CN114420928A - High-performance silicon-carbon negative electrode material for lithium ion battery, preparation method of high-performance silicon-carbon negative electrode material and lithium ion battery - Google Patents

High-performance silicon-carbon negative electrode material for lithium ion battery, preparation method of high-performance silicon-carbon negative electrode material and lithium ion battery Download PDF

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CN114420928A
CN114420928A CN202011172633.2A CN202011172633A CN114420928A CN 114420928 A CN114420928 A CN 114420928A CN 202011172633 A CN202011172633 A CN 202011172633A CN 114420928 A CN114420928 A CN 114420928A
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silicon
composite material
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graphene
nano tube
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CN114420928B (en
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张琪
鞠属元
李宏亮
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Shandong Haike Innovation Research Institute 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
    • H01M4/38—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
    • 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
    • H01M4/62—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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

Abstract

The invention provides a silicon-carbon composite material, which comprises a core composite material and a soft carbon layer coated on the surface of the core composite material; the core composite material is a carbon nano tube/silicon/graphene composite material. The composite material has a core-shell structure, and the carbon nano tube/silicon/graphene composite material with a specific structure is used as a core composite material to obtain the cathode material with a tubular matrix multilayer coating structure. The expansion and pulverization of silicon in the circulation process can be effectively limited by the rigid support of the carbon tube and the two-dimensional coating and porous characteristics of the graphene; the high conductivity can make up for the poor conductivity of silicon; the composite structure increases the contact area of the electrolyte and the negative electrode material, shortens the diffusion path of lithium ions, and simultaneously the external soft carbon layer is easy to form a stable SEI film with the electrolyte. When the silicon-carbon composite material provided by the invention is used for a lithium ion battery cathode material, the silicon-carbon composite material shows excellent electrochemical performance and has good cycle stability and rate capability.

Description

High-performance silicon-carbon negative electrode material for lithium ion battery, preparation method of high-performance silicon-carbon negative electrode material and lithium ion battery
Technical Field
The invention belongs to the technical field of lithium battery cathode materials, relates to a silicon-carbon composite material and a preparation method thereof, and a lithium ion battery, and particularly relates to a high-performance silicon-carbon cathode material for a lithium ion battery, a preparation method thereof, and a lithium ion battery.
Background
The lithium ion battery has the advantages of high working voltage, high specific energy, long cycle life, light weight, less self-discharge, no memory effect, high cost performance and the like, and becomes a main selection object of rechargeable power supplies in the fields of high-power electric vehicles, artificial satellites, aerospace and the like. In particular, in practical applications, lithium ion batteries have become ideal energy sources for various portable electronic devices, such as notebook computers, mobile phones, and the like. In recent years, novel electric equipment such as electric automobiles and the like is developed at a high speed, particularly, the cruising ability of new energy automobiles depends on the energy density of batteries, the requirement of consumers on the cruising mileage of the automobiles is continuously improved, the high energy density becomes the future development direction of power batteries, the energy density of lithium ion batteries mainly depends on the lithium storage capacity and the voltage of positive and negative electrode materials, and the solution to the problem has two directions, namely, the development of the positive electrode material with high capacity and high potential; secondly, developing a high-capacity and low-potential cathode material. Therefore, the negative electrode material also determines the performance of the lithium ion battery and is a key factor influencing the performance of the lithium ion battery. The currently widely used negative electrode materials are various carbon materials mainly comprising graphite, the theoretical capacity of the carbon materials is only 372mAh/g, the carbon materials are close to the theoretical capacity in the practical application process, the higher capacity requirement is difficult to achieve, the rate capability is poor, and lithium deposition is easily caused due to low discharge voltage, so that a series of safety problems are caused. Under the condition that the potential of the energy density of the traditional graphite cathode is fully developed, the power battery is further developed to improve the battery capacity, the research on a high-specific-capacity cathode active material is trended, the silicon-based cathode becomes one of the best means for solving the problem of energy density at present, the silicon-based material stores energy by adopting an alloying reaction process, and the theoretical specific capacity is 4200 mAh/g. However, the silicon negative electrode material also has several main problems, which cannot be applied to the silicon-based material of the lithium ion battery alone, and the volume expansion problem is: in the charging and discharging process, the volume of silicon can expand by 100-300%, continuous shrinkage and expansion can cause powdering of the silicon-carbon negative electrode material, a stable SEI film cannot be formed, and after several cycles, the capacity attenuation is serious, so that the comprehensive performance of the battery is greatly reduced, and the service life of the battery is seriously influenced. And secondly, the continuous expansion of silicon generates great stress in the battery, the pole piece is extruded by the stress, and the pole piece can be broken after being circulated for many times. And thirdly, due to the internal stress of the battery, the internal porosity of the battery is possibly reduced, lithium ion moving channels are reduced, lithium metal is separated out, and the safety of the battery is influenced. Silicon is a semiconductor, and the conductivity is much poorer than that of graphite, so that the irreversible degree in the lithium ion de-intercalation process is large, and the first coulombic efficiency of the lithium ion is reduced. Therefore, solving the defect of silicon materials is the subject of research at home and abroad, and the silicon-carbon composite active material is a great hot spot of research. The carbon material has high electrical conductivity, a relatively stable structure and small volume expansion in a circulation process, generally less than 10%, and has good flexibility and lubricity, so that the volume expansion of the silicon material in the circulation process can be inhibited to a certain extent, and therefore, the carbon material which has excellent electrical conductivity and can accommodate the volume change of silicon is required to be compounded to greatly improve the energy density and the circulation stability. The silicon-carbon composite active material can integrate respective advantages of the silicon material and the carbon material and exert more excellent performance.
