A kind of core-shell structure Si-C composite material and preparation method thereof
Technical field
The present invention relates to a kind of preparation methods of lithium ion battery negative material, have core-shell structure more particularly to one kind
Si-C composite material and preparation method thereof, belong to technical field of lithium ion.
Background technique
Since the 21th century, with the development of society and the progress of science and technology, electronic product, electric car and energy storage electricity
Station has increasing need for the lithium ion battery of high-energy density and long-life.However, commercialized lithium ion battery is adopted extensively at present
It is graphite negative electrodes material, theoretical capacity is lower (372mAh/g), has been difficult to meet demand.Silicon has as negative electrode material
There is high theoretical specific capacity (4200mAh/g), receives the extensive concern of researcher.Since silicon is in charge and discharge process,
The deintercalation of lithium ion will lead to its huge volume change, generate broken, the dusting of particle, so that silicon active material is from collector
On fall off, eventually lead to electrode interior structural damage, and then influence the chemical property of battery.By the study found that subtracting
The size of small silicon materials can effectively alleviate its volume change in charge and discharge process to nanoscale, while carbon coating can also
To play the role of improving material conductivity and inhibit volume expansion.Excellent properties possessed by Si-C composite material are expected to it
Graphite negative electrodes material is substituted, the stable nano-silicone wire/carbon composite material material of extensive, low cost preparation structure is to realize it
The basis of commercial applications.
Wang etc. uses resorcinol-formaldehyde for carbon source, and nano silicon material is added and obtains silicon-carbon aeroge, obtains after sintering
Carbon-coated silica-base material [G.X.Wang, et al.Electrochemistry Communications, 2004,6 (7):
689-692], but the carbon-coating coated is easy to be destroyed after iterative cycles, it is difficult to meet the needs of practical application.Patent
CN102623680A discloses a kind of preparation method of silicon-carbon composite cathode material with three-dimensional reserved pore structure, this method
By removing the surface coated silica of silicon particle in carbon base body, to be obtained between silicon particle and carbon base body three-dimensional reserved
Although expansion space, this method effectively improve the charge-discharge performance of material, but need first to generate silica
Silica is removed again, and step complexity is unfavorable for large-scale production, and without solving the problems, such as prepared by nano-silicon low cost.Patent
CN 104979539A does template using zinc oxide, layer of silicon dioxide and carbon-coating is deposited in template respectively, after magnesiothermic reduction
Obtain the silicon-carbon nanometer rod composite material of hollow structure, the same available preferable chemical property of this method, but mould
The preparation of plate and etching increase preparation cost, and CVD method complex process, is unfavorable for large-scale production used in carbon coating.
Using silica and magnesium powder occur reduction reaction prepare nano-silicon with method simple, low-cost advantage,
It is considered as one of the method for suitable large-scale application at present.But during preparing Si-C composite material, due to magnesium heat
Reduction is exothermic reaction, and local heat accumulation will lead to the generation of side reaction in system and generate silicon carbide impurity phase.Silicon carbide
Not with the reactivity of lithium, the decline of material specific capacity is not only resulted in, also affects lithium ion in electrode material
Interface transmitting.This substantially reduces the specific capacity and high rate performance of material prepared.How using magnesiothermic reduction structure is prepared steady
Fixed Si-C composite material has great importance to the industrial application for pushing silicon-carbon cathode material.
Summary of the invention
For deficiency existing for existing lithium ion battery silicon-carbon composite material, the purpose of the invention is to provide one kind
Si-C composite material with special core-shell structure, the Si-C composite material stability is good, and can buffer charge and discharge well
Silicon volume expansion in journey improves material conductivity, to guarantee the cyclical stability of electrode.
Another object of the present invention is to be that providing simple, the at low cost silicon-carbon for preparing without side reaction of one kind answers
The method of condensation material, this method can be mass produced.
