Positive electrode active electrolyte based on phenoxazine quaternary ammonium salt and its aqueous all-organic redox flow battery

Abstract

The present invention belongs to the field of flow batteries, and specifically provides a positive electrode active electrolyte based on phenoxazine quaternary ammonium salt and an all-aqueous organic flow battery. Phenoxazine and 1-halo-R-group-N,N-dimethylamine undergo a nucleophilic substitution reaction under the action of a phase transfer catalyst, and then react with methyl iodide to obtain phenoxazine quaternary ammonium salt iodide, which is then subjected to ion exchange to obtain phenoxazine quaternary ammonium salt chloride as the positive electrode active electrolyte. While retaining the electrochemical properties such as the electrochemical activity and high positive potential of the phenoxazine core and the physicochemical properties such as high chemical / thermal stability, the phenoxazine quaternary ammonium salt effectively improves the water solubility of the material, so that it can be used as a positive electrode active electrolyte material for high-capacity aqueous flow batteries. The aqueous organic flow battery obtained by combining with a viologen-based negative electrode active electrolyte has high energy efficiency and a long cycle life.

Description

Technical Field

[0001] The present invention belongs to the field of liquid flow batteries, and specifically provides a positive electrode active electrolyte based on phenoxazine quaternary ammonium salt and an aqueous all-organic liquid flow battery thereof. Background Art

[0002] Flow batteries offer advantages such as high energy conversion efficiency, high power density, long cycle life, and flexible design. Flow batteries store the electroactive materials in an external container, spatially separated from the battery pack, thereby decoupling power output from energy output. Flow batteries are categorized into aqueous and non-aqueous flow batteries, depending on the electrolyte solvent. Compared to non-aqueous flow batteries, aqueous flow batteries use water as a dielectric, offering high safety, environmental friendliness, and low cost, making them more suitable for large-scale energy storage applications. Over the past decade, organic-based redox-active materials for aqueous flow batteries have flourished, with a diverse range of organic molecules reported, including quinones, viologens, nitrogen-containing aromatic heterocyclic compounds, ferrocenes, nitroxide radicals (TEMPO), and azobenzenes. Although these reported organic materials exhibit high water solubility, excellent electrochemical reversibility, and suitable operating potentials, their energy density and high-current cycling performance still require further improvement.

[0003] The energy density of a flow battery depends on the effective concentration of the active material in the electrolyte system, the number of electrons involved in the redox reaction, and the potential difference between the positive and negative active electrolyte materials. Therefore, to maximize the energy density of a flow battery, it is necessary to develop positive active electrolyte materials with high solubility and high potential, and negative active electrolyte materials with high solubility and low potential. Due to molecular structure limitations, most organic materials have low redox potentials and can only be used as negative active electrolyte materials in flow batteries. Currently, only two derivative materials, ferrocene and TEMPO, have been reported as positive organic active electrolyte materials for neutral system flow batteries. Therefore, developing positive organic active electrolyte materials with high solubility and high electrochemical activity is one of the major challenges that need to be addressed in organic aqueous flow batteries.

[0004] Phenoxazine molecules have a high redox potential and fast electrochemical reaction kinetics. However, since phenoxazine molecules themselves are insoluble in water, they cannot be directly used in aqueous flow batteries. Summary of the Invention

[0005] The present invention aims to introduce a highly water-soluble quaternary ammonium salt group into the molecular structure of phenoxazine through nucleophilic substitution and subsequent quaternization reaction, thereby synthesizing a phenoxazine quaternary ammonium salt with high potential, high electrochemical reversibility, and high water solubility for use as a positive electrode active electrolyte material in liquid flow batteries. Furthermore, this can be combined with a viologen-based negative electrode active electrolyte to construct a high-performance neutral aqueous all-organic liquid flow battery.

[0006] The technical solution adopted in the present invention is:

[0007] The positive electrode active electrolyte based on phenoxazine quaternary ammonium salt has the structure shown in the following formula:

[0008]

[0009] In the structural formula of the phenoxazine quaternary ammonium salt, the structure of R includes but is not limited to a C1-6 straight chain or branched chain alkyl group.

