Aqueous redox flow battery and preparation method thereof

Abstract

The invention discloses an aqueous redox flow battery and a preparation method thereof, and relates to the technical field of flow batteries, the aqueous redox flow battery comprises a positive electrode electrolyte, a negative electrode electrolyte and a diaphragm, the positive electrode electrolyte adopts a complex of ferric chloride and crown ether as an active substance, the negative electrode electrolyte adopts anthraquinone-2, 7-disulfonic acid disodium salt as an active substance, and the diaphragm is prepared from a positive electrode electrolyte, a negative electrode electrolyte and a negative electrode electrolyte. The diaphragm is used for isolating the positive electrode electrolyte from the negative electrode electrolyte, preventing direct contact and allowing ions in the electrolyte to freely shuttle, the positive electrode electrolyte adopts a complex of ferric chloride and crown ether as an active substance, and the negative electrode electrolyte adopts anthraquinone-2, 5-diketone as an active substance. The 2, 7-disulfonic acid disodium salt is used as an active substance and has excellent oxidation-reduction performance and stability, the energy density of the battery is improved, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present disclosure relates to the field of energy storage systems, and in particular to an aqueous redox flow battery and a method for preparing the same. Background Art

[0002] With the rapid development of electronic products, electric vehicles, smart grids, aerospace and other fields, human demand for various energy sources has also increased. At the same time, the gradual depletion of fossil energy has made energy and environmental issues one of the most important challenges for the sustainable development of human society. Therefore, the efficient use of renewable energy has become the primary issue that energy development needs to face. However, most renewable energy cannot be used as a stable energy source alone, and cannot be used directly after being obtained. Due to the above problems, scientists are urgently needed to find efficient energy conversion devices and reliable energy storage systems.

[0003] Liquid flow battery is a new type of electrochemical energy storage technology, which has attracted wide attention due to its unique performance advantages. Liquid flow battery consists of key parts such as battery stack unit, electrolyte, electrolyte storage and supply unit, and management control unit. Its core working principle is to separate and circulate the positive and negative electrolytes separately, and realize the mutual conversion of electrical energy and chemical energy through the reversible redox reaction of the active substances in the positive and negative electrolyte solutions.

[0004] Liquid flow batteries have the characteristics of high capacity, wide application range, and long cycle life. Its active material is stored in the electrolyte and has fluidity, which makes the design of battery power and capacity relatively independent, and is particularly suitable for large-scale energy storage needs. According to the different electrode active materials, liquid flow batteries can be divided into many types, such as all-vanadium liquid flow batteries, lithium-ion liquid flow batteries, and lead-acid liquid flow batteries. Among them, all-vanadium liquid flow batteries have broad application prospects in the field of energy storage due to their advantages such as high safety, fast startup speed, and long battery life.

[0005] In recent years, with the accelerated advancement of global energy transformation and the rapid development of renewable energy, energy storage technology, as a key bridge connecting renewable energy generation with power grids and users, has become increasingly important. As an efficient and reliable energy storage technology, flow batteries have made significant progress in technological innovation, industrial upgrading, market demand, and policy support, injecting strong impetus into the optimization and adjustment of the global energy structure and the green and low-carbon transformation.

[0006] Traditional flow batteries still have many deficiencies in terms of electrode materials and electrolyte composition, which limits the improvement of their performance and the expansion of their application range. Therefore, it is of great significance to develop a flow battery with excellent performance and low cost. Summary of the invention

[0007] A first aspect of the present invention is to provide an aqueous redox flow battery.

[0008] The technical solution adopted by the present invention is as follows: An aqueous redox flow battery comprises a positive electrode electrolyte, a negative electrode electrolyte and a diaphragm, wherein the positive electrode electrolyte uses a complex of ferric chloride and crown ether as an active substance, the negative electrode electrolyte uses anthraquinone-2,7-disulfonic acid disodium salt as an active substance, and the diaphragm is used to isolate the positive electrode electrolyte and the negative electrode electrolyte to prevent direct contact, while allowing ions in the electrolyte to shuttle freely.

[0009] The present invention discloses an aqueous redox flow battery, wherein the positive electrode electrolyte uses a complex of ferric chloride and crown ether as an active substance, and the metal complex has excellent redox performance and stability; the negative electrode electrolyte uses anthraquinone-2,7-disulfonic acid disodium salt as an active substance, and the material can undergo redox reaction with the positive electrode active substance. The flow battery using the above materials has excellent redox performance and stability, and improves the energy density and cycle life of the battery.

