Method for preparing vanadium battery electrolyte by short process of alkaline vanadium solution

Abstract

The application relates to the field of vanadium batteries and discloses a method for preparing an electrolyte of a vanadium battery by a short process of an alkaline vanadium solution, which comprises the following steps: adding an adsorbent to the alkaline vanadium solution to remove impurities, so as to obtain vanadium solution after impurities are removed; wherein the adsorbent comprises mercapto chitosan microspheres; mixing and reacting the vanadium solution after impurities are removed and a conversion agent, so that V(OH)4 + in the vanadium solution after impurities are removed is converted into VO 2+ , and vanadium solution after conversion is obtained; wherein the conversion agent comprises ascorbic acid and sulfite; the vanadium solution after conversion is adjusted to be acidic and a stabilizer is added, so as to obtain an electrolyte to be electrolyzed, and the electrolyte to be electrolyzed is electrolyzed, so that an electrolyte containing V 3+ and VO 2+ is obtained. The application can effectively shorten the preparation process of the electrolyte, avoid the interference of impurities and improve the current efficiency.

Description

Technical Field

[0001] This invention relates to the field of vanadium battery technology, and specifically to a short-process method for preparing vanadium battery electrolyte using alkaline vanadium solution. Background Technology

[0002] Vanadium redox flow batteries (VRFBs) have become one of the preferred technologies for large-scale energy storage due to their excellent cycle stability and scalability. Commercial VRFB electrolytes typically use a sulfuric acid system (V... 3+ / V 4+ / V 5+ The pH value needs to be maintained within the range of 0 to 2 to obtain the best electrochemical performance. However, currently more than 90% of vanadium resource extraction processes use alkaline leaching methods (such as sodium roasting-water leaching), and the resulting leachate has a pH > 10 and contains various impurities such as Fe, Al, and Si. Traditional processes require repeated acid-base adjustments to convert it into an acidic electrolyte, resulting in a lengthy process and high costs.

[0003] Currently, there are three main technical challenges in the conversion of alkaline vanadium solutions:

[0004] (1) Impurities are not completely removed: Although the stepwise precipitation method is used, Fe and Al residues still reach 20~50ppm, which will form colloids that block the ion exchange membrane during the subsequent acidification process;

[0005] (2) Large acid and alkali consumption: It is necessary to first neutralize with sulfuric acid to pH=2 to precipitate silicon, then adjust back to pH=7 to remove iron and aluminum, and finally acidify to pH=0. The amount of acid and alkali used is 3 times the theoretical value.

[0006] (3) Low current efficiency: During acidic electrolysis, V is affected by impurities. 4+ / V 5+ The conversion current efficiency is only 82-85%, and the electrodes are easily passivated by silicon-aluminum deposits.

[0007] Recent attempts at improvement have all shown significant shortcomings. Solvent extraction, using P204 extractant, can remove impurities deeply, but the loss of organic phase increases costs by 30%. Biosorption utilizes sulfate-reducing bacteria to remove heavy metals, but the bacteria become inactive under strong acid conditions. Catalytic electrolysis introduces Ce... 3+ / Mn 2+ Catalysts can be used, but metal ions can contaminate the electrolyte and affect battery life.

[0008] Therefore, existing technologies need improvement. Summary of the Invention

[0009] The main objective of this invention is to provide a short-process method for preparing vanadium battery electrolyte using alkaline vanadium solution, in order to at least solve the following problems: existing methods for preparing vanadium battery electrolyte based on alkaline vanadium solution suffer from lengthy processes and incomplete impurity removal.

[0010] According to one aspect of the present invention, a method for preparing vanadium battery electrolyte using alkaline vanadium solution in a short process is provided, comprising: adding an adsorbent to an alkaline vanadium solution to remove impurities, thereby obtaining a purified vanadium solution; wherein the adsorbent comprises thiolated chitosan microspheres; mixing and reacting the purified vanadium solution with a conversion agent to reduce the V(OH)4 content in the purified vanadium solution. + Transform into VO 2+ The converted vanadium solution was obtained; the converting agent included ascorbic acid and sulfite; the converted vanadium solution was adjusted to acidity and a stabilizer was added to obtain the electrolyte, which was then electrolyzed to obtain a solution containing V. 3+ and VO 2+ The electrolyte.

[0011] According to one embodiment of the present invention, the thiolated chitosan microspheres have a particle size of 50-100 μm and a thiol content of 2.5-5 mmol / g.

