Bundled carbon nanotubes and manufacturing method therefor

Abstract

The present invention relates to novel bundled carbon nanotubes having excellent electrical conductivity and superior storage and transport efficiency, a method for manufacturing the bundled carbon nanotubes, a dispersion of bundled carbon nanotubes, an electrode structure comprising bundled carbon nanotubes, and a secondary battery comprising bundled carbon nanotubes.

Description

Bundle-type carbon nanotubes and methods for manufacturing the same

[0001] The present invention relates to a novel bundled carbon nanotube having excellent electrical conductivity and excellent storage and transport efficiency, a method for manufacturing said bundled 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 possess excellent electrical conductivity, high strength, and superior thermal conductivity, offering 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] Key indicators for evaluating the physical properties of carbon nanotubes include bulk density, angle of repose, powder resistance, and bundle size. These indicators have a significant impact on the productivity and performance of carbon nanotubes and are closely interconnected. Bulk density represents mass per unit volume and is directly related to the productivity of carbon nanotubes. High bulk density implies the presence of a larger quantity of carbon nanotubes within a given volume, serving as an important indicator in mass production. However, achieving high bulk density requires carbon nanotubes to exist in a dense form; during this process, the nanotubes may become entangled or aggregated, reducing internal voids and strengthening interactions. The angle of repose refers to the maximum angle at which particles remain stable when stacked on an inclined plane, and this is related to the bulk density and bundle size of the carbon nanotubes. Generally, particles with high bulk density tend to be stacked more densely, resulting in a lower angle of repose, whereas particles with low bulk density have larger interparticle spaces, which can lead to an increased angle of repose. In particular, the more uniform the distribution of bundle sizes, the more stably particles can stack, which is advantageous for lowering the angle of repose.

[0005] Meanwhile, powder resistance, an indicator of electrical conductivity, is closely related to the contact state between carbon nanotubes. Low powder resistance is an essential characteristic for conductive applications; generally, it is lower when inter-particle contact resistance is low and the structure is denser. However, manufacturing in a way that reduces aggregation to improve bundle uniformity can decrease inter-particle contact and increase powder resistance; this relationship also demonstrates the need for balancing between material properties.

[0006]

[0007] To improve the dispersibility of carbon nanotubes, it is important to form a uniform structure by maintaining a narrow distribution of bundle diameters. Bundles with evenly distributed diameters exhibit smooth dispersion and high processing stability; however, the processes required to achieve this are complex and can negatively affect other physical properties, such as bulk density and powder resistance.

[0008] Therefore, simultaneously satisfying mutually contradictory properties such as high bulk density, low angle of repose, low powder resistance, and small, uniform bundle diameters is a technically very challenging task. These properties are closely interrelated, resulting in a trade-off relationship where attempts to improve one characteristic negatively impact others. For example, making nanotubes denser to increase bulk density may widen the bundle diameter distribution and reduce dispersibility, while conversely, narrowing the diameter distribution to improve uniformity may lead to lower bulk density or increased powder resistance.

[0009]

[0010] Current technology faces limitations in manufacturing carbon nanotubes that simultaneously achieve high bulk density, low angle of repose, low powder resistance, and a uniform diameter distribution while maintaining a balance between such opposing characteristics, and a new technological approach is required to address this.

[0011]

[0012] Prior art literature

[0013] [Patent Document 1] Republic of Korea Published Patent No. 10-2017-0111973

[0014] [Patent Document 2] Republic of Korea Published Patent No. 10-2014-0032349

[0015] The present invention aims to overcome the mutually interfering trade-off relationship between bulk density, angle of repose, and bundle size to provide a carbon nanotube bundle having a uniform average diameter distribution while maintaining high bulk density and a low angle of repose. It also aims to provide a novel bundle-type carbon nanotube, a method for manufacturing said bundle-type carbon nanotube, a carbon nanotube dispersion, an electrode structure including carbon nanotubes, and a secondary battery including carbon nanotubes.

