Vanadium flow battery electrolyte, preparation method and application thereof

Abstract

This application discloses an all-vanadium redox flow battery electrolyte, its preparation method, and its application, relating to the field of flow batteries. The all-vanadium redox flow battery electrolyte contains vanadium ions, sulfate ions, a vanadium ion complexing stabilizer, and a passivating agent; the concentration of vanadium ions is >2.5 mol / L; the vanadium ion complexing stabilizer includes a vanadium ion complexing agent and a vanadium ion stabilizer, with a molar ratio of vanadium ion complexing agent, vanadium ion stabilizer, and vanadium ions of (0.2~1.2):(0.07~0.6):4; the concentration of the passivating agent is 0.04~2 mol / L. Adding the vanadium ion complexing stabilizer and passivating agent to the electrolyte increases the concentration of vanadium ions and effectively reduces the direct contact between pentavalent vanadium ions and the electrode. Furthermore, the passivating agent forms a passivation film on the electrode surface to block pentavalent vanadium ions, thereby achieving a vanadium ion concentration above 2.5 mol / L, suitable for higher operating voltages and higher operating temperatures.

Description

Technical Field

[0001] This application relates to the field of flow batteries, and in particular to an all-vanadium redox flow battery electrolyte, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow batteries are considered one of the most promising technologies in large-scale energy storage due to their flexible design, long lifespan, and high safety. Their electrochemical performance and commercial viability largely depend on the energy density and cost of the electrolyte.

[0003] Existing vanadium redox flow battery electrolytes typically use sulfuric acid as the supporting electrolyte, with a sulfuric acid concentration of 3–6 mol / L. This corresponds to a total vanadium ion concentration of 1–2.5 mol / L, not exceeding 2.5 mol / L. To improve the energy density and reduce the cost of vanadium redox flow battery electrolytes, increasing the vanadium ion concentration is commonly used, along with methods such as expanding the operating voltage window and widening the operating temperature range.

[0004] To increase the concentration of vanadium ions, the most common method is to use a mixture of sulfuric acid and hydrochloric acid as a supporting electrolyte to improve the solubility of vanadium ions and thus increase their concentration. However, the addition of hydrochloric acid can easily lead to the release of chlorine gas during use, posing a safety hazard.

[0005] For existing sulfuric acid-based electrolytes, increasing the operating voltage allows for storing more energy at the same current and widens the operating temperature range, particularly improving long-term operational stability at high temperatures (>40°C). However, these two conditions present a difficult-to-reconcile contradiction in traditional sulfuric acid-based electrolyte systems. Under high temperature or high charge conditions, pentavalent vanadium in the positive electrode electrolyte easily precipitates as vanadium pentoxide, leading to irreversible capacity decay. Furthermore, in high-potential and strongly oxidizing pentavalent vanadium environments, the carbon felt used as an electrode material is prone to oxidative corrosion, resulting in deteriorated electrode performance, increased resistance, and the potential for other side reactions, thus affecting battery life. Summary of the Invention

[0006] The main purpose of this application is to propose an all-vanadium redox flow battery electrolyte, its preparation method and application, aiming to solve the problems of existing all-vanadium electrolytes having low vanadium ion concentration and being unsuitable for stable operation at higher voltage windows and higher temperatures.

[0007] In a first aspect, this application provides an all-vanadium redox flow battery electrolyte, wherein the all-vanadium redox flow battery electrolyte contains vanadium ions, sulfate ions, vanadium ion complexing stabilizers and passivators;

[0008] Wherein, the concentration of vanadium ions is >2.5 mol / L, the vanadium ions include trivalent vanadium ions and tetravalent vanadium ions, and the molar ratio of the trivalent vanadium ions to the tetravalent vanadium ions is 1:1;

[0009] The concentration of sulfate ions is 3~6 mol / L;

