Graphite negative electrode material, negative electrode plate, lithium ion battery and preparation method thereof

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a high-power and long-cycle graphite negative electrode material, a negative electrode plate, a lithium ion battery and a preparation method of the lithium ion battery. The invention relates to the technical field of lithium ion battery graphite negative electrode materials. The graphite negative electrode material comprises a graphite inner core and a shell coating the graphite inner core, and the shell is an amorphous carbon layer doped with a fast ion conductor. The graphite inner core is artificial graphite particles subjected to spheroidization treatment. The fast ion conductor doped amorphous carbon layer is formed on the surface of the graphite core by mixing and heating a fast ion conductor, a carbon source and the graphite core. A negative electrode plate prepared from the graphite negative electrode material has abundant porosity, and shows excellent power performance, high-temperature performance and cycling stability on a lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a graphite anode material, anode sheet, lithium-ion battery, and its preparation method. Background Technology

[0002] Traditional graphite anode materials exhibit a relatively slow lithium-ion transport rate during high-power charge and discharge processes (10). -12 ~10 -11 cm 2 The low porosity and high tortuosity of the electrode sheets (on the order of / s) limit the battery's power performance. Furthermore, during long-term cycling, factors such as changes in graphite particle volume and thickening of the SEI film can easily lead to capacity decay and increased impedance, resulting in decreased cycle performance. The mainstream technology in the industry is to coat the graphite surface with amorphous carbon, but this offers limited improvement in fast-charging performance and significantly reduces its high-temperature performance. Summary of the Invention

[0003] In a first aspect, this application provides a graphite anode material comprising a graphite core and a shell covering the graphite core; the shell being an amorphous carbon layer doped with fast ion conductors.

[0004] This application designs a graphite anode material with optimized surface composition and low lithium-ion diffusion barrier, a high-porosity, low-torsivity anode sheet, and a high-power, high-thermal-stability, long-cycle lithium-ion battery by constructing fast-ion conductive channels and synergistically controlling the morphology and structure of artificial graphite anode materials.

[0005] The raw materials for the artificial graphite particles are selected from one or more of needle coke secondary particles, petroleum coke secondary particles, or medium-sulfur coke secondary particles. The aggregate particle size of the artificial graphite particles is 7.5-10μm.

[0006] By selecting graphite with low aggregate particle size, lithium ions migrate a shorter distance inside the graphite particles, thereby improving its fast charging performance.

[0007] In some embodiments, the fast ion conductor-doped amorphous carbon layer is formed on the surface of the graphite core by mixing and carbonizing the fast ion conductor, carbon source, and graphite core.

[0008] By mixing and heating a fast-ion conductor, a carbon source, and a graphite core, a fast-ion conductor-doped amorphous carbon layer is formed on the graphite surface, thereby constructing a composite interface with both high lithium-ion conductivity and electronic conductivity. This effectively reduces the lithium-ion diffusion barrier, improves the mechanical strength of the graphite surface, and optimizes the SEI film composition, thus simultaneously improving the material's fast-charging performance, high-temperature performance, and cycle stability.

[0009] In some embodiments, the graphite anode material satisfies at least one of the following conditions (1)-(2): (1) The fast ion conductor is selected from one or more of lithium phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium lanthanum titanate and their derivatives; (2) The carbon source is selected from one or more of asphalt oil, resin oil, rubber and its derivatives.

[0010] This application involves strong shaping of traditional artificial graphite particles to improve their sphericity and reduce their OI value. Improved sphericity helps to improve the packing density and flowability of the material, reduce the transport path (torsion) of lithium ions inside the electrode, and thus improve the lithium ion transport rate. The low OI value indicates that graphite has higher isotropy and lithium ion intercalation active site density, which is beneficial to high current density charge and discharge performance.

[0011] A second aspect of this application provides a method for preparing the aforementioned graphite anode material, the method comprising the following steps: S1: The raw material of graphite core is subjected to graphitization, carbonization and spheroidization treatment in sequence to obtain artificial graphite particles that have undergone spheroidization treatment; S2: The spheroidized artificial graphite particles, fast ion conductors and carbon source are mixed and carbonized to obtain artificial graphite particles coated with an amorphous carbon layer doped with fast ion conductors. S3: The artificial graphite particles coated with an amorphous carbon layer and doped with fast ion conductors are sieved to obtain graphite anode material.

[0012] This application first optimizes the geometric structure of graphite particles through spheroidization, then achieves uniform doping of amorphous carbon layers with fast ion conductors to coat the graphite particles, thereby synergistically improving the interfacial ion and electron transport capabilities of the material. Finally, through sieving, the particle size distribution of the final product is precisely controlled, thereby ensuring that the negative electrode material has a uniform and optimized stacking structure when it is made into an electrode, thus comprehensively improving the power performance and cycle life of the battery.

