Coal-based hard carbon material, preparation method and application of coal-based hard carbon material in sodium-ion battery

Abstract

The invention provides a preparation method of a coal-based hard carbon material and application of the coal-based hard carbon material in a sodium-ion battery. The preparation method comprises the following steps: (1) crushing and screening raw coal to obtain raw coal powder; (2) mixing the raw coal powder with an organic solvent, reacting at high temperature and high pressure, and cooling and filtering to obtain a reaction solution; (3) removing the organic solvent from the reaction liquid to obtain ultra-pure coal powder; and (4) carrying out high-temperature carbonization on the ultra-pure coal powder in an inert atmosphere to obtain the coal-based hard carbon material. The coal-based hard carbon material prepared by the method has larger carbon layer spacing and more defective sodium storage sites, and shows high reversible capacity and high dynamic performance when being used as a sodium ion battery negative electrode. The method provided by the invention is simple in process and low in cost, can meet the requirements of industrial mass production, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a hard carbon material taking coal as a raw material and a preparation method and application thereof in sodium ion batteries. BACKGROUND

[0002] Sodium ion batteries have the advantages of low cost, high safety, short commercialization cycle, etc., and are expected to be applied in fields with low energy density requirements and strong cost sensitivity. The negative electrode material is the core part of the sodium ion battery, which must meet the requirements of high electrochemical reaction activity, low oxidation-reduction potential, rich ion diffusion channel content, high theoretical specific capacity and good structural stability. According to the types and action mechanisms, the negative electrode materials of sodium ion batteries can be divided into three types of alloy, conversion and intercalation. Among them, the first two types will produce serious volume expansion during charging and discharging, which is easy to cause danger, limiting their commercial application. The intercalation type material has low volume change rate, low sodium intercalation platform potential, good cycle stability, simple preparation and rich source during charging and discharging, and has become the most promising negative electrode material of sodium ion batteries.

[0003] Among the many intercalation type materials, hard carbon material stands out due to its adjustable graphite microcrystalline layer spacing, controllable pore structure and rich sodium storage active sites. The precursors for preparing hard carbon include biomass, polymer and coal materials. Hard carbons prepared from different precursors will exhibit different structures and properties, and their sodium storage behaviors will also differ. If large-scale production is desired, a precursor with stable properties, abundant yield and low cost is needed, so the selection of hard carbon precursor is particularly important.

[0004] Coal is considered as a low-cost natural carbon source due to its low cost, high carbon content, abundant reserves, wide distribution and rich oxygen-containing functional groups. These advantages of coal also make coal a good precursor for preparing hard carbon negative electrode materials for sodium ion batteries. Coal-based hard carbon materials used in sodium ion battery negative electrodes exhibit excellent sodium storage performance and are potential hard carbon precursors. However, due to the complexity of coal composition, the sodium storage performance of carbon materials prepared from different coal types is different. At the same time, the existing coal-based carbon materials have problems such as low sodium storage capacity and poor kinetics, which limit their further development.

[0005] Therefore, it is particularly important to design and develop a coal-based hard carbon negative electrode material with high sodium storage capacity and good kinetics. SUMMARY

[0006] Therefore, the application provides a coal-based hard carbon material and a preparation method. A pure hard carbon negative electrode material with rich defect sites is prepared through hot melt extraction, rotary evaporation and high-temperature carbonization.

[0007] The method of the present application takes coal as raw material, adopts hot melt extraction method, removes ash content in coal by using the extraction of organic solvent, at the same time, the heteroatoms (such as N, S, etc.) in the organic solvent are mixed into the material to increase the defect site content, expand the carbon layer spacing, increase the active sodium storage site, and improve the sodium storage performance. The preparation method has the advantages of simple process, low cost, strong universality, and the prepared hard carbon negative electrode material has high capacity, high initial efficiency and high platform voltage, and has good application prospect.

