High-rate pitch-based hard carbon as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to high-rate pitch-based hard carbon as well as a preparation method and application thereof. Industrial asphalt is subjected to oxidation treatment and then subjected to first high-temperature carbonization treatment, a hard carbon precursor and a mixed solution containing a coating agent are obtained, the coating agent and an organic solvent are mixed and stirred for dissolution, the obtained mixed solution is filtered, and filtrate containing soluble substances and insoluble substances are obtained respectively; the filtrate containing the soluble substances and the insoluble substances are mixed again according to the mass ratio of the soluble substances to the insoluble substances being 1: (0.1-5), heat treatment and second high-temperature carbonization treatment are conducted, and the high-magnification pitch-based hard carbon is obtained. Through a strategy of combining oxidation treatment with synergistic coating modification of soluble and insoluble components, the electrochemical performance and the rate characteristic of the hard carbon material are effectively improved, the process is simple, the cost is low, the coating components can be flexibly regulated and controlled, and the method is suitable for industrial application.

Description

Technical Field

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

[0002] With the rapid development of the new energy industry, sodium-ion batteries have become a research hotspot in the field of large-scale energy storage due to their abundant resources and low cost. Hard carbon materials, with their unique disordered carbon layer structure and large interlayer spacing, can achieve reversible insertion / extraction of sodium ions and are widely recognized as one of the most promising anode materials for sodium-ion batteries. The electrochemical performance of hard carbon materials, such as initial efficiency, rate performance, and cycle stability, largely depends on the material's microstructure, specific surface area, and surface chemical properties.

[0003] Fossil fuel feedstocks, represented by industrial asphalt, are gradually becoming the mainstream precursors for hard carbon materials due to their advantages such as high carbon content, stable raw material sources, and low prices. Converting asphalt into hard carbon through oxidation and carbonization processes is currently a commonly used technical route. However, unmodified asphalt-based hard carbon materials often suffer from problems such as excessively high specific surface area and too many surface defect sites, leading to severe electrolyte decomposition during charge and discharge. This results in the formation of an excessively thick and unstable solid electrolyte interphase (SEI) film, increasing the resistance to sodium ion migration, thus significantly reducing the material's initial coulombic efficiency and limiting its high-rate performance.

[0004] To improve rate performance, effective coating treatment of pitch-based hard carbon is necessary. Currently common surface coating technologies, such as solid-phase mechanical fusion coating, liquid-phase impregnation coating, and chemical vapor deposition (CVD) coating, generally suffer from problems such as uneven coating thickness, difficulty in precisely controlling the coating structure and composition, complex processes, high energy consumption, and high costs. In particular, traditional coating methods struggle to achieve dense coating while effectively reducing the overall impedance of the material. One related technology discloses a solid-phase coating technique that mixes a hard carbon precursor and a solid coating agent through mechanical grinding followed by heat treatment. While this method is simple, its solid-phase mixing method makes it difficult to ensure uniform distribution of the coating agent on the surface of the hard carbon particles, easily leading to uneven coating thickness or even localized exposure. Furthermore, the composition and structure of the coating agent are difficult to precisely control, ultimately affecting the coating effect and product consistency. Another technique involves dissolving the coating agent in a solvent to form a mixture, filtering it, and then using only the soluble solution for impregnation coating. Although more uniform liquid-phase coating is achieved by using soluble substances, the complete elimination of insoluble components results in the coating layer lacking components with larger molecular weights and higher degrees of aromatization. During subsequent carbonization, the lighter components are prone to volatilization and shedding, affecting the continuity and stability of the coating layer.

