Graphitized porous carbon preparation method and supercapacitor electrode material

Abstract

The invention belongs to the technical field of new energy materials, and relates to a graphitized porous carbon preparation method and a supercapacitor electrode material. The method comprises the following steps: pretreating a biomass raw material to obtain pre-carbonized powder; mixing the pre-carbonized powder with potassium ferrite trioxalate, and performing high-temperature activation catalytic reaction in a first inert atmosphere to obtain an initial graphitized porous carbon material; and carrying out supercritical carbon dioxide treatment on the initial graphitized porous carbon material to optimize the pore structure of the initial graphitized porous carbon material through permeation and chambering effects of supercritical carbon dioxide so as to obtain the target graphitized porous carbon material. Based on the method, the porosity and graphitization of the biomass carbon are synchronously realized through a potassium ferrite trioxalate one-step method, the high-performance graphitized porous carbon is prepared by combining supercritical carbon dioxide post-treatment, and the process is simple, convenient and environment-friendly.

Description

Technical Field

[0001] This application relates to the field of new energy materials technology, and in particular to a method for preparing graphitized porous carbon and a supercapacitor electrode material. Background Technology

[0002] Supercapacitors, as highly efficient energy storage devices, have significant application prospects in the new energy field due to their high power density, rapid charge-discharge capability, and long cycle life. Electrode materials are a key factor determining the performance of supercapacitors, with porous carbon materials becoming a research hotspot due to their excellent conductivity and high specific surface area. Biomass-derived carbon materials are considered ideal precursors for electrode materials because of their wide availability, low cost, and naturally porous structure.

[0003] Traditional methods for preparing porous carbon from biomass typically employ KOH activation. While this effectively increases the specific surface area, the highly corrosive reagents cause significant damage to equipment. Furthermore, the activation process requires the introduction of transition metal catalysts (such as Fe and Co) to promote graphitization, resulting in a complex process, high energy consumption, and significant environmental pollution risks. In addition, conventional activation methods often leave impurities in the material, affecting electrochemical performance. In summary, traditional methods for preparing porous carbon from biomass require stepwise KOH activation and transition metal-catalyzed graphitization, which presents problems such as complex processes, the harmful effects of highly corrosive reagents, and the potential for impurity residues. Moreover, it is difficult to simultaneously achieve high specific surface area and high conductivity. Summary of the Invention

[0004] The present invention provides a method for preparing graphitized porous carbon and a supercapacitor electrode material, which at least solves the problems of complex processes, highly corrosive reagents, easy residue of impurities, and difficulty in achieving high specific surface area and high conductivity simultaneously in related technologies.

[0005] According to a first aspect of the present invention, a method for preparing graphitized porous carbon is provided, characterized in that it comprises:

[0006] Biomass raw materials are pretreated to obtain pre-carbonized powder;

[0007] The pre-carbonized powder was mixed with potassium trioxalatoferrate and then subjected to a high-temperature activation catalytic reaction under a first inert atmosphere to obtain the initial graphitized porous carbon material.

[0008] The initial graphitized porous carbon material is treated with supercritical carbon dioxide to optimize its pore structure through the permeation and pore-expanding effects of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material.

[0009] According to an embodiment of the present invention, the pretreatment of biomass raw materials to obtain pre-carbonized powder includes:

[0010] The biomass raw material is sequentially crushed, washed and dried to obtain biomass raw material powder;

[0011] The biomass raw material powder is pre-carbonized under a second inert atmosphere to obtain pre-carbonized powder.

[0012] According to an embodiment of the present invention, the second inert atmosphere is an argon atmosphere or a nitrogen atmosphere;

[0013] The step of pre-carbonizing the biomass raw material powder under a second inert atmosphere to obtain pre-carbonized powder includes:

[0014] The biomass raw material powder is transferred to a tube furnace and subjected to high-temperature pre-carbonization treatment under the atmosphere of argon or nitrogen to obtain the pre-carbonized powder. The temperature of the pre-carbonization treatment is 200℃~500℃ and the time is 1h~3h.

[0015] According to an embodiment of the present invention, the process of mixing the pre-carbonized powder with potassium trioxalatoferrate and then performing a high-temperature activation catalytic reaction under a first inert atmosphere to obtain an initial graphitized porous carbon material comprises:

[0016] The pre-carbonized powder and the potassium trioxalate ferrate were mixed in a ball mill to obtain a homogeneous mixture.

[0017] The homogeneous mixture is subjected to a high-temperature activation catalytic reaction under the first inert atmosphere to obtain the reaction product to be treated;

[0018] After cooling the reaction product to room temperature, it was repeatedly washed with dilute hydrochloric acid and deionized water until neutral, and then dried to obtain the initial graphitized porous carbon material.

[0019] According to an embodiment of the present invention, the mass ratio of the pre-carbonized powder to the potassium trioxalatoferrate is 1:5 to 5:1; the first inert atmosphere is an argon atmosphere or a nitrogen atmosphere; and the reaction temperature of the high-temperature activated catalytic reaction is 600°C.

[0020] The temperature is ~1200℃, and the reaction time is 1h to 5h; the rotation speed of the ball mill is 100rpm to 500rpm, and the mixing time is 10min to 60min.

[0021] According to an embodiment of the present invention, the step of treating the initial graphitized porous carbon material with supercritical carbon dioxide to optimize the pore structure of the initial graphitized porous carbon material through the permeation and pore-expanding effect of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material, includes:

[0022] The initial graphitized porous carbon material is placed in a high-pressure reaction vessel, and carbon dioxide is introduced into the high-pressure reaction vessel while the temperature and pressure are increased to make the carbon dioxide reach a supercritical state.

