Lavender straw-based nitrogen-doped porous carbon electrode modification material, and preparation method and application thereof

Abstract

The present application relates to a kind of lavender stalk base nitrogen-doped porous carbon electrode modification material and its preparation method and application, belong to electrochemical energy storage material technical field.The present application uses agricultural waste lavender stalk as carbon precursor, using the two-step method process of KOH chemical activation and melamine nitrogen-doped synergistic modification, nitrogen-doped porous carbon material is prepared.The material has hierarchical porous structure with micropore as the leading, auxiliary mesoporous, high specific surface area, high nitrogen-doped content, and high pyrrole nitrogen ratio.It is applied to supercapacitor electrode, shows very low equivalent series resistance, excellent rate performance and cycle stability, energy density and power density are superior.The present application realizes the high-value utilization of agricultural waste, simple and environment-friendly process, provides a new way for the development of high-performance supercapacitor electrode material.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, and particularly relates to a lavender straw-based nitrogen-doped porous carbon electrode modification material, its preparation method and application. Background Technology

[0002] Supercapacitors are considered highly promising energy storage devices due to their high power density, rapid charge / discharge capabilities, and long cycle life. However, their large-scale application remains a challenge due to their relatively low energy density. Electrode materials are a key factor determining the energy density of supercapacitors.

[0003] Currently, activated carbon is the most commonly used electrode material, but it is mainly derived from fossil fuels, resulting in high costs and often involving high energy consumption and environmental pollution during its preparation. Biomass carbon materials have attracted much attention due to their wide availability, renewability, and environmental friendliness. However, biomass carbon obtained through direct carbonization typically suffers from problems such as low specific surface area, unreasonable pore structure (excessive micropores leading to high ion transport resistance), and poor surface chemical activity (lack of pseudocapacitive contribution), making it difficult to meet the requirements of high-performance energy storage.

[0004] Therefore, developing a low-cost, green preparation method that can effectively regulate the pore structure and surface chemical properties of biomass carbon is an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a lavender stalk-based nitrogen-doped porous carbon electrode modification material, its preparation method, and its applications. The lavender stalk-based nitrogen-doped porous carbon electrode modification material prepared using the method of this invention exhibits excellent electrochemical performance and structural stability, making it particularly suitable for assembling flexible all-solid-state supercapacitors, meeting the requirements of wearable and implantable medical devices for energy storage devices that are thin, flexible, safe, and biocompatible.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material includes the following steps: Using lavender stalks as a precursor, a nitrogen-doped porous carbon electrode modified material was obtained through pretreatment, precarbonization, chemical activation and nitrogen doping synergistic pyrolysis and posttreatment. The activator used in the chemical activation and nitrogen doping synergistic pyrolysis step is potassium hydroxide; the nitrogen source is melamine.

[0007] Optionally, the steps of chemical activation and nitrogen doping synergistic pyrolysis are as follows: The pre-carbonized product, potassium hydroxide activator and nitrogen source melamine are mixed, ultrasonically dispersed in a mixed solvent, and then pyrolyzed. or, The pre-carbonized product and potassium hydroxide activator are mixed and ground for primary activation; then the product is mixed with melamine and ultrasonically dispersed in a mixed solvent for pyrolysis.

[0008] Optionally, the mass ratio of the pre-carbonized product, potassium hydroxide and melamine is 1:(2.5-4):(3.0-4.0).

[0009] Furthermore, the preferred mass ratio of the pre-carbonized product, potassium hydroxide, and melamine is 1:3:3.5.

[0010] Optionally, the pyrolysis temperature is 750-850℃, the holding time is 1-3h, and the heating rate is 3-10℃ / min.

[0011] Optionally, the pretreatment step specifically involves: chopping the lavender stalks, soaking them in a dilute alkaline solution with a concentration of 0.2-0.5 mol / L for 12-24 hours, and then washing and drying them.

[0012] Optionally, the pre-carbonization temperature is 450-550℃, the holding time is 1-3h, and the atmosphere is an inert atmosphere.

