A preparation method and application of all-vanadium liquid flow battery electrolyte

Abstract

The invention discloses a preparation method and application of an all-vanadium liquid flow battery electrolyte, belonging to the technical field of all-vanadium liquid flow batteries. The preparation method of the all-vanadium liquid flow battery electrolyte comprises the following steps: adding concentrated sulfuric acid to a mixture of solid V2O5 powder and metal lead to form a uniformly dispersed solid solution, stirring the reaction, filtering the clear liquid as a negative electrode electrolyte for electrolysis, and obtaining a vanadium ion sulfuric acid solution at the negative electrode of the electrolytic cell; wherein, metal lead is used as a chemical reducing agent, and its oxidation product is lead sulfate that is insoluble in the solution, thereby reducing the risk of impurities mixing in the electrolyte synthesis process. The invention avoids the problems caused by the residual traditional reducing agent, and realizes a method for preparing an electrolyte that is simple and convenient to operate and has low cost.

Description

Technical Field

[0001] The invention relates to the technical field of all-vanadium liquid flow batteries, and in particular to a method for preparing an all-vanadium liquid flow battery electrolyte and an application thereof. Background Art

[0002] All-vanadium flow battery is a new type of energy storage battery with the advantages of high energy conversion efficiency, long service life, convenient capacity adjustment, high safety and environmental friendliness. It can be used in large-scale energy storage fields such as renewable energy such as solar energy and wind energy and peak-shaving and valley-filling of power grids. It is one of the most promising energy storage devices. Among them, the electrolyte, as a carrier of active substances, is one of the most important components of all-vanadium flow batteries. The performance and concentration of the electrolyte directly affect the performance and energy density of the battery. How to obtain high-performance vanadium electrolyte has become a hot topic for researchers from all over the world. The synthesis of the electrolyte of all-vanadium flow battery mainly adopts chemical reduction combined with electrolysis. The chemical reduction part mainly uses vanadium oxide or other vanadium salt as raw materials, heats it in a certain concentration of sulfuric acid solution and adds a reducing agent (such as S, SO2, etc.) to dissolve it and reduce it to a low-priced and soluble vanadium compound, and then combines it with an electrolysis device to obtain a vanadium electrolyte of a certain concentration. However, the added reducing agent will remain in the vanadium electrolyte and is difficult to eradicate, affecting the purity and performance of the vanadium electrolyte. Summary of the invention

[0003] In view of the above problems, the present invention uses metallic lead as an additive and reducing agent in the electrolyte preparation process, and prepares a sulfuric acid solution electrolyte of vanadium ions with an average valence of 3.5 by chemical reduction combined with electrolysis. The characteristics of metallic lead and its oxidation product lead sulfate being insoluble in the solution are utilized to avoid the problems caused by the residual reducing agent, thereby realizing a method for preparing an electrolyte that is simple, convenient and low in cost.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a method for preparing an all-vanadium liquid flow battery electrolyte, comprising the following steps:

[0006] Concentrated sulfuric acid is added to a mixture of solid V2O5 powder and metallic lead to form a uniformly dispersed solid solution, which is stirred for reaction. The clear liquid after filtration is used as the negative electrode electrolyte for electrolysis to obtain a vanadium ion sulfuric acid solution electrolyte at the negative electrode of the electrolytic cell. Among them, metallic lead is used as a chemical reducing agent, and its oxidation product is lead sulfate, which is insoluble in the solution, thereby reducing the risk of impurities mixing in the electrolyte synthesis process.

[0007] The vanadium ion sulfuric acid solution electrolyte is obtained at the negative electrode of the electrolytic cell, wherein the average valence state of the vanadium ions is 3.5.

[0008] The temperature of the mixing and stirring reaction is 70° C.-90° C., and the stirring reaction time is 1 h-4 h.

[0009] The weight ratio of the V2O5 powder to metallic lead is (10-20):1.

[0010] The solid-liquid ratio of the mixture of the V2O5 powder and metallic lead to concentrated sulfuric acid is 50g:(100-200)mL.

[0011] The positive and negative electrodes of the electrolytic cell are both lead electrodes.

