Preparation method and system of silicon carbon material

Abstract

The invention relates to the field of batteries, in particular to a preparation method and system of a silicon-carbon material, and the preparation method comprises the following steps: pretreating porous carbon, conveying the pretreated porous carbon to a fluidized bed reactor, sequentially introducing a silicon source gas and a carrier gas for silicon deposition treatment, heating, introducing a carbon source gas, adjusting the flow of the carrier gas for carbon coating treatment, and discharging and cooling to obtain a finished product, meanwhile, reaction tail gas is recycled. The preparation system comprises a gas inlet unit, a fluidized bed reactor unit, a tail gas circulation unit, a feeding preheating unit and a discharging unit. The fluidized bed reactor comprises an outer shell, an up-down stirring device, a heat exchange assembly and an air distribution assembly, and efficient reaction and temperature control can be achieved. The silicon-carbon material prepared by the method has excellent electrochemical performance and is suitable for a lithium ion battery negative electrode material. The unique porous structure and the uniform carbon coating layer effectively improve the conductivity and the structural stability of the material, and meanwhile, the volume expansion effect of silicon in the charging and discharging process is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a preparation method and system of silicon-carbon material. BACKGROUND

[0002] The traditional graphite negative electrode is limited by the theoretical capacity limit of 372 mAh / g, and it is difficult to break through the industry threshold of 500 Wh / kg, while the silicon-based negative electrode with ultra-high theoretical capacity of 4200 mAh / g becomes the key to breaking through the limit. However, the volume expansion of 300% of silicon material during lithium intercalation causes the collapse of electrode structure and the continuous reconstruction of SEI film, resulting in a cycle life of less than 100 times. Therefore, the academic circle proposes a silicon-carbon composite strategy of anchoring nano-silicon particles in a porous carbon matrix - through the mechanical constraint and conductive network of the carbon skeleton, and appropriate carbon coating treatment, so that the lithium ion battery can maintain high specific capacity while greatly improving the cycle life, becoming the most feasible technical path for industrialization.

[0003] Although the current mainstream fluidized bed chemical vapor deposition (CVD) technology can realize the layer-by-layer construction of silicon / carbon structure through gas-solid fluidization, it exposes multiple bottlenecks in engineering scale-up: first, the traditional process adopts intermittent operation, and after reaction, it needs to be naturally cooled for 5-8 hours before discharging, which results in low equipment utilization rate and high-temperature retention, causing silicon particle sintering and carbon layer cracking; second, the strong exothermic characteristics of silane and acetylene cause large axial temperature difference of the fluidized bed, and local hot spots not only cause silicon particle melting and agglomeration, carbon layer over-graphitization, and even SiC impurity phase, but also easily trigger flash explosion risk; third, the single-pass conversion rate of carbon source gas is only 20-30%, and the high-temperature incineration of unreacted gas increases the energy consumption per ton of product, and the investment cost of tail gas purification system is high; fourth, although the laboratory can prepare ideal materials with silicon content > 50wt.% and specific surface area < 2m² / g, the industrial fluidized bed is forced to reduce the silicon content to maintain stability, and needs to be matched with a secondary coating in a rotary furnace, which increases the overall process and energy consumption, resulting in rising costs and performance shrinkage. The above technical bottlenecks form a vicious cycle of "high safety risk-low production efficiency-high cost investment", which seriously hinders the commercialization process of silicon-carbon negative electrode. SUMMARY

[0004] Therefore, the present application provides a preparation method and system of silicon-carbon material to overcome the problems of discontinuous process, low silicon / carbon deposition efficiency, high risk of reaction heat runaway, and uncontrollable product structure in the existing fluidized bed CVD method for preparing silicon-carbon negative electrode material, aiming to realize efficient, safe, and continuous production of silicon-carbon material through multi-stage temperature regulation, tail gas recycling, and reactor structure optimization, and precisely control the core performance indicators such as silicon content, carbon layer thickness, and specific surface area of the material.

[0005] To achieve the above purpose, in one aspect, the present application provides a preparation method of silicon-carbon material, comprising: Step S1, heating the porous carbon to 200-500℃ under inert atmosphere to obtain pretreated porous carbon; Step S2, feeding the pretreated porous carbon into a fluidized bed reactor, introducing a silicon source gas and a carrier gas into the fluidized bed reactor, and completing silicon deposition treatment at 450-540℃ for no more than 8h to obtain silicon deposition particles, then closing the silicon source gas and increasing the carrier gas flow to maintain a first superficial gas velocity; Step S3, heating the fluidized bed reactor to 545-600℃, introducing a carbon source gas, adjusting the carrier gas flow, and performing carbon coating treatment on the silicon deposition particles for no more than 8h to obtain a silicon-carbon material, then closing the carbon source gas and increasing the carrier gas flow to maintain a second superficial gas velocity; Step S4, discharging the silicon-carbon material from the fluidized bed reactor and cooling to obtain a finished silicon-carbon material; Step S5, recycling the reaction tail gas generated in the process of Step S2 and Step S3 to the gas inlet of the fluidized bed reactor, and introducing the corresponding reaction gas.

[0006] Further, the porous carbon in Step S1 includes any one or combination of phenolic resin carbon, coconut shell carbon, and pitch carbon; the particle size of the porous carbon is ≤12μm, and the specific surface area is ≥1500m 2 / g.

[0007] Further, the first superficial gas velocity in Step S2 is 0.02-0.15m / s; the axial temperature difference of the fluidized bed reactor is no more than 50℃; the reaction temperature fluctuation at the same axial measurement point is ≤±5℃; the second superficial gas velocity in Step S3 is 0.01-0.1m / s; the axial temperature difference of the fluidized bed reactor is no more than 20℃; the reaction temperature fluctuation at the same axial measurement point is ≤±5℃.

