Preparation method of nano silicon oxide

Abstract

The preparation method 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 range of 2: 3 to 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; after the step S1 and the step S2 are executed, the method further comprises the following steps that F1, a gas mixing device is arranged between the high-temperature area and the cooling area; f2, inert gas is introduced into the electric arc furnace, and silicon steam and carbon dioxide gas are conveyed to a gas mixing device through the inert gas; and F3, introducing oxidizing gas into the gas mixing device, so that the surfaces of part of the nanoscale silicon particles are oxidized in a graded manner, and a nano silicon oxide (SiOx, x is smaller than or equal to 2) surface passivation layer is formed.

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 oxide. 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 preparation method of nanometer silicon 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 the 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 the 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, it can be seen that 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, high preparation cost, inability to simultaneously prepare nanometer silicon, low purity of nanometer silicon, and uneven particle size distribution of the traditional preparation method of nanometer silicon oxide, the present application provides a preparation method of nanometer silicon oxide.

[0006] The technical problem of the present application is solved by providing a method for preparing nano-silicon oxide, comprising the following steps: S1: providing an electric arc furnace with a built-in graphite electrode, and passing a high-voltage power supply to 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 a molar ratio of silicon dioxide to carbon ranging from 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 vaporizes in the high-temperature region to generate silicon vapor; 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 a cooling region for condensation treatment, so that the silicon vapor condenses to generate nano-silicon particles; S4: providing a filtration system to filter out nano-silicon powder from the nano-silicon particles and collect the nano-silicon powder; after steps S1 to S2 are performed, the method further comprises the following steps: F1: providing a gas mixing device between the high-temperature region and the cooling region; F2: 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 gas mixing device; F3: passing oxidizing gas, including one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, into the gas mixing device, so that part of the nano-silicon particles are surface-graded oxidized to form a surface passivation layer of nano-silicon oxide (SiO x , x≤2).

[0007] Preferably, the condensation treatment comprises the following steps: S31: providing a heat-resistant conduit between the high-temperature region and the cooling region, and the inert gas sends the silicon vapor and carbon dioxide gas to the cooling region through the heat-resistant conduit; S32: providing 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 25nm to 35nm.

[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 60μm to 90μm, and the particle size of the nano-carbon powder is 40nm to 100nm; 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.

[0009] Preferably, the voltage for generating electric 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℃.

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

[0011] Preferably, the surface of part of the nanoscale silicon particles is 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 into the gas mixing device is oxygen; F32: introducing 5vol% oxygen into the first section to generate SiO x (x=0.8) first passivation layer; F33: introducing 15vol% oxygen into the second section to generate a SiO2 coating layer and SiO x (x=0.8) second passivation layer.

[0012] Preferably, the temperature of the first section is 800-400℃, generating SiO x (x=0.8) first passivation layer is 8-13nm; the temperature of the second section is 400℃ or below, generating a SiO2 coating layer with a thickness of 6-10nm, and SiO x (x=0.8) second passivation layer is 2-3nm.

[0013] Compared with the prior art, the preparation method of nanoscale silicon oxide provided by the application has the following advantages: 1. The preparation method of nanoscale silicon oxide provided by the embodiment of the application saves a large amount of energy consumption and reduces the preparation cost compared with the preparation of nanoscale silicon using a traditional heating method by introducing a high-voltage power supply into a graphite electrode to generate electric arc discharge to form a high-temperature environment for the reduction reaction of silicon dioxide and carbon; the filtering system can filter nanoscale silicon particles with a larger particle size to obtain nanoscale silicon powder with uniform particle size; the high temperature formed by electric arc discharge in the electric arc furnace can make the reaction of silicon dioxide and carbon more complete, and the nanoscale silicon powder obtained by using the filtering system has high purity. Further, a gas mixing device is arranged between the high-temperature region and the cooling region, and an oxidizing gas is introduced into the gas mixing device, which can be one, two or more of oxygen, ozone, oxygen plasma and oxygen radicals, to oxidize part of the surface of the nanoscale silicon particles and form a nanoscale silicon oxide (SiO x , x≤2) surface passivation layer; by arranging a mixing section of the gas mixing device, different concentrations of oxygen are introduced into the first section and the second section to cause the surface of the nanoscale silicon particles to be graded oxidation, and finally a SiO x (x≤2)@SiO2 composite nanoparticles with core-shell structure can be prepared.

