Catalyst for producing carbon nanotubes and carbon nanotubes produced using same

Abstract

The present invention relates to a catalyst for manufacturing carbon nanotubes and, particularly, to a catalyst for selectively manufacturing thin-walled carbon nanotubes, carbon nanotubes manufactured using same, a carbon nanotube dispersion, an electrode structure comprising the carbon nanotubes, and a secondary battery comprising the carbon nanotubes.

Description

Catalyst for manufacturing carbon nanotubes and carbon nanotubes manufactured using the same

[0001] The present invention relates to a catalyst for manufacturing carbon nanotubes, specifically a catalyst for the selective production of thin-walled carbon nanotubes, carbon nanotubes produced using the same, a carbon nanotube dispersion, an electrode structure containing carbon nanotubes, and a secondary battery containing carbon nanotubes.

[0002] Carbon nanomaterials are classified into fullerene, carbon nanotubes (CNT), graphene, and graphite nanoplates depending on the shape of the material. Among these, carbon nanotubes are nano carbon materials formed by rolling a graphene sheet, in which one carbon atom is bonded to three other carbon atoms to form a hexagonal honeycomb structure, into a cylindrical shape with a nanometer-sized diameter.

[0003] Carbon nanotubes possess excellent electrical conductivity, high strength, and outstanding thermal conductivity, giving them diverse application possibilities. In particular, their utilization as conductive electrode materials in electronic devices, composite materials, and energy storage devices is being actively researched.

[0004] Carbon nanotubes are classified into single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and rope carbon nanotubes based on their structure. Each of these forms exhibits different electrical, mechanical, and thermal properties.

[0005] Among them, single-walled carbon nanotubes (SWCNT) with one wall and multi-walled carbon nanotubes (MWCNT) with two to five walls are called thin-walled carbon nanotubes. These thin-walled carbon nanotubes provide a high specific surface area and excellent electrical and mechanical properties compared to multi-walled carbon nanotubes with more than five walls. Due to these properties, thin-walled carbon nanotubes have significant potential for application in various fields, such as electronic devices, energy storage devices, and high-strength composite materials.

[0006] Currently, single-walled carbon nanotubes boast very high electrical performance, but multi-walled carbon nanotubes with equivalent electrical performance are not yet known. In this context, thin-walled carbon nanotubes are attracting attention as a form with the potential to exhibit electrical performance similar to that of single-walled carbon nanotubes, and accordingly, research on the synthesis of thin-walled carbon nanotubes has been actively conducted recently.

[0007]

[0008] Meanwhile, crystallinity is used as a key indicator for evaluating the quality and performance of carbon nanotubes. Crystallinity represents the structural regularity and purity of carbon nanotubes, and carbon nanotubes with high crystallinity exhibit superior performance in terms of electrical conductivity, mechanical strength, and thermal conductivity.

[0009] High-crystallity carbon nanotubes are generally 1,000 by the FCCVD (Floating catalyst chemical vapor deposition) method oCarbon nanotubes are manufactured at high temperatures above C. Although there have been attempts to produce carbon nanotubes with high crystallinity using the Catalytic Chemical Vapor Deposition (CCVD) method, which operates at relatively low temperatures, the inherent characteristics of the process inevitably include amorphous carbon and multi-walled carbon nanotubes, resulting in carbon nanotubes with low crystallinity. To increase crystallinity, the obtained carbon nanotubes can be subjected to low-temperature oxidation; however, since amorphous carbon is oxidized at relatively low temperatures, it can be selectively removed. Conversely, because multi-walled carbon nanotubes are oxidized at relatively high temperatures, some of the highly crystallinated carbon nanotubes are inevitably removed as well, causing a low carbon nanotube yield. Therefore, to obtain highly crystallinated thin-walled carbon nanotubes at a commercially viable level using the CCVD process, it is necessary to develop an innovative manufacturing process capable of effectively inhibiting the growth of multi-walled carbon nanotubes during production.

