Method for detecting vanadium ion concentration in negative electrolyte of vanadium battery by two-step potential titration

Abstract

The present application belongs to the field of metal ion concentration detection, and particularly relates to a method for detecting the concentration of vanadium ions in the negative electrolyte of a vanadium battery by two-step potentiometric titration. In view of the problems of inaccurate measurement results, large errors and complicated operation of the negative electrolyte of the vanadium battery, the present application detects the concentration of vanadium ions in the negative electrolyte of the vanadium battery by two-step potentiometric titration. In the first step, the negative electrolyte is added to a solution containing excess pentavalent vanadium and sulfuric acid, and the pentavalent vanadium ions oxidize the divalent and trivalent vanadium ions in the solution into tetravalent vanadium ions, and at the same time, part of the pentavalent vanadium ions are reduced into tetravalent vanadium ions. Subsequently, the concentration of tetravalent vanadium ions in the solution is titrated with potassium permanganate to solve the problem of exposure of divalent vanadium ions to oxidation. In the second step, the concentration of vanadium ions in the negative electrolyte is directly titrated with potassium permanganate. The results prove that the present application has small detection result deviation, high precision and accuracy, and the instrument is light and portable, and is suitable for real-time monitoring of energy storage power stations.

Description

Technical Field

[0001] This invention belongs to the field of metal ion concentration detection, specifically relating to a two-step potentiometric titration method for detecting vanadium ion concentration and state of charge in vanadium battery negative electrode electrolyte. Background Technology

[0002] Electrolyte is the energy storage medium of vanadium batteries. The concentration of vanadium ions and the state of charge (SOC) in the electrolyte are important parameters characterizing the remaining capacity of the battery. Monitoring the electrolyte concentration and SOC is of great significance for the operation control, system design and maintenance of vanadium redox flow batteries.

[0003] Currently, the concentration of vanadium ions and the state of charge (SOC) in the negative electrode electrolyte can be measured by titration, UV-Vis spectroscopy, and voltage method. Titration yields accurate results, but because divalent vanadium ions in the negative electrode electrolyte are easily oxidized, measurements must be performed under nitrogen protection, which is cumbersome and requires bulky equipment (nitrogen cylinders), resulting in poor field applicability. While UV-Vis spectrophotometry can quickly monitor the full spectrum of optical signals and easily achieves online measurement and big data-based signal analysis, it currently only reads absorbance at one or a few specific wavelengths, failing to maximize the use of all optical test information. Furthermore, the peak positions of vanadium electrolytes shift with changes in electrolyte composition, and the absorption peaks of divalent, trivalent, and tetravalent vanadium ions overlap, meaning a fixed wavelength cannot represent the peak positions at all SOC levels. Therefore, the accuracy of measurements for vanadium battery negative electrode electrolytes is relatively poor. Patent CN117760996A proposes an improved UV-Vis spectrophotometric method for measuring the concentration and valence state of vanadium ions in negative electrode electrolytes. This method involves adding an excess of tetravalent vanadium ion standard solution to the negative electrode electrolyte, oxidizing all divalent vanadium ions to trivalent vanadium ions. The absorbance of the mixed trivalent and tetravalent vanadium electrolyte is then measured using a UV spectrophotometer to calculate the concentrations of divalent and trivalent vanadium ions in the negative electrode electrolyte. While this method solves the problem of divalent vanadium ion oxidation during UV-Vis spectroscopy analysis, the characteristic absorption peaks of trivalent and tetravalent vanadium ions partially overlap, interfering with the detection results and resulting in poor accuracy. Furthermore, UV-Vis spectroscopy is highly dependent on equipment, requiring calibration and standard curves, and the instruments are expensive and complex to maintain. Voltage-based methods offer fast response times and are suitable for online measurements. However, the circuit voltage used has poor specificity, and the voltage value is easily affected by substances other than vanadium in the electrolyte and the electrode state. Furthermore, they have strict requirements regarding the state of the reference side. For example, patent CN112415077A proposes a method that uses the voltage difference between a reference cell and a working cell to monitor valence state changes and then calculates the vanadium ion concentration based on the time taken. This method can measure vanadium ions in all valence states in the positive and negative electrode electrolytes, but the working cell and reference cell are connected by a tubing. The difference in SOC between the working and reference cells allows vanadium ions to migrate through the membrane, causing changes in SOC and voltage, resulting in inaccurate test results. Therefore, the core shortcomings of existing technologies are: inability to simultaneously handle rapid on-site detection (such as in energy storage power station operation and maintenance), poor anti-interference capabilities, and low accuracy. Summary of the Invention