[0012] According to one embodiment of the present invention, the method further includes preparing thiolated chitosan microspheres, comprising: dissolving chitosan in an acidic solution to obtain a solution; wherein the mass of chitosan is 2-10% of the mass of the acidic solution; adding sodium 2,3-dimercaptopropanesulfonate to the solution and reacting it at 50-90°C for 3-6 hours under an inert atmosphere to obtain a post-reaction solution; wherein the mass of sodium 2,3-dimercaptopropanesulfonate is 2-5% of the mass of the solution; and adding the post-reaction solution dropwise into an alkaline solution or spray drying it to obtain thiolated chitosan microspheres.

[0013] According to one embodiment of the present invention, the alkaline vanadium solution has a pH of 9 to 12 and contains at least one impurity selected from Fe, Al, and Si.

[0014] According to one embodiment of the present invention, adding an adsorbent to an alkaline vanadium solution to remove impurities includes: adding the adsorbent to the alkaline vanadium solution, shaking at 30~60°C for 1~3 hours, and then filtering, wherein the solid-liquid ratio of the adsorbent to the alkaline vanadium solution is 3~8 g / L.

[0015] According to one embodiment of the present invention, the molar ratio of ascorbic acid to sulfite in the conversion agent is (10~25):(2~5).

[0016] According to one embodiment of the present invention, the concentration of ascorbic acid in the conversion agent is 0.1~0.25 mol / L, and the concentration of sulfite is 0.02~0.05 mol / L; the vanadium solution after impurity removal and the conversion agent are mixed and reacted, including: mixing the vanadium solution after impurity removal and the conversion agent at a volume ratio of 1:(0.04~0.08) and reacting at 60~90°C for 20~40 min.

[0017] According to one embodiment of the present invention, the pH of the electrolyte is 1 to 1.5; the concentration of the stabilizer in the electrolyte is 0.02 to 0.1 mol / L; the method further includes adjusting the vanadium concentration of the electrolyte to 1.5 to 2.5 mol / L.

[0018] According to one embodiment of the present invention, the stabilizer comprises one or more of the following: inorganic stabilizers, organic acids, organic acid salts, alcohols, and surfactants.

[0019] According to one embodiment of the present invention, electrolysis includes: at 70~90 mA / cm 2 Electrolysis was carried out at a current density for 4-7 hours.

[0020] In the technical solution of this invention, thiolated chitosan is used as an adsorbent for impurity removal, which can effectively remove impurities such as Fe, Al, and Si from alkaline vanadium solutions; the use of a conversion agent containing ascorbic acid and sulfite can avoid the formation of V2O5 precipitate and directly obtain VO with high electrolytic activity. 2+ Stabilizers are used to improve the stability of the acidic electrolyte, allowing for direct electrolysis to generate V. 3+ / VO 2+ This eliminates the steps of vanadium precipitation, calcination, and dissolution. Therefore, this invention effectively shortens the electrolyte preparation process, avoids impurity interference, and improves current efficiency. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart illustrating a method for preparing vanadium battery electrolyte according to an embodiment of the present invention is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0024] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0025] As mentioned in the background section above, existing methods for preparing vanadium battery electrolytes based on alkaline vanadium solutions are lengthy and cannot achieve direct conversion from alkaline leachate to acidic electrolyte, requiring an intermediate pH transition stage. To address this issue, this application proposes a short-process method for directly preparing high-purity acidic electrolytes from alkaline vanadium solutions. This method employs a three-stage process route: deep alkaline impurity removal → directional conversion of vanadium speciation → high-efficiency acidic electrolysis.

[0026] refer to Figure 1 This invention proposes a short-process method for preparing vanadium battery electrolyte using alkaline vanadium solution, comprising the following steps:

[0027] S1, An adsorbent is added to an alkaline vanadium solution to remove impurities, resulting in a purified vanadium solution; wherein the adsorbent contains thiolated chitosan microspheres;

[0028] S2, the purified vanadium solution is mixed with the conversion agent and reacted to reduce the V(OH)4 in the purified vanadium solution. + Transform into VO 2+ (That is, converting pentavalent vanadium to tetravalent vanadium), to obtain vanadium solution after conversion; the conversion agent includes ascorbic acid and sulfite;

[0029] S3, the converted vanadium solution is adjusted to acidity and an aminopolycarboxylic acid ligand is added to obtain the electrolyte. The electrolyte is then electrolyzed to obtain a solution containing V. 3+ and VO 2+ The electrolyte.

