Vanadium battery electrolyte, preparation method and application thereof

Abstract

The application relates to the technical field of all-vanadium redox flow batteries, and provides a vanadium battery electrolyte as well as a preparation method and application thereof. The method comprises the following steps: (1) in the presence of a solvent, vanadium pentoxide and copper sulfide are subjected to a first reaction to obtain a vanadyl sulfate solution containing copper ions; and (2) the vanadyl sulfate solution containing copper ions is subjected to electrolysis treatment to obtain a vanadium battery electrolyte; wherein the mass ratio of the vanadium pentoxide to the copper sulfide is 7.5-8:1. The method for preparing the vanadium battery electrolyte can solve the problem that the performance of the electrolyte is reduced due to the excess of a reducing agent, and can also electrolytically separate the introduced copper ions, so that the pollution of the copper ions to the electrolyte is eliminated, the purity and activity of the electrolyte are improved; in addition, after the electrolysis of the copper ions, the copper element is separated out as a by-product, high economic benefits can be obtained, and the production cost of the vanadium electrolyte is further reduced.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, and in particular to a vanadium battery electrolyte, its preparation method, and its application. Background Technology

[0002] Vanadium electrolyte is the energy carrier and core material of vanadium redox flow batteries (hereinafter referred to as vanadium batteries). Vanadium batteries typically use vanadium electrolyte with an average vanadium valence of 3.5 as the initial electrolyte, adding equal volumes to the positive and negative electrodes to achieve a balance in charge and discharge capacity. Vanadium battery energy storage systems have high manufacturing costs, with the cost of the vanadium electrolyte accounting for more than 50% of the total system cost. The purity of the vanadium electrolyte can affect its electrochemical performance and stability.

[0003] The existing vanadium battery electrolyte production processes mainly include chemical reduction and electrolysis. The chemical reduction method uses vanadium pentoxide or vanadium oxysulfate crystals as raw materials, and adopts reducing agents or low-valence vanadium compounds to gradually reduce the average valence of vanadium and dissolve it in an acidic solution. Then, a mixed electrolyte of trivalent and pentavalent vanadium is generated through electrolysis or pre-charging.

[0004] Currently, commonly used reducing agents include sulfur dioxide, oxalic acid, and sulfur powder. However, all of these reducing agents have their own drawbacks: the amount of sulfur dioxide introduced is difficult to control, and it is difficult to remove if too much is introduced, which affects the performance of the electrolyte and has a negative impact on the safety and service life of the vanadium battery system; the oxalic acid reduction process produces a large amount of carbon dioxide gas, which not only increases carbon emissions, but also makes the reaction process difficult to control and poses a high risk; sulfur powder has a slow reaction rate, low production efficiency, and also poses an explosion risk and is difficult to store.

[0005] CN114497666A discloses a method for preparing an electrolyte for a vanadium redox flow battery using ferrous sulfide as a reducing agent. Solid V₂O₅ powder and ferrous sulfide are dispersed in a dilute sulfuric acid solution to form a uniformly dispersed solid solution. Through high-temperature stirring, ferrous sulfide dissolves in the dilute sulfuric acid to generate sulfide ions, which then undergo a redox reaction with V₂O₅ at high temperature, ultimately forming a sulfuric acid solution containing trivalent vanadium ions and divalent ferrous ions. Subsequently, V₂O₅ powder is added to the sulfuric acid solution containing trivalent vanadium ions and divalent ferrous ions according to a stoichiometric ratio and stirred uniformly to obtain a solution containing 3.5-valent vanadium ions and divalent ferrous ions, which serves as the mixed electrolyte for the vanadium redox flow battery.

[0006] However, in the aforementioned method, it is difficult for sulfur ions to directly reduce vanadium ions from pentavalent to trivalent, requiring a secondary reduction, which prolongs the reduction reaction time and reduces production efficiency. At the same time, using ferrous sulfide as a reducing agent easily introduces the impurity element iron, which reduces the purity of the electrolyte and affects its electrochemical performance and stability. In addition, the addition of ferrous ions will hinder the diffusion of vanadium ions, thereby reducing the activity of the electrolyte. Summary of the Invention

[0007] The main objective of this invention is to provide a vanadium battery electrolyte, its preparation method, and its application, in order to solve the problems of long reduction reaction time and low purity and activity of the obtained electrolyte in the existing vanadium battery electrolyte preparation process.

