Carbon nanotube aggregates, conductive materials, electrodes, secondary batteries, planar aggregates, laminates, filters, electromagnetic wave shields, and pellicles for extreme ultraviolet rays

Abstract

Provided is a carbon nanotube aggregate and the like that can be used to fabricate a battery having excellent cycle characteristics. [Solution] A carbon nanotube aggregate and its application satisfying the following conditions (1) and (2): (1) When a carbon nanotube dispersion is prepared in which the concentration of carbon nanotubes is 0.002 mass% relative to the total amount of the carbon nanotube dispersion, the average value of the fractal dimension calculated by the method described in the specification is 0.99 to 1.60, and (2) the cumulative 50% particle size D50 in the volume-based particle size distribution is 1.0 μm to 15.0 μm.

Description

[Technical Field]

[0001] The present disclosure relates to a carbon nanotube aggregate, a conductive material, an electrode, a secondary battery, a planar aggregate, a laminate, a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet rays. [Background technology]

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are substances with a cylindrical structure formed by rolling up graphene sheets in which carbon atoms are arranged in a hexagonal honeycomb pattern. CNTs are basically broadly classified into single-walled CNTs formed from a single layer of graphene sheets, and multi-walled CNTs formed from multiple layers of graphene sheets. 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 liquid that is defined based on an analysis of a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method.

[0004] Patent Document 2 discloses a CNT dispersion in which a CNT aggregate having a plurality of CNTs is dispersed in a dispersion medium, and the CNT concentration and viscosity of the CNT dispersion are each within a predetermined numerical range.

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

[0006] Patent Document 4 describes that a dispersion of CNTs containing 100 ppm or less of metals consisting of iron, nickel, and chromium has a median diameter of 100 μm or less, and has low viscosity and good storage stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2023 / 162937 [Patent Document 2] Japanese Patent Application Publication No. 2018-39722 [Patent Document 3] Special Publication No. 2018-530854 [Patent Document 4] Japanese Patent Publication No. 2022-034325 Summary of the Invention [Problem to be solved by the invention]

[0008] When a battery is produced using a CNT aggregate, there are cases where it is required to have excellent cycle characteristics.

[0009] The present disclosure has been made in consideration of the above circumstances. An object of an embodiment of the present disclosure is to provide an aggregate of carbon nanotubes that can be used to fabricate a battery having excellent cycle characteristics. Another problem to be solved by another embodiment of the present disclosure is to provide a conductive material, an electrode, a secondary battery, and a planar assembly, each including the carbon nanotube aggregate. Another problem to be solved by another embodiment of the present disclosure is to provide a laminate including the above-mentioned planar assembly. Another problem to be solved by another embodiment of the present disclosure is to provide a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet rays using the above-mentioned planar assembly. [Means for solving the problem]

[0010] <1> An aggregate of carbon nanotubes that satisfies the following conditions (1) and (2): (1) When the carbon nanotube concentration is 0.002 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 fractal dimension) The carbon nanotube dispersion is imaged using a scanning electron microscope to obtain multiple images of the carbon nanotube-attached regions. From the obtained images, images in which the carbon nanotube-attached regions are present throughout are selected. Using the selected images, the average value of the fractal dimension of the carbon nanotube structure is calculated by image analysis. (2) The cumulative 50% particle size D50 in the volume-based particle size distribution is 1.0 μm or more and 15.0 μm or less. <2> Satisfy the condition (3) below, <1> The carbon nanotube aggregate according to claim 1. (3) The bundle structure is included, and in the region observed by a scanning electron microscope, the cumulative 90% bundle diameter is more than 90 nm and 300 nm or less. <3> <1> or <2> A conductive material comprising the carbon nanotube aggregate according to claim 1. <4> an electrode active material; <3> and an electrode comprising the conductive material according to claim 1. <5> <4> A secondary battery comprising the electrode according to claim 1. <6> <1> or <2> A planar aggregate comprising the carbon nanotube aggregate according to claim 1. <7> A substrate; <6> A laminate comprising the planar assembly according to claim 1. <8> <6> A filter using the planar assembly described in 1. <9> <6> An electromagnetic wave shield using the planar assembly described in 1. <10> <6> A pellicle for extreme ultraviolet radiation using the planar assembly described in . [Effects of the Invention]

[0011] According to one embodiment of the present disclosure, there is provided an aggregate of carbon nanotubes that can be used to fabricate a battery having excellent cycle characteristics. According to another embodiment of the present disclosure, there are provided a conductive material, an electrode, a secondary battery, and a planar assembly, each including the carbon nanotube aggregate. According to another embodiment of the present disclosure, there is provided a laminate including the above-described planar assembly. According to other embodiments of the present disclosure, there are provided a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet radiation, which use the planar assembly. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 1 of Example 1. As shown in FIG. [Figure 2] FIG. 2 is a scanning electron microscope photograph showing one aspect of the CNT aggregate 2 of Example 2. As shown in FIG. [Figure 3] FIG. 3 is a scanning electron microscope photograph showing one aspect of the CNT aggregate 3 of Example 3. As shown in FIG. [Figure 4] FIG. 4 is a scanning electron microscope photograph showing one aspect of the CNT aggregate 4 of Example 4. As shown in FIG. [Figure 5] FIG. 5 is a scanning electron microscope photograph showing one aspect of the CNT aggregate 5 of Comparative Example 1. As shown in FIG. [Figure 6] FIG. 6 is a scanning electron microscope photograph showing one aspect of the CNT aggregate 6 of Comparative Example 2. As shown in FIG. [Figure 7] FIG. 7 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 7 of Comparative Example 3. As shown in FIG. [Figure 8] FIG. 8 is a scanning electron microscope photograph showing one embodiment of the CNT dispersion liquid 1 of Example 1. As shown in FIG. [Figure 9] FIG. 9 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 2 of Example 2. [Figure 10] FIG. 10 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 3 of Example 3. [Figure 11]FIG. 11 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 4 of Example 4. [Figure 12] FIG. 12 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 5 of Comparative Example 1. [Figure 13] FIG. 13 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 6 of Comparative Example 2. [Figure 14] FIG. 14 is a scanning electron microscope photograph showing one embodiment of CNT dispersion liquid 7 of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a carbon nanotube aggregate, a conductive material, an electrode, a secondary battery, a planar aggregate, a laminate, a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet radiation according to the present disclosure will be described in detail. The following description may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented by making appropriate modifications within the scope of the object of the present disclosure.

[0014] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0015] In the present disclosure, the terms "carbon nanotubes," "single-walled carbon nanotubes," "multi-walled carbon nanotubes," "carbon nanotube aggregate," "carbon nanotube structure," "carbon nanotubes having a maximum length of 1000 μm to 30000 μm," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "CNT aggregate," "CNT structure," "ULCNT," and "CNT dispersion," respectively.

[0016] [CNT aggregate] The CNT aggregate according to the present disclosure satisfies the following conditions (1) and (2). (1) When the CNT concentration of the CNT dispersion is 0.002 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 fractal dimension) The CNT dispersion is imaged using a scanning electron microscope to obtain multiple images of the CNT-attached regions. From the obtained images, images in which the CNT-attached regions are present throughout are selected. Using the selected images, the average value of the fractal dimension of the CNT structure is calculated by image analysis. (2) The cumulative 50% particle size D50 in the volume-based particle size distribution is 1.0 μm or more and 15.0 μm or less.

[0017] A CNT aggregate that satisfies the conditions (1) and (2), that is, a CNT aggregate according to the present disclosure, can produce a battery having excellent cycle characteristics. On the other hand, Patent Documents 1 to 4 do not mention conditions (1) and (2).

[0018] <Condition (1)> The CNT aggregate according to the present disclosure has an average fractal dimension of 0.99 or more and 1.60 or less, calculated by the following method, when the CNT concentration is 0.002 mass % relative to the total amount of the CNT dispersion. (Method for calculating the average value of fractal dimension) The CNT dispersion is imaged using a scanning electron microscope to obtain multiple images of the CNT-attached regions. From the obtained images, images in which the CNT-attached regions are present throughout are selected. Using the selected images, the average value of the fractal dimension of the CNT structure is calculated by image analysis.

[0019] The CNT aggregate according to the present disclosure makes it possible to fabricate a battery with excellent cycle characteristics. The present inventors have found that a CNT aggregate having an average fractal dimension calculated by a predetermined method of 0.99 to 1.60 forms a giant network structure in which CNTs are entangled with each other and can exist stably in a dispersion liquid. Fractal dimension is the absolute value of the slope of the approximate line of a plot of the logarithm of the number of boxes required to cover the figure for which the fractal dimension is to be calculated against the logarithm of the box (also called partition) size. When CNTs form a network structure, the number of boxes required to cover the figure of the network structure increases with smaller box sizes, so the absolute value of the slope of the approximate line increases, and the value of the fractal dimension increases. When the CNTs form a network structure, contact between the CNTs occurs at multiple points, forming huge conductive paths as a conductive material within the electrode, which is presumably why the cycle characteristics (i.e., the retention rate of discharge capacity) of the battery improves when the CNT aggregate according to the present disclosure is used as an electrode material. Therefore, it is possible to produce a battery with excellent cycle characteristics. It should be noted that the present disclosure is in no way limited to the above-mentioned presumed mechanism.

[0020] [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 the present disclosure is 0.99 or more and 1.60 or less. From the viewpoint of further improving the cycle characteristics of the battery, 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, and particularly preferably 1.00 or more and 1.30 or less. The average value of the fractal dimension is also preferably 1.10 or more and 1.45 or less, more preferably 1.10 or more and 1.40 or less, even more preferably 1.10 or more and 1.30 or less, still more preferably 1.12 or more and 1.30 or less, and particularly preferably 1.15 or more and 1.23 or less. A lower limit of 0.99 for the average fractal dimension allows for multiple contact points between CNTs, improving the cycle characteristics of the battery. Furthermore, an upper limit of 1.60 for the average fractal dimension ensures particularly good dispersibility of the CNT aggregate in the solvent. Furthermore, when used as a conductive additive in a battery, the CNT aggregate also exhibits good adhesion to the electrode active material within the electrode.

