Carbon nanotube dispersion composition, composite slurry, electrode film, secondary battery, and vehicle

Abstract

To provide: a carbon nanotube dispersion composition with excellent dispersibility and low initial viscosity, where the carbon nanotube dispersion composition enables provision of a composite slurry for forming an electrode film with high conductivity and adhesion; and more specifically, a secondary battery exhibiting excellent rate characteristics and high-temperature cycle characteristics, and a vehicle comprising the secondary battery thereby having high safety and improved fuel efficiency.SOLUTION: A carbon nanotube dispersion composition comprises carbon nanotubes, a copolymer, and an amide-based polar solvent, where the content of metallic foreign particles measured under a specific condition 1 is 1.0 mg or less. The copolymer comprises: 50 mass% or more and 75 mass% or less of alkylene structural units; and 25 mass% or more and 50 mass% or less of monomer units comprising a nitrile group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a carbon nanotube dispersion composition. More specifically, the present invention relates to a carbon nanotube dispersion composition including carbon nanotubes, a copolymer including a monomer unit having an alkylene structural unit and a nitrile group, and an amide-based organic solvent, a composite slurry including the carbon nanotube dispersion composition and an active material, an electrode film formed therefrom, a secondary battery including an electrode having the electrode film, and a vehicle including the secondary battery. [Background technology]

[0002] With the spread of electric vehicles and the miniaturization, weight reduction, and high performance of portable devices, there is a demand for secondary batteries with high energy density and further for high capacity of the secondary batteries. Under such a background, non-aqueous electrolyte secondary batteries using a non-aqueous electrolyte, particularly lithium ion secondary batteries, are being used in many devices because of their characteristics of high energy density and high voltage.

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

[0004] The conductive additive plays a role in forming a conductive path inside the electrode, and is required to be resistant to breakage due to the expansion and contraction of the electrode film. In order to maintain the conductive path with a small amount of conductive additive, it is effective to use a carbon material with a large specific surface area, in particular carbon nanotubes, which are a type of nanocarbon. However, although batteries using carbon nanotubes have excellent output characteristics, they often contain residual metal foreign matter derived from the metal catalyst used in the synthesis of carbon nanotubes, which causes problems with voltage drop.

[0005] In addition, the metal foreign particles contained in the carbon nanotube dispersion composition may dissolve inside the secondary battery, precipitate in the form of dendrites, and break through the separator, which may cause an internal short circuit. Furthermore, if the content of the metal foreign particles is high, the electrolyte and active material are likely to deteriorate due to high-temperature charging and discharging of the secondary battery, and the deterioration of high-temperature cycle characteristics becomes a problem. Therefore, it is required to reduce the amount of metal foreign particles contained in the carbon nanotube dispersion composition.

[0006] Therefore, Patent Document 1 considers a method of crushing carbon nanotubes containing foreign metal particles such as iron, cobalt, and nickel, and removing the foreign metal particles from the carbon nanotubes using an electromagnet.

[0007] Patent Documents 2 and 3 disclose a technique in which carbon nanotubes are disintegrated by a dispersion treatment, and then the metallic foreign particles are attached to a magnet to remove the metallic foreign particles from the carbon nanotubes.

[0008] Furthermore, Patent Document 4 proposes a method for removing metal foreign particles by circulating a dispersion containing a conductive assistant through a primary filter multiple times using a circulation method, and then passing the dispersion through at least two filters arranged in series once. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2010-174418 A [Patent Document 2] Patent No. 6962428 [Patent Document 3] Patent Publication No. 2021-065846 [Patent Document 4] Patent Publication No. 2022-046307 Summary of the Invention [Problem to be solved by the invention]

[0010] However, these conventional methods such as those described in Patent Documents 1 to 4 have limitations in reducing the metal content in the carbon nanotube dispersion composition, and there is a risk of problems such as an increase in viscosity due to the inhibition of dispersion stability by metal foreign particles, and insufficient characteristics when used as a secondary battery.

[0011] The problem to be solved by the present invention is to provide a carbon nanotube dispersion composition having good dispersibility and low initial viscosity, and a composite slurry capable of obtaining an electrode film having high conductivity and adhesion by using the carbon nanotube dispersion composition. More specifically, the problem to be solved by the present invention is to provide a secondary battery having excellent rate characteristics and high-temperature cycle characteristics, and a vehicle having the secondary battery, which is safe and has improved fuel efficiency. [Means for solving the problem]

[0012] The inventors of the present invention have conducted intensive research to solve the above problems. The inventors have found that a carbon nanotube dispersion composition containing carbon nanotubes, an amide-based polar solvent, and a copolymer having a specific structural unit in a specific ratio, and having a content of metal foreign particles of 1.0 mg or less as determined by condition 1, has good dispersibility and low initial viscosity, and that by using such a dispersion composition, an electrode with high conductivity and adhesion can be obtained. Furthermore, they have found that a secondary battery obtained by using this has excellent rate characteristics and high-temperature cycle characteristics. Based on these findings, the inventors have come up with the present invention.

[0013] That is, the present invention includes the following embodiments, but the embodiments of the present invention are not limited to the following. [1] A carbon nanotube dispersion composition comprising carbon nanotubes, a copolymer, and an amide-based polar solvent, The content of metallic foreign particles determined according to the following condition 1 is 1.0 mg or less, The copolymer has an alkylene structural unit content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less. Carbon nanotube dispersion composition. <Condition 1> The metal foreign particles in 20 kg of the carbon nanotube dispersion composition are collected using an electromagnet (an electromagnet having a magnetic flux density of 16,000 Gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and 31 grid screens of 1.3 cm thickness), and then washed with an amide-based polar solvent. The resulting metal foreign particles are deposited on a filter with a disk diameter of 47 mm and mesh openings of 5 μm, and the weight of the metal foreign particles on the filter is measured. [2] The carbon nanotube dispersion composition according to [1], wherein the total content of iron, cobalt, nickel, chromium, molybdenum and copper is 100 ppm or less. [3] The carbon nanotube dispersion composition according to [1] or [2], wherein the carbon nanotubes have an angle of repose of 40° or more. [4] Cumulative particle diameter D measured by laser diffraction method 90 is 6.0 μm or less, The carbon nanotube dispersion composition according to any one of items 1) to 3). [5] The carbon nanotube dispersion composition according to any one of [1] to [4], having a viscosity at 25°C measured with a Brookfield viscometer of less than 2,000 mPa·s. [6] A composite slurry comprising the carbon nanotube dispersion composition according to any one of [1] to [5] and an active material. [7] An electrode film formed from the composite slurry according to [6]. [8] A secondary battery having a positive electrode and a negative electrode, A secondary battery, in which at least one of a positive electrode and a negative electrode has the electrode film according to [6]. [9] A vehicle equipped with the secondary battery described in [8].

[10] A method for producing a carbon nanotube dispersion composition according to any one of [1] to [5], comprising all of the following steps (1) to (3): [Process (1): Crushing process] A process of applying shear stress to the carbon nanotubes to disintegrate them. [Process (2): Magnetic selection process] A process to remove metal foreign particles using an electromagnet with a magnetic flux density of 10,000 gauss or more and 20,000 gauss or less. [Step (3): Filtration step] A process of filtering using a depth filter with a filtering accuracy of 5 μm to 50 μm Effect of the Invention

[0014] The carbon nanotube dispersion composition of the present invention has good dispersibility and low initial viscosity, and by using this carbon nanotube dispersion composition, an electrode film excellent in conductivity and adhesion can be obtained. In addition, a secondary battery excellent in rate characteristics and high-temperature cycle characteristics can be obtained. As a result, it can be suitably used even in vehicle applications such as hybrid automobiles, plug-in hybrid automobiles, and electric automobiles, in which high capacity, high output, and high durability are required for the secondary battery to be mounted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The carbon nanotube dispersion composition, composite slurry, electrode film, and secondary battery of the present invention will be described in detail below, but are not limited thereto. Note that the numerical values ​​specified in this specification are values ​​obtained by the methods disclosed in the embodiments or examples.

[0016] In addition, in this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the lower limit and upper limit of the range. In this specification, carbon nanotubes may be referred to as "CNTs" and N-methyl-2-pyrrolidone may be referred to as "NMP." In addition, in this specification, the carbon nanotube dispersion composition may be referred to as the "CNT dispersion composition" or simply as the "dispersion composition." In the present invention, the foreign metallic particles are not limited to those of any size or shape, and include fine metal powders, but do not include those that are dissolved and exist in the form of metal ions. Unless otherwise noted, the various components appearing in this specification may be used independently as a single type or as a mixture of two or more types.

[0017] <Carbon nanotube dispersion composition> A carbon nanotube dispersion composition according to one embodiment of the present invention is a carbon nanotube dispersion composition comprising carbon nanotubes, a copolymer, and an amide-based polar solvent, The content of metallic foreign particles determined according to the following condition 1 is 1.0 mg or less, The copolymer has an alkylene structural unit content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less. <Condition 1> Metallic particles in 20 kg of the carbon nanotube dispersion composition were placed in an electromagnet (magnetic flux density 16 The particles are collected using an electromagnet equipped with 31 grid screens, each with a spatial volume of 1.7 L and a diameter of 10 cm and a thickness of 1.3 cm, and then washed with an amide-based polar solvent. The resulting metal foreign particles are deposited on a filter with a disk diameter of 47 mm and mesh size of 5 μm, and the weight of the metal foreign particles on the filter is measured.

[0018] Specifically, the content of metallic foreign particles can be determined, for example, by the method described in the Examples.

[0019] The content of metal foreign particles contained in the carbon nanotube dispersion composition as determined by condition 1 is 1.0 mg or less, and from the viewpoint of the storage stability and high-temperature cycle characteristics of the secondary battery, it is preferably 0.4 mg or less, and more preferably 0.1 mg or less. This makes it possible to obtain a carbon nanotube dispersion composition having good dispersibility and low initial viscosity. Furthermore, by using this carbon nanotube dispersion composition, a secondary battery having excellent rate characteristics and high-temperature cycle characteristics can be obtained.

[0020] The carbon nanotube dispersion composition of the present invention is characterized in that the content of metallic foreign particles collected by a magnet and recovered by a filter with a mesh size of 5 μm is 1.0 mg or less according to condition 1. If the content of metallic foreign particles of 5 μm or more collected by the magnet is large, the metallic foreign particles may be exposed from the electrode surface, causing a short circuit in the secondary battery, which may cause the secondary battery to fail to function. In addition, the metallic foreign particles may dissolve in the electrolyte, which may cause the secondary battery to spontaneously discharge more.

[0021] The inventors have discovered that simply reducing the content of metal ions contained in a carbon nanotube dispersion composition does not result in fully satisfactory electrical characteristics when used as a secondary battery, and that the content of metal foreign particles of 5 μm or more that are captured by a magnet is also important.

