Carbon nanotube aggregate

Abstract

A carbon nanotube aggregate according to an aspect of the present disclosure comprises a plurality of carbon nanotubes (CNTs), wherein, when at least 110 CNTs constituting the aggregate are observed with a transmission electron microscope, in a case in which the number of most frequently observed layers is defined as n, with respect to 100% of the total amount of all observed CNTs, the proportion of the total amount of CNTs in which the number of layers is n-1 to n+1 is 20-38%, and the proportion of the total amount of CNTs in which the number of layers is n-2 to n+2 is 35-80%, and in a case in which the average value of the outer diameters of the CNTs in which the number of layers is n is defined as X (nm), the average value of the outer diameters of the CNTs in which the number of layers is n-1 is X-2.8 (nm) to X+0.5 (nm), the average value of the outer diameters of the CNTs in which the number of layers is n+1 is X-0.5 (nm) to X+2.8 (nm), and the average value of the outer diameters of the all observed CNTs is X-1.5 (nm) to X+1.5 (nm).

Description

Carbon nanotube aggregate Cross-reference of related applications

[0001] This application claims priority under Japanese Patent Application No. 2025-020211, dated February 10, 2025, and incorporates all the provisions contained herein.

[0002] This disclosure relates to an aggregate of carbon nanotubes.

[0003] Carbon nanotubes are used in electrical and electronic equipment applications, as well as in transportation machinery applications. For example, carbon nanotube films are sometimes used in applications such as heaters (see, for example, Patent Document 1).

[0004] Japanese Patent Publication No. 2010-257971

[0005] This disclosure aims to provide a novel carbon nanotube aggregate.

[0006] One embodiment of a carbon nanotube (CNT) aggregate of the present disclosure includes a plurality of CNTs, and when 110 or more CNTs constituting the aggregate are observed with a transmission electron microscope (TEM), if the most frequently observed layer number is n (where n is an integer), then the total proportion of CNTs with n-1 to n+1 layers is 20-38% of the total observed CNTs (100%), and the total proportion of CNTs with n-2 to n+2 layers is 35-80%. Furthermore, if the average outer diameter of CNTs with n layers is X (nm), then the average outer diameter of CNTs with n-1 layers is X-2.8 (nm) to X+0.5 (nm), the average outer diameter of CNTs with n+1 layers is X-0.5 (nm) to X+2.8 (nm), and the average outer diameter of all observed CNTs is X-1.5 (nm) to X+1.5 (nm).

[0007] According to this disclosure, a novel carbon nanotube aggregate can be provided.

[0008] Figure 1 is an example of a TEM image of carbon nanotubes obtained in Example 1.

[0009] In this specification, the numerical range A to B means A or greater and B or less. In this specification, if the units of the numbers before and after the "~" indicating a numerical range are the same, the unit of the number before the "~" may be omitted. Throughout this specification, singular expressions should be understood to include the concept of their plural form unless otherwise specified. Therefore, singular articles (for example, "a," "an," and "the" in English) should be understood to include the concept of their plural form unless otherwise specified. Furthermore, terms used in this specification should be understood to be used in the sense commonly used in the field unless otherwise specified. The upper and / or lower limits of numerical ranges described in this specification can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of numerical ranges can be arbitrarily combined to define a preferred range. In this specification, carbon nanotubes are also referred to as "CNTs," carbon nanotube forests as "CNT forests," carbon nanotube fibers as "CNT fibers," and carbon nanotube webs as "CNT webs."

[0010] [Carbon Nanotube Aggregates] The carbon nanotube (CNT) aggregates of this disclosure include a plurality of CNTs. When 110 or more CNTs constituting the aggregate are observed with a transmission electron microscope (TEM), and the most frequently observed layer number is n (where n is an integer), the total percentage of CNTs with n-1 to n+1 layers is 20-38% of the total 100% of all observed CNTs, and the total percentage of CNTs with n-2 to n+2 layers is 35-80%. Furthermore, if we consider the average outer diameter of a CNT with n layers as X (nm), then the average outer diameter of a CNT with n-1 layers is between X-2.8 (nm) and X+0.5 (nm), the average outer diameter of a CNT with n+1 layers is between X-0.5 (nm) and X+2.8 (nm), and the average outer diameter of all observed CNTs is between X-1.5 (nm) and X+1.5 (nm).

[0011] The aggregate of CNTs of this disclosure comprises a plurality of CNTs. CNTs can be manufactured using methods such as thermochemical vapor deposition (thermal CVD), plasma CVD, laser ablation, arc discharge, or combustion.

[0012] The aggregate of CNTs in this disclosure is, for example, a CNT forest provided on a substrate, or an aggregate obtained from a CNT forest. A CNT forest refers to an aggregate of multiple CNTs provided on a substrate and oriented perpendicular to the surface of the substrate. In a CNT forest, multiple CNTs stand in a dense forest on the substrate. An aggregate obtained from a CNT forest is, for example, an aggregate of powdered CNTs. Note that an aggregate of powdered CNTs is also simply referred to as powdered CNTs.

[0013] The following describes the number of layers, outer diameter, and inner diameter of the CNTs, which are calculated by observing 110 or more CNTs constituting the aggregate of CNTs of this disclosure using a transmission electron microscope (TEM). Observing CNTs using a transmission electron microscope (TEM) is also called "TEM observation," and the image obtained by TEM observation is also called a "TEM image."

