A preparation method of asphalt-based sodium ion battery hard carbon negative electrode material

Abstract

The present invention relates to a method for preparing an asphalt-based hard carbon negative electrode material for sodium ion batteries, comprising the following steps: (S1) subjecting an asphalt-based substance to hydrogenation polycondensation and catalytic polycondensation in sequence to obtain a precursor; (S2) subjecting the precursor to acid washing, water washing, and drying, and then to oxidation treatment to obtain an oxidized precursor; (S3) subjecting the oxidized precursor to medium-temperature pre-carbonization treatment under an inert atmosphere; (S4) subjecting the pre-carbonized material of step (S3) to high-temperature carbonization under an inert atmosphere or a hydrocarbon gas atmosphere to obtain a hard carbon material. The asphalt-based hard carbon material of the present invention exhibits excellent electrochemical properties, has a higher sodium storage capacity, and has good cycle stability. The preparation method is simple, low-cost, and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery negative electrode materials, and in particular relates to a method for preparing an asphalt-based hard carbon negative electrode material for sodium ion batteries. Background Art

[0002] Amidst the current energy and environmental crises, the development of efficient and environmentally friendly energy storage technologies has become a key focus of global research. Lithium-ion batteries have become a market favorite due to their superior energy density and long cycle life. However, due to limited lithium resources and cost constraints, researchers are seeking sustainable alternatives. Sodium-ion batteries, in particular, have garnered widespread attention due to their abundance and low cost.

[0003] The working principle of sodium-ion batteries is similar to that of lithium-ion batteries. Both batteries store and release energy through the intercalation and deintercalation of ions in positive and negative electrode materials. However, the large ionic radius of sodium ions leads to poor intercalation performance in traditional graphite negative electrode materials, which directly limits their energy density and cycle stability. Therefore, the development of new negative electrode materials suitable for sodium-ion batteries has become a research focus. Hard carbon, as a non-graphitizable carbon material, exhibits good storage capacity for sodium ions due to its unique pore structure and high specific surface area. The preparation of hard carbon usually comes from natural organic matter or artificial organic polymers, but these materials often have problems such as high cost and limited sources. Asphalt, as a widely available and inexpensive by-product of petroleum processing, provides an economically viable hard carbon precursor option. Through appropriate heat treatment, asphalt can be converted into structurally stable hard carbon for use as a negative electrode material for sodium-ion batteries.

[0004] However, the development of pitch-based hard carbon is not without its challenges. First, pitch has a complex composition, and properties from different sources can vary significantly, which places high demands on its consistency and performance stability as a battery material. Second, controlling the pyrolysis temperature and atmosphere during the hard carbon preparation process to optimize its microstructure and electrochemical performance is also a technical challenge.

[0005] CN118545701A discloses a method for preparing asphalt-based hard carbon, wherein asphalt powder is pre-oxidized and carbonized at high temperature in sequence to obtain the asphalt-based hard carbon; the pre-oxidation comprises: laying the asphalt powder in a thickness of 0.2 to 2 cm in a carrier, and heat-treating it in an oxygen-containing atmosphere at 150 to 350°C for 2 to 12 hours.

[0006] CN118239467A discloses an asphalt-based hard carbon material for a sodium ion battery negative electrode, and its preparation method is as follows: (1) under the protection of an inert gas, oxidized asphalt, a cross-linking agent and a catalyst are mixed, heated with stirring, reacted, and cooled to room temperature after the reaction is completed; (2) the product of step (1) is placed in a coking furnace, first solidified under an inert atmosphere, and then coked, and then the pre-carbonized precursor is crushed to obtain a carbon material precursor powder; (3) the carbon material precursor powder of step (2) is subjected to a high-temperature carbonization treatment under an inert atmosphere to obtain a carbon negative electrode material for a sodium ion battery.

[0007] CN117776156A discloses a technology for preparing asphalt-based hard carbon negative electrode, which includes the following steps: S1, solid asphalt softening: heating solid asphalt at normal pressure to obtain softened asphalt; S2, softened asphalt oxidation reaction: in an oxygen atmosphere, the softened asphalt is subjected to negative pressure heating and negative pressure insulation operations in sequence to obtain a hard carbon precursor; S3, hard carbon precursor carbonization: in an inert gas atmosphere, the hard carbon precursor is subjected to high-temperature carbonization operations to obtain a carbonized material; S4, carbonized material crushing: the carbonized material is cooled and crushed in sequence to obtain the final asphalt-based hard carbon.

