Carbon nanotube liquid dispersion, laminate, production method for carbon nanotube liquid dispersion, and production method for carbon film

Abstract

The purpose of the present invention is to provide a carbon nanotube liquid dispersion that allows secondary battery electrodes to demonstrate a strong peel strength between an electrode mixture layer and a current collector formed from a metal, etc., and a weak peel strength for an electrode mixture layer provided with a release substrate made of a resin or the like, between the electrode mixture layer and the release substrate; and to allow a secondary battery to demonstrate superior rate performance, or realizes good film formation properties when a carbon film is formed. The carbon nanotube liquid dispersion according to the present invention contains carbon nanotubes and a solvent, wherein when a scattering curve obtained by the measurement conducted with ultra-small-angle X-ray scattering method is analyzed by the Beaucage model, the fractal dimension within a wavenumber range from 0.001 (1 / Å) to 0.3 (1 / Å) is in the range from 3 to 4.

Description

Carbon nanotube dispersion, laminate, method for producing carbon nanotube dispersion, and method for producing carbon film

[0001] The present invention relates to a carbon nanotube dispersion, a laminate, a method for producing a carbon nanotube dispersion, and a method for producing a carbon film.

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated in order to further improve the performance of secondary batteries.

[0003] Here, electrodes for secondary batteries such as lithium-ion secondary batteries typically include a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed by binding components such as an electrode active material together and / or between the electrode active material and the current collector with a binder. To improve the performance of secondary batteries such as lithium-ion secondary batteries, an electrode mixture layer in which carbon nanotubes are dispersed as a conductive material has been used. The electrode mixture layer is formed from a slurry composition containing the components of the electrode mixture layer, for example, by applying the slurry composition to a current collector and drying it. The slurry composition can also be prepared by mixing an electrode active material, a carbon nanotube dispersion, a binder, and optional additives such as a dispersant, as described in Patent Document 1, for example.

[0004] Meanwhile, in recent years, carbon nanotubes (hereinafter sometimes referred to as "CNTs") have been attracting attention as a material with excellent electrical conductivity, thermal conductivity, electromagnetic wave shielding performance, and mechanical properties. Taking note of these properties of CNTs, it has been proposed to produce a carbon nanotube film (hereinafter sometimes referred to as "CNT film" or "carbon film"), which is sometimes called "buckypaper" and is made up of a film-like assembly of multiple CNTs, and to use the CNT film as an electrically conductive sheet, a thermally conductive sheet, an electromagnetic wave absorbing sheet, etc.

[0005] However, because CNTs are minute structures with nanometer-sized diameters, they are difficult to handle and process when used alone. Therefore, it has been proposed to produce a carbon film by preparing a solution in which CNTs are dispersed (CNT dispersion), applying this solution to a substrate, etc., and removing components other than the CNTs to form a film of the CNT aggregates contained in the CNT dispersion. Examples of such CNT dispersions include a carbon nanotube dispersion (Patent Document 1) that includes a solvent having a predetermined viscosity and density range and a carbon nanotube aggregate dispersed in the solvent at a predetermined content range, and that is characterized by physical properties such as scale width and density being within predetermined ranges; a CNT dispersion (Patent Document 2) that includes a solvent, CNTs exhibiting predetermined physical properties, and ionic particles; and a CNT dispersion (Patent Document 3) that includes CNTs, a surfactant having a molecular weight equal to or less than a predetermined value, and a solvent.

[0006] JP 2020-057474 A Japanese Patent No. 6789529 A JP 2017-119586 A International Publication No. 2019 / 188978

[0007] Electrodes for secondary batteries such as lithium-ion secondary batteries have the form of a laminate of a current collector made of a metal or the like and an electrode mixture layer. In order to enhance the mechanical strength of such electrodes, a strong peel strength is required between the electrode mixture layer and the current collector.

[0008] Electrodes for secondary batteries such as lithium-ion secondary batteries can also be produced by transferring a pre-fabricated electrode mixture layer onto a current collector. A member used for transferring such an electrode mixture layer can be a release substrate-attached electrode mixture layer (transfer electrode mixture layer), which has the form of a laminate of a substrate (release substrate) made of resin or the like and an electrode mixture layer. Such an electrode mixture layer with a release substrate requires a weak peel strength between the electrode mixture layer and the release substrate to enhance the ease of releasability of the release substrate.

[0009] Furthermore, secondary batteries such as lithium ion secondary batteries are required to have excellent rate characteristics as battery performance.

[0010] On the other hand, when forming a carbon film using a CNT dispersion, a property is required in which the carbon film does not collapse during film formation and a good carbon film can be obtained (good film formability). Furthermore, if the conditions of a CNT dispersion suitable for achieving good film formability during carbon film formation are known in advance, it is expected that good film formability can be achieved during carbon film formation with high reproducibility by using a CNT dispersion that satisfies those conditions.

[0011] Therefore, an object of the present invention is to provide a carbon nanotube dispersion that, when used to prepare an electrode mixture layer, can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and can provide a release substrate-attached electrode mixture layer with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Another object of the present invention is to provide a laminate that can be used as a secondary battery electrode having strong peel strength between the electrode mixture layer and a current collector made of metal or the like. A further object of the present invention is to provide a laminate that can be used as a release substrate-attached electrode mixture layer having weak peel strength between the electrode mixture layer and a release substrate made of resin or the like.

[0012] Another object of the present invention is to provide a CNT dispersion that can achieve good film-forming properties when forming a carbon film using the CNT dispersion, and a method for producing the same. Another object of the present invention is to provide a method for producing a carbon film with good film-forming properties using a CNT dispersion.

[0013] The present inventors have conducted extensive research to achieve the above object, and have found that the fractal dimension obtained when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and the area ratio of carbon nanotubes in an image obtained by photographing a carbon nanotube dispersion, can be used as indicators of a dispersion suitable for preparing a slurry composition, and that the values ​​of the fractal dimension and area ratio of a CNT dispersion suitable for a slurry vary depending on the physical properties of the CNTs. Specifically, (Aspect A): a carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a solvent, wherein the fractal dimension in a predetermined wave number range when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model is in the range of 3 to 4; (Aspect B1): a carbon nanotube dispersion liquid containing single-walled carbon nanotubes and a solvent, wherein the area ratio of the carbon nanotubes in an image obtained by capturing an image of the carbon nanotube dispersion liquid at a concentration of 0.1 wt % is 55% or less; or (Aspect B2): a carbon nanotube dispersion liquid containing single-walled carbon nanotubes and a solvent, wherein the area ratio of the carbon nanotubes in an image obtained by capturing an image of the carbon nanotube dispersion liquid at a concentration of 0.1 wt % is 55% or less; The inventors have found that by producing a slurry composition for secondary battery electrodes using a carbon nanotube dispersion containing single-walled carbon nanotubes and a solvent in a ratio of 10 or more, where the area ratio of carbon nanotubes in an image obtained by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 75% or more, it is possible to produce a secondary battery electrode having strong peel strength between the electrode mixture layer and a collector made of metal or the like, an electrode mixture layer with a release substrate having weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, and a secondary battery with excellent rate characteristics, and have completed the present invention.

[0014] On the other hand, the present inventors have found that the area ratio of CNTs in an image obtained by photographing a CNT dispersion can be used as an indicator of the degree of film-formability when forming a carbon film using a CNT dispersion. Specifically, (Aspect C): They have found that good film-formability can be achieved by forming a carbon film using a carbon nanotube dispersion containing carbon nanotubes and a solvent, in which the area ratio of carbon nanotubes in an image obtained by photographing the carbon nanotube dispersion at a concentration of 0.1 wt % is 70% or less, and have completed the present invention.

[0015] That is, the present invention has an object to advantageously solve the above-mentioned problems. In Aspect A, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing carbon nanotubes and a solvent, characterized in that, when a scattering curve obtained by ultra-small-angle X-ray scattering measurement is analyzed using the Beaucage model, the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4. By having the fractal dimension measured above in the range of 3 to 4, a secondary battery electrode can exhibit strong peel strength between an electrode mixture layer and a current collector made of metal or the like, and an electrode mixture layer with a release substrate can exhibit weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Note that, in the present invention, the fractal dimension can be determined by the method described below.

[0016] In Aspect B1, the carbon nanotube dispersion of the present invention is characterized in that it contains single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent, and the carbon nanotube area ratio in an image obtained by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 55% or less. When single-walled carbon nanotubes having a G / D ratio of 5 or less are used as the carbon nanotubes, the carbon nanotube area ratio measured above of 55% or less can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and can provide a release substrate-attached electrode mixture layer with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Note that in the present invention, the G / D ratio and area ratio can be determined by the methods described in the Examples.

[0017] In addition, when single-walled carbon nanotubes having a G / D ratio of 5 or less are used as carbon nanotubes, the thickness of the nanotubes is 26,000 μm in the image. ２ It is further preferred that the carbon nanotube composition contains 5 to 100 carbon nanotubes having an aspect ratio of 10 or more per area corresponding to the surface area of ​​the electrode. By having the number of carbon nanotubes having an aspect ratio of 10 or more in the above range, a secondary battery electrode can be provided with an even stronger peel strength between the electrode mixture layer and a current collector made of metal or the like, and a release substrate-attached electrode mixture layer can be provided with an even stronger peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit even better rate characteristics. In the present invention, the number of carbon nanotubes having an aspect ratio (length / diameter) in a predetermined range can be determined by the method described in the Examples.

[0018] In Aspect B2, the carbon nanotube dispersion of the present invention is characterized in that it contains single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent, and the carbon nanotube area ratio in an image obtained by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 75% or more. When single-walled carbon nanotubes having a G / D ratio of 10 or more are used as the carbon nanotubes, the carbon nanotube area ratio measured above of 75% or more can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and can provide a release substrate-attached electrode mixture layer with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Note that in the present invention, the G / D ratio and area ratio can be determined by the methods described in the Examples.

[0019] In Aspect C, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing carbon nanotubes and a solvent, wherein the area ratio of carbon nanotubes in an image acquired by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 70% or less. By using a CNT dispersion having a carbon nanotube area ratio of 70% or less measured as described above, good film-formability can be achieved when forming a carbon film. Furthermore, it becomes possible to determine whether good film-formability can be achieved by using this carbon nanotube dispersion at a stage prior to actually forming a film. Note that in the present invention, the area ratio of the CNT dispersion can be determined by the method described in the Examples, and the film-formability of the carbon film can be evaluated by the method described in the Examples.

[0020] Furthermore, in the carbon nanotube dispersion, the area ratio of carbon nanotubes in an image obtained by photographing the carbon nanotube dispersion is preferably 20% to 70%, more preferably 55% to 70%. By using a CNT dispersion having an area ratio measured above in the range of 20% to 70%, preferably 55% to 70%, it is possible to obtain a carbon film having a high porosity, for example, 60% to 99%, which is useful for battery applications. In the present invention, the porosity of the carbon film can be determined by the method described in the Examples.

[0021] In aspects B1, B2, and C, the carbon nanotube dispersion of the present invention is further characterized in that, when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using the Beaucage model, the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4. When the fractal dimension measured above is in the range of 3 to 4, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics or enabling good film formability to be achieved during bare film formation.

[0022] In aspects A, B1, B2, and C, the carbon nanotube dispersion of the present invention preferably has a CNT persistent length of 100 nm or more in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) when the scattering curve obtained by ultra-small-angle X-ray scattering is analyzed using the Beaucage model. Having a CNT persistent length of 100 nm or more as measured above can further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in a secondary battery electrode, and can further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby further enhancing the excellent rate characteristics of the secondary battery or enabling good film formability during bare film formation. In the present invention, the CNT persistent length can be determined by the method described below.

[0023] In the carbon nanotube dispersions of Aspects A, B1, B2, and C, the solvent is preferably water, alcohol, or a mixture of water and alcohol. When water is used as such a solvent, when a carbon film made of the carbon nanotube dispersion using water is used in a battery, the affinity between the carbon film and the electrolyte is good, thereby improving battery performance. Furthermore, when alcohol is used as such a solvent, a carbon film can be easily produced using the carbon nanotube dispersion.

[0024] In the carbon nanotube dispersions of Aspects A, B1, B2, and C, it is preferable that the carbon nanotubes satisfy at least one of the following conditions (1) to (3): (1) A carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more is subjected to Fourier transform infrared spectroscopy, and in the spectrum obtained, a peak due to plasmon resonance of the carbon nanotube dispersion appears at a wave number of 300 cm. －１ Super 2000cm －１(2) The maximum peak in a pore distribution curve showing the relationship between pore diameter and log differential pore volume, obtained from the adsorption isotherm of liquid nitrogen at 77 K based on the Barrett-Joyner-Halenda method for the carbon nanotube aggregate, is in the pore diameter range of more than 100 nm and less than 400 nm. (3) The peak in the two-dimensional spatial frequency spectrum of an electron microscope image of the carbon nanotube aggregate is in the range of 1 μm －１ 100 μm or more －１ At least one of the following conditions is present. A carbon nanotube dispersion using such carbon nanotubes is suitable for obtaining a carbon film with high porosity because the carbon nanotubes have mesopores. The above conditions (1) to (3) can be confirmed by the method described below.

[0025] In one embodiment, the laminate of the present invention is characterized by being a laminate of a metal film having a surface tension of 400 mN / m or more and 2000 mN / m or less and a carbon nanotube-containing film formed using any of the carbon nanotube dispersions described above. Preferably, the laminate is formed by directly laminating the metal film and the carbon nanotube-containing film. In such a laminate, the high surface tension of the metal film provides strong peel strength between the carbon nanotube-containing film and the metal film, improving adhesion between the carbon nanotube-containing film and the metal film, resulting in a contact-type laminate useful as an electrode or the like. In the present invention, the surface tension of the metal film can be determined by the method described in the Examples.

[0026] In another embodiment, the laminate of the present invention is characterized by being a laminate of a substrate having a surface tension of 20 mN / m or more and 50 mN / m or less and a carbon nanotube-containing film formed using any of the carbon nanotube dispersions described above. Preferably, the laminate comprises the metal film and the carbon nanotube-containing film directly laminated together. Since the surface tension of the substrate is low in this laminate, the peel strength between the carbon nanotube-containing film and the substrate is weakened, forming a peelable laminate in which easy peeling is imparted between the carbon nanotube-containing film and the substrate. This peelable laminate can be used as a laminate (electrode mixture layer with release substrate) to which the carbon nanotube-containing film (electrode mixture layer) can be easily transferred. In the present invention, the surface tension of the substrate can be determined by the method described in the Examples.

[0027] In Aspect A, the method for producing a carbon nanotube dispersion of the present invention is characterized by comprising the steps of: dispersing a mixture of carbon nanotubes and a solvent to obtain a carbon nanotube dispersion; measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies Condition 1, in which the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less when the scattering curve obtained by the measurement by ultra-small angle X-ray scattering is analyzed using the Beaucage model is in the range of 3 or more and 4 or less; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy Condition 1. According to this manufacturing method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, it is possible to obtain a carbon nanotube dispersion liquid that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby providing excellent rate characteristics for the secondary battery.

[0028] Furthermore, the method for producing a carbon nanotube dispersion of the present invention preferably includes the steps of: obtaining a carbon nanotube dispersion by dispersing a mixture of carbon nanotubes and a solvent; measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, where the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4 and the CNT persistent length in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is in the range of 100 nm or more, when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using a Beaucage model; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2. According to this manufacturing method, by adding the additional condition that the CNT persistence length measured above is 100 nm or more, it is possible to obtain a carbon nanotube dispersion liquid that can further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in a secondary battery electrode, and can further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby enabling the secondary battery to exhibit even better rate characteristics.

[0029] In aspect B1, the method for producing a carbon nanotube dispersion of the present invention is characterized by comprising the steps of: dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent to obtain a carbon nanotube dispersion; photographing the obtained carbon nanotube dispersion at a concentration of 0.1 wt % to obtain an image; and evaluating the carbon nanotube dispersion as appropriate if condition 3, that is, the area ratio of carbon nanotubes in the obtained image is 55% or less, is satisfied, and evaluating the carbon nanotube dispersion as inappropriate if condition 3 is not satisfied. According to this manufacturing method, when a carbon nanotube dispersion is produced using single-walled carbon nanotubes with a G / D ratio of 5 or less, provided that the area ratio of the carbon nanotubes measured above is 55% or less, it is possible to obtain a carbon nanotube dispersion that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0030] The method for producing a carbon nanotube dispersion of the present invention includes the steps of: dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent to obtain a carbon nanotube dispersion; photographing the obtained carbon nanotube dispersion at a concentration of 0.1 wt % to obtain an image; and capturing an image of the carbon nanotube dispersion at a concentration of 0.1 wt % in which the area ratio of the carbon nanotubes in the obtained image is 55% or less and the area ratio of the carbon nanotubes in the image is 26,000 μm ２ and a step of evaluating the carbon nanotube dispersion as appropriate if condition 4 is satisfied, that is, if the carbon nanotube dispersion contains 5 to 100 carbon nanotubes having an aspect ratio of 10 or more per area corresponding to 26000 μm, and evaluating the carbon nanotube dispersion as inappropriate if condition 4 is not satisfied. ２By further adding the condition that the carbon nanotube dispersion contains 5 to 100 carbon nanotubes with an aspect ratio of 10 or more per area corresponding to the electrode mixture layer, it is possible to further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in an electrode for a secondary battery, and it is possible to further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby obtaining a carbon nanotube dispersion that can further enhance the excellent rate characteristics of a secondary battery.

[0031] In aspect B2, the method for producing a carbon nanotube dispersion of the present invention is characterized by comprising the steps of: dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent to obtain a carbon nanotube dispersion; photographing the obtained carbon nanotube dispersion at a concentration of 0.1 wt % to obtain an image; and evaluating the carbon nanotube dispersion as appropriate if condition 5, in which the area ratio of carbon nanotubes in the obtained image is 75% or more, is satisfied, and evaluating the carbon nanotube dispersion as inappropriate if condition 5 is not satisfied. According to this manufacturing method, when a carbon nanotube dispersion is produced using single-walled carbon nanotubes having a G / D ratio of 10 or more as the carbon nanotubes, provided that the area ratio of the carbon nanotubes measured above is 75% or more, it is possible to obtain a carbon nanotube dispersion that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0032] In Aspect C, the method for producing a carbon nanotube dispersion of the present invention includes the following steps: obtaining a carbon nanotube dispersion by dispersing a mixture of carbon nanotubes and a solvent; photographing the obtained carbon nanotube dispersion to obtain an image; and evaluating the carbon nanotube dispersion as appropriate if the area ratio of carbon nanotubes in the obtained image satisfies Condition A, and evaluating the carbon nanotube dispersion as inappropriate if Condition A is not satisfied. Condition A includes the area ratio of carbon nanotubes in the image obtained by photographing the carbon nanotube dispersion at a concentration of 0.1 wt % being 70% or less. Under the condition that the area ratio of carbon nanotubes measured above is 70% or less, good film-formability can be achieved when forming a carbon film by using the CNT dispersion produced by this production method. Furthermore, it is possible to determine whether good film-formability can be achieved by using the carbon nanotube dispersion produced by this production method even before actually forming a film.

[0033] Furthermore, in the above-described method for producing a carbon nanotube dispersion, it is preferable that the condition A further includes that the area ratio is 20% or more, and more preferably 55% or more. Under the condition that the area ratio of carbon nanotubes measured above is 20% or more and 70% or less, preferably 55% or more and 70% or less, by using the CNT dispersion obtained by this production method, it is possible to obtain a carbon film having a high porosity, for example, 60% or more and 99% or less, which is useful for battery applications. Furthermore, by using the carbon nanotube dispersion produced by this production method, it is possible to determine, even before actual film formation, whether a high porosity, for example, 60% or more and 99% or less, which is useful for battery applications, can be achieved.

[0034] The methods for producing carbon nanotube dispersions of aspects B1, B2, and C are characterized by further comprising the steps of: measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 1, that is, the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model is in the range of 3 or more and 4 or less; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 1. According to this manufacturing method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, a secondary battery electrode can be provided with strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and a release substrate-attached electrode mixture layer can be provided with weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics, or a carbon nanotube dispersion liquid can be obtained that enables good film-forming properties to be achieved when forming a bare film.

