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

Abstract

Provided is a carbon nanotube assembly with which a battery having excellent cycle characteristics can be manufactured. This carbon nanotube assembly satisfies conditions (1) and (2) below. (1) The peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum, exceeds 4.7. (2) The cumulative 50% particle size D50 in a volume-based particle size distribution is in the range of more than 0.45 μm but less than 25 μm.

Description

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

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

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are materials having a cylindrical structure formed by coaxially rolling up graphene sheets, which are composed of six-membered ring structures of carbon, in single or multilayer configurations. CNTs are broadly classified into single-walled CNTs, formed from a single layer of graphene sheet, and multilayered CNTs, formed from multiple layers of graphene sheet. CNTs exhibit excellent mechanical, electrical, and chemical properties, and these properties are expected to lead to applications in fields such as materials, catalysts, energy, and electronics. Various attempts have been proposed to further enhance the properties of CNTs.

[0003] For example, Patent Document 1 discloses a carbon nanotube aggregate that satisfies the following conditions (1) and (2): (1) The peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum of the carbon nanotube, is 0.70 to 10.0, and the ratio of the peak area ratio G2 / D2, which is the ratio of the peak area G2 of the G band to the peak area D2 of the D band, to the peak intensity ratio G1 / D1 is 1.20 to 3.00. (2) The BET specific surface area of ​​the carbon nanotube is 100 m ２ / g to 300m ２ / g. Patent Document 2 discloses a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a solvent, which satisfies (1) to (4). (1) Raman spectrum of carbon nanotubes at 1560 cm⁻¹ －１ ~1600cm －１ The maximum peak intensity within the range is G, 1310 cm. －１ ~1350cm －１(1) When the maximum peak intensity within the range is denoted as D, the G / D ratio of the carbon nanotubes is 5 to 100. (2) The dispersion contains 30 to less than 250 parts by mass of dispersant per 100 parts by mass of carbon nanotubes. (3) The complex modulus of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is 5 Pa or more and less than 650 Pa, and the phase angle is 5° or more and less than 50°. (4) The BET specific surface area of ​​the carbon nanotubes is 550 m². ２ / g to 1200m ２ It is / g.

[0004] Japanese Patent Publication No. 7528393, Japanese Unexamined Patent Publication No. 2022-63234

[0005] When manufacturing batteries using CNT assemblies, there were times when excellent cycle characteristics were required.

[0006] This disclosure has been made in view of the above circumstances. One embodiment of this disclosure aims to solve the problem of providing a carbon nanotube aggregate capable of producing a battery with excellent cycle characteristics. Another embodiment of this disclosure aims to solve the problem of providing a conductive material, electrode, secondary battery, and planar aggregate containing the carbon nanotube aggregate. Another embodiment of this disclosure aims to solve the problem of providing a laminate comprising the planar aggregate. Another embodiment of this disclosure aims to solve the problem of providing a filter, electromagnetic shield, and extreme ultraviolet pellicle using the planar aggregate.

[0007] The following embodiments are included as specific means to solve the above problems. <1> A carbon nanotube aggregate that satisfies the following conditions (1) and (2): (1) The peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum, is greater than 4.7. (2) The cumulative 50% particle size D50 in the volume-based particle size distribution is in the range of greater than 0.45 μm and less than 25 μm. <2> The carbon nanotube aggregate described in <1> that satisfies the following condition (3): (3) The elongation at break calculated from the tensile strength measured by the following measurement method is in the range of 2.0% or more and 4.0% or less. (Method for calculating elongation at break) A carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water are mixed to prepare a carbon nanotube dispersion in which the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%. A sample is prepared by pouring 15 mL of the prepared carbon nanotube dispersion onto a glass slide-type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heating and drying it at 100°C. The prepared sample is fixed to the gripping part of a tensile testing apparatus, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. The point at which the stress is maximum in the tensile test is considered to be the fracture point, and the elongation at fracture is calculated from the length of the sample at fracture and the length of the sample before the tensile test. <3> A carbon nanotube aggregate as described in <1> that satisfies the following condition (4). (4) The fracture energy density, which is the product of the tensile strength and the elongation at fracture measured by the measurement method below, is 14.5 MPa・% or more. (Method for measuring tensile strength and method for calculating elongation at break) A carbon nanotube dispersion is prepared by mixing a carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, so that the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%. 15 mL of the prepared carbon nanotube dispersion is poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heated and dried at 100°C to prepare a sample for measurement.The prepared sample is fixed to the gripping part of the tensile testing apparatus, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. The point where the stress is maximum in the tensile test is considered to be the fracture point, and the elongation at fracture is calculated from the length of the sample at fracture and the length of the sample before the tensile test. The tensile strength and the elongation at fracture are multiplied to determine the fracture energy density. <4> A conductive material containing a carbon nanotube aggregate as described in any one of <1> to <3>. <5> An electrode containing an electrode active material and the conductive material described in <4>. <6> A secondary battery equipped with the electrode described in <5>. <7> A planar aggregate containing a carbon nanotube aggregate as described in any one of <1> to <3>. <8> A laminate comprising a substrate and the planar aggregate described in <7>. <9> A filter using the planar aggregate described in <7>. <10> An electromagnetic shield using the planar aggregate described in <7>. <11> An extreme ultraviolet pellicle using the planar aggregate described in <7>.

[0008] According to one embodiment of the present disclosure, a carbon nanotube aggregate capable of producing a battery with excellent cycle characteristics is provided. According to another embodiment of the present disclosure, a conductive material, an electrode, a secondary battery, and a planar aggregate comprising the carbon nanotube aggregate are provided. According to another embodiment of the present disclosure, a laminate comprising the planar aggregate is provided. According to another embodiment of the present disclosure, a filter, an electromagnetic shield, and an extreme ultraviolet pellicle using the planar aggregate are provided.

[0009] This is a scanning electron microscope image showing one aspect of CNT aggregate 1 of Example 1. This is a scanning electron microscope image showing one aspect of CNT aggregate 2 of Example 2. This is a scanning electron microscope image showing one aspect of CNT aggregate 3 of Example 3. This is a scanning electron microscope image showing one aspect of CNT aggregate 4 of Example 4. This is a scanning electron microscope image showing one aspect of CNT aggregate 5 of Comparative Example 1. This is a scanning electron microscope image showing one aspect of powdered CNT aggregate 6 of Comparative Example 2.

[0010] The carbon nanotube assemblies, conductive materials, electrodes, secondary batteries, planar assemblies, laminates, filters, electromagnetic shields, and extreme ultraviolet pellicles related to this disclosure will be described in detail below. The following descriptions may be based on typical embodiments of this disclosure, but this disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the purpose of this disclosure.

[0011] In this disclosure, numerical ranges indicated using "~" mean ranges that include the numerical values ​​before and after "~" as the lower and upper limits, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the amount of each component means the total amount of multiple substances if there are multiple substances corresponding to each component, unless otherwise specified. In this disclosure, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0012] In this disclosure, the terms "carbon nanotube," "single-walled carbon nanotube," "multi-walled carbon nanotube," "carbon nanotube aggregate," "carbon nanotube having a maximum length of 1,000 μm to 30,000 μm," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "CNT aggregate," "ULCNT," and "CNT dispersion," respectively.

[0013] [CNT Aggregate] The CNT aggregate according to the present disclosure satisfies the following conditions (1) and (2). (1) A peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in a Raman spectrum, exceeds 4.7. (2) A cumulative 50% particle size D50 in a volume-based particle size distribution is in a range of more than 0.45 μm and less than 25 μm.

[0014] According to the CNT aggregate that satisfies conditions (1) and (2), that is, the CNT aggregate according to the present disclosure, a battery having excellent cycle characteristics can be manufactured.

[0015] <Condition (1)> In the CNT aggregate according to the present disclosure, a peak intensity ratio G1 / D1 (hereinafter also simply referred to as "peak intensity ratio G1 / D1"), which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in a Raman spectrum, exceeds 4.7.

[0016] The G band indicates the crystallinity and lattice vibration of graphene contained in the CNT aggregate, and is located at 1590 cm －１ A peak intensity G1 appears in the vicinity. The D band originates from structural disorder and defects of graphene contained in the CNT aggregate, and is located at 1350 cm －１ A peak intensity D1 appears in the vicinity. In the CNT aggregate according to the present disclosure, since the peak intensity ratio G1 / D1 exceeds 4.7, graphene has high crystallinity and tends to have few structural defects. Therefore, the CNT aggregate according to the present disclosure is excellent in electronic conductivity and excellent in stability as an electrode material. Accordingly, when the CNT aggregate according to the present disclosure is used as an electrode material, the cycle life of the battery can be prolonged and the performance of the battery can be improved. From the above viewpoint, the peak intensity ratio G1 / D1 is preferably 5.0 or more, more preferably 6.0 or more, still more preferably 7.0 or more, particularly preferably 8.0 or more, even more preferably 8.61 or more, especially preferably 10.0 or more, extremely preferably 11.0 or more, and most preferably 11.41 or more.

[0017] The upper limit of the peak intensity ratio G1 / D1 is not particularly limited, but is preferably 25.0 or less, more preferably 22.0 or less, even more preferably 20.0 or less, particularly preferably 18.0 or less, even more preferably 17.0 or less, and especially preferably 16.43 or less. When the peak intensity ratio G1 / D1 is 25.0 or less, the uniformity of the shape of the CNT aggregate is partially disrupted. When the shape of the CNT aggregate is moderately non-uniform, unnecessary aggregation of CNT aggregates can be avoided, thereby suppressing a decrease in the dispersibility of the CNT aggregate in the dispersion medium. As a result, the battery's cycle characteristics are less likely to be impaired. In another embodiment, the upper limit of the peak intensity ratio G1 / D1 is preferably 80.0 or less, and more preferably 60.0 or less, from the viewpoint of improving battery performance.

[0018] The peak intensity ratio G1 / D1 may be in the range of greater than 4.7 and less than or equal to 25.0, greater than 4.7 and less than or equal to 22.0, greater than 4.7 and less than or equal to 20.0, greater than 4.7 and less than or equal to 17.0, greater than 5.0 and less than or equal to 25.0, greater than 5.0 and less than or equal to 22.0, greater than 5.0 and less than or equal to 20.0, or greater than or equal to 5.0 and less than or equal to 17.0. Furthermore, the peak intensity ratio G1 / D1 may be in the range of 6.0 to 25.0, 6.0 to 22.0, 6.0 to 20.0, 6.0 to 17.0, 7.0 to 25.0, 7.0 to 22.0, 7.0 to 20.0, 7.0 to 17.0, 8.0 to 25.0, 8.0 to 22.0, 8.0 to 20.0, or 8.0 to 17.0. Furthermore, the peak intensity ratio G1 / D1 may be in the range of 9.0 to 25.0, 9.0 to 22.0, 9.0 to 20.0, 9.0 to 17.0, 10.0 to 25.0, 10.0 to 22.0, 10.0 to 20.0, 10.0 to 17.0, 11.0 to 25.0, 11.0 to 22.0, 11.0 to 20.0, or 11.0 to 17.0. Furthermore, the peak intensity ratio G1 / D1 may be in the range of 11.41 to 25.0, 11.41 to 22.0, 11.41 to 20.0, 11.41 to 17.0, or 11.41 to 16.43. When the peak intensity ratio G1 / D1 is within the above range, the battery's cycle characteristics can be further improved.When the peak intensity ratio G1 / D1 exceeds 4.7, the crystallinity and lattice structure of the graphene in the CNT aggregate are adjusted to an appropriate state. In addition, when the peak intensity ratio G1 / D1 is 25.0 or less, when the CNT aggregate is used as an electrode material, the CNT aggregate with appropriate graphene crystallinity and lattice structure is appropriately dispersed in the dispersion medium, improving the structural stability of the electrode. Improved structural stability of the electrode reduces volume changes and stress during the cycle, and suppresses electrode degradation due to swelling and contraction of the electrode active material due to charging and discharging. As a result, the battery's cycle characteristics are expected to be further improved.

[0019] In this disclosure, the peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum of a CNT aggregate, is determined by the following method. A Raman spectrum of the CNT aggregate is obtained using a Raman spectrometer under the following measurement conditions. The peak intensity G1 of the G band and the peak intensity D1 of the D band are read from the obtained Raman spectrum, and the peak intensity ratio G1 / D1 is determined. More specifically, the peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum of a CNT aggregate, is determined by the method described in the examples below. As the Raman spectrometer, for example, RAMAN-11 (product name), a Raman spectrometer manufactured by Nanophoton Inc., can be suitably used. However, the Raman spectrometer is not limited to this.

[0020] (Measurement conditions) Excitation laser wavelength: 532 nm Grating: 600 grooves / mm Objective lens: 20x Numerical aperture (N.A.): 0.45 Wavenumber range: 110 cm －１ ~2650cm －１

[0021] In peak analysis, peak fitting can be used to avoid the effects of peak overlap and improve resolution, allowing for more accurate calculation of peak intensity. As for the function used for fitting, the Lorentz function is preferable due to its high fitting ability. However, depending on the peak shape, the Gaussian function may be preferable due to its superior fitting ability.

