CN111082014A - Silicon/carbon nanotube composite material, preparation method thereof, lithium battery cathode and lithium battery - Google Patents

Silicon/carbon nanotube composite material, preparation method thereof, lithium battery cathode and lithium battery Download PDF

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CN111082014A
CN111082014A CN201911329766.3A CN201911329766A CN111082014A CN 111082014 A CN111082014 A CN 111082014A CN 201911329766 A CN201911329766 A CN 201911329766A CN 111082014 A CN111082014 A CN 111082014A
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silicon
composite material
carbon
nano tube
carbon nanotube
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姚曼
张正
赵微
詹世英
李海军
蔡惠群
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Yinlong New Energy Co Ltd
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Yinlong New Energy 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a silicon/carbon nanotube composite material, a preparation method thereof, a lithium battery cathode and a lithium battery. The preparation method comprises the following steps: step S1, dispersing the carbon nano tube and the polyvinylpyrrolidone in an alcohol solvent to obtain a carbon nano tube dispersion liquid; step S2, mixing tetraethoxysilane and carbon nano tube dispersion liquid under the stirring condition to obtain mixed liquid; step S3, hydrolyzing ethyl orthosilicate in the ammonia water catalytic mixed solution to obtain alcohol dispersion liquid of the carbon nano tube/silicon dioxide; step S4, carrying out solid-liquid separation on the alcohol dispersion liquid, and drying the obtained solid to obtain the carbon nano tube/silicon dioxide composite material; step S5, reducing the carbon nano tube/silicon dioxide composite material to obtain a carbon nano tube/silicon composite material; and step S6, arranging a carbon source on the surface of the carbon nano tube/silicon composite material and carbonizing the carbon source to obtain the silicon/carbon nano tube composite material. The problem of poor bonding force of silicon and carbon caused by poor mixing uniformity of the silicon and the carbon is solved.

Description

Silicon/carbon nanotube composite material, preparation method thereof, lithium battery cathode and lithium battery
Technical Field
The invention relates to the technical field of preparation of silicon-carbon composite materials, in particular to a silicon/carbon nanotube composite material, a preparation method thereof, a lithium battery cathode and a lithium battery.
Background
The lithium ion battery taking graphite as the cathode has excellent performance and is widely applied to the fields of electric automobiles, energy storage, digital codes and the like, wherein a ternary NCM/graphite system is considered to have better application prospect. However, with the gradual adjustment of the national subsidy policy, the lithium ion battery is gradually developed toward both high energy density and high power density. At present, the widely-viewed NCM 811/graphite system has become a main direction for research and development of enterprises, and mass production of some enterprises is realized.
Silicon has a theoretical specific capacity of 4200mAh/g, and has a good application potential compared with 372mAh/g of graphite, so that the silicon is expected to replace graphite to become an optimal choice for a new generation of high-energy density battery negative electrode material, and has recently received attention of many researchers. However, the volume change of silicon is large (300%) during the charge and discharge process, so that the SEI film is repeatedly cracked, the electrolyte is continuously consumed, the material structure is damaged, and the battery capacity is rapidly attenuated, which becomes an obstacle for the application of silicon as a new-generation negative electrode material.
In order to make up for the defects of the silicon material, researchers adopt the idea of material compounding to coat a layer of carbon or other materials outside the silicon material to avoid the direct contact between the silicon and the electrolyte, so as to reduce the occurrence of side reactions, relieve the volume change of the silicon, and improve the structural stability of the material, thereby realizing the improvement of the cycle life of the NCM811/Si system.
Due to the ultrahigh specific surface area, large length-diameter ratio, excellent conductivity and good mechanical stability of the multi-walled carbon nanotube (MWCNTs) material with the one-dimensional structure, the multi-walled carbon nanotube material is widely applied to various electrode materials, and a plurality of researches show that the electrochemical performance of an electrode can be effectively improved by compounding the multi-walled carbon nanotube material. Generally, a ball milling method is adopted to ball mill and mix the single-walled carbon nanotube and the silicon nanoparticles, and the prepared composite material of the carbon nanotube and the silicon is used as a cathode of the lithium ion battery, so that good electrochemical performance is obtained. However, the method has the disadvantages that the uniformity of the ball-milling mixing method is poor, the binding force between the carbon nano tube and silicon is poor, and silicon particles are easy to fall off from the carbon tube; and the silicon particles are attached to the surface of the carbon tube, part of the surface of the silicon tube is still exposed, and the volume change in the circulation process is not completely and effectively inhibited, so that the circulation stability of the battery cannot be improved.