[0035] Preferably, the method for producing a carbon nanotube dispersion of aspects B1, B2, and C further comprises the steps of: measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, where the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4 and the CNT persistent length in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is in the range of 100 nm or more, when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2. According to this manufacturing method, by adding the additional condition that the CNT persistence length measured above is 100 nm or more, it is possible to further enhance the strong peel strength between the electrode mixture layer and the current collector made of a metal or the like in a secondary battery electrode, and to further enhance the weak peel strength between the electrode mixture layer and the release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby enabling secondary batteries to exhibit even better excellent rate characteristics, or to obtain a carbon nanotube dispersion that enables good film-forming properties to be achieved when forming a bare film.

[0036] The method for producing a carbon film of the present invention includes a step of removing the solvent from the CNT dispersion liquid having a CNT area ratio of 70% or less to form a carbon film. According to this production method, by using the CNT dispersion liquid having a CNT area ratio of 70% or less, a carbon film can be obtained with good film-forming properties.

[0037] Furthermore, the method for producing a carbon film of the present invention includes a step of forming a carbon film by removing the solvent from a CNT dispersion obtained by the above-described method for producing a CNT dispersion and selected under the condition that the CNT area ratio is 70% or less. According to this production method, by using a CNT dispersion selected under the condition that the CNT area ratio is 70% or less, a carbon film can be obtained with good film-forming properties.

[0038] According to the present invention, a carbon nanotube dispersion can be provided that can provide a secondary battery electrode with strong peel strength between an electrode mixture layer and a current collector made of metal or the like, and can provide a release substrate-attached electrode mixture layer with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Furthermore, according to the present invention, a laminate can be provided that can be used as a secondary battery electrode having strong peel strength between an electrode mixture layer and a current collector made of metal or the like. Furthermore, according to the present invention, a laminate can be provided that can be used as an electrode mixture layer with a release substrate having weak peel strength between an electrode mixture layer and a release substrate made of resin or the like. Furthermore, according to the present invention, a CNT dispersion that can achieve good film-formability when forming a carbon film using the CNT dispersion, and a method for producing the same can be provided. Furthermore, according to the present invention, a method for producing a carbon film with good film-formability using the CNT dispersion can be provided.

[0039] FIG. 1 shows an optical microscope image of the CNT dispersion of Example 1. FIG. 2 shows an optical microscope image of the CNT dispersion of Example 2. FIG. 3 shows an optical microscope image of the CNT dispersion of Example 3. FIG. 4 shows an optical microscope image of the CNT dispersion of Comparative Example 1. FIG. 5 shows an SEM image of a CNT aggregate according to an example of the CNTs used in the CNT dispersion of the present invention. FIG. 6 shows a graph obtained by fitting the ultra-small angle X-ray scattering profiles of the CNT dispersions of Example 1 and Comparative Example 1 to Beaucage's equation. FIG. 7 shows a schematic configuration of the CNT production apparatus used in Examples 1, 3 to 7, and Comparative Examples 1, 3, and 4. FIG. 8 shows an optical microscope image of an example CNT dispersion. FIG. 9 shows an image of the optical microscope image of FIG. 10 after binarization processing. FIG. 11 shows an image of the CNT dispersion of Example 1 after binarization processing. FIG. 12 shows an image of the CNT dispersion of Example 2 after binarization processing. FIG. 13 shows an image of the CNT dispersion of Example 3 after binarization processing. The solid line indicates carbon nanotubes with an aspect ratio of 10 or more. This shows an image of the CNT dispersion of Comparative Example 1 after binarization. This shows an image of the CNT dispersion of Comparative Example 2 after binarization. This shows a photograph (top) of a grindmeter analysis of a slurry composition for a lithium ion secondary battery positive electrode produced using the CNT dispersion of Example 1, and a photograph (bottom) of a lithium ion secondary battery positive electrode produced using the same CNT dispersion. This shows a photograph (top) of a grindmeter analysis of a slurry composition for a lithium ion secondary battery positive electrode produced using the CNT dispersion of Example 2, and a photograph (bottom) of a lithium ion secondary battery positive electrode produced using the same CNT dispersion. This shows a photograph (top) of a grindmeter analysis of a slurry composition for a lithium ion secondary battery positive electrode produced using the CNT dispersion of Example 3, and a photograph (bottom) of a lithium ion secondary battery positive electrode produced using the same CNT dispersion. 1 shows a photograph (top) of a grindmeter analysis of a slurry composition for a lithium ion secondary battery positive electrode produced using the CNT dispersion of Comparative Example 1, and a photograph (bottom) of a lithium ion secondary battery positive electrode produced using the same CNT dispersion.

[0040] Hereinafter, embodiments of the present invention will be described in detail.

[0041] (Carbon nanotube dispersion) In Aspect A, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing carbon nanotubes and a solvent, and when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, the carbon nanotube dispersion has a fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) inclusive, in the range of 3 to 4. Since the fractal dimension measured above is in the range of 3 to 4 inclusive, when used to form an electrode mixture layer, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, and the secondary battery can exhibit excellent rate characteristics.

[0042] In Aspect B1, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent, wherein the area ratio of carbon nanotubes in an image obtained by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 55% or less. When single-walled carbon nanotubes having a G / D ratio of 5 or less are used as the carbon nanotubes, the area ratio of carbon nanotubes measured above being 55% or less means that, when used to form an electrode mixture layer, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, allowing the secondary battery to exhibit excellent rate characteristics.

[0043] In addition, when single-walled carbon nanotubes having a G / D ratio of 5 or less are used as carbon nanotubes, the 26000 μm ２Preferably, the carbon nanotube composition further comprises 5 to 100 carbon nanotubes having an aspect ratio (length / diameter) of 10 or more per area corresponding to the surface area of ​​the electrode mixture layer. By having the number of carbon nanotubes having an aspect ratio of 10 or more within the above range, when used to form an electrode mixture layer, the secondary battery electrode can exhibit even stronger peel strength between the electrode mixture layer and a current collector made of metal or the like, and the electrode mixture layer with release substrate can exhibit even stronger weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby allowing the secondary battery to exhibit even stronger excellent rate characteristics.

[0044] In Aspect B2, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent, wherein the area ratio of carbon nanotubes in an image obtained by capturing the carbon nanotube dispersion at a concentration of 0.1 wt % is 75% or more. When single-walled carbon nanotubes having a G / D ratio of 10 or more are used as the carbon nanotubes, the area ratio of carbon nanotubes measured above being 75% or more means that, when used to form an electrode mixture layer, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, allowing the secondary battery to exhibit excellent rate characteristics.

[0045] In Aspect C, the carbon nanotube dispersion of the present invention is a carbon nanotube dispersion containing carbon nanotubes and a solvent, wherein the area ratio of carbon nanotubes in an image acquired by capturing an image of the carbon nanotube dispersion is 70% or less. When the area ratio of carbon nanotubes measured above is 70% or less, good film-formability can be achieved when forming a carbon film using the CNT dispersion. Note that, in the present invention, the area ratio of the CNT dispersion can be determined by the method described in the Examples, and the film-formability of the carbon film can be evaluated by the method described in the Examples.

[0046] Furthermore, by setting the area ratio of carbon nanotubes in an image of the carbon nanotube dispersion to a predetermined range, it becomes possible to obtain a carbon film having a desired porosity range when forming a carbon film using the CNT dispersion. For example, by using a CNT dispersion having an area ratio measured above in the range of 20% to 70%, preferably 55% to 70%, it is possible to obtain a carbon film having a high porosity, for example, 60% to 99%, which is useful for battery applications. The correlation between the area ratio of the CNT dispersion and the porosity of the resulting carbon film strictly depends on the type of CNT, but generally, the porosity tends to increase as the area ratio value increases, and the porosity tends to decrease as the area ratio value decreases. As a measure of the correlation between the area ratio and the porosity, for example, when a CNT dispersion prepared using a CNT aggregate that satisfies at least one of the following conditions (1) to (3) is used as the CNTs, it can be estimated that a carbon film having a porosity of 80% to 99% can be obtained if the area ratio measured above is in the range of 55% to 70%: (1) In a spectrum obtained by Fourier transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more, a peak due to the plasmon resonance of the carbon nanotube dispersion appears at a wave number of 300 cm －１ Super 2000cm －１ (2) The maximum peak in a pore distribution curve showing the relationship between pore diameter and log differential pore volume, obtained from the adsorption isotherm of liquid nitrogen at 77 K based on the Barrett-Joyner-Halenda method for the carbon nanotube aggregate, is in the pore diameter range of more than 100 nm and less than 400 nm. (3) The peak in the two-dimensional spatial frequency spectrum of an electron microscope image of the carbon nanotube aggregate is in the range of 1 μm －１ 100 μm or more －１At least one of the following ranges exists. If a more precise correlation between area ratio and porosity is required, a calibration curve showing the correlation between area ratio and porosity can be created for each type of CNT, and the calibration curve can be used to determine an area ratio that can achieve a desired porosity. In the present invention, the porosity of the carbon film can be determined by the method described in the examples.

[0047] In aspects B1, B2, and C, the carbon nanotube dispersion of the present invention is further characterized in that, when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using the Beaucage model, the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4. When the fractal dimension measured above is in the range of 3 to 4, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics or enabling good film formability to be achieved during bare film formation.

[0048] In aspects A, B1, B2, and C, the carbon nanotube dispersion of the present invention preferably has a CNT persistent length of 100 nm or more in a wavenumber range of 0.05 (1 / Å) or more and 0.01 (1 / Å) or less when a scattering curve obtained by ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model. Having a CNT persistent length of 100 nm or more as measured above allows a secondary battery electrode, when used to form an electrode mixture layer, to exhibit even stronger peel strength between the electrode mixture layer and a current collector made of a metal or the like, or allows a release substrate-attached electrode mixture layer to exhibit even stronger peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit even better excellent rate characteristics or enabling good film formability to be achieved during bare film formation.

[0049] <Carbon Nanotubes> The carbon nanotubes (CNTs) used in the carbon nanotube dispersion of the present invention are not particularly limited. For example, single-walled carbon nanotubes (single-walled CNTs) are preferably used. In the cases of Aspects B1 and B2, single-walled carbon nanotubes (single-walled CNTs) are used. By using single-walled CNTs, a CNT dispersion with high conductivity can be prepared. Examples of CNTs include those that satisfy the conditions shown below or are obtained by the production method shown below. The proportion of CNTs that satisfy the conditions shown below or are obtained by the production method shown below relative to the total mass of CNTs is preferably more than 50% by mass, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.

[0050] The carbon nanotubes (CNTs) used in the carbon nanotube dispersion of the present invention are not particularly limited, and single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used, but it is preferable that the dispersion contains single-walled carbon nanotubes (single-walled CNTs) as the main component. Components other than single-walled CNTs that can be contained in the CNTs include multi-walled carbon nanotubes (multi-walled CNTs). Here, the ratio of single-walled CNTs to the total mass of the CNTs may be, for example, more than 50% by mass, preferably 90% by mass or more, more preferably 95% by mass or more, and even 100% by mass. When the CNTs include multi-walled CNTs, it is preferable that the number of walls of the multi-walled CNTs is 5 or less. Using single-walled CNTs makes it possible to prepare a CNT dispersion with higher conductivity than when multi-walled CNTs are used, or a CNT dispersion that can produce a self-supporting carbon film with high conductivity and porosity.

[0051] In one embodiment, single-walled carbon nanotubes with a G / D ratio of 5 or less are used as the CNTs. In this case, the G / D ratio of the CNTs is preferably 1 or more, more preferably 1.1 or more. Furthermore, the G / D ratio of the CNTs is 5 or less, preferably 4.9 or less. If the G / D ratio is equal to or less than the above upper limit, it is easy to form a CNT network. Conversely, a CNT aggregate with a G / D ratio below the above lower limit is thought to have low single-walled CNT crystallinity, a large amount of contamination such as amorphous carbon, and a high rate of multi-walled CNT contamination.

[0052] In another embodiment, single-walled carbon nanotubes having a G / D ratio of 10 or more are used as the CNTs. In this case, the G / D ratio of the CNTs is preferably 10 or more, more preferably 11 or more. Furthermore, the G / D ratio of the CNTs is preferably 100 or less, more preferably 60 or less. If the G / D ratio is equal to or greater than the lower limit, high crystallinity can be expected, and electrical conductivity can be imparted. Conversely, CNT aggregates having a G / D ratio exceeding the upper limit have high linearity, and the CNTs are likely to form bundles with few gaps, which may reduce the specific surface area.

[0053] The G / D ratio is an index commonly used to evaluate the quality of CNTs. The Raman spectrum of CNTs measured by a Raman spectrometer contains the G band (1600 cm －１ around 1350 cm －１ A vibration mode called the G band (near the G band) is observed. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibration mode derived from the amorphous portion. Therefore, the higher the peak intensity ratio (G / D ratio) of the G band to the D band, the higher the crystallinity (linearity) of the CNT can be evaluated. The G / D ratio can be determined, for example, by the method described in the Examples. Furthermore, when the CNT is a mixture of multiple types of CNT, it is sufficient that the G / D ratio of the CNT mixture is within the above range.

[0054] CNTs can be produced using known CNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD), without any particular limitation. Specifically, CNTs can be efficiently produced, for example, by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer for carbon nanotube production on its surface, and synthesizing CNTs by chemical vapor deposition (CVD), by adding a trace amount of oxidizing agent (catalytic activator) to the system, thereby dramatically improving the catalytic activity of the catalyst layer (super-growth method; see International Publication No. 2006 / 011655). Hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNT."

[0055] Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of the CNTs exhibits an upwardly convex shape.

[0056] Here, in materials with pores on the surface, the growth of a nitrogen gas adsorption layer can be classified into the following processes (1) to (3). The slope of the t-plot changes depending on the following processes (1) to (3): (1) The process of forming a monomolecular adsorption layer of nitrogen molecules on the entire surface; (2) The process of forming a multimolecular adsorption layer and the accompanying capillary condensation filling process within the pores; and (3) The process of forming a multimolecular adsorption layer on an apparently non-porous surface where the pores are filled with nitrogen.

[0057] In the t-plot showing an upward convex shape, the plot lies on a straight line passing through the origin in the region where the average thickness t of the nitrogen gas adsorption layer is small, whereas as t increases, the plot shifts downward from the straight line. CNTs having such a t-plot shape have a large ratio of internal specific surface area to total specific surface area of ​​the CNT, indicating that numerous openings are formed in the CNTs. As a result, when a dispersion is prepared using such CNTs, the CNTs are less likely to aggregate in the dispersion. When used to form an electrode mixture layer, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and an electrode mixture layer with a release substrate can exhibit weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics or enabling good film formability to be achieved during bare film formation.

[0058] The inflection point of the t-plot of the CNTs preferably falls within a range satisfying 0.2≦t (nm)≦1.5, more preferably within a range satisfying 0.45≦t (nm)≦1.5, and even more preferably within a range satisfying 0.55≦t (nm)≦1.0. When a dispersion is prepared using CNTs with an inflection point of the t-plot within this range, the CNTs are even less likely to aggregate in the dispersion. As a result, when used to form an electrode mixture layer, a secondary battery electrode can exhibit strong peel strength between the electrode mixture layer and a current collector composed of a metal or the like, and a release substrate-attached electrode mixture layer can exhibit weak peel strength between the electrode mixture layer and a release substrate composed of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics or achieving good film formability during bare film formation. Here, the "position of the inflection point" is the intersection of the approximate line A in the above-mentioned process (1) and the approximate line B in the above-mentioned process (3).

[0059] Furthermore, the CNT preferably have a ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from a t-plot of 0.05 or more and 0.30 or less. When a carbon nanotube dispersion is prepared using CNTs with an S2 / S1 value within this range, the CNTs are even less likely to aggregate in the dispersion. As a result, a carbon nanotube dispersion can be obtained that exhibits excellent stabilization of the CNT network in the dispersion.

[0060] Here, the total specific surface area S1 and the internal specific surface area S2 of the CNT can be determined from the t-plot. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximation line in step (1), and the external specific surface area S3 can be determined from the slope of the approximation line in step (3). Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

[0061] Measurement of the adsorption isotherm of CNT, creation of t-plots, and calculation of the total specific surface area S1 and the internal specific surface area S2 based on analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0062] In addition, the BET specific surface area of ​​CNT is 600 m ２ / g or more, and ２ / g or more is more preferable, and 2000m ２ / g or less, and ２ / g or less is more preferable, and 1600m ２ / g or less is even more preferable. If the BET specific surface area is within the above range, a CNT dispersion liquid with excellent dispersibility can be prepared. In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0063] The average diameter of the CNTs is preferably 1 nm or more, preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. The average length of the CNTs is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more, and preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. When a carbon nanotube dispersion is prepared using CNTs with an average diameter and / or average length within the above ranges, the CNTs are less likely to aggregate in the carbon nanotube dispersion, allowing for the production of a stabilized CNT dispersion.

[0064] The carbon nanotubes may be in the form of a CNT aggregate. As the CNT in the form of a CNT aggregate, for example, a CNT aggregate that satisfies at least one of the conditions (1) to (3) described below can be used.

[0065] <<CNT aggregate>> Here, it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3) as the CNT aggregate that can be used to prepare the carbon nanotube dispersion. A CNT dispersion prepared using a CNT aggregate that satisfies at least one of the conditions (1) to (3) below is excellent in performance with respect to strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed. Alternatively, the CNT dispersion is suitable for obtaining a carbon film with high porosity because the carbon nanotubes have mesopores.

[0066] (1) A carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more is subjected to Fourier transform infrared spectroscopy. In the spectrum obtained, a peak due to plasmon resonance of the carbon nanotube dispersion is observed at a wave number of 300 cm. －１ Super 2000cm －１(2) The maximum peak in a pore distribution curve showing the relationship between pore diameter and log differential pore volume, obtained from the adsorption isotherm of liquid nitrogen at 77 K based on the Barrett-Joyner-Halenda method for the carbon nanotube aggregate, is in the pore diameter range of more than 100 nm and less than 400 nm. (3) The peak in the two-dimensional spatial frequency spectrum of an electron microscope image of the carbon nanotube aggregate is in the range of 1 μm －１ 100 μm or more －１ At least one of the following ranges is present:

[0067] The reasons why a CNT dispersion formed from a CNT aggregate satisfying at least one of the above conditions (1) to (3) exhibits strong peel strength when a laminate between a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate between a release substrate and a carbon nanotube-containing film is formed, and excellent performance in terms of discharge rate characteristics when a secondary battery is formed, or why a CNT dispersion is suitable for obtaining a carbon film in which carbon nanotubes have mesopores and a high porosity, are not clear, but are presumed to be as follows. Figure 5 shows a scanning electron microscope (SEM) image of an example of a CNT aggregate satisfying at least one of the above conditions (1) to (3). As shown in Figure 5, the CNTs constituting a CNT aggregate satisfying at least one of the above conditions (1) to (3) have a wavy structure. Due to this "wavy structure," the CNTs form a network structure. As a result, it is presumed that this is reflected in the strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, the weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and excellent performance in terms of discharge rate characteristics when a secondary battery is formed, or in the suitability of carbon nanotubes to obtain a carbon film having mesopores and high porosity. Below, the above conditions (1) to (3) that can be satisfied by the CNT aggregate used in preparing the CNT dispersion of the present invention will be described in detail.

[0068] <<Condition (1)>> The condition (1) is that "in a spectrum obtained by Fourier transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more, a peak due to plasmon resonance of the carbon nanotube dispersion is at a wave number of 300 cm －１ Super 2000cm －１ At least one of the following is present in the range below. Here, strong absorption characteristics in the far-infrared region have been widely known as an optical property of CNTs. Such strong absorption characteristics in the far-infrared region are thought to be due to the diameter and length of the CNTs. Note that absorption characteristics in the far-infrared region, more specifically, the relationship between the peak due to the plasmon resonance of CNTs and the length of CNTs, have been discussed in detail in a non-patent document (T. Morimoto et al., "Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes", pp. 9897-9904, Vol. 8, No. 10, ACS NANO, 2014).

