A method for preparing hard carbon material and its application in sodium-ion batteries

Abstract

This invention provides a method for preparing hard carbon materials and their application in sodium-ion batteries. The preparation method includes uniformly mixing soft carbon precursor powder with a carboxylic acid diephile, obtaining a carboxylated soft carbon precursor through a Diels-Alder reaction in a reactor, and then subjecting it to high-temperature carbonization to obtain the hard carbon material. This invention regulates the thermal conversion process of the soft carbon precursor and enhances its crosslinking degree by introducing carboxyl groups, effectively preventing the rearrangement of adjacent graphite microcrystal segments, thus forming a hard carbon material with abundant closed-pore structures and extended interlayer spacing. Furthermore, the surface of the hard carbon material is coated with a carbon shell, effectively reducing surface defects. When the obtained hard carbon material is used as the anode in a sodium-ion battery, it exhibits excellent reversible sodium storage specific capacity and initial coulombic efficiency, realizing high-value utilization of petroleum coke. The carbonaceous precursor used in this invention is widely available, inexpensive, and readily available, and the preparation process is simple, safe, reliable, and cost-controllable, making it suitable for large-scale production and practical applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage. Specifically, it relates to a preparation method of hard carbon material and its application in sodium ion batteries. BACKGROUND

[0002] The increasing demand for key resources and large-scale energy storage devices has brought sodium ion batteries back into the spotlight. The commercialization of sodium ion batteries largely depends on the innovation of low-cost and high-performance electrode materials. Graphite anodes commonly used in lithium ion batteries lack electrochemical sodium storage activity, so the anode material has become a major bottleneck in the development of sodium ion batteries. Currently, research on sodium ion battery anodes mainly focuses on hard carbon materials and has made some progress. However, the reported hard carbon precursors, such as biomass, resins, and polymers, generally face high costs and low yields, which affect the overall cost-effectiveness of sodium ion batteries. Therefore, exploring low-cost precursors or optimizing the preparation process is crucial for promoting the large-scale application of sodium ion batteries.

[0003] Soft carbon precursors, such as petroleum coke, coal, and pitch, are considered ideal choices for electrode material precursors in large-scale energy storage equipment due to their low cost, high carbon content, and good electrical conductivity. However, during carbonization, soft carbon precursors tend to form highly graphitized structures with low interlayer spacing and regular structures, which are not conducive to the effective insertion of sodium ions between layers or the adsorption of sodium ions on defect sites, resulting in low reversible sodium storage specific capacity and initial coulombic efficiency. To overcome these challenges, researchers have explored various modification strategies. One Chinese invention patent (Publication No.: CN118083943A) introduces a method of activating petroleum coke with KOH and then mixing it with pitch for secondary high-temperature carbonization to prepare a porous core-shell structure sodium ion battery anode carbon material. Although this method can improve sodium storage performance to some extent, the improvement is limited, with a reversible specific capacity of only about 250mAh g -1 . Another patent (Publication No.: CN118289731A) proposes using mixed acid to treat petroleum coke to prepare a coated carbon material for coating the surface of hard carbon to reduce the pores and defects on the surface of hard carbon material, thereby increasing the initial coulombic efficiency and reversible specific capacity to 64.9% and 223.6mAh g -1At present, the sodium storage capacity of soft carbon precursor derived carbon is improved by acid oxidation, strong alkali activation and high temperature carbonization, etc. Although these methods improve the sodium storage performance to some extent, they still cannot meet the requirements of practical application, and there are problems such as complex operation, environmental pollution, safety and difficulty in commercialization in the process. In view of the above situation, it is urgent to develop a new type of sodium ion battery negative electrode material which is environment-friendly, low-cost and can significantly improve the sodium storage capacity and initial coulomb efficiency, in order to meet the demand of large-scale energy storage system for high-efficiency and reliable sodium ion battery in the future. SUMMARY

