Graphite negative electrode material and preparation method and application thereof

Abstract

The application provides a graphite negative electrode material and a preparation method and application thereof. The graphite negative electrode material has a macroporous structure and a mesoporous structure on the surface. In the macroporous structure, the ratio R of the macropore depth H to the pore diameter D satisfies 0 < R < 60, R = H / D; in the mesoporous structure, the ratio r of the mesopore depth h to the pore diameter d satisfies 0 < r < 250, r = h / d. The preparation method comprises the following steps: dispersing a pore-forming agent solution on the surface of graphite through mechanical force, and heat-treating under a protective atmosphere to obtain the graphite negative electrode material; the pore-forming agent is water-soluble. The graphite negative electrode material provided by the application has the macroporous structure and the mesoporous structure on the surface. The multi-level pore structure makes the basal plane and the end face of the graphite material have channels for allowing lithium ions to quickly enter the graphite interlayer, shortens the solid-phase diffusion path of the lithium ions, and thus improves the charging rate of the graphite negative electrode material, realizes fast charging, and the preparation process is safe and environmentally friendly, and low in cost.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 202211169275.9, filed on September 26, 2022, entitled "A graphite anode material and its preparation method and application". Technical Field

[0002] This invention belongs to the field of lithium-ion battery technology, and relates to a graphite anode material, its preparation method, and its application. Background Technology

[0003] The rapid development of lithium-ion rechargeable batteries has also led to higher demands for fast-charging performance in people's lives and work. As a crucial component of lithium-ion rechargeable batteries, graphite anode materials, currently the mainstream anode material, largely determine the fast-charging performance of lithium-ion rechargeable batteries due to their rapid lithium intercalation performance. Therefore, modifying graphite anode materials is an effective way to improve their lithium intercalation behavior. This includes carbon coating, element doping, oxidation etching, and pore creation on the graphite surface. Oxidation etching and pore creation both involve chemical reactions where oxidizing gases or reagents react with carbon to form pores on the carbon / graphite material surface, shortening the diffusion path of lithium ions from the graphite surface to the core, thereby improving the overall lithium intercalation performance of the graphite material.

[0004] The following problems exist in the current process of creating pores in graphite: (1) When using nano or micro metal oxides as pore-forming agents, it is difficult to disperse them evenly and they do not come into close contact with graphite, resulting in low effective utilization and high cost; (2) When using metal salts as pore-forming agents, a large amount of organic solvent is required for dissolution. The evaporation and drying process of organic solvents has high energy consumption, low production efficiency, high production cost and significant safety hazards; (3) In the existing technology, when using metal oxides or transition metal salts as pore-forming agents, the heat treatment pore-forming stage is usually carried out in oxygen or an oxygen-containing atmosphere, which poses a safety hazard of dust explosion; (4) After using metal oxides and metal salts as pore-forming agents to create pores in graphite materials, acid washing or high-temperature graphitization is required to remove the pore-forming agents, resulting in high production cost and safety and environmental pollution hazards.

[0005] For example, CN100499215A discloses a surface-modified lithium-ion battery anode material, obtained by depositing metal salts on the surface of coke or artificial graphite powder, followed by heat treatment of the powder under an oxidizing atmosphere. However, the use of organic solvents in the preparation process leads to high production costs, and a large amount of corrosive and harmful gases are generated during the heat treatment process. CN111048755A discloses a high-rate lithium-ion battery anode material and its preparation method, which involves preparing a mixture of potassium carbonate and nitrogen- and phosphorus-containing organic matter, then adding it to a hydrochloric acid solution, stirring evenly, adding flake graphite, mixing evenly to prepare a graphite mixed solution, filtering, carbonizing, and then obtaining a graphite composite material through gas surface modification. The nano- and micro-pores left by gas surface oxidation improve the lithium-ion insertion channels, thereby improving the rate performance and cycle performance of the anode material. However, the channel depth of the prepared material is limited, and the addition of hydrochloric acid solution and halogen gases are not friendly to the metal equipment used in conventional industrial production and the environment. For example, CN101908627A discloses a lithium-ion secondary battery anode material and its preparation method. It mainly adds additives to improve the graphitization degree and pore-forming agents to the carbonized raw coke. The resulting graphite anode material has a nanoporous structure, which can effectively improve the lithium insertion / extraction performance of the anode material and the liquid absorption performance of the electrode sheet. However, the poor uniformity of the pores prepared by the pore-forming agent affects the application of the material.

