Preparation method of lignin-based three-dimensional flaky carbon material

Abstract

According to the preparation method of the lignin-based three-dimensional flaky carbon material, the lignin-based three-dimensional flaky carbon material is of a three-dimensional flaky structure, the specific surface area is large, mass transfer is facilitated, electron transport is promoted, and the lignin-based three-dimensional flaky carbon material has high performance in the field of energy storage.

Description

Technical Field

[0001] This application relates to the field of energy storage material technology, specifically to a method for preparing lignin-based three-dimensional sheet-like carbon material. Background Technology

[0002] Biomass-derived carbon materials have attracted much attention due to their renewability and structural tunability, with lignin being a key research focus due to its unique molecular configuration and industrial applicability. As the most abundant natural aromatic macromolecule, lignin has a wide molecular weight distribution (1000 g / mol-20000 g / mol) and a three-dimensional aromatic network structure, giving it an inherently high carbon content (60 wt%-65 wt%, accounting for 30% of the organic carbon in the terrestrial biosphere). These structural characteristics enable it to be directionally transformed into a conductive carbon skeleton with a π-π conjugated system during pyrolysis, while spontaneously forming a hierarchical pore system spanning micro and mesoscales.

[0003] In energy storage devices such as supercapacitors, electrode performance is jointly regulated by the material's specific surface area, pore structure, and electrochemical activity. Although lignin-based carbon materials typically possess high specific surface area and microporosity, their narrow pore size distribution severely limits the electrolyte penetration depth, leading to a sharp decrease in capacitance at high current densities. Therefore, constructing a hierarchical pore structure that balances micropores (high specific surface area) and mesopores / macropores (ion diffusion channels) has become a key pathway to improve the energy density of lignin-based supercapacitors.

[0004] Current strategies for preparing lignin-based carbon energy storage materials mainly employ a template-activation synergistic method. This involves using a hard template to coat and pyrolyze precursors within a rigid framework to construct a controllable porous structure, while a soft template enables the assembly of amphiphilic molecules to form a mesoporous network. While hard templates offer structural control, they come with environmental costs, and soft templates are limited by insufficient graphitization. The dual-template approach can synergistically increase the specific surface area of ​​mesoporous carbon; however, it still suffers from problems such as excessively high microporosity, insufficient mesopore connectivity, and limitations in scalability due to complex pretreatment and high-cost templates. Therefore, there is an urgent need for an energy storage material and its preparation method that can improve energy storage performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this application is proposed. Embodiments of this application provide a method for preparing a lignin-based three-dimensional sheet-like carbon material.

[0006] According to one aspect of this application, a lignin-based three-dimensional sheet-like carbon material is provided, comprising carbon, nitrogen, and oxygen, wherein the lignin-based three-dimensional sheet-like carbon material has a three-dimensional sheet-like structure, and the specific surface area of ​​the lignin-based three-dimensional sheet-like carbon material is not less than 800 m². 2 / g.

[0007] In one embodiment, the lignin-based three-dimensional sheet-like carbon material includes four elements: carbon, nitrogen, oxygen, and sulfur.

[0008] According to another aspect of this application, a method for preparing a lignin-based three-dimensional sheet-like carbon material is provided, for preparing the aforementioned lignin-based three-dimensional sheet-like carbon material; the method for preparing the lignin-based three-dimensional sheet-like carbon material includes: mixing lignin, urea, polyvinylpyrrolidone, and ammonium chloride, adding a solvent and ball milling evenly to obtain a slurry, drying the slurry to obtain a solid, calcining the solid under an inert atmosphere to obtain a porous carbon material; mixing the porous carbon material and magnesium oxide evenly, and calcining again under an inert atmosphere; washing the calcined material with acid, filtering, rinsing with distilled water until pH=7, and drying to obtain the lignin-based three-dimensional sheet-like carbon material.

[0009] In one embodiment, the lignin comprises alkali lignin; the mass ratio of the lignin, the urea, the polyvinylpyrrolidone, and the ammonium chloride is 1:(0.5-1):(0.8-1):(1-1.2).

[0010] In one embodiment, the solvent is water or ethanol; the ball milling speed is 200-350 r / min, and the ball milling time is 1h-2h.

[0011] In one embodiment, the drying method is rotary evaporation, and the drying temperature is 50°C-60°C.

[0012] In one embodiment, the inert atmosphere is any one of 99.999% nitrogen, 99.999% argon, and 99.999% helium.

[0013] In one embodiment, the calcination temperature is 850℃-950℃, the heating rate is 5℃ / min, and the calcination time is 4.5h.

