A method for preparing nanosilicon
Nano-silicon was prepared by molten metal reduction and advanced alcohol grafting techniques, which solved the problem of high impurity content in silicon oxide and achieved efficient and low-cost preparation of nano-silicon with small particle size and good crystallinity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2024-04-16
- Publication Date
- 2026-06-26
AI Technical Summary
Existing methods for preparing nano-silicon have problems such as high levels of silicon oxide impurities, high equipment costs, and high energy consumption. In particular, nano-silicon products prepared by the reaction ball milling method contain a large amount of silicon oxide impurities.
Nano-silicon was prepared by molten metal reduction. The reducing metal was kept in a molten state by heating and reacted with silicon halide. Mechanical stirring was used to increase the contact area. Hydrophobic higher alcohols were used to form chemical bonds with the nano-silicon to prevent oxidation. The nano-silicon was then separated.
The efficient preparation of nano-silicon has been achieved, with small particle size and good crystallinity, reducing silicon oxide impurities, simplifying the separation process, and reducing costs and energy consumption.
Smart Images
Figure CN118387878B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon material technology, and in particular to a method for preparing nano-silicon. Background Technology
[0002] Compared to other battery technologies, lithium-ion batteries offer advantages such as high energy density, long lifespan, high output voltage, low self-discharge rate, and wide operating temperature range, making them one of the most popular battery technologies today. However, the theoretical specific capacity of commonly used graphite anodes is only 372 mAh / g, limiting the application scenarios of lithium-ion batteries. Silicon, as the second most abundant element on Earth, boasts a theoretical specific capacity of 4200 mAh / g for silicon-based anodes, approximately 10 times that of graphite anodes. Furthermore, its theoretical operating voltage is about 0.4V. The lower operating potential, higher specific capacity, and lower pollution make silicon-based anodes one of the most promising next-generation anode materials. However, silicon-based anodes have not yet achieved large-scale application. They exhibit significant volume deformation (approximately 300%) during cycling, leading to volume expansion during charge and discharge. They also suffer from poor conductivity and rapid capacity decay.
[0003] To address the above issues, various scholars have made numerous attempts to modify and control the morphology and structure of silicon-based anode materials. These include nano-sizing and amorphizing silicon-based materials. Nano-sizing of silicon can significantly improve the performance of lithium-ion batteries. The unique morphology and structure of nano-silicon can effectively alleviate its volume expansion problem and improve the cycle life of the electrode. Moreover, nano-silicon has a large specific surface area, which can improve the electrode reaction rate and accelerate the charging and discharging process. Currently, the main methods for preparing nano-silicon are as follows: (1) Mechanical ball milling. This method uses the mechanical grinding pressure and shear force generated by the interaction between grinding balls to grind coarse silicon with large particle size into micron or even nano powder. This method has low raw material cost, mature technology, and large output, but it is energy-intensive and the particle size is large. (2) Molten salt electrolysis. This method prepares nano-silicon by electrolytic reduction of SiO2 in molten salt. Its raw material price is low, but the operating temperature is high and the equipment requirements are stringent. (3) Chemical vapor deposition. This method utilizes plasma-enhanced chemical vapor deposition to decompose SiH4 under vacuum conditions. After dehydrogenation and condensation, nano-silicon is finally obtained. This method has relatively mature technology and equipment, and can achieve control over the particle size and morphology of nano-silicon. However, the raw material cost is high, and the raw material is flammable and explosive. (4) Laser ablation method. This method uses a high-power laser to bombard a solid silicon target to produce nano-silicon particles. The nano-silicon prepared by this method has high purity and small particle size, but the preparation cost is high.
