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

Abstract

Provided are a carbon nanotube aggregate having excellent conductivity, a carbon nanotube dispersion, a conductive material, an electrode, a secondary battery, a planar aggregate, and a composition. [Solution] 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, images in which the carbon nanotube-attached regions are present throughout are selected. Using the selected images, the average fractal dimension of the carbon nanotube structure is calculated by image analysis.

Description

[Technical Field]

[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. [Background technology]

[0002] Carbon nanotubes (also called "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 broadly divided into single-walled carbon nanotubes (also called "SWCNTs"), which are made from a single layer of graphene sheets, and multi-walled carbon nanotubes (also called "MWCNTs"), which are made 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 used in a variety of 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, which have a spherical secondary structure in which carbon nanotube units are entangled, and whose true density, bulk density, and metal content are each within a predetermined numerical range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2023 / 162937 [Patent Document 2] Japanese Patent Application Publication No. 2018-39722 [Patent Document 3] Special Publication No. 2018-530854 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one embodiment of the present disclosure is to provide an aggregate of carbon nanotubes having excellent electrical conductivity. Another problem to be solved by another embodiment of the present disclosure is to provide a carbon nanotube dispersion, a conductive material, a planar aggregate, and a composition, each of which includes the carbon nanotube aggregate. Another problem to be solved by another embodiment of the present disclosure is to provide an electrode including the above-mentioned conductive material. Another problem to be solved by another embodiment of the present disclosure is to provide a secondary battery including the above electrode. [Means for solving the problem]

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

[0009] According to an embodiment of the present disclosure, it is possible to provide an aggregate of carbon nanotubes having excellent electrical conductivity. According to another embodiment of the present disclosure, there can be provided a carbon nanotube dispersion, a conductive material, a planar aggregate, and a composition, each of which includes the carbon nanotube aggregate. According to another embodiment of the present disclosure, an electrode can be provided that includes the conductive material described above. According to another embodiment of the present disclosure, a secondary battery including the above electrode can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a scanning electron microscope photograph of CNT dispersion liquid 2 in Example 2. [Figure 2] FIG. 2 is a scanning electron microscope photograph of CNT dispersion C1 in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an example of an embodiment according to the present disclosure will be described in detail. The following description may be made based on typical embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and modifications can be appropriately made and implemented within the scope of the object of the present disclosure.

[0012] In the present disclosure, the numerical range indicated using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the 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, the amount of each component means the total amount of a plurality of substances corresponding to each component unless otherwise specified when there are a plurality of substances corresponding to each component. In this specification, the term "step" includes not only an independent step but also cases where it cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0013] In the present disclosure, each of the terms "carbon nanotube", "single-walled carbon nanotube", "multi-walled carbon nanotube", "multi-walled carbon nanotube having a maximum length of 500 μm to 30,000 μm (particularly, multi-walled carbon nanotube 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 calculated under the following conditions in a CNT dispersion liquid where the CNT concentration is 0.002 mass % relative to the total amount of the CNT dispersion liquid. Conditions: The CNT dispersion is photographed using a scanning electron microscope to obtain multiple images of the CNT-attached regions. From the obtained images, images in which the CNT-attached regions are present throughout are selected. Using the selected images, the average value of the fractal dimension of the CNT structure is calculated by image analysis.

[0015] The CNT aggregate according to the present disclosure has excellent electrical conductivity. The inventors have discovered that CNT aggregates with an average fractal dimension of 1.03 to 2.00 calculated under specified conditions form a giant network structure in which the CNTs are entangled with each other, which can exist stably in a dispersion liquid. Fractal dimension is the absolute value of the slope of the approximate line of a plot of the logarithm of the number of boxes required to cover the figure for which the fractal dimension is to be calculated against the logarithm of the box (also called partition) size. When CNTs form a network structure, the number of boxes required to cover the figure of the network structure increases with smaller box sizes, so the absolute value of the slope of the approximate line increases, and the value of the fractal dimension increases. It is presumed that the formation of a network structure by the CNTs results in multiple contacts between the CNTs, forming huge conductive paths and increasing the electrical conductivity. Therefore, the CNT aggregate according to the present disclosure has excellent electrical conductivity. It should be noted that the present disclosure is in no way limited to the above-mentioned presumed mechanism.

[0016] [Average value of fractal dimension] The average value of the fractal dimension of the CNT structure calculated under predetermined conditions using the CNT aggregate according to the present disclosure is 1.03 to 2.00. From the viewpoint of electrical conductivity, the average value 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. When the average fractal dimension is at the lower limit of 1.03, contact points between CNTs are generated at multiple points, improving conductivity. The upper limit of 2.00 for the average fractal dimension is the theoretical maximum value resulting from the fact that the average fractal dimension is calculated from a two-dimensional image. Furthermore, when the average fractal dimension is 1.60 or less, particularly good dispersibility in solvents 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 liquid is prepared in which the concentration of CNTs is 0.2 mass % relative to the total amount of the CNT dispersion liquid. The method for preparing a CNT dispersion liquid having a CNT concentration of 0.2 mass % relative to the total amount of the CNT dispersion liquid is not particularly limited, and the CNT dispersion liquid can be prepared by a known method. More specifically, first, CNT aggregates, water, and carboxymethyl cellulose are mixed to obtain a mixture with a CNT concentration of 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 to a dispersion treatment using a wet jet mill as a main dispersion, thereby obtaining a CNT dispersion with a CNT concentration of 0.2 mass%. In other words, a CNT aqueous dispersion with a CNT concentration of 0.2 mass% relative to the total amount of the CNT dispersion is prepared.