[0016] One aspect of the present invention is

[0017] A bundled carbon nanotube satisfying (1) to (4) below is provided:

[0018] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0019] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0020] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0021] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles are 0.15 ≤ σ / A ≤ 0.30.

[0022] The bulk density of the above carbon nanotubes is 100 to 160 kg / m³ 3 It could be

[0023] The angle of repose of the above carbon nanotube may be 30 to 38°.

[0024] The standard deviation (σ) of the average diameter of the carbon nanotube bundles may be 0.1 to 0.6 μm.

[0025] The average diameter (A) of the carbon nanotube bundles above may be 1.0 to 2.5 μm.

[0026]

[0027] Another aspect of the present invention is

[0028] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0029] (S2) A step of filling the reactor with the above catalyst;

[0030] (S3) A step of heating the reactor; and

[0031] (S4) A step of injecting carbon source gas into the reactor;

[0032] A method for manufacturing bundled carbon nanotubes is provided that includes and satisfies the following (1) to (4).

[0033] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0034] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0035] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0036] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles are 0.15 ≤ σ / A ≤ 0.30.

[0037] The content of cobalt (Co, Cobalt) in the catalyst prepared in step (S1) above may be 13 to 30 weight% based on the total weight of the catalyst.

[0038] The molar ratio of vanadium to cobalt in the catalyst prepared in step (S1) above (V / Co, Vanadium to Cobalt molar ratio) may be 0.05 to 0.6.

[0039] 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 5.0.

[0040] In the above step (S1), 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.

[0041]

[0042] Another aspect of the present invention is

[0043] A carbon nanotube dispersion comprising bundled carbon nanotubes according to one aspect of the present invention is provided.

[0044]

[0045] Another aspect of the present invention is

[0046] An electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0047]

[0048] Another aspect of the present invention is

[0049] An electrode structure comprising bundled carbon nanotubes according to one aspect of the present invention is provided.

[0050]

[0051] Another aspect of the present invention is

[0052] A secondary battery comprising an electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0053] The bundled carbon nanotubes according to the present invention exhibit high bulk density and a low angle of repose simultaneously, and have a small and uniform average diameter, which can provide excellent storage capacity and ease of handling.

[0054] In particular, due to its high bulk density characteristics, it can be used directly for the preparation of dispersions without separate processing or compression, which is advantageous for process simplification and productivity improvement. Additionally, its low powder resistance is advantageous in terms of electrical conductivity, and its small bundle structure with a uniform average diameter responds effectively to external shear forces, facilitating aggregation disintegration during the dispersion process and contributing to securing a uniform dispersion state.

[0055] Accordingly, the bundled carbon nanotubes according to the present invention can be utilized as high-performance carbon materials capable of simultaneously achieving process simplification and performance improvement in various application fields such as electrode materials, conductive materials, and composite materials, and are particularly expected to contribute to improving the productivity and efficiency of electrochemical device manufacturing processes.

[0056] The present invention will be described in more detail below.

[0057] 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.

[0058] 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 in wholly or partially in a bundle form or in a mixed group form. 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, or two or more of them.

[0059] Unless otherwise stated, the term “bundle type” as used herein may refer 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 the axes along the length direction of the units in substantially the same orientation, or are twisted or entangled after being arranged.

[0060] 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 -5It can be based on SEM images performed at (Pa or less). Therefore, the average bundle diameter (A) and the standard deviation of the bundle diameter (σ) of the carbon nanotube bundle according to the present invention are important indicators representing the structural uniformity of the bundle.

[0061] 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.

[0062]

[0063] 1. Bundle-type carbon nanotubes

[0064] One aspect of the present invention provides a bundled carbon nanotube satisfying (1) to (4) below.

[0065] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0066] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0067] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0068] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.30.