[0004] To address the problems of inaccurate measurement results, large measurement errors, and cumbersome operation in current vanadium battery negative electrode electrolyte measurements, this invention proposes a two-step potentiometric titration method for detecting vanadium ion concentration in vanadium battery negative electrode electrolytes without the need for a protective atmosphere. This method can rapidly and accurately analyze the vanadium ion concentration and state of charge (SOC) in vanadium battery negative electrode electrolytes, completely avoiding measurement errors caused by the oxidation of divalent vanadium ions by air. It achieves on-site quantitative detection without the need for inert gas protection and is easy to operate. This method requires only a portable potentiometric titrator, making it suitable for real-time monitoring in energy storage power stations; its accuracy is comparable to laboratory methods, and it can effectively promote the intelligent upgrading of vanadium battery management systems.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, the present invention provides a method for detecting the concentration of vanadium ions in the negative electrode electrolyte of a vanadium battery using a two-step potentiometric titration, comprising the following steps:

[0007] S1. Add a volume of V0 of vanadium battery negative electrode electrolyte A to 10 mL of sulfuric-phosphoric acid mixed solution and excess oxidant solution, and dilute to a concentration of C. KMnO4 Potassium permanganate standard solution was used as the titration solution for potentiometric titration. When the solution turned light pink or light red and the potentiometric titrator showed a sudden endpoint, the volume V1 of potassium permanganate solution consumed was recorded.

[0008] S2. Take another vanadium battery negative electrode electrolyte A with the same volume V0 as in step S1, add 10 mL of sulfuric-phosphoric acid solution to it, dilute it, and then titrate it with a potassium permanganate standard solution of the same concentration as in step S1. When the solution color turns light pink or light red and the potentiometric titrator shows three abrupt endpoints, record the volume of potassium permanganate consumed corresponding to the three abrupt endpoints, and label them as V1', V2', and V3' respectively. Calculate the total vanadium ion concentration C in the negative electrode electrolyte according to formulas (1) to (4). TV vanadium divalent ion concentration trivalent vanadium ion concentration and state of charge (SOC);

[0009]

[0010] In step S1, the volume fraction ratio of the sulfuric acid-phosphoric acid mixed solution is sulfuric acid:phosphoric acid:water = 1:1:1.

[0011] In step S1, the volume V0 of the vanadium battery negative electrode electrolyte is 0.2–2 mL, preferably 0.2–1 mL.

[0012] In step S1, the concentration C of the potassium permanganate standard solution is... KMnO4The concentration is 0.02–0.1 mol / L, preferably 0.03–0.06 mol / L.

[0013] In step S1, the vanadium battery negative electrode electrolyte is a sulfuric acid solution system with a total vanadium concentration of 0.1–4 mol / L.

[0014] In step S1, the oxidant solution is a solution containing pentavalent vanadium, with a vanadium ion concentration of 0.1–2 mol / L, preferably 0.2–1 mol / L.

[0015] Preferably, the vanadium source of the solution containing pentavalent vanadium comes from at least one of the following: a pentavalent vanadium electrolyte in a sulfuric acid system, a sodium vanadate solution, a potassium vanadate solution, or an ammonium metavanadate solution.

[0016] More preferably, if the vanadium source is a pentavalent vanadium electrolyte, the pentavalent vanadium electrolyte is diluted with water to 0.2–1.0 mol / L. If the pentavalent vanadium is vanadium pentoxide, vanadium pentoxide is first dissolved in sodium hydroxide, then acidified with 1:1 H2SO4, and finally brought to a final volume to a vanadium ion concentration of 0.2–1.0 mol / L.

[0017] More preferably, if the vanadium source is a sodium vanadate, potassium vanadate, or ammonium metavanadate solution, it is dissolved in 5% sulfuric acid and brought to a final volume to a vanadium ion concentration of 0.2–1.0 mol / L.

[0018] In step S1, the amount of oxidant solution added is in excess, preferably 20-30 mL.

[0019] In step S2, V1' corresponds to the volume of potassium permanganate consumed in the oxidation of divalent vanadium ions to trivalent vanadium ions, V2'-V1' corresponds to the volume of potassium permanganate consumed in the oxidation of trivalent vanadium ions to tetravalent vanadium ions, and V3'-V2' corresponds to the volume of potassium permanganate consumed in the oxidation of tetravalent vanadium ions to pentavalent vanadium ions. Since divalent vanadium is easily oxidized by air, the volumes of potassium permanganate consumed are selected from V2'-V1' and V3'-V2' when calculating the total vanadium ion concentration, with V3'-V2' being preferred.

