Silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a silicon-carbon negative electrode material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. The method comprises the following steps: filling a porous carbon rod into a chemical vapor deposition furnace; a motor is arranged at the outer bottom of the furnace body and connected with the bottom of the elbow through a magnetofluid sealing device to drive the elbow to rotate; a hollow interlayer is arranged on the outer wall of the furnace body and used for introducing circulating water; the preparation method comprises the following steps: in an inert atmosphere, heating a porous carbon rod by utilizing a power supply, introducing silicon source gas to carry out chemical vapor deposition reaction, heating the porous carbon rod, introducing carbon source gas to carry out carbon coating, taking out the deposited and coated silicon-carbon composite material rod, crushing, screening and grinding, adding the silicon-carbon composite material powder into a fluidized bed reactor, and carrying out fluidized bed reaction to obtain the silicon-carbon composite material. And then introducing a carbon source gas for secondary carbon coating to obtain the product. According to the method, deposition is more uniform, the conversion rate of the silicon source gas is higher, the structural stability of the silicon-carbon negative electrode material is kept, and the cycle life of the material is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and more specifically to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] With the replacement of electronic products and the rapid development of new energy vehicles, the demand for high energy density batteries is becoming more and more urgent. After years of commercial application and research optimization, the current specific capacity of traditional graphite anode materials can reach 340-360mAh g -1 , which is close to the theoretical specific capacity of graphite anode 372 mAh g -1 Among the negative electrode materials currently studied, silicon has a very high theoretical specific capacity (4200mAh g -1 ), which is the theoretical specific capacity of the traditional graphite negative electrode (372mAh g -1 ) times that of silicon. In addition, silicon has abundant reserves in nature and lower potential to lithium, making it an ideal negative electrode material for lithium-ion batteries.

[0003] The huge volume change of silicon during lithiation and delithiation (up to 300%) leads to the breaking and reformation of chemical bonds, the repeated formation, breaking and reformation of the solid electrolyte interface film (SEI film), and the large consumption of lithium, which causes the battery performance to decay rapidly; in addition, the poor intrinsic electronic conductivity of silicon also limits its cycle stability. To this end, researchers have improved the volume expansion of silicon during the cycle to a certain extent and improved its cycle stability through technical improvements to silicon-based materials, including silicon nano-sizing, silicon oxide, and carbon coating. However, silicon-based negative electrode materials prepared by these methods also expose many defects during the cycle process, such as the excessive consumption of lithium due to the huge specific surface area of ​​nano-silicon, the low initial efficiency and high production cost of silicon oxide, and the collapse of the coating structure of carbon-coated silicon negative electrode materials after long-term circulation, which makes it difficult for silicon-based negative electrode materials to meet commercial requirements.

[0004] Therefore, how to develop a silicon-carbon negative electrode material and its preparation method and application to solve the above-mentioned technical problems is an issue that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, the present invention provides a silicon-carbon negative electrode material and a preparation method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0008] (1) Loading the porous carbon rod into a chemical vapor deposition furnace;

[0009] The chemical vapor deposition furnace comprises: a furnace body, a gas delivery elbow pipe is provided at the bottom of the furnace body and is connected to the outside of the furnace body, the elbow pipe comprises a lower elbow pipe vertical section and an upper elbow pipe horizontal section that are connected to each other, a motor is provided at the bottom of the furnace body and is connected to the bottom of the elbow pipe through a magnetic fluid sealing device to drive the elbow pipe to rotate, an external gas source is connected to the magnetic fluid sealing device to supply gas to the elbow pipe, a hollow interlayer is provided on the inner wall of the furnace body, a circulating water inlet is provided on one side of the hollow interlayer, and a circulating water outlet is provided on the other side, and an exhaust gas outlet is provided on the top of the furnace body;

[0010] One end of the porous carbon rod is connected to the positive electrode of the power supply outside the furnace, and the other end is connected to the negative electrode of the power supply outside the furnace;

[0011] The porous carbon rod is heated by power supply, and circulating water is introduced into the hollow interlayer to control the temperature in the furnace, and then silicon source gas is introduced under an inert atmosphere to carry out chemical vapor deposition reaction;

[0012] (2) heating the porous carbon rod under an inert atmosphere, while circulating water is introduced into the hollow interlayer to control the temperature in the furnace, and then introducing a carbon source gas for carbon coating to obtain a deposited and coated silicon-carbon composite material rod;

[0013] (3) taking out the deposited and coated silicon-carbon composite material rod, crushing, screening, and grinding to obtain silicon-carbon composite material powder;

[0014] (4) Adding the silicon-carbon composite material powder into a fluidized bed reactor, heating it under an inert atmosphere, and then introducing a carbon source gas for secondary carbon coating to obtain the above-mentioned silicon-carbon negative electrode material.

