Carbon nanotubes and method for preparing same

Abstract

The present invention relates to novel carbon nanotubes having excellent dispersibility, a method for preparing the carbon nanotubes, a carbon nanotube dispersion, an electrode structure comprising the carbon nanotubes, and a secondary battery comprising the carbon nanotubes.

Description

Carbon nanotubes and methods for manufacturing the same

[0001] The present invention relates to a novel carbon nanotube having excellent dispersibility, a method for manufacturing said carbon nanotube, a carbon nanotube dispersion, an electrode structure comprising a carbon nanotube, and a secondary battery comprising a carbon nanotube.

[0002] Carbon nanomaterials are classified into fullerenes, carbon nanotubes (CNTs), graphene, and graphite nanoplates depending on their shape. 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. Recently, carbon nanotubes have been widely used as conductive materials in secondary batteries; however, there is a problem in that they are difficult to disperse uniformly within electrode slurry compositions and tend to aggregate easily. This aggregation 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 capable of uniformly dispersing carbon nanotubes is essential. Currently, attempts are being made to prevent carbon nanotube aggregation and improve dispersibility by using dispersants such as polyvinylpyrrolidone (PVP) or hydrogenated nitrile butadiene rubber (HNBR). However, when using these dispersants, a problem arises in which the viscosity of the dispersion increases rapidly as the carbon nanotube content increases.

[0003]

[0004] Maintaining low viscosity while increasing the carbon nanotube content in carbon nanotube dispersions is a technically challenging task. Carbon nanotubes are prone to aggregation due to strong van der Waals forces, and as the concentration increases, aggregation intensifies and viscosity rises. This leads to reduced fluidity of the dispersion, inconvenience in storage and transport, and decreased process efficiency. Furthermore, an increase in viscosity can still occur if the amount of dispersant increases or if dispersion is incomplete. Therefore, there is a need to develop novel carbon nanotubes that can maintain low viscosity while improving dispersibility in carbon nanotube dispersions.

[0005]

[0006] Prior art literature

[0007] [Patent Document 1] Republic of Korea Published Patent No. 10-2015-0027675

[0008] The present invention aims to provide a carbon nanotube having excellent dispersibility, a method for manufacturing said carbon nanotube, a carbon nanotube dispersion, an electrode structure including a carbon nanotube, and a secondary battery including a carbon nanotube.

[0009] One aspect of the present invention is

[0010] A carbon nanotube satisfying (1) to (3) below is provided.

[0011] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0012] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0013] (3) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0014] The powder resistance of the above carbon nanotube may be 10 to 11.5 mΩ·cm.

[0015] The specific surface area of ​​the above carbon nanotube is 230 to 500 m² 2 It can be / g.

[0016] The purity of the above carbon nanotubes may be 93 weight% or more.

[0017]

[0018] Another aspect of the present invention is

[0019] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0020] (S2) A step of filling the reactor with the above catalyst;

[0021] (S3) A step of heating the reactor; and

[0022] (S4) A step of injecting carbon source gas into the reactor;

[0023] A method for manufacturing carbon nanotubes is provided, comprising and satisfying the following (1) to (3):

[0024] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0025] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0026] (3) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0027] The content of cobalt (Co, Cobalt) in the catalyst prepared in step (S1) above may be 14 to 30 weight% based on the total weight of the catalyst.

[0028] 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 0.60.

[0029] 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 2.0.

[0030] 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.

[0031]

[0032] Another aspect of the present invention is

[0033] A carbon nanotube dispersion comprising carbon nanotubes according to one aspect of the present invention is provided.

[0034]

[0035] Another aspect of the present invention is

[0036] An electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0037]

[0038] Another aspect of the present invention is

[0039] An electrode structure comprising carbon nanotubes according to one aspect of the present invention is provided.

[0040]

[0041] Another aspect of the present invention is

[0042] A secondary battery comprising an electrode structure manufactured using the above carbon nanotube dispersion is provided.