[0022] The reason for this is presumably as follows. When carbon nanotubes are synthesized, metal catalysts are used in the manufacturing process. Therefore, metals derived from the metal catalyst remain and may be contained within the carbon nanotubes. When the metals derived from the metal catalyst contained within the carbon nanotubes and the abrasion powder that may be contained when dispersing the carbon nanotubes are finely divided by dispersion, it is difficult to capture only the metal foreign particles even when a filter with high filtration accuracy is used.

[0023] Furthermore, the metallic foreign particles may include wear powder from the inner walls and piping of the disperser used in the dispersion process of carbon nanotubes, and in some cases, wear powder from the dispersion media, stirring blades, etc. Wear powder originating from parts of piping and tanks containing SUS304 or SUS316 used in dispersers and piping changes the crystal structure of SUS304 or SUS316 when external stress is applied to the SUS304 or SUS316, becoming metallic foreign particles with magnetism, but because the magnetism is weak, it is difficult to remove.

[0024] These foreign metal particles deteriorate the dispersion stability in the carbon nanotube dispersion composition and cause an increase in viscosity. In addition, if the foreign metal particles are larger than the thickness of the separator, for example, 20 μm or more, they may break through the separator separating the positive and negative electrodes, causing an internal short circuit and resulting in voltage failure.

[0025] Furthermore, metal foreign particles often have an orientation, and even if a filter with a filtering accuracy of 20 μm is used when filtering the carbon nanotube dispersion composition, needle-shaped metal foreign particles of 20 μm or more may be mixed into the carbon nanotube dispersion composition. Such metal foreign particles are weakly magnetic, and only the metal foreign particles close to the magnetic pole are magnetically attracted to the magnet. Therefore, it is difficult to reduce the number of foreign metal particles simply by using a magnet with a strong magnetic force and increasing the number of times of magnetic separation processing. However, by using a magnet with a certain level of magnetic force and a narrow gap between the magnetic poles, such as an electromagnet, it is possible to remove weakly magnetic foreign metal particles and to reduce the content of foreign metal particles of 5 μm or more required by condition 1 to 1.0 mg or less, thereby making it possible to fabricate a secondary battery that is not only highly safe but also has good rate characteristics and high-temperature cycle characteristics.

[0026] The carbon nanotube dispersion composition means a state before the active material is added. In this respect, the carbon nanotube dispersion composition is distinguished from a composite slurry containing an active material. That is, the carbon nanotube dispersion composition does not substantially contain an active material. This is a concept excluding a state in which an active material is intentionally added to the carbon nanotube dispersion composition, and the active material may be 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less, or may be 0 mass %, based on the total mass of the carbon nanotube dispersion composition. The active material will be described later.

[0027] The carbon nanotube dispersion composition of the present invention contains carbon nanotubes, and when used as a conductive assistant in an electrode for a secondary battery, it is possible to form a conductive path even in a small amount, and it is possible to have excellent rate characteristics and high-temperature cycle characteristics.

[0028] As mentioned above, carbon nanotubes contain and / or retain metals derived from the metals used during production, and if the metals remain present, they can cause voltage drops and the like. Since the encapsulated metal powder is exposed and refined by dispersion, from the viewpoint of efficiency in removing metallic foreign matter, it is desirable to remove and reduce the amount of metal powder before it is refined, i.e., before or during the dispersion process.

[0029] In addition, metallic foreign particles that may be mixed in as wear debris from pipes or tanks containing SUS304 or SUS316 during the carbon nanotube dispersion process can change crystal structure due to external stress such as dispersion, become magnetic, and can cause voltage drops when used in secondary batteries. Therefore, it is desirable to reduce the amount of metallic foreign particles derived from these wear particles before they are pulverized in the dispersion step, and preferably, they are removed by a magnet before the dispersion step or simultaneously with the dispersion step. This not only prevents the magnetic attraction area of ​​the metal foreign particles from becoming smaller and the efficiency of foreign matter removal by the magnet from becoming difficult to sufficiently reduce the metal foreign matter particles, but also suppresses a decrease in the stability of the carbon nanotube dispersion liquid caused by the finely divided metal foreign matter particles.

[0030] The carbon nanotube dispersion composition of the present invention is capable of achieving excellent dispersibility and high-temperature cycle characteristics by controlling the content of metal foreign particles required by condition 1, which includes metal foreign particles resulting from the production of carbon nanotubes and metal foreign particles such as abrasion powder from the dispersing machine during the dispersion process, to 1.0 mg or less. The content of metallic foreign particles required by condition 1 can be controlled to 1.0 mg or less by reducing the amount of metallic foreign particles brought in from the raw materials as much as possible, removing metallic foreign particles from the dispersion equipment and the dispersion process during the process, filtering the dispersed carbon nanotube dispersion composition, etc. Furthermore, the content of metallic foreign particles can be further reduced by magnetic separation using a magnet with a narrow magnetic pole gap, such as an electromagnet. Since metallic foreign particles often have an orientation, it is preferable to pass the particles through a magnet or filter multiple times. These methods make it possible to achieve both dispersion stability, which cannot be achieved by simply reducing the metal element content in the carbon nanotube dispersion composition, and excellent battery characteristics.

[0031] The total content of iron, cobalt, nickel, chromium, molybdenum and copper in the carbon nanotube dispersion composition is preferably as small as possible, and is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less. When the content of metallic foreign particles required by condition 1 is 1.0 mg or less and the total content of iron, cobalt, nickel, chromium, molybdenum and copper is within the above range, voltage defects in the secondary battery can be further suppressed. The iron, cobalt, nickel, chromium and molybdenum contents are each preferably 10 ppm or less, more preferably 5 ppm or less, and more preferably 1 ppm or less, while the copper content is preferably 5 ppm or less, more preferably 1 ppm or less, and more preferably 0.1 ppm or less. Iron, cobalt, nickel, and molybdenum are used as catalyst raw materials when producing carbon nanotubes. Since carbon nanotubes are produced in a reducing atmosphere, the above-mentioned iron, cobalt, nickel, and molybdenum exist in the form of pure metals contained in carbon nanotubes, and since they have a low redox potential, they may dissolve into the electrolyte and precipitate on the negative electrode surface, which may lead to voltage defects and capacity reduction of the secondary battery. In addition, iron, nickel, and chromium may be mixed in from wear powder of the tank or stirrer used to produce the carbon nanotube dispersion composition, and copper may be mixed in from the motor of the dispersion equipment. Of these, copper has a low redox potential, so it may dissolve into the electrolyte and precipitate in the form of dendrites on the negative electrode surface, which may lead to voltage defects of the secondary battery. The amounts of these metal elements can be measured, for example, by ICP emission spectrometry.

[0032] The content of carbon nanotubes in the carbon nanotube dispersion composition is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less, and even more preferably 3% by mass or more and 6% by mass or less, based on the mass of the carbon nanotube dispersion composition (the mass of the carbon nanotube dispersion composition being 100% by mass).

[0033] The content of the copolymer is preferably 5 parts by mass or more and 200 parts by mass or less, more preferably 10 parts by mass or more and 100 parts by mass or less, and even more preferably 20 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the carbon nanotubes. When the amount of the copolymer containing the alkylene structural unit and the nitrile group-containing structural unit is within the above range, the dispersion stability of the carbon nanotubes in the carbon nanotube dispersion composition tends to be good. In addition, the peel strength of the electrode for the secondary battery is good.

[0034] The content of the amide polar solvent is preferably 90% by mass to 99% by mass, and more preferably 92% by mass to 98% by mass, based on the carbon nanotube dispersion composition (100% by mass). When it is within the above range, a carbon nanotube dispersion composition having excellent fluidity and dispersion stability is easily obtained. By using a carbon nanotube dispersion composition having excellent fluidity and dispersion stability, it is easy to remove metal foreign matter, an electrode film having stable conductivity is obtained, and the quality of the secondary battery is likely to be stable.

[0035] The carbon nanotube dispersion composition preferably has a water content of 100 ppm or more and 1500 ppm or less, and more preferably 200 ppm or more and 1000 ppm or less. When the water content of the carbon nanotube dispersion composition is within the above range, gelation of the composite slurry described below is suppressed, and it is easy to obtain a composite slurry and an electrode film with stable quality. When the water content exceeds the above range, the metal contained in the carbon nanotube may dissolve during dispersion, making it difficult to remove metal foreign matter during the manufacturing process.

[0036] The initial viscosity of the carbon nanotube dispersion composition is preferably less than 2,000 mPa·s, measured at 100 rpm and 25°C using a B-type viscometer. More preferably, it is less than 1,000 mPa·s, and even more preferably, it is less than 500 mPa·s. It may be 100 mPa·s or more. When the initial viscosity is within the above range, the dispersion state of the carbon nanotubes contained in the carbon nanotube dispersion composition is appropriate, and it is easy to remove metal foreign matter using a filter or an electromagnet. It is considered that the carbon nanotube dispersion composition having an initial viscosity within the above range has an appropriate composition ratio of the carbon nanotubes, the copolymer, and the amide polar solvent, and a dispersion process, and has good dispersion stability. Specifically, it can be measured by the method described in the Examples, for example.

[0037] The carbon nanotube dispersion composition has a cumulative particle diameter D measured by laser diffraction. 90is preferably 10 μm or less, more preferably 6.0 μm or less, and even more preferably 4.0 μm or less. Also, it is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. 90 In the case where the carbon nanotube dispersion composition is in the above range, a conductive network of the carbon nanotubes is easily formed in the electrode. In addition, the carbon nanotube dispersion composition has good filterability, and metal foreign particles can be removed using a filter with high filtering accuracy, so that the inclusion of metal foreign particles in the secondary battery can be suppressed, and the rate characteristics and cycle characteristics of the secondary battery are further improved.

[0038] <Carbon nanotubes> Carbon nanotubes have a structure in which planar graphite is wound into a cylindrical shape, and include single-walled carbon nanotubes and multi-walled carbon nanotubes, and these may be mixed. Among them, it is preferable to include multi-walled carbon nanotubes. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound, and single-walled carbon nanotubes have a structure in which one layer of graphite is wound. The sidewall of the carbon nanotube does not have to have a graphite structure. For example, carbon nanotubes with sidewalls having an amorphous structure can also be used as the carbon material.

[0039] The average outer diameter of the carbon nanotubes is preferably 1 nm to 25 nm, more preferably 3 nm to 20 nm, and even more preferably 4 nm to 15 nm. When the average outer diameter is within the above range, a good conductive network is easily formed in the electrode, and the active material inside the secondary battery is used uniformly during charging and discharging, so that deterioration of the active material is suppressed and the cycle characteristics of the secondary battery are further improved.

[0040] The BET specific surface area of ​​carbon nanotubes is 100m 2 / g or more 1000m 2 / g or less, and 2 / g or more 600m 2 / g or less is more preferable, and 2 / g or more 500m 2 / g or less is more preferable. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount, and the amount of conductive material in the electrode can be reduced. This increases the degree of freedom in battery design, such as increasing the amount of active material and binder resin. Furthermore, when preparing the composite slurry, the active material and the carbon nanotubes are more likely to be combined, so that an electrode film having a homogeneous conductive network in which the active material surface is covered with carbon nanotubes can be obtained, and the electrolyte decomposition reaction at the interface between the electrolyte and the active material can be suppressed, thereby improving the cycle characteristics of the battery. The BET specific surface area can be measured by the BET method described in JIS Z 8830.

