Carbon nanotube dispersion composition, composition for secondary battery electrodes, electrode film, secondary battery, and vehicle

Abstract

To provide a carbon nanotube dispersion composition that is excellent in terms of time stability and applicable to various application fields requiring high conductivity and durability, and a secondary battery having high conductivity and excellent electrode strength, an electrode film with excellent cycle characteristics and high-temperature storage characteristics, using the carbon nanotube dispersion composition and a secondary battery electrode composition using the carbon nanotube dispersion composition. [Solution] The problem is solved by a carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and an amide-based polar solvent, wherein the carbon nanotubes have an iron content of 170,000 ppm or less, and further comprise a carbon nanotube aggregate in which two or more carbon nanotube units, each having an average outer diameter of 3 nm to 8 nm and 3 to 15 layers, are bundled together in parallel by interaction, and the average outer diameter of the carbon nanotube aggregate is 10 nm to 50 nm.

Description

[Technical Field]

[0001] The present invention relates to a carbon nanotube dispersion composition. More specifically, it relates to a carbon nanotube dispersion composition, a composition for secondary battery electrodes comprising the carbon nanotube dispersion composition and an active material, an electrode film formed therefrom, and a secondary battery comprising the electrode film and an electrolyte. [Background technology]

[0002] With the spread of electric vehicles and the miniaturization, weight reduction, and increased performance of portable devices, there is a growing demand for secondary batteries with high energy density and higher capacity. Against this backdrop, non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, which utilize non-aqueous electrolytes due to their high energy density and high voltage characteristics, are increasingly being used in many devices.

[0003] The negative electrode materials used in these lithium-ion secondary batteries are carbon materials, such as graphite, which have a low potential close to that of lithium (Li) and a large charge / discharge capacity per unit mass. However, these electrode materials are being used up to near-theoretical levels of charge / discharge capacity per unit mass, and the energy density per unit mass of the battery is approaching its limit. Therefore, in order to increase the utilization rate of the electrodes, attempts are being made to reduce conductive additives and binders that do not contribute to the discharge capacity.

[0004] Conductive additives used include carbon black, Ketjenblack, fullerene, graphene, and fine carbon materials. Carbon nanotubes, a type of fine carbon fiber, are particularly frequently used. For example, it is known that adding carbon nanotubes to graphite or silicon negative electrodes improves electrode conductivity, adhesion, and electrode strength (such as expansion and contraction resistance), as well as the rate characteristics and cycle characteristics of lithium-ion secondary batteries (see, for example, Patent Document 1). Studies have also been conducted to reduce electrode resistance by adding carbon nanotubes to the positive electrode (see, for example, Patent Documents 2, 3, and 4).

[0005] However, when carbon nanotubes having a low G / D ratio determined by Raman spectroscopy are used in lithium ion secondary batteries, there has been a problem of poor storage characteristics. (See, for example, Patent Document 5)

[0006] As described above, it is known that when carbon nanotubes having a small average outer diameter and a large fiber length are used, a conductive network can be efficiently formed with a small amount, and the amount of conductive aid contained in positive electrodes and negative electrodes for lithium ion secondary batteries can be reduced. However, for lithium ion secondary batteries that are used for a long time in high-temperature environments and require durability in applications such as in-vehicle use, there is a demand for a carbon nanotube dispersion composition that can suppress deterioration of active materials and decomposition of electrolytic solutions, which are members constituting the battery and cause battery deterioration during high-temperature storage. [Prior Art Documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2021-72279 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2019-210173 [Patent Document 3] International Publication No. WO 2017 / 171291 [Patent Document 4] Japanese National Publication of International Patent Application No. 2022-521422 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2024-099986 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] However, since carbon nanotubes are fibrous and have strong cohesive force, it is difficult to obtain a carbon nanotube dispersion composition that is uniformly dispersed and maintains dispersibility for a long period of time.

[0009] In Patent Document 1, the average outer diameter is more than 3 nm and 25 nm or less, and the BET specific surface area is 150 m2 / g~800m 2 A carbon nanotube dispersion composition with a fiber length of 0.8 to 3.5 μm is prepared by dispersing carbon nanotubes (at a concentration of 1 / g), a dispersant, and a solvent using a high-pressure homogenizer. In Patent Document 2, carbon nanotubes with a G / D ratio of 1.5 to 5.0 are prepared by heat treatment of carbon nanotubes, and the dispersion treatment is performed using polyvinylpyrrolidone as a dispersant and zirconia beads. These carbon nanotube dispersions were dispersed to the point where the carbon nanotubes were broken down to individual units. While this improved the conductivity of the electrodes, it compromised the rigidity of the carbon nanotube aggregates, resulting in insufficient electrode strength. Furthermore, when carbon nanotubes were broken down to individual units, the increased surface area of ​​the electrodes containing the carbon nanotubes accelerated the decomposition reaction of the electrolyte, leading to insufficient battery performance, especially during high-temperature storage.

[0010] In other words, the problem that the present invention aims to solve is to provide a carbon nanotube dispersion composition that is excellent in terms of time stability, high conductivity, and durability, and is applicable to various application fields. Furthermore, the objective is to obtain an electrode film with high conductivity and excellent electrode strength using the carbon nanotube dispersion composition and the secondary battery electrode composition using the carbon nanotube dispersion composition. Additionally, the objective is to provide a secondary battery with excellent cycle characteristics and high-temperature storage characteristics. [Means for solving the problem]

[0011] In other words, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. [1] A carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and an amide-based polar solvent, The carbon nanotubes have an iron content of 170,000 ppm or less. Furthermore, it includes a carbon nanotube aggregate in which two or more carbon nanotube units, each having an average outer diameter of 3 nm to 8 nm and 3 to 15 layers, are bundled together in parallel by interaction. The average outer diameter of the carbon nanotube aggregate is between 10 nm and 50 nm. Carbon nanotube dispersion composition. [2]: The carbon nanotube dispersion composition according to [1], wherein the iron content of the carbon nanotube dispersion composition is 50 ppm or less. [3] The BET specific surface area of ​​the carbon nanotube is 100 m 2 / g or more 300m 2 A carbon nanotube dispersion composition according to [1] or [2], wherein the amount is less than or equal to / g. [4]: The carbon nanotube dispersion composition according to any one of [1] to [3], wherein the G / D ratio of the carbon nanotubes is 5.1 or more and 15 or less. [5]: The carbon nanotube dispersion composition according to any one of [1] to [4], wherein the 20-degree specular gloss of the carbon nanotube dispersion composition is 50 or more and 170 or less. [6] The carbon nanotube dispersion composition according to any one of [1] to [5], wherein the phase angle when the carbon nanotube dispersion composition is subjected to dynamic viscoelasticity measurement using a rheometer with a cone of 25 mm in diameter and 2°, at 25°C and a frequency of 1 Hz, with a strain from 0.01% to 500%, is greater than 20°. [7]: A composition for secondary battery electrodes comprising the carbon nanotube dispersion composition described in any of [1] to [6]. [8]: An electrode film comprising a coating film of the secondary battery electrode composition described in [7]. [9]: A secondary battery comprising the electrode film described in [8].

[10] : A vehicle containing the secondary battery described in [9]. [Effects of the Invention]

[0012] By using the carbon nanotube dispersion composition of the present invention, an electrode film with not only high conductivity but also excellent electrode strength, and a secondary battery electrode composition capable of forming such an electrode film can be obtained. Furthermore, a secondary battery with excellent cycle characteristics and high-temperature storage characteristics can be obtained. Thus, a carbon nanotube dispersion composition is obtained that is excellent in terms of time stability and applicable to various application fields where high conductivity and durability are required. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a photograph of a carbon nanotube (A-1) fabricated in the manufacturing example, observed at 1 million times magnification using a transmission electron microscope. [Figure 2] Figure 2 is a photograph of the carbon nanotube dispersion composition (D1-2) prepared in Example 2-15, observed at 500,000x magnification using a transmission electron microscope. [Figure 3] Figure 3 shows the viscoelasticity measurement results of the secondary battery electrode compositions prepared in Examples 2-6 and 2-15. [Figure 4] Figure 4 shows the viscosity measurement results for the secondary battery electrode compositions prepared in Examples 2-6 and 2-15. [Modes for carrying out the invention]

[0014] The carbon nanotube dispersion composition, secondary battery electrode composition, electrode film, and secondary battery according to embodiments of the present invention will be described in detail below, but are not limited thereto. The numerical values ​​specified herein are those obtained by the methods disclosed in the embodiments or examples.

[0015] Furthermore, in this specification, numerical ranges specified using "~" include the numbers written before and after "~" as the lower and upper limits. In this specification, carbon nanotubes may be referred to as "CNTs." Furthermore, in this specification, a carbon nanotube unit may be called a "CNT unit," a carbon nanotube aggregate may be called a "CNT aggregate," and a carbon nanotube dispersion composition may be called a "CNT dispersion composition," or simply "dispersion composition." A carbon nanotube aggregate in which two or more nanotubes are bundled together in parallel due to interaction is also called a "bundled CNT." Unless otherwise noted, the various components mentioned herein may be used individually or in combination of two or more.

[0016] Furthermore, the term "CNT dispersion composition" refers to the state before the addition of active material. In this respect, CNT dispersion compositions are distinguished from secondary battery electrode compositions that contain active material. That is, CNT dispersion compositions substantially do not contain active material. This concept excludes the state in which active material is intentionally added to the CNT dispersion composition, and the amount of active material relative to the total mass of the CNT dispersion composition may be 1% by mass or less, 0.5% by mass or less, 0.1% by mass or less, or even 0% by mass. The active material will be described later.

[0017] Carbon nanotube dispersion composition The carbon nanotube dispersion composition of the embodiment of the present invention comprises carbon nanotubes, a dispersant, and an amide-based polar solvent, wherein the carbon nanotubes have an iron content of 170,000 ppm or less, and further comprises carbon nanotube aggregates in which two or more carbon nanotube units, each having an average outer diameter of 3 nm to 8 nm and 3 to 15 layers, are bundled together in parallel by interaction, and the average outer diameter of the carbon nanotube aggregates is 10 nm to 50 nm.

[0018] A CNT unit is an individual carbon nanotube fiber, possessing a specific average outer diameter and number of layers. A CNT aggregate is a form in which multiple CNT units aggregate together through interactions such as van der Waals forces, resulting in two or more CNTs being bundled together in parallel, a state known as a bundle or ligature. By controlling the average outer diameter of CNT aggregates in a CNT dispersion composition to be between 10 nm and 50 nm, it is possible to create a CNT dispersion composition that exhibits not only high conductivity but also good durability. Some CNT units that do not form CNT aggregates, or other types of CNT aggregates, may be present.

[0019] The average outer diameter of the CNT aggregate can be adjusted by controlling the dispersion method, as described in the manufacturing method of the CNT dispersion composition later, so as to prevent the small-diameter, easily breakable CNTs from becoming excessively fine during dispersion, and so as to maintain the bundled state without completely unraveling each individual CNT. Methods for controlling dispersion include, for example, the disintegration of CNT aggregates using collision energy through media dispersion, the disintegration of CNT aggregates using shear energy through media-less dispersion, the control of resin adsorption to CNTs and suppression of re-aggregation of CNTs by adjusting the amount of dispersant, the adjustment of interactions with solvents or resins by modifying or surface-treating CNTs, and the suppression of CNT re-aggregation and sedimentation by stabilizers or thickeners.