[0013] In some implementations, the method satisfies at least one of the following conditions (3)-(16): (3) The temperature of graphitization treatment in step S1 is 2600-3400℃; (4) The graphitization treatment time in step S1 is 20-40 hours; (5) The carbonization temperature in step S1 is 900-1400℃; (6) The carbonization treatment time in step S1 is 1-8 hours; (7) The rotational speed of the air classifier wheel in the spheroidizing process in step S1 is 2000-12000 rpm; (8) The airflow pressure for the spheroidization process in step S1 is 0.6-1.0 MPa; (9) The feed particle size for the spheroidization process in step S1 is ≤200 mesh; (10) The mixing speed in step S2 is 20-400 r / min; (11) The mixing time in step S2 is 10-120 min; (12) The carbonization temperature in step S2 is 600-1200℃; (13) The carbonization time in step S2 is 1-8 hours; (14) The fast ion conductor is selected from one or more of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium lanthanum titanate and their derivatives; (15) The carbon source is selected from one or more of asphalt oil, resin oil, rubber and its derivatives; (16) The mass ratio of the fast ion conductor to the carbon source is 1-10:20-100, the sphericity is 0.8-0.95, the OI value is 2-3, the K value is 0.96-1.02 and the tortuosity is 10-20.

[0014] This application involves coating shaped graphite with a fast-ion conductor and amorphous carbon composite; traditional graphite has a slow lithium-ion diffusion rate (10). -11 ~10 -10 The S / cm scale leads to severe polarization during fast charging; conventional amorphous carbon (soft carbon or hard carbon) offers limited improvement in fast charging performance and severely impacts its high-temperature performance; in contrast, fast ion conductors exhibit high lithium-ion diffusion rates (10⁻⁶ S / cm). -3 ~10 -6 It has high mechanical strength (on the order of S / cm) and the SEI composition can be tuned to be rich in inorganic lithium salts; however, it is a fast ion conductor with extremely poor electronic conductivity (<10). -8 (on the order of S / cm), therefore, composite modification of the graphite surface with fast ion conductors and invisible carbon can significantly improve its lithium-ion diffusion rate, high-temperature performance and high mechanical stability, while ensuring high electronic conductivity.

[0015] This application involves sieving the coated graphite. By selecting appropriate screen mesh size and sieving equipment, and utilizing sieving methods such as vibrating sieving and airflow sieving, the particle size distribution of the graphite is reduced. A suitable particle size distribution allows the graphite particles to pack more densely and uniformly within the electrode, further optimizing the electrode's pore structure, increasing the electrode's compaction density, and simultaneously improving the consistency of lithium-ion transport within the electrode, thereby enhancing the overall performance of the battery.

[0016] A third aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode material layer coated on the surface of the current collector; The negative electrode material layer includes the graphite negative electrode material or the graphite negative electrode material prepared by the method; The negative electrode sheet has abundant porosity. Appropriate porosity is beneficial for electrolyte wetting and lithium ion transport. At the same time, it can accommodate the volume change of graphite during charging and discharging, reduce the damage to the electrode structure, and provide a guarantee for improving the power performance and cycle life of the battery.

[0017] A fourth aspect of this application provides a method for preparing the aforementioned negative electrode sheet, comprising the following steps: The negative electrode material, conductive agent, thickener and binder are mixed to obtain a slurry; The slurry is coated onto the current collector and dried to obtain the negative electrode sheet. The conductive agent is selected from one or more of Ketjen Black, acetylene black, and Super P; The thickener is selected from one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium polyacrylate, and polyacrylic acid; The adhesive is selected from one or more of styrene-butadiene rubber, nitrile rubber, polyvinylidene fluoride, and polytetrafluoroethylene.

[0018] A negative electrode slurry is prepared by mixing graphite negative electrode material with binder, conductive agent and other materials in a certain proportion and adding an appropriate amount of solvent. Then, the negative electrode slurry is uniformly coated on the negative electrode current collector (copper foil) by coating, rolling and other processes. After drying, slitting and other processes, the negative electrode sheet is obtained.

[0019] A fifth aspect of this application provides the application of the graphite anode material or the graphite anode material prepared by the method or the anode sheet in a battery.

[0020] The graphite anode material, its preparation method, or the application of the anode sheet containing the material in the battery can significantly improve the overall performance of the battery, enabling the battery to have excellent fast charging, high-temperature storage, and long cycle life.

[0021] A sixth aspect of this application provides a battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte; wherein the negative electrode is the negative electrode described in the third aspect.

