CN112436125A - Composite material for negative pole piece and preparation method and application thereof - Google Patents

Composite material for negative pole piece and preparation method and application thereof Download PDF

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CN112436125A
CN112436125A CN202011379480.9A CN202011379480A CN112436125A CN 112436125 A CN112436125 A CN 112436125A CN 202011379480 A CN202011379480 A CN 202011379480A CN 112436125 A CN112436125 A CN 112436125A
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boron
composite material
phenolic resin
doped
heating
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CN112436125B (en
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赵晓锋
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Svolt Energy Technology Co Ltd
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Svolt Energy 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/205—Preparation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B35/00—Boron; Compounds thereof
    • C01B35/02—Boron; Borides
    • C01B35/023—Boron
    • 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
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • H01M2004/021—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
    • 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 composite material for a negative pole piece, a preparation method and application thereof, wherein the composite material comprises an inner core and an outer shell; the core is graphite, the shell is a boron-doped hard carbon coating layer, the shell and the core form a composite material through chemical bonding, the compaction density of the material can be improved, the transmission of lithium ions is facilitated, the gram capacity exertion of the material is improved, the first efficiency of the battery can be further improved when the composite material is applied to the lithium ion battery, the structural stability of the composite material is good, the structural damage effect of a circulation process on the material is small, the structure is stable, and therefore the circulation performance of the lithium ion battery can be greatly improved.

Description

Composite material for negative pole piece and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a composite material for a negative electrode plate, and a preparation method and application thereof.
Background
At present, with the improvement of the energy density and rate capability requirement of the graphite in the market, the graphite cathode material is required to have high energy density and higher rate capability and safety performance. 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 discloses a graphite-hard carbon-coated material and a preparation method thereof, wherein graphite and oligomeric phenolic resin are mixed and then cured and pyrolyzed to realize in-situ coating of graphite and hard carbon. According to the invention, phenolic resin is pyrolyzed to prepare hard carbon, and the obtained hard carbon is coated on the surface of a graphite material to prepare the negative electrode material with high specific capacity. However, the soft carbon or hard carbon coated negative electrode material can only improve the transmission rate of lithium ions on the surface layer of the material, and the transmission rate of the lithium ions of the material is not improved; meanwhile, the voltage platform of the battery can be influenced due to poor electronic conductivity of the hard carbon or soft carbon coating layer.
CN103647055A discloses an epoxy resin modified graphite cathode material and a preparation method thereof, the epoxy resin modified graphite cathode material is obtained by grinding, curing, carbonizing and crushing organic silicon modified epoxy resin and natural graphite, an epoxy resin carbon film coated on the surface of the graphite really plays a role in preventing large-volume solvent molecules from being co-embedded, a graphite layer is reversibly expanded and contracted in a small range, and the graphite layer is prevented from rapidly collapsing and collapsing, so that the cycle life of the graphite cathode is prolonged. However, in the existing pyrolytic carbon coating process, the phenomena of particle adhesion and coating non-uniformity are easily caused by high-temperature pyrolysis or high-temperature curing. The improvement of the performance of the graphite material by different coating processes reaches a bottleneck, the performance requirements of the current lithium ion battery industry on the graphite cathode are difficult to meet (the first reversible capacity is higher than 360mAh/g, and the first coulombic efficiency is higher than 92%), and meanwhile, the problems of poor batch stability, high production cost and the like exist.
The scheme has the problems of low ion transmission rate, poor stability or high cost and the like, so that the development of the composite material with low manufacturing cost, good electronic conductivity, good power performance and good cycle performance is necessary.
Disclosure of Invention
The invention aims to provide a composite material for a negative pole piece, a preparation method and application thereof, wherein the composite material comprises an inner core and an outer shell; the core is graphite, the shell is a boron-doped hard carbon coating layer, the shell and the core form a composite material through chemical bonding, the compaction density of the material can be improved, the lithium ion transmission is facilitated, the gram capacity exertion of the material is improved, and the first efficiency is further improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a composite material for a negative pole piece, which comprises an inner core and an outer shell; wherein the core is graphite, and the shell is a boron-doped hard carbon coating.
