CN117712359B - Double-shell silicon-carbon composite anode material and preparation method and application thereof - Google Patents
Double-shell silicon-carbon composite anode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of lithium ion batteries, and discloses a double-shell silicon-carbon composite anode material and a preparation method and application thereof. The preparation method comprises the following steps: distributing amorphous silicon nano particles in the pores of the porous carbon by a chemical vapor deposition method to obtain a silicon-carbon substrate; and coating a carbon layer outside the silicon-carbon substrate by adopting a chemical vapor deposition method, and coating a metal oxide coating layer outside the carbon layer by adopting a liquid phase method and heat treatment to obtain the double-shell silicon-carbon composite anode material. According to the double-shell silicon-carbon composite anode material, the pores are reserved in the silicon-carbon substrate to accommodate the volume expansion of silicon, so that the stress generated by the volume change in the lithium intercalation process can be relieved, meanwhile, the double-shell cladding structure avoids the etching of electrolyte, reduces side reactions, ensures the integrity and stability of the silicon-carbon composite material, inhibits the generation of an SEI layer in the circulation process, and realizes the improvement of the electrochemical performance and the circulation stability of a battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a double-shell silicon-carbon composite anode material and a preparation method and application thereof.
Background
With the rapid development of electric vehicles, energy storage technologies, and portable electronic products, lithium Ion Batteries (LIBs) are receiving widespread attention as an indispensable power storage device. Silicon is a promising alloy negative electrode material with suitable operating voltages (0.1-0.4V), high theoretical specific capacities (4200 mAh g -1), and sufficient reserves on earth. However, silicon (Si) has several disadvantages as an anode active material. Si is a typical semiconductor material whose electron conductivity (< 10 -3 S cm-1) cannot meet the requirements of fast kinetics. In addition, more than 300% expansion occurs during the charge/discharge of Si, which leads to structural breakdown and loss of electrical contact between the active Si nanoparticles and the current collector. The consumption of electrolyte results in the continuous generation of a Solid Electrolyte Interface (SEI) film. These limitations of silicon cathodes should be overcome to increase the energy density of the LIB. If these problems cannot be overcome, silicon can only be used as a limited additive in the negative electrode material of lithium ion batteries to gradually increase the battery energy density.
In recent years, in order to overcome the above problems and realize commercialization, lithium battery researchers have proposed various improvements, such as the preparation of silicon-carbon composite materials. Chinese patent (CN 109713242A) discloses a titanium silicon carbon negative electrode material with a core-shell pomegranate structure and a preparation method thereof, wherein the titanium silicon carbon negative electrode material consists of a core composed of Si/SiO 2 secondary powder, a carbon element material shell layer coated on the surface of the Si/SiO 2 secondary powder and a titanium element material shell layer coated on the surface of the carbon element material shell layer and composed of a titanium source material. The titanium-silicon-carbon negative electrode material is prepared by carrying out carbon coating treatment on Si/SiO 2 secondary powder and then coating the obtained C/Si/SiO 2 tertiary particles with titanium element. According to the technical scheme, a part of space is reserved inside the carbon layer, the volume expansion of silicon in the circulation process can be relieved to a certain extent, however, the stress generated by the internal silicon expansion during circulation easily causes the cracking of the carbon layer and the titanium layer on the surface, so that the SEI layer is continuously generated and cracked, and the cycle life of the battery is poor. In addition, the coating on the surface of the nano material has extremely high difficulty, increases the production cost and is not beneficial to the industrialized practical application.