[0041] The G / D ratio (peak ratio of the G-band to the D-band) of carbon nanotubes is 1560 cm -1 ~1600cm -1 The maximum peak intensity in the range of G, 1310 cm -1 ~1350cm -1 When the maximum peak intensity within the range is D, The G / D ratio is preferably from 0.5 to 10, and more preferably from 0.7 to 4.5. When the G / D ratio of the carbon nanotubes is within the above range, it is believed that the contact resistance between the carbon nanotubes is small, and good electrical conductivity is easily obtained. It is also believed that the amount of functional groups on the multi-walled carbon nanotube surface is appropriate, and the affinity with the solvent is good, resulting in better dispersibility.

[0042] The volume resistivity of carbon nanotubes is 1.0×10 -2 Ω cm~3.0×10 -2 Ω cm is preferred, and 1.0×10 -2 Ω cm~2.0×10 -2 It is more preferable that the resistance is Ω·cm. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Nitto Seiko Analytech Co., Ltd.) When the volume resistivity is within the above range, the conductivity of the electrode film is good, and a secondary battery having excellent rate characteristics and cycle characteristics can be obtained.

[0043] The angle of repose of the carbon nanotubes is preferably 40° or more. More preferably, it is 45° or more, and even more preferably, it is 50° or more. Also, it is preferably 85° or less, and more preferably, it is 70° or less. The angle of repose is an index representing the fluidity of the powder, and the carbon nanotubes having the angle of repose in the above range are easy to remove the metal foreign matter particles contained in the carbon nanotubes, and it is easy to obtain a carbon nanotube dispersion composition having a low content of metal foreign matter particles. The angle of repose can be measured by the injection method. The injection method is a method in which the powder is deposited on a table having a disk-shaped upper surface and measured, and is not easily affected by the material of the table, and the angle between the powder deposited in a cone shape and the horizontal plane can be measured using a protractor or the like. The angle of repose can also be measured using a commercially available measuring device.

[0044] The angle of repose of carbon nanotubes can be controlled by processing using conventionally known pulverizing equipment. Examples of pulverizing equipment that can be used include a Henschel mixer, a super mixer, a Nauta mixer, a Trimix, a high-speed mixer, a mortar, a pin mill, a hammer mill, a pulverizer, an attritor, a jet mill, a cutter mill, a ball mill, a bead mill, a colloid mill, a conical mill, a disk mill, an edge mill, a wonder crusher, a vibration mill, and an ultrasonic homogenizer. Particularly preferred are an attritor, a pin mill, a hammer mill, a jet mill, a cutter mill, a ball mill, and a bead mill vibration mill.

[0045] It is preferable that the carbon nanotubes have been removed of metallic foreign matter particles by magnetic force using an electromagnet. For example, it is preferable to remove metallic foreign matter particles by passing the carbon nanotubes through an electromagnet in the crushing process or filling process of the carbon nanotubes. The higher the carbon purity of the carbon nanotubes, the more preferable. The carbon purity is preferably 98.0 mass % or more, more preferably 99.5 mass % or more, even more preferably 99.8 mass % or more, and particularly preferably 99.9 mass % or more, based on 100 mass % of the carbon nanotubes. That is, the lower the content of metallic foreign particles, the better; it is preferably 2.0 mass % or less, more preferably 0.5 mass % or less, even more preferably 0.2 mass % or less, and particularly preferably 0.1 mass % or less, based on 100 mass % of the carbon nanotubes. By using carbon nanotubes produced by a method that does not use a metal catalyst as a nucleus, or carbon nanotubes obtained by a conventional purification method such as acid treatment, the content of metal foreign particles can be reduced to 2.0 mass% or less relative to 100 mass% of carbon nanotubes, thereby reducing the content of metal foreign particles in the carbon nanotube dispersion composition and improving the characteristics of secondary batteries. The carbon purity of the carbon nanotubes was measured using an ICP emission spectrometer as described in the Examples. It can be found by the method.

[0046] <Copolymer> The copolymer of the present invention has an alkylene structural unit content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less. By using such a copolymer, a carbon nanotube composition having excellent dispersibility and oxidation resistance can be obtained, and since it has low solubility in the electrolyte, the ionic conductivity of the electrolyte is less likely to decrease, and secondary batteries using this can have excellent rate characteristics and high-temperature cycle characteristics. The copolymer can be prepared, for example, by copolymerizing a monomer mixture containing a conjugated diene monomer and a nitrile group-containing monomer, partially hydrogenating the carbon-carbon double bonds of the structural units derived from the conjugated diene monomer by hydrogenation, and obtaining a copolymer having an alkylene structural unit and a nitrile group-containing structural unit. Specifically, it can be produced by the method described below.

[0047] The Mooney viscosity of the copolymer is preferably 65 or less, more preferably 60 or less, further preferably 50 or less, and particularly preferably 35 or less. Also, it is preferably 20 or more, and more preferably 35 or more.

[0048] In the present invention, the "Mooney viscosity (ML 1+4 ", 100℃)" can be measured at a temperature of 100℃ in accordance with JIS K6300-1. It is presumed that by setting the Mooney viscosity in the above range, the copolymer adsorbed on the carbon nanotubes has a moderate repulsive force, and the dispersion stability can be improved. By setting the Mooney viscosity to 20 or more, the balance between the solubility in the amide-based polar solvent used as the solvent and the adsorption to the carbon nanotubes is good, and the dispersibility of the carbon nanotubes is improved. In addition, when the Mooney viscosity is 65 or less, the viscosity of the carbon nanotube dispersion composition does not become too high, the decrease in the energy transmission efficiency of the dispersing machine is suppressed, and metal foreign matter that is mixed in due to the raw material can be efficiently removed by a method such as magnet, filtration, and centrifugation, so that it is preferable to prevent voltage defects of secondary batteries caused by metal foreign matter particles.

[0049] The copolymer of the present invention may have suitable fluidity at room temperature as long as it has an alkylene structural unit content of 50% by mass or more and 75% by mass or less and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less.

[0050] The weight average molecular weight (Mw) of the copolymer is preferably 20,000 to 200,000, more preferably 20,000 to 150,000. When the weight average molecular weight is within the above range, the adsorption to carbon nanotubes and the affinity to the dispersion medium tend to be good. The weight average molecular weight is the weight average molecular weight converted into polystyrene and can be measured by gel permeation chromatography (GPC).

[0051] The method for adjusting the Mooney viscosity is not particularly limited, and the viscosity can be adjusted, for example, by changing the composition of the polymer (type and content of structural units, hydrogenation rate, etc.), structure (linearity rate, etc.), molecular weight, preparation conditions (polymerization temperature, amount of molecular weight regulator, etc.), etc.

[0052] The copolymer used is preferably one from which metallic foreign particles have been removed by a filtering process using a filter and / or a magnetic separation process using a magnetic force using an electromagnet. For example, it is preferable to remove metallic foreign particles by passing the copolymer through a filter or an electromagnet in the crushing process or filling process of the copolymer. The magnetic separation step of the copolymer may be carried out after dissolving the copolymer in an amide-based polar solvent or the like to prepare a copolymer solution.

[0053] [Alkylene structural unit] The alkylene structural unit is a structural unit containing an alkylene structure, and is preferably a structural unit consisting of only an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure, except for structural units having a nitrile group.

[0054] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1A).

[0055] General formula (1A) [ka]

[0056] In general formula (1A), n represents an integer of 1 or more. n is preferably an integer of 2 or more, and more preferably an integer of 3 or more. n is preferably an integer of 5 or less, and more preferably an integer of 4 or less. In particular, n is preferably 3.

[0057] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1B).

[0058] General formula (1B) [ka]

[0059] In general formula (1B), n represents an integer of 1 or more. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, and even more preferably an integer of 2 or less. In particular, n is preferably 2.

[0060] The method for introducing an alkylene structural unit into the copolymer is not particularly limited, but examples thereof include the following method (1a) or (1b).

[0061] In the method (1a), a copolymer is prepared by polymerization reaction using a monomer composition containing a conjugated diene monomer. The prepared copolymer contains monomer units derived from the conjugated diene monomer. In the present invention, the "monomer units derived from the conjugated diene monomer" may be referred to as "conjugated diene monomer units", and the same abbreviation is used for monomer units derived from other monomers. Then, the conjugated diene monomer units are hydrogenated to convert at least a part of the conjugated diene monomer units into alkylene structural units. Hereinafter, "hydrogenation" may be referred to as "hydrogenation". The finally obtained copolymer contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0062] The conjugated diene monomer unit includes at least a monomer unit having one carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, includes at least one monomer unit selected from the group consisting of a monomer unit having a cis-1,4 structure, a monomer unit having a trans-1,4 structure, and a monomer unit having a 1,2 structure, and may include two or more monomer units. The conjugated diene monomer unit may further include a monomer unit having no carbon-carbon double bond and including a branch point. In this specification, the "branch point" refers to a branch point in a branched polymer, and when the conjugated diene monomer unit includes a monomer unit having a branch point, the above-prepared copolymer and the copolymer are branched polymers.

[0063] In the method (1b), a copolymer is prepared by polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared copolymer contains α-olefin monomer units. The finally obtained copolymer contains the α-olefin monomer units as alkylene structural units.

[0064] Among these, the method (1a) is preferred because the copolymer can be easily produced. The carbon number of the conjugated diene monomer is 4 or more, preferably 4 to 6. Examples of the conjugated diene monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. The alkylene structural unit preferably contains a structural unit (hydrogenated conjugated diene monomer unit) obtained by hydrogenating a conjugated diene monomer unit, and more preferably contains a structural unit (hydrogenated 1,3-butadiene monomer unit) obtained by hydrogenating a 1,3-butadiene monomer unit. The conjugated diene monomer can be used alone or in combination of two or more kinds.

[0065] The hydrogenation is preferably a method capable of selectively hydrogenating conjugated diene monomer units. Examples of the hydrogenation method include known methods such as oil phase hydrogenation and aqueous phase hydrogenation.

[0066] The hydrogenation can be carried out by a conventional method. For example, the hydrogenation can be carried out by treating a copolymer having conjugated diene monomer units dissolved in a suitable solvent with hydrogen gas in the presence of a hydrogenation catalyst. Examples of the hydrogenation catalyst include nickel, palladium, platinum, copper, etc.

[0067] In the method (1b), the carbon number of the α-olefin monomer is 2 or more, preferably 3 or more, and more preferably 4 or more. The carbon number of the α-olefin monomer is preferably 6 or less, and more preferably 5 or less. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomer may be used alone or in combination of two or more.

[0068] The alkylene structural unit preferably includes at least one selected from the group consisting of a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, more preferably includes at least one selected from the group consisting of a structural unit consisting only of a linear alkylene structure and a structural unit consisting only of a branched alkylene structure, and is preferably selected from the group consisting of a structural unit represented by the above formula (1A) and a structural unit represented by the above formula (1B). It is more preferable that the compound contains at least one selected from the above.