In the boron-doped hard carbon-coated composite material, the shell and the core form the composite material through chemical bonding, and boron element doped hard carbon with high electronic conductivity is doped on the surface of the composite material to reduce the electronic conductivity of the composite material; the composite material with chemical bond connection can improve the compaction density of the material, is beneficial to the transmission of lithium ions, improves the gram capacity exertion of the material, and further improves the primary efficiency.
Preferably, the mass fraction of the boron-doped hard carbon coating layer is 0.5-2% based on 100% of the composite material, such as: 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or the like.
Preferably, the mass fraction of the graphite is 98-99.5%, for example: 98%, 98.2%, 98.4%, 98.6%, 98.8%, 99%, 99.3%, 99.5%, etc.
In a second aspect, the present invention provides a method for preparing a composite material for a negative electrode plate according to the first aspect, wherein the preparation method comprises the following steps:
(1) placing phenolic resin in a mixed atmosphere of boron trichloride and inert gas, heating, and adding the heated phenolic resin into N-methyl pyrrolidone to obtain a boron-doped phenolic resin solution;
(2) placing graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate for oxidation treatment, then diluting, adding hydrogen peroxide, filtering, washing to be neutral, and drying to obtain graphite oxide;
(3) adding the graphite oxide obtained in the step (2) into the boron-doped phenolic resin solution obtained in the step (1), uniformly mixing, stirring, drying and crushing to obtain a coated material;
(4) and (4) heating, cooling, crushing and graphitizing the coated material obtained in the step (3) to obtain the composite material for the negative pole piece.
According to the invention, the surface of the graphite is coated with boron-containing hard carbon by a chemical method, so that the electronic conductivity of the composite material is improved, and the power performance and the cycle performance of the material are improved.
Preferably, the phenolic resin in the step (1) is an alkaline phenolic resin.
Preferably, the inert gas comprises argon and/or nitrogen.
Preferably, the heating temperature is 800-1000 ℃, for example: 800 deg.C, 810 deg.C, 820 deg.C, 830 deg.C, 840 deg.C, 850 deg.C, 860 deg.C, 870 deg.C, 880 deg.C, 890 deg.C, 900 deg.C, 920 deg.C, 940 deg.C, 960 deg.C, 980 deg.C or 1000 deg.C, etc.
Preferably, the heating time is 30-120 min, for example: 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min and the like.
Preferably, the mass concentration of the boron-doped phenolic resin solution is 1-10 wt.%, for example: 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, or 10 wt.%, etc.
Preferably, the temperature of the oxidation treatment in the step (2) is 25-100 ℃, for example: 25 deg.C, 30 deg.C, 35 deg.C, 40 deg.C, 50 deg.C, 60 deg.C, 70 deg.C, 80 deg.C, 90 deg.C or 100 deg.C.
Preferably, the time of the oxidation treatment is 1-48 h, for example: 1h, 5h, 10h, 15h, 20h, 27h, 30h, 35h, 40h, 45h or 48h and the like.
Preferably, the diluent comprises water.
Preferably, the concentration of the hydrogen peroxide is 1 to 10 wt%, for example: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, etc.
Preferably, the washing detergent comprises dilute hydrochloric acid and deionized water.
Preferably, the concentration of the dilute hydrochloric acid is from 1 to 20% by weight, for example: 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, or the like.
Preferably, the mass ratio of the graphite powder to the deionized water to the hydrogen peroxide is 10 (100-300) to (1-10), for example: 10:100:1, 10:120:3, 10:150:6, 10:200:8, 10:250:3, 10:270:6, 10:300:10, etc.
Preferably, the mass ratio of the graphite oxide to the boron-doped phenolic resin solution in the step (3) is 2 (1-2), for example: 2:1, 2: 1.1, 2: 1.2, 2: 1.3, 2: 1.4, 2: 1.6, 2: 1.8 or 2: 2, etc.
Preferably, the means for agitating comprises a high speed mixer.
Preferably, the stirring speed is 100-1000 r/min, such as: 100r/min, 200r/min, 300r/min, 400r/min, 500r/min, 600r/min, 700r/min, 800r/min, 900r/min, 1000r/min, etc.
