Preparation method of nanometer silicon, nanometer silicon oxide and silicon-carbon nanometer composite material

Abstract

The application relates to the technical field of nanometer silicon, in particular to a preparation method of nanometer silicon, nanometer silicon dioxide and silicon-carbon nanometer composite material. The nanometer silicon preparation method comprises the following steps: S1, providing an electric arc furnace with a built-in graphite electrode, inputting a high-voltage power supply into the graphite electrode to generate electric arc discharge and form a high-temperature area; S2, providing solid silicon sources and carbon sources, mixing the silicon sources and the carbon sources according to a molar ratio of 2:3 to 3:2 of silicon dioxide and carbon, and then sending the mixture into the high-temperature area, so that silicon and carbon dioxide are generated through a reduction reaction, a chemical equation is SiO2+C->Si+CO2, the generated silicon is gasified into silicon vapor in the high-temperature area; S3, inputting an inert gas into the electric arc furnace, the inert gas sends the silicon vapor and the carbon dioxide gas to a cooling area to perform condensation treatment, so that the silicon vapor is condensed into nanometer silicon particles; and S4, providing a filtering system, filtering nanometer silicon powder from the nanometer silicon particles, and collecting the nanometer silicon powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer silicon, and particularly relates to a preparation method of nanometer silicon, nanometer silicon dioxide and silicon-carbon nanometer composite material. BACKGROUND

[0002] In recent years, with the rapid development of nanotechnology, nanometer silicon has shown revolutionary application potential in key technical fields such as energy, electronics and catalysis due to its unique physical and chemical properties, and has become a key research direction in the global new material field. However, the traditional nanometer silicon preparation method often has problems such as high energy consumption, low yield and uneven particle size distribution, which to some extent limits the wide application of nanometer silicon.

[0003] For example, in the preparation process of existing silicon-carbon negative electrode material in the field of lithium batteries, the nanometer silicon is deposited unevenly in the carbon, which leads to easy cracking of the silicon-carbon interface and easy pulverization of silicon, thereby greatly affecting the cycle performance. At the same time, the existing silicon-carbon negative electrode material is prepared by using silane gas, which has high cost and great safety risk, resulting in high price of the silicon-carbon negative electrode material and seriously affecting its large-scale application and promotion.

[0004] Therefore, although nanometer silicon material has significant performance advantages, its large-scale application is still limited by the problems of high energy consumption, low yield and structure control in the preparation process. SUMMARY

[0005] In order to solve the technical problems of high energy consumption and high cost of the traditional nanometer silicon preparation method, and low purity and uneven particle size distribution of the obtained nanometer silicon, the present application provides a preparation method of nanometer silicon, nanometer silicon dioxide and silicon-carbon nanometer composite material.

[0006] The technical problem of the present application is solved by providing a nanometer silicon preparation method, which comprises the following steps: S1: providing an electric arc furnace with a built-in graphite electrode, and passing a high-voltage power supply into the graphite electrode to generate electric arc discharge and form a high-temperature region; S2: providing solid silicon source and carbon source, mixing them according to the molar ratio of silicon dioxide to carbon in the range of 2:3 to 3:2, and then sending them into the high-temperature region to generate silicon and carbon dioxide through reduction reaction, the chemical equation is: SiO2+C→Si+CO2↑, and the generated silicon is gasified to generate silicon vapor in the high-temperature region; S3: passing inert gas into the interior of the electric arc furnace, and the inert gas sends the silicon vapor and carbon dioxide gas to the cooling region for condensation treatment, so that the silicon vapor is condensed to generate nanometer silicon particles; S4: providing a filtration system to filter out nanometer silicon powder from the nanometer silicon particles, and collecting the nanometer silicon powder.

[0007] Preferably, the condensing treatment comprises the following steps: S31: setting a heat-resistant conduit between the high-temperature region and the cooling region, and sending the silicon vapor and the carbon dioxide gas to the cooling region through the heat-resistant conduit; S32: setting a liquid nitrogen cold trap of -196℃ in the cooling region, and the liquid nitrogen cold trap promotes the silicon vapor to be cooled at a rate of at least 10 4 K / s, to generate amorphous silicon powder with an average particle size of 25 nm to 35 nm.