[0014] 2. In the method for preparing nano-silicon oxide provided in this embodiment of the invention, a heat-resistant conduit is set between the high-temperature region and the cooling region. Inert gas is used to deliver silicon vapor and carbon dioxide gas to the cooling region through the heat-resistant conduit. This design can prevent silicon vapor from condensing into silicon particles before reaching the cooling region, thereby improving the yield of nano-silicon. By setting a liquid nitrogen cold trap at -196°C in the cooling region, the silicon vapor is encouraged to evaporate at a rate of at least 10... 4 Rapid cooling at a rate of K / s ensures uniform particle size distribution of amorphous silicon powder, further improving the yield of nano-silicon.

[0015] 3. In the preparation method of nano-silica provided in the embodiments of the present invention, when the silicon source and carbon source are quartz sand and nano-carbon powder respectively, since quartz sand is a powder material and nano-carbon powder has a smaller particle size, it participates in the reduction reaction more completely, and is inexpensive and has a relatively high yield.

[0016] 4. In the method for preparing nano-silica provided in the embodiments of the present invention, 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 raised to 1350°C, making the reduction reaction of silicon dioxide and carbon more complete. Furthermore, when the input current and voltage are increased, the temperature of the high-temperature region can continue to rise, thereby increasing the content of silicon vapor in the reaction products.

[0017] 5. In the preparation method of nano-silicon oxide provided in the embodiments of the present invention, silicon and carbon sources with low price and high purity are mainly selected to reduce the cost of raw materials. Compared with the preparation of nano-silicon using silane gas, the embodiments of the present invention use one, two or more silicon sources from quartz sand, silica and photovoltaic waste silicon. When preparing the same amount of nano-silicon material, the cost of raw materials used can be reduced by 20 times. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of steps S1 to S4 in a method for preparing nano-silicon provided in an embodiment of the present invention.

[0020] Figure 2 This is a schematic flowchart of steps S31 to S32 in a method for preparing nano-silicon provided in an embodiment of the present invention.

[0021] Figure 3This is a schematic flowchart of steps F1 to F3 in a method for preparing nano-silica provided in an embodiment of the present invention.

[0022] Figure 4 This is a flowchart illustrating steps F31 to F33 in a method for preparing nano-silica provided in an embodiment of the present invention.

[0023] Figure 5 This is a schematic flowchart of steps P1 to P3 in a method for preparing silicon-carbon nanocomposite materials provided in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] In the embodiments provided by this invention, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B solely based on A; B can also be determined based on A and / or other information.

[0026] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, 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 recognize that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily essential to the invention.

[0027] In various embodiments of the present invention, it should be understood that the sequence number of each process does not necessarily imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0028] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. It is particularly important to note that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0029] The technical solution of the present invention will be described below.

[0030] Please see Figure 1 This invention provides a method for preparing nano-silicon, comprising the following steps: S1: An electric arc furnace with built-in graphite electrodes, through which a high-voltage power supply is applied to the graphite electrodes to generate an electric arc discharge, forming a high-temperature zone; S2: Provides solid silicon and carbon sources. After mixing silicon dioxide and carbon in a molar ratio of 2:3 to 3:2, it is sent to a high-temperature region and generates silicon and carbon dioxide through a reduction reaction. The chemical equation is: SiO2+C→Si+CO2↑. The generated silicon vaporizes in the high-temperature region to generate silicon vapor. S3: Inert gas is introduced into the interior of the electric arc furnace. The inert gas sends silicon vapor and carbon dioxide gas to the cooling zone for condensation treatment, so that the silicon vapor is condensed to generate nano-sized silicon particles. S4: Provides a filtration system to filter out nano-silicon powder from nano-sized silicon particles and collect the nano-silicon powder.

