Coal-based hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention provides a coal-based hard carbon negative electrode material as well as a preparation method and application thereof, and belongs to the related technical field of sodium ion batteries. According to the invention, pulverized coal is used as a raw material to prepare the negative electrode material by a self-template method, pores are formed by using functional groups contained in the pulverized coal and embedded metal ions, and a large number of closed pores are introduced into the negative electrode material through a self-sacrifice strategy, so that the carbonized negative electrode material has a micro-closed pore structure; the micro closed pore structure overcomes pi-pi interaction and graphitization trend among aromatic molecules, is beneficial to storage of sodium ions, can effectively transmit the sodium ions, and improves platform capacity; oxygen sites are introduced into the pulverized coal through hydrothermal treatment, regulation and control of a hard carbon microstructure in the carbonization process can be achieved, introduction of C = O can effectively limit movement of carbon atoms in the high-temperature carbonization process, then graphitization of a carbon layer is prevented, active hydrogen on carboxyl and hydroxyl can provide more active sites for metal cations, and the carbon layer is further prevented from being graphitized. And formation of closed pores is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field related to sodium ion batteries, and in particular to a coal-based hard carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] With the development of modern society, the irreversible consumption of traditional fossil energy and the environmental problems it causes have become increasingly prominent, and the development of a "low-carbon economy" has become a consensus among countries around the world. Lithium-ion batteries have been widely used in portable electronic products, electric vehicles, and energy storage due to their advantages such as high energy density and long cycle life. However, the rising prices and uneven distribution of lithium resources have severely restricted the development of lithium-ion batteries. Sodium-ion batteries have gradually become a potential substitute for lithium-ion batteries due to their advantages such as abundant resources and low cost. The working principles of sodium-ion batteries are similar to those of lithium-ion batteries, and the abundant sodium resources and low prices have made the research on sodium-ion batteries a focus of attention.

[0003] The negative electrode material is an important component of sodium-ion batteries, and its performance has an important impact on the overall energy density, power density and cycle life of the battery. In the past few years, some developed materials have been explored as Na + Anode materials for storage, such as oxides, alloys, phosphides, and organic materials. However, these anode materials usually have problems such as large irreversible capacity, high redox potential, and poor cycle performance. In contrast, carbonaceous materials, especially hard carbon, can ensure more Na+ due to their short-range carbon crystallites and increased interlayer spacing. + inserted into the carbon lattice and is considered a promising Na + Storage anode selection. Therefore, the development of high-capacity anode materials with high cycle performance and good rate performance will be the focus of sodium-ion battery research.

[0004] As the natural coal with the lowest cost and the highest carbon content in nature, it is not only abundant in reserves and diverse in types, but also has the characteristics of moderate molecular weight and easy-to-control molecular structure, making it a potential high-quality precursor for negative electrode materials of sodium ion batteries. However, sodium ion batteries require carbon materials to have characteristics such as low graphitization degree (large interlayer spacing) and loose structure (pore structure <0.5nm), while the π-π interaction and graphitization trend between planar aromatic molecules in coal limit the sodium ion storage capacity of coal. During the high-temperature carbonization process, the carbon structure will be highly ordered and the interlayer spacing will be narrow, resulting in the fact that sodium ion batteries prepared with coal as negative electrode materials are not satisfactory in practical applications. Therefore, conventional coal cannot be directly used as the negative electrode material of sodium ion batteries.

[0005] Therefore, how to broaden the microcrystalline interlayer spacing of coal-based carbon negative electrode materials and improve their sodium storage performance has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a coal-based hard carbon negative electrode material and a preparation method and application thereof. The coal-based hard carbon negative electrode material prepared by the present invention has a wider microcrystalline layer spacing, a larger number of micro-closed pores and a larger sodium ion storage capacity, and its reversible specific capacity reaches 350 mAh g -1 , showing excellent sodium storage performance, and at the same time has the advantages of high specific capacity, good rate performance and good cycle stability in sodium ion batteries.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a coal-based hard carbon negative electrode material, comprising the following steps:

[0009] (1) demineralizing the coal powder using an acid demineralization method to obtain deashed coal powder;

[0010] (2) mixing the deashed coal powder obtained in step (1) with water and performing a hydrothermal reaction to obtain hydrothermal coal powder;

[0011] (3) mixing the hydrothermal coal powder obtained in step (2) with a sodium hydroxide solution and performing an activation treatment to obtain a coal-based porous carbon material precursor;

[0012] (4) Carbonizing the coal-based porous carbon material precursor obtained in step (3) to obtain a coal-based hard carbon negative electrode material.