At the present stage, in order to achieve good dispersion of the carbon material and the nano silicon and complete coating of the carbon material on the nano silicon, especially to prepare a high-capacity silicon-carbon material (specific capacity >800mAh/g), it is often necessary to modify the surface functional groups of the carbon material and the nano silicon or to achieve the preparation by vapor deposition and other techniques. Because of this, the silicon carbon negative electrode faces a high technical barrier in research and development and application, so the application of the silicon negative electrode material in the lithium battery is not considerable.
Therefore, how to obtain a silicon-carbon composite material with more excellent comprehensive performance is more suitable for a lithium ion battery cathode material, and the silicon-carbon composite material is more beneficial to industrial large-scale production, has important practical significance, and also becomes one of the focuses of extensive attention of research and development type enterprises in the field.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a silicon-carbon composite material, a preparation method thereof, and a lithium ion battery, especially a silicon-carbon negative electrode material for a lithium ion battery with high performance.
The invention provides a silicon-carbon composite material, which comprises a core composite material and a soft carbon layer coated on the surface of the core composite material;
the core composite material is a carbon nano tube/silicon/graphene composite material.
Preferably, the silicon-carbon composite material has a core-shell structure;
the particle size of the core composite material is 35-40 mu m;
the thickness of the soft carbon layer is 0.1-0.6 mu m;
the mass ratio of the core composite material to the soft carbon is 1: (4-5);
the mass ratio of the carbon nanotubes to the silicon is 1: (5-7).
Preferably, the mass ratio of the carbon nanotubes to the graphene is 1: (4-6);
the silicon comprises silicon microparticles;
the graphene comprises one or more of single-layer graphene, few-layer graphene, multi-layer graphene and graphene nanoplatelets;
the carbon nanotubes include carbon nanotubes having defects on the surface;
in the carbon nano tube/silicon/graphene composite material, silicon microparticles are attached to the surface of the carbon nano tube;
the core composite material has a rough, particulate-packed surface topography.
Preferably, in the carbon nanotube/silicon/graphene composite material, carbon nanotubes and silicon microparticles are compounded on the surface of the graphene sheet layer and/or between the graphene sheet layers;
in the carbon nanotube/silicon/graphene composite material, carbon nanotubes are interlaced among silicon microparticles;
in the carbon nano tube/silicon/graphene composite material, silicon microparticles are attached to the defect positions on the surface of the carbon nano tube;
the carbon nano tube comprises an acid etched carbon nano tube;
the core composite material has a villous surface topography formed by carbon nanotubes;
the silicon-carbon composite material is a silicon-carbon composite negative electrode material.
Preferably, the diameter of the carbon nano tube is 30-50 nm;
the length of the carbon nano tube is 10-15 mu m;
the particle size of the silicon micron particles is 5-10 mu m;
the sheet diameter of the graphene sheet layer is 1-3 mu m;
the thickness of the graphene sheet layer is 1-30 nm;
the graphene is porous graphene.
The invention provides a preparation method of a silicon-carbon composite material, which comprises the following steps:
1) ultrasonically stirring the carbon nano tube/silicon composite material and the graphene solution to obtain the carbon nano tube/silicon/graphene composite material;
2) mixing the carbon nanotube/silicon/graphene composite material obtained in the step with a soft carbon precursor to obtain a carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor;
3) and carbonizing the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor obtained in the step under a protective atmosphere to obtain the silicon-carbon composite material.
Preferably, the carbon nanotube/silicon composite material is obtained by grinding the acidified carbon nanotube and the nano silicon powder, or is prepared by the following steps:
a) premixing a surfactant, alkali and water, adding the acidified carbon nanotube and a silicon source, continuously mixing, and reacting to obtain a carbon nanotube/silicon dioxide composite material;
b) under protective atmosphere, carrying out heat treatment on the carbon nano tube/silicon dioxide composite material obtained in the step and a reducing agent to obtain a carbon nano tube/silicon composite material;
the grinding time is 10-15 h;
the grinding comprises wet ball milling;
the rotating speed of the wet ball milling is 1200-1600 r/min;
the ball-material ratio of the wet ball milling is (4-6): 1.
preferably, the surfactant comprises cetyltrimethylammonium bromide;
the base comprises ammonia;
the premixing time is 1-2 h;
the continuous mixing time is 10-20 h;
the reaction temperature is 80-150 ℃;
the reaction time is 60-85 h;
the reducing agent comprises magnesium powder;
the temperature of the heat treatment is 600-850 ℃;
the heat treatment time is 4-7 h.
Preferably, the ultrasonic stirring time is 2-4 h;
the rotating speed of the ultrasonic stirring is 500-1000 r/min;
the soft carbon precursor comprises emulsified asphalt and/or petroleum coke;
the mixing time is 1-2 h;
the carbonization temperature is 300-500 ℃;
and the carbonization time is 2-4 h.
The invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode and electrolyte;
the material of the negative electrode comprises the silicon-carbon composite material prepared by the preparation method of any one of the above technical schemes or the silicon-carbon composite material prepared by the preparation method of any one of the above technical schemes.
The invention provides a silicon-carbon composite material, which comprises a core composite material and a soft carbon layer coated on the surface of the core composite material; the core composite material is a carbon nano tube/silicon/graphene composite material. Compared with the prior art, the invention aims at the defects that the existing graphite material cathode of the lithium ion battery has low specific capacity, poor compatibility with electrolyte, poor circulation stability, poor heavy-current charging and discharging performance, unsuitability for rapid charging and discharging and the like, and the silicon material cathode has poor practical performance and also has the problems of expensive raw materials, complex process, high energy consumption, high cost, unfriendly environment and the like in the preparation process. Particularly, when the silicon-based negative electrode material similar to the heterostructure is provided in the existing experiment, in order to realize good dispersion of the carbon material and the nano silicon and complete coating of the carbon material on the nano silicon, the surface functional groups of the carbon material and the nano silicon need to be modified or realized by vapor deposition and other technologies, the problems of complex process, high cost, low capacity and the like exist, effective industrial amplification is difficult to realize, and the problem of hindering the industrialization process of the silicon-carbon negative electrode material is solved.