[0021] The average value of the fractal dimension can be adjusted by the length, diameter, etc. of the CNT aggregate.

[0022] In the present disclosure, the CNT structure refers to a structure formed by CNTs, and can be confirmed by observing a CNT dispersion liquid with a scanning electron microscope.

[0023] In the present disclosure, the average value of the fractal dimension is calculated by the method described below using a CNT dispersion liquid in which the CNT concentration is 0.002 mass % relative to the total amount of the CNT dispersion liquid.

[0024] (Preparation of CNT dispersion) A CNT dispersion liquid is prepared in which the concentration of CNTs is 0.2 mass % relative to the total amount of the CNT dispersion liquid. The method for preparing a CNT dispersion liquid having a CNT concentration of 0.2 mass % relative to the total amount of the CNT dispersion liquid is not particularly limited, and the CNT dispersion liquid can be prepared by a known method. More specifically, first, CNT aggregates, water, and carboxymethyl cellulose are mixed to obtain a mixture with a CNT concentration of 0.2 mass% relative to the total amount. Next, the mixture is subjected to a dispersion treatment for 1 hour using a homogenizer as a pre-dispersion, and then to a dispersion treatment using a wet jet mill as a main dispersion, thereby obtaining a CNT dispersion with a CNT concentration of 0.2 mass%. In other words, a CNT aqueous dispersion with a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is prepared.

[0025] The detailed conditions for the pre-dispersion treatment are not particularly limited, and for example, the dispersion treatment is carried out using a homogenizer under conditions of 500 rpm to 20,000 rpm. The detailed conditions for this dispersion treatment are not particularly limited, and for example, the dispersion treatment is carried out using a wet jet mill under the following conditions: nozzle diameter: 0.15 mm to 0.70 mm, pressure: 10 MPa to 250 MPa, number of times: 1 to 30 times, method: circulation method.

[0026] (Image taken using a scanning electron microscope (SEM)) The CNT dispersion having a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is diluted with pure water so that the CNT concentration becomes 0.002 mass% relative to the total amount of the CNT dispersion, and this CNT dispersion having a CNT concentration of 0.002 mass% is imaged using an SEM to obtain multiple images of the CNT-attached region. The imaging method using an SEM is not particularly limited, and can be performed by a known method.

[0027] -Attaching CNT dispersion to a substrate for SEM observation- More specifically, first, the CNT dispersion liquid is attached to a substrate for SEM observation according to the following procedure. 1. A slide glass with Pt deposition is treated with UV and ozone, and then attached to a substrate for SEM observation with conductive tape. 2. Apply 0.001 μL to 1 μL of the CNT dispersion liquid to the slide glass. 3. The SEM observation substrate with the CNT dispersion attached is placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass on which the CNT dispersion liquid was frozen was placed on a 4.0 x 10 -3 Pa ~ 6.0 × 10 -3 A vacuum is drawn to a pressure of 0.05 Pa to sublimate the ice.

[0028] -Image capture- Next, the impregnated CNT dispersion is imaged using an SEM device (e.g., S-4800, manufactured by Hitachi High-Technologies Corporation) under the following conditions to obtain multiple images of the CNT-immobilized region. The CNT-immobilized region is the region 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: 10μA Measurement magnification: 500x Image size: 1280 pixels x 960 pixels

[0029] (Image selection) Among the obtained images, an image in which the CNT-attached region is present throughout is selected. More specifically, first, the following image processing is performed on all images of the CNT dispersion-attached region using image analysis software (for example, ImageJ).

[0030] - Image processing procedure - 1.Crop: 1280 pixels x 896 pixels 2.Filters: Gaussian Blur, Sigma(Radius)=3 3.Filters:Top Hat, Radius=9pixels 4. Binarization: Auto Threshold, 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

[0031] Next, the image after the image processing is divided into 64 parts (8 parts vertically and horizontally), and only images in which all 64 divided images have pixels with a pixel value of 255 (i.e., images in which the CNT-attached region is present throughout) are selected from the images of the attachment region. However, images in which CNTs have clearly not been extracted after the image processing compared to the image before the image processing (for example, images in which most of the SEM observation substrate region has pixels with a pixel value of 255) are excluded from selection in advance.

[0032] -Percentage of selected images- In this case, the proportion of images used to calculate the fractal dimension (i.e., selected images) among the total number of images in the CNT dispersion liquid-attached region 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 values.

[0033] (Calculation of the average value of the fractal dimension) Using the selected image, the average value of the fractal dimension of the CNT structure is calculated by image analysis. More specifically, all of the selected images after image processing are analyzed using image analysis software (for example, ImageJ), and the fractal dimension is calculated for each image using the following procedure.

[0034] -Calculation procedure- 1.Binary:Skeletonize 2.Analyze:Fractal Box Counter, Box Sizes=4,6,8,12,16,32,64,128, Black Background

[0035] Based on the fractal dimension calculated for each image, the average value of the fractal dimension is further calculated.

[0036] <Condition (2)> The CNT aggregate according to the present disclosure has a cumulative 50% particle size D50 in the volume-based particle size distribution of 1.0 μm or more and 15.0 μm or less. The CNT aggregate according to the present disclosure preferably has a cumulative 50% particle size D50 in the volumetric particle size distribution of 1.0 μm or more and 14.0 μm or less, and more preferably 1.0 μm or more and 13.0 μm or less. The cumulative 50% particle size D50 in the volumetric particle size distribution is also preferably 1.1 μm or more and 15.0 μm or less, more preferably 1.1 μm or more and 14.0 μm or less, and even more preferably 1.1 μm or more and 13.0 μm or less. When the cumulative 50% particle diameter D50 is within the above range, the particle size of the CNT aggregate is appropriately controlled, and uniform dispersion of the CNT aggregate in the dispersion liquid is achieved, making it possible to produce a battery with excellent cycle characteristics. In particular, when the cumulative 50% particle diameter D50 is in the range of 1.0 μm or more and 15.0 μm or less, the particle size of the CNT aggregates is appropriately small and uniform, which suppresses aggregation of the CNT aggregates in the dispersion and improves dispersibility. It is believed that the small particle size of the CNTs increases their surface area in the dispersion and strengthens their interaction with the dispersion medium, thereby improving dispersibility. Furthermore, a uniform particle size distribution stabilizes the viscosity of the CNT aggregate dispersion, improving processability when forming electrodes or other products using the CNT aggregates and ease of handling during use. Furthermore, when the cumulative 50% particle size D50 is within the above range, the particle size of the CNT aggregate is appropriately controlled, and a more uniform dispersion is achieved when a dispersion is prepared using the CNT aggregate. Therefore, by satisfying condition (2), the dispersibility of the CNT aggregates is further improved and the viscosity of the dispersion is optimized, making it possible to fabricate a battery with excellent cycle characteristics and to provide a high-performance CNT dispersion that is also excellent in conductivity and handleability.

[0037] By setting the cumulative 50% particle size D50 to 15.0 μm or less, the CNT aggregate and the electrode active material can be mixed in the electrode in a state of sufficient adhesion, making it easier to form a conductive path.

[0038] The cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is measured as follows. The CNT dispersion is thoroughly stirred and further diluted with pure water. Using the resulting diluted solution as a sample, the cumulative particle size D50 of the CNT dispersion is measured using a particle size distribution analyzer (LA-960, laser diffraction particle size distribution analyzer, manufactured by Horiba, Ltd.). The particle refractive index of the CNT to be measured is 1.920-0.522i. The refractive index of the solvent is set to 1.333. When measuring, the CNT dispersion is diluted by adding it dropwise to pure water while observing the transmittance, and measurements are carried out after confirming that the particle size distribution on the monitor has stabilized.

[0039] <Condition (3)> The CNT aggregate according to the present disclosure preferably has a bundle structure, and the cumulative 90% bundle diameter (hereinafter also referred to as the "cumulative 90% bundle diameter") in the region observed by a scanning electron microscope is more than 90 nm and not more than 300 nm. In this range, the CNT bundle structure is more appropriately formed, and a battery with better cycle characteristics can be fabricated.

[0040] In this disclosure, the bundle structure contained in a CNT aggregate refers to an aggregate in which multiple CNTs are aggregated together by van der Waals forces or the like to form a bundle. It is presumed that when a CNT aggregate contains bundle structures of an appropriate size, the handleability of the CNT aggregate as a whole is improved and stability is further improved. On the other hand, if the bundle structures contained in the CNT aggregate are too large, the size of the CNT aggregate itself becomes too large, and it becomes difficult to separate and disperse the CNTs contained in the bundle structures, which may result in reduced dispersibility in a dispersion medium.

[0041] The bundle structure in the CNT aggregate can be formed, for example, by controlling the catalyst particle size distribution in the production by chemical vapor deposition (CVD) method, by controlling the cooling rate in the cooling process, etc. Note that multiple bundle structures may form one large bundle structure.

[0042] From the viewpoint of achieving both ease of handling of the CNT aggregate and dispersibility in a solvent, the width of each bundle structure 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 the bundle structure in the CNT aggregate is preferably 10% by mass to 100% by mass, and more preferably 20% by mass to 90% by mass, relative to the total mass of the CNT aggregate. The presence or absence of a bundle structure in a 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 a photographed image of the bundle structure.

[0043] When the CNT aggregate according to the present disclosure is observed by SEM, the 90% cumulative bundle diameter exceeds 90 nm, which makes it easier for the CNT bundles to gather and form a long-distance conductive network. Furthermore, when the 90% cumulative bundle diameter is 300 nm or less, the dispersibility in the dispersion medium is improved and the conductivity is easily ensured.

[0044] Specifically, a cumulative 90% bundle diameter of over 90 nm allows CNTs to gather together 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 improves dispersibility in the dispersion medium, enhancing structural stability within the electrode and improving durability against volume changes and stress during battery cycling, thereby improving the battery's cycle characteristics.