[0008] To achieve the above effects, the technical scheme adopted by the present application is as follows:

[0009] In a first aspect, the present application provides a preparation method of coal-based hard carbon material, comprising the following steps:

[0010] (1) crushing and sieving raw coal to obtain raw coal powder;

[0011] (2) mixing the raw coal powder with an organic solvent and reacting at high temperature and high pressure, and then filtering to obtain a reaction liquid;

[0012] (3) removing the organic solvent from the reaction liquid to obtain ultra-pure coal powder;

[0013] (4) carbonizing the ultra-pure coal powder at high temperature in an inert atmosphere to obtain the coal-based hard carbon material.

[0014] In one embodiment, the raw coal in step (1) is one or more of lignite, bituminous coal and anthracite; preferably, it is bituminous coal.

[0015] In one embodiment, the particle size (D50) of the raw coal powder in step (1) is 5-300 μm, for example, 5, 10, 50, 100, 150, 200, 250, 300 μm, etc.; preferably, the particle size of the raw coal powder is 10-75 μm.

[0016] In one embodiment, the organic solvent in step (2) is one or more of organic solvents containing nitrogen and / or sulfur elements;

[0017] Alternatively, the organic solvent containing nitrogen elements is selected from one or more of N-methyl pyrrolidone, N,N-dimethylformamide, N-ethyl formamide, N-methyl acetamide, preferably N-methyl pyrrolidone;

[0018] Alternatively, the organic solvent containing sulfur elements is selected from one or more of carbon disulfide, dimethyl sulfoxide, dibutyl disulfide, preferably carbon disulfide;

[0019] In one embodiment, the amount of the organic solvent used in step (2) is 100-1000 mL / g of the raw coal powder, such as 100, 200, 400, 600, 800, 1000 mL / g, and the like; preferably, the amount of the organic solvent used is 100-500 mL / g of the raw coal powder.

[0020] In one embodiment, the reaction in step (2) is carried out at a temperature of 50-400°C, such as 50, 100, 150, 200, 250, 300, 350, 400°C, and the like, and a pressure of 0.1-10 MPaG, such as 0.1, 1, 3, 5, 7, 9, 10 MPaG, and the like, for a time period of 1-6 hours, such as 1, 2, 3, 4, 5, 6 hours, and the like; preferably, the reaction is carried out at a temperature of 150-350°C, a pressure of 1-5 MPa, and a time period of 2-4 hours.

[0021] The reaction in step (2) of the present application is carried out at high temperature and high pressure after the raw coal powder is mixed with the organic solvent. Analysis shows that the process mainly includes the following: pyrolysis reaction, the macromolecular structure of coal is decomposed by heat, covalent bonds are broken, free radicals and small molecular fragments are generated; the bridge bonds (-CH2-, -O-, -S-, and the like) between aromatic clusters are first broken, so that the macromolecule is disintegrated; swelling and dissolution process, the organic solvent penetrates into the microporous structure of coal, so that the coal particles are swelled, the crosslinking structure of coal is destroyed, and the dissolution ability of the solvent to the organic matter in coal is enhanced; and heteroatom transfer reaction involving the solvent, the organic solvent provides active nitrogen and sulfur to the free radicals generated by coal pyrolysis, stabilizes the intermediate products in pyrolysis, and promotes the depolymerization of macromolecules in coal into soluble small molecules. The final reaction product mainly includes a reaction liquid of the organic solvent and the macromolecular matter in coal, and a solid residue whose main component is ash.

[0022] In one embodiment, the method for removing the organic solvent from the reaction liquid in step (3) is not particularly required, and can be a conventional method in the art. For example, the separation of the solvent and coal can be achieved by processes such as rotary evaporation, vacuum distillation, back extraction, and the like, such as rotary evaporation at a pressure of 1-10 KPaA and a temperature of 10-90°C for 6-12 hours.

[0023] In one embodiment, the inert atmosphere in step (4) is one or more of argon, nitrogen, and the like; preferably, the inert atmosphere is argon.

[0024] In one embodiment, the carbonization in step (4) is carried out at a temperature of 800-1800°C, such as 800, 1000, 1200, 1400, 1600, 1800°C, and the like, and a heating rate of 0.5-10°C / min, such as 0.5, 2, 4, 6, 8, 10°C / min, and the like; preferably, the carbonization is carried out at a temperature of 1000-1600°C and a heating rate of 1-3°C / min.