[0020] Beneficial Effects: This invention employs a two-step potentiometric titration method to detect the vanadium ion concentration in the negative electrode electrolyte of vanadium batteries under conditions without inert gas protection. Before titration, an excess of a sulfuric-phosphoric acid solution is added to utilize the specific complexation of ferric ions by phosphoric acid, eliminating the interference of trivalent ferric ions on the titration process. In the first titration step, an excess of oxidant is added, which rapidly oxidizes all divalent and trivalent vanadium ions in the negative electrode electrolyte to tetravalent vanadium ions in an open system. Simultaneously, some pentavalent vanadium ions are reduced to tetravalent ions, solving the problem of exposed oxidation of divalent vanadium ions. Experimental results show that the detection method of this invention has small deviations and high precision and accuracy. The second titration step directly titrates the vanadium ion concentration in the negative electrode electrolyte with potassium permanganate. The two-step potentiometric titration detection method of this invention does not require the introduction of a protective gas during the testing process, making it simple and convenient to operate. It can achieve rapid detection of vanadium ions in the electrolyte of vanadium redox flow batteries, meeting analytical requirements. The analysis is fast, the operation is simple, and it has high application value. Detailed Implementation

[0021] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this application clearer, the following detailed description is provided in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as understood by one of ordinary skill in the art.

[0022] In one embodiment of the present invention, a method for detecting the vanadium ion concentration in a vanadium battery negative electrode electrolyte using a two-step potentiometric titration method is provided, comprising the following steps:

[0023] S1. Add a volume of V0 of vanadium battery negative electrode electrolyte A to 10 mL of sulfuric-phosphoric acid mixed solution and excess oxidant solution, and dilute to a concentration of C. KMnO4 Potassium permanganate standard solution was used as the titer solution for potentiometric titration. When the solution turned light pink or light red and the potentiometric titrator showed a sudden endpoint, the volume of potassium permanganate solution consumed, V1, was recorded.

[0024] S2. Take another vanadium battery negative electrode electrolyte A with the same volume V0 as in step S1, add 10 mL of sulfuric-phosphoric acid solution to it, dilute it, and then titrate it with a potassium permanganate standard solution of the same concentration as in step S1. When the solution color turns light pink or light red and the potentiometric titrator shows three abrupt endpoints, record the volume of potassium permanganate consumed corresponding to the three abrupt endpoints, and label them as V1', V2', and V3' respectively. Calculate the total vanadium ion concentration C in the negative electrode electrolyte according to formulas (1) to (4). TV vanadium divalent ion concentration trivalent vanadium ion concentration and the state of charge (SOC).

[0025] The principle of this invention for two-step potentiometric titration to detect vanadium ion concentration in vanadium battery negative electrode electrolyte is as follows:

[0026] In potentiometric titration, the concentration of vanadium ions and the concentrations of vanadium ions in different valence states in the solution are calculated by measuring the volume of potassium permanganate consumed during the potential abrupt change. Assuming the concentration of divalent vanadium ions in the solution is x, and the concentration of trivalent vanadium ions is y, then the total concentration of vanadium ions is C. TV =x + y.

[0027] Without an oxidizing agent, during the entire titration process, potassium permanganate first oxidizes all divalent vanadium ions in the negative electrode electrolyte to trivalent vanadium ions. As the titration proceeds, the trivalent vanadium ions are successively oxidized to tetravalent and pentavalent vanadium ions, resulting in three potential abrupt change points V1', V2', and V3', corresponding to V... 2+ →V 3+ V 3+ →V 4+ and V 4+ →V 5+ However, the titration process is carried out in air, and the divalent vanadium ions in the electrolyte are partially oxidized. Therefore, V1' cannot be used to calculate the concentration of divalent vanadium ions in the electrolyte. The concentration of vanadium ions in the electrolyte can be calculated by calculating V2'-V1' and V3'-V2'. Preferably, V3'-V2' is used to calculate the total vanadium concentration.

[0028]

[0029] When an excess of oxidizing agent is added, the pentavalent vanadium ions oxidize all the divalent and trivalent vanadium ions to tetravalent ions, and are themselves reduced to tetravalent ions, as shown in the following reaction:

[0030] One divalent vanadium ion consumes two pentavalent vanadium ions to produce three tetravalent vanadium ions; one trivalent vanadium ion reacts with one pentavalent vanadium ion to produce two tetravalent vanadium ions. Assuming the concentration of divalent vanadium ions in the solution is x and the concentration of trivalent vanadium ions is y, then after the reaction is complete, the total concentration of tetravalent vanadium ions is 3x + 2y. Through potentiometric titration, potassium permanganate oxidizes all tetravalent vanadium ions to pentavalent vanadium ions. The volume of potassium permanganate consumed when the potential changes abruptly is V1.