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

[0022] (Image taken 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 region. The imaging method using an SEM is not particularly limited, and can be performed by a known method.

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

[0024] -Image capture- Next, the impregnated CNT dispersion is imaged using an SEM device (e.g., S-4800, manufactured by Hitachi High-Technologies Corporation) under the following conditions to obtain multiple images of the CNT-immobilized region. The CNT-immobilized 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 value, it is preferable to obtain 10 or more images. Acceleration voltage: 1 kV Emission current: 10μA Measurement magnification: 500x Image size: 1280 pixels x 960 pixels

[0025] (Image selection) Among the obtained images, an image in which the CNT-attached region is present throughout is selected. More specifically, first, the following image processing is performed on all images of the CNT dispersion-attached region using image analysis software (for example, ImageJ).

[0026] - Image processing procedure - 1.Crop: 1280 pixels x 896 pixels 2.Filters: Gaussian Blur, Sigma(Radius)=3 3.Filters:Top Hat, Radius=9pixels 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 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-attached region is present throughout) are selected from the images of the attachment region. 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 region has pixels with a pixel value of 255) are excluded from selection in advance.

[0028] -Percentage 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-attached 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 the fractal dimension) Using the selected image, 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 (for example, ImageJ), and the fractal dimension is calculated for each image using the following procedure.

[0030] -Calculation procedure- 1.Binary:Skeletonize 2.Analyze:Fractal 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: Data x1, x2, . . ., x n When the mean value of is expressed as μ, the variance S 2 and standard deviation S are calculated by the following formulas (1) and (2), respectively.

[0033]

number

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

[0035]

number

[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. In light of electrical conductivity, the median value of the fractal dimension is preferably from 1.03 to 1.80, more preferably from 1.04 to 1.60, still more preferably from 1.04 to 1.40, and particularly preferably from 1.05 to 1.20.

[0037] [SWCNT, MWCNT] The CNTs in the CNT aggregate according to the present disclosure may be SWCNTs or MWCNTs, or may be a mixture of SWCNTs and MWCNTs. From the viewpoint of excellent thermal stability and chemical stability, and from the viewpoint of having a wall number distribution and therefore lower uniformity, making it easier to improve dispersibility, the CNTs preferably include MWCNTs, and more preferably are MWCNTs. The number of walls of the CNT can be controlled by selecting the method for producing the CNT.

[0038] [Fe atom] 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 CNTs and / or in a state where they are incorporated into the interior of the CNTs. From the viewpoint of dispersibility in a dispersion medium, the CNT aggregate according to the present disclosure preferably contains 450 mass ppm to 150,000 mass ppm of Fe atoms, and more preferably 500 mass ppm to 150,000 mass ppm 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 are more preferably 1,000 mass ppm to 100,000 mass ppm, even more preferably 5,000 mass ppm to 90,000 mass ppm, particularly preferably 10,000 mass ppm to 80,000 mass ppm, and especially preferably 30,000 mass ppm to 70,000 mass ppm, 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, making it easy for the CNTs to aggregate. Here, it is thought that if an appropriate amount of Fe atoms are attached to the surface of the CNT, the Fe atoms will moderately inhibit contact between multiple CNTs, thereby suppressing excessive aggregation. More specifically, in a CNT aggregate in which the content of Fe atoms is 150,000 mass ppm or less relative to the total mass of the CNT aggregate, even if Fe atoms are present, it is easy to ensure a certain number of contact points between the CNTs, making it easy to connect conductive paths and improving conductivity. On the other hand, in a CNT aggregate in which the content of Fe atoms is 450 mass ppm or more (particularly 500 mass ppm 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 conductivity is more likely to be improved.

[0040] The content ratio of Fe atoms to the total mass of the CNT aggregate can be measured, for example, by the following method. First, the CNT aggregates are completely dissolved in an acid such as hydrochloric acid or nitric acid. To completely dissolve the CNT aggregates in the acid, pretreatment such as dry ashing, wet ashing, or melting may be performed. The solution in which the CNT aggregates are completely dissolved in the acid can be subjected to inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS) to measure the Fe atom content. ICP-MS is preferred because it allows for more sensitive measurements.

[0041] [Maximum length] The maximum length of the CNTs in the CNT aggregate according 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, even 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. This is thought to be because 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 mentioned above, MWCNTs with 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 fiber may be a thread-like fiber with a circular cross section, a ribbon-like fiber with a rectangular cross section, hollow, or have another shape. From the viewpoint of increasing electrical conductivity, the cross section of the ULMWCNT is preferably circular, and hollow is preferred.

