CN108390049A - A kind of silicon@silicon carbide@carbon composite material of core-shell structure and preparation method thereof - Google Patents
A kind of silicon@silicon carbide@carbon composite material of core-shell structure and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a kind of silicon@silicon carbide@carbon composite material of core-shell structure, belong to lithium ion battery negative material field.The composite material contains internal layer, middle layer and outer layer three-decker；Wherein, internal layer is silicon Si hypothallus, middle layer is silicon carbide SiC hypothallus, and outer layer is carbon C hypothallus.In addition, the present invention also provides the preparation methods of the composite material.The specific capacity for the silicon@silicon carbide@carbon composite material of core-shell structure that the present invention is prepared is high, about 1800~2500mAh/g, and has excellent cyclical stability.
Description
Technical field
The present invention relates to technical field of lithium ion battery negative, more particularly to a kind of silicon Si@silicon carbide SiC@carbon C cores
Core-shell structure composite material and preparation method thereof.
Background technology
It is using lithium metal as cathode, because the high reduction potential of lithium makes this system that can carry first at the beginning of lithium battery develops
For quite high capacitance (mass energy density 3860mAh/g, volume energy density 2060mAh/cm3).However it was charging
Cheng Zhong, lithium ion can be deposited on lithium an- ode surface, generate dendrite.The lithium of these dendritic crystallines once punctures diaphragm, will cause
Internal short-circuit and so that battery is had the anxiety of combustion explosion, to improve its safety, Sony SONY is developed using carbon material as cathode
Second generation lithium ion battery.Until now, commercially available lithium ion battery is still mostly with various carbon materials for its negative material.But
Its theoretical capacity of carbon material is low (372mAh/g), and current battery has reached substantially to its theoretical capacity.Therefore many in recent years
Research is devoted to the material that development has more high-capacitance, may replace carbon-based negative electrode.
Silicon source is wide, at low cost, be applied to lithium ion battery negative material have theoretical specific capacity high (4200mAh/g),
Big (the 9786mAh/cm of volume energy density3) the characteristics of, and the averagely de- lithium platform rather moderate (0.4V) of silicium cathode, it is difficult to cause
Surface analyses lithium phenomenon and has good security performance, thus is considered as most potential next-generation negative electrode of lithium ion battery
One of material.Currently, the development bottleneck problem of silicium cathode material is it, there are huge volume is swollen during embedding lithium takes off lithium
It is swollen with blockage effect (＞ 300%), cause the easy dusting of silica flour, electrodes conduct Web Grafiti, solid electrolyte interface film (SEI,
Solid electrolyte interface) lasting formation, to cause the decaying of battery capacity, cyclical stability is deteriorated.
Silicon carbide (SiC) is a kind of wide band gap semiconducter, has broad-band gap, high intensity, high rigidity, excellent thermal shock resistance
And inoxidizability, it can be in room temperature and high-temperature field as excellent semi-conducting material application.It is several due to SiC high mechanical strengths
It is that silicon materials are evenly spread to SiC bases using SiC as a kind of " buffer substance " not have electro-chemical activity, Existing policies
Si/SiC composite materials are prepared in matter, are disperseed and are buffered the volume expansion of silicon using SiC in this way, improve electrode stability.
However, such Si/SiC composite materials have the following problems：1) disperse uneven.Ball milling the preparation method, this method are generally used at present
Although preparing simply, the adhesive force of Si and SiC matrix is poor, it is difficult to obtain evenly dispersed nanosizing particle, not fully
The aggregate of dispersion will seriously undermine the buffering expansion of SiC matrix；2) poorly conductive.Since Si and SiC are semiconductor
Material so that the electric conductivity of composite material is poor, and chemical property is difficult to be not fully exerted.
In conclusion although Si/SiC composite materials prepared by ball-milling method can inhibit the volume of Si swollen to a certain extent
It is swollen, its electrochemical cycle stability is improved, but the reversible electrochemical capacity of such material still needs to further increase with cycle performance,
Requirement of the next-generation negative material to height ratio capacity, high circulation stability could be met.
