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

Abstract

The invention relates to the technical field of nano silicon, in particular to a preparation method of nano silicon, nano silicon oxide and a silicon-carbon nano composite material. The preparation method of the nano silicon comprises the following steps: S1, providing an electric arc furnace with a built-in graphite electrode, and introducing a high-voltage power supply into the graphite electrode to generate arc discharge so as to form a high-temperature area; s2, providing a solid silicon source and a solid carbon source, mixing silicon dioxide and carbon according to a molar ratio of 2: 3-3: 2, feeding the mixture into a high-temperature area, carrying out a reduction reaction to generate silicon and carbon dioxide according to a chemical equation of SiO2 + C-Si + CO2, and gasifying the generated silicon in the high-temperature area to generate silicon steam; s3, inert gas is introduced into the electric arc furnace, the inert gas conveys the silicon steam and the carbon dioxide gas to a cooling area for condensation treatment, and the silicon steam is condensed to generate nanoscale silicon particles; and S4, providing a filtering system, filtering out nanometer silicon powder in 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 xThe thickness of the first passivation layer (x≈0.8) is 8nm to 13nm; the temperature of the second section is 400℃ or below, and the thickness of the SiO2 coating layer generated is 6nm to 10nm, and the SiO x The thickness of the second passivation layer (x≈0.8) 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: a porous carbon fiber support is arranged in the electric arc furnace, and porous carbon fibers are put into the porous carbon fiber support; P2: the current for generating electric arc discharge by passing a high-voltage power supply to the graphite electrode is set to be at least 120A, so that silicon vapor permeates into the porous carbon fibers to form amorphous silicon; P3: the temperature of the electric arc furnace is reduced 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: 1. The nanosilicon preparation method provided by the application forms a high-temperature environment by passing a high-voltage power supply to the graphite electrode to generate electric arc discharge, so that the reduction reaction of silicon dioxide and carbon occurs, 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.

[0018] 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; by arranging the liquid nitrogen cold trap at-196℃ in the cooling region, the silicon vapor is rapidly cooled at a rate of at least 10 4 K / s, which can ensure that the particle size distribution of the amorphous silicon powder is uniform, thereby further improving the yield of nanosilicon.

[0019] 3. In the nano-silicon preparation method provided in the embodiment of the present invention, when the silicon source and the carbon source are quartz sand and nano-carbon powder respectively, since quartz sand is a powder material and the particle size of nano-carbon powder is small, it participates in the reduction reaction more completely, is inexpensive, and has a relatively high yield.

[0020] 4. In the nano-silicon preparation method provided in the embodiment of the present invention, by setting the voltage and current for generating arc discharge in the arc furnace, the temperature of the high-temperature zone in the arc furnace can be increased to 1350°C, so that the reduction reaction of silicon dioxide and carbon is more complete, and when the input current and voltage are increased, the temperature of the high-temperature zone can continue to increase, thereby increasing the content of silicon vapor in the reaction product.

[0021] 5. In the nano-silicon preparation method provided in the embodiment of the present invention, low-priced and high-purity silicon sources and carbon sources are mainly selected to reduce raw material costs; compared with the use of silane gas to prepare nano-silicon, the embodiment of the present invention uses one, two or more silicon sources selected from quartz sand, silica stone and photovoltaic waste silicon. When preparing the same output of nano-silicon material, the raw material cost used can be reduced by 20 times.

[0022] 6. The present invention also provides a method for preparing nano-silicon oxide, wherein a gas mixing device is provided between a high temperature area and a cooling area, and an oxidizing gas is introduced into the gas mixing device. The oxidizing gas may be one, two or more of oxygen, ozone, oxygen plasma and oxygen free radicals, so as to gradedly oxidize the surface of some nano-sized silicon particles to form nano-silicon oxide (SiO x , x≤2) surface passivation layer; 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-scale silicon particles can be graded oxidized, and finally SiO with a core-shell structure can be prepared. x (x≤2)@SiO2 composite nanoparticles.

