CN106784741B - Carbon-silicon composite material, preparation method thereof and lithium ion battery containing composite material - Google Patents

Carbon-silicon composite material, preparation method thereof and lithium ion battery containing composite material Download PDF

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CN106784741B
CN106784741B CN201710086689.8A CN201710086689A CN106784741B CN 106784741 B CN106784741 B CN 106784741B CN 201710086689 A CN201710086689 A CN 201710086689A CN 106784741 B CN106784741 B CN 106784741B
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carbon
silicon composite
composite material
silicon
carbonization
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CN106784741A (en
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程钢
汪福明
任建国
岳敏
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Shenzhen Beiteri New Energy Technology Research Institute Co ltd
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BTR New Material Group 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M4/621—Binders
    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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 discloses a carbon-silicon composite material, a preparation method thereof and a lithium ion battery containing the composite material. The method is simple, easy to operate, environment-friendly and suitable for large-scale production, the prepared carbon-silicon composite material is stable in structure, the nano-silicon is good in dispersibility and high in coating degree, the carbon-silicon composite material serving as a negative electrode material of a lithium ion battery shows very high lithium removal specific capacity, good cycle performance and excellent quick charge characteristic, the lithium removal specific capacity is above 391.7mAh/g, the capacity retention rate of 1.0C constant-current charging and discharging for 50 times is above 95.3%, and the charging rate of 10min can reach 90.2%.

Description

Carbon-silicon composite material, preparation method thereof and lithium ion battery containing composite material
Technical Field
The invention belongs to the technical field of electrochemistry and lithium ion battery cathode materials, relates to a composite material, a preparation method thereof and a lithium ion battery containing the composite material, and particularly relates to a carbon-silicon composite material, a preparation method thereof and a lithium ion battery containing the carbon-silicon composite material as a cathode material.
Background
The rate performance and the low-temperature performance of the traditional graphite material are poor, and the theoretical capacity is only 372mAh/g, so that the application of the traditional graphite material in the field of power batteries is limited. The amorphous carbon (soft carbon and hard carbon) has excellent multiplying power, cycle and low-temperature performance, and is one of ideal materials for preparing power batteries. The defect is that the specific capacity of the amorphous carbon is low, wherein the capacity of pure soft carbon is difficult to reach more than 300mAh/g, the capacity of a mature pure hard carbon product can only reach 450mAh/g generally, and the tap density of the amorphous carbon is low, so that the amorphous carbon is not enough to meet the requirement of the cruising ability of an electric automobile in the long run.
Methods for improving the capacity performance of carbon materials include doping, compounding, oxidation, and the like. The silicon has high specific capacity (4200mAh/g), and the capacity performance of the composite material can be further improved on the basis of keeping the excellent multiplying power and low-temperature performance of the amorphous carbon by compounding the silicon and the amorphous carbon, so that the fast-charging high-capacity carbon composite negative electrode material suitable for the power battery is prepared.
The difficulty in preparing the silicon-containing composite negative electrode material is to improve the cycle performance of the silicon-containing composite negative electrode material. At present, common methods for preparing silicon-based materials are: nano-crystallizing, porous and alloying silicon; embedding silicon into a buffer matrix; a coating layer (the coating layer can be conductive polymer, high molecular pyrolytic carbon, metal, etc.) is formed on the silicon surface. The methods can inhibit the volume expansion of silicon in the process of lithium intercalation and deintercalation to a certain extent, thereby improving the cycle performance of the silicon.
For example, patent CN 103337612a discloses a nano porous silicon carbon composite negative electrode material and a preparation method thereof. According to the method, the nano porous silicon-carbon composite negative electrode material with high performance and high stability is obtained by etching the silicon-carbon ternary alloy material, and the operation is simple. However, the structure of the material is difficult to ensure higher first effect, and the cost is higher in practical application.
For example, patent CN103618074A discloses a method for embedding nano-silicon in polymer microspheres to improve the dispersibility of nano-silicon in a silicon-carbon composite negative electrode material, thereby alleviating the volume effect of silicon in the lithium embedding process and improving the cycle performance thereof, but the preparation method disclosed in the patent has more processes, is complicated in process, and has low value in practical application.
Therefore, it is an urgent technical difficulty to develop a method that can maintain the excellent rate, cycle and low temperature characteristics of the amorphous carbon negative electrode material, improve the capacity characteristics thereof, and is easy to operate and easy to implement industrial production.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a high-capacity carbon-silicon composite material, a preparation method thereof and a lithium ion battery containing the carbon-silicon composite material, the carbon-silicon composite material has a stable structure, good dispersibility of nano-silicon and high coating degree of the nano-silicon, shows very high lithium removal specific capacity as a negative electrode material of the lithium ion battery, has good cycle performance and excellent quick charge characteristic, the lithium removal specific capacity is above 391.7mAh/g, the capacity retention rate of 1.0C constant current charging and discharging for 50 times is above 95.3%, and the charging rate of 10min can reach 90.2%.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a carbon-silicon composite material, which includes an inner core and an outer shell coated on a surface of the inner core, wherein the inner core is amorphous carbon, and the outer shell is formed by dispersing nano-silicon in a pyrolytic carbon layer.
The carbon-silicon composite material preferably has a median particle diameter of 5 to 60 μm, and may be, for example, 5 to 25 μm, 7 to 8 μm, 10 to 12 μm, 15 to 17 μm, 19 to 22 μm, 24 to 25 μm, 26 to 28 μm, 30 to 33 μm, 35 to 38 μm, 40 to 45 μm, 48 to 52 to 56 μm, or 60 μm, preferably 8 to 30 μm, and more preferably 10 to 25 μm.
Preferably, the specific surface area of the carbon-silicon composite material is 0.8m2/g～3.5m2A/g, for example, of 0.8m2/g、1m2/g、1.2m2/g、1.4m2/g、1.6m2/g、1.8m2/g、2m2/g、2.3m2/g、2.6m2/g、3m2/g、3.2m2G or 3.5m2G, etc., preferably 1.1m2/g～2.0m2/g。
Preferably, the compacted density of the carbon-silicon composite material is 0.9g/cm3～2.0g/cm3For example, it may be 0.9g/cm3、1.1g/cm3、1.3g/cm3、1.5g/cm3、1.6g/cm3、1.7g/cm3、1.8g/cm3Or 2g/cm3Etc., preferably 1.0g/cm, for example3～1.4g/cm3。
Preferably, the amorphous carbon comprises soft carbon and/or hard carbon.
The "soft carbon and/or hard carbon" according to the present invention means: it may be soft carbon, hard carbon, or a mixture of soft carbon and hard carbon.
In the present invention, the inner core is amorphous carbon, and the median particle diameter of the amorphous carbon is preferably 5 to 30 μm, and may be, for example, 5 to 6 μm, 7 μm, 9 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 17 μm, 20 μm, 22 μm, 25 μm, 28 μm, or 30 μm, and the like, preferably 7 to 20 μm, and more preferably 9 to 15 μm;
preferably, the nano-silicon has a median particle size of 25nm to 300nm, and may be, for example, 25nm, 35nm, 45nm, 50nm, 60nm, 75nm, 80nm, 90nm, 100nm, 110nm, 125nm, 135nm, 140nm, 150nm, 160nm, 175nm, 190nm, 210nm, 230nm, 245nm, 260nm, 280nm, 300nm, or the like, preferably 80nm to 200 nm.