[0013] Preferably, the particle size of the coal powder in step (1) is ≤75 μm.

[0014] Preferably, the acid demineralization method in step (1) is an HCl-HF acid demineralization method.

[0015] Preferably, in step (2), the ratio of the mass of the deashed coal powder to the volume of water is (5-20) g:100 mL.

[0016] Preferably, the holding temperature of the hydrothermal reaction in step (2) is 180-250° C., and the holding time of the hydrothermal reaction is 0.5-3 h.

[0017] Preferably, the concentration of the sodium hydroxide solution in step (3) is 0.5-2 mol / L, and the ratio of the mass of the hydrothermal coal powder to the volume of the sodium hydroxide solution is 10 g: (30-60) mL.

[0018] Preferably, the temperature of the activation treatment in step (3) is 50 to 80° C., and the time of the activation treatment is 1 to 5 hours.

[0019] Preferably, the temperature of the carbonization treatment in step (4) is 1100-1400° C., the time of the carbonization treatment is 1-5 h, the heating rate to the carbonization treatment temperature is 3-8° C. / min, and the atmosphere of the carbonization treatment is an inert atmosphere.

[0020] The present invention provides a coal-based hard carbon negative electrode material prepared by the preparation method described in the above technical solution.

[0021] The present invention provides the application of the coal-based hard carbon negative electrode material described in the above technical solution in a sodium ion battery.

[0022] The present invention provides a method for preparing a coal-based hard carbon negative electrode material, comprising the following steps: (1) demineralizing coal powder using an acid demineralization method to obtain deashed coal powder; (2) mixing the deashed coal powder obtained in step (1) with water and then performing a hydrothermal reaction to obtain hydrothermal coal powder; (3) mixing the hydrothermal coal powder obtained in step (2) with a sodium hydroxide solution and then performing an activation treatment to obtain a coal-based porous carbon material precursor; (4) carbonizing the coal-based porous carbon material precursor obtained in step (3) to obtain a coal-based hard carbon negative electrode material. The present invention uses coal powder as a raw material to prepare a negative electrode material by a self-template method, utilizes the functional groups and embedded metal ions contained in the coal powder itself to form pores, introduces a large number of closed pores into the negative electrode material by a self-sacrificing strategy, and makes the carbonized negative electrode material have a micro-closed pore structure, which overcomes the π-π interaction and graphitization tendency between aromatic molecules, is conducive to the storage of sodium ions, can effectively transmit sodium ions, and improves the platform capacity. The oxygen sites introduced into the coal powder by hydrothermal treatment in the present invention can realize the regulation of the hard carbon microstructure during the carbonization process, wherein the introduction of C=O can effectively limit the movement of carbon atoms during the high-temperature carbonization process, thereby preventing the graphitization of the carbon layer, and the active hydrogen on the carboxyl and hydroxyl groups can provide more active sites for metal cations, promoting the formation of closed pores, and by regulating the microstructure of the hard carbon material, the synthesis of high-performance hard carbon negative electrode materials is achieved.

[0023] The raw materials used in the present invention are low-priced, the preparation process is simple, and large-scale production is possible. By using lignite powder as a raw material, high-value utilization of lignite is achieved, and the production cost of negative electrode materials is greatly reduced, which provides convenience for the manufacture of sodium ion batteries of different models, improves market competitiveness, and is suitable for large-scale industrial promotion. The preparation method provided by the present invention can also reduce the use of chemical reagents, thereby reducing the discharge of polluted wastewater, and further reducing the production cost of closed-cell carbon materials.