[0014] More than 110 CNTs for TEM observation can be arbitrarily selected from the CNT aggregate. However, if a CNT with a changing layer number is observed during TEM observation, more than 110 CNTs will be selected from the CNT aggregate so as not to include that CNT. If the CNT aggregate is a CNT forest provided on a substrate, selecting more than 110 CNTs from the CNT aggregate means sampling more than 110 CNTs from the CNT forest. Details of the observation method using TEM are described in the Examples section.

[0015] The CNT aggregate may also contain single-walled carbon nanotubes.

[0016] When TEM observations were performed on 110 or more CNTs, and the most frequently observed layer number was n (where n is an integer), the total percentage of CNTs with n-1 to n+1 layers was 20-38% of the total 100% of all observed CNTs, while the total percentage of CNTs with n-2 to n+2 layers was 35-80%.

[0017] The total proportion of CNTs with n-1 to n+1 layers refers to the ratio of the total number of CNTs with n-1 to n+1 layers to the total number of CNTs observed using TEM. The same applies to the total proportion of CNTs with n-2 to n+2 layers and the proportion of CNTs with n layers. When 110 or more CNTs are observed using TEM, if there are two or more layers that are observed most frequently, the layer number closest to the median of all observed layers is defined as n. The median refers to the median in the distribution of CNT layers, specifically the value (number of layers) at which the cumulative value in the cumulative distribution of CNT layers reaches 50%.

[0018] When n is 1, the total proportion of CNTs with n-1 to n+1 layers means the total proportion of CNTs with 1 to 2 layers, and the total proportion of CNTs with n-2 to n+2 layers means the total proportion of CNTs with 1 to 3 layers. When n is 2, the total proportion of CNTs with n-1 to n+1 layers means the total proportion of CNTs with 1 to 3 layers, and the total proportion of CNTs with n-2 to n+2 layers means the total proportion of CNTs with 1 to 4 layers.

[0019] n is preferably 3 or more, more preferably 3 to 20, even more preferably 4 to 15, even more preferably 5 to 15, and particularly preferably 7 to 13. The total proportion of CNTs with n-1 to n+1 layers is preferably 22 to 36%, more preferably 24 to 35%, and even more preferably 26 to 34%. The total proportion of CNTs with n-2 to n+2 layers is preferably 40 to 76%, more preferably 45 to 73%, and even more preferably 50 to 70%. When the total proportion of CNTs with n-1 to n+1 and n-2 to n+2 layers falls within the above ranges, the CNT aggregate, particularly the CNT forest provided on the substrate, exhibits excellent spinnability, and the CNT aggregate also exhibits excellent dispersibility. In other words, the CNT aggregate of this disclosure exhibits an excellent balance between spinnability and dispersibility.

[0020] The proportion of CNTs with n layers is preferably 10-30%, more preferably 15-29%, and even more preferably 17-28%. When the proportion of CNTs with n layers is within the above range, the CNT aggregate, particularly the CNT forest provided on the substrate, exhibits excellent spinability, and the CNT aggregate also exhibits excellent dispersibility. In other words, the CNT aggregate of this disclosure exhibits an excellent balance between spinability and dispersibility.

[0021] If the distribution of the number of layers of CNTs that make up an aggregate of CNTs is wide, the total proportion of CNTs with n, n-1 to n+1, and n-2 to n+2 layers will be small.

[0022] The value of n, and the total proportion of CNTs with layers of n, n-1 to n+1, and n-2 to n+2, can be adjusted, for example, in the CNT assembly manufacturing method described later, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure in the reaction chamber in the CVD method, and the flow rates of the raw material gas and carrier gas. These amounts may also be adjusted while performing sequential TEM observations.

[0023] When TEM observations were performed on more than 110 CNTs, if the average outer diameter of CNTs with n layers is denoted as X (nm), then the average outer diameter of CNTs with n-1 layers is between X-2.8 (nm) and X+0.5 (nm), and the average outer diameter of CNTs with n+1 layers is between X-0.5 (nm) and X+2.8 (nm). Furthermore, the average outer diameter of all CNTs observed using TEM (used to calculate n) is between X-1.5 (nm) and X+1.5 (nm).

[0024] The outer diameter of a CNT refers to the diameter of the outermost layer of the CNT, measured using images obtained by TEM observation. If amorphous material is attached to the outside of the outermost layer, the diameter includes the amorphous material as well.

[0025] X is preferably 1 to 30 nm, more preferably 3 to 25 nm, even more preferably 5 to 20 nm, and particularly preferably 10.0 to 20.0 nm, from the viewpoint of ensuring that the CNT aggregate, especially the CNT forest provided on the substrate, has excellent spinnability and that the CNT aggregate has excellent dispersibility. X may also be 22 nm or less, 20 nm or less, 18 nm or less, 16 nm or less, or 14 nm or less. X may also be 4 nm or more, 6 nm or more, 8 nm or more, or 10 nm or more. A range combining these may be set as appropriate for X. The average value of the outer diameter of CNTs with n layers refers to the arithmetic mean of the outer diameters of CNTs with n layers. The same applies to the average value of the outer diameter of CNTs with n-1 layers, the average value of the outer diameter of CNTs with n+1 layers, and the average value of the outer diameter of all CNTs observed by TEM.

[0026] The average outer diameter of a CNT with n-1 layers is preferably X-2.6 nm to X+0.5 nm, more preferably X-2.5 nm to X+0.5 nm, and even more preferably X-2.4 nm to X+0.4 nm, from the viewpoint that the CNT aggregate, especially the CNT forest provided on the substrate, has excellent spinnability and the CNT aggregate has excellent dispersibility.