[0045] By taking on a fibrous form, ULMWCNTs have the property of easily entangling with each other. The CNT aggregate preferably contains at least one ULMWCNT, and from the viewpoint that the CNTs are more likely to entangle with each other and form a more stable aggregate, an aggregate containing multiple 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 a CNT dispersion according to the present disclosure. The SEM photograph shown in Figure 1 shows that multiple 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 images taken at adjacent viewing angles. Here, "CNT length" refers to the measured length of the CNT in the longitudinal direction, and the maximum value of the measured lengths is taken as the "maximum length." When observing an SEM photograph, if one 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 from the viewpoint of further improving the stability of the CNT aggregate due to the entanglement of ULMWCNTs, it is preferable that 10% or more of the observed CNTs are MWCNTs (i.e., ULMWCNTs) with a maximum length in the range of 500 μm to 30,000 μm (particularly 1,000 μm to 30,000 μm), calculated as numbers, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0049] 〔diameter〕 The diameter of the CNTs in the CNT aggregate according to the present disclosure can be measured by observing SEM photographs or transmission electron microscope (TEM) photographs. 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, further preferably 3 nm to 50 nm, and particularly preferably 5 nm to 30 nm.

[0051] The length / diameter ratio of the CNT, 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 CNTs can be measured by thermogravimetric analysis. For example, a thermal analyzer (Shimadzu Corporation, DTG-60) is used to obtain a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the CNT aggregate. The largest exothermic peak in the DTA curve, which appears at a peak top near 650°C to 750°C, is considered to be the combustion of CNTs, and any other exothermic peaks are considered to be the combustion of substances other than CNTs. The purity of the CNTs is determined from the weight loss rate of the TG curve. From the viewpoint of the obtained 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] [Application] The use of the CNT aggregate according to the present disclosure is not particularly limited. The CNT aggregate according to the present disclosure has excellent electrical conductivity, and therefore has 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). Note that, in the present disclosure, the 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, plays a role in assisting 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 Ketjenblack. The CNT aggregate according to the present disclosure can be used, for example, as a conductive material. Examples of conductive materials to which the CNT aggregate according to the present disclosure is applied 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 producing a CNT aggregate according to the present disclosure (including the method for producing an SWCNT aggregate, the method for producing an MWCNT aggregate, and the method for producing an ULMWCNT aggregate) is not particularly limited. As a method for producing 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 method described in, for example, Japanese Patent Application Laid-Open No. 2016-102047 or Japanese Patent Application Laid-Open No. 2021-527611. Below, the method for producing a CNT aggregate according to the present disclosure will be described with examples, but the method for producing a 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 JP 2016-102047 A. That is, an example of a manufacturing method (hereinafter also referred to as "manufacturing method X") includes the steps of passing gaseous reactants containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in 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 production method X, the 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 production 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 can be exerted by a rotating spindle around which the agglomerates are wound. The fibrous CNT aggregates can be collected on the spindle or can be accumulated elsewhere by rotating around the spindle one or more times and then successively 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 a 25° angle 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 around two axes (e.g., two perpendicular axes). In particular, the spindle can rotate around axes perpendicular and parallel to the flow direction of the gaseous reactants. Such a spindle can pull and twist the agglomerates of fibrous CNT aggregates to control the twist number and length.

[0061] The spindle may be made of metal, ceramic, or resin. The spindle can have different suitable shapes depending on the material properties and the intended use of the CNT aggregate. The spindle can be used as a mold for producing carbon products, for example, by a spin coating process. Preferred spindle shapes are rod-shaped or box-shaped.

[0062] Fibrous CNT aggregates are deposited on the spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the application of an electric or other field 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 / minute; the same applies hereinafter) to 10,000 rpm, and more preferably 0.1 rpm to 100 rpm. The spinning speed (i.e., the rotational speed of the spindle) may be adjusted so that the material is collected at a similar rate to that which is produced. The rotational speed of the spindle may also control the thickness of the accumulated CNT filament. In a preferred embodiment, as the spindle rotates, the CNT filament is processed in the axial direction of the spindle. This processing ensures that the CNT filament is evenly wrapped along the spindle, rather than being wrapped only at one specific point on the spindle.

[0064] The CNT fiber aggregates 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 aggregates as they are collected. A suitable substrate arrangement for fiber technology is a substrate consisting of two guides positioned at right angles to each other.

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

[0066] Another force that can be applied to the product particles is electrostatic force, which is appropriately applied by a charged plate. The use of electrostatic force requires 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] The gaseous reactant(s) are preferably reacted at temperatures between 500°C and 1600°C, more preferably between 1000°C and 1500°C or 1600°C (particularly 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 keep the reactive sites on the catalyst intact and produce nanotubes.

[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 0.1 bar to 50 bar, more preferably 0.5 bar to 5 bar, and even more preferably 1 bar to 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 SWCNT, MWCNT, and / or ULMWCNT, 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] Carbon-containing compounds suitable as carbon sources include, for example, carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, and hydrocarbons containing mixtures of two or more thereof). The carbon-containing compound is preferably carbon monoxide, methane, ethylene or acetylene.

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

[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 used supported on a carrier, and preferred carriers include silica and magnesium oxide.

