A method for preparing an electrolyte for an all-vanadium redox flow battery using ferrous sulfide as a reducing agent

Abstract

The present invention discloses a method for preparing an all-vanadium liquid flow battery electrolyte using ferrous sulfide as a reducing agent. Specifically, the following operating steps are followed: solid V2O5 powder and ferrous sulfide are dispersed in a dilute sulfuric acid solution to form a uniformly dispersed solid solution. Through a high-temperature stirring process, the ferrous sulfide is dissolved in the dilute sulfuric acid to generate a reducing agent, sulfur ions, which undergo an oxidation-reduction reaction with V2O5 at high temperature, ultimately forming a sulfuric acid solution of trivalent vanadium ions and divalent iron ions. Subsequently, the V2O5 powder is added to the sulfuric acid solution of trivalent vanadium ions and divalent iron ions according to a stoichiometric ratio and uniformly stirred to ultimately obtain a 3.5-valent vanadium ion and divalent iron ion solution as a mixed electrolyte for an all-vanadium liquid flow battery. The preparation process of the present invention is simple to operate, energy-saving and environmentally friendly, low in cost, and can simultaneously achieve stable operation of the electrolyte in the battery.

Description

Technical Field

[0001] The invention belongs to the field of all-vanadium redox flow battery electrolyte preparation, and particularly relates to a method for preparing an all-vanadium redox flow battery electrolyte using ferrous sulfide as a reducing agent. Background Art

[0002] Vanadium flow batteries (VFBs) are a new type of pollution-free chemical energy storage power source, characterized by long life, deep charge and discharge capabilities, and easy operation and maintenance. VFBs are primarily used in energy storage systems for large-scale renewable energy generation, such as wind and solar power generation, as well as for peak load balancing in power plants. The electrolyte, the active substance in the VFB's electrochemical reactions and the carrier of electrical energy, directly determines its energy storage capacity. Depending on the application configuration, electrolyte costs can account for 30% to 60% of the energy storage system. Therefore, finding an effective electrolyte preparation method and reducing VFB production costs are crucial to accelerating VFB commercialization and practical application. VFBs use sulfuric acid solutions containing vanadium ions of varying valence states as the electrolyte. Typically, the cathode electrolyte uses a tetravalent vanadium solution, which is oxidized to a pentavalent vanadium solution during charging; the cathode electrolyte uses a trivalent vanadium solution, which is reduced to a divalent vanadium solution during charging. Therefore, preparing trivalent and tetravalent vanadium solutions is crucial for practical field operation.

[0003] However, V2O5 has a very low solubility in water and is not easily soluble in acid, so sulfuric acid solution cannot be used directly as the electrolyte for VFB. It needs to be reduced, and the main methods for this treatment are chemical reduction and electrolytic reduction. The chemical method mainly uses vanadium oxide or other vanadium salts as raw materials, heats them in a sulfuric acid solution of a certain concentration, and adds a reducing agent (such as S, SO2, etc.) to dissolve and reduce them to low-priced, easily soluble vanadium compounds, thereby producing a vanadium electrolyte of a certain concentration. The advantage of the chemical synthesis method is that the production equipment is simple, but the dissolution rate of the solid is slow, and the added reducing agent will remain in the vanadium electrolyte and is difficult to eradicate, affecting the purity and performance of the vanadium electrolyte. The electrolytic reduction method can overcome the shortcomings of the chemical method, but because the solubility of V2O5 powder is low, the initial electrolyte is a slurry, which has problems such as low initial electrolyte concentration and easy precipitation.

[0004] On the other hand, the solubility of the active substances in the electrolyte of all-vanadium flow batteries is low, whether in the positive or negative electrode. Excessive concentration will lead to decreased solubility and instability during the reaction process. Therefore, many researchers are considering whether to use a mixed electrolyte to increase the capacity of all-vanadium flow batteries. Among them, adding divalent iron ions to both the positive and negative electrodes and utilizing the appropriate potential range of iron ions can effectively increase the capacity of all-vanadium flow batteries, and therefore has received widespread attention. However, in the existing methods, the reducing properties of the iron-containing compounds themselves are not considered as the reducing agent of the electrolyte during the preparation process of the electrolyte. Instead, divalent iron ions are artificially added after the electrolyte preparation is completed. This leads to a disconnect between production and application. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing an electrolyte for an all-vanadium redox flow battery using ferrous sulfide as a reducing agent, so as to solve the problems raised in the above background technology.

