Cathode organic electrolyte with phenothiazine quaternary ammonium salt structure as well as preparation method and application of cathode organic electrolyte

Abstract

The invention belongs to the field of new energy, and particularly relates to a cathode organic electrolyte with a phenothiazine quaternary ammonium salt structure and a preparation method and application of the cathode organic electrolyte with the phenothiazine quaternary ammonium salt structure. Carrying out methylation reaction on the product and methyl iodide to obtain phenothiazine quaternary ammonium salt iodide, and carrying out ion exchange to obtain a final product. The cathode organic electrolyte with the phenothiazine quaternary ammonium salt structure has the characteristics of high positive electrode potential, electrochemical reversibility and water solubility. And the cathode organic electrolyte of the all-aqueous flow battery has good solubility, and is beneficial to improving the energy and power density of the flow battery. The cathode organic electrolyte can be applied to the field of new energy as a cathode organic electrolyte of a flow battery.

Description

Technical Field

[0001] The invention belongs to the field of new energy, and in particular relates to a cathode organic electrolyte with a phenothiazine quaternary ammonium salt structure, and a preparation method and application thereof. Background Art

[0002] Liquid flow batteries have the advantages of high energy conversion efficiency, high power density and long cycle life. Liquid flow batteries store electroactive materials in external containers, separated from the electrode stack, and can be stored independently without increasing the cost of the entire system. Depending on the electrolyte, liquid flow batteries are divided into aqueous and non-aqueous liquid flow batteries. Compared with non-aqueous liquid flow batteries, aqueous liquid flow batteries use water as a medium, have high safety, are green and environmentally friendly, low cost, and are more suitable for large-scale energy storage applications.

[0003] The energy density of a flow battery depends on the concentration (solubility) of the active material in the electrolyte, the number of electrons participating in the redox reaction, and the operating voltage, which is determined by the potential difference between the oxidation reaction at the cathode and the reduction reaction at the anode. Therefore, in order to maximize the energy density of a flow battery, materials with high solubility and high redox potential are required.

[0004] Phenothiazine and its derivatives have good electron donating properties, non-planar spatial geometric structures and good electrochemical stability. However, there are few reports on the use of phenothiazine derivatives as organic electrolytes for the cathode of aqueous liquid flow batteries. Existing phenothiazine derivatives are only used as electrode materials for solar cells and have extremely low or no water solubility, resulting in the energy density of the system still cannot meet the requirements of practical applications. Summary of the invention

[0005] The purpose of the present invention is to provide a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure and a preparation method, and to describe their application as cathode organic electrolytes for all-aqueous flow batteries. A cathode material phenothiazine quaternary ammonium salt having positive electrode potential, electrochemical reversibility and water solubility characteristics was synthesized, and a highly water-soluble all-aqueous flow battery was designed using methyl viologen as an anolyte. The all-aqueous flow battery, taking advantage of the high water solubility of both cathode and anode materials, can provide higher energy and power density for the flow battery.

[0006] In order to achieve the above object, the structural formula of the cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure of the present invention is shown in formula (I):

[0007]

[0008] The structure of R can be straight chain or branched chain, saturated or unsaturated, and the carbon chain length of R is between C 1 ~C 8When the length of the carbon chain is extended, the molecular weight of the overall structure increases, and the water solubility and unit molar solubility of the structure itself will decrease, but the corresponding risk of the organic electrolyte as a cathode penetrating the ion exchange membrane of the flow battery will decrease. Conversely, when the carbon chain length is shortened, the molecular weight of the overall structure decreases, the water solubility and unit molar solubility of the structure itself will increase, and the risk of the organic electrolyte as a cathode penetrating the ion exchange membrane of the flow battery will increase.

[0009] R is preferably C 1 -C 4 Saturated straight-chain or branched-chain aliphatic alkanes.

[0010] When X is a halogen, it refers to a halogen element, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts).

