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

Abstract

The present invention provides a carbon nanotube aggregate or the like, from which a battery having excellent cycle characteristics can be manufactured.　Provided are: a carbon nanotube aggregate that satisfies the following conditions (1), (2), and (3); and an application thereof. (1) When the carbon nanotube aggregate is formed into a carbon nanotube dispersion having a carbon nanotube concentration of 0.002 mass% relative to the total amount of the carbon nanotube dispersion, the average value of fractal dimensions calculated by the method described in the description is 0.99-1.60 inclusive. (2) The elongation at break measured by the measurement method described in the description is more than 0% to 3.0% or less. (3) The carbon nanotube aggregate includes a bundle structure, and in an observation region with a scanning electron microscope, the area ratio of bundles having a bundle diameter of 100 nm or more is more than 0.1.

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 applications.

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are materials having a cylindrical structure formed by rolling up a graphene sheet in which carbon atoms are arranged in a hexagonal honeycomb pattern. CNTs are basically classified into single-walled CNTs, which are formed from a single layer of graphene sheet, and multi-walled CNTs, which are formed from multiple layers of graphene sheet. CNTs have good mechanical and electronic properties and are expected to be used in a variety of applications, and in recent years, various attempts have been proposed to further improve the properties of CNTs.

[0003] For example, Patent Document 1 discloses a CNT dispersion defined based on the analysis of scattering curves obtained by measurement using ultra-small-angle X-ray scattering.

[0004] Patent Document 2 discloses a CNT dispersion in which a CNT aggregate comprising multiple CNTs is dispersed in a dispersion medium, wherein the concentration of CNTs and the viscosity of the CNT dispersion are both within predetermined numerical ranges.

[0005] Patent Document 3 discloses a conductive material for secondary batteries containing carbon nanotubes, having a spherical secondary structure in which carbon nanotube units are entangled, and in which the true density, bulk density, and metal content are each within predetermined numerical ranges.

[0006] Patent Document 4 describes that lithium-ion battery negative electrode materials in which the tensile strength of conductivity enhancers such as CNTs is within a specific range effectively suppress the volume expansion of the negative electrode material and improve the battery's cycle characteristics.

[0007] Patent Document 5 describes a CNT aggregate that satisfies the following conditions: powder X-ray diffraction analysis shows the presence of a 2θ peak at 24°±2°; Raman spectroscopy analysis at a wavelength of 532 nm shows a G-band to D-band height ratio (G / D ratio) of 30 or more; and the combustion peak temperature is between 550°C and 700°C.

[0008] Patent document 6 describes a CNT aggregate having a bundle structure, with each bundle having a diameter greater than 0.3 μm, and an average diameter of 0.5 μm or more.

[0009] International Publication No. 2023 / 162937, Japanese Patent Publication No. 2018-39722, Japanese Patent Publication No. 2018-530854, Japanese Patent Publication No. 2023-542766, Japanese Patent Publication No. 2009-029695, Chinese Patent Application Publication No. 116111043 (Specification)

[0010] When manufacturing batteries using CNT assemblies, there were times when excellent cycle characteristics were required.

[0011] 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.

[0012] <1> A carbon nanotube aggregate that satisfies the following conditions (1), (2), and (3). (1) When the carbon nanotube dispersion has a carbon nanotube concentration of 0.002% by mass relative to the total amount of the carbon nanotube dispersion, the average value of the fractal dimension calculated by the following method is 0.99 or more and 1.60 or less. (Method for calculating the average value of the fractal dimension) The carbon nanotube dispersion is imaged using a scanning electron microscope to obtain multiple images of the carbon nanotube attachment regions. From the obtained images, an image in which the carbon nanotube attachment region is present throughout is selected. Using the selected image, the average value of the fractal dimension of the carbon nanotube structure is calculated by image analysis. (2) The elongation at break measured by the following measurement method is greater than 0% and 3.0% or less. (Method for measuring elongation at break) A carbon nanotube aggregate is mixed with water to prepare a dispersion with a concentration of 0.20% by mass. The obtained dispersion is poured onto a 22 mm × 75 mm × 3 mm slide glass silicon plate, heated at 100°C for 30 minutes to dry and obtain a sample for measurement. The obtained sample for measurement is fixed to the gripping part of a tensile testing device, and a tensile test is performed at a speed of 1 mm / min. The point where the stress is maximum is considered the breaking point, and the elongation at break is calculated from the length of the sample for measurement at the breaking point and the length of the sample for measurement before measurement. (3) Contains a bundle structure, and in the area observed by a scanning electron microscope, the area ratio of bundles with a bundle diameter of 100 nm or more is greater than 0.1. <2> A carbon nanotube aggregate as described in <1> that satisfies the following condition (4). (4) Contains a bundle structure, and in the area observed by a scanning electron microscope, the bundle diameter that accounts for 90% of the cumulative bundle is greater than 90 nm and less than or equal to 300 nm. <3> A conductive material comprising the carbon nanotube aggregate described in <1> or <2>. <4> An electrode comprising an electrode active material and the conductive material described in <3>. <5> A secondary battery comprising the electrode described in <4>. <6> A planar aggregate comprising the carbon nanotube aggregate described in <1> or <2>. <7> A laminate comprising a substrate and the planar aggregate described in <6>. <8> A filter using the planar aggregate described in <6>. <9> An electromagnetic shield using the planar aggregate described in <6>.<10> A pellicle for extreme ultraviolet light using the planar aggregate described in <6>.

[0013] 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.

[0014] Figure 1 is a scanning electron microscope image showing one aspect of the CNT aggregate 1 of Example 1. Figure 2 is a scanning electron microscope image showing one aspect of the CNT aggregate 2 of Example 2. Figure 3 is a scanning electron microscope image showing one aspect of the CNT aggregate 3 of Example 3. Figure 4 is a scanning electron microscope image showing one aspect of the CNT aggregate 4 of Example 4. Figure 5 is a scanning electron microscope image showing one aspect of the CNT aggregate 5 of Comparative Example 1. Figure 6 is a scanning electron microscope image showing one aspect of the CNT aggregate 6 of Comparative Example 2. Figure 7 is a scanning electron microscope image showing one aspect of the CNT aggregate 7 of Comparative Example 3. Figure 8 is a scanning electron microscope image showing one aspect of the CNT dispersion 1 of Example 1. Figure 9 is a scanning electron microscope image showing one aspect of the CNT dispersion 2 of Example 2. Figure 10 is a scanning electron microscope image showing one aspect of the CNT dispersion 3 of Example 3. Figure 11 is a scanning electron microscope image showing one aspect of the CNT dispersion 4 of Example 4. Figure 12 is a scanning electron microscope image showing one aspect of the CNT dispersion 5 of Comparative Example 1. Figure 13 is a scanning electron microscope image showing one aspect of the CNT dispersion 6 of Comparative Example 2. Figure 14 is a scanning electron microscope image showing one aspect of the CNT dispersion 7 of Comparative Example 3.

[0015] The carbon nanotube assemblies, conductive materials, electrodes, secondary batteries, planar assemblies, laminates, filters, electromagnetic shields, and extreme ultraviolet pellicles related to this disclosure will be described in detail below. The following descriptions may be based on typical embodiments of this disclosure, but this disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the purpose of this disclosure.

[0016] In this disclosure, numerical ranges indicated using "~" mean ranges that include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, 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 disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the amount of each component means the total amount of multiple substances if there are multiple substances corresponding to each component, unless otherwise specified. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0017] In this disclosure, the terms "carbon nanotube," "single-walled carbon nanotube," "multi-walled carbon nanotube," "carbon nanotube aggregate," "carbon nanotube structure," "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," "CNT structure," "ULCNT," and "CNT dispersion," respectively.