[0015] The beneficial effects of the present invention are as follows: for a chemical vapor deposition furnace, a gas delivery elbow is provided at the bottom of the furnace body and communicated with the outside of the furnace body, and a motor is provided at the bottom of the furnace body and connected with the bottom of the elbow through a magnetic fluid sealing device to drive the elbow to rotate, thereby ensuring uniform delivery of inert atmosphere, silicon source gas, and carbon source gas in the furnace body, so as to facilitate diffusion and distribution of the gas in the furnace. A hollow interlayer is provided on the outer wall of the furnace body, and circulating water is introduced to cool the furnace to control the stability of the temperature in the furnace.

[0016] The present invention presses porous carbon into a carbon rod form, connects electrodes at both ends of the carbon rod to directly heat the carbon rod body, and introduces silicon source gas to perform chemical vapor deposition reaction on the carbon rod after the carbon rod reaches a preset temperature. The advantage of using a carbon rod is that, on the one hand, the carbon rod body can be directly heated by electric current, and the heating speed is fast; on the other hand, due to the heating of the carbon rod body, the concentrated cracking and deposition of the silicon source gas on the carbon rod body can be achieved. Compared with the fluidized bed porous carbon powder deposition method, this method has more uniform deposition and higher silicon source gas conversion rate.

[0017] In addition, the CVD method can be used to decompose and deposit silicon source gas to achieve silicon atomic-level deposition, forming uniform nano-silicon (about 2-5nm), which effectively reduces the volume expansion effect of silicon; after the formed silicon-carbon material is carbon-coated, the nano-silicon is encapsulated in the pores of porous carbon, which can provide a supporting skeleton and expansion buffer space for the nano-silicon, thereby maintaining the structural stability of the silicon-carbon negative electrode material and improving the cycle life of the material.

[0018] Furthermore, the porous carbon rod is an n-type hollow body pressed from porous carbon powder, with a height of 50-100 cm, an outer diameter of the porous carbon rod of 5-10 cm, a hollow inner diameter of 1-2 cm, and a pore with a diameter of 2-20 mm on the surface of the porous carbon rod column, preferably a pore with a diameter of 5-10 mm;

[0019] Porous carbon powder includes micropores, mesopores and macropores. The pore size range of micropores and mesopores is 2-30nm, the pore size range of macropores is 2-20mm, and the specific surface area is >1500m 2 / g, preferably 1800-2000m 2 / g.

[0020] The beneficial effect of adopting the above further technical solution is: in order to ensure the uniformity of gas deposition on the porous carbon rod, the porous carbon rod needs to be punched to form a uniform macroscopic pore distribution structure on the carbon rod to ensure the circulation and uniform distribution of the gas.

[0021] Furthermore, in step (1), the porous carbon rod is heated to 400-1000°C, and circulating water is introduced into the hollow interlayer at the same time, the temperature in the furnace is controlled at 400-1000°C, and then silicon source gas is introduced at a flow rate of 1.0-3.0L / min under an inert atmosphere to carry out chemical vapor deposition reaction. The reaction time is 4-8h, and the mass ratio of the porous carbon rod to the silicon source gas is (40-70):(30-60).

[0022] Furthermore, in step (1), the rotation speed of the above-mentioned curved pipe is 10-50 revolutions per minute, the diameter of the curved pipe is 5-12 mm, and the height is 10-15 cm.

[0023] Furthermore, in step (2), the heating temperature of the porous carbon rod is changed to 600-800°C under an inert atmosphere, and circulating water is introduced into the hollow interlayer at the same time, the temperature in the furnace is controlled to be 600-800°C, and then the carbon source gas is introduced at a flow rate of 1.0-3.0L / min for carbon coating. The carbon coating time is 1-2h, and the mass ratio of the porous carbon rod to the carbon source gas is (90-95):(5-10).