[0025] In an embodiment, the carbonization in step (4) has a carbonization time of 1-6 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0026] In a second aspect, the present application provides a coal-based hard carbon material.

[0027] The coal-based hard carbon material is prepared by the method described above, has an ash content of 0.01-0.05wt%, a carbon layer spacing of 0.35-0.39nm, and a specific surface area of 1-10m 2 / g.

[0028] In a third aspect, the present application also provides the use of the coal-based hard carbon material in a sodium ion battery.

[0029] Specifically, the coal-based hard carbon material is used as a negative electrode of a sodium ion battery.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] 1. The present application uses a hot melt extraction method to selectively dissolve the organic components in coal at high temperature, thereby realizing the separation of ash and organic matter, and an ultra-pure coal with an ash content of less than 0.05% can be prepared. The organic solvent involved can be recycled, and the present application has the advantages of environmental friendliness, simple process, and low cost. The prior art often uses chemical acid and alkali washing method to prepare ultra-pure coal, which has the problems of strong corrosion, serious pollution, and high waste water treatment cost.

[0032] 2. In an embodiment of the present application, an organic solvent containing N and S elements is used for hot melt extraction and ash removal treatment. During the reaction process, N and S atoms in the solvent are introduced into the ultra-pure coal, which has the effect of element doping. Specifically, it can increase the defect sites of the material, improve the electronic conductivity, enhance the sodium ion diffusion kinetics, and thus improve the reversible capacity and rate performance of the material. The coal-based hard carbon material prepared by the present application solves the problems of low sodium storage capacity and poor kinetics of such materials, effectively improves the sodium storage performance, and has high reversible capacity and high rate performance. The reversible specific capacity is 310mAh / g at a current density of 0.1C, the first cycle coulombic efficiency is 90.2%, and the secondary cycle platform voltage is 62mV. DETAILED DESCRIPTION

[0033] The technical solutions of the present application are further described below in combination with specific embodiments. The present application can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0034] It is to be understood that the endpoints of the ranges specified in the description and claims are too be understood as being approximate. Moreover, all ranges disclosed herein are to be understood to encompass both the range specifically disclosed and any other narrower range encompassed thereon. The disclosure of a range includes each possible sub-range as if each numerical value between the upper and lower limit of that range is expressly disclosed. The disclosure of a range could be a range including any and all sub-ranges assuming the base value and the top value are explicitly disclosed.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this description, the singular forms "a", "an" and "the" include plural references unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art, which can be obtained by commercial purchase, and the reagents involved can also be obtained by conventional methods in the art.

[0037] In the embodiments and comparative examples of the present application, the main raw materials used are as follows,

[0038] Lignite: Inner Mongolia Company of State Power Investment Corporation, Huolinhe Lignite HM30;

[0039] Bituminous coal: State Energy Group, Jungar long flame coal (CY);

[0040] Anthracite: Huayang Group, Yangquan anthracite WY01;

[0041] N-methyl pyrrolidone: Aladdin;

[0042] N,N-dimethylformamide: Aladdin;

[0043] N-ethyl formamide: Aladdin;

[0044] N-methyl acetamide: Aladdin;

[0045] Carbon disulfide: Aladdin;

[0046] Dimethyl sulfoxide: Aladdin;

[0047] Dibutyl disulfide: Aladdin.

[0048] The main analysis methods used in the embodiments and comparative examples of the present application are as follows:

[0049] Ash content: GB / T 212-2008;

[0050] Carbon interlayer spacing (d002 GB / T 24533-2019;

[0051] Specific surface area: GB / T 19587-2017;

[0052] Reversible specific capacitance, first-cycle coulombic efficiency and second-cycle plateau voltage: GB / T 43114-2023.

[0053] Example 1

[0054] The preparation of coal-based hard carbon anode materials, using bituminous coal as raw material, includes the following steps:

[0055] (1) The lumpy bituminous coal was crushed using a double roller crusher, and the powder was further crushed by an air jet mill to obtain raw coal powder with D50 = 5μm.

