Method for manufacturing small-diameter carbon nanotubes and carbon nanotubes produced thereby

Abstract

To provide a method for producing a carbon nanotube capable of synthesizing a small-diameter carbon nanotube with a high purity.SOLUTION: A method for producing a carbon nanotube in an embodiment comprises the steps of: (a) inputting a catalyst into a chemical vapor deposition reactor; and (b) injecting a carbon source gas to synthesize a carbon nanotube. A relation between an input amount of the catalyst and a flow rate of the carbon source gas satisfies the following formula 1: 0.1 L / g min≤a / b≤1.1 L / g min, wherein a represents a flow rate (L / min) of the carbon source gas and b represents an input amount (g) of the catalyst.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification relates to a method for producing small-diameter carbon nanotubes and carbon nanotubes produced thereby. [Background technology]

[0002] As interest in and demand for environmentally friendly energy and electric vehicles increase, the demand for rechargeable batteries and the need for performance improvements are rapidly increasing. In particular, rechargeable batteries for electric vehicles are required to be high-capacity batteries with high energy density, long lifespan, and low self-discharge rate, and the development of highly electrically conductive materials is essential to ensure these properties.

[0003] Conductive materials act as pathways for the movement of electric charge within a battery. Carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes can be used, and currently, conductive carbon black has been the primary material.

[0004] Carbon nanotubes are tubular materials with a hexagonal honeycomb lattice structure formed by the interconnection of carbon atoms. Their excellent electrical conductivity has made them a promising next-generation conductive material for secondary batteries. Using carbon nanotubes as a conductive material can improve the energy density and lifespan of secondary batteries, and reduce their overall size.

[0005] On the other hand, carbon nanotubes exhibit superior electrical conductivity as their diameter decreases. Therefore, using small-diameter carbon nanotubes as conductive materials for secondary batteries can further improve the capacity and lifespan characteristics of those batteries. Consequently, there is a need for the development of manufacturing technologies that can synthesize carbon nanotubes with reduced diameters compared to existing materials at high purity. [Overview of the project] [Problems that the invention aims to solve]

[0006] The information contained herein is intended to solve the problems of the prior art described above, and one of the objectives of this specification is to provide a method for producing carbon nanotubes that can synthesize small-diameter carbon nanotubes with high purity.

[0007] Another objective of this specification is to provide small-diameter carbon nanotubes with excellent electrical conductivity. [Means for solving the problem]

[0008] In one aspect, the present invention provides a method for producing carbon nanotubes, comprising the steps of (a) introducing a catalyst into a chemical vapor deposition reactor and (b) injecting a carbon source gas to synthesize carbon nanotubes, wherein the amount of catalyst introduced and the flow rate of the carbon source gas satisfy the following formula 1.

[0009] [Formula 1] 0.1L / g·min≦a / b≦1.1L / g·min In the above formula 1, a is the flow rate of the carbon source gas (L / min), and b is the amount of catalyst added (g).

[0010] In one embodiment, the catalyst comprises a main catalyst and a support, and the mole fraction of the main catalyst relative to the support may be 0.01 to 0.5.

[0011] In one embodiment, the catalyst may include i) a main catalyst selected from the group consisting of Co, Fe, Ni, and combinations thereof; ii) a support selected from the group consisting of Al, Ca, Mg, and combinations thereof; and iii) a co-catalyst selected from the group consisting of V, Mn, Mo, and combinations thereof.

[0012] In one embodiment, the carbon source gas may include one selected from the group consisting of saturated or unsaturated hydrocarbons having 1 to 4 carbon atoms, carbon monoxide, and mixtures of two or more of these.

[0013] According to another aspect, there is provided a carbon nanotube produced by the method for producing a carbon nanotube described above.

[0014] In one embodiment, the diameter of the carbon nanotube can be 7 to 12 nm.

[0015] In one embodiment, the purity of the carbon nanotube can be 90% or more.

[0016] In one embodiment, the length of the bundle of the carbon nanotube can be 50 to 200 μm.

[0017] In one embodiment, the BET specific surface area of the carbon nanotube is 250 to 400 m 2 / g.

