Fluidized bed preparation method of silicon-carbon composite material, silicon-carbon composite material and application

Abstract

The present invention discloses a fluidized bed preparation method of a silicon-carbon composite material, a silicon-carbon composite material and an application thereof, which at least include the following operating steps: step 1, preparing modified activated carbon: carbonizing the activated carbon under a carbonization temperature range of 500-800°C for at least 1 hour to obtain modified activated carbon; step 2, transferring the modified activated carbon to a fluidized bed device, and when the fluidized bed is in a working state, introducing a silane mixed gas into the fluidized bed, and floating the modified activated carbon by the airflow of the fluidized bed so that it is in a suspended state, thereby achieving deposition of nano-silicon in the modified activated carbon; step 3, stopping the introduction of the silane mixed gas into the fluidized bed, replacing it with a carbon source gas and a nitrogen-containing gas, raising the temperature to 700-1000°C and keeping the temperature for at least 0.5 hour to achieve carbon coating; the silicon-carbon composite material obtained by the present invention has the advantages of high production efficiency, good consistency and uniform particles, and can significantly improve the cycle performance and high-temperature storage performance of lithium-ion batteries used therein.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery material preparation, and specifically relates to a fluidized bed preparation method for a silicon-carbon composite material. The present invention also relates to a silicon-carbon composite material obtained by adopting the fluidized bed preparation method and its application. Background Art

[0002] Currently, most commercially available methods for preparing silicon-carbon composite materials use sand milling, which suffers from low efficiency and poor consistency. Silicon-carbon materials prepared using silane cracking offer advantages such as smaller silicon grains, less expansion, and excellent cycling performance. However, their porous structure leads to high impedance and significant safety risks, making them difficult to commercialize on a large scale.

[0003] The fluidized bed process has the advantages of high gas-solid mixing efficiency and strong adaptability to reaction conditions. It has been widely used in various gas-solid reaction situations. At present, there are still few application cases in the field of silicon-carbon composite material preparation. For example, although the prior patents CN111188022A and CN115663153A introduced the fluidized bed process, its effect on carbon source coating is still limited, and the circulation and high-temperature storage performance of the products still has room for improvement.

[0004] Therefore, based on the applicant's dedicated research experience in this field, we hope to seek new technical solutions to solve the above technical problems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a fluidized bed preparation method of silicon-carbon composite materials, silicon-carbon composite materials and applications, which have the advantages of high production efficiency, good consistency and uniform particles, and can significantly improve the cycle performance and high-temperature storage performance of lithium-ion batteries used therein.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A fluidized bed preparation method for a silicon-carbon composite material comprises at least the following steps:

[0008] Step 1: preparing modified activated carbon: placing the activated carbon in a carbonization device, first introducing an inert gas into the carbonization device to remove air, then introducing carbon dioxide gas into the carbonization device, and carbonizing the carbonized carbon at a temperature range of 500-800° C. for at least 1 hour to obtain modified activated carbon;

[0009] Step 2: Transfer the modified activated carbon obtained in step 1 above to a fluidized bed apparatus. While the fluidized bed is in operation, introduce a silane mixed gas into the fluidized bed, heat it to 300-500° C., and float the modified activated carbon by the airflow of the fluidized bed so that it is in a suspended state, thereby achieving deposition of nano-silicon in the modified activated carbon.

[0010] Step 3: Stop feeding the silane mixed gas into the fluidized bed, feed the carbon source gas and nitrogen-containing gas instead, raise the temperature to 700-1000° C. and keep it at that temperature for at least 0.5 hours to achieve carbon coating;

[0011] Step 4: obtaining the silicon-carbon composite material.

[0012] Preferably, in step 1, the gas flow rate of the carbon dioxide gas is in the range of 10-30 ml / min; and / or the carbonization temperature heating rate of the carbonization device is in the range of 1-10° C. / min; and / or the carbonization treatment time is 1-6 hours.

[0013] Preferably, in step 2, the silane mixed gas includes a mixed gas of SiH4 and CF3; wherein the volume ratio of SiH4:CF3 ranges from 10:1-10, preferably from 10:1-5.

[0014] Preferably, in step 2, the flow rate range of the silane mixed gas is

[0015] 100-500 ml / min, and the deposition time is 1-6 hours.

[0016] Preferably, in step 3, the volume ratio of the carbon source gas to the nitrogen-containing gas is in the range of 4:2-0.2, more preferably 4:1.5-0.5; and the total gas flow rate of the carbon source gas and the nitrogen-containing gas is 60-200 ml / min.

