Device and preparation method for improving deposition efficiency of silicon-carbon negative electrode prepared by CVD (Chemical Vapor Deposition)

Abstract

The invention relates to the technical field of silicon-carbon negative electrode material preparation devices, in particular to a device for improving the deposition efficiency of a silicon-carbon negative electrode prepared through CVD and a preparation method. The reaction cavity is used for containing the base material, and the base material is heated through the heating device so as to promote decomposition and deposition reaction of silane gas; an optimized stirring mechanism is designed in the reaction cavity so as to ensure that base materials can be fully mixed in the reaction process; meanwhile, the design of the lifting plate can ensure that the base material is uniformly lifted in the reaction process and is in full contact with the silane gas, so that the mixing uniformity is improved. The gas supply part is responsible for introducing silane gas into the reaction cavity in the stirring process; by accurately controlling the flow and the introduction time of the silane gas, the uniform distribution of the silane gas in the reaction cavity can be ensured. And the recycling part can recycle useful components in the tail gas, so that the resource utilization rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon negative electrode material preparation device, and in particular to a device and a preparation method for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD. Background Art

[0002] Lithium battery negative electrode material is one of the four main materials of lithium batteries. Graphite negative electrode is the mainstream at present. At present, the specific capacity of commercial graphite negative electrode materials is close to the theoretical limit, and there is little room for improvement. Silicon-carbon negative electrode materials have advantages such as high lithium storage capacity and low voltage platform. The emerging silicon-based materials have extremely high energy density (theoretical specific capacity is 4200mAh / g, which is 10 times that of graphite negative electrode materials). It is expected to replace graphite negative electrode and become the mainstream direction of negative electrode material research and development for the next generation of high energy density lithium batteries.

[0003] CVD vapor deposition of silicon requires a short production process, less equipment, and low theoretical cost, and is therefore regarded as the ultimate silicon negative electrode solution for each battery cell factory. Equipment for depositing silicon-carbon materials is currently divided into two categories: rotary kiln and fluidized bed, each with its own advantages and disadvantages. The rotary kiln process is relatively simple and highly repeatable, so overseas manufacturers generally use this equipment. However, the deposition efficiency of this process is average, there is a certain waste of silane, and the batch production volume is low, and the coverage of the particles is slightly insufficient, which in turn affects the increase in the cost of mass-produced silicon-carbon products. Although the fluidized bed does not have to worry about uneven deposition and low silane utilization, it has high requirements for the airtightness and air pressure of the equipment to meet the gaseous coating of small particles. It faces the difficulty of achieving mass production and expansion, so it needs to be solved urgently. Summary of the invention

[0004] In order to avoid and overcome the technical problems existing in the prior art, the present invention provides a device and a preparation method for improving the deposition efficiency of CVD silicon-carbon anode preparation. The device of the present invention can effectively improve the mixing uniformity of silane and base material, thereby improving the efficiency of preparing silicon-carbon anode materials.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD comprises a reaction chamber for heating and stirring a base material, a gas supply section for introducing silane gas into the reaction chamber in the stirring process, and a recovery section for recovering the tail gas in the reaction chamber, and a lifting plate for lifting and stirring the base material is installed in the reaction chamber.

[0007] As a further solution of the present invention, it includes a base and a furnace tube horizontally rotatably installed on the base, the furnace tube is a cylindrical shape that is thick in the middle and thin at both ends, and its transition section is a truncated cone; the middle section of the furnace tube and its two transition sections constitute the reaction chamber; the lifting plate includes a straight plate installed on the inner wall of the middle section of the furnace tube and a spiral plate installed on the inner walls of the two transition sections; the length directions of the straight plates uniformly distributed along the circumference of the furnace tube are parallel to the axis of the furnace tube, and the height directions of the straight plates extend along the radial direction of the furnace tube at their respective positions; the spiral plates at the two transition sections are distributed in a spiral shape, and the spiral directions of the spiral plates at the two end transition sections are opposite to each other.

