Countercurrent fluidized bed for preparing silicon-carbon anode materials and its preparation method

Abstract

This invention discloses a countercurrent fluidized bed for preparing silicon-carbon anode materials and its preparation method, comprising: a reaction cylinder, a stirring shaft rotatably disposed within the reaction cylinder, several stirring paddles connected to the stirring shaft, an annular tube disposed on the inner wall of the reaction cylinder, several nozzles evenly distributed on the upper circumference of the annular tube, the annular tube being connected to a sleeve, the sleeve sealingly passing through the side wall of the reaction cylinder and a heater, an annular plug disposed on the sleeve, the annular plug sealing the outer tube portion of the sleeve and communicating with the inner tube portion, the outer tube portion of the sleeve being connected to a carrier gas source, the annular plug being connected to both a silicon source process gas source and a carbon source process gas source, a central spray nozzle disposed within the reaction cylinder, the central spray nozzle extending through a gas pipe beyond the reaction cylinder and heater and connected to both a carrier gas source and a liquid carrier gas source, upper spray holes evenly distributed on the upper side wall of the central spray nozzle, and lower spray holes evenly distributed on the bottom wall of the central spray nozzle. This invention can eliminate dead zones and improve the efficiency and quality of the fluidized reaction.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation equipment technology, and in particular to a countercurrent fluidized bed for preparing silicon-carbon anode materials and its preparation method. Background Technology

[0002] Lithium-ion batteries are deeply penetrating fields such as electric vehicles and large-scale energy storage, placing extreme demands on the energy density and cycle life of anode materials. The theoretical specific capacity of traditional graphite anodes at 372 mAh / g is already approaching the physical ceiling. Silicon-carbon materials, with their ultra-high lithium storage potential of 4200 mAh / g and the buffering effect of carbon layer coating on volume expansion, have become the core carrier for reconstructing the performance boundaries of anodes. The essence of this performance breakthrough is the victory of microstructural uniformity—only when silicon nanoparticles are uniformly dispersed in the carbon matrix and the thickness of the carbon coating layer fluctuates little can a specific capacity of over 1800 mAh / g and a capacity retention rate of 90% after 1000 cycles be achieved, truly supporting the leap in energy density of power batteries.

[0003] Chemical vapor deposition (CVD) utilizes the controlled reaction of silicon (silane) and carbon (acetylene) sources on a carbon substrate surface to construct a core-shell structure that buffers volume expansion. This allows for an initial coulombic efficiency exceeding 92.5% and an expansion rate reduced to below 25%, making it a mainstream process in the 10,000-ton-scale silicon-carbon market. Fluidized bed reactors, with their highly efficient gas-solid two-phase contact characteristics, have increased single-batch production capacity from 20kg in batch equipment to 300kg, and continue to improve. However, their weakness in controlling microscopic uniformity remains a key constraint on material performance advancement. When the coating thickness deviates significantly, battery cycle life decreases substantially, and the root cause of this deviation lies precisely in the uncontrolled flow and temperature fields of the fluidized bed.

[0004] The imbalance in the flow field originates from the limitations of the annular gas inlet in the gas distributor of mainstream fluidized bed equipment for silicon-carbon material preparation. Traditional fluidized beds employ an annular slit gas distribution design. In laboratory settings (reactor diameter 300 mm), the slit can generate laminar airflow with small radial velocity deviation, achieving a 90% contact efficiency between silane and the carbon substrate. However, when the equipment is scaled up for industrial production (diameter 800 mm), the slit needs to be widened to match the gas flow rate. At this point, the Reynolds number of the airflow increases significantly, abruptly transitioning from laminar to turbulent flow, and a sharp increase in radial velocity deviation. In the high-speed airflow region, intense particle collisions cause uneven local silicon deposition and excessive carbon coating. Conversely, insufficient fluidization of particles in the low-speed region near the reactor wall leads to insufficient particle suspension, or even a static state, limiting silicon source diffusion and resulting in a thinner coating. This microscopic difference directly exacerbates the battery's cycle capacity decay rate. A more subtle influence comes from the transmission of temperature field fluctuations. The decomposition rate of silane at 500-600℃ is extremely sensitive to temperature, and the differences in local turbulent dissipation caused by uneven flow field are the main factors for temperature field runaway.

[0005] Therefore, to achieve the ultimate uniformity of the microstructure of silicon-carbon materials, the key lies in reconstructing the flow field and temperature field control logic of the fluidized bed—eliminating radial gas velocity deviation through flow field optimization and controlling temperature fluctuations through temperature field control, ultimately effectively improving the uniformity of silicon-carbon deposition and carbon coating, and providing stable and reliable material support for high-energy-density batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a countercurrent fluidized bed for preparing silicon-carbon anode materials, which can eliminate dead zones, improve fluidization efficiency, and ensure bed airflow density, as well as its preparation method.

