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

Abstract

One embodiment of the present invention relates to a carbon nanotube dispersion composition containing carbon nanotubes, a dispersant, and a solvent, the carbon nanotube dispersion composition having a content of metal foreign matter particles of 1.0 mg or less as determined according to specific condition 1.

Description

Technical Field

[0001] Embodiments of the present invention relate to a carbon nanotube dispersion composition, a composite material slurry, an electrode film, a secondary battery, and a vehicle. Background Art

[0002] With the popularization of electric vehicles or the miniaturization, light weight, and high performance of portable devices, a secondary battery with a high energy density is sought, and further, a high capacity of the secondary battery is required. Under such circumstances, due to the characteristics of high energy density and high voltage, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, particularly lithium-ion secondary batteries, are used in a large number of devices.

[0003] As the negative electrode material used in these lithium-ion secondary batteries, a carbon material represented by graphite, which has a low potential close to lithium (Li) and a large charge-discharge capacity per unit mass, is used. However, when these electrode materials have been used until the charge-discharge capacity per mass approaches the theoretical value, the energy density per mass of the battery approaches the limit. Therefore, in order to improve the utilization rate of the electrode, research has been conducted to reduce conductive aids or binders that do not contribute to the discharge capacity.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2010-174418

[0007] Patent Document 2: Japanese Patent No. 6962428

[0008] Patent Document 3: Japanese Patent Laid-Open No. 2021-065846

[0009] Patent Document 4: Japanese Patent Laid-Open No. 2022-046307

[0010] Patent Document 5: Specification of Chinese Patent Application Publication No. 118289749 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] The conductive aid plays a role of forming a conductive path inside the electrode and is required not to be cut off easily due to the expansion and contraction of the electrode film. In order to maintain the conductive path with a small amount of conductive aid, it is effective to use a carbon material with a large specific surface area, particularly carbon nanotubes, which are a kind of nanocarbon. However, although the battery using carbon nanotubes has excellent output characteristics, there are problems such as a large amount of metal foreign matters derived from the metal catalyst used in the synthesis of carbon nanotubes remaining and poor voltage drop.

[0013] In addition, metal foreign matter particles contained in the carbon nanotube dispersion composition sometimes dissolve inside the secondary battery and precipitate in a dendritic shape, piercing the separator and becoming a factor for internal short circuit. Furthermore, if the content of metal foreign matter particles is large, deterioration of the electrolyte or active material is likely to occur due to high-temperature charge and discharge of the secondary battery, and deterioration of the high-temperature cycle characteristics becomes a problem. Therefore, it is required to reduce the amount of metal foreign matter particles contained in the carbon nanotube dispersion composition.

[0014] Therefore, in Patent Document 1, the following method was studied: carbon nanotubes containing metal foreign matter particles such as iron, cobalt, and nickel were shredded, and the metal foreign matter particles of the carbon nanotubes were removed using an electromagnet.

[0015] In Patent Documents 2 and 3, the following technique was disclosed: after shredding carbon nanotubes by dispersion treatment of the carbon nanotubes, metal foreign matter particles were attached to a magnet to remove the metal foreign matter particles of the carbon nanotubes.

[0016] In addition, in Patent Document 4, the following method was proposed: a dispersion containing a conductive additive was circulated in a primary filter a plurality of times in a circulation manner, and at least two filters were arranged in series and passed through once, thereby removing metal foreign matter particles.

[0017] Furthermore, in Patent Document 5, the following method was proposed: after obtaining a carbon nanotube dispersion composition, it was passed through a magnetic filter and a filter membrane made of polypropylene, thereby removing metal foreign matter particles.

[0018] However, in these existing methods such as Patent Documents 1 to 5, there is a limit in reducing the metal content in the carbon nanotube dispersion composition, and there is a concern that problems such as an increase in viscosity caused by the hindrance of metal foreign matter particles to dispersion stability or insufficient characteristics when manufacturing a secondary battery may occur.

[0019] Therefore, the object of the problem to be solved by the present invention is to provide a carbon nanotube dispersion composition having good dispersibility and a low initial viscosity, and to provide a composite material slurry which can obtain an electrode film having high conductivity and close contact by using the carbon nanotube dispersion composition. More specifically, a secondary battery having excellent rate characteristics and high-temperature cycle characteristics, and a vehicle having high safety and improved fuel consumption rate by having the secondary battery are provided.

[0020] Technical means for solving the problem

[0021] The inventors of the present invention have made diligent studies to solve the above problems. The present inventors have found that a carbon nanotube dispersion composition containing carbon nanotubes, a dispersant, and a solvent, and having a content of metal foreign matter particles of 1.0 mg or less as determined according to Condition 1, has good dispersibility and a low initial viscosity. By using such a dispersion composition, an electrode with high conductivity and high adhesion can be obtained. Furthermore, it has been found that a secondary battery obtained by using the above electrode has excellent rate characteristics and high-temperature cycle characteristics. Based on the above findings, the present inventors have completed the present invention.

[0022] The present invention includes the following embodiments. The embodiments of the present invention are not limited to the following.

[0023] One embodiment relates to a carbon nanotube dispersion composition comprising: carbon nanotubes, a dispersant, and a solvent, wherein the content of metal foreign matter particles in the carbon nanotube dispersion composition as determined according to the following Condition 1 is 1.0 mg or less.

[0024] <Condition 1>

[0025] After recovering metal foreign matter particles in 20 kg of the carbon nanotube dispersion composition using an electromagnet (including an electromagnet with a grid screen having 31 pieces, a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), the electromagnet is cleaned with a solvent, and the obtained metal foreign matter particles are accumulated on a filter having a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metal foreign matter particles on the filter is measured.

[0026] Another embodiment relates to a composite material slurry comprising the carbon nanotube dispersion composition and an active material.

[0027] Another embodiment relates to an electrode film formed from the composite material slurry.

[0028] Another embodiment relates to a secondary battery including a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode in the secondary battery has the electrode film.

[0029] Another embodiment relates to a vehicle including the secondary battery.

[0030] Another embodiment relates to a manufacturing method, which is a manufacturing method of the carbon nanotube dispersion composition, and includes all of the following steps (1) to (3).

[0031] [Step (1): Disintegration step]

[0032] A step of applying a shear stress to carbon nanotubes to disintegrate the carbon nanotubes

[0033] [Step (2): Magnetic separation step]

[0034] The step of removing metallic foreign matter particles using an electromagnet with a magnetic flux density of 10,000 Gauss or more and 20,000 Gauss or less

[0035] [Step (3): Filtration and separation step]

[0036] The step of performing filtration and separation using a depth filter with a filtration accuracy of 5 μm or more and 50 μm or less

[0037] Effects of the invention

[0038] According to an embodiment of the present invention, the carbon nanotube dispersion composition has good dispersibility and a low initial viscosity. In addition, by using the carbon nanotube dispersion composition, an electrode film with excellent conductivity and adhesion can be obtained. In addition, a secondary battery with excellent rate characteristics and high-temperature cycle characteristics can be obtained. Thus, even for vehicle applications such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles that require high capacity, high output, and high durability for the mounted secondary battery, it can be preferably used. Description of the drawings

[0039] Figure 1 Figure 1 It is a photograph of the carbon nanotubes (J1) used in the examples observed at a magnification of 1 million times using a transmission electron microscope.

[0040] Figure 2 Figure 2 It is a photograph of the carbon nanotubes (K1) used in the examples observed at a magnification of 1 million times using a transmission electron microscope. Detailed description of the invention

[0041] Hereinafter, a carbon nanotube dispersion composition, a composite material slurry, an electrode film, and a secondary battery according to an embodiment of the present invention will be described in detail, but are not limited thereto. In addition, the numerical values determined in this specification are values obtained by the methods disclosed in the embodiments or examples.

[0042] In addition, the numerical range determined using "~" in this specification includes the range of the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0043] In this specification, carbon nanotubes (Carbon Nano Tube) are sometimes referred to as "CNT", and N-methyl-2-pyrrolidone is sometimes referred to as "NMP". In addition, in this specification, the carbon nanotube dispersion composition is sometimes referred to as "CNT dispersion composition" or simply as "dispersion composition".

[0044] ​​​​In the present invention, the so-called metallic foreign matter particles include fine metal powders and the like, regardless of their size or shape, and do not include substances that exist in the form of metal ions after dissolution.

[0045] As long as there are no special notes for the various components appearing in this specification, each can be used independently alone, or two or more can be mixed and used.

[0046] "Carbon Nanotube Dispersion Composition"

[0047] The carbon nanotube dispersion composition as an embodiment of the present invention contains carbon nanotubes, a dispersant, and a solvent. In the carbon nanotube dispersion composition, the content of metallic foreign matter particles obtained according to the following Condition 1 is 1.0 mg or less.

[0048] <Condition 1>

[0049] After recovering the metallic foreign matter particles in 20 kg of the carbon nanotube dispersion composition using an electromagnet (including an electromagnet with a grid screen having 31 pieces with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), the metallic foreign matter particles are washed with a solvent, and the obtained metallic foreign matter particles are piled up on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic foreign matter particles on the filter is measured.

[0050] Specifically, for example, the content of the metallic foreign matter particles can be obtained by the method described in the examples.

[0051] When the content of the metallic foreign matter particles contained in the carbon nanotube dispersion composition obtained according to Condition 1 is 1.0 mg or less, from the viewpoints 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. Thus, a carbon nanotube dispersion composition with good dispersibility and low initial viscosity can be prepared. In addition, by using the carbon nanotube dispersion composition, a secondary battery with excellent rate characteristics and high-temperature cycle characteristics can be obtained.

[0052] In addition, as the solvent used for washing the recovered metallic foreign matter particles in <Condition 1>, the same solvent as the solvent contained in the carbon nanotube dispersion composition can be used.

[0053] For example, in the case of a carbon nanotube dispersion composition containing carbon nanotubes, a dispersant, and a "solvent containing an amide-based polar solvent", the metallic foreign matter particles can be washed with the same "solvent containing an amide-based polar solvent". In the case where the solvent is a solvent composed only of an "amide-based polar solvent", the washing can be performed with the same "amide-based polar solvent".

[0054] For example, in the case of a carbon nanotube dispersion composition containing carbon nanotubes, a dispersant, and a "solvent containing water", the same "solvent containing water" can be used to clean the metal foreign matter particles. In the case where the solvent is a solvent composed only of "water", "water" can be used for cleaning.

[0055] An organic solvent can be used to clean the metal foreign matter particles deposited on the filter. As the organic solvent, for example, a water-soluble organic solvent such as alcohol (e.g., ethanol) can be used.

[0056] In the carbon nanotube dispersion composition, the content of metal foreign matter particles captured by a magnet according to Condition 1 and recovered through a filter with a mesh size of 5 μm is 1.0 mg or less. When the content of metal foreign matter particles larger than 5 μm captured by the magnet is large, sometimes the metal foreign matter particles expose from the electrode surface, causing a short circuit in the secondary battery and preventing it from functioning as a secondary battery. In addition, there is a possibility that the metal foreign matter particles dissolve into the electrolyte, increasing the self-discharge of the secondary battery.

[0057] The inventors of the present invention have found that simply reducing the content of metal elements such as metal ions contained in the carbon nanotube dispersion composition cannot sufficiently meet the electrical characteristics when manufacturing a secondary battery, and the content of metal foreign matter particles larger than 5 μm captured by a magnet is important.

[0058] It is speculated that the reason is as follows.

[0059] When carbon nanotubes are synthesized, a metal catalyst is used during manufacturing. Therefore, sometimes metals derived from the metal catalyst remain, and in addition, the metal catalyst is encapsulated. If the metal derived from the metal catalyst encapsulated in the carbon nanotubes or wear powder that may be included when dispersing the carbon nanotubes is refined by dispersion, it is difficult to capture only the metal foreign matter particles even when using a filter with a high filtration accuracy.

[0060] Furthermore, as metal foreign matter particles, sometimes wear powder caused by the wear of the inner wall, piping, dispersion medium, stirring blades, etc. of the disperser used in the dispersion process of carbon nanotubes is included. Wear powder from a part of the piping or tank containing stainless steel (SUS) 304 or SUS316 used in the disperser or piping, etc. changes its crystal structure under external stress applied to SUS304 or SUS316, becoming a magnetic metal foreign matter particle, but its magnetism is weak, so it is difficult to remove.