[0069] Under condition (1), the wave number is 300 cm －１ Super 2000cm －１ Within the following range, preferably within the wave number 500 cm －１ More than 2000cm －１ in the following range, more preferably in the range of 700 cm －１ More than 2000cm －１ If a peak due to the plasmon resonance of CNTs is present in the following range, when a CNT dispersion using such CNTs is used, it can exhibit strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and excellent performance in terms of discharge rate characteristics when a secondary battery is formed. Furthermore, because such CNTs have mesopores, a CNT dispersion using such CNTs is suitable for obtaining a carbon film with a high porosity.

[0070] In the spectrum obtained by Fourier transform infrared spectroscopy of the CNT aggregate, in addition to a relatively gentle peak due to the plasmon resonance of the CNT dispersion, a peak at a wave number of 840 cm －１ Near 1300 cm －１ and around 1700 cm －１ It can be seen that sharp peaks are observed around 840 cm. These sharp peaks do not correspond to "peaks based on plasmon resonance of the carbon nanotube dispersion," but each corresponds to infrared absorption derived from a functional group. More specifically, －１ The sharp peak around 1300 cm is due to the C-H out-of-plane bending vibration; －１ The sharp peak around 1700 cm is due to the epoxy three-membered ring stretching vibration; －１ The sharp peak around 2000 cm is due to the C=O stretching vibration. －１ In the region above 2000, a peak similar to the S1 peak is detected in addition to the plasmon resonance, as mentioned in the non-patent document by T. Morimoto et al., and therefore, in the present invention, the upper limit for determining the presence or absence of a peak based on the plasmon resonance of the CNT dispersion under condition (1) is set to 2000. －１ cm or less.

[0071] Here, in condition (1), when obtaining a spectrum by Fourier transform infrared spectroscopy, it is necessary to obtain a CNT dispersion by dispersing the CNT aggregate so that the bundle length is 10 μm or more. Here, for example, by blending a CNT aggregate, water, and a surfactant (e.g., sodium dodecylbenzenesulfonate) in an appropriate ratio and stirring the mixture for a predetermined period of time using ultrasound or the like, a dispersion liquid in which a CNT dispersion having a bundle length of 10 μm or more is dispersed in water can be obtained.

[0072] The bundle length of a CNT dispersion can be obtained by analysis using a wet image analysis particle size measuring device. This measuring device can calculate the area of ​​each dispersion from an image obtained by photographing the CNT dispersion, and obtain the diameter of a circle having the calculated area (hereinafter, sometimes referred to as the ISO area diameter). In this specification, the bundle length of each dispersion is defined as the value of the ISO area diameter obtained in this manner.

[0073] <<Condition (2)>> Condition (2) specifies that "the maximum peak in the pore distribution curve is in the range of pore diameters greater than 100 nm and less than 400 nm." The pore distribution of a carbon nanotube aggregate can be determined based on the BJH method from the adsorption isotherm of liquid nitrogen at 77 K. The fact that the peak in the pore distribution curve obtained by measuring the carbon nanotube aggregate is in the range of greater than 100 nm means that voids of a certain size exist between the CNTs in the carbon nanotube aggregate, and the CNTs are not in an excessively densely aggregated state. The upper limit of 400 nm is the measurement limit when, for example, a BELSORP-mini II is used as a measurement device.

[0074] Here, from the viewpoint of further improving the performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed, or making the CNTs have mesopores and the CNT dispersion suitable for obtaining a carbon film with high porosity, the value of the log differential pore volume at the maximum peak of the pore distribution curve of the CNT aggregate is 2.0 cm ３ / g or more is preferred.

[0075] <<Condition (3)>> The condition (3) is that "the peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is within 1 μm －１ 100 μm or more －１At least one of the following conditions is present in the range below." Whether or not this condition is satisfied can be determined as follows. First, the CNT aggregate to be determined is observed at a magnification (for example, 10,000 times) using an electron microscope (for example, a field emission scanning electron microscope), and multiple electron microscope images (for example, 10 images) are obtained in a field of view of 1 cm square. A fast Fourier transform (FFT) is performed on the multiple electron microscope images obtained, and a two-dimensional spatial frequency spectrum is obtained. The two-dimensional spatial frequency spectrum obtained for each of the multiple electron microscope images is binarized to find the average value of the peak positions that appear on the highest frequency side. If the average value of the obtained peak positions is less than 1 μm －１ 100 μm or more －１ If the difference is within the range below, it is determined that the condition (3) is satisfied. Here, the "peak" used in the above determination is a clear peak obtained by performing the isolated point extraction process (i.e., the reverse operation of the isolated point removal). Therefore, when the isolated point extraction process is performed, －１ 100 μm or more －１ If no clear peak is obtained within the range below, it is determined that condition (3) is not satisfied.

[0076] Here, from the viewpoint of further improving the performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed, or from the viewpoint of making the CNTs have mesopores and the CNT dispersion suitable for obtaining a carbon film with a high porosity, the peak of the two-dimensional spatial frequency spectrum is 2.6 μm －１ 100 μm or more －１ It is preferred that it is in the following range:

[0077] From the viewpoint of further improving the performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed, or making the CNTs have mesopores and the CNT dispersion suitable for obtaining a carbon film with high porosity, it is preferable that the CNT aggregate satisfy at least two of the above conditions (1) to (3), and it is more preferable that the CNT aggregate satisfy all of the conditions (1) to (3).

[0078] <<Other Properties>> In addition to the above conditions (1) to (3), the CNT aggregate that can be used to form the CNT dispersion of the present invention preferably has the following properties.

[0079] For example, the CNT aggregate preferably has a total specific surface area measured by the BET method of 600 m ２ / g or more, more preferably 800m ２ / g or more, preferably 2600m ２ / g or less, more preferably 1400m ２ / g or less. Furthermore, in the case of the opening treatment, ２ / g or more is preferable. A CNT aggregate with a high specific surface area enhances the bonding strength between the CNTs and the metal film, resulting in a strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, a weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and further improved performance in terms of discharge rate characteristics when a secondary battery is formed. Alternatively, good film formability can be achieved when forming a carbon film using a CNT dispersion. In cases other than aspects B1 and B2, the CNT aggregate may primarily contain single-walled CNTs, and may also contain double-walled CNTs and multi-walled CNTs to the extent that their function is not impaired. The total specific surface area of ​​CNTs measured by the BET method can be measured, for example, using a BET specific surface area measurement device in accordance with JIS Z8830.

[0080] The tap bulk density of the CNT aggregate is 0.001 g / cm ３ 0.2g / cm or more ３It is preferable that the tap bulk density of the CNT aggregate is 0.2 g / cm or less. In a CNT aggregate in this density range, the bonds between the CNTs are not excessively strong, so the aggregate has excellent dispersibility and can be molded into various shapes. ３ If the tap bulk density of the CNT aggregate is less than 0.001 g / cm, the bonds between the CNTs will be weak, making it easier to disperse the CNT aggregate homogeneously when stirred in a solvent or the like. ３ If the density is above this, the integrity of the CNT aggregate is improved and handling becomes easier. Tapped bulk density is the apparent bulk density in a densely packed state after a container is filled with powdered CNT aggregate and the voids between the powder particles are reduced by tapping or vibration or the like.

[0081] In cases other than modes B1 and B2, the G / D ratio of the CNT aggregate is preferably 1 or more and 50 or less. A CNT aggregate with a G / D ratio of less than 1 is thought to have low single-walled CNT crystallinity, a lot of contamination such as amorphous carbon, and a high content of multi-walled CNT. Conversely, a CNT aggregate with a G / D ratio of more than 50 is highly linear, and the CNTs tend to form bundles with few gaps, which may result in a reduced specific surface area. The G / D ratio is an index generally used to evaluate the quality of CNT. The Raman spectrum of CNT measured by a Raman spectrometer contains the G band (1600 cm －１ around 1350 cm －１ A vibration mode called the G band (near the G band) is observed. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibration mode derived from the amorphous part. Therefore, the higher the peak intensity ratio of the G band to the D band (G / D ratio), the higher the crystallinity (linearity) of the CNT can be evaluated.

[0082] In order to obtain a high specific surface area, it is desirable that the purity of the CNT aggregate be as high as possible. Purity here refers to carbon purity, and is a value that indicates what percentage of the mass of the CNT aggregate is made up of carbon. There is no upper limit to the purity in obtaining a high specific surface area, but in terms of production, it is difficult to obtain a CNT aggregate of 99.9999 mass% or more. If the purity is less than 95 mass%, it will be difficult to obtain a CNT aggregate of 1000 m without being subjected to opening treatment. ２ It becomes difficult to obtain a specific surface area exceeding 98% by mass / g. Furthermore, if the carbon purity is less than 95% by mass due to the presence of metal impurities, the metal impurities will react with oxygen during the opening treatment, hindering the opening of the CNTs, making it difficult to increase the specific surface area. From these points of view, the purity of single-walled CNTs is preferably 95% by mass or more. A predetermined CNT aggregate that satisfies at least one of the above conditions (1) to (3) can typically achieve a purity of 98% by mass or more, preferably 99.9% by mass or more, without purification treatment. The CNT aggregate is almost free of impurities, allowing the inherent properties of CNT to be fully exhibited. The carbon purity of a CNT aggregate can be obtained by elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

[0083] <<Method for manufacturing CNT aggregate>> The method for manufacturing a CNT aggregate is not particularly limited, and manufacturing conditions can be adjusted according to the desired properties. For example, when manufacturing a CNT aggregate that satisfies at least any of the above-mentioned conditions (1) to (3), the conditions during growth of the CNT aggregate need to satisfy all of the following (a) to (c). (a) The growth rate of the CNT aggregate is 5 μm / min or more. (b) The concentration of the catalyst activation material in the growth atmosphere of the CNT aggregate is 4 vol% or more. (c) During growth of the CNT aggregate, an obstacle is present in the growth direction of the CNTs that make up the CNT aggregate.

[0084] Then, a manufacturing method that satisfies all of the above-mentioned (a) to (c) can efficiently manufacture a CNT aggregate that satisfies at least any of the above-mentioned conditions (1) to (3). Furthermore, such a manufacturing method is not particularly limited as long as the above-mentioned conditions (a) to (c) are satisfied during the growth of the CNT aggregate, and a CNT synthesis step according to known methods such as a fluidized bed method, a moving bed method, and a fixed bed method can be adopted. Here, the fluidized bed method refers to a synthesis method in which CNTs are synthesized while fluidizing a granular support that supports a catalyst for synthesizing CNTs (hereinafter also referred to as a granular catalyst support). Furthermore, the moving bed method and the fixed bed method refer to synthesis methods in which CNTs are synthesized without fluidizing a support (a particulate support or a plate-like support) that supports a catalyst.

[0085] In one example, a manufacturing method that satisfies all of the above-mentioned (a) to (c) includes a catalyst support formation step of forming a catalyst support, a CNT synthesis step of synthesizing CNTs using the catalyst support obtained in the catalyst support formation step, and a recovery step of recovering the CNTs synthesized in the CNT synthesis step. The catalyst support formation step can be carried out according to a known wet or dry catalyst support method. The recovery step can be carried out using a known separation and recovery device such as a classification device.

[0086] [CNT Synthesis Process] In the CNT synthesis process, all of the above conditions (a) to (c) are satisfied during CNT growth. Specifically, by appropriately adjusting the concentration and temperature of the source gas serving as the carbon source in the CNT growth atmosphere, the condition (a) that "the growth rate of the carbon nanotube aggregate is 5 μm / min or more" can be satisfied. The source gas serving as the carbon source is not particularly limited, and hydrocarbon gases such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene, and acetylene; lower alcohol gases such as methanol and ethanol; and mixtures thereof can also be used. Furthermore, this source gas may be diluted with an inert gas. Furthermore, from the viewpoint of further improving the dispersibility of the obtained CNT aggregate while also improving the performance of the strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, the weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and the discharge rate characteristics when a secondary battery is formed, or from the viewpoint of achieving good film formability when a carbon film is formed using a CNT dispersion, the growth rate of the CNT aggregate is preferably 10 μm / min or more. The temperature can be adjusted, for example, in the range of 400° C. or higher and 1100° C. or lower.

[0087] In the CNT growth atmosphere, the raw material gas serving as the carbon source preferably contains ethylene. Heating ethylene within a predetermined temperature range (700°C or higher and 900°C or lower) promotes the decomposition reaction of ethylene, enabling rapid CNT growth when the decomposition gas comes into contact with the catalyst. However, if the thermal decomposition time is too long, the ethylene decomposition reaction proceeds too quickly, causing catalyst deactivation and carbon impurities to adhere to the CNT aggregate. In the production of CNT aggregates using the CNT dispersion liquid of the present invention, a thermal decomposition time of 0.5 seconds to 10 seconds is preferred for an ethylene concentration in the range of 0.1% by volume to 40% by volume. If the thermal decomposition time is less than 0.5 seconds, the ethylene thermal decomposition is insufficient, making it difficult to rapidly grow a CNT aggregate with a high specific surface area. If the time is longer than 10 seconds, the ethylene decomposition proceeds too quickly, generating a large amount of carbon impurities, which can deactivate the catalyst and reduce the quality of the CNT aggregate. The thermal decomposition time is calculated using the following formula: (Pyrolysis time)=(Heated flow path volume) / {(Feedstock gas flow rate)×(273.15+T) / 273.15} Here, the heated flow path volume is the volume of a flow path heated to a predetermined temperature T°C, through which the feedstock gas passes before contacting the catalyst, and the feedstock gas flow rate is the flow rate at 0°C and 1 atm.

[0088] Furthermore, by appropriately adjusting the supply rate of the catalytic activator supplied during CNT growth, it is possible to satisfy condition (b) that "the concentration of the catalytic activator in the growth atmosphere for the carbon nanotube aggregate is 4% by volume or more." From the viewpoint of further improving the performance of the strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, the weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and the discharge rate characteristics when a secondary battery is formed, or achieving good film formability when a carbon film is formed using a CNT dispersion, the concentration of the catalytic activator in the growth atmosphere for the CNT aggregate is preferably 5% by volume or more. Examples of catalytic activators include, but are not limited to, water, oxygen, ozone, acidic gases, nitrogen oxide, low-carbon oxygen-containing compounds such as carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; aldehydes; esters; and mixtures thereof. Among these, carbon dioxide is preferred. In addition, substances containing both carbon and oxygen, such as carbon monoxide and alcohols, may function as both a feed gas and a catalyst activator. For example, carbon monoxide acts as a catalyst activator when combined with a more reactive feed gas, such as ethylene, and acts as a feed gas when combined with a catalyst activator that exhibits significant catalyst activation even in trace amounts, such as water.

[0089] Furthermore, by selecting a fluidized bed method in the CNT synthesis process or adjusting the placement interval of the catalyst support in a moving bed method or a fixed bed method, the condition (c) that "an obstacle exists in the growth direction of the carbon nanotubes that constitute the carbon nanotube aggregate during synthesis of the carbon nanotube aggregate" can be satisfied.

[0090] Here, when synthesizing CNTs by the fluidized bed method, the CNT synthesis step may be carried out, for example, by supplying a raw material gas while supplying gas from below to fluidize the particulate catalyst support, or by supplying a raw material gas while continuously transporting the particulate catalyst support by screw rotation.

[0091] The catalyst carrier has a carrier and a catalyst supported on the surface of the carrier, and the carrier is a part that forms a matrix structure for supporting the catalyst on the surface of the carrier by adhering, fixing, forming a film, or forming. The carrier structure may be the carrier alone, or a carrier with an underlying layer, in which an optional underlying layer is provided on the surface of the carrier to favorably support the catalyst. The carrier is preferably in the form of particles, and the particle diameter is preferably 1 mm or less, more preferably 0.7 mm or less, even more preferably 0.4 mm or less, and preferably 0.05 mm or more, in terms of volume average particle diameter. If the particle diameter is equal to or less than the above upper limit, the growing CNT bundles will be thinner, which is advantageous for forming a wave-like structure. The particle density is 3.8 g / cm in apparent density. ３ It is preferable that the density is 5.8 g / cm or more. ３ More preferably, it is 8 g / cm or more. ３ It is preferable that the particle density is equal to or less than the above lower limit. If the particle density is equal to or greater than the above lower limit, the force applied to the growing CNT bundle increases, which is advantageous for forming a wave-like structure. The support material is preferably a metal oxide containing at least one of Al and Zr. Among these, zirconia beads containing a large amount of Zr are particularly preferable.

[0092] For example, when a particulate carrier is used, a method for supporting a catalyst on the surface of the particulate carrier can be, for example, a method using a rotary drum coating device equipped with a substantially cylindrical rotary drum. When a catalyst is supported on the surface of the particulate carrier after a base layer is formed on the surface, a solution containing components that can form the base layer is sprayed onto the surface of the particulate carrier and dried prior to spraying and drying the catalyst solution. This method allows the catalyst layer and base layer to be formed relatively easily and evenly.

[0093] In the CNT synthesis process, a "formation process" is performed prior to the "growth process" performed so as to satisfy the above conditions (a) to (c), in which the catalyst supported on the catalyst support is reduced. After the growth process is completed, a "cooling process" can be performed to cool the catalyst support on which the CNTs have grown. In the "formation process," for example, the atmosphere containing the catalyst support is a reducing gas atmosphere, and at least one of the reducing gas atmosphere or the catalyst support is heated to reduce and microparticulate the catalyst supported on the catalyst support. The temperature of the catalyst support or the reducing gas atmosphere in the formation process is preferably 400°C or higher and 1100°C or lower. The formation process can be performed for 3 minutes or longer and 120 minutes or shorter. Examples of the reducing gas that can be used include hydrogen gas, ammonia gas, water vapor, and mixtures thereof. The reducing gas may also be a mixture of these gases with an inert gas such as helium gas, argon gas, or nitrogen gas. On the other hand, in the "cooling step", the catalyst support on which the CNTs have been grown is cooled in an inert gas environment. Here, the inert gas may be the same as the inert gas that can be used in the growth step. In addition, in the cooling step, the temperature of the catalyst support on which the CNTs have been grown is lowered to preferably 400°C or less, more preferably 200°C or less.

[0094] <Dry pulverization treatment> When obtaining the CNT dispersion liquid of the present invention, if necessary, the CNT aggregate before dispersion can be subjected to a dry pulverization treatment. Note that, in this specification, "dry pulverization treatment" means a pulverization treatment in a state where the object to be pulverized does not substantially contain a solvent (for example, a state where the solid content concentration is 95% or more).

[0095] The grinding device that can be used in the dry grinding process is not particularly limited as long as it is a device that can apply a physical load to an aggregate of fine structures by stirring or the like. A mixer equipped with rotating blades can be used as such a device. The grinding conditions are not particularly limited. For example, when a mixer equipped with rotating blades is used as the grinding device, the rotation speed is preferably 500 rpm or more and 5000 rpm or less, and the grinding time is preferably 10 seconds or more and 20 minutes or less.

[0096] <Solvent> The solvent for the CNT dispersion (hereinafter sometimes simply referred to as "solvent") is not particularly limited, and examples thereof include alcohols such as water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amide-based polar organic solvents such as N,N-dimethylformamide and N-methylpyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, ortho-dichlorobenzene, and para-dichlorobenzene. These solvents may be used alone or in combination of two or more. Among these, in the cases of Aspects A, B1, and B2, it is more preferable to use NMP as the solvent for the CNT dispersion. In the case of aspect C, the solvent for the CNT dispersion is preferably water, an alcohol, or a mixture thereof, and more preferably water. When water is used as such a solvent, when a carbon film made of a carbon nanotube dispersion using the water is used in a battery, the affinity between the carbon film and the electrolyte is good, and battery performance can be improved. When alcohol is used as such a solvent, a carbon film can be easily produced using the carbon nanotube dispersion. Furthermore, the solvent for the CNT dispersion and the solvent for the slurry composition may be the same or different, but they are preferably the same from the viewpoint of maintaining a constant solvent composition throughout the production process of the slurry composition.

[0097] <Carbon nanotube content> The carbon nanotube content in the carbon nanotube dispersion is not particularly limited, but from the viewpoint of dispersibility, it is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Also, from the viewpoint of dispersibility, the carbon nanotube content in the carbon nanotube dispersion is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less.