[0006] Therefore, how to achieve uniform pore formation on the graphite surface, improve its electrochemical performance, reduce costs, and enhance the safety of the preparation process are urgent technical problems to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a graphite anode material, its preparation method, and its applications. The graphite anode material provided by this invention has both macroporous and mesoporous structures on its surface. This hierarchical porous structure provides channels for lithium ions to rapidly enter the graphite layers on both the basal and end faces of the graphite material, shortening the solid-phase diffusion path of lithium ions. This improves the charging rate of the graphite anode material, enabling fast charging and enhancing its fast-charging performance. Furthermore, the preparation process is safe, environmentally friendly, and low-cost.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a graphite anode material, wherein the surface of the graphite anode material has a macroporous structure and a mesoporous structure, wherein in the macroporous structure, the ratio R of the macroporous pore depth H to the pore diameter D satisfies 0 < R < 60, R = H / D; and in the mesoporous structure, the ratio r of the mesoporous pore depth h to the pore diameter d satisfies 0 < r < 250, r = h / d.

[0010] For example, R can be 0.5, 15, 10, 12, 15, 19, 20, 25, 30, 31, 35, 40, 45, 46, 49, 50, 55 or 59, etc., and r can be 0.5, 1, 2, 3, 5, 8, 9, 10, 13, 15, 18, 20, 23, 25, 28 or 29, etc.

[0011] In this invention, macropores are pores with a diameter greater than 50 nm, and mesopores are pores with a diameter between 2 and 50 nm.

[0012] The graphite anode material provided by this invention has both macroporous and mesoporous structures on its surface. This multi-level pore structure enables both the base and end faces of the graphite material to have channels that allow lithium ions to quickly enter the graphite layers, shortening the solid-phase diffusion path of lithium ions, thereby improving the charging rate of the graphite anode material, achieving fast charging, and enhancing its fast charging performance.

[0013] The graphite anode material provided by this invention differs from conventional porous graphite anode materials in that, under a scanning electron microscope at a magnification of no more than 10,000 times, the surface of the porous graphite anode material exhibits a uniform macroporous structure.

[0014] The porous graphite provided by this invention has significantly deeper pores than conventional porous graphite, and most of them are single-pore straight-through. Therefore, compared with conventional porous graphite, the pore size and depth of the porous graphite provided by this invention can be quantitatively measured.

[0015] Advantages: Larger pore size provides stronger electrolyte retention and larger electrolyte capacity. Deeper pores significantly shorten the solid-phase diffusion path of lithium ions between graphite layers, resulting in superior rate performance.

[0016] Preferably, in the macroporous structure, the macropore diameter is <2μm and the macropore depth is <3μm. For example, the macropore diameter can be 100nm, 300nm, 500nm, 800nm, 1μm, 1.3μm, 1.5μm, 1.8μm or 1.9μm, etc., and the macropore depth can be 500nm, 800nm, 1μm, 1.3μm, 1.5μm, 1.8μm, 2μm, 2.3μm, 2.5μm, 2.8μm or 2.9μm, etc.

[0017] In a second aspect, the present invention provides a method for preparing a graphite anode material as described in the first aspect, the method comprising the following steps:

[0018] The pore-forming agent solution is dispersed on the graphite surface by mechanical force, and then heat-treated under a protective atmosphere to obtain the graphite anode material;

[0019] The pore-forming agent is water-soluble.

[0020] In this invention, no special limitation is made on the type of mechanical force that can achieve the coating of the pore-forming agent solution. This invention is applicable to all types of mechanical forces, including but not limited to shear force and friction force.

