CN113871601B - Graphite material and preparation method thereof, negative plate and lithium ion battery - Google Patents

Graphite material and preparation method thereof, negative plate and lithium ion battery Download PDF

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CN113871601B
CN113871601B CN202111142564.5A CN202111142564A CN113871601B CN 113871601 B CN113871601 B CN 113871601B CN 202111142564 A CN202111142564 A CN 202111142564A CN 113871601 B CN113871601 B CN 113871601B
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particles
primary particles
graphite
carbon
carbon coating
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CN113871601A (en
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张保海
彭冲
李俊义
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • 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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a graphite material and a preparation method thereof, a negative plate and a lithium ion battery, wherein the graphite material graphite provided by the invention comprises the following components: secondary particles C and primary particles D; the secondary particles C and the primary particles D are carbon-coated graphite particles, the graphite particles in the secondary particles C and the graphite particles in the primary particles D have pore channel structures, and the number of carbon-coated layers of the secondary particles C is larger than that of the primary particles D. The secondary particles C and the primary particles D are coated with carbon, so that the dynamic performance of the material is improved. Meanwhile, the mixing of the secondary particles C and the primary particles D can effectively improve the compaction. The graphite particles in the secondary particles C and the primary particles D both have pore channel structures, so that the self expansion of graphite is reduced, the increase of pores also effectively increases lithium ion embedding channels, and the dynamic performance of the graphite is improved.

Description

Graphite material and preparation method thereof, negative plate and lithium ion battery
Technical Field
The invention relates to the technical field of batteries, in particular to a graphite material and a preparation method thereof, a negative plate and a lithium ion battery.
Background
With the rapid development of society, the technology of lithium ion batteries is also rapidly developed, and people have more and more demands on miniature electronic devices and portable electronic products. The lithium ion battery used by the precise electronic equipment is required to have the performance of small deformation, so that the precise electronic equipment cannot influence other parts of the precise electronic equipment due to factors such as expansion and deformation of the lithium ion battery in the long-term use process. The cathode material is an important component of the lithium ion battery, and has important influence on the cycle performance and the expansion performance of the battery. The artificial graphite has a complete layered structure characteristic, is beneficial to the intercalation/deintercalation reaction of lithium ions, has a lower lithium intercalation potential and higher energy density, has a theoretical specific capacity of 372mAh/g and an actual specific capacity of 360mAh/g, and is one of important lithium ion battery cathode materials. However, the traditional graphite has small interlayer diffusion coefficient and poor high-current charge and discharge performance. In the process of cyclic charge and discharge, the distance between graphite layers is increased, lithium ions and an organic solvent are embedded between the graphite layers, the graphite layers are easy to peel off, the negative electrode material is pulverized, the self expansion of the lithium ion battery is increased, the service life of the lithium ion battery is influenced, the use of precise electronic equipment is influenced, and the use of artificial graphite in partial lithium ion batteries is limited. Therefore, the problem that the conventional artificial graphite is integrally modified to improve the charge-discharge performance and the expansion performance of the artificial graphite so as to meet the practical requirement of the lithium ion battery cathode material in the field of lithium ion batteries is urgently needed to be solved.
Disclosure of Invention
In view of the above, the invention provides a graphite material and a preparation method thereof, a negative plate and a lithium ion battery.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a graphitic material comprising:
secondary particles C and primary particles D;
the secondary particles C and the primary particles D are carbon-coated graphite particles, the graphite particles in the secondary particles C and the graphite particles in the primary particles D both have pore channel structures, and the number of carbon-coated layers of the secondary particles C is larger than that of the primary particles D.
Further, the mass ratio of the secondary particles C to the primary particles D is 9:1 to 4:6.
further, the carbon coating amount of the secondary particles C is 3 to 20wt.%; and/or the carbon coating amount of the primary particles D is 1 to 4wt.%.
Further, the D50 of the secondary particles C is 9-17 μm, and the length-diameter ratio is 0.8-1.7; and/or the D50 of the primary particles D is 4-10 μm, and the length-diameter ratio is 0.9-3.
Further, the secondary particles are obtained by bonding a plurality of primary particles B and performing carbon coating, and the primary particles D are obtained by directly carbonizing the primary particles B.
Further, the surfaces of the secondary particles C and the primary particles D contain functional groups including C — O; c = C; C-F; C-N; c = N.
