Composite electrode for all-vanadium redox flow battery and preparation method thereof

Abstract

The application discloses a composite electrode for a vanadium redox flow battery and a preparation method thereof, and the preparation steps are as follows: S1, placing an aqueous dispersion of graphene oxide at a temperature of 55-65 DEG C to perform cross-linking concentration until the aqueous dispersion of graphene oxide is concentrated to 38-42 mg / g, and obtaining a printing base material; S2, taking the printing base material, vitamin C and conductive carbon black to perform sufficient stirring, and obtaining a printing ink raw material; S3, loading a syringe containing the printing ink raw material into a 3D printer to perform 3D printing, and obtaining a 3D printed electrode; S4, freezing the 3D printed electrode at-50 to-48 DEG C for 9-10 h, then performing vacuum drying on the 3D printed electrode in a stepwise heating mode for 30-35 h, then placing the electrode at a temperature of 90-95 DEG C for 2-3 h, naturally cooling to room temperature, fully washing and vacuum drying, and obtaining a graphene-conductive carbon black composite aerogel; and S5, placing the graphene-conductive carbon black composite aerogel into a tube furnace, heating at 300-900 DEG C under an argon atmosphere for 1.5-2.5 h, taking out and cooling to room temperature, and obtaining the graphene-conductive carbon black composite aerogel.

Description

Technical Field

[0001] This invention relates to a composite electrode for vanadium redox flow batteries and its preparation method, belonging to the field of electrode preparation technology. Background Technology

[0002] 3D printing, as an emerging rapid prototyping technology, has revolutionized the diversity and complexity of structures. Furthermore, the precise material deposition process of 3D printing not only improves material utilization but also avoids excessive material consumption, aligning with the sustainable development of renewable devices. As one of the 3D printing technologies, extrusion-based direct-flow (DIW) offers design flexibility, thereby improving the performance and functionality of energy storage devices. DIW technology has been successfully applied in fields such as supercapacitors, sensors, integrated microfluidic devices, sodium-ion batteries, lithium metal batteries, and lithium-ion batteries. Graphene, due to its high specific surface area, excellent mechanical strength, high chemical stability, and conductivity, has been widely used in energy storage devices. However, the stacking or agglomeration of graphene sheets, attributed to van der Waals forces, reduces the specific surface area and affects the material's mechanical and electrical properties. To overcome the agglomeration problem, a method combining 3D printing and freeze-drying is employed, using high-precision assembly and processing techniques to precisely control structural features. As a precursor to graphene, graphene oxide (GO) sheets possess amphiphilicity and unique viscoelasticity. Therefore, GO dispersions are widely used as printable inks for extruded DIW (Digital-Induced Wave) printing. Based on DIW, the macroscopic and microscopic pore structure of graphene aerogels can be flexibly controlled by changing the printing path and GO concentration. A rationally designed porous structure can provide more specific surface area for the reaction, reduce mass transfer paths, and improve ion accessibility, thereby helping to reduce electrochemical polarization and improve the accessibility of reactant ions. Furthermore, 3D-printed graphene composite aerogels possess advantages such as low density, rational pore structure, excellent mechanical properties, large specific surface area, and large electrochemically active surface area, making them applicable in energy storage, catalysis, environmental applications, interfacial thermal conductivity, interfacial electrical conductivity, and electronic devices. Therefore, 3D-printed graphene aerogels hold great promise for applications in all-vanadium redox flow batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a composite electrode for vanadium redox flow batteries and its preparation method. The composite electrode uses DIW extrusion ink and freeze-drying technology, and enhances the redox capability of the electrode by high-temperature heat treatment reduction and doping with conductive carbon black, thereby reducing the resistivity and increasing the conductivity of the electrode, thus improving the performance of the composite electrode in vanadium redox flow batteries and improving the energy efficiency of the battery.

[0004] The technical solution adopted by this invention to achieve its objective is: a composite electrode for an all-vanadium redox flow battery and its preparation method, wherein the preparation method of the composite electrode comprises the following steps:

[0005] S1. The aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is placed at a temperature of 55℃-65℃ for cross-linking and concentration until the aqueous dispersion of graphene oxide is concentrated to 38-42 mg / g to obtain the printing base material.