[0006] To achieve the above objectives, the present invention proposes a method for reducing V2O5 using ferrous sulfide as a reducing agent. Existing sulfur reducing agents have weak reducing power, and solid sulfur makes it difficult to evenly disperse and contact with the solid V2O5, resulting in low reaction efficiency. Furthermore, ferrous sulfide reduces V2O5 to produce trivalent vanadium ions and divalent iron ions, which can form a mixed electrolyte in a single step. Furthermore, V2O5 powder is added to a sulfuric acid solution containing trivalent vanadium ions according to a stoichiometric ratio and uniformly stirred, ultimately yielding a solution of 3.5-valent vanadium ions and divalent iron ions, which serves as the mixed electrolyte for all-vanadium redox flow batteries.

[0007] A method for preparing an electrolyte for an all-vanadium redox flow battery using ferrous sulfide as a reducing agent, comprising the following steps:

[0008] Ferrous sulfide is used as a primary chemical reducing agent to synthesize a sulfuric acid solution of trivalent vanadium ions and divalent iron ions, and then trivalent vanadium ions are used as a secondary reducing agent to obtain a sulfuric acid solution of 3.5-valent vanadium ions and divalent iron ions.

[0009] Preferably, the mixture of solid V2O5 powder and ferrous sulfide sulfuric acid forms a uniformly dispersed solid solution at 80-100°C and reacts for 2-4 hours.

[0010] Preferably, the weight ratio of V2O5 powder to ferrous sulfide is between 100:1 and 200:1.

[0011] Preferably, the solid-liquid ratio of V2O5 powder to sulfuric acid is between 100g:10ml and 100g:100ml.

[0012] Preferably, V2O5 powder is added to the solution obtained after ferrous sulfide reduction, mixed evenly, and reacted at 20-40°C for 2-5 hours.

[0013] Preferably, the solid-to-liquid ratio of the solution obtained by reducing V2O5 powder and ferrous sulfide is between 100g:10ml and 100g:50ml.

[0014] Technical effects and advantages of the present invention:

[0015] (1) The present invention proposes a method for preparing a sulfuric acid solution of 3.5-valent vanadium ions and divalent iron ions for all-vanadium redox flow batteries by chemically synthesizing ferrous sulfide and trivalent vanadium ions as reducing agents, thereby realizing a simple, convenient and low-cost mixed electrolyte preparation route.

[0016] (2) The present invention uses ferrous sulfide to replace traditional elemental sulfur, which can ensure that the reducing agent is evenly dispersed after being dissolved in sulfuric acid, thereby improving the reduction efficiency and eliminating the subsequent iron ion addition process, further combining production and application.

[0017] (3) The substances obtained after reducing V2O5 with the ferrous sulfide used in the present invention are all valuable substances, and no impurities will remain in the electrolyte, thereby ensuring the requirements for impurity content. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a performance test diagram of the solution-assembled all-vanadium redox flow battery in Comparative Example 1;

[0019] Figure 2 This is a performance test diagram of an all-vanadium redox flow battery assembled with the solution prepared in Example 1;

[0020] Figure 3 This is a performance test diagram of an all-vanadium redox flow battery assembled with the solution prepared in Example 2;

[0021] Figure 4 This is a performance test diagram of an all-vanadium redox flow battery assembled with the solution prepared in Example 3. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Comparative Example 1

[0024] A mixture of solid V2O5 powder and elemental sulfur was added to concentrated sulfuric acid and then heated at 90°C to form a uniformly dispersed solid solution. The weight ratio of V2O5 powder to elemental sulfur was 50:1, and the solid-liquid ratio of the V2O5 powder and sulfur mixture to sulfuric acid was 100g:100ml. After uniform mixing for 5 hours, Solution 1 was obtained. This solution was used to assemble an all-vanadium redox flow battery and perform performance tests to evaluate the electrolyte performance. Figure 1 .

