All-vanadium redox flow battery electrolyte and preparation method thereof

Abstract

The application discloses a kind of all-vanadium redox flow battery electrolyte and preparation method thereof, belong to all-vanadium redox flow battery electrolyte preparation field.Preparation raw materials of all-vanadium redox flow battery electrolyte include: vanadium pentoxide, thiourea, sodium dodecyl sulfonate, anhydrous ethanol, sulfur dioxide, sodium chloride, boric acid, sulfuric acid, phosphoric acid tributyl and perfluorobutyl sulfonic acid.Preparation steps of all-vanadium redox flow battery electrolyte include: preliminary reduction liquid preparation, preliminary reduction, secondary reduction and all-vanadium redox flow battery electrolyte preparation.The prepared all-vanadium redox flow battery electrolyte has the advantages of good stability, strong energy storage capacity, wide temperature range, etc.Solves the problem of poor stability, narrow temperature range, the need to equip complex, expensive, energy-consuming electrolyte temperature control device of high-concentration all-vanadium redox flow battery electrolyte.

Description

Technical Field

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

[0002] Vanadium redox flow batteries are currently the world's largest, most technologically advanced, and closest to industrialization high-efficiency rechargeable fuel cells. They possess advantages such as high power output, low cost, long lifespan, and zero pollution, and show promising application prospects in photovoltaic power generation, wind power generation, communication base stations, transportation and municipal infrastructure, and military energy storage. Vanadium redox flow batteries achieve the interconversion of chemical energy and electrical energy through electrochemical reactions circulated from bottom to top through electrodes by vanadium electrolytes in different valence states.

[0003] The positive and negative electrolytes of vanadium redox flow batteries are typically sulfuric acid solutions of VOSO4 and V2(SO4)3, respectively. As the storage site for the battery's electrical energy, the concentration and volume of the vanadium redox flow battery electrolyte determine the battery's capacity, while its stability and temperature adaptability determine the battery's lifespan and application range. Currently, the main methods for preparing vanadium redox flow battery electrolytes are physical dissolution, chemical reduction, and electrolysis. The physical dissolution method involves directly dissolving high-purity VOSO4 solid in sulfuric acid.

[0004] The resulting electrolyte has a low concentration, making large-scale production difficult. Electrolysis is a suitable method for large-scale production, but producing vanadium electrolyte requires high-purity V₂O₅ as a raw material, and the reaction rate is slow and the equipment requirements are high, making it difficult to implement. The chemical reduction method uses a reducing agent to reduce high-valent vanadium oxides or vanadates to prepare the electrolyte. Common reducing agents include oxalic acid, elemental sulfur, sulfurous acid, organic carboxylic acids, or alcohols, which reduce V₂O₅ to tetravalent or trivalent vanadium compounds at high temperatures. This method produces high-concentration vanadium redox flow battery electrolytes with strong energy storage capacity, but poor stability. High-concentration vanadium redox flow battery electrolytes easily hydrolyze and precipitate V₂O₅ at temperatures above 40°C, and easily saturate and precipitate V₂(SO₄)₃ crystals at temperatures below 10°C. This results in a narrow applicable temperature range and requires complex, expensive, and energy-intensive electrolyte temperature control devices. Therefore, there is an urgent need for a method to prepare a high-concentration all-vanadium redox flow battery electrolyte with high stability and a wide temperature adaptability range to overcome the problems of the narrow temperature application range of all-vanadium redox flow battery electrolyte and the need for complex, expensive, and energy-intensive electrolyte temperature control devices. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a vanadium redox flow battery electrolyte and its preparation method, so as to solve the problems of poor stability, narrow temperature range, and the need for complex, expensive and energy-consuming electrolyte temperature control devices in high-concentration vanadium redox flow battery electrolytes.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A vanadium redox flow battery electrolyte is provided, wherein the raw materials for preparing the vanadium redox flow battery electrolyte include: vanadium pentoxide, thiourea, sodium dodecyl sulfonate, anhydrous ethanol, thiourea dioxide, sodium chloride, boric acid, sulfuric acid, tributyl phosphate, and perfluorobutyl sulfonic acid.

