Annular nitroxide free radical positive electrode electrolyte and neutral aqueous organic flow battery

Abstract

The invention discloses a cyclic nitroxide free radical positive electrode electrolyte and a neutral aqueous organic flow battery, and belongs to the technical field of organic flow batteries. According to the positive electrode electrolyte, halide ions (such as chloride ions) in an existing supporting electrolyte are replaced by inorganic salt composed of anions such as sulfate ions and bis (trifluoromethanesulfonyl) imine ions, and the precipitation side reaction caused by the chloride ions in the charging and discharging process is avoided. Sulfate and bis (trifluoromethanesulfonyl) imine salt have wider electrochemical stability windows, and anions of the sulfate and bis (trifluoromethanesulfonyl) imine salt have a regulation effect on a free water structure, so that a more stable solvated water environment is favorably formed, strong solvating behaviors of H < + > and OH <-> are reduced, a decomposition reaction of water in the electrolyte is inhibited, and the tolerance of a system to pH fluctuation is improved; the working potential window of the electrolyte is widened, and the operation stability and the electrochemical performance of the flow battery under the neutral or near-neutral condition are improved. According to the scheme, a new material design thought and an application basis are provided for constructing a high-stability and high-safety aqueous organic flow battery.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and specifically relates to a cyclic nitroxide free radical cathode electrolyte and a neutral aqueous organic liquid flow battery. Background Art

[0002] Flow batteries are electrochemical energy storage technologies that store and release energy through reversible redox reactions in liquid electrolytes. They offer advantages such as flexible system design, high safety, and long cycle life, making them a key development direction for large-scale energy storage applications. In recent years, cyclic nitroxide-based organic molecules, due to their high redox potential, excellent air stability, and reversibility, have been widely used as cathode electrolyte systems in neutral aqueous organic flow batteries. However, like most organic molecules, these compounds generally have low solubility in aqueous solutions, limiting their practical application in high-energy-density batteries. To improve their water solubility, molecular structure modification by introducing hydrophilic functional groups is often required to enhance their solubility in the supporting electrolyte. Furthermore, although cyclic nitroxide compounds exhibit good structural stability in neutral environments, they are susceptible to disproportionation reactions, degradation reactions, or electrochemical deactivation in slightly acidic or alkaline conditions, resulting in the loss of active electrolyte sites. These unfavorable factors further lead to rapid capacity decay and shortened cycle life, severely restricting their large-scale and stable application in aqueous flow batteries. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a cyclic nitroxide free radical cathode electrolyte and a neutral aqueous organic liquid flow battery to solve the problem that commonly used supporting electrolytes (such as chlorides) in traditional liquid flow batteries are prone to electrolytic side reactions, thereby improving the electrochemical stability and cycle life of the system.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A cyclic nitroxide free radical positive electrode electrolyte comprises an organic active molecule and a supporting electrolyte, wherein the organic active molecule is a cyclic nitroxide free radical or a derivative thereof, and the supporting electrolyte is a sulfate solution, a bis(trifluoromethanesulfonyl)imide salt solution or a mixed solution thereof.

[0006] A further improvement of the present invention is:

[0007] Preferably, the sulfate in the sulfate solution is selected from one or more of potassium sulfate, sodium sulfate, rubidium sulfate, ammonium sulfate, cesium sulfate and magnesium sulfate.

[0008] Preferably, the sulfate in the sulfate solution is potassium sulfate.

[0009] Preferably, the bis(trifluoromethanesulfonyl)imide salt in the bis(trifluoromethanesulfonyl)imide salt solution is potassium bis(trifluoromethanesulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide.

[0010] Preferably, the cyclic nitroxide free radical or its derivative is any one of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical, 4-[3-(trimethylamino)propoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl free radical chloride and 4-[3-(trimethylammonium)acetylamino]propoxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical chloride.

[0011] Preferably, the concentration of the supporting electrolyte is 0.1 to 3.0 mol / L.

[0012] Preferably, the concentration of the organic active molecules in the positive electrode electrolyte is 0.05 to 4.0 mol / L.

