Process for the preparation of an iron-chromium battery electrolyte containing a complexing agent

Abstract

This invention discloses a method for preparing a complexing agent-containing iron-chromium battery electrolyte, comprising: solution preparation: preparing ferrous chloride solution and chromium chloride solution using an iron-chromium alloy; complexation reaction: mixing the chromium chloride solution and ferrous chloride solution, and adding a complexing agent solution; buffer system construction: adding ammonium chloride solution and a nonionic surfactant; electrode adjustment: adding sodium phosphate to obtain the positive electrode electrolyte; adding diethylenetriaminepentaacetic acid as the negative electrode electrolyte; and allowing it to stand for aging. The method for preparing a complexing agent-containing iron-chromium battery electrolyte disclosed in this invention utilizes a complexing agent to form stable complexes with ferrous and chromium ions, significantly inhibiting hydrolysis and precipitation, while simultaneously adjusting the ionic electrode potential and reducing hydrogen evolution during charging and discharging. Furthermore, the combined action of the buffer and hydrochloric acid can inhibit the oxidation of ferrous ions, ensuring the conductivity and electrochemical activity of the electrolyte.

Description

Technical Field

[0001] This invention relates to a method for preparing an iron-chromium battery electrolyte containing a complexing agent, belonging to the technical field of iron-chromium battery electrolytes. Background Technology

[0002] Iron-chromium redox flow batteries, as one of the core technologies in the field of large-scale energy storage, have advantages such as high safety, long cycle life, low cost, and environmental friendliness, and have broad application prospects in new energy storage, smart grid peak shaving, and other fields. The electrolyte, as a core component of iron-chromium redox flow batteries, directly determines the battery's charge-discharge efficiency, capacity stability, and cycle life, and is a key factor restricting the large-scale application of iron-chromium batteries.

[0003] Traditional iron-chromium electrolytes use ferrous chloride and chromium chloride as the main active substances and deionized water as the solvent, but they have significant technical drawbacks: Fe 2+ Fe 3+ Cr 3+ Metal ions readily undergo hydrolysis in aqueous solutions, generating hydroxide precipitates that cause electrolyte turbidity and loss of active materials. Simultaneously, the hydrogen evolution reaction is significant during charging and discharging, which not only causes electrolyte component loss but also leads to rapid battery capacity decay and poor cycle stability, severely impacting the lifespan and operational reliability of iron-chromium batteries.

[0004] Developing a stable iron-chromium battery electrolyte with low hydrogen evolution is of great practical significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an iron-chromium battery electrolyte containing a complexing agent. By adding a complexing agent and a buffer system, the electrolyte exhibits good stability, no significant precipitation, and low hydrogen evolution, thus providing comprehensive performance for iron-chromium batteries.

[0006] To solve the above-mentioned technical problems, the objective of this invention is achieved as follows: The present invention relates to a method for preparing an iron-chromium battery electrolyte containing a complexing agent, comprising the following steps: S1. Solution preparation: Ferrous chloride solution and chromium chloride solution were prepared using an iron-chromium alloy. S2, Complexation reaction: Heat chromium chloride solution and ferrous chloride solution to a set temperature and stir to obtain a first mixed solution; continue stirring the first mixed solution, add complexing agent solution, and keep warm at 70-80℃ for a set time to obtain a second mixed solution; The complexing agent solution is prepared by dissolving the complexing agent in water at 50-60°C; S3. Buffer system construction: Adjust the pH of the second mixed solution to 2.5±0.5 and heat it to 40-60℃. Then add ammonium chloride solution and nonionic surfactant, and mix evenly to obtain the third mixed solution; the ammonium chloride solution is obtained by adding ammonium chloride to water at 60-65℃. S4. Electrode Adjustment: The third mixed solution is divided into a fourth mixed solution and a fifth mixed solution; the pH of the fourth mixed solution is adjusted to 3±0.5, and sodium phosphate is added to obtain the positive electrode electrolyte; the pH of the fifth mixed solution is adjusted to 4±0.5, and diethylenetriaminepentaacetic acid is added to obtain the negative electrode electrolyte. S5. Standing and aging: After vacuum filtration of the positive and negative electrolytes using an organic filter membrane, place them in a sealed container and let them stand and age for 24-48 hours at room temperature (25±5℃) and in the dark. If a small amount of precipitation occurs, filter again to obtain the finished iron-chromium battery electrolyte.