[0024] Furthermore, in step (3), the deposited coated silicon-carbon composite material is crushed to a particle size of less than 5 mm, and after ball milling, the particle size of the silicon-carbon composite material powder is 5-15 μm. In step (4), the particle size of the silicon-carbon negative electrode material is 5-25 μm.

[0025] Furthermore, in step (4), the heating temperature of the fluidized bed reactor is 400-800°C, preferably 600-800°C, and then the carbon source gas is introduced at a flow rate of 0.5-1.5L / min for secondary carbon coating. The carbon coating time is 1-2h, and the mass ratio of the silicon-carbon composite material powder and the carbon source gas is (96-99):(1-4).

[0026] Furthermore, the inert atmosphere is a combination of one or more of nitrogen, argon or helium, and the flow rate is 10-30 L / min;

[0027] The silicon source gas is one or more of silane, hexachlorodisilane, trichlorosilane, dichlorosilane, chloromethyltrichlorosilane, trimethylchlorosilane, chloromethyltrichlorosilane, dichloromethyldichlorosilane, trichloromethylchlorosilane, trimethylchlorosilane, methyldichlorosilane, ethyldichlorosilane or propyldichlorosilane.

[0028] The carbon source gas is one or more of methane, acetylene, ethane, ethylene, propane, propylene, propyne, butane or isobutane.

[0029] The present invention also provides a silicon-carbon negative electrode material prepared by the above method.

[0030] The present invention also provides an application of the silicon-carbon negative electrode material in a lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall structure of the chemical vapor deposition furnace of the present invention.

[0032] Figure 2 This is a schematic diagram of the connection between the motor in the furnace body and the bent pipe through a magnetic fluid sealing device.

[0033] Among them, 1-furnace body, 2-bend pipe, 3-motor, 4-magnetic fluid sealing device, 5-hollow interlayer, 6-circulating water outlet, 7-circulating water inlet, 8-exhaust gas outlet, 9-porous carbon rod, 10-positive electrode, 11-negative electrode. DETAILED DESCRIPTION

[0034] 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.

[0035] Example 1

[0036] The method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0037] (1) Loading the porous carbon rod 9 into a chemical vapor deposition furnace;

[0038] The chemical vapor deposition furnace comprises: a furnace body 1, a gas delivery elbow 2 is provided at the bottom of the furnace body 1 and is connected to the outside of the furnace body 1, the elbow 2 has a diameter of 10 mm and a height of 12 cm, the elbow 2 comprises a lower elbow 2 vertical section and an upper elbow 2 horizontal section which are connected to each other, a motor 3 is provided at the bottom of the furnace body 1 and is connected to the bottom of the elbow 2 through a magnetic fluid sealing device 4 to drive the elbow 2 to rotate, an external gas source is connected to the magnetic fluid sealing device 4 to supply gas to the elbow 2, and the rotation speed of the elbow 2 is 30 revolutions per minute, a hollow interlayer 5 is provided on the outer wall of the furnace body 1, a circulating water inlet 7 is provided on one side of the hollow interlayer 5, and a circulating water outlet 6 is provided on the other side, and an exhaust gas outlet 8 is provided on the top of the furnace body 1;

[0039] One end of the porous carbon rod 9 is connected to the positive electrode 10 of the power supply outside the furnace body 1, and the other end is connected to the negative electrode 11 of the power supply outside the furnace body 1; the porous carbon rod 9 is an n-type hollow body pressed by porous carbon powder, with a height of 80 cm, an outer diameter of the porous carbon rod 9 of 7 cm, a hollow inner diameter of 1 cm, and a pore with a diameter of 5 mm on the surface of the porous carbon rod 9; the porous carbon powder includes micropores, mesopores and macropores, the pore size range of the micropores and mesopores is 2-30 nm, and the specific surface area is greater than 1500 m 2 / g.