Chinese patent (CN 107845797A) discloses a preparation method of a nano silicon-carbon composite negative electrode material, wherein nano crystal graphite is placed into a vacuum rotary tube furnace, a silicon source is added after the nano crystal graphite is heated to 850 ℃, a precursor is prepared, then the precursor and a carbonaceous binder are uniformly stirred in a mixer, then the precursor and the carbonaceous binder are placed into the vacuum rotary tube furnace, the mixture is heated to 600 ℃ under the protection of nitrogen, and the prepared material is crushed and screened to prepare the nano silicon-carbon composite negative electrode material. From the research results of the silicon-carbon composite material, the core-shell structure material has good circulation stability, which indicates that the carbon coating has obvious buffering effect on the volume deformation of the nano silicon particles. However, in the long-period cycle process of the battery, the carbon layer in the carbon-coated Si/C core-shell structure still cannot bear long-term volume deformation of the silicon particles to be broken, and the capacity and the service life of the electrode are directly affected.
It can be known how to realize structural optimization of the silicon-carbon composite material, reduce the volume expansion of the silicon-carbon composite material, improve the interface stability of silicon in a battery and realize the improvement of the cycling stability of the battery, which are the problems to be solved in the art.
Accordingly, there is a need for improvement and development in the art.
Disclosure of Invention
In view of the defects in the prior art, the invention provides a double-shell silicon-carbon composite anode material, and a preparation method and application thereof, and aims to solve the technical problem that the existing silicon-carbon anode material is reduced in cycling stability due to volume expansion.
Specifically, the technical scheme of the invention is as follows:
In a first aspect, the invention provides a preparation method of a double-shell silicon-carbon composite anode material, comprising the following steps:
s1, compositing porous carbon and silane by a chemical vapor deposition method to enable amorphous silicon nano particles to be distributed in internal pores of the porous carbon, so as to obtain a silicon carbon substrate;
S2, coating a carbon layer on the outer surface of the silicon-carbon substrate by adopting a chemical vapor deposition method, wherein the carbon layer is a first shell layer;
And S3, coating a metal oxide precursor outside the carbon layer by adopting a liquid phase method, and converting the metal oxide precursor into a metal oxide coating layer through heat treatment, wherein the metal oxide coating layer is a second shell layer, so as to obtain the double-shell silicon-carbon composite anode material.
In step S1, optionally, the step of compounding the porous carbon and the silane by a chemical vapor deposition method specifically includes:
Placing the porous carbon in a chemical vapor deposition furnace, introducing inert gas, heating, and introducing silane gas to enable amorphous silicon nano particles to be distributed in the pores of the porous carbon, thereby obtaining the silicon carbon substrate.
Wherein, optionally, the porous carbon is selected from one or more of resin porous carbon, biological porous carbon, petroleum-based porous carbon and coal-based porous carbon.
Optionally, the silane gas is one or more of monosilane, disilane, and silane derivatives.
Optionally, the pore size of the porous carbon is 0.1-50 nm, and the size of the amorphous silicon nano-particles is 0.1-50 nm.
Optionally, the heating is carried out to a temperature of 300-900 ℃.
In step S2, optionally, the coating a carbon layer on the outer surface of the silicon-carbon substrate by using a chemical vapor deposition method specifically includes:
and placing the silicon-carbon substrate in a chemical vapor deposition furnace, introducing inert gas, heating, introducing hydrocarbon gas, and performing pyrolysis to obtain the silicon-carbon substrate coated by the carbon layer.
Optionally, the heating is carried out to a temperature of 300-900 ℃.
Optionally, the hydrocarbon gas is one of acetylene, ethylene and methane.
In step S3, optionally, the step of obtaining the dual-shell silicon-carbon composite anode material specifically includes:
Preparing a metal oxide precursor solution, dispersing the silicon-carbon substrate coated by the carbon layer in the metal oxide precursor solution, and adding a dispersing agent to obtain a metal oxide precursor dispersion liquid;
Carrying out liquid phase coating on the precursor dispersion liquid on the surface of a carbon layer of a silicon-carbon substrate, and then carrying out solid-liquid separation;
And performing heat treatment in an inert atmosphere to convert the metal oxide precursor coated on the surface of the carbon layer into a metal oxide coating layer, thereby obtaining the double-shell silicon-carbon composite anode material.
