High-performance natural graphite negative electrode material, preparation method therefor, and use thereof

Abstract

Disclosed are a high-performance natural graphite negative electrode material, a preparation method therefor, and a use thereof. In the negative electrode material of the present invention, a uniform and thin amorphous carbon layer coated on surfaces of each curled flake graphite layer inside the natural graphite in a core can prevent organic molecules in an electrolyte from penetrating into spherical graphite during charging and discharging to generate a new SEI film, thereby preventing delamination of the curled graphite layers inside the spherical graphite; sulfonated graphene in the inner shell has good flexibility, which can alleviate the volume expansion of natural graphite during charging and discharging, improving the cycling performance of natural graphite up to 1500 cycles. An outermost amorphous carbon layer can reduce the specific surface area of the inner sulfonated graphene, preventing reduction of first-cycle efficiency of a lithium-ion battery caused by the graphene coating. In the natural graphite negative electrode material of the present invention, the amorphous carbon layer is uniform and thin, and does not reduce the tapped density and gravimetric capacity of the anode material.

Description

A high-performance natural graphite anode material, its preparation method and application

[0001] This application claims priority to an earlier application filed on July 31, 2024, with patent application number 2024110424719, entitled "A High-Performance Natural Graphite Anode Material and Its Preparation Method and Application," which is incorporated herein by reference in its entirety. Technical Field

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

[0003] Lithium-ion batteries are widely used in portable electronic devices such as laptops, mobile phones, and instruments due to their advantages including high specific capacity, high operating voltage, good safety, and no memory effect. With the popularization of new energy vehicles, their application has expanded to fields such as electric vehicles. In recent years, as electronic products and in-vehicle and energy storage devices have increasingly demanded miniaturization, lightweighting, multi-functionality, and long-duration operation, the requirements for high energy density, high rate performance, and long cycle life of lithium-ion batteries have continued to rise.

[0004] Commercial lithium-ion batteries primarily utilize carbon anode materials such as natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, natural graphite is widely used as an important anode material due to its high specific capacity, good charge-discharge platform, and low cost. However, the lithium-ion intercalation compound Li₂ formed during the lithium-ion intercalation process... x The interlayer spacing of C6 is larger than that of natural graphite, causing natural graphite to expand by about 10% during charge and discharge, resulting in graphite layer peeling and a decrease in the cycle performance of lithium-ion batteries. High-temperature amorphous carbon coating can reduce the specific surface area of ​​natural graphite, thereby improving the initial coulombic efficiency of natural graphite anode materials. However, conventional amorphous carbon coating methods result in excessively thick amorphous carbon coating layers, leading to a high amorphous carbon content, which reduces the compaction density of the natural graphite anode material, resulting in a decrease in the specific capacity of lithium-ion batteries and increased costs. Therefore, there is a need to develop a high-performance anode material that balances specific capacity, cycle life, and initial coulombic efficiency. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a high-performance natural graphite anode material, its preparation method, and its applications. The natural graphite anode material exhibits high compaction density and initial coulombic efficiency, along with excellent cycle performance. The preparation method does not require complex equipment or toxic organic solvents, meeting the requirements of green and low-cost chemistry, and is conducive to the large-scale production of high-performance natural graphite anode materials.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a natural graphite anode material, the method comprising the following steps:

[0008] (1) Mix hydrated tar and emulsifier to prepare an emulsion;

[0009] (2) Under vacuum conditions, natural graphite and the emulsion from step (1) are mixed and impregnated under pressure to obtain slurry 1;

[0010] (3) Spray dry the slurry 1 from step (2) to prepare powder 1;

[0011] (4) Mix the powder 1 and sulfonated graphene from step (3) with water to obtain slurry 2;

[0012] (5) Spray dry the slurry 2 from step (4) to prepare powder 2;

[0013] (6) Mix the powder 2 from step (5) with the emulsion from step (1) to obtain slurry 3;

[0014] (7) Spray dry the slurry 3 from step (6) to prepare powder 3;

[0015] (8) The powder 3 from step (7) is carbonized to prepare the natural graphite anode material.

