A method for recycling electrolyte of failed all-vanadium redox flow battery

Abstract

The application provides a recycling method of failed electrolyte of all-vanadium redox flow battery, which comprises the following steps: taking auxiliary electrolyte as an anode liquid and taking failed positive electrode electrolyte as a cathode liquid to electrolyze to obtain VOSO4 solution, evaporate and crystallize, and filter to obtain VOSO4 crystal and VOSO4 mother liquor; taking auxiliary electrolyte as an anode liquid and taking failed negative electrode electrolyte as a cathode liquid to electrolyze to obtain V2(SO4)3 solution, evaporate and crystallize, and filter to obtain V2(SO4)3 crystal and V2(SO4)3 mother liquor; and the V2(SO4)3 mother liquor is subjected to vanadium recovery, sulfuric acid recovery and waste liquid recovery respectively. The application combines electrolysis method and evaporation crystallization method, in-situ prepares VOSO4 crystal and V2(SO4)3 crystal, realizes efficient direct recovery of failed electrolyte of all-vanadium redox flow battery, and the prepared crystal has large particle size and high purity. The application realizes the purposes of green and environmental protection recycling and cost reduction and benefit increase of failed electrolyte of all-vanadium redox flow battery.

Description

Technical Field

[0001] This invention relates to electrolyte recovery technology, and more particularly to a method for recycling electrolyte from a failed vanadium redox flow battery. Background Technology

[0002] The global energy structure is undergoing revolutionary changes, and my country's energy structure adjustment is also deepening. After decades of research and exploration, flow battery technology has been continuously developed and improved, especially vanadium redox flow battery systems, iron-chromium flow battery systems, and zinc-bromine flow battery systems. Among all the flow battery technologies that have been researched and developed, the vanadium redox flow battery system is the most mature, with the highest degree of commercial application and industrialization. Its safety, long lifespan, and environmental friendliness have been practically verified both domestically and internationally. However, due to the limited crustal content of vanadium resources and the complexity of current vanadium extraction processes, the research and development of technologies for the low-cost, high-efficiency recycling and reuse of flow battery electrolytes has become a key focus for universities, research institutes, and enterprises. Currently, the main methods for treating spent vanadium electrolytes include:

[0003] CN 117142519 B discloses a method, apparatus, and application for recovering vanadium hydroxide from waste vanadium electrolyte. The method includes the following steps: performing bipolar membrane electrodialysis on the waste low-valent vanadium electrolyte to obtain low-valent vanadium hydroxide and / or vanadium hydroxide; oxidizing the low-valent vanadium hydroxide to obtain vanadium hydroxide; wherein, the low-valent vanadium is V 2+ V 3 + V 4+ The method can effectively recover vanadium ions from spent electrolytes, but the valence ratio of vanadium in the obtained product is uncertain, and the low-valence instability of low-valence vanadium can easily lead to product deterioration.

[0004] CN 116130692 A discloses a method for recycling waste vanadium battery electrolyte, belonging to the field of vanadium redox flow battery technology. Specifically targeting mixed-acid vanadium electrolyte systems, this method involves adding calculated amounts of vanadium sulfate, vanadium oxysulfate, and the corresponding acid to recover the entire system's electrolyte in batches, solving the problem of distinguishing between positive and negative electrodes in existing waste vanadium battery electrolyte treatments. This method effectively addresses the cumbersome recycling process of mixed-acid vanadium electrolyte systems and avoids ion contamination caused by the introduction of other ions. However, the raw materials added to the waste electrolyte cannot dissolve quickly, and insoluble crystals easily lead to electrolyte crystallization and precipitation, impairing electrochemical performance.

[0005] CN 110994061 B discloses a method for recovering vanadium electrolyte. The method involves adjusting the average valence state of vanadium in the electrolyte to not less than 4.9 by positive electrode charging or adding an oxidant. The electrolyte is then diluted with water, and an alkaline substance is added to adjust the pH. After filtration and washing, red vanadium is obtained. This red vanadium is then dissolved by heating with an alkaline substance, followed by the addition of a precipitant, stirring, and filtration to obtain high-purity ammonium metavanadate. While this method yields high-purity ammonium metavanadate, the recovery process involves the addition of large amounts of alkaline substances and ammonium salts, generating significant amounts of ammonia nitrogen wastewater, resulting in high costs for auxiliary materials and wastewater treatment.

