Carbon nanotube assembly, carbon nanotube dispersion, conductive material, electrode, secondary battery, planar assembly, and composition

Abstract

Provided are a carbon nanotube assembly excellent in conductivity, a carbon nanotube dispersion, a conductive material, an electrode, a secondary battery, a planar assembly, and a composition.　When this carbon nanotube assembly is formed into a carbon nanotube dispersion in which the concentration of carbon nanotubes is 0.002% by mass with respect to the total amount of the carbon nanotube dispersion, the average value of fractal dimensions calculated under the following condition is 1.03-2.00. Condition: the carbon nanotube dispersion is imaged using a scanning electron microscope to obtain a plurality of images of a carbon nanotube attachment region. Among the obtained images, an image in which the carbon nanotube attachment region is present throughout the image is selected. The average value of fractal dimensions of a carbon nanotube structure is calculated by image analysis using the selected image.

Description

Carbon nanotube aggregate, carbon nanotube dispersion, conductive material, electrode, secondary battery, planar aggregate, and composition

[0001] The present disclosure relates to a carbon nanotube aggregate, a carbon nanotube dispersion, a conductive material, an electrode, a secondary battery, a planar aggregate, and a composition.

[0002] Carbon nanotubes (also referred to as "CNTs") are substances with a cylindrical structure formed by rolling up graphene sheets in which carbon atoms are arranged in a hexagonal honeycomb pattern. CNTs are basically broadly classified into single-walled carbon nanotubes (also referred to as "SWCNTs") formed from a single layer of graphene sheets, and multi-walled carbon nanotubes (also referred to as "MWCNTs") formed from multiple layers of graphene sheets. CNTs have excellent properties such as electrical conductivity, thermal conductivity, and heat resistance, and are therefore expected to be applied to various electronic materials, including electrode materials for electricity storage devices.

[0003] Patent Document 1 discloses a CNT dispersion liquid that is defined based on an analysis of a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method.

[0004] Patent Document 2 discloses a CNT dispersion in which a CNT aggregate having a plurality of CNTs is dispersed in a dispersion medium, and the CNT concentration and viscosity of the CNT dispersion are each within a predetermined numerical range.

[0005] Patent Document 3 discloses a conductive material for secondary batteries containing carbon nanotubes, in which carbon nanotube units have an entangled spherical secondary structure, and the true density, bulk density, and metal content are each within a predetermined numerical range.

[0006] International Publication No. 2023 / 162937 Japanese Patent Application Laid-Open No. 2018-39722 Japanese Patent Application Laid-Open No. 2018-530854

[0007] An object of one embodiment of the present disclosure is to provide a carbon nanotube aggregate having excellent electrical conductivity.An object of another embodiment of the present disclosure is to provide a carbon nanotube dispersion, a conductive material, a planar aggregate, and a composition, each including the carbon nanotube aggregate.An object of another embodiment of the present disclosure is to provide an electrode including the conductive material.An object of another embodiment of the present disclosure is to provide a secondary battery including the electrode.

[0008] The present disclosure includes the following aspects. <1> An aggregate of carbon nanotubes, in which, when a carbon nanotube dispersion liquid has a carbon nanotube concentration of 0.002 mass % relative to the total amount of the carbon nanotube dispersion liquid, an average value of fractal dimension calculated under the following conditions is 1.03 to 2.00. Conditions: The carbon nanotube dispersion liquid is imaged using a scanning electron microscope to obtain a plurality of images of the carbon nanotube attachment region. From the obtained images, an image in which the carbon nanotube attachment region is present throughout is selected. Using the selected image, the average value of fractal dimension of the carbon nanotube structure is calculated by image analysis. <2> The carbon nanotube aggregate according to <1>, in which the carbon nanotubes are multi-walled carbon nanotubes. <3> The carbon nanotube aggregate according to <1> or <2>, containing 450 ppm by mass to 150,000 ppm by mass of Fe atoms relative to the total mass of the carbon nanotube aggregate. <4> The aggregate of carbon nanotubes according to any one of <1> to <3>, wherein the carbon nanotubes have a maximum length of 500 μm to 30,000 μm. <5> A carbon nanotube dispersion comprising the aggregate of carbon nanotubes according to any one of <1> to <4> and a dispersion medium. <6> A conductive material comprising the aggregate of carbon nanotubes according to any one of <1> to <4>. <7> An electrode comprising an electrode active material and the conductive material according to <6>. <8> A secondary battery comprising the electrode according to <7>. <9> A planar aggregate comprising the aggregate of carbon nanotubes according to any one of <1> to <4>. <10> A composition comprising the aggregate of carbon nanotubes according to any one of <1> to <4> and at least one selected from the group consisting of resin, ceramics and concrete.

[0009] According to one embodiment of the present disclosure, it is possible to provide a carbon nanotube aggregate having excellent conductivity. According to another embodiment of the present disclosure, it is possible to provide a carbon nanotube dispersion, a conductive material, a planar aggregate, and a composition, each including the carbon nanotube aggregate. According to another embodiment of the present disclosure, it is possible to provide an electrode including the conductive material. According to another embodiment of the present disclosure, it is possible to provide a secondary battery including the electrode.

[0010] Fig. 1 is a scanning electron microscope photograph of CNT dispersion liquid 2 in Example 2. Fig. 2 is a scanning electron microscope photograph of CNT dispersion liquid C1 in Comparative Example 1.

[0011] An example of an embodiment of the present disclosure will be described in detail below. The following description may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment and can be implemented by making appropriate modifications within the scope of the purpose of the present disclosure.

[0012] 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" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0013] In the present disclosure, the terms "carbon nanotubes," "single-walled carbon nanotubes," "multi-walled carbon nanotubes," "multi-walled carbon nanotubes having a maximum length of 500 μm to 30,000 μm (particularly multi-walled carbon nanotubes having a maximum length of 1,000 μm to 30,000 μm)," "carbon nanotube aggregate," "carbon nanotube structure," and "carbon nanotube dispersion" may be abbreviated as "CNT," "SWCNT," "MWCNT," "ULMWCNT," "CNT aggregate," "CNT structure," and "CNT dispersion," respectively.

[0014] <CNT aggregate> The CNT aggregate according to the present disclosure has an average fractal dimension of 1.03 to 2.00 when the CNT aggregate is a CNT dispersion having a CNT concentration of 0.002 mass% relative to the total amount of the CNT dispersion, calculated under the following conditions. Conditions: The CNT dispersion is imaged using a scanning electron microscope to obtain multiple images of the CNT-attached regions. Of the obtained images, an image in which the CNT-attached region is present throughout is selected. Using the selected images, the average fractal dimension of the CNT structure is calculated by image analysis.

[0015] The CNT aggregate according to the present disclosure exhibits excellent electrical conductivity. The inventors discovered that a CNT aggregate having an average fractal dimension of 1.03 to 2.00 calculated under specified conditions forms a huge network structure in which CNTs are entangled with each other, which can exist stably in a dispersion. The fractal dimension is the absolute value of the slope of the approximation line of a plot obtained by plotting the logarithm of the number of boxes required to cover the figure for which the fractal dimension is to be determined against the logarithm of the box (also referred to as compartment) size. When CNTs form a network structure, a smaller box size requires a larger number of boxes to cover the figure of the network structure, so the absolute value of the slope of the approximation line increases, and the value of the fractal dimension increases. It is presumed that the formation of a network structure by CNTs results in contact between CNTs at multiple points, forming huge conductive paths and thereby increasing electrical conductivity. Therefore, the CNT aggregate according to the present disclosure exhibits excellent electrical conductivity. Note that the present disclosure is in no way limited to the above-mentioned presumed mechanism.

[0016] [Average Fractal Dimension] The average fractal dimension of the CNT structure calculated under specified conditions using the CNT aggregate according to the present disclosure is 1.03 to 2.00. From the viewpoint of electrical conductivity, the average fractal dimension is preferably 1.03 to 1.80, more preferably 1.04 to 1.60, even more preferably 1.04 to 1.40, and particularly preferably 1.05 to 1.20. When the average fractal dimension is at the lower limit of 1.03, contact points between CNTs occur at multiple points, improving electrical conductivity. The upper limit of 2.00 for the average fractal dimension is the theoretical maximum value resulting from the calculation of the average fractal dimension from a two-dimensional image. Incidentally, when the average fractal dimension is 1.60 or less, particularly good dispersibility in a solvent can be ensured.

[0017] The average value of the fractal dimension can be adjusted by the length, diameter, etc. of the CNT aggregate.

[0018] In the present disclosure, the CNT structure refers to a structure formed by CNTs, and can be confirmed by observing a CNT dispersion liquid with a scanning electron microscope.

[0019] In the present disclosure, the average value of the fractal dimension is calculated under the conditions described below using a CNT dispersion liquid in which the CNT concentration is 0.002 mass % relative to the total amount of the CNT dispersion liquid.

[0020] (Preparation of CNT Dispersion) A CNT dispersion having a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is prepared. The method for preparing a CNT dispersion having a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is not particularly limited, and it can be prepared by a known method. More specifically, first, a mixture is obtained by mixing CNT aggregates, water, and carboxymethyl cellulose so that the CNT concentration is 0.2 mass% relative to the total amount. Next, the mixture is subjected to a dispersion treatment for 1 hour using a homogenizer as a pre-dispersion, and then further subjected to a dispersion treatment using a wet jet mill as a main dispersion, thereby obtaining a CNT dispersion having a CNT concentration of 0.2 mass%. In other words, a CNT aqueous dispersion having a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is prepared.

[0021] The detailed conditions for the preliminary dispersion treatment are not particularly limited, and for example, dispersion treatment is performed using a homogenizer under conditions of 500 rpm to 20,000 rpm. The detailed conditions for the main dispersion treatment are also not particularly limited, and for example, dispersion treatment is performed using a wet jet mill under conditions of nozzle diameter: 0.15 mm to 0.70 mm, pressure: 10 MPa to 250 MPa, number of times: 1 to 30 times, and method: circulation method.

