A system, method, single-walled carbon nanotube and battery for preparing single-walled carbon nanotubes by magnetic field assisted plasma CVD

Abstract

This invention discloses a system, method, single-walled carbon nanotubes (SHUs), and battery prepared by magnetic field-assisted plasma CVD, relating to the field of materials technology. The system includes a plasma evaporation unit, a magnetic field screening unit, and a CVD growth unit arranged sequentially. The magnetic field screening unit includes a magnetic field screening cavity, a temperature control component, and a magnetic field generating component. The magnetic field screening unit is positioned between the plasma evaporation unit and the CVD growth unit. By applying a magnetic field and coordinating with temperature control, catalyst particles are screened. This unit selectively removes large-diameter catalyst particles while retaining small-diameter ones, allowing for precise control of the particle size distribution. This reduces the defect density and ash content of the SHUs from the source, overcoming the bottleneck of traditional processes in the mass production of SHUs and significantly improving product purity and structural consistency.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and more specifically, to a system, method, single-walled carbon nanotubes, and battery prepared by magnetic field-assisted plasma CVD. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) are one-dimensional nanomaterials formed by rolling up a single layer of graphene. They possess extremely high mechanical strength (>100 GPa) and excellent electrical conductivity (10 GPa). 6 With its high efficiency (S / cm) and unique optical properties, single-walled carbon nanotubes (S nanotubes) have enormous application potential. However, their industrialization has long been limited by the bottlenecks of traditional preparation technologies: methods such as arc discharge and laser ablation have low yields (<1 g / h) and high energy consumption, and the products contain mixed multi-walled tubes and amorphous carbon; although traditional chemical vapor deposition (CVD) can control growth, the catalyst is prone to sintering and deactivation, making it difficult to achieve continuous mass production. Plasma CVD uses ultra-high temperature plasma to vaporize metal catalysts such as iron, cobalt, and nickel, which are then condensed to form nanocatalyst aerogels; combined with the stable growth environment provided by chemical vapor deposition (CVD), it achieves the efficient synthesis of single-walled carbon nanotubes. This method combines the advantages of instantaneous high temperature of plasma and controllable growth of CVD, breaking through the bottlenecks of traditional processes in mass production, significantly improving product purity and structural consistency, and is currently the core research and development direction for industrial mass production.

[0003] In the large-scale preparation of single-walled carbon nanotubes using plasma chemical vapor deposition (CVD), the catalyst particle size is difficult to control precisely during the condensation stage after plasma evaporation of the metal catalyst to form nanocatalysts. This results in a wide catalyst size distribution (ranging from a few nanometers to hundreds of nanometers). Excessively large catalyst sizes lead to increased product defects (lower GD ratio), higher ash content, and increased difficulty in subsequent purification processes. Therefore, achieving catalyst particle size control, improving the quality of single-walled carbon nanotubes, and ultimately realizing large-scale production are pressing technical challenges that need to be addressed in this field.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a system, method, single-walled carbon nanotubes, and battery for magnetic field-assisted plasma CVD preparation, so as to solve or improve the above-mentioned technical problems.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a system for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, the system comprising a plasma evaporation unit, a magnetic field screening unit, and a CVD growth unit connected in sequence, wherein:

[0008] The plasma evaporation unit is used to evaporate ferromagnetic catalyst materials and form catalyst particles;

[0009] The magnetic field screening unit includes a magnetic field screening chamber, a temperature control component, and a magnetic field generating component. The temperature control component is used to adjust the magnetic field screening chamber to a preset temperature. The magnetic field generating component is used to apply a magnetic field to the catalyst particles and selectively screen out catalyst particles that retain ferromagnetism at the preset temperature by utilizing whether the catalyst particles lose their ferromagnetism at the preset temperature.

[0010] The CVD growth unit is used to receive catalyst particles of the target particle size range after screening and to react them with carbon source cracking gas to grow single-walled carbon nanotubes.

[0011] The preset temperature is determined based on the relationship between the catalyst particle size and the Curie temperature, as well as the target particle size range.

[0012] Secondly, the present invention provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, wherein single-walled carbon nanotubes are prepared using a system as described in any of the foregoing embodiments.

[0013] Thirdly, the present invention provides a single-walled carbon nanotube, which is prepared by any of the systems or methods described in any of the foregoing embodiments.

[0014] Fourthly, the present invention provides a battery comprising a single-walled carbon nanotube prepared by a system as described in any of the foregoing embodiments or by a method as described in any of the foregoing embodiments.

[0015] The present invention has the following beneficial effects:

[0016] The magnetic field-assisted plasma CVD system for preparing single-walled carbon nanotubes provided in this invention includes a magnetic field screening unit between the plasma evaporation unit and the CVD growth unit. By applying a magnetic field and coordinating with temperature control, catalyst particles are screened. This unit selectively removes large-diameter catalyst particles while retaining small-diameter ones, allowing for precise control of the particle size distribution. This reduces the defect density and ash content of single-walled carbon nanotubes from the source, breaking through the bottleneck of traditional processes in the mass production of single-walled carbon nanotubes and significantly improving product purity and structural consistency. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the system from a first-person perspective.

[0019] Figure 2 The curve showing the relationship between the particle size of the ferromagnetic catalyst and the Curie temperature is shown.