[0045] In particular, in one embodiment, the cumulative 90% bundle diameter is preferably greater than 90 nm and not greater than 250 nm, more preferably greater than 90 nm and not greater than 230 nm, even more preferably greater than 90 nm and not greater than 200 nm, particularly preferably greater than 90 nm and not greater than 190 nm, even more preferably greater than 90 nm and not greater than 180 nm, and especially preferably greater than 90 nm and not greater than 170 nm. By appropriately controlling the CNT bundle diameter within this range, contact resistance between CNTs is reduced and electron conduction paths are efficiently formed, thereby improving conductivity. Furthermore, the CNT bundle structure is appropriately formed, stabilizing the structure as an electrode material, improving durability against volume changes and stress during battery cycling, and improving the battery's cycle characteristics.

[0046] In another embodiment, the cumulative 90% bundle diameter is preferably more than 90 nm and less than 190 nm, more preferably more than 90 nm and 180 nm or less, even more preferably more than 90 nm and 170 nm or less, particularly preferably more than 100 nm and 170 nm or less, and even more preferably 110 nm or more and 170 nm or less. Within this range, the CNT bundle diameter becomes appropriately small, increasing the surface area of ​​the dispersion and widening the contact area with the dispersion medium. This further improves dispersibility and maintains an appropriate viscosity of the dispersion.

[0047] Therefore, having a cumulative 90% bundle diameter in the range of more than 90 nm and not more than 300 nm (particularly, more than 90 nm and not more than 250 nm, more than 90 nm and not more than 230 nm, more than 90 nm and not more than 200 nm, more than 90 nm and not more than 190 nm, more than 90 nm and not more than 185 nm, more than 90 nm and not more than 180 nm, or more than 90 nm and not more than 170 nm) serves to further improve the cycle characteristics (i.e., the discharge capacity retention rate) of a battery made of a CNT aggregate.

[0048] Furthermore, in the CNT aggregate according to the present disclosure, the area ratio of bundles having a bundle diameter of 100 nm or more is preferably greater than 0.1 when observed with an SEM. When the area ratio of bundles having a bundle diameter of 100 nm or more is greater than 0.1, a CNT bundle structure is formed appropriately, and the mechanical strength and conductivity as an electrode material are improved. The area ratio of the bundle is preferably more than 0.1 and less than 0.6, more preferably more than 0.1 and less than 0.55, even more preferably more than 0.1 and less than 0.5, particularly preferably 0.12 or more and less than 0.5, even more preferably 0.14 or more and less than 0.5, even more preferably 0.15 or more and less than 0.5, and especially preferably 0.15 or more and 0.45 or less. In another embodiment, the ratio is preferably 0.14 or more and 0.43 or less, and more preferably 0.14 or more and 0.26 or less.

[0049] <Matters regarding bundle diameter and bundle diameter parameters> The bundle diameter of the CNT aggregate is measured by observation using an SEM. The CNT aggregate is photographed at a magnification of 100,000 to obtain multiple SEM photographs. The imaging method using an SEM is not particularly limited, and can be performed by a known method.

[0050] -Image capture- Using an SEM device (for example, S-4800 manufactured by Hitachi High-Technologies Corporation), images are taken under the following conditions to obtain multiple images of the CNT aggregate. From the viewpoint of reducing the variance of the analytical values ​​of the bundle diameter, it is preferable to obtain five or more images. Acceleration voltage: 0.5 kV Emission current: 10μA Measurement magnification: 100,000 times Image size: 1280 pixels x 960 pixels

[0051] -Image selection- From the obtained images, select two or more images in which CNT bundles are clearly observed.

[0052] - Overview of bundle diameter analysis using image analysis - The selected image is subjected to image processing and analysis using Python. In image processing, the CNT outline and center line are detected and combined with the original image. In image analysis, the bundle diameter is determined by calculating the distance from the center line to the outline of the created image. The product of the bundle diameter and the length of the center line is then calculated to calculate the area occupied by the CNT in the image.

[0053] -Detecting the outline of CNTs using image analysis- 1. The image is binarized to distinguish between CNTs and the background. 2. Create a contour for the CNT part using the edge detection function of the OpenCV library.

[0054] -Detecting CNT centerlines using image analysis- 1. Adjust the parameters to distinguish between CNTs and the background and perform binarization. 2. Create a skeleton for the CNT part using the skeletonize function of the scikit-image library. 3. For each coordinate of the skeleton, the number of skeletons within the surrounding two pixels is counted, and coordinates where five or more exist are recognized as skeleton intersections. 4. The skeleton is divided at the intersections by converting the intersections into background pixels. The divided skeleton is called a region. 5. Measure the length of the region and delete the short region. 6. Linear approximation is performed for each region. 7. For each line created, obtain the X-axis coordinate of the region that was the source of approximation. Convert the line into a line segment based on the range in which the obtained X-coordinate exists. Treat the line segment obtained here as the center line of the CNT. 8. Calculate the similarity based on the center coordinates and angle for all pairs of center lines. Pairs of center lines whose center coordinates are within 10 pixels of each other and whose angle between the two line segments is less than 10 degrees are treated as overlapping center lines, and the shorter one is deleted. 9. Overlay and save the contour and center line of the CNT on the original image. Treat the contour in red and the center line in blue.

[0055] - Detection of the bundle diameter of CNT by image analysis - 1. Read the image created by image processing and recognize the CNT, contour, background, and center line by hue recognition. 2. Measure the length of each center line. 3. Select random points on the center line and draw perpendicular lines from the points to the center line. 4. Detect the intersection points of the perpendicular lines and the contour, and save the distance from the random points on the center line to the intersection points as the bundle diameter. 5. Calculate the product of the line segment length of the center line and the bundle diameter as the exclusive area. Save the data as a histogram with the bundle diameter on the horizontal axis and the exclusive area on the vertical axis.

[0056] - Acquisition of bundle diameter parameters - Using the calculated bundle diameter histogram data, calculate the feature amount of the bundle diameter of each sample by the following method. 1. Add up the bundle diameters and exclusive areas of multiple fields of the same sample, and normalize them so that the sum is 1. Along with the normalization, set the unit of the vertical axis as the exclusive area ratio. 2. Obtain the total value of the exclusive area ratios of the bundles with a bundle diameter of 100 nm or more. 3. Calculate the cumulative exclusive area ratio, and obtain the bundle diameter when this value first exceeds 0.9 as the cumulative 90% bundle diameter.

[0057] <Other matters regarding the CNT aggregate> In the present disclosure, the CNTs included in the CNT aggregate may be SWCNTs or MWCNTs. From the perspective that having a layer number distribution and a slightly low uniformity contributes to satisfying conditions (1) and (2), the CNT aggregate preferably includes SWCNTs and MWCNTs.

[0058] The maximum length of the CNTs included in the CNT aggregate according to the present disclosure is not particularly limited.

[0059] In one embodiment, the CNT aggregate may be an aggregate that contains CNTs having a maximum length of 500 μm or less as a main component and does not contain CNTs having a maximum length of more than 500 μm and no more than 30,000 μm. Here, "main component" means that 90 mass % or more of the CNTs that make up the CNT aggregate are CNTs having a maximum length of 500 μm or less. The CNT aggregate may contain CNTs having a maximum length of 500 μm or less.

[0060] The CNT aggregate according to the present disclosure includes, for example, CNTs having a maximum length of 10 μm to 30,000 μm. The CNT aggregate according to the present disclosure preferably contains CNTs having a maximum length of 500 μm or more, more preferably contains CNTs having a maximum length of 500 μm to 30,000 μm, and even more preferably contains CNTs having a maximum length of 1,000 μm to 30,000 μm (i.e., ULCNTs).

[0061] Compared to general-purpose CNTs, ULCNTs are longer and can take the shape of fibers. When the maximum length of the CNTs contained in the CNT aggregate according to the present 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.

[0062] Being in the form of a fiber, ULCNTs have the property of easily entangling with each other. The CNT aggregate contains at least one ULCNT, and from the viewpoint that the CNTs are likely to entangle with each other and form a more stable aggregate, it is preferable that the CNT aggregate is an aggregate containing multiple ULCNTs. Hereinafter, an aggregate containing ULCNT may be abbreviated as "ULCNT aggregate."

[0063] 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 another shape. From the viewpoint of increasing electrical conductivity, the cross section of the CNTs contained in the CNT aggregate is preferably circular, and is preferably hollow.

[0064] The CNT aggregate may be an aggregate having a three-dimensional structure in which the CNTs are entangled with one another. The entangled state of the CNTs in the CNT aggregate according to the present disclosure can be confirmed by SEM observation.

[0065] The length of the CNTs contained in a CNT aggregate can be measured by focusing on a single CNT and observing multiple SEM images taken at adjacent viewing angles. Here, "CNT length" refers to the measured length of the CNT in the longitudinal direction, and the maximum value of the measured lengths is taken as the "maximum length." When observing an SEM photograph, if one CNT with a maximum length in the range of 1000 μm to 30000 μm is observed within the viewing angle of the SEM photograph, it can be confirmed that the observed CNTs include ULCNTs.

[0066] It is preferable that multiple ULCNTs are present within the viewing angle of the SEM photograph. Focusing on 100 CNTs within the viewing angle of the SEM photograph, the maximum length of each is measured, and from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULCNTs, it is preferable that 10% or more of the observed CNTs (i.e., ULCNTs) have a maximum length in the range of 1,000 μm to 30,000 μm, calculated as numbers, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0067] The diameter of ULCNT can be measured by observing SEM or transmission electron microscope (TEM) photographs. Here, the diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULCNT. The diameter is measured at 10 different locations on a single ULCNT, and the average value is taken as the diameter of that ULCNT.

[0068] 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 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.

[0069] The length / diameter ratio of ULCNT, so-called aspect ratio, is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 10,000 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.

[0070] 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 density and specific gravity of solids."

[0071] The purity of carbon in the ULCNT aggregate as CNT can be measured by thermogravimetric analysis. For example, using a thermal analyzer (manufactured by Shimadzu Corporation, DTG-60), the thermogravimetric (TG) curve and differential thermal analysis (DTA) curve of the ULCNT aggregate are obtained. The largest exothermic peak in the DTA curve where a peak top appears around 650 °C to 750 °C is regarded as the combustion of CNT, and the exothermic peaks that appear other than that are regarded as the combustion of substances other than CNT. The purity of CNT is determined from the weight loss rate of the TG curve. From the perspective of the conductivity obtained, the purity of the ULCNT aggregate is preferably 50% by mass or more, more preferably 65% by mass or more, still more preferably 80% by mass or more, and particularly preferably 95% by mass or more.