[0023] The supercritical state is maintained for a set time, allowing the supercritical carbon dioxide to permeate into the pore structure of the initial graphitized porous carbon material to obtain the target graphitized porous carbon material.

[0024] According to an embodiment of the present invention, the temperature of the supercritical carbon dioxide treatment is 100℃~200℃, the pressure is 10MPa~30MPa, and the set time is 1h~6h.

[0025] According to an embodiment of the present invention, the biomass raw material is a straw-type plant, which includes at least one of the following: bamboo, sunflower stalks, rush pith, rice stalks, wheat stalks, corn stalks, and sorghum stalks.

[0026] According to a second aspect of the present invention, a supercapacitor electrode material is provided, characterized in that the supercapacitor electrode material comprises graphitized porous carbon, the graphitized porous carbon being prepared according to the method described in the first aspect.

[0027] Beneficial effects of the embodiments of the present invention:

[0028] This invention provides a method for preparing graphitized porous carbon that simultaneously achieves the porosimetry and graphitization of biomass carbon in a one-step process using potassium tris(oxalato)ferrate. Combined with supercritical carbon dioxide post-treatment, this method yields graphitized porous carbon with high specific surface area, excellent conductivity, and a clean surface, significantly simplifying the preparation process and improving material performance. Specifically, this method involves pre-treating biomass raw materials to obtain pre-carbonized powder, mixing it with potassium tris(oxalato)ferrate, and conducting a high-temperature activation catalytic reaction under an inert atmosphere. Utilizing the dual function of potassium tris(oxalato)ferrate as both an activator and catalyst, the method achieves simultaneous porosimetry and graphitization of the biomass carbon material in one step, significantly simplifying the traditional step-by-step process. Subsequently, supercritical carbon dioxide treatment further optimizes the pore structure of the porous carbon and cleans the surface through its unique penetration and pore-expanding effects. The resulting graphitized porous carbon material possesses high specific surface area, a well-developed hierarchical pore structure, and excellent conductivity. In superelectrode applications, it exhibits high specific capacitance and good rate capability. Furthermore, the entire preparation process is green, environmentally friendly, and easy to operate, making it suitable for industrial production.

[0029] Details of one or more embodiments of the present invention are set forth in the following drawings and description, so that other features, objects and advantages of the invention will be more readily understood. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of a method for preparing graphitized porous carbon according to an embodiment of the present invention.

[0032] Figure 2 This is a scanning electron microscope image of bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention.

[0033] Figure 3 This is a transmission electron microscope image of bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention.

[0034] Figure 4 This is a schematic diagram of the nitrogen adsorption-desorption test results of bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention.

[0035] Figure 5 This is a schematic diagram of the constant current charge-discharge curves of bamboo-based graphitized porous carbon under different current densities, provided in Embodiment 1 of the present invention.

[0036] Figure 6 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based graphitized porous carbon under different current densities, as provided in Embodiment 1 of the present invention.

[0037] Figure 7 This is a schematic diagram illustrating the specific capacitance variation of corn straw-based graphitized porous carbon under different current densities, as provided in Embodiment 2 of the present invention.

[0038] Figure 8 This is a schematic diagram illustrating the specific capacitance variation of sorghum straw-based graphitized porous carbon under different current densities, as provided in Embodiment 3 of the present invention.

[0039] Figure 9 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based porous carbon under different current densities, as provided in Comparative Example 1 of the present invention.

[0040] Figure 10 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based porous carbon under different current densities, as provided in Comparative Example 2 of the present invention. Detailed Implementation

[0041] Embodiments of this embodiment will now be described in more detail with reference to the accompanying drawings. While some embodiments of this embodiment are shown in the drawings, it should be understood that this embodiment can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this embodiment. It should be understood that the accompanying drawings and embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this embodiment.

[0042] Supercapacitors hold significant promise in the new energy field due to their high power density, rapid charge-discharge, and long cycle life. Electrode materials are crucial, with porous carbon materials attracting considerable research attention due to their excellent conductivity and high specific surface area. Among these, biomass-derived carbon materials are considered ideal electrode precursors due to their wide availability, low cost, and naturally porous structure. Traditional preparation methods often employ KOH activation, which can increase the specific surface area. However, the highly corrosive reagent damages equipment, and the addition of transition metal catalysts after activation promotes graphitization, resulting in complex processes, high energy consumption, significant pollution risks, and the tendency for residual impurities to affect electrochemical performance. Furthermore, the stepwise operation makes it difficult to simultaneously achieve high specific surface area and high conductivity.

[0043] To address the aforementioned problems, this invention provides a method for preparing graphitized porous carbon and a supercapacitor electrode material.

[0044] Figure 1 This is a flowchart illustrating a method for preparing graphitized porous carbon according to an embodiment of the present invention. Figure 1 As shown, the method includes the following steps.

[0045] Step S101: Pre-treat the biomass raw material to obtain pre-carbonized powder.

[0046] In step S102, the pre-carbonized powder is mixed with potassium trioxalatoferrate and then subjected to a high-temperature activation catalytic reaction under a first inert atmosphere to obtain the initial graphitized porous carbon material.

[0047] Step S103: The initial graphitized porous carbon material is treated with supercritical carbon dioxide to optimize the pore structure of the initial graphitized porous carbon material through the permeation and pore-expanding effect of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material.

[0048] The method for preparing graphitized porous carbon provided in this invention achieves the preparation of high-performance porous carbon materials through an innovative three-step process.

[0049] First, the biomass raw materials are pretreated to obtain pre-carbonized powder.

[0050] In this embodiment, the biomass raw materials are first pretreated by crushing selected biomass materials such as bamboo and corn stalks to achieve a particle size suitable for subsequent processing. The crushed raw materials are then washed with water to remove surface impurities and dried to ensure complete moisture removal. The dried biomass powder is then transferred to a tube furnace and pre-carbonized under inert gas protection to obtain pre-carbonized powder. This step lays a stable carbon framework foundation for the subsequent activation catalytic reaction.

