3.5 valent vanadium electrolyte in hydrochloric acid system, its preparation method and battery

Abstract

This invention provides a vanadium electrolyte in a 3.5-valent hydrochloric acid system, its preparation method, and a battery, relating to the field of vanadium redox flow battery technology. It solves the problem of long preparation times caused by the need to completely oxidize tetravalent vanadium to pentavalent vanadium and completely reduce pentavalent vanadium to tetravalent vanadium in the preparation of vanadium electrolytes in both 3.5-valent hydrochloric acid and 3.5-valent sulfuric acid systems. The preparation steps of the vanadium electrolyte in the 3.5-valent hydrochloric acid system include: using a hydrochloric acid solution of tetravalent vanadium ions and a sulfuric acid solution of (4+x)valent vanadium ions as negative and positive solutions, respectively. Electrolysis of the electrolyte yields a vanadium electrolyte solution with a 3.5-valent hydrochloric acid system and a sulfuric acid solution containing (4+y)-valent vanadium ions at the negative and positive electrodes, respectively. The sulfuric acid solution containing (4+y)-valent vanadium ions is then reduced to prepare a sulfuric acid solution containing (4+x)-valent vanadium ions. This sulfuric acid solution containing (4+x)-valent vanadium ions can then be electrolyzed with a fresh hydrochloric acid solution containing tetravalent vanadium ions as the negative and positive electrolyte solutions for a full vanadium redox flow battery, yielding a fresh vanadium electrolyte solution with a 3.5-valent hydrochloric acid system and a sulfuric acid solution containing (4+y)-valent vanadium ions at the negative and positive electrodes, respectively.

Description

[0001] This application is a divisional application of Chinese patent application filed on February 21, 2023, with application number "202310146771.0" and entitled "Preparation Method of Vanadium Electrolyte in 3.5-valent Hydrochloric Acid System and 3.5-valent Sulfuric Acid System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of vanadium redox flow battery technology, and particularly to a vanadium electrolyte based on 3.5 valence hydrochloric acid, its preparation method, and the battery thereof. Background Technology

[0003] Vanadium redox flow batteries are the preferred choice for high-capacity, long-duration energy storage batteries and a key technological support for achieving the energy revolution and dual-carbon goals. They utilize vanadium electrolyte to circulate through the positive and negative electrodes to carry out electrochemical reactions, achieving the interconversion of electrical and chemical energy.

[0004] Patent application CN201310542929.2 discloses a method for preparing a 3.5-valent vanadium electrolyte. It employs an electrolysis apparatus, using half a volume of a tetravalent vanadium solution as the positive electrode electrolyte and one volume as the negative electrode electrolyte. Under the influence of a current supplied by a power source, the electrolysis charge is controlled to reduce the vanadium in the negative electrode electrolyte from tetravalent to 3.5 valence, and to oxidize the vanadium in the positive electrode electrolyte from tetravalent to pentavalent. After electrolysis, the 3.5-valent vanadium solution at the negative electrode is released, and the same volume of tetravalent vanadium is added. A reducing agent is then added to the positive electrode to reduce the pentavalent vanadium back to tetravalent, and the electrolysis process is repeated.

[0005] However, this method has the following serious drawbacks: First, it requires that the concentrations of tetravalent vanadium in half a volume of the positive electrode electrolyte and one volume of the negative electrode electrolyte be exactly equal in order for the vanadium in the negative electrode electrolyte to be reduced from tetravalent to 3.5 valence when the vanadium in the positive electrode electrolyte is oxidized from tetravalent to pentoxide. Second, electrolysis requires the complete oxidation of vanadium in the positive electrode electrolyte from tetravalent to pentoxide (otherwise the vanadium valence in the negative electrode electrolyte will be higher than 3.5 valence), which would take an extremely long time and be impractical. This is because as the electrolysis proceeds, the concentration of tetravalent vanadium in the positive electrode electrolyte decreases and approaches zero, the electrolysis reaction rate slows down and approaches zero, and the electrolysis current decreases and approaches zero. Theoretically, it would take an infinitely long time to completely oxidize the vanadium in the positive electrode electrolyte from tetravalent to pentoxide. In addition, a reducing agent needs to be added to the positive electrode electrolyte to reduce all pentavalent vanadium to tetravalent (otherwise, the vanadium valence state of the negative electrode electrolyte will not drop to 3.5 valence in the next electrolysis). If the reducing agent is added according to the stoichiometric ratio for completely reducing pentavalent vanadium to tetravalent, it would also take an extremely long time to completely reduce pentavalent vanadium to tetravalent, which is impractical. This is because as the reduction reaction proceeds, the concentration of pentavalent vanadium and the concentration of the reducing agent in the positive electrode electrolyte will decrease and approach zero, and the reduction reaction rate will also slow down and approach zero. Theoretically, it would take an infinitely long time to completely reduce the vanadium in the positive electrode electrolyte from pentavalent to tetravalent.

[0006] If the incompletely reduced positive electrolyte is used directly in the next electrolysis, the unreacted reducing agents (such as hydrazine hydrate, oxalic acid, etc.) in the positive electrolyte will undergo a redox reaction with the newly generated pentavalent vanadium, generating a large number of N2, CO2 and other bubbles in the positive electrolyte. This will frequently cause the positive electrolyte magnetic circulation pump to stop running, run dry, or even burn out, seriously affecting the smooth progress of the electrolysis reaction.

[0007] If an excessive amount of reducing agent is added, although the vanadium in the positive electrode electrolyte can be reduced from pentavalent to tetravalent in a short time, the remaining reducing agent in the positive electrode electrolyte (such as hydrazine hydrate, oxalic acid, etc.) will also undergo redox reactions with the newly generated pentavalent vanadium in the next electrolysis process. This will generate a large number of N2, CO2 and other bubbles in the positive electrode electrolyte, frequently causing the magnetic circulation pump of the positive electrode electrolyte to stop running, run dry, or even burn out. This seriously affects the smooth progress of the electrolysis reaction. Furthermore, due to the cumulative effect, the amount of remaining reducing agent in the positive electrode electrolyte will increase with each reaction, and the amount of N2, CO2 and other bubbles generated will increase with each reaction. The occurrence of the magnetic circulation pump of the positive electrode electrolyte stopping running dry or even burning out will become more frequent and severe, eventually causing the method to completely fail.

[0008] Therefore, there is an urgent need for a method to prepare vanadium electrolyte in a 3.5-valent hydrochloric acid system that is rapid in electrolysis, quick in reduction, safe, reliable, economical and efficient. Summary of the Invention

[0009] The technical problem to be solved by the present invention is that in the process of preparing 3.5 vanadium electrolyte, it is usually necessary to oxidize all tetravalent vanadium to pentavalent vanadium and reduce all pentavalent vanadium to tetravalent vanadium, which results in long preparation time and low preparation efficiency.

[0010] To solve the above-mentioned technical problems, the first aspect of the present invention provides a method for preparing vanadium electrolytes in a 3.5-valent hydrochloric acid system and a 3.5-valent sulfuric acid system.

[0011] A second aspect of the present invention provides an electrolyte.

[0012] A third aspect of the present invention provides a battery.

[0013] The method for preparing a vanadium electrolyte in a 3.5 valent hydrochloric acid system provided by the first aspect of the present invention includes the following steps:

[0014] Hydrochloric acid solution and sulfuric acid solution of tetravalent vanadium ions were used as negative and positive electrodes for electrolysis, respectively. A vanadium electrolyte with a 3.5-valent hydrochloric acid system was obtained at the negative electrode, and a sulfuric acid solution with (4+2)-valent vanadium ions was obtained at the positive electrode.

