Electrode material for regulating and controlling pseudocapacitance behavior of coconut shell biochar based on nitrogen-molybdenum dual-element synergistic doping and preparation method of electrode material

Abstract

The invention discloses an electrode material for regulating and controlling the pseudocapacitance behavior of coconut shell charcoal based on nitrogen and molybdenum dual-element synergistic doping and a preparation method thereof, and belongs to the technical field of supercapacitor electrode materials. Comprising the following steps: performing hydrothermal carbonization on coconut shells, and performing co-pyrolysis on the coconut shells, MoS2, urea and KOH to prepare activated carbon; mixing with acetylene black and PVDF (Polyvinylidene Fluoride), coating foamed nickel, and tabletting. According to the process, pore forming and doping are synchronously realized in one step, a Mo-N coordination structure is constructed, the specific capacitance and the cycling stability are remarkably improved, the production cost is reduced, and a green and low-cost solution is provided for a high-performance supercapacitor.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor electrode material technology, and particularly relates to an electrode material and its preparation method based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar. Background Technology

[0002] Clean energy development and ecological environmental protection have become the dual cornerstones of modern industrial civilization, and building a new energy system dominated by renewable energy has risen to the level of an international strategic need. According to the International Energy Agency (IEA), the share of global renewable energy generation needs to be increased to more than 65% by 2040, which places unprecedented technical demands on large-scale energy storage systems.

[0003] In the diversified energy storage technology matrix, supercapacitors, due to their unique charge storage mechanism, offer high power densities (10-100 kW kg⁻¹). -1 Cyclic stability (>10) 5 It exhibits significant advantages in terms of speed (multiple cycles) and rapid charge / discharge capability (second-level response), and has become a core component in key scenarios such as smart grid frequency regulation and new energy vehicle start-stop. However, existing commercially available activated carbon electrode materials are limited by the following technical bottlenecks: 2 The limited electron delocalization ability of carbon skeletons results in a volumetric specific capacitance generally below 200 F cm⁻¹. -3 Excessive micropore ratio (>90%) significantly increases ion transport resistance, manifested as Warburg impedance higher than 0.5Ω; and structural phase transitions in conventional electrode materials during long cycles cause capacity decay, typically exceeding 0.1% per cycle.

[0004] To overcome these limitations, heteroatoms co-doping strategies have shown great potential. By introducing heteroatoms such as nitrogen, sulfur, or molybdenum into the carbon matrix, the electronic structure of the material can be effectively controlled (e.g., nitrogen doping can increase the charge density at specific sites by up to 0.38e), and stable coordination structures such as Mo-NC can be constructed to suppress cycling volume changes. However, this technical approach still faces key bottlenecks: segregation of dopant atoms during high-temperature pyrolysis leads to uneven distribution of active sites, manifested as a redox peak half-width greater than 0.3V in the cyclic voltammetry curve; insufficient synergy between the hierarchical pore structure and surface chemical active sites results in an effective specific surface area utilization rate of less than 60%; in addition, the complex multi-step doping process significantly increases production costs by up to about 40%, severely restricting its industrialization process. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes an electrode material and its preparation method based on nitrogen-molybdenum dual-element co-doping to regulate the pseudocapacitive behavior of coconut shell biochar. By simultaneously optimizing pseudocapacitive behavior and electrode surface reactivity through a nitrogen-molybdenum dual-element co-doping strategy, and utilizing a directionally constructed Mo-N coordination structure to enhance ion adsorption energy and reduce charge transfer barrier, this invention provides an innovative solution for developing high-performance biomass carbon-based supercapacitors.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One objective of this invention is to provide a method for preparing an electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar, comprising the following steps:

[0008] After drying and crushing, coconut shell raw materials are mixed with deionized water, subjected to hydrothermal carbonization, and then separated into solid and liquid components to obtain biochar.

[0009] The obtained biochar was mixed with MoS2, urea and KOH, and pyrolyzed under a nitrogen atmosphere. After washing until neutral, activated carbon was obtained.

