Carbon nanotube aggregates, conductive material, electrode, secondary battery, planar aggregate, laminate, filter, electromagnetic wave shield, pellicle for extreme ultraviolet rays, and method for measuring average curvature

Abstract

Provided are carbon nanotube aggregates or the like excellent in conductivity when made into a carbon nanotube dispersion. Carbon nanotube aggregates in which the average curvature Z (um-1) of carbon nanotube structures in a region observed by a scanning electron microscope is from 0.005 to less than 0.088, and the cumulative 50% particle size D50 in a volume-based particle size distribution exceeds 0.65 μm.

Description

Carbon nanotube aggregates, conductive materials, electrodes, secondary batteries, planar aggregates, laminates, filters, electromagnetic shielding, pellicles for extreme ultraviolet radiation, and methods for measuring mean curvature.

[0001] This disclosure relates to carbon nanotube aggregates, conductive materials, electrodes, secondary batteries, planar aggregates, laminates, filters, electromagnetic shielding, pellicles for extreme ultraviolet radiation, and methods for measuring mean curvature.

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are materials having a cylindrical structure formed by rolling up graphene sheets, which are composed of six-membered ring structures of carbon, in a single or multilayer configuration on the same axis. CNTs are broadly classified into single-walled CNTs, which are formed from a single layer of graphene sheet, and multilayered CNTs, which are formed from multiple layers of graphene sheet. CNTs exhibit excellent mechanical, electrical, and chemical properties, and these properties are expected to lead to applications in fields such as materials, catalysts, energy, and electronics. Various attempts have been proposed to further enhance the properties of CNTs.

[0003] For example, Patent Document 1 describes a multi-walled carbon nanotube aggregate containing multi-walled carbon nanotubes with a maximum length of 1,000 μm to 30,000 μm and Fe atoms, wherein the Fe atom content ratio to the total mass of the aggregate is 0.5% by mass or more and less than 10% by mass. Furthermore, a scanning electron microscope (SEM) image showing one embodiment reveals that multiple fibrous multi-walled carbon nanotubes are intertwined to form a sheet-like aggregate. Patent Document 2 describes a conductive additive containing pulverized multi-walled carbon nanotubes with a tensile strength of 10 MPa to 100 MPa and an angle of repose of 10 to 90 degrees, which exhibits excellent conductivity-improving effects. Furthermore, a scanning electron microscope (SEM) image showing one embodiment reveals that multiple fibrous multi-walled carbon nanotubes are intertwined to form a sheet-like aggregate.

[0004] International Publication No. 2025 / 013504, Japanese Patent Publication No. 2025-010479

[0005] In some cases, when CNT aggregates are dispersed, it is required that they possess excellent conductivity.

[0006] This disclosure has been made in view of the above circumstances. One embodiment of this disclosure aims to solve the problem of providing a carbon nanotube aggregate that exhibits excellent conductivity when used as a carbon nanotube dispersion. Another embodiment of this disclosure aims to solve the problem of providing a conductive material, electrode, secondary battery, and planar aggregate containing the above carbon nanotube aggregate. Another embodiment of this disclosure aims to solve the problem of providing a laminate comprising the above planar aggregate. Another embodiment of this disclosure aims to solve the problem of providing a filter, electromagnetic shield, and extreme ultraviolet pellicle using the above planar aggregate. Another embodiment of this disclosure aims to solve the problem of providing a novel method for measuring the mean curvature of a carbon nanotube aggregate.

[0007] The means for solving the above problem include the following embodiments: <1> Mean curvature Z(um) of the carbon nanotube structure in the observation area by scanning electron microscope －１<1> A carbon nanotube aggregate having a particle size ratio of 0.005 or more and less than 0.088, and a cumulative 50% particle size D50 in the volume-based particle size distribution that exceeds 0.65 μm. <2> The carbon nanotube aggregate according to <1>, which includes a bundle structure, and in the area observed by a scanning electron microscope, the bundle diameter X that is cumulatively 90% is greater than 90 nm and less than 500 nm. <3> The carbon nanotube aggregate according to <1> or <2>, which includes a bundle structure, and in the area observed by a scanning electron microscope, the area ratio Y of bundles with a bundle diameter of 100 nm or more is greater than 0.1. <4> A conductive material containing the carbon nanotube aggregate according to any one of <1> to <3>. <5> An electrode containing an electrode active material and the conductive material according to <4>. <6> A secondary battery comprising the electrode according to <5>. <7> A planar aggregate containing the carbon nanotube aggregate according to any one of <1> to <3>. <8> A laminate comprising a substrate and the planar aggregate described in <7>. <9> A filter using the planar aggregate described in <7>. <10> An electromagnetic shield using the planar aggregate described in <7>. <11> An extreme ultraviolet pellicle using the planar aggregate described in <7>. <12> A method for measuring the mean curvature of a carbon nanotube aggregate, comprising performing the following steps 1 to 3 on two or more images of the carbon nanotube aggregate using the image analysis software ImageJ (version 1.54g) and Kappa plugin (version 2.0.0) to calculate the mean curvature. 1. Adjust the image size in Image:Adjust:Size, Width=1280. Set the image size to 1280×960 and the width to 1410nm. 2. Using the following conditions: Plugin:Analyze:Kappa, File:OpenActiveImage, and CurveFittingOptions:ChoosePoints=100,DataThreshold=10, Scale(μm / pixel)=0.16, the curve is finely adjusted to follow the center of the fiber. 3.1 After calculating approximately eight center lines per field of view, the curvature of each line and the mean curvature are calculated.

[0008] According to one embodiment of the present disclosure, a carbon nanotube aggregate exhibiting excellent conductivity when used as a carbon nanotube dispersion is provided. According to another embodiment of the present disclosure, a conductive material, an electrode, a secondary battery, and a planar aggregate containing the carbon nanotube aggregate are provided. According to another embodiment of the present disclosure, a laminate comprising the planar aggregate is provided. According to another embodiment of the present disclosure, a filter, an electromagnetic shield, and an extreme ultraviolet pellicle using the planar aggregate are provided. According to another embodiment of the present disclosure, a method for measuring the mean curvature of a novel carbon nanotube aggregate is provided.

[0009] This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 1 of Example 1. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 2 of Example 2. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 3 of Example 3. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 4 of Example 4. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 5 of Example 5. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 6 of Comparative Example 1. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 7 of Comparative Example 2.

[0010] The present disclosure is described in detail below. In this specification, a numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. In this specification, in numerical ranges described in stages, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this specification, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that is not clearly distinguishable from other processes, as long as the intended purpose of that process is achieved.

[0011] In this disclosure, the terms "carbon nanotube," "single-walled carbon nanotube," "multi-walled carbon nanotube," "carbon nanotube aggregate," "carbon nanotube having a maximum length of 1,000 μm to 30,000 μm," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "CNT aggregate," "ULCNT," and "CNT dispersion," respectively.

[0012] (Carbon Nanotube Assembly) The carbon nanotube assembly (also referred to as the "CNT assembly") relating to this disclosure has an average curvature Z (um) of the carbon nanotube structure in the area observed by a scanning electron microscope. －１ The mean curvature (where um represents unit meters) is between 0.005 and 0.088, and the cumulative 50% particle size D50 in the volume-based particle size distribution exceeds 0.65 μm. －１ This section explains "um (unit meter)" in this specification. "um" is a unit corresponding to the analysis based on the image size and set scale as defined in this invention, and is also used in the analysis of the examples and comparative examples in this specification. In Kappa, 1 μm is defined as 1 um. Note that the scale in Kappa is set to a different value from the scale of the actual image, and the conversion to the scale of the actual image is 1 um = 6.885 nm. Curvature is a value obtained by using a circle inscribed in the curve and finding the reciprocal of the radius "um" of the inscribed circle. Therefore, the reciprocal of the radius "um" －１ The unit is "n," and by unifying the screen size and scale, it becomes possible to compare the average curvature Z of each carbon nanotube structure. Using the image analysis software ImageJ (version 1.54g), when adjusting the image size with Image:Adjust:Size, Width=1280, set the image size to 1280 x 960 and the width to 1410 nm. When performing analysis with the Kappa plugin (version 2.0.0), set Scale(μm / pixel) = 0.16. By unifying the image size and scale here, it becomes possible to compare images.

[0013] The CNT aggregate described herein makes it possible to produce a battery that yields a carbon nanotube dispersion with appropriate viscosity. On the other hand, Patent Documents 1 and 2 do not contain any descriptions that focus on the curvature of the carbon nanotube structure.

[0014] While Patent Document 1 describes the length of multi-walled carbon nanotubes and their intertwined aggregates, it does not specifically describe the shape of the carbon nanotube aggregates. Furthermore, while viscosity is described, conductivity is not specifically described. Patent Document 2 describes the tensile strength of multi-walled carbon nanotubes before grinding, but does not describe the tensile strength after grinding. Furthermore, while the volume resistivity of the powder under pressurized conditions is described regarding conductivity, dispersibility is not described. In contrast, the CNT aggregates according to this disclosure have excellent conductivity when used as a carbon nanotube dispersion because the mean curvature Z of the carbon nanotube structure and the cumulative 50% particle size D50 in the volume-based particle size distribution satisfy the aforementioned range.

[0015] <Mean curvature Z> The CNT aggregate according to this disclosure provides a carbon nanotube aggregate that improves the cycle characteristics of a battery when used as an electrode conductive additive. The mean curvature Z (um) of the carbon nanotube structure (also called "bundle") in the carbon nanotube aggregate according to this disclosure －１ The value is between 0.005 and less than 0.088.

[0016] The average curvature (um) of the carbon nanotube structure in the CNT aggregate relating to this disclosure －１) is 0.005 or more and less than 0.088, may be 0.008 or more and 0.080 or less, may be 0.010 or more and 0.080 or less, may be 0.010 or more and 0.070 or less, may be 0.010 or more and 0.060 or less, may be 0.010 or more and 0.050 or less, may be 0.010 or more and 0.040 or less, may be 0.010 or more and 0.035 or less, may be 0.010 or more and 0.030 or less, may be 0.010 or more and 0.025 or less, and may be 0.010 or more and 0.021 or less. Among these, 0.010 or more and 0.035 or less is preferable, 0.010 or more and 0.030 or less is more preferable, 0.010 or more and 0.025 or less is even more preferable, and 0.010 or more and 0.021 or less is particularly preferable. The average curvature Z of carbon nanotube structures in a CNT aggregate (um －１ ) is 0.005 or more, which is preferable because it appropriately suppresses aggregation between CNT aggregates, prevents an increase in bundle diameter, and improves dispersibility in a dispersion solvent. In addition, the average curvature Z (um －１ ) is less than 0.088, which is preferable because the conductivity of the CNT aggregate is improved.

[0017] Specifically, when the average curvature Z of the carbon nanotube aggregate (um －１ ) is 0.010 or more and 0.035 or less, the linearity of the CNT aggregate is maintained, and the network structure becomes partially more linear. This prevents excessive entanglement between CNT aggregates and promotes uniform dispersion in the dispersion liquid. In addition, conductivity is improved. In one embodiment, the average curvature Z of the carbon nanotube aggregate (um －１The ratio is greater than 0.010 and less than or equal to 0.025, so for example, when the CNT aggregate according to this disclosure is used as a conductive additive in a lithium-ion battery, the cycle characteristics are improved. Although the mechanism is not clear, it is thought that the linear shape of the carbon nanotube aggregate shortens the conductive distance and reduces electrical resistance when it forms a network structure and conductive paths. Furthermore, the linear shape of the carbon nanotube aggregate increases its rigidity, and it is thought that the swelling and contraction of the electrode active material due to charging and discharging is effectively suppressed by the tightly packed carbon nanotube aggregate.

[0018] - Mean curvature: Calculation of the average value of curvature - Mean curvature Z (um) of a carbon nanotube aggregate －１ The carbon nanotube (CNT) can be measured, for example, by the following method. Suitable images include scanning electron microscope (SEM) images, which clearly show bundles of CNTs. The SEM imaging method and conditions will be described later.

[0019] Using the aforementioned images, the average curvature of the CNT structure is calculated by image analysis. More specifically, the average curvature is calculated by performing the following steps 1 to 3 on two or more images of carbon nanotube assemblies using the image analysis software ImageJ (Wayne Rasband (NIH) Version) (version 1.54g) and the Kappa plugin (version 2.0.0). 1. Adjust the image size using Image:Adjust:Size, Width=1280. Set the screen size to 1280 x 960 and the width to 1410 nm. 2. Using the following conditions: Plugin:Analyze:Kappa, File:OpenActiveImage, and CurveFittingOptions:ChoosePoints=100,DataThreshold=10, Scale(μm / pixel)=0.16, the curve is finely adjusted to follow the center of the fiber. 3.1 After calculating approximately eight center lines per field of view, the curvature of each line and the mean curvature are calculated.