Wherein, optionally, the metal oxide precursor is one or more of aluminum isopropoxide, titanium isopropoxide, copper isopropoxide, aluminum acetylacetonate and magnesium isopropoxide.
Optionally, the mass ratio of the metal oxide precursor to the silicon carbon substrate is 1-5:100.
In a second aspect, the invention provides a double-shell silicon-carbon composite anode material, which sequentially comprises a silicon-carbon substrate, a carbon layer and a metal oxide coating layer from inside to outside; the silicon-carbon substrate is composed of porous carbon and amorphous silicon nanoparticles, and the amorphous silicon nanoparticles are deposited in the internal pores of the porous carbon; the carbon layer is coated on the surface of the silicon carbon substrate, and the metal oxide coating layer is coated on the outer surface of the carbon layer;
Or the double-shell silicon-carbon composite anode material is prepared by the preparation method of the double-shell silicon-carbon composite anode material.
In a third aspect, the invention also provides application of the double-shell silicon-carbon composite anode material in a lithium ion battery.
The invention has the following beneficial effects:
The invention provides a double-shell silicon-carbon composite anode material, a preparation method and application thereof, wherein the double-shell silicon-carbon composite anode material is prepared by coating a double shell layer on the surface of a silicon-carbon substrate with a buffer pore space, so that on one hand, stress generated by volume expansion of silicon nano particles in a lithium intercalation process is relieved, on the other hand, a carbon layer in a double-shell structure also provides a buffer effect on volume change in a circulation process, contact between the silicon nano particles and electrolyte is blocked, and meanwhile, the conductivity of the silicon-carbon composite material is improved. The mechanical strength of the metal oxide coating layer further ensures the overall stability of the silicon-carbon anode material, and can avoid the problems of etching silicon nano particles by hydrofluoric acid generated in electrolyte and 'natural' generation of an SEI layer in the circulation process. Therefore, the double-shell silicon-carbon composite anode material provided by the invention realizes the remarkable improvement of the first cycle coulombic efficiency, the cycle coulombic efficiency and the cycle stability of the battery.
Drawings
Fig. 1 is a schematic structural diagram of a double-shell silicon-carbon composite anode material provided by the invention.
Fig. 2 is a transmission electron microscope image of the double-shell silicon-carbon composite anode material prepared in example 1 of the present invention.
FIG. 3 is a scanning electron microscope image of the double-shell silicon-carbon composite anode material prepared in example 1 of the present invention, wherein the scales in (a) and (b) are 1 μm and 300nm, respectively.
Fig. 4 is an X-ray diffraction (XRD) pattern of the dual-shell silicon-carbon composite anode material of example 1 of the present invention.
FIG. 5 is a graph showing the results of electrochemical performance tests of the double-shell silicon-carbon composite anode material prepared in example 1 of the present invention and the comparative composite material prepared in comparative example 1, wherein the circulation conditions of (a) and (b) were 500mA g -1 and 2000mA g -1, respectively.
Fig. 6 is a comparison chart of battery cycle test results of the double-shell silicon-carbon composite anode material prepared in example 2 of the present invention and the control composite material prepared in comparative example 1, wherein the cycle conditions of (a) and (b) are 500mA g -1 and 2000mA g -1, respectively.
Fig. 7 is a graph showing the battery cycle test results of the double-shell silicon-carbon composite anode material prepared in example 3 of the present invention and the control composite material prepared in comparative example 1 at 500mA g -1.
Fig. 8 is a battery cycle stability test chart of the double-shell silicon-carbon composite anode material prepared in example 4 of the present invention and the composite materials of the control group prepared in comparative examples 1 and 2.
Fig. 9 is an electrochemical performance test chart of the double-shell silicon-carbon composite anode material prepared in example 4 of the present invention and the composite materials of the control group prepared in comparative examples 1 and 2 at 500mA g -1.