[0056] (2) Add 10g of the raw coal powder obtained in step (1) to 4L of N-methylpyrrolidone solution, react at 350℃ and 5MPaG pressure for 4h, cool to room temperature and filter to obtain the reaction solution.

[0057] (3) The reaction solution obtained in step (2) was rotary evaporated at 60°C for 12 hours under a pressure of 3 kPaA to remove the solvent and obtain ultrapure coal powder.

[0058] (4) The ultrapure coal powder obtained in step (3) is placed in a tubular carbonization furnace and heated to 1300°C at a heating rate of 3°C / min under an argon atmosphere. It is then carbonized at this temperature for 4 hours and then cooled naturally to room temperature to obtain the coal-based hard carbon anode material.

[0059] The calculated carbon interlayer spacing is 0.370 nm. The ash content of the coal-based hard carbon material is measured to be 0.01%, and the specific surface area is 4.52 m². 2 / g.

[0060] The coal-based hard carbon material obtained in step (4) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode plates for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the above sodium-ion battery negative electrode plates were assembled into CR2032 coin cells.

[0061] The material was tested under constant current charge and discharge in the Xinwei Battery Testing System. The reversible specific capacity was measured to be 310 mAh / g, the first-cycle coulombic efficiency was 90.2%, and the second-cycle plateau voltage was 62 mV.

[0062] Example 2

[0063] The preparation of coal-based hard carbon anode materials using anthracite as raw material includes the following steps:

[0064] (1) The lumpy anthracite was crushed by a double roller crusher and the powder was further crushed by an air jet mill to obtain raw coal powder with D50 = 10μm.

[0065] (2) Add 10g of the raw coal powder obtained in step (1) to 1L of N-ethylformamide solution, react at 50℃ and 0.1MPaG pressure for 1h, cool to room temperature and filter to obtain the reaction solution.

[0066] (3) The reaction solution obtained in step (2) was rotary evaporated at 90°C for 6 hours under a pressure of 6 kPaA to remove the solvent and obtain ultrapure coal powder.

[0067] (4) The ultrapure coal powder obtained in step (3) is placed in a tubular carbonization furnace and heated to 800°C at a heating rate of 0.5°C / min under an argon atmosphere. It is then carbonized at this temperature for 2 hours and then cooled to room temperature to obtain the coal-based hard carbon anode material.

[0068] The calculated carbon interlayer spacing is 0.381 nm. The ash content of the coal-based hard carbon material is measured to be 0.05%, and the specific surface area is 8.69 m². 2 / g.

[0069] The coal-based hard carbon material obtained in step (4) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode plates for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the above sodium-ion battery negative electrode plates were assembled into CR2032 coin cells.

[0070] The material was tested under constant current charge and discharge in the Xinwei Battery Testing System. The reversible specific capacity was measured to be 279 mA h / g, the first-cycle coulombic efficiency was 90.0%, and the second-cycle plateau voltage was 58.5 mV.

[0071] Example 3

[0072] The preparation of coal-based hard carbon anode materials, using lignite as raw material, includes the following steps:

[0073] (1) The lump lignite was crushed by a double roller crusher, and the powder was crushed again by an air jet mill to obtain raw coal powder with D50 = 300 μm.

[0074] (2) Add 10g of the raw coal powder obtained in step (1) to 10L of dimethyl sulfoxide solution, react at 400℃ and 10MPaG pressure for 6h, cool to room temperature and filter to obtain the reaction solution.

[0075] (3) The reaction solution obtained in step (2) was rotary evaporated at 40°C for 10 hours under a pressure of 9 kPaA to remove the solvent and obtain ultrapure coal powder.

[0076] (4) The ultrapure coal powder obtained in step (3) is placed in a tubular carbonization furnace and heated to 1600°C at a heating rate of 10°C / min under an argon atmosphere. It is then carbonized at this temperature for 4 hours and then cooled naturally to room temperature to obtain the coal-based hard carbon anode material.

[0077] The calculated carbon interlayer spacing is 0.357 nm. The ash content of the coal-based hard carbon material is measured to be 0.04%, and the specific surface area is 1.40 m². 2 / g.

[0078] The coal-based hard carbon material obtained in step (4) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode plates for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the above sodium-ion battery negative electrode plates were assembled into CR2032 coin cells.