[0020] <D50> In the carbon nanotube aggregate according to the present disclosure, the cumulative 50% particle size D50 in the volume-based particle size distribution is more than 0.35 μm, and from the viewpoint of conductivity, it is preferably more than 0.35 μm and 45.0 μm or less, preferably more than 0.35 μm and 20.0 μm or less, more preferably more than 0.35 μm and 15 μm or less, even more preferably more than 0.35 μm and 14 μm or less, particularly preferably more than 0.35 μm and 13 μm or less, and most preferably more than 0.35 μm and 12 μm or less. In other embodiments, it is preferably more than 0.35 μm and 11 μm or less, more preferably more than 0.35 μm and 10 μm or less, even more preferably more than 0.35 μm and 9.0 μm or less, and particularly preferably more than 0.35 μm and 8.0 μm or less. Furthermore, from the viewpoint of achieving both conductivity and mechanical durability, the particle size is preferably greater than 0.35 μm and 45.0 μm or less, more preferably greater than 0.40 μm and 30.0 μm or less, even more preferably greater than 0.41 μm and 20.0 μm or less, particularly preferably greater than 0.42 μm and 15.0 μm or less, especially preferably greater than 0.43 μm and 14.0 μm or less, and even more preferably greater than 0.44 μm and 13.05 μm or less. Furthermore, from the viewpoint of achieving both conductivity and dispersibility, the cumulative 50% particle size D50 in the volume-based particle size distribution is preferably greater than 0.65 μm and 45 μm or less, more preferably greater than 0.65 μm and 20 μm or less, even more preferably greater than 0.65 μm and 15 μm or less, even more preferably greater than 0.65 μm and 14 μm or less, particularly preferably greater than 0.65 μm and 13 μm or less, and most preferably greater than 0.65 μm and 10 μm or less. When the cumulative 50% particle size D50 is within the above range, the particle size of the CNT aggregate is appropriately controlled, and uniform dispersion of the CNT aggregate in the dispersion is achieved. In particular, when the cumulative 50% particle size D50 is in the range of greater than 0.65 μm and less than or equal to 45 μm, more preferably greater than 0.65 μm and less than or equal to 15 μm, the particle size of the CNT aggregate is appropriately small and uniform, so aggregation of the CNT aggregate in the dispersion is suppressed and dispersibility is improved.The smaller particle size of the CNT aggregates increases their surface area in the dispersion, strengthening their interaction with the dispersion medium and thus improving dispersibility. Furthermore, a uniform particle size distribution stabilizes the viscosity of the CNT aggregate dispersion, resulting in better processability and handling when forming electrodes or other components using the CNT aggregates. Moreover, when the cumulative 50% particle size D50 is greater than 0.65 μm and less than or equal to 8.0 μm, the particle size of the CNT aggregates is appropriately controlled, achieving more uniform dispersion when preparing dispersions using the CNT aggregates. Therefore, by satisfying the above conditions, the dispersibility of the CNT aggregates is further improved and the viscosity of the dispersion is optimized, making it possible to provide a high-performance CNT dispersion with excellent conductivity and handling properties.

[0021] The cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is measured as follows: The CNT dispersion is thoroughly stirred and then diluted with pure water. The resulting diluted solution is used as a sample, and the cumulative particle size D50 of the CNT dispersion is measured using a particle size analyzer (LA-960, laser diffraction particle size analyzer, Horiba, Ltd.). The particle refractive index of the CNTs to be measured is assumed to be 1.920–0.522i. The refractive index of the solvent is assumed to be 1.333. During measurement, the CNT dispersion is diluted by dropping it into pure water while observing the transmittance, and the measurement is performed after confirming that the particle size distribution on the monitor is stable. The CNT dispersion is prepared by mixing carbon nanotube aggregates, 700 kDa of carboxymethylcellulose sodium, and water, with a concentration of 0.20 mass% of carbon nanotube aggregates and a concentration of 0.30 mass% of carboxymethylcellulose sodium.

[0022] <Bundle Structure> The CNT aggregate according to this disclosure includes a bundle structure, and preferably the bundle diameter at which 90% of the cumulative total is reached (hereinafter also referred to as the "90% cumulative bundle diameter") is greater than 90 nm and less than 500 nm in the area observed by a scanning electron microscope. Furthermore, the bundle diameter at which 90% of the cumulative total is reached may be 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less. Furthermore, the bundle diameter at which 90% of the cumulative total is reached may be 100 nm or more, or 110 nm or more. Within the range of the bundle diameter at which 90% of the cumulative total is reached, these upper and lower limits can be arbitrarily selected.

[0023] In this disclosure, the bundle structure included in a CNT aggregate refers to an aggregate in which multiple CNTs are aggregated together by van der Waals forces or the like, forming a bundle-like structure. It is presumed that including a bundle structure of an appropriate size in a CNT aggregate improves the handling properties of the CNT aggregate and further enhances its stability.

[0024] The bundle structure in the CNT aggregate can be formed, for example, by controlling the catalyst particle size distribution during manufacturing by chemical vapor deposition (CVD) or by controlling the cooling rate during the cooling process.

[0025] From the viewpoint of achieving both the handling properties and dispersibility in the solvent of the CNT aggregate, the individual bundle diameters contained in the CNT aggregate are preferably 5 nm to 500 nm, and more preferably 10 nm to 300 nm. The content of bundle structures in the CNT aggregate is preferably 10% to 100% by mass, and more preferably 20% to 90% by mass, based on the total mass of the CNT aggregate. The presence or absence of bundle structures in the CNT aggregate can be confirmed by observing the CNT aggregate with an optical microscope, a scanning electron microscope (SEM), etc. The bundle diameter can be determined by identifying the locations where bundle structures exist in the CNT aggregate and measuring the length using images of the bundle structures.

[0026] In SEM observation, the CNT aggregates described herein have a cumulative 90% bundle diameter exceeding 90 nm, which facilitates the aggregation of CNT bundles and the formation of long-distance conductive networks. Furthermore, having a cumulative 90% bundle diameter of less than 500 nm results in good dispersibility in the dispersion medium and makes it easier to ensure conductivity.

[0027] Specifically, a cumulative 90% bundle diameter exceeding 90 nm allows the CNTs to aggregate appropriately, forming efficient conductive paths. This improves the conductivity of the CNT aggregate and optimizes its performance as an electrode material. Furthermore, a cumulative 90% bundle diameter of 400 nm or less ensures good dispersibility in the dispersion medium, resulting in uniform dispersion. This maintains the viscosity of the dispersion containing the CNT aggregate within an appropriate range, improving dispersibility. As a result, battery performance can be improved.

[0028] In particular, the cumulative 90% bundle diameter is preferably greater than 90 nm and 350 nm or less, more preferably greater than 90 nm and 300 nm or less, more preferably greater than 90 nm and 250 nm or less, even more preferably greater than 90 nm and 230 nm, and especially preferably greater than 90 nm and 200 nm or less. Furthermore, the cumulative 90% bundle diameter is preferably 100 nm or more and 350 nm or less, more preferably greater than 100 nm and 300 nm or less, more preferably greater than 100 nm and 250 nm or less, even more preferably greater than 100 nm and 230 nm or less, and especially preferably greater than 100 nm and 200 nm or less. Furthermore, the cumulative 90% bundle diameter is preferably 110 nm or more and 350 nm or less, more preferably 110 nm or more and 300 nm or less, even more preferably 110 nm or more and 250 nm or less, especially preferably 110 nm or more and 230 nm or less, and particularly preferably 110 nm or more and 200 nm or less. Within this range, by appropriately controlling the bundle diameter of the CNTs, the contact resistance between CNTs is reduced, and electron conduction paths are efficiently formed, thereby improving conductivity. Furthermore, by appropriately controlling the bundle diameter, the viscosity of the dispersion containing the CNT aggregates is maintained within an appropriate range, improving dispersibility. As a result, battery performance can be improved.

[0029] Furthermore, in the CNT aggregate according to this disclosure, it is preferable that the area ratio of bundles with a bundle diameter of 100 nm or more is greater than 0.1 when observed by SEM. The area ratio of the bundles may also be 0.11 or more, 0.12 or more, or 0.13 or more. Moreover, the area ratio of bundles with a bundle diameter of 100 nm or more may be 0.8 or less, 0.7 or less, 0.6 or less, 0.55 or less, or 0.5 or less. The area ratio of bundles with a bundle diameter of 100 nm or more is calculated by dividing the area of ​​bundles with a bundle diameter of 100 nm or more by the total area of ​​the CNT aggregate in the SEM image of the CNT aggregate. The area ratio of the bundles is preferably greater than 0.1 and less than or equal to 0.8, more preferably between 0.11 and 0.8, even more preferably between 0.12 and 0.8, and particularly preferably between 0.13 and 0.8. In other embodiments, the area ratio of bundles is preferably greater than 0.1 and less than or equal to 0.6, more preferably between 0.11 and 0.6, even more preferably between 0.12 and 0.6, and particularly preferably between 0.13 and 0.6. In other embodiments, the area ratio of bundles is preferably greater than 0.1 and less than or equal to 0.6, more preferably greater than 0.1 and less than or equal to 0.55, even more preferably greater than 0.1 and less than or equal to 0.5, particularly preferably between 0.11 and 0.5, even more preferably between 0.12 and 0.5, and especially preferably between 0.13 and 0.5. When the area ratio of bundles with a bundle diameter of 100 nm or more is within the above range, the bundles of CNTs gather together, making it easier to form long-distance conductive networks, which in turn makes it easier to ensure conductivity and improves dispersibility in the dispersion medium.

[0030] Furthermore, in some embodiments, the area ratio of the bundle is preferably greater than 0.1 and less than or equal to 0.7, more preferably between 0.11 and 0.7, even more preferably between 0.12 and 0.7, and particularly preferably between 0.13 and 0.7, from the viewpoint of mechanical strength and conductivity.

[0031] The bundle diameter of the CNT aggregate is measured by observation using a scanning electron microscope (SEM). Multiple SEM images are obtained by photographing the CNT aggregate at a magnification of 100,000x. The imaging method using the SEM is not particularly limited and can be carried out using known methods.

[0032] -Imaging- Images of the CNT aggregate are obtained by imaging using an SEM device (for example, Hitachi High-Technologies Corporation, S-4800) under the following conditions. From the viewpoint of reducing the variance of the analyzed bundle diameter, it is preferable to obtain five or more images. Acceleration voltage: 0.5 kV Emission current: 10 μA Magnification: 100,000x Image size: 1280 pixels × 960 pixels

[0033] - Image Selection - From the obtained images, select two or more images in which CNT bundles are frequently observed.

[0034] - Overview of Bundle Diameter Analysis using Image Analysis - Image processing and image analysis are performed on the selected image using Python. In image processing, the contours and centerlines of the CNTs are detected and combined with the original image. In image analysis, the bundle diameter is determined by calculating the distance from the centerline to the contour in the created image. Then, the product of the bundle diameter and the length of the centerline is calculated to determine the area occupied by the CNTs in the image.

[0035] -Detection of CNT contours using image analysis- 1. Binarize the image to distinguish between CNTs and the background. 2. Create contours for the CNT portions using the edge detection function of the OpenCV library.

[0036] -Detection of CNT centerlines using image analysis- 1. Adjust parameters to distinguish between CNTs and background and perform binarization. 2. Create a skeleton for the CNT portion using the skeletonize function of the scikit-image library. 3. For each coordinate of the skeleton, count the number of skeletons in the surrounding 2 pixels and recognize coordinates with 5 or more skeletons as skeleton intersections. 4. Divide the skeleton at the intersections by converting the intersections to background pixels. The resulting skeletons are called regions. 5. Measure the length of the regions and delete the shorter regions. 6. Perform linear approximation for each region. 7. For each created line, obtain the X-axis coordinate of the region from which the approximation was made. Convert the line into a line segment based on the interval in which the obtained X-coordinate exists. Treat the line segment obtained here as the centerline of the CNT. 8. Calculate the similarity based on the center coordinates and angles for all sets of centerlines. If the distance between the center coordinates is within 10 pixels and the angle between the two line segments is less than 10 degrees, treat the pair of center lines as duplicate center lines and delete the shorter one. 9. Overlay the CNT contour and center lines onto the original image and save. The contour will be treated in red, and the center lines in blue.

[0037] -Detection of CNT bundle diameter by image analysis- 1. Load an image created by image processing and recognize CNTs, contours, background, and center lines using hue recognition. 2. Measure the length of each center line. 3. Select a random point on the center line and draw a perpendicular line from the point to the center line. 4. Detect the intersection point of the perpendicular line and the contour, and save the distance from the random point on the center line to the intersection point as the bundle diameter. 5. Calculate the occupied area as the product of the length of the center line segment and the bundle diameter. Save the data as a histogram with the bundle diameter on the horizontal axis and the occupied area on the vertical axis.

[0038] - Obtaining Bundle Diameter Parameters - Using the calculated bundle diameter histogram data, the bundle diameter features of each sample are calculated using the following method: 1. Add the bundle diameters and occupied areas of multiple fields of view of the same sample and normalize so that the sum is 1. With normalization, the unit of the vertical axis is set to occupied area ratio. 2. Find the sum of the occupied area ratios of bundles with a bundle diameter of 100 nm or more. 3. Calculate the cumulative occupied area ratio and determine the bundle diameter at which this value first exceeds 0.9 as the cumulative 90% bundle diameter.