[0043] The carbon nanotubes according to the present invention possess innovative characteristics that simultaneously satisfy high bulk density and a high specific surface area while exhibiting low powder resistance. Accordingly, the carbon nanotubes of the present invention can not only achieve significantly superior electrical conductivity compared to conventional carbon nanotubes but also provide high space utilization efficiency and stability during storage and transportation. Furthermore, these characteristics lead to ease of handling, reduced storage costs, and ensured transportation stability in mass logistics processes, thereby maximizing their industrial application value.

[0044] Furthermore, the carbon nanotubes of the present invention exhibit high bulk density, allowing them to be applied directly to the preparation of dispersions without the need for separate post-processing or compression processes. In particular, the carbon nanotubes of the present invention exhibit an excellent effect of stably maintaining low viscosity by suppressing a rapid increase in viscosity even when added to a dispersion in high amounts. Accordingly, the prepared dispersion secures excellent fluidity even under high concentration conditions, and handling, workability, and mass production efficiency can be dramatically improved throughout the entire process. As such, the dispersion containing the carbon nanotubes of the present invention provides a uniform and stable dispersion state during the preparation of electrode slurries along with excellent dispersibility, thereby significantly enhancing the ability to form a conductive network within the electrode; consequently, electrochemical performance such as high energy density, high power characteristics, and long lifespan characteristics can be maximized.

[0045] Therefore, the carbon nanotubes according to the present invention improve conductivity, increase storage and transport efficiency, and enable process simplification and cost reduction. Furthermore, by ensuring viscosity stability of the dispersion, various technical and industrial effects can be simultaneously achieved, such as maximizing mass production efficiency and improving the electrochemical performance of the final product. As a result, the present invention can provide innovative performance in next-generation secondary batteries and various electronic and energy applications.

[0046] Figure 1 is a graph showing the relationship between the content of carbon nanotubes in a dispersion and viscosity according to an experimental example of the present invention.

[0047] The present invention will be described in more detail below.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The unit of viscosity used in this specification is basically centipoise (cP). Viscosity can be measured according to methods generally accepted in the relevant technical field, and the viscosity of the dispersion of the present invention is based on the value measured at 25°C using a rotational viscometer (Brookfield DV2T) equipped with spindle No. 63 under a shear rate of 12 rpm. Meanwhile, 1 centipoise (cP) corresponds to 0.001 Pascal-second (Pa·s), and Pascal-second units may be indicated in this specification and drawings as necessary.

[0053]

[0054] 1. Carbon nanotubes

[0055] One aspect of the present invention is

[0056] A carbon nanotube satisfying (1) to (3) below is provided.

[0057] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0058] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0059] (3) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0060] 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, 81 kg / m² 3 Above, 82 kg / m² 3 Above, 83 kg / m² 3 Above, 84 kg / m² 3 Above, 85 kg / m² 3 Above, 86 kg / m² 3 Above, 87 kg / m² 3 Above, 88 kg / m² 3 Above, 89 kg / m² 3 Above, 90 kg / m² 3 Above, 91 kg / m² 3 Above, 92 kg / m² 3 Above, 93 kg / m² 3 Above, 94 kg / m² 3 95 kg / m² or more 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 Below, 130 kg / m² 3 Below, 125 kg / m² 3 Less than or equal to 120 kg / m³ 3It 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 , 81 kg / m 3 Up to 160 kg / m² 3 , 82 kg / m 3 Up to 155 kg / m² 3 , 83 kg / m 3 Up to 155 kg / m² 3 , 84 kg / m 3 up to 150 kg / m² 3 , 85 kg / m 3 up to 150 kg / m² 3 , 86 kg / m 3 Up to 145 kg / m² 3 , 87 kg / m 3 Up to 145 kg / m² 3 , 88 kg / m 3 up to 140 kg / m² 3 , 89 kg / m 3 up to 140 kg / m² 3 , 90 kg / m 3 Up to 135 kg / m² 3 , 91 kg / m 3 Up to 135 kg / m² 3 , 92 kg / m 3 Up to 130 kg / m² 3 , 93 kg / m 3 Up to 130 kg / m² 3 , 94 kg / m 3 up to 125 kg / m² 3 , or 95 kg / m² 3 up to 120 kg / m² 3 It may be. The bulk density of the carbon nanotube is 80 kg / m³ 3If 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 in electrode manufacturing processes. 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 electrode manufacturing processes 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).