[0020] Figure 3 Morphology analysis of the single-walled carbon nanotubes prepared in Example 1;

[0021] Figure 4 Morphology analysis of the single-walled carbon nanotubes prepared in Comparative Example 1;

[0022] Figure 5 Statistical analysis of the particle size of catalyst particles in the single-walled carbon nanotubes prepared in Example 1;

[0023] Figure 6 Statistical analysis of the particle size of catalyst particles in the single-walled carbon nanotubes prepared in Comparative Example 1;

[0024] Figure 7 The results of Raman analysis of the single-walled carbon nanotubes prepared in Example 1 are shown.

[0025] Figure 8 The results are Raman analysis of the single-walled carbon nanotubes prepared in Comparative Example 1.

[0026] Icons: 10-Plasma Evaporation Unit; 11-Plasma Evaporation Chamber; 12-Carrier Gas Inlet; 13-Inlet Component; 14-Gas Dispersant Component; 15-Gas Dispersant Hole; 16-Cathode Hollow Graphite Component; 17-Central Hole; 18-Anode Graphite Component; 20-Magnetic Field Screening Unit; 21-Magnetic Field Screening Chamber; 22-Temperature Control Component; 221-Thermocouple; 23-Magnetic Field Generating Component; 231-Induction Coil; 232-Electromagnet; 30-CVD Growth Unit; 31-Carbon Source Inlet; 32-Heating Component; 33-Gas Barrier Component; 34-CVD Growth Chamber; 40-Cooling Unit; 41-Cooling Chamber; 50-Collection Unit; 51-Collection Tank; 52-Nozzle; 53-Water Dispersant Component; 54-Discharge Valve; 55-Discharge Port; 56-Inlet; 100-System. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0028] In a first aspect, the present invention provides a system 100 for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, the system 100 comprising a plasma evaporation unit 10, a magnetic field screening unit 20, and a CVD growth unit 30 connected in sequence.

[0029] Understandably, due to the finite size effect, the Curie temperature (Tc) of nanomagnetic particles (iron, cobalt, nickel, etc.) decreases significantly as the diameter decreases (see [reference needed] for the relationship between particle size and Curie temperature of some ferromagnetic nanoparticle catalysts). Figure 2 The system 100 of this invention establishes a magnetic field screening unit 20 between the plasma evaporation unit 10 and the CVD growth unit 30, forming a region for screening catalyst particles by applying a magnetic field and coordinating temperature control. In this region, large-diameter catalyst particles are selectively removed, while small-diameter catalyst particles are retained. This allows for precise control of the particle size distribution, reducing the defect density and ash content of single-walled carbon nanotubes at the source. This overcomes the bottleneck of traditional processes in the mass production of single-walled carbon nanotubes, significantly improving product purity and structural consistency, and breaking through the bottleneck of high-purity mass production. A schematic diagram of the system 100 from a first-view perspective is shown below. Figure 1 .

[0030] The plasma evaporation unit 10 is used to evaporate ferromagnetic catalyst materials and form catalyst particles; the magnetic field screening unit 20 includes a magnetic field screening chamber 21, a temperature control component 22, and a magnetic field generating component 23. The temperature control component 22 is used to adjust the magnetic field screening chamber 21 to a preset temperature, and the magnetic field generating component 23 is used to apply a magnetic field to the catalyst particles and selectively screen out catalyst particles that retain ferromagnetism at the preset temperature by utilizing whether the catalyst particles lose ferromagnetism at the preset temperature; the CVD growth unit 30 is used to receive catalyst particles within the target particle size range after screening and to react them with carbon source pyrolysis gas to grow single-walled carbon nanotubes; the preset temperature is determined according to the relationship between the particle size of the catalyst particles and the Curie temperature and the target particle size range.

[0031] The plasma evaporation unit 10 includes a plasma evaporation chamber 11, a carrier air inlet, a gas dissipation component 14, a cathode hollow graphite component 16, and an anode graphite component 18, wherein:

[0032] One end of the plasma evaporation chamber 11 is connected to the magnetic field screening chamber 21; the carrier gas inlet is located at the end of the plasma evaporation chamber 11 away from the magnetic field screening unit 20, and is arranged along the axial direction of the system 100 on the end wall of the plasma evaporation chamber 11; the cathode hollow graphite element 16 penetrates the side wall of the plasma evaporation chamber 11 along the radial direction of the system 100, and is arranged opposite to the anode graphite element 18; the anode graphite element 18 is located inside the plasma evaporation chamber 11 and is arranged opposite to the cathode hollow graphite element 16; the gas diffuser 14 is connected to the carrier gas inlet 12, is located inside the plasma evaporation chamber 11, and is located on the side of the oppositely arranged anode graphite element 18 and cathode hollow graphite element 16 away from the magnetic field screening unit 20.

[0033] Furthermore, the air diffuser 14 may include 10 to 30 evenly arranged air diffuser holes 15 with a diameter of 1 mm to 3 mm; the air diffuser 14 is in the shape of a porous disc, and the cross-sectional shape is selected from any one of the circles, squares, triangles and rectangles.

[0034] In specific embodiments of the present invention, the air diffuser 14 is arranged perpendicularly to the carrier air inlet 13, which facilitates the more efficient introduction of protective gas and removes air and residual impurities from the cavity in a shorter time. The cavity of the system 100 of the present invention is cylindrical, and the radial cross-section of the air diffuser 14 is circular. Twenty air diffuser holes 15 with a diameter of 2 mm are evenly arranged on the air diffuser 14. In other embodiments of the present invention, the radial cross-sectional shape of the air diffuser 14, the number of air diffuser holes 15, and their diameter can be reasonably set according to actual conditions.

