Method for preparing supercapacitor electrode through high-temperature alkali activation

Abstract

The invention discloses a method for preparing a supercapacitor electrode through high-temperature alkali activation. The method comprises the steps of preparing porous carbon, preparing an electrode plate, preparing a supercapacitor, and carrying out electrochemical performance testing and material characterization testing. When the carbon precursor of the supercapacitor electrode material is prepared, organic components in walnut shells can be refined and removed and biochar is left by utilizing the effect of removing organic matters in biomass at high temperature of a tubular furnace; the potassium hydroxide with different concentrations is used as the activating agent to activate the biochar, the porosity and the internal structure richness of the porous carbon can be greatly improved, and compared with traditional solid alkali activation, the aqueous solution alkali activation has the advantages that the reliability and the possibility are improved, and the contact area of the activating agent and substances is increased. The electrode material prepared by the method has the advantages of low manufacturing cost, small environmental pollution and excellent service life, and is an ideal electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode preparation, and in particular to a method for preparing supercapacitor electrodes by utilizing high-temperature alkali activation. Background Art

[0002] In recent years, rapid economic development and population growth have led to a growing demand for energy. Since fossil fuels are non-renewable and have limited reserves, developing and utilizing new clean energy sources is one of the effective solutions to the energy crisis. Energy storage and utilization are crucial issues that require urgent attention. Energy storage is the technology that uses specific devices or physical media to store various forms of energy for later use. Its development has a significant impact on the development of the new energy sector. Many countries, including the United States, Japan, and the European Union, recognized the importance of energy storage and developed it early, now holding a leading position internationally. Currently, my country's energy storage development is still in its early stages. While certain technologies and industrial chain mechanisms are in place, overall improvement is still needed, requiring greater investment in policy, economic, and technological areas.

[0003] Supercapacitors are ideal energy storage components, with a Lagung curve intermediate between traditional capacitors and batteries. They balance the shortcomings of traditional capacitors' low energy density with the low power density of batteries. To achieve high power density and cycle performance, most researchers use metals as a manufacturing source. However, metal reserves and environmental pollution are issues. Consequently, research on carbon-based materials has gained significant momentum.

[0004] At present, most studies use strong alkaline substances such as NaOH and KOH to etch materials to make them porous, but the porosity and pore size distribution of carbon materials prepared by this method are poor; the micromorphology and pore structure are in a small amount. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention designs a method for preparing supercapacitor electrodes using high-temperature alkaline activation.

[0006] In order to achieve the above technical effects, the present invention is implemented by the following technical solutions: A method for preparing supercapacitor electrodes by high-temperature alkaline activation, characterized in that it includes the following steps:

[0007] S1. Biomass treatment: Clean walnut shells were crushed into blocks using a hammer; ultrasonic treatment was performed in deionized water using frequencies of 25 kHz and 40 kHz for 10 minutes, with the frequency switched every 5 minutes for 5 or 6 times to remove surface dust and impurities; the ultrasonically treated walnut shells were placed in an oven, heated to 130° C., and then kept warm for 12 hours to obtain clean walnut shells;

[0008] S2. Preparation of porous carbon precursor: Select the clean walnut shells prepared in S1 and perform high-temperature carbonization. The walnut shells can be oxidized and removed by high temperature. The powdered biochar obtained after grinding, drying, and cooling is the porous carbon precursor.

[0009] S3. Preparation of pure porous carbon: Biochar material and activator KOH are taken in a certain ratio, and then the powdered biochar material and activator KOH are dispersed in deionized water in sequence and uniformly treated with ultrasound to prepare alkaline porous carbon, and the alkaline porous carbon is carbonized at high temperature and acid-washed with HCl solution until neutral, and then dried and cooled to obtain pure porous carbon;

[0010] S4. Preparing an electrode sheet with pure porous carbon: weighing pure porous carbon material, carbon black and polytetrafluoroethylene solution in a mass ratio of pure porous carbon material: carbon black: polytetrafluoroethylene solution = 75-150:20-40:5-10, and dispersing the porous carbon material, carbon black and polytetrafluoroethylene solution in the order of porous carbon material, carbon black and polytetrafluoroethylene solution into 10-20 mL of anhydrous ethanol, ultrasonically treating the mixture evenly, heating to evaporate the anhydrous ethanol, and stopping heating when the mixture becomes a paste; cutting the nickel foam into pieces of 1 cm*9 cm and washing and drying it, applying the paste to the front end of the nickel foam, and vacuum drying to obtain the electrode sheet;

[0011] S5. Conducting electrochemical performance testing on the prepared electrode sheet;

[0012] S6. Perform morphology characterization tests on the prepared pure porous carbon material.

