A core-shell structure fast-charging long-cycling artificial graphite, a preparation method thereof, a negative electrode material and purposes thereof

Abstract

The application discloses a kind of core-shell structure fast charging long cycle artificial graphite, its preparation method, negative electrode material and purposes, including, petroleum coke or acicular coke aggregate D50 8~20 μm, non-biomass hard carbon raw material powder D50 1~10 μm and pitch are mixed according to the mass ratio hard carbon: pitch = 1:9~5:5, aggregate: composite coating agent = 95:5~85:15, pre-mixing S1 is carried out at 100~200 DEG C, 160~220 DEG C melt kneading granulation S2, carbonization S3 is carried out at 600~1000 DEG C, and graphitization S4 is carried out at 2800~3200 DEG C, and core-shell structure artificial graphite is prepared by one-step method.The shell layer is composed of uniformly dispersed graphitized hard carbon and soft carbon, and is densely coated outside the artificial graphite core.The first reversible specific capacity of the product is greater than or equal to 350 mAh / g, the first coulombic efficiency is greater than or equal to 93%, and the capacity retention rate at 5.0C / 0.2C is greater than or equal to 84%, with excellent fast charging performance and cycle stability, simple process and low cost.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a core-shell structured fast-charging long-cycle artificial graphite, its preparation method, negative electrode material and applications. Background Technology

[0002] With the increasing demand for fast charging and long cycle life from electric vehicles, portable electronic devices, and energy storage, the development of low-cost next-generation fast-charging, long-cycle lithium-ion batteries has become a research hotspot. This invention utilizes readily available and inexpensive raw materials, employing a one-step method to directly prepare core-shell structured fast-charging, long-cycle artificial graphite, simplifying the process and reducing production costs. The artificial graphite core is coated with uniformly dispersed hard carbon and graphite, resulting in a stable structure that balances fast charging and high-temperature performance. This solves the problem of traditional artificial graphite where secondary carbonization after graphitization improves fast charging performance, but high-temperature performance decreases due to the amorphous carbon coating on the particle surface.

[0003] Artificial graphite is the most mainstream anode material for lithium-ion batteries, and its performance is highly dependent on raw materials and preparation processes. Currently, high-performance artificial graphite typically uses soft carbon materials such as pitch as coating agents and binders, prepared by coating and granulating aggregates such as petroleum coke and needle coke before graphitization. However, existing technologies have significant drawbacks: the coating layer structure is singular, making it difficult to balance fast-charging performance and cycle life. Traditional single pitch coatings form a dense soft carbon shell after graphitization. While the cycle stability is acceptable, the dense structure and high crystallinity limit the rapid insertion and extraction of lithium ions, resulting in poor fast-charging performance and a tendency for lithium plating during high-current charging, posing safety hazards. Insufficient coating uniformity and density can lead to uneven coating, agglomeration, or excessively thick or thin coatings in certain areas if the process control is inadequate during dry or liquid-phase mixing. Uneven coatings generate structural stress during graphitization and are prone to cracking and peeling during battery cycling, causing direct contact between the aggregate core and the electrolyte, increasing side reactions, reducing initial efficiency, and shortening cycle life. The granulation effect and sphericity are not ideal. The single asphalt binder experiences significant volume shrinkage during carbonization, potentially leading to insufficient secondary particle strength after granulation. This results in easy breakage and fine powder formation during subsequent processing. Irregular particle morphology also reduces the compaction density of the negative electrode, affecting the battery's energy density. Furthermore, the raw material properties are limited. Using asphalt alone as a coating agent results in a fixed coking value and residual carbon content. The resulting coating layer's microstructure, such as pores and defects, has a narrow adjustable range, making it difficult to optimize the lithium-ion diffusion channels. Summary of the Invention

[0004] The purpose of this invention is to provide a core-shell structured fast-charging long-cycle artificial graphite, its preparation method, negative electrode material and applications, aiming to enable lithium-ion batteries to have high energy density while also having significantly improved fast-charging performance and long-cycle performance.

[0005] In a first aspect, the present invention provides a method for preparing core-shell structured fast-charging long-cycle artificial graphite, comprising the following steps:

[0006] S1 adds aggregate, non-biomass hard carbon raw material powder and asphalt into a mixer and premixes them at 100℃~200℃ to obtain a premixed material;

[0007] S2 transfers the premixed material to a heated kneading device, and under the protection of an inert atmosphere, heats it to 160°C~220°C for melting, kneading and granulation to form secondary particles with the aggregate as the core and the composite of the non-biomass hard carbon raw material and the asphalt as the shell.

