CN114242961A - Graphene/silicon oxide-coated nano-silicon composite material, and preparation method and application thereof - Google Patents
Graphene/silicon oxide-coated nano-silicon composite material, and preparation method and application thereof Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a graphene/silicon oxide-coated nano-silicon composite material, a preparation method and an application thereof. By continuously coating the graphene on the surface of the oxide coating layer of the silicon, the volume expansion effect of the nano silicon particles in the charging and discharging process can be effectively relieved, and meanwhile, the silicon particles are prevented from being directly contacted with the electrolyte to generate an excessively thick solid electrolyte interface film. Therefore, the graphene/silicon oxide coated nano silicon composite material provided by the invention has higher specific capacity, rate capability and cycling stability; the preparation method of the graphene/silicon oxide coated nano-silicon composite material is simple, low in manufacturing cost and easy for industrial production.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a graphene/silicon oxide coated nano-silicon composite material, and a preparation method and application thereof.
Background
Because the silicon negative electrode material has extremely high theoretical capacity, the capacity of the silicon negative electrode material can reach 4200mAh/g at high temperature, which is much higher than that of the graphite negative electrode material used commercially at present, and the storage capacity of silicon is extremely rich, the silicon negative electrode material is regarded as one of the most potential materials of the negative electrode material of the next generation commercial lithium ion battery. However, the silicon negative electrode material has poor conductivity, and the silicon negative electrode material expands about 300% in volume during lithiation, and a solid electrolyte film (SEI) is continuously formed during charge and discharge cycles, thereby causing a series of problems such as continuous decomposition of an electrolyte solution, rapid decrease in electrode capacity, reduction in coulombic efficiency, and reduction in cycle life.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a graphene/silicon oxide-coated nano-silicon composite material, and a preparation method and application thereof, and aims to solve the problems of serious volume expansion, poor performance and high preparation cost in the lithiation process when the existing silicon-based composite material is used as a negative electrode material.
The technical scheme of the invention is as follows:
a graphene/silicon oxide-coated nano-silicon composite material comprises a nano-silicon substrate, a silicon oxide coating layer coated on the surface of the nano-silicon substrate and a graphene coating layer coated on the surface of the silicon oxide coating layer.
The graphene/silicon oxide-coated nano-silicon composite material is characterized in that the raw material of the graphene coating layer is a single-layer graphene aqueous solution with oxidized edges.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material specifically comprises the following steps:
providing oxide coated nano silicon of silicon;
mixing the nano silicon coated by the silicon oxide with an organic solvent to obtain a suspension;
adding the single-layer graphene aqueous solution with oxidized edges into the suspension, and stirring, heating and drying to obtain the graphene/silicon oxide-coated nano silicon composite material with oxidized edges;
and carrying out heat treatment on the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge to obtain the graphene/silicon oxide-coated nano-silicon composite material.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material comprises the following steps:
mixing micron silicon with an organic solvent to obtain a mixed solution;
and carrying out high-energy ball milling on the mixed solution to prepare the silicon oxide coated nano-silicon.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material comprises the step of preparing a graphene/silicon oxide coated nano-silicon composite material, wherein the organic solvent is one or more of methanol, ethanol, ethylene glycol and propanol.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material comprises the step of preparing a graphene/silicon oxide coated nano-silicon composite material, wherein the mass of graphene in the edge-oxidized single-layer graphene aqueous solution is 0.1% -5% of that of micron silicon.
The preparation method of the graphene/silicon oxide-coated nano-silicon composite material comprises the following steps of:
and (3) placing the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge into a sintering furnace, and treating for 2-5 hours under the conditions of inert gas protection and heat treatment temperature of 600-1100 ℃ to obtain the graphene/silicon oxide-coated nano-silicon composite material.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material comprises the step of preparing a graphene/silicon oxide coated nano-silicon composite material, wherein the inert gas is one or more of nitrogen, argon and helium.
The preparation method of the graphene/silicon oxide coated nano-silicon composite material comprises the following steps of carrying out heat treatment on the graphene/silicon oxide coated nano-silicon composite material with oxidized edges at a heating rate of 3 ℃/min or 5 ℃/min or 10 ℃/min; the cooling rate is 5 ℃/min or 7 ℃/min.
