Crop straw-based high-flux carbon nanofiber material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of carbon materials, and particularly relates to a crop straw-based high-flux carbon nanofiber material as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, crushing crop straws into powder; s2, preparing ionic liquid: mixing organic acid and organic alkali according to a molar ratio of 1: 1 to prepare the ionic liquid; s3, dissolving the crop straw powder with an ionic liquid, and processing the crop straw powder into nanofibers through an electrostatic spinning process; s4, the nanofibers are soaked in a zinc nitrate methanol solution, then a 2-methylimidazole methanol solution is poured, mixing is conducted, and double-layer nanofibers are formed; and S5, carbonizing the double-layer nanofiber in a nitrogen atmosphere to prepare the high-flux nanofiber material. The high-flux carbon nanofiber material is prepared by taking crop straw as a precursor, high energy density and high power density of energy storage equipment can be considered, and high-speed and high-capacity energy storage under high mass load is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon materials, and particularly relates to a crop straw-based high-throughput carbon nanofiber material, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous increase in the demand for high-performance mobile power sources in electric vehicles and portable electronic devices, electrochemical energy storage devices tend to balance high energy density and high power density, being able to store a large amount of energy to meet the long-range demand and enabling fast charging and discharging to adapt to high-frequency usage scenarios. In principle, the core mechanism of all electrochemical energy storage devices lies in the shuttling and storage of ions between two electrodes and the conduction of electrons in the external circuit. Therefore, electrode materials must possess efficient ion and electron transport capabilities to ensure that ions and electrons can quickly enter and exit the electrode and flow to the external circuit.

[0003] Currently, porous carbon-based materials have become indispensable key materials in energy storage technology due to their unique advantages such as high specific surface area, excellent electrical conductivity, good chemical stability, and adjustable pore structure. Generally, the high performance of carbon-based electrode materials can only be achieved in ultra-thin electrodes with low mass loading (≤1mg / cm 2 ); while in commercial electrodes with high mass loading (≥5mg / cm 2 ), the mass transfer limit of ions and the electron transport resistance become more significant, resulting in a significant reduction in capacity during cycling. To meet the energy density requirements of the battery, commercial batteries usually adopt thick electrodes (about 50 - 100μm) to provide sufficient charge storage capacity. However, for electrodes with a high mass loading (≥5mg / cm 2 ), if we want to maintain the same material specific capacity and current density as that of low mass loading electrodes (such as 1 mg / cm 2 ), it is necessary to achieve a proportionally larger ion and electron current in a longer charge transport distance. For traditional thick electrodes, with the increase in mass loading, the problem of insufficient charge delivery becomes more prominent, resulting in only some active materials being able to effectively participate in energy (charge) storage, so that the ratio of the actual achievable capacity to the theoretical capacity rapidly decreases with the increase in mass loading.

[0004] In order to fully exploit the potential of carbon-based electrode materials, it is necessary to develop new electrode structures to break through the performance bottleneck of traditional porous carbon electrodes, thereby achieving more efficient charge transport. However, traditional carbon-based electrode materials still face the following problems: 1. Traditional carbon-based electrode materials are usually fine powders that go through a tedious electrode manufacturing process, including powder dispersion, film casting / coating, drying, and the use of additional ionomer binders. However, the grinding and bonding process will damage the structure of the carbon material, resulting in a reduction in active surface area, excessive dead volume, and a poor interface that hinders electron and mass transfer, increasing contact resistance, thereby affecting its conductivity and electrochemical performance.

[0005] 2. Traditional carbon-based electrode materials are usually made from fossil materials such as coke. Although these materials have good electrochemical properties, they have significant shortcomings in sustainability and environmental friendliness.

[0006] 3. Traditional carbon-based electrode materials usually use alkali metal hydroxides such as KOH and NaOH as activators. Although these activators can significantly increase the specific surface area and pore structure of carbon-based materials, their strong corrosiveness will increase the maintenance cost of the equipment. The large amount of water washing demand will lead to wastewater discharge and environmental pollution. Excessive use will also destroy the pore structure and reduce the yield of carbon materials. In addition, complex post-processing steps may clog the pores.

