CN111261862B - Modified graphite negative electrode material of lithium ion battery and preparation method thereof - Google Patents

Modified graphite negative electrode material of lithium ion battery and preparation method thereof Download PDF

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CN111261862B
CN111261862B CN202010076154.4A CN202010076154A CN111261862B CN 111261862 B CN111261862 B CN 111261862B CN 202010076154 A CN202010076154 A CN 202010076154A CN 111261862 B CN111261862 B CN 111261862B
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lithium ion
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modified graphite
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methylimidazole
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CN111261862A (en
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韩俊女
赵英杰
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Guangxi Baise Xinhao New Energy Technology Co ltd
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Jingmen Noviying New Material Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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Abstract

The invention discloses a modified graphite cathode material of a lithium ion battery and a preparation method thereof, wherein the method comprises the following steps: s1, immersing natural spherical graphite in a methanol solution of 2-methylimidazole, adding a methanol solution of zinc salt, uniformly mixing, sealing, standing, aging, centrifuging, washing and drying to obtain a ZIF 8/natural spherical graphite composite material; s2, carbonizing the composite material at high temperature to obtain an intermediate; s3, adding the intermediate into molten asphalt, cooling and crushing to obtain a precursor; and S4, carbonizing the precursor in a protective gas at high temperature to obtain the modified graphite cathode material of the lithium ion battery. According to the invention, the ZIF 8/natural spherical graphite composite material is carbonized at high temperature, coated with the asphalt and carbonized again, so that the graphite surface and pores contain soft carbon, thereby reducing the stripping of graphite on the surface layer, improving the de-intercalation rate of lithium ions and improving the rate capability of the lithium ions, and the preparation method is simple, mild in condition and good in application prospect.

Description

Modified graphite negative electrode material of lithium ion battery and preparation method thereof
Technical Field
The invention belongs to the technical field of graphite cathode materials, and particularly relates to a modified graphite cathode material of a lithium ion battery and a preparation method thereof.
Background
A lithium ion battery is a secondary battery (rechargeable battery) that mainly operates by movement of lithium ions between a positive electrode and a negative electrode. During charging and discharging, Li+Intercalation and deintercalation to and from two electrodes: upon charging, Li+The lithium ion battery is extracted from the positive electrode and is inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge. The lithium ion battery is widely applied to the fields of 3C products, power devices, energy storage equipment and the like by virtue of the advantages of high energy density, high average output voltage, excellent cycle performance, rapid charge and discharge, no toxic and harmful substances and the like.
The current commercialized negative electrode material is mainly a graphite negative electrode, wherein natural spherical graphite has rich resources and excellent performance; however, in the process of lithium deintercalation cycle of natural spherical graphite, the solvent co-intercalation and lattice expansion in the process of lithium deintercalation easily cause the graphite flakes to peel off and fall off, which causes capacity attenuation in the cycle process and even influences the service life. In order to improve the cycle performance of the natural crystalline flake graphite, the natural crystalline flake graphite is mechanically spheroidized to obtain the natural spherical graphite with rich internal pores. However, the surface structure of the pores cannot be perfected by common surface modification, and graphite on the surface layer is still easy to peel off in the lithium extraction process, so that the cycle performance is reduced.
Disclosure of Invention
In view of the above, the present invention provides a method for preparing a modified graphite negative electrode material for a lithium ion battery, which comprises preparing a ZIF 8/natural spherical graphite composite material, carbonizing the composite material to obtain an intermediate, coating the intermediate with pitch, and carbonizing the intermediate to coat the pores and the surface of the natural spherical graphite with soft carbon, thereby modifying the graphite.
The invention also aims to provide the modified graphite negative electrode material for the lithium ion battery, which is prepared by the preparation method.
The technical scheme adopted by the invention is that the preparation method of the modified graphite cathode material of the lithium ion battery comprises the following steps:
s1, uniformly mixing 2-methylimidazole and methanol to obtain a methanol solution of 2-methylimidazole, completely immersing natural spherical graphite in the methanol solution of 2-methylimidazole to obtain a mixed solution, adding a methanol solution of zinc salt into the mixed solution at the temperature of 5-15 ℃, uniformly stirring, sealing, standing, aging, centrifuging, washing and drying to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a protective gas atmosphere, and cooling to obtain an intermediate;
s3, heating the pitch to a molten state, adding the intermediate obtained in the step S2 into the pitch in the molten state under a stirring condition, cooling and crushing to obtain a precursor;
and S4, carbonizing the precursor at high temperature in a protective gas atmosphere, and cooling to obtain the modified graphite negative electrode material of the lithium ion battery.
Preferably, in the S1, the feed-to-liquid ratio of the 2-methylimidazole to the methanol is (6.56-13.12 g): 1L, the mass ratio of the natural spherical graphite to the 2-methylimidazole zinc salt is (10-15): 1: (0.25-0.5).
