In-situ growth single-walled carbon nanotube coated silicon-carbon composite material and preparation method and application thereof

Abstract

The invention discloses an in-situ growth single-walled carbon nanotube coated silicon-carbon composite material as well as a preparation method and application of the in-situ growth single-walled carbon nanotube coated silicon-carbon composite material. The preparation method comprises the following steps: carrying out a carbon-coated silicon reaction on a suspension containing nano silicon and a catalyst system and a carbon source reaction gas in a low-temperature reaction zone, and then inputting the obtained material into a high-temperature reaction zone for a catalytic cracking reaction to prepare the single-walled carbon nanotube-coated silicon-carbon composite material, wherein the catalyst system comprises a main catalyst, an accelerant and an organic solvent. The coating sequence of the carbon layer and the single-walled carbon nanotube layer can be controlled through sectional entering of the carbon source, in-situ preparation is carried out, the formed composite material coating layer is uniform, the single-walled carbon nanotubes are integrated to the surface of the silicon carbon material and are not prone to falling off in the machining process, and the silicon carbon material can be used as a negative electrode material without additionally adding carbon tube conductive slurry; meanwhile, the technological process of adding a carbon tube in the use process of the silicon-carbon negative electrode material is greatly reduced, the cost is reduced, and the important commercial application value is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterial preparation, and particularly relates to an in-situ grown single-walled carbon nanotube coated silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] Compared with traditional graphite negative electrode materials, silicon-based negative electrode materials have high specific capacity and excellent fast charging performance, but also have defects such as poor conductivity, high volume expansion rate and low cycle life. Therefore, in the process of use, high-performance conductive agents need to be added to make up for the above defects. Single-walled carbon nanotubes have only one layer of carbon atoms and a high aspect ratio, which can better build a three-dimensional conductive network at a very low addition amount. At the same time, it has better elastic modulus and mechanical strength, and its structure is not easy to be damaged under external force. At present, single-walled carbon nanotubes are considered to be the most suitable conductive agent for silicon-based negative electrode materials. The above advantages of single-walled carbon nanotubes can alleviate the stress of volume change of silicon-based negative electrode in the charging and discharging process, reduce the collapse of the negative electrode, thereby improving the cycle life of the battery.

[0003] The traditional method of mixing single-walled carbon nanotubes with silicon-carbon negative electrode materials is: first, the single-walled carbon nanotubes are configured into a slurry with a certain solid content, and then the slurry is added to the silicon-carbon negative electrode as a conductive slurry according to a certain ratio. Other methods are also used by mechanically mixing the two for composite use. The patent with publication number CN117682507A uses single-walled carbon nanotubes prepared by a fluidized bed, and after purification treatment, an aqueous slurry is prepared. The dispersed single-walled carbon nanotube aqueous slurry is used as a conductive agent for silicon-carbon negative electrode materials. The patent with publication number CN109830668A discloses a method for preparing a lithium ion battery silicon-carbon negative electrode material using carbon nanotubes. The silicon powder, carbon nanotubes and dispersing agent are mixed in a deionized water solvent and subjected to shearing dispersion by a high-speed shearing machine. The carbon nanotube / silicon-carbon negative electrode material is obtained after carbonization treatment. These methods are all through the dispersion of single-walled carbon nanotube raw materials and then mixed with silicon-carbon particles. In the process of carbon tube dispersion, the wet process of slurry preparation is involved. Not only many non-conductive dispersants are added, which reduces the conductivity of the carbon tube itself, but also the process is complex, and the carbon tube is easy to fall off when the carbon tube mixed silicon-carbon composite material is prepared.

[0004] In addition to the above traditional process, there is also a method of growing carbon tube coating by adding catalyst on the surface of the previously prepared silicon-carbon: the patent with publication number CN111326726A first uses silicon powder, a binder and a dispersing agent to obtain a silicon-carbon material by heat treatment, and then a catalyst is coated on the surface of the silicon-carbon material to grow carbon tubes by CVD to obtain a single-walled carbon nanotube-silicon-carbon composite material. This method introduces a large amount of impurities such as external additives and catalysts, which will affect the purity and conductivity of the composite material. SUMMARY

[0005] The main object of the present application is to provide an in-situ grown single-walled carbon nanotube coated silicon-carbon composite material and its preparation method and application to overcome the shortcomings of the prior art.

[0006] To achieve the above-mentioned objects, the technical scheme adopted by the present application comprises:

[0007] The present application provides a preparation method of an in-situ grown single-walled carbon nanotube coated silicon-carbon composite material, which comprises:

[0008] The suspension containing nanosilicon and a catalyst system, and a carbon source reaction gas are subjected to a carbon-coated silicon reaction in a low-temperature reaction zone, and then the obtained material is input into a high-temperature reaction zone to perform a catalytic cracking reaction, thereby obtaining a single-walled carbon nanotube coated silicon-carbon composite material; wherein the catalyst system comprises a main catalyst, a promoter, and an organic solvent.

[0009] The present application also provides a single-walled carbon nanotube coated silicon-carbon composite material prepared by the above-mentioned preparation method, which comprises a silicon-carbon material and single-walled carbon nanotubes in-situ grown on the surface of the silicon-carbon material.

[0010] The present application also provides the use of the above-mentioned single-walled carbon nanotube coated silicon-carbon composite material in the preparation of lithium negative electrode materials.

[0011] The present application also provides an electric negative electrode material, which comprises the above-mentioned single-walled carbon nanotube coated silicon-carbon composite material.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] (1) The present application first proposes to use in-situ grown single-walled carbon nanotubes to coat the generated silicon-carbon, which can be formed in one step to obtain this dry-made composite material. This in-situ preparation dry process avoids the traditional carbon tube dispersion preparation slurry process, greatly simplifying the preparation process.