[0022] (Imaging Using a Scanning Electron Microscope (SEM)) The CNT dispersion having a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is diluted with pure water so that the CNT concentration becomes 0.002 mass% relative to the total amount of the CNT dispersion, and this CNT dispersion having a CNT concentration of 0.002 mass% is imaged using an SEM to obtain multiple images of the CNT-attached regions. The imaging method using an SEM is not particularly limited, and can be performed using a known method.

[0023] -Attaching CNT dispersion to SEM observation substrate- More specifically, first, the CNT dispersion is attached to the SEM observation substrate in the following procedure. 1. A slide glass on which Pt has been vapor-deposited is UV-ozone treated and attached to the SEM observation substrate with conductive tape. 2. 0.001 μL to 1 μL of CNT dispersion is attached to the slide glass. 3. The SEM observation substrate with the CNT dispersion attached is placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass with the frozen CNT dispersion is placed on a 4.0 x 10 －３ Pa ~ 6.0 x 10 －３ A vacuum is drawn to a pressure of 0.05 Pa to sublimate the ice.

[0024] -Imaging- Next, the attached CNT dispersion is imaged using an SEM device (for example, S-4800 manufactured by Hitachi High-Technologies Corporation) under the following conditions to obtain multiple images of the CNT-attached region. The CNT-attached region is the region on the SEM observation substrate where the CNT network structure is located. From the viewpoint of reducing the variance of the fractal dimension values, it is preferable to obtain 10 or more images. Acceleration voltage: 1 kV Emission current: 10 μA Measurement magnification: 500x Image size: 1280 pixels x 960 pixels

[0025] (Image Selection) From the obtained images, images in which the CNT-attached region is present throughout are selected. More specifically, first, the following image processing is performed on all images of the CNT dispersion-attached region using image analysis software (e.g., ImageJ).

[0026] --Image processing procedure-- 1. Crop: 1280 pixels x 896 pixels 2. Filters: Gaussian Blur, Sigma (Radius) = 3 3. Filters: Top Hat, Radius = 9 pixels 4. Binarization: Auto Threshold, Otsu, White objects on black background 5. Morphology: Gray Morphology, Radius of the structure elements (pixels) = 3.0, Type of structure element=circle, operator=open

[0027] Next, the image after the image processing is divided into 64 parts (8 parts both vertically and horizontally), and only images in which all 64 divided images have pixels with a pixel value of 255 (i.e., images in which the CNT attachment area is present throughout) are selected from the images of the attachment area. However, images in which CNTs have clearly not been extracted after the image processing compared to the image before the image processing (for example, images in which most of the SEM observation substrate area has pixels with a pixel value of 255) are excluded from selection in advance.

[0028] —Proportion of Selected Images— In this case, the proportion of images used to calculate the fractal dimension (i.e., selected images) among the total number of images in the CNT dispersion liquid attachment region is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, particularly preferably 50% or more, and especially preferably 55% or more, from the viewpoint of reducing the variance of the fractal dimension values.

[0029] (Calculation of the average value of fractal dimension) Using the selected images, the average value of the fractal dimension of the CNT structure is calculated by image analysis. More specifically, all of the selected images after image processing are analyzed using image analysis software (e.g., ImageJ), and the fractal dimension is calculated for each image by the following procedure.

[0030] - Calculation procedure - 1. Binary: Skeletonize 2. Analyze: Fractional Box Counter, Box Sizes = 4, 6, 8, 12, 16, 32, 64, 128, Black Background

[0031] Based on the fractal dimension calculated for each image, the average value of the fractal dimension is further calculated.

[0032] Variance, Standard Deviation, and Median The variance, standard deviation, and median of the fractal dimension are calculated based on the following formulas: １ , x ２ , ..., x ｎ When the mean value of is expressed as μ, the variance S ２ and the standard deviation S are calculated by the following formulas (1) and (2), respectively.

[0033]

[0034] The data is sorted in ascending order and expressed as x (1) , x (2) , ..., x (n) Then, the median value Me can be calculated by the following formula (3).

[0035]

[0036] The dispersion of the fractal dimension is preferably 0.05 or less, more preferably 0.03 or less, and even more preferably 0.02 or less. The standard deviation of the fractal dimension is preferably 0.20 or less, more preferably 0.18 or less, and even more preferably 0.15 or less. From the viewpoint of electrical conductivity, the median of the fractal dimension is preferably 1.03 to 1.80, more preferably 1.04 to 1.60, even more preferably 1.04 to 1.40, and particularly preferably 1.05 to 1.20.

[0037] [SWCNT, MWCNT] The CNT in the CNT aggregate according to the present disclosure may be SWCNT or MWCNT, or may be a mixture of SWCNT and MWCNT. From the viewpoint of excellent thermal stability and chemical stability, and from the viewpoint of having a wall number distribution with lower uniformity and thus facilitating improved dispersibility, the CNT preferably includes MWCNT, and is more preferably MWCNT. The number of walls of the CNT can be controlled by selecting the manufacturing method for the CNT.

[0038] [Fe atoms] The CNT aggregate according to the present disclosure may contain Fe atoms. The Fe atoms are derived from, for example, iron, which is a catalyst that can be used during production. The CNT aggregate may contain Fe atoms, for example, in a state where they are adsorbed on the surface of the CNT and / or in a state where they are incorporated inside the CNT. From the viewpoint of dispersibility in a dispersion medium, the CNT aggregate according to the present disclosure preferably contains 450 ppm by mass to 150,000 ppm by mass of Fe atoms, and more preferably contains 500 ppm by mass to 150,000 ppm by mass of Fe atoms, relative to the total mass of the CNT aggregate. The Fe atoms contained in the CNT aggregate according to the present disclosure is more preferably 1,000 ppm by mass to 100,000 ppm by mass, even more preferably 5,000 ppm by mass to 90,000 ppm by mass, particularly preferably 10,000 ppm by mass to 80,000 ppm by mass, and especially preferably 30,000 ppm by mass to 70,000 ppm by mass, relative to the total mass of the CNT aggregate.

[0039] Since the average value of the fractal dimension of the CNT structure calculated under specified conditions using the CNT aggregate according to the present disclosure is 1.03 to 2.00, the CNTs in the network structure of the CNT aggregate are located close to each other, and CNT aggregation is likely to occur. Here, it is thought that if an appropriate amount of Fe atoms are attached to the surface of the CNT, the Fe atoms moderately inhibit contact between multiple CNTs, and excessive aggregation is suppressed. More specifically, in a CNT aggregate in which the content of Fe atoms is 150,000 mass ppm or less with respect to the total mass of the CNT aggregate, even in the presence of Fe atoms, a certain number of contact points between CNTs is likely to be secured, conductive paths are likely to be connected, and conductivity is likely to be improved. On the other hand, in a CNT aggregate in which the content of Fe atoms is 450 ppm by mass or more (particularly 500 ppm by mass or more) relative to the total mass of the CNT aggregate, the aggregation suppression effect due to the presence of Fe atoms is more likely to function, the network structure that acts as a conductive path is less likely to aggregate excessively, and the conductivity is more likely to improve.

[0040] The content ratio of Fe atoms to the total mass of a CNT aggregate can be measured, for example, by the following method. First, the CNT aggregate is completely dissolved in an acid such as hydrochloric acid or nitric acid. In order to completely dissolve the CNT aggregate in acid, pretreatment such as dry ashing, wet ashing, or melting treatment may be performed. The content ratio of Fe atoms can be measured by performing inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS) on a solution in which the CNT aggregate is completely dissolved in acid. ICP-MS is preferred because it allows for measurements with higher sensitivity.

[0041] [Maximum Length] The maximum length of the CNTs in the CNT aggregate related to the present disclosure is not particularly limited, and from the viewpoint of electrical conductivity, it is preferably 500 μm to 30,000 μm, more preferably 1,000 μm to 30,000 μm, even more preferably 1,000 μm to 25,000 μm, particularly preferably 1,100 μm to 20,000 μm, even more preferably 1,200 μm to 18,000 μm, still more preferably 1,300 μm to 15,000 μm, and most preferably 2,000 μm to 10,000 μm.

[0042] When the maximum length of the CNTs in the CNT aggregate according to the present disclosure is 500 μm or more (particularly 1,000 μm or more), the conductivity of the CNT aggregate tends to be higher. The reason for this is thought to be that the CNTs contained in the CNT aggregate are more likely to come into contact with each other, making it easier to form conductive paths. When the maximum length of the CNTs contained in the CNT aggregate according to the present disclosure is 30,000 μm or less, it tends to be easier to manufacture.

[0043] As described above, MWCNTs having a maximum length of 500 μm to 30,000 μm (particularly, 1,000 μm to 30,000 μm) are also called “ULMWCNTs.” ULMWCNTs have a maximum length of 500 μm to 30,000 μm (particularly, 1,000 μm to 30,000 μm), and are longer than general-purpose MWCNTs, making them more likely to take on a fibrous shape.

[0044] Here, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two. The fibers may be thread-like fibers with a circular cross section, ribbon-like fibers with a rectangular cross section, hollow, or have other shapes. From the viewpoint of increasing electrical conductivity, the cross section of ULMWCNTs is preferably circular, and hollow is preferred.

[0045] By taking on a fibrous shape, ULMWCNTs have the property of easily entangling with one another. The CNT aggregate preferably contains at least one ULMWCNT, and from the viewpoint that CNTs are more likely to entangle with one another and form a more stable aggregate, an aggregate containing a plurality of ULMWCNTs is more preferable. Hereinafter, an aggregate containing ULMWCNT may be abbreviated as "ULMWCNT aggregate."

[0046] The CNT aggregate may be an aggregate having a three-dimensional structure in which the CNTs are entangled with one another. Figure 1 is an SEM photograph of one embodiment of the CNT dispersion according to the present disclosure. The SEM photograph shown in Figure 1 shows that a plurality of fibrous CNTs are entangled to form a network. In this way, the entangled state of the CNTs can be confirmed by SEM observation.