[0010] The synthesis steps of phenoxazine quaternary ammonium salt are as follows:

[0011] (1) Phenoxazine, a phase transfer catalyst, and an alkaline solution were added to a reaction flask in sequence. After mixing, 1-halogenated-R-yl-N,N-dimethylamine was slowly added dropwise. After nucleophilic substitution reaction, an oily intermediate product was obtained, which was directly used for subsequent reactions without purification.

[0012] Among them, the phase transfer catalyst includes but is not limited to benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide, and the amount of the catalyst added is 5.0wt.% to 10.0wt.% of the total mass of phenoxazine and 1-halo-R-group-N,N-dimethylamine.

[0013] During the synthesis process, the base includes but is not limited to inorganic bases such as potassium hydroxide, sodium hydroxide, and calcium hydroxide, or organic bases such as potassium ethoxide, potassium tert-butoxide, and lithium diisopropylamide. The concentration of the base solution is 3 to 12 mol L -1 .

[0014] In the 1-halogenated-R-based-N,N-dimethylamine used in the reaction, the structure of R includes but is not limited to a C1-6 straight or branched alkyl group, and the molar ratio of the reactants phenoxazine and 1-halogenated-R-based-N,N-dimethylamine is 1:1 to 1:3.

[0015] The temperature of the nucleophilic substitution reaction is 50-120° C., and the reaction time is 6-12 h.

[0016] (2) The oily intermediate is dissolved in a polar solvent, and iodomethane is added to react to obtain phenoxazine quaternary ammonium salt iodide.

[0017] The polar solvent in the reaction includes, but is not limited to, acetone, ethyl acetate, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0018] The amount of iodomethane used is twice the molar amount of the raw material phenoxazine.

[0019] The reaction temperature is 20-50 °C, and the reaction time is 12-24.

[0020] (3) Dissolve the phenoxazine quaternary ammonium iodide in deionized water, and perform ion exchange with an ion exchange resin to obtain the phenoxazine quaternary ammonium chloride.

[0021] The ion exchange resin is a chlorine-form strong-base ion exchange resin.

[0022] The present invention also provides a neutral aqueous all-organic flow battery, which is composed of a negative electrode active material, a positive electrode active material, a supporting electrolyte, a separator, a porous carbon electrode, and a current collector.

[0023] The positive electrode active material of the aqueous flow battery is the phenoxazine quaternary ammonium salt prepared above, and the negative electrode active material is a viologen derivative.

[0024] The supporting electrolyte is ammonium chloride, sodium chloride, potassium chloride, or a mixture thereof. The pH of the supporting electrolyte solution is 5-8, and the solvent is water. The concentration of the supporting electrolyte is 1 mol / L -1 .

[0025] The separator is an anion-conducting membrane.

[0026] The porous carbon electrode is carbon paper, carbon cloth, carbon felt, or porous graphene felt.

[0027] Advantages of the present invention:

[0028] The phenoxazine quaternary ammonium salt disclosed in the present invention is obtained by introducing a highly water-soluble quaternary ammonium salt group through a chemical reaction on the phenoxazine skeleton. While retaining the electrochemical properties such as the electrochemical activity and high positive potential of the phenoxazine core, and the physicochemical properties such as high chemical / thermal stability, the water solubility of the material is effectively improved.

[0029] The present invention proposes a synthetic route for a hydrophilic functionalized phenoxazine electroactive material - phenoxazine quaternary ammonium salt. Its synthesis steps and post-treatment processes are simple, the cost is low, and it is conducive to large-scale manufacturing. And it is used as the positive electrode active substance of an aqueous all-organic flow battery for the first time, and an aqueous all-organic flow battery obtained by combining with the negative electrode active material viologen derivative. Due to the strong hydrogen bond interaction between the quaternary ammonium salt group and water, the synthetic design of introducing a highly water-soluble quaternary ammonium salt group on the phenoxazine skeleton effectively improves the water solubility of the phenoxazine-based material while retaining the electrochemical activity of the phenoxazine core unit, thus meeting the requirements of the flow battery for the system energy density in practical applications. Description of the Drawings

[0030] Figure 1 1H NMR spectrum of the ethyl phenoxazine quaternary ammonium salt (NEt-PXZ) prepared in Example 1.