[0061] These metallic foreign particles are factors that deteriorate the dispersion stability in the carbon nanotube dispersion composition and cause an increase in viscosity. Further, when the metallic foreign particles are larger than the thickness of the separator, for example, 20 μm or more, they sometimes puncture the separator that separates the positive electrode and the negative electrode, causing an internal short circuit and resulting in a voltage defect.

[0062] Furthermore, most of the metallic foreign particles have orientation. When filtering and separating the carbon nanotube dispersion composition, even if a filter with a filtration accuracy of 20 μm is used, for example, needle-shaped metallic foreign particles of 20 μm or more sometimes mix into the carbon nanotube dispersion composition. Such metallic foreign particles are weakly magnetic, and only the metallic foreign particles close to the magnetic pole part can be removed by a magnet. It is difficult to reduce the metallic foreign particles only by using a magnet with a high magnetic force and increasing the number of magnetic separation treatments. However, by using a magnet such as an electromagnet having a magnetic force of a certain level or more and a narrow space between magnetic poles, the weakly magnetic metallic foreign particles are removed, and the content of metallic foreign particles exceeding 5 μm obtained according to Condition 1 is set to 1.0 mg or less, whereby a secondary battery having not only high safety but also good rate characteristics and high-temperature cycle characteristics can be manufactured.

[0063] In addition, the carbon nanotube dispersion composition refers to the state before adding the active material. In this regard, the carbon nanotube dispersion composition is distinguished from the composite material slurry containing the active material. That is, the carbon nanotube dispersion composition substantially does not contain the active material. This is a concept other than the state where the active material is intentionally added to the carbon nanotube dispersion composition. As long as the active material is 1 mass% or less, 0.5 mass% or less, or 0.1 mass% or less, or may be 0 mass% with respect to the total mass of the carbon nanotube dispersion composition. The active material will be described later.

[0064] When the carbon nanotube dispersion composition is used as a conductive aid for an electrode of a secondary battery by containing carbon nanotubes, even a small amount can form a conductive path and can have excellent rate characteristics and high-temperature cycle characteristics.

[0065] As described above, metal powders derived from metals used in manufacturing remain and / or are included in the carbon nanotubes. However, if the metals exist as they are, voltage drops and the like sometimes occur.

[0066] Since these included metal powders are exposed and refined by dispersion, from the viewpoint of the removal efficiency of metallic foreign matters, it is desirable to remove and reduce them before being refined, that is, before the dispersion step or during the dispersion step.

[0067] In addition, metal foreign matter particles that can be mixed as wear powder from a part of piping or tanks containing SUS304 or SUS316 during the dispersion process of carbon nanotubes change their crystal structure due to external stresses such as dispersion and have magnetism. When used in secondary batteries, they sometimes cause voltage drops and the like.

[0068] Therefore, it is desirable to reduce the metal foreign matter particles from these wear powders before they are refined by the dispersion process. It is preferably removed using a magnet before or during the dispersion process.

[0069] Thereby, not only can it prevent the reduction in the foreign matter removal efficiency using a magnet due to the decrease in the magnetization area of the metal foreign matter particles, making it difficult to sufficiently reduce the metal foreign matter particles, but also it can suppress the decrease in the stability of the carbon nanotube dispersion caused by the refined metal foreign matter particles.

[0070] The carbon nanotube dispersion composition can make the dispersibility and high-temperature cycle characteristics of the carbon nanotube dispersion composition excellent by controlling the content of metal foreign matter particles obtained according to Condition 1, which are formed by combining metal foreign matter particles such as those from the production of such carbon nanotubes and metal foreign matter particles such as wear powder from the dispersing machine during the dispersion process, to 1.0 mg or less.

[0071] As a method for making the content of metal foreign matter particles obtained according to Condition 1 1.0 mg or less, for example, it can be controlled by infinitely reducing the introduction of metal foreign matter from the raw material source, removing metal foreign matter from the dispersion equipment and the dispersion process during the process, filtering the dispersed carbon nanotube dispersion composition through a filter, etc. In addition, for example, further by magnetic separation treatment using a magnet with a narrow gap between magnetic poles such as an electromagnet, the content of metal foreign matter particles can be further reduced. Since most metal foreign matter particles have orientation, it is preferably passed through a magnet or a filter multiple times.

[0072] By these methods, it is possible to balance the dispersion stability and excellent battery characteristics that cannot be achieved only by reducing the metal element content in the carbon nanotube dispersion composition.

[0073] In addition, the lower the total content of iron, cobalt, nickel, chromium, molybdenum, and copper in the carbon nanotube dispersion composition, the more preferable it is, and it is preferably 100 ppm or less. More preferably, it is 50 ppm or less, and still more preferably, it is 10 ppm or less.

[0074] When the content of metal foreign matter particles obtained according to 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, the voltage failure of the secondary battery can be further suppressed.

[0075] The contents of iron, cobalt, nickel, chromium and molybdenum are each preferably 10 ppm or less, more preferably 5 ppm or less, and still more preferably 1 ppm or less. In addition, the content of copper is preferably 5 ppm or less, more preferably 1 ppm or less, and still more preferably 0.1 ppm or less.

[0076] Iron, cobalt, nickel and molybdenum are used as catalyst raw materials for producing carbon nanotubes. Since carbon nanotubes are produced in a reducing environment, the iron, cobalt, nickel and molybdenum exist in the form of pure metals encapsulated in the carbon nanotubes. Due to their low redox potential, there is a concern that they may dissolve into the electrolyte, precipitate on the surface of the negative electrode, resulting in poor voltage and decreased capacity of the secondary battery. In addition, it is also considered that iron, nickel and chromium may be mixed in from the wear powder of the tank or mixer used to produce the carbon nanotube dispersion composition, and copper may be mixed in from the motor of the dispersion equipment, etc. Among them, copper has a low redox potential, so there is a concern that it may dissolve into the electrolyte and precipitate as dendrites on the surface of the negative electrode, resulting in poor voltage of the secondary battery.

[0077] The amounts of these metal elements can be measured, for example, by inductively coupled plasma (ICP) optical emission spectrometry.

[0078] The content rate of the carbon nanotubes contained in the carbon nanotube dispersion composition is preferably 0.4% by mass or more and 10% by mass or less, more preferably 0.6% by mass or more and 8% by mass or less, and still more preferably 1% by mass or more and 6% by mass or less, based on the mass of the carbon nanotube dispersion composition (assuming the mass of the carbon nanotube dispersion composition is 100% by mass). When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the content rate of the carbon nanotubes 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 still more preferably 3% by mass or more and 6% by mass or less, based on the mass of the carbon nanotube dispersion composition (assuming the mass of the carbon nanotube dispersion composition is 100% by mass). Regarding "copolymer N", it will be described later.

[0079] The content of the dispersant 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 still more preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the carbon nanotubes. When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the content of copolymer N 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 still more preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the carbon nanotubes. When the content of the dispersant is within the above range, the dispersion stability of the carbon nanotubes in the carbon nanotube dispersion composition is likely to be good. In addition, the peel strength of the electrode for the secondary battery becomes good.

[0080] The content rate of the solvent is preferably 90% by mass to 99.6% by mass, more preferably 92% by mass to 99.4% by mass, and still more preferably 94% by mass to 99% by mass based on the carbon nanotube dispersion composition (100% by mass). When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the content rate of the amide-based polar solvent is preferably 90% by mass to 99% by mass, more preferably 92% by mass to 98% by mass based on the carbon nanotube dispersion composition (100% by mass). When within the above range, it is easy to obtain a carbon nanotube dispersion composition excellent in fluidity and dispersion stability. By using a carbon nanotube dispersion composition excellent in fluidity and dispersion stability, it is easy to remove metal foreign matters, an electrode film having stable conductivity can be obtained, and the quality of the secondary battery is likely to be stable.

[0081] When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the water content of the carbon nanotube dispersion composition is preferably 100 ppm or more and 1500 ppm or less, and preferably 200 ppm or more and 1000 ppm or less. The carbon nanotube dispersion composition further contains a binder resin. When the water content is within the above range, the gelation of the composite material slurry described later is suppressed, and it is easy to obtain a composite material slurry and an electrode film having stable quality. Especially when the binder resin contains a fluororesin, a good effect of suppressing the gelation of water is easily obtained. When the water content is within the above range, there is a tendency to easily prevent the metal encapsulated in the carbon nanotubes from dissolving during dispersion. From the viewpoint of suppressing metal dissolution, the water content can be within the above range.

[0082] Regarding the initial viscosity of the carbon nanotube dispersion composition, the viscosity measured using a B-type viscometer at 100 rpm and 25°C is preferably less than 2,000 mPa·s. More preferably, it is less than 1,000 mPa·s, and even more preferably, it is less than 500 mPa·s. In addition, it can 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 matters using a filter or an electromagnet. It can be considered that the composition ratio or dispersion process of the carbon nanotubes, dispersant, and solvent in the carbon nanotube dispersion composition with the initial viscosity within the above range is appropriate, and the dispersion stability is good.

[0083] Specifically, for example, the measurement can be carried out using the method described in the examples. The initial viscosity can be the viscosity measured within 12 hours after manufacturing the carbon nanotube dispersion composition.

[0084] The cumulative particle size D of the carbon nanotube dispersion composition measured by the laser diffraction method 90 is preferably 10 μm or less, more preferably 6.0 μm or less, and even more preferably 4.0 μm or less. In addition, it is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. When the cumulative particle size D 90 is within the above range, it is easy to form a conductive network of carbon nanotubes in the electrode. In addition, the filterability of the carbon nanotube dispersion composition is good, and metal foreign matter particles can be removed using a filter with a high filtration accuracy. Therefore, the mixing of metal foreign matter particles inside the secondary battery can be suppressed, and the rate characteristics and cycle characteristics of the secondary battery are further improved.

[0085] <Carbon Nanotubes>

[0086] Carbon nanotubes have a structure in which planar graphite is wound into a cylindrical shape. Examples of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes. The carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes, and they can also be mixed. For example, the carbon nanotubes include multi-walled carbon nanotubes. Multi-walled carbon nanotubes have a structure formed by winding two or more layers of graphite, and single-walled carbon nanotubes have a structure formed by winding one layer of graphite. The side walls of the carbon nanotubes may not be a graphite structure. For example, carbon nanotubes including side walls with an amorphous structure can also be used as carbon materials.

[0087] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 1 nm or more and 9 nm or less, and still more preferably 1 nm or more and 5 nm or less. When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and still more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, it is easy to form a good conductive network in the electrode. During charge and discharge, the active substances inside the secondary battery are uniformly utilized, so the deterioration of the active substances is suppressed and the cycle characteristics of the secondary battery are further improved. The average outer diameter of the carbon nanotubes can be obtained by observing the carbon nanotubes with a transmission electron microscope, measuring the outer diameters of 300 arbitrarily extracted carbon nanotubes, and calculating the arithmetic average of the measured values.

[0088] The Brunauer-Emmett-Teller (BET) specific surface area of the carbon nanotubes is preferably 100 m 2 / g or more and 1000 m 2 / g or less. When the solvent contains an amide-based polar solvent, the BET specific surface area of the carbon nanotubes is preferably 100 m 2 / g or more and 1000 m 2 / g or less, more preferably 170 m 2 / g or more and 600 m 2 / g or less, and still more preferably 200 m 2 / g or more and 500 m 2 / g or less. When the solvent contains water, the BET specific surface area of the carbon nanotubes is preferably 150 m 2 / g or more and 1000 m 2 / g or less, more preferably 500 m 2 / g or more and 1000 m 2 / g or less. When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the BET specific surface area of the carbon nanotubes is preferably 100 m 2 / g or more and 1000 m 2 / g or less, more preferably 170 m 2 / g or more and 600 m 2 / g or less, and still more preferably 200 m 2 / g or more and 500 m 2 / g or less.

