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

Abstract

To provide a carbon nanotube aggregate excellent in conductivity when used as a carbon nanotube dispersion, and the application thereof.　The present invention provides a carbon nanotube aggregate, a carbon nanotube dispersion, a conductive material, an electrode, a secondary battery, a planar aggregate, a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet rays that satisfy conditions (1), (2), and (3). (1) At least one of Fe atoms and Co atoms is contained, and the total content of Fe atoms and Co atoms is 2000-100,000 mass ppm with respect to the total mass of the carbon nanotube aggregate. (2) At least one of Na atoms and K atoms is contained, and the total content of Na atoms and K atoms is 50-1000 mass ppm with respect to the total mass of the carbon nanotube aggregate. (3) The ratio of the volume resistivity under 20 kN pressurization and the volume resistivity under 1 kN pressurization is 0.21 or more.

Description

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

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

[0002] Carbon nanotubes are substances with a cylindrical structure formed by rolling up graphene sheets in which carbon atoms are arranged in a hexagonal honeycomb pattern. Carbon nanotubes are basically broadly classified into single-walled carbon nanotubes formed from a single layer of graphene sheets and multi-walled carbon nanotubes formed from multiple layers of graphene sheets. Carbon nanotubes have good mechanical and electronic properties and are expected to be used in a variety of applications. In recent years, various attempts have been proposed to further improve the properties of carbon nanotubes.

[0003] For example, Patent Document 1 describes carbon nanotubes containing 1,000 ppm to 30,000 ppm of cobalt, particles containing metal atoms with a specific mass magnetic susceptibility, and a G / D ratio of 0.7 to 1.5 in a Raman spectrum, a dispersion, and uses thereof. Patent Document 2 describes a conductive material for secondary batteries containing carbon nanotubes having a diameter of 20 nm to 150 nm, an entangled spherical secondary structure in which carbon nanotube units are intertwined, a true density (TD) to bulk density (BD) ratio (TD / BD) of 30 to 120, and a metal content of 50 ppm or less.

[0004] JP 2023-089806 A JP 2018-530854 A

[0005] A problem to be solved by one embodiment of the present disclosure is to provide a carbon nanotube aggregate that has excellent conductivity when made into a carbon nanotube dispersion.A problem to be solved by another embodiment of the present disclosure is to provide a carbon nanotube dispersion that contains the above carbon nanotube aggregate and has excellent conductivity.A problem to be solved by another embodiment of the present disclosure is to provide a conductive material, an electrode, and a secondary battery that contain the above carbon nanotube aggregate.A problem to be solved by another embodiment of the present disclosure is to provide a planar aggregate that contains the above carbon nanotube aggregate, the carbon nanotube aggregate having a maximum length of 1000 μm to 30000 μm.A problem to be solved by another embodiment of the present disclosure is to provide a filter, an electromagnetic wave shield, and an extreme ultraviolet pellicle that use the above planar aggregate.

[0006] <1> An aggregate of carbon nanotubes satisfying the following conditions (1), (2), and (3): (1) containing at least one of Fe atoms and Co atoms, wherein the total content of Fe atoms and Co atoms is 2000 ppm by mass to 100000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes; (2) containing at least one of Na atoms and K atoms, wherein the total content of Na atoms and K atoms is 50 ppm by mass to 1000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes; (3) a ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN is 0.21 or less; <2> The aggregate of carbon nanotubes according to <1>, comprising a bundle structure; <3> a pore volume of 0.60 cm ３ / g ~ 3.20 cm ３ / g. <4> A carbon nanotube dispersion liquid containing the carbon nanotube aggregate according to any one of <1> to <3> and a dispersion medium. <5> A conductive material containing the carbon nanotube aggregate according to any one of <1> to <3>. <6> An electrode containing an electrode active material and the conductive material according to <5>. <7> A secondary battery comprising the electrode according to <6>. <8> A planar aggregate of carbon nanotubes according to any one of <1> to <3>, wherein the carbon nanotube aggregate contains carbon nanotubes having a maximum length of 1000 μm to 30000 μm. <9> A filter using the planar aggregate according to <8>. <10> An electromagnetic wave shield using the planar aggregate according to <8>. <11> A pellicle for extreme ultraviolet radiation using the planar aggregate according to <8>. <12> A composition comprising an aggregate of carbon nanotubes and at least one selected from the group consisting of a dispersion medium, a resin, a ceramic, and concrete, which satisfies the following conditions (1) and (2): (1) Contains at least one of Fe atoms and Co atoms, wherein the total content of Fe atoms and Co atoms is 2500 ppm by mass to 60000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes. (2) Contains at least one of Na atoms and K atoms, wherein the total content of Na atoms and K atoms is 50 ppm by mass to 700 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes. <13> A composition comprising an aggregate of carbon nanotubes and at least one selected from the group consisting of a dispersion medium, a resin, a ceramic, and concrete, which satisfies the following conditions (1) and (2): (1) The aggregate of carbon nanotubes contains at least one of Fe atoms and Co atoms, and the total content of Fe atoms and Co atoms is 2500 ppm by mass to 60000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes. (2) The ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN is 0.21 or more.

[0007] According to one embodiment of the present disclosure, it is possible to provide a carbon nanotube aggregate that has excellent conductivity when made into a carbon nanotube dispersion. According to another embodiment of the present disclosure, it is possible to provide a carbon nanotube dispersion that contains the carbon nanotube aggregate and has excellent conductivity. According to another embodiment of the present disclosure, it is possible to provide a conductive material, an electrode, and a secondary battery that contain the carbon nanotube aggregate.

[0008] 1 is a scanning electron microscope photograph showing one embodiment of a specific CNT aggregate.

[0009] Hereinafter, the carbon nanotube aggregate, the carbon nanotube dispersion, the conductive material, the electrode, and the secondary battery according to the present disclosure will be described in detail. The following description may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0010] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when multiple substances corresponding to each component are present, the amount of each component means the total amount of multiple substances unless otherwise specified. In this specification, the term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0011] In the present disclosure, the terms "carbon nanotubes," "single-walled carbon nanotubes," "multi-walled carbon nanotubes," "multi-walled carbon nanotubes having a maximum length of 1000 μm to 30000 μm," "carbon nanotube aggregate," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "ULMWCNT," "CNT aggregate," and "CNT dispersion," respectively.

[0012] [Carbon nanotube aggregate] One embodiment of the present disclosure is a carbon nanotube aggregate that satisfies the following conditions (1), (2), and (3). (1) Contains at least one of Fe atoms and Co atoms, and the total content of Fe atoms and Co atoms with respect to the total mass of the aggregate is 2000 mass ppm to 100000 mass ppm. (2) Contains at least one of Na atoms and K atoms, and the total content of Na atoms and K atoms with respect to the total mass of the aggregate is 50 mass ppm to 1000 mass ppm. (3) The ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN is 0.21 or more. Hereinafter, the carbon nanotube aggregate of this embodiment will also be referred to as a "specific CNT aggregate".

[0013] The specific CNT aggregate has excellent electrical conductivity when made into a carbon nanotube dispersion. That is, a carbon nanotube dispersion (hereinafter also referred to as "specific CNT dispersion") containing a specific CNT aggregate and a dispersion medium that satisfy the above conditions (1), (2), and (3) has excellent electrical conductivity.

[0014] The specific CNT dispersion is another embodiment of the present disclosure, and details regarding the specific CNT dispersion other than the specific CNT aggregate will be described later.

[0015] On the other hand, Patent Document 1 specifies the content of Co atoms from the viewpoint of obtaining a carbon nanotube dispersion liquid having excellent conductivity, but does not focus on controlling the total content of N atoms and K atoms, or on setting the ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN as predetermined conditions. Patent Document 2 specifies the ratio (TD / BD) of true density (TD) to bulk density (BD) from the viewpoint of obtaining a carbon nanotube dispersion liquid having excellent conductivity, but does not focus on setting the total content of Fe atoms and Co atoms, the total content of N atoms and K atoms, or further the ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN as predetermined conditions.

[0016] The specific CNT aggregate will be described in detail below. However, the speculations described in the following description are not intended to limit the interpretation of the specific CNT aggregate, but are described as an example.

[0017] <Condition (1)> The specific CNT aggregate contains at least one of Fe atoms and Co atoms, and the total content of Fe atoms and Co atoms is 2000 ppm by mass to 100,000 ppm by mass relative to the total mass of the specific CNT aggregate. The Fe atoms and Co atoms contained in the specific CNT aggregate are thought to be derived from the metal catalyst used during CNT production. When CNTs are produced in the presence of a catalyst containing metal atoms such as Fe and Co, there is a concern that catalyst-derived Fe atoms, Co atoms, etc. will be contained in the CNT and conductivity will decrease. Therefore, in the past, after CNT production, the CNTs have been washed with acid to remove metal atoms such as Fe atoms and Co atoms. However, according to studies by the present inventors, it has been found that by having the total content of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate be 2000 ppm by mass to 100,000 ppm by mass, the conductivity of the CNT aggregate is maintained while the dispersibility in the dispersion medium is further improved. The total content of Fe atoms and Co atoms is 2,000 to 100,000 ppm by mass, preferably 2,500 to 80,000 ppm by mass, and more preferably 3,000 to 60,000 ppm by mass.

[0018] Fe atoms and Co atoms are located close to each other in the periodic table of atoms, and are thought to have similar mechanisms of action. By having the total content of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate be in the range of 2,000 ppm by mass to 100,000 ppm by mass, the contact points between the CNTs contained in the specific CNT aggregate are maintained within an appropriate range, and therefore, conductive paths are easily connected, and good conductivity is thought to be obtained in the resulting specific dispersion.