[0008] Preferably, the silicon source and the carbon source are quartz sand and nano-carbon powder respectively, the particle size of the quartz sand is 60 μm to 90 μm, and the particle size of the nano-carbon powder is 40 nm to 100 nm; and the molar ratio of silicon dioxide to carbon is 2:3, 1:1 or 3:2 when the quartz sand and the nano-carbon powder are mixed.

[0009] Preferably, the voltage for generating the arc discharge in the arc furnace is 15 kV to 25 kV, the current is 60 A to 100 A, and the temperature of the high-temperature region is at least 1350℃.

[0010] Preferably, the silicon source comprises one, two or more of quartz sand, silica and photovoltaic waste silicon; and the carbon source comprises one, two or more of nano-carbon powder, coke powder, graphite and carbon black.

[0011] The present application also provides a method for preparing nano-silicon, which comprises the method for preparing nano-silicon described above. x Preferably, the method for preparing nano-silicon further comprises the following steps: F1: setting a gas mixing device between the high-temperature region and the cooling region; F2: introducing an inert gas into the interior of the arc furnace, and the inert gas sends the silicon vapor and the carbon dioxide gas to the gas mixing device; and F3: introducing an oxidizing gas into the gas mixing device, the oxidizing gas comprises one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, and the surface of part of the nano-silicon particles is partially oxidized to form a surface passivation layer of nano-silicon (SiO x x≤2).

[0012] Preferably, the surface of part of the nano-silicon particles is partially oxidized, which comprises the following steps: F31: providing a mixing section of the gas mixing device, the mixing section comprises a first section and a second section arranged in sequence, and the oxidizing gas introduced into the gas mixing device is oxygen; F32: introducing 5 vol% oxygen into the first section to generate a first passivation layer of SiO x x≈0.8); and F33: introducing 15 vol% oxygen into the second section to generate a SiO2 coating layer and a second passivation layer of SiO x x≈0.8).

[0013] Preferably, the temperature of the first section is 800℃ to 400℃, and the first passivation layer of SiO x(x≈0.8) the thickness of the first passivation layer is 8nm to 13nm; the temperature of the second section is 400℃ and below, and the thickness of the SiO2 coating layer generated is 6nm to 10nm, SiO x (x≈0.8) the thickness of the second passivation layer is 2nm to 3nm.

[0014] The application further provides a silicon-carbon nanocomposite material preparation method, which comprises the above-mentioned nanosilicon preparation method; after the execution of steps S1 to S2, the silicon-carbon nanocomposite material preparation method further comprises the following steps: P1: setting a porous carbon fiber support in the electric arc furnace and putting porous carbon fibers into the porous carbon fiber support; P2: setting the current for generating electric arc discharge of the graphite electrode to be at least 120A, so that silicon vapor permeates into the porous carbon fibers to form amorphous silicon; P3: cooling at a rate of at least 10 4 K / s, so as to promote the deposition and growth of the amorphous silicon on the surface of the porous carbon fibers and form a silicon-carbon nanocomposite material.

[0015] Preferably, the porosity of the porous carbon fiber support is 85%, and the pore size is 50nm to 100nm.

[0016] Preferably, the silicon-carbon nanocomposite material comprises porous carbon fibers and silicon particles uniformly embedded in the porous carbon fibers, and the particle size of the silicon particles is 20nm to 50nm.

[0017] Compared with the prior art, the application has the following advantages:

[0018] 1. The nanosilicon preparation method provided by the application generates electric arc discharge of the graphite electrode to form a high-temperature environment for the reduction reaction of silicon dioxide and carbon, thereby saving a large amount of energy consumption and reducing the preparation cost compared with the preparation of nanosilicon by using a traditional heating method; the filtration system can filter the nanoscale silicon particles with a large particle size, thereby obtaining nanosilicon powder with uniform particle size; the high temperature formed by the electric arc discharge in the electric arc furnace can make the reaction of silicon dioxide and carbon more complete, and finally the nanosilicon powder obtained by using the filtration system has high purity.

[0019] 2. In the nanosilicon preparation method provided by the application, a heat-resistant conduit is arranged between the high-temperature region and the cooling region, and the inert gas sends the silicon vapor and the carbon dioxide gas to the cooling region through the heat-resistant conduit, so that the silicon vapor can be prevented from condensing to form silicon particles before reaching the cooling region, thereby improving the yield of nanosilicon; the-196℃ liquid nitrogen cold trap arranged in the cooling region promotes the rapid cooling of the silicon vapor at a rate of at least 10 4 K / s, which can ensure the uniform distribution of the particle size of the amorphous silicon powder and further improve the yield of nanosilicon.

