Method for detecting free acidity in electrolyte of sulfuric acid-based all-vanadium flow battery

Abstract

The application discloses a method for detecting free acidity in sulfuric acid-based all-vanadium liquid flow battery electrolyte, and relates to the field of liquid flow batteries. The method comprises the following steps: preparing a vanadium ion masking agent with a pH of 6.5-8.0 and a concentration of 1-2 mol / L; adding the vanadium ion masking agent into the electrolyte to be measured, adding standard alkali liquid dropwise, detecting the mass of the system before and after adding the standard alkali liquid, and obtaining the free acidity in the electrolyte to be measured by using a calculation formula of free acidity C. The addition of the vanadium ion masking agent effectively eliminates the influence of interference sources such as vanadium ion hydrolysis and oxidation and reduction on the detection result, and further guarantees the accuracy of the acid-base titration detection result.

Description

Technical Field

[0001] This application relates to the field of flow batteries, and in particular to a method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery. Background Technology

[0002] In vanadium redox flow batteries, the acidity of the sulfuric acid-based electrolyte plays a crucial role in the battery's performance and lifespan. Accurate detection of the free acidity in the sulfuric acid-based electrolyte is of great significance for optimizing battery operating conditions and improving battery efficiency and stability. Currently, the direct potentiometry method (pH meter) and acid-base titration method are commonly used to detect the free acidity in sulfuric acid-based vanadium redox flow battery electrolytes.

[0003] For the direct potentiometric method: the sulfuric acid-based electrolyte contains a high concentration of sulfuric acid, as well as a high concentration of vanadium ions in different valence states. The vanadium ions are in equilibrium between these different valence states (V0). 2+ / V 3+ , or V 4+ / V 5+ These multivalent vanadium ions can undergo redox reactions on the electrode surface, causing the potential response of the glass electrode to deviate from the actual value, thus affecting the accuracy of the detection results.

[0004] For acid-base titration, sodium hydroxide standard solution is commonly used as the titrant, with a pH of 2-4 at the titration endpoint. However, during titration, tetravalent vanadium ions can be oxidized, consuming hydrogen ions, and pentavalent vanadium ions also exhibit oxidizing properties, potentially interfering with detection. Furthermore, as the titration progresses, localized pH spikes can occur, causing vanadium ions, especially tetravalent vanadium ions, to readily hydrolyze, forming colloidal or precipitated compounds. This process consumes hydroxide ions, leading to higher detection values ​​and affecting the accuracy of the results. Summary of the Invention

[0005] The main objective of this application is to propose a method for detecting free acidity in the electrolyte of a vanadium redox flow battery based on sulfuric acid, aiming to solve the problem of low accuracy in existing acidity detection results in the electrolyte of a vanadium redox flow battery based on sulfuric acid.

[0006] Firstly, this application provides a method for detecting free acidity in a sulfuric acid-based vanadium redox flow battery electrolyte, comprising the following steps: S1. Provide a vanadium ion complexing agent, mix the vanadium ion complexing agent with water, adjust the pH to 6.5~8.0, and obtain a vanadium ion masking agent with a concentration of 1~2 mol / L; S2. Provide the electrolyte to be tested, and add the vanadium ion masking agent obtained in step S1 to the electrolyte to be tested to obtain a first mixture with a mass of m1. S3. Stir the first mixture obtained in step S2, and add a standard alkaline solution with a concentration of C0 dropwise to the first mixture until the pH is 2.98~3.05. The titration is then completed, and a second mixture with a mass of m2 is obtained. S4. Calculate the free acidity C in the electrolyte to be tested using the following formula. , In the formula, m1 and m2 are both in g; K1 is the correction parameter, with a value of 0.05 and a unit of g; K2 is the correction parameter, with a value of 1.01 and a unit of g / mL; V is the volume of the electrolyte to be tested, with a unit of mL; C0 is in mol / L; and C is in mol / L.

