A nano silicon-carbon composite material and SiF 4 Method for preparing nano silicon-carbon composite material

Abstract

The present invention discloses a nano-silicon-carbon composite material and a method for preparing the nano-silicon-carbon composite material by SiF4, which solves the problems of poor dispersion, low concentration and high energy consumption existing in the preparation of the existing nano-silicon-carbon composite material. The technical solution is to hydrolyze the purified SiF4 gas into an aqueous solution containing an additive to generate a slurry containing nano-SiO2 and fluoride salts. The solid matter separated after the slurry is aged and filtered is washed and then a carbon source is added for surface modification of SiO2 to obtain a modified SiO2 slurry. The modified nano-SiO2 slurry is dried to obtain modified nano-SiO2 powder, and the modified nano-SiO2 powder is carbonized under air isolation conditions to finally obtain the nano-silicon-carbon composite material. The nano-silicon-carbon composite material of the present invention is prepared by the above method. The method of the present invention is simple, low in cost, small in energy consumption, mild in reaction conditions, high in solid content concentration of silicon dioxide in the slurry and can effectively avoid agglomeration of SiO2 particles.

Description

Technical Field

[0001] The present invention relates to the field of battery material preparation, and more specifically to a nano silicon-carbon composite material and SiF 4 The invention discloses a method for preparing a nano silicon-carbon composite material. Background Art

[0002] With the continuous development of the new energy industry, higher requirements are also put forward for lithium-ion batteries, which requires improvements and upgrades in energy density, cycle life, high and low temperature charge and discharge performance, and safety performance. The electrode material of lithium batteries is one of the key materials that affect the above factors. At present, lithium is mostly carbon materials, such as natural graphite, graphitized mesophase carbon microspheres, etc. However, due to the limitations of the properties of carbon materials themselves, it is difficult to significantly increase the energy density of the battery. On the one hand, nano-silicon-carbon composite materials have extremely high theoretical specific capacity and low reaction voltage platform. On the other hand, the composite materials effectively alleviate the volume expansion phenomenon of pure silicon negative electrode during battery charging and discharging, and improve the cycle performance of negative electrode materials.

[0003] The existing wet phosphoric acid, sulfuric acid decomposition of fluorosilicic acid to produce anhydrous hydrogen fluoride, and fluorosilicate thermal decomposition process will produce a certain amount of SiF 4 Generally speaking, gas SiF 4 The treatment is usually to convert it into fluorosilicic acid and silica gel after absorption by water. Fluorosilicic acid is sold as a product or used as a raw material for downstream products. Silica gel is produced by rapid hydrolysis under strong acidic and fluorine-containing conditions, so its specific surface area is low and its adsorption capacity is much lower than that of general active silica, so it can only be treated as solid waste. 4 The value of SiF has not been fully realized. 4 Using silicon sources to prepare nano-silicon-carbon composite materials and using fluorine sources to prepare high-purity fluoride salts is an effective way to increase their added value.

[0004] To use SiF 4 To prepare silicon-carbon negative electrode materials, nano-silicon dioxide must first be prepared. CN114477197A discloses a method for preparing white carbon black using a microwave plasma torch. The patent mainly uses water vapor and SiF 4 Nano-silicon dioxide is obtained by high-temperature hydrolysis of the raw material in a plasma torch. This method requires the plasma torch to provide an ultra-high temperature, and the plasma torch has a short life and high maintenance costs. Therefore, this method has the disadvantage of high overall energy consumption.

[0005] CN 102351150 A discloses a SiF 4 A method for preparing hydrogen fluoride and co-producing white carbon black, in which crude SiF 4After the gas is dusted and dehumidified, it undergoes a hydrolysis reaction with the reactant amount of water vapor at 200-800°C. The obtained products are separated by gas and solid to obtain hydrogen fluoride and white carbon black, which are then separated to obtain white carbon black. 4 White carbon black is prepared by high-temperature hydrolysis, except that steam is used as the heat source. However, the generation of ultra-high temperature (200-800°C) steam also requires a lot of energy consumption. Secondly, the mixture of a large amount of high-temperature water vapor and hydrogen fluoride will place very high demands on the high temperature and corrosion resistance of the equipment material, thereby greatly increasing the cost of the equipment. Finally, the mixture of high-temperature water vapor and hydrogen fluoride needs to be separated, and if the high-level heat needs to be recovered, it will also place very demanding demands on the material of the heat exchange equipment. In summary, the implementation of this method will lead to a significant increase in overall costs. SiF 4 Hydrolysis produces SiO 2 and fluorosilicic acid, but the reaction rate is fast in water, and the obtained SiO 2 Partially crystallized, so the specific surface area is low. Adding during the hydrolysis process can effectively control the hydrolysis rate and obtain SiO with high specific surface area 2 .

