Graphite negative electrode material, preparation method thereof and secondary battery

Abstract

This invention relates to the field of battery technology, and in particular to a graphite anode material, its preparation method, and a secondary battery. The graphite anode material of this invention comprises multiple secondary graphite particles, each secondary particle comprising multiple primary graphite particles. The surface of each primary graphite particle is coated with a hard carbon layer, and each primary graphite particle has at least one pore containing hard carbon. The preparation method of the graphite anode material includes the following steps: granulating and graphitizing a mixture containing raw material coke and a hard carbon precursor sequentially to obtain the graphite anode material. In the graphite anode material of this invention, the hard carbon not only coats the surface of the primary graphite particles, forming secondary particles, but also penetrates into the interior of the primary graphite particles. The high disordered structure of the hard carbon is more conducive to lithium-ion intercalation. This graphite anode material exhibits excellent rate performance, initial charge-discharge efficiency, and cycle performance.

Description

Technical Field

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

[0002] Currently, artificial graphite anodes are widely used in the field of power batteries. However, due to the large number of active end faces on their surface, irreversible interfacial decomposition reactions occur at these active end faces during charging and discharging, resulting in a decrease in initial coulombic efficiency. Simultaneously, co-intercalation of solvent molecules occurs, damaging the graphite structure and reducing capacity and cycle performance. Furthermore, the small interlayer spacing of graphite limits its kinetic performance, further affecting its application in fast charging and high-power applications. Compared to uncoated graphite, graphite anodes coated with pyrolytic carbon show significant improvements in reversible capacity, cycle performance, and rate performance. Particle size affects the lithium-ion transport distance; smaller aggregate particle sizes can reduce the tortuosity of lithium ions in the electrode, thereby improving fast charging performance. The end faces on the particle surface are the migration path for lithium ions; the more end faces, the more favorable it is for lithium ion extraction. Therefore, particle surface coating and secondary granulation of small aggregate particles can shorten the lithium-ion extraction path, effectively improving the fast charging and discharging performance of the material.

[0003] The construction of secondary particles generally involves adding pitch to crushed raw coke and mixing it thoroughly. Then, a heat treatment process in a reactor is used to bond the single coke particles into uniformly distributed secondary particles. The pitch binder is then converted into an ordered graphitized structure through a high-temperature graphitization process, thus forming graphitized secondary particles. However, graphitized particles alone cannot meet the high-rate charge / discharge requirements of the market, necessitating subsequent coating modification of the material, which increases coating costs and simplifies the process.

[0004] In view of this, this invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a graphite anode material in which hard carbon not only coats the surface of primary graphite particles to form secondary particles, but also penetrates into the interior of primary graphite particles, giving it excellent rate performance, first charge-discharge efficiency, and cycle performance.

[0006] The second objective of this invention is to provide a method for preparing graphite anode material, which uses raw material coke and hard carbon precursor for granulation and graphitization treatment, eliminating the need for subsequent carbonization and coating steps, thereby improving rate performance, first charge and discharge efficiency and cycle performance, and achieving higher charging rate performance.

[0007] A third objective of this invention is to provide a secondary battery with excellent electrochemical performance.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a graphite anode material comprising a plurality of secondary graphite particles, wherein the secondary graphite particles comprise a plurality of primary graphite particles, the surface of the primary graphite particles is coated with a hard carbon layer, and the primary graphite particles have at least one pore, wherein hard carbon is disposed within the pore.

[0010] Furthermore, the thickness of the hard carbon layer is 4–15 nm, and the thickness of the hard carbon layer is the distance between the outer surface of the hard carbon layer and the surface of the primary graphite particles.

[0011] Furthermore, in the Raman spectrum of the graphite anode material, the average value of ID / IG is 0.10 to 0.20.

[0012] Furthermore, it includes at least one of the following features (1) to (4);

[0013] (1) The pore volume of the graphite anode material is 0.007–0.015 cm³. 3 / g;

[0014] (2) The graphite anode material includes micropores and mesopores, wherein the pore volume of the mesopores accounts for ≥70% of the total pore volume; preferably, the pore volume of the mesopores accounts for 70% to 85% of the total pore volume.

[0015] (3) The specific surface area of ​​the graphite anode material is 1.20–2.00 m². 2 / g;

[0016] (4) The tap density of the graphite anode material is 0.85–1.10 g / cm³. 3 .