[0020] In the CNT dispersion composition, two or more CNT units are bundled together in parallel by interactions, forming CNT aggregates. The average outer diameter of the CNT aggregates is 10 nm to 50 nm, preferably 15 nm to 30 nm. If the average outer diameter of the CNT aggregates is within the above range, it can be determined that the CNT aggregates are sufficiently dispersed and unraveled, resulting in a sufficient number of CNT aggregates in the CNT dispersion composition and enabling the formation of an efficient conductive network. Furthermore, the carbon nanotubes are arranged in a mesh-like structure within the electrode film, acting as a structural reinforcement material, thereby improving electrode strength. The average outer diameter of CNT aggregates in a CNT dispersion composition can be determined by measuring the outer diameters of 50 randomly selected CNT aggregates using a transmission electron microscope and calculating the arithmetic mean. Specifically, it can be measured by the method described in the examples.

[0021] The standard deviation of the outer diameter of the CNT aggregate is preferably 20 nm or less, and more preferably 10 nm or less. When the standard deviation of the outer diameter is within the above range, the storage modulus of the secondary battery electrode composition becomes appropriate, the bundled CNTs are uniformly dispersed within the electrode, and the electrode strength and the cycle characteristics of the secondary battery are further improved.

[0022] The average fiber length of the CNTs in the CNT dispersion composition is preferably 0.8 to 5 μm, and more preferably 1 to 3.5 μm. Within this range, a conductive network can be efficiently formed with a small amount, and the amount of CNTs contained in the positive and negative electrodes of the secondary battery can be reduced. When the average fiber length of the CNTs is 0.8 μm or more, the CNTs are spread in a mesh-like structure within the electrode film, acting as a structural reinforcement material, thereby further improving the strength of the electrode film. Furthermore, by using CNTs with a larger fiber length, the amount of CNTs contained in the electrode is reduced, which can suppress an increase in the surface area of ​​the electrode, suppressing the decomposition of the electrolyte during high-temperature storage in the secondary battery and further improving the cycle characteristics. Also, when the average fiber length of the CNTs is 5 μm or less, a sufficient amount of CNTs can be contained in the electrode, and a conductive network can be efficiently formed.

[0023] The average fiber length of CNTs in a CNT dispersion composition can be measured by the following method. The CNT dispersion composition is diluted with an amide-based polar solvent to a CNT concentration of 0.000001% by mass to 0.00001% by mass, and then a few drops of the CNT dispersion composition are dropped onto a mica substrate. The substrate is then dried on a hot plate at 140°C to prepare a substrate for observing the CNT fiber length. The prepared substrate is photographed using a scanning electron microscope, and the obtained SEM images are analyzed using image analysis software such as "WinROOF2015" (manufactured by Mitani Corporation) or "ImageJ" (open-source image processing and analysis software developed by the National Institutes of Health, USA). The fiber length of 100 CNT aggregates is measured, and the average fiber length of CNTs in the CNT dispersion composition can be determined by the arithmetic mean.

[0024] <Carbon nanotubes> The CNT dispersion composition of this embodiment contains carbon nanotubes, and carbon nanotubes This includes a CNT aggregate in which two or more CNT units, each having an iron content of 170,000 ppm or less, an average outer diameter of 3 nm to 8 nm, and 3 to 15 layers, are bundled together in parallel by interaction.

[0025] The iron content of the CNTs is 170,000 ppm or less, preferably 150,000 ppm or less, more preferably 5,000 ppm or less, and even more preferably 3,000 ppm or less. When the iron content of the CNTs is within the above range, gas generation due to electrolyte decomposition in the secondary battery is suppressed, and the cycle characteristics of the secondary battery tend to be good. In addition, the iron content of the CNT dispersion composition described later can be easily reduced. The lower limit of the iron content may be 0 ppm, and the iron contained in CNTs often originates from the catalyst used during CNT synthesis. If an iron-containing catalyst is used, the iron content may exceed 0 ppm.

[0026] The average outer diameter of the CNT units is between 3 nm and 8 nm. Preferably, it is between 3 nm and 6 nm, and more preferably between 3 nm and 5 nm. By having CNT units with an average outer diameter within the above range, electrodes with excellent conductivity and electrode strength can be obtained. The average outer diameter of the CNT units can be obtained by observing the CNT units using a transmission electron microscope, measuring the outer diameter of 50 randomly selected CNT units, and taking the arithmetic mean of the measured values.

[0027] The standard deviation of the outer diameter of the CNT unit is preferably 2 nm or less, more preferably 1.5 nm or less, and even more preferably 1.2 nm or less. CNT units with an outer diameter standard deviation within the above range tend to yield electrodes with superior electrode strength when used in secondary battery electrode compositions.

[0028] The number of layers of the CNT units is between 3 and 15. Preferably, it is between 3 and 13, and more preferably between 8 and 13. Having the number of CNT units within this range allows for good viscoelasticity of the secondary battery electrode composition after CNT dispersion, leading to improved electrode strength and enhanced cycle characteristics of the secondary battery. The CNT units may consist of a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0029] The number of layers in a CNT unit can be determined from the crystallite size (Lc002) and average interplanar spacing (d002) obtained by powder X-ray diffraction analysis of the CNTs, and can be calculated using the following formula (1). Equation (1): Number of layers = Crystallite size (Lc002) / Average interplanar spacing (d002) (In equation (1), the crystallite size (Lc002) and average interplanar spacing (d002) are the crystallite size (Lc002) and average interplanar spacing (d002) of the maximum peak at the diffraction angle 2θ = 25° ± 2° in powder X-ray diffraction analysis using CuKα rays.)

[0030] Specifically, it can be determined, for example, by performing powder X-ray diffraction analysis using the following method. First, the CNTs are packed into a designated sample holder so that the surface is flat, set in a powder X-ray diffraction analyzer, and measured under CuKa line conditions (wavelength: 1.54 Å) at a scanning speed of 87.5 seconds for every 0.02° from 2-Theta 10° to 90°. The diffraction angle 2θ at which the peak appears can be read to evaluate the CNTs. In graphite, a peak is usually detected around 26° for 2θ, and this is known to be a peak due to interlayer diffraction. Since CNTs also have a graphite structure, a peak due to graphite interlayer diffraction is detected around this point, but because CNTs have a cylindrical structure, 2θ will differ from that of graphite. The presence or absence of a peak at 25°±2° for 2θ can be used to determine whether it is a single-walled CNT or a composition with a multilayer structure. The peak appearing at 2θ ± 2° is due to interlayer diffraction in a multilayer structure. Therefore, in monowalled carbon nanotubes (WNTs) that have only one layer and do not have a multilayer structure, the peak at 2θ ± 2° does not appear. On the other hand, if the material is not composed solely of WNTs but also contains multilayered CNTs, the peak may appear at 2θ ± 2°. In other words, it can be confirmed that the CNT composition of the present invention contains multilayer CNTs, and the number of layers of these multilayer CNTs is between 3 and 15. When multilayer CNTs are included and the number of layers of these multilayer CNTs is within the above range, the CNT units form strong aggregates due to van der Waals forces, etc., which tends to improve conductivity and electrode strength.

[0031] For CNTs, the (Lc002) and (La100) values ​​can be obtained by measuring the full width at half maximum (FWHM) of the (002) crystal peak appearing at 2θ~30° and the full width at half maximum (FWHM) of the (100) crystal peak appearing around 38°~50°, and calculating them using the Scherrer formula.

[0032] The crystallite size (Lc002) of the CNTs is preferably 1.0 nm or larger, more preferably 1.9 nm or larger, and even more preferably 2.5 nm or larger. A crystallite size (Lc002) of 1.0 nm or larger allows π electrons to move easily within the crystal layer, enabling the creation of electrodes with excellent conductivity even with small amounts of additive. Furthermore, a crystallite size (Lc002) of less than 4.8 nm is preferable. A crystallite size (Lc002) of less than 4.8 nm allows for the creation of electrode films with superior flexibility, durability, and other strengths with small amounts of additive.

[0033] The crystallite size (La100) of the CNT is preferably between 10 and 100, more preferably between 20 and 100, and even more preferably between 30 and 100. The crystallite size (La100) is a parameter that reflects the growth unit length and crystallinity of the growth unit of the CNT. CNTs with a crystallite size (La100) within the above range tend to have fewer nodes, are not excessively fractured even when subjected to dispersion treatment using shear energy or collision energy, and can maintain a long fiber length, thus yielding electrodes with good conductivity and strength, making them preferable.

[0034] The BET specific surface area of ​​CNT is 100m². 2 / g~300m 2 It is preferable that it be / g, 100m 2 / g~199m 2 It is more preferable that the BET specific surface area is within the above range. When the CNT dispersion treatment is performed, excessive dispersion and subsequent miniaturization of CNTs can be suppressed, making it easier to obtain a secondary battery electrode composition with good conductivity. Furthermore, when used in a secondary battery, the decomposition of the electrolyte on the electrode surface can be suppressed, resulting in better cycle characteristics for the secondary battery. The BET specific surface area can be measured by the BET method of JIS Z 8830:2013.

[0035] The G / D ratio of CNTs is preferably 3 to 20, and more preferably 5.1 to 15. The G / D ratio is measured in the Raman spectrum at 1560 to 1600 cm⁻¹.-1 let G be the maximum peak intensity within the range of 1310 to 1350 cm -1 and D be the maximum peak intensity within the range, which is expressed as the G / D ratio. The Raman spectrum can be measured using laser light with a wavelength of 532 nm in accordance with Raman spectroscopy. When the G / D ratio of CNTs is 3 or more, the CNTs become more highly crystalline, thereby enabling the formation of a conductive network with excellent electrical conductivity. In addition, the network is toughened, which improves the toughness of the film. When the G / D ratio is 20 or less, a certain amount of defects remain, so both toughness and flexibility can be achieved, the contact surface with the active material increases, and an efficient conductive network can be formed.

[0036] The volume resistivity of CNTs is 1.0×10 -3 Ω·cm to 1.5×10 -2 Ω·cm, more preferably 1.0×10 -3 Ω·cm to 1.0×10 -2 Ω·cm. The volume resistivity of CNTs can be measured using a powder resistivity measuring device (Loresta-GP powder resistivity measurement system MCP-PD-51, manufactured by Nitto Seiko Analytech Co., Ltd.). When the volume resistivity is within the above range, the electrode membrane has good conductivity, and a secondary battery having excellent rate characteristics and cycle characteristics can be obtained.

[0037] The higher the carbon purity of CNTs, the more preferable it is. Based on 100% by mass of CNTs, the carbon purity is preferably 90% by mass or more, more preferably 98% by mass or more, still more preferably 99.5% by mass or more, even still more preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more. That is, the lower the content of foreign metal particles, the more preferable it is. Based on 100% by mass of CNTs, the content of foreign metal particles is preferably 2.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less. By using CNTs produced by a manufacturing method that does not use a metal catalyst as a core, or CNTs obtained by conventionally known purification methods such as acid treatment, the content of metal foreign particles can be reduced to 2.0% by mass or less per 100% by mass of CNTs, thereby improving the cycle characteristics of secondary batteries. The carbon purity of the CNTs can be determined by the method described in the examples using an ICP emission spectrometer.