[0021] The preparation method provided by this invention can uniformly coat the pore-forming agent solution onto the surface of graphite material through mechanical force, reducing the amount of pore-forming agent used, lowering production costs, and being more friendly to equipment and the environment during the production process. No oxidizing or halogen gases are added during the production process, reducing risks. The prepared material has a more uniform pore structure distribution and is easy to industrialize.

[0022] The water-soluble pore-forming agent provided by this invention produces a water-soluble substance after heat treatment, meaning that no additional substances requiring special treatment to remove are generated.

[0023] Preferably, the mass ratio of the pore-forming agent solution to the graphite material is (0.1 to 1):1, for example, 0.1:1, 0.13:1, 0.15:1, 0.18:1, 0.2:1, 0.23:1, 0.25:1, 0.28:1, 0.3:1, 0.33:1, 0.35:1, 0.38:1, 0.4:1, 0.43:1, 0.45:1, 0.48:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1, etc.

[0024] Preferably, the mass ratio of the pore-forming agent to the graphite material is (0.05-0.5):1, for example, 0.05:1, 0.08:1, 0.1:1, 0.13:1, 0.15:1, 0.18:1, 0.2:1, 0.23:1, 0.25:1, 0.28:1, 0.3:1, 0.33:1, 0.35:1, 0.38:1, 0.4:1, 0.43:1, 0.45:1, 0.48:1, or 0.5:1, etc.

[0025] In this invention, if the mass ratio of pore-forming agent to graphite material is too large, that is, if too much pore-forming agent is added, it is not conducive to forming a uniformly dispersed pore structure. If the mass ratio is too small, it will be difficult to form a large pore structure or to form a uniformly distributed pore structure on the surface of the graphite material.

[0026] As can be seen from the range of the mass ratio of pore-forming agent to graphite material provided by the present invention, the present invention achieves pore formation on graphite material with a very small amount of pore-forming agent, without the need to use a large amount of pore-forming agent or repeatedly soak the graphite material in the pore-forming agent solution. That is, the present invention uses a mechanical method to achieve a multi-level pore structure on the surface of graphite anode material with only a very small amount of pore-forming agent, and the pores are evenly distributed, which greatly reduces the production cost.

[0027] Preferably, the heat treatment temperature is 700-900℃, such as 700℃, 730℃, 750℃, 780℃, 800℃, 830℃, 850℃, 880℃ or 900℃.

[0028] If the heat treatment temperature provided by this invention is too high, it will result in an excessively large specific surface area of ​​the graphite material; if it is too low, it will be difficult to form a porous structure on the surface of the graphite material.

[0029] Preferably, the heat-treated material is sequentially washed with water and dried.

[0030] In this invention, byproducts and other impurities generated by the pore-forming agent can be removed simply by water washing, without the need for complex acid washing or other additional treatment processes.

[0031] Preferably, the water-soluble pore-forming agent comprises any one or a combination of at least two of inorganic bases, carbonates, chlorides, or inorganic acids.

[0032] Preferably, the inorganic base includes NaOH and / or KOH, the carbonate includes Na2CO3 and / or K2CO3, the chloride includes KCl and / or ZnCl2, and the inorganic acid includes H3PO4.

[0033] The pore-forming agents provided by this invention produce byproducts or impurities that are still water-soluble after heat treatment, without generating additional impurities that are difficult to remove.

[0034] Preferably, the solvent in the pore-forming agent solution is water, and the pore-forming agent solution also includes a dispersant.

[0035] In this invention, the pore-forming agent is water-soluble, so that carbonization will not cause the pore size to become too small during the heat treatment process.

[0036] In this invention, the addition of a dispersant can better achieve uniform dispersion and tight adhesion of the pore-forming agent on the surface of the graphite material.

[0037] Preferably, the dispersant comprises any one or a combination of at least two of PVP, PVA, or CMC.