[0010]

[0011] Prior art literature

[0012] [Patent Document 1] Republic of Korea Published Patent No. 10-2016-0107524

[0013] The present invention aims to provide a catalyst that inhibits the growth of multi-walled carbon nanotubes (MWNTs) and induces the selective growth of thin-walled carbon nanotubes (TWNTs) having an average number of walls of 1 to 5, carbon nanotubes prepared using said catalyst, a carbon nanotube dispersion, an electrode structure containing carbon nanotubes, and a secondary battery containing carbon nanotubes.

[0014] One aspect of the present invention is

[0015] It includes iron as a catalytic active metal,

[0016] 2θ = 33 in X-ray diffraction (XRD) analysiso A catalyst for manufacturing carbon nanotubes is provided in which no peak corresponding to bulk Fe2O3 is present. The XRD analysis can be performed using Cu Kα (λ = 1.541 Å) X-rays in the range 2θ = 10° to 80° under conditions of voltage 40 kV, current 40 mA, step size 0.02°, and scan rate 5° / min.

[0017] The carbon nanotubes above may have an average number of walls ranging from 1 to 5.

[0018]

[0019] Another aspect of the present invention is

[0020] Contains iron as the catalytic active metal, but 2θ = 33 when analyzed by X-ray diffraction (XRD). o Carbon nanotubes are grown on a catalyst in which the peak corresponding to bulk Fe2O3 is not present, satisfying (1) and (2) below.

[0021] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0022] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0023] (Here, the above I G / I D is 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I D When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D represents )

[0024] I of the above carbon nanotube G / I DIt can be 24 to 36 days.

[0025] The carbon nanotubes above may have an average number of walls ranging from 1 to 4.

[0026] The average number of walls of the carbon nanotubes above can be 1 to 3.

[0027]

[0028] Another aspect of the present invention is

[0029] (S1) Contains iron as the catalytic active metal, wherein 2θ = 33 when analyzed by X-ray diffraction (XRD). o A step of introducing a catalyst into a chemical vapor deposition reactor in which a peak corresponding to bulk Fe2O3 is not present;

[0030] (S2) A step of synthesizing Pristine carbon nanotubes by heating the chemical vapor deposition reactor and then injecting a carbon source gas; and

[0031] (S3) A step of obtaining carbon nanotubes by low-temperature oxidizing the above pristine carbon nanotubes.

[0032] A method for manufacturing carbon nanotubes is provided that includes and satisfies (1) and (2) below:

[0033] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0034] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0035] Here, the above I G / I D is 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 The maximum peak intensity within the range of the D band intensity (I D When referring to ), the strength of the G-band (I G ) and D-band strength (ID The ratio of )(I G / I D It represents ).

[0036] In the above (S2) step, the chemical vapor deposition reactor may be heated to a temperature of 800 to 900°C.

[0037] I of the pristine carbon nanotubes synthesized in the above (S2) step G / I D It can be 5 to 20 days.

[0038] In the above (S3) step, the low-temperature oxidation can be performed at a temperature of 400 to 600°C.

[0039] I of the above carbon nanotube G / I D It can be 24 to 36 days.

[0040]

[0041] Another aspect of the present invention is

[0042] A carbon nanotube dispersion comprising carbon nanotubes according to one aspect of the present invention is provided.

[0043]

[0044] Another aspect of the present invention is

[0045] An electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0046]

[0047] Another aspect of the present invention is

[0048] An electrode structure comprising carbon nanotubes according to one aspect of the present invention is provided.

[0049]

[0050] Another aspect of the present invention is

[0051] A secondary battery comprising an electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0052] The catalyst according to the present invention inhibits the growth of multi-walled carbon nanotubes (MWNTs) with more than 5 walls and effectively removes amorphous carbon, thereby enabling the selective production of thin-walled carbon nanotubes with 1 to 5 walls that have high crystallinity.

[0053] Accordingly, carbon nanotubes produced using the catalyst according to the present invention have a highly crystalline structure in which amorphous carbon is effectively removed even after calcination, and can have a thin-walled structure with an average number of walls of 1 to 5.

[0054] Figure 1 shows the results of confirming the thin-wall structure of carbon nanotubes prepared according to Example 1 through TEM.

[0055] Figure 2 shows the results of confirming the thin-wall structure of carbon nanotubes prepared according to Example 2 through TEM.

[0056] Figure 3 shows the results of confirming the thin-wall structure of carbon nanotubes prepared according to Example 3 through TEM.

