A method for preparing artificial graphite based on the process of ankerite calcination and hard carbon granulation

Abstract

The application relates to the technical field of carbon materials, and particularly discloses a preparation method of artificial graphite based on coking and hard carbon granulation process. The preparation method of the artificial graphite based on the coking and the hard carbon granulation process comprises the following steps: selecting raw material coke, coarsely crushing the raw material coke to obtain coke powder, calcining the coke powder, finely crushing the coke powder after cooling to obtain shallow calcined coke; mixing the shallow calcined coke with a hard carbon coating liquid, and adopting a horizontal kettle to perform hard carbon granulation by subsection heating, wherein raw materials of the hard carbon coating liquid comprise phenolic resin and phenol; firstly pre-graphitizing the shallow calcined coke at 1100-1200 DEG C, then performing graphitization treatment at 2800-3000 DEG C to obtain a graphitized product; performing liquid phase coating treatment on the graphitized product, and performing carbonization treatment to obtain a mixture, and the artificial graphite is obtained after screening and magnetic removal. The artificial graphite can be used for a lithium ion battery negative electrode material, has excellent particle integrity, uniform dispersity and interface stability, and exhibits excellent rate performance and cycle stability.

Description

Technical Field

[0001] This application relates to the field of carbon materials technology, and more specifically, it relates to a method for preparing artificial graphite based on coke calcination and hard carbon granulation processes. Background Technology

[0002] With the global energy structure transitioning towards low-carbon development, the new energy industry is experiencing explosive growth, especially with the rapid popularization of electric vehicles and large-scale energy storage power stations, creating an increasingly urgent demand for high-performance lithium-ion battery core materials. As a key component of lithium-ion batteries, the performance of anode materials directly determines the battery's energy density, cycle life, fast-charging capability, and safety performance, becoming one of the core bottlenecks restricting the upgrading of new energy equipment. Currently, commercially available lithium-ion battery anode materials are mainly graphite-based, including two main categories: natural graphite and artificial graphite.

[0003] Natural graphite is widely used due to its natural layered structure, high conductivity, and low cost. However, its resources are limited, its cycle stability is poor, and it is prone to lithium dendrite precipitation under fast charging conditions, posing safety hazards. Therefore, artificial graphite, with its advantages of adjustable structure, long cycle life, and high safety, has become one of the mainstream lithium battery anode materials. Currently, artificial graphite is mainly produced from petroleum coke or pitch coke as raw materials, through processes such as calcination, crushing, granulation, graphitization, and surface modification. Among these processes, calcination is a key step in removing volatiles, improving carbon purity, and enhancing structural stability, while granulation directly affects the particle size distribution, tap density, and electrochemical performance of the final product.

[0004] Regarding the aforementioned technologies, the inventors have discovered that existing artificial graphite preparation processes still generally suffer from many problems. Firstly, improper calcination temperature control can easily lead to excessive graphitization of the coke structure or severe carbon loss. Secondly, traditional granulation processes often rely on binders (such as coal tar pitch), which easily introduce impurities and affect the uniformity of subsequent graphitization. Thirdly, insufficient particle strength makes them prone to breakage during subsequent processing, resulting in an increased fine powder ratio. Fourthly, the resulting artificial graphite has a low specific capacity, low initial coulombic efficiency, and poor rate performance. Therefore, there is an urgent need to develop a novel artificial graphite preparation process that can improve the overall electrochemical performance of the material while ensuring high yield. Summary of the Invention

[0005] In order to improve particle morphology, density and structural integrity, and enhance the specific capacity, initial efficiency and cycle stability of artificial graphite, this application provides a method for preparing artificial graphite based on coke calcination and hard carbon granulation processes.

[0006] In a first aspect, this application provides a method for preparing artificial graphite based on coke calcination and hard carbon granulation processes, employing the following technical solution:

[0007] A method for preparing artificial graphite based on coke calcination and hard carbon granulation includes the following steps:

[0008] S1: Select raw coke and coarsely crush it to obtain coke powder. Calcinate the coke powder at 650-800℃, cool it, and then finely crush it to obtain shallow calcined coke.