[0010] The vanadium ion complexing stabilizer comprises a vanadium ion complexing agent and a vanadium ion stabilizer, wherein the molar ratio of the vanadium ion complexing agent, the vanadium ion stabilizer, and the vanadium ions is (0.2~1.2):(0.07~0.6):4; the vanadium ion complexing agent is selected from at least one of malonic acid, succinic acid, and tartaric acid, and the vanadium ion stabilizer is selected from at least one of benzoic acid and salicylic acid;

[0011] The concentration of the passivating agent is 0.04~2 mol / L, and the passivating agent is selected from at least one of aminosulfonic acid, p-toluenesulfonic acid and 2-pyridinecarboxylic acid.

[0012] By employing the above technical solution, the vanadium ion complexing agent can form a stable complex with vanadium ions, especially high-valence vanadium ions. Furthermore, the vanadium ion stabilizer can combine with the already formed complex to form a more stable and complex mixed ligand complex. The vanadium ion complexing agent and the vanadium ion stabilizer work together to form a relatively stable mixed ligand complex of vanadium ions, effectively inhibiting vanadium deposition, increasing the concentration of vanadium ions, and maintaining stable binding even in complex environments with higher operating voltages and temperatures. Moreover, the stable binding of vanadium ions by the vanadium ion complexing agent and the vanadium ion stabilizer effectively reduces the chemical activity of pentavalent vanadium ions on the electrode surface. Thus, while increasing the concentration of vanadium ions in the electrolyte, it also appropriately increases the upper limit of charging voltage and the upper limit of operating temperature.

[0013] The combination of vanadium ion complexing agents and vanadium ion stabilizers forms relatively stable complexes of vanadium ions. However, a very small portion of pentavalent vanadium ions remain in a free state. To further improve the operating voltage and stability, it is necessary to prevent these free pentavalent vanadium ions from causing potential corrosion to the electrode. This application adds a passivating agent to the electrolyte. The coordinating ability of the coordinating groups in the passivating agent preferentially and strongly adsorbs onto the active sites of the carbon electrode (carbon matrix) with water molecules and sulfate ions, forming an ordered adsorption layer. As the potential gradually increases to the V(Ⅳ) / V(Ⅴ) oxidation range during charging, the adsorption layer pre-formed on the carbon matrix reacts with the high-valence vanadium ions (especially tetravalent vanadium ions) migrating from the solution, as well as the carbon oxide groups generated on the electrode surface due to oxidation, forming an organic-inorganic hybrid passivation film. This passivation film is relatively dense and firmly bonded to the carbon substrate, effectively preventing direct contact between free pentavalent vanadium ions and the carbon matrix, thereby inhibiting chemical corrosion of the electrode. Meanwhile, the passivation film alters the catalytic properties of the electrode surface, increasing the overpotential required for water decomposition to generate oxygen. This allows for further increases in charging voltage during the charging process while ensuring operational stability.

[0014] In this technical solution, sulfuric acid is used as the supporting electrolyte, and a vanadium ion complexing stabilizer and a passivating agent are added to the electrolyte. The vanadium ion complexing stabilizer can stably and fully form vanadium ions into complexes, which not only increases the concentration of vanadium ions but also effectively reduces the direct contact between pentavalent vanadium ions and the electrode. In addition, the passivating agent forms a dense passivation film on the electrode surface, further blocking the direct contact between pentavalent vanadium ions and the electrode, effectively avoiding chemical corrosion of the electrode, so as to achieve a vanadium ion concentration of more than 2.5 mol / L. The resulting electrolyte can be used for higher operating voltages and higher operating temperatures, thereby effectively improving the energy density and operational stability of the electrolyte.

[0015] It should be noted that if the amount of passivating agent is too small, the passivation film may be incomplete or uneven, affecting the blocking effect of pentavalent vanadium ions. If the amount of passivating agent is too large, it may form an excessively thick multilayer film, increasing the interfacial charge transfer resistance. Furthermore, excessively thick multilayer films are not firmly bonded and may detach and enter the solution as impurities. Therefore, the feasible range for passivating agent concentration is 0.04~2 mol / L to achieve a better blocking effect.