[0057] Figure 4 shows the results of confirming the thin-wall structure of carbon nanotubes prepared according to Example 4 through TEM.

[0058] The present invention will be described in more detail below.

[0059] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0060] As used in this specification, the term “carbon nanotube (CNT)” comprises a structure composed of one or more carbon nanotube units, and may include not only a single CNT (SWCNT, DWCNT, or MWCNT) but also a secondary structure in which these CNTs are assembled in a bundle form or a group form in which multiple CNTs are mixed, either wholly or partially. The carbon nanotube unit has a structure in which a graphene sheet, which is a planar carbon atomic layer with a hexagonal honeycomb structure having an sp2 bonding structure, is rolled into a cylindrical shape to have a nanometer-sized diameter. At this time, depending on the rolling angle (or chiral angle) and structure of the graphene sheet, it may exhibit conductive or semiconductor properties. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of layers forming the walls, and generally, the thinner the wall thickness, the lower the resistance. Meanwhile, the term “pristine carbon nanotube” as used in this specification refers to carbon nanotubes in their original form, in which no chemical functional groups have been introduced to the surface, that is, without undergoing chemical modification or surface alteration.

[0061] The term “thin-walled carbon nanotube” as used in this specification refers to a carbon nanotube having an average number of walls of 1 to 5, and may include any one or a combination of single-walled, double-walled, triple-walled, quadruple-walled, and pentruple-walled carbon nanotube units.

[0062] As used herein, the term “crystallinity” refers to the degree to which atoms or molecules within carbon nanotubes form a regular and repetitive crystal lattice structure. A higher degree of crystallinity is evaluated as having fewer defects and a more uniform atomic arrangement within the carbon nanotubes, resulting in superior electrical, mechanical, and thermal properties. The crystallinity is [related to] the G band of the Raman spectrum (1550–1650 cm⁻¹). -1 ) and D band (1250~1400cm -1 It can be evaluated by measuring the peak intensity in the ) region. Here, the G band represents a regular graphene layer structure, and the D band represents structural defects or irregularities. Therefore, the intensity of the G band (I G ) and D band strength (I D The ratio of ) (I G / I D The larger ) is, the fewer defects and the better the crystal lattice is formed, that is, it indicates a high degree of crystallization.

[0063] As used herein, the term “catalytically active metal” refers to a metal component that actually induces a reaction in a catalyst.

[0064]

[0065] 1. Catalyst

[0066] One aspect of the present invention is

[0067] It includes iron as a catalytic active metal,

[0068] 2θ = 33 in X-ray diffraction (XRD) analysis o Provides a catalyst in which the peak corresponding to bulk Fe2O3 is not present.

[0069] Here, the XRD analysis can be performed using Cu Kα (λ = 1.541 Å) X-rays in the range 2θ = 10° to 80° under conditions of voltage 40 kV, current 40 mA, step size 0.02°, and scan rate 5° / min.

[0070] The above catalyst enables the production of thin-walled carbon nanotubes with a highly crystalline average number of walls, 1 to 5, preferably 1 to 4, more preferably 1 to 3, in which the growth of multi-walled carbon nanotubes (MWNTs) is suppressed and amorphous carbon is effectively removed.

[0071] The above catalyst can be manufactured by controlling the type and content of the metal used as a catalyst precursor and the type and content of the precipitating agent, and the specific manufacturing method is as described below.

[0072]

[0073] 2. Method for manufacturing a catalyst

[0074] Another aspect of the present invention is

[0075] (S1) A step of forming a metal precursor solution by adding a metal salt of iron (Fe) as a catalytically active metal to an aqueous solvent;

[0076] (S2) A step of adding a precipitating agent to the metal precursor solution to obtain a metal precursor solution containing a precipitating agent;

[0077] (S3) A step of obtaining a slurry by aging the above-mentioned metal precursor solution containing a precipitating agent at a temperature of 80°C to 150°C for 1 hour to 48 hours; and

[0078] (S4) A step of separating, washing, and drying the above slurry to obtain a dried catalyst body

[0079] When performing X-ray diffraction (XRD) analysis including , 2θ = 33 o A method for preparing a catalyst in which a peak corresponding to bulk Fe2O3 is not present is provided.

