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

Abstract

To provide a carbon nanotube dispersion composition that exhibits excellent temporal 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. [Solution] The solution is provided by a carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and water, wherein the carbon nanotubes include 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.

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 containing the carbon nanotube dispersion composition and an active material, an electrode film formed therefrom, and a secondary battery containing 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] Thus, it is known that when using carbon nanotubes with a small average outer diameter and a large fiber length, an electrically conductive network can be efficiently formed in a small amount, and the amount of conductive aids contained in the positive and negative electrodes of a lithium-ion secondary battery can be reduced.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, since carbon nanotubes are fibrous and have strong cohesive force, it is difficult to obtain a carbon nanotube dispersion liquid that is uniformly dispersed and retains its dispersibility over a long period.

[0008] In Patent Document 1, carbon nanotubes with an average outer diameter exceeding 3 nm and not exceeding 25 nm and a BET specific surface area of 150 m 2 / g to 800 m 2 / g, a dispersant, and a solvent are dispersed using a high-pressure homogenizer to produce a carbon nanotube dispersion composition with a fiber length of the carbon nanotubes of 0.8 to 3.5 μm. In Patent Document 2, carbon nanotubes with a G / D ratio of 1.5 to 5.0 are produced by heat-treating carbon nanotubes, and dispersion treatment is performed using zirconia beads with polyvinylpyrrolidone as a dispersant. These carbon nanotube dispersions were dispersed to the point where the carbon nanotubes were broken down into individual units. While this improved the conductivity of the electrodes, it compromised the rigidity of the carbon nanotube aggregates, resulting in insufficient electrode strength.

[0009] 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. It is also important to provide a secondary battery with excellent cycle characteristics. [Means for solving the problem]

[0010] In other words, the present invention includes the following embodiments. Embodiments of the present invention are not limited to the following. [1]: A carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and water, The carbon nanotube comprises 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]: Shear rate of the carbon nanotube dispersion composition 10s -1 Viscosity (V1) at 25°C measured by [method / tool ​​name] and shear rate 100s -1 A carbon nanotube dispersion composition according to any one of [1] to [5], wherein the viscosity ratio (V1 / V2) of the viscosity (V2) measured at 25°C is 4.0 or more and 7.5 or less. [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]

[0011] 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 can be obtained. Thus, a carbon nanotube dispersion composition is obtained that is excellent in terms of time stability and can be applied to various application fields where high conductivity and durability are required. [Brief explanation of the drawing]

[0012] [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 1-2, 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 Example 2-2, Comparative Example 2-6, and Comparative Example 2-7. [Figure 4] Figure 4 shows the viscosity measurement results for the secondary battery electrode compositions prepared in Example 2-2, Comparative Example 2-6, and Comparative Example 2-7. [Modes for carrying out the invention]

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Carbon nanotube dispersion composition The carbon nanotube dispersion composition according to an embodiment of the present invention comprises carbon nanotubes, a dispersant, and water, wherein the carbon nanotubes include 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.

[0017] A CNT unit is an individual carbon nanotube fiber, possessing a specific average outer diameter and number of layers. A CNT aggregate is formed when multiple CNT units interact through van der Waals forces, etc. The CNTs aggregate together through interactions, forming bundles of two or more CNTs in parallel, resulting in a bundle-like or tangled structure. By controlling the average outer diameter of the CNT aggregates in the CNT dispersion composition to be between 10 nm and 50 nm, a CNT dispersion composition with not only high conductivity but also good durability can be obtained. Some CNT units that do not form CNT aggregates, or other types of CNT aggregates, may be present.

[0018] The average outer diameter of the CNT aggregate is determined by the method for manufacturing the CNT dispersion composition described later, ensuring that the small-diameter, easily breakable CNTs are not excessively broken down during dispersion, and that the individual CNTs are not overly separated. The distribution method can be controlled to maintain the bundled state. 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.

[0019] 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 18 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 of these measurements. Specifically, it can be measured by the method described in the examples.

[0020] 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.

[0021] 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.

[0022] 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 water to a CNT concentration of 0.0001% to 0.001% 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 100°C to prepare a substrate for observing CNT fiber length. The prepared substrate is photographed using a scanning electron microscope (SEM), and the resulting 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). 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 calculating the arithmetic mean.

[0023] <Carbon nanotubes> The CNT dispersion composition of this embodiment contains carbon nanotubes, and the carbon nanotubes include CNT aggregates in which two or more CNT 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.

[0024] The average outer diameter of a CNT unit is between 3 nm and 8 nm. It is preferable that the average outer diameter be 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.

[0025] 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.

[0026] 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.

[0027] 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.)

[0028] 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°.

[0029] 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.

[0030] 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 a small amount 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 flexibility and... An electrode film excellent in strength such as durability can be obtained.

[0031] The crystallite size (La100) of CNT is preferably 10 or more and 100 or less, more preferably 20 or more and 100 or less, and even more preferably 30 or more and 100 or less. The crystallite size (La100) is a parameter that reflects the growth unit length and crystallinity of CNT. CNT with a crystallite size (La100) within the above range has few nodes and tends to maintain a long fiber length without being excessively broken even when subjected to dispersion treatment using shear energy or collision energy, which is preferable because an electrode with good conductivity and strength can be obtained.

[0032] The BET specific surface area of CNT is preferably 100 m 2 / g to 300 m 2 / g, and more preferably 100 m 2 / g to 199 m 2 / g. When the BET specific surface area is within the above range, when performing the dispersion treatment of CNT, it is possible to suppress the refinement of CNT due to excessive dispersion, and it is easy to obtain a composition for a secondary battery electrode with good conductivity. Also, when used as a secondary battery, it is possible to suppress the decomposition of the electrolyte on the electrode surface, and the cycle characteristics of the secondary battery tend to be good. The BET specific surface area can be measured by the BET method of JIS Z 8830:2013. [[ID=​​​​​​​When the G / D ratio of CNTs is 3 or higher, the CNTs become more crystalline, allowing for the formation of a conductive network with superior electrical conductivity. Furthermore, the network becomes tougher, improving the toughness of the film. When the G / D ratio is 20 or lower, a certain degree of defects remains, allowing for a balance between toughness and flexibility, and increasing the contact surface with the active material, enabling the formation of an efficient conductive network.

[0034] The volume resistivity of CNTs is 1.0 × 10⁻⁶ -3 Ω·cm~1.5×10 -2 It is preferable that the ratio is Ω·cm, and 1.0 × 10 -3 Ω·cm~1.0×10 -2 A value of Ω·cm is more preferable. The volume resistivity of CNTs can be measured using a powder resistivity measuring device (Rolestar GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Nitto Seikou Analytech Co., Ltd.). When the volume resistivity is within the above range, the conductivity of the electrode film is good, and a secondary battery with excellent rate characteristics and cycle characteristics can be obtained.