In order to achieve the above technical purposes, the present invention provides a kind of core-shell structure Si-C composite material, the silicon-carbon is compound
Material has core-shell structure;In the core-shell structure includes the shell being made of carbon-coating and is made of porous nano silicon
Core;There is void layer between the shell and kernel.
The Si-C composite material of offer of the invention has special core-shell structure, and core is porous nano silicon, and shell is carbon
Layer, especially there are void layers between kernel and shell.Carbon-coating can not only improve the electric conductivity of material, and silicon core can be prevented broken
It is granular to fall, ensure that the stability of material structure, and void layer provided for the volume expansion of silicon in battery charge and discharge process it is slow
Space is rushed, composite material is effectively prevent to rupture crushing due to volume change in charge and discharge process, to guarantee following for electrode
Ring is stablized.
Preferred scheme, the size of the kernel are 10nm~10 μm.
Preferred scheme, the shell with a thickness of 1~200nm.
The present invention also provides the preparation method of the core-shell structure Si-C composite material, this method includes following step
It is rapid:
1) silica dioxide granule carries out magnesiothermic reduction reaction by magnesium powder, obtains Si@SiO2Intermediate;
2) the Si@SiO2After intermediate carries out in-stiu coating by organic polymer carbon source, charing obtains C@Si@SiO2
Intermediate;
3) the C@Si@SiO2Intermediate using hydrofluoric acid corrode to get.
In technical solution of the present invention, by magnesium reduction process, so that silica sections is reduced generation silicon, mainly obtain
Silicon coated silica intermediate Si@SiO2;In-stiu coating method is used again, in Si@SiO2Surface prepares carbon-coating clad, then benefit
After the nano-silicon that silica is selectively removed in hydrofluoric acid and partial reduction generates, carbon-coating cladding silicon composite C is obtained
Si.The removing of silica and part silicon is not only corresponding spatial volume to be left between carbon-coating and silicon core, and generate
Porous nano silicon kernel, by the size for controlling void layer, it is ensured that free wxpansion and whole knot of the silicon particle in carbon-coating
Structure is not destroyed.
Preferred scheme, 1) in, silica dioxide granule and magnesium powder after mixing, are placed in full of the closed of protective atmosphere
In environment, 600~800 DEG C are warming up to the heating rate of 1~20 DEG C/min, 1~12h of reduction reaction is carried out, obtains Si@SiO2
Intermediate.The condition of preferred magnesiothermic reduction, can control magnesiothermic reduction degree, to realize porous nano silicon structure well
Control.Simultaneously 2Mg+SiO not only has occurred in the process of magnesiothermic reduction2The reaction of → Si+2MgO, also has occurred 2Mg+Si → Mg2Si and
Mg2Si+SiO2The a series of reaction such as → 2Si+2MgO, therefore not only the surface of silica has occurred reduction and generates silicon,
Inside also has small part reducing silica and generates silicon, so foring porous nano in subsequent hydrofluoric acid corrosion process
Silicon kernel;The silicon particle that silica surface restores simultaneously is very tiny, and activity is big, it is easy to corrode in hydroflouric acid
Cheng Zhongyu hydrofluoric acid reacts, and forms void layer between charcoal shell and porous nano silicon kernel.
The mass ratio of more preferably scheme, silica and magnesium powder is 1:0.4~1:1.
More preferably scheme, silica dioxide granule partial size are 10nm~10 μm.
Preferred scheme, 2) in, the Si@SiO2Intermediate and organic polymer carbon source are dissolved in solvent, after mixing,
Stirring is evaporated, and obtained solid mixture is polished, is placed under protective atmosphere, is heated up with the heating rate of 1~20 DEG C/min
To 600~1200 DEG C, 1~12h of charing is carried out, obtains C@Si@SiO2Intermediate.It, can be it is preferred that in-stiu coating and carbonization condition
Si@SiO2Intermediate surface prepares uniform carbon-coating.
Preferred scheme, organic polymer carbon source and Si@SiO2The mass ratio of intermediate is 100:1~1:100.