[0008] Further, the silicon source gas in Step S2 includes one or more of monosilane, disilane, and chlorosilane; the carbon source in Step S3 includes any one or combination of C1-C10 alkane, C2-C10 alkene, C2-C10 alkyne, and C6-C12 aromatic hydrocarbon; and the carrier gas is any one of nitrogen, argon, and helium.

[0009] Further, the reaction tail gas in Step S5 is divided into exhaust gas and recycled tail gas; the flow ratio of the recycled tail gas to the reaction gas is ≤10.

[0010] Further, the silicon content in the finished silicon-carbon material obtained in Step S4 is 40wt.%-55wt.%; the carbon content in the carbon coating process is no more than 5wt.%; and the specific surface area of the finished silicon-carbon material is ≤10 m 2 / g.

[0011] In another aspect, the present application provides a preparation system of silicon-carbon material, comprising a gas inlet unit, a fluidized bed reactor, a tail gas circulation unit, a feeding preheating unit and a discharging unit. The gas output end of the gas inlet unit is connected with the gas input end of the fluidized bed reactor, the gas output end of the fluidized bed reactor is connected with the tail gas circulation unit, the output end of the tail gas circulation unit is connected with the fluidized bed reactor and the gas inlet unit respectively, the feeding preheating unit is connected with the feeding end of the fluidized bed reactor, and the discharging unit is connected with the discharging end of the fluidized bed reactor.

[0012] Further, the fluidized bed reactor comprises an outer shell; The upper stirring device arranged at the top end of the outer shell and the lower stirring device arranged at the bottom end of the outer shell, the heat exchange assembly arranged in the outer shell for controlling the reaction temperature, and the air distribution assembly arranged at the lower end of the outer shell. The lower stirring device comprises a lower stirring motor and a lower stirrer arranged at the output end of the lower stirring motor. The air distribution assembly comprises an upper air distribution ring connected with the tail gas circulation unit and a lower air distribution ring connected with the gas inlet unit.

[0013] Further, the upper stirring device comprises an upper stirring motor, an upper stirring shaft arranged at the output end of the upper stirring motor, and a ribbon stirrer arranged at the output end of the upper stirring shaft, and the heat exchange assembly comprises a first vertical heat extraction pipe bundle and a second vertical heat extraction pipe bundle, the first vertical heat extraction pipe bundle and the second vertical heat extraction pipe bundle being arranged between the upper stirring shaft and the ribbon stirrer.

[0014] Further, the upper stirring device comprises an upper stirring motor, an upper stirring shaft arranged at the output end of the upper stirring motor, and a first upper stirring paddle and a second upper stirring paddle arranged at the output end of the upper stirring shaft, and the heat exchange assembly comprises a first horizontal heat extraction pipe bundle and a second horizontal heat extraction pipe bundle, wherein the first horizontal heat extraction pipe bundle is arranged between the first upper stirring paddle and the second upper stirring paddle, and the second horizontal heat extraction pipe bundle is arranged between the upper stirring device and the lower stirring device.

[0015] Compared with the prior art, the present application has the beneficial effects that the present application combines porous carbon preheating with fluidization process, shortens the silicon deposition induction period, shortens the reaction time to within 8 hours, and improves the production efficiency by more than 1.5 times.

[0016] Further, during the silicon deposition and carbon coating process, the axial temperature difference of the fluidized bed reactor and the reaction temperature fluctuation at the same axial measuring point are strictly controlled. The axial temperature difference is not higher than 50°C and 20°C respectively, and the temperature fluctuation is ≤±5°C, effectively avoiding the generation of local hot spots, preventing problems such as silicon particle melting and agglomeration, excessive graphitization of the carbon layer, and the formation of SiC impurity phases, improving the stability and consistency of product quality, reducing the risk of flash explosion, and ensuring production safety.

[0017] Further, the reaction tail gas is recycled, and the reaction tail gas generated in steps S2 and S3 is circulated to the gas inlet of the fluidized bed reactor and mixed with the corresponding reaction gas. This tail gas recycling method increases the effective concentration of gas in the reaction system, prolongs the residence time of gas in the reactor, thereby improving the single-pass conversion rate of the carbon source gas, reducing the emission of unreacted gas, reducing the energy consumption caused by high-temperature incineration of unreacted gas, and reducing the investment and operating costs of the tail gas purification system.

[0018] Further, by precisely controlling the process parameters of each step, such as reaction temperature, gas flow, reaction time, etc., the silicon content in the prepared silicon-carbon material product is 40wt.%~55wt.%, the carbon content in the carbon coating process is not higher than 5wt.%, and the specific surface area is ≤10 m² / g. Under the requirement of industrial production for material stability, excessive reduction of silicon content and addition of secondary coating process to maintain stability are avoided, achieving a good balance between product performance and production cost, reducing overall production cost, and ensuring that the product has good performance.

[0019] Further, the porous carbon can be any one or combination of phenolic resin carbon, coconut shell carbon, and pitch carbon, the silicon source gas includes one or more of monosilane, disilane, and chlorosilane, the carbon source includes any one or combination of C1-C10 alkane, C2-C10 alkene, C2-C10 alkyne, and C6-C12 aromatic hydrocarbon, and the carrier gas is any one of nitrogen, argon, and helium. This wide range of raw material selection provides greater flexibility for production, allowing the selection of appropriate raw materials based on resource conditions and cost factors in different regions, reducing raw material procurement costs.

[0020] Further, the system is equipped with a tail gas recycling unit, which collects and processes the reaction tail gas discharged from the fluidized bed reactor and then recycles part of it back to the reactor for further reaction. This design improves the utilization rate of gas, reduces the amount of fresh gas used, reduces resource consumption and production cost, and reduces the environmental impact of tail gas emissions.