[0022] In this disclosure, the peak intensity G1 of the G band in the Raman spectrum is defined as 1550 cm⁻¹. －１ ~1600cm －１ This refers to the maximum scattering intensity in the Raman shift. In this disclosure, the peak intensity D1 of the D band in the Raman spectrum is 1325 cm⁻¹. －１ ~1360cm －１ This represents the maximum scattering intensity in the Raman shift.

[0023] The peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum of a CNT aggregate, can be controlled by synthesis conditions such as the calcination temperature, gas flow rate, and gas introduction method when synthesizing the CNT aggregate. The peak intensity ratio G1 / D1 can be increased, for example, by increasing the calcination temperature when synthesizing the CNT aggregate, and decreased by decreasing the calcination temperature when synthesizing the CNT aggregate.

[0024] In the Raman spectrum of a CNT aggregate, the peak intensity D1 in the D band tends to be high when metal catalysts used in CNT synthesis remain in the CNTs. Therefore, by removing the remaining metal catalyst from the CNTs through chemical treatment (e.g., acid washing, chelating agent aqueous solution treatment, etc.), the peak intensity D1 decreases, and the peak intensity ratio G1 / D1 can be increased. The above chemical treatment of CNTs can be carried out, for example, in the step of purifying CNT aggregates in manufacturing method X, which is an example of a CNT manufacturing method described later. Furthermore, the peak intensity ratio G1 / D1 can be increased by increasing the purity of the CNTs. When the purity of the CNTs is increased by removing impurities contained in the CNTs (e.g., amorphous carbon, metal impurities, etc.), the overall crystallinity of the CNTs is improved. As a result, the peak intensity G1 in the G band increases relatively, and the peak intensity D1 in the D band decreases, thus increasing the peak intensity ratio G1 / D1.

[0025] <Condition (2)> The CNT aggregate relating to this disclosure has a cumulative 50% particle size D50 (hereinafter also simply referred to as "cumulative 50% particle size D50") in the volume-based particle size distribution that is in the range of greater than 0.45 μm and less than 25 μm.

[0026] The CNT aggregates according to this disclosure have a cumulative 50% particle size D50 within the above range, thereby appropriately controlling the particle size and dispersing with high uniformity in the dispersion. High dispersibility of the CNT aggregates in the dispersion leads to higher homogeneity of the electrode material when used as an electrode material, thus stabilizing the battery cycle life.

[0027] When the cumulative 50% particle size D50 is within the above range, the particle size of the CNT aggregates is appropriately small, and the uniformity of the particle size distribution of the CNT aggregates is high, which suppresses aggregation of CNT aggregates in the dispersion and improves dispersibility. This is thought to be because the small particle size of the CNT aggregates increases the surface area in the dispersion, strengthening the interaction with the dispersion medium, and the high uniformity of the particle size distribution of the CNT aggregates stabilizes the viscosity of the dispersion. Furthermore, when the viscosity of the dispersion of CNT aggregates is stable, the handling properties, such as processability when forming electrodes etc. using CNT aggregates and ease of handling during use, are improved. In addition, when the cumulative 50% particle size D50 is within the above range, by appropriately controlling the particle size of the CNT aggregates, a dispersion in which the CNT aggregates are dispersed with high uniformity can be obtained when preparing a dispersion using CNT aggregates. In other words, the CNT aggregates according to this disclosure have a cumulative 50% particle size D50 within the above range, allowing them to be dispersed with high uniformity in the dispersion. Therefore, when used as a conductive additive in electrodes, the conductive paths within the electrodes become stable. As a result, the battery's cycle characteristics are improved.

[0028] The cumulative 50% particle size D50 of the CNT aggregate according to this disclosure may be 0.50 μm or larger, 0.55 μm or larger, 0.60 μm or larger, 0.65 μm or larger, 0.70 μm or larger, 0.75 μm or larger, 0.80 μm or larger, 0.85 μm or larger, 0.90 μm or larger, 0.95 μm or larger, 1.0 μm or larger, greater than 1.01 μm, 1.3 μm or larger, or 1.51 μm or larger. Furthermore, the cumulative 50% particle size D50 of the CNT aggregate according to this disclosure may be 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, 13 μm or less, 12 μm or less, 11 μm or less, 10 μm or less, 9.0 μm or less, 8.0 μm or less, 7.0 μm or less, or 6.65 μm or less.

[0029] From the viewpoint of improving conductivity throughout the CNT aggregate, the cumulative 50% particle size D50 of the CNT aggregate according to this disclosure is preferably in the range of 0.70 μm to 15 μm, more preferably in the range of 0.80 μm to 15 μm, even more preferably in the range of 0.90 μm to 15 μm, and particularly preferably in the range of 1.0 μm to 15 μm. From the viewpoint of improving uniformity in the dispersion, the cumulative 50% particle size D50 of the CNT aggregate according to this disclosure is preferably in the range of 1.0 μm to 15 μm, more preferably in the range of 1.0 μm to 14 μm, even more preferably in the range of 1.0 μm to 13 μm, and particularly preferably in the range of 1.0 μm to 12 μm. The cumulative 50% particle size D50 of the CNT aggregate according to this disclosure is preferably in the range of 1.0 μm to 11 μm, more preferably in the range of 1.0 μm to 10 μm, even more preferably in the range of 1.0 μm to 9.0 μm, particularly preferably in the range of 1.0 μm to 8.0 μm, and most preferably in the range of 1.0 μm to 7.0 μm, from the viewpoint of improving the battery cycle characteristics. Furthermore, the cumulative 50% particle size D50 of the CNT aggregate is preferably in the range of 1.01 μm to 7.0 μm, more preferably in the range of greater than 1.1 μm and 7.0 μm, even more preferably in the range of 1.3 μm to 7.0 μm, and particularly preferably in the range of 1.51 μm to 6.65 μm.

[0030] In this disclosure, the cumulative 50% particle size D50 in the volume-based particle size distribution of a CNT aggregate is measured by the following method. A CNT dispersion is prepared by mixing a CNT aggregate with 700 kDa of carboxymethylcellulose sodium and water, so that the concentration of the CNT aggregate is 0.20 mass% and the concentration of the carboxymethylcellulose sodium is 0.30 mass%. The prepared CNT dispersion is thoroughly stirred and then diluted with water. The resulting diluted solution is used as a sample, and the volume-based particle size distribution of the CNT aggregate is measured using a laser diffraction particle size distribution analyzer. The particle refractive index of the CNTs is assumed to be 1.920-0.522i, and the refractive index of the solvent is assumed to be 1.333. During measurement, the CNT dispersion is diluted by dropping it into pure water while observing the transmittance, and the measurement is performed after confirming that the particle size distribution on the monitor is stable. As a laser diffraction particle size analyzer, for example, the LA-960 (product name), manufactured by Horiba, Ltd., can be suitably used. However, the laser diffraction particle size analyzer is not limited to this.

[0031] The CNT aggregates relating to this disclosure exhibit excellent electronic conductivity and excellent stability as electrode materials when condition (1) is met, and excellent homogeneity as electrode materials when condition (2) is met, thereby enabling the fabrication of batteries with excellent cycle characteristics.

[0032] <Condition (3)> The CNT aggregate relating to this disclosure preferably has a fracture elongation rate calculated by the calculation method described below that is in the range of 2.0% to 4.0%. By satisfying condition (3) in addition to conditions (1) and (2), the CNT aggregate relating to this disclosure makes it possible to manufacture a battery with superior cycle characteristics.

[0033] <Condition (4)> Preferably, the CNT assembly according to this disclosure has a fracture energy density (hereinafter also simply referred to as "fracture energy density") of 14.5 MPa・% or more, which is the product of the tensile strength measured by the measurement method described below and the elongation at break calculated by the calculation method described below. By satisfying condition (4) in addition to conditions (1) and (2), the CNT assembly according to this disclosure makes it possible to manufacture a battery with superior cycle characteristics.

[0034] (Method for measuring tensile strength and calculating elongation at break) A carbon nanotube dispersion is prepared by mixing a carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, so that the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%. 15 mL of the prepared carbon nanotube dispersion is poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heated and dried at 100°C to prepare a measurement sample. The prepared measurement sample is fixed to the gripping part of a tensile testing apparatus, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. The point where the stress is maximum in the tensile test is considered to be the fracture point, and the elongation at break is calculated from the length of the measurement sample at the fracture point and the length of the measurement sample before the tensile test. The fracture energy density is obtained by multiplying the tensile strength and the elongation at break. As a tensile testing apparatus, for example, the Autograph AG-IS (product name), a tensile testing apparatus manufactured by Shimadzu Corporation, can be suitably used. However, the tensile testing apparatus is not limited to this.

[0035] The elongation at break calculated in a tensile test is an important indicator for evaluating the durability and toughness of a material. When the elongation at break of the CNT aggregate according to this disclosure is 2.0% or higher, the mechanical strength as an electrode material is high, and the battery cycle life tends to be extended. Furthermore, when the elongation at break of the CNT aggregate according to this disclosure is 2.0% or higher, the length of the CNTs is sufficiently long, making it easier to manufacture batteries with excellent cycle characteristics. Specifically, the sufficient length of the CNTs increases the contact points between CNTs, allowing for smoother electron movement, which improves the conductivity of the entire CNT aggregate and improves the battery's cycle characteristics (i.e., the rate of discharge capacity maintenance).

[0036] The elongation at break of the CNT aggregate relating to this disclosure may be, for example, 2.1% or more, 2.2% or more, or 2.3% or more. The upper limit of the elongation at break of the CNT aggregate relating to this disclosure may be 3.9% or less, 3.8% or less, 3.7% or less, 3.6% or less, 3.5% or less, 3.4% or less, 3.3% or less, 3.2% or less, 3.1% or less, 3.0% or less, or 2.9% or less. The upper and lower limits can be combined in any way.

[0037] The CNT aggregates according to this disclosure are easier to process into a dispersion and easier to ensure dispersibility in the dispersion if the elongation at break is 4.0% or less. Furthermore, if the CNT aggregates according to this disclosure have an elongation at break of 3.0% or less, the flexibility and mechanical strength of the CNTs are well balanced, resulting in high uniformity in dispersion. This appropriately maintains the viscosity of the dispersion, further improving durability against volume changes and stress during the battery cycle, and consequently improving the discharge capacity retention rate, i.e., the battery's cycle characteristics.

[0038] From the viewpoint of improving processability into dispersions, the elongation at break of the CNT aggregate according to this disclosure is preferably in the range of 2.0% to 3.9%, more preferably in the range of 2.0% to 3.8%, even more preferably in the range of 2.0% to 3.7%, particularly preferably in the range of 2.0% to 3.6%, and most preferably in the range of 2.0% to 3.5%. From the viewpoint of improving the cycle characteristics of batteries, the elongation at break of the CNT aggregate according to this disclosure is preferably in the range of 2.0% to 3.4%, more preferably in the range of 2.0% to 3.3%, even more preferably in the range of 2.0% to 3.2%, and particularly preferably in the range of 2.0% to 3.1%. From the viewpoint of improving resistance during battery cycling, the elongation rate at break of the CNT aggregate according to this disclosure is preferably in the range of 2.0% to 3.0%, more preferably in the range of 2.0% to 2.9%, even more preferably in the range of 2.0% to 2.8%, particularly preferably in the range of 2.0% to 2.7%, and most preferably in the range of 2.0% to 2.4%.

[0039] The elongation at break of a CNT aggregate can be adjusted, for example, by the length and diameter of the CNT aggregate.

[0040] The product of the elongation at break and the tensile strength calculated in a tensile test is generally called the "breaking energy density (toughness)." Breaking energy density indicates the total amount of energy that a material can absorb before breaking, and is an important indicator for evaluating the durability and toughness of a material. When the breaking energy density of the CNT aggregate according to this disclosure is 14.5 MPa·% or higher, the mechanical strength as an electrode material is high, and therefore the battery cycle life tends to be extended. Furthermore, when the breaking energy density of the CNT aggregate according to this disclosure is 14.5 MPa·% or higher, the length of the CNTs is sufficiently long, making it easier to manufacture batteries with excellent cycle characteristics. Specifically, the sufficient length of the CNTs increases the contact points between CNTs, allowing for smoother electron movement, which improves the conductivity of the entire CNT aggregate and improves the battery's cycle characteristics (i.e., the rate of discharge capacity maintenance).

[0041] The fracture energy density of the CNT aggregate relating to this disclosure may be, for example, 15 MPa·% or more, 16 MPa·% or more, 17 MPa·% or more, 18 MPa·% or more, 19 MPa·% or more, 20 MPa·% or more, 21 MPa·% or more, 22 MPa·% or more, 23 MPa·% or more, 24 MPa·% or more, 25 MPa·% or more, or 27.1 MPa·% or more. The upper limit of the fracture energy density of the CNT aggregate relating to this disclosure is not particularly limited, but is usually 200 MPa·% or less, may be 180 MPa·% or less, 150 MPa·% or less, 120 MPa·% or less, 100 MPa·% or less, 90 MPa·% or less, 85 MPa·% or less, 80 MPa·% or less, 70 MPa·% or less, or 60.6 MPa·% or less. The upper and lower limits can be combined arbitrarily.

