Method for preparing hard carbon from medium-temperature coal tar-based pitch

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, in particular to a method for preparing hard carbon from medium-temperature coal tar-based pitch, which comprises the following steps: (S1) hydrogenating the medium-temperature coal tar-based pitch and a hydrogen donor solvent at high temperature and high pressure to obtain hydrogenated pitch; (S2) mixing the hydrogenated asphalt with a Lewis acid catalyst, and oxidizing in an oxygen-containing atmosphere to obtain first oxidized asphalt; (S3) uniformly mixing the first oxidized asphalt and a modifier, and carrying out secondary oxidation crosslinking to obtain second oxidized asphalt; and (S4) uniformly mixing the second oxidized asphalt and a pore-forming agent, and carrying out heat treatment in an inert atmosphere to obtain the product hard carbon material. The hard carbon material prepared by the method disclosed by the invention is benefited from a specific preparation process, shows relatively high specific capacity and first coulombic efficiency, and also has excellent rate capability. The preparation method is simple, low in cost and easy for large-scale production, and lays a foundation for large-scale production of the sodium-ion battery negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to a method for preparing hard carbon from medium-temperature coal tar-based pitch. Background Technology

[0002] Currently, due to the development of new energy sources, the price of lithium ore is rising, and the uneven distribution and limited reserves of lithium ore in the Earth's crust are gradually becoming a factor restricting further research and development of new energy sources. Compared with lithium, sodium has approximately 420 times the reserves in the Earth's crust and is more evenly distributed, reducing the material costs and supply chain risks of sodium-ion batteries. Sodium-ion batteries, as a promising alternative to lithium-ion batteries, have attracted much attention due to their abundant resources and lower cost. However, a problem with sodium-ion batteries is that sodium ions have a larger radius than lithium ions, requiring a negative electrode material with a larger interlayer spacing. Graphite anodes have a smaller interlayer spacing, approximately 0.335 nm, therefore, the already maturely industrialized graphite anode is not suitable for sodium-ion batteries.

[0003] Hard carbon materials are currently the most promising anode materials for practical application in sodium-ion batteries. Hard carbon is an amorphous carbon material that is difficult to graphitize at high temperatures. It possesses a disordered microcrystalline structure with larger interlayer spacing than graphite, which is beneficial for sodium ion transport. Despite the great potential of hard carbon materials in sodium-ion batteries, their commercialization still faces many challenges, mainly low initial coulombic efficiency, poor rate performance, and insufficient cycle stability. Current technologies for preparing hard carbon materials mostly use bio-based materials as carbon sources. Although bio-based sources are widely available and inexpensive, the hard carbon materials prepared using these methods are still far from practical application. Methods using pitch-based materials as carbon sources have also been developed. Medium-temperature coal tar pitch is a byproduct of medium-temperature coal carbonization and has the advantages of wide availability and low price. Compared with high-temperature coal tar pitch, medium-temperature coal tar pitch has a simpler production process, lower cost, a relatively narrower molecular weight distribution, and contains suitable proportions of aromatics and aliphatic hydrocarbons. These characteristics make it a potentially high-quality raw material for preparing hard carbon. However, hard carbon materials produced by direct carbonization of medium-temperature coal tar pitch suffer from poor electrochemical performance, manifested in low initial efficiency and poor rate performance. This may be due to uncontrollable thermal behavior caused by complex components and specific molecular structures, leading to easy graphitization under high-temperature carbonization conditions and a decline in the material's electrochemical performance. The mechanism of sodium storage and sodium intercalation / deintercalation is not yet fully understood. It is speculated that the complex composition of pitch, with some aromatic rings having high condensation degrees and others containing numerous aliphatic side chains and hydrogenated aromatic rings, may lead to a "hydrogen transfer" effect during carbonization. Hydrogen from aliphatic chains and hydrogenated aromatic rings breaks and transfers to polycyclic aromatic hydrocarbons, promoting the pyrolysis and condensation of large planar aromatic molecules, making them more prone to ordered stacking and ultimately forming a carbon structure with small interlayer spacing and a high degree of graphitization. Currently, a common practice is to pre-oxidize and / or cross-link pitch materials to increase the proportion of amorphous carbon and reduce the degree of graphitization. Considering the problems faced by hard carbon materials and the sodium storage mechanism of hard carbon, it can be seen that rationally controlling defects and interlayer spacing in hard carbon anode materials and reducing surface area are effective measures to improve the chemical performance of the materials.