[0022] Existing technologies mostly employ a layered coating approach, primarily aiming to optimize electrode material performance through functional separation (e.g., the inner layer focuses on enhancing ionic conductivity, while the outer layer enhances electronic conductivity or isolates the electrolyte) and synergistic effects. This addresses issues such as slow ion diffusion, low initial efficiency, and poor cycle stability in graphite or hard carbon materials. Simultaneously, layered design achieves interface optimization and process controllability. However, this approach also has drawbacks, including complex fabrication processes, high costs, the risk of weak interlayer bonding, challenges in thickness and uniformity control, and material compatibility issues, potentially affecting the feasibility and consistency of large-scale production. Overall, layered coating is a high-performance-oriented strategy, but a balance must be struck between process simplification and interface reliability.

[0023] Existing technologies often employ a layered coating approach to process electrode materials, as exemplified by patents CN120749142A and CN120261569A. The primary aim is to optimize electrode material performance through the functional separation and synergistic effects of different coating layers, while simultaneously utilizing layered design to achieve interface optimization and process controllability. However, layered coating also presents several drawbacks, including complex fabrication processes, the risk of weak interlayer bonding (requiring the addition of crosslinking agents to improve interlayer adhesion), challenges in thickness and uniformity control, and material compatibility issues.

[0024] Compared with existing technologies, this application combines material geometry, material interface modification, and electrode structure optimization with the improvement of ion transport kinetics to design a comprehensive solution. It introduces amorphous carbon coating doped with fast-ion conductors to form channels that facilitate both rapid lithium-ion and electron transport, significantly improving the migration rate of lithium ions in the electrode material. The resulting modified graphite exhibits high sphericity, low orientation, high lithium-ion diffusion rate, high interfacial mechanical strength, and stability, effectively enhancing the diffusion kinetics and high-temperature stability of lithium ions on the graphite surface. The resulting negative electrode sheet combines high compaction with abundant porosity, improving electrolyte wettability and reducing the tortuosity of lithium-ion transport within the electrode. The resulting lithium-ion battery demonstrates excellent power and high-temperature performance (6C constant current charge ratio ≥90%, capacity recovery rate ≥95% after 21 days of storage at 55℃). Attached Figure Description

[0025] Figure 1 This is a SEM image of the graphite anode material prepared in Example 1.

[0026] Figure 2 This is a SEM image of the graphite anode material prepared in Comparative Example 5.

[0027] Figure 3 This is a comparison diagram of the solid-phase diffusion coefficients of the graphite anode materials in Example 1 and Comparative Example 1.

[0028] Figure 4 HPPC curves are shown as a comparison of the graphite anode materials used in Example 1 and Comparative Example 1 for the fabricated pouch cells.

[0029] Figure 5 The graph shows the charge performance of the pouch cell prepared using the graphite anode material of Example 1.

[0030] Figure 6 This is a comparison chart of the high-temperature storage performance of pouch cells prepared using the graphite anode materials of Example 1 and Comparative Example 1.

[0031] Figure 7 The graph shows the overall performance data of the pouch cell prepared using the graphite anode material of Example 1 under high-temperature storage and high-rate charging conditions. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] For the sake of brevity, this document only discloses a few specific numerical ranges for a given parameter. However, any lower limit can be combined with any upper limit to form an unspecified range, and any lower limit can be combined with other lower limits to form an unspecified range; similarly, any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit, combined with any other point or single value, or with other lower or upper limits, to form an unspecified range. It should be understood that this disclosure is not limited to the specific methods, schemes, and reagents described herein, and is itself subject to variation. The terminology used herein is for the purpose of describing specific embodiments or aspects only and is not intended to limit the scope of this disclosure.

[0034] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application). Unless otherwise expressly stated, all reagents used in this application are commonly used reagents for chemical analysis or experiments and are derived from conventional commercial suppliers in the art.

[0035] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0036] In this article, needle coke secondary graphitized particles refer to secondary graphite particles obtained by bonding multiple primary particles together through a granulation process using needle coke (high-quality coke with obvious fibrous or needle-like structures) as raw material, followed by high-temperature graphitization treatment; petroleum coke secondary graphitized particles refer to secondary graphite particles made by granulation and high-temperature graphitization treatment using petroleum coke (obtained from the coking of heavy petroleum oil or residual oil) as raw material; and medium-sulfur coke secondary graphitized particles refer to secondary graphite particles obtained by granulation and graphitization treatment using coke with a medium sulfur content as raw material.

[0037] In this paper, fast ion conductors refer to a class of materials that can exhibit extremely high ionic conductivity under solid conditions; fast ion conductor doping refers to a composite process in which fast ion conductor powder is uniformly mixed with an organic carbon source during the preparation of an amorphous carbon coating, and the fast ion conductor is dispersed and fixed in the amorphous carbon matrix at the nano or micro scale through carbonization treatment.