[0006] S2. Take printing base material, vitamin C and conductive carbon black with a mass ratio of 45-50:1.8-2:0.9-1 and stir them thoroughly to obtain printing ink raw material. Then transfer the printing ink raw material to the syringe of the 3D printer and put the syringe into a centrifuge for centrifugation to remove air bubbles from the syringe.

[0007] S3. Insert the syringe containing printing ink into the 3D printer for 3D printing to obtain a 3D printed electrode. The 3D printing parameters are as follows: the printed shape is a square of 3-3.5cm × 3-3.5cm, the printing line width is 1.08-1.25mm, the printing path is a serpentine line with an interval of 2.5-3mm, the number of printing layers is 3-5, the printing height of each layer is 0.7-1.2mm, the printing speed is 3-7mm / s, and the printing air pressure is 15-30psi.

[0008] S4. Freeze the 3D printed electrode at -50 to -48℃ for 9 to 10 hours, then vacuum dry the 3D printed electrode for 30 to 35 hours in a stepwise heating method within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. Then place the freeze-dried electrode at 90℃ to 95℃ for 2 to 3 hours. After heating, allow it to cool naturally to room temperature. Wash the electrode with a large amount of deionized water until the pH of the washing liquid is neutral. Then vacuum dry the washed electrode to obtain graphene-conductive carbon black composite aerogel.

[0009] S5. Place the graphene-conductive carbon black composite aerogel into a tube furnace and heat it at 300℃~900℃ for 1.5~2.5h in an argon atmosphere. Remove it and cool it to room temperature to obtain the graphene aerogel-conductive carbon black composite electrode.

[0010] Furthermore, in step S1 of the present invention, the aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is subjected to crosslinking and concentration at a temperature of 60°C.

[0011] Furthermore, in step S2 of the present invention, the mass ratio of printing base material, vitamin C and conductive carbon black in the printing ink raw material is 50:2:1.

[0012] Furthermore, in step S3 of the present invention, the 3D printed graphic is a 3cm×3cm square, the printed line width is 1.24mm, the printed path is a serpentine line with a 3mm interval, and the number of printed layers is 4.

[0013] Furthermore, the 3D printing speed in step S3 of the present invention is 4-5 mm / s, and the printing air pressure is 20-25 psi.

[0014] Furthermore, in step S4 of the present invention, a stepped heating method is used to vacuum dry the 3D printed electrode for 30 to 35 hours within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. The specific operation is as follows: drying at -40℃ to -33℃ for 3 hours, drying at -25℃ to -23℃ for 2 hours, drying at -20℃ to -18℃ for 3 hours, drying at -10℃ to -8℃ for 2 hours, drying at -5℃ to -3℃ for 3 hours, drying at 0℃ to 2℃ for 3 hours, drying at 5℃ to 7℃ for 2 hours, drying at 10℃ to 12℃ for 3 hours, drying at 15℃ to 17℃ for 3 hours, drying at 25℃ to 27℃ for 3 hours, and drying at 33℃ to 37℃ for 3 hours.

[0015] Stepwise heating can reduce the shrinkage ratio of the aerogel electrode and prevent excessive shrinkage of the aerogel due to rapid heating. When drying at the above temperatures, each temperature is maintained for a certain period of time to ensure that the electrode is fully dried and forms a porous aerogel. The small difference between each temperature can reduce the shrinkage rate of the aerogel electrode during the drying process.

[0016] Furthermore, in step S4 of the present invention, the 3D printed electrode is frozen at -50°C for 10 hours, and then vacuum dried for 30 to 35 hours in a stepwise heating method within the temperature range of -40°C to -30°C to 33°C to 37°C. Then, the freeze-dried electrode is placed at 95°C for 2 hours, and after heating, it is naturally cooled to room temperature.

[0017] Furthermore, in step S4 of the present invention, the vacuum drying process of the washed electrode is carried out at a temperature of 35°C for a time of 12 hours.

[0018] Furthermore, in step S5 of the present invention, the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 900°C for 2 to 2.1 hours under an argon atmosphere.