Invention content
It is existing to solve an embodiment of the present invention provides a kind of Si@SiC@C composite material of core-shell structure and preparation method thereof
There is a problem of that the specific capacity of Si/SiC composite materials is low, cyclical stability is poor in technology.For one of the embodiment to disclosure
There are one basic understandings for a little aspects, and simple summary is shown below.The summarized section is not extensive overview, nor true
Determine key/critical component or describes the protection domain of these embodiments.Its sole purpose is to be presented one with simple form
A little concepts, in this, as the preamble of following detailed description.
According to a first aspect of the embodiments of the present invention, a kind of Si@SiC@C composite material of core-shell structure is provided.
In some exemplary embodiments, Si@SiC@C composite material of core-shell structure contains internal layer, middle layer and outer layer
Three-decker；Wherein, internal layer is silicon Si hypothallus, middle layer is silicon carbide SiC hypothallus, and outer layer is carbon C hypothallus.
In the above-described embodiments, Si hypothallus can be pure Si or be doped with other metals or nonmetalloid be with Si
The mixture of main body.Approximately, SiC hypothallus can be SiC or the mixture containing SiC.C hypothallus refers to based on carbon
Clad, can be pure carbon material, such as agraphitic carbon, graphene, graphitic carbon, or be doped with metal or nonmetalloid
Carbon material etc..
Preferably, internal layer is pure Si powder, and middle layer SiC, outer layer is agraphitic carbon or graphitic carbon.
Wherein, the non-SiC nanowires of SiC, but the SiC clads of fine and close cladding.
Within this material, three-decker is the shell core three-decker of fine and close cladded type, and it is negative to can be directly used for lithium ion battery
The preparation of pole material, and find after tested, nucleocapsid clad can effectively inhibit the volume change of Si in charge and discharge process, surely
The SEI films on fixed electrode surface, this composite material have specific capacity height, about 1800~2500mAh/g, the spies such as good cycling stability
Point.
In some optional embodiments, by the total weight of composite material it is in terms of 100% that the mass fraction of internal layer is 19~
96%, the mass fraction of middle layer is 3~80%, and the mass fraction of outer layer is 1~40%.Preferably, the mass fraction of internal layer
It is 60%~80%, the mass fraction of middle layer is 15~20%, and the mass fraction of outer layer is 5%~20%.
In some optional embodiments, if Si hypothallus is Si powder, particle diameter is 0.02~50 μm.It is preferred that
, the particle diameter of Si powder is 50nm, 70nm, 90nm, 5 μm, 10 μm and 20 μm.
In some optional embodiments, the thickness of middle layer is 2nm~20 μm, and the thickness of outer layer is 2nm~10 μm.It is excellent
Choosing, the thickness of middle layer is 5~300nm.The thickness of outer layer is 10~200nm.
Above-described embodiment gives each preferred mass fraction of hypothallus in Si@SiC@C composite material of core-shell structure, Si powder
The preferred thickness of the middle layer and outer layer of preferred particle diameter range and Si@SiC@C composite material of core-shell structure, into one
Step improves cyclical stability of the composite material as cell negative electrode material when.
According to a second aspect of the embodiments of the present invention, a kind of preparation side of Si@SiC@C composite material of core-shell structure is provided
Method.
In some exemplary embodiments, which includes：Carburising step and carbon coating step；Wherein：
Carburising step includes：Powder containing Si is heated to carburizing temperature under the protection of the first carrier gas, is passed through containing carbon source
The first reaction gas carry out carburizing reagent, obtain Si@SiC Core-shell structure materials；
Carbon coating step includes：Si@SiC Core-shell structure materials are heated or cooled to carbon packet under the protection of the second carrier gas
Temperature is covered, the second reaction gas containing carbon source and the second carrier gas is passed through and carries out chemical vapor deposition, obtain Si@SiC@C nucleocapsid knots
Structure composite material.
In carburising step：
First carrier gas can be with argon gas or the gaseous mixture of hydrogen and argon gas.Further, if the mixing of hydrogen and argon gas
Gas, then the volume ratio of hydrogen and argon gas is 0.01~0.4:1.Further, the gas velocity of the first carrier gas is 0.1~1L/min.It is excellent
Choosing, the gas velocity of the first carrier gas is 0.2,0.3,0.4,0.5L/min.
Carburizing temperature is 900~1400 DEG C.Preferably, 1100,1200 and 1300 DEG C of carburizing temperature.Further, will
During first powder is heated to carburizing temperature under the protection of the first carrier gas, heating rate is 1~20 DEG C/min.It is preferred that
, heating rate 5,10,15 DEG C/min.