The application of the graphene/silicon oxide-coated nano-silicon composite material is to use the graphene/silicon oxide-coated nano-silicon composite material or the graphene/silicon oxide-coated nano-silicon composite material prepared by the preparation method of the graphene/silicon oxide-coated nano-silicon composite material as a negative electrode material of a lithium ion battery.
Has the advantages that: the invention provides a graphene/silicon oxide-coated nano-silicon composite material, a preparation method and an application thereof. By continuously coating the graphene on the surface of the oxide coating layer of the silicon, the volume expansion effect of the nano silicon particles in the charging and discharging process can be effectively relieved, and meanwhile, the direct contact between the silicon particles and the electrolyte is avoided to generate an excessively thick solid electrolyte interface film; in addition, the graphene can effectively improve the electronic conductivity of the composite material. Therefore, the graphene/silicon oxide coated nano silicon composite material provided by the invention has higher specific capacity, rate capability and cycling stability; the preparation method of the graphene/silicon oxide coated nano-silicon composite material is simple, low in manufacturing cost and easy for industrial production.
Drawings
Fig. 1 is an X-ray powder diffraction pattern of the graphene/silicon oxide-coated nano-silicon composite material obtained in example 1 of the present invention;
FIG. 2 is a Raman spectrum of the graphene/silicon oxide-coated nano-silicon composite material obtained in example 1 of the present invention;
fig. 3 is a scanning electron microscope image of the graphene/silicon oxide-coated nano-silicon composite material obtained in example 1 of the present invention;
FIG. 4 is a TEM image of the graphene/silicon oxide-coated nano-silicon composite obtained in example 1 of the present invention;
FIG. 5 is a graph comparing rate capability tests of example 1 of the present invention and comparative example 1;
FIG. 6 is a graph showing the specific discharge capacity as a function of the number of cycles of example 1, example 2, example 3 and comparative example 1 according to the present invention;
FIG. 7 is a graph showing the change of specific discharge capacity with cycle number in examples 1, 4 and 5 of the present invention;
FIG. 8 is a comparative graph of AC impedance tests of example 1 of the present invention and comparative example 1.
Detailed Description
The invention provides a graphene/silicon oxide-coated nano-silicon composite material, and a preparation method and application thereof, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
At present, in order to solve the problems of poor conductivity and volume expansion of silicon materials in the prior art, modification methods such as silicon particle nanocrystallization and carbon coating are generally adopted to modify silicon materials, for example, in the invention patent with the application number of 201910900037.2, a synthesis method of porous silicon nanowires and application of the porous silicon nanowires on a lithium ion battery cathode are provided, the silicon oxide nanowires are prepared by a sol-gel method, magnesium thermal reduction and acid washing are utilized to obtain the silicon nanowires with porous structures, and the porous linear structures relieve the volume expansion of silicon in charge and discharge cycles, but cannot meet the social requirements. In the invention patent with the application number of 202010877236.9, polytetrafluoroethylene particles and silicon particles are mixed and then ball-milled, and the ball-milled powder is ignited, so that the carbon-coated silicon composite material is obtained. Therefore, how to prepare the silicon-based composite material with excellent electrochemical properties at low cost is an urgent problem to be solved for developing silicon cathode materials.
Based on this, as shown in fig. 4, the present invention provides a graphene/silicon oxide-coated nano-silicon composite material, which includes a nano-silicon substrate, a silicon oxide coating layer coated on the surface of the nano-silicon substrate, and a graphene coating layer coated on the surface of the silicon oxide coating layer.
In this embodiment, the silicon oxide coating layer may form lithium silicate after charging, and the lithium silicate has good ionic conductivity and higher modulus, which may improve the ionic conductivity of the graphene/silicon oxide coated nano-silicon composite material and inhibit the volume expansion effect of silicon.
In some embodiments, the graphene in the graphene coating layer is high-crystallinity graphene, and the raw material is an aqueous solution of single-layer graphene with oxidized edges; the graphene with oxidized edges is low in oxidation degree, and the pi plane is not damaged, so that the electronic conductivity of the graphene is high, and the electronic conductivity of the composite material is effectively improved.
In some embodiments, the silicon oxide coating layer is obtained by mixing micro silicon with an organic solvent and then performing high-energy ball milling, so as to obtain silicon oxide-coated nano silicon.
