Method for preparing spherical silicon-carbon composite material by using thermal plasma, prepared spherical silicon-carbon composite material and application of spherical silicon-carbon composite material

Abstract

The invention discloses a method for preparing a spherical silicon-carbon composite material through thermal plasma, the prepared spherical silicon-carbon composite material and application, and the method comprises the following steps: S1, raw material preparation: mechanically mixing micron-sized silicon powder and solid carbon source powder to obtain a mixed raw material; s2, plasma treatment: loading the mixed raw material obtained in the step S1 into a high-temperature hot plasma torch generated by a plasma generator through a powder feeder, and instantly heating the mixed raw material in the plasma torch to a gasified or molten state; and S3, rapid quenching and spheroidizing: spraying the gas / liquid phase material subjected to plasma treatment at a high speed to pass through a quenching medium to realize millisecond-level rapid cooling, solidification and spheroidizing, and directly collecting to obtain the spherical silicon-carbon composite material. By utilizing the extreme condition of the thermal plasma, the decomposition, compounding, spheroidization and crystallization processes of the raw materials are integrated into one step, so that the precise regulation and control of the microstructure of the material are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery material preparation, and particularly relates to a method for preparing spherical silicon-carbon composite material by using thermal plasma, and the prepared spherical silicon-carbon composite material and application thereof. BACKGROUND

[0002] Silicon-carbon composite material is one of the most effective ways to solve the huge volume effect of silicon negative electrode and improve its cycle stability. Traditional silicon-carbon composite material preparation methods, such as high-energy ball milling method, chemical vapor deposition method, sol-gel method, etc., generally have problems such as long process flow, high energy consumption, need to use toxic reagents, or difficult to realize uniform composite of silicon and carbon at nanoscale. For example, the ball milling method easily introduces impurities, and the nanocrystallization of silicon and the uniformity of mixing with carbon are not well controlled; the CVD method is high in cost, limited in silicon loading, and there is a risk of incomplete coating.

[0003] Thermal plasma technology is an advanced material preparation and processing technology with ultra-high temperature, high energy density, controllable reaction atmosphere and extremely fast reaction rate. It can melt or even vaporize almost all raw materials in an instant, and realize the synthesis, spheroidization and crystallization of materials through rapid quenching. At present, this technology has been successfully applied to the preparation of spherical ceramic powder, nanomaterials, etc. However, the application of thermal plasma technology to the synthesis of silicon-carbon composite negative electrode material and the precise control of process parameters to directly obtain spherical products with specific microstructure have not been reported. The existing technology lacks an industrial-friendly preparation method that can simultaneously realize atomic-level uniform mixing of silicon and carbon, in-situ spheroidization of materials, high graphitization of carbon phase, and short process flow.

[0004] CN202310510596.9 proposes a low-expansion silicon-carbon material and a preparation method thereof. The low-expansion silicon-carbon material has a porous core-shell structure, the inner core is graphene / metal-doped amorphous carbon coated nanosilicon, and the outer shell is boron-doped amorphous carbon. The preparation method comprises the following steps: first, add silicon oxide compounds, graphene oxide solution and organic metal polymers into an organic carbon source solution, spray dry, and react to obtain silicon-oxygen precursor material coated with graphene oxide and doped with metal; then, pass a mixed gas of boron source gas and argon gas into the silicon-oxygen precursor material coated with graphene oxide and doped with metal, and react to obtain boron-doped silicon-carbon composite material; soak the boron-doped silicon-carbon composite material in a hydrofluoric acid solution, and dry to obtain a low-expansion silicon-carbon material. Through the above technical solution, the problems of high expansion and poor rate performance of silicon-carbon materials in related technologies are solved. However, this technology uses a spray drying method to prepare silicon-carbon materials, which has a complex process flow and needs to use toxic reagents. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a novel method for preparing high-performance spherical silicon-carbon composite materials by one-step hot plasma technology.

[0006] Another object of the present application is to provide the spherical silicon-carbon composite materials with unique "island-in-sea" structure (nano-silicon islands embedded in continuous graphite carbon matrix) prepared by the above method.

[0007] Still another object of the present application is to provide the application of the above spherical silicon-carbon composite materials as anodes of lithium ion batteries.