[0038] In this paper, amorphous carbon layer refers to a thin film or coating composed of amorphous carbon, lacking a long-range ordered crystal structure, and derived from the pyrolysis of organic carbon source into soft carbon or hard carbon, wherein the residual carbon content is 0.5%~5%.

[0039] In this paper, aggregate particle size refers to the average particle size of the granular material after the graphite coke source has undergone coarse crushing and toner processing.

[0040] In this paper, sphericity refers to a geometric parameter that characterizes how close a particle is to a perfect sphere. Its value is between 0 and 1, and the higher the value, the closer the particle shape is to a sphere.

[0041] In this paper, the OI value refers to the parameter of the degree of order of the graphite sheet arrangement in the graphite material. It is measured by X-ray diffraction (XRD) and its value is defined as the ratio of the diffraction peak intensity I(002) of the (002) crystal plane to the diffraction peak intensity I(110) of the (110) crystal plane, that is, OI = I(002) / I(110).

[0042] In this paper, the K value refers to the parameter characterizing the width of the particle size distribution of powder materials. Its value is defined as (D90 - D10) / D50, where D10, D50, and D90 are the particle sizes corresponding to the cumulative particle size distribution percentages of 10%, 50%, and 90%, respectively.

[0043] In this paper, tortuosity refers to a physical quantity used to describe the degree of tortuosity of the pores in a porous electrode. It reflects the ratio of the length of the migration path of lithium ions in the actual pores to the length of the ideal straight path of the electrode thickness.

[0044] In this article, residual carbon refers to the percentage of the mass of solid carbon remaining after a specific high-temperature carbonization process of an organic carbon source relative to the mass of the original carbon source.

[0045] In this article, LATP refers to lithium aluminum titanium phosphate, LLZO refers to lithium lanthanum zirconium oxide, and LLTO refers to lithium lanthanum titanate.

[0046] In this article, SP refers to Super P, a commonly used conductive agent in carbon black.

[0047] In this article, CMC refers to carboxymethyl cellulose, which is used as a thickener in lithium-ion battery anode slurry.

[0048] In this article, SBR refers to styrene-butadiene rubber, a common water-based binder used in conjunction with CMC to provide adhesion to electrode active materials.

[0049] In this article, ACR refers to the AC internal resistance, which is the battery internal resistance measured by the AC impedance method.

[0050] In this paper, DCR refers to the DC internal resistance, which is the battery internal resistance calculated based on voltage changes under a specific pulse current and a specific SOC (state of charge).

[0051] In this article, the 6C constant current charge ratio refers to the ratio (expressed as a percentage) of the amount of electricity charged when the battery is discharged to the cutoff voltage and then charged at a constant current rate of 6C to the cutoff voltage, to the rated capacity of the battery. It is used to evaluate the fast charging capability of the battery.

[0052] In this article, 6C discharge / 1C discharge capacity refers to the ratio (expressed as a percentage) of the capacity that a battery can release when discharged at a high rate of 6C to the capacity that it can release when discharged at a high rate of 1C. This ratio is used to evaluate the battery's high-rate discharge performance retention rate.

[0053] In this paper, solid-phase diffusion coefficient testing refers to an electrochemical characterization method for quantitatively measuring the migration rate of ions (such as lithium ions) within a solid-phase lattice of a battery electrode material.

[0054] In this paper, GITT (Galvanostatic Intermittent Titration) refers to a key electrochemical testing method that measures the diffusion kinetics of lithium ions and other molecules in graphite materials by applying intermittent galvanostatic pulses followed by static relaxation.

[0055] In this article, HPPC testing refers to a standard test method that measures the internal resistance and power capability of a battery at different discharge depths by applying specific charge and discharge pulses.

[0056] In this document, the experimental methods used in the examples and comparative examples are all conventional techniques widely established in the art. Unless otherwise specified, the reagents, antibodies, or materials used are all commercially available generic products.

[0057] In this article, “EC” refers to ethylene carbonate, “PC” refers to propylene carbonate, “EMC” refers to ethyl methyl carbonate, “EA” refers to ethyl acetate, “LiPF6” refers to lithium hexafluorophosphate, “LiFSI” refers to lithium difluorosulfonyl imide, “VC” refers to vinylene carbonate, “FEC” refers to fluoroethylene carbonate, “DTD” refers to vinyl sulfate, “LiPO2F2” refers to lithium difluorophosphate, “MMDS” refers to methane disulfonate, and “DMC” refers to dimethyl carbonate.