Disclosure of Invention
The invention mainly aims to provide a silicon/carbon nanotube composite material, a preparation method thereof, a lithium battery cathode and a lithium battery, and aims to solve the problem that the silicon/carbon nanotube composite material in the prior art has poor binding force due to poor mixing uniformity of silicon and carbon nanotubes.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method of preparing a silicon/carbon nanotube composite material, comprising: step S1, dispersing the carbon nano tube and the polyvinylpyrrolidone in an alcohol solvent to obtain a carbon nano tube dispersion liquid; step S2, mixing tetraethoxysilane and carbon nano tube dispersion liquid under the stirring condition to obtain mixed liquid; step S3, hydrolyzing ethyl orthosilicate in the ammonia water catalytic mixed solution to obtain alcohol dispersion liquid of the carbon nano tube/silicon dioxide; step S4, carrying out solid-liquid separation on the alcohol dispersion liquid, and drying the obtained solid to obtain the carbon nano tube/silicon dioxide composite material; step S5, reducing the carbon nano tube/silicon dioxide composite material to obtain a carbon nano tube/silicon composite material; and step S6, arranging a carbon source on the surface of the carbon nano tube/silicon composite material and carbonizing the carbon source to obtain the silicon/carbon nano tube composite material.
Further, the mass ratio of the carbon nanotubes to the polyvinylpyrrolidone is 1.5: 1-5: 1, preferably 1.5: 1-2.5: 1, wherein the mass content of the carbon nanotubes in the carbon nanotube dispersion liquid is 1-10%, preferably 1-1.25%; preferably, the alcoholic solvent is ethanol or isopropanol.
Further, the stirring is performed in both step S1 and step S2, preferably at a speed of 200 to 1000rpm, preferably for 0.5 to 8 hours in step S1, and preferably for 10 to 30 minutes in step S2.
Further, the carbon source is asphalt, and the mass ratio of the carbon nano tubes to the tetraethoxysilane to the asphalt is 32.0-58.0: 25.0-59.0: 8.0-17.0.
Further, the amount of the aqueous ammonia added to the ethyl orthosilicate is 0.1 to 5mL/g, the hydrolysis temperature is preferably 50 to 70 ℃, and the hydrolysis time is preferably 8 to 24 hours.
Further, the step S4 includes: washing the alcohol dispersion liquid with alcohol solvent to remove ammonia water, and then carrying out centrifugal separation to obtain solid; and drying the solid at 50-80 ℃ for 12-48 hours to obtain the carbon nano tube/silicon dioxide composite material.
Further, the step S5 includes: reducing the silicon dioxide in the carbon nano tube/silicon dioxide composite material by using the reducing powder in an inert gas atmosphere or an argon atmosphere to obtain a reduced substance; and (3) carrying out acid treatment on the reduced matter to obtain the carbon nano tube/silicon composite material, wherein the preferable reducing powder is magnesium powder or carbon powder, the preferable reducing temperature is 500-1200 ℃, the preferable reducing time is 2-24 hours, the preferable acid used for the acid treatment is hydrochloric acid, and the further preferable concentration is 5-20% hydrochloric acid.
Further, the step S6 includes: mixing the carbon nanotube/silicon composite material with pitch to form a mixture; carbonizing the mixture in an inert gas atmosphere or a nitrogen atmosphere to obtain a silicon/carbon nanotube composite material; preferably, the carbonization temperature is 400-1000 ℃, and the carbonization time is 6-24 hours.
According to another aspect of the present invention, there is provided a silicon/carbon nanotube composite material prepared by any one of the above-mentioned preparation methods.
According to another aspect of the present invention, there is provided a lithium battery negative electrode including a silicon/carbon nanotube composite material, the silicon/carbon nanotube composite material being the silicon/carbon nanotube composite material described above.
According to still another aspect of the present invention, there is provided a lithium battery including a positive electrode and a negative electrode, the negative electrode being the negative electrode for a lithium battery described above.
By applying the technical scheme of the invention, in the step S1, polyvinylpyrrolidone is used as a surfactant to uniformly disperse the carbon nanotubes in the alcohol solvent as much as possible; in addition, the tetraethoxysilane used in the step S2 can be well compatible and mixed with the polyvinylpyrrolidone, so that the carbon nanotubes and the tetraethoxysilane in the obtained mixed solution are mixed more uniformly. In the alcohol dispersion of carbon nanotubes/silica obtained by hydrolysis in step S3, since hydrolysis of tetraethoxysilane is a relatively mild chemical reaction, the homogeneous system already formed in step S2 is not affected, and then silicon obtained by reducing silica in the carbon nanotube/silica composite material can be uniformly coated on the carbon nanotubes; finally, the carbon source arranged on the surface of the carbon nano tube/silicon composite material is carbonized to realize the coating of the silicon.