[0040] The porous carbon rod 9 is heated to 400° C. by using a power supply, and circulating water is introduced into the hollow interlayer 5 at the same time, and the temperature in the furnace is controlled to be 400° C. Then, silane gas is introduced at a flow rate of 1.0 L / min under a nitrogen atmosphere to carry out a chemical vapor deposition reaction. The reaction time is 8 hours, and the mass ratio of the porous carbon rod 9 to the silane gas is 70:30. In this embodiment, the flow rate of the nitrogen atmosphere in each step is 10 L / min;

[0041] (2) heating the porous carbon rod 9 to 600° C. in a nitrogen atmosphere, while circulating water is introduced into the hollow interlayer 5, controlling the temperature in the furnace to be 600° C., and then introducing acetylene gas at a flow rate of 1.0 L / min for carbon coating. The carbon coating time is 2 h, and the mass ratio of the porous carbon rod 9 to the acetylene gas is 95:5, to obtain a deposited and coated silicon-carbon composite material rod;

[0042] (3) taking out the deposited coated silicon-carbon composite material rod, crushing and screening it to a particle size of less than 5 mm, and grinding it to obtain a silicon-carbon composite material powder with a particle size of 5-15 μm;

[0043] (4) The silicon-carbon composite material powder is added to a fluidized bed reactor and heated under a nitrogen atmosphere at a heating temperature of 600°C. Then, acetylene gas is introduced at a flow rate of 0.5 L / min for secondary carbon coating. The carbon coating time is 2 h. The mass ratio of the silicon-carbon composite material powder and acetylene gas is 96:4, and a silicon-carbon negative electrode material with a particle size of 5-25 μm is obtained.

[0044] Example 2

[0045] The method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0046] (1) Loading the porous carbon rod 9 into a chemical vapor deposition furnace;

[0047] The chemical vapor deposition furnace comprises: a furnace body 1, a gas delivery elbow 2 is provided at the bottom of the furnace body 1 and is connected to the outside of the furnace body 1, the elbow 2 has a diameter of 10 mm and a height of 12 cm, the elbow 2 comprises a lower elbow 2 vertical section and an upper elbow 2 horizontal section which are connected to each other, a motor 3 is provided at the bottom of the furnace body 1 and is connected to the bottom of the elbow 2 through a magnetic fluid sealing device 4 to drive the elbow 2 to rotate, an external gas source is connected to the magnetic fluid sealing device 4 to supply gas to the elbow 2, and the rotation speed of the elbow 2 is 30 revolutions per minute, a hollow interlayer 5 is provided on the outer wall of the furnace body 1, a circulating water inlet 7 is provided on one side of the hollow interlayer 5, and a circulating water outlet 6 is provided on the other side, and an exhaust gas outlet 8 is provided on the top of the furnace body 1;

[0048] One end of the porous carbon rod 9 is connected to the positive electrode 10 of the power supply outside the furnace body 1, and the other end is connected to the negative electrode 11 of the power supply outside the furnace body 1; the porous carbon rod 9 is an n-type hollow body pressed by porous carbon powder, with a height of 80 cm, an outer diameter of the porous carbon rod 9 of 7 cm, a hollow inner diameter of 1 cm, and a pore with a diameter of 5 mm on the surface of the porous carbon rod 9; the porous carbon powder includes micropores, mesopores and macropores, the pore size range of the micropores and mesopores is 2-30 nm, and the specific surface area is greater than 1500 m 2 / g.

[0049] The porous carbon rod 9 is heated to 600° C. by using a power supply, and circulating water is introduced into the hollow interlayer 5 at the same time, and the temperature in the furnace is controlled to be 600° C. Then, silane gas is introduced at a flow rate of 2.0 L / min under a nitrogen atmosphere to carry out a chemical vapor deposition reaction. The reaction time is 5 h, and the mass ratio of the porous carbon rod 9 to the silane gas is 60:40. In this embodiment, the flow rate of the nitrogen atmosphere in each step is 20 L / min;

[0050] (2) heating the porous carbon rod 9 to 600° C. in a nitrogen atmosphere, while circulating water is introduced into the hollow interlayer 5, controlling the temperature in the furnace to be 600° C., and then introducing acetylene gas at a flow rate of 1.0 L / min for carbon coating. The carbon coating time is 2 h, and the mass ratio of the porous carbon rod 9 to the acetylene gas is 95:5, to obtain a deposited and coated silicon-carbon composite material rod;

[0051] (3) taking out the deposited coated silicon-carbon composite material rod, crushing and screening it to a particle size of less than 5 mm, and grinding it to obtain a silicon-carbon composite material powder with a particle size of 5-15 μm;

[0052] (4) The silicon-carbon composite material powder is added to a fluidized bed reactor and heated under a nitrogen atmosphere at a heating temperature of 600°C. Then, acetylene gas is introduced at a flow rate of 0.5 L / min for secondary carbon coating. The carbon coating time is 2 h. The mass ratio of the silicon-carbon composite material powder and acetylene gas is 97:3, and a silicon-carbon negative electrode material with a particle size of 5-25 μm is obtained.