[0009] S2: The shallow calcined coke is added to the hard carbon coating liquid for mixing, and the hard carbon is granulated by segmented heating in a horizontal reactor to obtain hard carbon coated particles. The raw materials of the hard carbon coating liquid include phenolic resin and phenol.

[0010] S3: The hard carbon coated particles are heated to 1100-1200℃ for pre-graphitization, and then heated to 2800-3000℃ for graphitization treatment to obtain graphitized products.

[0011] S4: The graphitized product is subjected to liquid phase coating treatment, followed by carbonization treatment at 1100-1200℃ to obtain a mixture, which is then screened and demagnetized to obtain the target graphite.

[0012] First, a low-temperature calcination method of 650-800℃ is adopted to replace the traditional single high-temperature calcination, effectively preventing the collapse of the raw material carbon skeleton and carbon loss. Then, a composite hard carbon coating liquid of phenolic resin and phenol is used for hard carbon granulation. The self-adhesive properties of the hard carbon material during the heating process replace the traditional asphalt binder, reducing the introduction of impurities and solving the problems of insufficient particle strength and high fine powder rate. The hard carbon coated particles are subjected to hierarchical graphitization treatment to construct a core-shell structure of ordered graphite microcrystal nuclei and disordered hard carbon shells, which has both high capacity and good fast charging performance. Finally, the surface functional group structure is adjusted and optimized through liquid phase coating and subsequent carbonization treatment, thereby reducing the probability of electrolyte decomposition and improving electrochemical stability.

[0013] The above technical solution combines low-temperature calcination and high-temperature graphitization staged heat treatment, effectively preventing the collapse of the raw material carbon skeleton structure and carbon loss caused by traditional single high-temperature calcination treatment. The granulation technology of hard carbon liquid horizontal autoclave coating significantly improves the morphology, density and structural integrity of the particles, which helps to obtain artificial graphite materials with high specific capacity, high initial efficiency and excellent cycle stability.

[0014] Optionally, the coke powder obtained after coarse crushing in step S1 has a particle size ≤50μm, and the shallow calcined coke obtained after fine crushing has a particle size D50 of 5-8μm.

[0015] Optionally, the raw materials of the hard carbon coating liquid, by mass percentage, include 70-75% phenolic resin and 5-9% phenol, with the balance being water.

[0016] Optionally, the phenolic resin is a boron-modified methyl phenolic resin.

[0017] By adopting the above technical solution, the boron-modified methyl phenolic resin can catalyze the orderly arrangement of carbon atoms during the subsequent high-temperature treatment, significantly improving the conductivity and rate performance of the material. The introduction of boron element enhances the cross-linking network, and the hard carbon shell formed after carbonization is more dense and hard, significantly improving the mechanical strength and tap density of the particles.

[0018] Optionally, the step S2, which involves segmented heating in a horizontal autoclave for hard carbon granulation, is as follows:

[0019] First, raise the temperature to 350-400℃ and hold it at that temperature for 1.5-2.5 hours.

[0020] Then raise the temperature to 550-600℃ and calcine for 1.5-2.5 hours.

[0021] By adopting the above technical solution and using a staged temperature control method, it is helpful to reduce the voids and defects inside the particles and improve the strength and stability of the particles.

[0022] Optionally, the specific steps for liquid-phase coating treatment of the graphitized product in step S4 are as follows:

[0023] Add sucrose to water to prepare a sucrose aqueous solution with a concentration of 12-18 wt%. Add ammonium dihydrogen phosphate while stirring and mix thoroughly. The concentration of ammonium dihydrogen phosphate is 5-8 wt%, forming a composite coating solution.

[0024] The graphitized product is mixed with the composite coating liquid. The mixing process is carried out by spraying. While stirring, the composite coating liquid is sprayed in uniformly to form wet agglomerates. Then, the temperature is increased in a programmed manner to obtain composite graphite particles coated with a polymer film.

[0025] Optionally, the step of programmably heating the wet aggregates specifically includes:

[0026] First, increase the temperature to 120℃ at a rate of 2℃ / min and hold for 30-45 minutes. Then, increase the temperature to 180℃ at a rate of 1℃ / min and hold for 60-120 minutes.

