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

Abstract

The invention provides a graphite negative electrode material and a preparation method thereof, a negative electrode plate and a lithium ion battery. The graphite negative electrode material comprises an inner core and a carbon coating layer arranged on the surface of the inner core, the inner core sequentially comprises first graphite particles, a carbon bonding layer and second graphite particles arranged on the surface of the carbon bonding layer from inside to outside, the D50 of the first graphite particles is larger than that of the second graphite particles, and the ratio of the D50 of the first graphite particles to the D50 of the second graphite particles is (1.3-6): 1; the second graphite particles have pore structures, and the porosity of the second graphite particles is 20-60%; and the particle size distribution width of the graphite negative electrode material is 0.5-1. The graphite negative electrode material has excellent rate capability and relatively high lithium ion transmission efficiency, and when the graphite negative electrode material is applied to a negative electrode plate as a negative electrode active material, the hole blocking phenomenon of the negative electrode plate can be inhibited, the tortuosity of the negative electrode plate is reduced, and the rate capability, the energy density and the cycle performance of the lithium ion battery are effectively improved.

Description

Technical Field

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

[0002] The anode material for lithium-ion batteries, especially graphite anode materials, is a key factor affecting the performance of lithium-ion batteries, particularly their cycle performance, rate performance, energy density, and safety. Currently, the demand for high-performance lithium-ion batteries is increasing. To achieve high-performance requirements such as rapid acceleration and efficient hill climbing, lithium-ion batteries need to output a large amount of electrical energy in a short time, i.e., possess high-rate discharge capability. In some fields, such as low-altitude flight, plug-in hybrid electric vehicles (PHEVs), and some devices requiring frequent start-stop operations, the discharge requirements for lithium-ion batteries are even greater than 10C. Therefore, research on the modification of graphite anode materials has received widespread attention.

[0003] In recent years, small-particle-size graphite (typically below 6 μm) has gained favor due to its superior performance in fast charge-discharge processes, demonstrating high application potential. Small-particle-size graphite not only provides faster lithium-ion transport paths but also possesses a larger specific surface area, promoting more efficient electrochemical reactions. Existing research has attempted to blend small-particle-size graphite with large-particle-size conventional graphite, hoping to combine the advantages of both. However, directly mixing graphite of different particle sizes leads to complex blending effects, especially during battery assembly into negative electrode sheets. The difference between the high fluidity of small-particle-size graphite and the low fluidity of large-particle-size graphite easily causes uneven distribution of pore structures, resulting in pore blockage and significantly increasing the tortuosity of the negative electrode sheet—that is, the complexity of the lithium-ion transport path within the material—thus severely affecting lithium-ion transport efficiency. Furthermore, increased tortuosity not only hinders effective charge transfer but also limits the rate performance of lithium-ion batteries, ultimately adversely affecting their rate and cycle performance.

[0004] In summary, the research and development of a graphite anode material with excellent rate performance and high lithium-ion transport efficiency, as well as its preparation method, is of great significance for improving the rate performance and cycle performance of lithium-ion batteries. Summary of the Invention

[0005] The main objective of this invention is to provide a graphite anode material and its preparation method, anode sheet, and lithium-ion battery, in order to solve the problems of poor rate performance of graphite anode materials in the prior art, and the increased tortuosity of the anode sheet caused by pore blockage during subsequent anode sheet preparation.

[0006] To achieve the above objectives, the present invention provides a graphite anode material comprising a core and a carbon coating layer disposed on the surface of the core; the core, from the inside out, comprises first graphite particles, a carbon binder layer, and second graphite particles disposed on the surface of the carbon binder layer, wherein the first graphite particles have a D... 50 D is larger than that of the second graphite particle 50 And both D 50 The ratio is (1.3~6):1; the second graphite particles have a porous structure and the porosity of the second graphite particles is 20~60%; the particle size distribution width of the graphite anode material is 0.5~1.

[0007] Furthermore, the D of graphite anode materials 10 The diameter is 5–15 μm, D 50 The diameter is 7–20 μm, D 90 The value is 9–25 μm, and D 10 <D 50 <D 90 .

[0008] Furthermore, the weight ratio of the core to the carbon coating is 100:(0.5-12).

[0009] Furthermore, the first graphite particle is artificial graphite, and the D of the first graphite particle... 50 It is 8–12 μm.

[0010] Furthermore, the D of the second graphite particle 50 Its diameter is 2–6 μm, its average pore size is 0.5–30 nm, and its specific surface area is 10–1000 m². 2 / g; Preferably, the second graphite particles are obtained by creating pores from natural graphite and / or artificial graphite.

[0011] Furthermore, in the graphite anode material, the weight percentage of the second graphite particles is 10–50 wt%.

[0012] To achieve the above objectives, another aspect of the present invention provides a method for preparing the graphite anode material provided in this application. The method includes: step S1, preparing first graphite particles; step S2, creating pores in graphite raw materials using a physical activation method or a chemical activation method to obtain second graphite particles; step S3, mixing the first graphite particles, the second graphite particles, and a coating material, and sequentially subjecting them to a first heat treatment and sieving to obtain the graphite anode material; wherein the coating material is selected from asphalt compounds and / or carbon-containing resins.

[0013] Further, in step S1, the method for preparing the first graphite particles includes: preheating, crushing, graphitizing, demagnetizing and sieving the amorphous carbon material in sequence to obtain the first graphite particles.

[0014] Furthermore, the preheating treatment temperature is 900–1400℃, and the time is 4–10 hours.

[0015] Furthermore, the graphitization temperature is 2800–3500℃, and the time is 4–24 hours.

[0016] Furthermore, the amorphous carbon material is selected from one or more of the group consisting of petroleum coke, needle coke, and pitch coke.

[0017] Furthermore, in step S2, the physical activation method includes: using an oxidizing gas to create pores in the graphite raw material to obtain second graphite particles.

[0018] Furthermore, the temperature for creating the pore is 800–1000℃, and the time is 1–5 hours.

[0019] Furthermore, the ratio of the weight of the graphite raw material to the volume of the oxidizing gas is 1 kg: (10–50) m³. 3 .

[0020] Furthermore, the oxidizing gas is selected from air and / or carbon dioxide.

[0021] Further, in step S2, the chemical activation method includes: mixing graphite raw material with a pore-forming agent in an inert gas atmosphere, and then obtaining second graphite particles after a second heat treatment.

[0022] Furthermore, the weight ratio of graphite raw material to pore-forming agent is 1:(0.5-4).

