CN114105133B - Graphite-silicon/silicon oxide-carbon composite material and preparation method and application thereof - Google Patents

Graphite-silicon/silicon oxide-carbon composite material and preparation method and application thereof Download PDF

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CN114105133B
CN114105133B CN202111216321.1A CN202111216321A CN114105133B CN 114105133 B CN114105133 B CN 114105133B CN 202111216321 A CN202111216321 A CN 202111216321A CN 114105133 B CN114105133 B CN 114105133B
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silicon
graphite
silicon oxide
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CN114105133A (en
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易旭
廖寄乔
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Hunan Jinsi Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • 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 graphite-silicon/silicon oxide-carbon composite material, and a preparation method and application thereof. Carrying out ball milling treatment on graphite powder and nano silicon to obtain graphite-silicon/silicon oxide composite particles; dispersing graphite-silicon/silicon oxide composite particles into an organic solvent, adding asphalt, heating, stirring and mixing to obtain a graphite-silicon/silicon oxide-asphalt composite material; the graphite-silicon/silicon oxide-asphalt composite material is subjected to pyrolysis treatment to obtain the graphite-silicon/silicon oxide-carbon composite material, the composite material is used as a negative electrode material for lithium ion electrons, the obtained lithium ion battery has the characteristics of high discharge specific capacity, good charge and discharge performance, higher cycle stability and the like, and the raw materials adopted in the preparation process of the composite material are cheap, the process flow is simple, and the preparation method is easy to implement and suitable for large-scale production.

Description

Graphite-silicon/silicon oxide-carbon composite material and preparation method and application thereof
Technical Field
The invention relates to a lithium ion battery cathode material, in particular to a graphite-silicon/silicon oxide-carbon composite material, a preparation method thereof and application of the graphite-silicon/silicon oxide-carbon composite material as a lithium ion battery cathode material; belongs to the technical field of lithium ion batteries.
Background
Along with the continuous updating and iteration of products such as electric automobiles, wearable electronic equipment, energy storage equipment and the like, the enthusiasm of consumers for the products is continuously increased, the demand of the market for the energy storage device is also increasingly eager and harsh, the lithium ion battery is used as the secondary battery which is most widely applied at present, but the existing factors such as capacity, multiplying power performance, safety, cycle performance and the like do not completely meet the demand of higher markets, and the development of novel lithium ion battery cathode materials is critical to improve the conditions. The theoretical capacity of the traditional graphite cathode is only 372mAh/g, and the development of the whole lithium ion battery industry is severely restricted. The silicon (Si) anode material has high theoretical capacity and low discharge platform (0.3-0.5V vs. Li/Li) + ) The advantages of rich resources, good safety performance and the like, the theoretical capacity of the material can reach 4200mAh/g, and the material is an electrode material which is very likely to replace a commercial graphite negative electrode. Therefore, silicon-based materials are increasingly attracting attention from researchers as negative electrodes of lithium ion batteries.