[0020] 3. In the method for preparing nano-silicon according to the embodiment of the present application, when the silicon source and the carbon source are quartz sand and nano-carbon powder respectively, the quartz sand is a powder material and the nano-carbon powder has a small particle size, so that the reduction reaction is more complete, and the cost is low and the yield is relatively high.

[0021] 4. In the method for preparing nano-silicon according to the embodiment of the present application, by setting the voltage and the current for generating the arc discharge in the electric arc furnace, the temperature in the high-temperature region of the electric arc furnace can be increased to 1350℃, so that the reduction reaction of the silicon dioxide and the carbon is more complete, and when the input current and voltage are increased, the temperature in the high-temperature region can continue to increase, so that the content of the silicon vapor in the reaction product is increased.

[0022] 5. In the method for preparing nano-silicon according to the embodiment of the present application, the silicon source and the carbon source with low cost and high purity are mainly selected to reduce the cost of raw materials; compared with the preparation of nano-silicon by using silane gas, one, two or more silicon sources of quartz sand, silica and photovoltaic waste silicon are used in the embodiment of the present application, and the cost of raw materials can be reduced by 20 times when the same yield of nano-silicon material is prepared.

[0023] 6. The embodiment of the present application further provides a method for preparing nano-silicon, by setting a gas mixing device between the high-temperature region and the cooling region, and introducing oxidizing gas into the gas mixing device, the oxidizing gas can be one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, so that the surface of part of the nano-silicon particles is graded and oxidized, and a surface passivation layer of nano-silicon oxide (SiO x x≤2) is formed; by setting the mixing section of the gas mixing device, different concentrations of oxygen are introduced into the first section and the second section, so that the surface of the nano-silicon particles is graded and oxidized, and finally the SiO x (x≤2)@SiO2 composite nanoparticles with core-shell structure can be prepared.

[0024] 7. The embodiment of the present application further provides a method for preparing silicon-carbon nano-composite material, by setting a porous carbon fiber support in the electric arc furnace and putting porous carbon fibers into the porous carbon fiber support, the silicon vapor can penetrate into the porous carbon fibers to form amorphous silicon under high-temperature environment, and then the amorphous silicon is deposited and grown on the surface of the porous carbon fibers by rapid cooling to form the silicon-carbon nano-composite material; at this time, the observation by the transmission electron microscope (TEM) shows that the silicon particles with a size of 20nm to 50nm are uniformly embedded in the porous carbon fibers, and the conductivity can be increased to 300 times of that of pure silicon material. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0026] Figure 1 is a flowchart of steps S1 to S4 in a method for preparing nano-silicon provided by an embodiment of the present application.

[0027] Figure 2 is a flowchart of steps S31 to S32 in a method for preparing nano-silicon provided by an embodiment of the present application.

[0028] Figure 3 is a flowchart of steps F1 to F3 in a method for preparing nano-silicon oxide provided by an embodiment of the present application.

[0029] Figure 4 is a flowchart of steps F31 to F33 in a method for preparing nano-silicon oxide provided by an embodiment of the present application.

[0030] Figure 5 is a flowchart of steps P1 to P3 in a method for preparing silicon-carbon nano-composite material provided by an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the following will further describe the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0032] In the embodiments provided by the present application, it should be understood that “B corresponding to A” means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0033] It should be understood that “one embodiment” or “an embodiment” mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, “in one embodiment” or “in an embodiment” appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in any suitable manner in one or more embodiments. Those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0034] In various embodiments of the present application, it should be understood that the size of the sequence number of the above processes does not mean the inevitable sequence of execution, and the execution sequence of the processes should be determined according to their functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] The flowcharts and block diagrams in the drawings of the present application illustrate the possible implementation architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each block in the flowchart or block diagram can represent a module, a program segment, or a part of code containing one or more executable instructions for implementing the specified logic function. It should also be noted that in some alternative implementations, the functions noted in the blocks can also occur in a different order from that noted in the drawings. For example, two blocks represented in succession can actually be executed substantially in parallel, and sometimes they can be executed in reverse order, based on the functions involved. It should be particularly noted that each block in the block diagram and / or flowchart, and the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of special-purpose hardware and computer instructions.