[0004] CN113233440A discloses a method for modifying and preparing a hard carbon anode material, comprising the following steps: S1, premixing 10 parts of NMP (whether to add Chinese name for the first time) with 10 parts of medium-temperature coal tar pitch; S2, placing 40 parts of biomass hard carbon in 30-60 parts of organic solution and stirring to form a suspension, adding 2.4-4.8 parts of carbon nanotube slurry to the suspension and stirring evenly; S3, adding the premixed pitch solution from S1 to the mixture obtained in S2 and stirring evenly; S4, heating the mixture obtained in S3 to dryness, calcining and cooling it in a CAD furnace under inert gas protection, and then screening to obtain the modified hard carbon anode material for sodium-ion batteries.

[0005] CN116161643A discloses a method for preparing a high-rate, low-temperature resistant hard carbon anode material, comprising: (1) mixing zinc salt, carbon precursor and nitrogen source uniformly to obtain a zinc-containing carbon precursor mixture; (2) drying the zinc-containing carbon precursor mixture prepared in step (1) to obtain a dried precursor mixture; and (3) pyrolyzing and carbonizing the dried precursor mixture prepared in step (2) in an inert atmosphere to obtain the hard carbon anode material.

[0006] However, existing methods for preparing hard carbon based on pitch-based materials are not applicable to medium-temperature coal tar pitch. The direct carbonization of medium-temperature coal tar pitch is characterized by an uncontrollable carbonization process, with π-π interactions between excess hydrogen and aromatics, which rearrange into sheet-like aromatic fused ring structures and stack them, resulting in a high degree of graphitization. This is not conducive to the insertion and extraction of sodium ions, leading to less than ideal electrochemical performance of the hard carbon materials produced.

[0007] A research team led by Professor Song Yan at the Shanxi Coal Chemistry Institute, Chinese Academy of Sciences, has made progress in the study of coal liquefaction pitch components. They have achieved a fractional extraction method using solvents to separate toluene-soluble (TS) and toluene-insoluble-pyridine-soluble (TI-PS) components. The TS component has a smaller molecular weight, is rich in aliphatic side chains, and has a looser structure, making it easier to combine with oxygen and form numerous cross-linked structures, preventing ordered stacking during carbonization. After carbonization at 1000℃, the TS-derived hard carbon (O-TS-1000) exhibits larger interlayer spacing and a more disordered carbon layer arrangement, providing more space and rapid pathways for sodium ion insertion. In contrast, TI-PS, due to its stable structure and lower oxidation degree, is more likely to form a graphite-like ordered structure after carbonization, which is unfavorable for sodium ion storage. This method, utilizing fractional extraction to obtain the toluene-soluble (TS) component followed by pyrolysis carbonization, significantly improves the electrochemical performance of hard carbon materials obtained from coal tar pitch as a carbon source. However, this method requires the use of a large amount of toluene solvent for extraction, which increases costs. The extracted toluene is also difficult to process, and hard carbon companies do not currently have large-scale extraction equipment, requiring additional purchases, which also increases production costs. Summary of the Invention

[0008] Given that existing technologies using medium-temperature coal tar pitch as raw material to prepare hard carbon materials have unsatisfactory electrochemical performance, particularly in terms of initial coulombic efficiency and rate performance, this invention proposes a method for preparing hard carbon from medium-temperature coal tar pitch. This invention first hydrogenates the medium-temperature coal tar pitch, then oxidatively crosslinks the hydrogenated pitch, followed by the addition of a pore-forming agent and uniform mixing. After solid-phase heat treatment, a hard carbon suitable as a negative electrode material for sodium-ion batteries is obtained, exhibiting significantly improved initial coulombic efficiency and rate performance. This invention achieves the above objectives through the following technical solutions:

[0009] A method for preparing hard carbon from medium-temperature coal tar-based pitch includes the following steps:

[0010] (S1) Hydrogenated pitch is obtained by hydrogenating medium-temperature coal tar-based pitch and hydrogen-donating solvent under high temperature and high pressure.

[0011] (S2) Hydrogenated bitumen and Lewis acid catalyst are mixed and oxidized in an oxygen-containing atmosphere to obtain the first oxidized bitumen;

[0012] (S3) The first oxidized asphalt and the modifier are mixed evenly and then subjected to secondary oxidative crosslinking to obtain the second oxidized asphalt;

[0013] (S4) The second oxidized asphalt and the pore-forming agent are mixed evenly and heat-treated under an inert atmosphere to obtain the product hard carbon material.