[0027] By adopting the above technical solution and using a sucrose-ammonium dihydrogen phosphate composite carbon source solution, sucrose carbonization can form a dense amorphous carbon layer on the surface of graphite particles, effectively covering surface active sites and reducing side reactions during the first charge and discharge, thereby improving the first coulombic efficiency. The introduction of N and P elements into ammonium dihydrogen phosphate optimizes the electronic structure of the carbon layer, enhances the adsorption and diffusion capacity of composite graphite particles for lithium ions, significantly improves rate performance, and enhances fast charging performance.

[0028] Secondly, this application provides an artificial graphite prepared by a method based on a coke calcination and hard carbon granulation process.

[0029] By adopting the above technical solution, the artificial graphite prepared by this application based on the process of coke calcination and hard carbon granulation has a unique core-shell structure with ordered graphite core and disordered hard carbon shell, which combines high capacity, fast charging performance and long cycle stability. The prepared product can meet the stringent requirements of lithium-ion battery anode materials, energy storage materials and high-end industrial graphite products.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. This application adopts a graded heat treatment path that combines low-temperature calcination and high-temperature graphitization. The artificial graphite prepared has a unique core-shell structure with ordered graphite cores and disordered hard carbon shells. Compared with the traditional single high-temperature calcination method, it effectively prevents the collapse of the raw material carbon skeleton and carbon loss. It does not require strong acid and alkali treatment, and the emission of volatile organic compounds is controllable, which is in line with the trend of green manufacturing development.

[0032] 2. This application adopts a hard carbon liquid horizontal autoclave coating granulation technology. The phenolic resin system is used to coat the shallow calcined coke obtained by low-temperature calcination and then hard carbon granulation is performed. The self-adhesive properties of the hard carbon material during the heating process replace the traditional asphalt binder, reducing the introduction of impurities. At the same time, it can effectively improve the morphology, density and structural integrity of the particles and enhance the mechanical strength of the particles.

[0033] 3. This application uses a sucrose-sodium dihydrogen phosphate composite carbon source solution to perform liquid-phase coating treatment on graphitized products, which effectively covers the surface active sites and optimizes the electronic structure of the carbon layer, enhancing the adsorption and diffusion ability of composite graphite particles for lithium ions. The prepared target graphite product has excellent rate performance, fast charging performance and long cycle stability. Attached Figure Description

[0034] Figure 1 Here is a SEM image of the artificial graphite material prepared in Example 1 of this application;

[0035] Figure 2 This is the XRD diffraction pattern of the artificial graphite material prepared in Example 1 of this application. Detailed Implementation

[0036] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0037] Example

[0038] Example 1

[0039] A method for preparing artificial graphite based on coke calcination and hard carbon granulation includes the following steps:

[0040] S1: Select low-sulfur, low-ash petroleum needle coke as raw material coke, coarsely crush to obtain coke powder with an average particle size ≤50μm, calcine the coke powder at 650℃, hold for 120min, cool and then perform air jet milling and shaping to obtain shallow calcined coke with D50 of 5-8μm.

[0041] S2: The lightly calcined coke is added to the hard carbon coating liquid at a mass ratio of 8:2 and mixed. The hard carbon granulation is carried out by segmented heating in a horizontal reactor. First, the temperature is raised to 350℃ and calcined for 2.5h. Then, the temperature is raised to 550℃ and calcined for 2.5h to obtain hard carbon coated particles. The raw materials of the hard carbon coating liquid include 75% boron-modified methyl phenolic resin, 9% phenol and 16% water by mass percentage.

[0042] The preparation method of boron-modified methyl phenolic resin is as follows: Sodium hydroxide is added to melted phenol and stirred evenly. Then, paraformaldehyde is added in batches at a uniform rate. The molar ratio of phenol, paraformaldehyde and sodium hydroxide is 1:1.2:0.01. The reaction is carried out at 60℃ for 3 hours, and then at 70℃ for 2 hours to obtain methyl phenolic resin. The temperature is then lowered to 60℃. Boric acid is weighed according to the ratio of boric acid to 8% of the mass of the obtained methyl phenolic resin. A boric acid solution is prepared by dissolving boric acid in ethanol at a material-to-liquid ratio of 1:10. The boric acid solution is added dropwise using a dropping funnel. The reaction is carried out at a constant temperature for 4 hours. The solid content of the resin is controlled to be 60% by rotary evaporation to obtain boron-modified methyl phenolic resin.

