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

Abstract

A carbon nanotube aggregate having higher tensile strength than conventional aggregates is provided. The present invention provides an aggregate of carbon nanotubes that includes a bundle structure and satisfies the following conditions (1) and (2). (1) The most frequent bundle class has a bundle diameter W in the range of 20 nm or more and 100 nm or less, and a total bundle length ratio K of 10.0% or more and less than 100.0%. (2) The bundle diameter W of the smallest bundle class is more than 20 nm.

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 filter, an electromagnetic wave shield and a pellicle for extreme ultraviolet rays, and a measurement method. [Background technology]

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are substances with a cylindrical structure in which graphene sheets, which are composed of six-membered carbon ring structures, are rolled up coaxially in single or multiple layers. CNTs are 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 exhibit excellent mechanical, electrical, and chemical properties, and these properties are expected to be utilized for applications in fields such as materials, catalysts, energy, and electronics. Various attempts have been proposed to further enhance the properties of CNTs.

[0003] Patent Document 1 describes a CNT aggregate that satisfies the following criteria: a 2θ peak at 24°±2° as determined by powder X-ray diffraction analysis; a height ratio (G / D ratio) of the G band to the D band as determined by Raman spectroscopy at a wavelength of 532 nm of 30 or more; and a combustion peak temperature of 550°C or more and 700°C or less. Patent Document 2 describes that the CNT aggregate has a bundle structure, the bundles have a diameter of more than 0.3 μm, and the average diameter is 0.5 μm or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-029695 [Patent Document 2] Chinese Patent Application Publication No. 116111043 Summary of the Invention [Problem to be solved by the invention]

[0005] There are cases where high tensile strength is required for CNT aggregates.

[0006] The present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide an aggregate of carbon nanotubes having a higher tensile strength than conventional aggregates. 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]

[0007] The present disclosure includes the following embodiments. <1> An aggregate of carbon nanotubes that includes a bundle structure and satisfies the following conditions (1) and (2): (1) The most frequent bundle class has a bundle diameter W in the range of 20 nm or more and 100 nm or less, and a total bundle length ratio K of 10.0% or more and less than 100.0%. (2) The bundle diameter W of the smallest bundle class is more than 20 nm. <2> Satisfy the condition (3) below, <1> The carbon nanotube aggregate according to claim 1. (3) The cumulative 50% particle size D50 in the volume-based particle size distribution is 0.5 μm or more. <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 . <11> A method for measuring the total bundle length ratio, comprising sequentially performing the following steps 1, 2, and 3 on a carbon nanotube aggregate including a bundle structure. (Step 1) A scanning electron microscope image of a carbon nanotube aggregate is processed to calculate the bundle diameter and the area occupied by the bundle structure within the field of view of the electron microscope image, and the result is converted into histogram data. (Step 2) Based on the histogram data obtained in Step 1, the abundance of bundle structures is classified according to the bundle diameter range. (Step 3) The total bundle length, which is the area occupied by the bundle structure within the field of view of the electron microscope image divided by the bundle diameter, is normalized so that the sum is 100, and the total bundle length ratio (%) is calculated. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, an aggregate of carbon nanotubes having a higher tensile strength than conventional ones is provided. 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. According to another embodiment of the present disclosure, a method for measuring a total bundle length ratio for a carbon nanotube aggregate including a bundle structure can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 1 of Example 1. [Figure 2] 1 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 2 of Example 2. [Figure 3] 10 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 3 of Example 3. [Figure 4] 1 is a scanning electron microscope photograph showing one aspect of a powdered CNT aggregate 4 of Comparative Example 1. [Figure 5] 10 is a scanning electron microscope photograph showing one aspect of a powdered CNT aggregate 5 of Comparative Example 2. [Figure 6] FIG. 10 is a diagram for explaining classification. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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, as well as a measurement method 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 with appropriate modifications within the scope of the object of the present disclosure.

[0011] 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.

[0012] In the present disclosure, the terms "carbon nanotubes," "single-walled carbon nanotubes," "multi-walled carbon nanotubes," "carbon nanotube aggregate," "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," "ULCNT," and "CNT dispersion," respectively.

[0013] [CNT aggregate] One embodiment of the CNT aggregate according to the present disclosure includes a bundle structure and satisfies the following conditions (1) and (2). (1) The most frequent bundle class has a bundle diameter W in the range of 20 nm or more and 100 nm or less, and a total bundle length ratio K of 10.0% or more and less than 100.0%. (2) The bundle diameter W of the smallest bundle class is more than 20 nm.

[0014] In one embodiment, the CNT aggregate according to the present disclosure may include a bundle structure, the most frequent bundle class may have a bundle diameter W in the range of 20 nm or more and 100 nm or less, a total bundle length ratio K of less than 100%, and the bundle diameter W of the smallest bundle class may be more than 30 nm.

[0015] In conditions (1) and (2), The most frequent bundle class is the class with the largest total length ratio of bundle structures when the abundance of bundle structures is classified according to the bundle diameter range based on histogram data calculated from the observation area of ​​a CNT aggregate using a scanning electron microscope. The total bundle length ratio is the ratio (%) of the total bundle length, which is the value obtained by dividing the area occupied by the bundle structure by the bundle diameter, based on histogram data calculated from the area observed by a scanning electron microscope of a CNT aggregate, normalized so that the sum is 100, and the total bundle length ratio K is the total bundle length ratio of the most frequent bundle class. The smallest bundle class is the class with the smallest bundle diameter range when classified according to the bundle diameter range based on histogram data calculated from the observation area of ​​the CNT aggregate using a scanning electron microscope. The bundle diameter W of the most frequent bundle class or the smallest bundle class is a value determined based on the peak position belonging to the most frequent bundle class or the smallest bundle class. The bundle diameter W of the most frequent bundle class and the bundle diameter W of the smallest bundle class may be the same value or may be different values.

[0016] A CNT aggregate that satisfies the conditions (1) and (2), that is, a CNT aggregate according to the present disclosure, has a higher tensile strength than conventional CNT aggregates. On the other hand, Patent Documents 1 and 2 do not mention conditions (1) and (2).

[0017] Patent Document 1 and Patent Document 2 describe bundles formed by CNTs, but do not pay attention to the conditions (1) and (2) satisfied by the CNT aggregate according to the present disclosure. Patent Document 1 describes forming a film by applying a dispersion liquid containing CNTs, but does not describe anything about the mechanical properties of the film. Patent Document 1 does not describe anything about the mechanical properties of the CNT aggregate. Furthermore, Patent Documents 1 and 2 describe CNTs as a conductive additive for electrodes, and controlling the bundle structure to maximize its function is an issue, but Patent Documents 1 and 2 do not consider this. In contrast, the CNT aggregate according to the present disclosure satisfies the conditions (1) and (2), and therefore has a higher tensile strength than conventional ones.

[0018] <Condition (1)> In one embodiment of the CNT aggregate according to the present disclosure, the most frequent bundle class has a bundle diameter W in the range of 20 nm or more and 100 nm or less, and a total bundle length ratio K of 10.0% or more and less than 100.0%.

[0019] In the present disclosure, the most frequent bundle class is the class with the largest number of bundle structures, which is determined by classifying the abundance of bundle structures according to the bundle diameter range from a histogram calculated from the observation area of ​​a CNT aggregate using a scanning electron microscope. In the present disclosure, the bundle total length ratio (hereinafter also referred to as "total length ratio") is a ratio (%) obtained by normalizing the total bundle length, which is the value obtained by dividing the area occupied by the bundle structure by the bundle diameter, based on histogram data calculated from the observation area of ​​a CNT aggregate using a scanning electron microscope, so that the sum is 100. The bundle total length ratio K (hereinafter also referred to as "total length ratio") is the total length ratio of the most frequent bundle class. The method for determining the most frequent bundle class and calculating the total length ratio will be described later.

[0020] By satisfying condition (1), the CNT aggregate according to the present disclosure forms a more appropriate CNT bundle structure, improving dispersibility in a solvent. Furthermore, the CNT bundles gather together, facilitating the formation of a long-distance conductive network. Furthermore, the number of contact points between the CNT aggregates increases, improving tensile strength. As a result, the CNT aggregate according to the present disclosure has a higher tensile strength than conventional ones.