[0069] The content of the alkylene structural unit is 50% by mass or more and 75% by mass or less based on the mass of the copolymer (i.e., when the mass of the copolymer is 100% by mass), preferably 55% by mass or more, and more preferably 70% by mass or less, and more preferably 65% ​​by mass or less. By setting the content of the alkylene structural unit within the above range, the adsorption to the carbon nanotubes and the affinity to the dispersion medium can be controlled, and the carbon nanotubes can be stably present in the dispersion medium, so that the stability of the dispersion composition is improved. In addition, the affinity of the copolymer to the electrolyte can be controlled, and problems such as the copolymer dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented.

[0070] [Nitrile group-containing structural unit] The nitrile group-containing structural unit is a structural unit having a nitrile group. A structural unit having an alkylene structure substituted with a nitrile group is preferred, and a structural unit consisting of only an alkylene structure substituted with a nitrile group is more preferred. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further include a structural unit including (or consisting of) an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one.

[0071] The nitrile group-containing structural unit preferably has a structural unit represented by the following general formula (2A).

[0072] General formula (2A) [ka]

[0073] In formula (2A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2.

[0074] The nitrile group-containing structural unit may include a structural unit represented by the following general formula (2B).

[0075] General formula (2B) [ka]

[0076] In general formula (2B), R represents a methyl group.

[0077] The method of introducing the nitrile group-containing structural unit into the copolymer is not particularly limited, but a method of preparing a copolymer by polymerization reaction using a monomer composition containing a nitrile group-containing monomer (method (2a)) can be preferably used. The finally obtained copolymer has a nitrile group-containing monostructural unit as a nitrile group-containing structural unit. Examples of the nitrile group-containing monomer capable of forming the nitrile group-containing structural unit include monomers having a polymerizable carbon-carbon double bond and a nitrile group. For example, an α,β-ethylenically unsaturated group-containing compound having a nitrile group, specifically, acrylonitrile, methacrylonitrile, etc. are mentioned. In particular, from the viewpoint of increasing the intermolecular force between the copolymers and / or between the copolymer and the dispersed substance (adsorbed substance), it is preferable that the nitrile group-containing monomer contains acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more kinds.

[0078] The content of the nitrile group-containing structural unit is from 25% by mass to 50% by mass based on the mass of the copolymer (i.e., when the mass of the copolymer is taken as 100% by mass), preferably 30% by mass or more, and more preferably 45% by mass or less, and more preferably 40% by mass or less. By setting the content of the nitrile group-containing structural unit within the above range, the adsorption to carbon nanotubes and the affinity to the dispersion medium can be controlled, and the carbon nanotubes can be stably present in the dispersion medium, so that the stability of the dispersion composition is improved. In addition, the affinity of the copolymer to the electrolyte can be controlled, and problems such as the copolymer dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented.

[0079] [Other structural units] As long as the effects of the present invention are not impaired, structural units other than the alkylene structural unit and the nitrile group-containing structural unit may be contained as necessary. Examples of the other structural units include an amide group-containing monomer and a carboxyl group-containing monomer.

[0080] <Amide-based polar solvent> Amide-based polar solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl- Examples of the monomer include 2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. Among these, it is more preferable to use at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0081] The water content of the amide-based polar solvent is preferably 100 ppm or more and 1500 ppm or less, more preferably 100 ppm or more and 1000 ppm or less. When it is in the above range, the alkali metal encapsulated in the carbon nanotubes dissolves in the carbon nanotube dispersion composition, and the carbon The dispersion stability of the carbon nanotube dispersion composition may be improved.

[0082] <Optional ingredients> The carbon nanotube dispersion composition may contain optional components such as other additives such as alkali metal hydroxides, wetting agents, pH adjusters, wetting penetrants, and leveling agents, and other conductive materials other than carbon nanotubes, as necessary, within a range that does not impair the object of the present invention. The optional components can be added at any timing, such as before the preparation of the carbon nanotube dispersion composition, during mixing, after mixing, or a combination thereof.

[0083] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. When an alkali metal hydroxide is used, the content is preferably 0.5 parts by mass or more and 4 parts by mass or less, more preferably 1 part by mass or more and 3 parts by mass or less, and more preferably 1.5 parts by mass or more and 2.5 parts by mass or less, relative to 100 parts by mass of the copolymer. When an alkali metal hydroxide is used, the wettability of the carbon nanotubes is improved, and the dispersibility is further improved. In addition, since the dispersion progresses to the target viscosity in a short time, the carbon nanotubes are less damaged, and it is easy to obtain an electrode film and a secondary battery with good conductivity.

[0084] <Method of Manufacturing Carbon Nanotube Dispersion Composition> The carbon nanotube dispersion composition of the present embodiment is obtained by dispersing a mixture containing carbon nanotubes, a copolymer, and an amide-based polar solvent using a disperser. In addition, the production method is not particularly limited, but preferably includes a step of crushing the carbon nanotubes by applying shear stress to the carbon nanotubes, and a metal foreign matter removal step such as a magnetic separation step for removing magnetic foreign matter, a filtering step, and a centrifugal separation step in order to make the content of metal foreign matter particles in the carbon nanotube dispersion composition determined by condition 1 1.0 mg or less. As these metal foreign matter removal steps, at least one of the magnetic separation step and the filtering step is preferable. The metal foreign matter removal step may be carried out at any timing, such as before, during, or after the dispersion of the carbon nanotube dispersion composition. The metallic foreign particles are preferably removed before being pulverized in the dispersion step, and it is preferable to have a metallic foreign particle removing step before and / or during the dispersion of the carbon nanotube dispersion composition.

[0085] A method for producing a carbon nanotube dispersion composition comprising the following steps (1) to (3) is preferred. [Process (1): Crushing process] A process of applying shear stress to the carbon nanotubes to disintegrate them. [Process (2): Magnetic selection process] A process to remove metal foreign particles using an electromagnet with a magnetic flux density of 10,000 gauss or more and 20,000 gauss or less. [Step (3): Filtration step] A process of filtering using a depth filter with a filtering accuracy of 5 μm to 50 μm

[0086] The order of steps (1), (2), and (3) is not particularly limited, and the metal foreign matter removal steps of steps (2) and (3) may be performed before or after step (1), simultaneously with step (1), or a combination of these. Preferably, the method comprises steps (1), (2), and (3) in that order, or steps (1) and (2) are carried out simultaneously, followed by step (3).

[0087] This is because, in [Step (1): Crushing step], the metallic foreign particles encapsulated in the carbon nanotubes are exposed, and then, or simultaneously, in [Step (2): Magnetic separation step], the magnetic metallic foreign particles can be removed by contacting them with a magnet, and then, in [Step (3): Filtering step], weakly magnetic metallic foreign particles that cannot be completely removed with a magnet (such as particles with a large particle size but weak magnetism, or particles with a particle size that is too small so that the magnetic attraction area is small and they are not captured by the magnet and are carried away by the liquid) can be removed.

[0088] [Process for crushing carbon nanotubes] In the step of applying a shear stress to the carbon nanotubes to disintegrate the carbon nanotubes, the carbon nanotubes can be subjected to a dry and / or wet disintegration treatment using a dispersing device or the like.

[0089] The dispersing device used for disintegrating the carbon nanotubes is not particularly limited. As the dispersing device, a dispersing machine normally used for dispersing pigments or the like can be used. For example, mixers such as a disperser, homomixer, and planetary mixer, homogenizers (Advanced Digital Sonifer (registered trademark) and MODEL 450DA manufactured by BRANSON, "Clearmix" manufactured by M Technique, "Filmix" manufactured by PRIMIX, "Abramix" manufactured by Silverson, etc.), paint conditioners (manufactured by Red Devil), colloid mills ("PUC Colloid Mill" manufactured by PUC, "Colloid Mill MK" manufactured by IKA), cone mills ("Cone Mill MKO" manufactured by IKA, etc.), ball mills, sand mills ("Dyno Mill" manufactured by Shinmaru Enterprises, etc.), attritors, pearl mills ("DCP Mill" manufactured by Eirich, etc.), etc. ), media-type dispersers such as a Coball mill, high-pressure homogenizers (such as Genus's "Genus PY," Sugino Machine's "Starburst," and Nanomizer's "Nanomizer"), media-less dispersers such as Sanmaru Machinery's "HC3 Series," Izumi Food Machinery's "HV-H Series," SPX Flow's "R-Model," M-Technique's "Claire SS-5," and Nara Machinery's "MICROS," as well as other roll mills, but are not limited to these. Since it is desirable to have less abrasion powder mixed in during the disintegration process, a media-less disperser is preferred. The rotor and stator of the disperser are preferably made of ceramics. When a bead mill is used in wet dispersion, the dispersion media is also preferably made of ceramics. When a bead mill is used as a wet disperser, it is preferable to use the media-less disperser after applying shear stress to the carbon nanotubes in advance to disintegrate the carbon nanotubes before the dispersion process using the bead mill. This is because the beads are easily worn when the bead mill is operated at a high peripheral speed on a low-viscosity dispersed material in which the carbon nanotubes have not been disintegrated. In addition, when a high-pressure homogenizer is used as a disperser, if abrasion powder from the beads is present during the dispersion process, there is a risk of nozzle clogging or valve damage of the high-pressure homogenizer.

[0090] When a high-pressure homogenizer is used as the dispersing machine, for example, a nozzle-type high-pressure homogenizer that discharges the treatment liquid from a nozzle, or a valve-type high-pressure homogenizer that discharges the treatment liquid from a homogenizing valve can be used. As the nozzle-type high-pressure homogenizer, the "Genus PY" manufactured by Genus, the "Starburst" manufactured by Sugino Machine Co., Ltd., and the "Nanomizer" manufactured by Nanomizer Co., Ltd. can be used. As the valve-type high-pressure homogenizer, the "HC3 Series" manufactured by Sanmaru Machinery Co., Ltd., the "HV-H Series" manufactured by Izumi Food Machinery Co., Ltd., and the "R-Model" manufactured by SPX Flow Co., Ltd. can be used, but are not limited to these. Among them, the valve-type high-pressure homogenizer can increase the flow rate of the treatment liquid, and when a carbon nanotube dispersion composition is produced by circulating dispersion, the homogeneity is improved, and the cumulative particle diameter D of the carbon nanotube dispersion composition can be increased. 90 The size of the filter is reduced, the filterability is improved, and a filter with excellent filtering accuracy can be used in the filtering process. In this case, a carbon nanotube dispersion composition with less carbon nanotube particles is more likely to be obtained.

[0091] The carbon nanotube dispersion composition of this embodiment is preferably dispersed by circulation dispersion or pass dispersion until there is substantially no uncrushed carbon nanotubes. In the case of circulation dispersion, when the holding tank is uniformly stirred, five passes are preferable because the probability of the presence of uncrushed particles can be reduced to 1 mass% or less, with 10 passes being more preferable, and 15 passes or more being even more preferable. In the case of pass dispersion, three passes or more are preferable, with five passes or more being more preferable, and 10 passes or more being even more preferable. When uncrushed carbon nanotubes are present, the cumulative particle diameter D 90 This may result in a decrease in the filterability of the carbon nanotube dispersion composition.