[0051] In this embodiment, the biomass raw material is straw-type plants, including at least one of the following: bamboo, sunflower straw, rush, rice straw, wheat straw, corn straw, and sorghum straw.

[0052] After pretreatment, the pre-carbonized powder was mixed with potassium trioxalatoferrate and then subjected to a high-temperature activation catalytic reaction under a first inert atmosphere to obtain the initial graphitized porous carbon material.

[0053] In this embodiment, the obtained pre-carbonized powder was thoroughly mixed with potassium tris(oxalato)ferrate (K3[Fe(C2O4)3]). In this step, potassium tris(oxalato)ferrate plays a dual role: acting as both an activator and a catalyst. The uniformly mixed material was subjected to high-temperature treatment under an inert atmosphere. During this process, the active components generated from the decomposition of potassium tris(oxalato)ferrate reacted with the carbon material, simultaneously achieving the formation of a porous structure and enhancing the degree of graphitization. After the reaction was completed, the product was acid-washed and water-washed to remove reaction residues, ultimately yielding an initial graphitized porous carbon material with a rich pore structure.

[0054] Finally, the initial graphitized porous carbon material was treated with supercritical carbon dioxide to optimize the pore structure of the initial graphitized porous carbon material through the permeation and pore-expanding effect of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material.

[0055] In this embodiment, to further optimize the pore structure of the material, the initial graphitized porous carbon material obtained above was placed in a supercritical carbon dioxide treatment device. Under specific temperature and pressure conditions, carbon dioxide reaches a supercritical state, and its unique physical properties allow it to deeply penetrate into the microporous structure of the carbon material. This treatment process not only effectively widens the original pore channels of the material but also cleans the pore surface, ultimately yielding a target graphitized porous carbon material with an ideal pore structure and excellent performance. The entire preparation process in this embodiment is simple and environmentally friendly, and the resulting product shows promising application prospects in fields such as supercapacitor electrode materials.

[0056] In one optional embodiment, when pretreating the biomass raw material, the biomass raw material can first be crushed, washed and dried in sequence to obtain biomass raw material powder; then the biomass raw material powder is pre-carbonized under a second inert atmosphere to obtain pre-carbonized powder.

[0057] In this embodiment, the second inert atmosphere can be an argon atmosphere or a nitrogen atmosphere. Specifically, during the pre-carbonization treatment, the biomass raw material powder can be transferred to a tube furnace and subjected to high-temperature pre-carbonization treatment under an argon atmosphere or a nitrogen atmosphere to obtain pre-carbonized powder. The pre-carbonization treatment temperature is 200℃~500℃, and the time is 1h~3h.

[0058] Taking bamboo as an example, in the pretreatment stage, freshly harvested bamboo can be cut into small sections of 3-5 cm, and then pre-crushed using a high-speed pulverizer. During the crushing process, the rotation speed is controlled at 8000-10000 rpm, and crushing is continued for 15-20 minutes until coarse powder with a particle size of 100-300 micrometers is obtained. To further refine the particles, the coarse powder can be transferred to a ball mill, with an appropriate amount of deionized water added as the medium, and zirconia balls used as the grinding medium. The ball-to-material ratio is controlled at 5:1, and ball milling is carried out at a speed of 300-400 rpm for 2-3 hours, finally obtaining fine biomass raw material powder with uniform particle size distribution and an average particle size of 50-100 micrometers.

[0059] The pulverized biomass raw material powder needs to undergo thorough cleaning. The powder is placed in an ultrasonic cleaning tank, and deionized water is added until completely submerged. The ultrasonic power is set to 500W, the frequency to 40kHz, and the cleaning is performed at 60℃ for 30 minutes. This process effectively removes impurities such as mud and dust adhering to the surface of the raw material. After cleaning, a vacuum filtration device is used for solid-liquid separation. A filter membrane with a pore size of 0.45 microns is selected, and the filtration pressure is controlled at 0.1–0.2 MPa to ensure thorough removal of moisture while preventing the loss of fine particles.

[0060] The drying process can be carried out using a gradient heating method. The wet material is spread evenly on a tray, with a thickness controlled at 2-3 cm. First, it is pre-dried at 60℃ for 4 hours, then the temperature is increased to 80℃ and maintained for 8 hours, and finally dried at 105℃ for 2 hours. Nitrogen gas is continuously purged during the drying process for protection, with the airflow velocity controlled at 0.5-1.0 m / s to prevent oxidation of the material. The moisture content of the dried biomass powder is controlled below 3%, and it is stored in a desiccator for later use.

[0061] The pre-carbonization treatment is carried out in a tube furnace, and the specific operation is as follows: the dried biomass raw material powder is evenly spread in an alumina crucible, and the packing density is controlled at 0.3-0.5 g / cm³. 3The crucible was placed in the constant-temperature zone of a tube furnace. The system was first evacuated to below 10 Pa using a mechanical pump, then high-purity argon gas (99.999% purity) was introduced at a flow rate of 5 L / min for atmosphere replacement. This evacuation and argon purging process was repeated three times. The heating program was set as follows: heating from room temperature to 200 °C at a rate of 5 °C / min, holding for 30 minutes to remove residual moisture; then heating to 350 °C at a rate of 3 °C / min, and holding at this temperature for 2 hours. Throughout the heating process, the argon flow rate was maintained at 200 mL / min, and the system pressure was maintained at a slightly positive pressure (approximately 1.05 atmospheres). After the reaction was complete, the sample was removed, yielding a dark brown pre-carbonized powder. This pre-carbonized powder should be sealed and stored in an argon-filled glove box to prevent moisture absorption and oxidation.

