Preparation method of vanadium electrolyte for all-vanadium redox flow battery, vanadium electrolyte and application

Abstract

The invention provides a preparation method of a vanadium electrolyte for an all-vanadium redox flow battery, the vanadium electrolyte and application. The method comprises the following steps: (1) dissolving concentrated sulfuric acid in water to obtain a sulfuric acid solution with a preset concentration, then adding vanadium pentoxide into the sulfuric acid solution, and reacting to obtain a first vanadium solution; (2) the temperature of the first vanadium solution is kept to be the preset temperature, low-valence vanadium oxide is added into the first vanadium solution for reaction, water or hydrochloric acid is supplemented in the reaction process, a second vanadium solution is obtained, and the low-valence vanadium oxide is vanadium oxide with the valence of 3-3.5; and (3) filtering the second vanadium solution to obtain the vanadium electrolyte. The method provided by the invention can save energy consumption, reduce cost and improve dissolution efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of vanadium batteries, and specifically relates to a preparation method of vanadium electrolyte for all-vanadium redox flow batteries, vanadium electrolyte and applications thereof. Background Art

[0002] An all-vanadium redox flow battery is a rechargeable and dischargeable battery in which both the positive and negative electrodes use circulating vanadium solutions as energy storage media. It has the advantages of intrinsic safety, long cycle life, low full-life cycle cost, suitability for long-duration energy storage, and rich resources, and is currently the most commercially promising redox flow battery. Vanadium electrolyte is an important component of all-vanadium redox flow batteries, accounting for more than 50% of the cost of vanadium batteries. The production cost and quality of vanadium electrolyte directly affect the cost and performance of vanadium batteries. Therefore, an excellent preparation method of vanadium electrolyte is the guarantee for reducing production costs and improving product quality.

[0003] The preparation methods of vanadium electrolyte can be divided into physical dissolution method, chemical reduction method, and electrolysis method. The physical dissolution method is to directly dissolve high-purity VOSO 4 solid in sulfuric acid to obtain electrolyte. The chemical reduction method is to use reducing agents (such as hydrogen, methane, sulfur, alcohol, etc.) to reduce high-valent vanadium oxides or vanadates to prepare electrolyte. The electrolysis method can be further divided into direct electrolysis and indirect electrolysis. In the direct electrolysis method, V 2 O 5 dissolved in sulfuric acid is introduced into the negative electrode of the electrolytic cell. After power-on, a reduction reaction occurs at the negative electrode to obtain a 3.5-valent electrolyte. Indirect electrolysis is to electrolyze vanadyl sulfate tetravalent obtained by reduction dissolution or extraction to obtain a 3.5-valent electrolyte. Both of these methods have the characteristics of high energy consumption and slow kinetic processes.

[0004] Patent document CN 116154244 A discloses a preparation method of vanadium electrolyte, which uses ammonium metavanadate to prepare vanadium oxide, uses vanadium oxide to prepare an electrolyte precursor, and uses an asymmetric electrolytic device to electrolyze the electrolyte precursor to obtain a 3.5-valent electrolyte. This method uses the electrolysis method and has high energy consumption.

[0005] Patent document CN 106941186 A discloses a vanadium electrolyte and its preparation method. Using ammonium metavanadate with a purity of 99.0-99.5 wt% as raw material, dissolve vanadium, filter to obtain a purified vanadium solution, and perform acid precipitation to obtain ammonium polyvanadate solid phase; (2) calcine the ammonium polyvanadate solid phase in a reducing atmosphere to obtain a mixture containing vanadium dioxide and vanadium trioxide; the molar ratio of vanadium dioxide to vanadium trioxide is (0.95-1.05):1; (3) dissolve the mixture in acid to obtain vanadium electrolyte. This method directly dissolves the mixture of vanadium dioxide and vanadium trioxide, with a slow kinetic process and poor dissolution efficiency.

[0006] Patent document CN 117832565 A discloses a method for preparing a 3.5-valent vanadyl sulfate electrolyte by gas-based reduction of ammonium metavanadate. The method includes: reducing and calcining ammonium metavanadate with a reducing gas to obtain a vanadium oxide; the vanadium oxide contains V 4 O 7 ; the reducing gas includes a mixed gas of NH 3 , CO and H 2 ; (2) mixing a sulfuric acid solution and the vanadium oxide for a dissolution reaction, and performing vanadium adjustment to obtain a 3.5-valent vanadyl sulfate electrolyte. This method directly dissolves V 4 O 7 , and the kinetic process is slow and the dissolution efficiency is poor.

