Device and method for preparing silicon-based material by magnesiothermic reduction of silicon-containing precursor

Abstract

The invention discloses a device and method for preparing a silicon-based material through magnesiothermic reduction of a silicon-containing precursor. The device comprises a furnace body, a vacuum or atmosphere control system, a double-temperature-zone heating control system, a furnace body tilting system, a furnace body rotating system, a water cooling system, a heat preservation pipe plug and a control panel. Feeding and discharging pipes are arranged at the two opposite ends of the furnace body; a hole-reserved partition plate is arranged in the cavity of the furnace body and divides the cavity of the furnace body into a magnesium material evaporation bin and a reduction reaction bin; and an air hole is formed in the hole-reserved partition plate and communicated with an air guide pipe with a hole, and the air guide pipe with the hole is located in the reduction reaction bin. A double-temperature-zone heating control system is adopted, the evaporation temperature and the reduction reaction temperature of a magnesium material can be independently adjusted, a magnesium steam perforated gas guide pipe of a special structure is designed inside, it is ensured that magnesium steam can be evenly distributed in a reduction reaction bin, meanwhile, the perforated gas guide pipe is prevented from being blocked, and the production efficiency is improved. The equipment can realize thermal reduction of the silicon-containing precursor by magnesium steam under a vacuum condition.

Description

Technical Field

[0001] The invention relates to a device for preparing silicon-based materials, and in particular to a device and method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. Background Art

[0002] Silicon-based materials refer to nano-silicon, porous silicon, silicon oxide, silicon carbide, silicon nitride and various composite materials. As these materials have excellent properties such as good lithium storage, wave absorption, thermal stability and / or acid and alkali corrosion resistance, they play a key role in strategic emerging industries such as new energy, energy conservation and environmental protection, and electronic information. At present, silicon-based materials have become one of the new material industries that my country is focusing on cultivating and developing.

[0003] There are many methods for preparing silicon-based materials, including high-energy ball milling, metal thermal reduction, and chemical vapor deposition. Among them, magnesium thermal reduction is a process that uses magnesium as a reducing agent to reduce silicon-containing precursors such as silicon dioxide, quartz, and clay minerals to silicon at a temperature of 650 to 1000°C. This method can effectively prevent the agglomeration of silicon particles and retain the porous structure of the precursor, so it is considered to be an effective and economical method for preparing high-performance silicon-based materials.

[0004] From an operational perspective, the traditional magnesium thermal reduction method usually involves mixing a silicon-containing precursor, micron-sized magnesium powder, and a heat regulator (such as NaCl) in a uniform proportion and placing them in a tube furnace. Under the protection of an inert atmosphere, the mixture is heated to several hundred degrees Celsius at a specific heating rate and kept at this temperature for several hours to obtain a crude reaction product. However, this preparation method has the following significant limitations:

[0005] (1) Safety issues: Micron-grade magnesium powder is highly flammable and explosive, so extremely strict safety measures must be taken during the production process, which greatly increases operational risks and production difficulties;

[0006] (2) Reaction efficiency and product quality issues: Uneven mixing of silicon-containing precursor and micron-sized magnesium powder, as well as uneven temperature field distribution, may lead to local excessive heat release, which will not only generate more by-products (such as magnesium silicide), but also cause silicon particle agglomeration and template structure destruction;

[0007] (3) Economic and cost issues: The traditional process requires a long reaction time, and micron-grade magnesium powder is expensive. At the same time, a large amount of inert gas and heat regulator are used, and excess hydrochloric acid (HCl) is required to remove the regulator. These factors significantly increase the production cost. Summary of the invention

[0008] The purpose of the present invention is to provide a device and method for preparing silicon-based materials by thermal reduction of silicon-containing precursors by magnesium. A dual-temperature zone heating control system is adopted so that the evaporation temperature and reduction reaction temperature of the magnesium material can be adjusted independently. A magnesium vapor perforated air duct with a special structure is designed inside to ensure that the magnesium vapor can be evenly distributed in the reduction reaction chamber while avoiding blockage of the perforated air duct. The device can realize thermal reduction of silicon-containing precursors by magnesium vapor under vacuum conditions.

[0009] In order to achieve the above-mentioned purpose, the present invention provides a device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, the device comprising: a furnace body, a vacuum or atmosphere control system, a dual-temperature zone heating control system, a furnace body tilting system, a furnace body rotation system, a water cooling system, a heat preservation pipe plug and a control panel; wherein, the opposite ends of the furnace body are provided with feed and discharge pipes; a perforated partition is provided in the cavity of the furnace body, dividing the cavity of the furnace body into two parts: a magnesium material evaporation bin and a reduction reaction bin; the magnesium material evaporation bin is used to place magnesium material; the reduction reaction bin is used to A silicon-containing precursor or a modified product thereof is placed; air holes are arranged on the perforated partition plate, and a perforated air duct is connected to the air holes of the perforated partition plate, and the perforated air duct is located in the reduction reaction chamber; insulation pipe plugs are arranged at the positions where the two opposite ends of the furnace body are connected to the feed and discharge pipes, which are used to separate the feed and discharge pipes from the magnesium material evaporation chamber and the reduction reaction chamber; the insulation pipe plug is a multi-layer metal sheet insulation pipe plug; the vacuum or atmosphere control system comprises: a vacuum valve, a pressure gauge and a vacuum sealing flange; a vacuum sealing flange is arranged at the end of the feed and discharge pipes, and the vacuum A gas pipeline is connected to the sealing flange, and a vacuum valve and a pressure gauge are arranged on the gas pipeline, and the pressure gauge is located between the vacuum sealing flange and the vacuum valve; the gas pipeline is externally connected to a vacuum pump or an inert gas; the dual-temperature zone heating control system comprises: a heater and a heat insulation layer; a heater is respectively arranged on the outer side wall of the furnace body corresponding to the magnesium material evaporation bin and the reduction reaction bin, for independently heating the magnesium material evaporation bin and the reduction reaction bin respectively; the heat insulation layer is arranged on the outer side wall of the furnace body; the furnace body tilting system is used to adjust the tilting of the furnace body so that the furnace body is tilted to dump the silicon-based crude product; the furnace body rotation system is used to adjust the rotation of the furnace body; the water cooling system is used to prevent the sealing ring of the vacuum sealing flange from leaking due to high temperature; the water cooling system comprises: a water cooling pipe, a water cooling liquid, and a circulating water pump; the water cooling pipe is wound around the feed and discharge pipe, and the circulating water pump is connected to the water cooling pipe; the water cooling liquid circulates in the water cooling pipe; the control panel is electrically connected to the furnace body tilting system and the furnace body rotation system, and is used to control the operation of the furnace body tilting system and the furnace body rotation system.

[0010] Preferably, the furnace body tilting system comprises: a support frame, an electric push rod and a rotating joint; the support frame is located below the furnace body, the electric push rod is fixedly connected to the support frame, the electric push rod is hinged to one end of the furnace body, and the rotating joint is hinged to the other end of the furnace body, and is used to tilt the furnace body to dump the silicon-based crude product; the control panel is electrically connected to the electric push rod, and the control panel is provided with a tilt angle adjustment button; or / and, the furnace body rotation system comprises: a tubular furnace rotating motor and a transmission component; the transmission component is connected between the tubular furnace rotating motor and the end of the furnace body, and is used to drive the rotation of the furnace body; the control panel is electrically connected to the tubular furnace rotating motor.

[0011] Preferably, a conical opening with a contracting opening is provided on the circumference of the perforated air duct; or, a plurality of vertical short tubes are symmetrically provided on the tube wall of the perforated air duct, and outlets are symmetrically provided on the side walls of the vertical short tubes; or, a plurality of T-shaped pipes are symmetrically provided on the tube wall of the perforated air duct, and the opposite ends of the T-shaped pipes are outlets.