[0072] The obtained fibrous ULCNT is preferably flexible and strong. Also, the conductivity of the ULCNT itself is preferably 5000 ohm -1 ·m -1 or more, more preferably 10000 ohm -1 ·m -1 or more. Note that the conductivity of the ULCNT itself is usually 1000000 ohm -1 ·m -1 or less.

[0073] <Method for manufacturing CNT> The method for manufacturing CNT in the present disclosure is not particularly limited. For example, as the method for manufacturing CNT in the present disclosure, methods such as a conventionally known chemical vapor deposition (CVD) method and a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst can be applied.

[0074] The CNT in the present disclosure can be manufactured, for example, by referring to the methods described in Japanese Patent Application Laid-Open No. 2016-102047, Japanese Patent Publication No. 2021-527611, etc.

[0075] Hereinafter, the method for manufacturing CNT in the present disclosure will be described with examples. However, the method for manufacturing CNT in the present disclosure is not limited to the following examples.

[0076] =Manufacturing method X= An example of a CNT manufacturing method referred to in this disclosure is described in JP 2016-102047 A. That is, the manufacturing method includes the steps of passing gaseous reactants containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in a reaction zone of the reactor in the presence of a catalyst to form product particles containing carbon, aggregating the product particles into aggregates, and applying force to the aggregates to continuously move the aggregates out of the reaction zone (hereinafter also referred to as "Manufacturing Method X").

[0077] According to production method X, CNTs including ULCNTs can be obtained in the form of fibrous aggregates or other aggregate forms that are easy to handle.

[0078] In production method X, the force applied to the product particles may be a mechanical force. When the agglomerates are fibrous CNTs, the mechanical force applied to the product particles can be exerted by a rotating spindle around which the agglomerates are wound, and the fibrous CNTs can be collected on the spindle or accumulated elsewhere by rotating around the spindle one or more times and then successively unwinding the spindle.

[0079] The spindle is preferably oriented with its axis perpendicular or parallel to the flow direction of the gaseous reactant(s), although other orientations are also possible, for example, a spindle with its axis oriented at a 25° angle to the flow direction of the gaseous reactants may also be suitable for applying mechanical forces to the product particles.

[0080] The spindle can rotate around two axes (e.g., two perpendicular axes). In particular, the spindle can rotate around axes perpendicular and parallel to the flow direction of the gaseous reactants. Such a spindle can pull and twist the fibrous CNT aggregates to control the twist number and length.

[0081] The spindle may be made of metal, ceramic, or resin. The spindle can have different suitable shapes depending on the material properties and the intended use of the CNTs. The spindle can be used as a mold for producing carbon products, for example, by a spin-coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0082] Fibrous CNTs are deposited on a spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the application of electric or other fields to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by gas flow forces.

[0083] The rotation speed of the spindle is preferably 0.01 rpm (revolutions / minute; the same applies hereinafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the rotational speed of the spindle) may be adjusted so that the material is collected at a similar rate as it is produced. The rotational speed of the spindle may also control the thickness of the accumulated CNT fiber. In a preferred embodiment, as the spindle rotates, the CNT fiber is processed in the axial direction of the spindle. This processing ensures that the CNT fiber is evenly wrapped along the spindle, rather than being wrapped only at one specific point on the spindle.

[0084] The CNT fibers may be collected, for example, on the reactor wall 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 CNT fibers as they are collected. A suitable substrate arrangement for fiber technology is a substrate consisting of two guides positioned at right angles to each other.

[0085] In production method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow may be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube downstream of the reaction zone. A vacuum may be applied to the product particles.

[0086] Another force that can be applied to the product particles is electrostatic force, which is suitably applied by a charged plate. Electrostatic force requires that the product particles be charged. By using a charged plate, the CNTs can be grown in the form of intertwined sheets on the charged plate.

[0087] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0088] Instead of a gaseous reactant containing a carbon source, the CNT precursor may be injected in the form of a liquid containing a carbon source. When a liquid is used as the CNT precursor, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0089] Preferably, the gaseous reactant(s) are reacted at a temperature between 500° C. and 1600° C., more preferably between 1000° C. and 1500° C. A temperature gradient is preferably maintained within the reactor, with the reaction zone being maintained at a higher temperature than the product zone of the reactor.

[0090] The gaseous reactants may be mixed with one or more gases that act as diluents. The gaseous reactants may also be mixed with gases that play a supporting but not direct role in the reaction. It is also preferred to use a diluent gas that can react with the amorphous carbon by-product, if any, to keep the reactive sites on the catalyst intact and produce nanotubes.

[0091] Gases that can be used as a diluent include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, helium, etc. Among these, hydrogen is particularly preferred as a gas that can be used as a diluent.

[0092] The composition of the product particles can be controlled by monitoring the agglomerates and modifying the reaction conditions based on the information obtained. For example, the agglomerates can be monitored by online Raman spectroscopy, which provides data indicating whether the CNTs are single-walled or multi-walled. It also provides data indicating the diameter and crystallinity of the CNTs. The agglomerates can also be monitored by online conductivity measurements, gas analysis, measuring the opacity of the reaction zone, and / or measuring the winding force.

[0093] When the agglomerate is removed from the reactor, it is preferable to prevent air from entering the reactor, which is particularly important when the diluent gas contains hydrogen, for example, in order to prevent an explosive mixture of hydrogen and air from forming in the reactor.

[0094] The product particles in production method X contain ULCNTs. Depending on the production conditions, SWCNTs and MWCNTs may also be contained.

[0095] The product particles may be produced by chemical vapor deposition, where a gaseous reactant, a carbon source, is reacted in the presence of a catalyst.

[0096] Carbon-containing compounds suitable 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, and hydrocarbons containing mixtures of two or more thereof). The carbon-containing compound is preferably carbon monoxide, methane, ethylene or acetylene.

[0097] Preferably, the carbon source contains oxygen. Ethanol is a particularly preferred carbon source. Oxygen can be introduced into the reactor by other methods, such as by using a diluent gas or a carbon source containing water.

[0098] The catalyst is preferably a transition metal, particularly a group VIB transition metal such as chromium (Cr), molybdenum (Mo), or tungsten (W), or a group VIIIB transition metal. Specifically, the catalyst is preferably, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or manganese (Mn), or a mixture 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, such as a mixture of Ni and Co (50 / 50 by mass), a mixture of Fe and Ni, or a mixture of Fe and Mo, are more preferred. Any of these transition metals, either alone or in combination with any of the other transition metals listed, can serve as a catalyst for CNT growth, with it being particularly preferred that the catalyst be a mixture of two or more of the listed metals.

[0099] The catalyst is preferably formed by decomposition of a precursor. The precursor is preferably a thermally, photo-, or plasma-decomposable compound of one or more of the above metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickelocene, and cobaltocene are particularly preferred precursors. In one embodiment, at least 0.01% by mass of the precursor is contained in the carbon source, preferably 0.2% to 30% by mass of the precursor, and more preferably 0.2% to 20% by mass of the precursor. In one embodiment, 0.23% to 2.3% by mass of the precursor may be contained in the carbon source, and 0.02% to 20% by mass of the precursor may be contained in the carbon source. The catalyst may be used supported on a carrier, and preferred carriers include silica and magnesium oxide.

[0100] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters are one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is also a preferred promoter. Suitably, up to 10% by weight of the promoter is included in the carbon source. Preferably, 0.2% to 6% by weight of the promoter is included in the carbon source. When high or low concentrations of thiophene are used as the promoter, MWCNTs are formed.

[0101] According to production method X, it is possible to obtain fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm. The fibrous CNTs can be in the form of threads or sheets. The length of the fibrous CNT can be controlled, for example, by the winding capacity of the spindle used in producing the fibrous CNT.

[0102] The manufacturing method X preferably includes the steps of reacting a carbon source in a reaction zone of a reactor to produce CNTs, and aggregating the CNTs into aggregates by applying force to the CNTs. This manufacturing method makes it possible to easily produce fibrous CNTs.

[0103] Preferably, production method X further comprises, after the step of aggregating the CNTs into aggregates, a step of passing the resulting CNT aggregates through a sieve. Also, it is preferable to recover the CNTs that have passed through the sieve. By passing the obtained CNT aggregate through a sieve, it becomes easy to obtain a CNT aggregate that satisfies the conditions (1) and (2).

[0104] The method for passing the material through a sieve is not particularly limited, and any commonly known method can be used. 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 (particularly 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 agglomerates through a sieve, the CNT agglomerates may be cut into pieces of an appropriate size.

[0105] It is also preferable to use two types of sieves with different mesh sizes and pass the material through the sieves at least twice. By using the sieve with the smaller mesh size of the two types of sieves, it is possible to remove amorphous carbon that has become dusty. By using the sieve with the larger mesh size of the two types of sieves, it is possible to remove foreign matter, coarse CNTs, etc. that have been mixed in from the outside.

[0106] The resulting CNT agglomerates are passed through a sieve and the CNTs that pass through the sieve are collected, thereby removing coarse CNTs and improving the stability of the CNT dispersion. Furthermore, in general, in the manufacture of electrodes, foreign matter that has been mixed in from the outside is removed, but by passing the obtained CNT agglomerates through a sieve, it is possible to more easily remove foreign matter that has been mixed in from the outside.

[0107] In another embodiment, a method may be adopted in which CNTs containing ULCNTs are generated in a reaction region by the above method, and then condensed to form CNTs containing ULCNTs, and the CNTs are continuously withdrawn from the vicinity of the reaction region. In another embodiment, a method may be adopted that includes producing CNTs containing ULCNTs in a reaction region, continuously electrostatically attracting the CNTs containing ULCNTs from the reaction region, and recovering the CNTs containing ULCNTs.

[0108] =Manufacturing method Y= In the present disclosure, the manufacturing method described in JP-A 2021-527611 can be referred to as an example of a method for manufacturing CNTs. That is, the manufacturing method includes a step (1) of supporting a mixture containing a main catalyst precursor and a co-catalyst precursor on γ-Al2O3 to manufacture an active support, a step (2) of drying the active support by multistage drying including vacuum drying, a step (3) of subjecting the dried active support to a heat treatment to manufacture a supported catalyst, and a step (4) of manufacturing CNTs in the presence of the supported catalyst (hereinafter also referred to as "manufacturing method Y").

