A method for preparing coal coke-based hard carbon by solvent-thermal assisted low-temperature heat treatment

Abstract

The present application belongs to the technical field of lithium / sodium ion battery negative electrode material, and particularly relates to a method for preparing coal tar-based hard carbon by solvent-thermal assisted low-temperature heat treatment. The method comprises the following steps: S1, crushing and sieving a hard carbon precursor to obtain a powdery raw material with uniform particle size; S2, acid washing the powdery raw material to remove ash, and cleaning until neutral, and then drying to obtain a purified raw material; S3, mixing the purified raw material with a polar organic solvent to perform a solvent-thermal reaction, and after the reaction, filtering, washing and drying to obtain a modified raw material; and S4, performing low-temperature heat treatment on the modified raw material to obtain a hard carbon material. The method is cheap in raw material, reliable in process, and can be produced on a large scale. The obtained hard carbon material can be used as a lithium ion battery and sodium ion battery negative electrode material, and provides a new way for low-cost preparation of hard carbon negative electrode material for energy storage.

Description

A method for preparing coal coke-based hard carbon by solvothermal-assisted low-temperature heat treatment Technical Field

[0001] This invention belongs to the technical field of lithium / sodium-ion battery anode materials, specifically relating to a method for preparing coal-based hard carbon through solvothermal-assisted low-temperature heat treatment. Background Technology

[0002] With the rapid development of electric vehicles, consumer electronics, and large-scale energy storage industries, the market demand for high-performance energy storage batteries is increasing. Sodium, due to its abundant reserves, low cost, and similar physicochemical properties to lithium, is considered a complementary system to lithium-ion batteries and has received widespread attention. However, graphite anode materials commonly used in lithium-ion batteries suffer from low sodium storage capacity due to the thermodynamic instability of the intercalation compounds formed with sodium ions and the small interlayer spacing, which hinders effective insertion / deposition. Therefore, there is an urgent need to develop anode materials suitable for both lithium-ion and sodium-ion battery systems to achieve the synergistic and rapid development of both energy storage systems. Hard carbon, due to its high degree of disorder, large interlayer spacing, and abundance of defects and pores, is conducive to the rapid insertion and deposition of lithium and sodium ions and is considered one of the most promising carbon anode materials.

[0003] Biomass, polymer resins, and coal-based materials such as coal and coal tar pitch have been used in the preparation of hard carbon materials. Compared to other materials, coal-based materials have high carbon content, high carbonization yield, low cost, and abundant resources, making them a class of hard carbon precursors with greater industrialization potential. However, current mainstream technologies typically require high-temperature treatment above 1000℃, resulting in significant energy consumption. Furthermore, the resulting coal-based hard carbon often exhibits small interlayer spacing and low ion transport rates, which are unfavorable for the construction of high-rate lithium-ion and sodium-ion battery systems. Therefore, developing novel coal-based hard carbon modification methods to effectively control the microcrystalline and pore structures of coal-based hard carbon, tailored to the inherent characteristics of coal-based hard carbon materials, is of great significance for the large-scale application of coal-based hard carbon. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing coal-based hard carbon through solvothermal-assisted low-temperature heat treatment. The aim is to obtain hard carbon materials that meet application requirements through simple and easy-to-implement control methods. This method is easily scaled up industrially, utilizes abundant raw material resources, and has a cost advantage. This invention is achieved through the following technical solutions.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A method for preparing coal coke-based hard carbon by solvothermal-assisted low-temperature heat treatment includes the following steps:

[0007] S1. The hard carbon precursor is crushed and sieved to obtain a powdered raw material with uniform particle size.

[0008] S2. The powdered raw material is acid-washed to remove ash, washed until neutral, and dried to obtain purified raw material;

[0009] S3. The purified raw material is mixed with a polar organic solvent and subjected to a solvothermal reaction. After the reaction is completed, the raw material is filtered, washed and dried to obtain the modified raw material.

[0010] S4. The modified raw materials are subjected to low-temperature heat treatment to obtain hard carbon materials.

[0011] Preferably, the hard carbon precursor in S1 is one or more of semi-coke, pitch coke, and coke; the powder raw material D50 is between 5μm and 50μm.

[0012] Preferably, in step S2, the pickling process uses hydrochloric acid with a concentration of 15% to 35% and hydrofluoric acid with a concentration of 3% to 30%, which are used together or sequentially.

[0013] Preferably, the polar organic solvent in S3 is one or more of alcohols, ketones, and aromatics; the volume ratio of the purified raw material to the polar organic solvent is 1:1 to 1:20.

[0014] Preferably, the solvothermal reaction temperature in S3 is 100–220°C, and the reaction time is 8–48 h; the washing solution used is one or more of acetone, methanol, and chloroform.

[0015] Preferably, the low-temperature heat treatment conditions in S4 are as follows: the atmosphere is one of argon, nitrogen, Ar / H2 mixture or N2 / H2 mixture, the heating rate is 1-10°C / min, the carbonization temperature is 400-800°C, and the holding time is 1-6h.