[0035] The carbon purity of the CNTs is preferably as high as possible, preferably 90% by mass or more out of 100% by mass of CNTs, preferably 98% by mass or more, more preferably 99.5% by mass or more, even more preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more. In other words, the content of metallic foreign particles is preferably as low as possible, preferably 2.0% by mass or less per 100% by mass of CNT, more preferably 0.5% by mass or less, even 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.

[0036] The iron content of the CNTs is preferably 5,000 ppm or less, and 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. Furthermore, as will be described later... The iron content of the CNT dispersion composition can be easily reduced.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] <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.

[0041] When selecting anionic surfactants, the type is not particularly limited. Specifically, examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfonates, alkylnaphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters.

[0042] Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Yes, there are, 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 dodecyl benzyltriethylammonium chloride. Examples of amphoteric surfactants include, but are not limited to, aminocarboxylate salts.

[0043] 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.

[0044] 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.

[0045] Specific 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, polyacrylic acid, and polyacrylonitrile polymers. Cellulose derivatives, polyvinyl butyral, polyvinylpyrrolidone, polyacrylic acid, and polyacrylonitrile polymers are particularly preferred. Among cellulose derivatives, methylcellulose, ethylcellulose, and carboxymethylcellulose are preferred. Carboxymethylcellulose, polyacrylic acid, polyvinylpyrrolidone, and polyacrylonitrile polymers are preferred resin-type dispersants, with carboxymethylcellulose, polyacrylic acid, and polyacrylonitrile polymers being particularly preferred.

[0046] As a resin-type dispersant, carboxymethylcellulose can be used in the form of a salt, such as a sodium salt of carboxymethylcellulose, in which the hydroxyl groups of carboxymethylcellulose are replaced with carboxymethyl sodium groups. The degree of etherification of carboxymethylcellulose as a resin-type dispersant is preferably 0.5 to 1.5, and more preferably 0.6 to 1.0. The degree of etherification of carboxymethylcellulose can be measured according to conventional methods. By setting the degree of etherification within the above range, it is possible to provide appropriate affinity for water and CNTs. Furthermore, when used in secondary batteries, it is possible to prevent problems such as the dispersant dissolving in the electrolyte within the battery and increasing the viscosity of the electrolyte. The degree of etherification can be measured, for example, by the following method.

[0047] Accurately weigh approximately 2.0 g of the sample and place it in a 300 mL stoppered Erlenmeyer flask. Add 100 mL of methanol nitrate (a solution of 1 L of anhydrous methanol and 100 mL of high-grade concentrated HNO3) and shake for 2 hours. Thus, Na-CMC is converted to H-CMC. The H-CMC is quantitatively transferred to a glass filter 1G3 and filtered by suction, then washed with 200 mL of 80% methanol. After that, it is replaced with 50 mL of anhydrous methanol, filtered by suction, and dried at 105°C for 2 hours. 1 to 1.5 g of the oven-dried H-CMC is accurately weighed and placed in a 300 mL stoppered Erlenmeyer flask, and the H-CMC is moistened with 15 mL of 80% methanol. N / 10 Add 50 mL of NaOH and shake at room temperature for 2 hours. Use phenol phthalein as an indicator. N / 10 Back titration of excess NaOH with H2SO4. The degree of etherification is calculated using the following formula. ((50×F'- N / 10 H2SO4 (mL) × F) / (Dry weight of H-CMC (g)) × (1 / 10) = A Degree of etherification (M / c6) = (0.162A / (1 - 0.058A)) F: N / 10 Factors of H2SO4 F': N / 10 NaOH Factor

[0048] 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 contains a copolymer (sometimes referred to as "Copolymer N") 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.

[0049] 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.

[0050] <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.

[0051] <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.

[0052] <Antifoaming agent> The CNT dispersion composition may further contain an antifoaming agent. Any commercially available antifoaming agent, wetting agent, etc. having an antifoaming effect can be arbitrarily used, and it may be used alone or in combination of a plurality.

[0053] <Optional component> The CNT dispersion composition may, if necessary, further appropriately contain other additives such as wetting agents, pH adjusters, wetting and penetrating agents, leveling agents, etc., and optional components such as other conductive materials other than CNTs, within a range not inhibiting the object of the present invention. The optional components can be added at any timing, such as before the production of the CNT dispersion composition, during mixing, after mixing, or a combination thereof.

[0054] <Method for producing CNT dispersion composition> The CNT dispersion composition can be produced, for example, by dispersing CNTs in water. The raw material CNTs used for the dispersion treatment may be added at any timing, once or divided into a plurality of times. The dispersion method for performing such treatment is not particularly limited.

[0055] In the present invention, it is important to crush the CNT aggregate firmly bundled by interactions such as van der Waals forces to an optimal thickness, and for that purpose, it is preferable to apply a strong shearing force under higher pressure conditions using a device such as a high-pressure homogenizer for dispersion. However, when the shearing force is excessive, all the CNT aggregates are crushed and reach the CNT unit, and although the conductivity of the electrode is improved, the rigidity due to the twisting and aggregation of the CNT aggregates is impaired, so the durability such as the electrode strength cannot be improved.

[0056] Furthermore, the CNTs used in the embodiment of the present invention may be in the form of cut sheet-like raw materials. In the case of sheet-like CNTs, in order to more quickly finish the cut or crushed CNTs to a fiber length of several micrometers, it is also effective to break them by impact force using bead dispersion or by shear force using plastomyll dispersion. The cutting method is not particularly limited, but for example, scissors can be used.

[0057] As the dispersion device, a disperser commonly used for pigment dispersion and the like can be used. For example, it may be either a media-less distributor or a media-type distributor. Examples of media-less distributors 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); colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"); and cone mills (IKA's "Corn Mill"). Examples include "Mill MKO," etc. Media-type dispersers include ball mills, sand mills (such as Shinmaru Enterprises' "Dino Mill"), atlighters, pearl mills (such as Eirich's "DCP Mill"), ball mills, bead mills (Ashizawa Finetech's Mugen Flow®), media-type paint conditioners, etc. 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.

[0058] 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.

[0059] 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 process of manufacturing the CNT dispersion composition, the iron content in the CNT dispersion composition can be easily reduced by using CNTs produced by a 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 step of the CNT dispersion composition and / or at the end of the dispersion step. The foreign matter removal step may be performed multiple times.

[0060] 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, the method of removal by magnetic force is preferred, and the process involves removal by magnetic force and filtration using a filter. A method that combines the removal process is more preferable.