[0008] S3 involves heating the granulated material to 600℃~1000℃ under an inert atmosphere at a heating rate of 1~5℃ / min for carbonization treatment, and holding the temperature for 1~4 hours.

[0009] S4 involves heating the carbonized material to 2800℃~3200℃ in an inert atmosphere at a heating rate of 3~10℃ / min for graphitization treatment, holding the temperature for 8~20 hours, and then cooling to obtain the core-shell structured fast-charging long-cycle artificial graphite.

[0010] The aggregate is petroleum coke or needle coke with an average particle size D50 of 8-20 μm; the non-biomass hard carbon raw material powder has an average particle size D50 of 1-10 μm; the mass ratio of the non-biomass hard carbon raw material powder to the asphalt is 1:9 to 5:5; the mass ratio of the aggregate to the composite coating agent is 95:5 to 85:15, and the composite coating agent is composed of the non-biomass hard carbon raw material powder and the asphalt.

[0011] In any embodiment of this application, the asphalt is coal tar pitch, petroleum asphalt, or modified asphalt, with a softening point of 80°C to 150°C.

[0012] In any embodiment of this application, the premixing temperature in S1 is 130°C to 180°C and the time is 30 to 120 minutes; the stirring speed for melt kneading and granulation in S2 is 20 to 60 rpm and the kneading time is 60 to 180 minutes.

[0013] In any embodiment of this application, the heating rate of the carbonization treatment in S3 is 2~3℃ / min, and the final carbonization temperature is 800℃~900℃; the heating rate of the graphitization treatment in S4 is 4~8℃ / min, and the final graphitization temperature is 2900℃~3100℃.

[0014] Secondly, the present invention provides a core-shell structured fast-charging long-cycle artificial graphite, which is prepared by any of the above-described preparation methods. The artificial graphite has a core-shell structure, wherein the core is artificial graphite and the shell is composed of uniformly dispersed graphitized hard carbon and soft carbon, and the shell densely covers the surface of the core.

[0015] In any embodiment of this application, the artificial graphite has a particle size D50 of 10~25μm, a tap density ≥1.0g / cm³, and a specific surface area of ​​1.0~3.0m² / g.

[0016] In any embodiment of this application, the artificial graphite, in the coin cell test, has an initial reversible specific capacity ≥350mAh / g, an initial coulombic efficiency ≥93%, and a capacity retention rate of ≥84% at 5.0C / 0.2C rates.

[0017] Thirdly, the present invention provides a lithium-ion battery anode material comprising, as described in any one of the above-mentioned core-shell structured fast-charging long-cycle artificial graphite, as an active material.

[0018] Fourthly, the present invention provides a lithium-ion battery comprising the above-mentioned negative electrode material.

[0019] Fifthly, the present invention provides the use of the above-mentioned core-shell structured fast-charging long-cycle artificial graphite in the preparation of fast-charging lithium-ion batteries.

[0020] To address the aforementioned shortcomings, this invention innovatively proposes using a composite coating agent and granulating agent made from non-biomass hard carbon raw materials and soft carbon raw material asphalt to prepare a core-shell structured artificial graphite, which has the following significant advantages and beneficial effects.

[0021] A synergistic composite coating layer was constructed. Hard carbon materials possess abundant nanopores and larger interlayer spacing, providing high-speed diffusion channels for lithium ions; soft carbon pitch exhibits good adhesion and flowability, forming a dense conductive network after graphitization. The combination of the two forms a synergistic coating layer where hard carbon provides the channels and soft carbon ensures stability and conductivity, while significantly improving the material's fast-charging performance, first-cycle efficiency, and cycle stability.

[0022] Optimize particle structure and strength. The composite coating agent has better plasticity and adhesion, making the coating and granulation process more uniform, resulting in secondary particles with high sphericity, smooth surface, and high strength. This is beneficial for improving the compaction density of the negative electrode and reducing electrode rebound and slurry processing difficulties during the preparation process.