Detailed Description
The invention provides a double-shell silicon-carbon composite anode material, a preparation method and application thereof, and aims to make the purposes, technical schemes and effects of the invention clearer and more definite, and the invention is further described in detail below. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The embodiment of the invention provides a preparation method of a double-shell silicon-carbon composite anode material, which comprises the following steps:
s1, compositing porous carbon and silane by a chemical vapor deposition method to enable amorphous silicon nano particles to be distributed in internal pores of the porous carbon, so as to obtain a silicon carbon substrate;
S2, coating a carbon layer on the outer surface of the silicon-carbon substrate by adopting a chemical vapor deposition method, wherein the carbon layer is a first shell layer, and the silicon-carbon substrate coated by the carbon layer is obtained;
And S3, coating a metal oxide precursor outside the carbon layer by adopting a liquid phase method, and converting the metal oxide precursor into a metal oxide coating layer through heat treatment, wherein the metal oxide coating layer is a second shell layer, so as to obtain the double-shell silicon-carbon composite anode material.
In the embodiment of the invention, in the step S1, a porous carbon material with pores distributed inside is selected, amorphous silicon nano particles are deposited in the gaps, and the stress generated by expansion in the Si circulation process is relieved mainly by utilizing the pores in the silicon carbon substrate.
And the carbon layer is coated on the surface of the silicon-carbon substrate in the step S2, so that the structural integrity of the silicon-carbon material in the circulation process can be improved.
The second coating layer, namely the metal oxide coating layer, is prepared on the outer surface of the carbon layer of the silicon-carbon substrate in the step S3, so that continuous generation of the SEI layer on the surface and etching of Si by electrolyte can be avoided.
In the embodiment of the invention, certain pores are reserved in the silicon carbon substrate to relieve stress generated by volume change in the lithium intercalation process. On the basis, the existence of the first coating layer, namely the carbon layer, in the double-shell structure is beneficial to improving the conductivity of the silicon-carbon substrate, and a certain buffer effect is provided to relieve the larger volume expansion of the silicon nano particles in the circulation process, so that the circulation performance of the battery is further improved, and the carbon layer can also block the contact of the silicon particles and electrolyte, so that the occurrence of side reaction is reduced. The existence of the second coating metal oxide in the double-shell structure can provide certain mechanical strength to coat the overall stability of the silicon-carbon anode material, prevent side reaction in the preparation process and avoid etching of silicon nano particles by hydrofluoric acid generated in the electrolyte; on the other hand, continuous consumption of lithium ions caused by 'natural' generation of an SEI layer in a cycling process can be avoided, so that the first cycle coulombic efficiency (ICE) and the cycle Coulombic Efficiency (CE) of the battery can be improved.
In some specific embodiments, the porous carbon has a pore size of 0.1 to 50nm and the silicon nanoparticles have a size of 0.1 to 50nm.
According to the embodiment of the invention, the porous carbon material is used as the carbon substrate, wherein the buffered micropores and mesopores are reserved to provide a space for accommodating silicon expansion, so that stress generated by volume change in the lithium intercalation process can be relieved, and the structural integrity of the silicon-carbon substrate can be further maintained after the surface of the silicon-carbon substrate is coated.
In step S1, in some embodiments, the step of compositing the porous carbon and the silane by a chemical vapor deposition method specifically includes:
And placing the porous carbon in a chemical vapor deposition furnace, introducing inert gas, heating, introducing silane gas, and distributing amorphous silicon nano particles in the pores of the porous carbon to obtain the silicon carbon substrate.
In some embodiments, the silane gas is monosilane, disilane, silane derivative gas, or the like, but is not limited thereto.
In some specific embodiments, the porous carbon is selected from one or more of resin porous carbon, bio-porous carbon, petroleum-based porous carbon, and coal-based porous carbon, but is not limited thereto.