[0092] In order to ensure that the content of metallic foreign particles required by condition 1 is 1.0 mg or less, it is preferable to use carbon nanotubes that have been crushed and then have the metallic foreign particles removed using a filter or magnetic force in the carbon nanotube dispersion composition of this embodiment.

[0093] [Process for removing metal foreign particles] The method for removing the metal foreign particles is not particularly limited, but examples thereof include a filtration step in which the particles are filtered out using a filter, and a magnetic separation step such as a magnetic separation treatment using an electromagnet. It is preferable to include a filtration step and a magnetic separation step, because the magnetic separation step can remove metallic foreign particles from carbon nanotubes that have grown around a metal catalyst as a nucleus, and the filtration step can recover metallic foreign particles that cannot be removed by a magnet. It is more preferable to carry out a magnetic separation process after the filtration process. By carrying out the filtration process at the end of the CNT dispersion composition before shipping, it is possible to remove metal foreign particles from piping, etc. This reduces the amount of metal foreign particles, which leads to better characteristics when the CNT dispersion composition is made into a battery.

[0094] (Magnetic selection process) As a method for removing metal foreign particles by using a magnetic force in the magnetic separation step, various conventionally known methods can be used. For example, a method for removing metal foreign particles by passing a carbon nanotube composition through an electromagnet during the production process of the carbon nanotube dispersion composition is preferred.

[0095] The magnetic flux density of the electromagnet is preferably from 5,000 to 20,000 gauss, and more preferably from 10,000 to 20,000 gauss. By using an electromagnet in the above range, not only the metallic foreign particles contained in the carbon nanotubes but also the metallic foreign particles mixed in during the manufacturing process can be removed.

[0096] Specifically, for example, CS-150HHH, CS-250HHH, CS-300HHH manufactured by Nippon Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Nippon Eriez Magnetics Co., Ltd., EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Taiho Magnetic Co., Ltd., and the like can be used.

[0097] The flow rate of the carbon nanotube dispersion composition when it comes into contact with the electromagnet is preferably 1 L / min to 200 L / min, more preferably 30 L / min to 100 L / min. If the flow rate when it comes into contact with the electromagnet is high, there is a possibility that the metallic magnetic foreign particles with small magnetic force captured by the electromagnet will flow again into the carbon nanotube dispersion composition.

[0098] The carbon nanotube dispersion composition is preferably passed through the electromagnet three or more times. If the number of passes is too few, there is a possibility that the metal foreign particles cannot be removed. If the stones are passed through, it is preferable to pass them through more times to ensure uniformity in the tanks used in the manufacturing process.

[0099] (filtration process) The filter for filtering out the foreign metal particles may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferable. Since foreign metal particles are not spherical and often have an orientation, the use of a depth filter can efficiently remove the foreign metal particles from the carbon nanotube dispersion composition.

[0100] Unlike surface filters (filters that capture particulate matter in a fluid mainly on the filter surface), depth filters capture particulate matter in a fluid mainly inside the filter medium and have the characteristics of high particle retention and low clogging. By using a depth filter, it is possible to more selectively remove metal foreign particles from a carbon nanotube dispersion composition.

[0101] As the depth filter, for example, 3M(TM) PP nonwoven fabric depth cartridge NT-T series can be used.

[0102] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. When a filter with a small pore size is used for the purpose of increasing the efficiency of removing metal foreign particles from the carbon nanotube dispersion composition, the efficiency of removing metal foreign particles may decrease due to clogging of the carbon nanotubes. By using a filter with a filtration accuracy in the above range, metal foreign particles can be efficiently removed, and a carbon nanotube dispersion composition with fewer metal foreign particles can be obtained.

[0103] Even if the filtration process is performed using a filter with a filtration accuracy of 5 μm, the metal foreign particles may have an orientation due to their needle-like shape, etc., and the metal foreign particles cannot be completely removed and remain in the carbon nanotube dispersion composition. Therefore, it is important to appropriately control the composition and viscosity of the carbon nanotube dispersion composition, the method of the dispersion process, or the metal foreign particle removal process, etc., to reduce the content of the metal foreign particles required by condition 1.

[0104] <Composition slurry> The composite slurry of the present embodiment contains at least a carbon nanotube dispersion composition and an active material. That is, the composite slurry contains at least carbon nanotubes, a copolymer containing an alkylene structural unit and a nitrile group-containing structural unit, an amide polar solvent, an active material, and preferably a binder resin.

[0105] The binder resin is a resin used to bond between substances. The binder resin is not particularly limited, but examples thereof include polymers or copolymers containing fluororesin, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as constituent units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; cellulose resin such as carboxymethylcellulose; rubbers such as styrene butadiene rubber; conductive resins such as polyaniline and polyacetylene. Among them, it is preferable to use fluororesin as the binder resin from the viewpoint of electrochemical oxidation-reduction resistance.

[0106] As the fluororesin of this embodiment, for example, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferable.

[0107] The weight average molecular weight of the fluororesin is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,500,000, and particularly preferably from 200,000 to 1,500,000.

[0108] An active material is a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on their electromotive force. In this specification, positive electrode active materials and negative electrode active materials may be simply referred to as "active materials." Active materials are a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on their electromotive force.

[0109] The positive electrode active material is not particularly limited, but may be a metal compound such as a metal oxide or metal sulfide capable of doping or intercalating lithium ions, or a conductive polymer. Examples of the material 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, VO, VO 13 Examples of the conductive material include transition metal oxide powders such as TiO2, composite oxide powders of lithium and transition metals such as lithium nickel oxide, lithium cobalt oxide, lithium manganate, and lithium manganate having a spinel structure, lithium iron phosphate-based materials that are phosphate compounds having an olivine structure, and transition metal sulfide powders such as TiS2 and FeS. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. The above inorganic compounds and organic compounds may also be used in combination.

[0110] The positive electrode active material is preferably a composite oxide of lithium containing a transition metal such as Al, Fe, Co, Ni, or Mn, more preferably a composite oxide of lithium containing any of Al, Co, Ni, or Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained in terms of battery characteristics.

[0111] The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, its alloys such as tin alloys, silicon alloys, and lead alloys, Li X Fe2O3, Li X Fe3O4, Li XWO2 (where x is a number between 0 and 1), metal oxide-based materials such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymer-based materials such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, and carbon fibers. These negative electrode active materials can be used alone or in combination of two or more.

[0112] The BET specific surface area of the active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less, more preferably 0.2 m 2 / g or more and 5 m 2 / g or less, even more preferably 0.3 m 2 / g or more and 3 m 2 / g or less.

[0113] The average particle diameter of the active material is preferably in the range of 0.05 μm to 100 μm, and more preferably in the range of 0.1 μm to 50 μm. The average particle diameter of the active material as used herein refers to the average value of the particle diameters measured by an electron microscope for the active material.

[0114] To obtain the composite material slurry of this embodiment, it is preferable to add the active material to the carbon nanotube dispersion composition and then perform a dispersion treatment. The dispersion device used for performing such treatment is not particularly limited. The composite material slurry can be obtained using the dispersion device described for the carbon nanotube dispersion composition. The composite material slurry can be obtained using the dispersion device described above.

[0115] The content of the active material in the composite material slurry is preferably 20% by mass to 85% by mass, and particularly preferably 40% by mass to 85% by mass, based on 100% by mass of the composite material slurry.

[0116] The content of carbon nanotubes in the composite slurry is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the active material.

[0117] The content of the binder resin in the composite slurry 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.

[0118] The solid content concentration of the composite slurry is preferably 30% by mass to 90% by mass, and more preferably 40% by mass to 85% by mass, based on 100% by mass of the composite slurry.

[0119] The water content in the composite slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0120] ≪Electrode≫ The electrode of this embodiment includes a current collector and an electrode film formed from a composite material slurry. The electrode film is a coating film of a composite material slurry, for example, a coating film formed by coating a composite material slurry on a current collector and drying the composite material slurry to form an electrode composite material layer.

[0121] The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. For example, the material of the current collector can be metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. In addition, as for the shape, a flat foil is generally used, but a current collector with a roughened surface, a perforated foil, or a mesh-shaped current collector can also be used.

[0122] The method of applying the composite slurry onto the current collector to form the electrode film is not particularly limited, and a known method can be used. Specifically, examples of the method include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. The drying method can be, but is not limited to, standing drying, a blower dryer, a hot air dryer, an infrared heater, or a far infrared heater.

[0123] After coating, the electrode mixture layer may be rolled using a lithographic press, a calendar roll, etc. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0124] ≪Secondary battery≫ The secondary battery of this embodiment includes an electrode having the electrode film of the present invention and an electrolyte. The carbon nanotube dispersion composition of this embodiment has excellent rate characteristics because it forms a good conductive network in the secondary battery electrode, and the active material is used uniformly during charging and discharging, so that the active material is less likely to deteriorate. Furthermore, overcharging and overdischarging during charging and discharging are suppressed. Furthermore, since there is little metal foreign matter derived from the carbon nanotube dispersion composition, deterioration of battery characteristics due to electrolyte decomposition and metal precipitation is less likely to occur, and the high-temperature cycle characteristics are excellent.

[0125] The positive electrode can be prepared by coating a composite slurry containing a positive electrode active material on a current collector and drying the coated composite slurry to form an electrode film.

[0126] The negative electrode may be prepared by coating a composite slurry containing a negative electrode active material on a current collector and drying the coated composite slurry to form an electrode film.

[0127] As the electrolyte, various conventionally known electrolytes capable of moving ions can be used. For example, those containing 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 (wherein Ph is a phenyl group) can be used, but are not limited thereto, and those containing sodium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0128] Examples of non-aqueous solvents include, but are not limited to, 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; glymes 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 alone or in combination of two or more.

[0129] The secondary battery of the present embodiment preferably includes a separator. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those that have been subjected to a hydrophilic treatment.

[0130] The structure of the secondary battery of the present embodiment is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator that is provided as necessary, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0131] The applications of the secondary battery of this embodiment are not particularly limited, and specifically, it can be used as a power source for consumer devices such as mobile phones, notebook computers, and digital cameras, an emergency power source for hospitals, factories, buildings, and the like, and for vehicles such as hybrid automobiles, plug-in hybrid automobiles, electric automobiles, power-assisted bicycles, and railroad cars. The secondary battery is, for example, used to recover regenerative energy for the motive power of a vehicle.

[0132] In particular, since the secondary battery has high charge / discharge performance and excellent cycle characteristics, it can be suitably used in vehicles, and a vehicle with high safety and improved fuel efficiency can be obtained. Furthermore, it can exert excellent effects in vehicle applications where charging and discharging at a large current is desired.