[0008] The technical scheme of the present application is as follows: a method for preparing spherical silicon-carbon composite materials by hot plasma, comprising the following steps: S1. Raw material preparation: mechanically mixing micron-sized silicon powder and solid carbon source powder to obtain a mixed raw material; S2. Plasma treatment: loading the mixed raw material obtained in step S1 into a high-temperature hot plasma torch generated by a plasma generator through a powder feeder, and instantaneously heating the mixed raw material in the plasma torch to a gasification or melting state; S3. Rapid quenching and spheroidization: rapidly spraying the gas / liquid phase material after plasma treatment through a quenching medium to achieve millisecond-level rapid cooling, solidification and spheroidization, and directly collecting the spherical silicon-carbon composite materials.

[0009] Further, in step S1, the particle size of the micron-sized silicon powder is 1-10 μm; the solid carbon source is at least one of pitch, graphite, carbon black and sucrose; and the mass ratio of the silicon powder to the solid carbon source is (10:90) to (60:40).

[0010] Further, in step S2, the plasma generator is one of a direct current transferred arc plasma torch, a radio frequency plasma torch or a microwave plasma torch; the plasma working gas is one or more of argon, hydrogen, nitrogen or helium; and the central temperature of the plasma torch is 5000-15000 K.

[0011] Further, in step S3, the quenching medium is an inert gas or a hydrocarbon gas reactive with the carbon source; when the quenching medium is an inert gas, the spherical silicon-carbon composite material is a silicon / carbon composite sphere; and when the quenching medium is a hydrocarbon such as methane or acetylene, it is cracked during the quenching process to form a carbon-coated layer on the surface of the sphere.

[0012] Furthermore, the quenching process controls the sphericity and shell thickness of the final product by adjusting the flow rate, temperature, and composition of the quenching gas; wherein the flow rate of the quenching gas is 10~100m / s, the temperature is 25℃~800℃, and the composition is one or more of argon, nitrogen, methane, ethane, propane, acetylene, and other hydrocarbons.

[0013] The spherical silicon-carbon composite material prepared by the above method is characterized in that the material consists of regular spherical particles with a particle size distribution of 50 nm - 2 μm, and has an "island-type" composite structure in which highly graphitized carbon serves as a continuous matrix and nano-silicon islands are uniformly dispersed.

[0014] Furthermore, the size of the nano-silicon islands is less than 50 nm and they are effectively separated by a carbon matrix; the carbon matrix has a high degree of graphitization crystallinity.

[0015] Furthermore, the surface of the spherical particles is coated with an amorphous or graphitized carbon shell of 2-20 nm thickness formed by the decomposition of carbon source gas in a quenching atmosphere.

[0016] A lithium-ion battery negative electrode comprising the above-mentioned spherical silicon-carbon composite material.

[0017] A lithium-ion battery comprising the aforementioned lithium-ion battery negative electrode.

[0018] The beneficial effects of this invention are: 1. Process advantages: fast reaction speed, great potential for continuous production, high product purity (avoiding solvent pollution), and green and environmentally friendly.

[0019] 2. Material Performance Advantages: ① The highly graphitized carbon matrix provides a "highway"-like electronic conductivity network; the nano-sized silicon islands shorten the lithium-ion diffusion path and are effectively buffered by carbon to prevent volume expansion. ② The spherical particles have high tap density; the "island" structure and surface carbon shell work together to provide multi-level buffering space for silicon volume changes, making the material structure extremely stable. ③ Good conductivity and nanoscale characteristics enable the material to have rapid charge and discharge capabilities. Attached Figure Description

[0020] Figure 1 This is a schematic cross-sectional view of the silicon-carbon material prepared by the method of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] The method for preparing spherical silicon-carbon composite materials using thermal plasma according to the present invention includes the following steps: S1. Raw material preparation: Micron-sized silicon powder and solid carbon source powder are mechanically mixed to obtain mixed raw materials; S2. Plasma treatment: The mixed raw material obtained in step S1 is loaded into a high-temperature thermal plasma torch generated by a plasma generator through a powder feeder. The mixed raw material is instantly heated to a gasified or molten state in the plasma torch. S3. Rapid quenching and spheroidization: The gaseous / liquid phase material after plasma treatment is sprayed at high speed through the quenching medium to achieve millisecond-level rapid cooling, solidification and spheroidization, and the spherical silicon-carbon composite material is directly collected.

[0023] Further, in step S1, the particle size of the micron-sized silicon powder is 1-10 μm; the solid carbon source is at least one of pitch, graphite, carbon black, and sucrose; and the mass ratio of the silicon powder to the solid carbon source is (10:90) to (60:40).

