System and method for preparing secondary battery composite anode material by CVD

Abstract

The application relates to the technical field of new energy material manufacturing, and discloses a system and a preparation method for preparing secondary battery composite negative electrode material by CVD, which comprises a solid-phase material conveying and metering system, a gas-phase material and carrier gas supply system, a CVD reaction and product screening system and a post-reaction material processing system.The first outlet quantitative feeder of the solid-phase material conveying and metering system is connected with the CVD reaction and product screening system through a pipeline; the first outlet carrier gas mixture of the gas-phase material and carrier gas supply system is connected with the CVD reaction and product screening system through a pipeline; and the first outlet CVD reactor of the CVD reaction and product screening system is connected with the post-reaction material processing system through a pipeline.Through a chemical vapor deposition process, the secondary battery composite negative electrode integrated material meeting the process requirements is formed by CVD coating of the gas-phase material, and the capacity density and service life of the secondary battery are improved, which is of great significance for promoting the progress of the secondary battery industry.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy material manufacturing, in particular to a system and a preparation method for preparing secondary battery composite negative electrode material by CVD. BACKGROUND

[0002] Secondary batteries, also known as rechargeable batteries or accumulators, are batteries that can be restored by using electric energy to repair the chemical system after a chemical reaction is converted into electric energy. The secondary batteries mainly rely on the movement of ionized ions between the positive electrode and the negative electrode to work. During the charging and discharging process, the ionized ions are embedded and de-embedded between the two electrodes. When charging, the ionized ions are de-embedded from the positive electrode and embedded into the negative electrode through the electrolyte, and the negative electrode is in a rich-ion state. When discharging, the situation is reversed. Taking lithium ion batteries as an example, lithium ion batteries are widely used in consumer electronics and new energy vehicles due to their high working voltage, large energy density, long cycle life and other advantages.

[0003] Secondary batteries are usually composed of positive electrode materials, negative electrode materials, separators, electrolytes and the like. The negative electrode material is an important component of the secondary battery, and its performance directly affects important indicators such as the energy density, power density and cycle stability of the battery. Taking lithium ion batteries as an example: currently, graphite is the main negative electrode material for lithium ion batteries, which occupies 90% of the negative electrode material market due to its mature technology, low cost and good performance. Although graphite materials have high electrical conductivity and good stability, the development of energy density has reached its theoretical maximum of 372 mAh / g. The theoretical capacity of pure silicon material can reach 4200 mAh / g, and the theoretical capacity of silicon-carbon negative electrode material can easily exceed 400 mAh / g. Silicon can provide channels for lithium ion insertion and extraction in all directions, and has excellent fast charging performance. Tesla and Panasonic have been applying silicon-carbon negative electrodes for many years to solve the problem of new energy vehicle range, improve the energy density, and silicon-carbon negative electrode is the only way.

[0004] Silicon-carbon anodes have solved the energy density of secondary batteries (such as lithium-ion batteries), but the cycle stability is also crucial for secondary batteries. Studies have shown that silicon carbide anode materials have excellent cycle stability and great development potential. Among them, "ELECTROCHEMICAL ENERGY STORAGE RESEARCH OF SILICON CARBIDE NANOWIRES" mentions that "CVD-prepared nanosilicon carbide is used as an electrode sheet for lithium-ion batteries without adding any binder and electronic conductive material, showing high capacity ratio and good cycle retention. In contrast, nanosilicon carbide wrapped in carbon material shows good electrochemical performance. CVD-prepared silicon carbide nanowire films grown on graphite paper in different growth states have different morphologies of silicon carbide materials, which are applied to supercapacitors to test their electrochemical performance. It is found that after 200 cycles, the silicon carbide active material is in complete contact with the electrolyte, the specific capacity increases, and the specific capacity remains unchanged after 1000 cycles, showing excellent cycle stability."

[0005] Therefore, by selecting different combinations of solid and gas phase materials, using CVD process, silicon-carbon anodes, silicon carbide-carbon anodes, silicon anodes, silicon carbide anodes, silicon carbide-silicon-carbon anodes, silicon-carbon-silicon-carbon anodes, carbon-silicon-carbon anodes and other composite anode materials with different performance parameters are prepared, which further improve the energy density and cycle stability of secondary batteries, which is of great significance for solving the storage of various non-fossil energy electric energy, the range anxiety of new energy vehicles and battery life, and is also a problem that needs to be solved by those skilled in the art. SUMMARY

[0006] Therefore, the present application provides a system for preparing composite anode materials for secondary batteries by CVD and a preparation method thereof, based on the summary of multiple pilot tests and focusing on industrial production. By using different solid and gas phase materials and their combinations, designing a reasonable CVD reaction system, and adjusting appropriate CVD process parameters for different material combinations and target products, silicon-carbon anodes, silicon carbide-carbon anodes, silicon anodes, silicon carbide anodes, silicon carbide-silicon-carbon anodes, silicon-carbon-silicon-carbon anodes, carbon-silicon-carbon anodes and other composite anode materials with different performance parameters can be prepared to meet the process requirements of various secondary batteries, achieving high energy density and high cycle stability of secondary batteries.

[0007] In order to achieve the purpose of the present application, the present application adopts the following technical solutions:

[0008] A system for preparing secondary battery composite negative electrode material by CVD, comprising: a solid-phase material conveying and metering system, a gas-phase material and carrier gas supply system, a CVD reaction and product screening system, and a post-reaction material processing system, wherein the solid-phase material conveying and metering system comprises a main bin for storing solid-phase material, an automatic feeding machine, a material storage box, a quantitative feeder, and inert sealing gas, and the first outlet quantitative feeder of the solid-phase material conveying and metering system is connected to the CVD reaction and product screening system through a pipeline;

[0009] The gas-phase material and carrier gas supply system comprises inert gas replacement, gas-phase material and carrier gas mixing, and the first outlet carrier gas mixing of the gas-phase material and carrier gas supply system is connected to the CVD reaction and product screening system through a pipeline;

[0010] The CVD reaction and product screening system comprises a CVD reactor, a screening device, a reject tank, a qualified product tank, and an automatic packaging machine, and the first outlet CVD reactor of the CVD reaction and product screening system is connected to the post-reaction material processing system through a pipeline;

[0011] The post-reaction material processing system comprises a filter, a vacuum unit, a vacuum unit exhaust buffer tank, a compressor, a condenser, a gas-liquid separator, a recycled material temporary storage tank, a recycled carrier gas storage tank, and a tail gas treatment system;

[0012] In the system, the surfaces inside the main bin that contact the material are sprayed with anti-static Teflon, the support bottom of the material storage box is provided with a pressure weighing sensor with an error of not more than 0.2%, and the weight signal is connected to a PLC to ensure that the material storage box feeds quantitatively and records the feeding and discharging; each bin is provided with a pneumatic knocking hammer that can be automatically knocked at a frequency set by a program or manually controlled, and the bins are replaced and sealed with inert gas to ensure that the oxygen content of the system is below 0.5%;

[0013] The CVD reactor furnace tail cover and the furnace head cover are provided with gas inlets for filling reaction gas into the furnace to adapt to the CVD process, the inert gas includes but is not limited to nitrogen, argon, helium, preferably argon and helium, and the gas phase material includes but is not limited to silane, methylsilane, trimethylsilane, methyltrichlorosilane, dichlorodihydrogenosilane, trichlorohydrogenosilane, silicon tetrachloride, methane, ethane, ethylene, acetylene, propane, propylene, acetone, benzene, ethanol, toluene and the like which are liquid at normal temperature but can be gasified into gas by heating; the mixing method is preferably static mixing gas mixing, one kind of silicon gas is introduced into a liquid carbon gas source to volatilize and carry for mixing, one kind of carbon gas is introduced into a liquid silicon source to volatilize and carry for mixing; the CVD reactor preferably has a drum type rotary structure composed of a furnace pipe, a furnace body, a heating element, a spiral feeder, a furnace pipe head / tail sealing cover, a furnace pipe support device, a furnace pipe driving device and a base CVD reactor lifting device, and the furnace pipe is preferably conical in design to avoid the formation of dead angles for gas flow in the furnace pipe;

[0014] The upper part of the material filter is provided with a 316L wire mesh demisting device with a cooling jacket, a cooling coil, built-in cooling fins or a combination of the above cooling methods, and a tank type filter, the filter is also provided with inert gas purging pipelines and control valves, condensate discharge pipelines and control valves, purge gas discharge pipelines and control valves, etc., the liquid discharge pipeline is connected to a recovered material temporary storage tank, and the purge gas discharge pipeline is connected to an exhaust gas treatment device;

[0015] The vacuum unit preferably has a combination of two, three or more of a rotary vane pump, a chemical pump or a Roots pump, the vacuum unit transmits signals to a PLC system, the PLC system controls the start and stop of the vacuum unit and monitors the running state of the vacuum unit, the vacuum unit also includes corresponding electric vacuum ball valves, pneumatic vacuum ball valves, manual vacuum ball valves, electromagnetic one-way valves, vacuum measuring instruments, corrugated pipes and vacuum pipelines, the vacuum pipelines are provided with vacuum pneumatic ball valves and KF interfaces, and a one-way valve is arranged in front of the vacuum unit; the compressor is a diaphragm compressor or an oil-free piston compressor, the compressor is provided with an air inlet and outlet pressure self-adjusting system, the compressor transmits signals to the PLC system, the PLC system controls the start and stop of the compressor and monitors the running state of the compressor;

[0016] The gas-liquid separator is provided with a cooling jacket, an embedded cooling coil and fins; the gas-liquid separator is provided with pressure, temperature and liquid level sensors and an online gas analyzer, and the related signals are transmitted to the PLC system for real-time monitoring and control; the gas-liquid separator comprises at least three discharge pipes, the first discharge pipe is a liquid phase discharge pipe, and electric and pneumatic valves, including but not limited to ball valves, butterfly valves and regulating valves, are arranged on the pipe, the pipe is connected to a recovered material temporary storage tank, the second discharge pipe is a gas phase discharge pipe, and electric and pneumatic valves, including but not limited to ball valves, butterfly valves and regulating valves, are arranged on the pipe, the pipe is connected to a recovered carrier gas storage tank, and the third discharge pipe is a tail gas discharge pipe, and electric and pneumatic valves, including but not limited to ball valves, butterfly valves and regulating valves, are arranged on the pipe, the pipe is connected to a tail gas treatment system, when the online analyzer analyzes that the purity of the carrier gas in the gas phase composition is lower than the set value and the content of impurity components exceeds the set value, the valves on the pipe are automatically opened according to the set program, and the material is discharged to the tail gas treatment system, and when the online analyzer analyzes that the purity of the carrier gas in the gas phase composition is higher than the set value and the content of impurity components is lower than the set value, the valves are closed, and the discharge to the tail gas treatment system is stopped.