[0023] Furthermore, the second heat treatment is carried out at a temperature of 700–900°C for a time of 1–5 hours.

[0024] Furthermore, the pore-forming agent is selected from one or more of the group consisting of potassium hydroxide, sodium hydroxide, phosphoric acid, sulfuric acid, and nitric acid.

[0025] Furthermore, in step S3, the weight ratio of the first graphite particle to the second graphite particle is (1-9):1.

[0026] Furthermore, the total weight ratio of the first graphite particles and the second graphite particles to the weight of the coating material is (88-99.5):(0.5-12).

[0027] Furthermore, the bituminous compounds are selected from one or more of the group consisting of tar pitch, petroleum pitch and natural bitumen; the carbon-containing resins are selected from one or more of the group consisting of phenolic resins, furan resins and epoxy resins.

[0028] Furthermore, the temperature of the first heat treatment is 400–1200℃, and the time is 2–12 hours.

[0029] Furthermore, in step S3, a conductive agent is introduced during the mixing process.

[0030] Furthermore, the weight ratio of the conductive agent to the coating material is (0.01 to 0.05):1.

[0031] Furthermore, the conductive agent is selected from one or more of graphene, carbon nanotubes, carbon nanofibers, and carbon black.

[0032] Another aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer stacked together, wherein the negative electrode active material layer comprises the graphite negative electrode material provided in this application.

[0033] A fourth aspect of the present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode is the aforementioned negative electrode provided in this application.

[0034] By applying the technical solution of this invention, compared with graphite anode materials that directly mix small-diameter graphite particles with large-diameter conventional graphite particles, the graphite anode material provided in this application has the second graphite particles tightly bonded to the first graphite particles through a carbon bonding layer. This effectively suppresses pore blockage caused by the difference in flowability between the second and first graphite particles during the preparation of the anode sheet, thereby reducing the tortuosity of the anode sheet and improving the lithium-ion transport efficiency and rate performance of the lithium-ion battery. 50 Smaller second graphite particles can provide rapid lithium-ion diffusion channels, D 50 Larger first graphite particles can improve the energy density and structural stability of graphite anode materials compared to other sizes. 50 When the ratio is limited to the specific range mentioned above, the two can exert a synergistic effect, improving the rate performance and cycle stability of lithium-ion batteries.

[0035] The carbon coating layer can create a continuous and stable conductive network, accelerating electron conduction and thus improving the rate performance of lithium-ion batteries. At the same time, it can also isolate the core from the electrolyte, inhibiting the electrolyte's erosion of the core, thereby improving the stability of lithium-ion batteries and extending their service life. In addition, the carbon coating layer can also alleviate the expansion of graphite anode materials during lithium-ion battery cycling, thereby improving the cycle performance of lithium-ion batteries.

[0036] Limiting the particle size distribution of graphite anode material within the aforementioned specific range can, on the one hand, improve the microstructure and pore distribution of the anode sheet containing the graphite anode material, enhance the uniformity of the pore distribution within the anode sheet, and reduce the tortuosity of the anode sheet, thereby improving the rate performance of the lithium-ion battery. On the other hand, it can suppress structural changes caused by the inconsistent expansion and contraction rates of the graphite anode material during charging and discharging, reduce local current density differences caused by the uneven particle size distribution of the graphite anode material, thereby improving the stability of the lithium-ion battery, ensuring that the anode sheet maintains a low tortuosity, and further improving the rate performance and cycle performance of the lithium-ion battery.

[0037] The porous structure of the second graphite particles can provide a fast transport channel for lithium ions. By limiting the porosity of the second graphite particles to the aforementioned specific range, the detour diffusion of lithium ions between layers can be reduced, thereby improving the transport efficiency of lithium ions and the rate performance of the graphite anode material.

[0038] The carbon binder layer enhances the adhesion between the second graphite particles and the first graphite particles, and it also forms a continuous conductive network with the carbon coating layer, promoting rapid electron conduction and thus improving the rate performance of the lithium-ion battery.

[0039] In summary, the graphite anode material provided in this application has excellent rate performance and high lithium-ion transport efficiency. When used as an anode active material in anode sheets, it can suppress pore blockage and reduce the tortuosity of the anode sheets, thereby effectively improving the rate performance, energy density, and cycle performance of lithium-ion batteries. Attached Figure Description

[0040] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0041] Figure 1 The SEM image of the graphite anode material prepared in Example 1 of this application is shown.

[0042] Figure 2 The image shows a cross-sectional SEM image of the negative electrode sheet prepared from the graphite negative electrode material obtained in Example 1 of this application. Detailed Implementation

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0044] As described in the background section, existing graphite anode materials suffer from poor rate performance and are prone to pore blockage during subsequent anode sheet fabrication, leading to increased tortuosity of the anode sheet. To address these technical problems, this application provides a graphite anode material comprising a core and a carbon coating layer disposed on the surface of the core. The core, from the inside out, comprises first graphite particles, a carbon binder layer, and second graphite particles disposed on the surface of the carbon binder layer. The first graphite particles have a D... 50 D is larger than that of the second graphite particle 50 And both D 50 The ratio is (1.3~6):1; the second graphite particles have a porous structure and the porosity of the second graphite particles is 20~60%; the particle size distribution width of the graphite anode material is 0.5~1.

[0045] Compared to graphite anode materials that directly blend small-diameter graphite particles with large-diameter conventional graphite particles, the graphite anode material provided in this application has the second graphite particles tightly bonded to the first graphite particles through a carbon bonding layer. This effectively suppresses pore blockage caused by the difference in flowability between the second and first graphite particles during the anode sheet fabrication process, thereby reducing the tortuosity of the anode sheet and improving lithium-ion transport efficiency and rate performance of the lithium-ion battery. 50 Smaller second graphite particles can provide rapid lithium-ion diffusion channels, D 50 Larger first graphite particles can improve the energy density and structural stability of graphite anode materials compared to other sizes. 50 When the ratio is limited to the specific range mentioned above, the two can exert a synergistic effect, improving the rate performance and cycle stability of lithium-ion batteries.

[0046] The carbon coating layer can create a continuous and stable conductive network, accelerating electron conduction and thus improving the rate performance of lithium-ion batteries. At the same time, it can also isolate the core from the electrolyte, inhibiting the electrolyte's erosion of the core, thereby improving the stability of lithium-ion batteries and extending their service life. In addition, the carbon coating layer can also alleviate the expansion of graphite anode materials during lithium-ion battery cycling, thereby improving the cycle performance of lithium-ion batteries.