[0024] Furthermore, in step S2, the plasma generator is one of a DC transfer arc plasma torch, a radio frequency plasma torch, or a microwave plasma torch; the plasma working gas is one or more of argon, hydrogen, nitrogen, or helium; and the center temperature of the plasma torch is 5000-15000K.

[0025] Furthermore, in step S3, the quenching medium is an inert gas or a hydrocarbon gas that is reactive with the carbon source; when the quenching medium is an inert gas, the spherical silicon-carbon composite material is a silicon / carbon composite sphere; when the quenching medium is a hydrocarbon such as methane or acetylene, it undergoes cracking during the quenching process, forming a carbon coating layer on the surface of the sphere.

[0026] Furthermore, the quenching process controls the sphericity and shell thickness of the final product by adjusting the flow rate, temperature, and composition of the quenching gas; wherein the flow rate of the quenching gas is 10~100m / s, the temperature is 25℃~800℃, and the composition is one or more of argon, nitrogen, methane, ethane, propane, acetylene, and other hydrocarbons.

[0027] The spherical silicon-carbon composite material prepared by the above method is characterized in that the material consists of regular spherical particles with a particle size distribution of 50 nm - 2 μm, and has an "island-type" composite structure in which highly graphitized carbon serves as a continuous matrix and nano-silicon islands are uniformly dispersed.

[0028] Furthermore, the size of the nano-silicon islands is less than 50 nm and they are effectively separated by a carbon matrix; the carbon matrix has a high degree of graphitization crystallinity.

[0029] Furthermore, the surface of the spherical particles is coated with an amorphous or graphitized carbon shell of 2-20 nm thickness formed by the decomposition of carbon source gas in a quenching atmosphere.

[0030] A lithium-ion battery negative electrode comprising the above-mentioned spherical silicon-carbon composite material.

[0031] A lithium-ion battery comprising the aforementioned lithium-ion battery negative electrode.

[0032] like Figure 1 The diagram shown is a cross-sectional view of the silicon-carbon material prepared by the method of this invention. 1 represents the carbon coating shell, 2 represents nano-silicon, and 3 represents graphitized carbon. The core of this invention lies in utilizing the ultra-high temperature characteristics of thermal plasma to enable a mixture of micron-sized silicon powder and solid carbon source to undergo a "gasification-mixing-nucleation-growth" process in a short time. Its innovation is reflected in: 1. One-step in-situ synthesis: The traditional multi-step process (such as nano-silicon preparation, mixing, coating, carbonization and graphitization) is integrated into a single plasma reactor and completed in one step, which greatly simplifies the process and reduces energy consumption and production costs.

[0033] 2. Unique "island" structure formation mechanism: Under the high temperature of plasma, both silicon and carbon are vaporized or form high-temperature droplets. Because carbon has a higher boiling point than silicon, during the subsequent rapid quenching process, carbon preferentially nucleates and crystallizes, forming a continuous phase; while silicon precipitates in a nanoscale "island" form and is naturally separated by the carbon matrix. This structure effectively suppresses the agglomeration and volume expansion stress of silicon particles during cycling.

[0034] 3. Self-spherification and high graphitization: Surface tension causes high-temperature droplets to automatically form spherical particles during flight, while the high-temperature environment of plasma provides the necessary conditions for in-situ graphitization of carbon without the need for additional high-temperature heat treatment, resulting in carbon matrix with better electrical conductivity.

[0035] 4. Adjustable surface coating: By selecting different quenching atmospheres (such as inert gas or hydrocarbon gas), in-situ carbon coating can be achieved on the surface of spherical particles to form a robust core-shell structure, further enhancing the mechanical strength and interfacial stability of the material.

[0036] Example 1 S1. Mix silicon powder and graphite powder with an average particle size of 5μm in a mixer at a mass ratio of 52:48 for 2 hours.

[0037] S2. The mixed raw materials are fed into the powder feeder of the DC transfer arc plasma torch. The plasma working gas is a mixture of argon and 5% hydrogen, with a power of 30 kW. The raw materials are fed into the center of the plasma flame at a temperature as high as 10,000 K by the carrier gas and are instantly heated and evaporated.

[0038] S3. The gaseous material then enters a quenching reaction chamber directly connected to the plasma torch, where it is quenched by a high-speed flow of argon gas. The material cools and condenses into spherical particles within milliseconds, which are then collected by a cyclone collector. The resulting product consists of regular spherical particles with a particle size distribution of 0.5–1.5 μm.