[0027] The average outer diameter of a CNT with n+1 layers is preferably X-0.5 nm to X+2.6 nm, more preferably X-0.5 nm to X+2.5 nm, and even more preferably X-0.4 nm to X+2.4 nm, from the viewpoint that the CNT aggregate, especially the CNT forest provided on the substrate, has excellent spinnability and the CNT aggregate has excellent dispersibility.

[0028] The average outer diameter of all CNTs observed by TEM is preferably X-1.3 nm to X+1.3 nm, more preferably X-1.1 nm to X+1.1 nm, and even more preferably X-0.9 nm to X+0.9 nm, from the viewpoint that the CNT aggregate, especially the CNT forest provided on the substrate, has excellent spinnability and the CNT aggregate has excellent dispersibility. From a similar viewpoint, in one embodiment, the average outer diameter of all CNTs observed by TEM may be, for example, 9.0 to 11.6 nm, 9.2 to 11.4 nm, 9.4 to 11.2 nm, 9.6 to 11.0 nm, 9.8 to 10.8 nm, or 10.0 to 10.6 nm.

[0029] The outer diameter of the CNTs can be adjusted, for example, in the CNT assembly manufacturing method described later, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure inside the reaction chamber in the CVD method, and the flow rates of the raw material gas and carrier gas. These quantities may also be adjusted while performing sequential TEM observations.

[0030] The average value of the inner diameters of all CNTs observed by TEM (used for calculating n by observing the number of layers) is preferably 1.0 to 6.0 nm, more preferably 3.5 to 6.0 nm, still more preferably 3.7 to 5.7 nm, and particularly preferably 4.0 to 5.5 nm from the viewpoints that the CNT aggregate, particularly the CNT forest provided on the substrate, has excellent spinability and the CNT aggregate has excellent dispersibility.

[0031] The inner diameter of the CNT refers to the diameter of the innermost layer of the CNT measured using an image obtained by TEM observation. The average value of the inner diameters of all CNTs observed by TEM refers to the arithmetic mean of the inner diameters of all CNTs observed by TEM.

[0032] The inner diameter of the CNT can be adjusted, for example, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure in the reaction chamber in the CVD method, and the flow rates of the raw material gas and the carrier gas in the method for producing the CNT aggregate described later. These amounts may be adjusted while sequentially performing TEM observation.

[0033] The average length of the CNTs constituting the CNT aggregate is preferably 10 to 1000 μm, more preferably 30 to 800 μm, and still more preferably 50 to 500 μm. The average length of the CNT can be adjusted, for example, by adjusting the time for performing the CVD method, that is, the growth time of the CNT. The average length of the CNT refers to the arithmetic mean of the lengths of all CNTs observed using a scanning electron microscope (SEM). Specifically, 10 images of the CNTs are obtained using an SEM. For each of the 10 images, 10 measurement points of the length are arbitrarily selected and measured, and the lengths of a total of 100 points are measured. Then, the average length of the CNT can be obtained by calculating the arithmetic mean of the measured values of the lengths of the 100 points.

[0034] The carbon purity of the CNTs constituting the CNT aggregate is preferably 95.0 to 99.999%. The lower limit of the carbon purity of the CNTs is preferably 96.0%, more preferably 97.0%, still more preferably 98.0%, even more preferably 99.0%, and particularly preferably 99.8%. The upper limit of the carbon purity of the CNTs may be, for example, 99.99% or 99.9%. The carbon purity of the CNTs can be determined, for example, by elemental analysis using fluorescent X-rays. In the present disclosure, % of carbon purity means mass%.

[0035] The crystallinity of the CNTs constituting the CNT aggregate can be evaluated, for example, using Raman spectroscopy. In the evaluation of crystallinity by Raman spectroscopy, the value of the D / G ratio is used as an index. The D / G ratio is the ratio of the peak intensity of the D band appearing near 1360 cm -1 to the peak intensity of the G band appearing near 1580 cm -1 in the Raman spectrum measured by Raman spectroscopy. The smaller the value of the D / G ratio, the higher the crystallinity of the carbon nanotubes. The D / G ratio of the CNTs is preferably 0.5 to 1.0, more preferably 0.6 to 0.8.

[0036] The carbon purity and crystallinity of the CNTs can be adjusted, for example, by adjusting the thickness of the buffer layer on the catalyst substrate, the type of material used for the buffer layer, the thickness of the catalyst layer, the type of catalyst, the type and flow rate of the source gas in the CVD method, and the temperature and pressure in the reaction chamber, in the method for producing the CNT aggregate described later.

[0037] [Method for Producing Aggregate of Carbon Nanotubes] The CNT aggregate of the present disclosure is, for example, a CNT forest provided on a substrate or an aggregate obtained from a CNT forest. The CNT forest can be produced, for example, by the method described later. An aggregate obtained from the CNT forest (for example, a powdery CNT aggregate) can be obtained, for example, by scraping off the CNTs from the substrate using a scraper or the like from the CNT forest.

[0038] A CNT forest can be obtained, for example, by performing chemical vapor deposition (CVD) on a catalyst substrate comprising a substrate and a catalyst layer provided on the substrate. The CVD method involves placing the catalyst substrate in a reaction chamber, supplying a raw material gas to the reaction chamber, and growing CNTs on the surface of the catalyst layer. Thermal CVD is preferred as the CVD method.

[0039] Examples of substrates include silicon substrates, alumina substrates, magnesium oxide substrates, glass substrates, sapphire substrates, titanium substrates, and stainless steel substrates.

[0040] From the viewpoint of handling and substrate cost, the thickness of the substrate is preferably 0.03 to 2.0 mm, more preferably 0.05 to 1.8 mm, even more preferably 0.07 to 1.6 mm, and particularly preferably 0.09 to 1.4 mm.