[0047] The length of a CNT can be measured by focusing on a single CNT and observing multiple SEM photographs 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 referred to as the "maximum length." When observing an SEM photograph, if one or more CNTs with a maximum length in the range of 500 μm to 30,000 μm (particularly 1,000 μm to 30,000 μm) are observed within the viewing angle of the SEM photograph, it can be confirmed that the observed CNTs include ULWMCNTs.

[0048] It is preferable that a plurality of ULMWCNTs 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 of the observed CNTs, it is preferable that MWCNTs (i.e., ULMWCNTs) having a maximum length in the range of 500 μm to 30,000 μm (particularly 1,000 μm to 30,000 μm) account for 10% or more in terms of number, from the viewpoint of further improving the stability of the CNT aggregate due to entanglement between ULMWCNTs, and it is more preferable that they account for 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0049] [Diameter] The diameter of the CNTs in the CNT aggregate according to the present disclosure can be measured by observing an SEM photograph or a transmission electron microscope (TEM) photograph. Here, the diameter refers to the length in the direction perpendicular to the longitudinal direction of the CNT, and the diameter is measured at 10 different locations on one CNT, and the average value is taken as the diameter of that CNT.

[0050] The diameter of the CNT is preferably 1 nm to 100 nm, more preferably 2 nm to 80 nm, even more preferably 3 nm to 50 nm, and particularly preferably 5 nm to 30 nm.

[0051] The length / diameter ratio of the CNT, or the so-called aspect ratio, is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 10,000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single CNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more CNTs.

[0052] [Specific Gravity] From the viewpoint of dispersibility, the specific gravity of the CNT 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 CNT aggregate can be measured by the method described in JIS Z8807:2012 "Method for measuring density and specific gravity of solids."

[0053] [Purity] The purity of the CNT aggregate as CNT can be measured by thermogravimetric analysis. For example, a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the CNT aggregate are obtained using a thermal analyzer (Shimadzu Corporation, DTG-60). The largest exothermic peak in the DTA curve, which has a peak top near 650°C to 750°C, is considered to be the combustion of CNT, and any other exothermic peaks are considered to be the combustion of substances other than CNT. The purity of the CNT is determined from the weight loss rate of the TG curve. From the viewpoint of the resulting conductivity, the purity of the CNT 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 93% by mass or more.

[0054] [Applications] The applications of the CNT aggregate according to the present disclosure are not particularly limited. The CNT aggregate according to the present disclosure has excellent conductivity, and therefore excellent cycle characteristics when used in a battery. The CNT aggregate according to the present disclosure can be used as a conductive additive (preferably, a conductive additive for a negative electrode). In this disclosure, a conductive additive refers to a substance that coexists with an electrode active material (specifically, a positive electrode active material or a negative electrode active material) in an electrode formed using an electrode material to assist conductivity and has the function of forming a conductive path. The CNT aggregate according to the present disclosure can be used together with, for example, known conductive additives such as graphite and ketjen black. The CNT aggregate according to the present disclosure can be used, for example, as a conductive material. Examples of conductive materials using the CNT aggregate according to the present disclosure include electrode materials in secondary batteries (e.g., lithium ion batteries), specifically, negative electrode materials and positive electrode materials.

[0055] [Method for manufacturing CNT aggregate] The method for manufacturing a CNT aggregate according to the present disclosure (including a method for manufacturing a SWCNT aggregate, a method for manufacturing a MWCNT aggregate, and a method for manufacturing a ULMWCNT aggregate) is not particularly limited. As a method for manufacturing a CNT aggregate according to the present disclosure, a conventionally known chemical vapor deposition (CVD) method, a method for reacting a gaseous reactant containing a carbon source in the presence of a catalyst, or the like can be applied.

[0056] The CNT aggregate according to the present disclosure can be manufactured by referring to the manufacturing methods described in, for example, Japanese Patent Application Laid-Open No. 2016-102047 or Japanese Translation of PCT International Publication No. 2021-527611. Below, examples of the manufacturing method of the CNT aggregate according to the present disclosure will be explained, but the manufacturing method of the CNT aggregate according to the present disclosure is not limited to the following examples.

[0057] (Manufacturing Method X) As an example of a manufacturing method for a CNT aggregate according to the present disclosure, reference can be made to the manufacturing method described in Japanese Patent Application Laid-Open No. 2016-102047. That is, there can be mentioned a manufacturing method (hereinafter also referred to as "Manufacturing Method X") comprising the steps of passing a gaseous reactant containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in the presence of a catalyst in a reaction zone of the reactor 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. According to Manufacturing Method X, a CNT aggregate according to the present disclosure can be obtained in the form of a fibrous aggregate or other aggregate form that is easy to handle.

[0058] In manufacturing method X, the force applied to the product particles may be a mechanical force. When the agglomerates are fibrous CNT aggregates, the mechanical force applied to the product particles may be exerted by a rotating spindle around which the agglomerates are wound. The fibrous CNT aggregate may be collected on the spindle, or may be accumulated elsewhere by rotating around the spindle one or more times and then continuously unwinding the spindle.

[0059] 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 an angle of 25° to the flow direction of the gaseous reactants may also be suitable for applying mechanical forces to the product particles.

[0060] The spindle can rotate about two axes (e.g., two perpendicular axes), specifically, about axes perpendicular and parallel to the flow direction of the gaseous reactants, and can pull and twist the agglomerates of fibrous CNT aggregates to control the twist number and length.

[0061] The spindle may be made of a metal, ceramic, or resin material. The spindle may have different suitable shapes depending on the properties of the material and the intended use of the CNT aggregate. The spindle may be used as a mold for producing carbon products, for example, by a spin coating method. A preferred spindle shape is a rod or box shape.

[0062] Fibrous CNT aggregates are deposited on a spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the conditions under which an electric or other field is applied to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by gas flow forces.

[0063] The rotation speed of the spindle is preferably 0.01 rpm (revolutions per minute; the same applies hereinafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the rotation speed of the spindle) may be adjusted so that the material is collected at a similar rate to that at which it is produced. The thickness of the accumulated fibrous CNT aggregate may be controlled by the rotation speed of the spindle. In a preferred embodiment, as the spindle rotates, the fibrous CNT aggregate is processed in the axial direction of the spindle. In the processing, the fibrous CNT aggregate is wound evenly along the spindle, rather than being wound only at one specific point on the spindle.

[0064] The CNT fiber aggregate may be collected, for example, on the wall of the reactor 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 fiber aggregate as it is collected. A suitable substrate arrangement for use in fiber technology is a substrate consisting of two guides positioned at right angles to each other.

[0065] In manufacturing method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow may be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube downstream of the reaction zone. A vacuum may be applied to the product particles.

[0066] Other forces that can be applied to the product particles include electrostatic forces, which are appropriately applied by a charged plate. Electrostatic forces require that the product particles be charged. By using a charged plate, the CNT aggregates can be formed on the charged plate in the form of intertwined sheets (also called mats).

[0067] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0068] The raw material for the CNT aggregate may be injected in the form of a liquid containing a carbon source instead of a gaseous reactant containing a carbon source. When a liquid is used as the raw material for the CNT aggregate, it can be injected through a single inlet or multiple inlets, for example, in a showerhead arrangement.

[0069] Preferably, the gaseous reactant or reactants are reacted at a temperature between 500° C. and 1600° C., more preferably between 1000° C. and 1500° C. or 1600° C. (especially 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.

[0070] The gaseous reactants may be mixed with one or more gases that act as diluents. The gaseous reactants may also be mixed with gases that play a supporting but not direct role in the reaction. It is also preferred to use a diluent gas that can react with the amorphous carbon by-product, if any, to maintain active sites on the catalyst for nanotube production.

[0071] Examples of gases that can be used as diluents include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, and helium. Among these, a mixed gas of nitrogen and argon or hydrogen is particularly preferred as a gas that can be used as a diluent. The flow rate of the gas used as a diluent is preferably 2000 mL (milliliters) / min or less, and more preferably 400 mL / min to 800 mL / min.

[0072] The gas pressure of the gaseous reactants and any diluents is preferably between 0.1 bar and 50 bar, more preferably between 0.5 bar and 5 bar, and even more preferably between 1 bar and 2 bar. If there is a gas effluent from the furnace, the effluent gas can be recycled with or without cleaning.

[0073] 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.

[0074] When the agglomerate is removed from the reactor, it is preferable to prevent air from entering the reactor. When the diluent gas contains hydrogen, preventing air from entering the reactor is desirable, for example, from the viewpoint of preventing an explosive mixture of hydrogen and air from being formed in the reactor.

[0075] The product particles in Production Method X may contain SWCNTs, MWCNTs, and / or ULMWCNTs, depending on the production conditions.

[0076] 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.

[0077] Examples of 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). Preferred carbon-containing compounds are carbon monoxide, methane, ethylene, or acetylene.

[0078] 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.

[0079] The gaseous reactant, which is a carbon source, is preferably injected into the reactor at a rate of 0.01 mL / min to 10 mL / min, more preferably 0.08 mL / min to 0.25 mL / min.

[0080] The catalyst is preferably a transition metal, particularly a Group VIB transition metal such as chromium (Cr), molybdenum (Mo), tungsten (W), or a Group VIIIB transition metal. Specifically, the catalyst may be, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or manganese (Mn), or a mixture thereof. Metals from the lanthanide and actinide series, such as yttrium (Y), may also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof, such as a 50 / 50 mixture of Ni and Co, a mixture of Fe and Ni, or a mixture of Fe and Mo, are more preferred. Any of these transition metals, alone or in combination with any of the other transition metals listed, may serve as a catalyst for CNT growth. It is particularly preferred that the catalyst is a mixture of two or more of the metals listed.