[0023] The process is highly adaptable and its performance is easily controllable. By adjusting the type, ratio, and particle size of hard carbon and soft carbon asphalt, the microstructure of the final coating layer, such as porosity, defect degree, and graphitization, can be precisely controlled. This allows for the customization of the electrochemical performance of the final product to meet the needs of different applications, such as power batteries and energy storage batteries.

[0024] Balancing raw material costs and performance. Non-biomass hard carbon is a stable and inexpensive source, partially replacing more expensive high-end coating agents such as mesophase pitch, thus improving product performance while effectively controlling production costs. Attached Figure Description

[0025] Figure 1 This is a flowchart of the process of the present invention;

[0026] Figure 2 This is a schematic diagram of the microstructure of core-shell structured artificial graphite particles. Detailed Implementation

[0027] The following details the core-shell structure fast-charging long-cycle artificial graphite, negative electrode sheet, and lithium-ion battery according to the present invention.

[0028] First, let me describe the core-shell structured fast-charging long-cycle artificial graphite according to the first aspect of the present invention. It has a core-shell structure, with the core material selected from artificial graphite, and the shell material composed of uniformly dispersed graphitized hard carbon and soft carbon. The shell densely coats the surface of the core. The aggregate is petroleum coke or needle coke with an average particle size D50 of 8-20 μm. The non-biomass hard carbon raw material powder has an average particle size D50 of 1-10 μm. The mass ratio of the non-biomass hard carbon raw material powder to the asphalt is 1:9 to 5:5, and the mass ratio of the aggregate to the composite coating agent is 95:5 to 85:15. Figure 2 As shown, the central region of the diagram is composed of agglomerates of larger petroleum coke or needle coke primary particles, exhibiting a dense structure and a high degree of graphitization. The shell is a uniform coating layer surrounding the core. This shell has a two-phase composite structure: ① Hard carbon phase: dispersed as irregular particles or dots, representing rapid lithium-ion migration channels. ② Soft carbon phase (graphitized pitch, labeled as graphite phase): serving as a continuous matrix, firmly bonding the hard carbon phase and the core together to form a dense and complete protective layer.

[0029] During battery charging, the negative electrode undergoes three electrochemical processes: lithium ions released from the positive electrode active material enter the electrolyte, pass through the separator, and migrate with the electrolyte to the surface of the negative electrode active material; lithium ions and electrons exchange charge on the surface of the negative electrode active material; and lithium ions are conducted from the surface of the negative electrode active material to its interior via solid-phase transfer. Among these, the charge exchange process is a crucial step and, in many cases, a decisive factor limiting the battery charging speed.

[0030] The hard carbon material in the shell layer possesses abundant nanopores and a larger interlayer spacing, providing high-speed diffusion channels for lithium ions. The soft carbon pitch, after graphitization, forms a dense conductive network, ensuring structural stability and conductivity. The combination of these two materials creates a synergistic coating layer where hard carbon provides the channels and soft carbon ensures stability and conductivity. This significantly improves the material's fast-charging performance, first-cycle efficiency, and cycle stability, greatly enhancing the battery's kinetic performance and fast-charging capability. Furthermore, the battery also features high energy density and long cycle life under high-rate fast charging. In addition, the core-shell structured fast-charging long-cycle artificial graphite of this invention is prepared using a one-step method, which is simple and can reduce battery costs.

[0031] When the mass ratio of non-biomass hard carbon raw material powder to asphalt is less than 1:9, the hard carbon content in the shell is too low, resulting in insufficient high-speed diffusion channels and minimal improvement in fast-charging performance. Furthermore, the excessively high proportion of soft carbon leads to an overly dense shell, hindering lithium-ion diffusion. While a mass ratio of non-biomass hard carbon raw material powder to asphalt greater than 5:5 provides sufficient diffusion channels, the insufficient soft carbon content reduces the stability and density of the shell structure, impairing cycle performance and resulting in poor granulation. The core-shell structure fast-charging long-cycle artificial graphite of this invention controls the mass ratio of non-biomass hard carbon raw material powder to asphalt within the range of 1:9 to 5:5, thus balancing fast-charging performance and cycle stability.