[0007] To achieve the above objectives, the technical solution adopted in this invention is: a countercurrent fluidized bed for preparing silicon-carbon anode materials, comprising: a reaction cylinder, on which a solid material inlet, a gas outlet, and a heater are provided; a thermocouple is provided at the lower end of the reaction cylinder; a stirring shaft is rotatably mounted at the lower end of the reaction cylinder, the stirring shaft is connected to a servo-driven geared motor, and several stirring paddles are connected to the stirring shaft, extending into the reaction cylinder; an annular tube is provided on the inner wall of the reaction cylinder, and several downwardly inclined nozzles are evenly distributed circumferentially on the lower side wall of the annular tube, the rotation direction of the gas flow ejected from the nozzles being consistent with the rotation direction of the stirring paddles; the annular tube is connected to a sleeve, and the sleeve is tightly sealed. The casing passes through the side wall of the reaction cylinder and the heater. An annular seal is installed on the casing, which seals the outer tube and connects to the inner tube. The outer tube is connected to the carrier gas source. The annular seal is connected to the silicon source process gas source and the carbon source process gas source, respectively. A central spray nozzle is installed in the reaction cylinder. The central spray nozzle is located above the agitator and is coaxial with the agitator shaft. The central spray nozzle extends out of the reaction cylinder and the heater through a gas pipe and is connected to the carrier gas source and the liquid carrier gas source, respectively. Several upward spray holes are evenly distributed around the upper side wall of the central spray nozzle. The upward spray holes are set at an elevation angle. Several downward spray holes are evenly distributed around the bottom wall of the central spray nozzle. The downward spray holes are set at a depression angle.

[0008] Furthermore, in the aforementioned countercurrent fluidized bed for preparing silicon-carbon anode materials, the annular tube is located at 40% to 60% of the bed height in the reaction chamber, the outer diameter of the annular tube is 0.7 to 0.8 times the inner diameter of the reaction chamber, the nozzle on the annular tube faces the inner wall of the reaction chamber, the inclination angle of the nozzle is 20° to 30°, and the orifice diameter of the nozzle is 1 to 3 mm.

[0009] Furthermore, in the aforementioned countercurrent fluidized bed for preparing silicon-carbon anode materials, the elevation angle of the upper nozzle is 25° to 35°, the spray coverage radius of the upper nozzle is 0.4 times the radius of the reaction cylinder, the depression angle of the lower nozzle is 50° to 70°, and the spray velocity of the lower nozzle is ≥40m / s.

[0010] Furthermore, in the aforementioned countercurrent fluidized bed for preparing silicon-carbon anode materials, the stirring paddle has a propulsion structure with a pitch ratio of 1:1 and a blade tilt angle of 25° to 35°. The diameter of each stirring paddle increases gradually from bottom to top and avoids the annular tube. The diameter of the stirring paddle at the bottom is 0.6 times the inner diameter of the reaction cylinder, and the diameter of the stirring paddle at the top is 0.9 times the inner diameter of the reaction cylinder.

[0011] Furthermore, in the aforementioned countercurrent fluidized bed for preparing silicon-carbon anode materials, the connection structure between the stirring shaft and the reaction cylinder is as follows: the bottom of the reaction cylinder is an open structure, a sealing cover is sealed at the bottom of the reaction cylinder, a connecting sleeve is fully welded inside the sealing cover, a thermocouple is fixed on the connecting sleeve, the connecting sleeve is connected to a support, a servo geared motor is fixed on the support, a skeleton oil seal and bearing are provided in the connecting sleeve, the stirring shaft passes through the connecting sleeve and is connected to the skeleton oil seal and bearing, the stirring shaft is connected to the output shaft of the servo geared motor through a coupling, a cooling groove is provided on the outer wall of the connecting sleeve, a cooling sleeve is sealed on the outer wall of the connecting sleeve and covers the cooling groove, and a cooling outlet and a cooling inlet are provided on the cooling sleeve.

[0012] Furthermore, in the aforementioned countercurrent fluidized bed for preparing silicon-carbon anode materials, the reaction cylinder has at least two gas outlets, each equipped with a metal filter, a backflow valve and a shut-off valve, a safety valve, and a pressure gauge.

[0013] The preparation method described above uses a countercurrent fluidized bed for preparing silicon-carbon anode materials, and its steps are as follows:

[0014] S1. Feeding: Porous carbon particles are fed into the reaction cylinder through the solid material inlet, and then the solid material inlet is closed.

[0015] S2. Fluidization and Dispersion: Turn on the carrier gas source. The carrier gas enters the annular tube through the outer tube of the sleeve, and then is sprayed onto the inner wall of the reaction cylinder through the nozzle on the annular tube. It then flows spirally downward along the inner wall and converges at the bottom of the reaction cylinder to form a spiral upward airflow, thereby rotating and fluidizing the porous carbon particles upward. At the same time, the carrier gas replaces the air in the reaction cylinder. Start the servo reduction motor to drive the stirring paddle to rotate. The stirring paddle rotating in the same direction stirs the fluidized porous carbon particles, which not only breaks up the agglomeration of porous carbon particles, but also enhances the upward efficiency of porous carbon particles and assists in fluidization. When there is only carrier gas in the reaction cylinder, start the heater to heat the reaction cylinder to a temperature of 700-900℃. Hold the temperature for 2-4 hours. The porous carbon particles are annealed under the protection of the carrier gas and then slowly cooled.