[0041] The catalyst layer can be formed, for example, by attaching catalyst particles to a substrate by sputtering. Examples of catalysts include metals, specifically iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo), gold (Au), and alloys containing at least one metal selected from the group consisting of these. Examples of alloys include iron alloys, nickel alloys, and cobalt alloys. The catalyst may also be a metal precursor, such as a metal oxide or metal compound. Examples of metal oxides include iron oxide, nickel oxide, and cobalt oxide. An example of a metal compound is iron chloride. When using a precursor, it is necessary to convert the precursor to a metal before performing the CVD method, for example, by heating it. By changing the type of catalyst, the number of layers, outer diameter, and inner diameter of the CNT can be changed.

[0042] The thickness of the catalyst layer is preferably 1 to 20 nm, more preferably 2 to 17 nm, even more preferably 3 to 15 nm, and particularly preferably 4 to 10 nm. The thicker the catalyst layer, the larger the number of CNT layers and outer diameter tend to be. The thinner the catalyst layer, the narrower the distribution of the number of CNT layers constituting the CNT aggregate tends to be.

[0043] The catalyst substrate may further include a buffer layer between the substrate and the catalyst layer. Examples of materials used for the buffer layer include silica (SiO2), alumina (Al2O3), silicon nitride (SiN), zinc oxide (ZnO), copper oxide (Cu2O), and nickel oxide (NiO). The buffer layer can be formed, for example, by sputtering. The outer and inner diameters of the CNTs can be changed by changing the type of material used for the buffer layer. For example, under certain manufacturing conditions, when the material used for the buffer layer is alumina (Al2O3), the outer and inner diameters of the CNTs tend to be smaller, while when the material is silica (SiO2), the outer and inner diameters of the CNTs tend to be larger.

[0044] The thickness of the buffer layer may be, for example, 10 to 100 nm, 20 to 80 nm, or 30 to 60 nm.

[0045] Sputtering for forming a catalyst layer and sputtering for forming a buffer layer can be carried out using known apparatus and conditions depending on the object to be sputtered. The pressure conditions for sputtering are preferably 0.01 to 10 Pa, more preferably 0.1 to 1 Pa.

[0046] As the raw material gas, carbon-containing raw material gases can be used, and examples include hydrocarbons, sulfur-containing organic gases, phosphorus-containing organic gases, carbon monoxide, and alcohols. Examples of hydrocarbons include alkane compounds such as methane and ethane, alkene compounds such as ethylene and butadiene, alkyne compounds such as acetylene, aryl hydrocarbon compounds such as benzene, toluene, and styrene, aromatic hydrocarbons having condensed rings such as indene, naphthalene, and phenanthrene, cycloalkane compounds such as cyclopropane and cyclohexane, cycloolefin compounds such as cyclopentene, and alicyclic hydrocarbon compounds having condensed rings such as steroids. Examples of alcohols include methanol and ethanol. From the viewpoint of the carbon purity of the resulting CNTs, the raw material gas is preferably hydrocarbons.

[0047] The flow rate of the raw material gas can be appropriately set according to the size of the reaction chamber and the size of the substrate in the CVD method. For example, in a CVD apparatus, if the volume of the quartz reaction tube is 2.0 × 10⁻⁶ －３ I understand ３ When using an apparatus in which the heating zone is 60% of the quartz reaction tube, and the size of the substrate is 2 inches in diameter, the flow rate of the raw material gas may be 5 to 100 sccm, 7 to 80 sccm, 10 to 60 sccm, or 15 to 40 sccm.

[0048] Along with the raw material gas, a carrier gas, which is a gas that transports the raw material gas, may also be supplied to the reaction chamber. Examples of carrier gases include helium, neon, argon, nitrogen, and hydrogen. Hydrogen is thought to contribute to the productivity and quality of carbon nanotubes and is also called a reactive carrier gas.

[0049] The carrier gas flow rate can be appropriately set according to the size of the apparatus used in the CVD process and the size of the substrate. For example, in a CVD apparatus, the volume of the quartz reaction tube is 2.0 × 10⁻⁶. －３ I understand ３ When using an apparatus in which the heating zone is 60% of the quartz reaction tube, and the size of the substrate is 2 inches in diameter, the carrier gas flow rate is preferably 50 to 2500 sccm, more preferably 200 to 2200 sccm, even more preferably 300 to 2000 sccm, and particularly preferably 400 to 1900 sccm.

[0050] In the CVD process, the temperature inside the reaction chamber is preferably 600 to 850°C, more preferably 650 to 800°C, from the viewpoint of the growth rate of CNTs and the carbon purity of the resulting CNTs. The pressure inside the reaction chamber in the CVD process is preferably atmospheric pressure, from the viewpoint of the growth rate of CNTs and the carbon purity. Depending on other conditions when carrying out the CVD process, the pressure inside the reaction chamber may be reduced or increased from atmospheric pressure. Under one manufacturing condition, the higher the pressure inside the reaction chamber, the narrower the distribution of the number of layers of CNTs constituting the CNT aggregate tends to be. In the production of the CNT aggregate according to this disclosure, the pressure inside the reaction chamber is preferably 450 to 800 torr, more preferably 480 to 750 torr, even more preferably 510 to 700 torr, and particularly preferably 540 to 650 torr.

[0051] The average length of CNTs in a CNT forest is similar to, for example, the average length of CNTs described above.