[0031] Solve equations (1) and (2) to calculate...

[0032]

[0033]

[0034] In this invention, the purpose of adding a sulfuric-phosphoric acid mixed solution is: 1. To provide a strongly acidic environment, preventing the hydrolysis of vanadium ions and ensuring the reaction proceeds stoichiometrically. 2. To utilize the specific complexation of phosphoric acid with iron ions to eliminate Fe. 3+ Interferences to the titration process are crucial for ensuring accurate results. 3. Improve the reaction system to make the endpoint of potentiometric titration more pronounced, resulting in more accurate and reliable results.

[0035] In one embodiment of the present invention, in step S1, the oxidant solution is a solution containing pentavalent vanadium, and the vanadium ion concentration is 0.1–2 mol / L, preferably 0.2–1 mol / L.

[0036] The oxidizing agent solution is added in excess, preferably 20-30 mL. The purpose of adding excess oxidizing agent solution is to oxidize all the divalent and trivalent vanadium ions in the solution to tetravalent ions.

[0037] The purpose of adding an excess of a solution containing pentavalent vanadium as an oxidant in this invention is to utilize the strong oxidizing property of pentavalent vanadium ions to rapidly oxidize all divalent and trivalent vanadium ions in the negative electrode electrolyte to tetravalent vanadium ions in an open system. Simultaneously, some pentavalent vanadium ions are reduced to tetravalent ions, thus solving the problem of exposed oxidation of divalent vanadium ions. The redox reaction process is as follows:

[0038] V 2+ +2VO2 + +2H + →3VO 2+ +H2O(1)

[0039] V 3+ +VO2 + →2VO 2+ (2)

[0040] In one embodiment of the present invention, in step S2, V1' corresponds to the volume of potassium permanganate consumed in the oxidation of divalent vanadium ions to trivalent vanadium ions in the solution, V2'-V1' corresponds to the volume of potassium permanganate consumed in the oxidation of trivalent vanadium ions to tetravalent vanadium ions, and V3'-V2' corresponds to the volume of potassium permanganate consumed in the oxidation of tetravalent vanadium ions to pentavalent vanadium ions. Since divalent vanadium is easily oxidized by air, V2'-V1' and V3'-V2' are selected when calculating the total vanadium ion concentration, with V3'-V2' being preferred.

[0041] In one embodiment of the invention, the purpose of dilution is to maintain the same volume of solution for each measurement.

[0042] The following specific embodiments will be provided to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0043] Example 1: Detection of pure divalent electrolyte (SOC = 100%)

[0044] (1) Add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1) and 20 mL of 0.2 mol / L pentavalent vanadium red electrolyte to a 100 mL beaker. Then transfer 0.3 mL (V0) of pure divalent vanadium red electrolyte (SOC = 100%) and dilute with water to 60 mL. Titrate with 0.04 mol / L potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows a sudden endpoint. Record the volume of potassium permanganate solution consumed, V1 = 7.510 mL.

[0045] (2) Take 0.3 mL of divalent vanadium electrolyte and add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1). Dilute with water to 60 mL and titrate with potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows 3 jump endpoints. Record the volumes of potassium permanganate solution consumed at the 2nd and 3rd jump points as V2' = 4.823 mL and V3' = 7.327 mL, respectively.

[0046] (3) Calculate the total vanadium ion concentration C in the solution according to formulas 1-4. TV The concentration was 1.669 mol / L, and the state of charge (SOC) was 99.92%.

[0047]

[0048] In the above formula:

[0049] C TV The total vanadium ion concentration in the negative electrode electrolyte is expressed in mol / L.

[0050] C KMnO4 The concentration of the potassium permanganate solution is in mol / L.

[0051] V1', V2', and V3' represent the volumes of potassium permanganate consumed when divalent vanadium ions are oxidized to trivalent, trivalent vanadium ions to tetravalent, and tetravalent vanadium ions to pentavalent vanadium ions, respectively; in mL.

