Hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses a kind of hard carbon negative electrode material and preparation method thereof, the preparation method includes: porous carbon is mixed with sugar class sealing agent and catalyst, first heat treatment is carried out under inert atmosphere, and primary coated porous carbon is obtained;The primary coated porous carbon is mixed with polymer sealing agent, and second heat treatment is carried out under inert atmosphere, and hard carbon negative electrode material is obtained.The application adopts two-step in-situ solid-phase sealing process, without using solvent and flammable and explosive carbon source gas, and the process is safe and environmentally friendly;The obtained hard carbon material has rich closed-cell structure, low specific surface area, and has high specific capacity and high initial coulomb efficiency when used as sodium-ion battery negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation technology, specifically to a hard carbon anode material and its preparation method. Background Technology

[0002] Under the global "dual carbon" goal, the large-scale utilization of renewable energy urgently requires low-cost, highly safe, and large-scale energy storage technologies. Lithium-ion batteries, affected by the scarcity and price fluctuations of lithium resources, are difficult to fully adapt to large-scale energy storage scenarios. Sodium-ion batteries, due to abundant sodium resources, low cost, and safety and reliability, have become an ideal alternative. Hard carbon, as an amorphous disordered carbon material, possesses a unique microstructure and can store sodium through various methods. Its laboratory specific capacity can reach 300-500 mAh / g, demonstrating significant performance advantages and making it a core research focus and the preferred material for practical application in sodium-ion battery anode materials. Research shows that constructing abundant closed-pore structures in hard carbon helps improve its low-voltage plateau capacity.

[0003] Sealing porous carbon is an effective method to obtain closed-cell structures. Existing technologies mainly fall into two categories: First, liquid-phase sealing, which involves dissolving a sealing agent in a solvent, adding porous carbon, evaporating the solvent, and then carbonizing to obtain hard carbon materials (e.g., patent applications CN202310412244.X, CN202511148826.7, and CN202510487039.9). This method involves the use and evaporation of solvents, increasing the process and cost. Second, gas-phase sealing, which uses carbon source gases for chemical vapor deposition (e.g., patent applications CN202511353448.6, CN202411345182.6, and CN202410340011.8). This method requires the use of alkane, alkene, benzene, or alkyne gases, whose flammable and explosive properties impose extremely high safety requirements on equipment and operation.

[0004] Therefore, developing a method for preparing hard carbon materials that requires no solvents or combustible gases, has a simple process, and can effectively construct a rich closed-pore structure is of great practical significance. Summary of the Invention

[0005] This invention aims to address the technical problems in existing technologies for sealing porous carbon: liquid-phase sealing requires solvents, increasing process costs and complexity, while gas-phase sealing requires flammable and explosive carbon source gases, posing safety hazards. This invention provides a simple two-step in-situ solid-phase sealing process to seal porous carbon without the use of solvents or combustible gases, resulting in a high-performance hard carbon anode material with abundant closed-pore structures, along with its preparation method and applications.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing a hard carbon anode material includes the following steps:

[0008] Porous carbon is mixed with a sugar-based sealing agent and a catalyst, and then subjected to a first heat treatment under an inert atmosphere to obtain one-time coated porous carbon.

[0009] The primary coated porous carbon is mixed with a polymer sealing agent and subjected to a second heat treatment under an inert atmosphere to obtain the hard carbon anode material.

[0010] This invention employs a two-step in-situ solid-phase sealing process, the core reaction mechanism of which is as follows:

[0011] First heat treatment (pre-sealing of pores with sugars):

[0012] Porous carbon (specific surface area 1000-2000 m² / g) is uniformly mixed with sugar sealing agents (sucrose, glucose or fructooligosaccharides) and catalyst ammonium chloride, and then subjected to programmed temperature rise heat treatment in an inert atmosphere.