[0004] While the aforementioned methods can achieve silicon nano-sizing, they all have some drawbacks, such as large particle size and high equipment costs. In recent years, some researchers have proposed using reactive ball milling to prepare silicon nanoparticles. This method utilizes active metals or active metal hydrides such as Mg and MgH2 to reduce silicon raw materials such as SiO2 and SiCl4 at room temperature to obtain nano-silicon. The ball milling reaction method mainly involves mixing MgH2, Mg, etc., with SiO2 or SiCl4 in a ball mill jar for grinding. After grinding, the product is collected, washed with dilute acid and ethanol, and dried to obtain nano-silicon powder. This method utilizes mature ball milling technology to convert inexpensive SiCl4 into nano-silicon, significantly reducing the cost of nano-silicon preparation. Furthermore, ball milling is suitable for large-scale production, and the particle size of the nano-silicon product can be controlled by adjusting conditions such as the ball-to-material ratio, rotation speed, and raw material ratio during the ball milling reaction. However, most nano-silicon products prepared by reactive ball milling currently contain a significant amount of silicon oxide impurities. Summary of the Invention
[0005] Therefore, it is necessary to provide a method for preparing nano-silicon that can reduce silicon oxide impurities in the product.
[0006] A method for preparing nano-silicon includes the following steps:
[0007] A reducing metal and a silicon halide are mixed and heated under sealed conditions to keep the reducing metal in a molten state while stirring to obtain the reaction product.
[0008] The reaction product was mixed with a hydrophobic higher alcohol and allowed to stand to obtain a reaction mixture;
[0009] The reaction mixture was mixed with water and stirred, and allowed to stand to form an aqueous layer and a hydrophobic colloidal layer. The hydrophobic colloidal layer was obtained and dried to prepare nano-silicon.
[0010] In one embodiment, the higher alcohol is selected from one or more of n-pentanol, isopentanol, neopentanol, n-hexanol, isohexanol, n-heptanol, isoheptanol, n-octanol, and isooctanol.
[0011] In one embodiment, the reaction product is mixed with the higher alcohol and allowed to stand for 3 to 24 hours.
[0012] In one embodiment, the mass-to-volume ratio of the silicon halide to the higher alcohol is 1 g:(2-10) mL.
[0013] In one embodiment, the reaction mixture is stirred at a speed of 800–1400 r / min for a duration of 10–60 min after being mixed with water.
[0014] In one embodiment, the volume ratio of the above reaction mixture to water is 1:(1-5).
[0015] In one embodiment, the reducing metal is selected from one or more of lithium, sodium, magnesium, and aluminum.
[0016] In one embodiment, the silicon halide is selected from one or more of silicon chloride, silicon bromide, and silicon iodide.
[0017] In one embodiment, in the step of preparing the above reaction product, the target heating temperature is 100-200°C, the stirring speed is 200-500 r / min, and the stirring time is 1-8 h.
[0018] In one embodiment, the molar ratio of the silicon halide to the reducing metal is 1:(4-6).
[0019] The above-described solution of the present invention has the following beneficial effects:
[0020] This invention is based on the molten metal reduction method, using an active reducing metal and silicon halide as raw materials. The reducing metal is kept molten during the reaction by heating, and reacts with the silicon halide to prepare nano-silicon. By using the molten active metal reduction method to prepare nano-silicon, the metal remains molten during the reaction, lowering the reaction energy barrier and increasing the contact area between materials. Mechanical stirring continuously refreshes the surface of the molten metal, exposing fresh surfaces and enabling continuous reaction. Compared with other methods for preparing nano-silicon, such as ball milling, this method has advantages such as simple operation, low cost, low energy consumption, simple process flow, and high yield. Furthermore, the particle size of the nano-silicon can be controlled by adjusting experimental parameters, resulting in nano-silicon with good crystallinity and small particle size.
[0021] This invention employs a hydrophobic higher alcohol grafting method to protect and separate prepared nano-silicon. The higher alcohol reduces the surface activity of the nano-silicon, preventing oxidation during air or water washing and reducing the generation of silicon oxide impurities. Specifically, nano-silicon prepared by molten metal reduction has high surface energy. Grafting allows chemical bonds to form between the nano-silicon and the higher alcohol, thereby reducing the surface energy and preventing oxidation during air or water washing. Simultaneously, due to the small particle size of the prepared nano-silicon, separation by centrifugation or filtration is impossible. However, the chemical bond formed between the higher alcohol and nano-silicon creates a hydrophobic colloid that separates from the water layer. This allows for successful separation of the nano-silicon while removing sodium chloride through liquid-liquid separation, achieving highly efficient separation, simplifying the operation process, and the lower boiling point of the higher alcohol also facilitates recovery and reduces costs. Attached Figure Description
[0022] Figure 1 The XRD patterns of the reaction product and the washed product in Example 1 of this invention are shown.