[0016] According to an embodiment of the present invention, in step (1), the hydrated tar is a recovered product of asphalt fumes, which can be prepared by methods known in the art or purchased commercially.

[0017] According to an embodiment of the present invention, in step (1), the hydrated tar includes water and tar.

[0018] According to an embodiment of the present invention, in step (1), the water content in the hydrated tar is 50-65 wt%, for example, 50 wt%, 55 wt%, 60 wt% or 65 wt%.

[0019] According to an embodiment of the present invention, in step (1), the mass percentage of tar in the hydrated tar is 35-50 wt%, for example, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0020] According to an embodiment of the present invention, in step (1), the carbon residue value of the hydrated tar after carbonization is ≤5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%.

[0021] According to an embodiment of the present invention, in step (1), the emulsifier is selected from nonionic emulsifiers, such as sucrose fatty acid ester, fatty acid sorbitan, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, or a mixture of several of them.

[0022] According to an embodiment of the present invention, in step (1), the mass ratio of the emulsifier to the hydrated tar is (2.5-8):100, preferably (2.5-6.5):100, for example 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, 5.5:100, 6:100 or 6.5:100.

[0023] According to an embodiment of the present invention, in step (1), the mixing is carried out under stirring conditions. The stirring speed is 20-80 r / min, and the stirring time is 40-120 min.

[0024] According to an embodiment of the present invention, in step (2), the mass ratio of the natural graphite to the emulsion is 100:(200-400), for example, 100:200, 100:250, 100:300, 100:350 or 100:400.

[0025] According to an embodiment of the present invention, in step (2), the natural graphite is at least one of spherical, nearly spherical, oval, and potato-shaped, and the D of the natural graphite... 50 The size is 5-17 μm, and the carbon content is ≥99.0%.

[0026] According to an embodiment of the present invention, in step (2), the vacuum degree of the vacuum condition is 0.07-0.09 MPa.

[0027] According to an embodiment of the present invention, in step (2), natural graphite is first placed under vacuum conditions, and then mixed with emulsion under vacuum conditions. Preferably, the natural graphite is first placed under vacuum conditions for a period of time, for example, more than 5 minutes, such as 10-180 minutes; the purpose of this operation is to remove as much air as possible from the interior of the natural graphite under vacuum conditions, thereby facilitating the penetration of the emulsion (actually tar) into and filling the surface of each curled flake graphite layer inside the natural graphite.

[0028] According to an embodiment of the present invention, step (2) is carried out in a reaction vessel. Preferably, natural graphite is placed in the reaction vessel, the reaction vessel is evacuated, and the vacuum degree inside the reaction vessel reaches 0.07-0.09 MPa and is maintained for more than 5 minutes, after which the emulsion is added. The method of adding the emulsion is, for example, to open the emulsion suction valve, draw the emulsion from step (1) into the reaction vessel, and close the suction valve after the liquid addition is completed. Preferably, after the emulsion is added, the evacuation is stopped, and the mixture (the mixture formed by natural graphite and emulsion) is stirred at the same time.

[0029] According to an embodiment of the present invention, in step (2), the pressure of the pressure impregnation is 2MPa-10MPa, for example 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa; the pressure impregnation time is 1-5 hours, for example 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.

[0030] According to an embodiment of the present invention, step (2) further includes a post-processing step: after the pressurized impregnation is completed, the pressure is reduced to make the pressure inside and outside the reactor the same, and then the material is discharged and centrifuged. The purpose of the centrifugation is to separate the water content in the mixed system, reduce the spray drying time, and save preparation costs.

[0031] According to an embodiment of the present invention, in step (3), the temperature of the spray drying process is 100-150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C. The time of the spray drying process is 1-6 hours, preferably 2-4 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0032] According to an embodiment of the present invention, in step (4), the mass ratio of the sulfonated graphene to powder 1 is (0.5-1.5):100, for example, 0.5:100, 0.6:100, 0.8:100, 0.9:100, 1:100, 1.2:100 or 1.5:100; the mass ratio of powder 1 to water is 100:(100-300), for example, 100:100, 100:120, 100:150, 100:160, 100:180, 100:200, 100:220, 100:250, 100:260, 100:280 or 100:300.

