Extracted asphalt double-layer coated modified natural graphite composite material as well as preparation method and application thereof

Abstract

The invention provides an extracted asphalt double-layer coated modified natural graphite composite material, and a preparation method and application thereof, the preparation method performs solid-liquid extraction on medium-temperature / high-temperature asphalt by means of an organic solvent, and realizes fine separation and classified utilization of components with different molecular weights and chemical structures in the asphalt; the heavy asphalt and refined asphalt components obtained through separation are used as raw materials, and natural graphite is subjected to twice coating and twice carbonization treatment to obtain the composite material sequentially composed of soft carbon, hard carbon and graphite materials from outside to inside. According to the method, the properties of the composite material are regulated and controlled by virtue of the difference of asphalt components, so that efficient utilization of asphalt and natural graphite is realized. The double-layer coated modified natural graphite composite material prepared by the method shows excellent rate capability in the field of lithium batteries, and compared with a traditional natural graphite negative electrode material, the first coulombic efficiency and the rate capability of the composite material are remarkably improved.

Description

A bilayer coated modified natural graphite composite material for extracting bitumen, its preparation method and application Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to an extracted pitch double-layer coated modified natural graphite composite material, its preparation method and application. Background Technology

[0002] In recent years, with the rapid development of industrialization, a large number of gasoline-powered vehicles have been used in various industries, leading to energy crises and environmental pollution that have become hot issues of our time. Against this backdrop, the energy focus is gradually shifting towards renewable energy, and electric vehicle sales have increased by approximately 500% in the past decade. Lithium-ion batteries, as the core energy source for electric vehicles, have become the most popular high-energy-density batteries on the market due to their environmental friendliness and superior performance. However, the charging time for lithium-ion batteries in electric vehicles is currently 20 to 100 times longer than that of refueling traditional vehicles. Insufficient driving range and fast-charging efficiency have become key bottlenecks restricting the widespread adoption of electric vehicles.

[0003] As a core component determining the charging rate of lithium-ion batteries, the anode material's kinetic properties directly affect the battery's fast-charging performance. Currently, commercially available lithium-ion batteries widely use natural graphite (including flake graphite and microcrystalline graphite) or artificial graphite as the anode material, with the core advantages being low cost and high theoretical capacity (~372 mAh g⁻¹). -1 Furthermore, it has a stable voltage platform, making it the most cost-effective anode substrate material currently available. However, the inherent structural defects of natural graphite severely limit its performance: First, the layered crystal structure and anisotropy result in a low lithium-ion diffusion coefficient, which easily leads to the precipitation of lithium metal on the surface and the formation of lithium dendrites under fast charging conditions, causing not only capacity decay but also serious safety hazards; Second, the large number of active sites exposed at the edges of graphite can induce side reactions in the electrolyte, leading to the formation of a heterogeneous solid electrolyte interphase (SEI) film, and the unstable film structure further exacerbates the degradation of battery cycle life; Third, after processing such as grading, shaping, and purification, the low structural strength of natural graphite still results in many defects on its surface, further inhibiting the full release of electrochemical performance.

[0004] Therefore, how to further improve the cycle life, fast charging performance, and energy density of graphite anode materials is a current research hotspot. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides an extractable bitumen double-layer coated modified natural graphite composite material, its preparation method and application. The method utilizes solvent polarity to finely separate bitumen, thereby constructing a synergistic structure of a heavy component hard carbon layer and a refined component soft carbon layer on the surface of natural graphite, so as to solve the problems of slow lithium-ion diffusion and poor fast-charging performance of natural graphite negative electrode.

