A method for preparing a graphene-transition metal oxide composite electrode material by using plasma

Abstract

The application belongs to the technical field of electrode material preparation, and particularly relates to a method for preparing a graphene-transition metal oxide composite electrode material by using plasma. The application adopts supercritical CO2 and microwave-assisted preparation of bio-based GO, and carries out deposition of transition metal oxides through a plasma reactor. High energy of the plasma can pre-activate metal organic salt, so that the metal organic salt is more easily reacted and deposited on the surface of graphene, and uniform loading of the transition metal oxides on the surface of graphene is realized. In addition, the plasma treatment process is short in time, low in energy consumption and high in preparation efficiency. The graphene-transition metal oxide composite electrode material prepared through the method of the application has a large specific surface area and good electrical conductivity, and good interface contact is formed between the transition metal oxides and the graphene, which is beneficial to the transmission of electrons and ions, so that the graphene-transition metal oxide composite electrode material has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of electrode material preparation technology, specifically relating to a method for preparing graphene-transition metal oxide composite electrode materials using plasma. Background Technology

[0002] Against the backdrop of the global energy structure's accelerated transition to clean energy, electrochemical energy storage devices such as supercapacitors and lithium-ion batteries are becoming increasingly crucial in fields such as smart grids and electric vehicles due to their advantages such as high power density and long cycle life. Electrode materials, as the core components of energy storage devices, directly determine the energy storage and release efficiency of the devices. Graphene-transition metal oxide composite electrode materials, with the excellent conductivity and high specific surface area of ​​graphene and the abundant redox active sites of transition metal oxides, have shown enormous application potential and have become a research focus in the field of materials science in recent years.

[0003] However, traditional methods for preparing graphene-transition metal oxide composite electrode materials face numerous unresolved issues. In the graphene oxide preparation stage, the commonly used Hummers method requires the use of strong oxidizing chemical reagents such as concentrated sulfuric acid and potassium permanganate, posing not only safety risks but also generating large amounts of highly acidic wastewater containing heavy metal ions such as manganese, resulting in high treatment costs and environmental risks. Furthermore, this method is time-consuming, and the degree of oxidation is difficult to control, easily leading to the destruction of the graphene sheet structure and affecting material performance.

[0004] In the composite process, common methods such as hydrothermal synthesis and sol-gel synthesis often fail to achieve uniform loading of transition metal oxides on the graphene surface, leading to particle agglomeration. This reduces active sites, hinders electron transport, and consequently degrades the electrochemical performance of the composite material. Furthermore, these methods often require high-temperature, high-pressure conditions or lengthy reaction processes, resulting in high energy consumption and low efficiency, which is unfavorable for large-scale industrial production. Summary of the Invention

[0005] The purpose of this invention is to address existing problems by providing a method for preparing graphene-transition metal oxide composite electrode materials using plasma.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing graphene-transition metal oxide composite electrode materials using plasma includes the following steps:

[0008] S1. Mix natural graphite with a bio-based oxidant and add it to a supercritical CO2 reactor. Introduce CO2 to form a supercritical CO2 fluid. Start the microwave-assisted system to react. After the reaction is completed, separate the CO2 by depressurization and recycle it to obtain a solid product. Disperse the solid product in deionized water by ultrasound to form a uniform suspension. After centrifugation, dialysis and purification (molecular weight cutoff of 8000~14000 Da) until neutral. Freeze-dry to obtain bio-based GO.

[0009] S2. The bio-based GO obtained in step S1 is ultrasonically dispersed in deionized water to form a dispersion. The dispersion is uniformly loaded onto the substrate. After loading is completed, the substrate is dried and then placed in the deposition zone of the plasma reactor.

[0010] S3. Dissolve the transition metal salt in supercritical CO2 to obtain a precursor solution. The precursor solution is then transported to an ultrasonic atomizer and ultrasonically atomized to obtain aerosol particles. These particles are then transported to the plasma reactor via a carrier gas.

[0011] S4. In the reactor inlet area, radio frequency plasma is applied to preactivate the organometallic salt, and then it enters the deposition zone through the carrier gas for deposition treatment.