[0024] The experimental results show that the coal-based hard carbon anode material provided by the present invention has a wider microcrystalline layer spacing, a larger number of micro-closed pores and a larger sodium ion storage capacity, and its reversible specific capacity reaches 350 mAh g -1, showing excellent sodium storage performance at 30mAg -1 The capacity retention rate after 400 cycles is 95%, 1000mA g -1 The capacity is 220mAh g -1 , which has the advantages of high specific capacity, good rate performance and good cycle stability in sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FTIR spectra of deashed coal powder and hydrothermal coal powder in Example 1;

[0026] Figure 2 XRD patterns of the coal-based hard carbon negative electrode material prepared in Example 1 and the hard carbon materials prepared in Comparative Examples 1 to 2;

[0027] Figure 3 The interlayer spacing distribution of the coal-based hard carbon negative electrode material prepared in Example 1 and the hard carbon materials prepared in Comparative Examples 1 to 2;

[0028] Figure 4 The charge and discharge curve diagram of the half-cell prepared in Application Example 1;

[0029] Figure 5 The charge and discharge curve diagram of the half-cell prepared in comparative application example 1;

[0030] Figure 6 The charge and discharge curve diagram of the half-cell prepared in comparative application example 2;

[0031] Figure 7 The cycle performance of the coal-based hard carbon negative electrode material prepared in Example 1;

[0032] Figure 8 This is the rate performance of the coal-based hard carbon negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a coal-based hard carbon negative electrode material, comprising the following steps:

[0034] (1) demineralizing the coal powder using an acid demineralization method to obtain deashed coal powder;

[0035] (2) mixing the deashed coal powder obtained in step (1) with water and performing a hydrothermal reaction to obtain hydrothermal coal powder;

[0036] (3) mixing the hydrothermal coal powder obtained in step (2) with a sodium hydroxide solution and performing an activation treatment to obtain a coal-based porous carbon material precursor;

[0037] (4) Carbonizing the coal-based porous carbon material precursor obtained in step (3) to obtain a coal-based hard carbon negative electrode material.

[0038] The present invention uses an acid demineralization method to extract coal powder to obtain deashed coal powder.

[0039] The present invention has no particular limitation on the specific type of the coal powder, and the coal powder can be prepared by using commercially available coal powder known to those skilled in the art or existing coal. In an embodiment of the present invention, the coal powder can be lignite powder. The present invention uses lignite powder as a raw material, which not only reduces the cost of the raw material, but also realizes the high-value utilization of lignite.

[0040] In the present invention, the particle size of the coal powder is preferably ≤75 μm. In the present invention, when the particle size of the coal powder does not meet the above conditions, the coal powder is preferably crushed and ground in sequence. The present invention has no special restrictions on the specific operations of the crushing and grinding, and the operations well known to those skilled in the art can be used to make the particle size of the coal powder meet the requirements. The present invention controls the particle size of the coal powder, which is conducive to demineralization by an acid demineralization method.

[0041] In the present invention, the acid demineralization method is preferably an HCl-HF acid demineralization method. The present invention has no special restrictions on the specific operation of the HCl-HF acid demineralization method and the specific concentration and dosage of the hydrochloric acid and hydrofluoric acid solutions used, and the operation of the HCl-HF acid demineralization method well known to those skilled in the art can be adopted. In the present invention, there are a large number of highly complex inorganic mineral components in coal, which will have an adverse effect on the performance of coal-based porous carbon materials, and impurities and minerals in coal can be removed by the acid demineralization method.

[0042] As an embodiment of the present invention, the HCl-HF acid demineralization method can be: coal powder and ultrapure water are mixed, and then hydrochloric acid and hydrofluoric acid solutions are added in sequence, and finally heated and stirred at 60°C for 8 hours to obtain deashed coal powder; the ratio of the mass of the coal powder, the volume of ultrapure water, the volume of hydrochloric acid and the volume of the hydrofluoric acid solution can be 10g:200mL:50mL:40mL; the hydrochloric acid can be concentrated hydrochloric acid; the concentration of the hydrochloric acid can be 12mol / L; the concentration of the hydrofluoric acid solution can be 22-29mol / L.

[0043] After obtaining the deashed coal powder, the present invention mixes the deashed coal powder with water and then performs a hydrothermal reaction to obtain hydrothermal coal powder.