[0011] The technical solution adopted by the present invention is: using cheap and easily available industrial-grade phenothiazine as a starting material, and through a nucleophilic substitution reaction between a halide and phenothiazine under base catalysis, a water-soluble group is attached to the phenothiazine structure. The synthetic scheme selected by the present invention is simple and reliable, and the raw materials are cheap and easily available. It is mainly divided into the following steps:

[0012]

[0013] (1) in a solvent and optionally in the presence of a base and / or a phase transfer catalyst, a nucleophilic substitution reaction occurs between phenothiazine and a compound of formula (IV) to obtain a compound of formula (III);

[0014] Wherein, the phase transfer catalyst is selected from one or more of benzyltriethylammonium chloride, tetrabutylammonium iodide, tetrabutylammonium bromide, trioctylmethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium iodide, and hexadecyltrimethylammonium bromide, and the added amount is 0.05-0.5 molar equivalent of phenothiazine;

[0015] The strength of the alkalinity is related to the activity of the leaving group, the choice of base is related to the nature of the solvent, whether to add a phase transfer catalyst, and what type of phase transfer catalyst to add are also related to the choice of base and solvent. 1 When X is iodine, iodine acts as a leaving group with high reaction activity. Potassium carbonate can be selected as a base and N,N-dimethylformamide as a solvent, without adding a phase transfer catalyst. 1 When it is chlorine, the reaction activity is significantly reduced. You can choose a stronger base, such as sodium hydride, and carry out the reaction in a non-polar solvent, such as toluene. You can also choose a relatively weaker sodium hydroxide and water as the solvent, and add tetrabutylammonium iodide as a phase transfer catalyst to enhance the reaction activity.

[0016] The base is selected from one or more of sodium hydride, potassium hydroxide, sodium hydroxide, potassium carbonate, potassium ethoxide, potassium tert-butoxide, and lithium diisopropylamide. Depending on the alkalinity, the amount of the base added is 1-5 molar equivalents of the amount of phenothiazine used.

[0017] The amount of the compound of formula (IV) added is 1-3 molar equivalents of phenothiazine; the reaction temperature is 50-120°C, and the reaction time is 1-16 hours.

[0018] (2) the compound of formula (III) undergoes a methylation reaction with methyl iodide in a solvent to obtain a phenothiazine quaternary ammonium salt of formula (II) iodide;

[0019] Iodomethane is selected as the methylating agent, and the amount of iodomethane added is 1-3 molar equivalents of the compound of formula (III); the reaction temperature is 0-50° C., and the reaction time is 1-12 hours.

[0020] The solvent may be one or more of the common ones such as water, methanol, ethanol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, acetonitrile, N,N-dimethylformamide, and dioxane.

[0021] (3) Using a strong base anion exchange resin of the hydroxide type, iodide ions can be replaced with hydroxide ions, and the corresponding quaternary ammonium salt can be obtained by adding the corresponding acid; or directly using the corresponding anion exchange resin for direct replacement, for example, using a strong base anion exchange resin of the chloride type can replace iodide ions with chloride ions.

[0022] Beneficial effects of the present invention:

[0023] The invention discloses a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure, which has the characteristics of high positive electrode potential, electrochemical reversibility and water solubility, and can be used as a cathode organic electrolyte for liquid flow batteries and applied in the field of new energy.

[0024] The organic electrolyte in the cathode of the flow battery has good solubility, which is conducive to improving the energy and power density of the flow battery. It also uses relatively cheap and readily available raw materials, and the synthesis process is simple and feasible, which is conducive to large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride (a) prepared in Example 4 was added to 1 mol L -1 CV graphs at different scan rates in KCl electrolyte; (b) Relationship between peak current density and scan rate (diffusion control); (c) -1 CV plot in KCl electrolyte at a larger potential window, scan rate 25 mV s -1 ; (d) at 1 mol L-1 Cyclic CV in KCl electrolyte (100 cycles), 100 mV s -1 .

[0026] Figure 2 (a) UV-visible absorption spectra of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride at different concentrations and saturated concentration diluted (diluted 100,000 times) N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride in deionized water prepared in Example 4; (b) line graph with the maximum absorbance recorded at λ=251 nm.

[0027] Figure 3 CV test graph of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride in Example 5 when the electrolyte pH is 0-9.

[0028] Figure 4 Capacity retention diagram of the NEt-PXZ / / MV aqueous organic liquid flow battery assembled in Example 6.

[0029] Figure 5 Capacity retention rate diagram of NEt-PXZ / / MV non-aqueous organic liquid flow battery assembled in Example 7. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with embodiments, but is not limited thereto.