[0080] The above XRD analysis can be performed using Cu Kα (λ = 1.541 Å) X-rays in the range of 2θ = 10° to 80° under conditions of voltage 40 kV, current 40 mA, step size 0.02°, and scan rate 5° / min.

[0081] In the above step (S1), the iron content may be 10 to 30 weight% based on the total weight of the catalyst. For example, the iron content may be 10 to 30 weight%, 10 to 25 weight%, or 10 to 20 weight% based on the total weight of the catalyst.

[0082] In the above (S1) step, the metal precursor solution may further include one or more metal salts selected from the group consisting of magnesium, aluminum, calcium, and silicon as a catalyst support in addition to the catalyst active metal.

[0083] In the above (S1) step, the aqueous solvent may include water, lower alcohols having 1 to 4 carbon atoms, or a combination thereof.

[0084] In step (S2) above, the precipitating agent may include ammonium carbonate ((NH₄)₂CO₃), water of ammonia (NH4OH), or a combination thereof. The precipitating agent may be added in a molar ratio of 1.5 to 7.0 (mol of precipitating agent / mol of total metal) based on the total metal including the catalyst active metal and the support metal. If the molar ratio of the precipitating agent to the total metal is less than 1.5, the structure of the catalyst may be incompletely formed due to unstable precipitation, and if the molar ratio of the precipitating agent to the total metal exceeds 7.0, unnecessary byproducts may be generated, resulting in a heterogeneous catalyst in the form of a mixture.

[0085]

[0086] 3. Carbon nanotubes

[0087] Another aspect of the present invention is

[0088] Contains iron as the catalytic active metal, but 2θ = 33 when analyzed by X-ray diffraction (XRD). o Carbon nanotubes are grown on a catalyst in which the peak corresponding to bulk Fe2O3 is absent, satisfying (1) and (2) below:

[0089] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0090] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0091] (Here, the above I G / I D 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I D When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D represents )

[0092] I of the above carbon nanotube G / I D Specifically, it may be 20 or more, 21 or more, 22 or more, 23 or more, or 24 or more, and may be 40 or less, 39 or less, 38 or less, 37 or less, or 36 or less. For example, I of the carbon nanotube above G / I D It may be 20 to 40, 21 to 39, 22 to 38, 23 to 37, or 24 to 36.

[0093] The average number of walls of the carbon nanotubes may be 1 to 5, preferably 1 to 4, and more preferably 1 to 3.

[0094]

[0095] 4. Method for manufacturing carbon nanotubes

[0096] Another aspect of the present invention is

[0097] (S1) Contains iron as the catalytic active metal, wherein 2θ = 33 when analyzed by X-ray diffraction (XRD). oA step of introducing a catalyst into a chemical vapor deposition reactor in which a peak corresponding to bulk Fe2O3 is not present;

[0098] (S2) A step of synthesizing Pristine carbon nanotubes by heating the chemical vapor deposition reactor and then injecting a carbon source gas; and

[0099] (S3) A step of obtaining carbon nanotubes by low-temperature oxidizing the above pristine carbon nanotubes.

[0100] A method for manufacturing carbon nanotubes satisfying the following (1) and (2) is provided, comprising:

[0101] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0102] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0103] Here, the above I G / I D 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I D When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D It represents ).

[0104] I of the pristine carbon nanotubes synthesized in the above step (S2) G / I D can be 5 to 20. I of the above pristine carbon nanotube G / I DSpecifically, it may be 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, or 11 or more, and may be 20 or less, 19 or less, 18 or less, 17 or less, or 16 or less. For example, I of the above pristine carbon nanotube G / I D may be 5 to 20, 6 to 19, 7 to 18, 8 to 18, 9 to 17, 10 to 17, or 11 to 16. I of the pristine carbon nanotube above G / I D When the above range is applied, the electrical and thermal conductivity of the carbon nanotubes can be excellent.

[0105] In the above step (S2), the temperature of the reactor may be 800 to 900°C. When the temperature of the reactor is in the above range, the yield of carbon nanotubes can be improved and it is advantageous to prevent the sintering of iron particles, thereby suppressing the formation of high-layer multi-walled carbon nanotubes.

