Carbon nanotube assembly, conductive material, electrode, secondary battery, planar assembly, laminate, filter, electromagnetic wave shield, and extreme ultraviolet pellicle

Abstract

Provided is a carbon nanotube assembly, etc., with which a battery having excellent cycle characteristics can be manufactured. This carbon nanotube assembly contains Fe atoms, and the amount X of Fe atoms relative to the total mass of the carbon nanotube assembly is more than 0 ppm but less than 5,000 ppm. The carbon nanotube assembly includes a bundle structure, and in a region observed by a scanning electron microscope, the cumulative 90% bundle diameter W is more than 90 nm but less than 500 nm.

Description

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

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

[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 states that a carbon nanotube aggregate in which the sum of the iron and cobalt content and the sum of the sodium and potassium content are within a specific range relative to the total mass of the carbon nanotube aggregate, and the ratio of the volume resistivity under two specific pressure conditions is within a specific range, exhibits excellent conductivity when used as a carbon nanotube dispersion.

[0004] Patent Document 2 states that bundles formed by carbon nanotubes have better dispersibility in the dispersion medium when the bundle diameter is small (for example, an average of 20 nm or less), and that the conductivity remains high even when the dispersion is applied to create a film.

[0005] Patent Document 3 describes a CNT aggregate having a bundle structure, where each bundle has a diameter greater than 0.3 μm, and the average diameter is 0.5 μm or more.

[0006] For example, Patent Document 4 discloses a multi-walled carbon nanotube assembly having high conductivity. It is described that the multi-walled carbon nanotubes are intertwined with each other, forming a large network structure that can exist stably in an aqueous dispersion.

[0007] Japanese Patent Publication No. 7556170, Japanese Unexamined Patent Publication No. 2009-029695, Chinese Patent Application Publication No. 116111043, International Publication No. 2025 / 013505

[0008] When manufacturing batteries using CNT assemblies, there were times when excellent cycle characteristics were required.

[0009] 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 capable of producing a battery with excellent cycle characteristics. Another embodiment of this disclosure aims to solve the problem of providing a conductive material, electrode, secondary battery, and planar aggregate containing the carbon nanotube aggregate. Another embodiment of this disclosure aims to solve the problem of providing a laminate comprising the planar aggregate. Another embodiment of this disclosure aims to solve the problem of providing a filter, electromagnetic shield, and extreme ultraviolet pellicle using the planar aggregate.

[0010] The means for solving the above-mentioned problems include the following embodiments: <1> A carbon nanotube aggregate containing Fe atoms, wherein the Fe atom content X relative to the total mass of the carbon nanotube aggregate is greater than 0 ppm and less than 5000 ppm, and which includes a bundle structure, wherein the bundle diameter W at a cumulative 90% in the observation area by scanning electron microscopy is greater than 90 nm and less than 500 nm. <2> The carbon nanotube aggregate according to <1>, wherein the carbon nanotube aggregate is mixed with 700 kDa of carboxymethylcellulose sodium and water, and at a liquid temperature of 25°C, the common logarithm of the viscosity of the dispersion, in which the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%, is 1.55 or more (the unit of viscosity is mPa·s). <3> A carbon nanotube aggregate according to <1> or <2>, which does not contain Si atoms and Co atoms, or contains at least one of Si atoms and Co atoms, and the total content Z of Si atoms and Co atoms relative to the total mass of the carbon nanotube aggregate is less than 1000 ppm. <4> A conductive material comprising the carbon nanotube aggregate according to any one of <1> to <3>. <5> An electrode comprising 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 comprising the carbon nanotube aggregate according to any one of <1> to <3>. <8> A laminate comprising a substrate and the planar aggregate according to <7>. <9> A filter using the planar aggregate according to <7>. <10> An electromagnetic shield using the planar aggregate according to <7>. <11> An extreme ultraviolet pellicle using the planar aggregate according to <7>.

[0011] According to one embodiment of the present disclosure, a carbon nanotube aggregate capable of producing a battery with excellent cycle characteristics is provided. According to another embodiment of the present disclosure, a conductive material, an electrode, a secondary battery, and a planar aggregate comprising 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.

[0012] 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 Comparative Example 1. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 4 of Comparative Example 2. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 5 of Comparative Example 3. This is an image obtained using a scanning electron microscope for carbon nanotube aggregate 6 of Comparative Example 4.

[0013] 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.

[0014] 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.

[0015] (Carbon Nanotube Assembly) The carbon nanotube assembly (also referred to as "CNT assembly") according to this disclosure contains Fe atoms, the Fe atom content X relative to the total mass of the carbon nanotube assembly is greater than 0 ppm and less than 5000 ppm, and it contains a bundle structure, and the bundle diameter W at which cumulative 90% is greater than 90 nm and less than 500 nm in the area observed by a scanning electron microscope.

[0016] The CNT aggregate described herein allows for the production of a carbon nanotube dispersion with appropriate viscosity and a battery with excellent cycle characteristics. On the other hand, Patent Documents 1, 2, 3, and 4 do not contain any descriptions focusing on the Fe atom content or the bundle diameter being 90% cumulative.

[0017] For example, Patent Document 1 does not describe the dispersibility of CNT aggregates in a dispersion medium, nor does it describe the characteristics of secondary batteries using the dispersion. Patent Document 2 states that bundles formed by carbon nanotubes have better dispersibility in a dispersion medium when the bundle diameter is small (for example, an average of 20 nm or less), and that the conductivity remains high even when the dispersion is applied to create a film. However, in recent years, Patent Document 3 has reported that when used as a conductive additive in electrodes, if the bundle diameter is small, the rigidity deteriorates and it becomes difficult to form long-distance conductive networks, so a bundle diameter of 500 nm or more is preferable, and controlling the bundle structure to have excellent cycle characteristics has been a challenge. Patent Document 4 describes the relationship between the median diameter in the volume-based particle size distribution obtained by centrifugal sedimentation when multi-walled carbon nanotubes are dispersed in an aqueous dispersion of a specific concentration, and the structure formed by the entanglement of multi-walled carbon nanotubes, but it does not describe how to obtain a carbon nanotube dispersion with appropriate viscosity. Furthermore, it does not describe how lithium-ion secondary batteries have excellent cycle characteristics. In contrast, the CNT aggregate according to this disclosure satisfies the above range by having an Fe atom content X and a bundle diameter of 90% cumulative Fe atoms, thereby enabling the production of a battery with excellent cycle characteristics.