[0014] Furthermore, in step (S1), the softening point of the medium-temperature coal tar-based pitch is 90-110℃ (obtained by ring and ball method test), the mass percentage of toluene insoluble matter is 15-25%, the ash content is ≤0.3wt%, and the mass percentage of quinoline insoluble matter is 5-8wt%.

[0015] Furthermore, the hydrogen-donating solvent is selected from at least one of tetrahydronaphthalene and hydroanthracene, and the mass ratio of the hydrogen-donating solvent to medium-temperature coal tar-based pitch is 50-80:100; the high temperature and high pressure are achieved by heating to 360-450℃ and applying a pressure of 3-6MPa, with a treatment time of 5-8h, a heating rate of 1-5℃ / min, and the pressurizing gas being an inert gas, such as nitrogen, helium, or argon.

[0016] In existing technologies for preparing hard carbon materials for sodium-ion batteries, oxidative dehydrogenation is generally performed, transforming asphalt into a disordered, rigid carbon network structure with large interlayer spacing at high temperatures. This transformation is achieved through dehydrogenation crosslinking. The inventors unexpectedly discovered that prior hydrogenation before oxidative crosslinking can hydrogenate and decompose excessively heavy and highly condensed components in medium-temperature asphalt into components with suitable molecular weights, thus improving reactivity. However, catalytic hydrogenation cannot be used for medium-temperature coal tar-based asphalt. This is because excessive hydrogenation in catalytic hydrogenation generates too many hydrogenated aromatics and cycloalkanes. These components are more prone to melting and orderly arrangement during heat treatment, tending to form a soft carbon-like structure, which is detrimental to the formation of hard carbon and may lead to a decrease in the material's capacity and initial efficiency. Simultaneously, the amount of hydrogen-donating solvent needs to be carefully controlled; otherwise, it can also easily lead to a decline in the electrochemical performance of the hard carbon material.

[0017] Further, in step (S2), the Lewis acid catalyst is selected from at least one of ferric chloride and ferric acetylacetonate, and the amount of Lewis acid catalyst used is 0.7-1.2 wt% of the hydrogenated asphalt mass. The oxygen-containing atmosphere is a gas with an oxygen content ≥15%, such as oxygen, air-rich air, preferably air. The oxidation temperature is 180-240℃, and the oxidation time is 2-3 h. The lower oxidation temperature, combined with the use of the catalyst, can stably perform preliminary pre-oxidation of the hydrogenated asphalt in S1. The inventors also speculate that the Fe in the Lewis acid catalyst added during the preparation of hydrogenated asphalt will catalyze the formation of short-range ordered carbon layers during the subsequent carbonization process. These carbon layers are divided and restricted by the overall cross-linked network, forming a macroscopic disordered structure containing a certain degree of order, that is, the presence of a certain graphite microcrystalline structure, which is conducive to the rapid insertion / extraction of sodium ions.

[0018] Further, in step (S3), the modifier is selected from at least one of sulfonate and 2,5-dimercapto-1,3,4-thiadiazole, and the amount of modifier is 6-10 wt% of the mass of the first oxidized asphalt. The second oxidative crosslinking is performed by heating to 400-500℃ and holding for 1-2 hours. The sulfonate is preferably at least one of sodium p-toluenesulfonate, potassium p-benzenesulfonate, sodium lignosulfonate, and potassium lignosulfonate; more preferably at least one of sodium lignosulfonate and potassium lignosulfonate. The lignin molecule itself is a huge three-dimensional network with a large number of active functional groups such as phenolic hydroxyl groups and methoxy groups. These functional groups can crosslink with the active sites on the molecular chain of the first oxidized asphalt, greatly enhancing the rigidity and stability of the final carbon network.

[0019] Preferably, the modifier is a mixture of lignin sulfonate and 2,5-dimercapto-1,3,4-thiadiazole in a mass ratio of 6-9:1. Both of these modifiers contain sulfur (S), which, after carbonization, is incorporated into the cross-linked carbon network framework as heteroatoms. Sulfur doping can increase the carbon interlayer spacing and introduce defect sites; it also facilitates the insertion and extraction of sodium ions.