[0004] In view of the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of hard carbon material and its application in sodium ion battery. The present application provides a low-cost, simple and safe and reliable preparation method, which improves the crosslinking degree of soft carbon precursor by carboxyl induction, effectively prevents the rearrangement of adjacent graphite crystallite fragments in the soft carbon precursor, and realizes the transformation of soft carbon precursor derived carbon from highly graphitized soft carbon to turbo-type structure hard carbon. The suitable carbon layer spacing and closed pore structure in the hard carbon provide a large number of effective storage sites for sodium ions; in addition, the surface of the hard carbon material is coated with a carbon shell, which effectively reduces the surface defects of the hard carbon material and significantly improves its initial coulomb efficiency; the obtained hard carbon material exhibits excellent reversible sodium storage capacity and initial coulomb efficiency, realizing the high value-added utilization of soft carbon precursor.

[0005] The technical scheme of the present application is as follows:

[0006] A preparation method of hard carbon material, comprising the following steps:

[0007] (1) uniformly mixing soft carbon precursor powder and carboxylic diene to carry out Diels-Alder reaction in a reaction kettle to obtain carboxylated soft carbon precursor;

[0008] (2) high temperature carbonization of the carboxylated soft carbon precursor to obtain hard carbon material.

[0009] The soft carbon precursor includes one or more of petroleum coke, pitch and coal.

[0010] The petroleum coke is one or more of low-sulfur petroleum coke, medium-sulfur petroleum coke and high-sulfur petroleum coke; the pitch includes one or more of low-temperature pitch, medium-temperature pitch and high-temperature pitch; the coal includes one or more of bituminous coal, anthracite and lignite.

[0011] Before the soft carbon precursor powder and the carboxylic diene are uniformly mixed in step (1), the soft carbon precursor powder is further subjected to ball milling pretreatment.

[0012] The ball milling speed is 400-1000 rpm, and the ball milling time is 0.1-4 h.

[0013] The carboxylic diene includes one or more of maleic acid, maleic anhydride, acrylic acid and acetylene dicarboxylic acid.

[0014] The mass ratio of the soft carbon precursor to the carboxylic diene is 1:(1-20).

[0015] The Diels-Alder reaction is carried out in a closed reaction kettle, the reaction temperature is 150-240 DEG C, and the reaction time is 1-15 h.

[0016] The step (1) further includes washing and drying the carboxylated soft carbon precursor. Further, the washing solvent includes one or more of water, acetone, tetrahydrofuran, benzene, chloroform.

[0017] The temperature of the high-temperature carbonization is 800-1600 DEG C, and the time of the high-temperature carbonization is 0.5-5 h.

[0018] The process of the high-temperature carbonization is carried out in an inert atmosphere.

[0019] The heating rate of the high-temperature carbonization is 1-10 DEG C / min.

[0020] The application further provides an application of the above-mentioned hard carbon material in a sodium ion battery, and the hard carbon material is used as a negative electrode of the sodium ion battery.

[0021] Compared with the prior art, the application has the following advantages:

[0022] 1. The application provides a preparation method of a low-cost and safe and reliable hard carbon material, which creatively changes a conventional path of directly carbonizing a traditional soft carbon precursor to form a high-graphitization-degree soft carbon, improves cross-linking degree of the soft carbon precursor through carboxyl induction, effectively prevents rearrangement of adjacent graphite microcrystal fragments in the soft carbon precursor, and realizes a change of the soft carbon precursor-derived carbon from the high-graphitization-degree soft carbon to a turbo-type structure hard carbon. The suitable carbon layer spacing and closed pore structure in the hard carbon provide a large number of effective storage sites for sodium ions, exhibit excellent reversible sodium storage specific capacity, and realize high-value-added utilization of the soft carbon precursor.

[0023] 2. The carboxylic diene used in the application can form a carbon shell in situ in a subsequent carbonization process, which is coated on the surface of the hard carbon, effectively reduces surface defects of the hard carbon material, and significantly improves initial coulombic efficiency.

[0024] 3. The preparation method disclosed by the application is simple in process, green and environmentally friendly, and low in cost, is suitable for large-scale production and practical application, and has important significance for future commercialized preparation of a sodium ion battery negative electrode.