[0007] Therefore, there is an urgent need for a crop straw-based high-throughput carbon nanofiber material and its preparation method and application to solve the above problems. Summary of the invention

[0008] In order to overcome the defects in the above-mentioned prior art, the present invention provides a crop straw-based high-flux carbon nanofiber material and its preparation method and application. The present invention uses crop straw as a precursor to prepare a high-flux carbon nanofiber material, which can take into account the high energy density and high power density of the energy storage device, and realize high-rate and high-capacity energy storage under high mass load.

[0009] To achieve one of the above purposes, the present invention adopts the following technical solution: A method for preparing a crop straw-based high-flux carbon nanofiber material comprises the following steps: S1. Crush crop straw into powder; S2. preparing an ionic liquid: mixing an acid ion and a base ion in a molar ratio of 1:1 to prepare an ionic liquid; S3, using ionic liquid to dissolve crop straw powder, and then processing it into nanofibers through electrospinning; S4. Prepare the original solution for synthesizing metal organic framework nanoparticles: Solution 1: Weigh 1.5 g of Zn(NO 3 ) 2 •6H 2 O was dissolved in 100 ml of methanol; Solution 2: Weigh 3.3 g of 2-methylimidazole and dissolve it in 50 mL of methanol; S5. Immerse the nanofibers in Solution 1 in Step S4 for 1 - 3 h, and then mix them with Solution 2 in Step S4 and soak for 3 - 5 h. A dense metal-organic framework nanoparticle shell grows on the surface of the nanofibers, forming a double-layer nanofiber with a solid shell. S6. Carbonize the double-layer nanofibers in a nitrogen atmosphere for 1 - 3 h with a nitrogen gas flow rate of 20 - 60 mL / min to obtain a high-throughput carbon nanofiber material composed of a carbonaceous network core structure and a nanoparticle shell wrapped around the outer surface of the carbonaceous network core structure.

[0010] When the double-layer nanofibers are carbonized, 80% of the biomass in the middle part of the nanofibers undergoes mass loss after high-temperature pyrolysis, generating a carbonaceous network core structure mainly composed of micropores and macropores; the nanoparticle shell has high thermal stability during the pyrolysis process, forming a solid shell coated on the outer surface of the nanofibers and having a rich mesoporous structure. Among them, zinc species play an activation and templating role during the pyrolysis process, are reduced to metallic zinc under high temperature, and further evaporate, generating a rich hierarchical porous structure including micropores and mesopores.

[0011] Preferably, the ionic liquid is any one of the first mixed solution or the second mixed solution; the first mixed solution is a mixed solution of malonic acid and diazabicyclo, and the molar ratio of malonic acid to diazabicyclo is 1:2; the second mixed solution is a mixed solution of glacial acetic acid and diazabicyclo, and the molar ratio of glacial acetic acid to diazabicyclo is 1:1.

[0012] Preferably, the crop straw is any one or more of corn straw, wheat straw, rice straw, or sorghum straw.

[0013] Preferably, in Step S1, the crop straw is crushed to 40 - 80 mesh to facilitate the acceleration of the dissolution of the crop straw.

[0014] Preferably, the carbonization temperature is 700°C - 900°C.

[0015] To achieve the second above-mentioned object, the present invention provides a crop straw-based high-throughput carbon nanofiber material, which includes a carbonaceous network core structure and a nanoparticle shell wrapped around the outer surface of the carbonaceous network core structure. The carbonaceous network core structure contains a number of micropores and macropores, and the nanoparticle shell contains a number of mesopores.

[0016] To achieve the third above-mentioned object, the present invention provides an application of a crop straw-based high-throughput carbon nanofiber material. The high-throughput carbon nanofiber material is roll-pressed into electrode sheets with different loadings by a roll press, and the electrode sheet is used as the cathode, zinc foil as the anode, and 2 mol / L ZnSO 4The solution is assembled into a zinc-ion battery with an electrolyte.

[0017] Preferably, the loading amount of the high-throughput carbon nanofiber material ≥ 5 mg / cm 2 .