[0061] 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, or 350 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 350 m 2 It can be / g. The specific surface area of ​​the carbon nanotube is 230 m². 2 If the value is 1 / g or higher, the electrical conductivity may be excellent, making it suitable as a conductive material for secondary batteries, and the specific surface area of ​​the carbon nanotube is 500 m² 2 When the value is less than 1 / g, the carbon nanotubes may have less tendency to clump or form aggregates, so excellent dispersibility may be achieved. The specific surface area of ​​the carbon nanotubes can be measured by methods commonly used in this technical field. 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.

[0062] 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, or 11.5 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, 9.6 mΩ·cm or more, 9.7 mΩ·cm or more, 9.8 mΩ·cm or more, 9.9 mΩ·cm or more, or 10 mΩ·cm or more. For example, the powder resistance of the carbon nanotube is 6 mΩ·cm to 12 mΩ·cm, 6.5 mΩ·cm to 12 mΩ·cm, 7 mΩ·cm to 12 mΩ·cm, 7.5 mΩ·cm to 12 mΩ·cm, 8 mΩ·cm to 12 mΩ·cm, 8.5 mΩ·cm to 12 mΩ·cm, 9 mΩ·cm to 12 mΩ·cm, 9.5 mΩ·cm to 12 mΩ·cm, 9.6 mΩ·cm to 11.9 mΩ·cm, 9.7 mΩ·cm to 11.8 mΩ·cm, 9.8 mΩ·cm to 11.7 mΩ·cm, 9.9 mΩ·cm to 11.6 mΩ·cm, 9.9 mΩ·cm to 11.6 mΩ·cm, or 10 mΩ·cm to It may be 11.5 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 may cause electrical interference or short-circuit problems, and if the powder resistance of the carbon nanotube exceeds 12 mΩ·cm, the 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.

[0063] 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:

[0064] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0065] According to one aspect of the present invention, when carbon nanotubes are added at a weight percent relative to the total weight of the dispersion during the preparation of a dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm may be 800 to 5,000 cP (0.8 to 5.0 Pa·s). This is a significantly lower viscosity range compared to conventional carbon nanotubes, and even when added at the same amount, the carbon nanotubes of the present invention effectively suppress the increase in viscosity. Therefore, the carbon nanotubes of the present invention can maintain excellent fluidity and stability even under high concentration conditions, and it is expected that the process suitability and mass production efficiency of the dispersion will be improved.

[0066] According to one aspect of the present invention, the carbon nanotube, that is, the carbon nanotube satisfying the conditions of (1) to (3), can be obtained by controlling the cobalt (Co) content in the catalyst, the molar ratio of vanadium to cobalt (V / Co), and the molar ratio of citric acid to vanadium (CA / V). This will be explained in detail below.

[0067]

[0068] 2. Method for manufacturing carbon nanotubes

[0069] Another aspect of the present invention is

[0070] (S1) A step of preparing a catalyst by mixing an active ingredient containing cobalt, vanadium, and citric acid with a catalyst support;

[0071] (S2) A step of filling the reactor with the above catalyst;

[0072] (S3) A step of heating the reactor; and

[0073] (S4) A step of injecting carbon source gas into the reactor;

[0074] A method for manufacturing carbon nanotubes is provided, comprising and satisfying the following (1) to (3):

[0075] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0076] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0077] (3) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0078] 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.

[0079] In the above (S1) step, as a vanadium precursor, ammonium vanadate (NH₄VO₃), sodium vanadate (NaVO₃), potassium vanadate (KVO₃), vanadium pentoxide (V₂O), vanadyl sulfate (VOSO₄), vanadyl acetylacetone (VO(acac)₂), vanadium trichloride (VCl₃) or vanadium oxotrifluoride (VOF₃) may be used, but are not limited thereto.