[0021] Further, the gas inlet unit, the material charging and preheating unit, and the material outlet unit are reasonably connected with the fluidized bed reactor, so as to ensure that the silicon source gas, the carbon source gas, the carrier gas, and the porous carbon and other raw materials can be stably and accurately delivered into the reactor, and at the same time, the prepared silicon-carbon material can be smoothly discharged. The optimized material delivery system helps to maintain a stable reaction environment in the reactor, improves the reaction efficiency and product quality.

[0022] Further, the upper stirring device and the lower stirring device arranged inside the fluidized bed reactor can effectively stir the reaction materials, promote the sufficient contact and reaction between the gas and the solid particles, and improve the uniformity and conversion rate of the reaction. The arrangement of the heat exchange assembly can accurately control the reaction temperature, so as to ensure that the reaction is carried out under suitable temperature conditions, and further improve the product quality.

[0023] Further, the air distribution assembly includes an upper air distribution ring pipe connected with the tail gas circulation unit and a lower air distribution ring pipe connected with the gas inlet unit. The design of the double air distribution ring pipes can uniformly distribute the gas in the reactor, avoid the local overlarge or over-small gas flow, ensure that the solid particles are in a good fluidized state in the fluidized bed, promote the uniform reaction, and improve the quality consistency of the product.

[0024] Further, the system provides two different structure schemes of the upper stirring device and the heat exchange assembly. In the first scheme, the upper stirring device adopts a screw ribbon stirrer, and the heat exchange assembly is a vertical heat extraction pipe bundle; in the second scheme, the upper stirring device adopts an upper stirring paddle, and the heat exchange assembly is a horizontal heat extraction pipe bundle. The two schemes can be selected according to different production process requirements and reaction characteristics, improve the adaptability and flexibility of the system, and better meet the diversified production demands.

[0025] The silicon-carbon material preparation method and system strictly control the axial temperature difference and temperature fluctuation of the reactor during silicon deposition and carbon coating, avoid various adverse problems, and ensure production safety. The system recycles the reaction tail gas, improves the gas utilization rate and carbon source conversion rate, reduces the cost and energy consumption, and reduces emissions. The process parameters are accurately controlled to balance the product performance and cost. The raw material selection range is wide, and the raw material can be flexibly selected according to resources and cost. In the system design, the tail gas circulation, material delivery, stirring and heat exchange, air distribution, and other units and components are reasonably designed, and two upper stirring and heat exchange structure schemes are provided to improve the adaptability and flexibility of the system and meet the diversified production demands. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A flow chart of a silicon-carbon material preparation method according to an embodiment of the present application; Figure 2 A flow chart of a silicon-carbon material preparation method according to an embodiment of the present application; Figure 3A fluidized bed reactor structure schematic diagram of an embodiment of the present application; Figure 4 Another fluidized bed reactor structure schematic diagram of an embodiment of the present application; In the figure: 11, gas cylinder group; 111, nitrogen cylinder; 112, carbon source gas cylinder; 113, silicon source gas cylinder; 12, flow controller; 13, preheating furnace; 31, metal filter column; 32, lye absorber; 33, circulating fan; 34, exhaust pipe; 41, feeding tank; 42, heating assembly; 51, unloading tank; 52, material collecting tank; 21, outer shell; 231, lower stirring motor; 232, lower stirrer; 251, upper air distribution ring pipe; 252, lower air distribution ring pipe; 221, upper stirring motor; 222, upper stirring shaft; 223, ribbon stirrer; 241, first vertical heat extraction pipe bundle; 242, second vertical heat extraction pipe bundle; 224, first upper stirring paddle; 225, second upper stirring paddle; 243, first horizontal heat extraction pipe bundle; 244, second horizontal heat extraction pipe bundle. DETAILED DESCRIPTION

[0027] In order to make the objectives and advantages of the present application clearer, the present application will be further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0028] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and do not limit the protection scope of the present application.

[0029] Please refer to Figures 1-4 The figure shows a flow chart of a method for preparing a silicon-carbon material according to an embodiment of the present application; a preparation flow chart of a silicon-carbon material according to an embodiment of the present application; a fluidized bed reactor structure schematic diagram according to an embodiment of the present application; another fluidized bed reactor structure schematic diagram according to an embodiment of the present application; In one aspect, a method for preparing a silicon-carbon material according to an embodiment of the present application comprises: Step S1, heating porous carbon to 200-500℃ under inert atmosphere to obtain pretreated porous carbon; Step S2, feeding the pretreated porous carbon into a fluidized bed reactor, introducing silicon source gas and carrier gas into the fluidized bed reactor, and completing silicon deposition treatment for no more than 8h at 450-540℃ to obtain silicon deposition particles, then closing the silicon source gas and increasing the carrier gas flow to maintain a first apparent gas velocity; Step S3, increasing the temperature of the fluidized bed reactor to 545-600℃, introducing carbon source gas, adjusting the carrier gas flow, and performing carbon coating treatment for no more than 8h on the silicon deposition particles to obtain a silicon-carbon material, then closing the carbon source gas and increasing the carrier gas flow to maintain a second apparent gas velocity; Step S4, after the silicon-carbon material is discharged from the fluidized bed reactor, the silicon-carbon material product is obtained after cooling; wherein, the specific operation mode of cooling after discharging is to open the discharge valve, and the silicon-carbon material obtained in step S3 is transported to the discharge tank and cooled to below 50°C, preferably below 30°C, by a water-cooled wall to obtain the silicon-carbon material product; Step S5, the reaction tail gas generated in the process of step S2 and step S3 is recycled to the gas inlet of the fluidized bed reactor, and the corresponding reaction gas is added.

[0030] Specifically, in step S1, the heating treatment of the porous carbon can effectively remove the water and impurities adsorbed on the surface of the porous carbon, improve the purity of the porous carbon, and provide a good foundation for the silicon deposition process. At the same time, the protection of inert atmosphere can prevent the reaction of porous carbon with oxygen during heating process, and avoid unnecessary side reactions.