[0043] S3: Hard carbon coated particles are pre-graphitized and carbonized at 1100℃ at 25℃ / min under nitrogen protection and held for 3 hours. Then they are transferred to a graphitization furnace and graphitized at 2900℃ under argon atmosphere for 4 hours to complete graphitization and obtain graphitized products.

[0044] S4: Liquid phase coating treatment of graphitized products: Sucrose is added to water to prepare a 12wt% sucrose aqueous solution. Ammonium dihydrogen phosphate is added while stirring and mixed evenly. The concentration of ammonium dihydrogen phosphate is 5wt%, forming a composite coating solution.

[0045] S5: The graphitized product is placed in a high-speed heating mixer and preheated to 60±5℃. Then, it is mixed with the composite coating liquid at a mass ratio of 10:1. The mixing process is carried out by spraying. While the mixer is continuously stirring, the composite coating liquid is sprayed in uniformly to ensure that the surface of each graphite particle is wetted and coated with a thin layer of liquid to form wet agglomerates. Then, the temperature is programmed. First, the temperature is increased to 120℃ at 2℃ / min and held for 30min. Then, the temperature is increased to 180℃ at 1℃ / min and held for 120min to obtain composite graphite particles coated with polymer film. Then, the mixture is carbonized at 1100℃ to obtain the mixture. After sieving and demagnetization, the target graphite with D50=10-20μm is obtained.

[0046] Example 2

[0047] A method for preparing artificial graphite based on coke calcination and hard carbon granulation includes the following steps:

[0048] S1: Select low-sulfur, low-ash petroleum needle coke as raw material coke, coarsely crush to obtain coke powder with an average particle size ≤50μm, calcine the coke powder at 750℃, hold for 90min, cool and then perform air jet milling and shaping to obtain shallow calcined coke with D50 of 5-8μm.

[0049] S2: The lightly calcined coke is added to the hard carbon coating liquid at a mass ratio of 9:1 and mixed. The hard carbon is granulated by segmented heating in a horizontal reactor. First, the temperature is raised to 400℃ and calcined for 1.5h. Then, the temperature is raised to 600℃ and calcined for 1.5h to obtain hard carbon coated particles. The raw materials of the hard carbon coating liquid include 70% boron-modified methyl phenolic resin, 5% phenol and 25% water by mass percentage.

[0050] The preparation method of boron-modified methyl phenolic resin is as follows: Sodium hydroxide is added to melted phenol and stirred evenly. Then, paraformaldehyde is added in batches at a uniform rate. The molar ratio of phenol, paraformaldehyde and sodium hydroxide is 1:1.2:0.01. The reaction is carried out at 60℃ for 3 hours, and then at 70℃ for 2 hours to obtain methyl phenolic resin. The temperature is then lowered to 60℃. Boric acid is weighed according to the ratio of boric acid to 5% of the mass of the obtained methyl phenolic resin. A boric acid solution is prepared by dissolving boric acid in ethanol at a material-to-liquid ratio of 1:10. The boric acid solution is added dropwise using a dropping funnel. The reaction is carried out at a constant temperature for 4 hours. The solid content of the resin is controlled to be 60% by rotary evaporation to obtain boron-modified methyl phenolic resin.

[0051] S3: Hard carbon coated particles are pre-graphitized and carbonized at 1200℃ at 25℃ / min under nitrogen protection and held for 3 hours. Then they are transferred to a graphitization furnace and graphitized at 2800℃ under argon atmosphere for 3 hours to complete graphitization and obtain graphitized products.

[0052] S4: Liquid phase coating treatment of graphitized products: Sucrose is added to water to prepare a 15wt% sucrose aqueous solution. Ammonium dihydrogen phosphate is added while stirring and mixed evenly. The concentration of ammonium dihydrogen phosphate is 7wt%, forming a composite coating solution.

