Bundled carbon nanotubes and manufacturing method therefor

Abstract

The present invention relates to: novel carbon nanotubes having excellent electrical conductivity while exhibiting outstanding storage and transportation efficiency; a method for manufacturing the carbon nanotubes; a carbon nanotube dispersion; an electrode structure comprising the carbon nanotubes; and a secondary battery comprising the carbon nanotubes.

Description

Bundle-type carbon nanotubes and methods for manufacturing the same

[0001] The present invention relates to a novel carbon nanotube having excellent electrical conductivity and excellent storage and transport efficiency, a method for manufacturing said carbon nanotube, a carbon nanotube dispersion, an electrode structure including carbon nanotubes, and a secondary battery including 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 graphene sheets, 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. Carbon nanotubes have excellent electrical conductivity, high strength, and outstanding thermal conductivity, giving them diverse application possibilities. In particular, their utilization as electrode conductive materials in electronic devices, composite materials, and energy storage devices is being actively researched.

[0003]

[0004] Carbon nanotubes play an important role in secondary batteries and conductive polymer compounds, and are particularly widely used as conductive materials in secondary batteries. To optimize the electrical conductivity of carbon nanotubes, uniform dispersion of carbon nanotubes is essential. However, carbon nanotubes are difficult to disperse uniformly within electrode slurry compositions and face the problem of easily aggregating. This aggregation phenomenon prevents the conductive material from being evenly distributed within the active material layer during the electrode formation process, which can lead to a degradation in the performance of the secondary battery. Therefore, a technical approach to uniformly disperse carbon nanotubes is essential.

[0005] For bundled carbon nanotubes, reducing bundle size and minimizing standard deviation is crucial for improving dispersion performance. Smaller bundles enhance dispersion by reducing aggregation among carbon nanotubes, but this process can complicate the manufacturing process. Furthermore, manufacturing carbon nanotubes with small standard deviation results in uniform diameters, leading to smoother dispersion, but this entails additional technical challenges.

[0006] Furthermore, one of the important indicators representing the productivity of carbon nanotubes is bulk density. Bulk density refers to mass per unit volume and is directly related to the productivity of carbon nanotubes. High bulk density indicates that a larger amount of carbon nanotubes is contained within the same volume, making it an important indicator for mass production.

[0007]

[0008] Therefore, reducing bundle size and standard deviation while maintaining high bulk density is a highly challenging task for simultaneously satisfying dispersibility and productivity. Current technology faces limitations in manufacturing carbon nanotubes that meet both of these requirements, and a new technological approach is needed to address this.

[0009]

[0010] Prior art literature

[0011] [Patent Document 1] Republic of Korea Published Patent No. 10-2017-0111973

[0012] [Patent Document 2] Republic of Korea Published Patent No. 10-2014-0032349

[0013] The present invention aims to provide a novel bundled carbon nanotube having excellent dispersibility and high bulk density, a method for manufacturing said carbon nanotube, a carbon nanotube dispersion, an electrode structure including carbon nanotubes, and a secondary battery including carbon nanotubes.

[0014] One aspect of the present invention is

[0015] A bundled carbon nanotube satisfying (1) to (3) below is provided:

[0016] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0017] (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and

[0018] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0019] [Equation 1]

[0020] 0.5 ≤ 3σ / A ≤ 0.9

[0021] The average diameter of the carbon nanotube bundles may be 1 to 2.5 μm.

[0022] The standard deviation (σ) of the above diameter may be 0.1 to 0.6.

[0023] The specific surface area of ​​the above carbon nanotube is 230 to 500 m² 2 It can be / g.

[0024]

[0025] Another aspect of the present invention is

[0026] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0027] (S2) A step of filling the reactor with the above catalyst;

[0028] (S3) A step of heating the reactor; and

[0029] (S4) A step of injecting carbon source gas into the reactor;

[0030] A method for manufacturing bundled carbon nanotubes is provided, comprising and satisfying the following (1) to (3):

[0031] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0032] (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and

[0033] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0034] [Equation 1]

[0035] 0.5 ≤ 3σ / A ≤ 0.9

[0036] The content of cobalt (Co, Cobalt) in the catalyst prepared in step (S1) above may be 10 to 30 weight% based on the total weight of the catalyst.

[0037] The molar ratio of vanadium to cobalt in the catalyst prepared in step (S1) above (V / Co, Vanadium to Cobalt molar ratio) may be 0.01 to 0.6.

[0038] The molar ratio of citric acid to vanadium in the catalyst prepared in step (S1) above (CA / V, Citric Acid to Vanadium molar ratio) may be 0.1 to 3.0.

[0039] The catalyst support may include one or more metal oxides or metal hydroxides selected from the group consisting of hydrotalcite, alumina (Al2O3), magnesium peroxide (MgO2), magnesium oxide (MgO), and boehmite.