[0031] Specifically, in the silicon deposition step of step S2, accurate control of reaction temperature and superficial gas velocity is a key factor to realize high-quality silicon deposition. The temperature range of 450-540°C can not only ensure the complete decomposition of silicon source gas and deposition on the surface of porous carbon, but also avoid the occurrence of silicon particle excessive growth or melting and agglomeration due to too high temperature. By adjusting the carrier gas flow to maintain a stable superficial gas velocity, it is helpful to maintain the good fluidization state of the particles in the fluidized bed, promote the uniform contact between the silicon source gas and the porous carbon particles, and obtain silicon particles with uniform particle size distribution and stable structure.

[0032] Specifically, the carbon coating treatment in step S3 further improves the performance of the silicon-carbon material. After the fluidized bed reactor is heated to a temperature range of 545-600°C, carbon source gas is introduced, so that a dense and uniform coating layer of carbon can be formed on the surface of the silicon particles. This carbon coating not only can effectively alleviate the volume expansion effect of silicon during charging and discharging process, improve the cycle stability of the material, but also can enhance the electrical conductivity of the material and improve its electrochemical performance. Adjusting the carrier gas flow to meet the needs of different reaction stages ensures the smooth progress of the carbon coating process.

[0033] Specifically, the cooling treatment of the silicon-carbon material product in step S4 also cannot be ignored. Cooling treatment can prevent the material from being exposed to high temperature for too long and causing oxidation or other adverse reactions, ensuring the quality and performance of the final product. The design of the discharge unit ensures the production efficiency while avoiding mechanical damage or contamination to the finished product.

[0034] Specifically, the tail gas recycling link of step S5 embodies the advantages of the present application in environmental protection and economy. By collecting, separating and recycling the tail gas generated during the reaction process, not only the utilization rate of raw materials can be significantly improved, the production cost can be reduced, but also the potential harm of direct emission of unreacted gas to the environment can be reduced. This closed-loop gas management strategy conforms to the development concept of modern green chemical industry, and provides a sustainable solution for large-scale industrial production of silicon-carbon materials.

[0035] Specifically, the porous carbon in step S1 includes any one or combination of phenolic resin carbon, coconut shell carbon, pitch carbon; the particle size of the porous carbon is ≤12 μm, the specific surface area is ≥1500 m 2 / g.

[0036] Specifically, phenolic resin carbon, coconut shell carbon and pitch carbon each has its own characteristics and can meet different process requirements. For example, phenolic resin carbon has high mechanical strength and good thermal stability, and is suitable for use in high temperature environment; coconut shell carbon has excellent adsorption performance due to its natural porous structure, which helps to improve the efficiency of silicon deposition; and pitch carbon is one of the ideal choices due to its low cost and good electrical conductivity. By reasonably matching these raw materials, not only the basic performance of silicon-carbon materials can be optimized, but also the formula can be flexibly adjusted according to the actual production conditions. In addition, the requirements for the particle size and specific surface area of the porous carbon are also strictly considered. Controlling the particle size below 12 μm ensures the uniform suspension and full contact of particles in the fluidized bed reactor, avoiding the problem of incomplete reaction or local blockage caused by too large particles. At the same time, the design target of specific surface area not less than 1500 m² / g provides sufficient reaction interface for silicon source gas, significantly improving the efficiency and quality of silicon deposition. This fine parameter setting makes the finally prepared silicon-carbon material more uniform and dense in microstructure, thereby showing more superior electrochemical performance.

[0037] Specifically, the first superficial gas velocity in step S2 is 0.02-0.15 m / s; the axial temperature difference of the fluidized bed reactor is not higher than 50°C; the reaction temperature fluctuation at the same axial measuring point is ≤±5°C, preferably ≤±2°C; the second superficial gas velocity in step S3 is 0.01-0.1 m / s; the axial temperature difference of the fluidized bed reactor is not higher than 20°C; the reaction temperature fluctuation at the same axial measuring point is ≤±5°C. In actual operation, strict monitoring of the superficial gas velocity, axial temperature difference and temperature fluctuation is the key to ensuring the stability of the reaction and the consistency of the product. A reasonable range of superficial gas velocity can effectively maintain the good suspension state of particles in the fluidized bed, avoiding poor fluidization or particle agglomeration caused by too fast or too slow gas velocity. At the same time, precise control of the axial temperature difference and temperature fluctuation can prevent local overheating, thereby avoiding problems such as silicon particle melting and agglomeration, excessive graphitization of the carbon layer, and impurity generation. This multi-dimensional parameter control not only improves the reaction efficiency, but also significantly improves the quality stability of the product. In addition, in steps S2 and S3, the design of superficial gas velocity at different stages also reflects the concept of process optimization. In the silicon deposition stage, setting the superficial gas velocity at 0.02-0.15 m / s helps to enhance the contact frequency between the silicon source gas and the porous carbon particles, thereby improving the deposition efficiency; while in the carbon coating stage, reducing the superficial gas velocity to 0.01-0.1 m / s is more conducive to the formation of a uniform and dense coating layer on the surface of the silicon deposition particles. By adjusting the gas velocity in stages and combining with the precise temperature management strategy, the reaction can be ensured to proceed fully while minimizing the occurrence of side reactions, providing protection for the high performance of the final product.

[0038] Specifically, the silicon source gas in step S2 includes one or more of monosilane, disilane, chlorosilane, preferably monosilane; the carbon source in step S3 includes any one or combination of C1-C10 alkane, C2-C10 alkene, C2-C10 alkyne and C6-C12 aromatic hydrocarbon, preferably acetylene; the carrier gas is any one of nitrogen, argon, helium, preferably nitrogen.