[0031] Figure 2 Cyclic voltammetry (CV) diagram of the ethylphenoxazine quaternary ammonium salt prepared in Example 1 in a KCl solution. The concentration of the KCl solution is 1 mol / L -1 , and the scan rate is 25 mV / s -1 .

[0032] Figure 3 CV diagrams of the ethylphenoxazine quaternary ammonium salt prepared in Example 1 in 1 mol / L -1 KCl: (a) CV diagrams at different scan rates; (b) relationship diagram between peak current density and scan rate; (c) CV diagrams under different potential windows, with a scan rate of 25 mV / s -1 ; (d) CV diagram of 100 cyclic scans, with a scan rate of 100 mV / s -1 .

[0033] Figure 4 CV diagrams of the ethylphenoxazine quaternary ammonium salt prepared in Example 1 in electrolytes with different pH values.

[0034] Figure 5 Ultraviolet-visible absorption spectra of the ethylphenoxazine quaternary ammonium salt prepared in Example 1 in deionized water: (a) spectra at different concentrations; (b) spectrum of a 33333-fold dilution at the saturated concentration; (c) relationship diagram between absorbance and concentration at the maximum absorption wavelength of 319 nm.

[0035] Figure 6 Rate performance data and capacity retention diagram of the NEt-PXZ / / methyl viologen (MV) all-aqueous organic redox flow battery assembled in Example 2.

[0036] Figure 7 1H NMR spectrum of the propylphenoxazine quaternary ammonium salt (NPr-PXZ) prepared in Example 3.

[0037] Figure 8 CV diagram of the propylphenoxazine quaternary ammonium salt prepared in Example 3 in a KCl solution. The concentration of the KCl solution is 1 mol / L -1 , and the scan rate is 25 mV / s -1 .

[0038] Figure 9 CV diagrams of the propylphenoxazine quaternary ammonium salt prepared in Example 3 in 1 mol / L -1 KCl: (a) CV diagrams at different scan rates; (b) relationship diagram between peak current density and scan rate; (c) CV diagrams under different potential windows, with a scan rate of 25 mV / s -1 ; (d) CV diagram of 100 cycles, with a scan rate of 100 mV / s -1 .

[0039] Figure 10Ultraviolet-visible absorption spectra of the propylphenoxazine quaternary ammonium salt (a) prepared in Example 3 at different concentrations; (b) ultraviolet-visible absorption spectrum after dilution by 1750 times at the saturated concentration; (c) graph of the relationship between absorbance and concentration at the maximum absorption wavelength of 319 nm.

[0040] Figure 11 Rate data and capacity retention graph of the NPr-PXZ / / MV aqueous all-organic flow battery assembled in Example 4. Detailed implementation manners

[0041] The present invention will be further described below in conjunction with examples, but not limited thereto.

[0042] Preparation of the ethylphenoxazine quaternary ammonium salt (NEt-PXZ) positive electrode active material in Example 1

[0043] (1) Material preparation

[0044] First step: Add phenoxazine (10.08 g, 0.055 mol), tetrabutylammonium bromide (1.61 g, 0.005 mol), and 3 mol L -1 NaOH aqueous solution (250 mL) in sequence, slowly add 2-chloro-N,N-dimethylethylamine (17.64 g, 0.165 mol), heat to 50 °C and stir the reaction overnight. Monitor the reaction by thin-layer chromatography until completion. The developing agent ratio of thin-layer chromatography is ethyl acetate: petroleum ether = 1:1. After cooling to room temperature, extract with dichloromethane 5 times, combine the organic phases, dry with anhydrous magnesium sulfate and then filter, and rotary evaporate under reduced pressure to dryness to obtain the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)ethan-1-amine. Without purification, directly proceed to the next reaction;

[0045] Second step: Dissolve the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)ethan-1-amine in acetone, slowly add methyl iodide (35.19 g, 0.109 mol) at room temperature, and react in a sealed container at 20 °C for 24 h. After filtration, wash with 20 mL of acetone and dry under reduced pressure to obtain 18.17 g of yellowish-brown powdery N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)ethan-1-ammonium iodide.