[0008] This invention also provides a method for preparing an electrolyte for an all-vanadium redox flow battery, as detailed below:

[0009] (1) Preparation of preliminary reducing solution: Thiourea and sodium dodecyl sulfonate were dissolved in anhydrous ethanol, and deionized water was added and stirred for 30-40 min to obtain the preliminary reducing solution;

[0010] (2) Preliminary reduction: Vanadium pentoxide was added to the preliminary reduction solution and ultrasonically dispersed for 10-20 min at 60-80 kHz, followed by heating and stirring to obtain a reduced suspension;

[0011] (3) Secondary reduction: Tributyl phosphate and perfluorobutyl sulfonic acid are added to the reduction suspension and mixed evenly. Thiourea dioxide is added and fully dissolved. The mixture is then poured into a reaction vessel and heated to obtain a secondary reduction slurry.

[0012] (4) Preparation of vanadium redox flow battery electrolyte: Add sulfuric acid, boric acid and sodium chloride to the secondary reduction slurry and stir until the precipitate completely disappears to obtain vanadium redox flow battery electrolyte.

[0013] Furthermore, in step (2), the heating and stirring temperature is 80-120℃ and the time is 10-20min.

[0014] Furthermore, in step (3), the temperature of the heating reaction is 140-180℃ and the time is 10-15min.

[0015] Furthermore, in step (1), the mass ratio of thiourea, sodium dodecyl sulfonate, anhydrous ethanol and deionized water is (1-2):(0.2-0.4):(1-2):(2-4).

[0016] Furthermore, in step (2), the mass ratio of vanadium pentoxide to the initial reducing solution is (1-2):(2-3).

[0017] Furthermore, in step (3), the mass ratio of tributyl phosphate, perfluorobutyl sulfonic acid, thiourea dioxide and the reducing suspension is (0.02-0.04):(0.02-0.04):(0.01-0.03):(1-3).

[0018] Furthermore, in step (4), the mass ratio of the secondary reduction slurry, sodium chloride, sulfuric acid, and boric acid is (1-2):(0.2-0.4):(2.0-3.0):(0.1-0.3).

[0019] This invention involves dissolving thiourea and dodecyl sulfonic acid in anhydrous ethanol, then adding water to prepare a preliminary reducing solution. Vanadium pentoxide is added to this preliminary reducing solution, and under the reduction of thiourea and the micellization of dodecyl sulfonic acid, the vanadium pentoxide is reduced to obtain a reduced suspension. The reduced suspension contains a large amount of tetravalent vanadium ions, with VS4 as the suspended matter. Adding tributyl phosphate and perfluorobutyl sulfonic acid to the reduced suspension and mixing it evenly with thiourea dioxide effectively avoids the generation of elemental sulfur during the redox process, thus preventing a decrease in the reduction effect. Under high temperature and high pressure conditions, a secondary reduced slurry is obtained. In the secondary reduced slurry, a portion of the suspended VS4 is converted into V2S3 particles, forming a VS4 and V2S3 coexisting system. Subsequently, sulfuric acid, boric acid, and sodium chloride are added, successfully converting VS4 to VOSO4 and V2S3 to V2(SO4)3, and S... 2- With SO4 2+ They also coexist in this system. The high concentration and good stability of VOSO4 and V2(SO4)3 in this system result in strong energy storage capacity of the electrolyte in the vanadium redox flow battery.

[0020] When VO2 in the system + When V2O5 precipitates out from the hydrolysate under high temperature conditions, S 2- It has a reducing effect in the system, reducing VO2 + Restore to VO 2+ Meanwhile, S 2- Hydrolysis and VO2 will also occur. + Competition arises, thus slowing down the precipitation of V2O5 under high-temperature conditions. Furthermore, the electrolyte contains dodecyl sulfonic acid, which can also effectively improve the precipitation of VO2. + The thermal stability of the system was improved, delaying the precipitation of V₂O₅ at high temperatures. At low temperatures, the S content in the system... 2- Anhydrous ethanol effectively increases the solubility of V₂(SO₄)₃, making it less likely for V₂(SO₄)₃ crystals to precipitate. In S 2- The combined effect of dodecyl sulfonic acid and anhydrous ethanol broadens the applicable temperature range of the electrolyte in vanadium redox flow batteries.