[0031] In the nano-silicon preparation method provided in this embodiment of the invention, an arc discharge is generated by passing a high voltage power supply to the graphite electrode, forming a high-temperature environment for silicon dioxide and carbon to undergo a reduction reaction. Compared with the traditional heating method for preparing nano-silicon, this method saves a lot of energy consumption and greatly reduces the preparation cost of nano-silicon.

[0032] 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 this embodiment must contain silicon dioxide, and the carbon source must contain carbon. This embodiment can reduce raw material costs by selecting inexpensive and high-purity silicon and carbon sources. Compared with the preparation of nano-silicon using silane gas, the present invention uses quartz sand, silica, and / or photovoltaic waste silicon, which can reduce the raw material cost by 20 times when preparing the same amount of nano-silicon material.

[0033] It should be noted that in step S1, by providing an electric arc furnace with built-in graphite electrodes, a high-temperature region is directly formed in the electric arc furnace using high-voltage electric arc discharge technology. It is only necessary to mix the silicon source and carbon source according to the molar ratio of silicon dioxide to carbon and then send them 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 relatively complete, the embodiments of the present invention can use the aforementioned low-cost and high-purity silicon source and carbon source.

[0034] In steps S1 and S2, when silicon dioxide and carbon undergo a reduction reaction at high temperature in an electric arc furnace to generate silicon and carbon dioxide gas, the generated silicon will vaporize in the high-temperature region to generate silicon vapor, which will facilitate the next process. The entire reaction process is carried out in a closed manner in the electric arc furnace. This design can effectively reduce harmful emissions and meet the requirements of green production.

[0035] In step S3, an inert gas is introduced into the electric arc furnace. This inert gas does not react with silicon vapor and carbon dioxide gas and is used to deliver the silicon vapor and carbon dioxide gas to the cooling zone. Condensation of the silicon vapor in the cooling zone allows it to condense into nanoscale silicon particles. In embodiments of the present invention, the rate at which the inert gas is introduced into the electric arc furnace needs to be adjusted according to actual conditions. A low rate will not effectively deliver the silicon vapor and carbon dioxide gas to the cooling zone, affecting the condensation effect of the silicon vapor. A high rate may result in incomplete reaction between the silicon dioxide in the silicon source and the carbon in the carbon source. Therefore, the size of the electric arc furnace, the distance between the high-temperature zone and the cooling zone, and the rate of the reduction reaction need to be considered to determine the rate at which the inert gas is introduced. The inert gas can be argon or nitrogen, preferably nitrogen.

[0036] In step S4, the filtration system can filter out larger nano-sized silicon particles, thereby obtaining nano-silicon powder with uniform particle size. Because the high temperature generated by the electric arc discharge in the electric arc furnace allows for a more complete reaction between silicon dioxide and carbon, the nano-silicon powder obtained by using the filtration system ultimately has a high purity. As one embodiment, the filtration system provided in this invention is a bag filter system.

[0037] This invention utilizes high-voltage arc discharge technology to create a high-temperature environment for the reduction reaction of silicon dioxide and carbon, saving significant energy consumption and reducing preparation costs. Using an electric arc furnace allows for a more complete reduction reaction of silicon dioxide and carbon at high temperatures. During filtration and collection, a filtration system can be used to obtain nano-silicon powder with uniform particle size and high purity. This technical solution solves the problems of high energy consumption, high cost, and low purity and uneven particle size distribution of traditional nano-silicon preparation methods.

[0038] For further details, please refer to Figure 2 The condensation process includes the following steps: S31: A heat-resistant conduit is installed between the high-temperature zone and the cooling zone, and inert gas is used to deliver silicon vapor and carbon dioxide gas to the cooling zone through the heat-resistant conduit. S32: A liquid nitrogen cold trap at -196°C is installed in the cooling area, which causes the silicon vapor to vaporize at a rate of at least 10... 4 Cooling at a rate of K / s produces amorphous silicon powder with an average particle size of 25 nm to 35 nm.

