Graphene supported nanosilicon material, preparation method and application thereof

Abstract

The application discloses a kind of graphene load nano silicon material and its preparation method and application, including the following steps: to cathode plasma torch continuous supply graphite powder, produce the first jet stream containing graphene sheet, simultaneously, to anode plasma torch continuous supply nano silicon powder, produce the second jet stream containing vaporized silicon powder;First jet stream and second jet stream converge together, then in order after quenching, fractional collection, graphene load nano silicon powder is obtained;Wherein, the gathering place is continuously passed into working medium gas, temperature control is at 1500-2000K.In high temperature atmosphere graphene and nano silicon rapidly compound, by gas quenching, fractional collection and obtain graphene load nano silicon powder body.The application realizes the continuous preparation of graphene load nano silicon powder body by plasma process, and the graphene load nano silicon powder body prepared has the characteristics such as high specific surface area, high purity and excellent conductivity, and can be used as silicon-carbon negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of carbon material preparation technology, and in particular to a graphene-supported nano-silicon material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as an important energy storage device with high energy density and long cycle life, have seen rapid development in recent years. Silicon, with its advantages of high theoretical specific capacity (4200 mAh / g), low lithium extraction / insertion potential, and abundant raw material reserves, is expected to become a new type of anode material for lithium-ion batteries.

[0003] Recent studies have found that graphene-supported silicon nanomaterials exhibit superior performance, mainly due to graphene's higher conductivity, large specific surface area, and interfacial benefits between graphene and silicon particles. Therefore, graphene-supported silicon nanomaterials are expected to become high-performance composite anode materials for lithium-ion batteries (Research progress on Si@G composite materials for lithium-ion battery anodes, New Chemical Materials, 2023, 51: 23-26).

[0004] Plasma is the fourth state of matter, distinct from solid, liquid, and gas, and is characterized by high temperature, high enthalpy, and high chemical reactivity. Currently, reports on the preparation of graphene-coated silicon nanoparticles using plasma are frequent, such as the preparation of graphene from hydrocarbon raw materials via plasma pyrolysis and the preparation of nano-silicon from crude silicon powder via plasma evaporation, demonstrating good technical feasibility. For example, Watanabe et al. reported a method for preparing carbon-coated silicon nanoparticles using radio frequency plasma. This process utilizes high-temperature radio frequency plasma to evaporate silicon powder to prepare nano-silicon powder, while simultaneously using ethylene to rapidly cool the silicon powder. The ethylene pyrolysis forms solid carbon, which coats the silicon powder to form carbon-coated silicon nanoparticles (Synthesis of carbon-coated silicon nanoparticles by induction thermal plasma for lithium ion battery, Powder Technology, 2020, 371: 26-36). To avoid silicon carbide formation, this method requires a very high quenching rate for ethylene, resulting in a predominantly amorphous carbon structure that cannot form graphene. Furthermore, this quenching process involves the pyrolysis of ethylene, leading to poor temperature control and often resulting in the presence of significant amounts of silicon carbide in the product, affecting its purity. Yang et al. reported a process for preparing two-dimensional sheet-like graphene-supported silicon nanospheres using silicon nanospheres as the silicon source and ethanol as the carbon source via radio frequency thermal plasma (In-situ synthesis of graphenenanosheets encapsulated silicon nanospheres by thermal plasma for ultra-stable lithium storage, Carbon, 2022, 199: 424-430). However, the reaction between the silicon nanospheres and ethanol at high temperatures results in numerous Si-C, Si-O, and CO bonds in the product, affecting its purity. Moreover, both of these methods are performed using radio frequency plasma, whose relatively low efficiency and difficulty in scale-up further complicate the industrialization of these approaches. Summary of the Invention

[0005] The purpose of this invention is to provide a graphene-supported nano-silicon material, its preparation method and application, to achieve continuous preparation of graphene-supported nano-silicon powder, with simple process, low cost and easy to scale up.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention discloses a method for continuously preparing graphene-supported silicon nanomaterials, comprising the following steps:

[0008] Graphite powder is continuously supplied to the cathode plasma torch to generate a first jet containing graphene sheets, while nano-silicon powder is continuously supplied to the anode plasma torch to generate a second jet containing vaporized silicon powder.

[0009] The first and second jets are converged, and then subjected to rapid cooling and staged collection to obtain graphene-supported silicon nanoparticles. A working gas is continuously introduced at the convergence point, and the temperature is controlled between 1500-2000 K. If the temperature exceeds 2000 K, the graphene and silicon nanoparticles will react to form silicon carbide; if the temperature is below 1500 K, the graphene and silicon nanoparticles cannot effectively and stably combine.

