Composite graphite negative electrode material and preparation method thereof

Abstract

This invention discloses a composite graphite anode material and its preparation method. The material comprises: a graphite matrix, wherein the graphite matrix is ​​a secondary particle formed by hard carbon granulation of single-particle artificial graphite, and an amorphous soft carbon layer coating the surface of the graphite matrix. By constructing a composite structure of secondary particles and soft carbon spray coating through hard carbon granulation, a rapid lithium-ion diffusion channel is formed in the graphite matrix, and the interface is stabilized, significantly improving the high-rate fast charging performance and cycle stability of the anode material.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically a composite graphite anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries have become the mainstream power source for portable electronic devices and electric vehicles due to their high energy density and long cycle life. Graphite anode materials are the most widely used anode materials due to their wide availability and stable electrochemical performance.

[0003] However, traditional graphite anode materials suffer from a low lithium-ion diffusion coefficient. During high-rate charging, the insertion process of lithium ions between graphite layers is slow, easily leading to the formation of deposited lithium on the graphite surface. This not only reduces the reversible capacity of the battery but may also induce lithium dendrite growth, causing internal short circuits and posing serious safety hazards. Although existing technologies have proposed modification strategies such as carbon coating and particle refinement, it remains difficult to achieve a good balance between fast-charging performance, cycle stability, and safety.

[0004] Therefore, there is an urgent need to provide a composite graphite anode material that can balance high-rate fast charging performance with high safety, as well as its preparation method and a lithium-ion battery containing the material. Summary of the Invention

[0005] In view of this, the present invention provides a composite graphite anode material and its preparation method. By constructing a composite structure of secondary particles and soft carbon spray coating through hard carbon granulation, a lithium-ion fast diffusion channel is formed in the graphite matrix and the interface is stabilized, which significantly improves the high-rate fast charging performance and cycle stability of the anode material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention discloses a composite graphite anode material, comprising: The graphite matrix is ​​a secondary particle formed by hard carbon granulation of single-particle artificial graphite. And an amorphous soft carbon layer covering the surface of the graphite matrix.

[0007] As a further aspect of the present invention: the particle size D50 of the single-particle artificial graphite is 7-9 μm; the particle size D50 of the secondary particles is 12-16 μm.

[0008] As a further aspect of the present invention, the artificial graphite is selected from at least one of low-sulfur petroleum coke, medium-sulfur petroleum coke, and needle coke.

[0009] As a further aspect of the present invention: the carbon source used for the hard carbon granulation is at least one of petroleum asphalt, phenolic resin, epoxy resin, furan resin and furfural resin.

[0010] As a further aspect of the present invention: the carbon source of the amorphous soft carbon layer is at least one of low-temperature liquid phase asphalt oil, anthracene oil, and wash oil.

[0011] Secondly, this invention discloses a method for preparing the composite graphite anode material as described above, comprising the following steps: S1: Mix single-particle artificial graphite with a hard carbon source and granulate to obtain secondary particles; S2: The secondary particles are subjected to high-temperature graphitization treatment; S3: The graphitized particles are mixed with a soft carbon source, and a soft carbon layer is coated on the surface of the material by spray drying to obtain coated particles. S4: The coated particles are carbonized to obtain composite graphite anode material.

[0012] As a further aspect of the present invention: in step S1, the mass ratio of single-particle artificial graphite to hard carbon source is 100:6-10.

[0013] As a further aspect of the present invention, the residual carbon content of the composite graphite anode material is 1-3%.

[0014] As a further aspect of the present invention: in step S2, the temperature of graphitization treatment is 2800-3200℃.

[0015] As a further aspect of the present invention: in step S4, the carbonization temperature is 1100-1300℃.

[0016] Thirdly, the present invention discloses a lithium-ion battery comprising the composite graphite anode material as described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The composite graphite anode material provided by this invention employs a composite structure of hard carbon granulation to construct secondary particles and soft carbon coating, forming a rapid lithium-ion diffusion channel within the graphite matrix, significantly improving the lithium-ion transport rate. Simultaneously, the amorphous soft carbon layer on the surface effectively isolates the electrolyte from direct contact with the graphite matrix, suppressing side reactions and forming a stable SEI film. This structural design balances fast charging performance and cycle stability, enabling the material to maintain excellent electrochemical performance under high-rate charge-discharge conditions. Lithium-ion batteries incorporating this composite graphite anode material, due to the anode material's combination of rapid lithium-ion transport capability and stable interface structure, can achieve rapid charge-discharge at high rates, while effectively suppressing lithium plating, reducing the risk of thermal runaway, and significantly improving battery safety and cycle life in high-power applications.