[0039] In the nano-silicon preparation method provided in this embodiment of the invention, condensation treatment refers to the process of dissolving silicon vapor at a temperature of at least 10°C. 4 Rapid cooling at a rate of K / s causes silicon vapor to condense and form nanoscale silicon particles.

[0040] Specifically, in step S31, an inert gas is introduced into the electric arc furnace by setting a heat-resistant conduit between the high-temperature zone and the cooling zone. The inert gas then carries silicon vapor and carbon dioxide gas to the cooling zone through the heat-resistant conduit. This design can prevent silicon vapor from condensing into silicon particles before it reaches the cooling zone, thereby improving the yield of nano-silicon.

[0041] It should be noted that the heat-resistant conduit has properties such as high thermal conductivity, electrical insulation, high temperature resistance and oxidation resistance. In the embodiments of the present invention, boron nitride conduit is preferably used to allow the flow of inert gas, silicon vapor and carbon dioxide gas.

[0042] Understandably, the method used to condense silicon vapor at high temperatures is vapor deposition. In step S32, by setting up a liquid nitrogen cold trap at -196°C in the cooling zone, the silicon vapor is condensed at a rate of at least 10... 4 Rapid cooling at a rate of K / s can ensure uniform particle size distribution of amorphous silicon powder and improve the yield of nano-silicon.

[0043] Among them, when silicon vapor is greater than 10 4When cooled at a rate of K / s, the particle size of the generated amorphous silicon powder is more concentrated, which further improves the final yield of nano-silicon. Specifically, this can be achieved by increasing the contact area between liquid nitrogen and silicon vapor, or by setting up a liquid nitrogen cold trap with a temperature below -196℃ to achieve a higher silicon vapor cooling rate.

[0044] In some embodiments, the silicon source and the carbon source are quartz sand and carbon nanoparticles, respectively, with the quartz sand having a particle size of 60 μm to 90 μm and the carbon nanoparticles having a particle size of 40 nm to 100 nm; as a preferred embodiment of this embodiment, the quartz sand has a particle size of 75 μm and the carbon nanoparticles have a particle size of 70 nm.

[0045] In the nano-silicon preparation method provided in this embodiment of the invention, when the silicon source and carbon source are quartz sand and nano-carbon powder respectively, since quartz sand is a powder material and nano-carbon powder has a smaller particle size, it participates in the reduction reaction more completely, and is inexpensive and has a relatively high yield.

[0046] In some embodiments, when silica sand and nano-carbon powder are mixed, the molar ratio of silicon dioxide (SiO2) to carbon (C) is 2:3, 1:1, or 3:2. The preparation method of this embodiment can obtain amorphous silicon powder with an average particle size of 30±5 nm using this raw material ratio. The relevant performance parameters of the amorphous silicon powder obtained by different raw material ratios are as follows: Table 1. Specific surface area, specific capacity, and first-efficiency parameters of amorphous silicon powder obtained with different raw material ratios.

[0047] (1) When the molar ratio of silicon dioxide to carbon is 2:3, the specific surface area of ​​the generated amorphous silicon powder is 415 m². 2 / g, with a capacity of 2870mAh / g and an initial efficiency of 93%; (2) When the molar ratio of silicon dioxide to carbon is 1:1, the specific surface area of ​​the generated amorphous silicon powder is 400 m². 2 / g, with a capacity of 3100mAh / g and an initial efficacy of 90%; (3) When the molar ratio of silicon dioxide to carbon is 3:2, the specific surface area of ​​the generated amorphous silicon powder is 420 m². 2 / g, with a capacity of 2750mAh / g and an initial efficacy of 87%.

[0048] It should be noted that the above data on specific surface area, specific capacity, and initial efficiency reflect the excellent performance of the nano-silicon prepared in the embodiments of this invention in the field of lithium batteries. Specific surface area (unit: m²) 2Specific surface area ( / g) refers to the total surface area per unit mass of material, usually referring to the specific surface area of ​​materials such as powders, fibers, and granules, which is generally obtained by a BET specific surface area tester; 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; First-time efficiency (unit %) refers to the ratio of the discharge capacity to the charging capacity of the negative electrode material particles during the first charge and discharge process.