[0061] While there are no particular limitations on the method of removal by magnetic force as long as it can remove iron particles, from the viewpoint of productivity and removal efficiency, a method is preferred in which a magnetic filter is placed in the manufacturing line of the CNT dispersion composition and the CNT dispersion composition is passed through it to remove the particles. The step of removing iron particles from the CNT dispersion composition by placing a magnetic filter and passing the 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. 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. 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.

[0062] 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 0.5 to 10 parts by mass, and particularly preferably 0.5 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.

[0063] In the CNT dispersion composition of the present embodiment, the amount of the dispersant 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 with respect to 100 parts by mass of CNT. Also, 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 it is within the above range, the dispersibility of the CNT dispersion composition becomes good, and the initial viscosity and stability over time tend to be good. When the amount of the dispersant in the CNT dispersion composition of the present embodiment is more important for the conductivity and strength of the electrode film described later than the ease of handling such as the initial viscosity and stability over time of CNT, the amount of the dispersant may be appropriately adjusted according to the amount of CNT added in the electrode film, and it may be 10 parts by mass or more and less than 100 parts by mass, or 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.

[0064] When the CNT dispersion composition contains other components in addition to CNT, the dispersant, and water, the amount of the 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 with respect to 100 parts by mass of the CNT dispersion composition.

[0065] When the CNT dispersion composition contains a basic compound, 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 part by mass, or 0.04 to 0.1 part by mass with respect to 100 parts by mass of the CNT dispersion composition. When the CNT dispersion composition contains a basic compound, the amount of the basic compound in the CNT dispersion composition is 1 to 20 parts by mass, 2 to 10 parts by mass, or 4 to 8 parts by mass with respect to 100 parts by mass of the dispersant.

[0066] When the CNT dispersion composition contains an antifoaming agent, 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 part by mass, or 0.04 to 0.1 part by mass with respect to 100 parts by mass of the CNT dispersion composition.

[0067] <Physical properties of CNT dispersion composition> [Iron content] The iron content of the CNT dispersion composition can be calculated using an ICP emission spectrometer as described in the examples, after drying the CNT dispersion composition to remove water. The iron content detected by ICP analysis includes iron particles and dissolved iron ions. In other words, the iron content of the CNT dispersion composition after the foreign matter removal process includes iron particles that could not be completely removed and dissolved iron ions.

[0068] The iron content of the CNT dispersion composition is preferably 50 ppm or less, and more preferably 30 ppm or less, based on 100% by mass of the CNT dispersion composition. By setting the iron content of the CNT dispersion composition within the above range, side reactions due to the decomposition of the electrolyte in the secondary battery electrode film are less likely to occur, and a secondary battery with superior cycle characteristics can be obtained.

[0069] [pH] The pH of the CNT dispersion composition is preferably 3 to 6, more preferably 4 to 6, and even more preferably 4 to 5. The pH may also be 9 to 11. The pH of the CNT dispersion composition can be measured using a pH meter (pH METER F-52, manufactured by Horiba, Ltd.). When the pH of the CNT dispersion composition is within the above range, a CNT dispersion composition with excellent viscosity stability is easily obtained due to surface charge repulsion of the CNTs.

[0070] [20-degree mirror finish] 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 glass 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.

[0071] [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 4.0 or higher, more preferably 5.0 or higher, and even more preferably 6.0 or higher. It is also preferably 7.5 or lower. (Shear rate 10s) -1 and 100s -1 By determining the ratio of shear viscosities (V1 / V2) in the given region, 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. This is possible. When using CNTs of a length such that the viscosity ratio (V1 / V2) is 4.0 or higher, the CNTs form a network state with each other, resulting in an improvement in the strength of the electrode film. Furthermore, by using CNTs with a large fiber length, the increase in the surface area of ​​the electrode can be suppressed, which suppresses the decomposition of the electrolyte during high-temperature storage in secondary batteries and improves the cycle characteristics. In addition, when using CNTs of a length such that the viscosity ratio (V1 / V2) is 7.5 or lower, the CNTs are broken down to an appropriate length, which increases the number of effective CNTs contained in the electrode film, allowing for the efficient formation of a conductive network with a small amount of material.

[0072] 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 finally 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.

[0073] [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 water, the structural viscosity of the CNTs themselves may result in a high 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 300 Pa or less, more preferably 150 Pa or less, and even more preferably 50 Pa or less. It is also preferably 1 Pa or more, more preferably 5 Pa or more, and even more preferably 10 Pa or more. The phase angle of the CNT dispersion composition is preferably 5° or more, more preferably 8° or more, and even more preferably 10° or more. It is also preferably 80° or less, more preferably 59° or less, and even more preferably 50° 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.

[0074] ≪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, a solvent, and an active material. It is also preferable to include a binder resin.

[0075] 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.

[0076] As for the fluororesin, polyvinylidene fluoride, polyvinyl fluoride, and polytetrafluoroethylene are preferred, for example.

[0077] 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.

[0078] 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 13, transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2 and FeS, etc. can be mentioned. Further, conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene, etc. can also be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0079] The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium ions. For example, metallic Li, alloy systems such as its alloys of tin alloy, silicon alloy, lead alloy, etc., Li X Fe2O3, Li X Fe3O4, Li X WO2 (x is a number where 0 < x < 1.), metal oxide systems such as lithium titanate, lithium vanadate, lithium silicate, etc., conductive polymer systems such as polyacetylene, poly-p-phenylene, etc., amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, carbon fibers, etc. can be mentioned. These negative electrode active materials can be used alone or in combination of two or more. Among these, it is preferable to use an alloy-based negative electrode active material as the negative electrode active material, and a silicon alloy is particularly preferable. The alloy-based negative electrode active material has a large theoretical capacity, but has a large volume change during charge and discharge of the secondary battery. By combining with the carbon nanotube dispersion composition of the present embodiment, deterioration of the electrode due to volume change of the alloy-based active material can be suppressed, and the cycle characteristics of the secondary battery can be improved.

[0080] The BET specific surface area of the negative electrode active material is preferably 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.

[0081] 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.

[0082] To obtain a composition for secondary battery electrodes, it is preferable to add an active material to the CNT dispersion composition and then perform a dispersion process. The dispersion apparatus used for such a process is not particularly limited. No. 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.

[0083] In viscoelastic measurements, when the shear strain of the secondary battery electrode composition 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 less than 8 Pa, more preferably less than 7 Pa, and even more preferably less than 6 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 stable and less prone to breakage. 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] ≪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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] ≪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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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 paper type, cylindrical type, button type, or laminated type. It can be made into various shapes depending on the purpose of use.

[0100] 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.

[0101] Among them, since it is a secondary battery having high charge-discharge performance and excellent cycle characteristics, it can be suitably used for vehicles, and a vehicle with high safety and expected fuel efficiency improvement can be obtained. Further, excellent effects can be exhibited even in the case of vehicle applications where charge-discharge at a large current is desired.