[0047] The particle size distribution width of graphite anode materials reflects the degree of difference in particle size. Limiting it within the aforementioned specific range can, on the one hand, improve the microstructure and pore distribution of the anode sheet containing the graphite anode material, increase the uniformity of the pore distribution within the anode sheet, and reduce the tortuosity of the anode sheet, thereby improving the rate performance of the lithium-ion battery. On the other hand, it can suppress structural changes caused by the inconsistent expansion and contraction rates of the graphite anode material during charging and discharging, reduce local current density differences caused by the uneven particle size distribution of the graphite anode material, thereby improving the stability of the lithium-ion battery, ensuring that the anode sheet maintains a low tortuosity, and further improving the rate performance and cycle performance of the lithium-ion battery.

[0048] The porous structure of the second graphite particles can provide a fast transport channel for lithium ions. By limiting the porosity of the second graphite particles to the aforementioned specific range, the detour diffusion of lithium ions between layers can be reduced, thereby improving the transport efficiency of lithium ions and the rate performance of the graphite anode material.

[0049] The carbon binder layer enhances the adhesion between the second graphite particles and the first graphite particles, and it also forms a continuous conductive network with the carbon coating layer, promoting rapid electron conduction and thus improving the rate performance of the lithium-ion battery.

[0050] In summary, the graphite anode material provided in this application has excellent rate performance and high lithium-ion transport efficiency. When used as an anode active material in anode sheets, it can suppress pore blockage and reduce the tortuosity of the anode sheets, thereby effectively improving the rate performance, energy density, and cycle performance of lithium-ion batteries.

[0051] It should be noted that the particle size distribution width (SPAN value) is an indicator of the uniformity of particle size distribution. Its size reflects the breadth of the particle size distribution. The larger the SPAN value, the wider the particle size distribution. The SPAN value is usually calculated by equation (I).

[0052] In a preferred embodiment, the D of the graphite anode material 10 The diameter is 5–15 μm, D 50 The diameter is 7–20 μm, D 90 The value is 9–25 μm, and D 10 <D 50 <D 90 D of graphite anode materials 10 D 50 and D 90Including but not limited to the above-mentioned scope, limiting it to the above-mentioned scope is beneficial to improving the dimensional consistency of graphite anode materials. On the one hand, it is beneficial to improve the microstructure and pore distribution of the anode sheet containing the graphite anode material, reduce the tortuosity of the anode sheet, and thus improve the rate performance of lithium-ion batteries. On the other hand, it is beneficial to suppress the structural changes caused by the inconsistency of the expansion rate and contraction rate of the graphite anode material during charging and discharging, reduce the local current density difference, and thus improve the rate performance and cycle performance of lithium-ion batteries.

[0053] In a preferred embodiment, the weight ratio of the core to the carbon coating layer is 100:(0.5-12). The thicknesses of the core and the carbon coating layer include, but are not limited to, the above-mentioned ranges. Limiting them to these ranges is beneficial for improving lithium-ion transport efficiency, improving the rate performance of the graphite anode material, and also for obtaining a carbon coating layer of suitable thickness. This helps to suppress electrolyte erosion of the core, alleviate the expansion of the graphite anode material during battery cycling, and thus improve the rate performance and stability of the lithium-ion battery.

[0054] Artificial graphite refers to graphite materials obtained through organic carbonization followed by high-temperature graphitization. Artificial graphite has a denser particle structure and higher compaction density, which can improve the energy density of lithium-ion batteries. In a preferred embodiment, the first graphite particle is artificial graphite, and the D of the first graphite particle... 50 The diameter is 8–12 μm. The D of the first graphite particle... 50 Including but not limited to the above-mentioned scope, limiting it to the above-mentioned scope is beneficial to improving the stability and compaction density of graphite anode materials, and is beneficial to improving the microstructure and pore distribution of anode sheets containing graphite anode materials, thereby reducing the tortuosity of anode sheets, improving lithium-ion transport efficiency, and further improving the rate performance and energy density of lithium-ion batteries.

[0055] To provide more lithium-ion transport channels while reducing the circuitous diffusion of lithium ions between dense graphite layers, thereby further improving lithium-ion transport efficiency and rate performance of lithium-ion batteries, in a preferred embodiment, the D of the second graphite particles... 50 Its diameter is 2–6 μm, its average pore size is 0.5–30 nm, and its specific surface area is 10–1000 m². 2 / g. Preferably, the specific surface area of ​​the second graphite particles is 400–1000 m². 2 / g.

[0056] This application focuses more on the D of the second graphite particles. 50 The optimization of its pore structure does not limit the specific type of raw material. In a preferred embodiment, the second graphite particles are obtained by creating pores from natural graphite and / or artificial graphite.

[0057] In a preferred embodiment, the weight percentage of the second graphite particles in the graphite anode material is 10–50 wt%. The weight percentage of the second graphite particles includes, but is not limited to, the above range. Limiting it to this range facilitates the introduction of a more suitable amount of second graphite particles, which is beneficial for maintaining high energy density and capacity while improving the rate performance of the graphite anode material, providing more fast transport paths for lithium ions, and thus improving the rate performance, energy density, and cycle performance of the lithium-ion battery. Specifically, the weight percentage of the second graphite particles can be 10 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%.

[0058] The second aspect of this application also provides a method for preparing the graphite anode material provided in this application. The method includes: step S1, preparing first graphite particles; step S2, creating pores in graphite raw materials using a physical activation method or a chemical activation method to obtain second graphite particles; step S3, mixing the first graphite particles, the second graphite particles, and a coating material, and sequentially subjecting them to a first heat treatment and sieving to obtain the graphite anode material; wherein the coating material is selected from asphalt compounds and / or carbon-containing resins.

[0059] In the preparation method of the graphite anode material provided in this application, first graphite particles can be prepared in step S1. Step S2 uses a physical activation method or a chemical activation method to create pores in the graphite raw material, resulting in second graphite particles with a porous structure. This provides a fast transport channel for lithium ions, reduces the detour-like diffusion of lithium ions between dense graphite layers, and improves the transport efficiency of lithium ions and the rate performance of the anode material. In step S3, by mixing the first and second graphite particles with a coating material and sequentially performing a first heat treatment and sieving, a graphite anode material with a uniform particle size distribution can be obtained. It should be noted that the coating material can both act as a binder and granulator, forming a carbon binder layer to bond the first and second graphite particles together, and simultaneously act as a coating, forming a carbon coating layer on the surface of the core, constructing a continuous conductive network, accelerating electron conduction, and inhibiting the erosion of the core by the electrolyte, thereby improving the rate performance and stability of the lithium-ion battery.