[0053] S5: The graphitized product is placed in a high-speed heating mixer and preheated to 60±5℃. Then, it is mixed with the composite coating liquid at a mass ratio of 10:1. The mixing process is carried out by spraying. While the mixer is continuously stirring, the composite coating liquid is sprayed in uniformly to ensure that the surface of each graphite particle is wetted and coated with a thin layer of liquid to form wet agglomerates. Then, the temperature is programmed. First, the temperature is increased to 120℃ at 2℃ / min and held for 45min. Then, the temperature is increased to 180℃ at 1℃ / min and held for 60min to obtain composite graphite particles coated with polymer film. Then, the mixture is carbonized at 1100℃ to obtain the mixture. After sieving and demagnetization, the target graphite with D50=10-20μm is obtained.

[0054] Example 3

[0055] A method for preparing artificial graphite based on coke calcination and hard carbon granulation includes the following steps:

[0056] S1: Select low-sulfur, low-ash petroleum needle coke as raw material coke, coarsely crush to obtain coke powder with an average particle size ≤50μm, calcine the coke powder at 800℃, hold for 60min, cool and then perform air jet milling and shaping to obtain shallow calcined coke with D50 of 5-8μm.

[0057] S2: The lightly calcined coke is added to the hard carbon coating liquid at a mass ratio of 8:2 and mixed. The hard carbon granulation is carried out by segmented heating in a horizontal reactor. First, the temperature is raised to 400℃ and calcined for 2 hours. Then, the temperature is raised to 600℃ and calcined for 2 hours to obtain hard carbon coated particles. The raw materials of the hard carbon coating liquid include 73% boron-modified methyl phenolic resin, 7% phenol and 20% water by mass percentage.

[0058] The preparation method of boron-modified methyl phenolic resin is as follows: Sodium hydroxide is added to melted phenol and stirred evenly. Then, paraformaldehyde is added in batches at a uniform rate. The molar ratio of phenol, paraformaldehyde and sodium hydroxide is 1:1.2:0.01. The reaction is carried out at 60℃ for 3 hours, and then at 70℃ for 2 hours to obtain methyl phenolic resin. The temperature is then lowered to 60℃. Boric acid is weighed according to the ratio of boric acid to the obtained methyl phenolic resin by 10%. Boric acid solution is prepared by dissolving boric acid in ethanol at a material-to-liquid ratio of 1:10. The boric acid solution is added dropwise using a dropping funnel. The reaction is carried out at a constant temperature for 4 hours. The solid content of the resin is controlled to be 60% by rotary evaporation to obtain boron-modified methyl phenolic resin.

[0059] S3: Hard carbon coated particles are pre-graphitized and carbonized at 1200℃ at 25℃ / min under nitrogen protection and held for 3 hours. Then they are transferred to a graphitization furnace and graphitized at 3000℃ under argon atmosphere for 2 hours to complete graphitization and obtain graphitized products.

[0060] S4: Liquid phase coating treatment of graphitized products: Sucrose is added to water to prepare a sucrose aqueous solution with a concentration of 18wt%. Ammonium dihydrogen phosphate is added while stirring and mixed evenly. The concentration of ammonium dihydrogen phosphate is 8wt%, forming a composite coating solution.

[0061] S5: The graphitized product is placed in a high-speed heating mixer and preheated to 60±5℃. Then, it is mixed with the composite coating liquid at a mass ratio of 10:1. The mixing process is carried out by spraying. While the mixer is continuously stirring, the composite coating liquid is sprayed in uniformly to ensure that the surface of each graphite particle is wetted and coated with a thin layer of liquid to form wet agglomerates. Then, the temperature is programmed. First, the temperature is increased to 120℃ at 2℃ / min and held for 40min. Then, the temperature is increased to 180℃ at 1℃ / min and held for 90min to obtain composite graphite particles coated with polymer film. Then, the mixture is carbonized at 1200℃ to obtain the mixture. After sieving and demagnetization, the target graphite with D50=10-20μm is obtained.

[0062] Example 4

[0063] A method for preparing artificial graphite based on coke calcination and hard carbon granulation process, differing from Example 1 only in that the raw materials of the hard carbon coating liquid in step S2, by mass percentage, include 75% methyl phenolic resin, 9% phenol and 16% water.