[0014] (2) The present application can accurately control the carbon layer thickness of the silicon-carbon material and the content of the grown single-walled carbon nanotubes by adjusting the carbon source ratio and the reaction time. At the same time, the material first passes through the low-temperature zone for carbon coating, and the catalyst system can also be evaporated at the same time. The formed vapor catalyst system enters the high-temperature zone to grow single-walled carbon nanotubes, greatly improving the catalytic efficiency. The process operation and control of the present application are convenient, efficient, and suitable for continuous batch production.

[0015] (3) The composite material prepared by the present application has no additional additives, high product purity, and good electrical conductivity. At the same time, the silicon-carbon coated by the in-situ grown single-walled carbon nanotubes is tightly connected and not easy to fall off, so that this composite material has better specific capacity and cycle stability when used as a lithium negative electrode material.

[0016] (4) The raw material used in the application adds ready-made silicon particles, the particle size is controllable and the distribution is uniform, and the raw material with appropriate parameters can be added according to the demand, which is more operable than the synthesized silicon substrate, and has higher quality. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings described below are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 It is a schematic diagram of the reaction process of single-walled carbon nanotube coated silicon-carbon composite material in a typical embodiment of the present application.

[0019] Figure 2 It is a scanning electron microscope photo of the composite material prepared in Example 1 of the present application.

[0020] Figure 3 It is a Raman spectrum of the composite material prepared in Example 1 of the present application.

[0021] Figure 4 It is a powder conductivity graph of the composite material prepared in Example 1 of the present application.

[0022] Figure 5 It is a cycle number graph of the composite material prepared in Example 1 of the present application.

[0023] Figures 6a-6b It is a comparison photo of the scanning electron microscope of the composite materials prepared in Example 1 and Comparative Example 1 of the present application.

[0024] Figure 7 It is a scanning electron microscope photo of the composite material prepared in Example 2 of the present application.

[0025] Figure 8 It is a scanning electron microscope photo of the composite material prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0026] In view of the defects of the prior art, the present inventors have long-term research and a large number of practices, and have proposed the technical solutions of the present application. The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] Specifically, as one aspect of the technical scheme of the present application, a preparation method of a single-walled carbon nanotube coated silicon-carbon composite material grown in situ includes:

[0028] a carbon-coated silicon reaction is performed on a suspension containing nanosilicon and a catalyst system and a carbon source reaction gas in a low-temperature reaction zone, and then the obtained material is input into a high-temperature reaction zone for a catalytic cracking reaction to obtain a single-walled carbon nanotube coated silicon-carbon composite material; wherein the catalyst system includes a main catalyst, a promoter and an organic solvent.

[0029] In some preferred embodiments, the preparation method specifically includes:

[0030] (1) mixing nanosilicon with a catalyst system to form a suspension;

[0031] (2) excluding air in the staged reaction device and filling a protective atmosphere, while raising the temperature of the low-temperature reaction zone in the staged reaction device to 500-900℃ and raising the temperature of the high-temperature reaction zone to 1000-1800℃;

[0032] (3) under the condition of a carrier gas and an auxiliary gas, inputting the suspension and the carbon source reaction gas into the low-temperature reaction zone for a carbon-coated silicon reaction to obtain a silicon-carbon material;

[0033] (4) transporting the product obtained in step (3) to the high-temperature reaction zone for a catalytic cracking reaction to generate single-walled carbon nanotubes in situ on the surface of the silicon-carbon material, thereby obtaining a single-walled carbon nanotube coated silicon-carbon composite material.

[0034] Further, the average particle size D50 of the nanosilicon is 10-85 nm.

[0035] Further, the content of nanosilicon in the suspension is 0.5-30 wt%.

[0036] Further, the mass percentage concentration in the suspension is 0.1-55%.

[0037] Further, the main catalyst includes an iron-based compound, which includes any one or more of combinations of ferrocene, carbonyl iron, iron oxide, and is not limited thereto.

[0038] Further, the promoter includes a compound containing sulfur and / or selenium, and is not limited thereto; wherein the compound containing sulfur and / or selenium includes thiophene, elemental sulfur, mercaptan, sulfide, elemental selenium, selenium oxide and the like.

[0039] Further, the organic solvent includes any one or more of combinations of benzene, ethylbenzene, xylene, methanol, ethanol, and is not limited thereto.

[0040] Further, the mass ratio of the main catalyst, the promoter and the organic solvent in the catalyst system is 20-1:0.01-5:79.99-94.

[0041] Further, the reaction zone interval of the low-temperature reaction zone is 300-1000 mm.

[0042] Further, the reaction zone interval of the high-temperature zone is 150-500 mm.

[0043] Further, the carrier gas comprises argon, and the flow rate of the carrier gas is 1.5-50 L / min.

[0044] Further, the auxiliary gas comprises any one or a combination of hydrogen sulfide, water vapor, carbon dioxide and hydrogen, and the flow rate of the auxiliary gas is 10%-150% of the flow rate of the carrier gas.

[0045] Further, the carbon source reaction gas comprises any one or a combination of ethylene, acetylene, propylene and propane, and the flow rate of the carbon source reaction gas is 0.15-25 L / min; the flow rate of the carbon source reaction gas is 10%-50% of the flow rate of the carrier gas.

[0046] Further, the injection rate of the suspension is 0.01-10 mL / min.

[0047] Further, the temperature of the carbon-coated silicon reaction in step (3) is 500-900℃.

