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CN114068923A - Modification method of graphite and application of graphite in lithium ion battery - Google Patents

Modification method of graphite and application of graphite in lithium ion battery Download PDF

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CN114068923A
CN114068923A CN202010753216.0A CN202010753216A CN114068923A CN 114068923 A CN114068923 A CN 114068923A CN 202010753216 A CN202010753216 A CN 202010753216A CN 114068923 A CN114068923 A CN 114068923A
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graphite
atmosphere
raw material
nitrogen
modifier
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李能
王志勇
任娜娜
皮涛
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Hunan Shinzoom Technology Co ltd
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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
    • 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H—ELECTRICITY
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    • 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
    • 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
    • H01M4/13—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
    • 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
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a modification method of graphite and application of the graphite in a lithium ion battery. The method comprises the following steps: 1) mixing a graphite raw material and a modifier to obtain a mixture; 2) carrying out primary carbonization treatment on the mixture at the carbonization temperature of 700-1100 ℃ in an inert atmosphere to obtain a graphite material with a porous surface; the modifier is a substance which can react with the graphite raw material at the primary carbonization temperature to generate CO. According to the method, the graphite raw material and the modifier are mixed and carbonized at a certain carbonization temperature and under an inert atmosphere, so that pores can be formed on the surface of the graphite raw material, the porous structure of the obtained graphite material is favorable for lithium ions to enter into graphite layers from pores of a basal plane, the rate capability of the graphite is greatly improved, the electronic conductivity of the graphite material is improved by the porous structure, and the porous structure is used as a negative electrode material to be applied to a lithium ion battery, so that the graphite material has the advantages of high rate capability and excellent dynamic performance.

Description

Modification method of graphite and application of graphite in lithium ion battery
Technical Field
The invention relates to the technical field of new energy, relates to a modification method of graphite and application of the modification method in a lithium ion battery, and particularly relates to a modification method of graphite, a negative electrode containing a graphite material prepared by the method and a lithium ion battery.
Background
Graphite is a layered crystal formed by stacking graphite sheets under van der waals forces. The graphite has rich resources and low price, and has the advantages of high reversible capacity, low charge-discharge voltage platform, no voltage hysteresis, good conductivity and the like when being used as a negative electrode material for a lithium battery, and is widely researched in the lithium battery industry.
Although lithium ions can be completely and reversibly intercalated and deintercalated in graphite in theory, capacity fading occurs during the first cycle in the practical application process, and the main reason is that the graphite negative electrode reacts with the electrolyte solution to generate a passivation film (SEI film) having lithium ion conductivity and electronic insulation when lithium is first intercalated. Moreover, since the anisotropic structure of graphite restricts the free diffusion of lithium ions in the graphite structure, the rate capability is poor, and it is difficult to meet the requirements of practical application.
CN109911892A discloses a preparation method of a composite graphite cathode material with high capacity and high multiplying power, which comprises the steps of carbonizing an artificial graphite particle material at low temperature, crushing the carbonized artificial graphite particle material to 8-11 mu m, carrying out normal-temperature surface modification on green spheres of mesocarbon microbeads, mixing the two materials with a binder, carrying out secondary coating modification granulation, and carrying out high-temperature graphitization treatment to obtain the composite graphite cathode material with high capacity and high multiplying power. The modification method can improve the capacity and rate capability.
CN105375030A discloses a preparation method of a graphite negative electrode material of a low-temperature high-rate power battery, which comprises the following steps: 1) adding natural crystalline flake graphite into a grinder to carry out stirring ball milling, and carrying out wet stirring milling and shaping; 2) mixing graphite powder with concentrated acid, ultrasonically stirring for 0.5-1h, separating the powder by a centrifuge, washing the powder with pure water and ethanol respectively until the pH value is 6-8, and drying at 80 ℃ for 10-24 h; preserving the heat for 1-10h in the protective atmosphere at the temperature of 500-900 ℃, and then cooling to room temperature; 3) adding the micro-expanded graphite, a carbon source and a solvent into a high-speed stirrer, and stirring for 1-4h at the stirring frequency of 30-50 HZ; 4) and placing the agglomerate coated with the carbon source in a protective atmosphere for carbonization sintering treatment for 10-48h, wherein the carbonization temperature is 1000-1500 ℃, and obtaining the low-temperature high-magnification graphite cathode material.