[0012] S5. After deposition, the substrate is removed from the plasma reactor and placed in a muffle furnace for annealing to obtain the graphene-transition metal oxide composite electrode material.

[0013] Furthermore, the bio-based oxidant mentioned in step S1 is phytic acid, and the mass ratio of natural graphite to bio-based oxidant is 1:(3.5~4.5).

[0014] Furthermore, in step S1, the microwave power is set to 400-500W and the reaction time is 40-50 minutes when the microwave-assisted system is started.

[0015] Furthermore, the centrifugation speed in step S1 is 8000~9000 r / min, and the centrifugation time is 30~40 min;

[0016] The freeze-drying temperature is -50 to -30℃, and the freeze-drying time is 30 to 40 hours.

[0017] Furthermore, the concentration of the dispersion in step S2 is 2~4 mg / mL;

[0018] The substrate is carbon cloth, nickel foam, or titanium sheet;

[0019] The loading capacity is 0.4~0.7 mg / cm³. 2 .

[0020] Furthermore, the drying temperature in step S2 is controlled at 60~70℃, and the drying time is 16~26h.

[0021] Furthermore, the transition metal salt mentioned in step S3 is any one of manganese acetate, cobalt nitrate, and nickel sulfate;

[0022] During ultrasonic atomization, the frequency of the ultrasonic atomizer is controlled at 1~3MHz, the atomization time is 6~9min, and the particle size of the aerosol particles formed is 200~400nm.

[0023] The carrier gas is Ar, and the flow rate is 100 sccm.

[0024] Furthermore, in step S4, the applied power of the radio frequency plasma is 50~150W, the frequency is 13.56MHz, and the residence time of the aerosol during pre-activation is controlled to be 0.2~0.5s;

[0025] The carrier gas is Ar;

[0026] During the deposition process, the temperature inside the reactor is maintained at room temperature to 80°C, and the pressure is 10~100Pa;

[0027] Furthermore, the annealing temperature in step S5 is 400~500℃, the annealing time is 2~3h, and the heating rate is 6~8℃ / min.

[0028] The present invention has the following advantages over the prior art:

[0029] This invention utilizes supercritical CO2 and microwave-assisted preparation of bio-based graphene oxide (GO). Supercritical CO2 possesses excellent solubility and diffusion properties, enabling uniform contact between phytic acid and natural graphite. Microwave assistance accelerates the reaction rate and improves oxidation efficiency. Furthermore, this process is environmentally friendly and safe as it does not use toxic or harmful chemical reagents. Transition metal oxides are deposited using a plasma reactor. The high energy of the plasma pre-activates the organometallic salts, facilitating their reaction and deposition on the graphene surface, achieving uniform loading of transition metal oxides. In addition, the plasma treatment process is short, energy-efficient, and highly efficient. The graphene-transition metal oxide composite electrode material ultimately prepared by this method possesses a large specific surface area and good conductivity. The transition metal oxides and graphene form a good interfacial contact, which is beneficial for electron and ion transport, resulting in excellent electrochemical performance. Detailed Implementation

[0030] To further explain the present invention, the following specific embodiments are described.

[0031] Example 1

[0032] A method for preparing graphene-transition metal oxide composite electrode materials using plasma includes the following steps:

[0033] S1. Natural graphite and phytic acid were mixed at a mass ratio of 1:3.5 and added to a supercritical CO2 reactor. CO2 was introduced to form a supercritical CO2 fluid. The microwave-assisted system was started, and the microwave power was set to 400W. The reaction time was 40min. After the reaction, CO2 was separated by depressurization and recycled to obtain a solid product. The solid product was ultrasonically dispersed in deionized water to form a uniform suspension. After centrifugation at 8000r / min for 30min, the suspension was purified by dialyzing (molecular weight cutoff of 8000Da) until neutral. The suspension was then freeze-dried at -50℃ for 30h to obtain bio-based GO.

[0034] S2. The bio-based GO obtained in step S1 is ultrasonically dispersed in deionized water to form a dispersion with a concentration of 2 mg / mL. The dispersion is then uniformly loaded onto a carbon cloth substrate at a loading rate of 0.4 mg / mL. 2 After loading is completed, the substrate is dried at 60°C for 16 hours, and then placed in the deposition zone of the plasma reactor.