[0133] The mounting position of the secondary battery in the vehicle of this embodiment is not particularly limited. For example, when the secondary battery is mounted in an automobile, the secondary battery can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle. EXAMPLES

[0134] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, so long as it does not depart from the gist of the invention. "Parts by mass" and "%" represent "% by mass." The blending amounts in the table are in parts by mass, and amounts other than the solvent are calculated as non-volatile contents. The blank spaces in the table indicate that no blend was made.

[0135] The materials used in the examples and comparative examples are shown below. Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural unit 66% by mass, nitrile group-containing structural unit content 34% by mass), was used as dispersant (A). Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35053, Mooney viscosity 35, weight average molecular weight 130,000, alkylene structural unit 64% by mass, content of nitrile group-containing structural unit 36% by mass), below, was used as dispersant (B). Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN28255, Mooney viscosity 50, weight average molecular weight 190,000, alkylene structural unit 72% by mass, content of nitrile group-containing structural unit 28% by mass), was used as dispersant (C). Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35056, Mooney viscosity 65, weight average molecular weight 180,000, alkylene structural unit 64% by mass, content of nitrile group-containing structural unit 36% by mass), was used as dispersant (D). Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35058, Mooney viscosity 85, weight average molecular weight 220,000, alkylene structural unit 64% by mass, content of nitrile group-containing structural unit 36% by mass), was used as dispersant (E). Hydrogenated nitrile butadiene rubber (ARLANXEO, Therban(R) 3406, Mooney viscosity 63, weight average molecular weight 200,000, alkylene structural unit 66% by mass, nitrile group-containing structural unit content 34% by mass), hereinafter referred to as dispersant (F). Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, liquid hydrogenated nitrile butadiene rubber, weight average molecular weight 30,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass) was used as dispersant (G). Polyvinylpyrrolidone (K-30, weight average molecular weight 40,000, manufactured by Nippon Shokubai Co., Ltd.) was used as the dispersant (H). Carbon nanotube (manufactured by JEIO, JENOTUBE10B) (hereinafter referred to as carbon nanotube (A1)). Carbon nanotube (manufactured by JEIO, JENOTUBE6A) (hereinafter referred to as carbon nanotube (B1)). The purified CNT described in paragraph 0098 of Japanese Patent No. 6586197 was used as carbon nanotube (I1).

[0136] <Preparation of Carbon Nanotubes (C1)> 1 kg of carbon nanotubes (A1) was weighed into a 100 L glass container, and 50 kg of 20% hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, followed by thorough stirring at 25°C using a stirrer. The mixture was then thoroughly diluted with ion-exchanged water and subjected to reduced pressure filtration using a membrane filter. After repeating the dilution and filtration process, the CNTs were transferred to a PTFE tray and dried in an oven at 80°C to obtain carbon nanotubes (C1).

[0137] <Preparation of Carbon Nanotubes (C2)> The carbon nanotubes (C1) were milled in a Dynamic Mill (manufactured by Nippon Coke & Co.) using zirconia beads with a diameter of 8 mm as milling media under operating conditions of 10.0 kg / h supply and a peripheral speed of 5.0 m / s to obtain carbon nanotubes (C2).

[0138] <Preparation of carbon nanotubes (D1)> 10 kg of carbon nanotubes (A1) were weighed into a 120 L heat-resistant container, and the heat-resistant container containing the carbon nanotubes was placed in a furnace. Nitrogen gas was then introduced into the furnace, While maintaining positive pressure, the air in the furnace was discharged. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the temperature in the furnace at 1600°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min to cool the furnace while maintaining positive pressure, and carbon nanotubes (D1) were obtained.

[0139] <Preparation of Carbon Nanotubes (E1)> 10 kg of carbon nanotubes (A1) were weighed into a 120 L heat-resistant container, and the heat-resistant container containing the carbon nanotubes was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 1800°C over 30 hours. While maintaining the temperature in the furnace at 1800°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min to cool the furnace while maintaining positive pressure, and carbon nanotubes (E1) were obtained.

[0140] <Preparation of Carbon Nanotubes (E2)> The carbon nanotubes (E1) were passed through an electromagnet (CG-150HHH manufactured by Japan Magnetics Co., Ltd.) three times to remove magnetic foreign matter from the raw material, thereby obtaining carbon nanotubes (E2). The electromagnetic separator used had a screen opening of 10 mm.

[0141] <Production of Carbon Nanotubes (E3)> Carbon nanotubes (E1) were fed into a dynamic mill (manufactured by Nippon Coke & Co., Ltd.) with zirconia beads of 8 mm diameter as a grinding medium, and were operated at 10.0 kg / h and processed at a peripheral speed of 5.0 m / s. The raw material was then passed through an electromagnet (CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove magnetic foreign matter from the raw material, and carbon nanotubes (E3) were obtained. The electromagnet used had a screen opening of 10 mm.

[0142] <Preparation of carbon nanotubes (F1)> 10 kg of carbon nanotubes (A1) were weighed into a 120 L heat-resistant container, and the heat-resistant container containing the carbon nanotubes was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 2000°C over 30 hours. While maintaining the temperature in the furnace at 2000°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min to cool the furnace while maintaining positive pressure, and carbon nanotubes (F1) were obtained.

[0143] <Preparation of carbon nanotubes (G1)> 10 kg of carbon nanotubes (A1) were weighed into a 120 L heat-resistant container, and the heat-resistant container containing the carbon nanotubes was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 3000°C over 30 hours. While maintaining the furnace temperature at 3000°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min to cool the furnace while maintaining positive pressure, and carbon nanotubes (G1) were obtained.

[0144] <Preparation of Carbon Nanotubes (H1)> Carbon nanotubes (B1) were weighed out in a 120 L heat-resistant container, and the heat-resistant container containing the carbon nanotubes was placed in a furnace. Nitrogen gas was then introduced into the furnace to maintain positive pressure while discharging the air from within the furnace. After the oxygen concentration within the furnace reached 0.1% or less, it was heated to 1800°C over 30 hours. While maintaining the temperature within the furnace at 1800°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min to cool the furnace while maintaining the positive pressure, after which the carbon nanotubes were removed and milled in a dynamic mill (manufactured by Nippon Coke & Co.) with zirconia beads of 8 mm in diameter as a grinding medium, at an operating condition of 10.0 kg / h and a peripheral speed of 5.0 m / s. After the treatment, the raw material was passed through an electromagnet (CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove metal foreign particles from the raw material, and carbon nanotubes (H1) were obtained. The electromagnet used had a screen opening of 10 mm.

[0145] Table 1 shows the physical properties of the carbon nanotubes used in the examples and comparative examples.

[0146] [Table 1]

[0147] <Measurement of weight average molecular weight of dispersant> The weight average molecular weight (Mw) of the dispersant was measured by gel permeation chromatography (GPC) equipped with an RI detector. HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, and three separation columns were connected in series. Tosoh Corporation's "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" were used as the packing materials, in that order, at an oven temperature of 40°C, and an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr was used as the eluent, and the measurement was performed at a flow rate of 0.6 mL / min. The concentration of the measurement sample was adjusted to 1% using a solvent consisting of the eluent, and 20 microliters were injected. The weight average molecular weight is a polystyrene equivalent value.

[0148] <Preparation of standard negative electrode> 0.5 parts by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka), 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt Sunrose special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%), and 98.4 parts by mass of water were added to a plastic container with a capacity of 150 ml, and then the mixture was stirred for 30 seconds at 2000 rpm using a centrifugal mixer (Thinky Awatori Rentaro, ARE-310). Furthermore, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) and 5 parts by mass of silicon (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5 μm, non-volatile content 100%) were added as active materials, and the mixture was stirred for 10 minutes at 3000 rpm using a high-speed stirrer. Next, 3.1 parts by mass of SBR (TRD2001, manufactured by JSR Corporation) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the centrifugal mixer to obtain a negative electrode composite slurry. The negative electrode composite slurry was then applied to the electrode using an applicator so that the weight per unit area of ​​the electrode became 8 mg / cm. 2 After coating on copper foil so that the thickness was 1.6g / cm, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, rolling was performed using a roll press (Thank Metal Co., Ltd., 3t hydraulic roll press) to reduce the density of the composite layer to 1.6g / cm. 3A standard negative electrode was prepared.

[0149] <Physical property measurement and evaluation method> The carbon nanotubes and carbon nanotubes used in the following examples and comparative examples The methods for measuring and evaluating the physical properties of the tube dispersion composition, the electrode film, and the secondary battery are as follows.

[0150] <Outer diameter of carbon nanotube> Using an electronic balance (made by Sartorius, MSA225S100DI), 0.2 g of carbon nanotubes was weighed into a 450 mL SM sample bottle (made by Sanshosha Co., Ltd.), 200 mL of toluene was added, and an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, made by BRANSON Co., Ltd.) was used to perform dispersion treatment under ice cooling at an amplitude of 30% for 5 minutes to prepare a carbon nanotube dispersion composition. Thereafter, the carbon nanotube dispersion composition was appropriately diluted, several μL was dropped onto a collodion film, and after drying at room temperature, it was directly observed using a transmission electron microscope (H-7650, made by Hitachi, Ltd.). The observation was performed at a magnification of 50,000 times, and multiple photographs containing 10 or more carbon nanotubes in the field of view were taken, and the average outer diameter of 300 carbon nanotubes randomly extracted was measured, and the average value was taken as the outer diameter (nm) of the carbon nanotubes.

[0151] <BET specific surface area of ​​carbon nanotubes> 0.03 g of carbon nanotubes was weighed out using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried for 15 minutes at 110° C. while degassing. Thereafter, the BET specific surface area of ​​the carbon nanotubes was measured using a fully automatic specific surface area measuring device (HM-model1208, manufactured by MOUNTECH).

[0152] <G / D ratio of carbon nanotubes> The carbon nanotube was placed in a Raman microscope (XploRA, manufactured by Horiba, Ltd.) and measurements were performed using a laser wavelength of 532 nm. The measurement conditions were: acquisition time 60 seconds, number of integrations 2, neutral density filter 10%, objective lens magnification 20 times, confocus hole 500, slit width 100 μm, measurement wavelength 100 cm -1 ~3000cm -1 The carbon nanotubes for measurement were separated onto a slide glass and flattened using a spatula. -1 ~1600cm -1 The maximum peak intensity within the range of G, 1310 cm -1 ~1350cm -1 The maximum peak intensity within the range was defined as D, and the G / D ratio was defined as the G / D ratio of the carbon nanotube.

[0153] <Angle of repose of carbon nanotubes> The angle of repose of the carbon nanotubes was measured using a bulk density measuring device (manufactured by Tsutsui Rikagaku Kikai Co., Ltd., JIS bulk specific gravity measuring device). First, the mass of the receiver was measured, and then the bulk density measuring device was horizontally placed, a funnel was attached to the funnel stand, a sieve was placed on the funnel, and the receiver was placed on the receiver stand. Then, the carbon nanotubes were placed on the sieve using a medicine spoon, and the carbon nanotubes were lightly and evenly spread over the entire surface of the sieve with a brush, and the sample that passed through the sieve was received in the receiver. This operation was repeated until the carbon nanotubes were piled up in the receiver. The angle between the horizontal plane and the powder piled up in a cone shape was measured using a protractor, and this was taken as the angle of repose of the carbon nanotubes.