Conventional silicon-carbon composite materials are usually obtained by embedding nano silicon in a carbon substrate with no reserved pores, and the volume expansion of the silicon in the circulation process is buffered by the property of the carbon, however, the expansion space capable of accommodating the silicon in the circulation process is limited, and the cracking of the silicon-carbon material in the circulation process is more easily caused. Compared with the method, the embodiment of the invention adopts the porous carbon with the reserved buffer pores to prepare the silicon-carbon substrate, so that the structural integrity of the silicon-carbon substrate in the circulation process can be ensured, and the circulation stability of the battery can be improved.
In some embodiments, the heating is to a temperature of 300-900 ℃.
In step S2, in some embodiments, the coating a carbon layer on the outer surface of the silicon-carbon substrate by using a chemical vapor deposition method specifically includes:
and placing the silicon-carbon substrate in a chemical vapor deposition furnace, introducing inert gas, heating, introducing hydrocarbon gas, and performing pyrolysis to obtain the silicon-carbon substrate coated by the carbon layer.
The carbon layer coating layer in the double-shell silicon-carbon composite anode material structure is beneficial to improving the conductivity of the silicon-carbon composite material, and provides a certain buffer effect to relieve the larger volume expansion of the silicon nano particles in the circulation process, so that the circulation performance of the battery is further improved. In addition, the carbon layer can also prevent the silicon particles from contacting with electrolyte, so that side reactions are reduced.
In some embodiments, the heating is to a temperature of 300-900 ℃.
In some embodiments, the hydrocarbon gas is one of acetylene, ethylene, and methane.
In step S3, in some embodiments, the step of obtaining the double-shell silicon-carbon composite anode material specifically includes:
Preparing a metal oxide precursor solution, dispersing a silicon-carbon substrate coated by a carbon layer in the metal oxide precursor solution, and adding a dispersing agent to obtain a metal oxide precursor dispersion liquid;
Carrying out liquid phase coating on the precursor dispersion liquid on the surface of a carbon layer of a silicon-carbon substrate, and then carrying out solid-liquid separation;
And performing heat treatment in an inert atmosphere to convert the metal oxide precursor coated on the surface of the carbon layer into a metal oxide coating layer, thereby obtaining the double-shell silicon-carbon composite anode material.
Wherein, in some specific embodiments, the metal oxide precursor may include at least one of aluminum isopropoxide, titanium isopropoxide, copper isopropoxide, magnesium isopropoxide, and aluminum acetylacetonate.
The dispersing agent is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivative, polyacrylamide, guar gum and fatty acid polyethylene glycol ester. The addition of the dispersing agent can improve the dispersibility of the precursor materials so as to realize better coating effect.
In some specific embodiments, the mass ratio of the metal oxide precursor to the silicon carbon substrate is 1-5:100.
According to the double-shell silicon-carbon composite anode material, the metal oxide is used as the second coating layer of the silicon-carbon substrate, so that the capacity retention rate, the first-cycle coulomb efficiency and the cycle coulomb efficiency of the battery can be obviously improved, wherein the first-cycle coulomb efficiency and the improvement of the coulomb efficiency can be attributed to the fact that the naturally formed SEI layer and side reaction in the battery are reduced by the metal oxide coating layer, and the volume expansion in the cycle process is further reduced.
The embodiment of the invention provides a double-shell silicon-carbon composite anode material which sequentially comprises a silicon-carbon substrate, a carbon layer and a metal oxide coating layer from inside to outside. Wherein the silicon carbon substrate is composed of porous carbon and amorphous silicon nanoparticles deposited in the internal pores of the porous carbon. The carbon layer is coated on the surface of the silicon carbon substrate, and the metal oxide coating layer is coated on the outer surface of the carbon layer.
Or the double-shell silicon-carbon composite anode material is prepared by adopting the preparation method of the double-shell silicon-carbon composite anode material.