[0023] 7. An embodiment of the present invention also provides a method for preparing a silicon-carbon nanocomposite material. By arranging a porous carbon fiber support in an electric arc furnace and placing porous carbon fibers into the porous carbon fiber support, silicon vapor can be allowed to penetrate into the porous carbon fibers under high temperature to form amorphous silicon. Rapid cooling is then used to cause amorphous silicon to deposit and grow on the surface of the porous carbon fibers to form a silicon-carbon nanocomposite material. At this time, observations using a transmission electron microscope (TEM) show that silicon particles of 20 nm to 50 nm are uniformly embedded in the porous carbon fibers, and the electrical conductivity can be increased to 300 times that of pure silicon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In various embodiments of the present application, it should be understood that the size of the sequence number of the above-mentioned processes does not mean the inevitable sequence of execution order, and the execution order 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.

[0034] 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 a 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 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 functions or operations, or can be implemented by a combination of special-purpose hardware and computer instructions.

[0035] The technical solutions of the present application will be described below.

[0036] Please refer to Figure 1 The embodiment of the present application provides a preparation method of nano-silicon, comprising the following steps: S1: providing an arc furnace with a built-in graphite electrode, passing a high-voltage power supply to the graphite electrode 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 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 is gasified in the high-temperature region to generate silicon vapor; S3: passing inert gas into the interior of the arc furnace, and the inert gas sends 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; S4: providing a filtering system to filter out nano-silicon powder from the nano-silicon particles and collect the nano-silicon powder.

[0037] In the preparation method of nano-silicon provided by the embodiment of the present application, the graphite electrode is passed through a high-voltage power supply to generate arc discharge and form a high-temperature environment for the reduction reaction of silicon dioxide and carbon, compared with the preparation of nano-silicon using a traditional heating method, a large amount of energy consumption is saved, and the preparation cost of nano-silicon is greatly reduced.

[0038] 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 embodiments must contain silicon dioxide, and the carbon source must contain carbon. By selecting silicon source and carbon source with low price and high purity, the raw material cost can be reduced in the embodiments. Compared with using silane gas to prepare nano-silicon, the quartz sand, silica and / or photovoltaic waste silicon are used in the embodiments, and the raw material cost can be reduced by 20 times when preparing the same yield of nano-silicon material.

[0039] It should be noted that in step S1, the high-temperature region is directly formed in the electric arc furnace by using high-voltage arc discharge technology by providing an electric arc furnace with a built-in graphite electrode. Only the silicon source and the carbon source mixed according to the molar ratio of silicon dioxide to carbon are sent into the high-temperature region to generate silicon and carbon dioxide gas through 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 embodiments.

[0040] In steps S1 and S2, when the reduction reaction of silicon dioxide and carbon at high temperature is generated in the electric arc furnace, 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, and through this design, harmful emissions can be effectively reduced, meeting the requirements of green production.

[0041] In step S3, inert gas is introduced into the interior of the electric arc furnace. The inert gas does not react with silicon vapor and 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 treatment in the cooling region. In the embodiments, the rate of introducing inert gas 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 silicon dioxide in the silicon source and 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 introducing inert gas. The inert gas can be argon or nitrogen, and is preferably nitrogen.

[0042] In step S4, the filtration system can filter the nano-silicon particles with larger particle size, and then obtain nano-silicon powder with uniform particle size. Since the high temperature formed by arc discharge in the electric arc furnace can make the reaction of silicon dioxide and carbon more complete, the nano-silicon powder obtained by using the filtration system has high purity. As an embodiment, the filtration system provided by the embodiments is a bag filter system.

[0043] The embodiment of the present application forms a high-temperature environment for the reduction reaction of silicon dioxide and carbon by high-voltage arc discharge technology, saves a large amount of energy consumption, reduces the preparation cost, and makes the reduction reaction of silicon dioxide and carbon at high temperature more complete by using an arc furnace. In the filtering and collecting process, the uniform particle size and high-purity nano silicon powder can be obtained by using a filtering system. Through the above technical scheme, the technical problems of the traditional nano silicon preparation method, such as high energy consumption, high cost, low purity of obtained nano silicon, and uneven particle size distribution, are solved.