[0012] The electrolysis current of the electrolytic cell is 40 mA / cm 2 -160mA / cm 2 .

[0013] The positive electrode electrolyte in the electrolytic cell is a 4 mol / L-6 mol / L sulfuric acid solution, and the volumes of the positive and negative electrode electrolytes are the same.

[0014] The diaphragm of the electrolytic cell is a Nafion diaphragm.

[0015] The present invention also provides an application of an all-vanadium liquid flow battery electrolyte in an all-vanadium liquid flow battery, and the all-vanadium liquid flow battery electrolyte is configured using the preparation method of the all-vanadium liquid flow battery electrolyte.

[0016] Advantages and effects of the present invention:

[0017] 1. The present invention proposes a method for preparing an electrolyte for an all-vanadium redox flow battery by combining a chemical method with an electrolytic method using metallic lead as a reducing agent. The electrolyte is a sulfuric acid solution of vanadium ions with an average valence of 3.5, which realizes a simple, convenient and low-cost electrolyte preparation route;

[0018] 2. The present invention uses metal lead which is hardly soluble in sulfuric acid to replace the traditional reducing agent, which can ensure that the reducing agent metal lead does not pollute the electrolyte; the reaction product of the traditional reducing agent contains water, which reduces the concentration of vanadium ions, while the reaction product of the present invention does not contain water;

[0019] 3. The present invention adopts a method combining chemistry and electrolysis, which solves the problem of low concentration in chemical preparation and high energy consumption in electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a performance test diagram of an all-vanadium redox flow battery assembled with an electrolyte prepared in Example 1 of the present invention;

[0021] Figure 2 This is a performance test diagram of an all-vanadium redox flow battery assembled with an electrolyte prepared in Example 2 of the present invention;

[0022] Figure 3This is a performance test diagram of an all-vanadium redox flow battery assembled with an electrolyte prepared in Example 3 of the present invention;

[0023] Figure 4 This is a performance test diagram of an all-vanadium redox flow battery assembled with an electrolyte prepared in Comparative Example 1 of the present invention;

[0024] Figure 5 This is a performance test diagram of the all-vanadium redox flow battery assembled with the electrolyte prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with embodiments.

[0026] Example

[0027] The mixture of solid V2O5 powder and metallic lead was mixed with concentrated sulfuric acid to form a uniformly dispersed solid solution at 70°C, and the reaction was stirred for 1 hour. The weight ratio of V2O5 powder to metallic lead was 10:1, and the solid-liquid ratio of the mixture of V2O5 powder and metallic lead to concentrated sulfuric acid was 50g:100mL. After filtration, the clear liquid was electrolyzed. Lead electrodes were used at both the positive and negative electrodes of the electrolytic cell. The electrolysis current of the electrolytic cell was 40mA / cm 2 The positive electrode electrolyte in the electrolytic cell is a 4 mol / L sulfuric acid solution, and the volumes of the positive and negative electrode electrolytes are the same; the electrolytic cell diaphragm is a Nafion diaphragm; after electrolysis for 3 hours, the solution of Example 1 is obtained, and its total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration are shown in Table 1. It can be seen from Table 1 that the total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration all meet the requirements for the main component content of the 3.5-valent electrolyte in "GB / T 37204-2018 Electrolyte for All-vanadium Redox Flow Batteries"; the all-vanadium redox flow battery is assembled with this solution for performance testing to evaluate the performance of the electrolyte, see Figure 1 As for the solution of Example 1 in Table 2, the battery efficiency and cycle performance are normal and significantly better than those of the comparative example.

