Preparation methods of high-performance supercapacitor electrode materials and supercapacitors

Abstract

This invention discloses a method for preparing a high-performance supercapacitor electrode material, comprising: raw material preparation; raw material pretreatment; composite system construction; self-template assembly; Joule thermal activation; post-treatment purification; surface functional modification; and finished product acquisition. A supercapacitor is manufactured using the aforementioned high-performance supercapacitor electrode material. This invention's method for preparing the high-performance supercapacitor electrode material and the supercapacitor itself utilizes green and renewable lignin as the core raw material. A graphene-carbon dot composite self-template system is constructed. Through synergistic Joule thermal ultrafast activation and ammonia nitrogen doping modification, a hierarchical porous structure with a sub-nanometer micropore ratio of ≥90% is achieved. This balances high specific surface area and rapid ion transport, resulting in a supercapacitor electrode material with high specific capacitance and long cycle stability. Furthermore, it is suitable for wide-temperature-range and multi-scenario applications, offering better commercial prospects and value. It is suitable for industrial-scale production and reduces industrial application costs.

Description

Technical Field

[0001] This invention relates to the field of electrical components, specifically to capacitors, and more particularly to a method for preparing high-performance supercapacitor electrode materials and supercapacitors. Background Technology

[0002] Supercapacitors, as a novel energy storage device combining high power density, long cycle life, and rapid charge-discharge characteristics, have irreplaceable application value in fields such as energy recovery from braking in new energy transportation, power supply for flexible electronic devices, and peak-shaving energy storage in smart grids. The performance of electrode materials directly determines the energy storage efficiency and service life of supercapacitors, making it one of the core directions of industry research and development. Currently, commercial supercapacitor electrode materials are mainly activated carbon and graphene. However, activated carbon has defects such as low specific surface area and uneven pore size distribution, resulting in high ion transport resistance. Graphene is prone to sheet aggregation, making it difficult to fully utilize its theoretical specific surface area advantage. At the same time, the above materials mostly rely on fossil-based raw materials for preparation, resulting in high cost and significant environmental impact.

[0003] Existing methods for preparing supercapacitors are insufficient to achieve the synergy of green raw materials, efficient preparation, and high-performance electrode materials. There is an urgent need to develop a method for preparing supercapacitor electrode materials that features renewable raw materials, efficient and controllable processes, and excellent performance. Summary of the Invention

[0004] The technical problem this invention aims to solve is: to address the difficulty of achieving green raw materials, efficient preparation, and synergistic effects of high-performance electrode materials in existing supercapacitor preparation methods. This invention provides a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. By constructing a graphene-carbon dot composite self-templating system and through the synergistic effect of Joule thermal ultrafast activation and ammonia nitrogen doping modification, a hierarchical porous structure with a sub-nanometer micropore ratio of ≥90% is achieved. This method balances high specific surface area and rapid ion transport, resulting in a supercapacitor electrode material with high specific capacitance and long cycle stability. This material is suitable for wide-temperature-range and multi-scenario applications, is suitable for industrial-scale production, and reduces industrial application costs.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for preparing a high-performance supercapacitor electrode material, comprising the following steps: S1. Raw material preparation: Lignin, graphene, carbon dots, potassium hydroxide activator, and ammonia water are used as raw materials; S2. Raw material pretreatment: Lignin is soaked in hydrochloric acid solution to remove ash, washed until neutral, dried, pulverized and sieved; graphene is dispersed into a dispersion. S3. Construction of composite system: Weigh the dry base of pretreated lignin and graphene dispersion and carbon dots and pour them into the reaction vessel. Add deionized water and disperse and stir to form a uniform mixed slurry. S4. Self-template assembly: Add potassium hydroxide activator to the mixed slurry, heat and stir to promote carbon dot cross-linking to form a high-density hydrogel, and construct a sub-nanometer microporous self-template; S5. Joule thermal activation: The hydrogel is transferred to an ultrafast Joule thermal reactor for carbonization activation, spontaneously forming a hierarchical porous network structure to obtain the activated product; S6. Post-purification treatment: The activated product is washed until neutral to remove residual potassium hydroxide, and then vacuum dried to obtain a porous carbon intermediate; S7. Surface functional modification: The porous carbon intermediate is placed in an ammonia atmosphere and nitrogen doped to introduce oxygen- and nitrogen-containing functional groups to obtain the modified material. S8. Finished Product Acquisition: Detect the specific surface area, pore size distribution and electrochemical performance of the modified material to obtain high-performance supercapacitor electrode materials with a specific surface area ≥2500m² / g and a sub-nanometer micropore ratio ≥90%.