[0013] Furthermore, in S2, a porous carbon precursor is prepared as follows:

[0014] S2.1. Weigh five 5g portions of clean walnut shells and place them in a porcelain boat. Using a push rod, place the boat in a tube furnace protected by a nitrogen atmosphere. Adjust the temperature of the tube furnace to 350°C at a heating rate of 5°C / min. Heat for 60 min, then cool naturally to obtain a carbonized product.

[0015] S2.2. The carbonized product is then placed in a grinder and ground into powder to obtain biochar.

[0016] Furthermore, in S3, pure porous carbon is prepared as follows:

[0017] S3.1. Weigh biochar powder and KOH in a mass ratio of biochar powder to KOH = 1:0, 1:1, 1:2, 1:3, and 1:4, and disperse the biochar powder and KOH into 40 mL of deionized water in the order of biochar powder → KOH. Ultrasonic treatment at a frequency of 25 kHz was performed for 30 min to ensure that the biochar powder and the activator were fully mixed. The solution was then dried in an oven at 130°C for 12 hours to remove excess water.

[0018] S3.2. Place the dried activated biochar powder into a porcelain boat and, under the action of a push rod, place the porcelain boat into a tube furnace protected by a nitrogen atmosphere. Heat it to 800°C at a heating rate of 5°C / min. Keep it at this temperature for 1 hour, then cool it naturally to room temperature and remove the product.

[0019] S3.3. The high-temperature calcined product was ground in a mortar and placed in a beaker. 40 mL of deionized water was added to the beaker and stirred for 10 minutes. An equal amount or an excess of 36% HCl solution was then added, depending on the KOH concentration. The solution was then ultrasonically treated at 40 kHz for 30 minutes to fully neutralize the acid and base solutions until the filtrate was neutral. The filtrate was then filtered using a sand-core filtration funnel with a 100 nm pore size polytetrafluoroethylene filter membrane and deionized water. This was repeated five times to obtain a black, powdery, granular substance.

[0020] S3.4. Transfer the powdered granular material into a beaker, place the beaker in an oven, and dry it at 130°C for 12 hours. Dry the solvent in the powdered granular material and gently stir to obtain a pure powdered porous carbon material.

[0021] Furthermore, in S4, preparing the electrode sheet includes the following steps:

[0022] S4.1. Wet a clean beaker with 5 ml of anhydrous ethanol, then add 20 ml of anhydrous ethanol, weigh 5 mg of carbon black, and sonicate for 10 minutes to disperse it evenly. Then, add 18.75 mg of pure porous carbon and sonicate for 10 minutes to disperse it evenly. Finally, add 1.25 mg of a 5% polytetrafluoroethylene solution and sonicate for 10 minutes to disperse it evenly. A black liquid is obtained.

[0023] S4.3. Heat the black liquid while stirring until it reaches 70°C, then maintain the temperature and continue stirring until the liquid becomes a black paste. Stop heating.

[0024] S4.3. Select nickel foam with a size of 1 cm*9 cm as the current collector; soak the nickel foam in anhydrous ethanol, ultrasonically clean it for 10 minutes, place it in an oven, and dry it at a temperature of 105-115°C for 10 hours to obtain a carrier;

[0025] S4.4. Use chamfered glass to evenly coat the black paste on the carrier without any obvious agglomeration or gaps. The coating position is at the front end of the carrier, and the coating area is a 1 cm*1 cm square. This yields an initial sheet.

[0026] S4.5. Place the coated initial sheet into a forced air drying oven at 780°C for 10 hours. After complete drying, the electrode sheet can be obtained.

[0027] Furthermore, in S5, the prepared electrode sheet is subjected to an electrochemical performance test, which specifically includes the following steps:

[0028] S5.1. Using an electrochemical workstation, test the electrodes using a three-electrode system, with a mercury-mercuric oxide electrode as the reference electrode, a platinum sheet measuring 1.5 cm x 1.5 cm as the counter electrode, and 1M KOH as the electrolyte.

[0029] S5.2. Activate the electrode using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential of -1 V, and a final potential of -1 V. The scan rate is 0.01 V / s and the number of scan segments is 10.

[0030] S5.3. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range from -1 V to 0 V, with the initial and final potentials both at -1 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, 500 mV / s, and 1000 mV / s, with 4 scan segments.

[0031] S5.4. Perform a chronopotentiometry (CP) test on the electrode sheet, setting the potential range to -1 V to 0 V, the anode and cathode currents to be the set value * load, with the set values ​​being 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and the number of scan segments to be 5;

[0032] S5.5. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz;

[0033] S5.6. Perform a life test on the electrode sheet using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential and a final potential of -1 V, a scan rate of 0.05 V / s, and 10,000 scan segments.