[0023] Figure 2 This is a TEM image of the nano-silicon prepared in Example 1 of the present invention;
[0024] Figure 3 The Raman spectrum of the nano-silicon prepared in Example 1 of this invention;
[0025] Figure 4 This is a comparison of the yield, oxygen content, and sodium chloride content of the nano-silicon prepared in the embodiments and comparative examples of the present invention. Detailed Implementation
[0026] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0028] This invention addresses the existing problems by providing a method for preparing nano-silicon, which includes the following steps:
[0029] S1. Mix the reducing metal and silicon halide, heat under sealed conditions to keep the reducing metal in a molten state, and stir to obtain the reaction product.
[0030] S2. The above reaction product is mixed with a hydrophobic higher alcohol and allowed to stand to obtain a reaction mixture.
[0031] S3. Mix the above reaction mixture with water and stir, let it stand to form an aqueous layer and a hydrophobic colloidal layer, obtain the above hydrophobic colloidal layer and dry it to obtain nano-silicon.
[0032] Currently, most nano-silicon products prepared by reactive ball milling contain a large amount of silicon oxide impurities. The inventors have discovered through research that this is mainly because the nano-silicon prepared by reaction has a high surface energy, making it easy to be oxidized in air or during washing with dilute acid or ethanol, thus generating silicon oxide impurities.
[0033] The preparation method of this invention uses a reducing metal and silicon halide as reactants. The active reducing metal and silicon halide are added to a reaction vessel, and the mixture is heated to keep the reducing metal in a molten state during the reaction. Simultaneously, stirring is performed. The molten reducing metal reacts with the silicon halide, generating nano-silicon on the surface of the molten metal. The stirring continuously refreshes the surface of the active metal, promoting the reaction between the molten active metal and silicon halide. Furthermore, the larger contact area between the molten active metal and silicon halide during the reaction accelerates the reaction rate and improves the efficiency of nano-silicon preparation. The prepared nano-silicon exhibits good crystallinity and a small particle size.
[0034] After the reaction, the generated nano-silicon is highly reactive and easily oxidized. Therefore, this invention adds a hydrophobic higher alcohol to the reaction vessel to protect the generated nano-silicon. The highly reactive nano-silicon can form chemical bonds with the higher alcohol, reducing the surface energy and preventing the nano-silicon from being oxidized in air or during washing to form silicon oxide impurities. Simultaneously, because the prepared nano-silicon particles are small in size, they cannot be separated by centrifugation, filtration, or other methods. Using a hydrophobic higher alcohol allows for separation of the nano-silicon through extraction. After thoroughly mixing the reaction mixture with water, the sodium chloride in the reaction product dissolves in the water, while the higher alcohol is immiscible with water. The nano-silicon reacts with the higher alcohol to form a hydrophobic colloid. By separating the hydrophobic colloidal layer, the nano-silicon is separated, achieving successful separation of nano-silicon while removing sodium chloride. Finally, drying removes the solvent, yielding the finished nano-silicon product.
[0035] In a specific example, the aforementioned higher alcohol is selected from one or more of n-pentanol, isopentanol, neopentanol, n-hexanol, isohexanol, n-heptanol, isoheptanol, n-octanol, and isooctanol. Preferably, the aforementioned higher alcohol is n-pentanol, which has the shortest carbon chain among the series of higher alcohols, its hydroxyl group has higher reactivity, and the chemical bond formed with nano-silicon is stronger. It is more effective in preventing oxidation than other higher alcohols, and n-pentanol has the lowest boiling point among water-immiscible alcohols, facilitating the purification of nano-silicon and the recycling of n-pentanol.