[0013] First, the temperature is raised to 110-180℃ and held for 1-1.5 hours. Within this temperature range, the sugar-based sealing agent melts and softens, utilizing its good fluidity to penetrate into the open pores of the porous carbon. Simultaneously, the catalyst ammonium chloride begins to sublimate or decompose at this temperature, producing ammonia (NH3) and hydrogen chloride (HCl) gases. These gases activate the sugar molecules and promote cross-linking.

[0014] Subsequently, the temperature is raised to 400-600℃ and held for 1-2 hours. Within this temperature range, the following key reactions occur:

[0015] Carbohydrate carbonization: Carbohydrate molecules that have penetrated into the pores of porous carbon undergo pyrolysis and carbonization to generate amorphous carbon, which covers the surface of the pore walls and initially fills the open pores, significantly reducing the specific surface area of ​​porous carbon from 1000-2000 m² / g to 80-120 m² / g.

[0016] Pore ​​shrinkage: The carbon layer formed by the carbonization of sugars is deposited at the opening of the open pores, and at the same time, the carbon atoms undergo preliminary rearrangement, turning the originally open pores into a semi-closed or closed state.

[0017] Second heat treatment (high-temperature sealing and densification of polymer):

[0018] The primary coated porous carbon, after undergoing initial heat treatment and crushing and grading, is mixed with a polymer sealing agent (polystyrene, polyethylene, or polypropylene powder) and then subjected to higher temperature heat treatment in an inert atmosphere.

[0019] First, the temperature is raised to 700-850℃ and held for 1-2 hours. Within this temperature range, the polymer sealing agent melts and undergoes pyrolysis and carbonization. Due to the relatively long polymer molecular chains, a continuous and dense carbon layer is formed after pyrolysis. Simultaneously, the polymer pyrolysis produces hydrocarbon gases, which undergo in-situ carbon deposition at high temperatures, further covering and filling any remaining open pores.

[0020] Subsequently, the temperature is raised to 1200-1600℃ and held for 1-2 hours. Within this high-temperature range, the following key reactions occur:

[0021] Formation of graphitized micro-regions in carbon layers: Amorphous carbon undergoes localized graphitization, the carbon layer structure tends to be ordered, the interlayer spacing decreases, and residual pores are further closed.

[0022] Defect repair: High temperatures induce carbon atoms to rearrange, repairing the defective structures between carbon atoms.

[0023] Significantly reduced specific surface area: After high-temperature densification, the specific surface area of ​​the material eventually drops to 5-10 m² / g, indicating that the vast majority of open pores have been effectively sealed.

[0024] Through the above two-step in-situ solid-phase sealing process, this invention successfully constructs abundant closed-pore structures in a porous carbon matrix without using any solvents or flammable and explosive carbon source gases. These closed-pore structures can provide additional active sites for sodium ion storage, thereby significantly improving the low-voltage plateau capacity and first coulombic efficiency of the hard carbon anode material.

[0025] Preferably, the porous carbon has a specific surface area of ​​1000-2000 m² / g.

[0026] Preferably, the sugar sealing agent is selected from at least one of sucrose, glucose or fructooligosaccharides; and the catalyst is ammonium chloride.

[0027] Preferably, the first heat treatment includes: heating to 110-180℃ at a heating rate of 5-10℃ / min and holding for 1-1.5 hours, and then heating to 400-600℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours.

[0028] Preferably, the second heat treatment includes: heating to 700-850℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours, and then heating to 1200-1600℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours.

[0029] Preferably, the polymer sealing agent is selected from at least one of polystyrene powder, polyethylene powder, or polypropylene powder.

[0030] Preferably, the amount of the saccharide sealing agent is 200%-500% of the mass of the porous carbon, and the amount of the catalyst is 0.5%-1.5% of the mass of the saccharide sealing agent.

[0031] Preferably, the amount of the polymer sealing agent is 4%-8% of the mass of the porous carbon coated in one step.