[0049] Furthermore, 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 zone is at least 1350℃.

[0050] In the nano-silicon preparation method provided in this embodiment of the invention, by setting the voltage and current of the electric arc furnace to generate an electric arc discharge, the temperature of the high-temperature area inside the electric arc furnace can be increased to 1350°C, making the reduction reaction of silicon dioxide and carbon more complete.

[0051] As an optional implementation method in this embodiment, the voltage for generating an arc discharge in the electric arc furnace is 20kV and the current is 80A, at which point the temperature of the high-temperature region rises to 1350℃. It should be noted that by increasing the input current and voltage, the temperature of the high-temperature region can continue to rise, thereby increasing the silicon vapor content in the reaction products.

[0052] In some embodiments, the silicon source includes one, two, or more of quartz sand, silica, and photovoltaic waste silicon; the carbon source includes one, two, or more of nano-carbon powder, coke powder, graphite, and carbon black.

[0053] The nano-silicon preparation method provided in this invention selects inexpensive and high-purity silicon and carbon sources to reduce raw material costs. Understandably, the chemical substances participating in the reaction within the silicon and carbon sources are silicon dioxide and carbon, respectively. Therefore, reduction reactions can occur between single or composite silicon sources, and between single or composite carbon sources, under high-temperature conditions. This design eliminates the need to specifically purchase or collect a single silicon or carbon source, thereby improving raw material utilization and achieving cost reduction and efficiency improvement in the preparation of nano-silicon.

[0054] It should be noted that, compared with the preparation of nano-silicon using silane gas, the embodiments of the present invention use one, two or more silicon sources from quartz sand, silica and photovoltaic waste silicon. When preparing the same amount of nano-silicon material, the cost of raw materials used can be reduced by 20 times.

[0055] Please see Figure 1 and Figure 3 The present invention also provides a method for preparing nano-silicon oxide, which includes the above-described method for preparing nano-silicon. The method for preparing nano-silica also includes the following steps after performing steps S1 to S2: F1: A gas mixing device is installed between the high-temperature zone and the cooling zone; F2: Inert gas is introduced into the interior of the electric arc furnace, and the inert gas sends the silicon vapor and carbon dioxide gas to the gas mixing device. F3: An 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, causing graded oxidation of the surface of some nanoscale silicon particles to form nano-silicon oxide (SiO₂). x Surface passivation layer (x≤2).

[0056] In the method for preparing nano-silicon oxide provided in this invention, a gas mixing device is set between the high-temperature region and the cooling region, and an oxidizing gas is introduced into the gas mixing device. The oxidizing gas can be one, two, or more of oxygen, ozone, oxygen plasma, and oxygen free radicals, so as to cause the surface of some nano-sized silicon particles to be oxidized in stages to form nano-silicon oxide (SiO2). x (x≤2) Surface passivation layer; by setting a mixing section of the gas mixing device, different concentrations of oxygen are introduced into the first and second sections, which can cause hierarchical oxidation of the surface of nanoscale silicon particles, and finally prepare SiO with a core-shell structure. x (x≤2)@SiO2 composite nanoparticles.

[0057] It should be noted that a core-shell structure is a special structure composed of nanomaterials or micromaterials, in which the core is covered by one or more layers of heterogeneous or homogeneous materials to form an outer shell. The core-shell structure tightly binds the core and the outer shell through electrostatic interactions or chemical bonds, and has unique physicochemical properties.

[0058] Please see Figure 4 The process involves hierarchical oxidation of the surface of some nanoscale silicon particles, including the following steps: F31: Provides a mixing section for a gas mixing device, the mixing section including a first section and a second section arranged sequentially, and the oxidizing gas introduced into the gas mixing device is oxygen. F32: Introduce 5 vol% oxygen in the first section to generate SiO2. x (x≈0.8) First passivation layer; F33: In the second section, 15 vol% oxygen is introduced to generate a SiO2 coating layer and SiO2. x (x≈0.8) Second passivation layer.