[0006] The invention, published under CN 201210514078 and titled "A Method for Preparing Vanadium Oxide Sulfate from Expired Vanadium Battery Electrolyte," discloses a method for preparing vanadium oxysulfate using electrolytes of varying vanadium concentrations under nitrogen protection. The positive electrode is charged to bring the vanadium valence state to pentavalent, the pH of the solution is adjusted to 47, and the solution is heated to 90°C and held at this temperature. A precipitant is added, and the mixture is stirred for 1 hour. Heating is stopped, and stirring continues for another 2 hours. After standing for 24 hours, a precipitate is obtained. A reducing agent (ethanol, acetic acid, acetaldehyde) is added for reduction, and the mixture is allowed to stand for another 24 hours. The precipitate is then centrifuged at 5000 rpm for 20 minutes to obtain vanadium oxysulfate crystals, with a recovery rate >90%. While this method achieves a high recovery rate of the vanadium electrolyte, the process is complex, lengthy, and costly, making it unsuitable for large-scale production.

[0007] In summary, current domestic research on electrolyte recycling technologies for flow batteries generally suffers from problems such as complex processes, high costs, low recovery rates, the introduction of new impurities during recycling, high packaging and transportation costs, and inability to meet the requirements of large-scale production. Therefore, developing a vanadium electrolyte recycling technology that is more widely applicable, avoids long-distance transportation, has a simple process, produces high-purity products, and can be directly reused is of significant practical importance. Summary of the Invention

[0008] The purpose of this invention is to address the problems of existing electrolyte recycling methods, such as complex processes, high costs, low recovery rates, introduction of new impurities during recycling, high packaging and transportation costs, and inability to meet the requirements of large-scale production. This invention proposes a method for recycling and utilizing spent vanadium redox flow battery electrolytes. This method uses the spent vanadium redox flow battery electrolyte as the vanadium source, eliminating the need for high-temperature calcination to prepare vanadium oxides. VOSO4 and V2(SO4)3 crystals can be prepared in situ through electrolysis and evaporation crystallization, achieving efficient and direct recycling of spent vanadium redox flow battery electrolytes. The VOSO4 and V2(SO4)3 crystals prepared by this invention have large particle size, high product purity, and low impurity content, saving raw material and equipment costs. It also solves the transportation radius problem of spent vanadium redox flow battery electrolytes, achieving the goals of green and environmentally friendly recycling and cost reduction and efficiency improvement.

[0009] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a method for recycling and utilizing electrolyte from a failed vanadium redox flow battery, comprising the following steps:

[0011] Step 1 uses auxiliary electrolyte (A1) as anolyte and failed positive electrode electrolyte (A2) as catholyte. The valence state of vanadium ions in the catholyte is reduced to 4.0±0.1 through electrolysis to obtain VOSO4 solution (A4).

[0012] Step 2: Evaporate the VOSO4 solution (A4) to crystallize, and filter to obtain VOSO4 crystals and VOSO4 mother liquor;

[0013] Step 3: Using the auxiliary electrolyte (A1) as the anolyte and the failed negative electrode electrolyte (B1) as the catholyte, the valence state of vanadium ions in the catholyte is electrolyzed to 3.0±0.1 to obtain V2(SO4)3 solution (B2);

[0014] Step 4: Evaporate and crystallize the V2(SO4)3 solution (B2), and filter to obtain V2(SO4)3 crystals and V2(SO4)3 mother liquor;

[0015] Step 5 involves recovering vanadium, sulfuric acid, and waste liquid from the V2(SO4)3 mother liquor.

[0016] The auxiliary electrolyte (A1) mentioned in steps 1 and 3 is a vanadium-containing sulfuric acid solution, such as a sulfuric acid solution containing VOSO4.

[0017] Furthermore, in the auxiliary electrolyte (A1) described in steps 1 and 3, the vanadium ion concentration is 1.5 mol / L to 1.8 mol / L, the vanadium ion valence state is 4.0 ± 0.1, and the sulfate ion concentration is 4.0 mol / L to 5.0 mol / L.