[0106] In the above step (S2), the carbon source gas may include an aliphatic alkane, an aliphatic alkene, an aliphatic alkyne, an aromatic compound, or a combination thereof. For example, the carbon source gas may include methane, ethane, ethylene, acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, acetylene, formaldehyde, or acetaldehyde.

[0107] In the above step (S2), a flowing gas may be injected into the reactor along with the carbon source gas. For example, the flowing gas may include hydrogen, helium, argon, nitrogen, oxygen, carbon dioxide, or methane.

[0108] In the above step (S3), low-temperature oxidation may be performed at 300 to 600°C. Specifically, the low-temperature oxidation may be performed at 300 to 600°C, 350 to 550°C, or 400 to 500°C, and preferably at 400 to 500°C. Pristine carbon nanotubes prepared using a catalyst according to one aspect of the present invention suppress the formation of high-layer multi-walled carbon nanotubes and consist mostly of thin-walled carbon nanotubes and amorphous carbon, in which the average number of walls is 1 to 5, preferably 1 to 4, more preferably 1 to 3, and so that the degree of crystallization can be significantly increased while minimizing the amount of loss due to oxidation by selectively removing only the amorphous carbon through low-temperature oxidation (see Examples 1 to 4). On the other hand, if the manufactured pristine carbon nanotubes contain a significant amount of high-layer multi-walled carbon nanotubes, there may not be a significant difference in the degree of crystallinity of the carbon nanotubes before and after low-temperature oxidation even if low-temperature oxidation is performed (see Comparative Examples 1 to 5).

[0109]

[0110] Another aspect of the present invention is

[0111] A carbon nanotube dispersion comprising a carbon nanotube satisfying (1) and (2) below and a dispersion medium is provided.

[0112] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0113] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0114] Here, the above I G / I D 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (ID When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D It represents ).

[0115] In the carbon nanotube dispersion above, one or more dispersion media selected from the group consisting of N-methylpyrrolidone, pyridine, dimethylaminobenzene, and diethylaminobenzene may be used.

[0116]

[0117] Another aspect of the present invention is

[0118] An electrode structure prepared by including the above-described carbon nanotube dispersion is provided. The electrode structure may be, for example, a secondary battery electrode structure.

[0119]

[0120] Another aspect of the present invention is

[0121] An electrode structure comprising the above carbon nanotube is provided. The carbon nanotube satisfies the conditions of (1) and (2) below and may exist in a dried solid state within the electrode structure, and the electrode structure may be, for example, a secondary battery electrode structure.

[0122] (1) I of carbon nanotubes G / I D It shall be 20 to 40 days,

[0123] (2) The average number of walls of the carbon nanotubes is 1 to 5.

[0124] Here, the above I G / I D 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I DWhen referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D It represents ).

[0125] In addition, the carbon nanotubes may be included in the electrode structure, for example, as a conductive material. Due to their excellent electrical conductivity and high crystallinity, the carbon nanotubes improve the electrical properties of the electrode and can contribute to improving the output characteristics and high-rate characteristics of the battery by improving the uniformity of current flow and the charge transfer efficiency within the electrode.

[0126]

[0127] Another aspect of the present invention is

[0128] The present invention provides a secondary battery comprising an electrode structure manufactured including the above-described carbon nanotube dispersion. Due to the excellent electrical conductivity and high crystallinity of the carbon nanotubes within the electrode structure, the secondary battery can exhibit excellent and stable electrochemical performance in terms of discharge capacity, output characteristics, and capacity retention rate.

[0129] As a result, the secondary battery of the present invention can be usefully applied to portable electronic devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles requiring high performance, such as hybrid electric vehicles (HEVs).