[0025] All-vanadium redox flow battery test conditions: positive and negative electrodes are 800cm 2 Carbon felt electrodes, positive and negative electrodes were made of the prepared solution, using 80mA / cm 2 The charge and discharge cycles were carried out at a current density of 1.5 V. The charge cut-off condition was that the voltage was no higher than 1.5 V, and the discharge cut-off condition was that the voltage was no lower than 0.1 V. All the following battery tests were conducted using this method.

[0026] Example 1

[0027] A mixture of solid V2O5 powder and ferrous sulfide was heated at 80°C to form a uniformly dispersed solid solution and reacted for 2 hours. The weight ratio of V2O5 powder to ferrous sulfide was 100:1. The solid-liquid ratio of V2O5 powder to sulfuric acid was 100g:10ml. Furthermore, V2O5 powder was added to the solution obtained after the ferrous sulfide reduction, mixed evenly, and reacted at 20°C for 2 hours. The solid-liquid ratio of V2O5 powder to the solution obtained after the ferrous sulfide reduction was 100g:10ml. This solution was used to assemble an all-vanadium redox flow battery for performance testing to evaluate the electrolyte performance. Figure 2 .

[0028] Example 2

[0029] A mixture of solid V2O5 powder and ferrous sulfide sulfuric acid forms a uniformly dispersed solid solution at 90°C and reacts for 3 hours. The weight ratio of V2O5 powder to ferrous sulfide is 150:1. The solid-liquid ratio of V2O5 powder to sulfuric acid is 100g:50ml. Further, V2O5 powder is added to the solution obtained after ferrous sulfide reduction, mixed evenly, and reacted at 30°C for 3 hours. The solid-liquid ratio of V2O5 powder to the solution obtained after ferrous sulfide reduction is 100g:25ml. This solution is used to assemble an all-vanadium redox flow battery for performance testing to evaluate the performance of the electrolyte. Figure 3 .

[0030] Example 3

[0031] A mixture of solid V2O5 powder and ferrous sulfide sulfuric acid was allowed to form a uniformly dispersed solid solution at 100°C and reacted for 4 hours. The weight ratio of V2O5 powder to ferrous sulfide was 200:1. The solid-liquid ratio of V2O5 powder to sulfuric acid was 100g:100ml. Further, V2O5 powder was added to the solution obtained after the ferrous sulfide reduction, mixed evenly, and reacted at 40°C for 5 hours. The solid-liquid ratio of V2O5 powder to the solution obtained after the ferrous sulfide reduction was 100g:50ml. This solution was used to assemble an all-vanadium redox flow battery for performance testing to evaluate the electrolyte performance. Figure 4 .

[0032] Performance comparison table:

[0033]

[0034] From the data in the table, it can be found that the battery performance and capacity of the electrolyte obtained by using elemental sulfur as a reducing agent are significantly lower than the battery performance of the electrolyte obtained by using hydrazine hydrate combined with trivalent vanadium ions as a reducing agent.

[0035] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an electrolyte for an all-vanadium redox flow battery using ferrous sulfide as a reducing agent, characterized in that: Ferrous sulfide is used as a primary chemical reducing agent to synthesize a sulfuric acid solution of trivalent vanadium ions and divalent iron ions, and then trivalent vanadium ions are used as a secondary reducing agent to obtain a sulfuric acid solution of 3.5-valent vanadium ions and divalent iron ions. A mixture of solid V2O5 powder and ferrous sulfide forms a uniformly dispersed solid solution at 80-100°C and reacts for 2-4 hours. The weight ratio of V2O5 powder to ferrous sulfide is between 100:1-200:1, and the solid-liquid ratio of V2O5 powder to sulfuric acid is between 100g:10ml and 100g:100ml. The V2O5 powder is added to the solution obtained after the ferrous sulfide reduction, mixed evenly, and reacted at 20-40°C for 2-5 hours. The solid-liquid ratio of the solution obtained after the V2O5 powder and ferrous sulfide reduction is between 100g:10ml and 100g:50ml.

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