[0080] The cobalt content in the catalyst prepared in step (S1) above may be 14 to 30 weight percent based on the total weight of the catalyst. If the cobalt content falls outside the above range, the powder resistance of carbon nanotubes obtained from the catalyst may increase, and in some cases, the specific surface area may increase, which may reduce the electrical conductivity of the carbon nanotubes. In addition, the purity of the carbon nanotubes may decrease, which may lead to a decrease in the performance of the final product.

[0081] 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, 0.4 or less, 0.3 or less, or 0.2 or less. For example, the molar ratio of vanadium to cobalt may be 0.01 to 0.6, 0.02 to 0.5, 0.03 to 0.4, 0.04 to 0.3, or 0.05 to 0.2. When the molar ratio of vanadium to cobalt is within the above range, the carbon nanotubes obtained from the catalyst may have reduced powder resistance and increased bulk density, which may be advantageous for productivity.

[0082] The molar ratio (CA / V) of citric acid to vanadium in the catalyst prepared in step (S1) above may be 0.1 to 2.0. Specifically, the molar ratio of citric acid to vanadium may be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more, and may be 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, or 1.5 or less. For example, the molar ratio of citric acid to vanadium may be 0.1 to 2.0, 0.2 to 1.9, 0.3 to 1.8, 0.4 to 1.7, 0.4 to 1.6, or 0.5 to 1.5. When the molar ratio of citric acid to vanadium is within the above range, the carbon nanotubes obtained from the catalyst may have reduced powder resistance and thus may be advantageous in terms of electrical conductivity.

[0083] 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.

[0084] 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.

[0085] In the above (S2) step, the reactor may include a chemical vapor deposition reactor, a fixed-bed reactor, or a fluidized-bed reactor.

[0086] 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.

[0087] 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.

[0088]

[0089] 3. Carbon nanotube dispersion

[0090] Another aspect of the present invention is

[0091] A carbon nanotube dispersion comprising a carbon nanotube satisfying (1) to (3) below and a dispersion medium is provided.

[0092] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0093] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0094] (3) When 2 wt% of carbon nanotubes are added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm is 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0095] The viscosity of the carbon nanotube dispersion may be 800 to 5,000 cP (0.8 to 5.0 Pa·s). For example, the viscosity of the carbon nanotube dispersion may be 800 to 5,000 cP (0.8 to 5.0 Pa·s), 800 to 4,900 cP (0.8 to 4.9 Pa·s), 800 to 4,800 cP (0.8 to 4.8 Pa·s), 800 to 4,700 cP (0.8 to 4.7 Pa·s), 800 to 4,600 cP (0.8 to 4.6 Pa·s), or 800 to 4,500 cP (0.8 to 4.5 Pa·s). The viscosity of the carbon nanotube dispersion may be measured by methods commonly used in the art. For example, the viscosity of the above dispersion can be calculated using a rotational viscometer (Brookfield DV2T) at 25 °C, using spindle No. 63 under a shear rate of 12 rpm.

[0096] One or more of the dispersion media selected from the group consisting of N-methylpyrrolidone, pyridine, dimethylaminobenzene, and diethylaminobenzene may be used.

[0097] The content of carbon nanotubes in the above carbon nanotube dispersion may be 0.05 to 10 weight%. When the carbon nanotube content in the dispersion is 0.05 weight% or more, a conductive network within the electrode is effectively formed, which may be advantageous for achieving sufficient and stable electrical conductivity. In addition, when the carbon nanotube content is 10 weight% or less, the aggregation of carbon nanotubes is suppressed, preventing a rapid increase in viscosity; thus, the dispersion can maintain low viscosity while ensuring excellent fluidity under high concentration conditions. As such, the carbon nanotube dispersion of the present invention can simultaneously satisfy the conflicting requirements of ensuring conductivity and viscosity stability, thereby enabling a revolutionary improvement in processability, process suitability, and mass production, which are difficult to achieve with conventional technology.

[0098]

[0099] Another aspect of the present invention is

[0100] 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.

[0101]

[0102] Another aspect of the present invention is

[0103] An electrode structure comprising the above carbon nanotube is provided. The carbon nanotube satisfies 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.