The invention creatively designs a silicon-carbon composite material with a special structure, the composite material has a core-shell structure, and the carbon nano tube/silicon/graphene composite material with a specific structure is used as a core composite material to obtain a cathode material with a tubular matrix multilayer coating structure. According to the invention, a carbon nano tube is used as a template, nano silicon particles are compounded on the outer layer, graphene is added for compounding, and finally soft carbon is coated on the outer layer to form the composite structure material. The multi-coating structure formed by the invention has the characteristics of rigid support of the carbon tube, two-dimensional coating and porosity of the graphene, and can effectively limit the expansion and pulverization of silicon in the circulation process; the high conductivity of the carbon tubes and the graphene makes up the problem of poor conductivity of silicon, the tubular substrate multilayer composite structure increases the contact area of the electrolyte and a negative electrode material, shortens the diffusion path of lithium ions, and meanwhile, a soft carbon layer on the outer surface of the tubular substrate is easy to form a stable SEI film with the electrolyte. When the silicon-carbon composite material provided by the invention is used for a lithium ion battery cathode material, the silicon-carbon composite material shows excellent electrochemical performance and has good cycle stability and rate capability.
In addition, the invention adopts a simpler preparation mode, realizes the uniform dispersion and preparation of the internal material of the silicon-carbon composite material, and does not need complicated processes and steps such as surface functional group modification or vapor deposition and the like. The invention simplifies the preparation method, reduces the cost, reduces the environmental pollution, has simple process route, good controllability and strong environmental protection property, and is more suitable for industrialized popularization and application.
Experimental results show that when the silicon-carbon composite material provided by the invention is used as a lithium ion battery cathode material, the silicon-carbon composite material shows excellent electrochemical performance and has good cycle stability and rate capability.
Drawings
FIG. 1 is a schematic structural diagram of a silicon-carbon composite material having a tubular substrate multi-layer coating structure provided by the present invention;
fig. 2 is an SEM scanning electron microscope image of the carbon nanotube/silicon/graphene composite material prepared in example 1 of the present invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
All raw materials of the invention are not particularly limited in purity, and the invention preferably adopts analytically pure or conventional purity used in the field of lithium ion battery cathode preparation.
The invention provides a silicon-carbon composite material, which comprises a core composite material and a soft carbon layer coated on the surface of the core composite material;
the core composite material is a carbon nano tube/silicon/graphene composite material.
The invention has no special limitation on the overall morphology of the silicon-carbon composite material in principle, and a person skilled in the art can select and adjust the overall morphology according to the actual application condition, the product requirement and the quality requirement.
The particle size of the core composite material is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the particle size of the core composite material is preferably 35-40 μm, more preferably 36-39 μm, and more preferably 37-38 μm.
The invention has no special limitation on the thickness of the soft carbon layer in principle, and a person skilled in the art can select and adjust the soft carbon layer according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphological structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the thickness of the soft carbon layer is preferably 0.1-0.6 μm, more preferably 0.2-0.5 μm, and more preferably 0.3-0.4 μm.
In the invention, the mass ratio of the core composite material to the soft carbon is not particularly limited in principle, and a person skilled in the art can select and adjust the core composite material according to the actual application condition, the product requirement and the quality requirement, so that the specific morphology structure of the composite material is further ensured, the deformation and pulverization of the silicon material are better relieved, the direct contact of the silicon material and the electrolyte is reduced, the contact area of the electrolyte and a negative electrode material is enhanced, the diffusion path of lithium ions is shortened, and the electrochemical performance in application is further improved, and the mass ratio of the core composite material to the soft carbon is preferably 1: (4-5), more preferably 1: (4.2 to 4.8), more preferably 1: (4.4-4.6).
In order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and a negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance during application, the mass ratio of the carbon nanotube to the silicon is preferably 1: (5-7), more preferably 1: (5.4-6.6), more preferably 1: (5.8-6.2).
In the invention, the mass ratio of the carbon nanotube to the graphene is not particularly limited in principle, and a person skilled in the art can select and adjust the mass ratio according to actual application conditions, product requirements and quality requirements, in order to further ensure a specific morphological structure of the composite material, better alleviate the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and an electrolyte, enhance the contact area of the electrolyte and a negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the mass ratio of the carbon nanotube to the graphene is preferably 1: (4-6), more preferably 1: (4.4 to 5.6), more preferably 1: (4.8-5.2).
The specific selection of the silicon is not particularly limited in principle, and a person skilled in the art can select and adjust the silicon according to the actual application condition, the product requirement and the quality requirement. More specifically, the particle size of the silicon microparticles is preferably 5-10 μm, more preferably 6-9 μm, and more preferably 7-8 μm.
The specific selection of the graphene is not particularly limited in principle, and a person skilled in the art can select and adjust the graphene according to the actual application condition, the product requirements and the quality requirements.
The invention has no special limitation on other morphological characteristics of the graphene in principle, and a person skilled in the art can select and adjust the morphological characteristics according to the actual application condition, the product requirement and the quality requirement.
The sheet diameter of the graphene sheet layer is preferably 1-3 μm, more preferably 1.4-2.6 μm, and even more preferably 1.8-2.2 μm, in order to further ensure the specific morphology structure of the composite material, better alleviate the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, and shorten the diffusion path of lithium ions, thereby improving the electrochemical performance in application.