[0016] S3, Silicon deposition: When the temperature inside the reaction chamber drops to 450-550℃, the carrier gas source is kept open, and then the silicon source process gas source is opened. The silicon source process gas enters the annular pipe through the inner tube of the sleeve and mixes with the carrier gas. The carrier gas in the outer tube isolates the heat radiation generated by the heater from the inner tube, preventing the silicon source process gas from cracking in the inner tube. The volume flow ratio between the silicon source process gas and the carrier gas is 1:2-10. Then they are sprayed into the reaction chamber together, and the silicon source process gas is evenly dispersed. The silicon source process gas cracks at high temperature to form nano-silicon particles. The nano-silicon particles and porous carbon particles are chemically vapor deposited to form silicon-carbon particles. During this process, the central spray nozzle sprays the carrier gas, and the upward airflow from the upper spray nozzle lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction chamber. The lower spray nozzle focuses the spray to destroy the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. Combined with the propulsion and stirring of the agitator, the axial temperature gradient around the agitator is less than 5℃.

[0017] S4. Carbon Coating: When the temperature inside the reaction chamber reaches 500-650℃, the carbon source process gas is turned on. The carbon source process gas enters the annular pipe through the inner tube of the casing and mixes with the carrier gas. The carrier gas in the outer tube isolates the heat radiation generated by the heater from the inner tube, preventing the carbon source process gas from cracking in the inner tube. The volume flow ratio between the carbon source process gas and the carrier gas is 1:4-20. Then, they are sprayed into the reaction chamber together, and the carbon source process gas is evenly dispersed. The carbon source process gas cracks at high temperature to form pyrolytic carbon. The pyrolytic carbon coats the surface of the silicon carbon particles, ultimately forming a silicon carbon anode material. During this process, the central spray nozzle sprays the carrier gas, and the upward airflow from the upper spray nozzle lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction chamber. The lower spray nozzle focuses the spray to disrupt the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. Combined with the propulsion and stirring of the agitator, the axial temperature gradient around the agitator is less than 5℃.

[0018] Furthermore, in the aforementioned preparation method, when the fluctuation deviation of the annular tube surface is greater than ±20%, the air velocity of the upper and lower spray holes on the central shower head increases by 15%.

[0019] Furthermore, in the aforementioned preparation method, the pulse frequency and pulse velocity of the carrier gas in the annular tube need to be dynamically adjusted according to the bed density in the reaction chamber: bed density < 400 kg / m³ 3 At that time, the pulse frequency was once every 8 minutes, the peak velocity of the carrier gas was 50 m / s, and the bed density was 400 kg / m³. 3 ~550kg / m 3 At that time, the pulse frequency was once every 5 minutes, the peak velocity of the carrier gas was 60 m / s, and the bed density was >550 kg / m³. 3 At that time, the pulse frequency was once every 3 minutes, and the peak velocity of the carrier gas was 70 m / s.

[0020] Furthermore, in the aforementioned preparation method, during the silicon deposition process in S3 and the carbon coating process in S4, the temperature of the bottom of the reaction cylinder is measured by a thermocouple, and the bottom of the reaction cylinder is controlled by a central spray nozzle to achieve zero-bottom high-temperature safety control. When the bottom heating rate of the reaction cylinder is 5-10℃ / min, including 10℃ / min, the carrier gas velocity of the upper and lower spray holes in the central spray nozzle is increased by 30%-40% until the bottom heating rate of the reaction cylinder does not exceed 5℃ / min; when the bottom of the reaction cylinder... When the heating rate is 10-20℃ / min (including 20℃ / min), liquid nitrogen is injected into the central shower head at a rate of 5L / min. At the same time, the rotation speed of the agitator is increased by 30% until the heating rate is no higher than 10℃ / min. When the heating rate decreases to 5-10℃ / min, room temperature carrier gas is injected into the central shower head for cooling until the heating rate at the bottom of the reaction cylinder is no higher than 5℃ / min. When the heating rate at the bottom of the reaction cylinder is greater than 20℃ / min and continues for 3 seconds, the pressure is released.

[0021] The advantages of this invention are as follows: the carrier gas and process gas are respectively transported to the annular tube through the outer and inner tubes of the casing for injection. The carrier gas in the outer tube can isolate the thermal radiation generated by the heater from the inner tube, preventing the process gas in the inner tube from prematurely decomposing due to high temperature. Thus, there is no need to set up a preheating device to preheat the process gas, and the gas velocities of the process gas and carrier gas can be adjusted separately to stabilize or meet process requirements, improving operational flexibility. The airflow ejected from the nozzles on the annular tube rotates in the same direction as the rotation of the agitator, so that the forward shear force generated by the agitator, combined with the spiral airflow, forms a dynamic flow field, thereby breaking down large agglomerates, improving the efficiency of breaking down residual agglomerates, and ensuring the fluidization effect of the particles. Since the annular tube is set on the inner wall of the reaction cylinder, and the nozzles on the annular tube face the reaction cylinder... The inner wall ensures that regardless of the reactor's diameter, the airflow from the nozzles acts directly on the inner wall and flows downwards along it, converging at the bottom to form a spiral airflow, thus eliminating dead zones at the bottom and side walls. During preparation, the upward spray from the central nozzle lifts particles, preventing sedimentation and maintaining bed expansion within the reactor. The downward spray focuses airflow to disrupt the stable flow field created by unidirectional rotation, breaking the axial concentration gradient. Combined with the stirring paddle, this ensures the axial temperature gradient within the reactor is less than 5°C, controlling the uniformity of temperature inside the reactor and preventing excessively rapid heating at the bottom. Furthermore, the thermocouple at the bottom of the reactor, in conjunction with the central nozzle, allows for zero-bottom high-temperature safety control of the reactor, effectively reducing the risk of flash explosion. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the countercurrent fluidized bed structure for preparing silicon-carbon anode materials according to the present invention.