[0012] Preferably, the closing sections at both ends of the furnace body have a trapezoidal structure; or / and, the furnace body has an arc-shaped structure with closing ends at both ends.

[0013] Preferably, two heaters are arranged between the outer wall of the furnace body and the insulation layer for heating the magnesium material evaporation bin and the reduction reaction bin respectively; the control panel is electrically connected to the two heaters, and a real-time temperature display screen and an indicator diode are provided on the control panel for monitoring the temperature and the operating status of the heater, and the control panel can control the heating temperature of the magnesium material evaporation bin and the reduction reaction bin respectively.

[0014] Preferably, the multi-layer metal sheet thermal insulation pipe plug is a multi-layer metal foil thermal insulation pipe plug.

[0015] Another object of the present invention is to provide a method for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor, the method using the device for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor, the method comprising:

[0016] S1. Put the magnesium material and the silicon-containing precursor into the magnesium material evaporation chamber and the reduction reaction chamber respectively, seal them, start the rotating motor of the tubular furnace to rotate the furnace body, and evacuate the furnace with an external vacuum pump;

[0017] The magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, or magnesium ingot and / or magnesium-containing alloy;

[0018] S2, evacuate the whole furnace body to make the vacuum degree less than 500Pa, and heat to induce reduction reaction; when the magnesium material is selected from magnesium ingot and / or magnesium-containing alloy, the heating temperature of the magnesium material evaporation bin is 650-1000°C; when the magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, the heating temperature of the magnesium material evaporation bin is 1100-1300°C; the heating temperature of the reduction reaction bin is 650-850°C;

[0019] S3, pickling, water washing and drying; wherein, after the pickling, the obtained solid is stirred and washed with hydrofluoric acid, the solid is collected and placed in a vacuum dryer for drying to obtain the target product; after the pickling, the liquid obtained by solid-liquid separation is adjusted in pH value, and a magnesium source or an aluminum source is added to prepare hydrotalcite.

[0020] Preferably, in step S1, before evacuating, the magnesium material evaporation chamber and the reduction reaction chamber are filled with inert gas; or / and, in step S1, when the pressure gauge shows that the vacuum degree is less than 500Pa, argon gas is filled at a rate of less than 50mL / min (preferably 5mL / min), and evacuation is continued until the reaction is completed; or / and, in step S1, after the inorganic salt (as a heat regulator) is mixed with the silicon-containing precursor material, the silicon-containing precursor is reduced by magnesium vapor; or / and, in step S1, the mass ratio of the ferrosilicon alloy, calcined white, and mineralizer is 6:(0.8-1.2):(0.1-0.2 ); or / and, in step S1, the Si content in the ferrosilicon alloy is higher than 70%, the S content is lower than 0.1%, and the Al content is lower than 0.5%; or / and, in step S1, the ferrosilicon alloy, calcined white, and mineralizer are all passed through a sieve of >100 mesh; or / and, in step S1, the furnace body speed is 1-100rpm; or / and, in step S2, the silicon-containing precursor is selected from at least one of the following: clay minerals, silicon-carbon precursors, nano-silicon dioxide, or modified products of these three precursors; the modification method includes at least one of heat treatment, acid treatment, mechanical treatment, organic modification, and inorganic modification; or / and, in step S2, a carbon source is added to the silicon-containing precursor; the modification method includes at least one of heat treatment, acid treatment, mechanical treatment, organic modification and inorganic modification; or / and, in step S2, the silicon-containing precursor or its modified product is pre-decontaminated and dried in an oven, and the selected particles are all screened by a sieve of >100 mesh; or / and, the molar ratio of the magnesium material to the silicon-containing precursor is 0.3 to 2.5:1; or / and, in step S2, the magnesium material evaporation chamber and the reduction reaction chamber are heated to their respective heating temperatures, and then each is independently kept warm; wherein the insulation time of the reduction reaction chamber covers the two The heat preservation time of the magnesium material evaporation bin is greater than or equal to the heat preservation time of the reduction reaction bin, and the heat preservation time covers the time difference between the two bins reaching the predetermined temperature; or / and, in step S3, the pickling is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, the volume concentration of the acid used is 1-20%, and the washing time lasts for 0.1-10h; the volume concentration of the hydrofluoric acid is 1-10%, and the washing time lasts for 1-60min; or / and, in step S3, the pickling solution obtained by solid-liquid separation is supplemented with a magnesium source or an aluminum source, and the pH is adjusted to 6-14 to prepare hydrotalcite.

[0021] Preferably, in step S1, the inorganic salt is selected from at least one of NaCl, LiCl, KCl, CaCl2 and MgCl2; or / and, in step S1, the mass ratio of the inorganic salt to the silicon-containing precursor is 0.1 to 5:1; or / and, in step S2, the clay mineral is selected from any one or more of montmorillonite, kaolinite, halloysite, palygorskite, talc, black talc, muscovite, saponite, biotite, illite, chlorite, sepiolite and pyrophyllite; or / and, in step S2, the silicon-carbon precursor is selected from any one or more of the following: rice husk, straw, bamboo leaves, reeds, bagasse, silicon-containing plastics, silicon-containing rubber, and waste clay adsorbing organic matter; or / and, in step S2, the carbon source is selected from any one or more of carbon powder, graphite, graphene, carbon nanotubes, carbon fiber, and carbon black.

[0022] The device and method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors of the present invention have the following advantages:

[0023] (1) The device of the present invention adopts an integrated design, and its main components include a furnace body (composed of a magnesium material evaporation chamber and a reduction reaction chamber), a vacuum or atmosphere control system, a dual-temperature zone heating control system, a furnace body tilting system, a furnace body rotation system, a water cooling system, a thermal insulation pipe plug and a control panel. The device separates the magnesium material from the silicon-containing precursor so that the selection of the magnesium material is not limited by the reaction temperature, thereby expanding the types of available magnesium materials. In addition, the device adopts a dual-temperature zone heating control system so that the evaporation temperature and the reduction reaction temperature of the magnesium material can be adjusted independently. The number of device interfaces is reduced, reducing the risk of leakage, and a thermal insulation pipe plug and a water cooling device are arranged on the extended part of the furnace body, so that lower-cost silica gel can be selected for sealing. A specially designed magnesium vapor perforated air duct is designed inside to ensure that the magnesium vapor can be evenly distributed in the reduction reaction chamber while avoiding blockage of the perforated air duct. The equipment can realize the thermal reduction of a silicon-containing precursor by magnesium vapor under vacuum conditions;

[0024] (2) Compared with the traditional magnesium thermal reduction process, the method of the present invention has significant advantages: the magnesium material used is cheaper and safer; the original morphology of the silicon-containing precursor is better preserved; due to less heat release, only a small amount of heat regulator is needed, or even no regulator is used, saving costs; saving inert gas; the reduction reaction is more uniform and faster, significantly reducing unreacted precursors and side reaction products. Overall, this method not only ensures production safety, but also successfully reduces costs, while significantly improving reduction efficiency and product quality;

[0025] (3) From the perspective of silicon-containing precursors, the method of the present invention has abundant reserves of clay minerals, is environmentally friendly and inexpensive, and naturally has microscopic morphologies such as flakes, clusters of flakes, fibers, tubes and needles. After mechanical treatment, acid treatment, heat treatment and other modifications, these nanostructures are retained or strengthened, and their size, morphology and surface chemical properties can be precisely adjusted. The present invention also uses silicon-carbon precursors, such as rice husks, straws, bamboo leaves, bagasse, silicon-containing plastics, silicon-containing rubber, waste white clay that absorbs organic matter, etc. These materials may not have nanoscale structures without special treatment, but after appropriate modification treatments (such as carbonization, pickling, pore expansion treatment, etc.), they can show nanostructures or nanoscale features. These characteristics make them ideal silicon carriers and show great application potential in the preparation of silicon-based materials. From the perspective of magnesium materials, this process uses safer and lower-cost magnesium materials, avoiding the potential safety risks brought about by the use of micro-nano magnesium powder particles. From the perspective of the magnesium thermal reduction method, compared with the traditional solid-state reaction, the reaction energy barrier between magnesium vapor and silicon-containing precursors is lower and less heat is generated. In addition, conducting the reaction under vacuum conditions not only reduces costs, but also allows magnesium vapor to diffuse and penetrate more freely in the vacuum, making the reduction reaction more uniform and faster, thereby reducing the residue of unreacted precursors and the generation of side reaction products, and avoiding morphological damage caused by local overheating. Therefore, even if inorganic salts are not used to adjust the heat, or only a small amount of inorganic salts are used to adjust the heat, products that are superior to traditional magnesium thermal methods can be obtained;

[0026] (4) The method of the present invention has the advantages of safety, economy and high efficiency, and can be used to prepare nano silicon, porous silicon, silicon oxide, silicon carbide, silicon nitride and their composite materials. This technology shows broad application prospects in emerging industries such as new energy, energy conservation and environmental protection, and electronic information. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic structural diagram of an apparatus for preparing silicon-based materials by magnesium thermal reduction of a silicon-containing precursor.