[0021] Beneficial effects:

[0022] 1. The vanadium redox flow battery electrolyte prepared by this invention has the advantages of good stability, strong energy storage capacity, and wide temperature range.

[0023] 2. Vanadium pentoxide was successfully and fully reduced by thiourea and thiourea dioxide under heating, stirring and high-temperature reaction conditions, respectively. The precipitation of V2O5 under high temperature conditions was delayed by anhydrous ethanol and sodium dodecyl sulfonate, and the solubility of V2(SO4)3 was increased, making it difficult for V2(SO4)3 crystals to precipitate.

[0024] 3. The electrolyte of the vanadium redox flow battery will not precipitate under temperature conditions of -10℃ to 60℃. At the same time, the energy efficiency of the electrolyte of the vanadium redox flow battery can reach 98.6%, the number of cycles when the discharge capacity drops to 70% of the initial discharge capacity can reach 352, and the conductivity is 681.2mS / cm. Detailed Implementation

[0025] The present invention will be described in detail below with reference to specific embodiments:

[0026] Example 1: Preparation of electrolyte for vanadium redox flow battery

[0027] (1) Preparation of preliminary reducing solution: Weigh 0.15 kg of thiourea and 0.03 kg of sodium dodecyl sulfonate respectively, dissolve them in 0.15 kg of anhydrous ethanol, add 0.3 kg of deionized water and stir for 35 min to obtain the preliminary reducing solution;

[0028] (2) Preliminary reduction: Weigh 0.15 kg of vanadium pentoxide and add it to 0.25 kg of preliminary reduction solution. After ultrasonic dispersion at 70 kHz for 15 min, heat to 100 ℃ and stir for 15 min to obtain a reduced suspension.

[0029] (3) Secondary reduction: Add 0.003 kg of tributyl phosphate and 0.003 kg of perfluorobutyl sulfonic acid to 0.2 kg of reduction suspension and mix evenly. Then add 0.002 kg of thiourea dioxide and dissolve it completely. Pour it into a reaction vessel and heat it to 160℃ for 12 min to obtain secondary reduction slurry.

[0030] (4) Preparation of vanadium redox flow battery electrolyte: Weigh 0.15 kg of secondary reduction slurry, add 0.25 kg of sulfuric acid, 0.03 kg of boric acid and 0.03 kg of sodium chloride, and stir until the precipitate completely disappears to obtain vanadium redox flow battery electrolyte.

[0031] Example 2: Preparation of electrolyte for vanadium redox flow battery

[0032] (1) Preparation of preliminary reducing solution: Weigh 0.2 kg of thiourea and 0.02 kg of sodium dodecyl sulfonate respectively, dissolve them in 0.1 kg of anhydrous ethanol, add 0.2 kg of deionized water and stir for 30 min to obtain the preliminary reducing solution;

[0033] (2) Preliminary reduction: Weigh 0.1 kg of vanadium pentoxide and add it to 0.3 kg of preliminary reduction solution. Disperse the solution by ultrasonication at 60 kHz for 20 min and stir for 10 min at 120 ℃ to obtain a reduced suspension.

[0034] (3) Secondary reduction: Add 0.002 kg of tributyl phosphate and 0.002 kg of perfluorobutyl sulfonic acid to 0.1 kg of reduction suspension and mix evenly. Then add 0.001 kg of thiourea dioxide and dissolve it completely. Pour it into a reaction vessel and heat it to 140°C. React for 15 min to obtain secondary reduction slurry.

