Carbon nanotube / silicon composite material, preparation method and application thereof

Abstract

The application discloses an in-situ preparation method of carbon nanotube / silicon composite material and belongs to the technical field of lithium ion battery negative electrode materials. A solution containing a carbon source and a catalyst is taken into a plasma reactor by a carrier gas and a reducing gas, and a silicon source gas is introduced at the same time; the material sequentially passes through a first double-electrode area (20-50 kW), arc discharge is cracked to generate carbon nanotubes and deposit silicon nanoparticles; then passes through a second double-electrode area (10-19 kW) to remove amorphous carbon impurities; and then passes through a third double-electrode area (1-9 kW) to reduce sp 3 Defects in the carbon nanotubes; after the reaction is finished, liquid nitrogen spraying, low-temperature nitrogen or water spraying is used for rapid cooling, gas flow grading or vibration screening is carried out to collect the carbon nanotube / silicon composite material. The in-situ growth of the carbon nanotubes, the silicon deposition, the removal of amorphous carbon and the repair are continuously completed in the same reactor, the reaction only takes a few minutes, the process is simple, the method is suitable for large-scale production, and the obtained composite material can be used for lithium ion battery negative electrodes.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to an in-situ preparation method of carbon nanotube / silicon composite material for lithium-ion battery anode materials. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have been widely used in portable electronic devices, electric vehicles, and energy storage systems. The anode material is one of the key factors determining battery performance. Currently, commercially available anodes are mainly graphite, but its theoretical specific capacity is only 372 mAh / g, which is insufficient to meet the ever-increasing demand for high energy density. Silicon, with a theoretical specific capacity as high as 3580 mAh / g at room temperature, is one of the most promising next-generation anode materials. However, silicon undergoes dramatic volume expansion (>300%) during charge and discharge, leading to electrode structure pulverization, repeated rupture and regeneration of the solid electrolyte interface film, and consequently, rapid capacity decay and poor cycle stability. To address these issues, combining silicon with carbon nanotubes is an effective strategy: the three-dimensional conductive network constructed from carbon nanotubes not only buffers the volume changes of silicon but also significantly reduces the contact resistance and charge transfer impedance within the electrode, improving rate performance and cycle life.

[0003] Currently, the main methods for preparing carbon nanotube / silicon composite materials include mechanical ball milling, high-energy ultrasonic dispersion, chemical vapor deposition (CVD), sol-gel method, and plasma-enhanced chemical vapor deposition (PECVD). However, existing technologies still have the following major technical shortcomings: 1. Primarily based on physical mixing followed by carbonization, lacking in-situ growth capability: Most existing technologies employ a stepwise method to prepare carbon nanotube / silicon composites. This involves first preparing or purchasing carbon nanotubes, then mixing them with silicon particles through physical methods such as mechanical stirring, ultrasonic dispersion, and ball milling, followed by high-temperature carbonization or reduction treatment. For example, Chinese invention patent publication CN112886015A prepares solution A with phenolic resin, graphene oxide, and hydroxylated carbon nanotubes, and solution B with a silane coupling agent and nano-silicon. After hydrothermal polymerization, the mixture is carbonized in a tube furnace at 800-1100℃ for 12-72 hours. In this method, the carbon nanotubes are not grown in situ; rather, they are externally added hydroxylated carbon nanotubes. The interfacial bonding with silicon depends on the silane coupling agent, still belonging to a post-composite mode with weak bonding strength. Chinese invention patent publication number CN112599747A directly mixes nano-silicon powder and carbon nanotube dispersion by mechanical stirring, and then reduces them with hydrogen at 600℃. This is the most typical physical mixing method. There are no chemical bonds between carbon nanotubes and silicon, and silicon particles are easy to fall off. The volume expansion during the cycle cannot be effectively suppressed.