[0013] Optionally, the mixed solvent is a mixture of deionized water and anhydrous ethanol in a volume ratio of 1:1.

[0014] A lavender straw-based nitrogen-doped porous carbon electrode modification material prepared by the above method.

[0015] Optionally, the lavender straw-based nitrogen-doped porous carbon electrode modification material has a micropore-dominant micro-mesopore hierarchical porous structure with a specific surface area of ​​500-1700 m² / g, a total pore volume of 0.3-0.8 cm³ / g, and an average pore size of 1.8-2.9 nm.

[0016] Optionally, the nitrogen doping content on the surface of the lavender straw-based nitrogen-doped porous carbon electrode modification material is 1-3 at.%, and the pyrrole nitrogen content is 10-40%.

[0017] The above-mentioned lavender straw-based nitrogen-doped porous carbon electrode modification material is used in supercapacitors.

[0018] An electrode whose active ingredient comprises the above-mentioned lavender straw-based nitrogen-doped porous carbon electrode modification material.

[0019] A supercapacitor comprising the electrodes described above.

[0020] Optionally, the supercapacitor is a symmetrical supercapacitor, and the electrolyte is a 6 M KOH aqueous solution or a PVA / KOH gel electrolyte.

[0021] Optionally, the supercapacitor has a power density of 498 W / kg and a capacity retention rate of not less than 98.98% after 10,000 charge-discharge cycles.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The preparation method of lavender straw-based nitrogen-doped porous carbon electrode modification material provided by this invention is simple, low-cost, and environmentally friendly. This invention uses lavender straw, a characteristic agricultural waste from Xinjiang, as a carbon precursor, which not only effectively solves the problem of agricultural waste treatment and realizes high-value utilization of "waste into treasure," but also significantly reduces the raw material cost of high-performance electrode materials. Through a synergistic modification strategy of KOH chemical activation and melamine nitrogen doping, combined with a two-step carbonization-activation process, precise control of the material's microstructure is achieved. This method does not require complex and expensive equipment, has mild reaction conditions, is easy to repeat and scale up, and conforms to the concepts of green chemistry and sustainable development.

[0023] (2) The nitrogen-doped porous carbon material prepared by this invention has excellent microstructure characteristics, providing a material basis for high-performance energy storage. By controlling the ratio of activator and pyrolysis temperature, a hierarchical porous structure dominated by micropores and assisted by mesopores (Vmi / Vme=3.02) was successfully constructed, with a specific surface area as high as 1648.78 m² / g, providing abundant active sites for ion adsorption. At the same time, the introduction of melamine achieved efficient nitrogen doping and a high pyrrole nitrogen ratio. This unique structure not only forms a smooth ion transport channel, effectively alleviating concentration polarization, but also significantly enhances the surface wettability and electronic conductivity of the material through the lone pair electrons of pyrrole nitrogen.

[0024] (3) The supercapacitor prepared by the present invention exhibits excellent electrochemical performance and cycle stability. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart illustrating the preparation of a lavender straw-based nitrogen-doped porous carbon electrode modification material in Example 1 of the present invention; Figure 2 Images are scanning electron microscope (SEM) images; where (a) is LNAC-800-1:2; (b) is LNAC-800-1:3; and (c) is LNAC-800-1:4. Figure 3 XRD diffraction patterns and Raman spectra of LNAC-850, LNAC-800, LNAC-750, and LAC; Figure 4 (a) shows the N2 adsorption-desorption isotherm; (b) shows the pore size distribution of LAC, LNAC-750, LNAC-800 and LNAC-850. Figure 5 This is a photograph of a porous carbon supercapacitor prepared using the lavender straw-based nitrogen-doped porous carbon electrode modification material of Example 1 of the present invention. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] This invention provides a method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material, comprising the following steps: Using lavender stalks as a precursor, a nitrogen-doped porous carbon electrode modified material was obtained through pretreatment, precarbonization, chemical activation and nitrogen doping synergistic pyrolysis and posttreatment.