Further, the structure of the primary particles D is graphite and a carbon coating layer coated on the surface of the graphite, and the thickness of the carbon coating layer is 3-10nm;
the secondary particle C is structurally composed of graphite, a first carbon coating layer coated on the surface of the graphite, and a second carbon coating layer coated on the surface of the first carbon coating layer, wherein the thickness of the first carbon coating layer is 3-10nm, and the thickness of the second carbon coating layer is 7-13nm.
Further, the graphitization degree of the primary particles D is 95% -98%; the graphitization degree of the secondary particles C is 91-96%.
In a second aspect, the present invention provides a method for preparing a graphite material, the method comprising: carrying out pre-expansion and pore-forming treatment on the raw material coke to obtain pre-treated coke; carrying out pre-carbonization treatment and carbonization on the pre-treated coke to obtain calcined coke, and crushing the calcined coke to obtain primary particles A, wherein the D50 of the primary particles A is 4-12 mu m, and the length-diameter ratio is 0.9-3; coating, carbonizing and screening the primary particles A by using a carbon material to obtain primary particles B; mixing, granulating, carbonizing and screening the primary particles B and a carbon source-containing carbonizable binder to obtain double-layer carbon-coated secondary particles C; carbonizing the primary particles B to obtain primary particles D; taking the secondary particles C and the primary particles D according to the mass ratio of 9:1 to 4:6, mixing to obtain the graphite material.
Further, the raw material coke comprises at least one of needle coke, petroleum coke, and pitch coke; and/or the carbon material comprises at least one of soft carbon, hard carbon, organic carbon; and/or the binder containing the carbon source and capable of being carbonized comprises asphalt micro powder, petroleum asphalt, coal pitch, phenolic resin, polyvinyl chloride and polystyrene.
Further, after the secondary particles C and the primary particles D are mixed, introducing mixed gas of nitrogen, argon and carbon tetrafluoride for high-temperature heat treatment to obtain a graphite material, wherein the temperature of the high-temperature heat treatment is 700-900 ℃.
Further, the carbon material is used in an amount of 3 to 6wt.% based on the amount of the primary particles a; and/or the carbon coating amount of the primary particles B is 1 to 4wt.%.
Further, the dosage of the binder containing carbon source and capable of carbonizing is 10-30 wt.%; and/or the secondary particles C have a carbon coating amount of 3 to 20wt.%.
Further, the pre-carbonization treatment of the pre-treated coke is as follows: calcining the pretreated coke at 400-650 ℃ for 3-10 h; the carbonization treatment of the pretreatment coke comprises the following steps: calcining the pretreated coke at 1400-1600 ℃ for 3-10 h after the pretreatment of carbonization; and/or the carbon material coats and carbonizes the primary particles A: mixing the carbon material with the primary particles A, and calcining at 800-1500 ℃ for 7-12 h; the primary particles B and the binder containing the carbon source and capable of being carbonized are subjected to granulation and carbonization treatment as follows: granulating the primary particles B and a binder containing a carbon source and capable of being carbonized, and calcining at 2800-3500 ℃ for 15-38 h; the treatment of carbonizing the primary particles B to obtain primary particles D comprises the following steps: calcining the primary particles B at 2800-3500 ℃ for 8-17 h.
In a third aspect, the present invention provides a negative electrode sheet comprising the graphite material described above.
Further, the thickness H of the negative electrode sheet and the D50 of the graphite material satisfy the following relationship: D50/H =0.20 to 0.28.
In a fourth aspect, the invention provides a lithium ion battery, and the lithium ion battery comprises the above negative electrode sheet.
The technical scheme of the invention has the following beneficial effects:
the present invention provides a graphite material comprising: secondary particles C and primary particles D; the secondary particles C and the primary particles D are carbon-coated graphite particles, the graphite particles in the secondary particles C and the graphite particles in the primary particles D both have pore channel structures, and the number of carbon-coated layers of the secondary particles C is larger than that of the primary particles D.
(1) The graphite particles in the secondary particles C and the primary particles D provided by the invention have pore channel structures, so that the expansion of graphite can be reduced, and meanwhile, the increase of pores can also effectively increase lithium ion insertion channels and improve the dynamic performance of graphite.
(2) The carbon coating of the primary particles D can improve the dynamic properties of the material.