[0019] As a catalyst containing Fe or Co atoms for use in CNT production, a metal catalyst such as iron (Fe) or cobalt (Co) may be used alone as a main catalyst, or the main catalyst may be used in the form of a main catalyst-co-catalyst composite catalyst together with a co-catalyst such as molybdenum (Mo), vanadium (V), or chromium (Cr). Specific examples of the composite catalyst include FeCo, CoMo, CoV, FeCoMo, FeMoV, FeV, and FeCoMoV, and mixtures of any one or more of these may also be used. The co-catalyst may be used in an amount of 0.01 mol to 1 mol, more specifically 0.05 mol to 0.5 mol, per 1 mol of the main catalyst.

[0020] The respective contents (ppm by mass) of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate can be measured by, for example, the following method. The specific CNT aggregate is completely dissolved in an acid such as hydrochloric acid or nitric acid. In order to completely dissolve the specific CNT aggregate in acid, pretreatment such as dry ashing, wet ashing, or melting treatment may be performed. The contents of Fe atoms and Co atoms can be measured by performing inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like on the solution in which the specific CNT aggregate is completely dissolved in acid. It is preferable to carry out ICP-MS since it allows for more sensitive measurement.

[0021] When the content of each of Fe atoms and Co atoms is less than 10 ppm, it becomes technically difficult to detect peaks derived from the element by ICP-MS or ICP-AES, and it may be difficult to accurately calculate the content. Therefore, a content of less than 10 ppm may be treated as 0.

[0022] The CNT may contain 0.01% by mass to 50% by mass of Fe atoms or Co atoms derived from the iron catalyst used during production. The CNT may also contain Fe atoms or Co atoms, for example, adsorbed on the surface of the CNT or incorporated into the fibrous CNT formed during production. That is, in the present disclosure, the Fe atoms and Co atoms contained in the specific CNT aggregate may each contain Fe atoms and Co atoms derived from the catalyst used in the production of the MWCNT. In the specific CNT aggregate, taking into account the content of the Fe atoms and Co atoms derived from the catalyst contained in the CNT, it is preferable to adjust the total content of Fe atoms and Co atoms relative to the total mass of the aggregate to the desired range of 4,000 ppm by mass to 60,000 ppm by mass. It goes without saying that when the total content of Fe atoms or Co atoms derived from the catalyst relative to the total mass of the aggregate is the target content, there is no need to take any special measures to adjust the content of Fe atoms.

[0023] When the total content of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate exceeds 60,000 ppm by mass, the total content of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate can be adjusted to 60,000 ppm by mass or less by using a known method, for example, by washing the aggregate with water, acid, or an aqueous acid solution (for example, a 35% by mass aqueous solution of hydrochloric acid) to wash and remove some of the Fe atoms. If the total content of Fe atoms and Co atoms relative to the total mass of the specific CNT aggregate is less than 2,000 ppm by mass, the aggregate can be immersed in an approximately 5% by mass aqueous iron nitrate solution or an approximately 40% by mass aqueous iron chloride solution as a source of Fe atoms to adsorb Fe atoms onto the surfaces of the fibrous ULMWCNT, thereby increasing the content of Fe atoms relative to the total mass of the aggregate, and the total content of Fe atoms and Co atoms can be adjusted to 2,000 ppm by mass or more. Furthermore, by immersing the aggregate in an approximately 5 mass% aqueous solution of cobalt nitrate or an approximately 40 mass% aqueous solution of cobalt chloride as a Co atom supply source, and causing Co atoms to be adsorbed onto the surface of the fibrous ULMWCNT, the content of Co atoms relative to the total mass of the aggregate can be increased, and the total content of Fe atoms and Co atoms can be adjusted to 2000 mass ppm or more.

[0024] <Condition (2)> The specific CNT aggregate contains at least one of Na atoms and K atoms, and the total content of Na atoms and K atoms relative to the total mass of the specific CNT aggregate is 50 ppm by mass to 1000 ppm by mass. The total content of Na atoms and K atoms relative to the total mass of the specific CNT aggregate is preferably 60 ppm by mass to 900 ppm by mass, and more preferably 70 ppm by mass to 700 ppm by mass. The Na atoms and K atoms contained in the specific CNT aggregate are thought to be derived from the catalyst raw material used during CNT production. The Na atoms and K atoms are preferably derived from atoms contained as impurities in the catalyst raw material, such as ferrocene. The dispersant used in preparing the CNT dispersion may contain Na atoms and K atoms as counter ions. According to the studies of the present inventors, it is believed that Na atoms and K atoms originating from the catalyst raw material, and being contained in a state of being adsorbed on the surface of the CNT during CNT production or being incorporated into the interior of the fibrous CNT formed during production, is effective for improving the conductivity of a carbon nanotube dispersion liquid. This is believed to be because the Na ions and K ions contained in the dispersant have unstable adsorption to CNT in the dispersion liquid.

[0025] Although it is unclear how the conductivity of the specific CNT dispersion is improved when the total content of Na atoms and K atoms relative to the total mass of the specific CNT aggregate is 50 ppm by mass to 1000 ppm by mass, the inventors believe as follows: After the reaction during CNT production, the surfaces of the catalyst-derived Fe atoms and Co atoms are partially covered with oxide, and the inventors speculate that the presence of at least one selected from Na atoms and K atoms during CNT production causes the formation of a composite oxide. The formation of the composite oxide increases the affinity of the specific CNT aggregate for water, enabling it to be more stably dispersed in the dispersion, and as a result, the obtained specific CNT dispersion is more likely to form conductive paths and achieve good conductivity.

[0026] As the composite oxide, NaFeO ３ , Na ２ FeO ４ , NaCoO ３ , Na ２ CoO４ , KFeO ３ , K. ２ FeO ４ , KCoO ３ , K. ２ CoO ４ It is presumed that the above-mentioned effects are achieved because the above-mentioned composite oxide is formed in minute amounts on the surfaces of Fe atoms, Co atoms, etc., which are catalyst residues.

[0027] In a specific CNT aggregate, if the total content of Fe atoms and Co atoms is too high, the formation of a conductive path tends to be inhibited, and if the total content of Fe atoms and Co atoms is too low, CNT aggregation tends to occur, and the dispersibility of the CNT aggregate in solvents such as water tends to decrease, making it difficult to achieve the effect of improving the conductivity of the dispersion. In addition, if the total content of Na atoms and K atoms is too high, the ionic strength on the surface becomes too strong, suggesting the possibility that the formation of a conductive path may become difficult due to some reason such as electrostatic repulsion between CNTs, and if the total content of Na atoms and K atoms is too low, it may be difficult to achieve the effect of improving the dispersibility of the CNT aggregate in solvents such as water, making it difficult to achieve the effect of improving the conductivity of the dispersion.

[0028] The respective contents of Na atoms and K atoms contained in the specific CNT aggregate can be measured by the same method as the method for measuring the Fe atom content described above.

[0029] The total content of Na atoms and K atoms contained in the specific CNT aggregate can be adjusted by controlling the content of Na atoms and K atoms contained as impurities in the catalyst raw material, such as ferrocene. For example, when ferrocene using sodium cyclopentadienyl and iron chloride is used as the catalyst starting material, the content of Na atoms contained as impurities may be high. By using a sodium compound and a potassium compound as starting materials for the catalyst raw material in this way, the respective contents of Na atoms and K atoms contained in the obtained CNT can be increased to a predetermined content. On the other hand, if CNTs having a total content of Na atoms and K atoms higher than the predetermined range are obtained, the total content can be adjusted to a predetermined value by appropriately performing acid washing treatment as described above to remove some of the Na atoms and K atoms.

[0030] <Condition (3)> The specific CNT aggregate has a ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN (hereinafter also simply referred to as "resistivity ratio") of 0.21 or less.

[0031] Because the specific CNT aggregate has a resistivity ratio of 0.21 or more, it does not tend to aggregate very much when in a powder state and has good dispersibility in the dispersion medium, allowing it to be widely and finely dispersed in the dispersion. Therefore, it is presumed that the conductive paths formed between the CNTs in the dispersion tend to be of an appropriate length, resulting in a dispersion with excellent conductivity. Furthermore, there is no particular limit to the upper limit of the resistivity ratio in the specific CNT aggregate, but it can be set to 0.35 or less, since the contact between the CNTs becomes moderately strong and conductive paths are likely to be stably formed.

[0032] In particular, in one embodiment, the resistivity ratio of the specific CNT aggregate is preferably 0.21 or more and 0.24 or less. When the resistivity ratio is 0.21 or more and 0.24 or less, the specific CNT aggregate does not have a very high agglomeration tendency in a powder state and dispersibility in a dispersion medium is easily ensured, so it is presumed that communication between the CNTs finely dispersed in the dispersion can be ensured and the conductivity of the dispersion is improved. Furthermore, in another embodiment, the resistivity ratio of the specific CNT aggregate is preferably 0.25 or more and 0.29 or less. When the resistivity ratio is 0.25 or more and 0.29 or less, it is presumed that agglomeration tendency in a powder state is not too high and the conductivity of the specific CNT dispersion can be more stably ensured.

[0033] In the present disclosure, the volume resistivity of a CNT aggregate is measured by a four-probe method at 25°C using a resistivity meter. A Loresta device can be used as the resistivity meter. Specifically, using a Loresta device (product names: powder resistivity measurement system MCP-PD51, low resistivity meter Loresta-GP, low resistance probe for powder MCP-PD511 (constant current application type four-probe method), all manufactured by Nitto Seiko Analytech Co., Ltd.), a measurement sample is introduced into a resistivity measurement probe unit, and a pressure of 1 kN or 20 kN is applied using an attached hydraulic pump until the target load is reached, at which point the volume resistivity (Ω cm) is measured.

[0034] A powder of a CNT aggregate is used as a sample for measuring volume resistivity. When the CNT aggregate is in a form other than powder (for example, fiber or sheet), the CNT aggregate may be pulverized to form a powder. The pulverization process is not particularly limited, and any pulverization process that can crush the CNT aggregate into small pieces may be used. As the pulverization process, a process using a freeze-pulverization method may be used.