[0019] The reaction mechanism of each step in this invention is as follows:

[0020] Step S1 involves heating and concentrating an aqueous solution of graphene oxide to induce esterification of the carboxyl and hydroxyl groups on the graphene oxide surface, forming self-crosslinks and giving the printing substrate a certain viscosity, thus obtaining a composite printing substrate. Step S4, after printing, uses a gradually increasing temperature freeze-drying technique to remove moisture from the printing electrode, forming an aerogel. The electrode is then placed at 90℃~95℃ for 2~3 hours, and after heating, it is naturally cooled to room temperature to fully reduce the graphene oxide. The electrode is then washed with a large amount of deionized water to remove water-soluble impurities after the reaction until the pH of the washing liquid is neutral. Finally, the washed electrode is vacuum dried to obtain a graphene-conductive carbon black composite aerogel. In step S5, the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 300℃~900℃ for 1.5~2.5h under an argon atmosphere to carry out thermal reduction carbonization treatment, further removing oxygen-containing functional groups to enhance the conductivity and carbon content of the electrode. After cooling to room temperature, the graphene aerogel-conductive carbon black composite electrode is obtained.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention first concentrates the aqueous solution of graphene oxide through a water bath, causing esterification of the carboxyl and hydroxyl groups on the graphene oxide surface, forming self-crosslinks. Vitamin C mainly reduces the epoxy functional groups and hydroxyl groups on the graphene oxide surface. Therefore, concentrating the aqueous solution of graphene oxide through a water bath reduces the degree of reduction of graphene oxide by vitamin C before printing, thereby reducing the impact of the added vitamin C reducing agent on printing. In addition, this invention adds a certain amount of conductive carbon black to the printing raw material, which can greatly enhance the conductivity of the electrode. In summary, this invention uses DIW extrusion ink and freeze-drying technology to prepare composite electrodes, reduces the electrode by reducing it with vitamin C, improves the yield of electrode preparation, and enhances the redox capability of the electrode through high-temperature heat treatment reduction and doping with conductive carbon black, reducing the electrode resistivity and increasing the electrode conductivity, thereby improving the performance of the composite electrode in vanadium redox flow batteries and improving the energy efficiency of the battery.

[0023] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the printing path of the 3D printed electrode in step S3 of an embodiment of the present invention.

[0025] Figure 2 The XPS full spectrum of the graphene aerogel-conductive carbon black composite electrodes of Examples 1-4 of this invention is shown.

[0026] Figure 3This is a schematic diagram showing the carbon and oxygen content of the graphene aerogel-conductive carbon black composite electrodes in Examples 1-4 of the present invention.

[0027] Figure 4 This is a schematic diagram showing the conductivity and resistivity of the graphene aerogel-conductive carbon black composite electrode in Examples 1-4 of the present invention. Detailed Implementation

[0028] Example

[0029] A composite electrode for an all-vanadium redox flow battery and its preparation method are disclosed. The preparation steps of the composite electrode are as follows:

[0030] S1. The aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is placed at a temperature of 55℃-65℃ for cross-linking and concentration until the aqueous dispersion of graphene oxide is concentrated to 38-42 mg / g to obtain the printing base material.

[0031] S2. Take printing base material, vitamin C and conductive carbon black with a mass ratio of 45-50:1.8-2:0.9-1 and stir them thoroughly to obtain printing ink raw material. Then transfer the printing ink raw material to the syringe of the 3D printer and put the syringe into a centrifuge for centrifugation to remove air bubbles from the syringe.

[0032] S3. Insert the syringe containing printing ink into the 3D printer for 3D printing to obtain a 3D printed electrode. The 3D printing parameters are as follows: the printed shape is a square of 3-3.5cm × 3-3.5cm; the line width is 1.08-1.25mm; the printing path is a serpentine line with intervals of 2.5-3mm; the number of printing layers is 3-5; the height of each layer is 0.7-1.2mm; the printing speed is 3-7mm / s; and the printing air pressure is 15-30psi. A schematic diagram of the printing path is shown below. Figure 1 As shown; Figure 1 In the image, (a) shows the printing path for odd-numbered layers, and (b) shows the printing path for even-numbered layers.