[0035] The cathode hollow graphite component 16 is a cathode hollow graphite electrode rod, and units respectively loading plasma, magnetic catalyst, and co-catalyst are connected to the outside of the cathode hollow graphite electrode rod. The anode graphite component 18 is an anode graphite crucible. The graphite crucible in this invention has a concave structure, and the lowest point of the concave structure is on the same straight line as the central hole 17 of the cathode hollow graphite electrode rod. A carrier air inlet 13 is provided at the carrier air inlet, which is connected to the gas dispersant 14 and is arranged vertically.

[0036] During the operation of the plasma evaporation unit 10, a protective gas (such as argon, helium, nitrogen, etc.) is continuously introduced. Molten material is added to the anode graphite crucible, and high-purity argon is introduced through the carrier gas inlet 12 as a protective gas for 0.8-1.5 hours to ensure that the air inside the plasma evaporation unit 10 is completely removed. Plasma gas is introduced through the cathode hollow graphite electrode rod, the plasma power supply is turned on and the power is adjusted to generate a plasma arc between the cathode and anode, raising the temperature of the plasma evaporation chamber 11 to 1200-2000℃. Argon gas carrying magnetic catalyst and co-catalyst is introduced through the central hole 17 of the cathode hollow graphite electrode rod. After evaporation in the high-temperature zone of the plasma evaporation unit 10, it forms vapor, which is condensed through the gas diffuser 14 to form catalyst particles. Under the action of the protective gas flow, these particles enter the magnetic field screening unit 20, and the generated catalyst particles are nanoscale particles.

[0037] In the plasma evaporation unit 10, the plasma power can be 30 kW-200 kW, the current can be 500A-2000 A, the voltage can be 60 V-100 V, and the temperature can be 1500℃-1800℃; the plasma material is selected from at least one of argon, hydrogen, nitrogen and helium, and the plasma flow rate can be 30 L / min-800 L / min.

[0038] The ferromagnetic catalyst is selected from at least one of iron, cobalt, nickel, ferrocene, cobalt dicene, and nickel dicene, and the co-catalyst is selected from at least one of sulfur powder, thiophene, carbon disulfide, ferrous sulfide, and molybdenum sulfide. Preferably, the addition rate of the ferromagnetic catalyst and / or co-catalyst is 0.1 g / min to 10 g / min. If the addition rate of the magnetic catalyst and / or co-catalyst is too fast, it cannot be uniformly dispersed and fully contacted with the reaction medium, easily leading to magnetic and non-magnetic agglomeration and the formation of large catalytic particles; if the addition rate is too slow, it will prolong the reaction time, resulting in a decrease in production efficiency.

[0039] The magnetic field screening unit 20 is designed based on the fact that the Curie temperature of ferromagnetic (iron, cobalt, nickel, etc.) nanoparticles decreases significantly with decreasing particle size. Above the Curie temperature, the ferromagnetism of the catalyst particles disappears, and they will not be attracted by a magnet. This is based on the relationship curve between the particle size and Curie temperature of the ferromagnetic catalyst particles (see [link to curve]). Figure 2 The temperature of the magnetic field screening unit 20 should be set appropriately. For example, to control the particle size of the iron catalyst below 20 nm, a temperature of approximately 697.5℃ should be selected. It should be noted that to screen catalysts with different target particle size ranges, the preset temperature value can be adjusted according to the correspondence between the selected catalyst particle size and Curie temperature, combined with the required target particle size range. For example, for iron catalysts, refer to... Figure 2 The particle size shown If the particle size of the iron catalyst particles needs to be controlled below 10 nm, the temperature of the magnetic field screening unit 20 can be preset to about 625℃.

[0040] Furthermore, it should be understood that although the magnetic field screening unit 20 of the present invention aims to control the catalyst particle size below a certain set value (such as 20 nm or other preset values), this does not mean that it can absolutely screen out all particles larger than that size. This is mainly because catalyst particles slightly larger than that size, although magnetic, have weak magnetism because their preset temperature is close to their Curie temperature. Even if a strong magnetic field is applied, it may not be sufficient to remove them by attracting and changing their trajectory. Figure 5 As shown, in actual operation, a very small number of catalyst particles with a diameter larger than the set value (mainly catalyst particles with a diameter slightly larger than the set value by 20 nm) may still pass through the magnetic field screening unit 20 and enter the CVD growth unit 30. Additionally, during the actual operation of the system 100, factors such as the lag in temperature regulation may also prevent the removal of all particles exceeding this size. However, compared to the system without a magnetic field (corresponding to...), Figure 6 Compared to the situation in the past, Figure 5 This invention demonstrates that it can significantly remove most large-diameter catalyst particles, thereby effectively reducing the average particle size of the final catalyst particles and achieving precise control over the catalyst particle size distribution. Therefore, by introducing the magnetic field screening unit 20, this invention can efficiently screen out large-diameter catalyst particles and optimize the particle size distribution.

[0041] The temperature control component 22 in the magnetic field screening unit 20 includes a first interlayer water-cooled component (not shown in the figure) and a thermocouple 221. The first interlayer water-cooled component is arranged around the magnetic field screening cavity 21, and the thermocouple 221 penetrates the side wall of the magnetic field screening cavity 21 radially and extends into the magnetic field screening cavity 21. The thermocouple 221 can monitor the temperature inside the cavity of the magnetic field screening unit 20 in real time, ensuring that the temperature of the cavity of the magnetic field screening unit 20 is within the preset temperature during the operation of the system 100.