[0007] Based on the above scheme and as a preferred embodiment of the above scheme: the complexing agent includes oxalic acid and / or formic acid.

[0008] Based on the above scheme and as a preferred embodiment of the above scheme: Step S1, solution preparation, includes: S1.1 Preparation of iron-chromium alloy solution: After dissolving the iron-chromium alloy in hydrochloric acid, the solution is obtained by filtration. S1.2 Add reduced iron powder: Add reduced iron powder to the iron-chromium alloy solution in the previous step; S1.3, Precipitate chromium ions: Control the pH of the iron-chromium alloy solution to 3.5±0.3 until Cr... 3+ The mixture is completely converted to Cr(OH)3, resulting in a solution containing impurities and a solid precipitate, wherein the solid precipitate includes Cr(OH)3, excess iron powder, and nickel. S1.4, Impurity Removal: Removes excess iron powder and nickel; S1.5 Filtration: Filter the filtrate from the previous step to separate the Cr(OH)3 solid precipitate from the ferrous chloride filtrate containing impurities. S1.6 Dissolving Cr(OH)3: Dissolve solid Cr(OH)3 in hydrochloric acid to obtain chromium chloride solution; S1.7 Filtrate removal: ferrous chloride solution is obtained.

[0009] Based on the above scheme and as a preferred embodiment of the above scheme: the nonionic surfactant is polyethylene glycol or polyvinylpyrrolidone.

[0010] Based on the above scheme and as a preferred option: in step S1.4, electromagnetic filtration is used to remove iron powder and nickel.

[0011] Based on the above scheme and as a preferred option: in step S1.7, the pH of the filtrate is adjusted to 56; ferrous sulfide is added to remove impurities.

[0012] The beneficial effects of this invention are as follows: The method for preparing an iron-chromium battery electrolyte containing a complexing agent disclosed in this invention uses a complexing agent to form stable complexes with ferrous ions and chromium ions, significantly inhibiting hydrolysis and precipitation, while simultaneously adjusting the ion electrode potential and reducing hydrogen evolution during charging and discharging. Furthermore, the combined action of the buffer and hydrochloric acid can also inhibit the oxidation of ferrous ions, ensuring the conductivity and electrochemical activity of the electrolyte. Detailed Implementation

[0013] The present invention will be further described below with reference to specific embodiments.

[0014] Example 1 The preparation method of an iron-chromium battery electrolyte containing a complexing agent involved in this embodiment includes the following steps: S1. Solution Preparation: Ferrous chloride solution and chromium chloride solution are prepared using an iron-chromium alloy; the preparation process includes: S1.1 Preparation of Ferrochromium Alloy Solution: The ferrochromium alloy is dissolved in hydrochloric acid to obtain a solution and an insoluble residue. The insoluble residue is then filtered to obtain the ferrochromium alloy solution. In this embodiment, the selected ferrochromium alloy includes C 0.1%–0.2%, Cr 18.0%–20.0%, Si 3.5%–4.0%, Mn 1.8%–2.1%, Ni 17.0%–19.0%, B 1.2%–1.8%, and Fe as the balance. Other ferrochromium alloys can also be used. When the ferrochromium alloy is dissolved in hydrochloric acid, the metal elements react with the hydrochloric acid to generate metal ions that dissolve in the solution. Non-metallic materials do not dissolve in hydrochloric acid, thus forming an insoluble residue that can be removed. The iron element forms ferric ions, and the chromium element forms chromium ions. The metals that are less reactive than iron are displaced, while the metal ions that are more reactive than iron remain in the solution.

[0015] S1.2 Adding Reduced Iron Powder: Add reduced iron powder to the iron-chromium alloy solution from the previous step. Reduced iron powder is elemental iron powder with strong reducing properties. It can react with ferric ions to generate ferrous ions and can also convert nickel ions to form metallic nickel. Since the reduced iron powder added at this time is in excess, the resulting solution is acidic, with a pH of approximately 2.