[0010] The obtained activated carbon, acetylene black and polyvinylidene fluoride were mixed, and N-methyl-2-pyrrolidone was added to make a slurry. The slurry was coated on nickel foam and pressed into a sheet to obtain the electrode material.

[0011] This invention achieves three functions simultaneously in one step: pore formation, doping, and activation through an integrated process of "coconut shell → hydrothermal carbonization → nitrogen-molybdenum co-doping pyrolysis → coating and pressing". This simplifies the traditional multi-step doping process, greatly reduces production costs, and significantly improves electrode specific capacity and cycle stability.

[0012] Furthermore, the specific operation steps of the hydrothermal carbonization treatment include: reacting for 1 hour at 1-5 MPa and 220-230℃ under a nitrogen atmosphere, with a heating rate of 10℃ / min and a stirring rate of 175-185 rpm.

[0013] This parameter is set to ensure that the coconut shell is fully carbonized and forms a uniform three-dimensional honeycomb porous structure, providing a high specific surface area framework for subsequent doping and improving ion transport efficiency.

[0014] Furthermore, the mass ratio of the coconut shell to deionized water is 1:10.

[0015] This invention optimizes the concentration of hydrothermal reaction materials, thereby avoiding reactor overload and ensuring complete carbonization, thus improving yield and process stability.

[0016] Furthermore, the mass ratio of the biochar, MoS2, urea and KOH is 2∶1∶2∶(4-6).

[0017] This invention ensures uniform doping of Mo and N and the formation of Mo-NC active sites by limiting the amount of raw materials used. At the same time, KOH and urea work together to create pores, resulting in a high mesopore / micropore ratio and reducing ion diffusion resistance.

[0018] Furthermore, the specific operation steps of the pyrolysis treatment are as follows: the heating rate is 5℃ / min, and the reaction is carried out at 600-800℃ for 2 hours.

[0019] The pyrolysis parameters selected in this invention can promote the formation of Mo2C nanocrystals and their embedding into the carbon framework, suppress the segregation of doped atoms at high temperatures, and improve the uniformity of active sites and cycle stability.

[0020] Furthermore, the mass ratio of activated carbon, acetylene black, and polyvinylidene fluoride is 8:1:1.

[0021] The electrode formulation selected in this invention optimizes the conductive network and bonding strength, reduces contact resistance, and improves rate performance.

[0022] Furthermore, the specific operation steps of the tablet compression molding include: pressing under a pressure of 10 MPa for 30 seconds.

[0023] The compression parameters selected in this invention ensure that the electrode sheets are dense and uniform, prevent active material from falling off, reduce interfacial polarization, and improve cycle life and mechanical stability.

[0024] A second objective of this invention is to provide an electrode material prepared using the aforementioned preparation method.

[0025] This electrode material combines the advantages of high specific capacitance, high specific surface area, and low cost, breaking through the performance bottleneck of traditional biomass carbon materials.

[0026] A third objective of this invention is to provide an application of the electrode material in a supercapacitor.

[0027] Applying this electrode material to supercapacitors significantly reduces the internal resistance of the device, meeting the needs of transient high-power scenarios such as frequency regulation in smart grids and start-stop systems for new energy vehicles.

[0028] The fourth objective of this invention is to provide a supercapacitor electrode comprising the electrode material.

[0029] This invention provides a supercapacitor electrode containing this electrode material, which can directly replace the traditional activated carbon electrode, achieve a synergistic improvement in device energy density and power density, and promote the large-scale application of biomass carbon materials in the field of energy storage.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] This invention provides an electrode material and its preparation method based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar. By introducing a nitrogen-molybdenum doping process, the characteristics of the electrode material are optimized, overcoming the defects in the prior art, improving specific capacity and reducing production costs, while reducing equipment corrosion problems and improving the rate performance of the electrode material. In addition, the embodiments of this invention expand the applicable range of different doping elements, promote the production of more efficient and environmentally friendly electrode materials, and provide a brand-new technical solution for the efficient conversion and utilization of supercapacitor electrode materials. Attached Figure Description

[0032] 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:

[0033] Figure 1 Scanning electron microscope images of the electrode materials prepared in Examples 1-3 and Comparative Examples 1-4;

[0034] Figure 2 XRD images of the electrode materials prepared in Examples 1-3;

[0035] Figure 3 The electrochemical performance of the electrode material prepared in Example 1. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] 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.