[0069] The bulk density of the above carbon nanotubes is 80 to 160 kg / m³ 3 It may be. Specifically, the bulk density of the above carbon nanotube is 80 kg / m³ 3 Above, 85 kg / m² 3 Above, 90 kg / m² 3 Above, 95 kg / m² 3 Above, 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 , 145 kg / m 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 / m 3 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 3If the bulk density is lower, the total volume of the carbon nanotubes increases, which limits the amount of carbon nanotubes that can be manufactured within a given reactor volume, potentially leading to reduced productivity. Furthermore, a lower bulk density results in reduced flowability and transportability of the powder, and easy scattering of the powder can occur, which may impair handling and processability in processes utilizing carbon nanotubes, such as electrode manufacturing. If additional processes, such as compression, are performed to suppress this scattering, there is a problem of increased manufacturing costs. On the other hand, the carbon nanotubes according to the present invention exhibit a high bulk density, thereby increasing the absolute amount of carbon nanotubes that can be processed within the same volume and improving overall productivity of the manufacturing process. Additionally, since they maintain excellent flowability and handling properties even in the powder state, operational stability is enhanced in processes such as slurry preparation and transport, and quality stability in the electrode manufacturing process can also be improved. Meanwhile, 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 nanotube can be calculated by filling a quantitative cup with carbon nanotube powder by free fall and then dividing the mass of the filled powder by the volume of the cup.

[0070] The angle of repose of the carbon nanotube may be 20° to 40°. Specifically, the angle of repose of the carbon nanotube may be 20° or more, 21° or more, 22° or more, 23° or more, 24° or more, 25° or more, 26° or more, 27° or more, 28° or more, 29° or more, 30° or more, and 40° or less, 39.5° or less, 39° or less, 38.5° or less, 38° or less, 37.5° or less, 37° or less, 36.5° or less, 36° or less, 35.5° or less, or 35° or less. For example, the angle of repose of the carbon nanotube may be 20° to 40°, 21° to 39.5°, 22° to 39°, 23° to 38.5°, 24° to 38°, 25° to 38°, 26° to 38°, 27° to 38°, 28° to 38°, 29° to 38°, 30° to 38°, 30° to 37.5°, 30° to 37°, 30° to 36.5°, 30° to 36°, 30° to 35.5°, or 30° to 35°, preferably 30° to 38°, more preferably 30° to 35°. If the angle of repose of the carbon nanotube is less than 20°, it is difficult to handle, and there is a risk of loss of the carbon nanotube. If the angle of repose of the carbon nanotube exceeds 40°, the carbon nanotube may clump together or form aggregates, which may reduce dispersibility. The angle of repose of the carbon nanotube can be measured by methods commonly used in this field of technology.

[0071] The average diameter (A) of the carbon nanotube bundle may be 1.0 to 2.5 μm. Specifically, the average diameter of the carbon nanotube bundle may be 1.0 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, 2.2 μm or less, or 2.15 μm or less. For example, the average diameter of the carbon nanotube bundle may be 1.0 to 2.5 μm, 1.1 to 2.4 μm, 1.2 to 2.3 μm, 1.3 to 2.3 μm, 1.4 to 2.2 μm, or 1.5 to 2.15 μm. The standard deviation of the diameter may be 0.1 to 0.6 μm. Specifically, the standard deviation of the diameter may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more, and 0.6 μm or less, or 0.5 μm or less. For example, the standard deviation of the diameter may be 0.1 to 0.6 μm, 0.2 to 0.6 μm, or 0.3 to 0.5 μm. At this time, σ / A is an indicator representing the uniformity of the diameter distribution of the carbon nanotube bundle, and may be 0.05 to 0.40. Specifically, σ / A may be 0.05 or more, 0.1 or more, 0.15 or more, or 0.2 or more, and 0.40 or less, 0.35 or less, 0.30 or less, or 0.27 or less. For example, the above σ / A may be 0.05 to 0.40, 0.1 to 0.35, 0.15 to 0.30, or 0.2 to 0.27. The above σ / A may preferably be 0.15 to 0.30, and more preferably 0.2 to 0.27. When the above σ / A is within the above range, the diameter distribution of the bundle is maintained uniformly, which can contribute to improved dispersibility and filling stability, and this may be advantageous for ensuring the quality of the dispersion or consistency of the processing process.