However, si negative electrode materials also face a number of problems during charge and discharge: 1) The material is pulverized, and huge volume expansion is generated in the charging and discharging process, so that the internal stress of the material is increased, when the internal stress of the material exceeds a certain limit, the material is separated from a current collector, si particles separated from the current collector lose electrochemical activity and cannot participate in the alloying reaction of lithium ions in a battery, and the cycle performance of the material is further quickly attenuated. 2) Repeated growth of SEI film when the voltage of the anode material is less than 1V (vs. Li/Li + ) In the cycling process of the lithium ion battery, an electrolyte film (SEI) which only allows ions but not electrons to pass through is formed on the surface of the electrode material, and the SEI film effectively prevents further decomposition of electrolyte and plays a great role in ensuring the long cycling performance of the Si material. However, when the Si material is in the discharge process, the volume of the material expands along with the alloying of lithium and Si, and the SEI film is formed on the surface of the materialWhen lithium and Si are dealloyed, the volume of the material is contracted, and the SEI film on the surface of the material is destroyed due to the change of the volume. Such repetition causes repeated formation of an SEI film, thereby resulting in consumption of lithium ions and electrolyte in a large amount, and lowering coulombic efficiency and cycle performance of the material. 3) The electrode is difficult to design, and because the Si anode material is accompanied with great change of volume in the charging and discharging process, active substances are separated from the current collector, so that a large amount of materials in the charging and discharging process of the material are deactivated, and the volume of the anode is changed in the whole process, the characteristics of the Si anode material are considered in the design process of the whole battery, and the design difficulty of the anode of the battery is increased. In addition, the Si anode material has the characteristic of low conductivity, and the Si anode material belongs to a semiconductor material, and has the conductivity of only 10 at room temperature -5 –10 -3 S cm-1, lithium ion diffusion rate is only 10 -14 -10 -13 cm 2 s -1 Resulting in lower rate capability of the material. In view of the above problems, researchers have explored various methods for improving the cycle performance of silicon anode materials, such as reducing the particle size of silicon particles, designing a specific structure, carbon coating, improving binders, and the like. The method is effectively used for preparing the silicon-based composite material to relieve the volume expansion in the charge and discharge process, and is widely applied to modification researches of lithium ion battery anode materials.
Chinese patent (CN 108565451 a) discloses a preparation method of a silicon-carbon negative electrode material: the amorphous carbon and graphite are adopted to coat the silicon particles, so that the conductivity of the battery material and the cycle performance of the battery are improved, but the method can not well relieve the volume expansion of the nano silicon in the discharging process.
Chinese patent (CN 106941164 a) discloses a preparation method of a silicon-carbon negative core-shell material: the amorphous carbon and the graphene are adopted to coat the silicon particles, so that the conductivity of the battery material and the cycle performance of the battery are improved to a certain extent, but the method can not well protect the pulverization of the nano silicon particles and the falling of active substances under the condition of high cycle times.
None of the above methods can well solve the problem of abrupt expansion of the volume of the silicon material during the charge and discharge processes.
Disclosure of Invention
In view of the drawbacks of the prior art, a first object of the present invention is to provide a graphite-silicon/silicon oxide-carbon composite material, which has a core-shell structure, wherein a pyrolytic carbon layer is a shell layer, and graphite-silicon/silicon oxide composite particles form an inner core, the shell layer is a pyrolytic carbon layer, which can effectively improve the conductivity of a silicon material, and can buffer the volume change of a nano silicon material in a charging and discharging process, the inner core uses graphite particles as a framework, silicon oxide is loaded on the surface of the framework to coat silicon nano particles, the graphite particles have high conductivity, and can cooperate with the pyrolytic carbon layer to realize the internal and external common buffer of the volume expansion of the nano silicon material in the discharging process, and the silicon oxide layer on the surface of the nano silicon can generate Li in the charging and discharging process 4 SiO 4 And the components are equal, so that the volume expansion of the nano silicon in the discharging process can be well buffered, the whole composite material can fundamentally and well solve the problem of the rapid volume expansion of the silicon material cathode in the discharging process, the charging and discharging performance of the silicon cathode lithium ion battery is improved, and the service life is prolonged.
The second object of the invention is to provide a preparation method of the graphite-silicon/silicon oxide-carbon composite material, which is simple to operate, low in raw material cost and beneficial to mass production.
The third object of the invention is to provide an application of the graphite-silicon/silicon oxide-carbon composite material, and the application of the graphite-silicon/silicon oxide-carbon composite material as a negative electrode material of a lithium ion battery can obtain the lithium ion battery with high specific capacity and good cycle performance.
In order to achieve the technical aim, the invention provides a preparation method of a graphite-silicon/silicon oxide-carbon composite material, which comprises the following steps:
1) Carrying out ball milling treatment on graphite powder and nano silicon to obtain graphite-silicon/silicon oxide composite particles;
2) Dispersing the graphite-silicon/silicon oxide composite particles into an organic solvent, adding asphalt, heating, stirring and mixing to obtain a graphite-silicon/silicon oxide-asphalt composite material;
3) And carrying out pyrolysis treatment on the graphite-silicon/silicon oxide-asphalt composite material to obtain the graphite-silicon/silicon oxide-carbon composite material.