[0039] <Viscosity> The carbon nanotube aggregate according to this disclosure is preferably prepared by mixing the carbon nanotube aggregate with 700 kDa of carboxymethylcellulose sodium and water, where the concentration of the carbon nanotube aggregate is 0.20% by mass and the concentration of the carboxymethylcellulose sodium is 0.30% by mass. The common logarithm of the viscosity of the dispersion is 1.0 or higher (the unit of viscosity is mPa·s). The viscosity in this disclosure is the viscosity at 25°C.

[0040] Furthermore, in one embodiment, the viscosity of the dispersion may be 7.0 mPa·s to 5000 mPa·s, 15 mPa·s to 5000 mPa·s, 20 mPa·s to 5000 mPa·s, 25 mPa·s to 5000 mPa·s, or 30 mPa·s to 5000 mPa·s. Moreover, it may be 30 to 3000 mPa·s, 30 to 2000 mPa·s, 30 to 1600 mPa·s, 50 to 1600 mPa·s, 80 to 900 mPa·s, 110 to 800 mPa·s, or 142.6 to 798.2 mPa·s.

[0041] The common logarithm of the viscosity of the above dispersion is preferably 1.0 or more and 5.0 or less. The upper limit may be 4.5 or less, 4.0 or less, 3.5 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.90 or less. The lower limit may be 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more. Furthermore, the upper and lower limits can be combined in any way.

[0042] By having a common logarithm of the viscosity of the above dispersion of 1.0 or higher, the dispersibility of CNTs is improved, and the performance as an electrode material is optimized.

[0043] The common logarithm of the viscosity of the above dispersion is more preferably 1.1 to 3.5, even more preferably 1.2 to 3.2, and particularly preferably 1.3 to 3.2. Furthermore, it is more preferably 1.4 to 3.2, even more preferably 1.5 to 3.2, and particularly preferably 1.54 to 2.90. In addition, when the common logarithm of the viscosity of the above dispersion is 1.1 to 3.5, the dispersion of CNTs is further improved, and the tensile strength of the CNT aggregate is improved. Specifically, when the common logarithm of the viscosity of the above dispersion is 1.6 to 3.2, the bundles of CNTs gather together, making it easier to form long-distance conductive networks, and the dispersibility in the dispersion medium is improved, and conductivity is easier to ensure. As a result, for example, when added as a conductive additive to an electrode, the conductivity of the electrode is improved, the internal resistance of the battery is reduced, the charge-discharge efficiency of the battery is improved, and the cycle characteristics are further improved. Therefore, by having a common logarithm of viscosity of 1.0 or higher, it becomes possible to achieve both a CNT film with excellent conductivity and an appropriate viscosity when used as a dispersion.

[0044] The carbon nanotube aggregate according to this disclosure is preferably obtained by mixing the carbon nanotube aggregate with 700 kDa of carboxymethylcellulose sodium and water, wherein the concentration of the carbon nanotube aggregate is 0.20% by mass and the concentration of the carboxymethylcellulose sodium is 0.30% by mass, and the common logarithm of the viscosity of the dispersion is 1.6 or higher (the unit of viscosity is mPa·s).

[0045] The common logarithm of the viscosity of the above dispersion is 1.54 or more and 5.0 or less, and 1.6 or more and 5.0 or less. The upper limit may be 4.5 or less, 4.0 or less, 3.5 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.90 or less. The lower limit may be 1.7 or more, 1.8 or more, 1.9 or more, 2.0 or more, 2.01 or more, or 2.1 or more. Furthermore, the upper and lower limits can be arbitrarily combined. Moreover, the common logarithm of the viscosity of the above dispersion is more preferably 1.8 or more and 3.2 or less, even more preferably 2.0 or more and 3.0 or less, and particularly preferably 2.1 or more and 2.9 or less. By appropriately controlling the viscosity of the CNTs, the dispersibility of the CNTs is improved and the tensile strength is improved. Specifically, when the common logarithm of the viscosity of the dispersion is between 1.8 and 3.2, the dispersion of CNTs is kept uniform and conductivity is easily ensured. As a result, for example, when added to electrodes as a conductive additive, the conductivity of the electrodes is improved, the internal resistance of the battery is reduced, the charge and discharge efficiency of the battery is improved, and the cycle characteristics are further enhanced.

[0046] Furthermore, when the common logarithm of the viscosity of the dispersion is between 2.0 and 3.0, the dispersion of CNTs is further improved, and conductivity is enhanced. As a result, for example, when added to electrodes as a conductive additive, the electrodes can be made more durable against volume changes and stress during the cycle, contributing to the battery life. In particular, when the common logarithm of the viscosity of the dispersion is between 2.1 and 2.9, the balance between the dispersibility and conductivity of CNTs is optimized, and for example, when added to electrodes as a conductive additive, the performance of the electrodes is maximized. Within this range, uniform dispersion of CNTs and high conductivity can be achieved simultaneously, and a significant improvement in the battery's cycle characteristics can be expected. Therefore, by satisfying the viscosity range mentioned above, it becomes possible to provide a CNT film with excellent conductivity and an appropriate viscosity when used as a dispersion.

[0047] The viscosity of the dispersion containing the CNT aggregates according to this disclosure is measured using a cone-plate viscometer (also known as an E-type viscometer). For example, a Brookfield DV-II+Pro Programmable Viscometer is used as the cone-plate viscometer. The measurement conditions are as follows: Measurement fixture: Cone-plate; Measurement mode: Rotational mode; Shear speed: 0.6 s －１ ~384 simultaneous －１ Temperature: 25°C. From the obtained data, read the viscosity at the following shear rate: Shear rate = 12s －１

[0048] The CNT aggregates relating to this disclosure have a high affinity for the dispersion medium, which tends to result in a lower viscosity of the dispersion. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the aggregates relating to this disclosure in the dispersion medium is good.

[0049] <Surface Resistivity> In this disclosure, the surface resistivity of the molded film can be measured by the four-terminal, four-probe method in accordance with the JIS K7194:1994 standard. As a resistivity meter, for example, a Loresta GXII manufactured by Nitto Seiko Analytech Co., Ltd. is used. The method for preparing the molded film will be described later.

[0050] In this disclosure, the surface resistivity of the tensile test film is preferably 0.01 Ω / □ to 15.4 Ω / □, more preferably 0.1 Ω / □ to 10.0 Ω / □, even more preferably 0.2 Ω / □ to 8.0 Ω / □, particularly preferably 0.3 Ω / □ to 5.0 Ω / □, especially preferably 0.9 Ω / □ to 3.5 Ω / □, particularly preferably 0.90 Ω / □ to 3.31 Ω / □, and most preferably 0.90 Ω / □ to 2.59 Ω / □, from the viewpoint of easily ensuring conductivity as a conductive additive and the stability of the dispersion.

[0051] <Elongation at Break, Tensile Strength, and Energy Density at Break> The CNT aggregate according to this disclosure preferably has an elongation at break of more than 0% and 5.0% or less, measured by the following measurement method, a tensile strength of 2.5 MPa or more and 50.0 MPa or less, and an energy density at break of more than 4.3 MPa·% and 100 MPa·% or less.

[0052] -Method for measuring tensile strength, elongation at break, and energy density at break- A carbon nanotube dispersion is prepared by mixing a carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, so that the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%. 15 mL of the obtained carbon nanotube dispersion is poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm, and heated at 100°C for 30 minutes to dry and obtain a measurement sample. The obtained measurement sample is fixed to the gripping part of a tensile testing apparatus, and a tensile test is performed at a speed of 1 mm / min. The point where the stress is maximum is considered the fracture point, and the elongation at break is calculated from the length of the measurement sample at the fracture point and the length of the measurement sample before measurement. The maximum test force is calculated as the tensile strength. Furthermore, the energy density at break is calculated from the product of the elongation at break and the tensile strength.

[0053] When the elongation at break of the CNT aggregate according to this disclosure exceeds 0% (preferably 0.5% or more), the length of the CNTs is sufficiently long, making it easier to ensure conductivity. Specifically, the sufficient length of the CNTs increases the number of contact points between CNTs, allowing for smoother electron movement, thus improving the conductivity of the entire CNT aggregate. Furthermore, maintaining an appropriate length of CNTs allows for efficient formation of conductive paths, optimizing conductivity. When the elongation at break of the CNT aggregate according to this disclosure is 6.0% or less, more preferably 5.0% or less, it is easy to process into a dispersion and ensure dispersibility in the dispersion. Specifically, an elongation at break of 5.0% or less maintains the flexibility of the CNTs appropriately, enabling uniform dispersion of CNTs in the dispersion. This appropriately maintains the viscosity of the dispersion, improves dispersibility, and further enhances durability against volume changes and stress during the battery cycle. This further improves the maintenance rate of discharge capacity. Therefore, having a fracture elongation rate of the CNT aggregate in the range of 0% to 6.0%, more preferably 0% to 5.0%, plays an important role in improving the battery cycle characteristics of the CNT aggregate. In particular, it is more preferable that the fracture elongation rate of the CNT aggregate be in the range of 0.5% to 6.0%, even more preferable that it be in the range of 0.7% to 5.7%, and especially preferable that it be in the range of 1.1% to 5.4%.

[0054] Furthermore, the elongation rate at break of the CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0055] The tensile strength of the CNT aggregate according to this disclosure is preferably 2.5 MPa or more and 50.0 MPa or less, more preferably 4.0 MPa or more and 50.0 MPa or less, even more preferably 5.0 MPa or more and 50.0 MPa or less, and particularly preferably 7.0 MPa or more and 50.0 MPa or less. In another embodiment, the tensile strength is preferably 3.0 MPa or more and 80.0 MPa or less, more preferably 5.0 MPa or more and 70.0 MPa or less, even more preferably 8.0 MPa or more and 60.0 MPa or less, particularly preferably 8.0 MPa or more and 50.0 MPa or less, and even more preferably 8.0 MPa or more and 32.6 MPa or less. When the tensile strength of the CNT aggregate according to this disclosure is 2.5 MPa or more, the length of the CNTs according to this disclosure is sufficiently long, making it possible to manufacture a battery with excellent cycle characteristics. Specifically, sufficient length of the CNTs increases the contact points between them, allowing for smoother electron movement. This improves the overall conductivity of the CNT assembly and enhances the battery's cycle characteristics (i.e., the rate of discharge capacity retention). When the tensile strength of the CNT assembly according to this disclosure is 50.0 MPa or less, it is easy to process into a dispersion and ensure dispersibility in the dispersion. Specifically, a tensile strength of 50.0 MPa or less maintains a good balance between the flexibility and mechanical strength of the CNTs, enabling uniform dispersion of the CNTs in the dispersion. This appropriately maintains the viscosity of the dispersion, further improving the battery's resistance to volume changes and stress during the cycle. This further improves the rate of discharge capacity retention.

[0056] Furthermore, the tensile strength of the CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0057] The fracture energy density of the CNT aggregate according to this disclosure is preferably greater than 4.3 MPa·% and 100.0 MPa·% or less, more preferably 5.0 MPa·% to 95.0 MPa·%, more preferably 6.0 MPa·% to 90.0 MPa·%, even more preferably 8.0 MPa·% to 80.0 MPa·%, and particularly preferably 8.6 MPa·% to 75.1 MPa·%. When the fracture energy density of the CNT aggregate according to this disclosure is greater than 4.3 MPa·% (preferably 6.0 MPa·% or more), the length of the CNTs according to this disclosure is sufficiently long, making it possible to manufacture a battery with excellent cycle characteristics. Specifically, the sufficient length of the CNTs increases the contact points between the CNTs, allowing for smoother electron movement, which improves the conductivity of the entire CNT aggregate and improves the battery's cycle characteristics (i.e., the rate of discharge capacity maintenance). When the fracture energy density of the CNT aggregate according to this disclosure is 100.0 MPa·% or less, it is easy to process into a dispersion and easy to ensure dispersibility in the dispersion. Specifically, when the fracture energy density is 100.0 MPa·% or less, the flexibility and mechanical strength of the CNTs are well balanced, and uniform dispersion of CNTs in the dispersion is achieved. As a result, the viscosity of the dispersion is appropriately maintained, and the durability against volume changes and stress during the battery cycle is further improved. As a result, the retention rate of discharge capacity is further improved.

[0058] Furthermore, the fracture energy density of a CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0059] <Amorphous Carbon> The CNT aggregate according to this disclosure preferably contains amorphous carbon. The CNT aggregate according to this disclosure preferably contains amorphous carbon in an amount of less than 2.0% by mass of the total mass of the CNT aggregate.

[0060] CNT aggregates may contain amorphous carbon, for example, adsorbed on the surface of the CNT aggregate, or incorporated into the interior of fibrous CNT aggregates formed during manufacturing.