[0060] Using the aforementioned specific type of coating material can enhance the adhesion between the first graphite particles and the second graphite particles, and it can also form a continuous conductive network with the carbon coating layer, thereby promoting rapid electron conduction and improving the rate performance and stability of lithium-ion batteries.

[0061] Moreover, compared to graphite anode materials that directly mix small-diameter graphite particles with large-diameter conventional graphite particles, the preparation method provided in this application binds the first graphite particles and the second graphite particles together through a carbon bonding layer. This effectively suppresses the pore blockage caused by the difference in flowability between the second and first graphite particles during the preparation of the anode sheet, thereby reducing the tortuosity of the anode sheet and improving the lithium-ion transport efficiency and the rate performance of the lithium-ion battery. Screening can yield graphite anode materials with uniform particle size distribution. On one hand, it can improve the microstructure and pore distribution of the anode sheet containing this graphite anode material, increase the uniformity of the pore distribution inside the anode sheet, and reduce the tortuosity of the anode sheet, thereby improving the rate performance of the lithium-ion battery. On the other hand, it can suppress structural changes caused by the inconsistent expansion and contraction rates of the graphite anode material during charging and discharging, reduce the local current density differences caused by the uneven particle size distribution of the graphite anode material, thereby improving the stability of the lithium-ion battery, ensuring that the anode sheet maintains a low tortuosity, and thus improving the rate performance and cycle performance of the lithium-ion battery.

[0062] In summary, the graphite anode material prepared by the above-mentioned preparation method provided in this application has excellent rate performance and high lithium-ion transport efficiency. When used as an anode active material in anode sheets, it can suppress the pore blockage phenomenon of anode sheets and reduce the tortuosity of anode sheets, thereby effectively improving the rate performance, energy density and cycle performance of lithium-ion batteries.

[0063] In order to further enhance the bonding force between the second graphite particles and the first graphite particles, and to further improve the conductivity of the graphite anode material and the electron conduction efficiency, thereby further improving the rate performance of the lithium-ion battery, in a preferred embodiment, the asphalt compounds include, but are not limited to, one or more of the group consisting of tar pitch, petroleum pitch and natural pitch, and the carbon-containing resins include, but are not limited to, one or more of the group consisting of phenolic resin, furan resin and epoxy resin.

[0064] In order to obtain first graphite particles with a more stable structure and higher compaction density and capacity, and further improve the lithium-ion transport efficiency, thereby further improving the electrochemical performance of lithium-ion batteries and increasing the rate performance and energy density of lithium-ion batteries, in a preferred embodiment, the preparation method of the first graphite particles in step S1 includes: preheating, crushing, graphitizing, demagnetizing and sieving amorphous carbon materials in sequence to obtain the first graphite particles.

[0065] It should be noted that in the preparation method of the first graphite particles described above in this application, the demagnetization process includes: separating magnetic particles using a magnetic separator.

[0066] To remove volatile components (such as moisture and organic solvents) and some impurities from amorphous carbon materials and improve the efficiency of subsequent graphitization, the preheating treatment is preferably carried out at a temperature of 900–1400°C for 4–10 hours. Specifically, the preheating treatment temperature can be 900°C, 1000°C, 1100°C, 1200°C, 1300°C, or 1400°C, and the time can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0067] In order to improve the graphitization degree of the first graphite particles and form a more ordered carbon layer structure, thereby further improving the lithium-ion transport efficiency and the rate performance of the lithium-ion battery, preferably, the graphitization temperature is 2800-3500℃ and the time is 4-24h.

[0068] In order to form first graphite particles with a more ordered carbon layer structure, thereby further improving the lithium-ion transport efficiency and the rate performance of lithium-ion batteries, more preferably, the amorphous carbon material includes, but is not limited to, one or more of the group consisting of petroleum coke, needle coke, and pitch coke.

[0069] In a preferred embodiment, step S2, the physical activation method includes: using an oxidizing gas to create pores in the graphite raw material to obtain second graphite particles. The oxidizing gas can react with the graphite raw material at high temperatures to generate carbon monoxide, thereby forming pores in situ on the graphite raw material, resulting in second graphite particles with a porous structure. Compared to other methods, using the physical activation method for pore creation is beneficial for controlling the size and distribution of the formed pore structure, increasing the specific surface area of ​​the second graphite particles, reducing damage to the graphite structure, and improving the structural stability of the second graphite particles.

[0070] To further control the size and distribution of the pore structure of the second graphite particles, while further reducing the destructiveness of the graphite structure and improving the stability of the second graphite particles, preferably, the pore-forming temperature is 800–1000℃ and the time is 1–5 hours. Specifically, the pore-forming temperature can be 800℃, 900℃, or 1000℃, and the time can be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours.

[0071] To improve the reaction efficiency between the oxidizing gas and the graphite raw material, and to further regulate the size and distribution of the pore structure of the second graphite particles, thereby giving the second graphite particles a more suitable porosity and specific surface area, preferably, the ratio of the weight of the graphite raw material to the volume of the oxidizing gas is 1 kg:(10-50) m³. 3 .

[0072] To further improve the reaction efficiency between the oxidizing gas and the graphite raw material, and to further regulate the size and distribution of the pore structure of the second graphite particles, preferably, the oxidizing gas includes, but is not limited to, air and / or carbon dioxide.

[0073] In a preferred embodiment, step S2, the chemical activation method includes: mixing graphite raw material with a pore-forming agent in an inert gas atmosphere, followed by a second heat treatment to obtain second graphite particles. The pore-forming agent can react with the graphite raw material at high temperature, corroding the surface of the graphite raw material and releasing gas in situ, thereby forming pores and obtaining second graphite particles with a porous structure. Compared with other methods, the chemical activation method makes it easier to control the size and distribution of the pore structure of the second graphite particles, forming a multi-level pore structure from micropores and mesopores to macropores. This is beneficial for providing more efficient transport channels for lithium ions, reducing their tortuous diffusion between dense graphite layers, and thus improving the rate performance of lithium-ion batteries.

[0074] To further control the size and distribution of the pore structure of the second graphite particles, preferably, the weight ratio of graphite raw material to pore-forming agent is 1:(0.5-4). Specifically, the weight ratio of graphite raw material to pore-forming agent can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4.