First reaction gas can be the gaseous mixture containing hydrogen and carbon source.Wherein, the volume ratio of hydrogen and carbon source be 0~
0.4:1.Further, during carburizing reagent, the gas velocity of the first reaction gas is 0.01~1L/min.Preferably, first
The gas velocity of reaction gas be 0.1,0.2,0.3,0.4,0.5L/min.
The carburizing reagent time is 0.2~2h.
Carbon source can be that methane, ethane, ethylene, acetylene, propylene, propane, ethyl alcohol, carbon monoxide or above-mentioned several substances are appointed
The mixture of meaning.Preferably, carbon source is methane, ethylene or acetylene.
Powder containing Si is a kind of powder containing Si, can be pure Si powder also or Si C composite material of core-shell structure.
In carbon coating step：
Second carrier gas can be the protective gas such as argon gas or nitrogen, and the gas velocity of the second carrier gas is 0.1~1L/min.It is preferred that
, the gas velocity of the second carrier gas is 0.2,0.3,0.4,0.5L/min.
Second reaction gas is the gaseous mixture containing carbon source and the second carrier gas, and the gas velocity of the second reaction gas is 0.01~0.5L/
min.Preferably, the gas velocity of the second reaction gas be 0.1,0.2,0.3,0.4,0.5L/min.
Wherein, carbon source and the volume ratio of the second carrier gas are 1.05~1.5:0.2~6.In addition, carbon source can be methane, second
Alkane, ethylene, acetylene, propylene, propane, ethyl alcohol, carbon monoxide or the above-mentioned arbitrary mixture of several substances.
Carbon coating temperature is 500~900 DEG C.Preferably, carbon coating temperature is 800,850,900 and 950 DEG C.
Further, the reaction time of carbon coating process is 0.1~3h.
In some optional embodiments, if powder containing Si is Si@C composite material of core-shell structure；Then walked in the carbonization
Further include that carbon coating is carried out to obtain the operation of the Si@C composite material of core-shell structure to Si powder in advance before rapid.It should be noted that
, carrying out carbon-coated operation to Si powder in advance not necessarily must be identical with the operation of the carbon coating in above-described embodiment,
As carbon source, carrier gas, reaction gas and carbon coating temperature do not need it is identical.
Pass through above-described embodiment, it is known that present invention offer two ways preparation Si@SiC@C composite material of core-shell structure, one
Kind mode is first to carry out carbonization to Si powder to generate Si SiC Core-shell structure materials, then carries out carbon coating again and generates Si SiC C cores
Core-shell structure composite material；Another mode is to carry out carbon coating in advance to Si powder to generate Si@C composite material of core-shell structure, so
Carbonization is carried out to Si@C composite material of core-shell structure again afterwards and generates Si@SiC Core-shell structure materials, finally again to Si@SiC nucleocapsid knots
Structure material carries out carbon coating and generates Si@SiC@C composite material of core-shell structure.Both the above mode can prepare specific capacity
Si@SiC@C composite material of core-shell structure high, cyclical stability is high.First way only has two steps, and operation is relatively easy, right
Carbonization and carbon-coated reaction environment and appointed condition are more demanding.The second way is although complicated for operation, needs pre- to Si powder
Carbon coating is first carried out, but reaction environment and appointed condition are required relatively low.
In addition, in above-mentioned carburising step and carbon coating step, fixed bed, moving bed, fluid bed may be used in reactor
Or combination thereof.
Carburising step and carbon coating step can carry out in the same reactor, can also distinguish in different reactor
It carries out.
Compared to Si/SiC composite materials prepared by traditional ball-milling method, the Si@SiC@C nucleocapsids that the present invention is prepared
Composite material has the following advantages：
1) specific capacity is high, about 1800~2500mAh/g.
2) excellent cyclical stability.
3) of low cost.
4) product is uniform, is uniformly dispersed.
5) good conductivity.
6) this preparation method is simple, pollution-free, yield is high, is easy to produce in batches.
7) product quality is controllable, can easily adjust each component content.
It should be understood that above general description and following detailed description is only exemplary and explanatory, not
It can the limitation present invention.