[0018] Further, a reducing agent is added to the auxiliary electrolyte after electrolysis in steps 1 and 3 to reduce the valence state of vanadium ions in the auxiliary electrolyte to 3.9 to 4.1 (i.e., restore it to the state before electrolysis), and an auxiliary electrolyte (Al) is prepared and sent back to steps 1 and / or 3 for recycling.

[0019] Furthermore, the reducing agent is one or more of citric acid, oxalic acid, formic acid, acetic acid, sulfite, and hydrogen peroxide.

[0020] Furthermore, the vanadium ion concentration in the failed positive electrode electrolyte (A2) described in step 1 is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence state is 4.3 to 4.8, and the sulfate ion concentration is 4.0 mol / L to 5.0 mol / L.

[0021] Furthermore, in the failed negative electrode electrolyte (B1) described in step 3, the vanadium ion concentration is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence state is 3.0 to 4.0, and the sulfate ion concentration is 4.0 mol / L to 5.0 mol / L.

[0022] Furthermore, the electrolysis parameters for steps 1 and 3 are: current density of 80 mA / cm². 2 ~120mA / cm 2 The voltage is greater than 0V and less than 62V.

[0023] Furthermore, the evaporation and crystallization temperature in step 2 is 50℃~100℃.

[0024] Furthermore, the evaporation and crystallization temperature in step 5 is 60℃~100℃.

[0025] Furthermore, the VOSO4 mother liquor from step 2 is mixed with the depleted negative electrode electrolyte (B1), and the mixture is used as the cathode liquid in step 3. Since the VOSO4 mother liquor has a low vanadium ion content, it is directly added to the next process to avoid waste.

[0026] Furthermore, the vanadium recovery described in step 5 involves extracting vanadium ions from the V2(SO4)3 mother liquor using an extraction method or an ion exchange method.

[0027] Further, the sulfuric acid recovery in step 5 involves first passing the obtained sulfuric acid solution through an ion exchange resin or nanofiltration membrane to remove dissolved impurity ions (such as vanadium, iron, zinc, etc.); then further removing organic impurities and color through activated carbon adsorption. Finally, the sulfuric acid solution is adjusted to the target concentration (approximately 1 mol / L to 3 mol / L) by evaporation or dilution, and recovered according to the ratio requirements of the flow battery electrolyte.

[0028] Furthermore, step 1 employs a first electrolysis system, in which the anolyte and catholyte circulate throughout the electrolysis process; step 3 employs a second electrolysis system, in which the anolyte and catholyte circulate throughout the electrolysis process.

[0029] Furthermore, both the first and second electrolysis systems include a cathode liquid storage tank, an anolyte storage tank, a cathode pump, an anode pump, an electrode stack assembly, a pipeline connecting the cathode liquid storage tank and the electrode stack, and a pipeline connecting the anolyte storage tank and the electrode stack. The cathode pump is installed on the pipeline connecting the cathode liquid storage tank and the electrode stack, and the anode pump is installed on the pipeline connecting the anolyte storage tank and the electrode stack. The cathode liquid circulates between the cathode liquid storage tank and the electrode stack via the cathode pump, and the anolyte circulates between the anolyte storage tank and the electrode stack via the anode pump.

[0030] Furthermore, the first electrolysis system also includes a VOSO4 mother liquor storage tank, a transfer pump, and a pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank. The transfer pump is installed on the pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank, and the VOSO4 mother liquor is transferred to the cathode liquid storage tank through the transfer pump.

[0031] Furthermore, the anode pump and cathode pump are centrifugal pumps, magnetic pumps, axial flow pumps, vacuum pumps, or magnetic levitation pumps.

[0032] Furthermore, both the first and second electrolysis systems use cell-type electrolysis devices.

[0033] Furthermore, the diaphragm of the fuel cell stack is an inorganic nanoparticle-doped Nafion membrane, an organic polymer / Nafion composite membrane, a Daramic membrane, or a Selemion CMV membrane.

[0034] Furthermore, the bipolar plate is a carbon-plastic composite bipolar plate, a flexible graphite plate, or an electrode-bipolar plate.

[0035] Furthermore, the material of the trough-type equipment is HEPE, PP, UPVC or PTFE.

[0036] Furthermore, filtration devices are installed in the anolyte storage tanks and catholyte storage tanks of the first and second electrolysis systems.