Preferred scheme, organic polymer carbon source are polyvinyl alcohol, polypropylene, pitch, phenolic resin, epoxy resin, Portugal
At least one of grape sugar, sugarcane sugar and starch.Preferred organic polymer carbon source is water-soluble high-molecular material, or is readily soluble
In the high molecular material of organic solvent, these organic polymer carbon sources are easy to by solvent medium to Si@SiO2Intermediate carries out
In-stiu coating.
Preferred scheme, 3) in, the C@Si@SiO2Intermediate use mass percent concentration for 1~40% hydrogen fluorine
Acid carries out 0.01~6h of impregnation.
More preferably scheme, protective atmosphere are at least one of nitrogen, argon gas and hydrogen.
The preparation method of core-shell structure Si-C composite material of the invention, comprising the following steps:
Step 1: silica dioxide granule (partial size is 10nm~10 μm) is mixed with magnesium powder according to quality 1:0.4~1:1
It after even, is placed in the closed environment full of protective atmosphere, is warming up to 600~800 DEG C with the heating rate of 1~20 DEG C/min
React 1~12h;After reaction, product is taken out, the product is added to the hydrochloric acid and/or sulfuric acid that concentration is 0.5~4mol/L
In solution washing 1~obtain intermediate product Si@SiO for 24 hours, after filtering drying2;
Step 2: by organic polymer carbon source and Si@SiO2100:1~1:100 is dissolved in solvent in mass ratio, and mixing is equal
Solution is stirred under the conditions of 60~120 DEG C after even and is evaporated, gained mixture grinding after under protective atmosphere, with 1~20 DEG C/
The heating rate of min is warming up to 600~1200 DEG C of 1~12h of reaction, obtains carbon-coated C@Si@SiO after reaction2;
Step 3: by C@Si@SiO2It is dissolved in 0.01~6h of immersion treatment in the hydrofluoric acid solution that concentration is 1~40wt%,
Remove residue SiO2And after a small amount of silicon, filtration washing obtains the final product C@Si with core-shell structure.
Compared with prior art, technical solution of the present invention has the advantage that
1) Si-C composite material that technical solution of the present invention obtains has special core-shell structure, including porous nano silicon
There are void layers between kernel and carbon-coating shell, especially kernel and shell.Carbon-coating can not only improve the electric conductivity of material, and
It can prevent silicon core is broken to be scattered, ensure that the stability of material structure, and void layer is the volume of silicon in battery charge and discharge process
Expansion provides cushion space, and composite material is effectively prevent to rupture crushing due to volume change in charge and discharge process, thus
Guarantee the stable circulation of electrode.
2) technical solution of the present invention during preparing Si-C composite material, first passes through magnesiothermic reduction silica, then wrap
Carbon is covered, the generation of the side reactions object such as silicon carbide is efficiently avoided.
3) for technical solution of the present invention by can be by controlling magnesium thermit degree, Lai Shixian Si-C composite material be hollow
The regulation of the size of gap layer and the regulation of porous nano silicon structure.
4) technical solution of the present invention is raw material without the use of nano-silicon, and raw material sources are wide, at low cost, and process is simple, can
Control is suitble to large-scale production without expensive manufacturing equipment, and practical application foreground is good.
Detailed description of the invention
[Fig. 1] is the X-ray diffractogram of reaction product prepared by comparative example 1: as can be seen from the figure first carbon coated magnesium again
The prepared material of thermal reduction has an apparent miscellaneous peak at 36 ° or so, shows that reaction generates carbonization silicon impurities.
[Fig. 2] is the transmission electron microscope picture of reaction product prepared by comparative example 2: as can be seen from the figure being divided after magnesiothermic reduction
Not there is apparent porous structure using the product that hydrochloric acid and hydrofluoric acid treatment obtain.
[Fig. 3] is the X-ray diffractogram of reaction product prepared by embodiment 1: as can be seen from the figure by the technology of the present invention
There is no silicon carbide impurity component in Si-C composite material prepared by scheme.