[0017] Preferably, in step three, the carbon source gas is selected from any one of methane, ethylene, and acetylene, or a mixture of several thereof; and the nitrogen-containing gas is selected from any one of nitrogen dioxide, nitric oxide, and ammonia, or a mixture of several thereof.

[0018] Preferably, in step 3, the insulation time is 0.5-4 hours, more preferably 0.5-2 hours.

[0019] Preferably, in step 1, the activated carbon is nanoporous carbon.

[0020] Preferably, a silicon-carbon composite material is prepared by the fluidized bed preparation method as described above.

[0021] Preferably, an application of the silicon-carbon composite material as described above is to use the silicon-carbon composite material as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0022] In this application, activated carbon is first subjected to high-temperature carbonization treatment by carbon dioxide gas to obtain modified activated carbon. The modified activated carbon is used as the raw material basis, and the modified activated carbon particles are put into a suspended fluidized state through fluidized bed technology. In this state, the gas nano-silicon particles are uniformly deposited in the modified activated carbon particles. Finally, the carbon source is cracked and coated to achieve a three-dimensional carbon coating effect on the material, ensuring that the final silicon-carbon composite material has the advantages of high production efficiency, good consistency and uniform particles. At the same time, the application also specifically uses modified activated carbon that has been carbonized as the raw material basis, and uses SiH4 and CF3 as specific silane mixed gases. While depositing nano-silicon particles, carbon is further deposited on the surface of the nano-silicon particles, further reducing the impedance, and carbon fluoride has good compatibility with the battery electrolyte, which can significantly improve the cycle performance and high-temperature storage performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flowchart of the steps for preparing a silicon-carbon composite material according to a specific embodiment of the present invention;

[0024] Figure 2 This is an SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] See Figure 1 As shown, this embodiment provides a fluidized bed preparation method for a silicon-carbon composite material, comprising the following steps:

[0026] Step 1. Preparation of modified activated carbon: Place activated carbon (specifically, nanoporous carbon that can be directly purchased on the market) in a carbonization device, first introduce inert gas into the carbonization device to exclude air, then introduce carbon dioxide gas into the carbonization device, and perform carbonization treatment under a carbonization temperature range of 500-800°C for at least 1 hour to obtain modified activated carbon; preferably, in this step one, the gas flow rate range of carbon dioxide gas is 10-30ml / min; and / or preferably, in this step one, the carbonization temperature heating rate range of the carbonization device is 1-10°C / min; and / or preferably, in this step one, the carbonization treatment time is 1-6 hours.

[0027] Step 2: Transfer the modified activated carbon obtained in the above step 1 to a fluidized bed device. When the fluidized bed is in working condition, introduce a silane mixed gas into the fluidized bed (the flow rate range is preferably 100-500 ml / min), heat it to 300-500°C, and float the modified activated carbon with the air flow of the fluidized bed to make it in a suspended state, thereby realizing the deposition of nano-silicon in the modified activated carbon, wherein the deposition time is preferably 1-6 hours; preferably, in this step 2, the silane mixed gas includes a mixed gas of SiH4 and CF3; wherein the volume ratio of SiH4:CF3 is in the range of 10:1-10, more preferably 10:1-5.

[0028] Step 3: Stop feeding the silane mixed gas into the fluidized bed and feed the carbon source gas and the nitrogen-containing gas instead, wherein the volume ratio of the carbon source gas to the nitrogen-containing gas is preferably in the range of 4:2-0.2, more preferably 4:1.5-0.5, and the total gas flow rate of the carbon source gas and the nitrogen-containing gas is preferably 60-200 ml / min; heating to a temperature condition of 700-1000° C. and keeping warm for at least 0.5 hour (the holding time is preferably 0.5-4 hours, more preferably 0.5-2 hours) to achieve carbon coating; preferably, in step 3, the carbon source gas is selected from any one or a mixture of methane, ethylene, and acetylene; the nitrogen-containing gas is selected from any one or a mixture of nitrogen dioxide, nitric oxide, and ammonia;

[0029] Step 4: Obtaining a silicon-carbon composite material.

[0030] Preferably, this embodiment provides a silicon-carbon composite material, which is prepared by the fluidized bed preparation method as described above in this embodiment.