[0018] <Fe atom content X> The carbon nanotube aggregate according to this disclosure contains Fe atoms, and the Fe atom content X relative to the total mass of the carbon nanotube aggregate is greater than 0 ppm and less than 5000 ppm. Unless otherwise specified, ppm in this disclosure refers to ppm by mass.

[0019] The Fe atom content X relative to the total mass of a carbon nanotube aggregate can be measured, for example, by the following method: The carbon nanotube aggregate according to this disclosure is completely dissolved in an acid such as hydrochloric acid or nitric acid. Pretreatment such as dry ashing, wet ashing, or melting may be performed to completely dissolve the aggregate according to this disclosure in the acid. The Fe atom content ratio of the solution obtained by completely dissolving the aggregate according to this disclosure in the acid can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS is preferred because it allows for more sensitive measurement.

[0020] The carbon nanotube aggregate may contain 0.01% to 50% by mass of Fe atoms derived from iron, which is a catalyst used in its manufacture. The carbon nanotube aggregate may contain Fe atoms, for example, adsorbed on the surface of the carbon nanotube aggregate or incorporated into the interior of the fibrous carbon nanotube aggregate formed during manufacture. That is, in this disclosure, the Fe atoms contained in the carbon nanotube aggregate may include Fe atoms derived from the catalyst used in the manufacture of the carbon nanotube aggregate. In the carbon nanotube aggregate of this disclosure, it is preferable to adjust the Fe atom content X relative to the total mass of the carbon nanotube aggregate to a target Fe atom content ratio within the range of more than 0 ppm and less than 5000 ppm, taking into consideration the content of catalyst-derived Fe atoms contained in the carbon nanotube aggregate. It goes without saying that if the content ratio of catalyst-derived Fe atoms relative to the total mass of the aggregate is the target content ratio, it is not necessary to take any special measures to adjust the Fe atom content ratio.

[0021] If the Fe atom content X relative to the total mass of the carbon nanotube aggregate is 5000 ppm or more, the Fe atom content relative to the total mass of the aggregate can be adjusted to less than 5000 ppm by washing the aggregate with water, acid, or an acidic aqueous solution (for example, a 1% to 37% by mass aqueous solution of hydrochloric acid, particularly a 35% by mass aqueous solution) using a known method, thereby washing and removing some of the Fe atoms. If the Fe content relative to the total mass of the carbon nanotube aggregate is 0 ppm or more, the Fe content relative to the total mass of the carbon nanotube aggregate can be adjusted to 20 ppm or more by immersing the aggregate in a 1% to 46% by mass (particularly about 5% by mass) iron nitrate aqueous solution or a 1% to 47% by mass (particularly about 40% by mass) iron chloride aqueous solution as a source of Fe atoms, thereby adsorbing Fe atoms onto the surface of the carbon nanotube aggregate.

[0022] The Fe atom content X relative to the total mass of the CNT aggregate relating to this disclosure may have a lower limit of 20 ppm or more, 30 ppm or more, 40 ppm or more, 50 ppm or more, 60 ppm or more, 70 ppm or more, 80 ppm or more, 90 ppm or more, 100 ppm or more, 150 ppm or more, 200 ppm or more, 250 ppm or more, 300 ppm or more, 350 ppm or more, 400 ppm or more, 450 ppm or more, 600 ppm or more, 800 ppm or more, or 1000 ppm or more. Furthermore, the upper limit may be 4950 ppm or less, 4900 ppm or less, 4850 ppm or less, or 4800 ppm or less. The upper and lower limits can be combined in any way.

[0023] The Fe atom content X relative to the total mass of the CNT aggregate relating to this disclosure may be 20 ppm or more and less than 5000 ppm, 35 ppm or more and less than 5000 ppm, 100 ppm or more and less than 5000 ppm, 450 ppm or more and less than 5000 ppm, 20 ppm or more and 4950 ppm or less, 35 ppm or more and 4950 ppm or less, 100 ppm or more and 4950 ppm or less, or 450 ppm or more and 4 It may be 950 ppm or less, 20 ppm to 4900 ppm or less, 35 ppm to 4900 ppm or less, 100 ppm to 4900 ppm or less, 450 ppm to 4900 ppm or less, 20 ppm to 4800 ppm or less, 35 ppm to 4800 ppm or less, 100 ppm to 4800 ppm or less, or 450 ppm to 4800 ppm or less.

[0024] In other embodiments of this disclosure, the concentration is preferably 20 ppm or more and less than 5000 ppm, more preferably 35 ppm or more and less than 5000 ppm, particularly preferably 100 ppm or more and less than 5000 ppm, and even more preferably 450 ppm or more and less than 5000 ppm. Furthermore, in other embodiments of this disclosure, the concentration is preferably 20 ppm or more and less than 4800 ppm, more preferably 35 ppm or more and less than 4800 ppm, particularly preferably 100 ppm or more and less than 4800 ppm, and even more preferably 450 ppm or more and less than 4800 ppm. Furthermore, in other embodiments of this disclosure, the concentration is preferably 3500 ppm or more and 5000 ppm or less, and even more preferably 3500 ppm or more and 4800 ppm or less. The Fe atom content X relative to the total mass of the CNT aggregate is preferable when it is within the above range because it moderately suppresses the aggregation of CNT aggregates, inhibits the increase in bundle diameter, and improves dispersibility in the dispersion solvent. Furthermore, it is preferable when it is 4900 ppm or less because it improves the conductivity of the CNT aggregate.

[0025] Specifically, the Fe content relative to the total mass of the CNT aggregate is between 20 ppm and 4900 ppm. This prevents excessive aggregation of CNT aggregates, promotes uniform dispersion in the dispersion, and improves conductivity. When used as a conductive additive in lithium-ion secondary batteries, this improves cycle characteristics. Although the mechanism is not entirely clear, it is thought that the carbon nanotube aggregates aggregate appropriately to form a bundle structure, creating a network structure and efficiently forming conductive paths. It is believed that the swelling and contraction of the electrode active material due to charging and discharging are effectively suppressed by the tightly packed carbon nanotube aggregates.

