Coal-based hard carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a coal-based hard carbon composite material as well as a preparation method and application thereof. The method specifically comprises the following steps: carrying out ball-milling mixing on pulverized coal with the particle size of less than 75 microns and glucose, collecting the material, transferring the collected material into a tubular furnace, carrying out pre-carbonization under the protection of inert gas, and then heating to carry out high-temperature carbonization treatment, so as to obtain the coal-based hard carbon composite material. According to the preparation method, coal and glucose are utilized for co-carbonization, two carbon structures are subjected to composite cross-linking to form a rich microporous structure, the pulping process is improved, so that excellent electrochemical performance is obtained, and the preparation method has the advantages of low raw material cost, simple treatment process and high material carbon yield and is suitable for industrial production. And the material is a commercial sodium ion battery negative electrode material with industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a coal-based hard carbon composite material, a preparation method thereof, and an application thereof. Background Art

[0002] As an emerging energy storage technology, sodium-ion batteries have gradually become an important alternative to lithium-ion batteries due to the abundance and low cost of sodium resources. The performance of sodium-ion batteries depends to a large extent on the selection and optimization of anode materials. Among them, hard carbon materials have become the focus of research on anode materials for sodium-ion batteries due to their excellent electrochemical performance and low cost.

[0003] As a widely existing and inexpensive natural carbon source, coal shows great potential to become an ideal precursor for hard carbon materials due to its high carbon yield, aromatic skeleton structure, and three-dimensional cross-linked network characteristics. However, due to the complex molecular structure and variety of coal types, the refined preparation of coal-based carbon materials suitable for sodium-ion batteries still poses great challenges.

[0004] In recent years, researchers have proposed various modification and process optimization methods for coal-based carbon materials. For example, CN118183739A proposes to introduce pore-forming agents and coating materials to increase the pore structure of the material, improve the sodium storage capacity and cycling performance, effectively inhibit high-temperature graphitization, expand the layer spacing, and enhance the sodium ion diffusion ability. CN118637616A proposes to precisely control the activation process to optimize the carbon layer spacing and disorder, thereby improving the electrochemical performance and initial Coulomb efficiency of the material, and enhancing the uniformity and cycling stability of the hard carbon anode material. CN118771356A adopts a multi-step process including low-temperature carbonization, wet grinding, spray drying, and high-temperature carbonization to gradually optimize the particle structure and carbon layer spacing of the hard carbon material, thereby improving the rate performance and fast charging performance, reducing the generation of sodium dendrites, and enhancing the cycling stability and fast charging ability. However, these methods do not combine coal with other carbon sources to fully utilize the synergistic advantages of different carbon sources. Therefore, there is an urgent need for a process to prepare hard carbon anodes from coals with different vitrinite contents, so as to achieve the wide application of coal materials in the energy storage field. Summary of the Invention

[0005] One object of the present invention is to provide a preparation method of a coal-based hard carbon composite material, using abundant coal and common glucose as carbon sources for preparing hard carbon materials.

[0006] Another object of the present invention is to provide a coal-based hard carbon anode material prepared by the above preparation method, which has high specific capacity and rate performance.

[0007] A third object of the present invention is to provide an application of the above coal-based hard carbon as an anode material for sodium-ion batteries.

[0008] To achieve the above-mentioned invention object, the present invention provides the following technical solutions:

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

[0010] (1) Crashing and screening the raw coal to obtain coal powder with a particle size less than 75 μm;

[0011] (2) Performing high-energy ball milling on the coal sample obtained in step (1) and glucose, transferring the mixture to an inert gas for pre-carbonization treatment after being uniformly mixed to obtain a precursor;

[0012] (3) Performing high-temperature carbonization treatment on the precursor obtained in step (2) in an inert gas to obtain a coal-based hard carbon composite material.

[0013] Preferably, the raw coal is at least one of anthracite, bituminous coal, and lignite, and the D50 particle size of the coal is 3 - 20 μm.

[0014] Preferably, in step (2), the coal sample and glucose are ball milled and mixed according to a mass ratio of 1:0.5 - 2.

[0015] Preferably, in step (2), the temperature of the pre-carbonization is 300 °C, the heat preservation time is 1 - 2 h, and the heating rate is 1 - 5 °C / min.

[0016] Preferably, in step (3), the temperature of the high-temperature carbonization is 1100 - 1500 °C, the heat preservation time is 1 - 6 h, and the heating rate is 1 - 5 °C / min.

[0017] Preferably, in step (2), the rotation speed of the high-energy ball milling is 400 r / min, the ball milling time is 3 h, and the ball-to-material ratio is 2:1.

[0018] In a second aspect, the present invention provides a coal-based hard carbon composite material prepared by the above preparation method.