[0020] Further, in step (S4), the pore-forming agent is selected from at least one of ammonium bicarbonate, ammonium carbonate, and gluconate, wherein the gluconate is selected from at least one of zinc gluconate, magnesium gluconate, ferrous gluconate, and calcium gluconate; the amount of pore-forming agent used is 1-3 wt% of the mass of the second oxidized asphalt. Preferably, the pore-forming agent is a mixture of ammonium bicarbonate and gluconate in a mass ratio of 1-2:1-2. A single pore-forming agent has a limited thermal decomposition temperature; ammonium bicarbonate has a low decomposition temperature and is consumed in the early stages of carbonization. Using a mixed pore-forming agent can yield a hard carbon material with a richer pore structure. According to reports, gluconate can also inhibit graphitization during the carbonization process.

[0021] Further, in step (S4), the inert atmosphere is nitrogen and / or argon; the heat treatment involves first heating to 300-500℃ and holding for 1-2 hours, then heating to 1000-1300℃ and holding for 4-6 hours. The heating rate is not particularly limited, for example, 1-20℃ / min, preferably 5-10℃ / min.

[0022] Further, in step (S4), the mixing method is grinding, ball milling, or high-speed mixing. Ball milling is preferred. After S3, the second oxidized asphalt becomes a brittle solid; ball milling effectively breaks it down into fine particles, increasing the specific surface area. Moreover, ball milling better mixes the second oxidized asphalt and the pore-forming agent, resulting in a more uniform pore structure distribution in the hard carbon material product. The ball milling parameters are a ball-to-material ratio of 10-20:1, a rotation speed of 60-80 rpm, and a milling time of 5-10 minutes. Ball milling is conducted under an inert atmosphere to prevent oxidation of the material during mechanical activation. Furthermore, the temperature during ball milling needs to be controlled below 50°C to prevent exceeding the decomposition temperature of the pore-forming agent.

[0023] This invention also protects a hard carbon material, which is prepared by the above-described method.

[0024] The present invention also protects a sodium-ion battery, the negative electrode of which comprises a hard carbon material prepared by the above preparation method.

[0025] The preparation method of this invention, through a process of hydrogenation followed by stepwise oxidation, produces a hard carbon material with excellent electrochemical performance, significantly improving initial efficiency and rate performance. This invention innovatively first hydrogenates medium-temperature coal tar-based pitch, hydrogenating and cracking excessively heavy and highly condensed components into components with suitable molecular weights, thus improving reactivity and laying the foundation for subsequent effective oxidative crosslinking. Then, preliminary oxidation is performed under mild conditions in the presence of a Lewis acid salt catalyst, followed by a deep crosslinking oxidation step with a modifier, and finally, solid-phase heat treatment with a pore-forming agent to obtain a hard carbon material with a certain porosity structure. This invention eliminates the need for complex extraction processes of medium-temperature coal tar-based pitch to obtain a hard carbon material with excellent electrochemical performance, offering advantages for industrial application. Attached Figure Description

[0026] Figure 1 This is a SEM image of the hard carbon material obtained in Example 1.

[0027] Figure 2 This is a magnified SEM image of the hard carbon material obtained in Example 1.

[0028] Figure 3 This is the XRD pattern of the hard carbon material obtained in Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0030] Unless otherwise specified, the term "parts" in the embodiments of this invention refers to parts by weight.

[0031] The softening point of the medium-temperature coal tar-based pitch is 104℃ (obtained by the ring and ball method), the mass percentage of toluene-insoluble matter is 21.4%, the ash content is ≤0.3wt%, and the mass percentage of quinoline-insoluble matter is 7.6wt%.

[0032] Example 1

[0033] (S1) 100 parts by weight of medium-temperature coal tar-based pitch and 60 parts by weight of tetrahydronaphthalene were fed into the mixture. The mixture was pressurized to 6 MPa with nitrogen and heated to 420°C at 2°C / min for 6 hours. The tetrahydronaphthalene was removed by distillation to obtain hydrogenated pitch.

[0034] (S2) 100 parts by mass of hydrogenated bitumen and 1 part by mass of iron acetylacetone are mixed evenly and heated to 220°C in air atmosphere for pre-oxidation for 3 hours to obtain the first oxidized bitumen.

[0035] (S3) 100 parts by weight of the first oxidized asphalt and 8.5 parts by weight of the modifier are mixed evenly. The modifier is a mixture of sodium lignosulfonate and 2,5-dimercapto-1,3,4-thiadiazole in a mass ratio of 7:1. The mixture is heated to 450℃ and kept at that temperature for 1 hour to obtain the second oxidized asphalt.

