An apparatus and method for preparing silicon-based materials by magnesiothermic reduction of silicon-containing precursors

Abstract

The present invention discloses a device and method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. The device includes: 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 thermal insulation pipe plug, and a control panel; wherein, feed and discharge pipes are provided at both opposite ends of the furnace body; a perforated partition is provided in the cavity of the furnace body, dividing the cavity of the furnace body into a magnesium material evaporation chamber and a reduction reaction chamber; air holes are provided on the perforated partition, and a perforated gas pipe is connected to the air holes of the perforated partition, and the perforated gas pipe is located in the reduction reaction chamber. The present invention adopts a dual-temperature zone heating control system, enabling independent adjustment of the evaporation temperature of the magnesium material and the reduction reaction temperature. A magnesium vapor perforated gas pipe 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 gas pipe. This device can achieve the thermal reduction of silicon-containing precursors by magnesium vapor under vacuum conditions.

Description

Technical Field

[0001] The present invention relates to a device for preparing silicon-based materials, and particularly to a device and method for preparing silicon-based materials by magnesiothermic reduction of silicon-containing precursors. Background Art

[0002] Silicon-based materials refer to nanosilicon, porous silicon, silicon oxides, silicon carbides, silicon nitrides, and their various composite materials. Due to the excellent properties of these materials, 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.

[0003] There are various methods for preparing silicon-based materials, including high-energy ball milling, metallothermic reduction, and chemical vapor deposition. Among them, magnesiothermic 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 650-1000°C. This method can effectively prevent the agglomeration of silicon particles and retain the porous structure of the precursor, so it is considered an effective and economical method for preparing high-performance silicon-based materials.

[0004] From an operational perspective, the traditional magnesiothermic reduction method usually involves uniformly mixing a silicon-containing precursor, micron-sized magnesium powder, and a heat regulator (such as NaCl) and placing them in a tube furnace. Under the protection of an inert atmosphere, it is heated to several hundred degrees Celsius at a specific heating rate and held 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-sized magnesium powder is highly flammable and explosive, so extremely strict safety measures must be taken during the production process, greatly increasing the operational risk and production difficulty;

[0006] (2) Reaction efficiency and product quality issues: The uneven mixing of the silicon-containing precursor and micron-sized magnesium powder, as well as the uneven temperature field distribution, may lead to local overheating, not only generating more by-products (such as magnesium silicide), but also causing silicon particle agglomeration and template structure damage;

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

[0008] The object of the present invention is to provide a device and method for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. A dual-temperature zone heating control system is adopted, so that the evaporation temperature of magnesium material and the reduction reaction temperature can be independently adjusted. A magnesium vapor porous gas pipe with a special structure is designed inside to ensure that magnesium vapor can be evenly distributed in the reduction reaction chamber, and at the same time prevent the porous gas pipe from being blocked. This device can realize the thermal reduction of silicon-containing precursors by magnesium vapor under vacuum conditions.

[0009] To achieve the above object, the present invention provides a device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors. The device includes: 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, heat preservation pipe plugs, and a control panel; wherein, feeding and discharging pipes are provided at both opposite ends of the furnace body; a partition plate with holes is provided in the cavity of the furnace body, dividing the cavity of the furnace body into a magnesium material evaporation chamber and a reduction reaction chamber; the magnesium material evaporation chamber is used for placing magnesium materials; the reduction reaction chamber is used for placing silicon-containing precursors or their modified products; air holes are provided on the partition plate with holes, and a porous gas pipe is connected to the air holes of the partition plate with holes, and this porous gas pipe is located in the reduction reaction chamber; heat preservation pipe plugs are provided at the positions where the two opposite ends of the furnace body are connected to the feeding and discharging pipes, for separating the feeding and discharging pipes from the magnesium material evaporation chamber and the reduction reaction chamber; the heat preservation pipe plugs are multi-layer metal sheet heat preservation pipe plugs; the vacuum or atmosphere control system includes: a vacuum valve, a pressure gauge, and a vacuum sealing flange; a vacuum sealing flange is provided at the end of the feeding and discharging pipe, a gas pipe is connected to the vacuum sealing flange, a vacuum valve and a pressure gauge are provided on this gas pipe, and the pressure gauge is located between the vacuum sealing flange and the vacuum valve; the gas pipe is externally connected to a vacuum pump or inert gas; the dual-temperature zone heating control system includes: a heater and a heat insulation layer; a heater is respectively provided on the outer side walls of the furnace body corresponding to the magnesium material evaporation chamber and the reduction reaction chamber, for independently heating the magnesium material evaporation chamber and the reduction reaction chamber respectively; the heat insulation layer is provided 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 tilts to pour out the silicon-based crude product; the furnace body rotating system is used to adjust the rotation of the furnace body; the water cooling system is used to prevent air leakage caused by the high temperature of the sealing ring of the vacuum sealing flange; the water cooling system includes: a water cooling pipe, a water cooling liquid, and a circulating water pump; the water cooling pipe is wound around the feeding and discharging 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 both the furnace body tilting system and the furnace body rotating system, for controlling the operation of the furnace body tilting system and the furnace body rotating system.

