CN113889596A - Preparation method of nitrogen-doped hard carbon-coated artificial graphite composite material - Google Patents
Preparation method of nitrogen-doped hard carbon-coated artificial graphite composite material Download PDFInfo
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- 229910021385 hard carbon Inorganic materials 0.000 title claims abstract description 74
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- 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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
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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
- 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
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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Abstract
The invention belongs to the field of secondary batteries, and particularly relates to a preparation method of a nitrogen-doped hard carbon-coated artificial graphite composite material. The nitrogen-doped hard carbon coated artificial graphite composite material obtained by the method is of a core-shell structure, the inner core is artificial graphite, the outer shell is a nitrogen-doped hard carbon coating layer, and the mass of the nitrogen-doped hard carbon coating layer is 0.5-2% of that of the inner core of the artificial graphite; the shell and the inner core are bonded through a chemical bond, wherein the chemical bond comprises an amido bond formed by the reaction of amino groups and/or imino groups on the shell and carboxyl groups on the artificial graphite. The nitrogen-doped hard carbon-coated artificial graphite composite material prepared by the method improves the coating quality and the electronic conductivity, and obviously improves the rate capability, the cycle performance and the consistency of the graphite cathode material.
Description
Technical Field
The invention belongs to the field of secondary battery cathode materials, and particularly relates to a preparation method of a nitrogen-doped hard carbon-coated artificial graphite composite material.
Background
At present, with the improvement of the energy density and rate capability of graphite in the market, the graphite material is required to have high energy density and higher rate capability. One of the methods for increasing the energy density and the rate of the negative electrode material is to perform surface coating, such as coating with soft carbon or hard carbon.
CN110797513A, the chinese patent application, discloses a graphite-hard carbon coated material and a preparation method thereof, wherein graphite and oligomeric phenolic resin are mixed, and then are cured and pyrolyzed, and hard carbon is coated on the surface of the graphite material, so as to prepare a high-capacity negative electrode material.
In the traditional soft carbon or hard carbon coated cathode material, the structural orientations of the coating layer materials are different, the impedance difference of the same batch of materials is large, and the rate performance and the cycle performance are easily influenced. And the coating and the graphite are bonded by physical mixing, the consistency and stability of the physical bonding are poor, the coating is usually completely or partially peeled off, and the rate, the cycle performance and the consistency of the graphite negative electrode material are further deteriorated.
Disclosure of Invention
The invention aims to provide a preparation method of a nitrogen-doped hard carbon-coated artificial graphite composite material, which aims to solve the problem that the existing graphite cathode material is poor in rate capability and cycle performance.
In order to achieve the purpose, the technical scheme of the preparation method of the nitrogen-doped hard carbon-coated artificial graphite composite material is as follows:
a preparation method of a nitrogen-doped hard carbon coated artificial graphite composite material is characterized in that the nitrogen-doped hard carbon coated artificial graphite composite material is of a core-shell structure, an inner core is artificial graphite, a shell is a nitrogen-doped hard carbon coating layer, and the mass of the nitrogen-doped hard carbon coating layer is 0.5-2% of that of the inner core of the artificial graphite; the shell and the inner core are bonded through a chemical bond, wherein the chemical bond comprises an amido bond formed by the reaction of amino groups and/or imino groups on the shell and carboxyl groups on the artificial graphite; the doping amount of nitrogen in the nitrogen-doped hard carbon coating layer is (0.5-2)%; the preparation method comprises the following steps:
1) uniformly dispersing a hard carbon precursor, an oxidant, tetrabutylammonium bromide and a surfactant in a solvent to obtain a precursor liquid; the hard carbon precursor contains amino groups and/or imino groups; the oxidant is one or more than two of ammonium persulfate, potassium persulfate, hydrogen peroxide and potassium permanganate;
carrying out oxidation treatment on the artificial graphite to obtain oxidized artificial graphite;
2) coating the oxidized artificial graphite with a precursor liquid, drying, carbonizing at 600-1000 ℃, and graphitizing at 2500-3000 ℃.