[0104] (1) Bulk density is 80 to 160 kg / m³ 3 will be,

[0105] (2) The resistance of the powder shall be 6 to 12 mΩ·cm, and

[0106] (3) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP (0.8 to 5.0 Pa·s).

[0107] 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.

[0108]

[0109] Another aspect of the present invention is

[0110] 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).

[0111]

[0112] 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.

[0113]

[0114] <Catalyst Preparation Example>

[0115] 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 heating to 680°C under an atmospheric atmosphere and calcining 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 below.

[0116] Co content of catalyst (wg%) V / CoCA / V Preparation Example 1130.10.5 Preparation Example 2140.10.5 Preparation Example 3160.10.5 Preparation Example 4180.10.5 Preparation Example 5200.10.5 Preparation Example 6220.10.5 Preparation Example 7240.10.5 Preparation Example 8260.10.5

[0117] <Examples and Comparative Examples>

[0118] 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 each example and comparative example are shown in Table 2 below.

[0119] Classification Catalyst Used Catalyst Characteristics Co Content (wt%) V / Co (Molar Ratio) CA / V (Molar Ratio) Comparative Example 1 Preparation Example 1 130.10.5 Example 1 Preparation Example 2 140.10.5 Example 2 Preparation Example 3 160.10.5 Example 3 Preparation Example 4 180.10.5 Example 4 Preparation Example 5 200.10.5 Example 5 Preparation Example 6 220.10.5 Example 6 Preparation Example 7 240.10.5 Example 7 Preparation Example 8 260.10.5

[0120] <Experimental Example>

[0121] 1. Confirmation of physical properties of carbon nanotubes

[0122] The 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%.

[0123]

[0124] 1) Bulk Density

[0125] 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.

[0126] 2) Specific Surface Area

[0127] 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.

[0128] 3) Powder Resistivity

[0129] 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 5 loads of 4, 8, 12, 16, and 20 kN were applied using a hydraulic pump, and the electrical resistance at each stage was measured. Subsequently, the powder resistance value at 1 g / cc was calculated through interpolation.

[0130] 4) Purity

[0131] 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 change in weight.

[0132] Purity (%) = {(Weight of carbon nanotubes - Weight of carbon nanotubes after combustion) / Weight of carbon nanotubes} x 100

[0133] The measured physical properties are shown in Table 3 below.

[0134]

[0135] Bulk density (kg / m³) 3 ) Specific surface area (m² 2 / g) Powder Resistance (mΩ·cm) Purity (weight%) Example 1 11531211.595.2 Example 2 10627511.295.8 Example 3 10229810.495.6 Example 4 10227510.396.1 Example 5 10125610.095.8 Example 69828610.095.8 Example 79527910.295.7 Comparative Example 1 11933512.492.4

[0136] As can be seen from Table 3 above, the carbon nanotubes according to Examples 1 to 7 all have a purity of 93% or higher and 80 kg / m² 3 High bulk density of over 230 m 2It was confirmed that the carbon nanotubes possess a low powder resistance of 12 mΩ·cm or less while simultaneously satisfying a high specific surface area of ​​more than 1g. These carbon nanotubes simultaneously realize four properties that are generally difficult to achieve together: high bulk density, high specific surface area, low powder resistance, and high purity. This demonstrates that excellent physical properties can be secured in terms of electrode slurry uniformity, electrical conductivity, and process stability. On the other hand, in the case of Comparative Example 1, the bulk density (119 kg / m³) and specific surface area (335 m² / g) were similar to those of the present invention, but the powder resistance was 12.4 mΩ·cm, exceeding the above range, and the purity was also 92.4%, which was lower than that of the embodiments of the present invention. These results suggest that the carbon nanotubes of Comparative Example 1 not only have limitations in securing conductivity but also have the potential for electrochemical performance degradation due to increased impurity content.

[0137] Therefore, the carbon nanotube according to the present invention can simultaneously achieve multifaceted effects such as improved conductivity, suppression of impurities, process suitability, and maximization of electrode performance, which provides a distinct advantage that is clearly different from conventional technology.