[Fig. 4] is the transmission electron microscope picture for the silica precursor that embodiment 1 uses: before as can be seen from the figure restoring
Silica is smooth medicine ball.
[Fig. 5] is Si@SiO prepared by embodiment 12The transmission electron microscope picture of intermediate product: as can be seen from the figure magnesium heat is also
The intermediate product that HCl treatment obtains after original has maintained whole pattern, and does not have apparent porous structure.
[Fig. 6] is the transmission electron microscope picture of C@Si product prepared by embodiment 1: as can be seen from the figure silicon core is by one layer without fixed
Type carbon is wrapped up, and internuclear there are obvious void layers for carbon shell and silicon.
[Fig. 7] is 50 charge and discharge when Si-C composite material prepared by embodiment 1 is used for lithium ion battery negative material
Capacity Plan: as can be seen from the figure the reversible specific capacity for the first time of the battery is 1791mAh/g, and reversible specific capacity is after 50 circle of circulation
1690mAh/g。
Specific embodiment
Illustrate specific steps of the invention by the following examples, but the range of the claims in the present invention protection is not implemented
Example limitation.
Term as used in the present invention generally there are those of ordinary skill in the art usually to manage unless otherwise indicated
The meaning of solution.
The present invention is described in further detail combined with specific embodiments below and referring to data.It should be understood that these embodiments are only
It is in order to demonstrate the invention, rather than to limit the scope of the invention in any way.
In the examples below, the various processes and method being not described in detail are conventional methods as known in the art.
The present invention is further described combined with specific embodiments below.
Comparative example 1
It takes the silica spheres that 1g diameter is about 250nm as raw material, is dissolved in ethyl alcohol according to mass ratio 1:1 with phenolic resin
In solvent, at 80 DEG C stirring to ethyl alcohol volatilization completely, be mixed object grinding it is careful after under an argon atmosphere, with 5 DEG C/min's
Heating rate is warming up to 800 DEG C of reaction 2h.Products therefrom C@SiO after reaction2After mixing with 0.8g metal magnesium powder, it puts
It sets in the closed environment full of argon gas, 700 DEG C of reaction 6h is warming up to the heating rate of 5 DEG C/min.After reaction, it takes out
Product, which is dissolved in the hydrochloric acid of 1mol/L, reacts 6h.It is re-dissolved in after filtering drying in the hydrofluoric acid of mass fraction 5% and reacts 0.5h, mistake
Reaction product is obtained after filter drying.The X-ray diffractogram of reaction product is as shown in Figure 1, contain a large amount of carbonization sila in product
Matter ingredient.
The material being prepared and conductive black and sodium alginate 8:1:1 in mass ratio are modulated into slurry, are coated in copper
On foil, anode plate for lithium ionic cell is made after 60 DEG C of dry 12h.Use button lithium battery CR2025 as simulated battery, lithium metal
Piece is used as to electrode, and electrolyte group becomes 1MLiPF6(ethylene carbonate: diethyl carbonate=1:1, v/v), diaphragm is
Celgard2400 is completed in the glove box full of argon gas.Current density of the preparation-obtained battery in 100mA/g
Under, charge and discharge section is that 0.01-1.5V completes charge-discharge test.The reversible specific capacity for the first time of the battery is 546mAh/g, circulation
Reversible specific capacity is 308mAh/g after 50 circles.
