A system and method for preparing nano-silicon based on gas phase decomposition method

Abstract

The present disclosure relates to a system and method for preparing nano-silicon based on a gas phase decomposition method, the system comprising: a thermal decomposition device, provided with a carrier gas inlet, a silane-containing gas inlet and a gas-solid mixture outlet; a nano-silicon collecting device, connected to the gas-solid mixture outlet and provided with a tail gas outlet, for gas-solid separation of the gas-solid mixture generated in the thermal decomposition device; the thermal decomposition device comprises an inner furnace tube and an outer furnace tube sleeved outside the inner furnace tube, the outer wall of the outer furnace tube is provided with a heating and heat preservation device, and a closed interlayer cavity is provided between the outer furnace tube and the inner furnace tube; the inner furnace tube is used as a thermal decomposition chamber of silane, one end of which is provided with a silane-containing gas inlet and the other end of which is provided with a gas-solid mixture outlet; the interlayer cavity is connected to the carrier gas inlet, and the inner furnace tube wall is provided with a carrier gas channel for the carrier gas to enter the inner furnace tube; the gas pressure of the interlayer cavity is greater than the gas pressure of the thermal decomposition chamber. The scheme of the present disclosure avoids the deposition of silicon particles on the inner wall of the chamber.

Description

Technical Field

[0001] The present disclosure relates to the technical field of nano-silicon powder preparation, and in particular to a system and method for preparing nano-silicon based on a gas phase decomposition method. Background Art

[0002] Silicon-based negative electrode materials are highly regarded battery negative electrode materials due to their abundant raw material reserves, ultra-high theoretical capacity (4200mAh / g) and excellent fast charging performance. However, the volume of silicon-based negative electrodes expands severely during the lithium insertion process. The change in volume causes the SEI film (Solid Electrolyte Interface) on the surface of the silicon electrode to break and form repeatedly, and causes cracks in the silicon-based negative electrode material until it is pulverized, destroying the contact between the electrode material and the current collector, causing the active material to detach from the pole piece, causing the battery capacity to decay rapidly. Moreover, the expansion will generate a lot of stress inside the battery, squeezing the pole piece. With multiple cycles, there is a risk of the pole piece breaking. In addition, this stress may also cause a decrease in the internal porosity of the battery, reduce the lithium ion movement channel, cause the precipitation of lithium metal, and affect the safety of the battery. Reducing the volume expansion of silicon-based negative electrodes is the key to improving battery cycle and safety performance, and nano-sizing of silicon particles is one of the important means to reduce volume expansion.

[0003] At present, the main methods for preparing nano silicon powder are mechanical ball milling, plasma evaporation condensation and chemical vapor deposition. Mechanical ball milling is currently a commonly used method for mass production of nano silicon powder. It has a simple process and low cost, but it cannot effectively control the particle size distribution, and the ball milling medium easily causes silicon powder pollution, which cannot meet the demand of the new energy market for high-quality nano silicon powder. The plasma evaporation condensation method uses high-temperature plasma as a heat source to vaporize silicon powder and then quickly cool it to obtain nano silicon powder. It can obtain silicon powder with a smaller particle size, but it is difficult to guarantee the yield. The chemical vapor deposition method heats silane to decompose, and then condenses it in the gas phase to form nano silicon powder. The particle size and purity of nano silicon can be controlled by adjusting the parameters.

[0004] Chemical vapor deposition is carried out in a thermal decomposition reaction device, and existing equipment mainly provides heat energy for the reaction by external heating or internal heating. The external heating method refers to heating the wall of the reaction equipment to provide decomposition heat energy for the substances in the equipment, but too high a wall temperature can easily cause silicon powder to deposit on the wall, and as the thickness of the deposition increases, the heating efficiency will gradually decrease, and the wall may burst. By setting a lining made of materials such as graphite and silicon carbide on the wall, the difference in thermal expansion coefficient can be reduced to avoid bursting, but the deposition of silicon powder on the wall cannot be avoided. The internal heating method refers to setting heating equipment such as heating tubes and heating elements in the chamber of the thermal decomposition reaction device. When using this heating method, the deposition of silicon powder is transferred from the wall to the heating device, which not only increases the cost of daily maintenance but also easily introduces new sources of pollution. In addition, there is also a method of zone heating, but this method has also failed to completely solve the problem of wall deposition.