[0017] A system for preparing a secondary battery composite negative electrode material by CVD, wherein the CVD reactor has a main furnace tube with a size of Ø50-1500xØ52-1550x1000-10880 mm and a reduced section with a size of Ø20-800xØ26-900x40-5000 mm, which extends into the main furnace tube and a conical furnace tube inside the main furnace tube, and the annular space formed by the main furnace tube and the conical furnace tube is filled with heat-resistant material to achieve heat insulation effect, and the heat-resistant material is preferably heat-resistant cotton board and high-purity graphite felt; a spiral feeder is arranged at the front section of the CVD reactor, and guide vanes are uniformly arranged inside the furnace tube, and the setting angle of the guide vanes is +36-56° and -46-66°; a pneumatic knocking hammer is arranged at the feeding end and the discharging end of the furnace tube of the CVD reactor, which has a knocking function controlled according to a set program or manually, and one or more knocking devices are arranged at the furnace head and the furnace tail, respectively; the heating part of the CVD reactor is divided into n independent temperature control zones, the heating power is independently set and controlled, and the material of the heating resistance wire is preferably 0Cr27Al7Mo2 and 0Cr21Al6Nb; the temperature zones in the CVD deposition chamber are separated by heat-resistant cotton board; the design temperature of the CVD reactor is 700-1200℃, the working temperature is 750-950℃, and the temperature is automatically controlled by an intelligent temperature control instrument, the PID is automatically adjusted, the power is adjusted by SCR, the control precision of the temperature control instrument is 0.1-0.3% FS, and the temperature difference of each temperature measuring point is ±1-5℃.

[0018] A system for preparing secondary battery composite negative electrode material by CVD, the CVD reactor feed device adopts screw feed mode, including a crushing shaft and a screw propulsion motor. The screw feed pipe and blade are preferably SUS314S, SUS310S, INCOLOY800H, the box material is preferably SUS316L, and the thickness is 3-12 mm. In addition to the screw feed pipe, screw shaft and guide blade, the other surfaces in contact with the powder are preferably sprayed with Teflon, with a thickness of 15-60 μm (if sprayed with tungsten carbide, the thickness is 100-500 μm), and the screw feed pipe inner wall and screw blade are pickled and polished. The feed screw is preferably of unequal pitch structure, with the pitch gradually increasing from back to front. The screw feeder feed port is directly connected to the heating zone, the furnace tube feed end is conical in structure, and the overall inclination angle of the equipment is 0-20°.

[0019] A system for preparing secondary battery composite negative electrode material by CVD, the CVD reactor tail discharge port is provided with a discharge valve, which is connected to a closed 316L stainless steel classifier. The classifier preferably adopts a special fluidized bed and a vibrating screen. The qualified material passes through the first outlet of the classifier into a qualified product tank, which is sealed with inert gas. A discharge valve is provided between the qualified product tank and the automatic packaging equipment. The valve is preferably an electrically or pneumatically controlled ball valve or butterfly valve. When the material in the qualified product tank reaches a set height, the discharge valve opens according to the set program, and the qualified material enters the automatic packaging equipment for packaging according to the set program and specifications.

[0020] A system for preparing secondary battery composite negative electrode material by CVD, the CVD reactor furnace head cover bottom is provided with a waste discharge port and a discharge valve, and the waste is collected into a waste box in a closed manner. Dustproof sealing covers are provided at both ends of the CVD reactor furnace pipe inlet and outlet. The sealing device preferably adopts an axial compression type graphite disc seal to prevent the overflow of heating gas phase or dust. The spring is sleeved on the screw rod, and the flange is extruded with the sealing ring to form a dynamic and static friction surface to ensure the sealing of the furnace chamber. The shell material of the CVD reactor furnace head cover and furnace tail cover is preferably SUS316L stainless steel, and the inner surface of the furnace head cover in contact with the material is sprayed with a Teflon coating. The sealing cover is provided with a pressure sensor to monitor the pressure in the furnace chamber near the sealing cover and realize overpressure alarm and safety interlocking.

[0021] A system for preparing secondary battery composite negative electrode material by CVD, the main furnace pipe is preferably a seamless steel pipe, the inner wall is polished to a roughness of 0.2-4.0 μm, and the guide blade and weld are pickled and polished. The furnace pipe material is preferably SUS314S, SUS310S, or INCOLOY800H.

[0022] A system for preparing secondary battery composite negative electrode material by CVD, a quantitative feeder, the material is preferably SUS304 or SUS316L, and the surface in contact with the powder is sprayed with Teflon. The quantitative feeder is connected to the feeder by a flexible connection, and the connecting pipe is provided with a star-shaped discharge valve. The preferred quantitative feeder is provided with a pneumatic knocking hammer to prevent material bridging.

[0023] A system for preparing secondary battery composite negative electrode material by CVD, the temperature control of the system is formed by a temperature controller, a power regulator, a heating body, and a thermocouple into a closed loop PID temperature control system. The temperature controller is preferably an FP-23 high-precision programmable temperature controller, the system can be heated according to the given heating curve, manual intervention can be adjusted, and different process heating curves can be stored. And with the temperature sensor to form a closed loop control system to realize program control temperature. The system is configured with a capacitive film gauge to measure the pressure in the CVD deposition chamber, together with the pressure sensor and the electric and pneumatic regulating valves on the gas outlet pipeline to form a constant pressure control system. The control system has the functions of over-temperature, disconnection, over-current, cooling water shortage, cooling water overpressure, cooling water overtemperature, CVD furnace overpressure and overtemperature alarm, over-temperature safety interlock protection, and gas leakage emergency shutdown.

[0024] A system for preparing secondary battery composite negative electrode material by CVD, the whole system is controlled by a programmable controller (PLC) and a touch screen, including but not limited to being able to realize pump, valve, heating, start-stop action control, parameter setting, device running real-time data display, temperature, power, pressure, flow curve display, data list display, alarm display, safety interlock, etc., with recording, data export functions, and can also realize permission management to prevent unauthorized operation of the device. The explosion-proof grade of the system is not less than dIICT4, the protection grade is not less than IP67, and the insulation level is not less than F level. Through the PLC programmable controller, touch screen, configuration interface, the automatic operation control, running state monitoring, running state simulation display, running fault alarm indication, safety emergency disposal of the whole system can be realized, and all control and monitoring signals can be transmitted to the DCS system of the central control room through the Modbus protocol, and the system is controlled by the DCS system.

[0025] A preparation method of a system for preparing secondary battery composite negative electrode material by CVD, the steps are as follows:

[0026] 1) Perform power-on inspection on the system, the insulation resistance between the heating element and the shell is not less than 500Ω, the system chambers are well sealed, the waterway is unobstructed, the pneumatic elements are normally and flexibly operated, and various mechanical action tests and position determination are performed;

[0027] 2) Vacuumize the system to 0.1-0.01 Pa, and ensure that the pressure rise rate of the process cavity is ≤0.5 Pa / h;

[0028] 3) The whole system is replaced by inert gas, the replacement pressure is 0.05-0.15 MPa, the continuous replacement is 3-5 times, the replacement gas is nitrogen, the last replacement gas after the nitrogen replacement is argon or helium, the oxygen concentration of the replacement gas in the tail gas system sampling port is lower than 0.5%, and the inert gas atmosphere of the system is maintained at 0.01-0.03 MPa;

[0029] 4) The solid-phase material is manually added to the main bin, the feeding program is started through the PLC control panel, the solid-phase material is fed from the main bin to the material storage box by the automatic feeding machine, and the solid-phase material is preferably nano silicon powder, porous silicon, nano silicon monoxide, various high-performance mesoporous carbon materials, and materials coated by the first or nth CVD;

[0030] 5) After the solid-phase material is gradually added to the CVD reactor according to the set program, the CVD reactor furnace tube rotation motor is started through the PLC control panel, the rotation speed of the furnace tube is controlled at 0.5-50 rpm, the material heating time is controlled within 5-100 min, and the material temperature is 600-1000℃;

[0031] 6) The gas-phase material feeding program is started through the PLC control panel, the whole system is replaced by the carrier gas first, then the specified carrier gas, reaction gas flow and proportion are controlled according to the set program, the carrier gas and the reaction gas are fully mixed and uniformly enter the CVD reactor, and the CVD reactor is reacted, including but not limited to two or more material reaction CVD deposition, single material self-decomposition CVD deposition, CVD deposition, internal pore CVI deposition of the solid-phase material and external CVD coating; the proportion of the carrier gas and the recovered carrier gas is 1:1-1:100, the proportion of the reaction gas and the carrier gas is 1:2-1:50, the proportion of the two or more reaction gases is calculated according to the chemical reaction equation, the carrier gas flow is 50-100 L / min, and the reaction gas flow is 20-50 L / min. The CVD deposition temperature is 600-950℃, and the rotation speed of the furnace tube is preferably 2-30 rpm;

[0032] 7) The material deposited, coated in the CVD reactor is transferred from the CVD reactor to the sifter through a pipeline; in the sifter, the material is classified into qualified products and unqualified products, the qualified product material is transferred to the qualified product tank, and the qualified product tank is at least two or more; when the material in a storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another qualified product tank, at the same time, the inert gas replacement valve is automatically opened, and the reaction gas in the qualified product tank filled with the material is replaced to the tail gas treatment device; the inert replacement gas is preferably nitrogen, argon, helium, the replacement pressure is 0.1-0.3 MPa, and the replacement is at least 5 times; when the replacement gas content measured by the on-line gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified; after the inert gas replacement of the qualified product tank is qualified, the PLC control system automatically opens the valve on the pipeline connecting the qualified product tank and the automatic packaging machine, and the material is fed to the automatic packaging machine according to a set amount, and the product packaging is completed;