Comparative example 2
The silica spheres that 1g diameter is about 250nm are taken after mixing with 0.8g metal magnesium powder to be placed on as raw material
In closed environment full of argon gas, 700 DEG C of reaction 6h are warming up to the heating rate of 5 DEG C/min.After reaction, product is taken out
It is dissolved in the hydrochloric acid of 1mol/L and reacts 6h.It is re-dissolved in after filtering drying in the hydrofluoric acid of mass fraction 5% and reacts 0.5h, cross diafiltration
Reaction product is obtained after washing drying.The transmission electron microscope picture of reaction product is as shown in Fig. 2, there are a large amount of holes in product.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
Test result shows that the reversible specific capacity for the first time of the battery is 2375mAh/g, and reversible specific capacity is 551mAh/ after 50 circle of circulation
g。
Embodiment 1
The silica spheres that 1g diameter is about 250nm are taken after mixing with 0.8g metal magnesium powder to be placed on as raw material
In closed environment full of argon gas, 700 DEG C of reaction 6h are warming up to the heating rate of 5 DEG C/min.After reaction, product is taken out
It is dissolved in the hydrochloric acid of 1mol/L and reacts 6h.By intermediate product Si@SiO obtained above after filtering drying2With phenolic resin according to
Mass ratio 1:1 is dissolved in alcohol solvent, at 80 DEG C stirring to ethyl alcohol volatilization completely, be mixed object grinding it is careful after in argon gas gas
Under atmosphere, 800 DEG C of reaction 2h are warming up to the heating rate of 5 DEG C/min.Products therefrom C@Si@SiO after reaction2It is dissolved in quality
0.5h is reacted in the hydrofluoric acid of score 5%, obtains reaction product C@Si after filtration washing drying.The X-ray of its product C@Si is spread out
Figure is penetrated as shown in figure 3, the transmission electron microscope picture of used silica precursor is as shown in figure 4, its gained intermediate product Si@
SiO2Transmission electron microscope picture as shown in figure 5, the transmission electron microscope picture of its product C@Si is as shown in Figure 6.The porous nano of products therefrom
Silicon nuclear diameter is about 250nm, and carbon layers having thicknesses are about 10nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
It is the battery charging and discharging 50 times charge/discharge capacity figures as shown in Figure 7, the reversible specific capacity for the first time of the battery is 1791mAh/g,
Reversible specific capacity is 1690mAh/g after 50 circle of circulation.
Embodiment 2
The silica spheres that 1g diameter is about 100nm are taken after mixing with 0.5g metal magnesium powder to be placed on as raw material
In closed environment full of argon gas and hydrogen, 650 DEG C of reaction 2h are warming up to the heating rate of 2 DEG C/min.After reaction, it takes
Product, which is dissolved in the sulfuric acid of 0.5mol/L, out reacts 4h.By intermediate product Si@SiO obtained above after filtering drying2With sucrose
Be dissolved in aqueous solution solvent according to mass ratio 1:10, at 100 DEG C stir it is complete to moisture evaporation, be mixed object grinding it is careful after
In a nitrogen atmosphere, 700 DEG C of reaction 4h are warming up to the heating rate of 10 DEG C/min.Products therefrom C@Si@after reaction
SiO2It is dissolved in the hydrofluoric acid of mass fraction 2% and reacts 2h, obtain reaction product C@Si after filtration washing drying.Products therefrom
Porous nano silicon nuclear diameter is about 100nm, and carbon layers having thicknesses are about 50nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
The reversible specific capacity for the first time of the battery is 982mAh/g, and reversible specific capacity is 924mAh/g after 50 circle of circulation.
Embodiment 3
It takes the silica dioxide granule that 1g diameter is about 500nm as raw material, after mixing with 0.7g metal magnesium powder, places
In the closed environment full of argon gas, 700 DEG C of reaction 4h are warming up to the heating rate of 10 DEG C/min.After reaction, it takes out
Product, which is dissolved in the hydrochloric acid of 2mol/L, reacts 8h.By intermediate product Si@SiO obtained above after filtering drying2With polyvinyl alcohol
Be dissolved in n-butanol solvent according to mass ratio 1:15, at 90 DEG C stirring to ethyl alcohol volatilization completely, be mixed object grinding it is careful after
Under argon gas and nitrogen mixture atmosphere, 900 DEG C of reaction 6h are warming up to the heating rate of 20 DEG C/min.Gained produces after reaction
Object C@Si@SiO2It is dissolved in the hydrofluoric acid of mass fraction 10% and reacts 0.5h, obtain reaction product C@Si after filtration washing drying.