[0013] A neutral aqueous organic liquid flow battery comprises a positive electrode liquid storage tank, a negative electrode liquid storage tank and a battery stack; the positive electrode liquid storage tank and the negative electrode liquid storage tank are both connected to the battery stack;

[0014] The positive electrode liquid storage tank is loaded with the above-mentioned cyclic nitroxide free radical positive electrode electrolyte; the negative electrode liquid storage tank is loaded with the negative electrode electrolyte.

[0015] Preferably, the supporting electrolyte in the negative electrode solution is a sulfate solution.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention discloses a cyclic nitroxide free radical cathode electrolyte. This electrolyte replaces the chloride ions in the commonly used supporting electrolyte with sulfate or bis(trifluoromethanesulfonyl)imide ions, significantly improving the problem of chlorine evolution side reaction that is prone to occur in the existing system. Specifically, sulfate (such as potassium sulfate, sodium sulfate) or bis(trifluoromethanesulfonyl)imide salt (such as potassium bis(trifluoromethanesulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide) is used as the supporting electrolyte, which not only effectively avoids the electrochemical chlorine evolution reaction of chloride ions at high potential, but also these salts have a wider electrochemical stability window, can promote the formation of more stable free water structure in aqueous solution, and inhibit H +and excessive solvation of OH-, thereby reducing the probability of water decomposition reaction, and improving the tolerance of the electrolyte to pH fluctuations, broadening the working potential window of the electrolyte, and improving the operating stability and electrochemical performance of the flow battery under neutral or near-neutral conditions. Although sulfate and bis(trifluoromethanesulfonyl)imide ions are different from chloride ions in chemical properties, they still have good ion conduction functions, can maintain charge balance during battery operation, ensure ion exchange and energy transfer between positive and negative electrodes, and contribute to stable operation and efficient circulation of the battery. Therefore, the cathode electrolyte modification strategy provided by the present invention provides a new design concept and technical path for improving the cycle stability, energy efficiency and service life of cyclic nitroxide free radical electrolytes in neutral aqueous organic flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical (OH-TEMPO) positive electrode electrolyte of the organic flow battery of Example 1 shows the normalized discharge capacity and coulombic efficiency curves of the cyclic charge and discharge.

[0019] Figure 2 1 is a curve showing the change in solution pH during the charge and discharge process of the organic flow battery containing the OH-TEMPO positive electrolyte of Example 1.

[0020] Figure 3 This is a time-dependent cyclic voltammetry curve of the solution of OH-TEMPO in Example 1 after circulating in 1 mol / L potassium chloride.

[0021] Figure 4 This is a time-dependent cyclic voltammetry curve of the solution of OH-TEMPO in Example 1 after circulating in 0.50 mol / L potassium sulfate.

[0022] Figure 5 The normalized discharge capacity and coulombic efficiency curves of the organic liquid flow battery containing 4-[3-(trimethylamino)propoxy]-2,2,6,6-tetramethylpiperidin-1-oxyl chloride (TMA-TEMPO) positive electrode electrolyte of Example 2 during cyclic charge and discharge.

[0023] Figure 6 This is a curve showing the change in solution pH during the charge and discharge process of the organic flow battery containing the TMA-TEMPO positive electrolyte of Example 2.

[0024] Figure 7 This is a time-dependent cyclic voltammetry curve of the solution of TMA-TEMPO in Example 2 after circulating in 1 mol / L potassium chloride.

[0025] Figure 8This is a time-dependent cyclic voltammetry curve of the solution of TMA-TEMPO in Example 2 after circulating in 0.50 mol / L potassium sulfate.

[0026] Figure 9 The normalized discharge capacity and coulombic efficiency curves of the organic liquid flow battery containing 4-[3-(trimethylammonium)acetylamino]propoxy-2,2,6,6-tetramethylpiperidin-1-oxyl chloride (TMAAcNH-TEMPO) positive electrode electrolyte of Example 3 are shown.

[0027] Figure 10 3 is a curve showing the change in solution pH during the charge and discharge process of the organic liquid flow battery containing the TMAAcNH-TEMPO positive electrode electrolyte of Example 3.