[0035] (4) Preparation of vanadium redox flow battery electrolyte: Weigh 0.1 kg of secondary reduction slurry, add 0.2 kg of sulfuric acid, 0.01 kg of boric acid and 0.02 kg of sodium chloride, and stir until the precipitate completely disappears to obtain vanadium redox flow battery electrolyte.

[0036] Example 3: Preparation of electrolyte for all-vanadium redox flow battery

[0037] (1) Preparation of preliminary reducing solution: Weigh 0.1 kg of thiourea and 0.04 kg of sodium dodecyl sulfonate respectively, dissolve them in 0.2 kg of anhydrous ethanol, add 0.4 kg of deionized water and stir for 40 min to obtain the preliminary reducing solution;

[0038] (2) Preliminary reduction: Weigh 0.2 kg of vanadium pentoxide and add it to 0.2 kg of preliminary reduction solution. Disperse the solution by ultrasonication at 80 kHz for 10 min and stir for 20 min at 80 ℃ to obtain a reduced suspension.

[0039] (3) Secondary reduction: Add 0.004 kg of tributyl phosphate and 0.004 kg of perfluorobutyl sulfonic acid to 0.3 kg of reduction suspension and mix evenly. Then add 0.003 kg of thiourea dioxide and dissolve it completely. Pour it into a reaction vessel and heat it to 180°C. React for 10 min to obtain secondary reduction slurry.

[0040] (4) Preparation of vanadium redox flow battery electrolyte: Weigh 0.2 kg of secondary reduction slurry, add 0.3 kg of sulfuric acid, 0.03 kg of boric acid and 0.04 kg of sodium chloride, and stir until the precipitate completely disappears to obtain vanadium redox flow battery electrolyte.

[0041] Comparative Example 1: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0042] This comparative example is compared with Example 1, the only difference being that in step (1) of Comparative Example 1, thiourea is replaced with elemental sulfur, and the other steps are the same as in Example 1. Step (1) is as follows:

[0043] (1) Preparation of preliminary reducing solution: Weigh 0.15 kg of elemental sulfur and 0.03 kg of sodium dodecyl sulfonate respectively, dissolve them in 0.15 kg of anhydrous ethanol, add 0.3 kg of deionized water and stir for 35 min to obtain the preliminary reducing solution;

[0044] Comparative Example 2: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0045] This comparative example is compared with Example 1. The only difference is that sodium dodecyl sulfonate is not added in step (1) of Comparative Example 2. Instead, sodium dodecyl sulfonate is replaced with thiourea. All other steps are the same as in Example 1. Step (1) is as follows:

[0046] (1) Preparation of preliminary reducing solution: Weigh 0.18 kg of thiourea and dissolve it in 0.15 kg of anhydrous ethanol. Add 0.3 kg of deionized water and stir for 35 min to obtain the preliminary reducing solution.

[0047] Comparative Example 3: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0048] This comparative example is compared with Example 1. The only difference is that in step (1) of Comparative Example 3, anhydrous ethanol is not added, but deionized water is used instead of anhydrous ethanol. All other steps are the same as in Example 1. Step (1) is as follows:

[0049] (1) Preparation of preliminary reducing solution: Weigh 0.15 kg of thiourea and 0.03 kg of sodium dodecyl sulfonate, mix them evenly, add 0.45 kg of deionized water and stir for 35 min to obtain the preliminary reducing solution.

[0050] Comparative Example 4: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0051] This comparative example is compared with Example 1. The only difference is that in step (3) of Comparative Example 3, thiourea dioxide is replaced with elemental sulfur. All other steps are the same as in Example 1. Step (3) is as follows:

[0052] (3) Secondary reduction: Add 0.003 kg of tributyl phosphate and 0.003 kg of perfluorobutyl sulfonic acid to 0.2 kg of reduction suspension and mix evenly. Then add 0.002 kg of elemental sulfur and dissolve it completely. Pour it into a reaction vessel and heat it to 160℃ for 12 min to obtain secondary reduction slurry.