Preferably, the stirring temperature is 100-300 ℃, for example: 100 deg.C, 120 deg.C, 140 deg.C, 160 deg.C, 180 deg.C, 200 deg.C, 210 deg.C, 230 deg.C, 250 deg.C, 270 deg.C, or 300 deg.C.
Preferably, the stirring time is 1-6 h, such as: 1h, 2h, 3h, 4h, 5h or 6h and the like.
Preferably, the heating of step (4) is performed under an inert atmosphere.
Preferably, the heated apparatus comprises a tube furnace.
Preferably, the heating rate is 1-10 ℃/min, for example: 1 deg.C/min, 2 deg.C/min, 3 deg.C/min, 4 deg.C/min, 5 deg.C/min, 6 deg.C/min, 7 deg.C/min, 8 deg.C/min, 9 deg.C/min or 10 deg.C/min, etc.
Preferably, the temperature of the heat is 600 to 1000 ℃, for example: 600 deg.C, 700 deg.C, 800 deg.C, 900 deg.C or 1000 deg.C, etc.
Preferably, the heating time is 1-6 h, such as: 1h, 2h, 3h, 4h, 5h or 6h and the like.
Preferably, the temperature of the temperature reduction is room temperature.
Preferably, the graphitization is performed under an inert atmosphere.
Preferably, the graphitization temperature is 2500-3000 ℃, for example: 2500 deg.C, 2600 deg.C, 2700 deg.C, 2800 deg.C, 2900 deg.C, 3000 deg.C, etc.
Preferably, the graphitization time is 48-480h, for example: 48h, 60h, 120h, 180h, 360h or 480h and the like.
As a preferable scheme of the invention, the preparation method comprises the following steps:
(1) placing phenolic resin in a mixed atmosphere of boron trichloride and inert gas, heating at 800-1000 ℃ for 30-120 min, and then adding into N-methyl pyrrolidone to obtain 1-10 wt.% boron-doped phenolic resin solution;
(2) placing graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate, oxidizing at 25-100 ℃ for 1-48 h, diluting with water, adding hydrogen peroxide, filtering, washing with dilute hydrochloric acid and deionized water to be neutral, and drying to obtain graphite oxide;
(3) adding the graphite oxide obtained in the step (2) into the boron-doped phenolic resin solution obtained in the step (1), uniformly mixing, transferring to a high-speed mixer, stirring at 100-1000 r/min and 100-300 ℃ for 1-6 h, drying, and crushing to obtain a coated material;
(4) and (4) transferring the coated material obtained in the step (3) to a tubular furnace, heating to 600-1000 ℃ at a speed of 1-10 ℃/min in an inert atmosphere, preserving heat for 1-6 h, naturally cooling to room temperature, crushing, and graphitizing … in the inert atmosphere at a temperature of 2500-3000 ℃ to obtain the composite material.
In a third aspect, the present invention provides a lithium ion battery negative electrode plate, which comprises the boron-doped hard carbon-coated composite material according to the first aspect.
In a fourth aspect, the invention further provides a lithium ion battery, where the lithium ion battery includes the lithium ion battery negative electrode sheet described in the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
1. in the boron-doped hard carbon-coated composite material, the shell and the core form the composite material through chemical bonding, and the surface of the cathode material is doped with boron element-doped hard carbon with high electronic conductivity, so that the electronic conductivity of the cathode material is reduced; the composite material with chemical bond connection can improve the compaction density of the material, is beneficial to the transmission of lithium ions, improves the gram capacity exertion of the material, and further improves the primary efficiency.
2. According to the preparation method of the boron-doped hard carbon-coated 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.
3. The first discharge capacity of a button cell prepared from the boron-doped hard carbon-coated composite material can reach more than 357.4mAh/g, the first efficiency is more than 93.7%, the liquid absorption capacity is more than 7.3mL/min, and the rate capability and the cycle performance of a soft package cell prepared from the boron-doped hard carbon-coated composite material are greatly improved.
Drawings
Fig. 1 is an SEM image of a boron doped hard carbon clad composite prepared for example 1.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The alkaline phenolic resins described in the examples and comparative examples of the invention are ZTS-968 phenolic resin; the purchasing manufacturer was a saint da foundry, ningjin county.