[0035] In the present disclosure, the resistivity ratio is calculated by dividing the measured volume resistivity under a pressure of 20 kN by the measured volume resistivity under a pressure of 1 kN, and rounding off to two decimal places.

[0036] The resistivity ratio of the specific CNT aggregate can be adjusted by a conventional method. Examples of methods for adjusting the resistivity ratio of the specific CNT aggregate include controlling the content of impurities contained in the CNT, controlling structural defects in the CNT, controlling the length of the CNT, and controlling the specific surface area of ​​the CNT.

[0037] Regarding impurities contained in CNTs, it is thought that when the load pressure is low, the impurities are sandwiched between CNTs, significantly blocking the conductive path and resulting in high resistivity. On the other hand, as the load pressure increases, the number of contact points between CNTs increases, reducing the effect of the impurities on the increase in resistance and lowering the resistivity. Therefore, for example, the resistivity ratio can be controlled by controlling the content of Fe atoms and / or Co atoms derived from the catalyst, which are important impurities. The amount of structural defects in CNTs can be measured by the G / D intensity ratio in Raman spectra. A high G / D intensity ratio tends to result in fewer structural defects and therefore lower resistivity. The G / D intensity ratio can be controlled by selecting the conditions of the CNT manufacturing method described below.

[0038] Longer CNTs tend to have lower resistivity. Taking this into consideration, one method of controlling resistivity is to incorporate ULMWCNTs. ULMWCNTs can be obtained, for example, by controlling the manufacturing method of CNTs.

[0039] The resistivity ratio of a specific CNT aggregate can also be controlled by the specific surface area of ​​the CNT. A small specific surface area makes it difficult to secure contact points between CNTs, but it is presumed that the effect of increasing contact points due to load and pressure is significant. On the other hand, a large specific surface area makes it easier to secure contact points between CNTs, but it is presumed that the effect of increasing contact points due to load and pressure is small. The specific surface area of ​​the CNT can be controlled by adjusting the conditions in the CNT manufacturing method described below. For example, the mixing ratio of CNTs with a large specific surface area and CNTs with a small G / D intensity ratio may be controlled, and the two may be mixed uniformly.

[0040] <Bundle structure> From the viewpoint of improving handleability, the specific CNT aggregate 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 to form a bundle, i.e., a bundle-like aggregate. It is presumed that the specific CNT aggregate includes a bundle structure of an appropriate size, which improves the handleability of the CNT aggregate and further improves its stability. However, on the other hand, if the bundle structure included in the specific 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 result in a decrease in dispersibility in a dispersion medium.

[0041] For this reason, from the viewpoint of achieving both the handleability of the CNT aggregate and its dispersibility in a solvent, the width of each bundle structure contained in the specific CNT aggregate, i.e., the size in the width direction of the fiber bundle, is preferably 5 nm to 500 nm, and more preferably 10 nm to 300 nm. The content of bundle structures in the specific CNT aggregate is preferably 10 mass % to 100 mass %, and more preferably 20 mass % to 90 mass %, with respect to the total mass of the specific CNT aggregate. The presence or absence of bundle structures in the specific CNT aggregate can be confirmed by observing the specific CNT aggregate with an optical microscope, a scanning electron microscope (SEM), or the like. The width of the bundle structure can be determined by identifying the location where the bundle structure exists in the specific CNT aggregate and measuring the length using a photographed image of the bundle structure.

[0042] The bundle structure in the specific CNT aggregate can be formed, for example, in production by chemical vapor deposition (CVD) by controlling the catalyst particle size distribution and by controlling the cooling rate in the cooling process.

[0043] <Pore Volume> The specific CNT aggregate of the present disclosure has a pore volume of 0.60 cm ３ / g ~ 3.20 cm ３ / g.

[0044] The specific CNT aggregate has a pore volume of 0.60 cm ３ / g ~ 3.20 cm ３ / g, friction between the specific CNT aggregates falls within a suitable range, and when the specific CNT aggregates are dispersed, it is presumed that conductive paths are easily formed stably, improving the conductivity of the dispersion.

[0045] In contrast, the pore volume is 0.60 cm ３ / g, the CNT aggregate has less unevenness on its surface, which reduces friction between the CNT aggregates and makes it difficult to maintain a stable contact state, which is presumably why the conductive path becomes unstable.

[0046] The pore volume is 3.20 cm ３ It is presumed that CNT aggregates with a particle size greater than 1 / g will have increased friction between the CNT aggregates, resulting in insufficient dispersion in the dispersion liquid and being disadvantageous in forming conductive paths.

[0047] Furthermore, the pore volume is 3.20 cm ３ If it is greater than / g, the amount of cavities in the CNT aggregate increases, which may reduce the physical strength of the CNT aggregate. This is not preferable because a reduction in the physical strength of the CNT aggregate may make it unable to withstand a process in which shear force is applied to the aggregate, such as a process of dispersing the CNT aggregate (for example, the pores may be partially blocked, or the CNT aggregate may be partially destroyed). Furthermore, if the pore volume is too large, the amount of cavities in the CNT aggregate may increase, which may make the conductive paths in the CNT aggregate too long and increase resistance, which is not preferable.

[0048] In the present disclosure, the pore volume of a CNT aggregate is the volume of pores (cm) that a CNT aggregate has per unit mass (g). ３ The form of the CNT aggregate to be measured for pore volume is not limited, and may be in any form such as powder, fiber, or sheet.

[0049] In the present disclosure, the pore volume of the CNT aggregate is measured using a constant volume method. A specific surface area / pore size distribution measuring device can be used as the measuring device.

[0050] Pore ​​volume of CNT aggregate (cm ３ / g) is specifically measured by the following procedure. First, a CNT aggregate to be measured is subjected to vacuum degassing treatment at 300°C for 3 hours to prepare a measurement sample. The nitrogen adsorption / desorption isotherm is measured for the prepared measurement sample using a constant volume method. The BJH method is used for analysis to calculate the pore volume. Measurement device: specific surface area / pore distribution measurement device (product name "BEL SORP-miniII", manufactured by Microtrac-Bell) Measurement temperature: 77K Adsorbate: nitrogen Saturated vapor pressure: measured Adsorbate cross-sectional area: 0.162nm ２ Waiting time after reaching adsorption equilibrium: 500 seconds

[0051] <Other Matters Related to Specific CNT Aggregate> In the present disclosure, the CNT contained in the specific CNT aggregate may be either SWCNT or MWCNT, but it is preferable that the specific CNT aggregate contains MWCNT from the viewpoint that it has a wall number distribution and is slightly less uniform, making it easier to improve dispersibility.

[0052] In general, SWCNTs have a lower volume resistivity than MWCNTs, and the lower the volume resistivity, the smaller the change in resistivity due to applied pressure. The number of walls of a CNT can be controlled by selecting the manufacturing method for the CNT.

[0053] The longer the CNT, the lower the volume resistivity tends to be. The length of the CNT can be controlled by selecting the method for producing the CNT.

[0054] In one embodiment, the specific CNT aggregate may be an aggregate containing MWCNTs having a maximum length of 500 μm or less as a main component, and not containing MWCNTs having a maximum length of more than 500 μm and 30,000 μm or less. Here, "main component" means that 90 mass% or more of the CNTs constituting the specific CNT aggregate are MWCNTs having a maximum length of 500 μm or less. The specific CNT aggregate may contain SWCNTs having a maximum length of 500 μm or less.

[0055] In one embodiment, the specific CNT aggregate preferably includes MWCNTs having a maximum length of 10 μm to 30,000 μm. In one aspect, the MWCNTs preferably include ULMWCNTs.

[0056] ULMWCNT is a MWCNT with a maximum length of 1,000 μm to 30,000 μm, which is longer than general-purpose MWCNT and can take the form of a fiber.

[0057] By taking on a fibrous shape, ULMWCNTs have the property of easily entangling with each other. MWCN contains at least one ULMWCNT, and from the viewpoint that the MWCNTs are likely to entangle with each other and form a more stable aggregate, it is preferable that the MWCN is an aggregate containing a plurality of ULMWCNTs. Hereinafter, an aggregate containing ULMWCNT may be abbreviated as "ULMWCNT aggregate."

[0058] Here, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two. The fibers may be thread-like fibers with a circular cross section, ribbon-like fibers with a rectangular cross section, hollow, or have other shapes. From the viewpoint of enhancing electrical conductivity, the cross section of ULMWCNT is preferably circular, and hollow.

[0059] The MWCNT aggregate may be an aggregate having a three-dimensional structure in which the MWCNTs are entangled with one another. FIG. 1 is a scanning electron microscope (SEM) photograph showing one embodiment of the MWCNT aggregate according to the present disclosure. The SEM photograph shown in FIG. 1 shows that a plurality of fibrous ULMWCNTs are entangled to form an aggregate. In this way, the entangled state of the ULMWCNTs according to the present disclosure can be confirmed by SEM observation.

[0060] The length of ULMWCNT can be measured by focusing on a single ULMWCNT and observing multiple SEM photographs taken at adjacent viewing angles. Here, "ULMWCNT length" refers to the measured length of the ULMWCNT in the longitudinal direction, and the maximum value of the measured lengths is referred to as the "maximum length." When observing an SEM photograph, if a single MWCNT with a maximum length in the range of 1,000 μm to 30,000 μm is observed within the viewing angle of the SEM photograph, it can be confirmed that the observed MWCNT includes ULWMCNT.