[0005] Silane is thermally decomposed to form silicon nuclei, which then gradually grow into silicon particles. The size of silicon particles is affected by the growth time, that is, the distance the particles travel in the reaction chamber. Therefore, in addition to the easy deposition of silicon powder on the wall of the reaction chamber or the surface of the built-in heating device, the existing thermal decomposition device / method also deposits silicon powder on the inner wall of the furnace tube, which will nucleate and grow continuously until it forms particles of hundreds of nanometers or micrometers, and then it will break away from the inner wall and enter the collection system, resulting in a wide size distribution of silicon powder, or even a multi-peak size distribution. Summary of the invention

[0006] One of the technical problems to be solved by the present disclosure is that the existing silane thermal decomposition device and method easily cause the product nano-silicon particles to be deposited on the wall surface of the reaction chamber or the surface of the built-in heating device.

[0007] The second technical problem to be solved by the present disclosure is that the existing silane thermal decomposition device and method cannot accurately control the particle size of the nano-silicon particle product.

[0008] Based on this, the present disclosure provides a system for preparing nano-silicon based on a gas phase decomposition method, aiming to solve at least one of the above technical problems. The system for preparing nano-silicon based on a gas phase decomposition method comprises:

[0009] A thermal decomposition device is provided with a carrier gas inlet, a silane-containing gas inlet and a gas-solid mixture outlet;

[0010] A nano-silicon collecting device, connected to the gas-solid mixture outlet and provided with an exhaust gas outlet, for performing gas-solid separation on the gas-solid mixture generated in the thermal decomposition device to obtain nano-silicon particles and exhaust gas;

[0011] The thermal decomposition device comprises an inner furnace tube and an outer furnace tube sleeved outside the inner furnace tube, the outer wall of the outer furnace tube is provided with a heating and heat preservation device, and a closed interlayer cavity is provided between the outer furnace tube and the inner furnace tube;

[0012] The inner furnace tube serves as a thermal decomposition chamber for silane, and is provided with an inlet for the silane-containing gas at one end and an outlet for the gas-solid mixture at the other end;

[0013] The interlayer cavity is provided with the carrier gas inlet, and the inner furnace tube wall is also formed with a plurality of channels for the carrier gas to diffuse evenly into the inner furnace tube to form a disturbed airflow near the inner wall of the inner furnace tube; the gas pressure of the interlayer cavity is greater than the gas pressure of the thermal decomposition chamber.

[0014] Preferably, the wall of the inner furnace tube is a porous structure;

[0015] More preferably, the porosity of the inner furnace tube wall is 3% to 50%, and the pore size is 100 nanometers to 50 micrometers.

[0016] The thermal decomposition device is a vertical structure, the silane-containing gas inlet is arranged at the lower end of the inner furnace tube, and the bottom end of the thermal decomposition device is provided with a cleaning chamber connected to the inner furnace tube.

[0017] Preferably, an annular air inlet distributor is provided at the inlet of the silane-containing gas, and the air inlet distributor comprises an air inlet, an air inlet pipe connected to the air inlet, and a gas distributor connected to the air inlet pipe, and the air inlet pipe is arranged around the gas distributor.

[0018] Preferably, the nano-silicon collecting device comprises a cooling mechanism, a powder separation mechanism and a collecting mechanism.

[0019] The cooling mechanism is connected to the gas-solid mixture outlet and is used to cool the gas-solid mixture;

[0020] The powder separation mechanism is connected to the outlet of the cooling mechanism and is used for performing gas-solid separation on the gas-solid mixture to obtain the nano silicon particles and the tail gas;

[0021] The collecting mechanism is connected to the powder separation mechanism and is used to store the separated nano silicon particles;

[0022] The tail gas outlet is connected to the powder separation mechanism.

[0023] Preferably, the carrier gas is selected from hydrogen, and the system further comprises a tail gas treatment device connected to the tail gas outlet, and the tail gas treatment device comprises an impurity removal device;

[0024] The impurity removal device is connected to the tail gas outlet and is used to remove remaining solid and gas impurities in the tail gas to obtain pure hydrogen, and the pure hydrogen is circulated and used as the carrier gas.