[0006] The present invention relates to a method for preparing high-performance supercapacitor electrode materials. Furthermore, in step S1, the lignin undergoes acid washing and deashing pretreatment, resulting in a carbon content ≥60% and an ash content ≤0.5%, ensuring the formation of a well-developed porous structure during subsequent carbonization and avoiding the adverse effects of impurities on electrode conductivity. The carbon dots are carbonized polymer dots with a particle size of 5-10 nanometers, precisely matching the self-template assembly requirements, ensuring crosslinking efficiency without damaging the microporous structure due to excessively large particles. The graphene has a purity ≥98%, and the potassium hydroxide activator has a purity ≥95%. This high-purity design avoids side reactions caused by impurity ions during activation, ensuring the uniformity of the pore structure. The ammonia solution has a concentration of 25%, providing a stable nitrogen source for the subsequent nitrogen doping process.

[0007] Further, in step S3, the lignin is soaked in a 5%-10% hydrochloric acid solution for 2 hours to remove ash, washed until neutral, dried at 105°C for 4 hours, and then pulverized through an 80-mesh sieve. The graphene is ultrasonically dispersed for 30 minutes to form a dispersion with a concentration of 0.5 mg / mL. The ultrasonic dispersion power is set to 300 watts and the ultrasonic frequency to 40 kHz, generating a highly efficient cavitation effect, effectively breaking the van der Waals forces between graphene sheets and avoiding aggregation. The magnetic stirring speed is 500 rpm, which can promote the polymerization of lignin. The molecular-level fusion of graphene and carbon dots, with the ambient temperature controlled at 25℃ during stirring, ensures uniform fusion of all components without significant agglomeration. This guarantees the reactivity of each component while preventing premature cross-linking of carbon dots due to excessively high temperatures. The dispersion effect is verified by laser particle size analyzer, ensuring that the particle agglomerates in the mixed slurry have a particle size not exceeding 500 nanometers, forming a uniform and stable composite system. This lays the foundation for subsequent self-templating assembly and the formation of hierarchical porous structures, significantly improving the structural consistency and electrochemical stability of the material.

[0008] Furthermore, in step S4, potassium hydroxide activator is added to the mixed slurry at an alkali-to-carbon ratio of 3:1-4:1. The potassium hydroxide activator is added in stages: first, 50% potassium hydroxide is added and stirred for 1 hour, then the remaining 50% potassium hydroxide is added and stirred for another 2 hours. This avoids excessive local alkali concentration that could lead to excessive degradation of lignin, while ensuring uniform distribution of the activator. The heating rate is controlled at 5°C per minute, and samples are taken every 30 minutes during the constant temperature stirring process at 80°C to ensure that the hydrogel forms uniformly without stratification.

[0009] Furthermore, in step S5, the ultrafast Joule heating device heats the material at a rate of 1100 K / s, with a pulsed current power of 10 kW. This rapidly bypasses the side reaction temperature range during lignin carbonization, reducing heteroatom loss. The activation temperature is 800℃-900℃, which facilitates the formation of abundant micropores, appropriately increasing the mesopore ratio and enabling precise control of pore size distribution. During activation, inert gas protection effectively isolates oxygen, preventing surface oxidation and inhibiting graphitization of the carbon material, preserving more active sites. Carbonization activation is completed within 3-8 seconds. This extremely short holding time balances the degree of carbonization and pore structure integrity, preventing over-carbonization and pore collapse. The innovative application of ultrafast Joule heating activation technology enables the rapid and efficient construction of a hierarchical porous network structure, significantly improving the specific surface area and conductivity of the material.

[0010] Furthermore, in step S6, the activated product is repeatedly washed with deionized water using vacuum filtration, which improves the washing efficiency by more than 40% while reducing water consumption, meeting energy-saving requirements. The water consumption for each wash is 10 times the product mass, ensuring full dissolution and removal of residual potassium hydroxide and reaction byproducts. Vacuum drying at 120℃ for 6 hours, with a vacuum degree ≥0.09MPa, can quickly remove moisture without damaging the microstructure of porous carbon. The product is turned over every 2 hours during the drying process to ensure uniform drying. The final product has a moisture content ≤1%, avoiding residual moisture from affecting the subsequent nitrogen doping effect and the electrochemical performance of the material, significantly improving the stability and reliability of the finished electrode material.

[0011] Furthermore, in step S7, the porous carbon intermediate is subjected to nitrogen doping at a constant temperature of 600℃ for 2 hours. The ammonia flow rate is controlled at 50 ml / min to ensure that the ammonia fully surrounds the porous carbon intermediate, achieving uniform doping, while avoiding waste and environmental pollution caused by excessive ammonia. The heating rate is set to 10℃ / min, and the slow heating allows nitrogen atoms to gradually penetrate into the lattice structure of the porous carbon, forming stable chemical bonds. After nitrogen doping, the nitrogen content of the material reaches 4-6 atomic percentages. This nitrogen content range can maximize the pseudocapacitive performance of the material without affecting its conductivity. During the nitrogen doping process, oxygen-containing functional groups such as carboxyl and hydroxyl groups are introduced simultaneously, increasing the number of oxygen-containing functional groups on the surface by 30% compared to before modification. X-ray photoelectron spectroscopy verification shows that graphitic nitrogen and pyrrole nitrogen form a synergistic effect with carboxyl and hydroxyl groups, significantly improving the hydrophilicity and ion adsorption capacity of the material, thereby enhancing the charge-discharge performance and cycle stability of the supercapacitor.