[0025] 4. The hard carbon material prepared by the preparation method provided by the application has a reversible specific capacity of 326.3 mAh g as a negative electrode material of a sodium ion battery, and an initial coulombic efficiency of 90%. -1 BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is an infrared spectrum picture of the petroleum coke and the carboxylated petroleum coke precursor.

[0027] Figure 2 is an XRD picture of the petroleum coke-based hard carbon material prepared in Example 1.

[0028] Figure 3 is a TEM picture of the petroleum coke-based hard carbon material prepared in Example 1.

[0029] Figure 4 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 1.

[0030] Figure 5 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 2.

[0031] Figure 6 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 3.

[0032] Figure 7 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 4.

[0033] Figure 8 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 5.

[0034] Figure 9 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Example 6.

[0035] Figure 10 is an XRD picture of the petroleum coke-based soft carbon material prepared in Comparative Example 1.

[0036] Figure 11 is a TEM picture of the petroleum coke-based soft carbon material prepared in Comparative Example 1.

[0037] Figure 12 is a constant current charge-discharge curve diagram of the first cycle charge-discharge process of the petroleum coke-based soft carbon material prepared in Comparative Example 1.

[0038] Figure 13 is an XRD picture of the petroleum coke-based hard carbon material prepared in Comparative Example 2.​

[0039] Figure 14 is a constant current charge-discharge curve of the first cycle charge-discharge process of the petroleum coke-based hard carbon material prepared in Comparative Example 2.

[0040] Figure 15 is a constant current charge-discharge curve of the first cycle charge-discharge process of the petroleum coke-based soft carbon material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0041] The present application is described in detail below through some representative examples, but the present application is not limited to these examples.

[0042] Example 1

[0043] This example provides a preparation method of a petroleum coke-based hard carbon material, and the specific operation steps are as follows:

[0044] Take 3 g of high-sulfur petroleum coke powder and ball mill for 1 h at 800 rpm to obtain a ball-milled petroleum coke. Mix 3 g of the ball-milled petroleum coke obtained above with 9 g of maleic anhydride uniformly by grinding, and then place it in a sealed reaction kettle for Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8 h. After the reaction is completed, naturally cool to room temperature, and clean with tetrahydrofuran to remove unreacted maleic anhydride, and dry in a vacuum oven at 50°C for 12 h to obtain a carboxylated petroleum coke precursor. Figure 1 is an infrared spectrum picture of petroleum coke and the carboxylated petroleum coke precursor, from which it can be seen that Diels-Alder reaction can precisely graft a large number of carboxyl groups on the surface of the petroleum coke. Place 1 g of the carboxylated petroleum coke precursor in a tube furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and keep the temperature at 1500°C for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then naturally cool to room temperature to obtain a hard carbon material. Figure 2 is an XRD pattern of the hard carbon material prepared in this example, from which it can be seen that the material exhibits amorphous structure characteristics, and the carbon interlayer spacing calculated according to the Bragg formula is 0.365 nm. Figure 3 is a TEM pattern of the hard carbon material prepared in this example, which exhibits a turbine-type structure feature rich in closed pores and expanded interlayer spacing, and is mainly composed of graphitic and pseudo-graphitic phases.

[0045] Example 2

[0046] This example provides a preparation method of a petroleum coke-based hard carbon material, and the specific operation steps are as follows:

[0047] Take 3 g of high-sulfur petroleum coke powder and mill for 2 h at 800 rpm to obtain milled petroleum coke. Mix 3 g of the milled petroleum coke obtained above with 9 g of maleic anhydride uniformly by grinding, and then place in a sealed reaction kettle to perform Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8 h. After the reaction is completed, cool naturally to room temperature, and clean with tetrahydrofuran to remove unreacted maleic anhydride, and dry in a vacuum oven at 50°C for 12 h to obtain a carboxylated petroleum coke precursor. Place 1 g of the carboxylated petroleum coke precursor in a tube-type carbonization furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain at this temperature for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then cool naturally to room temperature to obtain a hard carbon material.