[0061] It is preferable that a plurality of ULMWCNTs are present within the viewing angle of the SEM photograph. Focusing on 100 MWCNTs within the viewing angle of the SEM photograph, the maximum length of each is measured, and from the viewpoint of further improving the stability of the MWCNT aggregate due to entanglement between ULMWCNTs, it is preferable that 10% or more of the observed MWCNTs (i.e., ULMWCNTs) have a maximum length in the range of 1,000 μm to 30,000 μm, calculated as the number of MWCNTs, be present, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0062] The diameter of a ULMWCNT can be measured by observing an SEM photograph or a transmission electron microscope (TEM) photograph. Here, the diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULMWCNT. The diameter is measured at 10 different locations on a single ULMWCNT, and the average value is taken as the diameter of that ULMWCNT.

[0063] The length of the ULMWCNT is in the range of 1,000 μm to 30,000 μm, preferably in the range of 1,050 μm to 25,000 μm, more preferably in the range of 1,100 μm to 20,000 μm, even more preferably in the range of 1,200 μm to 18,000 μm, and particularly preferably in the range of 1,300 μm to 15,000 μm. The diameter of the ULMWCNT is preferably 1 nm to 100 nm, more preferably in the range of 2 nm to 80 nm, even more preferably in the range of 3 nm to 50 nm, and particularly preferably in the range of 5 nm to 30 nm.

[0064] The length / diameter ratio of the ULMWCNT, or the so-called aspect ratio, is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 10,000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single ULMWCNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more ULMWCNTs.

[0065] Furthermore, from the viewpoint of dispersibility, the specific gravity of the ULMWCNT 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 ULMWCNT aggregate can be measured by the method described in JIS Z8807:2012 "Method for measuring density and specific gravity of solids."

[0066] The purity of the ULMWCNT aggregate as MWCNT can be measured by thermogravimetric analysis. For example, a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the ULMWCNT aggregate are obtained using a thermal analyzer (Shimadzu Corporation, DTG-60). The largest exothermic peak in the DTA curve, which has a peak top near 650°C to 750°C, is considered to be the combustion of MWCNT, and any other exothermic peaks are considered to be the combustion of substances other than MWCNT. The purity of the MWCNT is determined from the weight loss rate of the TG curve. From the viewpoint of the resulting conductivity, the purity of the ULMWCNT 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.

[0067] ULMWCNT may contain 0.01% by mass to 50% by mass of Fe atoms derived from the iron catalyst used during production. ULMWCNT may contain Fe atoms, for example, in a state where the Fe atoms are adsorbed on the surface of the ULMWCNT or in a state where the Fe atoms are incorporated into the fibrous ULMWCNT formed during production.

[0068] The resulting fibrous ULMWCNT is preferably flexible and strong. The electrical conductivity of the ULMWCNT itself is 5000 ohms. －１ ・m－１ It is preferable that the resistance is 10,000 ohms or more. －１ ・m －１ It is more preferable that the conductivity of the ULMWCNT itself is 1,000,000 ohms or more. －１ ・m －１ The following is the result.

[0069] <Method for Producing CNTs> The method for producing CNTs in the present disclosure is not particularly limited. For example, the method for producing MWCNTs in the present 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 the like.

[0070] The CNTs in the present disclosure can be produced by referring to the methods described in, for example, JP-A-2016-102047 and JP-T-2021-527611.

[0071] The CNT manufacturing method according to the present disclosure will be described below using examples, although the CNT manufacturing method according to the present disclosure is not limited to the following examples.

[0072] =Manufacturing Method X= An example of a CNT manufacturing method referenced in this disclosure is the manufacturing method described in JP 2016-102047 A. That is, the manufacturing method (hereinafter also referred to as "Manufacturing Method X") includes the steps of passing gaseous reactants containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in a reaction zone of the reactor in the presence of a catalyst to form product particles containing carbon, aggregating the product particles into aggregates, and applying force to the aggregates to continuously move the aggregates out of the reaction zone.

[0073] According to production method X, MWCNTs including ULMWCNTs can be obtained in the form of fibrous aggregates or other aggregate forms that are easy to handle.

[0074] In production method X, the force applied to the product particles may be a mechanical force. If the agglomerates are fibrous MWCNTs, the mechanical force applied to the product particles may be applied by a rotating spindle around which the agglomerates are wound. The fibrous CNTs may be collected on the spindle, or may be accumulated elsewhere by rotating around the spindle one or more times and then successively unwinding the spindle.

[0075] The spindle is preferably oriented with its axis perpendicular or parallel to the flow direction of the gaseous reactant(s), although other orientations are also possible, for example, a spindle with its axis oriented at a 25° angle to the flow direction of the gaseous reactants may also be suitable for applying mechanical forces to the product particles.

[0076] The spindle can rotate about two axes (e.g., two perpendicular axes). In particular, the spindle can rotate about axes perpendicular and parallel to the flow direction of the gaseous reactants. Such a spindle can pull and twist the fibrous CNT aggregates to control the twist number and length.

[0077] The spindle material may be made of metal, ceramic, or resin. The spindle can have different suitable shapes depending on the properties of the material and the intended use of the MWCNTs. The spindle can be used as a mold for producing carbon products, for example, by a spin-coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0078] Fibrous MWCNTs are deposited on a spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the conditions under which an electric or other field is applied to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by gas flow forces.

[0079] The rotational speed of the spindle is preferably 0.01 rpm (revolutions per minute; hereinafter the same) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the rotational speed of the spindle) may be adjusted so that the material is collected at a similar rate to that at which it is produced. The rotational speed of the spindle may also control the thickness of the accumulated fibrous MWCNT. In a preferred embodiment, as the spindle rotates, the fibrous MWCNT is processed in the axial direction of the spindle. In this processing, the fibrous MWCNT is evenly wrapped along the spindle, rather than being wrapped only at one specific point on the spindle.

[0080] The MWCNT fibers may be collected, for example, on the reactor wall by a substrate placed in the reactor. The substrate may be a fixed substrate or a rotating guide used to apply a strong and equal force to the MWCNT fibers as they are collected. Suitable substrate configurations for fiber technology include a substrate consisting of two guides positioned at right angles to each other.

[0081] 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 may be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube downstream of the reaction zone. A vacuum may be applied to the product particles.

[0082] Other forces that can be applied to the product particles include electrostatic forces, suitably applied by charged plates. Electrostatic forces require that the product particles be charged. The use of charged plates allows the MWCNTs to grow in the form of intertwined sheets on the charged plates.

[0083] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0084] Instead of a gaseous reactant containing a carbon source, the CNT source may be injected in the form of a liquid containing a carbon source. When a liquid is used as the CNT source, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0085] Preferably, the gaseous reactant(s) are reacted at a temperature between 500° C. and 1600° C., more preferably between 1000° C. and 1500° C. A temperature gradient is maintained within the reactor, with the reaction zone preferably being maintained at a higher temperature than the product zone of the reactor.

[0086] The gaseous reactants may be mixed with one or more gases that act as diluents. The gaseous reactants may also be mixed with gases that play a supporting but not direct role in the reaction. It is also preferred to use a diluent gas that can react with the amorphous carbon by-product, if any, to maintain active sites on the catalyst for nanotube production.

[0087] Examples of 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 gas that can be used as a diluent. The flow rate of the gas used as a diluent is preferably 2000 mL (milliliters) / min or less, and more preferably 400 mL / min to 800 mL / min.

[0088] The gas pressure of the gaseous reactants and any diluents is preferably between 0.1 bar and 50 bar, more preferably between 0.5 bar and 5 bar, and even more preferably between 1 bar and 2 bar. If there is a gas effluent from the furnace, the effluent gas can be recycled with or without cleaning.

[0089] The composition of the product particles can be controlled by monitoring the agglomerates and modifying the reaction conditions based on the information obtained. For example, the agglomerates can be monitored by online Raman spectroscopy, which provides data indicating whether the CNTs are single-walled or multi-walled. It also provides data indicating the diameter and crystallinity of the CNTs. The agglomerates can also be monitored by online conductivity measurements, gas analysis, measuring the opacity of the reaction zone, and / or measuring the winding force.

[0090] When the agglomerate is removed from the reactor, it is preferable to prevent air from entering the reactor. When the diluent gas contains hydrogen, preventing air from entering the reactor is particularly important, for example, from the viewpoint of preventing an explosive mixture of hydrogen and air from forming in the reactor.

[0091] The product particles in Production Method X contain ULMWCNT. Depending on the production conditions, SWCNT may also be contained in addition to MWCNT.

[0092] The product particles may be produced by chemical vapor deposition, where a gaseous reactant, a carbon source, is reacted in the presence of a catalyst.

[0093] Suitable carbon-containing compounds as the carbon source include carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, and hydrocarbons containing mixtures of two or more thereof). Preferred carbon-containing compounds are carbon monoxide, methane, ethylene, or acetylene.

[0094] Preferably, the carbon source contains oxygen. Ethanol is a particularly preferred carbon source. Oxygen can be introduced into the reactor by other methods, such as by using a diluent gas or a carbon source containing water.

[0095] The gaseous reactant, which is a carbon source, is preferably injected into the reactor at a rate of 0.01 mL / min to 10 mL / min, more preferably 0.08 mL / min to 0.25 mL / min.

[0096] The catalyst is preferably a transition metal, particularly a Group VIB transition metal such as chromium (Cr), molybdenum (Mo), tungsten (W), or a Group VIIIB transition metal. Specifically, the catalyst may be, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or manganese (Mn), or a mixture thereof. Metals from the lanthanide and actinide series, such as yttrium (Y), may also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof, such as a 50 / 50 mixture of Ni and Co, a mixture of Fe and Ni, or a mixture of Fe and Mo, are more preferred. Any of these transition metals, alone or in combination with any of the other transition metals listed, may serve as a catalyst for CNT growth. It is particularly preferred that the catalyst is a mixture of two or more of the metals listed.