[0042] The CNT aggregates according to this disclosure are easier to process into a dispersion and easier to ensure dispersibility in the dispersion if the fracture energy density is 200 MPa·% or less. Furthermore, if the CNT aggregates according to this disclosure have a fracture energy density of 80.0 MPa·% or less, the flexibility and mechanical strength of the CNTs are well balanced, resulting in high uniformity in dispersion. This appropriately maintains the viscosity of the dispersion, further improving durability against volume changes and stress during battery cycling, and consequently improving the discharge capacity retention rate, i.e., the battery's cycle characteristics. From the above viewpoint, the fracture energy density of the CNT aggregate relating to this disclosure is preferably in the range of 14.5 MPa·% to 200 MPa·% from the viewpoint of improving the cycle characteristics of the battery, more preferably in the range of 14.5 MPa·% to 100 MPa·%, even more preferably in the range of 20 MPa·% to 100 MPa·%, particularly preferably in the range of 20 MPa·% to 80 MPa·%, especially preferably in the range of 25 MPa·% to 70 MPa·%, and most preferably in the range of 27.1 MPa·% to 60.6 MPa·%.

[0043] The fracture energy density of a CNT aggregate can be adjusted, for example, by the length and diameter of the CNT aggregate.

[0044] <Matters concerning bundle diameter and bundle diameter parameters> The CNT aggregate according to this disclosure preferably includes a bundle structure. A bundle structure refers to an aggregate in which multiple CNTs are aggregated together by van der Waals forces or the like, forming a bundle. The width of the bundle structure, that is, the size in the width direction of the fiber bundle, is the bundle diameter. It is presumed that including a bundle structure with an appropriate bundle diameter in the CNT aggregate improves the handling properties of the CNT aggregate and further improves its stability. On the other hand, if the bundle structure included in the CNT aggregate becomes too large, the size of the CNT aggregate itself becomes too large, and it becomes difficult to separate and disperse the CNTs included in the bundle structure, which may reduce the dispersibility in the dispersion medium.

[0045] The bundle structure in the CNT aggregate can be formed, for example, by controlling the catalyst particle size distribution during manufacturing by chemical vapor deposition (CVD) or by controlling the cooling rate during the cooling process.

[0046] From the viewpoint of achieving both the handling properties and dispersibility in solvents of the CNT aggregate, the individual bundle diameters contained in the CNT aggregate according to this disclosure are preferably 5 nm to 500 nm, and more preferably 10 nm to 300 nm. The content of bundle structures in the CNT aggregate according to this disclosure is preferably 10% to 100% by mass, and more preferably 20% to 90% by mass, based on the total mass of the CNT aggregate. The presence or absence of bundle structures in the CNT aggregate can be confirmed by observing the CNT aggregate with an optical microscope, a scanning electron microscope (SEM), etc. The bundle diameter can be determined by identifying the location where bundle structures exist in the CNT aggregate and measuring the length using an image of the bundle structure.

[0047] <<Area ratio of bundles with a bundle diameter of 100 nm or more>> The CNT aggregate according to this disclosure includes a bundle structure, and it is preferable that the area ratio of bundles with a bundle diameter of 100 nm or more exceeds 0.1 in the area observed by a scanning electron microscope (SEM). In the CNT aggregate according to this disclosure, when the area ratio of bundles with a bundle diameter of 100 nm or more exceeds 0.1 in the area observed by an SEM, the bundle structure of the CNTs is appropriately formed, improving the mechanical strength and conductivity as an electrode material. Specifically, a bundle diameter of 100 nm or more strengthens the bonding between CNTs, making the electron transport pathways connecting electrode active materials more robust, thereby improving the structural stability of the electrode. In addition, a large bundle diameter increases the electron conduction pathways within the electrode, promoting efficient current flow. This reduces the internal resistance of the battery and improves the charge and discharge efficiency. Therefore, in the SEM observation area, a battery with superior cycle characteristics can be obtained if the area ratio of bundles with a bundle diameter of 100 nm or more exceeds 0.1.

[0048] The area ratio of bundles with a bundle diameter of 100 nm or more is preferably in the range of 0.1 to less than 0.6, more preferably in the range of 0.1 to less than 0.55, and even more preferably in the range of 0.1 to less than 0.5. Within this range, the bundle structure of CNTs is appropriately formed, and the bonding between CNTs is strengthened, thereby improving the mechanical strength of the electrode. In addition, an appropriate bundle diameter improves the dispersibility of CNTs and ensures a uniform conductive path within the electrode. As a result, the overall conductivity of the electrode is improved, the internal resistance of the battery is reduced, and thus superior cycle characteristics are obtained.

[0049] Furthermore, from the viewpoint of increasing the elongation at break, the area ratio of bundles with a bundle diameter of 100 nm or more is more preferably in the range of 0.11 to 0.30, particularly preferably in the range of 0.12 to 0.25, even more preferably in the range of 0.13 to 0.25, and especially preferably in the range of 0.13 to 0.23. A higher elongation at break improves the flexibility and durability of the material containing the CNT aggregate.

[0050] Furthermore, it is preferable that the area ratio of bundles with a bundle diameter of 100 nm or more is in the range of greater than 0.1 and less than or equal to 0.45. In this range, the moderately small bundle diameter of the CNTs increases the surface area as an electrode material and widens the contact area with the electrode active material. This promotes ion movement and improves the charge and discharge efficiency of the battery. In addition, a moderately small bundle diameter also has the effect of increasing the flexibility of the electrode and improving its durability against volume changes during the cycle. Therefore, the cycle characteristics of the battery are further improved.

[0051] <<Cumulative 90% Bundle Diameter>> The CNT aggregate according to this disclosure includes a bundle structure, and in the area observed by a scanning electron microscope, the cumulative 90% bundle diameter (hereinafter also referred to as the "cumulative 90% bundle diameter") is preferably 500 nm or less, and more preferably in the range of greater than 80 nm and less than or equal to 500 nm. Furthermore, the cumulative 90% bundle diameter may be 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, 160 nm or less, or 150 nm or less. Furthermore, the cumulative 90% bundle diameter may be greater than 90 nm or 100 nm or more. Within the range of the cumulative 90% bundle diameter, these upper and lower limits can be arbitrarily selected. From the viewpoint of improving the battery's cycle characteristics, the cumulative 90% bundle diameter in the CNT aggregate according to this disclosure is preferably in the range of 80 nm to less than 200 nm, more preferably in the range of 80 nm to 180 nm, even more preferably in the range of greater than 90 nm to 180 nm, and particularly preferably in the range of greater than 90 nm to 150 nm. Furthermore, the cumulative 90% bundle diameter is preferably in the range of 100 nm to 150 nm, more preferably in the range of greater than 100 nm to 140 nm, and even more preferably in the range of 110 nm to 130 nm.

[0052] The bundle diameter of the CNT aggregate is measured by observation using a scanning electron microscope (SEM). Multiple SEM images are obtained by photographing the CNT aggregate at a magnification of 100,000x. The imaging method using the SEM is not particularly limited and can be carried out using known methods.

[0053] -Imaging- Images of the CNT aggregate are obtained by imaging using an SEM device (for example, Hitachi High-Technologies Corporation, S-4800) under the following conditions. From the viewpoint of reducing the variance of the analyzed bundle diameter, it is preferable to obtain five or more images. Acceleration voltage: 0.5 kV Emission current: 10 μA Magnification: 100,000x Image size: 1280 pixels × 960 pixels

[0054] - Image Selection - From the obtained images, select two or more images in which CNT bundles are frequently observed.

[0055] - Overview of Bundle Diameter Analysis using Image Analysis - Image processing and image analysis are performed on the selected image using Python. In image processing, the contour and centerline of the CNT are detected and combined with the original image. In image analysis, the bundle diameter is determined by calculating the distance from the centerline to the contour of the created image. Then, the product of the bundle diameter and the length of the centerline is calculated to determine the area occupied by the CNT in the image.

[0056] -Detection of CNT contours using image analysis- 1. Binarize the image to distinguish between CNTs and the background. 2. Create contours for the CNT portions using the edge detection function of the OpenCV library.

[0057] -Detection of CNT centerlines using image analysis- 1. Adjust parameters to distinguish between CNTs and background and perform binarization. 2. Create a skeleton for the CNT portion using the skeletonize function of the scikit-image library. 3. For each coordinate of the skeleton, count the number of skeletons in the surrounding 2 pixels and recognize coordinates with 5 or more skeletons as skeleton intersections. 4. Divide the skeleton at the intersections by converting the intersections to background pixels. The resulting skeletons are called regions. 5. Measure the length of the regions and delete the shorter regions. 6. Perform linear approximation for each region. 7. For each created line, obtain the X-axis coordinate of the region from which the approximation was made. Convert the line into a line segment based on the interval in which the obtained X-coordinate exists. Treat the line segment obtained here as the centerline of the CNT. 8. Calculate the similarity based on the center coordinates and angles for all sets of centerlines. If the distance between the center coordinates is within 10 pixels and the angle between the two line segments is less than 10 degrees, treat the pair of center lines as duplicate center lines and delete the shorter one. 9. Overlay the CNT contour and center lines onto the original image and save. The contour will be treated in red, and the center lines in blue.

[0058] -Detection of CNT bundle diameter by image analysis- 1. Load an image created by image processing and recognize CNTs, contours, background, and center lines using hue recognition. 2. Measure the length of each center line. 3. Select a random point on the center line and draw a perpendicular line from the point to the center line. 4. Detect the intersection point of the perpendicular line and the contour, and save the distance from the random point on the center line to the intersection point as the bundle diameter. 5. Calculate the occupied area by multiplying the length of the center line segment by the bundle diameter. Save the data as a histogram with the bundle diameter on the horizontal axis and the occupied area on the vertical axis.

[0059] - Obtaining Bundle Diameter Parameters - Using the calculated bundle diameter histogram data, the bundle diameter features of each sample are calculated using the following method: 1. The bundle diameters and occupied areas of multiple fields of view of the same sample are added together and normalized so that the sum is 1. Following normalization, the unit of the vertical axis is set to the occupied area ratio. 2. The sum of the occupied area ratios of bundles with a bundle diameter of 100 nm or more is calculated. 3. The cumulative occupied area ratio is calculated, and the bundle diameter at which this value first exceeds 0.9 is determined as the cumulative 90% bundle diameter.

[0060] <Viscosity of dispersion containing CNT aggregates> The viscosity of the dispersion containing CNT aggregates according to this disclosure is preferably 10 mPa·s to 1500 mPa·s, more preferably 30 mPa·s to 1300 mPa·s, even more preferably 35 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 1000 mPa·s, more preferably 100 mPa·s to 800 mPa·s, even more preferably 120 mPa·s to 710 mPa·s, and particularly preferably 210 mPa·s to 710 mPa·s. In other embodiments, the viscosity of the dispersion is preferably 10 mPa·s to 1600 mPa·s, more preferably 10 mPa·s to 1400 mPa·s, and even more preferably 100 mPa·s to 1400 mPa·s.

[0061] The viscosity of the dispersion containing the CNT aggregate according to this disclosure is the viscosity obtained by measuring the viscosity using a dispersion prepared by mixing the CNT aggregate, 700 kDa of carboxymethylcellulose sodium, and water, at a liquid temperature of 25°C, with a carbon nanotube aggregate concentration of 0.20% by mass and a carboxymethylcellulose sodium concentration of 0.30% by mass.

[0062] The viscosity of the dispersion containing the CNT aggregate according to this disclosure is measured using a cone-plate viscometer (also known as an E-type viscometer) under the following measurement conditions. For example, a Brookfield DV-II+Pro Programmable Viscometer can be suitably used as the cone-plate viscometer. However, the cone-plate viscometer is not limited to this.

[0063] (Measurement conditions) Measurement fixture: Cone plate Measurement mode: Rotation mode Shear speed: 0.6 s －１ ~384 simultaneous －１ Temperature: 25℃

[0064] From the obtained data, read the viscosity at the following shear rate: Shear rate = 12s －１

[0065] The CNT aggregates relating to this disclosure have a high affinity for the dispersion medium, which tends to result in a lower viscosity of the dispersion. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the CNT aggregates relating to this disclosure in the dispersion medium is good.

[0066] <Surface Resistivity W> The surface resistivity W of the CNT aggregate according to this disclosure is preferably 0.01 Ω / □ to 15.4 Ω / □, more preferably 0.01 Ω / □ to 12.0 Ω / □, even more preferably 0.01 Ω / □ to 10.0 Ω / □, particularly preferably 0.01 Ω / □ to 8.0 Ω / □, and most preferably 0.01 Ω / □ to 4.0 Ω / □, from the viewpoint of ensuring conductivity as a conductive additive and the stability of the dispersion. Furthermore, the surface resistivity W is preferably 0.1 Ω / □ to 4.0 Ω / □, more preferably 0.5 Ω / □ to 4.0 Ω / □, even more preferably 1.0 Ω / □ to 3.0 Ω / □, particularly preferably 1.2 Ω / □ to 2.7 Ω / □, and especially preferably 1.24 Ω / □ to 2.50 Ω / □.

