Biomass-derived hollow thin-wall two-stage porous carbon fiber material, preparation method thereof and supercapacitor

Abstract

The invention discloses a preparation method of a biomass-derived hollow thin-wall two-stage porous carbon fiber material. The preparation method comprises the following steps: (1) pretreating biomass; (2) degrading lignin and activating cellulose to obtain degraded biomass; (3) adding the degraded biomass into an acetic acid metal salt solution to carry out acetic acid treatment and metal coordination treatment, and then carrying out pre-oxidation treatment on the obtained product to obtain biomass-derived hollow thin-walled carbon fibers; and (4) carrying out pyrolysis treatment on the biomass-derived hollow thin-wall carbon fiber, and carrying out acid treatment on a pyrolysis treatment product to obtain the biomass-derived hollow thin-wall two-stage porous carbon fiber material. The invention also provides a biomass-derived hollow thin-wall two-stage porous carbon fiber material and a supercapacitor. The biomass-derived hollow thin-wall two-stage porous carbon fiber material disclosed by the invention has the advantages of adjustable wall thickness, high microporosity and large specific surface area.

Description

Technical Field

[0001] The present invention belongs to the field of capacitor materials, and particularly relates to an electrode material, a preparation method thereof, and a supercapacitor. Background Art

[0002] With the rapid development of electronic devices, electric vehicles, and renewable energy systems, the demand for high-efficiency energy storage devices is increasing day by day. Supercapacitors have become an important development direction in the energy storage field due to their advantages such as fast charge / discharge rates, excellent cycle stability, and high safety. Traditional carbon fibers have become ideal electrode materials due to their high chemical stability, light weight, and environmental friendliness. Compared with carbon fiber materials, hollow carbon fiber materials have broad application prospects in supercapacitors due to their excellent electrical conductivity, good electrolyte permeability, and high ion transport efficiency. The wall thickness, specific surface area, and microporosity of hollow carbon fibers are the key factors affecting the performance of supercapacitors. Among them, the carbon wall thickness affects the ion transport efficiency, the higher the specific surface area, the higher the charge storage capacity, and the microporosity determines the electrolyte permeability.

[0003] At present, the main preparation methods of hollow carbon fiber materials are as follows: electrospinning method and biological template method. The hollow carbon fibers prepared by the electrospinning method disclosed at present have a low specific surface area and microporosity, and cannot solve the problem of low charge storage capacity of carbon materials. In addition, due to instrument limitations, it is difficult to effectively adjust the carbon wall thickness to the nanoscale for the hollow carbon fibers prepared by coaxial electrospinning. For example, the patent document with the publication number CN119020889A discloses a hollow carbon fiber material loaded with trace ruthenium, a preparation method thereof, and an application. A hollow fiber precursor is obtained by coaxial electrospinning combined with soaking in water, and pre-oxidation and high-temperature carbonization are carried out to obtain a hollow carbon fiber material. The highest specific surface area of the obtained hollow carbon fiber material can reach 390m 2 / g. The above patent prepares a hollow structure by soaking in water, and water molecules will penetrate into the fiber interior, resulting in a change in the internal structure of the fiber and the arrangement of molecular chains becoming disordered, causing a decrease in the microporosity and specific surface area of the fiber. The hollow carbon fibers prepared by the biological template method disclosed at present have obtained a large specific surface area of 1000m 2 / g. However, its carbon wall thickness is fixed and cannot be adjusted, which is not conducive to enhancing the ion transport efficiency.

[0004] For the problems of poor nano-scale wall thickness tunability, small specific surface area, and low microporosity existing in hollow carbon fibers in the prior art, there is no mature and widely recognized solution. How to prepare hollow carbon fibers under mild conditions, regulate the wall thickness of hollow carbon fibers at the nano-scale, prepare hollow carbon fibers with a large specific surface area and high microporosity under simple conditions, and develop a new preparation method for hollow carbon fibers is imminent. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a biomass-derived hollow thin-walled double-stage porous carbon fiber material with high microporosity, large specific surface area, adjustable wall thickness, a preparation method thereof, and a supercapacitor.