[0018] [CNT aggregate] The CNT aggregate according to this disclosure satisfies the following conditions (1), (2), and (3). (1) When the CNT dispersion has a CNT concentration of 0.002% by mass relative to the total amount of the CNT dispersion, the average value of the fractal dimension calculated by the following method is 0.99 or more and 1.60 or less. (Method for calculating the average value of the fractal dimension) The CNT dispersion is imaged using a scanning electron microscope to obtain multiple images of the CNT attachment regions. From the obtained images, an image in which the CNT attachment region is present throughout is selected. Using the selected image, the average value of the fractal dimension of the CNT structure is calculated by image analysis. (2) The elongation at break measured by the following measurement method is greater than 0% and 3.0% or less. (Method for measuring elongation at break) A dispersion with a concentration of 0.20% by mass is prepared by mixing the CNT aggregate with water. The obtained dispersion is poured onto a 22 mm × 75 mm × 3 mm slide glass type silicon plate and heated at 100°C for 30 minutes to dry and obtain a sample for measurement. The obtained sample for measurement is fixed to the gripping part of a tensile testing device and a tensile test is performed at a speed of 1 mm / min. The point where the stress is maximum is considered to be the breaking point, and the elongation at break is calculated from the length of the sample for measurement at the breaking point and the length of the sample for measurement before measurement. (3) The material contains a bundle structure, and in the observation area by a scanning electron microscope, the area ratio of bundles with a bundle diameter of 100 nm or more is greater than 0.1.

[0019] A CNT assembly that satisfies conditions (1), (2), and (3), i.e., a CNT assembly according to the present disclosure, makes it possible to manufacture a battery with excellent cycle characteristics. On the other hand, Patent Documents 1 to 6 do not contain any descriptions that focus on conditions (1), (2), and (3).

[0020] <Condition (1)> The CNT aggregate relating to this disclosure is such that, when the CNT dispersion has a CNT concentration of 0.002% by mass relative to the total amount of the CNT dispersion, the average value of the fractal dimension calculated by the following method is 0.99 or more and 1.60 or less. (Method for calculating the average value of the fractal dimension) The CNT dispersion is imaged using a scanning electron microscope to obtain multiple images of the CNT attachment regions. From the obtained images, an image in which the CNT attachment region is present throughout is selected. Using the selected image, the average value of the fractal dimension of the CNT structure is calculated by image analysis.

[0021] The CNT aggregate described herein makes it possible to manufacture a battery with excellent cycle characteristics. The inventors have found that a CNT aggregate whose average fractal dimension, calculated by a predetermined method, is between 0.99 and 1.60 forms a huge network structure in which CNTs are intertwined, allowing it to exist stably in a dispersion. The fractal dimension is the absolute value of the slope of the approximation line of a plot when the logarithm of the number of boxes required to cover the figure for which the fractal dimension is to be determined is plotted against the logarithm of the box (also called a compartment) size. When CNTs form a network structure, for smaller box sizes, the number of boxes required to cover the network structure increases, so the absolute value of the slope of the approximation line increases, and the value of the fractal dimension increases. It is estimated that when CNTs form a network structure, contact between CNTs occurs at multiple points, and a huge conductive path is formed as a conductive material within the electrode, thereby improving the cycle characteristics of the battery (i.e., the discharge capacity maintenance rate) when used as an electrode material for a battery. Therefore, the CNT assembly relating to this disclosure makes it possible to manufacture a battery with excellent cycle characteristics. This disclosure is not limited in any way to the above-described estimation mechanism.

[0022] [Average value of fractal dimension] The average value of the fractal dimension of the CNT structure calculated by a predetermined method using the CNT aggregate according to this disclosure is 0.99 or more and 1.60 or less. From the viewpoint of further improving the battery cycle characteristics, the average value of the fractal dimension is preferably 0.99 or more and 1.50 or less, more preferably 1.00 or more and 1.45 or less, even more preferably 1.00 or more and 1.40 or less, particularly preferably 1.00 or more and 1.35 or less, and especially preferably 1.00 or more and 1.30 or less. Furthermore, the average value of the fractal dimension is also preferably 1.05 or more and 1.45 or less, more preferably 1.05 or more and 1.40 or less, even more preferably 1.05 or more and 1.35 or less, particularly preferably 1.05 or more and 1.30 or less, even more preferably 1.10 or more and 1.25 or less, and especially preferably 1.15 or more and 1.23 or less. The lower limit of the average value of the fractal dimension is 0.99, which allows for multiple contact points between CNTs, improving the battery's cycle characteristics. Furthermore, the upper limit of the average value of the fractal dimension is 1.60, which ensures particularly good dispersibility of the CNT aggregate in the solvent, and also results in good adhesion with the electrode active material within the electrode when used as a conductive additive in a battery.

[0023] The average value of the fractal dimension can be adjusted by the length, diameter, etc., of the CNT aggregate.

[0024] In this disclosure, the term "CNT structure" refers to a structure formed from carbon nanotubes (CNTs), which can be confirmed by observing a CNT dispersion using a scanning electron microscope.

[0025] In this disclosure, the average value of the fractal dimension is calculated using a CNT dispersion in which the concentration of CNTs is 0.002% by mass relative to the total volume of the CNT dispersion, by the method described below.

[0026] (Preparation of CNT dispersion) A CNT dispersion is prepared in which the concentration of CNTs is 0.2% by mass relative to the total volume of the CNT dispersion. The method for preparing a CNT dispersion in which the concentration of CNTs is 0.2% by mass relative to the total volume of the CNT dispersion is not particularly limited and can be prepared by known methods. More specifically, first, a mixture is obtained by mixing CNT aggregates, water, and carboxymethylcellulose so that the concentration of CNTs is 0.2% by mass relative to the total volume. Next, the mixture is subjected to a pre-dispersion treatment using a homogenizer for 1 hour, and then subjected to a final dispersion treatment using a wet jet mill to obtain a CNT dispersion in which the concentration of CNTs is 0.2% by mass. In other words, a CNT aqueous dispersion in which the concentration of CNTs is 0.2% by mass relative to the total volume of the CNT dispersion is prepared.

[0027] The detailed conditions for the pre-dispersion treatment are not particularly limited; for example, dispersion treatment can be performed using a homogenizer at a speed of 500 rpm to 20,000 rpm. The detailed conditions for this dispersion treatment are also not particularly limited; for example, dispersion treatment can be performed using a wet jet mill with the following conditions: nozzle diameter: 0.15 mm to 0.70 mm, pressure: 10 MPa to 250 MPa, number of cycles: 1 to 30, method: circulating method.

[0028] (Imaging using a Scanning Electron Microscope (SEM)) The CNT dispersion, in which the concentration of CNTs is 0.2% by mass relative to the total volume of the CNT dispersion, is diluted with pure water to a CNT concentration of 0.002% by mass relative to the total volume of the CNT dispersion. This CNT dispersion with a CNT concentration of 0.002% by mass is imaged using an SEM to obtain multiple images of the CNT-implanted regions. The imaging method using the SEM is not particularly limited and can be carried out using known methods.

[0029] -Implantation of CNT dispersion onto SEM observation substrate- More specifically, first, the CNT dispersion is implanted onto the SEM observation substrate using the following procedure. 1. A slide glass coated with Pt deposition is UV-ozone treated and attached to the SEM observation substrate with conductive tape. 2. 0.001 μL to 1 μL of CNT dispersion is implanted onto the slide glass. 3. The SEM observation substrate with the implanted CNT dispersion is placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass with the frozen CNT dispersion is placed on a 4.0 × 10⁻⁶ surface. －３ Pa ~ 6.0 x 10 －３ The ice is sublimated by creating a vacuum to achieve a pressure of Pa.

[0030] -Imaging- Next, the imprinted CNT dispersion is imaged using an SEM device (for example, Hitachi High-Technologies Corporation, S-4800) under the following conditions to obtain multiple images of the CNT imprinted region. The CNT imprinted region is the area on the SEM observation substrate where the CNT network structure is located. From the viewpoint of reducing the variance of the fractal dimension value, it is preferable to obtain 10 or more images. Acceleration voltage: 1 kV Emission current: 10 μA Magnification: 500x Image size: 1280 pixels × 960 pixels

[0031] (Image Selection) From the images obtained, select the image in which the entire area is covered by the CNTs. More specifically, first, the following image processing is performed on all images of the CNT dispersion's coated area using image analysis software (e.g., ImageJ).