Although the modification method of graphite can improve the electrochemical performance of graphite, the preparation process is complex and high in cost, and is not suitable for industrial production.
Disclosure of Invention
In view of the above problems in the prior art, the present invention aims to provide a modification method of graphite and its use in a lithium ion battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for modifying graphite, the method comprising the steps of:
(1) mixing a graphite raw material and a modifier to obtain a mixture;
(2) carrying out primary carbonization treatment on the mixture obtained in the step (1) at the carbonization temperature of 700-1100 ℃ in an inert atmosphere to obtain a graphite material with a porous surface;
the modifier is a substance which can react with the graphite raw material at the primary carbonization temperature to generate CO.
In the method of the present invention, the primary carbonization temperature is 700 ℃ to 1100 ℃, for example, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 975 ℃, 1000 ℃, 1050 ℃, 1100 ℃, or the like. If the temperature is too low, the CO generated by the reaction is insufficient, and the pore-forming is insufficient; if the temperature is too high, the reaction is too vigorous and the pore-forming is not uniform.
For a graphite negative electrode material, lithium ions can only enter from the end face of graphite due to the layered structure of the graphite, so that the rate capability of the graphite negative electrode material is poor, the invention provides a modification method of the graphite, a graphite raw material and a modifier are mixed and carbonized at a certain carbonization temperature and under an inert atmosphere, a hole can be formed on the surface of the graphite raw material, and the technical principle is as follows: the modifier is coated on the surface of the graphite raw material in the step (1), the modifier and the graphite raw material react to generate CO through carbonization treatment in the step (2), and CO escapes to generate an etching effect on the surface of the graphite raw material, so that the porous carbon with an integral structure is formed on the surface.
The graphite material with the porous surface prepared by the method has the advantages that the porous structure is beneficial to lithium ions entering the graphite layer from the pores of the base surface, the diffusivity of the lithium ions is improved, the rate capability of the graphite is greatly improved, the electronic conductivity of the graphite material is improved by the pore structure, and the graphite material is used as a negative electrode material to be applied to a lithium ion battery, so that the graphite material has the advantages of high rate capability and excellent dynamic performance.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
Preferably, the graphite matrix comprises artificial graphite and/or natural graphite.
Preferably, the artificial graphite comprises petroleum coke artificial graphite and/or needle coke artificial graphite.
Preferably, the graphite raw material in step (1) has an average particle diameter of 5 μm to 25 μm, for example, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 20 μm, 23 μm, 25 μm, or the like.
Preferably, the specific surface area of the graphite raw material in the step (1) is less than or equal to 5m2In g, e.g. 5m2/g、3.5m2/g、5m2(ii)/g or 1m2And/g, etc.
Preferably, the graphite raw material of the step (1) has a 5T compaction density of more than 0.8g/cm3E.g. 0.85g/cm3、0.9g/cm3、0.95g/cm3、1g/cm3、1.1g/cm3、1.2g/cm3Or 1.4g/cm3And the like.
Preferably, the degree of graphitization of the graphite starting material in step (1) is > 90%, such as 91%, 92%, 93%, 94%, 95%, 96%, 98%, or the like.
Preferably, the modifier comprises at least one of potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, and calcium carbonate.
Preferably, the mass ratio of the modifier to the graphite raw material in the step (1) is 0.2:9.8-3:7, such as 0.2:9.8, 0.3:9.7, 0.5:9.5, 0.7:9.3, 1:9, 1.2:8.8, 1.5:8.5, 2:8, 2.1:7.9, 2.4:7.6 or 3:7, etc., if the content of the modifier is too much, too much CO is generated, which leads to violent reaction and excessive etching, and the porous carbon structure formed on the surface of the graphite is easily damaged, which leads to too large specific surface area and first effect reduction; if the content of the modifier is too small, the generated CO is too small, so that the etching is insufficient, the pore distribution is not uniform, and the material performance is influenced, and the content is more preferably 1.2:8.8-2.4: 7.6.