[0008] Existing technologies use ferrous sulfide as a reducing agent, which makes it difficult to remove iron ions. Iron ions hinder the diffusion of vanadium ions, reduce electrolyte activity, and exacerbate the risk of precipitation at high temperatures (>40°C). Furthermore, the inventors discovered during their research that in the acidic environment of the electrolyte, combining chemical reduction and electrolysis followed by electrolytic removal easily reduces vanadium ions to divalent and causes hydrogen evolution. This not only lowers the valence state of the electrolyte but also affects the free hydrogen ion content, increasing the difficulty of electrolyte preparation. To address these issues, this invention creatively uses copper sulfide as a reducing agent, employing a combination of chemical reduction and electrolytic reduction to deeply reduce pentavalent vanadium pentoxide raw materials, obtaining a 3.5-valent vanadium electrolyte that meets the requirements. During electrolysis, copper ions are simultaneously reduced to elemental copper, removing impurities and improving electrolyte purity. This also yields high-purity metallic copper as a byproduct, adding value and further reducing the production cost of vanadium electrolyte. Based on this approach, the inventors have provided the solution of this invention.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a vanadium battery electrolyte, comprising the following steps: (1) In the presence of a solvent, vanadium pentoxide is reacted with copper sulfide to obtain a vanadium oxysulfate solution containing copper ions; (2) Electrolyze the vanadium oxysulfate solution containing copper ions to obtain the vanadium battery electrolyte; The mass ratio of vanadium pentoxide to copper sulfide is 7.5-8:1.

[0010] The method for preparing vanadium battery electrolyte provided by this invention combines chemical reduction and electrolysis, resulting in high production efficiency. First, copper sulfide is used as a reducing agent. By precisely controlling the amount added, the problem of electrolyte performance degradation caused by excessive reducing agent is solved. Then, electrolysis is used to further reduce vanadium ions to 3.5-valent vanadium electrolyte. Simultaneously, introduced copper ions are electrolyzed out, eliminating copper ion contamination of the electrolyte and improving electrolyte purity and activity. Furthermore, the precipitation of elemental copper as a byproduct after copper ion electrolysis yields significant economic benefits and further reduces the production cost of vanadium electrolyte.

[0011] In some embodiments, the solvent is sulfuric acid; Optionally, the concentration of the sulfuric acid is 1.0-4.0 mol / L, preferably 3.0-4.0 mol / L.

[0012] In some embodiments, the amount of vanadium pentoxide is controlled such that the concentration of vanadium ions in the solvent is 1.5-4.0 mol / L.

[0013] In some embodiments, the conditions for the first reaction are at least: a temperature of 60-90°C and a time of 4-6 hours.

[0014] In some embodiments, the conditions for the first reaction are at least: the temperature is 80-90°C.

[0015] In some embodiments, the electrolysis process includes the following steps: The vanadium oxysulfate solution containing copper ions is used as the cathode of the electrolysis device, and the sulfuric acid solution is used as the anode of the electrolysis device for electrolysis treatment. The electrolytic treatment time is T, and T = (0.5 × C × V × 96320) / (3600 × I × n × ŋ), Equation (I); In formula (I), C is the concentration of tetravalent vanadium ions, in mol / L; V represents the volume of the vanadium oxysulfate solution, in L; I represents the electrolysis current, measured in amperes (A). n is the number of individual cells in series in the electrolytic cell stack; ŋ represents the electrolysis efficiency of the electrolysis device.

[0016] In some embodiments, the electrolysis device includes a power unit, an electrolyte storage tank, and liquid pipelines; the power unit has an electrolyte circuit on both the positive and negative electrode sides. The electrolyte storage tank includes a positive electrode electrolyte storage tank for storing the sulfuric acid solution and a negative electrode electrolyte storage tank for storing the vanadium oxysulfate solution. Optionally, the electrolyte circuit includes a positive electrode side electrolyte circulation pipeline and a negative electrode side electrolyte circulation pipeline, and a circulation pump is provided on both the positive electrode side electrolyte circulation pipeline and the negative electrode side electrolyte circulation pipeline.

[0017] A second aspect of the present invention provides an electrolyte prepared by means of the method described in the first aspect.