[0072] 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, 450 m 2 / g or less, 400 m 2 / g or less, 350 m 2 / g or less, or 310 m 2 It 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 450 m 2 / g, 240 m 2 / g to 400 m 2 / g, 245 m 2 / g to 350 m 2 / g, or 250 m 2 / g to 310 m 2 It can 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 it 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 Micromeritics Tristar II.

[0073] 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, 11.7 mΩ·cm or less, 11.6 mΩ·cm or less, 11.5 mΩ·cm or less, 11.4 mΩ·cm or less, 11.3 mΩ·cm or less, or 11.2 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 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 11.8 mΩ·cm, 7.5 mΩ·cm to 11.7 mΩ·cm, 8 mΩ·cm to 11.6 mΩ·cm, 8.5 mΩ·cm to 11.5 mΩ·cm, 9 mΩ·cm to 11.4 mΩ·cm, 9.5 mΩ·cm to 11.3 mΩ·cm, or 9.8 mΩ·cm to 11.2 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.

[0074] 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:

[0075] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0076] Carbon nanotubes according to one aspect of the present invention exhibit high bulk density and a low angle of repose, 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 have a small average diameter and a small standard deviation of the diameter distribution, and thus possess a structurally uniform bundle shape, thereby ensuring excellent flowability and dispersibility. These uniform distribution characteristics not only dramatically improve the efficiency of the dispersion process but also contribute 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.

[0077] According to one aspect of the present invention, the carbon nanotube, that is, the carbon nanotube satisfying the conditions of (1) to (4), can be obtained by controlling the manufacturing raw materials, catalyst, manufacturing conditions, etc. This will be explained in detail below.

[0078]

[0079] 2. Method for manufacturing bundled carbon nanotubes

[0080] Another aspect of the present invention is

[0081] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0082] (S2) A step of filling the reactor with the above catalyst;

[0083] (S3) A step of heating the reactor; and

[0084] (S4) A step of injecting carbon source gas into the reactor;

[0085] A method for manufacturing bundled carbon nanotubes is provided, comprising and satisfying the following (1) to (4):

[0086] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0087] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0088] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0089] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.30.

[0090] 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.

[0091] 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.

[0092] The content of cobalt in the catalyst prepared in step (S1) above may be 13 to 30 weight% based on the total weight of the catalyst. Specifically, the content of cobalt may be 13 weight% or more, 14 weight% or more, or 15 weight% or more, and 30 weight% or less, 29 weight% or less, 28 weight% or less, 27 weight% or less, 26 weight% or less, 25 weight% or less, 24 weight% or less, or 23 weight% or less. For example, the content of cobalt may be 13 to 30 weight%, 13 to 29 weight%, 13 to 28 weight%, 13 to 27 weight%, 14 to 26 weight%, 14 to 25 weight%, 15 to 24 weight%, or 15 to 23 weight%. Carbon nanotubes obtained from a catalyst in which the cobalt content falls outside the above range may exhibit increased powder resistance, and in some cases, an increase in specific surface area may lead to a decrease in electrical conductivity. Additionally, the purity of the carbon nanotubes may be lowered, which may result in a degradation of the performance of the final product.

[0093] The molar ratio of vanadium to cobalt (V / Co) in the catalyst prepared in step (S1) above may be 0.05 to 0.6. Specifically, the molar ratio of vanadium to cobalt may be 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.1 or more, and may be 0.6 or less, 0.5 or less, or 0.4 or less. For example, the molar ratio of vanadium to cobalt may be 0.05 to 0.6, preferably 0.08 to 0.5, and 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 the bulk density may increase, which may be advantageous for productivity.

[0094] The molar ratio (CA / V) of citric acid to vanadium in the catalyst prepared in step (S1) above may be 0.1 to 5.0. 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 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less. For example, the molar ratio of citric acid to vanadium may be 0.1 to 5.0, 0.1 to 4.0, 0.2 to 4.0, 0.2 to 3.0, preferably 0.3 to 3.0, more preferably 0.3 to 2.0. When the molar ratio of citric acid to vanadium in the supported catalyst (CA / V) is within the above range, the resistance of the carbon nanotubes obtained from the catalyst may be reduced, and accordingly, it may be advantageous in terms of electrical conductivity.