[0023] Figure 2 yes Figure 1 A schematic diagram of the connection structure between the stirring shaft and the reaction vessel.

[0024] Figure 3 yes Figure 2 A schematic diagram of the nozzle distribution structure on the central annular tube. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0026] like Figure 1 , Figure 2 , Figure 3 As shown, the countercurrent fluidized bed for preparing silicon-carbon anode materials according to the present invention includes: a reaction cylinder 1, on which a solid material inlet 11, a gas outlet, and a heater 12 are provided. The reaction cylinder 1 has no less than two gas outlets, and a metal filter 13 is provided in the gas outlet. A backflow valve and a shut-off valve are provided on the metal filter 13. The heater 12 is a multi-stage electric heating furnace arranged around the reaction cylinder 1. Each stage of the electric heating furnace has an independently controlled temperature. The heating range is 200-900℃, and the temperature control accuracy is ±2℃. A temperature sensor is provided on the electric heating furnace. The temperature sensor is connected to an external control system to realize real-time monitoring and control of the internal temperature of the reaction cylinder 1. A safety valve 14 is provided on the reaction cylinder 1, and a pressure gauge 141 is provided on the safety valve 14. Porous carbon particles can be added to the reaction chamber 1 through the solid material inlet 11, and the carrier gas and residual process gas can be discharged through the gas outlet 1. The metal filter 13 can filter out solid particles. When one metal filter 13 becomes blocked, the shut-off valve of another metal filter 13 is opened and the shut-off valve of the blocked metal filter 13 is closed. The backflush valve of the blocked metal filter 13 is opened for backflush. During backflush, the same gas as the carrier gas needs to be used and the gas is preheated. When the pressure gauge 141 on the safety valve 14 detects that the pressure in the reaction chamber 1 is too high, the shut-off valves on all metal filters 13 are opened first to increase the gas output and reduce the pressure in the reaction chamber 1. If the pressure in the reaction chamber 1 is still too high, the safety valve 14 needs to be opened to release the pressure.

[0027] A stirring shaft 2 is rotatably mounted at the lower end of the reaction cylinder 1. The connection structure between the stirring shaft 2 and the reaction cylinder 1 is as follows: the bottom of the reaction cylinder 1 is an open structure, and a sealing cover 15 is sealed to the bottom of the reaction cylinder 1. An upper flange 151 is provided on the outer wall of the bottom of the reaction cylinder 1, and a lower flange 152 is provided on the outer wall of the sealing cover 15. The upper flange 151 and the lower flange 152 are fitted together and connected by bolts. A sealing gasket is provided between the upper flange 151 and the lower flange 152. A connecting sleeve 153 is fully welded into the sealing cover 15, and a thermocouple 1531 is provided on the connecting sleeve 153. The thermocouple 1531 extends into the sealing cover 15. The connecting sleeve 153 is connected to a bracket 16, and a servo reduction motor 17 is fixed on the bracket 16. The connecting sleeve 153 is equipped with a skeleton oil seal and bearings. The stirring shaft 2 passes through the connecting sleeve 153 and is connected to the skeleton oil seal and bearings. The stirring shaft 2 is connected to the output shaft of the servo geared motor 17 through a coupling. A cooling groove 154 is provided on the outer wall of the connecting sleeve 153. A cooling sleeve 155 is sealed on the outer wall of the connecting sleeve 153 and covers the cooling groove 154. A cooling outlet and a cooling inlet are provided on the cooling sleeve 155. Coolant is introduced into the cooling groove 154 through the cooling inlet and flows out from the cooling outlet. The coolant cools the connecting sleeve 153 and the stirring shaft 2 extending out of the reaction cylinder 1, preventing the heat on the reaction cylinder 1 from being radiated to the servo geared motor 17 and affecting the service life of the servo geared motor 17.