[0041] This invention provides a method for preparing an electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar, comprising the following steps:

[0042] 1) Preparation of biochar:

[0043] The coconut shell raw material is naturally air-dried for 12-24 hours, then dried at 65-85℃ for 12-48 hours, then crushed using a pulverizer and passed through an 80-mesh sieve for later use; the coconut shell raw material used in this invention is coconut shell biomass waste;

[0044] Mix the obtained coconut shell powder with deionized water at a mass ratio of 1:10 and place it in a hydrothermal reactor and stir evenly. The mass of the two should be 70-85% of the capacity of the hydrothermal reactor to ensure that there is enough material in the reactor, but not too much to affect the reaction efficiency.

[0045] The reactor was purged with nitrogen at a rate of 50 mL / min for 10 min to remove air. The initial temperature of the reactor was room temperature. The pressure gauge reading should be controlled within the range of 1-5 MPa. The temperature setting range was 220-230℃ (preferably 230℃). The reaction time was set to 1 h, and the heating rate was set to 10℃ / min. The reactor was run and magnetically stirred at a speed of 175-185 rpm (preferably 180 rpm). After the reaction was completed, the reactor was allowed to cool naturally at room temperature. The product was then subjected to solid-liquid separation, and the collected solid product was the biochar material.

[0046] 2) Preparation of activated carbon:

[0047] The biochar obtained in step 1) is mixed with molybdenum disulfide (MoS2), urea (CO(NH2)2) and potassium hydroxide (KOH) in a mass ratio of 2:1:2:(4-6) (preferably 2:1:2:4). The four components are placed in a beaker and stirred evenly with a magnetic stirrer, dried, placed in a quartz dish, and then placed in a tube furnace.

[0048] The tube furnace was purged with nitrogen at a rate of 60 mL / min for 5 min to remove air from the tube. The initial temperature of the tube furnace was room temperature, and the temperature setting range was 600-800℃ (e.g., 600℃, 700℃, or 800℃, preferably 800℃). The reaction time was set to 2 h, and the heating rate was set to 5℃ / min. After the reaction was completed, the tube furnace was allowed to cool naturally at room temperature. The product after the reaction was washed until neutral, and the collected solid was the activated carbon material.

[0049] 3) Electrode material forming:

[0050] The activated carbon obtained in step 2) was mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and 1-2 mL of N-methyl-2-pyrrolidone (NMP, 98%) was added to prepare a slurry.

[0051] Apply the slurry to a 1×1cm area 2 Place the nickel foam on it in an oven at 105℃ for 6-12 hours;

[0052] After drying, the electrode material is obtained by pressing it into tablets at 10 MPa pressure for 30 seconds using a tablet press.

[0053] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0054] All raw materials used in this invention were purchased from the market.

[0055] The technical solution of the present invention will be further illustrated by the following embodiments.

[0056] Example 1

[0057] A method for preparing an electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar, comprising the following steps:

[0058] 1) Preparation of biochar:

[0059] Coconut shell biomass waste is air-dried for 24 hours, then dried at 85°C for 12 hours, then crushed using a pulverizer and passed through an 80-mesh sieve to obtain coconut shell powder.

[0060] Place 6g of coconut shell powder and 60mL of deionized water in a hydrothermal reactor and stir until homogeneous.

[0061] The reactor was purged with nitrogen at a rate of 50 mL / min for 10 min to remove air from the reactor. The initial temperature of the reactor was room temperature. The pressure gauge reading should be controlled within 5 MPa. The temperature setting range was 230℃. The reaction time was set to 1 h. The heating rate was set to 10℃ / min. The reactor was run and magnetically stirred at a rate of 180 rpm. After the reaction was completed, the reactor was allowed to cool naturally at room temperature. The product was then subjected to solid-liquid separation. The collected solid product was biochar.