[0081] The catalyst is preferably formed by decomposition of a precursor. The precursor is preferably a thermally, photo-, or plasma-decomposable compound of one or more of the above metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickelocene, and cobaltocene are particularly preferred precursors. Suitably, at least 0.01% by weight of the precursor is contained in the carbon source, and preferably 0.2% to 2.5% by weight of the precursor is contained in the carbon source. In one embodiment, 0.23% to 2.3% by weight of the precursor is contained in the carbon source. The catalyst may be supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0082] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters include one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is one of the preferred promoters. Suitably, up to 10% by weight (10% by weight or less) of the promoter is contained in the carbon source. Preferably, 0.2% to 6% by weight of the promoter is contained in the carbon source. When a high or low concentration of thiophene is used as the promoter, MWCNTs are successfully formed. For example, MWCNTs are successfully formed using ethanol containing 0% by weight or 1.5% to 4.0% by weight of thiophene and 1.0% to 10.0% by weight (particularly 2.3% by weight) of ferrocene, under conditions of an injection rate of 5.0 mL / hour to 30.0 mL / hour (particularly 7.5 mL / hour), a hydrogen flow rate of 400 mL / min to 800 mL / min, and a synthesis temperature of 1100°C to 1180°C.

[0083] According to production method X, it is possible to obtain fibrous CNTs having a length of at least 500 μm, for example, at least 1,000 μm. The fibrous CNTs can take the form of threads or sheets. The length of the CNTs can be controlled, for example, by the winding capacity of the spindle used to produce the fibrous CNT aggregate.

[0084] 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 a fibrous CNT aggregate.

[0085] Another embodiment similar to production method X may involve producing CNTs in a reaction zone by the above method, then condensing them to form a CNT aggregate, and continuously withdrawing the CNT aggregate from near the reaction zone. Another embodiment may involve producing CNTs in a reaction zone, continuously electrostatically attracting the CNTs from the reaction zone, and recovering the CNT aggregate.

[0086] (Manufacturing Method Y) As another example of a manufacturing method for a CNT aggregate according to the present disclosure, reference can be made to the manufacturing method described in JP-T-2021-527611. That is, a mixture containing a main catalyst precursor and a co-catalyst precursor is mixed with γ-Al ２ O ３ a production method (hereinafter also referred to as "production method Y") that includes a step (1) of supporting a carbon nanotube on a support to produce an active support, a step (2) of drying the active support by multi-stage drying including vacuum drying, a step (3) of subjecting the dried active support to a heat treatment to produce a supported catalyst, and a step (4) of producing CNTs in the presence of the supported catalyst.

[0087] Step (1) In step (1), a mixture containing a main catalyst precursor and a co-catalyst precursor is added to a γ-Al ２ O ３ to produce an active support.

[0088] The main catalyst precursor and the co-catalyst precursor were ２ O ３ In order to uniformly support the catalyst precursor and the co-catalyst precursor on the catalyst support, the mixture may further contain a solvent, and the main catalyst precursor and the co-catalyst precursor may be dissolved in the solvent. The solvent may be one or more selected from the group consisting of water, methanol, and ethanol, and water is preferred.

[0089] γ-Al ２ O ３ has high porosity and a spinel structure, and therefore the main catalyst and co-catalyst are γ-Al. ２ O ３ The CNTs grown from the randomly arranged primary catalyst can be produced in an entangled state.

[0090] The main catalyst may be one or more selected from the group consisting of cobalt, iron, nickel, manganese and chromium, with cobalt being preferred.

[0091] 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.

[0092] The main catalyst precursor is Co(NO ３ ) ２ , Co(NO３ ) ２ ・6H ２ O, Co ２ (CO) ８ , Co ２ (CO) ６ [HC=C(C(CH ３ ) ３ )], Co(CH ３ CO ２ ) ２ , Fe(NO ３ ) ３ , Fe(NO ３ ) ２ ・nH ２ O, Fe(CH ３ CO ２ ) ２ , Ni(NO ３ ) ２ , Ni(NO ３ ) ２ ・6H ２ O, Mn(NO ３ ) ２ , Mn(NO ３ ) ２ ・6H ２ O, Mn(CH ３ CO ２ ) ２ ・n (H ２ O) and Mn(CO) ５ Br, and among these, Co(NO ３ ) ２ ・6H ２ O, Fe(NO ３ ) ２ ・nH ２ O, Ni(NO ３ ) ２ ・6H ２ O is preferred.

[0093] The promoter improves the dispersibility of the main catalyst and may be one or more selected from the group consisting of vanadium and molybdenum.

[0094] The cocatalyst precursor is NH ４ VO ３ , NaVO ３ , V ２ O ５ , V(C ５ H ７ O２ ) ３ , and (NH ４ ) ６ Mo ７ O ２４ ・4H ２ O, and NH ４ VO ３ and (NH ４ ) ６ Mo ７ O ２４ ・4H ２ O is preferred.

[0095] When the mixture contains two or more promoter precursors, i.e., when it contains both a vanadium precursor and a molybdenum precursor, the molar ratio of the sum of vanadium and molybdenum to vanadium can be 1:0.45 to 1:0.95 or 1:0.5 to 1:0.9, and preferably 1:0.5 to 1:0.9. When the above conditions are met, the CNT structure can be stably maintained and CNTs having the desired pore volume can be produced.

[0096] The mixture may contain the main catalyst precursor and the co-catalyst precursor such that the molar ratio of the main catalyst to the co-catalyst is 1:0.01 to 1:0.5, 1:0.1 to 1:0.4, or 1:0.1 to 1:0.25, and preferably 1:0.1 to 1:0.25. Satisfying the above molar ratios can improve the dispersibility of the main catalyst, allowing the production of CNTs with a desired pore volume.

[0097] The mixture may further include an organic acid which serves to inhibit precipitation of the main catalyst precursor and the co-catalyst precursor.

[0098] 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.

[0099] The mixture may contain the organic acid and the co-catalyst precursor in a molar ratio of 1:1 to 1:20, 1:2 to 1:10, or 1:3 to 1:6, preferably 1:3 to 1:6. When the ratio satisfies the above ranges, it is possible to prepare a transparent catalyst metal solution during catalyst production, and it is possible to prepare a catalyst in which fine particles are suppressed during impregnation.

[0100] After step (1), a step of aging may be further included.

[0101] The aging may be carried out for 1 minute to 60 minutes or 10 minutes to 50 minutes. It is preferably carried out for 10 minutes to 50 minutes. When the above conditions are satisfied, γ-Al ２ O ３ In addition, bubbles present in the support are removed to the maximum extent possible, allowing the main catalyst precursor and the co-catalyst precursor to be sufficiently supported even in the fine pores inside the support.

[0102] Step (2) Next, the active support is dried by multi-stage drying including vacuum drying.

[0103] 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.

[0104] The vacuum drying may be carried out at a temperature of 80° C. to 300° C. or 120° C. to 250° C., preferably 120° C. to 250° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Drying at atmospheric pressure may be carried out at 80° C. to 160° C. or 100° C. to 140° C., and is preferably carried out at 100° C. to 140° C. If the above conditions are met, the solvent present in the active support can be sufficiently removed, and energy consumption can be minimized.

[0109] Drying under atmospheric pressure may be carried out at 900 mbar to 1,100 mbar, preferably 950 mbar to 1,050 mbar. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0110] 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.

[0111] 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.

[0112] The primary vacuum drying can remove any solvent that may be present in the active support.

[0113] 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.

[0114] The primary vacuum drying can be performed for 1 to 12 hours, preferably 3 to 9 hours. If the above conditions are met, the solvent present in the active support can be sufficiently removed and energy consumption can be minimized.

[0115] 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.

[0116] The secondary vacuum drying is as described above in the description of the vacuum drying.

[0117] 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.

[0118] The secondary vacuum drying may be performed at 1 mbar to 200 mbar, 1 mbar to 150 mbar, or 1 mbar to 70 mbar, and more preferably at 1 mbar to 70 mbar. When the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

[0119] 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.

[0120] Step (3) Next, the dried active support is subjected to a heat treatment to produce a supported catalyst.

[0121] When heat treatment is performed, the main catalyst and the co-catalyst are converted into γ-Al ２ O ３A supported catalyst is produced in which the catalyst is present in a coated state on the surface and in the pores of the catalyst.

[0122] The heat treatment may be carried out at 600° C. to 800° C. or 620° C. to 750° C., and is preferably carried out at 620° C. to 750° C. When the above conditions are satisfied, the main catalyst and the co-catalyst are γ-Al. ２ O ３ Therefore, the supported catalyst can be produced with the surface and pores of the catalyst uniformly coated, and energy consumption can be minimized.

[0123] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, and is preferably carried out for 2 to 8 hours. ２ O ３ A supported catalyst can be produced in which the catalyst is present in a uniform coating on the surface and in the pores of the catalyst.

[0124] Step (4) Next, CNTs are produced in the presence of a supported catalyst.

[0125] Specifically, CNTs can be produced by contacting a supported catalyst with a carbon-based compound, and specifically, by chemical vapor synthesis.

[0126] To explain the steps of producing CNTs in detail, first, a supported catalyst can be loaded into a horizontal fixed-bed reactor or a fluidized-bed reactor. Then, at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the supported catalyst, a gaseous carbon-based compound or a mixture of a gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen) is injected to grow CNTs by chemical vapor synthesis through the decomposition of the gaseous carbon-based compound.

[0127] The CNTs produced by the above-mentioned chemical vapor synthesis method have a crystal growth direction that is nearly parallel to the tube axis, and the graphite structure has high crystallinity along the tube length. As a result, CNTs with small unit diameters and high electrical conductivity and strength can be produced.

[0128] The chemical vapor synthesis method may be carried out at a temperature of 600° C. to 800° C. or 650° C. to 750° C., and is preferably carried out at a temperature of 650° C. to 750° C. If the above temperature is satisfied, CNTs can be produced while minimizing the generation of amorphous carbon.

[0129] The heat source for the reaction may be induction heating, radiant heat, laser, IR, microwave, plasma, surface plasmon heating, or the like.

[0130] Any carbonaceous compound can be used without particular limitation as long as it can supply carbon and can exist in a gaseous state at a temperature of 300° C. or higher.

[0131] The carbon-based compound may be a carbon-based compound having 6 or less carbon atoms, and may be one or more compounds selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene.