[0021] In the CNT aggregate according to the present disclosure, when observed with a scanning electron microscope (SEM, the same applies hereinafter), the most frequent bundle class has a bundle diameter W of 20 nm to 100 nm and a total length ratio K of less than 100.0%, which makes it easier for the CNT bundles to gather and form a long-distance conductive network. In addition, there are many contact points between the carbon nanotube aggregates, which improves the tensile strength. In addition, the total length ratio K usually exceeds 0.

[0022] Specifically, when the total length ratio K is 10.0% or more, the CNT aggregates have good dispersibility in the dispersion medium, making it possible to obtain a CNT dispersion with an appropriate viscosity. Furthermore, when the total length ratio K is less than 100.0%, the CNTs gather together appropriately, facilitating the formation of a network structure. Furthermore, the number of contact points between the CNT aggregates increases, improving tensile strength.

[0023] In particular, in one embodiment, the total length ratio K may be 10.0% or more, 20.0% or more, 30.0% or more, 40.0% or more, or 50.0% or more, preferably more than 50.0% and less than 99.9%, more preferably more than 50.0% and less than 99.8%, even more preferably more than 50.0% and less than 99.7%, particularly preferably more than 50.0% and less than 99.6%, even more preferably more than 50.0% and less than 99.5%, even more preferably more than 50.0% and less than 99.4%, and especially preferably more than 50.0% and less than 99.2%. Furthermore, the total length ratio K is preferably more than 60.0% and less than 99.1%, more preferably more than 60.0% and less than 99.0%, and even more preferably more than 70.0% and less than 98.0%. Within this range, the CNT bundle diameter can be appropriately controlled, allowing the CNTs to gather together in an appropriate amount, facilitating the formation of a longer-distance network, improving electrical conductivity. Furthermore, the number of contact points between the CNT aggregates increases, further improving tensile strength.

[0024] In another embodiment, the total length ratio K may be 80.0% or more, or 83.6% or more, preferably more than 80.0% and less than 99.9%, and more preferably more than 83.6% and less than 99.9%. In another embodiment, the total length ratio K is preferably more than 75.0% and less than 98.0%, more preferably more than 78.0% and less than 98.0%, even more preferably more than 80.0% and less than 98.0%, and particularly preferably more than 83.0% and less than 98.0%. Within these ranges, the CNT bundle diameter becomes appropriately small, thereby increasing the area where bundles can contact each other. This increases the frictional force between the bundles, improving the tensile strength of the CNT aggregate.

[0025] Therefore, when the total length ratio K is in the range of more than 0% and less than 100.0%, more than 50.0% and not more than 99.9%, more than 60.0% and not more than 99.8%, more than 70.0% and not more than 99.7%, more than 75.0% and not more than 99.6%, more than 78.0% and not more than 99.5%, more than 80.0% and not more than 99.0%, or more than 83.0% and not more than 98.0%, a CNT aggregate with higher tensile strength than conventional CNT aggregates is provided.

[0026] In another embodiment, the total length ratio K may be greater than 0% and less than 100%, greater than 50.0% and not more than 99.9%, greater than 60.0% and not more than 99.0%, greater than 70.0% and not more than 98.0%, greater than 75.0% and not more than 98.0%, greater than 78.0% and not more than 98.0%, greater than 80.0% and not more than 98.0%, or greater than 83.0% and not more than 98.0%.

[0027] <Condition (2)> In one embodiment of the CNT aggregate according to the present disclosure, the bundle diameter W of the smallest bundle class exceeds 20 nm. In one embodiment, the bundle diameter W of the smallest bundle class can be greater than 30 nm.

[0028] In the present disclosure, the smallest bundle class is the class with the smallest bundle diameter range when classified according to the bundle diameter range based on histogram data calculated from an observation area of ​​a CNT aggregate using a scanning electron microscope. The bundle diameter W of the smallest bundle class is a value determined based on the peak position belonging to the smallest bundle class. The method for determining the minimum bundle class and the method for calculating the bundle diameter W will be described later.

[0029] In condition (2), the upper and lower limit values ​​can be arbitrarily combined as long as the bundle diameter of the smallest bundle class exceeds 20 nm. In condition (2), the bundle diameter may be 21 nm or more, 22 nm or more, 23 nm or more, 24 nm or more, 25 nm or more, 26 nm or more, 27 nm or more, 28 nm or more, 29 nm or more, 30 nm or more, 31 nm or more, 32 nm or more, 33 nm or more, 34 nm or more, 35 nm or more, or 40 nm or more. In condition (2), the bundle diameter may be 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, or 75 nm or less.

[0030] In the CNT aggregate according to the present disclosure, the bundle diameter is typically greater than 20 nm and less than 100 nm, preferably greater than 20 nm and less than 90 nm, more preferably greater than 20 nm and less than 95 nm, even more preferably greater than 20 nm and less than 85 nm, particularly preferably greater than 20 nm and less than 85 nm, and most preferably greater than 20 nm and less than 75 nm. In another aspect, the bundle diameter is typically greater than 21 nm and less than 100 nm, preferably greater than 21 nm and less than 90 nm, more preferably greater than 21 nm and less than 95 nm, even more preferably greater than 21 nm and less than 85 nm, particularly preferably greater than 21 nm and less than 85 nm, and most preferably greater than 21 nm and less than 75 nm. In another aspect, the bundle diameter is typically greater than 22 nm and less than 100 nm, preferably greater than 22 nm and less than 90 nm, more preferably greater than 22 nm and less than 95 nm, even more preferably greater than 32 nm and less than 85 nm, particularly preferably greater than 22 nm and less than 85 nm, and most preferably greater than 22 nm and less than 75 nm. In another embodiment, the bundle diameter is typically greater than 24 nm and less than 100 nm, preferably greater than 24 nm and less than 90 nm, more preferably greater than 24 nm and less than 95 nm, even more preferably greater than 24 nm and less than 85 nm, particularly preferably greater than 24 nm and less than 85 nm, and most preferably greater than 24 nm and less than 75 nm. In another embodiment, the bundle diameter is typically greater than 25 nm and less than 100 nm, preferably greater than 25 nm and less than 90 nm, more preferably greater than 25 nm and less than 95 nm, even more preferably greater than 25 nm and less than 85 nm, particularly preferably greater than 25 nm and less than 85 nm, and most preferably greater than 25 nm and less than 75 nm. In another embodiment, the bundle diameter is typically greater than 40 nm and less than 100 nm, preferably greater than 40 nm and less than 90 nm, more preferably greater than 40 nm and less than 95 nm, even more preferably greater than 40 nm and less than 85 nm, particularly preferably greater than 40 nm and less than 85 nm, and most preferably greater than 40 nm and less than 75 nm. Within these ranges, the CNT bundle structure is more appropriately formed, and the tensile strength is further improved.

[0031] In other embodiments, the bundle diameter may be greater than 30 nm to 100 nm, greater than 30 nm to 90 nm, greater than 30 nm to 95 nm, greater than 30 nm to 85 nm, greater than 30 nm to 85 nm, or greater than 30 nm to 75 nm. In other embodiments, the bundle diameter may be greater than 31 nm to 100 nm, greater than 31 nm to 90 nm, greater than 31 nm to 95 nm, greater than 31 nm to 85 nm, greater than 31 nm to 85 nm, or greater than 31 nm to 75 nm. In other embodiments, the bundle diameter may be greater than 32 nm to 100 nm, greater than 32 nm to 90 nm, greater than 32 nm to 95 nm, greater than 32 nm to 85 nm, greater than 32 nm to 85 nm, or greater than 32 nm to 75 nm. In other embodiments, the bundle diameter can be greater than 34 nm to 100 nm, greater than 34 nm to 90 nm, greater than 34 nm to 95 nm, greater than 34 nm to 85 nm, greater than 34 nm to 85 nm, or greater than 34 nm to 75 nm. In other embodiments, the bundle diameter can be greater than 35 nm to 100 nm, greater than 35 nm to 90 nm, greater than 35 nm to 95 nm, greater than 35 nm to 85 nm, greater than 35 nm to 85 nm, or greater than 35 nm to 75 nm.

[0032] In the CNT aggregate according to the present disclosure, when observed by SEM, the bundle diameter exceeds 20 nm, which makes it easier for the CNT bundles to gather and form a longer-distance network. The number of contact points between carbon nanotube aggregates increases, further improving tensile strength. Furthermore, when the bundle diameter is 100 nm or less, it becomes easier to ensure an area where the bundles can contact each other. This increases the frictional force between the bundles, improving the tensile strength of the CNT aggregate.