[0042] The magnetic field generating component 23 includes an electromagnet 232, which is located outside the first interlayer water-cooled component.

[0043] In the magnetic field screening unit 20, a typical magnetic field direction is configured such that the catalyst particles, which have passed through the magnetic field screening cavity 21 and remain ferromagnetic at a preset temperature, are attracted and moved towards the side wall of the magnetic field screening cavity 21 and trapped within it. Figure 1As shown, an electromagnet 232 is provided on one side of the magnetic field screening chamber 21. The catalyst particles that have passed through the magnetic field screening chamber 21 and remain ferromagnetic at a preset temperature are attracted to the side wall of the electromagnet 232 and thus trapped on the side wall of the magnetic field screening chamber 21.

[0044] It is understandable that the size of the catalyst particles to be screened can be adapted by adjusting the magnetic force of the electromagnet 232 or the size of the area affected by the electromagnet 232. For example, when the screening effect is poor (or the screening effect of catalysts larger than the target particle size range is poor), the magnetic force of the electromagnet 232 can be increased, or a larger model of electromagnet 232 can be selected, or multiple electromagnets 232 can be set.

[0045] Understandably, the catalyst particles trapped in the magnetic field screening chamber 21 will not affect long-term continuous production, and will be removed after the next production stoppage.

[0046] Furthermore, the core of electromagnet 232 can be selected from at least one of soft magnets, permanent magnets, and superconducting magnets; wherein, the permanent magnet is selected from at least one of neodymium iron boron, ferrite, samarium cobalt, and AlNiCo; and the superconducting magnet is selected from at least one of yttrium barium copper oxide and bismuth strontium calcium copper oxide; the specific selection can be made reasonably according to the needs.

[0047] Electromagnet 232 is wound with induction coil 231, which has 1500-2000 turns. Induction coil 231 is tightly wound around the periphery of electromagnet 232. The number of turns of induction coil 231 directly and strongly affects the coil's magnetic flux, induced voltage, inductance, and its ability to generate a magnetic field, and should be set appropriately according to actual needs. Furthermore, in magnetic field filtering unit 20, the current can be controlled at 80 A-120 A, the voltage at 24 V-48 V, and the magnetic field strength at 1 T-2 T. It is understood that these parameters are set to meet specific requirements and can be adjusted according to actual conditions.

[0048] Furthermore, the magnetic field screening unit 20 is also connected to a control unit for controlling the opening and closing of the magnetic field screening unit 20. The control unit can be a microcomputer or a PLC, or other known control units.

[0049] Specifically, when the system 100 is turned on, the magnetic field screening chamber 21 is precisely controlled at a predetermined temperature by the first interlayer water-cooling component, that is, the critical range from the magnetic field screening chamber 21 to the Curie point of the catalyst particles. At the same time, the magnetic field generating component 23 applies a magnetic field to the catalyst particles. By utilizing whether the catalyst particles lose ferromagnetism at the preset temperature, catalyst particles that retain ferromagnetism at the preset temperature are selectively screened out. In the embodiment of the present invention, large-diameter catalyst particles are screened out; small-diameter catalysts (target <20nm) can pass through the magnetic field screening chamber 21 and enter the subsequent unit because the superparamagnetism disappears, while large-diameter particles are adsorbed and retained because they retain magnetism.

[0050] The screened small-particle-size catalyst enters the CVD growth unit 30 and reacts with the decomposed carbon source to achieve highly selective growth of single-walled carbon nanotubes. The magnetic field screening unit 20 significantly improves catalyst utilization (low ash content), reduces catalyst particle size, and reduces carbon impurities (high GD ratio), providing key technical support for the mass production of high-purity single-walled carbon nanotubes.

[0051] The CVD growth unit 30 includes a CVD growth chamber 34, a carbon source inlet 31, an air separator 33, and a heating element 32. One end of the CVD growth chamber 34 is connected to the magnetic field screening chamber 21. The inner diameter of the CVD growth chamber 34 is larger than the inner diameter of the magnetic field screening chamber 21. The end of the air separator 33 near the CVD growth unit 30 is sealed to the end of the CVD growth chamber 34.

[0052] The carbon source inlet 31 is located on one side near the magnetic field screening unit 20; there are multiple carbon source inlets 31, which are evenly arranged along the circumferential sidewall of the CVD growth chamber 34.

[0053] Six to 24 carbon source inlets 31 can be evenly arranged along the circumferential sidewall of the CVD growth chamber 34; the carbon source inlets 31 are externally connected to the equipment for loading the carbon source. In an embodiment of the present invention, 12 inlets are provided.

[0054] The gas separator 33 is used to preheat the gas entering the CVD growth chamber 34 from the carbon source inlet 31. The gas separator 33 is cylindrical, located inside the CVD growth chamber 34, and has a gap with the side wall of the CVD growth unit 30. The carbon source inlet 31 is located in the gap so that the gas flowing out of the carbon source inlet 31 is preheated after passing through the gap and then enters the reaction zone of the CVD growth chamber 34 to contact the catalyst for reaction.

[0055] Specifically, the gas separator 33 can initially isolate the carbon source from the catalyst. The carbon source is preheated until it is fully decomposed into carbon source gas, and then the carbon source gas is allowed to react with the catalyst particles. This can increase the reaction contact area between the carbon source gas and the catalyst particles, making the reaction more thorough, increasing the yield and accelerating the reaction efficiency.