[0008] The above patent discloses the steps of softening and / or oxidizing asphalt, but current technology makes it difficult to fully condense small-molecule asphalt into large molecules or even more effective polymers, resulting in molecular rearrangement and reorganization in the subsequent carbonization process, causing the carbonized product to have a high degree of graphitization, and therefore the electrochemical performance is not excellent enough. Summary of the Invention

[0009] The present invention addresses the challenges of low sodium storage capacity, low ICE, and low platform capacity faced by existing pitch-based hard carbon materials used as negative electrodes for sodium-ion batteries. This invention provides a high-performance pitch-based hard carbon negative electrode material for sodium-ion batteries. This invention utilizes a staged polycondensation of the pitch, first with hydrogenation followed by catalytic polycondensation. By controlling the polycondensation conditions, the structural order and electrochemical performance of the hard carbon material are effectively improved. This not only improves the charge-discharge efficiency and cycle stability of sodium-ion batteries, but also offers cost-effectiveness and environmental friendliness, opening up new possibilities for the commercial application of sodium-ion batteries.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a pitch-based hard carbon negative electrode material for sodium ion batteries comprises the following steps:

[0012] (S1) subjecting the asphalt-based material to hydrogenation polycondensation and catalytic polycondensation in sequence to obtain a precursor;

[0013] (S2) acid-washing, water-washing, and drying the precursor, and then oxidizing it to obtain an oxidized precursor;

[0014] (S3) the oxidized precursor is subjected to a medium-temperature pre-carbonization treatment under an inert atmosphere;

[0015] (S4) Carbonizing the pre-carbonized material in step (S3) at high temperature in an inert atmosphere or a hydrocarbon gas atmosphere to obtain a hard carbon material.

[0016] The existing technology pre-oxidizes asphalt-based hard carbon materials with oxygen or other oxidants in the hope of improving the sodium storage performance of the material. However, even after high oxidation, it can only change the oxygen content of the asphalt, and does not change other structural characteristics of the asphalt molecules, so the effect on improving the sodium storage performance is limited. To the surprise of the inventors, after increasing the softening point of the asphalt through a two-stage polycondensation method, the electrochemical performance of the asphalt-based hard carbon negative electrode material can be significantly optimized. However, the order of the two-stage polycondensation cannot be reversed, nor can it be combined into a one-step synchronous polycondensation, otherwise the expected purpose, that is, the purpose of significantly improving the electrochemical performance of the carbon negative electrode material, cannot be achieved. Because it is easier to polymerize small molecules of asphalt into larger molecules after hydrogenation, and it is easier to avoid the subsequent rearrangement of carbon atoms in the chemical bonds, and the strength between the molecules of the prepared hard carbon material is higher, which is more conducive to obtaining a closed-pore structure that is conducive to sodium storage.

[0017] Furthermore, in step (S1), the asphalt material is selected from coal-based asphalt, petroleum asphalt, heavy petroleum oil and biomass asphalt, as well as heavy petroleum oil, naphthalene, anthracene and other aromatic hydrocarbons, and the softening point of the asphalt material is between 60°C and 130°C.

[0018] Furthermore, in step (S1), the hydrogenated polycondensation is performed by uniformly mixing the asphalt material and the hydrogen donor, heating to 350-450°C, the hydrogenated polycondensation pressure is 1-2 MPa, and the hydrogenated polycondensation time is 3-5 hours; and the catalytic polycondensation is performed by uniformly mixing the hydrogenated polycondensation product and the Lewis acid catalyst, carrying out catalytic polycondensation at 200-300°C, the catalytic polycondensation pressure is 2-4 MPa, and the catalytic polycondensation reaction time is 1-2 hours.

[0019] Furthermore, in step (S1), the mass ratio of the asphalt material, hydrogen donor, and catalyst is 100:5-10:1-3. Furthermore, the hydrogen donor includes, but is not limited to, at least one of polyethylene, polypropylene, and polystyrene; and the Lewis acid catalyst is selected from at least one of AlCl3, HF-BF3, and FeCl3.