[0028] Figure 11 This is a time-dependent cyclic voltammetry curve of the solution of TMAAcNH-TEMPO in Example 3 after cycling in 1 mol / L potassium chloride.

[0029] Figure 12 This is a time-dependent cyclic voltammetry curve of the solution of TMAAcNH-TEMPO in Example 3 after cycling in 0.50 mol / L potassium sulfate.

[0030] Figure 13 4 is the normalized discharge capacity and coulombic efficiency curve of the organic liquid flow battery containing TMA-TEMPO positive electrode electrolyte during cyclic charge and discharge.

[0031] Figure 14 This is a cyclic voltammetry curve of the positive electrode electrolyte test of the organic liquid flow battery containing TMA-TEMPO positive electrode electrolyte in Example 4 after 30 cycles of charge and discharge. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below with reference to the accompanying drawings:

[0033] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0034] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0035] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0036] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0037] Cyclic nitroxide radical electrolyte molecules are widely used in flow batteries as active materials in the anode electrolyte. These electrolytes require the addition of a supporting electrolyte, which alters the pH of the electrolyte. This pH directly impacts the stability of nitroxide radical cathode electrolytes. For example, acidic conditions exacerbate the disproportionation reaction of nitroxide radicals. Currently, potassium chloride (KCl) and sodium chloride (NaCl) are commonly used as the primary supporting electrolytes for the cathode electrolyte in aqueous organic flow batteries due to their high conductivity, low cost, and readily available availability. However, the use of KCl / NaCl supporting electrolytes can trigger electrolytic side reactions during long-term battery operation. For example, during battery charge and discharge, elevated chloride ion concentrations can easily trigger electrolytic chlorine evolution. The generated chlorine gas dissolves in water to form hypochlorous acid, causing a decrease in solution pH. Furthermore, due to the narrow electrochemical window of water, electrolytic oxygen evolution occurs during charge and discharge. These side reactions can cause changes in the electrolyte pH, thereby impacting the stability of the redox electrolyte molecules and shortening the life of the flow battery.

[0038] The present invention discloses a method for improving the cycling performance of a cyclic nitroxide-based cathode electrolyte in a neutral aqueous organic flow battery. The cathode electrolyte comprises an organic active molecule, a cyclic nitroxide or its derivative, and a supporting electrolyte, a sulfate solution, a bis(trifluoromethanesulfonyl)imide salt solution, or a mixture thereof. By replacing commonly used chloride ions with bis(trifluoromethanesulfonyl)imide salts or sulfates, the present invention effectively prevents the chloride ion from undergoing a chlorine evolution reaction.

[0039] In some embodiments of the present invention, the concentration of the organic active molecule is 0.05 to 4 mol / L

[0040] In some embodiments of the present invention, the cyclic nitroxide free radical compounds, such as the piperidine cyclic nitroxide free radical compounds, are 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical (OH-TEMPO), 4-[3-(trimethylamino)propoxy]-2,2,6,6-tetramethylpiperidin-1-oxyl free radical chloride (TMA-TEMPO) or 4-[3-(trimethylammonium)acetylamino]propoxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical chloride (TMAAcNH-TEMPO), and the corresponding structural formulas are:

[0041]

[0042] In some embodiments of the present invention, the bis(trifluoromethanesulfonyl)imide salt solution is a potassium bis(trifluoromethanesulfonyl)imide solution or a sodium bis(trifluoromethanesulfonyl)imide solution, and the chloride ions are replaced by bis(trifluoromethanesulfonyl)imide ions. While ensuring the important ion transport function, the charge balance of the electrolyte can be maintained in the electrode reaction, thereby promoting ion exchange between the positive and negative electrodes.

[0043] In some embodiments of the present invention, sulfate is one or more of potassium sulfate, sodium sulfate, rubidium sulfate, ammonium sulfate, cesium sulfate or magnesium sulfate. Sulfate (such as Na2SO4) is a strong acid and strong base salt, and its complete dissociation produces Na + and SO4 2- No hydrolysis occurs and the ionization balance of water is not destroyed. Therefore, the neutral environment of the electrolyte can be maintained, side reactions caused by changes in pH value can be avoided, and the stable operation of the battery system is more conducive to it.

