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

Abstract

Provided is a carbon nanotube aggregate and the like that can be used to fabricate a battery having excellent cycle characteristics. [Solution] A carbon nanotube aggregate and its application satisfying the following conditions (1) and (2): (1) The content of amorphous carbon is 0.1 mass % or more and less than 2.0 mass % with respect to the total mass of the carbon nanotube aggregate, and (2) The aggregate contains a bundle structure, and in an area observed with a scanning electron microscope, the area ratio of bundles having a bundle diameter of 100 nm or more exceeds 0.1.

Description

[Technical Field]

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

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

[0003] For example, Patent Document 1 describes a method for removing carbonaceous impurities from carbon nanotubes, which comprises a first step of providing sulfur and carbon nanotubes in a sealed space, and a second step of sulfurizing the surface of the carbon nanotubes to remove impurities attached to the carbon nanotubes. Patent Document 2 describes a CNT aggregate that satisfies the following criteria: a 2θ peak is present at 24°±2° in powder X-ray diffraction analysis; the height ratio of the G band to the D band (G / D ratio) is 30 or more in Raman spectroscopy analysis at a wavelength of 532 nm; and the combustion peak temperature is 550°C or higher and 700°C or lower. Patent Document 3 describes that the CNT aggregate has a bundle structure, the bundles have a diameter of more than 0.3 μm, and the average diameter is 0.5 μm or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-008803 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-029695 [Patent Document 3] Chinese Patent Application Publication No. 116111043 Summary of the Invention [Problem to be solved by the invention]

[0005] When a battery is produced using a CNT aggregate, there are cases where it is required to have excellent cycle characteristics.

[0006] The present disclosure has been made in consideration of the above circumstances. An object of an embodiment of the present disclosure is to provide an aggregate of carbon nanotubes that can be used to fabricate a battery having excellent cycle characteristics. Another problem to be solved by another embodiment of the present disclosure is to provide a conductive material, an electrode, a secondary battery, and a planar assembly, each including the carbon nanotube aggregate. Another problem to be solved by another embodiment of the present disclosure is to provide a laminate including the above-mentioned planar assembly. Another problem to be solved by another embodiment of the present disclosure is to provide a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet rays using the above-mentioned planar assembly. [Means for solving the problem]

[0007] <1> An aggregate of carbon nanotubes that satisfies the following conditions (1) and (2): (1) The content of amorphous carbon is 0.1 mass % or more and less than 2.0 mass % with respect to the total mass of the aggregate of carbon nanotubes. (2) The area ratio of bundles having a bundle diameter of 100 nm or more is more than 0.1 in an area observed by a scanning electron microscope, which includes a bundle structure. <2> Satisfy the condition (3) below, <1> The carbon nanotube aggregate according to claim 1. (3) When the aggregate of carbon nanotubes is mixed with water and the liquid temperature is 25°C and the concentration is 0.20 mass%, the common logarithm of the viscosity of the dispersion is more than 1.0 and less than 3.5. The unit of viscosity is mPa·s. <3> <1> or <2> A conductive material comprising the carbon nanotube aggregate according to claim 1. <4> an electrode active material; <3> and an electrode comprising the conductive material according to claim 1. <5> <4> A secondary battery comprising the electrode according to claim 1. <6> <1> or <2> A planar aggregate comprising the carbon nanotube aggregate according to claim 1. <7> A substrate; <6> A laminate comprising the planar assembly according to claim 1. <8> <6> A filter using the planar assembly described in 1. <9> <6> An electromagnetic wave shield using the planar assembly described in 1. <10> <6> A pellicle for extreme ultraviolet radiation using the planar assembly described in . [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, there is provided an aggregate of carbon nanotubes that can be used to fabricate a battery having excellent cycle characteristics. According to another embodiment of the present disclosure, there are provided a conductive material, an electrode, a secondary battery, and a planar assembly, each including the carbon nanotube aggregate. According to another embodiment of the present disclosure, there is provided a laminate including the above-described planar assembly. According to other embodiments of the present disclosure, there are provided a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet radiation, which use the planar assembly. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 1 of Example 1. [Figure 2] 1 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 2 of Example 2. [Figure 3] 10 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 3 of Example 3. [Figure 4] 10 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 4 of Example 4. [Figure 5] 10 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 5 of Example 5. [Figure 6] 10 is a scanning electron microscope photograph showing one aspect of a CNT aggregate 6 of Example 6. [Figure 7] 1 is a scanning electron microscope photograph showing one aspect of a powdered CNT aggregate 7 of Comparative Example 1. [Figure 8] 10 is a scanning electron microscope photograph showing one aspect of a powdered CNT aggregate 8 of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a carbon nanotube aggregate, a conductive material, an electrode, a secondary battery, a planar aggregate, a laminate, a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet radiation according to the present disclosure will be described in detail. The following description may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

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

[0012] In the present disclosure, the terms "carbon nanotubes," "single-walled carbon nanotubes," "multi-walled carbon nanotubes," "carbon nanotube aggregate," "carbon nanotubes having a maximum length of 1000 μm to 30000 μm," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "CNT aggregate," "ULCNT," and "CNT dispersion," respectively.

[0013] [CNT aggregate] The CNT aggregate according to the present disclosure satisfies the following conditions (1) and (2). (1) The content of amorphous carbon is 0.1 mass % or more and less than 2.0 mass % with respect to the total mass of the CNT aggregate. (2) The area ratio of bundles having a bundle diameter of 100 nm or more is more than 0.1 in an area observed by a scanning electron microscope, which includes a bundle structure.

[0014] A CNT aggregate that satisfies the conditions (1) and (2), that is, a CNT aggregate according to the present disclosure, can produce a battery having excellent cycle characteristics. On the other hand, Patent Documents 1 to 3 do not mention conditions (1) and (2).

[0015] In Patent Document 1, amorphous carbon is removed as an impurity that inhibits the inherent properties of CNTs, such as high conductivity. However, while removing amorphous carbon allows the CNTs to more easily exhibit their inherent properties, it also increases the tendency for CNTs to aggregate together. As a result, the dispersibility of the CNT aggregates in solvents and the like decreases, making them unsuitable for applications such as conductive additives. On the other hand, CNTs that contain an excessive amount of amorphous carbon tend to lose the inherent properties of CNTs, such as physical robustness (tensile strength and breaking strength) and high electrical conductivity. Furthermore, in Patent Documents 2 and 3, the bundle diameter is not sufficiently controlled. In contrast, the CNT aggregate according to the present disclosure satisfies the conditions (1) and (2), making it possible to fabricate a battery with excellent cycle characteristics.

[0016] <Condition (1)> The CNT aggregate according to the present disclosure has an amorphous carbon content of not less than 0.1 mass % and less than 2.0 mass % with respect to the total mass of the CNT aggregate.

[0017] The CNT aggregate according to the present disclosure contains amorphous carbon.

[0018] The CNT aggregate may contain amorphous carbon, for example, in a state where it is adsorbed on the surface of the CNT aggregate or in a state where it is incorporated into the interior of the fibrous CNT aggregate formed during production.

[0019] Amorphous carbon is produced as a by-product during the CNT manufacturing process. Because amorphous carbon and CNTs have different physical and chemical properties, controlling the amorphous carbon content is important. For example, amorphous carbon is produced when hydrocarbon gas is decomposed at high temperatures during CNT synthesis using chemical vapor deposition (CVD). During this process, carbon atoms precipitate on the catalyst metal surface, resulting in CNT growth, while amorphous carbon is simultaneously produced on the catalyst surface and substrate. The amorphous carbon content can be controlled by appropriately adjusting the CNT growth conditions (e.g., temperature, gas flow rate, catalyst type, etc.). In particular, in the CNT aggregate according to the present disclosure, controlling the amorphous carbon content to 0.1% by mass or more and less than 2.0% by mass improves the battery cycle characteristics.

[0020] From the viewpoint of further improving the cycle characteristics of the battery, the content of amorphous carbon is preferably 0.1 mass% or more and less than 1.9 mass% relative to the total mass of the CNT aggregate. Furthermore, the content of amorphous carbon is preferably 0.20 mass% or more and less than 2.0 mass%, more preferably 0.22 mass% or more and less than 2.0 mass%, even more preferably 0.22 mass% or more and less than 1.9 mass%, particularly preferably 0.22 mass% or more and less than 1.85 mass%, and most preferably 0.24 mass% or more and less than 1.80 mass%.

[0021] By ensuring that the amorphous carbon content is between 0.1% and 2.0% by mass of the total mass of the CNT aggregate, the amorphous carbon is dispersed appropriately on the surface of the CNTs, improving the electrical conductivity and mechanical strength of the electrode material. Specifically, the amorphous carbon reduces the contact resistance between the CNTs and promotes efficient current flow. The presence of amorphous carbon on the surface of the CNTs weakens the van der Waals forces between the CNTs, suppressing aggregation and facilitating widespread dispersion within the electrode. This allows connections between the electrode active materials to form uniform conductive paths within the electrode. Furthermore, amorphous carbon stabilizes the bundle structure of CNTs, improving the structural stability of the electrode and mitigating volume changes and stress during cycling. This is believed to result in a battery with excellent cycle performance. Furthermore, it suppresses electrode deterioration due to swelling and shrinkage of the electrode active material during charge and discharge, thereby improving the cycle performance of the battery.