[0028] Figure 2 It is a side view of the hole-retaining partition of the present invention.

[0029] Figure 3 It is a schematic structural diagram of Scheme 1 of the perforated airway tube of the present invention.

[0030] Figure 4 It is a schematic structural diagram of Scheme 2 of the perforated airway tube of the present invention.

[0031] Figure 5 It is a structural schematic diagram of Scheme 3 of the perforated airway tube of the present invention.

[0032] Figure 6This is the X-ray diffraction pattern of the micro-nano silicon prepared in Example 4.

[0033] Figure 7 This is a scanning electron microscope image of the micro-nano silicon prepared in Example 4.

[0034] Figure 8 The cycling performance of the micro-nano silicon prepared for application example as negative electrode material for lithium-ion batteries.

[0035] Label: 1-vacuum valve; 2-pressure gauge; 3-vacuum sealing flange; 4-feeding and discharging area; 5-insulation pipe plug; 6-tube furnace rotating motor; 7-magnesium material evaporation chamber; 8-heating element; 9-insulation layer; 10-perforated partition; 11-perforated air duct; 12-reduction reaction chamber; 13-upper shell; 14-electric push rod; 15-lower shell; 16-support body; 17-circulating water pump; 18-rotating joint; 19-control panel. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention provides a device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. The closing sections at both ends of the furnace body are designed as a trapezoidal structure, which contains two independent feeding and discharging pipes, which are respectively used to put in magnesium material / silicon-containing precursors or to recover magnesium slag / silicon-based material crude products. The perforated partition plate divides the furnace body into two parts: a magnesium material evaporation chamber and a reduction reaction chamber. Through the perforated partition plate and the perforated air duct, magnesium vapor is evenly distributed in the reduction reaction chamber, thereby achieving effective reduction of the silicon-containing precursor and avoiding blockage of the air duct.

[0038] The device of the present invention adopts a dual temperature control system, so that the evaporation temperature of the magnesium material and the temperature of the reduction reaction can be adjusted independently to meet the different requirements of the two process of evaporation and reduction. The device of the present invention can realize the reduction of silicon-containing precursors by magnesium vapor under vacuum conditions to prepare silicon-based materials.

[0039] The following is a detailed description of an apparatus for preparing silicon-based materials by magnesium thermal reduction of a silicon-containing precursor provided by the present invention through Example 1.

[0040] Example 1

[0041] A device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, the device comprising: a furnace body, a shell, a vacuum or atmosphere control system, a dual-temperature zone heating control system, a furnace body tilting system, a furnace body rotation system, a water cooling system, an insulation pipe plug and a control panel 19.

[0042] Both opposite ends of the furnace body are provided with feed and discharge pipes 4. A perforated partition plate 10 is provided in the cavity of the furnace body, dividing the cavity of the furnace body into two parts: a magnesium material evaporation chamber 7 and a reduction reaction chamber 12. The magnesium material evaporation chamber 7 is used to place magnesium materials, such as calcined white, magnesium ingots or magnesium-containing alloys; the reduction reaction chamber 12 is used to place silicon-containing precursors. The perforated partition plate 10 is provided with air holes, and the air holes of the perforated partition plate 10 are connected to a perforated air guide tube 11, which is in the reduction reaction chamber 12. The magnesium vapor is evaporated from the magnesium material evaporation chamber 7 and transferred to the reduction reaction chamber 12 through the perforated air guide tube 11, thereby realizing the reduction of the silicon-containing precursor.

[0043] The perforated air duct 11 is a hollow structure, and the hole position at one end thereof coincides with the hole position of the perforated partition plate 10, so as to ensure that the magnesium vapor in the magnesium material evaporation chamber 7 can be dispersed into the perforated air duct 11 from the perforated partition plate 10. The perforated air duct 11 is provided with a truncated cone-shaped opening on its circumference, so that the magnesium vapor can be dispersed in the reduction reaction chamber 12.

[0044] Insulation pipe plugs 5 are provided at the positions where the opposite ends of the above-mentioned furnace body are connected to the feed and discharge pipes 4, and a gap is left at the position where the insulation pipe plugs 5 are set, so as to separate the feed and discharge pipes 4 from the magnesium material evaporation bin 7 and the reduction reaction bin 12, thereby effectively ensuring a good thermal insulation effect while ensuring gas circulation without affecting the vacuum operation inside the furnace body.

[0045] The thermal insulation pipe plug 5 can be composed of multi-layer insulation material (Multi-layer insulation, MLI), and its structure includes two parts: a reflective screen and a spacer layer. It is composed of a reflective screen with low reflectivity and a spacer layer with low thermal conductivity alternately stacked. Generally, materials with a reflectivity of more than 90% are considered to have high reflectivity. The reflective screen uses a metal foil material with low emissivity, such as molybdenum foil, steel foil, and nickel foil. Gaps are maintained between the foils to avoid contact, thereby further improving the reflection efficiency. The spacer layer is made of a material with excellent thermal insulation performance, high temperature resistance, and stable dimensions, such as quartz fiber, high silica fiber, and aluminum silicate fiber. This multi-layer reflective screen structure can produce extremely high thermal resistance to radiant heat and has excellent thermal insulation performance in a vacuum environment.

[0046] The closing sections at both ends of the furnace body have a trapezoidal structure.

[0047] The housing may be composed of an upper housing 13 and a lower housing 15. The upper housing 13 is used to protect the magnesium material evaporation chamber 7, the reduction reaction chamber 12, the heating element 8 and the heat insulation layer 9, and further ensure the heat insulation effect.

[0048] The vacuum or atmosphere control system comprises: a vacuum valve 1, a pressure gauge 2 and a vacuum sealing flange 3. A vacuum sealing flange 3 is provided at the end of the feed and discharge pipe 4. A gas pipeline is connected to the vacuum sealing flange 3, and a vacuum valve 1 and a pressure gauge 2 are provided on the gas pipeline, and the pressure gauge 2 is located between the vacuum sealing flange 3 and the vacuum valve 1. The gas pipeline can be connected to an external vacuum pump or an inert gas for vacuuming or filling the furnace body with an inert gas such as argon or helium to realize the function of the atmosphere control system.

[0049] The dual-temperature zone heating control system includes: a heater 8 and a heat insulation layer 9. The heat insulation layer 9 is arranged on the outer wall of the furnace body, and two heaters 8 are arranged between the outer wall of the furnace body and the heat insulation layer 9 to heat the magnesium material evaporation bin 7 and the reduction reaction bin 12 respectively, so that the magnesium material evaporation bin and the reduction reaction bin can be individually controlled in temperature.