Preferably, in S1, the zinc salt is zinc chloride or zinc nitrate hexahydrate, and the mass concentration of the methanol solution of the zinc salt is 0.04 to 0.08 mol/L.
Preferably, in S1, the solution of zinc salt in methanol is added by atomization.
Preferably, in S1, the natural spherical graphite has an average particle size of 5 to 25 μm.
Preferably, in the step S1, the standing and aging time is 24-48 h; the specific conditions of the centrifugation are as follows: the centrifugation speed is 3000-8000 rpm, the centrifugation time is 10-15 min, and the drying temperature is 60-70 ℃.
Preferably, in S2, the ZIF 8/natural spherical graphite composite material is carbonized at high temperature under the following conditions: heating to 1000-1500 ℃ at the speed of 1-3 ℃/min, and preserving heat for 2-3 h, wherein the protective gas is at least one of argon, nitrogen and helium.
Preferably, in the S3, the mass ratio of the intermediate to the asphalt in the molten state is (0.5-1.5): 1;
the preparation process of the asphalt in the molten state comprises the following steps: heating the asphalt to 400-430 ℃, preserving heat for 4-5 h at normal pressure, and then carrying out vacuum distillation for 0.5-1 h to obtain the asphalt in a molten state.
Preferably, in S4, the high-temperature carbonization conditions of the precursor are as follows: heating to 800-1000 ℃ at the speed of 1-3 ℃/min, and preserving heat for 1-3 h, wherein the protective gas is at least one of argon, nitrogen and helium.
The invention also provides the modified graphite cathode material of the lithium ion battery prepared by the preparation method of the modified graphite cathode material.
The invention has the beneficial effects that: according to the invention, the ZIF 8/natural spherical graphite composite material is prepared, and is carbonized at high temperature to obtain an intermediate, and then the intermediate is coated with the asphalt and carbonized, so that the surface and the pores of the natural spherical graphite are coated with soft carbon uniformly and comprehensively, the stripping of graphite on the surface layer is reduced, and the modification of the graphite is realized; meanwhile, the interlayer spacing of the graphite material is smaller and is only 0.34nm, so that the intercalation and deintercalation rate of lithium ions is lower, and the rate capability is poorer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 4.92g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 7.2g of natural spherical graphite with the average particle size of 25 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 250mL of atomized methanol solution of zinc chloride into the mixed solution at 15 ℃, uniformly stirring, sealing, standing and aging for 36h, centrifugally washing and drying, specifically centrifuging the standing and aging product at 5000rpm for 13min, washing the centrifuged product with methanol for 4 times, and drying at 65 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1300 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain an intermediate;
s3, heating the asphalt to 415 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 900 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 2
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 4.92g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 9.00g of natural spherical graphite with the average particle size of 17.8 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 350mL of atomized methanol solution of zinc chloride into the mixed solution at 5 ℃, uniformly stirring, sealing, standing, aging for 24h, centrifugally washing and drying, specifically, centrifuging the statically aged product at 3000rpm for 15min, washing the centrifuged product with methanol for 5 times, and drying at 60 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1000 ℃ at the speed of 1 ℃/min, preserving heat for 3h, and cooling to obtain an intermediate;
s3, heating the asphalt to 400 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 0.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: heating to 800 ℃ at the speed of 1 ℃/min, preserving the heat for 3h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 3
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 6.56g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 10.80g of natural spherical graphite with the average particle size of 15.7 microns in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 500mL of atomized methanol solution of zinc chloride into the mixed solution at 5 ℃, uniformly stirring, sealing, standing, aging for 48 hours, centrifugally washing and drying, specifically, centrifuging the statically aged product at 8000rpm for 10 minutes, washing the centrifuged product with methanol for 3 times, then washing with ethanol for 3 times, and finally drying at 70 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1500 deg.C at a rate of 3 deg.C/min, maintaining for 1 hr, and cooling to obtain intermediate;
s3, heating the asphalt to 430 ℃, preserving heat for 5 hours at normal pressure, performing vacuum distillation for 1 hour to obtain asphalt in a molten state, adding the intermediate obtained in the step S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 1000 ℃ at the speed of 3 ℃/min, preserving the heat for 1h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 4
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 3.28g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 4.80g of natural spherical graphite with the average particle size of 5.38 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 250mL of atomized methanol solution of zinc chloride into the mixed solution at 10 ℃, uniformly stirring, sealing, standing, aging for 36h, centrifugally washing and drying, specifically centrifuging the statically aged product at 5000rpm for 13min, washing the centrifuged product with methanol for 4 times, and drying at 65 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1300 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain an intermediate;
s3, heating the asphalt to 415 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 900 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 5