[0039] Specifically, in step S5, the reaction tail gas is divided into purge gas and recycled tail gas to ensure pressure balance in the reactor, and the flow rate of the recycled tail gas is adjustable; the flow rate ratio of the recycled tail gas to the reaction gas is ≤10. Such a setting not only effectively prevents the reaction of porous carbon with oxygen, but also reduces the possibility of introducing impurities. This measure ensures the purity of the material from the source, laying a solid foundation for subsequent silicon deposition and carbon coating. Combined with the step of removing water and impurities through heating treatment, the active surface of the porous carbon can be further improved, making it exhibit higher reactivity in the silicon deposition process.

[0040] Specifically, the silicon content in the finished silicon-carbon material obtained in step S4 is 40wt.% to 55wt.%, preferably 50wt.%; the carbon content in the carbon coating process is not higher than 5wt.%, preferably 2wt.%; the specific surface area of the finished silicon-carbon material is ≤10 m2 / g, preferably ≤2 m 2 / g. This precise control of the silicon-carbon ratio ensures a balance between the electrochemical performance and mechanical stability of the material. A silicon content of 40wt.% to 55wt.% can significantly improve the specific capacity of the material, and a carbon coating with a carbon content not higher than 5wt.% effectively alleviates the volume expansion problem of silicon during charging and discharging, thereby prolonging the cycle life of the material. At the same time, by controlling the specific surface area of the finished product to be below 10 m2 / g, the interface properties of the material are further optimized, unnecessary side reactions are reduced, and the overall stability of the material is improved. In addition, this design also takes into account the operability in actual production, providing convenient conditions for large-scale industrial application.

[0041] In another aspect, the present application provides a preparation system of silicon-carbon material, comprising a gas inlet unit, a fluidized bed reactor, a tail gas circulation unit, a feeding preheating unit and a discharging unit; wherein the gas output end of the gas inlet unit is connected with the gas input end of the fluidized bed reactor, the gas output end of the fluidized bed reactor is connected with the tail gas circulation unit, the output end of the tail gas circulation unit is connected with the fluidized bed reactor and the gas inlet unit respectively, the feeding preheating unit is connected with the feeding end of the fluidized bed reactor, and the discharging unit is connected with the discharging end of the fluidized bed reactor; wherein the gas inlet unit comprises a gas cylinder group 11, the gas cylinder group 11 comprises a nitrogen cylinder 111, a carbon source cylinder 112 and a silicon source cylinder 113, and the output end of each cylinder is provided with a flow controller 12, wherein the output end of the flow controller 12 corresponding to the carbon source cylinder 112 is provided with a preheating furnace 13; the tail gas circulation unit comprises a metal filter column 31 connected with the top end of the fluidized bed reactor, an alkali liquor absorber 32 connected with the fixed end of the metal filter column 31, a circulating fan 33 connected with the gas output end of the alkali liquor absorber 32 and a vent gas pipe 34 arranged in the gas flow direction of the circulating fan 33; the feeding preheating unit comprises a feeding tank 41 arranged at the feeding end of the fluidized bed reactor and a heating assembly 42 arranged on the outer wall of the feeding tank 41; the discharging unit comprises a discharging tank 51 arranged at the discharging end of the fluidized bed reactor and a material collecting tank 52 connected with the discharging tank 51; in this way, efficient and stable operation of the silicon-carbon material preparation process can be realized. The gas inlet unit provides accurately proportioned reaction gas through the gas cylinder group 11, and the flow and temperature of the gas are accurately controlled by the flow controller 12 and the preheating furnace 13, thereby ensuring the stability of the reaction conditions. The metal filter column 31 in the tail gas circulation unit can effectively intercept solid particles in the tail gas, and the alkali liquor absorber 32 is used to remove acidic or harmful components, thereby realizing purification treatment of the tail gas. After the purification treatment, the purified tail gas is re-introduced into the reactor by the action of the circulating fan 33, forming a closed loop circulation, thereby maximizing the utilization rate of raw materials and reducing the risk of environmental pollution. The design of the feeding preheating unit focuses on sealing and controllability, and the pretreated porous carbon is uniformly fed into the fluidized bed reactor through the feeding tank 41, thereby avoiding the introduction of external impurities. The discharging tank 51 and the material collecting tank 52 of the discharging unit work cooperatively, thereby ensuring the smooth collection of finished products and preventing oxidation problems of high-temperature finished products during the discharging process.

[0042] Specifically, the fluidized bed reactor comprises an outer shell 21; an upper stirring device arranged at the top end of the outer shell 21 and a lower stirring device arranged at the bottom end of the outer shell 21, a heat exchange assembly arranged in the outer shell 21 for controlling the reaction temperature, and an air distribution assembly arranged at the lower end of the outer shell 21; the lower stirring device comprises a lower stirring motor 231 and a lower stirrer 232 arranged at the output end of the lower stirring motor 231; The air distribution assembly includes an upper air distribution ring pipe 251 connected to the tail gas circulation unit and a lower air distribution ring pipe 252 connected to the gas inlet unit.

[0043] Specifically, the upper stirring device includes an upper stirring motor 221, an upper stirring shaft 222 arranged at the output end of the upper stirring motor 221, and a ribbon stirrer 223 arranged at the output end of the upper stirring shaft 222, and the heat exchange assembly includes a first vertical heat extraction pipe bundle 241 and a second vertical heat extraction pipe bundle 242, which are arranged between the upper stirring shaft 222 and the ribbon stirrer 223.