[0018] In one embodiment, the apparent density of the carbon nanotube can be 0.005 to 0.5 g / ml.

Advantages of the Invention

[0019] The method for producing a carbon nanotube according to one aspect of the present specification can synthesize small-diameter carbon nanotubes having a diameter reduced from the existing comparison with high purity.

[0020] In addition, the carbon nanotube according to another aspect of the present specification has excellent electrical conductivity due to its small diameter, and when used as a conductive material for a secondary battery, it can improve the capacity and life characteristics of the secondary battery.

[0021] The effects of one aspect of the present specification are not limited to the above effects, and should be understood to include all effects inferable from the configurations described in the detailed description or claims of the present specification.

Brief Description of the Drawings

[0022] [Figure 1] It is a TEM image of the carbon nanotube synthesized according to the examples or comparative examples of the present specification. [Figure 2]This shows the diameter analysis results of carbon nanotubes synthesized according to the examples or comparative examples described herein. [Figure 3] These are SEM images of carbon nanotubes synthesized according to the examples or comparative examples described herein. [Modes for carrying out the invention]

[0023] In the following, one aspect of this specification will be described with reference to the attached drawings. However, the matters described herein can be embodied in a variety of different forms and are therefore not limited to the embodiments described herein. Furthermore, in order to clearly illustrate one aspect of this specification with the drawings, parts that are not relevant to the description have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0024] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected" but also cases where they are "indirectly connected" through other components in between. Furthermore, when a part is described as "containing" some component, this means that it may further contain other components, rather than excluding other components, unless otherwise stated.

[0025] When a range of numerical values ​​is described herein, unless otherwise specified, the value shall have the precision of significant figures provided by the standard rules for significant figures in chemistry. For example, 10 includes the range of 5.0 to 14.9, and the figure 10.0 includes the range of 9.50 to 10.49.

[0026] Hereinafter, an embodiment of this specification will be described in detail with reference to the attached drawings.

[0027] Method for manufacturing carbon nanotubes A method for producing carbon nanotubes according to one aspect of this specification includes (a) the step of introducing a catalyst into a chemical vapor deposition reactor; and (b) the step of injecting a carbon source gas to synthesize carbon nanotubes, wherein the amount of catalyst introduced and the flow rate of the carbon source gas satisfy the following formula 1.

[0028] [Formula 1] 0.1L / g·min≦a / b≦1.1L / g·min In the above formula 1, a is the flow rate of the carbon source gas (L / min), and b is the amount of catalyst added (g).

[0029] The carbon nanotube manufacturing method described above can produce small-diameter carbon nanotubes with a reduced diameter compared to existing ones by adjusting the ratio (a / b value) of the carbon source gas flow rate to the amount of catalyst input. The diameter of the carbon nanotubes produced by this method may be 7 to 12 nm, and the smaller the a / b value, the smaller the diameter of the produced carbon nanotubes can be.

[0030] The a / b value may be, for example, 0.1 L / g·min, 0.2 L / g·min, 0.3 L / g·min, 0.4 L / g·min, 0.5 L / g·min, 0.6 L / g·min, 0.7 L / g·min, 0.8 L / g·min, 0.9 L / g·min, 1.0 L / g·min, 1.1 L / g·min, or a range between these two values. If the a / b value is below the range, the catalytic activity may decrease excessively, and carbon nanotubes may not be synthesized. If it exceeds the range, the diameter of the synthesized carbon nanotubes may increase, and their electrical conductivity may decrease.

[0031] The catalyst may include, but is not limited to, i) a main catalyst selected from the group consisting of Co, Fe, Ni, and combinations thereof; ii) a support selected from the group consisting of Al, Ca, Mg, and combinations thereof; and iii) a co-catalyst selected from the group consisting of V, Mn, Mo, and combinations thereof.

