Halide-modified coal-based hard carbon material, preparation method and application thereof

Abstract

The invention discloses a halide modified coal-based hard carbon material as well as a preparation method and application thereof, the preparation method comprises the following steps: S1, mixing and grinding raw material coal and halide according to a mass ratio of 1: (0.1-0.5), and pre-sintering and activating in a closed environment with an inert atmosphere to prepare a mixed material; s2, grinding the mixed material into powder, performing acid pickling treatment, and then performing water washing and drying to obtain a powdery carbon material; and S3, carbonizing the powdery carbon material in an inert atmosphere to prepare the coal-based hard carbon material. The method is simple in process, low in production cost and suitable for industrial large-scale production, the prepared coal-based hard carbon material has a rich pore structure, the sodium storage performance is improved, and the problems that a battery is short in service life and low in energy density in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a halide-modified coal-based hard carbon material, its preparation method, and its application. Background Technology

[0002] The development and utilization of renewable energy is an inevitable trend. However, the utilization of renewable energy sources such as solar and wind power is intermittent and unstable. Therefore, efficient energy storage technology has become a key technological support for the development of renewable energy. Currently, lithium-ion batteries have achieved great success and dominate in consumer electronics, electric vehicles, and other fields. However, given the uneven distribution of lithium resources and the difficulty of mining them, the development of sodium-ion batteries to replace lithium-ion batteries has become a new trend. Based on this, research and development of sodium-ion battery technologies, including coal-based hard carbon anodes, has been promoted.

[0003] Coal, as a natural resource with abundant reserves, low price, and high carbon content, is one of the ideal precursor materials for preparing hard carbon anode materials. Theoretically, coal-based hard carbon materials prepared from coal possess unique microstructures and physicochemical properties, effectively meeting the key requirements of sodium-ion batteries for anode materials. Furthermore, the preparation process of coal-based hard carbon is relatively mature and cost-controllable. Using coal-based hard carbon materials to prepare anode materials could reduce the overall manufacturing cost of sodium-ion batteries. However, traditional coal-based hard carbon materials suffer from low specific capacity and poor rate performance. Improving these properties has become one of the research directions for enhancing the performance of sodium-ion battery anodes. Currently, there are also modified coal-based hard carbon solutions. For example, patent CN119750547A discloses a method for preparing coal-based hard carbon anode materials and its application, which requires deashing, micro-arc oxidation, and carbonization treatments. This method requires the introduction of micro-arc oxidation, making the preparation steps relatively cumbersome. Another approach involves using high-temperature graphitization of raw materials to produce hard carbon materials, but the reaction temperature is extremely high, making it difficult to reduce production costs. Based on this, the present invention proposes a halide-modified coal-based hard carbon material, which has a simple preparation process and effectively solves the above problems. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a halide-modified coal-based hard carbon material, its preparation method, and its application. The preparation process of the coal-based hard carbon material of the present invention is simple and the production cost is low, making it suitable for industrial-scale production. Furthermore, the coal-based hard carbon material has a rich pore structure, which improves sodium storage performance and solves the problems of short lifespan and low energy density in existing batteries.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a halide-modified coal-based hard carbon material, as follows:

[0007] S1. Mix and grind the raw coal and the halide at a mass ratio of 1:(0.1~0.5), and pre-calcine and activate them in a closed environment with an inert atmosphere to obtain a mixture.

[0008] S2. Grind the mixture, then acid wash and water wash, and dry to obtain powdered carbon material;

[0009] S3. Carbonize the powdered carbon material in an inert atmosphere to obtain coal-based hard carbon material.

[0010] Preferably, in step S1, the pre-calcination activation temperature is 300–600°C, the heating rate is 1–5°C / min, and the holding time is 1–3 h.

[0011] Preferably, the raw coal includes one or more of lignite, long-flame coal, bituminous coal, and anthracite.

[0012] Preferably, the halide includes one or more of ammonium fluoride, ammonium chloride, ammonium bromide and ammonium iodide.

[0013] Preferably, in step S2, pickling refers to treating the mixture with an acidic solution, wherein the acidic solution includes one or two of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid, and the total hydrogen ion concentration of the acidic solution is 6 to 12 mol / L.

[0014] More preferably, in step S2, the pickling time is 6 to 12 hours.

[0015] Preferably, in step S2, the drying temperature is 60-80°C and the drying time is 8-12 hours.