[0058] Experimental reagents: Needle coke single particles (FG1), needle coke secondary particles (FG2), petroleum coke secondary particles (FGB), lithium iron phosphate (GX100), electrolyte for soft-pack batteries (EV-05), and LATP (DQ7) are all produced by Guoxuan Company; asphalt oil was purchased from Liaoning Xinde New Material Technology (Group) Co., Ltd., with the product number XD200; SP was purchased from Supermicro high carbon black. P™-Li; CMC was purchased from Daicel, item number CMC2200; SBR was purchased from Dongguan Hongkai, item number DZ-8092; copper foil was purchased from Jiujiang Defu Technology Co., Ltd., item number GT-5μm; separator was purchased from Hebei Jinli New Energy Materials Technology Co., Ltd., item number C-09A; positive electrode sheet (lithium iron phosphate coated aluminum foil) was purchased from Kelude, item number LF06XX; lithium metal sheet was purchased from AlfaAesar, item number 10769; gaskets and springs were purchased from Shenzhen Luojia Electronics Co., Ltd., item number WJ-2032; positive / negative electrode shells were purchased from Xiamen TOB New Energy, item number TOB-2032-304 / 316; aluminum-plastic film was purchased from DNP, item number D-ND408. The electrolyte (EV-05) composition of the soft-pack battery (by weight) is as follows: 25 parts EC, 5 parts PC, 20 parts EMC, 50 parts EA, 3.5 parts VC, 0.7 parts FEC, 0.7 parts DTD, 0.3 parts LiPO2F2, 1 part MMDS, 0.7M LiPF6, and 0.4M LiFSI. The electrolyte of the CR2032 coin cell (1.0M LiPF6 in EC:DMC:EMC=1:1:1 wt% with 1.0% VC) was purchased from Zhengzhou Aikem Chemical Co., Ltd., product number LB-066.

[0059] Example 1 A method for preparing a high-power, long-cycle graphite anode material includes the following steps: S1: 20 kg of needle coke secondary particles are heated to 3000℃ at 10℃ / min and held for 30 h to complete the graphitization treatment. Then, the temperature is increased to 1150℃ at 5℃ / min and held for 2 h to carry out the carbonization treatment, which completes the graphitization of needle coke secondary particles into graphite (aggregate particle size of 8.5μm). The graphite is then added to an air jet mill shaping equipment with a classifying wheel speed of 8000rpm, an air pressure of 0.6MPa, a feed particle size of ≤200 mesh, and a processing time of 60 min to obtain spheroidized artificial graphite particles.

[0060] S2: Take 10 kg of the spheroidized artificial graphite particles obtained in S1, 50 g of fast ion conductor LATP, and 1 kg of asphalt oil (coking value 15%) and add them to a mechanical fusion device. Set the process speed to 200 r / min and maintain for 2 h to achieve uniform mixing of the three materials. Then transfer the mixture to a carbonization furnace and, under nitrogen atmosphere protection, heat it to 1150℃ at 5℃ / min and hold for 4 h to perform carbonization treatment, thereby obtaining artificial graphite coated with an amorphous carbon layer doped with fast ion conductor.

[0061] S3: The amorphous carbon layer doped with fast ion conductors obtained in S2 is coated with artificial graphite and then subjected to a turbine air classifier (classifier wheel speed 2000 rpm, airflow speed 8 m / s) and a vibrating screen (150 mesh screen) to remove fine powder and large particles, and the final product with optimized particle size sieving is obtained, namely graphite anode material.

[0062] Example 2 A method for preparing a high-power, long-cycle graphite anode material includes the following steps: S1: 20 kg of secondary petroleum coke particles are heated to 3000℃ at 10℃ / min and held for 30 h to complete the graphitization treatment. Then, the temperature is increased to 1150℃ at 5℃ / min and held for 2 h to carry out the carbonization treatment, which completes the graphitization of secondary petroleum coke particles into graphite (aggregate particle size of 10μm). The graphite is then added to an air jet mill shaping equipment with a classifying wheel speed of 8000 rpm, an air pressure of 0.6 MPa, a feed particle size of ≤200 mesh, and a processing time of 60 min to obtain spheroidized artificial graphite particles.

[0063] S2: Take 10 kg of the spheroidized artificial graphite particles obtained in S1, 50 g of the fast ion conductor LATP, and 1 kg of asphalt oil (15% residual carbon) and add them to a mechanical fusion device. Set the process speed to 200 r / min and maintain for 2 h to achieve uniform mixing of the three materials. Then transfer the mixture to a carbonization furnace and, under nitrogen atmosphere protection, heat it to 1150℃ at 5℃ / min and hold for 2 h to perform carbonization treatment, thereby obtaining artificial graphite coated with an amorphous carbon layer doped with a fast ion conductor.