The shell and the inner core are bonded together through the urethane bond, and compared with physical adhesion, the nitrogen-doped hard carbon-coated artificial graphite composite material prepared by the method has high and stable bonding force and is beneficial to improving the consistency of the material. In addition, through the bonding process, the orientation of the hard carbon coating layer tends to be consistent, which is beneficial to reducing the impedance of the material, thereby improving the rate capability and the cycle performance of the material. After the hard carbon is doped with nitrogen, on one hand, the fast charging performance of the hard carbon is improved by utilizing the characteristics of large spacing and fast lithium ion transmission of the hard carbon material layer, and on the other hand, the impedance is reduced by utilizing the characteristic of strong carrier density of nitrogen atoms doping, and the multiplying power performance and the power performance are improved. The composite material improves the coating quality and the electronic conductivity, and obviously improves the rate capability, the cycle performance and the consistency of the graphite cathode material.
In order to further improve the tap density of the negative electrode material and increase the energy density of the battery, the particle size of the nitrogen-doped hard carbon-coated artificial graphite composite material is preferably 8-15 μm.
According to the preparation method of the nitrogen-doped hard carbon-coated artificial graphite composite material, the shell and the core are chemically bonded to form the composite material, the preparation process is simple, and the preparation method is suitable for large-scale industrial production.
Step 1) preparing a precursor liquid by using a hard carbon precursor, an oxidant, tetrabutylammonium bromide and a surfactant, preferably, in the step 1), the mass ratio of the hard carbon precursor to the oxidant to the tetrabutylammonium bromide is 100 (1-3) to (1-3). In order to facilitate the subsequent coating, the mass ratio of the hard carbon precursor to the solvent is preferably 100: (500-1000). The use of an oxidizing agent, tetrabutylammonium bromide, promotes surface oxidation, and preferably, the precursor liquid is treated at (30-100) deg.C for (1-6) h. So as to facilitate the subsequent reaction.
The hard carbon precursor is amino resin or amino-containing modified epoxy resin.
The surfactant can promote the raw materials to be fully dispersed, preferably, in the step 1), the surfactant is sodium dodecyl benzene sulfonate, and the mass ratio of the sodium dodecyl benzene sulfonate to the hard carbon precursor is (0.1-1): 100.
preferably, in step 1), the oxidized artificial graphite is prepared by a method comprising the following steps: carrying out low-temperature oxidation reaction (1-24) on the mixed solution containing the artificial graphite and the oxidant at the temperature of 50-100 ℃ for 1-24 h, and then carrying out solid-liquid separation and drying; the oxidant is one or more than two of nitric acid, sulfuric acid, phosphoric acid, perchloric acid and ammonium persulfate. The oxidized surface of the artificial graphite is rich in oxygen-containing groups such as hydroxyl, carboxyl and the like, which is beneficial to the reaction with the hard carbon precursor.
Step 2) is a coating process of the precursor liquid. Preferably, the coating is realized by stirring for 1-6 hours at the temperature of (100-300) DEG C. The coating process can be carried out in a high-speed mixer, and the rotating speed can be controlled to be (100-1000) r/min.
The carbonization process is carried out to ensure that the reaction is fully carried out, preferably, in the step 2), the carbonization is carried out at the temperature of 600-1000 ℃ for 1-6 h. The graphitization process after carbonization can rearrange the hard carbon structure, improve the disorder degree of the material and remove the residual hydrophilic groups on the surface.
For further coating consistency of the coating layer, it is preferable that the mass of the hard carbon precursor in step 2) is (1 to 10) parts by mass per 100 parts by mass of the oxidized artificial graphite.
Drawings
Fig. 1 is an SEM image of a nitrogen-doped hard carbon-coated artificial graphite composite material prepared in example 1 of the present invention;
fig. 2 is an infrared spectrum of the nitrogen-doped hard carbon-coated artificial graphite composite material prepared in example 1 of the present invention.
Detailed Description
The following examples are provided to further illustrate the practice of the invention. In the following examples, the amino resin and the amino-containing modified epoxy resin are commercially available products or can be prepared according to the prior art. The amino resin is 9003-08-1, and is available from Shanghai weathercock chemical science and technology, Inc.
