A coal-based hard carbon negative electrode material and its preparation method and application

Abstract

The present invention provides a coal-based hard carbon negative electrode material and its preparation method and application, which belongs to the technical field related to sodium ion batteries. The present invention uses coal powder as raw material to prepare the negative electrode material by a self-template method, utilizes the functional groups contained in the coal powder itself and the embedded metal ions to form pores, 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, which overcomes the π-π interaction and graphitization trend 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 realize the regulation of the hard carbon microstructure during the carbonization process, 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.

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 resulting environmental problems have become increasingly prominent, and the development of a "low-carbon economy" has become a consensus among countries around the world. Lithium-ion batteries, due to their advantages such as high energy density and long cycle life, have been widely used in portable electronics, electric vehicles, and energy storage. However, problems such as rising prices and uneven distribution of lithium resources have severely restricted the development of lithium-ion batteries. Sodium-ion batteries, due to their abundant resources and low cost, have gradually become a potential alternative to lithium-ion batteries. Sodium-ion batteries work in a similar way to lithium-ion batteries, and the abundance and low price of sodium resources have made their research a hot topic.

[0003] The negative electrode material is an important component of sodium ion batteries, and its performance has a significant 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+ storage due to their short-range carbon microcrystals and increased interlayer spacing. + inserted into the carbon lattice and is considered a promising Na + Therefore, the development of high-capacity anode materials with high cycle performance and good rate performance will be the key direction of sodium-ion battery research.

[0004] As the lowest-cost and highest-carbon natural material in nature, coal is not only abundant in reserves and diverse in variety, but also has a moderate molecular weight and easily regulated molecular structure, making it a potential high-quality precursor for sodium-ion battery anode materials. However, sodium-ion batteries require carbon materials with low graphitization (large interlayer spacing) and loose structure (pore structure <0.5nm). However, the π-π interaction between planar aromatic molecules in coal and its tendency to graphitize limit its sodium ion storage capacity. The high-temperature carbonization process results in a highly ordered carbon structure with narrow interlayer spacing, resulting in unsatisfactory performance of sodium-ion batteries prepared using coal as the anode material in practical applications. Therefore, conventional coal cannot be directly used as the anode material for 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 its preparation method and application. 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 350mAh 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 pulverized coal using an acid demineralization method to obtain deashed pulverized coal;

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

[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 pulverized coal 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 50-80° C., and the time of the activation treatment is 1-5 hours.

[0019] Preferably, the temperature of the carbonization treatment in step (4) is 1100-1400°C, the time of the carbonization treatment is 1-5h, 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 the 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 through a self-sacrificing strategy, and makes the carbonized negative electrode material have a micro-closed pore structure. 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 improves the platform capacity. The present invention introduces oxygen sites into coal powder through hydrothermal treatment, which can achieve 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. The active hydrogen on the carboxyl and hydroxyl groups can provide more active sites for metal cations, promoting the formation of closed pores. By regulating the microstructure of the hard carbon material, the synthesis of high-performance hard carbon negative electrode materials is achieved.

[0023] The present invention utilizes inexpensive raw materials, a simple preparation process, and is suitable for large-scale production. By using lignite powder as a raw material, it achieves high-value utilization of lignite and significantly reduces the production cost of negative electrode materials. This facilitates the manufacture of various sodium-ion battery models, improves market competitiveness, and is suitable for large-scale industrial deployment. The preparation method provided by the present invention also reduces the use of chemical reagents, thereby reducing the discharge of polluting 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 interlayer 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 and 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 and 2;

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

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

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

[0031] Figure 7 Cycling 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 pulverized coal using an acid demineralization method to obtain deashed pulverized coal;

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

[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 does not specifically limit the specific type of pulverized coal; commercially available pulverized coal known to those skilled in the art or pulverized coal prepared from existing coal can be used. In embodiments of the present invention, the pulverized coal can be lignite pulverized coal. Using lignite pulverized coal as a raw material not only reduces raw material costs but also achieves high-value utilization of lignite.

[0040] In the present invention, the particle size of the pulverized coal is preferably ≤75 μm. In the present invention, when the particle size of the pulverized coal does not meet the above conditions, the pulverized coal is preferably crushed and then ground. The specific operations of crushing and grinding are not particularly limited in the present invention; procedures familiar to those skilled in the art can be employed to achieve the required particle size of the pulverized coal. By controlling the particle size of the pulverized coal, the present invention facilitates demineralization using an acid demineralization method.

[0041] In the present invention, the acid demineralization method is preferably an HCl-HF acid demineralization method. The present invention does not particularly limit the specific operation of the HCl-HF acid demineralization method and the specific concentrations and amounts of the hydrochloric acid and hydrofluoric acid solutions used. The operation of the HCl-HF acid demineralization method well known to those skilled in the art can be adopted. In the present invention, the presence of a large number of highly complex inorganic mineral components in coal can adversely affect the performance of the coal-based porous carbon material. The acid demineralization method can remove impurities and minerals in the coal.

[0042] As an embodiment of the present invention, the HCl-HF acid demineralization method can be: mixing coal powder and ultrapure water, then adding hydrochloric acid and hydrofluoric acid solutions in sequence, and finally heating and stirring 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 amounts of deashed coal powder and water, the present invention can fully disperse the deashed coal powder in the water, thereby improving the efficiency of C=O introduction into 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 an autoclave; the autoclave is preferably sealed during the hydrothermal reaction. The present invention does not particularly limit the specific model or source of the autoclave; any commercially available autoclave familiar to those skilled in the art can be used. By carrying out the hydrothermal reaction in the autoclave, the reaction temperature can be raised to the desired hydrothermal reaction temperature under high pressure.