[0015] Oxalic acid is added to a sulfuric acid solution of (4+z) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < z < 1.

[0016] Hydrochloric acid solution containing tetravalent vanadium ions and sulfuric acid solution containing (4+x) vanadium ions were used as negative and positive electrodes for electrolysis. A vanadium electrolyte with a 3.5 valence hydrochloric acid system was obtained at the negative electrode, and a sulfuric acid solution containing (4+y) vanadium ions was obtained at the positive electrode.

[0017] Oxalic acid is added to a sulfuric acid solution of (4+y) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < y < 1.

[0018] Repeat at least once the steps of using a sulfuric acid solution of (4+x) vanadium ions as the positive electrode electrolyte and a hydrochloric acid solution of 4 vanadium ions as the negative electrode for charging and electrolysis, and adding oxalic acid to the sulfuric acid solution of (4+y) vanadium ions obtained at the positive electrode to obtain a sulfuric acid solution of (4+x) vanadium ions, so as to continuously obtain a vanadium electrolyte system of 3.5 vanadium ions at the negative electrode.

[0019] Furthermore, x≥0.1, y≥0.9.

[0020] Furthermore, a hydrochloric acid solution of tetravalent vanadium ions is prepared by dissolving vanadium dichloride in hydrochloric acid.

[0021] Furthermore, vanadium pentoxide is prepared by reducing a sulfuric acid solution of tetravalent vanadium ions with a sulfuric acid-oxalic acid solution.

[0022] Furthermore, the charging electrolysis is carried out in a full vanadium redox flow battery.

[0023] This invention provides a method for preparing a vanadium electrolyte with a 3.5-valent hydrochloric acid system. The vanadium valence state of the positive electrode electrolyte is between 4 and 5. The method involves charging and electrolyzing a hydrochloric acid solution containing 4-valent vanadium ions and a sulfuric acid solution containing (4+x)-valent vanadium ions, respectively, as the negative and positive electrode electrolytes of a vanadium redox flow battery. At the negative electrode, a hydrochloric acid solution containing 3.5-valent vanadium ions is obtained, which is the 3.5-valent hydrochloric acid system vanadium electrolyte. At the positive electrode, a sulfuric acid solution containing (4+y)-valent vanadium ions is obtained. Oxalic acid is then added to the obtained (4+y)-valent vanadium ion sulfuric acid solution according to a stoichiometric ratio for reduction, resulting in a new sulfuric acid solution containing (4+x)-valent vanadium ions, where 0 < x < y < 1. This process is repeated continuously at the negative electrode to continuously prepare a new 3.5-valent hydrochloric acid system vanadium electrolyte.

[0024] Furthermore, the method for preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system provided by this invention does not require the concentration of tetravalent vanadium in the positive and negative electrode electrolytes of a full vanadium redox flow battery to be exactly equal, nor does it require the volumes to differ by a factor of two, making it simple and convenient. Moreover, during the charging and electrolysis of the full vanadium redox flow battery, this invention only requires oxidizing the vanadium in the positive electrode electrolyte from (4+x) valence to (4+y) valence, where 0 < x < y < 1. That is, only a portion of the tetravalent vanadium needs to be oxidized to pentavalent valence, without oxidizing all tetravalent vanadium to pentavalent valence, resulting in a fast electrolysis reaction rate and significantly shortening the electrolysis step time. Simultaneously, this invention only requires quantitatively adding oxalic acid according to a stoichiometric ratio to the sulfuric acid solution of (4+y) valence vanadium ions obtained from the positive electrode after charging and electrolysis of the full vanadium redox flow battery to regenerate a sulfuric acid solution of (4+x) valence vanadium ions, where 0 < x < y < 1. That is, only a portion of the pentavalent vanadium needs to be reduced to tetravalent valence, without reducing all pentavalent vanadium to tetravalent valence, resulting in a fast reduction reaction rate and significantly shortening the reduction step time.

[0025] More importantly, because the present invention maintains an excess of pentavalent vanadium relative to oxalic acid reducing agent in the reduction step of the positive electrode electrolyte after charging and electrolysis of the vanadium redox flow battery, the reduction reaction rate is fast and the reduction step time is short. Moreover, there is no oxalic acid reducing agent residue in the reduced positive electrode electrolyte, thereby fundamentally preventing the occurrence of situations such as liquid interruption, dry running, or even pump burnout of the positive electrode electrolyte magnetic circulation pump during the next charging and electrolysis, and ensuring the smooth progress of subsequent electrolysis steps.

[0026] Therefore, the method for preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system provided by the present invention completely overcomes the defects of the current method for preparing 3.5-valent vanadium electrolyte by using 4-valent vanadium for both the positive and negative electrodes. It has the characteristics of rapid electrolysis, fast reduction, safety and reliability, economy and efficiency, and recyclability.

[0027] The method for preparing a vanadium electrolyte in a 3.5-valent sulfuric acid system provided by the first aspect of the present invention includes the following steps:

[0028] A sulfuric acid solution containing tetravalent vanadium ions and a sulfuric acid solution containing tetravalent vanadium ions were used as negative and positive electrodes, respectively, for charging and electrolysis. A vanadium electrolyte with a 3.5-valent sulfuric acid system was obtained at the negative electrode, and a sulfuric acid solution containing (4+2)-valent vanadium ions was obtained at the positive electrode.

[0029] Oxalic acid is added to a sulfuric acid solution of (4+z) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < z < 1.

[0030] A sulfuric acid solution containing tetravalent vanadium ions and a sulfuric acid solution containing (4+x) vanadium ions were used as the negative and positive electrodes, respectively, for charging and electrolysis. A vanadium electrolyte with a 3.5 valence sulfuric acid system was obtained at the negative electrode, and a sulfuric acid solution containing (4+y) vanadium ions was obtained at the positive electrode.

[0031] Oxalic acid is added to a sulfuric acid solution of (4+y) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < y < 1.

[0032] Repeat at least once the steps of using a sulfuric acid solution of (4+x) vanadium ions as the positive electrode electrolyte and a sulfuric acid solution of tetravalent vanadium ions as the negative electrode, and adding oxalic acid to the sulfuric acid solution of (4+y) vanadium ions obtained at the positive electrode to obtain a sulfuric acid solution of (4+x) vanadium ions, so as to continuously obtain a vanadium electrolyte system of 3.5 valence sulfuric acid at the negative electrode.

[0033] Furthermore, x≥0.1, y≥0.9.

[0034] Furthermore, vanadium pentoxide is prepared by reducing a sulfuric acid solution of tetravalent vanadium ions with a sulfuric acid-oxalic acid solution.

[0035] Furthermore, the chemical equation for the reduction of vanadium pentoxide by sulfuric acid and oxalic acid solution is as follows:

[0036] 0.5V2O5+2.5H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+0.5H2SO4+CO2↑+2.5H2O.

[0037] Furthermore, the charging electrolysis is carried out in a full vanadium redox flow battery.