[0109] ·Process (1) In step (1), a mixture containing a main catalyst precursor and a co-catalyst precursor is supported on γ-Al 2 O 3 to produce an active support.

[0110] In order to uniformly support the main catalyst precursor and the co-catalyst precursor on γ-AlO, the mixture may further contain a solvent, and the main catalyst precursor and the co-catalyst precursor may be dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, and water is preferred.

[0111] Because γ-Al2O3 has high porosity and a spinel structure, the main catalyst and promoter can be randomly arranged in γ-Al2O3. CNTs grown from the randomly arranged main catalyst can be produced in an entangled state.

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

[0113] The main catalyst precursor may be one or more selected from the group consisting of nitrates, sulfates, carbonates and acetates of the main catalyst, with nitrates of the main catalyst being preferred.

[0114] The main catalyst precursor may be one or more selected from the group consisting of Co(NO3)2, Co(NO3)2·6H2O, Co2(CO)8, Co2(CO)6[HC=C(C(CH3)3)], Co(CH3CO2)2, Fe(NO3)3, Fe(NO3)2·nH2O, Fe(CH3CO2)2, Ni(NO3)2, Ni(NO3)2·6H2O, Mn(NO3)2, Mn(NO3)2·6H2O, Mn(CH3CO2)2·n(H2O) and Mn(CO)5Br, of which Co(NO3)2·6H2O, Fe(NO3)2·nH2O and Ni(NO3)2·6H2O are preferred.

[0115] The promoter improves the dispersibility of the main catalyst, and may be one or more selected from the group consisting of vanadium and molybdenum.

[0116] The promoter precursors were NH4VO3, NaVO3, V2O5, V(C5H7O2)3, and (NH4)6Mo7O. 24 4H2O, NH4VO3 and (NH4)6Mo7O 24 Preferably, one or more selected from the group consisting of 4H2O.

[0117] When the mixture contains two or more promoter precursors, i.e., 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 preferably 1:0.5 to 1:0.9. When the above conditions are met, the CNT structure can be stably maintained and CNTs with the desired pore volume can be produced.

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

[0119] The mixture may further include an organic acid which serves to inhibit precipitation of the main catalyst precursor and the co-catalyst precursor.

[0120] The organic acid may be one or more selected from the group consisting of citric acid, tartaric acid, fumaric acid, malic acid, acetic acid, butyric acid, palmitic acid and oxalic acid, with citric acid being preferred.

[0121] The mixture may 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, preferably 1:3 to 1:6. When the above range is satisfied, it is possible to produce a transparent catalyst metal solution during catalyst production, and it is advantageous in that it is possible to produce a catalyst in which fine particles are suppressed during impregnation.

[0122] After step (1), a step of aging may be further included.

[0123] The aging may be carried out for 1 to 60 minutes or 10 to 50 minutes. Preferably, it is carried out for 10 to 50 minutes. When the above conditions are satisfied, the main catalyst precursor and the co-catalyst precursor can be sufficiently supported on the γ-Al2O3. In addition, air bubbles present in the support are removed to the maximum extent possible, and the main catalyst precursor and the co-catalyst precursor can be sufficiently supported even in the fine pores inside the support.

[0124] ·Process (2) The active support is then dried by multi-stage drying, including vacuum drying.

[0125] Multi-stage drying may mean that a drying process including vacuum drying is performed two or more times. Specifically, multi-stage drying may include atmospheric drying and vacuum drying, or may include vacuum drying two or more times.

[0126] The vacuum drying may be carried out at 80° C. to 300° C. or 120° C. to 250° C., preferably at 120° C. to 250° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0127] The vacuum drying may be performed at 1 mbar to 200 mbar or 30 mbar to 150 mbar, preferably 30 mbar to 150 mbar. When the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0128] The vacuum drying can be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, preferably 10 minutes to 2 hours. If the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0129] On the other hand, when the multi-stage drying includes atmospheric drying and vacuum drying, atmospheric drying can be performed before the above-mentioned vacuum drying, and the atmospheric drying can remove solvent that may be present in the active support.

[0130] Drying at normal pressure 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. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0131] Drying at atmospheric pressure may be performed at 900 mbar to 1,100 mbar, preferably 950 mbar to 1,050 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0132] Drying under atmospheric pressure may be carried out for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0133] On the other hand, when the multi-stage drying includes two or more vacuum dryings, the multi-stage drying may include two or more vacuum dryings performed at different temperatures, more specifically, a primary vacuum drying performed at a first temperature and a secondary vacuum drying performed at a second temperature higher than the first temperature.

[0134] The primary vacuum drying can remove any solvent that may be present in the active support.

[0135] The first temperature may be 80° C. to 160° C., and preferably 100° C. to 140° C. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0136] The primary vacuum drying can be carried out for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0137] The primary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 80 mbar to 150 mbar, and is preferably performed at 80 mbar to 150 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

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

[0139] The second temperature may be 175 to 300° C., and preferably 180 to 280° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0140] The secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, and more preferably at 1 mbar to 70 mbar. If the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0141] The secondary vacuum drying may be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, preferably 10 minutes to 2 hours. If the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0142] ·Process (3) The dried active support is then subjected to a heat treatment to produce a supported catalyst.

[0143] By carrying out the heat treatment, a supported catalyst is produced in which the main catalyst and the promoter are present in a coated state on the surface and in the pores of γ-Al2O3.

[0144] The heat treatment may be carried out at 600 to 800°C or 620 to 750°C, preferably at 620 to 750°C. If the above conditions are met, a supported catalyst can be produced in which the main catalyst and the co-catalyst are uniformly coated on the surface and pores of the γ-Al2O3, and energy consumption can be minimized.

[0145] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, preferably 2 to 8 hours. When the above-mentioned time is satisfied, a supported catalyst can be produced in which the catalyst precursor is uniformly coated on the surface and in the pores of γ-AlO.

[0146] ·Process (4) CNTs are then produced in the presence of a supported catalyst.

[0147] Specifically, CNTs can be produced by contacting a supported catalyst with a carbon-based compound, and specifically, by chemical vapor synthesis.

[0148] To explain the steps for producing CNTs in detail, first, a supported catalyst is loaded into a horizontal fixed-bed reactor or a fluidized-bed reactor. Next, the gaseous carbon-based compound or a mixture of the 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 supported catalyst. CNTs can be grown by chemical vapor synthesis through the decomposition of the gaseous carbon-based compound.

[0149] The CNTs produced by the above-mentioned chemical vapor synthesis method have a crystal growth direction that is nearly parallel to the tube axis, and the graphite structure has high crystallinity along the tube length. As a result, CNTs with small unit diameters and high conductivity and strength can be produced.

[0150] The chemical vapor 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. If the above temperature is satisfied, CNTs can be produced while minimizing the generation of amorphous carbon.

[0151] The heat source for the reaction may be induction heating, radiant heat, laser, IR, microwave, plasma, surface plasmon heating, or the like.

[0152] In addition, the carbon-based compound can supply carbon and can be used without particular limitation as long as it can exist in a gaseous state at a temperature of 300°C or higher.

[0153] The carbon-based compound may be a carbon-based compound having 6 or less carbon atoms, and may be one or more selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene.

[0154] After growing CNTs by the above reaction, a cooling step may be selectively further performed to align the CNT arrays more regularly. Specifically, the cooling step can be performed by natural cooling by removing the heat source or using a cooler or the like.

[0155] The above manufacturing method X and manufacturing method Y are examples, and the manufacturing method of CNTs that can be included in the CNT aggregate is not limited to the above.

[0156] 〔Carbon nanotube dispersion〕 The carbon nanotube dispersion (CNT dispersion) according to the present disclosure includes a CNT aggregate and a dispersion medium. The CNT dispersion has good dispersibility of the CNT aggregate according to the present disclosure in the dispersion medium and excellent conductivity. The CNT dispersion is preferably used for forming electrodes, forming transparent conductive films, resin additives, conductive inks, coating agents, antistatic agents, paints, and the like.

[0157] <CNT aggregate> Since the CNT aggregate included in the CNT dispersion is the same as the CNT aggregate according to the present disclosure described above, the description thereof is omitted here.

[0158] <Dispersion medium> The dispersion medium preferably contains water, and more preferably contains water as a main component. "Containing water as a 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, and even more preferably 99% by mass or more, and may be, for example, 100% by mass.

[0159] The water is not particularly limited, but is preferably distilled water, ion-exchanged water, pure water, or the like, which contains fewer impurities.

[0160] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of hydrophilic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0161] The CNT dispersion may further contain other components that can be used in the dispersion in addition to the CNT aggregates and the dispersion medium. Examples of other components include dispersants, antifoaming agents, antistatic agents, conductive assistants other than the conductive assistant according to the present disclosure, etc. Furthermore, the composition may further contain trace amounts of impurity components, so-called inevitable impurities, etc.

[0162] <Dispersant> The CNT dispersion may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the CNT aggregates. The dispersant is not particularly limited and may be, for example, various surfactants. The dispersant may also be a polymer compound such as a resin. The dispersant is preferably a surfactant. The surfactant may be an ionic surfactant or a nonionic surfactant, and is not particularly limited. In the CNT dispersion, the surfactant may be used alone or in combination of two or more.

[0163] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzenesulfonates (e.g., dodecylbenzenesulfonic acid) and dodecylphenyl ether sulfonates; ether sulfate surfactants; phosphate surfactants; and carboxylic acid surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. As the ionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic ionic surfactant) is preferred, and aromatic sulfonic acid surfactants such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate are more preferred. Aromatic ionic surfactants tend to be excellent in dispersibility, dispersion stabilization, and concentration of CNT aggregates.

[0164] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers and polyoxyethylene polypropylene glycols; and aromatic nonionic surfactants such as polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, polyoxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl cumyl phenyl ether and polyoxyalkylene phenyl ether. As the nonionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic nonionic surfactant) is preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersing ability, dispersion stabilizing ability, and concentration enhancement for CNT aggregates.