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 3.28g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 6.00g of natural spherical graphite with the average particle size of 12.5 microns in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 400mL of atomized methanol solution of zinc chloride into the mixed solution at 15 ℃, uniformly stirring, sealing, standing, aging for 24h, centrifugally washing and drying, specifically centrifuging the statically aged product at 3000rpm for 15min, washing the centrifuged product with methanol for 5 times, and drying at 60 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1000 ℃ at the speed of 1 ℃/min, preserving heat for 3h, and cooling to obtain an intermediate;
s3, heating the asphalt to 400 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 0.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: heating to 800 ℃ at the speed of 1 ℃/min, preserving the heat for 3h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 6
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 3.28g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 7.20g of natural spherical graphite with the average particle size of 8.1 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 500mL of atomized zinc nitrate hexahydrate methanol solution into the mixed solution at 15 ℃, uniformly stirring, sealing, standing, aging for 48 hours, centrifugally washing and drying, specifically, centrifuging the statically aged product at 8000rpm for 10 minutes, washing the centrifuged product with methanol for 3 times, and drying at 70 ℃ to obtain a ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1500 ℃ at the speed of 3 ℃/min, preserving heat for 1h, and cooling to obtain an intermediate;
s3, heating the asphalt to 430 ℃, preserving heat for 5 hours at normal pressure, performing vacuum distillation for 1 hour to obtain asphalt in a molten state, adding the intermediate obtained in the step S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 1000 ℃ at the speed of 3 ℃/min, preserving the heat for 1h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 7
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 6.56g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 10.80g of natural spherical graphite with the average particle size of 25 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 250mL of atomized methanol solution of zinc nitrate hexahydrate into the mixed solution at 10 ℃, uniformly stirring, sealing, standing, aging for 36h, centrifuging, washing and drying, specifically centrifuging the standing and aging product at 5000rpm for 13min, washing the centrifuged product with methanol for 4 times, and drying at 65 ℃ to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1300 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain an intermediate;
s3, heating the asphalt to 415 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 900 ℃ at the speed of 2 ℃/min, preserving the heat for 2h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 8
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 6.56g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 12.00g of natural spherical graphite with the average particle size of 15.9 mu m in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 400mL of atomized methanol solution of zinc nitrate hexahydrate into the mixed solution at 5 ℃, uniformly stirring, sealing, standing, aging for 24h, centrifugally washing and drying, specifically, centrifuging the statically aged product at 3000rpm for 15min, washing the centrifuged product with methanol for 5 times, and drying at 60 ℃ to obtain a ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1000 ℃ at the speed of 1 ℃/min, preserving heat for 3h, and cooling to obtain an intermediate;
s3, heating the asphalt to 400 ℃, preserving heat for 4 hours at normal pressure, then carrying out vacuum distillation for 0.5 hour to obtain asphalt in a molten state, then adding the intermediate obtained in the S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 0.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: heating to 800 ℃ at the speed of 1 ℃/min, preserving the heat for 3h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Example 9
The embodiment provides a preparation method of a modified graphite negative electrode material of a lithium ion battery, which comprises the following steps:
s1, uniformly mixing 6.56g of 2-methylimidazole with 500mL of methanol to obtain a methanol solution of 2-methylimidazole, completely immersing 14.4g of natural spherical graphite with the average particle size of 10.6 microns in the methanol solution of 2-methylimidazole to obtain a mixed solution, spraying 500mL of atomized zinc nitrate hexahydrate methanol solution into the mixed solution at 15 ℃, uniformly stirring, sealing, standing, aging for 48 hours, centrifugally washing and drying, specifically, centrifuging the statically aged product at 8000rpm for 10 minutes, washing the centrifuged product with methanol for 3 times, and drying at 70 ℃ to obtain a ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a nitrogen protection atmosphere, and specifically: heating to 1500 ℃ at the speed of 3 ℃/min, preserving heat for 1h, and cooling to obtain an intermediate;
s3, heating the asphalt to 430 ℃, preserving heat for 5 hours at normal pressure, performing vacuum distillation for 1 hour to obtain asphalt in a molten state, adding the intermediate obtained in the step S2 into the asphalt in the molten state under the stirring condition according to the mass ratio of 1.5:1, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in an argon atmosphere, specifically: and heating to 1000 ℃ at the speed of 3 ℃/min, preserving the heat for 1h, and cooling to obtain the modified graphite cathode material of the lithium ion battery.
Comparative example 1
The same procedure was followed as in example 1, except that the addition temperature of the methanol solution of zinc chloride was 30 ℃.
Comparative example 2
The resulting intermediate was prepared by the preparation method of example 1.
Comparative example 3
The natural spherical graphite was subjected to the modified graphite materials prepared in S3 and S4 in the preparation method of example 1.
Comparative example 4
Commercially available natural spheroidal graphite materials.