[0048] Further, the reaction residence time of the carbon-coated silicon reaction in the low-temperature reaction zone in step (3) is 10-100 s.

[0049] Further, the temperature of the catalytic cracking reaction in step (4) is 1000-1800℃.

[0050] Further, the reaction residence time of the catalytic cracking reaction in the high-temperature reaction zone in step (4) is 0.5-50 s.

[0051] Further, the preparation method further comprises collecting the single-walled carbon nanotube-coated silicon-carbon composite material by using a collection system.

[0052] In some preferred embodiments, the method for preparing the in-situ grown single-walled carbon nanotube coated silicon-carbon composite material uses a segmented temperature field as different reaction zones, and a suspension containing nano-silicon powder and a catalyst system is injected into a low-temperature reaction zone to produce carbon-coated nano-silicon under a carbon source, and further catalytic cracking reaction of the catalyst in a high-temperature zone forms the in-situ grown single-walled carbon nanotube coated silicon-carbon composite material.

[0053] In some more specific embodiments, the method for preparing the in-situ grown single-walled carbon nanotube coated silicon-carbon composite material comprises the following steps:

[0054] S1) configuring nano-silicon powder and a catalyst system into a suspension and placing it in a liquid injection system for standby;

[0055] S2) removing air in the reactor and filling it with argon protection, and performing segmented heating on different zones of the reactor;

[0056] S3) after reaching the reaction temperature, stably injecting the suspension into the low-temperature reaction zone under certain atmosphere conditions, and simultaneously introducing a suitable amount of carbon source reaction gas into the front end of the reaction zone to complete the production of carbon-coated nano-silicon;

[0057] S4) the formed silicon-carbon particles enter the high-temperature zone under the driving of the gas flow, the catalyst system in the suspension catalyzes the cracking reaction in the high-temperature zone, single-walled carbon nanotubes are generated in-situ on the surface of the silicon-carbon, and finally the generated composite material product enters the collection system for collection.

[0058] Preferably, the average particle size D50 of the silicon powder in S1) is 10 nm to 85 nm, and the mass fraction of the silicon powder in the system is 0.5% to 30%.

[0059] Preferably, the catalyst system comprises an organic solvent as a carbon source, a promoter and a main catalyst, wherein the carbon source comprises at least one of benzene, ethylbenzene, xylene, methanol and ethanol to form a high-cracking-temperature solvent.

[0060] Preferably, the mass percentage concentration of the suspension is 0.1% to 55%.

[0061] Preferably, the reactor segmented heating in S2) is divided into a low-temperature zone to a high-temperature zone, wherein the reaction zone interval of the low-temperature zone is 300 mm to 1000 mm, and the temperature is 500°C to 900°C.

[0062] Preferably, the certain atmosphere conditions in S3) are carrier gas argon and auxiliary gas, wherein the argon flow is 1.5 L / min to 50 L / min.

[0063] As a preference, the auxiliary gas is at least one of hydrogen sulfide, water vapor, carbon dioxide, and hydrogen gas, which is mixed with argon and introduced at a flow rate of 10% to 150% of the flow rate of the argon.

[0064] As a preference, the injection rate of the suspension is 0.01 mL / min to 10 mL / min.

[0065] As a preference, the reaction residence time of the material in the low-temperature zone during the preparation of the carbon-coated silicon is 10 s to 100 s.

[0066] As a preference, the introduced carbon source reaction gas is at least one of ethylene, acetylene, propylene, and propane gas, which is introduced at a flow rate of 0.15 L / min to 25 L / min and at a flow rate of 10% to 50% of the flow rate of the argon.

[0067] As a preference, the introduction position of the carbon source gas is 1 cm to 10 cm above the injection port and 2 cm to 10 cm above the front end of the low-temperature zone.

[0068] As a preference, the reaction interval of the high-temperature zone in S4) is 150 mm to 500 mm, the temperature is 1100°C to 1700°C, and the reaction residence time of the material in the high-temperature zone is 0.5 s to 50 s.

[0069] As a preference, the thickness of the carbon layer in the composite silicon-carbon prepared by the method is 1 nm to 2.5 nm, and the content of the coated single-walled carbon nanotube is 0.01% to 5%, which can be directly used as an anode material and has important commercial application value.

[0070] The method of in-situ growth is adopted in the present application, which can form a core-shell structure of carbon-coated silicon particles in the first stage, and then directly grow single-walled carbon nanotubes around the silicon-carbon particles through high-temperature catalytic growth in the second stage, to directly form a composite material by a dry method, greatly reducing the process flow and cost, and meanwhile, no external additives are generated in the composite material, and the formed single-walled carbon nanotubes are not easy to fall off and have high conductivity.

[0071] Another aspect of the embodiments of the present application also provides a single-walled carbon nanotube-coated silicon-carbon composite material prepared by the aforementioned preparation method, which comprises a silicon-carbon material and single-walled carbon nanotubes in-situ grown on the surface of the silicon-carbon material.

[0072] In some preferred embodiments, the silicon-carbon material has a core-shell structure, and the thickness of the carbon layer in the silicon-carbon material is 1 nm to 2.5 nm.

[0073] In some preferred embodiments, the content of the single-walled carbon nanotubes in the single-walled carbon nanotube-coated silicon-carbon composite material is 0.01% to 5% by weight.

[0074] Another aspect of the embodiments of the present application also provides a use of the single-walled carbon nanotube-coated silicon-carbon composite material as described above in the preparation of a lithium negative electrode material.