[0004] 2. The process is lengthy and the equipment is highly dependent, making it difficult to achieve continuous production: Typical processes require multiple steps such as solution preparation, hydrothermal / polymerization reaction, filtration and drying, high-temperature carbonization (800~1100℃, 12~72 hours), pickling, and ball milling (Chinese invention patent publication numbers CN112886015A and CN112467134A). Frequent transfers between equipment result in intermittent production. The above methods are energy-intensive and inefficient, making them unsuitable for large-scale continuous production.

[0005] 3. Harsh reaction conditions and use of toxic or hazardous raw materials: Chinese invention patent publication number CN112467134A uses highly toxic SOCl2 for acyl chloride reaction, CN111732092A uses concentrated acid, and CN107658452A uses chlorosilane monomers that release HCl upon contact with water.

[0006] 4. Existing plasma or thermal CVD methods have failed to achieve integrated preparation of carbon nanotubes through in-situ growth and simultaneous purification. For example, Chinese invention patent publication CN120518058A uses carbon nanotubes as seed crystals to simultaneously deposit silicon-carbon in fluidized bed thermal CVD (450~600℃), followed by independent carbon coating, with a total reaction time of 5~20 hours. In this method, the carbon nanotubes are added as raw materials rather than grown in situ, resulting in weak interfacial bonding; a single temperature zone cannot remove amorphous carbon or repair sp. 3 Defects; subsequent carbon coating only masks rather than removes defects. For example, Qiao Yafeng et al. (Preparation of silicon-carbon anode materials for lithium-ion batteries by thermal plasma method [J]. Nonferrous Metals Engineering, 2023, 13(8): 28-35) used DC arc thermal plasma (11.7 kW single-stage) to vaporize silicon waste and graphite solid powder and then rapidly cooled it to obtain a spherical mixture of silicon nanoparticles and carbon nanoparticles. This method does not use a catalyst, does not generate carbon nanotubes, and the product is a physical mixture of silicon and carbon without a three-dimensional conductive network; single-stage power cannot achieve amorphous carbon removal or defect repair; natural cooling leads to a high defect density. The above-mentioned existing technologies have failed to solve the problem of in-situ integrated composite and simultaneous purification of carbon nanotubes and silicon.

[0007] Currently, there is no known method for continuously completing carbon nanotube growth, silicon deposition, amorphous carbon removal, and sp24-plasma deposition in the same plasma reactor using three power gradients. 3 Reports on defect repair. The three-segment series electrode structure and power segmentation control scheme of this invention are non-obvious. Summary of the Invention

[0008] To address the aforementioned technical bottlenecks, the present invention aims to provide a method for in-situ preparation of carbon nanotube / silicon composite materials using a three-stage continuous flow plasma method. In the carbon nanotube / silicon composite material prepared by this invention, carbon nanotubes are grown in situ from a carbon source and anchor silicon particles to form a three-dimensional network conductive structure. Silicon nanoparticles are uniformly distributed on the surface of the carbon nanotubes and in the network gaps. In the X-ray photoelectron spectroscopy (XPS) of the composite material, the C 1s peak shows a high concentration of silicon nanotubes. 3 The proportion of hybrid carbon (the proportion being the ratio of the peak area corresponding to sp³ hybrid carbon to the total peak area of ​​C 1s) is less than 10%. This method requires only a few minutes of reaction, operates at atmospheric pressure, uses inexpensive and readily available raw materials, and does not add sulfur-containing co-catalysts or strong acids throughout the process, making it green and environmentally friendly, and suitable for large-scale continuous production.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: An in-situ preparation method of carbon nanotube / silicon composite material for lithium-ion battery anode materials includes the following steps: S1. Carrier gas and reducing gas bring the precursor mixture containing carbon source and catalyst into the first dual-electrode region of the plasma reactor to crack the raw material by arc discharge with a power of 20~50 kW. At the same time, silicon source gas is introduced to generate carbon nanotubes and deposit silicon nanoparticles on the surface and in the network of carbon nanotubes. S2. The generated carbon nanotubes, silicon nanoparticles, and amorphous carbon impurities sequentially pass through the second and third dual-electrode regions along with the carrier gas. The second dual-electrode region removes amorphous carbon impurities at a power of 10–19 kW, and the third dual-electrode region reduces sp(II) content in the carbon nanotubes at a power of 1–9 kW. 3 The defects are then removed, and the carbon nanotube / silicon composite material is obtained by one or a combination of liquid nitrogen spraying, cryogenic nitrogen gas or water spraying.