[0062] 2) Preparation of activated carbon:

[0063] The biochar obtained in step 1) is mixed with MoS2, urea and KOH in a mass ratio of 2:1:2:4. The mixture is placed in a beaker and stirred evenly with a magnetic stirrer. After drying, the mixture is placed in a quartz dish and then placed in a tube furnace.

[0064] The tube furnace was purged with nitrogen at a rate of 60 mL / min for 5 min to remove air from the tube. The initial temperature of the tube furnace was room temperature, the temperature was set to 800℃, the reaction time was set to 2 h, and the heating rate was set to 5℃ / min. After the reaction was completed, the tube furnace was allowed to cool naturally at room temperature. The product after the reaction was washed until neutral, and the collected solid was activated carbon.

[0065] 3) Electrode material forming:

[0066] The activated carbon obtained in step 2), acetylene black, polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP, 98%) were mixed in a mass ratio of 8:1:0.5:0.5 to prepare a slurry; the slurry was then coated onto a 1×1 cm... 2 The electrode material is formed by placing it on nickel foam and drying it in an oven at 105℃ for 6-12 hours; after drying, it is pressed into tablets at 10MPa pressure for 30 seconds using a tablet press.

[0067] Example 2

[0068] Same as Example 1, except that the temperature in step 2) is set to 700°C.

[0069] Example 3

[0070] Same as Example 1, except that the temperature in step 2) is set to 600°C.

[0071] Comparative Example 1

[0072] Same as Example 1, except that urea is not added in step 2).

[0073] Comparative Example 2

[0074] Same as Example 1, except that molybdenum disulfide is not added in step 2).

[0075] Comparative Example 3

[0076] Same as Example 1, except that potassium hydroxide is not added in step 2).

[0077] Comparative Example 4

[0078] Same as Example 1, except that coconut shell biomass is replaced with cypress wood.

[0079] The electrode sheet materials prepared in Examples 1-3 and Comparative Examples 1-4 were analyzed, and the scanning electron microscope images were obtained as follows: Figure 1 As shown, according to Figure 1 It can be seen that, under the same reaction temperature and time, the co-doping of nitrogen and molybdenum significantly altered the microstructure of biochar. Compared with Comparative Examples 1-4, the activated carbon in Example 1 formed a more complete honeycomb porous structure with a uniformly distributed morphology. Comparative Example 1, without the addition of urea, only formed a honeycomb structure, failing to develop the 3D interconnected disordered channels seen in Example 1, indicating that the reaction of KOH and urea during pyrolysis produced CO2 gas. Comparative Example 2, without the addition of MoS2, resulted in only interconnected channels forming inside the sample, without the formation of micro / mesopores using Mo2C nanoparticles as a pore-forming template. Comparative Example 3, without the addition of KOH, resulted in an insignificant pore-forming effect. Comparative Example 4 used different biomass; although cypress wood had a higher mesopore area, it did not exhibit 3D interconnected disordered channels compared to coconut shell biomass. For electrochemical performance, 3D interconnected disordered channels can increase the transport between ions, thereby improving electrochemical performance. This effect can be confirmed in Table 1 below.

[0080] The electrode sheet materials prepared in Examples 1-3 were analyzed, and the scanning electron microscope images are as follows: Figure 1 As shown in the image, the three embodiments differ in their activation temperatures: 800℃, 700℃, and 600℃, respectively. The images clearly show that as the temperature increases, the connectivity between the pores strengthens, forming a three-dimensional network structure. This illustrates the crucial role of temperature in the pyrolysis process of carbon materials. This structure gives the sample a high specific surface area, and the pore outlines are clearly visible. The pore walls are thinner than in other samples, and this well-developed pore structure is essential for the electrochemical performance of activated carbon.

[0081] Figure 2 The images are XRD patterns of the electrode materials prepared in Examples 1-3. Figure 2As can be seen, in Examples 1-3, two broad and weak carbon characteristic peaks can be clearly observed near 24° and 43.5°, indicating that the activated carbon matrix is ​​an amorphous carbon material with a certain degree of graphitization. As shown in the figure, Example 1 shows a weak peak near 14°, which may correspond to the MoS2(002) crystal plane (2H phase), and a broad peak between 32-33°, indicating the presence of the MoS2(100) crystal plane. Compared with Examples 2 and 3, Example 1 not only has higher carbon crystallinity and the largest graphite crystallite size, but also contains a well-developed porous structure. The results show that the material has a high degree of graphitization.