[0018] In some embodiments, the electrolyte satisfies at least one of the following conditions: A. The average valence state of the electrolyte is 3.5 ± 0.01; B. The copper content in the electrolyte is no more than 0.1 mg / L; C. The iron content in the electrolyte is not greater than 10 mg / L; D. The concentration of vanadium ions in the electrolyte is not less than 1.5 mol / L; optionally, the concentration of vanadium ions in the electrolyte is 1.5-4 mol / L. E. The concentration of sulfate ions in the electrolyte is not less than 3 mol / L; optionally, the concentration of sulfate ions in the electrolyte is 3-5 mol / L.

[0019] A third aspect of the present invention provides a battery comprising an electrolyte as described in the second aspect; or The battery includes an electrolyte, which is prepared by the method described in the first aspect.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present application. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0023] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0024] It should be noted that the average valence state of the electrolyte, 3.5, refers to the equilibrium state in which the molar ratio of trivalent vanadium to tetravalent vanadium in the electrolyte reaches 1:1.

[0025] As described above, a first aspect of the present invention provides a method for preparing a vanadium battery electrolyte, comprising the following steps: (1) In the presence of a solvent, vanadium pentoxide is reacted with copper sulfide to obtain a vanadium oxysulfate solution containing copper ions; (2) Electrolyze the vanadium oxysulfate solution containing copper ions to obtain the vanadium battery electrolyte; The mass ratio of vanadium pentoxide to copper sulfide is 7.5-8:1.

[0026] The method for preparing vanadium battery electrolyte provided by this invention combines chemical reduction and electrolysis, resulting in high production efficiency. First, copper sulfide is used as a reducing agent. By precisely controlling the amount added, the problem of electrolyte performance degradation caused by excessive reducing agent is solved. Then, electrolysis is used to further reduce vanadium ions to 3.5-valent vanadium electrolyte. Simultaneously, introduced copper ions are electrolyzed out, eliminating copper ion contamination of the electrolyte and improving electrolyte purity and activity. Furthermore, the precipitation of elemental copper as a byproduct after copper ion electrolysis yields significant economic benefits and further reduces the production cost of vanadium electrolyte.

[0027] The mass ratio of vanadium pentoxide to copper sulfide can be, for example, any value between 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, 8:1, or 7.5:8:1. Insufficient reducing agent leads to incomplete chemical reduction, making subsequent electrolysis difficult. Excessive reducing agent, while reducing the electrolyte from pentavalent to tetravalent in a short time, results in a redox reaction between the remaining reducing agent and the newly generated pentavalent vanadium, producing large amounts of nitrogen and carbon dioxide bubbles, severely hindering the electrolysis process and degrading the performance of the finished electrolyte. The inventors discovered that precisely controlling the reducing agent dosage within the aforementioned range ensures a sufficient chemical reduction reaction while preventing excessive reducing agent from causing performance degradation in the finished electrolyte, resulting in an electrolyte with excellent energy efficiency and utilization.

[0028] It is worth noting that this invention utilizes the reducing properties of sulfur in copper sulfide to reduce vanadium pentoxide to tetravalent vanadium ions, which then dissolve and form a vanadium oxysulfate solution containing copper ions. The copper-containing vanadium oxysulfate solution is then electrolytically reduced to a 3.5-valent vanadium electrolyte. Simultaneously, during electrolysis, copper ions are reduced to elemental copper, which remains at the bottom of the electrolytic cell, thus removing copper impurities. The main reaction equations for the entire process are as follows: 3V2O5+12H + +S 2- →6VO 2+ +6H2O+SO3 2- Reaction formula (1) V2O5+4H + +SO3 2- →2VO 2+ +2H2O+SO4 2- , reaction formula (2) VO 2+ +2H + +e- →V3 + +H2O, reaction (3) Cu 2+ +2e→Cu, reaction (4) The above reaction formulas (1) and (2) are the process of copper sulfide reducing vanadium pentoxide to generate tetravalent vanadium oxysulfate solution; reaction formula (3) is the electrolytic treatment process, in which the vanadium oxysulfate solution is further electrolyzed and reduced to trivalent vanadium / tetravalent vanadium in a ratio of 1:1, i.e., 3.5 valence electrolyte; reaction formula (4) is the process of fine electrolysis of vanadium oxysulfate solution containing copper ions, in which copper ions are reduced to elemental copper and precipitate at the bottom of the electrolytic cell, thereby achieving the purpose of removing copper ions.

[0029] In some embodiments, the solvent is sulfuric acid.