[0064] S3: The amorphous carbon layer doped with fast ion conductors prepared in S2 is coated with artificial graphite and graded and vibrated by sieving (150 mesh screen) to remove fine powder and large particles. After sieving, graphite anode material is obtained with a particle size distribution K value of 1.05.

[0065] Example 3 The operation steps for preparing graphite anode material in Example 3 are the same as those in Example 1. The difference between Example 3 and Example 1 is that the aggregate particle size of the needle coke secondary graphitized graphite used in process S1 is 7.5 μm.

[0066] Example 4 The operation steps for preparing graphite anode material in Example 4 are the same as those in Example 1. The difference from Example 1 is that the linear velocity is controlled at 80 m / s during process S1.

[0067] Example 5 The operation steps for preparing graphite anode material in Example 5 are the same as those in Example 1. The difference between Example 5 and Example 1 is that the shaping process in S1 takes 6 hours.

[0068] Example 6 The operation steps for preparing the graphite anode material in Example 6 are the same as those in Example 1. The difference from Example 1 is that the amount of fast ion conductor LATP added during S2 is 20 g.

[0069] Example 7 The operation steps for preparing graphite anode material in Example 7 are the same as those in Example 1. The difference from Example 1 is that the amount of asphalt oil added in process S2 is 1.33 kg.

[0070] Example 8 The operation steps for preparing the graphite anode material in Example 8 are the same as those in Example 1. The difference between Example 8 and Example 1 is that the fast ion conductor used in the S2 process is LLZO.

[0071] Example 9 The operation steps for preparing the graphite anode material in Example 9 are the same as those in Example 1. The difference from Example 1 is that the carbonization temperature used in process S2 is 1100 ℃.

[0072] Example 10 Example 10 The operation steps for preparing graphite anode material are the same as those in Example 1. The difference from Example 1 is that the speed of the airflow stager used in process S3 is 3000 rpm.

[0073] Example 11 The operation steps for preparing graphite anode material in Example 11 are the same as those in Example 1. The difference between Example 1 and Example 1 is that the vibrating screen used in process S3 is 200 mesh.

[0074] Comparative Example 1 Comparative Example 1 uses untreated needle-shaped coke single-particle graphitized products as graphite anode materials.

[0075] Comparative Example 2 Comparative Example 2 uses untreated needle-shaped coke secondary particle graphitized products as graphite anode material.

[0076] Comparative Example 3 Comparative Example 3 uses untreated petroleum coke secondary particulate graphitized product as the graphite anode material.

[0077] Comparative Example 4 Comparative Example 4 used needle coke secondary particle coating (1.5% residual carbon) without any treatment as graphite anode material.

[0078] Comparative Example 5 The operation steps for preparing the graphite anode material in Comparative Example 5 are the same as those in Example 1. The difference from Example 1 is that the graphite core is coated in layers: First, the artificial graphite particles that have been spherized are coated with asphalt oil and carbonized to form an amorphous carbon layer on the surface of the artificial graphite particles. Then, the artificial graphite particles coated with the amorphous carbon layer are coated with a fast ion conductor and calcined to obtain artificial graphite particles coated with a fast ion conductor layer (outer layer) and an amorphous carbon layer (inner layer), which is the graphite anode material.

[0079] Comparative Example 6 The operation steps for preparing the graphite anode material in Comparative Example 6 are the same as those in Example 1. The difference from Example 1 is that the graphite core is coated in layers: First, the spheroidized artificial graphite particles are coated with fast ion conductors and calcined to form fast ion conductivity on the surface of the artificial graphite particles. Then, the artificial graphite particles coated with fast ion conductor layers are coated with asphalt oil and carbonized to obtain artificial graphite particles coated with an amorphous carbon layer (outer layer) and a fast ion conductor layer (inner layer), thus preparing the graphite anode material.

[0080] Experimental Example 1: Assembly of a Soft-Pack Battery 3 kg of graphite anode material, 0.0155 kg of SP, 73 kg of CMC03, and 0.1166 kg of SBR prepared in Examples 1-11 and Comparative Examples 1-6 were mixed to form a negative electrode slurry (viscosity 2000~6000 mPa·s, solid content 50~51%), resulting in a negative electrode slurry. The negative electrode slurry was then uniformly coated onto a 5 μm copper foil (double-sided areal density 164 g / m²) using a coating machine. 2 After further processes such as rolling and slitting, the negative electrode sheet is obtained. Finally, using lithium iron phosphate coated aluminum foil as the positive electrode, the prepared negative electrode sheet, positive electrode sheet, electrolyte, and separator are assembled into a pouch battery according to conventional processes.