[0047] In the present invention, the holding temperature of the hydrothermal reaction is preferably 180-250°C; the holding 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 they 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 regulating 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 can 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 can 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 pulverized coal. The present invention does not specifically limit the specific operation of the filtration; a filtration operation familiar to those skilled in the art can be used to achieve solid-liquid separation. The present invention does not specifically limit the specific operation of the drying; it can be performed to completely remove the moisture. As one embodiment of the present invention, the drying temperature can be 50-60°C; the drying time can be 20-24 hours; and the drying can be performed 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 then performs an 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 pulverized coal 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 activation treatment temperature is preferably 50-80°C, more preferably 60-70°C; the activation treatment time is preferably 1-5 hours, more preferably 2-4 hours, and even more preferably 2-3 hours. The activation treatment can introduce metal ions, facilitating subsequent pore formation using the embedded metal ions.

[0053] After the activation treatment is completed, the present invention preferably sequentially filters, washes, and dries the product obtained from the activation treatment to obtain a coal-based porous carbon material precursor. The present invention does not specifically limit the specific operations of filtration, washing, and drying, as long as the impurities in the product are removed and the product is dried. As an embodiment of the present invention, the drying temperature can be 50-60°C; the drying time can be 20-24 hours; and the drying can be carried out 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. At the same time, 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 transport sodium ions, and improve the platform capacity.

[0057] After the carbonization treatment is completed, the product obtained by the carbonization treatment is preferably sequentially acid-washed, water-washed, dried, and dispersed to obtain a coal-based hard carbon negative electrode material. The specific operations of acid-washing, water-washing, drying, and dispersed are not particularly limited in the present invention, and can be performed using procedures well known to those skilled in the art that can remove impurities and dry the material.

[0058] The present invention uses coal powder as a raw material to prepare negative electrode materials using a self-template method. The functional groups contained in the coal powder itself and the embedded metal ions are used to form pores. A large number of closed pores are introduced into the negative electrode material through a self-sacrificing strategy, so that the negative electrode material after carbonization has a micro-closed pore structure. 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 transport 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. 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. The active hydrogen on the carboxyl and hydroxyl groups can provide more active sites for metal cations, promoting the formation of closed pores. By regulating the microstructure of the hard carbon material, the synthesis of high-performance hard carbon negative electrode materials is achieved.

[0059] The present invention utilizes inexpensive raw materials, a simple preparation process, and is suitable for large-scale production. By using lignite powder as a raw material, it achieves high-value utilization of lignite and significantly reduces the production cost of negative electrode materials. This facilitates the manufacture of various sodium-ion battery models, improves market competitiveness, and is suitable for large-scale industrial deployment. The preparation method provided by the present invention also reduces the use of chemical reagents, thereby reducing the discharge of polluting 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 350mAh 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 particular limitation on the specific operation of the application, and any operation of using the negative electrode material in a sodium ion battery well known to those skilled in the art may be used.

[0064] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some 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 making creative efforts 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed 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. Finally, the mixture was 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0074] (2) adding the deashed pulverized coal 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 pulverized coal;

[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. Finally, the mixture was 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) was 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 was acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which was 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0080] (2) adding the deashed pulverized coal 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 pulverized coal;

[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. Finally, the mixture was 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) was 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 was acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which was 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0086] (2) adding the deashed pulverized coal 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 pulverized coal;

[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. Finally, the mixture was 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) was 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 was acid-washed, water-washed, dried and dispersed in sequence to obtain a coal-based hard carbon negative electrode material, which was 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0092] (2) adding the deashed pulverized coal 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 pulverized coal;

[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. Finally, the mixture was 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 broken up 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0098] (2) adding the deashed pulverized coal 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 pulverized coal;

[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. Finally, the mixture was 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 was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was 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 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 DCL-1300.

[0105] Comparative Example 2

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

[0107] (1) The lignite was 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 was demineralized using an HCl-HF acid demineralization method. 10 g of coal powder was mixed with 200 mL of ultrapure water, and then acid was injected into the water using a glass rod. 50 mL of hydrochloric acid (12 mol / L) and 40 mL of hydrofluoric acid solution (23 mol / L) were added in sequence. Finally, the mixture was heated and stirred at 60°C for 8 h, and filtered and dried to obtain deashed coal powder.

[0108] (2) adding the deashed pulverized coal 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 pulverized coal;

[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, and then N-methylpyrrolidone was added to grind into a slurry, which was 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 acetylene black as a conductive agent and polyvinylidene fluoride as a binder in a mass ratio of 8:1:1, then N-methylpyrrolidone was added and ground into a slurry, which was then coated onto 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 acetylene black as a conductive agent and polyvinylidene fluoride as a binder in a mass ratio of 8:1:1, then ground into a slurry with N-methylpyrrolidone, coated onto 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 patterns of the coal-based hard carbon negative electrode material prepared in Example 1 and the hard carbon materials prepared in Comparative Examples 1 and 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 and 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 and 2 are shown in the figure below: Figures 4-6 As shown. Figures 4-6 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 sodium ion batteries 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 principles of the present invention. These improvements and modifications should also be regarded as within 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 pulverized coal using an acid demineralization method to obtain deashed pulverized coal; (2) mixing the deashed pulverized coal obtained in step (1) with water and performing a hydrothermal reaction to obtain hydrothermal pulverized coal; (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; the concentration of the sodium hydroxide solution in step (3) is 0.5 to 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 to 60) mL; the temperature of the activation treatment in step (3) is 50 to 80° C., and the activation treatment time is 1 to 5 h; (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 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.

6. 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.

7. The coal-based hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 6.

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

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