[0008] As a further solution of the present invention: a support frame is also installed on the base, and two groups of rotating components respectively matched with the two ends of the furnace tube are installed on the support frame; each rotating component includes a plurality of supporting wheels installed on the support frame and rotating uniformly in sequence along the circumference of the furnace tube, and the rotation axis of each supporting wheel is parallel to the axis of the furnace tube; the wheel surface of each supporting wheel is concave to form an annular groove, and rolling rings are coaxially fixedly installed at both ends of the furnace tube, and the rolling rings are rollingly embedded in the annular grooves of each supporting wheel matched therewith; a driven sprocket is coaxially fixedly connected to one end of the furnace tube, a driving motor is fixedly installed on the base, a driving sprocket is coaxially fixedly connected to the motor shaft of the driving motor, and the driving sprocket and the driven sprocket are transmission-connected to each other through a transmission chain.

[0009] As a further solution of the present invention: a furnace shell is also installed on the base, and the interior of the furnace shell is formed with a cylindrical furnace chamber which is arranged coaxially with the furnace tube and contains the middle section of the furnace tube and two transition sections. A plurality of annular heating plates are coaxially and evenly installed on the inner wall of the furnace chamber along the axial direction of the furnace chamber, and the furnace tube is coaxially inserted in a heating cavity formed by the plurality of annular heating plates.

[0010] As a further solution of the present invention: the recovery part includes an exhaust pipe fixedly mounted on the base and coaxially rotating and sealingly cooperating with the exhaust end of the furnace tube, the exhaust end of the exhaust pipe extends into the sealed water tank and extends below the water surface of the water tank, and the water tank is connected to the clean water circulation system;

[0011] The gas pressure inside the furnace tube is calculated as follows:

[0012] P = (h1-h2)ρg;

[0013] In the formula, P represents the gas pressure in the furnace tube; h1 represents the liquid level in the water tank; h2 represents the liquid level difference between the exhaust pipe outlet and the bottom of the water tank; ρ represents the density of water; g represents the acceleration of gravity;

[0014] The gas pressure change in the furnace tube is calculated as follows:

[0015]

[0016] In the formula, ΔP represents the change in gas pressure in the furnace tube; Qv1 represents the flow rate of the water inlet of the clean water circulation system adding clean water into the water tank; Qv2 represents the flow rate of the water outlet of the clean water circulation system extracting clean water from the water tank; t represents the working time of the clean water circulation system; R1 represents the inner radius of the cylindrical water tank.

[0017] As a further solution of the present invention: a spiral sleeve is coaxially fixed in the tube cavity of the gas outlet end of the furnace tube, and an outer spiral plate is fixed on the inner surface of the spiral sleeve; an inner spiral plate is coaxially fixed in the tube cavity of the spiral sleeve, and the inner spiral plate and the outer spiral plate cooperate with each other to form a spiral channel connecting the reaction chamber and the exhaust pipe.

[0018] As a further solution of the present invention: the gas supply part includes an outer gas pipe which is coaxially rotatably sealed and sleeved on the gas inlet end of the furnace tube, the outer gas pipe extends into the reaction chamber and its extending end is a sealed end, and a plurality of gas holes are opened on the outer gas pipe only at the position where it coincides with the middle section of the furnace tube, and each gas hole is evenly arranged in sequence along the length direction of the outer gas pipe; an inner gas pipe is coaxially inserted in the outer gas pipe, and the gas outlet end of the inner gas pipe extends to the middle position of the furnace tube, the gas inlet end of the inner gas pipe is connected to each gas tank storing gas, and a mass flow meter is installed at the gas outlet end of each gas tank, and a gas static mixer for mixing gases to generate a mixed gas is installed at the aggregation point of various gases.

[0019] As a further solution of the present invention: the height of the straight board is calculated as follows:

[0020] h=0.3-0.4R;

[0021] Wherein, h is the width of the straight plate; represents the inner radius of the middle section of the furnace tube.