According to the invention, firstly, graphite powder and nano silicon are subjected to ball milling treatment, in the ball milling process, on one hand, nano silicon particles can be uniformly adhered on the surfaces of the graphite particles to form composite particles taking the graphite particles as a framework, and the surfaces of the graphite particles are adsorbed with nano silicon, on the other hand, in the ball milling process, the surfaces of the nano silicon are oxidized by utilizing mechanical ball milling energy and oxygen in air to generate a layer of thinner silicon oxide on the surfaces of the nano silicon, so that graphite-silicon/silicon oxide composite particles are formed, and then asphalt is further utilized as a carbon source to carry out carbon coating on the graphite-silicon/silicon oxide particles, finally, the graphite-silicon/silicon oxide-carbon composite material with a special structure is formed, the inner graphite particle framework and the outer pyrolytic carbon coating layer of the composite material not only can greatly improve the conductivity of the silicon material, but also realize the internal and external common buffering of volume expansion of the nano silicon in the discharging process, so as to improve the stability, and the silicon oxide layer generated on the surfaces of the nano silicon can generate Li in the charging and discharging process 4 SiO 4 And the like, which can well buffer the volume expansion of the nano silicon in the discharge process.
As a preferable scheme, the particle size of the graphite powder is in the range of 0.3-8 mu m; the grain diameter range of the nano silicon is 10 nm-200 nm. The graphite powder selected by the preferred scheme has micron-sized particles, and the nano silicon is nano-sized particles, so that a composite particle material which takes the graphite particles as a framework surface to adsorb the silicon nano particles is formed in the ball milling process.
As a preferable scheme, the mass ratio of the graphite powder to the nano silicon is 0.5-10:1. Further preferably 0.5 to 5:1.
As a preferable embodiment, the ball milling treatment conditions are as follows: the rotating speed is 300-1200 rad/s, the ball-material ratio is 5-25:1, and the ball milling time is 0.5-6 h. The ball milling process is carried out in a conventional air atmosphere. Under the preferable ball milling condition, the nano silicon particles can be uniformly adhered to the surfaces of the graphite particles, and the surface of the nano silicon can be promoted to be oxidized by utilizing mechanical ball milling, so that a layer of thinner silicon oxide is generated on the surface of the nano silicon. The thickness of the silicon oxide layer is generally 2 to 10nm. The ball milling speed is more preferably 500 to 1000rad/s. The ball-to-material ratio is more preferably 6 to 18:1. The ball milling time is more preferably 1 to 3 hours. If the simple mechanical mixing is carried out without ball milling, a layer of silicon oxide cannot be generated on the surface of the nano silicon, and nano silicon particles are difficult to uniformly adhere to the surface of graphite particles, so that the composite material cannot be formed.
As a preferable scheme, the mass ratio of the graphite-silicon/silicon oxide composite particles to the organic solvent is 1:50-600. The organic solvent is a common organic solvent capable of dissolving and dispersing asphalt, and is preferably cheap absolute ethyl alcohol. The mass ratio of the graphite-silicon/silicon oxide composite particles to the organic solvent is further preferably 1:200 to 300.
As a preferable scheme, the addition amount of the asphalt is 0.4-4 times of the mass of the graphite-silicon/silicon oxide composite particles. The addition amount of the pitch is more preferably 1 to 3 times the mass of the graphite-silicon/silicon oxide composite particles. The addition of asphalt mainly affects the thickness of the carbon coating layer, and even carbon coating layer is difficult to form on the surface of the silicon material due to the fact that the addition of asphalt is too small, and the electrochemical performance of the composite material is also affected due to the fact that the carbon coating layer is too thick.