(3) The secondary particles C are obtained by bonding a plurality of primary particles B and performing carbon coating again, so that on one hand, the carbon coating amount of the particles can be increased by performing the second carbon coating, and the dynamic performance of the material is further improved; on the other hand, a plurality of primary particles B are bonded together, which can further reduce the expansion rate of the material.
(4) The primary particles D with small particle size are filled between the secondary particles C with large particle size, so that the compaction can be improved, and the graphite material with high compaction, low expansion and high dynamic balance is manufactured.
(5) The graphite material prepared by the invention can be used as the negative active material of the lithium ion battery, so that the problem of expansion and deformation of the lithium ion battery can be effectively solved, and the cycle life of the lithium ion battery is prolonged.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention in conjunction with the following examples, but it will be understood that the description is intended to illustrate the features and advantages of the invention further, and not to limit the invention.
In a first aspect, the present invention provides a graphitic material comprising: secondary particles C and primary particles D; the secondary particles C and the primary particles D are carbon-coated graphite particles, the graphite particles in the secondary particles C and the graphite particles in the primary particles D have pore channel structures, and the number of carbon-coated layers of the secondary particles C is larger than that of the primary particles D.
According to some embodiments of the invention, the mass ratio of the secondary particles C to the primary particles D is 9:1 to 4:6.
according to some embodiments of the invention, the secondary particle C has a carbon coating in an amount of 3 to 20wt.%; and/or the carbon coating amount of the primary particles D is 1 to 4wt.%.
According to some embodiments of the invention, the secondary particles C have a D50 of 9 to 17 μm and an aspect ratio of 0.8 to 1.7; and/or the D50 of the primary particles D is 4-10 μm, and the length-diameter ratio is 0.9-3.
According to some embodiments of the invention, the surface of the secondary particles C and the primary particles D contain functional groups, including C-O; c = C; C-F; C-N; c = N.
The graphite material provided by the invention comprises secondary particles C and primary particles D, wherein the graphite particles in the secondary particles C and the primary particles D have pore structures, so that the expansion of graphite can be reduced, and meanwhile, the increase of pores can also effectively increase lithium ion intercalation channels and improve the dynamic performance of the graphite. The carbon coating layer of the primary particles D can improve the dynamic properties of the material. The secondary particles C are obtained by bonding a plurality of primary particles B and performing carbon coating again, so that on one hand, the carbon coating amount of the particles can be increased by performing the second carbon coating, and the dynamic performance of the material is further improved; on the other hand, a plurality of primary particles B are bonded together, which can further reduce the expansion rate of the material. According to the invention, the primary particles D with small particle size are filled between the secondary particles C with large particle size, so that the compaction can be improved, and the graphite material with high compaction, low expansion and high kinetics is manufactured. Finally, the surface of the graphite material contains C-O; c = C; C-F; C-N; and C = N functional groups and the like are favorable for electron transport and ion migration, so that the dynamic performance of the graphite is improved.
According to some embodiments of the present invention, the primary particle D has a structure of graphite and a carbon coating layer coated on a surface of the graphite, and a thickness of the carbon coating layer is 3 to 10nm;
the secondary particle C is structurally composed of graphite, a first carbon coating layer coated on the surface of the graphite, and a second carbon coating layer coated on the surface of the first carbon coating layer, wherein the thickness of the first carbon coating layer is 3-10nm, and the thickness of the second carbon coating layer is 7-13nm.
According to some embodiments of the invention, the degree of graphitization of the primary particles D is 95% to 98%; the graphitization degree of the secondary particles C is 91-96%.
In a second aspect, the present invention provides a method for preparing a graphite material, the method comprising:
carrying out pre-expansion and pore-forming treatment on the raw material coke to obtain pre-treated coke; carrying out pre-carbonization treatment and carbonization on the pre-treated coke to obtain calcined coke, and crushing the calcined coke to obtain primary particles A, wherein the D50 of the primary particles A is 4-10 mu m, and the length-diameter ratio is 0.9-3; coating, carbonizing and screening the primary particles A by using a carbon material to obtain primary particles B; mixing, granulating, carbonizing and screening the primary particles B and a carbon source-containing carbonizable binder to obtain double-layer carbon-coated secondary particles C; carbonizing the primary particles B to obtain primary particles D; taking the secondary particles C and the primary particles D according to the mass ratio of 9:1 to 4:6, mixing to obtain the graphite material.