[0095] In step (S1) above, a porous metal oxide may be used as the catalyst support. For example, the porous metal oxide 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.

[0096] 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 hour to 5 hours, and then calcined at 300°C to 750°C for 30 minutes to 3 hours to form a catalyst.

[0097] In the above (S2) step, the reactor may include a chemical vapor deposition reactor, a fixed-bed reactor, or a fluidized-bed reactor.

[0098] 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.

[0099] In the above step (S4), the carbon source gas is a carbon-containing gas capable of decomposing at high temperature 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.

[0100]

[0101] 3. Carbon nanotube dispersion

[0102] Another aspect of the present invention is

[0103] A carbon nanotube dispersion comprising a bundled carbon nanotube satisfying (1) to (4) below and a dispersion medium is provided:

[0104] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0105] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0106] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0107] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.30.

[0108] One or more of the dispersion media selected from the group consisting of N-methylpyrrolidone, pyridine, dimethylaminobenzene, and diethylaminobenzene may be used.

[0109] The content of carbon nanotubes in the above dispersion may be 0.05 to 10 weight%. Within this range, sufficient electrical conductivity is secured while the aggregation of carbon nanotubes is suppressed and the viscosity is appropriately maintained, thereby providing an advantageous effect of realizing excellent processability of the dispersion.

[0110]

[0111] Another aspect of the present invention is

[0112] 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.

[0113]

[0114] Another aspect of the present invention is

[0115] 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 (4) 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.

[0116] (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be,

[0117] (2) The angle of repose of the carbon nanotube is 20 to 40°,

[0118] (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and

[0119] (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.30.

[0120] In addition, the bundled 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.

[0121]

[0122] Another aspect of the present invention is

[0123] The present invention provides a secondary battery comprising an electrode structure manufactured using the above-described bundled 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).

[0124] 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.

[0125]

[0126] <Catalyst Preparation Example>

[0127] 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 temperature 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 as shown in Table 1 below.

[0128] Catalyst Co Content (WJ%) V / Co (Molar Ratio) CA / V (Molar Ratio) Calcination Temperature (°C) Preparation Example 1 160.11.0500 Preparation Example 2 160.71.0500 Preparation Example 3 160.10.3400 Preparation Example 4 160.70.3400 Preparation Example 5 160.41.0400 Preparation Example 6 220.12.0500 Preparation Example 7 220.251.0500 Preparation Example 8 220.10.4680 Preparation Example 9 100.31.5300 Preparation Example 106.500.5300 Preparation Example 116.50.30300 Preparation Example 126.50.30.1300

[0129] <Examples and Comparative Examples>

[0130] Carbon nanotubes were synthesized 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 synthesize carbon nanotubes. The catalysts used in the examples and comparative examples are shown in Table 2 below.

[0131] Classification Catalyst Used Catalyst Characteristics Co Content (Weight %) V / Co (Molar Ratio) CA / V (Molar Ratio) Calcination Temperature (°C) Example 1 Manufacturing Example 1 160.11.0500 Example 2 Manufacturing Example 3 160.10.3400 Example 3 Manufacturing Example 5 160.41.0400 Example 4 Manufacturing Example 6 220.12.0500 Example 5 Manufacturing Example 7 220.251.0500 Example 6 Manufacturing Example 8 220.10.4680 Comparative Example 1 Manufacturing Example 2 160.71.0500 Comparative Example 2 Manufacturing Example 4 160.70.3400 Comparative Example 3 Manufacturing Example 9 100.31.5300 Comparative Example 4 Manufacturing Example 106.500.5300 Comparative Example 5 Manufacturing Example 116.50.30300 Comparative Example 6 Manufacturing Example 126.50.30.1300

[0132] Comparative Example 7 used JO's carbon nanotube 6A product.