[0017] Secondly, the present invention also provides a method for preparing the graphite anode material as described above, comprising the following steps:

[0018] The mixture containing raw coke and hard carbon precursor is granulated and graphitized sequentially to obtain the graphite anode material.

[0019] Furthermore, the mass ratio of the raw coke to the hard carbon precursor is 100:(5-10);

[0020] And / or, the hard carbon precursor comprises a resin.

[0021] Furthermore, it includes at least one of the following features (1) to (4);

[0022] (1) The resin includes at least one of phenolic resin, ketol resin and epoxy resin;

[0023] (2) The mixture comprises solid resin, crosslinking agent and raw material coke; or, the mixture comprises liquid resin and raw material coke;

[0024] (3) The crosslinking agent includes at least one of aliphatic amine compounds, acid anhydrides, inorganic acids and organic acids;

[0025] (4) The raw material coke includes petroleum coke and / or needle coke.

[0026] Further, the granulation temperature is 10–35°C; or, the granulation temperature is 500–600°C;

[0027] Furthermore, the graphitization treatment temperature is 2500–3000℃, and the graphitization treatment time is 8–12 hours;

[0028] And / or, the graphitization process includes using an Atchison crucible furnace.

[0029] Thirdly, the present invention also provides a secondary battery comprising the graphite anode material as described above.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The graphite anode material of the present invention comprises a plurality of secondary graphite particles, each secondary graphite particle comprising a plurality of primary graphite particles. The surface of each primary graphite particle is coated with a hard carbon layer. Each primary graphite particle has at least one pore, within which hard carbon is disposed. The hard carbon not only coats the surface of the primary graphite particles to form secondary graphite particles, but also enters the pores of the primary graphite particles. The high disordered structure of the hard carbon is more conducive to the intercalation of lithium ions. This graphite anode material has excellent rate performance, initial charge-discharge efficiency, cycle performance, and fast charging performance.

[0032] 2. The method for preparing the graphite anode material of the present invention involves granulating and graphitizing the raw material coke and hard carbon precursor, which not only forms secondary particles but also retains a layer of hard carbon on the surface; this improves the rate performance, first charge and discharge efficiency and cycle performance, and can achieve a higher rate charging performance; furthermore, after graphitization, no subsequent carbonization coating step is required to achieve a fast charging capability comparable to that of soft carbon coating. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the graphite anode material of the present invention.

[0035] Figure 2 This is an HRTEM image of the graphite anode material of Embodiment 1 of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0037] The following provides a detailed description of a graphite anode material, its preparation method, and a secondary battery according to the present invention.

[0038] See Figure 1 In some embodiments of the present invention, a graphite anode material is provided, comprising a plurality of secondary graphite particles, each secondary graphite particle comprising a plurality of primary graphite particles, the surface of each primary graphite particle being coated with a hard carbon layer, each primary graphite particle having at least one pore, the pore containing hard carbon.

[0039] The graphite anode material of the present invention includes a plurality of secondary graphite particles, each secondary graphite particle comprising a plurality of primary graphite particles. The surface of each primary graphite particle is coated with a hard carbon layer, and each primary graphite particle has at least one pore containing hard carbon. The hard carbon not only coats the surface of the primary graphite particles to form secondary graphite particles, but also enters the pores of the primary graphite particles, thereby giving it excellent rate performance, initial charge-discharge efficiency, cycle performance, and fast-charging performance.

[0040] The graphite anode material of the present invention has a high degree of disorder in the hard carbon layer. The relatively disordered structure is more conducive to the intercalation of lithium ions, resulting in excellent fast charging performance and improved rate performance.

[0041] Compared to soft carbon, hard carbon offers advantages such as diverse structures, low cost, good conductivity, high lithium storage capacity, small volume deformation after lithium intercalation, environmental friendliness, and low redox potential. Compared to the ordered layered structure of graphite, its molecular structure is more complex, and its relatively disordered structure is more conducive to lithium storage, while also exhibiting excellent fast-charging performance. In terms of efficiency, the electrochemical plateau slope of hard carbon is lower than that of soft carbon, resulting in higher efficiency for hard carbon materials.

[0042] In some embodiments of the present invention, the thickness of the hard carbon layer is 4 to 15 nm, and the thickness of the hard carbon layer is the distance between the outer surface of the hard carbon layer and the surface of the primary graphite particles; typically, but not limitingly, for example, the thickness of the hard carbon layer can be 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 15 nm and any value between any two of them.