[0038] CNTs may be pulverized CNTs. Pulverization is a process that pulverizes CNTs without substantially involving any liquid substance, and is also called dry pulverization. Pulverization mainly has the effect of reducing the size of the secondary particles of CNTs, thereby improving the dispersibility of CNTs. Dry pulverization equipment includes dry attritors, ball mills, vibratory mills, bead mills, jet mills, and hammer mills, and the physical properties of CNTs can be controlled by optimizing the pulverization conditions. When using pulverization equipment, the pulverization process can be batch, pass, or circulating, but the pass or circulating method is preferred, and the circulating method is more preferred, due to the ease of controlling the physical properties of CNTs. The batch method is a method in which the process is carried out using only the dispersion device itself, without using piping, etc. The pass method is a method in which the pulverization device is equipped with a tank that supplies CNTs via piping and a tank that receives CNTs, and the CNTs pass through the pulverization device. The circulating method is a method in which the CNTs that have passed through the dispersion device are returned to the CNT supply tank and processed while being circulated. In both cases, the longer the processing time, the more the crushing process progresses. Therefore, it is sufficient to pass the material through or recirculate it until the desired state is reached, and the processing volume can be increased by changing the size of the tank or the processing time. As for the grinding equipment, grinders commonly used for grinding pigments can be used. Examples include bead mills such as the "Dynamic Mill" from Nippon Coke Industries Co., Ltd. and the "Drystar" from Ajisawa Finetech Co., Ltd., dry jet mills such as the "NanoJetmizer" from Aisin Nanotechnologies Corporation, the "Single Track Jet Mill" from Seishin Enterprise Co., Ltd., the "Spiral Jet Mill" and "Counter Jet Mill" from Hosokawa Micron Corporation, and hammer mills such as the "ACM Pulperizer" from Hosokawa Micron Corporation, the "Turbo Mill" from Freund Turbo Co., Ltd., and the "Drystr" from Sugino Machine Co., Ltd.

[0039] CNTs can be manufactured using any method. CNTs can generally be manufactured by laser ablation, arc discharge, FCCVD, thermal CVD, plasma CVD, and combustion, but are not limited to these methods.

[0040] The carbon nanotubes (CNTs) may be surface-treated CNTs. Alternatively, the CNTs may be CNT derivatives to which functional groups, such as carboxyl groups, have been added. Furthermore, CNTs containing organic compounds, metal atoms, or substances such as fullerenes can also be used.

[0041] <Dispersant> The carbon nanotube dispersion composition of this embodiment includes a dispersant. The dispersant has the function of dispersing and stabilizing CNTs in the dispersion composition, and other dispersants may be used in combination to the extent that they do not inhibit the effect. Although not particularly limited, it can be one or more selected from surfactants (anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants) and resin-type dispersants.

[0042] When selecting an anionic surfactant, the type is not particularly limited. Specifically, examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfons, alkylnaphthalene sulfons, dialkyl sulfons, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfons, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. Furthermore, specifically, examples include, but are not limited to, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salts of β-naphthalene sulfonic acid formalin condensates. The anionic surfactant is preferably a polycarboxylate or naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0043] Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specifically, these include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyl dioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride. Examples of amphoteric surfactants include, but are not limited to, aminocarboxylate salts.

[0044] Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

[0045] The selected surfactant is not limited to a single surfactant. Therefore, it is possible to use two or more surfactants in combination. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. In this case, the amount blended should preferably be an amount suitable for each surfactant component. A combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate salt or a naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0046] Examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile polymers. Methylcellulose, ethylcellulose, carboxymethylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile polymers are particularly preferred.

[0047] Polyacrylonitrile polymers are polymers having nitrile group-containing structural units, and may be copolymers having nitrile group-containing structural units and structural units other than nitrile group-containing structural units. When the polyacrylonitrile polymer is a copolymer, the content of nitrile group-containing structural units is preferably 15% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and even more preferably 25% by mass or more and 50% by mass or less. Examples of structural units other than nitrile group-containing structural units, based on the total structural units contained in the copolymer, include alkylene structural units, amide group-containing structural units, carboxyl group-containing structural units, etc. The polyacrylonitrile polymer preferably includes a copolymer having alkylene structural units in a content of 50% by mass or more and 75% by mass or less, and nitrile group-containing structural units in a content of 25% by mass or more and 50% by mass or less.

[0048] The weight-average molecular weight (Mw) of the resin-type dispersant is preferably 5,000 to 500,000, preferably 10,000 to 300,000, and more preferably 10,000 to 100,000. Using a dispersant with an appropriate weight-average molecular weight (Mw) improves adsorption to carbon nanotubes and further improves the stability of the carbon nanotube dispersion composition. Furthermore, if a dispersant exceeding the above range is used, the viscosity of the carbon nanotube dispersion composition increases, and the dispersion efficiency may decrease when using a disperser through which the composition to be dispersed passes through narrow channels, such as a nozzle-type or valve-type high-pressure homogenizer. Here, the weight-average molecular weight (Mw) of the resin-type dispersant can be measured using gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector.

[0049] <Inorganic bases, inorganic metal salts> The CNT dispersion composition may contain an inorganic base and / or an inorganic metal salt in addition to the dispersant. The inorganic base and inorganic metal salt are preferably compounds having at least one of an alkali metal and an alkaline earth metal, and more specifically, examples of alkali metals and alkaline earth metals include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates. Among these, alkali metals and alkaline earth metals are preferred because they can easily supply cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

[0050] <acid> The CNT dispersion composition may contain an acid in addition to the dispersant. Adding an acid can change the charge state and the balance between hydrophilic and hydrophobic parts in the dispersion system, which may improve dispersibility. The type of acid is not particularly limited, and one type or a combination of several may be used. The acid may be, for example, an organic acid or inorganic acid with 6 or fewer carbon atoms. Examples include oxalic acid, lactic acid, citric acid, acetic acid, malonic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, and phosphoric acid. If the active material contained in the secondary battery electrode composition described later is, for example, a lithium-containing negative electrode active material and is basic, the dispersibility of the carbon nanotube dispersion composition may be disrupted and it may thicken. However, if an acid is included in addition to the dispersant, the pH change during the manufacture of the electrode composition can be mitigated, and the rapid thickening of the secondary battery electrode composition can be suppressed. Therefore, the storage stability of the secondary battery electrode composition is excellent, coating unevenness of electrodes using the secondary battery electrode composition can be suppressed, and the quality of the secondary battery can be easily stabilized.

[0051] <Solvent> The CNT dispersion composition of this embodiment contains an amide-based polar solvent. The content of the amide-based polar solvent may be 50% by mass or more, more than 50% by mass, 75% by mass or more, or 90% by mass or more, based on 100% by mass of the solvent, preferably 95% by mass or more, more preferably 98% by mass or more, and may be substantially a single solvent of the amide-based polar solvent. The water content in the solvent containing the amide-based polar solvent is preferably 100 ppm to 1500 ppm, and more preferably 100 ppm to 1000 ppm. When the water content is within this range, alkali metals encapsulated in the carbon nanotubes may dissolve in the carbon nanotube dispersion composition, resulting in good dispersion stability of the carbon nanotube dispersion composition.

[0052] [Amide-based polar solvents] Examples of amide-based polar solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. Among these, it is more preferable to include at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0053] <Antifoaming agent> The CNT dispersion composition may further contain an antifoaming agent. Any commercially available antifoaming agent, such as a wetting agent or other agent with antifoaming properties, can be used, and one type or a combination of several types may be used.

[0054] <Optional ingredients> The CNT dispersion composition may optionally contain other additives such as wetting agents, pH adjusters, wetting and penetrating agents, leveling agents, and other conductive materials other than CNTs, as long as they do not hinder the objectives of the present invention. These optional components can be added at any time, such as before, during, or after the preparation of the CNT dispersion composition, or in combination thereof.

[0055] <Method for producing CNT dispersion composition> A CNT dispersion composition can be produced, for example, by subjecting CNTs to a dispersion treatment in an amide-based polar solvent. The raw material CNTs may be added once or in multiple portions at any timing during the dispersion treatment. The dispersion method for carrying out such treatment is not particularly limited.

[0056] In the present invention, it is important to disintegrate CNT aggregates firmly bound by interactions such as van der Waals force into an optimal size, and for this purpose, it is preferable to perform dispersion by applying a strong shearing force under higher pressure conditions using an apparatus such as a high-pressure homogenizer. However, if the shearing force is excessive, all CNT aggregates are disintegrated into individual CNT units; although the electrical conductivity of the electrode is improved, the rigidity derived from the aggregation and twisting of CNT aggregates is impaired, and thus durability such as electrode strength cannot be improved.

[0057] Furthermore, the CNTs used in the embodiment of the present invention may be in a form obtained by cutting a sheet-shaped raw material. In the case of sheet-shaped CNTs, breaking via impact force from bead dispersion or shearing force from plastomill dispersion is also effective for rapidly finishing cut or pulverized CNTs into a fiber length of about several micrometers. The cutting method is not particularly limited, and for example, scissors may be used.

[0058] As the dispersion device, a disperser commonly used for pigment dispersion, etc., can be used. For example, either a medialess disperser or a media-type disperser may be used. Examples of medialess dispersers include mixers such as dispersers, homomixers, and planetary mixers; homogenizers (such as Branson's Advanced Digital Sonifer®, MODEL 450DA, M-Technic's "Clearmix", PRIMIX's "Filmix", Silverson's "Abramix", etc.); paint conditioners (Red Devil), paint shakers (Paint Mixer Fast & Fluid's "SO400"), colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"), and cone mills (such as IKA's "Cone Mill MKO"). Examples of media-type dispersers include ball mills, sand mills (such as Shinmaru Enterprises' "Dino Mill"), attritors, pearl mills (such as Eirich's "DCP Mill"), ball mills, bead mills (Ashizawa Finetech's Mugen Flow®), and media-type paint conditioners. Furthermore, examples include high-pressure homogenizers (such as Genus's "Genus PY", Sugino Machine's "Starburst", and Nanomizer's "Nanomizer"), media-less dispersers such as M-Technique's "CREA SS-5" and Nara Machinery's "MICROS", and other roll mills. Dispersers are not limited to these. There are no particular restrictions on the disperser, but for example, it is preferable to use a high-pressure homogenizer from the viewpoint of adjusting the fiber length of the CNTs in the CNT dispersion composition to a preferred range, a high-shear mixer from the viewpoint of promoting wetting of the CNTs and breaking down coarse particles and agglomerations, and a media-type disperser such as a bead mill from the viewpoint of crushing agglomerated and solidified particles. Furthermore, it is more preferable to select and combine multiple of the above dispersers for dispersion, and the order of the dispersers can be changed arbitrarily. The pressure when using a high-pressure homogenizer is not particularly limited, but for example, it is preferably 30 to 150 MPa, and more preferably 60 to 150 MPa.

[0059] Dispersion methods using a dispersion device include batch dispersion, pass dispersion, and circulating dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method of dispersion using only the dispersion device itself, without the use of piping. Because it is easy to handle, it is preferable for small-scale production. Pass dispersion is a dispersion method in which the dispersion device is equipped with a tank to supply the liquid to be dispersed via piping and a tank to receive the liquid to be dispersed, and the liquid is dispersed by passing it through the dispersion device. Circulating dispersion is a method in which the liquid to be dispersed, after passing through the dispersion device, is returned to the tank to supply the liquid and dispersed while being circulated. In all cases, dispersion progresses as the processing time increases, so it is sufficient to repeat the pass or circulation until the desired dispersion state is achieved, and the processing volume can be increased by changing the size of the tanks or the processing time. Pass dispersion is preferable to circulating dispersion because it is easier to achieve a uniform dispersion state. Circulating dispersion is preferable to pass dispersion because the work and manufacturing equipment are simpler. In the dispersion process, the disintegration of aggregated particles, the unraveling of CNTs, wetting, stabilization, etc., proceed sequentially or simultaneously. Since the final dispersion state differs depending on how these processes proceed, it is preferable to control the dispersion state in each dispersion process by using various evaluation methods. For example, this can be controlled by the method described in the examples below.