[0028] Several agitator blades 3 are connected to the agitator shaft 2, and the agitator blades 3 extend into the reaction cylinder 1. The agitator blades 3 have a propeller structure with a pitch ratio of 1:1 and a blade inclination angle of 25° to 35°. The diameter of each agitator blade 3 increases gradually from bottom to top. The diameter of the agitator blade 3 at the bottom is 0.6 times the inner diameter of the reaction cylinder 1, and the diameter of the agitator blade 3 at the top is 0.9 times the inner diameter of the reaction cylinder 1, to enhance the upward force of the agitator blades 3. An annular tube 4 is provided on the inner wall of the reaction cylinder 1, located at 40% to 60% of the bed height in the reaction cylinder. The outer diameter of the annular tube is 0.7 to 0.8 times the inner diameter of the reaction cylinder. The stirring paddle 3 avoids the annular tube 4. Several downward-sloping nozzles 41 are evenly distributed circumferentially on the lower side wall of the annular tube 4. The nozzles 41 on the annular tube 4 face the inner wall of the reaction cylinder 1. The inclination angle of the nozzles 41 is 20°–30°, and the orifice diameter of the nozzles 41 is 1–3 mm. The airflow ejected from the nozzles 41 is tangential to the inner wall of the reaction cylinder 1, and the airflow spirals downwards along the inner wall of the reaction cylinder 1. When the rotating airflow converges at the bottom of the reaction cylinder 1, it forms a spiral airflow rotating in the same direction, thereby blowing the particulate material in the reaction cylinder 1 upwards for fluidization, eliminating dead zones at the bottom and side walls of the reaction cylinder 1. The annular tube… The airflow ejected from nozzle 41 on the ring tube 4 rotates in the same direction as the rotation of the agitator 3, so that the forward shear force generated by the agitator 3, combined with the spiral airflow, forms a dynamic flow field, thereby breaking down large agglomerates, improving the efficiency of breaking down residual agglomerates, and ensuring the fluidization effect of the particles. The annular tube 4 is connected to the sleeve 42, which passes through the side wall of the reaction cylinder 1 and the heater 12 in a sealed manner. An annular plug is provided on the sleeve 42, which seals the outer tube 421 of the sleeve 42 and is connected to the inner tube 422. The outer tube 421 of the sleeve 42 is connected to the carrier gas source 5, and the annular plug is connected to the silicon source process gas source. The process gas source 6 and the carbon source process gas source 7 are connected, and the process gas and carrier gas speeds can be adjusted separately to stabilize or meet process requirements, improving operational flexibility. A central shower head 8 is installed in the reaction cylinder 1. The central shower head 8 is located above the agitator 3 and is coaxially aligned with the agitator shaft 3. The central shower head 8 extends out of the reaction cylinder 1 and heater 12 through a gas pipe and is connected to the carrier gas source and liquid carrier gas source respectively. Several upper spray holes 81 are evenly distributed around the upper side wall of the central shower head 8. The upper spray holes 81 are set at an elevation angle of 25° to 35°, and the spray coverage radius of the upper spray holes 81 is 0.5 times the radius of the reaction cylinder 1.Four times stronger, the upward-spraying airflow can lift particles, prevent sedimentation, and maintain the expansion of the bed inside the reaction cylinder 1. Several downward-spraying holes 82 are evenly distributed circumferentially on the bottom wall of the central spray nozzle 8. The downward angle of the downward-spraying holes 82 is set at 50° to 70°, and the jet velocity of the downward-spraying holes 82 is ≥40m / s. The downward-spraying airflow can act on the agitator 3 to scour it, preventing particles from adhering to the agitator 3. To prevent the downward-spraying airflow from the downward-spraying holes 82 from affecting the fluidization effect, the agitator 3 adopts a propeller structure, and the diameter of each agitator 3 increases gradually from bottom to top. By enhancing the upward force of the agitator 3, the downward-spraying airflow from the downward-spraying holes 82 is balanced, thus maintaining the fluidization effect.

[0029] The preparation method uses the countercurrent fluidized bed used in the preparation of silicon-carbon anode materials described above, and its steps are as follows:

[0030] S1. Feeding: Porous carbon particles are fed into the reaction cylinder 1 through the solid material inlet 11, and the solid material inlet 11 is closed.

[0031] S2. Fluidization and Dispersion: The carrier gas source 5 is turned on, and the carrier gas enters the annular pipe 4 through the outer pipe 421 of the sleeve 42. Then, it is sprayed onto the inner wall of the reaction cylinder 1 through the nozzle 41 on the annular pipe 4, and flows spirally downwards along the inner wall. At the bottom of the reaction cylinder 1, it converges to form a spiraling upward airflow, thereby rotating and fluidizing the porous carbon particles. Simultaneously, the carrier gas replaces the air in the reaction cylinder 1. The servo reduction motor 17 is started to drive the stirring paddle 3 to rotate. The stirring paddle 3, rotating in the same direction, agitates the fluidized porous carbon particles. Stirring not only breaks up the agglomeration of porous carbon particles, but also enhances the upward efficiency of porous carbon particles, assists fluidization, and improves the fluidization effect. When there is only carrier gas in the reaction cylinder 1, the heater 12 is started to heat the reaction cylinder 1, so that the temperature inside the reaction cylinder 1 reaches 700-900℃, and is kept at this temperature for 2-4 hours. Under the protection of the carrier gas, the porous carbon particles are annealed to form a porous carbon skeleton. After the porous carbon particles have completed high-temperature activation, the reaction cylinder 1 is slowly cooled down at a cooling rate of 3-5℃ / min. Slow cooling can prevent the porous carbon skeleton from collapsing or the pores from shrinking.

[0032] In this step, the stirring paddle 3 first rotates at a low speed to avoid the porous carbon particles from agglomerating due to high-speed shearing. As the porous carbon particles gradually adapt to the shear force, the stirring paddle 3 gradually increases its rotation speed. At the same time, the fluidization gas velocity of the carrier gas is increased to maintain the bed fluidization state of the reaction chamber 1. Every time the stirring paddle 3 increases its rotation speed, it delays for 5 to 10 seconds before adjusting the fluidization gas velocity of the carrier gas to ensure that the porous carbon particles and the fluidization gas flow maintain dynamic balance.