[0032] When the mass ratio of aggregate to composite coating agent is less than 85:15, the coating layer is too thick. Although the kinetic performance is excellent, it is detrimental to energy density and increases side reactions, affecting cycle performance and high-temperature performance. When the mass ratio of aggregate to composite coating agent is greater than 95:5, the coating layer is too thin, making it impossible to form a complete core-shell structure. This affects fast-charging performance and cycle stability, and reduces granulation strength and sphericity. The core-shell structure fast-charging long-cycle artificial graphite of this invention has an aggregate to composite coating agent mass ratio between 95:5 and 85:15, allowing the battery to possess excellent kinetic performance, high energy density, and long cycle life under high-rate fast charging.

[0033] Preferably, the asphalt is coal tar pitch, petroleum asphalt, or modified asphalt, with a softening point of 80℃~150℃. The softening point of the asphalt affects the melt-kneading granulation process in step S2. If the softening point is too low, the asphalt is prone to softening and sticking during premixing in step S1, affecting the uniformity of mixing; if the softening point is too high, a higher temperature is required in step S2 to melt the asphalt, increasing energy consumption and potentially causing premature carbonization of the hard carbon raw materials. Controlling the asphalt softening point within the range of 80℃~150℃ allows the premixing and melt-kneading granulation processes to proceed smoothly, resulting in secondary particles with high sphericity, smooth surface, and high strength.

[0034] Preferably, the premixing temperature in S1 is 130℃~180℃, and the time is 30~120 minutes; the stirring speed of the melt kneading granulation in S2 is 20~60 rpm, and the kneading time is 60~180 minutes. If the premixing temperature is too low or the time is too short, the aggregate, hard carbon raw material and asphalt will not mix evenly, affecting the subsequent coating effect; if the premixing temperature is too high or the time is too long, the asphalt will soften prematurely, easily causing agglomeration. If the stirring speed of melt kneading granulation is too low or the time is too short, the asphalt will not be sufficiently wetted, and the coating layer will not be dense; if the speed is too high or the time is too long, energy consumption will increase and the particles will be easily over-crushed. Controlling the premixing and melt kneading granulation parameters within the above range can make the coating granulation process more uniform, and the resulting secondary particles will have high sphericity, smooth surface and high strength, which is beneficial to improving the compaction density of the negative electrode and reducing electrode rebound and slurry processing difficulties during the preparation process.

[0035] Preferably, the heating rate of the carbonization treatment in S3 is 2~3℃ / min, and the final carbonization temperature is 800℃~900℃; the heating rate of the graphitization treatment in S4 is 4~8℃ / min, and the final graphitization temperature is 2900℃~3100℃. If the heating rate of the carbonization treatment is too fast, the asphalt will not solidify and coke sufficiently, easily leading to cracks and pore defects; if the heating rate is too slow, production efficiency will be low. If the final carbonization temperature is too low, the asphalt coking degree will be insufficient, resulting in poor shell strength; if the final temperature is too high, energy consumption will increase and the hard carbon structure may shrink excessively. If the heating rate of the graphitization treatment is too fast, the temperature distribution will be uneven, and the degree of graphitization will be inconsistent; if the heating rate is too slow, the production cycle will be long. If the final graphitization temperature is too low, the degree of graphitization will be insufficient, resulting in poor material conductivity and structural stability; if the final temperature is too high, energy consumption will increase significantly and equipment wear will be aggravated. By controlling the carbonization and graphitization treatment parameters within the above range, the asphalt can be fully cured and coked to form a stable carbonized layer, which can then be transformed into a graphitized shell with excellent electrical conductivity and structural stability at high temperatures.

[0036] Next, the preparation method of the core-shell structured fast-charging long-cycle artificial graphite according to the second aspect of the present invention will be described, such as... Figure 1As shown, the process includes the following steps: S1, adding aggregate, non-biomass hard carbon raw material powder and asphalt into a mixer and premixing at 100℃~200℃ to obtain a premixed material; S2, transferring the premixed material to a heated kneading device, and melting, kneading and granulating it at 160℃~220℃ under an inert atmosphere to form secondary particles with the aggregate as the core and the composite of the non-biomass hard carbon raw material and the asphalt as the shell; S3, carbonizing the granulated material at 600℃~1000℃ under an inert atmosphere at a heating rate of 1~5℃ / min, and holding it at that temperature for 1~4 hours; S4, graphitizing the carbonized material at 2800℃~3200℃ under an inert atmosphere at a heating rate of 3~10℃ / min, and holding it at that temperature for 8~20 hours, and then cooling it to obtain the core-shell structured fast-charging long-cycle artificial graphite.