[0036] In one specific example, the reaction product is allowed to stand for 3–24 hours after being mixed with the higher alcohol. If the standing time is too long, the n-pentanol and nano-silicon will form a viscous colloid that adheres to the inside of the reaction vessel, increasing the difficulty of separating the mixture, reducing the yield of nano-silicon, and hindering the separation of sodium chloride. If the standing time is too short, the n-pentanol will not be able to fully contact the reaction product, resulting in the loss of some nano-silicon during separation, reducing the yield of nano-silicon, and insufficient contact will also lead to the oxidation of some nano-silicon. More preferably, the reaction product is allowed to stand for 10–14 hours after being mixed with the higher alcohol.
[0037] In one specific example, the mass-to-volume ratio of silicon halide to higher alcohol is 1 g:2 mL to 1 g:10 mL. This ratio range allows n-pentanol to completely wet the reaction product. Under these conditions, n-pentanol can fully contact the generated nano-silicon and form chemical bonds, thus improving the yield of nano-silicon. More preferably, the mass-to-volume ratio of silicon halide to higher alcohol is 1 g:4 mL to 1 g:7 mL.
[0038] In a specific example, the reaction mixture is stirred at a speed of 800–1400 r / min and for a time of 10–60 min after being mixed with water. Within this stirring speed and time range, the mixture can be fully mixed with water, which accelerates the dissolution of sodium chloride in water and improves the purity of nano-silicon. At the same time, within this time range, the contact time between nano-silicon and water is short, which can reduce the degree of oxidation of nano-silicon.
[0039] In a specific example, the volume ratio of the reaction mixture to water is 1:1 to 1:5. Within this volume ratio range, sodium chloride can be effectively removed. Considering the solubility of sodium chloride in water, this volume ratio range can ensure that the reaction byproduct sodium chloride is completely dissolved in water, thereby improving the purity of nano-silicon.
[0040] Optionally, the silicon halide is selected from one or more of silicon chloride, silicon bromide, and silicon iodide, for example, it can be a mixture of any two or three of the above silicon halides. Preferably, the silicon halide is silicon chloride, which is mainly derived from a byproduct of the preparation of crystalline silicon, and is widely available and inexpensive.
[0041] Optionally, the reducing metal is selected from one or more of lithium, sodium, magnesium, and aluminum, for example, it can be a mixture or alloy of any two or three of the above metals. Preferably, the reducing metal is sodium, as sodium is a relatively inexpensive alkali metal element with strong reducing properties, and can react with silicon chloride to produce sodium chloride and silicon.
[0042] Preferably, in the step of preparing the above reaction product, the target heating temperature is 100-200°C, the stirring speed is 200-500 r / min, and the stirring time is 1-8 h.
[0043] Preferably, the molar ratio of silicon halide to reducing metal is 1:4 to 1:6, so that the silicon halide can react completely.
[0044] Preferably, step S3 can be repeated multiple times before drying, that is, the obtained hydrophobic colloidal layer is mixed with water and stirred again, and left to stand until the water layer and the hydrophobic colloidal layer are formed, thereby improving the removal effect of sodium chloride.
[0045] In a specific example, the drying method is vacuum oven drying. Optionally, the drying temperature is 60–150°C, preferably 70–90°C, and the drying time is 6–24 hours, preferably 10–14 hours. It is understood that the drying method is not limited to this; static drying, rotary evaporation drying, spray drying, etc., can also be selected.
[0046] Optionally, a filtration step is included before mixing the reaction mixture with water to filter out insoluble impurities.
[0047] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.
[0048] Example 1
[0049] First, add 10g of metallic sodium and 18g of silicon tetrachloride into the ball mill jar of the reaction vessel, mix them evenly, seal the jar, then turn on the stirring device, stir at a speed of 350r / min, and heat the reaction vessel to maintain the temperature at 150℃ for 4 hours to allow the sodium and silicon tetrachloride to react fully.
[0050] After the reaction was complete, the reaction vessel was opened, and 100 mL of n-pentanol was added to the ball mill jar. The mixture was allowed to stand for 12 hours to ensure sufficient contact between the n-pentanol and the reaction product. The mixture was then filtered to obtain a solution of the reaction product and n-pentanol. Distilled water was added to the solution at a volume ratio of 1:3, and the mixture was vigorously stirred for 30 minutes at a speed of 1000 rpm to ensure sufficient contact between the solution and the water. The mixture was then allowed to stand for 30 minutes to allow the hydrophobic colloid and water to separate into layers. The water and hydrophobic colloid were then separated by liquid-liquid extraction. This process was repeated three times to obtain a mixture of nano-silicon and n-pentanol with sodium chloride removed. The mixture was then dried in a vacuum oven at 80°C for 12 hours to remove the n-pentanol from the sample, yielding nano-silicon.