[0032] The mole fraction of the main catalyst relative to the support may be 0.01 to 0.5. For example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.2 The values ​​may be 7, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, or a range between these two values. If the mole fraction of the main catalyst relative to the support is less than the above range, the synthesis yield of carbon nanotubes may decrease, and the dispersibility of the manufactured carbon nanotubes may decrease. If the mole fraction of the main catalyst relative to the support exceeds the above range, the durability of the catalyst may decrease due to the relatively low support content, and the electrical conductivity of the manufactured carbon nanotubes may decrease.

[0033] The catalyst may, but is not limited to, be manufactured by spray pyrolysis or a supported method.

[0034] When the catalyst is produced by spray pyrolysis, the catalyst may be produced by (a') preparing a catalyst mixed solution by dissolving the precursors of the main catalyst, the support, and the co-catalyst in a solvent; (b') spraying the catalyst mixed solution into the inside of a high-temperature reactor with a transport gas at 2 to 5 atmospheres using a gas spray method and pyrolysis at a temperature of 600 to 1200°C to form catalyst powder; and (c') obtaining the catalyst powder.

[0035] The aforementioned precursor may, but is not limited to, a nitrate, sulfate, alkoxide, or carbonate.

[0036] The solvent may, but is not limited to, deionized water.

[0037] The transported gas may, but is not limited to, air.

[0038] The thermal decomposition temperature may be between 600 and 1200°C, preferably between 600 and 1000°C, but is not limited thereto.

[0039] The pressure of the transport gas during pyrolysis may be 2 to 5 atmospheres, preferably 2 to 4 atmospheres, but is not limited to this.

[0040] The catalyst produced by this spray pyrolysis method can have an apparent density (bulk density) of 0.01 to 0.50 g / mL, preferably 0.03 to 0.40 g / mL.

[0041] The catalyst produced by the spray pyrolysis method in this way may have a hollow structure, with a hollow thickness of 0.5 to 10 μm, preferably 1 to 8 μm, and a hollow ratio of 50 volume% or more. Here, a hollow structure refers to a three-dimensional structure with an empty interior, such as a spherical or polyhedral structure with an empty interior, and includes closed structures where the hollow is completely sealed, open structures where part of the hollow is open, or any combination thereof. When the catalyst has such a hollow structure, it may be advantageous for the synthesis of small-diameter carbon nanotubes.

[0042] The chemical vapor deposition reactor may be, but is not limited to, a fixed-bed chemical vapor deposition reactor or a fluidized-bed chemical vapor deposition reactor.

[0043] The carbon source gas may include one selected from the group consisting of saturated or unsaturated hydrocarbons having 1 to 4 carbon atoms, carbon monoxide, and mixtures of two or more of these, for example, methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), butane (C4H4). 10 This may include, but is not limited to, acetylene (C2H2), carbon monoxide (CO), or a mixture of two or more of these.

[0044] In step (b) above, the internal temperature of the chemical vapor deposition reactor may be 600 to 1,000°C. For example, it may be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1,000°C, or a range between these two values. If the internal temperature of the reactor is below the above range, the growth of carbon nanotubes may be impossible or delayed, and if it is above the above range, the synthesized carbon nanotubes may be thermally decomposed or bonded together and unable to maintain their shape.

[0045] In step (b) above, the carbon source gas may be injected together with the transport gas. The transport gas may be, but is not limited to, one selected from the group consisting of helium, nitrogen, argon, and mixtures of two or more of these.

[0046] In step (b) above, the synthesis of carbon nanotubes may be carried out in which a carbon source gas, decomposed by high-temperature heat, permeates and saturates the catalyst, and then carbon is deposited.

[0047] carbon nanotubes The carbon nanotubes relating to another aspect of this specification may be manufactured by the carbon nanotube manufacturing method described above.

[0048] The diameter of the carbon nanotube may be 7 to 12 nm. For example, it may be 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, or a range between these two values. If the diameter is less than the range, structural defects may occur in the carbon nanotube or its dispersibility may decrease. If the diameter exceeds the range, its electrical conductivity may decrease, and when used as a conductive material for secondary batteries, the energy density, life characteristics, and self-discharge rate of the secondary battery may decrease.

[0049] The purity of the carbon nanotubes may be 90% or higher. If the purity is below this range, the electrical conductivity may decrease, and when used as a conductive material for secondary batteries, impurities may react inside the battery, potentially causing a safety accident.