[0082] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters are one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is also a preferred promoter. Suitably, up to 10% by weight (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 mass % or 1.5 mass % to 4.0 mass % thiophene and 1.0 mass % to 10.0 mass % (particularly 2.3 mass %) 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 be in the form of threads or sheets. The length of the CNTs can be controlled, for example, by the winding capacity of the spindle used in producing 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] In another embodiment similar to Production Method X, a method may be adopted in which CNTs are generated in a reaction region by the above-described method, and then condensed to form a CNT aggregate, and the CNT aggregate is continuously withdrawn from near the reaction region. In another embodiment, a method may be adopted that includes generating CNTs in a reaction region, continuously electrostatically attracting the CNTs from the reaction region, and collecting the CNT aggregates.

[0086] (Manufacturing method Y) As another example of the manufacturing method for a CNT aggregate according to the present disclosure, reference can be made to the manufacturing method described in JP-A No. 2021-527611. That is, one example of the manufacturing method (hereinafter also referred to as "manufacturing method Y") includes step (1) of supporting a mixture containing a main catalyst precursor and a co-catalyst precursor on γ-Al2O3 to manufacture an active support, step (2) of drying the active support by multistage drying including vacuum drying, step (3) of heat-treating the dried active support to manufacture a supported catalyst, and step (4) of manufacturing CNTs in the presence of the supported catalyst.

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

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

[0089] Because γ-Al2O3 has high porosity and a spinel structure, the main catalyst and promoter can be randomly arranged in γ-Al2O3. CNTs grown from the randomly arranged main catalyst can be produced in an entangled state.

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

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

[0094] The promoter precursors were NH4VO3, NaVO3, V2O5, V(C5H7O2)3, and (NH4)6Mo7O. 244H2O, NH4VO3 and (NH4)6Mo7O 24 Preferably, one or more selected from the group consisting of 4H2O.

[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 with 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 ratio improves the dispersibility of the main catalyst, enabling the production of CNTs with the 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 above range is satisfied, it is possible to produce a transparent catalyst metal solution during catalyst production, and it is possible to produce a catalyst in which fine powder is suppressed during impregnation.

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

[0101] The aging may be carried out for 1 to 60 minutes or 10 to 50 minutes. Preferably, it is carried out for 10 to 50 minutes. When the above conditions are satisfied, the main catalyst precursor and the co-catalyst precursor can be sufficiently supported on the γ-Al2O3. In addition, air bubbles present in the support are removed to the maximum extent possible, and the main catalyst precursor and the co-catalyst precursor can be sufficiently supported even in the fine pores inside the support.

[0102] ·Process (2) The active support is then 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 80° C. to 300° C. or 120° C. to 250° C., preferably at 120° C. to 250° C. If the above conditions are met, the main catalyst precursor, i.e., the coordinate bond of the main catalyst, can be easily decomposed to form the main catalyst oxide, and energy consumption can be minimized.

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

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

[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 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.

[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 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. If the above conditions are met, the main catalyst precursor, i.e., the main catalyst coordinated compound, is rapidly decomposed and discharged, making it easier to form the main catalyst oxide under vacuum conditions and minimizing energy consumption.

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

[0121] By carrying out the heat treatment, a supported catalyst is produced in which the main catalyst and the promoter are present in a coated state on the surface and in the pores of γ-Al2O3.

[0122] The heat treatment may be carried out at 600 to 800°C or 620 to 750°C, preferably at 620 to 750°C. If the above conditions are met, a supported catalyst can be produced in which the main catalyst and the co-catalyst are uniformly coated on the surface and pores of the γ-Al2O3, and energy consumption can be minimized.

[0123] The heat treatment may be carried out for 1 to 12 hours or 2 to 8 hours, preferably 2 to 8 hours. When the above-mentioned time is satisfied, a supported catalyst can be produced in which the catalyst precursor is uniformly coated on the surface and in the pores of γ-AlO.

[0124] ·Process (4) CNTs are then 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 for producing CNTs in detail, first, a supported catalyst is loaded into a horizontal fixed-bed reactor or a fluidized-bed reactor. Next, the gaseous carbon-based compound or a mixture of the gaseous carbon-based compound, a reducing gas (e.g., hydrogen), and a carrier gas (e.g., nitrogen) is injected at a temperature above the thermal decomposition temperature of the gaseous carbon-based compound or below the melting point of the catalyst supported on the supported catalyst. CNTs can be grown by chemical vapor synthesis through the decomposition of the gaseous carbon-based compound.

[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 conductivity and strength can be produced.

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

[0129] As a heat source for the reaction, induction heating, radiant heat, laser, IR, microwave, plasma, surface plasmon heating, etc. can be used.

[0130] Any carbonaceous compound can be used without particular limitations as long as it can supply carbon and can exist in a gaseous state at temperatures 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 performed to align the CNTs more regularly. Specifically, the cooling step may be performed by natural cooling by removing the heat source or by using a cooler or the like.

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

[0134] [CNT aggregate crushed material] The CNT aggregate according to the present disclosure may be a pulverized CNT aggregate. The pulverized CNT aggregate may be a frozen pulverized 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 aggregates are pulverized while they are 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 appropriately selected depending on the amount of CNT aggregates to be pulverized. For example, the ball mill "JFC-300" manufactured by Japan Analytical Industry Co., Ltd. can be used as the pulverizer. For example, the freezing pulverizer "JFC-2000" manufactured by Japan Analytical Industry Co., Ltd. can be used as the freezing pulverizer.