[0030] In some embodiments, the alkaline vanadium solution has a pH of 9-12 and contains at least one impurity selected from Fe, Al, and Si. The alkaline vanadium solution can be a leachate obtained by an alkaline leaching method (such as sodium roasting-water leaching). In some embodiments, the alkaline vanadium solution has a V concentration of 30-40 g / L, an Fe concentration of 1.5-3.0 g / L, an Al concentration of 1.0-2.0 g / L, and a Si concentration of 1.0-1.5 g / L.

[0031] Step S1 corresponds to the alkaline deep impurity removal stage. In this stage, thiolized chitosan, a biosorbent, is used as the adsorbent for impurity removal, effectively adsorbing and removing impurities such as Fe, Al, and Si from the alkaline vanadium solution. The adsorption mechanism is as follows: under alkaline conditions, thiol groups react with Fe... 3+ Al 3+ Stable coordination bonds are formed, with Si as SiO32- The form is electrostatically adsorbed by amino groups. The adsorption capacity of thiolated chitosan under strong alkalinity is 8 times higher than that of traditional resins, and it can be easily regenerated and reused after elution with 0.1 mol / L HCl. In some embodiments, the residual impurities in the vanadium solution obtained after impurity removal in step S1 are: Fe < 0.5 ppm, Al < 0.3 ppm, Si < 2 ppm, indicating a significant impurity removal effect.

[0032] In some embodiments, the thiolated chitosan microspheres have a particle size of 50-100 μm and a thiol content of 2.5-5 mmol / g, thereby ensuring good impurity removal effect. In some embodiments, an adsorbent is added to an alkaline vanadium solution to remove impurities, comprising: adding the adsorbent to the alkaline vanadium solution, shaking at 30-60°C for 1-3 h, and then filtering, wherein the solid-liquid ratio of the adsorbent to the alkaline vanadium solution is 3-8 g / L.

[0033] In some embodiments, the method of the present invention further includes preparing thiolated chitosan microspheres by crosslinking chitosan with sodium 2,3-dimercaptopropanesulfonate (DMPS). The preparation method specifically includes: dissolving chitosan in an acidic solution to obtain a solution; wherein the mass of chitosan is 2-10% of the mass of the acidic solution; adding sodium 2,3-dimercaptopropanesulfonate to the solution and reacting it at 50-90°C for 3-6 hours under an inert atmosphere (e.g., nitrogen) to obtain a post-reaction solution; wherein the mass of sodium 2,3-dimercaptopropanesulfonate is 2-5% of the mass of the solution; and adding the post-reaction solution dropwise into an alkaline solution or spray drying it to obtain thiolated chitosan microspheres. The degree of deacetylation of chitosan can be ≥95%. The acidic solution can be an acetic acid solution with a mass percentage concentration of 1-5% (e.g., 2%), or other dilute acids with a mass percentage concentration of 1-10%. The alkaline solution can be a NaOH solution with a mass percentage concentration of 3-8% (e.g., 5%). In some embodiments, the reacted solution is dropwise into an alkaline solution to form microspheres, which are then filtered, washed with ethanol, and vacuum dried to obtain thiolated chitosan microspheres. In other embodiments, the reacted solution is spray-dried at 130-180°C to obtain thiolated chitosan microspheres. It should be understood that although the present invention proposes the preferred method for preparing thiolated chitosan microspheres as described above, this application is not intended to limit it. Where feasible, other methods in the prior art can also be used to prepare thiolated chitosan microspheres.

[0034] Step S2 corresponds to the directional conversion stage of vanadium speciation. In this stage, the use of a composite system of ascorbic acid and sulfite avoids the formation of V₂O₅ precipitate, directly yielding VO₃ with high electrolytic activity. 2+ To achieve precise control of vanadium morphology and realize V(OH)4 + →VO 2+Highly efficient conversion (conversion rate >99%). The reaction mechanism is as follows: ascorbic acid provides a reducing hydroxyl group, promoting the reduction of V(V) to V(IV), while SO3... 2- Inhibit the polymerization reaction of vanadium and avoid the formation of V2O5 precipitate.