[0102] The mounting position of the secondary battery in the vehicle of this embodiment is not particularly limited. For example, when mounting the secondary battery in an automobile, the secondary battery can be mounted in the engine room of the vehicle, behind the vehicle body, or under the seat.

Example

[0103] The present invention will be described more specifically with reference to the following examples. The present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

[0104] 《Physical Property Measurement and Evaluation Method》 The physical property measurement and evaluation of CNT, CNT dispersion composition, composition for secondary battery electrode, electrode film, and secondary battery were performed by the following methods.

[0105] <Average Outer Diameter of CNT Unit> The CNT dispersion composition was diluted 50 to 200 times with ion-exchanged water, dropped onto a microgrid (Nisshin EM Holey Microgrid U1003), air-dried, and then observed using a transmission electron microscope (JEM2800, manufactured by JEOL Ltd.). The observation was carried out at an acceleration voltage of 200 kV and a magnification of 1 million times. A plurality of photographs containing 10 or more CNT aggregates in the visual field were taken, the outer diameters of 50 arbitrarily extracted CNTs were measured, and the arithmetic mean value was used to obtain the average outer diameter (nm) of the CNT unit and the standard deviation value was used as the standard deviation (nm) of the outer diameter of the CNT unit.

[0106] <Number of Layers of CNT Unit> The CNT was placed in the recess of a glass sample plate (outer diameter 5.0 cm × 3.5 cm, thickness 3 mm, sample part 2.0 cm × 2.0 cm, thickness 2 mm), and was flattened using a slide glass. Thereafter, a sample for powder X-ray diffraction analysis of the carbon material was installed in a fully automatic multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation), and was operated from 15° to 35° for analysis. Sampling was performed every 0.01°, and the scan speed was 1° / min. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα ray. Using the average interplanar spacing (d002) of the peaks obtained at diffraction angle 2θ = 25° ± 2° and the crystallite size (Lc002), the number of layers per unit of CNT was calculated by the following formula (1). Formula (1): Number of layers = crystallite size (Lc002) / average interplanar spacing (d002)

[0107] <Average outer diameter of CNT aggregate> The CNT dispersion composition was diluted 50 to 200 times using ion-exchanged water, dropped onto a microgrid (Nisshin 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 500,000 times, and photographs containing 10 or more CNT aggregates in the field of view were taken in plural, and the outer diameters of 50 arbitrarily extracted CNT aggregates were measured. The arithmetic mean value thereof was used as the average outer diameter (nm) of the CNT aggregates, and the standard deviation value was used as the standard deviation (nm) of the outer diameter of the CNT aggregates. The CNTs contained in the CNT dispersion compositions (D1-1 to D1-56) were CNT aggregates in which a plurality of CNTs had orientation and the CNT units were bundled in parallel by two or more due to interaction. The CNTs contained in the CNT dispersion compositions (D1-57 to D1-58) were crushed to the CNT unit and were not CNT aggregates. Therefore, the average outer diameter and standard deviation of the CNT aggregates in Table 3 were described as "-".

[0108] <000​​The CNT dispersion composition was diluted with water so that the CNT concentration became 0.0001% to 0.001% by mass, and then several drops of the CNT dispersion composition were dropped onto a mica substrate. Thereafter, it was dried on a hot plate at 100 °C to produce a substrate for observing the CNT fiber length. The produced substrate was photographed using a scanning electron microscope (SEM), and the obtained SEM image was analyzed using image analysis software "ImageJ" (open source image processing and analysis software developed by the National Institutes of Health, USA), and the fiber lengths of 100 CNTs were measured, and the average fiber length of the CNTs in the CNT dispersion composition was determined by arithmetic mean. The criteria for determining the average fiber length of CNTs in the CNT dispersion composition were 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. μm: C, less than 0.8 μm or 5.0 μm or more: D.

[0109] <Observation of CNT Images> Image observation was performed by the following method to confirm the state of the CNT aggregates of the powdery CNT. The powdery CNT was diluted about 50 to 200 times with a mixed solvent of acetone and MEK (acetone: MEK = 1: 1), dropped onto a microgrid (Nisshin EMHoley Microgrid U1003), and air-dried. Using JEM2800 (JEOL, transmission electron microscope image), at an accelerating voltage of 200 kV and a magnification of 1 million times, 10 to 12 specimens were measured based on the scale bar for arbitrarily selected CNTs, and the average value and standard deviation were calculated for all specimens.

[0110] <BET Specific Surface Area of CNT> 0.03 g of CNT was weighed using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried while degassing at 110 °C for 15 minutes. Thereafter, the BET specific surface area of the CNT was measured using a fully automatic specific surface area measuring device (manufactured by MOUNTECH, HM-model1208). The BET specific surface area was measured in accordance with the BET method of JIS Z 8830:2013.

[0111] <G / D Ratio of CNT> CNT was placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.), and measurements were performed using a laser wavelength of 532 nm. The measurement conditions were an acquisition time of 60 seconds, an integration number of 2 times, a dimming filter of 10%, an objective lens magnification of 20 times, a confocal hole of 500, a slit width of 100 μm, and a measurement wavelength of 100 cm -1 ~3,000 cm -1 The carbon nanotubes for measurement were separated on a slide glass and flattened using a spatula. Among the obtained peaks, within the spectrum range of 1,560 cm -1 ~1,600 cm -1 the maximum peak intensity was defined as G, and within the range of 1,310 cm -1 ~1,350 cm -1 the maximum peak intensity was defined as D, and the ratio of G / D was defined as the G / D ratio of CNT.

[0112] <Iron content of CNT> The CNT powder was decomposed by acid using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon nanotubes. Then, analysis was performed using a multi-type ICP emission spectroscopic analyzer (720-ES, manufactured by Agilent), and the iron content contained in the extract was calculated and defined as the iron content of the CNT powder. The iron content contained in the extract was calculated and defined as the iron content of the CNT powder.

[0113] <Iron content of CNT dispersion composition> The CNT dispersion composition was dried using a hot air oven, and then decomposed by acid using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon nanotubes. Then, analysis was performed using a multi-type ICP emission spectroscopic analyzer (720-ES, manufactured by Agilent), and the iron content contained in the extract was calculated and defined as the iron content of the CNT dispersion composition.

[0114] <20-degree specular gloss of CNT dispersion composition> The CNT dispersion composition was dropped by 1 mL onto a PET (polyethylene terephthalate) film and coated at 2 cm / second using a No. 7 bar coater. After that, a coating film prepared by baking and drying in a hot air oven at 140 °C for 5 minutes was used. 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, and measurements in accordance with JIS standard Z8741:1997 were performed once each in a parallel light method at 20°. The average value was taken as the gloss of the CNT dispersion composition. The criteria for judging the gloss of the CNT dispersion composition were as follows: 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.