[0032] In an optional embodiment, the pretreatment step includes: cutting the lavender stalks into small pieces, soaking them in a dilute alkaline solution with a concentration of 0.2-0.5 mol / L for 12-24 h, and then washing and drying them; The pre-carbonization temperature is 450-550℃, the holding time is 1-3h, and the atmosphere is an inert atmosphere.

[0033] Pre-carbonization is a crucial step in preserving the natural microstructure of biomass. Too low a temperature (<450℃) leads to incomplete removal of volatile organic compounds, making subsequent activation prone to violent reactions and pore collapse. Too high a temperature (>550℃) may cause excessive densification of the carbon skeleton, hindering the subsequent pore formation by the activator. This invention, by controlling pre-carbonization at 450-550℃, effectively preserves the cellulose skeleton of lavender stalks, providing an ideal precursor structure for subsequent pore formation.

[0034] In an optional embodiment, the chemical activation step includes: mixing the pre-carbonized product, potassium hydroxide activator and nitrogen source melamine in a specific ratio, adding them to a mixed solvent for ultrasonic dispersion, and then drying to obtain a mixed precursor.

[0035] Furthermore, the mass ratio of the pre-carbonized product (AC), potassium hydroxide (KOH), and melamine is 1:(2.5-4):(3.0-4.0), preferably 1:3:3.5.

[0036] Furthermore, the mixed solvent is a mixture of deionized water and anhydrous ethanol, the ultrasonic dispersion time is 20-60 min, and the drying temperature is 60-80℃.

[0037] In this invention, melamine is introduced as an exogenous nitrogen dopant, which works synergistically with KOH activation. Melamine decomposes at high temperatures, releasing nitrogen-containing gases, which not only aid in pore formation but also introduce high levels of pyrrole nitrogen and pyridine nitrogen active sites into the carbon framework. The specific mass ratio of KOH to melamine (1:3:3.5) is key to achieving a balance between high specific surface area and high nitrogen doping. Too low a ratio leads to incomplete pore development, while too high a ratio causes over-etching, damaging the conductive network of the carbon framework.

[0038] In an optional embodiment, the step of chemical activation and nitrogen doping synergistic pyrolysis includes: subjecting the dried mixture to high-temperature pyrolysis under an inert atmosphere and then naturally cooling it.

[0039] Furthermore, the high-temperature pyrolysis temperature is 750-850℃, the holding time is 1-3h, and the heating rate is 3-10℃ / min.

[0040] At high temperatures of 750-850℃, KOH undergoes a vigorous redox reaction with carbon, generating potassium vapor and potassium carbonate that further etch the carbon framework, forming abundant micropores and mesopores. This temperature range ensures sufficient reaction between KOH and carbon while avoiding excessive graphitization and loss of specific surface area due to excessively high temperatures. The pyrolysis products of melamine combine with the defect sites created by KOH etching at this temperature, achieving in-situ doping of nitrogen atoms.

[0041] In an optional embodiment, the post-processing includes: pouring the pyrolysis product into an acid solution and stirring and washing, then washing with deionized water until the filtrate is neutral and drying.

[0042] Furthermore, the acid solution is a 1M HCl solution; the drying temperature is 60-100℃, and the time is 10-24h.

[0043] The acid washing step aims to thoroughly remove residual potassium salts and activator byproducts, preventing impurity ions from affecting electrochemical performance. Thorough washing and drying ensure the purity and structural stability of the material, providing high-purity active material for subsequent electrode fabrication.

[0044] This invention provides a lavender straw-based nitrogen-doped porous carbon electrode modification material prepared by the above-mentioned method.