[0022] The amorphous carbon content in the CNT aggregate according to the present disclosure is calculated by thermogravimetric differential thermal analysis (TG-DTA). In thermogravimetric differential thermal analysis (TG-DTA), the temperature is raised to about 900°C at about 10°C / min, and the peak combustion temperature and residue are analyzed to evaluate the constituent elements and quality of the carbon material. For example, carbon materials obtained by floating catalyst chemical vapor deposition (FCCVD) are mixtures of metals (e.g., iron (Fe)) contained in the catalyst raw material, CNTs, amorphous carbon, and graphitic carbon. When the carbon material is heated under the above conditions, if it contains metals such as iron (Fe), an increase in mass due to oxidation of the metal is observed. Typically, amorphous carbon burns at around 300°C to 400°C, while CNTs and graphitic carbon begin to burn at around 400°C and are completely burned at around 700°C. Therefore, the amorphous carbon content can be calculated from the difference in the weight loss between 200°C and 400°C.

[0023] When measuring the content of amorphous carbon, a powder of CNT aggregates is used as the measurement sample. When the CNT aggregate is in a form other than powder (for example, fiber or sheet), the CNT aggregate may be pulverized to obtain a powder. The pulverization method is not particularly limited, and any pulverization method capable of crushing the CNT aggregate into small pieces may be used. As the pulverization method, a freeze-pulverization method may be used.

[0024] <Condition (2)> The CNT aggregate according to the present disclosure includes a bundle structure, and in an area observed with a scanning electron microscope (SEM), the area ratio of bundles having a bundle diameter of 100 nm or more exceeds 0.1.

[0025] The CNT aggregate according to the present disclosure includes a bundle structure. A bundle structure refers to an aggregate in which multiple CNTs are aggregated together due to van der Waals forces and other factors, forming a bundle. It is believed that if a CNT aggregate contains bundle structures of an appropriate size, it will be easier to handle as a CNT aggregate and its stability will be improved. On the other hand, if the bundle structures contained in the CNT aggregate become too large, the size of the CNT aggregate itself will become too large, and it will become difficult to separate and disperse the CNTs contained in the bundle structures, which may reduce dispersibility in the dispersion medium.

[0026] The bundle structure in the CNT aggregate can be formed, for example, by controlling the catalyst particle size distribution in production by chemical vapor deposition (CVD) method, or by controlling the cooling rate in the cooling step.

[0027] From the viewpoint of achieving both ease of handling of the CNT aggregate and dispersibility in a solvent, the width of each bundle structure contained in the CNT aggregate, i.e., the size in the width direction of the fiber bundle, is preferably 5 nm to 500 nm, and more preferably 10 nm to 300 nm. The content of the bundle structure in the CNT aggregate is preferably 10% by mass to 100% by mass, and more preferably 20% by mass to 90% by mass, relative to the total mass of the CNT aggregate. The presence or absence of a bundle structure in a CNT aggregate can be confirmed by observing the CNT aggregate with an optical microscope, a scanning electron microscope (SEM), etc. The width of the bundle structure can be determined by identifying the location where the bundle structure exists in the CNT aggregate and measuring the length using a photographed image of the bundle structure.

[0028] In the CNT aggregate according to the present disclosure, the area ratio of bundles having a bundle diameter of 100 nm or more exceeds 0.1 in the area observed by SEM, thereby forming an appropriate CNT bundle structure and improving the mechanical strength and conductivity of the electrode material. Specifically, a bundle diameter of 100 nm or more strengthens the bonds between CNTs, strengthening the electron transport pathways connecting the electrode active materials and improving the structural stability of the electrode. Furthermore, a large bundle diameter increases the electron conduction pathways within the electrode, promoting efficient current flow. This reduces the internal resistance of the battery and improves charge / discharge efficiency. Therefore, a battery with excellent cycle characteristics can be obtained by having the area ratio of bundles having a bundle diameter of 100 nm or more exceed 0.1 in the area observed by SEM.

[0029] In particular, the area ratio of the bundle is preferably more than 0.1 and not more than 0.6, more preferably more than 0.1 and not more than 0.55, even more preferably more than 0.1 and not more than 0.5, particularly preferably 0.13 or more and not more than 0.5, even more preferably 0.13 or more and not more than 0.45, and especially preferably 0.13 or more and not more than 0.41. The area ratio of the bundle is preferably more than 0.1 and less than 0.8, more preferably 0.11 or more and less than 0.6, and even more preferably 0.12 or more and 0.55 or less. Within this range, the CNT bundle structure is appropriately formed, strengthening the bonds between the CNTs and improving the mechanical strength of the electrode. Furthermore, a moderate bundle diameter improves CNT dispersion and ensures uniform conductive paths within the electrode. This improves the overall conductivity of the electrode and reduces the internal resistance of the battery, resulting in excellent cycle characteristics.

[0030] Furthermore, from the viewpoint of increasing the breaking elongation, the area ratio of the bundles is more preferably 0.20 to 0.55, particularly preferably 0.20 to 0.45. A high breaking elongation improves the flexibility and durability of the material containing the CNT aggregate. Furthermore, the area ratio of the bundles is particularly preferably 0.20 or more and 0.55 or less. A high breaking elongation improves the flexibility and durability of the material containing the CNT aggregate.

[0031] It is also preferable that the area ratio of the bundles is greater than 0.1 and not greater than 0.55. In this range, the CNT bundle diameter is appropriately small, increasing the surface area of ​​the electrode material and expanding the contact area with the electrode active material. This promotes ion migration and improves the charge / discharge efficiency of the battery. Furthermore, a moderately small bundle diameter also increases the flexibility of the electrode and improves its durability against volume changes during cycling. This further improves the cycle characteristics of the battery.

[0032] Furthermore, in observation by SEM, the bundle diameter at 90% of the cumulative total is preferably more than 90 nm and 300 nm or less. When the cumulative 90% bundle diameter exceeds 90 nm, the CNT bundles gather together and easily form a long-distance conductive network. Furthermore, when the cumulative 90% bundle diameter is 300 nm or less, the dispersibility in the dispersion medium is improved, making it easier to ensure conductivity. The cumulative 90% bundle diameter is preferably more than 90 nm and less than 250 nm, and more preferably more than 100 nm and less than 250 nm.

[0033] The bundle diameter of the CNT aggregate is measured by observation using an SEM. The CNT aggregate is photographed at a magnification of 100,000 to obtain multiple SEM photographs. The imaging method using an SEM is not particularly limited, and can be performed by a known method.

[0034] -Image capture- Using an SEM device (for example, S-4800 manufactured by Hitachi High-Technologies Corporation), images are taken under the following conditions to obtain multiple images of the CNT aggregate. From the viewpoint of reducing the variance of the analytical values ​​of the bundle diameter, it is preferable to obtain five or more images. Acceleration voltage: 0.5 kV Emission current: 10μA Measurement magnification: 100,000 times Image size: 1280 pixels x 960 pixels

[0035] -Image selection- From the obtained images, select two or more images in which CNT bundles are clearly observed.

[0036] - Overview of bundle diameter analysis using image analysis - The selected image is subjected to image processing and analysis using Python. In image processing, the CNT outline and center line are detected and combined with the original image. In image analysis, the bundle diameter is determined by calculating the distance from the center line to the outline of the created image. The product of the bundle diameter and the length of the center line is then calculated to calculate the area occupied by the CNT in the image.

[0037] -Detecting the outline of CNTs using image analysis- 1. The image is binarized to distinguish between CNTs and the background. 2. Create a contour for the CNT part using the edge detection function of the OpenCV library.

[0038] -Detection of CNT centerlines using image analysis- 1. Adjust the parameters to distinguish between CNTs and the background and perform binarization. 2. Create a skeleton for the CNT part using the skeletonize function of the scikit-image library. 3. For each coordinate of the skeleton, the number of skeletons within the surrounding two pixels is counted, and coordinates where five or more exist are recognized as skeleton intersections. 4. The skeleton is divided at the intersections by converting the intersections into background pixels. The divided skeleton is called a region. 5. Measure the length of the region and delete the short region. 6. Linear approximation is performed for each region. 7. For each line created, obtain the X-axis coordinate of the region that was the source of approximation. Convert the line into a line segment based on the range in which the obtained X-coordinate exists. Treat the line segment obtained here as the center line of the CNT. 8. Calculate the similarity based on the center coordinates and angle for all pairs of center lines. Pairs of center lines whose center coordinates are within 10 pixels of each other and whose angle between the two line segments is less than 10 degrees are treated as overlapping center lines, and the shorter one is deleted. 9. The CNT outline and center line are superimposed on the original image and saved. The outline is displayed in red and the center line in blue.