Example 1
The embodiment provides a boron-doped hard carbon-coated composite material, which is prepared by the following specific steps:
(1) placing 5g of alkaline phenolic resin in a mixed atmosphere of boron trichloride and argon (the volume ratio of the boron trichloride to the argon is 1:1), heating to 900 ℃ for reaction, preserving heat for 60min to obtain boron-doped phenolic resin, and then adding the boron-doped phenolic resin into 100ml of N-methyl pyrrolidone to obtain 5 wt.% boron-doped phenolic resin solution;
(2) placing 10g of graphite powder in a mixed solution of concentrated sulfuric acid and 10 wt% of potassium permanganate (the volume ratio of the concentrated sulfuric acid to the 10 wt% of potassium permanganate is 1:1), oxidizing at 80 ℃ for 24 hours, diluting with 200ml of water, adding 5g of hydrogen peroxide with the concentration of 5 wt%, filtering while hot, washing with dilute hydrochloric acid and deionized water to be neutral, and drying to obtain graphite oxide;
(3) boron-doped hard carbon-coated composite material
Adding 100g of graphite oxide obtained in the step (2) into 100ml of boron-doped phenolic resin solution obtained in the step (1), uniformly mixing, transferring into a high-speed mixer, stirring for 3h for coating under the conditions that the rotating speed is 500r/min and the temperature is 200 ℃, 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 heat for 3h, naturally cooling to room temperature, crushing, heating to 2800 ℃ under the inert atmosphere of nitrogen for graphitization for 240h, and naturally cooling to room temperature to obtain the boron-doped hard carbon coated composite material.
Example 2
The embodiment provides a boron-doped hard carbon-coated composite material, which is prepared by the following specific steps:
(1) placing 1g of alkaline phenolic resin in a mixed atmosphere of boron trichloride and nitrogen (the volume ratio of the boron trichloride to the nitrogen is 1:1), heating to 800 ℃ for reaction, preserving heat for 120min to obtain boron-doped phenolic resin, and then adding the boron-doped phenolic resin into 100ml of N-methylpyrrolidone to obtain 1 wt.% of boron-doped phenolic resin solution;
(2) placing 10g of graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate with the concentration of 10 wt% (the volume ratio of the concentrated sulfuric acid to the potassium permanganate with the concentration of 10 wt% is 1:1), oxidizing at 25 ℃ for 48 hours, diluting with 100ml of water, adding 1ml of hydrogen peroxide with the concentration of 10 wt%, filtering while hot, washing with dilute hydrochloric acid and deionized water to be neutral, and drying to obtain graphite oxide;
(3) adding 100g of graphite oxide into 50ml of boron-doped phenolic resin solution, uniformly mixing, transferring into a high-speed mixer, coating at the rotation speed of 100r/min and the temperature of 300 ℃ for 1h while stirring, drying, crushing, transferring the coated material into a tubular furnace, heating to 600 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 6h, naturally cooling to room temperature, crushing, heating to 2500 ℃ under the inert atmosphere, graphitizing for 240h, and naturally cooling to room temperature to obtain the boron-doped hard carbon coated composite material.
Example 3
The embodiment provides a boron-doped hard carbon-coated composite material, which is prepared by the following specific steps:
(1) placing 10g of alkaline phenolic resin in a mixed atmosphere of boron trichloride and argon (the volume ratio of the boron trichloride to the argon is 1:1), heating to 1000 ℃ for reaction, preserving heat for 30min to obtain boron-doped phenolic resin, and then adding the boron-doped phenolic resin into 100ml of N-methylpyrrolidone to obtain a 10 w.t% boron-doped phenolic resin solution;
(2) placing 10g of graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate with the concentration of 10 wt% (the volume ratio of the concentrated sulfuric acid to the potassium permanganate with the concentration of 10 wt% is 1:1), oxidizing at 80 ℃ for 24 hours, diluting with 300ml of deionized water, adding 10ml of hydrogen peroxide, filtering while hot, washing with dilute hydrochloric acid and deionized water to be neutral, and drying to obtain graphite oxide;
(3) adding 100g of graphite oxide into 100ml of boron-doped phenolic resin solution, uniformly mixing, transferring into a high-speed mixer, coating at the rotation speed of 1000r/min and the temperature of 100 ℃ for 6h under stirring, drying, crushing, transferring the coated material into a tubular furnace, heating to 1000 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of nitrogen, keeping the temperature for 1h, naturally cooling to room temperature, crushing, heating to 3000 ℃ under the inert atmosphere, graphitizing for 240h, and naturally cooling to room temperature to obtain the boron-doped hard carbon coated composite material.