[0067] In this disclosure, the surface resistivity W of a CNT aggregate is measured by the following method. A CNT dispersion is prepared by mixing a CNT aggregate with 700 kDa of sodium carboxymethylcellulose and water, so that the concentration of the CNT aggregate is 0.20 mass% and the concentration of sodium carboxymethylcellulose is 0.30 mass%. A sample is prepared by pouring 15 mL of the prepared CNT dispersion onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heating and drying it at 100°C. The surface resistivity of the prepared sample is measured at five arbitrarily selected locations on the film using a resistivity meter with a four-probe method, and the average of the five measured values ​​is taken as the surface resistivity W. As the resistivity meter, for example, a resistivity meter manufactured by Nitto Seiko Analytech Co., Ltd. (product name: Loresta GXII) can be suitably used. However, the resistivity meter is not limited to this.

[0068] <Other matters concerning CNT aggregates> The CNTs included in the CNT aggregates relating to this disclosure may be SWCNTs or MWCNTs. From the viewpoint that having a layer distribution and slightly lower uniformity contributes to satisfying conditions (1) and (2), it is preferable that the CNT aggregates relating to this disclosure include SWCNTs and MWCNTs.

[0069] The maximum length of the CNTs included in the CNT aggregate relating to this disclosure is not particularly limited.

[0070] In one embodiment, the CNT aggregate may mainly consist of CNTs with a maximum length of 500 μm or less, and may not contain CNTs in the range of 500 μm to 30,000 μm. Here, "main component" means that 90% by mass or more of the CNTs constituting the CNT aggregate are CNTs with a maximum length of 500 μm or less. The CNT aggregate according to this disclosure may also contain CNTs with a maximum length of 500 μm or less.

[0071] The CNT aggregates according to this disclosure include, for example, CNTs having a maximum length of 10 μm to 30,000 μm. The CNT aggregates according to this disclosure preferably include CNTs having a maximum length of 500 μm or more, more preferably include CNTs having a maximum length of 500 μm to 30,000 μm, and even more preferably include CNTs having a maximum length of 1,000 μm to 30,000 μm (i.e., ULCNTs).

[0072] ULCNTs are longer in length and can take the form of fibers compared to general-purpose CNTs. When the maximum length of the CNTs included in the CNT aggregate according to this disclosure is 500 μm or more, the entanglement between the CNTs becomes moderately strong, and the CNTs tend to form a network structure more easily.

[0073] By taking the form of fibers, ULCNTs have a tendency to entangle with each other. The CNT aggregate according to this disclosure contains at least one ULCNT, and from the viewpoint that the CNTs are more likely to entangle with each other and form a more stable aggregate, it is preferable that the aggregate contains multiple ULCNTs. Hereinafter, the aggregate containing ULCNTs may be abbreviated as "ULCNT aggregate".

[0074] Here, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two dimensions. The fiber may be a thread-like fiber with a circular cross-section, a ribbon-like fiber with a rectangular cross-section, hollow, or have other shapes. From the viewpoint of improving conductivity, the cross-section of the CNTs contained in the CNT aggregate according to this disclosure is preferably circular and preferably hollow.

[0075] The CNT aggregates relating to this disclosure may be aggregates of intertwined three-dimensional structures. The intertwined state of the CNTs in the CNT aggregate relating to this disclosure can be confirmed by SEM observation.

[0076] The length of the CNTs included in the CNT aggregate relating to this disclosure can be measured by focusing on one CNT and observing multiple SEM images of adjacent fields of view. Here, "CNT length" refers to the measured length in the longitudinal direction of the CNT, and the maximum value among the measured lengths is defined as the "maximum length." By observing the SEM image, if one CNT with a maximum length in the range of 1,000 μm to 30,000 μm is observed within the field of view of the SEM image, it can be confirmed that the observed CNT contains a ULCNT.

[0077] It is preferable that multiple ULCNs are present within the field of view of the SEM image. Focusing on 100 CNTs included in the field of view of the SEM image, the maximum length of each is measured, and of the observed CNTs, it is preferable that 10% or more (in numerical terms) of the CNTs have a maximum length in the range of 1000 μm to 30000 μm (i.e., ULCNs), from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULCNs, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0078] The diameter of an ULCNT can be measured by observing a SEM (Surface-Emission Microscope) or transmission electron microscope (TEM) image. Here, diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULCNT. The diameter is measured at 10 different points on a single ULCNT, and the average value is taken as the diameter of that ULCNT.

[0079] The length of the ULCNT is 1,000 μm to 30,000 μm, preferably 1,050 μm to 25,000 μm, more preferably 1,100 μm to 20,000 μm, even more preferably 1,200 μm to 18,000 μm, and particularly preferably 1,300 μm to 15,000 μm. The diameter of the ULCNT is preferably 1 nm to 100 nm, more preferably 2 nm to 80 nm, even more preferably 3 nm to 50 nm, and particularly preferably 5 nm to 30 nm.

[0080] The length / diameter ratio, or aspect ratio, of the ULCNT is preferably 1000 or more, more preferably 3000 or more, even more preferably 5000 or more, and particularly preferably 10000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single ULCNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more ULCNTs.

[0081] Furthermore, from the viewpoint of dispersibility, the specific gravity of the ULCNT aggregate is preferably in the range of 1.5 to 2.5, more preferably in the range of 1.7 to 2.4, and even more preferably in the range of 1.8 to 2.2. The specific gravity of the ULCNT aggregate can be measured by the method described in JIS Z8807:2012 "Method for measuring the density and specific gravity of solids".

[0082] The purity of carbon as CNTs in an ULCNT aggregate can be measured by thermogravimetric analysis. For example, a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the ULCNT aggregate are obtained using a thermal analyzer (Shimadzu Corporation, DTG-60). In the DTA curve, where the peak top appears around 650°C to 750°C, the largest exothermic peak is considered to be the combustion of CNTs, and other exothermic peaks are considered to be the combustion of substances other than CNTs. The purity of the CNTs is determined from the weight loss rate of the TG curve. From the viewpoint of the resulting conductivity, the purity of the ULCNT aggregate is preferably 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more.

[0083] The resulting fibrous ULCNT is preferably flexible and strong. Furthermore, the conductivity of the ULCNT itself should be 5000 ohms. －１ ・m －１ Preferably, it is 10,000 ohms or more. －１ ・m －１ The above is more preferable. The conductivity of the ULCNT itself is typically 1,000,000 ohms. －１ ・m －１ The following applies:

[0084] <Method for producing CNTs> The method for producing CNTs in this disclosure is not particularly limited. For example, the method for producing CNTs in this disclosure can be a conventionally known chemical vapor deposition (CVD) method, a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst, or other such methods.

[0085] The CNTs in this disclosure can be manufactured by referring to, for example, the methods described in Japanese Patent Publication No. 2016-102047, Japanese Patent Publication No. 2021-527611, etc.

[0086] The following describes the manufacturing method of CNTs in this disclosure with examples. However, the manufacturing method of CNTs in this disclosure is not limited to the following examples.

[0087] =Manufacturing Method X= An example of a method for manufacturing CNTs as referenced in this disclosure is the manufacturing method described in Japanese Patent Application Publication No. 2016-102047. That is, a manufacturing method (hereinafter also referred to as "Manufacturing Method X") that includes the steps of passing a gaseous reactant containing one or more carbon sources through a reactor, reacting one or more gaseous reactants in the reaction region of the reactor in the presence of a catalyst to form carbon-containing product particles, agglomerating the product particles into aggregates, and applying force to the aggregates to continuously move the aggregates out of the reaction region.

[0088] According to manufacturing method X, CNTs containing ULCNTs can be obtained in the form of easily handled fibrous aggregates or other aggregates.

[0089] In manufacturing method X, the force applied to the product particles may be a mechanical force. If the aggregate is fibrous CNT, the mechanical force applied to the product particles can be applied by a rotating spindle around which the aggregate is wound. The fibrous CNT may be collected on the spindle, or it may be accumulated elsewhere after being rotated around the spindle once or more times, as the spindle is continuously unwound.

[0090] Preferably, the spindle axis is positioned perpendicular or parallel to the flow direction of one or more gaseous reactants, but it may be positioned in other orientations. For example, a spindle with its axis positioned at a 25° angle to the flow direction of the gaseous reactants can also be suitably used to apply mechanical force to product particles.

[0091] The spindle can rotate around two axes (for example, two vertical axes). In particular, the spindle can rotate around axes perpendicular and parallel to the flow direction of the gaseous reactant. Such a spindle allows for the pulling and twisting of aggregates, which are fibrous carbon nanotubes, to control the number of twists and length.

[0092] The spindle material may be metal, ceramic, or resin. The spindle can take on different suitable shapes depending on the material properties and the intended use of the CNTs. The spindle can be used, for example, as a mold for producing carbon products by a spin-coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0093] Fibrous carbon nanotubes (CNTs) are accumulated on the spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and reaction conditions, or by applying an electric field or other field to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by the fluidity of the gas.

[0094] The spindle rotation speed is preferably 0.01 rpm (revolutions per minute; the same applies hereafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the spindle rotation speed) may be adjusted so that the material is recovered at the same rate as it is produced. The spindle rotation speed may be used to control the thickness of the accumulated fibrous CNTs. In one preferred embodiment, as the spindle rotates, the fibrous CNTs are processed in the axial direction of the spindle. In this processing, the fibrous CNTs are wound evenly along the spindle, rather than being wound at only one specific point on the spindle.

[0095] Fibrous CNTs may be recovered onto the reactor wall, for example, by a substrate placed in the reactor. The substrate may be a fixed substrate or a rotating guide used to apply a strong and equal force to the fibrous CNTs when they are recovered. A suitable substrate arrangement used in fiber technology is a substrate consisting of two guides positioned orthogonally to each other.

[0096] In manufacturing method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow can be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube located downstream of the reaction region. A vacuum may be applied to the product particles.

[0097] Other forces applied to the product particles include electrostatic forces appropriately applied by a charged plate. When using electrostatic forces, the product particles must be charged. By using a charged plate, CNTs can be generated on the plate in the form of intertwined sheets.

[0098] Furthermore, other forces applied to the generated particles may include magnetic force or photon pressure applied by a light source.

[0099] The raw material for CNTs may be injected in the form of a liquid containing a carbon source, instead of a gaseous reactant containing a carbon source. When a liquid is used as the raw material for CNTs, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0100] One or more gaseous reactants are preferably reacted at 500°C to 1600°C, and more preferably at 1000°C to 1500°C. The temperature gradient is maintained within the reactor, and the reaction region is preferably kept at a higher temperature than the product region of the reactor.

[0101] The gaseous reactant may be used in combination with one or more gases that act as diluents. The gaseous reactant may also be used in combination with gases that do not play a direct role in the reaction but play an auxiliary role. If amorphous carbon is produced as a byproduct, it is also preferable to use a gas as a diluent that can react with amorphous carbon to maintain the reaction sites on the catalyst and produce nanotubes.

[0102] Gases that can be used as diluents include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, and helium. Among these, hydrogen is particularly preferred as a diluent.

[0103] The composition of the product particles can be controlled by monitoring the aggregates and changing the reaction conditions based on the information obtained. For example, aggregates can be monitored by online Raman spectroscopy. Online Raman spectroscopy provides data indicating whether the CNTs are single-layer or multi-layer. It also provides data indicating the diameter and crystallinity of the CNTs. Aggregates can also be monitored by online conductivity measurement, gas analysis, measurement of the opacity of the reaction region, and / or measurement of the winding force.

[0104] When removing aggregates from the reactor, it is preferable to prevent air from entering the reactor. Preventing air inflow is particularly important, for example, when the diluent gas contains hydrogen, as it helps to prevent the formation of an explosive mixture of hydrogen and air in the reactor.

[0105] In manufacturing method X, it is preferable to control the reactor temperature to 200°C to 700°C when removing the aggregates from the reactor. The bundle diameter of the CNTs can be controlled by the temperature of the reaction region of the CNTs and the reactor temperature when removing the aggregates from the reactor. The higher the reactor temperature when removing the aggregates from the reactor, the larger the bundle diameter of the CNTs can be. For example, by setting the reactor temperature when removing the aggregates from the reactor to about 150°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 110 nm to 170 nm. By setting the reactor temperature when removing the aggregates from the reactor to about 500°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 200 nm to 230 nm. By setting the reactor temperature when removing the aggregates from the reactor to about 750°C, the bundle diameter, which is 90% of the cumulative CNTs, can be set to 300 nm to 400 nm. The "reactor temperature" refers to the temperature determined by measuring the gas temperature at the outlet from which the condensed material is removed from the reactor.

[0106] The product particles produced in manufacturing method X contain ULCN. Depending on the manufacturing conditions, SWCNTs and MWCNTs may also be present.

[0107] The product particles may be generated by chemical vapor deposition. When the product particles are generated by chemical vapor deposition, the carbon source, which is a gaseous reactant, reacts in the presence of a catalyst.

[0108] Suitable carbon-containing compounds as carbon sources include carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, or hydrocarbons containing two or more of these). Carbon monoxide, methane, ethylene, or acetylene are preferred as carbon-containing compounds.

[0109] The carbon source preferably contains oxygen. Ethanol is a particularly preferred carbon source. Oxygen can be introduced into the reactor by other means, for example, by using a carbon source containing a diluent gas or water.