[0012] Furthermore, it also includes step S71: performance regulation: The specific surface area, pore size distribution, and electrochemical performance of the modified material obtained in step S7 are detected. Specific surface area is used as the core regulation indicator, with other parameters serving as co-verification indicators. A multi-dimensional co-verification scheme is adopted for performance testing. Specific surface area is detected using the nitrogen adsorption-desorption method, with a testing accuracy of ±5 square meters per gram, accurately reflecting the porosity of the material. Pore size distribution is analyzed using density functional theory models, which can accurately distinguish the proportion and size distribution of micropores and mesopores, providing data support for process optimization. Electrochemical performance is tested using a three-electrode system in a 6 mol / L potassium hydroxide electrolyte, with the working electrode, counter electrode, and reference electrode all included. The combined design of the electrodes ensures the accuracy of the test results. A specific capacitance of ≥450 Farads per gram is set as the standard for compliance, which is much higher than that of traditional porous carbon materials. If the specific surface area is <2000 m² / g, step S5 is repeated and the holding time is extended by 1-2 seconds until the index is met. This avoids structural damage caused by over-activation and achieves precise control of material performance. Through this performance control process, the electrochemical performance of the final product is ensured to be stable and reliable, meeting the application requirements of high-performance supercapacitors. If the specific surface area meets the standard, but the pore size distribution or electrochemical performance does not, the raw material ratio, gel assembly parameters, or nitrogen doping process parameters are adjusted accordingly to achieve synergistic compliance of multiple performance indicators.

[0013] Furthermore, in step S8, the packing density of the high-performance supercapacitor electrode material is ≥0.7 g / cm³, ensuring good formability during electrode preparation. The total pore volume is ≥1.0 cm³ / g, providing ample space for ion storage. The mesoporous ratio is >35%, optimizing the ion transport path and reducing ion diffusion resistance. The ion transport resistance is ≤5Ω, significantly improving the rate performance of the material. The synergistic effect of these performance indicators enables the material to simultaneously possess high specific surface area, excellent conductivity, and rapid ion transport capability. This successfully solves the technical challenge of balancing specific surface area, conductivity, and ion transport efficiency in traditional porous carbon materials, meeting the dual requirements of high power density and high energy density for supercapacitors. This provides core support for the application of supercapacitors in wide temperature range and long-cycle scenarios.

[0014] Another technical solution adopted by the present invention to solve its technical problem is: a supercapacitor, made of the above-mentioned high-performance supercapacitor electrode material, wherein the preparation method of the supercapacitor includes the following steps: A1. Electrode preparation: The high-performance supercapacitor electrode material is mixed with polytetrafluoroethylene binder at a ratio of 95:5, and anhydrous ethanol is added to make a paste. The paste is uniformly coated on the nickel foam current collector with a coating thickness of 100μm. The electrode sheet is obtained by vacuum drying at 120℃ for 2 hours and pressing it with a pressure of 10MPa. A2. Device Components: Using electrode sheets as positive and negative electrodes, a polypropylene membrane as the isolation layer, and potassium hydroxide aqueous solution or tetraethylammonium tetrafluoroborate / acetonitrile organic electrolyte as the electrolyte, a button-type supercapacitor is assembled in an argon glove box. A3. Performance Testing: Conduct electrochemical performance tests on the assembled supercapacitors; The supercapacitor is used in flexible electronic devices, new energy transportation auxiliary energy storage systems, or smart grid energy storage systems.

[0015] The beneficial effects of this invention are: The present invention relates to a method for preparing high-performance supercapacitor electrode materials and a supercapacitor, which uses lignin as the core precursor to replace fossil-based raw materials, and has the characteristics of both renewability and low cost. After the raw materials are pretreated by acid washing and deashing, the interference of impurities on electrode performance is avoided, and the environmental impact and raw material cost of material preparation are significantly reduced.

[0016] The present invention relates to a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. The self-templating system breaks through the bottleneck of traditional template technology by innovatively adopting a graphene-carbon dot composite self-templating system. The carbon dots form a sub-nanometer microporous self-templating system through cross-linking. After subsequent carbonization, the template is directly converted into a carbon structure, eliminating the template removal step, avoiding structural damage, and solving the problems of unstable structure and low porosity of traditional template methods.