[0081] Test Example 2: Testing of Graphite Property Data The sphericity and particle size distribution (K value) of graphite particles were measured and calculated using a laser particle size analyzer (Malvin Mastersizer 3000). The OI value was measured and calculated using a Bruker D8 Advance X-ray diffractometer. The tortuosity was calculated by electrochemical impedance spectroscopy using a symmetrical cell.

[0082] The physical property data of the graphite anode materials of different embodiments and comparative examples are shown in Table 1. The SEM image of the graphite anode material of Example 1 is shown below. Figure 1 As shown; SEM image of the graphite anode material in Comparative Example 5 is shown below. Figure 2 As shown in Comparative Example 5, the graphite anode material obtained after calcination of the graphite treated with the graphite treatment method exhibits fast ion conductor agglomeration precipitation.

[0083] Table 1. Physical property data of different graphite anode materials

[0084] Experimental Example 3: Solid-phase diffusion coefficient test of graphite anode material (1) Preparation of CR2032 coin cell: Graphite active material and PVDF were weighed at a mass ratio of 95:5, NMP solvent was added and stirred to form a slurry, which was coated on copper foil with a wet film thickness of 100-150 μm. After standing at room temperature for 10 min, the film was vacuum dried at 80℃ for 12 h, and then rolled and punched into an electrode sheet with a diameter of 12 mm. The CR2032 battery was assembled in an argon glove box. Graphite electrode sheets were placed in the negative electrode shell in sequence, and 10-15 μL of electrolyte was added to soak for 5 min. After covering with a separator, 5-10 μL of electrolyte (1.0 M LiPF6 in EC:DMC:EMC=1:1:1 wt% with 1.0% VC) was added. Lithium metal sheet was placed, and gaskets and spring sheets were placed in sequence. After covering with the positive electrode shell, the battery was gently pressed and sealed. After sealing, the battery was left to stand for 24 h to obtain the CR2032 coin cell for later use.

[0085] (2) Solid-phase diffusion coefficient test of graphite anode material: The solid-phase diffusion coefficient of graphite anode material was obtained by GITT test using the assembled CR2032 half-cell as the test object. The GITT test method is as follows:

[0086] The solid-phase diffusion coefficient results of the graphite anode material are as follows: Figure 3 As shown.

[0087] Example 4: HPPC Test of Pouch Cells The HPPC test method for pouch batteries is as follows: (1) At 25℃, discharge the battery cell at 1C to 2.0V and let it stand for 60 minutes; (2) Then charge it at 1C constant current to 3.65V, maintain the voltage to 0.05C, and let it stand for 60 minutes; (3) Then discharge it at 1C constant current to 2.0V and let it stand for 60 minutes; (4) Repeat steps (2)-(3) above for 5 weeks, and take the average value of the discharge capacity of the last 3 weeks as C. a (5) Battery cell C a / 1h constant current discharge to 2.0V, then stand for 10min; (6) Battery cell C a / 1h constant current charging to 3.65V, then maintain the voltage to 0.05C and let stand for 60min; (7) Battery cell C a / 1h constant current discharge for 6min, then stand for 60min; (8) Battery cell 5xC a / 1h constant current discharge for 10s, rest for 40s; (9) Battery cell 3.75xCa / 1h constant current charge for 10s; (10) Battery cell C a / 1h constant current discharge 347.5s, stand for 60min; (11) Cycle steps (8)-(10) 9 times; (12) Battery cell Ca / 1h constant current discharge to 2.0V.

[0088] HPPC test results for pouch batteries are as follows Figure 4 As shown.

[0089] Test data of fast charging performance of pouch battery in Example 5 Table 2 shows the test data of the physical properties of the graphite anode materials in different embodiments and comparative examples. The charge performance of the pouch cell prepared using the graphite anode material of Example 1 is shown in the graph. Figure 5 As shown.

[0090] Table 2. Fast charging performance test data of different graphite anode materials in 2.5 Ah pouch batteries

[0091] Experiment 6: High-Temperature Storage Performance Test of Pouch Cells The high-temperature storage performance test method for pouch batteries is as follows: (1) At 25℃, after 1C constant capacity for 5 weeks, let stand for 30 minutes; (2) Then charge at 1C constant current to 3.65V, and stop at constant voltage to 0.05C, and test the voltage, internal resistance and thickness data of the battery cell; (3) Let stand at 55℃ for 7 days, and place at room temperature for about 5 hours to adapt to the ambient temperature, and test the voltage, internal resistance and thickness data of the battery cell; (4) Then discharge at 1C to 2.0V to obtain the retention capacity, and let stand for 60 minutes; (5) Then charge at 1C constant current to 3.65V, and stop at constant voltage to 0.05C, and let stand for 60 minutes; (6) Then discharge at 1C to 2.0V to obtain the recovery capacity, and let stand for 60 minutes.