[0044] Further, please refer to Figure 2 , the condensation treatment includes the following steps: 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; S32: A liquid nitrogen cold trap of -196℃ 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 amorphous silicon powder with an average particle size of 25nm to 35nm.

[0045] In the nano silicon 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 to condense the silicon vapor to generate nano silicon particles.

[0046] 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 arc furnace, and the silicon vapor and the carbon dioxide gas are sent to the cooling region through the heat-resistant conduit by the inert gas. Through this design, the silicon vapor can be prevented from condensing to form silicon particles before reaching the cooling region, thereby improving the yield of nano silicon.

[0047] It should be noted that the heat-resistant conduit has the characteristics of high thermal conductivity, electrical insulation, high temperature resistance, and oxidation resistance. The boron nitride conduit is preferably used for the inert gas, the silicon vapor, and the carbon dioxide gas to flow through.

[0048] It can be understood that the method for condensing the silicon vapor at high temperature is a vapor deposition method. In step S32, the liquid nitrogen cold trap of -196℃ is arranged in the cooling region to promote the silicon vapor to be rapidly cooled at a rate of at least 10 4 K / s, which can ensure that the particle size distribution of the amorphous silicon powder is uniform and improve the yield of nano silicon.

[0049] When the silicon vapor is cooled at a rate greater than 10 4When 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. In a preferred embodiment, the particle size of the quartz sand is 75 μm, and the particle size of the nano-carbon powder is 70 nm.

[0050] 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 60-90 μm, and the particle size of the nano-carbon powder is 40-100 nm. In a preferred embodiment, the particle size of the quartz sand is 75 μm, and the particle size of the nano-carbon powder is 70 nm.

[0051] In the preparation method of the nano-silicon provided by the embodiments 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 particle size of the nano-carbon powder is small, so that the reduction reaction is more complete, and the production rate is relatively high.

[0052] In some embodiments, the molar ratio of SiO2 to 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 embodiments of the present application can obtain amorphous silicon powder with an average particle size of 30±5 nm by using the raw material ratio. The performance parameters of the amorphous silicon powder obtained by using different raw material ratios are as follows: Table 1, specific surface area, gram capacity and initial efficiency of amorphous silicon powder obtained by using different raw material ratios

[0053] (1) When the molar ratio of SiO2 to C is 2:3, the specific surface area of the generated amorphous silicon powder is 415 m 2 / g, the gram capacity is 2870 mAh / g, and the initial efficiency is 93%; (2) When the molar ratio of SiO2 to C is 1:1, the specific surface area of the generated amorphous silicon powder is 400 m 2 / g, the gram capacity is 3100 mAh / g, and the initial efficiency is 90%; (3) When the molar ratio of SiO2 to C is 3:2, the specific surface area of the generated amorphous silicon powder is 420 m 2 / g, the gram capacity is 2750 mAh / g, and the initial efficiency is 87%.

[0054] It should be noted that the specific surface area, gram capacity and initial efficiency data reflect the good performance of the nano-silicon prepared by the embodiments of the present application in the field of lithium batteries. The specific surface area (unit m 2 / g) refers to the total area possessed by unit mass of material, usually refers to the specific surface area of materials such as powder, fiber and particle, and is generally obtained by a BET specific surface area tester; gram 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; the first efficiency (unit %) refers to the ratio of the discharge capacity to the charge capacity in the first charge-discharge process of the negative electrode material particles.

[0055] Further, the voltage for generating arc discharge in the electric arc furnace is 15kV to 25kV, the current is 60A to 100A, and the temperature of the high-temperature region is at least 1350℃.

[0056] In the preparation method of nanometer silicon 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.

[0057] As an optional implementation in the embodiment, the voltage for generating arc discharge in the electric arc furnace is 20kV, the current is 80A, and at this 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.

[0058] In some embodiments, the silicon source includes one, two or more of quartz sand, silica and photovoltaic waste silicon; and the carbon source includes one, two or more of nanometer carbon powder, coke powder, graphite and carbon black.