Preferably, the inert atmosphere in step (2) is selected from any one of nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere, xenon atmosphere, or radon atmosphere, or a mixed atmosphere of at least two of them.
Preferably, the rate of temperature rise to the primary carbonization temperature is 3 ℃/min to 10 ℃/min, such as 3 ℃/min, 4 ℃/min, 5 ℃/min, 7 ℃/min, 8 ℃/min, or 10 ℃/min, and the like.
Preferably, the heat preservation time of the primary carbonization treatment in the step (2) is 1h to 5h, such as 1h, 2h, 3h, 4h, 4.5h or 5 h.
As a preferred technical scheme of the method, the method also comprises the step (3) after the step (2): mixing the graphite material with the porous surface in the step (2) with a nitrogen-doped raw material, heating to a secondary carbonization temperature, and performing secondary carbonization treatment to obtain a graphite material with a nitrogen-doped porous layer on the surface;
the nitrogen-doped raw material can generate NH at the secondary carbonization temperature3The substance of (1).
According to the preferred technical scheme, the graphite material with the porous surface and the nitrogen-doped raw material are mixed and subjected to secondary carbonization treatment, so that nitrogen doping of the porous carbon on the surface of the graphite material can be realized, and the graphite material with the nitrogen-doped porous layer on the surface is obtained.
Preferably, in the step (3), the nitrogen-doped raw material comprises at least one of ammonium chloride, urea and melamine.
Preferably, in the step (3), the mass ratio of the nitrogen-doped raw material to the graphite material with porous surface is 0.2:9.8-3:7, such as 0.2:9.8, 0.4:9.7, 0.5:9.5, 0.7:9.3, 1:9, 1.2:8.8, 1.5:8.5, 2:8, 2.1:7.9, 2.4:7.6 or 3:7, etc., if the content of the nitrogen-doped raw material is too much, NH is generated3Too many defects are caused, the specific surface area is too large due to easy collapse of a pore structure, and the first effect is reduced; if the content of the nitrogen-doped raw material is too small, NH is generated3Too little, which in turn causes uneven doping and affects the product performance, preferably 1:9 to 2:8.
Preferably, the secondary carbonization temperature in step (3) is 800 ℃ to 1300 ℃, such as 800 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1200 ℃, 1300 ℃, or the like.
Preferably, the secondary carbonization treatment in the step (3) is performed under an inert gas atmosphere selected from any one of a nitrogen gas atmosphere, a helium gas atmosphere, a neon gas atmosphere, an argon gas atmosphere, a krypton gas atmosphere, a xenon gas atmosphere, or a radon gas atmosphere, or a mixed atmosphere of at least two kinds thereof.
Preferably, the rate of temperature increase from the primary carbonization temperature to the secondary carbonization temperature is 3 ℃/min to 10 ℃/min, such as 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 8 ℃/min, 9 ℃/min, or 10 ℃/min, and the like.
Preferably, the holding time of the secondary carbonization treatment in the step (3) is 1h to 4h, such as 1h, 2h, 3h or 4 h.
Preferably, the method further comprises the step of cooling and sieving after the secondary carbonization treatment.
In a second aspect, the present invention provides a negative electrode, including the graphite material prepared by the method in the first aspect, where the graphite material is a graphite material with a porous surface or a graphite material with a nitrogen-doped porous layer on the surface.
In a third aspect, the present invention provides a lithium ion battery comprising the negative electrode of the second aspect.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a modification method of graphite, which comprises the steps of (1) coating a modifier on the surface of a graphite raw material, carrying out carbonization treatment in the step (2), reacting the modifier with the graphite raw material to generate CO, and enabling CO to escape to have an etching effect on the surface of the graphite raw material, so that porous carbon with an integral structure is formed on the surface.