The thickness of the graphene sheet layer is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual application conditions, product requirements and quality requirements, the specific morphological structure of the composite material is further ensured, deformation and pulverization of the silicon material are better relieved, direct contact of the silicon material and an electrolyte is reduced, the contact area of the electrolyte and a negative electrode material is increased, the diffusion path of lithium ions is shortened, and further the electrochemical performance in application is improved, and the thickness of the graphene sheet layer is preferably 1-30 nm, more preferably 5-25 nm, and more preferably 10-20 nm.
The specific selection of the carbon nano tube is not particularly limited in principle, and a person skilled in the art can select and adjust the carbon nano tube according to the actual application condition, the product requirement and the quality requirement. Specifically, the carbon nanotube preferably includes a carbon nanotube having a defect on the surface. More preferably, the carbon nanotubes preferably comprise acid etched carbon nanotubes.
The diameter of the carbon nanotube is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the diameter of the carbon nanotube is preferably 30-50 nm, more preferably 34-46 nm, and more preferably 38-42 nm.
The length of the carbon nanotube is not particularly limited in principle, and a person skilled in the art can select and adjust the length according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the length of the carbon nanotube is preferably 10-15 μm, more preferably 11-14 μm, and more preferably 12-13 μm.
The invention relates to a complete and refined integral preparation scheme, in order to further ensure a specific morphological structure of a composite material, better relieve the deformation and pulverization of a silicon material, reduce the direct contact of the silicon material and an electrolyte, enhance the contact area of the electrolyte and a negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, in the carbon nanotube/silicon/graphene composite material, silicon microparticles are preferably attached to the surface of a carbon nanotube and can also be regarded as silicon microparticles forming a coated structure on the outer surface of the carbon nanotube.
The invention is a complete and refined integral preparation process, further ensures the specific morphological structure of the composite material, better relieves the deformation and pulverization of the silicon material, reduces the direct contact between the silicon material and an electrolyte, enhances the contact area between the electrolyte and a negative electrode material, shortens the diffusion path of lithium ions, and further improves the electrochemical performance in application. The above-mentioned compounding preferably includes attaching in the present invention.
The invention is a complete and refined integral preparation process, further ensures the specific morphology structure of the composite material, better relieves the deformation and pulverization of the silicon material, reduces the direct contact of the silicon material and the electrolyte, enhances the contact area of the electrolyte and the cathode material, shortens the diffusion path of lithium ions, and further improves the electrochemical performance in application.
The invention is a complete and refined integral preparation process, further ensures the specific morphology structure of the composite material, better relieves the deformation and pulverization of the silicon material, reduces the direct contact of the silicon material and the electrolyte, enhances the contact area of the electrolyte and the cathode material, shortens the diffusion path of lithium ions, and further improves the electrochemical performance in application.
The invention has no special limitation on the surface appearance of the core composite material in principle, and a person skilled in the art can select and adjust the surface appearance according to the actual application condition, the product requirement and the quality requirement. More preferably, the core composite preferably has a rough, particulate-packed surface topography.
The invention has no special limitation on the application direction of the silicon-carbon composite material in principle, and a person skilled in the art can select and adjust the silicon-carbon composite material according to the actual application condition, the product requirement and the quality requirement.
The invention provides a high-performance silicon-carbon negative electrode material for a lithium ion battery, which is a tubular matrix silicon-carbon negative electrode material with a non-strict multilayer composite structure, wherein the innermost layer of the core composite material is mostly carbon nanotubes, the middle layer is mostly silicon-based material, and the outermost layer is approximately a graphene coating layer. Due to the composition of the special structure, the contact area between the active material and the electrolyte can be layered, and lithium ions are allowed to be intercalated inside and outside the nanotube; the graphene layer has good conductivity, and the graphene shell can ensure silicon microparticles to be trapped in the graphene shell even after repeated circulation; the graphene nanometer on the surface forms a conductive layer with high conductivity, so that the conductivity of the material is improved. The tubular matrix structure of CNTs @ Si @ G can relieve stress generated by volume change in the charging and discharging process, so that crack formation and active material layering and falling off are reduced to the maximum extent. While the outermost carbon layer tends to form a stable SEI film with the electrolyte.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a silicon-carbon composite material having a tubular substrate multilayer coating structure according to the present invention.
The invention provides a preparation method of a silicon-carbon composite material, which comprises the following steps:
1) ultrasonically stirring the carbon nano tube/silicon composite material and the graphene solution to obtain the carbon nano tube/silicon/graphene composite material;
2) mixing the carbon nanotube/silicon/graphene composite material obtained in the step with a soft carbon precursor to obtain a carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor;
3) and carbonizing the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor obtained in the step under a protective atmosphere to obtain the silicon-carbon composite material.
The selection, composition and structure of the materials in the preparation method and the corresponding preferred principle of the invention can preferably correspond to the selection, composition and structure of the silicon-carbon composite material and the corresponding preferred principle, and are not described in detail herein.
According to the invention, the carbon nanotube/silicon composite material and the graphene solution are ultrasonically stirred to obtain the carbon nanotube/silicon/graphene composite material.
The ultrasonic stirring time is preferably 2-4 hours, more preferably 2.4-3.6 hours, and more preferably 2.8-3.2 hours, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, and shorten the diffusion path of lithium ions, thereby improving the electrochemical performance in application.
The rotating speed of the ultrasonic stirring is preferably 500-1000 r/min, more preferably 600-900 r/min, and more preferably 700-800 r/min, in order to further ensure the specific morphology structure of the composite material, better alleviate the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, and shorten the diffusion path of lithium ions, thereby improving the electrochemical performance in application.