[0079] The material was tested under constant current charge and discharge conditions using the Xinwei Battery Testing System. The reversible specific capacity was measured to be 283 mAh / g, the first-cycle coulombic efficiency was 89.8%, and the second-cycle plateau voltage was 56.5 mV.

[0080] Example 4

[0081] The preparation of coal-based hard carbon anode materials, using bituminous coal as raw material, includes the following steps:

[0082] (1) The lumpy bituminous coal was crushed using a double roller crusher, and the powder was further crushed by an air jet mill to obtain raw coal powder with D50 = 15μm.

[0083] (2) Add 10g of the raw coal powder obtained in step (1) to a 5L solution of carbon disulfide, react at 300℃ and 4MPaG pressure for 3h, cool to room temperature and filter to obtain the reaction solution.

[0084] (3) The reaction solution obtained in step (2) was rotary evaporated at 50°C for 8 hours under a pressure of 10 kPaA to remove the solvent and obtain ultrapure coal powder.

[0085] (4) The ultrapure coal powder obtained in step (3) is placed in a tubular carbonization furnace and heated to 1000°C at a heating rate of 6°C / min under an argon atmosphere. It is then carbonized at this temperature for 3 hours and then cooled naturally to room temperature to obtain the coal-based hard carbon anode material.

[0086] The calculated carbon interlayer spacing is 0.376 nm. The ash content of the coal-based hard carbon material is measured to be 0.01%, and the specific surface area is 3.10 m². 2 / g.

[0087] The coal-based hard carbon material obtained in step (4) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode plates for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the above sodium-ion battery negative electrode plates were assembled into CR2032 coin cells.

[0088] Constant current charge-discharge was performed on the Xinwei Battery testing system, and the reversible specific capacity of the material was measured to be 307 mA h / g, the first-cycle coulombic efficiency was 90.7%, and the second-cycle plateau voltage was 60.5 mV.

[0089] Example 5

[0090] The preparation of coal-based hard carbon anode materials, using bituminous coal as raw material, includes the following steps:

[0091] (1) The lumpy bituminous coal was crushed using a double roller crusher, and the powder was further crushed by an air jet mill to obtain raw coal powder with D50 = 50μm.

[0092] (2) Add 10g of the raw coal powder obtained in step (1) to a 3L ethanol solution, react at 100℃ and 2MPaG pressure for 2h, cool to room temperature and filter to obtain the reaction solution.

[0093] (3) The reaction solution obtained in step (2) was rotary evaporated at 30°C for 6 hours under a pressure of 1 kPaA to remove the solvent and obtain ultrapure coal powder.

[0094] (4) The ultrapure coal powder obtained in step (3) is placed in a tubular carbonization furnace and heated to 1200°C at a heating rate of 6°C / min under an argon atmosphere. It is then carbonized at this temperature for 6 hours and then cooled naturally to room temperature to obtain the coal-based hard carbon anode material.

[0095] The calculated interlayer spacing of the carbon layers was 0.373 nm. The ash content of the coal-based hard carbon material was measured to be 0.05%, and the specific surface area was 2.80 m². 2 / g.

[0096] The coal-based hard carbon material obtained in step (4) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode plates for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the above sodium-ion battery negative electrode plates were assembled into CR2032 coin cells.

[0097] Constant current charge-discharge was performed on the Xinwei Battery testing system, and the reversible specific capacity of the material was measured to be 265 mA h / g, the first-cycle coulombic efficiency was 88.2%, and the second-cycle plateau voltage was 53.4 mV.

[0098] Comparative Example 1

[0099] The preparation of coal-based hard carbon anode materials, using bituminous coal as raw material, includes the following steps:

[0100] (1) The lumpy bituminous coal was crushed using a double roller crusher, and the powder was further crushed by an air jet mill to obtain raw coal powder with D50 = 20μm.

[0101] (2) Place the ultrapure coal powder obtained in step (1) into a tubular carbonization furnace, and carbonize it at 8°C for 1 minute under an argon atmosphere. -1 The temperature was increased to 1400℃ at a certain rate and carbonized at this temperature for 1 hour. Then it was naturally cooled to room temperature to obtain the coal-based hard carbon anode material.