[0089] When the BET specific surface area is within the above range, a small amount of efficient conductive network can be formed, and the amount of conductive material in the electrode can be reduced. As a result, the degree of freedom in battery design such as active materials or binder resins is increased. Furthermore, when preparing the composite material slurry, the compounding of the active material and the carbon nanotubes can be easily promoted. Therefore, an electrode film with a homogeneous conductive network in which the surface of the active material is coated with carbon nanotubes can be obtained, the electrolyte decomposition reaction at the interface between the electrolyte and the active material can be suppressed, and the cycle characteristics of the battery can be improved.

[0090] The BET specific surface area can be measured by the BET method described in Japanese Industrial Standards (JIS) Z8830:2013.

[0091] When the maximum peak intensity in the range of 1560 cm -1 ~1600 cm -1 is defined as G and the maximum peak intensity in the range of 1310 cm -1 ~1350 cm -1 is defined as D in the Raman spectrum, the G / D ratio (peak ratio of G-band to D-band) of the carbon nanotubes is preferably 0.5 to 100. When the solvent contains an amide-based polar solvent, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5. When the solvent contains water, the G / D ratio is preferably 5 to 100, more preferably 10 to 50. When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, regarding the G / D ratio (peak ratio of G-band to D-band) of the carbon nanotubes, when the maximum peak intensity in the range of 1560 cm -1 ~1600 cm -1 is defined as G and the maximum peak intensity in the range of 1310 cm -1 ~1350 cm -1 is defined as D in the Raman spectrum, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5.

[0092] It is considered that when the G / D ratio of the carbon nanotubes is within the above range, the contact resistance between the carbon nanotubes becomes smaller, and good conductivity can be easily obtained. In addition, it is speculated that the reason is that the amount of functional groups on the surface of the multi-walled carbon nanotubes is appropriate, the affinity with the solvent is good, and the dispersibility becomes better.

[0093] When the solvent contains water and the G / D ratio of the carbon nanotubes is 5 or more, in most cases, it is an aggregate of carbon nanotubes with a small outer diameter. However, for carbon nanotubes having a BET specific surface area and a G / D ratio within the above range, the dispersant acts on the gaps between the carbon nanotubes, and by performing appropriate dispersion treatment, it is easy to obtain a carbon nanotube dispersion composition with good conductivity.

[0094] The volume resistivity of the carbon nanotubes is preferably 1.0×10 -3 Ω·cm to 3.0×10 -2 Ω·cm, more preferably 1.0×10 -3 Ω·cm to 2.0×10 -2 Ω·cm. When the carbon nanotube dispersion composition contains carbon nanotubes, copolymer N, and an amide-based polar solvent, the volume resistivity of the carbon nanotubes is preferably 1.0×10 -2 Ω·cm to 3.0×10 -2 Ω·cm, more preferably 1.0×10 -2 Ω·cm to 2.0×10 -2 Ω·cm.

[0095] The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (manufactured by Nittoseiko Analytech Co., Ltd.: Loresta GP powder resistivity measuring system MCP-PD-51). When the volume resistivity is within the above range, the conductivity of the electrode film becomes good, and a secondary battery with excellent rate characteristics and cycle characteristics can be obtained.

[0096] The angle of repose of the carbon nanotubes is preferably 40° or more. More preferably 45° or more, and further preferably 50° or more. In addition, it is preferably 85° or less, more preferably 70° or less. The angle of repose is an index indicating the fluidity of the powder. Among the carbon nanotubes with an angle of repose within the above range, it is easy to remove the metal foreign particles encapsulated in the carbon nanotubes, and it is easy to obtain a carbon nanotube dispersion composition with a small content of metal foreign particles. The angle of repose can be measured by the injection method. The injection method is a method of measuring by stacking powder on a table with a disk-shaped upper surface. It is not easily affected by the material of the table, and the angle formed by the powder stacked in a conical shape and the horizontal plane can be measured using a protractor or the like. In addition, a commercially available measuring machine can also be used to measure the angle of repose.

[0097] The angle of repose of carbon nanotubes can be controlled by processing using existing known pulverization equipment. As the pulverization equipment, for example, a Henschel mixer, a super mixer, a Nauta mixer, a trimix, a high-speed mixer, a mortar, a needle mill, a hammer mill, a pulverizer, an attritor, a jet mill, a shredder, a ball mill, a bead mill, a colloid mill, a conical ball mill, a disk mill, a crusher, a Wonder Crusher, a vibration mill, an ultrasonic homogenizer, etc. can be used. Particularly preferred are an attritor, a needle mill, a hammer mill, a jet mill, a shredder, a ball mill, a bead mill, and a vibration mill.

[0098] Preferably, an electromagnet is used for carbon nanotubes to remove metal foreign matter particles by magnetic force. For example, preferably, in the pulverization step or the filling step in the method for manufacturing carbon nanotubes, an electromagnet is set so that the carbon nanotubes pass through, thereby removing the metal foreign matter particles.

[0099] The higher the carbon purity of the carbon nanotubes, the more preferred. In 100% by mass of the carbon nanotubes, it is preferably 98.0% by mass or more, more preferably 99.5% by mass or more, still more preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more.

[0100] That is, the lower the content rate of metal foreign matter particles, the more preferred. In 100% by mass of the carbon nanotubes, it is preferably 2.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less.

[0101] By using carbon nanotubes produced by a method that does not use a metal catalyst as a core, or carbon nanotubes obtained by using an existing known purification treatment method such as acid treatment, the content rate of metal foreign matter particles is 2.0% by mass or less with respect to 100% by mass of the carbon nanotubes, whereby the content of metal foreign matter particles contained in the carbon nanotube dispersion composition can be reduced, and the characteristics of the secondary battery can be improved.

[0102] The carbon purity of the carbon nanotubes can be determined by an ICP emission spectroscopic analyzer using the method described in the examples.

[0103] <Dispersant>

[0104] The dispersant is not particularly limited as long as it can stabilize the dispersion of carbon nanotubes, and surfactants (excluding resins), resin-type dispersants, etc. can be used. The preferred type of dispersant can be appropriately used in a preferred blending amount according to the characteristics required for the dispersion of carbon nanotubes.

[0105] For example, as a dispersant, from the viewpoint of improving the wettability of carbon nanotubes with respect to a solvent and obtaining a homogeneous carbon nanotube dispersion composition, a surfactant is preferred. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric types. As the surfactant, polycarboxylate, naphthalene sulfonic acid formalin condensate, and polyoxyethylene phenyl ether can be used.

[0106] For example, from the viewpoints of electrochemical resistance, solubility in an electrolyte solvent, or viscosity stability of a composite material slurry, a resin-type dispersant is preferred. As the resin-type dispersant, cellulose derivatives, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylic acid, or a polyacrylonitrile-based polymer is preferred. Cellulose derivatives, polyvinyl butyral, polyvinylpyrrolidone, polyacrylic acid, and polyacrylonitrile-based polymers are particularly preferred. Among the cellulose derivatives, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose are preferred. The resin-type dispersant is preferably carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, and a polyacrylonitrile-based polymer, and carboxymethyl cellulose, polyacrylic acid, and polyacrylonitrile-based polymers are particularly preferred.

[0107] In the case of selecting an anionic surfactant, its type is not particularly limited. Specifically, examples include fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkyl aryl sulfonates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphonic acid sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters, but are not limited thereto. Further specifically, examples include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and the sodium salt of β-naphthalene sulfonic acid formalin condensate, but are not limited thereto. The anionic surfactant is preferably polycarboxylate and naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0108] Examples of the cationic surfactant include alkylamine salts and quaternary ammonium salts. Specifically, examples include stearylamine acetate, trimethylcoconut ammonium chloride, trimethyltallow ammonium chloride, dimethyldioleyl ammonium chloride, methyloleyl diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, lauryl pyridinium disulfate, cetylpyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride, but are not limited thereto.

[0109] Examples of the amphoteric surfactant include amino carboxylates, but are not limited thereto.

[0110] Examples of the nonionic surfactant include, but are not limited to, polyoxyethylene alkyl ether, polyoxyalkylene derivative, polyoxyethylene phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and alkyl allyl ether. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octyl phenyl ether.

[0111] The selected surfactant is not limited to a single surfactant. Therefore, two or more surfactants can also be combined and used. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. The blending amount at this time is preferably set to the preferred blending amount for each surfactant component. As the combination, a combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate or a naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0112] Specific examples of the resin type dispersant include cellulose derivatives (such as cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylic acid, polyacrylonitrile-based polymers, etc. Particularly preferred are cellulose derivatives, polyvinyl butyral, polyvinylpyrrolidone, polyacrylic acid, and polyacrylonitrile-based polymers. Among the cellulose derivatives, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose are preferred. The resin type dispersant is preferably carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, and polyacrylonitrile-based polymers, and particularly preferably carboxymethyl cellulose, polyacrylic acid, and polyacrylonitrile-based polymers.

[0113] Carboxymethyl cellulose as the resin type dispersant can be used in the form of a salt such as sodium carboxymethyl cellulose, which is obtained by substituting the hydroxyl group of carboxymethyl cellulose with a sodium carboxymethyl group. The degree of etherification of carboxymethyl cellulose as the resin type dispersant is preferably 0.5 to 1.5, more preferably 0.6 to 1.0. The degree of etherification of carboxymethyl cellulose can be measured by a conventional method. By setting the degree of etherification within the above range, it can have an appropriate affinity for water and CNTs. Further, in the case of being used in a secondary battery, it is possible to prevent adverse conditions such as the dispersant dissolving in the electrolyte in the battery and increasing the viscosity of the electrolyte. The degree of etherification can be measured, for example, by the following method.

[0114] Accurately weigh about 2.0 g of the sample and place it into a 300 mL stoppered conical flask. Add 100 mL of nitric acid methanol (a liquid prepared by adding 100 mL of super concentrated HNO3 to 1 L of anhydrous methanol), shake for 2 hours to convert Na-CMC into H-CMC. Quantitatively transfer the H-CMC to a glass filter 1G3 for suction filtration, and wash it with 200 mL of 80% methanol. Then, displace it with 50 mL of anhydrous methanol, perform suction filtration, and dry it at 105 °C for 2 hours. As the following indicator, that is, accurately weigh 1 g to 1.5 g of absolutely dry H-CMC, place it into a 300 mL stoppered conical flask, moisten the H-CMC with 15 mL of 80% methanol, add N / 10 50 mL of NaOH, shake at room temperature for 2 hours as the indicator, use phenolphthalein, and N / 10 back-titrate the excess NaOH with H2SO4.

[0115] The degree of etherification is calculated by the following formula.

[0116] ((50 × F' - N / 10 mL of H2SO4 × F) / (dry weight of H-CMC (g))) × (1 / 10) = A

[0117] Degree of etherification (M / c6) = (0.162A / (1 - 0.058A))

[0118] F: N / 10 Factor of H2SO4

[0119] F': N / 10 Factor of NaOH

[0120] The polyacrylonitrile-based polymer is a polymer having a structural unit containing a nitrile group, and may also be a copolymer having a structural unit containing a nitrile group and a structural unit other than the structural unit containing a nitrile group. When the polyacrylonitrile-based polymer is a copolymer, the content of the structural unit containing a nitrile group is preferably 15% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and still more preferably 25% by mass or more and 50% by mass or less. Based on all the structural units contained in the copolymer, examples of the structural unit other than the structural unit containing a nitrile group include: an alkylene structural unit, an amide group-containing structural unit, a carboxyl group-containing structural unit, etc. The polyacrylonitrile-based polymer is preferably a copolymer containing an alkylene structural unit having a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit having a content of 25% by mass or more and 50% by mass or less (sometimes referred to as "copolymer N").