[0110] As catalysts, transition metals are preferred, particularly chromium (Cr), molybdenum (Mo), tungsten (W), or VIII-B transition metals. Specifically, preferred catalysts include, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt) or manganese (Mn), or mixtures thereof. Metals from the lanthanide and actinide series (e.g., yttrium (Y)) can also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof are preferred, for example, a mixture of Ni and Co (mass ratio: 50 / 50), a mixture of Fe and Ni, or a mixture of Fe and Mo are more preferred. Any of these transition metals can be used alone or in combination with any of the other transition metals listed above to function as catalysts for the growth of CNTs. The catalyst is particularly preferably a mixture of two or more of the listed metals.

[0111] The catalyst is preferably formed by the decomposition of a precursor. The precursor is preferably a thermal, photocatalytic, or plasma-degradable compound of one or more of the above-mentioned metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickerocene, and cobaltocene are particularly preferred as precursors. In some embodiments, at least 0.01% by mass of the precursor is contained in the carbon source, preferably 0.2% to 30% by mass of the precursor, and more preferably 0.2% to 20% by mass of the precursor. In some embodiments, 0.23% to 2.3% by mass of the precursor may be contained in the carbon source, and 0.02% to 20% by mass of the precursor. The catalyst may also be used supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0112] The carbon source is preferably reacted in the presence of an accelerator. Suitable accelerators are one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is also a preferred accelerator. Preferably, the accelerator is contained in the carbon source at a concentration of up to 10% by mass. Preferably, the accelerator is contained in the carbon source at a concentration of 0.2% to 6% by mass. When high or low concentrations of thiophene are used as the accelerator, MWCNTs are formed.

[0113] According to manufacturing method X, fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm, can be obtained. The fibrous CNTs can take the form of threads or sheets. The length of the fibrous CNTs can be controlled, for example, by the winding capacity of the spindle used when manufacturing the fibrous CNTs.

[0114] The manufacturing method X preferably includes the steps of generating CNTs by reacting a carbon source in the reaction region of a reactor, and agglomerating the CNTs into aggregates by applying force to them. This manufacturing method makes it possible to easily produce fibrous CNTs.

[0115] The manufacturing method X preferably further includes a step of purifying the obtained CNT aggregates after the step of agglomerating CNTs into aggregates. Specifically, first, the CNT aggregates are washed with alcohol (e.g., methanol, ethanol, etc.). Next, they are washed with an alkaline solution (e.g., ammonia water). The pH of the alkaline solution is, for example, 8 to 11. Furthermore, they are washed with pure water.

[0116] The cleaning method is not particularly limited and may involve spraying a cleaning solution onto the CNT aggregates or immersing the CNT aggregates in a cleaning solution. Cleaning with alcohol removes alcohol-soluble components contained in the CNT aggregates. Cleaning with an alkaline solution hydrolyzes and removes impurities contained in the CNT aggregates. Cleaning with an acidic solution may also be performed.

[0117] It is preferable to dry the CNT aggregates after washing. The drying method is not particularly limited and can be carried out by commonly known methods.

[0118] By purifying the aggregates of carbon nanotubes (CNTs), the metal content in the CNTs can be reduced.

[0119] The manufacturing method X preferably further includes a step of passing the purified CNT aggregates through a sieve after the step of purifying the CNT aggregates. It is also preferable to recover the CNTs that have passed through the sieve.

[0120] The method of passing the material through the sieve is not particularly limited and can be carried out by commonly known methods. The mesh size of the sieve is, for example, 0.1 mm to 3.0 mm, preferably 0.5 mm to 2.0 mm, and more preferably 1.0 mm to 1.5 mm. The material of the sieve is not particularly limited and may be metal or resin. When the CNT aggregate is applied to an electrode (especially an electrode for a lithium-ion battery), it is preferable that the material does not impair the performance of the battery. The number of times the material is passed through the sieve is, for example, 1 to 3 times. Before passing the CNT aggregate through the sieve, the CNT aggregate may be crushed to an appropriate size beforehand. Crushing can be done using a crusher. Examples of crushers include roll mills, cutter mills, hammer mills, etc.

[0121] By passing the obtained CNT aggregates through a sieve and recovering the CNTs that pass through the sieve, coarse CNTs are removed, improving the stability of the CNT dispersion. In addition, while foreign matter introduced from the outside is generally removed during electrode manufacturing, passing the obtained CNT aggregates through a sieve allows for a simpler method of removing foreign matter introduced from the outside.

[0122] In other embodiments, the method may include generating CNTs containing ULCNTs in a reaction region by the above method, condensing them to form CNTs containing ULCNTs, and continuously withdrawing CNTs from near the reaction region. In yet other embodiments, the method may include generating CNTs containing ULCNTs in a reaction region, continuously electrostatically attracting CNTs containing ULCNTs from the reaction region, and recovering CNTs containing ULCNTs.

[0123] =Manufacturing Method Y= In this disclosure, as an example of a method for manufacturing CNTs, the manufacturing method described in Japanese Patent Publication No. 2021-527611 can be referenced. That is, a mixture containing a main catalyst precursor and a co-catalyst precursor is γ-Al ２ O ３A manufacturing method (hereinafter also referred to as "manufacturing method Y") includes the steps of: (1) supporting the active support on a material to produce an active support; (2) drying the active support by multi-stage drying including vacuum drying; (3) heat-treating the dried active support to produce a supported catalyst; and (4) producing CNTs in the presence of the supported catalyst.

[0124] Step (1) Step (1) involves mixing a main catalyst precursor and a co-catalyst precursor in γ-Al ２ O ３ The active support is manufactured by supporting it on a material.

[0125] The main catalyst precursor and co-catalyst precursor are γ-Al ２ O ３ To ensure uniform support, the mixture may further contain a solvent, and the main catalyst precursor and 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, with water being preferred.

[0126] γ-Al ２ O ３ Because it has high porosity and a spinel structure, the main catalyst and co-catalyst are γ-Al ２ O ３ They can be arranged irregularly. CNTs grown from an irregularly arranged main catalyst can be produced in an entangled manner.

[0127] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese, and chromium, with cobalt being preferred.

[0128] 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.

[0129] The main catalyst precursor is Co(NO ３ ) ２ Co(NO ３ ) ２ 6H ２ O, Co ２ (CO) ８ Co ２ (CO) ６ [HC=C(C(CH ３ )３ )], Co(CH ３ CO ２ ) ２ , Fe(NO ３ ) ３ , Fe(NO ３ ) ２ ·nH ２ O, Fe(CH ３ CO ２ ) ２ , Ni(NO ３ ) ２ , Ni(NO ３ ) ２ ·6H ２ O, Mn(NO ３ ) ２ , Mn(NO ３ ) ２ ·6H ２ O, Mn(CH ３ CO ２ ) ２ ·n(H ２ O) and Mn(CO) ５ Br may be one or more selected from the group consisting of, among these, Co(NO ３ ) ２ ·6H ２ O, Fe(NO ３ ) ２ ·nH ２ O, Ni(NO ３ ) ２ ·6H ２ O is preferred.

[0130] The co-catalyst improves the dispersibility of the main catalyst, and may be one or more selected from the group consisting of vanadium and molybdenum.

[0131] The co-catalyst precursor is NH ４ VO ３ , NaVO ３ , V ２ O ５ , V(C ５ H ７ O ２ ) ３ , and (NH ４ ) ６ Mo ７ O ２４ ·4H ２ O may be one or more selected from the group consisting of, NH４ V₂O₅ ３ and (NH₄ ４ )₆ ６ Mo₇ ７ O₂₄ ２４ ·4H₂ ２ O is preferably at least one selected from the group consisting of the above.

[0132] When the mixture contains two or more promoter precursors, that is, when it contains both a vanadium precursor and a molybdenum precursor, the mixture may be contained such that the molar ratio of vanadium to the sum of vanadium and molybdenum is 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and it is preferably contained such that the molar ratio is 1:0.5 to 1:0.9. When the above conditions are satisfied, the structure of CNTs can be stably maintained, and CNTs having a target pore volume can be produced.

[0133] The mixture may contain the main catalyst precursor and the promoter precursor such that the molar ratio of the main catalyst to the promoter is 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, and it is preferably contained such that the molar ratio is 1:0.1 to 1:0.25. When the above molar ratio is satisfied, the dispersibility of the main catalyst can be improved, and CNTs having a target pore volume can be produced.

[0134] The mixture may further contain an organic acid that functions to suppress precipitation of the main catalyst precursor and the promoter precursor.

[0135] The organic acid may be at least one 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.

[0136] The mixture may contain the organic acid and the promoter precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, and a molar ratio of 1:3 to 1:6 is preferred. When the above range is satisfied, there is an advantage that a transparent catalyst metal solution can be produced during catalyst production, and a catalyst with reduced fine powder generation during impregnation can be produced.

[0137] After step (1), a ripening step may be further included.

[0138] The maturation process may be carried out for 1 to 60 minutes or 10 to 50 minutes. It is preferable to carry it out for 10 to 50 minutes. When the above conditions are met, γ-Al ２ O ３ The main catalyst precursor and co-catalyst precursor can be sufficiently supported on the support. Furthermore, bubbles present within the support are removed to the maximum extent possible, allowing the main catalyst precursor and co-catalyst precursor to be sufficiently supported even in the fine pores inside the support.

[0139] Step (2) Next, the active support is dried by multi-stage drying, which includes vacuum drying.

[0140] Multi-stage drying can mean that a drying process, including vacuum drying, is performed two or more times. Specifically, multi-stage drying may include atmospheric pressure drying and vacuum drying, or it may include vacuum drying alone two or more times.

[0141] Vacuum drying may be carried out at 80°C to 300°C or 120°C to 250°C, with 120°C to 250°C being preferred. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0142] Vacuum drying may be performed at 1 mbar to 200 mbar or 30 mbar to 150 mbar, and is preferably performed at 30 mbar to 150 mbar. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, is rapidly decomposed and discharged, so that the main catalyst oxide can be formed more easily under vacuum conditions and energy consumption can be minimized.

[0143] Vacuum drying can be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, with 10 minutes to 2 hours being preferred. When the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0144] On the other hand, if multi-stage drying includes atmospheric pressure drying and vacuum drying, atmospheric pressure drying can be performed before the vacuum drying described above, and atmospheric pressure drying can remove any solvents that may be present in the active carrier.

[0145] Atmospheric pressure drying may be carried out at 80°C to 160°C or 100°C to 140°C, and is preferably carried out at 100°C to 140°C. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0146] Atmospheric pressure drying may be carried out at 900 mbar to 1,100 mbar, and preferably at 950 mbar to 1,050 mbar. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0147] Atmospheric pressure drying may be carried out for 1 to 12 hours, and preferably for 3 to 9 hours. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0148] On the other hand, if multi-stage drying includes two or more vacuum drying steps, it may include two or more vacuum drying steps performed at different temperatures, more specifically, a primary vacuum drying step performed at a first temperature and a secondary vacuum drying step performed at a second temperature higher than the first temperature.

[0149] Primary vacuum drying can remove any solvents that may be present in the active carrier.

[0150] The first temperature may be between 80°C and 160°C, and is preferably between 100°C and 140°C. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0151] Primary vacuum drying can be performed for 1 to 12 hours, preferably 3 to 9 hours. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0152] Primary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 80 mbar to 150 mbar, with 80 mbar to 150 mbar being preferred. When the above conditions are met, the solvent present in the active carrier can be sufficiently removed, and energy consumption can be minimized.

[0153] The explanation regarding secondary vacuum drying is as described in the explanation of vacuum drying above.

[0154] The second temperature may be between 175°C and 300°C, and is preferably between 180°C and 280°C. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0155] Secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, with 1 mbar to 70 mbar being more preferable. When the above conditions are met, the main catalyst precursor, i.e., the coordination bond of the main catalyst, is rapidly decomposed and discharged, so that the main catalyst oxide can be formed more easily under vacuum conditions and energy consumption can be minimized.

[0156] Secondary vacuum drying may be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, and is preferably performed for 10 minutes to 2 hours. When the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0157] Step (3) Next, the dried active support is subjected to heat treatment to produce a supported catalyst.

[0158] When heat treatment is performed, the main catalyst and co-catalyst are converted to γ-Al ２ O ３ A supported catalyst is manufactured that exists as a coating on the surface and pores of the material.

[0159] The heat treatment may be carried out at 600°C to 800°C or 620°C to 750°C, and is preferably carried out at 620°C to 750°C. When the above conditions are met, the main catalyst and co-catalyst are γ-Al２ O ３ The supported catalyst can be manufactured with a uniform coating on the surface and pores, while minimizing energy consumption.

[0160] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, and is preferably carried out for 2 to 8 hours. When the above time is met, the catalyst precursor is γ-Al ２ O ３ A supported catalyst can be manufactured that exists in a state where it is uniformly coated on the surface and pores.

[0161] Step (4) Next, CNTs are produced in the presence of a supported catalyst.

[0162] In detail, carbon nanotubes (CNTs) can be produced by contacting a supported catalyst with a carbon-based compound. Specifically, this may be done by chemical vapor phase synthesis.