[0133]

[0134] <Experimental Example>

[0135] The bulk density, specific surface area, powder resistance, angle of repose, purity, and bundle diameter of carbon nanotubes prepared according to the above examples and comparative examples were measured by the following method. Unless otherwise noted, all measurements were performed under conditions of room temperature (25 ± 5℃), atmospheric pressure (about 1 atm), and relative humidity of 40 to 60%.

[0136] 1) Bulk Density

[0137] 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 powder exceeding the top of the cup was then trimmed off, and the total weight of the powder filled without overflowing was measured using an electronic balance (Mettler Toledo, Balance XPR204V, precision: ± 0.0001 g). This was then 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.

[0138] 2) Specific Surface Area

[0139] Nitrogen gas adsorption isotherms were measured at liquid nitrogen temperature (77 K) using Micromeritics' Tristar II instrument, and the specific surface area was calculated according to the BET (Bruanauer-Emmett-Teller) method. Prior to measurement, the samples were vacuum dried at 150°C for at least 90 minutes, and the installed sample chamber was 10 - It was maintained at a vacuum of less than 2 Pa.

[0140] 3) Powder Resistivity

[0141] Measurements were performed in Density-Volume Resistivity mode using the Nittoseiko Analytech MCP-PD51 instrument (maximum load 20kN, probe volume 20×50mm, 4 Point Probe). 0.5 to 5g of CNT powder was weighed and filled into the measurement cell between the electrodes. Then, a total of 5 loads of 4, 8, 12, 16, and 20kN were applied using a hydraulic pump, and the electrical resistance at each stage was measured. Subsequently, the powder resistance value at 1g / cc was calculated through interpolation.

[0142] 4) Angle of Repose

[0143] A manual stainless steel hopper (K-One Co., Ltd., angle of repose measuring instrument BT-200) with a top section of 50 mm in diameter and an outlet of 2.5 mm in diameter was used. CNT powder was discharged by natural fall onto a SUS plate of 80 mm in diameter from a height of 76 mm, and the average value was calculated after measuring the formed conical inclined surface three times using a protractor.

[0144] 5) Purity

[0145] 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.

[0146] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0147] 6) Bundle Diameter (Diameter of CNT bundles)

[0148] 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 surface of the sample was observed at a magnification of 2,000x. SEM imaging was performed under vacuum conditions (approx. 10 -5The 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 and standard deviation were calculated, and the statistical characteristics of the bundle diameter distribution were evaluated.

[0149] The measured physical properties are shown in Table 3 below.

[0150] Classification Bulk Density (kg / m³) 3 ) Specific surface area (m² 2 / g) Powder Resistance (mΩ·cm) Angle of Repose (°) Purity (wt%) Bundle Diameter A (μm) σ (μm) σ / A Example 1 117287 10.9 34.3 95.3 1.6 90.4 40.26 Example 2 1292821 1.1 35.0 95.1 1.7 40.4 0.23 Example 3 117287 11.2 34.0 96.8 2.1 40.4 90.23 Example 4 124286 10.4 34.0 96.4 1.7 0.3 70.22 Example 5 108304 10.6 34.7 96.4 1.8 40.3 60.20 Example 61102571034.096.11.550.390.25 Comparative Example 110326215.338.096.42.140.520.24 Comparative Example 211429912.435.096.91.870.450.24 Comparative Example 3116-12.1-----Comparative Example 415938218.1-79.5---Comparative Example 514242919.2-89.1---Comparative Example 612054916.7-86.3---Comparative Example 77869010.649.398.20.650.470.72

[0151] (In the table, '-' indicates that the corresponding item is a value not measured in this experiment.)

[0152] As can be seen from Table 3 above, in the case of carbon nanotubes according to Comparative Examples 1 and 2, a high bulk density of 80 kg / m³ or more and 230 m 2Although a high specific surface area of ​​1 / g or higher was satisfied, a high powder resistance exceeding 12 mΩ·cm was exhibited. In the case of Comparative Examples 3 to 6, it was confirmed that the powder resistance exceeded 12 mΩ·cm or the purity was 90 wt% or less. Additionally, Comparative Example 7, which is commercially available, has a resistance of 80 kg / m² 3 It exhibited a low bulk density of less than and a very high angle of repose of more than 47°, and it was confirmed that σ / A increased significantly to more than 0.7.