[0035] S3. Dissolve manganese acetate in supercritical CO2 to obtain a precursor solution. The precursor solution is then transported to an ultrasonic atomizer. The frequency of the ultrasonic atomizer is controlled at 1MHz and the atomization time is 6min. The resulting aerosol particles have a particle size of 200nm. The aerosol is then transported to the plasma reactor via Ar carrier gas (flow rate of 100sccm).

[0036] S4. In the reactor inlet area, radio frequency plasma is applied to preactivate the organometallic salt. The applied power is 50W and the frequency is 13.56MHz. During preactivation, the residence time of the aerosol is controlled to be 0.2s. Then, it enters the deposition zone through the carrier gas for deposition treatment.

[0037] During the deposition process, the temperature inside the reactor is maintained between room temperature and 80°C, and the pressure is 10 Pa.

[0038] S5. After deposition, the substrate is removed from the plasma reactor and placed in a muffle furnace for annealing. The annealing temperature is 400℃, the annealing time is 2h, and the heating rate is 6℃ / min to obtain the graphene-transition metal oxide composite electrode material.

[0039] Example 2

[0040] A method for preparing graphene-transition metal oxide composite electrode materials using plasma includes the following steps:

[0041] S1. Natural graphite and phytic acid were mixed in a mass ratio of 1:4 and added to a supercritical CO2 reactor. CO2 was introduced to form a supercritical CO2 fluid. The microwave-assisted system was started, and the microwave power was set to 450W. The reaction time was 45min. After the reaction, CO2 was separated by depressurization and recycled to obtain a solid product. The solid product was ultrasonically dispersed in deionized water to form a uniform suspension. After centrifugation at 8500r / min for 35min, it was purified by dialyzing (molecular weight cutoff of 10000Da) until neutral. It was then freeze-dried at -40℃ for 35h to obtain bio-based GO.

[0042] S2. The bio-based GO obtained in step S1 is ultrasonically dispersed in deionized water to form a dispersion with a concentration of 3 mg / mL. The dispersion is then uniformly loaded onto a carbon cloth substrate at a loading rate of 0.5 mg / mL. 2 After loading is completed, the substrate is dried at 65°C for 21 hours, and then placed in the deposition zone of the plasma reactor.

[0043] S3. Dissolve manganese acetate in supercritical CO2 to obtain a precursor solution. The precursor solution is then transported to an ultrasonic nebulizer. The frequency of the ultrasonic nebulizer is controlled at 2MHz and the atomization time is 7.5min. The resulting aerosol particles have a particle size of 300nm. The aerosol is then transported to the plasma reactor via Ar carrier gas (flow rate of 100sccm).

[0044] S4. In the reactor inlet area, radio frequency plasma is applied to preactivate the organometallic salt. The applied power is 100W and the frequency is 13.56MHz. During preactivation, the residence time of the aerosol is controlled to be 0.4s. Then, it enters the deposition zone through the carrier gas for deposition treatment.

[0045] During the deposition process, the temperature inside the reactor is maintained between room temperature and 80°C, and the pressure is 50 Pa.

[0046] S5. After deposition, the substrate is removed from the plasma reactor and placed in a muffle furnace for annealing. The annealing temperature is 450℃, the annealing time is 2.5h, and the heating rate is 7℃ / min to obtain the graphene-transition metal oxide composite electrode material.

[0047] Example 3

[0048] A method for preparing graphene-transition metal oxide composite electrode materials using plasma includes the following steps:

[0049] S1. Natural graphite and phytic acid were mixed at a mass ratio of 1:4.5 and added to a supercritical CO2 reactor. CO2 was introduced to form a supercritical CO2 fluid. The microwave-assisted system was started, the microwave power was set to 500W, and the reaction time was 50min. After the reaction, CO2 was separated by depressurization and recycled to obtain a solid product. The solid product was ultrasonically dispersed in deionized water to form a uniform suspension. After centrifugation at 9000r / min for 40min, it was purified by dialyzing (molecular weight cutoff of 14000Da) to neutrality and freeze-dried at -30℃ for 40h to obtain bio-based GO.