[0046] Third step: Dissolve 5 g of N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)ethan-1-ammonium iodide in 200 mL of deionized water to obtain an aqueous solution. Then, at room temperature, use 1 mol L -1The chloride form strong base ion exchange resin soaked in NaCl aqueous solution for 12 h was used for ion exchange (the aqueous solution of N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)ethane-1-ammonium iodide was poured into the exchange column for passing through the column), and the exchanged aqueous solution was rotary evaporated to obtain N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)ethane-1-ammonium chloride (NEt-PXZ).

[0047] (2) Preparation of the active electrolyte solution

[0048] Weigh 30.4 mg of the above-mentioned ethyl phenoxazinium quaternary salt and dissolve it in 100 mL of 1 mol L -1 KCl solution (pH value is about 7.0) as the electrolyte solution. The glassy carbon electrode is used as the working electrode, the mercury / mercuric oxide electrode is used as the reference electrode, and the platinum plate electrode is used as the counter electrode. The electrochemical performance of the ethyl phenoxazinium quaternary salt is tested in a three-electrode system, and the whole test process is carried out under nitrogen protection.

[0049] Figure 1 It is the 1H NMR spectrum of the ethyl phenoxazinium quaternary salt positive electrode electrolyte prepared in Example 1. As can be seen from the figure, the characteristic peaks of various hydrogens in the 1H NMR spectrum of the ethyl phenoxazinium quaternary salt are clearly attributed, and there are no extra impurity peaks, indicating its high purity.

[0050] Figure 2 It is the CV diagram of the ethyl phenoxazinium quaternary salt in 1 mol L -1 KCl in Example 1, and the scanning rate is 25 mV s -1 . The ethyl phenoxazinium quaternary salt shows good redox electro-reversibility, and its equilibrium potential is 0.78 V.

[0051] Figure 3 It is the CV diagrams of the ethyl phenoxazinium quaternary salt in 1 mol L -1 KCl at different scanning rates, the relationship diagram between the peak current density and the scanning rate, the CV diagram under a larger potential window, and the CV diagram after 100 cycles in Example 1. The peak current is proportional to the square root of the scanning rate, indicating that the electrode process is diffusion-controlled. The CV diagram scanned under a larger potential window shows that the ethyl phenoxazinium quaternary salt has only a pair of redox peaks with good reversibility. After continuous cyclic scanning for 100 cycles, the peak potential and peak current change little, indicating good electrochemical stability of the ethyl phenoxazinium quaternary salt.

[0052] 1 mmol L -1 NEt-PXZ is dissolved in 100 mL of 1 mol L -1 NaCl as the initial active electrolyte solution, and its pH is measured to be 5.95. The pH value of the solution is adjusted with diluted hydrochloric acid or NaOH solution. Then the CV diagram of NEt-PXZ is measured using a three-electrode system.

[0053] Figure 4 This is the cyclic voltammogram (CV) of NEt-PXZ in the electrolyte with a pH range of 4 - 9. As can be seen from the figure, the redox potential of NEt-PXZ does not change with the change of pH, revealing that hydrogen ions or hydroxide ions do not participate in the redox reaction of NEt-PXZ.

[0054] Solubility test of NEt-PXZ in water. Aqueous solutions of NEt-PXZ with concentrations of 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1 mmol L -1 were prepared respectively, and the absorbance curves of the above solutions were measured using a UV-visible spectrophotometer. At the maximum absorbance, a linear dependence graph of absorbance and concentration was obtained according to the Lambert-Beer law. Furthermore, the concentration of the saturated aqueous solution of NEt-PXZ was measured.

[0055] Figure 5 These are the UV-visible absorption spectra of ethylphenoxazine quaternary ammonium salts with different concentrations in water, the UV-visible absorption spectra of the saturated concentration of ethylphenoxazine quaternary ammonium salts after dilution by 33333 times, and the absorbance-concentration relationship graph recorded at 319 nm. From the figure, it can be obtained that the solubility of ethylphenoxazine quaternary ammonium salt in water at room temperature is 2.56 mol L -1 .