[0016] Preferably, in step S3, the carbonization temperature is 900–1500°C, the carbonization heating rate is 1–5°C / min, and the holding time is 1–3 h.

[0017] In a second aspect, the present invention provides a halide-modified coal-based hard carbon material, prepared based on the above-described preparation method.

[0018] In a third aspect, the present invention proposes an application of a halide-modified coal-based hard carbon material, which is used in sodium-ion batteries.

[0019] Beneficial effects:

[0020] This invention utilizes the directional catalytic effect of halogen free radicals to deconstruct the aromatic rings of raw coal and generate halogen hydrides. This process creates porosity during carbonization, resulting in a coal-based hard carbon material with a layered structure (0.38-0.40 nm) suitable for sodium ions and high porosity. When used as a negative electrode material for sodium-ion batteries, the coal-based hard carbon prepared by this invention can significantly improve sodium storage capacity while maintaining a suitable specific surface area, achieving a capacity of 20 mA·g. -1 Reversible specific capacity at current density reaches 280–320 mAh·g -1 (of which the platform capacity accounts for >60%), it has excellent rate performance, at 1A·g -1 It still retains 150–200 mAh·g at current density -1 Reversible capacity (retention rate > 75%). Attached Figure Description

[0021] Figure 1 This is a SEM image of the coal-based hard carbon material prepared in Example 1 of this invention;

[0022] Figure 2 The image shows the XRD pattern of the coal-based hard carbon material prepared in Example 1 of this invention.

[0023] Figure 3 This is an adsorption-desorption curve of the coal-based hard carbon material prepared in Example 1 of the present invention;

[0024] Figure 4 The coal-based hard carbon material prepared in Example 1 of this invention is at 20 mA·g -1 Charge-discharge curves at current density;

[0025] Figure 5 The following is a rate performance diagram of the coal-based hard carbon material prepared in Example 1 of this invention at different current densities;

[0026] Figure 6 This is a SEM image of the coal-based hard carbon material prepared in Example 2 of the present invention;

[0027] Figure 7 The coal-based hard carbon material prepared in Example 2 of this invention is at 20 mAg -1 Charge-discharge curves at current density;

[0028] Figure 8 The graph shows the rate performance of the coal-based hard carbon material prepared in Example 2 of this invention at different current densities. Detailed Implementation

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0030] This invention proposes a halide-modified coal-based hard carbon material, prepared from coal raw materials and halides, and the specific preparation method is as follows:

[0031] S1. The raw coal and halide are mixed and ground, and then pre-calcined and activated in a closed environment with an inert atmosphere to obtain a mixture.

[0032] S2. Grind the mixture into powder, acid wash, then wash with water and dry to obtain powdered carbon material;

[0033] S3. Carbonize the powdered carbon material in an inert atmosphere to obtain coal-based hard carbon material.

[0034] In this invention, raw coal is mixed with halides and then subjected to low-temperature pre-carbonization treatment. During this process, a large number of halogen free radicals generated by the halides attack the aromatic structure of the coal itself, causing the aromatic rings to decompose and generating halogen hydrides. This promotes the transformation of the coal's molecular structure from ordered to disordered, forming a rich and stable porous structure. This results in a layered structure (0.38–0.40 nm) suitable for sodium ions and high porosity, thereby increasing the sodium storage capacity of the final coal-based hard carbon material. The layered structure refers to a microstructural feature in hard carbon materials where the interlayer spacing between carbon layers is enlarged, specifically manifested as the carbon interlayer spacing d. 002 The value is significantly larger than the interlayer spacing of graphite (approximately 0.335 nm). The extended layer structure can accommodate the large size of sodium ions (compared to lithium ions).

[0035] In step S1, the pre-calcination activation temperature is 300–600°C. Preferably, in step S1, the pre-calcination activation rate is 1–5°C / min, and the holding time is 1–3 hours, i.e., holding at the activation temperature for 1–3 hours after reaching the activation temperature. The inert atmosphere in step S1 is formed by an inert gas, such as nitrogen or argon, for pre-calcination activation.