Specifically, the method for preparing the graphite material provided by the invention has the following effects: the method comprises the steps of pre-expanding and pore-forming the raw material coke, and then pre-carbonizing, carbonizing and crushing the raw material coke to obtain the primary particles A. In addition, the invention also limits the primary particles A with the D50 of 4-10 mu m and the length-diameter ratio of 0.9-3 to be screened, so the particle size of the primary particles A is limited, mainly the secondary coating is needed in the subsequent process, and the secondary coating is not facilitated when the particles are too large or too small, so the expansion rate of the graphite is further reduced. After the primary particles A are obtained again, the carbon material is used for coating and carbonizing the primary particles A to obtain the primary particles B, and the purpose is mainly to improve the dynamic performance of the material through carbon coating. The method for secondary coating in the invention comprises the following steps: and mixing, granulating, carbonizing and screening the primary particles B and a carbonizable binder containing a carbon source to obtain double-layer carbon-coated secondary particles C. The secondary coating is mainly performed because the amount of the first carbon coating is small, and the secondary coating is performedThe carbon coating amount of the particles can be increased by performing the second carbon coating, so that the dynamic performance of the material is further improved; on the other hand, after the primary particles B are granulated by a binder containing a carbon source and being carbonizable, a plurality of the primary particles B are bonded together, and the expansion rate of the material can be further reduced. And finally, mixing the secondary particles C and the primary particles D according to a mass ratio of 9:1 to 4:6, mixing, filling the primary particles D with small particle size into the secondary particles C with large particle size, and improving compaction, thereby preparing the graphite with high compaction, low expansion and high dynamic balance. The graphite material prepared by the method has the particle size distribution of 3 mu m<D10<7μm，9μm<D50<16μm，19μm<D90<27 μm; the carbon coating amount is 15-25 wt.%; DET =1 to 2.5m 3 /g。
According to some embodiments of the invention, the method for pre-expanding and pore-forming the raw material coke comprises the following steps: and (3) carrying out pre-expansion and pore-forming treatment on the raw material coke of the artificial graphite by using a mixed solution of ammonia water and sodium chloride to obtain the pre-treated coke. The concentration of the mixed solution of the ammonia water and the sodium chloride is 1mol/L, wherein the ammonia water: the mass ratio of sodium chloride is 3:7 to 7:3, preferably 4:6.
according to some embodiments of the invention, the raw material coke comprises at least one of needle coke, petroleum coke and pitch coke, and/or the carbon-containing source carbonizable binder comprises pitch micropowder, petroleum pitch, coal pitch, phenolic resin, polyvinyl chloride, polystyrene. In the present invention, the raw material coke is preferably needle coke, and the binder containing a carbon source that can be carbonized is preferably pitch micropowder.
According to some embodiments of the invention, the pre-carbonization treatment of the pre-coke is: calcining the pretreated coke at 400-650 ℃ for 3-10 h; the carbonization treatment of the pretreatment coke comprises the following steps: the pre-treated coke is calcined at 1400-1600 ℃ for 3-10 h after being pre-carbonized to obtain calcined coke, and the calcined coke is crushed to obtain primary particles A, wherein the D50 of the primary particles A is 4-12 mu m, and the length-diameter ratio is 0.9-3.
According to some embodiments of the invention, the carbon material coats and carbonizes the primary particles a by: the carbon material is mixed with the primary particles A and then calcined at 800-1500 ℃ for 7-12 h.
According to some embodiments of the invention, the carbon material is present in an amount of 3 to 6wt.% of the primary particles a; and/or the carbon coating amount of the primary particles B is 1 to 4wt.%.
According to some embodiments of the invention, the carbon material comprises at least one of soft carbon, hard carbon, organic carbon.
According to some embodiments of the invention, the primary particles B and the carbon-source-containing carbonizable binder are granulated and carbonized by: granulating the primary particles B and a binder containing a carbon source and capable of being carbonized, and calcining at 2800-3500 ℃ for 15-38 h; and screening to obtain the double-layer carbon-coated secondary particles C. In the invention, the primary particles A are coated for the first time to obtain the primary particles B, but the carbon coating amount of the primary particles is less, and the secondary particles C can be coated for the second time after being granulated and carbonized with a caking agent containing a carbon source and capable of being carbonized. The carbon coating amount of the secondary particles C is increased, and the improvement of the dynamic performance is facilitated. Meanwhile, after the primary particles B are granulated by the carbon source-containing carbonizable binder, a plurality of the primary particles B are bonded together, so that the expansion rate of the material can be further reduced.