[0050] The furnace body tilting system includes: a support frame 16, an electric push rod 14 and a rotary joint 18. The support frame 16 is located below the furnace body, the electric push rod 14 is fixed on the support frame 16, the electric push rod 14 is hinged to one end of the furnace body, and the rotary joint 18 is hinged to the other end of the furnace body, which is used to tilt the furnace body to dump the silicon-based crude product. The electric push rod 14 can be built into the lower shell 15 and stabilized on the base through the support body 16. The upper shell 13 is connected to the lower shell 15 through the electric push rod 14 and the rotary joint 18 to achieve the tilting of the furnace body.

[0051] The control panel 19 is electrically connected to the tubular furnace rotating motor 6, the heater 8 and the electric push rod 14, and is equipped with a real-time temperature display screen and an indicator diode for monitoring the temperature and the operating status of the heater and the rotating motor. Through the programming function, the control panel can independently adjust the heating temperature of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12, and accurately control the rotation speed of the tubular furnace to ensure accurate regulation of the reaction process. In addition, the panel is equipped with a tilt angle adjustment button, allowing the operator to flexibly adjust the tilt angle of the furnace body by controlling the electric push rod 14, so as to facilitate the efficient dumping of the silicon-based crude product after the reaction is completed, thereby improving the operating efficiency.

[0052] The furnace body rotation system includes: a tubular furnace rotating motor 6 and a transmission component. The transmission component is used to connect the tubular furnace rotating motor 6 and the furnace body, and the continuous rotation of the furnace body is realized through the tubular furnace rotating motor 6. The transmission component is a structure known to those skilled in the art. For example, a driving gear is sleeved and fixedly connected on the output shaft of the tubular furnace rotating motor 6, and a passive gear is sleeved and fixed at both ends of the furnace body. The driving gear and the passive gear are meshed and connected, and the furnace body is rotated by rotating the tubular furnace rotating motor 6. There are many structures of such transmission components, and only one possible way of realization is listed here. Other transmission components can also be used to realize the transmission function.

[0053] The water cooling system includes: a water cooling pipe, a water cooling liquid, and a circulating water pump 17. The water cooling pipe is wound around the feed and discharge pipe 4, the circulating water pump 17 is connected to the water cooling pipe, and the water cooling liquid circulates in the water cooling pipe. The water cooling system helps to prevent the interface deformation or increase of the sealing gap caused by thermal expansion of the metal flange and the connecting parts, and prevents the sealing ring of the vacuum sealing flange from leaking due to high temperature, thereby more effectively ensuring the sealing performance of the furnace body at high temperature.

[0054] The method for using the device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors of the present invention is as follows:

[0055] During operation, magnesium material and silicon-containing precursor or its modified product are firstly loaded into magnesium material evaporation chamber 7 and reduction reaction chamber 12 respectively through feed and discharge pipe 4. In magnesium material evaporation chamber 7, magnesium material can be selected to use ferrosilicon alloy heat, calcined white and mineralizer, or magnesium ingot or magnesium-containing alloy.

[0056] Next, the insulation pipe plug 5 is inserted. The insulation pipe plug 5 is directly inserted into the furnace tube from both ends of the furnace body and is respectively arranged at the feed end and the discharge end. The size of the insulation pipe plug 5 matches the inner diameter of the furnace tube, which is convenient for installation and fixation. At the same time, a narrow gap is left between the feed pipe and the discharge pipe to ensure gas circulation, which does not affect the vacuum operation inside the furnace body and can effectively ensure a good thermal insulation effect. After insertion, the multi-layer insulation structure of the insulation pipe plug 5 effectively closes both ends of the furnace body, significantly reduces heat transfer by reflecting radiant heat, and prevents magnesium vapor from condensing in the low temperature area.

[0057] Then, seal through the vacuum sealing flange 3, start the tubular furnace rotation motor 6 to keep the furnace body rotating at a constant speed; fill the reaction device with inert gas before evacuating the vacuum, and then evacuate the vacuum with an external vacuum pump, the vacuum setting value is <500Pa, observe the vacuum degree of the pressure gauge 2 to the set value and then close the vacuum valve 1. Then, the temperature is controlled by the programming function of the control panel 19, the heating rate, target temperature, and holding time are pre-set, and then the heater 8 is turned on. The heating temperature of the ferrosilicon alloy thermal reduction calcination is 1100-1300°C, and the heating temperature of the calcined magnesium ingot / magnesium-containing alloy is 650-1000°C. The magnesium material evaporation chamber 7 is heated to the set temperature to produce magnesium vapor; the magnesium vapor is dispersed into the reduction reaction chamber 12 through the porous partition plate 10 and the perforated air guide pipe 11, and a reduction reaction occurs with the silicon-containing precursor. The heating temperature of the reduction reaction chamber 12 is 650-850°C, and the system is kept at the set temperature for a period of time. The holding time is based on the time difference between the two chambers reaching the predetermined temperature and then continues for 0.5-3h until the reaction is completed. The holding time of the reduction reaction chamber 12 should be synchronized with or slightly longer than that of the magnesium material evaporation chamber 7. Since the set temperature of the reduction reaction chamber 12 is usually equal to or lower than that of the magnesium material evaporation chamber 7, it may reach the target temperature earlier. To ensure sufficient reaction, the insulation time of the magnesium material evaporation chamber 7 should be calculated from the time it reaches the predetermined temperature, while the insulation time of the reduction reaction chamber 12 needs to be slightly longer, covering the time difference between the two chambers reaching the predetermined temperature. The dual-temperature zone heating control system controls the temperature of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 respectively through the control panel, independently sets the target temperature and insulation time, and ensures that the two chambers operate at the optimal temperature. After the heater 8 reaches the set temperature, it automatically enters the constant temperature mode, and the control panel programming function adjusts the heating power to keep the temperature stable. The temperature display screen and sensor monitor the furnace temperature in real time to ensure precise control of the reaction process.

[0058] After the reaction is finished, the solid matter generated in the reduction reaction chamber 12 is taken out; after post-treatment steps such as acid washing, water washing, and drying, the target silicon-based nanomaterial can be obtained.

[0059] Example 2

[0060] A device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors is basically similar to Example 1, except that:

[0061] The perforated air guide tube 11 is a hollow structure, and a plurality of T-shaped pipes are symmetrically arranged on the pipe wall, and the opposite ends of the T-shaped pipes are outlets.

[0062] Example 3

[0063] A device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors is basically similar to Example 1, except that:

[0064] The perforated air guide tube 11 is a hollow structure, and a plurality of vertical short tubes are symmetrically arranged on the tube wall, and outlets are symmetrically arranged on the side walls of the vertical short tubes.

[0065] The present invention also provides a method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, using safer magnesium materials, such as magnesium ingots, as raw materials, without the need to use flammable and explosive magnesium powder, and generating magnesium vapor through thermal reduction of ferrosilicon alloys, or calcining magnesium ingots or magnesium-containing alloys, and then fully contacting the silicon-containing precursors with magnesium vapor and undergoing reduction reactions to generate silicon-based crude products. The two reactions of the present invention are carried out in two isolated different reaction zones-magnesium material evaporation zones and reduction reaction zones. Since the reaction energy requirement of magnesium vapor is usually lower than that of solid-state reactions, the method uses a small amount of heat regulator, or does not use a regulator, which can also effectively reduce the generation of high-temperature phases and better maintain the original morphology of the precursor. At the same time, the entire reaction is carried out under vacuum conditions. Under vacuum conditions, the collisions between gas molecules are significantly reduced, and the mean free path of magnesium vapor is greatly increased, making the reduction reaction more uniform and faster. This not only reduces the generation of high-temperature byproducts, but also effectively avoids morphological damage caused by local overheating. Therefore, efficient reduction can be achieved without or with only a small amount of inorganic salt to regulate heat, while maintaining the integrity of the material's morphology and significantly reducing the generation of unreacted precursors and side reaction products.