[0051] The prepared silicon nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy.
[0052] Specific equipment and parameters: XRD was performed using a TD-3500X X-ray diffractometer manufactured by Dandong Tongda Technology Co., Ltd., China, with a copper target as the Kα radiation source, a voltage of 35kV, a current of 30mA, a step size of 0.02, and a scanning range of 5–80°. TEM was performed using a FEI TECAI G2 F20 transmission electron microscope manufactured by FEI Corporation, USA, with an accelerating voltage of 200kV, a magnification of 25K–1030K, a point resolution of 0.24nm, and a line resolution of 0.102nm. Raman spectroscopy was performed using an inVia micro Raman spectrometer manufactured by Renishaw Corporation, Hong Kong, China, with a spectral range of 200nm–1000nm and a spectral resolution of 1cm. -1 .
[0053] Characterization results: such as Figure 1 The XRD pattern of the reaction product in Example 1 is shown. According to the XRD results, the initial reaction product contains silicon and sodium chloride, which proves the feasibility of the above method. The preparation of nano-silicon crystals can be successfully achieved by reducing silicon halide with molten metal. After washing, the product only has diffraction peaks of silicon and no diffraction peaks of sodium chloride, which proves that sodium chloride in the reaction product can be removed by washing with distilled water.
[0054] To further verify the grain size of the prepared nano-silicon, transmission electron microscopy (TEM) analysis was performed on the nano-silicon sample. The results are as follows: Figure 2 As shown, the prepared nano-silicon has a sheet-like structure of about 100 nm, proving that nano-silicon can be prepared by this method and that the nano-silicon particles are small in size.
[0055] like Figure 3 As shown in the Raman spectroscopy results, there are obvious Si-Si bond peaks in the prepared nano-silicon samples, which further proves that nano-silicon was successfully prepared. The Si-O bond peaks are relatively weak, indicating that the method of grafting with higher alcohols can reduce the oxidation of nano-silicon.
[0056] like Figure 4 As shown, the yield of nano-silicon prepared in Example 1 was 91%, the oxygen content in the sample was 5%, and the sodium chloride content was 1%, indicating that the nano-silicon prepared by the above method has high purity and yield.
[0057] Comparative Example 1
[0058] This comparative example is basically the same as Example 1, except that:
[0059] After the reaction was completed, the reaction vessel was opened and the cooled reaction product was washed with 0.1M hydrochloric acid, then washed with distilled water and ethanol to remove the reaction byproduct sodium chloride. The nano-silicon was then separated from the sodium chloride by centrifugation. The above operation was repeated 3 times. Finally, the product obtained by centrifugation was dried in a vacuum drying oven at 80℃ to remove excess solvent, thus obtaining nano-silicon.
[0060] like Figure 4 As shown, the oxygen content in the nano-silicon sample without n-pentanol grafting was approximately 42%, and the yield was 54%, both of which were inferior to Example 1. This indicates that under these experimental conditions, the oxidation of nano-silicon could not be prevented, and the separation effect of nano-silicon was poor.
[0061] Example 2
[0062] This embodiment is basically the same as Embodiment 1, except that:
[0063] After the reaction was completed, n-pentanol was added to the ball mill jar after opening the reaction vessel, and the mixture was allowed to stand for 24 hours.
[0064] like Figure 4 As shown, the yield under these experimental conditions was approximately 59%, which was lower than that of Example 1. This indicates that a longer settling time causes the reaction mixture to adhere to the inside of the reaction vessel, increasing the difficulty of separation and thus reducing the yield of nano-silicon.
[0065] Example 3
[0066] This embodiment is basically the same as Embodiment 1, except that:
[0067] After the reaction is complete, n-pentanol is added, wherein the mass-to-volume ratio of silicon chloride to n-pentanol is 1 g: 2 mL.