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

[0138] The powder of CNT aggregates obtained by crushing CNT aggregates can be used as a conductive material, as well as for a variety of other applications such as conductive inks, fillers for reinforcing resins, antistatic agents, and transparent conductive film materials.

[0139] [Method for determining the conductivity of CNT aggregates] 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% relative 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. Condition: Image the CNT dispersion liquid using a scanning electron microscope to obtain a plurality of images of the attachment regions of the CNTs. Among the obtained images, select an image in which the attachment regions of the CNTs exist throughout. Using the selected image, calculate the average value of the fractal dimension of the CNT structure by image analysis.

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

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

[0142] 〔CNT aggregate〕 The details of the CNT aggregate according to the present disclosure are as described above. The content rate of the CNT aggregate according to the present disclosure in the CNT dispersion liquid according to the present disclosure is not particularly limited and can be appropriately set according to the purpose. From the perspective of conductivity, the content rate of the CNT aggregate according to the present disclosure in the CNT dispersion liquid according to the present disclosure is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, still more preferably 0.005% by mass or more, and particularly preferably 0.01% by mass or more with respect to the total mass of the CNT dispersion liquid. Also, from the perspective of dispersibility, the content rate of the CNT aggregate according to the present disclosure in the CNT dispersion liquid according to the present disclosure is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, particularly preferably 5% by mass or less, and especially preferably 1% by mass or less with respect to the total mass of the CNT dispersion liquid. 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 includes a dispersion medium. The dispersion medium preferably contains water, more preferably contains water as a main component, and even more preferably is water. "Containing water as a main component" means that the proportion of water in the dispersion medium is more than 50% by mass. The proportion of water in the dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, and may be, for example, 100% by mass.

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

[0146] [Other ingredients] 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 a dispersant, an antifoaming agent, an antistatic agent, a conductive assistant, CNTs other than the CNT aggregate according to the present disclosure, etc. The CNT dispersion according to the present disclosure may further contain a trace amount of impurity components, so-called inevitable impurities, etc.

[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 aggregates. The dispersant is not particularly limited and may be, for example, various surfactants. The dispersant may also be a polymer compound such as a resin. The dispersant is preferably a surfactant. The surfactant may be an ionic surfactant or a nonionic surfactant, and is not particularly limited. The surfactant may be used alone or in combination of two or more.

[0148] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzenesulfonates (e.g., dodecylbenzenesulfonic acid) and dodecylphenyl ether sulfonates; ether sulfate surfactants; phosphate surfactants; and carboxylic acid surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. As the ionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic ionic surfactant) is preferred, and aromatic sulfonic acid surfactants such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate are more preferred. Aromatic ionic surfactants tend to be excellent in dispersibility, dispersion stabilization, and concentration of CNTs.

[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 the nonionic surfactant, an ionic surfactant having an aromatic ring (so-called aromatic nonionic surfactant) is preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersing ability, dispersion stabilizing ability, and concentration enhancement for CNT aggregates.

[0150] Other dispersants that are excellent in dispersibility, dispersion stability, 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 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 liquid contains a dispersant, the content of the dispersant in the CNT dispersion liquid is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of CNT aggregates, the amount of dispersion medium, and the like. 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 relative to the total mass of the CNT dispersion.

[0152] [Application] The use of the CNT dispersion according to the present disclosure is not particularly limited. Because the CNT dispersion according to the present disclosure has high conductivity, it can be applied to 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 (especially 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 liquid] 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 step is a step of dispersing the CNT aggregate according to the present disclosure in a dispersion medium. In the dispersion step, a dispersant may be used from the viewpoint of improving the dispersibility and dispersion stability of the CNT aggregate according to the present disclosure. The 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 a dispersion device 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 known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, a vertical or horizontal agitator mill, an attritor, a colloid mill, a three-roll mill, a pearl mill, a super mill, an impeller, a disperser, a KD mill, a dynatron, a pressure kneader, and the like. As a dispersion method, a method using a jet mill is preferred, and a method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pumps a mixture in a solvent as a high-speed flow through a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, CNT aggregates are dispersed by collisions between opposing flows in the pressure-resistant container, collisions with the container wall, turbulence caused by the high-speed flow, shear flow, and the like. An ultra-high-pressure homogenizer (model numbers: NAGS20, NAGS100, JAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used as the wet jet mill. However, the wet jet mill is not limited to this. When the ultra-high pressure homogenizer is used as the dispersing device, the processing pressure for dispersion is preferably 10 MPa to 250 MPa.

[0156] (drying process) The method for producing a CNT dispersion 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] When 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, preventing adhesion of the CNT aggregates to each other due to moisture adhesion, and the dispersibility of the CNT aggregate according to the present disclosure in the dispersion medium can be further improved. The drying method is not particularly limited. Examples of the drying method 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 40°C to 100°C, for example. The drying time is not particularly limited and can be set appropriately depending on the drying temperature, the degree of moisture adhesion to the CNT aggregate in the present disclosure, and the like.