[0059] Understandably, setting the first and second sections in step F31 to mix in oxygen can promote different types of oxidation on the surface of nanoscale silicon particles.

[0060] Specifically, in steps F32 and F33, SiO is generated when 5 vol% oxygen is introduced into the first section. x (x≈0.8) The first passivation layer, when 15 vol% oxygen is introduced into the second section, can be further oxidized into a SiO2 coating layer and a SiO2 coating layer. x (x≈0.8) Second passivation layer, where the coating material SiO2 serves as SiO x (x≤2) The outer shell material in the SiO2 core-shell structure, the second passivation layer SiO x (x≈0.8) as SiO x (x≤2) The core material in the SiO2 core-shell structure.

[0061] It should be noted that the factors that promote the hierarchical oxidation of the surface of nanoscale silicon particles are: the volume percentage concentration of oxygen in the air (i.e., 5 vol% and 15 vol% in this embodiment), and the temperature of the first and second sections; by adjusting the oxygen concentration and the temperature of the oxygen supply section, a composite material of nanoscale silicon oxide can be prepared.

[0062] Furthermore, in some embodiments, the temperature of the first section is 400°C to 800°C, the oxygen concentration is 5 vol%, and SiO is ultimately generated. 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℃ or below, the oxygen concentration is 15 vol%, and the final SiO2 coating layer has a thickness of 6 nm to 10 nm. x (x≈0.8) The thickness of the second passivation layer is 2nm to 3nm; among which, the average thickness of the SiO2 coating layer is 8nm.

[0063] Please see Figure 1 and Figure 5 The present invention also provides a method for preparing silicon-carbon nanocomposite materials, which includes the above-mentioned method for preparing nano-silicon. The method for preparing silicon-carbon nanocomposites, after performing steps S1 to S2, also includes the following steps: P1: Set up a porous carbon fiber support in the electric arc furnace and put porous carbon fiber into the porous carbon fiber support. P2: Set the current to at least 120A to generate an arc discharge by applying a high voltage power supply to the graphite electrode, so that silicon vapor can penetrate into the porous carbon fiber to form amorphous silicon. P3: with at least 10 4 Cooling at a rate of K / s causes amorphous silicon to deposit and grow on the surface of porous carbon fibers, forming silicon-carbon nanocomposite materials.

[0064] Understandably, the preparation method of this embodiment can obtain silicon-carbon nanocomposite materials with high electrical conductivity. This composite material combines the high activity of silicon with the good conductivity of carbon, making it suitable for applications such as lithium-ion battery anode materials. In some embodiments, the porous carbon fiber scaffold has a porosity of 85% and a pore size of 50 nm to 100 nm.

[0065] Specifically, in steps P1 and P2, a porous carbon fiber support is set inside the electric arc furnace, and porous carbon fiber is placed into the porous carbon fiber support; the current set in this embodiment of the invention is at least 120A, so that the temperature inside the electric arc furnace reaches 1450°C or above, which can promote the permeation of silicon vapor into the porous carbon fiber to form amorphous silicon.

[0066] In step S3, amorphous silicon is deposited and grown on the surface of porous carbon fibers by rapid cooling to form silicon-carbon nanocomposite materials. It can be understood that the higher the cooling rate, the faster the amorphous silicon is deposited and grown on the surface of porous carbon fibers, which makes the application range of silicon-carbon nanocomposite materials wider.

[0067] In some embodiments, the silicon-carbon nanocomposite material includes 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.

[0068] It should be noted that, in the silicon-carbon nanocomposite material obtained by the preparation method provided in this embodiment, the silicon particles of 20 nm to 50 nm are uniformly embedded in the porous carbon fibers as observed by transmission electron microscopy (TEM), and the electrical conductivity can be increased to 300 times that of pure silicon material.