[0115] <Viscosity ratio of CNT dispersion composition> After the CNT dispersion composition was left standing in a constant temperature bath at 25 °C for 1 hour or more, using a cone with a diameter of 25 mm and 2°, and using a rheometer (MCR302e, manufactured by Anton Paar), at 25 °C and a shear rate of 0.01 s -1 to 1,000 s -1 the shear viscosity was measured. 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 were used to determine the viscosity ratio (V1 / V2). -1 From the viscosity (V1) at 25 °C measured at a shear rate of 100 s The evaluation criteria for the viscosity ratio (V1 / V2) were as follows: 6.0 or more and 7.5 or less: A, 5.0 or more and less than 6.0: B, 4.0 or more and less than 5.0 or exceeding 7.5 and 8.0 or less: C, less than 4.0 or exceeding 8.0: D.

[0116] <Complex elastic modulus and phase angle of CNT dispersion composition> After the CNT dispersion composition was left standing in a constant temperature bath at 25 °C for 1 hour or more, using a cone with a diameter of 25 mm and 2°, and using a rheometer (MCR302e, manufactured by Anton Paar), at 25 °C and a frequency of 1 Hz, within the range of shear strain from 0.01% to 5%, dynamic viscoelasticity measurement was performed to determine the complex elastic modulus and the phase angle.

[0117] <Viscosity over time of CNT dispersion composition> The secondary battery electrode composition was left to stand in a 40°C constant temperature bath for one week, then left to stand in a 25°C constant temperature bath for at least three hours. The CNT dispersion composition was then immediately analyzed using a Type B viscometer rotor at a rotation speed of 30 rpm. Rotor No. 4 was used. If the viscosity over time was less than 200 mPa·s, rotor No. 3 was used. The lower the viscosity of the CNT dispersion composition over time, the better the viscosity stability when used as a composition for secondary battery electrodes, the more coating unevenness can be suppressed, and a homogeneous electrode film and secondary battery can be obtained. [Evaluation Criteria] The evaluation criteria for viscosity over time were as follows: less than 4,000 mPa·s: Excellent (◎), 4,000 mPa·s or more but less than 6,000 mPa·s: Good (〇), 6,000 mPa·s or more but less than 9,000 mPa·s: Fair (△), 9,000 mPa·s or more: Poor (×).

[0118] <Viscosity of compositions for secondary battery electrodes> After allowing the secondary battery electrode composition to stand in a constant temperature bath at 25°C for at least one hour, a rheometer (MCR302e, manufactured by Anton Paar) was used with a 25 mm diameter, 2° cone to measure the temperature. °C, shear rate 0.01s ―1 from 1,000s -1 The shear viscosity was measured and evaluated. When the viscosity of the secondary battery electrode composition is within the following range, it can be said that the CNTs contained in the secondary battery electrode composition are uniformly dispersed, making it easier to improve the conductivity and strength of the electrode film. [Evaluation Criteria] The viscosity evaluation criteria for secondary battery electrode compositions is based on a shear rate of 1 s. -1 The viscosity was rated as follows: 2,000 mPa·s or more and less than 6,000 mPa·s: Excellent (◎), 6,000 mPa·s or more and less than 8,000 mPa·s: Good (〇), 8,000 mPa·s or more and less than 10,000 mPa·s: Fair (△), and less than 2,000 mPa·s or more than 10,000 mPa·s: Unacceptable (×).

[0119] <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 at least 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, within a shear strain range of 0.01% to 5%. Electrode strength was evaluated using 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 easily strained 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 Comparative Example 2-6, the elastic modulus changes even with slight strain, making the internal structure of the composition for secondary battery electrodes prone to damage. In Example 2-2 and Comparative Example 2-7, both are stable in regions without strain, but in Comparative Example 2-7, the dispersion state is inappropriate, resulting in high viscoelasticity during standing and a tendency to gel during standing, which is thought to affect the unevenness of the electrode at the start of coating and the handling of the product. The smaller the storage modulus value, the less prone the electrode is to unevenness and internal structure damage, indicating good electrode strength. [Evaluation Criteria] The evaluation criteria for electrode strength were as follows: Storage modulus less than 6 Pa: Excellent (◎), 6 Pa or more and less than 7 Pa: Good, 7 Pa or more and less than 8 Pa: Fair (△), 8 Pa or more: Poor.

[0120] <Evaluation of the conductivity of the negative electrode> The composition for the negative electrode of a secondary battery was measured using an applicator, and the basis weight per unit area of ​​the electrode was 8 mg / cm². 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. 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. 3A negative electrode was fabricated. Subsequently, the negative 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" for the operating mode, "MEDIUM" for the measurement speed, and "AUTO" for the measurement range. The thickness of the secondary battery electrode composition layer and the thickness of the copper foil were input, and the volume resistivity of the copper foil, "1.7000E-06", was selected. The film thickness of the secondary battery electrode composition layer was measured using a film thickness gauge (combination of digital microhead MH-15M (standard), measurement stand MS-5C, and counter TC-101, manufactured by Nikon Solutions Corporation), and the difference between the negative electrode film thickness and the copper foil film thickness was used. [Evaluation Criteria] The evaluation criteria for the conductivity of the negative electrode were as follows: Volume resistivity (Ω·cm) of the negative 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 (×).

[0121] <Fabrication of cells for battery evaluation> A negative electrode was punched out to a diameter of 16 mm to serve as the working electrode, and a metallic lithium foil (thickness 0.2 mm) was used as the counter electrode. A separator made of porous polypropylene film was inserted and laminated between the working and counter electrodes. After injecting 100 μL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate in a ratio of 38:30:28:3:1 (by weight), and then dissolving LiPF6 at a concentration of 1 M in the mixed solvent), a two-electrode cell (manufactured by Nippon Tom Cell Co., Ltd.) was assembled to produce a cell for battery evaluation.

[0122] <Evaluation of Cycle Characteristics of Secondary Batteries> A cell for battery evaluation was installed in a thermostatic chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (SM-8, manufactured by Hokuto Denko Corporation). The discharge current was set to 0.2C, and constant current constant voltage discharge (0.025C) was performed with a discharge cut-off voltage of 0V. Then, the charge current was set to 0.2C, and constant current charging was performed with a charge cut-off voltage of 1.5V. This operation was repeated 25 times. Here, 1C was defined as the current value that charges the theoretical capacity of the negative electrode in 1 hour. The cycle characteristics were calculated at 25°C using the ratio of the maximum 0.2C charge capacity within the 1st to 25th cycles to the 25th charge capacity, according to the following formula (2). (Formula 2) Cycle characteristics = 0.2C charge capacity at the 25th cycle / Maximum charge capacity within the 1st to 25th cycles × 100 (%) [Evaluation Criteria] For the cycle characteristics evaluation, when the cycle characteristics were 98% or more: Excellent (◎), 97% or more and less than 98%: Good (〇), 96% or more and less than 97%: Passable (△), less than 96%: Fail (×).

