Preparation method and application of coal-based hard carbon negative electrode material of sodium ion battery

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, and particularly discloses a sodium ion battery coal-based hard carbon negative electrode material preparation method, which comprises: S1, sequentially placing coal powder in an acid solution to carry out two-step impurity removal treatment, and carrying out water washing and drying; s2, dissolving the pretreated raw materials and an organic carbon source in deionized water according to a certain mass ratio, and uniformly stirring until a turbid liquid is formed; s3, dissolving a certain proportion of metal salt into the solution obtained in the step S2, uniformly stirring, washing with water, and drying; and S4, performing two-step carbonization treatment on the precursor powder in an inert atmosphere to obtain the coal-based hard carbon negative electrode material of the sodium-ion battery. According to the preparation method disclosed by the invention, the specific capacity of the coal-based hard carbon negative electrode material of the sodium-ion battery in a full-voltage region is synergistically improved through regulation and combination of a surface functional group and a microcrystalline structure, and excellent rate capability is obtained. The negative electrode material is wide in source and low in price, and has a relatively good industrial production prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery negative electrode materials, and specifically relates to a preparation method and application of a coal-based hard carbon negative electrode material for sodium ion batteries. Background Art

[0002] Sodium-ion batteries have shown great application potential in large-scale energy storage and low-speed electric vehicles due to their advantages such as abundant sodium resources, low cost and environmental friendliness. Hard carbon materials are considered to be ideal candidates for sodium-ion battery anodes due to their unique disordered carbon structure, high sodium storage capacity and good cycling stability. However, the practical application of hard carbon anodes still faces core problems such as multi-region capacity imbalance, sluggish kinetics and insufficient structural stability. The slope capacity of traditional hard carbon materials in the high voltage region mainly depends on surface redox reactions, but the number of active sites is limited and the reaction kinetics are slow; while the platform capacity in the low voltage region is limited by the diffusion rate of sodium ions embedded in the interlayer and the irreversible sodium retention of the closed-pore structure. Existing modification strategies such as heteroatom doping or metal composites can partially improve the performance of a certain region, but it is difficult to achieve coordinated optimization of the entire voltage range, and are often accompanied by problems such as complex processes, high costs or increased side reactions.

[0003] In recent years, researchers have tried to break through the above bottlenecks by combining surface chemical modification with bulk structure regulation, but most methods still have significant defects. For example, although surface functionalization treatment (such as oxygen doping) can improve the slope capacity, it can easily lead to electrolyte decomposition and decreased cycle stability; although the expansion of the bulk interlayer spacing is conducive to the embedding of sodium ions, it may destroy the closed-pore structure or reduce conductivity. In addition, existing processes often require multi-step complex processing or rely on expensive precursors, which is difficult to meet the needs of large-scale production. Therefore, the development of a low-cost, scalable and synergistically optimized surface and bulk structure hard carbon negative electrode preparation method has become the key to promoting the commercial application of sodium ion batteries. This invention is funded by the Energy Shaanxi Laboratory Science and Technology Project, and the project number is "The S&T Program of Energy Shaanxi Laboratory, Grant No. ESLB202402". Summary of the Invention

[0004] Purpose of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a coal-based hard carbon negative electrode material for a sodium ion battery, and to provide a hard carbon negative electrode material for a sodium ion battery with high specific capacity and high rate performance, and with low cost and high carbon yield.

[0006] Solution

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, characterized by comprising the following steps:

[0009] S1. Coal powder with a particle size of 50-200 μm is placed in an acid solution in sequence for two-step impurity removal treatment, followed by water washing and drying;

[0010] S2. Dissolve the pretreated pulverized coal and the organic carbon source in deionized water and stir evenly to form a suspension;

[0011] S3, dissolving the metal salt into the suspension obtained in step S2, stirring evenly, and then washing with water and drying to obtain a precursor powder;

[0012] S4. The precursor powder is subjected to a two-step carbonization treatment under an inert atmosphere to obtain a coal-based hard carbon negative electrode material for a sodium ion battery.

[0013] In the above S1, the acid selected in the pickling process includes one or more of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid. The pickling temperature is 40-80° C., and the pickling time is 2-8 hours.

[0014] The organic carbon source in S2 includes one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, polyvinylpyrrolidone, glucose, sucrose, citric acid, and hexadecyltrimethylammonium bromide. The mass ratio of coal powder to organic carbon source is 1.5 to 10:1, and the stirring temperature is 30 to 60°C.