[0050] The carbon nanotubes may be bundle-type carbon nanotubes in which a plurality of carbon nanotubes aggregate with each other, but are not limited thereto.

[0051] The length of the bundle of the carbon nanotubes can be 50 to 200 μm. For example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or a range between both values thereof. If the length of the bundle is less than the above range, the electrical conductivity may decrease, and if it exceeds the above range, the dispersibility may decrease.

[0052] The BET specific surface area of the carbon nanotubes can be 250 to 400 m 2 / g. For example, 250 m 2 / g, 260 m 2 / g, 270 m 2 / g, 280 m 2 / g, 290 m 2 / g, 300 m 2 / g, 310 m 2 / g, 320 m 2 / g, 330 m 2 / g, 340 m 2 / g, 350 m 2 / g, 360 m 2 / g, 370 m 2 / g, 380 m 2 / g, 390 m[[ID=4O]] 2 / g, 400 m 2 / g or a range between both values thereof. If the BET specific surface area is less than the above range, the electrical conductivity may decrease, and if it exceeds the above range, the dispersibility may decrease.

[0053] The apparent density (bulk density) of the carbon nanotube may be between 0.005 and 0.5 g / ml. For example, it may be 0.005 g / ml, 0.01 g / ml, 0.02 g / ml, 0.03 g / ml, 0.04 g / ml, 0.05 g / ml, 0.06 g / ml, 0.07 g / ml, 0.08 g / ml, 0.09 g / ml, 0.1 g / ml, 0.2 g / ml, 0.3 g / ml, 0.4 g / ml, 0.5 g / ml, or a range between these two values. The apparent density may be measured using carbon nanotube in powder form. If the apparent density is below the range, dispersibility may decrease, and if it exceeds the range, electrical conductivity may decrease.

[0054] Because the carbon nanotubes exhibit excellent electrical conductivity, even small amounts of these nanotubes can demonstrate the same or improved performance compared to existing materials when used as conductive materials for secondary batteries. This makes them applicable to the production of high-capacity secondary batteries with high energy density, long lifespan, and low self-discharge rate.

[0055] The following describes the examples of this specification in more detail. However, the following experimental results represent only representative results from the aforementioned examples, and the scope and content of this specification should not be narrowed or limited by these examples. The effects of various examples of this specification that are not explicitly presented below will be described in detail in the relevant sections.

[0056] Manufacturing Example 1 A precursor mixture solution was prepared by dissolving 0.76 moles of Co(NO3)3·6H2O, 2.36 moles of Al(NO3)3·9H2O, and 0.09 moles of NH4VO3 in deionized water. Subsequently, the catalyst was produced by spraying the precursor mixture solution into the inside of a reactor at 750°C and thermally decomposing it.

[0057] Manufacturing Example 2 A precursor mixture solution was prepared by dissolving 0.31 moles of Co(NO3)3·6H2O, 3.42 moles of Al(NO3)3·9H2O, and 0.04 moles of NH4VO3 in deionized water. Subsequently, the catalyst was produced by spraying the precursor mixture solution into the inside of a reactor at 750°C and thermally decomposing it.

[0058] Manufacturing Example 3 A precursor mixture solution was prepared by dissolving 0.62 moles of Co(NO3)3·6H2O, 2.61 moles of Al(NO3)3·9H2O, and 0.07 moles of NH4VO3 in deionized water. Subsequently, the catalyst was produced by spraying the precursor mixture solution into the inside of a reactor at 750°C and thermally decomposing it.

[0059] Manufacturing Example 4 After dissolving 0.07 moles of NH4VO3 and 0.07 moles of C6H8O7 in deionized water to prepare a clear solution, 0.8 moles of Fe(NO3)3·9H2O, 1.65 moles of Al(NO3)3·9H2O, and 0.78 moles of Mg(NO3)2·6H2O were added and dissolved to prepare a precursor mixture solution. Subsequently, the catalyst was produced by spraying the precursor mixture solution into the inside of a 750°C reactor and thermally decomposing it.