[0017] The present invention discloses a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. Joule thermal activation enables the efficient and controllable construction of a hierarchical porous structure, reduces the loss of heteroatoms, and achieves a hierarchical porous structure of micropores and mesopores. This ensures a high specific surface area and optimizes the ion transport path, thus solving the contradiction between high specific surface area and high ion transport efficiency in traditional carbon materials.

[0018] The present invention relates to a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. Surface modification synergistically enhances electrochemical performance, and simultaneously introduces oxygen-containing functional groups such as carboxyl and hydroxyl groups. Graphitic nitrogen and pyrrole nitrogen form a synergistic effect with the oxygen-containing functional groups, which not only improves the hydrophilicity and ion adsorption capacity of the material, but also enhances the contribution of pseudocapacitance.

[0019] The present invention discloses a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. The preparation process is highly efficient and energy-saving, and can be scaled up. Vacuum filtration washing efficiency is 40% higher than that of traditional static washing, and Joule thermal activation energy consumption is 30% lower than that of traditional high-temperature furnace activation. The step-by-step activation and precise control of the process steps are highly controllable, and the product performance is highly stable, making it suitable for industrial-scale production and reducing industrial application costs.

[0020] The present invention discloses a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. The high-performance supercapacitor electrode materials have excellent performance and wide application scenarios. At a current density of 1A / g, the specific capacitance is ≥400F / g, the energy density is ≥50Wh / kg, the capacity retention rate is ≥93% after 10,000 cycles, and it can work stably in a wide temperature range of -40℃ to 60℃. It can meet the energy storage needs of multiple scenarios such as new energy transportation, flexible electronics, and smart grids, and significantly expands the application scope of supercapacitors. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a flowchart outlining the steps of the method for preparing the high-performance supercapacitor electrode material of the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0024] Unless otherwise specified, all raw materials used in the preparation of the high-performance supercapacitor electrode material of this invention are commercially available; all instruments used in the tests are conventional laboratory instruments, and the testing standards comply with industry norms.

[0025] Raw material parameter description: Lignin: carbon content ≥60%, ash content ≤0.5%, purchased from Henan Xingtai Chemical Co., Ltd.; Graphene: purity ≥98%, flake size 1-5μm, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.; Carbon dots: carbonized polymer dots, particle size 5-10nm, purchased from Suzhou Carbonfeng Technology Co., Ltd.; Potassium hydroxide activator: purity ≥95%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Ammonia water: concentration 25%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0026] Example 1: like Figure 1 As shown, a method for preparing a high-performance supercapacitor electrode material includes the following steps: A high-performance supercapacitor electrode material, using a green and renewable lignin-based precursor as the core raw material, and constructing a self-templating system by combining graphene and carbon dots, is prepared as follows: S1: Raw material preparation, obtaining lignin, graphene, carbon dots, potassium hydroxide activator, and ammonia water, ensuring that all raw materials are free of heavy metal residues; S2: Raw material pretreatment: Lignin is soaked in 7% hydrochloric acid solution for 2 hours to remove ash, washed with deionized water until neutral, dried at 105℃ for 4 hours, and pulverized through an 80-mesh sieve; Graphene is ultrasonically dispersed for 30 minutes to form a dispersion with a concentration of 0.5mg / mL. S3: Construction of the composite system: Weigh the pretreated lignin, graphene dispersion dry base and carbon dots in a mass ratio of 10:2:3, pour them into a three-necked flask, add deionized water to adjust the solid-liquid ratio to 1:15, ultrasonically disperse at 300W power and 40kHz frequency for 40 minutes, and then magnetically stir at 500r / min speed for 2 hours at 25℃ to form a uniform mixed slurry; S4: Self-template assembly. Add potassium hydroxide activator to the mixed slurry in batches, control the alkali-to-carbon ratio to 3:1. First add 50% potassium hydroxide and stir for 1 hour, then add the remaining 50% potassium hydroxide. Heat to 80℃ at a rate of 5℃ / min and stir at a constant temperature for 3 hours. Take samples every 30 minutes to ensure that the carbon dots crosslink to form a uniform, non-layered, high-density hydrogel, thus completing the sub-nanometer microporous self-template construction. S5: Joule thermal activation: The hydrogel is transferred to an ultrafast Joule thermal reactor, inertly protected by argon gas, heated to 850°C at a rate of 1100K / s, and held for 5 seconds to complete carbonization activation, spontaneously forming a hierarchical porous network structure. S6: Post-processing purification: The activated product is washed with vacuum filtration-assisted washing and repeatedly washed with deionized water (each wash using 10 times the product mass) until pH=7 to remove residual potassium hydroxide; then it is placed in a vacuum drying oven and dried at 120℃ and vacuum degree ≥0.09MPa for 6 hours. During the drying process, the product is turned over every 2 hours to ensure uniform drying. The final product has a moisture content ≤1%, yielding a porous carbon intermediate; S7: Surface functional modification: The porous carbon intermediate was placed in an ammonia atmosphere, and the ammonia flow rate was controlled at 50 mL / min. The temperature was increased to 600℃ at a rate of 10℃ / min and held at the temperature for 2 hours to perform nitrogen doping, introducing oxygen- and nitrogen-containing functional groups. After modification, the nitrogen content of the material reached 4.2 atomic percentages, and the number of oxygen-containing functional groups on the surface increased by 30% compared with the unmodified material. S71: Performance Regulation: Detect the specific surface area, pore size distribution, and electrochemical performance of the modified material obtained in step S7, with specific surface area as the core regulation index and other parameters as co-verification indexes; when the specific surface area of ​​the material is <2000m² / g, repeat step S5 and extend the holding time by 1-2s until the index meets the standard; if the specific surface area meets the standard but the pore size distribution or electrochemical performance does not meet the standard, adjust the raw material ratio, gel assembly parameters, or nitrogen doping process parameters accordingly to achieve synergistic compliance of multiple performance indicators.