[0044] In a specific embodiment of the present invention, the supporting electrolyte is potassium sulfate solution.

[0045] In some embodiments of the present invention, the concentration of the supporting electrolyte is 0.1 to 3.0 mol / L. It should be noted that since the supporting electrolyte itself is a salt solution, the concentration corresponds to the concentration of the salt in water.

[0046] The present invention also discloses a neutral aqueous organic flow battery. The neutral aqueous organic flow battery is symmetrically centered on the diaphragm in the middle. The battery stack is composed of stainless steel end plates, copper plates, graphite plates, graphite felt electrodes, ion exchange membranes, graphite felt electrodes, graphite plates, copper plates, and stainless steel end plates from the outside to the inside. The remaining space is sealed with silicone pads and the edges are fixed with screws. The graphite felt electrodes used in the battery test are commercial graphite felt with a working area of ​​5 cm 2Use a pump tube to connect the assembled battery, peristaltic pump, and liquid storage bottle, inject the prepared electrolyte solution into the liquid storage bottle, and connect it to the pump tube section between the battery stack and the liquid storage tank in the battery device through the peristaltic pump. A circulation flow is formed between the battery device and the liquid storage bottle, and the electrolyte solution enters the carbon felt to complete the electrochemical reaction.

[0047] The positive electrode liquid storage tank is loaded with the above-mentioned cyclic nitroxide free radical positive electrode electrolyte; the negative electrode liquid storage tank is loaded with the negative electrode electrolyte.

[0048] The following is a further analysis in conjunction with specific comparative examples and embodiments.

[0049] Comparative Example 1

[0050] A positive electrolyte was prepared containing 0.05 mol / L OH-TEMPO and 1 mol / L potassium chloride as supporting electrolytes; the negative electrolyte consisted of 0.05 mol / L methyl viologen and 1 mol / L potassium chloride. During the battery cycling process, the pH change of the OH-TEMPO solution in the positive electrolyte was monitored in situ. The results showed that after six charge-discharge cycles, the pH value of the positive electrolyte dropped sharply from the initial 7.14 to 1.50. Subsequently, the positive and negative electrolytes after the battery cycle were taken and cyclic voltammetry tests were performed to further analyze the changes in electrolyte performance and electrode reaction characteristics.

[0051] Example 1

[0052] The positive electrode electrolyte was prepared, containing 0.05 mol / L OH-TEMPO and 0.50 mol / L potassium sulfate as supporting electrolytes; the negative electrode electrolyte consisted of 0.05 mol / L methyl viologen and 0.50 mol / L potassium sulfate. During the battery cycle, the pH change of the positive electrode OH-TEMPO solution was monitored in situ. The results showed that after 6 cycles of charge and discharge, the pH of the positive electrode electrolyte dropped from the initial 7.26 to 2.80. Subsequently, the positive and negative electrode electrolytes after the cycle were taken and cyclic voltammetry tests were carried out to evaluate the electrochemical behavior and stability of the active materials during battery operation.

[0053] Figure 1 The normalized discharge capacity and coulombic efficiency curves of the aqueous organic liquid flow battery with OH-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively, during cyclic charge and discharge.

[0054] Figure 2It represents an aqueous organic liquid flow battery with OH-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively. The changes in the solution pH during the charge and discharge process are monitored in situ. After charge and discharge cycles, the pH of the OH-TEMPO solution with 1 mol / L potassium chloride as the supporting electrolyte drops to 1.50, and the pH of the OH-TEMPO solution with 0.50 mol / L potassium sulfate as the supporting electrolyte drops to 2.80. It can be seen that the solution pH value of OH-TEMPO changes differently after battery charge and discharge in different supporting electrolytes.

[0055] Figure 3 It means that the time-dependent cyclic voltammetry curve test was performed on the solution of OH-TEMPO after circulating in 1 mol / L potassium chloride, with time intervals of 0, 1, 3, and 9 days. In the 1 mol / L potassium chloride OH-TEMPO solution, since its pH is 1.50, as time goes by, its oxidation peak and reduction peak current decrease, and the redox peak area decreases, indicating that the concentration of redox species decreases, and OH-TEMPO has poor stability in this medium environment.