[0045] The lavender straw-based nitrogen-doped porous carbon electrode material prepared by this invention possesses a micropore-dominated micro-mesopore hierarchical porous structure with a specific surface area of ​​up to 1648.78 m² / g and an average pore size of 1.88 nm. The material surface is rich in nitrogen (N) and oxygen (O) heteroatoms, with a nitrogen doping content of up to 2.59 at.% and a pyrrolic nitrogen (Pyrrolic-N) content as high as 12.06%. This unique structure not only provides a large number of double-layer charge adsorption sites, but the pyrrolic nitrogen also contributes significantly to pseudocapacitance and improves the surface wettability of the electrode material, reducing ion transport resistance, thereby significantly improving the specific capacitance and rate performance of the material.

[0046] This invention provides an application of the above-mentioned lavender straw-based nitrogen-doped porous carbon electrode modification material in supercapacitors.

[0047] The present invention provides an electrode in which the active ingredient includes the above-mentioned lavender straw-based nitrogen-doped porous carbon electrode modification material.

[0048] This invention provides a supercapacitor, including the electrodes described above; The supercapacitor is a symmetrical supercapacitor, and the electrolyte is a 6 M KOH aqueous solution.

[0049] This invention provides an application of the above-mentioned supercapacitor in energy storage devices.

[0050] All raw materials used in this invention were purchased from the market.

[0051] The technical solution of the present invention will be further illustrated by the following embodiments.

[0052] Example 1 like Figure 1 As shown, a method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material includes the following steps: S1. Soak Xinjiang Yili lavender stalks in a 0.3mol / L dilute alkaline solution for 12 hours, wash with deionized water, dry in an 80℃ oven for 12 hours, crush them initially with a crusher, then ball mill them for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 500°C at 5°C / min under a nitrogen atmosphere. It is then held at this temperature for 2 hours for pre-carbonization. After natural cooling, pre-carbonized carbon (denoted as AC) is obtained. S3. Pre-carbonized carbon, KOH solid and melamine are thoroughly ground and mixed in a mortar at a mass ratio of 1:3:3.5. A mixture of deionized water and ethanol is added and ultrasonically dispersed for 30 min. After drying, the mixture is transferred to a tube furnace and heated to 800℃ at 5℃ / min under a nitrogen atmosphere and held for 2 h for synergistic activation and nitrogen doping to obtain the activated product. S4. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain a biomass carbon-based electrode modification material, which is a nitrogen-doped porous carbon material based on lavender straw, denoted as LNAC-800 (LNAC-800-1∶3).

[0053] Based on Example 1, the pre-carbonized carbon, KOH solid and melamine in step S3 are now replaced by a mass ratio of 1:3:3.5 to 1:2:3.5 and 1:4:3.5, respectively, to obtain LNAC-800-1:2 and LNAC-800-1:4.

[0054] Example 2 A method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material includes the following steps: S1. Soak Xinjiang Yili lavender stalks in a 0.3mol / L dilute alkaline solution for 12 hours, wash with deionized water, dry in an 80℃ oven for 12 hours, crush them initially with a crusher, then ball mill them for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 500°C at 5°C / min under a nitrogen atmosphere. It is then held at this temperature for 2 hours for pre-carbonization. After natural cooling, pre-carbonized carbon (denoted as AC) is obtained. S3. Pre-carbonized carbon, KOH solid and melamine are thoroughly ground and mixed in a mortar at a mass ratio of 1:3:3. A mixture of deionized water and ethanol is added and ultrasonically dispersed for 30 min. After drying, the mixture is transferred to a tube furnace and heated to 750℃ at 5℃ / min under a nitrogen atmosphere. The temperature is maintained for 2 h to carry out synergistic activation and nitrogen doping to obtain the activated product. S4. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain a biomass carbon-based electrode modification material, which is a nitrogen-doped porous carbon material based on lavender straw, denoted as LNAC-750.

