Graphene-loaded nano silicon material and preparation method and application thereof

Abstract

The invention discloses a graphene-loaded nano silicon material and a preparation method and application thereof, and the preparation method comprises the following steps: continuously supplying graphite powder to a cathode plasma torch to generate a first jet flow containing graphene sheets, and continuously supplying nano silicon powder to an anode plasma torch to generate a second jet flow containing gasified silicon powder; and converging the first jet flow and the second jet flow together, and sequentially carrying out quenching and graded collection to obtain the graphene-loaded nano silicon powder. Wherein the working medium gas is continuously introduced into the convergence part, and the temperature is controlled to be 1500-2000K. Graphene and nano silicon are rapidly compounded in a high-temperature atmosphere, and graphene-loaded nano silicon powder is obtained through gas quenching and graded collection. The continuous preparation of the graphene-loaded nano silicon powder is realized through a plasma process, and the prepared graphene-loaded nano silicon powder has the characteristics of high specific surface area, high purity, excellent conductivity and the like, and can be used as a silicon-carbon negative electrode material.

Description

Technical Field

[0001] The invention relates to the technical field of carbon material preparation, in particular to a graphene-loaded nano-silicon material and a preparation method and application thereof. Background Art

[0002] As an important energy storage device with high energy density and long cycle life, lithium battery has developed rapidly in recent years. Silicon has the advantages of high theoretical specific capacity (4200mAh / g), low lithium extraction / insertion potential, and abundant raw material reserves, and is expected to become the negative electrode material of new lithium-ion batteries.

[0003] Recent studies have found that graphene-loaded nanosilicon materials exhibit better performance, which is mainly due to the higher conductivity of graphene, the large specific surface area and the interface effect between graphene and silicon particles. Therefore, graphene-loaded nanosilicon materials are expected to become excellent lithium-ion battery composite negative electrode materials (Research Progress of Si@G Composite Materials for Lithium-ion Battery Negative Electrodes, New Chemical Materials, 2023, 51: 23-26).

[0004] Plasma is the fourth state, different from solid, liquid and gas, and has the characteristics of high temperature, high enthalpy and high chemical activity. At present, reports on the preparation of graphene nano-silicon materials by plasma are common, such as plasma pyrolysis of hydrocarbon raw materials to prepare graphene, plasma evaporation of crude silicon powder to prepare nano-silicon, etc., which have good technical feasibility. For example, Watanabe et al. reported a method for preparing carbon-coated nano-silicon powder using radio frequency plasma. The process uses high-temperature radio frequency plasma to evaporate silicon powder to prepare nano-silicon powder, and at the same time uses ethylene to quench the silicon powder. The ethylene pyrolysis forms solid carbon, and the coated silicon powder forms carbon-coated nano-silicon powder (Synthesis of carbon-coated silicon nanoparticles by inductionthermal plasma for lithium ion battery, Powder Technology, 2020, 371: 26-36). In order to avoid the formation of silicon carbide, this method has very high requirements for the quenching rate of ethylene, resulting in a carbon structure dominated by amorphous carbon, and the graphene structure cannot be formed. In addition, the quenching process involves the pyrolysis reaction of ethylene, and the temperature controllability is poor. There is often a lot of silicon carbide in the product, which affects the purity of the product. Yang et al. reported a process for preparing two-dimensional graphene-loaded nanosilicon materials using silicon nanospheres as silicon source and ethanol as carbon source using a radio frequency thermal plasma system (In-situ synthesis of graphene nanosheets encapsulated silicon nanospheres by thermal plasma for ultra-stable lithium storage, Carbon, 2022, 199: 424-430). Since nanosilicon and ethanol react at high temperature, there are many Si-C bonds, Si-O bonds and CO bonds in the product, which affects the purity of the product. In addition, the above schemes are all carried out in radio frequency plasma. The relatively low efficiency of radio frequency plasma and the disadvantages of difficulty in amplification also increase the difficulty of industrialization of the above schemes. Summary of the invention

[0005] The purpose of the present invention is to provide a graphene-loaded nano-silicon material and a preparation method and application thereof, so as to realize the continuous preparation of graphene-loaded nano-silicon powder, with simple process, low cost and easy to realize large-scale expansion.