[0053] Comparative Example 5: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0054] This comparative example is compared with Example 1. The only difference is that in step (2) of Comparative Example 5, heating is not performed, but stirring is carried out at room temperature. All other steps are the same as in Example 1. Step (2) is as follows:

[0055] (2) Preliminary reduction: Weigh 0.15 kg of vanadium pentoxide and add it to 0.25 kg of preliminary reduction solution. Disperse the solution by ultrasonication at 70 kHz for 15 min and stir at room temperature for 15 min to obtain a reduced suspension.

[0056] Comparative Example 6: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0057] This comparative example is compared with Example 1. The only difference is that in step (3) of Comparative Example 6, the reaction is not heated, but stirred at room temperature. The other steps are the same as in Example 1. Step (3) is as follows:

[0058] (3) Secondary reduction: Add 0.003 kg of tributyl phosphate and 0.003 kg of perfluorobutyl sulfonic acid to 0.2 kg of reduction suspension and mix evenly. Then add 0.002 kg of thiourea dioxide and dissolve it completely. Stir at room temperature for 12 min to obtain secondary reduction slurry.

[0059] Comparative Example 7: Preparation of Electrolyte for Vanadium Redox Flow Battery

[0060] This comparative example demonstrates the preparation of vanadium redox flow battery electrolytes using the most commonly used chemical reduction method in current research.

[0061] Weigh 0.5 kg of vanadium pentoxide into a beaker, then add 1.0 kg of concentrated sulfuric acid and mix. Add 2.0 kg of deionized water, place the beaker in a constant temperature water bath, set the temperature to 80°C, and slowly add 3.5 kg of oxalic acid while stirring. After the addition is complete, continue stirring until the solution becomes a homogeneous blue solution to obtain the vanadium redox flow battery electrolyte.

[0062] Experiment 1: Thermal stability test of electrolyte in vanadium redox flow battery

[0063] The vanadium redox flow battery electrolytes prepared in Example 1, Comparative Examples 1-6 and Comparative Example 7 were placed in constant temperature ovens at -30℃, -10℃, 60℃ and 80℃ for 3 days, respectively. After filtration, the precipitate was collected, air-dried, and weighed. The supernatant was also collected, and the concentration of vanadium ions in the supernatant was determined by precipitation method. The results of three repeated experiments are shown in Table 1.

[0064] Table 1

[0065]

[0066] Experiment 2: Performance Testing of All-Vanadium Redox Flow Battery Electrolyte

[0067] The vanadium redox flow battery electrolytes prepared in Example 1 and Comparative Example 7 were tested for various parameters, and the test results are shown in Table 2 below:

[0068] Table 2

[0069]

[0070]

[0071] Results analysis:

[0072] Comparing the data from Example 1 and Comparative Example 7 in Table 1, it can be seen that the vanadium redox flow battery electrolyte prepared in Example 1 of this invention has better stability. No precipitation occurred at -10℃ and 60℃, with vanadium ion concentrations in the supernatant of 1.58 mol / L and 1.62 mol / L, respectively. At -30℃ and 80℃, only 80.1 g and 37.6 g of precipitate were formed, with vanadium ion concentrations in the supernatant of 1.39 mol / L and 1.51 mol / L, respectively. The data from Example 1 and Comparative Example 7 in Table 2 show that the energy efficiency of the vanadium redox flow battery electrolyte prepared in Example 1 is 98.6%, an increase of 4.5% compared to Comparative Example 7; the number of cycles to reduce the discharge capacity to 70% of the initial value reaches 352, an increase of 113 cycles compared to Comparative Example 7; and the conductivity is 681.2 mS / cm, an increase of 86.7 mS / cm compared to Comparative Example 7.