Comparative example 1:
the comparative example provides a boron-undoped carbon-coated composite material, and the specific preparation method comprises the following steps:
adding 10g of alkaline phenolic resin into 100ml of N-methyl pyrrolidone, uniformly mixing, adding 100g of graphite, uniformly mixing, transferring to a high-speed mixer, coating at the rotation speed of 1000r/min and the temperature of 300 ℃ for 6h while stirring, drying, crushing, transferring the coated material to a tube furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of nitrogen, preserving heat for 1h, naturally cooling to room temperature, crushing, and heating to 2800 ℃ under the inert atmosphere for graphitization for 240 h.
1. Testing the powder performance:
1.1, SEM test
The 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 composite material prepared in example 1 is granular, has uniform size distribution, and has a particle size of 10-20 μm.
1.2, testing the resistivity of the powder:
pressing the powder into a blocky structure, and then testing the resistivity of the powder by adopting a four-probe tester. The test results are shown in table 1.
1.3 powder compaction Density test
The composite materials of examples 1-3 and comparative example 1 were subjected to a powder compaction density test. The test method comprises the following steps: and (3) placing 1g of powder into a fixed kettle by using a powder compaction density instrument, pressing by using 2T pressure, standing for 10s, calculating the volume under pressing, and calculating the compaction density so as to calculate the powder compaction density. The test results are shown in table 1.
TABLE 1
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*10-5
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 composite material prepared by the invention is obviously smaller than that of the comparative example, so that the surface of the cathode material is doped with boron doped hard carbon with high electronic conductivity, and the electronic conductivity of the cathode material is improved; meanwhile, the composite material with chemical bond connection prepared by a chemical reaction method is adopted, so that the compaction density of the material is improved.
2. And (3) button cell testing:
the composites of examples 1-3 and comparative example 1 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 composite materials in examples 1 to 3 and comparative example 1, 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 glove box filled with argon, and the electrochemical performance test is carried out on a Wuhan blue CT2001A type battery tester, wherein the charging and discharging voltage range is 0.005V-2.0V, and the charging and discharging multiplying power is 0.1C. And simultaneously taking the negative plate, testing the liquid absorption and retention capacity of the negative plate, wherein the test result is shown in table 2:
TABLE 2
Item Example 1/A1 Example 2/A2 Example 3/A3 Comparative example 1/B1
Put for the first timeElectric 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) 7.8 7.3 7.8 2.4
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 comparative example 1, and thus, it can be seen that the use of the boron-doped hard carbon coating layer is beneficial to the transmission of lithium ions, the gram capacity exertion of the material is improved, and the first efficiency is further improved.
3. Testing the soft package battery:
the composite materials in examples 1-3 and comparative example 1 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 D1, D2, D3 and E1 are prepared. And then testing the cycle performance and the rate of the soft package batteryAnd (4) performance.
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.
The test results are shown in table 3:
TABLE 3
Figure BDA0002808078190000121
As can be seen from table 3, the cycle performance of the pouch battery prepared from the composite material of the present invention is superior to that of the comparative example, and thus it can be seen that 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 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 composite material.
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 table 4:
TABLE 4
Figure BDA0002808078190000122
As can be seen from Table 4, the laminate polymer battery prepared by the composite material of the invention has a better constant current ratio, and therefore, the surface of the material of the invention is coated with the hard carbon material doped with boron, so that the quick charge performance of the material is improved, and the constant current ratio of the lithium ion battery is improved.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. The composite material for the negative pole piece is characterized by comprising an inner core and an outer shell;
wherein the core is graphite, and the shell is a boron-doped hard carbon coating.
2. The composite material for the negative electrode plate of claim 1, wherein the mass fraction of the boron-doped hard carbon coating layer is 0.5 to 2% based on 100% by mass of the composite material;
preferably, the mass fraction of the graphite is 98-99.5%.