[0037] In step S1, the premixing temperature is below 100℃, resulting in poor asphalt fluidity and difficulty in uniformly mixing with aggregates and hard carbon raw materials; above 200℃, the asphalt softens excessively, causing materials to clump together. In step S2, the melting, kneading, and granulation temperature is below 160℃, resulting in insufficient asphalt melting, poor wettability and adhesion, and uneven coating; above 220℃, the asphalt is prone to oxidation and deterioration, and energy consumption increases. In step S3, the carbonization treatment heating rate is below 1℃ / min, resulting in excessively low production efficiency; above 5℃ / min, the asphalt undergoes severe pyrolysis, easily producing cracks and pores. A carbonization final temperature below 600℃ results in insufficient asphalt coking and insufficient shell strength; above 1000℃, the hard carbon structure may shrink excessively, and energy consumption increases. In step S4, the graphitization treatment heating rate is below 3℃ / min, resulting in an excessively long production cycle; above 10℃ / min, the temperature distribution is uneven, and the degree of graphitization is inconsistent. Graphitization temperatures below 2800℃ result in insufficient graphitization and poor material conductivity; temperatures above 3200℃ lead to a significant increase in energy consumption with limited performance improvement. By controlling the process parameters within these ranges, a one-step method for preparing core-shell structured, fast-charging, long-cycle artificial graphite can be achieved, resulting in a simpler and lower-cost process.

[0038] To reiterate, the lithium-ion battery anode material according to the third aspect of the present invention comprises the aforementioned core-shell structured fast-charging, long-cycle artificial graphite as the active material. This anode material exhibits good structural stability and fast-charging capability, as well as excellent cycle performance.

[0039] Finally, a lithium-ion battery according to a fourth aspect of the present invention is described, comprising the aforementioned negative electrode material. This lithium-ion battery, while possessing high energy density, also exhibits significantly improved fast-charging performance and long-cycle performance.

[0040] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0041] Example 1:

[0042] raw material:

[0043] Aggregate: Needle coke (Liaoning Dantan Technology Group Co., Ltd., D50=15μm), 900g.

[0044] Composite coating agent: 30g of non-biomass hard carbon raw material-1 (self-made according to the method of patent 3, D50=5μm) + 70g of medium-temperature coal tar pitch (Shandong Jiefuyi Zhenxing Chemical Co., Ltd., softening point 90℃).

[0045] Equipment: GH-10 high-speed heating mixer (Beijing Plastics Machinery Factory), NHZ-2 vacuum kneader (Zhengzhou Kecheng Temperature Control Equipment Co., Ltd.), KSL-1700X box furnace (Hefei Kejing Materials), ZGS-1 vacuum graphitization furnace (Shenyang Longji Electromagnetic Technology Co., Ltd.).

[0046] step:

[0047] 1. Put all raw materials into a high-speed mixer and mix at 150°C for 60 minutes.

[0048] 2. Transfer the material to a vacuum kneader, evacuate the vacuum, and fill with nitrogen for protection. Heat to 180°C and stir at 40 rpm for 90 minutes to melt and granulate.

[0049] 3. Take out the granulated product, place it in a box furnace, and carbonize it by heating it to 800℃ at 2℃ / min under a nitrogen atmosphere and holding it at that temperature for 2 hours.

[0050] 4. The carbonized product is placed in a graphite crucible and placed in a vacuum graphitization furnace. The temperature is increased to 3000℃ at 5℃ / min and held for 12 hours.

[0051] 5. After natural cooling, the product is crushed and sieved (400 mesh to remove iron) to obtain core-shell structured artificial graphite product AG-1.

[0052] Example 2:

[0053] raw material:

[0054] Aggregate: Petroleum coke (China Petroleum Jinzhou Petrochemical Branch, D50=10μm), 880g.

[0055] Composite coating agent: 48g of non-biomass hard carbon raw material-2 (self-made according to the method of patent 3, D50=2μm) + 72g of modified pitch (Baowu Carbon Materials Technology Co., Ltd., softening point 110℃).

[0056] Equipment: Same as in Example 1.

[0057] step:

[0058] 1. Premixing temperature: 130℃, time: 45 minutes.

[0059] 2. Kneading and granulation temperature: 200℃, rotation speed: 30rpm, time: 120 minutes.

[0060] 3. Carbonization process: Heat to 900℃ at a rate of 3℃ / min and hold for 1.5 hours.