[0068] like Figure 4 As shown, the oxygen content of the product was 33% and the yield was 68%, both slightly lower than that of Example 1. This indicates that the reduced proportion of higher alcohols reduced the protective effect on nano-silicon and also hindered the separation of nano-silicon.
[0069] Example 4
[0070] This embodiment is basically the same as Embodiment 1, except that:
[0071] To remove sodium chloride from the reaction products, water is added to the reaction mixture in a volume ratio of 1:1.
[0072] like Figure 4 As shown, the sodium chloride content of this sample is 21%, which is higher than that in Example 1. This indicates that a decrease in the proportion of distilled water added will result in a poorer removal effect of sodium chloride.
[0073] Example 5
[0074] This embodiment is basically the same as Embodiment 1, except that:
[0075] During the process of removing excess n-pentanol, the temperature of the vacuum oven is 120℃.
[0076] like Figure 4 As shown, the oxygen content in the nano-silicon prepared under these experimental conditions is higher than that in Example 1. Compared with Example 1, the drying temperature of the product is higher than that in Example 1, indicating that a higher drying temperature will intensify the oxidation of nano-silicon.
[0077] In summary, this invention provides a method for preparing nano-silicon by mechanically stirring molten metal reduction of silicon halides. This method uses an active metal to reduce silicon halides to prepare nano-silicon, and employs heating to keep the active metal in a molten state during the reaction, lowering the reaction energy barrier and increasing the contact area between materials. Mechanical stirring continuously refreshes the surface of the molten metal, exposing fresh surfaces and enabling continuous reaction. Compared to methods such as ball milling, this method has advantages such as simple operation and low energy consumption. Furthermore, after the reaction, higher alcohol grafting is used to protect the nano-silicon. Since the prepared nano-silicon has high surface energy and is easily oxidized, higher alcohols can form chemical bonds with the nano-silicon surface to lower the surface energy. Simultaneously, the hydrophobicity of higher alcohols allows for efficient separation of the nano-silicon, and the low boiling point of higher alcohols facilitates their recycling, reducing costs. Therefore, this method can efficiently separate and protect nano-silicon, simplify the operation process, and reduce costs and silicon oxide impurities in the nano-silicon preparation process.
[0078] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing nano-silicon, characterized in that, Includes the following steps: A reducing metal and a silicon halide are mixed and heated under sealed conditions to keep the reducing metal in a molten state. The mixture is stirred to obtain a reaction product containing nano-silicon. The reaction product is mixed with a hydrophobic higher alcohol and allowed to stand, allowing the higher alcohol to graft onto the nano-silicon to reduce the surface energy of the nano-silicon, thus obtaining a reaction mixture; wherein the higher alcohol is selected from one or more of n-pentanol, isopentanol, neopentanol, n-hexanol, isohexanol, n-heptanol, isoheptanol, n-octanol, and isooctanol; the reaction product is allowed to stand for 3 to 24 hours after mixing with the higher alcohol; The reaction mixture is mixed with water and stirred, and allowed to stand to form an aqueous layer and a hydrophobic colloidal layer. The hydrophobic colloidal layer is then obtained and dried to prepare the nano-silicon.
2. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the silicon halide to the higher alcohol is 1 g:(2~10) mL.
3. The preparation method according to claim 1, characterized in that, The reaction mixture is stirred at a speed of 800~1400 r / min for a time of 10~60 min after being mixed with water.
4. The preparation method according to claim 1, characterized in that, The volume ratio of the reaction mixture to water is 1:(1~5).
5. The preparation method according to claim 1, characterized in that, The reducing metal is selected from one or more of lithium, sodium, magnesium, and aluminum.
6. The preparation method according to claim 1, characterized in that, The silicon halide is selected from one or more of silicon chloride, silicon bromide, and silicon iodide.
7. The preparation method according to claim 1, characterized in that, In the step of preparing the reaction product, the target heating temperature is 100~200℃, the stirring speed is 200~500r / min, and the stirring time is 1~8h.
8. The preparation method according to any one of claims 1 to 7, characterized in that, The molar ratio of the silicon halide to the reducing metal is 1:(4~6).