[0007] By employing the above technical solution, a vanadium ion masking agent with a pH of 6.5–8.0 and a concentration of 1–2 mol / L is added to the electrolyte to be tested before acid-base titration. The addition of a specific pH and appropriate concentration of vanadium ion masking agent promotes the sufficient and stable complexation of vanadium ions in the electrolyte, forming an extremely stable complex. After the vanadium ions are stably complexed, the concentration of free vanadium ions in the electrolyte is reduced to an extremely low level, significantly reducing the redox activity of vanadium ions and preventing the hydrolytic tendency of vanadium ions to combine with hydroxide ions. The addition of the vanadium ion masking agent effectively eliminates the influence of interference sources such as vanadium ion hydrolysis and redox on the detection results, thereby ensuring the accuracy of the subsequent acid-base titration results.

[0008] It should be noted that if the pH value of the vanadium ion masking agent is too low, the complexing ability of the vanadium ion complexing agent will be significantly weakened under these conditions, and the stability of the complex will decrease, which may result in insufficient masking of vanadium ions. Unmasked vanadium ions will still participate in hydrolysis or redox reactions during titration, affecting the accuracy of the detection results. If the pH value of the vanadium ion masking agent is too high, although the vanadium ion complexing agent can effectively complex vanadium ions, there will be an excess of hydroxide ions in the system. These hydroxide ions will prematurely consume some of the free acid in the early stages of titration, affecting the accuracy of the detection results.

[0009] If the concentration of the vanadium ion masking agent is too low, the vanadium ion complexing agent will not be able to fully complex the vanadium ions in the electrolyte to be tested. The unmasked vanadium ions will still interfere with the titration process and affect the accuracy of the detection results. If the concentration of the vanadium ion masking agent is too high, it will not only waste reagents, but may also affect the pH of the system in the early stage of titration due to the buffering capacity of the complexing agent itself, thereby affecting the accurate judgment of the titration endpoint and reducing the accuracy of the detection results.

[0010] This application also proposes a formula for calculating free acidity C, and further improves the accuracy of the detection results by introducing correction and adjustment parameters into the formula. In specific calculations, since the concentration of the standard alkali solution is known, it is only necessary to measure the mass of the system before and after titration with the standard alkali solution and substitute it into the formula for calculating free acidity C to obtain the free acidity in the electrolyte to be tested. The entire detection method is simple, the detection time is short, and the detection results are highly accurate.

[0011] It is understandable that "vanadium ion masking agent with a concentration of 1~2 mol / L" refers to a vanadium ion masking agent with a concentration of 1~2 mol / L for the vanadium ion complexing agent.

[0012] Optionally, in step S1, the vanadium ion complexing agent and water are mixed to obtain a complexing agent solution, and sodium hydroxide is added to the complexing agent solution to adjust the pH to 7.0~7.5, thereby obtaining a vanadium ion masking agent with a concentration of 1.4~1.6 mol / L.

[0013] Preferably, the concentration of the vanadium ion complexing agent in the vanadium ion masking agent is 1.5 mol / L.

[0014] By adopting the above technical solution and further optimizing the pH value and concentration of the vanadium ion masking agent, the complexation effect of the vanadium ion complexing agent with the vanadium ions in the electrolyte to be tested can be further improved.

[0015] Optionally, in step S1, the temperature of the complexing agent solution is controlled at 50~70℃, the mixture is stirred at a stirring rate of 200~400rpm, and sodium hydroxide is added to the complexing agent solution.

[0016] By adopting the above technical solution, sodium hydroxide is added to the complexing agent solution under stirring conditions of 50~70℃ and 200~400rpm. By controlling the temperature of the complexing agent solution and stirring, the dispersion uniformity of each component is ensured, and a vanadium ion masking agent with relatively uniform performance is obtained.

[0017] Preferably, in step S1, the temperature of the complexing agent solution is controlled at 60°C, the mixture is stirred at a stirring rate of 300 rpm, and sodium hydroxide is added to the complexing agent solution.

[0018] Optionally, in step S1, the vanadium ion complexing agent is selected from at least one of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA.

[0019] Preferably, in step S1, the vanadium ion complexing agent is disodium ethylenediaminetetraacetate.