[0033] The unqualified product material is transferred to the unqualified product tank, and the unqualified product tank is at least two or more; when the material in a storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another unqualified product tank, and the inert gas replacement valve is automatically opened, and the reaction gas in the unqualified product tank filled with the material is replaced to the tail gas treatment device to ensure safety; the inert replacement gas is preferably nitrogen, argon, helium, the replacement pressure is 0.1-0.3 MPa, and the replacement is at least 5 times; when the replacement gas content measured by the on-line gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified; after the inert gas replacement of the unqualified product tank is qualified, the PLC control system or the DCS system automatically opens the valve on the pipeline connecting the unqualified product tank and the main material bin arranged on the ground, and the material is fed to the main material bin according to a set amount, and the CVD deposition and coating are performed again;

[0034] 8) The tail gas after the reaction of the CVD reactor is first transferred to a filter, the gas phase material liquefied at a certain temperature is separated by the filter, and a small amount of particulate matter in the gas phase is filtered out, the gas phase material liquefied by condensation is discharged to a temporary storage tank of the recovered material when reaching a certain liquid level, and when the pressure difference of the filter reaches a set value, the inert gas purging valve is opened by the PLC controller to purge the wire mesh demister; the filter is cooled by -35-5 ℃ refrigerated liquid, and the temperature of the reaction tail gas after cooling and condensation reaches 20-50 ℃ when the reaction tail gas is discharged from the filter;

[0035] The tail gas after condensation filtration enters the vacuum unit, is extracted by the vacuum unit, enters the buffer tank through the pipeline, the buffer tank is communicated with the compressor through the pipeline, the tail gas is pressurized by the compressor and enters the condenser, the compressed tail gas is reduced to the set temperature by the condenser, the tail gas gas-liquid mixture from the condenser enters the gas-liquid separator with a cold jacket, the carrier gas is recovered and discharged from the top of the gas-liquid separator and enters the carrier gas storage tank through the pipeline; the recovered material is discharged from the bottom of the gas-liquid separator, enters the recovered material temporary storage tank through the pipeline, enters the recovered material gasifier through the pipeline, returns to the static mixer, mixes with the carrier gas, and then enters the CVD reactor to participate in the reaction process; the vacuum degree of the vacuum unit is controlled to be 0.1-10000 Pa, the inlet pressure of the compressor is 0.001-0.05 MPa, the exhaust pressure of the compressor is 0.2-3.0 MPa, the temperature of the condenser refrigerant is-35-50 DEG C, the temperature of the tail gas gas-liquid mixture after condensation is-30-60 DEG C, the temperature of the gas-liquid separator refrigerant is-55-50 DEG C, the temperature of the recovered carrier gas after condensation is-30-50 DEG C, the temperature of the recovered material after condensation is-40-45 DEG C, and the temperature of the recovered material after heating and gasification by the recovered material gasifier is-10-150 DEG C;

[0036] 9) The gas-liquid separator is connected with an online analyzer, when the online analyzer detects that the pure component content of the carrier gas in the tail gas gas phase composition is less than 99.99%, the system PLC controller automatically closes the valve between the gas-liquid separator and the recovered carrier gas storage tank according to the parameters set in the program, and opens the valve on the pipeline between the gas-liquid separator and the tail gas treatment system, so that the gas phase material is discharged as tail gas to the tail gas treatment system for treatment.

[0037] 10) If CVD coating of different layers and different materials is needed, the material deposited by the first CVD according to the above process can be used as "raw material", and the CVD deposition is carried out again or multiple times according to the above process by adjusting the corresponding process parameters.

[0038] Due to the above technical scheme, the application has the following advantages:

[0039] The application discloses a system for preparing secondary battery composite negative electrode material by CVD and a preparation method thereof, various materials are recycled and fully reused according to their characteristics, flammable, explosive and corrosive products are not discharged, basically no waste is discharged, production cost is saved, overall energy consumption is low, and environmental protection and energy saving are achieved. The application discloses a system for preparing secondary battery composite negative electrode material by CVD and a preparation method thereof, which can adapt to various silicon, carbon solid phase and gas phase materials, complete nanoscale deposition and coating through the CVD mode, prepare negative electrode materials with excellent energy density, cycle stability and adaptability to various secondary battery process requirements, and has great significance for solving the storage of various non-fossil energy electric energy, the mileage anxiety of new energy vehicles and the service life of batteries, and will promote the revolutionary progress of secondary battery technology. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on the provided drawings without any creative effort;

[0041] Figure 1 This is a schematic diagram of the equipment composition and process system flow of the present invention;

[0042] Figure 2 The CV diagrams of the nano-silicon carbide carbon anode material of the present invention at different cycling cycles are shown.

[0043] Figure 3 This is a diagram showing the cycle retention of the nano-silicon carbide carbon anode material electrode sheet of the present invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of this application and are intended to explain the inventive concept. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] like Figure 1 , 2 As shown in Figure 3, a system for preparing composite negative electrode materials for secondary batteries by CVD belongs to the field of new energy material manufacturing technology. It includes: a solid-phase material conveying and metering system, a gaseous material and carrier gas supply system, a CVD reaction and product screening system, and a post-reaction material handling system. The first outlet of the solid-phase material conveying and metering system is connected to the CVD reaction and product screening system via a pipeline; the first outlet of the gaseous material and carrier gas supply system is connected to the CVD reaction and product screening system via a pipeline; and the first outlet of the CVD reaction and product screening system is connected to the post-reaction material handling system via a pipeline. The system has an explosion-proof rating of not less than dIICT4, a protection rating of not less than IP67, and an insulation rating of not less than F. It adopts complete automated control, and through a PLC programmable controller, touch screen, and configuration interface, it can realize automatic operation control, operation status monitoring, operation status simulation display, operation fault alarm indication, and safety emergency handling of the entire system. All control and monitoring signals can be transmitted to the DCS system in the central control room via the Modbus protocol for centralized control.

[0046] The solid-phase material conveying and metering system comprises a main bin for storing solid-phase material, an automatic feeding machine, a material storage box, a quantitative feeder and inert sealing gas. The main bin for automatic feeding is preferably placed on the ground and preferably made of SUS304. The surfaces inside the bin that contact the material are sprayed with anti-static Teflon. The bin is provided with a sealed cover. The solid-phase material in the main bin is conveyed to the sealed material storage box by a motor-driven screw conveyor or a vacuum suction device. A pressure sensor is installed on the top of the material storage box, which is provided with an inert sealing gas inlet hose. A pneumatic or electric gas inlet control valve is arranged on the hose. A pressure weighing sensor is arranged on the supporting bottom (the weighing error is not more than 0.2% of the total weight of the material in the full state of the bin). The weight signal is connected to a PLC to ensure the quantitative feeding of the material storage box and to realize the feeding and discharging record. Preferably, each bin is provided with a pneumatic knocking hammer to prevent the bridging of the material. The pneumatic knocking hammer can be automatically knocked at a frequency set by the program or manually controlled. The material storage box is connected to the quantitative feeder arranged below the material storage box through an outlet pipeline. A pneumatic or electric control valve (including but not limited to a butterfly valve, a ball valve and a gate valve) is arranged on the connecting pipeline. According to the set program, when it is detected that the quantitative feeder needs to be replenished with material, the valve on the pipeline is automatically opened to feed the material to the quantitative feeder. When the set amount is reached, the valve is automatically closed. The quantitative feeder is provided with a pressure weighing sensor (the weighing error is not more than 0.1% of the total weight of the material in the full state of the feeder). The material is replaced and sealed with inert gas before entering the material storage box and from the material storage box to the quantitative feeder, so as to ensure that the oxygen content of the system is below 0.5%.

[0047] The gas-phase material and carrier gas supply system comprises inert gas replacement, gas-phase material and carrier gas mixing. The gas-phase material and carrier gas supply system is connected to the inside of the heating zone of the furnace tube through the gas inlet pipeline arranged on the top of the CVD reactor furnace tail cover. As a preferred scheme of the present application, the CVD reactor furnace tail cover and the furnace head cover are both provided with gas inlets for filling the reaction gas into the furnace to adapt to the CVD process. The furnace head cover is provided with an exhaust port connected to the tail gas treatment device through a pipeline. As a preferred technical scheme of the present application, the inert gas includes but is not limited to nitrogen, argon, helium and the like, preferably argon and helium. The gas-phase material includes but is not limited to silane, methylsilane, trimethylsilane, methyltrichlorosilane, dichlorodihydrogenosilane, trichlorohydrogenosilane, silicon tetrachloride and the like which are silicon-containing; methane, ethane, ethylene, acetylene, propane, propylene and the like which are carbon-containing; and acetone, benzene, ethanol and toluene which are liquid at room temperature but can be gasified into gas by heating. The mixing method is preferably static mixing gas mixing, one kind of silicon gas is introduced into a liquid carbon gas source to carry and mix, one kind of carbon gas is introduced into a liquid silicon source to carry and mix, etc. As a preferred technical scheme of the present application, a mass flow controller is arranged for each gas source, and the flow and proportion of each gas source are controlled by a PLC according to the set program.

[0048] The CVD reaction and product screening system comprises a CVD reactor, a screening device, a reject tank, a qualified product tank and an automatic packaging machine. As a preferred technical solution of the present application, the CVD reactor preferably has a drum type rotary structure, and the material in the furnace tube is uniformly heated by heating (external heating) the rotary heat-resistant stainless steel furnace tube. The CVD reactor mainly comprises a furnace tube, a furnace body, a heating element (resistance wire, resistance block, etc.), a spiral feeder, a furnace tube head / tail sealing cover, a furnace tube support device, a furnace tube driving device, a base (CVD reactor lifting device), etc. As a preferred solution of the present application, the furnace tube is preferably designed in a conical shape to avoid the formation of dead angles for gas flow in the furnace tube.

[0049] The main furnace tube of the CVD reactor has a size of Ø50-1500xØ52-1550x1000-10880mm, and the reduced section has a size of Ø20-800xØ26-900x40-5000mm, which exceeds the size of the main furnace tube. The reduced section extends into the main furnace tube and the conical furnace tube is located inside the main furnace tube, forming an annular space with the main furnace tube. The annular space is filled with heat-resistant material to achieve heat insulation effect. The heat-resistant material is preferably heat-resistant cotton board and high-purity graphite felt. A spiral feeder is arranged at the front section of the CVD reactor to push the material into the preheating zone as soon as possible. Guiding vanes are uniformly arranged inside the furnace tube. The guiding vanes are preferably set at an angle of +36-56° and -46-66° to maximize the lifting and dispersion of the material, so that the material is in contact with hot gas, improving the dispersity of the material and the uniformity of CVD deposition.