[0158] <Conductive materials> 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. Because the conductive material according to the present disclosure contains the CNT aggregate according to the present disclosure, it has excellent conductive efficiency and can effectively impart high conductivity to an object of use. 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 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. Examples of 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). An example of use as a conductive auxiliary agent is, for example, when producing a positive electrode of a battery, a positive 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 positive electrode, dried, and stretched to produce a positive electrode.

[0162] Another example of the 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 contained in the electrode described below has the same meaning as 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. An 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, examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; lithium iron oxides such as LiFe3O4; and compounds with the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (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); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include lithium manganese composite oxides represented by Li2Mn3MO8 (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 Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion.

[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] As the graphite-based active material particles, at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, and graphitized mesocarbon microbeads may be used. By using artificial graphite as the graphite-based active material particles, the rate characteristics can be improved. As the silicon-based active material particles, 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) may be used. By using silicon-based active material particles, the battery can have a higher capacity.

[0170] The electrode active material layer may further contain a binder. The binder is not particularly limited, and the electrode active material layer can contain a binder commonly used for 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, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and polyacrylic acid, and polymers in which hydrogen atoms of these polymers are substituted with Li, Na, Ca, etc.

[0171] <Secondary battery> The secondary battery according to the present disclosure includes the 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. At least one of the positive electrode and the negative electrode is preferably an electrode according to the present disclosure, and the negative electrode is preferably an electrode according to the present disclosure.

[0172] The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move, and is not particularly limited as long as it is a separator that is typically used as a separator in a secondary battery. The separator preferably has low resistance to ion movement of the electrolyte and is excellent in the ability to retain moisture in the electrolyte solution. A specific example of the separator is a porous polymer film. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure in which two or more of these films are laminated. The separator may also be a typical porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. In order to ensure heat resistance or mechanical strength, the separator may also be coated with a ceramic component or a polymeric substance. The separator may optionally be of a 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 can include a non-aqueous organic solvent and a metal salt. Examples of non-aqueous organic solvents include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 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 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 and 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, which 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 - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -, CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Examples include:

[0177] In addition to the non-aqueous organic solvent and metal salt, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purposes of improving the battery's life characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[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 a medium to large device selected from the group consisting of, for example, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[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 the negative electrode is produced by mixing known artificial graphite as a negative electrode active material, the 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 negative electrode slurry 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. Thereafter, the current collector coated with the negative electrode slurry is further dried in an oven to produce a negative electrode. Next, a known positive electrode slurry 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 separator is interposed between the negative electrode and the positive electrode to produce a monocell, and an electrolyte 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 relative to the total mass of the planar aggregate. The planar aggregate according to the present disclosure may contain other components such as CNTs other than the CNT aggregate according to the present disclosure.

[0182] [Method for producing a planar assembly] The method for producing the planar assembly according to the present disclosure is not particularly limited. The planar aggregate according to the present disclosure can be produced, for example, as a nonwoven fabric-like planar aggregate, by dispersing the CNT aggregate according to the present disclosure, or the CNT aggregate according to the present disclosure and optionally other components, in water or other fluid and filtering once or more times.

[0183] The planar assembly according to the present disclosure can be, for example, a film, and is useful, for example, for filters, electromagnetic wave shields, and extreme ultraviolet (EUV) pellicles.

[0184] <Composition> The composition according to the present disclosure includes the CNT aggregate according to the present disclosure and at least one material selected from the group consisting of resin, ceramics, and concrete. Examples of the resin include thermoplastic resins and thermosetting resins, and preferred are olefin resins, polycarbonate resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, polysulfone resins, and silicone resins. Examples of ceramics include crystalline ceramics and non-crystalline ceramics. An example of concrete is Portland cement concrete. The composition according to the present disclosure may further contain 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 material selected from the group consisting of resin, ceramic, and concrete is usually 10 to 1,000,000 parts by mass, preferably 100 to 100,000 parts by mass, and more preferably 1,000 to 40,000 parts by mass, and when other components are included, the content is preferably 1 to 10,000 parts by mass, and more preferably 10 to 1,000 parts by mass. In the composition according to the present disclosure, the CNT aggregate, resin, ceramic, concrete, and other components may each be contained alone or in combination of two or more.

[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 resin, ceramics, or pre-hardened concrete. The resin may be in the form of powder, pellets, solution, or dispersion. The ceramic may be in the form of 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 uncured concrete and then molding it.

[0186] 〔Use of the composition〕 When the composition according to the present disclosure contains a resin or a ceramic, it is useful, for example, as a structural material, a conductive material, a thermal management material, or an antistatic material. When the composition according to the present disclosure contains concrete, it is useful as a building material with reduced weight and improved durability, or as an energy storage device (impregnated with an electrolyte if necessary).

Examples

[0187] Examples are given below to more specifically describe the CNT aggregate, CNT dispersion, conductive material, electrode, secondary battery, planar aggregate, and composition according to the present disclosure. 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 the gist thereof is not exceeded.