[0020] Furthermore, the inventors found that high-molecular-weight polyethylene (HMPE) is the most effective hydrogen donor, particularly for polyolefins with molecular weights between 700,000 and 1,000,000. This is likely due to the entanglement of the long molecular chains, which prevent hydrogen atoms from precipitating and are then readily absorbed by asphalt molecules. However, the molecular weight of the HMPE should not be too high, as this would increase the polymer's viscosity and prevent it from fully mixing with the asphalt, preventing the HM supply from being stable.

[0021] In the present invention, there is no particular limitation on the method for uniformly mixing the materials, including but not limited to ball milling, high-speed stirring, grinding, sand milling, etc.

[0022] Furthermore, in step (S2), the acid washing is performed by immersing the precursor in dilute hydrochloric acid to remove the added Lewis acid metal residues. The water washing is performed by washing with deionized water until the precursor is neutral.

[0023] Furthermore, in step (S2), the oxidant is one or more of oxygen, ozone, potassium permanganate, potassium nitrate, sulfuric acid, nitric acid, and ferric oxide. Depending on the selected oxidant, the oxidation method also needs to be adjusted accordingly, such as using ozone and oxygen for oxidation treatment, using a heating and ventilation method; using sulfuric acid and nitric acid for oxidation, using a liquid phase oxidation method; and using ferric oxide as the oxidant, using a solid phase mixing and heating method.

[0024] Furthermore, in step (S2), when using the heating and ventilation method, the temperature is increased to 250-350°C at a heating rate of 2-10°C / min and maintained at this temperature for 5-20 hours. When using the liquid phase oxidation method, the asphalt is ground and then immersed in an oxidant solution for oxidation for 4-20 hours. The concentration of the oxidant is 1 mol / L to 8 mol / L. When using ferric oxide as the oxidant, the asphalt is mixed with ferric oxide in an amount of 0.2 to 0.5 times the mass of the asphalt, and the temperature is increased to 250-350°C at a heating rate of 2-10°C / min and maintained at this temperature for 5-20 hours.

[0025] Furthermore, in step (S3), the medium temperature pre-carbonization treatment is carried out by heating the asphalt at a rate of 5-30°C / min to 500-800°C and keeping the temperature for 2-5 hours, and the inert atmosphere is at least one of argon, helium, and nitrogen. The purpose of pre-carbonization is to promote molecular cross-linking of the asphalt and obtain pre-carbonized material.

[0026] Furthermore, in step (S4), the inert atmosphere is at least one of argon, nitrogen, helium, and radon; and the hydrocarbon gas is at least one of methane, ethane, propane, butane, ethylene, acetylene, and toluene. Calcination in a hydrocarbon atmosphere is preferred to further enhance the initial efficiency and capacity of the hard carbon material.

[0027] Furthermore, in step (S4), the high-temperature carbonization is performed by heating the temperature to 1300-1600°C at a rate of 5-10°C / min and then maintaining the temperature for 5-10 hours. The faster heating rate during the pre-carbonization in step (S3) helps prevent asphalt melting and molecular rearrangement into soft carbon with a high degree of crystallinity, which facilitates the storage of sodium ions and improves the material's capacity.

[0028] This invention uses asphalt, a cost-effective and technologically mature raw material, as its key raw material. Through a two-step polycondensation and pre-oxidation process, the molecular structure of the asphalt precursor is optimized, effectively improving the sodium storage efficiency and initial Coulombic efficiency of the hard carbon. This low-cost, high-efficiency, and simple-to-use preparation method is highly suitable for large-scale production of hard carbon materials for use as negative electrode materials in sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is an SEM image of the hard carbon material obtained in Example 1.

[0030] Figure 2 This is a TEM image of the hard carbon material obtained in Example 1.

[0031] Figure 3 This is a constant current charge and discharge curve of the hard carbon material obtained in Example 1.

[0032] Figure 4 This is a cycle curve diagram of the hard carbon material obtained in Example 1.

[0033] Figure 5 This is the SEM image of the hard carbon material obtained in Comparative Example 1.