The carbon nanotube/silicon composite material is obtained by grinding acidified carbon nanotubes and nano silicon powder, and is preferably used for further ensuring the specific morphology structure of the composite material, better relieving the deformation and pulverization of the silicon material, reducing the direct contact of the silicon material and an electrolyte, enhancing the contact area of the electrolyte and a negative electrode material, shortening the diffusion path of lithium ions and further improving the electrochemical performance in application. Or, the preparation method comprises the following steps:
a) premixing a surfactant, alkali and water, adding the acidified carbon nanotube and a silicon source, continuously mixing, and reacting to obtain a carbon nanotube/silicon dioxide composite material;
b) and (3) carrying out heat treatment on the carbon nano tube/silicon dioxide composite material obtained in the step and a reducing agent in a protective atmosphere to obtain the carbon nano tube/silicon composite material.
The carbon nanotube/silicon composite material is preferably obtained by grinding the acidified carbon nanotube and the nano silicon powder.
The grinding time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the grinding time is preferably 10-15 h, more preferably 11-14 h, and more preferably 12-13 h.
The grinding mode is not particularly limited in principle, and a person skilled in the art can select and adjust the grinding mode according to the actual application condition, the product requirement and the quality requirement.
The rotating speed of the wet ball milling is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual application conditions, product requirements and quality requirements, in order to further ensure a specific morphological structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and an electrolyte, enhance the contact area of the electrolyte and a negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the rotating speed of the wet ball milling is preferably 1200-1600 r/min, more preferably 1250-1550 r/min, more preferably 1300-1500 r/min, and more preferably 1350-1450 r/min.
The ball-material ratio of the wet ball milling is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual application conditions, product requirements and quality requirements, in order to further ensure a specific morphological structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and an electrolyte, enhance the contact area of the electrolyte and a negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the ball-material ratio of the wet ball milling is preferably (4-6): 1, more preferably (4.4 to 5.6): 1, more preferably (4.8 to 5.2): 1.
the carbon nanotube/silicon composite material is preferably prepared by the following steps:
a) premixing a surfactant, alkali and water, adding the acidified carbon nanotube and a silicon source, continuously mixing, and reacting to obtain a carbon nanotube/silicon dioxide composite material;
b) and (3) carrying out heat treatment on the carbon nano tube/silicon dioxide composite material obtained in the step and a reducing agent in a protective atmosphere to obtain the carbon nano tube/silicon composite material.
Firstly, premixing surfactant, alkali and water, then adding acidified carbon nano tube and silicon source, continuously mixing them and making reaction so as to obtain the carbon nano tube/silicon dioxide composite material.
The specific selection of the surfactant is not particularly limited in principle, and a person skilled in the art can select and adjust the surfactant according to the actual application situation, the product requirements and the quality requirements.
The specific selection of the alkali is not particularly limited in principle, and a person skilled in the art can select and adjust the alkali according to the actual application condition, the product requirement and the quality requirement.
The specific selection of the silicon source is not particularly limited in principle, and a person skilled in the art can select and adjust the silicon source according to the actual application condition, the product requirement and the quality requirement.
The premixing time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual application conditions, product requirements and quality requirements, the specific morphology structure of the composite material is further ensured, the deformation and pulverization of the silicon material are better relieved, the direct contact of the silicon material and an electrolyte is reduced, the contact area of the electrolyte and a negative electrode material is enhanced, the diffusion path of lithium ions is shortened, and further the electrochemical performance in application is improved, wherein the premixing time is preferably 1-2 hours, more preferably 1.2-1.8 hours, and more preferably 1.4-1.6 hours.
The time for continuously mixing is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the time for continuously mixing is preferably 10-20 hours, more preferably 12-18 hours, and more preferably 14-16 hours.
The reaction temperature is preferably 80-150 ℃, more preferably 90-140 ℃, more preferably 100-130 ℃, and more preferably 110-120 ℃, in order to further ensure the specific morphology structure of the composite material, better alleviate the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, and shorten the diffusion path of lithium ions, thereby improving the electrochemical performance in application.
The reaction time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the reaction time is preferably 60-85 h, more preferably 65-80 h, and more preferably 70-75 h.
Finally, under protective atmosphere, the carbon nano tube/silicon dioxide composite material obtained in the step and a reducing agent are subjected to heat treatment to obtain the carbon nano tube/silicon composite material.
The specific selection of the reducing agent is not particularly limited in principle, and a person skilled in the art can select and adjust the reducing agent according to the actual application condition, the product requirement and the quality requirement.
The invention has no special limitation on the heat treatment temperature in principle, and a person skilled in the art can select and adjust the heat treatment temperature according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphological structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the cathode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the heat treatment temperature is preferably 600-850 ℃, more preferably 650-800 ℃, and more preferably 700-750 ℃.
The heat treatment time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the heat treatment time is preferably 4-7 hours, more preferably 4.5-6.5 hours, and more preferably 5-6 hours.
According to the invention, the carbon nanotube/silicon/graphene composite material obtained in the above step is mixed with the soft carbon precursor to obtain the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor.
The invention has no particular limitation on the specific selection of the soft carbon precursor in principle, and a person skilled in the art can select and adjust the soft carbon precursor according to the actual application condition, the product requirement and the quality requirement. Wherein the petroleum coke is one or more of sponge coke, honeycomb coke and needle coke.
The mixing time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the mixing time is preferably 1-2 hours, more preferably 1.2-1.8 hours, and more preferably 1.4-1.6 hours.
Finally, under a protective atmosphere, carbonizing the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor obtained in the step, and obtaining the silicon-carbon composite material.