The preparation method disclosed by the invention has the advantages of wide raw material source, simple and convenient process, easiness in operation, high efficiency and environmental friendliness; the silicon/carbon nanotube composite material obtained by the preparation method is of a hollow silicon-carbon nanotube composite structure, the nanotube can relieve the volume expansion of silicon, simultaneously compensates the defect of poor conductivity of silicon, has a large specific surface area, improves the conductivity of the material, and avoids the agglomeration of the material. According to the silicon/carbon nanotube composite material, silicon is uniformly distributed on the carbon nanotubes and is in close contact with the carbon nanotubes, and a carbon layer formed after carbonization covers the silicon, so that the silicon can stably exist in the composite material, therefore, the silicon/carbon nanotube composite cathode material has good cycling stability, tests show that some silicon/carbon nanotube composite materials prepared by the method are applied to a lithium battery, the lithium battery has initial discharge specific capacity of 634.3mAh/g under 0.5C multiplying power, after 50-week cycling, the discharge specific capacity of 547.4mAh/g and the capacity retention rate of 86.3 percent, and the problems of poor conductivity, poor cycling performance and the like of the materials are effectively solved.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is an SEM photograph of a silicon/carbon nanotube composite material prepared in example 1 of the present application;
fig. 2 is a graph of the charge-discharge cycle performance of the silicon carbon/nanotube composite material prepared in example 1 of the present application at a rate of 0.5C.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
As analyzed in the background of the present application, the silicon/carbon nanotube composite material in the prior art has poor binding force due to poor mixing uniformity of silicon and carbon nanotubes, and in order to solve the problem, the present application provides a silicon/carbon nanotube composite material, a preparation method thereof, a negative electrode of a lithium battery, and a lithium battery.
In an exemplary embodiment of the present application, there is provided a method of preparing a silicon/carbon nanotube composite material, the method comprising: step S1, dispersing the carbon nano tube and the polyvinylpyrrolidone in an alcohol solvent to obtain a carbon nano tube dispersion liquid; step S2, mixing tetraethoxysilane and carbon nano tube dispersion liquid under the stirring condition to obtain mixed liquid; step S3, hydrolyzing ethyl orthosilicate in the ammonia water catalytic mixed solution to obtain alcohol dispersion liquid of the carbon nano tube/silicon dioxide; step S4, carrying out solid-liquid separation on the alcohol dispersion liquid, and drying the obtained solid to obtain the carbon nano tube/silicon dioxide composite material; step S5, reducing the carbon nano tube/silicon dioxide composite material to obtain a carbon nano tube/silicon composite material; and step S6, arranging a carbon source on the surface of the carbon nano tube/silicon composite material and carbonizing the carbon source to obtain the silicon/carbon nano tube composite material.
In step S1, polyvinylpyrrolidone is used as a surfactant to disperse the carbon nanotubes in the alcohol solvent as uniformly as possible; in addition, the tetraethoxysilane used in the step S2 can be well compatible and mixed with the polyvinylpyrrolidone, so that the carbon nanotubes and the tetraethoxysilane in the obtained mixed solution are mixed more uniformly. In the alcohol dispersion of carbon nanotubes/silica obtained by hydrolysis in step S3, since hydrolysis of tetraethoxysilane is a relatively mild chemical reaction, the homogeneous system already formed in step S2 is not affected, and then silicon obtained by reducing silica in the carbon nanotube/silica composite material can be uniformly coated on the carbon nanotubes; finally, the carbon source arranged on the surface of the carbon nano tube/silicon composite material is carbonized to realize the coating of the silicon.
The preparation method disclosed by the invention has the advantages of wide raw material source, simple and convenient process, easiness in operation, high efficiency and environmental friendliness; the silicon/carbon nanotube composite material obtained by the preparation method is of a hollow silicon-carbon nanotube composite structure, the nanotube can relieve the volume expansion of silicon, simultaneously compensates the defect of poor conductivity of silicon, has a large specific surface area, improves the conductivity of the material, and avoids the agglomeration of the material. According to the silicon/carbon nanotube composite material, silicon is uniformly distributed on the carbon nanotubes and is in close contact with the carbon nanotubes, and a carbon layer formed after carbonization covers the silicon, so that the silicon can stably exist in the composite material, therefore, the silicon/carbon nanotube composite cathode material has good cycling stability, tests show that some silicon/carbon nanotube composite materials prepared by the method are applied to a lithium battery, the lithium battery has initial discharge specific capacity of 634.3mAh/g under 0.5C multiplying power, after 50-week cycling, the discharge specific capacity of 547.4mAh/g and the capacity retention rate of 86.3 percent, and the problems of poor conductivity, poor cycling performance and the like of the materials are effectively solved.
The carbon nanotubes of the present application are carbon nanotubes in a form conventional in the art, such as multi-walled carbon nanotubes or short single-walled carbon nanotubes, preferably carbon nanotubes having a diameter greater than 30 nm.
In a preferred embodiment of the present application, in order to improve the dispersion uniformity of the carbon nanotubes in the alcohol solvent, the mass ratio of the carbon nanotubes to the polyvinylpyrrolidone is preferably 1.5: 1-5: 1, preferably 1.5: 1-2.5: 1, wherein the mass content of the carbon nanotubes in the carbon nanotube dispersion liquid is 1-10%, preferably 1-1.25%; preferably, the alcoholic solvent is ethanol or isopropanol.