[0060] The CNT dispersion composition of this embodiment may contain iron particles or dissolved iron ions originating from the manufacturing processes of the CNTs, dispersant, and other materials, and iron particles or iron ions may also be introduced during the manufacturing process of the CNT dispersion composition. Since the presence of iron inside a secondary battery poses a risk of short-circuiting and ignition, removing iron contained in the CNT dispersion composition is extremely important from a safety standpoint when applying it to automotive applications. In the manufacturing process of the CNT dispersion composition, the iron content in the CNT dispersion composition can be easily reduced by using CNTs produced by a manufacturing method that does not use the aforementioned metal catalyst as a nucleus, or CNTs obtained by a purification method. Alternatively, it is preferable to include a step to remove contaminants such as iron particles (foreign matter removal step) at any arbitrary timing. From the viewpoint of efficiency, it is preferable to perform the foreign matter removal step in the middle of the dispersion process of the CNT dispersion composition and / or at the end of the dispersion process. The foreign matter removal step may be performed multiple times.

[0061] In the foreign matter removal process, the method for removing iron particles from the CNT dispersion composition is not particularly limited, and examples include removal by filtration using a filter, removal by centrifugal separation, and removal by magnetic force. Among these, since iron particles are magnetic, removal by magnetic force is preferred, and a method combining the removal by magnetic force and the removal by filtration using a filter is more preferred.

[0062] The method of removing iron particles by magnetism is not particularly limited as long as it can remove iron particles, but from the viewpoint of productivity and removal efficiency, it is preferable to remove them by placing a magnetic filter in the manufacturing line of the CNT dispersion composition and passing the CNT dispersion composition through it. The step of removing iron particles from the CNT dispersion composition by placing a magnetic filter and passing the CNT dispersion composition through it is preferably carried out by passing the composition through a magnetic filter having a magnetic flux density of 1,000 gauss or more. Since the removal efficiency of iron particles decreases if the magnetic flux density is low, it is preferably 5,000 gauss or more, more preferably 10,000 gauss or more, and most preferably 12,000 gauss or more, considering the removal of weakly magnetic iron particles such as stainless steel.

[0063] Since iron particles may pass through the magnetic filter depending on the filtration flow rate, it is preferable to include a step upstream of the magnetic filter in the manufacturing line to remove contaminants such as iron particles by filtration using a cartridge filter or similar filter. Furthermore, while passing the CNT dispersion composition through the magnetic filter only once is effective, it is more preferable to pass it through two or more times using a circulating system. Passing the CNT dispersion composition through the magnetic filter two or more times improves the efficiency of iron particle removal.

[0064] When a magnetic filter is placed in the manufacturing line for a CNT dispersion composition, there are no particular restrictions on where the magnetic filter is placed. However, it is preferable to place it before the filtration filter if there is a filtration step using a filtration filter immediately before filling the CNT dispersion composition into containers. By placing it in this way, if iron detaches from the magnetic filter, the iron particles will be captured by the filtration filter, preventing contamination of the product.

[0065] The amount of CNTs in the CNT dispersion composition of this embodiment is preferably 0.1 parts by mass or more, more preferably 0.2 to 20 parts by mass, even more preferably 0.3 to 10 parts by mass, and particularly preferably 0.3 to 3 parts by mass, per 100 parts by mass of the CNT dispersion composition. By setting the amount within the above range, the dispersibility of the CNT dispersion composition can be maintained more effectively. Furthermore, because the dispersibility of the CNT dispersion composition is maintained, when an electrode film is fabricated using the secondary battery electrode composition, the CNTs maintain linearity in the electrode film, the number of active material particles in contact with the CNTs increases, and the performance of the secondary battery can be further improved.

[0066] The amount of dispersant in the CNT dispersion composition of this embodiment is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 60 parts by mass or more, per 100 parts by mass of CNT. Furthermore, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less. When the amount is within the above range, the dispersibility of the CNT dispersion composition is good, and the initial viscosity and stability over time tend to be good. If the conductivity and strength of the electrode film described later are considered more important than the ease of handling such as the initial viscosity and stability over time of the CNT in the CNT dispersion composition of this embodiment, the amount of dispersant in the CNT dispersion composition of this embodiment may be adjusted appropriately according to the amount of CNT added to the electrode film, and may be 10 parts by mass or more and less than 100 parts by mass, 100 parts by mass or more and less than 200 parts by mass, or 200 parts by mass or more and less than 300 parts by mass, per 100 parts by mass of CNT.

[0067] If the CNT dispersion composition contains components other than CNTs, a dispersant, and an amide-based polar solvent, the amount of these other components in the CNT dispersion composition may be 0.1 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 3 parts by mass per 100 parts by mass of the CNT dispersion composition.

[0068] When a basic compound is contained in the CNT dispersion composition, the amount of the basic compound in the CNT dispersion composition may be 0.01 to 1 part by mass, 0.02 to 0.5 parts by mass, or 0.04 to 0.1 parts by mass relative to 100 parts by mass of the CNT dispersion composition. When a basic compound is contained in the CNT dispersion composition, the amount of the basic compound in the CNT dispersion composition may be 1 to 20 parts by mass, 2 to 10 parts by mass, or 4 to 8 parts by mass relative to 100 parts by mass of the dispersant.

[0069] When an antifoaming agent is contained in the CNT dispersion composition, the amount of the antifoaming agent in the CNT dispersion composition may be 0.01 to 1 part by mass, 0.02 to 0.5 parts by mass, or 0.04 to 0.1 parts by mass relative to 100 parts by mass of the CNT dispersion composition.

[0070] <Physical Properties of CNT Dispersion Composition> [Iron Content] The iron content of the CNT dispersion composition can be calculated by the method described in the Examples using an ICP optical emission spectrometer after drying the CNT dispersion composition to remove the amide polar solvent. The iron content detected by ICP analysis includes iron particles and dissolved iron ions. That is, the iron content of the CNT dispersion composition that has undergone the foreign matter removal step includes iron particles that have not been completely removed and dissolved iron ions.

[0071] The iron content of the CNT dispersion composition is preferably 50 ppm or less, and more preferably 30 ppm or less, relative to 100 mass% of the CNT dispersion composition. By setting the iron content of the CNT dispersion composition within the above range, side reactions caused by decomposition of the electrolyte solution in the secondary battery electrode film are less likely to occur, and a secondary battery with more excellent cycle characteristics can be obtained.

[0072] [20-degree Specular Gloss] The specular gloss of the CNT dispersion composition at 20 degrees Celsius is preferably 50 to 170, more preferably 70 or higher, and even more preferably 100 or higher. By setting it within the above range, a CNT dispersion composition with an appropriate dispersion state can be obtained. If it is below the above range, aggregated CNTs will be present, and if it is above the above range, a large number of finely cut CNTs will be generated, which may make it difficult to form an efficient conductive network. The specular gloss of the CNT dispersion composition at 20 degrees is measured at 20 degrees using a coating obtained by coating a PET (polyethylene terephthalate) film substrate and baking it dry (i.e., the intensity of reflected light at 20 degrees relative to the angle of incidence). When the dispersant content in the CNT dispersion composition is high, the 60-degree specular gloss measured according to Method 3 of JIS Standard Z8741:1997 may show high gloss, potentially reducing measurement accuracy. Therefore, it is preferable to measure the 20-degree specular gloss according to Method 5 of JIS Standard Z8741:1997.

[0073] [Viscosity ratio (V1 / V2)] The CNT-dispersed composition was measured using a rheometer at a shear rate of 10s. -1 Viscosity (V1) at 25°C measured by [method / tool ​​name] and shear rate 100s -1 The viscosity ratio (V1 / V2) of the viscosity (V2) measured at 25°C is preferably 6.0 or more and less than 7.0, more preferably 5.0 or more and less than 6.0, and even more preferably 2.0 or more and less than 5.0. Shear rate 10s -1 and 100s -1By determining the ratio of shear viscosities (V1 / V2) in the given state, the degree of structural viscosity originating from fibrous CNTs can be determined. When the fiber length of the CNTs is large, the viscosity ratio (V1 / V2) increases regardless of dispersibility. Within the above range, the fiber length of the CNTs is within an appropriate range, allowing for the efficient formation of a conductive network with a small amount of material, thereby reducing the amount of CNTs contained in the positive and negative electrodes of secondary batteries. In the case of CNTs with a length such that the viscosity ratio (V1 / V2) is 2.0 or higher, the CNTs form a network state, resulting in an improvement in the strength of the electrode film. Furthermore, using CNTs with a large fiber length can suppress the increase in the surface area of ​​the electrode, suppressing the decomposition of the electrolyte during high-temperature storage in secondary batteries and improving cycle characteristics. In addition, in the case of CNTs with a length such that the viscosity ratio (V1 / V2) is less than 7.0, the CNTs are broken down to an appropriate length, increasing the number of effective CNTs contained in the electrode film and allowing for the efficient formation of a conductive network with a small amount of material.

[0074] The viscosity of the CNT dispersion composition was determined by standing the CNT dispersion composition in a constant temperature bath at 25°C for at least one hour, then thoroughly stirring the CNT dispersion composition, and measuring it using a rheometer with a 25 mm diameter, 2° cone at 25°C and a shear rate of 10 s. -1 and 100s -1 The shear viscosity can be measured and determined. If the measured value includes decimal places, it should be rounded to an integer according to Rule B of JIS Z 8401:1999.

[0075] [Complex modulus of elasticity and phase angle] The dispersibility of a CNT dispersion composition can be evaluated by its complex modulus and phase angle, which are determined by dynamic viscoelasticity. The complex modulus indicates the hardness of the CNT dispersion composition; it decreases as the CNT dispersion is good and the viscosity of the CNT dispersion composition decreases. However, if the fiber length of the CNTs is large, even if the CNTs are uniformly and stably unraveled in the solution, the structural viscosity of the CNTs themselves may result in a high value for the complex modulus. The phase angle represents the phase shift of the stress wave when the strain applied to the CNT dispersion composition is considered as a sine wave, and thus indicates the flowability of the dispersion composition. The complex modulus of elasticity of the CNT dispersion composition is preferably 20 Pa or less, more preferably 10 Pa or less, and even more preferably 2 Pa or less. It is also preferably 0.001 Pa or more, more preferably 0.05 Pa or more, and even more preferably 0.1 Pa or more. The phase angle of the CNT dispersion composition is preferably 10° or more, more preferably 15° or more, and even more preferably 20° or more. It is also preferably 60° or less, more preferably 50° or less, and even more preferably 40° or less. When the phase angle and complex modulus of elasticity of the CNT dispersion composition are within the above ranges, the dispersibility of the CNTs is good, and an electrode film with excellent conductivity and strength is easily obtained. In this embodiment, the phase angle of the CNT dispersion is preferably 5° or more, more preferably 10° or more, and even more preferably 20° or more. When the phase angle of the CNT dispersion is within the above range, the dispersibility of the CNTs is good, and the storage characteristics of the battery tend to be good. The complex modulus and phase angle of the CNT dispersion composition are determined by dynamic viscoelasticity measurement using a rheometer with a 25 mm diameter, 2° cone, at 25°C and a frequency of 1 Hz, with strains ranging from 0.01% to 500%. Specifically, for example, using a rheometer (Anton Paar's "MCR 102e"), dynamic viscoelasticity measurements can be performed in the strain range of 0.01% to 500% with a cone plate of 2° / diameter of 25 mm, a measurement temperature of 25°C, and a frequency of 1 Hz, and the value at 1% strain can be used for the measurement.

[0076] ≪Composition for secondary battery electrodes≫ The secondary battery electrode composition of this embodiment comprises at least a CNT dispersion composition and an active material. That is, the secondary battery electrode composition comprises at least CNTs, a dispersant, an amide-based polar solvent, and an active material. It is also preferable to include a binder resin.