[0052] V0 is the volume of the electrolyte in the negative electrode vanadium battery, in mL;

[0053] The concentration of divalent vanadium ions in the negative electrode electrolyte, in mol / L;

[0054] The concentration of trivalent vanadium ions in the negative electrode electrolyte, in mol / L;

[0055] SOC refers to the state of charge of the negative electrode electrolyte, which is the proportion of divalent vanadium ions in the electrolyte to the total vanadium ion concentration.

[0056] Comparative experiment: Using the same sample, under nitrogen protection, the sample was measured by direct potentiometric titration with potassium permanganate. Three abrupt change points were obtained, corresponding to the oxidation of divalent vanadium to trivalent vanadium ions, the oxidation of trivalent vanadium ions to tetravalent vanadium ions, and the oxidation of tetravalent vanadium ions to pentavalent vanadium ions, respectively. The volumes of potassium permanganate consumed at the three potential jump points were recorded as V1” = 2.495 mL, V2” = 4.996 mL, and V3” = 7.496 mL, respectively. The total vanadium ion concentration C in the solution is then determined. TV The SOC and the state of charge are 1.667 mol / L and 99.80%, respectively, and the calculation formula is shown in Equation 5-8.

[0057]

[0058] Compared with conventional methods, the detection results of the negative electrode electrolyte obtained by this invention show a relative error of 0.12% in the total vanadium ion concentration and an error of 0.12% in the state of charge.

[0059] Example 2: Detection of mixed valence state electrolyte (SOC = 50%)

[0060] (1) Add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1) and 20 mL of 0.2 mol / L pentavalent vanadium electrolyte to a 100 mL beaker. Then transfer 0.3 mL (V0) of divalent and trivalent vanadium mixed electrolyte (SOC of 50%) and dilute with water to 60 mL. Titrate with 0.06 mol / L potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows a sudden endpoint. Record the volume of potassium permanganate solution consumed, V1 = 8.946 mL.

[0061] (3) Take 0.3 mL of the mixed electrolyte of divalent and trivalent vanadium (SOC of 50%), add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1), dilute with water to 60 mL, and titrate with potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows 3 jump endpoints. Record the volumes of potassium permanganate solution consumed at the 2nd and 3rd jump points as V2' = 5.224 mL and V3' = 8.788 mL, respectively.

[0062] (3) Calculate the total vanadium ion concentration C in the solution according to formulas 1-4. TV The concentration was 3.564 mol / L, and the state of charge (SOC) of the solution was 51.01%.

[0063] Comparative experiment: Using the same sample, under nitrogen protection, the sample was measured by direct potentiometric titration with potassium permanganate. Three abrupt change points were obtained, and the volumes of potassium permanganate consumed at each of the three potential jump points were recorded as V1” = 1.833 mL, V2” = 5.40 mL, and V3” = 8.969 mL, respectively. The total vanadium ion concentration C in the solution is then determined. TV The SOC and the state of charge are 3.569 mol / L and 51.36%, respectively, and the calculation formulas are shown in Equations 5-8.

[0064] Compared with conventional methods, the detection results of the negative electrode electrolyte obtained by this invention show a relative error of 0.14% in the total vanadium ion concentration and an error of 0.68% in the state of charge (SOC).

[0065] Example 3: Detection of low SOC electrolyte (SOC = 10%)

[0066] (1) Add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1) and 20 mL of 0.2 mol / L pentavalent vanadium electrolyte to a 100 mL beaker. Then transfer 0.5 mL (V0) of divalent and trivalent mixed electrolyte (SOC of 90%) and dilute with water to 60 mL. Titrate with 0.02 mol / L potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows a sudden endpoint. Record the volume of potassium permanganate solution consumed, V1 = 6.809 mL.

[0067] (2) Take 0.3 mL of the mixed divalent and trivalent electrolyte (SOC is 10%), add 10 mL of sulfur-phosphorus mixed acid solution (sulfur, phosphorus and water volume ratio 1:1:1), dilute with water to 60 mL, and titrate with potassium permanganate standard solution using potentiometric titration until the solution turns light pink or light red and the potentiometric titrator shows 3 jump endpoints. Record the volumes of potassium permanganate solution consumed at the 2nd and 3rd jump points as V2' = 3.53 mL and V3' = 6.775 mL, respectively.

[0068] (3) Calculate the total vanadium ion concentration C in the solution according to formulas 1-4. TV The concentration was 0.649 mol / L, and the state of charge (SOC) was 9.83%.