According to some embodiments of the invention, the carbon-containing source carbonizable binder is used in an amount of 10 to 30wt.%; and/or the amount of carbon coating of the secondary particles C is 3 to 20wt.%.
According to some embodiments of the invention, the carbonization of the primary particles B to obtain primary particles D is carried out by: and calcining the primary particles B at 2800-3500 ℃ for 8-17 h to obtain primary particles D.
According to some embodiments of the invention, the secondary particles C and the primary particles D are in a mass ratio of 9:1 to 4:6, mixing the secondary particles C with the primary particles D, and introducing a mixed gas of nitrogen, argon and carbon tetrafluoride for high-temperature heat treatment to obtain a graphite material, wherein the temperature of the high-temperature heat treatment is 700-900 ℃. In the present invention, the mass ratio of the secondary particles C to the primary particles D is 9:1 to 4: the advantage of 6 mixing is that it improves both compaction and kinetic performance. The purpose of introducing mixed gas of nitrogen, argon and carbon tetrafluoride for high-temperature heat treatment is as follows: and modifying the surface functional groups of the mixture of the secondary particles C and the primary particles D, wherein the nitrogen, the argon and the carbon tetrafluoride are mixed according to the volume ratio of 5:3:2, mixing, wherein the surface of the finally obtained graphite material contains C-O; c = C; C-F; C-N; and C = N functional groups and the like are favorable for electron transmission and ion migration, so that the dynamic performance of the graphite is improved.
In a third aspect, the present invention provides a negative electrode sheet, which includes the graphite material described above.
According to some embodiments of the present invention, the thickness H of the negative electrode sheet and the D50 of the graphite material satisfy the following relationship: D50/H =0.20 to 0.28. In the present invention, D50 of the graphite material and the thickness H of the negative electrode sheet satisfy the following relationship: in a fresh battery (full state) which is charged and discharged for the first time, the relation between the D50 particle size and the pole piece thickness H meets the requirement that D50/H = 0.20-0.28, and the pole piece thickness in the circulation process meets the following relation: 50T cycle (full power) D50 (50T)/H (50T) =0.25 to 0.32, and 200T cycle D50 (200T)/H (200T) =0.29 to 0.35.
In a fourth aspect, the invention provides a lithium ion battery, and the lithium ion battery comprises the above negative electrode sheet. The invention designs and manufactures a graphite material with high capacity, high compaction, low expansion, high multiplying power and long cycle life by starting from the raw material and the preparation process of graphite, and the graphite material serving as the negative active material of the lithium ion battery can effectively solve the problem of expansion deformation of the lithium ion battery, thereby improving the cycle life of the lithium ion battery.
The invention is further illustrated by the following specific examples.
Example 1
(1) Taking needle coke as raw material coke for preparing graphite, and preparing a mixed solution of 1mol/L ammonia water and sodium chloride, wherein the ammonia water: the mass ratio of the sodium chloride is 4:6. and soaking the needle coke in the mixed solution of the ammonia water and the sodium chloride for 24 hours, and then drying to obtain the pretreated needle coke.
(2) Calcining the needle coke pretreated in the step (1) at 500 ℃ for 5 hours for pre-carbonization treatment; then, solid-phase carbonization treatment is carried out for 5 hours under the condition of calcination at 1450 ℃, and calcined needle coke is obtained. And then crushing and screening the calcined needle coke to obtain primary particles A, wherein the average particle diameter D50 of the primary particles A is 7 microns, and the length-diameter ratio of the primary particles A is 0.9-1.5.
(3) And (3) mixing the primary particles A prepared in the step (2) with hard carbon by taking the hard carbon as a porous carbon material, wherein the using amount of the hard carbon is 2wt.%, carbonizing and coating the mixture of the primary particles A and the hard carbon at 1100 ℃ for 8h, and crushing and screening the coated and carbonized substances to obtain the primary particles B.
(4) Mixing the primary particles B prepared in the step (3) with the asphalt micro powder by taking the asphalt micro powder as a carbonizable binder containing a carbon source, wherein the using amount of the asphalt micro powder is 18wt%; placing the mixture in a roller furnace for granulation, then carrying out high-temperature carbonization for 20h at 3000 ℃, and screening to obtain double-layer carbon-coated secondary particles C;
and (4) carbonizing the primary particles B prepared in the step (3) at the high temperature of 3000 ℃ for 12h to obtain primary particles D.