[0043] In some embodiments of the present invention, the average value of ID / IG in the Raman spectrum of the graphite anode material is 0.10 to 0.20; typically, but not limitingly, for example, the average value of ID / IG in the Raman spectrum of the graphite anode material can be 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 and any value between any two of them.

[0044] Raman ID / IG testing: Peak intensity of the material's D peak (1350 cm⁻¹) was measured using a Renishaw microconfocal Raman spectrometer. -1 Nearby, the boundary vibration modes belonging to the disorder-induced hexagonal Brillouin zone (used for defect characterization) and the peak intensity of G peak (1580 cm⁻¹) -1 Nearby, the stretching vibration modes belonging to the in-plane bonds of carbon atoms (related to the degree of graphitization), where the peak intensity ratio of the D peak and the G peak is ID / IG. A 532nm semiconductor laser with a power ≥50mW was used; testing conditions: a neon lamp as the signal source, a high-resolution grating of ≥1800 lines, and a test depth of 17086 ABScm. -1 The luminous line has a full width at half maximum (FWHM) less than or equal to 1 wavenumber (FWHM ≤ 1 cm). -1 Spatial resolution: ≤0.3μm(XY); ≤1μm(Z); Scan step size: 5μm; Area scan range: -47μm≤X≤48μm; -47μm≤Y≤48μm; 400 points per area scan.

[0045] In some embodiments of the present invention, the pore volume of the graphite anode material is 0.007–0.015 cm³. 3 / g; typically, but not limitingly, the pore volume of graphite anode materials can be 0.007 cm³. 3 / g, 0.009cm 3 / g, 0.011cm 3 / g, 0.013cm 3 / g, 0.015cm 3 / g and any value between the two; preferably, the pore volume of the graphite anode material is 0.07–0.09 cm³. 3 / g.

[0046] In some embodiments of the present invention, the pores of the graphite anode material include micropores and mesopores, and the ratio of the pore volume of mesopores to the total pore volume is ≥70%; preferably, the ratio of the pore volume of mesopores to the total pore volume in the graphite anode material is 70% to 85%; typically, but not limitingly, for example, the ratio of the pore volume of mesopores to the total pore volume in the graphite anode material can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 85%, and any value between any two of them.

[0047] The graphitization process of resin granulation materials often results in an ordered mesoporous structure, which helps improve their thermal stability and electrical conductivity. The presence of mesopores makes graphite less prone to deformation or expansion at high temperatures, reduces electrode rebound rate, and improves high-temperature cycling stability. Furthermore, the electron transport channels within the mesopores facilitate current conduction, improving the material's rate performance. An appropriate amount of mesopores in graphite can also improve its mechanical properties, such as compressive strength.

[0048] In some embodiments of the present invention, the specific surface area of ​​the graphite anode material is 1.20–2.00 m². 2 / g; typically, but not limitingly, for example, the specific surface area of ​​graphite anode materials can be 1.20 m². 2 / g, 1.40m 2 / g, 1.60m 2 / g, 1.80m 2 / g, 2.00m 2 / g and any value between the two.

[0049] In some embodiments of the present invention, the tap density of the graphite anode material is 0.85–1.10 g / cm³. 3 Typical, but not limiting, examples include graphite anode materials with a tap density of 0.85 g / cm³. 3 0.90g / cm 3 0.95g / cm 3 0.10 g / cm 3 and any value between any two of them.

[0050] In some embodiments of the present invention, the average particle size Dv50 of the graphite anode material is 12–19 μm.

[0051] In some embodiments of the present invention, a method for preparing the above-mentioned graphite anode material is also provided, comprising the following steps:

[0052] The mixture containing raw coke and hard carbon precursor is granulated and graphitized sequentially to obtain graphite anode material.

[0053] The method for preparing graphite anode material of the present invention achieves the construction of secondary particles by granulating and graphitizing the raw material coke and hard carbon precursor. After graphitization, not only secondary particles are formed, but a layer of hard carbon is also retained on the surface. The surface of the secondary particles formed after graphitization is coated with a uniform layer of hard carbon.

[0054] Hard carbon precursors pyrolyze on the surface and inside of raw coke particles to form an amorphous carbon layer. During the formation of graphite microcrystals, the precursors not only coat the graphite surface to form secondary particles, but also penetrate into the interior of the graphite particles through micropores. This improves the tap density and electronic conductivity of the graphite anode material, thereby enhancing its initial charge-discharge efficiency and cycle performance. Furthermore, the high disorder structure of hard carbon is more conducive to lithium-ion intercalation, resulting in improved rate performance.