[0132] After growing CNTs by the above-mentioned reaction, a cooling step may be optionally further carried out to align the CNTs more regularly. Specifically, the cooling step may be carried out by natural cooling by removing the heat source or by using a cooler or the like.

[0133] The above manufacturing method X and manufacturing method Y are examples, and the manufacturing method of the CNT aggregate is not limited to the above.

[0134] [Pulverized Product of CNT Aggregate] The CNT aggregate according to the present disclosure may be a pulverized product of a CNT aggregate. The pulverized product of a CNT aggregate may be a frozen pulverized product of a CNT aggregate.

[0135] The pulverization process for obtaining a pulverized product of the CNT aggregate is not particularly limited, and any pulverization process capable of pulverizing the CNT aggregate into small pieces may be used.

[0136] The pulverization process may be a process in which the CNT aggregate is pulverized while it is still frozen. For the pulverization process, it is preferable to use a pulverizer (for example, a ball mill) or a freezing pulverizer. The pulverizer can be selected appropriately depending on the amount of CNT aggregate to be pulverized. As the pulverizer, for example, a ball mill "JFC-300" manufactured by Japan Analytical Industry Co., Ltd. can be used. As the freezing pulverizer, for example, a freezing pulverizer "JFC-2000" manufactured by Japan Analytical Industry Co., Ltd. can be used.

[0137] The shape of the CNT aggregate to be subjected to the pulverization treatment may be, for example, a sheet or thread, with a sheet being preferred since it is not too hard and a large amount can be processed at one time.

[0138] The powder of CNT aggregates obtained by crushing the CNT aggregates can be used as a conductive material, as well as for various other applications such as conductive ink, filler for reinforcing resin, antistatic agent, transparent conductive film material, etc.

[0139] [Method for determining the electrical conductivity of a CNT aggregate] The present disclosure also provides a method for determining the electrical conductivity of a CNT aggregate by calculating the average value of the fractal dimension. That is, in the present disclosure, the method for determining the electrical conductivity of a CNT aggregate includes: using a CNT aggregate to prepare a CNT dispersion liquid in which the CNT concentration is 0.002 mass% with respect to the total amount of the CNT dispersion liquid; calculating the average value of the fractal dimension using the prepared CNT dispersion liquid under the following conditions; and determining that the CNT aggregate has excellent electrical conductivity if the calculated average value of the fractal dimension is within the range of 1.03 to 2.00. Conditions: The CNT dispersion liquid is imaged using a scanning electron microscope to obtain multiple images of the CNT-attached region. From the obtained images, an image in which the CNT-attached region is present throughout is selected. Using the selected image, the average value of the fractal dimension of the CNT structure is calculated by image analysis.

[0140] In the method for determining the conductivity of a CNT aggregate, the method for preparing a CNT dispersion and the method for calculating the average value of the fractal dimension are the same as the method for preparing a CNT dispersion and the method for calculating the average value of the fractal dimension in the above <CNT aggregate>.

[0141] <CNT Dispersion> The CNT dispersion according to the present disclosure contains the CNT aggregate according to the present disclosure and a dispersion medium.

[0142] [CNT aggregate] Details of the CNT aggregate according to the present disclosure are as described above. The content of the CNT aggregate according to the present disclosure in the CNT dispersion according to the present disclosure is not particularly limited and can be set appropriately depending on the purpose. From the viewpoint of conductivity, the content of the CNT aggregate according to the present disclosure in the CNT dispersion according to the present disclosure is preferably 0.001 mass% or more, more preferably 0.002 mass% or more, even more preferably 0.005 mass% or more, and particularly preferably 0.01 mass% or more, relative to the total mass of the CNT dispersion. Furthermore, from the viewpoint of dispersibility, the content of the CNT aggregate according to the present disclosure in the CNT dispersion according to the present disclosure is preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 10 mass% or less, particularly preferably 5 mass% or less, and particularly preferably 1 mass% or less, relative to the total mass of the CNT dispersion. In an embodiment, the content of the CNT aggregate according to the present disclosure in the CNT dispersion according to the present disclosure may be 0.001 mass % to 20 mass %, 0.002 mass % to 10 mass %, 0.005 mass % to 5 mass %, or 0.01 mass % to 1 mass %, relative to the total mass of the CNT dispersion.

[0143] [Dispersion Medium] The CNT dispersion according to the present disclosure contains a dispersion medium. The dispersion medium preferably contains water, more preferably contains water as the main component, and even more preferably is water. "Contains water as the main component" means that the proportion of water in the dispersion medium is greater 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.

[0144] The water is not particularly limited, and is preferably, for example, distilled water, ion-exchanged water, pure water, or the like, which contains fewer impurities.

[0145] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of the hydrophilic solvent include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0146] [Other Components] The CNT dispersion according to the present disclosure may further contain other components in addition to the CNT aggregate and dispersion medium according to the present disclosure, as long as the effects of the CNT dispersion are not impaired. Examples of other components include dispersants, antifoaming agents, antistatic agents, conductive additives, CNTs other than the CNT aggregate according to the present disclosure, and the like. The CNT dispersion according to the present disclosure may further contain trace amounts of impurity components, so-called inevitable impurities, and the like.

[0147] The CNT dispersion according to the present disclosure may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the CNT aggregate. The dispersant is not particularly limited, and examples thereof include various surfactants. Further examples of the dispersant include polymer compounds such as resins. The dispersant is preferably a surfactant. The surfactant may be an ionic surfactant or a nonionic surfactant, and is not particularly limited. The surfactant may be used alone or in combination of two or more types.

[0148] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzene sulfonates (e.g., dodecylbenzene sulfonate) and dodecylphenyl ether 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. Examples of ionic surfactants include ionic surfactants having an aromatic ring (so-called aromatic ionic surfactants), and more preferably aromatic sulfonic acid surfactants such as alkylbenzene sulfonates and dodecylphenyl ether sulfonates. Aromatic ionic surfactants tend to have excellent CNT dispersibility, dispersion stability, and high concentration.

[0149] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene-polypropylene glycols; and aromatic nonionic surfactants such as polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, polyoxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl cumyl phenyl ether, and polyoxyalkylene phenyl ether. As nonionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic nonionic surfactants) are preferred, polyoxyalkylene phenyl ethers are more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersibility, dispersion stability, and concentration of CNT aggregates.

[0150] Other dispersants that are excellent in dispersibility, dispersion stabilization, and concentration of CNT aggregates include β-naphthalenesulfonic acid formalin condensate sodium salts, such as Demol N, Demol RN, and Demol T (manufactured by Kao Corporation), polyoxyethylene stearyl ether Brij S 100 (manufactured by Sigma-Aldrich), 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 an example. CMC is particularly preferred from the viewpoint of excellent dispersibility, dispersion stabilization ability, and high concentration of CNT aggregates.

[0151] When the CNT dispersion according to the present disclosure contains a dispersant, it may contain only one type of dispersant, or may contain two or more types of dispersants. When the CNT dispersion contains a dispersant, the content of the dispersant in the CNT dispersion 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, etc. An example of the content of the dispersant in the CNT dispersion according to the present disclosure is 0.001% by mass to 20% by mass with respect to the total mass of the CNT dispersion.

[0152] [Applications] The applications of the CNT dispersion according to the present disclosure are not particularly limited. The CNT dispersion according to the present disclosure has high conductivity and can be applied to, for example, conductive materials such as conductive inks, antistatic agents, conductive materials for forming circuit patterns, materials for transparent electrodes, and water-soluble polymer fillers. The CNT dispersion according to the present disclosure can be suitably used as a conductive ink for forming electrodes (particularly, negative electrodes) of various secondary batteries such as lithium-ion batteries. By using the CNT dispersion according to the present disclosure as a conductive ink, highly conductive electrodes can be easily produced.

[0153] [Method for producing CNT dispersion] The CNT dispersion according to the present disclosure can be produced by dispersing the CNT aggregate according to the present disclosure in a dispersion medium. That is, the CNT dispersion according to the present disclosure can be produced by a method including a step of dispersing the CNT aggregate according to the present disclosure 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.

[0154] (Dispersion process) The dispersion process is a process of dispersing the CNT aggregate according to the present disclosure in a dispersion medium. In the dispersion process, a dispersant may be used from the viewpoint of improving the dispersibility and dispersion stability of the CNT aggregate according to the present disclosure. Details of the CNT aggregate, dispersion medium and dispersant according to the present disclosure are as described above.

[0155] The dispersion method is not particularly limited. Examples of the dispersion method include methods using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Examples of the dispersion method include methods using known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressure kneader. As a dispersion method, a method using a jet mill is preferred, and a method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pressure-feeds a mixture in a solvent as a high-speed flow from a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, CNT aggregates are dispersed by collisions between opposing flows in a pressure-resistant container, collisions with the container wall, turbulence caused by high-speed flow, shear flow, etc. As a wet jet mill, an ultra-high-pressure homogenizer (model number: NAGS20, NAGS100, JAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used. However, the wet jet mill is not limited to this. When using the ultra-high-pressure homogenizer as the dispersion device, the dispersion treatment pressure is preferably 10 MPa to 250 MPa.

[0156] (Drying Step) The method for producing a CNT dispersion liquid may include a step of drying the CNT aggregate according to the present disclosure (also referred to as a "drying step") before the dispersion step.

[0157] If moisture adheres to the CNT aggregate, the CNT aggregates tend to adhere to each other due to the surface tension of the water, which raises concerns about reduced dispersibility. Therefore, by performing a drying process on the CNT aggregate before the dispersion process, moisture adhered to the CNT aggregate is removed, and adhesion between CNT aggregates due to moisture adhesion is suppressed, thereby further improving the dispersibility of the CNT aggregate according to the present disclosure in the dispersion medium. The drying method is not particularly limited. Examples of drying methods include heat drying, vacuum drying, and heat vacuum drying. Heat vacuum drying is preferred as the drying method. The drying temperature is not particularly limited, and is preferably, for example, 40°C to 100°C. The drying time is not particularly limited, and can be set appropriately depending on the drying temperature, the degree of moisture adhesion to the CNT aggregate according to the present disclosure, etc.