[0130]

[0131] Hereinafter, the present invention will be described in more detail through examples and experimental examples to specifically explain the invention, but the present invention is not limited by these examples and experimental examples. The embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0132]

[0133] <Catalyst Preparation Example>

[0134] As metal precursors, iron nitrate, magnesium nitrate, and aluminum nitrate were dissolved in distilled water to prepare an aqueous metal precursor solution. Next, a slurry solution was prepared by adding twice the molar amount of ammonia water or ammonium carbonate ((NH₄)₂CO₃) to the aqueous metal precursor solution relative to the molar amount of metal. The slurry solution was aged at a temperature of 90°C for 24 hours, and the solids were recovered from the aged slurry solution using a vacuum filter and then washed with distilled water. Subsequently, the washed solids were dried at a temperature of 120°C and calcined at 700°C to finally obtain a metal oxide catalyst. During the above process, catalysts of various compositions were prepared by adjusting the Fe content, Mg content, and Al content in the final catalyst, and the catalyst preparation conditions for each preparation example are shown in Table 1 below.

[0135] Classification Catalyst Composition (wt%) Precipitating Agent FeMgAl Preparation Example 1 10.04 0.08.9 (NH₄)₂CO₃ Preparation Example 2 20.031.97.1 (NH₄)₂CO₃ Preparation Example 3 10.05 0.1 -(NH₄)₂CO₃ Preparation Example 4 10.05 0.1 -NH₄OH Preparation Example 5 30.023.85.3 (NH₄)₂CO₃ Preparation Example 6 20.043.1 -(NH₄)₂CO₃ Preparation Example 7 30.034.4 -(NH₄)₂CO₃ Preparation Example 8 20.043.1 -NH₄OH Preparation Example 9 30.034.4 -NH₄OH

[0136] <Examples and Comparative Examples>

[0137] Carbon nanotubes were synthesized using a catalyst prepared according to the above catalyst preparation example. Specifically, 0.5 g of the prepared catalyst was loaded into a CCVD (Catalytic Chemical Vapor Deposition) reactor, 540 sccm of argon gas was injected into the reactor, and the internal temperature of the reactor was heated to 850°C. Subsequently, methane gas, which is a carbon source gas, was injected into the reactor at a flow rate of 105 sccm, and the reaction was continued for 30 minutes to synthesize pristine carbon nanotubes. The synthesized pristine carbon nanotubes were calcined at 450°C for 6 hours to remove impurities such as amorphous carbon.

[0138] Classification Catalyst Used Catalyst Composition (wt%) Precipitating Agent FeMgAl Example 1 Preparation Example 1 10.04 0.08 9 (NH₄)₂CO₃ Example 2 Preparation Example 2 20.03 1 9 7 1 (NH₄)₂CO₃ Example 3 Preparation Example 3 10.05 0.1 - (NH₄)₂CO₃ Example 4 Preparation Example 4 10.05 0.1 - NH₄OH Comparative Example 1 Preparation Example 5 30.02 3 8 5 3 (NH₄)₂CO₃ Comparative Example 2 Preparation Example 6 20.04 3 1 - (NH₄)₂CO₃ Comparative Example 3 Preparation Example 7 30.03 4 4 - (NH₄)₂CO₃ Comparative Example 4 Preparation Example 820.043.1-NH4OH Comparative Example 5 Preparation Example 930.034.4-NH4OH

[0139] <Experimental Example>

[0140] The crystal structure of the catalyst obtained in the above catalyst preparation example and the Fe2O3 peak within the catalyst, and the crystal structure of the carbon nanotubes prepared in the examples and comparative examples, and Raman spectrum analysis (I G / I D The number of average walls and the average number of walls were measured, and the results are shown in Table 3 below. Unless otherwise noted, all measurements were performed at room temperature (23 ± 2℃), atmospheric pressure (approx. 1 atm), and relative humidity (40–60%).

[0141] 1) Analysis of the Fe2O3XRD peak of the catalyst:

[0142] The catalyst was irradiated with Cu Kα (λ=1.541 Å) X-rays using a BRUKER D8 ENDEAVOR, and 2θ was 10 to 80 o XRD analysis was performed within the range under conditions of a voltage of 40 kV, a current of 40 mA, a step size of 0.02°, and a scan rate of 5° / min. From the analysis results, 2θ is approximately 33 o The presence or absence of Fe2O3 peaks observed in the vicinity was checked, and if a peak was present, the crystal grain size was calculated using Scherrer's equation below based on the full width at half maximum (FWHM) of the peak:

[0143]

[0144] (In the above formula,

[0145] D: Crystal grain size, K: Shape factor, λ: X-ray wavelength, β hkl : XRD peak full width at half maximum (FWHM) of the (hkl) plane, and θ hkl : Represents the Bragg angle.)