The graphite material with the porous surface prepared by the method has the advantages that the porous structure is beneficial to lithium ions entering the graphite layer from the pores of the base surface, the rate capability of the graphite is greatly improved, the electronic conductivity of the graphite material is improved by the porous structure, and the graphite material is used as a negative electrode material to be applied to a lithium ion battery, so that the graphite material has the advantages of high rate capability and excellent dynamic performance.
According to the preferred technical scheme, the graphite material with the porous surface is mixed with the nitrogen-doped raw material and subjected to secondary carbonization treatment, so that nitrogen doping of the porous carbon on the surface of the graphite material can be realized, and the graphite material with the nitrogen-doped porous layer on the surface is obtained.
The method can realize the regulation and control of the thickness of the porous carbon and the nitrogen doping amount in the porous carbon by controlling the dosage of the modifier and the nitrogen doping raw material and the technological parameters of the primary carbonization treatment and the secondary carbonization treatment. The method is simple and suitable for industrial production.
Drawings
FIG. 1 is a schematic view of a graphite material having a nitrogen-doped porous layer on the surface thereof.
Fig. 2 SEM of graphitic material with a nitrogen-doped porous layer on the surface.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1:
(1) potassium hydroxide was mixed with artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm394 percent of graphitization degree) according to the weight ratio of 15:85, placing the uniformly mixed mixture into a pushed slab kiln, and heating to the temperature of 3 ℃/min in the nitrogen atmosphereCarbonizing at 900 ℃, preserving heat for 4h, and naturally cooling to obtain a graphite material with a porous surface;
(2) VC mixing is carried out on the graphite material with porous surface and ammonium chloride according to the mass ratio of 90:10, the mixture is put into a pushed slab kiln for carbonization, the temperature is raised to 1100 ℃ at the temperature raising speed of 5 ℃/min under the nitrogen atmosphere, the carbonization time is 5h, and the finished product is obtained after natural temperature reduction and sieving.
Example 2:
(1) sodium carbonate and artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm3VC is uniformly mixed according to the weight ratio of 20:80, the uniformly mixed mixture is put into a rotary furnace, the temperature is increased to 1000 ℃ at the heating rate of 4 ℃/min under the nitrogen atmosphere for carbonization, the temperature is kept for 2h, and the graphite material with porous surface is obtained after natural cooling;
(2) VC mixing is carried out on the graphite material with porous surface and ammonium chloride according to the mass ratio of 85:15, the mixture is put into a rotary furnace for carbonization, the temperature is raised to 1200 ℃ at the temperature raising speed of 5 ℃/min under the argon atmosphere, the carbonization time is 1.5h, and the finished product is obtained after natural temperature reduction and sieving.
Example 3:
(1) uniformly mixing potassium hydroxide and artificial graphite secondary particles (the specific surface area is 1.2, the 5T compacted density is 2.06, and the graphitization degree is 94%) with the particle size d50 of 18 mu m according to the weight ratio of 25:75 by VC, putting the uniformly mixed mixture into a rotary furnace, heating to 800 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere for carbonization, preserving heat for 5h, and naturally cooling to obtain a graphite material with a porous surface;
(2) VC mixing is carried out on a graphite material with a porous surface and urea according to a mass ratio of 80:20, the mixture is put into a rotary furnace for carbonization, the temperature is raised to 1000 ℃ at a temperature rise speed of 5 ℃/min under the argon atmosphere, the carbonization time is 4h, and the finished product is obtained after natural cooling and sieving.
Example 4:
(1) uniformly mixing potassium hydroxide and natural graphite secondary particles (the specific surface area is 1.80, the 5T compacted density is 2.15, and the graphitization degree is 96.2%) with the particle size d50 of 17 mu m according to the weight ratio of 5:95 by VC, putting the uniformly mixed mixture into a rotary furnace, heating to 850 ℃ at the heating rate of 4 ℃/min in the nitrogen atmosphere for carbonization, preserving heat for 5h, and naturally cooling to obtain a graphite material with a porous surface;
(2) VC mixing is carried out on the graphite material with porous surface and ammonium chloride according to the mass ratio of 92:8, the mixture is put into a rotary furnace for carbonization, the temperature is raised to 1250 ℃ at the temperature raising speed of 10 ℃/min under the argon atmosphere, the carbonization time is 2h, and the finished product is obtained after natural temperature reduction and sieving.