[0050] S2. The bio-based GO obtained in step S1 is ultrasonically dispersed in deionized water to form a dispersion with a concentration of 4 mg / mL. The dispersion is then uniformly loaded onto a carbon cloth substrate at a loading rate of 0.7 mg / mL. 2 After loading is completed, the substrate is dried at 70°C for 26 hours, and then placed in the deposition zone of the plasma reactor.

[0051] S3. Dissolve manganese acetate in supercritical CO2 to obtain a precursor solution. The precursor solution is then transported to an ultrasonic atomizer. The frequency of the ultrasonic atomizer is controlled at 3MHz and the atomization time is 9min. The resulting aerosol particles have a particle size of 400nm. The aerosol is then transported to the plasma reactor via Ar carrier gas (flow rate of 100sccm).

[0052] S4. In the reactor inlet area, radio frequency plasma is applied to preactivate the organometallic salt. The applied power is 150W and the frequency is 13.56MHz. During preactivation, the residence time of the aerosol is controlled to be 0.5s. Then, it enters the deposition zone through the carrier gas for deposition treatment.

[0053] During the deposition process, the temperature inside the reactor is maintained between room temperature and 80°C, and the pressure is 100 Pa.

[0054] S5. After deposition, the substrate is removed from the plasma reactor and placed in a muffle furnace for annealing. The annealing temperature is 500℃, the annealing time is 3h, and the heating rate is 8℃ / min to obtain the graphene-transition metal oxide composite electrode material.

[0055] Comparative Example 1

[0056] Compared with Example 2, Comparative Example 1 omits the microwave processing in step S1, while the other steps are the same as in Example 2.

[0057] Comparative Example 2

[0058] Compared with Example 2, Comparative Example 2 omits the pre-activation treatment in step S4, while the other steps are the same as in Example 2.

[0059] Comparative Example 3

[0060] Comparative Example 3 uses a traditional solution mixing method to prepare graphene-transition metal oxide composite electrode materials, specifically as follows:

[0061] (1) Dissolve phytic acid in 100 mL of deionized water, then add natural graphite. The mass ratio of natural graphite to phytic acid is 1:3.5. Stir to form a uniform suspension.

[0062] (2) Transfer the suspension to a three-necked flask, heat and stir in an oil bath at 90°C under nitrogen protection for 20 h at 600 r / min. After the reaction is complete, cool naturally to room temperature, wash with deionized water by centrifugation until neutral, disperse the washed GO precipitate in 50 mL of deionized water, and sonicate for 30 min to obtain a GO suspension with a concentration of 10 mg / mL.

[0063] (3) Add manganese acetate to deionized water and stir to dissolve it. Then slowly drop the manganese acetate solution into the GO suspension. After the addition is complete, continue to sonicate so that manganese ions are uniformly adsorbed on the GO surface.

[0064] (4) Collect the precipitate by filtration of the mixture through a Buchner funnel, wash the precipitate alternately with 95% ethanol and deionized water, test the washing solution with silver nitrate solution, and if there is no white precipitate, it indicates that the residual ions have been washed away. Place the washed precipitate in a petri dish and dry it in a 70°C oven until it is completely dehydrated.

[0065] (5) Place the dried precursor powder into a tube furnace and anneal it under nitrogen protection. The annealing temperature is 450℃, the annealing time is 2.5h, and the heating rate is 7℃ / min.

[0066] Performance testing

[0067] 1. Specific capacitance test

[0068] A three-electrode system was used, with the prepared composite electrode material as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet electrode as the counter electrode. A 6 mol / L KOH solution was selected as the electrolyte. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were performed using an electrochemical workstation, and the specific capacitance was calculated based on the test results. The test results are shown in Table 1 below.