[0163] To describe in detail the steps for producing CNTs, first, a supported catalyst can be introduced into a horizontal fixed-bed reactor or a fluidized-bed reactor. Next, a gaseous carbon-based compound, or a mixed gas of a gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen), is injected at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the catalyst, and CNTs can be grown by chemical vapor-phase synthesis through the decomposition of the gaseous carbon-based compound.

[0164] CNTs produced by the chemical vapor phase synthesis method described above have crystal growth directions that are nearly parallel to the tube axis, and the graphite structure exhibits high crystallinity along the length of the tube. As a result, CNTs with small unit diameters and high conductivity and strength can be produced.

[0165] The chemical vapor phase synthesis method may be carried out at 600°C to 800°C or 650°C to 750°C, and is preferably carried out at 650°C to 750°C. By satisfying the above temperature range, CNTs can be produced while minimizing the generation of amorphous carbon.

[0166] Possible heat sources for the reaction include induction heating, radiant heat, lasers, IR, microwaves, plasma, and surface plasmon heating.

[0167] Furthermore, carbon-based compounds can be used without particular restrictions, as long as they can supply carbon and exist in a gaseous state at temperatures above 300°C.

[0168] The carbon-based compound may be a carbon-based compound having six or fewer carbon atoms, and may be one or more selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene.

[0169] After growing CNTs by the reaction described above, a cooling step may be selectively performed to further align the CNTs in a more regular manner. Specifically, the cooling step can be carried out by natural cooling by removing the heat source or by using a cooler or the like.

[0170] The above-described manufacturing methods X and Y are examples, and the manufacturing methods for CNTs that may be included in a CNT aggregate are not limited to those described above.

[0171] [Carbon Nanotube Dispersion] The carbon nanotube dispersion (CNT dispersion) according to this disclosure comprises a CNT aggregate and a dispersion medium. The CNT dispersion exhibits good dispersibility of the CNT aggregate in the dispersion medium and has excellent conductivity. The CNT dispersion is preferably used for electrode formation, transparent conductive film formation, resin additives, conductive inks, coatings, antistatic agents, paints, and the like.

[0172] <CNT aggregates> The CNT aggregates contained in the CNT dispersion are the same as the CNT aggregates related to this disclosure described above, so their explanation is omitted here.

[0173] <Dispersion Medium> The dispersion medium preferably contains water, and more preferably contains water as its main component. "Containing water as its main component" means that the proportion of water in the dispersion medium is more than 50% by mass. The proportion of water in the dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and may be, for example, 100% by mass.

[0174] The water is not particularly limited, but it is preferable to use distilled water, deionized water, or pure water, for example, because it contains fewer impurities.

[0175] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of hydrophilic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0176] The CNT dispersion may further contain other components that can be used in the dispersion, in addition to the CNT aggregate and dispersion medium. Examples of other components include dispersants, defoamers, antistatic agents, and conductive additives other than the conductive additives described herein. It may also further contain trace amounts of impurities, so-called unavoidable impurities.

[0177] <Dispersant> The CNT dispersion may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the CNT aggregate. The dispersant is not particularly limited and, for example, various surfactants can be used. Polymer compounds such as resins can also be used as dispersants. A surfactant is preferred as the dispersant. The surfactant may be an ionic surfactant or a nonionic surfactant and is not particularly limited. In the CNT dispersion, the surfactant can be used alone or in a mixture of two or more types.

[0178] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid-based surfactants such as alkylbenzene sulfonates (e.g., dodecylbenzenesulfonic acid) and dodecylphenyl ether sulfonates; ether sulfate-based surfactants; phosphate-based surfactants; and carboxylic acid-based surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine-based surfactants and amine oxide-based surfactants. As for ionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic ionic surfactants) are preferred, and aromatic sulfonic acid-based surfactants such as alkylbenzene sulfonates and dodecylphenyl ether sulfonates are more preferred. Aromatic ionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration properties for CNT aggregates.

[0179] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene polypropylene glycol; and aromatic nonionic surfactants such as polyoxyalkylene octylphenyl ether, polyoxyalkylene nonylphenyl ether, polyoxyalkyldibutylphenyl ether, polyoxyalkyl styrylphenyl ether, polyoxyalkyl benzylphenyl ether, polyoxyalkylbisphenyl ether, polyoxyalkylcumylphenyl ether, and polyoxyalkylene phenyl ether. As nonionic surfactants, ionic surfactants having aromatic rings (so-called aromatic nonionic surfactants) are preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration properties for CNT aggregates.

[0180] Other dispersants that excel in dispersibility, dispersion stability, and high concentration of CNTs include: Demol (registered trademark; hereinafter the same) N, Demol RN, and Demol T (manufactured by Kao Corporation), sodium salt of β-naphthalene sulfonic acid formalin condensate; Brij S 100 (manufactured by Sigma-Aldrich), polyvinylpyrrolidone K30 (e.g., manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (e.g., manufactured by Daicel Mirise Co., Ltd.); sodium deoxycholate (e.g., manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.); and SOLSPERSE. ＴＭ W100, SOLSPERSE ＴＭ Examples include W150 (manufactured by Lubrizol Japan Co., Ltd.). CMC is particularly preferred from the viewpoint of excellent dispersion ability, dispersion stability, and high concentration of CNT aggregates.

[0181] When the CNT dispersion contains a dispersant, the amount of dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of CNT aggregate, the amount of dispersion medium, etc.

[0182] [Method for Manufacturing CNT Dispersion] The method for manufacturing a CNT dispersion is not particularly limited. A CNT dispersion can be manufactured by dispersing CNT aggregates in a dispersion medium. That is, a CNT dispersion can be manufactured by a method that includes a step of dispersing CNT aggregates in a dispersion medium (also called the "dispersion step"). The dispersion mediums that can be used in the dispersion step are as described above.

[0183] The dispersion method is not particularly limited. Examples of dispersion methods include using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Other examples of dispersion methods include using known grinding means, such as ball milling (e.g., ball mill, vibrating ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressurized kneader. The method using a jet mill is preferred, and the method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pumps a mixture in a solvent as a high-speed flow from a nozzle placed in a sealed state inside a pressure vessel. In a wet jet mill, CNT aggregates are dispersed within a pressure vessel by collisions between opposing flows, collisions with the vessel wall, turbulence and shear flow generated by high-speed flow, etc. A suitable wet jet mill is an ultra-high pressure homogenizer manufactured by Jōkō Co., Ltd. (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.). However, the wet jet mill is not limited to these. When using the above-mentioned ultra-high pressure homogenizer as the dispersion device, the dispersion processing pressure is preferably 10 MPa to 250 MPa.

[0184] The method for producing a CNT dispersion may include a step of drying the CNT aggregate (also called a "drying step") before the dispersion step described above.

[0185] If moisture adheres to the CNTs, the surface tension of the water can cause the CNTs to stick together, potentially reducing their dispersibility. Therefore, by performing a drying step of the conductive additive before the dispersion step, moisture adhering to the CNTs is removed, preventing the CNTs from sticking together due to moisture, and further improving the dispersibility of the CNTs in the dispersion medium. The drying method is not particularly limited. Examples of drying methods include heating drying, vacuum drying, and heating vacuum drying. Heating vacuum drying is preferred as the drying method. The drying temperature is not particularly limited, but is preferably, for example, 40°C to 100°C. The drying time is not particularly limited and can be set appropriately depending on the drying temperature, the degree of moisture adhering to the CNT aggregate in this disclosure, etc.

[0186] The following are examples of CNT dispersion manufacturing methods, but the manufacturing of CNT dispersions is not limited to those shown below.

[0187] <Manufacturing Example 1: Example of Dispersion Production> 0.040 g of the CNT aggregate according to this disclosure is weighed and placed in a three-necked flask. After adding the CNT aggregate, a large excess of deionized water, which is the dispersion medium, is poured into the flask (for example, 20 mL), and the mixture is stirred at room temperature (25°C, the same applies hereafter). At this time, a known dispersant (for example, carboxymethylcellulose) may be added as appropriate. Next, the conductive additive is dispersed in the dispersion medium using a known dispersion device (for example, an ultrasonic irradiation device or a wet jet mill). The obtained dispersion is further stirred with a stirrer at room temperature for a long time (for example, 1 hour to 48 hours). In this way, a CNT dispersion is obtained.

[0188] [Conductive Material] The conductive material relating to this disclosure includes the CNT aggregate relating to this disclosure. As described above, the CNT aggregate relating to this disclosure contained in the conductive material relating to this disclosure has excellent conductivity when dispersed, and is therefore suitable as a conductive additive. Because the conductive material relating to this disclosure includes the CNT aggregate relating to this disclosure, it has excellent conductivity efficiency and can effectively impart high conductivity to the object to which it is used.

[0189] The conductive material relating to this disclosure may contain known conductive additives such as graphite and Ketjenblack. Furthermore, the conductive material relating to this disclosure may contain CNTs other than the CNT aggregate relating to this disclosure.

[0190] The conductive material relating to this disclosure can be used as one of the electrode materials. An example of an electrode formed using the electrode material is an electrode provided in a secondary battery. An embodiment of an electrode and a secondary battery equipped with the electrode will be described below.

[0191] <Electrode> The electrode according to this disclosure includes an electrode active material and a conductive material according to this disclosure. Because the electrode according to this disclosure includes a conductive material according to this disclosure, it has excellent conductivity for forming conductive paths within the electrode. Therefore, the secondary battery according to this disclosure has excellent cycle characteristics.

[0192] In electrodes, CNT aggregates can function as conductive additives. The CNT aggregates included in the electrodes described below are synonymous with the CNT aggregates in this disclosure, and the preferred embodiments are also the same; therefore, a description of the CNT aggregates will be omitted below.

[0193] The electrode may consist of at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, or it may include a current collector and an electrode active material layer disposed on the current collector.

[0194] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. Examples of current collectors include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, etc. Specifically, transition metals with good carbon adsorption properties, such as copper and nickel, may be used as current collectors.

[0195] The electrode active material layer may contain electrode active material. Preferably, the electrode active material is electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer may contain positive electrode active material commonly used for positive electrode materials. Specifically, as the positive electrode active material, lithium cobalt oxide (LiCoO) ２ ), lithium nickel oxide (LiNiO ２ ) Layered compounds such as, compounds substituted with one or more transition metals; LiFe ３ O ４ Lithium iron oxides such as Li １＋ｃ１ Mn ２－ｃ１ O ４ (0≦c1≦0.33), LiMnO ３ LiMn ２ O ３ LiMnO ２ Lithium manganese oxides such as lithium copper oxide (Li ２ CuO ２ ); LiV ３ O ８ , V ２ O ５ ,Cd ２ V ２ O ７ Vanadium oxides such as LiNi; chemical formula LiNi １－ｃ２ M ｃ２ O ２ Ni-site type lithium nickel oxide represented by the chemical formula LiMn (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c² ≤ 0.66). ２－ｃ３ M ｃ３ O ２ (Here, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1.), or Li ２ Mn ３ MO ８ Lithium manganese composite oxide represented by (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. ２ O ４These are some examples.

[0196] When the electrode is a negative electrode, the electrode active material is not particularly limited, and the electrode active material layer may include negative electrode active materials commonly used for negative electrode materials. Specifically, the negative electrode active material may include graphite-based active material particles or silicon-based active material particles. As graphite-based active material particles, at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads may be used. By using artificial graphite as graphite-based active material particles, rate characteristics can be improved. As silicon-based active material particles, at least one selected from the group consisting of Si, SiOx (0 < x < 2), Si-C composite, and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements, rare earth elements, and combinations thereof) may be used. By using silicon-based active material particles, the battery capacity can be increased.

[0197] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer may include binders commonly used in electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers are substituted with Li, Na, Ca, etc.

[0198] <Secondary Battery> The secondary battery according to this disclosure comprises electrodes according to this disclosure. The secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode is an electrode according to this disclosure.

[0199] A separator separates the negative electrode from the positive electrode and provides a passage for lithium ions to move. It is generally not limited to any separator commonly used in secondary batteries. Preferably, the separator has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, a porous polymer film can be used as a separator. The porous polymer film may be, for example, a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure in which two or more of these films are laminated. Alternatively, the separator may be a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, the separator may be coated with a ceramic component or polymer substance to ensure heat resistance or mechanical strength. The separator can selectively have a single-layer or multi-layer structure.

[0200] The electrolyte is not particularly limited and can include, for example, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0201] Specifically, the electrolyte may include non-aqueous organic solvents and metal salts. Examples of non-aqueous organic solvents include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate, which are aprotic organic solvents.

[0202] Among carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high dielectric constants as high-viscosity organic solvents and readily dissociate lithium salts. It is even more preferable to use a mixture of such cyclic carbonates with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions as a non-aqueous organic solvent, as this yields an electrolyte with high electrical conductivity.