[0040]

[0041] Another aspect of the present invention is

[0042] A carbon nanotube dispersion comprising bundled 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]

[0053] The carbon nanotubes according to the present invention simultaneously satisfy high bulk density and specific surface area while exhibiting low powder resistance, and thus possess excellent electrical conductivity along with superior storage and transport efficiency. Furthermore, they are easy to handle during storage and transport, allowing them to be utilized in various industrial fields.

[0054] In particular, due to its high bulk density characteristics, it can be used directly for manufacturing dispersions without separate processing or compression, which is advantageous for process simplification and productivity improvement.

[0055] In addition, the carbon nanotubes of the present invention have a uniform bundle diameter distribution, making individualization easy during the dispersion process, and thus exhibiting excellent stability. These characteristics can increase the efficiency of the dispersion process and contribute to ensuring the uniformity and stability of the conductive material in the electrode slurry.

[0056] As a result, the dispersion containing carbon nanotubes of the present invention provides not only excellent dispersibility but also a uniform and stable dispersion state when preparing an electrode slurry, thereby enabling excellent electrochemical performance.

[0057] Therefore, the carbon nanotubes according to the present invention can contribute significantly to the improvement of the electrochemical properties of the final product, as well as the simplification of the process and cost reduction effects.

[0058] Figure 1 shows a scanning electron microscope (SEM) image of carbon nanotubes according to Example 2 used to measure the average diameter of carbon nanotube bundles.

[0059] The present invention will be described in more detail below.

[0060] 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.

[0061] As used herein, the term “Carbon Nanotube (CNT)” refers to a structure comprising 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 wholly or partially in a bundle form or in a plurality of mixed groups. The carbon nanotube units are sp 2A graphene sheet, which is a planar carbon atomic layer with a hexagonal honeycomb structure having a bonding structure, has a structure in which it 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. The bundled carbon nanotube according to the present invention may include one or more of single-walled, double-walled, and multi-walled carbon nanotubes.

[0062] The term “bundle type” as used herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in parallel with a substantially identical orientation along the unit length axis, or are twisted or entangled after arrangement.

[0063] As used herein, the term “bundle diameter” refers to the transverse width of a carbon nanotube bundle. The average diameter of a carbon nanotube bundle is defined as the average of diameter values ​​measured for at least 100 bundles randomly selected from sharp, clearly focused areas among images taken from at least five different random areas of the sample. The diameter value is based on the visible width of each bundle, and the measurement is taken, for example, at a magnification of 2,000x, an acceleration voltage of 15 kV, and under vacuum conditions (approx. 10 -5 It can be based on SEM images performed at Pa or lower.

[0064] The term “Bulk Density” as used in this specification refers to the mass occupied by carbon nanotubes (powder) in a specific volume. This represents the density based on the total volume, including not only the interior of the carbon nanotube particles but also the porosity between the particles. The bulk density of carbon nanotubes is expressed in units of g / cm³ or kg / m³ and has a significant impact on the productivity of carbon nanotubes. Generally, carbon nanotubes with low bulk density have a large volume and weak inter-particle bonding forces, which causes the powder to easily swell or scatter. Due to these characteristics, transportation and handling are only possible after undergoing a separate compression or molding process. This increases production time and costs, and furthermore, can negatively affect the dispersibility and uniformity of the carbon nanotubes. On the other hand, the carbon nanotubes according to the present invention have a high bulk density in the range of 80 to 160 kg / m³, so they have the advantage of enabling efficient transportation and handling without a separate compression process during transport and handling.

[0065]

[0066] 1. Carbon nanotubes

[0067] One aspect of the present invention provides a bundled carbon nanotube satisfying (1) to (3) below:

[0068] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0069] (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and

[0070] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0071] [Equation 1]

[0072] 0.5 ≤ 3σ / A ≤ 0.9

[0073] The average diameter of the carbon nanotube bundle may be 1 to 2.5 μm. Specifically, the average diameter of the carbon nanotube bundle may be 1 μm or more, 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm or more, or 1.5 μm or more, and may be 2.5 μm or less, 2.4 μm or less, 2.3 μm or less, or 2.2 μm or less. For example, the average diameter of the carbon nanotube bundle may be 1 μm to 2.5 μm, 1.1 μm to 2.5 μm, 1.2 μm to 2.4 μm, 1.3 μm to 2.4 μm, 1.4 μm to 2.3 μm, 1.5 μm to 2.3 μm, or 1.5 μm to 2.2 μm.

[0074] The standard deviation of the diameter may be 0.1 to 0.6. Specifically, the standard deviation of the diameter may be 0.1 or more, 0.15 or more, 0.2 or more, 0.25 or more, 0.3 or more, or 0.35 or more, and may be 0.6 or less, 0.55 or less, or 0.5 or less. For example, the standard deviation of the diameter may be 0.1 to 0.6, 0.15 to 0.6, 0.2 to 0.55, 0.25 to 0.55, 0.3 to 0.5, or 0.35 to 0.5.