[0097] The catalyst is preferably formed by decomposition of a precursor. The precursor is preferably a thermally, photo-, or plasma-decomposable compound of one or more of the above metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickelocene, and cobaltocene are particularly preferred precursors. Suitably, at least 0.01% by mass of the precursor is contained in the carbon source, and preferably 0.2% to 2.5% by mass of the precursor is contained in the carbon source. In one embodiment, 0.23% to 2.3% by mass of the precursor is contained in the carbon source. The catalyst may be supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0098] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters include one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is one of the preferred promoters. Suitably, up to 10% by weight of the promoter is contained in the carbon source. Preferably, 0.2% to 6% by weight of the promoter is contained in the carbon source. When a high or low concentration of thiophene is used as the promoter, MWCNTs are formed. For example, MWCNTs are successfully formed using ethanol containing 0% by weight or 1.5% to 4.0% by weight of thiophene and 0.5% to 5.0% by weight (particularly 2.3% by weight) of ferrocene, with an injection rate of 3.0 mL / hr to 12.0 mL / hr (particularly 7.5 mL / hr), a hydrogen flow rate of 400 mL / min to 800 mL / min, and a synthesis temperature of 1100°C to 1180°C.

[0099] According to production method X, it is possible to obtain fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm. The fibrous CNTs can be in the form of threads or sheets. The length of the fibrous CNTs can be controlled, for example, by the winding capacity of the spindle used to produce the fibrous CNTs.

[0100] The manufacturing method X preferably includes the steps of reacting a carbon source in a reaction zone of a reactor to produce CNTs, and aggregating the CNTs into aggregates by applying force to the CNTs. This manufacturing method makes it possible to easily produce fibrous CNTs.

[0101] Another embodiment may include producing MWCNTs containing ULMWCNTs in a reaction zone by the above method, followed by condensation to form MWCNTs containing ULMWCNTs, and continuously withdrawing the MWCNTs from near the reaction zone. Another embodiment may include producing MWCNTs containing ULMWCNTs in a reaction zone, continuously electrostatically withdrawing the MWCNTs containing ULMWCNTs from the reaction zone, and recovering the MWCNTs containing ULMWCNTs.

[0102] =Production Method Y= In the present disclosure, as an example of a method for producing CNTs, the production method described in JP-A No. 2021-527611 can be referred to. That is, a mixture containing a main catalyst precursor and a co-catalyst precursor is mixed with γ-Al ２ O ３ a production method (hereinafter also referred to as "production method Y") that includes a step (1) of supporting a carbon nanotube on a support to produce an active support, a step (2) of drying the active support by multistage drying including vacuum drying, a step (3) of subjecting the dried active support to a heat treatment to produce a supported catalyst, and a step (4) of producing CNTs in the presence of the supported catalyst.

[0103] Step (1) In step (1), a mixture containing a main catalyst precursor and a co-catalyst precursor is added to a γ-Al ２ O ３ to produce an active support.

[0104] The main catalyst precursor and the co-catalyst precursor were ２ O ３ In order to uniformly support the catalyst precursor and the co-catalyst precursor on the catalyst support, the mixture may further contain a solvent, and the main catalyst precursor and the co-catalyst precursor may be dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, and water is preferred.

[0105] γ-Al ２ O ３ has high porosity and a spinel structure, and therefore the main catalyst and co-catalyst are γ-Al. ２ O ３ The CNTs grown from the randomly arranged primary catalyst can be produced in an entangled state.

[0106] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese and chromium, with cobalt being preferred.

[0107] 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.

[0108] 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)5Br, and among these, Co(NO ３ ) ２ ・6H ２ O, Fe(NO ３ ) ２ ・nH ２ O, Ni(NO ３ ) ２ ・6H ２ O is preferred.

[0109] The promoter improves the dispersibility of the main catalyst, and may be one or more selected from the group consisting of vanadium and molybdenum.

[0110] The cocatalyst precursor is NH ４ VO ３ , NaVO ３ , V ２ O ５ , V(C ５ H ７ O ２ ) ３, and (NH ４ ) 6Mo ７ O ２４ ・4H ２ O, and NH ４ VO ３ and (NH ４ ) 6Mo ７ O ２４ ・4H ２ O is preferred.

[0111] When the mixture contains two or more promoter precursors, i.e., when it contains both a vanadium precursor and a molybdenum precursor, the molar ratio of the sum of vanadium and molybdenum to vanadium can be 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and preferably 1:0.5 to 1:0.9. When the above conditions are met, the CNT structure can be stably maintained and CNTs having the desired pore volume can be produced.

[0112] The mixture may contain the main catalyst precursor and the co-catalyst precursor such that the molar ratio of the main catalyst to the co-catalyst is 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, and preferably 1:0.1 to 1:0.25. Satisfying the above molar ratios can improve the dispersibility of the main catalyst, allowing the production of CNTs with a desired pore volume.

[0113] The mixture may further include an organic acid which serves to inhibit precipitation of the main catalyst precursor and the co-catalyst precursor.

[0114] The organic acid may be one or more selected from the group consisting of citric acid, tartaric acid, fumaric acid, malic acid, acetic acid, butyric acid, palmitic acid and oxalic acid, with citric acid being preferred.

[0115] The mixture may contain the organic acid and the co-catalyst precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, preferably 1:3 to 1:6. When the ratio satisfies the above range, it is possible to prepare a transparent catalyst metal solution during catalyst production, and it is possible to prepare a catalyst in which fine particles are suppressed during impregnation.

[0116] After step (1), a step of aging may be further included.

[0117] The aging may be carried out for 1 minute to 60 minutes or 10 minutes to 50 minutes. It is preferably carried out for 10 minutes to 50 minutes. When the above conditions are satisfied, γ-Al ２ O ３ In addition, bubbles present in the support are removed to the maximum extent possible, allowing the main catalyst precursor and the co-catalyst precursor to be sufficiently supported even in the fine pores inside the support.

[0118] Step (2) Next, the active support is dried by multi-stage drying including vacuum drying.

[0119] Multi-stage drying may mean that a drying process including vacuum drying is performed two or more times. Specifically, multi-stage drying may include atmospheric drying and vacuum drying, or may include vacuum drying two or more times.

[0120] The vacuum drying may be carried out at a temperature of 80° C. to 300° C. or 120° C. to 250° C., preferably 120° C. to 250° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0121] The vacuum drying may be performed at 1 mbar to 200 mbar or 30 mbar to 150 mbar, preferably 30 mbar to 150 mbar. When the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0122] The vacuum drying can be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, preferably 10 minutes to 2 hours. If the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0123] On the other hand, when the multi-stage drying includes atmospheric drying and vacuum drying, atmospheric drying can be performed before the above-mentioned vacuum drying, and the atmospheric drying can remove solvent that may be present in the active support.

[0124] Drying at atmospheric pressure may be carried out at 80° C. to 160° C. or 100° C. to 140° C., and is preferably carried out at 100° C. to 140° C. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0125] Drying under atmospheric pressure may be carried out at 900 mbar to 1,100 mbar, preferably 950 mbar to 1,050 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0126] Drying under atmospheric pressure may be carried out for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0127] On the other hand, when the multi-stage drying includes two or more vacuum dryings, the multi-stage drying may include two or more vacuum dryings performed at different temperatures, more specifically, a primary vacuum drying performed at a first temperature and a secondary vacuum drying performed at a second temperature higher than the first temperature.

[0128] The primary vacuum drying can remove any solvent that may be present in the active support.

[0129] The first temperature may be 80° C. to 160° C., and preferably 100° C. to 140° C. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0130] The primary vacuum drying can be performed for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0131] The primary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 80 mbar to 150 mbar, and is preferably performed at 80 mbar to 150 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0132] The secondary vacuum drying is as described above in the description of the vacuum drying.

[0133] The second temperature may be 175 to 300° C., and preferably 180 to 280° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0134] The secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, and more preferably at 1 mbar to 70 mbar. When the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0135] The secondary vacuum drying may be performed for 10 minutes to 3 hours or 10 minutes to 2 hours, preferably 10 minutes to 2 hours. If the above conditions are met, the main catalyst precursor can be easily decomposed and converted into the main catalyst oxide, and energy consumption can be minimized.

[0136] Step (3) Next, the dried active support is subjected to a heat treatment to produce a supported catalyst.

[0137] When heat treatment is performed, the main catalyst and the co-catalyst are converted into γ-Al ２ O ３ A supported catalyst is produced in which the catalyst is present in a coated state on the surface and in the pores of the catalyst.

[0138] 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 satisfied, the main catalyst and the co-catalyst are γ-Al.２ O ３ Therefore, the supported catalyst can be produced with the surface and pores of the catalyst uniformly coated, and energy consumption can be minimized.

[0139] 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. ２ O ３ A supported catalyst can be produced in which the catalyst is present in a uniform coating on the surface and in the pores of the catalyst.

[0140] Step (4) Next, CNTs are produced in the presence of a supported catalyst.

[0141] Specifically, CNTs can be produced by contacting a supported catalyst with a carbon-based compound, and specifically, by chemical vapor synthesis.

[0142] To explain the steps of producing CNTs in detail, first, a supported catalyst can be loaded into a horizontal fixed-bed reactor or a fluidized-bed reactor. Then, at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the supported catalyst, a gaseous carbon-based compound or a mixture of a gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen) is injected to grow CNTs by chemical vapor synthesis through the decomposition of the gaseous carbon-based compound.

[0143] The CNTs produced by the above-mentioned chemical vapor synthesis method have a crystal growth direction that is nearly parallel to the tube axis, and the graphite structure has high crystallinity along the tube length. As a result, CNTs with small unit diameters and high electrical conductivity and strength can be produced.

[0144] The chemical vapor synthesis method may be carried out at a temperature of 600° C. to 800° C. or 650° C. to 750° C., and is preferably carried out at a temperature of 650° C. to 750° C. If the above temperature is satisfied, CNTs can be produced while minimizing the generation of amorphous carbon.