[0138]

[0139] Experimental Example 2. Confirmation of viscosity of carbon nanotube dispersion

[0140] 1 to 3 wt% of carbon nanotubes according to the above examples and comparative examples were mixed into a solution containing N-methylpyrrolidone, hydrogenated nitrile butadiene rubber (HNBR), and BYK180 (an acid group-containing copolymer composed of alkylolammonium salts). The mixed solution was pre-dispersed for 10 minutes at 5,000 rpm using an IKA T50 digital homogenizer, and then the final dispersion was prepared by passing the pre-dispersed solution three times through a Picomax MN400BF-EP high-pressure homogenizer at a pressure of 1,500 bar. The viscosity of the prepared dispersion was measured using a Brookfield DV2T viscometer at 25°C with spindle No. 63 mounted and a shear rate of 12 rpm, and the results (in cP and converted Pa·s units) are shown in Table 4 below.

[0141] 구분NMPHNBRBYK180CNT점도 (cP / Pa·s)실시예 198.6 wt%0.32 wt%0.08 wt%1 wt%280 cP / 0.280 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%4380 cP / 4.380 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%측정 불가실시예 298.6 wt%0.32 wt%0.08 wt%1 wt%120 cP / 0.120 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%2400 cP / 2.400 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%7750 cP / 7.750 Pa·s실시예 398.6 wt%0.32 wt%0.08 wt%1 wt%250 cP / 0.250 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%4100 cP / 4.100 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%측정 불가실시예 498.6 wt%0.32 wt%0.08 wt%1 wt%120 cP / 0.120 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%2550 cP / 2.550 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%8120 cP / 8.120 Pa·s실시예 598.6 wt%0.32 wt%0.08 wt%1 wt%45 cP / 0.045 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%830 cP / 0.830 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%5370 cP / 5.370 Pa·s실시예 698.6 wt%0.32 wt%0.08 wt%1 wt%250 cP / 0.250 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%3850 cP / 3.850 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%측정 불가실시예 798.6 wt%0.32 wt%0.08 wt%1 wt%150 cP / 0.150 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%2680 cP / 2.680 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%9520 cP / 9.520 Pa·sComparative example 198.6 wt%0.32 wt%0.08 wt%1 wt%420 cP / 0.420 Pa·s97.2 wt%0.64 wt%0.16 wt%2 wt%5050 cP / 5.050 Pa·s95.8 wt%0.96 wt%0.24 wt%3 wt%Not measurable.

[0142] As can be seen from Table 4 above, when the carbon nanotubes of Comparative Example 1 were added to the dispersion at 1 wt% and 2 wt%, the respective viscosities were 420 cP (0.42 Pa·s) and 5,050 cP (5.05 Pa·s), respectively, showing very high values. In contrast, the carbon nanotubes according to the embodiment of the present invention exhibited viscosities of 300 cP or less (0.3 Pa·s or less) and 4,500 cP or less (4.5 Pa·s or less) under the same conditions, respectively. It was confirmed that excellent dispersibility can be achieved by maintaining significantly lower viscosity compared to Comparative Example 1. In particular, while Comparative Example 1 showed a high viscosity of about 5,050 cP (5.05 Pa·s) when 2 wt% was added, the carbon nanotubes according to Example 5 of the present invention maintained a viscosity similar to that of Comparative Example 1 at 2 wt% even at a higher content of 3 wt%. This result clearly demonstrates that the carbon nanotubes of the present invention effectively suppress a rapid increase in viscosity even under high concentration conditions, thereby maximizing the process suitability of the dispersion along with excellent dispersion stability.

[0143] These excellent viscosity control capabilities and dispersion stability strongly suggest that the carbon nanotubes of the present invention enable more efficient and stable utilization in dispersion preparation and secondary battery electrode processes compared to existing technologies, and can significantly improve the quality and reliability of the final product through the improvement of electrode slurry uniformity and electrochemical performance.