[0032] -Image Processing Procedure- 1. Cropping: 1280 pixels × 896 pixels 2. Filters: Gaussian Blur, Sigma (Radius) = 3 3. Filters: Top Hat, Radius = 9 pixels 4. Binarization: Auto Threhold, Otsu, White objects on black background 5. Morphology: Gray Morphology, Radius of the structure elements (pixels) = 3.0, Type of structure element=circle, operator=open

[0033] Next, the image after image processing is divided into 64 sections (8 sections vertically and 8 sections horizontally), and only images in which all 64 divided images have pixels with a pixel value of 255 (i.e., images in which the entire CNT attachment region exists) are selected. However, images in which CNT extraction is clearly not possible after image processing compared to the image before image processing (for example, images in which most of the SEM observation substrate area has pixels with a pixel value of 255) are excluded from the selection beforehand.

[0034] - Proportion of selected images - In this case, the proportion of images used to calculate the fractal dimension (i.e., selected images) out of the total number of images of the impregnation region of the CNT dispersion is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, particularly preferably 50% or more, and especially preferably 55% or more, from the viewpoint of reducing the variance of the fractal dimension value.

[0035] (Calculation of the average value of the fractal dimension) Using the selected images, the average value of the fractal dimension of the CNT structure is calculated by image analysis. More specifically, all of the selected post-processed images are analyzed using image analysis software (e.g., ImageJ), and the fractal dimension is calculated for each using the following procedure.

[0036] - Calculation Procedure - 1. Binary: Skeletonize 2. Analyze: Fractal Box Counter, Box Sizes = 4, 6, 8, 12, 16, 32, 64, 128, Black Backround

[0037] Based on the fractal dimension calculated for each image, the average value of the fractal dimension is then calculated.

[0038] <Condition (2)> The CNT aggregate relating to this disclosure has a fracture elongation of more than 0% and 3.0% or less, as measured by the following measurement method. (Method for measuring fracture elongation) A dispersion with a concentration of 0.20% by mass is prepared by mixing the CNT aggregate with water. The obtained dispersion is poured onto a 22 mm × 75 mm × 3 mm slide glass type silicon plate, and heated at 100°C for 30 minutes to dry and obtain a measurement sample. The obtained measurement sample is fixed to the gripping part of a tensile testing device, and a tensile test is performed at a speed of 1 mm / min. The point where the stress is maximum is considered the fracture point, and the fracture elongation is calculated from the length of the measurement sample at the fracture point and the length of the measurement sample before measurement.

[0039] The elongation at break of a CNT aggregate is measured, for example, by the following method. A dispersion containing CNT aggregates is cast onto a 22 mm × 75 mm × 3 mm slide glass type silicon plate (manufactured by Dosaka E-M Co., Ltd., #08-1044), and a dried film (CNT-containing film) is prepared as a measurement sample by heating at 100°C for 30 minutes. The prepared measurement sample is fixed to the gripping part of a tensile testing device (manufactured by Shimadzu Corporation, Autograph AG-IS), and a tensile test is performed at a speed of 1 mm / min to calculate the tensile strength (MPa). At the same time, the point where the test force is maximum is considered to be the breaking point, and the elongation at break (%) is calculated. The elongation at break of the CNT aggregate according to this disclosure is more than 0% and 3.0% or less, preferably 1.0% or more and 2.6% or less, and more preferably 1.5% or more and 2.6% or less.

[0040] When the elongation at break of the CNT aggregate according to this disclosure exceeds 0% (preferably 1.0% 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, thereby improving the overall conductivity of the CNT aggregate and enhancing the battery's cycle characteristics (i.e., the rate of discharge capacity maintenance). When the elongation at break of the CNT aggregate according to this disclosure is 3.0% or less, it is easy to process into a dispersion and ensure dispersibility in the dispersion. Specifically, when the elongation at break is 3.0% or less, the flexibility and mechanical strength of the CNTs are well balanced, and uniform dispersion of CNTs in the dispersion is achieved. This appropriately maintains the viscosity of the dispersion, further improving the battery's durability against volume changes and stress during the cycle. This further improves the rate of discharge capacity maintenance. Therefore, having a fracture elongation rate of the CNT aggregate in the range of over 0% and 3.0% or less plays an important role in improving the cycle characteristics of the battery made from the CNT aggregate.

[0041] Furthermore, the elongation rate at break of the CNT aggregate can be adjusted by the length, diameter, and other factors of the CNT aggregate.

[0042] <Condition (3)> The CNT aggregate relating to this disclosure includes a bundle structure, and in the area observed by a scanning electron microscope (SEM), the area ratio of bundles with a bundle diameter of 100 nm or more is greater than 0.1.

[0043] The CNT aggregates relating to this disclosure include bundle structures. A bundle structure 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 the 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.

[0044] Bundle structures in CNT aggregates can be formed, for example, by controlling the catalyst particle size distribution during chemical vapor deposition (CVD) manufacturing, or by controlling the cooling rate during the cooling process. It should be noted that multiple bundle structures may also form a single large bundle structure.

[0045] From the viewpoint of achieving both the handling properties and dispersibility in the solvent of the CNT aggregate, the width of the individual bundle structures contained in the CNT aggregate, i.e., the size in the width direction of the fiber bundle, is 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 width of the bundle structure can be determined by identifying the location where the bundle structure exists in the CNT aggregate and measuring the length using an image of the bundle structure.

[0046] In the CNT aggregate according to this disclosure, the area ratio of bundles with a bundle diameter of 100 nm or more exceeds 0.1 in the SEM observation area, resulting in the appropriate formation of a CNT bundle structure and improved conductivity and dispersibility as an electrode material. Specifically, a bundle diameter of 100 nm or more strengthens the bonding between CNTs, making the electron transport pathways connecting electrode active materials more robust, thereby improving the structural stability of the electrode. Furthermore, a large bundle diameter increases the electron conduction pathways within the electrode, promoting efficient current flow. This reduces the internal resistance of the battery and improves charge-discharge efficiency. Moreover, a large bundle diameter promotes uniform dispersion in the dispersion, improving dispersibility and maintaining the viscosity of the dispersion appropriately. Therefore, in the SEM observation area, the area ratio of bundles with a bundle diameter of 100 nm or more exceeds 0.1, resulting in a battery with excellent cycle characteristics.

[0047] In particular, the area ratio of the bundle is preferably greater than 0.1 and less than 0.6, more preferably greater than 0.1 and less than 0.55, even more preferably greater than 0.1 and less than 0.5, especially preferably 0.13 or more and 0.5 or less, even more preferably 0.14 or more and 0.5 or less, even more preferably 0.14 or more and less than 0.5, and especially preferably 0.14 or more and 0.45 or less. In other embodiments, the area ratio of the bundle is preferably 0.14 or more and 0.43 or less, more preferably 0.14 or more and 0.35 or less, even more preferably 0.14 or more and 0.30 or less, and especially preferably 0.14 or more and 0.26 or less. Within this range, the bundle structure of the CNTs is appropriately formed, and the bonding between the CNTs is strengthened, thus improving the conductivity as an electrode material. In addition, an appropriate bundle diameter improves the dispersibility of the CNTs, and a uniform conductive path is ensured within the electrode. This improves the overall conductivity of the electrodes and reduces the internal resistance of the battery, resulting in excellent cycle characteristics.

[0048] Furthermore, the area ratio of the bundle is preferably 0.1 or more and less than 0.4, more preferably 0.1 or more and 0.3 or less, even more preferably 0.14 or more and 0.3 or less, and particularly preferably 0.15 or more and 0.3 or less. Within this range, the bundle diameter of the CNTs becomes appropriately small, increasing the surface area as an electrode material and widening the contact area with the electrode active material. This further improves dispersibility, maintains the viscosity of the dispersion appropriately, promotes ion movement, and improves the charge-discharge efficiency of the battery. In addition, an appropriately small bundle diameter also has the effect of increasing the flexibility of the electrode and improving its durability against volume changes during cycling. Having the area ratio of the bundle within the above range is important for optimizing the balance between conductivity and dispersibility as an electrode material. Therefore, the cycle characteristics of the battery are further improved.