[0006] To solve the above technical problems, the technical solution proposed by the present invention is as follows: A preparation method of a biomass-derived hollow thin-walled double-stage porous carbon fiber material, comprising the following steps: (1) Crushing and washing the biomass material to obtain pretreated biomass; (2) Degrading lignin and activating cellulose of the pretreated biomass to obtain degraded biomass; (3) Adding the degraded biomass into an acetic acid metal salt solution for acetylation treatment and metal coordination treatment, and then subjecting the obtained product to pre-oxidation treatment to obtain biomass-derived hollow thin-walled carbon fibers; (4) Pyrolyzing the biomass-derived hollow thin-walled carbon fibers, and subjecting the pyrolysis product to acid treatment to obtain a biomass-derived hollow thin-walled double-stage porous carbon fiber material.

[0007] In the above preparation method, preferably, the degradation of lignin and the activation of cellulose are carried out by fungal fermentation, and the fungi include one or more of white rot fungi, brown rot fungi, and soft rot fungi; during fermentation, the pH value is controlled to be 4-6, the fermentation temperature is 20-40 °C, the rotation speed is 100-200 rpm, and the fermentation time is 5-10 days. The specific process of the above fermentation treatment can be as follows: placing the pretreated biomass in a conical flask, supplementing a solid fermentation medium, adding the fungi to the solid fermentation medium, and fermenting the biomass material at a certain temperature and rotation speed under weak acid conditions to degrade lignin and activate cellulose. More preferably, white rot fungi are used as the fungi, and during fermentation, the pH value is controlled to be 5.5, the fermentation temperature is 30 °C, the rotation speed is 150 rpm, and the fermentation time is 5 days. The pH value and temperature will affect the activity of the fungi, thereby affecting the yield of laccase and cellulase, and further affecting the removal of lignin. If the fermentation time is too long, a large amount of cellulose will be removed by cellulase. It is necessary to reasonably control the above fermentation process conditions to ensure the fermentation efficiency and the fermentation purpose required by the present invention.

[0008] In the above preparation method, preferably, the metal acetate solution includes one or more of zinc acetate solution, lithium acetate solution and iron acetate solution. The concentration of the metal acetate solution is 0.1-0.5 mol / L. The temperature of acetylation treatment and the metal coordination system is 60-80 °C, the stirring rate is 100-200 rpm, and the treatment time is 1-4 h. More preferably, the metal acetate solution is zinc acetate solution with a concentration of 0.2 mol / L. The temperature of acetylation treatment and the metal coordination reaction system is 60 °C, the stirring rate is 150 rpm, and the treatment time is 2 h. The type and concentration of the metal acetate will affect the carbon wall thickness, and the acetylation cellulose and metal coordination time will affect the hollow structure in the subsequent pretreatment stage. The metal acetate solution should be sufficient. The above coordination process conditions can ensure the full reaction of the metal acetate with the degraded biomass, which is beneficial to obtaining the subsequent hollow structure and pore structure. In order to obtain a reasonable void structure and the mechanical strength of the material, it is necessary to control within the above process range. By changing the type of the metal acetate, the present invention constructs different metal coordination structures and metal oxide clusters to realize the regulation of the carbon wall thickness and the microporous structure.

[0009] In the above preparation method, preferably, the pre-oxidation treatment is carried out in air, controlling the pre-oxidation temperature to be 200-300 °C, the heating rate to be 5-8 °C / min, and the pre-oxidation time to be 1-3 h. More preferably, the pre-oxidation temperature is 200 °C, the heating rate is 5 °C / min, and the pre-oxidation time is 2 h. During the pre-oxidation treatment process, it is necessary to ensure the structural stability. If the temperature is too high and the time is too long, the hollow structure is likely to collapse. If the temperature is too low and the time is too short, the hollow structure may not be formed.