[0098] <Total Content of Carbon Nanotubes and Solvent> The carbon nanotube dispersion of the present invention is intended for use in producing a slurry composition for a secondary battery electrode by mixing it with components for a secondary battery electrode, such as an active material and a binder, and optionally a dispersant. From the viewpoint that the constancy of the dispersion state of the carbon nanotube dispersion may be impaired if other components are present, or from the viewpoint of minimizing the amount of impurities remaining in the carbon film formed by removing the solvent, it is preferable that the total content of components other than the carbon nanotubes and the solvent (i.e., the dispersant, the active material, the binder, etc.) is as low as possible, and in particular, it is more preferable that the carbon nanotube dispersion does not contain a dispersant. Conversely, it is preferable that the carbon nanotubes and the solvent account for the majority of the carbon nanotube dispersion of the present invention. Specifically, the total content of the carbon nanotubes and the solvent in the carbon nanotube dispersion of the present invention is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably that the carbon nanotube dispersion of the present invention does not contain any components other than the carbon nanotubes and the solvent.

[0099] <Dispersion Treatment> A carbon nanotube dispersion can be obtained by dispersing a mixture of carbon nanotubes and a solvent. In Aspects A, B1, and B2, the dispersion treatment can be carried out using a known mixing device. Examples of the mixing device include mixing devices that provide a cavitation effect, such as ultrasonic dispersers and jet mills, and dispersing devices that provide a crushing effect, such as bead mills, ball mills, roll mills, sand mills, pigment dispersers, crushers, homogenizers, planetary mixers, and Filmix. It is preferable to use a mixing device that provides a cavitation effect for the dispersion treatment, as this allows for more uniform dispersion of CNTs. These mixing devices may be used alone or in combination of two or more.

[0100] Here, in dispersion treatment using a mixer that can achieve the cavitation effect, dispersion is carried out by utilizing shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid. By using this dispersion method, CNTs can be dispersed even better.

[0101] When an ultrasonic disperser is used to disperse CNTs, the CNTs are added to a solvent, and then the resulting crude dispersion is irradiated with ultrasonic waves using the ultrasonic disperser. The irradiation time can be set appropriately depending on the amount of CNTs, and is, for example, preferably 3 minutes or more, more preferably 30 minutes or more, and preferably 5 hours or less, more preferably 2 hours or less. Furthermore, for example, the output is preferably 20 W or more and 500 W or less, more preferably 100 W or more and 500 W or less, and the temperature is preferably 15 ° C or more and 50 ° C or less.

[0102] Furthermore, when a jet mill is used, the number of times of treatment may be appropriately set depending on the amount of CNTs, etc., and is, for example, preferably 3 times or more, more preferably 6 times or more, and preferably 30 times or less, and more preferably 25 times or less. Furthermore, for example, the pressure is preferably 20 MPa or more and 250 MPa or less, and the temperature is preferably 15°C or more and 50°C or less.

[0103] It is more preferable that the dispersion treatment for obtaining the above-mentioned cavitation effect is carried out at a temperature of 50° C. or less.

[0104] Other dispersion treatment methods are not particularly limited, but a CNT dispersion can be obtained by dispersing CNT aggregates in a dispersion medium using known methods such as a dispersion method using an agitating blade, a dispersion method using ultrasonic waves, and a dispersion method using shear force. Here, preferred conditions for each dispersion method for obtaining the CNT dispersion of the present invention are as follows. When using a dispersion method using an agitating blade, dispersion of CNTs in a dispersion medium is preferably carried out at a rotation speed of the agitating blade of 1500 rpm to 12500 rpm, more preferably 2000 rpm to 10000 rpm, for 1 minute to 120 minutes, more preferably 5 minutes to 100 minutes. Dispersion using an agitating blade can be carried out using a known dispersion device equipped with an agitating blade. When using a dispersion method using ultrasonic waves, dispersion of CNTs in a dispersion medium is preferably carried out at a frequency of 50 kHz to 500 kHz, for 1 minute to 120 minutes, more preferably 2 minutes to 100 minutes. Dispersion using ultrasonic waves can be carried out using a known ultrasonic disperser.

[0105] In Aspect C, the method for dispersing CNTs in a solvent is not particularly limited, and a general dispersion method using a conventionally known dispersion device can be employed. From the viewpoint of easily obtaining a CNT dispersion having a desired area ratio (e.g., 70% or less, preferably 20% to 70%, and more preferably 55% to 70%) through dispersion treatment, it is preferable to prepare the dispersion by subjecting it to a dispersion treatment that produces a cavitation effect or a dispersion treatment that produces a crushing effect, as described in detail below. Furthermore, prior to the dispersion treatment, the CNTs may be pre-dispersed in the solvent using a stirrer or the like.

[0106] - Dispersion treatment that produces a cavitation effect - Dispersion treatment that produces a cavitation effect is a dispersion method that utilizes shock waves generated when vacuum bubbles generated in water burst when high energy is applied to the liquid. By using this dispersion method, CNTs can be dispersed well. It is more preferable to carry out dispersion treatment that produces a cavitation effect at a temperature of 50°C or less, as this suppresses concentration changes due to solvent evaporation.

[0107] Here, specific examples of dispersion treatments that can achieve a cavitation effect include dispersion treatment using ultrasonic waves, dispersion treatment using a jet mill, and dispersion treatment using high-shear stirring. Only one of these dispersion treatments may be performed, or multiple dispersion treatments may be combined. For dispersion treatments that can achieve a cavitation effect, for example, ultrasonic homogenizers, jet mills, and high-shear stirring devices are preferably used. These devices may be conventionally known devices.

[0108] When using an ultrasonic homogenizer, ultrasonic waves can be irradiated onto the preliminary dispersion or the mixed solution before dispersion using the ultrasonic homogenizer. The irradiation time can be set appropriately depending on the CNT concentration, degree of dispersion, etc. When using a jet mill, various conditions can be set appropriately depending on the CNT concentration, degree of dispersion, etc., but for example, the number of treatments is preferably 1 to 100 times. The pressure is preferably 20 MPa to 250 MPa, and the temperature is preferably 15°C to 50°C. As a jet mill dispersion device, a high-pressure wet jet mill is suitable, and specific examples include "Nanomaker (registered trademark)" (manufactured by Advanced Nano Technology Co., Ltd.), "Nanomizer" (manufactured by Nanomizer Co., Ltd.), "Nanovaita" (manufactured by Yoshida Kikai Kogyo Co., Ltd.), and "NanoJetPal (registered trademark)" (manufactured by Jokosha Co., Ltd.).

[0109] Furthermore, when high shear mixing is used, stirring and shearing can be applied to the preliminary dispersion or the mixed liquid before dispersion using a high shear mixer. The faster the rotation speed, the better. For example, the operating time (the time the machine is rotating) is preferably 3 minutes to 4 hours, the peripheral speed is preferably 20 m / s to 50 m / s, and the temperature is preferably 15°C to 50°C. Examples of high shear mixers include mixers such as "Ebara Milder" (manufactured by Ebara Corporation), "Cavitron" (manufactured by Eurotech), and "DRS2000" (manufactured by IKA); mixers such as "Clearmix (registered trademark) CLM-0.8S" (manufactured by M Technique); turbine mixers such as "TK Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.); and mixers such as "TK Filmix" (manufactured by Tokushu Kika Kogyo Co., Ltd.).

[0110] Dispersion Treatment with a Disintegration Effect In a dispersion treatment with a disintegration effect, shear force is applied to the pre-dispersion liquid or the mixed liquid before dispersion to disintegrate and disperse the CNTs. Furthermore, back pressure is applied, and cooling is performed as necessary. This allows the CNTs to be uniformly dispersed in the solvent while suppressing the generation of bubbles. Dispersion treatment with a disintegration effect is advantageous not only in that it can uniformly disperse the CNTs, but also in that it can suppress damage to the CNTs caused by shock waves generated when the bubbles disappear, compared to the dispersion treatment with a cavitation effect described above. Additionally, it is advantageous in that it can suppress the adhesion of bubbles to the CNTs and the energy loss caused by the generation of bubbles, thereby allowing the CNTs to be uniformly and efficiently dispersed. The back pressure can be applied by applying a load to the flow of the pre-dispersion liquid or the mixed liquid before dispersion. For example, a multi-stage pressure reducer can be disposed downstream of the disperser to apply a desired back pressure to the pre-dispersion liquid or the mixed liquid before dispersion. When applying back pressure to the preliminary dispersion or the mixed liquid before dispersion, the applied back pressure may be reduced to atmospheric pressure in one go, but it is preferable to reduce the pressure in multiple stages. This is because reducing the pressure in multiple stages using a multistage pressure reducer can prevent bubbles from being generated in the dispersion when the CNTs are finally released to atmospheric pressure.

[0111] The above-mentioned various dispersion treatments may be carried out alone or in any combination.

[0112] Among these, a preferred dispersion treatment for preparing a dispersion containing CNTs is to use a dispersion treatment device equipped with a capillary flow path, pump a preliminary dispersion into the capillary flow path, and apply shear force to the preliminary dispersion to disperse the fibrous carbon nanostructures. By pumping the preliminary dispersion into the capillary flow path and applying shear force to the preliminary dispersion to disperse the fibrous carbon nanostructures, the fibrous carbon nanostructures can be well dispersed while suppressing damage to the fibrous carbon nanostructures.

[0113] An example of a dispersion system having the above configuration is a product named "BERYU SYSTEM PRO" (manufactured by Biryu Co., Ltd.) Dispersion treatment that provides a disintegration effect can be carried out by using such a dispersion system and appropriately controlling the dispersion conditions.

[0114] <Ultra-Small-Angle X-Ray Scattering Measurement> The measurement by ultra-small-angle X-ray scattering in step (ii) can be performed as follows. A carbon nanotube dispersion is dropped onto a glass slide, and ultra-small-angle X-ray scattering measurement is performed on the dropped droplet of carbon nanotube dispersion to obtain a scattering image. In the present invention, the ultra-small-angle X-ray scattering measurement is performed under the following conditions: wavenumber q: 0.0004 (1 / Å) to 0.3 (1 / Å), X-ray source: CuKα, X-ray tube voltage: 45 kV, tube current: 200 mA, slit width: 10 mm, scan step: 0.0006 deg, scan range: 0 to 0.5 deg, scan speed: 0.034 deg / min, and X-ray detector: two-dimensional semiconductor detector. A scattering profile is then obtained, with the wavenumber q on the horizontal axis and the scattering intensity I(q) on the vertical axis.

[0115] <Fitting of Scattering Profile> Analysis of measurement data by ultra-small angle X-ray scattering in step (iii) and proper evaluation of the carbon nanotube dispersion liquid can be performed as follows. Fitting is performed on the above scattering profile using Beaucage's equation. Fitting of a scattering profile using Beaucage's equation is conventionally known and can be performed, for example, according to the method described in G. Beaucage, J. Appl. Cryst., 28, 717 (1995). Fitting can be performed using, for example, Igor Pro 8 (manufactured by WaveMetrics) as analysis software.

[0116] Specifically, the obtained scattering profile is fitted using the Beaucage equation represented by the following general formula (I) in the wave number range of 0.0004 (1 / Å) to 0.3 (1 / Å).

[0117] In the above general formula (I), q is the wave number (1 / Å), I(q) is the scattering intensity at wave number q, Bkgd is the background, G ｉ and B ｉ is the proportionality constant, P ｉ is the fractal dimension at layer i, R ｇ，ｉ represents the length of the structure at layer i, and N represents the number of layers.

[0118] As described above, by fitting the scattering profile using the general formula (I), the fractal dimension P ｉ In the present invention, the fractal dimension P ３ is in the range of 3 or more and 4 or less, it is determined that "the fractal dimension in the wave number range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is in the range of 3 or more and 4 or less."

[0119] In the ultra-small angle X-ray scattering profile of the carbon nanotube dispersion liquid according to the present invention, (1) scattering due to the diameter of one CNT (R ｇ,１ ), (2) Scattering due to the persistence length of a single CNT (R ｇ,２), and (3) scattering due to the bundle diameter of the CNT (R ｇ,３ ) can be observed. Since three scatterings are observed in this way, it is preferable to perform fitting with the number of layers set to 3. For example, in the wavenumber range of 0.1 (1 / Å) or more and 0.3 (1 / Å) or less, (1) scattering due to the diameter of a single CNT (R ｇ,１ ) in the wavenumber range of 0.01 (1 / Å) or more and 0.1 (1 / Å) or less, (2) scattering due to the persistence length of a single CNT (R ｇ,２ ) in the wavenumber range of 0.0001 (1 / Å) or more and 0.01 (1 / Å) or less, (3) scattering from CNT bundles (R ｇ,３ ) is observed. In addition, in the scattering profile, scattering (R ｇ,２ ) and scattering (R ｇ,３ ) from the slope of the surface roughness of the CNT bundle (P ３ ) can be analyzed.

[0120] When a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of a carbon film is fitted to Beaucage's equation, a carbon nanotube dispersion having a fractal dimension of 3 to 4 in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) can exhibit strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and excellent discharge rate characteristics when a secondary battery is formed. Although the reason is unclear, it is presumed to be as follows: CNTs contained in a carbon nanotube dispersion having a fractal dimension of 3 to 4 in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) are presumed to be unbundled, forming a CNT network. For this reason, it is presumed that the CNTs form a network when made into a carbon nanotube-containing film, and as a result, the carbon nanotube dispersion of the present invention can exhibit excellent performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed. When the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less exceeds 4, the CNTs in the CNT dispersion remain in bundles, and a CNT network is not well formed when made into a carbon nanotube-containing film. It is presumed that this results in poor performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed. Furthermore, if the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is less than 3, the CNTs in the CNT dispersion will be shortened, and a network will not be formed when the carbon nanotube-containing film is formed. This is presumably to result in a deterioration in performance with respect to strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed.

[0121] The dispersion state of the carbon nanotube dispersion of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 shows an optical microscope image of the CNT dispersion of Example 1. FIG. 2 shows an optical microscope image of the CNT dispersion of Example 2. FIG. 3 shows an optical microscope image of the CNT dispersion of Example 3. FIG. 4 shows an optical microscope image of the CNT dispersion of Comparative Example 1. As shown in FIGS. 1 to 3, the CNT dispersions of Examples 1 to 3, which have a fractal dimension of 3 or more and 4 or less within a predetermined wavenumber range, have CNT bundles that are loosened, the CNTs spread out, and a network structure is formed. In contrast, the CNT dispersion of Comparative Example 1, which has a fractal dimension of less than 3 within a predetermined wavenumber range, has numerous bundles and does not have the network structure of Examples 1 to 3. Therefore, in the CNT dispersion of Comparative Example 1, a CNT network is not well formed when the CNT dispersion is made into a carbon nanotube-containing film, and as a result, it is presumed that the resulting laminate is strong when formed from a metal film and a carbon nanotube-containing film, weak when formed from a laminate of a release substrate and a carbon nanotube-containing film, and poor performance in terms of discharge rate characteristics when a secondary battery is formed.

[0122] In addition, the fractal dimension P in the general formula (I) ｉ corresponds to the absolute value of the slope of the linear portion of the graph obtained by fitting the scattering profile to Beaucage's equation. FIG. 6 shows a graph obtained by fitting the ultra-small angle X-ray scattering profiles of the CNT dispersions of Example 1 and Comparative Example 1 to Beaucage's equation. In FIG. 6, the slope of the linear portion in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less in Example 1 is smaller than the slope of the linear portion in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less in Comparative Example 1. In other words, in the graph of Comparative Example 1 in FIG. 6, the slope of the linear portion in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is gentle, and it can be seen that the fractal dimension is closer to 4.

[0123] From the viewpoint of further improving performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed, the CNT dispersion liquid of the present invention has the fractal dimension of 3 or more, preferably 3.1 or more, and more preferably 3.2 or more, and 4 or less, preferably 3.9 or less, and more preferably 3.8 or less, in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less.

[0124] In the CNT dispersion of the present invention, the fractal dimension can be controlled, for example, by adjusting the CNT dispersion conditions (dispersion strength, dispersion time, presence or absence of a dispersant, etc.) when preparing the above-mentioned CNT dispersion, and by controlling the CNT bundle length, which will be described later, etc. For example, when CNT dispersion is performed using an agitating blade, the CNT bundle length can be changed by changing the rotation speed (rpm) of the agitating blade and / or the dispersion time and / or the shape of the agitating blade.

[0125] Furthermore, from the viewpoint of further improving performance in terms of strong peel strength when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed, the CNT dispersion of the present invention has, when the scattering profile obtained by ultra-small angle X-ray scattering measurement of the CNT dispersion is fitted to Beaucage's equation, the persistent length of the CNTs in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is preferably 100 nm or more, more preferably 105 nm or more, and even more preferably 110 nm or more. There is no particular upper limit for the persistent length of the CNTs in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å), but the persistent length of the CNTs is usually 1000 nm or less.

[0126] Here, the persistence length of the CNTs can be obtained in the same manner as the fractal dimension described above. Specifically, as described above, a carbon nanotube dispersion is dropped onto a slide glass, and the dropped droplet of the carbon nanotube dispersion is subjected to ultra-small angle X-ray scattering measurement to obtain a scattering profile. The obtained scattering profile is then fitted to the Beaucage equation expressed by general formula (I) as described above. When the analysis is performed with the number of layers set to 3, R ｇ，２ The CNT persistence length R ｇ，２ represents the persistence length of the CNT in layer 2. The persistence length of the CNT represents the tendency of the CNT to maintain its straightness in length, in other words, it indicates the length between adjacent bent portions (length between kinks) in a single CNT. It is presumed that within the range of the persistence length of the CNT of the present invention, a conductive path is formed and high conductivity can be exhibited. In the present invention, the persistence length R of the CNT when i = 1 and when i = 2 in general formula (I) is ｇ，１ , R ｇ，２ If the wavelength is 250 Å or less, it is determined that "the CNT persistence length in the wave number range of 0.05 (1 / Å) or more and 0.01 (1 / Å) or less is 100 nm or more."

[0127] In the CNT dispersion of the present invention, the CNT persistence length can be controlled, for example, by adjusting the CNT dispersion conditions (dispersion strength, dispersion time, presence or absence of a dispersant, etc.) when preparing the CNT dispersion, and by controlling the CNT bundle length, which will be described later. For example, when CNT dispersion is performed using an agitating blade, the CNT bundle length can be changed by changing the rotation speed (rpm) of the agitating blade and / or the dispersion time and / or the shape of the agitating blade.

[0128] (Uses of Carbon Nanotube Dispersion) The carbon nanotube dispersion of the present invention can be used for any application. It is particularly preferred to use it for forming an electrode composite layer of a secondary battery electrode. When used for such an application, the carbon nanotube dispersion of the present invention can be used, for example, to produce a slurry composition for a secondary battery electrode by mixing it with other components (e.g., an electrode active material, a binder, etc.). The slurry composition for a secondary battery electrode obtained in this manner can be used to produce a laminate (secondary battery electrode) of a metal film and a carbon nanotube-containing film by forming a carbon nanotube-containing film (electrode composite layer) on a metal film. The slurry composition for a secondary battery electrode obtained in this manner can also be used to produce a laminate (transfer electrode composite layer) of a release substrate and a carbon nanotube-containing film by forming a carbon nanotube-containing film (electrode composite layer) on a substrate such as a resin. An electrode obtained from the above-mentioned slurry composition for a secondary battery electrode can be used to produce a secondary battery. The secondary battery is preferably a nonaqueous secondary battery, and more preferably a lithium-ion secondary battery. The electrode can be a positive electrode or a negative electrode, with a positive electrode being preferred. The secondary battery electrode is most preferably a lithium ion secondary battery positive electrode. By using the carbon nanotube dispersion of the present invention, excellent performance can be obtained in terms of strong peel strength (i.e., mechanical strength of the electrode) when a laminate of a metal film and a carbon nanotube-containing film is formed, weak peel strength (i.e., easy peelability of the electrode in the transfer electrode mixture layer) when a laminate of a release substrate and a carbon nanotube-containing film is formed, and discharge rate characteristics when a secondary battery is formed. Furthermore, by preliminarily dispersing the carbon nanotubes in the slurry composition and the carbon nanotube-containing film (electrode mixture layer), the consistency and reproducibility of the dispersion state of the carbon nanotubes can be improved, making it suitable for repeated mass production and high yield production of products with the above-mentioned excellent performance (e.g., electrodes, transfer electrode mixture layers, secondary batteries) on an industrial scale.