[0049] <Condition (4)> The CNT aggregate according to this disclosure includes a bundle structure, and preferably the bundle diameter at which 90% of the total volume is accumulated (hereinafter also referred to as the "90% bundle diameter") is greater than 90 nm and less than or equal to 300 nm in the area observed by a scanning electron microscope. Within this range, the bundle structure of the CNTs is formed more appropriately, and a battery with better cycle characteristics can be manufactured.

[0050] The details regarding the bundle structure contained in the CNT aggregate have been described previously, and will not be explained here.

[0051] 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, a cumulative 90% bundle diameter of 300 nm or less results in good dispersibility in the dispersion medium and facilitates the assurance of conductivity.

[0052] Specifically, a cumulative 90% bundle diameter exceeding 90 nm allows 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 300 nm or less results in good dispersibility in the dispersion medium, increasing structural stability within the electrode, improving durability against volume changes and stress during battery cycling, and thus improving the battery's cycle characteristics.

[0053] In particular, in one embodiment, the cumulative 90% bundle diameter is preferably greater than 90 nm and 250 nm or less, more preferably greater than 90 nm and 230 nm or less, even more preferably greater than 90 nm and 200 nm or less, especially preferably greater than 90 nm and 190 nm or less, even more preferably greater than 90 nm and 180 nm or less, particularly preferably greater than 90 nm and 170 nm or less, especially preferably 100 nm or more and 170 nm or less, and most preferably 110 nm or more and 170 nm or less. In another embodiment, the cumulative 90% bundle diameter is preferably greater than 100 nm and 250 nm or less, more preferably greater than 110 nm and 250 nm or less, even more preferably greater than 110 nm and 250 nm or less, and especially preferably greater than 110 nm and 230 nm or less. Within these ranges, by appropriately controlling the bundle diameter of the CNTs, the contact resistance between CNTs is reduced and electron conduction paths are efficiently formed, thereby improving conductivity. Furthermore, the bundle structure of the CNTs is appropriately formed, stabilizing the structure as an electrode material, improving durability against volume changes and stress during battery cycling, and thus improving the battery's cycle characteristics.

[0054] In another embodiment, the cumulative 90% bundle diameter is preferably greater than 90 nm and less than 190 nm, more preferably greater than 90 nm and 185 nm or less, even more preferably greater than 90 nm and 180 nm or less, and particularly preferably greater than 90 nm and 170 nm or less. Within this range, the bundle diameter of the CNTs becomes appropriately small, increasing the surface area of ​​the dispersion and widening the contact area with the dispersion medium. This further improves dispersibility and appropriately maintains the viscosity of the dispersion.

[0055] Therefore, having a cumulative 90% bundle diameter in the range of 90 nm to 300 nm (especially 90 nm to 250 nm, 90 nm to 230 nm, 90 nm to 200 nm, 90 nm to 190 nm, 90 nm to 185 nm, 90 nm to 180 nm, or 90 nm to 170 nm) plays a role in further improving the cycle characteristics (i.e., the rate of discharge capacity maintenance) of the CNT assembly battery.

[0056] <Matters concerning bundle diameter and bundle diameter parameters> The bundle diameter of the CNT aggregate is measured by observation using a 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.

[0057] -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

[0058] - Image Selection - From the obtained images, select two or more images in which CNT bundles are frequently observed.

[0059] - 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.

[0060] -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.

[0061] -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.

[0062] -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.

[0063] - 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.

[0064] <Other matters concerning CNT aggregates> In this disclosure, the CNTs included in the CNT aggregate may be SWCNTs or MWCNTs. From the viewpoint that having a layer distribution and slightly lower uniformity contributes to satisfying conditions (1), (2), and (3), it is preferable that the CNT aggregate includes SWCNTs and MWCNTs.

[0065] The maximum length of the CNTs included in the CNT aggregate relating to this disclosure is not particularly limited.

[0066] In one embodiment, the CNT aggregate may mainly consist of CNTs with a maximum length of 500 μm or less, and may not contain CNTs with a length greater than 500 μm and less than or equal to 30,000 μm. Here, "main component" means that 90% by mass or more of the CNTs constituting the CNT aggregate are CNTs with a maximum length of 500 μm or less. The CNT aggregate may also contain CNTs with a maximum length of 500 μm or less.

[0067] The CNT aggregates according to this disclosure include, for example, CNTs having a maximum length of 10 μm to 30,000 μm. The CNT aggregates according to this disclosure preferably include CNTs having a maximum length of 500 μm or more, more preferably include CNTs having a maximum length of 500 μm to 30,000 μm, and even more preferably include CNTs having a maximum length of 1,000 μm to 30,000 μm (i.e., ULCNTs).

[0068] ULCNTs are longer in length and can take the form of fibers compared to general-purpose CNTs. When the maximum length of the CNTs included in the CNT aggregate according to this disclosure is 500 μm or more, the entanglement between the CNTs becomes moderately strong, and the CNTs tend to form a network structure more easily.

[0069] By taking the form of fibers, ULCNTs have a tendency to entangle with each other. A CNT aggregate is preferably an aggregate containing multiple ULCNTs, as this allows the CNTs to entangle with each other and form a more stable aggregate. Hereinafter, an aggregate containing ULCNTs may be abbreviated as an "ULCNT aggregate."

[0070] Here, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two dimensions. The fiber may be a thread-like fiber with a circular cross-section, a ribbon-like fiber with a rectangular cross-section, hollow, or have other shapes. From the viewpoint of improving conductivity, the cross-section of the CNTs contained in the CNT aggregate is preferably circular and preferably hollow.

[0071] The CNT aggregate may be an aggregate of three-dimensional structures in which the CNTs are intertwined. The intertwined state of the CNTs in the CNT aggregate according to this disclosure can be confirmed by SEM observation.

[0072] The length of individual carbon nanotubes (CNTs) within a CNT aggregate can be measured by focusing on a single CNT and observing multiple SEM images within adjacent fields of view. Here, "CNT length" refers to the measured length in the longitudinal direction of the CNT, and the maximum value among the measured lengths is defined as the "maximum length." If, by observing the SEM images, one CNT with a maximum length in the range of 1,000 μm to 30,000 μm is observed within the field of view of the SEM image, it can be confirmed that the observed CNT contains a ulcerative colloidal cell (ULCNT).

[0073] It is preferable that multiple ULCNs are present within the field of view of the SEM image. Focusing on 100 CNTs included in the field of view of the SEM image, the maximum length of each is measured, and of the observed CNTs, it is preferable that 10% or more (in numerical terms) of the CNTs have a maximum length in the range of 1000 μm to 30000 μm (i.e., ULCNs), from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULCNs, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0074] The diameter of an ULCNT can be measured by observing a SEM (Surface-Emission Microscope) or transmission electron microscope (TEM) image. Here, diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULCNT. The diameter is measured at 10 different points on a single ULCNT, and the average value is taken as the diameter of that ULCNT.

[0075] The length of the ULCNT is in the range of 1,000 μm to 30,000 μm, preferably in the range of 1,050 μm to 25,000 μm, more preferably in the range of 1,100 μm to 20,000 μm, even more preferably in the range of 1,200 μm to 18,000 μm, and particularly preferably in the range of 1,300 μm to 15,000 μm. The diameter of the ULCNT is preferably in the range of 1 nm to 100 nm, more preferably in the range of 2 nm to 80 nm, even more preferably in the range of 3 nm to 50 nm, and particularly preferably in the range of 5 nm to 30 nm.

[0076] The length / diameter ratio, or aspect ratio, of the ULCNT is preferably 1000 or more, more preferably 3000 or more, even more preferably 5000 or more, and particularly preferably 10000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single ULCNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more ULCNTs.