[0014] In one embodiment, the mass ratio of the porous carbon material to the magnesium oxide is 1:(1.5-2), and the re-calcination temperature is 300℃-400℃, the heating rate is 5℃ / min, and the calcination time is 3h.

[0015] In one embodiment, the acid solution is either hydrochloric acid or sulfuric acid with pH=3, the washing method is to put the re-calcined material into the acid solution and stir for 1 hour, and the drying method is to place it in an oven at 80°C and dry for 10 hours.

[0016] This application provides a method for preparing a lignin-based three-dimensional sheet-like carbon material. This lignin-based three-dimensional sheet-like carbon material has a three-dimensional sheet-like structure, a large specific surface area, which is beneficial for mass transfer and promotes electron transport, enabling the lignin-based three-dimensional sheet-like carbon material to achieve high performance in the field of energy storage. Attached Figure Description

[0017] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0018] Figure 1 This is a schematic diagram of the structure of a lignin-based three-dimensional sheet-like carbon material provided in an exemplary embodiment of this application.

[0019] Figure 2 This is a nitrogen adsorption-desorption curve of a lignin-based three-dimensional sheet-like carbon material provided in an exemplary embodiment of this application.

[0020] Figure 3 This is a schematic flowchart of a method for preparing lignin-based three-dimensional sheet-like carbon materials according to an exemplary embodiment of this application. Detailed Implementation

[0021] Hereinafter, exemplary embodiments according to this application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments of this application. It should be understood that this application is not limited to the exemplary embodiments described herein.

[0022] Figure 1 This is a schematic diagram of the structure of a lignin-based three-dimensional sheet-like carbon material provided in an exemplary embodiment of this application. The lignin-based three-dimensional sheet-like carbon material includes three elements: carbon, nitrogen, and oxygen. Figure 1 Scanning electron microscope image of lignin-based three-dimensional sheet-like carbon material, such as Figure 1 As shown, this lignin-based three-dimensional sheet-like carbon material has a three-dimensional sheet-like structure, such as... Figure 2 The figure shows the nitrogen adsorption-desorption curve of the lignin-based three-dimensional sheet-like carbon material. Calculations show that the specific surface area of ​​the lignin-based three-dimensional sheet-like carbon material is not less than 800 m². 2 / g ( Figure 2 The lignin-based three-dimensional sheet-like carbon material shown has a specific surface area of ​​950 m². 2 / g).

[0023] This application provides a lignin-based three-dimensional sheet-like carbon material and its preparation method. The lignin-based three-dimensional sheet-like carbon material has a three-dimensional sheet-like structure, a large specific surface area, which is beneficial for mass transfer and promotes electron transport, enabling the lignin-based three-dimensional sheet-like carbon material to achieve high performance in the field of energy storage.

[0024] In one embodiment, the lignin-based three-dimensional sheet-like carbon material may include four elements: carbon, nitrogen, oxygen, and sulfur.

[0025] Sulfur is a promising cathode material with a theoretical specific capacity of up to 1675 mAh / g and an energy density of 2600 Wh / kg, which is 3-5 times higher than traditional cathode materials based on transition metal oxides or phosphates. Sulfur also has other advantages, such as high abundance in various minerals, low price, and environmental friendliness. However, pure sulfur suffers from low conductivity, low specific capacity, low energy efficiency, and short cycle life due to the high solubility of polysulfide ions formed during charge and discharge. Therefore, this application utilizes the large surface area, chemical stability, high conductivity, and mechanical strength of carbon-based materials to immobilize sulfur, overcoming the low conductivity of sulfur for electrochemical energy storage.

[0026] Figure 3 This is a schematic flowchart of a method for preparing a lignin-based three-dimensional sheet-like carbon material according to an exemplary embodiment of this application. This method for preparing the lignin-based three-dimensional sheet-like carbon material is used to prepare the aforementioned lignin-based three-dimensional sheet-like carbon material; as... Figure 3 As shown, the preparation method of this lignin-based three-dimensional sheet-like carbon material includes the following steps: Step 310: Mix lignin, urea, polyvinylpyrrolidone, and ammonium chloride, add solvent, and ball mill evenly to obtain a slurry. After the slurry is dried, a solid is obtained. The solid is calcined under an inert atmosphere to obtain a porous carbon material.

[0027] In one embodiment, the lignin includes alkali lignin; the mass ratio of lignin, urea, polyvinylpyrrolidone, and ammonium chloride is 1:(0.5-1):(0.8-1):(1-1.2).

[0028] In one embodiment, the solvent is water or ethanol; the ball milling speed is 200-350 r / min, and the ball milling time is 1h-2h.