[0165] Other dispersants that are excellent in CNT dispersibility, dispersion stabilization, and concentration enhancement include DEMOL (registered trademark: the same applies hereinafter) N, DEMOL RN, and DEMOL T (manufactured by Kao Corporation), which are sodium salts of β-naphthalenesulfonic acid formalin condensates; Brij S 100 (manufactured by Sigma-Aldrich), which is a polyoxyethylene stearyl ether; polyvinylpyrrolidone K30 (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (manufactured by, for example, Daicel Miraize Co., Ltd.); sodium deoxycholate (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); and SOLSPERSE TM W100, SOLSPERSE TM W150 (manufactured by Lubrizol Japan, Inc.) is particularly preferred from the viewpoint of excellent dispersibility, dispersion stability and high concentration of multi-walled carbon nanotubes.

[0166] When the CNT dispersion liquid contains a dispersant, the amount of the dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of CNT aggregates, the amount of dispersion medium, and the like.

[0167] The CNT aggregate according to the present disclosure has a high affinity for the dispersion medium, and therefore tends to have a low viscosity when dispersed in a dispersion medium. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the aggregate according to the present disclosure in the dispersion medium is good. The viscosity of the dispersion is preferably 10 mPa·s to 1600 mPa·s, more preferably 10 mPa·s to 1500 mPa·s, even more preferably 30 mPa·s to 1300 mPa·s, particularly preferably 100 mPa·s to 1200 mPa·s, even more preferably 100 mPa·s to 1000 mPa·s, even more preferably 300 mPa·s to 900 mPa·s, and particularly preferably 434 mPa·s to 798 mPa·s. In another embodiment, from the viewpoint of achieving both dispersibility and battery performance, the viscosity of the dispersion is more preferably 30 mPa·s to 1600 mPa·s, further preferably 300 mPa·s to 1600 mPa·s, and particularly preferably 400 mPa·s to 1600 mPa·s.

[0168] The viscosity of the CNT aggregate dispersion is measured using a cone-and-plate viscometer (also known as an E-type viscometer). For example, a Brookfield DV-II+Pro Programmable Viscometer is used as the cone-and-plate viscometer. The measurement conditions are as follows. Measuring tool: cone and plate Measurement mode: Rotation mode Shear rate: 0.6s -1 ~384s -1 Temperature: 25℃ From the data obtained, the viscosity is read at the following shear rates: Shear rate=12s -1

[0169] [Method for producing CNT dispersion liquid] The method for producing the CNT dispersion liquid is not particularly limited. A CNT dispersion can be produced by dispersing a CNT aggregate in a dispersion medium. That is, a CNT dispersion can be produced by a method including a step of dispersing a CNT aggregate in a dispersion medium (also referred to as a "dispersion step"). The dispersion medium that can be used in the dispersion step is as described above.

[0170] The dispersion method is not particularly limited. Examples of the dispersion method include methods using a dispersion device such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Further, examples of the dispersion method include methods using known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, a vertical or horizontal agitator mill, an attritor, a colloid mill, a three-roll mill, a pearl mill, a super mill, an impeller, a disperser, a KD mill, a dynatron, a pressure kneader, or the like. As a dispersion method, a method using a jet mill is preferred, and a 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 through a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, CNT aggregates are dispersed by collisions between opposing flows in the pressure-resistant container, collisions with the container wall, turbulence caused by the high-speed flow, shear flow, and the like. An ultra-high-pressure homogenizer (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used as the wet jet mill. However, the wet jet mill is not limited to this. When the ultra-high pressure homogenizer is used as the dispersing device, the processing pressure for dispersion is preferably 10 MPa to 250 MPa.

[0171] The method for producing a CNT dispersion may include a step of drying the CNT aggregate (also referred to as a "drying step") before the dispersion step.

[0172] If water adheres to the CNTs, the surface tension of the water makes them more likely to adhere to each other, which can lead to a decrease in dispersibility. Therefore, by performing a drying process for the conductive additive before the dispersion process, the water adhering to the CNTs is removed, preventing adhesion of CNT aggregates to each other due to water adhesion, and further improving the dispersibility of the CNTs in the dispersion medium. The drying method is not particularly limited. Drying methods include, for example, heat drying, vacuum drying, and heat vacuum drying. The drying method is preferably heated vacuum drying. The drying temperature is not particularly limited, and is preferably 40°C to 100°C, for example. The drying time is not particularly limited and can be set appropriately depending on the drying temperature, the degree of moisture adhesion to the CNT aggregate in the present disclosure, and the like.

[0173] An example of producing a CNT dispersion liquid will be shown below, but the production of a CNT dispersion liquid is not limited to the following.

[0174] <Production Example 1: Example of production of dispersion liquid> 0.040 g of the CNT aggregate according to the present disclosure is weighed and placed in a three-neck flask. After the CNT aggregate is placed in the flask, a large excess of ion-exchanged water (e.g., 20 mL) is poured into the flask and stirred at room temperature (25°C, the same applies below). At this time, a known dispersant (e.g., carboxymethyl cellulose) may be added as appropriate. Next, a conductive additive is dispersed in the dispersion medium using a known dispersion device (e.g., an ultrasonic irradiation device or a wet jet mill). The obtained dispersion is further stirred with a stirrer at room temperature for a long period of time (e.g., 1 hour to 48 hours). In this way, a CNT dispersion is obtained.

[0175] [Conductive materials] The conductive material according to the present disclosure includes a CNT aggregate. As described above, the CNT aggregates contained in the conductive material according to the present disclosure have excellent conductivity when made into a dispersion, and are therefore suitable as a conductive auxiliary agent. The conductive material according to the present disclosure contains the CNT aggregate according to the present disclosure, and therefore has excellent conductive efficiency, and can effectively impart high conductivity to an object of use.

[0176] The conductive material according to the present disclosure may contain a known conductive aid such as graphite, Ketjen black, etc. Furthermore, the conductive material according to the present disclosure may contain CNTs other than the CNT aggregate according to the present disclosure.

[0177] The conductive material according to the present disclosure can be used as one of electrode materials. An example of an electrode formed using the electrode material is an electrode included in a secondary battery. Hereinafter, an embodiment of the electrode and the secondary battery including the electrode will be described.

[0178] <Electrode> An electrode according to the present disclosure includes an electrode active material and a conductive material according to the present disclosure. The electrode according to the present disclosure contains the conductive material according to the present disclosure, and therefore has excellent conductive path formation properties within the electrode, and therefore the secondary battery according to the present disclosure has excellent cycle characteristics.

[0179] In the electrode, the CNT aggregates can function as a conductive additive. The CNT aggregate contained in the electrode described below is synonymous with the CNT aggregate according to the present disclosure, and preferred embodiments are also the same, so description of the CNT aggregate will be omitted below.

[0180] The electrode may be at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, or may include a current collector and an electrode active material layer disposed on the current collector.

[0181] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. The current collector may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal such as copper or nickel that has good carbon adsorption properties may be used as the current collector.

[0182] The electrode active material layer can include an electrode active material. The electrode active material is preferably electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer can contain a positive electrode active material that is commonly used as an electrode material for a positive electrode. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≦c2≦0.66); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include lithium manganese composite oxides represented by Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion.

[0183] When the electrode is a negative electrode, the electrode active material is not particularly limited, and the electrode active material layer can contain a negative electrode active material commonly used in negative electrode materials. Specifically, the negative electrode active material can contain graphite-based active material particles or silicon-based active material particles. As the 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 the graphite-based active material particles, the rate characteristics can be improved. As the 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 can be made to have a higher capacity.

[0184] The electrode active material layer can further contain a binder. The binder is not particularly limited, and the electrode active material layer can contain a binder commonly used in electrode materials. Examples of the binder 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and polyacrylic acid, and polymers in which hydrogen atoms of these polymers are substituted with Li, Na, Ca, etc.

[0185] <Secondary battery> A secondary battery according to the present disclosure includes an electrode according to the present 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, wherein at least one of the positive electrode and the negative electrode is an electrode according to the present disclosure.

[0186] The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move, and is not particularly limited as long as it is a separator that is typically used as a separator in a secondary battery. The separator preferably has low resistance to ion movement of the electrolyte and is excellent in the ability to retain moisture in the electrolyte solution. A specific example of the separator is a porous polymer film. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure in which two or more layers of these films are laminated. The separator may also be a typical porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. The separator may also be coated with a ceramic component or a polymeric substance to ensure heat resistance or mechanical strength. The separator may optionally be of a single layer or multi-layer structure.

[0187] The electrolyte is not particularly limited, and examples thereof include electrolytes such as 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 producing lithium secondary batteries.

[0188] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt. Examples of non-aqueous organic solvents include aprotic organic solvents such as 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0189] Among carbonate organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high viscosity and high dielectric constants and dissociate lithium salts well. It is more preferred to use a non-aqueous organic solvent obtained by mixing such cyclic carbonates with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, in order to obtain an electrolyte having high electrical conductivity.

[0190] The metal salt may be a lithium salt. Lithium salts are substances that are easily dissolved in non-aqueous electrolytes. The anion portion of the lithium salt may be, for example, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3- , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Examples include:

[0191] In addition to the non-aqueous organic solvent and metal salt, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purposes of improving the battery's life characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[0192] The above-described secondary battery can be used to form a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack can be used as a power source for a medium to large device selected from the group consisting of, for example, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[0193] <Planar aggregate> The planar aggregate according to the present disclosure includes the CNT aggregate according to the present disclosure. The proportion of the CNT aggregate according to the present disclosure contained in the planar aggregate according to the present disclosure is typically 1 mass % or more relative to the total mass of the planar aggregate. The planar aggregate according to the present disclosure may contain components other than the CNT aggregate according to the present disclosure.

[0194] An example of the planar aggregate according to the present disclosure is a film including the CNT aggregate according to the present disclosure.

[0195] Planar assemblies according to the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0196] The method for producing the planar assembly according to the present disclosure is not particularly limited. The planar aggregate according to the present disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate by dispersing the CNT aggregate according to the present disclosure in water or other fluid and filtering it once or twice or more times.