[0059] The preparation method of nanometer silicon 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 the reduction reaction can occur between a single silicon source or a composite silicon source and a single carbon source or a composite carbon source under high-temperature conditions. Through this design, it is not necessary to specially purchase and collect a single specific silicon source or carbon source, so that the utilization rate of raw materials can be improved, and cost reduction and benefit increase can be realized in the preparation of nanometer silicon.

[0060] 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 of quartz sand, silica and photovoltaic waste silicon as the silicon source, and the cost of raw materials used in the preparation of the same output of nanometer silicon material can be reduced by 20 times.

[0061] Please refer to Figure 1 and Figure 3 The embodiment of the present application also provides a preparation method of nanometer silicon oxide, and the preparation method of nanometer silicon oxide includes the above-mentioned preparation method of nanometer silicon; The preparation method of nanometer silicon oxide further includes the following steps after the execution of steps S1 to S2: F1: a gas mixing device is arranged between the high-temperature region and the cooling region; F2: inert gas is introduced into the interior of the electric arc furnace, and the inert gas carries the silicon vapor and the carbon dioxide gas to the gas mixing device; F3: the gas mixing device is supplied with an oxidizing gas, and the oxidizing gas includes one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, so that part of the surfaces of the nano-sized silicon particles are graded oxidized to form a surface passivation layer of nano-silicon oxide (SiO x , x≤2).

[0062] In the nano-silicon oxide preparation method provided by the embodiment of the application, the gas mixing device is arranged between the high-temperature region and the cooling region, and the gas mixing device is supplied with an oxidizing gas, which can be one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, so that part of the surfaces of the nano-sized silicon particles are graded oxidized to form a surface passivation layer of nano-silicon oxide (SiO x , x≤2). By supplying different concentrations of oxygen to the first section and the second section through the mixing section of the gas mixing device, the surfaces of the nano-sized silicon particles can be graded oxidized, and finally the SiO x (x≤2)@SiO2 composite nanoparticles with a core-shell structure can be prepared.

[0063] It should be noted that the core-shell structure is a special structure composed of nano-materials or micro-materials, and the core is coated with one or more layers of heterogeneous or homogeneous materials to form a shell. The core-shell structure tightly combines the core and the shell through electrostatic action or chemical bonds, and has unique physical and chemical properties.

[0064] Please refer to Figure 4 to grade-oxidize part of the surfaces of the nano-sized silicon particles, including the following steps: F31: a mixing section of the gas mixing device is provided, the mixing section includes a first section and a second section arranged in sequence, and the oxidizing gas supplied to the gas mixing device is oxygen; F32: 5vol% oxygen is supplied to the first section to generate a first passivation layer of SiO x (x≈0.8); F33: 15vol% oxygen is supplied to the second section to generate a SiO2 coating layer and a second passivation layer of SiO x (x≈0.8).

[0065] It can be understood that the first section and the second section for mixing oxygen arranged in sequence in step F31 can promote the surfaces of the nano-sized silicon particles to be oxidized in different types.

[0066] Specifically, in steps F32 and F33, when 5vol% oxygen is introduced into the first section, SiO is generated x (x≈0.8) the first passivation layer, when 15vol% oxygen is introduced into the second section, the first passivation layer can be further oxidized into a SiO2 coating layer and SiO x (x≈0.8) the second passivation layer, at this time, the material of the coating layer, SiO2, is SiO x (x≤2) the outer shell material in the SiO2 core-shell structure, the second passivation layer, SiO x (x≈0.8) SiO x (x≤2) the core material in the SiO2 core-shell structure.

[0067] It should be noted that the factors that promote the surface grading oxidation of the nanoscale silicon particles are: the volume percentage concentration of oxygen in air (i.e. 5vol% and 15vol% 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, a nanosilica composite material can be prepared.