[0034] S5.7. Assemble the supercapacitor. Select two electrodes with similar load capacities, separate them with a diaphragm, clamp them together, and immerse them in the electrolyte.

[0035] S5.8. Using an electrochemical workstation, test a supercapacitor using a two-electrode system with 1 mol / L Na2SO4 as the electrolyte.

[0036] S5.9. Activate the electrode using cyclic voltammetry (CV) with a potential range of 0 V to 1.6 V, an initial potential of 0 V, and a final potential of 0 V. The scan rate is 0.01 V / s and the number of scan segments is 10.

[0037] S5.10. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the initial and final potentials both at 0 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, and 500 mV / s, with 4 scan segments.

[0038] S5.11. Perform chronopotentiometry (CP) testing on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the anode and cathode currents equal to the set value * load, with set values ​​of 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and a scan segment count of 5.

[0039] S5.12. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz.

[0040] S5.13. Perform a life test on the electrode sheet using cyclic voltammetry (CV), setting the potential range to 0 V to 1.6 V, with the initial and final potentials both at 0 V, a scan rate of 0.05 V / s, and 10,000 scan segments.

[0041] Furthermore, in S6, the prepared pure porous carbon material is subjected to a morphology characterization test, which specifically includes the following steps:

[0042] S6.1. Perform X-ray diffraction (XRD) testing on the pure porous carbon and analyze its XRD pattern to determine the degree of crystallinity of the material. The wide-angle diffraction scanning angle range is 5° to 85°, the wide-angle diffraction scanning rate is 8° / min, and the target material is Cu.

[0043] S6.2. Perform X-ray photoelectron spectroscopy (XPS) on pure porous carbon to analyze the element content and chemical bonds; the target material used in the test is Al;

[0044] S6.3. Perform scanning electron microscopy (SEM) and transmission electron microscopy (TEM) tests on the pure porous carbon to analyze its surface morphology and microstructure. TEM tests use a microgrid copper mesh and ethanol as the dispersant.

[0045] S6.4. Perform Raman spectroscopy on the pure porous carbon to analyze its defect level; the excitation wavelength is 532 nm and the test wavenumber range is 50 cm⁻¹ to 3400 cm⁻¹;

[0046] S6.5. Perform BET specific surface area test on pure porous carbon to analyze the specific surface area and pore distribution; nitrogen is selected as the adsorption gas and the sample degassing temperature is 200°C.

[0047] Furthermore, the resistivity of the deionized water is greater than 18.25 MΩ·cm.

[0048] The beneficial effects of the present invention are:

[0049] 1. This method of using high-temperature alkaline thermal activation of biochar to prepare supercapacitor electrodes is well designed. When preparing the carbon precursor of the supercapacitor electrode material, the aqueous solution can evenly fill the entire surface of the biochar, and the alkaline KOH can evenly etch the pore structure, making it suitable for preparing porous carbon materials.

[0050] 2. Using high-temperature aqueous solution for hot alkali activation, the optimal activation ratio can be obtained by uniformly mixing the precursor with alkali of different concentrations and ultrasonication, which improves the controllability and reliability compared with traditional alkali activation;

[0051] 3. Compared with the use of metal material composites as electrode materials for supercapacitors, the porous carbon material prepared by this method has the advantages of low cost, better environmental protection, and excellent lifespan, and is an ideal electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0053] Figure 1 This is a scanning electron microscope (SEM) image of the porous carbon material prepared in Example 1 of the present invention;

[0054] Figure 2 This is the X-ray diffraction (XRD) pattern of the porous carbon material prepared in Example 1 of the present invention;

[0055] Figure 3 This is an X-ray photoelectron spectroscopy (XPS) graph of the porous carbon material prepared in Example 1 of the present invention;

[0056] Figure 4 This is a Raman spectrum of the porous carbon material prepared in Example 1 of the present invention;

[0057] Figure 5 This is a comparative test diagram of the BET adsorption-desorption curves of the porous carbon material prepared in Example 1 of the present invention;

[0058] Figure 6 This is a BET specific surface area comparison test chart of the porous carbon material prepared in Example 1 of the present invention;

[0059] Figure 7 This is a cyclic voltammetry test diagram of the electrode sheet prepared in Example 1 of the present invention;

[0060] Figure 8 This is a chronopotentiometry test diagram of the electrode sheet prepared in Example 1 of the present invention;

[0061] Figure 9 This is a life test chart of a supercapacitor assembled with electrode sheets prepared in Example 1 of the present invention;

[0062] Figure 10 This is a flow chart of the method for preparing supercapacitor electrodes using high-temperature alkaline activation according to the present invention. DETAILED DESCRIPTION

[0063] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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 any creative efforts shall fall within the scope of protection of the present invention.