[0034] Figure 6 This is the SEM image of the hard carbon material obtained in Comparative Example 2. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0036] Example 1

[0037] (S1) 10 kg of coal-based asphalt with a softening point of 60 ° C and 1 kg of polyethylene with a molecular weight of about 1 million are mixed uniformly by ball milling, the ball mill speed is 500 rpm, the ball-to-material ratio is 20:1, and the ball milling time is 5 hours. The resulting mixture is placed in a reactor, and under the protection of an argon atmosphere, the temperature is increased to 400 ° C at a heating rate of 5 ° C / min and kept warm at a pressure of 2 MPa for 3 hours, and then naturally cooled to room temperature; the obtained material and 0.3 kg of aluminum trichloride are mixed uniformly by ball milling, the ball mill speed is 500 rpm, the ball-to-material ratio is 20:1, and the ball milling time is 5 hours. The resulting mixture is placed in a reactor again, and under the protection of an argon atmosphere, the temperature is increased to 240 ° C at a heating rate of 5 ° C / min, and kept warm at a pressure of 3 MPa for 1 hour to obtain a precursor.

[0038] (S2) The precursor obtained in step (S1) is immersed in dilute hydrochloric acid, stirred for 10 minutes, taken out, and repeatedly washed with deionized water until the effluent is neutral. The washed precursor is then dried and placed in a muffle furnace. It is heated in air at a heating rate of 5°C / min, a heating temperature of 300°C, and a holding time of 20 hours. After cooling, a pre-oxidized precursor is obtained.

[0039] (S3) Grinding the pre-oxidized precursor in step (S2) into powder, and then calcining it in a tube furnace at a heating rate of 5°C / min, raising it to 700°C and keeping it for 3 hours in an Ar gas atmosphere to obtain a pre-carbonized material.

[0040] (S4) Grinding the pre-carbonized material obtained in step (S3) into a fine powder, placing it in a high-temperature tubular furnace, introducing argon gas, and calcining it in an argon gas atmosphere at a heating rate of 5°C / min. After heating to 1300°C, keeping the temperature for 3 hours, and cooling it to room temperature, a hard carbon negative electrode material is obtained.

[0041] from Figure 1 It can be seen that the hard carbon material prepared in Example 1 has a smooth and compact surface. Figure 2 TEM images show that in the process of preparing hard carbon materials, pre-polymerization and oxidation significantly affect the material structure, forming interconnected closed pores. This is mainly because the pitch with a high softening point has a longer molecular chain and a higher degree of cross-linking, and oxidation prevents the random bending of macromolecules at high temperatures, which ultimately makes it easier for macromolecules to form closed pores during the stacking process. In addition, the high oxygen content prevents the fusion of aromatic rings and the rearrangement of molecules in the pre-carbonization stage; at the same time, during the carbonization process, oxygen atoms and their nearby carbon atoms are removed, which also triggers the formation of defects and closed pores. This closed-pore structure helps to form metal-like sodium clusters inside the hard carbon, and the increase in interlayer spacing is conducive to the migration of sodium ions between layers. Figure 5 This is the SEM image of the hard carbon material obtained in Comparative Example 1. Figure 6 This is the SEM image of the hard carbon material obtained in Comparative Example 2. Figure 5 , Figure 6 The hard carbon materials obtained by hydrogenation or catalytic condensation alone present a relatively regular layered structure, which cannot provide sufficient space to support effective sodium storage.

[0042] Example 2

[0043] Other conditions and operations are the same as those in Example 1, except that in step (S1), heavy petroleum oil is used as the raw material instead of coal-based asphalt.

[0044] Example 3

[0045] Other conditions and operations are the same as those in Example 1, except that in step (S1), the molecular weight of the polyethylene is 700,000.

[0046] Example 4

[0047] Other conditions and operations are the same as those in Example 1, except that in step (S1), the molecular weight of the polyethylene is 500,000.

[0048] Example 5

[0049] Other conditions and operations were the same as those in Example 1, except that in step (S1), the molecular weight of the polyethylene was 1.5 million.

[0050] Example 6

[0051] Other conditions and operations were the same as those in Example 1, except that step (S2) was changed to: immersing the precursor obtained in step (S1) in 3 times the mass of 1 mol / L nitric acid and oxidizing for 15 h.

[0052] Example 7

[0053] Other conditions and operations are the same as those in Example 1, except that in step (S1), 0.3 kg of aluminum chloride is replaced by 0.2 kg of HF-BF3

[0054] Comparative Example 1

[0055] Other conditions and operations were the same as in Example 1, except that step (S1) was modified to: 10 kg of coal-based pitch with a softening point of 60°C and 1 kg of polyethylene with a molecular weight of approximately 1,000,000 were uniformly mixed by ball milling at a ball mill speed of 500 rpm, a ball-to-material ratio of 20:1, and a milling time of 5 hours. The resulting mixture was placed in a reactor and heated to 400°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was maintained at 2 MPa for 3 hours, and the mixture was naturally cooled to room temperature to obtain a precursor. This omitted the catalytic polycondensation step.