[0007] The poor dissolution efficiency of vanadium oxide will cause an increase in insolubles in the electrolyte, easily block the reaction kettle pipeline, and at the same time increase the difficulty of removing insolubles from the electrolyte product, increase the cost of removing insolubles, and ultimately affect the quality of the electrolyte. Therefore, it is necessary to develop a vanadium electrolyte preparation technology with high dissolution efficiency and low cost to promote cost reduction of all-vanadium redox flow batteries. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems in the related art to some extent. The present invention provides a method for preparing a vanadium electrolyte for an all-vanadium redox flow battery, a vanadium electrolyte, and an application. Through the method provided by the present invention, a vanadium electrolyte can be rapidly prepared, and the cost is very low, and the dissolution rate of the prepared vanadium electrolyte is very high. The provided method can be used for industrial preparation of vanadium electrolyte, with low cost and controllable process.

[0009] Specifically, the present invention provides the following technical solutions:

[0010] In the first aspect of the present invention, a method for preparing a vanadium electrolyte for an all-vanadium redox flow battery is provided, including:

[0011] (1) Dissolve concentrated sulfuric acid in water to obtain a sulfuric acid solution with a predetermined concentration, and then add vanadium pentoxide to the sulfuric acid solution to react to obtain a first vanadium solution;

[0012] (2) Keep the temperature of the first vanadium solution at a predetermined temperature, add a low-valent vanadium oxide to the first vanadium solution to react, and supplement water or hydrochloric acid during the reaction to obtain a second vanadium solution, and the low-valent vanadium oxide is a 3-3.5-valent vanadium oxide;

[0013] (3) Filter the second vanadium solution to obtain a vanadium electrolyte.

[0014] The provided method first utilizes concentrated sulfuric acid to dissolve in water. During the process of dissolving in water, concentrated sulfuric acid generates heat, making the sulfuric acid solution itself have a certain temperature. Then, vanadium pentoxide is added to obtain a first vanadium solution. While maintaining the temperature of the first vanadium solution at a certain temperature, lower-valent vanadium oxide is slowly added, and water or hydrochloric acid is supplemented to obtain a second vanadium solution, and the vanadium electrolyte is obtained by filtration.

[0015] According to an embodiment of the present invention, the method for preparing the vanadium electrolyte for a vanadium redox flow battery described above may further include the following technical features:

[0016] According to an embodiment of the present invention, the predetermined concentration of the sulfuric acid solution in step (1) is 40 - 80%.

[0017] According to an embodiment of the present invention, the mass ratio of the vanadium pentoxide to the sulfuric acid solution is (1 - 6):100.

[0018] According to an embodiment of the present invention, the time for adding the lower-valent vanadium oxide to the first vanadium solution in step (2) is controlled within 2 hours;

[0019] The reaction time in step (2) is 6 - 8 hours.

[0020] According to an embodiment of the present invention, the mass ratio of the lower-valent vanadium oxide to the vanadium pentoxide is (2 - 15):1.

[0021] According to an embodiment of the present invention, the predetermined temperature in step (2) is 80 - 150 °C, for example, 90 °C - 140 °C. The first vanadium solution can be maintained at the predetermined temperature by continuous heating.

[0022] According to an embodiment of the present invention, the concentration of the vanadium electrolyte is 1.5 - 4.0 mol / L, the concentration of sulfate radical is 3 - 10 mol / L, and the concentration of chloride ion is 0 - 6 mol / L.

[0023] The second aspect of the present invention provides a vanadium electrolyte for a vanadium redox flow battery, obtained according to the preparation method described in any one of the first aspects.

[0024] The third aspect of the present invention provides the use of the vanadium electrolyte for a vanadium redox flow battery described in the second aspect above in the field of vanadium redox flow batteries.

[0025] The fourth aspect of the present invention provides a vanadium redox flow battery, including: a stack system, a positive electrode storage tank, a negative electrode storage tank, a circulation pump, and a management system;

[0026] The positive electrode storage tank stores positive electrode electrolyte; the negative electrode storage tank stores negative electrode electrolyte, and the positive electrode electrolyte and the negative electrode electrolyte respectively include the vanadium electrolyte for a vanadium redox flow battery described in the second aspect above.