[0075] The above 3σ / A may be 0.5 to 0.9. Specifically, the above 3σ / A may be 0.5 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, or 0.55 or more, and may be 0.9 or less, 0.89 or less, 0.87 or less, 0.88 or less, 0.86 or less, or 0.85 or less. For example, the 3σ / A may be 0.5 to 0.9, 0.51 to 0.89, 0.52 to 0.88, 0.53 to 0.87, 0.54 to 0.86, or 0.55 to 0.85. If the above 3σ / A is less than 0.5, it becomes difficult to disperse carbon nanotube bundles and aggregation may occur, and if the above 3σ / A exceeds 0.9, the dispersion becomes non-uniform, which may lead to a decrease in the performance of the final product.

[0076] The bulk density of the above carbon nanotubes is 80 to 160 kg / m³ 3 It may be. Specifically, the bulk density of the carbon nanotube is 80 kg / m³ 3 Above, 85 kg / m² 3 Above, 90 kg / m² 3 Above, 95 kg / m² 3 Above, or 100 kg / m² 3 Above, or 105 kg / m² 3 It may be greater than 160 kg / m² 3 Below, 155 kg / m² 3 Below, 150 kg / m² 3 Below, 145 kg / m² 3 Below, 140 kg / m² 3 Below, 135 kg / m² 3 Less than or equal to 130 kg / m³ 3 It may be less than or equal to. For example, the bulk density of the carbon nanotube is 80 kg / m³. 3 Up to 160 kg / m² 3 , 85 kg / m 3 Up to 155 kg / m² 3 , 90 kg / m 3 Up to 150 kg / m² 3 , 95 kg / m3 up to 140 kg / m² 3 , 100 kg / m 3 Up to 135 kg / m² 3 , or 105 kg / m² 3 Up to 130 kg / m² 3 It may be. The bulk density of the carbon nanotube is 80 kg / m³ 3 If the value is less than [amount], the low bulk density results in an excessive volume during slurry preparation, and reduced mixability and transportability may lead to reduced processability in the utilization process of carbon nanotubes, such as the electrode manufacturing process. The carbon nanotubes according to the present invention have a high bulk density, resulting in a large storage capacity within the same volume and exhibiting excellent flowability and handling properties even in a powder state; thus, workability is improved throughout processes such as slurry preparation, transport, and coating. Accordingly, not only transport and storage efficiency but also productivity and quality stability in the electrode manufacturing process can be dramatically improved. The bulk density of the carbon nanotubes can be measured by methods commonly used in the technical field. For example, the bulk density of the carbon nanotubes can be calculated by filling a quantitative cup with carbon nanotube powder via free fall and dividing the mass of the filled powder by the volume of the cup (kg / m³).

[0077] The specific surface area of ​​the above carbon nanotube is 230 to 500 m² 2 It may be / g. Specifically, the specific surface area of ​​the carbon nanotube is 230 m² 2 / g or more, 235 m 2 / g or more, 240 m 2 / g or more, 245 m 2 / g or more, or 250 m 2 It can be more than / g, and 500 m 2 / g or less, 480 m 2 / g or less, 460 m 2 / g or less, 420 m 2 / g or less, or 400 m 2It may be less than / g. For example, the specific surface area of ​​the carbon nanotube is 230 m² 2 / g to 500 m 2 / g, 235 m 2 / g to 480 m 2 / g, 240 m 2 / g to 460 m 2 / g, 245 m 2 / g to 420 m 2 / g, or 250 m 2 / g to 400 m 2 It may be / g. The specific surface area of ​​the carbon nanotube is 230 m². 2 If it is less than / g, electrical conductivity is reduced and may be unsuitable as a conductive material for secondary batteries, and the specific surface area of ​​the carbon nanotube is 500 m² 2 If it exceeds / g, the carbon nanotubes may clump together or form aggregates, which may reduce dispersibility. The specific surface area of ​​the carbon nanotubes can be measured by methods commonly used in this field of technology. For example, the specific surface area of ​​the carbon nanotubes measured by the BET (Brunauer-Emmett-Teller) method can be calculated by determining the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mini II from BEL Japan.