In the embodiment, a coating layer is formed on the surface of the nano silicon substrate by sequentially utilizing the silicon oxide and the graphene to obtain the graphene/silicon oxide coated nano silicon composite material, so that the volume expansion of the nano silicon in the lithiation process of the composite material can be effectively limited, and the SEI film is continuously generated due to the direct contact between the nano silicon substrate and the electrolyte solution; the silicon oxide coating layer can form lithium silicate after being charged, and the lithium silicate has good ionic conductivity and higher modulus, so that the volume expansion effect of silicon can be inhibited while the ionic conductivity of the composite material is improved; in addition, the graphene is used as an excellent conductive material, and the electronic conductivity of the graphene/silicon oxide-coated nano silicon composite material can be effectively improved. Therefore, the graphene/silicon oxide coated nano silicon composite material has high specific capacity, excellent rate performance and cycling stability.
Based on the same inventive concept, the invention also provides a preparation method of the graphene/silicon oxide coated nano-silicon composite material, which specifically comprises the following steps:
s10: providing oxide coated nano silicon of silicon;
s20: mixing the silicon oxide coated nano silicon with an organic solvent to obtain a suspension;
s30: adding the single-layer graphene aqueous solution with the oxidized edge into the suspension, and uniformly stirring, heating and drying to obtain the graphene/silicon oxide-coated nano silicon composite material with the oxidized edge;
s40: and carrying out heat treatment on the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge, and grinding and sieving after natural cooling to obtain the graphene/silicon oxide-coated nano-silicon composite material. At this time, the graphene/silicon oxide-coated nano-silicon composite material is in a powder form.
In some embodiments, the method for preparing the silicon oxide-coated nano-silicon specifically comprises:
s11: mixing micron silicon with an organic solvent to obtain a mixed solution;
s12: and carrying out high-energy ball milling on the mixed solution to prepare the silicon oxide coated nano silicon.
The method for forming the silicon oxide coating on the surface of the nano silicon substrate is simple in process, and can be used for large-scale preparation, so that the requirement of high-efficiency production is met.
In some embodiments, the organic solvent is one or more of methanol, ethanol, ethylene glycol, propanol.
In some embodiments, the mass of graphene in the aqueous edge-oxidized single-layer graphene solution is 0.1% -5% of the mass of the micron silicon. When the addition amount of the graphene is less than 0.1% of the mass of the micron silicon, the electrochemical performance of the prepared graphene/silicon oxide coated nano silicon composite material is not obviously improved due to the small amount of the graphene, and the requirement of using the graphene/silicon oxide coated nano silicon composite material as a negative electrode material cannot be met; when the addition amount of the graphene is more than 5% of the mass of the micron silicon, the silicon content is relatively reduced, so that the graphene/silicon oxide-coated nano silicon composite material has low capacity and low density, and is not beneficial to the development of commercialization.
In some embodiments, the thermal treatment of the edge-oxidized graphene/silicon oxide-coated nano-silicon composite material to obtain the graphene/silicon oxide-coated nano-silicon composite material comprises: and (3) placing the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge into a sintering furnace, and treating for 2-5 hours under the conditions of inert gas protection and heat treatment temperature of 600-1100 ℃ to obtain the graphene/silicon oxide-coated nano-silicon composite material. Under the heat treatment temperature and the treatment time, the graphene/silicon oxide-coated nano-silicon composite material with oxidized edges can be completely converted into the graphene/silicon oxide-coated nano-silicon composite material, so that the capacity and the electrochemical performance of the composite material are improved.
In some embodiments, the inert gas is one or more of nitrogen, argon, helium.
In some embodiments, the temperature rise rate of the heat treatment of the edge oxidized graphene/silicon oxide coated nano-silicon composite material may be, but is not limited to, 3 ℃/min or 5 ℃/min or 10 ℃/min; the cooling rate may be, but is not limited to, 5 deg.C/min or 7 deg.C/min. It should be noted that the heating rate and the cooling rate in the heat treatment process may be the same or different; by controlling the heating rate and the cooling rate during the heat treatment, the reaction process can be more stable, and the reaction can be more thoroughly carried out.