[0064] Example 1

[0065] A method for preparing supercapacitor electrodes using high-temperature alkaline activation, characterized in that it comprises the following steps:

[0066] S1. Preparation of porous carbon precursor: unpack the walnut shells and crush them into small pieces under the action of a hammer (for easy loading into a porcelain boat later), add ultrapure water (resistivity greater than 18.25MΩ·cm) to the crushed walnut shells, and use ultrasonic treatment at a frequency of 25kHz and 40kHz for 10 minutes, switching the frequency every 5 minutes; a large amount of mud and impurities can be observed floating out of the walnut shells, repeat the above operation 5 or 6 times, put the clean material into an oven, heat it to 130°C and keep it warm for 12 hours; weigh five 5g portions of clean walnut shells and put them into a porcelain boat, and place it in a tubular furnace protected by a nitrogen atmosphere under the action of a push rod, adjust the temperature to 350°C, and the heating rate is 5°C / min. After high-temperature treatment for 60 minutes, cool it naturally, remove impurities such as organic matter, and then place the carbonized product into a grinder and grind it into powder; a porous carbon precursor can be obtained; the precursor yield at this time is about 50%.

[0067] S2. Preparation of pure porous carbon, specifically as follows:

[0068] S2.1. Grind the precursor into powder in a mortar and pestle, and weigh the porous carbon precursor and potassium hydroxide in a mass ratio of 1:0, 1:1, 1:2, 1:3, and 1:4. Disperse the porous carbon precursor and KOH in 40 mL of deionized water in that order, and treat with ultrasound at frequencies of 25 kHz and 40 kHz for 30 min to fully mix the porous carbon precursor and the activator. Then, dry the solution in an oven at 130°C for 12 hours to remove excess water.

[0069] S2.2. Place the dried and activated porous carbon into a porcelain boat under the action of a push rod. Place the porcelain boat in a tube furnace protected by a nitrogen atmosphere and heat it to 800°C at a heating rate of 5°C / min. After holding for 1 hour, cool it naturally to room temperature and remove the product.

[0070] S2.3. The product was lightly crushed and added with 40 mL of deionized water, and stirred for 10 min. An equal amount of 36% HCl solution was added according to the KOH concentration, and the solution was treated with 40 kHz ultrasound for 10 min to fully neutralize the acid and base solutions. The solution was then filtered using a sand core filtration funnel with a 100 nm pore size polytetrafluoroethylene filter membrane, and the process was repeated five times. 400 mL of anhydrous ethanol was then added and the filtration was repeated once until the filtrate was neutral, thereby obtaining a black powdery granular carbon material.

[0071] S2.4. Transfer the black powdered granular carbon material into a beaker, place the beaker in an oven, and dry it at 130°C for 12 hours. Dry the solvent in the solution and lightly crush it to obtain a pure powdered porous carbon material.

[0072] S3. Prepare electrode sheets as follows:

[0073] S3.1. Take a clean beaker, add 10 ml of anhydrous ethanol, weigh 5 mg of carbon black, shake well, soak, and sonicate for 10 minutes to evenly disperse it. Then, add 18.75 mg of pure porous carbon and sonicate for 10 minutes to evenly disperse it. Finally, add 1.25 mg of 5% polytetrafluoroethylene solution and sonicate for 10 minutes to evenly disperse it. A black dispersion is obtained.

[0074] S3.2. Place the above black dispersion on a heating stirring table and heat while stirring. Heat to 60°C, then keep warm and continue stirring until the dispersion becomes a black paste. Stop heating.

[0075] S3.3. Select nickel foam with a size of 1cm*9cm as the current collector; soak the nickel foam in anhydrous ethanol, ultrasonically clean it for 20min, place it in an oven, and dry it at a temperature of 100℃ for 10h to obtain a carrier;

[0076] S3.4. Use chamfered glass to evenly coat the black paste on the carrier without any obvious agglomeration or gaps. The coating position is at the front end of the carrier, and the coating area is a 1 cm*1 cm square. This yields an initial sheet.

[0077] S3.5. Place the coated initial sheet in a blast drying oven at 80°C for 10 hours. After complete drying, the electrode sheet is obtained.

[0078] S4. Conduct electrochemical performance tests on the prepared electrode sheets, as follows:

[0079] S4.1. Using an electrochemical workstation, test the electrodes using a three-electrode system, with a mercury-mercuric oxide electrode as the reference electrode, a platinum sheet measuring 1.5 cm x 1.5 cm as the counter electrode, and 1 M KOH as the electrolyte.