[0145] The heat source for the reaction may be induction heating, radiant heat, laser, IR, microwave, plasma, surface plasmon heating, or the like.

[0146] Any carbonaceous compound can be used without particular limitation as long as it can supply carbon and can exist in a gaseous state at a temperature of 300° C. or higher.

[0147] The carbon-based compound may be a carbon-based compound having 6 or less carbon atoms, and may be one or more compounds selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene.

[0148] After growing CNTs through the above-described reaction, a cooling step may be optionally performed to arrange the CNTs more regularly. Specifically, the cooling step may be performed by natural cooling by removing the heat source or by using a cooler.

[0149] The above manufacturing method X and manufacturing method Y are examples, and the manufacturing methods for CNTs that can be contained in the specific CNT aggregate are not limited to the above.

[0150] [Carbon nanotube dispersion] The carbon nanotube dispersion (specific CNT dispersion) according to the present disclosure contains a specific CNT aggregate and a dispersion medium. The specific CNT dispersion has good dispersibility of the specific CNT aggregate according to the present disclosure in the dispersion medium and is excellent in conductivity. The specific CNT dispersion is preferably used for forming electrodes, forming transparent conductive films, as a resin additive, conductive ink, coating agent, antistatic agent, paint, etc.

[0151] <Specific CNT aggregate> The specific CNT aggregate contained in the specific CNT dispersion liquid is the same as the specific CNT aggregate according to the present disclosure described above, and therefore a description thereof will be omitted here.

[0152] <Dispersion medium> The dispersion medium preferably contains water, and more preferably contains water as a main component. "Containing water as a main component" means that the proportion of water in the dispersion medium is more than 50% by mass. The proportion of water in the dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, and may be, for example, 100% by mass.

[0153] The water is not particularly limited, but is preferably distilled water, ion-exchanged water, pure water, or the like, which contains fewer impurities.

[0154] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of the hydrophilic solvent include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0155] The specific CNT dispersion may further contain other components that can be used in the dispersion in addition to the specific CNT aggregate and the dispersion medium. Examples of other components include dispersants, antifoaming agents, antistatic agents, and conductive additives other than the conductive additives according to the present disclosure. The specific CNT dispersion may also contain trace amounts of impurity components, so-called inevitable impurities.

[0156] <Dispersant> The carbon nanotube dispersion liquid may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the specific CNT aggregate. The dispersant is not particularly limited, and examples thereof include various surfactants. The dispersant also includes polymer compounds such as resins. 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 specific CNT dispersion liquid, the surfactant may be used alone or in combination of two or more types.

[0157] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzene sulfonates (e.g., dodecylbenzene sulfonate) and dodecylphenyl ether sulfonate; ether sulfate surfactants; phosphate surfactants; and carboxylic acid surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. Examples of ionic surfactants include ionic surfactants having an aromatic ring (so-called aromatic ionic surfactants), and more preferably aromatic sulfonic acid surfactants such as alkylbenzene sulfonates and dodecylphenyl ether sulfonates. Aromatic ionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration of multi-walled carbon nanotubes.

[0158] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene-polypropylene glycols; and aromatic nonionic surfactants such as polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, polyoxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl cumyl phenyl ether, and polyoxyalkylene phenyl ether. As nonionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic nonionic surfactants) are preferred, polyoxyalkylene phenyl ethers are more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersibility, dispersion stability, and concentration of multi-walled carbon nanotubes.

[0159] Other dispersants that are excellent in CNT dispersibility, dispersion stabilization, and concentration enhancement include DEMOL (registered trademark: the same applies hereinafter) N, DEMOL RN, and DEMOL T (manufactured by Kao Corporation), which are sodium salts of β-naphthalenesulfonic acid formalin condensate; Brij S 100 (manufactured by Sigma-Aldrich), which is a polyoxyethylene stearyl ether; polyvinylpyrrolidone K30 (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (manufactured by, for example, Daicel Miraize Co., Ltd.); sodium deoxycholate (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); and SOLSPERSE ＴＭ W100, SOLSPERSE ＴＭ W150 (manufactured by Lubrizol Japan Co., Ltd.) etc. CMC is particularly preferred from the viewpoint of excellent dispersibility, dispersion stability and high concentration of multi-walled carbon nanotubes.

[0160] When the specific CNT dispersion liquid contains a dispersant, the amount of the dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of multi-walled carbon nanotubes, the amount of dispersion medium, and the like.

[0161] [Method for producing specific CNT dispersion] The method for producing the specific CNT dispersion is not particularly limited. The specific CNT dispersion can be produced by dispersing a specific CNT aggregate in a dispersion medium. That is, the specific CNT dispersion can be produced by a method including a step of dispersing a specific CNT aggregate in a dispersion medium (also referred to as a "dispersion step"). The dispersion medium that can be used in the dispersion step is as described above.

[0162] The dispersion method is not particularly limited. Examples of the dispersion method include methods using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Examples of the dispersion method include methods using known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressure kneader. As a dispersion method, a method using a jet mill is preferred, and a method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pressure-feeds a mixture in a solvent as a high-speed flow from a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, multi-walled carbon nanotubes are dispersed in a pressure-resistant container by collisions between opposing flows, collisions with the container wall, turbulence caused by high-speed flows, shear flows, etc. As a wet jet mill, an ultra-high-pressure homogenizer (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used. However, the wet jet mill is not limited to this. When using the ultra-high-pressure homogenizer as a dispersing device, the dispersion treatment pressure is preferably 10 MPa to 250 MPa.

[0163] The method for producing the specific CNT dispersion may include a step of drying the specific CNT aggregate (also referred to as a "drying step") before the dispersion step.

[0164] If moisture adheres to the CNTs, the surface tension of the water makes them more likely to adhere to each other, which raises concerns about reduced dispersibility. Therefore, by performing a drying process on the conductive additive body before the dispersion process, moisture adhered to the CNTs is removed, preventing adhesion between multi-walled carbon nanotubes due to moisture adhesion, and further improving the dispersibility of the CNTs in the dispersion medium. The drying method is not particularly limited. Examples of drying methods include heat drying, vacuum drying, and heat vacuum drying. Heat vacuum drying is preferred as the drying method. The drying temperature is not particularly limited, and 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 adhesion to the multi-walled carbon nanotubes in the present disclosure, and the like.

[0165] An example of the production of the specific CNT dispersion will be shown below, but the production of the specific CNT dispersion is not limited to the following.

[0166] <Production Example 1: Example of Production of Dispersion> 0.040 g of the specific CNT aggregate according to the present disclosure is weighed and placed in a three-neck flask. After the specific CNT aggregate is placed in the flask, a large excess of ion-exchanged water, which serves as a dispersion medium, is poured into the flask (e.g., 20 mL) and stirred at room temperature (25°C, the same applies below). At this time, a known dispersant (e.g., carboxymethyl cellulose) may be added as appropriate. Next, a conductive additive is dispersed in the dispersion medium using a known dispersion device (e.g., an ultrasonic irradiation device or a wet jet mill). The obtained dispersion is further stirred with a stirrer at room temperature for a long period of time (e.g., 1 hour to 48 hours). In this way, a specific CNT dispersion is obtained.

[0167] [Conductive Material] The conductive material according to the present disclosure contains a specific CNT aggregate. As described above, the specific CNT aggregate contained in the conductive material according to the present disclosure has excellent conductivity when made into a dispersion, and is therefore suitable as a conductive auxiliary. Because the conductive material according to the present disclosure contains the specific CNT aggregate according to the present disclosure, it has excellent conductive efficiency and can effectively impart high conductivity to an object to which it is used.

[0168] The conductive material according to the present disclosure may contain a known conductive additive such as graphite, ketjen black, etc. Furthermore, the conductive material according to the present disclosure may contain CNTs other than the specific CNT aggregate.

[0169] The conductive material according to the present disclosure can be used as one of electrode materials. An example of an electrode formed using the electrode material is an electrode included in a secondary battery. Hereinafter, an embodiment of the electrode and the secondary battery including the electrode will be described.

[0170] [Electrode and Secondary Battery] An electrode according to the present disclosure includes an electrode active material and a conductive material according to the present disclosure. A secondary battery according to the present disclosure includes an electrode according to the present disclosure. Since the electrode according to the present disclosure includes the conductive material according to the present disclosure, it is excellent in forming a conductive path within the electrode. Therefore, the secondary battery according to the present disclosure has excellent cycle characteristics. Hereinafter, one embodiment of an electrode and a secondary battery including the electrode will be described.

[0171] <Electrode> The electrode may contain a specific CNT aggregate. In the electrode, the specific CNT aggregate may function as a conductive additive. The CNT aggregate contained in the electrode described below is synonymous with the specific CNT aggregate, and preferred embodiments are also the same, so description of the CNT aggregate will be omitted below.

[0172] The electrode may be at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer, or may include a current collector and an electrode active material layer disposed on the current collector.

[0173] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, baked carbon, and aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals such as copper and nickel that have good carbon adsorption properties may be used as the current collector.

[0174] The electrode active material layer may contain an electrode active material. The electrode active material is preferably electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer may contain a positive electrode active material that is commonly used as an electrode material for a positive electrode. Specifically, the positive electrode active material may be lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), compounds substituted with one or more transition metals; LiFe ３ O ４ Lithium iron oxides such as those with the chemical formula 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 , Cu ２ V ２ O ７ Vanadium oxides such as LiNi １－ｃ２ M ｃ２ O ２ (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≦c2≦0.66); Ni-site type lithium nickel oxide represented by the chemical formula LiMn ２－ｃ３ M ｃ３ O ２(wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), or Li ２ Mn ３ MO ８ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn ２ O ４ Examples include:

[0175] When the electrode is a negative electrode, the electrode active material is not particularly limited, and the electrode active material layer can contain a negative electrode active material commonly used for negative electrode materials. Specifically, the negative electrode active material can contain graphite-based active material particles or silicon-based active material particles. The graphite-based active material particles may be at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads. Using artificial graphite as the graphite-based active material particles can improve rate characteristics. The silicon-based active material particles may be at least one selected from the group consisting of Si, SiOx (0<x<2), Si-C composites, and Si-Y alloys (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). The use of silicon-based active material particles can increase the capacity of the battery.

