Composite graphite felt material, preparation method thereof and all-vanadium redox flow battery

Abstract

The invention relates to the field of all-vanadium redox flow batteries, and discloses a composite graphite felt material and a preparation method thereof, and the composite graphite felt material can improve the battery performance of the all-vanadium redox flow battery. The method comprises the steps that magnesium salt and aluminum salt are dissolved in deionized water, and the molar ratio of Mg to Al in the solution ranges from 2: 1 to 4: 1; adding the prepared precipitant solution into the solution in which the magnesium salt and the aluminum salt are fully dissolved, and adjusting the pH value of the solution to 11-13 to obtain a precursor solution; the graphite felt is soaked in a dilute sulfuric acid solution for etching, impurities on the graphite felt are removed, and the etched graphite felt is dried for standby application; jointly transferring the precursor solution and the treated graphite felt into a hydrothermal reaction kettle, and putting the hydrothermal reaction kettle into a drying oven to react for 4-12 hours at the temperature of 60-180 DEG C; and cleaning the graphite felt material loaded with the catalyst material with deionized water, and drying in a drying oven.

Description

Technical Field

[0001] The invention belongs to the field of all-vanadium liquid flow batteries and relates to a MgAl-LDH composite graphite felt material and a preparation method thereof. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the present application as recited in the claims. The description herein is not admitted to be prior art as disclosed by virtue of its inclusion in this section.

[0003] Chemical energy storage technology is one of the key technologies to achieve large-scale utilization of renewable energy. Common chemical energy storage systems mainly include lead-acid batteries, lithium-ion batteries, redox flow batteries and sodium-sulfur batteries. Among them, redox flow batteries have attracted widespread attention due to their wide operating temperature range, long cycle life, high charge and discharge efficiency and good safety.

[0004] All-vanadium redox flow batteries use VO2 dissolved in sulfuric acid + / VO 2+ 、V 3+ / V 2+ The redox couple serves as the positive and negative active materials respectively and is stored in the electrolyte storage tank. The electrolyte is transported to the positive and negative chambers in the battery stack by pumping. The electrolyte produces an electrochemical reaction on the surface of the graphite felt bipolar plate to realize the charging and discharging process. However, the poor hydrophilicity and electrochemical activity of the electrode material restrict the overall performance of the all-vanadium liquid flow battery. At present, the modification methods for electrode materials mainly include the following methods: deposition of metal oxides on the electrode surface, heteroatom-doped electrodes, and carbon nanotubes or graphene on the modified electrode surface to improve the hydrophilicity of the electrode material and increase the electrochemical active area. However, the above methods are limited by high costs and complex processes and have not been widely promoted and used. Summary of the invention

[0005] The purpose of the present application is to provide a composite graphite felt material and a preparation method thereof, and an all-vanadium liquid flow battery, which realizes low-cost and simple-process electrode surface modification and improves the battery performance of the all-vanadium liquid flow battery.

[0006] The present application discloses a method for preparing a composite graphite felt material, comprising the following steps:

[0007] Dissolving a magnesium salt and an aluminum salt in deionized water, wherein the molar ratio of Mg / Al in the solution is 2:1 to 4:1;

[0008] Adding the prepared precipitant solution to a solution in which the magnesium salt and the aluminum salt are fully dissolved, and adjusting the pH value of the solution to 11 to 13, to obtain a precursor solution;

[0009] The graphite felt is immersed in a dilute sulfuric acid solution for etching and removing impurities on the graphite felt, and the etched graphite felt is dried for later use;

[0010] The precursor solution and the treated graphite felt are transferred to a hydrothermal reactor and placed in an oven at 60 to 180 degrees Celsius for 4 to 12 hours;

[0011] The graphite felt material treated as above will load the MgAl-LDH catalyst material. The obtained graphite felt material loaded with the catalyst material is washed with deionized water and then dried in an oven.

[0012] In a preferred example, the magnesium salt includes magnesium chloride, magnesium nitrate, magnesium carbonate, and magnesium hydroxide, and the aluminum salt includes aluminum chloride and aluminum nitrate.

[0013] In a preferred embodiment, the precipitant is 1M sodium carbonate and 1M sodium hydroxide solution, and the precipitant is added dropwise until the pH value of the solution is 11 to 13.

[0014] In a preferred embodiment, the pH value of the precursor solution is 12 to 13, and the aluminum salt and the magnesium salt in the precursor solution are magnesium chloride and aluminum chloride, respectively.

[0015] The present application also discloses a composite graphite felt material, which is prepared by the preparation method described above.

[0016] The present application also discloses an all-vanadium liquid flow battery, the electrodes of which use the composite graphite felt material described above.

[0017] In the embodiments of the present application, MgAl-LDH is adsorbed and deposited on the electrode surface by co-precipitation method for flaky magnesium aluminum hydrotalcite (MgAl-LDH), which is not only low-cost but also simple in process, improves the hydrophilicity of the electrode surface and the adsorption and desorption of vanadium ions of different valence states, accelerates the kinetic process of the battery reaction, and improves the battery performance of the all-vanadium liquid flow battery.

[0018] Specifically, it has the following advantages:

[0019] (1) The preparation process is simple and the raw materials used do not contain precious metals.

[0020] (2) The particle size of MgAl-LDH material is adjustable, which can significantly increase the electrochemical active sites of the electrode material.

[0021] (3) Graphite felt and MgAl-LDH materials can stably adsorb, ensuring good chemical and electrochemical stability.

[0022] (4) The hydroxyl group of MgAl-LDH material can effectively improve the hydrophilicity of graphite felt.