[0188] <Production of CNT aggregate> 〔Example 1〕 The MWCNT aggregate 1 of Example 1 was produced by the 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 an accelerator were introduced into the continuous flow of the carrier gas in a flow-through reactor whose temperature was controlled at 400°C to 700°C. A mixed gas of nitrogen and argon was used as the carrier gas, and the flow rate of the carrier gas was 30000 sccm (standard cubic centimeter per minute). By maintaining the temperature in the flow-through reactor within the above range, the metal catalyst precursor was generated as a particulate metal catalyst. The region where the metal catalyst is generated is referred to as the first temperature zone. Next, methane, a carbon source, was released into the carrier gas stream. The metal catalyst and carbon source were fed into a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce CNT agglomerates. In the second temperature zone, an electric field was generated within a temperature-controlled flow reactor, which produced MWCNT agglomerates. The generated aggregates were continuously discharged through the outlet of a flow reactor whose temperature was controlled between 100 and 500°C, and collected as sheet-like MWCNT aggregates by continuous discharge. The collected sheet-like MWCNT aggregates were washed with deionized water for 10 seconds. In this manner, the 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 freeze pulverizer (manufactured by Japan Analytical Industry Co., Ltd., JFC-2000) under the following conditions. More specifically, 5 g of MWCNT aggregate 1 was placed in a 75 mL sample container, and one tungsten carbide steel ball was then placed in the sample container, after which the sample container was attached to a crushing rod. The entire sample container was immersed in liquid nitrogen to cool the MWCNT aggregate 1 and the steel ball, and the crushing rod was then moved up and down to move the steel ball inside the sample container and crush the MWCNT aggregate 1. Freezing retention time: 5 minutes Grinding time: 2 minutes

[0190] Example 3 The MWCNT aggregate 3 of Example 3 was produced by the floating catalyst method (CVD method) which directly interacts with the self-assembly of CNT bundles in the gas phase, similar to the sheet-like MWCNT aggregate 1 collected in Example 1. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of a carrier gas in a through-flow reactor temperature-controlled at 400°C to 700°C. The carrier gas used was a mixed gas of nitrogen and argon. The flow rate of the carrier gas was 30,000 sccm. By maintaining the temperature in the through-flow 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 as a carbon source was released into the carrier gas flow. The metal catalyst and the carbon source were supplied to a second temperature zone temperature-controlled at 1400°C downstream of the first temperature zone. The second temperature zone was maintained at a temperature sufficient to produce aggregates of CNTs. In the second temperature zone, an electric field was generated in a temperature-controlled flow-through reactor, whereby aggregates of MWCNTs were produced. The produced aggregates were continuously discharged through the outlet of a flow-through reactor temperature-controlled at 100°C to 500°C and collected as a fibrous MWCNT aggregate by continuous discharging. The collected fibrous MWCNT aggregate was washed with deionized water for 10 seconds. In the above manner, the 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 was mixed with 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. The resulting mixture was subjected to a dispersion treatment at 8500 rpm for 1 hour using Labo-Lution (product name) manufactured by Primix Corporation as a pre-dispersion before the main dispersion, thereby obtaining a pre-dispersed solution 1. Note that, to prevent the MWCNT aggregate 1 from becoming tangled in the stirring section of the Labo-Lution, the MWCNT aggregate 1 was cut into small pieces of approximately 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 was mixed with 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. 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, 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 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 3 0.55 g of the MWCNT aggregate 3 of Example 3 was mixed with 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. The resulting 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, to prevent the MWCNT aggregate 3 from becoming tangled in the blades of the homogenizer, the MWCNT aggregate 3 was cut to a length of about 1 cm using scissors before mixing. 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 was mixed with 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. 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, 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 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)> [Attaching CNT dispersion to a substrate for SEM observation] The CNT dispersion was diluted with pure water so that the CNT concentration was 0.002% by mass relative to the total amount of the CNT dispersion. When observing the CNT dispersion (CNT concentration: 0.002% by 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 with Pt deposition was treated with UV and ozone, and then attached to a substrate for SEM observation with conductive carbon tape. 2. 0.1 μL of the CNT dispersion liquid was applied to the slide glass. 3. The SEM observation substrate with the CNT dispersion attached was placed on a metal cooled with liquid nitrogen to freeze the CNT dispersion. 4. The slide glass on which the CNT dispersion liquid was frozen is placed on a 4.0 x 10 -3 A vacuum was applied at a pressure of 100 Pa to sublimate the ice.

[0203] [Imaging] The CNT dispersion (CNT concentration: 0.002% by mass) was photographed using an SEM under the conditions below, and multiple images of the CNT-attached region were obtained. SEM equipment: S-4800 (Hitachi High-Technologies Corporation) Acceleration voltage: 1 kV Emission current: 10μA Measurement magnification: 500x Image size: 1280 pixels x 960 pixels

[0204] 1 shows an SEM photograph of CNT dispersion 2 in Example 2. The formation of a CNT network structure was confirmed. 2 shows an SEM photograph of CNT dispersion C1 in Comparative Example 1. The formation of a CNT network structure could not be confirmed.

[0205] <Image selection> All images of the area where the CNT dispersion liquid (CNT concentration: 0.002% by mass) was applied were subjected to the following image processing using ImageJ, an 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=9pixels 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 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. 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] [Percentage of selected images] The ratio of the images used for calculating the fractal dimension (ie, the selected images) to the total number of images of the CNT dispersion-attached region is shown in Table 1 below.

[0209] [Table 1]

[0210] <Calculation of the average value of fractal dimension> For all of the selected images after image processing, the fractal dimension was calculated using the image analysis software ImageJ according to the following procedure.