[0077] Furthermore, from the viewpoint of dispersibility, the specific gravity of the ULCNT aggregate is preferably in the range of 1.5 to 2.5, more preferably in the range of 1.7 to 2.4, and even more preferably in the range of 1.8 to 2.2. The specific gravity of the ULCNT aggregate can be measured by the method described in JIS Z8807:2012 "Method for measuring the density and specific gravity of solids".

[0078] The purity of carbon as CNTs in an ULCNT aggregate can be measured by thermogravimetric analysis. For example, a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the ULCNT aggregate are obtained using a thermal analyzer (Shimadzu Corporation, DTG-60). In the DTA curve, where the peak top appears around 650°C to 750°C, the largest exothermic peak is considered to be the combustion of CNTs, and other exothermic peaks are considered to be the combustion of substances other than CNTs. The purity of the CNTs is determined from the weight loss rate of the TG curve. From the viewpoint of the resulting conductivity, the purity of the ULCNT aggregate is preferably 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more.

[0079] The resulting fibrous ULCNT is preferably flexible and strong. Furthermore, the conductivity of the ULCNT itself should be 5000 ohms. －１ ・m －１ Preferably, it is 10,000 ohms or more. －１ ・m －１ The above is more preferable. The conductivity of the ULCNT itself is typically 1,000,000 ohms. －１ ・m －１ The following applies:

[0080] <Method for producing CNTs> The method for producing CNTs in this disclosure is not particularly limited. For example, the method for producing CNTs in this disclosure can be a conventionally known chemical vapor deposition (CVD) method, a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst, or other such methods.

[0081] 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.

[0082] 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.

[0083] =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.

[0084] According to manufacturing method X, CNTs containing ULCNTs can be obtained in the form of easily handled fibrous aggregates or other aggregates.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Furthermore, other forces applied to the generated particles may include magnetic force or photon pressure applied by a light source.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The product particles produced in manufacturing method X contain ULCN. Depending on the manufacturing conditions, SWCNTs and MWCNTs may also be present.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The catalyst is preferably formed by the decomposition of a precursor. The precursor is preferably a thermal, photocatalytic, or plasma-degradable compound of one or more of the above-mentioned metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickerocene, and cobaltocene are particularly preferred as precursors. In some embodiments, at least 0.01% by mass of the precursor is contained in the carbon source, preferably 0.2% to 30% by mass of the precursor, and more preferably 0.2% to 20% by mass of the precursor. In some embodiments, 0.23% to 2.3% by mass of the precursor may be contained in the carbon source, and 0.02% to 20% by mass of the precursor. The catalyst may also be used supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The manufacturing method X preferably further includes a step of passing the obtained CNT aggregates through a sieve after the step of agglomerating the CNTs into aggregates. It is also preferable to recover the CNTs that have passed through the sieve. By passing the obtained CNT aggregates through a sieve, it is easier to obtain CNT aggregates that satisfy conditions (1), (2), and (3).

[0111] 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 of 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 cut into appropriate sizes beforehand.

[0112] Furthermore, it is preferable to use two types of sieves with different mesh sizes and pass the material through the sieves two or more times. By using the sieve with the relatively smaller mesh size among the two types of sieves, it is possible to remove amorphous carbon and other particles that have become dusty. Alternatively, by using the sieve with the relatively larger mesh size among the two types of sieves, it is possible to remove foreign matter and coarse CNTs that may have entered from the outside.

[0113] 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.

[0114] As another aspect, after generating CNTs containing ULCNTs by the above method in the reaction region, they may be condensed to form CNTs containing ULCNTs, and means including continuously withdrawing CNTs from near the reaction region may be taken. Further, as another aspect, means including generating CNTs containing ULCNTs in the reaction region, continuously electrostatically attracting CNTs containing ULCNTs from the reaction region, and recovering CNTs containing ULCNTs may be taken.

[0115] = Manufacturing Method Y = In the present disclosure, as an example of a method for manufacturing CNTs, the manufacturing method described in Japanese Patent Application Laid-Open No. 2021-527611 can be referred to. That is, a step (1) of manufacturing an active support by supporting a mixture containing a main catalyst precursor and a cocatalyst precursor on γ-Al ２ O ３ ; a step (2) of drying the active support by multi-stage drying including vacuum drying; a step (3) of manufacturing a supported catalyst by subjecting the dried active support to heat treatment; and a step (4) of manufacturing CNTs in the presence of the supported catalyst (hereinafter, also referred to as "manufacturing method Y").

[0116] - Step (1) In step (1), a mixture containing a main catalyst precursor and a cocatalyst precursor is supported on γ-Al ２ O ３ to manufacture an active support.

[0117] 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 dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, and water is preferred.

[0118] Since γ-Al ２ O ３ has a high porosity and a spinel structure, 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 manufactured in a entangled state.

[0119] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese, and chromium, with cobalt being preferred.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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 NH ４ 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] The process may further include a maturation step after step (1).

[0130] 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.

[0131] Step (2) Next, the active support is dried by multi-stage drying, which includes vacuum drying.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] Primary vacuum drying can remove any solvents that may be present in the active carrier.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] The explanation regarding secondary vacuum drying is as described in the explanation of vacuum drying above.

[0146] The second temperature may be 175 to 300°C, and is preferably 180 to 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.

[0147] 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.

[0148] The secondary vacuum drying may be carried out for 10 minutes to 3 hours or 10 minutes to 2 hours, and it is preferably carried out for 10 minutes to 2 hours. When the above conditions are satisfied, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and the energy consumption can be minimized.

[0149] - Step (3): Next, the dried active support is heat-treated to produce a supported catalyst.

[0150] When the heat treatment is carried out, a supported catalyst is produced in which the main catalyst and the promoter are coated on the surface and pores of γ-Al ２ O ３ .

[0151] The heat treatment may be carried out at 600 °C to 800 °C or 620 °C to 750 °C, and it is preferably carried out at 620 °C to 750 °C. When the above conditions are satisfied, a supported catalyst can be produced in which the main catalyst and the promoter are uniformly coated on the surface and pores of γ-Al ２ O ３ , and the energy consumption can be minimized.

[0152] The heat treatment may be carried out for 1 hour to 12 hours or 2 hours to 8 hours, and it is preferably carried out for 2 hours to 8 hours. When the above time is satisfied, a supported catalyst can be produced in which the catalyst precursor is uniformly coated on the surface and pores of γ-Al ２ O ３ .

[0153] - Step (4): Next, CNT is produced in the presence of the supported catalyst.

[0154] Specifically, CNT can be produced by bringing the supported catalyst into contact with a carbon-based compound. Specifically, a chemical vapor synthesis method may be used.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] Possible heat sources for the reaction include induction heating, radiant heat, lasers, IR, microwaves, plasma, and surface plasmon heating.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] [Carbon Nanotube Dispersion] The carbon nanotube dispersion (CNT dispersion) according to this disclosure comprises 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, and the like.

[0164] <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.

[0165] <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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] <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.

[0170] 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.

[0171] 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.

[0172] Other dispersants that excel in dispersibility, dispersion stability, and high concentration of CNTs include: Demol (registered trademark: hereinafter the same) N, Demol RN, and Demol T (manufactured by Kao Corporation), sodium salt of β-naphthalene sulfonic acid formalin condensate; Brij S 100 (manufactured by Sigma-Aldrich), 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.); and SOLSPERSE. ＴＭ W100, SOLSPERSE ＴＭ Examples include W150 (manufactured by Lubrizol Japan Co., Ltd.). CMC is particularly preferred from the viewpoint of excellent dispersion ability, dispersion stability, and high concentration of multi-walled carbon nanotubes.

[0173] When the CNT dispersion contains a dispersant, the amount of the dispersant used is not particularly limited and can be appropriately set according to the type of the dispersant, the amount of the CNT aggregate, the amount of the dispersion medium, and the like.