[0020] By adopting the above technical solution, a specific vanadium ion complexing agent is used to effectively complex vanadium ions in the electrolyte to be tested.

[0021] Optionally, in step S2, an electrolyte to be tested is provided, and the electrolyte to be tested is diluted with water to obtain a diluted electrolyte. The vanadium ion masking agent obtained in step S1 is added to the diluted electrolyte to obtain a first mixture with a mass of m1. The volume ratio of the vanadium ion masking agent to the diluted electrolyte is (1~2):(25~35).

[0022] By adopting the above technical solution, the electrolyte to be tested can be appropriately diluted, which helps to optimize the titration environment without affecting the accuracy of the test results, and can also reduce the amount of standard alkali solution used.

[0023] It should be noted that the mass of the standard alkali solution consumed is directly obtained by accurately weighing the mass difference of the entire reaction system before and after titration. By introducing correction parameters K1 and K2, and combining this with the concentration C0 of the standard alkali solution, the mass difference of the system before and after titration is converted into the amount of standard alkali consumed. This amount of alkali is equal to the total amount of titratable hydrogen ions in the electrolyte to be tested. Combined with the volume of the electrolyte to be tested, the concentration of free acid in the electrolyte can be calculated. Therefore, there is no need to consider the volume correction factor resulting from appropriate sample dilution in the formula; the dilution step is used to optimize the titration environment.

[0024] Optionally, in step S2, the volume ratio of vanadium ion masking agent to diluted electrolyte is 2:30.

[0025] By adopting the above technical solution and further optimizing the ratio of vanadium ion masking agent to diluted electrolyte, it is possible to ensure that the vanadium ion complexing agent in the vanadium ion masking agent can stably and fully complex the vanadium ions in the electrolyte.

[0026] Preferably, in step S2, the volume of vanadium ion masking agent used is 2 mL, and the volume of diluted electrolyte used is 30 mL.

[0027] Optionally, in step S2, the volume ratio of the diluted electrolyte to the electrolyte to be tested is (20~50):1.

[0028] By adopting the above technical solution and controlling the appropriate dilution ratio, the amount of standard alkali solution used can be effectively reduced without affecting the accuracy of the test results.

[0029] Preferably, in step S2, the volume of the electrolyte to be tested is 1 mL, and the volume of the diluted electrolyte is 30 mL.

[0030] Optionally, in step S2, the total concentration of vanadium ions in the electrolyte to be tested is 0.1~2.0 mol / L.

[0031] By adopting the above technical solution, the free acidity detection method provided in this application is applicable to sulfuric acid-based vanadium electrolytes with a total vanadium ion concentration of 0.1~2.0 mol / L, and is applicable to the detection of free acidity in currently mainstream vanadium electrolytes, which can well meet the application requirements.

[0032] Preferably, in step S2, the total concentration of vanadium ions in the electrolyte to be tested is 1.0~2.0 mol / L. More preferably, in step S2, the total concentration of vanadium ions in the electrolyte to be tested is 2.0 mol / L.

[0033] Optionally, in step S3, the first mixture obtained in step S2 is stirred at a stirring rate of 550~650 rpm, and a standard alkaline solution with a concentration of C0 is added dropwise to the first mixture until the pH is 3.0.

[0034] By adopting the above technical solution, the standard alkali solution is titrated under stirring at a specific speed, ensuring that the standard alkali solution is quickly dispersed in the solution and guaranteeing the accuracy of the test results.

[0035] It should be noted that if the stirring rate is too low, the local pH may become too high momentarily, leading to a misjudgment of the titration endpoint and affecting the accuracy of the final test results. If the stirring rate is too high, solution may splash, reducing the amount of solution used, which will also lead to a misjudgment of the titration endpoint and affect the accuracy of the final test results.

[0036] Optionally, in step S3, the standard alkali solution is selected from a sodium hydroxide solution with a concentration of 0.1~1.0 mol / L.