[0062] In an optional embodiment, when preparing the initial graphitized porous carbon material, i.e., after mixing the pre-carbonized powder with potassium tris(oxalato)ferrate, and then carrying out a high-temperature activation catalytic reaction under a first inert atmosphere, the pre-carbonized powder and potassium tris(oxalato)ferrate can first be placed in a ball mill for mixing to obtain a homogeneous mixture; then the homogeneous mixture is carried out a high-temperature activation catalytic reaction under a first inert atmosphere to obtain the reaction product to be treated; finally, after cooling the reaction product to room temperature, it is repeatedly washed with dilute hydrochloric acid and deionized water until neutral and then dried to obtain the initial graphitized porous carbon material.

[0063] In this embodiment, the mass ratio of pre-carbonized powder to potassium trioxalatoferrate is 1:5 to 5:1; the first inert atmosphere is argon or nitrogen; the reaction temperature of the high-temperature activation catalytic reaction is 600℃ to 1200℃, and the reaction time is 1h to 5h; the rotation speed of the ball mill is 100rpm to 500rpm, and the mixing time is 10min to 60min.

[0064] In the activation and catalytic reaction stage, the pre-carbonized powder and potassium tris(oxalato)ferrate must first be thoroughly mixed. This step can be carried out in a ball mill. For example, the pre-carbonized biomass powder and potassium tris(oxalato)ferrate can be weighed according to a pre-set mass ratio and placed in a stainless steel ball mill jar. The ball mill jar is filled with zirconia grinding balls, and the ball-to-material ratio can be 10:1. The ball mill speed is set to 300 rpm, and the mixing time is controlled at 30 minutes. During the ball milling process, the material is subjected to the impact and friction of the grinding balls, achieving uniform mixing and ensuring the homogeneity of subsequent reactions. After ball milling, the mixture is removed and sieved to remove the grinding balls, resulting in a homogeneous mixture with a uniform texture.

[0065] Then, the mixed materials are transferred to a tube furnace for high-temperature activation and catalytic reaction. For example, the homogeneous mixture can be evenly spread in an alumina crucible, with a thickness controlled to about 5 mm, to ensure uniform heating. The crucible is placed in the constant temperature zone of the tube furnace, sealed, and high-purity argon gas (99.999% purity) is introduced for atmosphere replacement at a flow rate of 200 ml / min for 30 minutes to completely remove air from the system. Subsequently, the furnace temperature is increased to 800°C at a heating rate of 5°C / min and maintained at this temperature for 2 hours for activation and catalytic reaction. During the heating process, potassium trioxalatoferrate begins to decompose, initially decomposing into potassium oxalate and ferrous oxalate in the 200–300°C range. As the temperature continues to rise, these intermediate products further react with carbon materials, while iron begins to catalyze the rearrangement and graphitization of carbon atoms. After the reaction is complete, the mixture is cooled to room temperature at a cooling rate of 10°C / min, with argon gas protection maintained throughout the entire process.

[0066] After the reaction product is removed, post-processing is required. For example, it can first be soaked in 0.1 mol / L dilute hydrochloric acid. After acid washing, it is repeatedly washed with deionized water until the washing solution is neutral when tested with pH paper. The washed material is then dried in a vacuum drying oven at 80℃ for 12 hours to finally obtain a black, loosely textured initial graphitized porous carbon material.

[0067] The above-described treatment process in this embodiment effectively removes inorganic salt residues and metallic impurities generated during the reaction, ensuring the purity of the product. Throughout the activation and catalysis stage, key process parameters such as mixing ratio, ball milling conditions, reaction temperature, and time are strictly controlled to ensure that the final product has an ideal pore structure and degree of graphitization.

[0068] In an optional embodiment, when preparing the target graphitized porous carbon material, i.e., when treating the initial graphitized porous carbon material with supercritical carbon dioxide to optimize the pore structure of the initial graphitized porous carbon material through the permeation and pore-expanding effect of supercritical carbon dioxide, the initial graphitized porous carbon material can be placed in a high-pressure reaction vessel, and carbon dioxide can be introduced into the high-pressure reaction vessel and the temperature and pressure can be increased to make the carbon dioxide reach a supercritical state; then, the supercritical state is maintained for a set time to allow the supercritical carbon dioxide to permeate into the pore structure of the initial graphitized porous carbon material to obtain the target graphitized porous carbon material.

[0069] In this embodiment, the temperature of the supercritical carbon dioxide treatment is 100℃~200℃, the pressure is 10MPa~30MPa, and the set time is 1h~6h.

[0070] After the activation catalytic reaction is completed and the material is cleaned and dried, the initial graphitized porous carbon material needs to undergo pore structure optimization treatment.

[0071] For example, in practical applications, the pre-treated graphitized porous carbon material can first be loaded into a high-pressure reaction vessel. This reaction vessel must be made of high-pressure resistant stainless steel and equipped with a precise temperature and pressure control system, as well as a safety pressure relief device. During loading, it is important to control the packing density; for example, maintaining a powder layer thickness of 3–5 cm is recommended to ensure uniform penetration of the supercritical fluid during subsequent processing. After loading, the reaction vessel is sealed and connected to the carbon dioxide gas supply line.

[0072] At the start of the process, first open the carbon dioxide cylinder valve and control the gas flow rate using a precision pressure reducing valve, allowing carbon dioxide to be slowly introduced into the reaction vessel at a rate of 0.5–1.0 L / min. During this process, the pressure changes inside the vessel need to be monitored in real time. When the pressure reaches approximately 5 MPa, the heating system is activated. Heating employs a staged heating strategy: first, heat to 80°C at a rate of 3°C / min and maintain this temperature for 10 minutes to ensure uniform system temperature; then continue heating at a rate of 2°C / min to reach the target processing temperature (preferably within the range of 150–180°C). As the temperature rises, the pressure inside the vessel will naturally increase. At this point, precise adjustment using a back pressure valve is necessary to stabilize the final working pressure within the range of 20–25 MPa.