In the practical application process of the conventional silicon-based anode material, the volume expansion after lithium intercalation can reach 300%, but the interior of the conventional silicon-carbon material does not have enough space to accommodate the expansion of silicon, so that the cycle stability of the battery is directly affected. In the embodiment of the invention, a double-shell coating structure is carried out on the surface of a silicon-carbon substrate with a buffer pore space, wherein the first coating layer is a carbon layer, and the second coating layer is a metal oxide coating layer. The stress generated by expansion in the Si circulation process is relieved by utilizing the pores in the silicon-carbon substrate, the structural integrity of the silicon-carbon substrate in the circulation process is improved after the double-shell coating is carried out, and the continuous generation of the surface SEI layer and the etching of electrolyte to silicon are avoided.
The embodiment of the invention also provides application of the double-shell silicon-carbon composite anode material in a lithium ion battery.
The following is a further description of the present invention with reference to specific examples.
Example 1
(A) 1500g of porous carbon (particle size D50 of 5-10 μm) was charged into a Chemical Vapor Deposition (CVD) furnace, and nitrogen was introduced at a flow rate of 14L/min for 60min. And heating the temperature in the furnace to 520 ℃, introducing monosilane at a flow rate of 3L/min, and setting the ventilation time of the monosilane to be 500min to obtain the silicon-carbon substrate.
(B) And (c) introducing nitrogen into the silicon-carbon substrate prepared in the step (a) in a CVD furnace at a heating rate of 14L/min, heating to 550 ℃, introducing acetylene gas at a heating rate of 3L/min, and obtaining the silicon-carbon substrate coated by the carbon layer after the aeration time of the acetylene gas is 200 min.
(C) 10 g of the carbon-layer-coated silicon-carbon substrate is dispersed in 400mL of absolute ethyl alcohol, 3 wt% of aluminum isopropoxide (the mass of the aluminum isopropoxide is 3% of the mass of the carbon-layer-coated silicon-carbon substrate) is added, 0.1% of sodium carboxymethyl cellulose is added as a dispersing agent, and the mixture is uniformly stirred until the mixture is uniformly mixed, so that a precursor dispersion liquid is obtained. And uniformly coating the precursor dispersion liquid on the surface of the carbon layer by adopting a liquid phase coating method under the water bath condition of 80 ℃, heating to 500 ℃ under the nitrogen atmosphere, and preserving heat for 3 hours, so that the metal oxide precursor on the surface is converted into an alumina coating layer, and the double-shell silicon-carbon composite anode material is obtained.
Example 2
The only difference from example 1 is that: the mass of the aluminum isopropoxide added in the step (c) accounts for 1.0 weight percent of the mass of the silicon-carbon substrate coated by the carbon layer.
Example 3
The only difference from example 1 is that: the mass of the aluminum isopropoxide added in the step (c) accounts for 5.0 weight percent of the mass of the silicon-carbon substrate coated by the carbon layer.
Example 4
The difference from example 1 is that: the added metal oxide precursor is titanium isopropoxide.
The titanium oxide coating layer of the embodiment is a hard shell layer, so that the expansion of silicon carbon can be restrained better.
Comparative example 1
The difference from example 1 is that: the preparation process only comprises the steps (a) and (b), the metal oxide coating layer is not further coated, and finally the silicon-carbon substrate coated by the single-layer carbon layer is obtained.
Comparative example 2
The difference from example 1 is that: the carbon material used in step (a) is graphite, i.e., a non-porous carbon material.
Fig. 1 is a schematic structural diagram of a double-shell silicon-carbon composite anode material, wherein 1 is a metal oxide coating layer, 2 is a silicon-carbon substrate, 3 is a carbon layer, and 4 is an internal pore. It is known that the substrate material of the double-shell silicon-carbon composite anode material is a silicon-carbon substrate with pores inside, and the double-shell layers coated on the surface are a carbon layer and a metal oxide coating layer respectively.