[0033] According to an embodiment of the present invention, step (4) specifically involves mixing and stirring the powder 1 and sulfonated graphene from step (3) with water, followed by centrifugation to obtain slurry 2. The purpose of the centrifugation is to separate the water content in the mixture, reduce the spray drying time, and save preparation costs.

[0034] According to an embodiment of the present invention, in step (5), the temperature of the spray drying process is 100-150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C. The time of the spray drying process is 1-6 hours, preferably 2-4 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0035] According to an embodiment of the present invention, in step (6), the mass ratio of the emulsion to the powder 2 is (100-180):100, for example, 100:100, 120:100, 130:100, 140:100, 150:100, 160:100, 170:100 or 180:100.

[0036] According to an embodiment of the present invention, in step (6), after mixing is completed, the mixture can be centrifuged.

[0037] According to an embodiment of the present invention, in step (7), the temperature of the spray drying process is 100-150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C. The time of the spray drying process is 1-6 hours, preferably 2-4 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0038] According to an embodiment of the present invention, in step (8), the carbonization process is carried out under an inert atmosphere, such as nitrogen or argon.

[0039] According to an embodiment of the present invention, in step (8), the carbonization temperature is 800-1200℃, for example, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃. The carbonization time is 1-6 hours, preferably 2-4 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0040] The present invention also provides a natural graphite anode material prepared by the above method.

[0041] According to an embodiment of the present invention, the natural graphite anode material is a composite of natural graphite, sulfonated graphene, and amorphous carbon.

[0042] According to an embodiment of the present invention, the natural graphite anode material has a core-shell structure, including a core, an inner shell, and an outer shell; the inner shell covers the surface of the core, and the outer shell covers the surface of the inner shell; the core is natural graphite with amorphous carbon coated on the inner layer surface and the outer surface, the inner shell is sulfonated graphene, and the outer shell is amorphous carbon.

[0043] According to an embodiment of the present invention, the mass fraction of amorphous carbon in the natural graphite anode material is 1.0-3.5%, for example, 1.5%, 1.8%, 2.0%, 2.6%, 3.0%, 3.2%, or 3.5%; the mass fraction of sulfonated graphene in the natural graphite anode material is 0.6-2.5%, more preferably 0.6-2%, for example, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, or 2.5%.

[0044] The present invention also provides a use of the above-mentioned natural graphite anode material for preparing lithium-ion batteries, preferably for preparing the anode of lithium-ion batteries.

[0045] The present invention also provides a negative electrode for lithium-ion batteries, the negative electrode comprising the above-mentioned natural graphite negative electrode material.

[0046] The beneficial effects of this invention are:

[0047] This invention involves adding an emulsifier to hydrated tar to uniformly disperse the tar in water, thus obtaining an emulsion. Then, the air inside natural graphite is first removed under vacuum conditions. The natural graphite is then mixed with the emulsion, and under pressure, the tar in the emulsion penetrates into the coiled flake graphite layers inside the natural graphite. Spray drying is then performed, forming a uniform and thin tar coating layer on the surface of each coiled flake graphite layer inside the natural graphite, and simultaneously forming a uniform and thin tar coating layer on the outer surface of the natural graphite, thus obtaining powder 1. Powder 1 is mixed with sulfonated graphene and spray-dried again to coat the surface of natural graphite coated with tar, thus obtaining powder 2. Then, the natural graphite coated with sulfonated graphene is mixed with an emulsion, and the tar in the emulsion forms a uniform and thin tar coating layer on the surface of the sulfonated graphene, thus obtaining powder 3. During the carbonization process, the tar coating on the surface of each curled flake graphite layer inside the natural graphite, the outer surface of the natural graphite, and the surface of the sulfonated graphene carbonizes to form a uniform and thin amorphous carbon.