Preferably, the thickness of the shell is 0-3.0 μm, and 0 is not included.
Preferably, the pyrolytic carbon layer is obtained by pyrolyzing a binder and a carbon source, the binder preferably includes any one or a mixture of at least two of asphalt, polyvinyl alcohol or phenolic resin, but is not limited to the above-listed binders, and other binders that can be converted into pyrolytic carbon during carbonization and have a binding effect can also be used in the present invention.
Preferably, the carbon source preferably includes pitch and/or a high molecular compound.
The term "asphalt and/or polymer compound" as used herein means: the asphalt may be asphalt, or a polymer compound, or a mixture of asphalt and a polymer compound.
The polymer compound may be, for example, a polymer, a saccharide, etc., but is not limited to a polymer and a saccharide, and other kinds of polymer compounds may be used as a carbon source in the present invention.
Preferably, the polymer compound includes any one or a mixture of at least two of epoxy resin, phenolic resin, furfural resin, urea resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin or polyacrylonitrile, but is not limited to the above-mentioned polymer compound, and carbon sources for carbon coating commonly used in the art may also be used in the present invention.
In a second aspect, the present invention provides a method for preparing a carbon-silicon composite material as described in the first aspect, the method comprising the steps of:
(1) carrying out surface modification on amorphous carbon by adopting a binder;
(2) compounding the amorphous carbon modified by the binder obtained in the step (1) with nano-silicon, and performing first carbonization on the obtained composite product to obtain a first carbon-silicon composite precursor;
(3) and (3) coating and modifying the first carbon-silicon composite precursor obtained in the step (2) by adopting a carbon source to obtain a second carbon-silicon composite precursor, and performing second carbonization on the obtained second carbon-silicon composite precursor to obtain the carbon-silicon composite material.
As a preferable technical solution of the method of the present invention, the method further comprises a step of sieving the product obtained by the first carbonization after the first carbonization in the step (2), wherein the sieve has a mesh size of 200 mesh or 325 mesh, preferably 325 mesh.
As another preferable embodiment of the method of the present invention, the method further comprises the step of crushing, sieving and demagnetizing the product obtained by the second carbonization after the second carbonization in step (3) is completed.
Preferably, the amorphous carbon of step (1) comprises soft carbon and/or hard carbon, and may be, for example, soft carbon, hard carbon, or a mixture of soft carbon and hard carbon.
Preferably, the binder in step (1) includes any one or a mixture of at least two of asphalt, polyvinyl alcohol or phenolic resin, but is not limited to the above-listed binders, and other binders having a binding effect that can be converted into pyrolytic carbon by carbonization can also be used in the present invention.
The binder in the invention is converted into pyrolytic carbon in the subsequent carbonization process, so that the nano silicon is coated by the pyrolytic carbon converted from the carbon source added subsequently and also coated by the pyrolytic carbon converted from the binder, thereby improving the coating degree of the nano silicon.
The median particle size of the binder in step (1) is preferably 5 μm or less, and may be, for example, 5 μm, 4.5 μm, 4 μm, 3.5 μm, 3 μm, 2 μm, 1.5 μm, 1 μm, 0.8 μm or 0.5 μm, and preferably 2 μm or less.
Preferably, the surface modification in step (1) is performed by either a solid phase modification method or a liquid phase modification method. Wherein the preparation process of the solid phase modification method comprises the following steps: and (2) placing the binder and the amorphous carbon into a VC mixer for mixing, and then adding the mixed materials into a fusion machine for fusion to obtain the binder modified amorphous carbon.
The preparation process of the liquid phase modification method comprises the following steps: dissolving the binder in the solvent, adding the amorphous carbon, stirring, and evaporating the solvent to dryness to obtain the binder modified amorphous carbon.
In the solid phase modification method, the rotation speed of the VC mixer during mixing is preferably 500r/min to 3000r/min, and may be, for example, 500r/min, 700r/min, 800r/min, 1000r/min, 1200r/min, 1500r/min, 1750r/min, 1850r/min, 2000r/min, 2200r/min, 2300r/min, 2400r/min, 2500r/min, 2600r/min, 2800r/min, 3000r/min, or the like.
Preferably, in the solid phase modification method, the mixing (or scattering) time is not less than 15min, for example, 15min, 25min, 30min, 40min, 50min, 1h, 1.2h, 1.5h, 1.8h, 2h, 2.4h, 2.7h, 3h, 4h, 6h, 8h, 10h, 12h or 15h, etc., preferably 30 min;
preferably, in the solid phase modification method, the rotation speed of the fusion machine is 500r/min to 3000r/min, for example, 500r/min, 600r/min, 900r/min, 1000r/min, 1200r/min, 1400r/min, 1600r/min, 1800r/min, 2000r/min, 2200r/min, 2300r/min, 2400r/min, 2500r/min, 2600r/min, 2750r/min or 3000 r/min; the width of the knife gap in the fusion machine is preferably 0.01cm to 0.5cm, and may be, for example, 0.01cm, 0.03cm, 0.05cm, 0.1cm, 0.15cm, 0.2cm, 0.3cm, 0.35cm, 0.4cm, or 0.5 cm;
preferably, in the solid phase modification method, the fusion time is not less than 0.5h, for example, 0.5h, 1h, 1.5h, 2h, 2.4h, 3.5h, 4h, 5h, 6.5h, 7h, 8h, 9h, 10h, 12h, 15h, 20h, 24h, 28h, 30h, 32h, 34h or 36h, etc., preferably 45 min.
Preferably, in the liquid phase modification method, the solvent is any one or a mixture of at least two of tetrahydrofuran, toluene, carbon disulfide, alcohol or water.
Preferably, the compounding method in step (2) is as follows: and (2) adding the amorphous carbon modified by the binder obtained in the step (1) and nano-silicon into a solvent, stirring, and evaporating the solvent to dryness, so that the nano-silicon is bonded to the surface of the amorphous carbon modified by the binder obtained in the step (1) under the action of the binder, thereby obtaining a composite product.
Preferably, in the compounding method in step (2), the solvent is any one or a mixture of at least two of isopropanol, ethanol or water.
Preferably, the first carbonization in the step (2) is performed in an inert atmosphere, which includes any one of a nitrogen atmosphere, an argon atmosphere, a neon atmosphere, a helium atmosphere, a xenon atmosphere, or a krypton atmosphere, or a combination of at least two thereof.
Preferably, the temperature of the first carbonization in the step (2) is 400 to 800 ℃, and may be, for example, 400 ℃, 450 ℃, 475 ℃, 500 ℃, 550 ℃, 600 ℃, 620 ℃, 650 ℃, 700 ℃, 750 ℃, or 800 ℃.