[0146] 2) CNT Raman Spectrum Analysis (I G / I D ):

[0147] CNTs were mounted on a Thermo Scientific DXR Raman Microscope, and measurements were taken using a laser wavelength of 532 nm. The measurement conditions were an blowing time of 3 seconds, 5 accumulator cycles, an objective lens magnification of 50x, a slit width of 50 μm, and a measurement wavelength of 100–3000 cm⁻¹. -1 It was set to . CNTs for measurement were transferred onto a glass slide and flattened using a spatula. Among the obtained peaks, 1550–1650 cm⁻¹ -1 The maximum peak intensity within the spectral range is the intensity of the G band (I G It is called ), and 1250~1400cm -1 The maximum peak intensity within the range of the D band intensity (I DIt was set to ), and the intensity of the G band (I G ) and D-band strength (I D The ratio of ) to CNT's I G / I D It was defined as a ratio. This analysis was performed without applying baseline correction.

[0148] 3) XRD analysis of CNTs and calculation of average wall count:

[0149] CNTs were irradiated with Cu Kα (λ=1.541 Å) X-rays using a BRUKER D8 ENDEAVOR, and 2θ was 10 to 80 o XRD analysis was performed within the range under conditions of a voltage of 40 kV, a current of 40 mA, a step size of 0.02°, and a scan rate of 5° / min. The analysis results showed that 2θ was approximately 26 o The carbon (002) peak observed in the vicinity was identified, and based on this, the average number of CNT walls was calculated according to the following formula:

[0150]

[0151] (In the above formula,

[0152] L c : Carbon crystal grain size, d 002 : Distance between carbon (002) planes, K : Shape factor, β hkl : XRD peak full width at half maximum (FWHM) of the (hkl) plane, and θ hkl : Represents the Bragg angle)

[0153] 4) TEM (Transmission Electron Microscopy) Analysis:

[0154] To prepare the TEM sample, 1.6 g of SDS (Sodium dodecyl sulfate) was dissolved in 200 mL of water, 0.2 g of Calcined CNT was added, and the mixture was dispersed by sonication (20 minutes, 200 W). The dispersion was placed on a TEM grid and dried to prepare the sample. TEM analysis was performed using a Titan G2 80-200 Field Emission Transmission Electron Microscope at an acceleration voltage of 200 kV, and the number of CNT walls was analyzed at high magnification (1,000,000x).

[0155] Specific measurement results are shown in Table 3 below.

[0156]

[0157] Classification Catalyst Pristine CNTC Alcined CNTX RD Phase Presence / Absence of Fe2O3 peak Fe2O3 crystallite size (nm) I G / I D ratioCNT average wall number I G / I D ratio Example 1 XNA 11.7 23 1.2 Example 2 XNA 13.1 22 8.9 Example 3 XNA 14.8 23 5.6 Example 4 XNA 15.1 22 4.8 Comparative Example 1 O2 0.1 13.3 25 19.6 Comparative Example 2 O2 8.9 14.4 28 17.4 Comparative Example 3 O2 2.9 13.9 29 17.7 Comparative Example 4 O2 6.4 14.0 25 15.5 Comparative Example 5 O3 3.5 11.2 30 12.3

[0158] As can be seen from Table 3 and Figures 1 to 4 above, no bulk Fe₂O₃ peak was observed in XRD analysis of the catalysts used in the preparation of Examples 1 to 4, and accordingly, the prepared Pristine CNTs were found to contain TWNTs with an average wall number of 2 and amorphous carbon. As a result of calcining these Pristine CNTs, the IG / ID ratio in Raman analysis increased significantly to 24.8–35.6, which means that the amorphous carbon was effectively removed and the crystallinity was significantly improved. In addition, according to TEM analysis, it was confirmed that the CNTs prepared in Examples 1 to 3 all had a thin-walled structure with a wall count of 2 or less, and that they maintained this thin-walled structure and exhibited high crystallinity even after calcination treatment, demonstrating that only thin-walled CNTs can be selectively obtained. On the other hand, in Comparative Examples 1 to 5, a Bulk Fe₂O₃ peak was clearly observed in the XRD analysis of the catalyst, and a crystallinity peak characteristic of CNTs was also confirmed in the Pristine CNTs prepared using this, and it was found to contain high-layer multi-walled carbon nanotubes (MWNTs) with an average wall count of 25 or more. Furthermore, it was confirmed that the crystallinity was not improved, as the IG / ID ratio remained relatively low at 12.3 to 19.6 even after calcination treatment.