[0016] Optionally, the concentration of vanadium ions is 3~5 mol / L, and the molar ratio of the vanadium ion complexing agent, the vanadium ion stabilizer and the vanadium ions is (0.6~1.0):(0.2~0.4):4.

[0017] By adopting the above technical solution and further optimizing the vanadium ion concentration and the ratio of vanadium ion complexing agent and vanadium ion stabilizer, the vanadium ion complexing agent and vanadium ion stabilizer can work together to form a relatively stable mixed ligand complex of vanadium ions. This allows for stable binding even in complex environments with higher operating voltages and temperatures. Furthermore, the vanadium ion complexing agent and vanadium ion stabilizer effectively reduce the chemical activity of pentavalent vanadium ions on the electrode surface by binding vanadium ions more fully and stably. This allows for an appropriate increase in the upper limit of the electrolyte's charging voltage and operating temperature.

[0018] Preferably, the concentration of vanadium ions is 4 mol / L.

[0019] Optionally, the vanadium ion stabilizer includes benzoic acid and salicylic acid, and the molar ratio of benzoic acid to salicylic acid is (0.2~0.3):(0.1~0.2).

[0020] By adopting the above technical solution and further optimizing the composition and ratio of vanadium ion stabilizers, vanadium ion complexing agents can be used to form mixed ligand complexes more fully and stably with vanadium ions.

[0021] Preferably, the concentration of sulfate is 4-6 mol / L; more preferably, the concentration of sulfate is 5 mol / L.

[0022] Optionally, the concentration of the passivating agent is 0.5~1.2 mol / L.

[0023] By adopting the above technical solution and further optimizing the concentration of the passivating agent, the thickness and density of the passivation film formed by the passivating agent on the carbon electrode surface can be further improved. This not only can pentavalent vanadium ions be blocked more stably, but also ensure that the electrochemical reaction at the electrode and electrolyte interface can be carried out more stably.

[0024] Optionally, the passivating agent includes p-toluenesulfonic acid and 2-pyridinecarboxylic acid, and the molar ratio of p-toluenesulfonic acid to 2-pyridinecarboxylic acid is (0.7~0.9):(0.3~0.5).

[0025] By adopting the above technical solution and further optimizing the composition and ratio of the passivating agent, the thickness and density of the passivation film formed on the carbon electrode surface can be further improved.

[0026] Secondly, this application also proposes a method for preparing an all-vanadium redox flow battery electrolyte as described in any of the above claims, comprising the following steps:

[0027] S1. Mix water and sulfuric acid to prepare a sulfuric acid solution. Add a vanadium source to the sulfuric acid solution to obtain a pentavalent vanadium solution.

[0028] S2. Add the reducing agent to the pentavalent vanadium solution obtained in step S1 to reduce the pentavalent vanadium to tetravalent vanadium, thereby obtaining a tetravalent vanadium solution.

[0029] S3. Divide the tetravalent vanadium solution obtained in step S2 into two parts. Electrolyze one part of the tetravalent vanadium solution to obtain a trivalent vanadium solution. Mix the trivalent vanadium solution with the other part of the tetravalent vanadium solution to obtain a 3.5 valent basic vanadium electrolyte.

[0030] S4. Add vanadium ion complexing stabilizer and passivator to the 3.5-valent basic vanadium electrolyte obtained in step S3 to obtain the all-vanadium redox flow battery electrolyte.

[0031] By adopting the above technical solution, the electrolyte prepared in this application contains a high concentration of vanadium ions and is suitable for higher operating temperatures and higher operating voltages, effectively improving the energy density of the electrolyte.

[0032] Optionally, in step S1, the concentration of sulfuric acid is ≥95wt%, and the vanadium source is vanadium pentoxide; in step S2, the reducing agent is glycerol.