[0123] <Manufacture 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 Patent No. 7528392 and cutting with scissors until it became a sheet piece of about 1 mm × 3 mm.

[0124] (Production Example 2; CNT (A-2)) CNT (A-2) was obtained by the same method as in Production Example 1, except that the second temperature zone was changed from 1400°C to 1350°C.

[0125] (Production Example 3; CNT (A-3)) CNT (A-3) was obtained by the same method as in Production Example 1, except that the flow rate of the carrier gas was changed from 30,000 sccm to 45,000 sccm.

[0126] (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).

[0127] (Manufacturing example 5; CNT(A-5)) CNT(D) was crushed using a dry jet mill "NJ-50" (product name) manufactured by Aisin Nanotechnologies Inc., with a grinding air pressure of 1.2 MPa and a flow rate of 100 g / h, in a circulating grinding method to obtain CNT(A-5) at a processing speed of 30 g / h.

[0128] (Production example 6; CNT(A-6)) CNT(D) was processed using a bead mill in a 60L capacity dynamic mill (manufactured by Nippon Coke Industries Co., Ltd.) with 8mm diameter zirconia beads as the grinding media at a packing rate of 70%. 100kg of CNT(D) 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-6).

[0129] (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.

[0130] (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.

[0131] (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.

[0132] (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).

[0133] (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).

[0134] ·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

[0135] <Dispersant> • Dispersant (B-1): Polyacrylic acid (AC-10LP, weight-average molecular weight 50,000, manufactured by Toagosei Co., Ltd.) • Dispersant (B-2): Polyacrylic acid (AC-10P, weight-average molecular weight 9,000, manufactured by Toagosei Co., Ltd.) • Dispersant (B-3): Polyacrylic acid (molecular weight 1,000,000 to 1,600,000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Dispersant (B-4): Carboxymethylcellulose (Sunrose A, APP-084, weight-average molecular weight 18,000, manufactured by Nippon Paper Industries Co., Ltd.) • Dispersant (B-5): Polyvinyl alcohol (Kuraray Poval, SD1000, manufactured by Kuraray Co., Ltd.) • Dispersant (B-6); Polyvinylpyrrolidone (PVP) (K-30, weight-average molecular weight 40 ,000 (manufactured by Nippon Shokubai Co., Ltd.)

[0136] (Manufacturing Example 12; Dispersant (B-7)) 100 parts of acetonitrile were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen gas. The reaction vessel was heated to 70°C, and a mixture of 85.0 parts acrylonitrile, 15.0 parts acrylic acid, and 5.0 parts 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by NOF Corporation; V-65) was added dropwise over 2 hours to carry out the polymerization reaction. After the dropwise addition was complete, the reaction was continued at 70°C for another hour, then 0.5 parts of barbutyl O was added, and the reaction was continued at 70°C for another hour. Subsequently, the conversion rate was confirmed to be over 98% by measuring the non-volatile content, and the dispersion medium was completely removed by reducing the pressure and concentrating to obtain the dispersant (B-7). The weight-average molecular weight (Mw) of the dispersant (B-7) was 38,000.

[0137] (Method for measuring the weight-average molecular weight (Mw) of dispersants (B-1 to B-7)) The weight-average molecular weight (Mw) of the dispersants (B-1 to B-7) was measured using gel permeation chromatography (GPC) equipped with an RI detector, selecting either measurement method 1 or measurement method 2 depending on the solubility of the dispersant in water. The dispersant was added to a mixture of purified water and methanol (volume ratio) at a concentration of 0.2% by mass, and the mixture was sonicated for 10 minutes. If the dispersant was completely dissolved, it was measured using Measurement Method 1. On the other hand, if the dispersant did not completely dissolve, a precipitate formed, or the solution remained in a suspended state, it was measured using Measurement Method 2. (Measurement method 1) The apparatus used was a Shodex GPC-101 (manufactured by Showa Denko Corporation). Four columns were connected in series as separation columns: three Showa Denko "OHpak °SB-806M °HQ" columns and one Showa Denko "OHpak °SB-802.5 °HQ" column. The oven temperature was 40°C, and the eluent was a 50 mM lithium chloride solution of purified water / methanol = 3 / 7 (volume ratio). Measurements were taken at a flow rate of 1.0 mL / min. The sample was prepared at a concentration of 0.2% by mass in the mixture of the above eluents, and 0.1 mL was injected. Molecular weight is calculated on a polyethylene glycol basis. Based on the above measurement results, the weight-average molecular weight (Mw) of the dispersants (B-1 to B-7) was calculated. (Measurement Method 2) The apparatus used was the HLC-8320GPC (manufactured by Tosoh Corporation), and the separation columns used were, in order, Tosoh Corporation's "TSK-GELSUPER AW-4000", "AW-3000", and "A The "W-2500" was connected in series, the oven temperature was 40°C, and a 30 mM triethylamine and 10 mM lithium bromide N,N-dimethylformamide solution was used as the eluent, with a flow rate of 0 Measurements were taken at 0.6 mL / min. The sample was prepared at a concentration of 0.2% by mass in a solvent consisting of the above eluent, and 10 μL was injected. Molecular weight is expressed as polystyrene equivalent. Based on the above measurement results, the weight-average molecular weight (Mw) of the dispersants (B-1 to B-7) was calculated.

[0138] Table 1 shows the physical properties of the CNTs used in the examples and comparative examples.

[0139] [Table 1]

[0140] 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, third, and fourth dispersion steps.

[0141] [Table 2]

[0142] (Example 1-1) 98.05 parts of deionized water were added to a stainless steel container, and while stirring with a disperser, 0.90 parts of dispersant (B-1) and 0.05 parts of sodium carbonate were added and stirred with the disperser until homogeneous. Then, 1 part of CNT (A-4) was weighed out and added while stirring with the disperser, and a square-hole high-shear 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 homogeneous. This process is designated as the first dispersion step. Subsequently, the liquid to be dispersed was supplied from the stainless steel container through piping to a nozzle-type high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) and a circulating dispersion process was performed. The dispersion process was carried out using a single nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa, for 33 passes. This process is designated as the second dispersion step. By performing these processes, a CNT dispersion composition (D-1) was obtained.

[0143] (Examples 1-2 to 1-3) CNT-dispersed compositions (D-2 to D-3) were obtained by the same method as in Example 1-1, except that the second dispersion step was changed to the dispersion conditions described in Table 2.