[0129] <Slurry Composition for Secondary Battery Electrode> A slurry composition for a secondary battery electrode can be produced by mixing the carbon nanotube dispersion of the present invention with other components. Examples of the other components include an electrode active material, a binder, a solvent for the slurry composition, a dispersant, and the like. Mixing can be performed by stirring (kneading) using a planetary mixer, for example. The slurry composition obtained in this manner can be used to produce a laminate (used as a secondary battery electrode) of a metal film and a carbon nanotube-containing film.

[0130] <<Electrode Active Material>> An electrode active material is a material that transfers electrons at the electrodes (positive electrode, negative electrode) of a secondary battery. Examples of the electrode active material include a positive electrode active material and a negative electrode active material. The electrode active material is not particularly limited, and examples thereof include known electrode active materials used in secondary batteries. Specifically, for example, examples of electrode active materials that can be used to manufacture a composite used in an electrode of a lithium ion secondary battery, which is an example of a secondary battery, include, but are not particularly limited to, electrode active materials made of the following substances that can occlude and release lithium:

[0131] -Positive Electrode Active Material- Examples of positive electrode active materials for lithium ion secondary batteries include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and transition metals. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo. Examples of positive electrode active materials include conductive polymer compounds such as polyacetylene and poly-p-phenylene.

[0132] Examples of transition metal oxides include MnO, MnO ２ , V ２ O ５ , V ６ O １３ , TiO ２ , Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３Examples of the transition metal sulfide include TiS ２ , TiS ３ , amorphous MoS ２ , FeS, etc. Furthermore, examples of the lithium-containing composite metal oxide include lithium-containing composite metal oxides having a layered structure, lithium-containing composite metal oxides having a spinel structure, and lithium-containing composite metal oxides having an olivine structure.

[0133] The lithium-containing composite metal oxide having a layered structure includes, for example, lithium-containing cobalt oxide (LiCoO ２ ), lithium-containing nickel oxide (LiNiO ２ ), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium composite oxide, Ni—Co—Al lithium composite oxide, etc. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ２ O ４ ) or Li[Mn １．５ M ０．５ ]O ４ (wherein M is Cr, Fe, Co, Ni, Cu, etc.) Furthermore, examples of lithium-containing composite metal oxides having an olivine structure include Li Ｘ MPO ４ (wherein M represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, and X represents a number satisfying 0≦X≦2).

[0134] The above-mentioned positive electrode active materials may be used singly or in combination of two or more kinds in any ratio.

[0135] Negative electrode active material for lithium ion secondary batteries includes a negative electrode active material made of carbon. Examples of the negative electrode active material made of carbon include natural graphite, artificial graphite, and carbon black. Among these, graphite such as artificial graphite and natural graphite is preferred, and natural graphite is particularly preferred.

[0136] Another example of the negative electrode active material is a negative electrode active material containing a metal. In particular, a negative electrode active material containing at least one element selected from the group consisting of tin, silicon, germanium, and lead is preferred. A negative electrode active material containing these elements can reduce the irreversible capacity.

[0137] Among the metal-containing negative electrode active materials, silicon-containing negative electrode active materials are particularly preferred. By using silicon-containing negative electrode active materials, it is possible to increase the electric capacity of lithium-ion secondary batteries.

[0138] Examples of the silicon-containing negative electrode active material include silicon-containing compounds and metallic silicon. The silicon-containing compound is a compound of silicon and another element, such as SiO, SiO ２ , SiO ｘ (0.01≦x<2), SiC, SiOC, etc. Among these, SiO ｘ , SiOC and SiC are preferred. ｘ is SiO and SiO ２ It is a compound that can be formed from at least one of the above and metallic silicon. ｘ is, for example, SiO ２ and silicon metal, and then cooling and precipitating the resulting silicon monoxide gas.

[0139] The above-mentioned negative electrode active materials may be used singly or in combination of two or more kinds in any ratio.

[0140] Properties of the Electrode Active Material The electrode active material described above preferably has a median particle diameter (D50) of 0.001 μm or more and 100 μm or less, more preferably 0.01 μm or more and 50 μm or less, and even more preferably 0.1 μm or more and 30 μm or less. When the median particle diameter of the electrode active material is 0.001 μm or more, a slurry composition can be formed together with the carbon nanotube dispersion of the present invention, and the slurry composition can be used to successfully form an electrode mixture layer. When used as an electrode for a secondary battery, the electrode mixture layer can exhibit strong peel strength between a current collector made of metal or the like. When used as an electrode mixture layer with a release substrate, the electrode mixture layer can exhibit weak peel strength between a release substrate made of resin or the like, and when used as a secondary battery, the electrode mixture layer can exhibit excellent rate characteristics. Furthermore, when the median particle diameter of the electrode active material is 100 μm or less, the surface area of ​​the electrode active material can be sufficiently secured, and the rate characteristics of a secondary battery using such a slurry composition can be further improved.

[0141] <Binder> The binder is not particularly limited, and for example, a polymer compound such as an acrylic polymer, a fluorine-based polymer, a diene-based polymer, or a nitrile-based polymer can be used. These polymer compounds can be used alone or in combination of two or more. In the slurry composition, the binder may be dissolved in a solvent, or may be dispersed in a form such as particulates without being dissolved in a solvent.

[0142] Examples of the fluorine-based polymer, diene-based polymer, and nitrile-based polymer that can be used herein include the fluorine-based polymer, diene-based polymer, and nitrile-based polymer described in JP 2012-243476 A. Examples of the acrylic polymer that can be used include the acrylate-based polymer described in WO 2016 / 152262.

[0143] The binder is preferably the above-mentioned acrylic polymer. The acrylic polymer is a polymer containing repeating units (polymerization units) obtained by polymerizing acrylate or methacrylate (hereinafter sometimes abbreviated as "(meth)acrylate") and derivatives thereof, and specific examples thereof include homopolymers of (meth)acrylate, copolymers of (meth)acrylate, and copolymers of (meth)acrylate and other monomers copolymerizable with the (meth)acrylate.

[0144] Examples of the (meth)acrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate; alkoxyalkyl acrylates such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; 2-(perfluoroalkyl)ethyl acrylates such as 2-(perfluorobutyl)ethyl acrylate and 2-(perfluoropentyl)ethyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, tridecyl methacrylate, and stearyl methacrylate; and 2-(perfluoroalkyl)ethyl methacrylates such as 2-(perfluorobutyl)ethyl methacrylate and 2-(perfluoropentyl)ethyl methacrylate. In cases other than Aspects B1 and B2, among these, alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate; and alkoxyalkyl acrylates such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate are preferred because of their high adhesion to the inorganic solid electrolyte.

[0145] The content of polymerized units derived from (meth)acrylate in the acrylic polymer is usually 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more. The upper limit of the content of polymerized units derived from (meth)acrylate in the acrylic polymer is usually 100% by mass or less, preferably 95% by mass or less.

[0146] Examples of monomers copolymerizable with the (meth)acrylate include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; carboxylic acid esters having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; styrene-based monomers such as styrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; acrylamide, methacrylamide, N-methylolacrylamide, and 2-methylacrylamide; Examples of suitable copolymers include amide monomers such as methylpropanesulfonic acid; α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocycle-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole. Among these, styrene monomers, amide monomers, and α,β-unsaturated nitrile compounds are preferred. The content of polymerized units derived from the copolymerizable monomers in the acrylic polymer is typically 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less.

[0147] The amount of binder contained in the slurry composition for a secondary battery electrode is not particularly limited, and is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass. If the amount of binder is within the above range, when a secondary battery electrode is formed, strong peel strength can be exhibited between the electrode mixture layer and a current collector made of metal or the like, and when an electrode mixture layer with a release substrate is formed, weak peel strength can be exhibited between the electrode mixture layer and a release substrate made of resin or the like, and excellent rate characteristics can be exhibited when a secondary battery is formed.

[0148] <<Solvent for Slurry Composition>> The solvent for the slurry composition is not particularly limited, but examples thereof include those exemplified as solvents for the CNT dispersion. Among these, it is more preferable to use NMP as the solvent for the slurry composition. Furthermore, the solvent for the slurry composition and the solvent for the CNT dispersion may be the same or different, but are preferably the same from the viewpoint of maintaining a constant solvent composition throughout the production process of the slurry composition.

[0149] <<Dispersant>> A dispersant is an additive for improving the dispersibility of each component of the slurry composition (CNTs, electrode active material, binder, etc.) The dispersant is not particularly limited, and examples thereof include known surfactants such as sodium dodecyl sulfonate, sodium deoxycholate, sodium cholate, and sodium dodecylbenzenesulfonate, as well as synthetic or natural polymers that can function as dispersants.

[0150] <Contact-Type Laminate (Secondary Battery Electrode)> One aspect of the present invention provides a laminate of a metal film having a surface tension of 400 mN / m or more and 2000 mN / m or less and a carbon nanotube-containing film formed using the carbon nanotube dispersion of the present invention. Because the metal film has a high surface tension, this laminate provides strong peel strength between the carbon nanotube-containing film and the metal film, improving adhesion between the carbon nanotube-containing film and the metal film, forming a contact-type laminate. The contact-type laminate can be used as a component in which the carbon nanotube-containing film and the metal film are integrated, such as a secondary battery electrode, preferably a lithium-ion secondary battery positive electrode. In this case, the carbon nanotube-containing film corresponds to the electrode mixture layer, and the metal film corresponds to the current collector.

[0151] <<Metal Film>> The metal film is not particularly limited as long as it is made of a metal material that can be used as a current collector and has a surface tension within a predetermined range. Materials that are electrically conductive and electrochemically durable are used as the metal film. Specific examples of metal films include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among these, copper foil is particularly preferred as a metal film used as a negative electrode current collector. Aluminum foil is particularly preferred as a metal film used as a positive electrode current collector. The above materials may be used alone or in combination of two or more types in any ratio. The thickness of the metal film is preferably about 0.001 mm or more and 0.5 mm or less.

[0152] The surface tension of the metal film is 400 [mN / m] or more, preferably 430 [mN / m] or more, and more preferably 450 [mN / m] or more. The surface tension of the metal film is 2000 [mN / m] or less, preferably 1950 [mN / m] or less, and more preferably 1900 [mN / m] or less. When a carbon nanotube-containing film formed from the carbon nanotube dispersion of the present invention is used as the carbon nanotube-containing film and the surface tension of the metal film is within this range, a good carbon nanotube network is formed in the carbon nanotube-containing film, resulting in strong adhesion to the carbon nanotube-containing film and enabling the formation of a close-contact laminate. The surface tension can be measured, for example, by the method described in the Examples.

[0153] <<Method for Producing a Contact-Type Laminate>> The contact-type laminate of the present invention (e.g., secondary battery electrode) is produced, for example, through a step (coating step) of applying the above-described slurry composition for a secondary battery electrode onto a metal film, and a step (drying step) of drying the slurry composition for a secondary battery electrode applied onto the metal film to form a carbon nanotube-containing film (electrode composite layer) on the metal film.

[0154] [Coating Step] The method for applying the slurry composition for a secondary battery electrode onto a metal film is not particularly limited, and known methods can be used. Specifically, examples of the coating method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the slurry composition for a secondary battery electrode may be applied to only one side of the metal film, or may be applied to both sides. The thickness of the slurry film on the metal film after application and before drying can be appropriately set depending on the thickness of the carbon nanotube-containing film obtained by drying.

[0155] [Drying Step] The method for drying the slurry composition for a secondary battery electrode on the metal film is not particularly limited, and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams. By drying the slurry composition for a positive electrode on the current collector in this manner, a carbon nanotube-containing film can be formed on the metal film, and a laminate (contact-type laminate) of the metal film and the carbon nanotube-containing film can be obtained. Such a laminate can be used as a secondary battery electrode comprising a current collector and an electrode mixture layer.

[0156] Here, after the drying step, the carbon nanotube-containing film may be subjected to a pressure treatment using a mold press, a roll press, etc. The pressure treatment can improve the adhesion between the carbon nanotube-containing film and the metal film.

[0157] <Peelable Laminate (Transfer Electrode Composite Layer)> Another aspect of the present invention provides a laminate comprising a substrate having a surface tension of 20 mN / m or more and 50 mN / m or less and a carbon nanotube-containing film formed using the carbon nanotube dispersion of the present invention. This laminate uses a carbon nanotube-containing film formed from the carbon nanotube dispersion of the present invention as the carbon nanotube-containing film. Because the carbon nanotube-containing film maintains a good CNT network and the substrate has a low surface tension, the peel strength between the carbon nanotube-containing film and the substrate is weakened, forming a peelable laminate with easy peelability between the carbon nanotube-containing film and the substrate. The peelable laminate can be used as a component in which the carbon nanotube-containing film and the substrate are peelable from each other, such as a transfer electrode composite layer, preferably a transfer lithium-ion secondary battery positive electrode composite layer. When the peelable laminate is a transfer electrode composite layer, the carbon nanotube-containing film corresponds to the electrode composite layer, and the substrate corresponds to the peeling substrate. The electrode mixture layer for transfer can be used to produce a secondary battery electrode composed of the electrode mixture layer and the substrate or the current collector by peeling off the substrate from the electrode mixture layer for transfer and transferring the resulting electrode mixture layer to a current collector, or by transferring the electrode mixture layer side surface of the electrode mixture layer for transfer to a current collector and peeling off the substrate.

[0158] <<Substrate>> The substrate is not particularly limited as long as it has a surface tension within a predetermined range, but is preferably composed of a material that can be used as a release substrate. Resins can be used as the material for such substrates. Specific examples of resins include plastics (polyethylene, polypropylene, polystyrene, ABS resin, methacrylic resin, polyvinyl chloride, polyamide, polyacetal, polycarbonate, polybutylene terephthalate, polyethylene terephthalate, polyphenylene oxide, polyamide-imide, polyether ether ketone, polyphenylene sulfide, polytetrafluoroethylene, phenolic resin, urea resin, melamine resin, unsaturated polyester resin, epoxy resin, etc.), synthetic rubbers (isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene rubber, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, silicone rubber, etc.), and natural rubber. These materials may be used alone or in combination.

[0159] The surface tension of the substrate is 20 mN / m or more, preferably 21 mN / m or more, and more preferably 22 mN / m or more. The surface tension of the release substrate is 50 mN / m or less, preferably 49 mN / m or less, and more preferably 48 mN / m or less. If the surface tension of the substrate is within this range, a weak adhesive force with the carbon nanotube-containing film can be obtained, enabling the formation of a peelable laminate. The surface tension can be measured, for example, by the method described in the Examples.

[0160] <<Method for producing peelable laminate>> The peelable laminate of the present invention (e.g., transfer electrode mixture layer) is produced, for example, through a step of applying the above-mentioned secondary battery electrode slurry composition onto a substrate (application step), and a step of drying the secondary battery electrode slurry composition applied onto the substrate to form a carbon nanotube-containing film (electrode mixture layer) on the substrate (drying step). Each of these steps can be carried out in the same manner as in the method for producing a contact laminate.

[0161] <Secondary Battery> A secondary battery such as a lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, and a secondary battery electrode manufactured using the carbon nanotube dispersion of the present invention can be used as the positive electrode, the negative electrode, or both, preferably as the positive electrode. Such a secondary battery has excellent rate characteristics. Below, each component and a method for manufacturing the secondary battery will be illustrated using a lithium ion secondary battery in which the positive electrode of the lithium ion secondary battery is manufactured using the carbon nanotube dispersion of the present invention as an example.

[0162] <Negative Electrode> A known negative electrode can be used as the negative electrode. Specifically, the negative electrode can be, for example, a negative electrode made of a thin plate of metallic lithium, or a negative electrode formed by forming a negative electrode composite layer on a current collector. The current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The negative electrode composite layer can be a layer containing a negative electrode active material and a binder. The binder is not particularly limited, and any known material can be used.

[0163] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. In the case of a lithium ion secondary battery, for example, a lithium salt is used as the supporting electrolyte. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２Among them, LiPF is particularly preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred, and LiPF ６ is particularly preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0164] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) are suitable. Other suitable solvents include esters such as n-propyl propionate (PP), γ-butyrolactone, and methyl formate. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives can also be added to the electrolyte.

[0165] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the secondary battery and increasing the capacity per volume.

[0166] <Method for Manufacturing Secondary Battery> A secondary battery such as a lithium ion secondary battery can be manufactured by, for example, stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting structure as needed according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharge / discharge, and the like, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as needed. The shape of the secondary battery may be any type, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type.

[0167] (Method for Producing Carbon Nanotube Dispersion) The present invention provides a method for producing a carbon nanotube dispersion. In Aspect A, the method for producing a carbon nanotube dispersion of the present invention comprises the following steps: (A-i) obtaining a carbon nanotube dispersion by dispersing a mixture of carbon nanotubes and a solvent, (A-ii) measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering, and (A-iii) evaluating the carbon nanotube dispersion as appropriate if it satisfies Condition 1, that is, when a scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using a Beaucage model, the fractal dimension in the wavenumber range of 0.001 to 0.3 (1 / Å) is in the range of 3 to 4, and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy Condition 1. According to this manufacturing method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, it is possible to obtain a carbon nanotube dispersion liquid that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby providing excellent rate characteristics for the secondary battery.

[0168] Furthermore, in the method for producing a carbon nanotube dispersion of the present invention, the conditions for evaluating the suitability of step (A-iii) may further include a condition that the CNT persistent length in the wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more. That is, step (A-iii) is preferably performed by evaluating the carbon nanotube dispersion as suitable if it satisfies condition 2, that is, the fractal dimension in the wavenumber range of 0.001 to 0.3 (1 / Å) is 3 to 4 and the CNT persistent length in the wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more, when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and the carbon nanotube dispersion is evaluated as unsuitable if the condition 2 is not satisfied. According to this manufacturing method, by adding the additional condition that the CNT persistence length measured above is 100 nm or more, it is possible to obtain a carbon nanotube dispersion liquid that can further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in a secondary battery electrode, and can further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby enabling the secondary battery to exhibit even better rate characteristics.

[0169] The method for producing a carbon nanotube dispersion of the present invention may further include the following steps: (A-iv) further dispersing the carbon nanotube dispersion if it is determined that the carbon nanotube dispersion is not suitable; (A-v) performing steps (A-ii) and (A-iii) again to determine whether the carbon nanotube dispersion is suitable; and (A-vi) optionally repeating steps (A-iv) and (A-v).

[0170] The carbon nanotubes, solvent, and various content ratios in the mixture subjected to dispersion treatment (which will be the same as the various content ratios in the resulting carbon nanotube dispersion) used in the method for producing a carbon nanotube dispersion of the present invention can be those described above. Details of the dispersion treatments in steps (A-i) and (A-iv) are as described above. Details of the ultra-small angle X-ray scattering measurement in step (A-iii) are as described above.

[0171] The carbon nanotube dispersion liquid evaluated as suitable in the step (A-iii) or (A-v) may be used as it is, or may be used after further dispersion treatment within a range that satisfies the conditions of the fractal dimension and / or the CNT persistence length specified in the step (A-iii).

[0172] In aspect B1, the method for producing a carbon nanotube dispersion of the present invention comprises the following steps: (B1-i) a step of dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent to obtain a carbon nanotube dispersion; (B1-ii) a step of photographing the obtained carbon nanotube dispersion at a concentration of 0.1 wt % to obtain an image; and (B1-iii) a step of evaluating the carbon nanotube dispersion as appropriate if condition 3, that is, the area ratio of carbon nanotubes in the obtained image is 55% or less, is satisfied, and evaluating the carbon nanotube dispersion as inappropriate if condition 3 is not satisfied. According to this manufacturing method, when a carbon nanotube dispersion is produced using single-walled carbon nanotubes with a G / D ratio of 5 or less, provided that the area ratio of the carbon nanotubes measured above is 55% or less, it is possible to obtain a carbon nanotube dispersion that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0173] In addition, when a carbon nanotube dispersion is produced using single-walled carbon nanotubes having a G / D ratio of 5 or less as the carbon nanotubes, in the method for producing a carbon nanotube dispersion of the present invention, the appropriate evaluation conditions in the step (B1-iii) are: ２That is, in the step (B1-iii), the area ratio of carbon nanotubes in the acquired image is 55% or less, and the area ratio of carbon nanotubes in the acquired image is 26,000 μm or less. ２ It is preferable that the carbon nanotube dispersion is evaluated as appropriate when it satisfies condition 4, that is, when the carbon nanotube dispersion contains 5 to 100 carbon nanotubes having an aspect ratio of 10 or more per area corresponding to 26000 μm , and when it does not satisfy condition 4, the carbon nanotube dispersion is evaluated as inappropriate. ２ By further adding the condition that the carbon nanotube dispersion contains 5 to 100 carbon nanotubes with an aspect ratio of 10 or more per area corresponding to the electrode mixture layer, it is possible to further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in an electrode for a secondary battery, and it is possible to further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby obtaining a carbon nanotube dispersion that can further enhance the excellent rate characteristics of a secondary battery.