[0027] The beneficial effects achieved by the present invention are at least as follows:

[0028] The present invention provides a preparation method of a vanadium electrolyte for a vanadium redox flow battery. This method utilizes the fact that sulfuric acid dissolves in water to generate a large amount of heat, so that the sulfuric acid solution reaches a certain temperature, even up to 100 °C, which can save energy consumption and reduce costs. Then, vanadium pentoxide is added to the hot sulfuric acid solution and stirred to dissolve and hydrolyze into loose and porous flocculent vanadium pentoxide; the loose and porous flocculent vanadium pentoxide suspension reacts and dissolves with a low-valent vanadium oxide, such as the low-valent vanadium oxide obtained by reducing ammonium metavanadate. The liquid-solid reaction kinetics is faster and the dissolution efficiency is higher; the low-valent vanadium oxide is slowly added for dissolution, which can reduce the wear of the vanadium oxide solid on the stirring paddle and improve the dissolution efficiency at the same time. Description of the Drawings

[0029] Figure 1 is the preparation method of the vanadium electrolyte for a vanadium redox flow battery provided by the embodiment of the present invention.

[0030] Figure 2 is the charge-discharge curve of the electrolyte at a current density of 150 mA / cm 2 under the conditions provided by Embodiment 5 of the present invention. Detailed Embodiments

[0031] The embodiments of the present invention are described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as a limitation to the present invention.

[0032] The present invention provides a preparation method of a vanadium redox flow battery electrolyte, and the method includes the following steps:

[0033] S10: Dissolve concentrated sulfuric acid in water to obtain a sulfuric acid solution with a predetermined concentration, and then add vanadium pentoxide to the sulfuric acid solution to react to obtain a first vanadium solution;

[0034] S20: Keep the temperature of the first vanadium solution at a predetermined temperature, add a low-valent vanadium oxide to the first vanadium solution to react, and supplement water or hydrochloric acid during the reaction to obtain a second vanadium solution, where the low-valent vanadium oxide is a vanadium oxide with a valence of 3 to 3.5;

[0035] S30: Filter the second vanadium solution to obtain a vanadium electrolyte.

[0036] S10: Dissolve concentrated sulfuric acid in water to obtain a sulfuric acid solution with a predetermined concentration, and then add vanadium pentoxide to the sulfuric acid solution to react and obtain a first vanadium solution.

[0037] The pentavalent vanadium ions after the dissolution of vanadium pentoxide will hydrolyze at a higher temperature to form a loose and porous hydrated vanadium pentoxide flocculent precipitate. The obtained first vanadium solution is a suspension, and the loose and porous vanadium pentoxide is more conducive to the reaction with lower-valent vanadium oxides.

[0038] According to the specific embodiment, the concentration of the sulfuric acid solution is 40-80%, and examples are 50%, 60%, 70%, 80%.

[0039] According to the specific embodiment, the mass ratio of vanadium pentoxide to the sulfuric acid solution is (1-6):100, such as 1:100, 2:100, 3:100, 4:100, 5:100, 6:100. The amount of vanadium pentoxide is determined according to the amount and valence state of the lower-valent vanadium oxide. After adding vanadium pentoxide to the sulfuric acid solution, stir, and the stirring time is 0.5-2h, and examples are 0.5, 1, 1.5, 2h.

[0040] S20: Keep the temperature of the first vanadium solution at a predetermined temperature, add a lower-valent vanadium oxide to the first vanadium solution to react, and supplement water or hydrochloric acid during the reaction to obtain a second vanadium solution.

[0041] According to the specific embodiment, the lower-valent vanadium oxide is a vanadium oxide with a valence of 3-3.5. According to the preferred embodiment, the mentioned lower-valent vanadium oxide is a vanadium oxide with a valence of 3.1-3.3. The mentioned lower-valent vanadium oxide is obtained by reducing vanadium pentoxide or calcining ammonium metavanadate. According to the preferred embodiment, the mentioned lower-valent vanadium oxide is the lower-valent vanadium oxide reduced from ammonium metavanadate. These lower-valent vanadium oxides are loose and porous, which is more conducive to the dissolution reaction. The mass ratio of the lower-valent vanadium oxide to vanadium pentoxide is (2-15):1, and examples are 3:1, 5:1, 7:1, 9:1, 11:1, etc. At this ratio, the dissolution rate of the prepared vanadium electrolyte can be high.