[0030] In some embodiments, the concentration of the sulfuric acid is 1.0-4.0 mol / L, and the concentration of the sulfuric acid can be, for example, any value between 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, or 1.0-4.0 mol / L. Preferably, the concentration of the sulfuric acid is 3.0-4.0 mol / L.

[0031] In some embodiments, the amount of vanadium pentoxide is controlled such that the vanadium ion concentration in the solvent is 1.5-4.0 mol / L. The vanadium ion concentration in the solvent can be, for example, any value between 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, or 1.5-4.0 mol / L.

[0032] In some embodiments, the conditions for the first reaction at least satisfy the following: a temperature of 60-90°C and a time of 4-6 hours. The temperature of the first reaction can be, for example, any value between 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 60-90°C. Preferably, the temperature of the first reaction is 80-90°C.

[0033] In some embodiments, the electrolysis process includes the following steps: The vanadium oxysulfate solution containing copper ions is used as the cathode of the electrolysis device, and the sulfuric acid solution is used as the anode of the electrolysis device for electrolysis treatment. The electrolytic treatment time is T, and T = (0.5 × C × V × 96320) / (3600 × I × n × ŋ), Equation (I); In formula (I), C is the concentration of tetravalent vanadium ions, in mol / L; V represents the volume of the vanadium oxysulfate solution, in L; I represents the electrolysis current, measured in amperes (A). n is the number of individual cells in series in the electrolytic cell stack; optionally, the number n in series in the electrolytic device is not greater than 50; the number n in series in the electrolytic device can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 18, 19, 21, 23, 25, 28, 30, 32, 34, 35, 36, 40, 41, 43, 44, 46, 48, 50 or any value between 1 and 50.

[0034] ŋ represents the electrolysis efficiency of the electrolysis device.

[0035] When preparing vanadium trivalent electrolyte through electrolysis, the charging current and electrolysis voltage are adjusted according to the electrode area and the 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, resulting in the maximum charging current and the shortest electrolysis time, thus improving electrolysis efficiency. Alternatively, constant current charging followed by constant voltage charging can be performed first, which will result in a longer electrolysis time.

[0036] In some embodiments, the electrolysis device includes a power unit, an electrolyte storage tank, and liquid pipelines; the power unit has an electrolyte circuit on both the positive and negative electrode sides. The electrolyte storage tank includes a positive electrode electrolyte storage tank for storing the sulfuric acid solution and a negative electrode electrolyte storage tank for storing the vanadium oxysulfate solution.

[0037] Furthermore, the electrolyte circuit includes a positive electrode side electrolyte circulation pipeline and a negative electrode side electrolyte circulation pipeline, and a circulation pump is provided on both the positive electrode side electrolyte circulation pipeline and the negative electrode side electrolyte circulation pipeline. In some embodiments, the circulation pump on the positive electrode side electrolyte circulation pipeline is a positive electrode pump, and the circulation pump on the negative electrode side electrolyte circulation pipeline is a negative electrode pump.

[0038] It should be noted that during the electrolysis process, the vanadium oxysulfate solution obtained after the aforementioned reduction reaction is placed in the negative electrode electrolyte storage tank, and is transported by the negative electrode pump, flowing into the negative electrode side of the power unit and then flowing back to the negative electrode electrolyte storage tank; similarly, the sulfuric acid solution circulates between the power unit and the positive electrode electrolyte storage tank; after both the positive and negative sides have flowed back, the power supply of the electrolysis device is turned on.

[0039] It is worth noting that the present invention does not impose any special requirements on the electrolysis device; it only needs to be capable of electrolysis. Electrolysis devices known to those skilled in the art can be used, and will not be described in detail here, nor should this be construed as a limitation of the present invention. For example, a conventional vanadium redox flow battery can be used as the electrolysis device for electrolysis.

[0040] As previously described, a second aspect of the present invention provides an electrolyte prepared by means of the method described in the first aspect.

[0041] In some embodiments, the electrolyte satisfies at least one of the following conditions: A. The average valence state of the electrolyte is 3.5 ± 0.01; B. The copper content in the electrolyte is no more than 0.1 mg / L; preferably, no copper is detected in the electrolyte. C. The iron content in the electrolyte is not greater than 10 mg / L; the iron content in the electrolyte can be, for example, 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L or any value between 1 and 10 mg / L; D. The concentration of vanadium ions in the electrolyte is not less than 1.5 mol / L; optionally, the concentration of vanadium ions in the electrolyte is 1.5-4 mol / L; the concentration of vanadium ions in the electrolyte is any value between 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L or 1.5-4 mol / L.