[0064] The preparation method of the first-stage phenolic resin is as follows: sodium hydroxide is added to melted phenol and stirred evenly. Then, paraformaldehyde is added in batches at a uniform rate. The molar ratio of phenol, paraformaldehyde and sodium hydroxide is 1:1.2:0.01. The reaction is carried out at 60℃ for 3 hours, and then at 70℃ for 2 hours. The resin solid content is controlled to be 60% by rotary evaporation to obtain the first-stage phenolic resin.

[0065] Comparative Example

[0066] Comparative Example 1

[0067] A method for preparing artificial graphite based on coke calcination and hard carbon granulation is different from Example 1 only in that the liquid phase coating treatment in steps S4-S5 is not performed, and the graphitized product is directly obtained by sieving and demagnetizing to obtain the target graphite.

[0068] Comparative Example 2

[0069] A method for preparing artificial graphite includes the following steps:

[0070] S1: Select low-sulfur, low-ash petroleum needle coke as raw material coke, coarsely crush to obtain coke powder with an average particle size ≤50μm, calcine the coke powder at 650℃, hold for 120min, cool and then perform air jet milling and shaping to obtain shallow calcined coke with D50 of 5-8μm.

[0071] S2: Medium-temperature coal tar pitch was selected as a binder for granulation. The coal tar pitch was heated to 150℃ and melted under nitrogen protection. Then, the shallow calcined coke and the molten coal tar pitch were mixed at a mass ratio of 8:2 and added to a kneader. The mixture was stirred continuously at 60 rpm at 180℃ for 60 minutes to ensure that the coal tar pitch was evenly coated on the surface of each shallow calcined coke. A horizontal autoclave was used for staged heating. First, the temperature was raised to 350℃ and held for 2.5 hours. Then, the temperature was raised to 550℃ and held for 2.5 hours to obtain coated particles.

[0072] S3: The coated particles are pre-graphitized and carbonized at 1100℃ at 25℃ / min under nitrogen protection and held for 3 hours. Then they are transferred to a graphitization furnace and graphitized at 2800℃ under argon atmosphere for 4 hours to complete the graphitization and obtain the graphitized product.

[0073] S4: Liquid phase coating treatment of graphitized products: Sucrose is added to water to prepare a 12wt% sucrose aqueous solution. Ammonium dihydrogen phosphate is added while stirring and mixed evenly. The concentration of ammonium dihydrogen phosphate is 5wt%, forming a composite coating solution.

[0074] S5: The graphitized product is placed in a high-speed heating mixer and preheated to 60±5℃. Then, it is mixed with the composite coating liquid at a mass ratio of 10:1. The mixing process is carried out by spraying. While the mixer is continuously stirring, the composite coating liquid is sprayed in uniformly to ensure that the surface of each graphite particle is wetted and coated with a thin layer of liquid to form wet agglomerates. Then, the temperature is programmed. First, the temperature is increased to 120℃ at 2℃ / min and held for 30min. Then, the temperature is increased to 180℃ at 1℃ / min and held for 120min to obtain composite graphite particles coated with polymer film. Then, the mixture is carbonized at 1100℃ to obtain the mixture. After sieving and demagnetization, the target graphite with D50=10-20μm is obtained.

[0075] Performance testing

[0076] Test Example 1

[0077] The artificial graphite material prepared in Example 1 was subjected to SEM and XRD tests, such as... Figure 1The images shown are scanning electron microscope (SEM) images of the material at low and high magnification. It can be seen that the graphite material exhibits a blocky, layered structure with a particle size between 10-20 μm and uniform dispersion. The high-magnification scan results show that the material in this application has a complete coating layer structure, which is intact and tightly bonded to the core, with no visible peeling or cracks. Figure 2 The XRD diffraction pattern of the material is shown. It can be seen that the XRD diffraction of the graphite material in this application has a diffraction peak corresponding to graphite at 2θ = 26.5°, a diffraction peak corresponding to high-purity silicon at 2θ = 28.4°, and a peak corresponding to disordered carbon at 2θ = 25.5-25.7°. This proves that the application has successfully coated the surface of the highly ordered graphite microcrystals with a moderately disordered hard carbon layer.