[0066] The method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors of the present invention adopts the above-mentioned device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, and specifically comprises the following steps:

[0067] S1, putting magnesium material and silicon-containing precursor into magnesium material evaporation chamber 7 and reduction reaction chamber 12 respectively, sealing, then starting the tubular furnace rotation motor to rotate the furnace body, and then evacuating with an external vacuum pump;

[0068] The inventors have found that silicon-based materials with different morphologies can be prepared by using a self-template method of thermally reducing silicon-containing precursors with vacuum magnesium vapor. For example, montmorillonite can be used to prepare a flaky morphology, halloysite can be used to obtain a tubular morphology, and sepiolite can be used to obtain a fibrous morphology. This is because the magnesium vapor is dispersed at the atomic level, which reduces the energy barrier for reducing the silicon-containing precursor and reduces the heat generated, so its original morphology is relatively intact; under vacuum conditions, the collision between gas molecules is significantly reduced, and the mean free path of magnesium vapor is greatly increased, making the reduction reaction more uniform and faster. This not only reduces the generation of high-temperature by-products, but also effectively avoids morphological damage caused by local overheating. Therefore, efficient reduction can be achieved without or with only a small amount of inorganic salt to adjust the heat, while keeping the morphology of the material intact and significantly reducing the generation of unreacted precursors and side reaction products;

[0069] S2. The vacuum degree of the entire furnace body is evacuated to less than 500 Pa, and heating is performed to induce a reduction reaction; since the magnesium material evaporation chamber 7 is connected to the reduction reaction chamber 12 through the porous partition plate 10, the vacuum degrees of the two chambers are always consistent;

[0070] The furnace body is heated to generate magnesium vapor, and the generated magnesium vapor is used to reduce the silicon-containing precursor to prepare a crude product of silicon-based material. The temperatures of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 are synchronized during the heating process, and are finally heated to their respective required temperatures. When the magnesium material is selected from magnesium ingots and / or magnesium-containing alloys, the heating temperature range of the magnesium material evaporation chamber is 650-1000°C; when the magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, the heating temperature of the magnesium material evaporation chamber is 1100-1300°C; the heating temperature of the reduction reaction chamber is 650-850°C;

[0071] S3, pickling, washing and drying.

[0072] After the reduction reaction is completed, the crude silicon-based material product is acid-washed, water-washed and dried to obtain the target silicon-based nano-micron material.

[0073] Further, in step S1, before evacuating the magnesium material, the evaporation chamber and the reduction reaction chamber are filled with inert gas; or / and, when the pressure gauge shows that the vacuum degree is less than 500Pa, argon gas is filled in at a rate of 5mL / min, and evacuation is continued until the reaction is completed.

[0074] Furthermore, the pickling liquid obtained by solid-liquid separation is supplemented with a magnesium source or an aluminum source, and an alkaline solution, such as a sodium hydroxide solution or a sodium carbonate solution, is used to keep the pH constant between 6 and 14 to prepare hydrotalcite and realize full element utilization.

[0075] By adding different types of silicon-containing precursors and regulating parameters such as the magnesium-silicon ratio, the mass ratio of magnesium material to silicon-containing precursor, and reaction time, various types of silicon-based nano-micron materials can be prepared. For example, when the precursor is a silicon-carbon precursor, silicon carbide (SiC) may be generated; under conditions where the magnesium vapor concentration is too high, metal silicides such as magnesium silicide (Mg2Si) may be formed; when an iron source (such as iron powder, iron filings, or iron oxides Fe2O3, Fe3O4) is present in the precursor, iron silicides (FeSi, FeSi2) may be generated. Due to space limitations, only some examples are listed here, but the scope of application of the present invention is not limited to these. By appropriately regulating the reaction conditions, the prepared silicon-based nano-micron materials may include various types of materials such as single-substance silicon, silicon oxide, silicon carbide, silicon nitride, and metal silicides at nano-micron scales.

[0076] Furthermore, in step S1, the molar ratio of the magnesium material to the silicon-containing precursor is calculated according to the molar ratio of the magnesium vapor to the component to be reduced in the silicon-containing precursor, and the molar ratio of the two is 0.3 to 2.5: 1. In the magnesium material evaporation chamber 7, ferrosilicon alloy can be used to thermally reduce calcined white to produce magnesium vapor, and this magnesium material is a mixture of ferrosilicon alloy, calcined white, and mineralizer, and the mass ratio of the three is 6: (0.8 to 1.2): (0.1 to 0.2), or calcined magnesium ingots / magnesium-containing alloys can be used to produce magnesium vapor.

[0077] Furthermore, the silicon-containing precursor can be selected from at least one of the following categories: clay minerals, such as montmorillonite, kaolinite, halloysite, palygorskite, talc, black talc, muscovite, saponite, biotite, illite, chlorite, sepiolite, pyrophyllite; silicon-carbon precursors, such as rice husks, straw, bamboo leaves, bagasse, silicon-containing plastics, silicon-containing rubber, waste clay adsorbing organic matter, etc.; silicon dioxide; or modified products of these three precursors; the modification method includes at least one of heat treatment, acid treatment, mechanical treatment, organic modification and inorganic modification.

[0078] Furthermore, in step S1, the Si content in the ferrosilicon alloy is higher than 70%, the S content is lower than 0.1%, and the Al content is lower than 0.5%; the ferrosilicon alloy, calcined white, and the mineralizer are all passed through a sieve of >100 mesh.

[0079] Furthermore, in step S1, the silicon-containing precursor or its modified product is pre-decontaminated and dried in an oven, and the selected particles are all sieved with a mesh of >100 mesh.

[0080] Furthermore, in step S1, the furnace rotation speed is 1-100 rpm.

[0081] Furthermore, in step S1, after the inorganic salt is mixed with the silicon-containing precursor material, magnesium vapor is used to reduce the silicon-containing precursor. The inorganic salt is one or more of NaCl, LiCl, KCl, CaCl2 and MgCl2, and the mass ratio of the inorganic salt to the silicon-containing precursor is 0.1 to 5:1. Magnesium thermal reduction releases a large amount of heat, which can easily lead to local overheating, causing silicon melting or nanoparticle aggregation. Inorganic salts absorb heat, which helps to maintain the morphology and size of the material. Since magnesium vapor is dispersed at the atomic level, the reduction energy barrier is reduced, and the heat release and the generation of high-temperature by-products are reduced. Therefore, even without or with only a small amount of inorganic salt, efficient reduction can be achieved, but the addition of inorganic salts can better control the morphology and particle size of the material.

[0082] Further, in step S2, the vacuum degree of the entire furnace body is less than 500Pa, and the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 should be heated to their respective required temperatures at the same heating rate. When the magnesium material is selected from magnesium ingots and / or magnesium-containing alloys, the heating temperature of the magnesium material evaporation chamber 7 is 650-1000°C; when the magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, the heating temperature of the magnesium material evaporation chamber 7 is 1100-1300°C; the heating temperature of the reduction reaction chamber 12 is 650-850°C, and the reduction reaction duration is 0.5-3h.

[0083] Furthermore, the pickling is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, the volume concentration of the acid used is 1-20%, and the washing time lasts 0.1-10 hours; the volume concentration of hydrofluoric acid is 1-10%, and the washing time lasts 1-60 minutes.

[0084] The following is a detailed description of a method for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor provided by the present invention through Examples 4 to 10.

[0085] Example 4

[0086] A certain mass of magnesium ingot (Mg≥99.90wt%) and silicon-containing precursor (a mixture of halloysite and sodium chloride) are respectively fed into the magnesium material evaporation chamber and the reduction reaction chamber through two feed and discharge pipes. The mass ratio of magnesium ingot, halloysite and sodium chloride is 0.7:1:0.5.

[0087] Then, put in the insulation pipe plug and seal it with the vacuum sealing flange, start the tubular furnace rotation motor to make the furnace body rotate at a speed of 5rpm, then evacuate with an external vacuum pump, observe the vacuum degree of the pressure gauge to <500Pa and then close the vacuum valve.