[0044] In the present invention, the water is preferably distilled water; the ratio of the mass of the deashed coal powder to the volume of water is preferably (5-20) g: 100 mL. By controlling the amount of deashed coal powder and water, the deashed coal powder can be fully dispersed in water, thereby improving the introduction efficiency of C=O in the coal powder.

[0045] As an embodiment of the present invention, the ratio of the mass of the deashed coal powder to the volume of water can be 5g:100mL, 6g:100mL, 8g:100mL, 10g:100mL, 12g:100mL, 15g:100mL, 18g:100mL or 20g:100mL.

[0046] In the present invention, the hydrothermal reaction is preferably carried out in a high-pressure reactor; the high-pressure reactor is preferably sealed during the hydrothermal reaction. The present invention has no special restrictions on the specific model and source of the high-pressure reactor, and a commercially available high-pressure reactor well known to those skilled in the art can be used. The present invention can make the reaction temperature reach the required hydrothermal reaction temperature under high pressure by carrying out the hydrothermal reaction in the high-pressure reactor.

[0047] In the present invention, the insulation temperature of the hydrothermal reaction is preferably 180-250°C; the insulation time of the hydrothermal reaction is preferably 0.5-3h. The present invention has no special restrictions on the heating rate and heating time to the hydrothermal reaction temperature, and can be set according to common sense. The hydrothermal reaction of the present invention can introduce oxygen sites into the deashed coal powder, and the introduced oxygen sites are crucial for the regulation of the hard carbon microstructure during the carbonization process; among them, the introduction of C=O can effectively limit the movement of carbon atoms during high-temperature carbonization, thereby preventing the graphitization of the carbon layer, and the active hydrogen on the carboxyl and hydroxyl groups can provide more active sites for metal cations, promoting the formation of closed pores; the introduction efficiency of oxygen sites can be further improved by controlling the temperature and time of the hydrothermal reaction.

[0048] As an embodiment of the present invention, the insulation temperature of the hydrothermal reaction may be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C; the insulation time of the hydrothermal reaction may be 0.5h, 1h, 1.5h, 2h, 2.5h or 3h.

[0049] The present invention preferably filters and dries the product of the hydrothermal reaction in sequence to obtain hydrothermal coal powder. The present invention has no special limitation on the specific operation of the filtration, and the filtration operation well known to those skilled in the art can be used to separate the solid and the liquid. The present invention has no special limitation on the specific operation of the drying, and the water can be completely removed. As an embodiment of the present invention, the drying temperature can be 50 to 60°C; the drying time can be 20 to 24 hours; the drying can be carried out in a drying oven.

[0050] After obtaining the hydrothermal coal powder, the present invention mixes the hydrothermal coal powder with a sodium hydroxide solution and performs activation treatment to obtain a coal-based porous carbon material precursor.

[0051] In the present invention, the concentration of the sodium hydroxide solution is preferably 0.5-2 mol / L, more preferably 1-1.5 mol / L; the ratio of the mass of the hydrothermal coal powder to the volume of the sodium hydroxide solution is preferably 10 g: (30-60) mL, more preferably 10 g: (40-50) mL.

[0052] In the present invention, the temperature of the activation treatment is preferably 50-80°C, more preferably 60-70°C; the time of the activation treatment is preferably 1-5h, more preferably 2-4h, and further preferably 2-3h. The present invention can introduce metal ions through the activation treatment, which is convenient for subsequent pore formation using embedded metal ions.

[0053] After the activation treatment is completed, the present invention preferably performs suction filtration, water washing and drying in sequence on the product obtained by the activation treatment to obtain a coal-based porous carbon material precursor. The present invention has no special restrictions on the specific operations of the suction filtration, water washing and drying, and it is sufficient to remove impurities in the product and dry it. As an embodiment of the present invention, the drying temperature can be 50 to 60°C; the drying time can be 20 to 24 hours; and the drying can be performed in a drying oven.

[0054] After obtaining the coal-based porous carbon material precursor, the present invention performs carbonization treatment on the coal-based porous carbon material precursor to obtain a coal-based hard carbon negative electrode material.

[0055] In the present invention, the carbonization treatment is preferably carried out in a tube furnace. The present invention has no particular limitation on the specific model and source of the tube furnace, and a commercially available tube furnace well known to those skilled in the art can be used.