[0056] The CVD growth unit 30 maintains its chamber temperature at 1000℃-1300℃ via heating elements. The carbon source used is selected from at least one of methane, ethylene, propylene, acetylene, ethane, propane, and butane.

[0057] The material of the air-sealing component 33 is a high-temperature ceramic material, selected from at least one of corundum and silicon nitride.

[0058] The heating element 32 is used to heat the CVD growth chamber 34.

[0059] Considering that the generation of carbon nanotubes from carbon source pyrolysis inevitably produces byproducts such as amorphous carbon, carbon coatings, or graphene sheets with numerous defects, these byproducts can poison the catalyst, hinder carbon nanotube growth, or reduce product purity. By introducing carbon source and hydrogen together into the CVD growth unit 30, hydrogen can react with disordered, more reactive carbon species, vaporizing and removing them. Hydrogen can also weaken the interactions between catalyst nanoparticles, helping to inhibit their aggregation into large particles (sintering) at high temperatures. Furthermore, hydrogen can indirectly affect the carbon saturation and precipitation rate in the catalyst through its interaction with carbon, thereby regulating the growth rate and morphology of carbon nanotubes. Appropriate hydrogen partial pressure contributes to achieving stable and controllable growth.

[0060] System 100 also includes a cooling unit 40 and a collection unit 50, wherein the cooling unit 40 is located between the CVD growth unit 30 and the collection unit 50, wherein:

[0061] The cooling unit 40 includes a cooling cavity 41 and a second interlayer water-cooling component (not shown in the figure) disposed outside the cooling cavity 41; the single-walled carbon nanotubes generated in the cavity of the CVD growth unit 30 are cooled and enriched by the cooling unit 40 to form single-walled carbon nanotube fiber clusters; the generated single-walled carbon nanotube fiber clusters are in the form of aerogel.

[0062] The cooling unit 40 is also equipped with a thermocouple 221 penetrating the sidewall of the cooling unit 40 for real-time monitoring of the temperature of the cooling unit 40 cavity. The cooling unit 40 of this invention has a conical structure, with the side with a larger diameter closer to the CVD growth unit 30 and the side with a smaller diameter closer to the collection unit 50. This arrangement facilitates the collection of reaction products. Furthermore, the vertical height of the conical portion of the cooling unit 40 (i.e., the vertical height of the highest point of the sidewall of the cooling unit 40) is lower than the vertical height of the water distribution element 53 of the collection unit 50. This arrangement allows the cooling water discharged from the water distribution element 53 to carry the products into the discharge port 55 for collection. In other embodiments of this invention, the structure of the cooling unit 40 can be reasonably adjusted according to actual needs.

[0063] The collection unit 50 includes a collection tank 51, a nozzle 52, and a water distribution component 53. The collection tank 51 is provided with an inlet 56 connected to the cooling chamber 41 and a discharge port 55 for material discharge. The nozzle 52 is located on the top of the collection tank 51. The water distribution component 53 is located between the nozzle 52 and the inlet 56, and the inlet 56 is located between the water distribution component 53 and the discharge port 55. The water distribution component 53 is a perforated water distribution plate.

[0064] The nozzle 52 is connected to an external water supply unit. The porous design of the water diffuser 53 facilitates uniform water distribution. The vertical height of the water diffuser 53 is higher than the inlet 56, which helps to achieve more thorough cooling of the single-walled carbon nanotubes. The collection unit 50 has a discharge valve 54 on the outside of the discharge port 55. When a certain amount of material accumulates at the bottom of the collection unit 50, the discharge valve 54 opens, and the single-walled carbon nanotubes are discharged with the water flow. The porous water diffuser 53 has 30-50 holes with a diameter of 10 mm-15 mm, which can be adjusted according to actual needs. Specifically, in this embodiment of the invention, the porous water diffuser 53 has 50 holes with a diameter of 10 mm.

[0065] Specifically, the generated aerogel-like single-walled carbon nanotube fiber clusters enter the collection unit 50 with the airflow. The collection unit 50 uses a water spraying method. The water sprayed from the top nozzle 52 passes through the porous water diffuser 53 to form a uniform water curtain in the tank. The single-walled carbon nanotubes are further cooled and contracted in the collection unit 50 and carried to the bottom of the unit by the water curtain. When a certain amount of material accumulates at the bottom, the discharge valve 54 is opened, and the single-walled carbon nanotubes are discharged with the water flow.

[0066] In a second aspect, the present invention provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, wherein single-walled carbon nanotubes are prepared using system 100 as described in any of the foregoing embodiments.

[0067] In an optional implementation, the following steps are included:

[0068] Under a protective atmosphere, molten material is added to the plasma evaporation unit 10, and plasma is introduced. After the temperature of the plasma evaporation unit 10 rises to 1200℃-2000℃, ferromagnetic catalyst material and co-catalyst material are added to generate catalyst particles. The magnetic field screening chamber 21 is controlled to a preset temperature, and a magnetic field is generated in conjunction with the magnetic field generating component 23. The reaction temperature between the carbon source cracking gas and the catalyst particles in the CVD growth unit 30 is controlled to be 1000℃-1300℃. After being processed by the cooling unit 40 and the collection unit 50, single-walled carbon nanotubes are obtained.

[0069] Thirdly, the present invention provides a single-walled carbon nanotube, which is prepared by system 100 as described in any of the foregoing embodiments or by method as described in any of the foregoing embodiments.