[0075] In order to improve the reaction efficiency between the pore-forming agent and the graphite raw material, and to further control the size and distribution of the pore structure of the second graphite particles, preferably, the temperature of the second heat treatment is 700-900℃ and the time is 1-5h.

[0076] To further improve the reaction efficiency between the pore-forming agent and the graphite raw material, and to further control the size and distribution of the pore structure of the second graphite particles, preferably, the pore-forming agent includes, but is not limited to, one or more of the group consisting of potassium hydroxide, sodium hydroxide, phosphoric acid, sulfuric acid and nitric acid.

[0077] In a preferred embodiment, in step S3, the weight ratio of the first graphite particles to the second graphite particles is (1-9):1. The weight ratio of the first graphite particles to the second graphite particles includes, but is not limited to, the range described above. Limiting it to this range facilitates the introduction of an appropriate amount of second graphite particles, thereby improving the lithium-ion transport path and resulting in a graphite anode material with both high energy density and high rate performance. Specifically, the weight ratio of the first graphite particles to the second graphite particles can be 1:1, 1:2, 1:4, 1:5, 1:6, 1:8, or 1:9.

[0078] In a preferred embodiment, the total weight ratio of the first graphite particles and the second graphite particles to the coating material is (88-99.5):(0.5-12). This weight ratio includes, but is not limited to, the range described above. Limiting it to this range is beneficial in two ways: firstly, it enhances the bonding and granulation effects of the coating material, strengthening the bond between the first and second graphite particles and improving the stability of the core; secondly, it facilitates the formation of a carbon coating layer of suitable thickness, thereby promoting the construction of a continuous conductive network, accelerating electron conduction, and inhibiting electrolyte erosion of the core, ultimately improving the rate performance and stability of the lithium-ion battery.

[0079] In a preferred embodiment, the temperature of the first heat treatment is 400–1200°C, and the time is 2–12 hours. The temperature and time of the first heat treatment include, but are not limited to, the above ranges. Limiting them to these ranges facilitates the formation of a carbon bonding layer of suitable thickness, thereby achieving the bonding of the first graphite particles and the second graphite particles to obtain the core. Simultaneously, it facilitates the formation of a carbon coating layer of suitable thickness, which in turn facilitates the construction of a continuous conductive network, accelerates the transport of electrons and lithium ions, inhibits the erosion of the core by the electrolyte, and thus improves the rate performance and stability of the lithium-ion battery. Specifically, the temperature of the first heat treatment can be 400°C, 600°C, 700°C, 850°C, 900°C, 1000°C, 1100°C, or 1200°C, and the time can be 2 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 11 hours, or 12 hours.

[0080] In a preferred embodiment, a conductive agent is also introduced during the mixing process in step S3. The introduction of the conductive agent can synergistically work with the coating material to construct a continuous conductive network, alleviate the volume expansion effect of the graphite anode material during charging and discharging, and improve the electron and lithium-ion transport efficiency, thereby improving the rate performance and stability of the lithium-ion battery.

[0081] In a preferred embodiment, the weight ratio of the conductive agent to the coating material is (0.01 to 0.05):1. The weight ratio of the conductive agent to the coating material includes, but is not limited to, the above range. Limiting it to this range is beneficial for leveraging the synergistic effect of the conductive agent and the coating material, for forming a more stable and continuous conductive network, for mitigating the volume expansion effect of the graphite anode material during charging and discharging, and for improving the electron and lithium-ion transport efficiency, thereby enhancing the rate performance and stability of the lithium-ion battery. Specifically, the weight ratio of the conductive agent to the coating material can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, or 0.05:1.

[0082] To further improve the stability of graphite anode materials and further improve the electron and lithium-ion transport efficiency, preferably, the conductive agent includes, but is not limited to, one or more of the group consisting of graphene, carbon nanotubes, carbon nanofibers and carbon black.

[0083] A third aspect of this application also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer stacked together, wherein the negative electrode active material layer comprises the graphite negative electrode material provided in this application. The graphite negative electrode material provided in this application possesses excellent rate performance and high lithium-ion transport efficiency. Using it as a negative electrode active material in a negative electrode sheet can suppress pore blockage caused by the difference in flowability between the second and first graphite particles, reduce the tortuosity of the negative electrode sheet, and thus effectively improve the rate performance, energy density, and cycle performance of lithium-ion batteries.

[0084] A fourth aspect of this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrode, wherein the negative electrode is the aforementioned negative electrode provided in this application. The aforementioned negative electrode provided in this application includes the aforementioned graphite negative electrode material. This negative electrode is less prone to pore blockage and has low tortuosity, effectively improving the rate performance, energy density, and cycle performance of the lithium-ion battery.

[0085] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0086] It should be noted that in all embodiments and comparative examples of this application, the D of the first graphite particles and the second graphite particles... 50 The porosity, average pore size, and specific surface area of ​​the second graphite particles were measured using the method described in the national standard GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction"; the porosity, average pore size, and specific surface area of ​​the second graphite particles were measured using the method described in the national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0087] Example 1

[0088] A method for preparing a graphite anode material specifically includes the following steps:

[0089] (1) Preparation of the first graphite particles: Petroleum coke (Koppers Carbon Chemical Co., Ltd., KPC-30) was preheated at 1000℃ for 6 hours, then crushed, and then graphitized at 2800℃ for 20 hours. After cooling, it was demagnetized using a magnetic separator, and then sieved to obtain D. 50 The first graphite particle is 10 μm;

[0090] (2) Preparation of second graphite particles by chemical activation method: Under N2 protection, natural graphite (Yabot, ADT-05, D) was... 50 A mixture of 5 μm graphite particles and pore-forming agent KOH at a weight ratio of 1:1 was prepared and reacted at 700 °C (i.e., the second heat treatment) for 2 h to obtain second graphite particles; wherein, the D of the second graphite particles is... 50 It has a diameter of 5 μm, a porosity of 37%, an average pore size of 12 nm, and a specific surface area of ​​440 m². 2 / g;

[0091] (3) The first graphite particles obtained in step (1), the second graphite particles obtained in step (2), phenolic resin (Sumitomo, Japan, PR-53500), graphene (Xiamen Kaina Graphene Technology Co., Ltd., KNG-G2), and carbon nanotubes (Jiangsu Tiannai Technology Co., Ltd., 6121) were mixed in a weight ratio of 70:30:8:0.05:0.05, and then subjected to a first heat treatment at 900℃ for 5 hours. After cooling, the mixture was sieved to obtain D. 90 15μm, D 10 It is 7μm and D 50 It is a 13μm graphite anode material.