[0039] -Detecting CNT bundle diameter using image analysis- 1. The image created by image processing is read and the CNT, outline, background, and center line are recognized by color recognition. 2. Measure the length of each center line. 3. Choose a random point on the center line and draw a perpendicular line from the point to the center line. 4. Find the intersection of the perpendicular line and the contour, and save the distance from a random point on the centerline to the intersection as the bundle diameter. 5. Calculate the area occupied by the product of the length of the center line segment and the bundle diameter. Save the data as a histogram with the bundle diameter on the horizontal axis and the area occupied on the vertical axis.

[0040] - Obtaining bundle diameter parameters - Using the calculated bundle diameter histogram data, the feature amount of the bundle diameter of each sample is calculated by the following method. 1. The bundle diameters and occupied areas of multiple fields of view for the same sample are added together and normalized so that the total sum is 1. Following normalization, the unit of the vertical axis is the occupied area ratio. 2. Calculate the total area ratio of bundles with a bundle diameter of 100 nm or more. 3. Calculate the cumulative exclusive area ratio, and determine the bundle diameter when this value exceeds 0.9 for the first time as the cumulative 90% bundle diameter.

[0041] <Condition (3)> The CNT aggregate according to the present disclosure has a dispersion liquid in which the CNT aggregate is mixed with water at a liquid temperature of 25°C and a concentration of 0.20 mass%, and the common logarithm of the viscosity of the dispersion liquid is greater than 1.0 and less than 3.5. The unit of viscosity is mPa s.

[0042] When the common logarithm of the viscosity of the dispersion is greater than 1.0 and less than 3.5, the dispersibility of the CNTs is improved, and the performance as an electrode material is optimized.

[0043] The common logarithm of the viscosity of the dispersion is more preferably 1.1 or more and less than 3.5, and even more preferably 1.5 or more and less than 3.5. Furthermore, the common logarithm of the viscosity of the dispersion is more preferably greater than 1.0 and less than 3.3, even more preferably 1.1 or more and less than 3.3, even more preferably 1.5 or more and less than 3.3, and particularly preferably 1.52 or more and 2.98 or less. By properly controlling the viscosity of the dispersion, the dispersibility of CNTs is improved, optimizing their performance as an electrode material. Specifically, when the logarithm of the viscosity of the dispersion is 1.1 or more and less than 3.5, the CNTs are uniformly dispersed and conductive paths are efficiently formed within the electrode, improving the conductivity of the electrode and reducing the internal resistance of the battery, thereby improving the charge / discharge efficiency of the battery and further improving its cycle characteristics. Furthermore, when the logarithm of the viscosity of the dispersion is greater than 1.0 and less than 3.3, the dispersion of the CNTs is further improved, and the mechanical strength of the electrode material is enhanced, which makes the electrode more resistant to volume changes and stress during cycling and contributes to the battery life. In particular, when the logarithm of the viscosity of the dispersion is 1.1 or more and less than 3.3, the balance between the dispersibility and conductivity of the CNTs is optimized, and the performance as an electrode material is maximized. In this range, both uniform dispersion of the CNTs and high conductivity are achieved, and it is expected that the cycle characteristics of the battery will be significantly improved.

[0044] The viscosity of the CNT aggregate dispersion is measured using a cone-and-plate viscometer (also known as an E-type viscometer). For example, a Brookfield DV-II+Pro Programmable Viscometer is used as the cone-and-plate viscometer. The measurement conditions are as follows. Measuring tool: cone and plate Measurement mode: Rotation mode Shear rate: 0.6s -1 ~384s -1 Temperature: 25℃ From the data obtained, the viscosity is read at the following shear rates: Shear rate=12s -1

[0045] The CNT aggregate according to the present disclosure has a high affinity for the dispersion medium, and therefore tends to have a low viscosity when dispersed in a dispersion medium. When the viscosity of the dispersion is within an appropriate range, it can be determined that the dispersibility of the aggregate according to the present disclosure in the dispersion medium is good. The viscosity of the dispersion is preferably 10 mPa·s to 1600 mPa·s, more preferably 10 mPa·s to 1500 mPa·s, even more preferably 30 mPa·s to 1300 mPa·s, particularly preferably 100 mPa·s to 1200 mPa·s, even more preferably 100 mPa·s to 1000 mPa·s, even more preferably 300 mPa·s to 980 mPa·s, and particularly preferably 127.4 mPa·s to 953.2 mPa·s. In another embodiment, from the viewpoint of achieving both dispersibility and battery performance, the viscosity of the dispersion is more preferably 30 mPa·s to 1600 mPa·s, further preferably 300 mPa·s to 1600 mPa·s, and particularly preferably 400 mPa·s to 1600 mPa·s. In still other embodiments, from the perspective of prioritizing dispersibility in achieving both dispersibility and battery performance, the viscosity of the dispersion is more preferably 30 mPa·s to 1600 mPa·s, even more preferably 30 mPa·s to 1300 mPa·s, particularly preferably 30 mPa·s to 1200 mPa·s, even more preferably 30 mPa·s to 1000 mPa·s, and especially preferably 33.2 mPa·s to 953.2 mPa·s.

[0046] <Other matters regarding the CNT aggregate> In the present disclosure, the CNTs included in the CNT aggregate may be SWCNTs or MWCNTs. From the perspective that having a layer number distribution and slightly lower uniformity contributes to satisfying conditions (1) and (2), the CNT aggregate preferably contains SWCNTs and MWCNTs.

[0047] The maximum length of the CNTs included in the CNT aggregate according to the present disclosure is not particularly limited.

[0048] In one embodiment, the CNT aggregate may be an aggregate that mainly contains CNTs with a maximum length of 500 μm or less and does not contain CNTs with a length exceeding 500 μm and being 30000 μm or less. Here, the main component means that 90% by mass or more of the CNTs constituting the CNT aggregate are CNTs with a maximum length of 500 μm or less. The CNT aggregate may contain CNTs with a maximum length of 500 μm or less.

[0049] The CNT aggregate according to the present disclosure includes, for example, CNTs with a maximum length of 10 μm to 30000 μm. The CNT aggregate according to the present disclosure preferably contains CNTs with a maximum length of 500 μm or more, more preferably contains CNTs with a maximum length of 500 μm to 30000 μm, and even more preferably contains CNTs with a maximum length of 1000 μm to 30000 μm (i.e., ULCNTs).

[0050] Compared to general-purpose CNTs, ULCNTs are longer and can take the shape of fibers. When the maximum length of the CNTs contained in the CNT aggregate according to the present disclosure is 500 μm or more, the entanglement between the CNTs becomes moderately strong, and the CNTs tend to form a network structure more easily.

[0051] Being in the form of a fiber, ULCNTs have the property of easily entangling with each other. The CNT aggregate contains at least one ULCNT, and from the viewpoint that the CNTs are likely to entangle with each other and form a more stable aggregate, it is preferable that the CNT aggregate is an aggregate containing multiple ULCNTs. Hereinafter, an aggregate containing ULCNT may be abbreviated as "ULCNT aggregate."

[0052] Here, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two dimensions. The fiber may be a thread-like fiber with a circular cross section, a ribbon-like fiber with a rectangular cross section, hollow, or have another shape. From the viewpoint of increasing electrical conductivity, the cross section of the CNTs contained in the CNT aggregate is preferably circular, and is preferably hollow.

[0053] The CNT aggregate may be an aggregate having a three-dimensional structure in which the CNTs are entangled with one another. The entangled state of the CNTs in the CNT aggregate according to the present disclosure can be confirmed by SEM observation.

[0054] The length of the CNTs contained in a CNT aggregate can be measured by focusing on a single CNT and observing multiple SEM images taken at adjacent viewing angles. Here, "CNT length" refers to the measured length of the CNT in the longitudinal direction, and the maximum value of the measured lengths is taken as the "maximum length." When observing an SEM photograph, if one CNT with a maximum length in the range of 1000 μm to 30000 μm is observed within the viewing angle of the SEM photograph, it can be confirmed that the observed CNTs include ULCNTs.

[0055] It is preferable that multiple ULCNTs are present within the viewing angle of the SEM photograph. Focusing on 100 CNTs within the viewing angle of the SEM photograph, the maximum length of each is measured, and from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULCNTs, it is preferable that 10% or more of the observed CNTs (i.e., ULCNTs) have a maximum length in the range of 1,000 μm to 30,000 μm, calculated as numbers, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0056] The diameter of ULCNT can be measured by observing SEM or transmission electron microscope (TEM) photographs. Here, the diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULCNT. The diameter is measured at 10 different locations on a single ULCNT, and the average value is taken as the diameter of that ULCNT.