[0010] Furthermore, the plasma reactor includes a first, second, and third dual-electrode region connected in series in the same sealed cavity along the gas flow direction. Each dual-electrode region consists of a pair of parallel conductive electrodes with an electrode spacing of 1 to 10 mm.

[0011] Furthermore, the carrier gas is at least one of argon, nitrogen, helium, and neon; the reducing gas is at least one of hydrogen and ammonia; and the flow rates of the carrier gas and the reducing gas are each independently 1~10 L / min.

[0012] Further, the carbon source is at least one of anhydrous ethanol, acetonitrile, and xylene; the catalyst is at least one of ferrocene, cobalt styrene, nickel styrene, iron acetylacetonate, and cobalt acetylacetonate; the mass fraction of the catalyst in the precursor solution is 0.5~5.0 wt%; and the silicon source is at least one of silane, dimethylsilane, and tetramethylsilane, with a flow rate of 1~10 L / min.

[0013] Furthermore, the precursor mixture solution is introduced by heating and vaporizing the precursor mixture solution placed in a precision temperature-controlled evaporator, and then carrying it into the reaction chamber by carrier gas bubbling or by spraying it through a micro-pump; the heating temperature is controlled at 80~120℃.

[0014] Furthermore, the cooling method is one or a combination of liquid nitrogen spraying device, cryogenic nitrogen or water spraying for rapid cooling at the top outlet of the reaction chamber, with a spraying time of 0.1 to 1 second, liquid nitrogen flow rate of 0.5 to 5 L / min, cryogenic nitrogen flow rate of 0.5 to 5 L / min, and water spraying flow rate of 0.5 to 5 L / min.

[0015] Furthermore, after cooling, the reaction chamber is opened, and the carbon nanotube / silicon composite material deposited on the inner surface of the substrate is separated and collected by airflow classification or vibration sieving to obtain a high-purity composite material.

[0016] Compared with the prior art, the present invention provides an in-situ preparation method for carbon nanotube / silicon composite materials, which has the following beneficial effects: 1. In-situ growth and simultaneous deposition: In the first high-power region, carbon source is decomposed to generate carbon nanotubes, while silicon source gas is simultaneously decomposed and silicon nanoparticles are deposited on the surface and in the network of carbon nanotubes, forming a three-dimensional network structure in which carbon nanotubes anchor silicon particles. The interface is firmly bonded, avoiding the problem of silicon particles easily falling off in traditional physical mixing.

[0017] 2. Three-stage integrated continuous processing: By setting up three continuous zones with different power levels, the growth of carbon nanotube / silicon composite materials, the removal of amorphous carbon impurities, and the sp... are completed sequentially in the same reactor. 3 The repair of defects does not require transferring the product to a separate device for post-processing, which simplifies the process and reduces energy consumption and pollution risks.

[0018] 3. Rapid reaction, suitable for large-scale production: The entire reaction process takes only a few minutes, operates at atmospheric pressure, has simple equipment, and uses inexpensive and readily available raw materials, enabling continuous flow production and possessing good industrialization prospects.

[0019] 4. Excellent product structure: In the prepared carbon nanotube / silicon composite material, the carbon nanotubes are in a three-dimensional network structure, and the silicon nanoparticles are uniformly distributed and effectively anchored by the carbon nanotube network, which helps to buffer the volume expansion of silicon and improve the cycle stability and rate performance of the lithium-ion battery anode.