[0080] S4.2. Activate the electrode using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential of -1 V, and a final potential of -1 V. The scan rate is 0.01 V / s and the number of scan segments is 10.

[0081] S4.3. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range to -1 V to 0 V, with the initial and final potentials both at -1 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, 500 mV / s, and 1000 mV / s, with 4 scan segments.

[0082] S4.4. Perform a chronopotentiometry (CP) test on the electrode sheet, setting the potential range to -1 V to 0 V, the anode and cathode currents to be the set value * load, with the set values ​​being 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and the number of scan segments to be 5;

[0083] S4.5. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz.

[0084] S4.6. Perform a life test on the electrode sheet using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential and a final potential of -1 V, a scan rate of 0.05 V / s, and 10,000 scan segments.

[0085] S4.7. Assemble the supercapacitor by selecting two electrodes with similar load capacities, separating them with a diaphragm, clamping them together, and immersing them in the electrolyte.

[0086] S4.8. Using an electrochemical workstation, test a supercapacitor using a two-electrode system with 1 mol / L Na2SO4 as the electrolyte.

[0087] S4.9. Activate the electrode using cyclic voltammetry (CV) with a potential range of 0 V to 1.6 V, an initial potential of 0 V, and a final potential of 0 V. The scan rate is 0.01 V / s and the number of scan segments is 10.

[0088] S4.10. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the initial and final potentials both at 0 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, and 500 mV / s, with 4 scan segments.

[0089] S4.11. Perform chronopotentiometry (CP) testing on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the anode and cathode currents equal to the set value * load, with set values ​​of 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and a scan segment count of 5.

[0090] S4.12. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz.

[0091] S4.13. Perform a life test on the electrode using cyclic voltammetry (CV) with a potential range of 0 V to 1.6 V, an initial potential of 0 V, and a final potential of 0 V. The scan rate is 0.05 V / s and the number of scan segments is 10,000.

[0092] S5. Perform morphology characterization tests on the prepared pure porous carbon material, as follows:

[0093] S5.1. Perform X-ray diffraction (XRD) testing on the pure porous carbon and analyze its XRD pattern to determine the degree of crystallinity of the material. The wide-angle diffraction scanning angle range is 5° to 85°, the wide-angle diffraction scanning rate is 8° / min, and the target material is Cu.

[0094] S5.2. Perform X-ray photoelectron spectroscopy (XPS) on the pure porous carbon to analyze the element content and chemical bonds. The target material used in the test is Al.

[0095] S5.3. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were performed on the pure porous carbon to analyze its surface morphology and microstructure. TEM tests used a microgrid copper mesh and ethanol as the dispersant.

[0096] S5.4. Perform Raman spectroscopy on the pure porous carbon to analyze its defect level; the excitation wavelength is 532 nm and the test wavenumber range is 50 cm⁻¹ to 3400 cm⁻¹;

[0097] S5.5. Perform BET specific surface area test on pure porous carbon to analyze the specific surface area and pore distribution; nitrogen is selected as the adsorption gas and the sample degassing temperature is 200°C.

[0098] like Figure 1 As shown in a, the walnut shell-derived carbon material without activation treatment presents a unique block structure, similar to the stacking morphology of reverse fish scales. For PC-1 treated with a small amount of KOH, due to the limited amount of activator, only the surface is etched, the etching degree is low, and the carbon skeleton is relatively complete. With the increase of KOH dosage, PC-2 and PC-4 develop obvious porous structures. Specifically, PC-4 mainly presents a porous and gully-like structure, which may be due to the excess of activator. In contrast, PC-2 presents a bubble-like stacking morphology, as shown in Figure 1 As shown in the enlarged images in e and 1f.

[0099] Depend on Figure 2 As can be seen, this image is a typical XRD diffraction pattern of amorphous carbon. The distinct peaks at 10-30° and 40-50° in the XRD curve of the biomass carbon material obtained by direct carbonization of walnut shells indicate that the material has certain crystalline regions. The appearance of amorphous peaks represents the material's disordered structure, indicating that Sample 1 has low crystallinity and a loose structure.

[0100] Depend on Figure 3 It can be seen that the sample is mainly composed of C, O, and N elements; the corresponding element contents are: C: 87.93%, N: 2.1%, and O: 4.35%.

[0101] Depend on Figure 4 It can be seen that the ratio of the Raman spectrum ID / IG peak area is used to characterize the defects and irregularity of the carbon material; the Raman spectrum ID / IG value is greater than 2.4, indicating that the degree of defects and disorder is low but the conductivity is high; it can be observed that the half-peak width of the D band decreases, indicating that the carbon defects obtained by template directional regulation are reduced and the degree of graphitization is higher.