[0006] To achieve the above object, the present invention provides the following technical solutions:

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

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

[0009] The first jet and the second jet are converged together, and then quenched and graded to obtain graphene-loaded nano-silicon powder; wherein the working fluid gas is continuously introduced into the convergence point, and the temperature is controlled at 1500-2000 K. If the temperature exceeds 2000 K, the graphene and nano-silicon react to form silicon carbide; if the temperature is lower than 1500 K, the graphene and nano-silicon cannot be effectively and stably combined.

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

[0011] Further solution: the graphite powder has a particle size of 1-10 microns, and the silicon powder has a particle size of 20-80 microns. The graphite powder and silicon powder are continuously fed into the plasma torch discharge area through a powder feeding device. Graphite powder of 1-10 microns is an ideal raw material for exfoliation to form graphene, while silicon powder of 20-80 microns is convenient for silicon powder transportation and evaporation and condensation to form nano silicon powder.

[0012] Further solution: The mass flow ratio of the graphite powder and silicon powder is 2-10. By adjusting the flow ratio of graphite powder and silicon powder, the relative content of graphene and nano-silicon can be regulated. In order to ensure that the prepared graphene-loaded nano-silicon material has the structural characteristics of flaky graphene and reduce the excessive aggregation of nano-silicon, the mass flow rate of silicon powder should not be too large; in order to ensure that the composite material has the characteristics of nano-silicon material, the loading amount of silicon cannot be too small, so the flow rate of silicon cannot be too low. Preferably, the mass flow ratio of graphite powder and silicon powder is 3:1.

[0013] A further solution: the target temperature of the rapid cooling is 80-100°C.

[0014] In a second aspect, the present invention discloses a graphene-loaded nano-silicon material prepared by the above method, wherein the material has a sheet structure of graphene-loaded nano-silicon particles, wherein the number of graphene layers is not more than 10 layers, and the particle size of the nano-silicon is not more than 20 nanometers. The graphene-loaded nano-silicon 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] Further solution: Its specific surface area is not less than 200m 2 / g.

[0016] In a third aspect, the present invention discloses a device for continuously preparing graphene-loaded nano-silicon materials used in the above method, comprising:

[0017] A reaction chamber, wherein a first interface and a second interface are provided at an angle to each other at the upper portion of the reaction chamber, wherein a cathode plasma torch is accommodated in the first interface, and an anode plasma torch is accommodated in the second interface; the cathode plasma torch comprises a cathode carrier gas inlet; the first interface is provided with a first raw material inlet; the anode plasma torch comprises an anode carrier gas inlet; and the second interface is provided with a second raw material inlet;

[0018] A discharge port is provided at the bottom of the reaction chamber, and the discharge port is connected to a grading collection mechanism;

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

[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 present invention has the following beneficial effects:

[0022] 1. The present invention adopts plasma technology to realize continuous preparation of graphene-loaded nano-silicon powder, which has simple process, low cost and is easy to achieve large-scale expansion;

[0023] 2. The present invention adopts a dual-jet plasma torch, prepares graphene and nano-silicon separately, and then undergoes a process flow of combining at a suitable temperature, so as to achieve the control of the relative content of graphene and nano-silicon. Reasonable temperature adjustment can reduce the formation of silicon carbide;

[0024] 3. The graphene-loaded nano-silicon powder prepared by the present 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 negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The invention provides a graphene-loaded nano-silicon material device;

[0026] Figure 2This is an electron microscope image of the graphene-loaded nano-silicon material prepared in Example 1;

[0027] Figure 3 This is a high-magnification electron microscope image of the graphene-loaded nano-silicon material prepared in Example 1;

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

[0029] Figure 5 This is an electron microscope image of the graphene-loaded nano-silicon material prepared in Example 3;