[0092] The graphite anode material prepared in Example 1 has a particle size distribution width of 0.62 and a weight ratio of core to carbon coating layer of 100:8.

[0093] The SEM image of the graphite anode material prepared in Example 1 is shown below. Figure 1 As shown, by Figure 1 It can be seen that the graphite anode material is granular, and small-diameter graphite particles are adhered to the surface of the large-diameter graphite particles.

[0094] Example 2

[0095] The difference from Example 1 is that in step (2), 1000g of natural graphite (same type as in Example 1) is placed in a vacuum etching reactor, CO2 is introduced at 800°C, and the reaction is carried out at this temperature for 4 hours to obtain the second graphite particles; wherein, a total of 25m 3 Carbon dioxide gas, the D of the second graphite particles obtained 50 It has a diameter of 5 μm, a porosity of 27%, an average pore size of 7 nm, and a specific surface area of ​​120 m². 2 / g; the remaining steps are the same as in Example 1.

[0096] Example 3

[0097] The difference from Example 1 is that in step (2), the weight ratio of natural graphite to pore-forming agent KOH is 1:4, and the D of the resulting second graphite particles is... 50The micrometer diameter is 4.1 μm, the porosity is 54%, the average pore size is 24 nm, and the specific surface area is 930 m². 2 / g, the remaining steps are the same as in Example 1.

[0098] Example 4

[0099] The difference from Example 1 is that in step (2), the D of natural graphite is used. 50 The second graphite particles obtained are 6 μm in diameter and have a D-value of 6 μm. 50 The first graphite particle obtained in step (1) has a diameter of 6 μm and a density of 6 μm. 50 D of the second graphite particle mentioned above 50 The ratio is 5:3, and the remaining steps are the same as in Example 1.

[0100] Example 5

[0101] The difference from Example 1 is that in step (2), the D of natural graphite is used. 50 The second graphite particles obtained are 2μm in diameter and have a D-value of 2μm. 50 The first graphite particle obtained in step (1) has a diameter of 2 μm and a density of 2 μm. 50 D of the second graphite particle mentioned above 50 The ratio is 5:1, and the remaining steps are the same as in Example 1.

[0102] Example 6

[0103] The difference from Example 1 is that in step (3), the weight ratio of the first graphite particle to the second graphite particle is 9:1, and the remaining steps are the same as in Example 1.

[0104] Example 7

[0105] The difference from Example 1 is that in step (3), the weight ratio of the first graphite particle to the second graphite particle is 1:1, and the remaining steps are the same as in Example 1.

[0106] Example 8

[0107] The difference from Example 1 is that in step (3), the weight ratio of the first graphite particle to the second graphite particle is 19:1, and the remaining steps are the same as in Example 1.

[0108] Example 9

[0109] The difference from Example 1 is that in step (3), the total weight ratio of the first graphite particles and the second graphite particles to the weight of the phenolic resin is 99.5:0.5, and the remaining steps are the same as in Example 1.

[0110] Example 10

[0111] The difference from Example 1 is that in step (3), the total weight ratio of the first graphite particles and the second graphite particles to the phenolic resin is 88:12, and the remaining steps are the same as in Example 1.

[0112] Example 11

[0113] The difference from Example 1 is that in step (3), the total weight ratio of the first graphite particles and the second graphite particles to the weight of the phenolic resin is 80:20, and the remaining steps are the same as in Example 1.

[0114] Example 12

[0115] The difference from Example 1 is that in step (3), the conductive agent graphene and carbon nanotube mixture was not introduced, and an equal amount of phenolic resin was used instead. The remaining steps are the same as in Example 1.

[0116] Example 13

[0117] The difference from Example 1 is that in step (3), the weight ratio of the mixture of conductive agent graphene and carbon nanotubes to phenolic resin is 0.01:1, and the remaining steps are the same as in Example 1.

[0118] Example 14

[0119] The difference from Example 1 is that in step (3), the weight ratio of the mixture of conductive agent graphene and carbon nanotubes to phenolic resin is 0.05:1, and the remaining steps are the same as in Example 1.

[0120] Example 15

[0121] The difference from Example 1 is that in step (3), the weight ratio of the mixture of conductive agent graphene and carbon nanotubes to phenolic resin is 0.005:1, and the remaining steps are the same as in Example 1.

[0122] Example 16

[0123] The difference from Example 1 is that in step (3), the temperature of the first heating treatment is 1200℃ and the time is 2h, while the remaining steps are the same as in Example 1.

[0124] Example 17

[0125] The difference from Example 1 is that in step (3), the temperature of the first heating treatment is 400°C and the time is 12h, while the remaining steps are the same as in Example 1.

[0126] Example 18

[0127] The difference from Example 1 is that in step (3), the temperature of the first heating treatment is 300°C and the time is 6 hours, while the remaining steps are the same as in Example 1.

[0128] Comparative Example 1

[0129] The difference from Example 1 is that step (3) is omitted, and the first graphite particles obtained in step (1) and the second graphite particles obtained in step (2) are directly mixed in a weight ratio of 7:3 to obtain the graphite anode material. The remaining steps are the same as in Example 1.

[0130] Comparative Example 2

[0131] The difference from Example 1 is that step (2) is omitted, and unpore-free natural graphite (the same type as in Example 1) is used directly as the second graphite particle. The remaining steps are the same as in Example 1.

[0132] Comparative Example 3

[0133] The difference from Example 1 is that step (2) is omitted, and unpored natural graphite (the same type as in Example 1) is directly used as the second graphite particle. At the same time, step (3) is omitted, and the first graphite particle obtained in step (1) and the above-mentioned natural graphite are directly mixed in a weight ratio of 7:3 to obtain the graphite negative electrode material. The remaining steps are the same as in Example 1.

[0134] Comparative Example 4

[0135] The difference from Example 1 is that in step (3), no sieving was performed, and the graphite anode material was directly obtained after cooling. The remaining steps are the same as in Example 1. The graphite anode material obtained in Comparative Example 4 has a D... 90 54μm, D 10 3μm, D 50 The particle size is 28 μm, and its particle size distribution width is 1.82.