[0035] In some embodiments, the molar ratio of ascorbic acid to sulfite in the conversion agent is (10~25):(2~5). In some embodiments, the conversion agent is a composite solution containing ascorbic acid and sulfite, wherein the concentration of ascorbic acid in the conversion agent is 0.1~0.25 mol / L and the concentration of sulfite is 0.02~0.05 mol / L; the impurity-removed vanadium solution and the conversion agent are mixed and reacted, including: mixing the impurity-removed vanadium solution and the conversion agent at a volume ratio of 1:(0.04~0.08) and reacting at 60~90°C for 20~40 min. In some embodiments, the pH of the impurity-removed vanadium solution is 9.5~11. The sulfite may be one or more of Na2SO3, K2SO3, NaHSO3, and (NH4)2SO3.

[0036] Step S3 corresponds to the acidic high-efficiency electrolysis stage. In this stage, a stabilizer is used to improve the stability of the acidic electrolyte, allowing for direct electrolysis to generate V. 3+ / VO 2+ This method omits the vanadium precipitation-calcination-dissolution steps. In some embodiments, the pH is adjusted by adding an acid (e.g., concentrated sulfuric acid) to the converted vanadium solution, ultimately bringing the pH of the electrolyte to 1-1.5. In some embodiments, the method further includes adjusting the vanadium concentration of the electrolyte to 1.5-2.5 mol / L. In some embodiments, the concentration of the stabilizer in the electrolyte is 0.02-0.1 mol / L. The stabilizer may contain one or more of the following: inorganic stabilizers, organic acids, organic acid salts, alcohols, and surfactants. Specifically, the inorganic stabilizer may contain one or more of the following: phosphoric acid, phosphates, sulfates, and boric acid; the organic acid may contain one or more of the following: oxalic acid, citric acid, and aminopolycarboxylic acid ligands (e.g., EDTA (ethylenediaminetetraacetic acid), HEDTA (N-hydroxyethylethylenediaminetriacetic acid)); the alcohol may contain methanol and / or ethylene glycol; and the surfactant may contain PEG and / or Tween 20. Of course, this invention is not limited thereto, and other suitable stabilizers from the prior art may be used. In some embodiments, electrolysis includes: at 70~90 mA / cm 2 Electrolysis was performed at a current density of 4–7 h. Electrolysis can be carried out using a graphene / carbon felt composite electrode. The final electrolyte contained V... 3+ and VO 2+ The molar ratio is approximately 1:1, for example, 1:(0.95~1.05).

[0037] In summary, this invention relates to a method for preparing high-purity acidic vanadium electrolyte from alkaline vanadium leachate through a short process involving coupled bioadsorption, selective conversion, and electrochemical catalysis. This method employs a two-stage pH control strategy: first, a modified bioadsorbent is used to deeply remove impurities such as iron, aluminum, and silicon; then, through directional conversion of vanadium oxygen groups and a composite electrocatalytic system, efficient vanadium electrolysis is achieved in an acidic medium, with a current efficiency exceeding 95%. This invention solves the problems of repeated acid-base adjustments, lengthy processes, and impurity interference in traditional processes, and is suitable for high-performance vanadium redox flow battery energy storage systems.

[0038] The following description is based on specific embodiments.

[0039] Example 1

[0040] Alkaline deep impurity removal stage:

[0041] Step 1: Adsorbent preparation. Dissolve 5g of chitosan powder (degree of deacetylation ≥95%) in 100mL of 2% acetic acid solution and stir until completely dissolved; add 3.2g of sodium 2,3-dimercaptopropanesulfonate (DMPS) and react at 60℃ for 6h under nitrogen protection; drop the reaction solution into 5% NaOH solution to form microspheres, filter, wash with ethanol, and vacuum dry to obtain thiolated chitosan microspheres (particle size 80±15μm, thiol content 3.2mmol / g).

[0042] Step 2: Impurity Removal Process. Take 1L of alkaline vanadium leaching solution (pH=11.2, V content 35.3g / L, Fe content 2.8g / L, Al content 1.9g / L, Si content 1.4g / L); add the above adsorbent according to the solid-liquid ratio of adsorbent to vanadium leaching solution of 6g / L, and shake at 50℃ for 2h (150rpm). After filtration, the Fe content is 0.4ppm, Al content is 0.2ppm, Si content is 1.6ppm, and vanadium loss rate is <0.5%.