[0029] In one embodiment, the drying method is rotary evaporation, and the drying temperature is 50°C-60°C.

[0030] In one embodiment, the inert atmosphere is any one of 99.999% nitrogen, 99.999% argon, or 99.999% helium.

[0031] In one embodiment, the calcination temperature is 850℃-950℃, the heating rate is 5℃ / min, and the calcination time is 4.5h.

[0032] Step 320: Mix the porous carbon material and magnesium oxide evenly, and then calcine again under an inert atmosphere.

[0033] In one embodiment, the mass ratio of porous carbon material to magnesium oxide is 1:(1.5-2).

[0034] In one embodiment, the re-calcination temperature is 300℃-400℃, the heating rate is 5℃ / min, and the calcination time is 3h.

[0035] Step 330: The material after re-calcination is washed and filtered with acid, then rinsed with distilled water until pH=7, and dried to obtain lignin-based three-dimensional sheet carbon material.

[0036] In one embodiment, the acid solution is either hydrochloric acid or sulfuric acid with pH=3. The washing method is to put the material after re-calcination into the acid solution and stir for 1 hour. The drying method is to place it in an oven at 80°C and dry it for 10 hours.

[0037] This application provides a method for preparing a lignin-based three-dimensional sheet-like carbon material. This lignin-based three-dimensional sheet-like carbon material has a three-dimensional sheet-like structure and a large specific surface area, which is beneficial for mass transfer and promotes electron transport. This enables the lignin-based three-dimensional sheet-like carbon material to achieve high performance in the field of energy storage. Furthermore, the preparation method adopted in this application avoids the disadvantages of strong acid and strong alkali treatment under high temperature conditions, and reduces the environmental pollution caused by the preparation process.

[0038] This application uses the above-mentioned preparation method to prepare lignin-based three-dimensional sheet carbon material, and tests the energy storage performance of the lignin-based three-dimensional sheet carbon material. The specific testing method is as follows: First, the oxide layer on the surface of the nickel foam is removed using low-concentration hydrochloric acid and washed with distilled water; second, the lignin-based three-dimensional sheet carbon material to be tested is uniformly mixed with polytetrafluoroethylene (PTFE) at a mass ratio of 95:5, dried, and then made into an electrode material; then, the electrode material is uniformly coated and sandwiched between two pieces of nickel foam, and pressed under a pressure of 10MPa-15MPa for 15s to make a carbon material working electrode. The mass of the carbon material working electrode is determined by the subtraction method; finally, a three-electrode system is assembled with a platinum sheet as the counter electrode, a mercury / mercury oxide electrode (Hg / HgO) as the reference electrode, and the working electrode. In an electrolyte of 6 mol / L KOH, the three-electrode system is used to perform cyclic voltammetry, constant current charge-discharge, and AC impedance spectroscopy tests on the carbon material working electrode.

[0039] Example 1 This application provides a lignin-based three-dimensional sheet-like carbon material containing four elements: carbon, nitrogen, oxygen, and sulfur; the specific surface area of ​​this lignin-based three-dimensional sheet-like carbon material is 950 m². 2 / g, and has a three-dimensional sheet-like structure.

[0040] The preparation method of this lignin-based three-dimensional sheet-like carbon material includes the following steps: Step 1: Alkali lignin, urea, polyvinylpyrrolidone, and ammonium chloride are mixed evenly in a mass ratio of 1:0.8:1:1. Water is added and the mixture is ball-milled at a speed of 300 r / min for 1 hour to obtain a slurry. The slurry is then rotary evaporated at 50°C to obtain a solid. The solid is placed in a tube furnace and heated to 850°C at a heating rate of 5°C / min under a 99.999% nitrogen atmosphere and held for 4.5 hours to obtain a porous carbon material.

[0041] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:2 until homogeneous. Under a 99.999% nitrogen atmosphere, heat to 300℃ at a heating rate of 5℃ / min and hold for 3 hours to obtain a solid material.

[0042] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0043] All parameters in this embodiment are within the preferred range of the present invention. Electrochemical performance testing showed that the lignin-based three-dimensional sheet-like carbon material in this embodiment has a capacitance of 245 F / g at 1 A / g.

[0044] Example 2 This application provides a lignin-based three-dimensional sheet-like carbon material containing four elements: carbon, nitrogen, oxygen, and sulfur; the specific surface area of ​​this lignin-based three-dimensional sheet-like carbon material is 1050 m². 2 / g, and has a three-dimensional sheet-like structure.