[0174] In aspect B2, the method for producing a carbon nanotube dispersion of the present invention comprises the following steps: (B2-i) a step of dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent to obtain a carbon nanotube dispersion; (B2-ii) a step of photographing the obtained carbon nanotube dispersion at a concentration of 0.1 wt % to obtain an image; and (B2-iii) a step of evaluating the carbon nanotube dispersion as appropriate if condition 5, that is, the area ratio of carbon nanotubes in the obtained image is 75% or more, is satisfied, and evaluating the carbon nanotube dispersion as inappropriate if condition 5 is not satisfied. According to this manufacturing method, when a carbon nanotube dispersion is produced using single-walled carbon nanotubes having a G / D ratio of 10 or more as the carbon nanotubes, provided that the area ratio of the carbon nanotubes measured above is 75% or more, it is possible to obtain a carbon nanotube dispersion that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and a secondary battery electrode with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0175] In aspects B1 and B2, the method for producing a carbon nanotube dispersion of the present invention may further include the following steps: (B-iv) if the carbon nanotube dispersion is evaluated to be inappropriate, further dispersing the carbon nanotube dispersion; (B-v) in the case of aspect B1, repeating steps (B1-ii) and (B1-iii), or in the case of aspect B2, repeating steps (B2-ii) and (B2-iii), to evaluate whether the carbon nanotube dispersion is appropriate; (B-vi) optionally repeating steps (B-iv) and (B-v).

[0176] The carbon nanotubes, solvent, and various content ratios in the mixture subjected to dispersion treatment (which will be the same as the various content ratios in the resulting carbon nanotube dispersion) used in the method for producing a carbon nanotube dispersion of the present invention can be those described above. Details of the dispersion treatments in steps (B1-i), (B2-i), and (B-iv) are as described above. Details of image acquisition from the carbon nanotube dispersion and image analysis are as described above.

[0177] The carbon nanotube dispersion liquid evaluated as suitable in step (B1-iii), (B2-iii), or (B-v) may be used as is, or may be further dispersed to a degree that satisfies the conditions of the area ratio and / or the number of carbon nanotubes having an aspect ratio within a predetermined range specified in step (B1-iii) or (B2-iii), before use.

[0178] In Aspect C, the method for producing a carbon nanotube dispersion of the present invention includes the following steps: (i) obtaining a carbon nanotube dispersion by dispersing a mixture of carbon nanotubes and a solvent; (ii) photographing the obtained carbon nanotube dispersion to obtain an image; and (iii) evaluating the carbon nanotube dispersion as appropriate if the area ratio of carbon nanotubes in the obtained image satisfies Condition A, and evaluating the carbon nanotube dispersion as inappropriate if Condition A is not satisfied. Here, Condition A includes the area ratio of carbon nanotubes being 70% or less. Under the condition that the area ratio of carbon nanotubes measured above is 70% or less, good film-formability can be achieved when forming a carbon film by using the CNT dispersion produced by this production method. Furthermore, it becomes possible to determine whether good film-formability can be achieved by using the carbon nanotube dispersion produced by this production method even before actually forming a film.

[0179] Furthermore, by setting Condition A to a condition that the area ratio of carbon nanotubes in the acquired image is within a predetermined range, the above-described carbon nanotube dispersion manufacturing method can be used to manufacture a carbon film having a desired porosity range. For example, by setting Condition A to a condition that the area ratio of carbon nanotubes in the acquired image is 20% to 70%, preferably 55% to 70%, it is possible to obtain a CNT dispersion capable of producing a carbon film having a high porosity, for example, 60% to 99%, useful for battery applications. Furthermore, by using the carbon nanotube dispersion manufactured by this manufacturing method, it is possible to determine, even before actual film formation, whether a high porosity, for example, 60% to 99%, can be achieved. The correlation between the area ratio of the CNT dispersion and the porosity of the resulting carbon film is as described above.

[0180] The method for producing a carbon nanotube dispersion of the present invention may further include the following steps: (iv) if the carbon nanotube dispersion is evaluated to be inappropriate, further dispersing the carbon nanotube dispersion; (v) performing steps (ii) and (iii) again to evaluate whether the carbon nanotube dispersion is appropriate; and (vi) repeating steps (iv) and (v).

[0181] The carbon nanotubes, solvent, and various content ratios in the mixture subjected to dispersion treatment (which will be the same as the various content ratios in the resulting carbon nanotube dispersion) used in the method for producing a carbon nanotube dispersion of the present invention can be those described above. Details of the dispersion treatments in steps (i) and (iv) are as described above. Details of the area ratio measurement in step (iii) are as described above.

[0182] The carbon nanotube dispersion liquid evaluated as suitable in step (iii) or (v) may be used as is, or may be further dispersed within a range that satisfies the area ratio condition specified in step (iii) before use.

[0183] The methods for producing carbon nanotube dispersions of aspects B1, B2, and C are characterized by further comprising the steps of: measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 1, that is, the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model is in the range of 3 or more and 4 or less; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 1. According to this manufacturing method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, a secondary battery electrode can be provided with strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and a release substrate-attached electrode mixture layer can be provided with weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics, or a carbon nanotube dispersion liquid can be obtained that enables good film-forming properties to be achieved when forming a bare film.

[0184] Preferably, the method for producing a carbon nanotube dispersion of aspects B1, B2, and C further comprises the steps of: measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, where the fractal dimension in the wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4 and the CNT persistent length in the wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is in the range of 100 nm or more, when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model; and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2. According to this manufacturing method, by adding the additional condition that the CNT persistence length measured above is 100 nm or more, it is possible to further enhance the strong peel strength between the electrode mixture layer and the current collector made of a metal or the like in a secondary battery electrode, and to further enhance the weak peel strength between the electrode mixture layer and the release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby enabling secondary batteries to exhibit even better excellent rate characteristics, or to obtain a carbon nanotube dispersion that enables good film-forming properties to be achieved when forming a bare film.

[0185] In aspects B1, B2, and C, the method for producing a carbon nanotube dispersion of the present invention may further include the following steps: (α) a step of measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering; and (β) a step of evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 1, that is, the fractal dimension in the wavenumber range of 0.001 to 0.3 (1 / Å) when the scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using the Beaucage model is in the range of 3 or more and 4 or less, and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 1. According to this manufacturing method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, a secondary battery electrode can be provided with strong peel strength between the electrode mixture layer and a current collector made of a metal or the like, and a release substrate-attached electrode mixture layer can be provided with weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics, or a carbon nanotube dispersion liquid can be obtained that enables good film-forming properties to be achieved when forming a bare film.

[0186] Furthermore, in the method for producing a carbon nanotube dispersion of the present invention, the conditions for evaluating the suitability of step (β) may further include a condition that the CNT persistent length in the wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more. That is, step (β) is preferably performed by evaluating the carbon nanotube dispersion as suitable if it satisfies condition 2, that is, the fractal dimension in the wavenumber range of 0.001 to 0.3 (1 / Å) when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model is in the range of 3 to 4, and the CNT persistent length in the wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more, and by evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2. According to this manufacturing method, by adding the additional condition that the CNT persistence length measured above is 100 nm or more, it is possible to further enhance the strong peel strength between the electrode mixture layer and the current collector made of a metal or the like in a secondary battery electrode, and to further enhance the weak peel strength between the electrode mixture layer and the release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby enabling secondary batteries to exhibit even better excellent rate characteristics, or to obtain a carbon nanotube dispersion that enables good film-forming properties to be achieved when forming a bare film.

[0187] (Method for Evaluating Carbon Nanotube Dispersion) This specification discloses a method for evaluating a carbon nanotube dispersion. In Aspect A, the method for evaluating a carbon nanotube dispersion includes the following steps: (a) measuring the obtained carbon nanotube dispersion by ultra-small angle X-ray scattering, and (b) evaluating the carbon nanotube dispersion as appropriate if it satisfies Condition 1, that is, when a scattering curve obtained by the ultra-small angle X-ray scattering measurement is analyzed using a Beaucage model, the fractal dimension in the wavenumber range of 0.001 to 0.3 (1 / Å) is in the range of 3 or more and 4 or less, and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy Condition 1. According to this evaluation method, provided that the fractal dimension measured above is in the range of 3 or more and 4 or less, it is possible to select a carbon nanotube dispersion that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a current collector made of metal or the like, and can provide an electrode mixture layer with a release substrate with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0188] In the method for evaluating a carbon nanotube dispersion, the appropriate evaluation conditions in step (b) may further include a condition that the CNT persistent length in a wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more. That is, step (b) may be performed by evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, that is, the fractal dimension in a wavenumber range of 0.001 to 0.3 (1 / Å) is 3 to 4 inclusive and the CNT persistent length in a wavenumber range of 0.05 to 0.01 (1 / Å) is 100 nm or more when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and the carbon nanotube dispersion may be evaluated as inappropriate if condition 2 is not satisfied. According to this evaluation method, by adding the condition that the CNT persistence length measured above is 100 nm or more, it is possible to select a carbon nanotube dispersion that can further enhance the strong peel strength between the electrode mixture layer and the current collector made of metal or the like in a secondary battery electrode, and can further enhance the weak peel strength between the electrode mixture layer and the release substrate made of resin or the like in an electrode mixture layer with a release substrate, thereby further enabling the secondary battery to exhibit excellent rate characteristics.

[0189] The details of the ultra-small angle X-ray scattering measurement in step (b) are as described above.

[0190] In aspect B1, the method for evaluating a carbon nanotube dispersion is used to evaluate a carbon nanotube dispersion containing single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent, and includes the following steps: (a) a step of capturing an image of the obtained carbon nanotube dispersion when the concentration is 0.1 wt %, and (b) a step of evaluating the carbon nanotube dispersion as appropriate if condition 1 is met, that is, the area ratio of carbon nanotubes in the acquired image is 55% or less, and evaluating the carbon nanotube dispersion as inappropriate if condition 1 is not met. According to this evaluation method, when a carbon nanotube dispersion liquid containing single-walled carbon nanotubes with a G / D ratio of 5 or less and a solvent is used, provided that the area ratio of the carbon nanotubes measured above is 55% or less, it is possible to select a carbon nanotube dispersion liquid that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and can provide an electrode mixture layer with a release substrate with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics.

[0191] In the evaluation method for the carbon nanotube dispersion, the appropriate evaluation condition in the step (b) is 26000 μm in the image. ２ That is, the step (b) may further include a condition that the area ratio of carbon nanotubes in the acquired image is 55% or less and that the area ratio of carbon nanotubes in the acquired image is 26000 μm or less and that the area ratio of carbon nanotubes in the acquired image is 26000 μm or less. ２ In this case, the carbon nanotube dispersion is evaluated as being appropriate when it satisfies condition 2, that is, when the carbon nanotube dispersion contains 5 to 100 carbon nanotubes having an aspect ratio of 10 or more per area corresponding to 26,000 μm , and when it does not satisfy condition 2, the carbon nanotube dispersion is evaluated as being inappropriate. ２By further adding the condition that the carbon nanotube dispersion contains 5 to 100 carbon nanotubes with an aspect ratio of 10 or more per area corresponding to the electrode mixture layer, it is possible to further enhance the strong peel strength between the electrode mixture layer and a current collector made of a metal or the like in an electrode for a secondary battery, and to further enhance the weak peel strength between the electrode mixture layer and a release substrate made of a resin or the like in an electrode mixture layer with a release substrate, thereby making it possible to select a carbon nanotube dispersion that can further enhance the excellent rate characteristics of a secondary battery.

[0192] In aspect B2, the method for evaluating a carbon nanotube dispersion is used to evaluate a carbon nanotube dispersion containing single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent, and includes the following steps: (a) a step of capturing an image of the obtained carbon nanotube dispersion when the concentration is 0.1 wt %, and (b) a step of evaluating the carbon nanotube dispersion as appropriate if condition 3, that is, the area ratio of carbon nanotubes in the acquired image is 75% or more, is satisfied, and evaluating the carbon nanotube dispersion as inappropriate if condition 3 is not satisfied. According to this evaluation method, when a carbon nanotube dispersion liquid containing single-walled carbon nanotubes with a G / D ratio of 10 or more and a solvent is used, provided that the area ratio of the carbon nanotubes measured above is 75% or more, it is possible to select a carbon nanotube dispersion liquid that can provide a secondary battery electrode with strong peel strength between the electrode mixture layer and a collector made of metal or the like, and can provide an electrode mixture layer with a release substrate with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, and that can provide secondary batteries with excellent rate characteristics.

[0193] Details of image acquisition from the carbon nanotube dispersion and analysis of the images are as described above.

[0194] In Aspect C, the method for evaluating a carbon nanotube dispersion includes the following steps: (a) capturing an image of the carbon nanotube dispersion; and (b) evaluating the carbon nanotube dispersion as appropriate if the area ratio of carbon nanotubes in the acquired image satisfies Condition A, and evaluating the carbon nanotube dispersion as inappropriate if Condition A is not satisfied. Condition A includes the area ratio of carbon nanotubes being 70% or less. A carbon nanotube dispersion evaluated as appropriate by this evaluation method can be used for forming a carbon film. According to this evaluation method, if the CNT dispersion selected by this evaluation method is used under the condition that the area ratio of carbon nanotubes measured above is 70% or less, good film-formability can be achieved during carbon film formation. Furthermore, it can be determined before actual film formation that good film-formability can be achieved by using a carbon nanotube dispersion selected by this evaluation method. Details of the area ratio measurement in step (b) are as described above.

[0195] Furthermore, by setting Condition A to a condition that the area ratio of carbon nanotubes in the acquired image is within a predetermined range, the above-described carbon nanotube dispersion evaluation method can be used to select a carbon film having a desired porosity range. For example, by setting Condition A to a condition that the area ratio of carbon nanotubes in the acquired image is 20% to 70%, preferably 55% to 70%, using a CNT dispersion selected by this evaluation method, it becomes possible to obtain a carbon film having a high porosity, for example, of 60% to 99%. Furthermore, by using a carbon nanotube dispersion selected by this evaluation method, it becomes possible to determine, even before actual film formation, that a high porosity, for example, of 60% to 99% can be achieved. The correlation between the area ratio of a CNT dispersion and the porosity of the resulting carbon film is as described above.

[0196] The carbon nanotube dispersion evaluation method of Aspect A may be combined with any one of the carbon nanotube dispersion evaluation methods of Aspects B1, B2, and C.

[0197] (Method for producing a carbon film) The present invention also provides a method for producing a carbon film. In one aspect, the method for producing a carbon film of the present invention includes a step of removing the solvent from the above-mentioned CNT dispersion liquid having a CNT area ratio of 70% or less to form a carbon film. According to this production method, by using a CNT dispersion liquid having a CNT area ratio of 70% or less, it is possible to produce a carbon film with good film-forming properties.

[0198] Furthermore, in the above-described carbon film manufacturing method, if a CNT dispersion in which the area ratio of CNTs in an image acquired by photographing the CNT dispersion is within a predetermined range is used as the CNT dispersion, a carbon film having a porosity within a desired range can be obtained. For example, if a CNT dispersion in which the area ratio measured above is in the range of 20% to 70%, preferably 55% to 70%, is used, a carbon film having a high porosity, for example, of 60% to 99% can be obtained. The correlation between the area ratio of the CNT dispersion and the porosity of the resulting carbon film is as described above.

[0199] In another aspect, the method for producing a carbon film of the present invention includes a step of forming a carbon film by removing the solvent from a CNT dispersion obtained by the above-described method for producing a CNT dispersion and selected under conditions where the CNT area ratio is 70% or less. According to this production method, by using a CNT dispersion selected under conditions where the CNT area ratio is 70% or less, it is possible to produce a carbon film with good film-forming properties.

[0200] Furthermore, in the above-described carbon film manufacturing method, if a CNT dispersion selected under conditions in which the area ratio of CNTs in an image acquired by photographing the CNT dispersion falls within a predetermined range is used as the CNT dispersion, a carbon film having a porosity within a desired range can be obtained. For example, if a CNT dispersion selected under conditions in which the area ratio measured above falls within a range of 20% to 70%, preferably 55% to 70%, is used, a carbon film having a high porosity, for example, 60% to 99% can be obtained. The correlation between the area ratio of the CNT dispersion and the porosity of the resulting carbon film is as described above.

[0201] <Formation of Carbon Film by Solvent Removal> The step of forming a carbon film by removing the solvent from the CNT dispersion can be carried out using, for example, either of the following methods (A) and (B). (A) A method in which the CNT dispersion is applied to a film formation substrate and then the applied CNT dispersion is dried. (B) A method in which the CNT dispersion is filtered using a porous film formation substrate and the obtained filtrate is dried. Note that the carbon films obtained by the above methods (A) and (B) correspond to those obtained by peeling the aforementioned dried product from the growth substrate.

[0202] In the carbon film manufacturing method of the present invention, a porous structure with a highly developed network can be obtained by forming a film using a CNT dispersion liquid in which the area ratio of CNTs is 70% or less, and it is therefore presumed that a self-supporting carbon film can be obtained.

[0203] [Film-forming substrate] The film-forming substrate is not particularly limited, and known substrates can be used depending on the application of the carbon film to be produced. Specifically, examples of the film-forming substrate onto which the CNT dispersion is applied in method (A) include resin substrates, glass substrates, and metal substrates. Examples of resin substrates include substrates made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytetrafluoroethylene (PTFE), polyimide, polyphenylene sulfide, aramid, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polycarbonate, polymethyl methacrylate, alicyclic acrylic resin, cycloolefin resin, and triacetyl cellulose. Examples of glass substrates include substrates made of ordinary soda glass. Examples of metal substrates include substrates made of aluminum, copper, and the like. Examples of the film-forming substrate onto which the CNT dispersion is filtered in method (B) include filter paper and porous sheets made of cellulose, nitrocellulose, alumina, resin, and the like. Examples of the film-forming substrate include, for example, a membrane filter.

[0204] [Coating] In the above method (A), a known coating method can be used to coat the CNT dispersion onto the film-forming substrate. Specifically, examples of the coating method that can be used include dipping, roll coating, gravure coating, knife coating, air knife coating, roll knife coating, die coating, screen printing, spray coating, and gravure offset.

[0205] [Filtration] In the above method (B), a known filtration method can be used to filter the CNT dispersion using the film-forming substrate. Specifically, the filtration method can be natural filtration, reduced pressure filtration, pressure filtration, centrifugal filtration, or the like.

[0206] [Drying] A known drying method can be used to dry the CNT dispersion applied to the film-forming substrate in the above method (A) or the filtered product obtained in the above method (B). Examples of drying methods include hot air drying, vacuum drying, hot roll drying, and infrared irradiation. The drying temperature is not particularly limited, but is usually room temperature to 200°C, and the drying time is not particularly limited, but is usually 0.1 to 150 minutes.

[0207] <Post-Treatment of Carbon Film> In the method for producing a carbon film of the present invention, the carbon film formed in the film-forming step may be optionally washed.

[0208] The carbon film can be cleaned by washing away impurities remaining in the carbon film with a solvent. The solvent used for cleaning is not particularly limited, and the solvents described above that can be used as solvents for CNT dispersions, preferably the same solvents as those for CNT dispersions, can be used. The carbon film can be brought into contact with the solvent by immersing the carbon film in the solvent or by applying the solvent to the carbon film. Furthermore, the carbon film after cleaning can be dried using a known method.

[0209] In the carbon film manufacturing method of the present invention, the carbon film formed in the film formation step may be optionally press-formed to further increase its density. From the viewpoint of suppressing deterioration of properties due to damage or destruction of the fibrous carbon nanostructures, the pressing pressure during pressing is preferably less than 3 MPa, and it is more preferable not to perform pressing.