[0070] Fourthly, the present invention provides a battery comprising a system 100 as described in any of the foregoing embodiments or a single-walled carbon nanotube prepared by a method as described in any of the foregoing embodiments.

[0071] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0072] Example 1

[0073] This embodiment provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The method utilizes a system 100 for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, and includes the following steps:

[0074] (1) Add molten material (tungsten) to the anode graphite crucible of the plasma evaporation unit 10, and introduce protective gas (high-purity argon, 500L / min) through the carrier gas inlet 13 from the carrier gas inlet 12. Introduce the protective gas for 1 hour to ensure that the air in the cavity is removed; start the plasma evaporation unit 10 and adjust the power (voltage 50V, current 1000A, power 50kW), and introduce plasma gas from the cathode hollow graphite electrode rod to generate a plasma flame between the anode graphite crucible and the cathode hollow graphite electrode rod, raising the temperature of the plasma evaporation chamber 11 to 1800℃.

[0075] Argon gas (50 L / min) carrying magnetic catalyst (iron powder, 1.0 g / min) and co-catalyst (sulfur powder, 0.1 g / min) is introduced through the central hole 17 of the hollow graphite electrode rod in the cathode. After evaporation in the high-temperature plasma zone, it forms vapor, which is condensed through the gas diffuser 14 to form nano-catalyst particles (nano-iron particles). It then enters the magnetic field screening unit 20 with the airflow.

[0076] (2) Turn on and set the voltage of the electromagnet 232 in the magnetic field screening unit 20 to 24V and the current to 100A, and the output magnetic field strength to be about 1.5T; adjust the condensation rate and argon flow rate in the first interlayer water-cooled component of the magnetic field screening unit 20, and monitor it in real time through thermocouple 221 to keep the cavity temperature of the magnetic field screening unit 20 at 697.5℃; wherein, after the nano-iron particles obtained in step (1) enter the magnetic field screening unit 20 with the argon gas flow, the temperature is 697.5℃, the nano-iron particles with a particle size greater than 20 nm are adsorbed on the cavity wall by the influence of the magnetic field, and the iron particles with a particle size less than 20 nm enter the CVD growth unit 30 with the gas flow.

[0077] (3) Small-sized (less than 20 nm) iron nanoparticles after being screened by the magnetic field screening unit 20 enter the CVD growth unit 30; the temperature inside the CVD growth unit 30 cavity is maintained at 1300℃ by controlling the heating element of the CVD growth unit 30, and carbon source (ethylene, 5 L / min) and hydrogen (10 L / min) are introduced through the carbon source inlet 31; after the carbon source is preheated and decomposed into carbon source gas in the gas-isolating component 33, the carbon source gas is controlled to diffuse into the CVD growth unit 30 cavity to react with the iron nanoparticles.

[0078] (4) The single-walled carbon nanotubes grown in step (3) are cooled and enriched by gas flow into the cooling unit 40. The condensation rate and argon flow rate in the second interlayer water-cooled component of the cooling unit 40 are controlled and monitored in real time by thermocouple 221 to maintain the cavity temperature of the cooling unit 40 at 500℃, forming aerogel-like single-walled carbon nanotube fiber clusters.

[0079] (5) The aerogel-like single-walled carbon nanotube fiber clusters generated in step (4) enter the collection unit 50 with the flow. The collection unit 50 adopts the method of spraying water, spraying water from the top nozzle 52 (flow rate of 10L / min). After passing through the porous water diffuser 53, a uniform water curtain is formed in the tank. The single-walled carbon nanotubes are further cooled and contracted in the collection unit 50 and carried to the bottom of the unit by the water curtain. When a certain amount of material accumulates at the bottom, the discharge valve 54 is opened, and the single-walled carbon nanotubes are discharged with the water flow. The waste gas is discharged from the top of the collection unit 50.

[0080] Example 2

[0081] This embodiment provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The implementation steps are the same as in Example 1, with the only difference being:

[0082] (1) The magnetic catalyst is cobalt powder, which corresponds to the formation of cobalt nanoparticles.

[0083] (2) Adjust the cavity temperature of the magnetic field screening unit 20 to maintain it at 1036℃.

[0084] Example 3

[0085] This embodiment provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The implementation steps are the same as in Example 1, with the only difference being:

[0086] (1) The magnetic catalyst is nickel powder, which forms nano-nickel particles.

[0087] (2) Adjust the cavity temperature of the magnetic field screening unit 20 to maintain it at 334℃.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The implementation steps are the same as in Example 1, with the only difference being:

[0090] (2) Electromagnet 232 is not turned on.

[0091] Comparative Example 2

[0092] This comparative example provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The implementation steps are the same as in Example 2, with the only difference being:

[0093] (2) Electromagnet 232 is not turned on.

[0094] Comparative Example 3

[0095] This comparative example provides a method for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD. The implementation steps are the same as in Example 3, with the only difference being:

[0096] (2) Electromagnet 232 is not turned on.

[0097] Test Example 1

[0098] This test example uses scanning electron microscopy to analyze the morphology of the single-walled carbon nanotubes prepared in Example 1 and Comparative Example 1. The test results are shown in the figures below. Figures 3-4 ,in, Figure 3 Example 1, Figure 4 This is Comparative Example 1.