[0038] This invention provides a method for preparing a vanadium electrolyte in a 3.5-valent sulfuric acid system. The vanadium valence state of the positive electrode electrolyte is between 4 and 5. By using sulfuric acid solutions of 4-valent vanadium ions and (4+x)-valent vanadium ions as the negative and positive electrode electrolytes, respectively, in a vanadium redox flow battery, the method involves charging and electrolyzing. At the negative electrode, a sulfuric acid solution of 3.5-valent vanadium ions is obtained, i.e., the 3.5-valent sulfuric acid system vanadium electrolyte. At the positive electrode, a sulfuric acid solution of (4+y)-valent vanadium ions is obtained. Oxalic acid is then added to the (4+y)-valent vanadium ion sulfuric acid solution according to a stoichiometric ratio for reduction, resulting in a new sulfuric acid solution of (4+x)-valent vanadium ions, where 0 < x < y < 1. This process is repeated continuously at the negative electrode to continuously prepare new vanadium electrolyte in a 3.5-valent sulfuric acid system.

[0039] Furthermore, the method for preparing vanadium electrolyte in a 3.5-valent sulfuric acid system provided by this invention does not require the concentration of tetravalent vanadium in the positive and negative electrode electrolytes of a full vanadium redox flow battery to be exactly equal, nor does it require the volumes to differ by a factor of two, making it simple and convenient. Moreover, during the charging and electrolysis of the full vanadium redox flow battery, this invention only requires oxidizing the vanadium in the positive electrode electrolyte from (4+x) valence to (4+y) valence, where 0 < x < y < 1. That is, only a portion of the tetravalent vanadium needs to be oxidized to pentavalent valence, without oxidizing all tetravalent vanadium to pentavalent valence, resulting in a fast electrolysis reaction rate and significantly shortening the electrolysis step time. Simultaneously, this invention only requires quantitatively adding oxalic acid according to a stoichiometric ratio to the sulfuric acid solution of (4+y) valence vanadium ions obtained from the positive electrode after charging and electrolysis of the full vanadium redox flow battery to regenerate a sulfuric acid solution of (4+x) valence vanadium ions, where 0 < x < y < 1. That is, only a portion of the pentavalent vanadium needs to be reduced to tetravalent valence, without reducing all pentavalent vanadium to tetravalent valence, resulting in a fast reduction reaction rate and significantly shortening the reduction step time.

[0040] More importantly, because the present invention maintains an excess of pentavalent vanadium relative to oxalic acid reducing agent in the reduction step of the positive electrode electrolyte after charging and electrolysis of the vanadium redox flow battery, the reduction reaction rate is fast and the reduction step time is short. Moreover, there is no oxalic acid reducing agent residue in the reduced positive electrode electrolyte, thereby fundamentally preventing the occurrence of situations such as liquid interruption, dry running, or even pump burnout of the positive electrode electrolyte magnetic circulation pump during the next charging and electrolysis, and ensuring the smooth progress of subsequent electrolysis steps.

[0041] Therefore, the method for preparing vanadium electrolyte in a 3.5-valent sulfuric acid system provided by the present invention completely overcomes the defects of current methods for preparing 3.5-valent vanadium electrolyte by using 4-valent vanadium for both the positive and negative electrodes. It has the characteristics of rapid electrolysis, quick reduction, safety and reliability, economy and efficiency, and recyclability.

[0042] The second aspect of the present invention provides an electrolyte, which is prepared by the method for preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system provided by any one of the technical solutions of the first aspect of the present application, or by the method for preparing vanadium electrolyte in a 3.5-valent sulfuric acid system provided by any one of the technical solutions of the first aspect of the present application.

[0043] The third aspect of the present invention provides a battery, which includes the electrolyte provided in the second aspect of the present invention, or the battery includes an electrolyte prepared by a vanadium electrolyte preparation method of a 3.5 valent hydrochloric acid system provided in any one of the technical solutions of the first aspect of the present invention, or prepared by a vanadium electrolyte preparation method of a 3.5 valent sulfuric acid system provided in any one of the technical solutions of the first aspect of the present invention. Attached Figure Description

[0044] Figure 1 A flowchart illustrating the preparation method of vanadium electrolyte in a 3.5-valent hydrochloric acid system provided in this embodiment of the invention.

[0045] Figure 2 A flowchart illustrating the preparation method of vanadium electrolyte in a 3.5-valent sulfuric acid system provided in this embodiment of the invention. Detailed Implementation

[0046] like Figure 1 As shown in the embodiment of the present invention, the method for preparing vanadium electrolyte in a 3.5 valent hydrochloric acid system includes the following steps:

[0047] S102: Hydrochloric acid solution and sulfuric acid solution of tetravalent vanadium ions are used as negative and positive electrolytes respectively in a vanadium redox flow battery for charging and electrolysis. A vanadium electrolyte with a 3.5-valent hydrochloric acid system is obtained at the negative electrode, and a sulfuric acid solution with (4+2)-valent vanadium ions is obtained at the positive electrode.

[0048] S104: A sulfuric acid solution of (4+x) vanadium ions is prepared by adding oxalic acid to a sulfuric acid solution of (4+z) vanadium ions, where 0 < x < z < 1.

[0049] In the process of reducing (4+z) vanadium ions in a sulfuric acid solution with oxalic acid to obtain a (4+x) vanadium ion solution, the reaction is carried out according to the following reaction equation for the reduction of pentavalent vanadium to tetravalent vanadium by oxalic acid, and the amount of oxalic acid added is set accordingly:

[0050] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0051] Reduce (zx)×1mol VO2HSO4;

[0052] Generates (zx)×1mol VO(HSO4)2;

[0053] 0.5(zx)×1mol H2C2O4·2H2O needs to be added;

[0054] S106: Hydrochloric acid solution of tetravalent vanadium ions and sulfuric acid solution of (4+x) vanadium ions are used as negative and positive electrolytes for charging and electrolysis of a vanadium redox flow battery, respectively. A vanadium electrolyte with a 3.5 valence hydrochloric acid system is obtained at the negative electrode, and a sulfuric acid solution with (4+y) vanadium ions is obtained at the positive electrode.

[0055] S108: A sulfuric acid solution of (4+x) vanadium ions is prepared by adding oxalic acid to a sulfuric acid solution of (4+y) vanadium ions, where 0 < x < y < 1.

[0056] In the process of reducing (4+y) vanadium ions in a sulfuric acid solution with oxalic acid to obtain a (4+x) vanadium ion solution, the reaction is carried out according to the following reaction equation for the reduction of pentavalent vanadium to tetravalent vanadium by oxalic acid, and the amount of oxalic acid added is set accordingly:

[0057] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0058] Reduce (yx)×1mol VO2HSO4;

[0059] Generates (yx)×1mol VO(HSO4)2;

[0060] 0.5(yx)×1mol H2C2O4·2H2O needs to be added;

[0061] S110: Repeat at least once the steps of using a sulfuric acid solution of (4+x) vanadium ions as the positive electrode electrolyte and a hydrochloric acid solution of 4 vanadium ions as the negative electrode for charging and electrolysis, and adding oxalic acid to the sulfuric acid solution of (4+y) vanadium ions obtained at the positive electrode to obtain a sulfuric acid solution of (4+x) vanadium ions, so as to continuously obtain a vanadium electrolyte system of 3.5 vanadium ions at the negative electrode.

[0062] Where x≥0.1, y≥0.9.

[0063] The hydrochloric acid solution of tetravalent vanadium ions is prepared by dissolving vanadium dichloride in hydrochloric acid. The amounts of vanadium dichloride and hydrochloric acid are determined according to the total amount of vanadium and Cl in the prepared vanadium electrolyte system of 3.5 valent hydrochloric acid.