[0056] Example 2 Assembly of an aqueous all-organic redox flow battery based on ethylphenoxazine quaternary ammonium salt as the positive electrode active electrolyte

[0057] Using the ethylphenoxazine quaternary ammonium salt prepared in Example 1 as the positive electrode active electrolyte material, MV as the negative electrode active electrolyte material, DSV membrane as the separator, and 1 mol L -1 KCl as the supporting electrolyte, an aqueous all-organic redox flow battery was assembled and subjected to charge-discharge cycle experiments. The battery tests were carried out entirely in a nitrogen glove box. The flow rate of the electrolyte was 60 mL min -1 . The voltage range was 0.4 - 1.4 V.

[0058] Figure 6 These are the rate performance graph and capacity retention graph of the assembled NEt-PXZ / / MV battery, with a current density of 10 mA cm -2 . After 100 charge-discharge cycles, the Coulombic efficiency was 88.6%, the energy efficiency was 63.5%, and the discharge capacity retention rate reached 77.3%, revealing that the battery based on phenoxazine quaternary ammonium salt as the positive electrode active electrolyte has high energy efficiency and long cycle life.

[0059] Example 3 Preparation of propylphenoxazine quaternary ammonium salt (NPr-PXZ) as the positive electrode active material

[0060] (1) Material preparation

[0061] Step 1: Add phenoxazine (10.08 g, 0.055 mol), trioctylmethylammonium chloride (2.02 g, 0.005 mol), and 12 mol / L -1 aqueous NaOH solution (250 mL) in sequence. Slowly add 3-chloro-N,N-dimethylpropylamine (19.91 g, 0.164 mol), heat to 120 °C, stir and react overnight. Monitor the reaction by thin-layer chromatography until completion. The developing agent ratio for thin-layer chromatography is ethyl acetate:petroleum ether = 1:1. After cooling to room temperature, extract five times with dichloromethane. Combine the organic phases, dry over anhydrous magnesium sulfate, filter, and rotary evaporate under reduced pressure to dryness to obtain the crude product of N,N-dimethyl-3-(10H-phenoxazin-10-yl)propylamine as an oil. Proceed directly to the next step without purification.

[0062] Step 2: Dissolve the crude product of N,N-dimethyl-3-(10H-phenoxazin-10-yl)propylamine in acetone, slowly add methyl iodide (35.19 g, 0.109 mol) dropwise at room temperature, keep the temperature constant at 20 °C, seal and react overnight (12 h), filter, wash with 20 mL of acetone, and dry under reduced pressure to dryness to obtain 21.72 g of N,N,N-trimethyl-3-(10H-phenoxazin-10-yl)propylamine iodide as an off-white powdery substance (the two-step yield is 97%).

[0063] Step 3: Dissolve 5 g of the off-white powdery N,N,N-trimethyl-3-(10H-phenoxazin-10-yl)propylamine iodide in 200 mL of deionized water, perform ion exchange with a chloride-form strong-base ion-exchange resin soaked in 1 M aqueous NaCl solution (same as Example 1), and rotary evaporate the exchanged aqueous solution to obtain N,N,N-trimethyl-3-(10H-phenoxazin-10-yl)propylamine chloride (NPr-PXZ).

[0064] (2) Preparation of the active electrolyte solution

[0065] Take 31.8 mg of the above-mentioned propylphenoxazine quaternary ammonium salt and dissolve it in 100 mL of 1 mol / L -1 NH4Cl solution as the electrolyte. Use a glassy carbon electrode as the working electrode, a mercury / mercuric oxide electrode as the reference electrode, and a platinum plate electrode as the counter electrode to test the electrochemical performance of the propylphenoxazine quaternary ammonium salt in a three-electrode system. The entire test process is under nitrogen protection.

[0066] Figure 7 1H NMR spectrum of the propylphenoxazine quaternary ammonium salt prepared in Example 3. As can be seen from the figure, the 1H NMR characteristic peaks of the propylphenoxazine quaternary ammonium salt correspond to the hydrogen positions in the structural formula, and there are no extra impurity peaks, indicating its high purity.

[0067] Figure 8is the CV diagram of propylphenoxazine quaternary ammonium salt in 1 mol L -1 of NH4Cl. The scanning rate is 25 mV s -1 . As can be seen from the figure, propylphenoxazine quaternary ammonium salt exhibits good redox electroactivity, and its standard potential is 0.69 V.