[0056] Figure 4 It means that the time-dependent cyclic voltammetry curve test was performed on the solution of OH-TEMPO after circulating in 0.50 mol / L potassium sulfate, with time intervals of 0, 1, 3, and 9 days, respectively. Since the pH of the OH-TEMPO solution in 0.50 mol / L potassium sulfate is 2.80, its oxidation peak and reduction peak currents do not change significantly with the extension of time, and the redox peak area changes little, indicating that OH-TEMPO has good stability in this medium environment.

[0057] Comparative Example 2

[0058] A 0.05 mol / L TMA-TEMPO cathode electrolyte and a 0.05 mol / L methyl viologen cathode electrolyte were prepared. A 1 mol / L potassium chloride solution was added to both the cathode and anode electrolytes as a supporting electrolyte. The pH change of the TMA-TEMPO solution during battery cycling was monitored in situ. After five cycles, the pH of the potassium chloride-supporting electrolyte TMA-TEMPO solution changed from 8.04 to 2.03. Cyclic voltammetry curves were then taken from both solutions after the battery cycle.

[0059] Example 2

[0060] A positive electrode electrolyte of 0.05 mol / L TMA-TEMPO and a negative electrode electrolyte of 0.05 mol / L methyl viologen were prepared. A 0.50 mol / L potassium sulfate solution was added to both the positive and negative electrolytes for comparative testing. The pH change of the TMA-TEMPO solution during battery cycling was monitored in situ. After five cycles, the pH of the TMA-TEMPO solution with potassium sulfate as the supporting electrolyte changed from 7.83 to 2.55. Cyclic voltammetry curves were then taken from both solutions after the battery cycle.

[0061] Figure 5 The normalized discharge capacity and coulombic efficiency curves of the cyclic charge and discharge of an aqueous organic liquid flow battery with TMA-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively.

[0062] Figure 6 It represents an aqueous organic liquid flow battery with TMA-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively. The changes in the solution pH during the charge and discharge process are monitored in situ. After charge and discharge cycles, the pH of the TMA-TEMPO solution with 1 mol / L potassium chloride as the supporting electrolyte drops to 2.03, and the pH of the TMA-TEMPO solution with 0.50 mol / L potassium sulfate as the supporting electrolyte drops to 2.55. It can be seen that the pH value of the TMA-TEMPO solution changes differently after battery charge and discharge in different supporting electrolytes.

[0063] Figure 7 It means that the time-dependent cyclic voltammetry curve test is performed on the solution of TMA-TEMPO after circulating in 1 mol / L potassium chloride. The time intervals are 0, 1, 3, and 9 days. Since the pH of the TMA-TEMPO solution in 1 mol / L potassium chloride is 2.03, as time goes by, its oxidation peak and reduction peak current decrease, and the redox peak area decreases, which means that the concentration of TMA-TEMPO decreases.

[0064] Figure 8 It means that the time-dependent cyclic voltammetry curve test was performed on the solution of TMA-TEMPO after circulating in 0.50 mol / L potassium sulfate, with time intervals of 0, 1, 3, and 9 days, respectively. Since the pH of the TMA-TEMPO solution in 0.50 mol / L potassium sulfate is 2.55, the oxidation peak and reduction peak currents do not change significantly with the extension of time, and the redox peak area changes are small, indicating that TMA-TEMPO has good stability in this medium environment.

[0065] Comparative Example 3

[0066] A 0.05 mol / L TMAAcNH-TEMPO cathode electrolyte and a 0.05 mol / L methyl viologen cathode electrolyte were prepared. A 1 mol / L potassium chloride solution was added to both the cathode and anode electrolytes as a supporting electrolyte. The pH change of the TMAAcNH-TEMPO solution during battery cycling was monitored in situ. After six cycles, the pH of the TMAAcNH-TEMPO solution with potassium chloride as the supporting electrolyte changed from 9.83 to 1.97. Cyclic voltammetry curves were then taken from both solutions after the battery cycle.