[0077] A binder resin is a resin used to bond substances together. There are no particular restrictions on the binder resin, but examples include polymers or copolymers containing fluororesins, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, etc. as constituent units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; cellulose resins such as carboxymethylcellulose; rubbers such as styrene-butadiene rubber; and conductive resins such as polyaniline and polyacetylene. Among these, the use of styrene-butadiene rubber or fluororesins as binder resins is preferred from the viewpoint of electrochemical oxidation-reduction resistance.

[0078] As for the fluororesin, polyvinylidene fluoride, polyvinyl fluoride, and polytetrafluoroethylene are preferred, for example.

[0079] Active material refers to the material that forms the basis of a battery reaction. Active material can be divided into positive electrode active material and negative electrode active material based on its electromotive force. In this specification, positive electrode active material and negative electrode active material may sometimes be simply referred to as "active material." Active material refers to the material that forms the basis of a battery reaction. Active material can be divided into positive electrode active material and negative electrode active material based on its electromotive force.

[0080] The positive electrode active material is not particularly limited, but metal compounds such as metal oxides and metal sulfides that can be doped or intercalated with lithium ions, and conductive polymers can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, MnO, V2O5, V6O 13transition metal oxide powders such as TiO₂, composite oxide powders of lithium and transition metals such as lithium nickelate with layered structure, lithium cobaltate, lithium manganate, lithium manganate with spinel structure, lithium iron phosphate-based materials which are phosphate compounds with olivine structure, and transition metal sulfide powders such as TiS₂ and FeS. In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Further, a mixture of the above inorganic compounds and organic compounds may be used.

[0081] The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, alloys thereof such as tin alloys, silicon alloys, lead alloys and other alloy systems, Li X Fe₂O₃, Li X Fe₃O₄, Li X WO₂ (where x is a number satisfying 0 < x < 1), metal oxide systems such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymer systems such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and carbon-based materials such as carbon black, mesophase carbon black, resin-fired carbon materials, vapor-grown carbon fibers, and carbon fibers. One of these negative electrode active materials may be used alone, or two or more thereof may be used in combination. Among these, as the negative electrode active material, it is preferable to use an alloy-based negative electrode active material, and a silicon alloy is particularly preferable. Although alloy-based negative electrode active materials have large theoretical capacity, they undergo large volume changes during charge and discharge of secondary batteries. However, by combining with the carbon nanotube dispersion composition of the present embodiment, deterioration of the electrode accompanying the volume change of the alloy-based active material can be suppressed, and the cycle characteristics of the secondary battery can be improved.

[0082] The BET specific surface area of the negative electrode active material is 0.1 m 2 / g or more and 30 m 2 / g or less, more preferably 1.0 m 2 / g or more and 20 m 2 / g or less, and even more preferably 5.0 m 2 / g or more 15m 2 It is even more preferable that the amount is less than or equal to / g. The BET specific surface area can be measured by the BET method according to JIS Z 8830:2013.

[0083] Cumulative particle size D of the negative electrode active material 10 The particle size is preferably 0.05 μm or more and 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less. Cumulative particle size D 50 The particle size is preferably 0.5 μm to 5 μm, and more preferably 1 μm to 3 μm. Cumulative particle size D 90 The particle size is preferably 3 μm to 10 μm, and more preferably 3.0 to 5.0 μm. The cumulative particle size of the active material can be measured by the particle size analysis - laser diffraction and scattering method of JIS Z 8825:2013. As a measuring device, for example, a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) can be used, and the light intensity of the sample can be adjusted to 15 to 20% for measurement. When the cumulative particle size of the active material is within the above range, even if the negative electrode active material is an alloy system with a large volume change during charging and discharging of the secondary battery, the carbon nanotube dispersion composition of this embodiment maintains a strong conductive network, resulting in good cycle characteristics of the secondary battery.

[0084] To obtain a secondary battery electrode composition, it is preferable to add an active material to the CNT dispersion composition and then perform a dispersion process. The dispersion apparatus used for this process is not particularly limited. The secondary battery electrode composition can be obtained using the dispersion apparatus described above for the CNT dispersion composition. In the case of a secondary battery electrode composition containing a binder resin, the active material, binder resin, and a solvent may be added and mixed, and then the CNT dispersion composition may be added and dispersed. Alternatively, the CNT dispersion resin composition may be made by adding a binder resin to the CNT dispersion composition, and then the active material may be added to make a secondary battery electrode composition.

[0085] In viscoelastic measurements of secondary battery electrode compositions, when the shear strain is measured in the range of 0.01% to 500%, the difference between the storage modulus at 1% shear strain and the storage modulus at 100% shear strain is preferably 40 Pa or more and less than 50 Pa, more preferably 20 Pa or more and less than 40 Pa, and even more preferably less than 20 Pa. It is also preferably 1 Pa or more, and even more preferably 2 Pa or more. A secondary battery electrode composition with a large difference in storage modulus indicates that the hardness changes greatly depending on the shear force, i.e., it has a hard and brittle structure. On the other hand, a secondary battery electrode composition with a small difference in storage modulus indicates that the internal structure is less prone to breakage and is more stable. When the difference in storage modulus is within the above range, uneven coating during electrode film fabrication is less likely to occur, improving productivity, and the peel strength of the electrode and the uniformity of the coating film are improved, resulting in a secondary battery with stable quality.

[0086] The amount of active material in the secondary battery electrode composition is preferably 20 to 85 parts by mass, and particularly preferably 40 to 85 parts by mass, based on 100 parts by mass of the secondary battery electrode composition.

[0087] The amount of CNTs in the secondary battery electrode composition is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, and even more preferably 0.1 to 1 part by mass, based on 100 parts by mass of active material.

[0088] The amount of dispersant in the secondary battery electrode composition is preferably 10 to 300 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 40 to 120 parts by mass, based on 100 parts by mass of CNT.

[0089] When the secondary battery electrode composition contains a binder resin, the amount of binder resin in the secondary battery electrode composition is preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, and particularly preferably 1 to 5 parts by mass, based on 100 parts by mass of the active material.

[0090] The solid content concentration of the secondary battery electrode composition is preferably 30% to 90% by mass, and more preferably 40% to 85% by mass, based on 100% by mass of the secondary battery electrode composition.

[0091] ≪Electrode, electrode film≫ The electrode comprises a current collector and an electrode film formed from a secondary battery electrode composition. The electrode film is a coated film of the secondary battery electrode composition, for example, a coated film formed by coating the current collector with the secondary battery electrode composition and drying it to form a secondary battery electrode composition layer.

[0092] The material and shape of the current collector are not particularly limited, and can be appropriately selected to suit various types of secondary batteries. For example, the material of the current collector can be a metal or alloy such as aluminum, copper, nickel, titanium, or stainless steel. In terms of shape, a flat foil is generally used, but current collectors with roughened surfaces, perforated foils, and mesh-shaped current collectors can also be used.

[0093] There are no particular limitations on the method for coating a secondary battery electrode composition onto a current collector to form an electrode film, and known methods can be used. Specifically, die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, or electrostatic coating methods can be used, and drying methods such as standing drying, forced-air drying, hot-air drying, infrared heating, and far-infrared heating can be used, but are not limited to these.

[0094] Furthermore, rolling may be performed after coating using a flatbed press or calender roll. The thickness of the electrode film (composition layer for secondary battery electrodes) is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0095] ≪Secondary battery≫ The secondary battery of this embodiment comprises an electrode having an electrode film and an electrolyte. The secondary battery comprises a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode may have the aforementioned electrode film. In the carbon nanotube dispersion composition of this embodiment, carbon nanotubes exist as bundled aggregates within the electrodes of the secondary battery, contributing to good conductivity and improved electrode strength. As a result, the active material is utilized homogeneously during charging and discharging, and electrode degradation due to volume changes can be suppressed, thus improving the cycle characteristics of the secondary battery.

[0096] As the positive electrode, an electrode film can be used that has been prepared by coating a current collector with a composition for secondary battery electrodes containing a positive electrode active material and drying it.

[0097] As the negative electrode, an electrode film can be used that has been prepared by coating a secondary battery electrode composition containing a negative electrode active material onto a current collector and drying it.

[0098] Various conventionally known electrolytes that allow ion movement can be used. For example, lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is a phenyl group) can be used, but are not limited to these, and sodium salts can also be used. It is preferable to dissolve the electrolyte in a non-aqueous solvent and use it as an electrolyte solution.

[0099] Non-aqueous solvents are not particularly limited, but examples include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glycines such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used individually or in combination of two or more.

[0100] The secondary battery of this embodiment preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those treated to be hydrophilic, but are not limited to these.

[0101] The structure of the secondary battery in this embodiment is not particularly limited, but it typically consists of a positive electrode, a negative electrode, and a separator provided as needed, and can be in various shapes depending on the intended use, such as paper type, cylindrical type, button type, or laminated type.

[0102] The secondary battery of this embodiment is not particularly limited in its use, and can be used specifically as a power source for consumer electronics such as mobile phones, laptop computers, and digital cameras; as an emergency power source for hospitals, factories, and buildings; and for vehicles such as hybrid cars, plug-in hybrid cars, electric cars, electric assist bicycles, and railway vehicles. The secondary battery, for example, recovers regenerative energy from the power of a vehicle.

[0103] Among these, since the secondary battery has high charge-discharge performance and excellent durability, it can be suitably used in vehicles, and a vehicle with high safety and expected improvement in fuel efficiency can be obtained. Furthermore, excellent effects can be exhibited even in vehicle applications where charging and discharging with large current is desired.

[0104] The mounting position of the secondary battery in the vehicle of the present embodiment is not particularly limited. For example, when the secondary battery is mounted on an automobile, the secondary battery can be mounted in the engine room of the vehicle, at the rear of the vehicle body, or under a seat.

Examples

[0105] Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples as long as it does not exceed the gist thereof. Unless otherwise specified, "part" means "part by mass" and "%" means "% by mass".

[0106] <<Physical Property Measurement and Evaluation Methods>> Measurement and evaluation of physical properties of CNTs, CNT dispersion compositions, compositions for secondary battery electrodes, electrode films, and secondary batteries were carried out by the following methods.

[0107] <Average Outer Diameter of CNT Unit Bodies> The CNT dispersion composition was diluted 50 to 200 times with methanol, dropped onto a microgrid (Nissin EM Holey Microgrid U1003), air-dried, and then observed using a transmission electron microscope (JEM2800, manufactured by JEOL Ltd.). Observation was performed at an acceleration voltage of 200 kV and a magnification of 1,000,000 times. A plurality of photographs containing 10 or more CNT aggregates in the field of view were taken, the outer diameters of 50 arbitrarily extracted CNTs were measured, and the average outer diameter (nm) of CNT unit bodies was obtained from the arithmetic average value, and the standard deviation value was taken as the standard deviation (nm) of the outer diameter of CNT unit bodies.

[0108] <Number of Layers of CNT Unit Bodies> CNT was placed in the recess of a glass sample plate (outer diameter 5.0 cm × 3.5 cm, thickness 3 mm, sample portion 2.0 cm × 2.0 cm, thickness 2 mm), and flattened using a slide glass. Thereafter, the sample for powder X-ray diffraction analysis of CNT was placed in a fully automatic multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation), and analysis was performed by operating from 15° to 35°. Sampling was performed every 0.01°, and the scan speed was set to 1° / min. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα radiation. The number of layers per CNT unit was calculated by the following formula (1) using the average interplanar spacing (d002) of the peak obtained at a diffraction angle 2θ=25°±2° and the crystallite size (Lc002). Formula (1): Number of layers = Crystallite size (Lc002) / Average interplanar spacing (d002)

[0109] <CNT aggregate (Bundled CNTs) average outer diameter> The CNT dispersion composition was diluted 50 to 200 times with methanol, dropped onto a microgrid (Nissin EM Holey Microgrid U1003), air-dried, and then observed using a transmission electron microscope (JEM2800, manufactured by JEOL Ltd.). For observation, at an acceleration voltage of 200 kV and a magnification of 500,000 times, a plurality of photographs containing 10 or more CNT aggregates in the field of view were taken, the outer diameters of 50 arbitrarily extracted CNT aggregates were measured, and the arithmetic mean value was used to obtain the average outer diameter (nm) of the CNT aggregates, and the standard deviation value was taken as the standard deviation (nm) of the outer diameter of the CNT aggregates. The CNTs contained in the CNT dispersion compositions (D1-1 to D1-23) are CNT aggregates in which a plurality of CNTs have orientation, and two or more CNT units are bundled in parallel through interaction. The CNTs contained in the CNT dispersion compositions (D1-24 to D1-25) were disintegrated into individual CNT units and were not CNT aggregates. Therefore, the average outer diameter and standard deviation of CNT aggregates in Table 3 are indicated as "-".