[0121] The weight-average molecular weight of the resin-type dispersant is preferably 5,000 or more and 500,000 or less, more preferably 10,000 or more and 300,000 or less, and still more preferably 10,000 or more and 100,000 or less. If a dispersant having a moderate weight-average molecular weight is used, the adsorptivity to carbon nanotubes is improved, and the stability of the carbon nanotube dispersion is further improved. In addition, when a dispersant outside the above range is used, the viscosity of the carbon nanotube dispersion becomes high, and when a disperser such as a nozzle-type or valve-type high-pressure homogenizer is used to pass the dispersion liquid through a narrow flow path, the dispersion efficiency sometimes decreases. In addition, in addition to the dispersing ability, the resin-type dispersant sometimes has an adhesive ability. The resin-type dispersant having an adhesive ability also functions as an adhesive. When the resin-type dispersant has both functions as an adhesive, the weight-average molecular weight of the resin-type dispersant is preferably greater than that in the case where it does not have both functions as an adhesive. For example, in the case of a carbon nanotube dispersion composition in which the solvent contains an amide-based polar solvent, the weight-average molecular weight of the resin-type dispersant having both functions as an adhesive is preferably 20,000 or more and 250,000 or less, more preferably 50,000 or more and 200,000 or less. For example, in the case of a carbon nanotube dispersion composition in which the solvent contains water, the weight-average molecular weight of the resin-type dispersant having both functions as an adhesive is preferably 260,000 or more and 450,000 or less, more preferably 260,000 or more and 350,000 or less. Here, the weight-average molecular weight (Mw) of the resin-type dispersant can be measured using a gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector.

[0122] In addition to the dispersant, the carbon nanotube dispersion composition may further contain an inorganic base and / or an inorganic metal salt. As the inorganic base and the inorganic metal salt, compounds containing at least one of an alkali metal and an alkaline earth metal are preferred. Specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Among these, in terms of being able to easily supply cations, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferred. Examples of the hydroxides of alkali metals include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the hydroxides of alkaline earth metals include calcium hydroxide, magnesium hydroxide, etc. Examples of the carbonates of alkali metals include lithium carbonate, lithium hydrogencarbonate, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, etc. Examples of the carbonates of alkaline earth metals include calcium carbonate, magnesium carbonate, etc. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

[0123] In addition to a dispersant, the carbon nanotube dispersion composition may further contain an acid. By adding an acid, the charge state in the dispersion system or the balance between the hydrophilic part and the hydrophobic part changes, and sometimes the dispersibility is improved. The type of acid is not particularly limited, and one type may be used, or a combination of multiple types may be used. The acid may be, for example, an organic acid or an inorganic acid having 6 or less carbon atoms. Examples include: oxalic acid, lactic acid, citric acid, acetic acid, malonic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, etc. The active material contained in the composite material slurry described later is, for example, a negative electrode active material containing lithium. If it is alkaline, sometimes the dispersibility of the carbon nanotube dispersion composition collapses and thickens. However, when it contains an acid in addition to the dispersant, the change in the pH of the slurry can be alleviated, and the rapid thickening of the composite material slurry can be suppressed. Therefore, the storage stability of the composite material slurry is excellent, the coating unevenness of the electrode using the composite material slurry can be suppressed, and the quality of the battery is likely to become stable.

[0124] In addition to a dispersant, the carbon nanotube dispersion composition may further contain an antifoaming agent. Any commercially available antifoaming agent, wetting agent, or other substance having an antifoaming effect can be arbitrarily used, and one type may be used, or a combination of multiple types may be used.

[0125] [Copolymer N]

[0126] Copolymer N has an alkylene structural unit with a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit with a content of 25% by mass or more and 50% by mass or less.

[0127] By using such a copolymer N, a carbon nanotube dispersion composition excellent in dispersibility and oxidation resistance can be obtained. Since its solubility in the electrolyte is also low, the ionic conductivity of the electrolyte is not easily decreased, and the rate characteristics and high-temperature cycle characteristics of the secondary battery using the carbon nanotube dispersion composition can be made excellent.

[0128] Copolymer N can be obtained, for example, by copolymerizing a monomer mixture containing a conjugated diene monomer and a nitrile group-containing monomer, and hydrogenating the carbon-carbon double bond portion of the structural unit derived from the conjugated diene monomer to form a copolymer N having an alkylene structural unit and a nitrile group-containing structural unit. Specifically, it can be manufactured by the method described later.

[0129] The Mooney viscosity of copolymer N is preferably 65 or less, more preferably 60 or less, still more preferably 50 or less, and particularly preferably 35 or less. In addition, it is preferably 20 or more, more preferably 35 or more.

[0130] "Mooney viscosity (ML 1+4 , 100 °C)" in the embodiment of the present invention can be measured at a temperature of 100 °C in accordance with JIS K6300-1:2013.

[0131] It is presumed that by setting the Mooney viscosity within the above range, the copolymer N can have a moderate repulsive force in the state of being adsorbed on the carbon nanotubes, thereby improving the dispersion stability. When it is 20 or more, the balance between the solubility in the amide-based polar solvent used as the solvent and the adsorption property to the carbon nanotubes becomes 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 transfer efficiency of the disperser can be suppressed, and metal foreign matters mixed in the raw material source can be efficiently removed by methods such as magnet, filtration, and centrifugation. Therefore, voltage defects of the secondary battery caused by metal foreign matter particles can be prevented, which is thus preferred.

[0132] As long as the copolymer N has an alkylene structural unit with a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit with a content of 25% by mass or more and 50% by mass or less, it can have appropriate fluidity even at room temperature.

[0133] The weight average molecular weight (Mw) of the copolymer N is preferably 20,000 or more and 200,000 or less, and more preferably 20,000 or more and 150,000 or less. When the weight average molecular weight is within the above range, the adsorption property to the carbon nanotubes and the affinity to the dispersion medium are likely to be good. The weight average molecular weight is the weight average molecular weight in terms of polystyrene and can be measured by gel permeation chromatography (GPC).

[0134] The method for adjusting the Mooney viscosity is not particularly limited. For example, it can be adjusted by changing the composition of the polymer (type or content of structural units, hydrogenation rate, etc.), structure (linearity rate, etc.), molecular weight, preparation conditions (polymerization temperature, molecular weight adjustment dosage, etc.), and the like.

[0135] In addition, the copolymer N used is preferably one in which metal foreign matter particles are removed by a filtration separation process using a filter and / or a magnetic separation process using the magnetic force of an electromagnet. For example, it is preferred to set a filter or an electromagnet in the pulverization process or filling process of the copolymer N and pass the copolymer N through it to remove metal foreign matter particles.

[0136] The magnetic separation process of the copolymer N can also be carried out after dissolving the copolymer N in an amide-based polar solvent or the like to form a copolymer N solution.

[0137] (Alkylene structural unit)

[0138] The alkylene structural unit is a structural unit containing an alkylene structure, and is preferably a structural unit composed only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure. However, this does not include the case of a structural unit having a nitrile group.

[0139] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1A).

[0140] General formula (1A)

[0141] [Chemical formula 1]

[0142]

[0143] In general formula (1A), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more. n is preferably an integer of 5 or less, more preferably an integer of 4 or less. Particularly preferably, n is 3.

[0144] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1B).

[0145] General formula (1B)

[0146] [Chemical formula 2]

[0147]

[0148] 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, still more preferably an integer of 2 or less. Particularly preferably, n is 2.

[0149] The method for introducing the alkylene structural unit into the copolymer N is not particularly limited, and for example, the following methods (1a) or (1b) can be mentioned.

[0150] In the method (1a), a copolymer is prepared by a 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 embodiments of the present invention, the "monomer units derived from the conjugated diene monomer" are sometimes referred to as "conjugated diene monomer units", and the monomer units derived from other monomers are sometimes similarly omitted. Subsequently, at least a part of the conjugated diene monomer units is converted into alkylene structural units by hydrogenating the conjugated diene monomer units. Hereinafter, "hydrogenation" is sometimes referred to as "hydrogenation". The finally obtained copolymer N contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0151] In addition, the conjugated diene monomer unit contains at least a monomer unit having a carbon-carbon double bond. For example, the 1,3-butadiene monomer unit as the conjugated diene monomer unit contains 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 also contain two or more monomer units. In addition, the conjugated diene monomer unit may further contain a monomer unit that does not have a carbon-carbon double bond and contains a branching point. In the present specification, the "branching point" refers to the branching point in a branched polymer. When the conjugated diene monomer unit contains a monomer unit containing a branching point, the prepared copolymer and the copolymer are branched polymers.

[0152] In the method of (1b), a copolymer is prepared by a polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared copolymer contains an α-olefin monomer unit. The finally obtained copolymer N contains an α-olefin monomer unit as an alkylene structural unit.

[0153] Among these, in terms of ease of manufacturing the copolymer N, the method of (1a) is preferred. The number of carbon atoms of the conjugated diene monomer is 4 or more, preferably 4 or more and 6 or less. 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 them, 1,3-butadiene is preferred. The alkylene structural unit preferably contains a structural unit obtained by hydrogenating the conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably contains a structural unit obtained by hydrogenating the 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer may be used alone or in combination of two or more.

[0154] The hydrogenation is preferably a method capable of selectively hydrogenating the conjugated diene monomer unit. Examples of the hydrogenation method include known methods such as an oil-phase hydrogenation method or an aqueous-phase hydrogenation method.

[0155] The hydrogenation can be carried out by a usual method. The hydrogenation can be carried out, for example, by treating with hydrogen in the presence of a hydrogenation catalyst in a state where a copolymer having a conjugated diene monomer unit is dissolved in an appropriate solvent. Examples of the hydrogenation catalyst include nickel, palladium, platinum, copper, etc.

[0156] In the method of (1b), the number of carbon atoms of the α-olefin monomer is 2 or more, preferably 3 or more, more preferably 4 or more. The number of carbon atoms of the α-olefin monomer is preferably 6 or less, 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.

[0157] The alkylene structural unit preferably contains 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 contains at least one selected from the group consisting of a structural unit composed only of a linear alkylene structure and a structural unit composed only of a branched alkylene structure, and further preferably contains at least one selected from the group consisting of the structural unit represented by the formula (1A) and the structural unit represented by the formula (1B).

[0158] The content rate of the alkylene structural unit is 50% by mass or more and 75% by mass or less based on the mass of the copolymer N (that is, when the mass of the copolymer N is set to 100% by mass). It is preferably 55% by mass or more. In addition, it is preferably 70% by mass or less, more preferably 65% by mass or less.

[0159] By setting the content rate of the alkylene structural unit within the above range, the adsorptivity to carbon nanotubes and the affinity to the dispersion medium can be controlled, and the carbon nanotubes can exist stably in the dispersion medium, so that the stability of the dispersion composition becomes good. In addition, the affinity of the copolymer N to the electrolyte can also be controlled, and adverse conditions such as an increase in the resistance of the electrolyte due to the dissolution of the copolymer N in the electrolyte in the battery can be prevented.

[0160] (Structural unit containing a nitrile group)

[0161] The structural unit containing a nitrile group is a structural unit having a nitrile group. It is preferably a structural unit having an alkylene structure substituted with a nitrile group, more preferably a structural unit composed only of an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The structural unit containing a nitrile group may further contain a structural unit containing an alkyl structure substituted with a nitrile group (or composed only of it). The number of nitrile groups contained in the structural unit containing a nitrile group is preferably one.

[0162] The structural unit containing a nitrile group preferably has a structural unit represented by the following general formula (2A).

[0163] General formula (2A)

[0164] [Chemical formula 3]

[0165]

[0166] In general 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 still more preferably an integer of 3 or less. Particularly preferably, n is 2.

[0167] The nitrile group-containing structural unit may include a structural unit represented by the following general formula (2B).

[0168] General formula (2B)

[0169] [Chemical formula 4]

[0170]

[0171] In general formula (2B), R represents a methyl group.

[0172] The method for introducing the nitrile group-containing structural unit into the copolymer N is not particularly limited, and a method of preparing a copolymer by a polymerization reaction using a monomer composition containing a nitrile group-containing monomer ((2a) method) can be preferably used. The finally obtained copolymer N has a nitrile group-containing monomer unit as the nitrile group-containing structural unit. Examples of the nitrile group-containing monomer that can form the nitrile group-containing structural unit include monomers having a polymerizable carbon-carbon double bond and a nitrile group. For example, compounds having a nitrile group and an α,β-ethylenically unsaturated group, and specifically, acrylonitrile, methacrylonitrile, etc. can be cited. In particular, from the viewpoint of improving the intermolecular force between the copolymers N and / or between the copolymer N and the dispersed substance (adsorbed substance), the nitrile group-containing monomer is preferably acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more.