[0102] Depend on Figure 5It can be seen that in order to explore the influence of different mass ratios of potassium hydroxide on the properties of walnut shell carbon materials, a total of four samples were prepared: H-7024-1 (obtained by direct carbonization of walnut shells), H-7024-2 (activated with an aqueous potassium hydroxide solution with a mass ratio of 1:1), H-7024-3 (activated with an aqueous potassium hydroxide solution with a mass ratio of 1:2), and H-7024-4 (activated with an aqueous potassium hydroxide solution with a mass ratio of 1:4), and their N2 adsorption-desorption isotherms were measured. Figure 1 The test results are shown. By observation, we can find that when the relative pressure P / P0 is lower than 0.1, the N2 adsorption amounts of all samples show an upward trend. In particular, for the H-7024-2 sample, in the range of 0.4 < P / P0 < 0.9, the isotherm shows an obvious adsorption hysteresis phenomenon, forming a clear hysteresis loop, which strongly proves that the sample is rich in microporous and mesoporous structures inside. In contrast, the hysteresis loop of the H-7024-3 sample is significantly weakened, while almost no hysteresis loop can be observed for the H-7024-1 and H-7024-4 samples.

[0103] Generally speaking, after the activation treatment with potassium hydroxide, the adsorption amounts of the walnut shell carbon materials have been significantly improved, which fully shows that the potassium hydroxide activation has a profound impact on the specific surface area and pore structure of the walnut shell carbon materials. Specifically, the specific surface area of the unactivated H-7024-1 sample is only 457.3 m 2 / g, while after the activation with potassium hydroxide, the specific surface areas of the samples generally increase by 4 to 5 times. Among them, the increase in the specific surface area of H-7024-4 is relatively low, but it also reaches 1573.0 m 2 / g; the specific surface area of H-7024-2 is 1596.6 m [[ID=L10]] 2 / g; and the specific surface area of H-7024-3 is the largest, up to 1887.3 m 2 / g. This difference in specific surface area may be due to the etching effect of potassium hydroxide on the internal structure of the walnut shell carbon materials under high-temperature conditions. Appropriate etching can significantly increase the specific surface area, but excessive potassium hydroxide may lead to the collapse of the internal structure of the material, thus reducing the specific surface area.

[0104] As Figure 6 can be seen, from the perspective of pore size distribution, all samples show a hierarchical porous structure dominated by micropores and mesopores, and the pore sizes are generally less than 5.0 nm. The data in the figure further reveals the influence of potassium hydroxide activation on the pore structure of the walnut shell carbon materials. After the activation treatment, the pore sizes of the samples all decrease to varying degrees, while the pore volumes increase significantly. The pore size of the original sample H-7024-1 is 3.11 nm, and the pore volume is 0.329 cm 3 / g; while the pore sizes of H-7024-2, H-7024-3 and H-7024-4 samples after activation treatment were reduced to 2.17nm, 2.07nm and 2.24nm, respectively, and the pore volumes were increased to 0.744cm 3 / g, 0.839cm 3 / g and 0.736cm 3 / g. This finding once again emphasizes the important role of potassium hydroxide activation in optimizing the microscopic pore structure of walnut shell carbon materials.

[0105] Depend on Figure 7 It can be seen that the curves all show a symmetrical rectangular shape, which indicates that the material has an obvious double layer effect.

[0106] Depend on Figure 8 It can be seen that the charge and discharge curve shows an obvious triangle shape

[0107] Depend on Figure 9 It can be seen that after 5000 cycles, the capacity of the electrode sheet is 103% of the initial capacity. The initial increase in capacitance occurs due to the increased wetting level of the electrode material with the aqueous electrolyte solution, thus allowing a larger electrode surface area to participate in the formation of EDLC.

[0108] Example 2

[0109] Working principle: Porous carbon materials can effectively improve the performance of supercapacitors due to their high specific surface area and high porosity. Most traditional activation treatment methods etch the surface of the material, while the internal porosity is very small, which is not conducive to improving the capacity of the supercapacitor, resulting in a less obvious overall capacity improvement. During the high-temperature alkaline activation process, KOH is allowed to form effective contact in space through an aqueous solution, allowing the material to contact more fully and evenly. KOH is then removed by chemical means, leaving the corresponding pores. Compared with the traditional method of mixing solids with alkali, it has the advantage of high porosity and can be used as an electrode material for supercapacitors with extremely high controllability.

[0110] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention; therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is limited by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention; any figure signs in the claims should not be regarded as limiting the claims involved.