The carbonization temperature is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual application conditions, product requirements and quality requirements, the specific morphology structure of the composite material is further ensured, the deformation and pulverization of the silicon material are better relieved, the direct contact of the silicon material and an electrolyte is reduced, the contact area of the electrolyte and a negative electrode material is enhanced, the diffusion path of lithium ions is shortened, and the electrochemical performance in application is further improved, wherein the carbonization temperature is preferably 300-500 ℃, more preferably 340-460 ℃, and more preferably 380-420 ℃.
The carbonization time is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual application condition, the product requirement and the quality requirement, in order to further ensure the specific morphology structure of the composite material, better relieve the deformation and pulverization of the silicon material, reduce the direct contact of the silicon material and the electrolyte, enhance the contact area of the electrolyte and the negative electrode material, shorten the diffusion path of lithium ions and further improve the electrochemical performance in application, the carbonization time is preferably 2-4 h, more preferably 2.4-3.6 h, and more preferably 2.8-3.2 h.
The silicon-carbon composite material prepared in the steps is a composite material with a multi-layer tubular matrix structure CNTs @ Si @ G, and has a graphene and carbon nano tube electronic dual-channel, after the CNT is pre-treated and etched by acid, defects are formed on the outer tube wall of the CNT, a silicon-based material is added to form CNTs @ SiO2, the CNTs @ Si is obtained after reduction, and the CNTs @ Si is compounded with the graphene to obtain the composite structure material of the CNTs @ Si @ G. The double-coating structure formed by the invention has the characteristics of rigid support of the carbon tube, two-dimensional coating and porosity of the graphene, and can effectively limit the expansion and pulverization of silicon in the circulation process; the high conductivity of the carbon tubes and the graphene makes up for the problem of silicon conductivity. According to the invention, the conductivity of the Si-based negative electrode material can be improved by the external carbon layer and the internal carbon nano tube, and the contact area between the active material and the electrolyte can be increased, so that lithium ions are allowed to be intercalated inside and outside the nano tube; the high gram capacity is 1500-2000 mAh/g; the carbon layer can stabilize the interface of the active negative electrode material and the electrolyte, promote stable SEI formation and long cycle life; the tubular structure matrix of the CNTs @ Si @ G can relieve stress generated by volume change in the charging and discharging process, so that crack formation and active material layering and falling off are reduced to the maximum extent; the one-dimensional silicon micron line formed by the structure can effectively relieve the pulverization of materials in the charging and discharging process, thereby improving the electrochemical performance of the Si nanotube under the high current density. Meanwhile, the outer carbon layer is easy to form a stable SEI film with the electrolyte; when the material is used as a negative electrode material of a lithium ion battery, excellent electrochemical performance is shown.
The invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode and electrolyte;
the material of the negative electrode comprises the silicon-carbon composite material prepared by the preparation method of the technical scheme or the silicon-carbon composite material prepared by the preparation method of the technical scheme.
The invention provides a high-performance silicon-carbon negative electrode material for a lithium ion battery, a preparation method of the high-performance silicon-carbon negative electrode material and the lithium ion battery. The silicon-carbon cathode material is a silicon-carbon composite material with a special structure, the composite material has a core-shell structure, and a carbon nano tube/silicon/graphene composite material with a specific structure is used as a core composite material to obtain the cathode material with a tubular matrix multilayer coating structure. According to the invention, a carbon nano tube is used as a template, silicon dioxide is coated on the outer layer, the silicon dioxide is reduced into silicon through a magnesiothermic reduction reaction, and then graphene is added for coating, and then soft carbon is adopted for coating, so that the material with the composite structure is obtained. In the multiple coating structure formed by the invention, the carbon nano tube has good conductivity, the mechanical property of the good rigid support can improve and relieve the volume expansion of silicon in the charging and discharging process, the conductivity can be improved, and the two-dimensional coating and porous characteristics of graphene can effectively limit the expansion and pulverization of silicon in the circulating process; the tubular matrix three-layer composite structure increases the contact area between electrolyte and a negative electrode material, shortens the diffusion path of lithium ions, and simultaneously, a soft carbon layer on the outer surface of the tubular matrix is easy to form a stable SEI film with the electrolyte. When the silicon-carbon composite material provided by the invention is used for a lithium ion battery cathode material, the silicon-carbon composite material shows excellent electrochemical performance and has good cycle stability and rate capability.
In addition, the invention adopts a simpler preparation mode, realizes the uniform dispersion and preparation of the internal material of the silicon-carbon composite material, and does not need complicated processes and steps such as surface functional group modification or vapor deposition and the like. The invention simplifies the preparation method, reduces the cost, reduces the environmental pollution, has simple process route, good controllability and strong environmental protection property, and is more suitable for industrialized popularization and application.
Experimental results show that when the silicon-carbon composite material provided by the invention is used as a lithium ion battery cathode material, the silicon-carbon composite material shows excellent electrochemical performance and has good cycle stability and rate capability.
In order to further illustrate the present invention, the following will describe a silicon-carbon composite material, a method for preparing the same, and a lithium ion battery in detail with reference to the following examples, but it should be understood that the examples are implemented on the premise of the technical solution of the present invention, and the detailed embodiments and specific operation procedures are given, only for further illustrating the features and advantages of the present invention, but not for limiting the claims of the present invention, and the scope of the present invention is not limited to the following examples.