[0045] The preparation method of this lignin-based three-dimensional sheet-like carbon material includes the following steps: Step 1: Calcium lignosulfonate, urea, polyvinylpyrrolidone, and ammonium chloride are mixed evenly in a mass ratio of 1:1:0.8:1. Water is added and the mixture is ball-milled at a speed of 350 r / min for 1.5 h to obtain a slurry. The slurry is then rotary evaporated at 60°C to obtain a solid. The solid is placed in a tube furnace and heated to 900°C at a rate of 5°C / min under a 99.999% nitrogen atmosphere, and held for 4.5 h to obtain a porous carbon material.

[0046] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:1.5, and heat to 350℃ under a 99.999% nitrogen atmosphere at a heating rate of 5℃ / min and hold for 3 hours to obtain a solid material.

[0047] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0048] All parameters in this embodiment are within the preferred range of the present invention. Electrochemical performance testing showed that the lignin-based three-dimensional sheet-like carbon material in this embodiment has a capacitance of 230 F / g at 1 A / g.

[0049] Example 3 This application provides a lignin-based three-dimensional sheet-like carbon material containing four elements: carbon, nitrogen, oxygen, and sulfur; the specific surface area of ​​this lignin-based three-dimensional sheet-like carbon material is 850 m². 2 / g, and has a three-dimensional sheet-like structure.

[0050] The preparation method of this lignin-based three-dimensional sheet-like carbon material includes the following steps: Step 1: Alkali lignin, urea, polyvinylpyrrolidone, and ammonium chloride are mixed evenly in a mass ratio of 1:0.5:1:1.2. Water is added and the mixture is ball-milled at a speed of 200 r / min for 1 hour to obtain a slurry. The slurry is then rotary evaporated at 50°C to obtain a solid. The solid is placed in a tube furnace and heated to 850°C at a heating rate of 5°C / min under a 99.999% nitrogen atmosphere and held for 4.5 hours to obtain a porous carbon material.

[0051] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:1.5, and heat to 400℃ for 3 hours under a 99.999% nitrogen atmosphere at a heating rate of 5℃ / min to obtain a solid material.

[0052] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0053] All parameters in this embodiment are within the preferred range of the present invention. Electrochemical performance testing showed that the lignin-based three-dimensional sheet-like carbon material in this embodiment has a capacitance of 225 F / g at 1 A / g.

[0054] Comparative Example 1 A lignin-based carbon material containing carbon, nitrogen, oxygen, and sulfur; the specific surface area of ​​this carbon material is 350 m². 2 / g, with a clump structure and clump size of 2-5μm.

[0055] The preparation method of this carbon material includes the following steps: Step 1: Sodium lignosulfonate, urea, polyvinylpyrrolidone, and ammonium chloride are mixed evenly in a mass ratio of 1:0.5:1:1. A mixture of acetone and water is added and the mixture is ball-milled at a speed of 200 r / min for 1 h to obtain a slurry. The slurry is then rotary evaporated at 50 °C to obtain a solid. The solid is placed in a tube furnace and heated to 850 °C at a heating rate of 5 °C / min under a 99.999% nitrogen atmosphere and held for 4.5 h to obtain a porous carbon material.

[0056] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:1.5, and heat to 400℃ for 3 hours under a 99.999% nitrogen atmosphere at a heating rate of 5℃ / min to obtain a solid material.

[0057] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0058] The elements, material structure, and raw materials (sodium lignosulfonate) in this comparative example are not within the scope of this application; all other parameters are within the scope of this application. Electrochemical performance testing showed that the carbon material in this comparative example had a capacitance of 125 F / g at 1 A / g.

[0059] Comparative Example 2 A lignin-based carbon material containing carbon, nitrogen, and oxygen; the specific surface area of ​​this carbon material is 350 m². 2 / g; It has a clump-like structure with clump sizes ranging from 2μm to 3μm.

[0060] The preparation method of this carbon material includes the following steps: Step 1: Alkali lignin, urea, polyvinylpyrrolidone, and ammonium chloride are mixed evenly in a mass ratio of 1:0.5:1:1. Water is added and the mixture is ball-milled at a speed of 200 r / min for 1 hour to obtain a slurry. The slurry is then rotary evaporated at 50°C to obtain a solid. The solid is placed in a tube furnace and heated to 850°C at a rate of 5°C / min under a 99.999% nitrogen atmosphere, and held for 4.5 hours to obtain a porous carbon material.

[0061] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:0.5, and heat to 400℃ under a 99.999% nitrogen atmosphere at a heating rate of 5℃ / min and hold for 3 hours to obtain a solid material.