[0027] Specifically, the specific surface area was determined by nitrogen adsorption, the pore size distribution was analyzed by density functional theory model, and the electrochemical performance was tested in a 6 mol / L potassium hydroxide electrolyte using a three-electrode system. The specific surface area was found to be 2650 m² / g, which meets the requirement of ≥2500 m² / g, so step S5 does not need to be repeated. S8: Finished product acquisition, yielding a high-performance supercapacitor electrode material with a specific surface area of ​​2650 m² / g, a sub-nano micropore ratio of 92%, a bulk density of 0.75 g / cm³, a total pore volume of 1.12 cm³ / g, a mesopore ratio of 38%, and an ion transport resistance of 4.2 Ω.

[0028] The application steps for this electrode material are as follows: Step 1: Electrode preparation. The finished electrode material is mixed with polytetrafluoroethylene binder at a mass ratio of 95:5. Anhydrous ethanol is added to make a paste. The paste is uniformly coated on the nickel foam current collector with a coating thickness of 100μm. The paste is then vacuum dried at 120℃ for 2 hours and pressed into shape under a pressure of 10MPa. Step 2: Device assembly. Using the prepared electrode sheets as positive and negative electrodes, a polypropylene membrane as the isolation layer, and a 6 mol / L potassium hydroxide aqueous solution as the electrolyte, a button-type supercapacitor is assembled in an argon glove box. Step 3: Performance testing. The assembled supercapacitor was subjected to electrochemical performance testing. At a current density of 1 A / g, the specific capacitance was 468 F / g, the energy density was 52 Wh / kg, and the capacity retention rate was 94.5% after 10,000 cycles. Step 4: Practical application. This supercapacitor is used in flexible electronic devices and operates stably in a wide temperature range of -40℃ to 60℃.

[0029] Example 2: A high-performance supercapacitor electrode material, using a green and renewable lignin-based precursor as the core raw material, and constructing a self-templating system by combining graphene and carbon dots, is prepared as follows: S1: Raw material preparation, same as in Example 1; S2: Raw material pretreatment: Lignin was soaked in 8% hydrochloric acid solution for 2 hours to remove ash, and subsequent washing, drying and pulverizing steps were the same as in Example 1; the preparation of graphene dispersion was the same as in Example 1; S3: Construction of the composite system: Weigh the raw materials according to the mass ratio of 10:2:3, adjust the ultrasonic dispersion power to 350W, and follow the same parameters and operations as in Example 1 to form a uniformly mixed slurry. S4: Self-template assembly, control the alkali-to-carbon ratio at 3.5:1, add potassium hydroxide in batches, and use the same heating and constant temperature stirring parameters as in Example 1 to form a uniform high-density hydrogel. S5: Joule thermal activation, heating to 870°C at a rate of 1100K / s, holding for 6 seconds, and the remaining operations are the same as in Example 1, to form a hierarchical porous network structure. S6: Post-processing purification, the operation is the same as in Example 1, to obtain a porous carbon intermediate; S7: Surface functional modification, ammonia flow rate controlled at 60 mL / min, nitrogen doping isothermal treatment time extended to 2.5 hours, after modification the nitrogen content of the material reaches 5.1 atomic percentage, and the number of oxygen-containing functional groups on the surface increases by 35% compared with the unmodified material; S71: Performance adjustment, the specific surface area was measured to be 2820m² / g, which meets the requirements, so there is no need to repeat step S5; S8: Finished product acquisition, yielding a high-performance supercapacitor electrode material with a specific surface area of ​​2820 m² / g, a sub-nano micropore ratio of 93%, a bulk density of 0.78 g / cm³, a total pore volume of 1.25 cm³ / g, a mesopore ratio of 40%, and an ion transport resistance of 3.8 Ω.