[0057] The length of the ULCNT is in the range of 1,000 μm to 30,000 μm, preferably in the range of 1,050 μm to 25,000 μm, more preferably in the range of 1,100 μm to 20,000 μm, even more preferably in the range of 1,200 μm to 18,000 μm, and particularly preferably in the range of 1,300 μm to 15,000 μm. The diameter of the ULCNT is preferably 1 nm to 100 nm, more preferably in the range of 2 nm to 80 nm, even more preferably in the range of 3 nm to 50 nm, and particularly preferably in the range of 5 nm to 30 nm.

[0058] The length / diameter ratio of ULCNT, so-called aspect ratio, is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 10,000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single ULCNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more ULCNTs.

[0059] From the perspective of dispersibility, the specific gravity of the ULCNT aggregate is preferably in the range of 1.5 to 2.5, more preferably in the range of 1.7 to 2.4, and even more preferably in the range of 1.8 to 2.2. The specific gravity of the ULCNT aggregate can be measured by the method described in JIS Z8807:2012 "Methods for Measuring the Density and Specific Gravity of Solids".

[0060] The purity of carbon in the CNT of the ULCNT aggregate can be measured by thermogravimetric analysis. For example, using a thermal analyzer (manufactured by Shimadzu Corporation, DTG-60), obtain the thermogravimetric (TG) curve and differential thermal analysis (DTA) curve of the ULCNT aggregate. Regarding the DTA curve where a peak top appears around 650 °C to 750 °C, consider the largest exothermic peak as the combustion of CNT, and consider the other exothermic peaks that appear as the combustion of substances other than CNT. Determine the purity of CNT from the weight loss rate of the TG curve. From the perspective of the conductivity obtained, the purity of the ULCNT aggregate is preferably 50% by mass or more, more preferably 65% by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more.

[0061] The obtained fibrous ULCNT is preferably flexible and strong. Also, the conductivity of the ULCNT itself is preferably -1 ·m -1 or more, and more preferably -1 ·m -1 or more. Note that the conductivity of the ULCNT itself is usually -1 ·m -1 or less.

[0062] <Method for Manufacturing CNT> The method for manufacturing CNT in the present disclosure is not particularly limited. For example, as the method for manufacturing CNT in the present disclosure, methods such as a conventionally known chemical vapor deposition (CVD) method and a method of reacting a gaseous reactant containing a carbon source in the presence of a catalyst can be applied.

[0063] The CNTs in the present disclosure can be produced by, for example, referring to the methods described in JP-A-2016-102047 and JP-A-2021-527611.

[0064] The CNT manufacturing method according to the present disclosure will be described below with reference to examples, although the CNT manufacturing method according to the present disclosure is not limited to the following examples.

[0065] =Manufacturing method X= An example of a CNT manufacturing method referred to in this disclosure is described in JP 2016-102047 A. That is, the manufacturing method includes the steps of passing gaseous reactants containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in a reaction zone of the reactor in the presence of a catalyst to form product particles containing carbon, aggregating the product particles into aggregates, and applying force to the aggregates to continuously move the aggregates out of the reaction zone (hereinafter also referred to as "Manufacturing Method X").

[0066] According to production method X, CNTs including ULCNTs can be obtained in the form of fibrous aggregates or other aggregate forms that are easy to handle.

[0067] In production method X, the force applied to the product particles may be a mechanical force. When the agglomerates are fibrous CNTs, the mechanical force applied to the product particles can be exerted by a rotating spindle around which the agglomerates are wound, and the fibrous CNTs can be collected on the spindle or accumulated elsewhere by rotating around the spindle one or more times and then successively unwinding the spindle.

[0068] 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.

[0069] The spindle can rotate around two axes (e.g., two perpendicular axes). In particular, the spindle can rotate around axes perpendicular and parallel to the flow direction of the gaseous reactants. Such a spindle can pull and twist the fibrous CNT aggregates to control the twist number and length.

[0070] The spindle may be made of metal, ceramic, or resin. The spindle can have different suitable shapes depending on the material properties and the intended use of the CNTs. The spindle can be used as a mold for producing carbon products, for example, by a spin-coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0071] Fibrous CNTs are deposited on a spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the application of electric or other fields to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by gas flow forces.

[0072] The rotation speed of the spindle is preferably 0.01 rpm (revolutions / minute; the same applies hereinafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the rotational speed of the spindle) may be adjusted so that the material is collected at a similar rate as it is produced. The rotational speed of the spindle may also control the thickness of the accumulated CNT fiber. In a preferred embodiment, as the spindle rotates, the CNT fiber is processed in the axial direction of the spindle. This processing ensures that the CNT fiber is evenly wrapped along the spindle, rather than being wrapped only at one specific point on the spindle.

[0073] The CNT fibers may be collected, for example, on the reactor wall by a substrate placed in the reactor. The substrate may be a fixed substrate or a rotating guide used to apply a strong and equal force to the CNT fibers as they are collected. A suitable substrate arrangement for fiber technology is a substrate consisting of two guides positioned at right angles to each other.

[0074] In production method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow may be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube downstream of the reaction zone. A vacuum may be applied to the product particles.

[0075] Another force that can be applied to the product particles is electrostatic force, which is suitably applied by a charged plate. Electrostatic force requires that the product particles be charged. By using a charged plate, the CNTs can be grown in the form of intertwined sheets on the charged plate.

[0076] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0077] Instead of a gaseous reactant containing a carbon source, the CNT precursor may be injected in the form of a liquid containing a carbon source. When a liquid is used as the CNT precursor, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0078] Preferably, the gaseous reactant(s) are reacted at a temperature between 500° C. and 1600° C., more preferably between 1000° C. and 1500° C. A temperature gradient is preferably maintained within the reactor, with the reaction zone being maintained at a higher temperature than the product zone of the reactor.

[0079] The gaseous reactants may be mixed with one or more gases that act as diluents. The gaseous reactants may also be mixed with gases that play a supporting but not direct role in the reaction. It is also preferred to use a diluent gas that can react with the amorphous carbon by-product, if any, to keep the reactive sites on the catalyst intact and produce nanotubes.

[0080] Gases that can be used as a diluent include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, helium, etc. Among these, hydrogen is particularly preferred as a gas that can be used as a diluent.

[0081] 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.

[0082] When the agglomerate is removed from the reactor, it is preferable to prevent air from entering the reactor, which is particularly important when the diluent gas contains hydrogen, for example, in order to prevent an explosive mixture of hydrogen and air from forming in the reactor.

[0083] The product particles in production method X contain ULCNTs. Depending on the production conditions, SWCNTs and MWCNTs may also be contained.

[0084] 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.

[0085] Carbon-containing compounds suitable as carbon sources include carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, and hydrocarbons containing mixtures of two or more thereof). The carbon-containing compound is preferably carbon monoxide, methane, ethylene or acetylene.

[0086] 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.

[0087] The catalyst is preferably a transition metal, particularly a group VIB transition metal such as chromium (Cr), molybdenum (Mo), or tungsten (W), or a group VIIIB transition metal. Specifically, the catalyst is preferably, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or manganese (Mn), or a mixture thereof. Metals from the lanthanide and actinide series (e.g., yttrium (Y)) can also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof, such as a mixture of Ni and Co (50 / 50 by mass), a mixture of Fe and Ni, or a mixture of Fe and Mo, are more preferred. Any of these transition metals, either alone or in combination with any of the other transition metals listed, can serve as a catalyst for CNT growth, with it being particularly preferred that the catalyst be a mixture of two or more of the listed metals.

[0088] The catalyst is preferably formed by decomposition of a precursor. The precursor is preferably a thermally, photo-, or plasma-decomposable compound of one or more of the above metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickelocene, and cobaltocene are particularly preferred precursors. In one embodiment, at least 0.01% by mass of the precursor is contained in the carbon source, preferably 0.2% to 30% by mass of the precursor, and more preferably 0.2% to 20% by mass of the precursor. In one embodiment, 0.23% to 2.3% by mass of the precursor may be contained in the carbon source, and 0.02% to 20% by mass of the precursor may be contained in the carbon source. The catalyst may be used supported on a carrier, and preferred carriers include silica and magnesium oxide.

[0089] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters are one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is also a preferred promoter. Suitably, up to 10% by weight of the promoter is included in the carbon source. Preferably, 0.2% to 6% by weight of the promoter is included in the carbon source. When high or low concentrations of thiophene are used as the promoter, MWCNTs are formed.

[0090] According to production method X, it is possible to obtain fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm. The fibrous CNTs can be in the form of threads or sheets. The length of the fibrous CNT can be controlled, for example, by the winding capacity of the spindle used in producing the fibrous CNT.

[0091] 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.

[0092] Preferably, production method X further comprises, after the step of aggregating the CNTs into aggregates, a step of passing the resulting CNT aggregates through a sieve. Also, it is preferable to recover the CNTs that have passed through the sieve. By passing the obtained CNT aggregate through a sieve, it becomes easy to obtain a CNT aggregate that satisfies the conditions (1) and (2).