[0010] Further settings are as follows: The complex of ferric chloride and crown ether is obtained by the following method: ferric chloride and crown ether are added into water in proportion, stirred for reaction, and after the reaction is completed, vacuum rotary evaporation is performed, and then placed in an oven for drying to obtain the complex of ferric chloride and crown ether.

[0011] The crown ether is selected from any one of 12-crown-4, 15-crown-5 and 18-crown-6.

[0012] The molar ratio of the crown ether to ferric chloride is 1:0.1 to 1:1, preferably 1:1.

[0013] The complex of ferric chloride and crown ether is dissolved in an aqueous ammonium chloride solution and used as the positive electrode electrolyte of the liquid flow battery.

[0014] The anthraquinone-2,7-disulfonic acid disodium salt is dissolved in an aqueous solution of ammonium chloride and then subjected to a charging treatment to obtain a negative electrode electrolyte of a liquid flow battery.

[0015] The charging method is as follows: configure 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxide free base in ammonium chloride aqueous solution as the positive electrode electrolyte, and use anthraquinone-2,7-disulfonic acid disodium salt electrolyte as the negative electrode electrolyte, assemble the above-mentioned positive electrode electrolyte, negative electrode electrolyte and separator in order to assemble a liquid flow battery for charging.

[0016] A second aspect of the present invention is to provide a method for preparing an aqueous redox flow battery, comprising the following steps: (1) Preparation of positive electrode electrolyte: Crown ether and ferric chloride are added into water at a molar ratio of 1:0.1 to 1:1, and stirred for reaction. After the reaction is completed, vacuum rotary evaporation is performed, and then it is placed in an oven for drying to obtain a complex of ferric chloride and crown ether. The complex of ferric chloride and crown ether is dissolved in an aqueous ammonium chloride solution as a positive electrode electrolyte of a liquid flow battery.

[0017] (2) Preparation of negative electrode electrolyte: Dissolving anthraquinone-2,7-disulfonic acid disodium salt in an aqueous solution of ammonium chloride to obtain anthraquinone-2,7-disulfonic acid disodium salt electrolyte is then charged to obtain a negative electrode electrolyte after the charging is completed.

[0018] The charging process is as follows: configure 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxide free base in ammonium chloride aqueous solution as the positive electrode electrolyte, and use anthraquinone-2,7-disulfonic acid disodium salt electrolyte as the negative electrode electrolyte, assemble the above-mentioned positive electrode electrolyte, negative electrode electrolyte and separator in order to form a liquid flow battery for charging.

[0019] (3) Assembling the battery: The positive electrode electrolyte prepared in step (1), the negative electrode electrolyte prepared in step (2), and the diaphragm are assembled in sequence to obtain an aqueous redox flow battery.

[0020] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages: a complex of crown ether and ferric chloride is used as the positive electrode active material, and anthraquinone-2,7-disulfonic acid disodium salt is used as the negative electrode active material, which has excellent redox performance and stability, and improves the energy density and cycle life of the battery; and the preparation process is simple, and large-scale production is easy to achieve, thereby reducing the cost of the battery.

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of an aqueous redox flow battery of the present invention is shown in FIG.

[0023] Figure 2 This is a graph of the electrochemical properties of the 5 mM complex of 12-crown ether-4 and ferric chloride prepared in Example 1 measured using cyclic voltammetry (CV) in a 1 M potassium chloride aqueous solution.

[0024] Figure 3 This is a graph of the electrochemical properties of the 5 mM complex of 15-crown ether-5 prepared in Example 2 and ferric chloride measured using cyclic voltammetry (CV) in a 1 M potassium chloride aqueous solution.

[0025] Figure 4This is a graph of the electrochemical properties of the complex of 5 mM 18-crown ether-6 and ferric chloride prepared in Example 3 measured using cyclic voltammetry (CV) in 1 M potassium chloride aqueous solution.

[0026] Figure 5 This is a graph of the electrochemical properties of the 5 mM complex of 12-crown ether-4 and ferric chloride prepared in Example 1 measured using linear sweep voltammetry (LSV) in a 1 M potassium chloride aqueous solution.