[0010] In the above preparation method, preferably, the pyrolysis treatment is carried out in a protective atmosphere, controlling the pyrolysis temperature to be 700-900 °C, the heating rate to be 5-8 °C / min, and the pyrolysis time to be 2-4 h. More preferably, the pyrolysis temperature is 800 °C, the heating rate is 5 °C / min, and the pyrolysis time is 2 h. If the pyrolysis temperature is too low or the pyrolysis time is too short, the carbonization is incomplete. If the pyrolysis temperature is too high or the pyrolysis time is too long, the overall structure may collapse.

[0011] In the above preparation method, preferably, the acid treatment is carried out in a hydrochloric acid solution. The concentration of the hydrochloric acid solution is 1-3 mol / L, and it is stirred with the hydrochloric acid solution for 1-3 h. More preferably, the hydrochloric acid concentration is 2 mol / L and the stirring time is 2 h. The above acid concentration and treatment time can ensure the complete removal of metal oxide clusters.

[0012] In the above preparation method, preferably, the steps for obtaining the pretreated biomass by crushing and washing the biomass material are as follows: The biomass material is crushed by a ball mill and then classified by a mesh sieve. The surface dust is removed by distilled water washing, and then the metal impurities in the biomass material are removed by hydrochloric acid. After filtration, it is placed in an incubator for drying. The ball milling time of the ball mill is 2 - 6 h, the rotation speed is 400 - 600 rpm, and a 300 - 500 mesh sieve is used to obtain a biomass material with a particle size range of 10 - 50 μm. More preferably, the ball milling time is 4 h, the rotation speed is 500 rpm, a 500 - mesh sieve is selected, and the biomass particle size is 20 - 30 μm. When removing the metal impurities in the biomass material with hydrochloric acid, the hydrochloric acid concentration is 1 - 3 mol / L, and stirring is carried out for 1 - 3 h. More preferably, the hydrochloric acid concentration is 2 mol / L, and stirring is carried out for 2 h.

[0013] In the above preparation method, preferably, the biomass material includes one or more of moso bamboo, rice husk, straw, and reed. More preferably, moso bamboo is used.

[0014] As a general technical concept, the present invention also provides a biomass - derived hollow - walled double - stage porous carbon fiber material, which is prepared by using the above - mentioned preparation method. The specific surface area of the biomass - derived hollow - walled double - stage porous carbon fiber material is not less than 1100 m 2 / g, and the micropore proportion is not less than 72%.

[0015] As a general technical concept, the present invention also provides a supercapacitor. As the electrode material of the supercapacitor, when the current density is 0.5 A / g, the specific capacitance value can reach 360 F / g, with good electrochemical performance, and has strong application potential in the field of supercapacitors, which can meet the current requirements for high - performance energy storage devices.

[0016] The preparation method of the biomass - derived hollow - walled double - stage porous carbon fiber material of the present invention is more specifically composed of the following steps: (1) The biomass material is crushed by a ball mill and then classified by a mesh sieve. The surface dust is removed by distilled water washing, and then the metal impurities in the biomass material are removed by hydrochloric acid. After filtration, it is placed in an incubator for drying. (2) The biomass material is placed in a conical flask, and the solid - state fermentation medium is supplemented. The fungus is added to the solid - state fermentation medium, and the biomass material is fermented at a certain temperature and rotation speed under weak - acid conditions to degrade lignin and activate cellulose. (3) The above - mentioned materials are added to an acetic acid metal salt solution for acetylation treatment and metal coordination. The obtained product is pre - oxidized in the air to obtain a biomass - derived hollow - walled carbon fiber. During the subsequent high - temperature pyrolysis process, the coordination unit decomposes and forms uniformly distributed metal oxide clusters. The metal oxide clusters are finally removed by hydrochloric acid to obtain a hollow - walled double - stage porous carbon fiber.