[0030] The application steps for this electrode material are as follows: Step 1: Electrode preparation, same as in Example 1; Step 2: Device assembly. Tetraethylammonium tetrafluoroborate / acetonitrile organic electrolyte is selected. The remaining operations are the same as in Example 1. Assemble the button-type supercapacitor. Step 3: Performance testing. At a current density of 1 A / g, the specific capacitance is 485 F / g, the energy density is 55 Wh / kg, and the capacity retention rate is 95.2% after 10,000 cycles. Step 4: Practical application. This supercapacitor is used in new energy transportation auxiliary energy storage systems and operates stably over a wide temperature range.

[0031] Example 3: A high-performance supercapacitor electrode material, using a green and renewable lignin-based precursor as the core raw material, and constructing a self-templating system by combining graphene and carbon dots, is prepared as follows: S1: Raw material preparation, same as in Example 1; S2: Raw material pretreatment: Lignin was soaked in 10% hydrochloric acid solution for 2 hours to remove ash. Subsequent washing, drying, and pulverizing steps were the same as in Example 1; the preparation of graphene dispersion was the same as in Example 1. S3: Construction of the composite system: Weigh the raw materials according to the mass ratio of 10:2:3, adjust the ultrasonic dispersion power to 400W, increase the stirring speed to 550r / min, and keep the other parameters the same as in Example 1 to form a uniformly mixed slurry; S4: Self-template assembly, control the alkali-to-carbon ratio of 4:1, add potassium hydroxide in batches, take samples for observation every 20 minutes during constant temperature stirring, and perform the remaining operations as in Example 1 to form a uniform high-density hydrogel. S5: Joule thermal activation, heating to 900°C at a rate of 1100K / s, holding for 8 seconds, and the remaining operations are the same as in Example 1, to form a hierarchical porous network structure. S6: Post-processing purification, the operation is the same as in Example 1, to obtain a porous carbon intermediate; S7: Surface functional modification, ammonia flow rate controlled at 70 mL / min, nitrogen doping temperature raised to 620℃, constant temperature treatment for 2 hours, after modification the nitrogen content of the material reaches 5.8 atomic percentage, and the number of oxygen-containing functional groups on the surface increases by 40% compared with the unmodified material; S71: Performance adjustment, the specific surface area was measured to be 2980m² / g, which meets the requirements, so there is no need to repeat step S5; S8: Finished product acquisition, yielding a high-performance supercapacitor electrode material with a specific surface area of ​​2980 m² / g, a sub-nano micropore ratio of 94%, a bulk density of 0.82 g / cm³, a total pore volume of 1.38 cm³ / g, a mesopore ratio of 42%, and an ion transport resistance of 3.5 Ω.

[0032] The application steps for this electrode material are as follows: Step 1: Electrode preparation, same as in Example 1; Step 2: Device assembly. Tetraethylammonium tetrafluoroborate / acetonitrile organic electrolyte is used to assemble the soft-pack supercapacitor in an argon glove box. Step 3: Performance testing. At a current density of 1 A / g, the specific capacitance is 502 F / g, the energy density is 58 Wh / kg, and the capacity retention rate is 96.1% after 10,000 cycles. Step 4: Practical application. This supercapacitor is used in smart grid energy storage systems and operates stably over a wide temperature range.

[0033] Comparative Example 1: No carbon dots are added, and no self-template system is constructed. The remaining raw materials and preparation process are the same as in Example 1. Specifically, in S3, only the dry basis of lignin and graphene dispersion is weighed at a mass ratio of 10:2, and no carbon dots are added. In S4, since there is no carbon dot crosslinking, a high-density hydrogel cannot be formed, and it directly enters the Joule thermal activation step. The subsequent process remains unchanged.

[0034] Comparative Example 2: Traditional high-temperature calcination was used instead of Joule thermal activation, while the remaining raw materials and preparation process remained the same as in Example 1. Specifically, the ultrafast Joule thermal reaction device was removed in step S5, and the hydrogel was placed in a muffle furnace and heated to 850°C at a rate of 5°C / min, and held at that temperature for 2 hours to complete carbonization and activation. There was no inert gas protection, and the subsequent processes remained unchanged.

[0035] Comparative Example 3: The S7 surface functional modification (nitrogen doping) step is omitted, and the remaining raw materials and preparation processes are the same as in Example 1. That is, after the porous carbon intermediate is purified by the S6 post-treatment, it directly enters the S71 performance regulation step, without nitrogen doping treatment in an ammonia-free atmosphere.

[0036] Performance testing: 1. Basic material performance testing Standards: Specific surface area is tested by nitrogen adsorption-desorption method (GB / T19587-2004), pore size distribution is analyzed by density functional theory (DFT) model, bulk density is tested according to GB / T1479.1-2011, and ion transport resistance is tested by electrochemical impedance spectroscopy (EIS).

[0037] Indicators: specific surface area (m² / g), percentage of sub-nanometer micropores (%), bulk density (g / cm³), and ion transport resistance (Ω).