[0036] (S4) 100 parts by weight of second oxidized asphalt, 1 part by weight of ammonium bicarbonate, and 1 part by weight of zinc gluconate are ball-milled and mixed evenly (ball-to-material ratio 20:1, nitrogen atmosphere, rotation speed 80 rpm, ball milling time 5 min). The mixture is heated to 400℃ at a heating rate of 5℃ / min and held for 1 h under nitrogen atmosphere, and then heated to 1200℃ at a heating rate of 5℃ / min and held for 5 h. After cooling, the hard carbon material is obtained.

[0037] Figure 1 This is a SEM image of the hard carbon material obtained in Example 1. Figure 2 This is a magnified SEM image of the hard carbon material obtained in Example 1. It can be seen that the hard carbon material obtained in Example 1 has a size of approximately 10-20 μm and also possesses a rich porous structure. Figure 3 The image shows the XRD pattern of the hard carbon material obtained in Example 1. It can be seen that the broad peak of 002 appears around 24°. According to the Braggs equation, the interlayer spacing of the hard carbon in Example 1 can be calculated to be 0.394 nm.

[0038] Example 2

[0039] (S1) 100 parts by weight of medium-temperature coal tar-based pitch and 50 parts by weight of tetrahydronaphthalene were fed into the mixture. The mixture was pressurized to 6 MPa with nitrogen and heated to 450°C at 2°C / min for 5 hours. The tetrahydronaphthalene was removed by distillation to obtain hydrogenated pitch.

[0040] (S2) 100 parts by weight of hydrogenated bitumen and 1.2 parts by weight of ferric chloride are mixed evenly and heated to 200°C in air atmosphere for pre-oxidation for 3 hours to obtain the first oxidized bitumen.

[0041] (S3) 100 parts by weight of the first oxidized asphalt and 10 parts by weight of the modifier are mixed evenly. The modifier is a mixture of sodium lignosulfonate and 2,5-dimercapto-1,3,4-thiadiazole in a mass ratio of 6:1. The mixture is heated to 450℃ and kept at that temperature for 1 hour to obtain the second oxidized asphalt.

[0042] (S4) is the same as in Example 1.

[0043] Example 3

[0044] (S1) 100 parts by weight of medium-temperature coal tar-based pitch and 80 parts by weight of tetrahydronaphthalene were fed into the mixture. The mixture was pressurized to 6 MPa with nitrogen and heated to 450℃ at 2℃ / min for 5 hours. The tetrahydronaphthalene was removed by distillation to obtain hydrogenated pitch.

[0045] (S2) 100 parts by weight of hydrogenated asphalt and 0.7 parts by weight of acetylacetone iron are mixed evenly and heated to 180°C in air atmosphere for pre-oxidation for 3 hours to obtain the first oxidized asphalt.

[0046] (S3) 100 parts by weight of the first oxidized asphalt and 6 parts by weight of the modifier are mixed evenly. The modifier is a mixture of sodium lignosulfonate and 2,5-dimercapto-1,3,4-thiadiazole in a mass ratio of 9:1. The mixture is heated to 450℃ and kept at that temperature for 1 hour to obtain the second oxidized asphalt.

[0047] (S4) is the same as in Example 1.

[0048] Example 4

[0049] Everything else is the same as in Example 1, except that in step (S3), the modifier is a mixture of sodium p-toluenesulfonate and 2,5-dimercapto-1,3,4-thiadiazole in a mass ratio of 7:1.

[0050] Example 5

[0051] Everything else is the same as in Example 1, except that in step (S3), the modifier is sodium lignosulfonate.

[0052] Example 6

[0053] Everything else is the same as in Example 1, except that in step (S3), the modifier is 2,5-dimercapto-1,3,4-thiadiazole.

[0054] Comparative Example 1

[0055] Everything else is the same as in Example 1, except that step (S1) is omitted and the hydrogenated bitumen in step (S2) is replaced with an equal mass of medium-temperature coal tar-based bitumen.

[0056] Comparative Example 2

[0057] Everything else is the same as in Example 1, except that step (S2) is changed to: 100 parts by mass of hydrogenated asphalt is heated to 300°C in air for pre-oxidation for 3 hours to obtain the first oxidized asphalt. That is, acetylacetone iron is not added, and the pre-oxidation temperature is increased to 300°C.