[0043] Vanadium speciation directional conversion stage:

[0044] Step 3: Prepare the conversion agent: 0.1M ascorbic acid + 0.05M Na₂SO₃ (dissolved in deionized water); take 500mL of the purified solution (pH=10.8), add 25mL of conversion agent (volume ratio 1:0.05); react in a 75℃ water bath for 30min, and take a sample for analysis: V(OH)₄ + →VO 2+ The conversion rate was 99.3%, and the solution was blue (VO2+). 2+ (Characteristic color).

[0045] Acidic high-efficiency electrolysis stage

[0046] Step 4: Slowly add concentrated sulfuric acid to the converted solution until pH=1.3; add VOSO4 to adjust the total vanadium concentration to 2.0M, and add HEDTA to make the concentration 0.05M; use a graphene / carbon felt composite electrode (graphene loading 10mg / cm²) and electrolyze for 6 hours at a current density of 80mA / cm²; final electrolyte composition: V 3+ Concentration 1.02M, VO 2+ At a concentration of 0.98 M (molar ratio 1:0.96), the current efficiency was 95.7%.

[0047] Example 2

[0048] Alkaline deep impurity removal stage:

[0049] Step 1: Adsorbent Preparation. Dissolve 6g of medical-grade chitosan (97% degree of deacetylation) in 100mL of 2% acetic acid solution and stir until completely dissolved. Add 2.5g of sodium 2,3-dimercaptopropanesulfonate (DMPS) and react at 65℃ for 4.5h under nitrogen protection. Use a syringe pump (5mL / min) to dropwise add the reaction solution into a 5% NaOH coagulation bath. Collect the microspheres and wash with 50% ethanol. After vacuum drying for 48 hours, obtain microspheres with a particle size of 60±10μm and a thiol content of 3.8mmol / g.

[0050] Step 2: Impurity Removal Process. The vanadium leachate (pH=10.7, V content 32.5 g / L, Fe content 2.5 g / L, Al content 1.8 g / L, Si content 1.2 g / L) was treated by adding adsorbent at a solid-liquid ratio of 6 g / L. The solution was incubated at 45°C with shaking for 2 hours. After filtration, the results were: V content 32.3 g / L (recovery rate 99.4%), Fe content 0.3 ppm, Al content 0.2 ppm, and Si content 1.2 ppm. Adsorbent regeneration efficiency: After elution with 0.1 M HCl, the adsorbent can be reused 6 times.

[0051] Vanadium speciation directional conversion stage

[0052] Step 3: Prepare the conversion agent: 0.15M ascorbic acid and 0.02M Na₂SO₃; take 500mL of the purified solution and add 20mL of conversion agent (volume ratio 1:0.04); react in a 90℃ water bath for 30min, and take a sample for analysis: V(OH)₄ + →VO 2+ Conversion rate 99.7%, solution is blue (VO2+). 2+ (Characteristic color).

[0053] Acidic high-efficiency electrolysis stage

[0054] Step 4: Slowly add concentrated sulfuric acid to the converted solution until pH=1.5; add VOSO4 to adjust the total vanadium concentration to 1.8M, and add HEDTA to make the concentration 0.08M; use a graphene / carbon felt composite electrode (graphene loading 10mg / cm²) and electrolyze for 5h at a current density of 80mA / cm²; final electrolyte composition: V 3+ Concentration 1.01M, VO 2+ Concentration 0.99M (molar ratio 1.02:1), current efficiency 96.5%.

[0055] Example 3

[0056] Alkaline deep impurity removal stage:

[0057] Step 1: Adsorbent preparation. 7g of medical-grade chitosan (97% degree of deacetylation) was dissolved in 100mL of 2% acetic acid solution and stirred until completely dissolved. 3.2g of sodium 2,3-dimercaptopropanesulfonate (DMPS) was added, and the mixture was reacted at 55℃ for 3h under nitrogen protection. The mixture was then spray-dried directly at 160℃ to obtain particles with a diameter of 80±20μm and a thiol content of 3.0mmol / g.

[0058] Step 2: Impurity Removal Process. The vanadium leaching solution (pH=11.2, V content 37.7 g / L, Fe content 1.9 g / L, Al content 1.3 g / L, Si content 1.4 g / L) was treated by adding adsorbent at a solid-liquid ratio of 8 g / L. The solution was then shaken at 35°C for 2 hours. After filtration, the following results were obtained: V recovery rate 99.2%, Fe content 0.4 ppm, Al content 0.3 ppm, Si content 1 ppm; Adsorbent regeneration efficiency: after elution with 0.1 M HCl, it can be reused 6 times.