[0052] [Applications of Carbon Nanotube Aggregates] The CNT aggregates of this disclosure can be used, for example, in sports and leisure applications such as shoes, fishing rods, golf shafts and tennis rackets; in electrical and electronic equipment applications such as secondary batteries, heat dissipation materials, electrode sheets, electromagnetic shields, electromagnetic wave absorbing sheets, antistatic sheets, battery components, electronic components and casings for notebook computers, tablets and smartphones; in construction applications such as building materials; in transportation machinery applications such as automobiles, motorcycles, bicycles, railways, drones, rockets, aircraft and ships; in energy applications such as hydroelectric and wind power generators; and in fashion applications such as clothing and bags.

[0053] The aggregates of CNTs of this disclosure, particularly CNT forests provided on a substrate, are suitably used in applications that utilize carbon nanotube fibers (CNT fibers) or carbon nanotube webs (CNT webs). Examples of applications that utilize CNT fibers or CNT webs include applications that utilize CNT films, and specifically, in addition to the applications described above, heaters are also included.

[0054] A CNT web can be manufactured, for example, by using an aggregate of CNTs in the form of a CNT forest on a substrate, and extracting multiple CNTs from the CNT forest, specifically by extracting multiple CNTs in a sheet-like manner. More specifically, a CNT web can be manufactured, for example, by using a gripping tool such as tweezers to extract CNTs located at the ends of the CNT forest so that they move away from the CNT forest in a direction parallel to the surface of the substrate on which the CNT forest is provided. When CNTs located at the ends of the CNT forest are extracted, adjacent CNTs are successively extracted by van der Waals forces. The extracted CNTs are oriented so that their longitudinal direction aligns with the direction from which they were extracted. Therefore, the multiple CNTs constituting the CNT fiber are oriented in one direction. The multiple CNTs constituting the CNT fiber are bonded to each other by van der Waals forces. As a result, a CNT web is obtained, which is composed of multiple CNT fibers that extend in the direction from which the CNTs were extracted.

[0055] A CNT film containing CNT fibers can be manufactured, for example, by producing multiple sheets of CNT webs obtained by extracting multiple CNTs from a CNT forest, and then laminating each CNT web, or by manufacturing a roll by winding multiple CNT webs obtained by extracting multiple CNTs from a CNT forest around the circumferential surface of a roller, and then cutting open the roll along the rotation axis of the roller.

[0056] The CNT aggregates of this disclosure, particularly the CNT forests provided on a substrate, exhibit excellent spinability due to the fact that the physical properties of the CNTs, such as the number of layers, outer diameter, inner diameter, and length, are within the above range, and the CNT aggregates also exhibit excellent dispersibility. When the CNT aggregates exhibit excellent spinability, there is less risk of the CNT fibers and CNT webs breaking while the CNTs are being extracted from the CNT forest when manufacturing CNT fibers and CNT webs using the CNT forest. When the CNT aggregates exhibit excellent dispersibility, they are suitable as conductive additives in secondary batteries, such as lithium-ion secondary batteries.

[0057] Examples of dispersion media for the above-mentioned CNT aggregates include water and organic solvents. Examples of organic solvents include water-soluble organic solvents, specifically alcohol-based solvents, polyhydric alcohol ether-based solvents, amine-based solvents, amide-based solvents, heterocyclic solvents, sulfoxide-based solvents, sulfone-based solvents, lower ketone-based solvents, urea, and acetonitrile.

[0058] Examples of alcohol-based solvents include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol. Examples of polyhydric alcohol ether-based solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0059] Examples of amine solvents include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, and diethylenediamine. Examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam.

[0060] Examples of heterocyclic solvents include tetrahydrofuran, cyclohexylpyrrolidone, 2-oxazolidone, and 1,3-dimethyl-2-imidazolidinone. Examples of sulfoxide solvents include dimethyl sulfoxide. Examples of sulfone solvents include hexamethylphosphorotriamide and sulfolane. Examples of lower ketone solvents include acetone and methyl ethyl ketone.

[0061] This disclosure has, for example, the following aspects: [1] An aggregate of carbon nanotubes (CNTs) containing multiple CNTs, wherein when 110 or more CNTs constituting the aggregate are observed with a transmission electron microscope, the number of layers most frequently observed is n (where n is an integer), and the total percentage of CNTs with n-1 to n+1 layers is 20-38% of the total 100% of all observed CNTs, and the total percentage of CNTs with n-2 to n+2 layers is 35-80%, and the average outer diameter of CNTs with n layers is X (nm), the average outer diameter of CNTs with n-1 layers is X-2.8 (nm) to X+0.5 (nm), the average outer diameter of CNTs with n+1 layers is X-0.5 (nm) to X+2.8 (nm), and the average outer diameter of all observed CNTs is X-1.5 (nm) to X+1.5 (nm). An aggregate of carbon nanotubes. [2] The aggregate of carbon nanotubes according to [1], wherein the average value of the inner diameter of all the observed CNTs is 1.0 to 6.0 nm.

[0062] [3] The aggregate of carbon nanotubes according to [1] or [2], wherein n is 3 or more. [4] The aggregate of carbon nanotubes according to [3], wherein n is 3 to 15.

[0063] [5] An aggregate of carbon nanotubes according to any one of [1] to [4], wherein the total proportion of CNTs with n-1 to n+1 layers is 22 to 36%. [6] An aggregate of carbon nanotubes according to any one of [1] to [5], wherein the total proportion of CNTs with n-2 to n+2 layers is 50 to 70%.

[0064] [7] The aggregate of carbon nanotubes according to any one of [1] to [6], wherein the average length of the CNTs constituting the aggregate is 10 to 1000 μm. [8] The aggregate of carbon nanotubes according to any one of [1] to [7], wherein the aggregate of CNTs is a CNT forest provided on a substrate.