[0173] The content rate of the nitrile group-containing structural unit is 25% by mass or more and 50% by mass or less based on the mass of the copolymer N (that is, when the mass of the copolymer N is set to 100% by mass). It is preferably 30% by mass or more. In addition, it is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0174] By setting the content rate of the nitrile group-containing structural unit within the above range, the adsorptivity to carbon nanotubes and the affinity for 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 becomes good. In addition, the affinity of the copolymer N for the electrolyte can also be controlled, and it is possible to prevent problems such as the copolymer N dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte.

[0175] (Other structural units)

[0176] Within the range that does not hinder the effects of the present invention, if necessary, the copolymer N may also have structural units other than the alkylene structural unit and the nitrile group-containing structural unit. Examples of other structural units include amide group-containing structural units, carboxyl group-containing structural units, etc.

[0177] <Solvent>

[0178] As the solvent, as long as it is within the range where carbon nanotubes can be dispersed, there is no particular limitation. It is preferably any one selected from the group consisting of water and water-soluble organic solvents, or a mixed solvent containing two or more selected from these groups. For example, the solvent can be a solvent composed of only any one selected from the group consisting of water and water-soluble organic solvents, or a mixed solvent containing two or more selected from these groups.

[0179] As the water-soluble organic solvent, the following can be used: alcohol series (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, benzyl alcohol, etc.), polyol series (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexylene glycol, pentylene glycol, glycerol, hexanetriol, thiodiglycol, etc.), polyol ether series (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine series (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amide series (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic series (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide series (dimethyl sulfoxide, etc.), sulfone series (hexamethylphosphoric triamide, sulfolane, etc.), lower ketone series (acetone, methyl ethyl ketone, etc.), and tetrahydrofuran, urea, acetonitrile, etc.

[0180] [Water]

[0181] For example, the solvent preferably contains water. When the solvent contains water, the water content can be 50% by mass or more, more than 50% by mass, 75% by mass or more, or 90% by mass or more based on 100% by mass of the solvent, preferably 95% by mass or more, and more preferably 98% by mass or more, and it can also be a single solvent of water.

[0182] [Amide-based polar solvent]

[0183] For example, the solvent is preferably an amide-based polar solvent. Examples of the amide-based polar solvent include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, and the like. Among them, it is more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0184] When the solvent contains an amide-based polar solvent, the content of the amide-based polar solvent may be 50% by mass or more, more than 50% by mass, 75% by mass or more, or 90% by mass or more with respect to 100% by mass of the solvent, preferably 95% by mass or more, more preferably 98% by mass or more, and may substantially be a single solvent of the amide-based polar solvent.

[0185] The water content in the solvent containing an 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. In this range, the alkali metal encapsulated in the carbon nanotubes may dissolve in the carbon nanotube dispersion composition, and the dispersion stability of the carbon nanotube dispersion composition becomes good.

[0186] <Optional Components>

[0187] The carbon nanotube dispersion composition may optionally contain other additives such as alkali metal hydroxides, alkali metal carbonates, wetting agents, pH adjusters, wetting penetrants, leveling agents, etc., and other conductive materials other than carbon nanotubes within the scope not hindering the object of the present invention. The optional components can be added at any timing such as before the production of the carbon nanotube dispersion composition, during mixing, after mixing, or a combination thereof.

[0188] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like.

[0189] Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, potassium carbonate, and the like.

[0190] In the case of using an alkali metal hydroxide and / or an alkali metal carbonate, the content thereof 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, still more preferably 1.5 parts by mass or more and 2.5 parts by mass or less, based on 100 parts by mass of the copolymer N. In the case of using both the alkali metal hydroxide and the alkali metal carbonate, the total content is preferably within the above range. When using an alkali metal hydroxide and / or an alkali metal carbonate, the wettability of the carbon nanotubes is improved, and the dispersibility is further improved. In addition, since the dispersion proceeds to the target viscosity in a short time, there are few defects in the carbon nanotubes, and it is easy to obtain an electrode film and a secondary battery with good conductivity.

[0191] <Manufacturing method of carbon nanotube dispersion composition>

[0192] The carbon nanotube dispersion composition of the present embodiment is obtained by dispersing a mixture containing carbon nanotubes, a dispersant, and a solvent using a disperser.

[0193] In addition, the manufacturing method is not particularly limited, but preferably includes a step of applying a shear stress to the carbon nanotubes to break up the carbon nanotubes, and a magnetic separation step for removing magnetic foreign matters in order to make the content of metal foreign matter particles in the carbon nanotube dispersion composition obtained according to Condition 1 1.0 mg or less, a filtration separation step using a filter, and a centrifugation step and other metal foreign matter removal steps. As these metal foreign matter removal steps, at least any one of the magnetic separation step and the filtration separation step is preferred.

[0194] The metal foreign matter removal step can be performed at any timing such as before, during, or after the dispersion of the carbon nanotube dispersion composition.

[0195] The metal foreign matter particles are preferably removed before being refined by the dispersion step, and preferably include a metal foreign matter removal step before and / or during the dispersion of the carbon nanotube dispersion composition.

[0196] Furthermore, a manufacturing method of a carbon nanotube dispersion composition including the following steps (1) to (3) is preferred.

[0197] [Step (1): Disintegration step]

[0198] A step of applying a shear stress to the carbon nanotubes to break up the carbon nanotubes

[0199] [Step (2): Magnetic separation step]

[0200] A step of removing metal foreign matter particles using an electromagnet having a magnetic flux density of 10,000 Gauss or more and 20,000 Gauss or less

[0201] [Step (3): Filtration separation step]

[0202] A step of performing filtration separation using a depth filter with a filtration accuracy of 5 μm or more and 50 μm or less

[0203] There is no particular limitation on the order of step (1), step (2), and step (3). The metal foreign matter removal steps of step (2) and step (3) can also be before, simultaneous with, or a combination of them with respect to step (1).

[0204] Preferably, it includes each step in the order of step (1), step (2), and step (3), or step (1) and step (2) are performed simultaneously, and then step (3) is included.

[0205] The reason is that thereby, through [step (1): disintegration step], the metal foreign matter particles encapsulated in the carbon nanotubes can be exposed, and then or simultaneously through [step (2): magnetic separation step], the magnetic metal foreign matter particles can be removed by contacting with a magnet. Subsequently, through [step (3): filtration separation step], the weakly magnetic (large particle size but weak magnetism, or too small particle size and low magnetization area, not supplemented by the magnet and flowing in the liquid, etc.) metal foreign matter particles that cannot be completely removed by the magnet can be removed.

[0206] [Step of disintegrating carbon nanotubes]

[0207] In the step of disintegrating carbon nanotubes by applying a shear stress to the carbon nanotubes, the carbon nanotubes can be disintegrated by a dispersion device or the like in a dry and / or wet manner.

[0208] The dispersion device used for disintegrating carbon nanotubes is not particularly limited.

[0209] As a dispersion device, a disperser commonly used in pigment dispersion or the like can be used. For example, mixers such as dispersers, homogenizing mixers, planetary mixers, etc., homogenizers (Advanced Digital Sonifer (registered trademark) manufactured by BRANSON, MODEL 450DA, "clearmix" manufactured by M-technique, "filmix" manufactured by PRIMIX, "abramix" manufactured by Silverson, etc.), paint regulators (manufactured by Red Devil), colloid mills ("PUC colloid mill" manufactured by PUC, "colloid mill MK" manufactured by IKA, etc.), cone mills ("cone mill MKO" manufactured by IKA, etc.), ball mills, sand mills ("Dyno-mill" manufactured by SHINMARU ENTERPRISES, etc.), grinders, pearl mills ("DCPmill" manufactured by Eirich, etc.), bead mills and other media type dispersers, high-pressure homogenizers ("Jenius PY" manufactured by Jenius, "Star burst" manufactured by SUGINO Machine, "Nanomizer" manufactured by Nanomizer, etc.), "HC3 series" manufactured by Sanmaru Machinery Industry Co., Ltd., "HV-H series" manufactured by Izumi Food Machinery Co., Ltd., "R-Model" manufactured by SPXFLOW, "clear SS-5" manufactured by M-technique, "MICROS" manufactured by Nara Machinery Co., Ltd., and other mediumless dispersers, other roll mills, etc., but not limited to these.

[0210] It is ideal that the mixing of wear powder during the crushing process is small, so a medium-free disperser is preferably used. The rotor and stator of the disperser are preferably ceramics. When a bead mill is used in wet dispersion, the dispersion medium is also preferably ceramics. When a bead mill is used as a wet disperser, it is preferred to use a medium-free disperser to apply shear stress to the carbon nanotubes in advance and crush the carbon nanotubes before the dispersion treatment using the bead mill. The reason is that for the low-viscosity dispersed material where the crushing of the carbon nanotubes is not performed, the beads are easily worn when the bead mill is operated at a high peripheral speed. In addition, when a high-pressure homogenizer is used as a disperser, there is a concern that the nozzle of the high-pressure homogenizer is clogged or the valve is damaged when the wear powder of the beads during the dispersion process exists.

[0211] When a high-pressure homogenizer is used as a disperser, for example, a nozzle-type high-pressure homogenizer that ejects the treatment liquid from a nozzle, a valve-type high-pressure homogenizer that ejects the treatment liquid from a homogenization valve, etc. can be used. As a nozzle-type high-pressure homogenizer, "Jenius PY" manufactured by Jenius, "Star burst" manufactured by SUGINO Machine, "Nanomizer" manufactured by Nanomizer, etc. can be used. As a valve-type high-pressure homogenizer, "HC3 series" manufactured by Sanmaru Machinery Industry, "HV-H series" manufactured by Izumi Food Machinery, "R-Model" manufactured by SPX FLOW, etc. can be used, but it is not limited to these. Among them, the valve-type high-pressure homogenizer can increase the flow rate of the treatment liquid, and in the case of producing a dispersed composition of carbon nanotubes by circulating dispersion, the homogeneity is improved, and the cumulative particle size D of the dispersed composition of carbon nanotubes is reduced. 90 The smaller the particle size, the better the filterability. In the filtration step, a filter with excellent filtration accuracy can be used, and a carbon nanotube-dispersed composition with a small content of metallic foreign matter particles can be obtained more easily.

[0212] The carbon nanotube dispersion composition of this embodiment is preferably dispersed by circulating dispersion or channel dispersion until the unbroken carbon nanotubes are substantially eliminated. In the case of circulating dispersion, when the storage tank is uniformly stirred, 5 passes are performed, thereby making the probability of the existence of unbroken particles less than 1% by mass, so it is preferred, more preferably 10 passes, and more preferably 15 passes. In addition, in the case of channel dispersion, it is preferred to disperse 3 passes or more, more preferably 5 passes or more, and more preferably 10 passes or more. In the presence of unbroken carbon nanotubes, there is a cumulative particle size D 90 The particles are likely to become larger, and the filterability of the carbon nanotube-dispersed composition may be reduced.

[0213] In order to set the content of metallic foreign matter particles obtained under Condition 1 to 1.0 mg or less, the carbon nanotube dispersion composition of the present embodiment is preferably a substance obtained by removing metallic foreign matter particles by using a filter or magnetic force after subjecting carbon nanotubes to a disintegration treatment.

[0214] [Process of removing metallic foreign matter particles]

[0215] The method of removing metallic foreign matter particles is not particularly limited, and examples thereof include a filtration separation process of filtering and separating using a filter, and a magnetic separation process such as a magnetic separation treatment using an electromagnet.

[0216] It is preferably to include a filtration separation process and a magnetic separation process. The reason is that through the magnetic separation process, metallic foreign matter particles in carbon nanotubes grown with a metal catalyst as the core can be removed, and through the filtration separation process, metallic foreign matter particles that cannot be removed by a magnet can be recovered.

[0217] In addition, it is more preferably to perform the magnetic separation process after the filtration separation process. By performing the filtration separation process at the end before the CNT dispersion composition is shipped, metallic foreign matter particles from piping and the like can also be removed. Thus, by reducing the metallic foreign matter particles, the characteristics when manufacturing a battery can also be made more excellent.

[0218] (Magnetic separation process)

[0219] As a method of removing metallic foreign matter particles by using magnetic force through the magnetic separation process, various known methods can be used. For example, the following method is preferred: When manufacturing the carbon nanotube dispersion composition, an electromagnet is set and the carbon nanotube dispersion composition is passed through, thereby removing metallic foreign matter particles.