[0061] 4. Graphitization process: Heat to 2900℃ at a rate of 8℃ / min and hold for 15 hours.

[0062] 5. Following the same procedure as step 5 in Example 1, product AG-2 is obtained.

[0063] Example 3:

[0064] raw material:

[0065] Aggregate: needle coke (D50=18μm), 850g.

[0066] Composite coating agent: 45g of non-biomass hard carbon raw material-3 (self-made according to patent 3 method, D50=8μm) + 105g of petroleum asphalt (Sinopec, softening point 130℃).

[0067] Equipment: Same as in Example 1.

[0068] step:

[0069] 1. Premixing temperature: 180℃, time: 30 minutes.

[0070] 2. Kneading and granulation temperature: 210℃, rotation speed: 50rpm, time: 75 minutes.

[0071] 3. Carbonization process: Heat to 700℃ at a rate of 5℃ / min and hold for 3 hours.

[0072] 4. Graphitization process: Heat to 3100℃ at a rate of 4℃ / min and hold for 10 hours.

[0073] 5. Following the same procedure as step 5 in Example 1, product AG-3 is obtained.

[0074] Comparative example: Using the same aggregate and total coating agent amount (100g) as in Example 1, but only 100g of medium-temperature coal tar pitch was used as the coating agent, and other process conditions were exactly the same, conventional artificial graphite CG-1 was obtained.

[0075] Preparation of negative electrode sheet

[0076] The core-shell structured fast-charging long-cycle artificial graphite obtained in Examples 1-3 was used as the negative electrode active material. It was mixed with conductive agent Super P and binder SBR at a mass ratio of 95:2:3. Deionized water was added to make a slurry with a solid content of 50%. The slurry was coated on a copper foil current collector, dried at 80°C, rolled to a compaction density of 1.6 g / cm³, and cut into round sheets with a diameter of 12 mm to obtain the negative electrode sheet.

[0077] Preparation of positive electrode sheet

[0078] Lithium iron phosphate was used as the positive electrode active material. It was mixed with conductive agent Super P and binder PVDF at a mass ratio of 94:3:3. N-methylpyrrolidone was added to make a slurry with a solid content of 60%. The slurry was coated on an aluminum foil current collector, dried under vacuum at 120°C, rolled, and cut into round sheets with a diameter of 12 mm to obtain the positive electrode sheet.

[0079] Assembly of all batteries

[0080] The aforementioned negative electrode, positive electrode, separator, and electrolyte were assembled into a CR2032 coin cell. The separator was a polypropylene microporous membrane, and the electrolyte was a 1 mol / L LiPF6 mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate in a volume ratio of 1:1:1, with 2% vinylene carbonate as an additive. Battery assembly was completed in an argon-atmosphere glove box, where the water and oxygen content were both below 1 ppm. Electrochemical performance was tested after 24 hours of settling.

[0081] Electrochemical performance testing

[0082] The assembled full cells were subjected to charge-discharge tests at a constant temperature of 25°C. The test voltage range was 2.5V to 4.2V. Three activation cycles were performed at a 0.2C rate, followed by sequential testing of discharge capacity at 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C rates. Finally, the capacity retention was tested after 500 cycles at a 1.0C rate. The full cells assembled in Examples 1-3 exhibited a capacity retention rate exceeding 80% at both 5.0C and 0.2C rates, and a capacity retention rate exceeding 85% after 500 cycles, demonstrating excellent fast-charging performance and long-cycle stability.

[0083] Electrochemical performance comparison (coin cell test, vs. Li / Li+):

[0084] AG-1 357 93.5 99.8 85.1 AG-2 358 93.8 99.7 85.8 AG-3 356 93.0 99.5 84.5 CG-1 (Comparative Example) 355 92.5 99.0 78.8