[0075] Another aspect of the embodiments of the present application also provides an electric negative electrode material comprising the single-walled carbon nanotube-coated silicon-carbon composite material as described above.

[0076] The technical solutions of the present application will be further described in detail below in combination with several preferred embodiments and the accompanying drawings. The embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0077] The experimental materials used in the following embodiments are commercially available from conventional biochemical reagent companies, unless otherwise specified.

[0078] Embodiment 1

[0079] The reactor is opened, and after the system is vacuumed, inert gas protection is filled. A segmented temperature field is used as different reaction zones, and the first temperature segment, the low-temperature zone, is heated to 700°C. The reaction liquid system is configured, and an appropriate amount of silicon powder with an average particle size of 50 nm is dispersed into an ethanol solution, and an appropriate amount of ferrocene and thioether is added, and a suspension with a mass percentage concentration of 20% is prepared, and the mass fraction of silicon powder in the suspension is 15%. The suspension containing nanometer silicon powder and catalyst system is injected into the first low-temperature reaction zone at an injection rate of 5 mL / min to carry out the carbon-coated silicon reaction, wherein the reaction zone interval of the low-temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min, wherein the ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low-temperature zone. The second temperature segment, the high-temperature segment, is heated to 1300°C, and the baffle between the two reaction zones is adjusted so that the material generated in the first low-temperature zone enters the high-temperature zone for reaction, wherein the reaction zone interval of the high-temperature zone is 200 mm, and the reaction residence time of the material in the high-temperature zone is 20 s. At this time, the catalyst system evaporated in the low-temperature zone is carried into the high-temperature zone by the gas flow and carries out a catalytic cracking reaction, and single-walled carbon nanotubes are grown on the surface of the silicon-carbon product in the first stage to finally prepare a single-walled carbon nanotube-coated silicon-carbon composite material. The product is collected and characterized for testing and analysis.

[0080] Figure 1This is a schematic diagram of the reaction process of the present invention. As can be seen from the figure, after the silicon particles with uniform particle size in the raw material are coated with a low-temperature gaseous carbon source in the first stage, a carbon shell with a thickness of 1nm to 2.5nm is evenly coated on the outer surface of the silicon particles. The carbon-coated silicon material (silicon particles @ carbon layer) improves its conductivity in the negative electrode of the lithium-ion battery and limits its volume expansion during the charge and discharge process. When it further reaches the high-temperature zone of the second stage, the catalyst gasified in the low-temperature zone and the liquid carbon source vapor catalytically decompose in the high-temperature zone to grow single-walled carbon nanotubes. The formed single-walled carbon nanotubes use the silicon and carbon generated in the first stage as the matrix, and are coated around and on the surface, eventually forming a composite material of single-walled carbon nanotubes coated with silicon and carbon (denoted as: silicon particles @ carbon layer @ SWCNTs). After the formation of single-walled carbon nanotubes in the second stage, a three-dimensional conductive network is enhanced for the silicon-carbon negative electrode material, further improving the conductive properties of the composite material.

[0081] The scanning electron microscope photograph of the composite material prepared in this embodiment is as follows: Figure 2 As shown in the SEM image, upon magnification, silicon-carbon particles, measuring tens of nanometers in size, are encapsulated within the mesh-like conductive network of single-walled carbon nanotubes. The product is evenly distributed, demonstrating a good encapsulation effect. The single-walled carbon nanotubes are interwoven throughout, forming a well-developed conductive network. Figure 3 The Raman spectrum of the composite material prepared in Example 1 of the present invention shows that the product has obvious D peak and G peak, and the intensity ratio of the two is 1 G / I D It can reach more than 30, indicating that the material has good crystallization performance. 1 An obvious RBM peak appears nearby, which is a unique spectral characteristic of single-walled carbon nanotubes, indicating that single-walled carbon nanotubes are generated. Figure 4 This is the powder conductivity result diagram of the composite material prepared in Example 1 of the present invention. The resistivity of the powder sample gradually decreases under different pressures, and eventually tends to balance, close to the actual surface resistivity of the sample. It can be seen from the figure that when the pressure reaches 20MPa, the resistivity is 0.17Ωcm, and the converted conductivity reaches 588S / m, which has higher powder conductivity than conventional silicon-carbon materials. The composite material synthesized in this embodiment is configured as a negative electrode material and made into a button battery for cycle performance testing. Figure 5 As shown, at a current density of 300 mA / g, it cycles 60 times. After the specific capacity decreases in the first 10 cycles, it reaches 1200 mAh / g and remains stable, with high specific capacity and cycle performance.

[0082] Comparative Example 1

[0083] The reactor is opened, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section low temperature zone is heated to 700 DEG C. The reaction liquid system is configured, the appropriate amount of silicon powder with an average particle size of 50 nm is dispersed into the ethanol solution, and the appropriate amount of ferrocene and sulfide is added, and the suspension with a mass percentage concentration of 20% is prepared, and the mass fraction of silicon powder in the suspension is 15%. The suspension containing nanometer silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 5 mL / min to carry out the reaction of carbon-coated silicon, wherein the reaction zone interval of the low temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is respectively argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min, wherein the ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low temperature zone. The second temperature section is not heated, and the baffle between the two reaction zones is adjusted so that the material generated in the first low temperature zone enters the second section, wherein the interval length of the second section is 200 mm. The product is collected and characterized for testing and analysis.