[0042] The lower-valent vanadium oxide can be slowly added to the first vanadium solution (stirring can be carried out while adding), and the slow addition time is 0.5-4h, and examples are 0.5, 1, 2, 3, 4h. If the lower-valent vanadium oxide is added too quickly, there will be too many powders in the whole solution, which will cause relatively large wear on the stirring paddle; if the addition is too slow, the dissolution time will be increased, which will affect the cost to a certain extent. During the research process, it was found that if the lower-valent vanadium oxide was not slowly added but directly added, the dissolution rate of the prepared vanadium electrolyte would be significantly reduced.

[0043] The mass ratio of the water or hydrochloric acid to the sulfuric acid solution in step a is 20-70%, for example, 20%, 30%, 40%, 50%, 60%, 70%. The concentration of the added hydrochloric acid is 10-38%.

[0044] The time of the reaction mentioned is 4-12h. The predetermined temperature mentioned is 80-140°C (for example, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, etc.). According to a preferred embodiment, the predetermined temperature mentioned is 100-140 degrees Celsius, more preferably 110-130 degrees Celsius. At this temperature and time, the reaction can be complete, and the production cost will not be increased. If the reaction time is increased, the energy consumption will increase, the production cost will be greatly improved, and the reaction efficiency will not be improved. According to a preferred embodiment, the predetermined temperature is 120-130°C.

[0045] S30: filtering the second vanadium solution to obtain a vanadium electrolyte.

[0046] The vanadium electrolyte is obtained by filtration. The concentration of the obtained vanadium electrolyte is 1.5-4.0 mol / L, the sulfate concentration is 3-10 mol / L, and the chloride ion concentration is 0-6 mol / L (for example, 1-2 mol / L).

[0047] The provided vanadium electrolyte can be used to prepare an all-vanadium liquid flow battery. To this end, the present invention provides an all-vanadium liquid flow battery, comprising: a battery stack system, a positive electrode storage tank, a negative electrode storage tank, a circulation pump and a management system; the positive electrode storage tank stores a positive electrode electrolyte; the negative electrode storage tank stores a negative electrode electrolyte; the positive electrode electrolyte and the negative electrode electrolyte respectively include the vanadium electrolyte for an all-vanadium liquid flow battery mentioned in the present invention. The positive electrode electrolyte and the negative electrode electrolyte can contain vanadium electrolytes with different vanadium ion valence states as needed, and are used to prepare an all-vanadium liquid flow battery.

[0048] The stack system is the core part of the battery, including electrodes, ion exchange membranes, bipolar plates, current collectors, etc. The stack system is the place where electrochemical reactions occur, and the charging and discharging process is realized through the redox reaction on the electrode surface. The positive electrode electrolyte and the negative electrode electrolyte, as active substances, circulate in the stack through the circulation pump to participate in the electrochemical reaction. The circulation pump is used to transport the electrolyte from the storage tank to the stack and circulate it in the battery system to ensure that the electrolyte fully reacts on the electrode surface. The management system is used to monitor and manage the status of the battery to ensure the safe operation and performance optimization of the battery. In addition, the all-vanadium liquid flow battery can further include a power conversion system, which can be used to convert the direct current of the battery into alternating current for use by external devices.

[0049] The technical solution of the present invention will be described below through specific embodiments. It should be noted that these embodiments are only for the convenience of those skilled in the art and should not be regarded as a limitation on the protection scope of the present invention. Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products or can be prepared by known methods.

[0050] Example 1

[0051] Example 1 prepares a vanadium electrolyte by the following method, including:

[0052] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly, add 5.5 g of vanadium pentoxide, and stir for 2 h to obtain vanadium solution 1.

[0053] Heat vanadium solution 1 to 120 °C, continuously stir, and slowly add 3.3-valent vanadium oxide reduced from 34 g of ammonium metavanadate, and control to add it within 2 h.

[0054] Heat and react for 6 h, add 80 mL of pure water during the process, cool and filter, and make up the volume to 200 mL to obtain a 2.43 mol / L vanadium electrolyte with a sulfate ion concentration of 6.3 mol / L.

[0055] Example 2

[0056] Example 2 prepares a vanadium electrolyte by the following method, including:

[0057] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly, add 5.5 g of vanadium pentoxide, and stir for 2 h to obtain vanadium solution 1.