[0030] Figure 6 This is an electron microscope image of the product prepared in Comparative Example 1;

[0031] Figure 7 This is an electron microscope image of the product prepared in Comparative Example 2;

[0032] Figure 8 This is an electron microscope image 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- double jet plasma, 4- reaction chamber air inlet, 5- reaction chamber, 6- cooling gas inlet, 7- classification collection mechanism, 8- first interface, 81- first raw material inlet, 9- second interface, 91- second raw material inlet,. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inside", "outside", etc. are based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0036] See also Figure 1, the following embodiments are prepared in the device shown in the figure. The device includes a reaction chamber 5, the upper part of which is provided with a first interface 8 and a second interface 9 at an angle to each other, the first interface contains a cathode plasma torch 1, and the second interface 9 contains an anode plasma torch 2; the cathode plasma torch 1 includes a cathode carrier gas inlet 11; the first interface 8 is provided with a first raw material inlet 81; the anode plasma torch 2 includes an anode carrier gas inlet 21; the second interface 9 is provided with a second raw material inlet 91; a discharge port is provided at the bottom of the reaction chamber 5, and the discharge port is connected to a grading collection mechanism 7; the reaction chamber located above the discharge port is provided with a cooling gas interface 6; the upper part of the reaction chamber 5 is also provided with an air inlet 4 pointing to the intersection of the extension lines of the first interface 8 and the second interface 9. In the device, the cathode carrier gas inlet 11 and the anode carrier gas inlet 21 are simultaneously loaded with plasma working gas, the graphite powder raw material is introduced from the first raw material inlet 81, and the silicon powder raw material is introduced from the second raw material inlet 91, and they enter the double-jet plasma area 3 together and meet at the center. The working gas is introduced into the air inlet 4 to control the temperature of the dual-jet plasma area 3 within the target range, thereby regulating the composite process of graphene and nano-silicon. In the cathode plasma torch 1, graphite powder is peeled off 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, and the graphene sheets and nano-silicon powder are rapidly composited in the dual-jet plasma area 3. The cooling gas inlet 6 sprays cooling gas to terminate the above-mentioned composite reaction, and cools the above-mentioned reaction tail gas containing the powder product to below 100°C; the reaction tail gas containing the powder product is separated by the classification collection mechanism 7 to remove the graphite powder and silicon powder that have not reacted, and finally obtain a graphene-loaded nano-silicon powder product.

[0037] The preparation process of the following examples is as follows:

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

[0039] The first jet and the second jet are converged together, and then rapidly cooled and graded and collected in sequence to obtain graphene-loaded nano-silicon powder; wherein the convergence point is continuously fed with working fluid gas, and the cathode plasma torch and the anode plasma torch are continuously fed with plasma working fluid gas. Specific parameter settings are described in the embodiments.

[0040] Example 1

[0041] The parameters of the dual-jet plasma torches (including the cathode plasma torch 1 and the anode plasma torch 2) used in this embodiment are the same: 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 35Nm 3 / h; graphite powder with an average particle size of about 5 microns and a flow rate of 100g / hour is introduced into the cathode plasma torch; silicon powder with an average particle size of 50 microns and a flow rate of 20g / hour is introduced into the anode plasma torch; a mixture of argon and hydrogen is introduced into the reaction chamber air inlet 4 to reduce the temperature at the intersection of the double jet plasma, the volume ratio of argon and hydrogen is 5:1, and the temperature at the intersection of the double jets is controlled to be about 1800K; argon is introduced into the cooling gas inlet 6 at the bottom of the reaction chamber to cool the reaction tail gas to about 80°C. The reaction products after cooling are collected by classification to finally obtain a black powder product, i.e., graphene-loaded nano-silicon powder.