[0073] Once the system reaches the set supercritical state (e.g., 150°C, 20 MPa), timing begins. During this stage, supercritical carbon dioxide exhibits unique physical properties: its density is close to that of a liquid, its viscosity is close to that of a gas, its surface tension is almost zero, and it possesses extremely strong penetration and diffusion capabilities. These characteristics allow it to deeply penetrate the micropores and mesopores of porous carbon materials. The holding time can be set to 3–4 hours, during which the temperature and pressure parameters need continuous monitoring and fine-tuning, with fluctuations controlled within ±2°C and ±0.5 MPa.

[0074] During the treatment process, supercritical carbon dioxide optimizes the material structure primarily through three mechanisms: First, its strong dissolving ability removes residual organic impurities within the pores; second, under high pressure, carbon dioxide molecules cause a "swelling" effect on the pore walls, moderately enlarging narrow pores; and finally, the rapid diffusion characteristics of supercritical fluids help to connect previously blocked pores, forming a more complete three-dimensional interconnected pore network. These effects synergistically improve the material's specific surface area and pore accessibility.

[0075] After processing, a special decompression procedure can be used: first, slowly depressurize to 10 MPa at a rate of 0.3 MPa / min and maintain for 15 minutes; then depressurize to atmospheric pressure at a rate of 0.5 MPa / min. This staged decompression method can avoid material structure damage caused by sudden pressure changes. After decompression, allow the system to cool naturally to below 60°C before opening the container and removing the sample. The final obtained graphitized porous carbon material should be immediately transferred to a desiccator for storage to prevent re-adsorption of moisture and impurities from the air.

[0076] The entire supercritical treatment process in this embodiment needs to be carried out under strictly controlled conditions. The precise coordination of temperature, pressure, and time has a decisive impact on the final material's properties. By optimizing the experimental parameters, materials with ideal pore size distribution (mainly mesopores of 2–5 nm) and ultra-high specific surface area (>1300 m²) can be obtained. 2 High-quality porous carbon material (g / g). This material exhibits excellent rate performance when used as a supercapacitor electrode.

[0077] The following detailed description of a method for preparing graphitized porous carbon according to specific embodiments of the present invention is provided in conjunction with specific examples.

[0078] Example 1: Preparation of bamboo-based graphitized porous carbon

[0079] Raw material pretreatment stage: Fresh bamboo is selected as the raw material. First, a plant pulverizer is used to pulverize the bamboo to a particle size of 100-300μm. The pulverized bamboo powder is then ultrasonically cleaned in deionized water for 30 minutes (300W power, 40kHz frequency), repeated 3 times to thoroughly remove surface impurities. The cleaned bamboo powder is then dried in a vacuum drying oven at 80℃ for 12 hours to ensure the moisture content is below 5wt%.

[0080] Pre-carbonization treatment: The dried bamboo powder was evenly spread in an alumina crucible and placed in the reaction chamber of a tube furnace. High-purity argon gas (99.999%) was introduced for gas replacement at a flow rate of 200 mL / min for 30 minutes to ensure complete removal of air. The temperature was then increased to 350°C at a rate of 5°C / min and maintained at this temperature for 1 hour. The argon flow rate was maintained at 50 mL / min throughout the process. After the reaction, the mixture was allowed to cool naturally to room temperature to obtain black pre-carbonized bamboo charcoal powder.

[0081] Activation catalytic reaction: Pre-carbonized bamboo charcoal powder and potassium trioxalatoferrate (K3[Fe(C2O4)3]) were accurately weighed at a mass ratio of 1:1 and placed in a planetary ball mill. Zirconia grinding balls (5 mm in diameter) were used, and the milling speed was set to 300 rpm for 30 minutes. The uniformly mixed material was transferred to a graphite crucible and placed in the central temperature zone of a tube furnace. Under argon protection (100 mL / min), the temperature was increased to 800℃ at a rate of 10℃ / min and maintained at this temperature for 2 hours to carry out the activation catalytic reaction.

[0082] Post-processing purification: After cooling, the reaction product was first filtered and washed with 0.1 mol / L hydrochloric acid solution, and then repeatedly washed with deionized water until the pH of the filtrate was 7. The washed sample was dried for 12 hours to obtain black initial graphitized porous carbon material.

[0083] Supercritical CO2 treatment: 5g of initial graphitized porous carbon material was loaded into a 500mL supercritical reactor, sealed, and then food-grade CO2 gas was introduced. The pressure was first increased to 10MPa at a rate of 2MPa / min, then the heating program was started, raising the temperature to 150℃ at a rate of 3℃ / min. Finally, the pressure was adjusted to 20MPa, and the mixture was maintained under supercritical conditions for 3 hours. After treatment, the pressure was slowly released at a rate of 0.5MPa / min, and after cooling, the final product, bamboo-based graphitized porous carbon, was obtained.

[0084] Figure 2 This is a scanning electron microscope image of bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention, such as... Figure 2 As shown, the prepared bamboo-based target graphitized porous carbon material exhibits a three-dimensional interconnected network structure, which is beneficial for electrolyte penetration and rapid ion transport.

[0085] Figure 3 This is a transmission electron microscope image of bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention, such as... Figure 3 As shown, the microstructure characteristics of the prepared bamboo-based target graphitized porous carbon material are further revealed. Figure 3 Regular lattice stripes can be clearly seen in the material, which perfectly correspond to the 002 crystal plane of graphite, fully demonstrating that a highly ordered graphitized structure has been formed in local areas of the material.