[0078] The powder resistance of the carbon nanotube may be 6 mΩ·cm to 12 mΩ·cm. Specifically, the powder resistance of the carbon nanotube may be 12 mΩ·cm or less, 11.9 mΩ·cm or less, 11.8 mΩ·cm or less, or 11.7 mΩ·cm or less, and may be 6 mΩ·cm or more, 6.5 mΩ·cm or more, 7 mΩ·cm or more, 7.5 mΩ·cm or more, 8 mΩ·cm or more, 8.5 mΩ·cm or more, 9 mΩ·cm or more, 9.5 mΩ·cm or more, or 9.8 mΩ·cm or more. For example, the powder resistance of the carbon nanotube may be 6 mΩ·cm to 12 mΩ·cm, 6.5 mΩ·cm to 11.9 mΩ·cm, 7 mΩ·cm to 11.9 mΩ·cm, 7.5 mΩ·cm to 11.9 mΩ·cm, 8 mΩ·cm to 11.9 mΩ·cm, 8.5 mΩ·cm to 11.9 mΩ·cm, 9 mΩ·cm to 11.8 mΩ·cm, 9.5 mΩ·cm to 11.8 mΩ·cm, or 9.8 mΩ·cm to 11.7 mΩ·cm. If the powder resistance of the carbon nanotube is less than 6 mΩ·cm, the carbon nanotube may have excessively high conductivity, which could cause electrical interference or short-circuit problems; if the powder resistance of the carbon nanotube exceeds 12 mΩ·cm, electrical conductivity may be reduced, making it unsuitable as a conductive material for secondary batteries. The powder resistance of the carbon nanotube can be measured by methods commonly used in this technical field. For example, the powder resistance of the carbon nanotube can be calculated by measuring the resistance according to pressure at a compression density of 1 g / cc using the MCP-PD51 equipment of Nittoseiko Analytech.

[0079] The purity of the carbon nanotubes may be 93 wt% or more, 93.5 wt% or more, 94 wt% or more, or 95 wt% or more. Although there is no specific upper limit for the purity of the carbon nanotubes, a purity of typically 99.9 wt% or less may be used. The purity of the carbon nanotubes refers to the content of carbon nanotubes remaining after impurities within the carbon nanotubes have been removed, and can be calculated based on the weight change obtained by burning the carbon nanotubes:

[0080] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0081] Bundled carbon nanotubes according to one aspect of the present invention exhibit high bulk density, allowing them to be used directly in the preparation of dispersions without separate processing or compression processes. In particular, the bundled carbon nanotubes according to one aspect of the present invention are noteworthy for having a uniform bundle diameter distribution, which means that individualization can be easily achieved during the dispersion process, thereby ensuring excellent dispersibility. This uniform distribution characteristic not only dramatically improves the efficiency of the dispersion process but also contributes significantly to ensuring the uniformity and stability of the electrode slurry when applied as an electrode structure. Accordingly, when carbon nanotubes according to one aspect of the present invention are applied to various electronic devices, including secondary batteries and energy storage devices, they can substantially contribute to the improvement of electrochemical performance, and furthermore, simultaneously achieve process simplification and cost reduction effects.

[0082] According to one aspect of the present invention, the bundled carbon nanotube, that is, the carbon nanotube satisfying the conditions of (1) to (3), can be obtained by controlling the manufacturing raw materials, catalyst, manufacturing conditions, etc. This will be explained in detail below.

[0083]

[0084] 2. Method for manufacturing carbon nanotubes

[0085] Another aspect of the present invention is

[0086] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0087] (S2) A step of filling the reactor with the above catalyst;

[0088] (S3) A step of heating the reactor; and

[0089] (S4) A step of injecting carbon source gas into the reactor;

[0090] A method for manufacturing carbon nanotubes is provided, comprising and satisfying the following (1) to (3):

[0091] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0092] (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and

[0093] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0094] [Equation 1]

[0095] 0.5 ≤ 3σ / A ≤ 0.9

[0096] In the above step (S1), cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), cobalt chloride dihydrate (CoCl₂·2H₂O), cobalt sulfate heptahydrate (CoSO₄·7H₂O), cobalt acetate tetrahydrate (Co(CH₃COO)₂·4H₂O), cobalt oxalate dihydrate (CoC₂O₄·2H₂O), cobalt acetylacetone complex (Co(acac)₂), cobalt carbonate (CoCO₃), or cobalt oxide (Co₃O₄) may be used as the cobalt precursor, but is not limited thereto.

[0097] In the above (S1) step, as a vanadium precursor, ammonium vanadate (NH₄VO₃), sodium vanadate (NaVO₃), potassium vanadate (KVO₃), vanadium pentoxide (V₂O₅), vanadyl sulfate (VOSO₄), vanadyl acetylacetone (VO(acac)₂), vanadium trichloride (VCl₃) or vanadium oxotrifluoride (VOF₃) may be used, but are not limited thereto.

[0098] The cobalt content in the catalyst prepared in step (S1) above may be 10 to 30 weight% based on the total weight of the catalyst. Specifically, the cobalt content may be 10 weight% or more, 11 weight% or more, 12 weight% or more, or 13 weight% or more, and may be 30 weight% or less, 29 weight% or less, 28 weight% or less, 27 weight% or less, or 26 weight% or less. For example, the cobalt content may be 10 weight% to 30 weight%, 11 weight% to 29 weight%, 12 weight% to 28 weight%, 13 weight% to 27 weight%, or 13 weight% to 26 weight%. Carbon nanotubes obtained from a catalyst in which the cobalt content falls outside the above range may have increased powder resistance, and in some cases, the specific surface area may increase, resulting in decreased electrical conductivity. In addition, the purity of carbon nanotubes may decrease, which can lead to a degradation in the performance of the final product.