[0032] Preferably, after the first heat treatment and before the second heat treatment, the process further includes a step of crushing and classifying the first-coated porous carbon to 300-400 mesh.

[0033] The present invention also protects a hard carbon anode material, which is prepared by any of the preparation methods described above.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. Safe and environmentally friendly process: The process adopts two in-situ solid-phase sealing, completely avoiding the use of organic solvents and flammable and explosive carbon source gases, thus avoiding the cost and treatment problems caused by solvent evaporation, eliminating the safety hazards of gas leakage and explosion, and making the process green and safe.

[0036] 2. Abundant closed-cell structures: Through the synergistic effect of pre-sealing with sugars and high-temperature sealing with polymers, the high specific surface area of ​​porous carbon (1000-2000 m² / g) is effectively reduced to 5-10 m² / g, indicating that the open pores are fully filled or closed, forming a large number of stable closed-cell structures.

[0037] 3. Excellent electrochemical performance: The abundant closed-pore structure provides more storage sites for sodium ions. The hard carbon anode material prepared exhibits high specific capacity (≥400 mAh / g) and high first coulombic efficiency (≥88.9%), which is better than most existing hard carbon materials.

[0038] 4. Simple process and easy to scale up: The two-step method involves solid-phase mixing and conventional tubular furnace heat treatment, without involving complex liquid-phase treatment or vapor deposition equipment. It is easy to operate and can be easily industrialized. Attached Figure Description

[0039] Figure 1 This is a SEM image of the sodium-ion battery hard carbon material prepared in Example 1 of this invention.

[0040] Figure 2 This is a charge-discharge curve of the sodium-ion battery hard carbon material prepared in Example 1 of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0042] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0043] Example 1

[0044] Step 1: Mix 10g of porous carbon (specific surface area of ​​1500 m² / g), 35g of glucose and 0.35g of ammonium chloride evenly.

[0045] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and purge with nitrogen for protection. Heat to 110°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 400°C at a heating rate of 5°C / min and hold for 1 hour. Allow to cool naturally to room temperature before discharging, completing the first heat treatment. The specific surface area of ​​the porous carbon coated once was measured to be 85.2 m² / g.

[0046] Step 3: Crush and classify the single-coated porous carbon obtained in Step 2, and sieve it to 300-400 mesh.

[0047] Step 4: Take 10g of the one-time coated porous carbon obtained in Step 3 and mix it evenly with 0.5g of polystyrene powder.

[0048] Step 5: Transfer the mixture obtained in Step 4 to a tube furnace and purge with nitrogen for protection. Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 hour; then heat to 1400℃ at a heating rate of 5℃ / min and hold for 1 hour. Allow to cool naturally to room temperature before discharging to obtain the hard carbon anode material for sodium-ion batteries. The specific surface area of ​​the final material was measured to be 6.6 m² / g. Its SEM image is shown below. Figure 1 As shown, the charge-discharge curves are as follows: Figure 2 As shown.

[0049] Example 2

[0050] Step 1: Mix 10g of porous carbon (specific surface area of ​​1500 m² / g), 40g of sucrose and 0.4g of ammonium chloride evenly.

[0051] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and purge with argon gas for protection. Heat to 125°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 450°C at a heating rate of 5°C / min and hold for 1 hour. After natural cooling, discharge the material to complete the first heat treatment. The specific surface area of ​​the porous carbon coated once was measured to be 81.3 m² / g.

[0052] Step 3: Crush and classify the single-coated porous carbon obtained in Step 2, and sieve it to 300-400 mesh.

[0053] Step 4: Take 10g of the one-time coated porous carbon obtained in Step 3 and mix it evenly with 0.5g of polystyrene powder.

[0054] Step 5: Transfer the mixture obtained in Step 4 to a tube furnace and purge with argon gas for protection. Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 hour; then heat to 1400℃ at a heating rate of 5℃ / min and hold for 1 hour. Allow to cool naturally to room temperature and discharge to obtain the hard carbon anode material for sodium-ion batteries. The specific surface area of ​​the final material was measured to be 5.2 m² / g.