[0084] The sample particle size of the sample without the second stage high temperature growth of single-walled carbon nanotubes is obvious, and is not adhered to each other. Figures 6a-6b The scanning electron microscope comparison photos of the materials prepared in example 1 and comparative example 1 are prepared, and from the photos, it can be seen that in the scanning photo of the sample in example 1, a large number of convex silicon-carbon particles are clearly visible, which are wrapped by the reticular single-walled carbon nanotubes to form an integral network structure. In the scanning photo of the sample in comparative example 1, the silicon-carbon particles are accumulated together, and there is no connecting material between the particles, so that the simple silicon-carbon product is more prone to collapse when used as a lithium battery negative electrode material.

[0085] Comparative example 2

[0086] The reactor is opened, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section low temperature zone is heated to 700°C. Configure the reaction liquid system, take an appropriate amount of silicon powder with an average particle size of 50 nm and disperse it into an ethanol solution, add an appropriate amount of ferrocene and sulfide, and prepare a suspension with a mass percentage concentration of 20%, the mass fraction of silicon powder in the suspension is 15%. The suspension containing nano-silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 5 mL / min to react, the reaction zone interval of the low temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is argon 20 L / min, hydrogen 10 L / min, and ethylene 0 L / min, no carbon source gas is introduced in this comparative example, to compare whether the silicon-carbon product can be formed in the first stage. The second temperature section high temperature section is heated to 1300°C, the baffle between the two reaction zones is adjusted, the material generated in the first low temperature zone enters the high temperature zone for reaction, the reaction zone interval of the high temperature zone is 200 mm, and the reaction residence time of the material in the high temperature zone is 20 s, at this time the catalyst system evaporated in the low temperature zone is brought into the high temperature zone with the gas flow and carries out catalytic cracking reaction, the single-walled carbon nanotubes grow on the surface of the first stage product, and finally the composite material is prepared. After sampling, the product of the first stage is observed, it can be found that without adding carbon source gas, the added silicon powder does not change in the low temperature stage, it is still white powder, indicating that the addition of carbon source reaction gas is the key factor for the deposition of carbon layer on the surface of silicon powder.

[0087] Comparative Example 3

[0088] The reactor is opened, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, the first temperature section low temperature zone is not heated, and the room temperature state is maintained, that is, the experiment is carried out without low temperature zone reaction. The reaction liquid system is configured, and a proper amount of silicon powder with an average particle size of 50 nm is dispersed into an ethanol solution, and a proper amount of ferrocene and thioether is added, to prepare a suspension with a mass percentage concentration of 20%, and the mass fraction of silicon powder in the suspension is 15%. The suspension containing nano silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 5 mL / min, and the catalyst only passes through the low temperature zone and does not react. The gas flow used is respectively argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min, wherein the ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low temperature zone. The second temperature section high temperature section is heated to 1300℃, the baffle between the two reaction zones is adjusted, the material enters the high temperature zone for reaction, the reaction zone interval of the high temperature zone is 200 mm, and the reaction residence time of the material in the high temperature zone is 20 s, at this time, the catalyst system evaporated in the low temperature zone is brought into the high temperature zone by the gas flow and carries out catalytic cracking reaction, and single-walled carbon nanotubes are grown on the surface of the raw silicon powder, and finally the composite material is prepared. Without the reaction in the low temperature zone, the morphology of the silicon powder does not change, and finally only single-walled carbon nanotubes are formed on the surface of the silicon powder in the second stage high temperature zone.

[0089] Comparative Example 4

[0090] The reactor is opened, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, the first temperature section low temperature zone is heated to 700℃. The reaction liquid system is configured, and a proper amount of silicon powder with an average particle size of 50 nm is dispersed into an ethanol solution, and the mass fraction of silicon powder in the suspension is 15%, and no catalyst system is added to the solution for comparison experiment. The suspension prepared by the solution containing nano silicon powder without catalyst system is injected into the first low temperature reaction zone at an injection rate of 5 mL / min for carbon-coated silicon reaction, wherein the reaction zone interval of the low temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is respectively argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min, wherein the ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low temperature zone. The second temperature section high temperature section is heated to 1300℃, the baffle between the two reaction zones is adjusted, and the material generated in the first low temperature zone enters the high temperature zone for reaction, wherein the reaction zone interval of the high temperature zone is 200 mm, and the reaction residence time of the material in the high temperature zone is 20 s, at this time, no catalyst system evaporated in the low temperature zone can carry out catalytic cracking reaction, therefore, single-walled carbon nanotubes cannot be formed in the high temperature zone, and only silicon-carbon material is obtained.

[0091] Example 2

[0092] The reactor is started, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section, the low temperature zone, is heated to 800℃. The reaction liquid system is configured, an appropriate amount of silicon powder with an average particle size of 50 nm is dispersed into an ethanol solution, and an appropriate amount of carbonyl iron and thiophene is added, to prepare a suspension with a mass percentage concentration of 20%, and the mass fraction of silicon powder in the suspension is 15%. The suspension containing nano-silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 5 mL / min to carry out the carbon-coated silicon reaction, wherein the reaction zone interval of the low temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min, wherein the ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low temperature zone. The second temperature section, the high temperature section, is heated to 1400℃, and the baffle between the two reaction zones is adjusted so that the material generated in the first low temperature zone enters the high temperature zone for reaction, wherein the reaction zone interval of the high temperature zone is 200 mm, and the reaction residence time of the material in the high temperature zone is 20 s. At this time, the catalyst system evaporated in the low temperature zone is carried into the high temperature zone by the gas flow and carries out catalytic cracking reaction, and single-walled carbon nanotubes are grown on the surface of the silicon-carbon product in the first stage. Finally, a single-walled carbon nanotube coated silicon-carbon composite material is prepared. The product is collected and characterized for testing and analysis.