[0055] Example 3 A method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material includes the following steps: S1. Soak Xinjiang Yili lavender stalks in a 0.3mol / L dilute alkaline solution for 12 hours, wash with deionized water, dry in an 80℃ oven for 12 hours, crush them initially with a crusher, then ball mill them for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 500°C at 5°C / min under a nitrogen atmosphere. It is then held at this temperature for 2 hours for pre-carbonization. After natural cooling, pre-carbonized carbon (denoted as AC) is obtained. S3. Pre-carbonized carbon, KOH solid and melamine are thoroughly ground and mixed in a mortar at a mass ratio of 1:3:4. A mixture of deionized water and ethanol is added and ultrasonically dispersed for 30 min. After drying, the mixture is transferred to a tube furnace and heated to 850℃ at 5℃ / min under a nitrogen atmosphere. The temperature is maintained for 2 h to carry out synergistic activation and nitrogen doping to obtain the activated product. S4. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain a biomass carbon-based electrode modification material, which is a nitrogen-doped porous carbon material based on lavender straw, denoted as LNAC-850.

[0056] Example 4 A method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material includes the following steps: S1. Soak Xinjiang Yili lavender stalks in a 0.3mol / L dilute alkaline solution for 12 hours, wash with deionized water, dry in an 80℃ oven for 12 hours, crush them initially with a crusher, then ball mill them for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 500°C at 5°C / min under a nitrogen atmosphere. It is then held at this temperature for 2 hours for pre-carbonization. After natural cooling, pre-carbonized carbon (denoted as AC) is obtained. S3. Grind and mix the pre-carbonized carbon and KOH solid in a mortar at a mass ratio of 1:3, transfer to a tube furnace, heat to 800℃ at 5℃ / min under a nitrogen atmosphere, and hold for 2 hours to carry out a first chemical activation to obtain the first activated product. S4. The primary activation product and melamine were thoroughly ground and mixed in a mortar at a mass ratio of 1:3.5. A mixture of deionized water and ethanol was added and ultrasonically dispersed for 30 min. After drying, the mixture was transferred to a tube furnace and heated to 750℃ at 5℃ / min under a nitrogen atmosphere and held for 1.5 h to optimize nitrogen doping. S5. The optimized product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. Subsequently, it was dried in a vacuum oven at 80℃ for 12 hours to obtain a biomass carbon-based electrode modification material, which is an optimized lavender straw-based nitrogen-doped porous carbon material, denoted as LNAC-800-O.

[0057] The lavender straw-based nitrogen-doped porous carbon electrode modified material prepared in Example 4 has a specific surface area of ​​1215 m². 2 / g; Total pore volume 0.45 cm³ 3 / g; average pore size 2.34 nm.

[0058] Comparative Example 1 The preparation steps of a biochar material are as follows: S1. Wash the lavender stalks from Yili, Xinjiang with deionized water, dry them in an 80℃ oven for 12 hours, crush them initially with a crusher, then transfer them to a ball mill for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor (without pre-carbonization) and KOH solid were thoroughly ground and mixed in a mortar at a mass ratio of 1:3 (without adding melamine). The mixture was then transferred to a tube furnace and chemically activated under a nitrogen atmosphere by heating to 800°C at 5°C / min and holding for 2 hours to obtain the activated product. S3. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain biochar material, denoted as LAC.

[0059] Comparative Example 2 The preparation steps of a biochar material are as follows: S1. Wash the lavender stalks from Yili, Xinjiang with deionized water, dry them in an 80℃ oven for 12 hours, crush them initially with a crusher, then transfer them to a ball mill for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor (without pre-carbonization) and KOH solid were thoroughly ground and mixed in a mortar at a mass ratio of 1:1 (without adding melamine), transferred to a tube furnace, and chemically activated under a nitrogen atmosphere at a temperature of 5℃ / min to 800℃ and held for 2h to obtain the activated product. S3. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain biochar material, denoted as LAC-1-1.

[0060] Results Comparison: Due to insufficient KOH dosage (mass ratio 1:1), the activation reaction was incomplete, resulting in significantly lower specific surface area and pore volume of the prepared LAC-1-1 material compared to the material of this invention. Furthermore, the mesopores were poorly developed, and the hierarchical pore structure was not obvious. When assembled into a symmetrical supercapacitor, the equivalent series resistance was high, and the rate performance and cycle stability were significantly inferior to those of the embodiments of this invention. Specifically, at a current density of 1 A / g, the specific capacitance of the three-electrode system prepared from the biochar material of Comparative Example 2 (the preparation process and conditions in the following electrochemical performance tests were consistent) was 427.2 F / g, and at a high current density of 20 A / g, the capacitance retention was 59%.