[0068] Further, in some embodiments, the temperature of the first section is 400°C to 800°C, the concentration of the introduced oxygen is 5vol%, and finally SiO x (x≈0.8) the thickness of the first passivation layer is 8nm to 13nm. The temperature of the second section is 400°C and below, the concentration of the introduced oxygen is 15vol%, and finally the thickness of the SiO2 coating layer is 6nm to 10nm, and SiO x (x≈0.8) the thickness of the second passivation layer is 2nm to 3nm; wherein the average thickness of the SiO2 coating layer is 8nm.

[0069] Please refer to Figure 1 and Figure 5 The present embodiment also provides a silicon-carbon nanocomposite material preparation method, which comprises the above-mentioned nanosilicon preparation method. The silicon-carbon nanocomposite material preparation method further comprises the following steps after the execution of steps S1 to S2: P1: a porous carbon fiber support is arranged in the electric arc furnace, and the porous carbon fiber is placed into the porous carbon fiber support; P2: the current for generating electric arc discharge by introducing high-voltage power supply into the graphite electrode is set to be at least 120A, so that the silicon vapor permeates into the porous carbon fiber to form amorphous silicon; P3: the temperature of the electric arc furnace is controlled to be 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 fiber to form a silicon-carbon nanocomposite material.

[0070] It can be understood that the silicon-carbon nanocomposite material with high conductivity can be obtained by the preparation method of the embodiment, which combines the high activity of silicon and the good conductivity of carbon, and is suitable for the field of lithium ion battery negative materials and the like. In some embodiments, the porosity of the porous carbon fiber support is 85%, and the pore size is 50nm to 100nm.

[0071] Specifically, in steps P1 and P2, the porous carbon fiber support is arranged in the electric arc furnace, and the porous carbon fiber is placed in the porous carbon fiber support; the current set in the embodiment is at least 120A, so that the temperature inside the electric arc furnace reaches 1450℃ or above, which can promote the silicon vapor to penetrate into the porous carbon fiber to form amorphous silicon.

[0072] In step S3, the amorphous silicon is deposited and grown on the surface of the porous carbon fiber 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 amorphous silicon on the surface of the porous carbon fiber, so that the application range of the final silicon-carbon nanocomposite material is more extensive.

[0073] In some embodiments, the silicon-carbon nanocomposite material includes porous carbon fiber and silicon particles uniformly embedded in the porous carbon fiber, and the particle size of the silicon particles is 20nm to 50nm.

[0074] It should be noted that in the silicon-carbon nanocomposite material obtained by the preparation method provided in the embodiment, the transmission electron microscope (TEM) observation shows that the silicon particles with a particle size of 20nm to 50nm are uniformly embedded in the porous carbon fiber, and the conductivity can be increased to 300 times that of pure silicon material.

[0075] The preparation method of the nanosilicon, nanosilicon oxide and silicon-carbon nanocomposite material disclosed in the embodiment of the application is described in detail above, and specific examples are applied in this paper to describe the principles and implementation modes of the application. The above description of the embodiments is only used to help understand the method and core idea of the application. Meanwhile, for those skilled in the art, according to the idea of the application, the specific implementation mode and application range can be changed, and the above description of the application should not be understood as a limitation of the application. Any modification, equivalent replacement and improvement within the principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing nano-silicon, characterized in that: The following steps are involved: S1: Provide an arc furnace with built-in graphite electrodes. Apply high voltage power to the graphite electrodes to generate arc discharge, forming a high-temperature area. S2: Provide solid silicon source and carbon source, mix them in a molar ratio of silicon dioxide to carbon ranging from 2:3 to 3:2, and then send them into the high-temperature area to generate silicon and carbon dioxide through reduction reaction. The chemical equation is: SiO2+C→Si+CO2↑. The generated silicon is gasified in the high-temperature area to generate silicon vapor; S3: Inert gas is introduced into the interior of the electric arc furnace. The inert gas transports silicon vapor and carbon dioxide gas to the cooling area for condensation, causing the silicon vapor to condense into nano-sized silicon particles; S4: providing a filtering system to filter out nano-silicon powder from nano-sized silicon particles and collect the nano-silicon powder.