[0061] Amorphous carbon is produced as a by-product in the manufacturing process of carbon nanotubes (CNTs). Since amorphous carbon and CNTs have different physical and chemical properties, controlling the amorphous carbon content is important. For example, in the synthesis of CNTs using chemical vapor deposition (CVD), amorphous carbon is generated when hydrocarbon gas is decomposed at high temperatures. In this process, carbon atoms are deposited on the catalyst metal surface and CNTs grow, while amorphous carbon is simultaneously generated on the catalyst surface and substrate. The amorphous carbon content can be controlled by appropriately adjusting the CNT growth conditions (e.g., temperature, gas flow rate, catalyst type, etc.). In particular, in the CNT aggregate according to this disclosure, conductivity is improved by controlling the amorphous carbon content to less than 2.0 mass%.

[0062] From the viewpoint of improving the conductivity of the CNT aggregate, the amorphous carbon content is preferably less than 1.8% by mass, more preferably less than 1.7% by mass, even more preferably 1.6% by mass or less, and particularly preferably less than 1.6% by mass, based on the total mass of the CNT aggregate. Furthermore, from the viewpoint of improving the dispersibility and conductivity of the CNT aggregate, the amorphous carbon content is preferably 0% by mass, based on the total mass of the CNT aggregate, but from the viewpoint of maintaining the conductivity of the CNT aggregate, it may be 0.01% by mass or more, 0.02% by mass or more, or 0.03% by mass or more. The above upper and lower limits can be arbitrarily combined. The amorphous carbon content is preferably 0.01% by mass or more and less than 2.0% by mass, more preferably 0.01% by mass or more and less than 1.8% by mass, even more preferably 0.01% by mass or more and less than 1.7% by mass, and particularly preferably 0.01% by mass or more and 1.6% by mass or less, based on the total mass of the CNT aggregate. Furthermore, it is more preferable that the amount is 0.01% by mass or more and less than 1.6% by mass, even more preferable that it is 0.02% by mass or more and less than 1.6% by mass, and particularly preferable that it is 0.04% by mass or more and 1.43% by mass or less.

[0063] The amorphous carbon content in the CNT aggregates relating to this disclosure is calculated by thermogravimetric differential thermal analysis (TG-DTA). In thermogravimetric differential thermal analysis (TG-DTA), the constituent elements and quality of the carbon material are evaluated by analyzing the peak combustion temperature and residues after heating to approximately 900°C at a rate of approximately 10°C / min. For example, carbon material obtained by suspended catalytic chemical vapor deposition (FCCVD) is a mixture of metals (e.g., iron (Fe)) contained in the catalyst raw materials, CNTs, amorphous carbon, and graphite carbon. When the carbon material is heated under the above conditions, if it contains metals such as iron (Fe), an increase in mass due to oxidation of the metal is observed. Typically, amorphous carbon burns at around 300°C to 400°C, while CNTs and graphite carbon begin burning at around 400°C and completely burn at around 700°C. Therefore, the amorphous carbon content can be calculated from the difference in weight loss between 200°C and 400°C.

[0064] When measuring the amorphous carbon content, a powder of CNT aggregates is used as the measurement sample. If the CNT aggregates are in a form other than powder (e.g., fibers or sheets), the CNT aggregates can be pulverized to obtain a powder. The pulverization process is not particularly limited; any pulverization process that can break the CNT aggregates into small pieces can be used. As a pulverization process, freeze-drying can be used.

[0065] <Applications of Carbon Nanotube Assemblies> The applications of the CNT aggregates according to this disclosure are not particularly limited. Because the CNT aggregates according to this disclosure have high conductivity, they can be suitably used, for example, as conductive additives (especially conductive additives for negative electrodes). Because the CNTs in the CNT aggregates according to this disclosure intertwine with each other and easily form conductive paths, they can be used, for example, in combination with conductive materials such as positive electrode active materials and negative electrode active materials within an electrode to further improve the conductivity of the conductive materials. The CNT aggregates according to this disclosure can be used, for example, together with known conductive additives such as graphite and Ketjenbrak.

[0066] <Method for producing CNTs> The method for producing the CNTs constituting the CNT aggregates according to this disclosure is not particularly limited. For example, as a method for producing CNTs in this disclosure, conventionally known methods such as chemical vapor deposition (CVD) and a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst can be applied.

[0067] The CNTs in this disclosure can be manufactured by referring to, for example, the methods described in Japanese Patent Publication No. 2016-102047, Japanese Patent Publication No. 2021-527611, etc.

[0068] The following describes the manufacturing method of CNTs in this disclosure with examples. However, the manufacturing method of CNTs in this disclosure is not limited to the following examples.

[0069] =Manufacturing Method X= An example of a method for manufacturing CNTs as referenced in this disclosure is the manufacturing method described in Japanese Patent Application Publication No. 2016-102047. That is, a manufacturing method (hereinafter also referred to as "Manufacturing Method X") that includes the steps of passing a gaseous reactant containing one or more carbon sources through a reactor, reacting one or more gaseous reactants in the reaction region of the reactor in the presence of a catalyst to form carbon-containing product particles, agglomerating the product particles into aggregates, and applying force to the aggregates to continuously move the aggregates out of the reaction region.

[0070] According to manufacturing method X, CNTs containing ULCNTs can be obtained in the form of easily handled fibrous aggregates or other aggregates.

[0071] In manufacturing method X, the force applied to the product particles may be a mechanical force. If the aggregate is fibrous CNT, the mechanical force applied to the product particles can be applied by a rotating spindle around which the aggregate is wound. The fibrous CNT may be collected on the spindle, or it may be accumulated elsewhere after being rotated around the spindle once or more times, as the spindle is continuously unwound.

[0072] Preferably, the spindle axis is positioned perpendicular or parallel to the flow direction of one or more gaseous reactants, but it may be positioned in other orientations. For example, a spindle with its axis positioned at a 25° angle to the flow direction of the gaseous reactants can also be suitably used to apply mechanical force to product particles.

[0073] The spindle can rotate around two axes (for example, two vertical axes). In particular, the spindle can rotate around axes perpendicular and parallel to the flow direction of the gaseous reactant. Such a spindle allows for the pulling and twisting of aggregates, which are fibrous carbon nanotubes, to control the number of twists and length.

[0074] The spindle material may be metal, ceramic, or resin. The spindle can take on different suitable shapes depending on the material properties and the intended use of the CNTs. The spindle can be used, for example, as a mold for producing carbon products by a spin-coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0075] Fibrous carbon nanotubes (CNTs) are accumulated on the spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and reaction conditions, or by applying an electric field or other field to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by the fluidity of the gas.

[0076] The spindle rotation speed is preferably 0.01 rpm (revolutions per minute; the same applies hereafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the spindle rotation speed) may be adjusted so that the material is recovered at the same rate as it is produced. The spindle rotation speed may be used to control the thickness of the accumulated fibrous CNTs. In one preferred embodiment, as the spindle rotates, the fibrous CNTs are processed in the axial direction of the spindle. In this processing, the fibrous CNTs are wound evenly along the spindle, rather than being wound at only one specific point on the spindle.

[0077] Fibrous CNTs may be recovered onto the reactor wall, for example, by a substrate placed in the reactor. The substrate may be a fixed substrate or a rotating guide used to apply a strong and equal force to the fibrous CNTs when they are recovered. A suitable substrate arrangement used in fiber technology is a substrate consisting of two guides positioned orthogonally to each other.

[0078] In manufacturing method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow can be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube located downstream of the reaction region. A vacuum may be applied to the product particles.

[0079] Other forces applied to the product particles include electrostatic forces appropriately applied by a charged plate. When using electrostatic forces, the product particles must be charged. By using a charged plate, CNTs can be generated on the plate in the form of intertwined sheets.

[0080] Furthermore, other forces applied to the generated particles may include magnetic force or photon pressure applied by a light source.

[0081] The raw material for CNTs may be injected in the form of a liquid containing a carbon source, instead of a gaseous reactant containing a carbon source. When a liquid is used as the raw material for CNTs, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0082] One or more gaseous reactants are preferably reacted at 500°C to 1600°C, and more preferably at 1000°C to 1500°C. The temperature gradient is maintained within the reactor, and the reaction region is preferably kept at a higher temperature than the product region of the reactor.

[0083] The gaseous reactant may be used in combination with one or more gases that act as diluents. The gaseous reactant may also be used in combination with gases that do not play a direct role in the reaction but play an auxiliary role. If amorphous carbon is produced as a byproduct, it is also preferable to use a gas as a diluent that can react with amorphous carbon to maintain the reaction sites on the catalyst and produce nanotubes.

[0084] Gases that can be used as diluents include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, and helium. Among these, hydrogen is particularly preferred as a diluent.

[0085] The composition of the product particles can be controlled by monitoring the aggregates and changing the reaction conditions based on the information obtained. For example, aggregates can be monitored by online Raman spectroscopy. Online Raman spectroscopy provides data indicating whether the CNTs are single-layer or multi-layer. It also provides data indicating the diameter and crystallinity of the CNTs. Aggregates can also be monitored by online conductivity measurement, gas analysis, measurement of the opacity of the reaction region, and / or measurement of the winding force.

[0086] When removing aggregates from the reactor, it is preferable to prevent air from entering the reactor. Preventing air inflow is particularly important, for example, when the diluent gas contains hydrogen, as it helps to prevent the formation of an explosive mixture of hydrogen and air in the reactor.

[0087] In manufacturing method X, it is preferable to control the reactor temperature to 200°C to 700°C when removing the aggregates from the reactor. The bundle diameter of the CNTs can be controlled by the temperature of the reaction region of the CNTs and the reactor temperature when removing the aggregates from the reactor. The higher the reactor temperature when removing the aggregates from the reactor, the larger the bundle diameter of the CNTs can be. For example, by setting the reactor temperature when removing the aggregates from the reactor to about 150°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 110 nm to 170 nm. By setting the reactor temperature when removing the aggregates from the reactor to about 500°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 200 nm to 230 nm. By setting the reactor temperature when removing the aggregates from the reactor to about 750°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 300 nm to 400 nm. The "reactor temperature" refers to the temperature determined by measuring the gas temperature at the outlet from which the condensed material is removed from the reactor.

[0088] The product particles produced in manufacturing method X contain ULCN. Depending on the manufacturing conditions, SWCNTs and MWCNTs may also be present.

[0089] The product particles may be generated by chemical vapor deposition. When the product particles are generated by chemical vapor deposition, the carbon source, which is a gaseous reactant, reacts in the presence of a catalyst.

[0090] Suitable carbon-containing compounds as carbon sources include carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, or hydrocarbons containing two or more of these). Carbon monoxide, methane, ethylene, or acetylene are preferred as carbon-containing compounds.

[0091] The carbon source preferably contains oxygen. Ethanol is a particularly preferred carbon source. Oxygen can be introduced into the reactor by other means, for example, by using a carbon source containing a diluent gas or water.

[0092] As catalysts, transition metals are preferred, particularly chromium (Cr), molybdenum (Mo), tungsten (W), or VIII-B transition metals. Specifically, preferred catalysts include, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt) or manganese (Mn), or mixtures thereof. Metals from the lanthanide and actinide series (e.g., yttrium (Y)) can also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof are preferred, for example, a mixture of Ni and Co (mass ratio: 50 / 50), a mixture of Fe and Ni, or a mixture of Fe and Mo are more preferred. Any of these transition metals can be used alone or in combination with any of the other transition metals listed above to function as catalysts for the growth of CNTs. The catalyst is particularly preferably a mixture of two or more of the listed metals.

[0093] The catalyst is preferably formed by the decomposition of a precursor. The precursor is preferably a thermal, photocatalytic, or plasma-degradable compound of one or more of the above-mentioned metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickerocene, and cobaltocene are particularly preferred as precursors. In some embodiments, at least 0.01% by mass of the precursor is contained in the carbon source, preferably 0.2% to 30% by mass of the precursor, and more preferably 0.2% to 20% by mass of the precursor. In some embodiments, 0.23% to 2.3% by mass of the precursor may be contained in the carbon source, and 0.02% to 20% by mass of the precursor. The catalyst may also be used supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0094] The carbon source is preferably reacted in the presence of an accelerator. Suitable accelerators are one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is also a preferred accelerator. Preferably, the accelerator is contained in the carbon source at a concentration of up to 10% by mass. Preferably, the accelerator is contained in the carbon source at a concentration of 0.2% to 6% by mass. When high or low concentrations of thiophene are used as the accelerator, MWCNTs are formed.

[0095] According to manufacturing method X, fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm, can be obtained. The fibrous CNTs can take the form of threads or sheets. The length of the fibrous CNTs can be controlled, for example, by the winding capacity of the spindle used when manufacturing the fibrous CNTs.

[0096] The manufacturing method X preferably includes the steps of generating CNTs by reacting a carbon source in the reaction region of a reactor, and agglomerating the CNTs into aggregates by applying force to them. This manufacturing method makes it possible to easily produce fibrous CNTs.

[0097] The manufacturing method X preferably further includes a step of purifying the obtained CNT aggregates after the step of agglomerating CNTs into aggregates. Specifically, first, the CNT aggregates are washed with alcohol (e.g., methanol, ethanol, etc.). Next, they are washed with an alkaline solution (e.g., ammonia water). The pH of the alkaline solution is, for example, 8 to 11. Furthermore, they are washed with pure water.