[0061] Comparative Example 3 The preparation steps of a biochar material are as follows: S1. Wash the lavender stalks from Yili, Xinjiang with deionized water, dry them in an 80℃ oven for 12 hours, crush them initially with a crusher, then transfer them to a ball mill for 2 hours, and pass them through a 100-mesh sieve to obtain the precursor. S2. The precursor (without pre-carbonization), KOH solid and urea are ground and mixed in a mortar in a mass ratio of 1:3:3 (the amount of melamine used in this invention is also 3 parts). The mixture is then transferred to a tube furnace and heated to 800°C at 5°C / min under a nitrogen atmosphere. The mixture is then kept at this temperature for 2 hours to carry out chemical activation and nitrogen doping, thereby obtaining the activated product. S3. The activated product was washed with 1M HCl solution for 12 hours to remove residual potassium salts and impurities. Then it was washed with deionized water until the pH of the filtrate was neutral. After that, it was dried in a vacuum oven at 80℃ for 12 hours to obtain nitrogen-doped biochar material, denoted as NAC-urea.

[0062] Results: The three-electrode system prepared by biochar material in Comparative Example 3 had a specific capacitance of 405.2 F / g at a current density of 1 A / g, and a capacitance retention of 61.5% at a high current density of 20 A / g.

[0063] Figure 3 XRD diffraction patterns and Raman spectra of LNAC-850, LNAC-800, LNAC-750, and LAC are shown. The XRD patterns reveal diffraction peaks of the (002) and (100) crystal planes at approximately 25° and 43° 2θ, respectively, indicating a certain degree of graphitization. In the Raman spectra, all samples exhibit D and G bands, with ID / IG ratios of 1.03 (LNAC-850), 1.09 (LNAC-800), 1.01 (LNAC-750), and 0.98 (LAC), respectively. This suggests that the degree of graphitization increases with increasing processing temperature, and the defect density slightly increases.

[0064] Figure 4 (a) shows the N2 adsorption-desorption isotherm; (b) shows the pore size distribution of LAC, LNAC-750, LNAC-800 and LNAC-850. The nitrogen adsorption-desorption isotherm shows that the LNAC-850 sample has the highest adsorption capacity, indicating its large specific surface area. Figure 4 The pore size distribution diagram in (b) shows that all samples exhibit both microporous and mesoporous structures, with the LNAC-850 sample showing the most concentrated pore size distribution, primarily within the 2-5 nm range, indicating a relatively uniform pore structure. These results collectively reveal the influence of different processing temperatures on the microstructure and porosity of the samples.

[0065] Effect verification I. The specific surface area and pore structure of the lavender straw-based nitrogen-doped porous carbon materials prepared in Examples 1-3 and the biochar material prepared in Comparative Example 1 were tested using BET nitrogen adsorption; XPS was used to test the different nitrogen contents in the materials. The test results are shown in Tables 1 and 2.

[0066] Table 1. Analysis of Hole Structure Parameters Table 2 Elemental Composition Analysis Table As shown in Tables 1 and 2, the specific surface area and pore structure of the materials obtained in Examples 1-3 were detected by BET nitrogen adsorption testing. The results showed that LNAC-800 has an ultra-high specific surface area of ​​1648.78 m² / g and forms a micro-mesoporous hierarchical porous structure dominated by micropores, with an average pore size of 1.88 nm. XPS testing showed that the nitrogen doping content of this material reached 2.59 at.%, of which pyrrole nitrogen with high electrochemical activity accounted for as much as 61.95%.