Preferably, the first carbonization time in step (2) is 2h to 6h, and may be, for example, 2h, 2.3h, 2.5h, 2.7h, 3h, 3.4h, 3.7h, 4h, 4.5h, 4.8h, 5h, 5.2h, 5.5h, 5.8h, 6h, or the like.
Preferably, in the process of raising the temperature to the first carbonization temperature in the step (2), the temperature raising rate is 1 ℃/min to 10 ℃/min, and for example, the temperature raising rate can be 1 ℃/min, 3 ℃/min, 5 ℃/min, 6 ℃/min, 8 ℃/min, 10 ℃/min, or the like.
Preferably, the carbon source in step (3) comprises pitch and/or a high molecular compound, which may be, for example, a polymer, a saccharide, and the like.
Preferably, the polymer compound includes any one or a mixture of at least two of epoxy resin, phenol resin, furfural resin, urea resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin, or polyacrylonitrile, but is not limited to the above-mentioned polymer compound, and carbon-coated carbon sources commonly used in the art may also be used in the present invention.
Preferably, the mass percentage of the carbon source in the step (3) is 5 wt% to 20 wt%, for example, 5 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, or 20 wt%, etc., preferably 8 wt% to 13 wt%, based on 100 wt% of the total mass of the carbon source and the first carbon-silicon composite precursor.
Preferably, the coating modification in the step (3) is performed by any one of a solid-phase coating method, a liquid-phase coating method, a fusion coating method or a spray drying coating method. The preparation process of the solid phase coating method comprises the following steps: and (3) placing the first carbon-silicon composite precursor and a carbon source in a VC mixer, and mixing to obtain a second carbon-silicon composite precursor.
The preparation process of the liquid phase coating method comprises the following steps: and adding the first carbon-silicon composite precursor and a carbon source into a solvent, stirring, and evaporating the solvent to obtain a second carbon-silicon composite precursor.
The preparation process of the fusion coating method comprises the following steps: and adding the first carbon-silicon composite precursor and a carbon source into a fusion machine for fusion to obtain a second carbon-silicon composite precursor.
The preparation process of the spray drying coating method comprises the following steps: and adding the first carbon-silicon composite precursor and a carbon source into a solvent, stirring to obtain mixed slurry, and performing spray drying to obtain a second carbon-silicon composite precursor.
In the solid phase coating method, the rotation speed of the VC mixer during mixing is preferably 500r/min to 3000r/min, and may be, for example, 500r/min, 650r/min, 800r/min, 1000r/min, 1250r/min, 1450r/min, 1600r/min, 1900r/min, 2150r/min, 2300r/min, 2500r/min, 2700r/min, 3000r/min, or the like.
Preferably, in the solid phase coating method, the mixing (or scattering) time is not less than 15min, for example, 15min, 30min, 50min, 1h, 1.5h, 2h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 24h or 36h, etc., preferably 30 min;
preferably, in the liquid phase coating method, the solvent is any one or a mixture of at least two of tetrahydrofuran, toluene, carbon disulfide, alcohol or water.
Preferably, in the fusion coating method, the rotation speed of the fusion machine during fusion is 500r/min to 3000r/min, such as 500r/min, 800r/min, 1000r/min, 1250r/min, 1700r/min, 2000r/min, 2300r/min, 2600r/min, 2800r/min or 3000r/min, and the gap width of the cutter in the fusion machine is 0.01cm to 0.5cm, such as 0.01cm, 0.05cm, 0.1cm, 0.2cm, 0.3cm, 0.4cm or 0.5 cm.
Preferably, in the fusion coating method, the fusion time is not less than 0.5h, for example, 1h, 2h, 3h, 5h, 7h, 10h, 12h, 15h, 24h, 30h, 36h or 48h, etc., preferably 45 min.
Preferably, in the spray drying coating method, the solvent is any one or a mixture of at least two of tetrahydrofuran, toluene, carbon disulfide, alcohol or water.
Preferably, in the spray drying coating method, the spray drying conditions are as follows: the inlet temperature is 250-400 ℃, and the preferred temperature is 300 ℃; the outlet temperature is 90-115 ℃, and the preferred temperature is 110 ℃; the solid content of the mixed slurry for spray drying is 10-30 wt%; the feeding rate of the mixed slurry during spray drying is 10 mL/min-40 mL/min.
In the spray drying coating method, the inlet temperature is 250 to 400 ℃, for example, 250 ℃, 275 ℃, 300 ℃, 320 ℃, 350 ℃, 360 ℃, 380 ℃ or 400 ℃ and the like.
In the spray drying coating method, the outlet temperature is 90 ℃ to 115 ℃, for example, 90 ℃, 92 ℃, 95 ℃, 100 ℃, 103 ℃, 106 ℃, 110 ℃ or 115 ℃ and the like.
In the spray-drying coating method, the solid content of the slurry used for spray-drying is 10 wt% to 30 wt%, and may be, for example, 10 wt%, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, or the like.
In the spray drying coating method, the feed rate of the mixed slurry during spray drying is 10mL/min to 40mL/min, and may be, for example, 10mL/min, 15mL/min, 18mL/min, 20mL/min, 25mL/min, 30mL/min, 33mL/min, 36mL/min, or 40 mL/min.
Preferably, the second carbonization in the step (3) is performed in an inert atmosphere, and the inert atmosphere includes any one of a nitrogen atmosphere, an argon atmosphere, a neon atmosphere, a helium atmosphere, a xenon atmosphere, or a krypton atmosphere, or a combination of at least two thereof.
Preferably, the temperature of the second carbonization in step (3) is 900 to 1100 ℃, and may be 900 ℃, 920 ℃, 940 ℃, 960 ℃, 985 ℃, 1000 ℃, 1025 ℃, 1050 ℃, 1080 ℃, 1100 ℃, or the like, for example.
Preferably, the time of the second carbonization in the step (3) is 2h to 4h, and may be, for example, 2h, 2.5h, 3h, 3.2h, 3.5h, 3.6h, 3.8h, 4h, or the like.
Preferably, the temperature increase rate is 1 ℃/min to 10 ℃/min, for example, 1 ℃/min, 3 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, etc., in the process of increasing the temperature from the temperature of the first carbonization to the temperature of the second carbonization in step (2).
In a third aspect, the present invention provides an anode material, wherein the anode material is the carbon-silicon composite material according to the first aspect.
In a fourth aspect, the present invention provides a lithium ion battery comprising the carbon-silicon composite material according to the first aspect as a negative electrode material.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention selects an adhesive which can be converted into pyrolytic carbon by carbonization, carries out surface modification on amorphous carbon by the adhesive, then further compounds nano silicon under the adhesive action of the adhesive, carries out carbon source coating after first carbonization at a lower temperature, and finally carries out second carbonization at a higher temperature to obtain the carbon-silicon composite material. The method is simple to operate and suitable for large-scale production.