[0098] The cleaning method is not particularly limited and may involve spraying a cleaning solution onto the CNT aggregates or immersing the CNT aggregates in a cleaning solution. Cleaning with alcohol removes alcohol-soluble components contained in the CNT aggregates. Cleaning with an alkaline solution hydrolyzes and removes impurities contained in the CNT aggregates. Cleaning with an acidic solution may also be performed.

[0099] It is preferable to dry the CNT aggregates after washing. The drying method is not particularly limited and can be carried out by commonly known methods.

[0100] By purifying the aggregates of carbon nanotubes (CNTs), the metal content in the CNTs can be reduced.

[0101] The manufacturing method X preferably further includes a step of passing the purified CNT aggregates through a sieve after the step of purifying the CNT aggregates. It is also preferable to recover the CNTs that have passed through the sieve.

[0102] The method of passing the material through the sieve is not particularly limited and can be carried out by commonly known methods. The mesh size of the sieve is, for example, 0.1 mm to 3.0 mm, preferably 0.5 mm to 2.0 mm, and more preferably 1.0 mm to 1.5 mm. The material of the sieve is not particularly limited and may be metal or resin. When the CNT aggregate is applied to an electrode (especially an electrode for a lithium-ion battery), it is preferable that the material does not impair the performance of the battery. The number of times the material is passed through the sieve is, for example, 1 to 3 times. Before passing the CNT aggregate through the sieve, the CNT aggregate may be crushed to an appropriate size beforehand. Crushing can be done using a crusher. Examples of crushers include roll mills, cutter mills, hammer mills, etc.

[0103] By passing the obtained CNT aggregates through a sieve and recovering the CNTs that pass through the sieve, coarse CNTs are removed, improving the stability of the CNT dispersion. In addition, while foreign matter introduced from the outside is generally removed during electrode manufacturing, passing the obtained CNT aggregates through a sieve allows for a simpler method of removing foreign matter introduced from the outside.

[0104] In other embodiments, the method may include generating CNTs containing ULCNTs in a reaction region by the above method, condensing them to form CNTs containing ULCNTs, and continuously withdrawing CNTs from near the reaction region. In yet other embodiments, the method may include generating CNTs containing ULCNTs in a reaction region, continuously electrostatically attracting CNTs containing ULCNTs from the reaction region, and recovering CNTs containing ULCNTs.

[0105] =Manufacturing Method Y= In this disclosure, as an example of a method for manufacturing CNTs, the manufacturing method described in Japanese Patent Publication No. 2021-527611 can be referenced. That is, a mixture containing a main catalyst precursor and a co-catalyst precursor is γ-Al ２ O ３A manufacturing method (hereinafter also referred to as "manufacturing method Y") includes the steps of: (1) supporting the active support on a material to produce an active support; (2) drying the active support by multi-stage drying including vacuum drying; (3) heat-treating the dried active support to produce a supported catalyst; and (4) producing CNTs in the presence of the supported catalyst.

[0106] Step (1) Step (1) involves mixing a main catalyst precursor and a co-catalyst precursor in γ-Al ２ O ３ The active support is manufactured by supporting it on a material.

[0107] The main catalyst precursor and co-catalyst precursor are γ-Al ２ O ３ To ensure uniform support, the mixture may further contain a solvent, and the main catalyst precursor and co-catalyst precursor may be dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, with water being preferred.

[0108] γ-Al ２ O ３ Because it has high porosity and a spinel structure, the main catalyst and co-catalyst are γ-Al ２ O ３ They can be arranged irregularly. CNTs grown from an irregularly arranged main catalyst can be produced in an entangled manner.

[0109] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese, and chromium, with cobalt being preferred.

[0110] The main catalyst precursor may be one or more selected from the group consisting of nitrates, sulfates, carbonates, and acetates of the main catalyst, with nitrates of the main catalyst being preferred.

[0111] The main catalyst precursor is Co(NO ３ ) ２ Co(NO ３ ) ２ 6H ２ O, Co ２ (CO) ８ Co ２ (CO) ６ [HC=C(C(CH ３ )３ ) ], Co (CH ３ CO ２ ) ２ Fe(NO ３ ) ３ Fe(NO ３ ) ２ nH ２ O, Fe(CH ３ CO ２ ) ２ Ni (NO ３ ) ２ Ni (NO ３ ) ２ 6H ２ O, Mn (NO ３ ) ２ , Mn(NO ３ ) ２ 6H ２ O, Mn(CH ３ CO ２ ) ２ ・n(H ２ O) and Mn(CO) ５ It may be one or more selected from the group consisting of Br, and among these, Co(NO ３ ) ２ 6H ２ O, Fe (NO ３ ) ２ nH ２ O, Ni (NO ３ ) ２ 6H ２ O is preferred.

[0112] The co-catalyst improves the dispersibility of the main catalyst and may be one or more selected from the group consisting of vanadium and molybdenum.

[0113] The co-catalyst precursor is NH ４ VO ３ NaVO ３ , V ２ O ５ , V(C ５ H ７ O ２ ) ３ , and, (NH ４ ) ６ Mo ７ O ２４ 4H ２ It may be one or more selected from the group consisting of O, and NH４ VO ３ and (NH ４ ) ６ Mo ７ O ２４ ·4H ２ One or more selected from the group consisting of O is preferable.

[0114] When the mixture contains two or more cocatalyst precursors, that is, when it contains both a vanadium precursor and a molybdenum precursor, the mixture can be contained such that the molar ratio of the sum of vanadium and molybdenum to vanadium is 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and it is preferable that the mixture is contained such that the molar ratio is 1:0.5 to 1:0.9. When the above conditions are satisfied, the structure of CNTs can be stably maintained, and CNTs having a target pore volume can be produced.

[0115] The mixture can contain the main catalyst precursor and the cocatalyst precursor such that the molar ratio of the main catalyst to the cocatalyst is 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, and it is preferable that the mixture is contained such that the molar ratio is 1:0.1 to 1:0.25. When the above molar ratio is satisfied, the dispersibility of the main catalyst can be improved, and CNTs having a target pore volume can be produced.

[0116] The mixture may further contain an organic acid that functions to suppress precipitation of the main catalyst precursor and the cocatalyst precursor.

[0117] The organic acid may be one or more selected from the group consisting of citric acid, tartaric acid, fumaric acid, malic acid, acetic acid, butyric acid, palmitic acid, and oxalic acid, with citric acid being preferred.

[0118] The mixture can contain the organic acid and the cocatalyst precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, and a molar ratio of 1:3 to 1:6 is preferable. When the above range is satisfied, there is an advantage that a transparent catalytic metal solution can be produced during production of the catalyst, and a catalyst with suppressed fine powder during impregnation can be produced.

[0119] After step (1), a ripening step may be further included.

[0120] The maturation process may be carried out for 1 to 60 minutes or 10 to 50 minutes. It is preferable to carry it out for 10 to 50 minutes. When the above conditions are met, the main catalyst precursor and co-catalyst precursor can be sufficiently supported on the γ-Al2O3. Furthermore, air bubbles present within the support are removed to the maximum extent possible, and the main catalyst precursor and co-catalyst precursor can be sufficiently supported even in the micropores within the support.

[0121] Step (2) Next, the active support is dried by multi-stage drying, which includes vacuum drying.

[0122] Multi-stage drying can mean that a drying process, including vacuum drying, is performed two or more times. Specifically, multi-stage drying may include atmospheric pressure drying and vacuum drying, or it may include vacuum drying alone two or more times.

[0123] Vacuum drying may be carried out at 80°C to 300°C or 120°C to 250°C, with 120°C to 250°C being preferred. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0124] Vacuum drying may be performed at 1 mbar to 200 mbar or 30 mbar to 150 mbar, and is preferably performed at 30 mbar to 150 mbar. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, is rapidly decomposed and discharged, so that the main catalyst oxide can be formed more easily under vacuum conditions and energy consumption can be minimized.

[0125] Vacuum drying can be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, with 10 minutes to 2 hours being preferred. When the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0126] On the other hand, if multi-stage drying includes atmospheric pressure drying and vacuum drying, atmospheric pressure drying can be performed before the vacuum drying described above, and atmospheric pressure drying can remove any solvents that may be present in the active carrier.

[0127] Atmospheric pressure drying may be carried out at 80°C to 160°C or 100°C to 140°C, and is preferably carried out at 100°C to 140°C. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0128] Atmospheric pressure drying may be carried out at 900 mbar to 1,100 mbar, and preferably at 950 mbar to 1,050 mbar. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0129] Atmospheric pressure drying may be carried out for 1 to 12 hours, and preferably for 3 to 9 hours. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0130] On the other hand, if multi-stage drying includes two or more vacuum drying steps, it may include two or more vacuum drying steps performed at different temperatures, more specifically, a primary vacuum drying step performed at a first temperature and a secondary vacuum drying step performed at a second temperature higher than the first temperature.

[0131] Primary vacuum drying can remove any solvents that may be present in the active carrier.

[0132] The first temperature may be between 80°C and 160°C, and is preferably between 100°C and 140°C. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0133] Primary vacuum drying can be performed for 1 to 12 hours, preferably 3 to 9 hours. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0134] Primary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 80 mbar to 150 mbar, with 80 mbar to 150 mbar being preferred. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0135] The explanation regarding secondary vacuum drying is as described in the explanation of vacuum drying above.

[0136] The second temperature may be between 175°C and 300°C, and is preferably between 180°C and 280°C. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0137] Secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, with 1 mbar to 70 mbar being more preferable. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, is rapidly decomposed and discharged, so that the main catalyst oxide can be formed more easily under vacuum conditions and energy consumption can be minimized.

[0138] Secondary vacuum drying may be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, and is preferably performed for 10 minutes to 2 hours. When the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0139] Step (3) Next, the dried active support is subjected to heat treatment to produce a supported catalyst.

[0140] When heat treatment is performed, the main catalyst and co-catalyst are converted into γ-Al ２ O ３ A supported catalyst is manufactured that exists as a coating on the surface and pores of the material.

[0141] The heat treatment may be carried out at 600°C to 800°C or 620°C to 750°C, and is preferably carried out at 620°C to 750°C. When the above conditions are met, the supported catalyst can be manufactured in which the main catalyst and co-catalyst are uniformly coated on the surface and pores of γ-Al2O3, and energy consumption can be minimized.

[0142] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, and is preferably carried out for 2 to 8 hours. When the above time is met, the catalyst precursor is γ-Al ２ O ３ A supported catalyst can be manufactured that exists in a state where it is uniformly coated on the surface and pores.

[0143] Step (4) Next, CNTs are produced in the presence of a supported catalyst.

[0144] In detail, carbon nanotubes (CNTs) can be produced by contacting a supported catalyst with a carbon-based compound. Specifically, this may be done by chemical vapor phase synthesis.

[0145] To describe in detail the steps for producing CNTs, first, a supported catalyst can be introduced into a horizontal fixed-bed reactor or a fluidized-bed reactor. Next, a gaseous carbon-based compound, or a mixed gas of a gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen), is injected at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the catalyst, and CNTs can be grown by chemical vapor-phase synthesis through the decomposition of the gaseous carbon-based compound.

[0146] CNTs produced by the chemical vapor phase synthesis method described above have crystal growth directions that are nearly parallel to the tube axis, and the graphite structure exhibits high crystallinity along the length of the tube. As a result, CNTs with small unit diameters and high conductivity and strength can be produced.

[0147] The chemical vapor phase synthesis method may be carried out at 600°C to 800°C or 650°C to 750°C, and is preferably carried out at 650°C to 750°C. By satisfying the above temperature range, CNTs can be produced while minimizing the generation of amorphous carbon.

[0148] Possible heat sources for the reaction include induction heating, radiant heat, lasers, IR, microwaves, plasma, and surface plasmon heating.

[0149] Furthermore, carbon-based compounds can be used without particular restrictions, as long as they can supply carbon and exist in a gaseous state at temperatures above 300°C.

[0150] The carbon-based compound may be a carbon-based compound having six or fewer carbon atoms, and may be one or more selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene.

[0151] After growing CNTs by the reaction described above, a cooling step may be selectively performed to further align the CNTs in a more regular manner. Specifically, the cooling step can be carried out by natural cooling by removing the heat source or by using a cooler or the like.

[0152] The above-described manufacturing methods X and Y are examples, and the manufacturing methods for CNTs that may be included in a CNT aggregate are not limited to those described above.

[0153] <Carbon Nanotube Dispersion> In this disclosure, a carbon nanotube dispersion (CNT dispersion) is a dispersion containing a CNT aggregate and a dispersion medium. The CNT dispersion exhibits good dispersibility of the CNT aggregate in the dispersion medium and has excellent conductivity. The CNT dispersion is preferably used for electrode formation, transparent conductive film formation, resin additives, conductive inks, coatings, antistatic agents, paints, etc.

[0154] -CNT aggregates- The CNT aggregates contained in the CNT dispersion are the same as the CNT aggregates related to this disclosure described above, so their explanation is omitted here.