The preparation method of the amino-containing modified epoxy resin can refer to example 1 with application publication number CN105038516A, and the specific preparation process is as follows: the preparation method of the amino-containing modified epoxy resin comprises the following steps: 1) adding 400 parts of bisphenol A and 0.5 part of tetrabutylammonium bromide into 1000 parts of epoxy resin, and reacting at 160 ℃ for 12 hours to obtain a product 1; 2) then, 170 parts of soybean oil fatty acid and 0.5 part of tetrabutylammonium bromide are added into the product 1 and reacted for 12 hours at the temperature of 140 ℃ to obtain a product 2; 3) subsequently, to the product 2 were added 210 parts of ethylene glycol monobutyl ether, 80 parts of diethanolamine and 95 parts of ketimine of diethylenetriamine, and after reaction at 120 ℃ for 4 hours, 145 parts of methyl isobutyl ketone was added to obtain an amino group-containing modified epoxy resin.
First, a specific embodiment of the preparation method of the nitrogen-doped hard carbon-coated artificial graphite composite material of the present invention
Example 1
According to the preparation method of the nitrogen-doped hard carbon coated artificial graphite composite material, the obtained artificial graphite composite material is of a core-shell structure, the inner core is artificial graphite, the shell is the nitrogen-doped hard carbon coating layer, the mass of the nitrogen-doped hard carbon coating layer is 1% of the mass of the inner core of the artificial graphite, the doping amount of nitrogen in the nitrogen-doped hard carbon coating layer is 1%, and the shell and the inner core are bonded through chemical bonds.
The preparation method specifically comprises the following steps:
1) preparation of precursor liquid: 20g of amino-containing modified epoxy resin, 0.4g of ammonium persulfate, 0.4g of tetrabutylammonium bromide and 0.125g of sodium dodecyl benzene sulfonate are uniformly mixed in 160mL of tetrahydrofuran organic solvent and react for 2 hours at 50 ℃ to obtain precursor liquid.
2) Preparing modified artificial graphite: mixing 1000g of artificial graphite, 10g of sodium dodecyl benzene sulfonate, 10g of ammonium persulfate and 19380ml of water to prepare mixed solution with the mass concentration of 5%, carrying out low-temperature oxidation reaction at the temperature of 80 ℃ for 12h, filtering and drying to obtain the modified artificial graphite (namely the oxidized artificial graphite).
3) Preparing a nitrogen-doped hard carbon-coated artificial graphite composite material: adding the modified artificial graphite into a precursor liquid, uniformly mixing, transferring into a high-speed mixer, coating at the rotation speed of 500r/min, the temperature of 200 ℃ and the stirring time of 3h, drying, crushing, transferring the coated material into a tube furnace, heating to 800 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, preserving the temperature for 3h, naturally cooling to room temperature, crushing, heating to 2800 ℃ under the inert atmosphere of argon, graphitizing for 15 days, and naturally cooling to room temperature to obtain the artificial graphite composite material.
Example 2
According to the preparation method of the nitrogen-doped hard carbon coated artificial graphite composite material, the obtained artificial graphite composite material is of a core-shell structure, the inner core is artificial graphite, the shell is the nitrogen-doped hard carbon coating layer, the mass of the nitrogen-doped hard carbon coating layer is 0.5% of the mass of the inner core of the artificial graphite, the doping amount of nitrogen in the nitrogen-doped hard carbon coating layer is 0.5%, and the shell and the inner core are bonded through chemical bonds.
The preparation method specifically comprises the following steps:
1) preparation of precursor liquid: 10g of amino-containing modified epoxy resin, 0.1g of hydrogen peroxide, 0.1g of tetrabutylammonium bromide and 0.01g of sodium dodecyl benzene sulfonate are uniformly mixed in 5000ml of tetrahydrofuran organic solvent and react for 2 hours at 50 ℃ to obtain precursor liquid.