[0174] Since the CNT aggregate according to the present disclosure has a high affinity for the dispersion medium, the viscosity of the dispersion tends to be low. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the aggregate of the present disclosure in the dispersion medium is good. The viscosity of the above dispersion is preferably 10 mPa·s to 1600 mPa·s, more preferably 10 mPa·s to 1500 mPa·s, still more preferably 30 mPa·s to 1300 mPa·s, and particularly preferably 100 mPa·s to 1200 mPa·s. Further, it is preferably 100 mPa·s to 1100 mPa·s, more preferably 200 mPa·s to 900 mPa·s, and particularly preferably 218.5 mPa·s to 798.2 mPa·s. In another embodiment, from the viewpoint of achieving both dispersibility and battery performance, the viscosity of the above dispersion is more preferably 30 mPa·s to 1600 mPa·s, still more preferably 100 mPa·s to 1600 mPa·s, and particularly preferably 200 mPa·s to 1600 mPa·s.

[0175] The viscosity of the dispersion of the CNT aggregate is measured using a cone-plate viscometer (also known as an E-type viscometer). As the cone-plate viscometer, for example, DV-II+PROGRAMMABLE VISCOMETER manufactured by BROOKFIELD is used. The measurement conditions are as follows. Measurement jig: Cone-plate Measurement mode: Rotation mode Shearing rate: 0.6 s －１ ~384 s －１ Temperature: 25°C From the obtained data, the viscosity at the following shearing rate is read. Shearing rate = 12 s －１

[0176] [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.

[0177] The dispersion method is not particularly limited. Examples of dispersion methods include using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Other examples of dispersion methods include using known grinding means, such as ball milling (e.g., ball mill, vibrating ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressurized kneader. The method using a jet mill is preferred, and the method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pumps a mixture in a solvent as a high-speed flow from a nozzle placed in a sealed state inside a pressure vessel. In a wet jet mill, CNT aggregates are dispersed within a pressure vessel by collisions between opposing flows, collisions with the vessel wall, turbulence and shear flow generated by high-speed flow, etc. A suitable wet jet mill is an ultra-high pressure homogenizer manufactured by Jōkō Co., Ltd. (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.). However, the wet jet mill is not limited to these. When using the above-mentioned ultra-high pressure homogenizer as the dispersion device, the dispersion processing pressure is preferably 10 MPa to 250 MPa.

[0178] 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.

[0179] 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 adhesion between CNT aggregates due to moisture adhesion, 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 aggregates in this disclosure, etc.

[0180] The following are examples of CNT dispersion manufacturing methods, but the manufacturing of CNT dispersions is not limited to those shown below.

[0181] <Manufacturing Example 1: Example of Dispersion Production> 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 poured into the flask (for example, 20 mL), and the mixture is stirred at room temperature (25°C, the same applies hereafter). At this time, a known dispersant (for example, carboxymethylcellulose) may be added as appropriate. Next, the conductive additive is dispersed in the dispersion medium using a known dispersion device (for example, 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 (for example, 1 hour to 48 hours). In this way, a CNT dispersion is obtained.

[0182] [Conductive Material] The conductive material according to this disclosure includes a CNT aggregate. As described above, the CNT aggregate contained in the conductive material according to this disclosure has excellent conductivity when dispersed, and is therefore suitable as a conductive additive. Because the conductive material according to this disclosure includes the CNT aggregate according to this disclosure, it has excellent conductivity efficiency and can effectively impart high conductivity to the object to be used.

[0183] The conductive material relating to this disclosure may contain known conductive additives such as graphite and Ketjenblack. Furthermore, the conductive material relating to this disclosure may contain CNTs other than the CNT aggregate relating to this disclosure.

[0184] The conductive material relating to this disclosure can be used as one of the electrode materials. An example of an electrode formed using the electrode material is an electrode provided in a secondary battery. An embodiment of an electrode and a secondary battery equipped with the electrode will be described below.

[0185] <Electrode> The electrode according to this disclosure includes an electrode active material and a conductive material according to this disclosure. Because the electrode according to this disclosure includes a conductive material according to this disclosure, it has excellent conductivity for forming conductive paths within the electrode. Therefore, the secondary battery according to this disclosure has excellent cycle characteristics.

[0186] In electrodes, CNT aggregates can function as conductive additives. The CNT aggregates included in the electrodes described below are synonymous with the CNT aggregates in this disclosure, and the preferred embodiments are also the same; therefore, a description of the CNT aggregates will be omitted below.

[0187] The electrode may consist of at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, or it may include a current collector and an electrode active material layer disposed on the current collector.

[0188] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. Examples of current collectors include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, etc. Specifically, transition metals with good carbon adsorption properties, such as copper and nickel, may be used as current collectors.

[0189] The electrode active material layer may contain electrode active material. Preferably, the electrode active material is electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer may contain positive electrode active material commonly used for positive electrode materials. Specifically, as the positive electrode active material, 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 Li １＋ｃ１ Mn ２－ｃ１ O ４ (0≦c1≦0.33), LiMnO ３ LiMn ２ O ３ LiMnO ２ Lithium manganese oxides such as lithium copper oxide (Li ２ CuO ２ ); LiV ３ O ８ , V ２ O ５ ,Cd ２ V ２ O ７ Vanadium oxides such as LiNi; chemical formula LiNi １－ｃ２ M ｃ２ O ２ Ni-site type lithium nickel oxide represented by the chemical formula LiMn (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c² ≤ 0.66). ２－ｃ３ M ｃ３ O ２ (Here, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1.), or Li ２ Mn ３ MO ８ Lithium manganese composite oxide represented by (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. ２ O ４ These are some examples.

[0190] 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.

[0191] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer may include binders commonly used in electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers are substituted with Li, Na, Ca, etc.

[0192] <Secondary Battery> The secondary battery according to this disclosure comprises electrodes according to this disclosure. The secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode is an electrode according to this disclosure.

[0193] 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.

[0194] 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.

[0195] Specifically, the electrolyte may include non-aqueous organic solvents and metal salts. Examples of non-aqueous organic solvents include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate, which are aprotic organic solvents.

[0196] 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.

[0197] 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 － 、及び、(CF ３ CF ２ SO ２ ) ２ N － が挙げられる。

[0198] 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.

[0199] 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.

[0200] <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 contain components other than the CNT assembly relating to this disclosure.

[0201] Examples of planar aggregates relating to this disclosure include films containing the CNT aggregate relating to this disclosure.

[0202] The planar assemblies relating to this disclosure are useful, for example, in filters, electromagnetic shields, and pellicles for extreme ultraviolet (EUV) radiation.

[0203] 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 in water or other fluid and filtering it once or twice or more.

[0204] The planar assemblies relating to this disclosure are useful, for example, in filters, electromagnetic shielding, and pellicles for extreme ultraviolet (EUV) applications.

[0205] <Laminate> The laminate according to this disclosure comprises a substrate and a planar assembly according to this 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 this disclosure may be arranged on the substrate, and yet another layer may be arranged on the planar assembly.

[0206] The material constituting the substrate may be resin, glass, or fiber. Examples of resins include polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin polymer (COP), triacetate (TAC), cyclic olefin copolymer (COC), poly(vinyl chloride) (PVC), polyethylene 2,6-naphthalate (PEN), polyimide (PI), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), polyacetal (POM), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polyphenylene ether (PPE), polysulfone (PSU), polyether ether ketone (PEEK), and polyamide-imide (PAI). Examples of glass include float glass (SiO2). ２ Na ２ Examples include sodium chloride (containing O, CaO, and MgO), soda lime, aluminosilicate glass, and borosilicate glass. Examples of fibers include synthetic fibers such as polyester fibers, polyamide fibers, polyolefin fibers, and acrylic fibers; and natural fibers such as cotton, linen, silk, wool, cashmere, mohair, alpaca, jute, hemp, and ramie.

[0207] 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.

[0208] 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.

[0209] (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 in the gas phase. A cylindrical reactor with an inner diameter of 85 mm was used as the CNT reactor. First, ferrocene, as a metal catalyst precursor containing Fe atoms, and thiophene, as an accelerator, were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled to 200°C to 800°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.

[0210] 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, controlled to 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 thiophene / hydrogen gas flow rate ratio was set to range B in Table 1. The second temperature zone was maintained at a temperature sufficient to generate carbon nanotube aggregates.