[0158] <Conductive Material> The conductive material according to the present disclosure includes the CNT aggregate according to the present disclosure. As described above, the CNT aggregate according to the present disclosure contained in the conductive material according to the present disclosure has high conductivity and is therefore suitable as a conductive auxiliary. Since the conductive material according to the present disclosure includes the CNT aggregate according to the present disclosure, it has excellent conductive efficiency and can effectively impart high conductivity to an object to which it is used. The content ratio of the CNT aggregate in the conductive material according to the present disclosure may be any ratio relative to the total mass of the solid content.

[0159] The conductive material according to the present disclosure may contain a known conductive aid such as graphite, ketjen black, etc. Furthermore, the conductive material according to the present disclosure may contain CNTs and the like other than the CNT aggregate according to the present disclosure.

[0160] The conductive material according to the present disclosure may be the CNT aggregate according to the present disclosure. That is, the CNT aggregate according to the present disclosure itself may be used as the conductive material. Applications of the conductive material include use as an electrode material in batteries, for example, secondary batteries (e.g., lithium ion batteries), specifically, as a negative electrode active material, a positive electrode active material, etc.

[0161] The conductive material according to the present disclosure can be used as a conductive additive (preferably, a conductive additive for a negative electrode). One example of its use as a conductive additive is, for example, when manufacturing a positive electrode of a battery, mixing a positive electrode active material, the CNT aggregate according to the present disclosure, and a binder in a predetermined mass ratio, adding a solvent to the mixture to prepare a slurry, applying the slurry to a current collector for the positive electrode, drying it, and stretching it to produce a positive electrode.

[0162] Another example of use as a conductive auxiliary agent is, for example, when producing a negative electrode of a battery, a negative electrode active material, the CNT aggregate according to the present disclosure, and a binder are mixed in a predetermined mass ratio, a solvent is added to the mixture to prepare a slurry, which is then applied to a current collector for the negative electrode, dried, and stretched to produce a negative electrode.

[0163] <Electrode> The electrode according to the present disclosure includes an electrode active material and the conductive material according to the present disclosure described above. In the electrode according to the present disclosure, the CNT aggregate according to the present disclosure can function as a conductive assistant. The conductive material included in the electrode described below is synonymous with the conductive material according to the present disclosure, and the preferred embodiments are also the same.

[0164] The electrode according to the present disclosure may be at least one of a positive electrode and a negative electrode. The electrode according to the present disclosure may include an electrode active material layer, or may include a current collector and an electrode active material layer disposed on the current collector.

[0165] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, baked carbon, and aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals such as copper and nickel that have good carbon adsorption properties may be used as the current collector.

[0166] The electrode active material layer may contain an electrode active material, which is preferably electrode active material particles.

[0167] 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 can be, for example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), compounds substituted with one or more transition metals; LiFe ３ O ４ Lithium iron oxides such as those with the chemical formula Li １＋ｃ１ Mn ２－ｃ１ O ４ (0≦c1≦0.33), LiMnO ３ , LiMn ２ O ３ , LiMnO ２ Lithium manganese oxides such as lithium copper oxide (Li ２ CuO ２ ); LiV ３ O ８ , V ２ O ５ , Cu ２ V ２ O ７ Vanadium oxides such as LiNi １－ｃ２ M ｃ２ O ２ (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≦c2≦0.66); Ni-site type lithium nickel oxide represented by the chemical formula LiMn ２－ｃ３ M ｃ３ O ２ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), or Li ２ Mn ３ MO ８ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn ２ O ４ etc.

[0168] When the electrode is a negative electrode, the electrode active material is not particularly limited, and the electrode active material layer can include a negative electrode active material commonly used in negative electrode materials. Specifically, the negative electrode active material can include graphite-based active material particles or silicon-based active material particles.

[0169] The graphite-based active material particles may be at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads. By using artificial graphite as the graphite-based active material particles, the rate characteristics can be improved. The silicon-based active material particles may be Si, SiO ｘ (0<x<2), Si—C composites, and Si—Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, and combinations thereof). By using silicon-based active material particles, the capacity of the battery can be increased.

[0170] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer may contain a binder that is commonly used in electrode materials. Examples of the binder include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers have been substituted with Li, Na, Ca, or the like.

[0171] <Secondary Battery> A secondary battery according to the present disclosure includes an electrode according to the present disclosure. The secondary battery according to the present disclosure may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. It is preferable that at least one of the positive electrode and the negative electrode is an electrode according to the present disclosure, and that the negative electrode is an electrode according to the present disclosure.

[0172] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. It is not particularly limited as long as it is typically used as a separator in a secondary battery. The separator preferably has low resistance to ion migration of the electrolyte and excellent electrolyte humidification capacity. Specific examples of the separator include porous polymer films. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure comprising two or more layers of these films. The separator may also be a conventional porous nonwoven fabric, such as a nonwoven fabric made from high-melting-point glass fiber or polyethylene terephthalate fiber. To ensure heat resistance or mechanical strength, the separator may be coated with a ceramic component or a polymeric substance. The separator may have a selective single-layer or multi-layer structure.

[0173] 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 ion secondary batteries.

[0174] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt. Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0175] Among carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they have high viscosity, high dielectric constants, and effectively dissociate lithium salts. 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 or diethyl carbonate, in an appropriate ratio, in order to obtain an electrolyte having high electrical conductivity.

[0176] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte solution. The anion portion of the lithium salt may be, for example, F － , Cl － , I － , NO ３ － , N (CN) ２ － , B.F. ４ － , ClO ４ － , P.F. ６ － , (CF ３ ) ２ PF ４ － , (CF３ ) ３ PF ３ － 、(CF ３ ) ４ PF ２ － 、(CF ３ ) ５ PF － 、(CF ３ ) ６ P － 、CF ３ SO ３ － 、CF ３ CF ２ SO ３ － 、(CF ３ SO ２ ) ２ [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​In addition to the non-aqueous organic solvent and metal salt, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0178] The secondary battery according to the present disclosure can be used to form a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, for example.

[0179] An example of manufacturing an electrode and a secondary battery will be shown below, but the manufacturing of an electrode and a secondary battery according to the present disclosure is not limited to the following.

[0180] [Manufacturing Example: Manufacturing Example of Electrode (Negative Electrode) and Secondary Battery] A slurry for a negative electrode is prepared by mixing known artificial graphite as a negative electrode active material, a CNT dispersion according to the present disclosure and known carbon black as a negative electrode conductive additive, and known styrene butadiene rubber (SBR) and known carboxymethyl cellulose (CMC) as a negative electrode binder in a predetermined mass ratio with distilled water. The slurry for a negative electrode is applied to a negative electrode current collector (Cu), dried, and rolled to adjust the final thickness (i.e., the total thickness of the current collector and the negative electrode active material layer) to prepare a negative electrode. The current collector coated with the slurry for a negative electrode is then further dried in an oven to prepare a negative electrode. Next, a known slurry for a positive electrode is applied to a positive electrode current collector (Al), dried, and rolled to adjust the final thickness (i.e., the total thickness of the current collector and the positive electrode active material layer) to prepare a positive electrode. As the positive electrode slurry, for example, the positive electrode slurry described in paragraph

[0096] of JP-A No. 2022-521422 can be used. A mono-cell is produced by interposing a separator between the negative electrode and the positive electrode, and an electrolyte solution is injected to produce a lithium ion secondary battery.

[0181] <Planar aggregate> The planar aggregate according to the present disclosure includes the CNT aggregate according to the present disclosure. The ratio of the CNT aggregate according to the present disclosure contained in the planar aggregate according to the present disclosure is usually 1 mass % or more with respect to the total mass of the planar aggregate. The planar aggregate according to the present disclosure may include other components such as CNTs other than the CNT aggregate according to the present disclosure.

[0182] [Method for Producing Planar Assembly] There are no particular limitations on the method for producing the planar aggregate according to the present disclosure. 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, or the CNT aggregate according to the present disclosure and optionally other components, in water or other fluid, and filtering once or twice or more times.

[0183] The planar assembly according to the present disclosure can be, for example, a film, and is useful, for example, as a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet (EUV) radiation.

[0184] <Composition> The composition according to the present disclosure comprises the CNT aggregate according to the present disclosure and at least one selected from the group consisting of resin, ceramic, and concrete. Examples of the resin include thermoplastic resin and thermosetting resin, and preferably olefin-based resin, polycarbonate-based resin, polyester-based resin, polyamide-based resin, thermoplastic polyurethane resin, polysulfone-based resin, and silicone resin. Examples of the ceramic include crystalline ceramic and amorphous ceramic. Examples of the concrete include Portland cement concrete. The composition according to the present disclosure may further comprise other components such as water and an organic solvent. In the composition according to the present disclosure, when the content of the CNT aggregate is taken as 100 parts by mass, the content of at least one selected from the group consisting of resin, ceramic, and concrete is usually 10 to 1,000,000 parts by mass, preferably 100 to 100,000 parts by mass, and more preferably 1,000 to 40,000 parts by mass, and when other components are included, it is preferably 1 to 10,000 parts by mass, and more preferably 10 to 1,000 parts by mass. In the composition according to the present disclosure, the CNT aggregate, resin, ceramic, concrete, and other components may each be included singly or in combination of two or more types.

[0185] [Method for producing the composition] The composition according to the present disclosure can be produced, for example, by mixing the CNT aggregate according to the present disclosure with a resin, ceramics, or pre-hardened concrete. The resin may be in the form of a powder, pellets, solution, or dispersion. The ceramics may be in the form of a powder, precursor solution, or dispersion. The composition according to the present disclosure can also be produced, for example, by dispersing the CNT dispersion according to the present disclosure in a resin solution, a ceramic precursor or dispersion, or pre-hardened concrete, and then molding the resultant.