Description of the drawings
The drawings herein are incorporated into the specification and forms part of this specification, and shows the implementation for meeting the present invention
Example, and be used to explain the principle of the present invention together with specification.
Fig. 1 is Si@SiC@C composite material of core-shell structure structural schematic diagrams；
Fig. 2 is the typical scan electromicroscopic photograph under 15000 enlargement ratios of Si powder raw materials；
Fig. 3 is the typical scan electromicroscopic photograph under 40000 enlargement ratios of Si powder raw materials；
Fig. 4 is the typical scan electromicroscopic photograph under 17000 enlargement ratio of Si@SiC@C composite material of core-shell structure；
Fig. 5 is the typical scan electromicroscopic photograph under 40000 enlargement ratio of Si@SiC@C composite material of core-shell structure；
Fig. 6 is the low power TEM figures of Si@SiC@C composite material of core-shell structure；
Fig. 7 is the high power TEM figures of Si@SiC@C composite material of core-shell structure；
Fig. 8 is Si powder, Thermogravimetric Datas of the Si@SiC and Si@SiC@C under the atmosphere of oxygen；
Fig. 9 is the electrochemistry cycle performance that Si powder is enclosed with Si@SiC@C composite material of core-shell structure in 2A/g charge and discharge 250
Comparison diagram.
Specific implementation mode
The following description and drawings fully show specific embodiments of the present invention, to enable those skilled in the art to
Put into practice them.Embodiment only represents possible variation.Unless explicitly requested, otherwise individual components and functionality is optional, and
And the sequence of operation can change.The part of some embodiments and feature can be included in or replace other embodiments
Part and feature.
With reference to specific embodiment, invention is further explained, and however, it is not limited to this.
Embodiment 1
20g silica flours are placed in tubular fixed-bed reactor, are heated up with 10 DEG C/min under the carrier gas protection of 0.4L/min
Rate is heated to 1300 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.1:1.
Then, it is passed through the CH of 0.2L/min4Carburizing reagent 15min is carried out, cools to room temperature with the furnace after reaction to get Si@SiC cores
Shell structure powder.
By gained Si@SiC core-shell structured powders with 15 DEG C/min heating rates under the argon gas atmosphere protection of 0.3L/min
850 DEG C of heating is passed through the ethylene and argon gas mixed gas, wherein ethylene of 0.2L/min: the volume ratio of argon gas is 1: 2, passing through
It learns vapor deposition and carries out carbon coating 20min in particle surface.Products obtained therefrom is Si@SiC@C composite material of core-shell structure.Wherein
The grain size of Si powder is 150nm, and SiC layer thickness is 5~10nm, and the thickness of outermost layer carbon-coating is 10~25nm.The mass fraction of Si
It is 71.3%, it is about 7.4% that the mass fraction of SiC layer, which is about 21.3%, C layers of mass fraction,.
Characterization result：
Fig. 2~3 and the typical case that Fig. 4~5 are raw material Si powder and prepared Si@SiC@C composite material of core-shell structure respectively
Stereoscan photograph.It is well dispersed from Fig. 2~3 it is found that raw material Si powder is spherical in shape, average grain diameter 150nm.It can from Fig. 4~5
Know, Si@SiC@C composite material of core-shell structure prepared by the present invention is same spherical in shape and well dispersed, is not sintered.
Fig. 6~7 are the typical transmission electromicroscopic photograph of Si@SiC@C composite material of core-shell structure, SiC known to from Fig. 6~7
It is evenly coated completely with C, wherein C layer thickness is 5~10nm, and SiC layer thickness is 10~25nm.