[0016] S1.3, Precipitate chromium ions: Control the pH of the iron-chromium alloy solution to 3.5±0.3 until Cr... 3+The chromium alloy solution is completely converted to Cr(OH)3, resulting in a solution containing impurities and a solid precipitate, including Cr(OH)3, excess iron powder, and nickel. When the pH value is higher than 3, trivalent chromium ions precipitate as Cr(OH)3. Specifically, the pH value of the ferrochromium alloy solution is controlled at 3.5 ± 0.3. In this embodiment, it is controlled at 3.5.

[0017] S1.4, Impurity Removal: Remove excess iron powder and nickel. In this embodiment, electromagnetic filtration is used to remove iron powder, nickel and other metal impurities.

[0018] S1.5 Filtration: Filter the filtrate from the previous step to separate the Cr(OH)3 solid precipitate from the ferrous chloride filtrate containing impurities. Wash the solid solution to remove the ferrous chloride adhering to its surface.

[0019] S1.6 Dissolving Cr(OH)3: Dissolve solid Cr(OH)3 in hydrochloric acid to obtain a chromium chloride solution. Solid Cr(OH)3 reacts with hydrochloric acid to produce chromium trichloride and water, without introducing other impurities.

[0020] S1.7 Filtrate Removal: A ferrous chloride solution is obtained. In this embodiment, the pH of the filtrate is adjusted to 3.0-3.5; ferrous sulfide is added for impurity removal. This removes other metal ions from the ferrous chloride solution, such as manganese. Manganese ions combine with sulfur ions to form manganese sulfide precipitate. The weakly acidic solution contains some hydrogen ions. After precipitating the manganese ions, a pure ferrous chloride solution remains. The concentration of hydrochloric acid in both the chromium chloride solution and the ferrous chloride solution is less than 0.1 mol / L. In this embodiment, the concentration of chromium chloride is 3.2 mol / L, and the concentration of ferrous chloride is 3 mol / L.

[0021] S2. Complexation reaction: The chromium chloride solution and ferrous chloride solution are heated to a set temperature and stirred to obtain a first mixed solution; the first mixed solution is stirred continuously, a complexing agent solution is added, and the mixture is kept at 60-80℃ for a set time to obtain a second mixed solution; in this embodiment, the mixture is kept at 70℃ for 30 minutes. The chromium chloride solution and ferrous chloride solution are mixed in a 1:1 molar ratio.

[0022] The complexing agent solution is prepared by dissolving the complexing agent in water at 50-60°C; in this embodiment, it is dissolved in water at 55°C. The solution is added to the first mixed solution at 55°C. The complexing agent includes oxalic acid and / or formic acid. In this embodiment, oxalic acid and formic acid are mixed in a molar ratio of 1:1.

[0023] S3. Buffer System Construction: The pH of the second mixed solution was adjusted to 2.5 ± 0.5, and the temperature was raised to 40-60℃. Then, ammonium chloride solution and a nonionic surfactant were added, and the mixture was thoroughly mixed to obtain the third mixed solution. The ammonium chloride solution was prepared by adding ammonium chloride to water at 60-65℃. Specifically, in this embodiment, the pH of the second mixed solution was 4.5, and the temperature was raised to 50℃. The concentration of the ammonium chloride solution used was 1 mol / L.

[0024] Furthermore, the nonionic surfactant is polyethylene glycol or polyvinylpyrrolidone. As nonionic surfactants, polyethylene glycol and polyvinylpyrrolidone are hydrophilic and electrochemically inert, capable of adsorbing onto the electrode surface to form a nanoscale "water barrier," increasing proton transport resistance and raising the overpotential for hydrogen evolution. In this embodiment, polyvinylpyrrolidone is selected. The concentration of the nonionic surfactant is 50-200 ppm, and in this embodiment, it is 100 ppm.

[0025] S4. Electrode Adjustment: The third mixed solution is divided into a fourth mixed solution and a fifth mixed solution. The pH of the fourth mixed solution is adjusted to 3±0.5, and sodium phosphate is added to obtain the positive electrode electrolyte. The pH of the fifth mixed solution is adjusted to 4±0.5, and diethylenetriaminepentaacetic acid is added to obtain the negative electrode electrolyte. In this embodiment, the pH of the fourth mixed solution is 3, and the amount of sodium phosphate is 2.5 g / L. The pH of the fifth mixed solution is 4, and the amount of diethylenetriaminepentaacetic acid is 2 g / L.