[0006] The specific contents of the invention are as follows: Firstly, the present invention provides a method for preparing a double-layer coated modified natural graphite composite material from extracted asphalt. The preparation method includes: mixing medium-temperature asphalt powder with a first organic solvent, performing a first solid-liquid extraction, filtering, and drying and crushing the resulting filter residue to obtain a solid heavy asphalt component; mixing high-temperature asphalt powder with a second organic solvent, performing a second solid-liquid extraction, filtering, and distilling and drying the resulting filtrate to obtain a solid refined asphalt component; mixing the solid heavy asphalt component with natural graphite, transferring it to an inert atmosphere, and performing a first carbonization at 550 ℃-750 ℃ ​​to obtain a single-layer coated natural graphite composite material; dissolving the solid refined asphalt component in tetrahydrofuran, mixing the resulting liquid phase with the single-layer coated natural graphite composite material, distilling and drying, and then transferring it to an inert atmosphere at 750 ℃-1200 ℃. A second carbonization is carried out at ℃ to obtain the double-layer coated modified natural graphite composite material; the first organic solvent is selected from at least one of quinoline, tetrahydrofuran and pyridine; the second organic solvent is selected from at least one of ethanol, cyclohexane, n-heptane, n-butanol and toluene.

[0007] Optionally, the first solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the first organic solvent; and / or the second solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the second organic solvent.

[0008] Optionally, the solid-liquid ratio of the first solid-liquid extraction and the second solid-liquid extraction is 1:(3-5), and the extraction time is 2-3 hours.

[0009] Optionally, the mass ratio of the solid heavy asphalt component to the natural graphite is 1:5-15; and / or the mass ratio of the solid refined asphalt to the single-coated natural graphite composite material is 1:5-15.

[0010] Optionally, the particle size of the solid refined asphalt component and the single-coated natural graphite composite material is no greater than 200 mesh.

[0011] Optionally, the carbonization time is 2 h to 4 h.

[0012] Optionally, the second carbonization is carried out using a gradient heating method, including: heating to 400℃ at 10℃ / min, then reducing the heating rate to 1℃ / min and continuing to heat to 550℃, and then heating to 750℃-1200℃ at 5℃ / min, and holding at that temperature for 1 h-3 h.

[0013] Optionally, the natural graphite is selected from flake graphite and / or microcrystalline graphite.

[0014] In a second aspect, the present invention provides an extractable bitumen double-layer coated modified natural graphite composite material, wherein the extractable bitumen double-layer coated modified natural graphite composite material is obtained according to the preparation method described in the first aspect above.

[0015] Thirdly, the present invention provides an application of an extractable bitumen double-coated modified natural graphite composite material, characterized in that the extractable bitumen double-coated modified natural graphite composite material is obtained according to the preparation method described in the first aspect above; and the extractable bitumen double-coated modified natural graphite composite material is used as the negative electrode of a lithium-ion battery.