Electrochemical property test：
Under room temperature, by thickener sodium carboxymethylcellulose (CMC, Sodium Carboxymethyl Cellulose) powder
With ultra-pure deionized water with 1.5:98.5 mixing, stirring at normal temperature 12h obtain transparent sticky colloidal solution.According to active material
(Si@SiC@C composite material of core-shell structure)：Conductive agent super P：CMC=7：2：Each component substance is added in 1 mass ratio, adds
0.5h is stirred after entering active material, 1.5h is stirred after conductive agent super P are added, supplies the desired amount of solvent ultra-pure deionized water
Afterwards so that solid content is in 9wt.%, 12h is stirred, solution is in bright black state to get to negative electrode slurry
Scattered slurry is coated on copper foil of affluxion body, and film forming is dried in 60 DEG C of baking oven.It is to be cooled
It is punched into mold after to room temperatureDisk.After the electrode slice room temperature prepared is vacuumized 12 hours, knob is carried out
Detain battery assembling.Wherein battery size is 2032, and diaphragm is 2400 polypropylene screens of Celgard, just extremely metal lithium sheet, electrolysis
Liquid is ethylene carbonate (EC, Ethylene carbonate)/diethyl carbonate of 1mol/L lithium hexafluoro phosphates (LiPF6)
(DEC, Diethyl carbonate)/dimethyl carbonate (DMC, Dimethyl carbonate) solution (EC：DEC：The body of DMC
Product ratio 2:1:2) fluorinated ethylene carbonate (FEC, the Fluoroethylene that volume fraction is 10wt.%, are in addition added to
Carbonate) it is used as stabilizer.
Fig. 8 is Si powder, Thermogravimetric Datas of the Si@SiC and Si@SiC@C under the atmosphere of oxygen, as it can be observed in the picture that Si@SiC@C
The mass fraction of the carbon-coating of product outermost layer cladding is 7.4%.In addition it can be seen that coming, Si@SiC ratio Si powder has higher steady
Qualitative, surface carbonation is uniform during this also reflects that we are carbonized from side.
Fig. 9 is Si powder and the Si@SiC@C composite material of core-shell structure electrification that charge and discharge 250 are enclosed under 2A/g current densities
Learn cycle performance comparison diagram, as can be seen from Figure 9, the specific capacity of prepared Si@SiC@C composite material of core-shell structure, cycle performance
All it is far above Si@C.Main cause may be SiC very rigid, and SiC can effectively inhibit center during charge and discharge
The volume expansion of Si, and then the SEI films on protection materials surface.And Si@C-materials can not be effectively inhibited since carbon is soft
Its volume expansion, and then material surface can be made to destroy, surface SEI films are further destroyed, make the decaying of its chemical property quickly.
Embodiment 2
15g silica flours are placed in tubular fixed-bed reactor, are heated up with 15 DEG C/min under the carrier gas protection of 0.2L/min
Rate is heated to 1200 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.2:1.
Then, the ethylene for being passed through 0.1L/min carries out carburizing reagent 30min, after reaction, with 10 under 0.2L/min argon gas atmospheres
DEG C/rate of temperature fall of min, cool to 800 DEG C with the furnace.Then, the CO and argon gas mixed gas, wherein CO of 0.2L/min are passed through:
The volume ratio of argon gas is 2: 1, and carbon coating 20min is carried out in particle surface by chemical vapor deposition.Products obtained therefrom is Si@
SiC@C composite material of core-shell structure, wherein SiC mass fractions are 20.2wt.%, and C mass fractions are 8.6wt.%, Si contents
71.2wt.%.
Wherein, Si powder average diameter is 70nm, and C layer thickness is 12~15nm, and SiC layer thickness is 15~20nm.
Embodiment 3
20g silica flours are placed in fluidized-bed reactor, with 10 DEG C/min heating rates under the carrier gas protection of 0.5L/min
It is heated to 1325 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.3:1.Then,
The acetylene for being passed through 0.4L/min carries out carburizing reagent 40min, is cooled to room temperature under 0.5L/min argon gas atmospheres after reaction,
Up to Si@SiC core-shell structured powders.
Gained Si@SiC core-shell structured powders are placed in fluidized-bed reactor, are protected in the argon gas atmosphere of 0.35L/min
Under with 20 DEG C/min heating rates heat 850 DEG C, be passed through the ethyl alcohol of 0.2L/min and argon gas mixed gas, wherein ethyl alcohol: argon gas
Volume ratio be 1: 1, carbon coating 40min is carried out in particle surface by chemical vapor deposition.Products obtained therefrom is Si@SiC@C
Composite material of core-shell structure.Wherein, SiC mass fractions are 17.4wt.%, and C mass fractions are 15.9wt.%, Si contents
66.7wt.%.
Wherein, Si powder average diameter is 10 μm, and C layer thickness is 1~2 μm, and SiC thickness is 1~3 μm.