[0027] Figure 6 This is the Levich curve of limiting current and square root of rotation speed of the complex of 12-crown ether-4 and ferric chloride prepared in Example 1.

[0028] Figure 7 This is a Tafel curve obtained by comparing the overpotential and the logarithm of the kinetic current value of the complex of 12-crown ether-4 and ferric chloride prepared in Example 1.

[0029] Figure 8 This is a graph of the electrochemical properties of the 5 mM complex of 15-crown ether-5 prepared in Example 2 and ferric chloride measured in 1 M potassium chloride aqueous solution using linear sweep voltammetry (LSV).

[0030] Fig. 9 This is the Levich curve of limiting current and square root of rotation speed of the complex of 15-crown ether-5 and ferric chloride prepared in Example 2.

[0031] Fig.10 This is a Tafel curve obtained by comparing the overpotential and the logarithm of the kinetic current value of the complex of 15-crown ether-5 and ferric chloride prepared in Example 2.

[0032] Fig.11 This is a graph of the electrochemical properties of the complex of 5 mM 18-crown ether-6 and ferric chloride prepared in Example 3 measured using linear sweep voltammetry (LSV) in 1 M potassium chloride aqueous solution.

[0033] Fig.12 This is the Levich curve of limiting current and square root of rotation speed of the complex of 18-crown ether-6 and ferric chloride prepared in Example 3.

[0034] Fig.13 This is a Tafel curve obtained by comparing the overpotential and the logarithm of the kinetic current value of the complex of 18-crown ether-6 and ferric chloride prepared in Example 3.

[0035] Fig.14 This is a long cycle data diagram of the aqueous redox flow battery prepared in Example 1.

[0036] Fig.15 This is a long cycle data diagram of the aqueous redox flow battery prepared in Example 2.

[0037] Fig.16 This is a long cycle data diagram of the aqueous redox flow battery prepared in Example 3. DETAILED DESCRIPTION

[0038] like Figure 1 As shown, the aqueous redox flow battery described in the embodiment of the present invention includes a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, wherein: the positive electrode electrolyte uses a complex of ferric chloride and crown ether as an active substance, and the metal complex has excellent redox performance and stability; the negative electrode electrolyte uses anthraquinone-2,7-disulfonic acid disodium salt as an active substance, and anthraquinone-2,7-disulfonic acid disodium salt needs to obtain electrons before it can be used as the negative electrode electrolyte of the present invention, and the material can undergo redox reaction with the positive electrode active substance; the diaphragm uses an ion exchange membrane, and the Nature membrane is used in this embodiment to isolate the positive electrode electrolyte and the negative electrode electrolyte to prevent direct contact, while allowing ions in the electrolyte to shuttle freely; the flow battery of the present invention needs to be operated in a glove box, and the specific choice is the Itex single-sided workstation glove box, and the equipment model is Lab2000.

[0039] The following is a further detailed description of the implementation effects of the present invention in conjunction with embodiments of different process conditions.

[0040] Example 1

[0041] A method for preparing an aqueous redox flow battery comprises the following steps: (1) Preparation of positive electrode electrolyte: 12-crown ether-4 and ferric chloride were added to water in a molar ratio of 1:1, stirred for reaction, and after the reaction was completed, vacuum rotary evaporation was performed, and then placed in an oven for drying to obtain a metal complex. The metal complex was prepared in a concentration of 0.1M in 8mL of a 1M ammonium chloride aqueous solution, and the solution was used as the positive electrode electrolyte of the liquid flow battery.

[0042] (2) Preparation of negative electrode electrolyte: A 0.05M concentration of anthraquinone-2,7-disulfonic acid disodium salt is prepared in 10mL of a 1M ammonium chloride aqueous solution. The material needs to obtain electrons before it can be used as the negative electrode electrolyte of the liquid flow battery, as follows: a 0.1M concentration of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical) is prepared in 12mL of a 1M ammonium chloride aqueous solution, the prepared tempol electrolyte is used as the positive electrode of the liquid flow battery, the prepared anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode, the positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence, and the battery is charged. After the charging is completed, the obtained anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode electrolyte of the present invention.