[0005] In summary, existing coating technologies still suffer from problems such as poor coating uniformity, insufficient flexibility in controlling the composition and structure of the coating layer, and poor long-term stability of the coating layer, resulting in low rate performance and high impedance of the prepared coated hard carbon materials. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a high-ratio asphalt-based hard carbon, its preparation method and application. This invention can achieve fine control of the coating layer components, and the prepared high-ratio asphalt-based hard carbon has uniform coating and stable structure, with excellent rate performance and low impedance.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-ratio pitch-based hard carbon, comprising the following steps: Industrial asphalt is oxidized in an oxidizing atmosphere, and the resulting oxidized asphalt is subjected to a first high-temperature carbonization treatment in a first protective atmosphere to obtain a hard carbon precursor. The hard carbon precursor and the mixture containing the coating agent are mixed and then heat-treated to obtain a hard carbon precursor with a coating layer. The hard carbon precursor with the coating layer is subjected to a second high-temperature carbonization treatment in a second protective gas to obtain high-ratio pitch-based hard carbon. The preparation method of the coating agent-containing mixture is as follows: the coating agent and an organic solvent are mixed and stirred to dissolve the mixture; the resulting mixture is filtered to obtain a filtrate containing soluble matter and an insoluble matter; the filtrate containing soluble matter and the insoluble matter are mixed to obtain the coating agent-containing mixture. Based on the mass of soluble matter dissolved in the filtrate containing soluble matter, the mass ratio of soluble matter to insoluble matter in the mixture containing the coating agent is 1:0.1~5.

[0008] Preferably, the industrial asphalt includes one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch; the softening point of the industrial asphalt is not lower than 150°C.

[0009] Preferably, the coating agent includes asphalt-based substances and / or resin-based substances.

[0010] Preferably, the asphalt-based substances include one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch; the resin-based substances include one or more of phenolic resin, epoxy resin, polyurethane resin, polyethylene, polypropylene, and polyimide.

[0011] Preferably, the mass ratio of the hard carbon precursor to the total mass of the coating agent is 1:0.01~0.12; the total mass of the coating agent is the sum of the masses of soluble and insoluble substances in the mixture containing the coating agent.

[0012] Preferably, the oxidation treatment temperature is 250~350℃, and the holding time is 2~8h.

[0013] Preferably, the heat treatment temperature is 200~300℃ and the holding time is 0.5~2h.

[0014] Preferably, the temperature of the first high-temperature carbonization treatment and the second high-temperature carbonization treatment are independently 1100~1500℃, and the holding time is independently 1~5h.

[0015] This invention also provides high-ratio pitch-based hard carbon prepared by the preparation method described above, wherein the specific surface area of ​​the high-ratio pitch-based hard carbon is ≤10 m². 2 / g, with an average pore size of 5.0±1.0μm.

[0016] The present invention also provides the application of the high-rate asphalt-based hard carbon described in the above technical solution in sodium-ion batteries.

[0017] This invention provides a method for preparing high-ratio pitch-based hard carbon, comprising the following steps: Industrial asphalt is oxidized in an oxidizing atmosphere, and the resulting oxidized asphalt is subjected to a first high-temperature carbonization treatment in a first protective atmosphere to obtain a hard carbon precursor. The hard carbon precursor and the mixture containing the coating agent are mixed and then heat-treated to obtain a hard carbon precursor with a coating layer. The hard carbon precursor with the coating layer is subjected to a second high-temperature carbonization treatment in a second protective gas to obtain high-ratio pitch-based hard carbon. The preparation method of the coating agent-containing mixture is as follows: the coating agent and an organic solvent are mixed and stirred to dissolve the mixture; the resulting mixture is filtered to obtain a filtrate containing soluble matter and an insoluble matter; the filtrate containing soluble matter and the insoluble matter are mixed to obtain the coating agent-containing mixture. Based on the mass of soluble matter dissolved in the filtrate containing soluble matter, the mass ratio of soluble matter to insoluble matter in the mixture containing the coating agent is 1:0.1~5.