[0060] Examples 1-7 and Comparative Examples 1-3 The catalysts produced in Production Examples 1-4 were introduced into a 350 mm fluidized bed chemical vapor deposition reactor. The reactor's internal temperature was raised to 650-800°C under a nitrogen atmosphere, and then carbon source gas was injected to synthesize carbon nanotubes. At this time, the carbon source gas was injected according to the ratio of the carbon source gas flow rate to the catalyst input amount (a / b value) shown in Table 1 below, but the total amount of injected carbon source gas was kept constant.

[0061] Table 1 below shows the type of catalyst used in Examples 1-7 and Comparative Examples 1-3, the mole fraction of the main catalyst relative to the support, and the ratio of the carbon source gas flow rate relative to the amount of catalyst input.

[0062] [Table 1]

[0063] Experimental Example 1 The catalyst yield, purity, and structural properties of the carbon nanotubes synthesized according to the above examples and comparative examples were analyzed, and the results are shown in Table 2 and Figures 1-3 below.

[0064] 1) Catalyst yield: This refers to the total amount of carbon nanotubes synthesized relative to the amount of catalyst used, and was calculated using the following formula.

[0065] Catalyst yield (%) = Total amount of synthesized carbon nanotubes (g) / Amount of catalyst added (g) 2) Purity: After burning carbon nanotubes at 800°C using a thermal oxidation furnace, the purity was calculated using the following formula, based on the weight of the carbon nanotubes added and the weight after combustion.

[0066] Carbon nanotube purity (%) = [(Weight of added carbon nanotubes - Weight after combustion) / Weight of added carbon nanotubes] × 100 3) Average diameter: Measured at 200,000x magnification using a TEM (JEOL, JEM-2100F).

[0067] Figures 1 and 2 show TEM images and diameter analysis results of carbon nanotubes synthesized in Examples 1 and 4 and Comparative Example 2.

[0068] 4) Bundle length: Measured at 700x magnification using an FE-SEM (JEOL, JSM-7500F).

[0069] Figure 3 shows SEM images of carbon nanotubes synthesized in Examples 1 and 4 and Comparative Example 2.

[0070] 5) Apparent density: Carbon nanotube powder was filled into a 100 ml container whose weight was known, and its weight was measured. The apparent density was then calculated using the following formula.

[0071] Apparent density = Total amount of synthesized carbon nanotubes (g) / Volume of synthesized carbon nanotubes (ml) 6) BET specific surface area: Measured using TriStar II 3020 (Micrometritics).

[0072] [Table 2]

[0073] Referring to Table 2 above, the carbon nanotubes synthesized in Examples 1 to 7 had a diameter reduced by 7 to 12 nm and showed high catalyst yield and purity. Furthermore, it was confirmed that the diameter of the synthesized carbon nanotubes decreased as the ratio of the carbon source gas flow rate to the amount of catalyst input (a / b value) decreased.

[0074] As the a / b value decreased, the BET specific surface area value increased, and since it is generally known that the specific surface area increases as the diameter of carbon nanotubes decreases, the increased specific surface area value also confirms that the diameter of the carbon nanotubes decreased.

[0075] These results are achieved by adjusting the catalytic activity by controlling the ratio of the carbon source gas flow rate to the amount of catalyst input. As the ratio of the carbon source gas flow rate to the amount of catalyst input decreases, the catalytic activity decreases, which allows for the synthesis of small-diameter carbon nanotubes.

[0076] We confirmed that as the a / b value decreased, the catalytic activity decreased and the length of the carbon nanotube bundle increased. We also confirmed that as the diameter of the synthesized carbon nanotubes decreased and the length increased, the apparent density gradually decreased.

[0077] In the synthesis method described in Comparative Example 1, the a / b value was less than 0.1 L / g·min, and the catalytic activity was excessively low, resulting in the failure to synthesize carbon nanotubes.