[0099] The molar ratio (V / Co) of vanadium to cobalt in the catalyst prepared in step (S1) above may be 0.01 to 0.6. Specifically, the molar ratio of vanadium to cobalt may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more, and may be 0.6 or less, 0.5 or less, 0.49 or less, 0.48 or less, 0.47 or less, 0.46 or less, or 0.45 or less. For example, the molar ratio of vanadium to cobalt may be 0.01 to 0.6, preferably 0.05 to 0.5, more preferably 0.1 to 0.4. When the molar ratio of vanadium to cobalt is within the above range, the carbon nanotubes obtained from the catalyst may have significantly reduced powder resistance and increased bulk density, which may be advantageous for productivity.

[0100] The molar ratio (CA / V) of citric acid to vanadium in the catalyst prepared in step (S1) above may be 0.1 to 3.0. Specifically, the molar ratio of citric acid to vanadium may be 0.1 or more, 0.2 or more, or 0.3 or more, and may be 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, or 2.5 or less. For example, the molar ratio of citric acid to vanadium may be 0.1 to 3.0, 0.1 to 2.9, 0.1 to 2.8, 0.2 to 2.7, 0.2 to 2.6, or 0.3 to 2.5. When the molar ratio of citric acid to vanadium is within the above range, the powder resistance of the carbon nanotubes obtained from the catalyst may be reduced, and accordingly, it may be advantageous in terms of electrical conductivity.

[0101] In step (S1) above, a porous metal oxide may be used as the catalyst support. For example, one or more metal oxides or metal hydroxides selected from the group consisting of hydrotalcite, alumina (Al2O3), magnesium peroxide (MgO2), magnesium oxide (MgO), and boehmite may be used as the porous metal oxide.

[0102] In the above step (S1), the catalyst precursor mixed with the active ingredient and the catalyst support can be dried at 180°C to 200°C for 1 to 5 hours, and then calcined at 300°C to 750°C for 30 minutes to 3 hours to form a catalyst.

[0103] In the above (S2) step, the reactor may include a chemical vapor deposition reactor, a fixed-bed reactor, or a fluidized-bed reactor.

[0104] The step of heating the reactor in the above (S3) step may be performed at a temperature of 600 to 800°C. For example, the step of heating the reactor may be performed at a temperature of 600°C to 800°C, 610°C to 790°C, 620°C to 780°C, 630°C to 770°C, 640°C to 760°C, or 650°C to 750°C.

[0105] In the above step (S4), the carbon source gas is a carbon-containing gas capable of decomposing at high temperatures to form carbon nanotubes, and may be an aliphatic alkane, an aliphatic alkene, an aliphatic alkyne, or an aromatic compound. For example, the carbon source gas may be one or more selected from the group consisting of ethane, ethylene, acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, formaldehyde, and acetaldehyde.

[0106]

[0107] 3. Carbon nanotube dispersion

[0108] Another aspect of the present invention is

[0109] A carbon nanotube dispersion comprising a bundled carbon nanotube satisfying (1) to (3) below and a dispersion medium is provided.

[0110] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0111] (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and

[0112] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0113] [Equation 1]

[0114] 0.5 ≤ 3σ / A ≤ 0.9

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

[0116] The content of carbon nanotubes in the above dispersion may be 0.05 to 10 weight%. Within this range, while ensuring sufficient electrical conductivity, the aggregation of carbon nanotubes is suppressed and the viscosity is maintained appropriately, thereby providing an advantageous effect of achieving excellent processability of the dispersion.

[0117]

[0118] Another aspect of the present invention is

[0119] 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.

[0120]

[0121] Another aspect of the present invention is

[0122] The present invention provides an electrode structure comprising the above-described bundled carbon nanotubes. The above-described bundled carbon nanotubes satisfy the conditions of (1) to (3) 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.

[0123] (1) Bulk density of 80 to 160 kg / m³ 3 will be;

[0124] (2) The resistance of the powder shall be 6 to 12 mΩ·cm;

[0125] (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below:

[0126] [Equation 1]

[0127] 0.5 ≤ 3σ / A ≤ 0.9

[0128] In addition, the carbon nanotubes may be included in the electrode structure, for example, as a conductive material. The carbon nanotubes exhibit excellent dispersibility in the conductive material dispersion, which can increase the uniformity and stability of the electrode slurry, thereby contributing to the improvement of electrochemical performance.

[0129]

[0130] Another aspect of the present invention is

[0131] The present invention provides a secondary battery comprising an electrode structure manufactured including the above-described carbon nanotube dispersion. Due to the uniform dispersion of carbon nanotubes within the electrode structure, the secondary battery can stably exhibit excellent discharge capacity, output characteristics, and capacity retention rate. As a result, the secondary battery can be usefully applied in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles like hybrid electric vehicles (HEVs).

[0132] 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.