[0069] Table 1

[0070] Grouping Scan rate 5mV / s specific capacitance (F / g) Specific capacitance (F / g) at a scan rate of 100 mV / s Current density 1A / g specific capacitance (F / g) Current density 20 A / g specific capacitance (F / g) Example 1 360 230 350 190 Example 2 380 250 400 220 Example 3 370 230 380 200 Comparative Example 1 350 220 350 180 Comparative Example 2 340 220 330 170 Comparative Example 3 300 180 300 150

[0071] As can be seen from Table 1 above, compared with the comparative examples, especially compared with comparative example 3, the specific capacitance of Examples 1 to 3 is significantly better than that of comparative example 3, indicating that the composite electrode material prepared by the method of the present invention has stronger charge storage capacity and better energy density in practical applications.

[0072] 2. Cyclic stability test

[0073] A constant current charge-discharge cycle test was conducted at a current density of 10 A / g, with 5000 cycles. The charge-discharge curve was recorded every 500 cycles, and the specific capacitance retention rate was calculated to evaluate the cycle stability of the material. The test results are shown in Table 2 below.

[0074] Table 2

[0075] Grouping Capacitance retention rate (%) after 5000 cycles Example 1 87 Example 2 90 Example 3 88 Comparative Example 1 85 Comparative Example 2 83 Comparative Example 3 76

[0076] As can be seen from Table 2 above, compared with the comparative example, the composite electrode material of the embodiment exhibits slower capacitance degradation during long-term cyclic use, has a longer service life and more stable electrochemical performance, and can reduce the frequency of replacement due to material performance degradation in practical applications, thereby reducing costs.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-transition metal oxide composite electrode material using plasma, characterized by, It comprises the following steps: S1, mixing natural graphite with bio-based oxidant, adding supercritical CO2 reactor, starting microwave auxiliary system reaction, after reaction, obtaining solid product by reducing pressure, dispersing solid product into deionized water to form uniform suspension, centrifuging, purifying to neutral by dialysis, and freeze-drying to obtain bio-based GO; S2, ultrasonic dispersion of bio-based GO obtained in step S1 into deionized water to form dispersion liquid, uniformly loading dispersion liquid onto substrate, drying after loading, and then placing substrate in deposition area of plasma reactor; S3, dissolving transition metal salt in supercritical CO2 to obtain precursor solution, ultrasonic atomization to obtain aerosol particles, and transporting to plasma reactor by carrier gas; S4, applying radio frequency plasma at inlet area of reactor to pre-activate transition metal salt, and then entering deposition area by carrier gas to perform deposition treatment; S5, after deposition, taking substrate out of plasma reactor and placing it in muffle furnace for annealing treatment.

2. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The bio-based oxidant in step S1 is phytic acid, and the mass ratio of natural graphite to bio-based oxidant is 1:(3.5-4.5).

3. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The microwave power is set to 400-500 W when starting microwave auxiliary system reaction in step S1, and the reaction time is 40-50 min.

4. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The centrifugal speed in step S1 is 8000-9000 r / min, and the centrifugal time is 30-40 min. The freeze-drying temperature is-50--30℃, and the freeze-drying time is 30-40 h.

5. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The concentration of the dispersion liquid in step S2 is 2-4 mg / mL. The substrate is carbon cloth, foam nickel or titanium sheet. Load amount: 0.4-0.7 mg / cm2 2 .

6. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The drying temperature in step S2 is controlled to 60-70℃, and the drying time is 16-26 h.

7. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The transition metal salt in step S3 is any one of manganese acetate, cobalt nitrate and nickel sulfate. The frequency of the ultrasonic atomizer is controlled to 1-3 MHz during ultrasonic atomization, the atomization time is 6-9 min, and the particle size of the aerosol particles formed is 200-400 nm. The carrier gas is Ar, and the flow rate is 100 sccm.

8. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The applied power of the radio frequency plasma in step S4 is 50-150 W, the frequency is 13.56 MHz, and the residence time of the aerosol during pre-activation is controlled to 0.2-0.5 s. The carrier gas is Ar. During the deposition process, the temperature in the reactor is maintained at room temperature to 80℃, and the pressure is 10-100 Pa.

9. The method for preparing graphene-transition metal oxide composite electrode materials using plasma according to claim 1, characterized in that, The annealing temperature in step S5 is 400-500℃, the annealing time is 2-3 h, and the heating rate is 6-8℃ / min.