[0025] More preferably, it also includes a mixed gas preheating device, which is connected to the hydrogen storage tank and the silane gas storage tank respectively, and is used to preheat the silane gas and hydrogen introduced therein; the mixed gas outlet of the mixed gas preheating device is connected to the silane-containing gas inlet.

[0026] In order to solve the above technical problems, the present disclosure also provides a method for preparing nano-silicon in the above system, comprising the following steps:

[0027] S0: passing a carrier gas into the interlayer cavity to form a disturbed gas flow near the inner wall of the thermal decomposition chamber, and maintaining the gas pressure of the interlayer cavity greater than the gas pressure of the thermal decomposition chamber to prevent the nano-silicon particles produced in the subsequent silane thermal decomposition step from being deposited on the inner wall;

[0028] S1: heating a mixed gas containing silane gas and a carrier gas to a silane thermal decomposition temperature in a thermal decomposition chamber to obtain a gas-solid mixture containing nano-silicon particles;

[0029] S2: passing the gas-solid mixture into a nano-silicon collection device for cooling and separation to obtain nano-silicon particles and tail gas.

[0030] Preferably, the carrier gas is selected from hydrogen, and the mixed gas enters the thermal decomposition chamber uniformly along the lower circumference of the thermal decomposition chamber through a gas inlet distributor;

[0031] Before step S1, the method further includes mixing and preheating the silane gas and the carrier gas in a mixer preheating device;

[0032] After step S2, a purification step of removing remaining solid and gas impurities in the tail gas using a tail gas treatment device is also included, and the purified tail gas continues to be used as the carrier gas.

[0033] More preferably, before step S1, the mixed gas having a molar concentration of silane of 5% to 20% is preheated to 200 to 350° C.;

[0034] In step S1, the mixed gas is introduced into the thermal decomposition chamber at a flow rate of 30-300 L / h, and the temperature of the thermal decomposition chamber is 400-800° C.; the carrier gas is introduced into the interlayer cavity at a flow rate of 2000-3000 L / h.

[0035] The technical solution claimed in the present disclosure has achieved the following beneficial effects:

[0036] 1) The silane thermal decomposition device is set to a concentric double furnace tube structure with different diameters. The carrier gas can enter the inner furnace tube evenly through the interlayer cavity between the furnace tubes and the carrier gas channel on the tube wall of the inner furnace tube in sequence, forming a disturbed micro-airflow near the inner wall of the inner furnace tube, thereby preventing the thermal decomposition of silane near the inner wall of the inner furnace tube, thereby preventing the deposition and adhesion of silicon particle products on the inner wall, avoiding the silicon particles from nucleating and growing into large-sized particles on the inner wall and entering the subsequent collection system, so that the size of the obtained nano silicon particles is more uniform.

[0037] 2) Since the deposition of nano-silicon particles on the inner wall of the thermal decomposition chamber is avoided, the inner furnace tube is heated more evenly, the heating efficiency is improved, and the accidental rupture of the furnace tube wall caused by the deposition of silicon particles is avoided, thereby improving the efficiency and safety of silane thermal decomposition.

[0038] 3) Since the deposition of nano-silicon particles on the inner wall of the thermal decomposition chamber is avoided, the particle size distribution of nano-silicon particles can be accurately controlled by controlling the reaction temperature, silane concentration, flow rate of silane-containing gas, and flow rate of carrier gas, and other parameters to obtain nano-silicon particles of the desired size. When the nano-silicon particles are used in the negative electrode, the volume expansion of the silicon-based negative electrode can be effectively reduced, and the cycle and safety performance of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are merely embodiments of the present disclosure, and a person of ordinary skill in the art can obtain other drawings based on the provided drawings without paying any creative work.

[0040] Figure 1 Schematic diagram of the system for preparing nanosilicon based on gas phase decomposition method.

[0041] Figure 2 Schematic diagram of the inner furnace tube air inlet distributor.

[0042] Figure 3 The microstructure of nano-silicon particles obtained by the device and method disclosed in the present invention under a scanning electron microscope.