[0036] The technical solutions of the present application will be described below.

[0037] Please refer to Figure 1 The embodiment of the present application provides a method for preparing nano-silicon, comprising the following steps:

[0038] S1: providing an arc furnace with a built-in graphite electrode, passing high-voltage power to the graphite electrode to generate arc discharge and form a high-temperature region;

[0039] S2: providing solid silicon source and carbon source, mixing them according to a molar ratio of silicon dioxide to carbon of 2:3 to 3:2, and then sending them into the high-temperature region to generate silicon and carbon dioxide through a reduction reaction, with a chemical equation of SiO2+C→Si+CO2↑, and the generated silicon gasifies in the high-temperature region to generate silicon vapor;

[0040] S3: passing inert gas into the interior of the arc furnace, and sending the silicon vapor and carbon dioxide gas to a cooling region for condensation treatment, so that the silicon vapor is condensed to generate nano-silicon particles;

[0041] S4: providing a filtration system to filter out nano-silicon powder from the nano-silicon particles and collect the nano-silicon powder.

[0042] The preparation method of the nano-silicon provided by the embodiment of the present application saves a large amount of energy consumption and greatly reduces the preparation cost of the nano-silicon, compared with the preparation of the nano-silicon by using the traditional heating method.

[0043] In some embodiments, the silicon source provided in step S2 includes one, two or more of quartz sand, silica and photovoltaic waste silicon, and the carbon source includes one, two or more of nano-carbon powder, coke powder, graphite and carbon black. It can be understood that the silicon source in the embodiment must contain silicon dioxide, and the carbon source must contain carbon. By selecting the silicon source and the carbon source with low price and high purity, the raw material cost can be reduced. Compared with the preparation of the nano-silicon by using silane gas, the quartz sand, the silica and / or the photovoltaic waste silicon are used in the embodiment of the present application, and the raw material cost can be reduced by 20 times when the same yield of the nano-silicon material is prepared.

[0044] It should be noted that in step S1, the high-temperature region is directly formed in the electric arc furnace by using the high-voltage electric arc discharge technology by providing the electric arc furnace with the built-in graphite electrode. Only the silicon source and the carbon source mixed according to the molar ratio of silicon dioxide to carbon need to be sent into the high-temperature region to generate silicon and carbon dioxide gas through the reduction reaction. Since the reduction reaction of silicon dioxide and carbon at high temperature is complete, the silicon source and the carbon source mentioned above with low price and high purity can be used in the embodiment of the present application.

[0045] In steps S1 and S2, when the reduction reaction of silicon dioxide and carbon at high temperature is generated in the electric arc furnace to generate silicon and carbon dioxide gas, the generated silicon will be gasified to generate silicon vapor in the high-temperature region, so as to facilitate the next process. The whole reaction process is carried out in the electric arc furnace in a closed manner, which can effectively reduce harmful emissions and meet the requirements of green production.

[0046] In step S3, inert gas is introduced into the interior of the electric arc furnace. The inert gas does not react with the silicon vapor and the carbon dioxide gas, and is used to send the silicon vapor and the carbon dioxide gas to the cooling region. The silicon vapor can be condensed to generate nano-silicon particles by condensing the silicon vapor in the cooling region. In the embodiment of the present application, the rate of the inert gas introduced into the electric arc furnace needs to be adjusted according to the actual situation. When the rate is low, the silicon vapor and the carbon dioxide gas cannot be well sent to the cooling region, which will affect the condensation effect of the silicon vapor. When the rate is high, the reaction between the silicon dioxide in the silicon source and the carbon in the carbon source may not be complete. Therefore, the size of the electric arc furnace, the distance between the high-temperature region and the cooling region, and the rate of the reduction reaction need to be considered to determine the rate of the inert gas introduced. The inert gas can be argon or nitrogen, and nitrogen is preferred.

[0047] In step S4, the filtering system can filter the nanoscale silicon particles with large particle size, and then obtain the nanosilicon powder with uniform particle size; since the high temperature formed by the arc discharge in the electric arc furnace can make the reaction of silicon dioxide and carbon more complete, the nanosilicon powder obtained by using the filtering system has high purity. As an implementation form, the filtering system provided by the embodiment of the present application is a cloth bag filtering system.