The porous nano silicon nuclear diameter of products therefrom is about 500nm, and carbon layers having thicknesses are about 20nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
The reversible specific capacity for the first time of the battery is 853mAh/g, and reversible specific capacity is 798mAh/g after 50 circle of circulation.
Embodiment 4
The silica spheres that 1g diameter is about 1 μm are taken after mixing with 0.8g metal magnesium powder to be placed on and fill as raw material
In the closed environment of full argon gas, 750 DEG C of reaction 6h are warming up to the heating rate of 4 DEG C/min.After reaction, it is molten to take out product
4h is reacted in the hydrochloric acid of 3mol/L.By intermediate product Si@SiO obtained above after filtering drying2With epoxy resin according to matter
Amount be dissolved in acetone solvent than 2:1, at 80 DEG C stirring to acetone volatilization completely, be mixed object grinding it is careful after in argon gas and hydrogen
Under gas atmosphere, 1000 DEG C of reaction 5h are warming up to the heating rate of 10 DEG C/min.Products therefrom C@Si@SiO after reaction2It is molten
1h is reacted in the hydrofluoric acid of mass fraction 10%, obtains reaction product C@Si after filtration washing drying.Products therefrom it is porous
Nano-silicon nuclear diameter is about 1 μm, and carbon layers having thicknesses are about 10nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
The reversible specific capacity for the first time of the battery is 1956mAh/g, and reversible specific capacity is 1802mAh/g after 50 circle of circulation.
Embodiment 5
The silica dioxide granule that 1g diameter is about 2 μm is taken after mixing with 0.9g metal magnesium powder to be placed on as raw material
In closed environment full of hydrogen, 700 DEG C of reaction 8h are warming up to the heating rate of 5 DEG C/min.After reaction, product is taken out
It is dissolved in the sulfuric acid of 1mol/L and reacts 10h.By intermediate product Si@SiO obtained above after filtering drying2With polypropylene according to matter
Amount be dissolved in methanol solvate than 1:2, at 60 DEG C stirring to methanol volatilization completely, be mixed object grinding it is careful after in argon atmosphere
Under, 600 DEG C of reaction 8h are warming up to the heating rate of 20 DEG C/min.Products therefrom C@Si@SiO after reaction2It is dissolved in quality
2h is reacted in the hydrofluoric acid of score 5%, obtains reaction product C@Si after filtration washing drying.The porous nano silicon core of products therefrom
Diameter is about 2 μm, and carbon layers having thicknesses are about 20nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
The reversible specific capacity for the first time of the battery is 898mAh/g, and reversible specific capacity is 814mAh/g after 50 circle of circulation.
Embodiment 6
The silica dioxide granule that 1g diameter is about 8 μm is taken after mixing with 1g metal magnesium powder to be placed on and fill as raw material
In the closed environment of full argon gas, 650 DEG C of reaction 10h are warming up to the heating rate of 10 DEG C/min.After reaction, product is taken out
It is dissolved in the hydrochloric acid of 2mol/L and reacts 8h.By intermediate product Si@SiO obtained above after filtering drying2With glucose according to matter
Amount be dissolved in aqueous solvent than 1:1, at 110 DEG C stir it is complete to moisture evaporation, be mixed object grinding it is careful after in nitrogen atmosphere
Under, 800 DEG C of reaction 6h are warming up to the heating rate of 15 DEG C/min.Products therefrom C@Si@SiO after reaction2It is dissolved in quality
1h is reacted in the hydrofluoric acid of score 20%, obtains reaction product C@Si after filtration washing drying.The porous nano silicon of products therefrom
Nuclear diameter is about 8 μm, and carbon layers having thicknesses are about 5nm.
Anode plate for lithium ionic cell, and assembling test battery is made according to the method for comparative example 1 in the material being prepared.
The reversible specific capacity for the first time of the battery is 1690mAh/g, and reversible specific capacity is 1548mAh/g after 50 circle of circulation.