[0022] As a further solution of the present invention: the minimum inner radius of the transition section of the furnace tube is r, which is calculated as follows:

[0023] r=1.2-1.5(Q / πVa) 0.5 ;

[0024]

[0025] Wherein, Q represents the mixed gas flow rate entering the reaction chamber; Va represents the mixed gas flow rate entering the reaction chamber; K represents the correction parameter; L represents the length of the middle section of the furnace tube; n represents the furnace tube speed; δ represents the deposition efficiency of silane in the mixed gas; α represents the maximum angle at which the silane in the mixed gas can maintain a natural stable state when deposited on the base material, that is, the repose angle.

[0026] A preparation method, which uses the above-mentioned device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD, is characterized in that it includes the following preparation steps:

[0027] S1, assembling the device and placing the porous carbon as a base material in the furnace tube at the same time;

[0028] S2, silane, acetylene and nitrogen are mixed according to a set ratio, and the mixed gas is introduced into the reaction chamber, while the furnace tube rotates in a scroll direction opposite to that of the spiral plate, the annular heating plate heats the furnace tube, and the clean water circulation system operates at a set flow rate;

[0029] S3, the mixed gas contacts and reacts with the porous carbon, and the remaining gas enters the water tank and is extracted by the centrifugal fan according to the set power;

[0030] S4. After the reaction time is set, the device is stopped, and the preparation of the silicon-carbon negative electrode material is completed.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The reaction chamber of the present invention is used to accommodate the base material, and the base material is heated by a heating device to promote the decomposition and deposition reaction of the silane gas; the reaction chamber is designed with an optimized stirring mechanism to ensure that the base material can be fully mixed during the reaction process; at the same time, the design of the lifting plate can ensure that the base material is evenly lifted during the reaction process and fully contacted with the silane gas, thereby improving the mixing uniformity. The gas supply unit is responsible for introducing silane gas into the reaction chamber in the stirring process; by accurately controlling the flow rate and introduction time of the silane gas, it can ensure that the silane gas is evenly distributed in the reaction chamber. The recovery unit can also recycle the useful components in the tail gas to improve resource utilization.

[0033] 2. When the exhaust gas of the present invention passes through the spiral sleeve, the airflow rotates with the spiral channel, generating a certain centrifugal force. The powder carried in the exhaust gas is deposited under the influence of the centrifugal force. The deposited material gradually falls in the reverse direction to the spiral plate near it under the action of the spiral channel, and then re-enters the middle section of the furnace tube under the reverse push of the spiral plate, and continues to react with the base material, thereby reducing material loss.

[0034] 3. Based on the calculation formula of the gas pressure in the furnace tube, the present invention can change the gas pressure in the furnace tube according to actual needs by controlling the flow rate of the water inlet and outlet of the clean water circulation system, thereby stably controlling the furnace tube gas pressure and providing a stable atmosphere environment for high-temperature deposition of the gas in the furnace tube.

[0035] 4. The arrangement of the outer air duct and the inner air duct of the present invention, as well as the opening positions of the air duct holes, can enable the mixed gas to form an air curtain blowing toward the wall of the furnace tube during the discharge process, thereby improving the contact uniformity between the mixed gas and the base material, and further improving the reaction efficiency of silane and porous carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1It is a schematic diagram of the overall structure of the device of the present invention.

[0037] Figure 2 It is a structural schematic diagram of the furnace tube in the present invention.

[0038] Figure 3 It is a structural schematic diagram of the air supply part in the present invention.

[0039] Figure 4 It is a schematic diagram of the structure of the spiral sleeve in the present invention.

[0040] Figure 5 It is a structural schematic diagram of the recovery unit in the present invention.

[0041] Figure 6 It is a schematic diagram of the size structure of the straight plate in the present invention.