[0038] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the graphite anode material as described in the first aspect.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The graphite anode material provided by this invention has both macroporous and mesoporous structures on its surface. This hierarchical porous structure enables lithium ions to quickly enter the graphite interlayer on both the base and end faces of the graphite material, shortening the solid-phase diffusion path of lithium ions, thereby improving the charging rate of the graphite anode material, achieving fast charging, and enhancing its fast charging performance. The graphite material with a hierarchical porous structure provided by this invention is prepared by adding a dispersant and performing subsequent water washing treatment, combined with the control of the heat treatment temperature (700-900℃), so that the obtained graphite anode material has both macroporous and mesoporous hierarchical porous structures. The lithium removal capacity of the battery in this invention can reach more than 359.7 mAh / g, the first efficiency at 0.1C can reach more than 93.8%, and the rate performance at 2C / 0.2C can reach more than 72%.

[0041] (2) The preparation method provided by the present invention can uniformly coat the pore-forming agent solution onto the surface of the graphite material by mechanical force, which reduces the amount of pore-forming agent used, reduces production costs, is more friendly to equipment and environment during production, does not add oxidizing or halogen gases during production, reduces risks, and the pore structure of the prepared material is more uniform and easy to industrialize. Attached Figure Description

[0042] Figure 1 The image shows a SEM image of the graphite anode material provided in Example 2.

[0043] Figure 2 The image shows a SEM image of the graphite anode material provided in Example 2.

[0044] Figure 3 The image shows a SEM image of the graphite anode material provided in Example 7.

[0045] Figure 4 This is a TEM image of the graphite anode material provided in Example 7. Detailed Implementation

[0046] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0047] Example 1

[0048] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0049] The preparation method of the graphite anode material is as follows:

[0050] (1) Dissolve KOH, water and PVP in a mass ratio of 5:5:0.5 to obtain solution A;

[0051] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 0.5:1 (the mass ratio of pore-forming agent KOH to graphite powder is 0.24:1).

[0052] (3) The mixture B is placed in a carbonization furnace and heated to 900°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0053] Example 2

[0054] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0055] The preparation method of the graphite anode material is as follows:

[0056] (1) Dissolve KOH, water and PVA in a mass ratio of 5:5:0.5 to obtain solution A;

[0057] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by friction, and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 0.5:1.

[0058] (3) The mixture B is placed in a carbonization furnace and heated to 900°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 1 hour and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0059] Example 3

[0060] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0061] The preparation method of the graphite anode material is as follows:

[0062] (1) Dissolve KOH, water and PVA in a mass ratio of 5:5:0.5 to obtain solution A;

[0063] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 0.1:1 (the mass ratio of pore-forming agent KOH to graphite powder is 0.05:1).

[0064] (3) The mixture B is placed in a carbonization furnace and heated to 900°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 1 hour and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0065] Example 4

[0066] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0067] The preparation method of the graphite anode material is as follows:

[0068] (1) Dissolve K2CO3, water and CMC in a mass ratio of 5:5:0.1 to obtain solution A;

[0069] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 0.5:1.

[0070] (3) The mixture B is placed in a carbonization furnace and heated to 900°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0071] Example 5

[0072] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0073] The preparation method of the graphite anode material is as follows:

[0074] (1) Dissolve K2CO3, water and CMC in a mass ratio of 5:5:0.1 to obtain solution A;

[0075] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 0.5:1.

[0076] (3) The mixture B is placed in a carbonization furnace and heated to 700°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0077] Example 6

[0078] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0079] The preparation method of the graphite anode material is as follows:

[0080] (1) Dissolve ZnCl2, water and CMC in a mass ratio of 5:5:0.1 to obtain solution A;

[0081] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 1:1 (the mass ratio of pore-forming agent ZnCl2 to graphite powder is 0.5:1).

[0082] (3) The mixture B is placed in a carbonization furnace and heated to 700°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0083] Example 7

[0084] This embodiment provides a graphite anode material. The surface of the graphite anode material has a macroporous structure and a mesoporous structure. In the macroporous structure, the depth of the macropore is H and the diameter is D, and the ratio of the two is R = H / D. In the mesoporous structure, the depth of the mesopore is h and the diameter is d, and the ratio of the two is r = h / d. R and r are shown in Table 1.