[0144] (Examples 1-4) CNT dispersion composition (D-4) was obtained in the same manner as in Example 1-1, except that a valve-type high-pressure homogenizer (H3-1D, manufactured by Sanmaru Machinery Industry Co., Ltd.) was used instead of a nozzle-type high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machinery Co., Ltd.) and subjected to 50 passes at a pressure of 100 MPa.

[0145] (Examples 1-5) 98.05 parts of deionized water were added to a stainless steel container, and while stirring with a disperser, 0.90 parts of dispersant (B-1) and 0.05 parts of additive were added and stirred with the disperser until homogeneous. Then, 1 part of CNT (A-4) was weighed and added while stirring with the disperser, and a square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was homogeneous. This process is designated as the first dispersion process. Next, the mixture was circulated and dispersed from the stainless steel container through piping using a bead mill (Ashizawa Finetech Co., Ltd. "Star Mill LMZ2", bead filling rate 80%) filled with 1.0 mmφ zirconia beads, at a peripheral speed of 12 m / s and with a retention time of 16 minutes. This process is designated as the second dispersion process. Subsequently, the dispersion liquid was supplied from the stainless steel container through piping to a valve-type high-pressure homogenizer (H3-1D, manufactured by Sanmaru Machinery Industry Co., Ltd.) and circulating dispersion treatment was performed. For the homogenization step, a flat valve was used, and the mixture was processed in 50 passes at a pressure of 100 MPa. This step was designated as the third dispersion step. These processes were performed to obtain the CNT dispersion composition (D-5).

[0146] (Examples 1-6) 98.05 parts of deionized water were added to a stainless steel container, and while stirring with a disperser, 0.90 parts of dispersant (B-1) and 0.05 parts of additive were added and stirred with the disperser until homogeneous. Then, 1 part of CNT (A-4) was weighed and added while stirring with the disperser, and a square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was homogeneous. This process is designated as the first dispersion process. Next, the mixture was circulated and dispersed from the stainless steel container through piping using a bead mill (Ashizawa Finetech Co., Ltd. "Star Mill LMZ2", bead filling rate 80%) filled with 1.0 mmφ zirconia beads, at a peripheral speed of 12 m / s for 16 minutes. This process is designated as the second dispersion process. Next, the dispersion liquid was supplied from the stainless steel container to a nozzle-type high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion process was performed. The dispersion process was carried out using a single nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa for 40 passes. This process was designated as the third dispersion step. These processes were performed to obtain the CNT dispersion composition (D-6).

[0147] (Examples 1-7 to 1-11) CNT dispersion compositions (D-7 to D-11) were obtained in the same manner as in Examples 1-6, except that the second and third dispersion steps were changed to the bead diameter, dispersion time, nozzle diameter, pressure, and number of passes as shown in Table 2.

[0148] (Examples 1-12) 98.05 parts of deionized water were added to a stainless steel container, and while stirring with a disperser, 0.90 parts of dispersant (B-1) and 0.05 parts of additive were added and stirred with the disperser until homogeneous. Then, 1 part of CNT (A-4) was weighed and added while stirring with the disperser, and a square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the entire mixture was homogeneous. This process is designated as the first dispersion process. Next, the mixture was circulated and dispersed from the stainless steel container through piping using a bead mill (DynoMill MULTI LAB, manufactured by Shinmaru Enterprises, with a bead filling rate of 80%) filled with 2.0 mmφ zirconia beads, at a peripheral speed of 12 m / s and a residence time of 16 minutes. This process is designated as the second dispersion process. Next, the mixture was circulated and dispersed from the stainless steel container through piping using a bead mill (Ashizawa Finetech Co., Ltd. "Star Mill LMZ2", bead filling rate 80%) filled with 1.0 mmφ zirconia beads until it reached a peripheral speed of 12 m / s and remained in place for 16 minutes. This process was designated as the second dispersion step. Subsequently, the dispersion liquid was supplied from the stainless steel container through piping to a nozzle-type high-pressure homogenizer (Starburst Lab HJP-17007, Sugino Machine Co., Ltd.) for circulating dispersion treatment. The dispersion treatment was performed using a single-nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa for 40 passes. This process was designated as the fourth dispersion step. These processes were performed to obtain the CNT dispersion composition (D-12).

[0149] (Examples 1-13) 14.4 parts by mass of dispersant (B-1), 16 parts by mass of CNT (A-4), and 69.6 parts by mass of deionized water were charged into a Laboplast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the mixture was dispersed until the cumulative energy reached 2,000 MJ. This process is designated as the first dispersion process. Subsequently, the mixture was transferred to a stainless steel container, and 2565.6 parts by mass of deionized water and 1.07 parts by mass of sodium carbonate were added. A square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by Silverson), and the mixture was stirred at a speed of 7,000 rpm until uniform. This process is designated as the second dispersion process. The dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion process was performed. The dispersion process was carried out using a single-nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa for 40 passes. This process is designated as the third dispersion process. These processes were performed to obtain the CNT-dispersed composition (D-13).

[0150] (Examples 1-14) 14.4 parts by mass of dispersant (B-1), 16 parts by mass of CNT (A-4), and 69.6 parts by mass of deionized water were charged into a Laboplast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the mixture was dispersed until the cumulative energy reached 2,000 MJ. This process is designated as the first dispersion process. Subsequently, the mixture was transferred to a stainless steel container, and 2565.6 parts by mass of deionized water and 1.07 parts by mass of sodium carbonate were added. A square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by Silverson), and the mixture was stirred at a speed of 7,000 rpm until uniform. This process is designated as the second dispersion process. The dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion process was performed. The dispersion process was carried out using a single-nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa for 40 passes. This process is designated as the third dispersion process. Next, the mixture is circulated and dispersed from a stainless steel container through piping using a bead mill (Ashizawa Finetech Co., Ltd. "Star Mill LMZ2", bead filling rate 80%) filled with 1.0 mmφ zirconia beads, at a peripheral speed of 12 m / s for 16 minutes. This process is designated as the fourth dispersion step. These processes were performed to obtain the CNT dispersion composition (D-14).

[0151] (Examples 1-15) 14.4 parts by mass of dispersant (B-1), 16 parts by mass of CNT (A-4), and 69.6 parts by mass of deionized water were charged into a Laboplast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the mixture was dispersed until the cumulative energy reached 2,000 MJ. This process is designated as the first dispersion process. Subsequently, the mixture was transferred to a stainless steel container, and 2565.6 parts by mass of deionized water and 1.07 parts by mass of sodium carbonate were added. A square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. This process is designated as the second dispersion process. Next, the mixture was transferred from the stainless steel container via piping to a bead mill (Ashizawa Finetech Co., Ltd. "Star Mill LMZ2", bead filling rate 80%) filled with 1.0 mm diameter zirconia beads, and circulated dispersion was performed at a peripheral speed of 12 m / s for 16 minutes. This process is designated as the third dispersion process. The dispersion liquid was supplied from a stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion process was performed. The dispersion process was carried out using a single nozzle chamber, with a nozzle diameter of 0.20 mm and a pressure of 150 MPa for 40 passes. This process was designated as the fourth dispersion step. These processes were performed to obtain the CNT dispersion composition (D-15).