[0210] (Carbon Film) The carbon film obtained by the carbon film manufacturing method of the present invention contains CNTs contained in the CNT dispersion liquid having an area ratio of CNTs of 70% or less. Because the carbon film contains CNTs contained in the CNT dispersion liquid having an area ratio of CNTs of 70% or less, the carbon film is formed in a good state and becomes a self-supporting carbon film having high electrical conductivity and porosity.

[0211] Furthermore, the carbon film preferably contains CNTs contained in a CNT dispersion having a CNT area ratio within a predetermined range, thereby allowing the carbon film to have a desired range of porosity. For example, when the carbon film contains CNTs contained in a CNT dispersion having a CNT area ratio within the range of 20% to 70%, preferably 55% to 70%, the carbon film can have a high porosity of, for example, 60% to 99%. The correlation between the area ratio of the CNT dispersion and the porosity of the resulting carbon film is as described above.

[0212] (Uses of Carbon Film) The carbon film obtained by the carbon film production method of the present invention can be used, for example, as a conductive sheet (e.g., a conductive film for a solar cell or a touch panel), a heat conductive sheet, an electromagnetic wave absorbing sheet, a sheet for a battery, etc., based on the properties of CNTs such as electrical conductivity, thermal conductivity, electromagnetic wave shielding performance, mechanical properties, and high porosity.

[0213] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0214] <Fourier transform infrared spectroscopy (FT-IR)> 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1% by mass was added to 10 mg of CNT aggregate, and the mixture was stirred at 45 Hz for 1 minute using an ultrasonic bath to obtain 100 ml of a dispersion of each CNT aggregate. Each dispersion prepared as described above was diluted two-fold using a solvent of the same composition, and each was dropped onto a silicon substrate and dried, after which the plasmon effective length was measured using a Fourier transform infrared spectrophotometer from the plasmon far-infrared (FIR) resonance peak.

[0215] <Creating a pore distribution curve (CNT aggregate)> For 10 mg or more of CNT aggregate, the adsorption isotherm was measured using a BELSORP-mini II (manufactured by MicrotrackBell) at 77 K with liquid nitrogen (the adsorption equilibrium time was 500 seconds). As a pretreatment, vacuum degassing was performed at 100°C for 12 hours. From the adsorption amount of this adsorption isotherm, a pore distribution curve for each sample was obtained by the BJH method. Note that when creating the pore distribution curve for the CNT aggregate, the measurement range of pore diameter was set to be 1 nm or more and less than 400 nm.

[0216] <Two-dimensional spatial frequency spectrum analysis of electron microscope images> For the CNT aggregate (CNT_A) used in Examples 1 and 3 and Comparative Example 1, 0.01 mg was placed on carbon tape and blown with a blower to remove excess CNT to prepare a sample. The sample was observed at 10,000 magnification using a field emission scanning electron microscope, and 10 photographs were taken of an arbitrarily selected 1 cm square field of view. Each of the 10 captured electron microscope images was subjected to fast Fourier transform processing to obtain a two-dimensional spatial frequency spectrum. Each of the obtained two-dimensional spatial frequency spectra was subjected to binarization processing, and the outermost (high-frequency) peak position was determined to obtain an average value. Note that, during the binarization processing, values ​​greater than 0.75 obtained through fast Fourier transform processing were set to 1, and other values ​​were set to zero. Figure 5 shows one of the 10 images obtained for the above CNT aggregate.

[0217] <Ultra-Small-Angle X-Ray Scattering Measurement> The prepared dispersion was placed in a measurement capillary to obtain a test sample. Then, ultra-small-angle X-ray scattering measurement was performed on the obtained test sample under the following conditions to obtain a scattering image. [Measurement Conditions] X-ray source: CuKα Tube voltage: 45 kV Tube current: 200 mA Scan type: 2θ Scan mode: 0D (continuous) Scan range: -0.01 to 0.5 Scan step: 0.0006 Scan speed: 0.034° / min Optical system: Primary beam: Standard, Incident optical unit: Ge(220) Light receiving optical unit 1: U-SAXS CBO Type: Type 2 Selective slit: PB ISS: Soller slit open q (wavenumber) range: 0.0004 (1 / Å) to 0.3 (1 / Å) Detector: HyPix3000

[0218] <Calculation of fractal dimension and CNT persistence length by data processing of data obtained by ultra-small angle X-ray scattering measurement> A scattering profile was obtained from the scattering image obtained by ultra-small angle X-ray scattering measurement as described above. Using Igor Pro 8 (WaveMetrics) as analysis software and setting the wavenumber range to 0.0004 (1 / Å) to 0.3 (1 / Å), the obtained scattering profile was fitted to Beaucage's equation represented by the general formula (I) above to calculate the fractal dimension Pi at each layer i and the persistence length R of the CNT. ｇ，ｉ The number of layers was set to N = 3. Here, fitting indicates the error between the measured scattering profile and the calculated value. The value of P was set to 5 or less. If the value is 5 or less, it can be said that the fitting was successful. ３ , the persistence length of the CNT R ｇ，２ The values ​​are shown in Table 1.

[0219] <G / D ratio of CNT> The Raman spectrum of the CNT was measured using a microscopic laser Raman spectrophotometer (Nicolet Almega XR manufactured by Thermo Fisher Scientific Co., Ltd.). －１ The intensity of the G band peak observed near 1340 cm －１The intensity of the D band peak observed in the vicinity was determined, and the G / D ratio was calculated.

[0220] <CNT area ratio (jet mill CNT dispersion)> The CNT dispersion prepared by jet milling was adjusted to a concentration of 0.1 wt% with a solvent (the same solvent as used for the CNT dispersion), and 1 μL of the CNT dispersion was dropped onto each of five spots on a glass slide. The dropped CNT dispersion was observed at a magnification of 500 times using a digital microscope (manufactured by Keyence Corporation, product name "VHX-900"), and images were obtained. The obtained images were binarized using the image processing software in the same device, and then the 26,000 μm area of ​​the image was analyzed. ２ The area of ​​the aggregates of fibrous carbon nanostructures in the area corresponding to 100 μm was measured to determine the total area (Sc) of the aggregates of fibrous carbon nanostructures. The area ratio (S) of the aggregates of fibrous carbon nanostructures was then determined by dividing this value by the area (St) of the observation field. S = (Sc / St) x 100 (%) The average of the area ratios (S) determined for each spot was taken as the final CNT area ratio. An example of an image obtained from the CNT dispersion liquid using a digital microscope is shown in Figure 7. The image after binarization is shown in Figure 8.

[0221] <Number of CNTs in a Predetermined Range of Aspect Ratios> Using the binarized image obtained above, ２ The diameters and lengths of all carbon nanotubes in the area corresponding to this were measured to calculate the aspect ratio (ratio of diameter to length, i.e., length / diameter), and the number of CNTs with aspect ratios within a predetermined range was determined.

[0222] <Area ratio of CNT (high-shear agitated CNT dispersion)> The CNT dispersion prepared by high-shear agitation was adjusted to a concentration of 0.1 wt % with a solvent (the same solvent as used for the CNT dispersion), and 10 μL of the adjusted concentration CNT dispersion was applied to a 20 mm × 50 mm area on a glass slide. Five spots in the applied area were observed at 500x magnification using a digital microscope (manufactured by Keyence Corporation, product name "VHX-7000") to obtain images. The CNT area (black) was extracted using the automatic area measurement (particle count) software in the same device, and the area ratio of CNT (CNT area [μm ２ ] / Total image area area [μm２ ]) × 100. The average of the area ratios determined for each spot was taken as the final area ratio of CNT.

[0223] <Surface tension> A water droplet was dropped onto the measurement substrate using a contact angle meter B100 (Asumi Giken Co., Ltd.), and the surface tension was calculated using the image analysis software in the same device. The measurement substrate was cut into a 10 cm square to prepare a test piece.

[0224] <Mechanical Strength of Positive Electrode (Peel Strength of Positive Electrode Composite Layer Against Current Collector)> The fabricated positive electrode was cut into a rectangular shape measuring 100 mm in length and 10 mm in width to prepare a test specimen. This test specimen was placed with the surface of the positive electrode composite layer facing down, and cellophane tape was attached to the surface of the positive electrode composite layer. The cellophane tape used was specified in JIS Z1522. The cellophane tape was fixed to a test table. One end of the current collector was then pulled vertically upward at a pulling rate of 50 mm / min to measure the stress when peeled off. This measurement was performed three times, and the average value was calculated. This average value was used as the peel strength of the positive electrode composite layer against the current collector (metal film) and evaluated according to the following criteria. A higher peel strength indicates a stronger adhesive strength of the positive electrode composite layer to the current collector, i.e., a higher adhesion strength and superior mechanical strength of the positive electrode. OK (◯): Peel strength is 0.5 N / m or more NG (×): Peel strength is less than 0.5 N / m

[0225] <Transfer Ease of Positive Electrode Composite Layer (Peel Strength of Positive Electrode Composite Layer from Resin Substrate)> The prepared current collector transfer laminate was cut into a rectangle 100 mm long and 10 mm wide to prepare a test specimen. This test specimen was placed with the surface of the positive electrode composite layer facing down, and cellophane tape was attached to the surface of the positive electrode composite layer. The cellophane tape used was specified in JIS Z1522. The cellophane tape was fixed to a test table. One end of the resin substrate was then pulled vertically upward at a pulling rate of 50 mm / min to measure the stress when peeled off. This measurement was performed three times, and the average value was calculated. This average value was used as the peel strength of the positive electrode composite layer from the resin substrate and evaluated according to the following criteria. The smaller the peel strength, the smaller the adhesion strength of the positive electrode mixture layer to the resin substrate, and the better the ease of peeling (i.e., ease of transfer) of the positive electrode mixture layer from the resin substrate when a positive electrode is produced by peeling and transferring the positive electrode mixture layer from the resin substrate (peeling substrate) using a current collector transfer laminate. OK (◯): Peel strength is 0.5 N / m or less NG (×): Peel strength is more than 0.5 N / m

[0226] <Discharge Rate Characteristics of Lithium-Ion Secondary Battery> A charge-discharge test was performed seven times on the lithium-ion secondary batteries obtained in each Example and Comparative Example under the following conditions. The batteries were charged to an upper limit voltage and then discharged to a lower limit voltage. The discharge rate characteristics were calculated based on the following formula: Discharge rate characteristic [%] = (Capacity at 2.0 C) / (Capacity at 0.2 C) × 100. The obtained discharge rate characteristics were evaluated based on the following criteria. (Test Conditions) Upper limit voltage: 4.2 V Lower limit voltage: 3.0 V Charging condition: 0.2 C Constant current constant voltage (CCCV) Cutoff 0.05 C Discharging condition: The first discharge was performed using a constant current (CC) at 0.2 C, and the second to seventh discharges were performed using a CC from 1.0 C to 0.2 C. 1st: 0.2C CC 2nd: 1.0C CC → 0.2C CC 3rd: 1.5C CC → 0.2C CC 4th: 2.0C CC → 0.2C CC 5th: 2.5C CC → 0.2C CC 6th: 3.0C CC → 0.2C CC 7th: 3.5C CC → 0.2C CC Number of cycles: 1 cycle / each rate Temperature: 25°C (Evaluation criteria) OK (○): Discharge rate characteristics are 75% or more NG (×): Discharge rate characteristics are less than 75%

[0227] <Weight of Positive Electrode> The positive electrodes produced in the examples and comparative examples were placed in a 5 cm x 5 cm (area: 25 cm ２ The mass W (g) of the test piece was divided by the area of ​​the test piece to obtain the basis weight (g / cm) of the positive electrode. ２ ) was calculated as follows.

[0228] <Thickness of Positive Electrode> The positive electrodes produced in the examples and comparative examples were cut into 5 cm x 5 cm test pieces, and the thicknesses were measured using a "Digimatic Standard Outside Micrometer" manufactured by Mitutoyo Corporation.

[0229] <Positive Electrode Density> The positive electrodes produced in the Examples and Comparative Examples were cut into 5 cm x 5 cm test pieces, and the thickness was measured with a micrometer to determine the volume (cm ３ The mass W (g) of the test piece calculated in the same manner as in the above <Weight per unit area of ​​positive electrode> was then multiplied by the volume (cm ３ ) to obtain the density of the positive electrode (g / cm３ ) was calculated.

[0230] <Electrical Conductivity 1 of Positive Electrode Mixture Layer> The electrical conductivity 1 of the positive electrode mixture layer on the positive electrodes produced in the Examples and Comparative Examples was calculated using a low-resistivity resistivity meter (Loresta (registered trademark) GX, manufactured by Mitsubishi Chemical Analytical Co., Ltd.) in accordance with JIS K 7194:1994, by performing a four-probe method in which probes were placed on one side of a sheet.

[0231] <Electrical Conductivity 2 of Positive Electrode Mixture Layer> The electrical conductivity 2 of the positive electrode mixture layer on the positive electrodes produced in the Examples and Comparative Examples was calculated using a low-resistivity resistivity meter (Loresta (registered trademark) GX, manufactured by Mitsubishi Chemical Analytical Co., Ltd.) in accordance with JIS K 7194:1994, by performing a four-probe method in which probes were placed on one side of a sheet.

[0232] <Positive electrode axial winding strength> The positive electrodes produced in the examples and comparative examples were cut into 5 cm x 5 cm test pieces, which were then wound around an S stainless steel axial core (4 mmφ). The test pieces were then removed and visually inspected for cracks, chips, and peeling to evaluate the positive electrode axial winding strength. OK (○): No cracks, chips, or peeling. NG (×): Cracks, chips, or peeling in at least one place.

[0233] <Dust Falling Resistance of Positive Electrode Composite Layer> Five rectangular test pieces measuring 600 mm in length and 500 mm in width were prepared for the lithium-ion secondary battery positive electrodes fabricated in each Example and Comparative Example. The following operations and measurements were performed for each test piece. First, the initial electrode weight (P0) was measured for each test piece. Next, eleven 1 mm-wide cuts were made in the test piece using a utility knife, and the powder generated during the cutting was gently brushed off. The electrode weight (P1) after the cuts was then measured. The amount of powder falling off of the electrode was calculated using the following formula: Amount of powder falling off of electrode (mass%) = {(P0 - P1) / P0} × 100. The above operations and measurements were repeated five times, and the average amount of powder falling off of the five electrode samples was calculated. The powder falling resistance of the electrode composite layer was then evaluated according to the following criteria. The smaller the amount of powder falling off of the electrode, the better the resistance of the electrode composite layer to powder falling off. OK (○): The average amount of powder falling off the electrode is less than 10%. NG (×): The average amount of powder falling off the electrode is 10% or more.

[0234] <Electrolyte Impregnation of Positive Electrode> The positive electrodes produced in the Examples and Comparative Examples were cut into 5 cm x 5 cm pieces to obtain test pieces, and their masses were measured. The test pieces were then immersed in acetone at 25°C for 1 hour, removed, and their masses were measured. The electrolyte impregnation of the positive electrode was evaluated based on the rate of change in mass of the test pieces before and after immersion in the electrolyte. OK (○): The test piece did not peel off. NG (×): The test piece peeled off.

[0235] <Film-formability of carbon film> Regarding the film-formability of the obtained carbon film, if the film could maintain a size equivalent to that of the membrane filter (manufactured by Advantec Toyo Co., Ltd., made of PTFE) after peeling it off, it was evaluated as ○ (good), and if shrinkage or cracking was observed, it was evaluated as × (not good).

[0236] <Porosity> The porosity of the produced carbon membrane was measured by mercury intrusion porosimetry (Shimadzu Corporation, Autopore IV9510).

[0237] (Evaluation of CNT dispersion liquid produced by jet mill) (Example 1) <Synthesis of CNT_A> The CNTs used in Examples 1 and 3 and Comparative Example 1 (hereinafter referred to as "CNT_A") were produced by a method of supplying raw material gas while continuously transporting a particulate catalyst support by screw rotation in the CNT synthesis process. A schematic configuration of the CNT aggregate production apparatus 200 used is shown in FIG. 7. The CNT aggregate production apparatus 200 shown in FIG. 7 comprises a formation unit 202, a growth unit 204, a transport unit 207 that transports the base material from the formation unit 202 until it passes through the growth unit 204, a connection part 208 that spatially connects the formation unit 202 and the growth unit 204 to each other, and a gas mixing prevention device 203 that prevents gases from mixing with each other between the formation unit 202 and the growth unit 204. Furthermore, the CNT aggregate manufacturing apparatus 200 comprises components such as an inlet purge device 201 arranged in the stage before the formation unit 202, an outlet purge device 205 arranged in the stage after the growth unit 204, and a cooling unit 206 arranged in the stage after the outlet purge device 205. The formation unit 202 is composed of a formation furnace 202a for holding a reducing gas, a reducing gas injection device 202b for injecting the reducing gas, a heating device 202c for heating at least one of the catalyst and the reducing gas, an exhaust device 202d for discharging gas in the furnace to the outside of the system, etc. The gas mixing prevention device 203 comprises an exhaust device 203a and a purge gas injection device 203b for injecting a purge gas (seal gas). The growth unit 204 includes a growth furnace 204a for maintaining a source gas environment, a source gas injection device 204b for injecting the source gas, a heating device 204c for heating at least one of the catalyst and the source gas, and an exhaust device 204d for discharging gas in the furnace to the outside of the system. An inlet purge device 201 is attached to a connection part 209 that connects the formation furnace 202a to a front chamber 213, which is a component that introduces a substrate 211 into the system via a hopper 212. The cooling unit 206 includes a cooling container 206a for holding an inert gas, and a water-cooling device 206b arranged to surround the space inside the cooling container 206a.The conveying unit 207 is a unit that continuously conveys the substrate 211 by screw rotation. It is implemented by a screw blade 207a and a driving device 207b that can rotate the screw blade to achieve the substrate conveying function. The heating device 214 is configured to be able to heat the inside of the system at a temperature lower than the heating temperature in the formation unit, and heats the vicinity of the driving device 207b.

[0238] <<Catalyst Layer Formation Step>> Zirconia (zirconium dioxide) beads (ZrO ２ The zirconia beads were placed in a rotary drum coater. The zirconia beads were stirred at 20 rpm, and the aluminum-containing solution was sprayed with a spray gun (spray rate: 3 g / min, spray time: 940 seconds, spray air pressure: 10 MPa) while being dried by supplying compressed air (300 L / min) into the rotary drum. An aluminum-containing coating film was formed on the zirconia beads. The beads were then calcined at 480°C for 45 minutes to produce primary catalyst particles with an aluminum oxide layer. The primary catalyst particles were then placed in another rotary drum coater. The primary catalyst particles were stirred at 20 rpm, and the iron catalyst solution was sprayed with a spray gun (spray rate: 2 g / min, spray time: 480 seconds, spray air pressure: 5 MPa) while being dried by supplying compressed air (300 L / min) into the rotary drum. An iron-containing coating film was formed on the primary catalyst particles. Next, a baking treatment was carried out at 220° C. for 20 minutes to prepare a substrate on which an iron oxide layer was further formed.

[0239] <<CNT synthesis process>> The substrate having a catalyst on its surface produced in this manner was placed in the feeder hopper of a production device, and while being transported by a screw conveyor, it was subjected to the formation process, growth process, and cooling process in this order to produce a CNT aggregate.

[0240] <<Formation Step to Cooling Step>> Continuous CNT production was carried out by setting the conditions for the inlet purge device, formation unit, gas mixing prevention device, growth unit, outlet purge device and cooling unit of the CNT aggregate production apparatus as follows. Feeder hopper - Feed rate: 1.25 kg / h - Discharge volume: 10 sLm (natural exhaust from gap) Inlet purge device - Purge gas: Nitrogen 40 sLm Formation unit - Furnace temperature: 800°C - Reducing gas: Nitrogen 6 sLm, hydrogen 54 sLm - Discharge volume: 60 sLm - Treatment time: 20 minutes Gas mixing prevention device - Purge gas: 20 sLm - Discharge volume of exhaust device: 62 sLm ​​Growth unit - Furnace temperature: 830°C - Raw material gas: Nitrogen 15 sLm, ethylene 5 sLm, carbon dioxide 1 sLm, hydrogen 3 sLm - Discharge volume: 47 sLm - Treatment time: 10 minutes Outlet purge device - Purge gas: Nitrogen 45 sLm Cooling unit - Cooling temperature: Room temperature - Discharge volume: 10 sLm (natural exhaust from gap)

[0241] <<Separation and Recovery Process>> The CNT aggregates synthesized on the substrate were separated using a forced vortex classifier (rotation speed 2300 rpm, air flow rate 3.5 Nm ３ Separation and recovery were carried out using a flow rate of 1000 kJ / min. The recovery rate of the CNT aggregate was 96%. Typical properties of the produced CNT aggregate were G / D ratio: 1.3, tap bulk density: 0.02 g / cm ３ , CNT average length: 150 μm, BET specific surface area: 900 m ２ / g, average outer diameter: 4.0 nm, and carbon purity: 99%.