[0053] Example 3

[0054] The method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0055] (1) Loading the porous carbon rod 9 into a chemical vapor deposition furnace;

[0056] The chemical vapor deposition furnace comprises: a furnace body 1, a gas delivery elbow 2 is provided at the bottom of the furnace body 1 and is connected to the outside of the furnace body 1, the elbow 2 has a diameter of 10 mm and a height of 12 cm, the elbow 2 comprises a lower elbow 2 vertical section and an upper elbow 2 horizontal section which are connected to each other, a motor 3 is provided at the bottom of the furnace body 1 and is connected to the bottom of the elbow 2 through a magnetic fluid sealing device 4 to drive the elbow 2 to rotate, an external gas source is connected to the magnetic fluid sealing device 4 to supply gas to the elbow 2, and the rotation speed of the elbow 2 is 30 revolutions per minute, a hollow interlayer 5 is provided on the outer wall of the furnace body 1, a circulating water inlet 7 is provided on one side of the hollow interlayer 5, and a circulating water outlet 6 is provided on the other side, and an exhaust gas outlet 8 is provided on the top of the furnace body 1;

[0057] One end of the porous carbon rod 9 is connected to the positive electrode 10 of the power supply outside the furnace body 1, and the other end is connected to the negative electrode 11 of the power supply outside the furnace body 1; the porous carbon rod 9 is an n-type hollow body pressed by porous carbon powder, with a height of 80 cm, an outer diameter of the porous carbon rod 9 of 7 cm, a hollow inner diameter of 1 cm, and a pore with a diameter of 5 mm on the surface of the porous carbon rod 9; the porous carbon powder includes micropores, mesopores and macropores, the pore size range of the micropores and mesopores is 2-30 nm, and the specific surface area is greater than 1500 m 2 / g.

[0058] The porous carbon rod 9 is heated to 800° C. by using a power supply, and circulating water is introduced into the hollow interlayer 5 at the same time, and the temperature in the furnace is controlled to be 800° C. Then, silane gas is introduced at a flow rate of 3.0 L / min under a nitrogen atmosphere to carry out a chemical vapor deposition reaction. The purge reaction time is 4 h, and the mass ratio of the porous carbon rod 9 to the silane gas is 45:55. In this embodiment, the flow rate of the nitrogen atmosphere in each step is 30 L / min;

[0059] (2) heating the porous carbon rod 9 to 800° C. in a nitrogen atmosphere, while circulating water is introduced into the hollow interlayer 5, controlling the temperature in the furnace to 800° C., and then introducing acetylene gas at a flow rate of 2.0 L / min for carbon coating. The carbon coating time is 1.5 h, and the mass ratio of the porous carbon rod 9 to the acetylene gas is 92:8, to obtain a deposited and coated silicon-carbon composite material rod;

[0060] (3) taking out the deposited coated silicon-carbon composite material rod, crushing and screening it to a particle size of less than 5 mm, and grinding it to obtain a silicon-carbon composite material powder with a particle size of 5-15 μm;

[0061] (4) The silicon-carbon composite material powder is added to a fluidized bed reactor and heated under a nitrogen atmosphere at a heating temperature of 700°C. Then, acetylene gas is introduced at a flow rate of 1.5 L / min for secondary carbon coating. The carbon coating time is 1 h. The mass ratio of the silicon-carbon composite material powder and acetylene gas is 98:2, and a silicon-carbon negative electrode material with a particle size of 5-25 μm is obtained.