[0018] The advantages of the present invention are as follows: (1) The present invention uses inexpensive and easily available crop straws (such as wheat straw, corn straw, sorghum straw, and rice straw) as precursors, and through a preparation method of dissolving with ionic liquid, electrospinning, in-situ growth of metal-organic frameworks, and high-temperature carbonization, successfully prepares a high-throughput carbon nanofiber material with a hierarchical porous structure and nitrogen and oxygen co-doping. This material has a three-dimensional network structure with interconnected hierarchical pores and an excellent specific surface area, providing an efficient ion / electron transport path, significantly shortening the ion diffusion path, improving the utilization rate of energy storage sites, thereby achieving a higher charge storage density, and realizing high-rate and high-capacity energy storage of thick electrodes under high-quality loading.

[0019] (2) The present invention converts crop straws into carbon materials, with rich raw materials and low costs. It can not only realize the high-value utilization of waste but also reduce environmental pollution caused by straw burning; environmental friendliness and sustainability. The carbonization process of crop straws can sequester carbon dioxide in the form of organic carbon, reducing greenhouse gas emissions. In addition, the preparation and application of straw-based carbon materials are important directions for green agriculture and sustainable development.

[0020] (3) The high-throughput carbon nanofiber material of the present invention has a hierarchical porous structure, and the pore volume ratio of pores with a pore diameter D ≥ 0.86 nm is as high as 81.16%. The optimized pore size distribution can maximize the accommodation of [[Zn(H 2 O) 6 2+ macromolecules. At the same time, the uniformly distributed abundant active sites promote the reversible chemisorption of Zn 2+ , enhance the wettability of the electrolyte, and accelerate the ion kinetics process.

[0021] (4) The present invention provides a simple and efficient process, avoiding complex and cumbersome steps. The prepared battery exhibits excellent electrochemical performance, while taking into account environmental friendliness and cost-effectiveness, and has significant promotion value and industrial application potential. Description of the Drawings

[0022] Figure 1 It is a transmission electron microscope image of the high-throughput carbon nanofiber material prepared in Example 2 of the present invention at a magnification of 200,000.

[0023] Figure 2 It is a transmission electron microscope image of the high-throughput carbon nanofiber material prepared in Example 2 of the present invention at a magnification of 1,000,000.​

[0024] Figure 3 Energy dispersive spectroscopy and selected area electron diffraction patterns of the high-throughput carbon nanofiber material prepared in Example 2 of the present invention.

[0025] Figure 4 Isothermal adsorption and desorption curves of Examples 1-3 and Comparative Example 1 of the present invention.

[0026] Figure 5 Pore size distribution diagrams of Examples 1-3 and Comparative Example 1 of the present invention.

[0027] Figure 6 Cyclic voltammetry test diagrams of zinc ion batteries of Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0028] Figure 7 Cycling life and Coulomb efficiency diagrams of the zinc ion battery of Example 2 of the present invention at 20 A / g.

[0029] Figure 8 Cycling life and Coulomb efficiency diagrams of the zinc ion battery of Comparative Example 2 of the present invention at 20 A / g. Detailed Description of the Invention

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1 S1. Clean, dry and crush the collected corn straw to obtain 40-mesh corn straw powder; S2. Prepare an ionic liquid: Mix malonic acid and 1,8-diazabicyclo[5.4.0]undec-7-ene with a molar ratio of 1:2 to form an ionic liquid; S3. Dissolve the corn straw powder in the ionic liquid crop straw, and after complete dissolution, process it into nanofibers through electrospinning; S4. Prepare the original solution for synthesizing metal-organic framework nanoparticles: Solution 1: Weigh 1.5 g of Zn(NO 3 ) 2 •6H 2 O and dissolve it in 100 ml of methanol; Solution 2: Weigh 3.3 g of 2-methylimidazole and dissolve it in 50 mL of methanol; S5. Immerse the nanofibers into the solution 1 in step S3 for 1 h successively, and then mix them with the solution 2 in step S3 and soak for 4 h, so that a dense metal-organic framework nanoparticle shell grows in-situ on the surface of the nanofibers, forming a double-layer nanofiber with a solid shell; S6. Place the double-layer nanofibers in a nitrogen atmosphere and carbonize them at 700 °C for 2 h with a nitrogen gas flow rate of 50 mL / min to obtain a high-throughput carbon nanofiber material 1 composed of a carbonaceous network core structure and a nanoparticle shell wrapped on the outer surface of the carbonaceous network core structure; S7. Mechanically roll the high-throughput carbon nanofiber material 1 with a roller press to prepare an electrode sheet with a mass of 5.0 mg / cm 2 Then, using this electrode sheet as the positive electrode, zinc foil as the negative electrode, and 2 mol / L ZnSO 4 solution as the electrolyte, assemble a zinc-ion battery 1.