[0136] Comparative Example 5

[0137] The difference from Example 1 is that in step (2), the D of natural graphite is used. 50 The second graphite particles prepared therefrom have a diameter of 9 μm and a density of 0.5 μm. 50 The value is 9 μm, and the D of the first graphite particles obtained in step (1) is... 50 D of the second graphite particle mentioned above 50 The ratio was 1.1:1, and the remaining steps were the same as in Example 1. The D of the graphite anode material prepared in Comparative Example 5... 90 32μm, D 10 4μm, D 50 The particle size is 19 μm, and its particle size distribution width is 1.47.

[0138] Comparative Example 6

[0139] The difference from Example 1 is that in step (2), the weight ratio of natural graphite to pore-forming agent KOH is 1:0.2, and the D of the obtained second graphite particles is... 50 It has a diameter of 5 μm, a porosity of 15%, an average pore size of 3 nm, and a specific surface area of ​​56 m². 2 / g, the remaining steps are the same as in Example 1.

[0140] The specific surface area, particle size distribution width, and weight ratio of the core to the carbon coating layer of the graphite anode materials prepared in Examples 1 to 18 and Comparative Examples 1 to 6 of this application are shown in Table 1.

[0141] Table 1

[0142]

[0143] The graphite anode materials prepared in Examples 1 to 18 and Comparative Examples 1 to 6 of this application were mixed with conductive carbon black (Super P Li), binder carboxymethyl cellulose (Ashland, BVH9), and styrene-butadiene rubber (Shenzhen Haodian Technology Co., Ltd., HD3153) in a weight ratio of 96:1:1.5:1.5 to obtain anode slurry. The above anode slurry was coated onto a copper foil with a thickness of 6 μm and dried at 80°C to obtain anode sheet. Anode sheet was assembled using ternary cathode material NCM811 (Umicore Materials Technology Co., Ltd.) as cathode active material and aluminum foil with a thickness of 12 μm as cathode current collector. A lithium-ion battery was assembled using Xinzhoubang LBC448A17 electrolyte and Enjie Celgard2400 separator.

[0144] SEM image of the cross-section of the negative electrode sheet prepared from the graphite negative electrode material obtained in Example 1 is shown below. Figure 2 As shown, by Figure 2 It can be seen that the first graphite particle and the second graphite particle in the graphite anode material have a good composite state, and the surface of the second graphite particle has obvious pore structure.

[0145] The following electrochemical performance tests were performed on the lithium-ion batteries assembled in Examples 1 to 18 and Comparative Examples 1 to 6 of this application:

[0146] (1) Constant current charge ratio (i.e., the ratio of the battery charge capacity to the total charge capacity) test under constant current and constant voltage charging at different rates: Constant current and constant voltage charging at 1C, 2C, 3C, 4C and 5C rates were performed in the voltage range of 2.5 to 4.25V.

[0147] (2) Capacity retention test: at 25℃, the voltage range is 2.5~4.25V, and the cycle is 500 cycles at 1C.

[0148] The test results are shown in Table 2.

[0149] Table 2

[0150]

[0151]

[0152] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0153] Comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the constant current charge ratios of the lithium-ion batteries prepared in Comparative Examples 1 to 3 at 2C, 3C, 4C, and 5C are all lower than those in Example 1, and the cycle capacity retention is also lower than that in Example 1, indicating that the rate performance and cycle performance of the lithium-ion batteries prepared in Comparative Examples 1 to 3 are relatively poor. Therefore, compared to the graphite anode materials in Comparative Examples 1 to 3, which directly mix small-diameter graphite particles without pores with large-diameter conventional graphite particles, Example 1 of this application uses a carbon bonding layer to tightly bond the second graphite particles (small-diameter graphite particles) and the first graphite particles (large-diameter graphite particles) together. This effectively suppresses the pore blockage phenomenon caused by the difference in flowability between the second and first graphite particles during the preparation of the anode sheet, thereby reducing the tortuosity of the anode sheet and improving the lithium-ion transport efficiency and the rate performance and cycle performance of the lithium-ion battery. Simultaneously, creating pores in the second graphite particles can provide a fast transport channel for lithium ions, reducing the detour diffusion of lithium ions between layers, thereby improving the rate performance and cycle performance of the graphite anode material.

[0154] Comparing Example 1 and Comparative Example 4, it can be seen that limiting the particle size distribution width of the graphite anode material to the specific range described above in this application can, on the one hand, improve the microstructure and pore distribution of the anode sheet containing the graphite anode material, increase the uniformity of the pore distribution inside the anode sheet, reduce the tortuosity of the anode sheet, and improve the rate performance of the lithium-ion battery; on the other hand, it can suppress the structural changes caused by the inconsistency of the expansion rate and contraction rate of the graphite anode material during charging and discharging, reduce the local current density differences caused by the uneven particle size distribution of the graphite anode material, thereby improving the stability of the lithium-ion battery, ensuring that the anode sheet maintains a low tortuosity, and thus improving the rate performance and cycle performance of the lithium-ion battery.

[0155] Comparing Examples 1, 4, and 5 with Comparative Example 5, it can be seen that, compared to other ranges, the D of the first graphite particles... 50 D of the second graphite particles 50 The ratio is limited to the specific range mentioned above in this application, which allows the synergistic effect of the two to be better utilized. On the one hand, D 50 Smaller second graphite particles can provide more rapid lithium-ion diffusion channels, on the other hand, D 50Larger first graphite particles can improve the energy density and structural stability of graphite anode materials, thereby improving the rate performance and cycle stability of lithium-ion batteries.

[0156] Comparing Examples 1 to 3 and Comparative Example 6, it can be seen that, compared to other ranges, limiting the porosity of the second graphite particles to the above-mentioned specific range can reduce the detour diffusion of lithium ions between layers, improve the lithium ion transport efficiency and the rate performance of the anode material, thereby improving the rate performance and cycle stability of the lithium-ion battery.

[0157] Comparing Examples 1, 6 to 8, it can be seen that, compared to other ranges, limiting the weight ratio of the first graphite particles to the second graphite particles within the above range is beneficial for introducing an appropriate amount of second graphite particles, thereby improving the lithium-ion transport path and obtaining a graphite anode material with both high energy density and high rate performance.