[0155] -Dispersion medium- The dispersion medium preferably contains water, and more preferably contains water as its main component. "Containing water as its main component" means that the proportion of water in the dispersion medium is more than 50% by mass. The proportion of water in the dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and may be, for example, 100% by mass.

[0156] The water is not particularly limited, but it is preferable to use distilled water, deionized water, or pure water, for example, because it contains fewer impurities.

[0157] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of hydrophilic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0158] The CNT dispersion may further contain other components that can be used in the dispersion, in addition to the CNT aggregate and dispersion medium. Examples of other components include dispersants, defoamers, antistatic agents, and conductive additives other than the conductive additives described herein. It may also further contain trace amounts of impurities, so-called unavoidable impurities.

[0159] - Dispersant - The CNT dispersion may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the CNT aggregate. The dispersant is not particularly limited and, for example, various surfactants can be used. Polymer compounds such as resins can also be used as dispersants. A surfactant is preferred as the dispersant. The surfactant may be an ionic surfactant or a nonionic surfactant and is not particularly limited. In the CNT dispersion, the surfactant can be used alone or in a mixture of two or more types.

[0160] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid-based surfactants such as alkylbenzene sulfonates (e.g., dodecylbenzenesulfonic acid) and dodecylphenyl ether sulfonates; ether sulfate-based surfactants; phosphate-based surfactants; and carboxylic acid-based surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine-based surfactants and amine oxide-based surfactants. As for ionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic ionic surfactants) are preferred, and aromatic sulfonic acid-based surfactants such as alkylbenzene sulfonates and dodecylphenyl ether sulfonates are more preferred. Aromatic ionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration properties for CNT aggregates.

[0161] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene polypropylene glycol; and aromatic nonionic surfactants such as polyoxyalkylene octylphenyl ether, polyoxyalkylene nonylphenyl ether, polyoxyalkyldibutylphenyl ether, polyoxyalkyl styrylphenyl ether, polyoxyalkyl benzylphenyl ether, polyoxyalkylbisphenyl ether, polyoxyalkylcumylphenyl ether, and polyoxyalkylene phenyl ether. As nonionic surfactants, ionic surfactants having aromatic rings (so-called aromatic nonionic surfactants) are preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration properties for CNT aggregates.

[0162] Other dispersants that excel in dispersing ability, dispersion stability, and high concentration of CNTs include Demol (registered trademark: hereinafter the same) N, Demol RN, and Demol T (manufactured by Kao Corporation), which are sodium salts of β-naphthalene sulfonic acid formalin condensate; Brij S 100 (manufactured by Sigma-Aldrich), which is polyoxyethylene stearyl ether; polyvinylpyrrolidone K30 (e.g., manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (e.g., manufactured by Daicel Mirise Co., Ltd.); sodium deoxycholate (e.g., manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.); SOLSPERSET™ W100 and SOLSPERSET™ W150 (manufactured by Nippon Lubrizol Co., Ltd.). CMC is particularly preferred from the viewpoint of excelling in dispersing ability, dispersion stability, and high concentration of CNT aggregates.

[0163] When the CNT dispersion contains a dispersant, the amount of dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of CNT aggregate, the amount of dispersion medium, etc.

[0164] -Method for Manufacturing CNT Dispersion- The method for manufacturing a CNT dispersion is not particularly limited. A CNT dispersion can be manufactured by dispersing CNT aggregates in a dispersion medium. That is, a CNT dispersion can be manufactured by a method that includes a step of dispersing CNT aggregates in a dispersion medium (also called the "dispersion step"). The dispersion mediums that can be used in the dispersion step are as described above.

[0165] The dispersion method is not particularly limited. Examples of dispersion methods include using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Other examples of dispersion methods include using known grinding means, such as ball milling (e.g., ball mill, vibrating ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressurized kneader. The method using a jet mill is preferred, and the method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pumps a mixture in a solvent as a high-speed flow from a nozzle placed in a sealed state inside a pressure vessel. In a wet jet mill, CNT aggregates are dispersed within a pressure vessel by collisions between opposing flows, collisions with the vessel wall, turbulence and shear flow generated by high-speed flow, etc. A suitable wet jet mill is an ultra-high pressure homogenizer manufactured by Jōkō Co., Ltd. (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.). However, the wet jet mill is not limited to these. When using the above-mentioned ultra-high pressure homogenizer as the dispersion device, the dispersion processing pressure is preferably 10 MPa to 250 MPa.

[0166] The method for producing a CNT dispersion may include a step of drying the CNT aggregate (also called a "drying step") before the dispersion step described above.

[0167] If moisture adheres to the CNTs, the surface tension of the water can cause the CNTs to stick together, raising concerns about reduced dispersibility. Therefore, by performing a drying step of the conductive additive before the dispersion step, moisture adhering to the CNTs is removed, preventing the CNTs from sticking together due to moisture, and further improving the dispersibility of the CNTs in the dispersion medium. The drying method is not particularly limited. Examples of drying methods include heating drying, vacuum drying, and heating vacuum drying. Heating vacuum drying is preferred as the drying method. The drying temperature is not particularly limited, but is preferably, for example, 40°C to 100°C. The drying time is not particularly limited and can be set appropriately depending on the drying temperature, the degree of moisture adhering to the CNT aggregate in this disclosure, etc.

[0168] The following are examples of CNT dispersion manufacturing methods, but the manufacturing of CNT dispersions is not limited to those shown below.

[0169] -Example of Dispersion Preparation- 0.040 g of the CNT aggregate according to this disclosure is weighed and placed in a three-necked flask. After adding the CNT aggregate, a large excess of deionized water, which is the dispersion medium, is added to the flask (e.g., 20 mL), and the mixture is stirred at room temperature (25°C, the same applies hereafter). At this time, a known dispersant (e.g., carboxymethylcellulose) may be added as appropriate. Next, the conductive additive is dispersed in the dispersion medium using a known dispersion device (e.g., an ultrasonic irradiation device or a wet jet mill). The obtained dispersion is further stirred with a stirrer at room temperature for a long time (e.g., 1 hour to 48 hours). In this way, a CNT dispersion is obtained.

[0170] (Conductive Material) The conductive material relating to this disclosure includes the CNT aggregate relating to this disclosure. As described above, the CNT aggregate contained in the conductive material relating to this disclosure has high conductivity and excellent dispersibility when dispersed, making it suitable as a conductive additive. Because the conductive material relating to this disclosure includes the CNT aggregate relating to this disclosure, it has excellent conductivity and can effectively impart high conductivity to the object to be used.

[0171] The conductive material according to the present disclosure may contain a known conductive aid such as graphite, Ketjenblack, or the like. In addition, the conductive material according to the present disclosure may contain CNTs other than the CNT aggregate according to the present disclosure.

[0172] The conductive material according to the present disclosure can be used as one type of electrode material. An example of an electrode formed using the electrode material includes an electrode included in a secondary battery. Hereinafter, an embodiment of an electrode and a secondary battery including the electrode will be described.

[0173] (Electrode) The electrode can include the CNT aggregate according to the present disclosure described above. In the electrode, the CNT aggregate according to the present disclosure can function as a conductive aid. The CNT aggregate included in the electrode described below has the same definition as the CNT aggregate according to the present disclosure, and preferred embodiments thereof are also the same, so the description of the CNT aggregate is omitted herein.

[0174] The electrode may be at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, and may also include a current collector and an electrode active material layer disposed on the current collector.

[0175] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. Examples of the current collector include those obtained by surface-treating the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum or stainless steel with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal having good carbon adsorptivity, such as copper or nickel, may be used as the current collector.

[0176] The electrode active material layer can contain an electrode active material. The electrode active material is preferably electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer may contain a positive electrode active material that is commonly used for positive electrode materials. Specifically, examples of the positive electrode active material include lithium cobalt oxide (LiCoO ２ ), layered compounds such as lithium nickel oxide (LiNiO ２ ), compounds substituted with one or more transition metals; LiFe３ O ４ Lithium iron oxides such as Li １＋ｃ１ Mn ２－ｃ１ O ４ (0≦c1≦0.33), LiMnO ３ LiMn ２ O ３ LiMnO ２ Lithium manganese oxides such as lithium copper oxide (Li ２ CuO ２ ); LiV ３ O ８ , V ２ O ５ ,Cd ２ V ２ O ７ Vanadium oxides such as LiNi; chemical formula LiNi １－ｃ２ M ｃ２ O ２ Ni-site type lithium nickel oxide represented by the chemical formula LiMn (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c² ≤ 0.66). ２－ｃ３ M ｃ３ O ２ (Here, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1.), or Li ２ Mn ３ MO ８ Lithium manganese composite oxide represented by (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. ２ O ４ These are some examples.

[0177] When the electrode is a negative electrode, the electrode active material is not particularly limited, and the electrode active material layer may include negative electrode active materials commonly used for negative electrode materials. Specifically, the negative electrode active material may include graphite-based active material particles or silicon-based active material particles. As graphite-based active material particles, at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads may be used. By using artificial graphite as graphite-based active material particles, rate characteristics can be improved. As silicon-based active material particles, at least one selected from the group consisting of Si, SiOx (0 < x < 2), Si-C composite, and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements, rare earth elements, and combinations thereof) may be used. By using silicon-based active material particles, the battery capacity can be increased.

[0178] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer may include binders commonly used in electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers are substituted with Li, Na, Ca, etc.

[0179] (Secondary Battery) A secondary battery may comprise a negative electrode, a positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. At least one of the positive and negative electrodes is an electrode formed using an electrode material including a CNT aggregate according to this disclosure.

[0180] A separator separates the negative electrode from the positive electrode and provides a passage for lithium ions to move. It is generally not limited to any separator commonly used in secondary batteries. Preferably, the separator has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, a porous polymer film can be used as a separator. The porous polymer film may be, for example, a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure in which two or more of these films are laminated. Alternatively, the separator may be a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, the separator may be coated with a ceramic component or polymer substance to ensure heat resistance or mechanical strength. The separator can selectively have a single-layer or multi-layer structure.

[0181] The electrolyte is not particularly limited and can include, for example, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0182] Specifically, the electrolyte may include non-aqueous organic solvents and metal salts. Examples of non-aqueous organic solvents include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate, which are aprotic organic solvents.

[0183] Among carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high dielectric constants as high-viscosity organic solvents and readily dissociate lithium salts. It is even more preferable to use a mixture of such cyclic carbonates with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions as a non-aqueous organic solvent, as this yields an electrolyte with high electrical conductivity.

[0184] The metal salt may also be a lithium salt. Lithium salts are readily soluble in non-aqueous electrolytes. For example, the anion portion of the lithium salt may be F － , Cl － , I － NO ３ － , N (CN) ２ － BF ４ － , ClO ４ － , PF ６ － (CF ３ ) ２ PF ４ － (CF３ ) ３ PF ３ － , (CF ３ ) ４ PF ２ － , (CF ３ ) ５ PF － , (CF ３ ) ６ P － , CF ３ SO ３ － , CF ３ CF ２ SO ３ － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) ２ N － , CF ３ CF ２ (CF ３ ) ２ CO － , (CF ３ SO ２ ) ２ CH － , (SF ５ ) ３ C － , (CF ３ SO ２ ) ３ C － , CF ３ (CF ２ ) ７ SO ３ － , CF ３ CO ２ － , CH ３ CO ２ － , SCN － , and (CF ３ CF ２ SO ２ ) ２ N － may be mentioned.

[0185] In addition to non-aqueous organic solvents and metal salts, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycemic (glyme), hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride.

[0186] The secondary battery described above can constitute a battery module containing the secondary battery as a unit cell, and a battery pack containing the battery module. The battery module and battery pack can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0187] (Planar Assembly) The planar assembly relating to this disclosure includes the CNT assembly relating to this disclosure. The proportion of the CNT assembly relating to this disclosure contained in the planar assembly relating to this disclosure is usually 1% by mass or more with respect to the total mass of the planar assembly. The planar assembly relating to this disclosure may also contain other components such as CNT assemblies (in particular CNT assemblies) with a maximum length of less than 1000 μm.

[0188] <Method for producing a planar aggregate> The method for producing the planar aggregate according to this disclosure is not particularly limited. The planar aggregate according to this disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate by dispersing the CNT aggregate according to this disclosure, or the CNT aggregate according to this disclosure and other components such as CNT aggregates with a maximum length of less than 1000 μm (particularly CNT aggregates) in water or other fluid and filtering it once or twice or more.

[0189] Examples of planar aggregates relating to this disclosure include films.

[0190] The planar assemblies relating to this disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0191] (Laminate) The laminate according to the present disclosure comprises a substrate and a planar assembly according to the present disclosure. The substrate and the planar assembly may be in direct contact, or other layers may be arranged between the substrate and the planar assembly. Alternatively, the planar assembly according to the present disclosure may be arranged on the substrate, and yet another layer may be arranged on the planar assembly.