[0133]

[0134] <Catalyst Preparation Example>

[0135] As a vanadium precursor, NH₄VO₃ was first dissolved in water, followed by the addition of citric acid (CA), a multicarboxylic acid, as a complexing agent, and then the addition of Co(NO₃)₂·6H₂O as a cobalt precursor to prepare a precursor solution. After thoroughly stirring the precursor solution, it was supported on hydrotalcite, which served as a support. Subsequently, the catalyst was prepared by drying in an oven at 190°C for 4 hours, followed by calcination at the temperatures listed in Table 1 below for 1 hour. The cobalt content, the molar ratio of vanadium to cobalt (V / Co), and the molar ratio of citric acid to vanadium (CA / V) confirmed in the final prepared catalyst are shown in Table 1.

[0136] Catalyst Co Content (WJ%) V / Co (Molar Ratio) CA / V (Molar Ratio) Calcination Temperature (°C) Preparation Example 1 160.11.0500 Preparation Example 2 160.10.3400 Preparation Example 3 160.41.0400 Preparation Example 4 220.12.0500 Preparation Example 5 220.251.0500 Preparation Example 6 220.10.4680 Preparation Example 7 170.10.4500 Preparation Example 8 130.30.4500 Preparation Example 9 260.10.5680 Preparation Example 10 200.20.4300 Preparation Example 11 160.71.0500 Preparation Example 12 160.70.3400

[0137] <Examples and Comparative Examples>

[0138] Carbon nanotubes were prepared using the catalyst prepared in the above catalyst preparation example. Specifically, 6.4 g of the prepared catalyst was loaded into a fluidized bed reactor, nitrogen gas was injected into the reactor at 3,000 sccm, and the internal temperature of the reactor was heated to 690°C. Subsequently, ethylene gas, a carbon source gas, was injected at 1,000 sccm, and the reaction was continued for 120 minutes to produce carbon nanotubes. The catalysts used in the examples and comparative examples are shown in Table 2 below.

[0139] Classification Catalyst Used Catalyst Characteristics Co Content (Weight %) V / Co (Molar Ratio) CA / V (Molar Ratio) Calcination Temperature (°C) Example 1 Preparation Example 1 160.11.0500 Example 2 Preparation Example 2 160.10.3400 Example 3 Preparation Example 3 160.41.0400 Example 4 Preparation Example 4 220.12.0500 Example 5 Preparation Example 5 220.251.0500 Example 6 Preparation Example 6 220.10.4680 Example 7 Preparation Example 7 170.10.4500 Example 8 Preparation Example 8 130.30.4500 Example 9 Preparation Example 9 260.10.5680 Example 10 Preparation Example 10200.20.4300 Comparative Example 1 Manufacturing Example 11160.71.0500 Comparative Example 2 Manufacturing Example 12160.70.3400

[0140] Comparative Example 3

[0141] JO's carbon nanotube JENOTUBE 10B product was used.

[0142]

[0143] Comparative Example 4

[0144] JO's carbon nanotube JENOTUBE 6A product was used.

[0145]

[0146] <Experimental Example>

[0147] 1. Confirmation of physical properties of carbon nanotubes

[0148] The bundle diameter, bulk density, specific surface area, powder resistance, and purity of the carbon nanotubes prepared according to the above examples and comparative examples were measured by the following methods. Unless otherwise noted, all measurements were performed under conditions of room temperature (23 ± 2 ℃), atmospheric pressure (about 1 atm), and relative humidity of 40–60%.

[0149] 1) Bundle Diameter (Diameter of CNT bundles)

[0150] The diameter of the carbon nanotube bundles was measured using a scanning electron microscope (SEM, HITACHI Regulus 8220). During measurement, the acceleration voltage was set to 15 kV and the magnification was set to 2,000x to observe the surface of the sample. SEM imaging was performed under vacuum conditions (approx. 10 -5 The procedure was performed at Pa or lower, and at least 5 images were acquired from each of 5 or more different random regions on the sample surface. Among the acquired images, sharp and clearly focused regions were selected, and at least 100 carbon nanotube bundle strands were randomly selected from each image. Based on the diameter data (at least 100) obtained in this way, the mean value and standard deviation were calculated, and the statistical characteristics of the bundle diameter distribution were evaluated. As an example, the SEM image of carbon nanotubes according to Example 2 used in the above measurement is shown in Fig. 1.

[0151] 2) Bulk Density

[0152] Measurements were taken using a 50ml capacity stainless steel (SUS) measuring cup. During measurement, CNT powder was filled into the measuring cup by free fall from a height of approximately 5 cm above the top of the cup. The total weight of the powder, filled naturally without overflowing from the top of the cup, was measured using an electronic balance (Mettler Toledo, Balance XPR204V, precision: ± 0.0001 g), and this was divided by the volume of the cup (50ml) to convert it into bulk density (kg / m³). Repeated measurements were performed three times, and the average value was used as the final bulk density.

[0153] 3) Specific Surface Area

[0154] Using the BELSORP-mini II instrument from BEL Japan, the nitrogen gas adsorption isotherm was measured at liquid nitrogen temperature (77 K), and the specific surface area was calculated according to the BET (Brunauer-Emmett-Teller) method. Before measurement, the sample was vacuum dried at 150 °C for more than 90 minutes, and the mounted sample chamber was maintained at a vacuum of 10² Pa or less.