[0017] The principle analysis of the present invention is as follows: (1) Fungi produce laccase and cellulase during the secondary metabolism stage. Laccase opens the phenolic ring in lignin by oxidizing phenolic compounds, generating unstable free radicals that cause the chain breakage of lignin, thereby removing lignin and increasing the purity of cellulose, which is beneficial for obtaining porous materials with a large specific surface area and a high microporosity rate subsequently. Cellulase acts on the cellulose chain to generate smaller cellulose fragments, exposing the hydroxyl groups. Through fungal fermentation treatment, the degradation of lignin and the activation of cellulose can be achieved to obtain cellulose nanofibers, which is beneficial for subsequent pore-forming treatment. The present invention removes lignin and activates cellulose through fungal fermentation, avoiding the use of strong alkalis and ensuring the structural stability of carbon fibers.

[0018] (2) In the metal acetate solution, the metal acetate reacts with the hydroxyl groups on the side chain of cellulose through an esterification reaction to form cellulose acetate with a low melting point. Metal ions slowly diffuse to the surface thin layer of cellulose acetate and coordinate with the carboxyl functional groups on the cellulose acetate molecular chain. At the same time, metal acetate molecules adsorb on the surface of cellulose acetate and gradually form a dense layer, inhibiting the diffusion of metal ions into the core of cellulose acetate. The present invention generates cellulose acetate with a low melting point through an esterification reaction, avoiding the use of strong acid catalysts and protecting the surface and internal structures of the fibers.

[0019] (3) The surface melting point of cellulose acetate is increased through metal coordination, forming a melting point difference with the uncoordinated cellulose acetate. During the low-temperature pre-oxidation treatment stage, the uncoordinated cellulose acetate core decomposes to obtain a hollow thin-wall structure. In addition, the macromolecular chains form aromatic rings and conjugated molecular structures by introducing oxygen elements, thereby improving the structural stability of the undecomposed fibers. During the subsequent high-temperature pyrolysis process, the coordination units decompose to generate a primary microporous structure and form uniformly distributed metal oxide clusters. Removing the metal oxide clusters through hydrochloric acid generates a uniformly distributed secondary microporous structure. Through the above process, the preparation of a hollow structure and a secondary microporous structure can be achieved.

[0020] Compared with the prior art, the advantages of the present invention are as follows: 1. The preparation method of the biomass-derived hollow thin-wall double-stage porous carbon fiber material of the present invention in-situ prepares a hollow thin-wall double-stage porous structure. The in-situ formed double-stage porous structure and hollow thin-wall structure increase the specific surface area and ion transport channels of the material, shorten the transport path, and improve the mass transfer kinetics, having the advantages of a large specific surface area and a high microporosity rate. In addition, the formation of a hollow thin-wall structure during the low-temperature pre-oxidation stage avoids the deformation of the fiber structure under high temperature / strong acid / strong alkali, ensuring the integrity of the structure.

[0021] 2. By changing the types of metal acetates in the present invention, different metal coordination structures and metal oxide clusters can be constructed, enabling the regulation of the carbon wall thickness and microporous structure. For example, zinc ions usually form a helical or pocket-like microporous structure through monodentate coordination with carboxyl groups. The coordination environment is relatively open, occupying less space, which is conducive to the formation of a microporous structure with a high specific surface area. In addition, the relatively low coordination number of zinc ions and carboxyl groups results in a smaller number of ligands around the metal ions, thus generating a thin-wall structure.

[0022] 3. The biomass-derived hollow thin-wall double-stage porous carbon fiber material of the present invention has a large specific surface area (up to 1532 m 2 / g), a high microporosity (up to 82%), and a carbon wall thickness of 9 - 11 nm. When used as an electrode material for supercapacitors, the specific capacitance value can reach 360 F / g when the current density is 0.5 A / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 SEM image of the hollow thin-wall carbon fiber material obtained in Example 1.