(5) And (3) mixing the secondary particles C and the primary particles D prepared in the step (4) according to a mass ratio of 7:3, then introducing a mixed gas of nitrogen, argon and carbon tetrafluoride (volume ratio is 5.
The graphite material prepared in this example had a particle size distribution D10=6 μm by particle size testing; d50=13 μm; d90=25 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 15wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.53m 3 /g。
Example 2
(1) Examples (1) to (2) are the same as examples (1) to (2) in example 1.
(3) And (3) mixing the primary particles A prepared in the step (2) with soft carbon by taking the soft carbon as a porous carbon material, wherein the using amount of the soft carbon is 2wt.%, then putting the mixture of the primary particles A and the hard carbon at 1100 ℃ for 8h for carbonization and coating, and crushing and screening the coated and carbonized substances to obtain primary particles B.
(4) Mixing the primary particles B prepared in the step (3) with the asphalt micro powder by taking the asphalt micro powder as a carbonizable binder containing a carbon source, wherein the using amount of the asphalt micro powder is 18wt%; placing the mixture in a roller furnace for granulation, then carrying out high-temperature carbonization for 20h at 3000 ℃, and screening to obtain double-layer carbon-coated secondary particles C;
and (4) carbonizing the primary particles B prepared in the step (3) at the high temperature of 3000 ℃ for 12h to obtain primary particles D.
(5) And (5) mixing the secondary particles C prepared in the step (4) with the primary particles D according to the mass ratio of 7:3, then introducing a mixed gas of nitrogen, argon and carbon tetrafluoride (volume ratio is 5.
The graphite material prepared in this example had a particle size distribution D10=6 μm by the particle size test; d50=13 μm; d90=25 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 15wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.83m 3 /g。
Example 3
(1) Taking needle coke as raw material coke for preparing graphite, and preparing a mixed solution of 1mol/L ammonia water and sodium chloride, wherein the ammonia water: the mass ratio of the sodium chloride is 4:6. the needle coke is put into the above-mentioned mixed solution of ammonia and sodium chloride, followed by drying to obtain pretreated needle coke.
(2) Calcining the needle coke pretreated in the step (1) at 500 ℃ for 5 hours for pre-carbonization treatment; then the solid-phase carbonization treatment is carried out for 5 hours at the temperature of 1450 ℃, and the calcined needle coke is obtained. And then crushing and screening the calcined needle coke to obtain primary particles A, wherein the average particle size D50 of the primary particles A is 9 mu m, and the length-diameter ratio of the primary particles A is 1.5-2.2.
(3) Examples (4) to (5) are the same as examples (4) to (5) in example 2.
The graphite material prepared in this example had a particle size distribution D10=7 μm by the particle size test; d50=15 μ ι η; d90=26 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 15wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.26m 3 /g。
Example 4
(1) Examples (1) to (2) are the same as examples (1) to (2) of example 1.
(3) And (3) mixing the primary particles A prepared in the step (2) with soft carbon by taking the soft carbon as a porous carbon material, wherein the using amount of the soft carbon is 5wt.%, carbonizing and coating the mixture of the primary particles A and the hard carbon at 1100 ℃ for 8h, and crushing and screening the coated and carbonized substances to obtain the primary particles B.
(4) Mixing the primary particles B prepared in the step (3) with pitch micro powder by taking the pitch micro powder as a carbonizable binder containing a carbon source, wherein the use amount of the pitch micro powder is 18wt%; placing the mixture in a roller furnace for granulation, then carrying out high-temperature carbonization for 20h at 3000 ℃, and screening to obtain double-layer carbon-coated secondary particles C;
and (4) carbonizing the primary particles B prepared in the step (3) at the high temperature of 3000 ℃ for 12h to obtain primary particles D.
(5) And (3) mixing the secondary particles C and the primary particles D prepared in the step (4) according to a mass ratio of 7:3, then introducing a mixed gas of nitrogen, argon and carbon tetrafluoride (volume ratio is 5.
The graphite material prepared in this example had a particle size distribution D10=6 μm by the particle size test; d50=13 μm; d90=25 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 16.5wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.39m 3 /g。
Example 5
(1) Taking needle coke as raw material coke for preparing graphite, and preparing a mixed solution of 1mol/L ammonia water and sodium chloride, wherein the ammonia water: the mass ratio of sodium chloride is 3:7. and soaking the needle coke in the mixed solution of the ammonia water and the sodium chloride for 24 hours, and then drying to obtain the pretreated needle coke.