[0026] <Bundle diameter at 90% cumulative percentage> The carbon nanotube aggregate according to this disclosure includes a bundle structure, and in the area observed by a scanning electron microscope, the bundle diameter at 90% cumulative percentage (hereinafter also referred to as the "90% cumulative bundle diameter") is greater than 90 nm and less than 500 nm. Furthermore, the bundle diameter at 90% cumulative percentage may be 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less. Furthermore, the bundle diameter at 90% cumulative percentage may be 100 nm or more, or 110 nm or more. Within the range of the bundle diameter at 90% cumulative percentage, these upper and lower limits can be arbitrarily selected.

[0027] The CNT aggregates relating to this disclosure include bundle structures. 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. It is presumed that including bundle structures of an appropriate size in a CNT aggregate improves the handling properties of the CNT aggregate and further enhances its stability. On the other hand, if the bundle structures included in a CNT aggregate become too large, the size of the CNT aggregate itself becomes too large, and it becomes difficult to separate and disperse the CNTs included in the bundle structure, which may reduce its dispersibility in the dispersion medium.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 350 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.

[0032] In particular, the cumulative 90% bundle diameter is preferably greater than 90 nm and less than or equal to 350 nm, more preferably greater than 90 nm and less than or equal to 300 nm, and more preferably greater than 90 nm and less than or equal to 250 nm. Furthermore, the cumulative 90% bundle diameter is preferably between 100 nm and 350 nm, more preferably greater than 100 nm and less than or equal to 300 nm, and even more preferably greater than 100 nm and less than or equal to 250 nm. 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. In addition, by appropriately controlling the bundle diameter, the viscosity of the dispersion containing the CNT aggregate is maintained within an appropriate range, improving dispersibility. As a result, battery performance can be improved.

[0033] 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.

[0034] -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

[0035] - Image Selection - From the obtained images, select two or more images in which CNT bundles are frequently observed.

[0036] - 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.

[0037] -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.

[0038] -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.

[0039] -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.

[0040] - 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.

[0041] <Viscosity> The CNT aggregate according to this disclosure is preferably prepared by mixing the carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, and at a liquid temperature of 25°C, 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 preferably 1.55 or higher. The unit of viscosity is mPa·s. Furthermore, the viscosity in this disclosure is the viscosity at 25°C. The method for measuring viscosity will be described later.

[0042] The common logarithm of the viscosity of the above dispersion is 1.55 or higher, which improves the dispersibility of the CNTs and optimizes their performance as an electrode material. The common logarithm of the viscosity of the above dispersion may be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 3.1 or less, 3.2 or less, 3.3 or less, or 3.4 or less. The upper and lower limits can be combined in any way.

[0043] When the common logarithm of the viscosity of the above dispersion is between 1.55 and 5.0, the dispersibility of CNTs is further improved, and the performance as an electrode material is further optimized.

[0044] The common logarithm of the viscosity of the above dispersion is preferably 1.55 or more and 5.0 or less. Furthermore, the common logarithm of the viscosity of the above dispersion is more preferably 1.55 or more and 4.5 or less, even more preferably 1.55 or more and 4.0 or less, particularly preferably 1.55 or more and 3.5 or less, and most preferably 1.55 or more and 3.0 or less. By appropriately controlling the viscosity of the CNTs, the dispersibility of the CNTs is improved and the performance as an electrode material is optimized. Specifically, when the common logarithm of the viscosity of the above dispersion is 1.55 or more and 3.5 or less, the dispersion of CNTs is kept uniform, and conductive paths are efficiently formed within the electrode. As a result, the conductivity of the electrode is improved and the internal resistance of the battery is reduced, so the charge and discharge efficiency of the battery is improved and the cycle characteristics are further improved. Furthermore, when the common logarithm of the viscosity of the above dispersion is 1.55 or more and 3.4 or less, the dispersion of CNTs is further improved and the mechanical strength as an electrode material is improved. This allows the electrodes to be more durable against volume changes and stress during the cycle, contributing to battery life. In particular, when the common logarithm of the viscosity of the dispersion is between 1.55 and 3.3, the balance between the dispersibility and conductivity of the CNTs is optimized, and the performance as an electrode material 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 is expected.

[0045] 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

[0046] 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.

[0047] <Total content of Si and Co atoms Z> The carbon nanotube aggregate according to this disclosure either does not contain Si atoms and Co atoms, or contains at least one of Si atoms and Co atoms, and it is preferable that the total content Z of Si atoms and Co atoms relative to the total mass of the carbon nanotube aggregate is less than 1000 ppm. It is preferable that the total content of Si atoms and Co atoms contained in the CNT aggregate is less than 1000 ppm because it does not cause a decrease in battery performance when the CNT aggregate is used as a secondary battery (for example, as a conductive additive in a lithium-ion battery). Excess Si atoms and Co atoms totaling 1000 ppm or more may cause side reactions in the battery and degrade the battery performance, so it is important that the total content Z of Si atoms and Co atoms be within an appropriate range.

[0048] The lower limit of the total Si and Co content Z is not particularly limited and may be 0 ppm. However, if the individual Si and Co content is less than 10 ppm, it becomes technically difficult to detect peaks originating from these elements using ICP-MS or ICP-AES, making it difficult to accurately calculate the content. Therefore, content less than 10 ppm may be treated as 0 ppm. Achieving a total Si and Co content Z of 100 ppm or less is difficult from the viewpoint of CNT synthesis and handling. Specifically, in the CNT manufacturing process, it is unavoidable that trace amounts of Si and Co atoms, which are raw materials for the material, are mixed in as impurities from the reactor, making it technically difficult to achieve a total Si and Co content Z of 100 ppm or less. The contamination of these elements from the manufacturing process is presumed to originate from the reaction tube, raw material container, injector, recovery machine, etc. Ceramic materials containing Si, Al, etc., are sometimes used for the reaction tube because of their excellent heat resistance. Furthermore, MA23, which is known to contain up to 5% of Co as an active ingredient, may be used for the raw material container, injector, and recovery machine. Under harsh conditions such as high temperatures, trace amounts may be released and adhere to the carbon nanotube aggregate.