[0159]

[0160] In other words, the presence of Bulk Fe₂O₃ in the catalyst has a decisive influence on the structural characteristics and crystallinity of the CNT, and it has been experimentally proven that the catalyst according to the present invention can provide the advantage of selectively producing thin-walled carbon nanotubes with an average number of walls of 1 to 5 with high crystallinity.

Claims

1. Includes iron as a catalytic active metal, but, 2θ = 33 in XRD analysis o A catalyst for carbon nanotube manufacturing in which a peak corresponding to bulk Fe2O3 is absent.

2. In Paragraph 1, The above carbon nanotube is a catalyst for manufacturing carbon nanotubes, wherein the carbon nanotube is a thin-walled carbon nanotube having an average number of walls of 1 to 5.

3. Contains iron as the catalytic active metal, wherein 2θ = 33 when analyzed by X-ray diffraction (XRD). o Carbon nanotubes grown on a catalyst in which the peak corresponding to bulk Fe2O3 is not present, satisfying (1) and (2) below. (1) I of carbon nanotubes G / I D It shall be 20 to 40 days, (2) The average number of walls of the carbon nanotubes is 1 to 5. (Here, the above I G / I D is 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I D When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D It represents ).

4. In Paragraph 3, I of the above carbon nanotube G / I D Carbon nanotubes, ranging from 24 to 36.

5. In Paragraph 3, A carbon nanotube having an average number of walls of 1 to 4.

6. In Paragraph 3, Carbon nanotube having an average number of walls of 1 to 3. 7.(S1) Contains iron as the catalytic active metal, wherein 2θ = 33 when analyzed by X-ray diffraction (XRD). o A step of introducing a catalyst into a chemical vapor deposition reactor in which a peak corresponding to bulk Fe2O3 is not present; (S2) A step of synthesizing Pristine carbon nanotubes by heating the chemical vapor deposition reactor and then injecting a carbon source gas; and (S3) A step of obtaining carbon nanotubes by low-temperature oxidizing the above pristine carbon nanotubes. A method for manufacturing carbon nanotubes comprising and satisfying (1) and (2) below: (1) I of carbon nanotubes G / I D It shall be 20 to 40 days, (2) The average number of walls of the carbon nanotubes is 1 to 5. (Here, the above I G / I D is 1550–1650 cm in the Raman spectrum of carbon nanotubes -1 The maximum peak intensity within the range of the G band intensity (I G It is called ), and 1250~1400cm -1 Within the range of maximum peak intensity, the intensity of the D band (I D When referring to ), the strength of the G-band (I G ) and D-band strength (I D The ratio of )(I G / I D It represents ).

8. In Paragraph 7, A method for manufacturing carbon nanotubes, wherein in step (S2) above, the chemical vapor deposition reactor is heated to a temperature of 800 to 900°C.

9. In Paragraph 7, I of the pristine carbon nanotubes synthesized in the above step (S2) G / I D A method for manufacturing carbon nanotubes, wherein the nanotubes are 5 to 20.

10. In Paragraph 7, A method for manufacturing carbon nanotubes, wherein the low-temperature oxidation in step (S3) above is performed at a temperature of 400 to 600°C.

11. In Paragraph 7, I of the carbon nanotube obtained in the above step (S3) G / I D A method for manufacturing carbon nanotubes, wherein the nanotubes are 24 to 36 in number.

12. A carbon nanotube dispersion comprising carbon nanotubes according to any one of paragraphs 3 to 6.

13. An electrode structure manufactured using a carbon nanotube dispersion according to paragraph 12.

14. An electrode structure comprising carbon nanotubes according to any one of paragraphs 3 to 6.

15. A secondary battery comprising an electrode structure manufactured using a carbon nanotube dispersion according to paragraph 12.

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