[0048] In the natural graphite anode material of this invention, the uniform and thin amorphous carbon layer coating the surface of each curled-up flake graphite layer within the core of the natural graphite prevents organic molecules in the electrolyte from penetrating into the natural graphite during charging and discharging to form a new SEI film, thus preventing the peeling of the curled-up flake graphite layers within the natural graphite. The sulfonated graphene in the inner shell has good flexibility, which can mitigate the volume expansion of the natural graphite during charging and discharging, improving the cycle performance of the natural graphite to 1500 cycles. The amorphous carbon layer in the outer shell can reduce the specific surface area of ​​the sulfonated graphene in the inner shell, preventing the initial coulombic efficiency reduction of lithium-ion batteries caused by the sulfonated graphene coating. The uniform and thin amorphous carbon layer (low amorphous carbon content) in the natural graphite anode material of this invention does not reduce the compaction density and specific capacity of the anode material.

[0049] The preparation method of this invention does not require complex equipment or toxic organic solvents, meeting the requirements of green and low-cost chemistry, and is conducive to the large-scale production of anode materials. The method utilizes inexpensive asphalt fume recovery materials (i.e., hydrated tar) to prepare anode materials for lithium-ion batteries, realizing the utilization of waste resources. The method uses water as the dispersion medium, has a simple process, requires no post-treatment processes such as washing, and does not require complex equipment, making it easy to achieve large-scale production of graphite anode materials. Detailed Implementation

[0050] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0051] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0052] Example 1

[0053] (1) Mix 200g of hydrated tar (water content is 50% by mass, and the carbon residue value after carbonization of tar is 4%) and 7g of polysorbate, and stir (stirring speed is 60r / min) for 50min to obtain an emulsion.

[0054] (2) Place 100g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (3MPa) and impregnate for 3 hours. After depressurization to make the pressure inside and outside the reactor the same, discharge the material and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1.

[0055] (3) Mix 100g of powder 1 and 0.8g of sulfonated graphene with 180g of water in step (2), stir, centrifuge to obtain slurry 2, and spray dry slurry 2 at 130℃ for 2 hours to prepare powder 2.

[0056] (4) Prepare the emulsion again according to the method of step (1). Mix 100g of powder 2 from step (3) with 120g of emulsion and stir. Centrifuge to obtain slurry 3. Spray dry slurry 3 at 130℃ for 2 hours to obtain powder 3. Carbonize powder 3 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0057] In the high-performance natural graphite anode material, the mass percentage of amorphous carbon is 3.0%, and the mass percentage of sulfonated graphene is 0.8%.

[0058] Example 2

[0059] (1) Mix 200g of hydrated tar (water content is 60% by mass, and the carbon residue value after carbonization is 3.5%) and 8g of sucrose fatty acid ester and stir (stirring speed is 40r / min) for 40min to obtain an emulsion.

[0060] (2) Place 100g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (5MPa) and impregnate for 1 hour. After depressurization to make the pressure inside and outside the reactor the same, discharge the material and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1.

[0061] (3) Mix 100g of powder 1 and 0.6g of sulfonated graphene with 150g of water in step (2), stir, centrifuge to obtain slurry 2, and spray dry slurry 2 at 120℃ for 3 hours to prepare powder 2.

[0062] (4) Prepare the emulsion again according to the method of step (1). Mix 100g of powder 2 from step (3) with 100g of emulsion and stir. Centrifuge to obtain slurry 3. Spray dry slurry 3 at 120℃ for 3 hours to obtain powder 3. Carbonize powder 3 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0063] In the high-performance natural graphite anode material, the mass percentage of amorphous carbon is 2.6%, and the mass percentage of sulfonated graphene is 0.6%.

[0064] Example 3

[0065] (1) Mix 250g of hydrated tar (water content is 60% by mass and carbon residue value after carbonization is 5%) and 7g of fatty acid sorbitan and stir (stirring speed is 70r / min) for 30min to obtain an emulsion.

[0066] (2) Place 100g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (8MPa) and impregnate for 1 hour. After depressurization to make the pressure inside and outside the reactor the same, discharge the material and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1.

[0067] (3) Mix 100g of powder 1 and 1.0g of sulfonated graphene with 200g of water in step (2), stir, centrifuge to obtain slurry 2, and spray dry slurry 2 at 130℃ for 4 hours to prepare powder 2.