[0042] E. The concentration of sulfate ions in the electrolyte is not less than 3 mol / L; optionally, the concentration of sulfate ions in the electrolyte is 3-5 mol / L, and the concentration of sulfate ions in the electrolyte is any value between 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, 4.3 mol / L, 4.5 mol / L, 4.8 mol / L, 4.9 mol / L, 5 mol / L, or 3-5 mol / L.

[0043] It is worth noting that the vanadium battery electrolyte prepared using the method provided in this invention meets all standards in terms of parameters, and the content of the impurity element copper is significantly reduced to an undetectable level. Therefore, the vanadium battery electrolyte prepared by the method of this invention can achieve the purpose of removing copper ions.

[0044] As previously described, a third aspect of the present invention provides a battery comprising an electrolyte as described in the second aspect; or The battery includes an electrolyte, which is prepared by the method described in the first aspect.

[0045] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials and instruments used are commercially available products.

[0046] In the following embodiments, unless otherwise stated, the electrolysis efficiency of the electrolysis device is 95%.

[0047] In the following embodiments, the electrolysis time T = (0.5 × C × V × 96320) / (3600 × I × n × ŋ), where C is 1.65 M, V is 1.2 L, I is 6.25 A, and n is 3. Example 1

[0048] This embodiment provides a method for preparing a vanadium battery electrolyte, including the following steps: (1) Dilute 200mL of concentrated sulfuric acid to 1L, and add 182g of vanadium pentoxide powder and 23.9g of copper sulfide powder to the diluted sulfuric acid solution in sequence; keep it at 80℃ for 4h for reduction, and filter the solution after it turns into a clear blue liquid. (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.5h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte.

[0049] The vanadium battery electrolyte obtained in this embodiment was subjected to ICP testing. The electrolyte parameters and the content of impurity elements in the electrolyte are shown in Table 1 and Table 2, respectively.

[0050] Table 1 Electrolyte parameters of this embodiment Principal component parameters result V content / mol / L 1.65 <![CDATA[SO4 2- Content / mol / L]]> 4.33 Average price state 3.49 Table 2. Impurity element content in the electrolyte of this embodiment Element types Content / mg / L Al 5.0 As 1.0 Au Not detected Ca 5.0 Cr 1.0 Cl ＜20 Cu Not detected Fe 10 K 10 Mg 2.0 Mn 0.5 Mo 5 <![CDATA[NH4 + ]]> ＜20 Na 10 Ni 0.5 Pb 0.5 Pt Not detected Si 5 Example 2

[0051] The preparation method of the vanadium battery electrolyte provided in this embodiment is basically the same as that provided in Example 1, except that the ratio of vanadium pentoxide and copper sulfide in step (1) is different. (1) Dilute 200mL of concentrated sulfuric acid to 1L, and add 182g of vanadium pentoxide powder and 22.8g of copper sulfide powder to the diluted sulfuric acid solution in sequence; keep it at 80℃ for 4h for reduction, and filter the solution after it turns into a clear blue liquid.

[0052] (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.5h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte. Example 3

[0053] The preparation method of the vanadium battery electrolyte provided in this embodiment is basically the same as that provided in Example 1, except that the ratio of vanadium pentoxide and copper sulfide in step (1) is different. (1) Dilute 200mL of concentrated sulfuric acid to 1L, and add 182g of vanadium pentoxide powder and 23.3g of copper sulfide powder to the diluted sulfuric acid solution in sequence; keep it at 80℃ for 4h for reduction, and filter the solution after it turns into a clear blue liquid.

[0054] (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.5h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte.

[0055] Comparative Example 1 The preparation method of the vanadium battery electrolyte provided in this comparative example is basically the same as that provided in Example 1, except that the reducing agent in step (1) is: (1) Dilute 200mL of concentrated sulfuric acid to 1L, and add 182g of vanadium pentoxide powder and 90g of oxalic acid to the diluted sulfuric acid solution in sequence; keep it at 80℃ for 4h for reduction, and filter the solution after it turns into a clear blue liquid.

[0056] (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.5h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte.

[0057] Comparative Example 2 The preparation method of the vanadium battery electrolyte provided in this comparative example is basically the same as that provided in Example 1, except that the reducing agent in step (1) is: Dilute 200 mL of concentrated sulfuric acid to 1 L. Add 182 g of vanadium pentoxide powder and 19.5 g of ferrous sulfide to the diluted sulfuric acid solution. Keep the solution at 80 °C for 4 h for reduction. After the solution turns into a clear blue liquid, filter it.