[0033] Optionally, in step S1, the vanadium source is added to the sulfuric acid solution, the temperature is controlled at 50~75℃, and the mixture is stirred at a stirring rate of 100~500 rpm for 0.5~2 hours to obtain a pentavalent vanadium solution.

[0034] By adopting the above technical solution, after adding the vanadium source to the sulfuric acid solution, the temperature of the solution is controlled and stirring is used to ensure that the vanadium source is fully dissolved.

[0035] Optionally, in step S4, vanadium ion complexing stabilizer and passivator are added to a 3.5-valent vanadium electrolyte and ultrasonically dispersed for 30-90 minutes at an ultrasonic power of 200-500W to obtain the all-vanadium redox flow battery electrolyte.

[0036] By adopting the above technical solution, vanadium ion complexing stabilizer and passivator are added to a 3.5 valent vanadium electrolyte, and then ultrasonic dispersion is used to effectively promote the full dispersion of each component, resulting in an electrolyte with relatively uniform performance.

[0037] Preferably, in step S2, the vanadium source is added to the sulfuric acid solution, the temperature is controlled at 60°C, and the mixture is stirred at a stirring rate of 300 rpm for 1 hour to obtain a pentavalent vanadium solution.

[0038] Preferably, in step S4, vanadium ion complexing stabilizer and passivator are added to a 3.5-valent vanadium electrolyte and ultrasonically dispersed for 50 minutes at an ultrasonic power of 300W to obtain the all-vanadium redox flow battery electrolyte.

[0039] Thirdly, this application also proposes a flow battery, including a positive electrode electrolyte and a negative electrode electrolyte, wherein both the positive electrode electrolyte and the negative electrode electrolyte are vanadium redox flow battery electrolytes as described in any of the above claims.

[0040] By adopting the above technical solution, the electrolyte prepared in this application is suitable for the positive and negative electrodes of flow batteries, thus improving the applicability of the electrolyte.

[0041] In summary, this application includes at least one of the following beneficial technical effects:

[0042] 1. In the technical solution of this application, sulfuric acid is used as the supporting electrolyte, and vanadium ion complexing stabilizer and passivating agent are added to the electrolyte. The vanadium ion complexing stabilizer can stably and fully form vanadium ions into complexes, which not only increases the concentration of vanadium ions, but also effectively reduces the direct contact between pentavalent vanadium ions and the electrode. In addition, the passivating agent forms a dense passivation film on the electrode surface, which further blocks the direct contact between pentavalent vanadium ions and the electrode, effectively avoiding chemical corrosion of the electrode, so as to achieve a vanadium ion concentration of more than 2.5 mol / L. The resulting electrolyte can be used for higher operating voltages and higher operating temperatures, thereby effectively improving the energy density and operational stability of the electrolyte.

[0043] 2. Vanadium ion complexing agents can form stable, soluble complexes with vanadium ions. Furthermore, vanadium ion stabilizers can combine with the existing complexes to form a more stable and complex mixed-ligand complex, effectively inhibiting vanadium precipitation, increasing vanadium ion concentration, and maintaining stable binding even under complex environments with higher operating voltages and temperatures. The combination of vanadium ion complexing agents and vanadium ion stabilizers stably binds vanadium ions, effectively reducing the chemical activity of pentavalent vanadium ions on the electrode surface. Thus, while increasing the vanadium ion concentration in the electrolyte, it also appropriately raises the upper limits of charging voltage and operating temperature.