[0048] The embodiment of the present application forms a high-temperature environment for the reduction reaction of silicon dioxide and carbon by using the high-voltage arc discharge technology, thereby saving a large amount of energy consumption and reducing the preparation cost; the use of the electric arc furnace can make the reduction reaction of silicon dioxide and carbon at high temperature more complete; in the filtering and collecting process, the filtering system can be used to obtain the nanosilicon powder with uniform particle size and high purity; by using the above technical solution, the technical problems of the traditional nanosilicon preparation method, such as high energy consumption, high cost, low purity of obtained nanosilicon and uneven particle size distribution, are solved.

[0049] Further, please refer to Figure 2 , the condensation treatment includes the following steps:

[0050] S31: A heat-resistant conduit is arranged between the high-temperature region and the cooling region, and the inert gas sends the silicon vapor and the carbon dioxide gas to the cooling region through the heat-resistant conduit;

[0051] S32: A liquid nitrogen cold trap of -196 DEG C is arranged in the cooling region, and the liquid nitrogen cold trap promotes the silicon vapor to be cooled at a rate of at least 10 4 K / s, to generate the amorphous silicon powder with an average particle size of 25nm to 35nm.

[0052] In the nanosilicon preparation method provided by the embodiment of the present application, the condensation treatment refers to rapidly cooling the silicon vapor at a rate of at least 10 4 K / s, so that the silicon vapor is condensed to generate the nanoscale silicon particles.

[0053] Specifically, in step S31, the heat-resistant conduit is arranged between the high-temperature region and the cooling region, the inert gas is introduced into the electric arc furnace, and the inert gas sends the silicon vapor and the carbon dioxide gas to the cooling region through the heat-resistant conduit; by this design, the silicon vapor can be prevented from being condensed to form silicon particles before reaching the cooling region, thereby improving the yield of nanosilicon.

[0054] It should be noted that the heat-resistant conduit has the characteristics of high thermal conductivity, electrical insulation, high temperature resistance and oxidation resistance, and the boron nitride conduit is preferably used for the inert gas, the silicon vapor and the carbon dioxide gas to flow through.

[0055] It can be understood that the method applied to condense the silicon vapor at high temperature is a vapor deposition method. In step S32, by setting a liquid nitrogen cold trap at -196℃ in the cooling area, the silicon vapor is rapidly cooled at a rate of at least 10 4 K / s, which can ensure uniform particle size distribution of the amorphous silicon powder and improve the yield of the nano-silicon.

[0056] When the silicon vapor is cooled at a rate of greater than 10 4 K / s, the particle size of the generated amorphous silicon powder is more concentrated, so that the yield of the final nano-silicon is further improved. Specifically, a higher silicon vapor cooling rate can be achieved by increasing the contact area between the liquid nitrogen and the silicon vapor, or by setting a liquid nitrogen cold trap with a temperature lower than -196℃.

[0057] In some embodiments, the silicon source and the carbon source are quartz sand and nano-carbon powder, respectively, the particle size of the quartz sand is 60μm to 90μm, and the particle size of the nano-carbon powder is 40nm to 100nm; as a preferred implementation of the embodiment, the particle size of the quartz sand is 75μm, and the particle size of the nano-carbon powder is 70nm.

[0058] In the nano-silicon preparation method provided by the embodiment, when the silicon source and the carbon source are quartz sand and nano-carbon powder, respectively, the quartz sand is a powder material, and the nano-carbon powder has a smaller particle size, so that the reduction reaction is more complete, and the price is low, and the yield is relatively high.

[0059] In some embodiments, the molar ratio of silicon dioxide (SiO2) to carbon (C) is 2:3, 1:1 or 3:2 when the quartz sand and the nano-carbon powder are mixed; the preparation method of the embodiment can obtain amorphous silicon powder with an average particle size of 30±5nm by using the raw material ratio, wherein the amorphous silicon powder obtained by different raw material ratios has the following performance parameters:

[0060] Table 1, specific surface area, gram capacity and initial efficiency parameters of amorphous silicon powder obtained by different raw material ratios

[0061]

[0062] (1) When the molar ratio of silicon dioxide to carbon is 2:3, the specific surface area of the generated amorphous silicon powder is 415m 2 / g, the gram capacity is 2870mAh / g, and the initial efficiency is 93%;

[0063] (2) When the molar ratio of silicon dioxide to carbon is 1:1, the specific surface area of the generated amorphous silicon powder is 400m 2 / g, the gram capacity is 3100mAh / g, and the initial efficiency is 90%;

[0064] (3) when the molar ratio of silicon dioxide to carbon is 3:2, the specific surface area of the amorphous silicon powder generated is 420 m 2 / g, the specific capacity is 2750 mAh / g, and the initial efficiency is 87%.