[0197] Planar assemblies according to the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0198] <Laminate> A laminate according to the present disclosure includes a substrate and a planar assembly according to the present disclosure. The substrate and the planar assembly may be in direct contact with each other, or another layer may be disposed between the substrate and the planar assembly. Alternatively, the planar assembly according to the present disclosure may be disposed on a substrate, and another layer may be disposed on the planar assembly.

[0199] 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). Glasses include, for example, float glass (containing SiO2, Na2O, CaO, 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.

[0200] The planar aggregate preferably contains a binder in addition to the CNT aggregate according to the present disclosure. The binder is preferably a polymer, and preferably contains at least one selected from the group consisting of polymers containing structural 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. [Example]

[0201] The CNT aggregate and the like according to the present disclosure will be described more specifically below with reference to examples. The present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure.

[0202] Example 1 1. Production of sheet-shaped CNT aggregate 1 Sheet-like CNT aggregate 1 was produced by the floating catalyst method (CVD method), which directly interacts with the self-assembly of CNT bundles 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 a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled between 200 and 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 is decomposed. The region where the metal catalyst precursor is decomposed is referred to as the first temperature zone.

[0203] Next, methane, a carbon source, was released into the carrier gas flow. The metal catalyst and carbon source were supplied to a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The total gas supply flow rate of the carrier gas and source gas was 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 produce carbon nanotube aggregates.

[0204] [Table 1]

[0205] In the second temperature zone, a reaction field was created in a temperature-controlled flow reactor to form catalytic nuclei and rapidly grow CNTs, thereby producing CNT aggregates. The aggregates of CNTs were continuously discharged through the outlet of a flow reactor whose temperature was controlled at 200°C to 700°C, and the sheet-like CNT aggregates were collected. The obtained sheet-like CNT aggregate was washed with pure water for 10 seconds, then crushed into powder, and passed through a sieve with 1.0 mm openings twice. The CNT aggregate that passed through the sieve was collected and designated as CNT aggregate 1.

[0206] 2. Preparation of CNT Dispersion 1 The following materials were mixed and pre-dispersed by processing for 1 hour using an Ace Homogenizer manufactured by Nippon Seiki Co., Ltd., to obtain pre-dispersion liquid 1.

[0207] (Dispersion liquid composition) CNT aggregate 1 obtained above...1.1g ·CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (manufactured by MP Biomedicals) …1.65g ·Pure water…547.25g

[0208] The pre-dispersion liquid 1 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain a CNT dispersion liquid 1 with a concentration of 0.20 mass %. (dispersion condition) Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 Method: Circulation method

[0209] 3. Evaluation <Calculation of fractal dimension> (Image taken using a scanning electron microscope (SEM)) -Attaching CNT dispersion to a substrate for SEM observation- The above CNT dispersion 1 was diluted with pure water so that the CNT concentration was 0.002 mass% relative to the total amount of the CNT dispersion. When observing the CNT dispersion (CNT concentration: 0.002 mass%) with an SEM, the CNT dispersion was attached to a substrate for SEM observation using the following procedure to prevent excessive aggregation of the CNTs.

[0210] 1. A slide glass with Pt deposition was treated with UV and ozone, and then attached to a substrate for SEM observation with conductive carbon tape. 2. 0.1 μL of the CNT dispersion liquid was applied to the slide glass. 3. The SEM observation substrate with the CNT dispersion attached was placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass on which the CNT dispersion liquid was frozen is placed on a 4.0 x 10 -3 A vacuum was applied at a pressure of 100 Pa to sublimate the ice.

[0211] -Image capture- The CNT dispersion (CNT concentration: 0.002% by mass) was photographed using an SEM device under the conditions below, and multiple images of the CNT-attached region were obtained. SEM equipment: S-4800 (Hitachi High-Technologies Corporation) Acceleration voltage: 1 kV Emission current: 10μA Measurement magnification: 500x Image size: 1280 pixels x 960 pixels

[0212] 8 shows an SEM photograph of CNT dispersion 1 in Example 1. The formation of a CNT network structure was confirmed.

[0213] (Image selection) All images of the area where the CNT dispersion liquid (CNT concentration: 0.002% by mass) was applied were subjected to the following image processing using ImageJ, an image analysis software.

[0214] - Image processing procedure - 1.Crop: 1280 pixels x 896 pixels 2.Filters: Gaussian Blur, Sigma(Radius)=3 3.Filters:Top Hat, Radius=9pixels 4. Binarization: Auto Threshold, 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

[0215] Next, the image after the image processing was divided into 64 parts (8 parts vertically and horizontally), and only images in which all 64 divided images contained pixels with a pixel value of 255 (i.e., images in which the CNT-attached region was present throughout) were selected. However, images in which CNTs were clearly not extracted after the image processing compared to the images before the image processing (for example, images in which most of the SEM observation substrate region contained pixels with a pixel value of 255) were excluded from selection in advance.

[0216] That is, as a result of the image selection, five of the total five images of the CNT dispersion liquid-attached region were used to calculate the fractal dimension.

[0217] (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 according to the following procedure.

[0218] -Calculation procedure- 1.Binary:Skeletonize 2.Analyze:Fractal Box Counter, Box Sizes=4,6,8,12,16,32,64,128, Black Background

[0219] When the fractal dimension in Example 1 was calculated based on the fractal dimension calculated for each image, the average value of the fractal dimension was 1.23.

[0220] <Cumulative 50% particle size D50 in volume-based particle size distribution> CNT dispersion 1 was thoroughly stirred and further diluted with pure water. Using the resulting diluted solution as a sample, the cumulative 50% particle diameter D50 of the CNT aggregate was measured using a particle size distribution analyzer (LA-960, laser diffraction particle size distribution analyzer, manufactured by Horiba, Ltd.). The particle refractive index of the CNT was set to 1.920-0.522i. The refractive index of the solvent was set to 1.333. During the measurement, while observing the transmittance, CNT dispersion liquid 1 was dropped into pure water for dilution, and the measurement was carried out after confirming that the particle size distribution on the monitor was stable. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of CNT aggregate 1 was 12.53 μm.

[0221] <Characteristic quantity of bundle diameter> Regarding CNT aggregate 1 of Example 1, imaging was performed using a scanning electron microscope (SEM: Scanning Electron Microscope), and out of the obtained images, 2 images in which CNT bundles were well observed were selected (one of the 2 selected images is shown in FIG. 1). For the selected images, image processing and image analysis were performed using Python. In image processing, the contour of CNT and the center line of CNT were respectively detected and synthesized with the original image. In image analysis, the bundle diameter was obtained by calculating the distance from the center line to the contour of the created image. Then, the product of the bundle diameter and the length of the center line was calculated, and the exclusive area of CNT in the image was calculated. A histogram of the bundle diameter and the exclusive area was made.

[0222] Using the calculated bundle diameter histogram, the characteristic quantity of the bundle diameter of each sample was calculated by the following method. 1. The bundle diameters and exclusive areas of multiple fields of the same sample were added together and normalized so that the sum was 1. Along with the normalization, the unit of the vertical axis was set as the exclusive area ratio. 2. The total value of the exclusive area ratio of bundles with a bundle diameter of 100 nm or more was obtained. 3. The cumulative exclusive area ratio was calculated, and the bundle diameter when this value first exceeded 0.9 was obtained 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.

[0223] <Viscosity of dispersion liquid of CNT aggregate> The viscosity of CNT dispersion 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, the viscosity was measured using a cone-plate viscometer (BROOKFIELD DV-II+Pro PROGRAMMABLE VISCOMETER). Measuring tool: cone and plate Measurement mode: Rotation mode Shear rate: 0.6s -1 ~384s -1 Temperature: 25℃ From the obtained data, a shear rate of 12 s -1 The viscosity was read. The viscosity of the dispersion was 434.0 mPa·s.

[0224] Example 2 1. Production of CNT aggregate 2 CNT aggregate 2 was produced in the same manner as CNT aggregate 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.

[0225] 2. Preparation of CNT Dispersion 2 Using the obtained CNT aggregate 2, a pre-dispersion liquid 2 was obtained in the same manner as in Example 1.

[0226] The pre-dispersion liquid 2 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 2. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 200 MPa Number of times: 8 Method: Circulation method

[0227] 3. Evaluation <Calculation of fractal dimension> Among the total six images of the attachment area of the CNT dispersion liquid, except that two images were used for calculating 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 each image is shown in Fig. 9.

[0228] <Cumulative 50% particle size D50 in volume-based particle size distribution> Except for using CNT dispersion liquid 2, the particle size distribution was analyzed in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 1.06 μm.

[0229] <Characteristic quantity of bundle diameter> Regarding the CNT aggregate 2 of Example 2, imaging was performed using SEM, and among the obtained images, three images in which CNT bundles were frequently observed were selected (one of the three selected images is shown in Fig. 2). Except for this, the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1. As a result, the area ratio of the bundle diameter of 100 nm or more was 0.43. The cumulative 90% bundle diameter was 190 nm.

[0230] <Viscosity of the dispersion liquid of the CNT aggregate> Regarding CNT dispersion liquid 2, the viscosity was measured in the same manner as in Example 1. As a result, the viscosity was 33.2 mPa·s.

[0231] (Example 3) 1. Production of CNT aggregate 3 CNT aggregate 3 was produced by mixing the following CNT aggregate 3A and the following CNT aggregate 3B. CNT aggregate 3A was produced in the same manner as CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and the raw material gas was set to 35 NL / min. CNT aggregate 3B was produced in the same manner as CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and the raw material gas was set to 36 NL / min.

[0232] 2. Preparation of CNT Dispersion 3 Using the obtained CNT aggregate 3, a preliminary dispersion 3 was obtained in the same manner as in Example 1.

[0233] The final dispersion of the preliminary dispersion 3 was carried out using a high-pressure homogenizer (model number: NAGS100) manufactured by Tsunehiro Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion 3. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 50 MPa [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ The resulting viscosity was 798.2 mPa·s.

[0238] Example 4 1. Preparation of CNT aggregate 4 CNT aggregate 4 was produced in the same manner as CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 33.9 NL / min and the flow rate ratio of thiophene / hydrogen gas was set to range A in Table 1.