[0211]

[0212] In the second temperature zone, a reaction field was generated within the temperature-controlled flow reactor, forming catalytic nuclei and causing rapid growth of CNTs, thereby generating CNT aggregates. The aggregates were discharged as continuous discharge through the outlet of the flow-type reactor, which was temperature-controlled between 200°C and 700°C, and sheet-like CNT aggregates were collected. The obtained sheet-like CNT aggregates were washed with pure water for 10 seconds, 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.

[0213] 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.

[0214] (Dispersion composition) - CNT aggregate 1 obtained above... 1.1 g - CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (manufactured by MP Biomedicals)... 1.65 g - Purified water... 547.25 g

[0215] The pre-dispersion 1 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: 85 MPa Number of passes: 8 Method: Circulation method

[0216] 3. Evaluation <Calculation of Fractal Dimension> (Imaging using a Scanning Electron Microscope (SEM)) -Implantation of CNT dispersion onto SEM observation substrate- The above CNT dispersion 1 was diluted with pure water so that the CNT concentration was 0.002% by mass relative to the total volume of the CNT dispersion. In order to prevent excessive aggregation of CNTs when observing the CNT dispersion (CNT concentration: 0.002% by mass) with an SEM, the CNT dispersion was implanted onto the SEM observation substrate using the following procedure.

[0217] 1. A Pt-deposited glass slide was UV-ozone treated and attached to a SEM observation substrate with conductive carbon tape. 2. 0.1 μL of CNT dispersion was applied to the glass slide. 3. The SEM observation substrate with the CNT dispersion was placed on a metal cooled with liquid nitrogen, and the CNT dispersion was frozen. 4. The glass slide with the frozen CNT dispersion was placed on a 4.0 × 10⁻⁶ surface. －３ The ice was sublimated by creating a vacuum using Pa pressure.

[0218] - Imaging - Images of the CNT-implanted region were obtained by imaging a CNT dispersion (CNT concentration: 0.002% by mass) using a SEM device under the following conditions. SEM device: S-4800 (manufactured by Hitachi High-Technologies Corporation) Acceleration voltage: 1 kV Emission current: 10 μA Magnification: 500x Image size: 1280 pixels × 960 pixels

[0219] Figure 8 shows an SEM image of the CNT dispersion 1 in Example 1. The formation of a network structure of CNTs was confirmed.

[0220] (Image Selection) For all images of the impregnation area of ​​the CNT dispersion (CNT concentration: 0.002 mass%), the following image processing was performed using the image analysis software ImageJ.

[0221] -Image Processing Procedure- 1. Cropping: 1280 pixels × 896 pixels 2. Filters: Gaussian Blur, Sigma (Radius) = 3 3. Filters: Top Hat, Radius = 9 pixels 4. Binarization: Auto Threhold, Otsu, White objects on black background 5. Morphology: Gray Morphology, Radius of the structure elements (pixels) = 3.0, Type of structure element=circle, operator=open

[0222] Next, the processed image was divided into 64 sections (8 sections vertically and 8 sections horizontally), and only images in which all 64 divided images contained pixels with a pixel value of 255 (i.e., images in which the entire CNT attachment region was present) were selected. However, images in which CNT extraction was clearly not achieved after the above image processing compared to the image before image processing (for example, images in which most of the SEM observation substrate area contained pixels with a pixel value of 255) were excluded from the selection process.

[0223] In other words, as a result of image selection, five out of the five total images of the impregnation region of the CNT dispersion were used to calculate the fractal dimension.

[0224] (Calculation of the average value of the fractal dimension) For all of the selected images after image processing, the fractal dimension was calculated using the image analysis software ImageJ in the following procedure.

[0225] - Calculation Procedure - 1. Binary: Skeletonize 2. Analyze: Fractal Box Counter, Box Sizes = 4, 6, 8, 12, 16, 32, 64, 128, Black Backround

[0226] Based on the fractal dimensions calculated for each image, the fractal dimension in Example 1 was calculated, and the average value of the fractal dimension was 1.23.

[0227] <Elongation 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 point where the test force was maximum was considered the breaking point, and the elongation at break was calculated. As a result, the elongation at break was 1.5%.

[0228] <Bundle Diameter Features> For the CNT aggregate 1 of Example 1, imaging was performed using a scanning electron microscope (SEM), and two images in which CNT bundles were clearly observed were selected from the obtained images (one of the two selected images 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 obtained.

[0229] 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. 3. The cumulative occupied area ratio was calculated, and the bundle diameter at which this value first exceeded 0.9 was determined as the cumulative 90% bundle diameter. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.17. The cumulative 90% bundle diameter was 170 nm.

[0230] <Viscosity of CNT dispersion> The viscosity of CNT dispersion 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, a cone-plate viscometer (BROOKFIELD DV-II+Pro PROGRAMMABLE VISCOMETER) was used to measure the viscosity. Measurement fixture: Cone-plate Measurement mode: Rotation mode Shear speed: 0.6 s －１ ~384 simultaneous －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 434.0 mPa·s.

[0231] (Example 2) 1. Manufacturing of CNT assembly 2 CNT assembly 2 was manufactured in the same manner as CNT assembly 1, except that the temperature of the second temperature zone was controlled to 1320°C, the total gas supply flow rate of the carrier gas and raw material gas was set to 17 NL / min, and the flow rate ratio of thiophene / hydrogen gas was set to range A in Table 1.

[0232] 2. Preparation of CNT dispersion 2 Using the obtained CNT aggregate 2, a pre-dispersion 2 was obtained in the same manner as in Example 1.

[0233] The pre-dispersion 2 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 CNT dispersion 2. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 200 MPa Number of passes: 8 Method: Circulation method

[0234] 3. Evaluation <Calculation of Fractal Dimension> Except for using two of the six total images of the impregnation region of the CNT dispersion for the calculation of the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 1.01. One of the images is shown in Figure 9.

[0235] <Elongation at Break> The elongation at break was calculated using CNT dispersion 2 in the same manner as in Example 1. As a result, the elongation at break was 2.0%.

[0236] <Bundle Diameter Features> For CNT aggregate 2 of Example 2, imaging was performed using SEM, and three images in which CNT bundles were clearly observed were selected from the obtained images (one of the three selected images is shown in Figure 2). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area percentage of bundles with a diameter of 100 nm or more was 0.43. The cumulative 90% bundle diameter was 190 nm.

[0237] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 2 was measured in the same manner as in Example 1. As a result, the viscosity was 33.2 mPa·s.

[0238] (Example 3) 1. Manufacturing of CNT Assembly 3 CNT assembly 3 was manufactured by mixing the following CNT assembly 3A and CNT assembly 3B. CNT assembly 3A was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 35 NL / min. CNT assembly 3B was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 36 NL / min.

[0239] 2. Preparation of CNT dispersion 3 A pre-dispersion 3 was obtained using the obtained CNT aggregate 3 in the same manner as in Example 1.

[0240] The pre-dispersion 3 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill under the following conditions to obtain the CNT dispersion 3. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 50 MPa Number of passes: 3 Method: Circulation method

[0241] 3. Evaluation <Calculation of Fractal Dimension> Except for using two of the six total images of the impregnation region of the CNT dispersion for the calculation of the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 1.15. One of the images is shown in Figure 10.

[0242] <Elongation at Break> The elongation at break was calculated using CNT dispersion 3 in the same manner as in Example 1. As a result, the elongation at break was 2.6%.

[0243] <Bundle Diameter Features> For the CNT aggregate 3 of Example 3, imaging was performed using an SEM, and four images in which CNT bundles were clearly observed were selected from the obtained images (one of the four selected images is shown in Figure 3). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a diameter of 100 nm or more was 0.26. The cumulative 90% bundle diameter was 150 nm.

[0244] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 3 was measured in the same manner as in Example 1. As a result, the viscosity was 798.2 mPa·s.

[0245] (Example 4) 1. Manufacturing of CNT assembly 4 CNT assembly 4 was manufactured in the same manner as CNT assembly 1, except that the flow rate ratio of thiophene / hydrogen gas was set to range A.