[0064] The preparation method involves reducing vanadium pentoxide with sulfuric acid oxalic acid solution from a tetravalent vanadium ion solution. The reaction proceeds completely according to the following reaction equation:

[0065] 0.5V2O5+2H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2.5H2O;

[0066] The charging and electrolysis are carried out in a full vanadium redox flow battery, which includes a stack, pipelines, positive and negative electrode vanadium electrolyte containers, etc. The vanadium electrolyte of 3.5 valence hydrochloric acid system is prepared by charging and electrolyzing the corresponding vanadium electrolyte in the positive and negative electrode electrolyte containers of the full vanadium redox flow battery.

[0067] When preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system via electrolysis, the charging current and electrolysis voltage are adjusted according to the electrode area and number of individual cells connected in series in the vanadium redox flow battery stack. The electrolysis time is determined by the charging current, the volume and concentration of the negative electrode vanadium electrolyte. Constant voltage charging can be performed using the stack's charging limit voltage as the electrolysis voltage, maximizing the charging current and minimizing the electrolysis time, thus improving efficiency. Alternatively, constant current charging followed by constant voltage charging can be performed first, but this will result in a longer electrolysis time.

[0068] After charging and electrolyzing a sulfuric acid solution containing (4+x) valence vanadium ions at the positive electrode, some tetravalent vanadium ions lose electrons to become pentavalent vanadium ions, causing the average valence state of vanadium ions to rise to (4+y). By quantitatively adding oxalic acid to reduce the (4+y) valence vanadium back to the (4+x) valence, it can be paired with a newly prepared hydrochloric acid solution containing tetravalent vanadium ions (as the negative electrode solution) for a new round of charging and electrolysis. At the negative electrode, a vanadium electrolyte with a 3.5 valence hydrochloric acid system is obtained, and the valence state of vanadium ions in the positive electrode electrolyte rises to the (4+y) valence again, which can be reduced back to the (4+x) valence by quantitatively adding oxalic acid. ······ This process is repeated, and new vanadium electrolyte in a 3.5-valent hydrochloric acid system can be continuously prepared at the negative electrode.

[0069] Currently, oxalic acid is usually added artificially to the positive electrode electrolyte after charging and electrolysis. The reduction of some pentavalent vanadium ions to tetravalent vanadium ions by oxalic acid is an ionic reaction that releases CO2 gas. Although the process is relatively fast, it still takes several hours to complete the reaction. Stirring will speed up the process.

[0070] After each charging and electrolysis, the positive electrode (4+y) vanadium electrolyte container needs to be removed and oxalic acid added for reduction. At the same time, another positive electrode (4+x) vanadium electrolyte container that has been pre-reduced completely is replaced to start a new round of charging and electrolysis. This can greatly improve production efficiency.

[0071] If oxalic acid is added to the positive electrode electrolyte for reduction during charging and electrolysis, the CO2 bubbles continuously generated in the positive electrode electrolyte will frequently cause the magnetic circulation pump of the positive electrode electrolyte to stop running, run dry, or even burn out, seriously affecting the smooth progress of the electrolysis reaction.

[0072] The following examples illustrate the preparation method of the vanadium electrolyte in the 3.5-valent hydrochloric acid system provided by the present invention.

[0073] In one embodiment, a vanadium electrolyte is prepared using a 2.5M 0.5(VOCl2+VCl3+2HCl)3.5 valence hydrochloric acid system (M represents mol / L, the same below);

[0074] Step 1: Preparation of 800L 2.5M VOCl2 + 1.5HCl tetravalent vanadium electrolyte;

[0075] VOCl2: 800×2.5×1×137.85=275.7(kg);

[0076] HCl: 800×2.5×1.5×36.46=109.4(kg);

[0077] Add 200L of pure water to the reaction vessel, and slowly add 109.4kg of HCl while stirring, stirring until well mixed. Then, slowly add 275.7kg of VOCl2 while stirring, continuing to stir until completely dissolved. Filter the solution into a 1000L container, add pure water to adjust the volume to 800L, obtaining 800L of 2.5MVOCl2 + 1.5HCl tetravalent vanadium electrolyte.

[0078] Step 2: Preparation of 625L 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte;

[0079] 0.5V2O5+3H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+H2SO4+CO2↑+2.5H2O;

[0080] V2O5: 625×2×0.5×182=113.8(kg);

[0081] H2SO4: 625×2×3×98.1=368(kg);

[0082] H2C2O4·2H2O: 625×2×0.5×126=78.8(kg);

[0083] Add 300L of pure water to the reaction vessel, and slowly add 368kg of H2SO4 and 78.8kg of H2C2O4·2H2O while stirring. Stir well, and slowly add 113.8kg of V2O5 while stirring until no more bubbles are generated. Filter the solution into a 1000L container, add pure water to adjust the volume to 625L, and obtain 625L of 2MVO(HSO4)2+H2SO4 vanadium tetravalent electrolyte.

[0084] Step 3: Preparation of the first 800L vanadium electrolyte in a 2.5M 0.5(VOCl2+VCl3+2HCl) 3.5 valence hydrochloric acid system;

[0085] The 800L 2.5M VOCl2+1.5HCl tetravalent vanadium electrolyte prepared in step 1 was used as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries, and the 625L 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte prepared in step 2 was used as the positive electrode electrolyte. The battery was charged at a constant voltage of 60V for 724.3Ah. That is, the hydrochloric acid solution for tetravalent vanadium ions was vanadium dichloride and hydrochloric acid, and the sulfuric acid solution for tetravalent vanadium ions was vanadium hydrooxysulfate and sulfuric acid.

[0086] SOC － =37×724.3 / (800×2.5×26.8)=50%, SOC － The electrolyte is in a negative electrode state of charge.

[0087] SOC + =37×724.3 / (625×2×26.8)=80%, SOC + The positive electrode electrolyte is in a charged state;

[0088] Negative electrode: VOCl2 + HCl + H+ + +e=VCl3+H2O;

[0089] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0090] The negative electrode yielded the first 800 L of vanadium electrolyte in a 2.5 M 0.5 (VOCl2 + VCl3 + 2HCl) 3.5 valence hydrochloric acid system, while the positive electrode yielded 625 L of vanadium electrolyte in a 2 M 0.8 VO2HSO4 + 0.2 VO(HSO4)2 + 1.8 H2SO4 4.8 valence hydrochloric acid system.

[0091] Step 4: Preparation of 4.1-valent vanadium electrolyte: 625L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4;

[0092] Add 55.1 kg of H2C2O4·2H2O to the 625L 2M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8 vanadium electrolyte obtained in step 2, and stir for about 2 hours until no more bubbles are generated, to obtain the 625L 2M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1 vanadium electrolyte.

[0093] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0094] H2C2O4·2H2O: 0.7×625×2×0.5×126=55.1(kg);

[0095] Step 5: Preparation of vanadium electrolyte in 800L 2.5M 0.5(VOCl2+VCl3+2HCl)3.5 valence hydrochloric acid system;

[0096] Repeat step 1, using 800L of freshly prepared 2.5M VOCl2 + 1.5HCl tetravalent vanadium electrolyte as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries, and 625L of 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4 tetravalent vanadium electrolyte as the positive electrode electrolyte. Charge at a constant voltage of 60V for 724.3Ah.

[0097] SOC － =37×724.3 / (800×2.5×26.8)=50%;

[0098] SOC + =10% + 37 × 724.3 / (625 × 2 × 26.8) = 90%;

[0099] Negative electrode: VOCl2 + HCl + H+ + +e=VCl3+H2O;

[0100] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0101] The negative electrode yields 800 L of 2.5 M 0.5 (VOCl2 + VCl3 + 2HCl) 3.5 valent hydrochloric acid system vanadium electrolyte, and the positive electrode yields 625 L of 2 M 0.9 VO2HSO4 + 0.1 VO(HSO4)2 + 1.9 H2SO4 4.9 valent vanadium electrolyte.