[0033] S3, Silicon deposition: When the temperature inside the reaction chamber 1 drops to 450-550℃, the carrier gas source 5 remains open, and then the silicon source process gas source 6 is opened. The silicon source process gas enters the annular pipe 4 through the inner tube 422 of the sleeve 42 and mixes with the carrier gas. The carrier gas in the outer tube 421 isolates the heat radiation generated by the heater 12 from the inner tube 422, preventing the silicon source process gas from cracking in the inner tube 422. The volumetric flow rate ratio between the silicon source process gas and the carrier gas is 1:2-10. Then, they are sprayed together into the reaction chamber 1, and the silicon source process gas is evenly distributed. In the process, the silicon source gas is decomposed at high temperature to form nano-silicon particles. The nano-silicon particles and porous carbon particles are chemically vapor-deposited to form silicon-carbon particles. During this process, the central spray nozzle 8 sprays carrier gas, and the upward airflow from the upper spray nozzle 81 lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction cylinder 1. The lower spray nozzle 82 focuses the spray to destroy the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. Combined with the propulsion and stirring of the stirring paddle 3, the axial temperature gradient of the bed in the reaction cylinder 1 is less than 5°C, thereby controlling the uniformity of the internal temperature of the reaction cylinder 1.

[0034] S4. Carbon Coating: When the temperature inside the reaction cylinder 1 reaches 500-650℃, the carbon source process gas source 7 is turned on. The carbon source process gas enters the annular pipe 4 through the inner tube 422 of the sleeve 42 and mixes with the carrier gas. The volume flow ratio between the carbon source process gas and the carrier gas is 1:4-20. Then, they are sprayed into the reaction cylinder 1 together. The carbon source process gas is evenly dispersed. The carbon source process gas is decomposed at high temperature to form pyrolytic carbon. The pyrolytic carbon coats the surface of the silicon carbon particles and finally forms the silicon carbon anode material. During this process, the central spray nozzle 8 sprays the carrier gas, and the upward airflow from the upper spray hole 81 lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction cylinder 1. The lower spray hole 82 focuses the spray to destroy the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. With the propulsion and stirring of the stirring paddle 3, the axial temperature gradient of the bed in the reaction cylinder 1 is <5℃, thereby controlling the uniformity of the internal temperature of the reaction cylinder 1.

[0035] During the preparation process, when the fluctuation deviation on the surface of the annular tube 4 is greater than ±20%, the air velocity of the upper spray hole 81 and lower spray hole 82 on the central spray nozzle 8 is increased by 15%. The fluctuation on the surface of the annular tube 4 refers to the unstable changes in temperature, pressure or fluidization state near the annular tube 4, which will affect the fluidization stability and reaction efficiency in the reaction cylinder 1. Increasing the air velocity of the upper spray hole 81 and lower spray hole 82 of the central spray nozzle 8 can promote bubble breakage, improve particle distribution uniformity, and maintain the bed stability in the reaction cylinder 1. When the carrier gas sprayed out from the central spray nozzle 8 flows in the gas pipe, its temperature will be increased by the heat radiation of the heater 12. Increasing the air velocity can also introduce a large amount of heated carrier gas into the low-temperature zone in the middle of the reaction cylinder 1 to balance the temperature and pressure in the reaction cylinder 1. Increasing the air velocity of the central spray nozzle 8 can maintain the fluctuation deviation on the surface of the annular tube 4 ≤20% by maintaining bed stability and balancing pressure and temperature. However, an increase of 15% in air velocity is the limit value. Exceeding this value will result in excessively high air velocity, increasing system resistance and causing a entrapment effect, which will affect the fluidization effect.

[0036] The pulse frequency and pulse velocity of the carrier gas in the annular tube 4 need to be dynamically adjusted according to the bed density in reaction cylinder 1: bed density < 400 kg / m³ 3 At that time, the pulse frequency was once every 8 minutes, the peak velocity of the carrier gas was 50 m / s, and the bed density was 400 kg / m³. 3 ~550kg / m 3 At that time, the pulse frequency was once every 5 minutes, the peak velocity of the carrier gas was 60 m / s, and the bed density was >550 kg / m³. 3 At that time, the pulse frequency is once every 3 minutes, and the peak velocity of the carrier gas is 70 m / s. The periodic instantaneous high-speed airflow can force the agglomeration of particles to be broken, causing the particles to be violently fluidized.

[0037] During the silicon deposition process in S3 and the carbon coating process in S4, the temperature of the bottom of the reaction cylinder 1 is measured by thermocouple 1531, and the bottom of the reaction cylinder 1 is controlled by the central spray nozzle 8 to achieve zero-bottom high-temperature safety control. When the bottom heating rate of the reaction cylinder 1 is 5-10℃ / min (inclusive), the carrier gas velocity of the upper spray hole 81 and lower spray hole 82 in the central spray nozzle 8 is increased by 30%-40%. By increasing the carrier gas content, the reaction in the reaction cylinder 1 is suppressed, and the risk of heat accumulation is reduced, until the bottom heating rate of the reaction cylinder 1 is no higher than 5℃ / min; when the bottom heating rate of the reaction cylinder 1 is 10-20℃ / min (inclusive), the temperature of the bottom of the reaction cylinder 1 is measured by thermocouple 1531, and the temperature of the bottom of the reaction cylinder 1 is controlled by the central spray nozzle 8 to achieve zero-bottom high-temperature safety control. When the temperature rises to 20℃ / min, the central shower head 8 switches to the liquid carrier gas passage and injects liquid carrier gas into the central shower head 8 at a rate of 5L / min. At the same time, the speed of the stirring paddle is increased by 30% until the heating rate is no higher than 10℃ / min. The rapid heat absorption characteristics of the liquid carrier gas can quickly cool down the temperature, while increasing the stirring speed can force convection for rapid temperature uniformity. When the heating rate decreases to 5-10℃ / min, the central shower head 8 switches to the carrier gas source for cooling. When the bottom heating rate of the reaction cylinder 1 is greater than 20℃ / min and lasts for 3 seconds, the safety valve 14 is opened to release pressure and prevent the reaction cylinder 1 from exploding due to high temperature and overpressure.