[0220] The magnetic flux density of the electromagnet is preferably 5000 Gauss or more and 20000 Gauss or less, and more preferably 10000 Gauss or more and 20000 Gauss or less. By using an electromagnet within the above range, not only can metallic foreign matter particles contained in the carbon nanotubes be removed, but also metallic foreign matter particles mixed in during the manufacturing process of the carbon nanotube dispersion composition can be removed.

[0221] Specifically, for example, CS-150HHH, CS-250HHH, CS-300HHH manufactured by Nippon Magnetics, DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Eriez Magnetics Japan, EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Daebo Magnetic Co., Ltd. etc. can be used.

[0222] The flow rate of the carbon nanotube dispersion composition when in contact with the electromagnet is preferably 1 L / min or more and 200 L / min or less, more preferably 30 L / min or more and 100 L / min or less. When the flow rate is large when in contact with the electromagnet, there is a possibility that the metal magnetic foreign matter particles captured by the electromagnet with a small magnetic force may flow back into the carbon nanotube dispersion composition.

[0223] The number of times the carbon nanotube dispersion composition passes through the electromagnet is preferably three or more. When the number of passes is small, there is a possibility that the metal foreign matter particles cannot be removed. When passing through the electromagnet in a cyclic manner, considering the uniformity in the tank used in the manufacturing process, it is preferably passed through more times.

[0224] (Filtration and separation process)

[0225] As the filter for filtering and separating metal foreign matter particles, it can be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferred. The metal foreign matter particles are not spherical and mostly have orientation. Therefore, by using a depth filter, the metal foreign matter particles in the carbon nanotube dispersion composition can be efficiently removed.

[0226] Different from the surface filter (a filter that mainly captures particulate matter in the fluid on the filter surface), the depth filter is a filter that mainly captures particulate matter in the fluid inside the filter medium, and has the characteristics of high particle retention performance and not being easily blocked. By using a depth filter, the metal foreign matter particles in the carbon nanotube dispersion composition can be removed more selectively.

[0227] As the depth filter, for example, a non-woven fabric depth cartridge NT-T series made of 3M(TM) polypropylene (PP) or Profile II manufactured by Pall Corporation in Japan, and a Depth Filter Cartridge ShearScreen made of PP manufactured by Roki Corporation can be used.

[0228] The filtration accuracy of the filter is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 50 μm or less, and particularly preferably 10 μm or more and 40 μm or less. When using a filter with a small filter pore diameter to improve the removal efficiency of metal foreign matter particles in the carbon nanotube dispersion composition, there is a possibility that the removal efficiency of the metal foreign matter particles may decrease due to blockage of the carbon nanotubes, etc. By using a filter with the filtration accuracy within the above range, the metal foreign matter can be efficiently removed, and a carbon nanotube dispersion composition with fewer metal foreign matter particles can be obtained.

[0229] In addition, even when performing filtration separation using a filter with a filtration accuracy of 3 μm or 5 μm, etc., metal foreign matter particles sometimes have orientation due to their needle-like shape, etc., and it is impossible to completely remove the metal foreign matter particles, and sometimes they remain in the carbon nanotube dispersion composition. Therefore, it is preferable to appropriately control the composition or viscosity of the carbon nanotube dispersion composition, the dispersion process, or the metal foreign matter removal process, etc., to reduce the content of metal foreign matter particles determined under Condition 1.

[0230] "Evaluation Method of Carbon Nanotube Dispersion Composition"

[0231] The evaluation method of the carbon nanotube dispersion composition of the present embodiment includes determining the content of metal foreign matter particles in the carbon nanotube dispersion composition containing carbon nanotubes, a dispersant, and a solvent according to the following Condition 2.

[0232] <Condition 2>

[0233] After recovering the metal foreign matter particles in the carbon nanotube dispersion composition using an electromagnet, wash with a solvent, stack the obtained metal foreign matter particles on a filter, and measure the weight of the metal foreign matter particles on the filter.

[0234] As Condition 2, Condition 1 can also be implemented. According to the evaluation method of the present embodiment, the carbon nanotube dispersion composition can be evaluated based on a criterion corresponding to the content of metal foreign matter particles contained in the composition.

[0235] "Composite Material Slurry"

[0236] The composite material slurry of the present embodiment at least contains a carbon nanotube dispersion composition and an active material. That is, the composite material slurry preferably contains at least carbon nanotubes, a dispersant, a solvent, and an active material, and contains an adhesive resin.

[0237] The so-called adhesive resin is a resin for bonding between substances. There is no particular limitation on the adhesive resin. For example, polymers or copolymers containing fluororesin, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as structural units can be cited;

[0238] Polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin;

[0239] Cellulose resins such as carboxymethyl cellulose;

[0240] Rubber-like substances such as styrene-butadiene rubber;

[0241] Conductive resins such as polyaniline and polyacetylene. Among them, from the viewpoint of the oxidation-reduction resistance of electrochemistry, it is preferable to use a fluororesin as the binder resin.

[0242] The composite material slurry may also contain a resin-type dispersant having a function as a binder resin.

[0243] As the fluororesin, for example, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferably used.

[0244] The weight-average molecular weight of the fluororesin is preferably 10,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,500,000 or less, and particularly preferably 200,000 or more and 1,500,000 or less. The weight-average molecular weight is the weight-average molecular weight in terms of polystyrene and can be measured by gel permeation chromatography (GPC).

[0245] The so-called active material is the material that forms the basis of the battery reaction. In terms of electromotive force, the active material is divided into a positive electrode active material and a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material are sometimes simply referred to as "active materials". The so-called active material is the material that forms the basis of the battery reaction. In terms of electromotive force, the active material is divided into a positive electrode active material and a negative electrode active material.

[0246] There is no particular limitation on the positive electrode active material, and metal compounds such as metal oxides and metal sulfides that can dope or intercalate lithium ions, and conductive polymers, etc. can be used. For example, oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. can be cited. Specifically, powders of transition metal oxides such as MnO, V2O5, V6O 13 , TiO2, etc., composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials as olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2 and FeS, etc. can be cited. In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. In addition, the above-mentioned inorganic compounds or organic compounds can be mixed and used.

[0247] The positive electrode active material preferably contains a composite oxide of lithium and a transition metal such as Al, Fe, Co, Ni, and Mn, more preferably a composite oxide of lithium and any one of Al, Co, Ni, and Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When these active materials are used, particularly good battery characteristics can be obtained.

[0248] As the negative electrode active material, there is no particular limitation as long as it can dope or intercalate lithium ions. For example, the following can be listed: metallic Li, alloy systems such as tin alloys, silicon alloys, and lead alloys which are alloys thereof, Li x Fe2O3, Li x Fe3O4, Li x WO2 (x is a number where 0 < x < 1), metal oxide systems such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymer systems such as polyacetylene and poly(phenylene), amorphous carbonaceous materials such as soft carbon or hard carbon, or artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin calcined carbon materials, gas layer grown carbon fibers, carbon fiber and other carbon-based materials. These negative electrode active materials can also be used alone or in combination of two or more.

[0249] 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, and still more preferably 0.3 m 2 / g or more and 3 m 2 / g or less.

[0250] The average particle size of the active material is preferably in the range of 0.05 μm to 100 μm, and still more preferably in the range of 0.1 μm to 50 μm. The average particle size of the active material as described in this specification is the average value of the particle sizes measured by an electron microscope for the active material.

[0251] In order to obtain the composite material slurry, it is preferable to perform a treatment of adding the active material to the carbon nanotube dispersion composition and then dispersing it. The dispersion device for performing the treatment is not particularly limited. Regarding the composite material slurry, the dispersion device described in the carbon nanotube dispersion composition can be used to obtain the composite material slurry.

[0252] Based on 100% by mass of the composite material slurry, the content rate 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.

[0253] Based on 100 parts by mass of the active material, the content of carbon nanotubes in the composite material slurry is preferably 0.05 parts by mass to 10 parts by mass, preferably 0.1 parts by mass to 5 parts by mass, and preferably 0.1 parts by mass to 3 parts by mass.

[0254] The content of the dispersant in the composite material slurry 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 still more preferably 20 parts by mass or more and 50 parts by mass or less, based on 100 parts by mass of the carbon nanotubes.

[0255] When the composite material slurry contains an adhesive resin, the content of the adhesive resin in the composite material slurry is preferably 0.5 parts by mass to 20 parts by mass, still more preferably 1 part by mass to 10 parts by mass, and particularly preferably 1 part by mass to 5 parts by mass, based on 100 parts by mass of the active material.

[0256] The solid content concentration of the composite material slurry is preferably 30% by mass to 90% by mass, and preferably 40% by mass to 85% by mass, based on 100% by mass of the composite material slurry.

[0257] When the solvent contains an amide-based polar solvent, the water content in the composite material slurry is preferably 500 ppm or less, still more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0258] "Electrode, Electrode Film"

[0259] The electrode of this embodiment includes an electrode film formed from a current collector and the composite material slurry of this embodiment. The electrode film is a coating film of the composite material slurry. The electrode film is, for example, a coating film formed by coating the composite material slurry on the current collector and drying to form an electrode composite material layer.

[0260] The material or shape of the current collector is not particularly limited, and the material and shape suitable for various secondary batteries can be appropriately selected. For example, as the material of the current collector, metals such as aluminum, copper, nickel, titanium, or stainless steel, or alloys can be cited. In addition, as the shape, generally a foil on a flat plate can be used, but a current collector with a roughened surface, or a perforated foil-shaped current collector, and a mesh-shaped current collector can also be used.

[0261] As a method of coating the composite material slurry on the current collector to form an electrode film, there is no particular limitation, and known methods can be used. Specifically, methods such as die coating, dip coating, roll coating, knife coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating can be cited. As the drying method, air drying, hot air dryer, warm air dryer, infrared heater, far-infrared heater, etc. can be used, but it is not particularly limited to these.

[0262] In addition, calendering treatment using a flat plate press or a calender roll can also be performed after coating. The thickness of the electrode film (electrode composite material layer) is generally 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0263] Secondary Battery

[0264] The secondary battery of this embodiment includes an electrode having an electrode film and an electrolyte. The secondary battery may include a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode may have the electrode film of this embodiment. Since the carbon nanotube dispersion composition of this embodiment forms a good conductive network in the electrode of the secondary battery, its rate characteristics are excellent. During charge and discharge, the active material is utilized uniformly, so the deterioration of the active material is not easily aggravated. Furthermore, overcharge and over-discharge during charge and discharge are suppressed. Moreover, since there are few metal foreign matters derived from the carbon nanotube dispersion composition, the deterioration of battery characteristics caused by electrolyte decomposition or metal precipitation is not likely to occur, and the high-temperature cycle characteristics are excellent.

[0265] As the positive electrode, a material obtained by coating a composite material slurry containing a positive electrode active material on a current collector, drying it, and forming an electrode film can be used.

[0266] As the negative electrode, a material obtained by coating a composite material slurry containing a negative electrode active material on a current collector, drying it, and forming an electrode film can be used.

[0267] As the electrolyte, various known electrolytes through which ions can move can be used. For example, electrolytes 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 (where Ph is a phenyl group) can be cited, but it is not limited to these, and electrolytes containing sodium salts can also be used. The electrolyte is preferably used as an electrolytic solution after being dissolved in a non-aqueous solvent.

[0268] There is no particular limitation on the non-aqueous solvent. For example, 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-octanolactone; glycol dimethyl ethers (glyme) 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 can be cited. These solvents can be used alone or in combination of two or more.

[0269] The secondary battery of the present embodiment preferably includes a separator. Examples of the separator include polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and non-woven fabrics subjected to hydrophilic treatment, but are not particularly limited thereto.

[0270] The structure of the secondary battery of the present embodiment is not particularly limited, and generally includes a positive electrode, a negative electrode, and a separator provided as needed, and can be formed into various shapes corresponding to the use purpose, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

[0271] The use of the secondary battery of the present embodiment is not particularly limited. Specifically, it can be used for power supply purposes of civilian devices such as mobile phones, laptop computers, digital cameras, etc.; emergency power supplies for hospitals, factories, buildings, etc.; vehicle uses such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles, auxiliary bicycles, railway vehicles, etc. The secondary battery recovers, for example, the regenerative energy of vehicle power.