[0016] This invention provides a method for preparing a double-layer coated modified natural graphite composite material from extracted asphalt. The method includes: mixing medium-temperature asphalt powder with a first organic solvent, performing a first solid-liquid extraction, filtering, and drying and crushing the resulting filter residue to obtain a solid heavy asphalt component; mixing high-temperature asphalt powder with a second organic solvent, performing a second solid-liquid extraction, filtering, and distilling and drying the resulting filtrate to obtain a solid refined asphalt component; mixing the solid heavy asphalt component with natural graphite, transferring it to an inert atmosphere, and carbonizing it at 550℃-750℃ to obtain a single-layer coated natural graphite composite material; dissolving the solid refined asphalt component in tetrahydrofuran, mixing the resulting liquid phase with the single-layer coated natural graphite composite material, distilling and drying it, and then transferring it to an inert atmosphere, gradually increasing the temperature to 750℃-1200℃. Carbonization at ℃ yields the double-layer coated modified natural graphite composite material. The first organic solvent is selected from at least one of quinoline, tetrahydrofuran, and pyridine; the second organic solvent is selected from at least one of ethanol, cyclohexane, n-heptane, n-butanol, and toluene. Compared with the prior art, this invention has the following advantages: This preparation method utilizes organic solvents for solid-liquid extraction of medium / high temperature asphalt, achieving fine separation and classification of components with different molecular weights and chemical structures in the asphalt; using the separated heavy asphalt and refined asphalt components as raw materials, natural graphite undergoes two coating and two carbonization treatments to obtain a composite material composed of soft carbon, hard carbon, and graphite materials from the outside to the inside. This method utilizes the differences in asphalt components to regulate the properties of the composite material, thereby achieving efficient utilization of asphalt and natural graphite. The double-layer coated modified natural graphite composite material prepared by this method exhibits excellent rate performance in the lithium battery field. Compared with traditional natural graphite anode materials, the composite material provided by this invention shows a significant improvement in initial coulombic efficiency and rate performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 shows a flowchart of the preparation method of the extracted bitumen double-layer coated modified natural graphite composite material provided in the embodiment of the present invention; Figure 2 shows a scanning electron microscope image of the extracted bitumen double-layer coated modified natural graphite composite material provided in the embodiment of the present invention; Figure 3 shows a scanning electron microscope image of the natural microcrystalline graphite material provided in the present invention; Figure 4 shows a magnification performance diagram of the extracted bitumen double-layer coated modified natural graphite composite material provided in the embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0020] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0021] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Asphalt, a chemical raw material abundant in my country, boasts significant advantages such as high carbon content, low ash content, and low cost, making it an ideal precursor for coating modified graphite anodes. However, the molecular composition of asphalt is extremely complex: on the one hand, differences in raw material sources (coal tar pitch, petroleum tar pitch) lead to significant variations in molecular structure and functional group distribution; on the other hand, fluctuations in the production process environment can trigger complex reactions such as intermolecular pyrolysis and polymerization, resulting in substantial differences in the physicochemical properties of different batches of asphalt. This uncertainty in composition leads to unstable composite effects of asphalt and graphite in traditional direct coating processes, making it difficult to precisely control the performance of composite materials and fully realize the resource value of asphalt.

[0024] Furthermore, given that the components of medium-temperature asphalt are characterized by moderately polar light components (saturated components, aromatic components, and some resins) and extremely high molecular association of heavy components (asphaltite and macromolecules rich in heteroatoms), while the components of high-temperature asphalt are characterized by weakly polar low-molecular-weight aromatic compounds and highly polar or highly associated heavy impurities (macromolecules and inert asphaltite), this invention aims to utilize the polarity of organic solvents to perform solid-liquid extraction on medium-temperature and high-temperature asphalt to obtain asphalt components with significantly different properties for graded coating of natural graphite. After carbonization, this forms asphalt-carbon composite coating layers with different structural properties.

[0025] Specifically, this invention selects a highly polar organic solvent to perform solid-liquid extraction on medium-temperature asphalt to obtain a heavy asphalt component that is insoluble in the highly polar solvent. Based on the fact that the heavy component is rich in heteroatom functionalities such as N, O, and S, it is used to coat natural graphite. During carbonization, an inner hard carbon coating structure with porous defects is formed on the graphite surface. This defect structure leads to an uneven distribution of the electron cloud, providing a rapid transport channel for lithium ions. Further, this invention selects a weakly polar organic solvent to perform solid-liquid extraction on high-temperature asphalt to obtain a refined asphalt component (mainly composed of low molecular weight, highly active aromatic compounds) soluble in the weakly polar solvent. Based on the fact that the refined asphalt component is prone to graphitization, it is further used to coat graphite. During carbonization, the aromatic compounds readily undergo thermal polymerization to form large-molecule polycyclic aromatic hydrocarbons, which are transformed into a graphite-like structure at high temperatures. This further forms an ordered soft carbon layer structure on the surface of the inner hard carbon coating structure, ultimately obtaining a composite material with a "soft carbon-hard carbon-graphite" structure.