[0068] (4) Prepare the emulsion again according to the method of step (1). Mix 100g of powder 2 from step (3) with 150g of emulsion and stir. Centrifuge to obtain slurry 3. Spray dry slurry 3 at 130℃ for 4 hours to obtain powder 3. Carbonize powder 3 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0069] In the high-performance natural graphite anode material, amorphous carbon accounts for 3.0% by mass, and sulfonated graphene accounts for 1.1% by mass.

[0070] Example 4

[0071] (1) Mix 200g of hydrated tar (water content is 53% by mass, and the carbon residue value after carbonization is 5%) and 8g of sucrose fatty acid ester and stir (stirring speed is 60r / min) for 50min to obtain an emulsion.

[0072] (2) Place 100g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (10MPa) and impregnate for 2 hours. After depressurization to make the pressure inside and outside the reactor the same, discharge the material and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1.

[0073] (3) Mix 100g of powder 1 and 1.3g of sulfonated graphene from step (2) with 200g of aqueous solution, stir, centrifuge to obtain slurry 2, and spray dry slurry 2 at 130℃ for 5 hours to prepare powder 2.

[0074] (4) Prepare the emulsion again according to the method of step (1). Mix 100g of powder 2 from step (3) with 160g of emulsion and stir. Centrifuge to obtain slurry 3. Spray dry slurry 3 at 130℃ for 5 hours to obtain powder 3. Carbonize powder 3 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0075] In the high-performance natural graphite anode material, the mass percentage of amorphous carbon is 3.5%, and the mass percentage of sulfonated graphene is 1.5%.

[0076] Comparative Example 1

[0077] (1) Mix 200g of hydrated tar (water content is 50% by mass, and the carbon residue value after carbonization of tar is 3.5%) and 7g of polysorbate and stir (stirring speed is 60r / min) for 50min to obtain an emulsion;

[0078] (2) Place 120g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (3MPa) and impregnate for 3 hours. After depressurization to make the pressure inside and outside the reactor the same, discharge and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1. Carbonize powder 1 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0079] In the high-performance natural graphite anode material, the mass percentage of amorphous carbon is 3.3%.

[0080] Comparative Example 2

[0081] (1) Mix 200g of hydrated tar (water content is 50% by mass, and the carbon residue value after carbonization of tar is 3.5%) and 7g of polysorbate and stir (stirring speed is 60r / min) for 50min to obtain an emulsion;

[0082] (2) Place 120g of natural graphite into the reactor and vacuum for 50min. When the vacuum degree of the reactor reaches 0.07MPa, open the emulsion suction valve and suck all the emulsion obtained in step (1) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture at high speed (30r / min) for 40min, pressurize (3MPa) and impregnate for 3 hours. After depressurization to make the pressure inside and outside the reactor the same, discharge the material and centrifuge to obtain slurry 1. Spray dry slurry 1 at 120℃ for 2 hours to prepare powder 1.

[0083] (3) Mix 100g of powder 1, 0.8g of sulfonated graphene and 180g of water from step (2), stir and centrifuge to obtain slurry 2. Spray dry slurry 2 at 130℃ for 3 hours to prepare powder 2. Carbonize powder 2 at 1200℃ in nitrogen for 2 hours and cool to room temperature to obtain high-performance natural graphite anode material.

[0084] In the high-performance natural graphite anode material, the mass percentage of amorphous carbon is 2.9%, and the mass percentage of sulfonated graphene is 0.7%.

[0085] Electrode compaction density testing was conducted in accordance with national standard GB / T 24533-2019.

[0086] Electrochemical performance testing:

[0087] Half-cell test method: The negative electrode material prepared in the examples and comparative examples: conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 95:1:1.5:2.5 (mass ratio) was mixed evenly and coated on copper foil. The coated electrode was placed in a vacuum drying oven at 120°C and dried for 12 hours. Simulated battery assembly was carried out in an argon-protected Braun glove box. The electrolyte was 1M-LiPF6+EC:DEC:DMC (volume ratio of 1:1:1). The lithium metal sheet was used as the counter electrode. Simulated battery testing was carried out in a 5V, 1000mA Xinwei battery test cabinet. The charge and discharge voltage was 0.01-1.5V and the charge and discharge rate was 0.1C. The 0.1C first charge capacity and 0.1C first coulombic efficiency were tested and the test results are listed in Table 1 (Comparative Example 3 in Table 1 uses spherical natural graphite, specifically the natural graphite in step (2) of Example 1).