[0093] The method for passing the material through a sieve is not particularly limited, and any commonly known method can be used. The mesh size of the sieve is, for example, 0.1 mm to 3.0 mm, preferably 0.5 mm to 2.0 mm, and more preferably 1.0 mm to 1.5 mm. The material of the sieve is not particularly limited, and may be metal or resin. When the CNT aggregate is applied to an electrode (particularly an electrode of a lithium ion battery), it is preferable that the material does not impair the performance of the battery. The number of times the material is passed through the sieve is, for example, 1 to 3 times. Before passing the CNT agglomerates through a sieve, the CNT agglomerates may be cut into pieces of an appropriate size.

[0094] It is also preferable to use two types of sieves with different mesh sizes and pass the material through the sieves at least twice. By using the sieve with the smaller mesh size of the two types of sieves, it is possible to remove amorphous carbon that has become dusty. By using the sieve with the larger mesh size of the two types of sieves, it is possible to remove foreign matter, coarse CNTs, etc. that have been mixed in from the outside.

[0095] The resulting CNT agglomerates are passed through a sieve and the CNTs that pass through the sieve are collected, thereby removing coarse CNTs and improving the stability of the CNT dispersion. Furthermore, in general, in the manufacture of electrodes, foreign matter that has been mixed in from the outside is removed, but by passing the obtained CNT agglomerates through a sieve, it is possible to more easily remove foreign matter that has been mixed in from the outside.

[0096] In another embodiment, a method may be adopted in which CNTs containing ULCNTs are generated in a reaction region by the above method, and then condensed to form CNTs containing ULCNTs, and the CNTs are continuously withdrawn from the vicinity of the reaction region. In another embodiment, a method may be adopted that includes producing CNTs containing ULCNTs in a reaction region, continuously electrostatically attracting the CNTs containing ULCNTs from the reaction region, and recovering the CNTs containing ULCNTs.

[0097] =Manufacturing method Y= In the present disclosure, the manufacturing method described in JP-A 2021-527611 can be referred to as an example of a method for manufacturing CNTs. That is, the manufacturing method includes a step (1) of supporting a mixture containing a main catalyst precursor and a co-catalyst precursor on γ-Al2O3 to manufacture an active support, a step (2) of drying the active support by multistage drying including vacuum drying, a step (3) of subjecting the dried active support to a heat treatment to manufacture a supported catalyst, and a step (4) of manufacturing CNTs in the presence of the supported catalyst (hereinafter also referred to as "manufacturing method Y").

[0098] ·Process (1) In step (1), a mixture containing a main catalyst precursor and a co-catalyst precursor is supported on γ-Al 2 O 3 to produce an active support.

[0099] In order to uniformly support the main catalyst precursor and the co-catalyst precursor on γ-AlO, the mixture may further contain a solvent, and the main catalyst precursor and the co-catalyst precursor may be dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, and water is preferred.

[0100] Because γ-Al2O3 has high porosity and a spinel structure, the main catalyst and promoter can be randomly arranged in γ-Al2O3. CNTs grown from the randomly arranged main catalyst can be produced in an entangled state.

[0101] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese and chromium, with cobalt being preferred.

[0102] 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.

[0103] The main catalyst precursor may be one or more selected from the group consisting of Co(NO3)2, Co(NO3)2·6H2O, Co2(CO)8, Co2(CO)6[HC=C(C(CH3)3)], Co(CH3CO2)2, Fe(NO3)3, Fe(NO3)2·nH2O, Fe(CH3CO2)2, Ni(NO3)2, Ni(NO3)2·6H2O, Mn(NO3)2, Mn(NO3)2·6H2O, Mn(CH3CO2)2·n(H2O) and Mn(CO)5Br, of which Co(NO3)2·6H2O, Fe(NO3)2·nH2O and Ni(NO3)2·6H2O are preferred.

[0104] The promoter improves the dispersibility of the main catalyst, and may be one or more selected from the group consisting of vanadium and molybdenum.

[0105] The promoter precursors were NH4VO3, NaVO3, V2O5, V(C5H7O2)3, and (NH4)6Mo7O. 24 4H2O, NH4VO3 and (NH4)6Mo7O 24 Preferably, one or more selected from the group consisting of 4H2O.

[0106] When the mixture contains two or more promoter precursors, i.e., when it contains both a vanadium precursor and a molybdenum precursor, the molar ratio of the sum of vanadium and molybdenum to vanadium can be 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and preferably 1:0.5 to 1:0.9. When the above conditions are met, the CNT structure can be stably maintained and CNTs with the desired pore volume can be produced.

[0107] The mixture may contain the main catalyst precursor and the co-catalyst precursor such that the molar ratio of the main catalyst to the co-catalyst is 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, and preferably 1:0.1 to 1:0.25. Satisfying the above molar ratio improves the dispersibility of the main catalyst, enabling the production of CNTs with the desired pore volume.

[0108] The mixture may further include an organic acid which serves to inhibit precipitation of the main catalyst precursor and the co-catalyst precursor.

[0109] 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.

[0110] The mixture may contain the organic acid and the co-catalyst precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, preferably 1:3 to 1:6. When the above range is satisfied, it is possible to produce a transparent catalyst metal solution during catalyst production, and it is advantageous in that it is possible to produce a catalyst in which fine particles are suppressed during impregnation.

[0111] After step (1), a step of aging may be further included.

[0112] The aging may be carried out for 1 to 60 minutes or 10 to 50 minutes. Preferably, it is carried out for 10 to 50 minutes. When the above conditions are satisfied, the main catalyst precursor and the co-catalyst precursor can be sufficiently supported on the γ-Al2O3. In addition, air bubbles present in the support are removed to the maximum extent possible, and the main catalyst precursor and the co-catalyst precursor can be sufficiently supported even in the fine pores inside the support.

[0113] ·Process (2) The active support is then dried by multi-stage drying, including vacuum drying.

[0114] 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.

[0115] The vacuum drying may be carried out at 80° C. to 300° C. or 120° C. to 250° C., preferably at 120° C. to 250° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] Drying at normal pressure may be carried out at 80°C to 160°C or 100°C to 140°C, and is preferably carried out at 100°C to 140°C. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0120] Drying at atmospheric pressure may be performed at 900 mbar to 1,100 mbar, preferably 950 mbar to 1,050 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0121] 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.

[0122] 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.

[0123] The primary vacuum drying can remove any solvent that may be present in the active support.

[0124] 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.

[0125] The primary vacuum drying can be carried out for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0126] 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.

[0127] The secondary vacuum drying is as described above in the description of vacuum drying.

[0128] 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.

[0129] The secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, and more preferably at 1 mbar to 70 mbar. If the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0130] 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.

[0131] ·Process (3) The dried active support is then subjected to a heat treatment to produce a supported catalyst.

[0132] By carrying out the heat treatment, a supported catalyst is produced in which the main catalyst and the promoter are present in a coated state on the surface and in the pores of γ-Al2O3.

[0133] The heat treatment may be carried out at 600 to 800°C or 620 to 750°C, preferably at 620 to 750°C. If the above conditions are met, a supported catalyst can be produced in which the main catalyst and the co-catalyst are uniformly coated on the surface and pores of the γ-Al2O3, and energy consumption can be minimized.

[0134] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, preferably 2 to 8 hours. When the above-mentioned time is satisfied, a supported catalyst can be produced in which the catalyst precursor is uniformly coated on the surface and in the pores of γ-AlO.

[0135] ·Process (4) CNTs are then produced in the presence of a supported catalyst.

[0136] Specifically, CNTs can be produced by contacting a supported catalyst with a carbon-based compound, and specifically, by chemical vapor synthesis.

[0137] To explain the steps for producing CNTs in detail, first, a supported catalyst is loaded into a horizontal fixed-bed reactor or a fluidized-bed reactor. Next, the gaseous carbon-based compound or a mixture of the gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen) is injected at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the supported catalyst. CNTs can be grown by chemical vapor synthesis through the decomposition of the gaseous carbon-based compound.

[0138] The CNTs produced by the above-mentioned chemical vapor synthesis method have a crystal growth direction that is nearly parallel to the tube axis, and the graphite structure has high crystallinity along the tube length. As a result, CNTs with small unit diameters and high conductivity and strength can be produced.

[0139] The chemical vapor synthesis method may be carried out at 600° C. to 800° C. or 650° C. to 750° C., and is preferably carried out at 650° C. to 750° C. If the above temperature is satisfied, CNTs can be produced while minimizing the generation of amorphous carbon.

[0140] The heat source for the reaction may be induction heating, radiant heat, laser, IR, microwave, plasma, surface plasmon heating, or the like.

[0141] In addition, the carbon-based compound can supply carbon and can be used without particular limitation as long as it can exist in a gaseous state at a temperature of 300°C or higher.

[0142] The carbon-based compound may be a carbon-based compound having 6 or less carbon atoms, and may be at least one 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.

[0143] After growing CNTs by the above reaction, a cooling process for more regularly aligning the CNT arrays may be selectively further performed. Specifically, the cooling process can be performed by natural cooling by removing the heat source or using a cooler or the like.