[0093] The scanning electron microscope photo of the composite material prepared in this example is shown in Figure 7 From the scanning electron microscope photo, it can be seen that the formed reticular single-walled carbon nanotube conductive network is wrapped with dozens of nanometer-sized silicon-carbon particles, the product is uniformly distributed, the wrapping effect is good, and the silicon particle size is slightly larger after agglomeration.

[0094] Example 3

[0095] The reactor was started, evacuated, and then filled with inert gas. A segmented temperature field was used to create distinct reaction zones, with the first low-temperature zone heated to 850°C. The reaction system was prepared by weighing an appropriate amount of silicon powder with an average particle size of 50 nm and dispersing it in an ethanol solution. Appropriate amounts of iron oxide and mercaptan were added to create a suspension with a 20% by weight concentration and a 15% by weight fraction of silicon powder. This suspension containing nano-silicon powder and the catalyst system was injected into the first low-temperature reaction zone at an injection rate of 5 mL / min. The carbon-coated silicon reaction took place in the low-temperature zone, with a reaction interval of 500 mm and a residence time of 30 seconds. Gas flow rates were 20 L / min for argon, 10 L / min for hydrogen, and 5 L / min for ethylene. The ethylene was introduced 5 cm above the injection port, directly above the front end of the low-temperature zone. The second high-temperature section was heated to 1500°C. The baffles between the two reaction zones were adjusted to allow the material generated in the first low-temperature section to enter the high-temperature section for reaction. The reaction interval in the high-temperature section was 200 mm, and the material stayed in the high-temperature section for 20 seconds. The catalyst system, which had evaporated in the low-temperature section, was carried by the airflow into the high-temperature section for catalytic cracking. Single-walled carbon nanotubes (SWCNTs) formed on the surface of the silicon-carbon products in the first stage, ultimately producing a SWCNT-coated silicon-carbon composite. The product was collected and characterized and analyzed.

[0096] The scanning electron microscope photograph of the composite material prepared in this embodiment is as follows Figure 8 As shown in the SEM image, silicon-carbon particles, each tens of nanometers in size, are encapsulated within the sparse, conductive network of single-walled carbon nanotubes. While the encapsulation is effective, the size of the silicon-carbon particles increases. This suggests that during the first stage of the reaction, the increased temperature in the low-temperature zone leads to premature initial cracking of the catalyst, causing the silicon-carbon particles to aggregate and aggregate, thus affecting the uniformity of the particle size.

[0097] Table 1 Comparison of performance parameters of samples synthesized in Examples 1-3 and Comparative Examples 1, 2, and 4

[0098] Performance test parameters Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 4 Example 2 Example 3 Average Raman I G / I D ]]> 31.2 12.5 25.4 2.6 33.9 35.6 Particle size D50 (pm) 0.8 0.6 0.7 0.3 1.8 2.2 Powder conductivity (S / m) 588 107 254 98 577 554 Specific capacity (mAh / g) 1250 774 435 116 959 937

[0099] From the results in Table 1 above, it can be seen that Example 1, Example 2 and Example 3 respectively use higher temperatures for carbon layer coating and carbon tube growth. When the temperature is increased, the Raman spectroscopy results of the products are as follows: G / I DThe amount of carbon nanotubes in the final product is reduced and the uniformity of the particles is decreased, thereby affecting the conductivity of the product and the final specific capacity. In Comparative Example 1, after stopping heating in the second stage high-temperature zone, the silicon-carbon product generated in the first stage cannot continue to grow to form a single-walled carbon nanotube coated composite material, so the overall test performance of the product is reduced. Similarly, in Comparative Example 4, in the absence of a catalyst system, single-walled carbon nanotubes cannot be formed in the second stage high-temperature reaction, and the overall performance of the product is also reduced. In Comparative Example 2, in the absence of a carbon source reaction gas in the low-temperature zone CVD reaction, carbon layers cannot be deposited on the surface of the silicon particles, resulting in a composite material of silicon particles and single-walled carbon nanotubes, which greatly affects the cycle stability of the material.

[0100] Example 4

[0101] The reactor is opened, the system is vacuumed, and then filled with inert gas protection. A segmented temperature field is used as different reaction zones. The first temperature segment, the low-temperature zone, is heated to 750°C. The reaction liquid system is configured. An appropriate amount of silicon powder with an average particle size of 30 nm is dispersed in an ethanol solution, and an appropriate amount of ferrocene and elemental sulfur is added. A suspension with a mass percentage concentration of 15% is prepared, and the mass fraction of silicon powder in the suspension is 10%. The suspension containing nano-silicon powder and the catalyst system is injected into the first low-temperature reaction zone at an injection rate of 5 mL / min to perform the carbon-coated silicon reaction. The reaction zone interval of the low-temperature zone is 500 mm, and the reaction residence time is controlled to be 30 s. The gas flow used is argon 20 L / min, hydrogen 10 L / min, and ethylene 5 L / min. The ethylene inlet position is 5 cm higher than the liquid injection port and is located 5 cm above the front end of the low-temperature zone. The second temperature segment, the high-temperature segment, is heated to 1350°C. The baffles between the two reaction zones are adjusted so that the material generated in the first low-temperature zone enters the high-temperature zone for reaction. The reaction zone interval of the high-temperature zone is 200 mm, and the reaction residence time of the material in the high-temperature zone is 20 s. At this time, the catalyst system evaporated in the low-temperature zone is carried into the high-temperature zone by the gas flow and undergoes catalytic cracking reaction, and single-walled carbon nanotubes are grown on the surface of the silicon-carbon product in the first stage, finally preparing a single-walled carbon nanotube coated silicon-carbon composite material.