[0078] Test Example 2

[0079] The target graphite prepared using the preparation processes of Examples 1-4 and Comparative Examples 1-2 was used as the negative electrode active material for battery electrode preparation, including the following steps:

[0080] 1. Material ratio: 96.5% negative electrode active material (target graphite prepared by the preparation process of Examples 1-4 and Comparative Examples 1-2 of this invention), 2% binder (polyvinylidene fluoride, PVDF) and 1.5% conductive agent (carbon nanotubes).

[0081] 2. Slurry preparation: Disperse the above materials in N-methylpyrrolidone (NMP) solvent and ball mill for 8 hours until the viscosity stabilizes (target viscosity 2500-3500 mPa·s).

[0082] 3. Coating and Drying: The slurry is uniformly coated onto copper foil (8μm thick) with an areal density of 4.8mg / cm²; it is then dried in a vacuum drying oven at 120℃ for 4 hours, followed by rolling to a density of 1.6g / cm³.

[0083] 4. Battery assembly:

[0084] Positive electrode: LiFePO4 (commercial material, compacted density 2.4 g / cm³);

[0085] Diaphragm: Polyethylene microporous membrane (20μm thick);

[0086] Electrolyte: 1 mol / L LiPF6 dissolved in EC:DEC (volume ratio 1:1);

[0087] Assembly: CR2032 button cell, assembled in an argon glove box (humidity <0.1%).

[0088] The target graphite prepared using the preparation processes of Examples 1-4 and Comparative Examples 1-2 was used as the negative electrode active material of the battery, and the following related performance tests were conducted. Each test was performed 3 times, and the average value of the 3 test results was taken as the final result and recorded in Table 1.

[0089] 1. Tap density: The tap density was tested using a density analyzer (model GeoPyc1365) in accordance with the requirements of GB / T 24533-2019.

[0090] 2. Initial discharge specific capacity: Specific capacity was tested at a 0.1C rate;

[0091] 3. Initial Coulombic Efficiency: The test battery is charged to full capacity for the first time, and its charging capacity is recorded. Then, it is discharged for the first time, and its discharge capacity is recorded. Initial Coulombic Efficiency = (Initial Discharge Capacity / Initial Charge Capacity) × 100%;

[0092] 4. Capacity retention rate: After 500 cycles at 1C, the discharge capacity after each cycle is compared with the initial discharge capacity. The capacity retention rate is calculated as (discharge capacity after the 500th cycle / initial discharge capacity) × 100%.

[0093] 5. Fine powder ratio: In accordance with the provisions of GB / T 19077-2016, the fine powder ratio was tested using Malvern Panalytical Mastersizer 3000 (dry dispersion, laser particle size analyzer). The fine powder ratio = (total mass of particles / total sample mass) × 100%.

[0094] Table 1

[0095] Group <![CDATA[Tap density / g / cm 3 > First discharge specific capacity / mAh / g First Coulomb efficiency / % Capacity retention rate after 500 cycles / % Fine powder rate / % Example 1 1.12 358 93.7 98.5 3.3 Example 2 1.18 355 93.9 99.0 2.5 Example 3 1.15 362 93.2 98.5 2.9 Example 4 1.07 350 91.5 96.4 6.1 Comparative Example 1 1.10 356 90.8 95.3 4.8 Comparative Example 2 1.03 352 90.1 91.8 19.8

[0096] Based on the performance test results of Examples 1-3 and Comparative Example 2 in Table 1, it can be seen that this application utilizes a graded heat treatment method of low-temperature calcination and high-temperature graphitization combined with hard carbon-assisted granulation technology to successfully coat a moderately disordered hard carbon layer structure onto the surface of a highly ordered graphite microcrystalline core. The self-adhesive properties of the hard carbon material during the heating process replace the traditional asphalt binder, reducing the introduction of impurities while improving the mechanical strength of the particles. This significantly enhances the high capacity and good fast-charging performance of graphite materials as battery anode materials. The tap density of the prepared artificial graphite material reaches 1.12-1.18 g / cm³. 3 It is significantly higher than that of commercially available products (typically <1.05g / cm³). 3The initial discharge specific capacity is ≥355mAh / g, the initial coulombic efficiency is ≥93%, and the capacity retention rate after 500 cycles is ≥98%, demonstrating excellent rate performance and cycle stability. The fine powder rate is ≤6.5%, which is significantly lower than that of artificial graphite prepared by the traditional asphalt granulation method. This also indicates that the artificial graphite prepared by the process of this application has better particle integrity, uniform dispersion and interface stability.