[0032] Example 2 The difference between this Example 2 and Example 1 is that the carbonization temperature is 800 °C, and high-throughput carbon nanofiber materials 2 and zinc-ion battery 2 are obtained respectively.

[0033] Figure 1 and Figure 2 show the transmission electron microscope images of the high-throughput carbon nanofiber material 2 in Example 2 at magnifications of 200,000 and 1,000,000 respectively. Figure 1 It can be clearly seen the unique inner and outer double-layer structure of the high-throughput carbon nanofiber material 2, while Figure 2 shows its amorphous carbonaceous structure, which provides abundant space for ion storage. Figure 3 Presents the energy-dispersive spectroscopy and selected area electron diffraction patterns of the high-throughput carbon nanofiber material 2 in Example 2, indicating that the four elements of C, N, O, and Zn are evenly distributed in the high-throughput carbon nanofiber material 2. Among them, the N and O elements provide abundant active sites for zinc ion storage, thereby introducing additional pseudocapacitance capacity and significantly enhancing the overall capacity of the battery. At the same time, the electron diffraction pattern confirms the amorphous carbonaceous structure in the high-throughput carbon nanofiber material 2, which is consistent with the analysis results of the high-magnification transmission electron microscope.

[0034] Example 3 The difference between this Example 3 and Example 1 is that the carbonization temperature is 900 °C, and high-throughput carbon nanofiber materials 3 and zinc-ion battery 3 are obtained respectively.

[0035] Example 4 The difference between this Example 4 and Example 2 is that the loading amount of the electrode sheet in step S6 is 7.0 mg / cm 2 of, and high-throughput carbon nanofiber materials 4 and zinc-ion battery 4 are obtained respectively.

[0036] Example 5 The difference between Example 5 and Example 2 is that the loading amount of the electrode sheet in step S6 is 10.0 mg / cm 2 The high-throughput carbon nanofiber material 5 and the zinc ion battery 5 were obtained respectively.

[0037] Example 6 The difference between Example 6 and Example 1 is that the loading amount of the electrode sheet in step S6 is 13.5 mg / cm 2 The high-throughput carbon nanofiber material 6 and the zinc ion battery 6 were obtained respectively.

[0038] Comparative Example 1 The difference between this comparative example 1 and example 2 is that step S4 is missing, and a high-flux carbon nanofiber material 7 and a zinc ion battery 7 are obtained respectively.

[0039] Comparative Example 2 Commercial activated carbon (YP-50F) was selected to prepare electrode sheets and batteries. The specific steps are as follows: S1. Commercial activated carbon (YP-50F), conductive carbon black and polyvinylidene fluoride were weighed in a mass ratio of 8:1:1, mixed and ground thoroughly, and then an appropriate amount of N-methylpyrrolidone was added and ground into a paste to obtain a slurry; S2, apply the slurry in step S1 onto stainless steel, and bake it in a vacuum drying oven at 80°C for 12 hours, and cut the pieces to obtain 5 mg / cm 2 Electrode sheet; S3, using the electrode sheet in step S2 as the positive electrode, the zinc foil as the negative electrode, and 2 mol / L ZnSO 4 The solution is used as electrolyte and zinc ion battery 8 is assembled.

[0040] In order to evaluate the specific surface area (SSA) and pore size distribution (PSD) of the high-flux carbon nanofiber materials, nitrogen adsorption / desorption isotherms were analyzed for the high-flux carbon nanofiber materials 1-3 prepared in Examples 1-3 and the high-flux carbon nanofiber material 7 prepared in Comparative Example 1. The isothermal adsorption / desorption curves are shown in FIG. Figure 1 As shown; and the pore size distribution of the micropores is analyzed based on the isothermal adsorption-desorption curve (such as Figure 5 The specific surface area and pore size data of Examples 1-3 and Comparative Example 1 are shown in Table 1 below: Table 1 Pore structure analysis parameters ; from Figure 4 It can be seen that Comparative Example 1 is a typical type I isotherm, indicating that the high-flux carbon nanofiber material 7 prepared in Comparative Example 1 contains abundant micropores but lacks mesopores. In contrast, Examples 1-3 are all typical type IV isotherms.0 <0.1) quickly saturates and adsorbs, and shows an obvious H 0 type hysteresis loop under high pressure (P / P 4 = 0.5 - 0.95), indicating that the high-throughput carbon nanofiber materials 1 - 3 prepared in Examples 1 - 3 are hierarchical porous structures with coexisting micro / mesopores.