[0154] <Carbon purity of carbon nanotubes> Carbon nanotubes were decomposed with acid using a microwave sample pretreatment device (Milestone General, ETHOS1) to extract the metals contained in the carbon nanotubes. After that, analysis was performed using a multi-type ICP emission spectrometer (Agilent, 720-ES) to calculate the amount of metals (total amount of iron, cobalt, nickel, copper, and molybdenum) contained in the extract. The carbon purity of the carbon nanotubes was calculated as follows. Carbon purity of carbon nanotubes (%) = ((mass of carbon nanotubes - amount of metal) ÷ ​​mass of carbon nanotubes) x 100

[0155] <Initial Viscosity of Carbon Nanotube Dispersion Composition> The carbon nanotube dispersion composition was left to stand in a thermostatic bath at 25°C for at least 1 hour, and then immediately subjected to measurement with a Brookfield viscometer rotor at a rotation speed of 100 rpm. A No. 4 rotor was used for the measurement. The initial viscosity was evaluated as follows: less than 500 mPa·s: ◎ (excellent), 500 mPa·s or more but less than 1000 mPa·s: ◯ (good), 1000 mPa·s or more but less than 2000 mPa·s: △ (fair), and 2000 mPa·s or more: × (poor).

[0156] <Content of Metallic Foreign Particles in Carbon Nanotube Dispersion Composition> 20 kg of the carbon nanotube dispersion composition was passed through an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) via a hose pump at a flow rate of 30 L / min 5 times. Then, N-methyl-2-pyrrolidone (NMP) was passed through an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss), and the carbon nanotube dispersion composition in the hose pump and electromagnet was extruded and washed until the solid content was substantially eliminated. Further, after that, the power supply of the electromagnet was turned off, and after confirming that the magnetic force of the filter was eliminated, 10 kg of NMP was passed through the electromagnet at a flow rate of 30 L / min to obtain 10 kg of NMP containing metal foreign particles. Then, 10 kg of NMP containing metal foreign particles was ultrasonically treated for 2 minutes using an ultrasonic cleaner (manufactured by Aiwa Medical Industry, ultrasonic cleaner) at an output of 300 W and a frequency of 28 kHz to disperse the mixture, and then the mixture was passed through a filter (weight (W1), material: polyester, disk diameter: 47 mm, mesh size: 5 μm) using a filter bell, and the metal foreign particles deposited on the filter were washed using 100 g of ethanol. Further, the filter on which the metal foreign particles were deposited was removed, and the filter was dried at 60 ° C. for 10 minutes using a hot air oven, and the weight (W2) was measured. The filter weight (W1) was subtracted from the filter weight (W2) after drying on which the metal foreign particles were deposited, and the content of the metal foreign particles in the carbon nanotube dispersion composition (metal foreign particle weight) was calculated. The measurement results for the amount of metal foreign particles are as follows: A: 0.1 mg or less; B: greater than 0.1 mg but less than 0.4 mg; C: greater than 0.4 mg but less than 1.0 mg; D: greater than 1.0 mg.

[0157] <Amount of Metal Elements in Carbon Nanotube Dispersion Composition> The carbon nanotube dispersion composition was dried using a hot air oven, and then decomposed with acid using a microwave sample pretreatment device (Milestone General, ETHOS1) to extract the metals contained in the carbon nanotubes. Then, analysis was performed using a multi-type ICP emission spectrometer (Agilent, 720-ES) to calculate the amount of metal elements (total content of iron, cobalt, nickel, chromium, molybdenum and copper) contained in the extract. The smaller the amount of metal elements, the more effectively voltage defects in the secondary battery can be suppressed. The evaluation criteria for the amount of metal elements were as follows: 30 ppm or less: ◎ (excellent), over 30 ppm to 50 ppm or less: ◯ (good), over 50 ppm to 100 ppm: △ (passable), and over 100 ppm: × (unacceptable).

[0158] <Particle size of carbon nanotube dispersion composition> Cumulative particle size D due to particle size distribution 90 The measurement was performed using a laser diffraction / scattering particle size distribution analyzer (HORIBA, Ltd. Partical LA-960V2). The laser wavelength of this measurement device is 650 nm, and the detectors are one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. The measurement section uses a flow-type cell (sample cell) made of synthetic quartz. First, NMP, which is the same solvent as the carbon nanotube dispersion composition, was put into a sample bath containing a sample cell, and circulation / ultrasonic cleaning was performed. The operation modes were circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, and stirring mode: continuous. Then, air was removed. Therefore, after ultrasonic operation with ultrasonic intensity: 7 and ultrasonic time: 5 seconds, blank (background) measurement was performed. The particle size standard was volume, the particle refractive index was set to 1.920-0.522i (carbon nanotube), and the solvent refractive index was set to 1.468 (NMP). The carbon nanotube dispersion composition was dripped so that the laser light transmittance during measurement was 60% ± 1%, and sample adjustment was performed. The operation mode during measurement was circulation speed: 3, stirring speed: 7, and stirring mode: continuous. Cumulative particle size D 90 are A: 4.0 μm or less, B: more than 4.0 μm to 6.0 μm or less, C: more than 6.0 μm to 10 μm or less, and D: more than 10 μm.

[0159] <Initial Viscosity of Carbon Nanotube Dispersion Composition> The carbon nanotube dispersion composition was left to stand in a thermostatic bath at 25°C for at least 1 hour, and then immediately subjected to measurement with a Brookfield viscometer rotor at a rotation speed of 100 rpm. A No. 4 rotor was used for the measurement. The initial viscosity was evaluated as follows: less than 500 mPa·s: ◎ (excellent), 500 mPa·s or more but less than 1000 mPa·s: ◯ (good), 1000 mPa·s or more but less than 2000 mPa·s: △ (fair), and 2000 mPa·s or more: × (poor).

[0160] <Conductivity> The electrical conductivity was evaluated based on the volume resistivity of the electrode film. The composite slurry is applied to the electrode using an applicator so that the weight per unit area is 20 mg / cm 2 After coating on aluminum foil so that the coating was as above, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. The surface resistivity (Ω / □) of the coating after drying was then measured using a resistivity meter (Nitto Seiko Analytech Co., Ltd.: Loresta GP (MCP-T610), probe: AP2 probe (RMH333)). After measurement, the surface resistivity was multiplied by the thickness of the electrode mixture layer formed on the aluminum foil to obtain the volume resistivity (Ω·cm) of the electrode film. The thickness of the electrode mixture layer was measured at three points in the electrode film using a film thickness meter (NIKON, DIGIMICRO MH-15M), and the average value was subtracted from the film thickness of the aluminum foil to obtain the volume resistivity (Ω·cm) of the electrode film. The evaluation criteria for volume resistivity were as follows: less than 8 Ω·cm: ◎ (excellent), 8 Ω·cm to less than 12 Ω·cm: ◯ (good), 12 Ω·cm to less than 15 Ω·cm: △ (fair), 15 Ω·cm or more (poor).

[0161] <Adhesion> The adhesion was evaluated based on the peel strength of the electrode film. The composite slurry is applied to the electrode using an applicator so that the weight per unit area is 20 mg / cm 2 After coating on aluminum foil so that the coating was as above, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, the film was cut into two 90mm x 20mm rectangles with the coating direction as the long axis. Peel strength was measured using a tabletop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and evaluated by a 180-degree peel test method. Specifically, a double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) measuring 100mm x 30mm was attached to a stainless steel plate, the prepared battery electrode composite layer was attached to the other side of the double-sided tape, and the layer was peeled off while being pulled from the bottom to the top at a constant speed (50mm / min). The average value of the stress at this time was taken as the peel strength. The evaluation criteria for peel strength were as follows: 0.7 N / cm or more: ◎ (excellent), 0.5 N / cm or more but less than 0.7 N / cm: ◯ (good), 0.3 N / cm or more but less than 0.5 N / cm: △ (passable), and less than 0.3 N / cm: × (poor).

[0162] <Evaluation of rate characteristics of lithium-ion secondary batteries> The laminated lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (Hokuto Denko Corporation, SM-8). The battery was charged at a constant current and constant voltage (cut-off current 1.0mA (0.02C)) with a charge current of 10mA (0.2C) and a charge end voltage of 4.2V. After this, constant current discharge was performed at a discharge current of 10 mA (0.2 C) with a discharge end voltage of 2.5 V. This operation was repeated three times, and then constant current / constant voltage charging (cutoff current (1.0 mA 0.02 C)) was performed with a charge current of 10 mA (0.2 C) with a charge end voltage of 4.2 V, and constant current discharge was performed at discharge currents of 0.2 C and 3 C until the discharge end voltage of 2.5 V was reached, and the discharge capacity was calculated for each. The rate characteristic can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, using the following formula 2. (Formula 2) Rate characteristic = 3C discharge capacity / 3rd 0.2C discharge capacity × 100 (%) The rate characteristic evaluation criteria were as follows: 80% or more rate characteristic was rated as ◎ (excellent), 70% or more but less than 80% rate characteristic was 〇 (good), 60% or more but less than 70% rate characteristic was △ (fair), and less than 60% rate characteristic was × (poor).

[0163] <Evaluation of high-temperature cycle characteristics of lithium-ion secondary batteries> The laminated lithium-ion secondary battery was placed in a thermostatic chamber at 45°C, and charge / discharge measurements were performed using a charge / discharge device (Hokuto Denko Corporation, SM-8). After constant-current constant-voltage charging (cutoff current 1.25mA (0.025C)) was performed with a charge current of 50mA (1C) and a charge end voltage of 4.2V, constant-current discharging was performed with a discharge current of 50mA (1C) and a discharge end voltage of 2.5V. This operation was repeated 200 times. 1C was the current value at which the theoretical capacity of the positive electrode was discharged in 1 hour. The high-temperature cycle characteristics can be expressed as the ratio of the 3rd 1C discharge capacity at 45°C to the 100th 1C discharge capacity, as shown in the following formula 3. (Formula 3) High temperature cycle characteristics = 100th 1C discharge capacity / 3rd 1C discharge capacity x 100 (%) The high temperature cycle characteristics were evaluated as follows: 90% or more was rated as ◎ (excellent), 85% or more but less than 90% was rated as ○ (good), 80% or more but less than 85% was △ (fair), and less than 80% was rated as × (poor).