[0239] 2. Preparation of CNT Dispersion 4 Using the obtained CNT aggregate 4, a pre-dispersion liquid 4 was obtained in the same manner as in Example 1.

[0240] The pre-dispersion liquid 4 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 4. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of times: 8 Method: Circulation method

[0241] 3. Evaluation <Calculation of fractal dimension> The fractal dimension was calculated using a scanning electron microscope (SEM) in the same manner as in Example 1, except that 10 of the 17 total images of the CNT dispersion-imparted region were used to calculate the fractal dimension, and the average value of the fractal dimension was 1.23. One of the images is shown in Figure 11.

[0242] <Cumulative 50% particle size D50 in volume-based particle size distribution> The particle size distribution was analyzed in the same manner as in Example 1, except that CNT dispersion liquid 4 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 2.31 μm.

[0243] <Features of bundle diameter> Regarding the CNT aggregate 4 of Example 4, imaging was performed using SEM, and among the obtained images, four images in which CNT bundles were well observed were selected (one of the four selected images is shown in FIG. 4). Except for this, the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1. As a result, the area ratio of the bundle diameter of 100 nm or more was 0.14. The cumulative 90% bundle diameter was 110 nm.

[0244] <Viscosity of the dispersion of the CNT aggregate> Regarding the CNT dispersion 4, the viscosity was measured in the same manner as in Example 1. As a result, the viscosity was 218.5 mPa·s.

[0245] (Comparative Example 1) 1. Preparation of the powdered CNT aggregate 5 As the powdered CNT aggregate 5, carbon nanotubes manufactured by C-nano (catalog number: FT9100) were prepared.

[0246] 2. Preparation of the CNT dispersion 5 Using the prepared powdered CNT aggregate 5, a CNT dispersion 5 was obtained in the same manner as in Example 1.

[0247] 3. Evaluation <Calculation of the average value of the fractal dimension> Among the 17 total images of the adhesion area of the CNT dispersion, except that 3 images were used 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. As a result, the average value of the fractal dimension was 0.86. One of the images is shown in FIG. 12.

[0248] <Cumulative 50% particle size D50 in the volume-based particle size distribution><L Except for using the CNT dispersion 5, the particle size distribution was analyzed in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 0.35 μm.

[0249] <Characteristic quantity of the bundle diameter> For the CNT aggregate 5 of Comparative Example 1, imaging was performed using SEM, and among the obtained images, three images in which CNT bundles were well observed were selected (one of the three selected images is shown in FIG. 5). Except for this, the characteristic amount of the bundle diameter was calculated in the same manner as in Example 1. The results are shown in Table 2.

[0250] <Viscosity of the dispersion of CNT aggregates> For the CNT dispersion 5, the viscosity was measured in the same manner as in Example 1. As a result, the viscosity was 5.7 mPa·s.

[0251] (Comparative Example 2) 1. Preparation of powder CNT aggregate 6 As the powder CNT aggregate 6, carbon nanotubes (catalog number: FT7000) manufactured by C-nano were prepared.

[0252] 2. Preparation of CNT dispersion 6 Using the prepared powder CNT aggregate 6, a CNT dispersion 6 was obtained in the same manner as in Example 1.

[0253] 3. Evaluation <Calculation of the average value of the fractal dimension> Among the 22 full images of the adhesion area of the CNT dispersion 6, except that 6 images were used 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. As a result, the average value of the fractal dimension was 0.98. One of the images is shown in FIG. 13.

[0254] <Cumulative 50% particle size D50 in the volume-based particle size distribution> Except for using the CNT dispersion 6, the particle size distribution was analyzed in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 0.65 μm.

[0255] <Characteristic amount of the bundle diameter> Regarding the CNT aggregate 6 of Comparative Example 2, imaging was performed using SEM, and among the obtained images, two images in which CNT bundles were well observed were selected (one of the two selected images is shown in FIG. 6). Except for this, the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1. The results are shown in Table 2.

[0256] <Viscosity of the dispersion of CNT aggregates> For the CNT dispersion 6, the viscosity was measured in the same manner as in Example 1. As a result, the viscosity was 6.4 mPa·s.

[0257] (Comparative Example 3) 1. Preparation of CNT aggregate 7 As the CNT aggregate 7, a carbon nanotube manufactured by C-nano (catalog number: FT6120) was prepared.

[0258] 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.

[0259] 3. Evaluation <Calculation of the average value of the fractal dimension> Among the 21 full images of the attachment area of the CNT dispersion 7, except that 9 images were used 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. As a result, the average value of the fractal dimension was 1.02. One of the images is shown in FIG. 14.

[0260] <Cumulative 50% particle size D50 in the volume-based particle size distribution> Except for using the CNT dispersion 7, the particle size distribution was analyzed in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 0.48 μm.

[0261] <Characteristic quantity of the bundle diameter> For the CNT aggregate 7 of Comparative Example 3, imaging was performed using SEM, and among the obtained images, six images in which CNT bundles were well observed were selected (one of the six selected images is shown in FIG. 7), and the characteristic amount of the bundle diameter was calculated in the same manner as in Example 1. The results are shown in Table 2.

[0262] <Viscosity of the dispersion of the CNT aggregate> For the CNT dispersion 7, the viscosity was measured in the same manner as in Example 1. As a result, the viscosity was 9.3 mPa·s.

[0263] Next, a lithium-ion secondary battery was fabricated.

[0264] 1. Fabrication of the positive electrode for the lithium secondary battery The positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2), the conductive material (acetylene black), and the binder (PVdF) were mixed at a ratio such that the composition was positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and N-methyl-2-pyrrolidone was added and kneaded to prepare a paste-like positive electrode mixture. The obtained positive electrode mixture was applied to an Al foil with a thickness of 15 μm serving as a current collector, vacuum dried at 80°C for 1 hour, and then roll pressed to obtain a positive electrode for the lithium secondary battery. The positive electrode area was 1.65 cm 2 , the areal density was 16 mg / cm 2 , and the density was adjusted to be 3.0 g / cm 3 .

[0265] 2. Fabrication of the negative electrode for the lithium secondary battery The negative electrode for the lithium secondary battery was prepared by mixing artificial graphite MAG-E and SiO coated with carbon in a mass ratio of 9:1 as the negative electrode active material, using CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Corporation) as the binder, and using the above CNT dispersion as the conductive assistant, and adding and kneading them so that the composition was negative electrode active material:binder:conductive assistant = 94.9:5.0:0.1 (weight ratio) to prepare a paste-like negative electrode mixture. When preparing the negative electrode mixture, ion-exchanged water was used as the solvent. The resulting negative electrode mixture was applied to a 20 μm thick Cu foil using a single-sided continuous coater, dried at 120°C, and then roll-pressed to obtain a negative electrode for a lithium secondary battery. The negative electrode area was 1.77 cm. 2 , basis weight 9.3mg / cm 2 , density is 1.4g / cm 3 It was adjusted so that

[0266] 3. Fabrication of Lithium Secondary Batteries The positive electrode for the lithium secondary battery was placed on the bottom cover of a coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator consisting of a polyethylene porous film with a 16 μm heat-resistant porous layer laminated thereon was placed on top of it. 300 μL of electrolyte was poured into the separator. The electrolyte was a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with 1% vinylene carbonate added by volume, and LiPF6 dissolved therein to a concentration of 1.3 mol / L. Next, the negative electrode for the lithium secondary battery was placed on top of the laminated film separator, and the top cover was placed with a gasket in between. The assembly was then crimped using a crimping machine to produce a coin-type full-cell R2032 lithium secondary battery. These operations were carried out in a glove box under an argon atmosphere.

[0267] 4. Cycle test The fabricated lithium ion battery was subjected to a 200-cycle cycle test under the conditions shown below, and the discharge capacity retention rate after 200 cycles was calculated using the following formula: A higher discharge capacity retention rate after 200 cycles indicates better life characteristics. Discharge capacity retention rate after 200 cycles (%) = 200th discharge capacity / 1st discharge capacity × 100

[0268] <Cycle test conditions> Test temperature: 25℃ 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 Downtime after charging: 10 minutes In this test, one cycle was defined as a cycle in which charging, discharging, discharging, and charging were performed in that order.

[0269] The evaluation results for Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 2.

[0270] [Table 2]

[0271] As shown in Table 2, the CNT aggregates of Examples 1 to 4 satisfy the conditions (1) and (2), and therefore have a high discharge capacity retention rate and excellent cycle characteristics. This confirms that the CNT aggregates of the Examples have excellent performance as a conductive additive for batteries. The favorable dispersibility reflects that the CNTs are in an appropriate state of stacking, which indicates 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 aggregate that is excellent in discharge capacity retention rate when a CNT dispersion liquid is used as a conductive assistant.

Claims

1. An aggregate of carbon nanotubes that satisfies the following conditions (1) and (2): (1) When the carbon nanotube concentration of the carbon nanotube dispersion is 0.002 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 fractal dimension) The carbon nanotube dispersion is imaged using a scanning electron microscope to obtain multiple images of the carbon nanotube-attached regions. From the obtained images, images in which the carbon nanotube-attached regions are present throughout are selected. Using the selected images, the average value of the fractal dimension of the carbon nanotube structure is calculated by image analysis. (2) The cumulative 50% particle size D50 in the volume-based particle size distribution is 1.0 μm or more and 15.0 μm or less.

2. The carbon nanotube aggregate according to claim 1, which satisfies the following condition (3): (3) The particle contains a bundle structure, and in an area observed by a scanning electron microscope, the cumulative 90% bundle diameter is more than 90 nm and 300 nm or less.

3. A conductive material comprising the carbon nanotube aggregate according to claim 1 or 2.

4. An electrode comprising an electrode active material and the conductive material according to claim 3 .

5. A secondary battery comprising the electrode according to claim 4.

6. A planar aggregate comprising the carbon nanotube aggregate according to claim 1 or 2.

7. A laminate comprising a substrate and the planar assembly according to claim 6.

8. A filter using the planar assembly according to claim 6.

9. An electromagnetic wave shield using the planar assembly according to claim 6.

10. A pellicle for extreme ultraviolet rays, which uses the planar assembly according to claim 6.

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