[0042] In the figure: 1, base; 11, telescopic rod; 2, base; 21, support frame; 211, supporting wheel; 3, furnace tube; 3a, middle section; 3b, transition section; 31, lifting plate; 311, straight plate; 312, spiral plate; 32, rolling ring; 33, driven sprocket; 34, reaction chamber; 4, spiral sleeve; 41, outer spiral plate; 42, inner spiral plate; 43, spiral channel; 5, recovery part; 51, exhaust pipe; 52, clean water circulation system; 53, centrifugal fan; 54, water tank; 541, liquid level meter; 6, air supply part; 61, gas tank; 62, mass flow meter; 63, gas static mixer; 64, outer air duct; 641, air guide hole; 65, inner air duct. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] See also Figure 1 to Figure 6 When the device of the present invention is used, the base 1 is first fixedly installed at the corresponding position, and then the base 2 hinged on the base 1 is driven by the hydraulic cylinder as the telescopic rod 11 to be leveled. Then, the porous carbon as the base material is put into the reaction chamber 34 from the feed port on the right side of the furnace tube 3 according to the set amount, and then the rotating sleeve and the inner spiral plate 42 are fixedly installed in the tube cavity at the feed port on the right side of the furnace tube 3. Finally, the gas supply part 6 and the recovery part 5 are connected to the two ends of the furnace tube 3 in sequence.

[0045] In one embodiment of the present invention, four gas tanks 61 are used, two of which are filled with nitrogen, and one of the nitrogen tanks 61 is used as a backup. The other two gas tanks 61 are respectively filled with silane and acetylene. After acetylene, silane and nitrogen pass through the corresponding mass flow meters 62, nitrogen and acetylene are evenly mixed in a gas static mixer 63, and nitrogen and silane are evenly mixed in another gas static mixer 63. The two mixed gases are mixed again in the inner gas guide tube 65 to form a final mixed gas, which is then delivered to the reaction chamber 34 through the gas guide hole 641 in the outer gas guide tube 64. The mixed gas flow Q entering the reaction chamber 34 is calculated by formula (1):

[0046]

[0047] In the process of using mass flow meter 62 to monitor the flow of raw gas, the ratio of silane and nitrogen is controlled to be 1:3, and the ratio of acetylene and nitrogen is also 1:3. At the same time, a spare nitrogen tank 61 is used to continuously pass nitrogen into the interlayer between the inner air guide tube 65 and the outer air guide tube 64, so as to reduce the temperature in the composite tube composed of the outer air guide tube 64 and the inner air guide tube 65, thereby reducing the process gas temperature, avoiding that the mixed gas temperature is too high, after the mixed gas enters the furnace tube 3 and before contacting the porous carbon, it begins to decompose, thereby affecting the coating quality. At the same time, the composite tube adopts a commonly used coaxial rotary seal to be inserted in the air inlet end of the furnace tube 3, and is fixed on the base 2, so that during the rotation of the furnace tube 3, the composite tube remains fixed, and the stability of the gas guide is improved.

[0048] Mixed gas continuously enters in furnace tube 3, and furnace tube 3 is under the effect of driving motor, and driven sprocket 33 drives furnace tube 3 to rotate based on the transmission of driving sprocket and transmission chain. Each supporting wheel 211 installed on support frame 21 begins to cooperate with rolling ring 32, and provides rotation basis for the rotation of furnace tube 3, improves the stability of rotation. Horizontally arranged furnace tube 3 rotates continuously, and its turning direction is opposite to the scroll direction of spiral plate 312 in transition section 3b, so that spiral plate 312 pushes porous carbon diffused on transition section 3b to return to furnace tube 3 midsection 3a, and continuously turns over and stirs under the lifting action of straight plate 311 in lifting plate 31, so as to realize full contact and reaction with mixed gas. The spiral plates 312 at two ends of furnace tube 3 rotate in opposite directions, and spiral plate 312 on the right side of furnace tube 3 is right-handed, and spiral plate 312 on the left side of furnace tube 3 is left-handed. During sintering, the furnace tube 3 rotates counterclockwise, and the straight plate 311 can achieve uniform lifting of the middle material and increase the uniformity of particle coating. The spiral plates 312 at both ends can prevent the lifted powder from diffusing to both ends and push the powder accumulated in the transition section 3b of the furnace tube 3 to the middle of the furnace tube 3. The temperature difference between the transition section 3b and the middle section 3a of the furnace tube 3 is large, which prevents uneven coating of the powder at both ends. During discharge, the furnace tube 3 rotates in the opposite direction to push the material out of the furnace tube 3.