[0016] A coal-based hard carbon prepared by the method described above.

[0017] A negative electrode material composed of coal-coke-based hard carbon as described above.

[0018] A lithium-ion battery comprising the negative electrode material as described above.

[0019] A sodium-ion battery comprising the negative electrode material as described above.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The solvothermal reaction dissolves the small organic molecules remaining in the precursor, avoiding the increase in specific surface area and the decrease in interlayer spacing caused by the pyrolysis of small organic molecules, which is conducive to the rapid diffusion of metal ions inside the carrier gas and accelerates the charging speed of the battery.

[0022] (2) Compared with high temperature heat treatment, low temperature heat treatment can effectively reduce energy consumption and is also conducive to maintaining large interlayer spacing, providing a feasible solution for low-cost preparation of high-rate battery anode materials.

[0023] (3) This invention provides a new approach for the low-cost, high-value-added material application of coke powder, and increases the source of hard carbon anode materials. Attached Figure Description

[0024] Figure 1 is a SEM image of the hard carbon in Example 1 of the present invention;

[0025] Figure 2 is a TEM image of the hard carbon in Example 2 of the present invention;

[0026] Figure 3 shows the XRD pattern of hard carbon in Example 2 of the present invention;

[0027] Figure 4 shows the rate curve of hard carbon applied to the negative electrode of a lithium-ion battery in Example 2 of the present invention.

[0028] Figure 5 shows the cycle life curve of hard carbon applied to the negative electrode of a sodium-ion battery in Example 3 of this invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0030] The present invention aims to purify coal and modify its molecular structure by using a solvothermal method on ball-milled purified coal powder, thereby obtaining a solvothermal modified coal-based hard carbon material with a unique microcrystalline structure and surface functional groups under appropriate carbonization conditions.

[0031] Example 1

[0032] S1. The coal-based semi-coke precursor is crushed and sieved to obtain a powdery raw material with a D50 of approximately 15 μm.

[0033] S2. The raw material was removed by acid washing with 10% hydrofluoric acid and 18% hydrochloric acid, washed until neutral, and dried to obtain purified raw material.

[0034] S3. The purified raw material was mixed with ethylene glycol at a volume ratio of 1:3 and placed in a closed system. The mixture was heated to 160°C and reacted for 12 hours. After the reaction was completed, the product was filtered, washed with acetone, and dried to obtain the modified raw material.

[0035] S4. The modified raw materials are heated to 500℃ in nitrogen at a rate of 5℃ / min and reacted for 3 hours to obtain hard carbon materials.

[0036] Figure 1 is a SEM image of the hard carbon material obtained in Example 1. It can be seen from the figure that the hard carbon material has a relatively uniform particle size.

[0037] Example 2

[0038] S1. The pitch coke precursor is crushed and sieved to obtain a powdery raw material with a D50 of about 10μm.

[0039] S2. The raw material was removed by acid washing with 20% hydrochloric acid and 12% hydrofluoric acid, washed until neutral, and dried to obtain purified raw material.

[0040] S3. The purified raw material was mixed with N-methylpyrrolidone at a volume ratio of 1:5 and placed in a closed system. The mixture was heated to 180°C and reacted for 12 hours. After the reaction was completed, the product was filtered, washed with acetone, and dried to obtain the modified raw material.

[0041] S4. The modified raw materials are heated to 400℃ in argon at 5℃ / min and reacted for 3 hours to obtain hard carbon materials.

[0042] Figures 2 and 3 show the TEM electron microscope image and XRD pattern of the hard carbon material. It can be seen from the figures that the prepared material has a typical hard carbon disordered microcrystalline structure.

[0043] The hard carbon material prepared in Example 2 was mixed with conductive carbon black and a binder (PVDF) in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone was added and ground into a slurry, which was then coated onto copper foil and dried in a vacuum oven at 80°C. The resulting electrode was the negative electrode, lithium metal was the positive electrode, 1M LiPF6(EC+DEC) was used as the electrolyte (volume ratio 1:1), and glass fiber was used as the separator. A 2032 coin cell was assembled in an argon-filled glove box. As shown in Figure 4, this hard carbon material, used as the negative electrode in a lithium-ion battery, exhibits a specific capacity of 394 mAh / g at a current density of 0.1 A / g, 235 mAh / g at a current density of 1 A / g, and 133 mAh / g at a high current density of 5 A / g. Furthermore, it maintains high capacity even after reducing the current density, indicating that the obtained hard carbon has excellent rate performance and reversibility.

[0044] Example 3

[0045] S1. The coke precursor is crushed and sieved to obtain a powdery raw material with a D50 of approximately 12 μm.

[0046] S2. The raw material was removed by acid washing with 20% hydrochloric acid and 15% hydrofluoric acid, washed until neutral, and dried to obtain purified raw material.