[0037] Preferably, in step S3, the standard alkali solution is selected from a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0038] In summary, this application includes at least one of the following beneficial technical effects: 1. In the technical solution of this application, before acid-base titration, a vanadium ion masking agent with a pH of 6.5-8.0 and a concentration of 1-2 mol / L is added to the electrolyte to be tested. By adding a vanadium ion masking agent with a specific pH and suitable concentration, the vanadium ion complexing agent in the vanadium ion masking agent can sufficiently and stably complex the vanadium ions in the electrolyte to be tested, forming an extremely stable complex. After the vanadium ions are stably complexed, the concentration of free vanadium ions in the electrolyte to be tested drops to an extremely low level, significantly reducing the redox activity of vanadium ions and avoiding the tendency of vanadium ions to combine with hydroxide ions through hydrolysis. The addition of the vanadium ion masking agent effectively eliminates the influence of interference sources such as vanadium ion hydrolysis and redox on the detection results, thereby ensuring the accuracy of the subsequent acid-base titration detection results.

[0039] 2. This application also proposes a formula for calculating free acidity C, and further improves the accuracy of the detection results by introducing correction and adjustment parameters into the formula. In specific calculations, since the concentration of the standard alkali solution is known, it is only necessary to measure the mass of the system before and after titration with the standard alkali solution and substitute it into the formula for calculating free acidity C to obtain the free acidity in the electrolyte to be tested. The detection method is simple, the detection time is short, and the accuracy of the detection results is high. Detailed Implementation

[0040] The present application will be further described in detail below with reference to the embodiments. Example 1

[0041] A method for detecting free acidity in a vanadium redox flow battery electrolyte based on sulfuric acid, comprising the following steps: S1. Provide 0.15 mol of disodium ethylenediaminetetraacetate (EDTA). Add 0.15 mol of disodium EDTA to 70 mL of deionized water, and then add deionized water to bring the volume to 100 mL to obtain a complexing agent solution. Control the temperature of the complexing agent solution at 60℃ and stir the complexing agent solution at a stirring speed of 300 rpm for 2 min. Under the stirring conditions of 60℃ and 300 rpm, add sodium hydroxide (analytical grade) to adjust the pH of the system to 7.0 to obtain a vanadium ion masking agent.

[0042] S2. Provide 50 mL of the electrolyte to be tested (a standard sample of sulfuric acid-based vanadium electrolyte, with a tetravalent vanadium ion concentration of 1 mol / L, a pentavalent vanadium ion concentration of 1 mol / L, and a free acidity of 4.50 mol / L), and ultrasonically disperse it at 200 W for 15 min; take 1 mL (V) of the ultrasonically dispersed electrolyte to be tested, add 29 mL of deionized water to the electrolyte to be tested, and obtain 30 mL of diluted electrolyte; take 2 mL of the vanadium ion masking agent obtained in step S1, and add 2 mL of the vanadium ion masking agent to the 30 mL diluted electrolyte, and weigh it to obtain the first mixture with a mass of m1; wherein, m1 includes the mass of the container, the stirring device, and the mixture.

[0043] S3. Stir the first mixture obtained in step S2 at a stirring rate of 600 rpm. Add a sodium hydroxide solution with a concentration of 1 mol / L (CO) dropwise to the first mixture until the pH value is 3.0. The titration is then completed. After weighing, a second mixture with a mass of m2 is obtained.

[0044] S4. Calculate the free acidity C in the electrolyte to be tested using the following formula. , Wherein, m1=92.00g, m2=96.58g, K1=0.05g, K2=1.01g / mL, V=1mL, C0=1mol / L; the calculated free acidity C=4.49mol / L. Example 2

[0045] This embodiment is based on Example 1, the difference being that the pH value of the vanadium ion masking agent is different in step S1, while the other steps remain the same as in Example 1. Specifically, Step S1 in this embodiment is as follows: 0.15 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH of the system to 6.5 to obtain a vanadium ion masking agent.

[0046] After titration, the free acidity C = 4.46 mol / L was obtained by using the same calculation method as in Example 1. Example 3

[0047] This embodiment is based on Example 1, the difference being that the pH value of the vanadium ion masking agent is different in step S1, while the other steps remain the same as in Example 1. Specifically, Step S1 in this embodiment is as follows: 0.15 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH of the system to 7.5 to obtain a vanadium ion masking agent.