[0023] Each technical feature disclosed in the above invention content, each technical feature disclosed in each implementation mode and example below, and each technical feature disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions should be deemed to have been recorded in this specification), unless such combination of technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed, and features C and D are equivalent technical means that play the same role. Technically, only one of them can be used, and it is impossible to use them at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be deemed to have been recorded because it is technically infeasible, while the solution of A+B+C+E should be deemed to have been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the crystal structure diagram of MgAl-LDH material. DETAILED DESCRIPTION

[0025] In the following description, many technical details are provided to help readers better understand the present application. However, those skilled in the art can understand that the technical solution claimed in the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0026] Flaky magnesium aluminum hydrotalcite (MgAl-LDH) is a type of ionic layered compound, which is composed of positively charged brucite-like layers, and the interlayers contain charge-compensating anions and solvated molecules. The MgAl-LDH material is modified on the surface of the electrode of the all-vanadium liquid flow battery, but the effect on electron transfer and the hydrophilicity of graphite felt is still a research gap. Therefore, the present invention adopts a simple, economical and green method to successfully deposit the MgAl-LDH material on the graphite felt material, and studies the effect of MgAl-LDH materials with different deposition thicknesses on the comprehensive performance of the all-vanadium liquid flow battery.

[0027] In some embodiments of the present application, the preparation method of the MgAl-LDH composite graphite felt material is as follows:

[0028] (1) The cut graphite felt is immersed in 0.1 M sulfuric acid solution for 15 min and then dried for later use.

[0029] (2) The pH values ​​of the prepared precursor solutions were 12 and 13, respectively, and were marked and reacted at 120°C for 6 hours. The aluminum salt and magnesium salt in the precursor solution were magnesium chloride and aluminum chloride, respectively, and the molar ratio of Mg / Al in the solution was 2:1, 3:1 and 4:1; to prevent magnesium chloride and aluminum chloride from hydrolyzing and becoming insoluble, 200 microliters of concentrated hydrochloric acid solution was first added to 100 mL of deionized water. After the aluminum salt and magnesium salt were fully dissolved, a mixed solution of 1M sodium carbonate and 1M sodium hydroxide in a volume ratio of 2:1 was slowly added to the solution and stirred continuously, while the pH value was monitored, and the three precursor solutions with pH values ​​of 12 and 13 were all transferred to different hydrothermal reactors. The dried graphite felt material was added to the hydrothermal reactor, and the reactor was transferred to an oven and reacted at 120°C for 6 hours.

[0030] (3) The graphite felt material after the hydrothermal reaction is washed with deionized water for 3 to 5 times, dried in an oven, and assembled into a battery to test the electrochemical performance.

[0031] The ingredients of the specific embodiment are as follows:

[0032]

[0033] For the specific embodiment in the above table, the battery was assembled and tested. The test temperature was 25°C, the charge cut-off voltage was 1.65V, the discharge cut-off voltage was 0.8V, and the charge and discharge apparent current density was 100mA·h -1 , the electrolyte flow rate was set to 20 mL min -1 The battery was tested for 80 charge and discharge cycles, and the voltage efficiency data obtained after processing were 82.1%, 84.3%, 85.5%, 86.7%, 86.0% and 85.4%, respectively. The original graphite felt and the graphite felt soaked in sulfuric acid were tested under the same test conditions, and the voltage efficiency obtained after data processing was 70.2% and 75.6%, respectively. It can be seen that the MgAl-LDH composite graphite felt material prepared by the method of the present application can significantly improve the voltage efficiency of the all-vanadium liquid flow battery.

[0034] In one embodiment, at least one electrode of an all-vanadium liquid flow battery uses the composite graphite felt material prepared in the above embodiment.

[0035] This specification includes combinations of the various embodiments described herein. Individual references to an embodiment (e.g., "one embodiment" or "some embodiments" or "preferred embodiments") do not necessarily refer to the same embodiment; however, these embodiments are not mutually exclusive unless indicated as mutually exclusive or it is clear to a person skilled in the art that they are mutually exclusive. It should be noted that the word "or" is used in this specification in a non-exclusive sense unless the context clearly indicates or requires otherwise.

[0036] All documents mentioned in this application are considered to be included in the disclosure of this application as a whole, so that they can be used as the basis for modification when necessary. In addition, it should be understood that after reading the content of this application, those skilled in the art can make various changes or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A method for preparing a composite graphite felt material, characterized in that: The following steps are involved: Dissolving a magnesium salt and an aluminum salt in deionized water, wherein the molar ratio of Mg / Al in the solution is 2:1 to 4:1; Adding the prepared precipitant solution to a solution in which the magnesium salt and the aluminum salt are fully dissolved, and adjusting the pH value of the solution to 11 to 13, to obtain a precursor solution; The graphite felt is immersed in a dilute sulfuric acid solution for etching and removing impurities on the graphite felt, and the etched graphite felt is dried for later use; The precursor solution and the treated graphite felt are transferred to a hydrothermal reactor and placed in an oven at 60 to 180 degrees Celsius for 4 to 12 hours; The obtained graphite felt material loaded with MgAl-LDH catalyst material was washed with deionized water and then dried in an oven.

2. The method according to claim 1, characterized in that The magnesium salts include magnesium chloride, magnesium nitrate, magnesium carbonate and magnesium hydroxide; the aluminum salts include aluminum chloride and aluminum nitrate.

3. The method according to claim 1, characterized in that: The precipitant is 1M sodium carbonate and 1M sodium hydroxide solution, and the precipitant is added dropwise until the pH value of the solution is 11 to 13.

4. A composite graphite felt material, characterized in that: The composite graphite felt material is prepared by the preparation method described in any one of claims 1 to 3.

5. An all-vanadium liquid flow battery, characterized in that: The electrode of the battery uses the composite graphite felt material according to claim 5.

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