[0056] Comparative Example 2

[0057] Other conditions and operations were the same as in Example 1, except that step (S1) was modified to: 10 kg of coal-based pitch with a softening point of 60°C and 0.3 kg of aluminum trichloride were uniformly mixed by ball milling at a ball mill speed of 500 rpm, a ball-to-material ratio of 20:1, and a milling time of 5 h. The resulting mixture was again placed in a reactor and heated to 240°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was then maintained at a pressure of 4 MPa for 1 h to obtain a precursor. This omitted the hydrocondensation step.

[0058] Comparative Example 3

[0059] Other conditions and operations were the same as in Example 1, except that step (S1) was modified to: 10 kg of coal-based pitch with a softening point of 60°C and 0.3 kg of aluminum trichloride were uniformly mixed by ball milling at a ball mill speed of 500 rpm, a ball-to-material ratio of 20:1, and a ball milling time of 5 h. The resulting mixture was again placed in a reactor and heated to 240°C at a heating rate of 5°C / min under an argon atmosphere and kept at that temperature for 1 h at a pressure of 4 MPa. After cooling to room temperature, the resulting material was uniformly mixed with 1 kg of polyethylene with a molecular weight of approximately 1,000,000 by ball milling at a ball mill speed of 500 rpm, a ball-to-material ratio of 20:1, and a ball milling time of 5 h. The resulting mixture was placed in a reactor and heated to 400°C at a heating rate of 5°C / min under an argon atmosphere and kept at that temperature for 3 h at a pressure of 2 MPa. The precursor was obtained. The order of hydrogenation and catalytic polycondensation was reversed.

[0060] Comparative Example 4

[0061] Other conditions and operations were the same as in Example 1, except that step (S1) was modified to: 10 kg of coal-based pitch with a softening point of 60°C, 1 kg of polyethylene with a molecular weight of approximately 1,000,000, and 0.3 kg of aluminum trichloride were uniformly mixed by ball milling at a ball mill speed of 500 rpm, a ball-to-material ratio of 20:1, and a ball milling time of 5 h. The resulting mixture was again placed in a reactor and heated to 400°C at a heating rate of 5°C / min under an argon atmosphere. The mixture was then kept at this temperature for 3 h at a pressure of 2 MPa and naturally cooled to room temperature to obtain a precursor. That is, hydrogenation and catalytic polycondensation were carried out simultaneously.

[0062] Comparative Example 5

[0063] Other conditions and operations were the same as in Example 1, except that step (S1) was modified to: coal-based pitch with a softening point of 60°C was placed in a reaction kettle. The temperature was then raised to 400°C at a rate of 5°C / min under an argon atmosphere with stirring. The temperature was maintained for 5 hours and then naturally cooled to room temperature to obtain a precursor. In other words, Comparative Example 5 employed a conventional heating and softening process.

[0064] Application Examples

[0065] The method for preparing and testing the negative electrode material is as follows: the hard carbon obtained in the examples and control experiments was used as the negative electrode material, mixed with Super P and the binder CMC / SBR in a ratio of 94:2:4, and an appropriate amount of water was added and stirred to obtain a uniform electrode slurry; the slurry was then evenly coated on a copper foil and vacuum-dried at 60°C for 12 hours before cutting. Sodium metal was used as the counter electrode, glass fiber as the separator, and 1 mol / L NaPF6 (dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte. Button-type batteries were assembled in an argon glove box. Constant current charge and discharge experiments were then carried out with a current density of 20 mA / g and a voltage range of 0.001-2.0 V. The experimental results are recorded in Table 1.

[0066] Figure 3 This is a constant current charge and discharge curve diagram of the hard carbon material obtained in Example 1; Figure 4 This is a cycle curve diagram of the hard carbon material obtained in Example 1.