[0049] Furthermore, in the case of Co, it may originate from the catalyst used in the production of the carbon nanotube aggregate. When Co is used as the catalyst during the production of the carbon nanotube aggregate, it may contain 0.01% to 50% by mass of Co atoms. The carbon nanotube aggregate may contain Co atoms, for example, adsorbed on the surface of the carbon nanotube aggregate or incorporated into the interior of the fibrous carbon nanotube aggregate formed during production. That is, in this disclosure, the Co atoms contained in the carbon nanotube aggregate may include Co atoms derived from the catalyst used in the production of the carbon nanotube aggregate. In the carbon nanotube aggregate according to this disclosure, it is preferable to adjust the Co atom content ratio to the total mass of the carbon nanotube aggregate to the desired Co atom content ratio, taking into consideration the content of catalyst-derived Co atoms contained in the carbon nanotube aggregate, so that the Co atom content ratio to the total mass of the carbon nanotube aggregate is less than 1000 ppm. Needless to say, if the content ratio of catalyst-derived Co atoms to the total mass of the aggregate is the desired content ratio, it is not necessary to take any special measures to adjust the Co atom content ratio.

[0050] The inventors' studies have shown that stable CNTs can be obtained in the manufacturing process if the total content Z of Si and Co atoms is 400 ppm or less, and that even if the total content Z of Si and Co atoms is 400 ppm or more, there is little concern about a decrease in the conductivity or dispersibility of the CNT aggregate. The results of the examples and comparative examples described later also confirm that stable CNTs can be obtained in the manufacturing process if the total content of Si and Co atoms is 400 ppm or less.

[0051] Methods to reduce the total content Z of Si and Co atoms to less than 1000 ppm include, for example, washing the CNT aggregate with water, acid, an acidic aqueous solution (e.g., a 35% by mass aqueous solution of hydrochloric acid), or a chelating agent aqueous solution to reduce the content. In particular, washing with an aqueous solution containing hydrofluoric acid or an aqueous solution containing a tetraalkylammonium salt of fluoride ions is effective for Si atoms. Furthermore, the Si and Co atom content can be adjusted by using methods such as immersing the aggregate in an aqueous solution of nitrate or chloride containing approximately 5% by mass of Co atoms to adsorb Mn and Co atoms onto the surface of the CNT aggregate, thereby increasing the total Co atom content relative to the total mass of the aggregate; or immersing the aggregate in tetraethoxysilane and hydrolyzing it to adsorb Si atoms onto the surface of the CNT aggregate, thereby increasing the Si atom content relative to the total mass of the aggregate. However, such adjustments to the content increase the process load and lead to increased costs, so it is preferable to avoid them.

[0052] The Si atom content (ppm) relative to the total mass of the CNT aggregate according to this disclosure can be measured, for example, by the following method: The CNT aggregate is completely dissolved in an alkali. Pretreatment such as dry ashing or wet ashing may be performed to completely dissolve the CNT aggregate in an alkali. After dissolving in an alkali, it is dissolved in an acid. The Ca atom content relative to the total mass of the CNT aggregate can be measured by performing inductively coupled plasma atomic emission spectroscopy (ICP-AES) on the solution obtained by completely dissolving the CNT aggregate in an acid as a sample. From the viewpoint of being able to measure with higher sensitivity, it is preferable to perform ICP-AES. In this disclosure, the Co atom content (mass ppm) relative to the total mass of the CNT aggregate can be measured, for example, using the same measurement method as for the Fe atom content described above.

[0053] Furthermore, when the Si and Co atom content in a CNT aggregate is less than 10 ppm, it becomes technically difficult to detect peaks originating from Si and Co atoms, even when using ICP-MS, ICP-AES, etc., making it difficult to accurately calculate the content. Therefore, in this disclosure, when the Si and Co atom content measured above is less than 10 ppm, the Si and Co atom content may be treated as 0, but this does not negate the presence of Si and Co atoms in the CNT aggregate.

[0054] From the above viewpoint, the total content Z of Si atoms and Co atoms may be less than 1000 ppm, 900 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, 500 ppm or less, or 400 ppm or less. Furthermore, the total content Z of Si atoms and Co atoms may be greater than 0 ppm, 10 ppm or more, 20 ppm or more, 30 ppm or more, 40 ppm or more, 50 ppm or more, 60 ppm or more, 70 ppm or more, 80 ppm or more, 90 ppm or more, or 100 ppm or more. The total content Z can be set by combining the above upper and lower limits.

[0055] The content of one atom selected from the group consisting of Si atoms and Co atoms in the CNT aggregate can be set by combining the above upper and lower limits. In one embodiment, the total content of one or more atoms selected from the group consisting of Si atoms and Co atoms is 0 ppm or more and 1000 ppm or less, preferably 0 ppm or more and 950 ppm or less, may be 0 ppm or more and 900 ppm or less, may be 0 ppm or more and 850 ppm or less, may be 0 ppm or more and 800 ppm or less, or may be 0 ppm or more and 750 ppm or less. Furthermore, the total content is preferably 10 ppm to 1000 ppm, more preferably 10 ppm to 950 ppm, may be 10 ppm to 900 ppm, may be 10 ppm to 850 ppm, may be 10 ppm to 800 ppm, or may be 10 ppm to 750 ppm. In one embodiment, the total content of one or more atoms selected from the group consisting of Si atoms and Co atoms is preferably more than 0 ppm and 400 ppm or less, more preferably 10 ppm to 400 ppm, or may be 50 ppm to 400 ppm. In one embodiment, the total content of one or more atoms selected from the group consisting of Si atoms and Co atoms is preferably more than 100 ppm and 1000 ppm or less, more preferably 100 ppm or more and 950 ppm or less, may be 100 ppm or more and 900 ppm or less, may be 100 ppm or more and 850 ppm or less, may be 100 ppm or more and 800 ppm or less, may be 100 ppm or more and 750 ppm or less, may be 100 ppm or more and 700 ppm or less, may be 100 ppm or more and 650 ppm or less, may be 100 ppm or more and 600 ppm or less, may be 100 ppm or more and 550 ppm or less, may be 100 ppm or more and 500 ppm or less, may be 100 ppm or more and 450 ppm or less, or may be 100 ppm or more and 400 ppm or less. Within the above range, the dispersibility of the CNT aggregate as a dispersion, and the balance between the appropriate viscosity and conductivity of the dispersion can be optimized, resulting in improved battery performance.Furthermore, the purification costs incurred when removing these components from CNTs can be kept within a reasonable range.

[0056] <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.

[0057] 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 / □, and still more preferably 0.3 Ω / □ to 4.0 Ω / □, from the viewpoint of ensuring conductivity as a conductive additive and the stability of the dispersion.