2) Preparing modified artificial graphite: preparing mixed water solution with the concentration of 1% Wt by 1000ml of artificial graphite, 5g of sodium dodecyl benzene sulfonate, 5g of nitric acid and 100000ml of deionized water, carrying out low-temperature oxidation reaction at 50 ℃ for 24 hours, filtering and drying to obtain modified artificial graphite;
3) preparing a nitrogen-doped hard carbon-coated artificial graphite composite material: adding the modified artificial graphite into a precursor liquid, uniformly mixing, transferring into a high-speed mixer, coating at the rotating speed of 100r/min and the temperature of 100 ℃ for 6h under stirring, drying, crushing, transferring the coated material into a tube furnace, heating to 1000 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, preserving heat for 1h, naturally cooling to room temperature, crushing, heating to 2500 ℃ under the inert atmosphere, graphitizing for 15 days, and naturally cooling to room temperature to obtain the artificial graphite composite material.
Example 3
According to the preparation method of the nitrogen-doped hard carbon coated artificial graphite composite material, the obtained artificial graphite composite material is of a core-shell structure, the inner core is artificial graphite, the shell is the nitrogen-doped hard carbon coating layer, the mass of the nitrogen-doped hard carbon coating layer is 2% of the mass of the inner core of the artificial graphite, the doping amount of nitrogen in the nitrogen-doped hard carbon coating layer is 2%, and the shell and the inner core are bonded through chemical bonds.
The preparation method specifically comprises the following steps:
1) preparation of precursor liquid: 100g of amino resin, 3g of potassium persulfate, 3g of tetrabutylammonium bromide and 1g of sodium dodecyl benzene sulfonate are uniformly mixed in 10000 of tetrahydrofuran organic solvent, and the mixture reacts for 2 hours at the temperature of 50 ℃ to obtain precursor liquid.
2) Preparing modified artificial graphite: mixing 1000g of artificial graphite, 2g of sodium dodecyl benzene sulfonate, 2g of phosphoric acid and 10000ml of deionized water to prepare mixed water solution with the concentration of 10% Wt, carrying out low-temperature oxidation reaction at the temperature of 100 ℃ for 1 hour, filtering and drying to obtain the modified artificial graphite.
3) Preparing a nitrogen-doped hard carbon-coated artificial graphite composite material: adding the modified artificial graphite into a precursor liquid, uniformly mixing, transferring into a high-speed mixer, coating at the rotating speed of 1000r/min and the temperature of 300 ℃ for 1h, drying, crushing, transferring the coated material into a tubular furnace, heating to 600 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, preserving heat for 6h, naturally cooling to room temperature, crushing, heating to 3000 ℃ under the inert atmosphere of argon for graphitization, and naturally cooling to room temperature to obtain the artificial graphite composite material.
Second, comparative example
Dissolving 20g of asphalt in 5000ml of tetrahydrofuran, adding 1000g of artificial graphite, stirring, filtering, drying, crushing, transferring to a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under an argon inert atmosphere, keeping the temperature for 3h, naturally cooling to room temperature, crushing, heating to 2800 ℃ under an inert atmosphere, graphitizing for 15 days, and naturally cooling to room temperature to obtain the artificial graphite composite material.
Third, Experimental example
Experimental example 1 test of physical and chemical Properties
1.1SEM test and Infrared test
The artificial graphite composite material prepared in example 1 was subjected to SEM test, and the test results are shown in fig. 1.
As can be seen from FIG. 1, the artificial graphite composite material prepared in example 1 was in the form of particles having a uniform size distribution and a particle diameter of (8-15) μm.
In FIG. 2, 1300cm-1The position is a C-N stretching vibration characteristic absorption peak on the molecular structure.
1.2 powder conductivity test:
pressing the powder into a blocky structure, and then testing the conductivity of the powder by adopting a four-probe tester. The test results are shown in table 1.
1.3 powder compaction Density test
The artificial graphite composite materials of examples 1 to 3 and comparative example were subjected to a powder compaction density test. During testing, powder with a certain mass is weighed and placed in a mold, 2T pressure pressing is adopted (1 g of powder is placed in a fixed kettle and then pressed by 2T pressure by adopting a powder compaction density instrument, the powder is static for 10S, the volume under pressing is calculated, and the compaction density is calculated), and the powder compaction density is calculated. The test results are shown in table 1.