[0069] The preparation method of nano-silicon, nano-silicon oxide, and silicon-carbon nanocomposite materials disclosed in the embodiments of the present invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nano-silica, characterized in that, Includes the following steps: S1: An electric arc furnace with built-in graphite electrodes, through which a high-voltage power supply is applied to the graphite electrodes to generate an electric arc discharge, forming a high-temperature zone; S2: Provides solid silicon and carbon sources. After mixing them with a molar ratio of silicon dioxide to carbon ranging from 2:3 to 3:2, they are sent to a high-temperature region. Silicon and carbon dioxide are generated through a reduction reaction. The chemical equation is: SiO2+C→Si+CO2↑. The generated silicon vaporizes in the high-temperature region to generate silicon vapor. S3: Inert gas is introduced into the interior of the electric arc furnace. The inert gas sends silicon vapor and carbon dioxide gas to the cooling zone for condensation treatment, so that the silicon vapor is condensed to generate nano-sized silicon particles. S4: Provides a filtration system to filter out nano-silicon powder from nano-sized silicon particles and collect the nano-silicon powder; After performing steps S1 to S2, the following steps are also included: F1: A gas mixing device is installed between the high-temperature zone and the cooling zone; F2: Inert gas is introduced into the interior of the electric arc furnace, and the inert gas sends the silicon vapor and carbon dioxide gas to the gas mixing device. F3: An 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, causing graded oxidation of the surface of some nanoscale silicon particles to form nano-silicon oxide (SiO₂). x Surface passivation layer (x≤2).

2. The method for preparing nano-silica as described in claim 1, characterized in that, The condensation process includes the following steps: S31: A heat-resistant conduit is installed between the high-temperature zone and the cooling zone, and inert gas is used to deliver silicon vapor and carbon dioxide gas to the cooling zone through the heat-resistant conduit. S32: A liquid nitrogen cold trap at -196°C is installed in the cooling area, which causes the silicon vapor to vaporize at a rate of at least 10... 4 Cooling at a rate of K / s produces amorphous silicon powder with an average particle size of 25 nm to 35 nm.

3. The method for preparing nano-silica as described in claim 2, characterized in that: The silicon source and carbon source are quartz sand and carbon nanoparticles, respectively. The particle size of the quartz sand is 60μm to 90μm, and the particle size of the carbon nanoparticles is 40nm to 100nm. When silica sand and nano-carbon powder are mixed, the molar ratio of silica to carbon is 2:3, 1:1 or 3:

2.

4. The method for preparing nano-silica as described in claim 3, characterized in that: The voltage for generating arc discharge in the electric arc furnace is 15kV to 25kV, the current is 60A to 100A, and the temperature in the high-temperature zone is at least 1350℃.

5. The method for preparing nano-silica as described in claim 1, characterized in that: Silicon sources include one, two, or more of the following: quartz sand, silica, and photovoltaic waste silicon. Carbon sources include one, two, or more of the following: nano-carbon powder, coke powder, graphite, and carbon black.

6. The method for preparing nano-silica as described in claim 1, characterized in that, The process of hierarchical oxidation of the surface of some nanoscale silicon particles includes the following steps: F31: Provides a mixing section for a gas mixing device, the mixing section including a first section and a second section arranged sequentially, and the oxidizing gas introduced into the gas mixing device is oxygen. F32: Introduce 5 vol% oxygen in the first section to generate SiO2. x (x≈0.8) First passivation layer; F33: In the second section, 15 vol% oxygen is introduced to generate a SiO2 coating layer and SiO2. x (x≈0.8) Second passivation layer.

7. The method for preparing nano-silica as described in claim 6, characterized in that: The temperature in the first section is from 800℃ to 400℃, during which SiO is generated. x (x≈0.8) The thickness of the first passivation layer is 8nm to 13nm; The temperature in the second section is 400℃ or below, resulting in a SiO2 coating layer with a thickness of 6nm to 10nm. x (x≈0.8) The thickness of the second passivation layer is 2nm to 3nm.

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