[0028] All-vanadium liquid flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrode, positive and negative electrodes are using Example 1 solution, using 80mA / cm 2 The charge and discharge cycle is carried out at a current density of , the charge cut-off condition is that the voltage is not higher than 1.5V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0029] Example 2

[0030] The mixture of solid V2O5 powder and metallic lead was mixed with concentrated sulfuric acid to form a uniformly dispersed solid solution at 80°C, and stirred for 2 hours. The weight ratio of V2O5 powder to metallic lead was 15:1, and the solid-liquid ratio of the mixture of V2O5 powder and metallic lead to concentrated sulfuric acid was 50g:150mL. The positive and negative electrodes of the electrolytic cell were both lead electrodes, and the electrolysis current of the electrolytic cell was 160mA / cm 2 The positive electrode electrolyte in the electrolytic cell is a 5 mol / L sulfuric acid solution, the positive and negative electrode electrolytes have the same volume, and the electrolytic cell diaphragm is a Nafion diaphragm; after electrolysis for 3 hours, the solution of Example 2 is obtained, and its total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration are shown in Table 1. It can be seen from Table 1 that the total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration all meet the requirements for the main component content of 3.5-valent electrolyte in "GB / T37204-2018 Electrolyte for All-vanadium Redox Flow Batteries"; an all-vanadium redox flow battery is assembled with this solution for performance testing to evaluate the performance of the electrolyte, see Figure 2 As for the solution of Example 2 in Table 2, the battery efficiency and cycle performance are normal and significantly better than those of the comparative example.

[0031] All-vanadium liquid flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrode, positive and negative electrodes are using Example 2 solution, using 80mA / cm 2 The charge and discharge cycle is carried out at a current density of , the charge cut-off condition is that the voltage is not higher than 1.5V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0032] Example 3

[0033] The mixture of solid V2O5 powder and metallic lead was mixed with concentrated sulfuric acid to form a uniformly dispersed solid solution at 90°C, and stirred for 4 hours. The weight ratio of V2O5 powder to metallic lead was 20:1, and the solid-liquid ratio of the mixture of V2O5 powder and metallic lead to concentrated sulfuric acid was 50g:200mL. Lead electrodes were used for both the positive and negative electrodes of the electrolytic cell, and the electrolysis current of the electrolytic cell was 80mA / cm 2 The positive electrode electrolyte in the electrolytic cell is a 6 mol / L sulfuric acid solution, the positive and negative electrode electrolytes have the same volume, and the electrolytic cell diaphragm is a Nafion diaphragm; after electrolysis for 3 hours, the solution of Example 3 is obtained, and its total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration are shown in Table 1. It can be seen from Table 1 that the total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration all meet the requirements for the main component content of 3.5-valent electrolyte in "GB / T37204-2018 Electrolyte for All-vanadium Redox Flow Batteries"; the all-vanadium redox flow battery is assembled with this solution for performance testing to evaluate the performance of the electrolyte, see Figure 3 As for the solution of Example 3 in Table 2, the battery efficiency and cycle performance are normal, which are significantly better than those of the comparative example.

[0034] All-vanadium liquid flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrode, positive and negative electrodes are using Example 3 solution, using 80mA / cm 2 The charge and discharge cycle is carried out at a current density of , the charge cut-off condition is that the voltage is not higher than 1.5V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0035] Comparative Example 1

[0036] The mixture of solid V2O5 powder and sulfur was mixed with concentrated sulfuric acid to form a uniformly dispersed solid solution at 70°C. The reaction was stirred for 1 hour. The weight ratio of V2O5 powder to sulfur was 50:1, and the solid-liquid ratio of V2O5 powder and sulfur mixture to concentrated sulfuric acid was 50g:100ml. The positive and negative electrodes of the electrolytic cell were both lead electrodes, and the electrolysis current of the electrolytic cell was 10mA / cm 2 The positive electrode electrolyte in the electrolytic cell is a 5 mol / L sulfuric acid solution, and the volumes of the positive and negative electrode electrolytes are the same; the electrolytic cell diaphragm is a Nafion diaphragm; after electrolysis for 3 hours, the solution of Comparative Example 1 is obtained, and its total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration are shown in Table 1. Since sulfur is used as a reducing agent, sulfur residue exists. It can be seen from Table 1 that the final sulfate concentration of the electrolyte exceeds the design value (4.5 mol / L); an all-vanadium redox flow battery is assembled with this solution for performance testing to evaluate the performance of the electrolyte, see Figure 4 As for the solution of comparative example 1 in Table 2, the coulombic efficiency of the battery is lower than the normal value (about 95%) due to the residual sulfur impurities.