[0033] Specifically, when the bundle diameter is greater than 20 nm, the CNTs can be gathered together appropriately and efficiently form a network structure. This improves the mechanical strength of the CNT aggregate, thereby improving its tensile strength. Furthermore, when the bundle diameter is 100 nm or less, it becomes easier to ensure an area where the bundles can contact each other. This increases the frictional force between the bundles, improving the tensile strength of the CNT aggregate.

[0034] In particular, in one embodiment, the bundle diameter is preferably 22 nm or more and 100 nm or less, more preferably 24 nm or more and 100 nm or less, even more preferably 26 nm or more and 100 nm or less, and particularly preferably 28 nm or more and 100 nm or less. Furthermore, the bundle diameter is preferably 31 nm or more and 100 nm or less, more preferably 32 nm or more and 95 nm or less, even more preferably 34 nm or more and 90 nm, particularly preferably 35 nm or more and 85 nm or less, and most preferably 35 nm or more and 75 nm or less. Within this range, the bundle diameter of the CNTs is appropriately controlled, increasing the number of contact points between the CNTs and efficiently forming a network structure, thereby improving the tensile strength. This makes it easier to ensure a contactable area between the bundles. This increases the frictional force between the bundles, improving the tensile strength of the CNT aggregate.

[0035] In another embodiment, the bundle diameter is preferably more than 20 nm and less than 85 nm, preferably 22 nm or more and less than 85 nm, more preferably 24 nm or more and less than 85 nm, even more preferably 26 nm or more and less than 85 nm, particularly preferably 28 nm or more and less than 85 nm, and may be more than 30 nm and less than 85 nm. The bundle diameter is more preferably 35 nm or more and less than 80 nm, even more preferably 35 nm or more and less than 75 nm, and particularly preferably 40 nm or more and less than 75 nm. Within this range, the CNT bundle diameter becomes appropriately small, making it easier to ensure a contact area between the bundles. This increases the frictional force between the bundles and improves the tensile strength of the CNT aggregate.

[0036] Therefore, having a bundle diameter in the range of more than 20 nm and not more than 100 nm (particularly, 31 nm or more and 95 nm or less, 21 nm or more and 95 nm or less, 22 nm or more and 90 nm or less, 24 nm or more and 85 nm or less, 25 nm or more and 75 nm or less, 34 nm or more and 85 nm or less, 35 nm or more and 75 nm or less, or 40 nm or more and 75 nm or less) serves to improve the tensile strength of the CNT aggregate.

[0037] <Matters regarding bundle structure, bundle diameter, and bundle diameter parameters> Hereinafter, matters relating to the bundle structure, bundle diameter, and bundle diameter parameters contained in the CNT aggregate according to the present disclosure will be described in detail.

[0038] A bundle structure refers to an aggregate in which multiple CNTs are aggregated together by van der Waals forces and other factors, forming a bundle. It is believed that if a CNT aggregate contains bundle structures of an appropriate size, the handleability of the CNT aggregate as a whole will improve, and its stability will also be improved. On the other hand, if the bundle structures contained in the CNT aggregate are too large, the size of the CNT aggregate itself will become too large, and the contact area between the bundles will decrease. This may reduce the frictional force between the bundles, reducing the tensile strength of the CNT aggregate.

[0039] The bundle structure in the CNT aggregate can be formed, for example, by controlling the catalyst particle size distribution in production by chemical vapor deposition (CVD) method, or by controlling the cooling rate in the cooling step.

[0040] From the viewpoint of achieving both ease of handling of the CNT aggregate and dispersibility in a solvent, the diameter of each bundle contained in the CNT aggregate is preferably 5 nm to 500 nm, more preferably 10 nm to 300 nm, and even more preferably 15 nm to 300 nm.

[0041] 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.

[0042] 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 bundle diameter 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] In the present disclosure, the "bundle diameter" refers to the width of an individual bundle structure and the width of an aggregate of multiple bundle structures, each calculated as a single bundle diameter. The bundle diameter can be calculated based on the number of aggregates of bundle structures obtained from an image obtained by SEM and their occupied area.

[0044] 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 more than 0.1 in the region observed by SEM. In the CNT aggregate according to the present disclosure, the area ratio of bundles having a bundle diameter of 100 nm or more exceeds 0.1 in the region observed by SEM, which allows the CNT bundle structure to be formed appropriately and improves tensile strength. Specifically, a bundle diameter of 100 nm or more allows the CNTs to gather together appropriately and efficiently form a network structure. This improves the mechanical strength of the CNT aggregate, thereby improving tensile strength.

[0045] In particular, 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 0.15 or more and less than 0.5, and even more preferably 0.15 or more and 0.45 or less. In another embodiment, 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 0.14 or more and 0.45 or less, and even more preferably 0.14 or more and 0.23 or less. Within this range, the CNT bundle diameter can be appropriately controlled to increase the number of contact points between CNTs, efficiently forming a network structure and improving tensile strength. This makes it easier to ensure a sufficient contact area between bundles. This increases the frictional force between the bundles and improves the tensile strength of the CNT aggregate.

[0046] Furthermore, from the viewpoint of increasing the breaking elongation, the area ratio of the bundles is particularly preferably 0.20 or more and 0.45 or less. A high breaking elongation improves the flexibility and durability of the material containing the CNT aggregate, and also improves the tensile strength.

[0047] The CNT aggregate according to the present disclosure includes a bundle structure, and in the region observed by a scanning electron microscope, the cumulative 90% bundle diameter (hereinafter also referred to as "cumulative 90% bundle diameter") is typically 500 nm or less, and preferably more than 80 nm and 500 nm or less. The cumulative 90% bundle diameter may be 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less. The cumulative 90% bundle diameter may be more than 90 nm, 100 nm or more, or 110 nm or more. Within the range of the cumulative 90% bundle diameter, these upper and lower limit values ​​can be selected arbitrarily.

[0048] In the CNT aggregate according to the present disclosure, when observed by SEM, the cumulative 90% bundle diameter exceeds 90 nm, which makes it easier for the CNT bundles to gather and form a long-distance network structure. Furthermore, when the cumulative 90% bundle diameter is 400 nm or less, it becomes easier to ensure tensile strength.

[0049] Specifically, when the cumulative 90% bundle diameter is greater than 90 nm, CNTs can be gathered together appropriately and come into efficient contact with each other to form a network structure. This improves the tensile strength of the CNT aggregate. Furthermore, when the cumulative 90% bundle diameter is 300 nm or less, it becomes easier to ensure an area where bundles can contact each other. This increases the frictional force between the bundles, improving the tensile strength of the CNT aggregate.

[0050] In particular, the cumulative 90% bundle diameter is preferably more than 90 nm and not more than 350 nm, more preferably more than 90 nm and not more than 300 nm, more preferably more than 90 nm and not more than 270 nm, even more preferably more than 90 nm and not more than 250 nm, particularly preferably more than 90 nm and not more than 230 nm, and even more preferably more than 90 nm and not more than 200 nm. Furthermore, the cumulative 90% bundle diameter is preferably 100 nm or more and 350 nm or less, more preferably 100 nm or more and 300 nm or less, even more preferably 100 nm or more and 270 nm or less, even more preferably 100 nm or more and 250 nm or less, particularly preferably 100 nm or more and 230 nm or less, even more preferably 100 nm or more and 200 nm or less, and especially preferably 100 nm or more and 170 nm or less. Furthermore, it is preferably 110 nm or more and 350 nm or less, more preferably 110 nm or more and 300 nm or less, more preferably 110 nm or more and 270 nm or less, even more preferably 110 nm or more and 250 nm or less, particularly preferably 110 nm or more and 230 nm or less, even more preferably 110 nm or more and 200 nm or less, and especially preferably 110 nm or more and 170 nm or less. Within this range, the CNT bundle diameter is appropriately controlled, ensuring sufficient contact between CNTs and efficiently forming a network structure, improving tensile strength. It also makes it easier to ensure sufficient contact area between bundles. This increases the frictional force between bundles, improving the tensile strength of the CNT aggregate.

[0051] 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.

[0052] -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

[0053] -Image selection- From the obtained images, select two or more images in which CNT bundles are clearly observed.

[0054] - 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 found by calculating the distance from the center line to the outline in 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 CNTs in the image. Note that using Python for image analysis is preferable in terms of work efficiency as it allows the analysis to proceed efficiently, but manual analysis is also possible.