[0058] Heat vanadium solution 1 to 120 °C, continuously stir, and slowly add 3.3-valent vanadium oxide reduced from 34 g of vanadium pentoxide, and control to add it within 2 h.

[0059] Heat and react for 6 h, add 80 mL of pure water during the process, cool and filter, and make up the volume to 200 mL to obtain a 2.4 mol / L vanadium electrolyte with a sulfate ion concentration of 6.3 mol / L.

[0060] Example 3

[0061] Example 3 prepares a vanadium electrolyte by the following method, including:

[0062] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly, add 9.6 g of vanadium pentoxide, and stir for 2 h to obtain vanadium solution 1.

[0063] Heat vanadium solution 1 to 120 °C, continuously stir, and slowly add 3.1-valent vanadium oxide reduced from 34 g of ammonium metavanadate, and control to add it within 2 h.

[0064] Heat the reaction for 6 h, add 80 mL of pure water during the process, cool and filter, and make up the volume to 200 mL to obtain a vanadium electrolyte with a concentration of 2.47 mol / L and a sulfate ion concentration of 6.3 mol / L.

[0065] Example 4

[0066] Vanadium electrolyte was prepared in Example 4 by the following method, including:

[0067] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly, add 5.5 g of vanadium pentoxide, and stir for 2 h to obtain vanadium solution 1.

[0068] Heat vanadium solution 1 to 90 °C, keep stirring, and slowly add 3.3-valent vanadium oxide reduced from 34 g of ammonium metavanadate, and control to add it within 2 h.

[0069] Heat the reaction for 6 h, add 52 mL of 19% hydrochloric acid during the process, cool and filter, and make up the volume to 200 mL to obtain a vanadium electrolyte with a concentration of 2.45 mol / L, a sulfate ion concentration of 6.3 mol / L, and a chloride ion concentration of 2 mol / L.

[0070] Example 5

[0071] Vanadium electrolyte was prepared in Example 5 by the following method, including:

[0072] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly, add 5.5 g of vanadium pentoxide, and stir for 2 h to obtain vanadium solution 1.

[0073] Heat vanadium solution 1 to 130 °C, keep stirring, and slowly add 3.1-valent vanadium oxide reduced from 34 g of ammonium metavanadate, and control to add it within 2 h.

[0074] Heat the reaction for 6 h, add 80 mL of pure water during the process, cool and filter, and make up the volume to 200 mL to obtain a vanadium electrolyte with a concentration of 2.48 mol / L and a sulfate ion concentration of 6.3 mol / L.

[0075] Comparative Example 1

[0076] Vanadium electrolyte was prepared in Comparative Example 1 by the following method, including:

[0077] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stir evenly. Heat to keep the solution at 100 °C, add 5.5 g of vanadium pentoxide, stir for 2 h, and add 3.3-valent vanadium oxide reduced from 34 g of ammonium metavanadate.

[0078] Heat to 100 °C and react for 6 h, add 80 mL of pure water during the process, cool and filter, and make up the volume to 200 mL to obtain a vanadium electrolyte with a concentration of 2.35 mol / L and a sulfate ion concentration of 6.3 mol / L.

[0079] Comparative Example 2

[0080] Comparative Example 2 prepared a vanadium electrolyte by the following method, including:

[0081] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stirring evenly. Heat to keep the solution at 120 °C, add 5.5 g of vanadium pentoxide, stir for 2 h, and add 3.3-valent vanadium oxide reduced from 34 g of vanadium pentoxide.

[0082] Heat to 120 °C and react for 6 h. During the process, add 80 mL of pure water, cool and filter, and make up the volume to 200 mL to obtain a 2.2 mol / L vanadium electrolyte with a sulfate ion concentration of 6.3 mol / L.

[0083] Comparative Example 3

[0084] Comparative Example 3 prepared a vanadium electrolyte by the following method, including:

[0085] Take 60 mL of concentrated sulfuric acid and slowly add it to 60 mL of water, stirring evenly. Heat to keep the solution at 120 °C, add 5.5 g of vanadium pentoxide, and simultaneously add 3.3-valent vanadium oxide reduced from 34 g of ammonium metavanadate.

[0086] Heat to 120 °C and react for 6 h. During the process, add 80 mL of pure water, cool and filter, and make up the volume to 200 mL to obtain a 2.2 mol / L vanadium electrolyte with a sulfate ion concentration of 6.3 mol / L.