[0186] [Uses of the Composition] When the composition according to the present disclosure contains a resin or ceramic, it is useful as, for example, a structural material, a conductive material, a heat management material, or an antistatic material. When the composition according to the present disclosure contains concrete, it is useful as a lightweight, durable building material or an electricity storage device (optionally impregnated with an electrolyte).

[0187] The CNT aggregate, CNT dispersion, conductive material, electrode, secondary battery, planar aggregate, and composition according to the present disclosure will be described in more detail below with reference to examples. The CNT aggregate, CNT dispersion, conductive material, electrode, secondary battery, planar aggregate, and composition according to the present disclosure are not limited to the following examples as long as they do not deviate from the gist of the disclosure.

[0188] <Preparation of CNT Aggregate> [Example 1] The MWCNT aggregate 1 of Example 1 was prepared by a floating catalyst method (CVD method) that directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled at 400°C to 700°C. A mixture of nitrogen and argon was used as the carrier gas, and the flow rate of the carrier gas was 30,000 sccm (standard cubic centimeters per minute). By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst was produced is referred to as the first temperature zone. Next, methane, a carbon source, was released into the carrier gas flow. A metal catalyst and a carbon source were supplied to a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce CNT aggregates. In the second temperature zone, an electric field was generated in a temperature-controlled flow reactor, thereby producing MWCNT aggregates. The produced aggregates were continuously discharged through an outlet of the flow reactor, which was temperature-controlled at 100°C to 500°C, and collected as a sheet-like MWCNT aggregate by continuous discharge. The collected sheet-like MWCNT aggregate was washed with deionized water for 10 seconds. In this manner, MWCNT aggregate 1 of Example 1 was obtained.

[0189] [Example 2] The MWCNT aggregate 2 of Example 2 was obtained by pulverizing the sheet-like MWCNT aggregate 1 collected in Example 1 using a freezing pulverizer (manufactured by Japan Analytical Industry Co., Ltd., JFC-2000) under the following conditions. More specifically, 5 g of the MWCNT aggregate 1 was placed in a 75 mL sample container, and one steel ball made of tungsten carbide was further placed in the sample container, and then the sample container was attached to a pulverizing rod. The entire sample container was immersed in liquid nitrogen to cool the MWCNT aggregate 1 and the steel ball, and then the pulverizing rod was moved up and down to move the steel ball inside the sample container and pulverize the MWCNT aggregate 1. Freezing retention time: 5 minutes Pulverization time: 2 minutes

[0190] Example 3 Similar to the sheet-like MWCNT aggregate 1 collected in Example 1, the MWCNT aggregate 3 of Example 3 was produced by a floating catalyst method (CVD method) that directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled between 400°C and 700°C. A mixture of nitrogen and argon was used as the carrier gas. The carrier gas flow rate was 30,000 sccm. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst was produced is referred to as the first temperature zone. 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, whose temperature was controlled at 1,400°C. The second temperature zone was maintained at a temperature sufficient to produce CNT aggregates. In the second temperature zone, an electric field was generated in a temperature-controlled flow reactor, thereby producing MWCNT aggregates. The produced aggregates were continuously discharged through an outlet of the flow reactor, which was temperature-controlled at 100°C to 500°C, and collected as fibrous MWCNT aggregates by continuous discharge. The collected fibrous MWCNT aggregate was washed with deionized water for 10 seconds. In this manner, MWCNT aggregate 3 of Example 3 was obtained.

[0191] [Comparative Example 1] MWCNT aggregate C1 (product number: 901019, MWCNT aggregate, manufactured by Sigma-Aldrich) was used as Comparative Example 1. [Comparative Example 2] MWCNT aggregate C2 (product number: FT7000, MWCNT aggregate, manufactured by C-nano) was used as Comparative Example 2. [Comparative Example 3] MWCNT aggregate C3 (product number: FT6120, MWCNT aggregate, manufactured by C-nano) was used as Comparative Example 3.

[0192] <Preparation of CNT Dispersion> [Example 1: CNT Dispersion 1] 1.1 g of the MWCNT aggregate 1 of Example 1, 1.65 g of carboxymethyl cellulose (trade name: CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY, manufactured by MP Biomedicals) as a dispersant, and 547.25 g of ion-exchanged water were mixed. The obtained mixture was subjected to a dispersion treatment at 8,500 rpm for 1 hour using Labo-Lusion (product name) manufactured by Primix Corporation as a pre-dispersion before the main dispersion, thereby obtaining a pre-dispersion treatment liquid 1. Note that, in order to prevent the MWCNT aggregate 1 from becoming entangled in the stirring part of the Labo-Lusion, the MWCNT aggregate 1 was cut into small pieces of about 1 cm square using scissors before mixing. Next, the pre-dispersion treatment liquid 1 obtained above was subjected to a main dispersion treatment under the following conditions using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd., which is a wet jet mill, to obtain CNT dispersion liquid 1.

[0193] -Conditions- Nozzle diameter: 0.30 mm Pressure: 50 MPa Number of times: 1 Method: Circulation method

[0194] [Example 2: CNT Dispersion 2] 0.55 g of the MWCNT aggregate 2 of Example 2, 0.825 g of carboxymethyl cellulose (trade name: CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY, manufactured by MP Biomedicals) as a dispersant, and 273.625 g of ion-exchanged water were mixed. The resulting mixture was subjected to a dispersion treatment at 10,000 rpm for 1 hour using an Ace Homogenizer (product name) manufactured by Nippon Seiki Seisakusho Co., Ltd. as a pre-dispersion before the main dispersion, thereby obtaining a pre-dispersion treatment liquid 2. Next, the pre-dispersion treatment liquid 2 obtained above was subjected to a main dispersion treatment under the following conditions using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd., which is a wet jet mill, to obtain a CNT dispersion liquid 2.

[0195] -Conditions- Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 18 Method: Circulation method

[0196] [Example 3: CNT dispersion liquid 3] 0.55 g of the MWCNT aggregate 3 of Example 3, 0.825 g of carboxymethyl cellulose (trade name: CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY, manufactured by MP Biomedicals) as a dispersant, and 273.625 g of ion-exchanged water were mixed. The obtained mixture was subjected to a dispersion treatment at 10,000 rpm for 3.5 hours using an Ace Homogenizer (product name) manufactured by Nippon Seiki Seisakusho Co., Ltd. as a pre-dispersion before the main dispersion, thereby obtaining a pre-dispersion treatment liquid 3. Note that the MWCNT aggregate 3 was cut to a length of about 1 cm using scissors before mixing so that the MWCNT aggregate 3 would not become entangled in the blades of the homogenizer. Next, the pre-dispersion treatment liquid 3 obtained above was subjected to a main dispersion treatment under the following conditions using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd., which is a wet jet mill, to obtain CNT dispersion liquid 3.

[0197] -Conditions- Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 Method: Circulation method

[0198] [Comparative Example 1: CNT Dispersion C1] 1.1 g of the MWCNT aggregate C1 of Comparative Example 1, 1.65 g of carboxymethyl cellulose (trade name: CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY, manufactured by MP Biomedicals) as a dispersant, and 547.25 g of ion-exchanged water were mixed. The obtained mixture was subjected to a dispersion treatment at 10,000 rpm for 1 hour using an Ace Homogenizer (product name) manufactured by Nippon Seiki Seisakusho Co., Ltd. as a pre-dispersion before the main dispersion, to obtain a pre-dispersion treatment liquid C1. Next, the pre-dispersion treatment liquid C1 obtained above was subjected to a main dispersion treatment under the same conditions as the main dispersion treatment in Example 3: CNT dispersion liquid 3 above, using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Corporation, which is a wet jet mill, to obtain CNT dispersion liquid C1.

[0199] [Comparative Example 2: CNT dispersion C2] A CNT dispersion C2 was obtained in the same manner as in [Comparative Example 1: CNT dispersion C1], except that the MWCNT aggregate C2 was used as the MWCNT aggregate.

[0200] [Comparative Example 3: CNT dispersion C3] A CNT dispersion C3 was obtained in the same manner as in [Comparative Example 1: CNT dispersion C1], except that MWCNT aggregate C3 was used as the MWCNT aggregate.

[0201] <Imaging using a scanning electron microscope (SEM)> [Attachment of CNT dispersion to a substrate for SEM observation] The above CNT dispersion was diluted with pure water so that the CNT concentration was 0.002 mass% relative to the total amount of the CNT dispersion. When observing the CNT dispersion (CNT concentration: 0.002 mass%) with an SEM, the CNT dispersion was attached to a substrate for SEM observation using the following procedure to prevent excessive aggregation of the CNTs.

[0202] 1. A slide glass on which Pt had been vapor-deposited was subjected to UV-ozone treatment and attached to a substrate for SEM observation with conductive carbon tape. 2. 0.1 μL of CNT dispersion was applied to the slide glass. 3. The substrate for SEM observation to which the CNT dispersion had been applied was placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass on which the CNT dispersion had been frozen was placed on a 4.0 × 10 －３ A vacuum was drawn at a pressure of 100 Pa to sublimate the ice.

[0203] [Imaging] The CNT dispersion (CNT concentration: 0.002% by mass) was imaged using an SEM under the following conditions to obtain multiple images of the CNT-attached region: SEM device: S-4800 (manufactured by Hitachi High-Technologies Corporation) Acceleration voltage: 1 kV Emission current: 10 μA Measurement magnification: 500x Image size: 1280 pixels × 960 pixels

[0204] An SEM photograph of CNT dispersion 2 in Example 2 is shown in Figure 1. The formation of a CNT network structure was confirmed. An SEM photograph of CNT dispersion C1 in Comparative Example 1 is shown in Figure 2. The formation of a CNT network structure was not confirmed.

[0205] <Image Selection> All images of the region where the CNT dispersion liquid (CNT concentration: 0.002% by mass) was attached were subjected to the following image processing using ImageJ, which is image analysis software.