[0272] Among them, since it is a secondary battery with high charge-discharge performance and excellent cycle characteristics, it can be preferably used for vehicles, and a vehicle with high safety and an expected improvement in fuel consumption rate can be obtained. Furthermore, even in the case of vehicle uses where charging and discharging at a large current are desired, excellent effects can be exhibited.

[0273] The mounting position of the secondary battery in the vehicle of the present embodiment is not particularly limited. For example, when the secondary battery is mounted on an automobile, the secondary battery can be mounted in the engine compartment, behind the vehicle body, or under the seat of the vehicle.

[0274] The present invention includes, for example, the following embodiments. The embodiments of the present invention are not limited to the following.

[0275] 〔1〕A carbon nanotube dispersion composition, comprising: carbon nanotubes, a dispersant, and a solvent, in the carbon nanotube dispersion composition,

[0276] The content of metal foreign matter particles determined according to the following condition 1 is 1.0 mg or less.

[0277] <Condition 1>

[0278] After recovering the metal foreign matter particles in 20 kg of the carbon nanotube dispersion composition by using an electromagnet (including an electromagnet with a grid screen having 31 pieces with a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), cleaning is performed with a solvent, and the obtained metal foreign matter particles are accumulated on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metal foreign matter particles on the filter is measured.

[0279] 〔2〕The carbon nanotube dispersion composition according to 〔1〕, wherein the dispersant contains at least one selected from the group consisting of carboxymethyl cellulose, polyacrylic acid, and acrylonitrile-based polymers.

[0280] 〔3〕The carbon nanotube dispersion composition according to 〔1〕 or 〔2〕, wherein the dispersant contains a copolymer.

[0281] The copolymer has an alkylene structural unit with a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit with a content of 25% by mass or more and 50% by mass or less.

[0282] 〔4〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔3〕, wherein the solvent contains an amide-based polar solvent.

[0283] 〔5〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔4〕, wherein the solvent contains water.

[0284] 〔6〕A carbon nanotube dispersion composition comprising: carbon nanotubes, a copolymer, and an amide-based polar solvent. In the carbon nanotube dispersion composition,

[0285] the content of metal foreign particles determined according to the following Condition 1 is 1.0 mg or less.

[0286] The copolymer has an alkylene structural unit with a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit with a content of 25% by mass or more and 50% by mass or less.

[0287] <Condition 1>

[0288] After recovering the metal foreign particles in 20 kg of the carbon nanotube dispersion composition using an electromagnet (including an electromagnet with 31 grid meshes having a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), washing with an amide-based polar solvent, piling up the obtained metal foreign particles on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and measuring the weight of the metal foreign particles on the filter.

[0289] 〔7〕A carbon nanotube dispersion composition comprising: carbon nanotubes, a dispersant, and water. In the carbon nanotube dispersion composition,

[0290] the content of metal foreign particles determined according to the following Condition 1 is 1.0 mg or less.

[0291] <Condition 1>

[0292] After recovering the metallic foreign particles in 20 kg of the carbon nanotube dispersion composition using an electromagnet (including an electromagnet with a grid screen having 31 pieces, a magnetic flux density of 16,000 Gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), it is washed with water, and the obtained metallic foreign particles are accumulated on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic foreign particles on the filter is measured.

[0293] 〔8〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔7〕, wherein the total content of iron, cobalt, nickel, chromium, molybdenum, and copper is 100 ppm or less.

[0294] 〔9〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔8〕, wherein the angle of repose of the carbon nanotubes is 40° or more.

[0295] 〔10〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔9〕, wherein the cumulative particle size D 90 measured by the laser diffraction method is 6.0 μm or less.

[0296] 〔11〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔10〕, wherein the cumulative particle size D 90 measured by the laser diffraction method is 6.0 μm or less.

[0297] 〔12〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔11〕, wherein the viscosity at 25 °C measured by a B-type viscometer is less than 2,000 mPa·s.

[0298] 〔13〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔12〕, wherein the BET specific surface area of the carbon nanotubes is 150 m 2 / g to 1200 m 2 / g.

[0299] 〔14〕The carbon nanotube dispersion composition according to any one of 〔1〕 to 〔13〕, wherein, when the maximum peak intensity in the range of 1560 cm -1 to 1600 cm -1 in the Raman spectrum of the carbon nanotubes is set as G, and the maximum peak intensity in the range of 1310 cm -1 to 1350 cm -1 is set as D, the G / D ratio is 5 to 100.

[0300] 〔15〕A composite material slurry, comprising the carbon nanotube dispersion composition according to any one of 〔1〕 to 〔14〕 and an active material.

[0301] 〔16〕An electrode film is formed from the composite material slurry according to 〔15〕.

[0302] 〔17〕A secondary battery includes a positive electrode and a negative electrode. In this secondary battery,

[0303] at least one of the positive electrode and the negative electrode has the electrode film according to 〔16〕.

[0304] 〔18〕A vehicle includes the secondary battery according to 〔17〕.

[0305] 〔19〕A manufacturing method is the manufacturing method of the carbon nanotube dispersion composition according to any one of 〔1〕 to 〔14〕, and includes all of the following steps (1) to (3).

[0306] [Step (1): Disintegration step]

[0307] A step of applying shear stress to carbon nanotubes to disintegrate the carbon nanotubes

[0308] [Step (2): Magnetic separation step]

[0309] A step of removing metal foreign particle using an electromagnet with a magnetic flux density of 10,000 Gauss or more and 20,000 Gauss or less

[0310] [Step (3): Filtration and separation step]

[0311] A step of performing filtration and separation using a depth filter with a filtration accuracy of 5 μm or more and 50 μm or less

[0312] The disclosure of the present application is related to the subject matters described in Japanese Patent Application No. 2023-184181 filed on October 26, 2023 and Japanese Patent Application No. 2024-109392 filed on July 8, 2024, and the entire disclosure content thereof is incorporated herein by reference.

[0313] Examples

[0314] Examples are listed below to more specifically illustrate the present invention. The present invention is not limited to the following examples as long as it does not exceed its gist. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". In addition, the compounding amounts in the tables are parts by mass, and are values in terms of non-volatile components except for the solvent. In addition, the blank columns in the tables indicate non-formulation.

[0315] The materials used in the examples and comparative examples are shown below.

[0316] · Hydrogenated nitrile rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass) or less, to prepare dispersant (A).

[0317] · Hydrogenated nitrile rubber (manufactured by 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) or less, to prepare dispersant (B).

[0318] · Hydrogenated nitrile rubber (manufactured by 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) or less, to prepare dispersant (C).

[0319] · Hydrogenated nitrile rubber (manufactured by 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) or less, to prepare dispersant (D).

[0320] · Hydrogenated nitrile rubber (manufactured by 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) or less, to prepare dispersant (E).

[0321] · Hydrogenated nitrile rubber (manufactured by ARLANXEO, Therban (R) 3406, Mooney viscosity 63, weight average molecular weight 200,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass) or less, to prepare dispersant (F).

[0322] · Hydrogenated nitrile rubber (manufactured by Zannan Scitech, liquid hydrogenated nitrile rubber, weight average molecular weight 30,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass or less), to prepare dispersant (G).

[0323] · Polyvinyl pyrrolidone (PVP) (manufactured by Nippon Catalyst Co., Ltd., K-30, weight average molecular weight 40,000) or less, to prepare dispersant (H).

[0324] · Polyacrylic acid (manufactured by Dong-A Synthetic Co., Ltd., AC-10LP, weight-average molecular weight 50,000) or less was made into dispersant (I).

[0325] · Sodium carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., Sunrose A, APP-84, weight-average molecular weight 18,000, degree of etherification 0.71) or less was made into dispersant (J).

[0326] · Carbon nanotubes (manufactured by JEIO, JENOTUBE 10B) or less were made into carbon nanotubes (CNT) (A1).

[0327] · Carbon nanotubes (manufactured by JEIO, JENOTUBE 6A) or less were made into carbon nanotubes (CNT) (B1).

[0328] · The purified CNT described in paragraph 0098 of Japanese Patent No. 6586197 was made into carbon nanotubes (CNT) (I1).

[0329] · FT2020 (manufactured by Cnano) or less was made into carbon nanotubes (CNT) (J1).

[0330] · TUBALL 01RW03 (manufactured by OCSiAl) or less was made into carbon nanotubes (CNT) (K1).

[0331] <Production of carbon nanotubes (C1)>

[0332] 1 kg of carbon nanotubes (A1) was metered and added into a 100 L glass container. After adding 50 kg of 20% hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Corporation), it was sufficiently stirred using a stirrer at 25°C. Then, it was sufficiently diluted with ion-exchanged water and subjected to vacuum filtration using a membrane filter. After repeating the operations of dilution and filtration, the carbon nanotubes were transferred to a barrel made of polytetrafluoroethylene (PTFE) and dried in an oven at 80°C to obtain carbon nanotubes (C1).

[0333] <Production of carbon nanotubes (C2)>

[0334] For carbon nanotubes (C1), using a dynamic mill (manufactured by Nippon Coke & Engineering Co., Ltd.), zirconia beads with a diameter of 8 mm were charged as a grinding medium, supplied at an operating condition of 10.0 kg / h, and processed at a circumferential speed of 5.0 m / s to obtain carbon nanotubes (C2).

[0335] <Production of carbon nanotubes (D1)>

[0336] Weigh and add 10 kg of carbon nanotubes (A1) into a 120 L heat-resistant container, and place the heat-resistant container containing the carbon nanotubes in the furnace. Then, introduce nitrogen into the furnace, maintain a positive pressure, and at the same time, discharge the air in the furnace. After the oxygen concentration in the furnace reaches 0.1% or less, heat it to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, introduce chlorine at a rate of 50 L / min for 50 hours. Then, introduce nitrogen at a rate of 50 L / min and cool it while maintaining a positive pressure to obtain carbon nanotubes (D1).

[0337] <Fabrication of Carbon Nanotubes (E1)>

[0338] Weigh and add 10 kg of carbon nanotubes (A1) into a 120 L heat-resistant container, and place the heat-resistant container containing the carbon nanotubes in the furnace. Then, introduce nitrogen into the furnace, maintain a positive pressure, and at the same time, discharge the air in the furnace. After the oxygen concentration in the furnace reaches 0.1% or less, heat it to 1800 °C over 30 hours. While maintaining the furnace temperature at 1800 °C, introduce chlorine at a rate of 50 L / min for 50 hours. Then, introduce nitrogen at a rate of 50 L / min and cool it while maintaining a positive pressure to obtain carbon nanotubes (E1).

[0339] <Fabrication of Carbon Nanotubes (E2)>

[0340] For the carbon nanotubes (E1), pass them through an electromagnet (electromagnetic separator CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove magnetic foreign substances in the carbon nanotubes (E1) and obtain carbon nanotubes (E2). A separator with a screen mesh of 10 mm was used for the electromagnetic separator.

[0341] <Fabrication of Carbon Nanotubes (E3)>

[0342] For the carbon nanotubes (E1), use a dynamic mill (manufactured by Nippon Coke & Engineering Co., Ltd.), load zirconia beads with a diameter of 8 mm as the grinding medium, supply them at an operating condition of 10.0 kg / h, process them at a circumferential speed of 5.0 m / s, and then pass them through an electromagnet (electromagnetic separator CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove magnetic foreign substances in the raw materials and obtain carbon nanotubes (E3). A separator with a screen mesh of 10 mm was used for the electromagnetic separator.

[0343] <Fabrication of Carbon Nanotubes (F1)>

[0344] Weigh 10 kg of carbon nanotubes (A1) in a 120 L heat-resistant container, and place the heat-resistant container containing the carbon nanotubes in a furnace. Then, introduce nitrogen into the furnace, maintain a positive pressure, and at the same time discharge the air in the furnace. After the oxygen concentration in the furnace reaches 0.1% or less, heat it to 2000 °C over 30 hours. While maintaining the furnace temperature at 2000 °C, introduce chlorine at a rate of 50 L / min for 50 hours. Then, introduce nitrogen at a rate of 50 L / min and cool it while maintaining a positive pressure to obtain carbon nanotubes (F1).