[0065] It should be noted that the data of the specific surface area, the specific capacity and the initial efficiency reflect the good performance of the nano-silicon prepared by the embodiment of the present application in the field of lithium batteries. The specific surface area (unit: m 2 / g) refers to the total area per unit mass of material, and is usually referred to as the specific surface area of powders, fibers and particles, and is generally obtained by a BET specific surface area tester; the specific capacity (unit: mAh / g) refers to the ratio of the discharge capacity of the negative electrode material particles to the mass of the negative electrode material particles; and the initial efficiency (unit: %) refers to the ratio of the discharge capacity to the charge capacity of the negative electrode material particles in the first charge-discharge process.

[0066] Further, the voltage for generating arc discharge in the electric arc furnace is 15 kV to 25 kV, the current is 60 A to 100 A, and the temperature of the high-temperature region is at least 1350℃.

[0067] In the nano-silicon preparation method provided by the embodiment of the present application, by setting the voltage and current for generating arc discharge in the electric arc furnace, the temperature of the high-temperature region in the electric arc furnace can be increased to 1350℃, so that the reduction reaction of silicon dioxide and carbon is more complete.

[0068] As an optional embodiment in the present embodiment, the voltage for generating arc discharge in the electric arc furnace is 20 kV, and the current is 80 A, at which time the temperature of the high-temperature region is increased to 1350℃. It should be noted that when the input current and voltage are increased, the temperature of the high-temperature region can continue to increase, so that the content of silicon vapor in the reaction product is increased.

[0069] In some embodiments, the silicon source includes one, two or more of quartz sand, quartz and photovoltaic waste silicon; and the carbon source includes one, two or more of nano-carbon powder, coke powder, graphite and carbon black.

[0070] The nano-silicon preparation method provided by the embodiment of the present application selects silicon sources and carbon sources with low price and high purity to reduce the cost of raw materials. Understandably, the chemical substances participating in the reaction in the silicon source and the carbon source are silicon dioxide and carbon, respectively, so that the single silicon source or the composite silicon source, the single carbon source or the composite carbon source can all undergo reduction reaction under high-temperature conditions. Through this design, it is not necessary to specially purchase and collect single specific silicon sources or carbon sources, so that the utilization rate of raw materials can be improved, and cost reduction and benefit increase can be realized in the preparation of nano-silicon.

[0071] It should be noted that, compared with the preparation of nanometer silicon by using silane gas, the embodiment of the present application uses one, two or more silicon sources of quartz sand, silica and photovoltaic waste silicon, and the cost of raw materials can be reduced by 20 times when preparing the same output of nanometer silicon material.

[0072] Please refer to Figure 1 and Figure 3 , the embodiment of the present application also provides a preparation method of nanometer silicon oxide, which comprises the above-mentioned preparation method of nanometer silicon.

[0073] The preparation method of nanometer silicon oxide further comprises the following steps after the execution of steps S1 to S2:

[0074] F1: a gas mixing device is arranged between the high-temperature region and the cooling region;

[0075] F2: inert gas is introduced into the interior of the electric arc furnace, and the inert gas sends the silicon vapor and the carbon dioxide gas to the gas mixing device;

[0076] F3: the gas mixing device is introduced with oxidizing gas, and the oxidizing gas comprises one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, so that part of the surface of the nanometer silicon particles is graded oxidation to form a nanometer silicon oxide (SiO x , x≤2) surface passivation layer.

[0077] In the preparation method of nanometer silicon oxide provided by the embodiment of the present application, the gas mixing device is arranged between the high-temperature region and the cooling region, and the gas mixing device is introduced with oxidizing gas, which can be one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, so that part of the surface of the nanometer silicon particles is graded oxidation to form a nanometer silicon oxide (SiO x , x≤2) surface passivation layer; by arranging the mixing section of the gas mixing device, different concentrations of oxygen are introduced into the first section and the second section, so that the surface of the nanometer silicon particles is graded oxidation, and finally the SiO x (x≤2)@SiO2 composite nanoparticles with core-shell structure can be prepared.