[0055] Example 3

[0056] Step 1: Mix 10g of porous carbon (specific surface area of ​​1500 m² / g), 30g of fructooligosaccharides and 0.3g of ammonium chloride evenly.

[0057] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and purge with nitrogen for protection. Heat to 150°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 500°C at a heating rate of 5°C / min and hold for 1 hour. After natural cooling, discharge the material to complete the first heat treatment. The specific surface area of ​​the porous carbon coated once was measured to be 92.5 m² / g.

[0058] Step 3: Crush and classify the single-coated porous carbon obtained in Step 2, and sieve it to 300-400 mesh.

[0059] Step 4: Take 10g of the one-time coated porous carbon obtained in Step 3 and mix it evenly with 0.5g of polystyrene powder.

[0060] Step 5: Transfer the mixture obtained in Step 4 to a tube furnace and purge with nitrogen for protection. Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 hour; then heat to 1400℃ at a heating rate of 5℃ / min and hold for 1 hour. Allow to cool naturally to room temperature and discharge to obtain the hard carbon anode material for sodium-ion batteries. The specific surface area of ​​the final material was measured to be 7.2 m² / g.

[0061] Example 4

[0062] Step 1: Mix 10g of porous carbon (specific surface area of ​​1500 m² / g), 35g of glucose and 0.35g of ammonium chloride evenly.

[0063] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and purge with nitrogen for protection. Heat to 110°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 400°C at a heating rate of 5°C / min and hold for 1 hour. After natural cooling, discharge the material to complete the first heat treatment. The specific surface area of ​​the porous carbon coated once was measured to be 86.0 m² / g.

[0064] Step 3: Crush and classify the single-coated porous carbon obtained in Step 2, and sieve it to 300-400 mesh.

[0065] Step 4: Take 10g of the one-time coated porous carbon obtained in Step 3 and mix it evenly with 0.6g of polyethylene powder.

[0066] Step 5: Transfer the mixture obtained in Step 4 to a tube furnace and purge with nitrogen for protection. Heat to 800℃ at a heating rate of 5℃ / min and hold for 1 hour; then heat to 1400℃ at a heating rate of 5℃ / min and hold for 1 hour. Allow to cool naturally to room temperature and discharge to obtain the hard carbon anode material for sodium-ion batteries. The specific surface area of ​​the final material was measured to be 5.9 m² / g.

[0067] Example 5

[0068] Step 1: Mix 10g of porous carbon (specific surface area of ​​1500 m² / g), 35g of glucose and 0.35g of ammonium chloride evenly.

[0069] Step 2: Transfer the mixture obtained in Step 1 to a tube furnace and purge with nitrogen for protection. Heat to 110°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 400°C at a heating rate of 5°C / min and hold for 1 hour. After natural cooling, discharge the material to complete the first heat treatment. The specific surface area of ​​the porous carbon coated once was measured to be 86.3 m² / g.

[0070] Step 3: Crush and classify the single-coated porous carbon obtained in Step 2, and sieve it to 300-400 mesh.

[0071] Step 4: Take 10g of the one-time coated porous carbon obtained in Step 3 and mix it evenly with 0.6g of polypropylene powder.

[0072] Step 5: Transfer the mixture obtained in Step 4 to a tube furnace and purge with nitrogen for protection. Heat to 850°C at a heating rate of 5°C / min and hold for 1 hour; then heat to 1400°C at a heating rate of 5°C / min and hold for 1 hour. Allow to cool naturally to room temperature before discharging to obtain the hard carbon anode material for sodium-ion batteries. The specific surface area of ​​the final material was measured to be 8.8 m² / g.