[0018] The beneficial effects of this invention are as follows: First, it achieves precise design and controllable regulation of the coating layer components. The coating agent is separated into soluble and insoluble components through dissolution filtration, and these two components are innovatively used synergistically in a specific ratio. The insoluble components are mostly heavy polycyclic aromatic hydrocarbons with high molecular weight and thermal stability, serving as the "skeleton" of the coating layer to ensure structural stability. The soluble components are mostly light components with moderate molecular weight and good rheological properties, serving as "binders" and "fillers," effectively wetting the hard carbon core and filling surface micropores. By adjusting the ratio of the two components, the chemical composition and microstructure of the coating layer can be precisely designed, thereby customizing its electrochemical performance.

[0019] Secondly, the electrochemical performance of hard carbon materials, especially their rate performance, is significantly improved. This coating effectively reduces the specific surface area of ​​hard carbon, minimizing defect exposure and thus suppressing side reactions in the electrolyte during charge and discharge, resulting in a thinner and more stable SEI film. Simultaneously, the uniform and dense carbon coating exhibits excellent electronic conductivity, constructing a highly efficient electron transport network and greatly reducing charge transfer impedance. This significantly enhances the diffusion kinetics of sodium ions, enabling the hard carbon material prepared by this invention to possess excellent high-rate charge and discharge capabilities and low impedance.

[0020] Third, it is cost-effective. This method has broad requirements for the raw materials of the coating agent, and can utilize a variety of inexpensive and readily available asphalt or resin, effectively reducing raw material costs. At the same time, the process is simple and economical. Attached Figure Description

[0021] Figure 1 The graph shows a comparison of the rate performance of batteries assembled using the pitch-based hard carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Figure 2 The impedance comparison diagram shows the batteries assembled using the pitch-based hard carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0022] This invention provides a method for preparing high-ratio pitch-based hard carbon, comprising the following steps: Industrial asphalt is oxidized in an oxidizing atmosphere, and the resulting oxidized asphalt is subjected to a first high-temperature carbonization treatment in a first protective atmosphere to obtain a hard carbon precursor. The hard carbon precursor and the mixture containing the coating agent are mixed and then heat-treated to obtain a hard carbon precursor with a coating layer. The hard carbon precursor with the coating layer is subjected to a second high-temperature carbonization treatment in a second protective gas to obtain high-ratio pitch-based hard carbon. The preparation method of the coating agent-containing mixture is as follows: the coating agent and an organic solvent are mixed and stirred to dissolve the mixture; the resulting mixture is filtered to obtain a filtrate containing soluble matter and an insoluble matter; the filtrate containing soluble matter and the insoluble matter are mixed to obtain the coating agent-containing mixture. Based on the mass of soluble matter dissolved in the filtrate containing soluble matter, the mass ratio of soluble matter to insoluble matter in the mixture containing the coating agent is 1:0.1~5.

[0023] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0024] The present invention oxidizes industrial asphalt in an oxidizing atmosphere, and then performs a first high-temperature carbonization treatment on the resulting oxidized asphalt in a first protective gas to obtain a hard carbon precursor.

[0025] In one embodiment, the industrial asphalt includes one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch; the softening point of the industrial asphalt is not lower than 150°C, and in a specific embodiment it is 210°C or 220°C; before the oxidation treatment, the process further includes: pulverizing the industrial asphalt; the particle size of the industrial asphalt powder obtained after pulverization is ≤100μm.

[0026] In one embodiment, the oxidizing atmosphere is an air atmosphere or an oxygen atmosphere, specifically an air atmosphere; the air intake rate of the oxidizing atmosphere during the oxidation process is 100 mL / min to 1 L / min, specifically 500 mL / min; the heating rate to the oxidation treatment temperature is 0.5 to 5 °C / min, specifically 2 °C / min; the oxidation treatment temperature is 250 to 350 °C, specifically 300 °C, and the holding time is 2 to 8 hours, specifically 5 hours; based on industrial asphalt, the mass gain rate of the oxidized asphalt is ≥8%, specifically 9.5%.