[0088] Next, the heating program was started to heat the magnesium material evaporation chamber to 750°C and the reduction reaction chamber to 700°C. The reduction reaction lasted for 1 hour.

[0089] After the reaction is completed, the obtained solid is stirred and washed with hydrochloric acid having a volume concentration of 5% for 10 hours. After solid-liquid separation, a silicon-based crude product is obtained, which is stirred and washed with hydrofluoric acid having a volume concentration of 1% for 15 minutes to wash away SiO2. After solid-liquid separation, it is repeatedly washed with ultrapure water until the washing liquid is neutral. After solid-liquid separation, the solid is collected in a tray, placed in a vacuum dryer at 60°C and stirred and dried for 8 hours to obtain a product, which is elemental Si.

[0090] like Figure 6 The figure shows the X-ray diffraction pattern of the obtained product. The results show that the product has the characteristic diffraction peak of typical elemental silicon, and no diffraction peaks of other impurity phases.

[0091] like Figure 7As shown is the SEM image of the obtained product, it can be seen that the obtained elemental silicon is tubular, retaining the original one-dimensional morphology of halloysite, with a small grain size and a large aspect ratio. Its length can reach micrometer level and its diameter is less than 100nm.

[0092] Table 1 shows the element mass ratio of the silicon-based crude product in this example.

[0093]

[0094] The reduction rate of the silicon-based crude product was calculated by the following formula:

[0095]

[0096] Through calculation, the reduction rate of the silicon-based crude product obtained in this example is 92.2%.

[0097] Example 5

[0098] A certain mass of magnesium ingot (Mg≥99.90wt%) and silicon-containing precursor (acid-washed montmorillonite obtained by stirring and pickling in 1mol / L HNO3 for 5h, the purpose of adding HNO3 is to remove metal impurities such as iron and aluminum in montmorillonite, enrich the silicon content, and obtain relatively pure SiO2) are respectively put into the magnesium material evaporation bin and the reduction reaction bin through two feed and discharge pipes. Among them, the mass ratio of magnesium ingot to acid-washed montmorillonite is 0.9:1.

[0099] Then, put in the insulation pipe plug and seal the vacuum sealing flange. Start the rotating motor to make the furnace rotate at a speed of 5rpm.

[0100] Next, an external vacuum pump is used to evacuate the chamber, and then the heating program is started. While heating, the vacuum can be continuously drawn until the temperature rises to 500°C. At this time, the vacuum degree of the entire furnace is <500Pa. The magnesium material evaporation chamber and the reduction reaction chamber are then heated to 700°C. After reaching the specified temperature, they are kept warm for 1 hour.

[0101] After the reaction is completed, the obtained solid is stirred and washed with hydrochloric acid at a volume concentration of 5% for 10 hours. After solid-liquid separation, it is stirred and washed with hydrofluoric acid at a volume concentration of 1% for 15 minutes. After solid-liquid separation, it is repeatedly washed with ultrapure water until the washing liquid is neutral. After solid-liquid separation, the solid is collected in a tray, placed in a vacuum dryer at 60°C and stirred and dried for 8 hours to obtain the product. The obtained acid-activated montmorillonite-derived nanosilicon has the diffraction peak of elemental silicon, and the microscopic morphology is irregular granular, less than 100nm, and the tap density is 0.81g / cm 3 .

[0102] The liquid after washing with hydrochloric acid is rich in magnesium, aluminum, iron and other ions. The proportions are adjusted by supplementing ions, and the pH is stabilized at 10±0.2 using sodium hydroxide and sodium carbonate solutions. After aging and standing, hydrotalcite is finally obtained.

[0103] Table 2 shows the element mass ratio of the silicon-based crude product in this example.

[0104]

[0105] Through calculation, the reduction rate of the silicon-based crude product obtained in this example is 94.6%.

[0106] Example 6

[0107] A certain mass of forged white (MgO to CaO molar ratio of 1), ferrosilicon alloy (silicon content of 78.22%, S content of 0.03%, Al content of 0.09%), and fluorite (CaF2 content of 95.1%) are uniformly mixed in a mass ratio of 6:1.2:0.2, ball-milled and sieved through a 200-mesh sieve, and put into a magnesium material evaporation bin, and a certain mass of silicon-containing precursor (silicon ash) is put into a reduction reaction bin, and the molar ratio of magnesium element to silicon ash is 1:1.

[0108] Then, put in the insulation pipe plug and seal the vacuum sealing flange. Fill the tube furnace with argon gas with 200ml / L plastic for 30 minutes. Start the rotating motor to make the furnace rotate at 5rpm.

[0109] Next, the heating program is started. During heating, vacuum is continuously drawn until the furnace temperature reaches 500°C, at which time the vacuum degree of the entire furnace is <500Pa. The magnesium material evaporation chamber is then heated to 1200°C and the reduction reaction chamber is heated to 650°C. The reduction reaction lasts for 2 hours.

[0110] After the reaction is completed, the obtained solid is stirred and washed with hydrochloric acid with a volume concentration of 5% for 10 hours. After solid-liquid separation, it is stirred and washed with hydrofluoric acid with a volume concentration of 1% for 15 minutes. After solid-liquid separation, it is repeatedly washed with ultrapure water until the washing liquid is neutral. After solid-liquid separation, the solid is collected in a tray, placed in a vacuum dryer at 60°C and stirred and dried for 8 hours to obtain the product. The obtained product shows the diffraction peak of elemental silicon, retains the original morphology of silica ash, and presents a spherical structure of varying sizes, with an average particle size of 100 to 300nm.

[0111] The liquid after washing with hydrochloric acid is rich in magnesium, aluminum, iron and other ions. The proportions are adjusted by ion supplementation. Sodium hydroxide and sodium carbonate solutions are used to stabilize the pH at 10±0.2. After aging and standing, hydrotalcite is finally obtained.

[0112] Table 3 shows the element mass ratio of the silicon-based crude product in this example.

[0113]

[0114] Through calculation, the reduction rate of the silicon-based crude product obtained in this example is 90.7%.

[0115] Example 7

[0116] The steps are similar to those in Example 4, except that:

[0117] An external vacuum pump was used for evacuation. When the pressure gauge showed that the vacuum degree was less than 500Pa, a small amount of argon was filled in at a rate of 5mL / min, and the evacuation was continued until the reaction was completed. The small amount of argon further diluted the oxygen molecules in the device, increasing the reduction rate from 92.2% to 95.6%. The increase in the reduction rate means that more raw materials are successfully converted into the target product, thereby increasing the yield and reducing the production cost.

[0118] Example 8

[0119] The steps are similar to those in Example 4, except that the rice husks were pickled with 1M hydrochloric acid for 3 h, filtered and vacuum dried at 80°C for 24 h, and then pre-carbonized at 700°C for 3 h to obtain a precursor containing 63wt% carbon and 37wt% silicon dioxide. The mass ratio of the magnesium ingot to the precursor was 0.4:1. The final product contained 15.9wt% silicon, 83.4wt% carbon and 0.7wt% silicon carbide, and the reduction rate of the silicon-based crude product was 91.8%.

[0120] Example 9

[0121] The steps are similar to those in Example 4, except that the silicon-containing precursor used is a mixture of silicon dioxide and graphite, the mass ratio of the two is 0.7:0.3, and the mass ratio of the magnesium ingot to the silicon-containing precursor is 0.7:1. Among the reaction products, 47.6wt% is elemental silicon, 51.1wt% is elemental carbon, and 1.3wt% is silicon carbide. The reduction rate of the silicon-based crude product obtained in this example is 91.1%.