[0056] In the present invention, the temperature of the carbonization treatment is preferably 1100-1400°C, more preferably 1200-1300°C; the time of the carbonization treatment is preferably 1-5h, more preferably 2-4h, and further preferably 2-3h; the heating rate to the carbonization treatment temperature is preferably 3-8°C / min, more preferably 4-7°C / min, and further preferably 5-6°C / min; the atmosphere of the carbonization treatment is preferably an inert atmosphere, more preferably argon, helium or nitrogen, and further preferably nitrogen. The present invention can regulate the pore structure and microstructure of the material through high-temperature carbonization treatment, and the porous carbon after carbonization has a micro-closed-pore structure. The micro-closed-pore structure overcomes the π-π interaction and graphitization tendency between aromatic molecules, can effectively transmit sodium ions, and improve the platform capacity.

[0057] After the carbonization treatment is completed, the present invention preferably sequentially pickles, washes with water, dries and breaks up the product obtained by the carbonization treatment to obtain a coal-based hard carbon negative electrode material. The present invention has no particular limitation on the specific operations of pickling, washing with water, drying and breaking up, and the operations well known to those skilled in the art can be used to remove impurities and dry the product.

[0058] The present invention uses coal powder as a raw material to prepare negative electrode materials by a self-template method, utilizes the functional groups and embedded metal ions contained in the coal powder itself to form pores, and introduces a large number of closed pores into the negative electrode material through a self-sacrificing strategy, so that the carbonized negative electrode material has a micro-closed pore structure, and the micro-closed pore structure overcomes the π-π interaction and graphitization tendency between aromatic molecules, is conducive to the storage of sodium ions, can effectively transmit sodium ions, and improve the platform capacity. The oxygen sites introduced into the coal powder by hydrothermal treatment can achieve the regulation of the hard carbon microstructure during the carbonization process, wherein the introduction of C=O can effectively limit the movement of carbon atoms during the high-temperature carbonization process, thereby preventing the graphitization of the carbon layer, and the active hydrogen on the carboxyl and hydroxyl groups can provide more active sites for metal cations, promote the formation of closed pores, and achieve the synthesis of high-performance hard carbon negative electrode materials by regulating the microstructure of the hard carbon material.

[0059] The raw materials used in the present invention are low-priced, the preparation process is simple, and large-scale production is possible. By using lignite powder as a raw material, high-value utilization of lignite is achieved, and the production cost of negative electrode materials is greatly reduced, which provides convenience for the manufacture of sodium ion batteries of different models, improves market competitiveness, and is suitable for large-scale industrial promotion. The preparation method provided by the present invention can also reduce the use of chemical reagents, thereby reducing the discharge of polluted wastewater, and further reducing the production cost of closed-cell carbon materials.

[0060] The present invention also provides a coal-based hard carbon negative electrode material prepared by the preparation method described in the above technical solution.

[0061] The coal-based hard carbon negative electrode material provided by the present invention has a wider microcrystalline layer spacing, a larger number of micro-closed pores and a larger sodium ion storage capacity, and its reversible specific capacity reaches 350 mAh g -1 , showing excellent sodium storage performance, and thus can obtain sodium-ion batteries with high energy density, long cycle life, excellent rate performance and lower cost. Among sodium-ion batteries, it has the advantages of high specific capacity, good rate performance and good cycle stability.

[0062] The present invention also provides the use of the coal-based hard carbon negative electrode material described in the above technical solution in a sodium ion battery.

[0063] The present invention has no special limitation on the specific operation of the application, and the operation of using the negative electrode material in the sodium ion battery well known to those skilled in the art can be used.

[0064] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] Example 1

[0066] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0067] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain degreased lignite;

[0068] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal lignite;

[0069] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L sodium hydroxide solution, and then activated at 60° C. for 2 h, and finally filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0070] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-Na-1300.

[0071] Example 2

[0072] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0073] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0074] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0075] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L potassium hydroxide solution, and then activated at 60° C. for 2 h, and finally filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0076] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-K-1300.

[0077] Example 3

[0078] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0079] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0080] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0081] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L calcium chloride solution, and then activated at 60° C. for 2 h, and then filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0082] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-Ca-1300.