[0025] Figure 2 TEM image of the hollow thin-wall carbon fiber material obtained in Example 1.

[0026] Figure 3 SEM image of the hollow thin-wall double-stage porous carbon fiber material obtained in Example 1.

[0027] Figure 4 BET image of the hollow thin-wall double-stage porous carbon fiber material obtained in Example 1.

[0028] Figure 5 Cyclic test chart of the hollow thin-wall double-stage porous carbon fiber material obtained in Example 1 at 0.5 A / g. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in combination with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention.

[0031] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0032] Example 1: A method for preparing a biomass-derived hollow thin-walled double-stage porous carbon fiber material, comprising the following steps: S1: Ball-mill the bamboo material at a speed of 500 rpm for 4 h to break it, classify it through a 500-mesh sieve so that the particle size of the bamboo is 20 - 30 μm. Wash away the surface dust with distilled water, and then stir it with 2 mol / L hydrochloric acid for 2 h to remove the metal impurities in the bamboo material, filter it and place it in an incubator for drying.

[0033] S2: Place the above-mentioned bamboo material in a conical flask, supplement the solid-state fermentation medium, add white rot fungi to the solid-state fermentation medium, and ferment the bamboo material at 30 °C and 150 rpm for 5 days under the condition of pH value of 5.5 to degrade lignin and activate cellulose.

[0034] S3: Add the activated cellulose into 0.2 mol / L zinc acetate solution, stir it at 60 °C at 150 rpm for 2 h for acetylation treatment and metal coordination; heat-treat the obtained product in the air at 200 °C with a heating rate of 5 °C / min and a heat-treatment time of 2 h to obtain bamboo-derived hollow thin-walled carbon fiber (HTWC-Zn-200). Subsequently, perform high-temperature pyrolysis at 800 °C with a heating rate of 5 °C / min and hold for 2 h, resulting in the decomposition of the metal coordination unit and the formation of uniformly distributed ZnO clusters; finally, stir it with 2 mol / L hydrochloric acid for 2 h to remove the ZnO clusters to finally obtain hollow thin-walled double-stage porous carbon fiber (HTWC-Zn-800).

[0035] To prove that HTWC-Zn-200 has a hollow thin-walled structure, SEM and TEM tests were performed on HTWC-Zn-200, and the test results are as Figure 1 and Figure 2 shown, HTWC-Zn-200 has a hollow thin-walled structure with a wall thickness of 9 - 11 nm.

[0036] To prove that HTWC-Zn-800 has a hollow thin-walled double-stage porous structure, SEM test was performed on HTWC-Zn-800, and the test results are as Figure 3 shown, HTWC-Zn-800 has a hollow thin-walled double-stage porous structure.

[0037] To prove that HTWC-Zn-800 has a good specific surface area and pore structure, nitrogen adsorption / desorption tests were carried out on HTWC-Zn-800, and the test results are as Figure 4 shown. It can be seen from Figure 4 that the specific surface area of HTWC-Zn-800 is 1532 m 2 / g and the micropore proportion is 82%.

[0038] To evaluate the feasibility of HTWC-Zn-800 as a supercapacitor electrode material, the prepared HTWC-Zn-800 was subjected to constant current charge-discharge tests to evaluate its electrochemical performance. The test results are as Figure 5 shown. When the current density is 0.5 A / g, the specific capacitance value reaches 360 F / g.

[0039] Example 2: The difference between this example and Example 1 is only that: in step S3, the high-temperature pyrolysis temperature is 700 °C, and the prepared material is marked as HTWC-Zn-700.

[0040] According to the same method as in Example 1, constant current charge-discharge tests were carried out to evaluate its electrochemical performance. When the current density is 0.5 A / g, the specific capacitance value reaches 306 F / g.