[0019] The specific surface area of the coal-based hard carbon negative electrode material prepared by the present invention is 0.6 - 40 m 2 / g, the first charge capacity is 255 - 383 mAh / g, and the first discharge capacity is 338 - 577 mAh / g, showing excellent sodium ion battery performance. Particularly when the mixing ratio of coal and glucose is appropriate (1:1 - 2), the first charge capacity > 330 mAh / g.

[0020] In a third aspect, the present invention provides the application of the above coal-based hard carbon composite material as a negative electrode material for a sodium ion battery.

[0021] The coal-based hard carbon composite material prepared by the present invention, a binder, and conductive carbon black are placed in a certain amount of N-methylpyrrolidone (NMP) according to a certain ratio, ball-milled and mixed for 2-4 h, then coated, and after vacuum drying, tablets are made and assembled into a sodium-ion battery.

[0022] Preferably, the binder is polyvinylidene fluoride (PVDF) or carboxymethyl cellulose (CMC); when the binder is PVDF, the mass ratio of the composite material, PVDF, and conductive carbon black is 8:1:1 or 90:5:5; when the binder is CMC, the mass ratio of the composite material, CMC, and conductive carbon black is 8:1:1.

[0023] Preferably, the temperature of the vacuum drying is 70-90 °C and the time is 8-12 h.

[0024] Compared with the prior art, the preparation process provided by the present invention has a lower cost, does not require pickling operation, effectively reduces the additional cost brought by pickling and avoids the problem of difficult waste liquid treatment. The coal-based hard carbon negative electrode material prepared by this method has a rich closed pore structure, and at the same time, the surface defect degree of the prepared composite material is improved. The present invention provides a coal-based hard carbon negative electrode material with high energy density, long cycle life, excellent rate performance, and low cost, which can well meet the industrial demand. Description of the Drawings

[0025] Figure 1 SEM diagram of the material prepared in Example 1;

[0026] Figure 2 SEM diagram of the material prepared in Comparative Example 1;

[0027] Figure 3 Pore size distribution diagram of the materials prepared in Example 1 and Comparative Example 1;

[0028] Figure 4 Charge and discharge curve diagram of the coal-based sodium-ion battery prepared in Examples 1-5;

[0029] Figure 5 Charge and discharge curve diagram of the coal-based sodium-ion battery prepared in Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0030] Figure 6 Rate performance and long cycle performance curve diagram of Examples 1, 2, and 3; Detailed Description of the Invention

[0031] The present invention will be further described in detail below with reference to the drawings and specific examples.

[0032] Example 1

[0033] This embodiment provides a method for preparing a high-performance coal-based hard carbon / carbon composite material, comprising the following steps:

[0034] (1) Put Xinjiang Jilangde bituminous coal (vitrinite content > 50%) into a universal crusher and crush it to 200 mesh, then sieve it and take the undersize;

[0035] (2) Take 6 g of sieved coal powder, weigh glucose according to the mass ratio of coal powder to glucose of 1:1, place it in a high-energy ball milling tank, add grinding balls, with a ball-to-material ratio of 2:1, and carry out high-energy ball milling at a rotation speed of 400 r / min for 3 h to fully mix the coal and glucose;

[0036] (3) Take the mixed sample obtained in step (2) and put it into a tubular furnace. Under nitrogen protection, heat it to 300 °C at a heating rate of 2 °C / min, hold for 2 h, then heat it to 1300 °C at a heating rate of 2 °C / min, hold for 2 h, and cool it to room temperature to obtain a coal-based hard carbon composite material;

[0037] (4) Place the composite material, PVDF, and conductive carbon black in a mass ratio of 8:1:1 into 1.3 mL of NMP, and carry out ball milling and mixing for 2 - 4 h to make a slurry.

[0038] Example 2

[0039] The difference between this example and Example 1 is that the ratio of coal to glucose is 1:0.5.

[0040] Example 3

[0041] The difference between this example and Example 1 is that the ratio of coal to glucose is 1:2.

[0042] Example 4

[0043] The difference between this example and Example 1 is that in step (1), Tianchi bituminous coal (vitrinite content < 50%) is used, and the slurry-making ratio in step (4) is 90:5:5.

[0044] Example 5

[0045] (1) Put Tianchi bituminous coal (vitrinite content < 50%) into a universal crusher and crush it to 200 mesh, then sieve it and take the undersize;

[0046] (2) Take 6 g of sieved coal powder, carry out step-by-step pickling of the coal powder with HCl-HF, after pickling, rinse the coal with deionized water, rinse it 7 - 8 times and then transfer it to a blast drying oven for drying;

[0047] (3) Take the pickled sample obtained in step (2) and put it into a tubular furnace. Directly under nitrogen protection, heat it to 1300 °C at a heating rate of 2 °C / min, hold for 2 h, and cool it to room temperature;

[0048] (4) Place the composite material, CMC, and conductive carbon black in deionized water at a ratio of 8:1:1, ensuring a solid content of about 30%. Ball mill and mix for 2 - 4 h to make a slurry.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that in step (2), Xinjiang Jilangde coal (vitrinite content > 50%) is directly placed in the ball mill tank, and the remaining steps are the same as those in Example 1.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 4 is that in step (2), Tianchi bituminous coal (vitrinite content < 50%) is directly placed in the ball mill tank, and the remaining steps are the same as those in Example 4.