[0211] [Calculation procedure] 1.Binary:Skeletonize 2.Analyze:Fractal 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 each comparative example was further calculated. Table 2 shows the results of the average values ​​of the fractal dimensions for MWCNT aggregates 1 to 3 of Examples 1 to 3 and MWCNT aggregates C1 to C3 of Comparative Examples 1 to 3.

[0213] [Dispersion, Standard Deviation, and Median] The dispersion, standard deviation, and median of the fractal dimension in each example and each comparative example were obtained based on the following formulas. The results are shown in Table 2. When the average of the data x1, x2, ···, x n is represented by μ, the dispersion S 2 and the standard deviation S were obtained by the following mathematical formulas (1) and (2), respectively.

[0214] [[ID=!3]]

Equation

[0215] When the data is sorted in ascending order as x (1) , x (2) , ···, x (n) , the median Me was obtained by the following mathematical formula (3).

[0216] <00..01014> [[ID=!31]]

Equation

[0217] [Content of Fe Atoms with Respect to the Total Mass of the CNT Aggregate] Using an inductively coupled plasma mass spectrometer (ICP-MS) (manufactured by PerkinElmer, NexION 2000C), the content ratios of Fe atoms contained in MWCNT aggregates 1 to MWCNT aggregates 3 of Examples 1 to 3 and MWCNT aggregates C1 to MWCNT aggregates C3 of Comparative Examples 1 to 3 were measured. As a pretreatment, the CNT aggregates were subjected to low-temperature ashing / acid fusion. The results are shown in Table 2.

[0218] [Maximum Length of CNT] [Example 1: MWCNT Aggregate 1]<0..01027>When observing 100 MWCNTs by looking at a plurality of SEM photographs (magnification: 5000 times) adjacent to each other in 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 aggregates 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 aggregates 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 glass substrates cut to a size of 10 cm × 10 cm, and films were formed using a stainless steel applicator with a gap size of 150 μm. The glass substrates were then heated on a hot plate at 110°C for 10 minutes to dry the films, 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 thus obtained 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. 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 electrical conductivity was excellent. An evaluation result of "AA" is most preferable.

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

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

[0224] 1. Preparation of positive electrodes for lithium-ion secondary batteries Cathode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2), a conductive material (acetylene black), and a binder (PVdF) were mixed in a ratio of positive electrode active material:conductive material:binder = 92:5:3 (mass ratio), and N-methyl-2-pyrrolidone was added and kneaded to prepare a paste-like positive electrode mixture. The resulting positive electrode mixture was applied to a 15 μm thick Al foil as a current collector, and the resulting mixture was vacuum dried at 80°C for 1 hour, followed by roll pressing to obtain a positive electrode for a lithium ion secondary battery. The positive electrode area was 1.65 cm. 2 , basis weight 16mg / cm 2 , density is 3.0g / cm 3 It was adjusted so that

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

[0226] 3. Fabrication of Lithium-ion Secondary Batteries The positive electrode for a lithium-ion secondary battery was placed on the bottom cover of a coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator consisting of a polyethylene porous film with a 16 μm heat-resistant porous layer was placed on top of it. 300 μL of electrolyte was poured into the separator. The electrolyte was a 20:75:5 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with 1% vinylene carbonate added by volume, and LiPF6 dissolved therein to a concentration of 1.3 mol / L. Next, the negative electrode for a lithium-ion secondary battery was placed on top of the laminated film separator, and the top cover was placed with a gasket in between. The assembly was then crimped using a crimping machine to produce a coin-type full-cell R2032 lithium-ion secondary battery. These operations were carried out in a glove box under an argon atmosphere.

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

[0228] -Cycle test conditions- Test temperature: 25℃ Charging conditions: Constant current constant voltage charging, maximum charging voltage 4.2V, charging time 5 hours, charging current 0.3CA Pausing time after discharge: 10 minutes Discharge conditions: Constant current discharge, minimum discharge voltage 2.5V, discharge current 0.3CA Downtime after charging: 10 minutes In this test, one cycle consisted of charging, resting from discharge, discharging, and resting from charge. The evaluation results for Example 1, Example 3, Comparative Example 2, and Comparative Example 3 are shown in Table 2.

[0229] [Table 2]

[0230] From the above, it was shown that the MWCNT aggregates 1 to 3 of Examples 1 to 3 were CNT aggregates excellent in conductivity. Furthermore, according to the MWCNT aggregates 1 and 3 of Examples 1 and 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 calculated under the following conditions when the concentration of carbon nanotubes having an aspect ratio of 3000 or more is 0.002 mass% relative to the total amount of the carbon nanotube dispersion. Conditions: The carbon nanotube dispersion is photographed using a scanning electron microscope to obtain multiple images of the carbon nanotube-attached regions. From the obtained images, images in which the carbon nanotube-attached regions are present throughout are selected. Using the selected images, the average value of the 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. 3. The carbon nanotube aggregate according to claim 1, containing 450 mass ppm to 150,000 mass ppm of Fe atoms relative to the total mass of the carbon nanotube aggregate.

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

5. A carbon nanotube dispersion liquid comprising the aggregate of carbon nanotubes 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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