[0042] Figure 2 This is a transmission electron microscope image of the black powder product prepared in this example. It can be seen that there are obvious graphene sheets and a large number of nano-silicon particles distributed on the graphene sheets in the product. Figure 3 The corresponding high-magnification transmission electron microscope image is given, and it can be found that the nano-silicon particles are tightly attached to or embedded in the surface of the graphene sheet, confirming that the graphene and silicon nano-particles in this embodiment can be tightly combined to form a stable composite powder. Among them, the particle size of the nano-silicon particles in this embodiment is about 2-10nm, and the number of graphene layers is about 2. Table 1 shows the performance list of the product prepared in Example 1. It can be found that the graphene content in the graphene-loaded nano-silicon powder in this embodiment is 65%, the silicon content is 29%, and the silicon carbide content is about 3%. Due to the lamellar structure of graphene, its specific surface area is as high as 360m 2 / g.

[0043] Example 2

[0044] The parameters of the dual-jet plasma torches (including the cathode plasma torch 1 and the anode plasma torch 2) used in this embodiment are the same, namely: 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 45Nm 3 / h; graphite powder with an average particle size of about 3 microns and a flow rate of 100g / hour is introduced into the anode plasma torch; silicon powder with an average particle size of 40 microns and a flow rate of 35g / hour is introduced into the cathode plasma torch; argon gas is introduced into the reaction chamber air inlet 4 to reduce the temperature at the intersection of the double jet plasma, and the temperature at the intersection of the double jets is controlled to be about 1700K; argon gas is introduced into the cooling gas inlet at the bottom of the reaction chamber to cool the reaction tail gas to about 90°C. The cooled reaction products are collected by classification to finally obtain black powder products.

[0045] Figure 4 The transmission electron microscope image of the black powder product prepared in this embodiment shows that there are obvious graphene sheets and silicon nanoparticles in the product, confirming the formation of graphene-loaded nano-silicon material. Compared with Example 1, the flow rate ratio of silicon powder in this embodiment is increased, so there are more nano-silicon particles in the product. Table 1 shows the performance list of the product prepared in Example 2, and it can be found that the silicon content in this embodiment is 43%, which is higher than that in Example 1.

[0046] Example 3

[0047] The parameters of the dual-jet plasma torches (including the cathode plasma torch 1 and the anode plasma torch 2) used in this embodiment are the same, namely: discharge current 500A, total power 140kW, plasma working gas argon, and gas flow rate of each torch 90Nm 3 / h; graphite powder with an average particle size of about 8 microns and a flow rate of 150g / hour is introduced into the anode plasma torch; silicon powder with an average particle size of 40 microns and a flow rate of 30g / hour is introduced into the cathode plasma torch; a mixture of argon and hydrogen is introduced into the reaction chamber air inlet 4 to reduce the temperature at the intersection of the double jet plasma, and the temperature at the intersection of the double jets is controlled to be about 1800K; argon is introduced into the cooling gas inlet at the bottom of the reactor to cool the reaction tail gas to about 90°C. The cooled reaction product is collected by classification to finally obtain a black powder product.