[0020] 5. Compared with existing thermal CVD methods using carbon nanotubes as seed crystals (such as CN120518058A) and single-stage thermal plasma methods (such as the preparation of silicon-carbon anode materials for lithium-ion batteries by thermal plasma method reported by Qiao Yafeng et al. [J]. Nonferrous Metals Engineering, 2023, 13(8): 28-35), this invention has the following essential differences and advantages: Carbon nanotube source: In this invention, carbon nanotubes are grown in situ by in-situ pyrolysis in plasma using inexpensive carbon sources such as ethanol, forming a three-dimensional conductive network to anchor silicon particles; while in the comparative method, carbon nanotubes are added seed crystals or no carbon nanotubes are generated (only carbon particles), and the interface bonding is weak or there is no conductive network.

[0021] Process integration: This invention continuously completes growth, selective etching of amorphous carbon, and sp³ defect repair in the same reactor through three power gradients (20~50 kW→10~19 kW→1~9 kW), without post-processing; the comparative method is a single power or a single temperature zone, which cannot be purified in situ and requires an additional carbon coating step (CN120518058A) or natural cooling (Qiao Yafeng et al.).

[0022] Reaction efficiency: The total reaction time of this invention is only a few minutes, while CN120518058A requires 5 to 20 hours. Although the method of Qiao Yafeng et al. is continuous, the product structure is simple and the defects cannot be controlled.

[0023] Product structure: The product of this invention is a composite structure of silicon nanoparticles anchored by a three-dimensional carbon nanotube network, with low amorphous carbon content (sp³ carbon accounts for only 8.21% in Example 1) and high degree of graphitization; the product of the comparative method is a physical mixture of silicon and carbon or a disordered carbon matrix with high defect density.

[0024] Cooling method: The present invention uses one or a combination of liquid nitrogen spray, low temperature nitrogen gas or water spray for rapid cooling to lock in the highly crystalline structure; the comparative method does not use rapid cooling, and the defects are easily regenerated. Attached Figure Description

[0025] Figure 1 This is a SEM image of the carbon nanotube / silicon composite material prepared in Example 1 of the present invention.

[0026] Figure 2 The graphs show the electrochemical performance of the carbon nanotube / silicon composite material prepared in Example 1 of this invention, (a) cycling performance (0.1 A / g), and (b) rate performance.

[0027] Figure 3 This is a SEM image of the carbon nanotube / silicon composite material prepared in Example 2 of the present invention.

[0028] Figure 4 The Raman spectrum of the pure carbon nanotubes prepared in Comparative Example 1 of this invention (D peak ~1350 cm⁻¹) -1 G peak ~1580cm -1 ).

[0029] Figure 5 This is a SEM image of the carbon nanotube / silicon composite material prepared in Comparative Example 2 of this invention.

[0030] Figure 6 The graphs show the electrochemical performance of the carbon nanotube / silicon composite material prepared in Comparative Example 2 of this invention, (a) cycling performance (0.1 A / g), and (b) rate performance.

[0031] Figure 7 This is a SEM image of the carbon nanotube / silicon composite material prepared in Comparative Example 3 of this invention.

[0032] Figure 8 The image shows the XRD pattern of the carbon nanotube / silicon composite material prepared in Comparative Example 3 of this invention.

[0033] Figure 9 The image shows the Raman spectrum of the carbon nanotube / silicon composite material prepared in Comparative Example 4 of this invention (Si peak ~520.3 cm⁻¹). -1 D peak ~1350 cm -1 G peak ~1580 cm -1 2 D peak ~2700 cm -1 ).

[0034] Figure 10 XPS C 1s spectra of the carbon nanotube / silicon composite materials prepared in Examples 1(a), 5(b), and 6(c) of this invention.

[0035] Figure 11 The Raman spectrum of the pure carbon nanotubes prepared in Comparative Example 7 of this invention (D peak ~1350 cm⁻¹) -1 G peak ~1580cm -1 ).

[0036] Figure 12 The Raman spectrum of the carbon nanotube / silicon composite material prepared in Example 1 of this invention (Si peak ~520.3 cm⁻¹) is shown. -1 D peak ~1350 cm -1 G peak ~1580 cm -1 ). Detailed Implementation

[0037] The embodiments and comparative examples of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in various ways as defined in the claims.