[0078] It should be noted that the core-shell structure is a special structure composed of nanometer materials or micrometer materials, and the core is coated with one or more layers of heterogeneous or homogeneous materials to form a shell; the core and the shell are tightly combined by electrostatic action or chemical bond, and have unique physical and chemical properties.

[0079] Please refer to Figure 4 , part of the surface of the nanometer silicon particles is graded oxidation, which comprises the following steps:

[0080] F31: providing a mixing section of the gas mixing device, the mixing section comprising a first section and a second section arranged in sequence, and the oxidizing gas supplied into the gas mixing device is oxygen;

[0081] F32: supplying 5 vol% oxygen into the first section to generate a SiO x (x≈0.8) first passivation layer;

[0082] F33: supplying 15 vol% oxygen into the second section to generate a SiO2coating layer and a SiO x (x≈0.8) second passivation layer.

[0083] It can be understood that the first section and the second section arranged in sequence in step F31 can promote the surface of the nanoscale silicon particles to be oxidized in different types.

[0084] Specifically, in step F32 and F33, when 5 vol% oxygen is supplied into the first section to generate a SiO x (x≈0.8) first passivation layer, and when 15 vol% oxygen is supplied into the second section, the first passivation layer can be further oxidized into a SiO2coating layer and a SiO x (x≈0.8) second passivation layer, at this time, the material SiO2of the coating layer serves as the SiO x (x≤2) outer shell material in the SiO2core-shell structure, the second passivation layer SiO x (x≈0.8) as the SiO x (x≤2) core material in the SiO2core-shell structure.

[0085] It should be noted that the factors for promoting the surface of the nanoscale silicon particles to be oxidized in stages include the volume percentage concentration of oxygen in air (i.e., 5 vol% and 15 vol% in the present embodiment) and the temperature of the first section and the second section; by adjusting the oxygen concentration and the temperature of the oxygen supply section, the composite material of nanoscale silicon oxide can be prepared.

[0086] Further, in some embodiments, the temperature of the first section is 400°C to 800°C, the concentration of the supplied oxygen is 5 vol%, and finally a SiO x (x≈0.8) first passivation layer is generated, and the thickness of the first passivation layer is 8 nm to 13 nm. The temperature of the second section is 400°C or below, the concentration of the supplied oxygen is 15 vol%, and finally a SiO2coating layer with a thickness of 6 nm to 10 nm and a SiO x (x≈0.8) second passivation layer is generated, and the thickness of the second passivation layer is 2 nm to 3 nm; wherein the average thickness of the SiO2coating layer is 8 nm.

[0087] Please refer to Figure 1 and Figure 5The embodiment of the present application also provides a silicon-carbon nanocomposite material preparation method, which comprises the above-mentioned nanosilicon preparation method.

[0088] The silicon-carbon nanocomposite material preparation method further comprises the following steps after the execution of the step S1 to the step S2:

[0089] P1: a porous carbon fiber support is arranged in an arc furnace, and porous carbon fibers are placed into the porous carbon fiber support;

[0090] P2: a current for generating arc discharge by inputting a high-voltage power supply to the graphite electrode is set to be at least 120 A, so that silicon vapor permeates into the porous carbon fibers to form amorphous silicon;

[0091] P3: the temperature of the arc furnace is reduced at a rate of at least 10 4 K / s, so that the amorphous silicon is deposited and grown on the surface of the porous carbon fibers to form a silicon-carbon nanocomposite material.

[0092] It can be understood that the silicon-carbon nanocomposite material with high conductivity can be obtained by the preparation method of the embodiment, the composite material combines the high activity of silicon and the good conductivity of carbon, and is suitable for the field of lithium ion battery negative electrode materials and the like. In some embodiments, the porosity of the porous carbon fiber support is 85%, and the pore size is 50 nm to 100 nm.

[0093] Specifically, in the step P1 and the step P2, the porous carbon fiber support is arranged in the arc furnace, and the porous carbon fibers are placed into the porous carbon fiber support; the current set by the embodiment of the present application is at least 120 A, so that the temperature inside the arc furnace reaches 1450 DEG C or above, which can promote the silicon vapor to permeate into the porous carbon fibers to form amorphous silicon.