[0176] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer may contain a binder that is commonly used in electrode materials. Examples of the binder include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers have been substituted with Li, Na, Ca, or the like.

[0177] <Secondary Battery> The secondary battery may be configured to 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 formed using a conductive material containing a specific CNT aggregate as an electrode material.

[0178] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. It is not particularly limited as long as it is typically used as a separator in a secondary battery. The separator preferably has low resistance to ion migration of the electrolyte and excellent electrolyte humidification capacity. Specific examples of the separator include porous polymer films. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure comprising two or more layers of these films. The separator may also be a conventional porous nonwoven fabric, such as a nonwoven fabric made from high-melting-point glass fiber or polyethylene terephthalate fiber. The separator may also be coated with a ceramic component or a polymeric substance to ensure heat resistance or mechanical strength. The separator may be selectively formed into a single-layer or multi-layer structure.

[0179] The electrolyte is not particularly limited, and examples thereof include electrolytes such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in producing lithium secondary batteries.

[0180] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt. Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0181] Among carbonate organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high viscosity and high dielectric constants and dissociate lithium salts well. It is more preferred to use a non-aqueous organic solvent obtained by mixing such cyclic carbonates with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, in order to obtain an electrolyte having high electrical conductivity.

[0182] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte. The anion portion of the lithium salt may be, for example, F － , Cl － , I － , NO ３ － , N (CN) ２ － , B.F. ４ － , ClO ４ － , P.F. 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 )<​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​In addition to the non-aqueous organic solvent and metal salt, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0184] The above-described secondary battery can be used to form a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0185] The planar aggregate of the present disclosure is a carbon nanotube aggregate of the present disclosure, which includes carbon nanotubes having a maximum length of 1000 μm to 30000 μm. The proportion of carbon nanotubes having a maximum length of 1000 μm to 30000 μm included in the planar aggregate of the present disclosure is usually 1 mass % or more. The planar aggregate of the present disclosure may include other components, such as a carbon nanotube aggregate including carbon nanotubes having a maximum length of less than 1000 μm, i.e., a carbon nanotube aggregate that does not include carbon nanotubes having a maximum length of 1000 μm to 30000 μm. The planar aggregate of the present disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate, by dispersing a carbon nanotube aggregate containing carbon nanotubes with a maximum length of 1000 μm to 30000 μm, or the carbon nanotube aggregate and other components such as a carbon nanotube aggregate containing carbon nanotubes with a maximum length of less than 1000 μm, in water or other fluid, and filtering the resultant once or twice or more times.

[0186] The planar assembly of the present disclosure includes, for example, a film, which is useful, for example, as a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet (EUV) radiation.

[0187] [Composition] The composition according to the present disclosure is a composition comprising the CNT aggregate according to the present disclosure and at least one selected from the group consisting of a dispersion medium, a resin, ceramics, and concrete. The dispersion medium preferably contains water, more preferably contains water as a main component, and even more preferably is water. The second most preferred solvent after water is N-methylpyrrolidone. Examples of resins include thermoplastic resins and thermosetting resins, and preferred are olefin-based resins, polycarbonate-based resins, polyester-based resins, polyamide-based resins, thermoplastic polyurethane resins, polysulfone-based resins, and silicone resins. Examples of ceramics include crystalline ceramics and amorphous ceramics. Examples of concrete include Portland cement concrete. The composition according to the present disclosure may further contain other components such as water and organic solvents. In the composition according to the present disclosure, when the content of the CNT aggregate is taken as 100 parts by mass, the content of at least one selected from the group consisting of resin, ceramic, and concrete is usually 10 to 1,000,000 parts by mass, preferably 100 to 100,000 parts by mass, and more preferably 1,000 to 40,000 parts by mass, and when other components are included, the content is preferably 1 to 10,000 parts by mass, and more preferably 10 to 1,000 parts by mass. In the composition according to the present disclosure, the CNT aggregate, resin, ceramic, concrete, and other components may each be included singly or in combination of two or more types.

[0188] <Method for producing the composition> The composition according to the present disclosure can be produced, for example, by mixing the CNT aggregate according to the present disclosure with resin, ceramic, or pre-hardened concrete. The resin may be in the form of a powder, pellets, solution, or dispersion. The ceramic may be in the form of a powder, precursor solution, or dispersion. The composition according to the present disclosure can also be produced, for example, by dispersing the CNT dispersion according to the present disclosure in a resin solution, a ceramic precursor or dispersion, or pre-hardened concrete, and then molding the resultant.

[0189] <Uses of the Composition> When the composition according to the present disclosure contains a resin or ceramic, it is useful as, for example, a structural material, a conductive material, a heat management material, or an antistatic material. When the composition according to the present disclosure contains concrete, it is useful as a lightweight, durable building material, or an electricity storage device (impregnated with an electrolyte as needed).

[0190] The specific CNT aggregate according to the present disclosure, the dispersion containing the specific CNT aggregate, and the like will be described in more detail below with reference to examples. The aggregate and dispersion according to the present disclosure are not limited to the following examples as long as they do not deviate from the gist of the disclosure. Unless otherwise specified, "%" means "% by mass" and "ppm" means "ppm by mass".

[0191] (Example 1) 1. Production of Sheet-like CNT Aggregate 1 The sheet-like CNT aggregate 1 was produced by a floating catalyst method (CVD method) that directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled at 400°C to 700°C. A mixed gas of nitrogen and argon was used as the carrier gas. The flow rate of the carrier gas was 30,000 sccm (standard cubic centimeters per minute). By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst is produced is called the first temperature zone.

[0192] Next, methane, a carbon source, was released into the carrier gas stream. The metal catalyst and the carbon source were fed into a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0193] In the second temperature zone, an electric field was generated in the temperature-controlled flow reactor, thereby generating CNT aggregates. The aggregates were continuously discharged through the outlet of the flow reactor, which was temperature-controlled to 100°C to 500°C, and a sheet-like CNT aggregate was collected by continuous discharge. The obtained sheet-like CNT aggregate 1 contains MWCNTs. The obtained sheet-like CNT aggregate was washed with pure water for 10 seconds in order to adjust the contents of Fe atoms, Co atoms, Na atoms, and K atoms, and a sheet-like CNT aggregate 1, which is a specific CNT aggregate, was obtained.

[0194] 2. Preparation of CNT Dispersion Liquid 1 The following materials were mixed and pre-dispersed by processing for 1 hour with an Ace Homogenizer manufactured by Nippon Seiki Co., Ltd. to obtain pre-dispersion liquid 1. Note that the sheet-like CNT aggregate 1 was cut into small pieces of 1 cm x 1 cm with scissors before mixing so that the sheet-like CNT aggregate 1 would not become tangled in the blades of the homogenizer.

[0195] (Dispersion composition) Sheet-shaped CNT aggregate 1 obtained above 1.1 g Carboxymethyl Cellulose Sodium Salt High Viscosity (manufactured by MP Biomedicals) 1.65 g Pure water 547.25 g

[0196] The pre-dispersion liquid 1 was subjected to main dispersion using an ultra-high pressure homogenizer (model: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain a specific CNT dispersion liquid, CNT dispersion liquid 1. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 Method: Circulation method

[0197] 3. Evaluation 3-1. Contents of Fe atoms, Co atoms, Na atoms, and K atoms relative to the total mass of the aggregate Using an inductively coupled plasma mass spectrometry (ICP-MS) device (NexION 2000C, manufactured by PerkinElmer), the contents of Fe atoms, Co atoms, Na atoms, and K atoms contained in the sheet-like CNT aggregate 1 of Example 1 were measured. As a result of low-temperature ashing / acid dissolution of the sheet-like CNT aggregate 1 as a pretreatment and measurement with the above device, the content of Fe atoms relative to the total mass of the aggregate of the sheet-like CNT aggregate 1 of Example 1 was 56,000 ppm, the content of Co atoms was less than 10 ppm (below the lower detection limit), the content of Na atoms was 100 ppm, and the content of K atoms was 500 ppm. That is, the total content of Fe atoms and Co atoms was 56,000 ppm, and the total content of Na atoms and K atoms was 600 ppm.

[0198] 3-2. Volume resistivity The sheet-like CNT aggregate 1 of Example 1 was pulverized using a freeze-pulverization method. Using a Loresta device (product name: powder resistivity measurement system MCP-PD51, low resistivity meter Loresta-GP, low resistance probe for powder MCP-PD511 (constant current application type 4-probe method), all manufactured by Nitto Seiko Analytech Co., Ltd.), the pulverized sheet-like CNT aggregate 1 was introduced into a powder resistivity measurement probe unit, and pressed at 1 kN and 20 kN using an attached hydraulic pump, and after reaching the target load, the volume resistivity (Ω cm) was measured. As a result, the volume resistivity was 1.7 x 10 at 1 kN. -２ Ω cm, and 5.0 x 10 at 20 kN -３ The ratio of the volume resistivity at 20 kN to the volume resistivity at 1 kN (shown as "resistivity ratio" in Table 1) was 0.29.

[0199] 3-3. Conductivity of Dispersion Liquid CNT Dispersion Liquid 1 was dropped onto a glass substrate (10 cm x 10 cm) and a film was formed using a stainless steel applicator with a gap size of 150 μm. It was then heated on a hot plate at 110°C for 10 minutes and dried. The surface resistivity of the film was measured using a Loresta GXII manufactured by Nitto Seiko Analytech Co., Ltd. Measurements were performed at five locations on the film, and the average of the five values ​​was taken as the surface resistivity. The resulting surface resistivity was 164.42 Ω / □.