Example 5:
(1) potassium hydroxide was mixed with artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm3And the graphitization degree is 94%) according to the weight ratio of 10:90, uniformly mixing the VC, putting the uniformly mixed mixture into a pushed slab kiln, heating to 900 ℃ at the heating rate of 3 ℃/min under the nitrogen atmosphere for carbonization, preserving heat for 4h, and naturally cooling to obtain the graphite material with porous surface.
Example 6:
the difference from example 1 is that the mass ratio of potassium hydroxide to artificial graphite secondary particles was 0.1: 99.9.
Example 7:
the difference from example 1 is that the mass ratio of potassium hydroxide to artificial graphite secondary particles was 40: 60.
Example 8:
the difference from example 1 is that the mass ratio of the graphite material with porous surface to the ammonium chloride is 99.9: 0.1.
Example 9:
the difference from example 1 is that the mass ratio of the graphite material with porous surface to the ammonium chloride is 50: 50.
Comparative example 1:
ammonium chloride and artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm394 percent of graphitization degree) according to the mass ratio of 10:90, placing the mixture into a pushed slab kiln for carbonization, and raising the temperature at the speed of 5 ℃/min in nitrogen atmosphereHeating to 1100 deg.C, carbonizing for 5 hr, naturally cooling, and sieving to obtain the final product.
Comparative example 2:
the difference from example 1 is that the temperature for carbonization in step (1) is 550 ℃.
Comparative example 3:
the difference from example 1 is that the temperature for carbonization in step (1) was 1300 ℃.
And (3) testing:
firstly, specific surface area test:
and testing by using a full-automatic nitrogen adsorption specific surface area tester.
Secondly, testing the compaction density:
and testing by using a compression and bending integrated testing machine.
Thirdly, testing electrochemical performance:
and (3) carrying out button cell test on the prepared negative pole piece, assembling the cell in an argon glove box, and carrying out test by taking a metal lithium piece as a negative pole and 1mol/L LiPF as electrolyte6+ EC + EMC, the diaphragm is a polyethylene/propylene composite microporous membrane, the electrochemical performance is carried out on a Xinwei battery test cabinet (5V,1A), the charging and discharging voltage is 0.01-1.5V, the charging and discharging speed is 0.1C, and the buckling capacitance and the first coulombic efficiency are tested.
TABLE 1
Figure BDA0002610678380000091
Figure BDA0002610678380000101
Comparing examples 6-7 with example 1, it can be seen that the quality ratio of the modifier to the graphite raw material has an important influence on the product structure and performance, and compared with example 1, in example 6, the use amount of KOH is too small, the generated CO is insufficient, the etching is insufficient, the pore distribution is not uniform, and the capacity and 5C reversible capacity are reduced; in example 7, compared to example 1, the use amount of KOH was too large, so that the generated CO was too large, the reaction was severe, the specific surface area was increased, and the first effect was reduced.
Comparing examples 8-9 with example 1, it can be seen that the mass ratio of the nitrogen-doped raw material to the graphite material with porous surface has an important influence on the structure and performance of the product. Example 8 compared to example 1, the amount of ammonium chloride used was too small and NH was generated3The defects result in uneven nitrogen doping, slightly reduced capacity and initial coulombic efficiency, and obvious degradation of 5C reversible capacity; example 9 excess ammonium chloride relative to example 1 produced NH3Too much defects are caused, the specific surface area is large, the capacity is improved, the first effect is reduced, and the 5C reversible capacity is reduced.
Comparative example 1 no pore-forming was performed on the graphite surface but nitrogen doping was directly performed on graphite with ammonium chloride, and since there was no porous carbon coating and only N doping, the compaction density was reduced and the 5C reversible capacity was significantly deteriorated.