[0065] [9] The aggregate of carbon nanotubes according to any one of [1] to [7], wherein the aggregate of CNTs is an aggregate obtained from a CNT forest.

[0066] Hereinafter, the aggregate of CNTs of the present disclosure will be described more specifically based on examples, but the aggregate of CNTs of the present disclosure is not limited to these examples.

[0067] [Example 1] First, vertically aligned CNTs were grown from a catalyst by the following steps (1) to (6) to produce a vertically aligned CNT forest vertically aligned with respect to a wafer. (1) On a titanium metal foil substrate having a diameter of 2 inches and a thickness of 0.1 mm, silicon (Si) was used as a target by reactive sputtering, and 200 sccm of argon and 50 sccm of oxygen were introduced to react with silicon while forming a buffer layer of silica (SiO ２ ) with a thickness of 40 nm. (2) A catalyst layer of iron with a thickness of 5 nm was uniformly formed on the buffer layer of silica by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed in the center of the heating zone in the CVD apparatus, evacuated, and then the temperature inside the furnace (reaction chamber) was raised until the furnace temperature reached 730 ° C. to activate the catalyst particles (iron particles). As the CVD apparatus, an apparatus having a volume of the quartz reaction tube of 2.0 × 10 －３ m ３ , and a heating zone of 60% of the quartz reaction tube was used. (4) 1497 sccm of nitrogen gas was introduced, and the inside of the furnace was set to a carrier gas (nitrogen gas) atmosphere while maintaining the pressure inside the furnace at 600 torr. (5) After the furnace temperature stabilized at 729 ° C., without changing the amount of nitrogen gas introduced, further acetylene gas (C ２ H ２(6) 20 sccm of ) and 100 sccm of hydrogen gas were introduced, and the CNTs were grown for 10 minutes.

[0068] Next, the CNT forest formed on the catalyst substrate was scraped off the substrate using a scraper to obtain powdered CNTs.

[0069] The carbon purity of the CNTs constituting the CNT forest was 99.8% or higher, and the crystallinity (D / G ratio) was 0.6 to 0.8. Furthermore, 114 CNTs were arbitrarily selected from the obtained powdered CNTs and subjected to TEM observation, as described later. The observation results are shown in Table 1.

[0070]

[0071] Observations of a total of 114 carbon nanotubes (CNTs) revealed that the most frequently observed number of layers was 10. The total percentage of CNTs with 9 to 11 layers was 32.5%, while the total percentage of CNTs with 8 to 12 layers was 64.0%.

[0072] The average outer diameter of CNTs with 10 layers was 10.1 nm, the average outer diameter of CNTs with 9 layers was 10.4 nm, and the average outer diameter of CNTs with 11 layers was 12.4 nm. The average outer diameter of the 114 CNTs observed by TEM was 10.3 nm, and the average inner diameter was 4.9 nm. The average length of each CNT constituting the CNT forest observed by SEM was 250 μm.

[0073] Figure 1 shows an example of a TEM image of a CNT obtained in Example 1. In Figure 1, length D is an example of the outer diameter of the CNT, and length d is an example of the inner diameter.

[0074] [Comparative Example 1] First, vertically oriented CNTs were grown from a catalyst by the following steps (1) to (6) to fabricate a vertically oriented CNT forest oriented perpendicular to the wafer. (1) On a titanium metal foil substrate with a diameter of 2 inches and a thickness of 0.1 mm, aluminum (Al) was targeted by reactive sputtering, and 98 sccm of argon and 21 sccm of oxygen were introduced to react with the aluminum, while a 40 nm thick layer of alumina (Al) was grown. ２ O ３ (1) A buffer layer of alumina was deposited. (2) A 5 nm thick iron catalyst layer was uniformly deposited on the alumina buffer layer by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed in the center of the heating zone in the CVD apparatus, and after vacuuming, the furnace (reaction chamber) was heated to 730°C to activate the catalyst particles (iron particles). The CVD apparatus had a quartz reaction tube with a volume of 2.0 × 10 －３ I understand ３ , an apparatus was used in which the heating zone occupied 60% of the quartz reaction tube. (4) 1498 sccm of nitrogen gas was introduced, and the furnace was kept in a carrier gas (nitrogen gas) atmosphere while maintaining the furnace pressure at 749 torr. (5) After the furnace temperature stabilized at 730°C, acetylene gas (C) was introduced without changing the amount of nitrogen gas introduced. ２ H ２ (6) A 21 sccm of ferrous oxide and a 99 sccm of hydrogen gas were introduced, and the CNTs were grown for 10 minutes.

[0075] Next, the CNT forest formed on the catalyst substrate was scraped off the substrate using a scraper to obtain powdered CNTs.

[0076] The carbon purity of the CNTs constituting the CNT forest was 99.8% or higher, and the crystallinity (D / G ratio) was 0.6 to 0.8. Furthermore, 161 CNTs were arbitrarily selected from the obtained powdered CNTs and subjected to TEM observation, as described later. The observation results are shown in Table 2.

[0077]

[0078] Observations of a total of 161 carbon nanotubes (CNTs) revealed that the most frequently observed number of layers was 6. The total percentage of CNTs with 5 to 7 layers was 47.8%, while the total percentage of CNTs with 4 to 8 layers was 80.1%.