[0038] In S3 and S4, if the process gas cracks in the annular pipe 4, causing the nozzle 41 on the annular pipe 4 to become blocked, the gas velocity of the carrier gas in the outer pipe section 421 of the sleeve 42 can be increased to flush out the blockage, keep the nozzle 41 unobstructed, and ensure mass transfer efficiency.

[0039] In this embodiment, the carrier gas is either nitrogen or argon, the liquid carrier gas is either liquid nitrogen or liquid argon, and the carrier gas and liquid carrier gas are the same gas; the silicon source process gas is any one or more of silane, silane, hexamethyldisilane, chlorosilane, and tetrafluorosilane; and the carbon source process gas is any one or more of methane, ethane, ethylene, acetylene, and propylene.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A countercurrent fluidized bed for preparing silicon-carbon anode materials, comprising: A reaction cylinder, equipped with a solid material inlet, a gas outlet, and a heater, is characterized by: a thermocouple at the lower end of the reaction cylinder; a stirring shaft rotatably mounted at the lower end of the reaction cylinder, connected to a servo-driven geared motor; several stirring paddles connected to the stirring shaft, extending into the reaction cylinder; an annular tube on the inner wall of the reaction cylinder; and several downward-sloping nozzles evenly distributed around the lower side wall of the annular tube, the airflow ejected from the nozzles rotating in the same direction as the rotation of the stirring paddles; the annular tube being connected to a sleeve, the sleeve sealingly passing through the side wall of the reaction cylinder and the heater; and the sleeve... An annular seal is provided at the top, which seals the outer tube of the sleeve and connects to the inner tube. The outer tube of the sleeve is connected to the carrier gas source. The annular seal is connected to the silicon source process gas source and the carbon source process gas source respectively. A central shower is provided in the reaction cylinder. The central shower is located above the agitator and is coaxial with the agitator shaft. The central shower extends out of the reaction cylinder and heater through a gas pipe and is connected to the carrier gas source and the liquid carrier gas source respectively. Several upward spray holes are evenly distributed around the upper side wall of the central shower with an upward angle. Several downward spray holes are evenly distributed around the bottom wall of the central shower with a downward angle.

2. The countercurrent fluidized bed for preparing silicon-carbon anode materials according to claim 1, characterized in that: The annular tube is located at 40% to 60% of the bed height in the reaction chamber. The outer diameter of the annular tube is 0.7 to 0.8 times the inner diameter of the reaction chamber. The nozzle on the annular tube faces the inner wall of the reaction chamber, with an inclination angle of 20° to 30° and an orifice diameter of 1 to 3 mm.

3. The countercurrent fluidized bed for preparing silicon-carbon anode materials according to claim 1, characterized in that: The elevation angle of the upper spray hole is 25° to 35°, the spray coverage radius of the upper spray hole is 0.4 times the radius of the reaction cylinder, the depression angle of the lower spray hole is 50° to 70°, and the spray velocity of the lower spray hole is ≥40m / s.

4. The countercurrent fluidized bed for preparing silicon-carbon anode materials according to claim 1, characterized in that: The agitator has a propulsion structure with a pitch ratio of 1:1 and a blade tilt angle of 25° to 35°. The diameter of each agitator increases gradually from bottom to top and avoids the annular tube. The diameter of the agitator at the bottom is 0.6 times the inner diameter of the reaction cylinder, and the diameter of the agitator at the top is 0.9 times the inner diameter of the reaction cylinder.

5. The countercurrent fluidized bed for preparing silicon-carbon anode materials according to claim 1, characterized in that: The connection structure between the stirring shaft and the reaction cylinder is as follows: the bottom of the reaction cylinder is an open structure, a sealing cover is sealed at the bottom of the reaction cylinder, a connecting sleeve is fully welded in the sealing cover, a thermocouple is fixed on the connecting sleeve, the connecting sleeve is connected to the bracket, the servo geared motor is fixed on the bracket, a skeleton oil seal and bearing are provided in the connecting sleeve, the stirring shaft passes through the connecting sleeve and is connected to the skeleton oil seal and bearing, the stirring shaft is connected to the output shaft of the servo geared motor through a coupling, a cooling groove is provided on the outer wall of the connecting sleeve, a cooling sleeve is sealed on the outer wall of the connecting sleeve and covers the cooling groove, and a cooling outlet and a cooling inlet are provided on the cooling sleeve.

6. The countercurrent fluidized bed for preparing silicon-carbon anode materials according to claim 1, characterized in that: The reaction cylinder has at least two gas outlets, each equipped with a metal filter, a backflow valve, and a shut-off valve. The reaction cylinder is also equipped with a safety valve and a pressure gauge.