[0027] In one embodiment, the first protective gas is nitrogen, helium, or argon, with nitrogen being used in a specific embodiment; the temperature of the first high-temperature carbonization treatment is 1100~1500℃, with 1300℃ being used in a specific embodiment, and the holding time is 1~5h, with 2h being used in a specific embodiment; the heating rate to the temperature of the first high-temperature carbonization treatment is 3~10℃ / min, with 5℃ / min being used in a specific embodiment; after the first high-temperature carbonization treatment, the process further includes: cooling the product of the first high-temperature carbonization treatment and then pulverizing it to a particle size ≤20μm.

[0028] After obtaining the hard carbon precursor, the present invention mixes the hard carbon precursor with a mixture containing a coating agent and then heat-treats it to obtain a hard carbon precursor with a coating layer.

[0029] In one embodiment, the preparation method of the coating agent-containing mixture is as follows: the coating agent and an organic solvent are mixed and stirred to dissolve; the resulting mixture is filtered to obtain a filtrate containing soluble matter and an insoluble matter; the filtrate containing soluble matter and the insoluble matter are mixed to obtain the coating agent-containing mixture. This invention does not have a particular limitation on the stirring rate, as long as it is sufficient to fully dissolve the coating agent.

[0030] In one embodiment, the coating agent includes asphalt-based substances and / or resin-based substances, with asphalt-based substances being used in a specific embodiment; the asphalt-based substances include one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch, with coal tar pitch being used in a specific embodiment; the resin-based substances include one or more of phenolic resin, epoxy resin, polyurethane resin, polyethylene, polypropylene, and polyimide, with polyimide being used in a specific embodiment.

[0031] In one embodiment, the organic solvent includes one or more of quinoline, N-methylpyrrolidone, tetrahydrofuran, toluene, xylene, cyclohexane, n-hexane, and ethanol, with N-methylpyrrolidone being a specific example. Depending on the required solubility and polarity for dissolving the coating agent, one or more of the above organic solvents may be selected and mixed in any proportion.

[0032] As one implementation method, based on the mass of soluble matter dissolved in the filtrate containing soluble matter, the mass ratio of soluble matter to insoluble matter in the mixture containing the coating agent is 1:0.1~5, specifically 1:0.5 or 1:1; the mass ratio of the hard carbon precursor to the total mass of the coating agent is 1:0.01~0.12, specifically 1:0.02, 1:0.05 or 1:0.1; the total mass of the coating agent is the sum of the masses of soluble matter and insoluble matter in the mixture containing the coating agent.

[0033] In one embodiment, the hard carbon precursor and the mixture containing the coating agent are mixed under stirring conditions; the stirring rate is 300~1000 rpm, and in a specific embodiment it is 500 rpm.

[0034] In one embodiment, the heat treatment temperature is 200~300℃, specifically 250℃ in this embodiment, and the holding time is 0.5~2h, specifically 1h in this embodiment; the heating rate to the heat treatment temperature is 1~3℃ / min, specifically 2℃ / min in this embodiment; the heat treatment is carried out in an oxidizing atmosphere or a protective atmosphere; the oxidizing atmosphere is an air atmosphere or an oxygen atmosphere, specifically air in this embodiment; the protective gas is nitrogen or argon, specifically nitrogen in this embodiment; before the heat treatment, the process further includes: evaporating the solvent from the mixture obtained by mixing the hard carbon precursor and the coating agent-containing mixture. This invention does not have a specific limitation on the temperature for evaporating the solvent; a suitable temperature can be selected according to the organic solvent used.

[0035] After obtaining the hard carbon precursor with the coating layer, the present invention performs a second high-temperature carbonization treatment on the hard carbon precursor with the coating layer in a second protective gas to obtain high-ratio pitch-based hard carbon.

[0036] In one embodiment, the second protective gas is nitrogen, helium, or argon, with argon being used in a specific embodiment; the temperature of the second high-temperature carbonization treatment is 1100~1500℃, with 1400℃ being used in a specific embodiment, and the holding time is 1~5h, with 2h being used in a specific embodiment; the heating rate to the temperature of the second high-temperature carbonization treatment is 3~10℃ / min, with 5℃ / min being used in a specific embodiment; after the second high-temperature carbonization treatment, the process further includes: cooling the product of the second high-temperature carbonization treatment and then pulverizing it to a particle size ≤20μm.