[0102] Step 6: Preparation of vanadium electrolyte in 625L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4 (4.1 valence vanadium);

[0103] Add 63 kg of H₂C₂O₄·2H₂O to 625 L of 2M vanadium electrolyte (0.9VO₂HSO₄ + 0.1VO(HSO₄)₂ + 1.9H₂SO₄, 4.9 valent vanadium, and stir for about 2 hours until no more bubbles are generated, to obtain 625 L of 2M vanadium electrolyte (0.1VO₂HSO₄ + 0.9VO(HSO₄)₂ + 1.1H₂SO₄, 4.1 valent vanadium).

[0104] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0105] H2C2O4·2H2O: 0.8×625×2×0.5×126=63(kg);

[0106] Step 7: Repeat steps 5 and 6 in this cycle to continuously prepare new vanadium electrolyte in a 3.5 valence hydrochloric acid system at the negative electrode.

[0107] In another embodiment, a vanadium electrolyte is prepared using a 3M 0.5(VOCl2+VCl3+HCl)3.5 valence hydrochloric acid system.

[0108] Step 1: Preparation of 800L 3M VOCl2+HCl tetravalent vanadium electrolyte;

[0109] VOCl2: 800×3×1×137.85=330.8(kg);

[0110] HCl: 800×3×1×36.46=87.5(kg);

[0111] Add 200L of pure water to the reaction vessel, and slowly add 87.5kg of HCl while stirring. Stir well, and then slowly add 330.8kg of VOCl2 while stirring. Continue stirring until completely dissolved. Filter the solution into a 1000L container, add pure water to adjust the volume to 800L, and obtain 800L of 3MVOCl2+HCl tetravalent vanadium electrolyte.

[0112] Step 2: Preparation of 750L 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte;

[0113] 0.5V2O5+3H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+H2SO4+CO2↑+2.5H2O;

[0114] V2O5: 750×2×0.5×182=136.5(kg);

[0115] H2SO4: 750×2×3×98.1=441.5(kg);

[0116] H2C2O4·2H2O: 750×2×0.5×126=94.5(kg);

[0117] Add 300L of pure water to the reaction vessel, and slowly add 441.5kg of H2SO4 and 94.5kg of H2C2O4·2H2O while stirring. Stir well, and slowly add 136.5kg of V2O5 while stirring until no more bubbles are generated. Filter the solution into a 1000L container, add pure water to adjust the volume to 750L, and obtain 750L of 2MVO(HSO4)2+H2SO4 vanadium tetravalent electrolyte.

[0118] Step 3: Preparation of the first 800L 3M 0.5(VOCl2+VCl3+HCl) 3.5 valence hydrochloric acid system vanadium electrolyte;

[0119] The 800L 3M VOCl2+HCl tetravalent vanadium electrolyte prepared in step 1 was used as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries, and the 750L 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte prepared in step 2 was used as the positive electrode electrolyte. The battery was charged at a constant voltage of 60V for 869.2Ah.

[0120] SOC － =37×869.2 / (800×3×26.8)=50%;

[0121] SOC + =37×869.2 / (750×2×26.8)=80%;

[0122] Negative electrode: VOCl2 + HCl + H+ + +e=VCl3+H2O;

[0123] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0124] The negative electrode yielded the first 800 L 3M 0.5(VOCl2+VCl3+HCl) 3.5 valence hydrochloric acid system vanadium electrolyte, and the positive electrode yielded 750 L 2M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8 valence vanadium electrolyte.

[0125] Step 4: Preparation of 4.1-valent vanadium electrolyte: 750L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4;

[0126] Add 66.15 kg of H2C2O4·2H2O to the 750 L 2M 0.8VO2HSO4 + 0.2VO(HSO4)2 + 1.8H2SO4 4.8 vanadium electrolyte prepared in step 2, and stir for about 2 hours until no more bubbles are generated, to obtain 750 L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4 4.1 vanadium electrolyte.

[0127] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0128] H2C2O4·2H2O: 0.7×750×2×0.5×126=66.15(kg);

[0129] Step 5: Preparation of vanadium electrolyte in 800L 3M 0.5(VOCl2+0.5VCl3+HCl) 3.5 valence hydrochloric acid system;

[0130] Repeat step 1, using 800L of freshly prepared 3M VOCl2+HCl tetravalent vanadium electrolyte as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries, and 750L of 2M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 tetravalent vanadium electrolyte as the positive electrode electrolyte. Charge at a constant voltage of 60V to achieve 869.2Ah.

[0131] SOC － =37×869.2 / (800×3×26.8)=50%;

[0132] SOC + =10% + 37 × 869.2 / (750 × 2 × 26.8) = 90%;

[0133] Negative electrode: VOCl2 + HCl + H+ + +e=VCl3+H2O;

[0134] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0135] The negative electrode yields 800 L of 3M 0.5(VOCl2+VCl3+HCl)3.5 valent hydrochloric acid system vanadium electrolyte, and the positive electrode yields 750 L of 2M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO44 valent vanadium electrolyte.

[0136] Step 6: Preparation of 4.1-valent vanadium electrolyte: 750L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4;

[0137] Add 75.6 kg of H₂C₂O₄·2H₂O to 750 L of 2M vanadium electrolyte (0.9VO₂HSO₄ + 0.1VO(HSO₄)₂ + 1.9H₂SO₄, 4.9 valent vanadium, and stir for about 2 hours until no more bubbles are generated, to obtain 750 L of 2M vanadium electrolyte (0.1VO₂HSO₄ + 0.9VO(HSO₄)₂ + 1.1H₂SO₄, 4.1 valent vanadium).

[0138] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0139] H2C2O4·2H2O: 0.8×750×2×0.5×126=75.6(kg);

[0140] Step 7: Repeat steps 5 and 6 in this cycle to continuously prepare new vanadium electrolyte in a 3.5 valence hydrochloric acid system at the negative electrode.

[0141] In addition, all references to VO(HSO4)2 in this specification refer to vanadium hydrogen oxysulfate, V(HSO4)3 to vanadium hydrogen sulfate, V2O5 to vanadium pentoxide, H2SO4 to sulfuric acid, H2C2O4·2H2O to oxalic acid with two molecules of water of crystallization, CO2 to carbon dioxide, H2O to water, VO2HSO4 to vanadium hydrogen oxysulfate, VOCl2 to vanadium dichloride, VCl3 to vanadium chloride, and HCl to hydrochloric acid.

[0142] The vanadium electrolyte in a 3.5 valence hydrochloric acid system is a hydrochloric acid system electrolyte in which the average valence state of vanadium ions is 3.5.

[0143] The present invention provides a method for preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system, wherein the vanadium valence state of the positive electrode electrolyte is between 4 and 5 valence. This method completely overcomes the serious defects of conventional methods for preparing 3.5-valent vanadium electrolytes where both the positive and negative electrode electrolytes are 4-valent vanadium. It has outstanding advantages such as rapid electrolysis, quick reduction, simplicity, reliability, and cyclic operation, and can be effectively used for the efficient and low-cost preparation of vanadium electrolyte in a 3.5-valent hydrochloric acid system.