[0111] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing supercapacitor electrodes using high temperature alkaline activation, characterized in that: The following steps are involved: S1. Biomass treatment: Clean walnut shells were crushed into blocks using a hammer; ultrasonic treatment was performed in deionized water using frequencies of 25 kHz and 40 kHz for 10 minutes, with the frequency switched every 5 minutes for 5 or 6 times to remove surface dust and impurities; the ultrasonically treated walnut shells were placed in an oven, heated to 130° C., and then kept warm for 12 hours to obtain clean walnut shells; S2. Preparation of porous carbon precursor: Select the clean walnut shells prepared in S1 and perform high-temperature carbonization. The walnut shells can be oxidized and removed by high temperature. The powdered biochar obtained after grinding, drying, and cooling is the porous carbon precursor. S3. Preparation of pure porous carbon: Biochar material and activator KOH are taken in a certain ratio, and then the powdered biochar material and activator KOH are dispersed in deionized water in sequence and uniformly treated with ultrasound to prepare alkaline porous carbon, and the alkaline porous carbon is carbonized at high temperature and acid-washed with HCl solution until neutral, and then dried and cooled to obtain pure porous carbon; S4. Preparing an electrode sheet with pure porous carbon: weighing pure porous carbon material, carbon black and polytetrafluoroethylene solution in a mass ratio of pure porous carbon material: carbon black: polytetrafluoroethylene solution = 75-150:20-40:5-10, and dispersing the porous carbon material, carbon black and polytetrafluoroethylene solution in the order of porous carbon material, carbon black and polytetrafluoroethylene solution into 10-20 mL of anhydrous ethanol, ultrasonically treating the mixture evenly, heating to evaporate the anhydrous ethanol, and stopping heating when the mixture becomes a paste; cutting the nickel foam into pieces of 1 cm*9 cm and washing and drying it, applying the paste to the front end of the nickel foam, and vacuum drying to obtain the electrode sheet; S5. Conducting electrochemical performance testing on the prepared electrode sheet; S6. Perform morphology characterization tests on the prepared pure porous carbon material.

2. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: In S2, a porous carbon precursor is prepared as follows: S2.

1. Weigh five 5g portions of clean walnut shells and place them in a porcelain boat. Using a push rod, place the boat in a tube furnace protected by a nitrogen atmosphere. Adjust the temperature of the tube furnace to 350°C at a heating rate of 5°C / min. Heat for 60 min, then cool naturally to obtain a carbonized product. S2.

2. The carbonized product is then placed in a grinder and ground into powder to obtain biochar.

3. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: In S3, pure porous carbon is prepared as follows: S3.

1. Weigh biochar powder and KOH in a mass ratio of biochar powder to KOH = 1:0, 1:1, 1:2, 1:3, and 1:4, and disperse the biochar powder and KOH into 40 mL of deionized water in the order of biochar powder → KOH. Ultrasonic treatment at a frequency of 25 kHz was performed for 30 min to ensure that the biochar powder and the activator were fully mixed. The solution was then dried in an oven at 130°C for 12 hours to remove excess water. S3.

2. Place the dried activated biochar powder into a porcelain boat and, under the action of a push rod, place the porcelain boat into a tube furnace protected by a nitrogen atmosphere. Heat it to 800°C at a heating rate of 5°C / min. Keep it at this temperature for 1 hour, then cool it naturally to room temperature and remove the product. S3.

3. The high-temperature calcined product was ground in a mortar and placed in a beaker. 40 mL of deionized water was added to the beaker and stirred for 10 minutes. An equal amount or an excess of 36% HCl solution was then added, depending on the KOH concentration. The solution was then ultrasonically treated at 40 kHz for 30 minutes to fully neutralize the acid and base solutions until the filtrate was neutral. The filtrate was then filtered using a sand-core filtration funnel with a 100 nm pore size polytetrafluoroethylene filter membrane and deionized water. This was repeated five times to obtain a black, powdery, granular substance. S3.

4. Transfer the powdered granular material into a beaker, place the beaker in an oven, and dry it at 130° C. for 12 h; dry the solvent in the powdered granular material, and gently stir to obtain a pure powdered porous carbon material.

4. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: In S4, preparing the electrode sheet includes the following steps: S4.

1. Wet a clean beaker with 5 ml of anhydrous ethanol, then add 20 ml of anhydrous ethanol, weigh 5 mg of carbon black, and sonicate for 10 minutes to disperse it evenly. Then, add 18.75 mg of pure porous carbon and sonicate for 10 minutes to disperse it evenly. Finally, add 1.25 mg of a 5% polytetrafluoroethylene solution and sonicate for 10 minutes to disperse it evenly. A black liquid is obtained. S4.