In order to improve the mixing uniformity of the polyvinylpyrrolidone and the carbon nanotubes, it is preferable that the step S1 includes dissolving the polyvinylpyrrolidone in isopropanol to form a primary solution; adding the carbon nano tubes into the primary solution in batches under the condition of continuous stirring, and increasing the stirring speed to continue stirring after the carbon nano tubes are added to obtain the carbon nano tube dispersion liquid.
In addition, in order to improve the mixing uniformity and mixing efficiency of the solid materials in the mixed liquid, the stirring is preferably performed in both the step S1 and the step S2, the stirring speed is preferably 200 to 1000rpm, the stirring time in the step S1 is preferably 0.5 to 8 hours, and the stirring time in the step S2 is preferably 10 to 30 minutes.
The thickness of a silicon layer coated on the carbon nano tube is adjusted by controlling the mass ratio of the carbon nano tube to the tetraethoxysilane so as to obtain a composite structure with high capacity and stable structure, asphalt is used as a carbon source, certainly, carbon sources of other materials such as acetylene can also be used, and the mass ratio of the carbon nano tube to the tetraethoxysilane to the asphalt is preferably 32.0-58.0: 25.0-59.0: 8.0-17.0, and is preferably 32.9-57.9: 25.5-58.3: 8.0 to 16.6.
In order to accelerate the hydrolysis reaction and avoid silicon falling off from the carbon nanotubes due to too fast hydrolysis, the addition amount of the aqueous ammonia to the tetraethoxysilane is preferably 0.1-5 mL/g, the hydrolysis temperature is preferably 50-70 ℃, and the hydrolysis time is preferably 8-24 hours.
In an embodiment of the present application, the step S4 includes: washing the alcohol dispersion liquid with alcohol solvent to remove ammonia water, and then carrying out centrifugal separation to obtain solid; and drying the solid at 50-80 ℃ for 12-48 hours to obtain the carbon nano tube/silicon dioxide composite material. In order to hydrolyze the tetraethoxysilane as completely as possible, the ammonia water may be in excess, and the ammonia water is separated from the alcohol dispersion after the washing and centrifugal separation to avoid the influence of the ammonia water on the subsequent reduction; the drying is then carried out slowly at the above-mentioned temperature to avoid too rapid a drying movement of the material to cause a large amount of silica to fall off the carbon nanotubes.
The reducing agent used in the present application for reducing the carbon nanotube/silica composite material is mainly used for reducing silica, and therefore can be selected from reducing agents commonly used in silica reduction in the prior art, in a preferred embodiment, the step S5 includes: reducing the silicon dioxide in the carbon nano tube/silicon dioxide composite material by using the reducing powder in an inert gas atmosphere or an argon atmosphere to obtain a reduced substance; and carrying out acid treatment on the reduced matter to obtain the carbon nano tube/silicon composite material. After the reduction, the reduced product is subjected to an acid treatment for further removing the reduced powder.
In a preferred embodiment, the preferable reducing powder is magnesium powder or carbon powder, the preferable reducing temperature is 500-1200 ℃, and the preferable reducing time is 2-24 hours, so as to realize sufficient reduction of the silicon dioxide; preferably, the acid used for the acid treatment is hydrochloric acid, and further preferably, the concentration of the hydrochloric acid is 5-20% so as to remove the reducing powder under a mild condition and avoid silicon on the carbon nano tube from falling off due to excessive and violent reaction of the acid treatment.
Various ways of arranging and carbonizing the carbon source on the surface of the carbon nanotube/silicon composite material can be realized, such as carbonizing after chemical deposition of the carbon source, in order to realize more sufficient coating of the silicon by simple operation, the step S6 preferably includes: mixing the carbon nanotube/silicon composite material with pitch to form a mixture; and carbonizing the mixture in an inert gas atmosphere or a nitrogen atmosphere to obtain the silicon/carbon nanotube composite material, wherein the preferable carbonization temperature is 400-1000 ℃, and the carbonization time is 6-24 hours.
In another exemplary embodiment of the present application, there is provided a silicon/carbon nanotube composite material, which is prepared by any one of the above-mentioned preparation methods.
The silicon/carbon nanotube composite material obtained by the preparation method is of a hollow silicon-carbon nanotube composite structure, the nanotube can relieve the volume expansion of silicon, simultaneously compensates the defect of poor conductivity of silicon, has a large specific surface area, improves the conductivity of the material, and avoids the agglomeration of the material. According to the silicon/carbon nanotube composite material, silicon is uniformly distributed on the carbon nanotubes and is in close contact with the carbon nanotubes, and a carbon layer formed after carbonization covers the silicon, so that the silicon can stably exist in the composite material, therefore, the silicon/carbon nanotube composite cathode material has good cycling stability, tests show that some silicon/carbon nanotube composite materials prepared by the method are applied to a lithium battery, the lithium battery has initial discharge specific capacity of 634.3mAh/g under 0.5C multiplying power, after 50-week cycling, the discharge specific capacity of 547.4mAh/g and the capacity retention rate of 86.3 percent, and the problems of poor conductivity, poor cycling performance and the like of the materials are effectively solved.