[0043] Reference numerals:

[0044] 1-inner furnace tube; 2-outer furnace tube; 3-heating and heat preservation equipment; 4-interlayer cavity; 5-silane-containing gas inlet; 6-gas-solid mixture outlet; 7-cleaning chamber; 8-carrier gas inlet; 9-gas inlet distributor; 10-gas inlet; 11-gas inlet pipe; 12-gas distributor; 13-cooling mechanism; 14-powder separation mechanism; 15-impurity removal equipment; 16-induced draft fan; 17-hydrogen storage tank; 18-mixed gas preheating device; 19-silane gas storage tank; 20-thermal decomposition chamber; 21-heat preservation furnace shell. Implementation

[0045] In order to make the purpose, technical solution and beneficial effects of the embodiments of the present disclosure clearer, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure. Example

[0046] Reference Figure 1 The system for preparing nano-silicon based on the gas phase decomposition method in this embodiment is composed of a vertical thermal decomposition device, a nano-silicon collection device and an exhaust gas treatment device.

[0047] The vertical thermal decomposition device comprises an inner furnace tube 1 and an outer furnace tube 2 sleeved outside the inner furnace tube. The outer wall of the outer furnace tube 2 is provided with a heating and heat preservation device 3, which is composed of a heating tube and a heat insulation material. The heating temperature of the heating tube is 0-1200°C. An interlayer cavity 4 is also provided between the outer furnace tube 2 and the inner furnace tube 1 to seal the outside of the thermal decomposition device. The inner furnace tube 1 is used as a thermal decomposition chamber 20 of silane, and a silane-containing gas inlet 5 is provided at the lower part thereof, and a gas-solid mixture outlet 6 is provided at the other end. In order to enhance the heat preservation effect of the thermal decomposition chamber 20, a heat preservation furnace shell 21 is also provided at the upper and lower ends of the thermal decomposition chamber 20.

[0048] The gas-solid mixture comprises a carrier gas that does not participate in the reaction, nano silicon particles of silane thermal decomposition product and hydrogen. In the present embodiment, in order to facilitate the separation and recovery of the gas, the carrier gas is preferably the hydrogen identical to the silane thermal decomposition gas product. The bottom of the thermal decomposition device is provided with a cleaning chamber 7 communicated with the inner furnace tube 1. The large-sized or aggregated silicon particles generated in the silane thermal decomposition process can fall into the cleaning chamber 7 under the influence of airflow and gravity. The interlayer cavity 4 is connected to the carrier gas inlet 8, and the inner furnace tube 1 tube wall is also provided with a plurality of carrier gas channels for the carrier gas to uniformly diffuse into the inner furnace tube 1. Through the carrier gas channel, a disturbed micro-airflow can be formed in the inner furnace chamber, disturbing silane so that it does not decompose near the inner wall of the inner furnace tube, avoiding the deposition and attachment of nano silicon particles on the inner wall of the inner furnace tube, ensuring the consistency of the nano silicon size, and also reducing the risk of equipment operation and maintenance during large-scale production.

[0049] The outer furnace tube 2 can be made of ceramic, graphite or metal, and the inner furnace tube 1 can be made of graphite, carbon-carbon composite material, metal or ceramic. In a preferred embodiment, the tube wall of the inner furnace tube 1 is a porous structure, and the pores constitute an inert carrier gas channel. In a more preferred embodiment, the porosity of the tube wall of the inner furnace tube 1 is 3% to 50%, and the pore size is 100 nanometers to 50 microns. Alternatively, a flow guide channel can be further added to the inner wall of the inner furnace tube 1 to change the near-wall flow rate of the gas.

[0050] In order to evenly distribute the silane-containing gas in the chamber of the inner furnace tube 1, a ring-shaped gas inlet distributor 9 is also provided at the inlet of the silane-containing gas. The exemplary structure of the gas inlet distributor 9 can be referred to in the attached Figure 2 , wherein the air inlet distributor 9 includes an air inlet 10, an air inlet pipe 11 connected to the air inlet 10, and a gas distributor 12 connected to the air inlet pipe 11, and the gas distributor 12 is a porous structure made of ceramic or metal. The inner diameter of the gas distributor 12 is consistent with that of the thermal decomposition chamber, and the air inlet pipe 11 is arranged around the gas distributor 12. The annular structure of the air inlet distributor 9 allows the mixed gas to enter the thermal decomposition chamber 20 evenly along the circumference of the lower part of the thermal decomposition chamber, which helps to further avoid the occurrence of uneven gas distribution and uneven internal air pressure, and avoid the phenomenon of uneven silane thermal decomposition reaction.