[0068] Figure 9 are the CV diagrams of the propylphenoxazine quaternary ammonium salt prepared in Example 3 at different scanning rates, the relationship diagram between peak current density and scanning rate, the CV diagram under a larger potential window, and the CV diagram after 100 cycles. The scanning rate is 100 mV s -1 . The peak current density of propylphenoxazine quaternary ammonium salt shows a linear relationship with the square root of the scanning rate, indicating that its electrochemical behavior is controlled by diffusion. Two pairs of well-shaped redox peaks appear on the CV diagram of propylphenoxazine quaternary ammonium salt under a larger potential window.

[0069] The solubility of propylphenoxazine quaternary ammonium salt in water was tested by the same method as in Example 1. Aqueous solutions of propylphenoxazine quaternary ammonium salt with concentrations of 0.2, 0.24, 0.28, 0.32, and 0.36 mmol L -1 were prepared respectively, and the absorbance curves of the above solutions were tested using a UV-visible spectrophotometer.

[0070] Figure 10 are the UV-visible absorption spectra of propylphenoxazine quaternary ammonium salt at different concentrations, the UV-visible absorption spectrum of the saturated solution of propylphenoxazine quaternary ammonium salt diluted 1750 times, and the relationship diagram between the maximum absorbance and concentration at 319 nm. The solubility of propylphenoxazine quaternary ammonium salt in water at room temperature is 0.81 mol L -1 .

[0071] Example 4

[0072] Assembly of an aqueous all-organic redox flow battery based on a propylphenoxazine quaternary ammonium salt positive electrode electrolyte

[0073] Using the propylphenoxazine quaternary ammonium salt prepared in Example 3 as the positive electrode active material, methyl viologen as the negative electrode active material, and an AEM membrane as the separator, 1 mol L -1 NH4Cl as the supporting electrolyte. Charge-discharge tests were carried out on the above battery. The battery tests were carried out in a glove box. The voltage range of the charge-discharge experiment was 0.3 - 1.3 V. The flow rate of the electrolyte was 60 mL min -1 .

[0074] Figure 11Rate performance and capacity retention of the NEt-PXZ / / MV battery assembled in Example 4. After 200 charge-discharge cycles, the Coulombic efficiency was 98.4% and the energy efficiency reached 82.9%. There was almost no decay in the discharge capacity, revealing that the battery based on the propylphenoxazine quaternary ammonium salt cathode active electrolyte has high energy efficiency and outstanding long cycle life.

[0075] Preparation of hexylphenoxazine quaternary ammonium salt cathode active material in Example 5

[0076] (1) Material preparation

[0077] First step: Successively add phenoxazine (10.08 g, 0.055 mol), tetrabutylammonium bromide (2.07 g, 0.005 mol), 3 mol L -1 NaOH aqueous solution (250 mL), slowly dropwise add 2-chloro-N,N-dimethylhexanamine (5.88 g, 0.055 mol), heat to 50 °C and stir the reaction overnight. Monitor the reaction by thin-layer chromatography until completion. The developing agent ratio of thin-layer chromatography is ethyl acetate:petroleum ether = 1:1. After cooling to room temperature, extract with dichloromethane five times, combine the organic phases, dry with anhydrous magnesium sulfate and then filter. Rotate and evaporate under reduced pressure until dry to obtain the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)hexan-1-amine as an oily substance, which is directly used for the next reaction without purification;

[0078] Second step: Dissolve the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)hexan-1-amine in acetone, slowly dropwise add methyl iodide (35.19 g, 0.109 mol) at room temperature, and react in a sealed container at 20 °C for 24 h. After filtration, wash with 20 mL of acetone and dry under reduced pressure to obtain 18.17 g of yellowish-brown powdery N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)hexan-1-ammonium iodide.

[0079] Third step: Dissolve 5 g of N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)hexan-1-ammonium iodide in 200 mL of deionized water, and perform ion exchange using a chlorine-form strong-base ion exchange resin soaked in 1 mol L -1 NaCl aqueous solution (same as Example 1). Rotate and evaporate the exchanged aqueous solution to obtain N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)hexan-1-ammonium chloride.