[0041] BET tests were carried out on HTWC-Zn-700, and the results are shown in Table 1 below. The specific surface area is 1256 m 2 / g, the micropore proportion is 77% and the carbon wall thickness is (8 - 10 nm). The specific surface area of the material surface is relatively low and the micropore structure is relatively less.

[0042] Example 3: The difference between this example and Example 1 is only that: in step S3, the high-temperature pyrolysis temperature is 900 °C, and the prepared material is marked as HTWC-Zn-900.

[0043] According to the same method as in Example 1, constant current charge-discharge tests were carried out to evaluate its electrochemical performance. When the current density is 0.5 A / g, the specific capacitance value reaches 279 F / g.

[0044] BET tests were carried out on HTWC-Zn-900, and the results are shown in Table 1 below. The specific surface area is 1106 m 2 / g, the micropore proportion is 74% and the carbon wall thickness is (10 - 12 nm). The pore structure of the material surface is poor, and the specific surface area is smaller than that of Example 1 and Example 2.

[0045] By comparing Example 1, Example 2 and Example 3, it can be seen that the high-temperature pyrolysis temperature has an impact on the electrochemical performance of the material. When the carbonization temperature is 800 °C, it is the optimal temperature for the preparation process of the present invention.

[0046] Example 4: The difference between this example and Example 1 is only that: in step S3, the zinc acetate solution is replaced with lithium acetate, and the prepared material is marked as HTWC-Li-800.

[0047] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density was 0.5 A / g, the specific capacitance value reached 326 F / g. The data such as the specific surface area of the material are shown in Table 1 below. The specific surface area is 1425 m 2 / g, the micropore ratio is 77%, and the carbon wall thickness is (14 - 19 nm).

[0048] Example 5: The difference between this example and Example 1 is only that: in step S3, the zinc acetate solution is replaced with iron acetate, and the prepared material is marked as HTWC-Fe-800.

[0049] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density was 0.5 A / g, the specific capacitance value reached 320 F / g. The data such as the specific surface area of the material are shown in Table 1 below. The specific surface area is 1362 m 2 / g, the micropore ratio is 72%, and the carbon wall thickness is (21 - 26 nm).

[0050] By comparing Example 1, Example 4 and Example 5, it can be seen that specific metal acetates have a great influence on the pore structure and carbon wall thickness of the material, and zinc acetate is the best metal acetate for the preparation process of the present invention.

[0051] Comparative Example 1: The difference between this comparative example and Example 1 is only that: step S2 is not passed through (that is, biological fermentation is not used), and the prepared material is marked as C-Zn-800.

[0052] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density was 0.5 A / g, the specific capacitance value reached 220 F / g. The data such as the specific surface area of the material are shown in Table 1 below. The specific surface area is 1100 m 2 / g, the micropore ratio is 57%.

[0053] Comparative Example 2: The difference between this comparative example and Example 1 is only that: no metal acetate solution is used for coordination in step S3, and the prepared material is marked as C-800.

[0054] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density was 0.5 A / g, the specific capacitance value reached 180 F / g. Data such as the specific surface area of the material are shown in Table 1 below. The specific surface area was 920 m 2 / g, and the proportion of micropores was 52%.

[0055] Comparative Example 3: The difference between this comparative example and Example 1 was only that: pre-oxidation was not carried out in step S3, and the prepared material was labeled C-Zn-800. When the current density was 0.5 A / g, the specific capacitance value reached 166 F / g. Data such as the specific surface area of the material are shown in Table 1 below. The specific surface area was 356 m 2 / g, and the proportion of micropores was 24%.

[0056] The specific surface area and the proportion of micropores of the material play an important role in the electrochemical performance of the material. Some studies have shown that the presence of micropores greatly increases the specific surface area of porous carbon, thus providing more active sites, and micropores can serve as storage sites to improve the specific capacitance of the material through physical adsorption or chemical adsorption. In addition, the hollow thin-wall structure increases both the specific surface area and the ion transport channels of the material, and shortens the transport path to improve the mass transfer kinetics. HTWC-Zn-800 in Example 1 exhibited the highest specific surface area of 1532 m 2 / g, a micropore proportion of 82%, and a thin carbon wall thickness (9 - 11 nm), and HTWC-Zn-800 had a large specific capacitance (360 F / g) and a short discharge time (10 min).