[0026] The following is a detailed description of the embodiments of the present invention: In a first aspect, the present invention provides a method for preparing a double-layer coated modified natural graphite composite material from extracted asphalt. Figure 1 shows a flowchart of the preparation method of the double-layer coated modified natural graphite composite material from extracted asphalt provided in the embodiment of the present invention. As shown in Figure 1, the preparation method includes: S1, mixing medium-temperature asphalt powder with a first organic solvent, performing a first solid-liquid extraction, filtering, and drying and crushing the resulting filter residue to obtain a solid heavy asphalt component; in this specific implementation, the first organic solvent is selected from strongly polar organic solvents, specifically selected from at least one of quinoline, tetrahydrofuran, and pyridine; the first organic solvent reacts with the medium-temperature asphalt... During solid-liquid extraction, the light components (saturated components, aromatic components, etc.) with moderate polarity and small molecular weight in medium-temperature asphalt form stable interactions, achieving efficient dissolution. The heavy components in medium-temperature asphalt are mainly highly associated asphaltenes and are rich in heteroatom functional groups such as N, O, and S, with extremely strong intermolecular forces (hydrogen bonds, π-π stacking interactions). Strongly polar solvents cannot break their molecular association structure and are filtered out as insoluble substances. This invention, through extraction with strongly polar solvents, can accurately remove light components in medium-temperature asphalt that are not conducive to the formation of hard carbon structures, avoiding their impact on the porosity and defect structure of the inner coating, and finally obtaining a high-purity hard carbon precursor (heavy asphalt component) with abundant heteroatom content.

[0027] In some embodiments, the first solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the selected organic solvent to ensure efficient dissolution of the light component by the highly polar organic solvent. The solid-liquid ratio of the first solid-liquid extraction is preferably 1:(3-5), and the extraction time is controlled at 2-3 hours.

[0028] S2. High-temperature asphalt powder is mixed with a second organic solvent and subjected to a second solid-liquid extraction. After filtration, the resulting filtrate is distilled and dried to obtain a solid refined asphalt component. In this step, the second organic solvent is selected from at least one of weakly polar organic solvents, specifically ethanol, cyclohexane, n-heptane, n-butanol, and toluene. Using a weakly polar organic solvent for solid-liquid extraction of high-temperature asphalt allows the weakly polar solvent to match the polarity of low-molecular-weight, highly active aromatic ring compounds in the high-temperature asphalt (like dissolves like), enabling rapid dissolution of these target components without destroying their aromatic ring structure. The remaining insoluble matter is mostly macromolecular polymeric impurities and inert asphaltene. These substances are highly polar or have a high degree of molecular association, and their interaction with the weakly polar solvent is extremely weak, making them unsoluble and thus removed by filtration. Through extraction with a weakly polar solvent, the lightweight components in high-temperature asphalt that are conducive to the formation of soft carbon structures can be accurately enriched in the weakly polar solvent. After subsequent distillation and drying to remove the organic solvent, a highly active, easily graphitized solid refined asphalt component is obtained.

[0029] In some embodiments, the second solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the selected organic solvent to ensure efficient dissolution of the light component by the highly polar organic solvent. The solid-liquid ratio of the second solid-liquid extraction is preferably 1:(3-5), and the extraction time is controlled at 2-3 hours.

[0030] It should be noted that the solid refined asphalt components and solid heavy asphalt components obtained by solid-liquid extraction are ground before being used for coating. The large agglomerated particles are lightly ground into micro powder and then passed through a 200-mesh sieve to achieve uniform coating.

[0031] S3. After mixing the solid heavy asphalt component with natural graphite, transfer it to an inert atmosphere and perform a first carbonization at 550 ℃-750 ℃ ​​to obtain a single-coated natural graphite composite material. In this step, the heavy asphalt component obtained after medium-temperature asphalt solid-liquid extraction is used to coat the natural graphite, based on the fact that the heavy asphalt component is rich in highly associated macromolecular and heteroatom functional groups. This step is carried out at a relatively low temperature (550 ℃-750 ℃). During the carbonization process, the heteroatom functional groups in the heavy asphalt component restrict the formation of a large-scale ordered carbon structure. After carbonization, a hard carbon layer structure with voids and defects can be formed on the graphite surface. Such defect structures lead to the uneven distribution of electron clouds, which can provide a fast transport channel for lithium ions.

