anode electrolyte and cathode electrolyte, respectively, referred to as 1.5M diol-Vi / 0.8MMiAcNH-TEMPO.

[0079] Step 3: Assemble the neutral aqueous organic redox flow battery and perform performance testing;

[0080] Place the fixture prepared in step 1 and the solution in step 2 in the 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 then you can perform the charge and discharge test.

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

[0082] Therefore, the above battery tests show that this type of molecule has excellent stability. The R-diol-Vi and S-diol-Vi after chiral separation have greater molecular water solubility, up to 2.76M, and a larger theoretical capacity, which can test batteries with larger concentrations. This type of chirally split viologen derivative can be used as the anode electrolyte of a neutral aqueous organic liquid flow battery.

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

[0084]

[0085] (wherein the value of n is 1-10) etc. can also be modified to improve the solubility by chiral separation to obtain a better anolyte material.

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

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

[0088] The present invention discloses a method for improving electrolyte solubility through chiral splitting strategy. After the viologen molecule is split, its solubility is improved, and TEMPO derivatives or ferrocene are used as cathode electrolytes. The electrolyte materials are dissolved in 1M NaCl to increase the conductivity of the solution, and DSVN membrane is used as an anion exchange membrane to form a neutral aqueous organic flow battery with single or double electron storage. With Ar=Ar0, n=1, R=R a , X=Cl as an example, recorded as diol-Vi, when the current density is 60mA / cm 2 At a concentration of 1.5 M, the neutral aqueous organic flow battery based on R-diol-Vi / MiAcNH-TEMPO showed good cycling stability over 200 cycles. After 200 cycles, the capacity retention rate was 96.67% and the single-cycle capacity decay rate was 0.0167%.

[0089] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A chiral viologen derivative for improving electrolyte solubility, characterized in that: The structural formula is as follows: Wherein, X represents the counterparticle, which is Cl or Br; R1 and R6 are hydrophilic groups capable of chiral separation, including the following structures R a -R e Any of: n is 1 to 10; R2, R5, R7 and R 10 Any one of -Me, -OMe, -OEt, -COOH and -COONH4; R3, R4 and R8, R9 are connected via S, Se, Te or a double bond.

2. The chiral viologen derivative for improving electrolyte solubility according to claim 1, characterized in that: Structure R a -R e The structure is as follows by chiral resolution: n is 1 to 10.

3. A chiral viologen derivative for improving electrolyte solubility according to claim 1 or 2, characterized in that: The structural formula is shown below:

4. Use of the chiral viologen derivative for improving electrolyte solubility according to any one of claims 1 to 3 in the preparation of negative electrode electrolyte materials for neutral aqueous organic redox flow batteries.

5. The use according to claim 4, characterized in that The chiral 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 the DSVN / AMVN membrane is used as the anion exchange membrane to prepare a single cell or a battery stack composed of multiple cells; wherein the single cell or the battery stack uses carbon felt as the positive and negative electrodes, and copper sheets and graphite plates as current collectors to form a neutral aqueous liquid flow battery.

6. The use according to claim 5, 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.

7. The use according to claim 5, characterized in that The concentration of the supporting electrolyte is 0.5-2 mol / L.

8. The method for synthesizing a chiral viologen derivative for improving electrolyte solubility according to any one of claims 1 to 3, characterized in that: include: Precursors A and XR are dissolved in water, reacted at 120°C for 12-24 hours to obtain a reaction solution, cooled to room temperature and stirred evenly, then water is added, and then ethanol and acetone are slowly added dropwise, the product is precipitated by the difference in solvent polarity, and then filtered and dried to obtain the target viologen derivative; The structural formula of precursor A is as follows: R2, R5, R7 and R 10 Any one of -Me, -OMe, -OEt, -COOH and -COONH4; R3, R4 and R8, R9 are connected by S, Se, Te or double bonds; The structural formula of XR is shown in any of the following structures: X represents a counter particle, which is Cl or Br.

9. The method for synthesizing a chiral viologen derivative for improving electrolyte solubility according to claim 8, characterized in that: The structural formula of XR is specifically selected as follows:

10. The method for synthesizing a viologen derivative according to claim 8, characterized in that: The molar ratio of precursor A to XR is 1:2 to 2.5.

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