[0015] In S3, the metal salt includes one or more of anhydrous ferric chloride, nickel chloride hexahydrate, cobalt chloride hexahydrate, anhydrous manganese chloride, zinc chloride, nickel acetate, anhydrous zinc acetate, manganese acetate tetrahydrate, and ferrocene, the molar ratio of the metal salt to the organic carbon source is 1 to 5:10, and the stirring time is 3 to 8 hours.

[0016] In the step S4, the inert atmosphere is one or more of nitrogen and argon.

[0017] In S4, the temperature of the low-temperature pre-carbonization treatment is 400-700°C, the carbonization time is 1-3h, and the heating rate is 1-5°C / min; the temperature of the high-temperature carbonization treatment is 800-1400°C, the carbonization time is 2-4h, the heating rate is 1-5°C / min, and the cooling rate is 1-5°C / min.

[0018] The present invention provides a coal-based hard carbon negative electrode material for a sodium ion battery, which is prepared by the preparation method of the coal-based hard carbon negative electrode material for a sodium ion battery.

[0019] The present invention provides an application of a coal-based hard carbon negative electrode material for a sodium ion battery in preparing a negative electrode sheet of the sodium ion battery.

[0020] The present invention provides a sodium ion battery negative electrode plate, comprising the coal-based hard carbon negative electrode material for sodium ion batteries.

[0021] The present invention also provides a sodium ion battery negative electrode plate, characterized in that it is made of electrode negative electrode slurry and metal foil;

[0022] The electrode negative electrode slurry comprises the following components in parts by mass: 80-95 parts of the coal-based hard carbon negative electrode material for sodium ion batteries according to claim 7, 2-10 parts of a conductive agent, and 3-10 parts of a binder;

[0023] The conductive agent is Super P and the binder is PVDF;

[0024] The metal foil is copper foil;

[0025] The loading amount of the coal-based hard carbon negative electrode slurry on the metal foil is 0.7-1.2 mg / cm 2 ;

[0026] The sodium ion battery negative electrode plate is prepared by the following steps:

[0027] The aforementioned coal-based hard carbon negative electrode material for sodium ion batteries, a conductive agent, and a binder are uniformly dissolved in N-methylpyrrolidone to prepare the electrode negative electrode slurry;

[0028] The negative electrode slurry is coated on the surface of the metal foil and vacuum dried to obtain the negative electrode sheet of the sodium ion battery.

[0029] The present invention provides a sodium ion battery, which includes the above-mentioned sodium ion battery coal-based hard carbon negative electrode material or the above-mentioned sodium ion battery negative electrode plate.

[0030] Preferably, the counter electrode of the sodium ion battery is metallic sodium, and the separator is glass fiber.

[0031] Preferably, the sodium salt of the electrolyte includes sodium hexafluorophosphate (1.0 mol / L NaPF6), and the solvent is ethylene glycol dimethyl ether (DME).

[0032] Beneficial effects

[0033] The coal-based hard carbon negative electrode material for sodium ion batteries of the present invention has the following beneficial technical effects:

[0034] The present invention significantly enhances the slope capacity in the high-voltage region through the synergistic effect of the surface C=O functional group and the Fe3C phase. At the same time, the expanded interlayer spacing and the optimized closed-pore structure synergistically improve the platform capacity in the low-voltage region, thereby achieving balanced optimization of the sodium storage capacity in the entire voltage range. Secondly, the nitrogen-doped carbon coating layer can effectively inhibit the side reactions between the electrolyte and the active material, improve the first-cycle coulombic efficiency of the material, and the closed pores and interlayer spacing synergistically optimize the sodium ion embedding / filling kinetics, which solves the contradiction between surface and bulk performance in traditional modifications. In addition, the present invention provides a way to obtain a hard carbon negative electrode for sodium ion batteries with high specific capacity and high rate performance, and the precursor cost is low and the carbon yield is high, which is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a scanning electron microscope image of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Comparative Example 1 of the present invention;

[0036] Figure 2 This is a scanning electron microscope image of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention;

[0037] Figure 3 This is the X-ray diffraction pattern of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Comparative Example 1 of the present invention;

[0038] Figure 4 This is the X-ray diffraction pattern of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention;