[0053] Comparative Example 3

[0054] (1) Put Xinjiang Jilangde bituminous coal (vitrinite content > 50%) into a universal crusher and crush it to 200 mesh. Screen and take the undersize.

[0055] (2) Take 6 g of screened coal powder and perform step - by - step pickling of the coal powder with HCl - HF. After pickling, rinse the coal with deionized water. After rinsing 7 - 8 times, transfer it to a blast drying oven for drying. Then, weigh glucose according to the ratio of coal to glucose of 1:1, place it in a high - energy ball mill tank, add grinding balls, with a ball - to - material ratio of 2:1, and perform high - energy ball milling at a speed of 400 r / min for 3 h to fully mix the coal and glucose.

[0056] (3) Put the pickled sample obtained in step (2) into a tubular furnace. Under nitrogen protection, heat it to 300 °C at a heating rate of 2 °C / min, hold for 2 h, then heat it to 1300 °C at a heating rate of 2 °C / min, hold for 2 h, and cool to room temperature to obtain a coal - based hard carbon composite material.

[0057] (4) Place the composite material, PVDF, and conductive carbon black in 1.3 mL of NMP at a ratio of 8:1:1, and ball mill and mix for 2 - 4 h to make a slurry.

[0058] Physical and chemical property testing

[0059] Figure 1 The SEM image of the material prepared for Example 1 shows that the surface of the coal - based hard carbon composite material is relatively smooth, with no large number of attached particles. At the same time, there are a large number of closed pores on the surface of the intercalated lamellae, thus improving the electrochemical performance of the material.

[0060] Figure 2 The SEM image of the material prepared for Comparative Example 1 shows that there are many attached particles on the surface of the material, which may fall off during the charge - discharge process, hindering the performance of the battery.

[0061] Figure 3 Pore size distribution diagrams of the materials prepared in Example 1 and Comparative Example 1; it can be seen that there is a macropore distribution in the coal-based hard carbon composite material of Example 1 around 20 - 60 nm, while there is no obvious pore distribution in the coal-based hard carbon composite material of Comparative Example 1 within this range. In addition, the pore distribution of the coal-based hard carbon composite material of Example 1 with <10 nm is also more than that of Comparative Example 1. In addition, the specific surface area of Example 1 is 25.85 m 2 / g, which is higher than 0.6 m 2 / g of Comparative Example 1. A higher specific surface area can endow the hard carbon material with better sodium storage performance.

[0062] Assembly and testing of the battery

[0063] Coat the above slurry on a copper foil (the areal density is controlled at about 3 mg / cm 2 ), and place it in a vacuum drying oven to dry at 70 °C for 10 h. Then use a slicing machine to make a 10 mm electrode sheet, and dry the electrode sheet at 120 °C for 5 h under vacuum conditions. Use a sodium metal sheet as the negative electrode, and the electrode sheets of the examples and comparative examples as the positive electrode. 1 mol / L sodium hexafluorophosphate (NaPF 6 ) diglyme (1 mol / L sodium hexafluorophosphate (NaPF 6 ) in diglyme) is used as the electrolyte, and a CR2032 coin cell is assembled in a glove box. Use a high-precision battery tester (Wuhan Blue Electric) to perform constant current charge and discharge tests at a current density of 0.1C (1C = 200 mA / g) and a voltage range of 0 - 3.0V. The test results are shown in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] It can be seen from the specific surface area data in Table 1 that if the proportion of glucose is too high, its initial Coulombic efficiency will be greatly reduced. For example, in Example 3, its initial Coulombic efficiency is 59.92%. When the mixing ratio of coal to glucose is 1:1 and 1:0.5, the initial Coulombic efficiencies are not much different. In addition, the initial Coulombic efficiency of the negative electrode material is also related to the slurry preparation ratio. For example, in Example 4, the initial Coulombic efficiency can reach 77.26%, which is not much different from that of Example 5 with an aqueous slurry, indicating that even when using an organic slurry, appropriately increasing the proportion of the negative electrode material can effectively improve the initial Coulombic efficiency of the sodium-ion battery. Comparing Example 1 and Comparative Example 3, it is found that the initial Coulombic efficiency of the material obtained by compounding the pickled coal sample and glucose does not increase, indicating that this process can completely eliminate the pickling step.