[0037] The method for recycling and utilizing the failed vanadium redox flow battery electrolyte of the present invention has the following advantages compared with the prior art:

[0038] 1) This invention uses the electrolyte of a failed vanadium redox flow battery as the vanadium source, eliminating the need for high-temperature calcination to prepare vanadium oxides. Instead, VOSO4 crystals and V2(SO4)3 crystals can be prepared in situ through electrolysis and evaporation crystallization, achieving a short-process, efficient, and direct recovery of the electrolyte from a failed vanadium redox flow battery.

[0039] 2) The vanadium electrolyte recovery method of the vanadium redox flow battery described in this invention can achieve a vanadium recovery rate of greater than or equal to 95% in the vanadium electrolyte, and the VOSO4 crystals and V2(SO4)3 crystals prepared have low impurity content.

[0040] 3) This invention uses electrolysis and distillation crystallization to directly recover the electrolyte from failed vanadium redox flow batteries, saving raw material and equipment costs, solving the problem of transportation radius of failed vanadium redox flow battery electrolyte, and achieving the goal of green and environmentally friendly recycling and cost reduction and efficiency improvement.

[0041] 4) This invention uses V2(SO4)3 mother liquor as sulfuric acid source. Without going through high-temperature reduction or toxic and harmful gas processes, the sulfuric acid solution in the mother liquor is recovered by evaporation or dilution methods, and industrial sulfuric acid that meets the standards of vanadium redox flow battery electrolyte is obtained, realizing the direct recycling of a large amount of sulfuric acid waste liquid. Attached Figure Description

[0042] Figure 1 This is a process flow diagram for the recycling of electrolyte from a failed vanadium redox flow battery.

[0043] Figure 2 The particle size distribution diagram is shown for the VOSO4 crystals prepared in Example 1.

[0044] Figure 3 The particle size distribution diagram is shown for the V2(SO4)3 crystals prepared in Example 1.

[0045] Figure 4 The XRD pattern of the VOSO4 crystal prepared in Example 2;

[0046] Figure 5 The XRD pattern of the V2(SO4)3 crystal prepared in Example 2;

[0047] Figure 6 The graph shows the charge-discharge efficiency of the vanadium battery electrolyte prepared in Example 3.

[0048] Figure 7 The energy efficiency diagram is shown for the vanadium battery electrolyte prepared in Example 3.

[0049] Figure 8 The diagram shows the energy density of the vanadium battery electrolyte prepared in Example 3. Detailed Implementation

[0050] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0051] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0052] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0053] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0054] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0055] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0056] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0057] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0058] Unless otherwise specified, % in this invention refers to mass percentage.

[0059] In Examples 1-3, both the first electrolysis system (the system used in S2 electrolysis) and the second electrolysis system (the system used in S5 electrolysis) include a cathode liquid storage tank, an anolyte storage tank, a cathode pump, an anode pump, and an electrode stack assembly. The electrode stack assembly includes bipolar plates, a cathode cell, a diaphragm, an anode cell, carbon felt, a plate frame, a single-cell voltage detector, and 40 single cells. Each electrolysis system includes pipes connecting the cathode liquid storage tank and the electrode stack, as well as pipes connecting the anolyte storage tank and the electrode stack. The cathode pump is installed on the pipes connecting the cathode liquid storage tank and the electrode stack, and the anode pump is installed on the pipes connecting the anolyte storage tank and the electrode stack. Valves are installed at the inlets and outlets of the electrode stack assembly, the anolyte storage tank, the cathode liquid storage tank, the anode pump, and the cathode pump.

[0060] The anode pump and cathode pump are magnetic pumps; the electrolysis devices in the electrolysis system are all tank-type electrolysis devices; the diaphragm of the stack device is an inorganic nanoparticle-doped Nafion membrane; the bipolar plates are carbon-plastic composite bipolar plates; the material of the tank-type equipment is PTFE; and filtration devices are installed in the anode liquid storage tank and cathode liquid storage tank of each electrolysis system.

[0061] Example 1

[0062] This embodiment discloses a method for recycling and utilizing electrolyte from a failed vanadium redox flow battery, such as... Figure 1 As shown, it includes the following steps:

[0063] S1: Add 650g of VOSO4 crystals to 500mL of pure water, add 200mL of concentrated sulfuric acid, and then dilute with pure water to 1.5L to obtain auxiliary electrolyte A1.