[0102] Example 5

[0103] The reactor is started, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section low temperature zone is heated to 650℃. The reaction liquid system is configured, an appropriate amount of silicon powder with an average particle size of 15 nm is dispersed into ethanol solution, and an appropriate amount of ferrocene and mercaptan is added, to prepare a suspension with a mass percentage concentration of 5%, and the mass fraction of silicon powder in the suspension is 10%. The suspension containing nano-silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 8 mL / min to carry out the carbon-coated silicon reaction, wherein the reaction zone interval of the low temperature zone is 800 mm, and the reaction residence time is controlled to be 60 s. The gas flow used is argon 30 L / min, hydrogen 20 L / min, and ethylene 10 L / min, wherein the ethylene inlet position is 3 cm higher than the liquid injection port and is located 3 cm above the front end of the low temperature zone. The second temperature section high temperature section is heated to 1350℃, and the baffle between the two reaction zones is adjusted so that the material generated in the first low temperature zone enters the high temperature zone for reaction, wherein the reaction zone interval of the high temperature zone is 160 mm, and the reaction residence time of the material in the high temperature zone is 15 s. At this time, the catalyst system evaporated in the low temperature zone is carried into the high temperature zone by the gas flow and carries out catalytic cracking reaction, single-walled carbon nanotubes are grown on the surface of the silicon-carbon product in the first stage, and finally a single-walled carbon nanotube coated silicon-carbon composite material is prepared.

[0104] Example 6

[0105] The reactor is started, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section low temperature zone is heated to 550℃. The reaction liquid system is configured, an appropriate amount of silicon powder with an average particle size of 25 nm is dispersed into xylene solution, and an appropriate amount of ferrocene and elemental sulfur is added, to prepare a suspension with a mass percentage concentration of 15%, and the mass fraction of silicon powder in the suspension is 25%. The suspension containing nano-silicon powder and catalyst system is injected into the first low temperature reaction zone at an injection rate of 1 mL / min to carry out the carbon-coated silicon reaction, wherein the reaction zone interval of the low temperature zone is 900 mm, and the reaction residence time is controlled to be 90 s. The gas flow used is argon 30 L / min, water vapor 20 L / min, and propylene 10 L / min, wherein the propylene inlet position is 4 cm higher than the liquid injection port and is located 4 cm above the front end of the low temperature zone. The second temperature section high temperature section is heated to 1250℃, and the baffle between the two reaction zones is adjusted so that the material generated in the first low temperature zone enters the high temperature zone for reaction, wherein the reaction zone interval of the high temperature zone is 250 mm, and the reaction residence time of the material in the high temperature zone is 25 s. At this time, the catalyst system evaporated in the low temperature zone is carried into the high temperature zone by the gas flow and carries out catalytic cracking reaction, single-walled carbon nanotubes are grown on the surface of the silicon-carbon product in the first stage, and finally a single-walled carbon nanotube coated silicon-carbon composite material is prepared.

[0106] Example 7

[0107] The reactor was opened, and after the system was vacuumed, it was filled with inert gas protection. A segmented temperature field was used as different reaction zones. The first temperature segment, the low-temperature zone, was heated to 850°C. The reaction liquid system was configured. An appropriate amount of silicon powder with an average particle size of 75 nm was dispersed into a benzene solution, and an appropriate amount of ferrocene and selenium oxide was added. A suspension with a mass percentage concentration of 10% was prepared, and the mass fraction of silicon powder in the suspension was 20%. The suspension containing nano-silicon powder and the catalyst system was injected into the first low-temperature reaction zone at an injection rate of 0.5 mL / min to perform the carbon-coated silicon reaction, wherein the reaction zone interval of the low-temperature zone was 400 mm, and the reaction residence time was controlled to be 30 s. The gas flow used was argon 35 L / min, carbon dioxide 25 L / min, and acetylene 15 L / min, wherein the acetylene inlet position was 2 cm higher than the injection port and located 2 cm above the front end of the low-temperature zone. The second temperature segment, the high-temperature segment, was heated to 1650°C. The baffles between the two reaction zones were adjusted so that the material generated in the first low-temperature zone entered the high-temperature zone for reaction, wherein the reaction zone interval of the high-temperature zone was 200 mm, and the reaction residence time of the material in the high-temperature zone was 20 s. At this time, the catalyst system evaporated in the low-temperature zone was carried into the high-temperature zone by the gas flow and performed a catalytic cracking reaction. Single-walled carbon nanotubes were wrapped and grown on the surface of the silicon-carbon product in the first stage, and finally a single-walled carbon nanotube-coated silicon-carbon composite material was prepared.

[0108] Example 8

[0109] The reactor is opened, the system is vacuumed and filled with inert gas protection, a segmented temperature field is used as different reaction zones, and the first temperature section low temperature zone is heated to 800℃. The reaction liquid system is configured, an appropriate amount of silicon powder with an average particle size of 65 nm is dispersed into a methanol solution, and an appropriate amount of ferrocene and elemental selenium is added, to prepare a suspension with a mass percentage concentration of 10%, and the mass fraction of silicon powder in the suspension is 20%. The suspension containing nanometer silicon powder and the catalyst system is injected into the first low temperature reaction zone at an injection rate of 1.5 mL / min to carry out the carbon-coated silicon reaction, wherein the reaction zone interval of the low temperature zone is 450 mm, and the reaction residence time is controlled to be 35 s. The gas flow used is argon 5 L / min, hydrogen sulfide 1 L / min, and propane 2 L / min, wherein the propane inlet position is 3 cm higher than the liquid injection port and is located 3 cm above the front end of the low temperature zone. The second temperature section high temperature section is heated to 1550℃, and the baffle between the two reaction zones is adjusted so that the material generated in the first low temperature zone enters the high temperature zone for reaction, wherein the reaction zone interval of the high temperature zone is 250 mm, and the reaction residence time of the material in the high temperature zone is 25 s. At this time, the catalyst system evaporated in the low temperature zone is carried into the high temperature zone by the gas flow and carries out catalytic cracking reaction, the single-walled carbon nanotube grows on the surface of the silicon-carbon product in the first stage, and finally the single-walled carbon nanotube coated silicon-carbon composite material is prepared.