[0010] Preferably, the furnace body tilting system includes: a support frame, an electric push rod, and a rotary 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 rotary joint is hinged to the other end of the furnace body for tilting the furnace body to pour out the silicon-based crude product; the control panel is electrically connected to the electric push rod, and the control panel is provided with a tilting angle adjustment button; or / and, the furnace body rotation system includes: a tube furnace rotation motor and a transmission component; the transmission component is connected between the tube furnace rotation motor and the end of the furnace body for driving the rotation of the furnace body; the control panel is electrically connected to the tube furnace rotation motor.

[0011] Preferably, the circumferential wall of the perforated gas guide pipe is provided with a frustum-shaped opening with a shrinking opening; or, a plurality of vertical short pipes are symmetrically arranged on the pipe wall of the perforated gas guide pipe, and outlets are symmetrically arranged on the side walls of the vertical short pipes; or, a plurality of T-shaped pipes are symmetrically arranged on the pipe wall of the perforated gas guide pipe, and the opposite ends of the T-shaped pipes are outlets.

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

[0013] Preferably, two heaters for heating the magnesium material evaporation chamber and the reduction reaction chamber respectively are arranged between the outer side wall of the furnace body and the heat insulation layer; the control panel is electrically connected to both heaters, and the control panel is provided with a real-time temperature display screen and indicator diodes for monitoring the temperature and the operating state of the heaters, and the control panel can respectively control the heating temperatures of the magnesium material evaporation chamber and the reduction reaction chamber.

[0014] Preferably, the multi-layer metal sheet heat preservation pipe plug is a multi-layer metal foil heat preservation 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. This method uses the device for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor, and this method includes:

[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 tube furnace rotation motor, rotate the furnace body, and connect an external vacuum pump to pump vacuum;

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

[0018] S2. Evacuate to make the vacuum degree in the whole furnace body < 500 Pa, and carry out heating to initiate the reduction reaction; when the magnesium material is selected from magnesium ingots or / and magnesium-containing alloys, the heating temperature of the magnesium material evaporation bin is 650 - 1000 °C; when the magnesium material is selected from calcined dolomite, ferrosilicon alloy and mineralizing agent, 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. Carry out pickling, water washing and drying; wherein, after pickling, the obtained solid is further stirred and washed with hydrofluoric acid, the solid is collected and placed in a vacuum dryer for drying to obtain the target product; after pickling, the pH value of the liquid obtained by solid-liquid separation is adjusted, and a magnesium source or an aluminum source is supplemented to prepare hydrotalcite.

[0020] Preferably, in step S1, before vacuum pumping, the magnesium material evaporation chamber and the reduction reaction chamber are filled with an inert gas; or / and, in step S1, when the pressure gauge shows that the vacuum degree < 500 Pa, argon is filled at a rate of < 50 mL / min (preferably 5 mL / min), and at the same time, vacuum pumping continues until the reaction ends; 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 dolomite, 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 dolomite, and mineralizer all pass through a sieve with a mesh size > 100; or / and, in step S1, the rotational speed of the furnace body is 1 - 100 rpm; or / and, in step S2, the silicon-containing precursor is selected from at least one of the following: clay minerals, silicon-carbon precursors, nano-silica, or modified products of these three precursors; the modification methods include 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 methods include 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-treated for impurity removal and dried in an oven, and the selected particles all pass through a sieve with a mesh size > 100; or / and, the molar ratio of the magnesium material to the silicon-containing precursor is 0.3 - 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 insulated independently; wherein, the insulation time of the reduction reaction chamber is 0.5 - 8 h based on covering the time difference when the two chambers reach the predetermined temperature; the insulation time of the magnesium material evaporation chamber is greater than or equal to the insulation time of the reduction reaction chamber, and its insulation time covers the time difference when the two chambers reach 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 h; the volume concentration of hydrofluoric acid is 1 - 10%, and the washing time lasts for 1 - 60 min; or / and, in step S3, the acid washing 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 NaCl, LiCl, KCl, CaCl 2 and MgCl 2at least one of them; and / or, in step S1, the mass ratio of the inorganic salt to the silicon-containing precursor is 0.1-5:1; and / or, in step S2, the clay mineral is selected from any one or more of montmorillonite, kaolinite, halloysite, palygorskite, talc, black talc, muscovite, soapstone, biotite, illite, chlorite, sepiolite and pyrophyllite; and / or, 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, waste clay soil adsorbed with organic matter; and / or, in step S2, the carbon source is selected from any one or more of carbon powder, graphite, graphene, carbon nanotube, carbon fiber, carbon black.