The modified graphite anode materials of the embodiments 1 to 9 of the present invention all have better cycle performance, and we take the modified graphite anode material of the embodiment 1 as an example, and perform the battery performance test together with the samples of the comparative examples 1 to 4, and the test results are shown in table 1:
TABLE 1 Battery Performance data sheet for each sample
Figure BDA0002378542010000111
Figure BDA0002378542010000121
As can be seen from table 1, the first coulombic efficiency of example 1 is high, the rate capability is good, and the cycle performance is good, because the coating integrity and uniformity of example 1 are good, the stability of the modified graphite negative electrode material in the electrolyte is effectively improved; in the sample of the comparative example 1, as the addition temperature of the zinc salt methanol solution is higher, part of monomers formed by ZIF8 do not coat the surface of graphite, and the ZIF8 monomer exists, the initial coulombic efficiency is lower, the rate capability is better, but the cycle performance is poorer; in the sample of the comparative example 2, only the product obtained by carbonizing the ZIF8 exists on the graphite, and the ZIF8 has partial micropores after carbonization, so that the discharge capacity is high, the rate capability is good, but the first effect is low, and the cycle retention rate is slightly poor; the sample of comparative example 3 is only the carbonized product coating of asphalt, and the graphite surface coating is not uniform and complete due to the high viscosity of asphalt, and the rate capability is poor.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. A preparation method of a modified graphite cathode material of a lithium ion battery is characterized by comprising the following steps:
s1, uniformly mixing 2-methylimidazole and methanol to obtain a methanol solution of 2-methylimidazole, completely immersing natural spherical graphite in the methanol solution of 2-methylimidazole to obtain a mixed solution, adding a methanol solution of zinc salt into the mixed solution at the temperature of 5-15 ℃, uniformly stirring, sealing, standing, aging, centrifuging, washing and drying to obtain the ZIF 8/natural spherical graphite composite material;
s2, carbonizing the ZIF 8/natural spherical graphite composite material obtained in the S1 at a high temperature in a protective gas atmosphere, and cooling to obtain an intermediate;
wherein the ZIF 8/natural spherical graphite composite material is carbonized at high temperature under the following conditions: heating to 1000-1500 ℃ at the speed of 1-3 ℃/min;
s3, heating the pitch to a molten state, adding the intermediate obtained in the step S2 into the pitch in the molten state under a stirring condition, cooling and crushing to obtain a precursor;
s4, carbonizing the precursor at high temperature in a protective gas atmosphere, and cooling to obtain the modified graphite negative electrode material of the lithium ion battery;
wherein the high-temperature carbonization conditions of the precursor are as follows: heating to 800-1000 ℃ at the speed of 1-3 ℃/min, and preserving heat for 1-3 h.
2. The preparation method of the modified graphite anode material for the lithium ion battery according to claim 1, wherein in the step S1, the feed-liquid ratio of the 2-methylimidazole to the methanol is (6.56-13.12 g): 1L, wherein the mass ratio of the natural spherical graphite to the 2-methylimidazole zinc salt is (10-15): 1: (0.25-0.5).
3. The preparation method of the modified graphite anode material for the lithium ion battery according to claim 1 or 2, wherein in the step S1, the zinc salt is zinc chloride or zinc nitrate hexahydrate, and the mass concentration of the methanol solution of the zinc salt is 0.04-0.08 mol/L.
4. The method for preparing the modified graphite anode material of the lithium ion battery according to claim 3, wherein in the step S1, the addition mode of the methanol solution of the zinc salt is atomized and sprayed.
5. The method for preparing the modified graphite anode material for the lithium ion battery according to claim 1, wherein in the step S1, the average particle size of the natural spherical graphite is 5-25 μm.
6. The preparation method of the modified graphite anode material for the lithium ion battery according to claim 1, wherein in the step S1, the standing and aging time is 24-48 h; the specific conditions of the centrifugation are as follows: the centrifugation speed is 3000-8000 rpm, the centrifugation time is 10-15 min, and the drying temperature is 60-70 ℃.
7. The method of claim 1, wherein in step S2, the shielding gas is at least one of argon, nitrogen, and helium.
8. The method for preparing the modified graphite anode material of the lithium ion battery according to claim 1, wherein in the step S3, the mass ratio of the intermediate to the molten asphalt is (0.5-1.5): 1;
the preparation process of the asphalt in the molten state comprises the following steps: heating the asphalt to 400-430 ℃, preserving heat for 4-5 h at normal pressure, and then carrying out vacuum distillation for 0.5-1 h to obtain the asphalt in a molten state.
9. The method of claim 1, wherein in step S4, the shielding gas is at least one of argon, nitrogen, and helium.
10. The modified graphite anode material for lithium ion batteries, which is prepared by the preparation method of the modified graphite anode material according to any one of claims 1 to 9.
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