[0192] The material constituting the substrate may be resin, glass, or fiber. Examples of resins include polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin polymer (COP), triacetate (TAC), cyclic olefin copolymer (COC), poly(vinyl chloride) (PVC), polyethylene 2,6-naphthalate (PEN), polyimide (PI), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), polyacetal (POM), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polyphenylene ether (PPE), polysulfone (PSU), polyether ether ketone (PEEK), and polyamide-imide (PAI). Examples of glass include float glass (SiO2). ２ Na ２ Examples include sodium chloride (containing O, CaO, and MgO), soda lime, aluminosilicate glass, and borosilicate glass. Examples of fibers include synthetic fibers such as polyester fibers, polyamide fibers, polyolefin fibers, and acrylic fibers; and natural fibers such as cotton, linen, silk, wool, cashmere, mohair, alpaca, jute, hemp, and ramie.

[0193] The planar aggregate preferably contains a binder in addition to the CNT aggregate according to this disclosure. The binder is preferably a polymer and preferably contains at least one selected from the group consisting of polymers containing constituent units derived from vinylidene chloride (e.g., polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer, etc.), polyimide, polysiloxane, and epoxy resin.

[0194] (Method for measuring the mean curvature in carbon nanotube aggregates) The method for measuring the mean curvature in carbon nanotube aggregates according to this disclosure involves performing the following steps 1 to 3 on two or more images of the carbon nanotube aggregate using the image analysis software ImageJ (version 1.54g) and the Kappa plugin (version 2.0.0) to calculate the mean curvature. 1. Adjust the image size using Image:Adjust:Size, Width=1280. Set the screen size to 1280 x 960 and the width to 1410 nm. 2. Using the following conditions: Plugin:Analyze:Kappa, File:OpenActiveImage, and CurveFittingOptions:ChoosePoints=100,DataThreshold=10, Scale(μm / pixel)=0.16, the curve is finely adjusted to follow the center of the fiber. 3.1 After calculating approximately eight center lines per field of view, the curvature of each line and the mean curvature are calculated.

[0195] ImageJ is open-source, public-domain image processing software. By using it and employing the Kappa curvature analysis mode, it becomes possible to draw lines around each bundle in a carbon nanotube assembly for analysis, and the curvature of each bundle can be easily calculated.

[0196] The following examples will provide a more detailed explanation of the CNT aggregates, etc., related to this disclosure. This disclosure is not limited to the following examples, unless it exceeds the spirit of the disclosure.

[0197] (Example 1) 1. Production of Sheet-like CNT Assembly 1 Sheet-like CNT assembly 1 was produced by a floating catalyst method (CVD method) in which the self-assembly of CNT bundles directly interacts with the catalyst in the gas phase. A cylindrical reactor with an inner diameter of 85 mm was used as the CNT reactor. First, ferrocene, as a metal catalyst precursor containing Fe atoms, and thiophene, as an accelerator, were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled to 120°C. Hydrogen gas was used as the carrier gas. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor decomposes. The region in which the metal catalyst precursor decomposes is referred to as the first temperature zone.

[0198] Next, methane, the carbon source, was released into the carrier gas stream. The metal catalyst and carbon source were supplied to a second temperature zone, located downstream of the first temperature zone and controlled to 1400°C. The total gas supply flow rate for the carrier gas and source gas was set to 36 NL / min (NL is normal liters). The second temperature zone was maintained at a temperature sufficient to generate carbon nanotube aggregates.

[0199] In the second temperature zone, a reaction field was created within the temperature-controlled flow reactor, forming catalytic nuclei and rapidly growing CNTs, thereby generating CNT aggregates. The aggregates were discharged as continuous discharge through the outlet of the flow-type reactor, which was temperature-controlled to 500°C, and sheet-like CNT aggregates were collected.

[0200] The obtained sheet-like CNT aggregates were washed with methanol, immersed in a pH 10 diluted aqueous ammonia solution for 10 minutes, washed with pure water for 10 minutes, dried, crushed into a powder, and then passed through a sieve with a mesh size of 1.0 mm twice. The CNT aggregates that passed through the sieve were collected and designated as CNT aggregate 1.

[0201] 2. Preparation of CNT dispersion 1 The following materials were mixed and pre-dispersed by treating them with an Ace homogenizer manufactured by Nippon Seiki Co., Ltd. for 1 hour to obtain pre-dispersion 1.

[0202] -Dispersion composition- • CNT aggregate obtained above: 1.1 g • CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (manufactured by MP Biomedicals): 1.65 g • Purified water: 547.25 g

[0203] The main dispersion of pre-dispersion 1 was carried out using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion 1 with a concentration of 0.20% by mass. -Dispersion conditions- Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of passes: 8 Method: Circulation method

[0204] 3. Evaluation <Calculation of Mean Curvature> Images were taken of the CNT aggregate 1 of Example 1 using a scanning electron microscope (SEM), and eight images were selected from the obtained images in which the CNT bundles were clearly observed (one of which is Figure 1).

[0205] Using the above image, the average curvature of the CNT structure was calculated by image analysis. More specifically, the curvature of each image was calculated using image analysis software (ImageJ) following the procedure below.

[0206] - Calculation Procedure - 1. Image: Adjust: Size, Width = 1280 2. Plugin: Analyze: Kappa 3. File: OpenActiveImage 4. CurveFittingOptions: ChoosePoints = 100, DataThreshold = 10, Scale (μm / pixel) = 0.16 5. Select ControlPointTool and left-click along the center line of the CNT structure. 6. Press Enter and fine-tune the curve to follow the center of the fiber. 7. After calculating about 8 center lines per field of view, press ExportAveragePoints.

[0207] Based on the curvature calculated for each image, the average curvature was further calculated. The calculated average curvature Z(um) －１ The value was 0.010.

[0208] <Bundle Diameter Features> Image processing and analysis were performed on the selected images using Python. In image processing, the contours and centerlines of the CNTs were detected and combined with the original image. In image analysis, the bundle diameter was determined by calculating the distance from the centerline to the contour in the created image. Then, the product of the bundle diameter and the length of the centerline was calculated to determine the area occupied by the CNTs in the image. A histogram of bundle diameter and occupied area was created.

[0209] Using the calculated bundle diameter histogram, the bundle diameter features of each sample were calculated using the following method: 1. The bundle diameters and occupied areas of multiple fields of view of the same sample were added together and normalized so that the sum equaled 1. Following normalization, the unit of the vertical axis was set to occupied area ratio. 2. The total occupied area ratio of bundles with a bundle diameter of 100 nm or more was calculated. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.49. The cumulative 90% bundle diameter was 230 nm.

[0210] <Measurement of Cumulative 50% Particle Size D50 in Volume-Based Particle Size Distribution> CNT dispersion 1 was thoroughly stirred and then diluted with pure water. The resulting diluted solution was used as a sample, and the cumulative particle size D50 of the CNT dispersion was measured using a particle size analyzer (LA-960, laser diffraction particle size analyzer, Horiba, Ltd.). The particle refractive index of the CNTs was set to 1.920-0.522i. The refractive index of the solvent was set to 1.333. During measurement, CNT dispersion 1 was diluted by dropping it into pure water while observing the transmittance, and the measurement was performed after confirming that the particle size distribution on the monitor was stable. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of CNT aggregate 1 was 1.25 μm. The evaluation results are shown in Table 1 below.

[0211] <Viscosity of CNT dispersion> The viscosity of CNT dispersion 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, a cone-plate viscometer (BROOKFIELD DV-II+Pro PROGRAMMABLE VISCOMETER) was used to measure the viscosity. Measurement fixture: Cone-plate Measurement mode: Rotation mode Shear speed: 0.6 s －１ ~384 simultaneous －１Temperature: 25°C. From the obtained data, the shear rate was 12 s. －１ The viscosity was measured. The viscosity of the dispersion was 142.6 mPa·s. The common logarithmic representation of the viscosity was 2.15. It was determined that a CNT dispersion with appropriate viscosity was obtained if the viscosity of the dispersion was in the range of 10 mPa·s to 1500 mPa·s.

[0212] <Evaluation of CNT aggregate dispersion 1: Tensile strength, elongation at break, and energy density at break> A carbon nanotube dispersion was prepared by mixing CNT aggregate 1, 700 kDa of carboxymethylcellulose sodium, and water, with a carbon nanotube aggregate concentration of 0.20 mass% and a carboxymethylcellulose sodium concentration of 0.30 mass%. 15 mL of the obtained carbon nanotube dispersion was poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm, and heated at 100°C for 30 minutes to dry and obtain a measurement sample. The measurement sample was fixed to the gripping part of a tensile testing apparatus (Shimadzu Corporation, Autograph AG-IS), and a tensile test was performed at a speed of 1 mm / min. The maximum test force was calculated as the tensile strength. The point at which the test force was maximum was considered the breaking point, and the elongation at break was calculated. Furthermore, the energy density at break was calculated from the product of the elongation at break and the tensile strength. As a result, the tensile strength was 8.0 MPa, the elongation at break was 1.1%, and the energy density at break was 8.6 MPa·%.

[0213] <Evaluation of CNT aggregate dispersion 1: Surface resistivity> A carbon nanotube dispersion was prepared by mixing CNT aggregate 1, 700 kDa of carboxymethylcellulose sodium, and water, with a carbon nanotube aggregate concentration of 0.20 mass% and a carboxymethylcellulose sodium concentration of 0.30 mass%. 15 mL of the obtained carbon nanotube dispersion was poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm, and heated at 100°C for 30 minutes to dry and obtain a sample for measurement. The surface resistivity of the film was measured using a Loresta GXII manufactured by Nitto Seikou Analytech Co., Ltd. Measurements were taken at five locations on the film, and the average of the five values ​​was taken as the surface resistivity. As a result, the surface resistivity was 2.59 Ω / □. The results are shown in Table 1 below.

[0214] <Amorphous carbon content relative to the total mass of the CNT aggregate> The amount of amorphous carbon in CNT aggregate 1 was quantified by thermogravimetric differential thermal analysis (TG-DTA). Thermogravimetric differential thermal analysis was performed using a thermal analyzer (model: STA200, manufactured by Hitachi High-Tech Corporation) under air flow at a heating rate of 10°C / min. Approximately 10 mg of the sample was weighed into a Pt pan and heated to 900°C at a rate of 10°C / min. The amorphous carbon content was calculated from the difference in weight loss between 200°C and 400°C. As a result, the amorphous carbon content of CNT aggregate 1 was 0.04 mass%.

[0215] (Example 2) 1. Manufacturing of CNT assembly 2 CNT assembly 2 was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 39 NL / min, and the gas was continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 150°C.

[0216] 2. Preparation of CNT dispersion 2 Using the obtained CNT aggregate 2, a CNT dispersion 2 was obtained in the same manner as in Example 1.

[0217] 3. Evaluation <Calculation of Mean Curvature> Using CNT assembly 2, seven SEM images were selected (one of which is shown in Figure 2), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１The value was 0.021.

[0218] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 2 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.23. The cumulative 90% bundle diameter was 160 nm.

[0219] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 1.07 μm. The evaluation results are shown in Table 1 below.

[0220] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 2 was used. The viscosity of the dispersion was 102.2 mPa·s. The common logarithmic scale of the viscosity was 2.01.

[0221] <Tensile Strength, Elongation at Break, and Energy Density at Break> These were calculated in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the tensile strength was 28.5 MPa, the elongation at break was 2.5%, and the energy density at break was 71.5 MPa·%.

[0222] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the surface resistivity was 3.31 Ω / □. The results are shown in Table 1 below.

[0223] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 2 was used. As a result, the amorphous carbon content was 0.10% by mass.

[0224] (Example 3) 1. Manufacturing of CNT assembly 3 CNT assembly 3 was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 34 NL / min, and continuous discharge was performed through the outlet of a flow-through reactor with a temperature controlled to 150°C.

[0225] 2. Preparation of CNT dispersion 3 A pre-dispersion 3 was obtained using the obtained CNT aggregate 3 in the same manner as in Example 1.

[0226] The pre-dispersion 3 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain a CNT dispersion 3 with a concentration of 0.20% by mass. -Dispersion conditions- Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of passes: 8 Method: Circulation method

[0227] 3. Evaluation <Calculation of Mean Curvature> Using the CNT assembly 3, five SEM images were selected (one of which is shown in Figure 3), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１ The value was 0.012.

[0228] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 4 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.14. The cumulative 90% bundle diameter was 120 nm.

[0229] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 1.47 μm. The evaluation results are shown in Table 1 below.

[0230] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 3 was used. The viscosity of the dispersion was 34.6 mPa·s. The common logarithmic scale of the viscosity was 1.54.

[0231] <Tensile Strength, Elongation at Break, and Energy Density at Break> These were calculated in the same manner as in Example 1, except that CNT dispersion 3 was used. As a result, the tensile strength was 32.6 MPa, the elongation at break was 2.3%, and the energy density at break was 75.1 MPa·%.

[0232] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 3 was used. As a result, the surface resistivity was 1.07 Ω / □. The results are shown in Table 1 below.

[0233] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 3 was used. As a result, the amorphous carbon content was 0.39% by mass.

[0234] (Example 4) 1. Manufacturing of CNT Assembly 4 CNT assembly 4 was manufactured by mixing the following CNT assembly 4A and CNT assembly 4B. CNT assembly 4A was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 35 NL / min and that it was continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 150°C. CNT assembly 4B was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 36 NL / min and that it was continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 150°C.