[0033] S4. Freeze the 3D printed electrode at -50 to -48℃ for 9 to 10 hours, then vacuum dry the 3D printed electrode for 30 to 35 hours in a stepwise heating method within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. Then place the freeze-dried electrode at 90℃ to 95℃ for 2 to 3 hours. After heating, allow it to cool naturally to room temperature. Wash the electrode with a large amount of deionized water until the pH of the washing liquid is neutral. Then vacuum dry the washed electrode to obtain graphene-conductive carbon black composite aerogel.

[0034] S5. Place the graphene-conductive carbon black composite aerogel into a tube furnace and heat it at 300℃~900℃ for 1.5~2.5h in an argon atmosphere. Remove it and cool it to room temperature to obtain the graphene aerogel-conductive carbon black composite electrode.

[0035] Preferably, in step S1, the aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is subjected to crosslinking and concentration at a temperature of 60°C.

[0036] Preferably, in step S2, the mass ratio of printing base material, vitamin C, and conductive carbon black in the printing ink raw material is 50:2:1.

[0037] Preferably, the 3D printed graphic in step S3 is a 3cm×3cm square, the printed line width is 1.24mm, the printed path is a serpentine line with a 3mm interval, and the number of printed layers is 4.

[0038] Preferably, the 3D printing speed in step S3 is 4-5 mm / s, and the printing air pressure is 20-25 psi.

[0039] Preferably, in step S4, a stepped heating method is used to vacuum dry the 3D printed electrode for 30 to 35 hours within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. The specific operation is as follows: drying at -40℃ to -33℃ for 3 hours, drying at -25℃ to -23℃ for 2 hours, drying at -20℃ to -18℃ for 3 hours, drying at -10℃ to -8℃ for 2 hours, drying at -5℃ to -3℃ for 3 hours, drying at 0℃ to 2℃ for 3 hours, drying at 5℃ to 7℃ for 2 hours, drying at 10℃ to 12℃ for 3 hours, drying at 15℃ to 17℃ for 3 hours, drying at 25℃ to 27℃ for 3 hours, and drying at 33℃ to 37℃ for 3 hours.

[0040] Preferably, in step S4, the 3D printed electrode is frozen at -50°C for 10 hours, and then vacuum dried for 30 to 35 hours in a stepwise heating method within the temperature range of -40°C to -30°C to 33°C to 37°C. Then, the freeze-dried electrode is placed at 95°C for 2 hours, and after heating, it is naturally cooled to room temperature.

[0041] Preferably, in step S4, the vacuum drying process of the washed electrode is carried out at a temperature of 35°C for 12 hours.

[0042] Preferably, in step S5, the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 900°C for 2–2.1 h in an argon atmosphere.

[0043] Example 1

[0044] A composite electrode for an all-vanadium redox flow battery and its preparation method are disclosed. The preparation steps of the composite electrode are as follows:

[0045] S1. The aqueous dispersion of graphene oxide with a concentration of 20 mg / g was placed at 60°C for crosslinking and concentration until the aqueous dispersion of graphene oxide was concentrated to 40 mg / g to obtain the printing base material.

[0046] S2. Take printing base material, vitamin C and conductive carbon black with a mass ratio of 45:1.8:0.9 and stir them thoroughly to obtain printing ink material. Then transfer the printing ink material to the syringe of the 3D printer and put the syringe into a centrifuge for centrifugation to remove air bubbles from the syringe.

[0047] S3. Insert the syringe containing printing ink into the 3D printer to perform 3D printing and obtain a 3D printed electrode. The 3D printing parameters are as follows: the printed shape is a 3cm×3cm square, the printing line width is 1.24mm, the printing path is a serpentine line with a 3mm interval, the number of printing layers is 3 to 5, the printing height of each layer is 1mm, the printing speed is 5mm / s, and the printing air pressure is 20psi.

[0048] S4. Freeze the 3D printed electrode at -50℃ for 10 hours, then use a step heating method to vacuum dry the 3D printed electrode for 35 hours in the temperature range of -35℃ to 37℃. Then place the freeze-dried electrode at 95℃ for 2 hours. After heating, allow it to cool naturally to room temperature. Wash the electrode with a large amount of deionized water until the pH of the washing liquid is neutral. Then vacuum dry the washed electrode at 35℃ for 12 hours to obtain graphene-conductive carbon black composite aerogel.