[0055] -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.

[0056] -Detection of 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. The CNT outline and center line are superimposed on the original image and saved. The outline is displayed in red and the center line in blue.

[0057] -Detecting CNT bundle diameter using image analysis- 1. The image created by image processing is read and the CNT, outline, background, and center line are recognized by color recognition. 2. Measure the length of each center line. 3. Choose a random point on the center line and draw a perpendicular line from the point to the center line. 4. Find the intersection of the perpendicular line and the contour, and save the distance from a random point on the centerline to the intersection as the bundle diameter. 5. Calculate the area occupied by the product of the length of the center line segment and the bundle diameter. Save the data as a histogram with the bundle diameter on the horizontal axis and the area occupied on the vertical axis.

[0058] - Obtaining bundle diameter parameters - The bundle diameter feature quantity of each sample is calculated using the calculated bundle diameter histogram data. Hereinafter, a method for calculating the bundle diameter feature quantity will be specifically described along with the measurement method according to the present disclosure, i.e., the method for measuring the number of bundle structures and the total length ratio.

[0059] The measurement method for measuring the total length ratio according to the present disclosure (hereinafter also referred to as "measurement method A") is as follows: The method includes sequentially performing the following steps 1, 2, and 3 on a carbon nanotube aggregate including a bundle structure. (Step 1) A scanning electron microscope image of a carbon nanotube aggregate is processed to calculate the bundle diameter and the area occupied by the bundle structure within the field of view of the electron microscope image, and the result is converted into histogram data. (Step 2) Based on the histogram data obtained in Step 1, the existence of bundle structures is determined. The amount of stock is classified according to the bundle diameter range. (Step 3) The total bundle length, which is the area occupied by the bundle structure within the field of view of the electron microscope image divided by the bundle diameter, is normalized so that the sum is 100, and the total bundle length ratio (%) is calculated.

[0060] The above steps 1, 2, and 3 will be explained below.

[0061] (Step 1) In the measurement method A, in step 1, a scanning electron microscope image of a carbon nanotube aggregate is processed to calculate the bundle diameter and the area occupied by the bundle structure within the field of view of the electron microscope image, and the result is converted into histogram data. The details of the method for performing step 1 are specifically as explained in the section <<Measurement of bundle diameter>> above.

[0062] (Step 2) In the measurement methods A and B, in step 2, the abundance of bundle structures is classified according to the bundle diameter range based on the histogram data obtained in step 1. Specifically, classification will be carried out according to the following (i), (ii), and (iii). (i): Based on the histogram data obtained in step 1, the bundle diameters and occupied areas of multiple fields of view for the same sample are added together and normalized so that the total sum is 1. Following normalization, the vertical axis is the occupied area ratio, and the horizontal axis is the bundle diameter. (ii): In the normalized histogram data, a search is performed for "valleys" defined as follows, and the range from valley to valley is determined as one class. Valley: A point where the normalized area expressed as the exclusive area ratio (vertical axis) and bundle diameter (horizontal axis) is less than 0.02. However, if there are consecutive points where the area is less than 0.02, only the point with the smallest area will be considered a valley. (iii): Of the determined classes, the class with the smallest bundle diameter range is designated as Class A, followed by Class B, Class C, etc.

[0063] The bundle diameter of each class is determined based on the peak position belonging to each class. If there are multiple peak positions within one class, the peak with the largest value is selected. Therefore, the "smallest bundle class" in condition (2) means the class with the smallest bundle diameter range classified as class A in the above classification. In addition, the bundle diameter W of the smallest bundle class is determined based on the peak position belonging to the smallest bundle class (class A).

[0064] Here, classification will be explained using Fig. 6. However, Fig. 6 is used only for explaining classification. FIG. 6 shows an example of normalized histogram data obtained from a CNT aggregate, with the vertical axis representing the occupied area ratio and the horizontal axis representing the bundle diameter (nm). In FIG. 6, V1 to V5 each represent a searched "valley," and the normalized region determined from valley to valley is determined as one class. In FIG. 6, region A determined from V1 to V2 is classified into class A. Similarly, region B determined from V2 to V3 is classified into class B, region C determined from V3 to V4 is classified into class C, and region D determined from V4 to V5 is classified into class D. In FIG. 6, the peak belonging to the region divided into class A is determined as the bundle diameter of class A (i.e., the bundle diameter of the smallest bundle class).

[0065] (Step 3) In step 3 of measurement method A, the total bundle length, which is the value obtained by dividing the area occupied by the bundle structure within the field of view of the electron microscope image by the bundle diameter, is normalized so that the sum is 100 to calculate the total length ratio (%). The total length ratio is calculated as follows: The value of the occupied area of ​​the histogram data before normalization obtained in step 1 is divided by the value of the bundle diameter to convert it to total length. The converted histogram is normalized so that the total of the vertical axis becomes 100%. Following normalization, the unit of the vertical axis becomes the total length ratio (%).

[0066] For each class divided in step 1, the sum of the total length ratios is calculated, and the class with the highest total length ratio is designated as the "most frequent bundle class." The total length ratio of the most frequent bundle class is designated as the "total length ratio K."

[0067] <Condition (3)> The aggregate of carbon nanotubes according to the present disclosure preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution of 0.5 μm or more, and more preferably 0.5 μm or more and 25 μm or less.

[0068] In condition (2), the cumulative 50% particle size D50 in the volume-based particle size distribution is 0.5 μm or more, and may be 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1.0 μm. The cumulative 50% particle size D50 is 25 μm or less, 24 μm or less, 23 μm or less, 22 μm or less, 21 μm or less, 20 μm or less, 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, or 13 μm or less. These upper and lower limits can be combined in any manner.

[0069] The cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate according to the present disclosure is preferably 0.9 μm or more and 25 μm or less, more preferably 0.9 μm or more and 24 μm or less, even more preferably 0.9 μm or more and 23 μm or less, still more preferably 0.9 μm or more and 22 μm or less, especially preferably 0.9 μm or more and 21 μm or less, particularly preferably 0.9 μm or more and 20 μm or less, extremely preferably 0.9 μm or more and 19 μm or less, even extremely preferably 0.9 μm or more and 18 μm or less, and particularly preferably 0.9 μm or more and 17 μm or less. In another aspect, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is preferably 0.9 μm or more and 16 μm or less, more preferably 0.9 μm or more and 15 μm or less, even more preferably 0.9 μm or more and 14 μm or less, and particularly preferably 0.9 μm or more and 13 μm or less. In another aspect, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is preferably 0.9 μm or more and 25 μm or less, more preferably 0.9 μm or more and 24 μm or less, even more preferably 0.9 μm or more and 23 μm or less, even more preferably 0.9 μm or more and 22 μm or less, still more preferably 0.9 μm or more and 21 μm or less, especially preferably 0.9 μm or more and 20 μm or less, extremely preferably 0.9 μm or more and 19 μm or less, even extremely preferably 0.9 μm or more and 18 μm or less, and particularly preferably 0.9 μm or more and 17 μm or less. In another aspect, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is preferably 0.9 μm or more and 16 μm or less, more preferably 0.9 μm or more and 15 μm or less, even more preferably 0.9 μm or more and 14 μm or less, and particularly preferably 0.9 μm or more and 13 μm or less. In another aspect, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is preferably 1.0 μm or more and 13 μm or less, more preferably 1.0 μm or more and 8 μm or less, even more preferably 1.0 μm or more and 5 μm or less, and particularly preferably 1.07 μm or more and 2.31 μm or less.

[0070] The CNT aggregate according to the present disclosure preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution of 0.7 μm or more and 17 μm or less, and more preferably 1.0 μm or more and 15 μm or less. It is more preferable that the thickness is 1.0 μm or more and 13 μm or less, and particularly preferable that the thickness is 1.0 μm or more and 13 μm or less. When the cumulative 50% particle diameter D50 is within the above range, contact points between the CNT aggregates are sufficiently secured and a network structure is efficiently formed, resulting in improved tensile strength. In particular, when the cumulative 50% particle diameter D50 is in the range of 1.0 μm to 15 μm, the contact points between the CNTs are sufficiently secured and a network structure is efficiently formed, improving the tensile strength. Furthermore, a uniform particle size distribution stabilizes the viscosity of the dispersion of the CNT aggregate, resulting in better mechanical strength when, for example, an electrode is formed using the CNT aggregate.