[0039] Figure 5 Graph showing the cycle performance of coal-based hard carbon anode materials for sodium ion batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2 of the present invention;

[0040] Figure 6 This is a rate performance diagram of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2 of the present invention;

[0041] Figure 7 This is a long cycle performance diagram of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without inventive effort are all within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0045] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 60℃ for 5h, then wash with water and dry;

[0046] S2. Dissolve 250 mg of pretreated coal powder and 100 mg of ethylenediaminetetraacetic acid in 60 ml of deionized water and stir thoroughly at 50°C until a suspension is formed;

[0047] S3. Dissolve 13 mg of anhydrous ferric chloride in the suspension obtained in step S2, stir for 7 h until completely dissolved, then wash with water and dry;

[0048] S4. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0049] Example 2

[0050] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0051] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 60℃ for 5h, then wash with water and dry;

[0052] S2. Dissolve 250 mg of pretreated coal powder and 50 mg of ethylenediaminetetraacetic acid in 60 ml of deionized water and stir thoroughly at 50°C until a suspension is formed;

[0053] S3. Dissolve 8 mg of anhydrous ferric chloride in the suspension obtained in step S2, stir for 5 h until completely dissolved, then wash with water and dry;

[0054] S4. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0055] Example 3

[0056] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0057] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 60℃ for 5h, then wash with water and dry;

[0058] S2. Dissolve 250 mg of pretreated coal powder and 50 mg of ethylenediaminetetraacetic acid in 60 ml of deionized water and stir thoroughly at 50°C until a suspension is formed;

[0059] S3. Dissolve 13 mg of anhydrous ferric chloride in the suspension obtained in step S2, stir for 7 h until completely dissolved, then wash with water and dry;

[0060] S4. The precursor powder is heated to 500°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1000°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0061] Example 4

[0062] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0063] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 60℃ for 5h, then wash with water and dry;

[0064] S2. Dissolve 250 mg of pretreated coal powder and 50 mg of polyvinyl pyrrolidone in 60 ml of deionized water and stir thoroughly at 55°C until a suspension is formed;

[0065] S3. Dissolve 10 mg of anhydrous manganese chloride in the suspension obtained in step S2, stir for 8 h until completely dissolved, then wash with water and dry;

[0066] S4. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0067] Example 5

[0068] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0069] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 60℃ for 5h, then wash with water and dry;

[0070] S2. Dissolve 250 mg of pretreated coal powder and 150 mg of glucose in 60 ml of deionized water and stir thoroughly at 30°C until a suspension is formed;

[0071] S3. Dissolve 12 mg of zinc chloride in the suspension obtained in step S2, stir for 4 h until completely dissolved, then wash with water and dry;

[0072] S4. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1400°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 4 hours, and then the temperature is cooled at a rate of 5°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0073] Example 6

[0074] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0075] S1. Take 150μm pulverized coal and place it in hydrochloric acid and hydrofluoric acid to remove impurities, pickle and stir at a constant temperature of 70℃ for 8h, then wash with water and dry;

[0076] S2. Dissolve 250 mg of pretreated coal powder and 100 mg of disodium ethylenediaminetetraacetate in 60 ml of deionized water and stir thoroughly at 60°C until a suspension is formed;

[0077] S3, dissolving 13 mg of ferrocene into the suspension obtained in step S2, stirring for 5 h until completely dissolved, then washing with water and drying;

[0078] S4. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1000°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0079] Example 7

[0080] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery. The only difference from Example 2 is that the 50°C in the second step is replaced by 65°C, and the other steps are exactly the same as Example 2.

[0081] Example 8

[0082] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery. The only difference from Example 2 is that 8 mg in the third step is replaced by 13 mg, and the other steps are exactly the same as Example 2.

[0083] Example 9

[0084] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery. The only difference from Example 2 is that the high-temperature carbonization temperature of 1200°C in the fourth step is replaced with 1400°C, and the other steps are exactly the same as Example 2.