3. Heat the black liquid while stirring until it reaches 70°C, then maintain the temperature and continue stirring until the liquid becomes a black paste. Stop heating. S4.

3. Select nickel foam with a size of 1 cm*9 cm as the current collector; soak the nickel foam in anhydrous ethanol, ultrasonically clean it for 10 minutes, place it in an oven, and dry it at a temperature of 105-115°C for 10 hours to obtain a carrier; S4.

4. Use chamfered glass to evenly coat the black paste on the carrier without any obvious agglomeration or gaps. The coating position is at the front end of the carrier, and the coating area is a 1 cm*1 cm square. This yields an initial sheet. S4.

5. Place the coated initial sheet into a forced air drying oven at 780°C for 10 hours. After complete drying, the electrode sheet is obtained.

5. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: In S5, the prepared electrode sheet is subjected to an electrochemical performance test, which specifically includes the following steps: S5.

1. Using an electrochemical workstation, test the electrodes using a three-electrode system, with a mercury-mercuric oxide electrode as the reference electrode, a platinum sheet measuring 1.5 cm x 1.5 cm as the counter electrode, and 1M KOH as the electrolyte. S5.

2. Activate the electrode using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential of -1 V, and a final potential of -1 V. The scan rate is 0.01 V / s and the number of scan segments is 10. S5.

3. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range from -1 V to 0 V, with the initial and final potentials both at -1 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, 500 mV / s, and 1000 mV / s, with 4 scan segments. S5.

4. Perform a chronopotentiometry (CP) test on the electrode sheet, setting the potential range to -1 V to 0 V, the anode and cathode currents to be the set value * load, with the set values ​​being 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and the number of scan segments to be 5; S5.

5. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz; S5.

6. Perform a life test on the electrode sheet using cyclic voltammetry (CV) with a potential range of -1 V to 0 V, an initial potential and a final potential of -1 V, a scan rate of 0.05 V / s, and 10,000 scan segments. S5.

7. Assemble the supercapacitor. Select two electrodes with similar load capacities, separate them with a diaphragm, clamp them together, and immerse them in the electrolyte. S5.

8. Using an electrochemical workstation, test a supercapacitor using a two-electrode system with 1 mol / L Na2SO4 as the electrolyte. S5.

9. Activate the electrode using cyclic voltammetry (CV) with a potential range of 0 V to 1.6 V, an initial potential of 0 V, and a final potential of 0 V. The scan rate is 0.01 V / s and the number of scan segments is 10. S5.

10. Perform cyclic voltammetry (CV) on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the initial and final potentials both at 0 V, and scan rates of 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, and 500 mV / s, with 4 scan segments. S5.

11. Perform chronopotentiometry (CP) testing on the electrode sheet, setting the potential range from 0 V to 1.6 V, with the anode and cathode currents equal to the set value * load, with set values ​​of 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g, and a scan segment count of 5. S5.

12. Perform an electrochemical impedance spectroscopy (EIS) test on the electrode sheet, setting the minimum frequency to 0.1 Hz and the maximum frequency to 100,000 Hz. S5.

13. Perform a life test on the electrode sheet using cyclic voltammetry (CV), setting the potential range to 0 V to 1.6 V, with the initial and final potentials both at 0 V, a scan rate of 0.05 V / s, and 10,000 scan segments.

6. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: In S6, the prepared pure porous carbon material is subjected to morphology characterization testing, which specifically includes the following steps: S6.

1. Perform X-ray diffraction (XRD) testing on the pure porous carbon and analyze its XRD pattern to determine the degree of crystallinity of the material. The wide-angle diffraction scanning angle range is 5° to 85°, the wide-angle diffraction scanning rate is 8° / min, and the target material is Cu. S6.

2. Perform X-ray photoelectron spectroscopy (XPS) on pure porous carbon to analyze the element content and chemical bonds; the target material used in the test is Al; S6.

3. Perform scanning electron microscopy (SEM) and transmission electron microscopy (TEM) tests on the pure porous carbon to analyze its surface morphology and microstructure. TEM tests use a microgrid copper mesh and ethanol as the dispersant. S6.

4. Perform Raman spectroscopy on the pure porous carbon to analyze its defect level; the excitation wavelength is 532 nm and the test wavenumber range is 50 cm⁻¹ to 3400 cm⁻¹; S6.

5. Perform BET specific surface area test on pure porous carbon to analyze the specific surface area and pore distribution; nitrogen is selected as the adsorption gas and the sample degassing temperature is 200°C.

7. The method for preparing supercapacitor electrodes by high temperature alkali activation according to claim 1, characterized in that: The resistivity of the deionized water is greater than 18.25 MΩ·cm.

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