[0051] The nano-silicon collecting device is connected to the gas-solid mixture outlet of the inner furnace tube 1 and is provided with an exhaust gas outlet. The nano-silicon collecting device is used to perform gas-solid separation on the gas-solid mixture generated in the thermal decomposition device to obtain nano-silicon particles and exhaust gas. Exemplarily, the nano-silicon collecting device includes a cooling mechanism 13, a powder separation mechanism 14 and a collecting mechanism. Among them, the cooling mechanism 13 can be set as a cooling pipe, which is connected to the gas-solid mixture outlet and is used to cool the gas-solid mixture. The powder separation mechanism 14 is connected to the cooling mechanism outlet and is used to separate the cooled gas-solid mixture to obtain nano-silicon particles and exhaust gas. In this embodiment, any existing device for separating powders can be used for gas-solid separation. The collecting mechanism is connected to the powder separation mechanism for storing separated nano-silicon particles. The exhaust gas outlet is connected to the powder separation mechanism for discharging the exhaust gas after gas-solid separation.

[0052] The tail gas treatment device is connected to the tail gas outlet for purifying and recovering the tail gas. Exemplarily, the tail gas treatment device includes an impurity removal device 15 and a gas drainage device, and the gas drainage device can be an induced draft fan 16. The impurity removal device 15 is connected to the tail gas outlet for removing the remaining solid and gas impurities in the tail gas to obtain pure hydrogen. For example, in the tail gas treatment device, most of the solid impurities in the tail gas can be removed by a dust collection device, and then the residual solid and gas impurities in the tail gas can be further removed by setting a section of ultra-high temperature cavity (such as 1000°C) or setting a gas washing device, so as to recover high-purity tail gas. In addition, a reasonable silane ratio in the mixed gas is also conducive to improving the purity of the recovered tail gas. The induced draft fan 16 is connected to the outlet of the impurity removal device 15 for introducing the purified tail gas into the hydrogen storage tank 17, and the hydrogen storage tank 17 is connected to the carrier gas inlet 8, so as to realize the recycling of the carrier gas. Since hydrogen does not participate in the reaction and silane decomposition also generates hydrogen, the whole process does not need to be supplemented with hydrogen from the outside.

[0053] In a preferred embodiment, the system further comprises a mixed gas preheating device 18. The mixed gas preheating device 18 is respectively connected to the hydrogen storage tank 17 and the silane gas storage tank 19, and is used to preheat the silane gas and hydrogen introduced therein, and the mixed gas preheating device 18 can be heated by an external heating pipe or hydrogen recovered from the combustion tail gas. The mixed gas outlet of the mixed gas preheating device 18 is connected to the silane-containing gas inlet 5, and is used to pass the preheated mixed gas into the inner furnace tube 1 for thermal decomposition reaction of silane.

[0054] In the system of this embodiment, the preparation of nano-silicon by thermal decomposition of silane includes the following steps:

[0055] S: Silane gas with a purity greater than 99.999% and hydrogen are mixed and preheated to 200-350°C, preferably to 300-350°C, and the molar concentration of silane in the mixed gas is 5%-20%.

[0056] S0: A carrier gas is introduced into the interlayer cavity at a flow rate of 2000-3000 L / h to form a disturbed micro-flow near the inner wall of the inner furnace tube. After the hydrogen is introduced, the gas pressure of the interlayer cavity is 0.1-5 MPa, and the pressure is controlled to be always greater than the gas pressure of the silane thermal decomposition chamber to prevent the nano-silicon particles produced in the subsequent silane thermal decomposition step from being deposited on the inner wall;

[0057] S1: A mixed gas containing silane gas and carrier gas is uniformly introduced into the inner furnace tube through an air inlet distributor at a flow rate of 30-300 L / h, and the inner furnace tube is heated to 400-800°C, preferably to 550-750°C, by a heating device on the outer wall of the outer furnace tube to perform thermal decomposition of silane to obtain a gas-solid mixture containing nano-silicon particles.