[0037] This invention, based on the concept of component separation and reconstruction, provides a controllable preparation process for coating layer structures, aiming to achieve precise control over the surface chemistry and microstructure of hard carbon materials. The core of this method lies in the selective dissolution and separation of the coating agent using a solvent, followed by recombining as needed. This recombinant agent is then combined with a hard carbon precursor that has undergone oxidation and a first high-temperature carbonization treatment. Finally, through heat treatment and a second carbonization treatment, a high-performance hard carbon material with a uniform, dense, and structurally stable coating layer is formed. The technology first constructs a hard carbon precursor core with a preliminary carbon skeleton structure by pulverizing, oxidizing, and initially carbonizing high-softening-point industrial asphalt. Subsequently, the coating agent is dissolved in an organic solvent and filtered to separate it into soluble and insoluble components. The mixing ratio of soluble and insoluble substances is precisely adjusted to control the composition and structure of the coating layer at the molecular level. After thoroughly mixing this recombined coating system with the hard carbon precursor, the coating layer is initially solidified and firmly adhered to the core surface through solvent evaporation and medium-low temperature heat treatment. Finally, the organic coating layer is transformed into a well-crystallized carbon layer through high-temperature carbonization, completing the final preparation of the material. This process route not only achieves flexible control over the composition and structure of the coating layer, but also ensures the uniformity and consistency of the coating through liquid-phase composite, providing a reliable and cost-effective technical route for the mass production of high-performance hard carbon materials.

[0038] The present invention also provides high-ratio pitch-based hard carbon prepared by the preparation method described in the above technical solution.

[0039] As one embodiment, the specific surface area of ​​the high-ratio pitch-based hard carbon is ≤10m². 2 / g, specifically 7.33m in the embodiment. 2 / g, with an average pore size of 5.0±1.0μm, and 4.92μm in the specific embodiment.

[0040] The present invention also provides the application of the high-rate asphalt-based hard carbon described in the above technical solution in sodium-ion batteries.

[0041] The present invention does not impose any particular limitation on the application of the high-rate asphalt-based hard carbon in sodium-ion batteries; any application method known in the art can be used.

[0042] In this embodiment of the invention, the negative electrode of the sodium-ion battery is the high-rate asphalt-based hard carbon, the positive electrode is a metallic sodium sheet, and the electrolyte includes a solute and a solvent; the solute is NaClO4 or NaPF6; the solvent is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1; the concentration of the solute in the electrolyte is 1 mol / L; the sodium-ion battery is a CR2032 button cell; and the sodium-ion battery is assembled in an argon-filled glove box.

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 200g of coal tar pitch with a softening point of 220℃ was crushed and passed through a 150-mesh sieve to obtain pitch powder with a particle size ≤100μm. It was oxidized in an air atmosphere with an air intake of 500mL / min at a temperature of 2℃ / min to 300℃ for 5h. The oxidized pitch obtained had a weight increase of 9.5% compared with coal tar pitch. Subsequently, the oxidized pitch was subjected to a first high-temperature carbonization treatment in a nitrogen atmosphere at a temperature of 5℃ / min to 1300℃ for 2h. After cooling, it was crushed to a particle size ≤20μm to obtain hard carbon precursor A. Coal tar pitch was placed in N-methylpyrrolidone and stirred at 500 rpm to dissolve it completely. The resulting mixture was filtered to separate the filtrate containing soluble matter and the insoluble matter. Based on the mass of soluble matter, the two were mixed at a mass ratio of soluble matter:insoluble matter = 1:0.5 to obtain a mixture containing the coating agent. Take 5g of the total mass of the coating agent (the sum of the masses of soluble and insoluble matter) and mix it with 100g of hard carbon precursor A. Stir at 500rpm, evaporate the solvent, and then heat-treat in air at 250℃ / min for 1h to solidify the coating layer. Finally, perform a second high-temperature carbonization in argon atmosphere at 5℃ / min to 1400℃ for 2h. After cooling, pulverize to a particle size ≤20μm to obtain high-ratio pitch-based hard carbon with a specific surface area of ​​7.33m². 2 / g, with an average pore size of 4.92μm.