[0153] Meanwhile, in the case of the carbon nanotubes according to Examples 1 to 6 of the present invention, all have a high purity of 93% or more and a density of 80 kg / m² 3 Bulk density of the above, 230 m 2 It exhibited a specific surface area of ​​1 / g or more, a powder resistance of 12 mΩ·cm or less, and a low angle of repose of 40° or less. In addition, it was confirmed that σ / A was in the range of 0.15 to 0.30, as all had an average bundle diameter of 2.5 μm or less and a standard deviation of 0.6 or less.

[0154] That is, the bundled carbon nanotubes according to the present invention can have excellent electrical conductivity, flowability, storage and transport characteristics by simultaneously securing a high bulk density of 80 kg / m³ or more and a high specific surface area of ​​230 m² / g or more, while exhibiting a low powder resistance of 12 mΩ·cm or less and a low angle of repose of 40° or less. In addition, based on structural characteristics in which the average diameter is 2.5 μm or less, the standard deviation of the diameter is 0.6 μm or less, and σ / A is in the range of 0.15 or more and 0.30 or less, the uniformity of the bundle diameter distribution is ensured, so that it can effectively respond to external shear force during the dispersion process and improve dispersibility.

[0155] Due to this combination of physical and electrical properties, the bundled carbon nanotubes of the present invention can provide a stable and uniform dispersion state when preparing a dispersion, thereby contributing to the improvement of electrode slurry quality and the performance of electrochemical devices. Furthermore, these properties provide process simplification and cost reduction effects, and are expected to be usefully utilized as high-performance carbon materials in various industrial fields such as secondary batteries, supercapacitors, antistatic materials, conductive materials, and fillers for composite materials.

Claims

1. Bundle-type carbon nanotube satisfying (1) to (4) below. (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be, (2) The angle of repose of the carbon nanotube is 20 to 40°, (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.

30.

2. In Paragraph 1, The bulk density of the above carbon nanotubes is 100 to 160 kg / m³ 3 Phosphorus, bundled carbon nanotubes.

3. In Paragraph 1, A bundled carbon nanotube having an angle of repose of 30 to 38°.

4. In Paragraph 1, A bundled carbon nanotube having a standard deviation (σ) of the average diameter of the carbon nanotube bundles of the above-mentioned carbon nanotubes of 0.1 to 0.6 μm.

5. In Paragraph 1, A bundled carbon nanotube, wherein the average diameter (A) of the carbon nanotube bundle is 1.0 to 2.5 μm.

6. (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 that includes and satisfies the following (1) to (4). (1) The bulk density of carbon nanotubes is 80 to 160 kg / m³ 3 will be, (2) The angle of repose of the carbon nanotube is 20 to 40°, (3) The powder resistance of the carbon nanotubes shall be 6 to 12 mΩ·cm, and (4) The average bundle diameter (A) and standard deviation of bundle diameter (σ) of the carbon nanotube bundles shall be 0.15 ≤ σ / A ≤ 0.

30.

7. In Paragraph 6, A method for manufacturing bundled carbon nanotubes, wherein the cobalt content in the catalyst prepared in step (S1) is 13 to 30 weight% based on the total weight of the catalyst.

8. In Paragraph 6, 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 0.05 to 0.

6.

9. In Paragraph 6, 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 5.

0.

10. In Paragraph 6, A method for manufacturing bundled 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.

11. A carbon nanotube dispersion comprising bundled carbon nanotubes according to any one of claims 1 to 5.

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

13. An electrode structure comprising bundled carbon nanotubes according to any one of claims 1 to 5.

14. A secondary battery comprising an electrode structure manufactured using a carbon nanotube dispersion according to paragraph 11.