[0079] The average outer diameter of CNTs with 6 layers was 7.6 nm, the average outer diameter of CNTs with 5 layers was 7.4 nm, and the average outer diameter of CNTs with 7 layers was 7.5 nm. The average outer diameter of the 161 CNTs observed by TEM was 7.5 nm, and the average inner diameter was 4.1 nm. The average length of each CNT constituting the CNT forest observed by SEM was 250 μm.

[0080] [Comparative Example 2] First, vertically oriented CNTs were grown from a catalyst by following the steps (1) to (6) below, and a vertically oriented CNT forest oriented perpendicular to the wafer was fabricated. (1) On a titanium metal foil substrate with a diameter of 2 inches and a thickness of 0.1 mm, silicon (Si) was targeted by reactive sputtering, and 201 sccm of argon and 49 sccm of oxygen were introduced to react with the silicon, while a 40 nm thick silica (SiO ２ (1) A buffer layer of silica was deposited. (2) A 5 nm thick iron catalyst layer was uniformly deposited on the silica buffer layer by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed in the center of the heating zone in the CVD apparatus, and after vacuuming, the furnace (reaction chamber) was heated to 730°C to activate the catalyst particles (iron particles). The CVD apparatus had a quartz reaction tube with a volume of 2.0 × 10 －３ I understand ３ , an apparatus was used in which the heating zone occupied 60% of the quartz reaction tube. (4) 1502 sccm of nitrogen gas was introduced, and the furnace was kept in a carrier gas (nitrogen gas) atmosphere while maintaining the furnace pressure at 751 torr. (5) After the furnace temperature stabilized at 730°C, acetylene gas (C) was introduced without changing the amount of nitrogen gas introduced. ２ H ２(6) A 20 sccm solution of ferrous metal and a 98 sccm solution of hydrogen gas were introduced, and the CNTs were grown for 10 minutes.

[0081] Next, the CNT forest formed on the catalyst substrate was scraped off the substrate using a scraper to obtain powdered CNTs.

[0082] The carbon purity of the CNTs constituting the CNT forest was 99.8% or higher, and the crystallinity (D / G ratio) was 0.6 to 0.8. Furthermore, 166 CNTs were arbitrarily selected from the obtained powdered CNTs and subjected to TEM observation, as described later. The observation results are shown in Table 3.

[0083]

[0084] Observation of a total of 166 carbon nanotubes (CNTs) revealed that the most frequently observed number of layers was 6. The total percentage of CNTs with 5 to 7 layers was 42.2%, and the total percentage of CNTs with 4 to 8 layers was 65.1%. The average outer diameter of CNTs with 6 layers was 9.3 nm, the average outer diameter of CNTs with 5 layers was 8.3 nm, and the average outer diameter of CNTs with 7 layers was 10.7 nm. The average outer diameter of the 166 CNTs observed using TEM was 11.5 nm, and the average inner diameter was 5.4 nm. The average length of each CNT constituting the CNT forest observed using SEM was 246 μm.

[0085] [Comparative Example 3] First, vertically oriented CNTs were grown from a catalyst by the following procedure (1) to (5) to create a vertically oriented CNT forest oriented perpendicular to the wafer. (1) A catalyst substrate was manufactured by uniformly depositing a 3 nm thick iron catalyst layer on a silicon wafer with a diameter of 2 inches and a thickness of 0.725 mm using the sputtering method, with iron (Fe) as the target. (2) The catalyst substrate was placed in the center of the heating zone in the CVD apparatus, and after vacuuming, the furnace temperature (reaction chamber) was raised to 730°C to activate the catalyst particles (iron particles). The CVD apparatus had a quartz reaction tube with a volume of 2.0 × 10 －３ I understand ３, an apparatus was used in which the heating zone occupied 60% of the quartz reaction tube. (3) 1502 sccm of nitrogen gas was introduced, and the furnace was kept at a pressure of 751 torr, creating a carrier gas (nitrogen gas) atmosphere inside the furnace. (4) After the furnace temperature stabilized at 732°C, acetylene gas (C) was introduced without changing the amount of nitrogen gas introduced. ２ H ２ (5) 20 sccm of ) and 279 sccm of hydrogen gas were introduced, and the CNTs were grown for 10 minutes. (6) After that, the furnace was cooled and the catalyst substrate and the CNT forest (a forest of CNTs on the substrate) were removed.

[0086] Next, the CNT forest formed on the catalyst substrate was scraped off the substrate using a scraper to obtain powdered CNTs.

[0087] The carbon purity of the CNTs constituting the CNT forest was 99.8% or higher, and the crystallinity (D / G ratio) was 0.6 to 0.8. Furthermore, 115 CNTs were arbitrarily selected from the obtained powdered CNTs and subjected to TEM observation, as described later. The observation results are shown in Table 4.

[0088]

[0089] Observation of a total of 115 carbon nanotubes (CNTs) revealed that the median number of layers observed was 6, with 6 being the most frequently observed number of layers. 83.5% of CNTs had 5 to 7 layers, while 95.7% had 4 to 8 layers.

[0090] The average outer diameter of CNTs with 6 layers was 9.2 nm, the average outer diameter of CNTs with 5 layers was 8.1 nm, and the average outer diameter of CNTs with 7 layers was 10.6 nm. The average outer diameter of 115 CNTs observed with TEM was 9.2 nm, and the average inner diameter was 3.9 nm. The average length of each CNT constituting the CNT forest observed with SEM was 247 μm.