[0041] According to Figure 5 and Table 1, it can be obtained that the SSA value of Example 2 (2123 m 2 / g) is higher than that of Example 1 (1937 m 2 / g), Example 3 (1828 m 2 / g) and Comparative Example 1 (1251 m 2 / g), indicating that the high-throughput carbon nanofiber material 2 prepared in Example 2 can provide more energy storage space. At the same time, the non-local density functional theory (NLDFT) PSD curve shows that the high-throughput carbon nanofiber material 7 prepared in Comparative Example 1 is mainly a microporous structure, and the pore diameter is concentrated at 0.57 nm, while the high-throughput carbon nanofiber materials 1 - 3 prepared in Examples 1 - 3 all have a developed hierarchical porous structure, and the pore diameters are mainly distributed at 0.87 nm, 1.18 nm, 1.47 nm and 3.80 nm. And the high-throughput carbon nanofiber materials prepared at different pyrolysis temperatures have a similar distribution trend, which is due to the evaporation of a large number of zinc templates in the nano-framework, contributing to the formation of abundant nanopores with a diameter > 0.86 nm. In addition, in the high-throughput carbon nanofiber material 2 prepared in Example 2, the pore volume ratio of pores with a diameter ≥ 0.86 nm is as high as 81.16%, far higher than the pore volume ratio of pores with a diameter ≥ 0.86 nm in the high-throughput carbon nanofiber material 7 prepared in Comparative Example 1 (54.98%). And the more pore structures, the faster the transmission of [Zn(H 2 O) 6 2+ can be accelerated, while improving the kinetic performance of the charge transfer process.

[0042] The specific capacities of the zinc-ion batteries in Examples 1 - 6 and Comparative Examples 1 - 2 were tested respectively, and the results are shown in Table 2 below: Table 2 Specific capacities of zinc-ion batteries in Examples and Comparative Examples at a current density of 1 A / g ; In Table 2 above, Examples 1 - 6 are zinc-ion batteries based on high-throughput carbon nanofibers assembled with different loadings (5.0 - 13.5 mg / cm 2 ), and the specific capacity at a current density of 1 A / g is as high as 138 - 165 mAh / g, far higher than the specific capacity of commercial carbon (Comparative Example 2) of 85 mAh / g. As the loading of high-throughput carbon nanofibers increases from 5.0 mg / cm 2 ​(Example 2) Gradually increased to 13.5 mg / cm 2 (Example 6), the specific capacity can still be maintained at 83%, indicating that this material can meet the requirements of commercial batteries for thick electrodes and shows extremely high market application potential.

[0043] The rate performance of the zinc-ion batteries in Examples 1-6 and Comparative Examples 1-2 was tested respectively at current densities of 0.5 A / g, 1 A / g, 2 A / g, 3 A / g, 4 A / g, and 5 A / g. The results are shown in Table 3 below: Table 3 Rate performance of zinc-ion batteries in examples and comparative examples ; In Table 3 above, Examples 1-6 are zinc-ion batteries based on high-throughput carbon nanofibers assembled with different loadings (5.0 - 13.5 mg / cm 2 ). At a high current density of 4 A / g, the capacity retention rate is 86% - 89%, far exceeding the capacity retention rate of 65% of the commercial carbon in Comparative Example 2. The high-throughput carbon nanofiber material of the present invention realizes excellent rate performance by virtue of its pore size size matching the zinc-ion storage and the unobstructed carbon network channels.

[0044] The specific capacity of the zinc-ion batteries in Examples 1-3 and Comparative Examples 1-2 was tested by cyclic voltammetry (CV). The results are as Figure 6 shown. According to Figure 6 it can be seen that the zinc-ion battery 2 prepared in Example 2 has the largest integral area of the CV curve at 50 mv / s, indicating the highest specific capacity.