In another exemplary embodiment of the present application, a lithium battery negative electrode is provided, which includes a silicon/carbon nanotube composite material, wherein the silicon/carbon nanotube composite material is the silicon/carbon nanotube composite material described above. Because the silicon/carbon nanotube composite material has good cycle stability and rate characteristics, the lithium battery cathode with the silicon/carbon nanotube composite material also has good cycle stability and rate characteristics.
In another exemplary embodiment of the present application, there is provided a lithium battery including a positive electrode and a negative electrode, the negative electrode being the negative electrode for a lithium battery described above. The lithium battery with the lithium battery cathode also has good cycle stability and rate characteristics.
The advantageous effects of the present application will be further described below with reference to examples and comparative examples.
Example 1
0.2g of PVP is added into 45ml of isopropanol to be dissolved, 0.375g of carbon nano tube is added into the solution in a small amount for a plurality of times under continuous stirring, and then the solution is stirred for 2 hours at 800rpm to obtain carbon nano tube dispersion liquid.
And (3) keeping high-speed stirring, dropwise and slowly adding 0.32g of TEOS into the carbon nano tube dispersion liquid, and stirring for 30min to obtain a mixed liquid.
Stirring at high speed, slowly adding 0.8ml ammonia water drop by drop into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 50 ℃, and reacting for 24 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Washing the ethanol dispersion of carbon nanotube/silicon dioxide with anhydrous ethanol for several times until the washing solution is neutral, centrifuging, and drying at 70 deg.C for 24 hr to obtain carbon nanotube/SiO2A composite material.
0.47g of carbon nanotube/SiO2Reacting the composite material with magnesium powder for 4 hours at the high temperature of 650 ℃ in the argon atmosphere to obtain a reduced substance, then reacting the reduced substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
0.42g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture in high purity N2And (3) performing heat treatment at 600 ℃ for 20 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 2
0.2g of PVP was added to 35ml of an ethanol dispersion (1%) containing 0.35g of carbon nanotubes, and the mixture was dissolved with stirring to obtain a carbon nanotube dispersion.
Stirring at high speed, slowly adding 0.371g TEOS into the carbon nanotube dispersion liquid drop by drop, and stirring for 20min to obtain a mixed solution.
Stirring at high speed, slowly adding 1.0ml ammonia water dropwise into the mixed solution, sealing with preservative film, maintaining the temperature of the reaction system at 55 deg.C, and reacting for 20 hr to obtain carbon nanotube/SiO2The ethanol dispersion of (1);
mixing carbon nanotube/SiO2Washing the ethanol dispersion with anhydrous ethanol for several times, centrifuging, and drying at 80 deg.C for 12 hr to obtain carbon nanotube/SiO2A composite material.
0.46g of carbon nanotube/SiO2The composite material and carbon powder react for 8 hours at 550 ℃ in the argon atmosphere to obtain a reduced substance, and then the reduced substance reacts in 8% diluted hydrochloric acid, and the carbon nanotube/Si composite material is obtained after washing, centrifugation and drying.
0.4g of carbon nanotube/Si composite was mixed with 0.125g of pitch in high purity N2And (3) performing heat treatment at 700 ℃ for 12h under the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 3
0.2g of PVP is added into 35ml of absolute ethyl alcohol for dissolving, 0.42g of carbon nano tube is added for a plurality of times in a small amount under continuous stirring, and then the mixture is stirred at high speed for 4 hours to obtain the carbon nano tube dispersion liquid.
And (3) keeping high-speed stirring, dropwise and slowly adding 0.297g of TEOS into the carbon nano tube dispersion liquid, and stirring for 25min to obtain a mixed liquid.
Stirring at high speed, slowly adding 0.7ml ammonia water dropwise into the mixed solution, sealing with preservative film, maintaining the temperature of the reaction system at 60 deg.C, and reacting for 18h to obtain carbon nanotube/SiO2The ethanol dispersion of (1).
Mixing carbon nanotube/SiO2Washing the ethanol dispersion with anhydrous ethanol for several times, centrifuging, and drying at 60 deg.C for 48 hr to obtain carbon nanotube/SiO2A composite material.
0.506g of carbon nanotube/SiO2The composite material and magnesium powder react for 2 hours at the high temperature of 750 ℃ in the nitrogen atmosphere to obtain a reducing substance, and then the reducing substance reacts in 9% diluted hydrochloric acid, and the carbon nano tube/Si composite material is obtained after washing, centrifugation and drying.
0.46g of carbon nano tube/Si composite material is mixed with 0.063g of asphalt, and the asphalt is carbonized through heat treatment at 800 ℃ for 8 hours in the atmosphere of high-purity argon, so that the final product, namely the silicon/carbon nano tube composite material, is obtained.