In the embodiment, the preparation method of the graphene/silicon oxide coated nano-silicon composite material is simple, low in cost and easy for large-scale industrial production; meanwhile, the graphene/silicon oxide-coated nano silicon composite material prepared by the simple method realizes that the silicon oxide and the high-crystallinity graphene are sequentially and uniformly coated on the surface of the nano silicon, effectively limits the volume expansion of the nano silicon substrate, reduces the direct contact between electrolyte and the nano silicon substrate, and simultaneously obviously improves the electronic conductivity of the composite material. Therefore, the graphene/silicon oxide coated nano silicon composite material has higher specific discharge capacity, excellent rate performance and charge-discharge cycling stability.
Based on the same inventive concept, the invention also provides an application of the graphene/silicon oxide-coated nano-silicon composite material, and the graphene/silicon oxide-coated nano-silicon composite material or the graphene/silicon oxide-coated nano-silicon composite material prepared by the preparation method of the graphene/silicon oxide-coated nano-silicon composite material is used as a negative electrode material of a lithium ion battery.
The present invention will be described in further detail with reference to examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings.
Example 1
Mixing precursors: mixing 8mL of suspension (the concentration of which is 100mg/mL) formed by silicon oxide-coated nano silicon and an ethanol solvent with 8mL of edge graphene oxide aqueous solution (the concentration of which is 1mg/mL), uniformly stirring, heating and drying to obtain an edge graphene oxide/silicon oxide-coated nano silicon composite material;
and (3) heat treatment: and (3) putting the obtained graphene/silicon oxide-coated nano-silicon composite material with the edge into a tube furnace, carrying out heat treatment for 3 hours at the temperature of 900 ℃ in the argon atmosphere, wherein the heating rate is 5 ℃/min, naturally cooling, grinding and sieving to obtain the powdery graphene/silicon oxide-coated nano-silicon composite material.
Example 2
Mixing precursors: mixing 8mL of suspension (the concentration of which is 100mg/mL) formed by silicon oxide-coated nano silicon and an ethanol solvent with 4mL of edge graphene oxide aqueous solution (the concentration of which is 1mg/mL), uniformly stirring, heating and drying to obtain an edge graphene oxide/silicon oxide-coated nano silicon composite material;
and (3) heat treatment: and (3) putting the obtained graphene/silicon oxide-coated nano-silicon composite material with the edge into a tube furnace, carrying out heat treatment for 3 hours at the temperature of 900 ℃ in the argon atmosphere, wherein the heating rate is 5 ℃/min, naturally cooling, grinding and sieving to obtain the powdery graphene/silicon oxide-coated nano-silicon composite material.
Example 3
Mixing precursors: mixing 8mL of suspension (the concentration of which is 100mg/mL) formed by silicon oxide-coated nano silicon and an ethanol solvent with 12mL of edge graphene oxide aqueous solution (the concentration of which is 1mg/mL), uniformly stirring, heating and drying to obtain an edge graphene oxide/silicon oxide-coated nano silicon composite material;
and (3) heat treatment: and (3) putting the obtained graphene/silicon oxide-coated nano-silicon composite material with the edge into a tube furnace, carrying out heat treatment for 3 hours at the temperature of 900 ℃ in the argon atmosphere, wherein the heating rate is 5 ℃/min, naturally cooling, grinding and sieving to obtain the powdery graphene/silicon oxide-coated nano-silicon composite material.
Example 4
Mixing precursors: mixing 8mL of suspension (the concentration of which is 100mg/mL) formed by silicon oxide-coated nano silicon and an ethanol solvent with 8mL of edge graphene oxide aqueous solution (the concentration of which is 1mg/mL), uniformly stirring, heating and drying to obtain an edge graphene oxide/silicon oxide-coated nano silicon composite material;
and (3) heat treatment: and (3) putting the obtained graphene/silicon oxide-coated nano-silicon composite material with the edge into a tube furnace, carrying out heat treatment for 3 hours at the temperature of 800 ℃ in the argon atmosphere, wherein the heating rate is 5 ℃/min, naturally cooling, grinding and sieving to obtain the powdery graphene/silicon oxide-coated nano-silicon composite material.
Example 5
Mixing precursors: mixing 8mL of suspension (the concentration of which is 100mg/mL) formed by silicon oxide-coated nano silicon and an ethanol solvent with 8mL of edge graphene oxide aqueous solution (the concentration of which is 1mg/mL), uniformly stirring, heating and drying to obtain an edge graphene oxide/silicon oxide-coated nano silicon composite material;
and (3) heat treatment: and (3) putting the obtained graphene/silicon oxide-coated nano silicon composite material with the edge into a tube furnace, carrying out heat treatment for 3 hours at the temperature of 1000 ℃ in the argon atmosphere, wherein the heating rate is 5 ℃/min, naturally cooling, grinding and sieving to obtain the powdery graphene/silicon oxide-coated nano silicon composite material.