[0085] The preparation method of the graphite anode material is as follows:

[0086] (1) Dissolve NaOH, water and CMC in a mass ratio of 1:5:0.1 to obtain solution A;

[0087] (2) Liquid A is coated on the surface of graphite powder with a particle size DV50 of 10 μm by shear force and dried at 150℃ for 2 h to obtain mixture B. The mass ratio of solution A to graphite powder is 1:1.

[0088] (3) The mixture B is placed in a carbonization furnace and heated to 700°C at 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours and then cooled to room temperature to obtain carbonized material C. Carbonized material C is washed and filtered several times with water until neutral and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0089] Figure 1 The image shown is a SEM image of the graphite anode material provided in Example 2 at a magnification of 10,000x. Figure 1 As can be seen, the surface of graphite particles has pits below the graphite surface, i.e., a porous structure. The large pores are uniformly dispersed on the graphite surface, and mesopores can be observed between the large pores. This diagram allows for accurate measurement of the pore size. Figure 2 The SEM image of the cross-section of the graphite anode material provided in Example 2 is shown. It can be seen that the pores on the surface of the graphite particles extend into the graphite core and have a certain depth. Therefore, the depth of the pores can be quantitatively measured by this method. The macropore depth of the graphite anode material reaches 3 μm.

[0090] Figure 3 SEM images of the graphite anode material provided in Example 7 are shown. Figure 3 It can be seen that the surface of the graphite particles has uniformly dispersed mesopores and macropores with smaller diameters.

[0091] Figure 4 A TEM image of the graphite anode material provided in Example 7 is shown. Figure 4 As can be seen, the pores on the surface of the graphite particles extend into the graphite core and have a certain depth. Therefore, this method can be used to quantitatively measure the pore size and depth of small pores that are difficult to observe with SEM. The pores in this figure are mesopores.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 1 is that PVP is not added in step (1) of this embodiment.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 9

[0096] The difference between this embodiment and embodiment 1 is that water washing is not performed in step (2) of this embodiment.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Example 10

[0099] The difference between this embodiment and embodiment 1 is that the heat treatment temperature in step (3) of this embodiment is 650°C.

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that KOH is not added in this comparative example.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Comparative Example 2

[0105] This comparative example provides a method for preparing a graphite anode material: the preparation method is as follows:

[0106] (1) Iron oxide with a pore-forming agent DV50 of 0.5 μm was mixed with graphite powder with a particle size DV50 of 10 μm to obtain mixture A, wherein the mass ratio of iron oxide to graphite was 0.24:1.

[0107] (2) Mixture A is placed in a carbonization furnace and heated to 900°C at 1°C / min under a nitrogen atmosphere, and kept at that temperature for 1 hour. Then it is cooled to room temperature to obtain carbonized material B. Carbonized material B is washed and filtered several times with water and then dried at 150°C for 1 hour. After drying, the graphite anode material is obtained.

[0108] The graphite anode materials provided in Examples 1-10 and Comparative Examples 1-2 were tested, including:

[0109] (1) The specific surface area of ​​the graphite anode material was tested using the N2 adsorption method;

[0110] (2) The graphite anode material was observed by scanning electron microscopy, and the size and area of ​​the macropores were measured.

[0111] (3) The graphite anode material was cut and polished by argon ion beam, observed by scanning electron microscope, and the ratio of pore depth to pore diameter was statistically obtained.

[0112] (4) For graphite anode materials, the mesopore size was observed using a transmission electron microscope, and the ratio of pore depth to pore diameter was statistically obtained.

[0113] (5) Electrochemical performance testing: The graphite anode materials provided in Examples 1-10 and Comparative Examples 1-2 were prepared by slurry preparation with a graphite:CMC:SP:SBR ratio of 93.5:1.5:2:3, followed by coating, drying, and rolling to obtain anode sheets. CR2430 coin cells were then prepared, with lithium metal sheets as the counter electrode. Capacity, initial efficiency, and rate performance of the graphite anode materials were tested.