[0071] Furthermore, when the cumulative 50% particle diameter D50 is within the above range, contact points between the CNT aggregates are sufficiently secured and a network structure is efficiently formed, resulting in improved tensile strength. Therefore, by satisfying condition (2), contact points between CNT aggregates are sufficiently secured, and a network structure is efficiently formed, thereby improving the tensile strength.

[0072] The cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate is measured as follows. The CNT dispersion was 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 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 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.

[0073] <Matters regarding tensile strength and elongation at break> In the present disclosure, the tensile strength and elongation at break of a CNT aggregate are measured, for example, by the following method. CNT aggregates, 700 kDa sodium carboxymethylcellulose, and water are mixed to prepare a CNT dispersion with a CNT aggregate concentration of 0.20 mass% and a sodium carboxymethylcellulose concentration of 0.30 mass%. 15 mL of the prepared CNT dispersion is poured onto a glass slide-type silicon plate with inner dimensions of 22 mm x 75 mm x 3 mm and heated and dried at 100 °C to prepare a measurement sample. The prepared measurement sample is fixed to the grip of a tensile tester, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. The point at which the stress is maximum in the tensile test is considered to be the break point, and the break elongation is calculated from the length of the measurement sample at the break point and the length of the measurement sample before the tensile test.

[0074] <Tensile strength> The tensile strength of the CNT aggregate according to the present disclosure is preferably 8.5 MPa or more and 50.0 MPa or less, more preferably 10.0 MPa or more and 30.0 MPa or less, even more preferably 12.6 MPa or more and 28.5 MPa or less, and particularly preferably 26.2 MPa or more and 28.5 MPa or less. When the tensile strength of the CNT aggregate according to the present disclosure is 8.5 MPa or more, the CNTs according to the present disclosure are sufficiently long, making it possible to produce a battery with excellent cycle characteristics. Specifically, when the CNTs are sufficiently long, the number of contact points between the CNTs increases, allowing for smooth electron transfer, improving the conductivity of the entire CNT aggregate and improving the cycle characteristics of the battery (i.e., the discharge capacity retention rate). When the tensile strength of the CNT aggregate according to the present disclosure is 50.0 MPa or less, it is easy to process it into a dispersion and ensure its dispersibility in the dispersion. Specifically, a tensile strength of 50.0 MPa or less maintains a good balance between the flexibility and mechanical strength of the CNTs, realizing uniform dispersion of the CNTs in the dispersion. This maintains the viscosity of the dispersion appropriately, further improving durability against volume changes and stress during battery cycling. This further improves the discharge capacity retention rate.

[0075] Note that the tensile strength of the CNT aggregate can be adjusted by the length, diameter, etc. of the CNT aggregate.

[0076] <Viscosity of the dispersion containing the CNT aggregate> The viscosity of the dispersion containing the CNT aggregate according to the present disclosure is preferably 10 mPa·s to 1600 mPa·s, more preferably 10 mPa·s to 1500 mPa·s, still more preferably 30 mPa·s to 1300 mPa·s, and particularly preferably 100 mPa·s to 1200 mPa·s. Furthermore, the viscosity of the above dispersion is preferably 100 mPa·s to 1100 mPa·s, more preferably 100 mPa·s to 700 mPa·s, still more preferably 100 mPa·s to 500 mPa·s, and particularly preferably 102 mPa·s to 434 mPa·s. In another embodiment, from the viewpoint of achieving both dispersibility and tensile strength, the viscosity of the above dispersion is preferably 100 mPa·s to 1600 mPa·s.

[0077] The viscosity of the dispersion containing the CNT aggregate according to the present disclosure is the viscosity obtained by mixing the CNT aggregate with sodium carboxymethyl cellulose of 700 kDa and water, and using the dispersion when the liquid temperature is 25°C, the concentration of the carbon nanotube aggregate is 0.20% by mass, and the concentration of sodium carboxymethyl cellulose is 0.30% by mass.

[0078] The viscosity of the dispersion containing the CNT aggregate according to the present disclosure is measured using a cone-plate viscometer (also known as an E-type viscometer). As the cone-plate viscometer, for example, DV-II+Pro PROGRAMMABLE VISCOMETER manufactured by BROOKFIELD is used. The measurement conditions are as follows. Measurement jig: Cone-plate Measurement mode: Rotation mode Shear rate: 0.6 s -1 ~384 s -1 Temperature: 25°C Read the viscosity at the following shear rates from the obtained data. Shear rate = 12 s -1

[0079] Since the CNT aggregate according to the present disclosure has a high affinity for the dispersion medium, the viscosity of the dispersion tends to be low. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the aggregate of the present disclosure in the dispersion medium is good.

[0080] <Surface resistivity> From the viewpoints of ensuring conductivity as a conductive aid and the stability of the dispersion, the surface resistivity of the film containing the CNT aggregate according to the present disclosure is preferably from 0.01 Ω / sq to 15.4 Ω / sq, more preferably from 0.1 Ω / sq to 12.0 Ω / sq, particularly preferably from 0.2 Ω / sq to 10.0 Ω / sq, and even more preferably from 0.2 Ω / sq to 8.0 Ω / sq. Furthermore, the surface resistivity of the film containing the CNT aggregate is preferably from 0.5 Ω / sq to 5.0 Ω / sq, more preferably from 0.8 Ω / sq to 4.0 Ω / sq, even more preferably from 1.1 Ω / sq to 3.3 Ω / sq, and particularly preferably from 2.3 Ω / sq to 3.3 Ω / sq.

[0081] In the present disclosure, the surface resistivity is measured by the following method. Mix the CNT aggregate, sodium carboxymethyl cellulose with a molecular weight of 70 kDa, and water to prepare a CNT dispersion in which the concentration of the CNT aggregate is 0.20% by mass and the concentration of sodium carboxymethyl cellulose is 0.30% by mass. While flowing 15 mL of the prepared carbon nanotube dispersion onto a slide glass-shaped silicon plate with an inner diameter of 22 mm × 75 mm × 3 mm, heat and dry it at 100 °C to prepare a measurement sample. For the prepared measurement sample, measure the surface resistivity at five arbitrarily selected locations on the film by the four-probe method using a resistivity meter, and take the average value of the five measured values as the surface resistivity.

[0082] <Other matters regarding the CNT aggregate> In the present disclosure, the CNTs contained in the CNT aggregate may be SWCNTs, MWCNs, T. From the viewpoint that having a distribution of the number of layers and having a slightly low uniformity contributes to satisfying the conditions (1) and (2), the CNT aggregate preferably contains SWCNTs and MWCNTs.

[0083] The maximum length of the CNTs contained in the CNT aggregate according to the present disclosure is not particularly limited.

[0084] 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.

[0085] 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).

[0086] 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.

[0087] 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."

[0088] 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.

[0089] 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.

[0090] 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.

[0091] It is preferable that a plurality of ULCNTs are present within the viewing angle of the SEM photograph. Focusing on 100 CNTs included in the viewing angle of the SEM photograph, the maximum length of each is measured, and among the observed CNTs, CNTs with a maximum length in the range of 1000 μm to 30000 μm (i.e. , ULCNT) is present in an amount of preferably 10% or more in terms of number, from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULCNTs, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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 "Methods for Measuring the Density and Specific Gravity of Solids".

[0096] The purity of carbon in the CNT of the ULCNT aggregate can be measured by thermogravimetric analysis. For example, using a thermal analyzer (manufactured by Shimadzu Corporation, DTG-60), obtain the thermogravimetric (TG) curve and differential thermal analysis (DTA) curve of the ULCNT aggregate. Consider the largest exothermic peak in the DTA curve where a peak top appears around 650 °C to 750 °C as the combustion of CNT, and the other exothermic peaks that appear as the combustion of substances other than CNT. Determine the purity of CNT 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.

[0097] The obtained fibrous ULCNT is preferably flexible and strong. Also, the conductivity of the ULCNT itself is preferably -1 ·m -1 or more, and more preferably -1 ·m -1 or more. Note that the conductivity of the ULCNT itself is usually -1 ·m -1 or less.

[0098] <Manufacturing method of CNT> The manufacturing method of CNT in the present disclosure is not particularly limited. For example, as the manufacturing method of CNT in the present disclosure, methods such as conventionally known chemical vapor deposition (CVD) method, a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst, etc. can be applied.