[0044] 3. The coordinating ability of the coordinating groups in the passivating agent preferentially and strongly adsorbs onto the active sites of the carbon electrode (carbon matrix) with water molecules and sulfate ions, forming an ordered adsorption layer. As the potential gradually increases to the V(Ⅳ) / V(Ⅴ) oxidation range during charging, the adsorption layer pre-formed on the carbon matrix reacts with free migrating high-valence vanadium ions (especially tetravalent vanadium ions) from the solution, as well as the carbonyl groups generated on the electrode surface due to oxidation, forming an organic-inorganic hybrid passivation film. This passivation film is relatively dense and firmly bonded to the carbon substrate, which can greatly prevent free pentavalent vanadium ions from directly contacting the carbon matrix, thereby inhibiting chemical corrosion of the electrode. At the same time, this passivation film changes the catalytic properties of the electrode surface, increasing the overpotential required for water decomposition to generate oxygen. Thus, the charging voltage can be further increased during charging, while ensuring operational stability. Attached Figure Description

[0045] Figure 1 This is a graph showing the energy efficiency of the electrolyte prepared in Example 1 of this application.

[0046] Figure 2 This is a graph showing the capacity retention rate of the electrolyte prepared in Example 1 of this application. Detailed Implementation

[0047] The present application will be further described in detail below with reference to the embodiments. Example 1

[0048] A method for preparing an all-vanadium redox flow battery electrolyte includes the following steps:

[0049] S1. Mix 1088g of deionized water with 1000g of 98wt% sulfuric acid to obtain a sulfuric acid solution. Add 731.17g of vanadium pentoxide (purity 99.5wt%) to the sulfuric acid solution, control the temperature of the mixture at 60℃, and stir at 300rpm for 1h to obtain a pentavalent vanadium solution.

[0050] S2. Add 52.57g of glycerol (purity ≥99.7wt%) to the pentavalent vanadium solution obtained in step S1, stir at 300rpm for 1h, cool naturally to 25℃, add deionized water to make up to 2L, and obtain a tetravalent vanadium solution.

[0051] S3. Divide the tetravalent vanadium solution obtained in step S2 into two portions, resulting in a first portion with a volume of 1500 mL and a second portion with a volume of 500 mL. Divide the 1500 mL first portion into two equal portions, and add the two equal portions to the positive and negative electrode electrolytic cells of the electrolytic cell, respectively. These portions are then pumped into the battery chamber. During charging, the external circuit provides electrons, and at the negative electrode / electrolyte interface, V... 4+ After gaining electrons at the electrode surface, it is reduced to V. 3+ During electrolysis, the concentration of tetravalent vanadium ions in the negative electrode electrolytic cell is monitored until V... 4+ The molar concentration is 0, V 4+ Completely restored to V 3+ A trivalent vanadium solution was obtained; 500 mL of the trivalent vanadium solution was taken and mixed with 500 mL of the second solution to obtain a 3.5 valent basic electrolyte.

[0052] S4. Add 0.6 mol of malonic acid (99.5 wt%), 0.2 mol of benzoic acid (99.9 wt%), and 0.5 mol of aminosulfonic acid (99.5 wt%) to the 3.5 valence basic electrolyte in sequence, and disperse by ultrasonication at 300 W for 50 min to obtain the vanadium redox flow battery electrolyte.

[0053] Examples 2-4

[0054] Examples 2-4 are based on Example 1, the difference being that in step S4, the molar amounts of malonic acid and benzoic acid added are changed, while the other steps remain the same as in Example 1. Specifically,

[0055] In Example 2, the molar amount of malonic acid was 0.2 mol and the molar amount of benzoic acid was 0.07 mol.

[0056] In Example 3, the molar amount of malonic acid was 1.0 mol and the molar amount of benzoic acid was 0.4 mol.

[0057] In Example 4, the molar amount of malonic acid was 1.2 mol and the molar amount of benzoic acid was 0.6 mol.

[0058] Examples 5-7

[0059] Examples 5-7 are based on Example 3, except that the molar amount of aminosulfonic acid changed in step S4, while the other steps remained the same as in Example 3. Specifically,

[0060] In Example 5, the molar amount of aminosulfonic acid was 0.04 mol.