[0085] Comparative Example 1

[0086] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0087] S1. Take the coal powder and place it in hydrochloric acid and hydrofluoric acid in turn to remove impurities, pickle and stir at a constant temperature of 60℃ for 5 hours, then wash with water and dry;

[0088] S2. The pretreated precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0089] Comparative Example 2

[0090] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0091] S1. Take the coal powder and place it in hydrochloric acid and hydrofluoric acid in turn to remove impurities, pickle and stir at a constant temperature of 60℃ for 5 hours, then wash with water and dry;

[0092] S2. Dissolve 250 mg of the pretreated raw material and 50 mg of ethylenediaminetetraacetic acid in 60 ml of deionized water, stir thoroughly at 50°C until a suspension is formed, then wash with water and dry;

[0093] S3. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0094] Comparative Example 3

[0095] This embodiment provides a method for preparing a coal-based hard carbon negative electrode material for a sodium ion battery, the preparation method specifically comprising the following steps:

[0096] S1. Take the coal powder and place it in hydrochloric acid and hydrofluoric acid in turn to remove impurities, pickle and stir at a constant temperature of 60℃ for 5 hours, then wash with water and dry;

[0097] S2. Dissolve 250 mg of the pretreated raw material and 8 mg of anhydrous ferric chloride in 60 ml of deionized water, stir thoroughly at 50°C until completely dissolved, then wash with water and dry;

[0098] S3. The precursor powder is heated to 600°C at a rate of 2°C / min under an argon atmosphere for low-temperature pre-carbonization treatment. After keeping the temperature for 2 hours, the temperature is further raised to 1200°C at a rate of 2°C / min for high-temperature carbonization. The holding time is 3 hours, and then the temperature is cooled at a rate of 2°C / min to obtain a coal-based hard carbon negative electrode material for sodium ion batteries.

[0099] Performance Testing

[0100] Electrochemical performance test:

[0101] Test samples: coal-based hard carbon negative electrode materials for sodium ion batteries provided in Examples 1-9 and Comparative Examples 1-3;

[0102] Test method:

[0103] (1) Preparation of sodium ion battery negative electrode sheet: 80 parts by mass of coal-based hard carbon negative electrode material, 10 parts of Super P, and 10 parts of PVDF were weighed and dissolved in N-methylpyrrolidone to obtain battery negative electrode slurry; the battery negative electrode slurry was coated on the surface of copper foil, and its loading was controlled to be 1.0 mg / cm 2 , and dried in a vacuum drying oven at 70° C. for 12 h to obtain the sodium ion battery negative electrode sheet.

[0104] (2) Assembly of sodium ion battery: Sodium foil was used as the counter electrode, the electrolyte was 1 mol / L NaPF6 and 100 wt.% DME solvent, and the separator was glass fiber. CR2032 button cells were assembled in an argon-filled glove box.

[0105] (3) Battery electrochemical performance test: The battery testing system of Shenzhen Xinweier Electronics Co., Ltd. was selected for testing.

[0106] like Figure 1As shown in the figure, it is a scanning electron microscope image of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Comparative Example 1 of the present invention. It can be seen that the hard carbon material synthesized from coal powder has a larger size, a rich pore structure on the surface, and a higher specific surface area. The specific surface area is calculated to be 288.6 m 2 / g, which provides more adsorption sites for sodium ions on the carbon surface.

[0107] like Figure 2 As shown, this is a scanning electron microscope image of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention. It can be seen that the pores on the surface of the prepared coal-based hard carbon material are reduced, which is mainly due to the transformation of open pores to closed pores, which helps to improve the capacity in the low-voltage platform area.

[0108] like Figure 3 , which is the X-ray diffraction pattern of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Comparative Example 1 of the present invention, it can be seen that the negative electrode material exhibits characteristic peaks of carbon.

[0109] like Figure 4 As shown, this is the X-ray diffraction pattern of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention. It can be seen that the prepared hard carbon negative electrode material has a weak diffraction peak at around 45°, which is attributed to the Fe3C phase.

[0110] like Figure 5 As shown, this is a cycle performance diagram of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2, Comparative Example 1 and Comparative Example 2 of the present invention. At a current density of 0.1 A / g, the capacity of the hard carbon negative electrode material prepared in Example 2 still maintains 173.77 mAh / g after 200 cycles, showing higher specific capacity and cycle performance.

[0111] like Figure 6 As shown in the figure, it is a rate performance graph of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2, Comparative Example 1 and Comparative Example 2 of the present invention. It can be seen that at current densities of 0.03, 0.05, 0.1, 0.3, 0.5, 1.0 and 2.0 A / g, the capacity of the hard carbon negative electrode material prepared in Example 2 is 192.5, 178.88, 170.81, 159.6, 151.27, 138.43 and 120.04 mAh / g, respectively, which is much higher than the performance of Comparative Example 1 and Comparative Example 2, showing outstanding rate performance.