[0038] Reactor Structure Description: The plasma reactor of this invention is a DC arc plasma reactor, comprising three dual-electrode regions connected in series within the same sealed chamber along the gas flow direction. Each dual-electrode region consists of a pair of parallel conductive electrodes with an adjustable electrode spacing, preferably 1-3 mm. The carrier gas carries the reactants sequentially through the first, second, and third electrode regions, each independently connected to a high-frequency DC power supply, with its output power set separately. Controlling the electrode spacing within the range of 1-3 mm ensures stable arc discharge and the formation of a uniform plasma region, while avoiding insufficient energy density due to excessive spacing or gas flow blockage due to insufficient spacing.

[0039] Reaction mechanism explanation: The second stage power range (10~19 kW) of this invention does not remove amorphous carbon through oxidation, but rather utilizes the long-lived hydrogen radicals (H+) generated by the high-power discharge in the first stage. * Selective chemical etching of amorphous carbon. Because amorphous carbon has more dangling bonds and structural defects, its reactivity with hydrogen radicals is much higher than that of crystalline carbon nanotubes. Therefore, under the premise of appropriately reducing the power to avoid damage to carbon nanotubes, hydrogen radicals can preferentially etch amorphous carbon to generate gaseous hydrocarbons (such as CH4, C2H2), thus achieving selective removal.

[0040] The third stage of low power (1~9 kW) for sp 3 The defect repair mechanism is low-energy plasma annealing. Within this power range, the plasma provides a local temperature of 300–600 °C and low-energy ion bombardment of 10–50 eV, sufficient to interrupt sp... 3 CH bonds at the defects promote carbon atom surface migration, causing carbon atoms to rehybridize into an sp² structure, repairing the graphite lattice, and improving I. G / I D The ratio. Excessive power can introduce new defects, therefore the power selection in this invention is of critical technical significance.

[0041] Example 1; The carbon source in this example is ethanol; the catalyst is ferrocene with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution is 100°C; the carrier gas is nitrogen with a flow rate of 4.0 L / min; the reducing gas is hydrogen with a flow rate of 1.0 L / min; the silicon source is silane with a flow rate of 2.0 L / min; the power of the first stage is 30 kW, the power of the second stage is 10 kW, and the power of the third stage is 3 kW; the total reaction time is 5 minutes; the liquid nitrogen spraying time is 0.5 seconds with a flow rate of 2 L / min; the collection method is gas flow staged collection.

[0042] SEM characterization: such as Figure 1 As shown, the obtained product is a carbon nanotube / silicon composite material. Scanning electron microscopy observation shows that the carbon nanotubes have a three-dimensional network structure, and silicon nanoparticles are uniformly distributed on the surface of the carbon nanotubes and in the gaps between the networks. The diameter of the nanotubes is 10~19 nm, and there are very few amorphous carbon impurities.

[0043] Raman characterization: such as Figure 12 As shown, the Raman G / D ratio of the product at this time is 0.863, the Si peak is sharp, and it has a high Si content. The composite material prepared under this condition has a good Si and carbon nanotube coating structure.

[0044] XPS characterization: such as Figure 10 (a) shows the C 1s peak of the obtained product. Peak fitting of the C 1s peak revealed that the peak near 284.8 eV belongs to sp² hybrid carbon (graphite carbon), and the peak near 285.5–286.5 eV belongs to sp² hybrid carbon. 3 Hybrid carbon (amorphous carbon / defective carbon). Calculations show that sp... 3 Hybrid carbon accounts for 8.21% of the total carbon products, indicating that the content of amorphous carbon in the products is extremely low and the degree of graphitization of carbon nanotubes is high.