[0155] 4) Powder Resistivity

[0156] Measurements were performed in Density-Volume Resistivity mode using the Nittoseiko Analytech MCP-PD51 instrument (maximum load 20 kN, probe volume 20 × 50 mm, 4-point probe). 0.5 to 5 g of CNT powder was weighed and filled into the measurement cell between the electrodes. Then, a total of five load levels of 4, 8, 12, 16, and 20 kN were applied using a hydraulic pump, and the electrical resistance at each level was measured. Subsequently, the powder resistance value at 1 g / cc was calculated through interpolation.

[0157] 5) Purity

[0158] After the reaction was finished, the CNT powder was heated to 750°C for 2 hours and maintained for 4 hours to burn, and the purity was calculated based on the weight change.

[0159] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0160] The measured physical properties are shown in Table 3 below.

[0161]

[0162] Classification Bundle Diameter Bulk Density (kg / m³) 3 ) Specific surface area (m² 2 / g) Powder Resistance (mΩ·cm) Purity (Weight%) A (μm) σ3σ / A Example 1 1.69 0.44 0.78 117 28 710.99 5.3 Example 2 1.74 0.4 0.69 129 28 211.19 5.1 Example 3 2.14 0.49 0.69 117 28 711.29 6.8 Example 4 1.7 0.37 0.65 124 28 610.49 6.4 Example 5 1.84 0.36 0.59 108 304 10.69 6.4 Example 6 1.55 0.39 0.75 11025 7109 6.1 Example 7 1.56 0.43 0.83 101 304 11.79 5.2 Example 81.520.390.771183859.897.1 Example 91.600.410.77962389.896.7 Example 101.670.360.70872861196.7 Comparative Example 12.140.520.7310326215.396.4 Comparative Example 21.870.450.7211429912.496.9 Comparative Example 32.071.081.567121410.197.7 Comparative Example 40.650.472.187869010.698.2

[0163] As can be seen from Table 3 above, the average diameter (A) of the bundled carbon nanotubes according to Examples 1 to 10 of the present invention was uniformly controlled to be 2.5 μm or less, and the standard deviation (σ) was also narrowly distributed to be 0.6 or less. In particular, since 3σ / A, which is the ratio of the average bundle diameter (A) to the standard deviation of the diameter (σ), satisfies the range of 0.5 to 0.9, it was confirmed that the carbon nanotubes of the present invention are high-quality bundled carbon nanotubes exhibiting a uniform diameter distribution. This uniform bundle diameter distribution plays a decisive role in ensuring dispersibility and uniformity of the conductive material within the electrode, and can have the effect of significantly improving stability and reproducibility in the electrode slurry manufacturing process. Furthermore, the carbon nanotubes according to Examples 1 to 10 have a density of 80 kg / m² 3 While having a high bulk density of over 230 m 2 It maintains an excellent specific surface area of ​​more than 1 / g, thereby simultaneously securing high charge density and surface activity. This means that it can significantly contribute to improving the energy density of the electrode by maximizing the active surface area required for electrochemical reactions and increasing spatial efficiency within the electrode. Furthermore, excellent electrical conductivity was secured, with a low powder resistance of 12 mΩ·cm or less. This suggests that by forming a smooth electron transport path within the electrode, it can have a direct positive impact on improving the battery's output characteristics and lifespan. In terms of purity, it achieved a high carbon purity of over 93%, minimizing electrical and chemical performance degradation caused by impurities.

[0164] On the other hand, the carbon nanotubes of Comparative Examples 1 and 2 were found to have disadvantages in terms of conductivity, as their powder resistance was significantly higher than that of the embodiments of the present invention, with powder resistances of 15.3 mΩ·cm and 12.4 mΩ·cm, respectively. Comparative Examples 3 and 4 were found to have problems such as reduced dispersibility, with 3σ / A, an indicator of the uniformity of bundle diameter distribution, exceeding 1.0, and low bulk density, which resulted in reduced charging efficiency and electrical connectivity within the electrode.

[0165] Therefore, it has been clearly demonstrated that the carbon nanotube according to the present invention is an excellent conductive material capable of improving electrochemical performance and increasing process efficiency by simultaneously achieving high bulk density, low powder resistance, excellent specific surface area, and high purity.

[0166]

[0167] 2. Characterization of Carbon Nanotube Dispersion

[0168] 1) Maximum dispersion concentration

[0169] A mixture of carbon nanotubes and N-methylpyrrolidone (NMP, 99.5% purity) was pre-dispersed at 5,000 rpm for 10 minutes using an IKA T50 digital homogenizer, and then a dispersion was prepared by passing the pre-dispersed solution three times at a pressure of 1,500 bar using a Picomax MN400BF-EP high-pressure homogenizer. Subsequently, the maximum dispersion concentration of the dispersion was calculated using a Brookfield DV2T viscometer at 25°C with spindle No. 63 within the viscosity measurement range (maximum 10,000 cP).