[0048] Figure 5 The transmission electron microscope image of the black powder product prepared in this embodiment shows that there are obvious graphene sheets and silicon nanoparticles in the product, confirming the formation of graphene-loaded nano-silicon materials. Table 1 lists the properties of the product prepared in Example 3. It can be found that the content of graphene in this embodiment is 64%, the content of silicon is 28%, the content of silicon carbide is about 3%, and the specific surface area is 350m 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 The transmission electron microscope image of the black powder product prepared in this comparative example shows that there are obvious graphene sheets in the product, but the nano silicon particles are not obvious. This is because the temperature at the intersection of the two jets is low, and it is difficult for graphene and nano silicon particles to effectively combine. They separate from each other during the quenching and collection process, making it difficult to effectively form graphene-loaded nano silicon materials. Table 1 shows the performance list of the product prepared in comparative example 1. It can be found that the graphene content in this comparative example is 67% and the silicon content is 31%. Although the product composition is close to that of Example 1, a stable graphene / nano silicon composite structure is not 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 The transmission electron microscope image of the black powder product prepared in this comparative example shows that there are obvious graphene sheets in the product, and there are also large-sized, agglomerated particles. Characterizations such as XPS confirm that these particles are mainly silicon carbide particles. This is because the temperature at the intersection of the two jets is high, and graphene and nano-silicon particles undergo a strong chemical reaction to form silicon carbide particles, which affects the composition of the product and makes it difficult for the final product to effectively form graphene-loaded nano-silicon materials. Table 1 gives a list of the properties of the product prepared in comparative example 2, and it can be found 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 mixed and fed, that is, after the graphite powder and silicon powder raw materials are evenly mixed, they are introduced into the raw materials from the first raw material inlet 81 and the second raw material inlet 91 in two ways, the flow rate of the first raw material inlet 81 is 100 g / hour, and the flow rate of the second raw material inlet 91 is 20 g / hour. Figure 8 The transmission electron microscope image of the black powder product prepared for this comparative example shows that there are obvious graphene sheets in the product, and there are also particles with larger particle size and agglomeration. Characterizations such as XPS confirm that this particle is mainly silicon carbide particles. This is because the graphite powder and silicon powder are mixed and then enter the plasma torch. The high temperature environment (greater than 4000K) in the torch causes a strong chemical reaction between graphite / graphene and silicon particles to form silicon carbide particles, which affects the composition of the product and makes it difficult for the final product to effectively form graphene-loaded nano-silicon materials. Table 1 gives a performance list of the product prepared in comparative example 3, in which the specific surface area is measured by nitrogen adsorption method and the mass fraction is measured by thermogravimetry. It can be found that the silicon carbide content in this comparative example is as high as 45%.

[0055] Table 1: Performance list of products prepared in various embodiments and comparative examples

[0056]

[0057] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0058] Therefore, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of implementation of the present application; that is, all equivalent changes made according to the scope of the claims of the present application are within the protection scope of the claims of the present application.

Claims

1. A method for continuously preparing graphene-loaded nano-silicon materials, characterized in that: The following steps are involved: Graphite powder is continuously supplied to the cathode plasma torch to generate a first jet containing graphene sheets, and 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-loaded nano-silicon powder; wherein the working fluid gas is continuously introduced into the convergence point, and the temperature is controlled at 1500-2000K.

2. The method for continuously preparing graphene-loaded nano-silicon material 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 less than 4000K, and the plasma working fluid gas is at least one of argon and hydrogen.

3. The method for continuously preparing graphene-loaded nano-silicon material according to claim 1, characterized in that: The graphite powder has a particle size of 1-10 microns, and the silicon powder has a particle size of 20-80 microns.

4. The method for continuously preparing graphene-loaded nano-silicon materials 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 continuously preparing graphene-loaded nano-silicon materials according to claim 1, characterized in that: The target temperature of the quenching is 80-100°C.

6. The graphene-supported nano-silicon material prepared by the method according to any one of claims 1 to 5, characterized in that: The invention has a lamellar structure of graphene-loaded nano-silicon particles, wherein the number of graphene layers is not higher than 10 and the particle size of the nano-silicon is not greater than 20 nanometers.

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

8. Use of the graphene-loaded nano-silicon material according to claim 6 or 7 as a silicon-carbon negative electrode material.

9. The device for continuously preparing graphene-loaded nano-silicon materials used in the method according to any one of claims 1 to 5, characterized in that: include: A reaction chamber, wherein a first interface and a second interface are provided at an angle to each other at the upper portion of the reaction chamber, wherein a cathode plasma torch is accommodated in the first interface, and an anode plasma torch is accommodated in the second interface; the cathode plasma torch comprises a cathode carrier gas inlet; the first interface is provided with a first raw material inlet; the anode plasma torch comprises an anode carrier gas inlet; and the second interface is provided with a second raw material inlet; A discharge port is provided at the bottom of the reaction chamber, and the discharge port is connected to a grading collection mechanism; The reaction chamber located above the discharge port is provided with a cooling gas interface; 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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