Comparison of comparative example 2 with example 1 shows that the temperature of primary carbonization is too low, which results in incomplete decomposition of carbon dioxide into CO, insufficient pore formation, slight decrease in capacity and primary coulombic efficiency, and significant deterioration of 5C reversible capacity.
Comparison of comparative example 3 with example 1 shows that the primary carbonization temperature is too high, the reaction is severe, and pore formation is not uniform, resulting in significant deterioration of the 5C reversible capacity.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (10)

1. A method for modifying graphite, comprising the steps of:
(1) mixing a graphite raw material and a modifier to obtain a mixture;
(2) carrying out primary carbonization treatment on the mixture obtained in the step (1) at the carbonization temperature of 700-1100 ℃ in an inert atmosphere to obtain a graphite material with a porous surface;
the modifier is a substance which can react with the graphite raw material at the primary carbonization temperature to generate CO.
2. The modification method according to claim 1, wherein the graphite raw material of step (1) comprises artificial graphite and/or natural graphite, preferably the artificial graphite comprises petroleum coke artificial graphite and/or needle coke artificial graphite;
preferably, the average particle size of the graphite raw material in the step (1) is 5-25 μm;
preferably, the specific surface area of the graphite raw material in the step (1) is less than or equal to 5m2/g；
Preferably, the graphite raw material of the step (1) has a 5T compaction density of more than 2.0g/cm3；
Preferably, the graphitization degree of the graphite raw material in the step (1) is more than 90%.
3. The modification method according to claim 1 or 2, wherein the modifier of step (1) comprises at least one of potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate and calcium carbonate;
preferably, the mass ratio of the modifier to the graphite raw material in the step (1) is 0.2:9.8-3:7, preferably 1.2:8.8-2.4: 7.6.
4. The modification method according to any one of claims 1 to 3, wherein the inert atmosphere in the step (2) is selected from any one of a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, an argon atmosphere, a krypton atmosphere, a xenon atmosphere, or a radon atmosphere, or a mixed atmosphere of at least two thereof;
preferably, the heating rate of heating to the primary carbonization temperature is 3-10 ℃/min;
preferably, the heat preservation time of the primary carbonization treatment in the step (2) is 1h-5 h.
5. The modification method according to any one of claims 1 to 4, characterized in that the method further comprises performing step (3) after step (2): mixing the graphite material with the porous surface in the step (2) with a nitrogen-doped raw material, heating to a secondary carbonization temperature, and performing secondary carbonization treatment to obtain a graphite material with a nitrogen-doped porous layer on the surface;
the nitrogen-doped raw material can generate NH at the secondary carbonization temperature3The substance of (1).
6. The modification method according to claim 5, wherein in the step (3), the nitrogen-doped raw material comprises at least one of ammonium chloride, urea and melamine;
preferably, in the step (3), the mass ratio of the nitrogen-doped raw material to the graphite material with porous surface is 0.2:9.8-3:7, preferably 1:9-2: 8.
7. The modification method according to claim 5 or 6, wherein the secondary carbonization temperature in the step (3) is 800 ℃ to 1300 ℃;
preferably, the secondary carbonization treatment in the step (3) is performed under an inert atmosphere selected from any one of a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, an argon atmosphere, a krypton atmosphere, a xenon atmosphere, or a radon atmosphere, or a mixed atmosphere of at least two of them;
preferably, the heating rate of heating from the primary carbonization temperature to the secondary carbonization temperature is 3 ℃/min-10 ℃/min;
preferably, the heat preservation time of the secondary carbonization treatment in the step (3) is 1h-4 h.
8. The method according to any one of claims 5 to 7, further comprising the step of cooling and sieving after the secondary carbonization treatment.
9. A negative electrode comprising the graphite material prepared by the method according to any one of claims 1 to 8, wherein the graphite material is a graphite material with a porous surface or a graphite material with a porous layer doped with nitrogen on the surface.
10. A lithium ion battery, characterized in that it comprises the negative electrode of claim 9.
CN202010753216.0A 2020-07-30 2020-07-30 Modification method of graphite and application of graphite in lithium ion battery Pending CN114068923A (en)

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