[0059] Vanadium speciation directional conversion stage

[0060] Step 3: Prepare the conversion agent: 0.2M ascorbic acid and 0.05M Na₂SO₃; take 500mL of the purified solution and add 25mL of conversion agent (volume ratio 1:0.05); react in an 80℃ water bath for 20min, and take a sample for analysis: V(OH)₄ + →VO 2+ The conversion rate was 98.8%, and the solution was blue (VO2+). 2+ (Characteristic color).

[0061] Acidic high-efficiency electrolysis stage

[0062] Step 4: Slowly add concentrated sulfuric acid to the converted solution until pH=1.3; add VOSO4 to adjust the total vanadium concentration to 2.2M, and add HEDTA to make the concentration 0.01M; use a graphene / carbon felt composite electrode (graphene loading 10mg / cm²) and electrolyze for 5h at a current density of 75mA / cm²; final electrolyte composition: V 3+ Concentration 1M, VO 2+ Concentration 1.01M (molar ratio 1:1.01), current efficiency 95.2%.

[0063] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for preparing vanadium battery electrolyte using alkaline vanadium solution in a short-process manner, characterized in that, include: An adsorbent is added to an alkaline vanadium solution to remove impurities, resulting in a purified vanadium solution. The adsorbent described herein comprises thiolated chitosan microspheres; The purified vanadium solution and the conversion agent are mixed and reacted to remove V(OH)4 from the purified vanadium solution. + Transform into VO 2+ The converted vanadium solution was obtained; The converting agent comprises ascorbic acid and sulfite; The converted vanadium solution was adjusted to acidity and a stabilizer was added to obtain the electrolyte. The electrolyte was then electrolyzed to obtain a solution containing V. 3+ and VO 2+ Electrolyte; The method for preparing the thiolated chitosan microspheres includes: Chitosan is dissolved in an acidic solution to obtain a solution; wherein the mass of chitosan is 2-10% of the mass of the acidic solution. Sodium 2,3-dimercaptopropanesulfonate was added to the solution, and the mixture was reacted at 50-90°C for 3-6 hours under an inert atmosphere to obtain the post-reaction solution; wherein the mass of sodium 2,3-dimercaptopropanesulfonate was 2-5% of the mass of the solution. The reaction solution is added dropwise to an alkaline solution or spray-dried to obtain the thiolized chitosan microspheres.

2. The method according to claim 1, characterized in that, The thiolized chitosan microspheres have a particle size of 50-100 μm and a thiol content of 2.5-5 mmol / g.

3. The method according to claim 1, characterized in that, The alkaline vanadium solution has a pH of 9-12 and contains at least one impurity selected from Fe, Al, and Si.

4. The method according to claim 1, characterized in that, Adding an adsorbent to an alkaline vanadium solution to remove impurities includes: adding the adsorbent to the alkaline vanadium solution, shaking at 30-60°C for 1-3 hours, and then filtering, wherein the solid-liquid ratio of the adsorbent to the alkaline vanadium solution is 3-8 g / L.

5. The method according to claim 1, characterized in that, In the conversion agent, the molar ratio of ascorbic acid to sulfite is (10~25):(2~5).

6. The method according to claim 1, characterized in that, In the conversion agent, the concentration of ascorbic acid is 0.1~0.25 mol / L, and the concentration of sulfite is 0.02~0.05 mol / L; the vanadium solution after impurity removal and the conversion agent are mixed and reacted, including: mixing the vanadium solution after impurity removal and the conversion agent at a volume ratio of 1:(0.04~0.08) and reacting at 60~90℃ for 20~40 min.

7. The method according to claim 1, characterized in that, The pH of the electrolyte is 1 to 1.5; the concentration of the stabilizer in the electrolyte is 0.02 to 0.1 mol / L; the method further includes adjusting the vanadium concentration of the electrolyte to 1.5 to 2.5 mol / L.

8. The method according to claim 1, characterized in that, The stabilizer comprises one or more of the following: inorganic stabilizers, organic acids, organic acid salts, alcohols, and surfactants.

9. The method according to claim 1, characterized in that, Electrolysis includes: at 70~90 mA / cm 2 Electrolysis was carried out at a current density for 4-7 hours.

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