[0246] 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.

[0247] 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 the CNT dispersion 4. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of passes: 8 Method: Circulation method

[0248] 3. Evaluation <Calculation of Fractal Dimension> Except for using two of the six total images of the impregnation region of the CNT dispersion for the calculation of the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 1.23. One of the images is shown in Figure 11.

[0249] <Elongation at Break> The elongation at break was calculated using CNT dispersion 4 in the same manner as in Example 1. As a result, the elongation at break was 2.3%.

[0250] <Bundle Diameter Features> For the CNT aggregate 4 of Example 4, imaging was performed using an SEM, and six images in which CNT bundles were clearly observed were selected from the obtained images (one of the six selected images is shown in Figure 4). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area percentage of bundles with a diameter of 100 nm or more was 0.14. The cumulative 90% bundle diameter was 110 nm.

[0251] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 4 was measured in the same manner as in Example 1. As a result, the viscosity was 218.5 mPa·s.

[0252] (Comparative Example 1) 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.

[0253] 2. Preparation of CNT dispersion 5: Using the prepared powdered CNT aggregate 5, a CNT dispersion 5 was obtained in the same manner as in Example 1.

[0254] 3. Evaluation <Calculation of the average value of the fractal dimension> Except for using 3 out of a total of 17 images of the impregnation region of the CNT dispersion to calculate the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 0.86. One of the images is shown in Figure 12.

[0255] <Elongation at Break> The elongation at break was calculated using CNT dispersion 5 in the same manner as in Example 1. The results are shown in Table 2.

[0256] <Bundle diameter features> For the CNT aggregate 5 of Comparative Example 1, imaging was performed using an SEM, and three images in which CNT bundles were clearly observed were selected from the obtained images (one of the three selected images is shown in Figure 5). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. The results are shown in Table 2.

[0257] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 5 was measured in the same manner as in Example 1. As a result, the viscosity was 5.7 mPa·s.

[0258] (Comparative Example 2) 1. Preparation of Powdered CNT Assembly 6 As the powdered CNT assembly 6, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT7000) were prepared.

[0259] 2. Preparation of CNT dispersion 6: Using the prepared powdered CNT aggregate 6, a CNT dispersion 6 was obtained in the same manner as in Example 1.

[0260] 3. Evaluation <Calculation of the average value of the fractal dimension> Except for using 6 out of a total of 22 images of the impregnation region of the CNT dispersion 6 for the calculation of the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 0.98. One of the images is shown in Figure 13.

[0261] <Elongation at Break> The elongation at break was calculated using CNT dispersion 6 in the same manner as in Example 1. The results are shown in Table 2.

[0262] <Bundle diameter features> For the CNT aggregate 6 of Comparative Example 2, imaging was performed using SEM, and two images in which CNT bundles were clearly observed were selected from the obtained images (one of the two selected images is shown in Figure 6). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. The results are shown in Table 2.

[0263] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 6 was measured in the same manner as in Example 1. As a result, the viscosity was 6.4 mPa·s.

[0264] (Comparative Example 3) 1. Preparation of CNT aggregate 7 As CNT aggregate 7, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT6120) were prepared.

[0265] 2. Preparation of CNT dispersion 7: Using the prepared CNT aggregate 7, a CNT dispersion 7 was obtained in the same manner as in Example 1.

[0266] 3. Evaluation <Calculation of the average value of the fractal dimension> Except for using 9 out of a total of 21 images of the impregnation region of the CNT dispersion 7 for the calculation of the fractal dimension, the fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, and the average value of the fractal dimension was 1.02. One of the images is shown in Figure 14.

[0267] <Elongation at Break> The elongation at break was calculated using CNT dispersion 7 in the same manner as in Example 1. The results are shown in Table 2.

[0268] <Bundle diameter features> For the CNT aggregate 7 of Comparative Example 3, imaging was performed using SEM, and six images in which CNT bundles were clearly observed were selected from the obtained images (one of the six selected images is shown in Figure 7). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. The results are shown in Table 2.

[0269] <Viscosity of CNT aggregate dispersion> The viscosity of CNT dispersion 7 was measured in the same manner as in Example 1. As a result, the viscosity was 9.3 mPa·s.

[0270] Next, we fabricated a lithium-ion secondary battery.

[0271] 1. Fabrication of positive electrode for lithium secondary battery: Positive electrode active material (LiNi ０．８ Co ０．１ Mn ０．１ O ２ A positive electrode mixture was prepared by mixing a conductive material (acetylene black) and a binder (PVdF) in a ratio of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and then kneading with N-methyl-2-pyrrolidone. The obtained positive electrode mixture was applied to a 15 μm thick Al foil to be used as a current collector, vacuum-dried at 80°C for 1 hour, and then roll-pressed to obtain a positive electrode for a lithium secondary battery. The positive electrode area was 1.65 cm². ２ The estimated amount is 16 mg / cm³. ２ The density is 3.0 g / cm³. ３ I adjusted it so that it would be as follows.

[0272] 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 (weight 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.

[0273] 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.

[0274] 4. Cycle Test Using the manufactured 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

[0275] <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.

[0276] The evaluation results for Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 2.

[0277]

[0278] As shown in Table 2, the CNT assemblies of Examples 1 to 4 satisfy conditions (1), (2), and (3), and were found to have a high discharge capacity retention rate and excellent cycle characteristics. This confirms that the CNT assemblies of the examples have excellent performance as conductive additives for batteries. The suitable dispersibility reflects that the stacking of CNTs is suitable, indicating good conductive path formation and excellent conductivity as an electrode material. Therefore, according to one embodiment of the present disclosure, it is possible to provide a CNT assembly with excellent discharge capacity retention rate when a CNT dispersion is used as a conductive additive.

Claims

A carbon nanotube aggregate that satisfies the following conditions (1), (2), and (3). (1) When the carbon nanotube dispersion has a carbon nanotube concentration of 0.002% by mass relative to the total volume of the carbon nanotube dispersion, the average value of the fractal dimension calculated by the following method is 0.99 or more and 1.60 or less. (Method for calculating the average value of fractal dimensions) The carbon nanotube dispersion is imaged using a scanning electron microscope to obtain multiple images of the carbon nanotube attachment regions. From the obtained images, an image in which the carbon nanotube attachment region is present throughout is selected. Using the selected image, the average value of the fractal dimension of the carbon nanotube structure is calculated by image analysis. (2) The elongation at break measured by the following measurement method is greater than 0% and 3.0% or less. (Method for measuring elongation at break) A dispersion with a concentration of 0.20% by mass is prepared by mixing a carbon nanotube aggregate with water. The resulting dispersion is poured onto a 22 mm × 75 mm × 3 mm glass slide silicon plate and heated at 100°C for 30 minutes to dry and obtain a sample for measurement. The obtained sample is fixed to the gripping part of a tensile testing apparatus, and a tensile test is performed at a speed of 1 mm / min. The point where the stress is maximum is considered the fracture point, and the elongation at fracture is calculated from the length of the sample at the fracture point and the length of the sample before measurement. (3) The bundle structure is included, and in the area observed by a scanning electron microscope, the area ratio of bundles with a bundle diameter of 100 nm or more is greater than 0.

1. A carbon nanotube aggregate according to claim 1, satisfying the following condition (4). (4) The bundle structure is included, and in the area observed by scanning electron microscopy, the bundle diameter that is 90% of the cumulative area is greater than 90 nm and less than or equal to 300 nm. 　 A conductive material comprising a carbon nanotube aggregate according to claim 1 or claim 2. 　 An electrode comprising an electrode active material and the conductive material described in claim 3. 　 A secondary battery comprising the electrode described in claim 4. 　 A planar aggregate comprising the carbon nanotube aggregate described in claim 1 or claim 2. 　 A laminate comprising a substrate and the planar assembly described in claim 6. 　 A filter using the planar assembly described in claim 6. 　 Electromagnetic shielding using the planar assembly described in claim 6. 　 A pellicle for extreme ultraviolet radiation using the planar aggregate described in claim 6.

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