[0049] In this embodiment, the height of the straight plate 311 is also required, which is calculated by formula (2). When the number of the lifting plates 31 is 6, R < 600 mm; when the number of the straight plates 311 is 8, 600 mm ≤ R < 1000 mm.

[0050] h=0.3-0.4R (2)

[0051] At the same time, the minimum inner radius of the transition section 3b of the furnace tube 3 is r, which is calculated as shown in formula (3):

[0052] r=1.2-1.5(Q / πVa) 0.5 (3)

[0053] During the sintering process, the furnace is wrapped with a heat-insulating material made of high-quality ceramic fiber material, and a ring-shaped heating plate is embedded in the heat-insulating material to wrap the furnace tube 3 for a circle. The furnace tube 3 is heated evenly, the temperature difference in the cross section of the furnace tube 3 is small, and the silane is heated and decomposed and deposited at the same efficiency. The heat collecting plate can use a conventional plate body composed of a resistance wire, and of course other materials or structures that can be heated in time are also feasible.

[0054] The waste gas generated after the mixed gas reacts with the porous carbon will pass through the spiral channel 43 formed by the outer spiral plate 41 and the inner spiral plate 42 in the leakage sleeve, and then enter the exhaust pipe 51. At the same time, the exhaust pipe 51 is inserted at the gas outlet end of the furnace tube 3 using a commonly used coaxial rotary seal and fixed on the base 2, so that during the rotation of the furnace tube 3, the exhaust pipe 51 remains fixed, thereby improving the stability of the exhaust.

[0055] The high temperature resistant packing sealing material on the outside of the spiral sleeve 4 can ensure the seal between the rotating sleeve and the pipe wall to prevent the material from leaking from this part. The exhaust pipe 51 sends the exhaust gas to below the water surface of the water tank 54, so that some substances in the exhaust gas are dissolved in the water and taken away by the clean water circulation system 52. The remaining gas floats in the upper space of the water tank 54 and is sucked away by the centrifugal fan 53 for centralized treatment.

[0056] Numerical liquid flow meters are installed at the water inlet and outlet of the clean water circulation system 52 connected to the water tank 54, and the corresponding flow rate can be measured in real time by the numerical liquid flow meter. The liquid level meter 541 is set at the bottom of the water tank 54, and collects the height data h1 of the water surface in real time and transmits it to the control system. At the same time, the distance between the exhaust pipe 51 and the bottom of the water tank 54 is h2. The gas pressure in the reaction chamber 34 can be calculated by combining formula (4).

[0057] P=(h1-h2)ρg (4)

[0058] Since the water in the water tank 54 is always in a circulating state, the value of ρ remains basically unchanged, and the gas pressure in the furnace tube 3 is proportional to the vertical distance h1-h2 between the water tube and the water surface. The volume flow rates Qv1 and Qv2 of the inlet and outlet water are controlled by a numerical liquid flow meter to adjust the pressure P of the furnace tube 3. The pressure change of the furnace tube 3 is shown in formula (5).

[0059]

[0060] The above-mentioned gas pressure control method of the furnace tube 3 stably controls the gas pressure of the furnace tube 3 and provides a stable atmosphere environment for high-temperature deposition of gas in the furnace tube 3 .