[0086] Figure 4 This is a schematic diagram of nitrogen adsorption-desorption test results for bamboo-based graphitized porous carbon provided in Embodiment 1 of the present invention, as shown below. Figure 4 As shown, the measured specific surface area is as high as 1308 m². 2 / g, such a high specific surface area provides ample active sites for charge storage.

[0087] Figure 5 This is a schematic diagram of the constant current charge-discharge curves of bamboo-based graphitized porous carbon at different current densities provided in Embodiment 1 of the present invention, as shown below. Figure 5 As shown, all curves exhibit a typical isosceles triangle shape. This symmetrical charge-discharge characteristic fully demonstrates that the material has ideal double-layer capacitance properties and exhibits excellent electrochemical reversibility.

[0088] Figure 6 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based graphitized porous carbon under different current densities, as provided in Embodiment 1 of the present invention. Figure 6 As shown, as the current density increases from 1 A / g to 20 A / g, the specific capacitance gradually decreases from 241 F / g to 152 F / g, and the capacitance retention rate reaches 63%. This result fully demonstrates that the material has excellent rate performance and can meet the application requirements of supercapacitors under high power output conditions.

[0089] Example 2: Preparation of graphitized porous carbon based on corn stalks

[0090] Raw material pretreatment stage: Mature corn stalks are selected as raw materials. First, a multi-functional pulverizer is used to pulverize the stalks to a particle size of 150-400 μm. The pulverized stalk powder is then placed in deionized water and stirred and washed (500 rpm) for 45 minutes. This washing process is repeated three times to thoroughly remove surface mud and soluble impurities. The washed stalk powder is then dried in a forced-air drying oven at 85℃ for 15 hours to ensure a moisture content of less than 3 wt%.

[0091] Pre-carbonization treatment: The dried straw powder was evenly packed into a quartz boat and transferred to the isothermal zone of a tube furnace. High-purity argon gas (99.999%) was introduced for gas replacement at a flow rate of 250 mL / min for 40 minutes to ensure complete removal of air. The temperature was then increased to 350 °C at a rate of 4 °C / min and maintained at this temperature for 1 hour. The argon flow rate was maintained at 80 mL / min throughout the process. After the reaction, the mixture was cooled to room temperature under controlled conditions and removed to obtain black pre-carbonized straw carbon powder.

[0092] Activation catalytic reaction: Pre-carbonized straw carbon powder and potassium trioxalatoferrate were accurately weighed at a mass ratio of 1:1 and placed in a planetary ball mill. A stainless steel grinding jar and zirconia grinding balls (3-8 mm in diameter) were used, with a milling speed of 300 rpm and a milling time of 30 minutes. The uniformly mixed material was then loaded into an alumina crucible and placed in the central temperature zone of a tube furnace. Under argon protection (120 mL / min), the temperature was increased to 800℃ at a rate of 8℃ / min and maintained at this temperature for 2 hours to carry out the activation catalytic reaction.

[0093] Post-processing purification: After the reaction product cooled naturally, it was first filtered and washed with 0.2 mol / L hydrochloric acid solution, and then repeatedly washed with deionized water until the pH of the filtrate was 7. The washed sample was dried for 24 hours to obtain a dark black initial graphitized porous carbon material.

[0094] Supercritical CO2 treatment: 8g of initial graphitized porous carbon material was loaded into a 1L supercritical reactor, sealed, and then high-purity CO2 gas (99.99%) was introduced. The pressure was first increased to 12MPa at a rate of 1.5MPa / min, then the heating program was started, raising the temperature to 150℃ at a rate of 2.5℃ / min. Finally, the pressure was adjusted to 20MPa, and maintained under supercritical conditions for 3 hours. After treatment, a gradient depressurization method was used: first, the pressure was reduced to 15MPa at a rate of 0.3MPa / min and maintained for 30 minutes, then reduced to atmospheric pressure at a rate of 0.7MPa / min to obtain the final corn stalk-based graphitized porous carbon.

[0095] The corn stalk-based graphitized porous carbon material prepared in Example 2 was used as an electrode material for a supercapacitor. Constant current charge-discharge tests were conducted at different current densities to evaluate its electrochemical performance. A schematic diagram illustrating the specific capacitance variation of the corn stalk-based graphitized porous carbon at different current densities is shown below. Figure 7 As shown, the sample exhibits a specific capacitance of 223 F / g at a current density of 1 A / g.

[0096] Example 3: Preparation of graphitized porous carbon based on sorghum straw

[0097] Raw material pretreatment stage: Mature sorghum stalks are selected as raw materials. First, a high-speed pulverizer is used to pulverize the stalks to a particle size of 150–400 μm. The pulverized stalk powder is then placed in deionized water and magnetically stirred for 45 minutes, repeated three times to thoroughly remove surface ash and soluble impurities. The washed stalk powder is then dried in a forced-air drying oven at 85°C for 15 hours, ensuring the moisture content is below 3 wt%.

[0098] Pre-carbonization treatment: The dried straw powder was evenly packed into a quartz boat and placed in the constant temperature zone of a tube furnace. High-purity argon (99.999%) was introduced for a three-stage gas replacement: first, a vacuum was drawn to 0.1 MPa, then argon was introduced to atmospheric pressure, repeated three times. Subsequently, the temperature was increased to 350°C at a rate of 8°C / min and maintained at this temperature for 1 hour. The argon flow rate was maintained at 80 mL / min throughout the process. After the reaction was complete, the mixture was cooled to room temperature under controlled conditions and removed, yielding black pre-carbonized straw carbon powder.