[0050] The main furnace tube is preferably a seamless steel tube, and the inner wall is polished to a roughness of 0.2-4.0μm. The main furnace tube has one welding seam with the conical tube, and the small furnace tube has one welding seam with the conical tube. The conical tube is made of a steel plate wound in a conical shape, and the conical tube has one welding seam on the side surface. The guiding vanes are pickled and polished. The material of the furnace tube is preferably SUS314S, SUS310S, INCOLOY800H, etc., which can be used at 1080℃ for a long time.

[0051] As a preferred technical solution of the present application, the CVD reactor furnace tube feeding end and discharging end are provided with pneumatic knocking hammers, which have a knocking function controlled by a set program or manually, and are used to shake off the material adhered to the inner wall of the furnace tube. One or more knocking devices are arranged at the furnace head and the furnace tail.

[0052] The heating part of the CVD reactor is divided into n independent temperature control zones, and the heating power is independently set and controlled. As a preferred technical solution of the present application, the heating resistance wire is made of 0Cr27Al7Mo2 and 0Cr21Al6Nb. The temperature measuring thermocouple is preferably located at a position slightly below the temperature zone to be as close as possible to the temperature of the powder in the furnace tube. The temperature zones in the CVD deposition chamber are separated by heat-resistant cotton board to enhance the independence and control accuracy of the temperature between the temperature zones.

[0053] The CVD reactor is designed to have a temperature of 700-1200°C, preferably a working temperature of 750-950°C. Preferably, an intelligent temperature control instrument is used to automatically control the temperature, and a PID is used for automatic adjustment, and a power adjustment is applied to an SCR adjustment. The temperature control instrument has a control precision of 0.1-0.3% FS, and the temperature difference of each temperature measuring point is ±1-5°C. The furnace body insulation layer is preferably constructed from standard fiberboard modules and cotton blankets, which meet the requirements of environmental protection and energy saving.

[0054] The CVD reactor feeding device adopts a spiral feeding mode, and includes a crushing shaft and a spiral propelling motor. The spiral feeding pipe and the blade are preferably made of SUS314S, SUS310S and INCOLOY800H, and the box body material is preferably SUS316L, and the thickness is 3-12 mm. Except the spiral feeding pipe, the spiral shaft and the guide blade, other surfaces in contact with the powder are preferably sprayed with Teflon, and the thickness is 15-60 μm (if tungsten carbide is sprayed, the thickness is 100-500 μm). The inner wall of the spiral feeding pipe and the spiral blade are acid washed and polished. The feeding screw is preferably of a variable pitch structure, and the pitch gradually increases from the rear to the front, so as to improve the dispersivity of the material at the front end of the screw. The feeding port of the spiral feeder is directly connected to the heating zone, the furnace pipe feeding end is of a conical structure, and the whole equipment is inclined (the angle is 0-20°), so as to ensure that the material cannot backflow to the outside of the heating zone. When the CVD reactor reaches the maximum inclination angle, the material bin is not interfered with the feeding device, and the front idler wheel is not interfered with the material bin and the weighing system. The upper part of the feeder is preferably provided with a quantitative feeder, and the material is SUS304 and SUS316L. The surfaces in contact with the powder are all sprayed with Teflon. The quantitative feeder is connected to the feeder by a soft connection, and the connecting pipe is provided with a star-shaped discharge valve. The quantitative feeder is preferably provided with a pneumatic knocking hammer to prevent the bridging of the material. The quantitative feeder is provided with a material level meter, and the top is provided with a feeding port. At the same time, a protective gas inlet and an exhaust port are provided to ensure the inert atmosphere environment in the bin. The top of the quantitative feeder is preferably provided with a layered operation platform, which is connected to the whole system platform as a whole.

[0055] The CVD reactor tail end is provided with a discharge valve, and is connected to a closed 316L stainless steel classifier. The classifier is preferably a special fluidized bed and a vibrating screen. The qualified material passes through the first outlet of the classifier and enters a qualified product tank, and the qualified product tank is sealed by inert gas. A discharge valve is arranged between the qualified product tank and an automatic packaging device, and the valve is preferably an electrically or pneumatically controlled ball valve or butterfly valve. When the material in the qualified product tank reaches a certain height, the discharge valve is opened according to the set program, the qualified material enters the automatic packaging device, and is packaged according to the set program and specification.

[0056] The bottom of the CVD reactor furnace head cover is provided with a waste discharge port, and is provided with a discharge valve. The waste is collected into a waste box in a closed manner.

[0057] The CVD reactor furnace tube import and export ends are provided with dustproof sealing covers, preferably the sealing device adopts axial compression type graphite disc sealing, preventing heating gas phase or dust overflow. The spring is sleeved on the screw rod, extruding the flange and the sealing ring to form a dynamic and static friction surface to ensure the furnace chamber sealing.

[0058] The CVD reactor furnace head cover and furnace tail cover shell material is preferably SUS316L stainless steel, the inner surface of the furnace head cover in contact with the material is preferably sprayed with a Teflon coating. The sealing cover is provided with a pressure sensor to monitor the pressure in the furnace chamber near the sealing cover and realize overpressure alarm and safety interlocking.

[0059] The post-reaction material processing system comprises a filter, a vacuum unit, a vacuum unit exhaust buffer tank, a compressor, a condenser, a gas-liquid separator, a recycled material temporary storage tank, a recycled carrier gas storage tank and a tail gas treatment system. The material filter is preferably a tank filter provided with a 316L wire mesh demisting device at the upper portion, and provided with a cooling jacket, a cooling coil, built-in cooling fins or a combination of the above cooling methods. The filter is also provided with inert gas purging pipelines and control valves, condensate discharge pipelines and control valves, purging gas discharge pipelines and control valves, etc. The liquid discharge pipelines are connected to the recycled material temporary storage tank, and the purging gas discharge pipelines are connected to the tail gas treatment device. As a preferred technical solution of the present application, the vacuum unit is preferably a combination of two, three or more of a rotary vane pump, a chemical pump or a Roots pump. The vacuum unit transmits signals to the PLC system, which controls the start and stop of the vacuum unit and monitors the operating state of the vacuum unit. The vacuum unit also includes corresponding electric vacuum ball valves, pneumatic vacuum ball valves, manual vacuum ball valves, electromagnetic one-way valves, vacuum measuring instruments, bellows, vacuum pipelines, etc. A vacuum pneumatic ball valve is provided on the vacuum pipeline to control the opening of the vacuum system. A one-way valve is preferably provided before the vacuum unit to prevent the return of vacuum pump oil to the vacuum pipeline when the vacuum unit suddenly stops. A total exhaust pipeline is provided at a suitable position of the CVD reactor feed pipe of the vacuum unit, and two branch exhaust pipelines are preferably provided on the total exhaust pipeline, one for vacuum process and the other for CVD deposition process. All the vacuum exhaust pipelines and flanges are made of 316L stainless steel, and KF interfaces are provided on the vacuum pipelines for system leak detection. The vacuum exhaust buffer tank is preferably made of 316L material, and its volume is matched with the exhaust capacity. The tank body is provided with a pressure gauge and a thermometer with remote transmission function. The buffer tank is also provided with a safety valve, which automatically releases pressure when the pressure exceeds the set value, and is connected to the tail gas treatment system through a pipeline. The compressor is preferably a diaphragm compressor or an oil-free piston compressor, and is provided with an inlet and outlet pressure self-adjusting system. The compressor transmits signals to the PLC system, which controls the start and stop of the compressor and monitors the operating state of the compressor. The condenser includes but is not limited to a tube heat exchanger, a plate heat exchanger, a spiral tube plate heat exchanger, etc., preferably a tube heat exchanger. The outlet of the condenser is connected to the gas-liquid separator through a pipeline. The gas-liquid separator is provided with a built-in wire mesh demister made of 316L stainless steel, which is tightly connected to the steel ring welded inside the gas-liquid separator to ensure tight cooperation and connection with the wall of the gas-liquid separator. The gas-liquid separator includes but is not limited to a cooling jacket, built-in cooling coils (fins), etc. The gas-liquid separator is provided with pressure, temperature and liquid level sensors and an online gas analyzer, and the related signals are transmitted to the PLC system for real-time monitoring and control.The gas-liquid separator comprises at least three discharge pipes, the first discharge pipe is a liquid phase discharge pipe, an electric or pneumatic valve, including but not limited to a ball valve, a butterfly valve, and a regulating valve, is arranged on the pipe, the pipe is connected to a temporary storage tank for recovered materials, when the liquid level reaches a set level, the valve on the pipe is automatically opened according to a set program, and the recovered materials are discharged to the temporary storage tank, when the liquid level drops to a set value, the valve is closed, and the discharge is stopped. The second discharge pipe is a gas phase discharge pipe, an electric or pneumatic valve, including but not limited to a ball valve, a butterfly valve, and a regulating valve, is arranged on the pipe, the pipe is connected to a recovered carrier gas storage tank, when the pressure reaches a set value, the valve on the pipe is automatically opened according to a set program, and the recovered carrier gas is discharged to the recovered carrier gas storage tank, when the pressure drops to a set value, the valve is closed, and the discharge is stopped. The third discharge pipe is a tail gas discharge pipe, an electric or pneumatic valve, including but not limited to a ball valve, a butterfly valve, and a regulating valve, is arranged on the pipe, the pipe is connected to a tail gas treatment system, when an online analyzer analyzes that the purity of carrier gas in a gas phase component is lower than a set value and the content of impurity components exceeds a set value, the valve on the pipe is automatically opened according to a set program, and the tail gas is discharged to the tail gas treatment system, when the online analyzer analyzes that the purity of carrier gas in the gas phase component is higher than the set value and the content of impurity components is lower than the set value, the valve is closed, and the discharge to the tail gas treatment system is stopped. The tail gas treatment system comprises but is not limited to an alkali liquid spraying treatment device, an activated carbon adsorption device, an ultraviolet light catalytic decomposition device, and a flare incineration device, and the alkali liquid spraying treatment device is preferred. Pressure, temperature, flow, PH value sensors, pump start-stop faults and an online gas analyzer and other related signals are transmitted to a PLC system, which is monitored and controlled in real time. The tail gas spraying treatment device is preferably made of an acid- and alkali-resistant anticorrosion material, is provided with two or more spraying heads, and can effectively treat a small amount of non-condensable gas such as silane, methylsilane, trimethylsilane, trichlorosilane, silicon tetrachloride, ethanol, and hydrogen chloride in the tail gas. The tail gas is discharged through a pipeline with a length of more than 25 meters after being treated by the tail gas treatment system, and a flame arrester is arranged on the discharge pipeline. The tail gas spraying device is also provided with a nitrogen gas supplementing channel with flow control, which is used for diluting and replacing residual hydrogen in the spraying tower to ensure the safety of equipment use. The tail gas treatment device is also provided with a fast-charging nitrogen gas channel, which ensures that all equipment in the entire tail gas treatment system is maintained in an inert atmosphere, and avoids safety accidents of personnel during equipment maintenance.