As a preferable embodiment, the heating and stirring conditions are as follows: the temperature is 50-150 ℃, the stirring speed is 100-500 r/min, and the stirring time is 10-150 min. Under the preferable condition, the asphalt can be promoted to be dissolved and dispersed, and is uniformly adsorbed on the surface of the graphite-silicon/silicon oxide composite particles, thereby being beneficial to the generation of a carbon coating layer. The temperature is more preferably 50 to 150 ℃. The stirring speed is further 200-300 r/min. The stirring time is more preferably 30 to 120 minutes.
As a preferable embodiment, the pyrolysis treatment conditions are as follows: the temperature is 500-950 ℃ and the time is 0.5-5 h; the atmosphere is an inert atmosphere. The temperature is more preferably 550 to 800 ℃. The time is more preferably 0.5 to 3 hours; the inert atmosphere is one of nitrogen, argon or helium. If the pyrolysis temperature is too low, the asphalt is not completely pyrolyzed, and if the pyrolysis temperature is too high, carbothermic reduction easily occurs, and part of the silicon oxide is reduced to silicon.
The invention also provides a graphite-silicon/silicon oxide-carbon composite material, which is obtained by the preparation method.
The graphite-silicon/silicon oxide-carbon composite material has a core-shell structure, a pyrolytic carbon layer is taken as a shell layer, graphite-silicon/silicon oxide composite particles form a core, the shell layer is taken as the pyrolytic carbon layer, the conductivity of a silicon material can be effectively improved, the core can play a role in buffering the volume change of the nano silicon material in the charging and discharging process, graphite particles are taken as a framework, silicon oxide is loaded on the surface of the framework to coat silicon nano particles, the graphite particles have high conductivity, the pyrolytic carbon layer can be matched to realize the internal and external common buffering of the volume expansion of the nano silicon material in the discharging process, and the silicon oxide layer on the surface of the nano silicon can generate Li in the charging and discharging process 4 SiO 4 And the like, the volume expansion of the nano silicon in the discharging process can be well buffered, so that the whole composite material can fundamentally and well solve the problem of sharp expansion of the volume of the silicon material cathode in the discharging process, thereby improving the charging and discharging performance of the silicon cathode lithium ion battery and prolonging the service life.
The graphite-silicon/silicon oxide-carbon composite material provided by the invention is applied as a negative electrode material of a lithium ion battery.
The graphite-silicon/silicon oxide-carbon composite material is used for lithium ion batteries: and uniformly mixing the graphite-silicon/silicon oxide-carbon composite material, a binder, a conductive agent and the like, coating the mixture on a copper foil, drying the mixture in a drying oven at 80 ℃, and slicing the dried mixture to form the electrode slice. In an argon-filled airtight glove box, an electrode sheet loaded with an active material is used as a working electrode, a microporous polypropylene film is used as a diaphragm, and 1.0M LiPF 6 The mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio of 1:1 and VC with 5 percent is taken as electrolyte, and the metal lithium sheet is taken as a counter electrode, so that the CR2025 button cell is assembled.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) The graphite-silicon/silicon oxide-carbon composite material provided by the invention has a special core-shell structure, a pyrolytic carbon layer is taken as a shell layer, the graphite-silicon/silicon oxide composite particles form an inner core, the shell layer is taken as the pyrolytic carbon layer, the conductivity of the silicon material can be effectively improved, the inner core can play a role in buffering the volume change of the nano silicon material in the charging and discharging process, the inner core takes graphite particles as a framework, silicon oxide coated silicon nano particles are loaded on the surface of the framework, the graphite particles have high conductivity, the inner and outer parts can be matched with the pyrolytic carbon layer to realize the volume expansion of the nano silicon material in the discharging process, and the silicon oxide layer on the surface of the nano silicon can generate Li in the charging and discharging process 4 SiO 4 And the components are equal, so that the volume expansion of the nano silicon in the discharging process can be well buffered, the whole composite material can fundamentally and well solve the problem of the rapid volume expansion of the silicon material cathode in the discharging process, the charging and discharging performance of the silicon cathode lithium ion battery is improved, and the service life is prolonged.