[0058] <D50> The CNT aggregate according to this disclosure preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution greater than 0.35 μm and 25 μm or less. The CNT aggregate according to this disclosure is more preferably greater than 0.35 μm and 20 μm or less, even more preferably greater than 0.35 μm and 15 μm or less, particularly preferably greater than 0.35 μm and 10 μm or less, and most preferably greater than 0.35 μm and 8.0 μm or less. In another embodiment, the CNT aggregate according to the present disclosure preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution of 0.70 μm or more and 25 μm or less, more preferably 0.70 μm or more and 20 μm or less, even more preferably 0.70 μm or more and 15 μm or less, particularly preferably 0.70 μm or more and 10 μm or less, and most preferably 0.70 μm or more and 8.0 μm or less. In another embodiment, the CNT aggregate according to the present disclosure preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution of 1.0 μm or more and 25 μm or less, more preferably 1.0 μm or more and 20 μm or less, even more preferably 1.0 μm or more and 15 μm or less, particularly preferably 1.0 μm or more and 10 μm or less, and most preferably 1.0 μm or more and 8.0 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 0.70 μm to 10 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. It is thought that the small particle size of the CNT aggregate increases the surface area in the dispersion, strengthening the interaction with the dispersion medium, resulting in further improvement of dispersibility. In addition, the uniform particle size distribution stabilizes the viscosity of the CNT aggregate dispersion, resulting in better processability and handling when forming electrodes or the like using the CNT aggregate. Furthermore, when the cumulative 50% particle size D50 is between 0.70 μm and 8.0 μm, the particle size of the CNT aggregate is appropriately controlled, and a more uniform dispersion is achieved when preparing the dispersion using the CNT aggregate.Therefore, by satisfying the above conditions, the dispersibility of the CNT aggregate 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. Furthermore, when this dispersion is added to electrodes as a conductive additive, the cycle characteristics of the battery can be improved.

[0059] The cumulative 50% particle size D50 in the volume-based particle size distribution of a 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.

[0060] <Tensile Test> The CNT aggregate according to this disclosure preferably has a fracture elongation of more than 0% and 5.0% or less as measured by the following measurement method, a tensile strength of 2.5 MPa or more and 50.0 MPa or less, and a fracture energy density of more than 4.3 MPa·% and 100 MPa·% or less.

[0061] -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 prepared measurement sample is fixed to the gripping part of a tensile testing apparatus, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. The point where the stress is maximum in the tensile test is considered to be 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 the tensile test. Furthermore, the energy density at break is calculated from the product of the elongation at break and the tensile strength.

[0062] 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 according to this disclosure 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, by maintaining an appropriate length of CNTs, conductive paths are efficiently formed, optimizing conductivity. When the elongation at break of the CNT aggregate according to this disclosure is 5.0% or less, it is easy to process into a dispersion and ensure dispersibility in the dispersion. Specifically, when the elongation at break is 5.0% or less, the flexibility of the CNTs is appropriately maintained, 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 over 0% and 5.0% or less plays an important role in improving the battery cycle characteristics of the CNT aggregate.

[0063] Furthermore, the elongation rate at break of the CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0064] 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 8.5 MPa or more and 50.0 MPa or less, even more preferably 10.0 MPa or more and 50.0 MPa or less, and particularly preferably 15.0 MPa or more and 50.0 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, 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 cycle characteristics of the battery (i.e., the rate of maintenance of discharge capacity). When the tensile strength of the CNT aggregate according to this disclosure is 50.0 MPa or less, it is easy to process into a dispersion and easy to ensure dispersibility in the dispersion. Specifically, a tensile strength of 50.0 MPa or less ensures a good balance between the flexibility and mechanical strength of the CNTs, resulting in uniform dispersion of the CNTs in the dispersion. This appropriately maintains the viscosity of the dispersion, further improving its durability against volume changes and stress during the battery cycle. As a result, the retention rate of discharge capacity is further improved.

[0065] Furthermore, the tensile strength of the CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0066] The fracture energy density of the CNT aggregate according to this disclosure is 30.0 MPa·% or more and 100.0 MPa·% or less, preferably 40.0 MPa·% or more and 80.0 MPa·% or less. When the fracture energy density of the CNT aggregate according to this disclosure is 30.0 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 cycle characteristics of the battery (i.e., the rate of maintenance of discharge capacity). 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. This ensures that the viscosity of the dispersion is properly maintained, further improving its resistance to volume changes and stress during the battery cycle, and consequently, the retention rate of discharge capacity is further improved.

[0067] Furthermore, the fracture energy density of a CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0068] <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.

[0069] <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.

[0070] 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.

[0071] 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.

[0072] =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.

[0073] According to manufacturing method X, CNTs containing ULCNTs can be obtained in the form of easily handled fibrous aggregates or other aggregates.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Furthermore, other forces applied to the generated particles may include magnetic force or photon pressure applied by a light source.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] The product particles produced in manufacturing method X contain ULCN. Depending on the manufacturing conditions, SWCNTs and MWCNTs may also be present.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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, nickelocene, and cobaltocene are particularly preferred as precursors. In one embodiment, 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 another embodiment, 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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. Alternatively, impurities may be removed by cleaning the CNT aggregates with an acidic gas such as hydrogen chloride using a dry cleaning device such as the MDC8540L (manufactured by Maple Co., Ltd.).

[0102] 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.

[0103] By purifying the aggregates of carbon nanotubes (CNTs), the metal content in the CNTs can be reduced.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] In other embodiments, the method may include generating CNTs containing ULCNTs in a reaction region by the above method, then 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.

[0108] =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 step (1) of supporting on a support to produce an active support; a step (2) of drying the active support by multi-stage drying including vacuum drying; a step (3) of subjecting the dried active support to heat treatment to produce a supported catalyst; and a step (4) of producing CNTs in the presence of the supported catalyst (hereinafter also referred to as "production method Y").

[0109] ・Step (1) In step (1), a mixture containing a main catalyst precursor and a cocatalyst precursor is mixed with γ-Al ２ O ３ to produce an active support.

[0110] In order to uniformly support the main catalyst precursor and the cocatalyst precursor on γ-Al ２ O ３ , the mixture may further contain a solvent, and the main catalyst precursor and the cocatalyst precursor may be in a state of being 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.