[0055] After graphitization, no subsequent carbonization coating step is required to achieve a fast charging capability comparable to that of soft carbon coating. This eliminates the need for secondary high-temperature carbonization coating of the graphitized product, thus optimizing the process and reducing costs.

[0056] The existing preparation process of graphite anode materials is as follows: raw material coke and soft carbon precursor (asphalt) are mixed, and then subjected to heat treatment to construct secondary particles (heated at 550℃ for 5h) and graphitization treatment, followed by soft carbon coating and carbonization (heated at 1100~1200℃ for 6h).

[0057] The preparation process of the graphite anode material of the present invention is as follows: the raw material coke and hard carbon precursor are mixed, and then granulated to form secondary particles and graphitized in sequence, without the need for subsequent carbonization and coating steps.

[0058] The soft carbon precursor requires heating to granulate, and graphitization will completely form graphite; the hard carbon precursor of the present invention can not only form secondary particles after graphitization, but also retain hard carbon on the surface.

[0059] The raw materials for soft carbon granulation need to be coated with a layer of amorphous carbon after graphitization before being applied in the field of power graphite. The hard carbon on the surface of the graphite anode material in this invention has a high degree of disorder, which can achieve a higher charging rate. After graphitization, the raw materials can achieve a fast charging capability comparable to that of soft carbon coating without carbonization.

[0060] In some embodiments of the present invention, the mass ratio of raw coke to hard carbon precursor is 100:(5 to 10); typically, but not limitingly, for example, the mass ratio of raw coke to hard carbon precursor may be a range of 100:5, 100:6, 100:7, 100:8, 100:9, 100:10 or any combination thereof; preferably 100:(7 to 8).

[0061] In some embodiments of the present invention, the hard carbon precursor comprises a resin.

[0062] Hard carbon anode precursors are complex and diverse, including biomass, resin-based precursors, pitch, pyrolytic carbon from organic polymers (PVA, PVC, PVDF, PVN, etc.), and carbon black. Different precursors result in hard carbon with significant performance differences and varying structures, leading to variations in residual carbon content. Furthermore, the microstructures of different hard carbon precursors after high-temperature carbonization differ considerably, resulting in varying wettability to graphite. Therefore, these differences significantly impact the coating and modification effects on the anode material. Resin-based precursors yield hard carbon with better particle size uniformity and higher purity, and the raw materials are controllable, making them suitable for large-scale production. Additionally, resin-based hard carbon precursors meet requirements such as isotropy, high residual carbon content, and the ability to form stable amorphous carbon layers.

[0063] Using resin-coated raw coke instead of graphitized finished product can eliminate the need for secondary high-temperature carbonization coating of graphitized finished product, thus optimizing the process and reducing costs.

[0064] In some embodiments of the present invention, the resin includes at least one of phenolic resin, ketol resin and epoxy resin.

[0065] The selection of resin is crucial. The aforementioned resin can maintain its amorphous structure under high temperature and inert atmosphere and does not damage the graphite sheet structure of the raw material coke during the graphitization process, thus ensuring the capacity of the finished product while also forming a core-shell coating.

[0066] In some embodiments of the present invention, the mixture comprises a solid resin, a crosslinking agent, and raw material coke; or, the mixture comprises a liquid resin and raw material coke.

[0067] Solid-phase resins require the addition of crosslinking agents, while liquid-phase resins do not require the addition of crosslinking agents and can form uniform secondary particles before graphitization.

[0068] In some embodiments of the present invention, the crosslinking agent includes at least one of aliphatic amine compounds, acid anhydrides, inorganic acids, and organic acids; the present invention does not strictly limit the specific type of crosslinking agent, and conventional aliphatic amine compounds, acid anhydrides, inorganic acids, and organic acids that can be used as crosslinking agents can be used.

[0069] In some embodiments of the present invention, the feed coke includes petroleum coke and / or needle coke; preferably, the average particle size Dv50 of the feed coke is 7 to 10 μm; typically, but not limitingly, for example, the average particle size Dv50 of the feed coke can be 7 μm, 8 μm, 9 μm, 10 μm and any value between any two of them.

[0070] In some embodiments of the present invention, the granulation temperature is 10–35°C (room temperature); or, the granulation temperature is 500–600°C.

[0071] In some embodiments of the present invention, the granulation time is 6 to 10 hours.

[0072] In some embodiments of the present invention, the particle size of the granulation is 12 to 19 μm; typically, but not limitingly, for example, the particle size of the granulation can be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm and any value between any two of them.