(2) In the carbon-silicon composite material, the addition of the binder improves the acting force of the amorphous carbon and the nano-silicon, inhibits the self-aggregation phenomenon of nano-silicon particles, enables the nano-silicon to be uniformly compounded on the surface of the amorphous carbon material, and reduces the volume effect of silicon and the influence on the structure of the silicon in the lithium removal process; on the other hand, the binder is converted into pyrolytic carbon in the carbonization process, and the pyrolytic carbon converted from the carbon source coat the nano silicon together, so that the coating degree of the nano silicon is improved, the coating effect is good, the expansion of the silicon can be effectively inhibited, and the electrochemical properties such as cycle performance and the like are improved. Moreover, the pyrolytic carbon dispersed with the nano-silicon forms a conductive network, makes up for the disadvantage of poor conductivity of the silicon, and is beneficial to exerting and improving the capacity and the first effect of the silicon.
(3) The carbon-silicon composite material prepared by the invention has a stable structure, nano-silicon is uniformly dispersed and has a high coating degree, and the carbon-silicon composite material is very suitable for being used as a negative electrode material of a lithium ion battery, and a battery prepared by the carbon-silicon composite material shows very high lithium removal specific capacity, good cycle performance and excellent quick charge characteristic, the lithium removal specific capacity is more than 391.7mAh/g, the capacity retention rate of 1.0C constant current charging and discharging for 50 times is more than 95.3%, and the charging rate of 10min can reach 90.2%.
Drawings
FIG. 1 is a schematic diagram illustrating the mechanism of preparing a carbon-silicon composite material according to the present invention;
fig. 2A and 2B are SEM images of the composite products of comparative example 1 and example 1, respectively;
FIG. 3A is an SEM photograph of amorphous carbon (i.e., soft carbon) before modification in example 1;
FIG. 3B is an SEM image of modified amorphous carbon (i.e., high temperature pitch modified soft carbon) of example 1;
fig. 3C and 3D are SEM images of the carbon-silicon composite material of example 1 at 10000 times and 10000 times, respectively;
FIG. 4A is the XRD curves of the carbon silicon composite materials of example 1 and example 2;
fig. 4B is a first charge-discharge curve obtained by performing an electrochemical performance test on a battery made of the carbon-silicon composite material prepared in examples 1 and 2 as a negative electrode material under a power-off test condition;
FIG. 5 is a cycle performance curve obtained by performing a cycle performance test at a rate of 1.0C under a power-off condition on batteries made of the composite materials of example 1 and comparative example 1 as a negative electrode material;
fig. 6 shows that the carbon-silicon composite material of example 1 is used as a negative electrode material to prepare a battery, and the battery is tested under the cylindrical battery test condition to obtain a quick-charging performance curve; wherein SSC-1 corresponds to the carbon-silicon composite material of example 1, SSC-2 corresponds to the carbon-silicon composite material of example 2, and Ref-1 corresponds to the composite material of comparative example 1.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
The mechanism for preparing the carbon-silicon composite material is schematically illustrated in the figure 1.
Batteries were fabricated under the same conditions using the composite materials prepared in examples 1-5 and comparative example 1 as negative electrode materials.
The preparation of a specific button cell is carried out by methods known in the art.
The preparation method of the specific cylindrical battery comprises the following steps: dissolving the negative electrode material, the conductive agent and the binder in a solvent according to the mass percentage of 94:1:5, mixing, controlling the solid content to be 50%, coating the mixture on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate; then, a ternary positive pole piece prepared by a traditional mature process, 1mol/L LiPF6/EC + DMC + EMC (v/v is 1:1:1) electrolyte, a Celgard2400 diaphragm and an outer shell are assembled into the 18650 cylindrical single-cell battery by adopting a conventional production process.
Testing the charge and discharge performance and the first effect of the battery under the condition of power-on test: wherein, the electricity deduction test condition is as follows: the discharge was performed in a CC + CV mode (i.e., constant current followed by constant voltage), and then the charge was performed in a CC mode (constant current), and the constant current multiplying factor during the charge and discharge was 0.1C, and the cut-off voltage for constant current to constant voltage was 5mV, and the test results are shown in table 2.
The multiplying power performance of the battery is tested under the cylindrical battery test condition, the battery is tested on a Land battery test system of Wuhanjinnuo electronic Limited company at normal temperature, the charging and discharging voltage is limited to 2.0V-4.2V, and the test result is shown in table 2.
The quick charging performance of the battery is tested under the cylindrical battery test condition, and the CC + CV charging is carried out by adopting 6C in the test process, and the test result is shown in figure 6.
Example 1
(1) Surface modification: the amorphous carbon is subjected to surface modification by a binder through a solid phase modification method, specifically, 47.6g of high-temperature asphalt and 456.4g of soft carbon are accurately weighed and placed in a VC mixer to be mixed for 30min, and the rotating speed of the VC mixer is 3000 r/min. Then, the obtained materials are put into a fusion machine for fusion for 45min, and the rotating speed of the fusion machine is 3000r/min, so that the high-temperature asphalt modified soft carbon is obtained and is marked as SC @ LQ;
(2) compounding: adding nano silicon powder and a dispersing agent into isopropanol, and performing high-energy ball milling for 24 hours at a rotating speed of 300r/min to obtain silicon slurry. Accurately weighing silicon slurry (2.8 g silicon in terms of conversion, and isopropanol as solvent), and ultrasonically dispersing for 30min for later use. Under the condition of stirring at room temperature, 36.0g of high-temperature asphalt modified soft carbon (SC @ LQ) is added into the silicon slurry subjected to ultrasonic treatment, magnetic stirring is carried out for 45min, then water bath heating is carried out, the solvent is evaporated to dryness, the obtained material is scattered and then transferred into a 120 ℃ drying oven to be dried, and a composite product is obtained;
(3) first carbonization: carbonizing the composite product obtained in the step (2) at 600 ℃ for 3h under the protection of inert gas, wherein the heating rate in the process of heating from room temperature to 600 ℃ is 3 ℃/min, cooling to room temperature after carbonization is completed, and sieving by a 325-mesh sieve to obtain a first carbon-silicon composite precursor;
(4) coating modification: adopting 9.3 wt% (based on the total mass of the asphalt and the first carbon-silicon composite precursor being 100 wt%) of asphalt to carry out solid phase coating, wherein the specific coating steps are as follows: weighing a first carbon-silicon composite precursor and pitch according to a mass ratio, and uniformly mixing the first carbon-silicon composite precursor and the pitch to obtain a second carbon-silicon composite precursor;
(5) and (3) second carbonization: and (3) heating the second carbon-silicon composite precursor obtained in the step (4) from room temperature to 980 ℃ at the speed of 3 ℃/min under the protection of inert gas, carbonizing for 3 hours at 980 ℃, cooling to room temperature after carbonization is completed, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material, which is named as SSC-1.
The carbon-silicon composite material of the embodiment is used as a negative electrode material for a lithium ion battery, and the obtained battery has excellent characteristics of quick charge, high capacity and the like.
The specific surface area and particle size data of the carbon silicon composite material of this example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium intercalation capacity) and rate charge capacity of the 18650 cylindrical battery, which were obtained using the carbon-silicon composite material of this example as a negative electrode, are shown in table 2.