[0111] γ-Al ２ O ３ has high porosity and a spinel structure, so the main catalyst and the cocatalyst can be irregularly arranged on γ-Al ２ O ３ . CNTs grown from the irregularly arranged main catalyst can be produced in an entangled form.

[0112] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese and chromium, with cobalt being preferred.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 It is preferable to select one or more from the group consisting of O.

[0117] When the mixture contains two or more co-catalyst precursors, that is, when it contains both a vanadium precursor and a molybdenum precursor, the molar ratio of the sum of vanadium and molybdenum to vanadium can be 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and is preferably 1:0.5 to 1:0.9. When the above conditions are met, the structure of the CNTs can be stably maintained and CNTs with the desired pore volume can be produced.

[0118] The mixture may contain a main catalyst precursor and a co-catalyst precursor in molar ratios of 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, with a preferred ratio of 1:0.1 to 1:0.25. Satisfying the above molar ratios improves the dispersibility of the main catalyst, enabling the production of CNTs with the desired pore volume.

[0119] The mixture may further contain an organic acid that plays a role in suppressing the precipitation of the main catalyst precursor and the co-catalyst precursor.

[0120] 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.

[0121] The mixture can contain the organic acid and the co-catalyst precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, with a ratio of 1:3 to 1:6 being preferred. Satisfying the above range has the advantage of enabling the production of a transparent catalyst metal solution during catalyst manufacturing and the production of a catalyst with suppressed fine powder formation during impregnation.

[0122] The process may further include a maturation step after step (1).

[0123] 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, γ-Al ２ O ３ The main catalyst precursor and co-catalyst precursor can be sufficiently supported on the support. Furthermore, bubbles present within the support are removed to the maximum extent possible, allowing the main catalyst precursor and co-catalyst precursor to be sufficiently supported even in the fine pores inside the support.

[0124] Step (2) Next, the active support is dried by multi-stage drying, which includes vacuum drying.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] Primary vacuum drying can remove any solvents that may be present in the active carrier.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] The explanation regarding secondary vacuum drying is as described in the explanation of vacuum drying above.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] Step (3) Next, the dried active support is subjected to heat treatment to produce a supported catalyst.

[0143] 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.

[0144] 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 main catalyst and co-catalyst are γ-Al２ O ３ The supported catalyst can be manufactured with a uniform coating on the surface and pores, while minimizing energy consumption.

[0145] 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.

[0146] Step (4) Next, CNTs are produced in the presence of a supported catalyst.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] Possible heat sources for the reaction include induction heating, radiant heat, lasers, IR, microwaves, plasma, and surface plasmon heating.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] <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.

[0157] -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.

[0158] -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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] - 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] -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.

[0168] The dispersion method is not particularly limited. Examples of dispersion methods include using dispersion devices such as stirrers, homogenizers, colloid mills, flow jet mixers, dissolvers, paint conditioners, Manton emulsifiers, jet mills, and ultrasonic devices. Other examples of dispersion methods include using known grinding means, such as ball milling (e.g., ball mills, vibrating ball mills, planetary ball mills, bead mills, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mills, attritors, colloid mills, three-roll mills, pearl mills, super mills, impellers, despersers, KD mills, dynatrons, and pressurized kneaders. 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.

[0169] 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.

[0170] 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.

[0171] The following are examples of CNT dispersion manufacturing methods, but the manufacturing of CNT dispersions is not limited to those shown below.

[0172] -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.

[0173] (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.

[0174] The conductive material according to the present disclosure may contain a known conductive aid such as graphite or Ketjen black. The conductive material according to the present disclosure may also contain CNTs other than the CNT aggregate according to the present disclosure.

[0175] The conductive material according to the present disclosure can be used as one type of electrode material. An example of an electrode formed using an electrode material is an electrode included in a secondary battery. Hereinafter, an embodiment of an electrode and a secondary battery including the electrode will be described.

[0176] (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 meaning as the CNT aggregate according to the present disclosure, and preferred embodiments are also the same, so the description of the CNT aggregate is omitted herein.

[0177] The electrode may be at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, or may include a current collector and an electrode active material layer disposed on the current collector.

[0178] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. As the current collector, for example, one 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 may be used. Specifically, a transition metal having good carbon adsorption properties such as copper or nickel may be used as the current collector.

[0179] 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 can contain a positive electrode active material commonly used for positive electrode materials. Specifically, examples of the positive electrode active material include lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ) layered compounds such as, compounds substituted with one or more transition metals; LiFe３ O ４ lithium iron oxides such as; chemical formula 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 , Cu ２ V ２ O ７ vanadium oxides such as; chemical formula LiNi １－ｃ２ M ｃ２ O ２ (wherein 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) Ni-site type lithium nickel oxide represented by; chemical formula LiMn ２－ｃ３ M ｃ３ O ２ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01 ≤ c3 ≤ 0.1), or Li ２ Mn ３ MO ８ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn) lithium manganese composite oxide represented by; LiMn in which a part of Li in the chemical formula is substituted with alkaline earth metal ions ２ O ４ and the like can be mentioned.

[0180] 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.

[0181] 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, tetrafluoroethylene, 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.

[0182] (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.

[0183] 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.

[0184] 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.

[0185] 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, tetrahydroxyfuran, 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] (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.

[0191] <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.

[0192] Examples of planar aggregates relating to this disclosure include films.

[0193] The planar assemblies relating to this disclosure are useful, for example, in filters, electromagnetic shielding, and extreme ultraviolet (EUV) pellicles.

[0194] (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.

[0195] 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), poly(ethylene 2,6-naphthalate) (PEN), polyimide (PI), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), polyacetal (POM), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polyacetal (POM), polyphenylene ether (PPS), 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.

[0196] 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.

[0197] 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.

[0198] (Example 1) 1. Production of Sheet-Shaped CNT Assembly 1 Sheet-shaped 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 for 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 temperature-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.

[0199] 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, temperature-controlled at 1400°C, located downstream of the first temperature zone. The total gas supply flow rate for the carrier gas and source gas was set to 34 NL / min (NL is normal liters). The second temperature zone was maintained at a temperature sufficient to generate carbon nanotube aggregates.

[0200] 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 reactor, which was temperature-controlled to 150°C, and sheet-like CNT aggregates were collected.

[0201] 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.

[0202] 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.