[0114] A coin cell was discharged to 0.005V at 0.1C, allowed to stand for 10 minutes, then discharged to 0.005V at 0.01C, allowed to stand for 10 minutes, and then charged to 2V at 0.1C. This yielded the lithium insertion and extraction capacities, respectively. The ratio of lithium extraction capacity to lithium insertion capacity is the first-efficiency characteristic. The lithium insertion capacity was obtained by discharging to 0.01V at 0.2C, followed by constant-voltage discharge to 0.01C at 0.01V, and allowed to stand for 10 seconds; then charging to 1.5V at 0.2C, allowed to stand for 10 seconds, followed by discharge to 0.01V at 2C, constant-voltage discharge to 0.01C at 0.01V, and charging to 1.5V at 2C. This yielded the lithium insertion capacity under 0.2C and 2C conditions, respectively.

[0115] The data results of the above tests are shown in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] The data from Examples 1-7 show that increasing the proportion of pore-forming agent significantly increases the macropore R, micropore r, surface pore area ratio, and BET of the prepared porous graphite anode material, resulting in a significant improvement in kinetic performance.

[0120] The data from Examples 1 and 8 show that the absence of a dispersant in the pore-forming agent solution is not conducive to the uniform dispersion of pores, reduces the proportion of pore area on the graphite surface, and reduces the ratio of R to r.

[0121] The data from Examples 1 and 9 show that without water washing, the capacity and initial efficiency will be significantly reduced due to the failure to remove the pore-forming agent and its byproducts.

[0122] The data results from Examples 1 and 10 show that if the heat treatment temperature is too low, it will be difficult to form a porous structure.

[0123] The data from Example 1 and Comparative Example 1 show that without the addition of a pore-forming agent, pores cannot be formed, the specific surface area of ​​the material is small, and the dynamic performance, especially the fast-charging performance, is significantly poor.

[0124] The data results from Example 1 and Comparative Example 2 show that conventional pore-forming methods have the drawbacks of difficulty in uniformly dispersing the pore-forming agent on the surface of graphite particles, resulting in local accumulation of the pore-forming agent. Furthermore, the harsh pore-forming atmosphere conditions ultimately lead to weak pore-forming ability and poor pore uniformity. Specifically, it is easy to form aggregates of multiple large pores and retain the outline of multiple pores in the aggregated large pores, with a pore diameter greater than 4 μm. Due to the uneven dispersion of pores and insufficient pore depth, the electrochemical performance is poor. In addition, iron oxide is reduced to iron, which cannot be removed by water washing, and the iron cannot be intercalated into lithium ions, resulting in a low test capacity.

[0125] In summary, the graphite anode material provided by this invention possesses both macroporous and mesoporous structures on its surface. This hierarchical porous structure provides channels for lithium ions to rapidly enter the graphite layers on both the basal and end faces of the graphite material, shortening the solid-phase diffusion path of lithium ions. This improves the charging rate of the graphite anode material, enabling fast charging and enhancing its fast-charging performance. Furthermore, the preparation process is simple, safe, and low-cost, making it suitable for industrial production. The multi-level porous graphite material provided by this invention incorporates a dispersant during preparation, undergoes subsequent water washing, and is combined with controlled heat treatment temperature (700–900°C). This results in a graphite anode material with both macroporous and mesoporous hierarchical structures. The lithium removal capacity of the battery in this invention can reach over 359.7 mAh / g, the first-stage efficiency at 0.1C can reach over 93.8%, and the rate performance at 2C / 0.2C can reach over 72%.