[0110] <Average fiber length of CNTs in CNT dispersion composition> After diluting the CNT dispersion composition with an amide-based polar solvent such that the CNT concentration is 0.000001 mass% to 0.00001 mass%, several drops of the CNT dispersion composition were dropped onto a mica substrate. Thereafter, the substrate was dried on a hot plate at 140°C to prepare a substrate for observing CNT fiber lengths. The prepared substrate was photographed using a scanning electron microscope (SEM), the obtained SEM image was analyzed using the image analysis software "ImageJ" (an open-source image processing and analysis software developed by the National Institutes of Health, USA), the fiber lengths of 100 CNTs were measured, and the average fiber length of CNTs in the CNT dispersion composition was obtained by arithmetic mean. The criteria for determining the average fiber length of CNTs in the CNT dispersion composition are as follows: 1.0 µm or more and less than 3.5 µm: A; 0.8 µm or more and less than 1.0 µm: B; 3.5 µm or more and less than 5.0 µm: C; less than 0.8 µm or 5.0 µm or more: D.

[0111] <Image Observation of CNT> Image observation was performed by the method described below, and the state of CNT aggregates in powdered CNT was confirmed. Powdered CNT was diluted 50 to 200 times with a mixed solvent of acetone and MEK (acetone:MEK = 1:1), subjected to dispersion treatment using an ultrasonic disperser, then dropped onto a microgrid (Nisshin EM Holey Microgrid U1003) and air-dried. Using JEM2800 (a transmission electron microscope manufactured by JEOL Ltd.), 10 to 12 specimens were measured based on the scale bar for arbitrarily selected CNTs in a transmission electron image with an acceleration voltage of 200 kV and a magnification of 1,000,000 times, and the average value and standard deviation were calculated for all specimens.

[0112] <BET Specific Surface Area of CNT> After weighing 0.03 g of CNTs using an electronic balance (MSA225S100DI, manufactured by Sartorius), the CNTs were dried while being degassed at 110°C for 15 minutes. Thereafter, the BET specific surface area of the CNTs was measured using a fully automatic specific surface area analyzer (HM-model1208, manufactured by MOUNTECH Co., Ltd.). The BET specific surface area was measured in accordance with the BET method specified in JIS Z 8830:2013.

[0113] <G / D Ratio of CNT> CNT was placed in a Raman microscope (XploRA, manufactured by HORIBA, Ltd.), and measurement was performed using a laser wavelength of 532 nm. The measurement conditions were as follows: acquisition time of 60 seconds, 2 integrations, neutral density filter of 10%, objective lens magnification of 20×, confocal aperture of 500, slit width of 100 μm, and measurement wavelength ranging from 100 cm -1 −1 to 3,000 cm -1 −1. Carbon nanotubes for measurement were fractionated on a slide glass and flattened using a spatula. Among the obtained peaks, let G be the maximum peak intensity within the range of 1,560 cm -1 −1 to 1,600 cm -1 −1, and let D be the maximum peak intensity within the range of 1,310 cm -1 −1 to 1,350 cm -1 −1, and the G / D ratio was defined as the G / D ratio of the CNT.

[0114] <Volume Resistivity of CNT> Using a powder resistivity measurement apparatus (Loresta GP Powder Resistivity Measurement System MCP-PD-51, manufactured by Nitto Seiko Analytech Co., Ltd.), with a sample mass of 1.2 g, the volume resistivity [Ω·cm] of CNT powder was measured at a pressure that achieves a density of 1 g / cm 3 −3 using a powder probe unit (four-probe ring electrode, electrode interval: 5.0 mm, electrode radius: 1.0 mm, sample radius: 12.5 mm) with an applied voltage limiter set to 90 V.

[0115] <Iron Content of CNT> CNT powder was acid-decomposed using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract metals contained in the carbon nanotubes. Thereafter, analysis was performed using a multiplex ICP optical emission spectrometer (720-ES, manufactured by Agilent), the iron content contained in the extract was calculated, and this was taken as the iron content of the CNT powder.

[0116] <Iron Content of CNT Dispersion Composition> After the CNT dispersion composition was dried to solidness using a hot air oven, it was subjected to acid decomposition using a microwave sample pretreatment device (manufactured by Milestone General, ETHOS1) to extract metals contained in the carbon nanotubes. Thereafter, analysis was performed using a multiplex ICP optical emission spectrometer (manufactured by Agilant, 720-ES), and the iron content contained in the extract was calculated, which was taken as the iron content of the CNT dispersion composition.

[0117] <20-degree specular gloss of CNT dispersion composition> 1 mL of the CNT dispersion composition was dropped onto a PET (polyethylene terephthalate) film, coated at 2 cm / sec with a No. 7 bar coater, then baked and dried for 5 minutes in a 140°C hot air oven to prepare a coating film. Using a gloss meter (VG-7000, manufactured by Nippon Denshoku Industries Co., Ltd.), three locations within the coating film surface excluding the edges were randomly selected. Measurements were performed once each at 20° by the parallel light method in accordance with JIS Z8741:1997, and the average value was taken as the gloss of the CNT dispersion composition. The criteria for evaluating the gloss of the CNT dispersion composition are defined as: 100 or more and 170 or less: A, 70 or more and less than 100: B, 50 or more and less than 70: C, less than 50: D, 170 or more: E.

[0118] <Viscosity ratio of CNT dispersion composition> After allowing the CNT dispersion composition to stand in a constant temperature bath at 25°C for 1 hour or longer, the shear viscosity was measured using a rheometer (MCR302e, manufactured by Anton Paar) with a 25 mm diameter, 2° cone, at 25°C, at shear rates from 0.01 s -1 to 1,000 s -1 . From the viscosity (V1) at 25°C measured at a shear rate of 10 s -1 and the viscosity (V2) at 25°C measured at a shear rate of 100 s -1 , the viscosity ratio (V1 / V2) was obtained. The evaluation criteria for the viscosity ratio (V1 / V2) are defined as: 2.0 or more and less than 5.0: A, 5.0 or more and less than 6.0: B, 6.0 or more and 7.0 or less: C, less than 2.0 or more than 7.0: D.

[0119] <Complex modulus and phase angle of CNT dispersion composition> The complex modulus and phase angle of the CNT dispersion composition were measured after allowing the CNT dispersion composition to stand still in a thermostatic bath at 25°C for 1 hour or more, using a rheometer ("MCR 102e" manufactured by Anton Paar) with a cone plate of 2° / 25 mm diameter, a measurement temperature of 25°C, a frequency of 1 Hz, dynamic viscoelasticity measurement was performed within a strain rate range from 0.01% to 500%, and the value at a strain rate of 1% was used.

[0120] <Viscosity of CNT dispersion composition over time> After allowing the composition for a secondary battery electrode to stand still in a thermostatic bath at 40°C for 1 week, and then stand still in a thermostatic bath at 25°C for 3 hours or more, the viscosity measurement of the CNT dispersion composition was immediately performed using a B-type viscometer with a rotor rotation speed of 30 rpm. A No. 4 rotor was used. When the viscosity over time was less than 200 mPa·s, a No. 3 rotor was used. The lower the viscosity over time of the CNT dispersion composition, the more excellent the viscosity stability when the composition is used as a composition for a secondary battery electrode, coating unevenness can be suppressed, and a homogeneous electrode film and a secondary battery can be obtained. [Evaluation Criteria] The evaluation criteria for viscosity over time were defined as follows: less than 3,000 mPa·s: Excellent (◎), 3,000 mPa·s or more and less than 5,000 mPa·s: Good (〇), 5,000 mPa·s or more and less than 8,000 mPa·s: Fair (△), 8,000 mPa·s or more: Poor (×).

[0121] <Viscosity of composition for secondary battery electrode> After allowing the composition for a secondary battery electrode to stand still in a thermostatic bath at 25°C for 1 hour or more, shear viscosity measurement was performed using a rheometer (MCR302e, manufactured by Anton Paar) with a 25 mm diameter, 2° cone at 25°C and a shear rate of 0.01s ―1 to 1,000s -1 , and the result was evaluated. When the viscosity of the composition for a secondary battery electrode is within the following range, it can be considered that CNTs contained in the composition for a secondary battery electrode are uniformly dispersed, which is likely to improve the conductivity and strength of the electrode film. [Evaluation Criteria] The viscosity evaluation criteria for secondary battery electrode compositions were as follows: viscosity at a shear rate of 1 s⁻¹: Excellent (◎), 40,000 mPa·s or more and less than 60,000 mPa·s: Good (〇), 8,000 mPa·s or more and less than 15,000 mPa·s: Fair (△), less than 8,000 mPa·s or more and greater than 60,000 mPa·s: Unacceptable (×).

[0122] <Electrode strength of compositions for secondary battery electrodes> After allowing the secondary battery electrode composition to stand in a constant temperature bath at 25°C for more than one hour, dynamic viscoelasticity measurements were performed using a rheometer (MCR302e, manufactured by Anton Paar) with a 25 mm diameter, 2° cone at 25°C and a frequency of 1 Hz, in the range of shear strain from 0.01% to 500%. The electrode strength was evaluated by the storage modulus, which was determined by the difference between the storage modulus G' at 1% shear strain and 100% shear strain. The evaluation is performed in regions where strain is less likely to occur at a shear strain of 1% (e.g., during standing), and in regions where the liquid structure is more likely to strain due to increased force at a shear strain of 100% (e.g., during liquid transfer). For example, as shown in Figures 3 and 4, when CNTs are mixed without dispersion as in Example 2-6, the elastic modulus changes even with slight strain, making the internal structure prone to damage as a secondary battery electrode composition. Furthermore, the high viscoelasticity during standing and the tendency to gel during standing are thought to affect the unevenness of the electrode at the start of coating and the handling of the product. The smaller the value of the storage modulus, the less likely the electrode is to have unevenness and the less likely the internal structure is to break, and the better the electrode strength. [Evaluation Criteria] The evaluation criteria for electrode strength were as follows: difference in storage modulus less than 20 Pa: Excellent (◎), 20 Pa or more but less than 40 Pa: Good, 40 Pa or more but less than 50 Pa: Fair (△), 50 Pa or more: Poor.