[0083] Example 4

[0084] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0085] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0086] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0087] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L magnesium chloride solution, and then activated at 60° C. for 2 h, and finally filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0088] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-Mg-1300.

[0089] Example 5

[0090] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0091] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0092] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0093] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L sodium hydroxide solution, and then activated at 60° C. for 2 h, and finally filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0094] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1200°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-Na-1200.

[0095] Example 6

[0096] A method for preparing a coal-based hard carbon negative electrode material comprises the following steps:

[0097] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0098] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0099] (3) 10 g of the hydrothermal coal powder obtained in step (2) was mixed with 40 mL of a 1 mol / L sodium hydroxide solution, and then activated at 60° C. for 2 h, and finally filtered, washed with water, and dried in a drying oven at 50° C. for 24 h to obtain a coal-based porous carbon material precursor;

[0100] (4) The coal-based porous carbon material precursor obtained in step (3) is placed in a tubular furnace and heated to 1400°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which is recorded as HCL-Na-1400.

[0101] Comparative Example 1

[0102] A method for preparing a hard carbon material comprises the following steps:

[0103] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0104] (2) The deashed pulverized coal obtained in step (1) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min for carbonization treatment for 2 hours under a nitrogen atmosphere. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and broken up in sequence to obtain a hard carbon material, which is recorded as DCL-1300.

[0105] Comparative Example 2

[0106] A method for preparing a hard carbon material comprises the following steps:

[0107] (1) The lignite is crushed and ground in sequence, passed through a 200-mesh sieve to obtain coal powder with a particle size of ≤75 μm, and then the coal powder is demineralized using an HCl-HF acid demineralization method. 10 g of coal powder is mixed with 200 mL of ultrapure water, and then 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) are added in sequence by draining and injecting acid into the water with a glass rod, and finally heated and stirred at 60° C. for 8 h, and filtered and dried to obtain deashed coal powder;

[0108] (2) adding the deashed coal powder obtained in step (1) into a high-pressure reactor, then adding 100 mL of distilled water, closing the high-pressure reactor, adjusting the heating jacket to a preset temperature of 200° C., then heating to 200° C. for hydrothermal reaction for 1 hour, then cooling to room temperature, filtering, and drying in a drying oven at 50° C. for 24 hours to obtain hydrothermal coal powder;

[0109] (3) The hydrothermal pulverized coal obtained in step (2) is placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment for 2 hours. After naturally cooling to room temperature, it is acid-washed, water-washed, dried and broken up in sequence to obtain a hard carbon material, which is recorded as HCL-1300.

[0110] Application Example 1

[0111] The assembly method of the half-cell is:

[0112] 1) The coal-based hard carbon negative electrode material HCL-Na prepared in Example 1 was mixed with a conductive agent acetylene black and a binder polyvinylidene fluoride in a mass ratio of 8:1:1, then N-methylpyrrolidone was added to grind into a slurry, coated on a copper foil, and dried in a vacuum oven at 120° C. to obtain an electrode;

[0113] 2) The electrode obtained in step 1) is used as the negative electrode, metallic sodium is used as the positive electrode, and the electrolyte is a 1 mol / L NaClO4 / (EC+DEC) mixed system to assemble into a half-cell.

[0114] Comparative application example 1

[0115] The assembly method of the half-cell is:

[0116] 1) The hard carbon material DCL prepared in Comparative Example 1 was mixed with a conductive agent acetylene black and a binder polyvinylidene fluoride in a mass ratio of 8:1:1, then N-methylpyrrolidone was added to grind into a slurry, coated on a copper foil, and dried in a vacuum oven at 120° C. to obtain an electrode;

[0117] 2) The electrode obtained in step 1) is used as the negative electrode, metallic sodium is used as the positive electrode, and the electrolyte is a 1 mol / L NaClO4 / (EC+DEC) mixed system to assemble into a half-cell.

[0118] Comparative Application Example 2

[0119] The assembly method of the half-cell is:

[0120] 1) The hard carbon material HCL prepared in Comparative Example 2 was mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride in a mass ratio of 8:1:1, then N-methylpyrrolidone was added to grind into a slurry, coated on a copper foil, and dried in a vacuum oven at 120° C. to obtain an electrode;

[0121] 2) The electrode obtained in step 1) is used as the negative electrode, metallic sodium is used as the positive electrode, and the electrolyte is a 1 mol / L NaClO4 / (EC+DEC) mixed system to assemble into a half-cell.