Comparative example 1
8mL of suspension (the concentration of the suspension is 100mg/mL) formed by the silicon oxide coated nano silicon and the ethanol solvent is heated and dried to obtain the silicon oxide coated nano silicon composite material.
In order to test that the composite material provided by the invention has energy storage characteristics and can be used as a lithium battery cathode material, tests such as X-ray diffraction, Raman spectroscopy, scanning electron microscope, transmission electron microscope, multiplying power performance of the composite material, cycle performance of the composite material, alternating current impedance spectrogram of the composite material and the like are carried out on the energy storage materials obtained in the examples and the comparative examples, and the test results are shown in figures 1 to 8.
As can be seen from the analysis of fig. 1 to 8, fig. 1 is an X-ray diffraction pattern of the powdery graphene/silicon oxide-coated nano-silicon composite material obtained in example 1, and it can be seen from the pattern that the diffraction peak of the composite material matches the PDF card of pure silicon, indicating that the main component thereof is silicon.
Fig. 2 is a raman spectrum of the materials obtained in example 1 and comparative example 1, in example 1, a D peak, a G peak, and a 2D peak unique to the graphite structure are increased compared to comparative example 1, and the existence of graphene in the graphene/silicon oxide-coated nano-silicon composite material is proved.
Fig. 3 is a scanning electron microscope photograph of the single-layer graphene-coated nano-silicon composite material obtained in example 1 (the single-layer graphene-coated nano-silicon composite material is the graphene/silicon oxide-coated nano-silicon composite material of the present invention), and the composite material after heat treatment has relatively uniform particle size, the particle diameter is mainly concentrated between 400 and 600nm, and the nano-sized silicon is more favorable for prolonging the cycle life of the composite material.
Fig. 4 is a transmission electron microscope photograph of the graphene/silicon oxide-coated nano-silicon composite material obtained in example 1, and observing the morphology features thereof can clearly see the lattice stripes of silicon and the graphene with uniform surfaces of the silicon oxide coating layer and the silicon oxide coating layer.
FIG. 5 is a graph showing the rate capability tests of the materials obtained in comparative example 1 and example 1, wherein the composite material of the present invention has average discharge capacities of 1650.82mAh/g, 1663.10mAh/g, 1445.99mAh/g, 1167.68mAh/g, 874.45mAh/g and 1684.68mAh/g at current densities of 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, 2A/g and 0.1A/g, respectively.
Fig. 6 is a graph showing the change of specific discharge capacity of the composite materials with different graphene contents obtained in comparative example 1, example 2 and example 3 with the cycle number, i.e., a cycle performance test graph, the composite material prepared in example 1 of the present invention still has specific discharge capacity of 1151.0mAh/g after 140 cycles at a current density of 0.5A/g, and the first coulombic efficiency reaches 83.55%; the specific discharge capacities of the composite materials prepared in comparative example 1, example 2 and example 3 after 140 cycles at a flow density of 0.5A/g were 527.5mAh/g, 927.9mAh/g and 1058.7mAh/g, respectively.
Fig. 7 is a graph of specific discharge capacity of the composite material obtained in example 1, example 4 and example 5 at different heat treatment temperatures as a function of cycle number, i.e., a cycle performance test graph, and the composite material prepared in the example of the present invention has better capacity and stability.
Fig. 8 is an ac impedance test chart of the materials obtained in comparative example 1 and example 1, and compared with comparative example 1, the charge transfer resistance of example 1 is reduced from 294.3 Ω to 202.4 Ω, and the preparation method of the invention can significantly reduce the charge transfer resistance of the electrode and improve the electronic conductivity of the composite material.