[0032] In some embodiments, the mass ratio of the solid heavy bitumen component to the natural graphite is 1:5-15, and the carbonization time is preferably 2 h-4 h.

[0033] It should also be noted that the natural graphite is preferably selected from flake graphite and / or microcrystalline graphite. Before the obtained single-coated natural graphite composite material is used for secondary coating, it is first ground to lightly grind the agglomerated large particles into micro powder and then pass the whole material through a 200-mesh sieve to achieve uniform coating.

[0034] S4. The solid refined asphalt component is dissolved in tetrahydrofuran, and the resulting liquid phase is mixed with the single-coated natural graphite composite material. After distillation and drying, it is transferred to an inert atmosphere and subjected to a second carbonization at a gradient temperature of 750 ℃-1200 ℃ to obtain the double-coated modified natural graphite composite material. In this step, the solid refined asphalt component is fully dissolved in the organic solvent tetrahydrofuran to form a mixture, which is then mixed with the single-coated natural graphite composite material (the mass ratio of solid refined asphalt to the single-coated natural graphite composite material is 1:5-15). The mixture is thoroughly stirred and dissolved in a sealed container. After a mixing process of 2-3 hours, the temperature is raised to 10-30 ℃ below the boiling point of the solvent for distillation to slowly evaporate the solvent and ensure uniform deposition of asphalt on the surface of the single-coated natural graphite composite material. When the viscosity of the mixture significantly increases, it is transferred to a ventilated area for drying. The solvent is then rapidly removed from the system below the softening point of the refined asphalt to obtain the composite material precursor. Further, the obtained composite material precursor is transferred to an inert atmosphere and carbonized at 750℃-1200℃ to obtain the double-layer coated modified natural graphite composite material.

[0035] In some embodiments, the solid refined asphalt component is mainly composed of low molecular weight, highly active aromatic ring compounds, which are prone to graphitization transformation at high temperatures. This step is combined with gradient heating to promote carbon layer rearrangement. The specific gradient heating process includes: heating to 400 ℃ at 10 ℃ / min, then reducing the heating rate to 1 ℃ / min and continuing to heat to 550 ℃, and then heating to 750 ℃-1200 ℃ at 5 ℃ / min, and holding at this temperature for 1 h-3 h.

[0036] In a second aspect, the present invention provides an extractable bitumen double-layer coated modified natural graphite composite material, wherein the extractable bitumen double-layer coated modified natural graphite composite material is obtained according to the preparation method described in the first aspect above.

[0037] Thirdly, the present invention provides an application of an extractable bitumen double-coated modified natural graphite composite material, characterized in that the extractable bitumen double-coated modified natural graphite composite material is obtained according to the preparation method described in the first aspect above; and the extractable bitumen double-coated modified natural graphite composite material is used as the negative electrode of a lithium-ion battery.

[0038] To enable those skilled in the art to better understand the present invention, the following examples illustrate the present invention's method of preparing a modified natural graphite composite material with double-layer coating for extracting asphalt, and its application. The invention utilizes organic solvents of different polarities to perform solid-liquid extraction and separation of the target asphalt components. The resulting asphalt components, exhibiting significant differences in properties, are then used to grade and coat natural graphite. After carbonization, a modified natural graphite composite material with double coating layers (different coating layers possess different structural properties due to different components) is formed.

[0039] Example 1: S1. Medium-temperature petroleum asphalt and tetrahydrofuran were mixed at a ratio of 1:5, and after being stirred at a constant temperature for 3 hours, the mixture was hot-filtered. The filter residue was washed and dried to obtain a solid heavy asphalt component. S2. High-temperature coal tar pitch and toluene were mixed at a ratio of 1:5, and after being stirred at a constant temperature for 3 hours, the mixture was hot-filtered. The filtrate was distilled and dried to obtain a solid refined asphalt component.