The morphology of the double-shell silicon-carbon composite anode material prepared in the embodiment 1 is characterized, as shown in fig. 2, it can be seen that the surface of the silicon-carbon substrate is coated with a double-shell structure, wherein 1 is a metal oxide coating layer, 2 is a carbon layer, and 3 is a silicon-carbon substrate. The carbonized acetylene is formed into a carbon layer coated on the surface of the silicon-carbon substrate, and the metal oxide coating layer is coated outside the carbon layer.
In fig. 3 (a) is a feature representation of the double-shell silicon-carbon composite anode material, and in fig. 3 (b) is a feature of the double-shell silicon-carbon composite anode material locally enlarged, it can be seen that the feature of the double-shell silicon-carbon composite anode material is a random block, and a layer of coating substance obviously exists on the surface of the silicon-carbon substrate, namely, the second layer of coating layer aluminum oxide.
As shown in fig. 4, the XRD pattern of the dual-shell silicon-carbon composite anode material showed no significant Si crystallization peak and Al 2O3 crystallization peak, indicating that both silicon and aluminum oxide exist in amorphous form in the dual-shell silicon-carbon composite anode material.
Fig. 5 (a) is an electrochemical performance test result of the double-shell silicon-carbon composite anode material prepared in example 1 and the composite material prepared in comparative example 1 circulating at 500mA g -1, and fig. 5 (b) is an electrochemical performance test result of the double-shell silicon-carbon composite anode material prepared in example 1 and the composite material prepared in comparative example 1 circulating at 2000mA g -1. By comparing the electrochemical properties of the double-shell silicon-carbon composite anode material with those of the silicon-carbon substrate coated by the carbon layer in comparative example 1, it can be found that the first-effect cycle, the cycle coulombic efficiency and the capacity retention rate of the double-shell silicon-carbon composite anode material after double-layer coating are all obviously improved, which means that the capacity retention rate, the first-cycle coulombic efficiency and the cycle coulombic efficiency of a battery can be obviously improved by adopting the metal oxide as the second coating layer. Among them, the first cycle coulombic efficiency and the improvement of the coulombic efficiency can be attributed to the metal oxide coating layer reducing the occurrence of naturally occurring SEI layers and side reactions in the battery and further reducing the volume expansion during the cycle.
Fig. 6 (a) is an electrochemical performance test result of the double-shell silicon-carbon composite anode material prepared in example 2 and the composite material prepared in comparative example 1, which was circulated at 500mA g -1, and fig. 6 (b) is an electrochemical performance test result of the double-shell silicon-carbon composite anode material prepared in example 2 and the composite material prepared in comparative example 1, which was circulated at 2000mA g -1. When the addition amount of the aluminum isopropoxide is 1wt%, the circulation capacity retention rate of the battery formed by the prepared double-shell silicon-carbon composite anode material is obviously improved, but the circulation retention rate is lower than that of the battery formed by the aluminum isopropoxide when the addition amount of the aluminum isopropoxide is 3wt% because the coating layer is too thin.
As shown in fig. 7, when the addition amount of aluminum isopropoxide is 5wt%, the cycle data of the prepared double-shell silicon-carbon composite anode material constituting the battery can show that the cycle retention rate and cycle coulombic efficiency of the battery are improved to some extent as compared with the silicon-carbon substrate coated only with the carbon layer in comparative example 1, but the metal oxide coating layer is too thick due to the higher addition amount of the metal oxide precursor, and instead, the capacity reduction phenomenon occurs during the cycle because the lithium ion intercalation resistance is too large during the cycle due to the too thick coating layer, thereby affecting the electrochemical performance.