[0043] (3) Assembling the battery: The complex solution of 12-crown ether-4 and ferric chloride prepared in step (1) is used as the positive electrode electrolyte, the anthraquinone-2,7-disulfonic acid disodium salt electrolyte after charging in step (2) is used as the negative electrode electrolyte, and the positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence to obtain the first aqueous redox flow battery of the present invention.

[0044] Example 2

[0045] A method for preparing an aqueous redox flow battery comprises the following steps: (1) Preparation of positive electrode electrolyte: 15-crown ether-5 and ferric chloride were added to water in a molar ratio of 1:1, stirred for reaction, and after the reaction was completed, vacuum rotary evaporation was performed, and then placed in an oven for drying to obtain a metal complex. The metal complex was prepared in a concentration of 0.1M in 8mL of 1M ammonium chloride aqueous solution, and the solution was used as the positive electrode electrolyte of the liquid flow battery.

[0046] (2) Preparation of negative electrode electrolyte: A 0.05M concentration of anthraquinone-2,7-disulfonic acid disodium salt is prepared in 10mL of a 1M ammonium chloride aqueous solution. This material needs to obtain electrons before it can be used as the negative electrode electrolyte of the liquid flow battery, as follows: a 0.1M concentration of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical) is prepared in 12mL of a 1M ammonium chloride aqueous solution. The prepared tempol electrolyte is used as the positive electrode of the liquid flow battery, and the prepared anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode. The positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence, and charged. After charging is completed, the obtained anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode electrolyte of the present invention.

[0047] (3) Assembling the battery: The complex solution of 15-crown ether-5 and ferric chloride prepared in step (1) is used as the positive electrode electrolyte, the anthraquinone-2,7-disulfonic acid disodium salt electrolyte after charging in step (2) is used as the negative electrode electrolyte, and the positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence to obtain the second aqueous redox flow battery of the present invention.

[0048] Example 3

[0049] A method for preparing an aqueous redox flow battery comprises the following steps: (1) Preparation of positive electrode electrolyte: 18-crown ether-6 and ferric chloride were added to water in a molar ratio of 1:1, stirred for reaction, and after the reaction was completed, vacuum rotary evaporation was performed, and then placed in an oven for drying to obtain a metal complex. The metal complex was prepared in a concentration of 0.1M in 8mL of 1M ammonium chloride aqueous solution, and the solution was used as the positive electrode electrolyte of the liquid flow battery.

[0050] (2) Preparation of negative electrode electrolyte: A 0.05M concentration of anthraquinone-2,7-disulfonic acid disodium salt is prepared in 10mL of a 1M ammonium chloride aqueous solution. This material needs to obtain electrons before it can be used as the negative electrode electrolyte of the liquid flow battery, as follows: a 0.1M concentration of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical) is prepared in 12mL of a 1M ammonium chloride aqueous solution. The prepared tempol electrolyte is used as the positive electrode of the liquid flow battery, and the prepared anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode. The positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence, and charged. After charging is completed, the obtained anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode electrolyte of the present invention.

[0051] (3) Assembling the battery: The complex solution of 18-crown ether-6 and ferric chloride prepared in step (1) is used as the positive electrode electrolyte, the anthraquinone-2,7-disulfonic acid disodium salt electrolyte after charging in step (2) is used as the negative electrode electrolyte, and the positive electrode electrolyte, the negative electrode electrolyte and the diaphragm are assembled into a liquid flow battery in sequence to obtain the third aqueous redox flow battery of the present invention.

[0052] Performance Test: The positive electrode active material (complex of crown ether and ferric chloride) and aqueous redox flow battery prepared in Examples 1-3 were subjected to performance tests using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and long cycle performance tests: The CV curve data was recorded using a ZIVE SP1 electrochemical workstation. The glassy carbon working electrode, Ag / AgCl reference electrode, and platinum wire were used to test the electrode. The test results are shown in Figure 2-Figure 4 shown.

[0053] like Figure 2-Figure 4 As shown, the complex of crown ether and ferric chloride exhibits excellent reversible redox performance in water. The redox potential of the complex of crown ether and ferric chloride does not change with the scanning rate. From the data in the figure, the average median voltage of the complex of 12-crown ether-4 and ferric chloride is 474.31 mV ( Figure 2 ), the average median voltage of the complex of 15-crown ether-5 and ferric chloride is 468.35 mV ( Figure 3), the average median voltage of the complex of 18-crown ether-6 and ferric chloride is 469.21 mV ( Figure 4 ). CV data show that the complex of crown ether and ferric chloride has a high redox potential and is a potential positive electrode material for flow batteries.