[0085] Test results show that, compared with the conventional artificial graphite of the comparative example, the core-shell structure fast-charging long-cycle artificial graphite in Examples 1-3 all exhibited an initial reversible specific capacity of over 356 mAh / g, which is basically the same as the 355 mAh / g of the comparative example, indicating that the composite coating layer of the present invention did not sacrifice the bulk capacity of the material. The initial coulombic efficiency was all above 93.0%, higher than the 92.5% of the comparative example, indicating that the core-shell structure coating layer of the present invention is more uniform and dense, reducing irreversible lithium loss during the first charge and discharge process. The capacity retention rates at 0.5C and 0.2C were all above 99.5%, slightly improved compared to the 99.0% of the comparative example, indicating that the material of the present invention has good cycle stability at low rates. The capacity retention rates at 5.0C and 0.2C were all above 84.5%, significantly higher than the 78.8% of the comparative example, with an improvement of 6.3 to 7.0 percentage points, indicating that the synergistic coating layer formed by the hard carbon and soft carbon composite of the present invention provides a high-speed diffusion channel for lithium ions, greatly improving the high-rate fast-charging performance of the material. The test results fully verify that the core-shell structure fast-charging long-cycle artificial graphite of the present invention, while maintaining high capacity and high first-cycle efficiency, also has excellent fast-charging performance and cycle stability. The technical effect is significantly better than that of traditional single soft carbon coated artificial graphite.

[0086] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing core-shell structured fast-charging long-cycle artificial graphite, characterized in that, Includes the following steps: S1 adds aggregate, non-biomass hard carbon raw material powder and asphalt into a mixer and premixes them at 100℃~200℃ to obtain a premixed material; S2 transfers the premixed material to a heated kneading device, and under the protection of an inert atmosphere, heats it to 160°C~220°C for melting, kneading and granulation to form secondary particles with the aggregate as the core and the composite of the non-biomass hard carbon raw material and the asphalt as the shell. S3 involves heating the granulated material to 600℃~1000℃ under an inert atmosphere at a heating rate of 1~5℃ / min for carbonization treatment, and holding the temperature for 1~4 hours. S4 involves heating the carbonized material to 2800℃~3200℃ in an inert atmosphere at a heating rate of 3~10℃ / min for graphitization treatment, holding the temperature for 8~20 hours, and then cooling to obtain the core-shell structured fast-charging long-cycle artificial graphite. The aggregate is petroleum coke or needle coke with an average particle size D50 of 8-20 μm; the non-biomass hard carbon raw material powder has an average particle size D50 of 1-10 μm; the mass ratio of the non-biomass hard carbon raw material powder to the asphalt is 1:9 to 5:5; the mass ratio of the aggregate to the composite coating agent is 95:5 to 85:15, and the composite coating agent is composed of the non-biomass hard carbon raw material powder and the asphalt.

2. The preparation method according to claim 1, characterized in that, The asphalt is coal tar pitch, petroleum asphalt, or modified asphalt, with a softening point of 80℃~150℃.

3. The preparation method according to claim 1, characterized in that, The premixing temperature in S1 is 130℃~180℃, and the time is 30~120 minutes; the stirring speed for melt kneading and granulation in S2 is 20~60 rpm, and the kneading time is 60~180 minutes.

4. The preparation method according to claim 1, characterized in that, The heating rate of the carbonization treatment in S3 is 2~3℃ / min, and the final carbonization temperature is 800℃~900℃; the heating rate of the graphitization treatment in S4 is 4~8℃ / min, and the final graphitization temperature is 2900℃~3100℃.

5. A core-shell structured fast-charging long-cycle artificial graphite, prepared by the method according to any one of claims 1-4, characterized in that, The artificial graphite has a core-shell structure, wherein the core is artificial graphite and the shell is composed of uniformly dispersed graphitized hard carbon and soft carbon, and the shell densely covers the surface of the core.

6. The core-shell structured fast-charging long-cycle artificial graphite according to claim 5, characterized in that, The artificial graphite has a particle size D50 of 10~25μm, a tap density ≥1.0g / cm³, and a specific surface area of ​​1.0~3.0m² / g.

7. The core-shell structured fast-charging long-cycle artificial graphite according to claim 5, characterized in that, In coin cell testing, the artificial graphite exhibits an initial reversible specific capacity ≥350mAh / g, an initial coulombic efficiency ≥93%, and a capacity retention rate ≥84% at 5.0C / 0.2C rates.

8. A lithium-ion battery anode material, characterized in that, The active material includes the core-shell structured fast-charging long-cycle artificial graphite as described in any one of claims 5-7.

9. A lithium-ion battery, characterized in that, It includes the negative electrode material as described in claim 8.

10. The use of the core-shell structured fast-charging long-cycle artificial graphite according to any one of claims 5-7 in the preparation of fast-charging lithium-ion batteries.

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