[0058] S2: Cooling the gas-solid mixture through a cooling tube, and separating the gas and solid through a nano-silicon collection device to obtain nano-silicon particles and tail gas;

[0059] S3: The tail gas is passed into the tail gas treatment device to remove the remaining solid and gas impurities in the tail gas, and high-purity hydrogen is recovered. The recovered hydrogen is further used as a carrier gas.

[0060] Specifically, hydrogen is used as a carrier gas, and the hydrogen in the hydrogen storage tank 17 is passed into the interlayer cavity 4 in the thermal decomposition device at a flow rate of 2500L / h, and then the hydrogen enters the inner furnace tube through the pores on the tube wall of the inner furnace tube 1, and a disturbed airflow is generated near the inner wall of the inner furnace tube 1. Among them, the length of the inner furnace tube is set to 1.8 meters, the tube wall thickness is 5 mm, the porosity is 30%, and the pore size is 1-5 microns. After the hydrogen is passed, the gas pressure of the interlayer cavity is controlled at 0.14MPa, and the gas pressure in the inner furnace tube 1 is normal pressure. The whole process keeps the gas pressure of the interlayer cavity 4 greater than the gas pressure in the inner furnace tube 1.

[0061] The hydrogen in the hydrogen storage tank 17 and the silane in the silane gas storage tank 19 are introduced into the mixed gas preheating device 18, wherein the molar concentration ratio of silane is 7%, and the mixed gas is preheated to 300° C. Then, the preheated mixed gas is introduced into the inner furnace tube 1 through the gas distributor 12 at a flow rate of 60 L / h, and the thermal decomposition of silane is carried out at a temperature of 550° C. Due to the influence of the hydrogen flow on the tube wall of the inner furnace tube 1, the silane will not decompose near the inner wall of the inner furnace tube, thereby avoiding the deposition of the product nano silicon particles on the inner wall.

[0062] The decomposition products of silane are nano silicon particles and hydrogen. The gas-solid mixture is transported to the cooling pipe through the gas-solid mixture outlet 6, and then transported to the powder separation mechanism 14 after being cooled by the cooling pipe. The gas-solid mixture is separated into gas and solid in the powder separation mechanism, and the obtained nano silicon particles are sent to the collection mechanism. The tail gas is further transported to the tail gas treatment device through the induced draft fan 16 for purification and recovery.

[0063] In the tail gas treatment device, the tail gas is passed through the impurity removal device 15 to remove solid and gas impurities therein to obtain purified hydrogen, and the purified hydrogen is then transported to the hydrogen storage tank 17 for recycling.

[0064] Attached Figure 3 The microscopic view of the nano-silicon particles obtained under the conditions of this embodiment under a scanning electron microscope is shown. It can be seen from the figure that the obtained nano-silicon particles are uniform in size, with a particle size of only about 10~50nm, indicating that the particle size distribution of the nano-silicon particles can be effectively controlled. When nano-silicon particles of this size are used in the negative electrode, the volume expansion of the silicon-based negative electrode can be effectively reduced, and the cycle and safety performance of the battery can be improved.

[0065] The embodiments described above are merely illustrative descriptions of the present disclosure and are not intended to limit the scope of the present disclosure. Without departing from the design spirit of the present disclosure, various modifications and improvements made to the technical solutions of the present disclosure by ordinary technicians in this field should all fall within the protection scope determined by the present disclosure.