[0144]

[0145] Therefore, the carbon nanotubes of the present invention provide innovative properties that surpass existing technologies in terms of dispersibility and viscosity control, thereby dramatically expanding the potential for application in next-generation energy storage devices and various electronic materials.

[0146]

[0147] Experimental Example 3. Measurement of Maximum Dispersion Concentration and Viscosity of Carbon Nanotubes

[0148] The maximum dispersion concentration of carbon nanotubes prepared according to the above examples and comparative examples and the viscosity of the dispersion were measured and are shown in Table 5 below.

[0149] 1) Maximum dispersion concentration

[0150] 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).

[0151] 2) Viscosity

[0152] 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).

[0153] Classification Maximum Dispersion Concentration (wt%) Viscosity Addition Amount (wt%) Viscosity (cP / Pa·s) Comparative Example 1 2.0~2.2 2.050 cP / 5.050 Pa·s Example 1 2.1~2.3 2.04380 cP / 4.380 Pa·s Example 2 3.0~3.2 3.07750 cP / 7.750 Pa·s Example 3 2.2~2.4 2.04100 cP / 4.100 Pa·s Example 4 3.0~3.2 3.08120 cP / 8.120 Pa·s Example 5 3.5~3.7 3.58950 cP / 8.950 Pa·s Example 6 2.5~2.7 2.56650 cP / 6.650 Pa·s Example 73.0~3.23.09520 cP / 9.520 Pa·s

[0154] As can be seen from Table 5 above, the maximum dispersion concentration of carbon nanotubes according to Comparative Example 1 was only about 2.0 to 2.2 wt%, whereas the maximum dispersion concentration of carbon nanotubes according to Examples 1 to 7 of the present invention was confirmed to have increased compared to Comparative Example 1. These results demonstrate that the carbon nanotubes of the present invention have the ability to stably disperse a larger amount compared to conventional carbon nanotubes. Furthermore, when comparing cases where 2.0 wt% of carbon nanotubes were added to the dispersion, the viscosity of Comparative Example 1 was 5,050 cP (5.05 Pa·s), while the viscosity of Example 1 was 4,380 cP (4.38 Pa·s) and the viscosity of Example 3 was 4,100 cP (4.10 Pa·s). The carbon nanotubes according to the examples of the present invention exhibited significantly lower viscosity compared to the Comparative Example under the same conditions. This demonstrates that the carbon nanotubes of the present invention can suppress a rapid increase in viscosity even when added at a high concentration, thereby ensuring excellent dispersion stability.

[0155] Accordingly, the carbon nanotubes according to the present invention not only have improved dispersion stability compared to conventional carbon nanotubes, but also maintain low viscosity even under high concentration conditions and exhibit the effect of significantly improving fluidity and processability in the electrode slurry manufacturing process. These results support the fact that the carbon nanotubes of the present invention can have excellent industrial value as next-generation electrode materials.

Claims

1. A 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) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP.

2. In Paragraph 1, A carbon nanotube having a powder resistance of 10 to 11.5 mΩ·cm.

3. In Paragraph 1, The specific surface area of ​​the above carbon nanotube is 230 to 500 m² 2 / g, carbon nanotube.

4. In Paragraph 1, Carbon nanotubes having a purity of 93 weight% or more.

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 carbon nanotubes comprising, and 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) When preparing a dispersion, if 2% by weight of carbon nanotubes is added relative to the total weight of the dispersion, the viscosity of the dispersion measured using a rotational viscometer at 25°C under a shear rate of 12 rpm shall be 800 to 5,000 cP.

6. In Paragraph 5, A method for manufacturing carbon nanotubes, wherein the cobalt content in the catalyst prepared in step (S1) is 14 to 30 weight% based on the total weight of the catalyst.

7. In Paragraph 5, A method for manufacturing 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 carbon nanotubes, wherein the molar ratio (CA / V) of citric acid to vanadium in the catalyst prepared in step (S1) is 0.1 to 2.

0.

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

10. An electrode structure manufactured using a carbon nanotube dispersion according to claim 9.

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

12. A secondary battery comprising an electrode structure manufactured using a carbon nanotube dispersion according to claim 9.

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