[0040] S3. After grinding the solid heavy asphalt component into a fine powder (through a 200-mesh sieve), mix it thoroughly with high-purity spherical natural microcrystalline graphite at a ratio of 1:10. Spread the mixture evenly in a crucible, heat it to 650℃, carbonize it at low temperature for 3 hours, and then cool it to room temperature to obtain a single-coated natural microcrystalline graphite composite material.

[0041] S4. Add the single-coated natural graphite composite material and solid refined asphalt component to a mixing container at a ratio of 10:1. Add 50 ml of tetrahydrofuran to completely dissolve the refined asphalt. Stir in a sealed environment until fully dissolved. After 3 hours of thorough stirring, perform distillation. After the organic solvent has completely left the system, transfer the mixture to a ventilated area until completely dry. Transfer the obtained composite material precursor to an inert gas heating device for gradient heating carbonization. Specifically, heat to 400 ℃ at a rate of 10 ℃ / min, then to 550 ℃ at a rate of 1 ℃ / min, and finally to 1000 ℃ at a rate of 5 ℃ / min. Maintain the temperature for 3 hours, then cool to room temperature to obtain a double-coated modified natural microcrystalline graphite composite material (scanning electron microscope image shown in Figure 2).

[0042] Compared with Example 1, Example 2 differs in that the natural graphite material used is selected from flake graphite, while the rest of the operation is the same as in Example 1.

[0043] Compared with Example 1, Example 3 differs in that in S4, the temperature is gradually increased to 1200 °C for 3 h for carbonization, while the rest of the operation is the same as in Example 1.

[0044] Compared with Example 1, Example 4 differs in that in S4, the temperature is gradually increased to 800 °C for 3 hours for carbonization, while the rest of the operation is the same as in Example 1.

[0045] In a comparative example, high-temperature coal tar pitch and toluene were mixed at a ratio of 1:5, and after being stirred at a constant temperature for 3 hours, the mixture was hot filtered. The filtrate was then distilled and dried to obtain a solid refined asphalt component.

[0046] High-purity spherical natural microcrystalline graphite and solid refined asphalt components were added to a mixing container at a ratio of 10:1. 50 ml of tetrahydrofuran was added to completely dissolve the refined asphalt, and the mixture was stirred in a sealed environment until fully dissolved. After 3 hours of thorough stirring, distillation was performed. After the organic solvent completely left the system, the mixture was transferred to a ventilated area until completely dry. The obtained composite precursor was then transferred to an inert gas heating device for gradient heating carbonization. Specifically, the temperature was increased to 400 °C at a rate of 10 °C / min, then to 550 °C at a rate of 1 °C / min, and finally to 1000 °C at a rate of 5 °C / min, held at this temperature for 3 hours, and then cooled to room temperature to obtain a single-coated modified natural microcrystalline graphite composite material.

[0047] Compared with Example 1, the difference in this comparative example is that steps S1 and S3 are not performed.

[0048] The raw material sample is high-purity spherical natural microcrystalline graphite (scanning electron microscope image shown in Figure 3), without any coating treatment.

[0049] Performance testing involved using the composite materials and raw material samples obtained in Examples 1-4 and the comparative example to prepare coin cells. Specifically, the composite materials and raw material samples obtained in Examples 1-4 and the comparative example were mixed with conductive carbon black, CMC, and SBR in deionized water at a mass ratio of 90:5:3:2 to form a slurry. This slurry was then coated onto copper foil, dried, and stamped to obtain a lithium-ion battery negative electrode. This negative electrode was then combined with a lithium foil to form a lithium-ion half-cell. Using LiPF6 as the organic electrolyte, a CR2032 type coin cell was assembled and subjected to constant current charge-discharge testing. The test results are shown in Table 1 and Figure 4.