[0061] After reaching the set reaction time, sintering is stopped, the exhaust pipe 51 is disconnected from the furnace tube 3, and the spiral sleeve 4 is removed. At this time, under the action of the hydraulic cylinder, one end of the base 2 is lifted, and under the action of the drive motor, the furnace tube 3 is reversed, so that all the materials in the furnace tube 3 are poured into the collection box, and this round of silicon-carbon negative electrode material preparation is completed.

[0062] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A device for improving the deposition efficiency of silicon-carbon anode prepared by CVD, characterized in that: The invention comprises a reaction chamber (34) for heating and stirring a base material, a gas supply section (6) for introducing silane gas into the reaction chamber (34) in the stirring process, and a recovery section (5) for recovering tail gas in the reaction chamber (34), and a lifting plate (31) for lifting and stirring the base material is installed in the reaction chamber (34).

2. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 1, characterized in that: The invention comprises a base (2) and a furnace tube (3) mounted on the base (2) in a horizontally rotatable manner, wherein the furnace tube (3) is in the shape of a cylinder with a thick middle and thin ends, and its transition section (3b) is in the shape of a truncated cone; the middle section (3a) of the furnace tube (3) and its two transition sections (3b) constitute the reaction chamber (34); the material lifting plate (31) comprises a straight plate (311) mounted on the inner wall of the middle section (3a) of the furnace tube (3) and a spiral plate (312) mounted on the inner wall of the two transition sections (3b); the length directions of the straight plates (311) uniformly distributed along the circumference of the furnace tube (3) are parallel to the axis of the furnace tube (3), and the height directions of the straight plates (311) extend along the radial direction of the furnace tube (3) at their respective positions; the spiral plates (312) at the two transition sections (3b) are distributed in a spiral shape, and the spiral directions of the spiral plates (312) at the two transition sections (3b) are opposite to each other.

3. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 2, characterized in that: A support frame (21) is also mounted on the base (2), and two groups of rotating components respectively matched with the two ends of the furnace tube (3) are mounted on the support frame (21); each rotating component comprises a plurality of supporting wheels (211) mounted on the support frame (21) and rotating uniformly in sequence along the circumference of the furnace tube (3), and the rotating axis of each supporting wheel (211) is parallel to the axis of the furnace tube (3); the wheel surface of each supporting wheel (211) is concave to form an annular groove, and rolling rings (32) are coaxially fixedly mounted on both ends of the furnace tube (3), and the rolling rings (32) are rollingly embedded in the annular grooves of each supporting wheel (211) matched therewith; a driven sprocket (33) is coaxially fixedly connected to one end of the furnace tube (3), and a driving motor is fixedly mounted on the base (2), and a driving sprocket is coaxially fixedly connected to the motor shaft of the driving motor, and the driving sprocket and the driven sprocket (33) are connected to each other through a transmission chain.

4. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 3, characterized in that: A furnace shell is also mounted on the base (2), and a cylindrical furnace chamber is formed inside the furnace shell, which is arranged coaxially with the furnace tube (3) and contains the middle section (3a) and two transition sections (3b) of the furnace tube (3). A plurality of annular heating plates are coaxially and evenly mounted on the inner wall of the furnace chamber along the axis of the furnace chamber, and the furnace tube (3) is coaxially inserted into a heating cavity formed by the cooperation of the plurality of annular heating plates.