[0058] Application examples

[0059] The hard carbon material prepared in the above examples and comparative examples, along with the conductive agent Super P and the binder sodium carboxymethyl cellulose, were mixed in a mass ratio of 8:1:1 and N-methylpyrrolidone was used as a solvent to prepare a slurry. This slurry was then coated onto a 20 μm aluminum foil current collector to form a negative electrode (active material 1.5 g / cm²). 2 The electrolyte is a 1M sodium hexafluorophosphate solution, the solvent is a mixture of EC and DMC in a 1:1 volume ratio, and the diaphragm is a glass fiber diaphragm.

[0060] Electrochemical performance testing conditions: The charge / discharge voltage range is 0.01V to 2.0V. The initial discharge specific capacity is tested at a rate of 0.1C. The initial discharge specific capacity and initial coulombic efficiency of the coin cell are tested. The rate performance is tested at 2C. The percentage of the capacity at 2C compared to the capacity at 0.1C is calculated as the rate performance. The capacity retention rate after 100 cycles at 2C is also calculated. The results are shown in Table 1 below.

[0061] Table 1 Performance Tests of Hard Carbon Materials

[0062] .

Claims

1. A process for the preparation of hard carbon from a medium temperature coal tar pitch, characterized in that, The method comprises the following steps: (S1) hydrogenating a medium-temperature coal tar-based pitch and a hydrogen-donating solvent under high temperature and high pressure to obtain a hydrogenated pitch; (S2) mixing the hydrogenated pitch and a Lewis acid catalyst, and performing oxidation under an oxygen-containing atmosphere to obtain a first oxidized pitch; (S3) uniformly mixing the first oxidized pitch and a modifier, and performing secondary oxidation crosslinking to obtain a second oxidized pitch; (S4) uniformly mixing the second oxidized pitch and a pore-forming agent, and performing heat treatment under an inert atmosphere to obtain a product hard carbon material.

2. The production method according to claim 1, characterized by, In step (S1), the medium-temperature coal tar-based pitch has a softening point of 90-110°C, a toluene insoluble mass fraction of 15-25%, an ash content of ≤0.3wt%, and a quinoline insoluble mass fraction of 5-8wt%.

3. The preparation method according to claim 1, characterized in that, In step (S1), the hydrogen-donating solvent is at least one selected from tetrahydronaphthalene and hydrogenated anthracene, and the mass ratio of the hydrogen-donating solvent to the medium-temperature coal tar-based pitch is 50-80:

100. Preferably, the high temperature and high pressure are heating to 360-450°C and a pressure of 3-6MPa, the treatment time is 5-8h, the heating rate is 1-5°C / min, and the pressurized gas is an inert gas.

4. The method of claim 1, wherein, In step (S2), the Lewis acid catalyst is at least one selected from ferric chloride and iron acetylacetonate, and the amount of the Lewis acid catalyst is 0.7-1.2wt% of the mass of the hydrogenated pitch.

5. The preparation method according to claim 1, characterized in that, In step (S2), the oxygen-containing atmosphere is a gas with an oxygen content of ≥15%, the oxidation temperature is 180-240°C, and the oxidation time is 2-3h.

6. The method of claim 1, wherein, In step (S3), the modifier is at least one selected from sulfonate and 2,5-dimercapto-1,3,4-thiadiazole, the amount of the modifier is 6-10wt% of the mass of the first oxidized pitch, the secondary oxidation crosslinking is heating to 400-500°C for 1-2h, the sulfonate is preferably at least one selected from sodium p-toluenesulfonate, potassium p-toluenesulfonate, sodium lignosulfonate, and potassium lignosulfonate, and more preferably at least one selected from sodium lignosulfonate and potassium lignosulfonate.

7. The preparation method according to claim 1, characterized in that, The modifier is a mixture of lignosulfonate and 2,5-dimercapto-1,3,4-thiadiazole at a mass ratio of 6-9:

1.

8. The method of claim 1, wherein, In step (S4), the pore-forming agent is at least one selected from ammonium bicarbonate, ammonium carbonate, and gluconate, the gluconate is at least one selected from zinc gluconate, magnesium gluconate, ferrous gluconate, and calcium gluconate, and the amount of the pore-forming agent is 1-3wt% of the mass of the second oxidized pitch. Further, in step (S4), the inert atmosphere is nitrogen and / or argon, and the heat treatment is first heating to 300-500°C for 1-2h, and then heating to 1000-1300°C for 4-6h.

9. A hard carbon material, characterized by, The hard carbon material is prepared by the preparation method of any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The negative electrode of the sodium ion battery comprises the hard carbon material prepared by the preparation method of any one of claims 1-8.

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