[0054] The LSV curve data was recorded using a SIN-RRDE rotating ring disk electrode device. The Ag / AgCl reference electrode and the platinum wire counter electrode were used for testing. The test results are shown in Figure 5-Figure 13 shown.

[0055] Combination Figure 5-Figure 7 As shown, the LSV scan was performed at 10 mV s -1 The rotation speed was increased from 400 rpm to 4000 rpm. At all rotation speeds, the LSV curves showed a limiting current controlled by mass transport and exhibited a clear platform shape. The limiting current of the crown ether ferric chloride complex ( I ) are all related to the square root of the speed ( ω 1 / 2 ) is linearly dependent, which conforms to the Levich equation. According to the slope of the Levich plot of the complex of 12-crown ether-4 and ferric chloride, it is -15.48 ( Figure 6 ), the calculated diffusion coefficient D is 6.47×10 -6 cm 2 s -1 In order to determine the rate constant of the charge transfer process, the overpotential (η) of the oxidation of the complex of 12-crown ether-4 with ferric chloride was plotted against the logarithm of the kinetic current (Logi K ) of the graph ( Figure 7 ). The electron transfer rate obtained from the fitted Tafel plot is 1.27×10 -3 cm 2 s -1 The LSV curve data show that the complex of 12-crown ether-4 and ferric chloride has excellent diffusion properties in water systems and excellent electron transfer ability, and is a potential electrode material for liquid flow batteries.

[0056] Combination Figure 8-Figure 10 As shown, the LSV scan was performed at 10 mV s -1 The rotation speed was increased from 400 rpm to 4000 rpm. At all rotation speeds, the LSV curves showed a limiting current controlled by mass transport and exhibited a clear platform shape. The limiting current of the crown ether ferric chloride complex ( I ) are all related to the square root of the speed ( ω 1 / 2) is linearly dependent, which conforms to the Levich equation. According to the slope of the Levich plot of the complex of 15-crown ether-5 and ferric chloride, it is -15.85 ( Fig. 9 ), the calculated diffusion coefficient D is 6.37×10 -6 cm 2 s -1 In order to determine the rate constant of the charge transfer process, the overpotential (η) of the oxidation of the complex of 15-crown ether-5 with ferric chloride was plotted against the logarithm of the kinetic current (Logi K ) of the graph ( Fig.10 ). The electron transfer rate obtained from the fitted Tafel plot is 6.71×10 -3 cm 2 s -1 The LSV curve data show that the complex of 15-crown ether-5 and ferric chloride has excellent diffusion properties in water systems and excellent electron transfer ability, and is a potential electrode material for liquid flow batteries.

[0057] Combination Figure 11-13 As shown, the LSV scan was performed at 10 mV s -1 The rotation speed was increased from 400 rpm to 4000 rpm. At all rotation speeds, the LSV curves showed a limiting current controlled by mass transport and exhibited a clear platform shape. The limiting current of the crown ether ferric chloride complex ( I ) are all related to the square root of the speed ( ω 1 / 2 ) is linearly dependent, which conforms to the Levich equation. According to the slope of the Levich plot of the complex of 18-crown ether-6 and ferric chloride, it is -21.42 ( Fig.12 ), the calculated diffusion coefficient D is 5.21×10 -6 cm 2 s -1 In order to determine the rate constant of the charge transfer process, the overpotential (η) of the oxidation of the complex of 18-crown ether-6 with ferric chloride was plotted against the logarithm of the kinetic current (Logi K ) of the graph ( Fig.13 ). The electron transfer rate obtained from the fitted Tafel plot is 3.28×10 -6 cm 2 s -1 The LSV curve data show that the complex of 18-crown ether-6 and ferric chloride has excellent diffusion properties in water systems and excellent electron transfer ability, and is a potential electrode material for liquid flow batteries.

[0058] The long cycle performance data of the flow battery is recorded using BTSDA software. The test results are as follows Figure 14-16 shown.