[0094] In the step S3, the amorphous silicon is deposited and grown on the surface of the porous carbon fibers by rapid cooling to form a silicon-carbon nanocomposite material; it can be understood that the higher the cooling rate, the faster the rate of deposition and growth of the amorphous silicon on the surface of the porous carbon fibers, so that the application range of the final silicon-carbon nanocomposite material is more extensive.

[0095] In some embodiments, the silicon-carbon nanocomposite material comprises the porous carbon fibers and the silicon particles uniformly embedded in the porous carbon fibers, and the particle size of the silicon particles is 20 nm to 50 nm.

[0096] It should be noted that, in the silicon-carbon nanocomposite material obtained by the preparation method provided by the embodiment, the transmission electron microscope (TEM) observation shows that the silicon particles with a particle size of 20 nm to 50 nm are uniformly embedded in the porous carbon fibers, and the conductivity can be increased to 300 times that of pure silicon material.

[0097] The preparation method of the nano-silicon, nano-silicon oxide and silicon-carbon nano-composite material disclosed in the above embodiments of the present application is described in detail. The principles and implementation manners of the present application are described by using specific examples. The above embodiment descriptions are only used to help understand the method of the present application and its core idea. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges can be changed. In summary, the content of the present description should not be understood as a limitation of the present application. Any modification, equivalent replacement, improvement and the like within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a silicon-carbon nanocomposite material, characterized by, The method comprises the following steps: S1: providing an arc furnace with built-in graphite electrodes, and supplying high-voltage power to the graphite electrodes to generate arc discharge and form a high-temperature region; S2: providing solid silicon source and carbon source, mixing them according to a molar ratio of silica to carbon ranging from 2:3 to 3:2, and then feeding them into the high-temperature region to generate silicon and carbon dioxide through a reduction reaction, with a chemical equation of SiO2+C→Si+CO2↑, and the generated silicon gasifies in the high-temperature region to generate silicon vapor; S3: supplying inert gas into the arc furnace, and the inert gas carries the silicon vapor and carbon dioxide gas to a cooling region for condensation treatment to generate nano-sized silicon particles; S4: providing a filtering system to filter out nano silicon powder from the nano-sized silicon particles and collect the nano silicon powder; After the steps S1 to S2, the method further comprises the following steps: P1: setting a porous carbon fiber support in the arc furnace, and placing porous carbon fibers into the porous carbon fiber support; P2: setting the current supplied to the graphite electrodes to generate arc discharge to be at least 120 A, so that the silicon vapor permeates into the porous carbon fibers to form amorphous silicon; P3: at a rate of at least 10 4 K / s to cause amorphous silicon to deposit and grow on the surface of the porous carbon fibers to form a silicon-carbon nanocomposite; The condensation treatment comprises the following steps: S31: setting a heat-resistant conduit between the high-temperature region and the cooling region, and the inert gas carries the silicon vapor and carbon dioxide gas through the heat-resistant conduit to the cooling region; S32: A liquid nitrogen cold trap of -196°C is provided at the cooling zone, and the liquid nitrogen cold trap causes the silicon vapor to be condensed at a rate of at least 10 4 K / s, generating amorphous silicon powder having an average particle diameter of 25 nm to 35 nm.

2. The method according to claim 1, wherein: the silicon source and the carbon source are quartz sand and nano carbon powder respectively, the particle size of the quartz sand is 60-90 μm, and the particle size of the nano carbon powder is 40-100 nm; the molar ratio of silica to carbon when mixing the quartz sand and the nano carbon powder is 2:3, 1:1 or 3:

2.

3. The method according to claim 2, wherein: the voltage for generating arc discharge in the arc furnace is 15-25 kV, the current is 60-100 A, and the temperature of the high-temperature region is at least 1350 °C.

4. The method according to claim 1, wherein: the silicon source comprises one, two or more of quartz sand, silica stone and photovoltaic waste silicon; the carbon source comprises one, two or more of nano carbon powder, coke powder, graphite and carbon black.

5. The method according to claim 1, wherein: the porosity of the porous carbon fiber support is 85%, and the pore size is 50-100 nm.

6. The method according to claim 5, wherein: the silicon-carbon nanocomposite material comprises porous carbon fibers and silicon particles uniformly embedded in the porous carbon fibers, and the particle size of the silicon particles is 20-50 nm.

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