[0080] The solubility of hexylphenoxazine quaternary ammonium salt in water at room temperature is 0.62 mol L -1 .

[0081] (2) Preparation of active electrolyte solution

[0082] Weigh 30.4 mg of the above-mentioned hexylphenoxazine quaternary ammonium salt and dissolve it in 100 mL of 1 mol L -1 NaCl solution (pH value is about 7.0) as the electrolyte solution. A glassy carbon electrode is used as the working electrode, a mercury / mercuric oxide electrode is used as the reference electrode, and a platinum plate electrode is used as the counter electrode. The electrochemical performance of the hexylphenoxazine quaternary ammonium salt is tested in a three-electrode system, and the whole testing process is carried out under nitrogen protection.

[0083] Using the hexylphenoxazine quaternary ammonium salt prepared in Example 5 as the positive electrode active material, methyl viologen as the negative electrode active material, and an AEM membrane as the separator, 1 mol L -1 NH4Cl is used as the supporting electrolyte. Charge-discharge test experiments were carried out on the above battery. The battery test was carried out in a glove box. The voltage range of the charge-discharge experiment is 0.3 - 1.3 V. The flow rate of the electrolyte solution is 60 mL min -1 . After 200 charge-discharge cycles of the assembled battery, the Coulombic efficiency is 97.4%, and the energy efficiency reaches 78.6%.

[0084] Preparation of isobutylphenoxazine quaternary ammonium salt positive electrode active material in Example 6

[0085] (1) Material preparation

[0086] First step: Add phenoxazine (10.08 g, 0.055 mol), tetrabutylammonium bromide (2.07 g, 0.005 mol), and 3 mol L -1 NaOH aqueous solution (250 mL) in sequence, slowly dropwise add 3-chloro-N,N-dimethylisobutylamine (29.46 g, 0.11 mol), heat to 50 °C and stir the reaction overnight. Monitor the reaction by thin-layer chromatography until it is completed. The developing agent ratio of thin-layer chromatography is ethyl acetate:petroleum ether = 1:1. After cooling to room temperature, extract with dichloromethane 5 times, combine the organic phases, dry with anhydrous magnesium sulfate and then filter, and rotary evaporate under reduced pressure until dry to obtain the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)isobutane-1-amine, which can be directly used for the next reaction without purification;

[0087] Second step: Dissolve the crude product of N,N-dimethyl-2-(10H-phenoxazin-10-yl)isobutane-1-amine with acetone, slowly dropwise add methyl iodide (35.19 g, 0.109 mol) at room temperature, and react in a sealed container at 20 °C for 24 h. After filtration, wash with 20 mL of acetone and dry under reduced pressure to obtain 18.17 g of yellowish-brown powdery N,N,N-trimethyl-2-(10H-phenoxazin-10-yl)isobutane-1-iodide ammonium.

[0088] Step 3: Dissolve 5 g of N,N,N-trimethyl-2-(10H-phenoxazin-10-yl) isobutane-1-ammonium iodide in 200 mL of deionized water, and perform ion exchange using a chloride-form strongly basic ion exchange resin soaked in 1 mol L -1 aqueous NaCl solution (the same as in Example 1). Rotate evaporate the exchanged aqueous solution to obtain N,N,N-trimethyl-2-(10H-phenoxazin-10-yl) isobutane-1-ammonium chloride.

[0089] The solubility of isobutylphenoxazine quaternary ammonium salt in water at room temperature is 0.48 mol L -1 .

[0090] (2) Preparation of active electrolyte solution

[0091] Weigh 30.4 mg of the above isobutylphenoxazine quaternary ammonium salt and dissolve it in 100 mL of 1 mol L -1 aqueous NaCl solution (pH value is about 7.0) as the electrolyte. Use a glassy carbon electrode as the working electrode, a mercury / mercuric oxide electrode as the reference electrode, and a platinum plate electrode as the counter electrode to test the electrochemical performance of hexylphenoxazine quaternary ammonium salt in a three-electrode system. The whole test process is carried out under nitrogen protection.