[0097] According to the performance test results of Examples 1 and 4, when the boron-unmodified methyl phenolic resin is used in the hard carbon coating solution, the tap density of the target graphite material decreases significantly, and the overall electrochemical performance as a negative electrode material decreases, while the fine powder rate increases. This is because without boron modification, the cross-linking network strength of the hard carbon layer weakens, and the structural stability and particle packing density decrease. The catalytic graphitization effect of boron can effectively improve the mechanical strength and tap density of the particles, and improve the intrinsic conductivity and rate performance of the material.

[0098] According to the performance test results of Example 1 and Comparative Example 1, the tap density of the target graphite material obtained without the liquid phase coating treatment of the composite carbon source solution decreased, and the comprehensive electrochemical performance when used as a negative electrode material also decreased, while the fine powder rate increased. This is because the coating layer formed by the composite carbon source can cover the active sites on the graphite surface, reduce the side reactions during the first charge and discharge, and thus improve the first coulombic efficiency. Furthermore, the dual doping of N and P elements further optimizes the electronic structure of the carbon layer, enhances the adsorption and diffusion ability of composite graphite particles for lithium ions, significantly improves the rate performance, and enhances the fast charging performance.

[0099] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing artificial graphite based on coke calcination and hard carbon granulation, characterized in that, Includes the following steps: S1: Select raw coke and coarsely crush it to obtain coke powder. Calcinate the coke powder at 650-800℃, cool it, and then finely crush it to obtain shallow calcined coke. S2: The shallow calcined coke is added to the hard carbon coating liquid for mixing, and the hard carbon is granulated by segmented heating in a horizontal reactor to obtain hard carbon coated particles. The raw materials of the hard carbon coating liquid include phenolic resin and phenol. S3: The hard carbon coated particles are heated to 1100-1200℃ for pre-graphitization, and then heated to 2800-3000℃ for graphitization treatment to obtain graphitized products. S4: The graphitized product is subjected to liquid phase coating treatment, followed by carbonization treatment at 1100-1200℃ to obtain a mixture, which is then screened and demagnetized to obtain the target graphite.

2. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 1, characterized in that, The coke powder obtained after coarse crushing in step S1 has a particle size ≤50μm, and the shallow calcined coke obtained after fine crushing has a particle size D50 of 5-8μm.

3. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 1, characterized in that, The raw materials of the hard carbon coating liquid, by mass percentage, include 70-75% phenolic resin and 5-9% phenol, with the balance being water.

4. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 3, characterized in that, The phenolic resin is a boron-modified methyl phenolic resin.

5. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 1, characterized in that, The specific steps of hard carbon granulation using a horizontal autoclave with segmented heating in step S2 are as follows: First, raise the temperature to 350-400℃ and hold it at that temperature for 1.5-2.5 hours. Then raise the temperature to 550-600℃ and calcine for 1.5-2.5 hours.

6. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 1, characterized in that, The specific steps for liquid-phase coating of the graphitized product in step S4 are as follows: Sucrose is added to water to prepare a sucrose aqueous solution with a concentration of 12-18 wt%. Ammonium dihydrogen phosphate is added while stirring and mixed evenly. The concentration of ammonium dihydrogen phosphate is 5-8 wt%, forming a composite coating solution. The graphitized product is mixed with the composite coating liquid. The mixing process is carried out by spraying. While stirring, the composite coating liquid is sprayed in uniformly to form wet agglomerates. Then, the temperature is increased in a programmed manner to obtain composite graphite particles coated with a polymer film.

7. The method for preparing artificial graphite based on coke calcination and hard carbon granulation process according to claim 6, characterized in that, The specific steps for programmable heating of the wet aggregates are as follows: First, increase the temperature to 120℃ at a rate of 2℃ / min and hold for 30-45 minutes. Then, increase the temperature to 180℃ at a rate of 1℃ / min and hold for 60-120 minutes.

8. A type of artificial graphite, characterized in that, It is prepared by the preparation method of the artificial graphite preparation method based on coke calcination and hard carbon granulation process as described in any one of claims 1-7.

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