[0060] The system temperature control is formed by a temperature controller, a power regulator, a heating body and a thermocouple into a closed loop PID temperature control system. As a preferred scheme of the present application, the temperature controller is preferably an FP-23 high-precision programmable temperature controller, the system can be heated according to a given heating curve, manual intervention can be adjusted, and different process heating curves can be stored. And with the temperature sensor to form a closed loop control system to realize program temperature control. As a preferred scheme of the present application, the system uses a C-type tungsten-rhenium thermocouple to measure and monitor the temperature in the furnace, and the thermocouple tube has no effect on the vacuum when it is damaged. As a preferred scheme of the present application, the system is configured with a capacitive diaphragm gauge to measure the pressure in the CVD deposition chamber, and together with the pressure sensor and the electric and pneumatic regulating valves on the gas outlet pipeline to form a constant pressure control system. As a preferred scheme of the present application, the system control cabinet and power supply cabinet are dustproof and waterproof, and fully consider the isolation of carbon dust. As a preferred scheme of the present application, the control system has the functions of over-temperature, broken couple, over-current, cooling water shortage, cooling water overpressure, cooling water over-temperature, CVD furnace overpressure and over-temperature alarm, and has over-temperature safety interlocking protection and gas leakage emergency shutdown function, to ensure the safe and reliable operation of the system.

[0061] The whole system adopts a programmable controller (PLC) and a touch screen for control, including but not limited to being able to realize pump, valve, heating, start-stop action control, parameter setting, device running real-time data display, temperature, power, pressure, flow curve display, data list display, alarm information display, safety interlocking, etc., having recording, data export functions, and can also realize permission management to prevent unauthorized operation of the device. As a preferred scheme of the present application, the PLC control system can transmit all control and monitoring signals to the DCS system in the central control room through the Modbus protocol for centralized control through the DCS system.

[0062] A preparation method of a system for preparing secondary battery composite negative electrode material by CVD is disclosed. The system uses different solid-phase materials (such as nano-silicon powder, porous silicon, nano-silicon monoxide, high-performance mesoporous carbon material, material coated by CVD for the first or nth time, etc.) and gas-phase materials (such as silane, methylsilane, methane, propylene, propane, trimethylsilane, methyltrichlorosilane, silicon trichloride, silicon tetrachloride, ethanol, toluene, etc.), and adjusts appropriate CVD process parameters in the CVD reactor to prepare silicon-carbon negative electrode, silicon carbide-carbon negative electrode, silicon negative electrode, silicon carbide negative electrode, silicon carbide-silicon-carbon negative electrode, silicon-carbon-silicon-carbon negative electrode, carbon-silicon-carbon negative electrode and other composite negative electrode materials that meet the process requirements of corresponding secondary batteries (such as lithium batteries, sodium batteries, etc.). The following method is used to prepare the secondary battery composite negative electrode material:

[0063] 1) Turn on the system, check the mechanical, electrical and components are working properly. Measure the insulation resistance between the heating element and the shell, the resistance is not less than 500Ω. Check the sealing state of each chamber of the system. Check the water system, each water supply and backwater, check the gas system to ensure that the pressure is suitable for the normal operation of the pneumatic components, flexible. Check the test of various mechanical actions and the determination of the position;

[0064] 2) Start the vacuum unit, vacuum the system to 0.1-0.01Pa, ensure that the pressure rise rate of the process cavity is ≤0.5Pa / h, and ensure the sealing performance of the system;

[0065] 3) Open the inert sealing gas valve of the material storage tank, fill the entire system with inert gas for replacement, the replacement pressure is 0.05-0.15MPa, and the continuous replacement is 3-5 times. The preferred replacement gas is nitrogen, and the last replacement gas after nitrogen replacement is preferably argon or helium. Each replacement gas is discharged into the tail gas system, and the last replacement gas is tested by an oxygen content analyzer at the sampling port of the tail gas system. The oxygen concentration is less than 0.5% for replacement. Then, fill the system with inert gas, preferably argon or helium, and maintain the inert gas atmosphere of the system at 0.01-0.03Mpa;

[0066] 4) Manually add solid-phase material to the main material bin on the ground, cover the sealing cover. Start the feeding program through the PLC control panel, and the automatic feeding machine transports the solid-phase material from the main material bin to the material storage tank. After the set amount is transported, the feeding termination program is triggered, and the automatic feeding machine is stopped. As a preferred embodiment of the present application, in addition to manually adding material to the main material bin, all processes such as inert gas sealing, feeding to the material storage tank, discharging from the material storage tank to the quantitative feeder, and feeding from the quantitative feeder to the CVD reactor are automatically detected and operated according to the set program. As a preferred embodiment of the present application, the solid-phase material is preferably nano silicon powder, porous silicon, nano silicon monoxide, various high-performance mesoporous carbon materials, and materials coated by the first or nth CVD;

[0067] 5) After the solid-phase material is gradually added to the CVD reactor according to the set program, start the CVD reactor furnace tube rotation motor through the PLC control panel to control the furnace tube rotation speed at 0.5-50 revolutions / min. As a preferred embodiment of the present application, the furnace tube rotation speed is automatically adjusted by a frequency converter in a stepless speed regulation manner according to the set program. At the same time, the PLC controller starts the material heating program, and heats the material according to the set program, controls the material heating time within 5-100min, and the material temperature is 600-1000℃;

[0068] 6) Open the valve of each gas phase material and carrier gas, and the carrier gas recovery valve in the gas cabinet, and start the gas phase material supply program through the PLC control panel. As a preferred embodiment of the present application, the entire system is first replaced with carrier gas, and the replacement gas is discharged into the tail gas system. Then, according to the set program, the specified carrier gas, reaction gas flow and ratio are controlled, so that the carrier gas and the reaction gas are fully mixed and uniformly mixed in the static mixer, and then enter the CVD reactor, and react (including but not limited to two or more material reaction CVD deposition, single material self-decomposition CVD deposition) in the CVD reactor, CVD deposition, internal pore CVI deposition and external CVD coating of solid phase material. As a preferred embodiment of the present application, the gas phase material includes but is not limited to silane, methylsilane, trimethylsilane, methyltrichlorosilane, dichlorodihydrogen silane, trichlorohydrogen silane, silicon tetrachloride and the like which are silicon-containing; methane, ethane, ethylene, acetylene, propane, propylene and the like which are carbon-containing, and acetone, benzene, ethanol, toluene and the like which are liquid at room temperature but can be gasified into gas by heating. As a preferred embodiment of the present application, the ratio of the carrier gas and the recovered carrier gas is 1:1 to 1:100, the ratio of the reaction gas and the carrier gas is 1:2 to 1:50, the ratio of the two or more reaction gases is calculated according to the chemical reaction equation, the carrier gas flow is 0.5 to 100 L / min, and the reaction gas flow is 0.2 to 50 L / min;

[0069] 7) The solid phase material is heated to a specified temperature in the CVD reactor, and the material is heated very fully as the furnace tube rotates and slowly migrates. The gas phase material and the carrier gas are mixed and then enter the CVD reactor, and immediately react and deposit with the material as the carrier to form a CVD deposition layer of a certain thickness on the pores and surface of the material, forming an excellent material meeting the requirements of the corresponding negative electrode of the secondary battery. As a preferred embodiment of the present application, the CVD deposition temperature is preferably 600 to 950°C, and the furnace tube rotation speed is preferably 2 to 30 revolutions / min. The thickness and uniformity of the deposition layer depend on the temperature, furnace tube rotation speed, gas phase flow and the like. The reactions occurring in the CVD reactor include but are not limited to:

[0070] CnHm==nC+1 / 2mH2 (CnHm represents a carbon-containing compound)

[0071] SiH4==Si+2H2

[0072] CH3SiH3==SiC+3H2

[0073] 2SiHCl3+CH4==SiC+6HCl

[0074] SiHCl3+H2==Si+3HCl

[0075] SiCl4+2H2==Si+4HCl

[0076] 8) The material deposited, coated in the CVD reactor is transferred from the CVD reactor to the sieve through a pipeline. In the sieve, the material is sieved into qualified and unqualified products. The qualified product material enters the qualified product tank, and the qualified product tank is preferably provided with a pressure sensing weighing module. The qualified product tank is at least two or more. When the material in one storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another qualified product tank. At the same time, the inert gas replacement valve is automatically opened, and the reaction gas in the qualified product tank filled with material is replaced to the tail gas treatment device to ensure safety. The inert replacement gas is preferably nitrogen, argon, or helium, and the replacement pressure is 0.1-0.3 MPa. The replacement is at least 5 times. When the replacement gas content measured by the online gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified. After the inert gas replacement of the qualified product tank is qualified, the PLC control system automatically opens the valve on the pipeline connecting the qualified product tank and the automatic packaging machine, and feeds the material to the automatic packaging machine according to a set amount, to complete the product packaging;

[0077] The unqualified product material enters the unqualified product tank, and the unqualified product tank is preferably provided with a pressure sensing weighing module. The unqualified product tank is at least two or more. When the material in one storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another unqualified product tank. The inert gas replacement valve is automatically opened, and the reaction gas in the unqualified product tank filled with material is replaced to the tail gas treatment device to ensure safety. The inert replacement gas is preferably nitrogen, argon, or helium, and the replacement pressure is 0.1-0.3 MPa. The replacement is at least 5 times. When the replacement gas content measured by the online gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified. After the inert gas replacement of the unqualified product tank is qualified, the PLC control system automatically opens the valve on the pipeline connecting the unqualified product tank and the main material bin arranged on the ground, and feeds the material to the main material bin according to a set amount, to perform CVD deposition and coating again;