[0067] Example 3

[0068] A positive electrode electrolyte of 0.05 mol / L TMAAcNH-TEMPO and a negative electrode electrolyte of 0.05 mol / L methyl viologen were prepared. A 0.50 mol / L potassium sulfate solution was added to both the positive and negative electrolytes for comparative testing. The pH change of the TMAAcNH-TEMPO solution during battery cycling was monitored in situ. After six cycles, the pH of the TMAAcNH-TEMPO solution with potassium sulfate as the supporting electrolyte changed from 9.81 to 2.80. Cyclic voltammetry curves were then taken from both solutions after the battery cycle.

[0069] Figure 9 The normalized discharge capacity and coulombic efficiency curves of the cyclic charge-discharge of an aqueous organic liquid flow battery with TMAAcNH-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively.

[0070] Figure 10 It represents an aqueous organic liquid flow battery with TMAAcNH-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium sulfate, respectively. The changes in the solution pH during the charge and discharge process are monitored in situ. After charge and discharge cycles, the pH of the TMAAcNH-TEMPO solution with 1 mol / L potassium chloride as the supporting electrolyte drops to 1.97, and the pH of the TMAAcNH-TEMPO solution with 0.50 mol / L potassium sulfate as the supporting electrolyte drops to 2.80. It can be seen that the pH value of the TMAAcNH-TEMPO solution changes differently after battery charge and discharge in different supporting electrolytes.

[0071] Figure 11It means that the time-dependent cyclic voltammetry curve test was performed on the solution of TMAAcNH-TEMPO after circulating in 1 mol / L potassium chloride. The time intervals were 0, 1, 3, and 9 days. Since the pH of the TMAAcNH-TEMPO solution in 1 mol / L potassium chloride is 1.97, as time goes by, its oxidation peak and reduction peak current decrease, and the redox peak area decreases, which means that the concentration of TMAAcNH-TEMPO decreases.

[0072] Figure 12 It means that the time-dependent cyclic voltammetry curve test was performed on the solution of TMAAcNH-TEMPO after circulating in 0.50 mol / L potassium sulfate, with time intervals of 0, 1, 3, and 9 days, respectively. Since the pH of the TMAAcNH-TEMPO solution in 0.50 mol / L potassium sulfate is 2.80, its oxidation peak and reduction peak currents do not change significantly with the extension of time, and the redox peak area changes little, indicating that TMAAcNH-TEMPO has good stability in this medium environment.

[0073] Comparative Example 4

[0074] A positive electrolyte of 0.05 mol / L TMA-TEMPO and a negative electrolyte of 0.05 mol / L methyl viologen were prepared. A 1 mol / L potassium chloride solution was added to both the positive and negative electrolytes as a supporting electrolyte. The cycling performance of the battery with potassium chloride as the supporting electrolyte was tested. Cyclic voltammetry curves were performed on the two positive electrolyte solutions after 30 cycles of charge and discharge.

[0075] Example 4

[0076] A positive electrolyte of 0.05 mol / L TMA-TEMPO and a negative electrolyte of 0.05 mol / L methyl viologen were prepared. A 0.50 mol / L potassium bis(trifluoromethanesulfonyl)imide solution was added to both the positive and negative electrolytes for comparative testing. The cycling performance of batteries with potassium chloride and potassium bis(trifluoromethanesulfonyl)imide as supporting electrolytes was tested, respectively. Cyclic voltammetry curves were performed on batteries subjected to 30 charge-discharge cycles using both positive electrolytes.

[0077] Figure 13 It shows the cyclic charge-discharge curve test of an aqueous organic liquid flow battery with TMA-TEMPO as the positive electrode electrolyte, methyl viologen as the negative electrode electrolyte, and supporting electrolytes of 1 mol / L potassium chloride and 0.50 mol / L potassium bis(trifluoromethanesulfonyl)imide, respectively. After cyclic charge and discharge, the capacity of the aqueous organic liquid flow battery with 1 mol / L potassium chloride as the supporting electrolyte decays rapidly.