[0048] After titration, the free acidity C = 4.50 mol / L was obtained by using the same calculation method as in Example 1. Example 4

[0049] This embodiment is based on Example 1, the difference being that the pH value of the vanadium ion masking agent is different in step S1, while the other steps remain the same as in Example 1. Specifically, Step S1 in this embodiment is as follows: 0.15 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH of the system to 8.0 to obtain a vanadium ion masking agent.

[0050] After titration, the free acidity C = 4.48 mol / L was obtained by using the same calculation method as in Example 1. Example 5

[0051] This embodiment is based on Example 3, the difference being that the amount of disodium ethylenediaminetetraacetate used in step S1 is different, while the other steps remain the same as in Example 3. Specifically, Step S1 in this embodiment is as follows: 0.1 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH of the system to 7.5 to obtain a vanadium ion masking agent.

[0052] After titration, the free acidity C = 4.47 mol / L was obtained by using the same calculation method as in Example 3. Example 6

[0053] This embodiment is based on Example 3, the difference being that the amount of disodium ethylenediaminetetraacetate used in step S1 is different, while the other steps remain the same as in Example 3. Specifically, Step S1 in this embodiment is as follows: 0.2 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH of the system to 7.5 to obtain a vanadium ion masking agent.

[0054] After titration, the free acidity C = 4.54 mol / L was obtained by using the same calculation method as in Example 3. Example 7

[0055] This embodiment is based on Example 3, the difference being that the amount of vanadium ion masking agent used in step S2 is different, while the other steps remain the same as in Example 3. Specifically, Step S2 in this embodiment is as follows: Provide 50 mL of the electrolyte to be tested (a standard sample of sulfuric acid-based vanadium electrolyte, with a concentration of 1 mol / L for tetravalent vanadium ions, a concentration of 1 mol / L for pentavalent vanadium ions, and a free acidity of 4.5 mol / L), and ultrasonically disperse it at 200 W for 15 min; take 1 mL (V) of the ultrasonically dispersed electrolyte to be tested, add 29 mL of deionized water to the electrolyte to be tested, and obtain 30 mL of diluted electrolyte; take 1 mL of the vanadium ion masking agent obtained in step S1, and add 1 mL of the vanadium ion masking agent to the 30 mL diluted electrolyte, and weigh it to obtain the first mixture with a mass of m1.

[0056] After titration, the free acidity C = 4.48 mol / L was obtained by using the same calculation method as in Example 3. Example 8

[0057] This embodiment is based on Example 3, the difference being that: in step S2, the valence state of vanadium ions in the 50 mL electrolyte to be tested changes, while the other steps remain the same as in Example 3. Specifically, in the 50 mL electrolyte to be tested provided in this embodiment, the concentration of divalent vanadium ions is 1 mol / L, the concentration of trivalent vanadium ions is 1 mol / L, and the free acidity is 4.50 mol / L.

[0058] After titration, the free acidity C = 4.53 mol / L was obtained by using the same calculation method as in Example 3. Comparative Example 1

[0059] This comparative example is based on Example 2, the difference being that the pH value of the vanadium ion masking agent is different in step S1, while the other steps remain the same as in Example 2. Specifically, Step S1 in this embodiment is as follows: 0.15 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH to 6.0 to obtain a vanadium ion masking agent.

[0060] After titration, the free acidity C = 4.39 was obtained by using the same calculation method as in Example 2. Comparative Example 2

[0061] This comparative example is based on Example 2, the difference being that the pH value of the vanadium ion masking agent is different in step S1, while the other steps remain the same as in Example 2. Specifically, Step S1 in this embodiment is as follows: 0.15 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH to 8.5 to obtain a vanadium ion masking agent.

[0062] After titration, the free acidity C = 4.38 mol / L was obtained by using the same calculation method as in Example 2. Comparative Example 3

[0063] This comparative example is based on Example 2, the difference being that the amount of disodium ethylenediaminetetraacetate used in step S1 is different, while the other steps remain the same as in Example 2. Specifically, Step S1 in this embodiment is as follows: 0.05 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH to 6.5 to obtain a vanadium ion masking agent.