[0078] 9) The tail gas after the CVD reactor reaction, including but not limited to carrier gas, unreacted reaction gas, and a small amount of solid-phase particles, first enters a filter. The filter is at least two or more, and can be automatically controlled and switched by the PLC controller according to the filter pressure difference. The gas-phase material liquefied at a certain temperature is separated by the filter, and a small amount of particulate matter in the gas phase is filtered out. When the condensed liquefied gas-phase material reaches a certain liquid level, the valve between the condensate liquid pipeline and the recovery material temporary storage tank is automatically opened by the PLC controller according to a set program, and the condensate liquid is automatically discharged to the recovery material temporary storage tank. When the filter pressure difference reaches a set value, the inert gas purging valve is opened by the PLC controller to purge the wire mesh demister. The filter is cooled by -35-5℃ freezing liquid, and the temperature of the reaction tail gas after cooling and condensation reaches 20-50℃ when it exits the filter;

[0079] The tail gas after condensation filtration enters the vacuum unit, is extracted by the vacuum unit, and then enters the buffer tank through the pipeline. The state monitoring and control of the vacuum unit are automatically controlled by the PLC controller according to the set parameters. The material of the buffer tank is 316L, and the volume of the buffer tank should match the exhaust capacity of the vacuum unit. The buffer tank is communicated with the compressor through the pipeline. The state monitoring and control of the compressor are automatically controlled by the PLC controller according to the set parameters. The tail gas is pressurized by the compressor and then enters the condenser, and the compressed tail gas is reduced to the set temperature by the condenser. The gas-liquid mixture from the condenser enters the gas-liquid separator with a cold jacket, the carrier gas is recovered from the top of the gas-liquid separator and enters the carrier gas storage tank through the pipeline. The recovered carrier gas is mixed with the supplementary carrier gas through the pipeline, and then is used as the carrier gas to mix with the gas-phase material and enter the CVD reactor to participate in the reaction process. The pipeline from the carrier gas storage tank to the static mixer is provided with a flow meter, an adjusting valve and the like, and the flow control of the recovered carrier gas is automatically adjusted and controlled by the PLC controller according to the set parameters. The recovered material is discharged from the bottom of the gas-liquid separator through the discharge pipe, enters the recovered material temporary storage tank through the pipeline, and enters the recovered material gasifier through the pipeline. If necessary, the high-boiling-point material can be gasified into the gas phase and returned to the static mixer to mix with the carrier gas and enter the CVD reactor to participate in the reaction process. The pipeline from the recovered material temporary storage tank to the recovered material gasifier to the static mixer is provided with a flow meter, an adjusting valve and the like, and the temperature and flow control of the recovered carrier gas are automatically adjusted and controlled by the PLC controller according to the set parameters. As a preferred scheme of the present application, the vacuum degree of the vacuum unit is controlled to be 0.1-10000 Pa, the inlet pressure of the compressor is 0.001-0.05 MPa, the exhaust pressure of the compressor is 0.2-3.0 MPa, the temperature of the condenser refrigerant is-35-50℃, the temperature of the gas-liquid mixture after condensation is-30-60℃, the temperature of the gas-liquid separator refrigerant is-55-50℃, the temperature of the recovered carrier gas after condensation is-30-50℃, the temperature of the recovered material after condensation is-40-45℃, and the temperature of the recovered material after being heated and gasified by the recovered material gasifier is-10-150℃.

[0080] 10) The gas-liquid separator is connected with an online analyzer. When the online analyzer detects that the pure component content of the carrier gas in the tail gas gas phase composition is less than 99.99% (or the content of a specific impurity component is detected according to the process requirement), the system PLC controller automatically closes the valve between the gas-liquid separator and the recovered carrier gas storage tank, and opens the valve on the pipeline between the gas-liquid separator and the tail gas treatment system, so that the gas-phase material is discharged as tail gas to the tail gas treatment system for treatment.

[0081] 11) If the CVD coating of different layers and different materials in different layers is required, the material deposited by the first CVD according to the above process can be used as the "raw material", and the CVD deposition is performed again or multiple times according to the above process by adjusting the corresponding process parameters.

[0082] Example 1

[0083] 1) Power on the system, perform pre-boot checks, vacuum leak detection, argon replacement, and maintain the solid-phase material system argon atmosphere pressure at 0.01 MPa;

[0084] 2) Start the vacuum unit and maintain the CVD reactor to a vacuum degree of 1000 Pa;

[0085] 3) Start the alkali spray tower circulating pump of the tail gas treatment system, and start the tail gas recovery system;

[0086] 4) Add high-performance mesoporous carbon material JK-01 to the main bin, with specific indicators of: specific surface area 280 m 2 / g, average pore size 13 nm, tap density 0.56 g / ml, ash content ≤0.5%, average particle size 6 um, resistivity 0.08 Ω·cm, and metal content 40 ppm;

[0087] 5) Start the PLC control panel of the system, perform self-checking, and manually start JK-1 material feeding after self-checking is completed, with a feeding amount set at 10 kg / h;

[0088] 6) Set the CVD reactor furnace tube rotation speed at 2 revolutions / min, and the heating temperature at 780℃, and manually start the material heating program;

[0089] 7) Open the valve of the silane (SiH4) gas cylinder and the valve of the hydrogen gas cylinder in the gas cabinet, with a silane purity of 99.9995% and a hydrogen purity of 99.999%. Set the silane flow rate at 0.6 L / min and the hydrogen flow rate at 6 L / min, and manually start the gas-phase material feeding program to perform gas-phase material feeding;

[0090] 8) Keep the solid-phase material and gas-phase material feeding amounts stable, keep the CVD reactor furnace tube rotation speed and heating temperature stable, and perform CVD deposition coating of the high-performance mesoporous carbon material JK-1 by silane;

[0091] 9) After the CVD runs stably, when the vacuum buffer tank pressure rises to 0.05 MPa, start the compressor, keep the compressor outlet pressure at 1.2 MPa, and use the condenser and gas-liquid separator, with a condenser cooling water outlet temperature of -35℃. Gradually supplement the system with recovered carrier gas and gas-phase material, and the production system will enter a stable internal circulation state;

[0092] 10) After the system runs stably for 8 hours, analyze and test the silicon-carbon negative electrode materials with different coating conditions, with results as shown in the following table:

[0093]

[0094] Example 2

[0095] 1) Power on the system, perform pre-boot checks, vacuum leak detection, argon replacement, and maintain the solid-phase material system argon atmosphere pressure at 0.01 MPa;

[0096] 2) Start the vacuum unit and maintain the CVD reactor to a vacuum degree of 800 Pa;

[0097] 3) Start the circulating pump of the caustic soda spray tower of the tail gas treatment system, and start the tail gas recovery system;

[0098] 4) Add nano silicon powder to the main bin, with specific indicators of: silicon content 99.999%, average particle size 80 nm, and metal content 10 ppm;

[0099] 5) Start the PLC control panel of the system, perform self-checking, and manually start the nano silicon powder feeding after self-checking is completed, with a feeding amount set at 20 kg / h;

[0100] 6) Set the CVD reactor furnace tube rotation speed at 0.5 revolutions / min, and the heating temperature at 960°C, and manually start the material heating program;

[0101] 7) Open the propane (C3H8) gas cylinder valve and argon gas cylinder valve in the gas cabinet, with the purity of propane being 99.999% and the purity of hydrogen being 99.999%. Set the propane flow rate at 1.2 L / min and the hydrogen flow rate at 3 L / min, and manually start the gas-phase material feeding program to feed the gas-phase material;

[0102] 8) Keep the solid-phase material and gas-phase material feeding amount stable, keep the CVD reactor furnace tube rotation speed and heating temperature stable, and perform CVD deposition coating of the nano silicon powder by propane;

[0103] 9) After the CVD runs stably, when the vacuum buffer tank pressure rises to 0.02 MPa, start the compressor, keep the compressor outlet pressure at 0.8 MPa, and use the condenser and gas-liquid separator, with the condenser cooling water return temperature being 5°C. Gradually supplement the system with recovered carrier gas and gas-phase material, and the production system will enter a stable running state of internal circulation;

[0104] 10) After the system runs stably for 24 hours, analyze and test the silicon-carbon negative electrode material with different coating conditions, with the results shown in the following table:

[0105]

[0106] Example 3

[0107] 1) Power on the system, carry out pre-starting checks, vacuum leak detection, argon replacement, and maintain the argon atmosphere pressure of the solid-phase material system at 0.01 MPa;

[0108] 2) Start the vacuum unit, and maintain the CVD reactor to a vacuum degree of 600 Pa of the vacuum unit;

[0109] 3) Start the circulating pump of the alkali spray tower of the tail gas treatment system, and start the tail gas recovery system;

[0110] 4) Add high-performance mesoporous carbon material JK-01 to the main bin, and the specific indexes are as follows: specific surface area 280 m 2 / g, average pore size 13 nm, tap density 0.56 g / ml, ash content ≤0.5%, average particle size 6 um, resistivity 0.08 Ω·cm, and metal content 40 ppm;

[0111] 5) Start the PLC control panel of the system, and perform self-checking on the entire system; after the self-checking is completed, manually start the JK-1 material feeding, and set the feeding amount to 35 kg / h;

[0112] 6) Set the CVD reactor furnace tube rotating speed to 5 revolutions / min, and the heating temperature to 820℃, and manually start the material heating program;

[0113] 7) Open the methylsilane (CH3SiH3) gas cylinder valve and the argon gas cylinder valve in the gas cabinet, set the flow rate of the methylsilane to 0.8 L / min and the flow rate of the argon to 10 L / min, manually start the gas-phase material feeding program, and perform gas-phase material feeding;

[0114] 8) Keep the feeding amount of the solid-phase material and the gas-phase material stable, keep the CVD reactor furnace tube rotating speed and the heating temperature stable, and perform CVD deposition coating of the high-performance mesoporous carbon material JK-1 by methylsilane;

[0115] 9) After the CVD runs stably, when the pressure of the vacuum buffer tank rises to 0.03 MPa, start the compressor, keep the outlet pressure of the compressor at 1.2 MPa, and use the condenser and the gas-liquid separator, and the outlet water temperature of the condenser cooling water is -10℃. Gradually supplement the system with the recovered carrier gas and the recovered gas-phase material, and the production system will enter a stable running state of internal circulation;

[0116] 10) After the system runs stably for 12 hours, analyze and test the coated siliconized silicon-carbon negative electrode material, and the results are shown in Figure 2 , the CV graph of the nano-carbide silicon-carbon negative electrode material in different cycle periods, and the cycle retention graph of the nano-carbide silicon-carbon negative electrode material electrode sheet is shown in Figure 3 ;

[0117] From the above experimental results, it can be seen that the nano-silicon carbide carbon negative electrode material directly as an electrode sheet for electrochemical testing shows high specific capacity and superior cycle stability.