[0039] Example 2 S1. Same as Example 1.

[0040] S2. Same as Example 1.

[0041] S3. Change the quenching medium to a mixture of methane and argon (methane volume fraction 10%). During the quenching process, methane decomposes on the surface of the high-temperature particles, forming a carbon coating layer approximately 5 nm thick.

[0042] The resulting product has a core-shell structure, with the core structure being similar to that of Example 1, and the outer shell being a dense carbon layer.

[0043] Comparative Example Silicon powder and graphite were ball-milled and mixed for 10 hours using a traditional high-energy ball milling method, and then annealed under argon protection at 1000°C for 2 hours. The mass ratio of silicon powder to graphite was the same as in Example 1.

[0044] Performance data: The prepared material was used as the active material and mixed with conductive agent acetylene black and binder polyvinylidene fluoride in a mass ratio of 8:1:1 to form a slurry. This slurry was then coated onto copper foil to form a negative electrode. A lithium metal sheet was used as the counter electrode to assemble a CR2032 coin cell for testing.

[0045] Table 1 Material property test data

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing spherical silicon-carbon composite materials using thermal plasma, characterized in that, Includes the following steps: S1. Raw material preparation: Micron-sized silicon powder and solid carbon source powder are mechanically mixed to obtain mixed raw materials; S2. Plasma treatment: The mixed raw material obtained in step S1 is loaded into a high-temperature thermal plasma torch generated by a plasma generator through a powder feeder. The mixed raw material is instantly heated to a gasified or molten state in the plasma torch. S3. Rapid quenching and spheroidization: The gaseous / liquid phase material after plasma treatment is sprayed at high speed through the quenching medium to achieve millisecond-level rapid cooling, solidification and spheroidization, and the spherical silicon-carbon composite material is directly collected.

2. The method for preparing spherical silicon-carbon composite materials using thermal plasma according to claim 1, characterized in that, In step S1, the particle size of the micron-sized silicon powder is 1-10 μm; the solid carbon source is at least one of pitch, graphite, carbon black, and sucrose; and the mass ratio of silicon powder to solid carbon source is (10:90) to (60:40).

3. The method for preparing spherical silicon-carbon composite materials using thermal plasma according to claim 1, characterized in that, In step S2, the plasma generator is one of a DC transfer arc plasma torch, a radio frequency plasma torch, or a microwave plasma torch; the plasma working gas is one or more of argon, hydrogen, nitrogen, or helium; and the center temperature of the plasma torch is 5000-15000K.

4. The method for preparing spherical silicon-carbon composite materials by thermal plasma according to claim 1, characterized in that, In step S3, the quenching medium is an inert gas or a hydrocarbon gas that is reactive with the carbon source; when the quenching medium is an inert gas, the spherical silicon-carbon composite material is a silicon / carbon composite sphere; when the quenching medium is a hydrocarbon such as methane or acetylene, it undergoes cracking during the quenching process, forming a carbon coating layer on the surface of the sphere.

5. The method for preparing spherical silicon-carbon composite materials by thermal plasma according to claim 4, characterized in that, The quenching process controls the sphericity and shell thickness of the final product by adjusting the flow rate, temperature and composition of the quenching gas; wherein the flow rate of the quenching gas is 10~100m / s, the temperature is 25℃~800℃, and the composition is one or more of argon, nitrogen, methane, ethane, propane, acetylene and other hydrocarbons.

6. The spherical silicon-carbon composite material prepared by the method according to any one of claims 1-5, characterized in that, The material consists of regular spherical particles with a particle size distribution of 50 nm - 2 μm, and has an "island-type" composite structure with highly graphitized carbon as a continuous matrix and nano-silicon islands uniformly dispersed within it.

7. The spherical silicon-carbon composite material according to claim 6, characterized in that, The nano-silicon islands are smaller than 50 nm in size and are effectively separated by a carbon matrix; the carbon matrix has a high degree of graphitization crystallinity.

8. The spherical silicon-carbon composite material according to claim 6 or 7, characterized in that, The spherical particles are coated with an amorphous or graphitized carbon shell 2-20 nm thick, formed by the decomposition of carbon source gas in a quenching atmosphere.

9. A lithium-ion battery negative electrode, characterized in that, It includes the spherical silicon-carbon composite material according to any one of claims 6-8.

10. A lithium-ion battery, characterized in that, It includes the lithium-ion battery negative electrode as described in claim 9.

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