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

[0023] (1) The device of the present invention adopts an integrated design. The 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 rotating system, a water cooling system, a heat preservation pipe plug and a control panel. By separating the magnesium material from the silicon-containing precursor, the selection of the magnesium material is not limited by the reaction temperature, thus expanding the types of available magnesium materials. In addition, the device adopts a dual-temperature zone heating control system, enabling independent adjustment of the evaporation temperature of the magnesium material and the reduction reaction temperature. The number of device interfaces is reduced, reducing the leakage risk, and a heat preservation pipe plug and a water cooling device are configured at the extended part of the furnace body, so that silica gel with lower cost can be selected for sealing. A magnesium vapor porous gas pipe 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 porous gas pipe. This device can realize the thermal reduction of the silicon-containing precursor by magnesium vapor under vacuum conditions;

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

[0025] (3) In the method of the present invention, from the perspective of silicon-containing precursors, clay minerals are abundant in reserves, environmentally friendly, and inexpensive, and naturally have microscopic morphologies such as sheet-like, sheet cluster-like, fibrous, tubular, and needle-like. After modification by mechanical treatment, acid treatment, heat treatment, etc., these nanostructures are retained or strengthened, and their size, morphology, and surface chemical properties can be precisely adjusted. The present invention also selects silicon-carbon precursors such as rice husks, straws, bamboo leaves, bagasse, silicon-containing plastics, silicon-containing rubbers, waste bleaching clay adsorbed with organic matter, etc. These materials may not have nanostructures without special treatment, but after appropriate modification treatments (such as carbonization, pickling, pore expansion treatment, etc.), they can exhibit nanostructures or nano-scale characteristics, and these characteristics make them ideal carriers of silicon elements 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 by using micro-nano magnesium powder particles. From the perspective of the magnesium thermal reduction method, compared with traditional solid-state reactions, the reaction energy barrier between magnesium vapor and silicon-containing precursors is lower, and less heat is generated. In addition, the reaction is carried out under vacuum conditions, which not only reduces costs but also enables magnesium vapor to diffuse and penetrate more freely in 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 the morphology damage caused by local overheating. Therefore, even without using inorganic salts to regulate heat, or only using a small amount of inorganic salts to regulate heat, products 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 oxides, silicon carbides, silicon nitrides, 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. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors of the present invention.

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

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

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

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

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

[0033] Figure 7 Scanning electron microscope image of the micro-nano silicon obtained in Example 4.

[0034] Figure 8 Cycling performance of the micro-nano silicon obtained in the application example as the anode material of a lithium-ion battery.

[0035] Labels: 1 - Vacuum valve; 2 - Pressure gauge; 3 - Vacuum sealing flange; 4 - Feed and discharge area; 5 - Heat preservation pipe plug; 6 - Tube furnace rotation motor; 7 - Magnesium material evaporation chamber; 8 - Heating element; 9 - Heat insulation layer; 10 - Partition with holes; 11 - Gas pipe with holes; 12 - Reduction reaction chamber; 13 - Upper housing; 14 - Electric push rod; 15 - Lower housing; 16 - Support body; 17 - Circulating water pump; 18 - Rotary joint; 19 - Control panel. Specific implementation manners

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope 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 two end closing sections of the furnace body are both designed as trapezoidal structures, which contain two independent feed and discharge pipes, respectively used for feeding magnesium materials / silicon-containing precursors, or recovering magnesium slag / crude silicon-based materials. The partition with holes divides the furnace body into a magnesium material evaporation chamber and a reduction reaction chamber. Through the partition with holes and the gas pipe with holes, magnesium vapor is evenly distributed in the reduction reaction chamber, thereby realizing the effective reduction of the silicon-containing precursor and avoiding blockage of the gas pipe.

[0038] The device of the present invention adopts a dual-temperature control system, enabling the evaporation temperature of the magnesium material and the reduction reaction temperature to be independently adjusted to meet the different requirements of the evaporation and reduction processes. 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 provides a detailed description of a device for preparing silicon-based materials by magnesium thermal reduction of silicon-containing precursors 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 housing, 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 19.

[0042] Feeding and discharging pipes 4 are provided at both opposite ends of the above-mentioned furnace body. A perforated partition plate 10 is provided in the cavity of the furnace body, dividing the cavity of the furnace body into a magnesium material evaporation chamber 7 and a reduction reaction chamber 12. Among them, the magnesium material evaporation chamber 7 is used to place magnesium materials such as calcined dolomite, magnesium ingots or magnesium-containing alloys, etc.; the reduction reaction chamber 12 is used to place silicon-containing precursors. The perforated partition plate 10 is provided with air holes, and a perforated gas pipe 11 is connected to the air holes of the perforated partition plate 10. The perforated gas pipe 11 is located in the reduction reaction chamber 12, and magnesium vapor is evaporated and transferred from the magnesium material evaporation chamber 7 to the reduction reaction chamber 12 through the perforated gas pipe 11, so as to realize the reduction of silicon-containing precursors.