[0122] Example 10

[0123] The steps are similar to those in Example 4, except that the mass ratio of magnesium ingot, halloysite and sodium chloride is 1.4:1:0.5. After 30 minutes of heat preservation, carbon dioxide at -0.1 MPa is introduced as a carbon source and the temperature is continued to be maintained for 30 minutes. Among the reaction products, 76 wt% is elemental silicon and 24 wt% is elemental carbon. The reduction rate of the silicon-based crude product obtained in this example is 92.9%.

[0124] Comparative Example 1

[0125] The steps are similar to those in Example 4, except that:

[0126] Instead of using a vacuum pump to evacuate the furnace, the furnace body is filled with argon. Due to the mutual collision between magnesium atoms and argon molecules, the mean free path of magnesium vapor is reduced, so the uniformity and rate of the reduction reaction are reduced, resulting in most of the silicon-containing precursor remaining unreduced.

[0127] Comparative Example 2

[0128] The steps are similar to those in Example 4, except that:

[0129] Micron-sized magnesium powder is used as raw material, mixed with a silicon-containing precursor, and then put into a reduction reaction chamber. The direct contact between the magnesium powder and the silicon-containing precursor causes an excess of magnesium powder and excessive temperature in some areas, which leads to an increase in the amount of magnesium silicide generated, and the aluminum element combines with magnesium oxide or silicon oxide compounds to form high-temperature impurity phases such as spinel and mullite.

[0130] Comparative Example 3

[0131] The steps are similar to those in Example 4, except that:

[0132] The mass ratio of magnesium ingot, halloysite and sodium chloride is 0.7:1:5. Too much sodium chloride is mixed with the precursor, which hinders the contact between magnesium vapor and the precursor, resulting in a low reduction rate of the precursor.

[0133] Comparative Example 4

[0134] The steps are similar to those in Example 4, except that:

[0135] During this period, the furnace body is not rotated, so that the magnesium vapor and the precursor are not in uniform contact. A part of the halloysite reacts with the excess magnesium vapor to form magnesium silicide, and a part of the halloysite is not reduced because it cannot fully contact with the magnesium vapor.

[0136] Comparative Example 5

[0137] The steps are similar to those in Example 4, except that:

[0138] The whole furnace body was evacuated to a vacuum degree of 5 KPa. Since there was residual oxygen in the furnace body, although the reduction reaction produced some elemental silicon, the reduction of halloysite was not complete, and the diffraction peak of halloysite was still present in the XRD results.

[0139] Comparative Example 6

[0140] The steps are similar to those in Example 4, except that:

[0141] Without adding sodium chloride to the silicon-containing precursor, the nanotubes show a certain degree of agglomeration and the particle size of the product becomes larger.

[0142] Comparative Example 7

[0143] The steps are similar to those in Example 4, except that:

[0144] The mass ratio of magnesium ingot, halloysite and sodium chloride in the silicon-containing precursor is 0.7:1:5. Excessive sodium chloride hinders the diffusion of magnesium vapor, thereby reducing the reduction rate of the product.

[0145] Comparative Example 8

[0146] The steps are similar to those in Example 6, except that:

[0147] The magnesium material evaporation chamber and the reduction reaction chamber are heated to 1200℃, resulting in the formation of high-temperature phases such as spinel and mullite in the final product that are difficult to remove by pickling. Due to the high temperature and violent reaction, the particles not only become larger due to excessive recrystallization, but also the particles are over-sintered, and the original morphology of halloysite is destroyed.

[0148] Comparative Example 8

[0149] The steps are similar to those in Example 6, except that:

[0150] The mass ratio of ferrosilicon, ferrosilicon alloy and fluorite is 2:1.2:0.1. Since the proportion of ferrosilicon alloy is too small, its magnesium vapor generation rate is too low and halloysite cannot be fully reduced.

[0151] Comparative Example 10

[0152] The steps are similar to those in Example 6, except that:

[0153] The Si content in ferrosilicon alloy is 51.7%, the S content is 1.1%, and the Al content is 3.5%. The residue in the magnesium material area increases, and sulfides (such as magnesium sulfide) and more metal silicides are generated.

[0154] Comparative Example 11

[0155] The steps are similar to those in Example 6, except that:

[0156] Forged white, ferrosilicon alloy and fluorite were not ball-milled and sieved, and the average particle size of the particles used was >2mm. The reaction was incomplete, part of the ferrosilicon alloy did not fully participate in the reaction, and the reduction efficiency was low.

[0157] Application Examples

[0158] The elemental silicon obtained in Example 4 is used as the negative electrode material of the lithium ion battery to assemble button cells. Preparation of the working electrode: The active material (elemental silicon), acetylene black and sodium alginate are mixed evenly in a mass ratio of 7:1.5:1.5, then coated on a copper foil, and cut into discs with a diameter of 12 mm after vacuum drying. Both the counter electrode and the reference electrode are metallic lithium sheets. The electrolyte is ethylene carbonate / dimethyl carbonate in a volume ratio of 1:1 containing 1 mol / L LiPF6, to which 10 wt.% of fluorinated ethylene carbonate is added. The assembly process of the lithium ion battery is carried out in an argon glove box (water and oxygen concentrations are both less than 0.1 ppm).

[0159] The cycling performance results of the simple silicon prepared in Example 1 at a current density of 1.0 A / g (the first three cycles were activated at a low current density of 0.2 A / g) are shown in the figure ( Figure 8 ), the first cycle coulombic efficiency of this material is 81.1%, the specific capacity is as high as 1778mAh / g at a current density of 1.0A / g, and the specific capacity remains above 87.8% after 100 cycles, showing good cycle stability and good application potential in the field of lithium-ion batteries.

[0160] In summary, the embodiments of the present invention provide a production device and method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. Under vacuum conditions, the reduction of silicon-containing precursors by magnesium vapor is more uniform, and less heat is generated during the reaction, thereby reducing the generation of unreacted precursors and by-products, while better maintaining the original morphology of the silicon-containing precursor. The obtained silicon-based material is used as the negative electrode material of a lithium-ion battery, exhibiting good electrochemical lithium storage performance, proving its feasibility in lithium-ion battery applications.

[0161] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, characterized in that: The device comprises: a furnace body, a vacuum or atmosphere control system, a dual-temperature zone heating control system, a furnace body tilting system, a furnace body rotating system, a water cooling system, a heat preservation pipe plug and a control panel (19); Wherein, the furnace body is provided with a feed and discharge pipe (4) at both opposite ends; a perforated partition plate (10) is provided in the cavity of the furnace body, dividing the cavity of the furnace body into two parts, a magnesium material evaporation chamber (7) and a reduction reaction chamber (12); the magnesium material evaporation chamber (7) is used to place magnesium material; the reduction reaction chamber (12) is used to place a silicon-containing precursor or a modified product thereof; the perforated partition plate (10) is provided with air holes, and the air holes of the perforated partition plate (10) are connected to a perforated air guide pipe (11), and the perforated air guide pipe (11) is located in the reduction reaction chamber (12); Insulation pipe plugs (5) are provided at the positions where the two opposite ends of the furnace body are connected to the feed and discharge pipes (4), and are used to separate the feed and discharge pipes (4) from the magnesium material evaporation chamber (7) and the reduction reaction chamber (12); the insulation pipe plugs are multi-layer metal sheet insulation pipe plugs; The vacuum or atmosphere control system comprises: a vacuum valve (1), a pressure gauge (2) and a vacuum sealing flange (3); the end of the feed and discharge pipe (4) is provided with a vacuum sealing flange (3), the vacuum sealing flange (3) is connected to a gas pipeline, the gas pipeline is provided with a vacuum valve (1) and a pressure gauge (2), the pressure gauge (2) is located between the vacuum sealing flange (3) and the vacuum valve (1); the gas pipeline is externally connected to a vacuum pump or an inert gas; The dual-temperature zone heating control system comprises: a heater (8) and a heat insulation layer (9); a heater (8) is respectively arranged on the outer side wall of the furnace body corresponding to the magnesium material evaporation chamber (7) and the reduction reaction chamber (12), and is used to independently heat the magnesium material evaporation chamber (7) and the reduction reaction chamber (12); the heat insulation layer (9) is arranged on the outer side wall of the furnace body; The furnace body tilting system is used to adjust the tilting of the furnace body so that the furnace body is tilted to dump the silicon-based crude product; The furnace body rotation system is used to adjust the rotation of the furnace body; The water cooling system is used to prevent the sealing ring of the vacuum sealing flange from leaking due to high temperature; the water cooling system comprises: a water cooling pipe, a water cooling liquid, and a circulating water pump (17); the water cooling pipe is wound around the feed and discharge pipe (4), and the circulating water pump (17) is connected to the water cooling pipe; the water cooling liquid circulates in the water cooling pipe; The control panel (19) is electrically connected to the furnace body tilting system and the furnace body rotating system, and is used to control the operation of the furnace body tilting system and the furnace body rotating system.