[0048] Example 3

[0049] This example provides a method for preparing a petroleum coke-based hard carbon material, with the specific operation steps as follows:

[0050] Take 3 g of high-sulfur petroleum coke powder and mill for 2 h at 800 rpm to obtain milled petroleum coke. Mix 3 g of the milled petroleum coke obtained above with 9 g of maleic anhydride uniformly by grinding, and then place in a sealed reaction kettle to perform Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8 h. After the reaction is completed, cool naturally to room temperature, and clean with tetrahydrofuran to remove unreacted maleic anhydride, and dry in a vacuum oven at 50°C for 12 h to obtain a carboxylated petroleum coke precursor. Place 1 g of the carboxylated petroleum coke precursor in a tube-type carbonization furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain at this temperature for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then cool naturally to room temperature to obtain a hard carbon material.

[0051] Example 4

[0052] This example provides a method for preparing a petroleum coke-based hard carbon material, with the specific operation steps as follows:

[0053] Take 3 g of high-sulfur petroleum coke powder and mill for 2 h at 800 rpm to obtain milled petroleum coke. Mix 3 g of the milled petroleum coke obtained above with 9 g of maleic anhydride uniformly by grinding, and then place in a sealed reaction kettle to perform Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8 h. After the reaction is completed, cool naturally to room temperature, and clean with tetrahydrofuran to remove unreacted maleic anhydride, and dry in a vacuum oven at 50°C for 12 h to obtain a carboxylated petroleum coke precursor. Place 1 g of the carboxylated petroleum coke precursor in a tube-type carbonization furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain at this temperature for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then cool naturally to room temperature to obtain a hard carbon material.

[0054] Example 5

[0055] The present embodiment provides a method for preparing a petroleum coke-based hard carbon material, and the specific operation steps are as follows:

[0056] Take 3g of high-sulfur petroleum coke powder and ball mill it at 800 rpm for 1h to obtain a ball-milled petroleum coke. Mix 3g of the ball-milled petroleum coke obtained above with 9g of acrylic acid uniformly, and then place it in a sealed reaction kettle to perform a Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8h. After the reaction is completed, naturally cool it to room temperature, and wash it with water to remove unreacted acrylic acid. Dry it in a vacuum oven at 50°C for 12h to obtain a carboxylated petroleum coke precursor. Place 1g of the carboxylated petroleum coke precursor in a tube-type carbonization furnace, heat it to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain it at this temperature for 2h. Then, cool it to 1000°C at a cooling rate of 2°C / min, and then naturally cool it to room temperature to obtain a hard carbon material.

[0057] Example 6

[0058] The present embodiment provides a method for preparing a petroleum coke-based hard carbon material, and the specific operation steps are as follows:

[0059] Take 3g of high-sulfur petroleum coke powder and ball mill it at 800 rpm for 2h to obtain a ball-milled petroleum coke. Mix 3g of the ball-milled petroleum coke obtained above with 9g of maleic anhydride uniformly, and then place it in a sealed reaction kettle to perform a Diels-Alder reaction, with a reaction temperature of 220°C and a reaction time of 8h. After the reaction is completed, naturally cool it to room temperature, and wash it with tetrahydrofuran to remove unreacted maleic anhydride. Dry it in a vacuum oven at 50°C for 12h to obtain a carboxylated petroleum coke precursor. Place 1g of the carboxylated petroleum coke precursor in a tube-type carbonization furnace, heat it to 1400°C at a heating rate of 3°C / min under an argon atmosphere, and maintain it at this temperature for 2h. Then, cool it to 1000°C at a cooling rate of 2°C / min, and then naturally cool it to room temperature to obtain a hard carbon material.

[0060] Comparative Example 1

[0061] Take 1g of high-sulfur petroleum coke powder and place it in a tube-type carbonization furnace, heat it to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain it at this temperature for 2h. Then, cool it to 1000°C at a cooling rate of 2°C / min, and then naturally cool it to room temperature to obtain a soft carbon material. Figure 10 The XRD pattern of the soft carbon material prepared in this comparative example shows that the material exhibits high graphitization structure characteristics, and the carbon layer spacing calculated according to the Bragg formula is 0.342nm. Figure 11 The TEM pattern of the soft carbon material prepared in this comparative example shows that the material exhibits a long-range ordered structure of carbon layer directional arrangement, and is mainly composed of graphite phase and graphite-like phase.