[0158] Comparing Examples 1, 9 to 11, it can be seen that the cycle performance of Example 11 is much lower than that of Examples 1, 9 and 10, indicating that the lithium-ion battery prepared in Example 11 has poor cycle stability. Therefore, compared to other ranges, limiting the total weight ratio of the first and second graphite particles to the weight of the coating material within the above-mentioned range is beneficial in two ways: firstly, it helps to leverage the bonding and granulation effects of the coating material, enhancing the adhesion between the first and second graphite particles and improving the structural stability of the graphite anode material; secondly, it facilitates the formation of a carbon coating layer of suitable thickness, inhibiting the erosion of the core by the electrolyte, thereby improving the cycle stability of the lithium-ion battery.

[0159] Comparing Examples 1 and 12, it can be seen that although the cycle capacity retention rate of the lithium-ion battery prepared in Example 12 is comparable to that of Example 1, its constant current charge ratio at 2C, 3C, 4C, and 5C is lower than that of Example 1. This indicates that the rate performance of the lithium-ion battery prepared in Example 12 is poor. Therefore, the introduction of a conductive agent can synergistically work with the coating material to construct a continuous conductive network, improving the transport efficiency of electrons and lithium ions, thereby contributing to improved rate performance of the lithium-ion battery.

[0160] Comparing Examples 1, 13 to 15, it can be seen that, compared with other ranges, limiting the weight ratio of the conductive agent to the coating material within the above range is beneficial to exert the synergistic effect of the conductive agent and the coating material, forming a more stable and continuous conductive network, improving the transmission efficiency of electrons and lithium ions, and also helping to alleviate the volume expansion effect of graphite anode material during charging and discharging, thereby improving the rate performance and cycle life of lithium-ion batteries.

[0161] Comparing Examples 1, 16 to 18, it can be seen that, compared to other ranges, limiting the temperature and time of the first heat treatment within the above range is beneficial to forming a carbon bonding layer of suitable thickness, thereby achieving the bonding of the first graphite particles and the second graphite particles. At the same time, it is also beneficial to form a carbon coating layer of suitable thickness, thereby constructing a continuous conductive network, accelerating the transport of electrons and lithium ions, suppressing the erosion of the core by the electrolyte, and thus improving the rate performance and cycle stability of the lithium-ion battery.

[0162] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0163] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graphite anode material, characterized in that, The graphite anode material includes a core and a carbon coating layer disposed on the surface of the core; the core, from the inside out, includes first graphite particles, a carbon binder layer, and second graphite particles disposed on the surface of the carbon binder layer, wherein the first graphite particles have a D... 50 D greater than the second graphite particle 50 And both D 50 The ratio is (1.3~6):1; the second graphite particle has a porous structure, and the porosity of the second graphite particle is 20~60%; the particle size distribution width of the graphite anode material is 0.5~1.

2. The graphite anode material according to claim 1, characterized in that, The D of the graphite anode material 10 The diameter is 5–15 μm, D 50 The diameter is 7–20 μm, D 90 The value is 9–25 μm, and D 10 <D 50 <D 90 ; Preferably, the weight ratio of the core to the carbon coating is 100:(0.5-12).

3. The graphite anode material according to claim 1 or 2, characterized in that, The first graphite particle is artificial graphite, and the D of the first graphite particle is... 50 It is 8–12 μm; Preferably, the D of the second graphite particle 50 Its diameter is 2–6 μm, its average pore size is 0.5–30 nm, and its specific surface area is 10–1000 m². 2 / g; More preferably, the second graphite particles are obtained by creating pores from natural graphite and / or artificial graphite; Preferably, in the graphite anode material, the weight percentage of the second graphite particles is 10-50 wt%.

4. A method for preparing a graphite anode material according to any one of claims 1 to 3, characterized in that, The preparation method includes: Step S1: Prepare the first graphite particles; Step S2: Pores are created in the graphite raw material using physical or chemical activation methods to obtain second graphite particles; Step S3: The first graphite particles, the second graphite particles, and the coating material are mixed and then subjected to a first heat treatment and sieving to obtain the graphite anode material; wherein the coating material is selected from asphalt compounds and / or carbon-containing resins.

5. The method for preparing the graphite anode material according to claim 4, characterized in that, In step S1, the method for preparing the first graphite particles includes: preheating, crushing, graphitizing, demagnetizing and sieving the amorphous carbon material in sequence to obtain the first graphite particles. Preferably, the preheating treatment is performed at a temperature of 900–1400°C for 4–10 hours. Preferably, the graphitization temperature is 2800–3500℃ and the time is 4–24 hours; More preferably, the amorphous carbon material is selected from one or more of the group consisting of petroleum coke, needle coke, and pitch coke.

6. The method for preparing the graphite anode material according to claim 4, characterized in that, In step S2, the physical activation method includes: using an oxidizing gas to create pores in the graphite raw material to obtain the second graphite particles; Preferably, the temperature for creating the pore is 800–1000°C, and the time is 1–5 hours. Preferably, the weight ratio of the graphite raw material to the volume of the oxidizing gas is 1 kg:(10-50) m³. 3 ; Preferably, the oxidizing gas is selected from air and / or carbon dioxide.

7. The method for preparing the graphite anode material according to claim 4, characterized in that, In step S2, the chemical activation method includes: mixing the graphite raw material with a pore-forming agent in an inert gas atmosphere, and then subjecting it to a second heat treatment to obtain the second graphite particles; Preferably, the weight ratio of the graphite raw material to the pore-forming agent is 1:(0.5-4); Preferably, the temperature of the second heat treatment is 700–900°C, and the time is 1–5 hours; Preferably, the pore-forming agent is selected from one or more of the group consisting of potassium hydroxide, sodium hydroxide, phosphoric acid, sulfuric acid, and nitric acid.

8. The method for preparing the graphite anode material according to any one of claims 4 to 7, characterized in that, In step S3, the weight ratio of the first graphite particle to the second graphite particle is (1-9):

1. Preferably, the total weight of the first graphite particles and the second graphite particles to the weight of the coating material is (88-99.5):(0.5-12); Preferably, the asphalt compound is selected from one or more of the group consisting of tar pitch, petroleum pitch, and natural pitch; the carbon-containing resin is selected from one or more of the group consisting of phenolic resin, furan resin, and epoxy resin. Preferably, the temperature of the first heat treatment is 400–1200°C, and the time is 2–12 hours; Preferably, in step S3, a conductive agent is introduced during the mixing process; more preferably, the weight ratio of the conductive agent to the coating material is (0.01-0.05):1; even more preferably, the conductive agent is selected from one or more of graphene, carbon nanotubes, carbon nanofibers and carbon black.

9. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer stacked together, characterized in that, The negative electrode active material layer comprises the graphite negative electrode material according to any one of claims 1 to 3.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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