[0006] As CN1267634A discloses a method of producing SiF from phosphate fertilizer by-products 4 A method for preparing activated white carbon black by one-step hydrolysis. In this patent, SiF 4 The solution containing surfactant is passed through and the SiF 4 After hydrolysis, nano-silicon dioxide is obtained. However, the solid content of silicon dioxide in the patent is 0.2-1.5wt%, and the overall concentration is low. When the concentration is greater than 1.5wt%, the nano-silicon dioxide solvent agglomerates, which will lead to a decrease in production efficiency. In addition, due to the SiO 2 The concentration is low, and there is no corresponding surfactant and fluoride recovery, so the implementation of this method will produce a large amount of organic fluoride-containing wastewater. 4 The process conditions of the hydrolysis process must be strictly controlled, otherwise the SiO 2 Lattice fluorine will appear in the nano-SiO 2 quality. Summary of the invention

[0007] The purpose of the present invention is to solve the above technical problems and provide a method which is simple, low in cost, low in energy consumption, mild in reaction conditions, high in solid content of silicon dioxide in the slurry and can effectively avoid SiO 2 SiF particles agglomerated 4 A method for preparing nano silicon dioxide, and a method for obtaining a high value-added silicon-carbon composite material by carbon coating the nano silicon dioxide.

[0008] The present invention also provides a nano silicon-carbon composite material having advantages in terms of material uniformity and preparation economy.

[0009] SiF 4 The method for preparing nano silicon carbon composite material comprises: 4 The gas is mixed with an inert gas and diluted to a concentration of 30-90%wt of SiF4 to obtain a raw gas, and the raw gas is passed into an aqueous solution containing an additive for hydrolysis to generate a solution containing nano-SiO 2 and fluoride salt slurry, the slurry is aged, filtered, and the solid separated is washed and then added with a carbon source for SiO 2 Surface modification to obtain modified SiO 2 Slurry, modified SiO 2 The slurry is dried to obtain modified SiO 2 Powder, modified SiO 2 The powder is calcined in an air-tight condition to obtain a nano-silicon-carbon composite material.

[0010] Preferably, the inert gas is N 2 Or dry air.

[0011] Preferably, the additive consists of monoalcohol, polyol and inorganic base.

[0012] Preferably, the monoalcohol is at least one of methanol, ethanol, propanol (such as n-propanol or isopropanol), and butanol (such as n-butanol or isobutanol).

[0013] Preferably, the polyol is at least one of ethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol or glucose.

[0014] Preferably, the inorganic base is NH 3 ·H 2 O, NaOH, KOH, Ca(OH) 2 or Mg(OH) 2 At least one of .

[0015] Preferably, the additive consists of 10-70%wt of monoalcohol, 10-30%wt of polyol and 10-15%wt of inorganic base; further preferably, the additive consists of 50-70%wt of monoalcohol, 20-30%wt of polyol and 5-10%wt of inorganic base, and the total amount of the three is 100%wt.

[0016] Preferably, the additive is added in an amount of 0.1-5.0%wt of the aqueous solution, preferably 0.5-3.0%wt.

[0017] Preferably, during the hydrolysis process, the reaction temperature is controlled at 20-90°C and the pH value is controlled at 5-10. After hydrolysis, SiO 2 The concentration is 0.5-5%wt. The preferred temperature is 25-60°C and the pH value is 7.5-9.5.

[0018] Preferably, during the aging process, the slurry is placed in an ultrasonic dispersion tank for aging, the aging temperature is 20-60°C, the aging time is 0.5-3h, and the aging pH value is controlled at 5-10; the preferred aging temperature is 30-50°C, the aging time is 0.5-1.5h, and the aging pH value is 7-9.

[0019] Preferably, the filtration includes two stages of filtration, firstly using microfiltration or ceramic membrane for primary filtration to remove SiO 2 The particles, solid impurities and suspended matter are then separated into solid and liquid by a high-speed three-dimensional cyclone separator to separate SiO 2 Solids and mixed solutions containing fluoride salts and modifiers.