[0122] The FTIR spectra of deashed coal powder and hydrothermal coal powder in Example 1 are as follows: Figure 1 As shown. Figure 1 It can be seen that carbonyl groups were successfully introduced into lignite after hydrothermal treatment.

[0123] The XRD spectra of the coal-based hard carbon negative electrode material prepared in Example 1 and the hard carbon materials prepared in Comparative Examples 1 to 2 are as follows: Figure 2 As shown. Figure 2 It can be seen that the unique hard carbon diffraction pattern features of the three carbonaceous materials appear at approximately 22° and 43°, corresponding to the (002) and (100) graphite crystallite lattice planes, respectively.

[0124] The interlayer spacing distribution of the coal-based hard carbon negative electrode material prepared in Example 1 and the hard carbon materials prepared in Comparative Examples 1 to 2 is as follows: Figure 3 As shown. Figure 3 It can be seen that the coal-based hard carbon negative electrode material prepared by the present invention has a wider microcrystalline layer spacing.

[0125] The charge and discharge curves of the half-cells prepared in Application Example 1 and Comparative Application Examples 1 to 2 are shown in the figure below: Figures 4 to 6 As shown. Figures 4 to 6 It can be seen that the reversible specific capacity of the half-cell prepared by using the coal-based hard carbon negative electrode material provided by the present invention reaches 350 mAh g -1 , which is significantly higher than that of comparative application examples 1 to 2, indicating that the coal-based hard carbon negative electrode material provided by the present invention can enable the sodium ion battery to have the advantage of high specific capacity.

[0126] The cycle performance of the coal-based hard carbon negative electrode material prepared in Example 1 is as follows Figure 7 As shown. Figure 7 It can be seen that at 30mAg -1 The capacity retention rate is 95% after 400 cycles.

[0127] The rate performance of the coal-based hard carbon negative electrode material prepared in Example 1 is as follows Figure 8 As shown. Figure 8 It can be seen that 1000mAg -1 The capacity is 220mAh g -1 .

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a coal-based hard carbon negative electrode material, comprising the following steps: (1) demineralizing the coal powder using an acid demineralization method to obtain deashed coal powder; (2) mixing the deashed coal powder obtained in step (1) with water and performing a hydrothermal reaction to obtain hydrothermal coal powder; (3) mixing the hydrothermal coal powder obtained in step (2) with a sodium hydroxide solution and performing an activation treatment to obtain a coal-based porous carbon material precursor; (4) Carbonizing the coal-based porous carbon material precursor obtained in step (3) to obtain a coal-based hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: The particle size of the coal powder in step (1) is ≤75 μm.

3. The preparation method according to claim 1, characterized in that: The acid demineralization method in step (1) is an HCl-HF acid demineralization method.

4. The preparation method according to claim 1, characterized in that: In the step (2), the ratio of the mass of the deashed coal powder to the volume of water is (5-20) g:100 mL.

5. The preparation method according to claim 1, characterized in that: The insulation temperature of the hydrothermal reaction in the step (2) is 180-250° C., and the insulation time of the hydrothermal reaction is 0.5-3 h.

6. The preparation method according to claim 1, characterized in that: The concentration of the sodium hydroxide solution in step (3) is 0.5-2 mol / L, and the ratio of the mass of the hydrothermal coal powder to the volume of the sodium hydroxide solution is 10 g: (30-60) mL.

7. The preparation method according to claim 1, characterized in that: The temperature of the activation treatment in step (3) is 50 to 80° C., and the time of the activation treatment is 1 to 5 hours.

8. The preparation method according to claim 1, characterized in that: The temperature of the carbonization treatment in step (4) is 1100-1400° C., the time of the carbonization treatment is 1-5 hours, the heating rate to the carbonization treatment temperature is 3-8° C. / min, and the atmosphere of the carbonization treatment is an inert atmosphere.

9. The coal-based hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the coal-based hard carbon negative electrode material according to claim 9 in sodium ion batteries.

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