[0062] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0063] Except for the material structure and the ratio of porous carbon material to magnesium oxide, which are outside the scope of this application, all other parameters in this comparative example are within the scope of this application. Electrochemical performance testing showed that the carbon material in this comparative example had a capacitance of 120 F / g at 1 A / g.

[0064] Comparative Example 3 A lignin-based carbon material containing carbon, nitrogen, and oxygen; the specific surface area of ​​this carbon material is 320 m². 2 / g, with a clump structure and clump size of 5μm-8μm.

[0065] The preparation method of this carbon material includes the following steps: Step 1: Mix alkali lignin, urea, polyvinylpyrrolidone, and ammonium chloride in a mass ratio of 1:0.6:0.9:1.1 until homogeneous. Add water and ball mill at 200 r / min for 1 h to obtain a slurry. Rotary evaporate the slurry at 50°C to obtain a solid. Place the solid in a tube furnace and heat it to 600°C at a rate of 5°C / min under a 99.999% nitrogen atmosphere, and hold for 4.5 h.

[0066] Step 2: Mix porous carbon material and magnesium oxide at a mass ratio of 1:1.5 until homogeneous. Under a 99.999% nitrogen atmosphere, heat to 800℃ at a heating rate of 5℃ / min and hold for 3 hours to obtain a solid material.

[0067] Step 3: Place the solid material obtained in step 2 into hydrochloric acid with pH=3 and stir for 1 hour. Filter, then rinse with distilled water until pH=7. Dry in an oven at 80℃ for 10 hours to obtain sheet-like porous carbon material.

[0068] In this comparative example, the first and second calcination temperatures are outside the scope of this application; all other parameters are within the scope of this application. Electrochemical performance testing showed that the carbon material in this embodiment had a capacitance of 115 F / g at 1 A / g.

[0069] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0070] The block diagrams of devices, apparatuses, devices, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0071] It should also be noted that in the apparatus, equipment, and methods of this application, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered as equivalent solutions of this application.

[0072] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0073] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A method for preparing a lignin-based three-dimensional sheet-like carbon material, characterized in that, The lignin-based three-dimensional sheet-like carbon material comprises four elements: carbon, nitrogen, oxygen, and sulfur, and has a three-dimensional sheet-like structure. The specific surface area of ​​the lignin-based three-dimensional sheet-like carbon material is not less than 800 m². 2 / g; The preparation method of the lignin-based three-dimensional sheet-like carbon material includes: Lignin, urea, polyvinylpyrrolidone, and ammonium chloride are mixed, a solvent is added, and the mixture is ball-milled to obtain a slurry. After the slurry is dried, a solid is obtained. The solid is then calcined under an inert atmosphere to obtain a porous carbon material. The porous carbon material and magnesium oxide are mixed and stirred evenly, and then calcined again under an inert atmosphere; The material after re-calcination is washed and filtered with acid, then rinsed with distilled water until pH=7, and dried to obtain the lignin-based three-dimensional sheet carbon material.

2. The method for preparing lignin-based three-dimensional sheet-like carbon materials according to claim 1, characterized in that, The lignin includes alkali lignin; the mass ratio of the lignin, the urea, the polyvinylpyrrolidone, and the ammonium chloride is 1:(0.5-1):(0.8-1):(1-1.2).

3. The method for preparing lignin-based three-dimensional sheet-like carbon materials according to claim 1, characterized in that, The solvent is water or ethanol; the ball milling speed is 200-350 r / min, and the ball milling time is 1h-2h.

4. The method for preparing lignin-based three-dimensional sheet-like carbon materials according to claim 1, characterized in that, The drying method is rotary evaporation, and the drying temperature is 50℃-60℃.

5. The method for preparing lignin-based three-dimensional sheet-like carbon material according to claim 1, characterized in that, The inert atmosphere is any one of 99.999% nitrogen, 99.999% argon, or 99.999% helium.

6. The method for preparing lignin-based three-dimensional sheet-like carbon material according to claim 1, characterized in that, The calcination temperature is 850℃-950℃, the heating rate is 5℃ / min, and the calcination time is 4.5h.

7. The method for preparing lignin-based three-dimensional sheet-like carbon material according to claim 1, characterized in that, The mass ratio of the porous carbon material to the magnesium oxide is 1:(1.5-2), and the re-calcination temperature is 300℃-400℃, the heating rate is 5℃ / min, and the calcination time is 3h.

8. The method for preparing lignin-based three-dimensional sheet-like carbon material according to claim 1, characterized in that, The acid solution is either hydrochloric acid or sulfuric acid with a pH of 3. The washing method is to put the material after re-calcination into the acid solution and stir for 1 hour. The drying method is to place it in an oven at 80°C and dry it for 10 hours.

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