[0020] Preferably, the mixed solution containing the fluoride salt and the modifier is distilled to separate the light components methanol and ethanol, and the remaining medium and heavy components containing the fluoride salt and the modifier are concentrated by membrane and then crystallized to obtain fluoride salt solid.

[0021] Preferably, the carbon source modifier is at least one of polyols, polycarboxylic acids, polysaccharides, and cellulose.

[0022] Specifically, the polyols include triols, sorbitol, glucose, etc.; the polycarboxylates include ternary polycarboxylic acids, polyacrylic acid; the polysaccharides include fructose, mannan, starch, etc.; the celluloses include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, etc.

[0023] Preferably, the amount of the carbon source added is 2-15%wt of the solid mass of silica.

[0024] The nano silicon-carbon composite material of the present invention is prepared by the above method.

[0025] In view of the problems existing in the background technology, the inventor has made the following improvements:

[0026] (1) In order to better control SiO 2 The purity and particle size distribution of the purified SiF 4 A certain amount of dilution was carried out, and the rate of hydrolysis reaction was controlled by diluting the raw material SiF4 with inert gas, thereby controlling the SiO 2 The diluent gas is usually dried nitrogen or air. 4The concentration after dilution is controlled at 30-90%wt, preferably 50-80%wt, SiF 4 If the concentration is too low, the reaction rate will be low, resulting in reduced production capacity of the equipment and increased product costs, while if the concentration is too high, the hydrolysis reaction rate will be accelerated. 2 The particle size distribution becomes wider.

[0027] (2) An aqueous solution containing additives is used in the hydrolysis process, wherein the additives are composed of monoalcohols, polyols and inorganic bases, wherein the monoalcohols are mainly methanol, ethanol, propanol (such as n-propanol or isopropanol) or butanol (such as n-butanol or isobutanol), preferably methanol, ethanol and propanol. The monoalcohols can be used in combination of two or more, mainly considering that small molecule alcohols below C4 are easily adsorbed on SiO2 through the combination of alcohol hydroxyl groups and silanol groups on the surface of silica. 2 surface, thereby realizing SiO 2 The surface properties are regulated to reduce the aggregation of nano-silica through adsorption of silanol groups, thereby effectively increasing the SiO 2 Concentration (up to 5% without agglomeration). The selected small molecule monoalcohol has a relatively low boiling point, and the additive can be easily reused by distillation, thereby reducing costs and energy consumption. Further preferably, the monoalcohol in the additive is 50-70%wt to ensure that a large number of silanols can be adsorbed and occupied by small molecule alcohols, but all or excessive use of small molecule alcohols as additives will result in SiF 4 During the hydrolysis process, nano-SiO2 with small particle size is more likely to be formed. 2 , which is not conducive to the realization of nano-SiO 2 Particle size regulation, and too little addition will result in the silanol groups on the SiO2 surface not being fully occupied, which is prone to SiO 2 The aggregation of particles cannot increase the SiO 2 In addition to the monoalcohol, a certain amount of polyol needs to be added to the additive, preferably 10-30% wt. The addition of high molecular weight polyol is to 2 A certain amount of polyol is adsorbed on the surface. Since the molecular weight of polyol is large and the amount added is relatively small compared to monoalcohol, 2 The surface will form a part of the polyol adsorbed, and the small molecular unit alcohol will be adsorbed in the gap of the polyol, which can ensure the SiO 2 The surface silanols are fully covered, and on the other hand, the macromolecular polyols are beneficial to improve the nano-SiO 2 The repulsion of particles prevents the nano-SiO 2 However, excessive addition of polyols will be detrimental to SiO 2The surface silanols are completely covered, and the macromolecular polyols are also covered by nano-SiO 2 It is difficult to diffuse in the micropores of SiO, which increases the aging time. At the same time, the cost and boiling point of polyols are relatively high, which will also increase the cost of raw materials and recycling. Too little addition of polyols will affect the synergistic effect between the monools, which is not conducive to the realization of SiO 2 Particle size regulation; Inorganic alkali accounts for 10-15%wt. Too much addition will lead to too high pH of the system, increase the difficulty of subsequent wastewater treatment and increase the cost. Too little addition will lead to too low pH of the system. SiF 4 SiO formed by hydrolysis 2 The specific surface area is greatly reduced.