Fig. 2A and 2B are SEM images of the composite products of comparative example 1 and example 1, respectively. As can be seen from the graph, in comparative example 1, amorphous carbon was not modified with a binder but directly composited with nanosized silicon, and the nanosized silicon exhibited a very serious self-agglomeration phenomenon and was unevenly dispersed on the surface and in the gaps of amorphous carbon particles (fig. 2A); in example 1, the high-temperature pitch is used to modify the soft carbon, and then the high-temperature pitch modified soft carbon is compounded with the nano-silicon, so that the nano-silicon is uniformly adhered to the surface of the amorphous carbon soft carbon (fig. 2B), thereby showing that the binder can modify the amorphous carbon to promote the nano-silicon to be uniformly dispersed.
FIG. 3A is an SEM photograph of amorphous carbon (i.e., soft carbon) before modification in example 1; FIG. 3B is an SEM image of modified amorphous carbon (i.e., high temperature pitch modified soft carbon) of example 1; fig. 3C and 3D are SEM images of the carbon silicon composite material of example 1 at 10000 times and 10000 times, respectively. As can be seen, after the solid phase modification, a binder coating layer, i.e., a high temperature pitch coating layer, is formed on the surface of the soft carbon (fig. 3B), as compared to before the solid phase modification of the soft carbon (fig. 3A). Amorphous carbon modified with a binder is compounded with silicon, which can be uniformly and densely compounded to the surface of soft carbon (FIGS. 3C and 3D)
Fig. 4A is an XRD profile of the carbon silicon composite of example 1 and example 2. The figure shows that the characteristic peaks of soft carbon and silicon can be respectively found in the XRD curves of SSC-1 and SSC-2, and the material prepared by the invention is really a soft carbon and silicon composite material.
Fig. 4B is a first charge-discharge curve obtained by performing an electrochemical performance test on a battery made of the carbon-silicon composite material prepared in example 1 and example 2 as a negative electrode material under a power-off test condition. As can be seen from the figure, the charge and discharge curves of the silicon-carbon composite material obtained by solid-phase and liquid-phase modification almost coincide, and the charge and discharge curve shape peculiar to the soft carbon is basically kept, so that the capacity performance of the soft carbon is improved on the basis of the soft carbon by performing the silicon-carbon composite modification on the soft carbon.
Fig. 5 is a cycle performance curve obtained by performing electrochemical performance tests on batteries made of the composite materials of example 1 and comparative example 1 as negative electrode materials under the condition of a power-on test. It can be seen from the figure that the cycle performance of the SSC-1 obtained in example 1 is obviously superior to that of Ref-1 obtained in comparative example 1, the amorphous carbon (soft carbon in example 1) is subjected to surface modification by using a binder (high-temperature pitch in example 1), so that the acting force between the soft carbon and the nano silicon is improved, the self-aggregation phenomenon of nano silicon particles is inhibited, the nano silicon is uniformly compounded on the surface of the amorphous carbon, and the coated degree of the nano silicon is greatly enhanced because the binder and a subsequently added carbon source are converted into pyrolytic carbon after a carbonization process, and the uniform dispersion and the coating of silicon in the carbon-silicon composite material are favorable for reducing the influence of the volume effect of the silicon in a lithium removal process on the structure of the carbon-silicon composite material, so that the cycle performance of the carbon-silicon composite material is improved.
Fig. 6 is a fast-charging performance curve of the carbon-silicon composite material of example 1. The battery prepared by SSC-1 of example 1 is subjected to constant current charging and then constant voltage charging under the multiplying power of 6C, and the charging rate is 76.2% when the battery is subjected to constant current charging for 7.8 min; when the constant voltage charging is continued for 10min, the charging rate is 90.2%, and the very excellent quick charging performance is shown.
Example 2
(1) Surface modification: performing surface modification on amorphous carbon by using a binder through a liquid phase modification method, accurately weighing 3.4g of high-temperature asphalt, adding the high-temperature asphalt into 100mL of Tetrahydrofuran (THF) solution under the condition of room-temperature magnetic stirring, stirring for 1h to obtain a THF solution of the asphalt, adding 32.6g of soft carbon into the THF solution of the asphalt, and heating to evaporate a solvent to dryness to obtain the soft carbon modified by the high-temperature asphalt.
(2) Compounding: adding nano silicon powder and a dispersing agent into isopropanol, and performing high-energy ball milling for 24 hours at the rotating speed of 300r/min to obtain a silicon slurry solution. And (2) sequentially adding the high-temperature asphalt modified soft carbon obtained in the step (1) and silicon slurry (2.8 g of silicon in terms of conversion and isopropanol as a solvent) subjected to ultrasonic dispersion for 1h into 80mL of isopropanol solvent, stirring at a high speed for 45min at room temperature, heating to evaporate the solvent, scattering the obtained material, and transferring the scattered material to a 120-DEG C drying oven for drying to obtain a composite product.
(3) First carbonization: and (3) carbonizing the composite product obtained in the step (2) at 600 ℃ for 3h under the protection of inert gas, heating the composite product from room temperature to 600 ℃ at a heating rate of 3 ℃/min, cooling the carbonized product to room temperature after carbonization is completed, and sieving the carbonized product by using a 325-mesh sieve to obtain a first carbon-silicon composite precursor.
(4) Coating modification: adopting 9.3 wt% (based on the total mass of the asphalt and the first carbon-silicon composite precursor being 100 wt%) of asphalt to carry out solid phase coating, wherein the specific coating steps are as follows: and weighing the first carbon-silicon composite precursor and the pitch according to the mass ratio, and uniformly mixing the first carbon-silicon composite precursor and the pitch to obtain a second carbon-silicon composite precursor.
(5) And (3) second carbonization: and then under the protection of inert gas, heating the obtained second carbon-silicon composite precursor from room temperature to 980 ℃ at the speed of 3 ℃/min, carbonizing for 3h at 980 ℃, cooling to room temperature after carbonization is finished, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material, which is named as SSC-2.
The carbon-silicon composite material of the embodiment is used as a negative electrode material for a lithium ion battery, and the obtained battery has excellent characteristics of quick charge, high capacity and the like.
The specific surface area and particle size data of the carbon silicon composite material of this example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium intercalation capacity) and rate charge capacity of the 18650 cylindrical battery, which were obtained using the carbon-silicon composite material of this example as a negative electrode, are shown in table 2.
Example 3
(1) Surface modification: amorphous carbon is surface-modified by a liquid phase modification method using a binder. Accurately weighing 3.4g of phenolic resin, adding high-temperature asphalt into 100mL of ethanol under the condition of room-temperature magnetic stirring, stirring for 1h to obtain an ethanol solution of the phenolic resin, adding 32.6g of soft carbon into the ethanol of the phenolic resin, and heating to evaporate the solvent to dryness to obtain the soft carbon modified by the phenolic resin.