[0064] S2: Using the failed positive electrode electrolyte A2 with a vanadium ion concentration of 1.70 mol / L and a vanadium ion valence state of 4.85 as the cathode liquid, and the auxiliary electrolyte A1 obtained in S1 as the anolyte, at a current of 120 mA / cm². 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered through a filter to obtain 1L of VOSO4 solution. The average valence state of vanadium ions in the solution was 4.0. The solution was a mixture of VOSO4 and sulfuric acid.

[0065] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 80℃ for 6h, and then solid-liquid separation was performed to obtain 261g of VOSO4 crystals and 213mL of VOSO4 mother liquor.

[0066] S4: Transfer the VOSO4 mother liquor obtained in S3 to the failed negative electrode electrolyte to obtain 1L of failed negative electrode electrolyte B1 with a vanadium ion concentration of 3.10mol / L and a vanadium ion valence state of 3.6; add 250g of citric acid to the auxiliary electrolyte obtained in S2 and react fully to obtain 1.5L of auxiliary electrolyte A1.

[0067] S5: Use the failed negative electrode electrolyte B1 obtained in S4 as the cathode liquid and the auxiliary electrolyte A1 obtained in S4 as the anolyte, 120 mA / cm 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered to obtain 1 L of V2(SO4)3 solution. The average valence state of vanadium ions in the solution was 3.0. The solution was a mixture of V2(SO4)3 and sulfuric acid.

[0068] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 70℃ for 8h, and then solid-liquid separation was performed to obtain 1147g of V2(SO4)3 crystals and 255mL of V2(SO4)3 mother liquor.

[0069] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6 to extract vanadium ions and other dissolved impurity metal ions from the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color, yielding 265 mL of SO4. 2- A sulfuric acid solution with a concentration of 6.5 mol / L.

[0070] S8: Adding 0.88 L of pure water to the sulfuric acid solution obtained in S7 yields 1.15 L of SO4. 2- A dilute sulfuric acid solution with a concentration of 1.5 mol / L.

[0071] Example 2

[0072] This embodiment discloses a method for recycling and utilizing electrolyte from a failed vanadium redox flow battery, comprising the following steps:

[0073] S1: Add 650g of VOSO4 crystals to 500mL of pure water, add 250mL of concentrated sulfuric acid, and then dilute with pure water to 1.5L to obtain auxiliary electrolyte A1.

[0074] S2: Using the failed positive electrode electrolyte A2 with a vanadium ion concentration of 1.64 mol / L and a vanadium ion valence state of 4.75 as the cathode electrolyte, and the auxiliary electrolyte A1 obtained in S1 as the anolyte, at a current of 100 mA / cm². 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered through a filter to obtain 1L of VOSO4 solution. The average valence state of vanadium ions in the solution was 4.05. The solution was a mixture of VOSO4 and sulfuric acid.

[0075] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 70℃ for 6h, and then solid-liquid separation was performed to obtain 267g of VOSO4 crystals and 205mL of VOSO4 mother liquor.

[0076] S4: Transfer the VOSO4 mother liquor obtained in S3 to the failed negative electrode electrolyte to obtain 1L of failed negative electrode electrolyte B1 with a vanadium ion concentration of 3.13mol / L and a vanadium ion valence state of 3.55; add 250g of citric acid to the auxiliary electrolyte obtained in S2 and react fully to obtain 1.5L of auxiliary electrolyte A1.

[0077] S5: Use the failed negative electrode electrolyte B1 obtained in S4 as the cathode liquid and the auxiliary electrolyte A1 obtained in S4 as the anolyte, 100mA / cm 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered to obtain 1 L of V2(SO4)3 solution. The average valence state of vanadium ions in the solution was 3.05. The solution was a mixture of V2(SO4)3 and sulfuric acid.

[0078] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 70℃ for 12h, and then solid-liquid separation was performed to obtain 1160g of V2(SO4)3 crystals and 230mL of V2(SO4)3 mother liquor.