[0073] The granulation method of the present invention can be either room temperature granulation or heated granulation; the hard carbon precursor can be granulated at room temperature, and the room temperature granulation process of raw coke and hard carbon precursor is adopted, which optimizes the process and reduces costs.

[0074] In some embodiments of the present invention, the graphitization temperature is 2500–3000°C and the graphitization time is 8–12 hours.

[0075] In some embodiments of the invention, the graphitization process includes using an Atchison crucible furnace.

[0076] In some embodiments of the present invention, a secondary battery is also provided, comprising the above-mentioned graphite anode material.

[0077] In some embodiments of the present invention, the secondary battery includes a lithium-ion battery.

[0078] Examples 1-6

[0079] The method for preparing the graphite anode material provided in this embodiment includes the following steps:

[0080] The mixture of hard carbon precursor and petroleum coke, or the mixture of hard carbon precursor, petroleum coke and crosslinking agent, is granulated and then graphitized in an Atchison crucible furnace to obtain graphite anode material.

[0081] The types and amounts of raw materials used in the preparation methods of graphite anode materials in Examples 1 to 6 are shown in Table 1; the parameter settings for each step are shown in Table 2.

[0082] Table 1

[0083]

[0084] Table 2

[0085]

[0086]

[0087] Comparative Examples 1-4

[0088] The preparation method of the graphite anode material provided in this comparative example includes the following steps:

[0089] Petroleum coke and granulated carbon source are mixed and then heated and granulated (heat-treated at 550℃ for 5 hours); then graphitized in an Atchison crucible furnace to obtain graphite anode material; or, petroleum coke and granulated carbon source are mixed and then heated and granulated (heat-treated at 550℃ for 5 hours); then graphitized in an Atchison crucible furnace to obtain graphite; after solid phase pitch gas flow pulverization, it is mixed with graphite and carbonized and coated to obtain graphite anode material.

[0090] Table 3

[0091]

[0092] Table 4

[0093]

[0094]

[0095] Test case

[0096] HRTEM of the graphite anode material in Example 1 is as follows: Figure 2 As shown; Figure 2 In Figure a, HRTEM image of the graphite anode material of Example 1 is shown. Figure 2 Image b is another HRTEM image of the graphite anode material of Example 1.

[0097] from Figure 2 It is known that after the hard carbon precursor and raw coke are granulated and graphitized at room temperature, the hard carbon precursor coated on the surface of the raw coke is graphitized, and the raw coke becomes graphite. The hard carbon precursor is not completely graphitized, forming a disordered hard carbon layer coated on the graphite surface. The hard carbon layer and graphite have different degrees of graphitization.

[0098] The performance of the graphite anode materials prepared in Examples 1-6 and Comparative Examples 1-4 was tested, and the results are shown in Table 5.

[0099] Particle size D50 test: Refer to GB / T19077-2016, using Malvern Master Size 3000 laser particle size analyzer.

[0100] Tap density test: Refer to Appendix M of GB / T 24533-2019, using Dandong Baite (BT-313).

[0101] Specific surface area, pore size and pore volume testing: Refer to GB / T 19587-2017, and use the American Mack physical adsorption analyzer ASAP 2460.

[0102] Specific capacity and first-efficiency testing: Refer to GB / T 24533-2019; the negative electrode composition is SP:PVDF:active material = 1.8:6.6:91.6 (mass ratio), the binder is NMP:PVDF = 135:9.9 (mass ratio), using 16mm diameter electrode sheets, 18mm diameter lithium sheets, 26mm diameter separators, and electrolyte to form a coin cell, model CR2430. Half-cell testing uses the American Arbin multi-channel battery testing system, with test steps of: 0.6mA to 5.0mV, 0.3mA to 5.0mV, 0.6mA to 2.0V. The test temperature is 25±0.5℃.

[0103] Single cell DCR test: adopts industry standard, test temperature is 25℃ and 0℃. The test steps are as follows: 1) Charge at 1C and discharge at 0.5C (3.0~4.4V), record the 0.5C discharge capacity as C0; 2) Adjust the temperature of the temperature chamber to 25℃ (0℃), and let the cell rest in the temperature chamber for 4 hours; 3) 0.7C0 (0℃ is 0.1C0) CC to 4.4V and CV to I≤0.025C0; 4) Let stand for 10 minutes; 5) 0.1C0 (25℃ and 0℃ are the same) DC to 3.4V, this capacity is used as the capacity reference C for adjusting SOC; 6) Let stand for 10 minutes; 7) 0.1C CC to 60 minutes, adjust to 50% SOC; 8) 1C CC 1s; The calculation method is as follows: DCR charging = |U1-U0| / I; U1 is the voltage at the end of 1s pulse charging, U0 is the voltage before 1s pulse charging, and I is the pulse current.