[0049] S5. The graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 900°C for 2 hours under an argon atmosphere. It is then removed and cooled to room temperature to obtain the graphene aerogel-conductive carbon black composite electrode. The composite electrode prepared in this embodiment is denoted as V-rGO+P900.

[0050] In step S4 of this example, a stepped heating method is used to vacuum dry the 3D printed electrode for 35 hours within the temperature range of -35℃ to 37℃. The specific operation is as follows: dry for 3 hours at -35℃ to -33℃, dry for 2 hours at -25℃ to -23℃, dry for 3 hours at -20℃ to -18℃, dry for 2 hours at -10℃ to -8℃, dry for 3 hours at -5℃ to -3℃, dry for 3 hours at 0℃ to 2℃, dry for 2 hours at 5℃ to 7℃, dry for 3 hours at 10℃ to 12℃, dry for 3 hours at 15℃ to 17℃, dry for 3 hours at 25℃ to 27℃, and dry for 3 hours at 33℃ to 37℃.

[0051] Example 2

[0052] This embodiment is basically the same as Embodiment 1, except for step S5 of the preparation process. Step S5 in this embodiment is as follows: the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 700°C for 2 hours under an argon atmosphere. After cooling to room temperature, the graphene aerogel-conductive carbon black composite electrode is obtained. The composite electrode prepared in this embodiment is denoted as V-rGO+P700.

[0053] Example 3

[0054] This embodiment is basically the same as Embodiment 1, except for step S5 of the preparation process. Step S5 in this embodiment is as follows: the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 500°C for 2 hours under an argon atmosphere. After being removed and cooled to room temperature, the graphene aerogel-conductive carbon black composite electrode is obtained. The composite electrode prepared in this embodiment is denoted as V-rGO+P500.

[0055] Example 4

[0056] This embodiment is basically the same as Embodiment 1, except for step S5 of the preparation process. Step S5 in this embodiment is as follows: the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 300°C for 2 hours under an argon atmosphere. After being removed and cooled to room temperature, the graphene aerogel-conductive carbon black composite electrode is obtained. The composite electrode prepared in this embodiment is denoted as V-rGO+P300.

[0057] The X-ray photoelectron spectra of the graphene aerogel-conductive carbon black composite electrodes of Examples 1, 2, 3, and 4 were detected using an X-ray photoelectron spectrometer. The composite electrodes of each example were used as samples and tested in a vacuum environment at room temperature. Figure 2 The figures show the XPS full spectrum of the graphene aerogel-conductive carbon black composite electrodes of Examples 1-4. The two peaks in the figures correspond to C (~285 eV) and O (~532 eV), respectively. As can be seen from the figures, the graphene aerogel-conductive carbon black composite electrodes of this invention have obvious C and O peaks. The O peak of the composite electrode heat-treated at 900℃ is significantly reduced, indicating that the composite electrode heat-treated at 900℃ has a lower oxygen content. Figure 3 This diagram illustrates the carbon and oxygen content of the graphene aerogel-conductive carbon black composite electrodes in Examples 1-4. As can be seen from the diagram, the graphene aerogel-conductive carbon black composite electrodes of this invention have a lower oxygen content and a higher carbon content. Specifically, the composite electrode heat-treated at 900℃ exhibits a significantly lower oxygen content and a significantly higher carbon content, indicating that the composite electrode heat-treated at 900℃ has a higher carbon-to-oxygen ratio.

[0058] The conductivity and resistivity of the graphene aerogel-conductive carbon black composite electrodes of Examples 1, 2, 3, and 4 were tested on a four-probe testing system. The composite electrodes of each example were used as samples, and the test temperature was room temperature. Figure 4 This diagram illustrates the conductivity and resistivity of the graphene aerogel-conductive carbon black composite electrodes in Examples 1-4 of this invention. As can be seen from the diagram, the graphene aerogel-conductive carbon black composite electrodes of this invention exhibit low resistivity and high conductivity. Specifically, the resistivity of the composite electrode heat-treated at 900℃ decreases significantly, while the conductivity increases significantly, indicating that the composite electrode heat-treated at 900℃ has higher conductivity.