[0073] Comparing Example 1 and Comparative Examples 1-4 in Table 1, it can be seen that, compared with Example 1, Comparative Examples 1-4 do not add thiourea in step (1), do not add sodium dodecyl sulfonate in step (1), do not add anhydrous ethanol in step (1), and do not add thiourea dioxide in step (3). The stability of the vanadium redox flow battery electrolytes prepared in all these cases decreased, and the concentration of vanadium ions in the supernatant also decreased significantly. This indicates that the initial reduction solution preparation requires thiourea, sodium dodecyl sulfonate, and anhydrous ethanol. The absence of any one of these will affect the initial reduction effect in step (2), thereby reducing the stability of the prepared vanadium redox flow battery electrolyte and decreasing the concentration of vanadium ions in the electrolyte. Furthermore, without sodium dodecyl sulfonate and anhydrous ethanol, the electrolyte system... + The thermal stability of V2O5 decreases, causing it to precipitate rapidly at high temperatures. At the same time, the solubility of V2(SO4)3 decreases at low temperatures, leading to the rapid crystallization and precipitation of V2(SO4)3. Thiourea dioxide is not added in step (3) because it affects the secondary reduction effect, resulting in a decrease in the stability of the vanadium redox flow battery electrolyte and a decrease in the concentration of vanadium ions in the electrolyte.

[0074] Comparing Example 1 and Comparative Examples 5-6 in Table 1, it can be seen that, compared with Example 1, Comparative Examples 5-6 do not involve heating and stirring in step (2) and do not involve a temperature increase reaction in step (3). This affects the effectiveness of the initial reduction in step (2) and the secondary reduction in step (3), resulting in a decrease in the stability of the vanadium redox flow battery electrolyte and a decrease in the concentration of vanadium ions in the electrolyte. This indicates that there is a synergistic effect between steps (2) and (3). It is necessary to fully reduce vanadium ions through a stepwise reduction method to obtain a vanadium redox flow battery electrolyte with high stability and a wide temperature range.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A vanadium redox flow battery electrolyte, characterized in that, The raw materials for preparing the electrolyte of the vanadium redox flow battery include: vanadium pentoxide, thiourea, sodium dodecyl sulfonate, anhydrous ethanol, thiourea dioxide, sodium chloride, boric acid, sulfuric acid, tributyl phosphate, and perfluorobutyl sulfonic acid. The preparation method of the all-vanadium redox flow battery electrolyte is as follows: (1) Preparation of preliminary reducing solution: Thiourea and sodium dodecyl sulfonate were dissolved in anhydrous ethanol, and deionized water was added and stirred for 30-40 min to obtain the preliminary reducing solution; (2) Preliminary reduction: Vanadium pentoxide is added to the preliminary reduction solution and ultrasonically dispersed, then heated and stirred to obtain a reduced suspension; (3) Secondary reduction: Tributyl phosphate and perfluorobutyl sulfonic acid are added to the reduction suspension and mixed evenly. Thiourea dioxide is added and fully dissolved. The mixture is poured into a reaction vessel and heated to obtain a secondary reduction slurry. (4) Preparation of vanadium redox flow battery electrolyte: Add sulfuric acid, boric acid and sodium chloride to the secondary reduction slurry and stir until the precipitate completely disappears to obtain vanadium redox flow battery electrolyte.

2. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The heating and stirring temperature in step (2) is 80-120℃, and the time is 10-20min.

3. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 2, characterized in that, The temperature of the heating reaction in step (3) is 140-180℃ and the time is 10-15min.

4. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 3, characterized in that, In step (1), the mass ratio of thiourea, sodium dodecyl sulfonate, anhydrous ethanol and deionized water is (1-2):(0.2-0.4):(1-2):(2-4).

5. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 4, characterized in that, In step (2), the mass ratio of vanadium pentoxide to the initial reducing solution is (1-2):(2-3).

6. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 5, characterized in that, In step (3), the mass ratio of tributyl phosphate, perfluorobutyl sulfonic acid, thiourea dioxide and the reducing suspension is (0.02-0.04): (0.02-0.04): (0.01-0.03): (1-3).

7. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 6, characterized in that, In step (4), the mass ratio of the secondary reduction slurry, sodium chloride, sulfuric acid and boric acid is (1-2):(0.2-0.4):(2.0-3.0):(0.1-0.3).

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