Example 4
0.2g of PVP was dissolved in 45ml of isopropanol, and 1.860g of carbon nanotubes were added in small amounts several times with continuous stirring, followed by stirring at 800rpm for 2 hours to obtain a carbon nanotube dispersion.
And (3) keeping high-speed stirring, dropwise and slowly adding 1.587g of TEOS into the carbon nano tube dispersion liquid, and stirring for 30min to obtain a mixed liquid.
Keeping stirring at a high speed, dropwise and slowly adding 1mL of ammonia water into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 50 ℃, and reacting for 24 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Washing the ethanol dispersion of carbon nanotube/silicon dioxide with anhydrous ethanol for several times until the washing solution is neutral, centrifuging, and drying at 70 deg.CDrying for 24h to obtain the carbon nano tube/SiO2A composite material.
2.318g of carbon nanotube/SiO2Reacting the composite material with magnesium powder for 4 hours at the high temperature of 650 ℃ in the argon atmosphere to obtain a reduced substance, then reacting the reduced substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
2.074g of carbon nanotube/Si composite was mixed with 0.496g of pitch to form a mixture in high purity N2And (3) performing heat treatment at 600 ℃ for 20 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 5
0.2g of PVP was dissolved in 45ml of isopropanol, and 4.820g of carbon nanotubes were added in small amounts several times with continuous stirring, and then stirred at 1000rpm for 8 hours to obtain a carbon nanotube dispersion.
And (3) keeping high-speed stirring, dropwise and slowly adding 4.115g of TEOS into the carbon nano tube dispersion liquid, and stirring for 30min to obtain a mixed liquid.
Stirring at a high speed, slowly adding 3mL of ammonia water dropwise into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 50 ℃, and reacting for 24 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Washing the ethanol dispersion of carbon nanotube/silicon dioxide with anhydrous ethanol for several times until the washing solution is neutral, centrifuging, and drying at 70 deg.C for 24 hr to obtain carbon nanotube/SiO2A composite material.
6.007g of carbon nano tube/SiO2Reacting the composite material with magnesium powder for 4 hours at the high temperature of 650 ℃ in the argon atmosphere to obtain a reduced substance, then reacting the reduced substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
5.374g of carbon nanotube/Si composite was mixed with 1.285g of pitch to form a mixture in high purity N2And (3) performing heat treatment at 600 ℃ for 20 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 6
0.2g of PVP is added into 45ml of isopropanol to be dissolved, 0.375g of carbon nano tube is added into the solution in a small amount for a plurality of times under continuous stirring, and then the solution is stirred for 2 hours at 800rpm to obtain carbon nano tube dispersion liquid.
And (3) keeping high-speed stirring, dropwise and slowly adding 0.664g of TEOS into the carbon nano tube dispersion liquid, and stirring for 30min to obtain a mixed liquid.
Keeping stirring at a high speed, dropwise and slowly adding 1mL of ammonia water into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 50 ℃, and reacting for 24 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Washing the ethanol dispersion of carbon nanotube/silicon dioxide with anhydrous ethanol for several times until the washing solution is neutral, centrifuging, and drying at 70 deg.C for 24 hr to obtain carbon nanotube/SiO2A composite material.
0.855g of carbon nano tube/SiO2Reacting the composite material with magnesium powder for 4 hours at the high temperature of 650 ℃ in the argon atmosphere to obtain a reduced substance, then reacting the reduced substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
0.599g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture in high purity N2And (3) performing heat treatment at 600 ℃ for 20 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 7
0.2g of PVP is added into 45ml of isopropanol to be dissolved, 0.375g of carbon nano tube is added into the solution in a small amount for a plurality of times under continuous stirring, and then the solution is stirred for 2 hours at 800rpm to obtain carbon nano tube dispersion liquid.
And (3) keeping high-speed stirring, dropwise and slowly adding 0.154g of TEOS into the carbon nano tube dispersion liquid, and stirring for 30min to obtain a mixed liquid.
Keeping stirring at a high speed, dropwise and slowly adding 0.5mL of ammonia water into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 50 ℃, and reacting for 24 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Washing the ethanol dispersion of carbon nanotube/silicon dioxide with anhydrous ethanol for several times until the washing solution is neutral, centrifuging, and drying at 70 deg.C for 24 hr to obtain carbon nanotube/SiO2A composite material.
0.42g of carbon nano-particlestube/SiO2Reacting the composite material with magnesium powder for 4 hours at the high temperature of 650 ℃ in the argon atmosphere to obtain a reduced substance, then reacting the reduced substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
0.396g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture in high purity N2And (3) performing heat treatment at 600 ℃ for 20 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 8
The difference from example 1 is that the hydrolysis of ethyl orthosilicate is: keeping stirring at a high speed, dropwise and slowly adding 0.5mL of ammonia water into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 70 ℃, and reacting for 8 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Example 9
The difference from example 1 is that the hydrolysis of ethyl orthosilicate is: keeping stirring at a high speed, dropwise and slowly adding 0.5mL of ammonia water into the mixed solution, sealing with a preservative film, keeping the temperature of the reaction system at 75 ℃, and reacting for 5 hours to obtain the ethanol dispersion of the carbon nano tube/silicon dioxide.