(2) Compounding: adding nano silicon powder and a dispersing agent into isopropanol, and performing high-energy ball milling for 24 hours at a rotating speed of 300r/min to obtain silicon slurry. Accurately weighing silicon slurry (2.8 g silicon in terms of conversion, isopropanol as solvent), and ultrasonically dispersing for 45min to obtain silicon slurry for later use. Under the condition of stirring at room temperature, adding 3.6g of polyvinyl alcohol modified soft carbon into the silicon slurry subjected to ultrasonic treatment, stirring for 60min, heating in a water bath, evaporating the solvent to dryness, scattering the obtained material, and transferring the scattered material into a 120 ℃ drying oven for drying to obtain a composite product;
(3) first carbonization: carbonizing the composite product obtained in the step (2) at 600 ℃ for 3h under the protection of inert gas, wherein the heating rate in the process of heating from room temperature to 400 ℃ is 3 ℃/min, cooling to room temperature after carbonization is completed, and sieving by a 325-mesh sieve to obtain a first carbon-silicon composite precursor;
(4) coating modification: the solid phase coating is carried out by adopting 9.3 wt% (based on the total mass of the asphalt, the phenolic resin and the first carbon-silicon composite precursor as 100 wt%) of a mixture of the asphalt and the phenolic resin, and the specific coating steps are as follows: weighing a first carbon-silicon composite precursor and a mixture of asphalt and phenolic resin according to a mass ratio, adding the first carbon-silicon composite precursor, the asphalt and the phenolic resin into a fusion machine, fusing for 45min, wherein the rotating speed of the fusion machine is 2750r/min, the gap width of a cutter in the fusion machine is 0.2cm, and fusing to obtain a second carbon-silicon composite precursor;
(5) and (3) second carbonization: and (3) carbonizing the second carbon-silicon composite precursor obtained in the step (4) at 1000 ℃ for 3h under the protection of inert gas, wherein the temperature rising rate in the process of rising the temperature from room temperature to 1000 ℃ is 5 ℃/min, cooling to room temperature after the carbonization is finished, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material, which is named as SSC-3.
The carbon-silicon composite material of the embodiment is used as a negative electrode material for a lithium ion battery, and the obtained battery has excellent characteristics of quick charge, high capacity and the like.
The specific surface area and particle size data of the carbon silicon composite material of this example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium intercalation capacity) and rate charge capacity of the 18650 cylindrical battery, which were obtained using the carbon-silicon composite material of this example as a negative electrode, are shown in table 2.
Example 4
(1) Surface modification: and carrying out surface modification on the hard carbon by using a binder through a liquid phase modification method. Accurately weighing 3.4g of high-temperature asphalt, adding the high-temperature asphalt into 100mL of Tetrahydrofuran (THF) solution under the condition of magnetic stirring at room temperature, stirring for 1h to obtain a THF solution of the asphalt, adding 32.6g of hard carbon into the THF solution of the asphalt, and heating to evaporate the solvent to dryness to obtain the hard carbon modified by the high-temperature asphalt.
(2) Compounding: adding nano silicon powder and a dispersing agent into isopropanol, and performing high-energy ball milling for 24 hours at the rotating speed of 300r/min to obtain a silicon slurry solution. Accurately weighing silicon slurry (2.8 g of silicon in terms of conversion, and isopropanol as a solvent), and ultrasonically dispersing for 2h for later use. Under the condition of stirring at room temperature, adding 36g of high-temperature asphalt modified hard carbon into the silicon slurry subjected to ultrasonic treatment, stirring for 35min, heating in a water bath, evaporating the solvent, scattering the obtained material, and transferring the scattered material to a 110 ℃ drying oven for drying to obtain a composite product;
(3) first carbonization: carbonizing the composite product obtained in the step (2) at 800 ℃ for 2h under the protection of inert gas, wherein the heating rate in the process of heating from room temperature to 800 ℃ is 3 ℃/min, cooling to room temperature after carbonization is completed, and sieving by a 325-mesh sieve to obtain a first carbon-silicon composite precursor;
(4) coating modification: adopting 9.3 wt% (based on the total mass of the asphalt and the first carbon-silicon composite precursor being 100 wt%) of asphalt to carry out solid phase coating, wherein the specific coating steps are as follows: and weighing the first carbon-silicon composite precursor and the pitch according to the mass ratio, and uniformly mixing the first carbon-silicon composite precursor and the pitch to obtain a second carbon-silicon composite precursor.
(5) And (3) second carbonization: and (3) heating the second carbon-silicon composite precursor obtained in the step (4) from room temperature to 980 ℃ at a speed of 3 ℃/min under the protection of inert gas, carbonizing for 2 hours at 980 ℃, cooling to room temperature after carbonization is completed, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material, which is named as SSC-4.
The carbon-silicon composite material of the embodiment is used as a negative electrode material for a lithium ion battery, and the obtained battery has excellent characteristics of quick charge, high capacity and the like.
The specific surface area and particle size data of the carbon silicon composite material of this example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium intercalation capacity) and rate charge capacity of the 18650 cylindrical battery, which were obtained using the carbon-silicon composite material of this example as a negative electrode, are shown in table 2.
Example 5
(1) Surface modification: performing surface modification on amorphous carbon by using a binder through a liquid phase modification method, accurately weighing 3.4g of phenolic resin, dissolving the phenolic resin in 100mL of ethanol solution under the condition of magnetic stirring at room temperature to obtain ethanol solution of the phenolic resin, adding 32.6g of hard carbon into the ethanol solution of the phenolic resin, and heating to evaporate the solvent to obtain the phenolic resin modified hard carbon.
(2) Compounding: and (2) adding the phenolic resin modified hard carbon obtained in the step (1) and silicon slurry (2.8 g of silicon in terms of conversion and isopropanol as a solvent) subjected to ultrasonic dispersion for 1.3h into 80mL of isopropanol solvent, stirring at a high speed for 40min at room temperature, heating to evaporate the solvent, scattering the obtained material, and transferring the scattered material into a 95 ℃ oven to dry the dried material to obtain a composite product.
(3) First carbonization: and (3) carbonizing the composite product obtained in the step (3) at 700 ℃ for 4h under the protection of inert gas, heating the composite product from room temperature to 700 ℃ at a heating rate of 5 ℃/min, cooling the carbonized product to room temperature after the carbonization is finished, and sieving the carbonized product by using a 325-mesh sieve to obtain a first carbon-silicon composite precursor.
(4) Coating modification: spray drying and coating by using 9.3 wt% (based on 100 wt% of the total mass of the asphalt and the first carbon-silicon composite precursor), wherein the specific coating steps are as follows: weighing a first carbon-silicon composite precursor and asphalt according to a mass ratio, mixing the first carbon-silicon composite precursor and the asphalt, adding the mixture into an isopropanol solvent, stirring to obtain mixed slurry with the solid content of 20 wt%, and performing spray drying (the conditions of the spray drying are that the inlet temperature is 300 ℃, the outlet temperature is 110 ℃, and the feeding rate is 30mL/min) to obtain a second carbon-silicon composite precursor;
(5) and (3) second carbonization: and carbonizing the obtained second carbon-silicon composite precursor at 980 ℃ for 3h under the protection of inert gas, wherein the heating rate in the process of heating from room temperature to 980 ℃ is 3 ℃/min, cooling to room temperature after carbonization is finished, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material, which is named as SSC-5.
The carbon-silicon composite material of the embodiment is used as a negative electrode material for a lithium ion battery, and the obtained battery has excellent characteristics of quick charge, high capacity and the like.