[0061] In Example 6, the molar amount of aminosulfonic acid was 1.2 mol.

[0062] In Example 7, the molar amount of aminosulfonic acid was 2 mol.

[0063] Examples 8-9

[0064] Examples 8 and 9 are based on Example 6, except that in step S4, a mixture of benzoic acid and salicylic acid (99.5 wt% purity) is used instead of benzoic acid, while maintaining the total molar amounts of benzoic acid and salicylic acid at 0.4 mol. The other steps are the same as in Example 6. Specifically,

[0065] In Example 8, the molar amount of benzoic acid was 0.2 mol and the molar amount of salicylic acid was 0.2 mol.

[0066] In Example 9, the molar amount of benzoic acid was 0.3 mol and the molar amount of salicylic acid was 0.1 mol.

[0067] Examples 10-11

[0068] Examples 10-11 are based on Example 8, the difference being that in step S4, a mixture of p-toluenesulfonic acid (99wt% purity) and 2-pyridinecarboxylic acid (99wt% purity) is used to replace aminosulfonic acid, while maintaining the sum of the molar amounts of p-toluenesulfonic acid and 2-pyridinecarboxylic acid at 1.2 mol. The other steps are the same as in Example 8. Specifically,

[0069] In Example 10, the molar amount of p-toluenesulfonic acid was 0.7 mol, and the molar amount of 2-pyridinecarboxylic acid was 0.5 mol.

[0070] In Example 11, the molar amount of p-toluenesulfonic acid was 0.9 mol, and the molar amount of 2-pyridinecarboxylic acid was 0.3 mol.

[0071] Comparative Examples 1-3

[0072] Comparative Examples 1-3 are based on Example 2, except that step S4 does not contain one or both of benzoic acid and aminosulfonic acid; the other steps are the same as in Example 2. Specifically,

[0073] Step S4 of Comparative Example 1: 0.6 mol of malonic acid and 0.5 mol of aminosulfonic acid were added sequentially to the 3.5 valence basic electrolyte, and the mixture was ultrasonically dispersed at 300 W for 50 min to obtain the vanadium redox flow battery electrolyte.

[0074] Step S4 of Comparative Example 2: 0.6 mol of malonic acid and 0.2 mol of benzoic acid were added sequentially to the 3.5 valence basic electrolyte, and the mixture was ultrasonically dispersed at 300 W for 50 min to obtain the vanadium redox flow battery electrolyte.

[0075] Step S4 of Comparative Example 3: Add 0.6 mol of malonic acid to the 3.5 valence basic electrolyte and sonicate at 300 W for 50 min to obtain the vanadium redox flow battery electrolyte.

[0076] Performance testing

[0077] The electrolytes prepared in Examples 1-11 and Comparative Examples 1-3 were used as positive and negative electrode electrolytes to assemble vanadium redox flow batteries. The constant current charge-discharge performance of the obtained electrolytes was tested, and the test results are shown in Table 1 below.

[0078] Among them, 160mA / cm 2 The current density was tested at a constant current of 8A for 100 effective charge-discharge cycles. The charge and discharge cutoff voltages were 1.68V and 0.8V, respectively. The ambient temperature was 45℃, and nitrogen was used as the protective gas. The average energy efficiency (%) of the battery after 100 effective charge-discharge cycles and the capacity retention rate (%) of the battery after 100 effective charge-discharge cycles were tested.

[0079] in, In the formula, Ei refers to the energy efficiency corresponding to the i-th effective cycle, and the value of i is an integer from 1 to 100.

[0080] Battery capacity retention rate = (Q 100 / Q)*100%, where Q 100 Q refers to the discharge energy at the 100th effective cycle, while Q refers to the maximum discharge energy obtained in 100 effective cycles.

[0081] Table 1 Average energy efficiency and capacity retention of the electrolyte

[0082]

[0083] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the principles of this application should be covered within the scope of protection of this application.