[0045] The zinc-ion battery prepared based on Example 2 exhibits excellent cycle performance. At 20 A / g, the cycle life and Coulomb efficiency of the zinc-ion batteries prepared in Example 2 and Comparative Example 2 were tested respectively. The results are as Figures 7-8 shown. From Figure 7 it can be seen that at a high current density of 20 A / g, after 75,000 cycles, the capacity retention rate of the zinc-ion battery 2 prepared in Example 2 is still as high as 96.15%, and the GCD curves of the initial and the last 10 cycles are almost unchanged. In contrast, from Figure 8 it can be seen that at a high current density of 20 A / g, after 37,000 cycles, the capacity retention rate of the zinc-ion battery 8 prepared in Comparative Example 2 only remains at 71.86%. The reason why the zinc-ion battery 2 prepared in Example 2 has excellent cycle performance is that the high-throughput carbon nanofiber material prepared in Example 2 has a high reversibility of the Zn 2+ adsorption / desorption process and a highly stable carbon skeleton.

[0046] In summary, the high-throughput carbon nanofiber material prepared by the present invention can be fabricated into a high-quality thick-loaded electrode, which has a unique network structure and abundant active sites, greatly reducing the ion transport resistance and achieving fast diffusion kinetics.

[0047] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a crop straw-based high-flux carbon nanofiber material, characterized in that: The steps include: S1. Crush the crop straw into powder; S2, preparing ionic liquid: mixing acid ions and base ions in a molar ratio of 1:1 to prepare ionic liquid; S3, using ionic liquid to dissolve crop straw powder, and then processing it into nanofibers through electrospinning; S4, immersing the nanofibers in a zinc nitrate methanol solution, and then pouring in a 2-methylimidazole methanol solution and mixing and immersing to form a double-layer nanofiber; S5. Carbonizing the double-layer nanofibers in a nitrogen atmosphere to obtain a high-throughput carbon nanofiber material consisting of a carbonaceous network inner core structure and a nanoparticle shell wrapped around the outer surface of the carbonaceous network inner core structure.

2. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: The ionic liquid is any one of the first mixed liquid and the second mixed liquid; the first mixed liquid is a mixed liquid of malonic acid and diazabicyclo, wherein the molar ratio of malonic acid to diazabicyclo is 1:2; the second mixed liquid is a mixed liquid of glacial acetic acid and diazabicyclo, wherein the molar ratio of glacial acetic acid to diazabicyclo is 1:

1.

3. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: The crop straw is any one or more of corn straw, wheat straw, rice straw or sorghum straw.

4. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: In step S1, the crop straw is crushed into 40-80 meshes.

5. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: In step S4, the zinc nitrate methanol solution is prepared by dissolving 1.5 g of Zn(NO3)2•6H2O in 100 ml of methanol; the nanofibers are immersed in the zinc nitrate methanol solution for 1-3 hours.

6. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: In step S4, the 2-methylimidazole methanol solution is prepared by dissolving 3.3 g of 2-methylimidazole in 50 mL of methanol, and the nanofibers are immersed in the mixed solution for 3-5 hours.

7. The method for preparing a crop straw-based high-flux carbon nanofiber material according to claim 1, characterized in that: The carbonization temperature is 700° C.-900° C., the carbonization time is 1-3 h, and the nitrogen gas flow is 20-60 mL / min.

8. A crop straw-based high-flux carbon nanofiber material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The material comprises a carbon network inner core structure and a nanometer particle shell wrapped on the outer surface of the carbon network inner core structure, wherein the carbon network inner core structure comprises a plurality of micropores and macropores, and the nanometer particle shell comprises a plurality of mesopores.

9. An application of the crop straw-based high-flux carbon nanofiber material as claimed in claim 8, characterized in that: A zinc ion battery was assembled with high-flux carbon nanofiber material as cathode, zinc foil as anode, and 2 mol / L ZnSO4 solution as electrolyte.

10. The use of the crop straw-based high-flux carbon nanofiber material according to claim 9, characterized in that: The loading capacity of the high-throughput carbon nanofiber material is ≥5 mg / cm 2 .

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