[0087] Then, the vanadium electrolytes prepared in the above Examples 1 to 5 and Comparative Examples 1 to 2 were characterized as follows. The dissolution rate of the vanadium electrolyte refers to the dissolution degree of vanadium oxide (in this application, vanadium pentoxide and low-valent vanadium oxide in each example and comparative example) in sulfuric acid solution under specific conditions. The dissolution rate can be used to describe the dissolution effect of vanadium oxide and is one of the important indicators for evaluating the electrolyte preparation process. A higher dissolution rate of the vanadium electrolyte indicates a more advanced process method.

[0088] Table 1 Characterization Results

[0089]

[0090]

[0091] The above results show that the dissolution rates of Examples 1 to 5 are higher than those of Comparative Examples 1 and 2. Since hydrochloric acid was added in Example 4, the chloride ion concentration was also detected.

[0092] Then, taking Example 5 as an example, a vanadium electrolyte was prepared by the following method. The vanadium electrolyte was diluted to 2.0 mol / L and subjected to charge-discharge tests, and the results are as Figure 2 shown. Figure 2The three curves respectively represent the discharge capacity (Ah), current efficiency (%), and energy efficiency (%). Among them: (1) Discharge capacity (Ah): Initial stage: When the number of cycles is small (about 0 to 100 times), the discharge capacity drops rapidly, from about 8 Ah to about 4 Ah. Stable stage: After the number of cycles reaches 100 times, the discharge capacity tends to be stable, with small fluctuations, about 4 Ah. (2) Current efficiency (%): Stable stage: The current efficiency remains relatively stable throughout the cycle, about 11%, without obvious fluctuations or changes. (3) Energy efficiency (%): Initial stage: When the number of cycles is small (about 0 to 100 times), the energy efficiency drops from about 80% to about 60%. Stable stage: After the number of cycles reaches 100 times, the energy efficiency tends to be stable, with small fluctuations, about 60%.

[0093] The results show that the vanadium electrolyte prepared by the method of the present invention has excellent performance.

[0094] In the description of this specification, the descriptions of reference terms such as "one embodiment", "some embodiments", "example", "specific implementation manner", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example.

[0095] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a vanadium electrolyte for an all-vanadium redox flow battery, characterized in that: include: (1) dissolving concentrated sulfuric acid in water to obtain a sulfuric acid solution of a predetermined concentration, and then adding vanadium pentoxide to the sulfuric acid solution to react and obtain a first vanadium solution; (2) maintaining the temperature of the first vanadium solution at a predetermined temperature, adding a low-valent vanadium oxide to the first vanadium solution, reacting, and adding water or hydrochloric acid during the reaction to obtain a second vanadium solution, wherein the low-valent vanadium oxide is a vanadium oxide with a valence of 3 to 3.5; (3) Filtering the second vanadium solution to obtain a vanadium electrolyte.

2. The preparation method according to claim 1, characterized in that: The predetermined concentration of the sulfuric acid solution in step (1) is 40 to 80%.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the vanadium pentoxide to the sulfuric acid solution in step (1) is (1-6):

100.

4. The preparation method according to claim 1, characterized in that: The time for adding low-valent vanadium oxide to the first vanadium solution in step (2) is controlled to be 0.5 to 4 hours.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the supplementary amount of the water or hydrochloric acid to the sulfuric acid solution is (0.2-0.7):

1.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the low-valent vanadium oxide to the vanadium pentoxide is (2-15):

1.

7. The preparation method according to claim 1, characterized in that: The predetermined temperature in step (2) is 80-150° C., and the first vanadium solution is maintained at the predetermined temperature by continuous heating.

8. The preparation method according to claim 1, characterized in that: The vanadium electrolyte has a concentration of 1.5-4.0 mol / L, a sulfate concentration of 3-10 mol / L, and a chloride ion concentration of 0-6 mol / L.

9. A vanadium electrolyte for an all-vanadium liquid flow battery, characterized in that: Obtained according to the preparation method according to any one of claims 1 to 8.

10. An all-vanadium liquid flow battery, characterized in that: include: Battery stack system, cathode storage tank, anode storage tank, circulation pump and management system; The positive electrode storage tank stores a positive electrode electrolyte; the negative electrode storage tank stores a negative electrode electrolyte, and the positive electrode electrolyte and the negative electrode electrolyte respectively include the vanadium electrolyte for all-vanadium liquid flow battery according to claim 9.

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