[0031] Preferably, this embodiment further proposes an application of a silicon-carbon composite material, and the silicon-carbon composite material provided by this embodiment is used as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0032] Those skilled in the art may carry out specific applications according to actual needs during implementation. The specific application methods should belong to the conventional technical means of those skilled in the art. Therefore, this embodiment does not impose any special limitation on its application method.

[0033] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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 making creative efforts should fall within the scope of protection of the present invention.

[0034] Based on the above-described embodiments, the present application further proposes the following specific embodiments:

[0035] Example 1: In this example 1, a silicon-carbon composite material was prepared according to the following steps:

[0036] Step 1, preparation of modified activated carbon: activated carbon (specifically, nanoporous carbon) is transferred to a tubular furnace (as a carbonization device), argon inert gas is first introduced to remove the air in the tube, and then carbon dioxide gas is introduced at a gas flow rate of 20 ml / min, a heating rate of 5°C / min, a carbonization temperature condition set at 600°C, and a carbonization time of 3 hours to obtain a modified activated carbon material;

[0037] Step 2: Transfer the modified activated carbon obtained in the above step 1 to the cavity of the fluidized bed equipment. The fluidized bed equipment is in the working state. First, a silane mixed gas (the volume ratio of SiH4:CF3 in the silane mixed gas is 10:3, and the flow rate is set to 300 ml / min) is introduced through the inlet at the lower end of the fluidized bed equipment. Heat it to 400°C, and float the modified activated carbon with the air flow of the fluidized bed to make it in a suspended state, thereby achieving the deposition of nano-silicon in the modified activated carbon. The deposition time is 3 hours;

[0038] Step 3: Stop feeding the silane mixed gas into the fluidized bed and replace it with methane gas and nitrogen dioxide gas, wherein the volume ratio of methane gas to nitrogen dioxide gas is 4:1, the total gas flow rate is set to 100 ml / min, and the temperature is raised to 800° C. and kept for 1 hour to achieve a three-dimensional carbon coating effect on the material;

[0039] Step 4: Obtain the silicon-carbon composite material of Example 1.

[0040] The present application conducted a SEM (scanning electron microscope) morphology test on the silicon-carbon composite material obtained in Example 1, and the test results are as follows: Figure 2 As shown, we pass Figure 2 It can be seen that the material presents a spherical structure, and the particle size distribution of the material is uniform and reasonable, and the particle size D50 is between 5-10 μm.

[0041] Example 2: In this example 2, a silicon-carbon composite material was prepared according to the following steps:

[0042] Step 1, preparation of modified activated carbon: activated carbon (specifically, nanoporous carbon) is transferred to a tubular furnace (as a carbonization device), argon inert gas is first introduced to remove the air in the tube, and then carbon dioxide gas is introduced at a gas flow rate of 20 ml / min, a heating rate of 5°C / min, a carbonization temperature condition set at 600°C, and a carbonization time of 3 hours to obtain a modified activated carbon material;

[0043] Step 2: Transfer the modified activated carbon obtained in the above step 1 to the cavity of the fluidized bed equipment. The fluidized bed equipment is in the working state. First, a silane mixed gas (the volume ratio of SiH4:CF3 in the silane mixed gas is 10:1, and the flow rate is set to 100 ml / min) is introduced through the inlet at the lower end of the fluidized bed equipment. The mixture is heated to 300°C, and the modified activated carbon is floated by the air flow of the fluidized bed to make it in a suspended state, thereby achieving the deposition of nano-silicon in the modified activated carbon. The deposition time is 6 hours;

[0044] Step 3: Stop feeding the silane mixed gas into the fluidized bed and replace it with acetylene gas and ammonia gas, wherein the volume ratio of acetylene gas to ammonia gas is 4:1.5, the total gas flow rate is set to 60 ml / min, and the temperature is raised to 700° C. and kept at this temperature for 2 hours to achieve a three-dimensional carbon coating effect on the material;

[0045] Step 4: Obtain the silicon-carbon composite material of Example 2.