[0110] In addition, the inventors of the present case also refer to the foregoing examples, and conduct tests on other raw materials, process operations and process conditions described in the specification, and all obtain relatively ideal results.

[0111] It should be understood that the technical solutions of the present application are not limited to the specific implementation cases described above, and any technical modification made according to the technical solutions of the present application without departing from the purpose of the present application and the scope protected by the claims falls within the protection scope of the present application.

Claims

1. A method for preparing an in-situ grown single-walled carbon nanotube-coated silicon-carbon composite material, characterized in that: include: A suspension containing nano-silicon and a catalyst system and a carbon source reaction gas are placed in a low-temperature reaction zone to undergo a carbon-coated silicon reaction, and the resulting material is then fed into a high-temperature reaction zone for a catalytic cracking reaction to produce a single-walled carbon nanotube-coated silicon-carbon composite material; wherein the catalyst system includes a main catalyst, a promoter, and an organic solvent.

2. The preparation method according to claim 1, characterized in that Specifically include: (1) mixing nano-silicon with a catalyst system to form a suspension; (2) removing air from the staged reaction device and filling it with a protective atmosphere, while simultaneously heating the low-temperature reaction zone in the staged reaction device to 500° C. to 900° C. and the high-temperature reaction zone to 1000° C. to 1800° C.; (3) Under the conditions of carrier gas and auxiliary gas, the suspension and carbon source reaction gas are input into a low-temperature reaction zone to carry out a carbon-coated silicon reaction to obtain a silicon-carbon material; (4) The product obtained in step (3) is transported to a high-temperature reaction zone for catalytic cracking reaction, and single-walled carbon nanotubes are generated in situ on the surface of the silicon-carbon material, thereby preparing a single-walled carbon nanotube-coated silicon-carbon composite material.

3. The preparation method according to claim 2, wherein: The average particle size D50 of the nano-silicon is 10nm to 85nm; and / or, the content of nano-silicon in the suspension is 0.5 to 30 wt%; and / or, the mass percentage concentration in the suspension is 0.1 to 55%; and / or, the main catalyst comprises an iron-based compound, and the iron-based compound comprises any one or more combinations of ferrocene, carbonyl iron, and iron oxide; and / or, the promoter comprises a sulfur and / or selenium-containing compound; and / or, the organic solvent comprises any one or more combinations of benzene, ethylbenzene, xylene, methanol, and ethanol; And / or, the mass ratio of the main catalyst, the promoter and the organic solvent in the catalyst system is 20-1:0.01-5:79.99-94.

4. The preparation method according to claim 2, wherein: The reaction interval of the low temperature reaction zone is 300mm to 1000mm; And / or, the reaction range of the high temperature zone is 150 mm to 500 mm.

5. The preparation method according to claim 2, wherein: The carrier gas includes argon, and the flow rate of the carrier gas is 1.5 L / min to 50 L / min; And / or, the auxiliary gas includes any one or more of hydrogen sulfide, water vapor, carbon dioxide, and hydrogen, and the flow rate of the auxiliary gas is 10% to 150% of the flow rate of the carrier gas; And / or, the carbon source reaction gas includes any one or more of ethylene, acetylene, propylene, and propane, and the flow rate of the carbon source reaction gas is 0.15 L / min to 25 L / min; the flow rate of the carbon source reaction gas is 10% to 50% of the carrier gas flow rate; And / or, the injection rate of the suspension is 0.01 mL / min to 10 mL / min: and / or, the temperature of the carbon-coated silicon reaction in step (3) is 500° C. to 900° C.; And / or, the residence time of the carbon-coated silicon reaction in the low-temperature reaction zone in step (3) is 10s to 100s.

6. The preparation method according to claim 2, wherein: The temperature of the catalytic cracking reaction in step (4) is 1000° C. to 1800° C.; and / or, the reaction residence time of the catalytic cracking reaction in the high temperature reaction zone in step (4) is 0.5s to 50s; And / or, the preparation method further comprises: collecting the single-walled carbon nanotube-coated silicon-carbon composite material using a collection system.

7. The single-walled carbon nanotube-coated silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: It includes silicon-carbon material and single-walled carbon nanotubes grown in situ on the surface of the silicon-carbon material.

8. The single-walled carbon nanotube-coated silicon-carbon composite material according to claim 7, characterized in that: The silicon-carbon material has a core-shell structure, and the thickness of the carbon layer in the silicon-carbon material is 1 nm to 2.5 nm. And / or, the single-walled carbon nanotube content in the single-walled carbon nanotube-coated silicon-carbon composite material is 0.01 to 5 wt%.

9. Use of the single-walled carbon nanotube-coated silicon-carbon composite material according to claim 7 or 8 in preparing a lithium battery negative electrode material.

10. An electric negative electrode material, characterized in that The invention comprises the single-walled carbon nanotube-coated silicon-carbon composite material according to claim 7 or 8.

Images