[0088] Full cell testing method: Using the negative electrode materials prepared in the examples and comparative examples as negative electrodes, lithium cobalt oxide as positive electrodes, and 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1) solution as electrolyte, full cells were assembled and charged and discharged at room temperature at a rate of 0.1C, with a voltage range of 3.0-4.2V. The cycle performance obtained from the tests is listed in Table 1.

[0089] Table 1 Electrochemical performance test results

[0090] In Table 1, Comparative Example 3 showed a 0.1C cycle capacity retention rate of 80.6% after 300 cycles, but after 1500 cycles, the 0.1C cycle capacity retention rate was less than 64.6%.

[0091] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a natural graphite anode material, characterized in that, The preparation method includes the following steps: (1) Mix hydrated tar and emulsifier to prepare an emulsion; (2) Under vacuum conditions, natural graphite and the emulsion from step (1) are mixed and impregnated under pressure to obtain slurry 1; (3) Spray dry the slurry 1 from step (2) to prepare powder 1; (4) Mix the powder 1 and sulfonated graphene from step (3) with water to obtain slurry 2; (5) Spray dry the slurry 2 from step (4) to prepare powder 2; (6) Mix the powder 2 from step (5) with the emulsion from step (1) to obtain slurry 3; (7) Spray dry the slurry 3 from step (6) to prepare powder 3; (8) The powder 3 from step (7) is carbonized to prepare the natural graphite anode material.

2. The method according to claim 1, characterized in that, In step (1), the water content in the hydrated tar is 50-65 wt%; and / or, in step (1), the tar content in the hydrated tar is 35-50 wt%; and / or, in step (1), the carbon residue value of the hydrated tar after carbonization is ≤5%; and / or, in step (1), the emulsifier is selected from nonionic emulsifiers, such as one or a mixture of several of sucrose fatty acid esters, fatty acid sorbitan, polysorbate, polyoxyethylene fatty acid esters, and polyoxyethylene fatty alcohol ethers. and / or, in step (1), the mass ratio of the emulsifier to the hydrated tar is (2.5-8):

100.

3. The method according to claim 1 or 2, characterized in that, In step (2), the mass ratio of the natural graphite to the emulsion is 100:(200-400); and / or, in step (2), the vacuum degree of the vacuum condition is 0.07-0.09 MPa; and / or, in step (2), the pressure of the pressure impregnation is 2 MPa-10 MPa.

4. The method according to any one of claims 1-3, characterized in that, In step (4), the mass ratio of sulfonated graphene to powder 1 is (0.5-1.5):100; the mass ratio of powder 1 to water is 100:(100-300); in step (6), the mass ratio of emulsion to powder 2 is (100-180):

100.

5. The method according to any one of claims 1-4, characterized in that, In step (8), the carbonization process is carried out under an inert atmosphere at a temperature of 800-1200°C.

6. The natural graphite anode material prepared by the method according to any one of claims 1-5.

7. The natural graphite anode material according to claim 6, characterized in that, The natural graphite anode material has a core-shell structure, including a core, an inner shell, and an outer shell; the inner shell covers the surface of the core, and the outer shell covers the surface of the inner shell; the core is natural graphite with amorphous carbon coated on the inner and outer surfaces of the natural graphite, the inner shell is sulfonated graphene, and the outer shell is amorphous carbon.

8. The natural graphite anode material according to claim 7, characterized in that, The natural graphite anode material contains 1.0-3.5% amorphous carbon by mass; the natural graphite anode material contains 0.6-2.5% sulfonated graphene by mass.

9. Use of the natural graphite anode material according to any one of claims 6-8, for the preparation of lithium-ion batteries.

10. A negative electrode for a lithium-ion battery, characterized in that, The negative electrode comprises the natural graphite negative electrode material as described in any one of claims 6-8.