[0043] The above-mentioned perforated gas pipe 11 is of a hollow structure, and the hole positions at one end thereof coincide with the hole positions of the perforated partition plate 10 to ensure that the magnesium vapor in the magnesium material evaporation chamber 7 can disperse into the perforated gas pipe 11 from the perforated partition plate 10. The circumference of the perforated gas pipe 11 is provided with a frustum-shaped opening with a shrinking opening, so that the magnesium vapor diverges in the reduction reaction chamber 12.

[0044] Thermal insulation pipe plugs 5 are provided at the positions where the two opposite ends of the above-mentioned furnace body are connected to the feeding and discharging pipes 4, and gaps are left at the set positions of the thermal insulation pipe plugs 5 to separate the feeding and discharging pipes 4 from the magnesium material evaporation chamber 7 and the reduction reaction chamber 12. While effectively ensuring good heat insulation effect, it can also ensure gas circulation and does not affect the vacuum pumping operation inside the furnace body.

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

[0046] Both end closing sections of the above-mentioned furnace body have a trapezoidal structure.

[0047] The above-mentioned housing can 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, further ensuring the heat insulation effect.

[0048] The vacuum or atmosphere control system includes: 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. The pressure gauge 2 is located between the vacuum sealing flange 3 and the vacuum valve 1. The gas pipeline can be externally connected to a vacuum pump or inert gas, used for vacuum pumping or filling inert gases such as argon and helium into the furnace body to achieve 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. A heat insulation layer 9 is provided on the outer side wall of the furnace body, and two heaters 8 for heating the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 respectively are provided between the outer side wall of the furnace body and the heat insulation layer 9, enabling separate temperature control of the magnesium material evaporation chamber and the reduction reaction chamber.

[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, used to tilt the furnace body to pour out the silicon-based crude product. The electric push rod 14 can be built into the lower housing 15 and be firmly fixed on the base through the support 16. The upper housing 13 is connected to the lower housing 15 through the electric push rod 14 and the rotary joint 18 to achieve tilting of the furnace body.

[0051] The control panel 19 is electrically connected to the tube furnace rotation motor 6, the heater 8, and the electric push rod 14, and is equipped with a real-time temperature display screen and indicator diodes, used to monitor the temperature and the operating status of the heater and the rotation motor. Through the programming function, the control panel can independently adjust the heating temperatures of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12, and precisely control the rotation speed of the tube furnace to ensure precise regulation of the reaction process. In addition, the panel is equipped with tilt angle adjustment buttons, allowing the operator to flexibly adjust the tilt angle of the furnace body by controlling the electric push rod 14, facilitating efficient pouring of the silicon-based crude product after the reaction and improving the operation efficiency.

[0052] The furnace body rotation system includes: a tube furnace rotation motor 6 and transmission components. The transmission components are used to connect the tube furnace rotation motor 6 and the furnace body, and the continuous rotation of the furnace body is achieved through the tube furnace rotation motor 6. The transmission components are structures known to those skilled in the art. For example, a driving gear is sleeved and fixedly connected on the output shaft of the tube furnace rotation motor 6, and driven gears are sleeved and fixed at both ends of the furnace body. The driving gear and the driven gears are meshed and connected, and the rotation of the furnace body is achieved through the rotation of the tube furnace rotation motor 6. There are many such transmission component structures, and only one feasible way is listed here. Other transmission components can also be used to achieve the transmission function.

[0053] The water cooling system includes: water cooling pipes, water cooling liquid, and a circulation water pump 17. The water cooling pipes are wound around the feed and discharge pipe 4, the circulation water pump 17 is communicated with the water cooling pipes, and the water cooling liquid circulates in the water cooling pipes. The water cooling system helps to prevent the interface deformation or the increase of the sealing gap caused by thermal expansion of the metal flange and the connecting components, and to prevent the leakage of air caused by the high temperature of the sealing ring of the vacuum sealing flange, thereby more effectively ensuring the sealing performance of the furnace body at high temperature.

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

[0055] During the operation process, first, the magnesium material and the silicon-containing precursor or its modified product are respectively loaded into the magnesium material evaporation bin 7 and the reduction reaction bin 12 through the feed and discharge pipe 4. In the magnesium material evaporation bin 7, ferrosilicon alloy thermal, calcined dolomite, and mineralizer can be selected as the magnesium material, or magnesium ingots or magnesium-containing alloys can be selected.

[0056] Then, the heat preservation pipe plugs 5 are inserted. The heat preservation pipe plugs 5 are directly inserted into the furnace tubes from both ends of the furnace body and are respectively arranged at the feed end and the discharge end. The size of the heat preservation pipe plugs 5 matches the inner diameter of the furnace tubes, which is convenient for installation and fixation. At the same time, there are narrow gaps between the heat preservation pipe plugs 5 and the feed pipe and the discharge pipe to ensure gas circulation, which neither affects the vacuum pumping operation inside the furnace body nor can effectively ensure a good heat insulation effect. After insertion, the multi-layer heat insulation structure of the heat preservation pipe plugs 5 effectively seals both ends of the furnace body, and significantly reduces heat transfer by reflecting radiant heat, preventing the condensation of magnesium vapor in the low-temperature area.