[0028] (3) Furthermore, in order to avoid SiO 2 The particles showed obvious agglomeration during the aging step, which was carried out in an ultrasonic dispersion tank, using ultrasonic vibration to keep the SiO 2 The dispersibility of the ultrasonic conditions is not particularly limited, and those skilled in the art can reasonably select them according to their needs; and the inventors also found that the aging temperature should be controlled at 20-60°C to ensure that the surface silanol groups of the nano-SiO2 particles are fully adsorbed and occupied by the modifier. Too high a temperature will cause the adsorption layer formed on the surface of the SiO2 particles to desorb significantly at high temperatures. Low temperatures are generally conducive to adsorption, but too low a temperature will not continue to increase the adsorption amount, and additional cooling capacity will be required, resulting in increased costs.

[0029] (4) Two-stage filtration is performed by step filtration, which can not only separate large particle impurities, but also meet the requirements of solid-liquid separation. 2 While separating, SiO 2 The particle size is screened twice to further adjust the particle size distribution. The liquid after solid-liquid separation is a fluoride salt solution, which can be concentrated and crystallized to produce high-purity fluoride salt solids or used as raw materials for the production of other downstream fluorides.

[0030] (5) After washing the nano-SiO2, a carbon source is added to replace the alcohol substances desorbed from the surface of the nano-SiO2 during the washing process to form a sufficient carbon precursor coating layer. The amount of the carbon source added is preferably 2-15%wt of the SiO2 content. Too much addition will increase the cost of the product, and too little addition will lead to uneven coating of the SiO2 surface, ultimately affecting the quality of the formed silicon-carbon material.

[0031] In the present invention, the SiF 4 The gas purification method is an existing technology, which can be separated by concentrated sulfuric acid washing, distillation, low-temperature separation and adsorption. 4The purity can be as high as 99.99 wt %. The specific method will not be described in detail here.

[0032] Furthermore, the drying temperature is 30-150°C, and the drying pressure is 0.3-1.0 atm. Preferably, the drying temperature is 50-120°C, and the pressure is 0.5-1.0 atm.

[0033] The SiO 2 The powder is calcined in an airtight condition, the calcination temperature is 400-900°C, the calcination time is 1-5h, preferably the calcination temperature is 500-700°C, the calcination time is 1-2h.

[0034] The process of the present invention is simple, and a battery-grade composite material is produced by low-temperature hydrolysis of SiF4, and a portion of fluorine salt is produced as a by-product, which can effectively maintain the dispersibility of SiO2 particles and avoid obvious agglomeration of SiO2 particles. The reaction conditions are mild, and compared with the existing process, the silane stage is not required, the process is simpler, and the energy consumption and cost are reduced. The nano silicon-carbon composite material prepared by the present invention has the advantages of high material uniformity and low preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the present invention.

[0036] Figure 2 This is a histogram of the particle size distribution of nano-silicon dioxide in Example 1 of the present invention.

[0037] Figure 3 This is an electron microscope picture of nano-silicon dioxide in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] Description: SiF 4 The gas purification method is a prior art. In the following example, the crude SiF 4 After the gas is washed with concentrated sulfuric acid, extracted and distilled, separated at low temperature and adsorbed, SiF with a purity of up to 99.99% can be obtained. 4 gas.