[0144] like Figure 2 As shown in the embodiment of the present invention, the method for preparing vanadium electrolyte in a 3.5-valent sulfuric acid system includes the following steps:

[0145] S202: A sulfuric acid solution containing tetravalent vanadium ions is used as the negative and positive electrolytes of a vanadium redox flow battery for charging and electrolysis, respectively. A vanadium electrolyte with a 3.5-valent sulfuric acid system is obtained at the negative electrode, and a sulfuric acid solution with (4+2)-valent vanadium ions is obtained at the positive electrode.

[0146] S204: A sulfuric acid solution of (4+x) vanadium ions is prepared by adding oxalic acid to a sulfuric acid solution of (4+z) vanadium ions, where 0 < x < z < 1.

[0147] In the process of reducing (4+z) vanadium ions in a sulfuric acid solution with oxalic acid to obtain a (4+x) vanadium ion solution, the reaction is carried out according to the following reaction equation for the reduction of pentavalent vanadium to tetravalent vanadium by oxalic acid, and the amount of oxalic acid added is set accordingly:

[0148] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0149] Reduce (zx)×1mol VO2HSO4;

[0150] Generates (zx)×1mol VO(HSO4)2;

[0151] 0.5(zx)×1mol H2C2O4·2H2O needs to be added;

[0152] S206: A sulfuric acid solution containing tetravalent vanadium ions and a sulfuric acid solution containing (4+x) vanadium ions are used as the negative and positive electrolytes, respectively, in a vanadium redox flow battery for charging and electrolysis. A vanadium electrolyte with a 3.5 valence sulfuric acid system is obtained at the negative electrode, and a sulfuric acid solution containing (4+y) vanadium ions is obtained at the positive electrode.

[0153] S208: A sulfuric acid solution of (4+x) vanadium ions is prepared by adding oxalic acid to a sulfuric acid solution of (4+y) vanadium ions, where 0 < x < y < 1.

[0154] In the process of reducing (4+y) vanadium ions in a sulfuric acid solution with oxalic acid to obtain a (4+x) vanadium ion solution, the reaction is carried out according to the following reaction equation for the reduction of pentavalent vanadium to tetravalent vanadium by oxalic acid, and the amount of oxalic acid added is set accordingly:

[0155] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0156] Reduce (yx)×1mol VO2HSO4;

[0157] Generates (yx)×1mol VO(HSO4)2;

[0158] 0.5(yx)×1mol H2C2O4·2H2O needs to be added;

[0159] S210: Repeat at least once the steps of using a sulfuric acid solution of (4+x) vanadium ions as the positive electrode electrolyte and a sulfuric acid solution of tetravalent vanadium ions as the negative electrode, and adding oxalic acid to the sulfuric acid solution of (4+y) vanadium ions obtained at the positive electrode to obtain a sulfuric acid solution of (4+x) vanadium ions, so as to continuously obtain a vanadium electrolyte system of 3.5 valence sulfuric acid at the negative electrode.

[0160] Where x≥0.1, y≥0.9.

[0161] The preparation method involves reducing vanadium pentoxide with sulfuric acid oxalic acid solution from a tetravalent vanadium ion solution. The reaction proceeds completely according to the following reaction equation:

[0162] 0.5V2O5+2H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2.5H2O;

[0163] Furthermore, the amounts of vanadium pentoxide, oxalic acid, and sulfuric acid are determined based on the total vanadium and sulfur content of the prepared vanadium electrolyte in a 3.5-valent sulfuric acid system. The concentration of the sulfuric acid and oxalic acid solution can be increased to accelerate the reaction. After the reaction is complete, pure water is added to dilute the solution to the required volume and concentration of a vanadium tetravalent sulfuric acid solution.

[0164] The charging and electrolysis are carried out in a full vanadium redox flow battery, which includes a stack, pipelines, positive and negative electrode vanadium electrolyte containers, etc. The vanadium electrolyte of the 3.5 valence sulfuric acid system is prepared by charging and electrolyzing the corresponding vanadium electrolyte into the positive and negative electrode electrolyte containers of the full vanadium redox flow battery.

[0165] When preparing vanadium electrolyte in a 3.5-valent sulfuric acid system via electrolysis, the charging current and electrolysis voltage are adjusted according to the electrode area and number of individual cells connected in series in the vanadium redox flow battery stack. The electrolysis time is determined by the charging current, the volume and concentration of the negative electrode vanadium electrolyte. Constant voltage charging can be performed using the stack's charging limit voltage as the electrolysis voltage, maximizing the charging current and minimizing the electrolysis time, thus improving efficiency. Alternatively, constant current charging followed by constant voltage charging can be performed first, but this will result in a longer electrolysis time.

[0166] After charging and electrolyzing a sulfuric acid solution containing (4+x) valence vanadium ions at the positive electrode, some tetravalent vanadium ions lose electrons to become pentavalent vanadium ions, causing the average valence state of vanadium ions to rise to (4+y). By quantitatively adding oxalic acid to reduce the (4+y) valence vanadium back to the (4+x) valence, it can be paired with a newly prepared sulfuric acid solution containing tetravalent vanadium ions (as the negative electrode solution) for a new round of charging and electrolysis. At the negative electrode, a vanadium electrolyte system with a 3.5 valence sulfuric acid system is obtained. The valence state of vanadium ions in the positive electrode electrolyte rises to the (4+y) valence again, and can be reduced back to the (4+x) valence by quantitatively adding oxalic acid. ······This process is repeated, and new vanadium electrolyte in a 3.5 valent sulfuric acid system can be continuously prepared at the negative electrode.

[0167] Currently, oxalic acid is usually added artificially to the positive electrode electrolyte after charging and electrolysis. The reduction of some pentavalent vanadium ions to tetravalent vanadium ions by oxalic acid is an ionic reaction that releases CO2 gas. Although the process is relatively fast, it still takes several hours to complete the reaction. Stirring will speed up the process.

[0168] After each charging and electrolysis, the positive electrode (4+y) vanadium electrolyte container needs to be removed and oxalic acid added for reduction. At the same time, another positive electrode (4+x) vanadium electrolyte container that has been pre-reduced completely is replaced to start a new round of charging and electrolysis. This can greatly improve production efficiency.

[0169] If oxalic acid is added to the positive electrode electrolyte for reduction during charging and electrolysis, the CO2 bubbles continuously generated in the positive electrode electrolyte will frequently cause the magnetic circulation pump of the positive electrode electrolyte to stop running, run dry, or even burn out, seriously affecting the smooth progress of the electrolysis reaction.

[0170] The following examples illustrate the preparation method of the vanadium electrolyte in the 3.5-valent sulfuric acid system provided by the present invention.

[0171] In one embodiment, a vanadium electrolyte is prepared using a 1.5M 0.5(VO(HSO4)2+V(HSO4)3)3.5 valence sulfuric acid system (M represents mol / L, the same below);

[0172] Step 1: Preparation of two 800L portions of 1.5MVO(HSO4)2+0.5H2SO4 tetravalent vanadium electrolyte; 0.5V2O5+2.5H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+0.5H2SO4+CO2↑+2.5H2O;

[0173] V2O5: 2×800×1.5×0.5×182=218.4(kg);

[0174] H2SO4: 2×800×1.5×2.5×98.1=588.6 (kg);

[0175] H2C2O4·2H2O: 2×800×1.5×0.5×126=151.2(kg);

[0176] Add 600L of pure water to the reaction vessel, and slowly add 588.6kg of H2SO4 and 151.2kg of H2C2O4·2H2O while stirring. Stir well, and slowly add 218.4kg of V2O5 while stirring until no more bubbles are generated. Filter the solution and divide it into two 1000L containers. Add pure water to each container to adjust the volume to 800L, and obtain two 800L portions of 1.5MVO(HSO4)2+0.5H2SO4 vanadium tetravalent electrolyte.