Example 1
1. Treated with nitric acidThe carbon nano tube is used as a template, and the acidification process is as follows: putting a certain amount of multi-walled carbon nano-tubes with the inner layer diameter of about 30 nanometers into a 250mL conical flask, adding nitric acid into the conical flask, carrying out ultrasonic treatment for 8 hours, carrying out solid-liquid separation by using a centrifugal machine, centrifuging for a plurality of times, washing by using distilled water until eluate is clear, removing impurity metal catalysts in the carbon nano-tubes, and drying in a vacuum oven at 80 ℃ for 2 hours when the pH value is close to neutral. 2g of multi-walled carbon nanotube was added to a 100mL conical flask, and 40mL (concentrated H) of mixed acid was added thereto2SO4(98%): concentrated HNO3(60%) < 3: 1), ultrasonic treating at room temperature for 8h, diluting with distilled water, standing, precipitating carbon nanotube, removing supernatant, filtering with polytetrafluoroethylene film (pore size of 0.22 μm), washing with water for several times until the pH value of the filtrate is about 6, and drying at 80 deg.C for 24h to obtain acidified carbon nanotube.
2. 1g of CTAB (cetyl trimethyl ammonium bromide), 100ml of deionized water and 10ml of ammonia water are taken in sequence, uniformly stirred for 1h to form a transparent solution, then 2g of pretreated carbon nano tube and 4ml of tetraethoxysilane are added, ultrasonic stirring is continued for 12h, finally the obtained solution is added into a 100ml reaction kettle, and the solution is subjected to heat preservation at 100 ℃ for 72h, then separated and cleaned to obtain CNTs @ SiO2。
3. 0.5g of magnesium powder is put in a crucible, and 0.5g of CNTs @ SiO2Covering on magnesium powder, placing into a tube furnace, heating to 750 deg.C at a rate of 5 deg.C/min under the protection of argon gas, maintaining for 5 hr, cooling with the furnace, and removing MgO and unreacted SiO by acid washing2And (3) filtering, washing and drying impurities to obtain the CNTs @ Si.
4. And dispersing the prepared 300mg of CNTs @ Si into 50ml of graphene solution, ultrasonically stirring for 2h, filtering, washing and drying to obtain the material with the tubular multilayer composite structure of CNTs @ Si @ G.
The CNTs @ Si @ G composite material prepared in the embodiment 1 of the invention is characterized.
Referring to fig. 2, fig. 2 is an SEM scanning electron microscope image of the carbon nanotube/silicon/graphene composite material prepared in example 1 of the present invention.
As can be seen from FIG. 2, the particle size of the core composite material of the silicon-carbon composite material prepared by the present invention is about 35 μm, the core composite material has a rough surface morphology of particle-like accumulation, the morphology of graphene lamellar coating can be seen, and the carbon nanotubes are interlaced and interlaced among the silicon microparticles, and simultaneously the surface of the core composite material also has a fluffy surface formed by the carbon nanotubes
5. And (2) uniformly mixing the carbon nanotube/silicon/graphene composite material with a soft carbon precursor, namely needle coke for 1h to obtain the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor, and carbonizing at 300 ℃ for 2h under the condition of argon to obtain the silicon-carbon composite material.
The performance of the silicon-carbon composite negative electrode material prepared in the embodiment 1 of the invention is detected.
The result shows that the silicon-carbon composite negative electrode material prepared by the invention has the first discharge capacity of 481mAh/g, the efficiency of 83 percent and the average weekly capacity attenuation of 1.5mAh/g after circulation for 10 weeks.
Example 2
1. Using a carbon nano tube treated by nitric acid as a template, carrying out wet ball milling (1500r/min, ball-to-material ratio: 4: 1) on silicon powder in superfine ball milling equipment by taking water as a medium, and stopping ball milling after ball milling for 10 hours to obtain CNTs @ Si silicon slurry;
2. and dispersing the prepared 300mg of CNTs @ Si into 50ml of graphene solution, ultrasonically stirring for 2h, filtering, washing and drying to obtain the material with the tubular multilayer composite structure of CNTs @ Si @ G.
3. Then adding soft carbon precursor needle coke, and treating for 1h at 300 ℃ to obtain the material with the composite structure.
The following are the specific parameters in example 2 and the related experiments performed with varying silicon content, respectively:
experiment one: the silicon-carbon negative electrode material comprises the following components in percentage by weight: slurry containing nano silicon powder: 15 wt%; the carbon nanotubes with the average diameter of the internal filament of about 30 nanometers are single-wall carbon nanotubes or multi-wall carbon nanotubes: 20 wt%; emulsified asphalt: 48 wt%; the silicon-carbon composite negative electrode material prepared in embodiment 2 of the invention.
The silicon-carbon composite anode material prepared in the first experiment of example 2 of the invention was tested.
Referring to table 1, table 1 shows performance parameters of the silicon-carbon composite anode material prepared in example 2 of the present invention.
Experiment two: the silicon-carbon negative electrode material comprises the following components in percentage by weight: slurry containing nano silicon powder: 20 wt%; the carbon nanotubes with the average diameter of the internal filament of about 30 nanometers are single-wall carbon nanotubes or multi-wall carbon nanotubes: 20 wt%; emulsified asphalt: 48 wt%; the silicon-carbon composite negative electrode material prepared in embodiment 2 of the invention.
The silicon-carbon composite anode material prepared in experiment two of example 2 of the invention was tested.
Referring to table 1, table 1 shows performance parameters of the silicon-carbon composite anode material prepared in example 2 of the present invention.
Experiment three: the silicon-carbon negative electrode material comprises the following components in percentage by weight: slurry containing nano silicon powder: 25 wt%; the carbon nanotubes with the average diameter of the internal filament of about 30 nanometers are single-wall carbon nanotubes or multi-wall carbon nanotubes: 20 wt%; emulsified asphalt: 48 wt%; the silicon-carbon composite negative electrode material prepared in embodiment 2 of the invention.
The silicon-carbon composite anode material prepared in experiment three of example 2 of the invention was tested.
Referring to table 1, table 1 shows performance parameters of the silicon-carbon composite anode material prepared in example 2 of the present invention.