[0099] The CNT in the present disclosure can be manufactured, for example, by referring to the methods described in JP 2016-102047 A, WO 2021 -527611 A, etc.

[0100] The CNT manufacturing method according to the present disclosure will be described below with reference to examples, although the CNT manufacturing method according to the present disclosure is not limited to the following examples.

[0101] =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").

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] In production method X, it is preferable to control the temperature of the reactor to 200°C to 700°C when removing the agglomerates from the reactor. The CNT bundle diameter can be controlled by the temperature of the CNT reaction region and the temperature of the reactor when removing the agglomerates from the reactor. The higher the reactor temperature when removing the agglomerates from the reactor, the larger the CNT bundle diameter can be. For example, by setting the temperature of the reactor at about 150° C. when the aggregates are removed from the reactor, the bundle diameter, which is 90% of the cumulative diameter of the CNTs, can be set to 110 nm to 170 nm. By setting the temperature of the reactor at about 500° C. when the aggregates are removed from the reactor, the bundle diameter, which is 90% of the cumulative diameter of the CNTs, can be set to 200 nm to 230 nm. By setting the temperature of the reactor at about 750° C. when the aggregates are removed from the reactor, the bundle diameter, which is 90% of the cumulative diameter of the CNTs, can be set to 300 nm to 400 nm. The "reactor temperature" is a temperature determined by measuring the gas temperature at the outlet through which the condensate is taken out of the reactor.

[0120] The product particles in production method X contain ULCNTs. Depending on the production conditions, SWCNTs and MWCNTs may also be contained.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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, and 0.2% to 30% by mass of the precursor is contained in the carbon source. Preferably, the precursor is contained in the carbon source in an amount of 0.2 to 20 mass %, more preferably 0.2 to 20 mass %. In one embodiment, the precursor may be contained in the carbon source in an amount of 0.23 to 2.3 mass %, and the precursor is contained in the carbon source in an amount of 0.02 to 20 mass %. The catalyst may be used supported on a carrier, and preferred carriers include silica and magnesium oxide.

[0126] 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.

[0127] 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 a thread or a sheet. The length of the fibrous CNT can be controlled, for example, by the winding capacity of the spindle used in producing the fibrous CNT.

[0128] 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.

[0129] Preferably, production method X further comprises, after the step of aggregating CNTs into aggregates, a step of purifying the resulting CNT aggregates. Specifically, first, the CNT aggregates are washed with alcohol (for example, methanol, ethanol, etc.). Next, they are washed with an alkaline solution (for example, ammonia water). The pH of the alkaline solution is, for example, 8 to 11. Then, they are washed with pure water.

[0130] The cleaning method is not particularly limited, and may be a method of spraying a cleaning liquid onto the CNT aggregates, or a method of immersing the CNT aggregates in the cleaning liquid. Washing with alcohol removes alcohol-soluble components contained in the CNT aggregates. Furthermore, washing with an alkaline solution hydrolyzes and removes impurities contained in the CNT aggregates. Incidentally, washing with an acid solution may also be carried out.

[0131] After washing, the CNT aggregates are preferably dried. The drying method is not particularly limited, and can be carried out by a commonly known method.

[0132] By purifying the CNT agglomerates, the metal content in the CNTs can be reduced.

[0133] Preferably, production method X further comprises, after the step of purifying the CNT agglomerates, a step of passing the purified CNT agglomerates through a sieve. Also, it is preferable to recover the CNTs that have passed through the sieve.

[0134] 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 applied to electrodes (particularly electrodes of lithium ion batteries), 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, they may be crushed to an appropriate size. Crushing can be carried out using a crusher. Examples of crushers include a roll mill, a cutter mill, and a hammer mill.

[0135] 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.

[0136] 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.

[0137] =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").

[0138] ·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.

[0139] 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.

[0140] Because γ-Al2O3 has a high porosity and a spinel structure, the main catalyst and the promoter can be randomly arranged in γ-Al2O3. The CNTs grown from the randomly arranged main catalyst can be produced in an entangled state.

[0141] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese and chromium, with cobalt being preferred.

[0142] 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.

[0143] The main catalyst precursors were 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, and 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.

[0144] The promoter improves the dispersibility of the main catalyst, and may be one or more selected from the group consisting of vanadium and molybdenum.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] The mixture may further include an organic acid which serves to inhibit precipitation of the main catalyst precursor and the co-catalyst precursor.

[0149] 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.

[0150] 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.

[0151] After step (1), a step of aging may be further included.

[0152] 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.

[0153] ·Process (2) The active support is then dried by multi-stage drying, including vacuum drying.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] The primary vacuum drying can remove any solvent that may be present in the active support.

[0164] 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.

[0165] 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.

[0166] The primary vacuum drying may be carried out at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 80 mbar to 150 mbar, and is preferably carried out at 80 mbar to 150 mbar. When the above conditions are satisfied, the solvent present in the active support can be sufficiently removed. and energy consumption can be minimized.

[0167] The secondary vacuum drying is as described above in the description of vacuum drying.

[0168] The second temperature may be 175° C. to 300° C., and preferably 180° C. to 280° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinated bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0169] 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.

[0170] 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.

[0171] ·Process (3) The dried active support is then subjected to a heat treatment to produce a supported catalyst.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] ·Process (4) CNTs are then produced in the presence of a supported catalyst.

[0176] Specifically, CNTs can be produced by contacting a supported catalyst with a carbon-based compound, and specifically, by chemical vapor synthesis.

[0177] 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.

[0178] In the CNTs produced by the above-mentioned chemical vapor synthesis method, the crystal growth direction is almost parallel to the tube axis, and the graphite structure has high crystallinity in the tube length direction. CNTs with small diameters and high electrical conductivity and strength can be produced.

[0179] 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.

[0180] The heat source for the reaction is induction heating and radiant heat. , laser, IR, microwave, plasma, surface plasmon heating, etc. may be used.

[0181] Any carbonaceous compound can be used without particular limitations as long as it can supply carbon and can exist in a gaseous state at temperatures of 300° C. or higher.

[0182] The carbon-based compound may be a carbon-based compound having 6 or less carbon atoms, and may be one or more compounds 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.

[0183] After growing CNTs by the above-mentioned reaction, a cooling step may be optionally performed to align the CNTs more regularly. Specifically, the cooling step may be performed by natural cooling by removing the heat source or by using a cooler.

[0184] The above manufacturing methods X and Y are merely examples, and the manufacturing methods for CNTs that can be contained in a CNT aggregate are not limited to the above.

[0185] [Carbon nanotube dispersion liquid] 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 is excellent in 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.

[0186] <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.

[0187] <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, still more preferably 99% by mass or more, and may be, for example, 100% by mass.

[0188] Water is not particularly limited, but is preferably distilled water, ion-exchanged water, pure water, etc. in terms of having few impurities.

[0189] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of the hydrophilic solvent 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 still more preferably 1% by mass or less.

[0190] 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.

[0191] <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.

[0192] 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.

[0193] 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 nonionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic surfactants) Nonionic surfactants are preferred, polyoxyalkylene phenyl ethers are more preferred, and polyoxyethylene phenyl ethers are even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersing ability, dispersion stabilizing ability, and concentration enhancement for CNT aggregates.

[0194] Other dispersants that are excellent in CNT dispersibility, dispersion stabilization, and high concentration include Demol (registered trademark: the same applies hereinafter) N, a sodium salt of β-naphthalenesulfonic acid formalin condensate; Demol RN, Demol T (Kao Corporation), polyoxyethylene stearyl ether Brij S 100 (Sigma-Aldrich), polyvinylpyrrolidone K30 (e.g., Fujifilm Wako Pure Chemical Industries, Ltd.), carboxymethylcellulose (CMC) (e.g., Daicel Miraize Co., Ltd.), sodium deoxycholate (e.g., Fujifilm Wako Pure Chemical Industries, Ltd.), SOLSPERSETM W100, SOLSPERSE TM W150 (manufactured by Lubrizol Japan, Inc.) is particularly preferred from the viewpoint of excellent dispersibility, dispersion stabilization ability, and high concentration of CNT aggregates.

[0195] 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.

[0196] [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.

[0197] 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.

[0198] 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.

[0199] When water adheres to CNTs, the surface tension of the water makes it easier for the CNTs to adhere to each other. Therefore, by performing a drying process for the conductive additive before the dispersion process, the moisture adhering to the CNTs is removed, preventing adhesion of the CNTs to each other due to moisture 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.