[0039] Example 1

[0040] SiF 4 After purification, the purity is 99%, and then mixed with N2. The final concentration of SiF4 in the raw gas is 50%wt. 1940kg of raw gas is passed into the hydrolysis tank for hydrolysis reaction. The hydrolysis temperature is controlled at 25℃, the pH is controlled at 7.5, and the amount of additives added is 3.0%wt of the mass of the aqueous solution. After the hydrolysis is completed, nano-SiO 2The solid concentration is 2.5%wt of the solution mass. The methanol content of the additive is 50%wt, the ethanol content is 20%wt, the ethylene glycol content is 15%wt, the glucose content is 10%wt, and the NH3·H 2 O content is 5%wt. After hydrolysis is completed, SiO 2 The slurry is sent for ultrasonic aging, the aging time is 1h, the pH is controlled at 7, and the aging temperature is 30℃. The aged slurry is first filtered through a primary filter, and then filtered through a ceramic membrane to remove SiO2 with a particle size greater than 100nm, and then the SiO2 solid and the mixed solution containing fluoride salt and modifier are separated by three-dimensional cyclone. After the mixed solution is distilled, the light components methanol and ethanol are separated and recycled, and the remaining heavy components containing fluoride salt and modifier are mixed and concentrated by membrane and crystallized to obtain fluoride salt solid. The separated SiO2 solid is washed with water to remove impurities and residual fluoride salt, and then glucose is added to the water-containing SiO2 solid and mixed evenly to prepare SiO 2 The slurry was dried, wherein the amount of glucose added was 15%wt of the SiO2 solid content, the SiO2 content in the prepared slurry was 30%wt, the drying pressure was normal pressure, the temperature was 110°C, and the modified SiO2 was obtained after drying. 2 Powder, totaling 580 kg. Subsequently modified SiO 2 The powder was sent to an atmosphere furnace for calcination and carbonization. The calcination temperature was 500°C, the calcination time was 1.5 hours, and the atmosphere was nitrogen. After calcination, 530 kg of nano-silicon-carbon composite material was obtained.

[0041] Figure 2 The particle size distribution bar graph of nano-silicon dioxide shows that the particle size distribution of silicon dioxide prepared by the method of the present invention is in the range of 10-100 nm, which belongs to nano-scale silicon dioxide, followed by SiO2 in the range of 40-80 nm. 2 It accounts for 67% and has a narrow particle size distribution; Figure 3 This is a transmission electron microscope picture of a nano-silicon-carbon composite material. From the middle picture, it can be seen that the particles of the silicon-carbon composite material prepared by this method are uniform in size.

[0042] Example 2

[0043] SiF 4 After purification, the purity is 99%, and then mixed with dried air, the final concentration of SiF4 in the raw gas is 60%wt. 700kg of raw gas is passed into the hydrolysis tank for hydrolysis reaction, the hydrolysis temperature is controlled at 30℃, the pH is controlled at 8.0, the amount of additives added is 2.0%wt of the solution mass, and after the hydrolysis is completed, SiO 2 The concentration is 3.0%. The additive contains 30% ethanol, 40% isopropanol, 25% neopentyl glycol and 5% NaOH. 2The slurry was sent to an ultrasonic aging tank for aging. The aging time was 1.5 hours, the pH was controlled at 8.5, and the aging temperature was 35°C. The aged slurry was first filtered through a ceramic membrane to remove solid impurities with a particle size of >100 nm, and then the SiO2 solid and the mixed solution containing fluoride salts and modifiers were separated by three-dimensional cyclone. After distillation of the mixed solution, the light components ethanol and isopropanol were separated and recycled, and the remaining heavy components containing fluoride salts and modifiers were mixed and concentrated by membrane and crystallized to obtain fluoride salt solids. The separated SiO 2 The solid is washed with water to remove impurities and residual fluoride salts, and the obtained liquid is mainly fluoride salt brine, which is concentrated by membrane and then crystallized to obtain fluoride salt solid. The solid is washed with water to remove impurities, and then starch is added to the water-containing SiO2 solid and mixed evenly to prepare SiO2 slurry and dry it, wherein the amount of starch added is 10%wt of the SiO2 solid content, and the SiO2 content in the prepared slurry is 25%wt and dried, the drying pressure is 0.8atm, the temperature is 90℃, and the SiO2 slurry is obtained after drying. 2 Powder, totaling 270 kg. Then SiO 2 The powder was sent to an atmosphere furnace for calcination at a temperature of 700°C for 2 hours in a nitrogen atmosphere. After calcination, 230 kg of a nano-silicon-carbon composite material was obtained.