[0031] Example 1 Preparation of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium chloride

[0032] 1.1N,N-Dimethyl-2-(10H-phenothiazin-10-yl)ethane-1-amine

[0033] Dissolve 5g of phenothiazine in 35mL of toluene, cool to 15℃, control the internal temperature not to exceed 25℃, add 2.11g of sodium hydride (37.6mmol, 1.5eq.) in 5 batches, maintain the internal temperature, and stir for 1 hour. In addition, add 7.23g of 2-chloroethyldimethylamine hydrochloride (CAS No.: 4584-46-7) into water and stir to dissolve, add 2.82g of potassium hydroxide (50.2mmol, 2eq.), stir to dissolve, and extract the free 2-chloroethyldimethylamine twice with toluene. Slowly drop the toluene solution of 2-chloro-N,N-dimethylethylamine obtained by extraction into the reaction system, and continue stirring at 40℃ for 2 hours after the addition is completed. Add 35mL of purified water, wash once, wash once with saturated brine, add anhydrous sodium sulfate to remove water, and concentrate to dryness. After purification by column chromatography, 3.73 g of yellow oily N,N-dimethyl-2-(10H-phenothiazin-10-yl)ethane-1-amine was obtained with a yield of 55%.

[0034] 1.2N,N,N-Trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium iodide

[0035] The oil obtained in 1.1 was dissolved in methyl tert-butyl ether, the temperature was raised to 35°C, 3.92 g of methyl iodide (27.6 mmol, 2 eq.) was slowly added dropwise, the internal temperature was maintained and stirred for 8 hours, the temperature was lowered and filtered, and 10 mL of methyl tert-butyl ether was rinsed and dried under reduced pressure to obtain 5.4 g of light yellow powdered N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium iodide with a yield of 95%.

[0036] 1.3N,N,N-Trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium chloride

[0037] 5 g of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium iodide was dissolved in 200 mL of deionized water, and ion exchange was performed using a chloride-type strong base anion exchange resin. The aqueous solution after the ion exchange was dried under reduced pressure to obtain N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium chloride.

[0038] Example 2 Preparation of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium bromide

[0039] 2.1N,N-Dimethyl-2-(10H-phenothiazin-10-yl)propan-1-amine

[0040] Add 5 g of phenothiazine, 50 mL of 50% sodium hydroxide aqueous solution, and 0.93 g of tetrabutylammonium bromide (2.5 mmol, 0.1 eq.) to the reaction flask in sequence, stir evenly, heat to 70°C, add 7.93 g of chloro-1-(N,N-dimethyl)propylamine hydrochloride (CAS No.: 5407-04-5) (50.2 mmol, 2 eq.) in 3 batches, continue to maintain the internal temperature and stir for 2 hours, extract twice with ethyl acetate, wash once with water and saturated sodium chloride solution respectively, remove water with anhydrous sodium sulfate, and concentrate to dryness to obtain a brown-red oil, which is directly used in the next reaction without purification.

[0041] 2.2N,N,N-Trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium iodide

[0042] The oil obtained in 2.1 was dissolved in 50 mL of acetone, the temperature was raised to 40°C, and 7.12 g of iodomethane (50.2 mmol, 2 eq, since it was not purified in the previous step, the equivalent was calculated based on the amount of phenothiazine added in 2.1) was slowly added dropwise. After the addition was completed, the internal temperature was maintained and stirred for 5 hours, filtered, rinsed with 10 mL of acetone, and dried under reduced pressure to obtain 8.77 g of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium iodide as an off-white powder (yield: 82%).

[0043] 2.3N,N,N-Trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium bromide

[0044] 5 g of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium iodide was dissolved in 200 mL of deionized water, and ion exchange was performed using a hydroxide-type strong base anion exchange resin. 1 M hydrobromic acid was added dropwise to the aqueous solution after the ion exchange to neutralize the hydroxide, and the mixture was dried under reduced pressure to obtain N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)propane-1-ammonium bromide.