[0067] Table 1 Electrochemical performance test of asphalt-based hard carbon negative electrode materials

[0068]

[0069] It can be seen from the half-cell test results of each embodiment in Table 1 that during the preparation process, after increasing the softening point of the asphalt-based precursor and fully oxidizing it, the capacity, first coulombic efficiency and cycle stability of the obtained hard carbon sample are significantly improved.

Claims

1. A method for preparing a pitch-based sodium ion battery hard carbon negative electrode material, characterized in that: The following steps are involved: (S1) sequentially subjecting an asphalt-based substance to hydrogenation polycondensation and catalytic polycondensation to obtain a precursor; wherein the hydrogenation polycondensation comprises uniformly mixing the asphalt-based substance and a hydrogen donor, heating to 350-450° C., a hydrogenation polycondensation pressure of 1-2 MPa, and a hydrogenation polycondensation time of 3-5 hours; and wherein the catalytic polycondensation comprises uniformly mixing the hydrogenation polycondensation product and a Lewis acid catalyst, and conducting catalytic polycondensation at 200-300° C., a catalytic polycondensation pressure of 2-4 MPa, and a catalytic polycondensation reaction time of 1-2 hours; (S2) acid-washing, water-washing, and drying the precursor, and then oxidizing it to obtain an oxidized precursor; (S3) the oxidized precursor is subjected to a medium-temperature pre-carbonization treatment under an inert atmosphere; (S4) Carbonizing the pre-carbonized material in step (S3) at high temperature in an inert atmosphere or a hydrocarbon gas atmosphere to obtain a hard carbon material.

2. The preparation method according to claim 1, characterized in that In step (S1), the asphalt material is selected from coal-based asphalt, petroleum asphalt, biomass asphalt, heavy petroleum oil, and aromatic hydrocarbons, and the softening point of the asphalt material is between 60°C and 130°C.

3. The preparation method according to claim 1, characterized in that The aromatic hydrocarbon is selected from naphthalene and anthracene.

4. The preparation method according to claim 1, characterized in that In step (S1), the mass ratio of the asphalt material, the hydrogen donor and the catalyst is 100:5-10:1-3.

5. The preparation method according to claim 1, characterized in that The hydrogen donor is a polyolefin, selected from at least one of polyethylene, polypropylene, and polystyrene; the Lewis acid catalyst is selected from at least one of AlCl3, HF-BF3, and FeCl3.

6. The preparation method according to claim 5, characterized in that The molecular weight of the polyolefin is 700,000 to 1,000,000.

7. The preparation method according to claim 1, characterized in that In step (S2), the oxidant is one or a mixture of oxygen, ozone, potassium permanganate, potassium nitrate, sulfuric acid, nitric acid, and ferric oxide.

8. The preparation method according to claim 7, characterized in that Depending on the oxidant selected, when ozone and oxygen are used for oxidation treatment, the heating and ventilation method is adopted; when sulfuric acid and nitric acid are used for oxidation, liquid phase oxidation is adopted; when ferric oxide is used as the oxidant, the solid phase mixed heating method is adopted.

9. The preparation method according to claim 8, characterized in that When using the heating and ventilation method, the temperature is raised to 250~350℃ at a heating rate of 2~10℃ / min and kept warm for 5-20 hours. When using the liquid phase oxidation method, the asphalt is ground and then immersed in an oxidant solution for oxidation for 4~20 hours. The concentration of the oxidant is 1 mol / L~8 mol / L. When using ferric oxide as the oxidant, the asphalt is mixed with ferric oxide, the amount of ferric oxide is 0.2~0.5 times the mass of the asphalt, and the temperature is raised to 250~350℃ at a heating rate of 2~10℃ / min and kept warm for 5-20 hours.

10. The preparation method according to claim 1, characterized in that In step (S3), the medium-temperature pre-carbonization treatment is performed by heating the temperature to 500-800°C at a heating rate of 5-30°C / min and keeping the temperature for 2-5 hours, and the inert atmosphere is at least one of argon, helium, and nitrogen.

11. The preparation method according to claim 1, characterized in that In step (S4), the inert atmosphere is at least one of argon, nitrogen, helium, and radon; and the hydrocarbon gas is at least one of methane, ethane, propane, butane, ethylene, acetylene, and toluene.

12. The preparation method according to claim 1, characterized in that In step (S4), the high-temperature carbonization is carried out by heating the temperature to 1300-1600°C at a heating rate of 5-10°C / min and calcining at the temperature for 5-10 hours.

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