[0099] Activation catalytic reaction: Pre-carbonized straw carbon powder and potassium trioxalatoferrate were accurately weighed at a mass ratio of 1:1 and mixed for 30 minutes using a planetary ball mill (300 rpm) with zirconia grinding balls (3 mm and 5 mm in diameter mixed in a 1:2 ratio). The mixture was placed in a high-purity graphite crucible and placed in the central temperature zone of a tube furnace. Under argon protection, the temperature was increased to 800℃ at a rate of 12℃ / min and maintained at this temperature for 2 hours to complete the activation catalytic reaction.

[0100] Post-processing purification: After cooling, the reaction product was first filtered and washed with 0.2 mol / L hydrochloric acid solution, followed by repeated washing with deionized water until the pH of the filtrate was 7. The washed sample was dried for 24 hours to obtain a dark black initial graphitized porous carbon material.

[0101] Supercritical CO2 treatment: 6g of initial graphitized porous carbon material was loaded into a 600mL supercritical reactor. A staged pressurization method was used: first, the pressure was increased to 8MPa at 1.5MPa / min and held for 10 minutes; then, the pressure was increased to 20MPa at 1MPa / min. A gradient heating program was used: first, the temperature was increased to 100℃ at 5℃ / min and held for 20 minutes; then, it was increased to 150℃ at 3℃ / min. Finally, the temperature was maintained at 150℃ and 20MPa for 3 hours. The depressurization process used a two-step method: first, the pressure was reduced to 10MPa at 0.3MPa / min and held for 30 minutes; then, the pressure was reduced to atmospheric pressure at 0.5MPa / min, yielding sorghum straw-based graphitized porous carbon.

[0102] The sorghum straw-based graphitized porous carbon material prepared in Example 3 was used as an electrode material for a supercapacitor. Constant current charge-discharge tests were conducted at different current densities to evaluate its electrochemical performance. A schematic diagram illustrating the specific capacitance variation of the sorghum straw-based graphitized porous carbon at different current densities is shown below. Figure 8 As shown, the sample exhibits a specific capacitance of 227 F / g at a current density of 1 A / g.

[0103] Comparative Example 1: Preparation of bamboo-based porous carbon without activation catalysis

[0104] Raw material pretreatment stage: Bamboo raw materials from the same batch as in Example 1 were selected and processed into particles of 100-300μm using a plant pulverizer. The same cleaning process was used: three ultrasonic cleanings with deionized water (300W power, 40kHz frequency, 30 minutes each time), followed by drying in a vacuum drying oven at 80℃ for 12 hours to ensure the moisture content was below 5wt%.

[0105] Pre-carbonization treatment: The treated bamboo powder was evenly loaded into an alumina crucible and placed in a tube furnace. High-purity argon (99.999%) was introduced to replace the air at a flow rate of 200 mL / min for 30 minutes. Under the protection of an argon flow rate of 50 mL / min, the temperature was increased to 350°C at a rate of 5°C / min and held at a constant temperature for 1 hour to obtain pre-carbonized bamboo charcoal powder. The process parameters for this step were completely consistent with those in Example 1.

[0106] Supercritical CO2 treatment (activation catalysis step omitted): 5g of pre-carbonized powder was directly loaded into a 500mL supercritical reactor without any activating agent. The same supercritical conditions as in Example 1 were used: the pressure was first increased to 10MPa, then the temperature was raised to 150℃ and finally adjusted to 20MPa, maintained for 3 hours, and then slowly released. The entire process used only supercritical CO2 treatment, without the introduction of potassium tris(oxalato)ferrate for activation catalysis.

[0107] The core difference between Comparative Example 1 and Example 1 is that the activation and catalysis steps are completely omitted. Potassium trioxane ferrate is not used as an activation / catalyst. Instead, the pre-carbonized product is directly subjected to supercritical treatment. Figure 9 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based porous carbon under different current densities, as provided in Comparative Example 1 of this invention. Figure 9 As shown, under the same test conditions, the specific capacitance of this material at a current density of 1 A / g is only 44 F / g (approximately 18% of that in Example 1). This result fully demonstrates that the absence of the activation catalysis step leads to insufficient graphitization and poor conductivity in the material; the simultaneous activation-catalysis effect of potassium trioxalatoferrate is irreplaceable in improving the material's performance; and the excellent performance observed in Example 1 is the result of the synergistic effect of pretreatment, activation catalysis, and supercritical treatment. It should be noted that all experimental conditions in this Comparative Example 1 (except for the omission of the activation catalysis step) are consistent with those in Example 1, ensuring the reliability of the comparative results.

[0108] Comparative Example 2: Preparation of bamboo-based graphitized porous carbon without supercritical treatment

[0109] Raw material pretreatment stage: The same batch of bamboo as in Example 1 was selected as raw material and processed into 100-300μm particles using the same pulverization process. The same cleaning process was adopted: three ultrasonic cleanings with deionized water (300W, 40kHz, 30 minutes each time), followed by vacuum drying at 80℃ for 12 hours until the moisture content was <5wt%.

[0110] Pre-carbonization treatment: Dry bamboo powder was placed in an alumina crucible and then placed in a tube furnace. After purging the air at an argon flow rate of 200 mL / min for 30 minutes, the temperature was increased to 350°C at a rate of 5°C / min and held at that temperature for 1 hour (argon flow rate of 50 mL / min). After cooling, pre-carbonized bamboo charcoal powder was obtained, and its physical properties were basically the same as those of the sample in Example 1.

[0111] Activation of the catalytic reaction: Pre-carbonized bamboo charcoal and potassium trioxalatoferrate (1:1 mass ratio) were accurately weighed and mixed for 30 minutes using the same planetary ball mill (zirconia grinding balls, 300 rpm). The mixture was placed in a graphite crucible and heated to 800℃ at 10℃ / min under argon protection (100 mL / min), and reacted at this temperature for 2 hours.