2. The device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to claim 1, characterized in that: The furnace body tilting system comprises: a support frame (16), an electric push rod (14) and a rotary joint (18); the support frame (16) is located below the furnace body, the electric push rod (14) is fixedly connected to the support frame (16), the electric push rod (14) is hinged to one end of the furnace body, and the rotary joint (18) is hinged to the other end of the furnace body, and is used to tilt the furnace body to dump the silicon-based crude product; the control panel (19) is electrically connected to the electric push rod (14), and the control panel (19) is provided with a tilt angle adjustment button; Or / and, the furnace body rotation system comprises: a tubular furnace rotating motor (6) and a transmission component; the transmission component is connected between the tubular furnace rotating motor (6) and the end of the furnace body, and is used to drive the rotation of the furnace body; the control panel (19) is electrically connected to the tubular furnace rotating motor (6).

3. The device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to claim 1, characterized in that: The perforated air guide tube (11) is provided with a truncated cone-shaped opening on its circumference; Alternatively, a plurality of vertical short tubes are symmetrically arranged on the tube wall of the perforated air guide tube (11), and outlets are symmetrically arranged on the side walls of the vertical short tubes; Alternatively, a plurality of T-shaped pipes are symmetrically arranged on the wall of the perforated air guide pipe (11), and the two opposite ends of the T-shaped pipes are outlets.

4. The device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to claim 1, characterized in that: The closing sections at both ends of the furnace body have a trapezoidal structure; or / and, the furnace body has an arc-shaped structure with closing ends at both ends.

5. The device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to any one of claims 1 to 4, characterized in that: Two heaters (8) are arranged between the outer wall of the furnace body and the heat insulation layer (9) for heating the magnesium material evaporation chamber (7) and the reduction reaction chamber (12) respectively; The control panel (19) is electrically connected to both of the two heaters (8). The control panel (19) is provided with a real-time temperature display screen and an indicator diode for monitoring the temperature and the operating status of the heaters. The control panel (19) can control the heating temperatures of the magnesium material evaporation chamber (7) and the reduction reaction chamber (12) respectively.

6. A method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors, characterized in that: The method uses the device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors as described in any one of claims 1 to 5, and the method comprises: S1, placing magnesium material and silicon-containing precursor into magnesium material evaporation chamber (7) and reduction reaction chamber (12) respectively, sealing, starting the tubular furnace rotation motor (6), rotating the furnace body, and evacuating the furnace body with an external vacuum pump; The magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, or magnesium ingot and / or magnesium-containing alloy; the mineralizer is selected from fluorite; S2, evacuating the whole furnace body to a vacuum degree of less than 500 Pa, heating to initiate a reduction reaction; when the magnesium material is selected from magnesium ingots and / or magnesium-containing alloys, the heating temperature of the magnesium material evaporation chamber (7) is 650-1000° C.; when the magnesium material is selected from calcined white, ferrosilicon alloy and mineralizer, the heating temperature of the magnesium material evaporation chamber (7) is 1100-1300° C.; the heating temperature of the reduction reaction chamber (12) is 650-850° C.; S3, pickling, water washing and drying; wherein, after the pickling, the obtained solid is stirred and washed with hydrofluoric acid, the solid is collected and placed in a vacuum dryer for drying to obtain the target product; after the pickling, the liquid obtained by solid-liquid separation is adjusted in pH value, and a magnesium source or an aluminum source is added to prepare hydrotalcite.

7. The method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to claim 6, characterized in that: In step S1, before evacuating the magnesium material, the magnesium material evaporation chamber (7) and the reduction reaction chamber (12) are filled with inert gas; or / and, in step S1, when the pressure gauge shows that the vacuum degree is less than 500 Pa, argon gas is charged at a rate of less than 50 mL / min, and vacuum is continuously drawn until the reaction is completed; or / and, in step S1, after the inorganic salt is mixed with the silicon-containing precursor material, the silicon-containing precursor is reduced by magnesium vapor; Or / and, in step S1, the mass ratio of the ferrosilicon alloy, calcined white and mineralizer is 6:(0.8-1.2):(0.1-0.2); Or / and, in step S1, the Si content in the ferrosilicon alloy is higher than 70%, the S content is lower than 0.1%, and the Al content is lower than 0.5%; Or / and, in step S1, the ferrosilicon alloy, calcined white and mineralizer are all passed through a sieve of >100 mesh; Or / and, in step S1, the furnace rotation speed is 1-100 rpm; Or / and, in step S2, the silicon-containing precursor is selected from at least one of the following: clay mineral, silicon-carbon precursor, nano-silicon dioxide, or a modified product of these three precursors; the modification method includes at least one of heat treatment, acid treatment, mechanical treatment, organic modification and inorganic modification; or / and, in step S2, a carbon source is added to the silicon-containing precursor; Or / and, in step S2, the silicon-containing precursor or its modified product is pre-decontaminated and dried in an oven, and the selected particles are all sieved with a mesh of >100 mesh; Or / and, the molar ratio of the magnesium material to the silicon-containing precursor is 0.3 to 2.5:1; Or / and, in step S2, the magnesium material evaporation chamber (7) and the reduction reaction chamber (12) are heated to their respective heating temperatures, and then are kept warm independently; wherein the heat preservation time of the reduction reaction chamber (12) is further kept warm for 0.5 to 8 hours on the basis of covering the time difference between the two chambers reaching the predetermined temperature; the heat preservation time of the magnesium material evaporation chamber (7) is greater than or equal to the heat preservation time of the reduction reaction chamber (12), and its heat preservation time covers the time difference between the two chambers reaching the predetermined temperature; Or / and, in step S3, the pickling is selected from at least one of hydrochloric acid, sulfuric acid and nitric acid, the volume concentration of the acid used is 1-20%, and the washing time lasts for 0.1-10 hours; the volume concentration of the hydrofluoric acid is 1-10%, and the washing time lasts for 1-60 minutes; Or / and, in step S3, the pickling liquid obtained by solid-liquid separation is supplemented with a magnesium source or an aluminum source, and the pH is adjusted to 6 to 14 to prepare hydrotalcite.

8. The method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors according to claim 7, characterized in that: In step S1, the inorganic salt is selected from at least one of NaCl, LiCl, KCl, CaCl2 and MgCl2; Or / and, in step S1, the mass ratio of the inorganic salt to the silicon-containing precursor is 0.1 to 5:1; Or / and, in step S2, the clay mineral is selected from any one or more of montmorillonite, kaolinite, halloysite, palygorskite, talc, black talc, muscovite, saponite, biotite, illite, chlorite, sepiolite and pyrophyllite; Or / and, in step S2, the silicon-carbon precursor is selected from any one or more of the following: rice husk, straw, bamboo leaf, reed, bagasse, silicon-containing plastic, silicon-containing rubber, and waste clay adsorbing organic matter; Or / and, in step S2, the carbon source is selected from any one or more of carbon powder, graphite, graphene, carbon nanotubes, carbon fiber, and carbon black.

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