As shown in fig. 8, by comparing the cycle performance of the double-layer coated composite material prepared by using the carbon material without pores inside, it can be seen that the double-shell silicon-carbon composite anode material prepared by using the porous carbon material in example 1 has better cycle stability, which is attributable to the existence of pores inside, and the silicon nanoparticles of the silicon-carbon substrate are distributed in the pores, so that the damage of the stress generated by the silicon intercalation of lithium to the silicon-carbon structure during the cycle is dispersed. The conventional silicon-carbon composite material is prepared by embedding nano silicon in a carbon substrate, and buffering the volume expansion of the silicon in the circulation process by means of the property of the carbon, so that the silicon-carbon composite material is broken in the circulation process due to the limited expansion space for accommodating the silicon in the circulation process. Meanwhile, compared with the silicon-carbon substrate coated by the single-layer carbon layer in the comparative example 1, the cycle performance of the double-shell silicon-carbon composite anode material is further improved after the double-shell layers of the carbon layer and the metal oxide coating layer are coated.
As shown in fig. 9, the metal oxide coating layer using titanium oxide as the double-shell silicon-carbon composite anode material has an effect of improving electrochemical performance.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (7)
1. The preparation method of the double-shell silicon-carbon composite anode material is characterized by comprising the following steps of:
s1, compositing porous carbon and silane by a chemical vapor deposition method to enable amorphous silicon nano particles to be distributed in internal pores of the porous carbon, so as to obtain a silicon carbon substrate;
S2, coating a carbon layer on the outer surface of the silicon-carbon substrate by adopting a chemical vapor deposition method, wherein the carbon layer is a first shell layer;
s3, preparing a metal oxide precursor solution, dispersing a silicon-carbon substrate coated by a carbon layer in the metal oxide precursor solution, and adding a dispersing agent to obtain a metal oxide precursor dispersion liquid;
Carrying out liquid phase coating on the precursor dispersion liquid on the surface of a carbon layer of a silicon-carbon substrate, and then carrying out solid-liquid separation;
Performing heat treatment in an inert atmosphere to convert the metal oxide precursor coated on the surface of the carbon layer into a metal oxide coating layer to obtain the double-shell silicon-carbon composite anode material;
Wherein the dispersing agent is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivative, polyacrylamide, guar gum and fatty acid polyethylene glycol ester;
the metal oxide precursor is aluminum isopropoxide and/or aluminum acetylacetonate;
The mass ratio of the metal oxide precursor to the silicon-carbon substrate coated by the carbon layer is 3:100;
the size of the internal pores of the porous carbon is 0.1-50 nm, and the particle size of the amorphous silicon nano particles is 0.1-50 nm.
2. The method for preparing the double-shell silicon-carbon composite anode material according to claim 1, wherein in step S1, the porous carbon and silane are compounded by a chemical vapor deposition method, specifically comprising:
Placing the porous carbon in a chemical vapor deposition furnace, introducing inert gas, heating, and introducing silane gas to enable amorphous silicon nano particles to be distributed in the pores of the porous carbon, so as to obtain the silicon carbon substrate;
Wherein the porous carbon is selected from one or more of resin porous carbon, biological porous carbon, petroleum-based porous carbon and coal-based porous carbon;
the silane gas is one or more of monosilane, disilane and silane derivatives.
3. The preparation method of the double-shell silicon-carbon composite anode material according to claim 2, wherein the heating temperature is raised to 300-900 ℃.
4. The method for preparing a double-shell silicon-carbon composite anode material according to claim 1, wherein in step S2, a carbon layer is coated on the outer surface of the silicon-carbon substrate by chemical vapor deposition, and the method specifically comprises the following steps:
and placing the silicon-carbon substrate in a chemical vapor deposition furnace, introducing inert gas, heating, introducing hydrocarbon gas, and performing pyrolysis to obtain the silicon-carbon substrate coated by the carbon layer.
5. The preparation method of the double-shell silicon-carbon composite anode material according to claim 4, wherein the heating is carried out to 300-900 ℃; the hydrocarbon gas is one of acetylene, ethylene and methane.
6. The double-shell silicon-carbon composite anode material is characterized by being prepared by the preparation method of the double-shell silicon-carbon composite anode material in any one of claims 1-5.
7. Use of the double-shell silicon-carbon composite anode material of claim 6 in lithium ion batteries.
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