[0044] Example 3

[0045] SiF 4 After purification, the purity is 99%, and then mixed with N2, the final concentration of SiF4 in the raw gas is 70%wt. 117kg of raw gas is passed into the hydrolysis tank for hydrolysis reaction, the hydrolysis temperature is controlled at 35℃, the pH is controlled at 8.5, the amount of additives added is 3% of the solution mass, and after the hydrolysis is completed, SiO 2 The concentration is 3.5%. The methanol content in the additive is 50%, the isopropanol content is 20%, the pentaerythritol content is 20%, and the KOH content is 10%. SiO 2 The slurry was sent to an ultrasonic aging tank for aging. The aging time was 0.5 h, the pH was controlled at 9.0, and the aging temperature was 40 ° C. The aged slurry was first filtered through a ceramic membrane to remove solid impurities with a particle size of >100 nm, and then the SiO2 solid and the mixed solution containing fluoride salt and modifier were separated by three-dimensional cyclone. After distillation of the mixed solution, the light components ethanol and isopropanol were separated and recycled, and the remaining heavy components containing fluoride salt and modifier were mixed and concentrated by membrane and crystallized to obtain fluoride salt solid. The separated SiO 2The liquid obtained by washing the solid with water to remove impurities and residual fluorinated salts is mainly fluorinated salt brine, which is crystallized after evaporation and concentration to obtain solid fluorinated salts. The solid is washed with water to remove impurities, then polyethylene glycol is added and mixed evenly with hydrated SiO2 solid to prepare SiO2 slurry and dried. The addition amount of hydroxymethyl cellulose is 7% wt of the SiO2 solid content. The SiO2 content in the prepared slurry is 20% wt and dried. The drying operation pressure is 0.7 atm and the temperature is 75 °C. After drying, modified SiO 2 powder is obtained, with a total of 60 kg. Subsequently, the modified SiO 2 powder is sent to an atmosphere furnace for roasting. The roasting temperature is 700 °C, the roasting time is 1.5 h, and the atmosphere is nitrogen. After roasting, 53 kg of nano silicon-carbon composite material is obtained.

[0046] Example 4

[0047] SiF 4 After purification, the purity is 99%, and then it is mixed with N2. Finally, the concentration of SiF4 in the raw material gas is 80% wt. 40 kg of the raw material gas is introduced into a hydrolysis tank for hydrolysis reaction. The hydrolysis temperature is controlled at 40 °C, the pH is controlled at 9, and the addition amount of the additive is 1%. After hydrolysis, the SiO 2 concentration is 4%. The isopropanol content in the additive is 40%, the ethylene glycol content is 30%, the pentaerythritol content is 20%, and the NH3·H2O content is 10%. The SiO 2 slurry is sent to an ultrasonic aging tank for aging. The aging time is 2.5 h, the pH is controlled at 9.0, and the aging temperature is 45 °C. The aged slurry is first filtered through a ceramic membrane to remove solid impurities with a particle size > 100 nm, and then the SiO2 solid and the mixed solution containing fluorinated salts and modifiers are separated by three-dimensional cyclone. The light components ethanol and isopropanol in the mixed solution are separated and recycled after distillation, while the remaining heavy components in the mixed solution containing fluorinated salts and modifiers are crystallized after membrane concentration to obtain solid fluorinated salts. The separated SiO 2 solid is washed with water to remove impurities and residual fluorinated salts. The liquid obtained is mainly fluorinated salt brine, which is crystallized after evaporation and concentration to obtain solid fluorinated salts. The solid is washed with water to remove impurities, then polyacrylic acid is added and mixed evenly with hydrated SiO2 solid to prepare SiO2 slurry and dried. The addition amount of polyacrylic acid is 5% wt of the SiO2 solid content. The SiO2 content in the prepared slurry is 25% wt and dried. The drying operation pressure is 0.6 atm and the temperature is 60 °C. After drying, SiO 2 powder is obtained, with a total of 60 kg. Subsequently, the SiO 2 powder is sent to an atmosphere furnace for roasting. The roasting temperature is 700 °C, the roasting time is 1.5 h, and the atmosphere is nitrogen. After roasting, 37 kg of nano silicon-carbon composite material is obtained.