[0010] A further proposed solution: The dual-jet transferred arc plasma torch (cathode plasma torch and anode plasma torch) is a DC transferred arc plasma torch. Compared to a non-transferred arc plasma torch, the transferred arc plasma has higher electrothermal conversion efficiency and higher plasma temperature, promoting the exfoliation of graphite to form graphene and the evaporation of silicon to form silicon nanoparticles. The parameters of the cathode and anode plasma torches are as follows: discharge current of 50-1000A, average plasma temperature not lower than 4000K to ensure effective graphite exfoliation and effective silicon powder vaporization; the plasma working gas is at least one of argon and hydrogen. Argon is an inexpensive inert gas that can avoid side reactions with graphite and silicon, and it is also the plasma working gas that is easiest to maintain a stable discharge; hydrogen has reducing properties and can remove trace amounts of oxygen from graphite and silicon raw materials, thereby improving the purity of the product.

[0011] A further embodiment: The graphite powder has a particle size of 1-10 micrometers, and the silicon powder has a particle size of 20-80 micrometers. The graphite powder and silicon powder are continuously fed into the plasma torch discharge area using a powder feeding device. 1-10 micrometer graphite powder is an ideal raw material for exfoliation to form graphene, while 20-80 micrometer silicon powder facilitates silicon powder transport and evaporation / condensation to form nano-silicon powder.

[0012] A further embodiment: the mass flow rate ratio of graphite powder to silicon powder is 2-10. By adjusting the flow rate ratio of graphite powder to silicon powder, the relative content of graphene and nano-silicon can be controlled. To ensure that the prepared graphene-supported nano-silicon material has the structural characteristics of sheet graphene and to reduce excessive aggregation of nano-silicon, the mass flow rate of silicon powder should not be too high; to ensure that the composite material has the characteristics of nano-silicon material, the silicon loading should not be too low, therefore the silicon flow rate should not be too low. Preferably, the mass flow rate ratio of graphite powder to silicon powder is 3:1.

[0013] A further option: the target temperature for the rapid cooling is 80-100℃.

[0014] Secondly, this invention discloses a graphene-supported silicon nanomaterial prepared by the above method. This material has a layered structure consisting of graphene-supported silicon nanoparticles, wherein the number of graphene layers is no more than 10, and the particle size of the silicon nanoparticles is no greater than 20 nanometers. This graphene-supported silicon nanoparticle powder material has the characteristics of high specific surface area, high purity, and excellent conductivity, and can be used as a negative electrode material for lithium batteries.

[0015] A further proposed solution: its specific surface area should be no less than 200 m². 2 / g.

[0016] Thirdly, the present invention discloses an apparatus for the continuous preparation of graphene-supported silicon nanomaterials using the above method, comprising:

[0017] The reaction chamber has a first interface and a second interface at an angle to each other at its upper part. The first interface houses a cathode plasma torch, and the second interface houses an anode plasma torch. The cathode plasma torch includes a cathode carrier gas inlet. The first interface has a first raw material inlet. The anode plasma torch includes an anode carrier gas inlet. The second interface has a second raw material inlet.

[0018] The bottom of the reaction chamber is provided with a discharge port, which is connected to a graded collection mechanism;

[0019] The reaction chamber located above the discharge port is equipped with a cooling gas inlet;

[0020] The upper part of the reaction chamber is also provided with an air inlet pointing to the intersection of the extension lines of the first interface and the second interface.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention uses plasma technology to achieve continuous preparation of graphene-supported nano-silicon powder, which is simple, low-cost, and easy to scale up.

[0023] 2. This invention uses a dual-jet plasma torch to prepare graphene and nano-silicon separately, and then combines them at a suitable temperature. This process can control the relative content of graphene and nano-silicon, and proper temperature adjustment can reduce the formation of silicon carbide.