[0046] Example 3: In this Example 3, a silicon-carbon composite material was prepared according to the following steps:

[0047] Step 1, preparation of modified activated carbon: activated carbon (specifically, nanoporous carbon) is transferred to a tubular furnace (as a carbonization device), argon inert gas is first introduced to remove the air in the tube, and then carbon dioxide gas is introduced at a gas flow rate of 20 ml / min, a heating rate of 5°C / min, a carbonization temperature condition set at 600°C, and a carbonization time of 3 hours to obtain a modified activated carbon material;

[0048] Step 2: Transfer the modified activated carbon obtained in the above step 1 to the cavity of the fluidized bed equipment. The fluidized bed equipment is in the working state. First, a silane mixed gas (the volume ratio of SiH4:CF3 in the silane mixed gas is 10:5, and the flow rate is set to 500ml / min) is introduced through the inlet at the lower end of the fluidized bed equipment. The mixture is heated to 500°C, and the modified activated carbon is floated by the air flow of the fluidized bed to make it in a suspended state, thereby achieving the deposition of nano-silicon in the modified activated carbon. The deposition time is 1 hour;

[0049] Step 3: Stop feeding the silane mixed gas into the fluidized bed and replace it with ethylene gas and nitric oxide gas, wherein the volume ratio of ethylene gas to nitric oxide gas is 4:0.5, the total gas flow rate is set to 200 ml / min, and the temperature is raised to 1000° C. and kept for 0.5 hour to achieve a three-dimensional carbon coating effect on the material;

[0050] Step 4: Obtain the silicon-carbon composite material of Example 3.

[0051] Example 4: The remaining technical solutions of Example 4 are the same as those of Example 1, except that step 3 of Example 4 adopts the following solution:

[0052] Stop feeding the silane mixed gas into the fluidized bed and switch to methane gas (flow rate of 100 ml / min), raise the temperature to 800°C and keep it for 1 hour to achieve a three-dimensional carbon coating effect on the material.

[0053] Comparative Example 1: In this comparative example 1, the nanoporous carbon (the same as in Example 1) was transferred to a tubular furnace, the tubular furnace was evacuated, and silane gas was introduced, and the temperature was heated to 500°C and kept warm for 1 hour; then the silane gas was stopped, and methane gas was introduced instead, and the temperature was heated to 700°C and kept warm for 3 hours, and then the temperature was cooled to room temperature in an argon atmosphere to obtain the silicon-carbon composite material of comparative example 1.

[0054] Comparative Example 2: In this Comparative Example 2, the porous carbon (the same as Example 1) is transferred to a tubular furnace, the tubular furnace is evacuated, and a SiH4 silane mixed gas is introduced (SiH4:CF3 in the silane mixed gas is 10:3, and the introduction flow rate is set to 300 ml / min), and the temperature is heated to 500°C and kept warm for 1 hour. After that, the silane gas is stopped and replaced with methane gas and nitrogen dioxide gas (the volume ratio of methane gas to nitrogen dioxide gas is 4:1, and the total gas flow rate is set to 100 ml / min). The temperature is raised to 800°C and kept warm for 1 hour to achieve carbon coating of the material, thereby obtaining the silicon-carbon composite material of Comparative Example 2.

[0055] Comparative Example 3: In this Comparative Example 3, the porous carbon used in Example 1 is transferred to the cavity of a fluidized bed device, and the fluidized bed device is in the working open state. First, a silane mixed gas is introduced through the inlet located at the lower end of the fluidized bed device (the volume ratio of SiH4:CF3 in the silane mixed gas is 10:3, and the introduction flow rate is set to 300ml / min), and heated to 400°C. The modified activated carbon is floated by the air flow of the fluidized bed to make it in a suspended state, thereby realizing the deposition of nano-silicon in the porous carbon, and the deposition time is 3 hours; the introduction of the silane mixed gas into the fluidized bed is stopped, and methane gas and nitrogen dioxide gas are introduced instead, wherein the volume ratio of methane gas to nitrogen dioxide gas is 4:1, and the total gas flow rate is set to 100ml / min. The temperature is raised to 800°C and kept warm for 1 hour to achieve the carbon coating effect on the material; the silicon-carbon composite material of Comparative Example 3 is obtained.

[0056] In order to compare and verify the effects of the above examples and comparative examples, the present application conducted the following physical and chemical properties and button battery tests on the silicon-carbon composite materials obtained in the above examples 1-4 and comparative examples 1-3:

[0057] 1). According to the method in the national standard GB / T 38823-2020 "Silicon Carbon", the specific surface area, tap density, and carbon content of each silicon-carbon composite material obtained in Examples 1-4 and Comparative Examples 1-3 were respectively measured, and the electrical conductivity of each silicon-carbon composite material was tested using a four-probe tester, and the silicon grains of each silicon-carbon composite material were tested by XRD; the test results are shown in Table 1 below.