[0099] Combination Figures 3-4 It can be seen that the single-walled carbon nanotubes prepared using the technical solution of Example 1 of this invention exhibit a fibrous structure, while the particulate material is catalyst particles. (Observation based on scale bar) Figure 3 The catalyst particles in the nanotubes are small in diameter, with most particles smaller than 20 nm, a few larger than 20 nm, and none larger than 50 nm. This indicates that the single-walled carbon nanotubes prepared by the method described in this invention have small catalyst particle sizes and no large-particle catalysts. Figure 4 The catalyst particles in the sample were large, with many approaching 50 nm in diameter. This demonstrates that magnetic field sieving removed the large catalyst particles, reducing the average particle size of the catalyst.

[0100] Test Example 2

[0101] This test example characterizes the particle size of the catalyst particles in the single-walled carbon nanotubes prepared in Example 1 and Comparative Example 1 using scanning electron microscopy. A scanning electron microscope at a magnification of ×100k was randomly selected. Figure 3 Zhang used ImageJ software to statistically analyze the particle size of 200-300 catalyst nanoparticles, and used Origin software to generate bar charts and perform statistical analysis. The test results are shown in the figures below. Figures 5-6 ,in, Figure 5 Example 1, Figure 6 This is Comparative Example 1.

[0102] Combination Figures 5-6 It can be seen that the average particle size of the catalyst particles in Example 1 is 9.9 nm, while the average particle size of the catalyst particles in Comparative Example 1 is 17.7 nm. Furthermore, Comparative Example 1 contains a large number of large-particle-size catalyst particles, while Example 1 contains virtually none. This demonstrates that the addition of the magnetic field screening unit 20 can efficiently remove large-particle-size catalyst particles, thereby reducing the average particle size of the final catalyst particles.

[0103] Test Example 3

[0104] This test example uses Raman spectroscopy to analyze the structure, electronic properties, and defects of single-walled carbon nanotubes prepared in Example 1 and Comparative Example 1. The test results are shown in the figures below. Figures 7-8 ,in, Figure 7 Example 1, Figure 8 This is Comparative Example 1.

[0105] Combination Figures 7-8 It can be seen that, Example 1 ( Figure 7 The obtained single-walled carbon nanotubes at a wavenumber of 1500 cm⁻¹ -1 -1650cm -1 The peak at 1300 cm⁻¹ is called the G peak, representing the vibration of the carbon atom rings on the single-walled carbon nanotube. -1 -1350 cm -1 This is called the D peak, representing the sp peak of a single-walled carbon nanotube. 2 Defects in carbon. The defect rate of single-walled carbon nanotubes is assessed using the ratio of the G peak to the D peak (G / D ratio); a higher ratio indicates fewer defects. Figure 7 The average G / D ratio in Example 1 was calculated to be 102, which is higher than the results of other similar patented methods for preparing single-walled carbon nanotubes (CN118785563A, CN120291048A, CN118306980A). This proves that the single-walled carbon nanotubes prepared by the technical solution of this invention have fewer defects and better crystallinity. The reason is that this invention removes large catalyst particles, improves the overall catalyst activity, and prepares single-walled carbon nanotubes with fewer impurities and defects.

[0106] The D peak in Example 1 is significantly different from that in Comparative Example 1 ( Figure 8 If the D peak in the sample is small, the calculated G / D ratio is greater than that of Example 1 (102) than that of Comparative Example 1 (33). This demonstrates that after adding the magnetic field screening unit 20, the particle size of the catalyst particles is smaller, which improves the crystallinity of the single-walled carbon nanotubes.

[0107] The performance data of the single-walled carbon nanotubes prepared in Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1.

[0108] Table 1 Summary of Performance Data

[0109]

[0110] As can be seen from the data in Table 1, the magnetic catalyst particles of iron, cobalt, and nickel are screened using the technical solution of the present invention, and large catalyst particles are effectively removed, which can improve the yield and crystallinity of single-walled carbon nanotubes and reduce ash content.

[0111] In summary, the magnetic field-assisted plasma CVD system 100 for preparing single-walled carbon nanotubes provided in this embodiment of the invention establishes a magnetic field screening unit 20 between the plasma evaporation unit 10 and the CVD growth unit 30. By applying a magnetic field and coordinating temperature control, a region is used to screen catalyst particles. This region selectively removes large-diameter catalyst particles and retains small-diameter catalyst particles, which can precisely control the particle size distribution of catalyst particles. This reduces the defect density and ash content of single-walled carbon nanotubes from the source, breaks through the bottleneck of traditional processes in the mass production of single-walled carbon nanotubes, significantly improves the purity and structural consistency of the product, and breaks through the bottleneck of high-purity mass production.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for preparing single-walled carbon nanotubes by magnetic field-assisted plasma CVD, characterized in that, The system comprises a plasma evaporation unit, a magnetic field screening unit, and a CVD growth unit connected in sequence, wherein: The plasma evaporation unit is used to evaporate ferromagnetic catalyst materials and form catalyst particles; The magnetic field screening unit includes a magnetic field screening cavity, a temperature control component, and a magnetic field generating component. The temperature control component is used to adjust the magnetic field screening cavity to a preset temperature. The magnetic field generating component is used to apply a magnetic field to the catalyst particles and selectively screen out catalyst particles that retain ferromagnetism at the preset temperature by utilizing whether the catalyst particles lose ferromagnetism at the preset temperature. The CVD growth unit is used to receive catalyst particles within the target particle size range after screening and to react with carbon source pyrolysis gas to grow single-walled carbon nanotubes. The preset temperature is determined based on the relationship between the particle size of the catalyst particles and the Curie temperature, as well as the target particle size range.