[0024] 3. The graphene-supported nano-silicon powder prepared by this invention has the characteristics of both graphene and nano-silicon, and has the advantages of high specific surface area, high purity and excellent conductivity, and has application potential in the field of lithium battery anode materials. Attached Figure Description

[0025] Figure 1 This is an illustration of the graphene-supported nano-silicon material device of the present invention;

[0026] Figure 2Electron micrograph of the graphene-supported silicon nanomaterial prepared in Example 1;

[0027] Figure 3 Here is a high-magnification electron microscope image of the graphene-supported silicon nanomaterial prepared in Example 1;

[0028] Figure 4 This is an electron microscope image of the graphene-supported silicon nanomaterial prepared in Example 2;

[0029] Figure 5 Electron micrograph of the graphene-supported silicon nanomaterial prepared in Example 3;

[0030] Figure 6 Electron micrograph of the product prepared in Comparative Example 1;

[0031] Figure 7 Electron micrograph of the product prepared in Comparative Example 2;

[0032] Figure 8 Electron micrograph of the product prepared in Comparative Example 3;

[0033] Figure 1 In the middle: 1-Cathode plasma torch, 11-Cathode carrier gas inlet, 2-Anode plasma torch, 21-Anode carrier gas inlet, 3-Dual jet plasma, 4-Reaction chamber inlet, 5-Reaction chamber, 6-Cooling gas inlet, 7-Grading collection mechanism, 8-First interface, 81-First raw material inlet, 9-Second interface, 91-Second raw material inlet. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0036] Please see Figure 1The following embodiments are prepared in the apparatus shown in the figure. This apparatus includes a reaction chamber 5, with a first interface 8 and a second interface 9 at an angle to each other on the upper part of the reaction chamber 5. The first interface houses a cathode plasma torch 1, and the second interface 9 houses an anode plasma torch 2. The cathode plasma torch 1 includes a cathode carrier gas inlet 11. The first interface 8 has a first raw material inlet 81; the anode plasma torch 2 includes an anode carrier gas inlet 21; the second interface 9 has a second raw material inlet 91. A discharge port is located at the bottom of the reaction chamber 5, connected to a graded collection mechanism 7. A cooling gas interface 6 is located above the discharge port. An air inlet 4 is also located on the upper part of the reaction chamber 5, pointing to the intersection of the extended lines of the first interface 8 and the second interface 9. In this apparatus, the cathode carrier gas inlet 11 and the anode carrier gas inlet 21 simultaneously carry plasma working gas. Graphite powder is introduced through the first raw material inlet 81, and silicon powder is introduced through the second raw material inlet 91, both entering the dual-jet plasma region 3 and converging at the center. Inlet 4 introduces working gas to control the temperature of the dual-jet plasma region 3 within the target range, thus regulating the composite process of graphene and nano-silicon. In the cathode plasma torch 1, graphite powder is exfoliated by high-temperature plasma to form graphene sheets; in the anode plasma torch 2, silicon powder is evaporated and condensed by high-temperature plasma to form nano-silicon powder. The graphene sheets and nano-silicon powder are rapidly composited in the dual-jet plasma region 3. Cooling gas is injected through cooling gas inlet 6 to terminate the composite reaction and cool the reaction tail gas containing powder products to below 100°C. The reaction tail gas containing powder products is separated by the classification and collection mechanism 7 to remove unreacted graphite and silicon powder, ultimately yielding a graphene-supported nano-silicon powder product.

[0037] The preparation process for the following embodiments is as follows:

[0038] Graphite powder is continuously supplied to the cathode plasma torch to generate a first jet containing graphene sheets, while nano-silicon powder is continuously supplied to the anode plasma torch to generate a second jet containing vaporized silicon powder.

[0039] The first and second jets are converged, and then subjected to rapid cooling and staged collection to obtain graphene-supported silicon nanoparticles. A working gas is continuously introduced at the convergence point, and the cathode and anode plasma torches are continuously supplied with plasma working gas. Specific parameter settings are detailed in the embodiments.

[0040] Example 1

[0041] The dual-jet plasma torches used in this embodiment (including cathode plasma torch 1 and anode plasma torch 2) have the same parameters: discharge current 200A, total power 100kW, plasma working gas is a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 5:1, and the gas flow rate of each torch is 35Nm³. 3 The cathode plasma torch introduces graphite powder with an average particle size of approximately 5 micrometers at a flow rate of 100 g / h; the anode plasma torch introduces silicon powder with an average particle size of 50 micrometers at a flow rate of 20 g / h; a mixture of argon and hydrogen is introduced through the reaction chamber inlet 4 to lower the temperature at the intersection of the two plasma jets, with an argon to hydrogen volume ratio of 5:1, controlling the temperature at the intersection of the two jets to approximately 1800 K; argon is introduced through the cooling gas inlet 6 at the bottom of the reaction chamber to cool the reaction tail gas to approximately 80 °C. The cooled reaction products are collected in stages to finally obtain a black powder product, namely graphene-supported nano-silicon powder.