2) The graphite-silicon/silicon oxide-carbon composite material provided by the invention is used as a negative electrode material to be assembled into a lithium ion battery, the first-cycle discharge specific capacity is up to 1046.3mAh/g under the current density of 1A/g in the voltage range of 0.01-1V, after 200 cycles, the discharge specific capacity can be up to 938.5mAh/g, the coulomb efficiency is basically maintained to be more than 99% in the cycle process, and the composite material has stable structure and good charge and discharge performance.
3) The preparation method of the graphite-silicon/silicon oxide-carbon composite material provided by the invention has the advantages of relatively low price of raw materials, simple process and suitability for industrial production.
Drawings
Fig. 1 is an SEM electron microscope image of the graphite-silicon/silicon oxide-carbon composite material prepared in example 1 of the present invention.
Fig. 2 is an SEM electron microscope image of the graphite-silicon/silicon oxide composite particles prepared in example 1 of the present invention.
Fig. 3 is an HRTEM image of a graphite-silicon/silicon oxide-carbon composite material prepared in example 1 of the present invention.
FIG. 4 is a graph showing the cycle performance of the graphite-silicon/silicon oxide-carbon composite anode material prepared in example 1 of the present invention at a current density of 1A/g.
Detailed Description
The following description is of the preferred embodiments of the present invention, and it should be noted that, for those skilled in the art, it is possible to make several improvements and modifications without departing from the principle of the embodiments of the present invention, and these improvements and modifications are also considered as the protection scope of the embodiments of the present invention.
The graphite powder and nano silicon in the following examples are commercial materials, the particle size range of the graphite powder is 0.3-8 μm, and the particle size range of the nano silicon is 10-200 nm.
Example 1
Placing 5g of graphite and 5g of nano silicon into a ball mill for ball milling, wherein the rotating speed is 800rad/s, the ball-material ratio is 10:1 (mass ratio), and the ball milling time is 3 hours, so as to synthesize graphite-silicon/silicon oxide composite particles; placing 1g of graphite-silicon/silicon oxide composite particles into 300ml of absolute ethyl alcohol, and adding 1.5g of asphalt into the absolute ethyl alcohol to form a mixed solution; placing the mixed solution in a magnetic stirrer at 85 ℃ with the stirring speed of 200r/min and stirring for 90min to obtain a graphite-silicon/silicon oxide-asphalt composite material; and carrying out high-temperature heat treatment on the obtained graphite-silicon/silicon oxide-asphalt composite material for 2 hours at 750 ℃ in an argon atmosphere to obtain the graphite-silicon/silicon oxide-carbon composite anode material. As shown in fig. 2, in an SEM electron microscope image of the graphite-silicon/silicon oxide composite particles obtained in this example, it can be observed that nano silicon particles are well adsorbed on the surface of graphite particles; fig. 1 is an SEM electron microscope image of a graphite-silicon/silicon oxide-carbon composite anode material prepared in this embodiment, from which it can be seen that nano silicon particles are well adsorbed on the surface of graphite particles, and a layer of complete amorphous carbon is coated on the surface of the material, the material uses graphite as a skeleton, the surface of the particles is coated with carbon, and the volume expansion of nano silicon in the discharge process is buffered by both inside and outside, so as to improve the electrochemical performance of the material; FIG. 3 is a HRTEM image of a graphite-silicon/silicon oxide-carbon composite anode material prepared in this example, from which nano-silicon can be seenA thinner silicon oxide layer is formed on the surface, and Li is generated in the process of charging and discharging 4 SiO 4 And the like, which can further buffer the volume expansion of the nano silicon in the discharge process and improve the cycle performance of the material.