[0018] This invention employs a process of granulation followed by spray coating. Single-particle artificial graphite is assembled into secondary particles through hard carbon granulation, and then graphitized before being coated with soft carbon using a spray drying method. This process yields a uniform and dense coating layer, effectively controlling residual carbon content and avoiding the problems of uneven coating and numerous interface defects found in traditional coating processes. This method is controllable, simple to operate, and suitable for large-scale production. Detailed Implementation

[0019] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; unless otherwise specified, the parts in the following embodiments refer to parts by weight.

[0022] Example 1 This embodiment provides a high-power composite graphite anode material and a high-safety lithium-ion battery. The specific preparation steps are as follows: (1) The medium sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution.

[0023] (2) Place the crushed and shaped artificial graphite material in a vertical kettle, add 7% of the graphite material mass of phenolic resin as a hard carbon source, and heat up to granulate to obtain secondary particles with a particle size D50 controlled at 14-15μm.

[0024] (3) The secondary particles obtained in step (2) are placed in the Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0025] (4) Using liquid anthracene oil as a soft carbon coating agent, the graphitized material obtained in step 3 was coated in liquid phase by spray drying, and then carbonized at high temperature at 1150℃ to obtain a composite graphite anode material. The residual carbon content of the composite graphite anode material was measured to be 2%.

[0026] (5) The above-mentioned composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0027] (6) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0028] (7) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0029] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack battery cell, and then injected with electrolyte to obtain the lithium-ion battery of this embodiment.

[0030] Example 2 This embodiment provides a high-power composite graphite anode material and a high-safety lithium-ion battery. The specific preparation steps are as follows: (1) The medium-sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution.

[0031] (2) Place the crushed and shaped artificial graphite material in a vertical kettle, add 7% of the graphite material mass of petroleum asphalt as a hard carbon source, heat up and granulate to obtain secondary particles, and control the particle size D50 at 15-16μm.

[0032] (3) The secondary particles obtained in step (2) are placed in the Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0033] (4) Using liquid anthracene oil as a soft carbon coating agent, the graphitized material obtained in step 3 was coated in liquid phase by spray drying, and then carbonized at high temperature at 1150℃ to obtain a composite graphite anode material. The residual carbon content of the composite graphite anode material was measured to be 3%.

[0034] (5) The above-mentioned composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0035] (6) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0036] (7) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0037] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack battery cell, and then injected with electrolyte to obtain the lithium-ion battery of this embodiment.

[0038] Example 3 This embodiment provides a high-power composite graphite anode material and a high-safety lithium-ion battery. The specific preparation steps are as follows: (1) The petroleum coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution.

[0039] (2) Place the crushed and shaped artificial graphite material in a vertical reactor, add 7% of the mass of the graphite material of furan resin as a hard carbon source, and heat up to granulate to obtain secondary particles with a particle size D50 controlled at 14-15μm.

[0040] (3) The secondary particles obtained in step (2) are placed in the Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0041] (4) Using liquid anthracene oil as a soft carbon coating agent, the graphitized material obtained in step (3) was coated in liquid phase by spray drying, and then carbonized at high temperature at 1150℃ to obtain a composite graphite anode material. The residual carbon content of the composite graphite anode material was measured to be 1%.

[0042] (5) The above-mentioned composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0043] (6) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0044] (7) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0045] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack battery cell, and then injected with electrolyte to obtain the lithium-ion battery of this embodiment.

[0046] Example 4 This embodiment provides a high-power composite graphite anode material and a high-safety lithium-ion battery. The specific preparation steps are as follows: (1) The medium sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution.

[0047] (2) Place the crushed and shaped artificial graphite material in a vertical kettle, add 7% of the graphite material mass of phenolic resin as a hard carbon source, and heat up to granulate to obtain secondary particles with a particle size D50 controlled at 14-15μm.