[0026] S5. Static Aging: After vacuum filtration of the positive and negative electrolytes using an organic filter membrane, place them in a sealed container and allow them to stand and age for 24-48 hours at room temperature (25±5℃) in the dark. If a small amount of precipitation occurs, filter again to obtain the finished iron-chromium battery electrolyte. In this embodiment, the aging time is 36 hours.

[0027] Test results: Hydrogen evolution rate was 0.003%. (At 140 mA / cm²) 2 At current density, the coulombic efficiency can reach over 96.8%, and the energy efficiency can reach over 85%. The capacity retention rate is 91% after 50 cycles. The hydrogen evolution rate is significantly lower than that of existing flow batteries.

[0028] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing an iron-chromium battery electrolyte containing a complexing agent, characterized in that, Includes the following steps: S1. Solution preparation: Ferrous chloride solution and chromium chloride solution were prepared using an iron-chromium alloy. S2, Complexation reaction: The chromium chloride solution and the ferrous chloride solution are heated to a set temperature and stirred to obtain the first mixed solution; Continue stirring the first mixed solution, add the complexing agent solution, and keep it at 70-80℃ for a set time to obtain the second mixed solution; The complexing agent solution is prepared by dissolving the complexing agent in water at 50-60°C; S3. Buffer system construction: Adjust the pH of the second mixed solution to 2.5±0.5 and heat it to 40-60℃. Then add ammonium chloride solution and nonionic surfactant, and mix evenly to obtain the third mixed solution; the ammonium chloride solution is obtained by adding ammonium chloride to water at 60-65℃. S4, Polarization Adjustment: Divide the third mixed solution into a fourth mixed solution and a fifth mixed solution; The pH of the fourth mixed solution was adjusted to 3±0.5, and sodium phosphate was added to obtain the positive electrode electrolyte; the pH of the fifth mixed solution was adjusted to 4±0.5, and diethylenetriaminepentaacetic acid was added to obtain the negative electrode electrolyte. S5. Standing and aging: After vacuum filtration of the positive and negative electrolytes using an organic filter membrane, place them in a sealed container and let them stand and age for 24-48 hours at room temperature (25±5℃) and in the dark. If a small amount of precipitation occurs, filter again to obtain the finished iron-chromium battery electrolyte.

2. The method for preparing an iron-chromium battery electrolyte containing a complexing agent according to claim 1, characterized in that, The complexing agent includes oxalic acid and / or formic acid.

3. The method for preparing an iron-chromium battery electrolyte containing a complexing agent according to claim 1, characterized in that, Step S1, solution preparation, includes: S1.1 Preparation of iron-chromium alloy solution: After dissolving the iron-chromium alloy in hydrochloric acid, the solution is obtained by filtration. S1.2 Add reduced iron powder: Add reduced iron powder to the iron-chromium alloy solution in the previous step; S1.3, precipitating the chromium ions: controlling the pH of the ferrochrome alloy solution to 3.5 ± 0.3, until Cr 3+ is completely converted into Cr(OH)3, resulting in a solution containing impurities and a solid precipitate comprising Cr(OH)3, excess iron powder and nickel; S1.4, Impurity Removal: Removes excess iron powder and nickel; S1.5 Filtration: Filter the filtrate from the previous step to separate the Cr(OH)3 solid precipitate from the ferrous chloride filtrate containing impurities. S1.6 Dissolving Cr(OH)3: Dissolve solid Cr(OH)3 in hydrochloric acid to obtain chromium chloride solution; S1.7 Filtrate removal: ferrous chloride solution is obtained.

4. The method for preparing an iron-chromium battery electrolyte containing a complexing agent according to claim 1, characterized in that, The nonionic surfactant is polyethylene glycol or polyvinylpyrrolidone.

5. The method for preparing an iron-chromium battery electrolyte containing a complexing agent according to claim 3, characterized in that, In step S1.4, electromagnetic filtration is used to remove iron powder and nickel.

6. The method for preparing an iron-chromium battery electrolyte containing a complexing agent according to claim 3, characterized in that, In step S1.7, the pH of the filtrate is adjusted to 56, and ferrous sulfide is added to remove impurities.