[0067] II. Electrochemical performance testing: Preparation of the working electrode: Using ANAC-800 prepared in Example 1 as the active ingredient, it was mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) binder at a mass ratio of 7:2:1. N-methylpyrrolidone (NMP) was added to prepare a slurry with a solid content of 15%. The slurry was uniformly coated on a 1 cm × 1 cm nickel foam current collector, dried under vacuum at 80 °C for 12 h, and then pressed into a sheet under a pressure of 10 MPa to obtain the working electrode. The active material loading was about 2.0 mg / cm².

[0068] 1. The working electrode, the platinum counter electrode, and the reference electrode Hg / HgO prepared above were assembled into a three-electrode system in a 6M KOH aqueous electrolyte. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were performed using an electrochemical workstation. The results showed that ANAC-800 exhibited a specific capacitance of 635.1 F / g at a current density of 1 A / g. Even at a high current density of 20 A / g, the capacitance retention rate remained at 74%, demonstrating excellent rate performance. Its CV curve showed a highly symmetrical rectangular shape, indicating that its double-layer capacitance behavior was dominant and that it possessed good reversibility.

[0069] 2. Using the ANAC-800 prepared in Example 1 as the positive and negative electrode active materials, and PVA / KOH gel as the electrolyte and separator, a flexible all-solid-state symmetric supercapacitor was assembled. See the physical image below. Figure 5 Test results show that the supercapacitor achieves an energy density of 13.69 Wh / kg at a power density of 498 W / kg. Further testing revealed that after 10,000 charge-discharge cycles, the capacity retention rate reached 98.98%, demonstrating excellent cycle stability.

[0070] In summary, the nitrogen-doped porous carbon material prepared from lavender straw biomass as a precursor provided by this invention has an ultra-high specific surface area, a reasonable hierarchical pore structure, and excellent electrochemical performance. Its preparation method is simple and environmentally friendly. This material is particularly suitable as an electrode material for high-performance supercapacitors and has broad application prospects in the field of flexible wearable and implantable medical devices.

[0071] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material, characterized in that, Includes the following steps: Using lavender stalks as a precursor, a nitrogen-doped porous carbon electrode modified material was obtained through pretreatment, precarbonization, chemical activation and nitrogen doping synergistic pyrolysis and posttreatment. The activator used in the chemical activation and nitrogen doping synergistic pyrolysis step is potassium hydroxide; the nitrogen source is melamine.

2. The method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 1, characterized in that, The steps of chemical activation and nitrogen doping synergistic pyrolysis are as follows: The pre-carbonized product, potassium hydroxide and melamine were mixed, ultrasonically dispersed in a mixed solvent, and then pyrolyzed. or, The pre-carbonized product and potassium hydroxide were mixed and ground for initial activation; then the product and melamine were ultrasonically dispersed in a mixed solvent and then pyrolyzed.

3. The method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 2, characterized in that, The mass ratio of the pre-carbonized product, potassium hydroxide and melamine is 1:(2.5-4):(3.0-4.0).

4. The preparation method of a lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 3, characterized in that, The mass ratio of the pre-carbonized product, potassium hydroxide, and melamine is 1:3:3.

5.

5. The method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 2, characterized in that, The pyrolysis temperature is 750-850℃, the holding time is 1-3h, and the heating rate is 3-10℃ / min.

6. The method for preparing a lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 1, characterized in that, The pre-carbonization temperature is 450-550℃, and the holding time is 1-3 hours.

7. A lavender straw-based nitrogen-doped porous carbon electrode modification material prepared by the preparation method according to any one of claims 1-6.

8. The lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 7, characterized in that, It has a micro-mesoporous hierarchical porous structure dominated by micropores, with a specific surface area of ​​500-1700 m². 2 / g, total pore volume is 0.3-0.8 cm³ 3 / g, with an average pore size of 1.8-2.9 nm.

9. The lavender straw-based nitrogen-doped porous carbon electrode modification material according to claim 7, characterized in that, The nitrogen doping content is 1-3 at.%, and the pyrrole nitrogen content is 10-40%.

10. The application of the lavender straw-based nitrogen-doped porous carbon electrode modification material as described in claim 7 in supercapacitors.

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