TABLE 1 physicochemical Properties of graphite materials in examples and comparative examples
| Item | Example 1 | Example 2 | Example 3 | Comparative example 1 |
| Resistivity of powder (. OMEGA. m) | 8*10-6 | 5*10-6 | 6*10-6 | 8*10-7 |
| Powder compacted density (g/cm)3) | 1.67 | 1.64 | 1.63 | 1.51 |
As can be seen from table 1, the powder resistivity of the artificial graphite composite material prepared by the invention is obviously lower than that of the comparative example, because the surface of the negative electrode material is doped with nitrogen doped hard carbon with high electronic conductivity, the electronic conductivity is reduced; meanwhile, the hard carbon coating material prepared by the chemical reaction method has the advantages of high density, few pores and the like, so that the compaction density of the material is improved.
Experimental example 2 button cell test
The artificial graphite composites of examples 1-3 and comparative example were assembled into button cells a1, a2, A3, B1, respectively. The assembling method comprises the following steps: and adding a binder, a conductive agent and a solvent into the negative electrode material, stirring and pulping, coating the mixture on copper foil, and drying and rolling to obtain the negative electrode plate. The binder used was LA132 binder, the conductive agent was SP, the negative electrode materials were the graphite composite materials in examples 1 to 3 and comparative example, respectively, and the solvent was secondary distilled water. The proportion of each component is as follows: and (3) anode material: SP: LA 132: 95g of secondary distilled water: 1 g: 4 g: 220 mL; the electrolyte is LiPF6/EC+DEC(LiPF6The concentration of the lithium ion battery is 1.2mol/L, the volume ratio of EC to DEC is 1:1), the metal lithium sheet is used as a counter electrode, and the diaphragm is a Polyethylene (PE), polypropylene (PP) or polyethylene propylene (PEP) composite membrane. The button cell is assembled in a hydrogen-filled glove box, the electrochemical performance test is carried out on a Wuhan blue electricity CT2001A type battery tester, the charging and discharging voltage range is 0.005V-2.0V, and the charging and discharging multiplying power is 0.1C. The test results are shown in table 2.
And simultaneously taking the negative plate, and testing the liquid absorption and retention capacity of the negative plate.
Table 2 comparison of performance of lithium ion batteries prepared from artificial graphite composites of examples 1-3 and comparative example
| Item | Example 1/A1 | Example 2/A2 | Example 3/A3 | Comparative example 1/B1 |
| First discharge capacity (mAh/g) | 358.3 | 357.4 | 358.5 | 350.4 |
| First efficiency (%) | 94.1 | 93.8 | 93.7 | 91.2 |
| Liquid suction capacity (mL/min) | 9.8 | 9.3 | 8.8 | 5.4 |
As can be seen from table 2, the first discharge capacity and the first charge-discharge efficiency of the lithium ion battery using the graphite composite negative electrode material obtained in examples 1 to 3 are significantly higher than those of the comparative examples, because the use of the nitrogen-doped hard carbon coating layer is beneficial to the transmission of lithium ions, the gram capacity exertion of the material is improved, the first efficiency is further improved, and the porosity of the coating layer in the examples is high (nano-micron pores left by the gas generated in the carbonization process of the hard carbon precursor), which is beneficial to the liquid absorption of the material.
Experimental example 3 pouch cell test
The artificial graphite composite materials in examples 1 to 3 and comparative example were used as negative electrode materials to prepare negative electrode sheets. With ternary materials (LiNi)1/3Co1/3Mn1/3O2) As the positive electrode, LiPF6Solution (solvent EC + DEC, volume ratio 1:1, LiPF)6Concentration of 1.3mol/L) is used as electrolyte, celegard2400 is used as a diaphragm, and 2Ah soft package batteries A10, A20, A30 and B10 are prepared. And testing the cycle performance and the rate performance of the soft package battery.