[0062] Comparative Example 1

[0063] The method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0064] (1) Loading the porous carbon rod 9 into a chemical vapor deposition furnace;

[0065] The chemical vapor deposition furnace includes: a furnace body 1, a gas delivery elbow 2 is provided at the bottom of the furnace body 1 and is connected to the outside of the furnace body 1, the elbow 2 has a diameter of 10 mm and a height of 12 cm, the elbow 2 includes a lower elbow 2 vertical section and an upper elbow 2 horizontal section that are connected to each other, a motor 3 is provided at the bottom of the furnace body 1 and is connected to the bottom of the elbow 2 through a magnetic fluid sealing device 4 to drive the elbow 2 to rotate, and an external gas source is connected to the magnetic fluid sealing device 4 to supply gas to the elbow 2. The rotation speed of the elbow 2 is 30 revolutions per minute, a hollow interlayer 5 is provided on the outer wall of the furnace body 1, a circulating water inlet 7 is provided on one side of the hollow interlayer 5, and a circulating water outlet 6 is provided on the other side, and an exhaust gas outlet 8 is provided at the top of the furnace body 1;

[0066] One end of the porous carbon rod 9 is connected to the positive electrode 10 of the power supply outside the furnace body 1, and the other end is connected to the negative electrode 11 of the power supply outside the furnace body 1; the porous carbon rod 9 is an n-type hollow body pressed by porous carbon powder, with a height of 80 cm, an outer diameter of the porous carbon rod 9 of 7 cm, a hollow inner diameter of 1 cm, and a pore with a diameter of 5 mm on the surface of the porous carbon rod 9; the porous carbon powder includes micropores, mesopores and macropores, the pore size range of the micropores and mesopores is 2-30 nm, and the specific surface area is greater than 1500 m 2 / g.

[0067] The porous carbon rod 9 is heated to 800° C. by using a power supply, and circulating water is introduced into the hollow interlayer 5 at the same time, and the temperature in the furnace is controlled to be 800° C. Then, silane gas is introduced at a flow rate of 4.0 L / min under a nitrogen atmosphere to carry out a chemical vapor deposition reaction. The reaction time is 4 hours, and the mass ratio of the porous carbon rod 9 to the silane gas is 30:70. In this embodiment, the flow rate of the nitrogen atmosphere in each step is 30 L / min;

[0068] (2) heating the porous carbon rod 9 to 800° C. in a nitrogen atmosphere, while circulating water is introduced into the hollow interlayer 5, controlling the temperature in the furnace to 800° C., and then introducing acetylene gas at a flow rate of 2.0 L / min for carbon coating. The carbon coating time is 1.5 h, and the mass ratio of the porous carbon rod 9 to the acetylene gas is 92:8, to obtain a deposited and coated silicon-carbon composite material rod;

[0069] (3) taking out the deposited coated silicon-carbon composite material rod, crushing and screening it to a particle size of less than 5 mm, and grinding it to obtain a silicon-carbon composite material powder with a particle size of 5-15 μm;

[0070] (4) The silicon-carbon composite material powder is added to a fluidized bed reactor and heated under a nitrogen atmosphere at a heating temperature of 700°C. Then, acetylene gas is introduced at a flow rate of 1.5 L / min for secondary carbon coating. The carbon coating time is 1 hour. The mass ratio of the silicon-carbon composite material powder and acetylene gas is 99:1, and a silicon-carbon negative electrode material with a particle size of 5-25 μm is obtained.

[0071] Comparative Example 2

[0072] The method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0073] (1) Loading the porous carbon rod 9 into a chemical vapor deposition furnace;

[0074] The chemical vapor deposition furnace includes: a furnace body 1, a gas delivery elbow 2 is provided at the bottom of the furnace body 1 and is connected to the outside of the furnace body 1, the elbow 2 has a diameter of 10 mm and a height of 12 cm, the elbow 2 includes a lower elbow 2 vertical section and an upper elbow 2 horizontal section that are connected to each other, a motor 3 is provided at the bottom of the furnace body 1 and is connected to the bottom of the elbow 2 through a magnetic fluid sealing device 4 to drive the elbow 2 to rotate, and an external gas source is connected to the magnetic fluid sealing device 4 to supply gas to the elbow 2. The rotation speed of the elbow 2 is 30 revolutions per minute, a hollow interlayer 5 is provided on the outer wall of the furnace body 1, a circulating water inlet 7 is provided on one side of the hollow interlayer 5, and a circulating water outlet 6 is provided on the other side, and an exhaust gas outlet 8 is provided at the top of the furnace body 1;