[0044] Specifically, the upper stirring device includes an upper stirring motor 221, an upper stirring shaft 222 arranged at the output end of the upper stirring motor 221, and a first upper stirring paddle 224 and a second upper stirring paddle 225 arranged at the output end of the upper stirring shaft 222, and the heat exchange assembly includes a first horizontal heat extraction pipe bundle 243 and a second horizontal heat extraction pipe bundle 244, wherein the first horizontal heat extraction pipe bundle 243 is arranged between the first upper stirring paddle 224 and the second upper stirring paddle 225, and the second horizontal heat extraction pipe bundle 244 is arranged between the upper stirring device and the lower stirring device.

[0045] Specifically, the two schemes can be selected according to different production process requirements and reaction characteristics, improving the adaptability and flexibility of the system, and better meeting the diversified production needs. This design can also effectively optimize the heat distribution and mass transfer in the reaction process, thereby improving the product quality and production efficiency. By flexibly adjusting the cooperation mode of the air distribution assembly and the stirring device, the stability and controllability of the system can be further enhanced, providing greater convenience for actual operation. At the same time, the modular structure of the system also facilitates later maintenance and upgrading, reducing the long-term operation cost.

[0046] The present application strictly controls the reactor axial temperature difference and temperature fluctuation during silicon deposition and carbon coating through the preparation method and system of silicon-carbon material, avoids various adverse problems, and ensures production safety; recycles reaction tail gas, improves gas utilization rate and carbon source conversion rate, reduces cost and energy consumption, and reduces emissions; accurately controls process parameters, balances product performance and cost; the selection range of raw materials is wide, and the raw materials can be flexibly selected according to resources and cost; in the system design, the tail gas circulation, material conveying, stirring and heat exchange, air distribution and other units and components are reasonably designed, and two lower stirring and heat exchange structure schemes are provided, which improves the adaptability and flexibility of the system and meets the diversified production needs. Example 1

[0047] The present application utilizes the above-mentioned preparation system of silicon-carbon material to produce finished silicon-carbon material, and the method conditions adopted include the following: Step S1, heating the porous carbon to 200-500℃ under inert atmosphere to obtain a pretreated porous carbon; Phenolic resin carbon (particle size D50=8 μm, specific surface area 1800 m² / g) was selected as the raw material, and was preheated to 350℃ under nitrogen protection by electric heating method, and the preheating time was 30 min.

[0048] Step S2, the pretreated porous carbon was transported into a fluidized bed reactor, and a silicon source gas and a carrier gas were introduced into the fluidized bed reactor, and the silicon deposition treatment was completed at 450-540℃ for not more than 8h to obtain silicon deposition particles, and then the silicon source gas was turned off and the carrier gas flow was increased to maintain the first apparent gas velocity; The pretreated porous carbon was transported into a fluidized bed reactor (configured with an anchor stirring paddle, rotating speed 80 r / min), and a mixture of silane and nitrogen gas (volume ratio 1:5) was introduced, the apparent gas velocity was controlled at 0.08 m / s, the reaction temperature was 480℃. The axial temperature difference was maintained at ≤10℃ by the built-in heat extraction tube bundle, and the temperature fluctuation was ≤±2℃, and the reaction time was 6h. The heat extraction tube bundle includes a first vertical heat extraction tube bundle 241 and a second vertical heat extraction tube bundle 242, or a first horizontal heat extraction tube bundle 243 and a second horizontal heat extraction tube bundle 244.

[0049] Step S3, the fluidized bed reactor was heated to 545-600℃, a carbon source gas was introduced, and the carrier gas flow was adjusted, and the silicon deposition particles were subjected to carbon coating treatment for not more than 8h to obtain a silicon-carbon material, and then the carbon source gas was turned off and the carrier gas flow was increased to maintain the second apparent gas velocity; The temperature was raised to 550℃, and a mixture of acetylene and nitrogen gas (volume ratio 1:6) was switched in, the apparent gas velocity was 0.05 m / s, the axial temperature difference was ≤10℃, the reaction time was 4h, and a silicon-carbon material was obtained.

[0050] Step S4, after the silicon-carbon material was discharged from the fluidized bed reactor and cooled, a silicon-carbon material finished product was obtained; A high-temperature resistant discharge valve (material Inconel 600) was opened, the silicon-carbon material was cooled to 25℃ by the water-cooled wall (cooling water flow 5 m³ / h) within 3 min, and a silicon-carbon material finished product was obtained.

[0051] Step S5, the reaction tail gas generated in the process of step S2 and step S3 was circulated to the gas inlet of the fluidized bed reactor, and the corresponding reaction gas was introduced.

[0052] After the reaction tail gas was circulated by the circulating fan and mixed with the reaction gas, in the silicon deposition stage of step S2, the volume flow ratio of the reaction tail gas to the reaction gas was controlled at 3:1, and in the carbon coating stage of step 3, the volume flow ratio of the reaction tail gas to the reaction gas was controlled at 5:1.

[0053] To implement the operation steps of the above method, the preparation system of the silicon-carbon material used in this embodiment is mainly configured as follows: A fluidized bed reactor sequentially performs silicon deposition and carbon coating, and is internally provided with a loop-type gas distributor, a nitrogen heat-removal tube bundle, and an anchor stirring paddle. An exhaust gas circulation unit: circulation fan (air volume adjustable range 10-1000 m³ / h). A discharge unit: high-temperature-resistant valve (temperature resistance > 600°C); water-cooled wall (cooling rate ≥ 50°C / min).