[0036] In this invention, halides decompose at 300–600°C, generating a large number of halogen free radicals (·X). These free radicals attack the aromatic rings in the coal, breaking the C-C bonds and preventing the rearrangement and graphitization of the aromatic layers during subsequent heating. This temperature range allows for sufficient release of free radicals, preserving the defects and micropores created by the free radicals, without causing the carbon layers to close immediately. If the temperature exceeds 600°C, the aromatic layers rapidly grow laterally and stack, d 002When the size is reduced to <0.37nm, sodium ions are difficult to insert, resulting in a decrease in sodium storage capacity. Furthermore, the microporous / mesoporous sintering and porosity of the final product are reduced, leading to a deterioration in both rate capability and ICE (internal emission factor).

[0037] In step S1, the mass ratio of raw coal to halide is 1:(0.1~0.5). Excessive halide will release too high a concentration of X, which will "shred" the aromatic flakes too finely, leading to a decrease in the rigidity of the carbon layer. This makes it prone to collapse during subsequent high-temperature carbonization, which in turn makes d... 002 When the layer shrinks to <0.37nm, the extended structure disappears.

[0038] Raw coal refers to coal that has undergone acid washing and deashing treatment. Preferably, this invention selects coal types that are easily decomposed by halogen free radicals based on the characteristics of coal such as aroma, large interlayer spacing, and many defects. Specifically, raw coal includes one or more of lignite, long-flame coal, bituminous coal, and anthracite.

[0039] Halides include one or more of ammonium fluoride (NH4F), ammonium chloride (NH4Cl), ammonium bromide (NH4Br), and ammonium iodide (NH4I).

[0040] Preferably, ammonium halides are chosen in this invention because: NH4X undergoes one-step pyrolysis in the low-temperature range, simultaneously releasing 1. active free radicals ·X (Cl·, Br·, I·, etc.) that directly attack aromatic rings; 2. reducing gas HX, which simultaneously etches and creates pores; and 3. NH3, providing a localized reducing atmosphere and inhibiting excessive oxidation. This synergistic effect cannot be fully provided by alkali metal halides (NaCl, KBr, etc.) or metal halides (FeCl3, AlCl3) in a single heat treatment. Moreover, the use of metal halides easily leaves residual metal impurities.

[0041] This invention includes two grinding processes. The grinding in step S1 ensures that the coal and halides are fully and evenly mixed. The grinding in step S2 is because the pre-calcined and activated mixture will slightly clump together and needs to be further ground and dispersed. Grinding into powder also facilitates acid washing.

[0042] In step S2, the pickling process uses one or two acidic solutions of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid. Preferably, the total hydrogen ion concentration of the acidic solution is 6–12 mol / L, and the acidic solution is in excess relative to the mixture. Preferably, the pickling process uses hydrochloric acid with a concentration of 6–12 mol / L, more preferably 6–10 mol / L.

[0043] The pickling process of this invention can remove residual halides. More importantly, the pickling process is related to the ash content after coal pre-calcination and activation, that is, it is related to the type of coal. If the silicate content in the ash is high, hydrofluoric acid is required, i.e., hydrofluoric acid + hydrochloric acid / nitric acid / sulfuric acid. Hydrofluoric acid removes silicates, and hydrochloric acid / nitric acid / sulfuric acid removes metal oxides such as iron and aluminum. The two acids are used together, and the pickling can be completed in a short time at room temperature.

[0044] In step S2, the pickling time is 6 to 12 hours. Specifically, the mixture is immersed in acid solution for pickling, and magnetic stirring is used to assist the process, for example, the stirring speed is 500 rpm.

[0045] In step S2, drying is carried out in a forced-air drying oven at a temperature of 60-80°C. After acid washing and water washing, the moisture needs to be fully removed before drying, and the drying time is 8-12 hours.

[0046] In step S3, the carbonization temperature is 900–1500℃. Preferably, the carbonization heating rate is 1–5℃ / min, and the holding time is 1–3 hours, meaning the holding time after reaching the carbonization temperature is 1–3 hours. The inert atmosphere in step S3 is formed by an inert gas, such as nitrogen or argon. If the carbonization temperature in step S3 is too high, the hard carbon material will transform into a "graphite-like" structure, losing its unique advantages of large interlayer spacing and multiple closed pores, resulting in a significant deterioration in sodium storage capacity and rate performance.

[0047] The preferred particle size of the halide-modified coal-based hard carbon material prepared by the above method is 5–10 μm. The halide-modified coal-based hard carbon material can be used to prepare anode materials. For example, halide-modified coal-based hard carbon material, SP carbon black, and sodium carboxymethyl cellulose are added to a ball mill jar in a mass ratio of 80%:10%:10%, and ball-milled to obtain anode slurry. The anode slurry is then coated onto the surface of a copper foil and dried to obtain anode sheet, which can be used to prepare sodium-ion batteries.