[0075] One end of the porous carbon rod 9 is connected to the positive electrode 10 of the power supply outside the furnace body 1, and the other end is connected to the negative electrode 11 of the power supply outside the furnace body 1; the porous carbon rod 9 is an n-type hollow body pressed by porous carbon powder, with a height of 80 cm, an outer diameter of the porous carbon rod 9 of 7 cm, a hollow inner diameter of 1 cm, and a pore with a diameter of 5 mm on the surface of the porous carbon rod 9; the porous carbon powder includes micropores, mesopores and macropores, the pore size range of the micropores and mesopores is 2-30 nm, and the specific surface area is greater than 1500 m 2 / g.

[0076] The porous carbon rod 9 is heated to 800° C. by using a power supply, and circulating water is introduced into the hollow interlayer 5 at the same time, and the temperature in the furnace is controlled to be 800° C. Then, silane gas is introduced at a flow rate of 1.0 L / min under a nitrogen atmosphere to carry out a chemical vapor deposition reaction. The purge reaction time is 5.5 h, and the mass ratio of the porous carbon rod 9 to the silane gas is 80:20. In this embodiment, the flow rate of the nitrogen atmosphere in each step is 30 L / min;

[0077] (2) heating the porous carbon rod 9 to 800° C. in a nitrogen atmosphere, while circulating water is introduced into the hollow interlayer 5, controlling the temperature in the furnace to be 800° C., and then introducing acetylene gas at a flow rate of 2.0 L / min for carbon coating. The carbon coating time is 1.5 h, and the mass ratio of the porous carbon rod 9 to the acetylene gas is 92:8, to obtain a deposited and coated silicon-carbon composite material rod;

[0078] (3) taking out the deposited coated silicon-carbon composite material rod, crushing and screening it to a particle size of less than 5 mm, and grinding it to obtain a silicon-carbon composite material powder with a particle size of 5-15 μm;

[0079] (4) The silicon-carbon composite material powder is added to a fluidized bed reactor and heated under a nitrogen atmosphere at a heating temperature of 700°C. Then, acetylene gas is introduced at a flow rate of 1.5 L / min for secondary carbon coating. The carbon coating time is 1 h. The mass ratio of the silicon-carbon composite material powder and acetylene gas is 98:2, and a silicon-carbon negative electrode material with a particle size of 5-25 μm is obtained.

[0080] The above embodiment and comparative example 3 (artificial graphite) and comparative example 4 (pure nano silicon powder) were used as negative electrode active materials for performance testing and comparison. The performance testing method is as follows:

[0081] The negative electrode material, conductive agent (acetylene black), and binder (polyacrylic acid PAA) were weighed in a mass ratio of 91:6:3, and these substances were stirred into electrode slurry, which were then coated on the copper foil current collector respectively with a coating thickness of 200 μm. After drying and roller pressing, the negative electrode sheet was prepared. Metal lithium was used as the counter electrode, and 1 mol / L LiPF6 EC (ethylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) (EC:DMC:EMC volume ratio of 1:1:1) was used as the electrolyte. The button half-cell was assembled for electrochemical testing.

[0082] Table 1 Performance test results

[0083]

[0084] The silicon-carbon negative electrode material prepared by the present invention has a significantly higher discharge capacity than the traditional graphite negative electrode material, and has excellent first cycle efficiency performance. The material can be applied to lithium-ion batteries by completely replacing the graphite negative electrode or partially replacing and blending, which can effectively improve the energy density of the battery.