[0038] 2. Electrochemical performance testing Standard: The three-electrode system was used for testing in 6 mol / L potassium hydroxide electrolyte. Cyclic stability testing was performed according to GB / T33818-2017, with current densities set at 1 A / g and 5 A / g (rate performance).

[0039] Specifications: 1A / g specific capacitance (F / g), 5A / g specific capacitance (F / g), capacity retention after 10,000 cycles (%), energy density (Wh / kg).

[0040] The table below shows the basic performance test results of Examples 1 to 3 and Comparative Examples 1 to 3:

[0041] The table below shows the electrochemical performance test results of Examples 1 to 3 and Comparative Examples 1 to 3.

[0042] As shown in the table above, the electrode materials prepared in Examples 1 to 3 all have a specific surface area ≥2500m² / g, a sub-nanometer micropore ratio ≥92%, excellent electrochemical performance, a specific capacitance of ≥468F / g at 1A / g, a capacity retention rate of ≥94.5% after 10,000 cycles, and an energy density of ≥52Wh / kg. This demonstrates the synergistic effect of the lignin-based precursor with the graphene and carbon dot self-templating system, as well as the performance enhancement effect of Joule thermal activation and nitrogen doping processes.

[0043] Table of Pseudocapacitance Performance Testing Parameters and Comparison Data:

[0044] This invention utilizes high-temperature nitrogen doping modification in an ammonia atmosphere to stably introduce a large number of graphitic nitrogen, pyrrole nitrogen, and pyridine nitrogen active sites onto the surface of lignin-based hierarchical porous carbon materials, while simultaneously enriching oxygen-containing functional groups such as hydroxyl and carboxyl groups. These heteroatom functional groups can undergo highly reversible redox reactions in an alkaline electrolyte system, generating stable pseudocapacitance. Unlike traditional pure carbon materials that rely solely on the double-layer energy storage mechanism of physical adsorption, this invention achieves a synergistic effect of double-layer physical energy storage combined with reversible chemical energy storage of heteroatoms.

[0045] Meanwhile, the highly interconnected hierarchical porous network structure constructed by the ultrafast Joule thermal activation process of this invention has the structural advantages of high specific surface area and reasonable mesopore / micropore ratio, which can provide sufficient active reaction interface and fast ion transport channel for pseudocapacitive redox reaction, and completely solve the technical contradictions of high pseudocapacitance, poor rate performance and weak cycle stability of traditional modified carbon materials.

[0046] Comparative Example 1, lacking carbon dots, could not construct an effective self-template, resulting in a significant decrease in specific surface area and micropore ratio, increased ion transport resistance, and a substantial decline in electrochemical performance. Comparative Example 2, using traditional calcination instead of Joule thermal activation, resulted in severe material oxidation and uneven pore size distribution, with performance superior to Comparative Example 1 but far inferior to the examples. Comparative Example 3, omitting the nitrogen doping step, resulted in insufficient pseudocapacitance contribution, decreased specific capacitance and cycle stability, further confirming the necessity of each core process.

[0047] This invention provides a method for preparing high-performance supercapacitor electrode materials and a supercapacitor. A graphene-carbon dot composite self-templating system is constructed. Through Joule thermal ultrafast activation and ammonia nitrogen doping modification, a hierarchical porous structure with a sub-nanometer micropore ratio of ≥90% is achieved. This method balances high specific surface area and fast ion transport, resulting in a supercapacitor electrode material with high specific capacitance and long cycle stability. It is suitable for wide temperature range and multi-scenario applications, and is suitable for industrial-scale production, reducing industrial application costs.

[0048] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a high-performance supercapacitor electrode material, characterized in that: Includes the following steps: S1. Raw material preparation: Lignin, graphene, carbon dots, potassium hydroxide activator, and ammonia water are used as raw materials; S2. Raw material pretreatment: Lignin is soaked in hydrochloric acid solution to remove ash, washed until neutral, dried, pulverized and sieved; graphene is dispersed into a dispersion. S3. Construction of composite system: Weigh the dry base of pretreated lignin and graphene dispersion and carbon dots and pour them into the reaction vessel. Add deionized water and disperse and stir to form a uniform mixed slurry. S4. Self-template assembly: Add potassium hydroxide activator to the mixed slurry, heat and stir to promote carbon dot cross-linking to form a high-density hydrogel, and construct a sub-nanometer microporous self-template; S5. Joule thermal activation: The hydrogel is transferred to an ultrafast Joule thermal reactor for carbonization activation, spontaneously forming a hierarchical porous network structure to obtain the activated product; S6. Post-purification treatment: The activated product is washed until neutral to remove residual potassium hydroxide, and then vacuum dried to obtain a porous carbon intermediate; S7. Surface functional modification: The porous carbon intermediate is placed in an ammonia atmosphere and nitrogen doped to introduce oxygen- and nitrogen-containing functional groups to obtain the modified material. S8. Finished Product Acquisition: Detect the specific surface area, pore size distribution and electrochemical performance of the modified material to obtain high-performance supercapacitor electrode materials with a specific surface area ≥2500m² / g and a sub-nanometer micropore ratio ≥90%.

2. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S1, the lignin undergoes acid washing and deashing pretreatment, and the carbon content of the lignin is ≥60% and the ash content is ≤0.5%; the carbon dots are carbonized polymer dots with a particle size of 5-10 nanometers; the purity of the graphene is ≥98%; the purity of the potassium hydroxide activator is ≥95%; and the concentration of the ammonia water is 25%.

3. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S3, the lignin is soaked in a 5%-10% hydrochloric acid solution for 2 hours to remove ash, washed until neutral, dried at 105°C for 4 hours, and then pulverized through an 80-mesh sieve. The graphene is ultrasonically dispersed for 30 minutes to form a dispersion with a concentration of 0.5 mg / mL. The ultrasonic dispersion power is set to 300 watts, the ultrasonic frequency is 40 kHz, the magnetic stirring speed is 500 rpm, and the ambient temperature is controlled at 25°C during the stirring process to ensure that the components are uniformly fused and there is no obvious agglomeration.

4. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S4, potassium hydroxide activator is added to the mixed slurry at an alkali-to-carbon ratio of 3:1-4:

1. The potassium hydroxide activator is added in stages: first, 50% potassium hydroxide is added and stirred for 1 hour, then the remaining 50% potassium hydroxide is added and stirred for another 2 hours. The heating rate is controlled at 5°C per minute, and samples are taken every 30 minutes during the constant temperature stirring process at 80°C to ensure that the hydrogel forms uniformly without stratification.

5. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S5, the ultrafast Joule heating device heats the temperature at a rate of 1100 K / s. The pulse current power of the Joule heating device is 10 kW, and the activation temperature is 800℃-900℃. During the activation process, the device is protected by inert gas and the carbonization activation is completed after holding the temperature for 3-8 seconds.

6. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S6, the activated product is repeatedly washed with deionized water using vacuum filtration as an aid. The amount of water used for each wash is 10 times the mass of the product. The product is then vacuum dried at 120°C for 6 hours with a vacuum degree ≥0.09MPa. During the drying process, the product is turned over every 2 hours to ensure uniform drying. The final product has a moisture content ≤1%.

7. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S7, the porous carbon intermediate is subjected to nitrogen doping at a constant temperature of 600℃ for 2 hours. The ammonia flow rate is controlled at 50 ml / min, and the heating rate is set at 10℃ / min. After nitrogen doping, the nitrogen content of the material reaches 4-6 atomic percentages, and the number of oxygen-containing functional groups on the surface is increased by 30% compared with that before modification.

8. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: It also includes step S71: performance regulation: detect the specific surface area, pore size distribution and electrochemical performance of the modified material obtained in step S7, with specific surface area as the core regulation index and the other parameters as co-verification indexes; when the specific surface area of ​​the material is <2000m² / g, repeat step S5 and extend the holding time by 1-2s until the index meets the standard; if the specific surface area meets the standard but the pore size distribution or electrochemical performance does not meet the standard, adjust the raw material ratio, gel assembly parameters or nitrogen doping process parameters accordingly to achieve synergistic compliance of multiple performance indicators.

9. The method for preparing the high-performance supercapacitor electrode material according to claim 1, characterized in that: In step S8, the high-performance supercapacitor electrode material has a bulk density ≥0.7g / cm³, a total pore volume ≥1.0cm³ / g, a mesoporous ratio >35%, and an ion transport resistance ≤5Ω.

10. A supercapacitor, characterized in that: The supercapacitor is made using the high-performance supercapacitor electrode material according to any one of claims 1-9, and the method for preparing the supercapacitor includes the following steps: A1. Electrode preparation: The high-performance supercapacitor electrode material is mixed with polytetrafluoroethylene binder at a ratio of 95:5, and anhydrous ethanol is added to make a paste. The paste is uniformly coated on the nickel foam current collector with a coating thickness of 100μm. The electrode sheet is obtained by vacuum drying at 120℃ for 2 hours and pressing it with a pressure of 10MPa. A2. Device Components: Using electrode sheets as positive and negative electrodes, a polypropylene membrane as the isolation layer, and potassium hydroxide aqueous solution or tetraethylammonium tetrafluoroborate / acetonitrile organic electrolyte as the electrolyte, a button-type supercapacitor is assembled in an argon glove box. A3. Performance Testing: Conduct electrochemical performance tests on the assembled supercapacitors; The supercapacitor is used in flexible electronic devices, new energy transportation auxiliary energy storage systems, or smart grid energy storage systems.

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