[0045] Electrochemical testing: The prepared silicon composite carbon nanotube material, conductive carbon black and CMC binder were uniformly mixed in a mass ratio of 7:2:1. An appropriate amount of deionized water was added and the mixture was ground to form a uniform slurry. The slurry was uniformly coated onto the copper foil current collector using a 100 μm coating blade and dried in a vacuum drying oven at 80℃ for 8 h. The dried electrode was cut into circular electrode sheets with a diameter of 14 mm, and the mass of the active material of the single electrode sheet was accurately weighed. The assembly of coin cells was carried out in a high-purity argon glove box with water and oxygen content both below 0.01 ppm. The battery casing was CR2032, the separator was a Celgard 2400 membrane with a diameter of 18 mm, and the electrolyte was a 1 mol / L LiPF6 EC / EMC mixture (EC to EMC volume ratio 1:1). After the assembled batteries were allowed to stand for 12 h, electrochemical tests were conducted. The charge-discharge voltage window was 0.01 V to 3 V, the current density for 50 cycles was 0.1 A / g, and the current densities for rate performance tests were 0.1 A / g, 0.2 A / g, 0.5 A / g, 0.8 A / g, and 1 A / g, respectively.

[0046] The results show that: Figure 2 As shown in (a), the initial discharge specific capacity was 1089 mAh / g, and the discharge specific capacity after 50 cycles was 984 mAh / g, with a capacity retention of 90.3%. Figure 2(b) For rate performance testing, the decrease in battery capacity at various current densities is small and stable, and the capacity is still 600 mAh / g at a current density of 1 A / g.

[0047] Example 2; The carbon source in this example is ethanol; the catalyst is ferrocene with a mass fraction of 0.8 wt%; the heating temperature of the precursor mixture solution is 100℃; the carrier gas is nitrogen with a flow rate of 4.0 L / min; the reducing gas is hydrogen with a flow rate of 1.0 L / min; the silicon source is silane with a flow rate of 2.0 L / min; the power of the first stage is 30 kW, the power of the second stage is 10 kW, and the power of the third stage is 3 kW; the total reaction time is 5 minutes; the liquid nitrogen spraying time is 0.5 seconds with a flow rate of 2 L / min; the collection method is gas flow staged collection.

[0048] SEM characterization: such as Figure 3 As shown, the diameter of carbon nanotubes in the product is slightly increased, the distribution of silicon particles is still relatively uniform, and the content of amorphous carbon is slightly higher than that in Example 1.

[0049] Example 3; The carbon source in this example is ethanol; the catalyst is ferrocene with a mass fraction of 0.8 wt%; the heating temperature of the precursor mixture solution is 100℃; the carrier gas is nitrogen with a flow rate of 5.0 L / min; the reducing gas is ammonia with a flow rate of 2.0 L / min; the silicon source is dimethylsilane with a flow rate of 3.0 L / min; the power of the first stage is 30 kW, the power of the second stage is 10 kW, and the power of the third stage is 3 kW; the total reaction time is 5 minutes; the liquid nitrogen spraying time is 0.5 seconds with a flow rate of 2 L / min; the collection method is airflow staged collection.

[0050] Results and characterization: The product structure is similar to that of Example 1, the electrochemical performance is comparable to that of Example 1, the silicon deposition is slightly higher, and the carbon nanotube network is intact.

[0051] Comparative Example 1; The carbon source in this comparative example was ethanol; the catalyst was ferrocene with a mass fraction of 0.8 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen with a flow rate of 5.0 L / min; the reducing gas was ammonia with a flow rate of 2.0 L / min; no silicon source gas was introduced; the power of the first stage was 30 kW, the power of the second stage was 10 kW, and the power of the third stage was 3 kW; the total reaction time was 5 minutes; the liquid nitrogen spraying time was 0.5 seconds and the flow rate was 2 L / min; the collection method was gas flow staged collection.

[0052] Raman characterization: such as Figure 4 As shown, the Raman ratio of the product at this time is 1.521, indicating a high degree of graphitization.

[0053] Comparative Example 2; The carbon source in this comparative example was ethanol; the catalyst was ferrocene, with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen, with a flow rate of 4.0 L / min; the reducing gas was hydrogen, with a flow rate of 1.0 L / min; the silicon source was silane, with a flow rate of 2.0 L / min; the power of the first stage was 10 kW, the power of the second stage was 10 kW, and the power of the third stage was 3 kW; the total reaction time was 5 minutes; the liquid nitrogen spraying time was 0.5 seconds, with a flow rate of 2 L / min; the collection method was gas flow staged collection.