[0050] Table 1 shows the electrochemical performance test results. As can be seen from the data in Table 1, the double-layer coating modified natural graphite anode material using pitch extract, as described in this invention, with its unique composite coating structure, combines the synergistic effects of different carbon layer regions, thus achieving a significant improvement in electrochemical performance. Specifically, the outer layer of refined pitch-based carbon, with its good graphitization tendency and high electronic conductivity, provides an efficient and continuous electron transport network for the graphite substrate, effectively reducing interfacial impedance. Meanwhile, the inner layer of heavy carbon, due to its abundant nanopores and wider interlayer spacing, serves as a fast lithium-ion transport channel and buffer region, effectively improving the interfacial lithium-ion migration kinetics. The synergistic effect of these two layers ultimately leads to a systematic improvement in the material's first-efficiency performance, rate performance, and capacity retention under high current.

[0051] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0052] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0053] The foregoing has provided a detailed description of the extracted bitumen double-layer coated modified natural graphite composite material, its preparation method, and its application. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a double-layer coated modified natural graphite composite material for extracting bitumen, characterized in that, The preparation method includes: mixing medium-temperature asphalt powder with a first organic solvent, performing a first solid-liquid extraction, filtering, and drying and crushing the resulting filter residue to obtain a solid heavy asphalt component; mixing high-temperature asphalt powder with a second organic solvent, performing a second solid-liquid extraction, filtering, and distilling and drying the resulting filtrate to obtain a solid refined asphalt component; mixing the solid heavy asphalt component with natural graphite, transferring it to an inert atmosphere, and performing a first carbonization at 550 ℃-750 ℃ ​​to obtain a single-coated natural graphite composite material; dissolving the solid refined asphalt component in tetrahydrofuran, mixing the resulting liquid phase with the single-coated natural graphite composite material, distilling and drying, and then transferring it to an inert atmosphere, gradually increasing the temperature to 750 ℃-1200 ℃. A second carbonization is carried out at ℃ to obtain the double-layer coated modified natural graphite composite material; the first organic solvent is selected from at least one of quinoline, tetrahydrofuran and pyridine; the second organic solvent is selected from at least one of ethanol, cyclohexane, n-heptane, n-butanol and toluene.

2. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The first solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the first organic solvent; and / or the second solid-liquid extraction is carried out at a temperature 10°C to 50°C below the boiling point of the second organic solvent.

3. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The solid-liquid ratio of the first solid-liquid extraction and the second solid-liquid extraction is 1:(3-5), and the extraction time is 2 h-3 h.

4. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The mass ratio of the solid heavy asphalt component to the natural graphite is 1:5-15; and / or the mass ratio of the solid refined asphalt to the single-coated natural graphite composite material is 1:5-15.

5. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The particle size of the solid refined asphalt component and the single-coated natural graphite composite material is no greater than 200 mesh.

6. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The carbonization time is 2 h to 4 h.

7. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The second carbonization is carried out using a gradient heating method, including: heating to 400 ℃ at 10 ℃ / min, then reducing the heating rate to 1 ℃ / min and continuing to heat to 550 ℃, and then heating to 750 ℃-1200 ℃ at 5 ℃ / min, and holding at that temperature for 1 h-3 h.

8. The method for preparing the double-layer coated modified natural graphite composite material according to claim 1, characterized in that, The natural graphite is selected from flake graphite and / or microcrystalline graphite.

9. A composite material for extracting bitumen with a double-layer coating modified natural graphite, characterized in that, The extracted bitumen double-layer coated modified natural graphite composite material is obtained according to the preparation method described in any one of claims 1-8.

10. An application of a double-layer coated modified natural graphite composite material for extracting bitumen, characterized in that, The extracted bitumen double-layer coated modified natural graphite composite material is obtained according to any one of the preparation methods described in claims 1-8; the extracted bitumen double-layer coated modified natural graphite composite material is used as the negative electrode of a lithium-ion battery.

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