[0048] (3) The secondary particles obtained in step (2) are placed in the Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0049] (4) Using liquid anthracene oil as a soft carbon coating agent, the graphitized material obtained in step 3 was coated in liquid phase by spray drying, and then carbonized at high temperature at 1150℃ to obtain a composite graphite anode material. The residual carbon content of the composite graphite anode material was measured to be 2%.

[0050] (5) The above-mentioned composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0051] (6) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0052] (7) The electrolyte uses LiPF6 as the lithium salt and EC and DMC mixed in a volume ratio of 1:1 as the solvent.

[0053] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack battery cell, and then injected with electrolyte to obtain the lithium-ion battery of this embodiment.

[0054] Comparative Example 1 This comparative example provides a graphite anode material and a lithium-ion battery. The only difference from Example 1 is that it does not involve hard carbon granulation or soft carbon coating; instead, it directly uses ungranulated and uncoated graphite material as the anode active material. The specific preparation steps are as follows: (1) The medium sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution to obtain single-particle artificial graphite.

[0055] (2) Place the single-particle artificial graphite obtained in step (1) into an Atchison graphitization furnace and perform high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0056] (3) The above-mentioned graphitized material is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0057] (4) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0058] (5) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0059] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack cell, and then injected with electrolyte to obtain the lithium-ion battery of this comparative example.

[0060] Comparative Example 2 This comparative example provides a graphite anode material and a lithium-ion battery. The only difference from Example 1 is that it does not use hard carbon granulation; instead, it directly uses single-particle artificial graphite for soft carbon coating. The specific preparation steps are as follows: (1) The medium sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution to obtain single-particle artificial graphite.

[0061] (2) Place the single-particle artificial graphite obtained in step (1) into an Atchison graphitization furnace and perform high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0062] (3) Using liquid anthracene oil as a soft carbon coating agent, the graphitized material obtained in step (2) is coated in liquid phase by spray drying and then carbonized at high temperature at 1150℃ to obtain composite graphite anode material.

[0063] (4) The above composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8. Deionized water is added as a solvent and the mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0064] (5) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0065] (6) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0066] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack cell, and then injected with electrolyte to obtain the lithium-ion battery of this comparative example.

[0067] Comparative Example 3 This comparative example provides a graphite anode material and a lithium-ion battery. The only difference from Example 1 is that it does not involve soft carbon coating; instead, it undergoes only hard carbon granulation and carbonization. The specific preparation steps are as follows: (1) The medium sulfur coke is crushed to a particle size D50 of 7-9 μm and then shaped to narrow the particle size distribution.

[0068] (2) Place the crushed and shaped artificial graphite material in a vertical kettle, add 7% of the graphite material mass of phenolic resin as a hard carbon source, and heat up to granulate to obtain secondary particles with a particle size D50 controlled at 14-15μm.

[0069] (3) The secondary particles obtained in step (2) are placed in the Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃ to obtain graphitized material.

[0070] (4) The graphitized particles are carbonized at a temperature of 1150℃ to obtain composite graphite anode material.

[0071] (5) The above-mentioned composite graphite is mixed with conductive agent acetylene black, thickener CMC and binder SBR in a mass ratio of 96.5:0.5:1.2:1.8, and deionized water is added as a solvent. The mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The slurry is uniformly coated on the surface of copper foil, and after drying, cold pressing and slitting, a negative electrode sheet is obtained.

[0072] (6) The positive electrode active material LiFePO4, the conductive agent acetylene black, the graphene conductive paste, and the binder PVDF are mixed in a mass ratio of 96.8:0.7:0.5:2. NMP solvent is added and the mixture is stirred until homogeneous to obtain the positive electrode paste. The paste is uniformly coated on the surface of aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0073] (7) The electrolyte uses LiPF6 as the lithium salt, and the solvent is a mixture of EC and DMC in a volume ratio of 1:1. TMP flame retardant with a mass fraction of 18% and lithium nitrate with a mass fraction of 0.5% are added.

[0074] The above-mentioned positive electrode, negative electrode and polyethylene separator are wound and assembled into a small soft-pack cell, and then injected with electrolyte to obtain the lithium-ion battery of this comparative example.

[0075] Test case The aforementioned pouch cells were placed at 25°C and charged at a constant current to 3.65V, then charged at a constant voltage of 3.65V until the cutoff current reached 0.02C, and finally discharged at a constant current to 2.5V. Under these conditions, charge-discharge tests were conducted at rates of 0.33C, 1C, 2C, 3C, 4C, 5C, and 6C, and a 100-cycle test was performed at a 4C / 1C rate. The test results include the initial coulombic efficiency (%), the capacity retention rate at 6C, and the capacity retention rate after 100 cycles at 4C. Specific data are shown in Table 1.