[0045] Example 3 Preparation of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride

[0046] 3.1N,N-Dimethyl-1-(10H-phenothiazin-10-yl)propyl-2-amine

[0047] Dissolve 5 g of phenothiazine in 40 mL of N,N-dimethylformamide, stir until dissolved, add 10.4 g of anhydrous potassium carbonate (75.3 mmol, 3 eq.), heat to 60 ° C and stir for 1 hour, slowly add 6.25 g of 2-dimethylaminopropane bromide (CAS No.: 53929-74-1) (37.6 mmol, 1.5 eq.), maintain the internal temperature, continue stirring for 7 hours, add water and dichloromethane, collect the dichloromethane layer, wash with water 3 times, dry over anhydrous magnesium sulfate, and concentrate to dryness to obtain a brown oily N,N-dimethyl-1-(10H-phenothiazin-10-yl)propyl-2-amine crude product, which is directly used in the next step without purification.

[0048] 3.2N,N,N-Trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium iodide

[0049] The oil obtained in 3.1 was dissolved in 50 mL of acetonitrile, the temperature was raised to 45°C, and 7.12 g of iodomethane (50.2 mmol, 2 eq, since it was not purified in the previous step, the equivalent was calculated based on the amount of phenothiazine added in 3.1) was slowly added dropwise. After the addition was completed, the internal temperature was maintained and stirred for 3 hours, filtered, rinsed with 10 mL of acetone, and dried under reduced pressure to obtain 8.45 g of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium iodide as an off-white powder (yield: 79%).

[0050] 3.3N,N,N-Trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride

[0051] 5 g of N,N,N-trimethyl-2-(10H-phenothiazin-10-yl)ethane-1-ammonium iodide was dissolved in 200 mL of deionized water, and ion exchange was performed using a hydroxide-type strong base anion exchange resin. 1 M hydrochloric acid was added dropwise to the aqueous solution after the ion exchange to neutralize the hydroxide, and the mixture was dried under reduced pressure to obtain N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride.

[0052] Example 4 Electrochemical performance test:

[0053] Weigh 29.9 mg of the N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride material prepared in Example 3 above and dissolve it in 100 mL of 1 mol L -1 The electrochemical performance of N,N,N-trimethyl-1-(10H-phenothiazine-10-yl)propyl-2-ammonium chloride was tested in a three-electrode system with a glassy carbon electrode as the working electrode, a mercury / mercuric oxide electrode as the reference electrode, and a platinum electrode as the counter electrode. The entire test process was under nitrogen protection. The electrolyte was 1 mol L -1KCl solution, neutral electrolyte.

[0054] Figure 1 This is the CV graph of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride in a neutral electrolyte. The concentration of the electrolyte is 1 mol L -1 The scan rate was 25 mV s -1 As can be seen from the figure, under neutral conditions, N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride has good redox electroactivity, and its equilibrium potential is 0.902V.

[0055] Figure 2 (a) UV-visible absorption spectra of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride at different concentrations and saturated concentration diluted (100,000 times) N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride in deionized water; (b) Line graph between the maximum absorbance recorded at λ = 251 nm. The solubility of N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride in 1L deionized water was calculated to be 2.69M at 25±1℃.

[0056] Example 5

[0057] When the electrochemical performance test was performed using a three-electrode system, 1 mM N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride was weighed and dissolved in 100 mL of 1 M NaCl aqueous solution as the initial solution, and the initial pH value was measured to be 7. The pH was then adjusted with diluted hydrochloric acid solution and sodium hydroxide solution for CV testing.

[0058] Figure 3 This is the CV test graph of N,N,N-trimethyl-1-(10H-phenothiazine-10-yl)propyl-2-ammonium chloride in electrolyte pH = 0-9. It can be seen from the figure that the electrochemical performance of N,N,N-trimethyl-1-(10H-phenothiazine-10-yl)propyl-2-ammonium chloride material is not affected in the pH range from strong acid to weak base.

[0059] Example 6: Assembly of an all-aqueous organic flow battery based on N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride cathode electrolyte

[0060] The N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride prepared in Example 3 was used as the cathode electrolyte, methyl viologen was used as the anode electrolyte, the pretreated DSV membrane was used as the ion exchange membrane of the flow battery, and 1M KCl was used as the cathode and anode supporting electrolyte. The charge and discharge test of the above-assembled aqueous organic flow battery was carried out using the Xinwei battery test system.

[0061] The entire battery testing process was carried out under nitrogen protection, which prevented oxygen in the air from participating in the electrochemical reaction and affecting battery performance. The voltage range was 0.5-1.5V and the flow rate of the electrolyte was 60mL / min.