[0069] Comparative experiment: Using the same sample, under nitrogen protection, the sample was measured by direct potentiometric titration with potassium permanganate. Three abrupt change points were obtained, and the volumes of potassium permanganate consumed at each of the three potential jump points were recorded as V1” = 0.322 mL, V2” = 3.582 mL, and V3” = 6.843 mL, respectively. The total vanadium ion concentration C in the solution is then determined. TV The SOC and the state of charge are 0.652 mol / L and 9.87%, respectively, and the calculation formula is shown in Equation 5-8.

[0070] Compared with conventional methods, the detection results of the negative electrode electrolyte obtained by this invention show that the relative error of the total vanadium ion concentration is 0.56%, and the error of the state of charge (SOC) is 0.41%.

[0071] Example 4: Precision of the detection method described in this invention

[0072] Experimental method: Five different electrolyte samples were selected, and the total vanadium ion concentration and state of charge of the negative electrode electrolyte were determined according to the detection method in Example 1. The relative standard deviation was calculated, and the experimental results are shown in Table 1.

[0073] Table 1. Precision test results of the detection method described in this invention.

[0074]

[0075] The experimental results above show that the detection method described in this invention has small deviations, high precision and accuracy, meets analytical requirements, has fast analysis speed, and is simple to operate, thus having high value for promotion and application.

Claims

1. A method for determining the concentration of vanadium ions in the negative electrode electrolyte of a vanadium battery using a two-step potentiometric titration, characterized in that, Includes the following steps: S1. Add a volume of V0 of vanadium battery negative electrode electrolyte A to 10 mL of sulfuric-phosphoric acid mixed solution and excess oxidant solution, and dilute to a concentration of C. KMnO4 Potassium permanganate standard solution was used as the titration solution for potentiometric titration. When the solution turned light pink or light red and the potentiometric titrator showed a sudden endpoint, the volume of potassium permanganate solution consumed, V1, was recorded. S2. Take another vanadium battery negative electrode electrolyte A with the same volume V0 as in step S1, add 10 mL of a sulfuric-phosphoric acid mixed solution, dilute, and then titrate with a potassium permanganate standard solution of the same concentration as in step S1. When the solution color turns light pink or light red and the potentiometric titrator shows three abrupt endpoints, record the volume of potassium permanganate consumed corresponding to each of the three abrupt endpoints, and label them as follows: , , The total vanadium ion concentration C in the negative electrode electrolyte is calculated according to formulas (1) to (4). TV vanadium divalent ion concentration vanadium trivalent ion concentration and state of charge (SOC); .

2. The method according to claim 1, characterized in that, In step S1, the volume fraction ratio of the sulfuric acid-phosphoric acid mixed solution is sulfuric acid:phosphoric acid:water = 1:1:

1.

3. The method according to claim 1, characterized in that, In step S1, the volume V0 of the vanadium battery negative electrode electrolyte is 0.2 to 2 mL.

4. The method according to claim 1, characterized in that, In step S1, the concentration C of the potassium permanganate standard solution is... KMnO4 The concentration is 0.02–0.1 mol / L.

5. The method according to claim 1, characterized in that, In step S1, the vanadium battery negative electrode electrolyte is a sulfuric acid solution system with a total vanadium concentration of 0.1–4 mol / L.

6. The method according to claim 1, characterized in that, In step S1, the oxidant solution is a solution containing pentavalent vanadium, and the vanadium ion concentration is 0.1–2 mol / L.

7. The method according to claim 6, characterized in that, In step S1, the oxidant solution is a solution containing pentavalent vanadium, and the vanadium ion concentration is 0.2–1 mol / L.

8. The method according to claim 6, characterized in that, The vanadium source in the solution containing pentavalent vanadium comes from at least one of the following: pentavalent vanadium electrolyte in a sulfuric acid system, sodium vanadate solution, potassium vanadate solution, or ammonium metavanadate solution.

9. The method according to claim 1, characterized in that, In step S1, the amount of oxidant solution added is 20-30 mL.

10. The method according to claim 1, characterized in that, In step S2, the The volume of potassium permanganate consumed in the oxidation of divalent vanadium ions to trivalent vanadium ions in the corresponding solution. The volume of potassium permanganate consumed in the oxidation of trivalent vanadium ions to tetravalent vanadium ions. The volume of potassium permanganate consumed in the oxidation of tetravalent vanadium ions to pentavalent vanadium ions.

11. The method according to claim 10, characterized in that, When calculating the total vanadium ion concentration, the volume of potassium permanganate consumed is selected as... and .

12. The method according to claim 11, characterized in that, When calculating the total vanadium ion concentration, the volume of potassium permanganate consumed is selected as... .

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