[0076] Table 1

[0077] Table 1 shows that hard carbon granulation in Comparative Example 2 significantly improves the fast charging capability of the battery cell at high rates. After graphitization, hard carbon forms a hard carbon layer between graphite particles, providing a fast buffer channel between particles and improving the rapid transport of lithium ions. Soft carbon coating does not significantly improve the kinetics of lithium ion transport as hard carbon granulation, but the soft carbon layer can effectively modify the defects on the surface of hard carbon, improving the initial coulombic efficiency and cycle stability. However, comparing Example 1 with Comparative Examples 2 and 3, soft carbon coating modifies the defects on the surface of hard carbon, and the graphitization degree of soft carbon is slightly higher, which can seal the internal pores and prevent electrolyte etching, reducing the specific surface area and improving the initial coulombic efficiency and cycle performance. Comparing Example 1 with Examples 4 and 5, 3% residual carbon content results in better fast charging performance but slightly worse cycle performance than 1% residual carbon. Selecting appropriate residual carbon can balance fast charging performance with improved cycle performance of the battery cell. Compared with Example 4, TMP exhibits excellent compatibility with graphite due to its strong solubility for lithium salts and wide voltage window. The improved interface stability is attributed to the addition of a small amount of lithium nitrate. The mechanism is as follows: lithium nitrate is preferentially reduced at higher potentials, and its reduction products participate in the formation of the SEI film, generating an interface layer rich in LiF and ROCO2Li. This SEI film effectively inhibits the co-intercalation and decomposition of TMP, thereby achieving reversible insertion and extraction of lithium ions in the graphite electrode, improving the safety and rate performance of high-rate charge and discharge. The resulting SEI is rich in salt decomposition products LiF and solvent decomposition products ROCO2Li, thus effectively preventing the co-intercalation and decomposition of TMP, ultimately achieving reversible insertion and extraction of lithium ions in the graphite electrode. This improves the safety of lithium ions during high-rate rapid charge and discharge while also satisfying the requirement for rapid insertion and extraction of lithium ions in graphite at high power.

[0078] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0079] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A composite graphite anode material, characterized in that, include: The graphite matrix is ​​a secondary particle formed by hard carbon granulation of single-particle artificial graphite. And an amorphous soft carbon layer covering the surface of the graphite matrix.

2. The composite graphite anode material according to claim 1, characterized in that, The particle size D50 of the single-particle artificial graphite is 7-9 μm; the particle size D50 of the secondary particles is 12-16 μm.

3. The composite graphite anode material according to claim 1, characterized in that, The artificial graphite is selected from at least one of low-sulfur petroleum coke, medium-sulfur petroleum coke, and needle coke.

4. The composite graphite anode material according to claim 1, characterized in that, The carbon source used in the hard carbon granulation is at least one of petroleum asphalt, phenolic resin, epoxy resin, furan resin, and furfural resin.

5. The composite graphite anode material according to claim 1, characterized in that, The carbon source of the amorphous soft carbon layer is at least one of low-temperature liquid phase asphalt oil, anthracene oil, and wash oil.

6. A method for preparing the composite graphite anode material according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Mix single-particle artificial graphite with a hard carbon source and granulate to obtain secondary particles; S2: The secondary particles are subjected to high-temperature graphitization treatment; S3: The graphitized particles are mixed with a soft carbon source, and a soft carbon layer is coated on the surface of the material by spray drying to obtain coated particles. S4: The coated particles are carbonized to obtain composite graphite anode material.

7. The preparation method according to claim 6, characterized in that, In step S1, the mass ratio of single-particle artificial graphite to hard carbon source is 100:6-10.

8. The preparation method according to claim 6, characterized in that, The residual carbon content of the composite graphite anode material is 1-3%.

9. The preparation method according to claim 6, characterized in that, In step S2, the graphitization treatment temperature is 2800-3200℃; and / or, In step S4, the carbonization temperature is 1100-1300℃.

10. A lithium-ion battery, characterized in that, It comprises the composite graphite anode material as described in any one of claims 1-5.

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