[0170] 2) Viscosity

[0171] The viscosity of the carbon nanotube dispersion prepared at the maximum dispersion concentration was measured using a Brookfield DV2T viscometer. Under temperature conditions of 25°C, using Spindle No. 63, the average viscosity value was recorded after stabilization for 1 minute at a shear rate of 12 rpm. Viscosity measurements were repeated three times, and the average value was calculated (in cP and converted Pa·s units).

[0172] Classification Maximum Dispersion Concentration (Weight%) Viscosity Measurement Amount Added Viscosity (cP / Pa·s) Example 6 3.5~3.7 3.5 8800 cP / 8800 Pa·s

[0173] As can be seen from Table 4 above, it was confirmed that the carbon nanotubes according to Example 6 are stably dispersed while maintaining a viscosity of approximately 8,800 cP (8,800 Pa·s) even at a high concentration of about 3.5 wt%. This means that the increase in viscosity is suppressed even under high concentration conditions, thereby ensuring excellent fluidity and dispersion stability simultaneously. Generally, as the concentration of carbon nanotubes increases, problems arise where the processability of the slurry is significantly degraded due to inter-particle aggregation and a rapid increase in viscosity. However, the carbon nanotubes of the present invention effectively overcome these problems through an optimal balance design between bulk density, specific surface area, powder resistance, and bundle diameter distribution. In particular, high bulk density and a uniform bundle diameter distribution suppress aggregation to improve dispersion stability, while low powder resistance ensures electrical connectivity, which can contribute to improving the electrochemical performance of the dispersion.

[0174] Consequently, the carbon nanotube dispersion of the present invention can provide excellent workability in slurry manufacturing and electrode processes by minimizing the decrease in processability caused by increased viscosity even under high concentration conditions. This enables the simultaneous securing of process efficiency and quality stability during the manufacturing of secondary batteries and other electronic devices, and is expected to significantly enhance practical advantages by maintaining a stable dispersion state even during storage and transportation.

[0175] Therefore, it has been clearly proven that the carbon nanotubes of the present invention are an innovative material that dramatically increases the commercial potential of dispersions for electrode conductive materials due to their excellent physicochemical properties optimized for the preparation of high-concentration dispersions.

Claims

1. Bundle-type carbon nanotube satisfying (1) to (3) below. (1) Bulk density of 80 to 160 kg / m³ 3 will be; (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below: [Equation 1] 0.5 ≤ 3σ / A ≤ 0.9 2. In Paragraph 1, Bundle-type carbon nanotubes having an average diameter of 1 to 2.5 μm.

3. In Paragraph 1, Bundled carbon nanotubes, wherein the above standard deviation (σ) is 0.1 to 0.

6.

4. In Paragraph 1, The specific surface area of ​​the above carbon nanotube is 230 to 500 m² 2 Bundle carbon nanotubes in g.

5. (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support; (S2) A step of filling the reactor with the above catalyst; (S3) A step of heating the reactor; and (S4) A step of injecting carbon source gas into the reactor; A method for manufacturing bundled carbon nanotubes comprising and satisfying the following (1) to (3). (1) Bulk density of 80 to 160 kg / m³ 3 will be; (2) The resistance of the powder shall be 6 to 12 mΩ·cm; and (3) The average diameter (A) and standard deviation (σ) of the carbon nanotube bundles satisfy the relationship in Equation 1 below: [Equation 1] 0.5 ≤ 3σ / A ≤ 0.9 6. In Paragraph 5, A method for manufacturing bundled carbon nanotubes, wherein the cobalt content in the catalyst prepared in step (S1) is 10 to 30 weight% based on the total weight of the catalyst.

7. In Paragraph 5, A method for manufacturing bundled carbon nanotubes, wherein the molar ratio of vanadium to cobalt (V / Co) in the catalyst prepared in step (S1) above is 0.01 to 0.

6.

8. In Paragraph 5, A method for manufacturing bundled carbon nanotubes, wherein the molar ratio (CA / V) of citric acid to vanadium in the catalyst prepared in step (S1) is 0.1 to 3.

0.

9. In Paragraph 5, A method for manufacturing carbon nanotubes, wherein the catalyst support comprises one or more metal oxides or metal hydroxides selected from the group consisting of hydrotalcite, alumina (Al2O3), magnesium peroxide (MgO2), magnesium oxide (MgO), and boehmite.

10. A carbon nanotube dispersion comprising bundled carbon nanotubes according to any one of claims 1 to 4.

11. An electrode structure manufactured using a carbon nanotube dispersion according to paragraph 10.

12. An electrode structure comprising bundled carbon nanotubes according to any one of claims 1 to 4.

13. A secondary battery comprising an electrode structure manufactured using a carbon nanotube dispersion according to paragraph 10.

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