[0126] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A graphite anode material, characterized in that, The graphite anode material has a macroporous structure and a mesoporous structure on its surface. In the macroporous structure, the ratio R of the macropore depth H to the pore diameter D satisfies 5 ≤ ​​R ≤ 49, R = H / D. In the mesoporous structure, the ratio r of the mesopore depth h to the pore diameter d satisfies 1 ≤ r ≤ 29, r = h / d. In the macroporous structure, the macropore diameter D satisfies 50 nm < D < 2 μm and the macropore depth < 3 μm. In the mesoporous structure, the mesopore diameter is 2~50 nm. The macroporous structure includes a single-hole direct-entry hole structure, and the mesoporous structure includes a single-hole direct-entry hole structure.

2. The graphite anode material according to claim 1, characterized in that, In the aforementioned large-hole structure, the ratio R of the large-hole depth H to the hole diameter D satisfies 8 ≤ R ≤ 49.

3. The graphite anode material according to claim 1, characterized in that, In the aforementioned large-hole structure, the ratio R of the large-hole depth H to the hole diameter D satisfies 40 ≤ R ≤ 49.

4. The graphite anode material according to claim 1, characterized in that, In the mesoporous structure, the ratio r of the mesoporous pore depth h to the pore diameter d satisfies 1≤r≤9.

5. The graphite anode material according to claim 4, characterized in that, In the mesoporous structure, the ratio r of the mesoporous pore depth h to the pore diameter d satisfies 2≤r≤9.

6. The graphite anode material according to claim 5, characterized in that, In the mesoporous structure, the ratio r of the mesoporous pore depth h to the pore diameter d satisfies 6≤r≤9.

7. The graphite anode material according to claim 1, characterized in that, In lithium-ion batteries made from the graphite anode material, the 2C / 0.2C rate performance reaches over 72%.

8. The graphite anode material according to claim 7, characterized in that, In lithium-ion batteries made from the graphite anode material, the 2C / 0.2C rate performance is 85-91%.

9. The graphite anode material according to claim 1, characterized in that, The macroporous structure and the mesoporous structure enable both the base and end faces of the graphite material to have channels for lithium ions to rapidly enter the graphite layers.

10. The graphite anode material according to claim 1, characterized in that, Under a scanning electron microscope at a magnification of no more than 10,000x, the surface of the graphite anode material has a uniform macroporous structure; And / or, the mesopores are between the macropores.

11. The graphite anode material according to claim 10, characterized in that, In the macroporous structure, the pore diameter D satisfies 100nm≤D<2μm.

12. The graphite anode material according to claim 1, characterized in that, In the macroporous structure, the depth H of the macropore satisfies 500nm < H < 3μm.

13. The graphite anode material according to claim 12, characterized in that, In the macroporous structure, the depth H of the macropores satisfies 500nm≤H≤2.9μm.

14. A method for preparing a graphite anode material as described in any one of claims 1-13, characterized in that, The preparation method includes the following steps: The pore-forming agent solution is dispersed on the graphite surface by mechanical force, and then heat-treated under a protective atmosphere to obtain the graphite anode material; The pore-forming agent is water-soluble.

15. The method for preparing the graphite anode material according to claim 14, characterized in that, The mass ratio of the pore-forming agent solution to the graphite material is (0.1~1):1; the mass ratio of the pore-forming agent to the graphite material is (0.05~0.5):

1. And / or, the temperature of the heat treatment is 700~900℃; And / or, the heat-treated material is sequentially washed with water and dried; And / or, the water-soluble pore-forming agent includes any one or a combination of at least two of inorganic bases, carbonates, chlorides, or inorganic acids.

16. The method for preparing the graphite anode material according to claim 15, characterized in that, The inorganic base includes NaOH and / or KOH, the carbonate includes Na2CO3 and / or K2CO3, the chloride includes KCl and / or ZnCl2, and the inorganic acid includes H3PO4.

17. The method for preparing the graphite anode material according to claim 14, characterized in that, The water-soluble pore-forming agent includes KOH, K2CO3, ZnCl2, or NaOH.

18. The method for preparing the graphite anode material according to claim 14, characterized in that, The solvent in the pore-forming agent solution is water, and the pore-forming agent solution also includes a dispersant.

19. A lithium-ion battery, characterized in that, The lithium-ion battery includes the graphite anode material as described in any one of claims 1-13.

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