2. The method for preparing nano-silicon according to claim 1, wherein: The condensation process includes the following steps: S31: A heat-resistant conduit is provided between the high-temperature area and the cooling area, and the inert gas transports the silicon vapor and the carbon dioxide gas to the cooling area through the heat-resistant conduit; S32: A liquid nitrogen cold trap at -196°C is set in the cooling area. The liquid nitrogen cold trap causes the silicon vapor to be heated to at least 10 4 The amorphous silicon powder is cooled at a rate of K / s to generate an average particle size of 25nm to 35nm.

3. The method for preparing nano-silicon according to claim 2, wherein: The silicon source and 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; When the quartz sand and the nano-carbon powder are mixed, the molar ratio of silicon dioxide to carbon is 2:3, 1:1 or 3:

2.

4. The method for preparing nano-silicon according to claim 3, wherein: 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 in the high temperature zone is at least 1350°C.

5. The method for preparing nano-silicon according to claim 1, wherein: The silicon source includes one, two or more of quartz sand, silica stone and photovoltaic waste silicon; The carbon source includes one, two or more of nano carbon powder, coke powder, graphite and carbon black.

6. A method for preparing nano-silicon oxide, characterized in that: The method for preparing nano-silicon oxide comprises the method for preparing nano-silicon according to any one of claims 1 to 5; After executing steps S1 to S2, the method for preparing nano-silicon oxide further includes the following steps: F1: A gas mixing device is set between the high temperature area and the cooling area; F2: Inert gas is introduced into the interior of the electric arc furnace, and the inert gas transports silicon vapor and carbon dioxide gas to the gas mixing device; F3: The oxidizing gas is introduced into the gas mixing device. The oxidizing gas includes one, two or more of oxygen, ozone, oxygen plasma and oxygen free radicals, so that the surface of some nano-scale silicon particles is oxidized in stages to form nano-silicon oxide (SiO x , x≤2) surface passivation layer.

7. The method for preparing nano-silicon oxide according to claim 6, wherein: The surface of a portion of the nano-sized silicon particles is subjected to graded oxidation, comprising the following steps: F31: providing a mixing section of a gas mixing device, the mixing section comprising a first section and a second section arranged in sequence, and the oxidizing gas introduced by the gas mixing device is oxygen; F32: 5 vol% oxygen is introduced into the first section to generate SiO x (x≈0.8) first passivation layer; F33: In the second section, 15 vol% oxygen is introduced to form a SiO2 coating layer and SiO x (x≈0.8) second passivation layer.

8. The method for preparing nano-silicon oxide according to claim 7, wherein: The temperature of the first section is 800℃ to 400℃, generating SiO x (x≈0.8) the thickness of the first passivation layer is 8 nm to 13 nm; The temperature of the second section is 400℃ and below, and the thickness of the SiO2 coating layer is 6nm to 10nm. x (x≈0.8) The thickness of the second passivation layer is 2 nm to 3 nm.

9. A method for preparing a silicon-carbon nanocomposite material, characterized in that: The method for preparing a silicon-carbon nanocomposite material comprises the method for preparing nano-silicon according to any one of claims 1 to 5; After executing steps S1 to S2, the method for preparing the silicon-carbon nanocomposite material further comprises the following steps: P1: A porous carbon fiber support is set in an electric arc furnace, and porous carbon fibers are placed into the porous carbon fiber support; P2: Set the current of the arc discharge generated by the high-voltage power supply to at least 120A through the graphite electrode, so that the silicon vapor penetrates into the porous carbon fiber to form amorphous silicon; P3: At least 10 4 The cooling rate of 0.1K / s causes amorphous silicon to deposit and grow on the surface of the porous carbon fibers to form a silicon-carbon nanocomposite material.

10. The method for preparing the silicon-carbon nanocomposite material according to claim 9, wherein: The porous carbon fiber scaffold has a porosity of 85% and a pore size of 50nm to 100nm.

11. The method for preparing the silicon-carbon nanocomposite material according to claim 10, wherein: The silicon-carbon nanocomposite material comprises porous carbon fibers and silicon particles uniformly embedded in the porous carbon fibers, wherein the particle size of the silicon particles is 20 nm to 50 nm.

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