[0079] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6 to extract vanadium ions and other dissolved impurity metal ions from the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color, yielding 235 mL of SO4. 2- A sulfuric acid solution with a concentration of 6.35 mol / L.

[0080] S8: Add 0.77 L of pure water to the sulfuric acid solution obtained in S7 to obtain 1 L of SO4. 2- A dilute sulfuric acid solution with a concentration of 1.49 mol / L.

[0081] Example 3

[0082] This embodiment discloses a method for recycling and utilizing electrolyte from a failed vanadium redox flow battery, comprising the following steps:

[0083] S1: Add 620g of VOSO4 crystals to 500mL of pure water, add 225mL of concentrated sulfuric acid, and then dilute with pure water to 1.5L to obtain auxiliary electrolyte A1.

[0084] S2: Using the failed positive electrode electrolyte A2 with a vanadium ion concentration of 1.55 mol / L and a vanadium ion valence state of 4.95 as the cathode liquid, and the auxiliary electrolyte A1 obtained in S1 as the anolyte, at a current of 80 mA / cm². 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered through a filter to obtain 1 L of VOSO4 solution. The average valence state of vanadium ions in the solution was 4.1. The solution was a mixture of VOSO4 and sulfuric acid.

[0085] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 80℃ for 8h, and then solid-liquid separation was performed to obtain 270g of VOSO4 crystals and 195mL of VOSO4 mother liquor.

[0086] S4: Transfer the VOSO4 mother liquor obtained in S3 to the failed negative electrode electrolyte to obtain 1L of failed negative electrode electrolyte B1 with a vanadium ion concentration of 2.95mol / L and a vanadium ion valence state of 3.46; add 250g of citric acid to the auxiliary electrolyte obtained in S2 and react fully to obtain 1.5L of auxiliary electrolyte A1.

[0087] S5: Use the failed negative electrode electrolyte B1 obtained in S4 as the cathode liquid and the auxiliary electrolyte A1 obtained in S4 as the anolyte, 80 mA / cm 2 Electrolysis was performed at a current density, and the catholyte after electrolysis was precisely filtered to obtain 1 L of V2(SO4)3 solution. The average valence state of vanadium ions in the solution was 3.10. The solution was a mixture of V2(SO4)3 and sulfuric acid.

[0088] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 60℃ for 12h, and then solid-liquid separation was performed to obtain 1158g of V2(SO4)3 crystals and 210mL of V2(SO4)3 mother liquor.

[0089] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6 to extract vanadium ions and other dissolved impurity metal ions from the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color, yielding 215 mL of SO4. 2- A sulfuric acid solution with a concentration of 6.66 mol / L.

[0090] S8: Adding 0.68 L of pure water to the sulfuric acid solution obtained in S7 yields 0.9 L of SO4. 2- A dilute sulfuric acid solution with a concentration of 1.6 mol / L.

[0091] The VOSO4 crystals and V2(SO4)3 crystals from Examples 1-3 were tested respectively, and the test results are as follows:

[0092] Figure 2 The particle size distribution diagram is shown for the VOSO4 crystals prepared in Example 1; Figure 2 It can be seen that the particle sizes of the VOSO4 crystals prepared in Example 1 are Dv(10): 46.3 μm, Dv(50): 125 μm, Dv(90): 447 μm, and Dv(97): 612 μm. The VOSO4 crystals have large particle size and high crystallinity.

[0093] Figure 3 The particle size distribution diagram of the V2(SO4)3 crystals prepared in Example 1 is shown. Figure 3 It can be seen that the particle sizes of the V2(SO4)3 crystals prepared in Example 1 are Dv(10): 8.10μm, Dv(50): 21.5μm, Dv(90): 40.2μm, and Dv(97): 49.8μm. The V2(SO4)3 crystals have high crystallinity, small particle size, and uniform size.

[0094] Figure 4 The XRD pattern of the VOSO4 crystal prepared in Example 2; by Figure 4 As can be seen, the VOSO4 crystals prepared in Example 2 did not show any impurity characteristic peaks, and were consistent with the characteristic peaks of standard card 01-072-0912. Therefore, the main form of the VOSO4 crystals prepared in Example 2 is VOSO4·3H2O.