[0057] Then, seal it through the vacuum sealing flange 3, start the tube furnace rotating motor 6 to keep the furnace body rotating at a constant speed; before vacuum pumping, fill the reaction device with inert gas, and then connect an external vacuum pump to pump vacuum. The set value of the vacuum degree is <500 Pa. Observe the vacuum degree of the pressure gauge 2 until it reaches the set value, and then close the vacuum valve 1. Then, perform temperature control through the programming function of the control panel 19. Preset the heating rate, target temperature, and holding time in advance, and then turn on the heater 8. The heating temperature for the thermal reduction of calcined dolomite with ferrosilicon alloy is 1100 - 1300 °C, and the heating temperature for using calcined magnesium ingot / magnesium-containing alloy is 650 - 1000 °C. Heat the magnesium material evaporation chamber 7 to the set temperature to produce magnesium vapor; the magnesium vapor is dispersed into the reduction reaction chamber 12 through the pore-retaining partition 10 and the perforated gas pipe 11, and undergoes a reduction reaction with the silicon-containing precursor. The heating temperature of the reduction reaction chamber 12 is 650 - 850 °C. Keep the system insulated at the set temperature for a period of time. The holding time is 0.5 - 3 h based on the time difference when the two chambers reach the predetermined temperature 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 holding time of the magnesium material evaporation chamber 7 should be calculated starting from when it reaches the predetermined temperature, while the holding time of the reduction reaction chamber 12 needs to be slightly longer to cover the time difference between the two chambers reaching the predetermined temperature. The dual-temperature zone heating control system controls the temperatures of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 respectively through the control panel, independently sets the target temperature and holding time, and ensures that the two chamber areas 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 sensors monitor the furnace body temperature in real time to ensure precise control of the reaction process.

[0058] After the reaction is completed, take out the solid substance generated in the reduction reaction chamber 12; through post-treatment steps such as pickling, washing, and drying, the target silicon-based nanomaterial can be obtained.

[0059] Example 2

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

[0061] The above-mentioned perforated gas pipe 11 is of a hollow structure, and a number of T-shaped pipes are symmetrically arranged on its 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 magnesiothermic reduction of silicon-containing precursors is basically similar to that of Example 1, except that:

[0064] The above-mentioned perforated gas guide tube 11 is of a hollow structure, and a number of vertical short tubes are symmetrically arranged on its 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 a silicon-based material by magnesium thermal reduction of a silicon-containing precursor. A safer magnesium material, such as magnesium ingot, is used as a raw material, and there is no need to use flammable and explosive magnesium powder. Ferrosilicon alloy is used to thermally reduce calcined dolomite, or magnesium ingot or magnesium-containing alloy is calcined to generate magnesium vapor, and then the magnesium vapor is brought into full contact with the silicon-containing precursor to undergo a reduction reaction to generate a crude silicon-based product. The two reactions of the present invention are carried out in two isolated different reaction zones - a magnesium material evaporation zone and a reduction reaction zone. Since the reaction energy requirement of magnesium vapor is usually lower than that of a solid-state reaction, this method uses a small amount of heat regulator, or does not use a regulator, and can also effectively reduce the generation of high-temperature phases and better maintain the original morphology of the precursor. At the same time, the whole 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 by-products, but also effectively avoids the morphological damage caused by local overheating. Therefore, high-efficiency reduction can be achieved without or with only a small amount of inorganic salts to regulate heat, while maintaining the integrity of the material morphology and significantly reducing the generation of unreacted precursors and side reaction products.

[0066] The method for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor of the present invention uses the above-mentioned device for preparing a silicon-based material by magnesium thermal reduction of a silicon-containing precursor, and specifically includes the following steps:

[0067] S1. Put the magnesium material and the silicon-containing precursor into the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 respectively, seal them, then start the tube furnace rotation motor to rotate the furnace body, and then externally connect a vacuum pump to evacuate.

[0068] Through research by the inventor, it is found that silicon-based materials with different morphologies can be prepared by using a self-template method of vacuum magnesium vapor thermal reduction of a silicon-containing precursor. For example, sheet-like morphologies can be prepared using montmorillonite, tubular morphologies can be obtained using halloysite, and fibrous morphologies can be obtained using sepiolite. This is because magnesium vapor is dispersed at the atomic level, reducing the energy barrier for reducing the silicon-containing precursor and reducing the generated heat, so its original morphology is relatively completely retained; 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 by-products, but also effectively avoids the morphological damage caused by local overheating. Therefore, high-efficiency reduction can be achieved without or with only a small amount of inorganic salts to regulate heat, while maintaining the integrity of the material morphology and significantly reducing the generation of unreacted precursors and side reaction products;

[0069] S2. The vacuum degree of the whole furnace body is pumped to <500 Pa, and then heating is carried out to initiate the reduction reaction. Since the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 are connected through the porous partition plate 10, the vacuum degrees of the two chambers are always the same.