[0203] The metal salt may also be a lithium salt. Lithium salts are readily soluble in non-aqueous electrolytes. For example, the anion portion of the lithium salt may be F － , Cl － , I － NO ３ － , N (CN) ２ － BF ４ － , ClO ４ － , PF ６ － (CF ３ ) ２ PF ４ － (CF３ ) ３ PF ３ － , (CF ３ ) ４ PF ２ － , (CF ３ ) ５ PF － , (CF ３ ) ６ P － , CF ３ SO ３ － , CF ３ CF ２ SO ３ － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) ２ N － , CF ３ CF ２ (CF ３ ) ２ CO － , (CF ３ SO ２ ) ２ CH － , (SF ５ ) ３ C － , (CF ３ SO ２ ) ３ C － , CF ３ (CF ２ ) ７ SO ３ － , CF ３ CO ２ － , CH ３ CO ２ － , SCN － , and (CF ３ CF ２ SO ２ ) ２ N － can be mentioned.

[0204] In addition to non-aqueous organic solvents and metal salts, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycemic (glyme), hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride.

[0205] The secondary battery described above can constitute a battery module containing the secondary battery as a unit cell, and a battery pack containing the battery module. The battery module and battery pack can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0206] <Planar Assembly> The planar assembly relating to this disclosure includes the CNT assembly relating to this disclosure. The proportion of the CNT assembly relating to this disclosure contained in the planar assembly relating to this disclosure is usually 1% by mass or more with respect to the total mass of the planar assembly. The planar assembly relating to this disclosure may contain components other than the CNT assembly relating to this disclosure.

[0207] Examples of planar aggregates relating to this disclosure include films containing the CNT aggregate relating to this disclosure.

[0208] The planar assemblies relating to this disclosure are useful, for example, in filters, electromagnetic shields, and pellicles for extreme ultraviolet (EUV) radiation.

[0209] The method for producing the planar aggregate according to this disclosure is not particularly limited. The planar aggregate according to this disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate by dispersing the CNT aggregate according to this disclosure in water or other fluid and filtering it once or twice or more.

[0210] <Laminate> The laminate according to this disclosure comprises a substrate and a planar assembly according to this disclosure. The substrate and the planar assembly may be in direct contact, or other layers may be arranged between the substrate and the planar assembly. Alternatively, the planar assembly according to this disclosure may be arranged on the substrate, and yet another layer may be arranged on the planar assembly.

[0211] The material constituting the substrate may be resin, glass, or fiber. Examples of resins include polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin polymer (COP), triacetate (TAC), cyclic olefin copolymer (COC), poly(vinyl chloride) (PVC), polyethylene 2,6-naphthalate (PEN), polyimide (PI), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), polyacetal (POM), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polyphenylene ether (PPE), polysulfone (PSU), polyether ether ketone (PEEK), and polyamide-imide (PAI). Examples of glass include float glass (SiO2). ２ Na ２ Examples include sodium chloride (containing O, CaO, MgO, etc.), 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.

[0212] The planar aggregate preferably contains a binder in addition to the CNT aggregate according to this disclosure. The binder is preferably a polymer and preferably contains at least one selected from the group consisting of polymers containing constituent units derived from vinylidene chloride (e.g., polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer, etc.), polyimide, polysiloxane, and epoxy resin.

[0213] The following examples will provide a more detailed explanation of the CNT aggregates, etc., related to this disclosure. This disclosure is not limited to the following examples, unless it exceeds the spirit of the disclosure.

[0214] <Example 1> 1. Production of CNT Assembly 1 CNT assembly 1 was produced by a floating catalyst method (CVD method) in which the self-assembly of CNT bundles directly interacts with the gas phase. A cylindrical reactor with an inner diameter of 85 mm was used as the CNT reactor. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as an accelerator were introduced into a continuous flow of carrier gas in a once-through reactor temperature-controlled to 150°C. Hydrogen gas was used as the carrier gas. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor decomposes. The region in which the metal catalyst precursor decomposes is referred to as the first temperature zone.

[0215] Next, methane, the carbon source, was released into the carrier gas stream. The metal catalyst and carbon source were supplied to a second temperature zone, located downstream of the first temperature zone and controlled to 1400°C. The total gas supply flow rate of the carrier gas and source gas was set to 34.0 NL / min (NL is normal liter; the same applies hereafter). The flow rate ratio of methane / thiophene gas was set to range A in Table 1. The second temperature zone was maintained at a temperature sufficient to generate CNT aggregates.

[0216]

[0217] In the second temperature zone, a reaction field was created within the temperature-controlled flow reactor, forming catalytic nuclei and rapidly growing CNTs, thereby generating CNT aggregates. The aggregates were continuously discharged through the outlet of the flow reactor, which was temperature-controlled at 150°C, and collected as sheet-like CNT assemblies.

[0218] The obtained sheet-like CNT aggregate was washed with methanol and then immersed in a pH 10 diluted aqueous ammonia solution for 10 minutes. After immersion, the sheet-like CNT aggregate was washed with pure water for 10 minutes and then dried to obtain sheet-like CNT aggregate 1. The obtained sheet-like CNT aggregate 1 was crushed into a powder and then passed through a sieve with a mesh size of 1.0 mm twice. The CNT aggregate that passed through the sieve was collected and became CNT aggregate 1.

[0219] 2. Preparation of CNT dispersion 1 The following materials were mixed and treated for 1 hour in an Ace homogenizer manufactured by Nippon Seiki Co., Ltd. to predisperse the CNT aggregate 1 and obtain predispersion 1.

[0220] (Dispersion composition) - CNT aggregate 1 obtained above...1.1g - CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (700kDa, manufactured by MP Biomedicals)...1.65g - Pure water...547.25g

[0221] The pre-dispersion 1 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill, under the following dispersion conditions, to obtain a CNT dispersion 1 with a CNT aggregate 1 concentration of 0.20% by mass.

[0222] (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of cycles: 8 Method: Circulation method

[0223] <Evaluation of CNT dispersion 1: Viscosity> The viscosity of CNT dispersion 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, a cone-plate viscometer (DV-II+Pro PROGRAMMABLE VISCOMETER manufactured by Brookfield) was used, and the measurement was performed under the following conditions.

[0224] (Measurement conditions) Measurement fixture: Cone plate Measurement mode: Rotation mode Shear speed: 0.6 s －１ ~384 simultaneous －１ Temperature: 25℃

[0225] From the obtained data, the shear rate was 12s. －１The viscosity was measured. As a result, the viscosity of CNT dispersion 1 was 705.2 mPa·s.

[0226] 3. Evaluation <Raman Spectrum> The Raman spectrum of CNT aggregate 1 was measured, and the peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band, was determined. The Raman spectrum of CNT aggregate 1 was measured using CNT aggregate 1 as the measurement sample and a Raman spectrometer (product name: RAMAN-11) manufactured by Nanophoton Inc. under the following measurement conditions.

[0227] (Measurement conditions) Excitation laser wavelength: 532 nm Grating: 600 grooves / mm Objective lens: 20x Numerical aperture (N.A.): 0.45 Wavenumber range: 110 cm －１ ~2650cm －１

[0228] The CNT aggregate 1 was fixed to the sample stage, and Raman spectra were measured at 10 locations. In the obtained Raman spectra, at 1550 cm⁻¹ －１ ~1600cm －１ The peak detected in the Raman shift region was identified as a peak originating from the G band, at 1325 cm. －１ ~1360cm －１ Peaks detected in the Raman shift region were identified as peaks originating from the D band. Furthermore, peak fitting was performed using the Lorentz function for each band-derived peak, and the intensity of the fitted peaks was calculated. The peak intensity of the G band was defined as G1, and the peak intensity of the D band as D1, and the peak intensity ratio G1 / D1 was determined. The result showed that the peak intensity ratio G1 / D1 was 11.41.

[0229] (Measurement conditions) Measurement temperature: 77 K (Kelvin) Adsorbate: Nitrogen Saturated vapor pressure: Measured Adsorbate cross-sectional area: 0.162 nm ２ Waiting time after reaching adsorption equilibrium: 500 seconds

[0230] <Bundle Diameter Features> Images were taken of CNT aggregate 1 using a scanning electron microscope (SEM), and six images in which CNT bundles were frequently observed were selected (one of which is shown in Figure 1). Image processing and image analysis were performed on the selected images using Python. In image processing, the contours and midlines of the CNTs were detected and combined with the original image. In image analysis, the bundle diameter was determined by calculating the distance from the midline to the contour of the created image. Then, the product of the bundle diameter and the length of the midline was calculated to determine the area occupied by the CNTs in the image. A histogram of bundle diameter and occupied area was then created.

[0231] Using the calculated bundle diameter histogram data, the bundle diameter features of each sample were calculated using the following method: 1. The bundle diameters and occupied areas of multiple fields of view of the same sample were added together and normalized so that the sum equaled 1. Following normalization, the unit of the vertical axis was set to the occupied area ratio. 2. The total occupied area ratio of bundles with a bundle diameter of 100 nm or more was calculated. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.23, and the cumulative 90% bundle diameter was 130 nm.

[0232] <Measurement of Cumulative 50% Particle Size D50 in Volume-Based Particle Size Distribution> The CNT dispersion 1 was thoroughly stirred and then diluted with pure water. The resulting diluted solution was used as a sample, and the volume-based particle size distribution of the CNT aggregate 1 was measured using a laser diffraction particle size distribution analyzer (product name: LA-960) manufactured by Horiba, Ltd. The particle refractive index of the CNTs was set to 1.920-0.522i, and the refractive index of the solvent was set to 1.333. During measurement, the CNT dispersion 1 was diluted by dropping it into pure water while observing the transmittance, and the measurement was performed after confirming that the particle size distribution on the monitor was stable. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 6.65 μm.

[0233] <Tensile Test> CNT dispersion 1 was poured onto a slide-type silicon plate (product name: #08-1044, inner dimensions: 22 mm x 75 mm x 3 mm) manufactured by Dosaka E-M Co., Ltd., and dried by heating at 100°C. The resulting dried material, measuring 22 mm x 75 mm x 3 mm, was used as the measurement sample. The measurement sample was fixed to the gripping part of a tensile testing apparatus (product name: Autograph AG-IS) manufactured by Shimadzu Corporation, and a tensile test was performed at a tensile speed of 1 mm / min to measure the tensile strength. The point at which the stress was maximum in the tensile test was considered as the fracture point, and the elongation at fracture was calculated from the length of the measurement sample at the fracture point and the length of the measurement sample before the tensile test. As a result, the tensile strength was 11.3 MPa, the elongation at fracture was 2.4%, and the fracture energy density, which is the product of the tensile strength and the elongation at fracture, was 27.1 MPa・%.

[0234] <Surface Resistivity W of Tensile Test Sample> The surface resistivity of the tensile test sample was measured using a resistivity meter (product name: Loresta GXII) manufactured by Nitto Seiko Analytech Co., Ltd., by the four-probe method. Measurements were taken at five arbitrarily selected locations on the film, and the average of the five measured values ​​was taken as the surface resistivity W. As a result, the surface resistivity W was 1.24 Ω / □.

[0235] <Example 2> 1. Production of CNT aggregate 2 CNT aggregate 2 was produced in the same manner as CNT aggregate 1, except that the aggregates of CNTs generated in the second temperature zone were continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 150°C and collected as sheet-like CNT aggregates, and the time for washing the sheet-like CNT aggregates with pure water was set to 1 hour.

[0236] 2. Preparation of CNT dispersion 2 Using the obtained CNT aggregate 2, a pre-dispersion 2 was obtained in the same manner as in Example 1.

[0237] The pre-dispersion 2 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill, under the following dispersion conditions, to obtain a CNT dispersion 2 with a CNT aggregate concentration of 0.20% by mass.

[0238] (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of cycles: 8 Method: Circulation method

[0239] <Evaluation of CNT dispersion 2: Viscosity> The viscosity of CNT dispersion 2 was measured using the same method as in Example 1. As a result, the viscosity was 127.4 mPa·s.

[0240] 3. Evaluation <Raman Spectrum> The Raman spectrum was measured in the same manner as in Example 1, except that CNT aggregate 2 was used. As a result, the peak intensity ratio G / D was 8.61.

[0241] <Bundle Diameter Features> For CNT aggregate 2, imaging was performed using SEM, and five images in which CNT bundles were frequently observed were selected from the obtained images (one of which is shown in Figure 2). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.14, and the cumulative 90% bundle diameter was 120 nm.

[0242] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The volume-based particle size distribution of CNT aggregate 2 was measured in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 1.01 μm.

[0243] <Tensile Test> A tensile test was performed in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the tensile strength was 10.4 MPa, the elongation at break was 2.0%, and the energy density at break was 20.7 MPa·%.

[0244] <Surface resistivity W of the tensile test sample> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 2 was used. As a result, the surface resistivity W was 1.33 Ω / □.

[0245] <Example 3> 1. Manufacturing of CNT aggregate 3 CNT aggregate 3 was manufactured 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 34.2 NL / min, and the aggregates of CNTs generated in the second temperature zone were continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 150°C and collected as a sheet-like CNT aggregate.

[0246] 2. Preparation of CNT dispersion 3 Using the obtained CNT aggregate 3, pre-dispersion and main dispersion were carried out in the same manner as in Example 1 to obtain CNT dispersion 3.