[0092] The results of the high-temperature storage performance test of the pouch battery are as follows: Figure 6 As shown, the fabricated soft-pack battery exhibits excellent power and high-temperature performance (6C constant current charge ratio ≥90%, capacity recovery rate ≥95% after 21 days of storage at 55℃), such as... Figure 7 As shown.

[0093] The embodiments described in this invention are merely illustrative examples. The embodiments of this invention are not limited to the above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this invention shall be considered equivalent substitutions and are included within the protection scope of this invention.

Claims

1. A graphite anode material, characterized in that, The graphite anode material includes a graphite core and a shell covering the graphite core; the shell is an amorphous carbon layer doped with fast ion conductors.

2. The graphite anode material as described in claim 1, characterized in that, The raw material for the graphite core is selected from one or more of needle coke secondary particles, petroleum coke secondary particles, or medium-sulfur coke secondary particles. The aggregate particle size of the raw material for the graphite core is 7.5-10 μm.

3. The graphite anode material as described in claim 1, characterized in that, The fast ion conductor-doped amorphous carbon layer is formed on the surface of the graphite core by mixing and carbonizing the fast ion conductor, carbon source, and graphite core.

4. The graphite anode material as described in claim 3, characterized in that, The graphite anode material satisfies at least one of the following conditions (1)-(2): (1) The fast ion conductor is selected from one or more of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium lanthanum titanate and their derivatives; (2) The carbon source is selected from one or more of asphalt oil, resin oil, rubber and its derivatives.

5. A method for preparing graphite anode materials, characterized in that, The method includes the following steps: S1: The raw material of the graphite core is subjected to graphitization, carbonization and spheroidization treatment in sequence to obtain artificial graphite particles that have undergone spheroidization treatment; S2: The spheroidized artificial graphite particles, fast ion conductors and carbon source are mixed and carbonized to obtain artificial graphite particles coated with an amorphous carbon layer doped with fast ion conductors. S3: The artificial graphite particles coated with an amorphous carbon layer and doped with fast ion conductors are sieved to obtain graphite anode material.

6. The method as described in claim 5, characterized in that, The method satisfies at least one of the following conditions (3)-(16): (3) The temperature of graphitization treatment in step S1 is 2600-3400℃; (4) The graphitization treatment time in step S1 is 20-40 hours; (5) The carbonization temperature in step S1 is 900-1400℃; (6) The carbonization treatment time in step S1 is 1-8 hours; (7) The rotational speed of the air classifier wheel in the spheroidizing process in step S1 is 2000-12000 rpm; (8) The airflow pressure for the spheroidization process in step S1 is 0.6-1.0 MPa; (9) The feed particle size for the spheroidization process in step S1 is ≤200 mesh; (10) The mixing speed in step S2 is 20-400 r / min; (11) The mixing time in step S2 is 10-120 min; (12) The carbonization temperature in step S2 is 600-1200℃; (13) The carbonization time in step S2 is 1-8 hours; (14) The fast ion conductor is selected from one or more of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium lanthanum titanate and their derivatives; (15) The carbon source is selected from one or more of asphalt oil, resin oil, rubber and its derivatives; (16) The mass ratio of the fast ion conductor to the carbon source is 1-10:20-100, the sphericity is 0.7-0.95, the OI value is 1-4, the K value is 0.5-1.5 and the tortuosity is 10-40.

7. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode material layer coated on the surface of the current collector; The negative electrode material layer includes the graphite negative electrode material as described in any one of claims 1-4 or the graphite negative electrode material prepared by the method described in claim 5 or 6.

8. A method for preparing the negative electrode sheet as described in claim 7, characterized in that, Includes the following steps: The negative electrode material, conductive agent, thickener and binder as described in any one of claims 1-4 are mixed to obtain a slurry; The slurry is coated onto the current collector and dried to obtain the negative electrode sheet. The conductive agent is selected from one or more of Ketjen Black, acetylene black, and Super P; The thickener is selected from one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium polyacrylate, and polyacrylic acid; The adhesive is selected from one or more of styrene-butadiene rubber, nitrile rubber, polyvinylidene fluoride, and polytetrafluoroethylene.

9. The application of the graphite anode material as described in any one of claims 1-4, or the graphite anode material prepared by the method described in claim 5 or 6, or the anode sheet as described in claim 7, in a battery.

10. A battery, characterized in that, It includes a negative electrode, a positive electrode, a separator, and an electrolyte; the negative electrode is the negative electrode as described in claim 7.

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