[0070] Heating the furnace body generates magnesium vapor, and the generated magnesium vapor is used to carry out a reduction reaction on the silicon-containing precursor to prepare a crude product of the silicon-based material. During the heating process, the temperatures of the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 are synchronized, and finally they are heated to their respective required temperatures. When the magnesium material is selected from magnesium ingots or / and 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 dolomite, 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 with water and drying.

[0072] After the reduction reaction is completed, the crude product of the silicon-based material is pickled, washed with water and dried to obtain the target silicon-based nano / micro material.

[0073] Further, in step S1, before vacuum pumping, the magnesium material evaporation chamber and the reduction reaction chamber are filled with inert gas; or / and, when the pressure gauge shows that the vacuum degree <500 Pa, argon is filled at a rate of 5 mL / min, and at the same time, vacuum pumping continues until the reaction ends.

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

[0075] By adding different types of silicon-containing precursors and regulating parameters such as the magnesium-silicon ratio, the mass ratio of the magnesium material to the silicon-containing precursor, and the reaction time, various different types of silicon-based nano / micro materials can be prepared. For example, when the precursor is a silicon-carbon precursor, silicon carbide (SiC) may be generated; under the condition of too high magnesium vapor concentration, metal silicides, such as magnesium silicide (Mg 2 Si), may be formed; when there is an iron source (such as iron powder, iron filings or iron oxide Fe 2 O 3 , Fe 3 O 4 ) in the precursor, iron silicides (FeSi, FeSi 2 ) 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 / micro materials can include various types of materials such as nano / micro-scale elemental silicon, silicon monoxide, silicon carbide, silicon nitride, and metal silicides.

[0076] Further, in step S1, the molar ratio of the magnesium material to the silicon-containing precursor is calculated according to the molar ratio of magnesium vapor to the component to be reduced in the silicon-containing precursor, and the molar ratio of the two is 0.3-2.5:1. In the magnesium material evaporation chamber 7, ferrosilicon alloy can be selected to thermally reduce calcined dolomite to produce magnesium vapor. This magnesium material is prepared by mixing ferrosilicon alloy, calcined dolomite, and mineralizer, and the mass ratio of the three is 6:(0.8-1.2):(0.1-0.2), or calcined magnesium ingot / magnesium-containing alloy can be selected 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, soapstone, biotite, illite, chlorite, sepiolite, pyrophyllite; silicon-carbon precursors such as rice husk, straw, bamboo leaves, bagasse, silicon-containing plastics, silicon-containing rubbers, waste clay for adsorbing organic substances, etc.; silicon dioxide; or modified products of these three precursors; the modification methods include at least one of heat treatment, acid treatment, mechanical treatment, organic modification, and inorganic modification.

[0078] Further, 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 dolomite, and mineralizer all pass through a sieve with a mesh size of >100 meshes.

[0079] Further, in step S1, the silicon-containing precursor or its modified product is pre-removed of impurities and dried in an oven, and the selected particles all pass through a sieve with a mesh size of >100 meshes.

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

[0081] Further, in step S1, after the inorganic salt is mixed with the silicon-containing precursor material, the silicon-containing precursor is reduced by magnesium vapor. The inorganic salt is one or more of NaCl, LiCl, KCl, CaCl 2 and MgCl 2 The mass ratio of the inorganic salt to the mass of the silicon-containing precursor is 0.1-5:1. Magnesium thermal reduction releases a large amount of heat, which easily causes local overheating, leading to the melting of silicon or the aggregation of nanoparticles. Utilizing the heat absorption of the inorganic salt helps to maintain the morphology and size of the material. Since magnesium vapor is atomically dispersed, it reduces the reduction energy barrier, reduces heat release and the generation of high-temperature by-products. Therefore, even without or only requiring a small amount of inorganic salt, efficient reduction can be achieved, but adding inorganic salt can better control the morphology and particle size of the material.

[0082] Further, in step S2, the vacuum degree of the whole furnace body < 500 Pa, and the magnesium material evaporation chamber 7 and the reduction reaction chamber 12 should finally be heated to their respective required temperatures at the same heating rate. When the magnesium material is selected from magnesium ingots or / and 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 dolomite, 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 - 3 h.

[0083] Further, 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 h; the volume concentration of hydrofluoric acid is 1 - 10%, and the washing time lasts for 1 - 60 min.