[0247] <Evaluation of CNT dispersion 3: Viscosity> The viscosity of CNT dispersion 3 was measured using the same method as in Example 1. As a result, the viscosity of CNT dispersion 3 was 578.1 mPa·s.

[0248] 3. Evaluation <Raman Spectrum> The Raman spectrum was measured in the same manner as in Example 1, except that CNT aggregate 3 was used. As a result, the peak intensity ratio G / D was 14.67.

[0249] <Bundle Diameter Features> For CNT aggregate 3, imaging was performed using SEM, and six images in which CNT bundles were frequently observed were selected from the obtained images (one of which is shown in Figure 3). The bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.13, and the cumulative 90% bundle diameter was 110 nm.

[0250] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The volume-based particle size distribution of the CNT aggregate 3 was measured in the same manner as in Example 1, except that the CNT dispersion 3 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 1.51 μm.

[0251] <Tensile Test> A tensile test was performed in the same manner as in Example 1, except that CNT dispersion 3 was used. As a result, the tensile strength was 18.1 MPa, the elongation at break was 2.4%, and the energy density at break was 43.4 MPa·%.

[0252] <Surface resistivity W of the tensile test sample> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 3 was used. As a result, the surface resistivity W was 1.89 Ω / □.

[0253] <Example 4> 1. Manufacturing of CNT assembly 4 CNT assembly 4 was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 33.9 NL / min, and the flow rate ratio of methane / thiophene gas was set to range C in Table 1.

[0254] 2. Preparation of CNT dispersion 4 A pre-dispersion 4 was obtained using the obtained CNT aggregate 4 in the same manner as in Example 1.

[0255] The pre-dispersion 4 was subjected to the final dispersion using a high-pressure homogenizer (model number: NAGS100) manufactured by Jōkō Co., Ltd. as a wet jet mill, under the following dispersion conditions, to obtain a CNT dispersion 4 with a CNT aggregate concentration of 0.20% by mass.

[0256] (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of cycles: 8 Method: Circulation method

[0257] <Evaluation of CNT dispersion 4: Viscosity> The viscosity of CNT dispersion 4 was measured using the same method as in Example 1. As a result, the viscosity of CNT dispersion 3 was 218.5 mPa·s.

[0258] 3. Evaluation <Raman Spectrum> The Raman spectrum was measured in the same manner as in Example 1, except that CNT aggregate 4 was used. As a result, the peak intensity ratio G / D was 16.43.

[0259] <Bundle Diameter Features> For the CNT aggregate 4, imaging was performed using an SEM, and six images in which CNT bundles were frequently observed were selected from the obtained images (one of which is shown in Figure 4). The bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.14, and the cumulative 90% bundle diameter was 110 nm.

[0260] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The volume-based particle size distribution of the CNT aggregate 4 was measured in the same manner as in Example 1, except that the CNT dispersion 4 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 2.31 μm.

[0261] <Tensile Test> A tensile test was performed in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the tensile strength was 26.2 MPa, the elongation at break was 2.3%, and the energy density at break was 60.6 MPa·%.

[0262] <Surface resistivity W of the tensile test sample> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 4 was used. As a result, the surface resistivity W was 2.50 Ω / □.

[0263] <Comparative Example 1> 1. Manufacturing of CNT Assembly 5 CNT assembly 5 was manufactured in the same manner as CNT assembly 1, except that the total gas supply flow rate of the carrier gas and raw material gas was set to 41.9 NL / min, and the aggregates of CNTs generated in the second temperature zone were continuously discharged through the outlet of a flow-through reactor with a temperature controlled to 500°C and collected as a sheet-like CNT assembly.

[0264] 2. Preparation of CNT dispersion 5 A pre-dispersion 5 was obtained using the obtained CNT aggregate 5 in the same manner as in Example 1.

[0265] The pre-dispersion 5 was dispersed in the same manner as in Example 2 to obtain the CNT dispersion 5.

[0266] <Evaluation of CNT dispersion 5: Viscosity> The viscosity of CNT dispersion 5 was measured using the same method as in Example 1. As a result, the viscosity of CNT dispersion 5 was 34.6 mPa·s.

[0267] 3. Evaluation <Raman Spectrum> The Raman spectrum was measured in the same manner as in Example 1, except that CNT aggregate 5 was used. As a result, the peak intensity ratio G / D was 4.69.

[0268] <Bundle Diameter Features> For the CNT aggregate 5, imaging was performed using an SEM, and six images in which CNT bundles were frequently observed were selected from the obtained images (one of which is shown in Figure 5). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.41, and the cumulative 90% bundle diameter was 200 nm.

[0269] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The volume-based particle size distribution of the CNT aggregate 5 was measured in the same manner as in Example 1, except that the CNT dispersion 5 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 0.44 μm.

[0270] <Tensile Test> A tensile test was performed in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the tensile strength was 3.5 MPa, the elongation at break was 4.1%, and the energy density at break was 14.4 MPa·%.

[0271] <Surface resistivity W of the tensile test sample> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 5 was used. As a result, the surface resistivity W was 4.20 Ω / □.

[0272] <Comparative Example 2> 1. Preparation of Powdered CNT Assembly 6 As the powdered CNT assembly 6, carbon nanotubes manufactured by C-nano Co., Ltd. (catalog number: FT9100) were prepared.

[0273] 2. Preparation of CNT dispersion 6: Using the prepared powdered CNT aggregate 6, a CNT dispersion 6 was obtained in the same manner as in Example 1.

[0274] <Evaluation of CNT dispersion 6: Viscosity> The viscosity of CNT dispersion 6 was measured using the same method as in Example 1. As a result, the viscosity of CNT dispersion 6 was 5.7 mPa·s.

[0275] 3. Evaluation <Raman Spectrum> The Raman spectrum was measured in the same manner as in Example 1, except that powdered CNT aggregate 6 was used. As a result, the peak intensity ratio G / D was 0.87.

[0276] <Bundle diameter features> For the powder CNT aggregate 6, imaging was performed using an SEM, and three images in which CNT bundles were clearly observed were selected from the obtained images (one of which is shown in Figure 6). Except for this, the bundle diameter features were calculated in the same manner as in Example 1. As a result, the area ratio of bundles with a bundle diameter of 100 nm or more was 0.08, and the cumulative 90% bundle diameter was 80 nm.

[0277] <Measurement of cumulative 50% particle size D50 in volume-based particle size distribution> The volume-based particle size distribution of the powder CNT aggregate 6 was measured in the same manner as in Example 1, except that the CNT dispersion 6 was used. As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution was 0.35 μm.

[0278] <Tensile Test> A tensile test was performed in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the tensile strength was 2.3 MPa, the elongation at break was 1.9%, and the energy density at break was 4.4 MPa·%.

[0279] <Surface resistivity W of the tensile test sample> The surface resistivity was measured in the same manner as in Example 1, except that CNT dispersion 6 was used. As a result, the surface resistivity W was 15.49 Ω / □.

[0280] Next, we fabricated a lithium-ion secondary battery.

[0281] 1. Fabrication of positive electrode for lithium secondary battery: Positive electrode active material (LiNi ０．８ Co ０．１ Mn ０．１ O ２ A positive electrode mixture was prepared by mixing the positive electrode active material, conductive material (acetylene black), and binder (PVdF) in a composition of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and then kneading with N-methyl-2-pyrrolidone. The obtained positive electrode mixture was applied to a 15 μm thick Al foil to be used as a current collector, vacuum-dried at 80°C for 1 hour, and then roll-pressed to obtain a positive electrode for a lithium secondary battery. The positive electrode area was 1.65 cm². ２ The estimated amount is 16 mg / cm³. ２ The density is 3.0 g / cm³. ３ I adjusted it so that it would be as follows.

[0282] 2. Preparation of a Negative Electrode for Lithium Secondary Batteries A negative electrode for lithium secondary batteries was prepared by mixing artificial graphite MAG-E and carbon-coated SiO in a 9:1 (mass ratio) ratio as the negative electrode active material, using CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a binder, and adding the above CNT dispersion as a conductive additive, so that the composition was negative electrode active material:binder:conductive additive = 94.9:5.0:0.1 (weight ratio), and kneading to prepare a paste-like negative electrode mixture. Ion-exchanged water was used as the solvent during the preparation of the negative electrode mixture. The obtained negative electrode mixture was coated onto a 20 μm thick Cu foil using a single-sided continuous coating machine, dried at 120°C, and then roll-pressed to obtain a negative electrode for lithium secondary batteries. The negative electrode area was 1.77 cm². ２ The estimated amount is 9.3 mg / cm³. ２ The density is 1.4 g / cm³. ３ I adjusted it so that it would be as follows.

[0283] 3. Fabrication of a Lithium Secondary Battery The positive electrode for the lithium secondary battery was placed on the lower cover of a part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator, which consists of a 16 μm heat-resistant porous layer laminated on a polyethylene porous film, was placed on top of it. 300 μL of electrolyte was injected into this. As the electrolyte, a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was added, and 1 volume% of vinylene carbonate was added to it, and LiPF ６ A solution of 1.3 mol / L was used. Next, the negative electrode for the lithium secondary battery was placed on top of the laminated film separator, the top cover was placed on top via a gasket, and the lithium secondary battery of coin-type full cell R2032 was fabricated by crimping with a crimping machine. These operations were performed in a glove box under an argon atmosphere.

[0284] 4. Cycle Test Using the manufactured lithium-ion battery, a cycle test was conducted for 200 cycles under the conditions shown below, and the discharge capacity retention rate after 200 cycles was calculated using the following formula. Note that a higher discharge capacity retention rate after 200 cycles indicates better lifespan characteristics. Discharge capacity retention rate after 200 cycles (%) = Discharge capacity at 200th cycle / Discharge capacity at 1st cycle × 100

[0285] <Cycle Test Conditions> Test temperature: 25°C Charging conditions: Constant current constant voltage charging Maximum voltage during charging: 4.2V Charging time: 5 hours Charging current: 0.3CA Rest time after discharge: 10 minutes Discharge conditions: Constant current discharge Minimum voltage during discharge: 2.5V Discharge current: 0.3CA Rest time after charging: 10 minutes In this test, one cycle is defined as the process of charging, resting the discharge, discharging, and resting the charge in sequence.

[0286] The evaluation results for Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 2.

[0287]

[0288] As shown in Table 2, the CNT assemblies of the examples satisfy conditions (1) and (2), and were found to have a high discharge capacity retention rate and excellent cycle characteristics.

Claims

1. A carbon nanotube aggregate that satisfies the following conditions (1) and (2): (1) The peak intensity ratio G1 / D1, which is the ratio of the peak intensity G1 of the G band to the peak intensity D1 of the D band in the Raman spectrum, is greater than 4.

7. (2) The cumulative 50% particle size D50 in the volume-based particle size distribution is in the range of greater than 0.45 μm and less than 25 μm.

2. The carbon nanotube aggregate according to claim 1 that satisfies the following condition (3). (3) The elongation at break calculated from the tensile strength measured by the following measurement method is in the range of 2.0% to 4.0%. (Method for calculating elongation at break) A carbon nanotube dispersion is prepared by mixing the carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, so that the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of the carboxymethylcellulose sodium is 0.30 mass%. 15 mL of the prepared carbon nanotube dispersion is poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heated and dried at 100°C to prepare a measurement sample. The prepared measurement sample is fixed to the gripping part of a tensile testing device, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. In a tensile test, the point where the stress is maximum is considered the fracture point, and the elongation at fracture is calculated from the length of the sample at the fracture point and the length of the sample before the tensile test.

3. The carbon nanotube aggregate according to claim 1 that satisfies the following condition (4). (4) The fracture energy density, which is the product of the tensile strength and the elongation at break measured by the following measurement method, is 14.5 MPa・% or more. (Method for measuring tensile strength and method for calculating elongation at break) A carbon nanotube dispersion is prepared by mixing a carbon nanotube aggregate, 700 kDa of carboxymethylcellulose sodium, and water, so that the concentration of the carbon nanotube aggregate is 0.20 mass% and the concentration of carboxymethylcellulose sodium is 0.30 mass%. 15 mL of the prepared carbon nanotube dispersion is poured onto a slide glass type silicon plate with inner dimensions of 22 mm × 75 mm × 3 mm and heated and dried at 100°C to prepare a measurement sample. The prepared measurement sample is fixed to the gripping part of a tensile testing device, and a tensile test is performed at a tensile speed of 1 mm / min to measure the tensile strength. In a tensile test, the point where the stress is maximum is considered the fracture point. The elongation at fracture is calculated from the length of the sample at the fracture point and the length of the sample before the tensile test. The fracture energy density is determined by multiplying the tensile strength by the elongation at fracture.

4. A conductive material comprising a carbon nanotube aggregate according to any one of claims 1 to 3.

5. An electrode comprising an electrode active material and the conductive material described in claim 4.

6. A secondary battery comprising the electrodes described in claim 5.

7. A planar aggregate comprising the carbon nanotube aggregate described in any one of claims 1 to 3.

8. A laminate comprising a substrate and the planar assembly described in claim 7.

9. A filter using the planar assembly described in claim 7.

10. An electromagnetic shield using the planar assembly described in claim 7.

11. A pellicle for extreme ultraviolet radiation using the planar aggregate described in claim 7.

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