In summary, the graphene/silicon oxide-coated nano-silicon composite material and the preparation method and application thereof provided by the invention include a nano-silicon substrate, a silicon oxide coating layer coated on the surface of the nano-silicon substrate, and a graphene coating layer coated on the surface of the silicon oxide coating layer. By continuously coating the graphene on the surface of the oxide coating layer of the silicon, the volume expansion effect of the nano silicon particles in the charging and discharging process can be effectively relieved, and meanwhile, the direct contact between the silicon particles and the electrolyte is avoided to generate an excessively thick solid electrolyte interface film; in addition, the graphene can effectively improve the electronic conductivity of the composite material. Therefore, the graphene/silicon oxide coated nano silicon composite material provided by the invention has higher specific capacity, rate capability and cycling stability; the preparation method of the graphene/silicon oxide coated nano-silicon composite material is simple, low in manufacturing cost and easy for industrial production. Secondly, the capacity of the graphene/silicon oxide coated nano silicon composite material is superior to that of a commercial graphene coated nano silicon material, and the voltage range of the graphene/silicon oxide coated nano silicon composite material is between 0.01 and 2V; when the composite material is at current densities of 0.1A/g, 0.2A/g, 0.5A/g, 1A/g and 2A/g, the average discharge capacity of the composite material is 1650.82mAh/g, 1663.10mAh/g, 1445.99mAh/g, 1167.68mAh/g and 874.45mAh/g respectively.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. The graphene/silicon oxide-coated nano-silicon composite material is characterized by comprising a nano-silicon substrate, a silicon oxide coating layer coated on the surface of the nano-silicon substrate and a graphene coating layer coated on the surface of the silicon oxide coating layer.
2. The graphene/silicon oxide-coated nano-silicon composite material according to claim 1, wherein a raw material of the graphene coating layer is an aqueous solution of single-layer graphene with oxidized edges.
3. The preparation method of the graphene/silicon oxide-coated nano-silicon composite material according to any one of claims 1 to 2, which specifically comprises the steps of:
providing oxide coated nano silicon of silicon;
mixing the nano silicon coated by the silicon oxide with an organic solvent to obtain a suspension;
adding the single-layer graphene aqueous solution with oxidized edges into the suspension, and stirring, heating and drying to obtain the graphene/silicon oxide-coated nano silicon composite material with oxidized edges;
and carrying out heat treatment on the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge to obtain the graphene/silicon oxide-coated nano-silicon composite material.
4. The method according to claim 3, wherein the method for preparing the silicon oxide-coated nano-silicon composite material specifically comprises:
mixing micron silicon with an organic solvent to obtain a mixed solution;
and carrying out high-energy ball milling on the mixed solution to prepare the silicon oxide coated nano-silicon.
5. The method for preparing the graphene/silicon oxide-coated nano-silicon composite material according to claim 4, wherein the organic solvent is one or more of methanol, ethanol, ethylene glycol and propanol.
6. The method for preparing the graphene/silicon oxide-coated nano-silicon composite material according to claim 4, wherein the mass of graphene in the edge-oxidized single-layer graphene aqueous solution is 0.1-5% of the mass of the micron silicon.
7. The method for preparing the graphene/silicon oxide-coated nano-silicon composite material according to claim 4, wherein the step of performing heat treatment on the edge-oxidized graphene/silicon oxide-coated nano-silicon composite material to obtain the graphene/silicon oxide-coated nano-silicon composite material comprises the following steps:
and (3) placing the graphene/silicon oxide-coated nano-silicon composite material with the oxidized edge into a sintering furnace, and treating for 2-5 hours under the conditions of inert gas protection and heat treatment temperature of 600-1100 ℃ to obtain the graphene/silicon oxide-coated nano-silicon composite material.
8. The method for preparing the graphene/silicon oxide-coated nano-silicon composite material according to claim 7, wherein the inert gas is one or more of nitrogen, argon and helium.
9. The method of preparing the graphene/silicon oxide-coated nano-silicon composite material according to claim 7, wherein the temperature increase rate of the heat treatment of the edge-oxidized graphene/silicon oxide-coated nano-silicon composite material is 3 ℃/min or 5 ℃/min or 10 ℃/min; the cooling rate is 5 ℃/min or 7 ℃/min.
10. An application of the graphene/silicon oxide-coated nano-silicon composite material is characterized in that the graphene/silicon oxide-coated nano-silicon composite material prepared by the preparation method of the graphene/silicon oxide-coated nano-silicon composite material according to any one of claims 1 to 2 or the graphene/silicon oxide-coated nano-silicon composite material according to any one of claims 3 to 9 is used as a negative electrode material of a lithium ion battery.
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