[0118] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above embodiments are exemplary and should not be construed as limiting the present application. Various changes and modifications can be made to the present application without departing from the spirit and scope of the present application, and such changes and modifications fall within the scope of the present application.

Claims

1. A system for CVD preparation of a secondary battery composite anode material, comprising: a CVD reactor, characterized in that: Further comprising: solid phase material conveying and metering system, gas phase material and carrier gas supply system, product screening system and post-reaction material processing system; The post-reaction material processing system comprises: a filter, a mixed gas material processing system, a recycled material temporary storage tank, a recycled carrier gas storage tank, a tail gas processing system and a recycled material gasifier; The filter is in communication with the mixed gas material processing system through a pipeline, the carrier gas output end of the mixed gas material processing system is in communication with the carrier gas supply system through the recycled carrier gas storage tank, and the gas phase output end of the mixed gas material processing system is in communication with the gas phase supply system through the recycled material temporary storage tank and the recycled material gasifier; The filter has an input port for receiving tail gas material after the reaction of the CVD reactor at the upper portion, one end of the lower portion of the filter is provided with a filter dust discharge pipeline for discharging filter dust to an unqualified product tank of the product screening system, and the filter dust and unqualified product material of the unqualified product tank are recycled to the solid phase material conveying and metering system; The other end of the lower portion of the filter is provided with a condensate liquefaction discharge pipeline and a control valve for controlling the discharge of the condensate liquefaction gas phase material to the recycled material temporary storage tank; The top of the filter is provided with an inert gas purging pipeline and a control valve for controlling the inert gas to purge the filter dust discharge pipeline, the condensate liquefaction discharge pipeline and the tail gas discharge pipeline connected to the tail gas processing system, and the output end of the filter is provided with a mixed gas material processing system for processing the filtered mixed gas containing gas phase and carrier gas; The filter is a tank filter, the upper portion of the filter is provided with a 316L wire mesh demisting device, the tank filter is provided with a cooling structure, and the cooling structure is one or more of a cooling jacket, a cooling coil and an embedded cooling fin; The mixed gas material processing system is composed of a vacuum unit, a vacuum unit exhaust buffer tank, a compressor, a condenser and a gas-liquid separator; the vacuum unit is in sequence communication with the vacuum unit exhaust buffer tank, the compressor, the condenser and the gas-liquid separator through pipelines; The operation signal of the vacuum unit is connected to a PLC system, and the start-stop and operation state of the vacuum unit are monitored by the PLC; the vacuum unit further comprises an electric vacuum ball valve, a pneumatic vacuum ball valve, a manual vacuum ball valve, an electromagnetic one-way valve, a vacuum measuring instrument, a bellows and a vacuum pipeline; the vacuum pipeline is provided with a vacuum pneumatic ball valve and a KF interface, and a one-way valve is arranged in front of the vacuum unit; The compressor is a diaphragm compressor or an oil-free piston compressor, and the compressor is provided with an inlet and outlet pressure self-adjusting system; the operation signal of the compressor is connected to a PLC system, and the start-stop and operation state of the compressor are monitored by the PLC; The gas-liquid separator comprises at least three discharge pipelines: a first discharge pipeline is a liquid phase discharge pipeline connected to the recycled material temporary storage tank; the recycled material temporary storage tank is in communication with the gas phase material supply system through the recycled material gasifier; a second discharge pipeline is a gas phase discharge pipeline connected to the recycled carrier gas storage tank, and the recycled carrier gas storage tank is in communication with the carrier gas supply system through a pipeline; and a third discharge pipeline is a tail gas discharge pipeline connected to the tail gas processing system, a tail gas end pipeline of the vacuum unit exhaust buffer tank and a tail gas end pipeline of the compressor, for tail gas discharge. The discharge pipes are provided with electric and pneumatic valves, including ball valves and butterfly valves; The gas-liquid separator is provided with a cooling jacket, an internal cooling coil and fins, and is also provided with pressure, temperature and liquid level sensors and an online gas analyzer, and the related signals are transmitted into a PLC system through a cable connection, and are monitored and controlled in real time through the PLC system; The online gas analyzer is controlled as follows: when the online gas analyzer analyzes the gas phase components and the carrier gas purity is lower than the set value and the impurity component content exceeds the set value, the valve on the pipeline is automatically opened according to the set program, and the discharge is performed to a tail gas treatment system; when the online gas analyzer analyzes the gas phase components and the carrier gas purity is higher than the set value and the impurity component content is lower than the set value, the valve is closed according to the set program, and the discharge to the tail gas treatment system is stopped; The solid-phase material conveying and metering system comprises a main material bin for storing solid-phase materials, an automatic feeding machine, a material storage box, a quantitative feeder and inert sealing gas, and the outlet of the solid-phase material conveying and metering system is communicated with the CVD reactor through a pipeline; The inner surface of the main material bin contacting the materials is sprayed with anti-static Teflon, the supporting bottom of the material storage box is provided with a pressure weighing sensor with an error of not more than 0.2%, and the weight signal is connected to the PLC to ensure the quantitative feeding of the material storage box and realize the feeding and discharging record; each bin is provided with a pneumatic knocking hammer, the pneumatic knocking hammer is automatically knocked at a frequency set according to the program or is manually controlled, the inert gas is used to replace and seal each bin, and the oxygen content of the system is ensured to be below 0.5%; The quantitative feeder is made of SUS304 and SUS316L, and the surface contacting the powder is sprayed with Teflon; the quantitative feeder and the feeder are connected through a soft connection, the connecting pipe is provided with a star-shaped unloading valve, and the quantitative feeder is provided with a pneumatic knocking hammer to prevent the bridging of the materials; The gas-phase material and carrier gas supply system comprises: inert gas replacement, gas-phase material and carrier gas mixing; the outlet of the gas-phase material and carrier gas supply system is communicated with the input end of a static mixer through a pipeline, the output end of the static mixer is communicated with the input end of the CVD reactor through a pipeline; and the output end of the CVD reactor is communicated with a product screening system and a post-reaction material treatment system through pipelines respectively; The gas-phase material includes silane, methylsilane, trimethylsilane, methyltrichlorosilane, dichlorodisilane, trichlorosilane, silicon tetrachloride, methane, ethane, ethylene, acetylene, propane, propylene, acetone, benzene, ethanol and toluene which are liquid at normal temperature but can be gasified into gas by heating; and the inert gas includes nitrogen, argon and helium; The mixing method includes: static mixing gas mixing method, volatilization carrying mixing method of introducing silicon gas into liquid carbon gas source, and volatilization carrying mixing method of introducing carbon gas into liquid silicon gas source; The CVD reactor is a drum-type rotary structure furnace, comprising: a furnace tube, a furnace body, a heating element, a spiral feeder, a furnace tube head sealing cover, a furnace tube tail sealing cover, a furnace tube supporting device, a furnace tube driving device and a base. The furnace tube is conical in design to avoid the formation of dead angles for gas flow in the furnace tube; the CVD reactor comprises a main furnace tube and a reduced-section conical furnace tube extending into the interior of the main furnace tube; the conical furnace tube is located in the interior of the main furnace tube and fills the annular space formed with the main furnace tube with heat-resistant material to achieve a heat insulation effect; the heat-resistant material is heat-resistant cotton board or high-purity graphite felt; The CVD reactor furnace tube inlet and outlet are both provided with a pneumatic hammer, which has a set program or manual control knocking function, and the furnace head and the furnace tail are each provided with one or more knocking devices; The front section of the CVD reactor is provided with a spiral feeder, and the interior of the furnace tube is uniformly provided with guide vanes, which are arranged at an angle of +36-56° and -46-66°. The CVD reactor feeding device adopts a spiral feeder, which comprises a spiral shaft, a spiral propelling motor, a box body, a spiral feeding pipe and spiral vanes; the spiral feeding pipe and the spiral vanes are made of SUS314S, SUS310S or INCOLOY800H, and the box body is made of SUS316L with a thickness of 3-12 mm; except the spiral feeding pipe, the spiral shaft and the spiral vanes, other surfaces in contact with the powder are sprayed with Teflon with a thickness of 15-60 μm or tungsten carbide with a thickness of 100-500 μm; the spiral feeding pipe inner wall and the spiral vanes are pickled and polished; the spiral feeder has a variable pitch structure, and the pitch gradually increases from the rear to the front; the spiral feeder inlet is directly connected to the heating zone; the furnace tube inlet end is conical in structure, and the overall equipment inclination angle is 0-20°. The heating part of the CVD reactor is divided into n independent temperature control zones, the heating power is independently set and controlled, and the heating resistance wire is made of 0Cr27Al7Mo2 or 0Cr21Al6Nb; the temperature zones in the CVD deposition chamber are separated by heat-resistant cotton board; the design temperature of the CVD reactor is 700-1200℃, the working temperature is 750-950℃, and the temperature is automatically controlled by an intelligent temperature control instrument; the PID is automatically adjusted; the power adjustment is adjusted by SCR; the temperature control instrument control precision is 0.1-0.3% FS, and the temperature difference of each temperature measuring point is ±1-5℃. The CVD reactor furnace tube inlet and outlet are both provided with a dustproof sealing device, which adopts an axial compression type graphite disc seal to prevent the overflow of heated gas phase or dust; the spring is sleeved on the screw rod, and the flange is extruded with the sealing ring to form a dynamic and static friction surface to ensure the sealing of the furnace chamber; the sealing device is provided with a pressure sensor to monitor the pressure of the furnace chamber near the sealing cover and realize overpressure alarm and safety interlocking; The CVD reactor furnace tail cover and the furnace head cover are both provided with an air inlet for filling reaction gas into the furnace to adapt to the CVD process; the bottom of the furnace head cover is provided with a waste material outlet, and a discharge valve is arranged; the waste material is collected into a waste material box in a sealed manner; The CVD reactor furnace head cover and the furnace tail cover shell are made of SUS316L stainless steel, and the inner surface of the furnace head cover in contact with the material is sprayed with a Teflon coating, The main furnace tube is a seamless steel tube, the inner wall of which is polished to a roughness of 0.2-4.0 μm, and the guide vane and the weld are pickled and polished, and the material of the tube is selected from SUS314S, SUS310S and INCOLOY800H; The tail discharge port of the CVD reactor is provided with a discharge valve, and the discharge valve is connected to a closed 316L stainless steel sifter; The product screening system comprises a sifter, a non-conforming product tank, a conforming product tank and an automatic packaging device, the sifter is a stainless steel sifter, the stainless steel sifter adopts a special fluidized bed and a vibrating screen; the conforming material enters the conforming product tank through a first outlet of the stainless steel sifter, and the conforming product tank is sealed by inert gas; A discharge valve is arranged between the conforming product tank and the automatic packaging device, the valve is an electrically or pneumatically controlled ball valve or butterfly valve, when the material in the conforming product tank reaches a set height, the discharge valve is opened according to a set program, and the conforming material enters the automatic packaging device and is packaged according to a set program and specification; The temperature control of the system for preparing the secondary battery composite negative electrode material by CVD is formed by a temperature controller, a power regulator, a heating body and a thermocouple into a closed loop PID temperature control system, the temperature controller is an FP-23 high-precision programmable temperature controller, the system is heated according to a given heating curve, has manual intervention adjustment, can store different process heating curves, and forms a closed loop control system with the temperature measuring sensor to realize program temperature control; The system for preparing the secondary battery composite negative electrode material by CVD is provided with a capacitive diaphragm gauge for measuring the pressure in the CVD deposition chamber, and together with a pressure sensor and an electrically or pneumatically regulated valve on the gas outlet pipeline, forms a constant pressure control system, the control system has functions of over-temperature, disconnection, over-flow, lack of cooling water, over-pressure, over-temperature of cooling water, over-pressure and over-temperature in the CVD furnace, alarm functions and over-temperature safety interlocking protection, gas leakage emergency cut-off function; The overall control of the system for preparing the secondary battery composite negative electrode material by CVD is realized by a programmable controller PLC and a touch screen, which can realize action control, parameter setting, real-time data display of equipment operation, curve display of temperature, power, pressure and flow, data list display, alarm information display, safety interlocking, record and data export functions, and permission management to prevent unauthorized operation of the equipment, the system has an explosion-proof level of dIICT4, a protection level of IP67 and an insulation level of F, and adopts the PLC programmable controller, the touch screen and the configuration interface to realize automatic operation control, operation state monitoring, operation state simulation display, operation fault alarm indication and safety emergency disposal of the whole system, and all the control and monitoring signals are transmitted to the DCS system in the central control room through the Modbus protocol for centralized control by the DCS system.