And (3) battery assembly: uniformly mixing graphite-silicon/silicon oxide-carbon composite anode material, sodium carboxymethylcellulose and Super P according to the mass ratio of 8:1:1, coating the mixture on copper foil to form a composite material with consistent thickness, drying the composite material in a drying oven at 80 ℃, and slicing the composite material to form the electrode slice. In an argon-filled airtight glove box, an electrode sheet loaded with an active material is used as a working electrode, a microporous polypropylene film is used as a diaphragm, and 1.0M LiPF 6 The mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio of 1:1 and VC with 5 percent is taken as electrolyte, and the metal lithium sheet is taken as a counter electrode, so that the CR2025 button cell is assembled. The battery is tested for charge and discharge performance within the voltage range of 0.01-1V. The cycle performance curve of the graphite-silicon/silicon oxide-carbon composite anode material is shown in FIG. 4, at 1A g -1 The first-turn discharge specific capacity is up to 1046.3mAh/g, after 200 turns of the material are circulated, the discharge specific capacity can be up to 938.5mAh/g, and the coulomb efficiency is basically maintained to be more than 99% in the circulating process, which indicates that the material has stable structure and good charge and discharge performance.
Example 2
5g of graphite and 10g of nano silicon are placed in a ball mill for ball milling, the rotating speed is 800rad/s, the ball-material ratio is 10:1, the ball milling time is 3 hours, and the graphite-silicon/silicon oxide composite particles are synthesized; placing 1g of graphite-silicon/silicon oxide composite particles in 300ml of absolute ethyl alcohol, and adding 0.67g of asphalt into the absolute ethyl alcohol to form a mixed solution; placing the mixed solution in a magnetic stirrer at 60 ℃ with the stirring speed of 200r/min and stirring for 20min to obtain a graphite-silicon/silicon oxide-asphalt composite material; and carrying out high-temperature heat treatment on the obtained graphite-silicon/silicon oxide-asphalt composite material for 2 hours at 600 ℃ in an argon atmosphere to obtain the graphite-silicon/silicon oxide-carbon composite anode material. The nano silicon particles in the graphite-silicon/silicon oxide composite particles obtained in the embodiment can be well adsorbed on the surfaces of graphite particles, and amorphous carbon coated on the surfaces of materials is thinner and incomplete.
And (3) battery assembly: the graphite-silicon/silicon oxide-carbon composite anode material, sodium carboxymethylcellulose and Super P are uniformly mixed according to the mass ratio of 8:1:1, then coated on a copper foil to form a composite material with consistent thickness, dried in a drying oven at 80 ℃, and sliced to form an electrode slice. In an argon-filled airtight glove box, an electrode sheet loaded with an active material is used as a working electrode, a microporous polypropylene film is used as a diaphragm, and 1.0M LiPF 6 The mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio of 1:1 and VC with 5 percent is taken as electrolyte, and the metal lithium sheet is taken as a counter electrode, so that the CR2025 button cell is assembled. The battery is tested for charge and discharge performance within the voltage range of 0.01-1V. The cycle performance curve of the graphite-silicon/silicon oxide-carbon composite anode material shows that the initial discharge specific capacity is 1865.7mAh/g under the current density of 1A/g, and the discharge specific capacity still remains 569.5mAh/g after 200 cycles, so that the coulomb efficiency basically keeps more than 99% in the cycle process, which indicates that the structural stability of the composite material is general.
Example 3
3g of graphite and 1g of nano silicon are placed in a ball mill for ball milling, the rotating speed is 800rad/s, the ball-material ratio is 15:1, the ball milling time is 4 hours, and the graphite-silicon/silicon oxide composite particles are synthesized; placing 1g of graphite-silicon/silicon oxide composite particles in 300ml of absolute ethyl alcohol, and adding 2g of asphalt into the absolute ethyl alcohol to form a mixed solution; placing the mixed solution in a magnetic stirrer at the temperature of 100 ℃ and stirring at the stirring speed of 300r/min for 150min to obtain a graphite-silicon/silicon oxide-asphalt composite material; and carrying out high-temperature heat treatment on the obtained graphite-silicon/silicon oxide-asphalt composite material for 3 hours at 800 ℃ in an argon atmosphere to obtain the graphite-silicon/silicon oxide-carbon composite anode material. The nano silicon particles in the graphite-silicon/silicon oxide composite particles obtained by the embodiment can be well adsorbed on the surfaces of graphite particles, and amorphous carbon coating on the surfaces of materials is complete.