[0048] The technical solution of the present invention will be described in detail below with specific embodiments.

[0049] Example 1

[0050] 10g of acid-washed and deashed anthracite was ground and mixed with 3g of NH4Br (mass ratio 1:0.3) for 30min, placed in a covered porcelain boat, and pre-carbonized at 400℃ for 2h under argon atmosphere at a rate of 3℃ / min to obtain the mixture.

[0051] The mixture was ground into powder, and then acid-washed with a mixture of 6 mol / L HCl and 6 mol / L HF for 10 h. After vacuum filtration and washing with water until neutral, the mixture was dried at 70°C for 10 h.

[0052] The coal-based hard carbon material was carbonized in argon gas at a rate of 5℃ / min to 1000℃ for 2 hours to obtain a halide-modified material.

[0053] The coal-based hard carbon material, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. This paste was coated onto copper foil, vacuum dried at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 coin cells were assembled in an argon glove box. Electrochemical performance tests were then conducted on the Xinwei Battery Testing System.

[0054] Characterization tests were performed on coal-based hard carbon materials, such as... Figure 1 The SEM images show that the surface of coal-based hard carbon becomes rough (approximately 10 μm in diameter) after high-temperature carbonization treatment, and from... Figure 2 The XRD images showed relatively obvious (002) and (100) peaks. Further analysis of the specific surface area of ​​the hard carbon material by CO2 adsorption-desorption was performed. Figure 3 From this, we can conclude that the specific surface area of ​​the hard carbon is 9 cm². 2 g -1 .

[0055] The electrochemical performance test results are as follows: Figure 4-5 As shown, where Figure 4 The coal-based hard carbon material HC-1 prepared in Example 1 was subjected to a temperature of 20 mA·g. -1 Charge-discharge curves at current density Figure 5 This is a rate performance graph of the coal-based hard carbon material HC-1 prepared in Example 1 at different current densities. Figure 5 It can be seen that the half-cell with HC-1 as the negative electrode material has a capacitance of 0.02 A·g -1 The reversible specific capacity at current density can reach 300 mAh·g -1 , in 1A·g -1 It can still retain 150-200 mAh·g under high current density -1 .

[0056] Example 2

[0057] 10g of acid-washed deashed bituminous coal was ground and mixed with 4g of NH4I (mass ratio 1:0.4) for 40min, and then pre-carbonized in argon at 500℃ for 1h by heating at 1℃ / min to obtain the mixture.

[0058] The mixture was ground into powder, and then acid-washed with 12 mol / L HCl for 6 hours, followed by washing with water and drying.

[0059] Carbonization was carried out at 1℃ / min up to 1500℃ for 1 hour to finally obtain coal-based hard carbon materials.

[0060] The coal-based hard carbon material, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. This paste was coated onto copper foil, vacuum dried at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 coin cells were assembled in an argon glove box. Electrochemical performance tests were then conducted on the Xinwei Battery Testing System.

[0061] Characterization tests were performed on hard carbon materials, such as... Figure 6 The SEM images show that the hard carbon surface becomes rough (approximately 10 μm in diameter) after high-temperature carbonization.

[0062] The electrochemical performance test results are shown in the figure below. Figure 7 The coal-based hard carbon material HC-2 prepared in Example 2 was subjected to a temperature of 20 mA·g. -1 Charge-discharge curves at current density Figure 8 This is a rate performance graph of the coal-based hard carbon material HC-2 prepared in Example 2 at different current densities. Figure 7 It can be seen that the half-cell with HC-2 as the negative electrode material has a capacitance of 0.02 A·g -1 The reversible specific capacity at current density can reach 310 mAh·g -1 , in 1A·g -1 It can still retain 200-210 mAh·g even under high current density -1 .

[0063] Example 3

[0064] Take 10g of acid-washed deashed bituminous coal and grind it with 2g of NH4Cl (mass ratio 1:0.2), and pre-carbonize it at 300℃ for 3h by heating at 5℃ / min to obtain a mixture.

[0065] The mixture was ground into powder, and then acid-washed with a mixed solution of 8 mol / L H2SO4 + 6 mol / L HNO3 for 12 h, and dried at 60℃ for 12 h.

[0066] Carbonization was carried out at 3℃ / min up to 900℃ for 3 hours to finally obtain coal-based hard carbon materials.