[0058] 2). Button battery test:

[0059] The silicon-carbon composite materials obtained in Examples 1-4 and Comparative Examples 1-3 were used as active materials for the negative electrode plates of batteries and were respectively prepared and assembled into seven button batteries. The specific preparation process of each button battery was as follows:

[0060] Preparation of battery negative electrode sheets: A binder, a conductive agent, and a solvent were added to the corresponding silicon-carbon composite materials (as the active material of the battery negative electrode sheets) of Examples 1-4 and Comparative Examples 1-3, respectively, and the mixture was stirred to form a slurry. The slurry was then coated on a copper foil, and dried and rolled to obtain the battery negative electrode sheets. LA132 binder was used as the binder, SP (conductive carbon black) was used as the conductive agent, and NMP was used as the solvent. The ratios of the mixture were: silicon-carbon composite material: SP: LA132: NMP = 95 g: 1 g: 4 g: 220 mL.

[0061] Preparation of button cells: The electrolyte used was a LiPF6 solution, wherein the concentration of LiPF6 was 1 mol / L, and the solvent used was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a weight ratio of 1:1; a metal lithium sheet was used as the counter electrode, and a polypropylene (PP) film was used as the separator. The simulated battery was assembled in an argon-filled glove box, and the electrochemical performance was measured on a Wuhan Blue Electric CT2001A battery tester under the following test conditions: the charge and discharge voltage range was 0.005 V to 2.0 V, and the charge and discharge rate was 0.1C; a full-charge expansion test was also conducted: the thickness D1 of the negative electrode sheet of the button cell after rolling was measured, and then the negative electrode sheet of the button cell was dissected when it was fully charged to 100% SOC, and the thickness D2 of the negative electrode sheet was measured, and then the full-charge expansion rate was calculated as (D2-D1) / D1*100%; the test results are shown in Table 1 below.

[0062] Table 1

[0063]

[0064] It can be seen from Table 1 above that the button batteries made of the silicon-carbon composite materials provided in Examples 1-4 of the present application have significantly better first discharge specific capacity and first efficiency than comparative examples 1-3; the reason may be that the present application uses modified activated carbon that has been carbonized at high temperature, and at the same time uses a silane mixed gas composed of SiH4 and CF3 to deposit carbon on the surface of nano-silicon particles, reduce impedance, and improve specific capacity. At the same time, fluidized bed technology is used to achieve three-dimensional and uniform carbon coating on the surface of nano-silicon, thereby improving the powder conductivity of the material.

[0065] 3).Soft pack battery test:

[0066] The silicon-carbon composite materials obtained in Examples 1-4 and Comparative Examples 1-3 were doped with 90% artificial graphite as negative electrode materials (i.e., negative electrode sheets), and the ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 5Ah soft-pack batteries were assembled using O2 as the positive electrode material, electrolyte, and separator. The separator of the soft-pack battery was Celegard 2400, and the electrolyte was LiPF6 solution. The solvent of the LiPF6 solution was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 was 1.3 mol / L. The following performance tests were conducted on each soft-pack battery:

[0067] a. Liquid absorption capacity test: Use a 1mL burette and draw VmL of electrolyte. Add one drop of electrolyte to the surface of the negative electrode and measure the time until the electrolyte is completely absorbed. Record the time t and calculate the liquid absorption rate V / t of the negative electrode. The test results are shown in Table 2.

[0068] b. Liquid retention rate test: Calculate the theoretical liquid absorption of the negative electrode m1 according to the electrode parameters, and weigh the weight of the negative electrode m2. Then, place the negative electrode in the electrolyte and soak it for 24 hours. Weigh the weight of the negative electrode m3 and calculate the liquid absorption of the negative electrode m3-m2. Calculate according to the following formula:

[0069] Liquid retention rate = (m3-m2)*100% / m1; the test results are shown in Table 2 below.

[0070] Table 2

[0071] Liquid absorption speed (V / t) Fluid retention rate Example 1 54 91.4％ Example 2 58 90.1％ Example 3 63 89.9％ Example 4 59 90.0％ Comparative Example 1 98 85.9％ Comparative Example 2 123 84.7％ Comparative Example 3 84 89.7％

[0072] It can be seen from Table 2 above that the liquid absorption and liquid retention capabilities of the silicon-carbon composite materials provided in Examples 1-4 of the present application are significantly higher than those of Comparative Examples 1-3.