[0045] Example 2 The difference from Example 1 is that: after dissolving coal tar pitch in N-methylpyrrolidone and filtering, the filtrate containing soluble matter and the insoluble matter are mixed at a mass ratio of soluble matter:insoluble matter = 1:1 to obtain a mixture containing a coating agent. The remaining steps and raw material amounts are the same as in Example 1.

[0046] Example 3 The difference from Example 1 is that the industrial asphalt raw material is 200g of petroleum asphalt with a softening point of 210℃, and the remaining steps and raw material amounts are the same as in Example 1.

[0047] Example 4 The difference from Example 1 is that the coating agent is polyimide. 20g of polyimide is placed in 200mL of N-methylpyrrolidone and stirred at 500rpm to dissolve it completely. After the resulting mixture is filtered and separated, the filtrate containing soluble matter and the insoluble matter are mixed at a mass ratio of soluble matter:insoluble matter = 1:0.5 to obtain a mixture containing the coating agent. The remaining steps and raw material amounts are the same as in Example 1.

[0048] Example 5 The difference from Example 1 is that the coating amount is different. The above-mentioned mixture containing the coating agent, equivalent to 2g of the total mass of the coating agent, is mixed with 100g of hard carbon precursor A. The remaining steps are the same as in Example 1.

[0049] Example 6 The difference from Example 1 is that the coating amount is different. The above-mentioned mixture containing the coating agent, equivalent to 10g of the total mass of the coating agent, is mixed with 100g of hard carbon precursor A. The remaining steps are the same as in Example 1.

[0050] Comparative Example 1 The difference from Example 1 is that only the filtrate containing soluble matter is used as the coating agent. 20g of coal tar pitch is placed in 200mL of N-methylpyrrolidone and stirred at 500rpm to dissolve it completely. After the resulting mixture is filtered and separated, only the filtrate containing soluble matter is taken. The amount equivalent to 5g of soluble matter is taken and mixed with 100g of hard carbon precursor A (i.e., the total mass of the coating agent is only 5g of soluble matter). The remaining steps are the same as in Example 1.

[0051] Comparative Example 2 The difference from Example 1 is that: the unfiltered and unseparated complete coating mixture is used as the coating agent. After preparing 200 mL of N-methylpyrrolidone mixture of 20 g of coal tar pitch, the mixture is not filtered and separated. Instead, the original mixture containing 5 g of coal tar pitch is directly mixed and stirred with 100 g of hard carbon precursor A (i.e., the soluble and insoluble substances exist in their inherent proportions in the original coating agent). The remaining steps are the same as in Example 1.

[0052] Performance testing Using the hard carbon materials obtained in Examples 1-6 and Comparative Examples 1-2 as the negative electrode, and a sodium metal sheet as the counter electrode, a CR2032 button cell was assembled in an argon-filled glove box using a 1 mol / L NaClO4 or NaPF6 EC / DMC (1:1, volume ratio) solution as the electrolyte.

[0053] Charge and discharge tests were conducted on the LAND CT2001A battery testing system (Wuhan Landian Electronics Co., Ltd.) to test the battery's specific capacity, cycle performance, and rate performance.

[0054] The rate testing current densities are 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C.

[0055] The test results of the above embodiments and comparative examples are detailed in Table 1.

[0056] Table 1 Test results of the examples and comparative examples

[0057] As shown in Table 1, the pitch-based hard carbon materials prepared by the method of the present invention (Examples 1-6) have significantly better rate performance (5C charging specific capacity and 5C / 0.1C capacity retention rate) than Comparative Example 1 (using only soluble matter) and Comparative Example 2 (using the original mixture that has not been separated).