Claims

1. A method for preparing nano-silicon, characterized in that: A system for performing the method comprises: A thermal decomposition device is provided with a carrier gas inlet, a silane-containing gas inlet and a gas-solid mixture outlet; a nano-silicon collecting device is connected to the gas-solid mixture outlet and is provided with an exhaust gas outlet, and is used to separate the gas-solid mixture generated in the thermal decomposition device into gas and solid to obtain nano-silicon particles and exhaust gas; wherein the thermal decomposition device comprises an inner furnace tube and an outer furnace tube sleeved outside the inner furnace tube, the outer wall of the outer furnace tube is provided with a heating and heat preservation device, and a closed interlayer cavity is provided between the outer furnace tube and the inner furnace tube; The inner furnace tube serves as a thermal decomposition chamber for silane, and is provided with an inlet for the silane-containing gas at one end and an outlet for the gas-solid mixture at the other end; The interlayer cavity is provided with the carrier gas inlet, and the inner furnace tube wall is also formed with a plurality of channels for the carrier gas to diffuse uniformly into the inner furnace tube to form a disturbed airflow near the inner wall of the inner furnace tube, and the carrier gas does not participate in the reaction; the gas pressure of the interlayer cavity is greater than the gas pressure of the thermal decomposition chamber; the inner wall of the inner furnace tube is also provided with a guide channel to change the near-wall flow velocity of the carrier gas; The inner furnace tube wall is a porous structure; The thermal decomposition device is a vertical structure, the silane-containing gas inlet is arranged at the lower end of the inner furnace tube, and the bottom end of the thermal decomposition device is provided with a cleaning chamber connected to the inner furnace tube; The method comprises the following steps: S0: passing a carrier gas into the interlayer cavity to form a disturbed gas flow near the inner wall of the thermal decomposition chamber, and maintaining the gas pressure of the interlayer cavity greater than the gas pressure of the thermal decomposition chamber to prevent the nano-silicon particles produced in the subsequent silane thermal decomposition step from being deposited on the inner wall; S1: heating a mixture of silane-containing gas and the carrier gas to a silane thermal decomposition temperature in a thermal decomposition chamber to obtain a gas-solid mixture containing nano-silicon particles; S2: passing the gas-solid mixture into a nano-silicon collection device for cooling and separation to obtain nano-silicon particles and tail gas.

2. The method according to claim 1, characterized in that: The porosity of the inner furnace tube wall is 3% to 50%, and the pore size is 100 nanometers to 50 micrometers.

3. The method according to claim 1, characterized in that: The carrier gas is selected from hydrogen, and the mixed gas enters the thermal decomposition chamber uniformly along the lower circumference of the thermal decomposition chamber through the gas inlet distributor; Before step S1, the method further includes mixing and preheating the silane gas and the carrier gas in a mixed gas preheating device; After step S2, the method further includes a purification step of using an exhaust gas treatment device to remove remaining solid and gas impurities in the exhaust gas, and the purified exhaust gas continues to be used as the carrier gas.

4. The method according to claim 3, characterized in that: Before step S1, the mixed gas with a molar concentration of silane of 5% to 20% is preheated to 200 to 350°C; in step S1, the mixed gas is introduced into the thermal decomposition chamber at a flow rate of 30 to 300 L / h, and the temperature of the thermal decomposition chamber is 400 to 800°C; the carrier gas is introduced into the interlayer cavity at a flow rate of 2000 to 3000 L / h.

5. The method according to claim 3, characterized in that: The gas inlet distributor is arranged at the inlet of the silane-containing gas, and comprises a gas inlet, a gas inlet pipe connected to the gas inlet, and a gas distributor connected to the gas inlet pipe, wherein the gas inlet pipe is arranged around the gas distributor.

6. The method according to claim 3, characterized in that: The nano-silicon collecting device comprises a cooling mechanism, a powder separation mechanism and a collecting mechanism. The cooling mechanism is connected to the gas-solid mixture outlet and is used to cool the gas-solid mixture; The powder separation mechanism is connected to the outlet of the cooling mechanism and is used to perform gas-solid separation on the gas-solid mixture to obtain the nano-silicon particles and the tail gas; the collection mechanism is connected to the powder separation mechanism and is used to store the separated nano-silicon particles; The tail gas outlet is connected to the powder separation mechanism.

7. The method according to claim 3, characterized in that The tail gas treatment device is connected to the tail gas outlet and includes impurity removal equipment; The impurity removal equipment is connected to the tail gas outlet and is used to remove remaining solid and gas impurities in the tail gas to obtain pure hydrogen.

8. The method according to claim 3, characterized in that: The mixed gas preheating device is connected to the hydrogen storage tank and the silane gas storage tank respectively, and is used to preheat the silane gas and hydrogen introduced therein; the mixed gas outlet of the mixed gas preheating device is connected to the silane-containing gas inlet.

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