2. The preparation method of the system for preparing composite anode materials for secondary batteries by CVD as described in claim 1, characterized in that: The steps are as follows: 【1】Preparation 1) The system is powered on for inspection, the insulation resistance between the heating element and the shell is not less than 500Ω, the system chambers are well sealed, the waterway is unobstructed, the pneumatic elements operate normally and flexibly, and various mechanical actions are tested and positioned. ​ 2) The system is vacuumed to 0.1-0.01 Pa, and the pressure rise rate of the process cavity is ensured to be ≤0.5 Pa / h; 3) The entire system is replaced by inert gas, the replacement pressure is 0.05-0.15 MPa, continuous replacement is performed for 3-5 times, the replacement gas is nitrogen, the last replacement gas after nitrogen replacement is argon or helium, the oxygen concentration of the replacement gas analyzed at the tail gas system sampling port is lower than 0.5%, and the inert gas atmosphere of the system is maintained at 0.01-0.03 MPa; 【2】Solid phase material is added, and the solid phase material supply system is started 1) The solid phase material is manually added to the main material bin, the feeding program is started through the PLC control panel, the automatic feeding machine transports the solid phase material from the main material bin to the material storage box, and the solid phase material is nano silicon powder, porous silicon, nano silicon monoxide, various high-performance mesoporous carbon materials, and materials coated by CVD for the first time or the nth time; 【3】Start the CVD reactor 1) After the solid phase material is gradually added to the CVD reactor according to the set program, the CVD reactor furnace tube rotation motor is started through the PLC control panel, the furnace tube rotation speed is controlled to be 0.5-50 revolutions / min, and the material heating time is controlled to be within 5-100 min and the material temperature is controlled to be 600-1000℃; 【4】Start the gas phase material supply system 1) The gas phase material supply program is started through the PLC control panel, the entire system is first replaced by a carrier gas, then the specified carrier gas and reaction gas flow and proportion are controlled according to the set program, the carrier gas and reaction gas are fully mixed and uniformly enter the CVD reactor, react in the CVD reactor, including two or more material reaction CVD deposition, single material self-decomposition CVD deposition, and internal pore CVI deposition and external CVD coating of the solid phase material; the proportion of the carrier gas and the recovered carrier gas is 1:1-1:100, the proportion of the reaction gas and the carrier gas is 1:2-1:50, the proportion of the two or more reaction gases is calculated according to the chemical reaction equation, the carrier gas flow is 0.5-100 L / min, and the reaction gas flow is 0.2-50 L / min; the CVD deposition temperature is 600-950℃, and the furnace tube rotation speed is 0.5-30 revolutions / min; 【5】Material reaction in the CVD reactor 1) The solid phase material is heated to a specified temperature in the CVD reactor, and rotates and migrates slowly with the rotation of the furnace tube; the gas phase material and the carrier gas are mixed and then enter the CVD reactor to react and deposit on the solid phase material as a carrier, forming a CVD deposition layer with a certain thickness on the pores and surface of the solid phase material, and forming an excellent material meeting the requirements of the corresponding negative electrode of the secondary battery; the thickness and uniformity of the deposition layer depend on the temperature, the furnace tube rotation speed, and the gas phase flow; 【6】Screening of the material product completed by the CVD reactor 1) In the CVD reactor, the deposition, coating of solid phase material is completed, and the solid phase material is introduced into the sizer through the pipeline from the CVD reactor; in the sizer, the solid phase material is sieved into qualified products and unqualified products, the qualified product material is introduced into the qualified product tank, and the qualified product tank is at least two or more; when the material in a storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another qualified product tank, at the same time, the inert gas replacement valve is automatically opened, and the reaction gas in the qualified product tank filled with material is replaced into the tail gas treatment device; the inert replacement gas is nitrogen, argon or helium, the replacement pressure is 0.1-0.3 MPa, and the replacement is at least 5 times; when the replacement gas content measured by the on-line gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified; after the inert gas replacement of the qualified product tank is qualified, the PLC control system automatically opens the valve on the pipeline connecting the qualified product tank and the automatic packaging machine, feeds the material into the automatic packaging machine according to a set amount, and completes the product packaging; 2) The unqualified product material is introduced into the unqualified product tank, and the unqualified product tank is at least two or more; when the material in a storage tank reaches a specified amount, the feeding valve is automatically closed according to a set program, and the material is automatically switched to another unqualified product tank, and the inert gas replacement valve is automatically opened, and the reaction gas in the unqualified product tank filled with material is replaced into the tail gas treatment device to ensure safety; the inert replacement gas is nitrogen, argon or helium, the replacement pressure is 0.1-0.3 MPa, and the replacement is at least 5 times; when the replacement gas content measured by the on-line gas analyzer arranged on the replacement gas exhaust pipeline is greater than 99.9%, the replacement is qualified; after the inert gas replacement of the unqualified product tank is qualified, the PLC control system automatically opens the valve on the pipeline connecting the unqualified product tank and the main material bin arranged on the ground, feeds the material into the main material bin according to a set amount, and performs CVD deposition and coating again; 【7】Tail gas treatment after CVD reactor reaction 1) The tail gas after the CVD reactor reaction is first introduced into a filter, and the gas phase material liquefied at a certain temperature is separated out by the filter, and a small amount of particulate matter in the gas phase is filtered out; the condensed and liquefied gas phase material is discharged to a temporary storage tank for recovered material when reaching a certain liquid level; when the pressure difference of the filter reaches a set value, the inert gas purging valve is opened by the PLC controller to purge the wire mesh demister; the filter is cooled by -35-5 ℃ frozen liquid; the temperature of the reaction tail gas out of the filter after cooling and condensation is 20-50 ℃; The tail gas after condensation and filtration is introduced into a vacuum unit, and is extracted by the vacuum unit and then introduced into a buffer tank through a pipeline; the buffer tank is communicated with a compressor through a pipeline; the tail gas is pressurized by the compressor and then introduced into a condenser; the condensed gas is cooled to a set temperature by the condenser; the gas-liquid mixture out of the condenser is introduced into a gas-liquid separator with a cold jacket; the recovered carrier gas is discharged from the top of the gas-liquid separator and introduced into a recovered carrier gas storage tank through a pipeline; the recovered material is discharged from the bottom of the gas-liquid separator through a discharge pipe and introduced into a temporary storage tank for recovered material through a pipeline; the recovered material is introduced into a recovered material gasifier through a pipeline, mixed with the carrier gas in the static mixer, and then introduced into the CVD reactor to participate in the reaction process; 2) When the on-line analyzer detects that the pure component content of the carrier gas in the tail gas gas phase composition is less than 99.99%, the system PLC controller automatically closes the valve between the gas-liquid separator and the carrier gas recovery tank according to the parameters set in the program, and opens the valve between the gas-liquid separator and the tail gas treatment system, and discharges the gas phase material to the tail gas treatment system as tail gas for treatment; 3) If CVD coating of different layers and different materials with multiple levels and structures is required, the material deposited by the first CVD according to the above process is used as "raw material", and the CVD deposition is performed again or multiple times according to the above process by adjusting the corresponding process parameters.

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