2. The system according to claim 1, characterized in that, The temperature control component includes a first interlayer water-cooled component and a thermocouple. The first interlayer water-cooled component is arranged around the magnetic field screening cavity, and the thermocouple passes through the side wall of the magnetic field screening cavity and extends into the magnetic field screening cavity along the radial direction of the magnetic field screening cavity.

3. The system according to claim 2, characterized in that, The magnetic field generating component includes an electromagnet, which is located outside the first sandwich water-cooled component.

4. The system according to claim 3, characterized in that, The core of the electromagnet is selected from at least one of soft magnets, permanent magnets, or superconducting magnets; wherein the permanent magnet is selected from at least one of neodymium iron boron, ferrite, samarium cobalt, or alnico; and the superconducting magnet is selected from at least one of yttrium barium copper oxide or bismuth strontium calcium copper oxide.

5. The system according to claim 3, characterized in that, The electromagnet is wound with an induction coil, and the induction coil has 1500-2000 turns.

6. The system according to claim 1, characterized in that, The magnetic field filtering unit is connected to a control unit for controlling the opening and closing of the magnetic field filtering unit.

7. The system according to claim 1, characterized in that, The plasma evaporation unit includes a plasma evaporation chamber, a carrier inlet, a gas dissipation component, a hollow graphite cathode, and a graphite anode, wherein: One end of the plasma evaporation chamber is connected to the magnetic field screening cavity.

8. The system according to claim 7, characterized in that, The carrier air inlet is located at the end of the plasma evaporation chamber away from the magnetic field screening unit, and is arranged along the axial direction of the system on the end wall of the plasma evaporation chamber.

9. The system according to claim 7, characterized in that, The hollow graphite cathode extends through the sidewall of the plasma evaporation chamber along the radial direction of the system and is positioned opposite to the graphite anode.

10. The system according to claim 7, characterized in that, The anode graphite element is disposed inside the plasma evaporation chamber and is disposed opposite to the cathode hollow graphite element.

11. The system according to claim 7, characterized in that, The gas diffuser is connected to the carrier gas inlet, is disposed in the plasma evaporation chamber, and is located on the side away from the magnetic field screening unit of the oppositely disposed anode graphite and cathode hollow graphite.

12. The system according to claim 7, characterized in that, The air diffuser includes 10 to 30 evenly spaced air diffusers with a diameter of 1 mm to 3 mm.

13. The system according to claim 7, characterized in that, The air diffuser is in the shape of a porous disc, and its cross-sectional shape is selected from any one of the following: circular, square, triangular, and rectangular.

14. The system according to claim 1, characterized in that, The CVD growth unit includes a CVD growth chamber, a carbon source inlet, an air barrier, and a heating element, wherein: One end of the CVD growth chamber is connected to the magnetic field screening chamber.

15. The system according to claim 14, characterized in that, The carbon source inlet is located on one side close to the magnetic field screening unit.

16. The system according to claim 14, characterized in that, The gas separator is used to preheat the gas entering the CVD growth chamber from the carbon source inlet.

17. The system according to claim 14, characterized in that, The heating element is used to heat the CVD growth chamber.

18. The system according to claim 14, characterized in that, The carbon source inlet is provided in multiple ways, and the multiple carbon source inlets are evenly arranged circumferentially along the side wall of the CVD growth chamber.

19. The system according to claim 14, characterized in that, The gas separator is cylindrical and located inside the CVD growth chamber, with a gap between it and the side wall of the CVD growth unit. The carbon source inlet is located within the gap, so that the gas flowing out of the carbon source inlet is preheated after passing through the gap and enters the reaction zone of the CVD growth chamber to react with the catalyst.

20. The system according to claim 14, characterized in that, The gas barrier is made of high-temperature ceramic material, selected from at least one of corundum or silicon nitride.

21. The system according to claim 14, characterized in that, The inner diameter of the CVD growth chamber is larger than the inner diameter of the magnetic field screening chamber, and the end of the gas-isolating component near the CVD growth unit is sealed to the end of the CVD growth chamber.

22. The system according to claim 1, characterized in that, The system further includes a cooling unit and a collection unit, wherein the cooling unit is located between the CVD growth unit and the collection unit, wherein: The cooling unit includes a cooling cavity and a second sandwich water-cooled component disposed on the outside of the cooling cavity; The collection unit includes a collection tank, a nozzle, and a water distribution component. The collection tank is provided with an inlet connected to the cooling chamber and a discharge port for material discharge. The nozzle is located at the top of the collection tank. The water distribution component is located between the nozzle and the inlet. The inlet is located between the water distribution component and the discharge port. The water distribution component is a porous water distribution plate.

23. A method for preparing single-walled carbon nanotubes, characterized in that, Single-walled carbon nanotubes were prepared using the system described in any one of claims 1-22.

24. The method according to claim 23, characterized in that, Includes the following steps: Under a protective atmosphere, molten material is added to the plasma evaporation unit, and plasma is introduced. After the temperature of the plasma evaporation unit rises to 1200℃-2000℃, ferromagnetic catalyst material and co-catalyst material are added to generate catalyst particles. The magnetic field screening cavity is controlled to the preset temperature, and a magnetic field is generated in conjunction with the magnetic field generating component; The reaction temperature between the carbon source cracking gas and the catalyst particles in the CVD growth unit is controlled at 1000℃-1300℃. Single-walled carbon nanotubes were obtained after processing by a cooling unit and a collection unit.

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