[0144] The above production method X and production method Y are examples, and the production method of CNTs that can be included in the CNT aggregate is not limited to the above.

[0145] 〔Carbon nanotube dispersion〕 The carbon nanotube dispersion (CNT dispersion) according to the present disclosure includes a CNT aggregate and a dispersion medium. The CNT dispersion has good dispersibility of the CNT aggregate according to the present disclosure in the dispersion medium and excellent conductivity. The CNT dispersion is preferably used for forming electrodes, forming transparent conductive films, resin additives, conductive inks, coating agents, antistatic agents, paints, and the like.

[0146] <CNT aggregate> Since the CNT aggregate included in the CNT dispersion is the same as the CNT aggregate according to the present disclosure described above, the description thereof is omitted here.

[0147] <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.

[0148] The water is not particularly limited, but is preferably distilled water, ion-exchanged water, pure water, or the like, which contains fewer impurities.

[0149] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of hydrophilic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0150] The CNT dispersion may further contain other components that can be used in the dispersion in addition to the CNT aggregates and the dispersion medium. Examples of other components include dispersants, antifoaming agents, antistatic agents, conductive assistants other than the conductive assistant according to the present disclosure, etc. Furthermore, the composition may further contain trace amounts of impurity components, so-called inevitable impurities, etc.

[0151] <Dispersant> The CNT dispersion may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the CNT aggregates. The dispersant is not particularly limited and may be, for example, various surfactants. The dispersant may also be a polymer compound such as a resin. The dispersant is preferably a surfactant. The surfactant may be an ionic surfactant or a nonionic surfactant, and is not particularly limited. In the CNT dispersion, the surfactant may be used alone or in combination of two or more.

[0152] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzenesulfonates (e.g., dodecylbenzenesulfonic acid) and dodecylphenyl ether sulfonates; ether sulfate surfactants; phosphate surfactants; and carboxylic acid surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. As the ionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic ionic surfactant) is preferred, and aromatic sulfonic acid surfactants such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate are more preferred. Aromatic ionic surfactants tend to be excellent in dispersibility, dispersion stabilization, and concentration of CNT aggregates.

[0153] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers and polyoxyethylene polypropylene glycols; and aromatic nonionic surfactants such as polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, polyoxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl cumyl phenyl ether and polyoxyalkylene phenyl ether. As the nonionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic nonionic surfactant) is preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersing ability, dispersion stabilizing ability, and concentration enhancement for CNT aggregates.

[0154] Other dispersants that are excellent in CNT dispersibility, dispersion stabilization, and concentration enhancement include DEMOL (registered trademark: the same applies hereinafter) N, DEMOL RN, and DEMOL T (manufactured by Kao Corporation), which are sodium salts of β-naphthalenesulfonic acid formalin condensates; Brij S 100 (manufactured by Sigma-Aldrich), which is a polyoxyethylene stearyl ether; polyvinylpyrrolidone K30 (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (manufactured by, for example, Daicel Miraize Co., Ltd.); sodium deoxycholate (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); and SOLSPERSE TM W100, SOLSPERSE TM W150 (manufactured by Lubrizol Japan, Inc.) is particularly preferred from the viewpoint of excellent dispersibility, dispersion stabilization ability, and high concentration of CNT aggregates.

[0155] When the CNT dispersion liquid contains a dispersant, the amount of the dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of CNT aggregates, the amount of dispersion medium, and the like.

[0156] [Method for producing CNT dispersion liquid] The method for producing the CNT dispersion liquid is not particularly limited. A CNT dispersion can be produced by dispersing a CNT aggregate in a dispersion medium. That is, a CNT dispersion can be produced by a method including a step of dispersing a CNT aggregate in a dispersion medium (also referred to as a "dispersion step"). The dispersion medium that can be used in the dispersion step is as described above.

[0157] The dispersion method is not particularly limited. Examples of the dispersion method include methods using a dispersion device such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Further, examples of the dispersion method include methods using known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, a vertical or horizontal agitator mill, an attritor, a colloid mill, a three-roll mill, a pearl mill, a super mill, an impeller, a disperser, a KD mill, a dynatron, a pressure kneader, or the like. As a dispersion method, a method using a jet mill is preferred, and a method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pumps a mixture in a solvent as a high-speed flow through a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, CNT aggregates are dispersed by collisions between opposing flows in the pressure-resistant container, collisions with the container wall, turbulence caused by the high-speed flow, shear flow, and the like. An ultra-high-pressure homogenizer (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used as the wet jet mill. However, the wet jet mill is not limited to this. When the ultra-high pressure homogenizer is used as the dispersing device, the processing pressure for dispersion is preferably 10 MPa to 250 MPa.

[0158] The method for producing a CNT dispersion may include a step of drying the CNT aggregate (also referred to as a "drying step") before the dispersion step.

[0159] If water adheres to the CNTs, the surface tension of the water makes them more likely to adhere to each other, which can lead to a decrease in dispersibility. Therefore, by performing a drying process for the conductive additive before the dispersion process, the water adhering to the CNTs is removed, preventing the CNTs from adhering to each other due to water adhesion, and further improving the dispersibility of the CNTs in the dispersion medium. The drying method is not particularly limited. Drying methods include, for example, heat drying, vacuum drying, and heat vacuum drying. The drying method is preferably heated vacuum drying. The drying temperature is not particularly limited, and is preferably 40°C to 100°C, for example. The drying time is not particularly limited and can be set appropriately depending on the drying temperature, the degree of moisture adhesion to the CNT aggregate in the present disclosure, and the like.

[0160] An example of producing a CNT dispersion liquid will be shown below, but the production of a CNT dispersion liquid is not limited to the following.

[0161] <Production Example 1: Example of production of dispersion liquid> 0.040 g of the CNT aggregate according to the present disclosure is weighed and placed in a three-neck flask. After the CNT aggregate is placed in the flask, a large excess of ion-exchanged water (e.g., 20 mL) is poured into the flask and stirred at room temperature (25°C, the same applies below). At this time, a known dispersant (e.g., carboxymethyl cellulose) may be added as appropriate. Next, a conductive additive is dispersed in the dispersion medium using a known dispersion device (e.g., an ultrasonic irradiation device or a wet jet mill). The obtained dispersion is further stirred with a stirrer at room temperature for a long period of time (e.g., 1 hour to 48 hours). In this way, a CNT dispersion is obtained.

[0162] [Conductive materials] The conductive material according to the present disclosure includes a CNT aggregate. As described above, the CNT aggregates contained in the conductive material according to the present disclosure have excellent conductivity when made into a dispersion, and are therefore suitable as a conductive auxiliary agent. The conductive material according to the present disclosure includes the CNT aggregate according to the present disclosure, and therefore has excellent conductive efficiency and can effectively impart high conductivity to an object of use.

[0163] 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.

[0164] 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.

[0165] <Electrode> An electrode according to the present disclosure includes an electrode active material and a conductive material according to the present disclosure. The electrode according to the present disclosure contains the conductive material according to the present disclosure, and therefore has excellent conductive path formation properties within the electrode, and therefore the secondary battery according to the present disclosure has excellent cycle characteristics.

[0166] In the electrode, the CNT aggregates can function as a conductive additive. The CNT aggregate contained in the electrode described below is synonymous with the CNT aggregate according to the present disclosure, and preferred embodiments are also the same, so description of the CNT aggregate will be omitted below.

[0167] 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.

[0168] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has electrical conductivity. The current collector may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal such as copper or nickel that has good carbon adsorption properties may be used as the current collector.

[0169] The electrode active material layer can include an electrode active material. The electrode active material is preferably electrode active material particles. When the electrode is a positive electrode, the electrode active material is not particularly limited, and the electrode active material layer can contain a positive electrode active material that is commonly used as an electrode material for a positive electrode. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2Ni-site type lithium nickel oxide represented by O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.66); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1), or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion.

[0170] 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 usually used for negative electrode materials. Specifically, the negative electrode active material can contain graphite-based active material particles or silicon-based active material particles. As the graphite-based active material particles, at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads may be used. By using artificial graphite as the graphite-based active material particles, the rate characteristics can be improved. As the silicon-based active material particles, at least one selected from the group consisting of Si, SiOx (0 < x < 2), Si-C composite, and Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a transition metal, a Group 13 element, a Group 14 element, a rare earth element, and a combination thereof) may be used. By using the silicon-based active material particles, the battery can be made to have a higher capacity.

[0171] The electrode active material layer can further contain a binder. The binder is not particularly limited, and the electrode active material layer can contain a binder usually used for electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers have been substituted with Li, Na, Ca, or the like.

[0172] <Secondary battery> A secondary battery according to the present disclosure includes an electrode according to the present disclosure. The secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode according to the present disclosure.