[0112] like Figure 7As shown in FIG, this is a long cycle performance diagram of the coal-based hard carbon negative electrode material for sodium ion batteries prepared in Example 2 of the present invention. It can be seen that at a high current density of 1.0 A / g, the hard carbon negative electrode material prepared in Example 2 still has a specific capacity of 135.86 mAh / g after 1000 cycles, proving its good cycle stability.

[0113] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries, characterized in that: The following steps are involved: S1. Coal powder with a particle size of 50-200 μm is placed in an acid solution in sequence for two-step impurity removal treatment, followed by water washing and drying; S2. Dissolve the pretreated pulverized coal and the organic carbon source in deionized water and stir evenly to form a suspension; S3, dissolving the metal salt into the suspension obtained in step S2, stirring evenly, and then washing with water and drying to obtain a precursor powder; S4. The precursor powder is subjected to a two-step carbonization treatment under an inert atmosphere to obtain a coal-based hard carbon negative electrode material for a sodium ion battery.

2. The method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries according to claim 1, characterized in that: In the above S1, the acid selected in the pickling process includes one or more of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid. The pickling temperature is 40-80° C., and the pickling time is 2-8 hours.

3. The method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries according to claim 2, characterized in that: The organic carbon source in S2 includes one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, polyvinylpyrrolidone, glucose, sucrose, citric acid, and hexadecyltrimethylammonium bromide. The mass ratio of coal powder to organic carbon source is 1.5 to 10:1, and the stirring temperature is 30 to 60°C.

4. The method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries according to claim 3, characterized in that: In S3, the metal salt includes one or more of anhydrous ferric chloride, nickel chloride hexahydrate, cobalt chloride hexahydrate, anhydrous manganese chloride, zinc chloride, nickel acetate, anhydrous zinc acetate, manganese acetate tetrahydrate, and ferrocene, the molar ratio of the metal salt to the organic carbon source is 1 to 5:10, and the stirring time is 3 to 8 hours.

5. The method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries according to claim 4, characterized in that: In the step S4, the inert atmosphere is one or more of nitrogen and argon.

6. The method for preparing a coal-based hard carbon negative electrode material for sodium ion batteries according to claim 5, characterized in that: In S4, the two-step carbonization treatment includes a low-temperature pre-carbonization treatment and a high-temperature carbonization treatment. The temperature of the low-temperature pre-carbonization treatment is 400-700°C, the carbonization time is 1-3h, and the heating rate is 1-5°C / min; the temperature of the high-temperature carbonization treatment is 800-1400°C, the carbonization time is 2-4h, the heating rate is 1-5°C / min, and the cooling rate is 1-5°C / min.

7. A coal-based hard carbon negative electrode material for sodium ion batteries, characterized in that: The coal-based hard carbon negative electrode material for sodium ion batteries is prepared by the preparation method of the coal-based hard carbon negative electrode material for sodium ion batteries according to any one of claims 1 to 6.

8. Use of the coal-based hard carbon negative electrode material for sodium ion batteries according to claim 7 in preparing negative electrode sheets for sodium ion batteries.

9. A negative electrode plate for a sodium ion battery, characterized in that: Made of electrode negative electrode slurry and metal foil; The electrode negative electrode slurry includes the following components in parts by mass: 80-95 parts of the coal-based hard carbon negative electrode material for sodium ion batteries according to claim 7, 2-10 parts of a conductive agent, and 3-10 parts of a binder; The conductive agent is Super P and the binder is PVDF; The metal foil is copper foil; The loading amount of the coal-based hard carbon negative electrode slurry on the metal foil is 0.7-1.2 mg / cm 2 ; The sodium ion battery negative electrode plate is prepared by the following steps: The coal-based hard carbon negative electrode material for sodium ion batteries according to claim 7, a conductive agent and a binder are uniformly dissolved in N-methylpyrrolidone to prepare the electrode negative electrode slurry; The negative electrode slurry is coated on the surface of the metal foil and vacuum dried to obtain the negative electrode sheet of the sodium ion battery.

10. A sodium ion battery, characterized in that: It includes the coal-based hard carbon negative electrode material for sodium ion batteries as claimed in claim 7 or the sodium ion battery negative electrode sheet as claimed in claim 9.

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