[0177] Step 2: Preparation of the first 800L vanadium electrolyte in a 1.5M 0.5(V(HSO4)3+VO(HSO4)2) 3.5 valent sulfuric acid system;

[0178] One batch of 800L of 1.5MVO(HSO4)2+0.5H2SO4 tetravalent vanadium electrolyte obtained in step 1 was used as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries. Another batch of 500L of 1.5MVO(HSO4)2+0.5H2SO4 tetravalent vanadium electrolyte was taken out and used as the positive electrode electrolyte. The battery was charged at a constant voltage of 60V for 435Ah. That is, the sulfuric acid solution of tetravalent vanadium ions is vanadium hydroxide sulfate and sulfuric acid.

[0179] SOC － =37×435 / (800×1.5×26.8)=50%, SOC － The electrolyte is in a negative electrode state of charge.

[0180] SOC + =37×435 / (500×1.5×26.8)=80%, SOC + The positive electrode electrolyte is in a charged state;

[0181] Negative electrode: VO(HSO4)2 + H2SO4 + H + +e=V(HSO4)3+H2O;

[0182] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0183] The negative electrode yielded the first 800L of vanadium electrolyte in a 1.5M 0.5(V(HSO4)3+VO(HSO4)2) 3.5 valence sulfuric acid system, while the positive electrode yielded 500L of vanadium electrolyte in a 1.5M 0.8VO2HSO4+0.2VO(HSO4)2+1.3H2SO4 4.8 valence.

[0184] Step 3: Preparation of 4.1 vanadium electrolyte: 500 L 1.5 M 0.1 VO₂HSO₄ + 0.9 VO(HSO₄)₂ + 0.6 H₂SO₄;

[0185] Add 33.1 kg of H2C2O4·2H2O to the 500 L 1.5 M 0.8VO2HSO4 + 0.2VO(HSO4)2 + 1.3H2SO4 4.8 vanadium electrolyte prepared in step 2, and stir for about 2 hours until no more bubbles are generated, to obtain 500 L 1.5 M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 0.6H2SO4 4.1 vanadium electrolyte.

[0186] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0187] H2C2O4·2H2O: 0.7×500×1.5×0.5×126=33.1(kg);

[0188] Step 4: Preparation of 800L 1.5M 0.5(V(HSO4)3+VO(HSO4)2)3.5 vanadium electrolyte;

[0189] Repeat step 1, using the newly prepared 800L 1.5M VO(HSO4)2+0.5H2SO4 tetravalent vanadium electrolyte as the negative electrode electrolyte for 37 5kW all-vanadium redox flow batteries, and using 500L 1.5M0.1VO2HSO4+0.9VO(HSO4)2+0.6H2SO4 tetravalent vanadium electrolyte as the positive electrode electrolyte, charging at a constant voltage of 60V for 435Ah.

[0190] SOC － =37×435 / (800×1.5×26.8)=50%;

[0191] SOC + =10% + 37 × 435 / (500 × 1.5 × 26.8) = 90%;

[0192] Negative electrode: VO(HSO4)2 + H2SO4 + H + +e=V(HSO4)3+H2O;

[0193] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0194] The negative electrode yields 800L of vanadium electrolyte in a 1.5M system of 0.5(VO(HSO4)2+V(HSO4)3)3.5 valence sulfuric acid, while the positive electrode yields 500L of vanadium electrolyte in a 1.5M system of 0.9VO2HSO4+0.1VO(HSO4)2+1.4H2SO44.

[0195] Step 5: Preparation of 4.1 vanadium electrolyte: 500 L 1.5 M 0.1 VO₂HSO₄ + 0.9 VO(HSO₄)₂ + 0.6 H₂SO₄;

[0196] Add 37.8 kg of H2C2O4·2H2O to 500 L of 1.5 M 0.9VO2HSO4 + 0.1VO(HSO4)2 + 1.4H2SO4 4.9 vanadium electrolyte, stir for about 2 h until no more bubbles are generated, to obtain 500 L of 1.5 M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 0.6H2SO4 4.1 vanadium electrolyte;

[0197] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0198] H2C2O4·2H2O: 0.8×500×1.5×0.5×126=37.8(kg);

[0199] Step 6: Repeat steps 4 and 5 in this cycle to continuously prepare new vanadium electrolyte in a 3.5 valence sulfuric acid system at the negative electrode.

[0200] In another embodiment, a 2M 0.5(V(HSO4)3+VO(HSO4)2+H2SO4)3.5 vanadium electrolyte is prepared;

[0201] Step 1: Preparation of two 800L portions of 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte;

[0202] 0.5V2O5+3H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+H2SO4+CO2↑+2.5H2O;

[0203] V2O5: 2×800×2×0.5×182=291.2(kg);

[0204] H2SO4: 2×800×2×3×98.1=941.8(kg);

[0205] H2C2O4·2H2O: 2×800×2×0.5×126=201.6 (kg);

[0206] Add 600L of pure water to the reaction vessel, and slowly add 941.8kg of H2SO4 and 201.6kg of H2C2O4·2H2O while stirring. Stir well, and slowly add 291.2kg of V2O5 while stirring until no more bubbles are generated. Filter the solution and divide it into two 1000L containers. Add pure water to each container to adjust the volume to 800L, and obtain two 800L portions of 2MVO(HSO4)2+H2SO4 vanadium tetravalent electrolyte.

[0207] Step 2: Preparation of the first 800L 2M 0.5(V(HSO4)3+VO(HSO4)2+H2SO4)3.5 vanadium electrolyte;

[0208] One batch of 800 L of 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte prepared in step 1 was used as the negative electrode electrolyte for 37 5kW vanadium redox flow batteries. Another batch of 500 L of 2MVO(HSO4)2+H2SO4 tetravalent vanadium electrolyte was used as the positive electrode electrolyte. The battery was charged at a constant voltage of 60V for 579.5 Ah.

[0209] SOC － =37×579.5 / (800×2×26.8)=50%;

[0210] SOC + =37×579.5 / (500×2×26.8)=80%;

[0211] Negative electrode: VO(HSO4)2 + H2SO4 + H + +e=V(HSO4)3+H2O;

[0212] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0213] The negative electrode yielded the first 800 L of 2M 0.5(V(HSO4)3+VO(HSO4)2+H2SO4)3.5 valent sulfuric acid system vanadium electrolyte, and the positive electrode yielded 500 L of 2M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO44 valent vanadium electrolyte.

[0214] Step 3: Preparation of 4.1 vanadium electrolyte: 500 L 2M 0.1V₂HSO₄ + 0.9V₂(HSO₄)₂ + 1.1V₂SO₄;

[0215] In step 2, 44.1 kg of H2C2O4·2H2O was added to the 500 L 2M 0.8VO2HSO4 + 0.2VO(HSO4)2 + 1.8H2SO4 4.8 vanadium electrolyte obtained. The mixture was stirred for about 2 hours until no more bubbles were generated, resulting in a 500 L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4 4.1 vanadium electrolyte.

[0216] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0217] H2C2O4·2H2O: 0.7×500×2×0.5×126=44.1(kg);

[0218] Step 4: Preparation of 800L 2M 0.5(V(HSO4)3+VO(HSO4)2+H2SO4)3.5 vanadium electrolyte;

[0219] Repeat step 1, using the freshly prepared 800L 2M VO(HSO4)2+H2SO4 tetravalent vanadium electrolyte as the negative electrode electrolyte for 37 5kW all-vanadium redox flow batteries, and using 500L 2M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 tetravalent vanadium electrolyte as the positive electrode electrolyte. Charge at a constant voltage of 60V for 579.5Ah.