[0123] <Evaluation of positive electrode conductivity> The composition for the positive electrode of a secondary battery was measured using an applicator, and the basis weight per unit area of ​​the electrode was 15 mg / cm². 2After coating the aluminum foil in this manner, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Subsequently, it was rolled using a roll press (manufactured by Sanku Metal Co., Ltd., 3t hydraulic roll press) to obtain a density of 1.6 g / cm³ for the secondary battery electrode composition layer. 3 A negative electrode was fabricated. Subsequently, the positive electrode was punched out to a size of 50 mm x 45 mm, and the volume resistivity and interfacial resistance of the secondary battery electrode composition layer were measured using an electrode resistance meter (electrode resistance measurement system RM2610, manufactured by HIOKI E.E. CORPORATION). The measurement conditions were set to "potential measurement + calculation" as the operating mode, "MEDIUM" as the measurement speed, and "AUTO" as the measurement range. The thickness of the secondary battery electrode composition layer and the thickness of the aluminum foil were input, and the volume resistivity of the aluminum foil, "2.7000E-06", was selected. The film thickness of the secondary battery electrode composition layer was measured using a film thickness gauge (Nikon Solutions Corporation, combination of digital micro head MH-15M (standard), measurement stand MS-5C, and counter TC-101), and the difference between the positive electrode film thickness and the aluminum foil film thickness was used. [Evaluation Criteria] The evaluation criteria for the conductivity of the positive electrode were as follows: Volume resistivity (Ω·cm) of the positive electrode: less than 0.08: Excellent (◎), 0.08 or more and less than 0.1: Good (〇), 0.1 or more and less than 0.12 (△), 0.12 or more: Unacceptable (×).

[0124] <Evaluation of the cycle characteristics of secondary batteries> The secondary battery was placed in a constant temperature room at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). Constant current constant voltage charging (cutoff current 1.25mA (0.025C)) was performed with a charging current of 25mA (0.5C) and a charging termination voltage of 4.2V, followed by constant current discharge at a discharge current of 50mA (1C) and a discharge termination voltage of 2.5V. This operation was repeated 25 times. Note that 1C was defined as the current value required to discharge the theoretical capacity of the positive electrode in one hour. The cycle characteristics were calculated at 25°C using the ratio of the maximum 1C charge capacity among cycles 3 to 25 to the charge capacity of cycle 25, as shown in Equation 1 below. (Equation 1) Cycle characteristics = 1C charging capacity at the 25th cycle / Maximum 1C charging capacity between cycles 3 and 25 × 100% (%) [Evaluation Criteria] For cycle characteristic evaluation, cycle characteristics of 98% or higher are rated as Excellent (◎), and 97% or higher and less than 98% are rated as Good (〇), 96% or higher and less than 97% are rated as Acceptable (△), and less than 96% are rated as Unacceptable (×).

[0125] <Evaluation of High-Temperature Storage Characteristics of Secondary Batteries> After evaluating the above cycle characteristics, the secondary battery was similarly charged at a charging current of 25 mA (0.5C), then subjected to constant current discharge at a discharging current of 50 mA (1C) with a discharge end voltage of 2.5 V, thereby performing charge and discharge. After being charged at a charging current of 25 mA (0.5C), the secondary battery was taken out from the charge-discharge device, left to stand in a constant temperature tank at 80°C for 24 hours, and stored at high temperature. The secondary battery was again placed in a constant temperature room at 25°C and left to stand for about 12 hours, after which charge-discharge measurement was performed using a charge-discharge device. After constant current and constant voltage charging (cut-off current: 1.25 mA (0.025C)) was performed at a charging current of 25 mA (0.5C) with a charge end voltage of 4.2 V, constant current discharge was performed at a discharging current of 50 mA (1C) with a discharge end voltage of 2.5 V. Thereafter, after similarly charging at a charging current of 25 mA (0.5C), constant current discharge was performed at a discharging current of 150 mA (3C) with a discharge end voltage of 2.5 V, DCIR after high-temperature storage was measured, and the high-temperature storage characteristics of the secondary battery were evaluated. The high-temperature storage characteristics of a secondary battery can be calculated from the ratio of the voltage drop after 3 seconds during 3C discharge at 25°C to the applied current, using Equation 2 below. (Equation 2): High-temperature storage characteristics (DCIR) of secondary battery = (Voltage at 0 seconds of 3C discharge – Voltage at 3 seconds of 3C discharge) / Applied current (Ω) The evaluation criteria for the high-temperature storage characteristics of secondary batteries are as follows. [Evaluation Criteria] For the evaluation criteria of high-temperature storage characteristics of secondary batteries, DCIR of less than 1.7 is rated as Excellent (◎), 1.7 or more and less than 1.9 is rated as Good (〇), 1.9 or more and less than 2.2 is rated as Acceptable (△), and 2.2 or more is rated as Unacceptable (×).

[0126] <Production of CNT> (Production Example 1: CNT (A-1)) CNT(A-1) was obtained by manufacturing in the same manner as the sheet-like CNT aggregate 1 described in Example 1 of Japanese Patent No. 7528392, and cutting it with scissors until it became a sheet piece of about 1 mm x 3 mm.

[0127] (Production example 2; CNT(A-2)) CNT(A-2) was obtained using the same method as in Manufacturing Example 1, except that the second temperature zone was changed from 1,400°C to 1,350°C.

[0128] (Production example 3; CNT(A-3)) CNT(A-3) was obtained using the same method as in Production Example 1, except that the carrier gas flow rate was changed from 30,000 sccm to 45,000 sccm.

[0129] (Production example 4; CNT(A-4)) Ten portions of CNT(A-1) prepared in Manufacturing Example 1 were placed in a graphite crucible with a diameter of 10 cm and a height of 10 cm. The crucible containing the above CNTs was placed in a multi-purpose high-temperature furnace (High Multi 5000, manufactured by Fuji Denpa Kogyo Co., Ltd.) and subjected to heat treatment under reduced pressure and vacuum as follows. First, nitrogen gas was introduced into the multi-purpose high-temperature furnace, and nitrogen gas replacement was performed twice. Next, the furnace pressure was reduced using an oil rotary pump and adjusted to 9.8-9.5 Pa. Subsequently, the pressure was further reduced using an oil diffusion pump and adjusted to 0.03-2 Pa. Then, while maintaining the reduced pressure using the oil diffusion pump, the temperature was raised to 1,500°C at a heating rate of 20°C / min and held at 1,500°C for 2 hours. After that, the furnace was allowed to cool naturally until the internal temperature fell below 50°C to obtain CNT(A-4).

[0130] (Manufacturing example 5; CNT(A-5)) CNT(A-4) was crushed using a dry jet mill "NJ-50" (product name) manufactured by Aisin Nanotechnologies Inc., with a crushing air pressure of 1.2 MPa and a flow rate of 100 g / h, in a circulating crushing method to obtain CNT(A-5) at a processing speed of 30 g / h.

[0131] (Production example 6; CNT(A-6)) CNT(A-4) was processed using a 60L capacity dynamic mill (manufactured by Nippon Coke Industries Co., Ltd.) bead mill, with 8mm diameter zirconia beads as the grinding media at a packing rate of 70%. 100kg was supplied at a flow rate of 120±20kg / h (hour), and the process was carried out for 3 hours using a circulating grinding method at a peripheral speed of 3m / s (seconds) to obtain CNT(A-6).

[0132] (Production example 7; CNT(A-7)) CNT(A-7) was obtained using the same method as in Manufacturing Example 4, except that the carrier gas flow rate was changed from 30,000 sccm to 60,000 sccm, and CNTs prepared using the same method as in Manufacturing Example 1 were used.

[0133] (Production example 8; CNT(A-8)) CNT(A-8) was obtained using the same method as in Manufacturing Example 4, except that the carrier gas flow rate was changed from 30,000 sccm to 105,000 sccm, and CNTs prepared using the same method as in Manufacturing Example 1 were used.

[0134] (Production example 9; CNT(A-9)) CNT(A-9) was obtained using the same method as in Production Example 4, except that the temperature was raised to 1,800°C at a heating rate of 20°C / min and held at 1,800°C for 2 hours.

[0135] (Production example 10; CNT(A-10)) CNT(A-9) was processed using a 60L capacity dynamic mill (manufactured by Nippon Coke Industries Co., Ltd.) bead mill, with 8mm diameter zirconia beads as the grinding media at a packing rate of 70%. 100kg of CNT(A-9) was supplied at a flow rate of 120±20kg / h (hour) and processed for 3 hours using a circulating grinding method at a peripheral speed of 3m / s (seconds) to obtain CNT(A-10).

[0136] (Production example 11; CNT(A-11)) CNT(A-11)) was obtained by the same method as in Manufacturing Example 9, except that CNT(A-3) was used instead of CNT(A-1).

[0137] ·CNT (A-12); MIRALON (manufactured by HUNTSMAN, multilayer CNT) ·CNT(A-13); CNT described in Example 4 of Japanese Patent No. 6586197 ·CNT(A-14); CNT described in paragraph 0133 of Japanese Patent No. 6801806

[0138] <Dispersant> • Dispersant (B-1): Hydrogenated nitrile butadiene rubber polymer (manufactured by Zeon Corporation, Zetpole 2000L, acrylonitrile content 36%) • Dispersant (B-2): Zetpole(R) 3300 (manufactured by Nippon Zeon Co., Ltd., hydrogenated acrylonitrile rubber, acrylonitrile content 23%) • Dispersant (B-3): Thermon(R) 4307 (manufactured by ARLANXEO Corporation, hydrogenated acrylonitrile rubber, acrylonitrile content 43.0%) • Dispersant (B-4): Polyvinylpyrrolidone (manufactured by Nippon Shokubai, K-30) • Dispersant (B-5): Polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., BL-10)

[0139] Table 1 shows the physical properties of the CNTs used in the examples and comparative examples.

[0140] [Table 1]

[0141] Table 2 shows the dispersion conditions for producing the CNT-dispersed compositions prepared in the examples and comparative examples. The CNT-dispersed compositions were prepared by combining the first, second, and third dispersion steps.

[0142] [Table 2]

[0143] (Example 1-1) In a stainless steel container, an NMP solution containing hydrogenated nitrile butadiene rubber polymer (Zetpole2000L, manufactured by Nippon Zeon Co., Ltd.), which is an 8% dispersant (B-1), along with NaOH (Tosoh Pearl, manufactured by Tosoh Corporation), and NMP were added to adjust the amount to 0.30 parts by mass of the polymer, 0.01 parts by mass of NaOH, and a total of 99.29 parts by mass of NMP. To this solution, 0.40 parts by mass of CNT(A-4) were weighed and added while stirring with a disperser. A round-hole screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was uniform. This process is designated as the first dispersion process. Next, the contents of the stainless steel container were transferred and subjected to a circulating dispersion process (80% bead filling, peripheral speed 12 m / s) with a residence time of 10 minutes using a bead mill (Star Mill LMZ2, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. This process is referred to as the second dispersion process. Next, the dispersion liquid was supplied to a nozzle-type high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst Lab) and subjected to a 10-cycle circulating dispersion process. The dispersion process was performed using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After the dispersion process, the mixture was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 40 μm). This process was designated as the third dispersion step. In this way, a CNT dispersion composition (D-1) was prepared under dispersion condition X3.

[0144] (Examples 1-2 to 1-10, Examples 15-22), (Comparative Examples 1-1 to 1-3) CNT dispersion compositions (D-2 to D-10, D-15 to D-25) were prepared in the same manner as in Example 1-1, except for the changes made to the conditions described in Table 2.

[0145] (Examples 1-11) An NMP solution containing polyvinylpyrrolidone (manufactured by Nippon Shokubai, K-30), which is an 8% dispersant (B-4), and NMP were added to a stainless steel container, and the mixture was adjusted so that the polymer amounted to 0.30 parts by mass and the total amount of NMP was 99.30 parts by mass. To this solution, 0.40 parts by mass of CNT(A-4) were weighed and added while stirring with a disperser. A round-hole screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was uniform. This process is designated as the first dispersion process. Next, the contents of the stainless steel container were transferred and subjected to a circulating dispersion process (80% bead filling, peripheral speed 12 m / s) with a residence time of 10 minutes using a bead mill (Star Mill LMZ2, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. This process is referred to as the second dispersion process. Next, the dispersion liquid was supplied to a nozzle-type high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst Lab) and subjected to a 10-cycle circulating dispersion process. The dispersion process was carried out using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After the dispersion process, the mixture was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 40 μm). This process was designated as the third dispersion step. In this way, a CNT dispersion composition (D-11) was prepared under dispersion condition X3.