Embodiment 4
5kg silica flours are placed in fluidized-bed reactor, are added with 10 DEG C/min heating rates under the carrier gas protection of 1L/min
Heat is to 950 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.1:1.Then, lead to
Enter 0.4L/min ethylene carry out carbon coating 60min, be cooled to room temperature under 1L/min argon gas atmospheres after reaction to get
Si@C core-shell structured powders.
Obtained Si@C powders 5kg is placed in fixed bed reactors, 0.5L/min carrier gas protection under with 20 DEG C/
Min heating rates are heated to 1300 DEG C, keep constant temperature 20min, then Temperature fall to obtain Si@SiC to room temperature, wherein carrier gas is argon
Gas：Hydrogen=10：1.
Gained Si@SiC core-shell structured powders are placed in fluidized-bed reactor, are protected in the argon gas atmosphere of 0.85L/min
Under with 20 DEG C/min heating rates heat 850 DEG C, be passed through the ethyl alcohol of 0.2L/min and argon gas mixed gas, wherein ethyl alcohol: argon gas
Volume ratio be 1: 1, carbon coating 120min is carried out in particle surface by chemical vapor deposition.Products obtained therefrom is Si@SiC@C
Composite material of core-shell structure.Wherein, it is 12%, Si contents 65.5% that SiC mass fractions, which are 22.5%, C mass fractions,.
Wherein, Si powder average diameter is 50 μm, and C layer thickness is 10~20 μm, and SiC thickness is 10~20 μm.
Embodiment 5
5g silica flours are placed in tubular fixed-bed reactor, with 15 DEG C/min heating speed under the carrier gas protection of 0.2L/min
Rate is heated to 1270 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.3:1.So
Afterwards, be passed through 0.1L/min acetylene carry out carburizing reagent 50min, after reaction, under 0.2L/min argon gas atmospheres with 10 DEG C/
The rate of temperature fall of min cools to 700 DEG C with the furnace.Then, the CO and argon gas mixed gas, wherein CO: argon gas of 0.2L/min are passed through
Volume ratio be 2: 1, carbon coating 40min is carried out in particle surface by chemical vapor deposition.Products obtained therefrom is Si@SiC@C
Composite material of core-shell structure, wherein SiC mass fractions are 60.3wt.%, and C mass fractions are 20.2wt.%, Si contents
19.5wt.%.
Wherein, Si powder average diameter is 100nm, and C layer thickness is 30~35nm, and SiC layer thickness is 35~43nm.
Embodiment 6
1g silica flours are placed in tubular fixed-bed reactor, with 15 DEG C/min heating speed under the carrier gas protection of 0.3L/min
Rate is heated to 1330 DEG C, wherein the carrier gas is the gaseous mixture of argon gas and hydrogen, hydrogen: the volume ratio of argon gas is 0.4:1.So
Afterwards, be passed through 0.1L/min methane carry out carburizing reagent 10min, after reaction, under 0.2L/min argon gas atmospheres with 10 DEG C/
The rate of temperature fall of min cools to 750 DEG C with the furnace.Then, the ethylene and argon gas mixed gas, wherein ethylene of 0.2L/min are passed through:
The volume ratio of argon gas is 1: 1.5, and carbon coating 30min is carried out in particle surface by chemical vapor deposition.Products obtained therefrom is Si@
SiC@C composite material of core-shell structure, wherein SiC mass fractions are 3.3wt.%, and C mass fractions are 38.4wt.%, Si contents
58.3wt.%.
Wherein, Si powder average diameter is 100nm, and C layer thickness is 43~52nm, and SiC layer thickness is 13~23nm.
Table 1 is the Si@SiC@C composite material of core-shell structure electrochemical property tests of Examples 1 to 5 preparation as a result, wherein
The electrochemical test method of embodiment 2,3,4 and 5 is identical as method described in embodiment 1, here without repeating.
Cell testing results in the different embodiments of table 1
As known from Table 1 a process for preparing Si@SiC@C composite material of core-shell structure specific capacity it is high, about 1900~
2300mAh/g, specific capacity is still relatively high after recycling 100 circles or even 250 circles, has excellent cyclical stability.Therefore, originally
The Si@SiC@C of invention have higher cyclical stability, meet next-generation negative material to height ratio capacity, high circulation stability
It is required that.