[0203] -Dispersion composition- • CNT aggregate obtained above: 1.1 g • CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (700 kDa, manufactured by MP Biomedicals): 1.65 g • Purified water: 547.25 g

[0204] 2. Preparation of CNT dispersion 1 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: 85 MPa Number of passes: 8 Method: Circulation method

[0205] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> The content ratio of Fe atoms and Co atoms contained in the sheet-like ULMWCNT aggregate 1 of Example 1 was measured using an inductively coupled plasma mass spectrometer (ICP-MS) (NexION 2000C, PerkinElmer). The sheet-like ULMWCNT aggregate 1 was pretreated by low-temperature ashing / acid dissolution, and the results measured with the above apparatus showed that the Fe atom content relative to the total mass of the carbon nanotube aggregate 1 of Example 1 was 3900 ppm. The Co atom content was 0 ppm.

[0206] <Si content relative to the total mass of the CNT aggregate> The Si content relative to the total mass of CNT aggregate 1 was measured using an inductively coupled plasma mass spectrometer (ICP-AES) (NexION 2000C, PerkinElmer). The CNT aggregate 1 obtained above was pretreated by ashing / alkaline fusion / acid dissolution and then measured using the above apparatus. The Si content was 400 ppm.

[0207] <Bundle Diameter Features> For the CNT aggregate 1 of Example 1, imaging was performed using a scanning electron microscope (SEM), and five images in which CNT bundles were clearly observed were selected (one of which is shown in Figure 1). Image processing and image 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 of 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 then created.

[0208] 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 area ratio of bundles with a bundle diameter of 100 nm or more was 0.14. The cumulative 90% bundle diameter was 120 nm.

[0209] <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 1.01 μm. The evaluation results are shown in Table 1 below.

[0210] <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 rate: 0.6 s －１ ~384 simultaneous －１ Temperature: 25°C. From the obtained data, the shear rate was 12 s. －１ The viscosity was measured. The viscosity of the dispersion was 127.4 mPa·s. The common logarithmic representation of the viscosity was 2.11. 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.

[0211] <Evaluation of CNT aggregate dispersion 1: Tensile strength, elongation at break, and energy density at break> CNT dispersion 1 was poured onto a 22 mm x 75 mm x 3 mm slide glass type silicon plate (manufactured by Dosaka E-M Co., Ltd., #08-1044), heated at 100°C for 30 minutes and dried to prepare the measurement sample. The measurement sample was fixed to the gripping part of a tensile testing apparatus (manufactured by 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 32.6 MPa, the elongation at break was 2.3%, and the energy density at break was 75.1 MPa·%.

[0212] <Evaluation of CNT aggregate dispersion 1: Surface resistivity> CNT dispersion 1 was poured onto a 22 mm x 75 mm x 3 mm slide glass type silicon plate (manufactured by Dosaka E-M Co., Ltd., #08-1044), heated to 100°C, and dried for 30 minutes to be used as the measurement sample. The surface resistivity of the film was measured using a Loresta GXII manufactured by Nitto Seiko 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 1.07 Ω / □. The results are shown in Table 1 below.

[0213] (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 34 NL / min, and the gas was continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 500°C, and further, impurities were removed by washing with hydrogen chloride using a dry washing device MDC8540L (manufactured by Maple Co., Ltd.).

[0214] 2. Preparation of CNT dispersion 2 A dispersion 2 was obtained using the obtained CNT aggregate 2 in the same manner as in Example 1.

[0215] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> Measurements were taken in the same manner as in the example, except that CNT aggregate 2 was used. The content of Fe atoms was 4800 ppm. The content of Co atoms was 0 ppm.

[0216] <Si atom content relative to the total mass of the CNT aggregate> The measurement was performed in the same manner as in Example 1, except that CNT aggregate 2 was used. The Si atom content was 400 ppm.

[0217] <Bundle Diameter Characteristics> Using CNT aggregate 2, five SEM images were selected (one of which is shown in Figure 2), and the calculations were performed in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.41. The cumulative 90% bundle diameter was 230 nm.

[0218] <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. The cumulative 50% particle size D50 in volume-based particle size distribution was 1.48 μm. The evaluation results are shown in Table 1 below.

[0219] <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 585.9 mPa·s. The common logarithmic scale of the viscosity was 2.77.

[0220] <Evaluation of CNT aggregate dispersion 2: Tensile strength, elongation at break, and energy density at break> Measurements were taken in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the tensile strength was 23.5 MPa, the elongation at break was 2.2%, and the energy density at break was 51.7 MPa·%.

[0221] <Evaluation of CNT aggregate dispersion 2: Surface resistivity> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the surface resistivity was 0.78 Ω / □. The results are shown in Table 1 below.

[0222] (Comparative Example 1) 1. Preparation of Powdered CNT Assembly 3 As Powdered CNT Assembly 3, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT7000) were prepared.

[0223] 2. Preparation of CNT dispersion 3 Using the obtained CNT aggregate 3, a CNT dispersion 3 was obtained in the same manner as in Example 1.

[0224] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> Measurements were taken in the same manner as in the example, except that CNT aggregate 3 was used. The content of Fe atoms was 17,000 ppm. The content of Co atoms was 0 ppm.

[0225] <Si atom content relative to the total mass of the CNT aggregate> The measurement was performed in the same manner as in Example 1, except that CNT aggregate 3 was used. The Si atom content was 0 ppm.

[0226] <Bundle Diameter Characteristics> Using CNT aggregate 3, two SEM images were selected (one of which is shown in Figure 3), and the calculations were performed in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.10. The cumulative 90% bundle diameter was 90 nm.

[0227] <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 3 was used. 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.

[0228] <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 6.4 mPa·s. The common logarithmic scale of the viscosity was 0.81.

[0229] <Evaluation of CNT aggregate dispersion 3: Tensile strength, elongation at break, and energy density at break> Measurements were taken in the same manner as in Example 1, except that CNT dispersion 3 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·%.

[0230] <Evaluation of CNT aggregate dispersion 3: Surface resistivity> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 3 was used. As a result, the surface resistivity was 16.52 Ω / □. The results are shown in Table 1 below.

[0231] (Comparative Example 2) 1. Manufacturing of CNT Assembly 4 CNT assembly 4 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 42 NL / min, and the gas was continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 500°C.

[0232] 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.