[0054] SEM characterization: such as Figure 5 As shown, the carbon nanotube yield is low, the tube diameter is uneven, silicon particles are severely agglomerated, and a large amount of amorphous carbon remains.

[0055] Electrochemical testing: such as Figure 6 As shown in (a), the initial discharge specific capacity was 1049 mAh / g, and the discharge specific capacity after 50 cycles was 519 mAh / g, with a capacity retention of 49.5%. Figure 6 (b) For rate performance testing, the battery capacity decreased significantly and was unstable at various current densities, with a capacity of only about 250 mAh / g at a current density of 1 A / g.

[0056] Comparative Example 3; The carbon source in this comparative example was ethanol; the catalyst was ferrocene, with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen, with a flow rate of 4.0 L / min; the reducing gas was hydrogen, with a flow rate of 1.0 L / min; the silicon source was silane, with a flow rate of 2.0 L / min; the power of the first stage was 30 kW, the power of the second stage was 30 kW, and the power of the third stage was 30 kW; the total reaction time was 5 minutes; the liquid nitrogen spraying time was 0.5 seconds, and the flow rate was 2 L / min; the collection method was gas flow staged collection.

[0057] SEM characterization: such as Figure 7 As shown, the product has a high content of amorphous carbon and many defects in carbon nanotubes. At this point, the power is too high, and too much amorphous carbon accumulates.

[0058] XRD characterization: such as Figure 8 As shown, the three main diffraction peaks of Si in the XRD pattern are assigned to 28.448°, 47.313° and 56.135°, respectively. It can be seen that the product has many impurity peaks at this time, indicating that excessive power will lead to the generation of too many impurities.

[0059] Comparative Example 4; The carbon source in this comparative example was ethanol; the catalyst was ferrocene, with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen, with a flow rate of 4.0 L / min; the reducing gas was hydrogen, with a flow rate of 1.0 L / min; the silicon source was silane, with a flow rate of 2.0 L / min; the power of the first stage was 30 kW, the power of the second stage was 10 kW, and the power of the third stage was 3 kW; the total reaction time was 5 minutes; and the mixture was allowed to cool naturally to room temperature.

[0060] Raman characterization: such as Figure 9 As shown, in the Raman spectrum of the product of Comparative Example 4, the intensity ratio of the G peak to the D peak is approximately 0.8, lower than 0.863 in Example 1; the Si peak is weaker than in Example 1. This indicates that natural cooling leads to the generation of more amorphous carbon and structural defects, confirming the key role of rapid cooling in the present invention for high crystallinity structures and suppressing defect regeneration.

[0061] Comparative Example 5; The carbon source in this comparative example was ethanol; the catalyst was ferrocene, with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen, with a flow rate of 4.0 L / min; the reducing gas was hydrogen, with a flow rate of 1.0 L / min; the silicon source was silane, with a flow rate of 2.0 L / min; the power of the first stage was 30 kW, the power of the second stage was 0 kW, and the power of the third stage was 3 kW; the total reaction time was 5 minutes; the liquid nitrogen spraying time was 0.5 seconds, with a flow rate of 2 L / min; the collection method was gas flow staged collection.

[0062] XPS characterization: such as Figure 10 (b) shows the C 1s peak of the obtained product. Using the same peak fitting method as in Example 1, sp... 3 Hybrid carbon accounted for 26.12% of the total carbon products, significantly higher than in Example 1 (8.21%), indicating that the second stage power of 0 kW could not effectively remove amorphous carbon, resulting in a large amount of defective carbon remaining.