[0200] 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.

[0201] <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.

[0202] [Conductive materials] The conductive material according to the present disclosure includes the CNT aggregate according to the present disclosure. 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.

[0203] 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.

[0204] 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.

[0205] <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.

[0206] 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.

[0207] 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.

[0208] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has electrical 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.

[0209] 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 c2Ni-site type lithium nickel oxide represented by O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.66); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (where 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 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion.

[0210] 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 for 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 an alkali metal, an alkaline earth metal, a transition metal, a Group 13 element, a Group 14 element, a rare earth element, and combinations thereof) may be used. By using silicon-based active material particles, the battery can be made to have a higher capacity.

[0211] 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 for electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers have been substituted with Li, Na, Ca, or the like.

[0212] <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.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] Among carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high 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.

[0217] 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:

[0218] 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.

[0219] 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.

[0220] <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.

[0221] An example of the planar aggregate according to the present disclosure is a film including the CNT aggregate according to the present disclosure.

[0222] Planar assemblies according to the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0223] 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.

[0224] Planar assemblies according to the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0225] <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.

[0226] The material constituting the substrate may be resin, glass, or fiber. good. 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.

[0227] 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]

[0228] 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.

[0229] 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 temperature-controlled at 120°C. Hydrogen gas was used as the carrier gas. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor is decomposed. The region where the metal catalyst precursor is decomposed is referred to as the first temperature zone.

[0230] 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 17 NL / min (NL is normal liters). The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0231] 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 150°C, and the sheet-like CNT aggregates were collected. The obtained sheet-like CNT aggregate was washed with methanol, immersed in a diluted ammonia water solution of pH 10 for 10 minutes, washed with pure water for 10 minutes, dried, 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. Ta.

[0232] 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.

[0233] (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

[0234] 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 cycles: 8 times Method: Circulation method

[0235] <Evaluation of CNT aggregate dispersion liquid 1: Viscosity> The viscosity of CNT dispersion liquid 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, a cone-plate viscometer (DV-II + Pro PROGRAMMABLE VISCOMETER manufactured by BROOKFIELD) was used to measure the viscosity. Measurement fixture: Cone-plate Measurement mode: Rotation mode Shear rate: 0.6 s -1 ~384 s -1 Temperature: 25 °C From the obtained data, the viscosity at a shear rate of 12 s -1 was read. The viscosity of the dispersion liquid was 434.0 mPa·s. The results are shown in Table 1.

[0236] 3. Evaluation <Characteristic quantity of bundle diameter> Regarding CNT aggregate 1 of Example 1, imaging was performed using a scanning electron microscope (SEM: Scanning Electron Microscope). Among the obtained images, two images in which CNT bundles were well observed were selected. One of the two images is shown in Figure 1. For the selected images, image processing and image analysis were performed using Python. In image processing, the contour and center line of the CNTs were 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 to calculate the exclusive area of CNTs in the image. A histogram of the bundle diameter and exclusive area was created.

[0237] Using the calculated bundle diameter histogram, the characteristic quantity of the bundle diameter of each sample was calculated by the following method.

[0238] 1. Classification of bundle diameter: The bundle diameter histograms calculated from the two images were added together to create a histogram that was normalized so that the sum was 1. Following normalization, the unit of the vertical axis was set to the exclusive area ratio. Bundle classes were classified based on the occupied area ratio of the bundle diameter histogram. There were two classes, with the smaller bundle diameter range designated "Class A" and the larger designated "Class B." Class A is the smallest bundle class. After classification, the bundle diameter of each class was determined from the peak position of the occupied area ratio of the histogram.

[0239] 2. Calculation of total bundle length ratio K: The area occupied by the histogram before normalization, which was added up in "1. Classification of bundle diameter," was divided by the bundle diameter, and the vertical axis was converted to total length. The converted histogram was normalized so that the total of the vertical axis was 100%. Following normalization, the vertical axis unit was changed to total length ratio. Class A was the most frequent bundle class. The sum of the total length ratio (%) for each class classified in "1. Bundle diameter classification" was calculated. As a result, the class with the highest total length ratio (%) was determined as the most frequent bundle class. Class A was the most frequent bundle class. In addition, the total length ratio (%) of the most frequent bundle class was defined as the total length ratio K. As a result, the bundle diameter W of the most frequent bundle class was 73.1 nm, and the total length ratio K was 83.7%. The bundle diameter W of the smallest bundle class was 73.1 nm.

[0240] 3. Calculation of the cumulative 90% bundle diameter and the area ratio of bundle diameters of 100 nm or more Using the bundle diameter histogram calculated above, the cumulative 90% bundle diameter of each sample was calculated by the following method. The bundle diameters and occupied areas of multiple fields of view for the same sample were added together and normalized so that the total sum was 1. Following normalization, the unit of the vertical axis was changed to the occupied area ratio. The total value of the occupied area ratio of bundles with a bundle diameter of 100 nm or more was calculated. The cumulative exclusive area ratio was calculated, and the bundle diameter when this value exceeded 0.9 for the first time was determined as the cumulative 90% bundle diameter. As a result, the area ratio of bundle diameters of 100 nm or more was 0.17, and the cumulative 90% bundle diameter was 170 nm.

[0241] <Measurement of 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 particle size D50 of the CNT dispersion 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. When measuring, CNT dispersion 1 was diluted by adding it dropwise to pure water while observing the transmittance, and measurements were performed after confirming that the particle size distribution on the monitor had stabilized. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate 1 was 12.53 μm.

[0242] <Tensile test> A measurement sample was prepared by pouring 15 mL of CNT dispersion 1 onto a glass slide-type silicon plate (Dosaka EM Co., Ltd., #08-1044) with inner dimensions of 22 mm × 75 mm × 3 mm, and heating and drying it at 100°C for 30 minutes. The prepared measurement sample was fixed to the grip of a tensile testing device (Shimadzu Corporation, Autograph AG-IS), and a tensile test was carried out at a tensile speed of 1 mm / min to measure the tensile strength. The point where the stress was maximum in the tensile test was considered to be the breaking point, and the breaking elongation was calculated from the length of the measured sample at the breaking point and the length of the measured sample before the tensile test. The resulting tensile strength was 12.6 MPa, and the breaking elongation was 1.5%.

[0243] <Surface resistivity> 15 mL of the CNT dispersion liquid 1 was poured onto a slide glass-shaped silicon plate (manufactured by Dozank EM Co., Ltd., #08 - 1044) with an inner diameter of 22 mm × 75 mm × 3 mm, and heated and dried at 100 °C to prepare a measurement sample. The surface resistivity of the film was measured using Loresta GXII manufactured by Nitto Seiko Analytic Co., Ltd. The measurement was performed at 5 locations on the film, and the average value of the 5 measurement values was taken as the surface resistivity. As a result, the surface resistivity was 1.1 Ω / □.

[0244] (Example 2) 1. Production of CNT aggregate 2 The CNT aggregate 2 was produced in the same manner as the CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and the raw material gas was set to 34 NL / min. 2. Preparation of CNT dispersion liquid 2 Using the obtained CNT aggregate 2, a preliminary dispersion liquid 2 was obtained in the same manner as in Example 1.

[0245] The final dispersion of the preliminary dispersion liquid 2 was carried out using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Tokuyama Seisakusho Co., Ltd. as a wet jet mill under the following conditions to obtain the CNT dispersion liquid 2. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of times: 8 times Method: Circulation method

[0246] <Evaluation of CNT aggregate dispersion liquid 2: Viscosity> The viscosity of the CNT dispersion liquid 2 was measured in the same manner as in Example 1. The viscosity of the dispersion liquid was 218.5 mPa·s. 3. Evaluation

[0247] <Characteristic quantity of bundle diameter> Regarding the CNT aggregate 2 of Example 2, imaging was performed using SEM, and the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1, except that 6 images in which CNT bundles were well observed were selected from the obtained images. One of the 6 images is shown in Figure 2. As a result, the bundle diameter W of the most frequent bundle class was 51.8 nm, and the total length ratio K was 93.0%. The bundle diameter W of the smallest bundle class was 51.8 nm. The area ratio of bundle diameters of 100 nm or more was 0.14, and the cumulative 90% bundle diameter was 110 nm.

[0248] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> For CNT dispersion 2, the cumulative 50% particle size D50 in the volume-based particle size distribution was measured in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate 1 was 2.31 μm.