[0042] Figure 2 The transmission electron microscope image of the black powder product prepared in this embodiment shows that there are obvious graphene sheets and a large number of nano-silicon particles distributed on the graphene sheets. Figure 3 High-magnification transmission electron microscopy (TEM) images are provided, revealing that the silicon nanoparticles are tightly adhered to or embedded in the graphene sheet surface, confirming that graphene and silicon nanoparticles in this embodiment can be tightly bonded to form a stable composite powder. In this embodiment, the silicon nanoparticles have a particle size of approximately 2-10 nm, and the graphene layer number is approximately two. Table 1 lists the performance of the product prepared in Example 1. It can be seen that the graphene-supported silicon nanoparticle powder in this embodiment contains 65% graphene, 29% silicon, and approximately 3% silicon carbide. Due to the sheet structure of graphene, its specific surface area is as high as 360 m². 2 / g.

[0043] Example 2

[0044] The dual-jet plasma torches used in this embodiment (including cathode plasma torch 1 and anode plasma torch 2) have the same parameters: discharge current 300A, total power 140kW, plasma working gas is a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 10:1, and the gas flow rate of each torch is 45Nm³. 3 The anode plasma torch introduces graphite powder with an average particle size of approximately 3 micrometers at a flow rate of 100 g / h; the cathode plasma torch introduces silicon powder with an average particle size of 40 micrometers at a flow rate of 35 g / h; argon gas is introduced through inlet 4 of the reaction chamber to lower the temperature at the intersection of the two plasma jets, controlling the temperature at the intersection to approximately 1700 K; argon gas is introduced through the cooling gas inlet at the bottom of the reaction chamber to cool the reaction tail gas to approximately 90 °C. The cooled reaction products are collected in stages to ultimately obtain a black powder product.

[0045] Figure 4 Transmission electron microscopy (TEM) images of the black powder product prepared in this example reveal the presence of distinct graphene sheets and silicon nanoparticles, confirming the formation of graphene-supported silicon nanoparticles. Compared to Example 1, the silicon powder flow rate is increased in this example, resulting in a greater number of silicon nanoparticles in the product. Table 1 lists the performance of the product prepared in Example 2, showing that the silicon content in this example is 43%, higher than that in Example 1.

[0046] Example 3

[0047] The dual-jet plasma torches used in this embodiment (including cathode plasma torch 1 and anode plasma torch 2) have the same parameters: discharge current 500A, total power 140kW, plasma working gas is argon, and gas flow rate of 90Nm³ / g for each torch. 3 The anode plasma torch introduces graphite powder with an average particle size of approximately 8 micrometers at a flow rate of 150 g / h; the cathode plasma torch introduces silicon powder with an average particle size of 40 micrometers at a flow rate of 30 g / h; a mixture of argon and hydrogen is introduced into the reaction chamber inlet 4 to lower the temperature at the intersection of the two plasma jets, controlling the temperature at the intersection to approximately 1800 K; argon is introduced into the cooling gas inlet at the bottom of the reactor to cool the reaction tail gas to approximately 90 °C. The cooled reaction products are collected in stages to ultimately obtain a black powder product.

[0048] Figure 5 Transmission electron microscopy (TEM) images of the black powder product prepared in this example reveal the presence of distinct graphene sheets and silicon nanoparticles, confirming the formation of graphene-supported silicon nanomaterials. Table 1 lists the properties of the product prepared in Example 3, showing that the graphene content in this example is 64%, the silicon content is 28%, the silicon carbide content is approximately 3%, and the specific surface area is 350 m². 2 / g.

[0049] Comparative Example 1

[0050] The only difference between Comparative Example 1 and Example 1 is that the temperature at the intersection of the two jets is about 1000K. Figure 6 Transmission electron microscopy (TEM) images of the black powder product prepared for this comparative example reveal the presence of distinct graphene sheets, but the silicon nanoparticles are not prominent. This is because the temperature at the junction of the two jets is low, making it difficult for the graphene and silicon nanoparticles to bond effectively. They separate during rapid cooling and collection, hindering the formation of graphene-loaded silicon nanoparticles. Table 1 lists the properties of the product prepared in Comparative Example 1. It shows that the graphene content in this comparative example is 67%, and the silicon content is 31%. Although the product composition is similar to that of Example 1, a stable graphene / silicon nanoparticle composite structure has not been formed.