[0048] Example 5

[0049] SiF 4 After purification, the purity is 99%, and then mixed with air, the final concentration of SiF4 in the raw gas is 50%wt. 16kg of raw gas is passed into the hydrolysis tank for hydrolysis reaction, the hydrolysis temperature is controlled at 40℃, the pH is controlled at 9.5, the additive amount is 0.5%, and after the hydrolysis is completed, SiO 2 The concentration is 5%. The methanol content of the additive is 50%, the neopentyl glycol content is 15%, the pentaerythritol content is 25%, and the Ca(OH) 2 The content is 10%. SiO 2 The slurry was sent to an ultrasonic aging tank for aging. The aging time was 2.5 hours, the pH was controlled at 9.0, and the aging temperature was 50°C. The aged slurry was first filtered through a ceramic membrane to remove solid impurities with a particle size of >100 nm, and then the SiO2 solid and the mixed solution containing fluoride salts and modifiers were separated by three-dimensional cyclone. After distillation of the mixed solution, the light components ethanol and isopropanol were separated and recycled, and the remaining heavy components containing fluoride salts and modifiers were mixed and concentrated by membrane and crystallized to obtain fluoride salt solids. The separated SiO 2 The solid is washed with water to remove impurities and residual fluoride salts. The liquid obtained is mainly fluoride salt brine. After membrane concentration, it is crystallized to obtain fluoride salt solid. The solid is washed with water to remove impurities, and then hydroxymethyl cellulose and aqueous SiO 2 After the solids are mixed evenly, SiO 2 The slurry is dried, wherein the amount of hydroxymethyl cellulose added is SiO 2 Solid content is 2%wt, SiO in the prepared slurry 2 The content is 25%wt and dried, the drying operation pressure is 0.5atm, the temperature is 50℃, and the modified SiO 2 Powder, total 6.0 kg. Subsequently modified SiO 2 The powder was sent to an atmosphere furnace for calcination at a temperature of 900° C. for 1.5 h in a nitrogen atmosphere. After calcination, 53 kg of a nano-silicon-carbon composite material was obtained.

[0050] Comparative Examples 1-4 are different additives, and the rest are the same as Example 1. The comparison results are shown in the table below.

[0051] Examples and Comparative Examples

[0052]

[0053] Example 1 Metal ion content of nano-silicon dioxide

[0054] Metal Type Fe Co Ca Na Mg Cu Ni Cr Mn Content (ppm) 17 2 - 0.5 - 4 10 14 7

Claims

1. A SiF 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The purified SiF 4 The gas is mixed with an inert gas and diluted to a concentration of 30-90%wt of SiF4 to obtain a raw gas, and an aqueous solution containing an additive is introduced into the raw gas for hydrolysis to generate a solution containing nano-SiO 2 and fluoride salt slurry, the slurry is aged, filtered, and the solid separated is washed and then added with a carbon source for SiO 2 Surface modification to obtain modified nano-SiO 2 Slurry, modified nano-SiO 2 The slurry is dried to obtain modified nano-SiO 2 Powder, modified nano-SiO 2 The powder is calcined under air-tight conditions to obtain a nano-silicon-carbon composite material; the additive is composed of 10-70%wt of monoalcohol, 10-30%wt of polyol and 10-15%wt of inorganic base, which is 100wt% in total; the monoalcohol is at least one of methanol, ethanol, propanol and butanol; the polyol is at least one of ethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol or glucose; the inorganic base is NH 3 ·H 2 O, NaOH, KOH, Ca(OH) 2 At least one of .

2. The SiF according to claim 1 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The additive is added in an amount of 0.5-5%wt of the aqueous solution.

3. The SiF according to claim 1 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that During the hydrolysis process, the hydrolysis reaction temperature is controlled at 20-60°C and the pH value is controlled at 5-10. After hydrolysis, nano-SiO 2 The solid concentration is 0.5-5%wt.

4. The SiF according to claim 1 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that During the aging process, the slurry is placed in an ultrasonic dispersion tank for aging at a temperature of 20-60° C. for 0.5-3 h. During the aging process, the pH value is controlled at 5-10.

5. The SiF according to claim 1 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The filtration includes two stages of filtration, firstly using microfiltration or ceramic membrane for primary filtration to remove SiO2 particles larger than 100 nm. 2 The particles, solid impurities and suspended matter are then separated into solid and liquid by a high-speed three-dimensional cyclone separator to separate the nano-SiO 2 A mixed solution of a solid, fluoride-containing salt and a modifier.

6. The SiF according to claim 1 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The carbon source is at least one of polymer polyols, polycarboxylic acids, polysaccharides and cellulose.

7. SiF according to claim 1 or 5 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The amount of carbon source added is nano-SiO 2 2-15wt% of solid mass.

8. The SiF according to claim 5 4 A method for preparing a nano silicon-carbon composite material, It is characterized in that The mixed solution containing the fluoride salt and the modifier is distilled to separate the light components methanol and ethanol, and the remaining medium and heavy components containing the fluoride salt and the modifier are concentrated by membrane and then crystallized to obtain fluoride salt solid.

9. A nano silicon-carbon composite material, It is characterized in that Prepared by the method according to any one of claims 1 to 8.

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