[0233] The pre-dispersion 4 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 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

[0234] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> Measurements were taken in the same manner as in the example, except that CNT aggregate 4 was used. The content of Fe atoms was 110,000 ppm. The content of Co atoms was 0 ppm.

[0235] <Si atom content relative to the total mass of the CNT aggregate> The measurement was performed in the same manner as in Example 1, except that CNT aggregate 4 was used. The Si atom content was 1000 ppm.

[0236] <Bundle Diameter Characteristics> Using CNT aggregate 4, six SEM images were selected (one of which is shown in Figure 4), and the calculations were performed in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.41. The cumulative 90% bundle diameter was 200 nm.

[0237] <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. The cumulative 50% particle size D50 in volume-based particle size distribution was 0.44 μm. The evaluation results are shown in Table 1 below.

[0238] <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 34.6 mPa·s. The common logarithmic scale of the viscosity was 1.54.

[0239] <Evaluation of CNT aggregate dispersion 4: Tensile strength, elongation at break, and energy density at break> Measurements were taken in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the tensile strength was 3.5 MPa, the elongation at break was 4.1%, and the energy density at break was 14.2 MPa·%.

[0240] <Evaluation of CNT aggregate dispersion 4: Surface resistivity> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the surface resistivity was 4.21 Ω / □. The results are shown in Table 1 below.

[0241] (Comparative Example 3) 1. Preparation of Powdered CNT Assembly 5 As the powdered CNT assembly 5, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT9100) were prepared.

[0242] 2. Preparation of CNT dispersion 5 Using the obtained CNT aggregate 5, a CNT dispersion 5 was obtained in the same manner as in Example 1.

[0243] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> Measurements were taken in the same manner as in the example, except that CNT aggregate 5 was used. The content of Fe atoms was 7400 ppm. The content of Co atoms was 0 ppm.

[0244] <Si atom content relative to the total mass of the CNT aggregate> The measurement was performed in the same manner as in Example 1, except that CNT aggregate 5 was used. The Si atom content was 0 ppm.

[0245] <Bundle Diameter Characteristics> Using CNT aggregate 5, three SEM images were selected (one of which is shown in Figure 5), and the calculations were performed in the same manner as in Example 1. As a result, the area percentage of bundle diameters of 100 nm or more was 0.08. The cumulative 90% bundle diameter was 80 nm.

[0246] <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. 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.

[0247] <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 5.7 mPa·s. The common logarithmic scale of the viscosity was 0.75.

[0248] <Evaluation of CNT aggregate dispersion 5: Tensile strength, elongation at break, and energy density at break> Measurements were taken in the same manner as in Example 1, except that CNT dispersion 5 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·%.

[0249] <Evaluation of CNT aggregate dispersion 5: Surface resistivity> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the surface resistivity was 15.49 Ω / □. The results are shown in Table 1 below.

[0250] (Comparative Example 4) 1. Preparation of Powdered CNT Assembly 6 As the powdered CNT assembly 6, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT6120) were prepared.

[0251] 2. Preparation of CNT dispersion 6 A CNT dispersion 6 was obtained using the obtained CNT aggregate 6 in the same manner as in Example 1.

[0252] 3. Evaluation <Content of Fe and Co atoms relative to the total mass of the CNT aggregate> Measurements were taken in the same manner as in the examples, except that CNT aggregate 6 was used. The content of Fe atoms was 18 ppm. The content of Co atoms was 0 ppm.

[0253] <Si atom content relative to the total mass of the CNT aggregate> The measurement was performed in the same manner as in Example 1, except that CNT aggregate 6 was used. The Si atom content was 1000 ppm.

[0254] <Bundle diameter characteristics>

[0255] Except for selecting six SEM images using CNT aggregate 6 (one of which is shown in Figure 6), the calculations were performed in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.08. The cumulative 90% bundle diameter was 90 nm.

[0256] <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. The cumulative 50% particle size D50 in volume-based particle size distribution was 0.48 μm. The evaluation results are shown in Table 1 below.

[0257] <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 9.3 mPa·s. The common logarithmic scale of the viscosity was 0.97.

[0258] <Evaluation of CNT aggregate dispersion 6: Tensile strength, elongation at break, and energy density at break> Measurements were taken in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the tensile strength was 8.2 MPa, the elongation at break was 3.7%, and the energy density at break was 29.9 MPa·%.

[0259] <Evaluation of CNT aggregate dispersion 6: Surface resistivity> The measurement was performed in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the surface resistivity was 21.29 Ω / □. The results are shown in Table 1 below.

[0260] [Fabrication of Lithium-ion Rechargeable Batteries] Next, lithium-ion rechargeable batteries were fabricated.

[0261] 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 the positive electrode active material, conductive material (acetylene black), and binder (PVdF) in a ratio of 92:5:3 (mass ratio) and then kneading with N-methyl-2-pyrrolidone. The resulting positive electrode mixture was applied to a 15 μm thick Al foil to serve 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.

[0262] 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. ２ The 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.

[0263] 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.

[0264] 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

[0265] <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.

[0266] The evaluation results for Examples 1 and 2, and Comparative Examples 1 to 4 are shown in Table 1.

[0267]

[0268] As shown in Table 1, the CNT assemblies of Examples 1 and 2, in which the Fe atom content X and the bundle diameter W (which represents 90% of the cumulative total) satisfy the above range, yielded a carbon nanotube dispersion with appropriate viscosity, and it was found that batteries with high discharge capacity retention and excellent cycle characteristics could be fabricated.

Claims

1. A carbon nanotube aggregate containing Fe atoms, wherein the Fe atom content X relative to the total mass of the carbon nanotube aggregate is greater than 0 ppm and less than 5000 ppm, and which contains a bundle structure, wherein the bundle diameter W at which 90% of the cumulative volume is greater than 90 nm and less than 500 nm in the area observed by a scanning electron microscope.

2. The carbon nanotube aggregate according to claim 1, wherein the carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water are mixed, and at a liquid temperature of 25°C, 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 1.55 or higher (the unit of viscosity is mPa·s).

3. The carbon nanotube aggregate according to claim 1, which does not contain Si atoms and Co atoms, or contains at least one of Si atoms and Co atoms, wherein the total content Z of Si atoms and Co atoms relative to the total mass of the carbon nanotube aggregate is less than 1000 ppm.

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 a carbon nanotube aggregate as 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.

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