[0062] Comparative Example 2

[0063] Take 3 g of high-sulfur petroleum coke powder and ball mill for 1 h at 800 rpm to obtain a ball-milled petroleum coke. Place 1 g of the ball-milled petroleum coke in a tube furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain at this temperature for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then cool naturally to room temperature to obtain a hard carbon material. Figure 13 The XRD pattern of the hard carbon material prepared in this comparative example shows that ball milling can cause the structure of the petroleum coke-derived carbon to develop in the direction of disorder. The carbon interlayer spacing calculated according to Bragg's formula is 0.353 nm.

[0064] Comparative Example 3

[0065] Place 3 g of high-sulfur petroleum coke powder in a tube furnace, heat to 260°C at a heating rate of 3°C / min under an oxygen atmosphere, and maintain at this temperature for 3 h to obtain an oxygen pre-oxidized petroleum coke. Place 1 g of the pre-oxidized petroleum coke obtained above in a tube furnace, heat to 1500°C at a heating rate of 3°C / min under an argon atmosphere, and maintain at this temperature for 2 h, then cool to 1000°C at a cooling rate of 2°C / min, and then cool naturally to room temperature to obtain a soft carbon material.

[0066] Assembly and testing of simulated batteries

[0067] Grind and mix the carbon materials prepared in the above examples and comparative examples with SP and LA133+CMC binder in a mass ratio of 8:1:1, add an appropriate amount of pure water, place in a glass bottle, stir to form a uniformly dispersed slurry, then coat the slurry on a copper current collector foil, vacuum dry at 100°C for 12 h, cut into a circular piece with a diameter of 12 mm after drying, and the average mass loading of the active material is 1.5 mg.

[0068] The assembly of simulated batteries was carried out in an Ar atmosphere glove box, with metallic sodium as the counter electrode, 1 mol / L NaPF6(solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) as the electrolyte, glass fiber filter paper as the separator, and the electrode sheets of the examples and comparative examples as the negative electrode to assemble CR2032 button cells. Use Neware CT4008 (Shenzhen, China) battery testing equipment to perform constant current charge and discharge tests at a constant temperature of 30°C and a current density of 20 mA / g -1 The discharge cutoff voltage is 0.01 V and the charge cutoff voltage is 3 V. The test results are shown in Table 1, Figures 4-9 , Figure 12 , Figures 14-15 ,

[0069] Table 1 Comparison of electrochemical performance of negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-2

[0070]

[0071] Analysis:

[0072] From the above table, it can be seen that the hard carbon material preparation method provided by the application has significant innovation and practicality. The method creatively changes the conventional path of directly carbonizing the traditional soft carbon precursor to form a highly graphitized soft carbon, and improves the crosslinking degree of the soft carbon precursor by introducing carboxyl induction, effectively inhibits the rearrangement of the graphite crystallite fragments inside the soft carbon precursor, and promotes the transformation from the highly graphitized soft carbon to the turbine type structure hard carbon; the suitable carbon layer spacing and closed pore structure inside the hard carbon provide a large number of effective storage sites for sodium ions. The surface of the hard carbon material is coated with a carbon shell, which effectively reduces the surface defects of the hard carbon material and significantly improves the initial coulombic efficiency, showing excellent reversible sodium storage specific capacity and initial coulombic efficiency, greatly improving the application value of the soft carbon precursor.

[0073] From Example 1 and Comparative Example 2, Example 3 and Comparative Example 1, it can be seen that by adding maleic anhydride to direct grafting carboxyl groups on the surface of petroleum coke, a highly crosslinked structure can be formed during pyrolysis, delaying the graphitization process of the petroleum coke, expanding the interlayer spacing and increasing the closed pore content, and the surface of the hard carbon material is coated with a carbon shell, which effectively reduces the surface defects of the petroleum coke-based carbon material, thereby significantly improving the reversible specific capacity and initial coulombic efficiency of the petroleum coke-based carbon.