[0051] Comparative Example 2

[0052] The only difference between Comparative Example 2 and Example 1 is that the temperature at the intersection of the two jets is about 2400K. Figure 7 Transmission electron microscopy (TEM) images of the black powder product prepared for this comparative example reveal the presence of distinct graphene sheets, as well as large, agglomerated particles. XPS characterization confirmed that these particles are primarily silicon carbide particles. This is because the high temperature at the junction of the two jets causes a strong chemical reaction between the graphene and the silicon nanoparticles, forming silicon carbide particles, which affects the product composition and makes it difficult to effectively form graphene-supported silicon nanoparticles in the final product. Table 1 lists the properties of the product prepared in Comparative Example 2, showing that the silicon carbide content in this comparative example is as high as 26%.

[0053] Comparative Example 3

[0054] The only difference between Comparative Example 3 and Example 1 is that graphite powder and silicon powder are fed together. That is, after the graphite powder and silicon powder raw materials are mixed evenly, they are fed into the first raw material inlet 81 and the second raw material inlet 91 through two channels. The flow rate of the first raw material inlet 81 is 100g / hour, and the flow rate of the second raw material inlet 91 is 20g / hour. Figure 8 Transmission electron microscopy (TEM) images of the black powder product prepared for this comparative example reveal the presence of distinct graphene sheets, as well as large, agglomerated particles. XPS characterization confirmed that these particles are primarily silicon carbide particles. This is because the high-temperature environment (greater than 4000 K) within the plasma torch after the graphite / graphene mixture enters the plasma, causing a strong chemical reaction between the graphite / graphene and silicon particles to form silicon carbide particles. This affects the composition of the product, making it difficult to effectively form graphene-supported silicon nanomaterials in the final product. Table 1 lists the performance of the product prepared in Comparative Example 3. The specific surface area was measured using nitrogen adsorption, and the mass fraction was measured using thermogravimetric analysis. It can be seen that the silicon carbide content in this comparative example is as high as 45%.

[0055] Table 1: Performance List of Products Prepared in Each Example and Comparative Example

[0056]

[0057] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0058] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for continuously preparing graphene-supported silicon nanomaterials, characterized in that, Includes the following steps: Graphite powder is continuously supplied to the cathode plasma torch to generate a first jet containing graphene sheets, while nano-silicon powder is continuously supplied to the anode plasma torch to generate a second jet containing vaporized silicon powder. The first jet and the second jet are converged together, and then subjected to rapid cooling and graded collection in sequence to obtain graphene-supported nano-silicon powder; wherein, a working gas is continuously introduced at the convergence point and the temperature is controlled at 1500-2000K.

2. The method for continuous preparation of graphene-supported silicon nanomaterials according to claim 1, characterized in that, The parameters of the cathode plasma torch and the anode plasma torch are as follows: the discharge current is 50-1000A, the average plasma temperature is not lower than 4000K, and the plasma working gas is at least one of argon and hydrogen.

3. The method for continuous preparation of graphene-supported silicon nanomaterials according to claim 1, characterized in that, The graphite powder has a particle size of 1-10 micrometers, and the silicon powder has a particle size of 20-80 micrometers.

4. The method for continuous preparation of graphene-supported silicon nanomaterials according to claim 1, characterized in that, The mass flow ratio of the graphite powder to the silicon powder is 2-10.

5. The method for continuous preparation of graphene-supported silicon nanomaterials according to claim 1, characterized in that, The target temperature for rapid cooling is 80-100℃.

6. The graphene-supported silicon nanomaterial prepared by the method according to any one of claims 1-5, characterized in that, It has a sheet structure consisting of graphene-supported silicon nanoparticles, wherein the number of graphene layers is no more than 10 and the particle size of the silicon nanoparticles is no greater than 20 nanometers.

7. The graphene-supported silicon nanomaterial according to claim 6, characterized in that, Its specific surface area is not less than 200m² 2 / g.

8. The application of the graphene-supported nano-silicon material according to claim 6 or 7 as a silicon-carbon anode material.

9. The apparatus for continuous preparation of graphene-supported silicon nanomaterials as described in any one of claims 1-5, characterized in that, include: The reaction chamber has a first interface and a second interface at an angle to each other at its upper part. The first interface houses a cathode plasma torch, and the second interface houses an anode plasma torch. The cathode plasma torch includes a cathode carrier gas inlet. The first interface has a first raw material inlet. The anode plasma torch includes an anode carrier gas inlet. The second interface has a second raw material inlet. The bottom of the reaction chamber is provided with a discharge port, which is connected to a graded collection mechanism; The reaction chamber located above the discharge port is equipped with a cooling gas inlet; The upper part of the reaction chamber is also provided with an air inlet pointing to the intersection of the extension lines of the first interface and the second interface.

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