[0037] All-vanadium liquid flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrode, positive and negative electrodes are using the solution of comparative example 1, using 80mA / cm 2 The charge and discharge cycle is carried out at a current density of , the charge cut-off condition is that the voltage is not higher than 1.5V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0038] Comparative Example 2

[0039] The mixture of solid V2O5 powder and sulfur was mixed with concentrated sulfuric acid to form a uniformly dispersed solid solution at 90°C. The reaction was stirred for 2 hours. The weight ratio of V2O5 powder to sulfur was 100:1, and the solid-liquid ratio of V2O5 powder and sulfur mixture to concentrated sulfuric acid was 50g:200ml. Lead electrodes were used for both the positive and negative electrodes of the electrolytic cell, and the electrolysis current of the electrolytic cell was 10mA / cm 2The positive electrode electrolyte in the electrolytic cell is a 5 mol / L sulfuric acid solution, the positive and negative electrode electrolytes have the same volume, and the electrolytic cell diaphragm is a Nafion diaphragm; after 5 hours of electrolysis, the comparative example 2 solution is obtained, and its total vanadium ion concentration, the ratio of trivalent and tetravalent vanadium ion concentrations and sulfate concentration are shown in Table 1. Since sulfur is used as a reducing agent, sulfur residue exists. It can be seen from Table 1 that the final electrolyte sulfate concentration exceeds the design value (4.5 mol / L); the all-vanadium redox flow battery is assembled with this solution for performance testing to evaluate the electrolyte performance, see Figure 5 As for the solution of comparative example 2 in Table 2, the coulombic efficiency of the battery is lower than the normal value (about 95%) due to the residual sulfur impurities.

[0040] All-vanadium liquid flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrode, positive and negative electrodes are using the solution of comparative example 2, using 80mA / cm 2 The charge and discharge cycle is carried out at a current density of , the charge cut-off condition is that the voltage is not higher than 1.5V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0041] Table 1 Electrolyte ion concentration table

[0042]

[0043] Table 2 Battery efficiency comparison table

[0044]

[0045] From the data in the table, it can be found that the battery performance of the electrolyte obtained by using chemical reduction combined with electrolysis and using traditional sulfur as a reducing agent is significantly lower than the battery performance of the electrolyte obtained by using metallic lead as a reducing agent.

Claims

1. A method for preparing an all-vanadium redox flow battery electrolyte, characterized in that: The following steps are involved: Concentrated sulfuric acid is added to a mixture of solid V2O5 powder and metallic lead to form a uniformly dispersed solid solution, which is stirred for reaction. The clear liquid after filtration is used as the negative electrode electrolyte for electrolysis to obtain a vanadium ion sulfuric acid solution at the negative electrode of the electrolytic cell. Among them, metallic lead is used as a chemical reducing agent, and its oxidation product is lead sulfate, which is insoluble in the solution, thereby reducing the risk of impurities mixing in the electrolyte synthesis process.

2. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: The vanadium ion sulfuric acid solution electrolyte is obtained at the negative electrode of the electrolytic cell, wherein the average valence state of the vanadium ions is 3.

5.

3. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The temperature of the mixing and stirring reaction is 70° C.-90° C., and the stirring reaction time is 1 h-4 h.

4. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The weight ratio of the V2O5 powder to metallic lead is (10-20):

1.

5. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The solid-liquid ratio of the mixture of the V2O5 powder and metallic lead to concentrated sulfuric acid is 50g:(100-200)mL.

6. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The positive and negative electrodes of the electrolytic cell are both lead electrodes.

7. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The electrolysis current of the electrolytic cell is 40 mA / cm 2 -160mA / cm 2 .

8. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The positive electrode electrolyte in the electrolytic cell is a 4 mol / L-6 mol / L sulfuric acid solution, and the volumes of the positive and negative electrode electrolytes are the same.

9. The method for preparing an electrolyte for an all-vanadium redox flow battery according to claim 1, characterized in that: The diaphragm of the electrolytic cell is a Nafion diaphragm.

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