[0173] The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move, and is not particularly limited as long as it is a separator that is typically used as a separator in a secondary battery. The separator preferably has low resistance to ion movement of the electrolyte and is excellent in the ability to retain moisture in the electrolyte solution. A specific example of the separator is a porous polymer film. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure in which two or more layers of these films are laminated. The separator may also be a typical porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. The separator may also be coated with a ceramic component or a polymeric substance to ensure heat resistance or mechanical strength. The separator may optionally be of a single layer or multi-layer structure.

[0174] 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.

[0175] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt. Examples of non-aqueous organic solvents include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0176] 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.

[0177] The metal salt may be a lithium salt. Lithium salts are substances that are easily dissolved in non-aqueous electrolytes. The anion portion of the lithium salt may be, for example, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Examples include:

[0178] In addition to the non-aqueous organic solvent and metal salt, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purposes of improving the battery's life characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[0179] The above-described secondary battery can be configured into a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack can be used as a power source for a medium to large device selected from the group consisting of, for example, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[0180] <Planar aggregate> The planar aggregate according to the present disclosure includes the CNT aggregate according to the present disclosure. The proportion of the CNT aggregate according to the present disclosure contained in the planar aggregate according to the present disclosure is typically 1 mass % or more relative to the total mass of the planar aggregate. The planar aggregate according to the present disclosure may contain components other than the CNT aggregate according to the present disclosure.

[0181] An example of the planar aggregate according to the present disclosure is a film including the CNT aggregate according to the present disclosure.

[0182] Planar assemblies according to the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0183] The method for producing the planar assembly according to the present disclosure is not particularly limited. The planar aggregate according to the present disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate by dispersing the CNT aggregate according to the present disclosure in water or other fluid and filtering it once or twice or more times.

[0184] <Laminate> A laminate according to the present disclosure includes a substrate and a planar assembly according to the present disclosure. The substrate and the planar assembly may be in direct contact with each other, or another layer may be disposed between the substrate and the planar assembly. Alternatively, the planar assembly according to the present disclosure may be disposed on a substrate, and another layer may be disposed on the planar assembly.

[0185] The material constituting the substrate may be resin, glass, or fiber. Examples of resins include polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin polymer (COP), triacetate (TAC), cyclic olefin copolymer (COC), poly(vinyl chloride) (PVC), polyethylene 2,6-naphthalate (PEN), polyimide (PI), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), polyacetal (POM), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polyphenylene ether (PPE), polysulfone (PSU), polyether ether ketone (PEEK), and polyamide imide (PAI). Glasses include, for example, float glass (containing SiO2, Na2O, CaO, MgO), soda lime, aluminosilicate glass, and borosilicate glass. Examples of fibers include synthetic fibers such as polyester fibers, polyamide fibers, polyolefin fibers, and acrylic fibers; and natural fibers such as cotton, linen, silk, wool, cashmere, mohair, alpaca, jute, hemp, and ramie.

[0186] The planar aggregate preferably contains a binder in addition to the CNT aggregate according to the present disclosure. The binder is preferably a polymer, and preferably contains at least one selected from the group consisting of polymers containing structural units derived from vinylidene chloride (e.g., polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer, etc.), polyimide, polysiloxane, and epoxy resin. [Example]

[0187] The CNT aggregate and the like according to the present disclosure will be described more specifically below with reference to examples. The present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure.

[0188] Example 1 1. Production of sheet-shaped CNT aggregate 1 Sheet-like CNT aggregate 1 was produced by the floating catalyst method (CVD method), which directly interacts with the self-assembly of CNT bundles in the gas phase. A cylindrical reactor with an inner diameter of 85 mm was used as the CNT reactor. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled between 200 and 800°C. Hydrogen gas was used as the carrier gas. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor is decomposed. The region where the metal catalyst precursor is decomposed is referred to as the first temperature zone.

[0189] Next, methane, a carbon source, was released into the carrier gas flow. The metal catalyst and carbon source were supplied to a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The total gas supply flow rate of the carrier gas and source gas was 34 NL / min (NL is normal liters). The thiophene / hydrogen gas flow rate ratio was set to Range A in Table 1. The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0190] [Table 1]

[0191] In the second temperature zone, a reaction field was generated in the temperature-controlled flow reactor to form catalyst nuclei and rapidly grow CNTs, thereby generating aggregates of CNTs. The aggregates were continuously discharged through the outlet of the flow reactor whose temperature was controlled at 200°C to 700°C, and the sheet-like CNT aggregates were collected. The obtained sheet-like CNT aggregates were washed with pure water for 10 seconds, then crushed into powder, and further passed through a sieve with a mesh size of 1.0 mm twice. The CNT aggregates passing through the sieve were collected and designated as CNT aggregate 1.

[0192] 2. Preparation of CNT dispersion 1 The following materials were mixed and pre-dispersed by treating them with an Ace homogenizer manufactured by Nippon Seiki Co., Ltd. for 1 hour to obtain pre-dispersion liquid 1.

[0193] (Dispersion liquid composition) · 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

[0194] The main dispersion of pre-dispersion liquid 1 was carried out using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Tokuyama Corporation as a wet jet mill under the following conditions to obtain CNT dispersion 1 with a concentration of 0.20% by mass. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 times Method: Circulation method

[0195] <Content of amorphous carbon with respect to the total mass of CNT aggregates> The amount of amorphous carbon was quantified by thermogravimetric differential thermal analysis (TG-DTA). Using a thermal analyzer (model number: STA200, manufactured by Hitachi High-Tech Corporation), thermogravimetric differential thermal analysis was performed under air circulation at a heating rate of 10 °C / min. Approximately 10 mg of the sample was weighed into a Pt pan, and the content of amorphous carbon was calculated from the difference in weight loss at 200 °C and 400 °C when the temperature was raised to 900 °C at a rate of 10 °C / min.

[0196] <Ratio of area with bundle diameter of 100 nm or more> Regarding the CNT aggregate 1 of Example 1, imaging was performed using a scanning electron microscope (SEM: Scanning Electron Microscope). Among the obtained images, two images in which CNT bundles were well observed were selected (one of them is Figure 1). Image processing and image analysis were performed on the selected images using Python. In image processing, the contour of the CNT and the center line of the CNT were detected and synthesized with the original image. In image analysis, the bundle diameter was obtained by calculating the distance from the center line to the contour of the created image. Then, the product of the bundle diameter and the length of the center line was calculated to calculate the exclusive area of CNTs in the image. A histogram of the bundle diameter and the exclusive area was made.

[0197] Using the calculated bundle diameter histogram, the characteristic quantity of the bundle diameter of each sample was calculated by the following method. 1. The bundle diameters and exclusive areas of multiple fields of the same sample were added together and normalized so that the sum was 1. Along with the normalization, the unit of the vertical axis was set as the exclusive area ratio. 2. The total value of the exclusive area ratio of bundles with a bundle diameter of 100 nm or more was obtained. As a result, the area ratio with a bundle diameter of 100 nm or more was 0.17.

[0198] <Viscosity of the dispersion of CNT aggregates> The viscosity of the CNT dispersion 1 was measured using a cone-plate viscometer (also known as an E-type viscometer). Specifically, the viscosity was measured using a cone-plate viscometer (DV-II+Pro PROGRAMMABLE VISCOMETER manufactured by BROOKFIELD). Measuring tool: cone and plate Measurement mode: Rotation mode Shear rate: 0.6s -1 ~384s -1 Temperature: 25℃ From the obtained data, a shear rate of 12 s -1 The viscosity was read. The viscosity of the dispersion was 434.0 mPa·s. Table 2 lists the common logarithm of the viscosity.

[0199] <Elongation at break> CNT dispersion liquid 1 was poured onto a 22 mm × 75 mm × 3 mm slide-type silicon plate (Dosaka EM Co., Ltd., #08-1044), heated to 100 °C, and dried for 30 minutes to prepare a measurement sample. The measurement sample was fixed to the gripper of a tensile testing device (Shimadzu Corporation, Autograph AG-IS), and a tensile test was performed at a speed of 1 mm / min. The point where the test force was maximum was regarded as the breaking point, and the breaking elongation was calculated, which was 1.5%.

[0200] Example 2 1. Production of CNT aggregate 2 CNT aggregate 2 was produced in the same manner as CNT aggregate 1, except that the temperature of the second temperature zone was controlled to 1320°C and the total gas supply flow rate of the carrier gas and raw material gas was set to 17 NL / min.

[0201] 2. Preparation of CNT Dispersion 2 Using the obtained CNT aggregate 2, a pre-dispersion liquid 2 was obtained in the same manner as in Example 1.

[0202] The pre-dispersion liquid 2 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 2. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 200 MPa Number of times: 8 Method: Circulation method The viscosity of the dispersion was measured in the same manner as in Example 1 and was found to be 33.2 mPa·s.

[0203] 3. Evaluation CNT aggregate 2 of Example 2 was imaged using an SEM, and from the obtained images, three images in which the CNT bundles were clearly observed were selected (one of which is Figure 2), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0204] Example 3 1. Production of CNT aggregate 3 The CNT aggregate 3 was produced by mixing the following CNT aggregate 3A and the following CNT aggregate 3B. The CNT aggregate 3A was produced in the same manner as the CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and the raw material gas was set to 35 NL / min. The CNT aggregate 3B was produced in the same manner as the CNT aggregate 1, except that the total gas supply flow rate of the carrier gas and the raw material gas was set to 36 NL / min.