[0092] Use the isobutylphenoxazine quaternary ammonium salt prepared in Example 6 as the positive electrode active material, methyl viologen as the negative electrode active material, an AEM membrane as the separator, and 1 mol L -1 NH4Cl as the supporting electrolyte. Perform charge-discharge test experiments on the above battery. The battery test is carried out in a glove box. The voltage range of the charge-discharge experiment is 0.3 - 1.3 V. The flow rate of the electrolyte is 60 mL min -1 . After 200 charge-discharge cycles of the assembled battery, the Coulomb efficiency is 95.8%, and the energy efficiency reaches 76.4%.

Claims

1. A positive electrode active electrolyte based on phenoxazine quaternary ammonium salt, characterized in that: The positive electrode active electrolyte based on phenoxazine quaternary ammonium salt has the structure shown by the following formula: ， The structure of R is: C1-6 straight-chain or branched-chain alkyl group.

2. A synthesis method of a positive electrode active electrolyte based on phenoxazine quaternary ammonium salt according to claim 1, characterized in that: The synthesis method comprises the following steps: (1) Sequentially add phenoxazine, a phase transfer catalyst and an alkali solution into a reaction flask. After mixing evenly, dropwise add 1-halo-R-group-N,N-dimethylamine, and obtain an oily intermediate through a nucleophilic substitution reaction. Without purification, directly proceed to the next step of the reaction; (2) Dissolve the oily intermediate with a polar solvent, add methyl iodide for reaction, and obtain phenoxazine quaternary ammonium iodide; (3) Dissolve the phenoxazine quaternary ammonium iodide in deionized water, and perform ion exchange with a chlorine-form strongly basic ion exchange resin to obtain phenoxazine quaternary ammonium chloride.

3. The synthesis method of the positive electrode active electrolyte based on phenoxazine quaternary ammonium salt according to claim 2, characterized in that: In step (1), the phase transfer catalyst is benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogensulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride or cetyltrimethylammonium bromide.

4. The synthesis method of the positive electrode active electrolyte based on phenoxazine quaternary ammonium salt according to claim 2, characterized in that: The addition amount of the phase transfer catalyst in step (1) is 5.0 wt.% to 10.0 wt.% of the total mass of phenoxazine and 1-halo-R-group-N,N-dimethylamine; the concentration of the alkali solution is 3 to 12 mol / L -1 , and the alkali is potassium hydroxide, sodium hydroxide, calcium hydroxide, potassium ethoxide, potassium tert-butoxide, or lithium diisopropylamide.

5. The synthesis method of the positive electrode active electrolyte based on phenoxazine quaternary ammonium salt according to claim 2, characterized in that: In step (1), the molar ratio of phenoxazine to 1-halo-R-group-N,N-dimethylamine is 1:1 to 1:3; the temperature of the nucleophilic substitution reaction is 50-120 °C, and the reaction time is 6-12 h.

6. The synthesis method of the positive electrode active electrolyte based on phenoxazine quaternary ammonium salt according to claim 2, characterized in that: In step (2), the polar solvent is acetone, ethyl acetate, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; the dosage of methyl iodide is twice the molar amount of phenoxazine; the temperature of the quaternization reaction is 20-50 °C, and the reaction time is 12-24 h.

7. An aqueous all-organic redox flow battery based on a phenoxazine quaternary ammonium salt positive electrode active electrolyte, characterized in that: The aqueous all-organic flow battery described above is composed of a negative electrode active electrolyte material viologen derivative, the positive electrode active electrolyte material based on phenoxazine quaternary ammonium salt as claimed in claim 1, a supporting electrolyte, a separator, a porous carbon electrode and a current collector; the electrolyte is a neutral salt solution.

8. The all-aqueous organic redox flow battery based on the phenoxazine quaternary ammonium salt positive electrode active electrolyte according to claim 7, characterized in that: The supporting electrolyte is ammonium chloride, sodium chloride, potassium chloride or a mixture thereof. The pH of the supporting electrolyte solution is 5 to 8, the solvent is water, and the concentration of the supporting electrolyte is 1 mol / L -1 .

9. The aqueous all-organic redox flow battery based on a phenoxazine quaternary ammonium salt positive electrode active electrolyte according to claim 7, wherein: [[ID=...]]The separator is an anion conductive membrane; the porous carbon electrode is carbon paper, carbon cloth, carbon felt or porous graphene.

Images