The specific surface area and particle size data of the carbon silicon composite material of this example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium intercalation capacity) and rate charge capacity of the 18650 cylindrical battery, which were obtained using the carbon-silicon composite material of this example as a negative electrode, are shown in table 2.
Comparative example 1
The preparation method and conditions were the same as in example 1 except that the surface modification of the soft carbon was not performed.
Specifically, the method comprises the following steps:
(1) preparing Soft Carbon (SC) for standby;
(2) compounding: accurately weighing silicon slurry (2.8 g silicon in terms of conversion, and isopropanol as solvent), and ultrasonically dispersing for 30min to obtain silicon slurry for later use. Under the condition of stirring at room temperature, adding 36.0g of Soft Carbon (SC) into the silicon slurry subjected to ultrasonic treatment, stirring for 45min, heating in a water bath, evaporating the solvent to dryness, scattering the obtained material, and transferring the scattered material to a 120 ℃ oven for drying to obtain a composite product;
(3) first carbonization: carbonizing the composite product obtained in the step (3) at 600 ℃ for 3h under the protection of inert gas, wherein the heating rate in the process of heating from room temperature to 600 ℃ is 3 ℃/min, cooling to room temperature after carbonization is completed, and sieving by a 325-mesh sieve to obtain a first carbon-silicon composite precursor;
(4) coating modification: adopting 9.3 wt% (based on the total mass of the asphalt and the first carbon-silicon composite precursor being 100 wt%) of asphalt to carry out solid phase coating, wherein the specific coating steps are as follows: weighing a first carbon-silicon composite precursor and pitch according to a mass ratio, and uniformly mixing the first carbon-silicon composite precursor and the pitch to obtain a second carbon-silicon composite precursor;
(5) and (3) second carbonization: and (3) carbonizing the second carbon-silicon composite precursor obtained in the step (4) at 980 ℃ for 3h under the protection of inert gas, wherein the heating rate in the process of heating from the room temperature to 980 ℃ in the step (3) is 3 ℃/min, cooling to the room temperature after the carbonization is finished, and sieving by using a 325-mesh sieve to obtain the carbon-silicon composite material which is named as Ref-1.
The specific surface area and particle size data for the carbon silicon composite of this comparative example are shown in table 1.
The results of the lithium removal capacity, first effect (lithium removal capacity/lithium insertion capacity) and rate charge capacity of the 18650 cylindrical battery made with the composite material of this comparative example as the negative electrode are shown in table 2.
TABLE 1
Figure BDA0001227631340000201
TABLE 2
Figure BDA0001227631340000202
As can be seen from Table 2, the battery prepared by using the carbon-silicon composite material as the negative electrode material has very excellent rate performance, and the charge capacity retention rate of 5C/1C is as high as 85.7%.
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 (59)

1. The carbon-silicon composite material is characterized by comprising an inner core and an outer shell coated on the surface of the inner core, wherein the inner core is amorphous carbon, and the outer shell is formed by dispersing nano-silicon in a pyrolytic carbon layer;
the preparation method of the carbon-silicon composite material comprises the following steps:
(1) carrying out surface modification on amorphous carbon by adopting a binder;
(2) compounding the amorphous carbon modified by the binder obtained in the step (1) with nano-silicon, and then performing first carbonization on the obtained composite product, wherein the first carbonization temperature is 400-800 ℃, so as to obtain a first carbon-silicon composite precursor;
(3) coating and modifying the first carbon-silicon composite precursor obtained in the step (2) by adopting a carbon source to obtain a second carbon-silicon composite precursor, and then performing second carbonization at the second carbonization temperature of 900-1100 ℃ to obtain a carbon-silicon composite material;
the compounding method in the step (2) comprises the following steps: adding the amorphous carbon modified by the binder obtained in the step (1) and nano-silicon into a solvent, stirring, and evaporating the solvent to dryness, so that the nano-silicon is bonded to the surface of the amorphous carbon modified by the binder obtained in the step (1), and a composite product is obtained;
the surface modification in the step (1) adopts a solid phase modification method.
2. The carbon-silicon composite material according to claim 1, wherein the carbon-silicon composite material has a median particle diameter of 5 to 60 μm.
3. The carbon-silicon composite material according to claim 2, wherein the carbon-silicon composite material has a median particle diameter of 8 to 30 μm.
4. The carbon-silicon composite material according to claim 3, wherein the carbon-silicon composite material has a median particle diameter of 10 to 25 μm.
5. According to the rightThe carbon-silicon composite material according to claim 1, wherein the carbon-silicon composite material has a specific surface area of 0.8m2/g～3.5m2/g。
6. The carbon-silicon composite material according to claim 5, wherein the carbon-silicon composite material has a specific surface area of 1.1m2/g～2.0m2/g。
7. The carbon-silicon composite material according to claim 1, wherein the carbon-silicon composite material has a compacted density of 0.9g/cm3～2.0g/cm3。
8. The carbon-silicon composite material according to claim 7, wherein the carbon-silicon composite material has a compacted density of 1.0g/cm3～1.4g/cm3。
9. The carbon silicon composite material according to claim 1, wherein the amorphous carbon comprises soft carbon and/or hard carbon.
10. The carbon-silicon composite material according to claim 1, wherein the amorphous carbon has a median particle diameter of 5 to 30 μm.
11. The carbon-silicon composite material according to claim 10, wherein the amorphous carbon has a median particle diameter of 7 to 20 μm.
12. The carbon-silicon composite material according to claim 11, wherein the amorphous carbon has a median particle diameter of 9 to 15 μm.
13. The carbon-silicon composite material according to claim 1, wherein the nano-silicon has a median particle diameter of 25nm to 300 nm.
14. The carbon-silicon composite material according to claim 13, wherein the nano-silicon has a median particle size of 80nm to 200 nm.
15. The carbon-silicon composite material according to claim 1, wherein the shell has a thickness of 0 to 3.0 μm, excluding 0.
16. The carbon-silicon composite material as claimed in claim 1, wherein the pyrolytic carbon layer is obtained by pyrolysis of a binder and a carbon source.
17. The carbon-silicon composite material of claim 16, wherein the binder comprises any one or a mixture of at least two of pitch, polyvinyl alcohol, or phenolic resin.
18. The carbon-silicon composite material of claim 16, wherein the carbon source comprises pitch and/or a polymer compound.
19. The carbon-silicon composite material according to claim 18, wherein the polymer compound comprises any one or a mixture of at least two of epoxy resin, phenolic resin, furfural resin, urea resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin, or polyacrylonitrile.