[0146] (Examples 1-12 to 1-13) CNT dispersion compositions (D-12) and (D-13) were prepared in the same manner as in Example 1-11, except that dispersants (B-5) and (B-1) were used instead of dispersant (B-4).

[0147] (Examples 1-14) In a stainless steel container, an NMP solution containing hydrogenated nitrile butadiene rubber polymer (Zetpole2000L, manufactured by Nippon Zeon Co., Ltd.), which is an 8% dispersant (B-1), and ethanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and NMP were added to adjust the mixture to contain 0.30 parts by mass of the polymer, 0.02 parts by mass of ethanolamine, and a total of 99.28 parts by mass of NMP. To this solution, 0.40 parts by mass of CNT(A-4) were weighed and added while stirring with a disperser. A round-hole screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was uniform. This process is designated as the first dispersion process. Next, the contents of the stainless steel container were transferred and subjected to a circulating dispersion process (80% bead filling, peripheral speed 12 m / s) with a residence time of 10 minutes using a bead mill (Star Mill LMZ2, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. This process is referred to as the second dispersion process. Next, the dispersion liquid was supplied to a nozzle-type high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst Lab) and subjected to a 10-cycle circulating dispersion process. The dispersion process was carried out using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After the dispersion process, the mixture was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 40 μm). This process was designated as the third dispersion step. In this way, a CNT dispersion composition (D-11) was prepared under dispersion condition X3.

[0148] (Examples 1-15) In a stainless steel container, an NMP solution containing a hydrogenated nitrile butadiene rubber polymer (Zetpole2000L, manufactured by Nippon Zeon Co., Ltd.), which is an 8% dispersant (B-1), along with NaOH (Tosoh Pearl, manufactured by Tosoh Corporation), and NMP were added to adjust the mixture to contain 0.75 parts by mass of the polymer, 0.03 parts by mass of NaOH, and a total of 98.22 parts by mass of NMP. To this solution, 1.0 part by mass of CNT(A-4) was weighed and added while stirring with a disperser. A square-hole screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was uniform. This process is designated as the first dispersion process. Next, the contents of the stainless steel container were transferred and subjected to a circulating dispersion process (80% bead filling, peripheral speed 12 m / s) with a residence time of 15 minutes using a bead mill (Star Mill LMZ2, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. This process is referred to as the second dispersion process. Next, the dispersion liquid was supplied to a nozzle-type high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst Lab) and subjected to 42 circulating dispersion treatments. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. This process was designated as the third dispersion step. After the dispersion treatment, the mixture was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 40 μm). In this way, a CNT dispersion composition (D-15) was prepared under dispersion condition Y1.

[0149] (Examples 1-18) In a stainless steel container, an NMP solution containing hydrogenated nitrile butadiene rubber polymer (Zetpole2000L, manufactured by Nippon Zeon Co., Ltd.), which is an 8% dispersant (B-1), along with NaOH (Tosoh Pearl, manufactured by Tosoh Corporation), and NMP were added to adjust the amount to 0.30 parts by mass of the polymer, 0.01 parts by mass of NaOH, and a total of 99.29 parts by mass of NMP. To this solution, 0.40 parts by mass of CNT(A-7) were weighed and added while stirring with a disperser. A round-hole screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was uniform. This process is designated as the first dispersion process. Next, the contents of the stainless steel container were transferred and supplied to a nozzle-type high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst Lab) for 50 circulating dispersion treatments. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After the dispersion treatment, the mixture was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 40 μm). This process was designated as the second dispersion step. In this way, a CNT dispersion composition (D-18) was prepared under dispersion condition Z1.

[0150] Table 3 shows the composition, physical properties, and evaluation results of the CNT dispersion compositions prepared in the examples and comparative examples.

[0151] [Table 3-1]

[0152] [Table 3-2]

[0153] (Example 2-1) <Preparation of Binder Composition> Capacity 150cm 3 In a plastic container, the CNT dispersion composition (D-1) and PVdF (polyvinylidene fluoride, Solef 5130, manufactured by Solvay, 100% non-volatile content), which had been pre-dissolved in NMP (N-methyl-2-pyrrolidone) to a concentration of 8%, were added. Then, the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro, ARE-310). In this way, binder composition (D-1) was obtained.

[0154] <Preparation of electrode compositions> The binder composition (D-1) contains NMC (S800, LiNi) as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 After adding O2 (manufactured by Kinwa), the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Subsequently, the clumps were broken up with a spatula, and then the mixture was stirred at 2,000 rpm for 300 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310) to obtain secondary battery electrode composition (D-1). The non-volatile content of the electrode composition was set to 70.0%. Of the non-volatile portion of the electrode composition, the non-volatile content ratio of NMC:CNT:PVdF was set to 98.4:0.1:1.5.

[0155] (Examples 2-2 to 2-22), (Comparative Examples 2-1 to 2-3) Binder compositions (D-1 to D-25) and secondary battery electrode compositions (D-1 to D-25) were obtained by the same method as in Example 2-1, except that the CNT dispersion composition was changed to the one shown in Table 4.

[0156] [Table 4]

[0157] (Example 3-1) <Fabrication of electrode films> The composition for secondary battery electrodes (D-1) was measured using an applicator, and the basis weight per unit of the electrode was 17 mg / cm³. 2 The material was coated onto aluminum foil in the manner described above. After coating, the coating was dried in an electric oven at 120°C ± 5°C for 15 minutes to obtain electrode film (D-1). Subsequently, electrode film (D-1) was rolled using a roll press (Sankmetal, 3t hydraulic roll press) to obtain positive electrode (D-1). The basis weight per unit of the composite layer was 17 mg / cm². 2 The density of the asphalt layer after rolling was set to 3.2 g / cc.

[0158] (Examples 3-2 to 3-22), (Comparative Examples 3-1 to 3-3) Positive electrodes (D-2 to D-25) were prepared in the same manner as in Example 3-1, except that secondary battery electrode composition (D-1) was replaced with secondary battery electrode compositions (D-2 to D-25).

[0159] Table 5 shows the evaluation results of the positive electrodes prepared in the examples and comparative examples.

[0160] [Table 5]

[0161] (Example 4-1) <Manufacturing of secondary batteries> The positive electrode (D-1) and the standard negative electrode were punched out to 45mm x 40mm and 50mm x 45mm, respectively. These electrodes, along with the separator (porous polypropylene film) to be inserted between them, were placed in an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Subsequently, 2 mL of electrolyte (non-aqueous electrolyte) was injected into a glove box filled with argon gas, and then an aluminum laminate was sealed to create a laminate-type secondary battery (D-1). The standard negative electrode and non-aqueous electrolyte were prepared as follows. (Standard negative electrode) In a 150ml plastic container, 0.5 parts by mass of acetylene black (Denka Black® HS-100, manufactured by Denka), 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt, Sunrose special type MAC500L, manufactured by Nippon Paper Industries, 100% non-volatile content), and 98.4 parts by mass of water were added. The mixture was then stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Furthermore, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry, CGB-20) and 5 parts by mass of silicon oxide (manufactured by Osaka Titanium Technology, SILICON MONOOXIDE SiO 1.3C 5μm, 100% non-volatile content) were added as active materials, and the mixture was stirred at 3,000 rpm for 10 minutes using a high-speed stirrer. Next, 3.1 parts by mass of styrene-butadiene rubber (SBR) (TRD2001, manufactured by JSR Corporation) were added, and the mixture was stirred at 2,000 rpm for 30 seconds using the aforementioned rotating / revolving mixer to obtain a negative electrode mixture slurry. After that, the negative electrode mixture slurry was measured using an applicator to obtain an electrode weight of 8 mg / cm³ per unit area. 2 After coating the copper foil in this manner, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Furthermore, it was rolled using a roll press (manufactured by Sankumetal Co., Ltd., 3t hydraulic roll press) to obtain a density of 1.6 g / cm³ in the asphalt layer. 3 A standard negative electrode was fabricated. (Non-aqueous electrolyte) First, a mixed solvent was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 1:1:1 (volume ratio). Next, 2 parts by mass of VC (vinylene carbonate) was added as an additive to 100 parts by mass of this mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M to obtain a non-aqueous electrolyte.

[0162] Secondary batteries (D-2 to D-25) were manufactured in the same manner as in Example 4-1, except that the positive electrode (D-1) was changed to positive electrodes (D-2 to D-25).

[0163] Table 6 shows the evaluation results of the secondary batteries prepared in the examples and comparative examples.

[0164] [Table 6]

[0165] In the above example, a CNT dispersion composition was used that included CNTs, a dispersant, and an amide-based polar solvent, wherein the CNTs included CNT aggregates in which two or more CNT units, each having an iron content of 170,000 ppm or less, an average outer diameter of 3 nm to 8 nm, and 3 to 15 layers, were bundled together in parallel by interaction, and the average outer diameter of the CNT aggregates was 10 nm to 50 nm. This type of CNT dispersion composition demonstrates excellent long-term stability and high conductivity, making it applicable to various fields where durability is required.

[0166] Furthermore, the examples showed that the CNT dispersion composition exhibited superior stability over time compared to the comparative example, resulting in a secondary battery electrode composition with excellent viscosity and peel strength, and a secondary battery with excellent cycle characteristics and high-temperature storage characteristics. Therefore, it has become clear that the present invention can provide a secondary battery with high capacity, high output, and high durability that is difficult to achieve with conventional CNT dispersion compositions. A vehicle equipped with the secondary battery of the present invention has high charge and discharge performance and excellent cycle characteristics, resulting in a vehicle that is highly safe and has improved fuel efficiency.

[0167] Although the present invention has been described above with reference to embodiments, the present invention is not limited thereto. Various modifications to the structure and details of the present invention can be made that are understandable to those skilled in the art within the scope of the invention.

Claims

1. A carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and an amide-based polar solvent, The carbon nanotube has an iron content of 170,000 ppm or less, and further includes a bundled carbon nanotube formed from two or more carbon nanotube units having an average outer diameter of 3 nm or more and 8 nm or less and 3 or more layers or less and 15 or fewer layers. The average outer diameter of the bundled carbon nanotubes is 10 nm or more and 50 nm or less. Carbon nanotube dispersion composition.

2. The carbon nanotube dispersion composition according to claim 1, wherein the iron content of the carbon nanotube dispersion composition is 50 ppm or less.

3. The BET specific surface area of ​​the carbon nanotube is 100 m ２ / g or more 300m ２ The carbon nanotube dispersion composition according to claim 1, wherein the amount is less than or equal to / g.

4. The carbon nanotube dispersion composition according to claim 1, wherein the G / D ratio of the carbon nanotubes is 5.1 or more and 15 or less.

5. The carbon nanotube dispersion composition according to claim 1, wherein the 20-degree specular gloss of the carbon nanotube dispersion composition is 50 or more and 170 or less.

6. The carbon nanotube dispersion composition according to claim 1, wherein the phase angle when the carbon nanotube dispersion composition is subjected to dynamic viscoelasticity measurement using a rheometer with a cone of 25 mm in diameter and 2°, at 25°C and a frequency of 1 Hz, with a strain from 0.01% to 500%, is 20° or more.

7. A composition for secondary battery electrodes comprising the carbon nanotube dispersion composition according to any one of claims 1 to 6.

8. An electrode film comprising a coating film of the secondary battery electrode composition according to claim 7.

9. A secondary battery comprising the electrode film according to claim 8.

10. A vehicle comprising the secondary battery described in claim 9.

Images