[0164] (Example 1-1) 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (A) were added to a stainless steel container and stirred at 80°C using a disperser to completely dissolve the dispersant (A). The mixture was then passed through a nylon mesh with 48 μm openings and then through a high-magnetic magnet filter (manufactured by Eishin, surface magnetic flux density 17,000 Gauss) to prepare an 8% solution of dispersant (A). Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 7.5 parts of 8% solution of dispersant (A) were added to a stainless steel container and stirred with a disperser until it was uniform. Then, 3 parts of carbon nanotubes (C1) were taken and added while stirring with a disperser. A fine emulsion screen was attached to a high shear mixer (L5M-A, Silverson), and the mixture was dispersed in a batch manner at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size was 200 μm or less using a grind gauge. The mixture was then passed through a high magnetic force mag filter (Eishin, surface magnetic flux density 17000 Gauss) to prepare a carbon nanotube preliminary dispersion (C1). After that, the carbon nanotube preliminary dispersion liquid was sent, and a circulation type dispersion process (beads filling rate 80%, peripheral speed 12 m / s) was performed with a bead mill (Mugen Flow (registered trademark), manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ for a residence time of 15 minutes. Dispersion was performed while adjusting the discharge amount so that the number of passes per minute of residence time was 4 passes, and the total number of passes during the residence time of 15 minutes was 60 passes. Next, the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Co., Ltd.), and a 15-pass dispersion process was performed. Dispersion processing was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The liquid to be dispersed was then supplied to an electromagnet (manufactured by Taiho Magnetics, EMF-100S, magnetic flux density 16,000 gauss, space volume 1.7 L, electromagnet equipped with 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm) and subjected to three passes. After that, the liquid was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series to remove the carbon nanotubes. Dispersion composition 1 was prepared.

[0165] (Examples 1-2 to 1-20), (Comparative Examples 1-1 to 1-13) Except for changing the dispersion conditions, carbon nanotubes, dispersant, and NMP listed in Table 2, dispersion compositions 1-1 to 1-12 and comparative dispersion compositions 1-1 to 1-9 were obtained in the same manner as in Example 1-1. The depth filter in the examples and comparative examples was a PP nonwoven fabric depth cartridge NT-T series manufactured by 3M, and the surface filter was a nylon mesh. When using a nylon mesh, instead of passing through two depth filters (PP nonwoven fabric depth cartridge NT-T series manufactured by 3M, filtration accuracy 20 μm) installed in series, a filter was used to pass through the nylon mesh to obtain carbon nanotube dispersion compositions in the examples and comparative examples. The dispersion compositions in comparative examples 1-4 and 1-11 could not be filtered through a filter with a filtration accuracy of 3 μm, and could not be produced.

[0166] [Table 2]

[0167] Table 3 shows the evaluation results of the dispersion compositions prepared in (Examples 1-1 to 1-20) and (Comparative Examples 1-1 to 1-13).

[0168] [Table 3]

[0169] (Example 2-1) Capacity 150cm 3Into the plastic container, 18.8 parts by mass of NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvey, Solef#5130) was dissolved, and 5.8 parts by mass of NMP were weighed. Then, 13.3 parts by mass of carbon nanotube dispersion composition (dispersion composition 1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation-revolution mixer (Awatori Rentaro, ARE-310). Further, 98.1 parts by mass of positive electrode active material (BASF Toda Battery Materials, LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotation-revolution mixer (Awatori Rentaro, ARE-310) to obtain a composite slurry (composite slurry 1).

[0170] Next, the composite slurry (composite slurry 1) was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm2. 2 After coating on an aluminum foil so that the coating was as follows: the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (electrode film 1). The electrode film (electrode film 1) was then rolled using a roll press (3t hydraulic roll press, manufactured by Sun Metals) to obtain a positive electrode (positive electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. 2 The density of the composite layer after rolling was 3.1 g / cc.

[0171] (Examples 2-2 to 2-20), (Comparative Examples 2-1 to 2-13) As shown in Table 4, the composite slurry 2 to the comparative composite slurry 13 were prepared in the same manner as in Example 2-1, except that the dispersion composition 2 to the comparative dispersion composition 13 were used instead of the dispersion composition 1. An electrode film 2 to a comparative electrode film 13, and a positive electrode 2 to a comparative positive electrode 13 were obtained.

[0172] Table 4 shows the evaluation results of the electrode films produced in Examples 2-1 to 2-20 and Comparative Examples 2-1 to 2-13.

[0173] [Table 4]

[0174] (Example 3-1) The positive electrode (positive electrode 1) and the standard negative electrode were punched out to 45 mm x 40 mm and 50 mm x 45 mm, respectively, and the separator (porous polypropylene film) between them was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. After that, in a glove box filled with argon gas, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 1:1:1 (volume ratio) and adding 2 parts by mass of VC (vinylene carbonate) as an additive to 100 parts by mass of the mixed solvent, and then dissolving LiPF6 at a concentration of 1M) was injected, and the aluminum laminate was sealed to prepare a laminated lithium-ion secondary battery (secondary battery 1).

[0175] (Example 3-2 to Example 3-20), (Comparative Example 3-1 to Comparative Example 3-13) Laminated lithium ion secondary batteries (secondary battery 2) to (comparative secondary battery 13) were produced in the same manner as in the production of the laminated lithium ion secondary battery (secondary battery 1), except that the positive electrode was changed as shown in Table 5.

[0176] [Table 5]

[0177] (Examples 1-21) 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (F) were added to a stainless steel container and stirred at 80°C using a disperser to completely dissolve the dispersant (F). The mixture was then passed through a nylon mesh with 48 μm openings and then through a high-magnetic magnet filter (manufactured by Eishin, surface magnetic flux density 17,000 Gauss) to prepare an 8% solution of dispersant (F). Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 15 parts of an 8% solution of dispersant (F) were added to a stainless steel container and stirred with a disperser until it became uniform. Then, 3 parts of carbon nanotubes (H1) were taken and added while stirring with a disperser. A fine emulsion screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was dispersed in a batch manner at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size was 200 μm or less using a grind gauge. Then, the mixture was passed through a high magnetic force mag filter (manufactured by Eishin, surface magnetic flux density 17000 Gauss) to prepare a carbon nanotube preliminary dispersion. After that, the carbon nanotube preliminary dispersion was sent and subjected to a circulation dispersion treatment (beads filling rate 80%, peripheral speed 12 m) with a bead mill (manufactured by Ashizawa Finetech Co., Ltd., Mugen Flow (registered trademark)) filled with zirconia beads having a diameter of 1.0 mmφ for a residence time of 15 minutes. / s) was performed. Dispersion was performed while adjusting the discharge amount so that the number of passes per minute of residence time was 4 passes, and the total number of passes during the 15-minute residence time was 60 passes. Next, the liquid to be dispersed was supplied to a valve-type high-pressure homogenizer (manufactured by Sanmaru Machinery Co., Ltd., HC3-5 (product name)) and a circulation-type dispersion process was performed. The dispersion process was performed at a pressure of 80 MPa, a processing flow rate of 2000 L / H, and a total number of passes was 15. After the dispersion process, the liquid to be dispersed was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss, space volume 1.7 L, diameter: 10 cm, electromagnet equipped with 31 grid screens with a thickness of 1.3 cm) and a three-pass process was performed, and the liquid was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series to produce a carbon nanotube dispersion composition 21.

[0178] (Examples 1-22) Carbon nanotube dispersion composition 22 was prepared in the same manner as in Example 1-21, except that the total number of passes through the bulb-type homogenizer was set to 10 passes.

[0179] (Examples 1-23) Carbon nanotube dispersion composition 23 was prepared in the same manner as in Example 1-21, except that the total number of passes through the bulb-type homogenizer was set to 5 passes.

[0180] (Examples 2-21 to 2-23) Except for using (carbon nanotube dispersion composition 21) to (carbon nanotube dispersion composition 23) instead of carbon nanotube dispersion composition 1, (composite slurry 21) to (composite slurry 23), (electrode film 21) to (electrode 23), and (positive electrode 21) to (positive electrode 23) were prepared in the same manner as in Example 2-1.

[0181] (Examples 3-21 to 3-23) Except for using (cathode 21) to (cathode 23) instead of the positive electrode 1, (secondary battery 21) to (secondary battery 23) were produced in the same manner as in Example 3-1.

[0182] Table 6 shows the evaluation results of the carbon nanotube dispersion compositions prepared in (Examples 1-21 to 1-23) and the electrode films and secondary batteries prepared using them.

[0183] [Table 6]

[0184] In the above embodiment, a carbon nanotube dispersion composition is provided, which contains carbon nanotubes, a copolymer, and an amide-based polar solvent, and has a content of metal foreign particles of 1.0 mg or less as determined by condition 1, and the copolymer has an alkylene structural unit content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less. In the examples, the initial viscosity of the carbon nanotube dispersion composition was lower than that of the comparative examples, and a lithium ion secondary battery having excellent secondary battery characteristics, particularly high-temperature cycle characteristics, was obtained. Therefore, it has become clear that the present invention can provide a lithium ion secondary battery having high capacity, high output, and high durability that are difficult to achieve with conventional carbon nanotube dispersion compositions. A vehicle having the lithium ion secondary battery of the present invention has high charge / discharge performance and excellent high-temperature cycle characteristics, and therefore a vehicle with high safety and improved fuel economy can be obtained.

[0185] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

Claims

1. A carbon nanotube dispersion composition comprising carbon nanotubes, a copolymer, and an amide-based polar solvent, The content of metallic foreign particles determined according to the following condition 1 is 1.0 mg or less, The copolymer has an alkylene structural unit content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit content of 25% by mass or more and 50% by mass or less. Carbon nanotube dispersion composition. <Condition 1> The metallic foreign particles in 20 kg of the carbon nanotube dispersion composition were collected using an electromagnet (an electromagnet having a magnetic flux density of 16,000 Gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and 31 grid screens of 1.3 cm thickness), and then washed with an amide-based polar solvent. The resulting metallic foreign particles were deposited on a filter with a disk diameter of 47 mm and mesh openings of 5 μm, and the weight of the metallic foreign particles on the filter was measured.

2. 2. The carbon nanotube dispersion composition according to claim 1, wherein the total content of iron, cobalt, nickel, chromium, molybdenum and copper is 100 ppm or less.

3. 2. The carbon nanotube dispersion composition according to claim 1, wherein the carbon nanotubes have an angle of repose of 40° or more.

4. Cumulative particle diameter D measured by laser diffraction method ９０ The carbon nanotube dispersion composition according to claim 1 , wherein the average particle size is 6.0 μm or less.

5. 2. The carbon nanotube dispersion composition according to claim 1, which has a viscosity at 25° C. measured with a Brookfield viscometer of less than 2,000 mPa·s.

6. A composite slurry comprising the carbon nanotube dispersion composition according to any one of claims 1 to 5 and an active material.

7. An electrode film formed from the composite slurry according to claim 6.

8. A secondary battery including a positive electrode and a negative electrode, A secondary battery, wherein at least one of a positive electrode and a negative electrode has the electrode film according to claim 7.

9. A vehicle comprising the secondary battery according to claim 8.

10. The method comprises all of the following steps (1) to (3): A method for producing the carbon nanotube dispersion composition according to any one of claims 1 to 5. [Step (1): Crushing step] A process of applying shear stress to the carbon nanotubes to disintegrate them. [Process (2): Magnetic separation process] A process for removing metal foreign particles using an electromagnet with a magnetic flux density of 10,000 Gauss or more and 20,000 Gauss or less. [Step (3): Filtration step] A step of filtering the mixture using a depth filter having a filtering accuracy of 5 μm or more and 50 μm or less.

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