5. A device for improving the deposition efficiency of silicon-carbon anode prepared by CVD according to any one of claims 1 to 4, characterized in that: The recovery part (5) comprises an exhaust pipe (51) fixedly mounted on the base (2) and coaxially rotating with the exhaust end of the furnace tube (3) in a sealed manner, the exhaust end of the exhaust pipe (51) extends into a sealed water tank (54) and extends below the water surface of the water tank (54), and the water tank (54) and the clean water circulation system (52) are in communication with each other; The gas pressure in the furnace tube (3) is calculated as follows: P = (h1-h2)ρg; In the formula, P represents the gas pressure in the furnace tube (3); h1 represents the liquid level in the water tank (54); h2 represents the liquid level difference between the exhaust pipe (51) outlet and the bottom of the water tank (54); ρ represents the density of water; g represents the acceleration due to gravity; The gas pressure change in the furnace tube (3) is calculated as follows: In the formula, ΔP represents the change in gas pressure in the furnace tube (3); Qv1 represents the flow rate of the water inlet of the clean water circulation system (52) adding clean water to the water tank (54); Qv2 represents the flow rate of the outlet of the clean water circulation system (52) for extracting clean water from the water tank (54); t represents the working time of the clean water circulation system (52); and R1 represents the inner radius of the cylindrical water tank (54).

6. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 5, characterized in that: A spiral sleeve (4) is coaxially fixedly connected in the tube cavity of the gas outlet end of the furnace tube (3), and an outer spiral plate (41) is fixedly connected to the inner surface of the spiral sleeve (4); an inner spiral plate (42) is coaxially fixedly connected in the tube cavity of the spiral sleeve (4), and the inner spiral plate (42) and the outer spiral plate (41) cooperate with each other to form a spiral channel (43) connecting the reaction chamber (34) and the exhaust pipe (51).

7. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 6, characterized in that: The gas supply part (6) comprises an outer gas guide pipe (64) coaxially rotatably sealed and sleeved on the gas inlet end of the furnace tube (3); the outer gas guide pipe (64) extends into the reaction chamber (34) and its extending end is a sealed end; a plurality of gas guide holes (641) are provided in the outer gas guide pipe (64) only at a position where it coincides with the middle section (3a) of the furnace tube (3); and each gas guide hole (641) is evenly arranged in sequence along the length direction of the outer gas guide pipe (64); an inner gas guide pipe (65) is coaxially inserted into the outer gas guide pipe (64); and the gas outlet end of the inner gas guide pipe (65) extends to the middle position of the furnace tube (3); the gas inlet end of the inner gas guide pipe (65) is connected to each gas tank (61) storing gas, and each gas tank (61) is equipped with a mass flow meter (62); and a gas static mixer (63) for mixing gases to generate mixed gas is installed at the aggregation of various gases.

8. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 7, characterized in that: The height of the straight plate (311) is calculated as follows: h=0.3-0.4R; In the formula, h represents the width of the straight plate (311); represents the inner radius of the middle section (3a) of the furnace tube (3).

9. The device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD according to claim 8, characterized in that: The minimum inner radius of the transition section (3b) of the furnace tube (3) is r, which is calculated as follows: r=1.2-1.5(Q / πVa) 0.5 ; In the formula, Q represents the flow rate of the mixed gas entering the reaction chamber (34); Va represents the flow velocity of the mixed gas entering the reaction chamber (34); K represents the correction parameter; L represents the length of the middle section (3a) of the furnace tube (3); n represents the rotation speed of the furnace tube (3); δ represents the deposition efficiency of silane in the mixed gas; and α represents the maximum angle at which the silane in the mixed gas can maintain a natural stable state when deposited on the base material, i.e., the repose angle.

10. A preparation method, wherein the preparation method uses the device for improving the deposition efficiency of silicon-carbon negative electrode prepared by CVD as claimed in claim 9, characterized in that: The method comprises the following preparation steps: S1, assembling the device and placing the porous carbon as a base material in the furnace tube (3); S2, mixing silane, acetylene and nitrogen in a set ratio, and introducing the mixed gas into the reaction chamber (34), while the furnace tube (3) rotates in a scroll direction opposite to that of the spiral plate (312), the annular heating plate heats the furnace tube (3), and the clean water circulation system (52) operates at a set flow rate; S3, the mixed gas contacts and reacts with the porous carbon, and the remaining gas enters the water tank (54) and is extracted by the centrifugal fan (53) according to the set power; S4. After the reaction time is set, the device is stopped, and the preparation of the silicon-carbon negative electrode material is completed.

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