[0059] Combination Figure 14-16 As shown in the figure, the long cycle data of the flow battery shows that the complex of crown ether and ferric chloride shows excellent charge and discharge efficiency, which is always maintained at 100%. The flow battery using the complex of 12-crown ether-4 and ferric chloride still maintains 100% of the battery capacity after 200 cycles, showing excellent cycle performance. However, the flow battery using the complex of 15-crown ether-5, 18-crown ether-6 and ferric chloride does not show excellent cycle performance compared to the flow battery using the complex of 12-crown ether-4 and ferric chloride. The long cycle performance data shows that the flow battery using the complex of 12-crown ether-4 and ferric chloride has better charge and discharge efficiency and cycle performance, and is an excellent positive electrode material for flow batteries.

Claims

1. An aqueous redox flow battery comprising a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, characterized in that: The positive electrode electrolyte uses a complex of ferric chloride and crown ether as an active substance, and the negative electrode electrolyte uses anthraquinone-2,7-disulfonic acid disodium salt as an active substance. The diaphragm is used to isolate the positive electrode electrolyte and the negative electrode electrolyte to prevent direct contact, while allowing ions in the electrolyte to shuttle freely.

2. An aqueous redox flow battery according to claim 1, characterized in that: The complex of ferric chloride and crown ether is obtained by the following method: ferric chloride and crown ether are added into water in proportion, stirred for reaction, and after the reaction is completed, vacuum rotary evaporation is performed, and then placed in an oven for drying to obtain the complex of ferric chloride and crown ether.

3. The aqueous redox flow battery according to claim 1, characterized in that: The crown ether is selected from any one of 12-crown-4, 15-crown-5 and 18-crown-6.

4. The aqueous redox flow battery according to claim 1, characterized in that: The molar ratio of the crown ether to ferric chloride is 1:0.1 to 1:

1.

5. An aqueous redox flow battery according to claim 4, characterized in that: The molar ratio of the crown ether to ferric chloride is 1:

1.

6. The aqueous redox flow battery according to claim 1, characterized in that: The complex of ferric chloride and crown ether is dissolved in an aqueous ammonium chloride solution and used as the positive electrode electrolyte of the liquid flow battery.

7. The aqueous redox flow battery according to claim 1, characterized in that: The anthraquinone-2,7-disulfonic acid disodium salt is dissolved in an aqueous solution of ammonium chloride and then subjected to a charging treatment to obtain a negative electrode electrolyte of a liquid flow battery.

8. An aqueous redox flow battery according to claim 7, characterized in that: The charging process is as follows: configure 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxide free base in ammonium chloride aqueous solution as the positive electrode electrolyte, anthraquinone-2,7-disulfonic acid disodium salt solution as the negative electrode electrolyte, and then assemble into a liquid flow battery for charging.

9. A method for preparing an aqueous redox flow battery, characterized in that: The following steps are involved: (1) Preparation of positive electrode electrolyte: The crown ether and ferric chloride are added into water in a molar ratio of 1:0.1 to 1:1, and stirred for reaction. After the reaction is completed, vacuum rotary evaporation is performed, and then the complex of ferric chloride and crown ether is dried in an oven to obtain the complex of ferric chloride and crown ether. The complex of ferric chloride and crown ether is dissolved in an aqueous ammonium chloride solution as a positive electrode electrolyte of a liquid flow battery; (2) Preparation of negative electrode electrolyte: Dissolving anthraquinone-2,7-disulfonic acid disodium salt in an aqueous solution of ammonium chloride to obtain an anthraquinone-2,7-disulfonic acid disodium salt electrolyte, and then charging the electrolyte to obtain a negative electrode electrolyte after the charging is completed; (3) Assembling the battery: The positive electrode electrolyte prepared in step (1), the negative electrode electrolyte prepared in step (2), and the diaphragm are assembled in sequence to obtain an aqueous redox flow battery.

10. The method for preparing an aqueous redox flow battery according to claim 9, characterized in that: In step (2), the anthraquinone-2,7-disulfonic acid disodium salt electrolyte is charged, and the charging process is as follows: 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxide free base in an aqueous solution of ammonium chloride is prepared as the positive electrode electrolyte, and the anthraquinone-2,7-disulfonic acid disodium salt electrolyte is used as the negative electrode electrolyte, and then assembled into a liquid flow battery for charging.

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