[0054] Based on the method and system of the embodiment, the prepared porous carbon has a silicon content of 48 wt.%, a carbon coating amount of 2.3 wt.%, a specific surface area of 1.8 m² / g, and a D90 particle size of 10.5 μm. The capacity retention rate is 83.5% after 300 cycles of discharge test (0.5C charge and discharge). Embodiment 2

[0055] This embodiment provides a preparation method and system of a silicon-carbon material, which is different from Embodiment 1 in that: The system configuration adopts a structure of double upper stirring paddles and lower stirring in the fluidized bed reactor, and the heat-removal tube bundle and the stirring paddle are arranged in a spatial staggered manner in the axial direction. The silicon deposition reactor has a temperature of 540°C, a silane / nitrogen volume ratio of 1:8, and an apparent gas velocity of 0.12 m / s; the carbon coating reactor has a temperature of 580°C, an ethylene / nitrogen volume ratio of 1:15; The exhaust gas is circulated, and the silicon deposition circulation gas / reaction gas supply ratio is 5:1, and the carbon coating circulation ratio is 8:1; As a result, the silicon content is 53 wt.%, the specific surface area is 2.2 m² / g, the capacity retention rate is 81.2% after 500 cycles, and the production capacity is increased by 40% to 72 kg / h. Embodiment 3

[0056] This embodiment provides a preparation method and system of a silicon-carbon material, which is different from Embodiment 1 in that: The silicon deposition time is 4 h; The carbon coating amount is 2.0 wt.%; The stirring mode in the fluidized bed reactor is a combination of screw belt stirring and frame stirring for the upper stirring, and frame stirring for the lower stirring.

[0057] As a result, the silicon content is 42.5 wt.%, the specific surface area is 1.5 m² / g, the silicon content deviation of the same batch is ≤0.8 wt.%, and the retention rate is 84.7% after 300 cycles. Embodiment 4

[0058] This embodiment provides a preparation method and system of a silicon-carbon material, which is different from Embodiment 1 in that: The preheating temperature is 200°C; Silicon deposition parameters: temperature 450℃, reaction time 8h, gas velocity 0.02m / s; Carbon-coating gas velocity: 0.01m / s; As a result, silicon content 40wt.%, specific surface area 9.8m² / g. Example 5

[0059] This example provides a method and system for preparing silicon-carbon material, referring to Example 1, the difference is: Raw material composition: porous carbon is a mixture of phenolic resin carbon and coconut shell carbon with a mass ratio of 1:1; Carbon-coating carbon source: acetylene / propylene volume ratio 2:1.

[0060] As a result, silicon content 49wt.%, carbon-coating layer forms cross-linking structure (observed by TEM); specific surface area 1.6m² / g; capacity retention rate 85.9% after 300 cycles, anti-swelling performance is improved, volume expansion rate <100%. Example 6

[0061] This example provides a method for preparing silicon-carbon material, referring to Example 1, the difference is only: Carbon-coating carbon source: switched to ethylene, ethylene / nitrogen volume ratio 1:8; Carbon-coating temperature: 520℃, reaction time 6h.

[0062] As a result, carbon layer thickness uniformity is improved, deviation ≤±1.5nm, Example 1 is ±3nm; specific surface area 1.2m² / g, silicon content 50wt.%; initial efficiency is improved to 92.5%, retention rate 86.3% after 300 cycles.

[0063] Comparative Example 1 This comparative example provides a method for preparing silicon-carbon material, referring to Example 1, the difference is: No preheating, initial temperature of porous carbon 25℃; Natural cooling, discharging time 7h; Tail gas is directly discharged without recycling.

[0064] As a result, silicon content 36wt.%, specific surface area 23m² / g, production capacity 32kg / h, which is 38% of Example 1, retention rate 68% after 200 cycles.

[0065] Comparative Example 2 This comparative example provides a method for preparing silicon-carbon material, referring to Example 1, the difference is only: Silicon deposition cycle ratio: 12:1; Carbon-coating cycle ratio: 15:1; As a result, the reactor pressure fluctuation is >0.3 MPa, and the safety relief is triggered 3 times, the SiC impurity in the silicon-carbon product is 0.6 wt.%, and the cycle retention rate is reduced to 75%.

[0066] Comparative Example 3 This comparative example provides a method for preparing a silicon-carbon material, which is similar to Example 1, except that: The stirring paddle and the heat removal tube bundle are removed; The temperature is controlled only by relying on the gas distributor.

[0067] As a result, the axial temperature difference in the silicon deposition section is >100°C, the silicon particles are fused and agglomerated, and the flash combustion alarm is triggered.

[0068] Effect comparison: using the methods and systems of Examples 1-6 and Comparative Examples 1-3 to prepare silicon-carbon materials, the obtained silicon-carbon materials are used to make negative electrode sheets and assemble button-type half batteries, and the performance of the batteries is tested, and the energy consumption and safety of the systems used in the examples and comparative examples are compared. The specific data are shown in Table 1.

[0069] Table 1 Test results

[0070] Through the comparative analysis of the series of examples and comparative examples, the effectiveness and innovativeness of the technical solutions are fully verified. All examples strictly follow the parameter range of the claims, among which Example 1 is used as a benchmark process, which realizes excellent performance of 48 wt.% silicon content and 1.8 m² / g specific surface area, a cycle retention rate of 83.5% after 300 cycles, and a product energy consumption of 18 kWh per ton; the fluidized bed system used in Example 2 adopts a staggered arrangement form for stirring and heat removal, which maintains a production capacity of 72 kg / h while increasing the silicon content to 53 wt.%, confirming the advantages of multi-reactor cooperation; Examples 5-6 further improve the cycle retention rate to 86.3% by using a combination of porous carbon (phenolic resin carbon + coconut shell carbon) and optimizing the ethylene carbon source, and the carbon layer uniformity deviation is compressed to ±1.5 nm, and the initial efficiency breaks through 92.5%, reaching the standard of vehicle-grade battery materials. The boundary parameter verification (Example 4) shows that even under extreme conditions such as a preheating temperature of 200°C and a silicon deposition gas velocity of 0.02 m / s, qualified materials with a silicon content of 40 wt.% can still be stably prepared, highlighting the scientificity and operability of the parameter range of the claims. The data of the comparative examples inversely prove the necessity of the core design: after removing key features such as preheating, tail gas recycling, or stirring cooling, the specific surface area of the material increases to 23-28 m² / g, the cycle performance decays to 58%-68%, and safety hazards such as flash explosion and pressure loss of control occur. Through the structural innovation of the fluidized bed and the synergistic regulation of the process parameters, the industrialization contradiction of "high silicon content-low expansion rate-high safety" is successfully solved, providing a solution with high efficiency, safety, and economy for the large-scale commercialization of silicon-carbon negative electrodes.