[0249] <Tensile test> A tensile test was carried out in the same manner as in Example 1, except for using CNT dispersion liquid 2. The results were a tensile strength of 26.2 MPa and an elongation at break of 2.3%.

[0250] <Surface resistivity> The surface resistivity of the film was measured in the same manner as in Example 1, except for using CNT dispersion liquid 2. As a result, the surface resistivity was 2.5 Ω / □.

[0251] Example 3 1. Production of CNT aggregate 3 CNT aggregate 3 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 39 NL / min. 2. Preparation of CNT Dispersion 3 Using the obtained CNT aggregate 3, a pre-dispersion liquid 3 was obtained in the same manner as in Example 1.

[0252] The pre-dispersion liquid 3 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 3. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of times: 8 Method: Circulation method

[0253] <Evaluation of CNT aggregate dispersion liquid 3: Viscosity> The viscosity of CNT dispersion liquid 3 was measured in the same manner as in Example 1. The viscosity of the dispersion liquid was 102.2 mPa·s. 3. Evaluation

[0254] <Characteristic quantity of bundle diameter> Regarding the CNT aggregate 3 of Example 3, imaging was performed using SEM, and the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1, except that 7 images in which CNT bundles were well observed were selected from the obtained images. One of the 7 images is shown in Figure 3. As a result, the bundle diameter of the most frequent bundle class was 40.9 nm, and the total length ratio K was 93.0%. The bundle diameter W of the minimum bundle class was 40.9 nm. Also, the area ratio of the bundle diameter of 100 nm or more was 0.23. The cumulative 90% bundle diameter was 160 nm.

[0255] <Measurement of cumulative 50% particle diameter D50 in volume-based particle size distribution> Regarding CNT dispersion liquid 3, the cumulative 50% particle diameter D50 in the volume-based particle size distribution was measured in the same manner as in Example 1. As a result, the cumulative 50% particle diameter D50 in the volume-based particle size distribution of CNT aggregate 3 was 1.07 μm. The evaluation results are shown in Table 1 below

[0256] <Tensile test> A tensile test was conducted in the same manner as in Example 1, except that CNT dispersion liquid 3 was used. As a result, the tensile strength was 28.5 MPa and the elongation at break was 2.5%.

[0257] <Surface resistivity> The surface resistivity of the film was measured in the same manner as in Example 1, except that CNT dispersion liquid 3 was used. As a result, the surface resistivity was 3.3 Ω / □.

[0258] (Comparative Example 1) 1. Preparation of Powder CNT Aggregate 4 As the powder CNT aggregate 4, carbon nanotubes (catalog number: FT9100) manufactured by C-nano were prepared.

[0259] 2. Preparation of CNT Dispersion 4 Using the prepared powder CNT aggregate 4, a CNT dispersion 4 was obtained in the same manner as in Example 1.

[0260] <Evaluation of CNT Aggregate Dispersion 4: Viscosity> The viscosity of the CNT dispersion 4 was measured in the same manner as in Example 1. The viscosity of the dispersion was 5.7 mPa·s. 3. Evaluation <Characteristic Quantity of Bundle Diameter> Regarding the CNT aggregate 4 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, and the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1. One of the three images is shown in FIG. 4. As a result, the bundle diameter W of the most frequent bundle class was 30.0 nm, and the total length ratio K was 1.10%. The bundle diameter W of the minimum bundle class was 30.0 nm. In addition, the area ratio of the bundle diameter of 100 nm or more was 0.08. The cumulative 90% bundle diameter was 80 nm.

[0261] <Measurement of Cumulative 50% Particle Size D50 in Volume-Based Particle Size Distribution> Regarding the CNT dispersion 4, the cumulative 50% particle size D50 in the volume-based particle size distribution was measured in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate 4 was 0.35 μm.

[0262] <Tensile Test> A tensile test was performed in the same manner as in Example 1 except that the CNT dispersion 4 was used. As a result, the tensile strength was 2.3 MPa and the elongation at break was 1.9%.

[0263] <Surface Resistivity> The surface resistivity of the film was measured in the same manner as in Example 1 except that CNT dispersion liquid 4 was used. As a result, the surface resistivity was 15.5 Ω / sq.

[0264] (Comparative Example 2) 1. Preparation of Powder CNT Aggregate 5 As the powder CNT aggregate 5, carbon nanotubes (catalog number: FT6120) manufactured by C-nano were prepared.

[0265] 2. Preparation of CNT Dispersion Liquid 5 Using the prepared powder CNT aggregate 5, CNT dispersion liquid 5 was obtained in the same manner as in Example 1.

[0266] <Evaluation of CNT Aggregate Dispersion Liquid 5: Viscosity> The viscosity of CNT dispersion liquid 5 was measured in the same manner as in Example 1. The viscosity of the dispersion liquid was 9.3 mPa·s.

[0267] 3. Evaluation <Characteristic Quantity of Bundle Diameter> Regarding the CNT aggregate 5 of Comparative Example 2, imaging was performed using SEM, and the characteristic quantity of the bundle diameter was calculated in the same manner as in Example 1 except that 6 images in which CNT bundles were frequently observed were selected from the obtained images. One of the 6 images is shown in FIG. 5. As a result, the bundle diameter of the most frequent bundle class was 16.3 nm, and the total length ratio K was 100.0%. The bundle diameter W of the minimum bundle class was 16.3 nm. In addition, the area ratio of the bundle diameter of 100 nm or more was 0.08. The cumulative 90% bundle diameter was 90 nm.

[0268] <Measurement of Cumulative 50% Particle Size D50 in Volume-Based Particle Size Distribution> Regarding CNT dispersion liquid 5, the cumulative 50% particle size D50 in the volume-based particle size distribution was measured in the same manner as in Example 1. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution of the CNT aggregate 5 was 0.48 μm.

[0269] <Tensile test> A tensile test was carried out in the same manner as in Example 1, except for using CNT dispersion liquid 5. As a result, the tensile strength was 8.2 MPa and the elongation at break was 3.7%.

[0270] <Surface resistivity> The surface resistivity of the film was measured in the same manner as in Example 1, except for using CNT dispersion liquid 5. As a result, the surface resistivity was 16.5 Ω / □.

[0271] Next, a lithium ion secondary battery was fabricated.

[0272] 1. Preparation of a positive electrode for lithium secondary batteries Cathode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2) and conductive material (acetylene black The positive electrode mixture paste was prepared by mixing the positive electrode active material (C) and a binder (PVdF) in a ratio of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), adding N-methyl-2-pyrrolidone and kneading the mixture. The resulting positive electrode mixture was applied to a 15 μm thick Al foil as a current collector, and the resulting mixture was vacuum dried at 80°C for 1 hour, followed by roll pressing to obtain a positive electrode for a lithium secondary battery. The positive electrode area was 1.65 cm. 2 , basis weight 16mg / cm 2 , density is 3.0g / cm 3 It was adjusted so that

[0273] 2. Preparation of a negative electrode for lithium secondary batteries The negative electrode for the lithium secondary battery was prepared by mixing a 9:1 (mass ratio) mixture of artificial graphite MAG-E and carbon-coated SiO as the negative electrode active material, CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the binder, and the CNT dispersion as the conductive additive in a weight ratio of 94.9:5.0:0.1 to prepare a paste-like negative electrode mixture. Ion-exchanged water was used as the solvent for preparing the negative electrode mixture. 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

[0274] 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.

[0275] The evaluation results for Examples 1, 2, 3, Comparative Examples 1 and 2 are shown in Table 1.

[0276] [Table 1]

[0277] As shown in Table 1, the CNT aggregates of Example 1, Example 2, and Example 3 satisfy the conditions (1) and (2), and therefore, compared to Comparative Example 1 and Comparative Example 2, it was found that they have higher tensile strength.

Claims

1. An aggregate of carbon nanotubes that includes a bundle structure and satisfies the following conditions (1) and (2): (1) The most frequent bundle class has a bundle diameter W in the range of 20 nm or more and 100 nm or less, and a total bundle length ratio K of 10.0% or more and less than 100.0%. (2) The bundle diameter W of the smallest bundle class is more than 20 nm.

2. The carbon nanotube aggregate according to claim 1, which satisfies the following condition (3): (3) The cumulative 50% particle size D50 in the volume-based particle size distribution is 0.5 μm or more.

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.

Images