[0082] In addition, the specific capacitance of the electrode materials prepared in Examples 1-3 and Comparative Examples 1-4 was measured (all at a current density of 1 Ag). -1 The electrochemical performance of the electrode material prepared in Example 1 (as measured below) is as follows: Figure 3 As shown in the figure; the specific values ​​for BET calculation are shown in Table 1.

[0083] Table 1

[0084]

[0085] This invention innovatively develops a green preparation process for coconut shell biochar electrode materials with nitrogen and molybdenum dual-element synergistic doping. Through a hydrothermal-pyrolysis synergistic mechanism, a Mo-N coordination structure is directionally constructed, achieving three technological breakthroughs simultaneously: First, a resource recycling path is established using coconut shell biomass waste as raw material, significantly reducing raw material costs and environmental impact; second, a pioneering one-step pyrolysis method simultaneously completes pore formation and doping, improving the uniformity of active site distribution to a new level and reducing costs by approximately 32% compared to traditional multi-step processes; third, the synergistic effect of the dual active centers formed by Mo2C nanoparticles and the N-doped carbon framework drives a specific capacitance of 450 F g. -1 (10Ag -1 With a retention rate of 73%, a specific surface area utilization rate exceeding 75%, and a capacity decay rate of <6% after 5000 cycles, this invention not only overcomes the challenges of uniformity and cost control in the industrialization process of heterogeneous atom doping, but its high power characteristics also provide an ideal electrode solution for transient high-power scenarios such as start-stop systems for new energy vehicles, promoting the large-scale application of biomass-derived carbon materials in the field of advanced energy storage.

[0086] This invention not only overcomes the challenges of uniformity and cost control in the industrialization process of heterogeneous atom doping, but also opens up new avenues for the large-scale application of biomass-derived carbon materials in the field of high-performance supercapacitors.

[0087] 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. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar, characterized in that, Includes the following steps: Coconut shell biochar was mixed with MoS2, urea and KOH, and pyrolyzed under a nitrogen atmosphere. The mixture was then washed until neutral to obtain activated carbon. The obtained activated carbon, acetylene black and polyvinylidene fluoride were mixed, and N-methyl-2-pyrrolidone was added to make a slurry. The slurry was coated on nickel foam and pressed into a sheet to obtain the electrode material.

2. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 1, characterized in that, The preparation steps of the coconut shell biochar include: drying and crushing the coconut shell raw material, mixing it with deionized water, hydrothermal carbonization treatment, solid-liquid separation, and obtaining biochar.

3. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 2, characterized in that, The specific operation steps of the hydrothermal carbonization treatment include: reacting for 1 hour at 1-5 MPa and 220-230℃ under a nitrogen atmosphere, with a heating rate of 10℃ / min and a stirring rate of 175-185 rpm.

4. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 1, characterized in that, The mass ratio of coconut shell biochar, MoS2, urea and KOH is 2:1:2:(4-6).

5. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 1, characterized in that, The specific operation steps of the pyrolysis treatment are as follows: the heating rate is 5℃ / min, and the reaction is carried out at 600-800℃ for 2 hours.

6. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 1, characterized in that, The mass ratio of activated carbon, acetylene black, and polyvinylidene fluoride is 8:1:

1.

7. The method for preparing electrode material based on nitrogen-molybdenum dual-element synergistic doping to regulate the pseudocapacitive behavior of coconut shell biochar according to claim 1, characterized in that, The specific steps for tablet compression include: pressing under a pressure of 10 MPa for 30 seconds.

8. An electrode material prepared by the preparation method according to any one of claims 1-7.

9. The application of the electrode material as described in claim 8 in a supercapacitor.

10. A supercapacitor electrode, characterized in that, It includes the electrode material as described in claim 8.

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