Cycle performance test conditions: the charging and discharging current is 1C/1C, the voltage range is 2.8-4.2V, and the cycle times are 500 times.
Multiplying power performance test conditions: charging rate: 1C/2C/3C/5C, discharge multiplying power of 1C; voltage range: 2.8-4.2V.
The test results are shown in tables 3 and 4.
Table 3 comparison of cycle performance of lithium ion batteries prepared from graphite materials of examples 1-3 and comparative examples
As can be seen from table 3, the cycle performance of the pouch battery prepared from the artificial graphite composite material of the present invention is superior to that of the comparative example because the materials of the examples have characteristics of small impedance and high lithium ion transfer rate in terms of 1C/1C rate cycle performance. And the artificial graphite composite material of the embodiment has good structural stability, small structural damage effect on the material in the circulating process and stable structure, thereby improving the circulating performance of the artificial graphite composite material.
Table 4 multiplying power charging performance comparison table
As can be seen from table 4, the soft-package battery prepared from the artificial graphite composite material of the present invention has a better constant current ratio, and the reason is that the surface of the material in the embodiment is coated with the nitrogen-doped hard carbon material, such that the fast charging performance of the material is improved, and the constant current ratio of the lithium ion battery is improved.
Claims (6)
1. The preparation method of the nitrogen-doped hard carbon-coated artificial graphite composite material is characterized in that the nitrogen-doped hard carbon-coated artificial graphite composite material is of a core-shell structure, the inner core is artificial graphite, the shell is a nitrogen-doped hard carbon coating layer, and the mass of the nitrogen-doped hard carbon coating layer is 0.5-2% of that of the inner core of the artificial graphite; the shell and the inner core are bonded through a chemical bond, wherein the chemical bond comprises an amido bond formed by the reaction of amino groups and/or imino groups on the shell and carboxyl groups on the artificial graphite; the doping amount of nitrogen in the nitrogen-doped hard carbon coating layer is (0.5-2)%; the preparation method comprises the following steps:
1) uniformly dispersing a hard carbon precursor, an oxidant, tetrabutylammonium bromide and a surfactant in a solvent to obtain a precursor liquid; the hard carbon precursor contains amino groups and/or imino groups; the oxidant is one or more than two of ammonium persulfate, potassium persulfate, hydrogen peroxide and potassium permanganate;
carrying out oxidation treatment on the artificial graphite to obtain oxidized artificial graphite;
2) coating the oxidized artificial graphite with a precursor liquid, drying, carbonizing at 600-1000 ℃, and graphitizing at 2500-3000 ℃.
2. The method for preparing the nitrogen-doped hard carbon-coated artificial graphite composite material according to claim 1, wherein in the step 1), the mass ratio of the hard carbon precursor to the oxidant to the tetrabutylammonium bromide is 100 (1-3) to (1-3).
3. The preparation method of the nitrogen-doped hard carbon-coated artificial graphite composite material according to claim 1, wherein in the step 1), the surfactant is sodium dodecyl benzene sulfonate, and the mass ratio of the sodium dodecyl benzene sulfonate to the hard carbon precursor is (0.1-1): 100.
4. the method for preparing the nitrogen-doped hard carbon-coated artificial graphite composite material according to claim 1, wherein in the step 1), the oxidized artificial graphite is prepared by a method comprising the following steps: carrying out low-temperature oxidation reaction (1-24) on the mixed solution containing the artificial graphite and the oxidant at the temperature of 50-100 ℃ for 1-24 h, and then carrying out solid-liquid separation and drying; the oxidant is one or more than two of nitric acid, sulfuric acid, phosphoric acid, perchloric acid and ammonium persulfate.
5. The method for preparing the nitrogen-doped hard carbon-coated artificial graphite composite material according to claim 1, wherein in the step 2), the carbonization is performed at a temperature of (600-1000) DEG C for 1-6 h.
6. The method for preparing the nitrogen-doped hard carbon-coated artificial graphite composite material according to any one of claims 1 to 5, wherein in the step 2), the mass of the hard carbon precursor is (1 to 10) parts by mass per 100 parts by mass of the oxidized artificial graphite.
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