[0091] [TEM Observation] The powdered CNTs produced in the examples and comparative examples were observed using TEM, and the number of layers, outer diameter, and inner diameter of the CNTs were measured using the following methods (1) to (3). (1) The obtained powdered CNTs were dispersed in ethanol and dropped onto a microgrid. (2) The dried samples were observed using an FE-TEM (JEM-2100F, manufactured by JEOL Ltd.) to obtain TEM images. A predetermined number of CNTs were arbitrarily selected at this time. (3) For each TEM image, the number of layers, outer diameter, and inner diameter of the CNTs were measured using ImageJ. For the outer diameter and inner diameter of the CNTs, measurements were taken at three locations each on the CNTs visible in the TEM image, and the average value was used. If the outer or inner diameter of a carbon nanotube (CNT) visible in the TEM image changes noticeably along the CNT, three measurement points were selected: a section with a narrow outer or inner diameter, a section with a wide outer or inner diameter, and a section with a medium outer or inner diameter.

[0092] [Spinability Evaluation] Three evaluators, each with experience extracting CNT webs from over 100 CNT forests, evaluated the spinability of CNT forests manufactured under the same conditions as the examples and comparative examples by extracting CNT webs from the ends of the forests, according to the following criteria. Each evaluator performed the above operation on five CNT forests, and the average value was used as their evaluation. The average of the evaluations from the three evaluators was used as the spinability of the CNT aggregate.

[0093] The spinality of the CNT aggregate in Example 1 was 3.8, the spinality of the CNT aggregate in Comparative Example 1 was 1.1, the spinality of the CNT aggregate in Comparative Example 2 was 1.2, and the spinality of the CNT aggregate in Comparative Example 3 was 4.4.

[0094] 5: The CNT web can be traced from one end of the CNT forest to the other in one step. 4: The CNT web can be traced from one end of the CNT forest to the other in two steps. 3: The CNT web can be traced from one end of the CNT forest to the other in three steps. 2: The CNT web can be traced from one end of the CNT forest to the other in four to six steps. 1: The CNT web can be traced from one end of the CNT forest to the other in seven or more steps, or it cannot be traced from one end to the other.

[0095] [Dispersibility Evaluation] In the CNT forests obtained in the examples and comparative examples, CNTs were scraped off the wafers using a scraper to obtain aggregates of powdered CNTs. Three evaluators, each with experience in preparing CNT dispersions more than 100 times, performed the following operations and then evaluated the dispersions according to the following criteria.

[0096] 0.002 g of powdered carbon nanotube (CNT) aggregates were weighed into a glass screw-top tube, 5 ml of ethanol was added, and 40,000 Hz ultrasound was irradiated for 2 minutes. Visual observation was performed, and the dispersibility was evaluated according to the following criteria. Each evaluator evaluated each powdered CNT aggregate three times, and the average of these evaluations was used as each evaluator's score. The average of the evaluations from the three evaluators was used as the evaluation of the dispersibility of the CNT aggregates.

[0097] The dispersibility of the CNT aggregate in Example 1 was 2.8, the dispersibility of the CNT aggregate in Comparative Example 1 was 3.3, the dispersibility of the CNT aggregate in Comparative Example 2 was 3.2, and the dispersibility of the CNT aggregate in Comparative Example 3 was 1.4. 4: Uniformly dispersed within 2 minutes after ultrasonic irradiation. 3: Within 2 minutes after ultrasonic irradiation, slight clumps were observed, but dispersed to a degree that did not pose a practical problem. 2: Clumps were observed at 2 minutes after ultrasonic irradiation, and additional dispersion of up to 3 minutes was required to disperse to a degree that did not pose a practical problem. 1: Clumps were observed at 2 minutes after ultrasonic irradiation, and additional dispersion of more than 3 minutes was required to disperse to a degree that did not pose a practical problem.

[0098] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various omissions, substitutions, modifications, and changes are possible within the scope of the gist of the present invention as described in the claims. These embodiments and their variations are included in the scope and gist of the invention, as well as in the scope of the invention and its equivalents as described in the claims.

Claims

1. An aggregate of carbon nanotubes (CNTs) containing multiple CNTs, wherein when 110 or more CNTs constituting the aggregate are observed with a transmission electron microscope, and the most frequently observed layer number is n (where n is an integer), then, out of 100% of the total observed CNTs, the proportion of CNTs with n-1 to n+1 layers is 20-38%, and the proportion of CNTs with n-2 to n+2 layers is 35-80%. If the average outer diameter of CNTs with n layers is X (nm), then the average outer diameter of CNTs with n-1 layers is X-2.8 (nm) to X+0.5 (nm), the average outer diameter of CNTs with n+1 layers is X-0.5 (nm) to X+2.8 (nm), and the average outer diameter of all observed CNTs is X-1.5 (nm) to X+1.5 (nm). An aggregate of carbon nanotubes.

2. The aggregate of carbon nanotubes according to claim 1, wherein the average value of the inner diameter of all the observed CNTs is 1.0 to 6.0 nm.

3. The aggregate of carbon nanotubes according to claim 1, wherein n is 3 or more.

4. The aggregate of carbon nanotubes according to claim 3, wherein n is 3 to 15.

5. The aggregate of carbon nanotubes according to claim 1, wherein the total proportion of CNTs with n-1 to n+1 layers is 22 to 36%.

6. The aggregate of carbon nanotubes according to claim 1, wherein the total proportion of CNTs with n-2 to n+2 layers is 50 to 70%.

7. The carbon nanotube aggregate according to claim 1, wherein the average length of the CNTs constituting the aggregate is 10 to 1000 μm.

8. The carbon nanotube aggregate according to claim 1, wherein the aggregate of CNTs is a CNT forest provided on a substrate.

9. The carbon nanotube aggregate according to claim 1, wherein the aggregate of CNTs is an aggregate obtained from a CNT forest.

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