[0095] Figure 5 The XRD pattern of the V2(SO4)3 crystal prepared in Example 2; by Figure 5 As can be seen, the V2(SO4)3 crystal prepared in Example 2 did not show any impurity characteristic peaks, and its characteristic peaks were consistent with those of standard card 00-023-0723. Therefore, the main form of the V2(SO4)3 crystal prepared in Example 2 is V2(SO4)3.

[0096] The ICP detection results of the VOSO4 crystals prepared in Example 3 are shown in the table below:

[0097] Element types K Na Fe Al Mo Cr Mn Ca W Mg <![CDATA[VOSO4 crystal]]> 0.0005 0.0005 0.0002 0.0006 0.0003 0.0001 0.0000 0.0003 0.0002 0.0001 Element types B Pb Cu Bi Ti Co Zn Si Ni <![CDATA[VOSO4 crystal]]> 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0016 0.0000

[0098] The ICP test results of the VOSO4 crystals prepared in Example 3 show that the contents of all impurity ions such as K, Na, Fe, Al, Mo, Cr, Ca, W, Mg and Si in the VOSO4 crystals prepared in Example 3 meet the requirements of the national standard for Grade I products.

[0099] The ICP detection results of the V2(SO4)3 crystals prepared in Example 3 are shown in the table below:

[0100] Element types K Na Fe Al Mo Cr Mn Ca W Mg <![CDATA[V2(SO4)3 crystal]]> 0.0008 0.0004 0.0002 0.0007 0.0002 0.0002 0.0000 0.0001 0.0001 0.0001 Element types B Pb Cu Bi Ti Co Zn Si Ni <![CDATA[V2(SO4)3 crystal]]> 0.0000 0.0000 0.0001 0.0000 0.0001 0.0000 0.0000 0.0011 0.0000

[0101] The ICP test results of the V2(SO4)3 crystal prepared in Example 3 show that the contents of all impurity ions such as K, Na, Fe, Al, Mo, Cr, Ca, W, Mg, Cu, Ti and Si in the V2(SO4)3 crystal prepared in Example 3 meet the requirements of national standard grade 1 products.

[0102] Electrochemical performance testing

[0103] Using the VOSO4 crystals and V2(SO4)3 crystals prepared in Example 3, a standard sulfuric acid electrolyte system with a vanadium concentration of 1.65 mol / L and a sulfate concentration of 4.10 mol / L was prepared and incubated at 30°C for 48 cm⁻¹. 2 carbon felt area, 80 Ma / cm 2 Electrochemical performance tests were conducted under current density and a cutoff voltage of 1.55V. The test results are as follows: Figures 6-8 As shown:

[0104] Figure 6 The graph shows the charge-discharge efficiency of the vanadium battery electrolyte prepared in Example 3. Figure 7 The energy efficiency diagram is shown for the vanadium battery electrolyte prepared in Example 3. Figure 8 This is an energy density diagram of the vanadium battery electrolyte prepared in Example 3. Figures 6-8 Electrochemical test results show that at 30℃, 48cm 2 carbon felt area, 80 mA / cm 2 Under conditions of current density and a cutoff voltage of 1.55V, the electrolyte was charged and discharged using a constant current and constant voltage method, and the current was reduced to 40mA / cm under constant voltage conditions. 2The current density was such that after 50 cycles, the electrolyte's energy retention (EE) remained at 87%, the energy retention (CE) remained at 95.7%, the highest energy density was 26 Wh / L, and the energy retention rate after 50 cycles was over 70%. This indicates that the VOSO4 crystals and V2(SO4)3 crystals prepared in Example 3 exhibit good electrochemical performance and both meet the raw material standards for preparing vanadium redox flow battery electrolytes.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling electrolyte from a failed vanadium redox flow battery, characterized in that, Includes the following steps: Step 1 uses an auxiliary electrolyte as the anolyte and a failed positive electrode electrolyte as the catholyte. Through electrolysis, the valence state of vanadium ions in the catholyte is reduced to 4.0 ± 0.1 to obtain a VOSO4 solution. The auxiliary electrolyte is a vanadium-containing sulfuric acid solution. Step 2: Evaporate the VOSO4 solution to crystallize it, and filter it to obtain VOSO4 crystals and VOSO4 mother liquor; Step 3 uses an auxiliary electrolyte as the anolyte and a failed negative electrode electrolyte as the catholyte to electrolyze the vanadium ion valence state in the catholyte to 3.0±0.1, obtaining a V2(SO4)3 solution; the auxiliary electrolyte is a vanadium-containing sulfuric acid solution. Step 4: Evaporate and crystallize the V2(SO4)3 solution, and filter to obtain V2(SO4)3 crystals and V2(SO4)3 mother liquor; Step 5 involves recovering vanadium and sulfuric acid from the V2(SO4)3 mother liquor, respectively. In the auxiliary electrolyte described in steps 1 and 3, the vanadium ion concentration is 1.5 mol / L to 1.8 mol / L, the vanadium ion valence state is 4.0 ± 0.1, and the sulfate ion concentration is 4.0 mol / L to 5.0 mol / L. The vanadium ion concentration in the failed positive electrode electrolyte described in step 1 is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence state is 4.3 to 4.8, and the sulfate ion concentration is 4.0 mol / L to 5.0 mol / L. In step 3, the concentration of vanadium ions in the failed negative electrode electrolyte is 1.5 mol / L to 1.85 mol / L, the valence state of vanadium ions is 3.0 to 4.0, and the concentration of sulfate ions is 4.0 mol / L to 5.0 mol / L. Add a reducing agent to the auxiliary electrolyte after electrolysis in steps 1 and 3 to reduce the valence state of vanadium ions in the auxiliary electrolyte to 3.9~4.1, and prepare the auxiliary electrolyte, which can be returned to step 1 and / or step 3 for recycling; The reducing agent is one or more of citric acid, oxalic acid, formic acid, acetic acid, sulfite, and hydrogen peroxide; The VOSO4 mother liquor from step 2 is mixed with the failed negative electrode electrolyte, and the mixture is used as the cathode liquid in step 3.

2. The method for recycling the electrolyte of a failed vanadium redox flow battery according to claim 1, characterized in that, The electrolysis parameters for steps 1 and 3 are: current density of 80 mA / cm². 2 ~120mA / cm 2 The voltage is greater than 0V and less than 62V.

3. The method for recycling the electrolyte of a failed vanadium redox flow battery according to claim 1, characterized in that, The evaporation and crystallization temperature in step 2 is 50℃~100℃; And / or, the evaporation and crystallization temperature in step 5 is 60℃~100℃.

4. The method for recycling the electrolyte of a failed vanadium redox flow battery according to claim 1, characterized in that, The vanadium recovery described in step 5 involves extracting vanadium ions from the V2(SO4)3 mother liquor using either extraction or ion exchange methods. And / or, the sulfuric acid recovery in step 5 involves first removing dissolved impurity ions from the obtained sulfuric acid solution through an ion exchange resin or nanofiltration membrane; then further removing organic impurities and color through activated carbon adsorption; and finally adjusting the sulfuric acid solution to the target concentration through evaporation or dilution, and recovering it according to the ratio requirements of the flow battery electrolyte.

5. The method for recycling the electrolyte of a failed vanadium redox flow battery according to claim 1, characterized in that, Step 1 employs a first electrolysis system, in which the anolyte and catholyte circulate throughout the electrolysis process. Step 3 employs a second electrolysis system, in which the anolyte and catholyte circulate throughout the electrolysis process.

6. The method for recycling the electrolyte of a failed vanadium redox flow battery according to claim 5, characterized in that, Both the first electrolysis system and the second electrolysis system include a cathode liquid storage tank, an anolyte storage tank, a cathode pump, an anode pump, an electric stack assembly, a pipeline connecting the cathode liquid storage tank and the electric stack, and a pipeline connecting the anolyte storage tank and the electric stack. The cathode pump is installed on the pipeline connecting the cathode liquid storage tank and the electric stack, and the anode pump is installed on the pipeline connecting the anolyte storage tank and the electric stack. The cathode liquid circulates between the cathode liquid storage tank and the electric stack through the cathode pump, and the anolyte circulates between the anolyte storage tank and the electric stack through the anode pump. And / or, the first electrolysis system further includes a VOSO4 mother liquor storage tank, a transfer pump, and a pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank. The transfer pump is installed on the pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank, and the VOSO4 mother liquor is transferred to the cathode liquid storage tank through the transfer pump.

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