[0068] This process can effectively improve the charge-discharge capacity of the material. By comparing Example 1, Example 2, Example 3 with Comparative Example 1, it is found that the charge-discharge capacity of the composite material is higher than that of the non-composite material. The same conclusion can also be drawn by comparing Example 4 and Comparative Example 2. At the same time, the capacity is not directly proportional to the proportion of glucose. The more glucose there is, the more the capacity decreases, and the initial Coulombic efficiency also decreases. Therefore, this process needs to adjust the proportion according to the coal type and pretreatment method.

[0069] Figure 4 Charge-discharge curves of the coal-based sodium-ion batteries prepared for Examples 1 to 5. From Figure 4 it can be seen that different coal types and different pretreatment methods result in different battery performances prepared by this process. By comparing Examples 1 - 3, Example 1 has higher capacities in the slope region and the plateau region, Example 3 has the second-highest capacities in the slope region and the plateau region, and Example 2 has the lowest. Excessive glucose content will introduce more defects in the hard carbon material, and experiments prove that these defects are irreversible. Therefore, the first efficiency of Example 3 is the lowest. If the glucose content is too low, the capacity of the material cannot be increased. Therefore, an appropriate glucose content can improve the sodium storage performance of the hard carbon material. By comparing Examples 4 and 5, the capacities in the slope region and the plateau region of Example 4 are both higher than those of Example 5.

[0070] Figure 5 Charge-discharge curves of the coal-based sodium-ion batteries prepared for Comparative Example 1, Comparative Example 2 and Comparative Example 3. By comparing Comparative Example 1 and Comparative Example 2, it shows that the charge-discharge performance of the uncomposite Girande coal is lower than that of Tianchi bituminous coal. And through compounding with glucose, the performance of Girande coal can be better than that of Tianchi coal, indicating that this process has certain advantages. At the same time, different coal types have a certain impact on the application of this process. Compared with Example 1, the capacities in the slope region and the plateau region of Comparative Example 3 both decrease. Compared with Example 4, Comparative Example 3 has a higher slope region and a lower plateau region, indicating that compounding the pickled coal sample will hinder the intercalation and pore filling of sodium ions in the material.

[0071] Figure 6 Long cycle diagrams of the coal-based sodium-ion batteries prepared for Example 1, Example 2 and Example 3. From Figure 6 it can be seen that Example 1 exhibits good rate performance and long cycle performance.

[0072] As mentioned above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a coal-based hard carbon composite material, characterized in that: The following steps are involved: (1) crushing and screening the raw coal to obtain coal powder with a particle size of less than 75 μm; (2) subjecting the coal sample obtained in step (1) and glucose to high-energy ball milling, mixing them evenly and then transferring them to an inert gas for pre-carbonization treatment to obtain a precursor; (3) subjecting the precursor obtained in step (2) to high-temperature carbonization treatment in an inert gas to obtain a coal-based hard carbon composite material.

2. The method for preparing a coal-based hard carbon composite material according to claim 1, characterized in that: The raw coal is at least one of anthracite, bituminous coal and lignite, and the D50 particle size of the coal is 3-20 μm.

3. The method for preparing a coal-based hard carbon composite material according to claim 1, characterized in that: In step (2), the coal sample and glucose are mixed by ball milling at a mass ratio of 1:0.5-2.

4. The method for preparing a coal-based hard carbon composite material according to claim 1, characterized in that: The pre-carbonization temperature in step (2) is 300° C., the holding time is 1-2 h, and the heating rate is 1-5° C. / min.

5. The method for preparing a coal-based hard carbon composite material according to claim 1, characterized in that: The high temperature carbonization temperature in step (3) is 1100-1500°C, the insulation time is 1-6h, and the heating rate is 1-5°C / min.

6. The method for preparing a coal-based hard carbon composite material according to claim 1, characterized in that: The rotation speed of the high-energy ball mill in step (2) is 400 r / min, the ball milling time is 3 h, and the ball-to-material ratio is 2:

1.

7. A coal-based hard carbon composite material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

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

9. The use according to claim 8, characterized in that: The coal-based hard carbon composite material, the binder and the conductive carbon black are placed in N-methylpyrrolidone in proportion, ball-milled and mixed for 2-4 hours, then coated, vacuum-dried and sliced, and assembled into a sodium ion battery.

10. The use according to claim 9, characterized in that: The binder is polyvinylidene fluoride or carboxymethyl cellulose; when the binder is polyvinylidene fluoride, the mass ratio of the composite material, polyvinylidene fluoride and conductive carbon black is 8:1:1 or 90:5:5; when the binder is carboxymethyl cellulose, the mass ratio of the composite material, carboxymethyl cellulose and conductive carbon black is 8:1:1.

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