[0058] (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.5h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte.

[0059] The vanadium battery electrolyte obtained in this comparative example was subjected to ICP testing. The electrolyte parameters and the content of impurity elements in the electrolyte are shown in Tables 3 and 4, respectively.

[0060] Table 3 Electrolyte parameters of this comparative example Principal component parameters result V content / mol / L 1.65 <![CDATA[SO4 2- Content / mol / L]]> 4.32 Average price state 3.492 Table 4. Impurity element content in the electrolyte of this embodiment Element types Content / mg / L Al 5.0 As 1.0 Au Not detected Ca 5.0 Cr 1.0 Cl ＜20 Cu 0.5 Fe 4500 K 10 Mg 2.2 Mn 0.5 Mo 5 <![CDATA[NH4 + ]]> ＜20 Na 10 Ni 0.5 Pb 0.5 Pt Not detected Si 3 As can be seen from the table above, when ferrous sulfide is used as a reducing agent, the iron content in the finished electrolyte is seriously excessive, indicating that the introduced iron ions are difficult to remove.

[0061] Comparative Example 3 The preparation method of the vanadium battery electrolyte provided in this comparative example is basically the same as that provided in Example 1, except that the ratio of vanadium pentoxide and copper sulfide in step (1) is different. (1) Dilute 200mL of concentrated sulfuric acid to 1L, and add 182g of vanadium pentoxide powder and 20.2g of copper sulfide powder to the diluted sulfuric acid solution in sequence; keep it at 80℃ for 4h for reduction, and filter the solution after it turns into a clear blue liquid.

[0062] (2) Place the blue clear liquid in the negative electrode electrolyte storage tank of the electrolysis device. The positive electrode electrolyte storage tank of the electrolysis device is a dilute sulfuric acid solution. Turn on the circulation pump. After the electrolysis tank is filled with solution, start electrolysis. The electrolysis time is 1.35h. After the electrolysis is completed, take out the electrolyte on the negative electrode side, filter it, detect the vanadium ion concentration and sulfate concentration, add water and sulfuric acid, and adjust the electrolyte to obtain the vanadium battery electrolyte.

[0063] The vanadium battery electrolyte obtained in this comparative example was subjected to ICP testing. The electrolyte parameters and the content of impurity elements in the electrolyte are shown in Tables 5 and 6, respectively.

[0064] Table 5 Electrolyte parameters of this comparative example Principal component parameters result V content / mol / L 1.61 <![CDATA[SO4 2- Content / mol / L]]> 4.28 Average price state 3.5 Table 6. Impurity element content in the electrolyte of this comparative example. Element types Content / mg / L Al 4.2 As 0.9 Au Not detected Ca 4.5 Cr 0.9 Cl ＜20 Cu Not detected Fe 9 K 9 Mg 1.8 Mn 0.5 Mo 4 <![CDATA[NH4 + ]]> ＜20 Na 9 Ni 0.5 Pb 0.5 Pt Not detected Si 4 Test Example 1 The electrolytes obtained in the examples and comparative examples were subjected to an A / cm² temperature of 200 mA / cm². 2 The charge-discharge performance was tested at the current density, and the specific test results are shown in Table 7.

[0065] The formula for calculating current efficiency is: discharge capacity (Ah) / charge capacity (Ah).

[0066] The formula for calculating electrolyte utilization rate is: discharge capacity (Ah) / theoretical discharge capacity (Ah).

[0067] The theoretical discharge Ah capacity calculation formula is: C'×n'×96320 / 3600; In the formula: C' is the concentration of vanadium ions in the electrolyte, mol / L; n' represents the number of electrons gained or lost by a single vanadium ion, which is 1 in this formula.

[0068] Table 7 Current efficiency / % Voltage efficiency / % Energy efficiency / % Discharge capacity / Ah Electrolyte utilization rate / % Example 1 97.2 83.2 80.9 32.3 75.5 Example 2 97.5 83.1 81 32.5 76.0 Example 3 97.4 83.2 81 32.4 75.7 Comparative Example 1 97 82.7 80.2 30.2 70.2 Comparative Example 2 93 80.5 74.9 28.5 66.2 Comparative Example 3 97.2 83.4 81.1 30.2 75.1 As can be seen from the table above, the electrolyte parameters and impurity element content prepared by the method provided by the present invention all meet the standard GB / T37204-2018 "Electrolytes for Vanadium Redox Flow Batteries". The various efficiencies of the electrolyte are significantly improved during the charging and discharging process, especially the energy efficiency and electrolyte utilization rate.