[0220] SOC － =37×579.5 / (800×2×26.8)=50%;

[0221] SOC + =10% + 37 × 579.5 / (500 × 2 × 26.8) = 90%;

[0222] Negative electrode: VO(HSO4)2 + H2SO4 + H + +e=V(HSO4)3+H2O;

[0223] Positive electrode: VO(HSO4)2 + H2O → H + -e = VO₂HSO₄ + H₂SO₄;

[0224] The negative electrode yields 800 L of 2M 0.5(V(HSO4)3+VO(HSO4)2+H2SO4)3.5 valent sulfuric acid system vanadium electrolyte, and the positive electrode yields 500 L of 2M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO44 valent vanadium electrolyte.

[0225] Step 5: Preparation of 4.1 vanadium electrolyte: 500 L 2M 0.1VO2HSO4 + 0.9VO(HSO4)2 + 1.1H2SO4;

[0226] Add 50.4 kg of H₂C₂O₄·2H₂O to 500 L of 2M vanadium electrolyte (0.9VO₂HSO₄ + 0.1VO(HSO₄)₂ + 1.9H₂SO₄, 4.9 valent vanadium, and stir for about 2 hours until no more bubbles are generated, to obtain 500 L of 2M vanadium electrolyte (0.1VO₂HSO₄ + 0.9VO(HSO₄)₂ + 1.1H₂SO₄, 4.1 valent vanadium).

[0227] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2↑+2H2O;

[0228] H2C2O4·2H2O: 0.8×500×2×0.5×126=50.4(kg);

[0229] Step 6: Repeat steps 4 and 5 in this cycle to continuously prepare new vanadium electrolyte in a 3.5 valence sulfuric acid system at the negative electrode.

[0230] In addition, all references to VO(HSO4)2 in this specification are vanadium hydrogen oxysulfate, V(HSO4)3 is vanadium hydrogen sulfate, V2O5 is vanadium pentoxide, H2SO4 is sulfuric acid, H2C2O4·2H2O is oxalic acid with two molecules of water of crystallization, CO2 is carbon dioxide, H2O is water, and VO2HSO4 is vanadium hydrogen oxysulfate.

[0231] The vanadium electrolyte in a 3.5 valence sulfuric acid system is a vanadium electrolyte in which the average valence state of vanadium ions is 3.5.

[0232] The present invention provides a method for preparing vanadium electrolyte in a 3.5-valent sulfuric acid system, wherein the vanadium valence state of the positive electrode electrolyte is between 4 and 5 valence. This method completely overcomes the serious defects of conventional methods for preparing 3.5-valent vanadium electrolytes where both the positive and negative electrode electrolytes are 4-valent vanadium. It has outstanding advantages such as rapid electrolysis, quick reduction, simplicity, reliability, and cyclic operation, and can be effectively used for the efficient and low-cost preparation of vanadium electrolyte in a 3.5-valent sulfuric acid system.

[0233] The second aspect of the present invention provides an electrolyte. The electrolyte provided in this embodiment is prepared by the vanadium electrolyte preparation method of the 3.5 valent hydrochloric acid system provided by any one of the technical solutions of the first aspect of the present application, or by the vanadium electrolyte preparation method of the 3.5 valent sulfuric acid system provided by any one of the technical solutions of the first aspect of the present application.

[0234] A third aspect of the present invention provides a battery, which includes the electrolyte provided in the second aspect of the present invention, or the battery includes an electrolyte prepared by a vanadium electrolyte preparation method based on a vanadium electrolyte in a 3.5-valent hydrochloric acid system provided in any one of the technical solutions of the first aspect of the present application, or prepared by a vanadium electrolyte preparation method based on a vanadium electrolyte in a vanadium sulfuric acid system provided in any one of the technical solutions of the first aspect of the present application.

[0235] In embodiments of the present invention, the terms "first," "second," and "third" are used only for descriptive purposes and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in embodiments of the present invention based on the specific circumstances.

[0236] Furthermore, although the operations are depicted in a specific order, this should be understood as requiring that such operations be performed in the specific order shown or in sequential order, or requiring that all illustrated operations be performed to achieve the desired result. In certain environments, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the invention. Certain features described in the context of individual embodiments can also be implemented in combination in a single implementation.

[0237] Although the subject matter has been described using language describing specific structural features and / or methodological logic, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are merely illustrative examples of implementing the claims.

[0238] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a vanadium electrolyte in a 3.5 valent hydrochloric acid system, characterized in that, Includes the following steps: Hydrochloric acid solution and sulfuric acid solution of tetravalent vanadium ions were used as negative and positive electrodes respectively for charging and electrolysis. A vanadium electrolyte with a 3.5-valent hydrochloric acid system was obtained at the negative electrode, and a sulfuric acid solution with (4+2)-valent vanadium ions was obtained at the positive electrode. Oxalic acid is added to a sulfuric acid solution of (4+z) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < z < 1. Hydrochloric acid solution containing tetravalent vanadium ions and sulfuric acid solution containing (4+x) vanadium ions were used as negative and positive electrodes for electrolysis. A vanadium electrolyte with a 3.5 valence hydrochloric acid system was obtained at the negative electrode, and a sulfuric acid solution containing (4+y) vanadium ions was obtained at the positive electrode. Oxalic acid is added to a sulfuric acid solution of (4+y) vanadium ions to produce a sulfuric acid solution of (4+x) vanadium ions, where 0 < x < y < 1. Repeat at least once the steps of using a sulfuric acid solution of (4+x) vanadium ions as the positive electrode electrolyte and a hydrochloric acid solution of 4 vanadium ions as the negative electrode for charging and electrolysis, and adding oxalic acid to the sulfuric acid solution of (4+y) vanadium ions obtained at the positive electrode to obtain a sulfuric acid solution of (4+x) vanadium ions, so as to continuously obtain a vanadium electrolyte system of 3.5 vanadium ions at the negative electrode. The hydrochloric acid solution of the tetravalent vanadium ions was prepared by dissolving vanadium oxychloride in hydrochloric acid; The amounts of vanadium dichloride and hydrochloric acid are determined based on the total vanadium and Cl elements in the prepared vanadium electrolyte system of 3.5 valence hydrochloric acid.

2. The method for preparing vanadium electrolyte in a 3.5 valent hydrochloric acid system according to claim 1, characterized in that, x ≥ 0.1, y ≥ 0.

9.

3. The method for preparing vanadium electrolyte in a 3.5 valent hydrochloric acid system according to claim 1 or 2, characterized in that, The sulfuric acid solution of the tetravalent vanadium ions is prepared by reducing vanadium pentoxide with sulfuric acid and oxalic acid solution.

4. The method for preparing vanadium electrolyte in a 3.5 valent hydrochloric acid system according to claim 1 or 2, characterized in that, The charging electrolysis is carried out in a vanadium redox flow battery.

5. An electrolyte, characterized in that, The electrolyte is prepared by the method for preparing vanadium electrolyte in a 3.5-valent hydrochloric acid system as described in any one of claims 1 to 4.

6. A battery, characterized in that, The battery includes the electrolyte as described in claim 5; or The battery includes an electrolyte, which is prepared by the method for preparing a vanadium electrolyte based on a 3.5-valent hydrochloric acid system as described in any one of claims 1 to 4 of this application.

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