[0206] [Image processing procedure] 1. Crop: 1280 pixels x 896 pixels 2. Filters: Gaussian Blur, Sigma (Radius) = 3 3. Filters: Top Hat, Radius = 9 pixels 4. Binarization: Auto Threshold, Otsu, White objects on black background 5. Morphology: Gray Morphology, Radius of the structure elements (pixels) = 3.0, Type of structure element=circle, operator=open

[0207] Next, the image after the image processing was divided into 64 parts (8 parts both vertically and horizontally), and only images in which all 64 divided images contained pixels with a pixel value of 255 (i.e., images in which the CNT-attached region was present throughout) were selected from the images of the attachment region. However, images in which CNTs were clearly not extracted after the image processing compared to the images before the image processing (for example, images in which most of the SEM observation substrate region contained pixels with a pixel value of 255) were excluded from selection in advance.

[0208] [Proportion of Selected Images] The proportion of images used for calculating the fractal dimension (i.e., selected images) among the total number of images of the CNT dispersion-attached region is as shown in Table 1 below.

[0209]

[0210] <Calculation of Average Value of Fractal Dimension> The fractal dimension of each of the selected images after image processing was calculated using the image analysis software ImageJ in the following procedure.

[0211] [Calculation Procedure] 1. Binary: Skeletonize 2. Analyze: Fractional Box Counter, Box Sizes = 4, 6, 8, 12, 16, 32, 64, 128, Black Background

[0212] Based on the fractal dimension calculated for each image, the average value of the fractal dimension for each example and comparative example was further calculated. Table 2 shows the results of the average value of the fractal dimension for MWCNT aggregates 1 to 3 of examples 1 to 3 and MWCNT aggregates C1 to C3 of comparative examples 1 to 3.

[0213] [Variance, Standard Deviation, and Median] The variance, standard deviation, and median of the fractal dimension in each Example and Comparative Example were calculated based on the following formulas. The results are shown in Table 2. Data x １ , x ２ , ..., x ｎ When the mean is expressed as μ, the variance S ２ and standard deviation S were calculated using the following formulas (1) and (2), respectively.

[0214]

[0215] The data is sorted in ascending order and expressed as x (1) , x (2) , ..., x (n) Then, the median value Me was calculated by the following formula (3).

[0216]

[0217] <Fe atom content relative to total mass of CNT aggregate> Using an inductively coupled plasma mass spectrometry (ICP-MS) device (NexION 2000C, manufactured by PerkinElmer), the content ratios of Fe atoms contained in MWCNT aggregates 1 to 3 of Examples 1 to 3, and MWCNT aggregates C1 to C3 of Comparative Examples 1 to 3 were measured. As a pretreatment, the CNT aggregates were subjected to low-temperature ashing / acid melting. The results are shown in Table 2.

[0218] <Maximum Length of CNT> [Example 1: MWCNT aggregate 1] When observing 100 MWCNTs in a plurality of SEM photographs (magnification: 5000x) of adjacent MWCNT aggregate 1, the maximum length was 3,500 µm.

[0219] [Example 2: MWCNT aggregate 2] When observing 100 MWCNTs in a plurality of SEM photographs (magnification: 5000 times) of adjacent MWCNT aggregate 2, the maximum length was 3,500 µm.

[0220] Example 3 MWCNT Aggregate 3 When observing 100 MWCNTs in a plurality of SEM photographs (magnification: 5000 times) of adjacent MWCNT aggregate 3, the maximum length was 4,000 μm.

[0221] <Conductivity> MWCNT Dispersions 1 to 3 of Examples 1 to 3 and MWCNT Dispersions C1 to C3 of Comparative Examples 1 to 3 (CNT concentration: 0.2 mass%) were dropped onto a glass substrate cut to a size of 10 cm x 10 cm, and a film was formed using a stainless steel applicator with a gap size of 150 μm. The glass substrate was then heated on a hot plate at 110°C for 10 minutes to dry the film, thereby obtaining MWCNT Assembly Films 1 to 3 and MWCNT Assembly Films C1 to C3, respectively. The surface resistivities of the MWCNT Assembly Films 1 to 3 and MWCNT Assembly Films C1 to C3 obtained in this manner were measured using a resistivity meter, Loresta GXII (trade name), manufactured by Nitto Seiko Analytech Co., Ltd. The surface resistivity was measured at five different points on the CNT aggregate film, and the average value was taken as the surface resistivity of the MWCNT aggregate. Furthermore, based on the surface resistivity of the CNT aggregate, the conductivity of the MWCNT aggregate was evaluated according to the following evaluation criteria. The results are shown in Table 2. If the evaluation result was "AA", "A", or "B", it was determined that the conductivity was excellent. An evaluation result of "AA" is most preferable.

[0222] -Evaluation criteria- AA: The surface resistivity of the MWCNT aggregate is 1.00 x 10 ２A: The surface resistivity of the MWCNT aggregate is less than 1.00 × 10 ２ Ω / sq or more 1.80×10 ２ B: The surface resistivity of the MWCNT aggregate is in the range of 1.80 × 10 ２ Ω / sq or more 3.00×10 ２ C: The surface resistivity of the MWCNT aggregate is in the range of less than 3.00 × 10 ２ Ω / sq or more 1.00×10 ５ D: The surface resistivity of the MWCNT aggregate is in the range of less than 1.00 × 10 ５ It is Ω / sq or more.

[0223] <Battery Evaluation> A lithium ion secondary battery was fabricated.

[0224] 1. Preparation of positive electrode for lithium ion secondary battery Positive electrode active material (LiNi ０．８ Co ０．１ Mn ０．１ O ２ ), 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 obtained positive electrode mixture was applied to a 15 μm thick Al foil that served as a current collector, and vacuum dried at 80°C for 1 hour, followed by roll pressing to obtain a positive electrode for a lithium ion secondary battery. The positive electrode area was 1.65 cm ２ , basis weight 16 mg / cm ２ , density is 3.0 g / cm ３ It was adjusted so that

[0225] 2. Preparation of a negative electrode for a lithium ion secondary battery A negative electrode for a lithium ion secondary battery was prepared by mixing artificial graphite MAG-E and carbon-coated SiO in a ratio of 9:1 (by mass) as the negative electrode active material, CLPA-C07 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the binder, and MWCNT dispersion 1 of Example 1, MWCNT dispersion 3 of Example 3, MWCNT dispersion C2 of Comparative Example 2, and MWCNT dispersion C3 of Comparative Example 3 as the conductive additive, and adding and kneading them so that the composition was a negative electrode active material:binder:conductive additive = 94.9:5.0:0.1 (by mass), to prepare a paste-like negative electrode mixture. Ion-exchanged water was used as the solvent when preparing the negative electrode mixture. The obtained negative electrode mixture was applied to a Cu foil having a thickness of 20 μm using a single-sided continuous coater, dried at 120° C., and then roll-pressed to obtain a negative electrode for a lithium ion secondary battery. The negative electrode area was 1.77 cm ２ , basis weight 9.3 mg / cm ２ , density is 1.4 g / cm ３ It was adjusted so that

[0226] 3. Preparation of Lithium-ion Secondary Battery The positive electrode for the lithium-ion secondary battery was placed on the bottom cover of a coin-type battery R2032 part (manufactured by Hosen Co., Ltd.), and a laminated film separator consisting of a polyethylene porous film and a 16 μm heat-resistant porous layer was placed on top of it. 300 μL of electrolyte was poured into this. The electrolyte was a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, to which 1 volume % of vinylene carbonate was added, and LiPF ６ The lithium ion secondary battery negative electrode was placed on top of a laminated film separator, and a top cover was placed on top of the separator via a gasket. The battery was then crimped with a crimping machine to prepare a coin-type full-cell R2032 lithium ion secondary battery. These operations were carried out in a glove box under an argon atmosphere.

[0227] 4. Cycle Test Using the fabricated lithium ion secondary battery, a cycle test was performed 200 times under the conditions shown below, and the discharge capacity retention rate after 200 cycles was calculated using the following formula. Note that a higher discharge capacity retention rate after 200 cycles indicates better life characteristics. Discharge capacity retention rate after 200 cycles (%) = 200th discharge capacity / 1st discharge capacity × 100

[0228] - Cycle test conditions - Test temperature: 25°C Charging conditions: constant current / constant voltage charging, maximum charging voltage 4.2V, charging time 5 hours, charging current 0.3CA Rest time after discharge: 10 minutes Discharging conditions: constant current discharging, minimum discharging voltage 2.5V, discharging current 0.3CA Rest time after charge: 10 minutes In this test, a process of charging, discharging rest, discharging, and discharging rest in this order was counted as one cycle. The evaluation results for Example 1, Example 3, Comparative Example 2, and Comparative Example 3 are shown in Table 2.

[0229]

[0230] From the above, it was shown that the MWCNT aggregates 1 to 3 of Example 1 to Example 3 are CNT aggregates excellent in conductivity. Furthermore, according to the MWCNT aggregates 1 and 3 of Example 1 and Example 3, the discharge capacity retention rate after 200 cycle tests was high, that is, a lithium ion secondary battery excellent in cycle characteristics was obtained.

Claims

1. A carbon nanotube aggregate having an average fractal dimension of 1.03 to 2.00 when the carbon nanotube concentration is 0.002 mass % relative to the total amount of the carbon nanotube dispersion, as calculated under the following conditions: The carbon nanotube dispersion is imaged using a scanning electron microscope to obtain multiple images of the carbon nanotube-attached regions. From the obtained images, an image in which the carbon nanotube-attached regions are present throughout is selected. Using the selected images, the average fractal dimension of the carbon nanotube structure is calculated by image analysis.

2. The carbon nanotube aggregate according to claim 1, wherein the carbon nanotubes are multi-walled carbon nanotubes.

3. The aggregate of carbon nanotubes according to claim 1 or 2, containing 450 mass ppm to 150,000 mass ppm of Fe atoms relative to the total mass of the aggregate of carbon nanotubes.

4. The carbon nanotube aggregate according to claim 1 or 2, wherein the maximum length of the carbon nanotubes is 500 μm to 30,000 μm.

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

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

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

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

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

10. A composition comprising the aggregate of carbon nanotubes according to claim 1 or 2 and at least one material selected from the group consisting of resin, ceramics and concrete.

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