Claims

1. A vanadium redox flow battery electrolyte, characterized in that, The electrolyte of the vanadium redox flow battery contains vanadium ions, sulfate ions, vanadium ion complexing stabilizers, and passivators. Wherein, the concentration of vanadium ions is >2.5 mol / L, the vanadium ions include trivalent vanadium ions and tetravalent vanadium ions, and the molar ratio of the trivalent vanadium ions to the tetravalent vanadium ions is 1:1; The concentration of sulfate ions is 3~6 mol / L; The vanadium ion complexing stabilizer includes a vanadium ion complexing agent and a vanadium ion stabilizer, wherein the molar ratio of the vanadium ion complexing agent, the vanadium ion stabilizer, and the vanadium ions is (0.2~1.2):(0.07~0.6):4; the vanadium ion complexing agent is malonic acid, and the vanadium ion stabilizer is selected from at least one of benzoic acid and salicylic acid; The concentration of the passivating agent is 0.04~2 mol / L, and the passivating agent is aminosulfonic acid, or a mixture of p-toluenesulfonic acid and 2-pyridinecarboxylic acid.

2. The all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The concentration of vanadium ions is 3~5 mol / L, and the molar ratio of the vanadium ion complexing agent, the vanadium ion stabilizer and the vanadium ions is (0.6~1.0):(0.2~0.4):

4.

3. The all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The vanadium ion stabilizer includes benzoic acid and salicylic acid, and the molar ratio of benzoic acid to salicylic acid is (0.2~0.3):(0.1~0.2).

4. The all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The concentration of the passivating agent is 0.5~1.2 mol / L.

5. The all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The passivating agent comprises p-toluenesulfonic acid and 2-pyridinecarboxylic acid, and the molar ratio of p-toluenesulfonic acid to 2-pyridinecarboxylic acid is (0.7~0.9):(0.3~0.5).

6. A method for preparing the all-vanadium redox flow battery electrolyte as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Mix water and sulfuric acid to obtain a sulfuric acid solution. Add a vanadium source to the sulfuric acid solution to obtain a pentavalent vanadium solution. S2. Add the reducing agent to the pentavalent vanadium solution obtained in step S1 to reduce the pentavalent vanadium to tetravalent vanadium, thereby obtaining a tetravalent vanadium solution. S3. Divide the tetravalent vanadium solution obtained in step S2 into two parts. Electrolyze one part of the tetravalent vanadium solution to obtain a trivalent vanadium solution. Mix the trivalent vanadium solution with the other part of the tetravalent vanadium solution to obtain a 3.5 valent basic vanadium electrolyte. S4. Add vanadium ion complexing stabilizer and passivator to the 3.5-valent basic vanadium electrolyte obtained in step S3 to obtain the all-vanadium redox flow battery electrolyte.

7. The method for preparing the all-vanadium redox flow battery electrolyte according to claim 6, characterized in that, In step S1, the concentration of sulfuric acid is ≥95wt%, and the vanadium source is vanadium pentoxide; in step S2, the reducing agent is glycerol.

8. The method for preparing the all-vanadium redox flow battery electrolyte according to claim 6, characterized in that, In step S1, the vanadium source is added to the sulfuric acid solution, the temperature is controlled at 50~75℃, and the mixture is stirred at a stirring rate of 100~500 rpm for 0.5~2 hours to obtain a pentavalent vanadium solution.

9. The method for preparing the all-vanadium redox flow battery electrolyte according to claim 6, characterized in that, In step S4, vanadium ion complexing stabilizer and passivator are added to a 3.5-valent vanadium electrolyte and ultrasonically dispersed at 200-500W for 30-90 minutes to obtain the all-vanadium redox flow battery electrolyte.

10. A flow battery, characterized in that, It includes a positive electrode electrolyte and a negative electrode electrolyte, both of which are vanadium redox flow battery electrolytes as described in any one of claims 1 to 5.

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