Experiment four: the silicon-carbon negative electrode material comprises the following components in percentage by weight: slurry containing nano silicon powder: 30 wt%; the carbon nanotubes with the average diameter of the internal filament of about 30 nanometers are single-wall carbon nanotubes or multi-wall carbon nanotubes: 20 wt%; emulsified asphalt: 48 wt%; the silicon-carbon composite negative electrode material prepared in embodiment 2 of the invention.
The silicon-carbon composite anode material prepared in experiment four of example 2 of the invention was tested.
Referring to table 1, table 1 shows performance parameters of the silicon-carbon composite anode material prepared in example 2 of the present invention.
TABLE 1
Item Specific capacity of first discharge (mAh/g) First discharge efficiency Cycle retention at 300 weeks
Experiment one 463.8 87.5％ 81.1％
Experiment two 468.0 88.3％ 82.3％
Experiment three 473.3 89.3％ 83.1％
Experiment four 474.0 89.9％ 83.8％
The present invention provides a high performance silicon carbon negative electrode material for lithium ion battery, a method for preparing the same, and a lithium ion battery, which are described in detail above, and the principle and embodiments of the present invention are described herein by using specific examples, and the description of the above examples is only for helping to understand the method and the core idea of the present invention, including the best mode, and also for enabling anyone skilled in the art to practice the present invention, including making and using any device or system, and implementing any method in combination. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (10)

1. The silicon-carbon composite material is characterized by comprising a core composite material and a soft carbon layer coated on the surface of the core composite material;
the core composite material is a carbon nano tube/silicon/graphene composite material.
2. The composite material of claim 1, wherein the silicon carbon composite material has a core-shell structure;
the particle size of the core composite material is 35-40 mu m;
the thickness of the soft carbon layer is 0.1-0.6 mu m;
the mass ratio of the core composite material to the soft carbon is 1: (4-5);
the mass ratio of the carbon nanotubes to the silicon is 1: (5-7).
3. The composite material according to claim 1, wherein the mass ratio of the carbon nanotubes to the graphene is 1: (4-6);
the silicon comprises silicon microparticles;
the graphene comprises one or more of single-layer graphene, few-layer graphene, multi-layer graphene and graphene nanoplatelets;
the carbon nanotubes include carbon nanotubes having defects on the surface;
in the carbon nano tube/silicon/graphene composite material, silicon microparticles are attached to the surface of the carbon nano tube;
the core composite material has a rough, particulate-packed surface topography.
4. The composite material according to claim 3, wherein in the carbon nanotube/silicon/graphene composite material, carbon nanotubes and silicon microparticles are composited on the surface of the graphene sheets and/or between the graphene sheets;
in the carbon nanotube/silicon/graphene composite material, carbon nanotubes are interlaced among silicon microparticles;
in the carbon nano tube/silicon/graphene composite material, silicon microparticles are attached to the defect positions on the surface of the carbon nano tube;
the carbon nano tube comprises an acid etched carbon nano tube;
the core composite material has a villous surface topography formed by carbon nanotubes;
the silicon-carbon composite material is a silicon-carbon composite negative electrode material.
5. The composite material of claim 3, wherein the carbon nanotubes have a diameter of 30 to 50 nm;
the length of the carbon nano tube is 10-15 mu m;
the particle size of the silicon micron particles is 5-10 mu m;
the sheet diameter of the graphene sheet layer is 1-3 mu m;
the thickness of the graphene sheet layer is 1-30 nm;
the graphene is porous graphene.
6. The preparation method of the silicon-carbon composite material is characterized by comprising the following steps:
1) ultrasonically stirring the carbon nano tube/silicon composite material and the graphene solution to obtain the carbon nano tube/silicon/graphene composite material;
2) mixing the carbon nanotube/silicon/graphene composite material obtained in the step with a soft carbon precursor to obtain a carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor;
3) and carbonizing the carbon nanotube/silicon/graphene composite material coated with the soft carbon precursor obtained in the step under a protective atmosphere to obtain the silicon-carbon composite material.
7. The preparation method according to claim 6, wherein the carbon nanotube/silicon composite material is obtained by grinding acidified carbon nanotubes and nano silicon powder, or is prepared by the following steps:
a) premixing a surfactant, alkali and water, adding the acidified carbon nanotube and a silicon source, continuously mixing, and reacting to obtain a carbon nanotube/silicon dioxide composite material;
b) under protective atmosphere, carrying out heat treatment on the carbon nano tube/silicon dioxide composite material obtained in the step and a reducing agent to obtain a carbon nano tube/silicon composite material;
the grinding time is 10-15 h;
the grinding comprises wet ball milling;
the rotating speed of the wet ball milling is 1200-1600 r/min;
the ball-material ratio of the wet ball milling is (4-6): 1.
8. the method of claim 7, wherein the surfactant comprises cetyltrimethylammonium bromide;
the base comprises ammonia;
the premixing time is 1-2 h;
the continuous mixing time is 10-20 h;
the reaction temperature is 80-150 ℃;
the reaction time is 60-85 h;
the reducing agent comprises magnesium powder;
the temperature of the heat treatment is 600-850 ℃;
the heat treatment time is 4-7 h.
9. The preparation method according to claim 6, wherein the ultrasonic stirring time is 2-4 h;
the rotating speed of the ultrasonic stirring is 500-1000 r/min;
the soft carbon precursor comprises emulsified asphalt and/or petroleum coke;
the mixing time is 1-2 h;
the carbonization temperature is 300-500 ℃;
and the carbonization time is 2-4 h.
10. A lithium ion battery is characterized by comprising a positive electrode, a negative electrode and electrolyte;
the material of the negative electrode comprises the silicon-carbon composite material as defined in any one of claims 1 to 4 or the silicon-carbon composite material prepared by the preparation method as defined in any one of claims 5 to 8.
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