[0074] From Examples 1-3, it can be seen that appropriate ball milling treatment can destroy the microcrystalline structure and C-C bonds of the petroleum coke, increase the active carbon layer edge, improve the modification effect of maleic anhydride, further expand the interlayer spacing and increase the closed pore content, and improve the reversible specific capacity and initial coulombic efficiency of the petroleum coke-based carbon.

[0075] From Examples 1 and 4, it can be seen that increasing the amount of maleic anhydride will increase the number of carboxyl groups grafted on the surface of the petroleum coke, effectively preventing the rearrangement process of the carbon layer, realizing the transformation of the soft carbon precursor derived carbon from a highly graphitized soft carbon to a turbine type structure hard carbon, increasing the closed pore content, and increasing the platform specific capacity.

[0076] From Examples 1 and 5, it can be seen that the method provided by the application has wide applicability for different carboxylic acid dienophiles. Acrylic acid can also undergo Diels-Alder reaction with petroleum coke to achieve surface carboxyl grafting, achieving similar modification effect as maleic anhydride, and obtaining petroleum coke-based hard carbon material with excellent performance.

[0077] As can be seen from Examples 1 and 6, reducing the high-temperature carbonization temperature affects the closure of the pore structure formed in the low-temperature carbonization stage, resulting in an increase in the specific surface area of the hard carbon material and a decrease in the closed pore volume, thereby affecting the initial coulombic efficiency and platform specific capacity of the material. However, a lower carbonization temperature helps to retain more reversible sodium storage sites and maintain a lower graphitization degree, so the slope specific capacity is increased.

[0078] As can be seen from Examples 3, Comparative Example 1 and Comparative Example 3, due to the dense structure and surface inertness of petroleum coke, the conventional oxygen oxidation method cannot graft carboxyl and other oxygen-containing functional groups on the surface of petroleum coke, and the structural regulation of petroleum coke-based carbon materials is limited, and the sodium storage performance is less improved.

[0079] The above has described the present application in detail, the purpose is to let the person who knows this field technology can understand the content of the present application and implements, and cannot limit the protection scope of the present application with this, all equivalent changes or modifications according to the spirit of the present application should be covered in the protection scope of the present application.

Claims

1. A method for producing a hard carbon material, characterized by: The method comprises the following steps: S1: uniformly mixing a soft carbon precursor powder and a carboxylic dienophile, and performing a Diels-Alder reaction in a reaction kettle to obtain a carboxylated soft carbon precursor; S2: high-temperature carbonizing the carboxylated soft carbon precursor to obtain a hard carbon material; Before the soft carbon precursor powder and the carboxylic dienophile are uniformly mixed in step S1, the soft carbon precursor powder is subjected to a ball milling pretreatment; The mass ratio of the soft carbon precursor to the carboxylic dienophile is 1:(1-20).

2. The method of claim 1, wherein: The soft carbon precursor comprises one or more of petroleum coke, pitch and coal.

3. The method of claim 1, wherein: The ball milling speed is 400-1000 rpm, and the ball milling time is 0.1-4 h.

4. The method of claim 1, wherein: The carboxylic dienophile comprises one or more of maleic acid, maleic anhydride, acrylic acid and acetylene dicarboxylic acid.

5. The method of claim 1, wherein: The method of claim 1, wherein the Diels-Alder reaction is performed in a sealed reaction kettle, the reaction temperature is 150-240 ℃, and the reaction time is 1-15 h.

6. The method of claim 1, wherein: Step S1 further comprises cleaning and drying the carboxylated soft carbon precursor.

7. The method of claim 1, wherein: The high-temperature carbonization temperature is 800-1600 ℃, and the high-temperature carbonization time is 0.5-5 h.

8. Use of the hard carbon material obtained by the method according to any one of claims 1 to 7 in a sodium-ion battery, characterized in that: The hard carbon material is used as a negative electrode of a sodium ion battery.

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