[0067] The coal-based hard carbon, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. The paste was coated onto copper foil, dried under vacuum at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0068] Example 4

[0069] 10g of acid-washed and de-ashed lignite was mixed with 1g of NH4F (mass ratio 1:0.1), and the mixture was pre-carbonized at 350℃ for 2.5h by heating at 2℃ / min to obtain the mixture.

[0070] The mixture was ground into powder, and then acid-washed with 10 mol / L HF for 8 hours and dried at 75°C for 9 hours.

[0071] Carbonization was carried out at 1200℃ for 1.5 hours at a rate of 4℃ / min to finally obtain coal-based hard carbon materials.

[0072] The coal-based hard carbon, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. The paste was coated onto copper foil, dried under vacuum at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0073] Example 5

[0074] Take 10g of acid-washed and deashed long-flame coal and grind it together with 2.5g of NH4Br / NH4I mixture (1:1, coal:halide = 1:0.25), and pre-carbonize it at 450℃ for 2h by heating at 4℃ / min.

[0075] The mixture was ground into powder, and then acid-washed with a 9 mol / L HCl + HF mixture for 9 h and dried at 65 °C for 11 h.

[0076] Carbonization was carried out at 1300℃ for 2 hours at a rate of 2℃ / min to finally obtain coal-based hard carbon materials.

[0077] The coal-based hard carbon, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. The paste was coated onto copper foil, dried under vacuum at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0078] Example 6

[0079] 10g of acid-washed and deashed bituminous coal and 3.5g of NH4Cl+NH4Br mixture (mass ratio 1:1, coal:halide = 1:0.35) were ground together for 40min and then pre-carbonized at 450℃ for 2.5h in argon atmosphere at a temperature of 4℃ / min to obtain the mixture.

[0080] The mixture was ground into powder, and then acid-washed with a mixture of 10 mol / L HCl and 8 mol / L HF for 11 h. After being vacuum filtered and washed with water until neutral, it was dried at 75°C for 10 h.

[0081] Coal-based hard carbon was obtained by carbonizing in argon gas at a temperature of 1100℃ for 2 hours at a rate of 3℃ / min.

[0082] The coal-based hard carbon, SP carbon black, and sodium carboxymethyl cellulose were ball-milled and mixed at a mass ratio of 80:10:10. Deionized water was added and stirred into a paste. The paste was coated onto copper foil, dried under vacuum at 60°C for 12 hours, and then cut into negative electrode sheets. Using sodium metal as the counter electrode, a glass fiber membrane as the separator, and 1M NaPF6 DME as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0083] The embodiments provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention, and the descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a halide-modified coal-based hard carbon material, characterized in that, as follows: S1. Mix and grind the raw coal and the halide at a mass ratio of 1:(0.1~0.5), and pre-calcine and activate them in a closed environment with an inert atmosphere to obtain a mixture. S2. Grind the mixture into powder, acid wash, then wash with water and dry to obtain powdered carbon material; S3. Carbonize the powdered carbon material in an inert atmosphere to obtain coal-based hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step S1, the pre-calcination activation temperature is 300–600°C, the heating rate is 1–5°C / min, and the holding time is 1–3 h.

3. The preparation method according to claim 1, characterized in that, Raw coal includes one or more of lignite, long-flame coal, bituminous coal, and anthracite.

4. The preparation method according to claim 1, characterized in that, Halides include one or more of ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide.

5. The preparation method according to claim 1, characterized in that, In step S2, pickling refers to treating the mixture with an acidic solution, wherein the acidic solution includes one or two of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid, and the total hydrogen ion concentration of the acidic solution is 6 to 12 mol / L.

6. The preparation method according to claim 5, characterized in that, In step S2, the pickling time is 6 to 12 hours.

7. The preparation method according to claim 1, characterized in that, In step S2, the drying temperature is 60-80℃ and the drying time is 8-12h.

8. The preparation method according to claim 1, characterized in that, In step S3, the carbonization temperature is 900–1500℃, the carbonization heating rate is 1–5℃ / min, and the holding time is 1–3h.

9. A halide-modified coal-based hard carbon material, characterized in that, Prepared according to the preparation method described in any one of claims 1-8.

10. An application of a halide-modified coal-based hard carbon material, characterized in that, The coal-based hard carbon material of claim 9 is used in sodium-ion batteries.

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