[0073] Electrochemical performance testing

[0074] The hard carbon anode materials prepared in Examples 1-5 were subjected to half-cell tests. The specific methods are as follows:

[0075] Hard carbon material, Super-P, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were homogenized for 30 minutes at ratios of 92%, 3%, 1.5%, and 3.5% respectively to obtain a uniform electrode slurry. The slurry was coated onto an aluminum foil current collector to a thickness of 100 micrometers. The electrode was then vacuum-dried at 80°C for 12 hours to obtain the electrode sheet. A sodium sheet was used as the counter electrode, 1M sodium hexafluorophosphate (solvents being ethylene carbonate and diethyl carbonate, volume ratio 1:1) as the electrolyte, and a glass fiber membrane as the separator. CR2032 coin cells were assembled in an argon-filled glove box. The test results are shown in Table 1 below.

[0076] Table 1 shows the specific surface area and electrochemical performance test results of the examples.

[0077] project <![CDATA[Specific surface area after primary sealing (m 2 / g)]]> <![CDATA[Specific surface area after secondary sealing (m 2 / g)]]> Initial charge capacity (mAh / g) First-time efficiency (%) Example 1 85.2 6.6 420 90.9 Example 2 81.3 5.2 411 91.5 Example 3 92.5 7.2 405 89.6 Example 4 86.0 5.9 425 91.1 Example 5 86.3 8.8 409 88.9

[0078] As can be seen from the test data in Table 1, the specific surface area of ​​porous carbon decreased significantly after two in-situ solid-phase sealing processes. Furthermore, due to the abundant closed-pore structure of the resulting hard carbon material, it exhibited high capacity and first-pass efficiency.

[0079] Figure 1 This indicates that after two in-situ solid-phase sealing processes, the material surface is smooth, and the porous carbon is fully coated. From Figure 2 It can be seen that the coated hard carbon material has a long plateau capacity, indicating the formation of abundant closed-cell structures. At the same time, due to the low specific surface area and few surface defects of the resulting hard carbon material, its first-pass efficiency is very high.

[0080] The above embodiments illustrate in detail the specific implementation of the technical solution of the present invention, the logical and connection relationships of each component, and the complete working process. Those skilled in the art will understand that various changes and modifications can be made to the above embodiments without departing from the principles and spirit of the present invention, and all such changes and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, Includes the following steps: Porous carbon is mixed with a sugar-based sealing agent and a catalyst, and then subjected to a first heat treatment under an inert atmosphere to obtain one-time coated porous carbon. The primary coated porous carbon is mixed with a polymer sealing agent and subjected to a second heat treatment under an inert atmosphere to obtain the hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the porous carbon is 1000-2000 m² / g.

3. The preparation method according to claim 1, characterized in that, The pore-sealing agent is selected from at least one of sucrose, glucose, or fructooligosaccharides; the catalyst is ammonium chloride.

4. The preparation method according to claim 1, characterized in that, The first heat treatment includes: heating to 110-180℃ at a heating rate of 5-10℃ / min and holding for 1-1.5 hours, and then heating to 400-600℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours.

5. The preparation method according to claim 1, characterized in that, The second heat treatment includes: heating to 700-850℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours, and then heating to 1200-1600℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours.

6. The preparation method according to claim 1, characterized in that, The polymer sealing agent is selected from at least one of polystyrene powder, polyethylene powder, or polypropylene powder.

7. The preparation method according to claim 1, characterized in that, The amount of the saccharide sealing agent is 200%-500% of the mass of the porous carbon, and the amount of the catalyst is 0.5%-1.5% of the mass of the saccharide sealing agent.

8. The preparation method according to claim 1, characterized in that, The amount of the polymer sealing agent is 4%-8% of the mass of the porous carbon coated in one step.

9. The preparation method according to claim 1, characterized in that, After the first heat treatment, the specific surface area of ​​the porous carbon decreases to 80-120 m² / g; after the second heat treatment, the specific surface area of ​​the hard carbon anode material decreases to 5-10 m² / g.

10. A hard carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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