Example 10
The difference from example 1 is that 0.47g of carbon nanotubes/SiO2The composite material and magnesium powder react for 24 hours in an argon atmosphere at a high temperature of 500 ℃ to obtain a reduced substance, and then the reduced substance reacts in 10% diluted hydrochloric acid, and the carbon nano tube/Si composite material is obtained by washing, centrifuging and drying.
Example 11
The difference from example 1 is that 0.47g of carbon nanotubes/SiO2The composite material and magnesium powder react for 2 hours in an argon atmosphere at a high temperature of 1200 ℃ to obtain a reduced substance, and then the reduced substance reacts in 10% diluted hydrochloric acid, and the carbon nano tube/Si composite material is obtained after washing, centrifugation and drying.
Example 12
The difference from example 1 is that 0.47g of carbon nanotubes/SiO2Reacting the composite material with magnesium powder for 1h in an argon atmosphere at the high temperature of 1300 ℃ to obtain the composite materialAnd reacting the original substance in 10% diluted hydrochloric acid, washing, centrifuging and drying to obtain the carbon nano tube/Si composite material.
Example 13
The difference from example 1 is that 0.42g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture containing high purity N2And (3) performing heat treatment at 400 ℃ for 24 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 14
The difference from example 1 is that 0.42g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture containing high purity N2And (3) performing heat treatment at 1000 ℃ for 6 hours in the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Example 15
The difference from example 1 is that 0.42g of carbon nanotube/Si composite was mixed with 0.1g of pitch to form a mixture containing high purity N2And (3) carrying out heat treatment at 1200 ℃ for 4h under the atmosphere to carbonize the asphalt, so as to obtain the final product, namely the silicon/carbon nanotube composite material.
Comparative example 1
The difference from example 1 is that 0.375g of carbon nanotubes and 45ml of isopropyl alcohol were mixed, and then stirred at 800rpm for 2 hours to obtain a carbon nanotube dispersion, and 0.32g of TEOS was added dropwise and slowly to the carbon nanotube dispersion while maintaining high-speed stirring, and stirred for 60 minutes to obtain a mixed solution.
The rest is the same as the example 1, and the final product, namely the silicon/carbon nanotube composite material is obtained.
Performance testing
The silicon-carbon nanotube composite material prepared in each example and comparative example is mixed with CMC and SBR according to the mass percentage of 90: 5: 5, uniformly mixing the mixture with deionized water to prepare slurry, coating the slurry on copper foil to prepare an electrode plate with the diameter of 14mm, then assembling the electrode plate with a metal lithium sheet with the diameter of 14mm, a polyethylene diaphragm with the diameter of 16mm and 1MLiPF6, wherein the EC/DMC/EMC molar ratio is 1:1:1 to assemble a button cell, and carrying out electrochemical performance test, wherein the voltage range is 0.05-1.5V, and the current density is 400 mA/g. The test results are shown in table 1, and fig. 1 is an SEM picture of the silicon carbon nanotube composite material prepared in example 1. FIG. 2 is a graph of the cycle performance of the silicon carbon nanotube composite material prepared in example 1 with 0.5C rate of charging and discharging. As can be seen from the figure, the initial specific discharge capacity is 634.3mAh/g, after 50-week charge-discharge cycling, the specific discharge capacity is 547.4mAh/g, and the capacity retention rate is 90.87%.
TABLE 1
Figure BDA0002329274580000101
Figure BDA0002329274580000111
In example 7, the initial specific capacity is small due to a slightly unsatisfactory ratio of the carbon nanotube, the tetraethoxysilane and the asphalt, but the specific capacity retention rate is high due to the fact that the components are uniformly dispersed by the preparation method of the present application.
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
in step S1, polyvinylpyrrolidone is used as a surfactant to disperse the carbon nanotubes in the alcohol solvent as uniformly as possible; in addition, the tetraethoxysilane used in the step S2 can be well compatible and mixed with the polyvinylpyrrolidone, so that the carbon nanotubes and the tetraethoxysilane in the obtained mixed solution are mixed more uniformly. In the alcohol dispersion of carbon nanotubes/silica obtained by hydrolysis in step S3, since hydrolysis of tetraethoxysilane is a relatively mild chemical reaction, the homogeneous system already formed in step S2 is not affected, and then silicon obtained by reducing silica in the carbon nanotube/silica composite material can be uniformly coated on the carbon nanotubes; finally, the carbon source arranged on the surface of the carbon nano tube/silicon composite material is carbonized to realize the coating of the silicon.