[0062] Figure 4 Example 6 Assembled N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride

[0063] / / MV aqueous organic liquid flow battery rate data chart and capacity retention rate chart, the charge and discharge current is 50mA, after 300 cycles, the average current efficiency reaches 88.56%, and the average energy efficiency reaches 63.52%. This fully demonstrates that the aqueous organic liquid flow battery based on phenothiazine quaternary ammonium salt cathode organic electrolyte has a good application prospect.

[0064] Example 7: Assembly of a non-aqueous organic flow battery based on N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride cathode electrolyte

[0065] The N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride prepared in Example 3 was used as the cathode electrolyte, methyl viologen was used as the anode electrolyte, the pretreated DSV membrane was used as the ion exchange membrane of the flow battery, 1M KCl was used as the cathode supporting electrolyte, and acetonitrile was used as the cathode solvent. The above-assembled aqueous organic flow battery was charged and discharged using the Xinwei battery test system.

[0066] The entire battery testing process was carried out under nitrogen protection, which prevented oxygen in the air from participating in the electrochemical reaction and affecting battery performance. The voltage range was 0.9-2.2V and the flow rate of the electrolyte was 60mL / min.

[0067] Figure 5 Example 7 Assembled N,N,N-trimethyl-1-(10H-phenothiazin-10-yl)propyl-2-ammonium chloride

[0068] / / MV non-aqueous organic liquid flow battery capacity retention rate diagram, the charge and discharge current is 50mA, after 300 cycles, the average current efficiency reaches 87.76%, and the average energy efficiency reaches 63.39%. This fully demonstrates that the organic electrolyte based on the phenothiazine quaternary ammonium salt cathode also has good application prospects in the field of non-aqueous organic liquid flow batteries.

[0069] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure, characterized in that: The cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure has a structure shown in formula (I): Wherein, R is a saturated or unsaturated straight chain or branched alkyl group having carbon atoms of C1 to C8, and X is a halogen.

2. A method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 1, characterized in that: The reaction formula of the preparation method is: Wherein, R is a saturated or unsaturated straight or branched alkyl group having carbon atoms of C1 to C8, and X is a halogen; The specific steps are as follows: (1) reacting phenothiazine with a compound of formula (IV) in a solvent and in the presence of a base and / or a phase transfer catalyst to obtain a compound of formula (III); (2) reacting the compound of formula (III) with iodomethane in a solvent to obtain a phenothiazine quaternary ammonium salt of formula (II) iodide; (3) using a hydroxide-type strong base anion exchange resin to replace the iodide ion of the iodide of formula (II) with hydroxide, and adding a corresponding acid to obtain a corresponding quaternary ammonium salt; or directly using a corresponding anion exchange resin to replace to obtain a corresponding quaternary ammonium salt.

3. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (1), the amount of the compound of formula (IV) added is 1-3 molar equivalents of phenothiazine.

4. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (1), the phase transfer catalyst is selected from one or more of benzyltriethylammonium chloride, tetrabutylammonium iodide, tetrabutylammonium bromide, trioctylmethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium iodide, and hexadecyltrimethylammonium bromide, and the added amount is 0.05-0.5 molar equivalent of phenothiazine.

5. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (1), the base is selected from one or more of sodium hydride, potassium hydroxide, sodium hydroxide, potassium carbonate, potassium ethoxide, potassium tert-butoxide, and lithium diisopropylamide, and the added amount is 1-5 molar equivalents of phenothiazine.

6. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (1), the reaction temperature is 50-120° C. and the reaction time is 1-16 hours.

7. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (2), the amount of iodomethane added is 1-3 molar equivalents of the compound of formula (III); the reaction temperature is 0-50° C., and the reaction time is 1-12 hours.

8. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: The organic solvent used in step (1) and step (2) is selected from one or more of water, methanol, ethanol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, acetonitrile, N,N-dimethylformamide and dioxane.

9. The method for preparing a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 2, characterized in that: In step (3), the anion exchange resin is a chloride-type strong base anion exchange resin.

10. An application of a cathode organic electrolyte having a phenothiazine quaternary ammonium salt structure according to claim 1, characterized in that: The cathode organic electrolyte with the phenothiazine quaternary ammonium salt structure is used as the cathode organic electrolyte of the liquid flow battery.

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