[0085] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The steps include: (1) Loading the porous carbon rod into a chemical vapor deposition furnace; The chemical vapor deposition furnace comprises: a furnace body, a gas delivery elbow is provided at the bottom of the furnace body and is connected to the outside of the furnace body, the elbow comprises a lower elbow vertical section and an upper elbow horizontal section that are connected to each other, a motor is provided at the bottom of the furnace body and is connected to the bottom of the elbow through a magnetic fluid sealing device, driving the elbow to rotate, an external gas source is connected to the magnetic fluid sealing device to supply gas to the elbow, a hollow interlayer is provided on the inner wall of the furnace body, a circulating water inlet is provided on one side of the hollow interlayer, and a circulating water outlet is provided on the other side, and an exhaust gas outlet is provided at the top of the furnace body; One end of the porous carbon rod is connected to the positive electrode of the power supply outside the furnace, and the other end is connected to the negative electrode of the power supply outside the furnace; The porous carbon rod is heated by power supply, and circulating water is introduced into the hollow interlayer to control the temperature in the furnace. Then, silicon source gas is introduced under an inert atmosphere to carry out chemical vapor deposition reaction. (2) heating the porous carbon rod under an inert atmosphere while circulating water is introduced into the hollow interlayer to control the temperature in the furnace, and then introducing a carbon source gas for carbon coating to obtain a deposited and coated silicon-carbon composite material rod; (3) taking out the deposited and coated silicon-carbon composite material rod, crushing and screening it, and grinding it to obtain silicon-carbon composite material powder; (4) Adding the silicon-carbon composite material powder into a fluidized bed reactor, heating it under an inert atmosphere, and then introducing a carbon source gas for secondary carbon coating to obtain the silicon-carbon negative electrode material.

2. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: The porous carbon rod is an n-type hollow body made by pressing porous carbon powder, with a height of 50-100 cm, an outer diameter of 5-10 cm, a hollow inner diameter of 1-2 cm, and a hole with a diameter of 2-20 mm on the surface of the porous carbon rod cylinder; Porous carbon powder includes micropores, mesopores and macropores. The pore size range of micropores and mesopores is 2-30nm, the pore size range of macropores is 2-20mm, and the specific surface area is greater than 1500m 2 / g.

3. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: In step (1), the porous carbon rod is heated to 400-1000°C, and circulating water is introduced into the hollow interlayer at the same time, and the temperature in the furnace is controlled at 400-1000°C. Then, silicon source gas is introduced at a flow rate of 1.0-3.0 L / min under an inert atmosphere to carry out chemical vapor deposition reaction. The reaction time is 4-8 hours, and the mass ratio of the porous carbon rod to the silicon source gas is (40-70): (30-60).

4. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: In step (2), the heating temperature of the porous carbon rod is changed to 600-800°C under an inert atmosphere, and circulating water is introduced into the hollow interlayer at the same time to control the temperature in the furnace to 600-800°C. Then, the carbon source gas is introduced at a flow rate of 1.0-3.0 L / min for carbon coating. The carbon coating time is 1-2 h, and the mass ratio of the porous carbon rod to the carbon source gas is (90-95):(5-10).

5. The method for preparing a silicon-carbon negative electrode material according to claim 1, characterized in that: In step (3), the deposited coated silicon-carbon composite material is crushed to a particle size of less than 5 mm, and the particle size of the silicon-carbon composite material powder obtained after ball milling is 5-15 μm. In step (4), the particle size of the silicon-carbon negative electrode material is 5-25 μm.

6. The method for preparing a silicon-carbon negative electrode material according to claim 1, characterized in that: In step (4), the heating temperature of the fluidized bed reactor is 400-800°C, and then the carbon source gas is introduced at a flow rate of 0.5-1.5 L / min for secondary carbon coating. The carbon coating time is 1-2 hours, and the mass ratio of the silicon-carbon composite material powder and the carbon source gas is (96-99): (1-4).

7. The method for preparing a silicon-carbon negative electrode material according to claim 1, characterized in that: The inert atmosphere is a combination of one or more of nitrogen, argon or helium, with an inlet flow rate of 10-30 L / min; The silicon source gas is a combination of one or more of silane, hexachlorodisilane, trichlorosilane, dichlorosilane, chloromethyltrichlorosilane, trimethylchlorosilane, chloromethyltrichlorosilane, dichloromethyldichlorosilane, trichloromethylchlorosilane, trimethylchlorosilane, methyldichlorosilane, ethyldichlorosilane or propyldichlorosilane; The carbon source gas is one or more of methane, acetylene, ethane, ethylene, propane, propylene, propyne, butane or isobutane.

8. A silicon-carbon negative electrode material prepared by the method according to any one of claims 1 to 7.

9. Use of the silicon-carbon negative electrode material according to claim 8 in a lithium-ion battery.

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