[0235] 2. Preparation of CNT dispersion 4 A pre-dispersion 4 was obtained using the obtained CNT aggregate 4 in the same manner as in Example 1.

[0236] The pre-dispersion 4 was subjected to final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain the CNT dispersion 4. -Dispersion conditions- Nozzle diameter: 0.22 mm Pressure: 50 MPa Number of passes: 3 Method: Circulation method

[0237] 3. Evaluation <Calculation of Mean Curvature> Using the CNT assembly 4, four SEM images were selected (one of which is Figure 4), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１ The value was 0.010.

[0238] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 4 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.26. The cumulative 90% bundle diameter was 150 nm.

[0239] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> Measurement was performed in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 13.05 μm. The evaluation results are shown in Table 1 below.

[0240] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 4 was used. The viscosity of the dispersion was 798.2 mPa·s. The common logarithmic scale of the viscosity was 2.90.

[0241] <Tensile strength, elongation at break, and energy density at break> These were calculated in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the tensile strength was 15.5 MPa, the elongation at break was 2.6%, and the energy density at break was 40.6 MPa·%.

[0242] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the surface resistivity was 0.90 Ω / □. The results are shown in Table 1 below.

[0243] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 4 was used. As a result, the amorphous carbon content was 1.43% by mass.

[0244] (Example 5) 1. Manufacturing of CNT assembly 5 CNT assembly 5 is a CNT assembly manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 34.2 NL / min.

[0245] 2. Preparation of CNT dispersion 5 A pre-dispersion 5 was obtained using the obtained CNT aggregate 5 in the same manner as in Example 1.

[0246] The pre-dispersion 5 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain the CNT dispersion 5. -Dispersion conditions- Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of passes: 8 Method: Circulation method

[0247] 3. Evaluation <Calculation of Mean Curvature> Using the CNT assembly 5, four SEM images were selected (one of which is shown in Figure 5), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１ The value was 0.011.

[0248] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 5 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.13. The cumulative 90% bundle diameter was 110 nm.

[0249] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 40.1 μm. The evaluation results are shown in Table 1 below.

[0250] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 5 was used. The viscosity of the dispersion was 499.1 mPa·s. The common logarithmic scale of the viscosity was 2.70.

[0251] <Tensile Strength, Elongation at Break, and Energy Density at Break> These were calculated in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the tensile strength was 15.6 MPa, the elongation at break was 2.2%, and the energy density at break was 34.7 MPa·%.

[0252] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the surface resistivity was 1.40 Ω / □. The results are shown in Table 1 below.

[0253] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 5 was used. As a result, the amorphous carbon content was 0.24% by mass.

[0254] (Comparative Example 1) 1. Preparation of Powdered CNT Assembly 6 As the powdered CNT assembly 6, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT7000) were prepared. 2. Preparation of CNT Dispersion 6 Using the obtained CNT assembly 6, a pre-dispersion 6 was obtained in the same manner as in Example 1.

[0255] The pre-dispersion 6 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain the CNT dispersion 6. -Dispersion conditions- Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of passes: 8 Method: Circulation method

[0256] 3. Evaluation <Calculation of Mean Curvature> Using the CNT assembly 6, two SEM images were selected (one of which is Figure 6), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１ The value was 0.095.

[0257] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 6 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.10. The cumulative 90% bundle diameter was 90 nm.

[0258] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 0.65 μm. The evaluation results are shown in Table 1 below.

[0259] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 6 was used. The viscosity of the dispersion was 6.4 mPa·s. The common logarithmic scale of the viscosity was 0.81.

[0260] <Tensile Strength, Elongation at Break, and Energy Density at Break> These were calculated in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the tensile strength was 6.9 MPa, the elongation at break was 2.6%, and the energy density at break was 18.0 MPa·%.

[0261] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the surface resistivity was 16.52 Ω / □. The results are shown in Table 1 below.

[0262] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 6 was used. As a result, the amorphous carbon content was 0.07% by mass.

[0263] (Comparative Example 2) 1. Preparation of Powdered CNT Assembly 7 As the powdered CNT assembly 7, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT9100) were prepared.

[0264] 2. Preparation of CNT dispersion 7 A CNT dispersion 7 was obtained using the obtained CNT aggregate 7 in the same manner as in Comparative Example 1.

[0265] 3. Evaluation <Calculation of Mean Curvature> Using the CNT assembly 7, three SEM images were selected (one of which is shown in Figure 7), and the mean curvature was calculated in the same manner as in Example 1. Mean curvature Z(um －１ The value was 0.088.

[0266] <Bundle Diameter Characteristics> The calculations were performed in the same manner as in Example 1, except that CNT aggregate 7 was used. As a result, the proportion of bundles with a bundle diameter of 100 nm or more was 0.08. The cumulative 90% bundle diameter was 80 nm.

[0267] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 7 was used. As a result, the cumulative 50% particle size D50 in volume-based particle size distribution was 0.35 μm. The evaluation results are shown in Table 1 below.

[0268] <Viscosity of CNT aggregate dispersion> The viscosity was measured in the same manner as in Example 1, except that CNT dispersion 7 was used. The viscosity of the dispersion was 5.7 mPa·s. The common logarithmic scale of the viscosity was 0.75.

[0269] <Tensile strength, elongation at break, and energy density at break> These were calculated in the same manner as in Example 1, except that CNT dispersion 7 was used. As a result, the tensile strength was 2.3 MPa, the elongation at break was 1.9%, and the energy density at break was 4.3 MPa·%.

[0270] <Surface Resistivity> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 7 was used. As a result, the surface resistivity was 15.49 Ω / □. The results are shown in Table 1 below.

[0271] <Amorphous Carbon Content> The amount of amorphous carbon was quantified in the same manner as in Example 1, except that CNT aggregate 7 was used. As a result, the amorphous carbon content was 0.09% by mass.

[0272] [Fabrication of Lithium-ion Rechargeable Batteries] Next, lithium-ion rechargeable batteries were fabricated.

[0273] 1. Fabrication of positive electrode for lithium secondary battery: Positive electrode active material (LiNi ０．８ Co ０．１ Mn ０．１ O ２ A positive electrode mixture was prepared by mixing a conductive material (acetylene black) and a binder (PVdF) in a ratio of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and then kneading with N-methyl-2-pyrrolidone. The obtained positive electrode mixture was applied to a 15 μm thick Al foil to be used as a current collector, vacuum-dried at 80°C for 1 hour, and then roll-pressed to obtain a positive electrode for a lithium secondary battery. The positive electrode area was 1.65 cm². ２ The estimated amount is 16 mg / cm³. ２ The density is 3.0 g / cm³. ３ I adjusted it so that it would be as follows.

[0274] 2. Preparation of a Negative Electrode for Lithium Secondary Batteries A negative electrode for lithium secondary batteries was prepared by mixing artificial graphite MAG-E and carbon-coated SiO in a 9:1 (mass ratio) ratio as the negative electrode active material, using CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a binder, and adding the above CNT dispersion as a conductive additive, so that the composition was negative electrode active material:binder:conductive additive = 94.9:5.0:0.1 (mass ratio), and kneading to prepare a paste-like negative electrode mixture. Ion-exchanged water was used as the solvent during the preparation of the negative electrode mixture. The obtained negative electrode mixture was coated onto a 20 μm thick Cu foil using a single-sided continuous coating machine, dried at 120°C, and then roll-pressed to obtain a negative electrode for lithium secondary batteries. The negative electrode area was 1.77 cm². ２The estimated amount is 9.3 mg / cm³. ２ The density is 1.4 g / cm³. ３ I adjusted it so that it would be as follows.

[0275] 3. Fabrication of a Lithium Secondary Battery The positive electrode for the lithium secondary battery was placed on the lower cover of a part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator, which consists of a 16 μm heat-resistant porous layer laminated on a polyethylene porous film, was placed on top of it. 300 μL of electrolyte was injected into this. As the electrolyte, a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was added, to which 1 volume% of vinylene carbonate was added, and LiPF was added. ６ A solution of 1.3 mol / L was used. Next, the negative electrode for the lithium secondary battery was placed on top of the laminated film separator, the top cover was placed on top via a gasket, and the lithium secondary battery of coin-type full cell R2032 was fabricated by crimping with a crimping machine. These operations were performed in a glove box under an argon atmosphere.

[0276] 4. Cycle Test Using the prepared lithium-ion battery, a cycle test was conducted for 200 cycles under the conditions shown below, and the discharge capacity retention rate after 200 cycles was calculated using the following formula. Note that a higher discharge capacity retention rate after 200 cycles indicates better lifespan characteristics. Discharge capacity retention rate after 200 cycles (%) = Discharge capacity at 200th cycle / Discharge capacity at 1st cycle × 100

[0277] <Cycle Test Conditions> Test temperature: 25°C Charging conditions: Constant current constant voltage charging, maximum charging voltage 4.2V, charging time 5 hours, charging current 0.3CA Pause time after discharge: 10 minutes Discharge conditions: Constant current discharge, minimum discharge voltage 2.5V, discharge current 0.3CA Pause time after charging: 10 minutes In this test, one cycle is defined as the process of charging, discharging pause, discharging, and charging pause performed in that order.

[0278] The evaluation results for Examples 1 to 5, as well as Comparative Examples 1 and 2, are shown in Table 1.

[0279]

[0280] The CNT dispersions obtained by dispersing the CNT aggregates of Examples 1, 2, 3, 4, and 5 satisfy the ranges of the mean curvature Z and D50, indicating excellent conductivity. The surface resistivity values ​​of Examples 1, 2, 3, 4, and 5 are 2.59 Ω / □, 3.31 Ω / □, 1.07 Ω / □, 0.90 Ω / □, and 1.40 Ω / □, respectively. The viscosities of the dispersions are 142.6 mPa·s, 102.2 mPa·s, 34.6 mPa·s, 798.2 mPa·s, and 499.1 mPa·s, respectively. The common logarithmic representations of the viscosities are 2.15, 2.01, 2.11, 2.90, and 2.70, which are appropriate values. This confirms that the CNT aggregates of the examples have excellent conductivity and dispersibility. Therefore, it can be seen that the CNT assemblies of Examples 1, 2, 3, 4, and 5 are excellent as conductive materials. On the other hand, the surface resistivity values ​​of the CNT dispersions of Comparative Examples 1 and 2 were high, at 16.52 Ω / □ and 15.49 Ω / □, respectively, indicating low conductivity. Furthermore, the viscosity of the dispersions was 6.4 mPa·s and 5.7 mPa·s, respectively, and the common logarithmic expression of viscosity was 0.81 and 0.75, which is too low and makes them difficult to handle, resulting in poor workability and difficulty in using them as dispersions. These evaluation results show that the CNT assemblies of Comparative Examples 1 and 2 are inferior as conductive materials. Therefore, it has been confirmed that the CNT assemblies of this disclosure can provide CNT assemblies that have excellent conductivity when used as a CNT dispersion, and that can obtain a CNT dispersion with appropriate viscosity and excellent dispersibility.

Claims

1. Mean curvature Z(um) of carbon nanotube structures in the area observed by scanning electron microscopy. －１ A carbon nanotube aggregate in which the particle size ratio is 0.005 or greater and less than 0.088, and the cumulative 50% particle size D50 in the volume-based particle size distribution exceeds 0.65 μm.

2. The carbon nanotube aggregate according to claim 1, comprising a bundle structure, wherein the bundle diameter X, which represents 90% of the cumulative bundle in the area observed by a scanning electron microscope, is greater than 90 nm and less than 500 nm.

3. The carbon nanotube aggregate according to claim 1, comprising a bundle structure, wherein the area ratio Y of bundles with a bundle diameter of 100 nm or more in the area observed by a scanning electron microscope is greater than 0.

1.

4. A conductive material comprising a carbon nanotube aggregate according to any one of claims 1 to 3.

5. An electrode comprising an electrode active material and the conductive material described in claim 4.

6. A secondary battery comprising the electrodes described in claim 5.

7. A planar aggregate comprising the carbon nanotube aggregate described in any one of claims 1 to 3.

8. A laminate comprising a substrate and the planar assembly described in claim 7.

9. A filter using the planar assembly described in claim 7.

10. An electromagnetic shield using the planar assembly described in claim 7.

11. A pellicle for extreme ultraviolet radiation using the planar aggregate described in claim 7.

12. A method for measuring the mean curvature of a carbon nanotube aggregate, comprising performing the following steps 1 to 3 on two or more images of the carbon nanotube aggregate using the image analysis software ImageJ to calculate the mean curvature.

1. Adjust the image size using Image:Adjust:Size, Width=1280. Set the screen size to 1280 x 960 and the width to 1410 nm.

2. Fine-tune the curve to follow the center of the fiber using Plugin:Analyze:Kappa, File:OpenActiveImage, and CurveFittingOptions:ChoosePoints=100, DataThreshold=10, Scale(μm / pixel)=0.

16.

3. After calculating approximately 8 center lines per field of view, calculate each curvature and the mean curvature.

Images