[0064] After titration, the free acidity C = 4.41 mol / L was obtained by using the same calculation method as in Example 2. Comparative Example 4

[0065] This comparative example is based on Example 2, the difference being that the amount of disodium ethylenediaminetetraacetate used in step S1 is different, while the other steps remain the same as in Example 2. Specifically, Step S1 in this embodiment is as follows: 0.25 mol of disodium ethylenediaminetetraacetate was added to 70 mL of deionized water, and the volume was adjusted to 100 mL with more deionized water to obtain a complexing agent solution. The temperature of the complexing agent solution was controlled at 60 °C, and the solution was stirred at 300 rpm for 2 min. Under the stirring conditions of 60 °C and 300 rpm, sodium hydroxide (analytical grade) was added to adjust the pH to 6.5 to obtain a vanadium ion masking agent.

[0066] After titration, the free acidity C = 4.60 mol / L was obtained by using the same calculation method as in Example 2.

[0067] 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 method for detecting free acidity in a sulfate-based vanadium redox flow battery electrolyte, characterized in that, Includes the following steps: S1. Provide a vanadium ion complexing agent, mix the vanadium ion complexing agent with water, adjust the pH to 6.5~8.0, and obtain a vanadium ion masking agent with a concentration of 1~2 mol / L, wherein the vanadium ion complexing agent is an ethylenediaminetetraacetic acid-based complexing agent; S2. Provide the electrolyte to be tested, and add the vanadium ion masking agent obtained in step S1 to the electrolyte to be tested to obtain a first mixture with a mass of m1. S3. Stir the first mixture obtained in step S2, and add a standard alkaline solution with a concentration of C0 dropwise to the first mixture until the pH is 2.98~3.

05. The titration is then completed, and a second mixture with a mass of m2 is obtained. S4. Calculate the free acidity C in the electrolyte to be tested using the following formula. ， In the formula, m1 and m2 are both in g; K1 is the correction parameter, with a value of 0.05 and a unit of g; K2 is the correction parameter, with a value of 1.01 and a unit of g / mL; V is the volume of the electrolyte to be tested, with a unit of mL; C0 is in mol / L; and C is in mol / L.

2. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S1, the vanadium ion complexing agent and water are mixed to obtain a complexing agent solution. Sodium hydroxide is added to the complexing agent solution to adjust the pH to 7.0~7.5, thereby obtaining a vanadium ion masking agent with a concentration of 1.4~1.6 mol / L.

3. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 2, characterized in that, In step S1, the temperature of the complexing agent solution is controlled at 50~70℃, and the solution is stirred at a stirring rate of 200~400rpm. Sodium hydroxide is added to the complexing agent solution.

4. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S1, the vanadium ion complexing agent is selected from at least one of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA.

5. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S2, the electrolyte to be tested is provided, and the electrolyte to be tested is diluted with water to obtain a diluted electrolyte. The vanadium ion masking agent obtained in step S1 is added to the diluted electrolyte to obtain a first mixture with a mass of m1. The volume ratio of vanadium ion masking agent to diluted electrolyte is (1~2):(25~35).

6. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 5, characterized in that, In step S2, the volume ratio of vanadium ion masking agent to diluted electrolyte is 2:

30.

7. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 5, characterized in that, In step S2, the volume ratio of the diluted electrolyte to the electrolyte to be tested is (20~50):

1.

8. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S2, the total concentration of vanadium ions in the electrolyte to be tested is 0.1~2.0 mol / L.

9. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S3, the first mixture obtained in step S2 is stirred at a stirring rate of 550~650 rpm, and a standard alkaline solution with a concentration of C0 is added dropwise to the first mixture until the pH is 3.

0.

10. The method for detecting free acidity in the electrolyte of a sulfuric acid-based vanadium redox flow battery according to claim 1, characterized in that, In step S3, the standard alkaline solution is selected from sodium hydroxide solution with a concentration of 0.1~1.0 mol / L.

Images