[0200] 3-4. Confirmation of bundle structure When the obtained sheet-shaped CNT aggregate 1 of Example 1 was observed with an SEM (device name: S-4800, manufactured by Hitachi High-Technologies Corporation), it was confirmed that it contained a bundle structure. Measurements were taken at 20 points and the average value was calculated, and the width of the bundle structure was 70 nm.

[0201] 3-5. Pore volume The pore volume was measured using a gas adsorption measurement device (product name "BELSORP-miniII", manufactured by Microtrac-Bell). The sheet-like CNT aggregate 1 obtained in Example 1 was used as a measurement sample. The pore volume was measured after vacuum degassing treatment was performed on the sheet-like CNT aggregate 1 at 300°C for 3 hours using a pretreatment device (product name "BELPREP-vacII", manufactured by Microtrac-Bell). The adsorption and desorption isotherm with nitrogen was measured for the sheet-like CNT aggregate 1 after the vacuum degassing treatment using a constant volume method. The measurement temperature was 77K, the adsorbate was nitrogen, the saturated vapor pressure was actually measured, and the adsorbate cross-sectional area was 0.162nm ２ The waiting time after reaching the adsorption equilibrium state was set to 500 seconds. The BJH method was used for the analysis to calculate the pore volume from the obtained adsorption / desorption isotherm. As a result, the pore volume of the sheet-shaped CNT aggregate 1 was 2.06 cm ３ / g.

[0202] The evaluation results are shown in Table 1. In the section on confirmation of bundle structure, if a bundle structure was confirmed, it was recorded as "Yes", and if not confirmed, it was recorded as "-".

[0203] (Example 2) 1. Production of fibrous CNT aggregate 2 Like the sheet-like CNT aggregate 1, the fibrous CNT aggregate 2 was also produced by the floating catalyst method (CVD method) which directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled to 400°C to 700°C. A mixed gas of nitrogen and argon was used as the carrier gas. The flow rate of the carrier gas was 30,000 sccm. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst is produced is called the first temperature zone.

[0204] Next, methane, a carbon source, was released into the carrier gas stream. The metal catalyst and the carbon source were fed into a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0205] In the second temperature zone, an electric field was generated in the temperature-controlled flow reactor, thereby generating a fibrous CNT aggregate. The aggregate was continuously discharged as carbon nanotube aggregates through the outlet of the flow reactor, which was temperature-controlled at 100°C to 500°C, and the fibrous CNT aggregate was collected by continuous discharge. The obtained fibrous CNT aggregate contains MWCNT. The obtained fibrous CNT aggregate was washed with pure water for 10 seconds in order to adjust the contents of Fe atoms, Co atoms, Na atoms, and K atoms, and a fibrous CNT aggregate 2 was obtained.

[0206] 2. Preparation of CNT Dispersion 2 Using the obtained fibrous CNT aggregate 2, a CNT dispersion 2 was obtained in the same manner as in Example 1.

[0207] 3. Evaluation The fibrous CNT aggregate 2 and CNT dispersion 2 of Example 2 were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0208] (Example 3) 1. Production of sheet-like CNT aggregate 3 The sheet-like CNT aggregate obtained in Example 1 was immersed in a polytetrafluoroethylene (PTFE) tray containing hydrochloric acid (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) for 24 hours. After that, the sheet-like CNT aggregate was taken out of the tray and washed with deionized water until the pH of the washing water reached 7, and a sheet-like CNT aggregate 3 was obtained.

[0209] 2. Preparation of CNT Dispersion 3 Using the obtained sheet-shaped CNT aggregate 3, a CNT dispersion 3 was obtained in the same manner as in Example 1.

[0210] 3. Evaluation The sheet-shaped CNT aggregate 3 and CNT dispersion 3 of Comparative Example 1 were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0211] (Comparative Example 1) 1. Preparation of Powdered CNT Aggregate 4 As the powdered CNT aggregate 4, "multi-walled carbon nanotubes" (catalog number: 901019, 50-90 nm diameter, >95% carbon basis, manufactured by Sigma-Aldrich) was prepared.

[0212] 2. Preparation of CNT Dispersion Liquid 4 Using the prepared powdered CNT aggregate 4, a CNT dispersion liquid 4 was obtained in the same manner as in Example 1.

[0213] 3. Evaluation The powdered CNT aggregate 4 and the CNT dispersion liquid 4 of Comparative Example 1 were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0214] (Comparative Example 2) 1. Preparation of powdered CNT aggregate 5 As the powdered CNT aggregate 5, "multi-walled carbon nanotubes" (catalog number: FT7000, manufactured by C-nano Co., Ltd.) was prepared.

[0215] 2. Preparation of CNT Dispersion Liquid 5 Using the prepared powdered CNT aggregate 4, a CNT dispersion liquid 5 was obtained in the same manner as in Example 1.

[0216] 3. Evaluation The powdered CNT aggregate 5 and CNT dispersion liquid 5 of Comparative Example 2 were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0217] (Comparative Example 3) 1. Preparation of powdered CNT aggregate 6 As the powdered CNT aggregate 6, "single-walled carbon nanotubes" (catalog number: TUBALL ＴＭ , manufactured by OCSiAl Co., Ltd.) was prepared.

[0218] 2. Preparation of CNT Dispersion Liquid 6 Using the prepared powdered CNT aggregate 6, a CNT dispersion liquid 6 was obtained in the same manner as in Example 1.

[0219] 3. Evaluation The powdered CNT aggregate 6 and the CNT dispersion liquid 6 of Comparative Example 3 were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0220] (Comparative Example 4) 1. Preparation of powdered CNT aggregate 7 As the powdered CNT aggregate 7, "multi-walled carbon nanotubes" (catalog number: FT6120, manufactured by C-nano Co., Ltd.) was prepared.

[0221] 2. Preparation of CNT Dispersion Liquid 7 Using the prepared powdered CNT aggregate 7, a CNT dispersion liquid 7 was obtained in the same manner as in Example 1.

[0222] 3. Evaluation The powdered CNT aggregate 7 and the CNT dispersion liquid 7 of Comparative Example 4 were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0223]

[0224] As shown in Table 1, it can be seen that the CNT dispersion obtained by dispersing the CNT aggregates of the Examples has good conductivity. On the other hand, the CNT aggregates of Comparative Examples 1 and 2, in which the total content of Na atoms and K atoms is less than 50 ppm or exceeds 1000 ppm and the ratio of the volume resistivity at 20 kN to the volume resistivity at 1 kN is less than 0.21, had problems with the conductivity of the CNT dispersion obtained by dispersion. It can be seen that the CNT aggregates of Comparative Examples 1 and 2 are inferior as conductive materials. Furthermore, the CNT aggregate of Comparative Example 3, in which the total content of Fe atoms and Co atoms is greater than 100,000 ppm and the total content of Na atoms and K atoms is greater than 1,000 ppm, and the CNT aggregate of Comparative Example 4, in which the total content of Fe atoms and Co atoms is less than 2,000 ppm, both had problems with the conductivity of the CNT dispersion obtained by dispersion. It is clear that the CNT aggregates of Comparative Examples 3 and 4 are inferior as conductive materials.

Claims

1. An aggregate of carbon nanotubes satisfying the following conditions (1), (2), and (3): (1) containing at least one of Fe atoms and Co atoms, wherein the total content of Fe atoms and Co atoms is 2000 ppm by mass to 100000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes; (2) containing at least one of Na atoms and K atoms, wherein the total content of Na atoms and K atoms is 50 ppm by mass to 1000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes; and (3) the ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN is 0.21 or more.

2. The carbon nanotube aggregate according to claim 1, which comprises a bundle structure.

3. The pore volume is 0.60 cm ３ / g ~ 3.20 cm ３ The carbon nanotube aggregate according to claim 1 or claim 2, wherein the aggregate has a surface area of ​​1 / g.

4. A carbon nanotube dispersion liquid comprising the carbon nanotube aggregate according to claim 1 or 2 and a dispersion medium.

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

6. An electrode comprising an electrode active material and the conductive material according to claim 5.

7. A secondary battery comprising the electrode according to claim 6.

8. A carbon nanotube aggregate according to claim 1 or 2, wherein the carbon nanotube aggregate is a planar aggregate containing carbon nanotubes having a maximum length of 1000 μm to 30000 μm.

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

10. An electromagnetic wave shield using the planar assembly according to claim 8.

11. A pellicle for extreme ultraviolet rays using the planar assembly according to claim 8.

12. A composition comprising an aggregate of carbon nanotubes and at least one selected from the group consisting of a dispersion medium, a resin, a ceramic, and a concrete, which satisfies the following conditions (1) and (2): (1) The composition comprises at least one of Fe atoms and Co atoms, and the total content of the Fe atoms and the Co atoms is 2500 ppm by mass to 60000 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes, and (2) The composition comprises at least one of Na atoms and K atoms, and the total content of the Na atoms and the K atoms is 50 ppm by mass to 700 ppm by mass with respect to the total mass of the aggregate of carbon nanotubes.

13. A composition comprising an aggregate of carbon nanotubes and at least one selected from the group consisting of a dispersion medium, a resin, a ceramic, and a concrete, which satisfies the following conditions (1) and (2): (1) The composition comprises at least one of Fe atoms and Co atoms, and the total content of Fe atoms and Co atoms is 2500 mass ppm to 60000 mass ppm with respect to the total mass of the aggregate of carbon nanotubes. (2) The ratio of the volume resistivity under a pressure of 20 kN to the volume resistivity under a pressure of 1 kN is 0.21 or more.

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