[0063] Comparative Example 6; The carbon source in this comparative example was ethanol; the catalyst was ferrocene, with a mass fraction of 1.5 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen, with a flow rate of 4.0 L / min; the reducing gas was hydrogen, with a flow rate of 1.0 L / min; the silicon source was silane, with a flow rate of 2.0 L / min; the power of the first stage was 30 kW, the power of the second stage was 10 kW, and the power of the third stage was 0 kW; the total reaction time was 5 minutes; the liquid nitrogen spraying time was 0.5 seconds, with a flow rate of 2 L / min; the collection method was gas flow staged collection.

[0064] XPS characterization: such as Figure 10 (c) shows the C 1s peak of the obtained product. Using the same peak fitting method as in Example 1, sp...3 Hybrid carbon accounted for 32.43% of the total carbon products, approximately four times that of Example 1, indicating that the third stage with a power of 0 kW could not effectively repair sp. 3 Defects result in a large amount of defective carbon remaining.

[0065] Comparative Example 7; The carbon source in this comparative example was ethanol; the catalyst was ferrocene with a mass fraction of 0.8 wt%; the heating temperature of the precursor mixture solution was 100℃; the carrier gas was nitrogen with a flow rate of 5.0 L / min; the reducing gas was ammonia with a flow rate of 2.0 L / min; no silicon source gas was introduced; the power of the first stage was 30 kW, the power of the second stage was 10 kW, and the power of the third stage was 3 kW; the total reaction time was 5 minutes; water spray cooling was used, with a spray time of 0.5 seconds and a spray flow rate of 2 L / min; the collection method was airflow staged.

[0066] Raman characterization: such as Figure 11 As shown, the Raman ratio at this time is 1.507, which is close to the Raman ratio of Comparative Example 1, indicating that water spray cooling can also achieve a high degree of graphitization.

[0067] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for preparing a carbon nanotube / silicon composite material, characterized in that: Includes the following steps: S1. The carrier gas and reducing gas bring the precursor mixture solution containing carbon source and catalyst into the first dual electrode region of the plasma reactor to crack the raw material by arc discharge with a power of 20~50 kW. At the same time, silicon source gas is introduced to generate carbon nanotubes and deposit silicon nanoparticles on the surface and in the network of carbon nanotubes. S2. The generated carbon nanotubes, silicon nanoparticles, and amorphous carbon impurities are sequentially passed through the second and third dual-electrode regions along with the carrier gas. The second dual-electrode region removes amorphous carbon impurities at a power of 10–19 kW, and the third dual-electrode region reduces sp(II) content in the carbon nanotubes at a power of 1–9 kW. 3 The defects were removed, and then the carbon nanotube / silicon composite material was obtained through cooling treatment.

2. The preparation method according to claim 1, characterized in that: The carrier gas is at least one of argon, nitrogen, helium, and neon; the reducing gas is at least one of hydrogen and ammonia; and the flow rates of the carrier gas and the reducing gas are each independently 1~10 L / min.

3. The preparation method according to claim 1, characterized in that: The carbon source is at least one of anhydrous ethanol, acetonitrile, and xylene; the catalyst is at least one of ferrocene, cobalt styrene, nickel styrene, iron acetylacetonate, and cobalt acetylacetonate; the mass fraction of the catalyst in the precursor mixed solution is 0.5~5.0 wt%; the silicon source is at least one of silane, dimethylsilane, and tetramethylsilane, with a flow rate of 1~10 L / min.

4. The preparation method according to claim 1, characterized in that: The cooling method is at least one of liquid nitrogen spray, cryogenic nitrogen, and rapid water spray cooling.

5. A carbon nanotube / silicon composite material prepared by the method according to any one of claims 1-4, characterized in that: In the composite material, carbon nanotubes exhibit a three-dimensional network structure, with silicon nanoparticles uniformly distributed on the surface of the carbon nanotubes and within the network gaps; in the C 1s peak of the X-ray photoelectron spectroscopy of the composite material, sp 3 The peak area corresponding to hybrid carbon accounts for less than 10% of the total carbon peak area.

6. The application of a carbon nanotube / silicon composite material prepared by the method according to any one of claims 1-4 in a lithium-ion battery anode material.

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