3. The method for preparing the composite material for the negative electrode sheet according to claim 1 or 2, characterized by comprising the steps of:
(1) placing phenolic resin in a mixed atmosphere of boron trichloride and inert gas, heating, and adding the heated phenolic resin into N-methyl pyrrolidone to obtain a boron-doped phenolic resin solution;
(2) placing graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate for oxidation treatment, then diluting, adding hydrogen peroxide, filtering, washing to be neutral, and drying to obtain graphite oxide;
(3) adding the graphite oxide obtained in the step (2) into the boron-doped phenolic resin solution obtained in the step (1), uniformly mixing, stirring, drying and crushing to obtain a coated material;
(4) and (4) heating, cooling, crushing and graphitizing the coated material obtained in the step (3) to obtain the composite material for the negative pole piece.
4. The method according to claim 3, wherein the phenol resin in the step (1) is an alkaline phenol resin;
preferably, the inert gas comprises argon and/or nitrogen;
preferably, the heating temperature is 800-1000 ℃;
preferably, the heating time is 30-120 min;
preferably, the mass concentration of the boron-doped phenolic resin solution is 1-10 wt.%.
5. The method according to claim 3 or 4, wherein the temperature of the oxidation treatment in the step (2) is 25 to 100 ℃;
preferably, the time of the oxidation treatment is 1-48 h;
preferably, the diluent comprises water;
preferably, the concentration of the hydrogen peroxide is 1-10 wt%;
preferably, the washing detergent comprises dilute hydrochloric acid and deionized water;
preferably, the concentration of the dilute hydrochloric acid is 1-20 wt%;
preferably, the mass ratio of the graphite powder to the deionized water to the hydrogen peroxide is 10 (100-300) to 1-10.
6. The preparation method according to any one of claims 3 to 5, wherein the mass ratio of the graphite oxide to the boron-doped phenolic resin solution in the step (3) is 2 (1-2);
preferably, the means for agitating comprises a high speed mixer;
preferably, the stirring speed is 100-1000 r/min;
preferably, the stirring temperature is 100-300 ℃;
preferably, the stirring time is 1-6 h.
7. The method according to any one of claims 3 to 6, wherein the heating in step (4) is carried out under an inert atmosphere;
preferably, the heated apparatus comprises a tube furnace;
preferably, the heating rate is 1-10 ℃/min;
preferably, the temperature of the heat is 600-1000 ℃;
preferably, the heating time is 1-6 h;
preferably, the temperature for reducing the temperature is room temperature;
preferably, the graphitization is performed under an inert atmosphere;
preferably, the graphitization temperature is 2500-3000 ℃;
preferably, the graphitization time is 48-480 h.
8. The method of any one of claims 3 to 7, comprising the steps of:
(1) placing phenolic resin in a mixed atmosphere of boron trichloride and inert gas, heating at 800-1000 ℃ for 30-120 min, and then adding into N-methyl pyrrolidone to obtain 1-10 wt.% boron-doped phenolic resin solution;
(2) placing graphite powder in a mixed solution of concentrated sulfuric acid and potassium permanganate, oxidizing at 25-100 ℃ for 1-48 h, diluting with water, adding hydrogen peroxide, filtering, washing with dilute hydrochloric acid and deionized water to be neutral, and drying to obtain graphite oxide;
(3) adding the graphite oxide obtained in the step (2) into the boron-doped phenolic resin solution obtained in the step (1), uniformly mixing, transferring to a high-speed mixer, stirring at 100-1000 r/min and 100-300 ℃ for 1-6 h, drying, and crushing to obtain a coated material;
(4) and (4) transferring the coated material obtained in the step (3) into a tubular furnace, heating to 600-1000 ℃ at a speed of 1-10 ℃/min under an inert atmosphere, preserving heat for 1-6 h, naturally cooling to room temperature, crushing, and graphitizing for 48-480h under an inert atmosphere at a temperature of 2500-3000 ℃ to obtain the composite material.
9. A lithium ion battery negative electrode sheet, characterized in that it comprises the composite material for negative electrode sheets according to claim 1 or 2.
10. A lithium ion battery comprising the lithium ion battery negative electrode tab of claim 9.
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