[0242] <<Characteristics of CNT>> The electron microscope image (SEM image) of the obtained CNT aggregate (CNT_A) was as shown in FIG.

[0243] <Production of CNT dispersion and measurement of each physical property> A mixture of 0.3 g of the CNT_A synthesized above as CNTs and 300 g of N-methylpyrrolidone (NMP) as a solvent was subjected to 12 passes of dispersion treatment for 15 minutes at 100 MPa using a jet mill (NanoVeita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) to obtain a CNT dispersion. An optical microscope image of the CNT dispersion is shown in Figure 1. The fractal dimension and CNT persistence length of the obtained CNT dispersion were measured. The results are shown in Table 1. An optical microscope image of the obtained CNT dispersion was binarized to obtain an image (Figure 10), and the area ratio of CNTs in the obtained image and the area ratio of CNTs in the obtained image were measured. ２ The number of carbon nanotubes with an aspect ratio of 10 or more contained in an area corresponding to the above was measured. The results are shown in Table 1.

[0244] <Production of Slurry Composition for Positive Electrode> LiNi as Positive Electrode Active Material ０．５ Co ０．３ Mn ０．２ O ２ A slurry composition for a positive electrode was produced by stirring 100.0 parts of (NCM532), 0.1 parts of a CNT dispersion as a conductive material dispersion, 0.2 parts of polyvinylpyrrolidone as a binder, 1.0 part of hydrogenated NBR as a dispersant, and 50 parts of NMP as a solvent for the slurry composition using a planetary mixer.

[0245] <Production of Positive Electrode> The positive electrode slurry composition obtained above was applied to the surface of a current collector made of aluminum foil having a thickness of 20 μm and a surface tension of 900 mN / m using a comma coater, dried at 60° C. for 20 minutes, and then heat-treated at 150° C. for 1 hour to obtain a positive electrode blank. The obtained positive electrode blank was then rolled using a roll press to produce a positive electrode (laminate) having a thickness controlled to 50 μm, which included a current collector (metal film) and a positive electrode composite layer (carbon nanotube-containing film) formed on the current collector.

[0246] <Production of current collector transfer laminate> The positive electrode slurry composition obtained above was applied using a comma coater to the surface of a transfer release substrate made of a polypropylene resin substrate having a thickness of 20 μm and a surface tension of 30 mN / m, dried at 60° C. for 20 minutes, and then heat-treated at 150° C. for 1 hour to obtain a current collector transfer laminate raw sheet. The obtained current collector transfer laminate raw sheet was then rolled using a roll press to produce a current collector transfer laminate having a thickness controlled to 50 μm, which included a release substrate (resin substrate) and a positive electrode composite layer (carbon nanotube-containing film) formed on the release substrate.

[0247] <Production of Lithium-Ion Secondary Battery> Next, the lithium-ion secondary battery positive electrode obtained above was cut into a disk shape with a diameter of 16 mm. A separator (polypropylene porous membrane, disk-shaped, diameter 18 mm, thickness 25 μm), a negative electrode (metallic lithium, disk-shaped, diameter 18 mm, thickness 0.5 mm), and an expanded metal were stacked in this order on the positive electrode composite layer side of the obtained disk-shaped positive electrode to obtain a laminate. The resulting laminate was placed in a stainless steel coin-shaped outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) equipped with a polypropylene packing. The electrolyte was then poured into the container so that no air remained, and a 0.2 mm-thick stainless steel cap was placed on the outer container via the polypropylene packing and fixed, and the battery can was sealed to produce a coin-shaped lithium-ion secondary battery with a diameter of 20 mm and a thickness of approximately 2 mm. The electrolyte solution was a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of EC:DEC = 1:2 (volume ratio at 20°C), and LiPF ６ The resulting coin-type lithium ion secondary battery was evaluated for rate characteristics. The results are shown in Table 1.

[0248] Example 2 The CNT dispersion was produced, physical property measurements were performed, and a carbon film was produced and its performance evaluated in the same manner as in Example 1, except that single-walled carbon nanotubes, such as Tuball™ (manufactured by OCSiAl Corporation, CNT diameter: 1.6±0.4 nm, specific surface area ≧300 m / g, G / D ratio: >90, length: 5 μm), were used as the CNTs in the production of the CNT dispersion. The G / D ratio of the CNTs was 90. The results are shown in Tables 1 and 2. An optical microscope image and a binarized image of the CNT dispersion are shown in FIGS. 2 and 11, respectively. A photograph of the grindmeter analysis of the slurry composition and a photograph of the positive electrode are shown in FIG. 16. Since the grindmeter analysis exceeded the 40 μm line, it was confirmed that there were no aggregates or particles in the dispersion and that the degree of dispersion was good.

[0249] Example 3: The CNT dispersion was produced, various physical properties were measured, and a carbon film was produced and various performances were evaluated in the same manner as in Example 1, except that a mixture containing 9 parts CNT_A and 1 part CNT obtained by the super-growth method (product name "ZEONANO SG101" manufactured by Zeon Corporation) was used as the CNTs in the production of the CNT dispersion (the total amount was the same as in Example 1). The G / D ratio of the CNT mixture was 1.2. The results are shown in Tables 1 and 2. Optical microscope images and binarized images of the CNT dispersion are shown in Figures 3 and 12, respectively (solid lines indicate carbon nanotubes with an aspect ratio of 10 or more). A photograph of the grindmeter analysis of the slurry composition and a photograph of the positive electrode are shown in Figure 17. Since the grindmeter analysis exceeded the 40 μm line, it was confirmed that there were no aggregates or particles in the dispersion and that the degree of dispersion was good.

[0250] Comparative Example 1 A CNT dispersion was produced, physical property values ​​were measured, and a carbon film was produced and performance was evaluated in the same manner as in Example 1, except that nine passes of dispersion treatment using a jet mill were performed in the production of the CNT dispersion. The results are shown in Tables 1 and 2. An optical microscope image and a binarized image of the CNT dispersion are shown in Figures 4 and 13, respectively. A photograph of the grindometer analysis of the slurry composition and a photograph of the positive electrode are shown in Figure 18.

[0251] (Comparative Example 2) In producing the CNT dispersion, the production of the CNT dispersion, measurement of each physical property, production of the carbon film, and evaluation of each performance were carried out in the same manner as in Example 1, except that in producing the CNT dispersion, CNTs with the product name "K-nanos 100T" (manufactured by KNANO GRAPHENE COMPANY, CNT diameter: 7 to 23 nm, CNT length: 26 nm, carbon purity: up to 95%) were used. The G / D ratio of the CNT was 0.9. The results are shown in Table 1. FIG. 14 shows an image obtained by binarizing an optical microscope image of the CNT dispersion.

[0252]

[0253]

[0254] In the table, "◯" indicates a good evaluation result (OK), and "×" indicates a bad evaluation result (NG).

[0255] Table 1 shows that when the CNT dispersions of Examples 1 to 3 within the scope of the present invention were used, excellent performance was exhibited in all of the adhesion of the electrode mixture layer to the metal film, the ease of peeling the electrode mixture layer from the substrate, and the rate characteristics of the secondary battery.

[0256] (Evaluation of CNT dispersion prepared by high shear stirring) (Example 4) <Preparation of CNT dispersion> A mixture of 2 g of CNT obtained by the super growth method (product name "ZEONANO SG101", manufactured by Zeon Corporation) as the CNT and 1998 g of water as the solvent was subjected to a dispersion treatment under the condition A shown in Table 3 using a high shear stirrer Cavitron CD1000 (manufactured by Eurotech) as the disperser, to obtain a CNT dispersion. Images of this CNT dispersion were captured and analyzed, and the area ratio of CNT in the image was calculated. The results are shown in Table 4.

[0257] <Membrane Formation> Filtration was carried out under a condition of 0.09 MPa using a vacuum filtration device equipped with a membrane filter. Air was then passed through for 4 hours, and the carbon membrane was peeled off from the carbon membrane / membrane filter to obtain a carbon membrane. The obtained carbon membrane was evaluated for membrane formability and its porosity was measured. The results are shown in Table 4.

[0258] (Example 5) In preparing the CNT dispersion, the preparation of the CNT dispersion and the carbon film, and the measurement or evaluation of each physical property were carried out in the same manner as in Example 4, except that the dispersion treatment was carried out under condition B shown in Table 3. The results are shown in Table 4.

[0259] Example 6 <Synthesis of CNT_A> The CNTs used in Examples 6 and 7 (hereinafter referred to as "CNT_A") were produced by the same method as in Example 1.

[0260] <Preparation of CNT dispersion and carbon film> A CNT dispersion and a carbon film were prepared, and their physical properties were measured or evaluated, in the same manner as in Example 4, except that CNT_A produced above was used as the CNTs in preparing the CNT dispersion. The results are shown in Table 4.

[0261] (Example 7) In preparing the CNT dispersion, the preparation of the CNT dispersion and the carbon film, and the measurement or evaluation of each physical property were carried out in the same manner as in Example 6, except that the dispersion treatment was carried out under condition B shown in Table 3. The results are shown in Table 4.

[0262] (Comparative Example 3) In preparing the CNT dispersion, a CNT dispersion and a carbon film were prepared, and their physical properties were measured or evaluated in the same manner as in Example 4, except that CNTs with the product name "K-nanos 100T" (manufactured by KNANO GRAPHENE COMPANY) were used. The results are shown in Table 4.

[0263] (Comparative Example 4) In the preparation of the CNT dispersion, the preparation of the CNT dispersion and the carbon film, and the measurement or evaluation of each physical property were carried out in the same manner as in Comparative Example 3, except that the dispersion treatment was carried out under the condition B shown in Table 3. The results are shown in Table 4.

[0264]

[0265]

[0266] In the table, "◯" indicates a good evaluation result (OK), and "×" indicates a bad evaluation result (NG).

[0267] Table 4 shows that carbon films were produced with good film-forming properties in Examples 4 to 7, which fall within the scope of the present invention. Furthermore, the results of Examples 4 to 7 show that adjusting the area ratio of CNTs in a CNT dispersion can serve as a guide for obtaining a carbon film with a porosity in a desired range.

[0268] According to the present invention, a carbon nanotube dispersion can be provided that can provide a secondary battery electrode with strong peel strength between an electrode mixture layer and a current collector made of metal or the like, and can provide a release substrate-attached electrode mixture layer with weak peel strength between the electrode mixture layer and a release substrate made of resin or the like, thereby enabling the secondary battery to exhibit excellent rate characteristics. Furthermore, according to the present invention, a laminate can be provided that can be used as a secondary battery electrode having strong peel strength between an electrode mixture layer and a current collector made of metal or the like. Furthermore, according to the present invention, a laminate can be provided that can be used as an electrode mixture layer with a release substrate having weak peel strength between an electrode mixture layer and a release substrate made of resin or the like. Furthermore, according to the present invention, a CNT dispersion that can achieve good film-formability when forming a carbon film using the CNT dispersion, and a method for producing the same can be provided. Furthermore, according to the present invention, a method for producing a carbon film with good film-formability using the CNT dispersion, and a carbon film with good film formation state can be provided.

[0269] 200 CNT aggregate manufacturing apparatus 201 Inlet purge device 202 Formation unit 202a Formation furnace 202b Reducing gas injection device 202c Heating device 202d Exhaust device 203 Gas mixing prevention device 203a Exhaust device 203b Purge gas injection device 204 Growth unit 204a Growth furnace 204b Raw material gas injection device 204c Heating device 204d Exhaust device 205 Outlet purge device 206 Cooling unit 206a Cooling vessel 206b Water-cooled cooling device 207 Conveying unit 207a Screw blade 207b Driving device 208 to 210 Connection part 211 Substrate 212 Hopper 214 Heating device

Claims

1. A carbon nanotube dispersion liquid containing carbon nanotubes and a solvent, A carbon nanotube dispersion liquid, in which the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is in the range of 3 or more and 4 or less when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model.

2. A carbon nanotube dispersion liquid containing single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent, A carbon nanotube dispersion in which the area ratio of carbon nanotubes in an image obtained by photographing the carbon nanotube dispersion at a concentration of 0.1 wt % is 55% or less.

3. 26000 μm in the image ２ 3. The carbon nanotube dispersion according to claim 2, wherein 5 to 100 carbon nanotubes having an aspect ratio of 10 or more are contained per area corresponding to said surface area.

4. A carbon nanotube dispersion liquid containing single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent, A carbon nanotube dispersion in which the area ratio of carbon nanotubes in an image obtained by capturing an image of the carbon nanotube dispersion at a concentration of 0.1 wt % is 75% or more.

5. A carbon nanotube dispersion liquid containing carbon nanotubes and a solvent, A carbon nanotube dispersion in which the area ratio of carbon nanotubes in an image obtained by photographing the carbon nanotube dispersion at a concentration of 0.1 wt % is 70% or less.

6. The carbon nanotube dispersion liquid according to claim 5 , wherein the area ratio is 55% or more and 70% or less.

7. 6. The carbon nanotube dispersion liquid according to claim 2, wherein the fractal dimension in the wavenumber range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is in the range of 3 or more and 4 or less when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model.

8. 6. The carbon nanotube dispersion according to claim 1, wherein the CNT persistence length in the wavenumber range of 0.05 (1 / Å) or more and 0.01 (1 / Å) or less is 100 nm or more when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model.

9. 6. The carbon nanotube dispersion liquid according to claim 1, wherein the solvent is water, an alcohol, or a mixture of water and an alcohol.

10. 6. The carbon nanotube dispersion liquid according to claim 1, wherein the carbon nanotubes satisfy at least one of the following conditions (1) to (3): (1) A carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more is subjected to Fourier transform infrared spectroscopy. In the spectrum obtained, a peak due to the plasmon resonance of the carbon nanotube dispersion is observed at a wave number of 300 cm. －１ Super 2000cm －１ At least one of the following ranges is present: (2) For the aggregate of carbon nanotubes, the maximum peak in a pore distribution curve showing the relationship between pore diameter and log differential pore volume, which is obtained based on the Barrett-Joyner-Halenda method from the adsorption isotherm of liquid nitrogen at 77 K, is in the pore diameter range of more than 100 nm and less than 400 nm. (3) The peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm －１ 100 μm or more －１ At least one of the following ranges is present:

11. 6. A laminate comprising a metal film having a surface tension of 400 mN / m or more and 2000 mN / m or less and a carbon nanotube-containing film formed using the carbon nanotube dispersion liquid according to claim 1.

12. 6. A laminate comprising a substrate having a surface tension of 20 mN / m or more and 50 mN / m or less and a carbon nanotube-containing film formed using the carbon nanotube dispersion liquid according to claim 1.

13. a step of dispersing the mixture of carbon nanotubes and a solvent to obtain a carbon nanotube dispersion; a step of measuring the obtained carbon nanotube dispersion liquid by ultra-small angle X-ray scattering; The carbon nanotube dispersion is evaluated as being appropriate when it satisfies condition 1, in which the fractal dimension in the wave number range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is in the range of 3 or more and 4 or less when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and a step of evaluating the carbon nanotube dispersion liquid as being inappropriate if the condition 1 is not satisfied; A method for producing a carbon nanotube dispersion, comprising:

14. a step of dispersing the mixture of carbon nanotubes and a solvent to obtain a carbon nanotube dispersion; a step of measuring the obtained carbon nanotube dispersion liquid by ultra-small angle X-ray scattering; a step of evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, in which a fractal dimension in a wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4 and a CNT persistent length in a wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is in the range of 100 nm or more when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2; A method for producing a carbon nanotube dispersion, comprising:

15. a step of dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent to obtain a carbon nanotube dispersion; a step of capturing an image of the carbon nanotube dispersion liquid obtained when the concentration is 0.1 wt %; a step of evaluating the carbon nanotube dispersion liquid as appropriate when condition 3 is satisfied, that is, the area ratio of carbon nanotubes in the acquired image is 55% or less, and evaluating the carbon nanotube dispersion liquid as inappropriate when condition 3 is not satisfied; A method for producing a carbon nanotube dispersion, comprising:

16. a step of dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 5 or less and a solvent to obtain a carbon nanotube dispersion; a step of capturing an image of the carbon nanotube dispersion liquid obtained when the concentration is 0.1 wt %; The area ratio of carbon nanotubes in the acquired image is 55% or less, and the area of ​​26000 μm ２ a step of evaluating the carbon nanotube dispersion as appropriate if condition 4 is satisfied, that is, the carbon nanotube dispersion contains 5 to 100 carbon nanotubes having an aspect ratio of 10 or more per area corresponding to the above condition, and evaluating the carbon nanotube dispersion as inappropriate if condition 4 is not satisfied; A method for producing a carbon nanotube dispersion, comprising:

17. a step of dispersing a mixture of single-walled carbon nanotubes having a G / D ratio of 10 or more and a solvent to obtain a carbon nanotube dispersion; a step of capturing an image of the carbon nanotube dispersion liquid obtained when the concentration is 0.1 wt %; a step of evaluating the carbon nanotube dispersion liquid as appropriate when condition 5 is satisfied, that is, the area ratio of carbon nanotubes in the acquired image is 75% or more, and evaluating the carbon nanotube dispersion liquid as inappropriate when condition 5 is not satisfied; A method for producing a carbon nanotube dispersion, comprising:

18. a step of dispersing the mixture of carbon nanotubes and a solvent to obtain a carbon nanotube dispersion; a step of capturing an image of the obtained carbon nanotube dispersion; a step of evaluating the carbon nanotube dispersion liquid as appropriate when the area ratio of the carbon nanotubes in the acquired image satisfies condition A, and evaluating the carbon nanotube dispersion liquid as inappropriate when the area ratio of the carbon nanotubes in the acquired image does not satisfy condition A; Including, The condition A includes that the area ratio of carbon nanotubes in an image obtained by capturing an image of a carbon nanotube dispersion liquid at a concentration of 0.1 wt % is 70% or less. A method for producing a carbon nanotube dispersion.

19. The method for producing a carbon nanotube dispersion liquid according to claim 18 , wherein the condition A further includes the area ratio being 55% or more.

20. a step of measuring the obtained carbon nanotube dispersion liquid by ultra-small angle X-ray scattering; The carbon nanotube dispersion is evaluated as being appropriate when it satisfies condition 1, in which the fractal dimension in the wave number range of 0.001 (1 / Å) or more and 0.3 (1 / Å) or less is in the range of 3 or more and 4 or less when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and a step of evaluating the carbon nanotube dispersion liquid as being inappropriate if the condition 1 is not satisfied; The method for producing a carbon nanotube dispersion liquid according to any one of claims 15 to 18, further comprising:

21. a step of measuring the obtained carbon nanotube dispersion liquid by ultra-small angle X-ray scattering; a step of evaluating the carbon nanotube dispersion as appropriate if it satisfies condition 2, in which a fractal dimension in a wavenumber range of 0.001 (1 / Å) to 0.3 (1 / Å) is in the range of 3 to 4 and a CNT persistent length in a wavenumber range of 0.05 (1 / Å) to 0.01 (1 / Å) is in the range of 100 nm or more when a scattering curve obtained by measurement using an ultra-small angle X-ray scattering method is analyzed using a Beaucage model, and evaluating the carbon nanotube dispersion as inappropriate if it does not satisfy condition 2; The method for producing a carbon nanotube dispersion liquid according to any one of claims 15 to 18, further comprising:

22. A method for producing a carbon film, comprising the step of removing the solvent from the carbon nanotube dispersion liquid according to claim 1 to form a carbon film.

23. A method for producing a carbon film, comprising the step of removing the solvent from the carbon nanotube dispersion obtained by the method for producing a carbon nanotube dispersion according to any one of claims 13 to 18, to form a carbon film.