[0102] The calculated carbon interlayer spacing is 0.365 nm. The ash content of the coal-based hard carbon material is measured to be 8.4%, and the specific surface area is 12.10 m². 2 / g.

[0103] The coal-based hard carbon material obtained in step (2) was mixed with conductive carbon black and binder (5% LA133 + 1% CMC) in a mass ratio of 8:1:1. The mixture was then loaded onto a copper current collector, dried, and cut into 12mm diameter discs to serve as the negative electrode for sodium-ion batteries. The average loading of active material was 1.5mg. Using the sodium disc as the counter electrode, a glass fiber membrane (Whatman, GF / F) as the separator, and 1M NaPF6 (EC:DMC = 1:1) as the electrolyte, the sodium-ion battery negative electrode was assembled into a CR2032 coin cell.

[0104] The material was tested under constant current charge and discharge in the Xinwei Battery testing system. The reversible specific capacity was measured to be 254 mA h / g, the first-cycle coulombic efficiency was 86.2%, and the second-cycle plateau voltage was 50.1 mV.

[0105] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be covered by the protection of the invention.

Claims

1. A method for producing a coal-based hard carbon material, characterized by, The method comprises the following steps: (1) crushing and screening raw coal to obtain raw coal powder; (2) mixing the raw coal powder with an organic solvent and reacting at high temperature and high pressure to obtain a reaction liquid after filtration; (3) removing the organic solvent from the reaction liquid to obtain ultra-pure coal powder; (4) carbonizing the ultra-pure coal powder at high temperature in an inert atmosphere to obtain the coal-based hard carbon material.

2. The production method according to claim 1, characterized by, The raw coal in step (1) is one or more of lignite, bituminous coal, and anthracite; preferably, it is bituminous coal; and / or, The particle size (D50) of the raw coal powder in step (1) is 5-300 μm, preferably 10-75 μm.

3. The production method according to claim 1 or 2, characterized by, The organic solvent in step (2) is one or more of organic solvents containing nitrogen and / or sulfur elements; Optionally, the organic solvent containing nitrogen elements is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N-ethylformamide, and N-methylacetamide, preferably N-methylpyrrolidone; Optionally, the organic solvent containing sulfur elements is selected from one or more of carbon disulfide, dimethyl sulfoxide, and dibutyl disulfide, preferably carbon disulfide.

4. The production method according to any one of claims 1 to 3, characterized by, The amount of the organic solvent in step (2) is 100-1000 mL / g of raw coal powder, preferably 100-500 mL / g of raw coal powder.

5. The method of any one of claims 1-4, wherein, The reaction in step (2) is carried out at a temperature of 50-400 ℃, a pressure of 0.1-10 MPaG, and a reaction time of 1-6 hours; Preferably, the reaction is carried out at a temperature of 150-350 ℃, a pressure of 1-5 MPaG, and a reaction time of 2-4 hours.

6. The method of any one of claims 1-5, wherein, The method for removing the organic solvent from the reaction liquid in step (3) is rotary evaporation, vacuum distillation, or back extraction.

7. The method of any one of claims 1-6, wherein, The inert atmosphere in step (4) is one or more of argon and nitrogen; preferably, it is argon.

8. The method of any one of claims 1-7, wherein, The carbonization in step (4) is carried out at a temperature of 800-1800 ℃ and a heating rate of 0.5-10 ℃ / min; Preferably, the carbonization is carried out at a temperature of 1000-1600 ℃ and a heating rate of 1-3 ℃ / min; and / or, The carbonization in step (4) is carried out for 1-6 hours.

9. A coal-based hard carbon material prepared by the method of any one of claims 1-8. Optionally, the ash content is 0.01-0.05wt%, the carbon interlayer spacing is 0.35-0.39nm, and the specific surface area is 1-10m 2 / g.

10. Use of the coal-based hard carbon material prepared by the method of any one of claims 1-8 in a sodium ion battery. Optionally, the coal-based hard carbon material is used as a negative electrode of a sodium ion battery.