[0152] (Examples 1-16 to 1-53), (Comparative Examples 1-1 to 1-5) CNT dispersion compositions (D-16 to D-58) were prepared by changing the CNTs, dispersants, additives, water type and amount (parts by mass), and dispersion conditions as described in Table 3.

[0153] Table 3 shows the composition, physical properties, and evaluation results of the CNT dispersion compositions prepared in the examples and comparative examples.

[0154] [Table 3-1]

[0155] [Table 3-2]

[0156] [Table 3-3]

[0157] [Table 3-4]

[0158] (Example 2-1) Capacity 150cm 3 In a plastic container, 0.63 parts by mass of CNT dispersion composition (D-1), 12.5 parts by mass of an aqueous solution containing 2% by mass of CMC (manufactured by Daicel Finechem Co., Ltd., #1190), and 13.8 parts by mass of ion-exchanged water were weighed out. Then, using a rotation / revolution mixer (Awatori Rentaro, ARE-310, manufactured by Thinky Co., Ltd.), the mixture was stirred at 2,000 rpm for 30 seconds to obtain CNT resin composition (D-1). Next, 2.92 parts by mass of silicon monoxide (SILICON MONOOXIDE, SiO₂ 1.3C 5μm / 5μm, manufactured by Osaka Titanium Technologies Co., Ltd.) was added, and the mixture was stirred at 1,500 rpm for 10 minutes using a disperser. Furthermore, 21.44 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industry Co., Ltd.) was added, and the mixture was stirred at 6,000 rpm for 10 minutes using a disperser. Subsequently, 0.78 parts by mass of styrene-butadiene emulsion (manufactured by ENEOS Material Co., Ltd., TRD2001) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using the above-mentioned rotating / revolving mixer to obtain secondary battery electrode composition (D-1).

[0159] (Examples 2-2 to 2-53), (Comparative Examples 2-1 to 2-5) Secondary battery electrode compositions (D-2 to D-58) were obtained in the same manner as in Example 2-1, except that the CNT dispersion composition was changed to the one listed in Table 4, and the amount of CNT dispersion composition and ion-exchanged water added was adjusted so that the amount of CNT in 100% by mass of the secondary battery electrode composition was 0.025% by mass.

[0160] (Comparative Example 2-6) Secondary battery electrode composition (D-59) was obtained by the same method as in Example 2-1, except that the amount of CNT (A-4) and ion-exchanged water added was adjusted to replace the CNT dispersion composition so that the amount of CNT in 100% by mass of the secondary battery electrode composition was 0.025% by mass.

[0161] (Comparative Example 2-7) A secondary battery electrode composition (D-60) was obtained by the same method as in Example 2-1, except that the amount of a single-walled CNT dispersion (TUBALL BATT 02H017) containing carboxymethylcellulose with a CNT concentration of 0.4% by mass and deionized water was adjusted so that the amount of CNTs in 100% by mass of the secondary battery electrode composition was 0.025% by mass.

[0162] Table 4 shows the evaluation results of the secondary battery electrode compositions prepared in the examples and comparative examples.

[0163] [Table 4-1]

[0164] [Table 4-2]

[0165] (Example 3-1) The composition for secondary battery electrodes (D-1) was measured using an applicator, and the basis weight per unit area of ​​the electrode was 7.2 mg / cm². 2 After coating the copper foil in this manner, the coating was dried on a hot plate at 80°C for 10 minutes, and then dried in an electric oven at 120°C for 15 minutes to obtain electrode film D-1). Subsequently, the electrode film was rolled using a roll press (manufactured by Sanku Metal Co., Ltd., 3t hydraulic roll press) to obtain a composite layer density of 1.6 g / cm³. 3 A negative electrode (D-1) was fabricated.

[0166] (Examples 3-2 to 3-53), (Comparative Examples 3-1 to 3-7) The negative electrodes (D-2 to D-60) were prepared in the same manner as in Example 3-1, except that the secondary battery electrode composition (D-1) was changed to secondary battery electrode compositions (D-2 to D-60).

[0167] Table 5 shows the evaluation results of the negative electrodes prepared in the examples and comparative examples.

[0168] [Table 5-1]

[0169] [Table 5-2]

[0170] (Example 4-1) A negative electrode (D-1) was punched out to a diameter of 16 mm to serve as the working electrode, and a metallic lithium foil (thickness 0.2 mm) was used as the counter electrode. A separator made of porous polypropylene film was inserted and laminated between the working electrode and the counter electrode. After injecting 100 μL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate in a ratio of 38:30:28:3:1 (by weight), and then dissolving LiPF6 at a concentration of 1 M in the mixed solvent), a two-electrode cell (manufactured by Nippon Tom Cell Co., Ltd.) was assembled to produce a secondary battery (D-1).

[0171] (Examples 4-2 to 4-53), (Comparative Examples 4-1 to 4-7) A secondary battery (D-2 to D-60) was fabricated in the same manner as in Example 4-1, except that the negative electrode (D-1) was changed to the negative electrodes (D-2 to D-60).

[0172] Table 6 shows the evaluation results of the secondary batteries prepared in the examples and comparative examples.

[0173] [Table 6-1]

[0174] [Table 6-2]

[0175] In the above embodiment, a CNT dispersion composition was used, comprising CNTs, a dispersant, and water, wherein the CNTs included CNT aggregates in which two or more CNT 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 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.

[0176] Furthermore, the examples showed superior temporal stability of the CNT dispersion composition compared to the comparative example, and yielded a secondary battery electrode composition with excellent viscosity and peel strength, as well as a secondary battery with excellent cycle 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.

[0177] 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 water, The carbon nanotube comprises a carbon nanotube aggregate in which two or more carbon nanotube units, each having an average outer diameter of 3 nm or more and 8 nm or less and 3 to 15 layers, are bundled together in parallel by interaction. The average outer diameter of the carbon nanotube aggregate 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 m². 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. Shear rate of the carbon nanotube dispersion composition 10s －１ Viscosity (V1) at 25°C measured by [method / tool ​​name] and shear rate 100 s －１ The carbon nanotube dispersion composition according to claim 1, wherein the viscosity ratio (V1 / V2) of the viscosity (V2) measured at 25°C is 4.0 or more and 7.5 or less.

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.

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