[0057] Table 1: Performance data of porous carbon materials in examples and comparative examples

Claims

1. A method for preparing a biomass-derived hollow thin-walled dual-stage porous carbon fiber material, characterized in that: The following steps are involved: (1) crushing and washing the biomass material to obtain pretreated biomass; (2) degrading lignin and activating cellulose on the pretreated biomass to obtain degraded biomass; (3) adding the degraded biomass into an acetic acid metal salt solution for acetic acidization and metal coordination treatment, and then pre-oxidizing the obtained product to obtain biomass-derived hollow thin-walled carbon fibers; (4) The biomass-derived hollow thin-walled carbon fiber is subjected to pyrolysis treatment, and the pyrolysis product is subjected to acid treatment to obtain a biomass-derived hollow thin-walled dual-stage porous carbon fiber material.

2. The preparation method according to claim 1, characterized in that: The treatment of degrading lignin and activating cellulose is a treatment using fungal fermentation, wherein the fungi include one or more of white rot fungi, brown rot fungi and soft rot fungi; during fermentation, the pH value is controlled to be 4-6, the fermentation temperature is 20-40°C, the rotation speed is 100-200rpm, and the fermentation time is 5-10 days.

3. The preparation method according to claim 1, characterized in that: The metal acetate solution includes one or more of a zinc acetate solution, a lithium acetate solution and a ferric acetate solution, and the concentration of the metal acetate solution is 0.1-0.5 mol / L.

4. The preparation method according to claim 1, characterized in that: During the acetic acid treatment and the metal coordination treatment, the temperature of the reaction system is controlled to be 60-80° C., the stirring rate is 100-200 rpm, and the time of the acetic acid treatment and the metal coordination treatment is 1-4 hours.

5. The preparation method according to claim 1, characterized in that: The pre-oxidation treatment is carried out under air, the pre-oxidation temperature is controlled to be 200-300°C, the heating rate is 5-8°C / min, and the pre-oxidation time is 1-3h.

6. The preparation method according to claim 1, characterized in that: The pyrolysis treatment is carried out under a protective atmosphere, the pyrolysis temperature is controlled to be 700-900°C, the heating rate is 5-8°C / min, and the pyrolysis time is 2-4h.

7. The preparation method according to claim 1, characterized in that: The acid treatment is carried out in a hydrochloric acid solution having a concentration of 1-3 mol / L, and the hydrochloric acid solution is stirred for 1-3 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The process of crushing and washing the biomass material to obtain the pretreated biomass includes the following steps: crushing the biomass material with a ball mill and then grading it with a mesh sieve, washing the surface dust with distilled water, and then removing the metal impurities in the biomass material with hydrochloric acid, filtering and placing it in a constant temperature box to dry; the ball milling time is 2-6 hours, the rotation speed is 400-600rpm, and a 300-500 mesh sieve is used to obtain a biomass material with a particle size range of 10-50μm.

9. A biomass-derived hollow thin-walled dual-stage porous carbon fiber material, characterized in that: The biomass-derived hollow thin-walled dual-stage porous carbon fiber material is prepared by the preparation method according to any one of claims 1 to 8, wherein the specific surface area of ​​the biomass-derived hollow thin-walled dual-stage porous carbon fiber material is not less than 1100 m 2 / g, and the proportion of micropores is not less than 72%.

10. A supercapacitor, characterized in that: The electrode is prepared by the preparation method described in any one of claims 1 to 8 to obtain a biomass-derived hollow thin-walled dual-stage porous carbon fiber material or by the biomass-derived hollow thin-walled dual-stage porous carbon fiber material described in claim 9.

Images