The preparation method disclosed by the invention has the advantages of wide raw material source, simple and convenient process, easiness in operation, high efficiency and environmental friendliness; the silicon/carbon nanotube composite material obtained by the preparation method is of a hollow silicon-carbon nanotube composite structure, the nanotube can relieve the volume expansion of silicon, simultaneously compensates the defect of poor conductivity of silicon, has a large specific surface area, improves the conductivity of the material, and avoids the agglomeration of the material. According to the silicon/carbon nanotube composite material, silicon is uniformly distributed on the carbon nanotubes and is in close contact with the carbon nanotubes, and a carbon layer formed after carbonization covers the silicon, so that the silicon can stably exist in the composite material, therefore, the silicon/carbon nanotube composite cathode material has good cycling stability, tests show that some silicon/carbon nanotube composite materials prepared by the method are applied to a lithium battery, the lithium battery has initial discharge specific capacity of 634.3mAh/g under 0.5C multiplying power, after 50-week cycling, the discharge specific capacity of 547.4mAh/g and the capacity retention rate of 86.3 percent, and the problems of poor conductivity, poor cycling performance and the like of the materials are effectively solved.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (11)

1. A preparation method of a silicon/carbon nanotube composite material is characterized by comprising the following steps:
step S1, dispersing the carbon nano tube and the polyvinylpyrrolidone in an alcohol solvent to obtain a carbon nano tube dispersion liquid;
step S2, mixing tetraethoxysilane and the carbon nano tube dispersion liquid under the stirring condition to obtain a mixed liquid;
step S3, catalyzing ethyl orthosilicate in the mixed solution by ammonia water to hydrolyze, and obtaining alcohol dispersion liquid of carbon nano tubes/silicon dioxide;
step S4, performing solid-liquid separation on the alcohol dispersion liquid, and drying the obtained solid to obtain the carbon nano tube/silicon dioxide composite material;
step S5, reducing the carbon nano tube/silicon dioxide composite material to obtain a carbon nano tube/silicon composite material; and
step S6, arranging a carbon source on the surface of the carbon nanotube/silicon composite material and carbonizing the carbon source to obtain the silicon/carbon nanotube composite material.
2. The method according to claim 1, wherein the mass ratio of the carbon nanotubes to the polyvinylpyrrolidone is 1.5: 1-5: 1, preferably 1.5: 1-2.5: 1, wherein the mass content of the carbon nanotubes in the carbon nanotube dispersion liquid is 1-10%, preferably 1-1.25%; preferably, the alcohol solvent is ethanol or isopropanol.
3. The method according to claim 1, wherein the step S1 and the step S2 are stirred, preferably at a speed of 200-1000 rpm, preferably for a time of 0.5-8 hours in the step S1, preferably for a time of 10-30 min in the step S2.
4. The preparation method of claim 1, wherein the carbon source is pitch, and the mass ratio of the carbon nanotubes to the tetraethoxysilane is 32.0-58.0: 25.0-59.0: 8.0-17.0.
5. The preparation method according to claim 1, wherein the addition amount of the ammonia water to the tetraethoxysilane is 0.1-5 mL/g, the hydrolysis temperature is preferably 50-70 ℃, and the hydrolysis time is preferably 8-24 hours.
6. The method for preparing a composite material according to claim 1, wherein the step S4 includes:
washing the alcohol dispersion liquid by using an alcohol solvent to remove ammonia water, and then carrying out centrifugal separation to obtain a solid;
and drying the solid at the temperature of 50-80 ℃ for 12-48 hours to obtain the carbon nano tube/silicon dioxide composite material.
7. The method for preparing a composite material according to claim 1, wherein the step S5 includes:
reducing the silicon dioxide in the carbon nano tube/silicon dioxide composite material by using reducing powder in an inert gas atmosphere or an argon atmosphere to obtain a reduced substance;
carrying out acid treatment on the reducing substance to obtain the carbon nano tube/silicon composite material,
preferably, the reducing powder is magnesium powder or carbon powder, the reducing temperature is preferably 500-1200 ℃, the reducing time is preferably 2-24 hours, the acid used for acid treatment is preferably hydrochloric acid, and the hydrochloric acid with the concentration of 5-20% is further preferably selected.
8. The method for preparing a composite material according to claim 1, wherein the step S6 includes:
mixing the carbon nanotube/silicon composite material with pitch to form a mixture;
carbonizing the mixture in an inert gas atmosphere or a nitrogen atmosphere to obtain the silicon/carbon nanotube composite material;
preferably, the carbonization temperature is 400-1000 ℃, and the carbonization time is 6-24 hours.
9. A silicon/carbon nanotube composite material, characterized in that the silicon/carbon nanotube composite material is prepared by the preparation method of any one of claims 1 to 8.
10. A negative electrode for a lithium battery comprising a silicon/carbon nanotube composite, wherein the silicon/carbon nanotube composite is the silicon/carbon nanotube composite of claim 9.
11. A lithium battery comprising a positive electrode and a negative electrode, wherein the negative electrode is the negative electrode for a lithium battery according to claim 10.
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