And (3) battery assembly: uniformly mixing the graphite-silicon/silicon oxide-carbon composite anode material, sodium carboxymethylcellulose and Super P according to the mass ratio of 8:1:1, and then coating the mixture on a batteryAnd forming a composite material with consistent thickness on the copper foil, drying in a drying oven at 120 ℃, and slicing to form the electrode plate. In an argon-filled airtight glove box, an electrode sheet loaded with an active material is used as a working electrode, a microporous polypropylene film is used as a diaphragm, and 1.0M LiPF 6 The mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio of 1:1 and VC with 5 percent is taken as electrolyte, and the metal lithium sheet is taken as a counter electrode, so that the CR2025 button cell is assembled. The battery is tested for charge and discharge performance within the voltage range of 0.01-1V. The cycle performance curve of the graphite-silicon/silicon oxide-carbon composite anode material shows that the initial discharge specific capacity is 679.1mAh/g under the current density of 1A/g, the discharge specific capacity still remains 420.6mAh/g after 200 cycles, and the coulomb efficiency is basically maintained to be more than 99% in the cycle process, which indicates that the composite material has better structural stability.
Example 4 (comparative example)
5g of graphite and 10g of nano silicon are placed in a ball mill for ball milling, the rotating speed is 800rad/s, the ball-material ratio is 10:1, the ball milling time is 3 hours, and the graphite-silicon/silicon oxide composite particles are synthesized; placing 1g of graphite-silicon/silicon oxide composite particles into 300ml of absolute ethyl alcohol, and adding 0.1g of asphalt into the absolute ethyl alcohol to form a mixed solution; placing the mixed solution in a magnetic stirrer at 100 ℃ with the stirring speed of 200r/min and stirring for 150min to obtain a graphite-silicon/silicon oxide-asphalt composite material; and carrying out high-temperature heat treatment on the obtained graphite-silicon/silicon oxide-asphalt composite material for 2 hours at 600 ℃ in an argon atmosphere to obtain the graphite-silicon/silicon oxide-carbon composite anode material. The nano silicon particles in the graphite-silicon/silicon oxide composite particles obtained by the embodiment can be well adsorbed on the surfaces of the graphite particles, and amorphous carbon on the surfaces of materials is coated, so that the amorphous carbon formed by the nano silicon particles is low in integrity due to the fact that the amount of asphalt is small, the heat treatment temperature is low.
And (3) battery assembly: the graphite-silicon/silicon oxide-carbon composite anode material, sodium carboxymethylcellulose and Super P are uniformly mixed according to the mass ratio of 8:1:1, then coated on a copper foil to form a composite material with consistent thickness, dried in a drying oven at 120 ℃, and sliced to form an electrode slice. In a closed glove box filled with argon1.0M LiPF with active material-loaded electrode sheet as working electrode and microporous polypropylene film as separator 6 The mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio of 1:1 and VC with 5 percent is taken as electrolyte, and the metal lithium sheet is taken as a counter electrode, so that the CR2025 button cell is assembled. The battery is tested for charge and discharge performance within the voltage range of 0.01-1V. The cycle performance curve of the graphite-silicon/silicon oxide-carbon composite anode material shows that the initial discharge specific capacity is 1453.6mAh/g under the current density of 1A/g, and after 200 cycles, the discharge specific capacity is only 486.6mAh/g, and the initial discharge specific capacity is higher, but the coulombic efficiency is poor in the cycle process.
Example 5 (comparative example)
5g of graphite and 5g of nano silicon are placed in a ball mill for ball milling, the rotating speed is 800rad/s, the ball-material ratio is 10:1, the ball milling time is 3 hours, and the graphite-silicon/silicon oxide composite particles are synthesized; placing 1g of graphite-silicon/silicon oxide composite particles in 300ml of absolute ethyl alcohol, and adding 5g of asphalt into the absolute ethyl alcohol to form a mixed solution; placing the mixed solution in a magnetic stirrer at 100 ℃ with the stirring speed of 200r/min and stirring for 150min to obtain a graphite-silicon/silicon oxide-asphalt composite material; and carrying out high-temperature heat treatment on the obtained graphite-silicon/silicon oxide-asphalt composite material for 3 hours at 750 ℃ in an argon atmosphere to obtain the graphite-silicon/silicon oxide-carbon composite anode material. The nano silicon particles in the graphite-silicon/silicon oxide composite particles obtained in the embodiment can be well adsorbed on the surfaces of graphite particles, and thick amorphous carbon coating is formed on the surfaces of materials.