[0104] Table 5

[0105]

[0106] As shown in Table 5, the average particle size and tap density of the graphite anode materials in Examples 1-6 and Comparative Examples 1-4 are similar. The specific surface area of ​​Comparative Examples 1-4 is slightly lower. This is because during the graphitization process, the soft carbon forms graphitized particles, which are used to repair the pores and defects formed during the graphitization of the raw material coke. In contrast, hard carbon granulation, which does not undergo heat treatment in a reaction vessel before graphitization, has a higher volatile content than soft carbon granulation, thus forming some nanopores and defects. However, hard carbon can still maintain a certain degree of amorphous structure at the high graphitization temperature of around 3000℃, which is equivalent to coating the graphite surface with a layer of amorphous carbon, compensating for the larger specific surface area caused by the escape of volatiles. Therefore, overall, the two granulation methods do not cause a significant difference in specific surface area and do not affect the high-temperature storage and cycle performance of the finished battery.

[0107] A comparison of the DCR of individual cells shows that the DCR of uncoated hard carbon granules formed at room temperature is lower than that of coated soft carbon after high-temperature carbonization. This indicates that the high disorder structure of hard carbon is more conducive to lithium-ion intercalation, thus improving the rate performance.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A graphite negative electrode material, characterized by, It includes multiple secondary graphite particles, each of which includes multiple primary graphite particles. The surface of each primary graphite particle is coated with a hard carbon layer, and each primary graphite particle has at least one pore containing hard carbon.

2. The graphite negative electrode material of claim 1, wherein, The thickness of the hard carbon layer is 4–15 nm, and the thickness of the hard carbon layer is the distance between the outer surface of the hard carbon layer and the surface of the primary graphite particles.

3. The graphite negative electrode material of claim 1, wherein, In the Raman spectrum of the graphite anode material, the average value of ID / IG is 0.10 to 0.

20.

4. The graphite negative electrode material of claim 1, wherein, Includes at least one of the following features (1) to (4); (1) the graphite negative electrode material has a pore volume of 0.007 to 0.015 cm 3 / g; (2) The graphite anode material includes micropores and mesopores, wherein the pore volume of the mesopores accounts for ≥70% of the total pore volume; preferably, the pore volume of the mesopores accounts for 70% to 85% of the total pore volume. (3) the specific surface area of the graphite negative electrode material is 1.20-2.00 m 2 / g; (4) the tap density of the graphite negative electrode material is 0.85-1.10 g / cm 3 .

5. The method of producing a graphite negative electrode material according to any one of claims 1 to 4, characterized by, Includes the following steps: The mixture containing raw coke and hard carbon precursor is granulated and graphitized sequentially to obtain the graphite anode material.

6. The method of claim 5, wherein the graphite negative electrode material is prepared by the steps of: The mass ratio of the raw coke to the hard carbon precursor is 100:(5-10); ​ And / or, the hard carbon precursor comprises a resin.

7. The method of claim 6, wherein the graphite negative electrode material is prepared by the steps of: mixing graphite powder with a binder to form a mixture; and compressing the mixture to form a graphite negative electrode material. Includes at least one of the following features (1) to (4); (1) The resin includes at least one of phenolic resin, ketol resin and epoxy resin; (2) The mixture comprises solid resin, crosslinking agent and raw material coke; or, the mixture comprises liquid resin and raw material coke; (3) The crosslinking agent includes at least one of aliphatic amine compounds, acid anhydrides, inorganic acids and organic acids; (4) The raw material coke includes petroleum coke and / or needle coke.

8. The method of claim 5, wherein the graphite negative electrode material is prepared by the steps of: The granulation temperature is 10–35°C; or, the granulation temperature is 500–600°C. ​ 9. The method of claim 5, wherein the graphite negative electrode material is prepared by the steps of: The graphitization treatment temperature is 2500–3000℃, and the graphitization treatment time is 8–12 hours; ​ And / or, the graphitization process includes using an Atchison crucible furnace.

10. A secondary battery characterized by comprising: Includes the graphite anode material as described in any one of claims 1 to 4.

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