[0078] In the synthesis methods for Comparative Examples 2 and 3, the a / b value exceeded 1.1 L / g·min. Due to the excessively high catalytic activity, the synthesis of carbon nanotubes proceeded rapidly, resulting in the synthesis of carbon nanotubes with a diameter exceeding 12 nm. Furthermore, as the diameter increased, the specific surface area decreased, and short carbon nanotubes were synthesized due to the excessively high catalytic activity. This resulted in a tendency for the apparent density to increase with larger diameter and shorter length.

[0079] Experimental Example 2 To evaluate the electrical conductivity of the carbon nanotubes synthesized according to the above examples and comparative examples, the surface resistance and viscosity of the carbon nanotubes were measured, and the results are shown in Table 3 below.

[0080] The carbon nanotube dispersion was evaluated by adding 0.5% carbon nanotubes and 0.25% polyvinylpyrrolidone (PVP) as a dispersant to 100 ml of N-methylpyrrolidone (NMP), using an ultrasonic device (SONICS & MATERIALS, VC750). During dispersion preparation, the ultrasonic device was operated for 20 minutes, and then the dispersion preparation was completed.

[0081] The surface resistance of carbon nanotubes was measured using a 4-point probe after bar coating.

[0082] Viscosity was measured using a portable viscometer (Hydramotion, Viscolite 700).

[0083] [Table 3]

[0084] Referring to Table 3 above, the carbon nanotubes synthesized in Examples 1, 2, and 4 exhibited excellent electrical conductivity due to their low surface resistance, and it was confirmed that the smaller the diameter of the carbon nanotubes, the better the coating electrical conductivity using the dispersion.

[0085] The carbon nanotubes synthesized in Comparative Example 2 had a higher surface resistance compared to the examples, and it was confirmed that their electrical conductivity was reduced.

[0086] The descriptions herein provided herein are illustrative, and a person with ordinary skill in the art to which one aspect of this specification belongs will understand that the technical ideas and essential features described herein can be easily modified into other specific forms without alteration. Therefore, the embodiments described herein should be understood in all respects as illustrative and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

[0087] The scope of this specification is defined by the claims set forth below, and all modifications or alterations derived from the meaning and scope of the claims and the concept of equivalents thereof should be construed as being included within the scope of this specification.

Claims

1. (a) the step of obtaining a catalyst by spray pyrolysis and introducing the catalyst into a chemical vapor deposition reactor; and (b) A step of synthesizing carbon nanotubes by injecting a carbon source gas; The catalyst has a hollow structure, The catalyst comprises i) one main catalyst selected from the group consisting of Co, Fe, Ni and combinations thereof; ii) one support selected from the group consisting of Al, Ca, Mg and combinations thereof; and iii) one co-catalyst selected from the group consisting of V, Mn, Mo and combinations thereof. The mole fraction of the main catalyst relative to the support is 0.01 to 0.

33. A method for producing carbon nanotubes with an average diameter of 7 nm to 12 nm, wherein the amount of catalyst added and the flow rate of the carbon source gas satisfy the following equation 1: [Formula 1] 0.1L / g・min≦a / b≦0.82L / g・min In the above formula 1, a is the flow rate of the carbon source gas (L / min), and b is the amount of catalyst added (g).

2. The above [Equation 1] is, 0.52L / g・min≦a / b≦0.80L / g・min The method for producing carbon nanotubes according to claim 1.

3. The method for producing carbon nanotubes according to claim 1 or 2, wherein the carbon source gas comprises one selected from the group consisting of saturated or unsaturated hydrocarbons having 1 to 4 carbon atoms, carbon monoxide, and mixtures of two or more thereof.

4. The method for producing carbon nanotubes according to claim 1 or 2, wherein the purity of the carbon nanotubes is 90% or higher.

5. The method for producing carbon nanotubes according to claim 1 or 2, wherein the length of the carbon nanotube bundle is 50 to 200 μm.

6. The BET specific surface area of ​​the carbon nanotube is 250 to 400 m². ２ A method for producing carbon nanotubes according to claim 1 or 2, wherein the amount is / g.

7. The method for producing carbon nanotubes according to claim 1 or 2, wherein the apparent density of the carbon nanotubes is 0.005 to 0.5 g / ml.

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