[0047] S3. The purified raw material was mixed with N-methylpyrrolidone at a volume ratio of 1:2 and placed in a closed system. The mixture was heated to 180°C and reacted for 12 hours. After the reaction was completed, the product was filtered, washed with acetone, and dried to obtain the modified raw material.

[0048] S4. The modified raw materials are reacted in a mixed gas (90% Ar / 10% H2) at a temperature of 2℃ / min to 600℃ for 5h to obtain hard carbon material.

[0049] The hard carbon material prepared in Example 3 was mixed with conductive carbon black and a binder (PVDF) in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone was added and the mixture was ground into a slurry. This slurry was then coated onto copper foil and dried in a vacuum oven at 80°C. The resulting electrode was the negative electrode, lithium metal was the positive electrode, the electrolyte was 1M NaClO4 (EC+DMC) (volume ratio 1:1), and the separator was glass fiber. The mixture was assembled into a 2032 coin cell in an argon-filled glove box. As shown in Figure 5, this hard carbon material, used as the negative electrode in a sodium-ion battery, maintained 86% capacity after 500 cycles at a current density of 1 A / g.

[0050] Example 4

[0051] S1. The semi-coke precursor is crushed and sieved to obtain a powdered raw material with a D50 of approximately 8 μm.

[0052] S2. The raw material was removed by acid washing with 15% hydrochloric acid and 10% hydrofluoric acid, washed until neutral, and dried to obtain purified raw material.

[0053] S3. The purified raw material and isopropanol were mixed at a volume ratio of 1:8 and placed in a closed system. The mixture was heated to 160°C and reacted for 24 hours. After the reaction was completed, the product was filtered, washed with acetone, and dried to obtain the modified raw material.

[0054] S4. The modified raw materials are reacted in a mixed gas (95% N2 / 5% H2) at a temperature of 10℃ / min to 500℃ for 5 hours to obtain hard carbon material.

[0055] Example 5

[0056] S1. The pitch coke precursor is crushed and sieved to obtain a powdery raw material with a D50 of about 15μm.

[0057] S2. The raw material was removed by acid washing with 20% hydrochloric acid and 15% hydrofluoric acid, washed until neutral, and dried to obtain purified raw material.

[0058] S3. The purified raw material was mixed with ethylene glycol at a volume ratio of 1:8 and placed in a closed system. The mixture was heated to 170°C and reacted for 24 hours. After the reaction was completed, the product was filtered, washed with acetone, and dried to obtain the modified raw material.

[0059] S4. The modified raw materials are heated to 800℃ in argon at 10℃ / min and reacted for 2 hours to obtain hard carbon materials.

[0060] The above description is only for better explaining the embodiments of the present invention and is not intended to limit them. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing coal coke-based hard carbon through solvothermal-assisted low-temperature heat treatment, characterized in that, Includes the following steps: S1. The hard carbon precursor is crushed and sieved to obtain a powdered raw material with uniform particle size; S2. The powdered raw material is acid-washed to remove ash, washed until neutral, and dried to obtain a purified raw material; S3. The purified raw material is mixed with a polar organic solvent for a solvothermal reaction. After the reaction is completed, it is filtered, washed, and dried to obtain a modified raw material; S4. The modified raw material is subjected to low-temperature heat treatment to obtain hard carbon material; The low-temperature heat treatment conditions in S4 are: the atmosphere is one of argon, nitrogen, Ar / H2 mixture or N2 / H2 mixture, the heating rate is 1~10 ℃ / min, the carbonization temperature is 400~800 ℃, and the holding time is 1-6 h.

2. The method for preparing coal coke-based hard carbon by solvothermal assisted low-temperature heat treatment according to claim 1, characterized in that, The hard carbon precursor in S1 is one or more of semi-coke, pitch coke, and coke; the powder raw material D50 is between 5 μm and 50 μm.

3. The method for preparing coal coke-based hard carbon by solvothermal assisted low-temperature heat treatment according to claim 1, characterized in that, In S2, the pickling process uses hydrochloric acid with a concentration of 15% to 35% and hydrofluoric acid with a concentration of 3% to 30%, which are used together or sequentially.

4. The method for preparing coal coke-based hard carbon by solvothermal assisted low-temperature heat treatment according to claim 1, characterized in that, The polar organic solvent in S3 is one or more of alcohols, ketones, and aromatics; the volume ratio of the purified raw material to the polar organic solvent is 1:1 to 1:

20.

5. The method for preparing coal coke-based hard carbon by solvothermal assisted low-temperature heat treatment according to claim 1, characterized in that, The solvothermal reaction temperature in S3 is 100~220 ℃, and the reaction time is 8~48 h; the washing solution used is one or more of acetone, methanol, and chloroform.

6. A coal-based hard carbon prepared by the method according to any one of claims 1 to 5.

7. A negative electrode material, characterized in that, It is composed of the coal-coke-based hard carbon as described in claim 6.

8. A lithium-ion battery, characterized in that, Includes the negative electrode material as described in claim 7.

9. A sodium-ion battery, characterized in that, Includes the negative electrode material as described in claim 7.

Images