[0071] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will all fall within the protection scope of the present application.

[0072] The above description is only the preferred embodiments of the present application and is not intended to limit the present application; for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a silicon-carbon material, characterized in that, include: Step S1: The porous carbon is heated to 200~500℃ in an inert atmosphere using a feeding preheating unit to obtain pretreated porous carbon; Step S2: The pretreated porous carbon is transported to a fluidized bed reactor. Silicon source gas and carrier gas are introduced into the fluidized bed reactor. Silicon deposition treatment is carried out at 450~540℃ for no more than 8 hours to obtain silicon particles. Then the silicon source gas is turned off and the carrier gas flow rate is increased to maintain the first apparent gas velocity. Step S3: Heat the fluidized bed reactor to 545~600℃, introduce carbon source gas, adjust the carrier gas flow rate, and perform carbon coating treatment on the silicon particles for no more than 8 hours to obtain silicon-carbon material. Then, turn off the carbon source gas and increase the carrier gas flow rate to maintain the second apparent gas velocity. Step S4: After the silicon-carbon material is discharged from the fluidized bed reactor and cooled, the finished silicon-carbon material is obtained. Step S5: The reaction tail gas generated in steps S2 and S3 is recycled to the inlet of the fluidized bed reactor and incorporated into the corresponding reaction gas.

2. The method for preparing silicon-carbon material according to claim 1, characterized in that, The porous carbon in step S1 includes any one or a combination of phenolic resin carbon, coconut shell carbon, and asphaltene carbon; the particle size of the porous carbon is ≤12μm, and the specific surface area is ≥1500m². 2 / g.

3. The method for preparing silicon-carbon material according to claim 1, characterized in that, In step S2, the first apparent gas velocity is 0.02~0.15 m / s; the axial temperature difference of the fluidized bed reactor is not higher than 50℃; the reaction temperature fluctuation at the same axial measuring point is ≤±5℃. In step S3, the second apparent gas velocity is 0.01~0.1 m / s; the axial temperature difference of the fluidized bed reactor is not higher than 20℃; the reaction temperature fluctuation at the same axial measuring point is ≤±5℃.

4. The method for preparing silicon-carbon material according to claim 1, characterized in that, The silicon source gas in step S2 includes one or more of silane, silane, and chlorosilane; the carbon source in step S3 includes any one or a combination of C1-C10 alkanes, C2-C10 alkenes, C2-C10 alkynes, and C6-C12 aromatic hydrocarbons; and the carrier gas is any one of nitrogen, argon, and helium.

5. The method for preparing silicon-carbon material according to claim 4, characterized in that, In step S5, the reaction tail gas is divided into purge gas and recirculation tail gas; the flow ratio of the recirculation tail gas to the reaction gas is ≤10.

6. The method for preparing silicon-carbon material according to claim 5, characterized in that, The silicon content of the silicon-carbon material obtained in step S4 is 40 wt.% to 55 wt.%; the carbon content during the carbon coating process is no higher than 5 wt.%; and the specific surface area of ​​the silicon-carbon material is ≤10 m². 2 / g.

7. A system for preparing silicon-carbon materials, comprising using the method for preparing silicon-carbon materials according to any one of claims 1-6, characterized in that, It includes an air inlet unit, a fluidized bed reactor, a tail gas recirculation unit, a feeding and preheating unit, and a discharge unit; The gas output end of the air inlet unit is connected to the gas input end of the fluidized bed reactor, the gas output end of the fluidized bed reactor is connected to the tail gas circulation unit, the output end of the tail gas circulation unit is connected to both the fluidized bed reactor and the air inlet unit, the feeding preheating unit is connected to the feeding end of the fluidized bed reactor, and the discharge unit is connected to the discharge end of the fluidized bed reactor.

8. The silicon-carbon material preparation system according to claim 7, characterized in that, The fluidized bed reactor includes an outer shell; An upper stirring device is provided at the top of the outer shell and a lower stirring device is provided at the bottom of the outer shell; a heat exchange component is provided inside the outer shell to control the reaction temperature; and an air distribution component is provided at the bottom of the outer shell. The lower stirring device includes a lower stirring motor and a lower stirrer disposed at the output end of the lower stirring motor; The air distribution assembly includes an upper air distribution ring pipe connected to the exhaust gas recirculation unit and a lower air distribution ring pipe connected to the intake unit.

9. The silicon-carbon material preparation system according to claim 8, characterized in that, The upper stirring device includes an upper stirring motor, an upper stirring shaft disposed at the output end of the upper stirring motor, and a ribbon agitator disposed at the output end of the upper stirring shaft. The heat exchange assembly includes a first vertical heat extraction tube bundle and a second vertical heat extraction tube bundle, which are disposed between the upper stirring shaft and the ribbon agitator.

10. The silicon-carbon material preparation system according to claim 8, characterized in that, The upper stirring device includes an upper stirring motor, an upper stirring shaft disposed at the output end of the upper stirring motor, and a first upper stirring blade and a second upper stirring blade disposed at the output end of the upper stirring shaft. The heat exchange assembly includes a first transverse heat extraction tube bundle and a second transverse heat extraction tube bundle, wherein the first transverse heat extraction tube bundle is disposed between the first upper stirring blade and the second upper stirring blade, and the second transverse heat extraction tube bundle is disposed between the upper stirring device and the lower stirring device.

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