[0069] Comparing Example 1 with Comparative Examples 1 and 2, it was found that the method provided by the present invention, compared with the method using oxalic acid as a reducing agent, yields an electrolyte with a higher discharge capacity and a higher electrolyte utilization rate. Compared with the method using ferrous sulfide as a reducing agent, the method of the present invention using copper sulfide and electrolytic reduction not only yields an electrolyte with iron ions that meet the requirements for use, but also effectively removes copper ions, resulting in a significant improvement in the electrical performance of the electrolyte.

[0070] Comparing Example 1 and Comparative Example 3, it was found that the present invention can obtain an electrolyte with higher discharge capacity by precisely controlling the mass ratio of vanadium pentoxide to copper sulfide.

[0071] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0072] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the present invention specification under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing vanadium battery electrolyte, characterized in that, Includes the following steps: (1) In the presence of a solvent, vanadium pentoxide is reacted with copper sulfide to obtain a vanadium oxysulfate solution containing copper ions; (2) Electrolyze the vanadium oxysulfate solution containing copper ions to obtain the vanadium battery electrolyte; The mass ratio of vanadium pentoxide to copper sulfide is 7.5-8:

1.

2. The method according to claim 1, characterized in that, The solvent is sulfuric acid; Optionally, the concentration of the sulfuric acid is 1.0-4.0 mol / L, preferably 3.0-4.0 mol / L.

3. The method according to claim 2, characterized in that, The amount of vanadium pentoxide used is controlled so that the concentration of vanadium ions in the solvent is 1.5-4.0 mol / L.

4. The method according to claim 1, characterized in that, The conditions for the first reaction must at least be met: temperature 60-90℃ and time 4-6h.

5. The method according to claim 4, characterized in that, The conditions for the first reaction must at least be met: the temperature is 60-90℃.

6. The method according to any one of claims 1-5, characterized in that, The electrolysis process includes the following steps: The vanadium oxysulfate solution containing copper ions is used as the negative electrode of the electrolysis device, and the sulfuric acid solution is used as the positive electrode of the electrolysis device for electrolysis treatment. The electrolytic treatment time is T, and T = (0.5 × C × V × 96320) / (3600 × I × n × ŋ), Equation (I); In formula (I), C is the concentration of tetravalent vanadium ions, in mol / L; V represents the volume of the vanadium oxysulfate solution, in L; I represents the electrolysis current, measured in amperes (A). n is the number of individual cells in series in the electrolytic cell stack; ŋ represents the electrolysis efficiency of the electrolysis device.

7. The method according to claim 6, characterized in that, The electrolysis device includes a power unit, an electrolyte storage tank, and liquid pipelines; the power unit has electrolyte circuits on both the positive and negative electrode sides. The electrolyte storage tank includes a positive electrode electrolyte storage tank for storing the sulfuric acid solution and a negative electrode electrolyte storage tank for storing the vanadium oxysulfate solution. Optionally, the electrolyte circuit includes a positive electrode side electrolyte circulation pipeline and a negative electrode side electrolyte circulation pipeline, and a circulation pump is provided on both the positive electrode side electrolyte circulation pipeline and the negative electrode side electrolyte circulation pipeline.

8. An electrolyte, characterized in that, The electrolyte is prepared by the method described in any one of claims 1-7.

9. The electrolyte according to claim 8, characterized in that, The electrolyte satisfies at least one of the following conditions: A. The average valence state of the electrolyte is 3.5 ± 0.01; B. The copper content in the electrolyte is no more than 0.1 mg / L; C. The iron content in the electrolyte is not greater than 10 mg / L; D. The concentration of vanadium ions in the electrolyte is not less than 1.5 mol / L; optionally, the concentration of vanadium ions in the electrolyte is 1.5-4 mol / L. E. The concentration of sulfate ions in the electrolyte is not less than 3 mol / L; optionally, the concentration of sulfate ions in the electrolyte is 3-5 mol / L.

10. A battery, characterized in that, The battery includes the electrolyte as described in claim 8 or 9; or The battery includes an electrolyte, which is prepared by the method described in any one of claims 1-7.