(2) Calcining the needle coke pretreated in the step (1) at 500 ℃ for 5 hours for pre-carbonization treatment; then the solid-phase carbonization treatment is carried out for 5 hours at the temperature of 1450 ℃, and the calcined needle coke is obtained. And then crushing and screening the calcined needle coke to obtain primary particles A, wherein the average particle diameter D50 of the primary particles A is 7 microns, and the length-diameter ratio of the primary particles A is 0.9-1.5.
(3) Examples (4) to (5) are the same as examples (4) to (5) in example 2.
The graphite material prepared in this example had a particle size distribution D10=5 μm by the particle size test; d50=12 μ ι η; d90=23 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 15wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.67m 3 /g。
Example 6
(1) Examples (1) to (4) in example 2 are the same as examples (1) to (4).
(5) And (3) mixing the secondary particles C and the primary particles D prepared in the step (4) according to a mass ratio of 5: and 5, mixing, introducing a mixed gas of nitrogen, argon and carbon tetrafluoride (volume ratio is 5.
The graphite material prepared in this example had a particle size distribution D10=5.5 μm by particle size testing; d50=12.5 μm; d90=23 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was measured to be 13.5wt.%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.61m 3 /g。
Example 7
(1) Examples (1) to (4) in example 2 are the same as examples (1) to (4).
(5) And (3) mixing the secondary particles C and the primary particles D prepared in the step (4) according to a mass ratio of 5:5, mixing, and carrying out high-temperature heat treatment at 800 ℃ for 8h to obtain the graphite material.
The graphite material prepared in this example had a particle size distribution D10=6 μm by the particle size test; d50=13 μm; d90=25 μm.
The graphite material prepared in this example was tested for carbon coating, and the carbon coating of the graphite material prepared in this example was found to be 15.5%.
The graphite material prepared in this example was tested for carbon coating, and the graphite material prepared in this example had a BET =1.75m 3 /g。
Comparative example 1
(1) Examples (1) to (2) are the same as examples (2) of example 2.
(3) Mixing the primary particles A prepared in the step (2) with the pitch micro powder by taking the pitch micro powder as a carbonizable binder containing a carbon source, wherein the use amount of the pitch micro powder is 18wt%; placing the mixture in a roller furnace for granulation, then carrying out high-temperature carbonization for 8 hours at 3000 ℃, and screening to obtain double-layer carbon-coated secondary particles C1; and (3) carbonizing the primary particles A prepared in the step (2) at 3000 ℃ for 20h to obtain primary particles D1.
(4) Mixing the secondary particles C1 prepared in the step (3) with the primary particles D1 according to a mass ratio of 7:3, then introducing a mixed gas of nitrogen, argon and carbon tetrafluoride (volume ratio is 5.
The graphite material prepared in this comparative example had a particle size distribution D10=5 μm by particle size testing; d50=12 μ ι η; d90=23 μm.
The graphite material prepared in this comparative example was tested for carbon coating and was measured to have a carbon coating of 12.5wt.%.
The graphite material prepared in the comparative example was tested for the amount of carbon coating, and BET =1.1m was measured for the graphite material prepared in the comparative example 3 /g。
Comparative example 2
(1) Examples (1) to (2) are the same as examples (2) of example 2.
(3) And (3) carbonizing the primary particles A prepared in the step (2) at a high temperature of 3000 ℃ for 12 hours, and then carbonizing the carbonized substances, and crushing and screening the carbonized substances to obtain primary particles B2.
(4) And (4) mixing the primary particles B2 prepared in the step (3) with soft carbon by taking the soft carbon as a porous carbon material, wherein the using amount of the soft carbon is 3wt.%, carbonizing and coating the mixture of the primary particles B2 and the hard carbon at 1100 ℃ for 8h, and crushing and screening the coated and carbonized substances to obtain the graphite particles C2.
The graphite particles C2 prepared in this comparative example had a particle size distribution D10=7 μm by the particle size test; d50=14 μ ι η; d90=26 μm.
The graphite material prepared in this comparative example was tested for carbon coating, and the carbon coating of the graphite material prepared in this comparative example was measured to be 1.8wt.%.