[0058] Figure 1 This is a comparison chart of the rate performance of batteries assembled using the asphalt-based hard carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0059] Depend on Figure 1 As can be seen, Example 1 achieved a capacity retention rate of 81.66% at 5C / 1C. By separating the coating agent into soluble and insoluble components and using them synergistically according to the specified ratio, the chemical composition and microstructure of the coating layer were precisely designed and controllably regulated. The insoluble polycyclic aromatic hydrocarbons served as the structural "skeleton," while the soluble components acted as the "binder," jointly constructing a uniform, dense, and stable composite coating layer. This effectively reduced the specific surface area of ​​the hard carbon and created a highly efficient electron conduction network.

[0060] Figure 2 The impedance comparison diagram shows the batteries assembled using the pitch-based hard carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0061] Depend on Figure 2 As can be seen, the hard carbon material prepared in Example 1 exhibits the lowest impedance, confirming its faster sodium ion diffusion rate. This fully demonstrates that the technical solution of synergistic coating after filtration separation and precise control of the ratio of soluble and insoluble components can effectively combine the advantages of the two components to form a denser and more stable coating layer, thereby comprehensively improving the electrochemical performance of the material, especially its high-rate characteristics.

[0062] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-ratio pitch-based hard carbon, characterized in that, Includes the following steps: Industrial asphalt is oxidized in an oxidizing atmosphere, and the resulting oxidized asphalt is subjected to a first high-temperature carbonization treatment in a first protective atmosphere to obtain a hard carbon precursor. The hard carbon precursor and the mixture containing the coating agent are mixed and then heat-treated to obtain a hard carbon precursor with a coating layer. The hard carbon precursor with the coating layer is subjected to a second high-temperature carbonization treatment in a second protective gas to obtain high-ratio pitch-based hard carbon. The preparation method of the coating agent-containing mixture is as follows: the coating agent and an organic solvent are mixed and stirred to dissolve the mixture; the resulting mixture is filtered to obtain a filtrate containing soluble matter and an insoluble matter; the filtrate containing soluble matter and the insoluble matter are mixed to obtain the coating agent-containing mixture. Based on the mass of soluble matter dissolved in the filtrate containing soluble matter, the mass ratio of soluble matter to insoluble matter in the mixture containing the coating agent is 1:0.1~5.

2. The preparation method according to claim 1, characterized in that, The industrial asphalt includes one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch; the softening point of the industrial asphalt is not lower than 150°C.

3. The preparation method according to claim 1, characterized in that, The coating agent includes asphalt-based substances and / or resin-based substances.

4. The preparation method according to claim 3, characterized in that, The asphalt-like substances include one or more of coal tar pitch, coal liquefaction pitch, petroleum pitch, and ethylene tar pitch; the resin-like substances include one or more of phenolic resin, epoxy resin, polyurethane resin, polyethylene, polypropylene, and polyimide.

5. The preparation method according to claim 1, characterized in that, The ratio of the mass of the hard carbon precursor to the total mass of the coating agent is 1:0.01~0.12; the total mass of the coating agent is the sum of the masses of soluble and insoluble substances in the mixture containing the coating agent.

6. The preparation method according to claim 1, characterized in that, The oxidation treatment is carried out at a temperature of 250~350℃ for 2~8 hours.

7. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 200~300℃, and the holding time is 0.5~2h.

8. The preparation method according to claim 1, characterized in that, The temperatures for the first and second high-temperature carbonization treatments are independently 1100~1500℃, and the holding times are independently 1~5h.

9. The high-ratio pitch-based hard carbon prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The specific surface area of ​​the high-ratio asphalt-based hard carbon is ≤10m². 2 / g, with an average pore size of 5.0±1.0μm.

10. The application of the high-rate asphalt-based hard carbon according to claim 9 in sodium-ion batteries.

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