And (3) battery assembly: the graphite-silicon/silicon oxide-carbon composite anode material, sodium carboxymethylcellulose and Super P are uniformly mixed according to the mass ratio of 8:1:1, then coated on a copper foil to form a composite material with consistent thickness, dried in a drying oven at 120 ℃, and sliced to form an electrode slice. In an argon-filled airtight glove box, an electrode sheet loaded with an active material is used as a working electrode, a microporous polypropylene film is used as a diaphragm, and 1.0M LiPF 6 A mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) with 5% of VC in a volume ratio of 1:1 is used as an electrolyte, and metalThe lithium sheet was used as a counter electrode to assemble a CR2025 button cell. The battery is tested for charge and discharge performance within the voltage range of 0.01-1V. The cycle performance curve of the graphite-silicon/silicon oxide-carbon composite anode material shows that under the current density of 1A/g, the first-cycle discharge specific capacity is 635.1mAh/g, after 200 cycles, the discharge specific capacity is 386.9mAh/g, the coulomb efficiency is lower in the cycle process, the amorphous carbon coating on the surface of the material is thicker due to the fact that the asphalt adding amount is more, more holes are generated in the thick amorphous carbon layer, the conductivity is lower than that of the normal amorphous carbon coating, and the first-cycle discharge specific capacity and the coulomb efficiency are lower.

Claims (6)

1. A preparation method of a graphite-silicon/silicon oxide-carbon composite material is characterized by comprising the following steps: the method comprises the following steps:
1) Carrying out ball milling treatment on graphite powder and nano silicon to obtain graphite-silicon/silicon oxide composite particles; the ball milling is carried out in an air atmosphere; the particle size range of the graphite powder is 0.3-8 mu m; the grain diameter range of the nano silicon is 10 nm-200 nm; the ball milling treatment conditions are as follows: the rotating speed is 300-1200 rad/s, and the ball-to-material ratio is 5-25: 1, ball milling time is 0.5-6 h;
2) Dispersing the graphite-silicon/silicon oxide composite particles into an organic solvent, adding asphalt, heating, stirring and mixing to obtain a graphite-silicon/silicon oxide-asphalt composite material; the addition amount of the asphalt is 1 to 3 times of the mass of the graphite-silicon/silicon oxide composite particles;
3) Carrying out pyrolysis treatment on the graphite-silicon/silicon oxide-asphalt composite material to obtain a graphite-silicon/silicon oxide-carbon composite material; the pyrolysis treatment conditions are as follows: the temperature is 500-950 ℃ and the time is 0.5-5 h; the atmosphere is an inert atmosphere.
2. The method for preparing a graphite-silicon/silicon oxide-carbon composite material according to claim 1, wherein: the mass ratio of the graphite powder to the nano silicon is 0.5-10:1.
3. The method for preparing a graphite-silicon/silicon oxide-carbon composite material according to claim 1, wherein: the mass ratio of the graphite-silicon/silicon oxide composite particles to the organic solvent is 1:50-600; the organic solvent is absolute ethyl alcohol.
4. The method for preparing a graphite-silicon/silicon oxide-carbon composite material according to claim 1, wherein: the conditions of heating and stirring are as follows: the temperature is 50-150 ℃, the stirring speed is 100-500 r/min, and the stirring time is 10-150 min.
5. A graphite-silicon/silicon oxide-carbon composite material characterized by: obtained by the production process according to any one of claims 1 to 4.
6. Use of a graphite-silicon/silicon oxide-carbon composite material according to claim 5, characterized in that: the material is applied as a negative electrode material of a lithium ion battery.
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