The graphite material prepared in the comparative example was tested for the amount of carbon coating, and BET =0.95m was measured for the graphite material prepared in the comparative example 3 /g。
EXAMPLE 8 preparation of Battery
Preparing a negative plate: respectively taking the graphite particles prepared in the embodiments 1 to 7 and the comparative examples 1 to 2 as negative electrode active substances, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black, the styrene butadiene rubber and the sodium carboxymethyl cellulose into a stirring tank according to a mass ratio of 96.9; coating the negative electrode slurry on a copper foil current collector by using a double-layer coating machine, and drying at the temperature of 100 ℃ to prepare an initial negative electrode piece; and cutting the initial pole piece according to actual requirements to prepare the negative pole piece. The relationship between the graphite particles and the thickness H of the negative electrode sheet is shown in table 1.
Preparing a positive plate: lithium cobaltate is used as a positive electrode active material, then the positive electrode active material, a conductive agent and polyvinylidene fluoride are added into a stirring tank according to the mass ratio of 97.2 to 1.5, an NMP solvent is added, the materials are fully stirred according to the batching process in the prior art, and the materials are screened by a 200-mesh screen to prepare positive electrode slurry, wherein the solid content of the positive electrode slurry is 70-75%; coating the positive electrode slurry on an aluminum foil current collector by using a coating machine, and drying at the temperature of 120 ℃ to prepare an initial positive electrode piece; and cutting the initial pole piece according to actual requirements to prepare the positive pole piece.
Assembling the battery cell: and winding the positive plate, the negative plate and the diaphragm together to form a winding core, packaging by using an aluminum plastic film, baking to remove moisture, injecting electrolyte, and forming by adopting a hot-pressing formation process to obtain the battery core.
The battery cell assembled from the positive electrode sheets prepared in each example was subjected to 3C charging/0.7C cycling at 25 ℃, and the cycle life and energy density thereof were tested. The specific test method is as follows: using a blue test apparatus, a test cycle was performed 1000 times at 25 ℃ using 3C charging to the upper limit voltage, and then 0.7V discharging to 3.0V. The cycle life and swell data are shown in table 1.
Table 1 test results of lithium ion batteries provided in examples 1 to 7 and comparative examples 1 to 2
Figure BDA0003284533620000141
Figure BDA0003284533620000151
Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (8)

1. The negative plate is characterized in that the negative plate comprises a graphite material; the graphite material is characterized by comprising:
secondary particles C and primary particles D;
the secondary particles C and the primary particles D are carbon-coated graphite particles, the graphite particles in the secondary particles C and the primary particles D have pore channel structures, and the number of carbon-coated layers of the secondary particles C is larger than that of the primary particles D;
the thickness H of the negative electrode sheet and the D50 of the graphite material satisfy the following relation:
D50/H＝0.20～0.28。
2. the negative electrode sheet according to claim 1, wherein the mass ratio of the secondary particles C to the primary particles D is 9:1 to 4:6.
3. the negative electrode sheet according to claim 1, wherein the secondary particles C have a carbon coating amount of 3 to 20wt.%; and/or
The carbon coating amount of the primary particles D is 1-4 wt.%.
4. The negative electrode sheet according to claim 1, wherein the secondary particles C have a D50 of 9 to 17 μm, an aspect ratio of 0.8 to 1.7; and/or
The D50 of the primary particles D is 4-10 mu m, and the length-diameter ratio is 0.9-3.
5. The negative electrode sheet according to claim 1, wherein the surfaces of the secondary particles C and the primary particles D contain functional groups, the functional groups including C — O; c = C; C-F; C-N; c = N.
6. The negative electrode sheet according to claim 1, wherein the primary particles D have a structure of graphite and a carbon coating layer coated on the surface of the graphite, and the thickness of the carbon coating layer is 3 to 10nm; and/or
The secondary particle C is structurally composed of graphite, a first carbon coating layer coated on the surface of the graphite, and a second carbon coating layer coated on the surface of the first carbon coating layer, wherein the thickness of the first carbon coating layer is 3-10nm, and the thickness of the second carbon coating layer is 7-13nm.
7. The negative electrode sheet according to claim 6, wherein the graphitization degree of the primary particles D is 95% to 98%; the graphitization degree of the secondary particle C is 91-96%.
8. A lithium ion battery, characterized in that the lithium ion battery comprises the negative electrode sheet of claim 1.
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