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

[0085] Example 4

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

[0087] Then, a heat preservation pipe plug was placed, and the vacuum sealing flange was used for sealing. The tube furnace rotation motor was started to make the furnace body rotate at a speed of 5 rpm, and then an external vacuum pump was used to pump vacuum. After observing that the vacuum degree of the pressure gauge was < 500 Pa, the vacuum valve was closed.

[0088] Next, the heating program was started, the magnesium material evaporation chamber was heated to 750 °C, the reduction reaction chamber was heated to 700 °C, and the reduction reaction duration was 1 h.

[0089] After the reaction ended, the obtained solid was stirred and washed with hydrochloric acid with a volume concentration of 5% for 10 h. After solid-liquid separation, a silicon-based crude product was obtained, which was stirred and washed with hydrofluoric acid with a volume concentration of 1% for 15 min to wash away SiO 2 . After solid-liquid separation, it was repeatedly washed with ultrapure water several times until the washing liquid was neutral. After solid-liquid separation, the solid was collected in a tray and placed in a vacuum dryer for stirring and drying at 60 °C for 8 h to obtain a product, and the product was elemental Si.

[0090] As Figure 6 shown, it is the X-ray diffraction pattern of the obtained product. The results show that the product shows typical characteristic diffraction peaks of elemental silicon, and no diffraction peaks of other impurity phases appear.

[0091] AsFigure 7 As shown in the figure, it 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, having small grain size and large aspect ratio. Its length can reach the micron level and the diameter is less than 100 nm.

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

[0093]

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

[0095]

[0096] By calculation, the reduction rate of the crude silicon-based 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 (pickled montmorillonite obtained by stirring and pickling in 1mol / L HNO 3 for 5 h, adding HNO 3 The purpose is to remove metal impurities such as iron and aluminum in montmorillonite, enrich the silicon content, and obtain relatively pure SiO 2 ) are respectively fed into the magnesium material evaporation chamber and the reduction reaction chamber through two feed and discharge pipes. Among them, the mass ratio of magnesium ingot to pickled montmorillonite is 0.9:1.

[0099] Then, a heat preservation pipe plug is put in and the flange is vacuum-sealed. The rotating motor is started to make the furnace body rotate at a speed of 5 rpm.

[0100] Next, an external vacuum pump is used to pump vacuum, and then the heating program is started. While heating, vacuum can be continuously pumped until the temperature rises to 500 °C. At this time, the vacuum degree of the whole furnace body <500 Pa. Then, both the magnesium material evaporation chamber and the reduction reaction chamber are heated to 700 °C and kept at the specified temperature for 1 h.

[0101] After the reaction is completed, the obtained solid is stirred and washed with 5% (volume concentration) hydrochloric acid for 10 h. After solid-liquid separation, it is stirred and washed with 1% (volume concentration) hydrofluoric acid for 15 min. After solid-liquid separation, it is repeatedly washed with ultrapure water for many times until the washing liquid is neutral. After solid-liquid separation, the solid is collected in a tray and placed in a vacuum dryer to be stirred and dried at 60 °C for 8 h to obtain the product. The obtained acid-activated montmorillonite-derived nanosilicon shows a diffraction peak of elemental silicon, and its microscopic morphology is irregular granular, less than 100 nm, and the tapped density is 0.81 g / 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 amount of forged white (MgO to CaO molar ratio of 1), ferrosilicon alloy (Si content of 78.22%, S content of 0.03%, Al content of 0.09%), fluorite (CaF 2 The magnesium material is uniformly mixed with a mass ratio of 6:1.2:0.2, passed through a 200-mesh sieve after ball milling, and put into a magnesium material evaporation bin, and a certain mass of silicon-containing precursor (silica ash) is put into a reduction reaction bin, and the molar ratio of magnesium element to silica 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] Similar to the steps of Example 4, the difference is only that:

[0117] An external vacuum pump was used to evacuate. When the pressure gauge showed that the vacuum degree was less than 500 Pa, a small amount of argon was filled at a rate of 5 mL / min, and at the same time, the evacuation was continued until the reaction ended. The small amount of argon filling 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] Similar to the steps of Example 4, the difference is that: the rice husk was pickled with 1 M hydrochloric acid for 3 h, filtered and then vacuum dried at 80 °C for 24 h, and then pre-carbonized at 700 °C for 3 h to obtain a precursor containing 63 wt% carbon and 37 wt% silicon dioxide. The mass ratio of magnesium ingot to the precursor was 0.4:1. The final product contained 15.9 wt% silicon, 83.4 wt% carbon and 0.7 wt% silicon carbide, and the reduction rate of the silicon-based crude product was 91.8%.

[0120] Example 9

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

[0122] Example 10

[0123] Similar to the steps of Example 4, the difference is that: the mass ratio of magnesium ingot, halloysite and sodium chloride was 1.4:1:0.5. After holding for 30 min, carbon dioxide at -0.1 MPa was introduced as a carbon source and holding was continued for 30 min. In the reaction product, 76 wt% was elemental silicon and 24 wt% was elemental carbon. The reduction rate of the silicon-based crude product obtained in this example was 92.9%.