[0205] 2. Preparation of CNT Dispersion 3 Using the obtained CNT aggregate 3, a pre-dispersion liquid 3 was obtained in the same manner as in Example 1.

[0206] The pre-dispersion liquid 3 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 CNT dispersion liquid 3, which is a specific CNT dispersion liquid. (dispersion condition) Nozzle diameter: 0.22 mm Pressure: 50 MPa Number of times: 3 Method: Circulation method The viscosity of the dispersion was measured in the same manner as in Example 1 and was found to be 798.2 mPa·s.

[0207] 3. Evaluation CNT aggregate 3 of Example 3 was imaged using an SEM, and from the obtained images, four images in which CNT bundles were clearly observed were selected (one of which is FIG. 3), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0208] Example 4 1. Preparation of CNT aggregate 4 CNT aggregate 4 was produced in the same manner as CNT aggregate 1, except that the temperature of the second temperature zone was controlled to 1400°C and the total gas supply flow rate of the carrier gas and raw material gas was set to 34.2 NL / min.

[0209] 2. Preparation of CNT Dispersion 4 Using the obtained CNT aggregate 4, a pre-dispersion liquid 4 was obtained in the same manner as in Example 1.

[0210] The pre-dispersion liquid 4 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 4. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 Method: Circulation method The viscosity of the dispersion was measured in the same manner as in Example 1 and was found to be 953.2 mPa·s.

[0211] 3. Evaluation CNT aggregate 4 of Example 4 was imaged using an SEM, and from the obtained images, three images in which CNT bundles were clearly observed were selected (one of which is FIG. 4), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0212] Example 5 1. Production of CNT aggregate 5 CNT aggregate 5 was produced in the same manner as CNT aggregate 1, except that the temperature of the second temperature zone was controlled to 1400°C and the total gas supply flow rate of the carrier gas and raw material gas was set to 34.1 NL / min.

[0213] 2. Preparation of CNT Dispersion 5 Using the obtained CNT aggregate 5, a pre-dispersion liquid 5 was obtained in the same manner as in Example 1.

[0214] The pre-dispersion liquid 5 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 5. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 150 MPa Number of times: 8 Method: Circulation method The viscosity of the dispersion was measured in the same manner as in Example 1 and was found to be 127.4 mPa·s.

[0215] 3. Evaluation CNT aggregate 5 of Example 5 was imaged using an SEM, and from the obtained images, three images in which CNT bundles were clearly observed were selected (one of which is FIG. 5), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0216] Example 6 1. Production of CNT aggregate 6 The CNT aggregate 6 was produced in the same manner as the CNT aggregate 1, except that the temperature of the second temperature zone was controlled to 1400°C, the total gas supply flow rate of the carrier gas and the raw material gas was set to 41.9 NL / min, and the flow rate ratio of thiophene / hydrogen gas was set to range B in Table 1.

[0217] 2. Preparation of CNT Dispersion 6 Using the obtained CNT aggregate 6, a pre-dispersion liquid 6 was obtained in the same manner as in Example 1.

[0218] The pre-dispersion liquid 6 was subjected to main dispersion using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill under the following conditions to obtain CNT dispersion liquid 6. (Dispersion conditions) Nozzle diameter: 0.22 mm Pressure: 250MPa Number of times: 8 Method: Circulation method The viscosity of the dispersion was measured in the same manner as in Example 1 and was found to be 14.4 mPa·s.

[0219] 3. Evaluation CNT aggregate 6 of Example 6 was imaged using an SEM, and from the obtained images, three images in which CNT bundles were clearly observed were selected (one of which is FIG. 6), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0220] (Comparative Example 1) 1. Preparation of Powdered CNT Aggregates 7 As the powdered CNT aggregate 7, carbon nanotubes manufactured by C-nano (catalog number: FT9100) were prepared.

[0221] 2. Preparation of CNT Dispersion 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 Powdered CNT aggregate 7 of Comparative Example 1 was imaged using an SEM, and from the obtained images, three images in which CNT bundles were clearly observed were selected (one of which is FIG. 7), and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0223] (Comparative Example 2) 1. Preparation of Powdered CNT Aggregates 8 As the powdered CNT aggregate 8, carbon nanotubes manufactured by C-nano (catalog number: FT7000) were prepared.

[0224] 2. Preparation of CNT Dispersion 8 Using the prepared powdered CNT aggregate 8, a CNT dispersion liquid 8 was obtained in the same manner as in Example 1.

[0225] 3. Evaluation The powdered CNT aggregate 8 of Comparative Example 2 was imaged using an SEM, and from the obtained images, two images in which the CNT bundles were clearly observed were selected (one of which is FIG. 8), and evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0226] Next, a lithium ion secondary battery was fabricated.

[0227] 1. Preparation of a positive electrode for lithium secondary batteries Cathode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2), a conductive material (acetylene black), and a binder (PVdF) were mixed in a ratio of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and N-methyl-2-pyrrolidone was added and kneaded to prepare a paste-like positive electrode mixture. The resulting positive electrode mixture was applied to a 15 μm thick Al foil as a current collector, and the resulting mixture was vacuum dried at 80°C for 1 hour, followed by roll pressing to obtain a positive electrode for a lithium secondary battery. The positive electrode area was 1.65 cm2 and the coating weight was 16 mg / cm2. 2 , density is 3.0g / cm 3 It was adjusted so that

[0228] 2. Preparation of a negative electrode for lithium secondary batteries The negative electrode for the lithium secondary battery was prepared by mixing a 9:1 (mass ratio) mixture of artificial graphite MAG-E and carbon-coated SiO as the negative electrode active material, CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the binder, and the CNT dispersion as the conductive additive in a weight ratio of 94.9:5.0:0.1 to prepare a paste-like negative electrode mixture. Ion-exchanged water was used as the solvent for preparing the negative electrode mixture. The resulting negative electrode mixture was applied to a 20 μm thick Cu foil using a single-sided continuous coater, dried at 120°C, and then roll-pressed to obtain a negative electrode for a lithium secondary battery. The negative electrode area was 1.77 cm. 2 , basis weight 9.3mg / cm 2 , density is 1.4g / cm 3It was adjusted so that

[0229] 3. Fabrication of Lithium Secondary Batteries The positive electrode for the lithium secondary battery was placed on the bottom cover of a coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator consisting of a polyethylene porous film with a 16 μm heat-resistant porous layer was placed on top of it. 300 μL of electrolyte was poured into the separator. The electrolyte was a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with 1% vinylene carbonate added by volume, and LiPF6 dissolved therein to a concentration of 1.3 mol / L. Next, the negative electrode for the lithium secondary battery was placed on top of the laminated film separator, and the top cover was placed with a gasket in between. The assembly was then crimped using a crimping machine to produce a coin-type full-cell R2032 lithium secondary battery. These operations were carried out in a glove box under an argon atmosphere.

[0230] 4. Cycle test The fabricated lithium ion battery was subjected to a 200-cycle cycle test under the conditions shown below, and the discharge capacity retention rate after 200 cycles was calculated using the following formula: A higher discharge capacity retention rate after 200 cycles indicates better life characteristics. Discharge capacity retention rate after 200 cycles (%) = 200th discharge capacity / 1st discharge capacity × 100

[0231] <Cycle test conditions> Test temperature: 25℃ Charging conditions: Constant current constant voltage charging, maximum charging voltage 4.2V, charging time 5 hours, charging current 0.3CA Pausing time after discharge: 10 minutes Discharge conditions: Constant current discharge, minimum discharge voltage 2.5V, discharge current 0.3CA Downtime after charging: 10 minutes In this test, one cycle was defined as a cycle in which charging, discharging, discharging, and charging were performed in that order.

[0232] The evaluation results for Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 2.

[0233] [Table 2]

[0234] As shown in Table 2, the CNT aggregates of Examples 1 to 6 satisfy the conditions (1) and (2), and therefore it was found that they had high discharge capacity retention rates and excellent cycle characteristics.

Claims

1. An aggregate of carbon nanotubes that satisfies the following conditions (1) and (2): (1) The content of amorphous carbon is 0.1 mass % or more and less than 2.0 mass % with respect to the total mass of the aggregate of carbon nanotubes. (2) The area ratio of bundles having a bundle diameter of 100 nm or more is more than 0.1 in an area observed by a scanning electron microscope.

2. The carbon nanotube aggregate according to claim 1, which satisfies the following condition (3): (3) When the aggregate of carbon nanotubes is mixed with water to a concentration of 0.20 mass %, the viscosity of the dispersion liquid has a common logarithm of more than 1.0 and less than 3.5 when the liquid temperature is 25° C. The unit of viscosity is mPa·s.

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

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

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

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

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

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

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

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

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