[0112] Post-processing purification: The reaction product was washed with 0.1 mol / L hydrochloric acid and stirred, then washed with deionized water until neutral (pH=7), and vacuum dried at 60℃ for 12 hours to obtain black initial graphitized porous carbon material.

[0113] This comparative example strictly maintains the same raw material processing and activation catalytic process parameters as Example 1, but deliberately omits the key step of supercritical CO2 treatment and directly tests the performance of the activated initial graphitized porous carbon material.

[0114] The electrochemical performance of the sample prepared in this embodiment without supercritical CO2 treatment was tested under the same conditions. Figure 10 This is a schematic diagram illustrating the specific capacitance variation of bamboo-based porous carbon under different current densities, as provided in Comparative Example 2 of the present invention. Figure 10 As shown, the results indicate that the specific capacitance at a current density of 1 A / g is 215 F / g, which is 10.8% lower than that in Example 1; when the current density increases to 20 A / g, the specific capacitance retention drops to 53%, and the rate performance decreases significantly.

[0115] This invention also provides a supercapacitor electrode material comprising graphitized porous carbon, wherein the graphitized porous carbon is prepared by the graphitized porous carbon preparation method of this invention.

[0116] It should be noted that the term "comprising" and its variations used in the embodiments of the present invention are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "multiple" mentioned in the embodiments of the present invention are illustrative and not restrictive. Those skilled in the art should understand that, unless explicitly indicated otherwise in the context, they should be understood as "one or more".

[0117] The steps described in the method embodiments provided by this invention can be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of protection of this invention is not limited in this respect.

[0118] The term "embodiment" in this specification refers to a specific feature, structure, or characteristic described in connection with an embodiment that may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily imply the same embodiment, nor does it imply independence or alternativeity from other embodiments. The various embodiments in this specification are described in a related manner, with reference to each other for similar or identical parts. In particular, for apparatus, device, and system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, and relevant details are referred to in the description of the method embodiments.

[0119] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing graphitized porous carbon, characterized in that, include: Biomass raw materials are pretreated to obtain pre-carbonized powder; The pre-carbonized powder was mixed with potassium trioxalatoferrate and then subjected to a high-temperature activation catalytic reaction under a first inert atmosphere to obtain the initial graphitized porous carbon material. The initial graphitized porous carbon material is treated with supercritical carbon dioxide to optimize its pore structure through the permeation and pore-expanding effects of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material.

2. The method according to claim 1, characterized in that, The process of pre-treating biomass raw materials to obtain pre-carbonized powder includes: The biomass raw material is sequentially crushed, washed and dried to obtain biomass raw material powder; The biomass raw material powder is pre-carbonized under a second inert atmosphere to obtain pre-carbonized powder.

3. The method according to claim 2, characterized in that, The second inert atmosphere is an argon atmosphere or a nitrogen atmosphere; The step of pre-carbonizing the biomass raw material powder under a second inert atmosphere to obtain pre-carbonized powder includes: The biomass raw material powder is transferred to a tube furnace and subjected to high-temperature pre-carbonization treatment under the atmosphere of argon or nitrogen to obtain the pre-carbonized powder. The temperature of the pre-carbonization treatment is 200℃~500℃ and the time is 1h~3h.

4. The method according to claim 1, characterized in that, The process involves mixing the pre-carbonized powder with potassium trioxalatoferrate and then subjecting it to a high-temperature activation catalytic reaction under a first inert atmosphere to obtain an initial graphitized porous carbon material, comprising: The pre-carbonized powder and the potassium trioxalate ferrate were mixed in a ball mill to obtain a homogeneous mixture. The homogeneous mixture is subjected to a high-temperature activation catalytic reaction under the first inert atmosphere to obtain the reaction product to be treated; After cooling the reaction product to room temperature, it was repeatedly washed with dilute hydrochloric acid and deionized water until neutral, and then dried to obtain the initial graphitized porous carbon material.

5. The method according to claim 4, characterized in that, The mass ratio of the pre-carbonized powder to the potassium trioxalatoferrate is 1:5 to 5:1; the first inert atmosphere is an argon atmosphere or a nitrogen atmosphere; the reaction temperature of the high-temperature activation catalytic reaction is 600℃ to 1200℃, and the reaction time is 1 h to 5 h; the rotation speed of the ball mill is 100 rpm to 500 rpm, and the mixing time is 10 min to 60 min.

6. The method according to claim 1, characterized in that, The step of treating the initial graphitized porous carbon material with supercritical carbon dioxide to optimize the pore structure of the initial graphitized porous carbon material through the permeation and pore-expanding effects of supercritical carbon dioxide, thereby obtaining the target graphitized porous carbon material, includes: The initial graphitized porous carbon material is placed in a high-pressure reaction vessel, and carbon dioxide is introduced into the high-pressure reaction vessel while the temperature and pressure are increased to make the carbon dioxide reach a supercritical state. The supercritical state is maintained for a set time, allowing the supercritical carbon dioxide to permeate into the pore structure of the initial graphitized porous carbon material to obtain the target graphitized porous carbon material.

7. The method according to claim 6, characterized in that, The temperature of the supercritical carbon dioxide treatment is 100℃~200℃, the pressure is 10MPa~30MPa, and the set time is 1h~6h.

8. The method according to claim 1, characterized in that, The biomass raw material is a straw-type plant, which includes at least one of the following: bamboo, sunflower straw, rush, rice straw, wheat straw, corn straw, and sorghum straw.

9. A supercapacitor electrode material, characterized in that, The supercapacitor electrode material comprises graphitized porous carbon, which is prepared by the method according to any one of claims 1 to 8.

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