[0124] Comparative Example 1

[0125] Similar to the steps of Example 4, the difference is only that:

[0126] Instead of using a vacuum pump to evacuate the air, argon gas was filled into the furnace body. Due to the mutual collision between magnesium atoms and argon molecules, the mean free path of magnesium vapor decreased, resulting in a reduction in the uniformity and rate of the reduction reaction. As a result, most of the silicon-containing precursors remained unreduced.

[0127] Comparative Example 2

[0128] Similar to the steps of Example 4, the only difference is that:

[0129] Using micron-sized magnesium powder as the raw material, after mixing with the silicon-containing precursor, they were jointly put into the reduction reaction chamber. The direct contact between the magnesium powder and the silicon-containing precursor caused local magnesium powder to be excessive and the temperature to be too high, resulting in an increase in the amount of magnesium silicide formed, and the combination of aluminum elements with magnesium oxide or silicon oxide compounds to form high-temperature heterophases such as spinel and mullite.

[0130] Comparative Example 3

[0131] Similar to the steps of Example 4, the only difference is that:

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

[0133] Comparative Example 4

[0134] Similar to the steps of Example 4, the only difference is that:

[0135] During the process, the furnace body was not rotated, resulting in uneven contact between magnesium vapor and the precursor. Part of the halloysite reacted with excessive magnesium vapor to form magnesium silicide, and part of the halloysite was not reduced because it could not come into sufficient contact with magnesium vapor.

[0136] Comparative Example 5

[0137] Similar to the steps of Example 4, the only difference is that:

[0138] The furnace body was evacuated to a vacuum degree of 5 KPa. Due to the residual oxygen in the furnace body, although part of the elemental silicon was generated in the reduction reaction, the reduction of halloysite was not complete, and there were still diffraction peaks of halloysite in the XRD results.

[0139] Comparative Example 6

[0140] Similar to the steps of Example 4, the only difference is that:

[0141] Sodium chloride was not added to the silicon-containing precursor, resulting in a certain degree of aggregation of the nanotubes and an increase in the particle size of the product.

[0142] Comparative Example 7

[0143] Similar to the steps of Example 4, the only difference is that:

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

[0145] Comparative Example 8

[0146] Similar to the steps of Example 6, the only difference is that:

[0147] Both the magnesium material evaporation chamber and the reduction reaction chamber are heated to 1200 °C, 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 too high temperature, the reaction is intense, and the particles not only become larger due to over-recrystallization, but also are over-sintered between the particles, destroying the original morphology of the halloysite.

[0148] Comparative Example 8

[0149] Similar to the steps of Example 6, the only difference is that:

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

[0151] Comparative Example 10

[0152] Similar to the steps of Example 6, the only difference is that:

[0153] The Si content in the 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] Similar to the steps of Example 6, the only difference is that:

[0156] The calcined dolomite, ferrosilicon alloy, and fluorite are not ball-milled and sieved, and the average particle size of the particles used is >2 mm. The reaction is incomplete, and part of the ferrosilicon alloy does not participate in the reaction sufficiently, resulting in a low reduction efficiency.

[0157] Application Example

[0158] The elemental silicon obtained in Example 4 is used as the anode material of a lithium-ion battery, and a coin cell is assembled. Preparation of the working electrode: The active material (elemental silicon), acetylene black, and sodium alginate are mixed evenly according to the mass ratio of 7:1.5:1.5, then coated on a copper foil, and cut into a 12-mm-diameter disc after vacuum drying. The counter electrode and the reference electrode are both lithium metal foils. The electrolyte is 1 mol / L LiPF 6The volume ratio is 1:1 ethylene carbonate / dimethyl carbonate, with 10 wt.% fluorinated ethylene carbonate added. The assembly process of the lithium-ion battery is carried out in an argon glove box (both the water and oxygen concentrations are lower than 0.1 ppm).

[0159] The cycling performance results of the elemental silicon prepared in Example 1 at a current density of 1.0 A / g (activated at a small current density of 0.2 A / g in the first three cycles) are shown as follows ( Figure 8 ), the initial Coulombic efficiency of this material is 81.1%, the specific capacity is as high as 1778 mAh / g at a current density of 1.0 A / g, and the specific capacity remains above 87.8% after 100 cycles, showing good cycling stability and having 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 magnesiothermic reduction of silicon-containing precursors. The reduction of the silicon-containing precursors by magnesium vapor is more uniform under vacuum conditions, and less heat is generated during the reaction process, reducing the generation of unreacted precursors and by-products. At the same time, the original morphology of the silicon-containing precursors is better maintained. Using the obtained silicon-based materials as the anode materials of lithium-ion batteries shows good electrochemical lithium storage performance, demonstrating its feasibility in the application of lithium-ion batteries.

[0161] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined 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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