[0078] Figure 14It means that a cyclic voltammetry curve test is performed on a solution of TMA-TEMPO after 30 cycles in 1 mol / L potassium chloride and 0.50 mol / L potassium bis(trifluoromethanesulfonyl)imide. The oxidation peak and reduction peak currents of the CV curve of the TMA-TEMPO solution in 1 mol / L potassium chloride are low, and the redox peak area is small, which means that the concentration of TMA-TEMPO is low and TMA-TEMPO has poor stability in this medium environment.

[0079] Example 5

[0080] 1 mol / L TMA-TEMPO was prepared as the positive electrode electrolyte, 1 mol / L methyl viologen was prepared as the negative electrode electrolyte, and 0.50 mol / L sodium bis(trifluoromethanesulfonyl)imide solution was added to both the positive and negative electrode electrolytes as the supporting electrolyte. An anion exchange membrane was used as the diaphragm and carbon felt was used as the electrode to form an aqueous liquid flow battery.

[0081] Example 6

[0082] The positive electrode electrolyte was 0.05 mol / L OH-TEMPO, the negative electrode electrolyte was 0.05 mol / L methyl viologen, 0.1 mol / L sodium sulfate solution was added to both the positive and negative electrolytes as a supporting electrolyte, an anion exchange membrane was used as a diaphragm, and carbon felt was used as an electrode to form an aqueous liquid flow battery.

[0083] Example 7

[0084] The positive electrode electrolyte was 0.3 mol / L OH-TEMPO, the negative electrode electrolyte was 0.3 mol / L methyl viologen, 3.0 mol / L ammonium sulfate solution was added to both the positive and negative electrolytes as a supporting electrolyte, an anion exchange membrane was used as a diaphragm, and carbon felt was used as an electrode to form an aqueous liquid flow battery.

[0085] Example 8

[0086] The positive electrode electrolyte was prepared as 4 mol / L OH-TEMPO, the negative electrode electrolyte was prepared as 4 mol / L methyl viologen, 0.9 mol / L magnesium sulfate solution was added to both the positive and negative electrolytes as a supporting electrolyte, an anion exchange membrane was used as a diaphragm, and carbon felt was used as an electrode to form an aqueous liquid flow battery.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cyclic nitroxide free radical cathode electrolyte, characterized in that: The invention comprises organic active molecules and supporting electrolytes. The organic active molecules are cyclic nitrogen oxide free radicals or derivatives thereof. The supporting electrolytes are sulfate solution, bis(trifluoromethanesulfonyl)imide salt solution or mixed solution thereof.

2. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The sulfate in the sulfate solution is selected from one or more of potassium sulfate, sodium sulfate, rubidium sulfate, ammonium sulfate, cesium sulfate and magnesium sulfate.

3. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The sulfate in the sulfate solution is potassium sulfate.

4. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The bis(trifluoromethanesulfonyl)imide salt in the bis(trifluoromethanesulfonyl)imide salt solution is potassium bis(trifluoromethanesulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide.

5. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The cyclic nitrogen oxide free radical or its derivative is any one of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical, 4-[3-(trimethylamino)propoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl free radical chloride and 4-[3-(trimethylammonium)acetylamino]propoxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical chloride.

6. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The concentration of the supporting electrolyte is 0.1-3.0 mol / L.

7. The cyclic nitroxide free radical cathode electrolyte according to claim 1, characterized in that: The concentration of the organic active molecules in the positive electrode electrolyte is 0.05-4.0 mol / L.

8. A neutral aqueous organic flow battery, characterized in that: It includes a positive electrode liquid storage tank, a negative electrode liquid storage tank and a battery stack; the positive electrode liquid storage tank and the negative electrode liquid storage tank are both connected to the battery stack; The positive electrode liquid storage tank is loaded with the cyclic nitroxide free radical positive electrode electrolyte according to claim 1; the negative electrode liquid storage tank is loaded with the negative electrode electrolyte.

9. The neutral aqueous organic flow battery according to claim 8, characterized in that: The supporting electrolyte in the negative electrode solution is a sulfate solution.

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