Through analysis and research find, compared to traditional ball-milling method prepare Si/SiC composite materials, what the present invention was prepared
Si@SiC@C composite material of core-shell structure has the following advantages：
1) specific capacity is high
The initial capacity of material is 3 times of commercial graphite electrode or more in 1800mAh/g or more.
2) excellent cyclical stability
100 circle capacity of cycle, which maintains the circles of 1000mAh/g or more 250, can also maintain 700mAh/g or more.
3) of low cost
Present CVD technology is ripe, by preparing material on a large scale, can produce product by qurer very much
4) product is uniform, is uniformly dispersed.
SiC even compacts are coated on each Si powder particles surface, uniformly divide so that Si and SiC reaches granular-grade
It dissipates, avoids the formation of Si or SiC from aggregate.
5) good conductivity.
The carbon coating layer of outer layer can effectively improve the electric conductivity of composite material, while can also inhibit Si's to a certain extent
Volume expansion.
6) this preparation method is simple, pollution-free, yield is high, is easy to produce in batches.
7) product quality is controllable
Product quality is controllable, can easily adjust the content of each component.
To sum up, since this Si@SiC@C composite material of core-shell structure itself has, product is uniform, well dispersed, Si contents
The characteristics of height, good conductivity, as lithium ion battery negative material, nucleocapsid clad can effectively inhibit charge and discharge
The volume change of Si in journey, the SEI films on stabilized electrodes surface have the characteristics that specific capacity height, good cycling stability.
It should be understood that the invention is not limited in the flow and structure that are described above and are shown in the accompanying drawings,
And various modifications and changes may be made without departing from the scope thereof.The scope of the present invention is only limited by the attached claims
System.
Claims (10)
1. a kind of silicon@silicon carbide@carbon composite material of core-shell structure, which is characterized in that the composite material contains internal layer, middle layer
With outer layer three-decker；Wherein, the internal layer is silicon Si hypothallus, the middle layer is silicon carbide SiC hypothallus, the outer layer
For carbon C hypothallus.
2. composite material as described in claim 1, which is characterized in that by the total weight of the composite material be 100% in terms of, institute
The mass fraction for stating internal layer is 19~96%, and the mass fraction of the middle layer is 3~80%, and the mass fraction of the outer layer is
1~40%.
3. composite material as described in claim 1, which is characterized in that the internal layer is Si powder, and the middle layer is SiC, institute
It is amorphous carbon or graphitic carbon to state outer layer.
4. composite material as claimed in claim 3, which is characterized in that the particle diameter of the Si powder is 0.02~50 μm, institute
The thickness for stating middle layer is 2nm~20 μm, and the thickness of the outer layer is 2nm~10 μm.
5. a kind of preparation method of silicon@silicon carbide@carbon composite material of core-shell structure, which is characterized in that including：Carburising step and carbon
Encapsulation steps；Wherein：
The carburising step includes：Powder containing Si is heated to carburizing temperature under the protection of the first carrier gas, is passed through containing carbon source
The first reaction gas carry out carburizing reagent, obtain Si@SiC Core-shell structure materials；
The carbon coating step includes：The Si@SiC Core-shell structure materials are heated or cooled under the protection of the second carrier gas
Carbon coating temperature is passed through the second reaction gas containing carbon source and second carrier gas and carries out chemical vapor deposition, obtains the Si@
SiC@C composite material of core-shell structure.
6. preparation method as claimed in claim 5, which is characterized in that if the powder containing Si is Si@C nucleocapsid composite woods
Material；Further include that carbon coating is carried out to obtain the Si@C nucleocapsid composite woods to Si powder in advance then before the carburising step
The operation of material.
7. preparation method as claimed in claim 5, which is characterized in that first carrier gas is the gaseous mixture of hydrogen and argon gas
Body, wherein the volume ratio of the hydrogen and the argon gas is 0.01~0.4:1.
8. preparation method as claimed in claim 5, which is characterized in that the gas velocity of first reaction gas is 0.01~0.5m/
s。
9. preparation method as claimed in claim 5, which is characterized in that in second reaction gas, the carbon source with it is described
The volume ratio of second carrier gas is 1.05~1.5:0.2~6.
10. the preparation method as described in any one of claim 5-9, which is characterized in that the carburizing temperature is 900~1400
DEG C, the reaction time is 0.2~2h；The carbon coating temperature is 500~900 DEG C, and the reaction time is 0.1~3h.
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