7. The preparation method, characterized in that: The steps for preparing silicon-carbon anode materials using a countercurrent fluidized bed according to any one of claims 1 to 6 are as follows: S1. Feeding: Porous carbon particles are fed into the reaction cylinder through the solid material inlet, and then the solid material inlet is closed. S2. Fluidization and Dispersion: Turn on the carrier gas source. The carrier gas enters the annular tube through the outer tube of the sleeve, and then is sprayed onto the inner wall of the reaction cylinder through the nozzle on the annular tube. It then flows spirally downward along the inner wall and converges at the bottom of the reaction cylinder to form a spiral upward airflow, thereby rotating and fluidizing the porous carbon particles upward. At the same time, the carrier gas replaces the air in the reaction cylinder. Start the servo reduction motor to drive the stirring paddle to rotate. The stirring paddle rotating in the same direction stirs the fluidized porous carbon particles, which not only breaks up the agglomeration of porous carbon particles, but also enhances the upward efficiency of porous carbon particles and assists in fluidization. When there is only carrier gas in the reaction cylinder, start the heater to heat the reaction cylinder to a temperature of 700-1000℃. Hold the temperature for 2-4 hours. The porous carbon particles are annealed under the protection of the carrier gas and then slowly cooled. S3, Silicon deposition: When the temperature inside the reaction chamber drops to 450–550°C, the carrier gas source remains open, then the silicon source process gas source is opened. The silicon source process gas enters the annular tube through the inner tube of the casing and mixes with the carrier gas. The carrier gas in the outer tube isolates the heat radiation generated by the heater from the inner tube, preventing the silicon source process gas from decomposing in the inner tube. The volumetric flow rate ratio between the silicon source process gas and the carrier gas is 1:2–10. Then, they are both sprayed into the reaction chamber, where the silicon source process gas is evenly dispersed. The silicon source gas decomposes at high temperature to form… Nano-silicon particles are chemically vapor-deposited with porous carbon particles to form silicon-carbon particles. During this process, a carrier gas is sprayed from the central nozzle, and the upward airflow from the upper nozzle lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction chamber. The lower nozzle focuses the spray to disrupt the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. Combined with the propulsion and stirring of the agitator, the axial temperature gradient around the agitator is kept below 5°C. After silicon deposition is completed, the reaction chamber is heated. During the heating process, the silicon source process gas source is shut off, while the carrier gas is continuously introduced. S4. Carbon Coating: When the temperature inside the reaction chamber rises to 500-650℃, the carbon source process gas is turned on. The carbon source process gas enters the annular pipe through the inner tube of the casing and mixes with the carrier gas. The carrier gas in the outer tube isolates the heat radiation generated by the heater from the inner tube, preventing the carbon source process gas from cracking in the inner tube. The volume flow ratio between the carbon source process gas and the carrier gas is 1:4-20. Then, they are sprayed into the reaction chamber together, and the carbon source process gas is evenly dispersed. The carbon source process gas cracks at high temperature to form pyrolytic carbon. The pyrolytic carbon coats the surface of the silicon carbon particles, ultimately forming the silicon carbon anode material. During this process, the central spray nozzle sprays the carrier gas, and the upward airflow from the upper spray nozzle lifts the particles to prevent sedimentation and maintain the expansion of the bed inside the reaction chamber. The lower spray nozzle focuses the spray to disrupt the stable flow field formed by unidirectional rotation, thereby breaking the axial concentration gradient. Combined with the propulsion and stirring of the agitator, the axial temperature gradient around the agitator is less than 5℃.

8. The preparation method according to claim 7, characterized in that: When the fluctuation deviation of the annular pipe surface is greater than ±20%, the air velocity of the upper and lower spray holes on the central shower head increases by 15%.

9. The preparation method according to claim 7, characterized in that: The pulse frequency and pulse velocity of the carrier gas in the annular tube need to be dynamically adjusted according to the bed density in the reaction chamber: bed density < 400 kg / m³ 3 At that time, the pulse frequency was once every 8 minutes, the peak velocity of the carrier gas was 50 m / s, and the bed density was 400 kg / m³. 3 ~550kg / m 3 At that time, the pulse frequency was once every 5 minutes, the peak velocity of the carrier gas was 60 m / s, and the bed density was >550 kg / m³. 3 At that time, the pulse frequency was once every 3 minutes, and the peak velocity of the carrier gas was 70 m / s.

10. The preparation method according to claim 7, characterized in that: During the silicon deposition process in S3 and the carbon coating process in S4, the temperature of the bottom of the reaction cylinder is measured by thermocouples. A central spray nozzle is used to control the bottom temperature of the reaction cylinder for safety. When the bottom temperature rise rate of the reaction cylinder is 5–10°C / min (including 10°C / min), the carrier gas velocity of the upper and lower spray holes of the central spray nozzle is increased by 30%–40% until the bottom temperature rise rate of the reaction cylinder does not exceed 5°C / min. When the bottom temperature rise rate of the reaction cylinder is 10–… At a rate of 20℃ / min (including 20℃ / min), liquid nitrogen is injected into the central shower head at a rate of 5L / min. Simultaneously, the rotation speed of the agitator is increased by 30% until the heating rate is no higher than 10℃ / min. When the heating rate decreases to 5-10℃ / min, ambient temperature carrier gas is injected into the central shower head for cooling until the heating rate at the bottom of the reaction chamber is no higher than 5℃ / min. When the heating rate at the bottom of the reaction chamber exceeds 20℃ / min and remains so for 3 seconds, the pressure is released.

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