20. A method of preparing a carbon silicon composite material according to any one of claims 1 to 19, comprising the steps of:
(1) carrying out surface modification on amorphous carbon by adopting a binder;
(2) compounding the amorphous carbon modified by the binder obtained in the step (1) with nano-silicon, and then performing first carbonization on the obtained composite product, wherein the first carbonization temperature is 400-800 ℃, so as to obtain a first carbon-silicon composite precursor;
(3) coating and modifying the first carbon-silicon composite precursor obtained in the step (2) by adopting a carbon source to obtain a second carbon-silicon composite precursor, and then performing second carbonization at the second carbonization temperature of 900-1100 ℃ to obtain a carbon-silicon composite material;
the compounding method in the step (2) comprises the following steps: adding the amorphous carbon modified by the binder obtained in the step (1) and nano-silicon into a solvent, stirring, and evaporating the solvent to dryness, so that the nano-silicon is bonded to the surface of the amorphous carbon modified by the binder obtained in the step (1), and a composite product is obtained;
the surface modification in the step (1) adopts a solid phase modification method.
21. The method according to claim 20, further comprising a step of sieving the product obtained by the first carbonization after the first carbonization in the step (2), wherein the sieve is used with a mesh number of 200 or 325.
22. The method of claim 21 wherein said screen uses a mesh size of 325 mesh.
23. The method as set forth in claim 20, further comprising the steps of pulverizing, sieving and demagnetizing a product obtained by the second carbonization after the second carbonization in the step (3) is completed.
24. The method as recited in claim 20, wherein the amorphous carbon of step (1) comprises soft carbon and/or hard carbon.
25. The method of claim 20, wherein the binder of step (1) comprises any one of or a mixture of at least two of asphalt, polyvinyl alcohol, or phenolic resin.
26. The method of claim 20, wherein the median particle size of the binder of step (1) is 5 μ ι η or less.
27. The method of claim 26, wherein the median particle size of the binder of step (1) is 2 μ ι η or less.
28. The method of claim 20, wherein the solid phase modification method is prepared by: and (2) placing the binder and the amorphous carbon into a VC mixer for mixing, and then adding the mixed materials into a fusion machine for fusion to obtain the binder modified amorphous carbon.
29. The method according to claim 28, wherein in the solid phase modification method, the rotation speed of the VC mixer is 500 to 3000r/min at the time of mixing.
30. The method of claim 28, wherein the mixing time is not less than 15min in the solid phase modification method.
31. The method of claim 30, wherein the mixing time is 30min in the solid phase modification method.
32. The method according to claim 28, wherein the rotation speed of the fusion machine is 500 to 3000r/min during the fusion in the solid phase modification method.
33. The method according to claim 28, wherein in the solid phase modification method, the width of the knife gap in the fusion machine is 0.01cm to 0.5 cm.
34. The method of claim 28, wherein the time for the fusion in the solid phase modification method is not less than 0.5 h.
35. The method of claim 34, wherein the time for the fusion in the solid phase modification method is 45 min.
36. The method according to claim 20, wherein in the compounding method in step (2), the solvent is any one or a mixture of at least two of isopropanol, ethanol or water.
37. The method according to claim 20, wherein the first carbonization in step (2) is performed in an inert atmosphere comprising any one of a nitrogen atmosphere, an argon atmosphere, a neon atmosphere, a helium atmosphere, a xenon atmosphere, or a krypton atmosphere, or a combination of at least two thereof.
38. The method according to claim 20, wherein the time of the first carbonization in the step (2) is 2 to 6 hours.
39. The method as set forth in claim 20, wherein the temperature is raised to the temperature of the first carbonization in the step (2) at a rate of 1 ℃/min to 10 ℃/min.
40. The method of claim 20, wherein the carbon source of step (3) comprises pitch and/or a polymeric compound.
41. The method of claim 40, wherein the polymer compound comprises any one or a mixture of at least two of epoxy resin, phenolic resin, furfural resin, urea resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin, or polyacrylonitrile.
42. The method according to claim 20, wherein the mass percentage of the carbon source in the step (3) is 5 wt% to 20 wt% based on 100 wt% of the total mass of the carbon source and the first carbon-silicon composite precursor.
43. The method of claim 42, wherein the mass percentage of the carbon source in the step (3) is 8 wt% to 13 wt% based on 100 wt% of the total mass of the carbon source and the first carbon-silicon composite precursor.
44. The method according to claim 20, wherein the coating modification in step (3) is performed by any one of a solid-phase coating method, a liquid-phase coating method, a fusion coating method or a spray-drying coating method; the preparation process of the solid phase coating method comprises the following steps: placing the first carbon-silicon composite precursor and a carbon source in a VC mixer, and mixing to obtain a second carbon-silicon composite precursor;
the preparation process of the liquid phase coating method comprises the following steps: adding the first carbon-silicon composite precursor and a carbon source into a solvent, stirring, and evaporating the solvent to obtain a second carbon-silicon composite precursor;
the preparation process of the fusion coating method comprises the following steps: adding the first carbon-silicon composite precursor and a carbon source into a fusion machine for fusion to obtain a second carbon-silicon composite precursor;
the preparation process of the spray drying coating method comprises the following steps: and adding the first carbon-silicon composite precursor and a carbon source into a solvent, stirring to obtain mixed slurry, and performing spray drying to obtain a second carbon-silicon composite precursor.
45. The method according to claim 44, wherein in the solid phase coating method, the rotation speed of the VC mixer is 500 to 3000r/min during mixing.
46. The method of claim 44, wherein the mixing time is not less than 15min in the solid phase coating method.
47. The method of claim 44, wherein the mixing time is 30min in the solid phase coating method.
48. The method of claim 44, wherein in the liquid phase coating method, the solvent is one or a mixture of at least two of tetrahydrofuran, toluene, carbon disulfide, alcohol and water.
49. The method according to claim 44, wherein in the fusion coating method, the rotation speed of the fusion machine is 500r/min to 3000r/min and the gap width of the cutter in the fusion machine is 0.01cm to 0.5cm during fusion.
50. The method of claim 44, wherein the fusion coating is performed for a time period of not less than 0.5 h.
51. The method of claim 50, wherein in the fusion coating method, the fusion time is 45 min.
52. The method of claim 44, wherein the solvent in the spray drying coating method is one or a mixture of at least two of tetrahydrofuran, toluene, carbon disulfide, alcohol and water.
53. The method of claim 44, wherein the spray drying conditions in the spray drying coating process are: the inlet temperature is 250-400 ℃; the outlet temperature is 90-115 ℃; the solid content of the mixed slurry for spray drying is 10-30 wt%; the feeding rate of the mixed slurry during spray drying is 10 mL/min-40 mL/min.
54. The method of claim 53, wherein the inlet temperature is 300 ℃ and the outlet temperature is 110 ℃.
55. The method according to claim 20, wherein the second carbonization in step (3) is performed in an inert atmosphere, which includes any one of a nitrogen atmosphere, an argon atmosphere, a neon atmosphere, a helium atmosphere, a xenon atmosphere, or a krypton atmosphere, or a combination of at least two thereof.
56. The method according to claim 20, wherein the time of the second carbonization in the step (3) is 2 to 4 hours.
57. The method according to claim 20, wherein the temperature increase rate is 1 ℃/min to 10 ℃/min in the process of increasing the temperature from the first carbonization temperature to the second carbonization temperature in the step (3).
58. A negative electrode material, characterized in that the negative electrode material is the carbon-silicon composite material according to any one of claims 1 to 57.
59. A lithium ion battery comprising the negative electrode material of claim 58.
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