Claims

1. A method for preparing a composite electrode for an all-vanadium redox flow battery, characterized in that, Includes the following steps: S1. The aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is placed at a temperature of 55℃-65℃ for cross-linking and concentration until the aqueous dispersion of graphene oxide is concentrated to 38-42 mg / g to obtain the printing base material. S2. Take printing base material, vitamin C and conductive carbon black with a mass ratio of 45-50:1.8-2:0.9-1 and stir them thoroughly to obtain printing ink material. Then transfer the printing ink material to the syringe of the 3D printer and put the syringe into a centrifuge for centrifugation to remove air bubbles from the syringe. S3. Insert the syringe containing printing ink into the 3D printer for 3D printing to obtain a 3D printed electrode. The 3D printing parameters are as follows: the printed shape is a square of 3-3.5cm × 3-3.5cm, the printing line width is 1.08-1.25mm, the printing path is a serpentine line with an interval of 2.5-3mm, the number of printing layers is 3-5, the printing height of each layer is 0.7-1.2mm, the printing speed is 3-7mm / s, and the printing air pressure is 15-30psi. S4. Freeze the 3D printed electrode at -50 to -48℃ for 9 to 10 hours, then vacuum dry the 3D printed electrode for 30 to 35 hours in a stepwise heating method within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. Then place the freeze-dried electrode at 90℃ to 95℃ for 2 to 3 hours. After heating, allow it to cool naturally to room temperature. Wash the electrode with a large amount of deionized water until the pH of the washing liquid is neutral. Then vacuum dry the washed electrode to obtain graphene-conductive carbon black composite aerogel. S5. Place the graphene-conductive carbon black composite aerogel into a tube furnace and heat it at 300℃~900℃ for 1.5~2.5h in an argon atmosphere. Remove it and cool it to room temperature to obtain the graphene aerogel-conductive carbon black composite electrode.

2. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S1, the aqueous dispersion of graphene oxide with a concentration of 15-20 mg / g is subjected to crosslinking and concentration at 60°C.

3. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S2, the mass ratio of printing base material, vitamin C, and conductive carbon black in the printing ink raw material is 50:2:

1.

4. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: The 3D printed graphic in step S3 is a 3cm×3cm square, the printed line width is 1.24mm, the printed path is a serpentine line with a 3mm interval, and the number of printed layers is 4.

5. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: The 3D printing speed in step S3 is 4-5 mm / s, and the printing air pressure is 20-25 psi.

6. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S4, a stepped heating method is used to vacuum dry the 3D printed electrode for 30 to 35 hours within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. The specific operation is as follows: dry for 3 hours at -40℃ to -33℃, dry for 2 hours at -25℃ to -23℃, dry for 3 hours at -20℃ to -18℃, dry for 2 hours at -10℃ to -8℃, dry for 3 hours at -5℃ to -3℃, dry for 3 hours at 0℃ to 2℃, dry for 2 hours at 5℃ to 7℃, dry for 3 hours at 10℃ to 12℃, dry for 3 hours at 15℃ to 17℃, dry for 3 hours at 25℃ to 27℃, and dry for 3 hours at 33℃ to 37℃.

7. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S4, the 3D printed electrode is frozen at -50℃ for 10 hours, and then vacuum dried for 30 to 35 hours in a stepped heating method within the temperature range of -40℃ to -30℃ to 33℃ to 37℃. Then, the freeze-dried electrode is placed at 95℃ for 2 hours, and after heating, it is naturally cooled to room temperature.

8. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S4, the washed electrode is vacuum dried at a temperature of 35°C for 12 hours.

9. The method for preparing a composite electrode for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S5, the graphene-conductive carbon black composite aerogel is placed in a tube furnace and heated at 900°C for 2–2.1 h in an argon atmosphere.

10. A composite electrode for an all-vanadium redox flow battery, characterized in that: The composite electrode is prepared by any one of the preparation methods according to claims 1-9.

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