[0073] c. Rate and cycle performance: Cycle performance test and rate test were performed on each soft pack battery. The test conditions of the cycle performance test were: charge and discharge voltage range of 2.5~4.2V, temperature of 25±3.0℃, charge and discharge rate of 1.0C / 1.0C, and cycle number of 500 times; the test conditions of the rate test were: testing the constant current ratio of the material under 2C conditions; the test results are shown in Table 3 below.

[0074] Table 3

[0075]

[0076]

[0077] As can be seen from Table 3 above, the soft-pack lithium-ion batteries prepared using the silicon-carbon composite materials provided in Examples 1-4 of the present application perform better than those in Comparative Examples 1-3 in terms of rate performance and cycle performance. The main reason for this may be that the silicon-carbon composite materials provided in the examples of the present application have excellent electronic conductivity and high specific surface area, which ultimately makes the soft-pack lithium-ion batteries have excellent battery performance.

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0079] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A fluidized bed preparation method for a silicon-carbon composite material, characterized in that: At least the following steps are included: Step 1: preparing modified activated carbon: placing the activated carbon in a carbonization device, first introducing an inert gas into the carbonization device to remove air, then introducing carbon dioxide gas into the carbonization device, and carbonizing the carbonized carbon at a temperature range of 500-800° C. for at least 1 hour to obtain modified activated carbon; In the step 1, the activated carbon is nanoporous carbon; the gas flow rate of the carbon dioxide gas is in the range of 10-30 ml / min; the carbonization temperature of the carbonization device is in the range of 1-10° C. / min; and the carbonization treatment time is 1-6 hours; Step 2: Transfer the modified activated carbon obtained in step 1 to a fluidized bed apparatus. While the fluidized bed is in operation, introduce a silane mixed gas into the fluidized bed, heat the fluidized bed to 300-500° C., and float the modified activated carbon by the airflow of the fluidized bed so that the modified activated carbon is in a suspended state, thereby achieving deposition of nano-silicon in the modified activated carbon. In step 2, the silane mixed gas comprises a mixed gas of SiH4 and CF4, wherein the volume ratio of SiH4:CF4 is in the range of 10:1-10. Step 3: Stop feeding the silane mixed gas into the fluidized bed, feed the carbon source gas and nitrogen-containing gas instead, raise the temperature to 700-1000° C. and keep it at that temperature for at least 0.5 hours to achieve carbon coating; Step 4: obtaining the silicon-carbon composite material.

2. The fluidized bed preparation method of silicon-carbon composite material according to claim 1, characterized in that: In the step 2, the silane mixed gas includes a mixed gas of SiH4 and CF4; wherein the volume ratio of SiH4:CF4 ranges from 10:1 to 5.

3. The fluidized bed preparation method of the silicon-carbon composite material according to claim 1 or 2, characterized in that: In the step 2, the flow rate of the silane mixed gas is in the range of 100-500 ml / min, and the deposition time is 1-6 hours.

4. The fluidized bed preparation method of silicon-carbon composite material according to claim 1, characterized in that: In the step 3, the volume ratio of the carbon source gas to the nitrogen-containing gas is in the range of 4:0.2-2; and the total gas flow rate of the carbon source gas and the nitrogen-containing gas is in the range of 60-200 ml / min.

5. The fluidized bed preparation method of silicon-carbon composite material according to claim 1, characterized in that: In the step 3, the volume ratio of the carbon source gas to the nitrogen-containing gas is in the range of 4:0.5-1.

5.

6. The fluidized bed preparation method of the silicon-carbon composite material according to claim 1 or 4, characterized in that: In step three, the carbon source gas is selected from any one of methane, ethylene, and acetylene, or a mixture of several thereof; and the nitrogen-containing gas is selected from any one of nitrogen dioxide, nitric oxide, and ammonia, or a mixture of several thereof.

7. The fluidized bed preparation method of silicon-carbon composite material according to claim 1, characterized in that: In the step 3, the insulation time is 0.5-4 hours.

8. The fluidized bed preparation method of silicon-carbon composite material according to claim 1, characterized in that: In the step 3, the insulation time is 0.5-2 hours.

9. A silicon-carbon composite material, characterized in that: The fluidized bed preparation method according to any one of claims 1 to 8 is used for preparation.

10. An application of the silicon-carbon composite material according to claim 9, characterized in that: The silicon-carbon composite material is used as an active material raw material for preparing battery pole pieces.

11. The use of the silicon-carbon composite material according to claim 10, characterized in that: The silicon-carbon composite material is used as the active material raw material of the negative electrode plate of a lithium-ion battery.

Images