[0345] <Fabrication of Carbon Nanotubes (G1)>

[0346] Weigh 10 kg of carbon nanotubes (A1) in a 120 L heat-resistant container, and place the heat-resistant container containing the carbon nanotubes in a furnace. Then, introduce nitrogen into the furnace, maintain a positive pressure, and at the same time discharge the air in the furnace. After the oxygen concentration in the furnace reaches 0.1% or less, heat it to 3000 °C over 30 hours. While maintaining the furnace temperature at 3000 °C, introduce chlorine at a rate of 50 L / min for 50 hours. Then, introduce nitrogen at a rate of 50 L / min and cool it while maintaining a positive pressure to obtain carbon nanotubes (G1).

[0347] <Fabrication of Carbon Nanotubes (H1)>

[0348] Weigh 10 kg of carbon nanotubes (B1) in a 120 L heat-resistant container, and place the heat-resistant container containing the carbon nanotubes in a furnace. Then, introduce nitrogen into the furnace, maintain a positive pressure, and at the same time discharge the air in the furnace. After the oxygen concentration in the furnace reaches 0.1% or less, heat it to 1800 °C over 30 hours. While maintaining the furnace temperature at 1800 °C, introduce chlorine at a rate of 50 L / min for 50 hours. Then, introduce nitrogen at a rate of 50 L / min and cool it while maintaining a positive pressure, and then take out the carbon nanotubes. For the carbon nanotubes, use a dynamic mill (manufactured by Nippon Coke & Engineering Co., Ltd.), load zirconia beads with a diameter of 8 mm as the grinding medium, supply them at an operating condition of 10.0 kg / h, process them at a circumferential speed of 5.0 m / s, and then pass them through an electromagnet (electromagnetic separator CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove metal foreign particles in the raw material and obtain carbon nanotubes (H1). The electromagnetic separator used is a separator with a screen mesh of 10 mm.

[0349] Table 1 shows the physical properties of the carbon nanotubes used in the examples and comparative examples.

[0350] [Table 1]

[0351] Table 1

[0352]

[0353] <Determination of weight-average molecular weight of dispersant>

[0354] The weight-average molecular weight (Mw) of the dispersant is determined by gel permeation chromatography (GPC) equipped with a refractive index (RI) detector. The conditions are as follows.

[0355] (Determination method for polyacrylonitrile-based polymers)

[0356] Use HLC-8320GPC (manufactured by Tosoh Corporation) as the device, connect three separation columns in series, and use "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" manufactured by Tosoh Corporation as the packing materials in sequence. Use a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide as the eluent at an oven temperature of 40°C, and perform the determination at a flow rate of 0.6 mL / min. The concentration of the measurement sample is adjusted to 1% with a solvent containing the eluent, and 20 μL is injected. The weight-average molecular weight is the polystyrene conversion value.

[0357] (Determination method for cellulose derivatives)

[0358] As the device, use HLC-8320GPC (manufactured by Tosoh Corporation), use "TSKgel SuperMultiporePW-M" manufactured by Tosoh Corporation as the column, and use 0.1 M aqueous NaCl solution as the eluent at a temperature of 25°C, and perform the determination at a flow rate of 1.0 mL / min. Prepare the measurement sample into a 0.1 mass% aqueous solution and inject 100 μL. The weight-average molecular weight is the pullulan conversion value.

[0359] (Determination method for dispersants other than acrylonitrile-based polymers and cellulose derivatives)

[0360] Select either Measurement Method 1 or Measurement Method 2 according to the solubility of the dispersant in water and perform the determination.

[0361] Add the dispersant to a mixed solution of purified water / methanol = 3 / 7 (volume ratio) to make it 0.2 mass%, perform ultrasonic irradiation for 10 minutes, and use Measurement Method 1 for the determination when the dispersant is completely dissolved. On the other hand, use Measurement Method 2 for the determination when the dispersant is not completely dissolved, forms a precipitate, or is in a suspended state.

[0362] (Measurement Method 1)

[0363] The apparatus used Shodex GPC-101 (manufactured by Resonac Co., Ltd.) as the separation column. A total of four columns, namely three "OHpak SB-806M HQ" and one "OHpak SB-802.5HQ", all manufactured by Resonac Co., Ltd., were connected in series. At an oven temperature of 40°C, a solution of 50 mM lithium chloride in purified water / methanol = 3 / 7 (volume ratio) was used as the eluent, and the measurement was carried out at a flow rate of 1.0 mL / min. The sample was prepared at a concentration of 0.2 mass% in a mixture containing the above eluent and 0.1 mL was injected. The weight-average molecular weight was the value in terms of polyethylene glycol conversion.

[0364] (Measurement method 2)

[0365] The apparatus used HLC-8320GPC (manufactured by Tosoh Corporation) as the separation column. "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500", all manufactured by Tosoh Corporation, were connected in series. At an oven temperature of 40°C, an N,N-dimethylformamide solution containing 30 mM triethylamine and 10 mM lithium bromide was used as the eluent, and the measurement was carried out at a flow rate of 0.6 mL / min. The sample was prepared at a concentration of 0.2 mass% in a solvent containing the above eluent and 10 μL was injected. The weight-average molecular weight was the value in terms of polystyrene conversion.

[0366] <Fabrication of standard positive electrode>

[0367] 93 parts by mass of the positive electrode active material (manufactured by BASF TODA Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100), 4 parts by mass of acetylene black (manufactured by DENKA Co., Ltd., DENKA BLACK (registered trademark) HS100), and 3 parts by mass of polyvinylidenefluoride (PVDF) (manufactured by Kureha Battery Materials Japan Co., Ltd., Kureha KF Polymer W#1300) were added to a container with a volume of 150 cm 3After the plastic container, use a spatula to mix until the powder is uniform. Then, add 20.5 parts by mass of N-methyl-2-pyrrolidone (NMP), and use a planetary mixer (Degassing Ryorotaro, ARE-310 manufactured by Thinky Corporation) to stir at 2000 rpm for 30 seconds. Then, use a spatula to mix the mixture in the plastic container until uniform, and use the planetary mixer to stir at 2000 rpm for 30 seconds. Then, add 14.6 parts by mass of NMP, and use the planetary mixer to stir at 2000 rpm for 30 seconds. Finally, use a high-speed mixer to stir at 3000 rpm for 10 minutes to obtain a composite material slurry for the positive electrode. Then, after coating the composite material slurry for the positive electrode onto an aluminum foil with a thickness of 20 μm as a current collector using a coater, dry it in an electric oven at 120 °C ± 5 °C for 25 minutes, and adjust the unit area weight per unit area of the electrode to 20 mg / cm 2 . Furthermore, perform a rolling process using a rolling press (Thank-Metal Co., Ltd. manufactured, 3t hydraulic rolling press) to make the density of the composite material layer 3.1 g / cm 3 of the standard positive electrode.

[0368] <Fabrication of Standard Negative Electrode>

[0369] Add 0.5 part by mass of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA), 1 part by mass of MAC500LC (sodium carboxymethyl cellulose Sunrose special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile component 100%), and 98.4 parts by mass of water into a 150 ml plastic container, and use a planetary mixer (Degassing Ryorotaro, ARE-310 manufactured by Thinky) to stir at 2000 rpm for 30 seconds. Further add 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries, CGB-20) and 5 parts by mass of silicon (manufactured by OSAKA Titanium Technologies Co., Ltd., silicon monoxide SiO1.3C5μm, non-volatile component 100%) as active materials, and use a high-speed mixer to stir at 3000 rpm for 10 minutes. Then, add 3.1 parts by mass of styrene butadiene rubber (SBR) (TRD2001, manufactured by JSR Corporation), and use the planetary mixer to stir at 2000 rpm for 30 seconds to obtain a composite material slurry for the negative electrode. Then, use a coater so that the unit area weight per unit area of the electrode becomes 8 mg / cm 2After applying the negative electrode composite material paste to the copper foil in the above-described manner, the coating film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Further, calendering treatment was performed using a roll press (manufactured by Thank-Metal Co., Ltd., 3t hydraulic roll press) to produce a standard negative electrode with a density of the composite material layer of 1.6 g / cm 3

[0370] "Physical Property Measurement and Evaluation Methods"

[0371] The physical property measurement and evaluation methods for the carbon nanotubes, carbon nanotube dispersion compositions, electrode films, and secondary batteries used in the following respective examples and comparative examples are as described below.

[0372] <Average Outer Diameter of Carbon Nanotubes>

[0373] For the carbon nanotubes, using an electronic balance (manufactured by Sartorius, MSA225S100DI), 0.2 g of carbon nanotubes was weighed into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.). 200 mL of toluene was added, and an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON) was used to perform a dispersion treatment for 5 minutes with an amplitude of 30% under ice bath cooling to prepare a carbon nanotube dispersion composition. Then, the carbon nanotube dispersion composition was appropriately diluted, and several μL was dropped in the form of a collodion film. After drying at room temperature, a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.) was used for direct observation. The observation was performed at a magnification of 50,000 times, and multiple photos containing 10 or more carbon nanotubes in the field of view were taken. The outer diameters of 300 arbitrarily extracted carbon nanotubes were measured, and their average value was taken as the average outer diameter (nm) of the carbon nanotubes.

[0374] In the case where the carbon nanotubes form a bundled aggregate, a transmission electron microscope (manufactured by JEOL Ltd., JEM2800) was used to observe at a magnification of 1,000,000 times, and the same measurement was performed as the outer diameter of the carbon nanotubes.

[0375] <BET Specific Surface Area of Carbon Nanotubes>

[0376] For the carbon nanotubes, after weighing 0.03 g using an electronic balance (manufactured by Sartorius, MSA225S100DI), it was dried while degassing at 110°C for 15 minutes. Then, a fully automatic specific surface area measuring device (manufactured by MOUNTECH, HM-model 1208) was used to measure the BET specific surface area of the carbon nanotubes. ​

[0377] <G / D ratio of carbon nanotubes>

[0378] The carbon nanotubes were placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.), and measurements were performed using a laser wavelength of 532 nm. The measurement conditions were set as follows: integration time of 60 seconds, number of accumulations of 2 times, neutral density filter of 10%, objective lens magnification of 20 times, confocal aperture of 500, slit width of 100 μm, and measurement wavelength range of 100 cm -1 ~3000 cm -1 . The carbon nanotubes for measurement were separated and taken out onto a glass slide, and flattened using a spatula. Among the obtained peaks, the maximum peak intensity in the spectrum within the range of 1560 cm -1 ~1600 cm -1 was set as G, and the maximum peak intensity within the range of 1310 cm -1 ~1350 cm -1 was set as D, and the ratio of G / D was taken as the G / D ratio of the carbon nanotubes.

[0379] <Angle of repose of carbon nanotubes>

[0380] The angle of repose of the carbon nanotubes was measured using a bulk density measuring device (manufactured by Tsutsui Rika Kikai Co., Ltd., JIS bulk specific gravity measuring device). First, the mass of the reservoir was measured. Then, the bulk density measuring device was horizontally installed with a funnel on the funnel stand, a sieve was placed on the funnel, and the reservoir was overlapped on the reservoir stand. Then, the carbon nanotubes were placed on the sieve using a spatula, and the carbon nanotubes were gently and evenly wiped across the entire surface of the sieve using a brush, and the sample passing through the sieve was received in the reservoir. The above operation was repeated until the reservoir was filled with carbon nanotubes. The angle formed by the conical powder pile and the horizontal plane when filled was measured using a protractor as the angle of repose of the carbon nanotubes.

[0381] In the case where the carbon nanotubes are difficult to pass through the sieve, the sieve is not placed on the funnel, and the angle of repose is measured by the same method.

[0382] <Carbon purity of carbon nanotubes>

[0383] The carbon nanotubes were acid-decomposed using a microwave sample pretreatment device (manufactured by Milestone-general, ETHOS 1) to extract the metals contained in the carbon nanotubes. Then, analysis was performed using a multi-type ICP emission spectroscopic analyzer (manufactured by 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.

[0384] Carbon purity (%) of carbon nanotubes = ((mass of carbon nanotubes - mass of metal) ÷ mass of carbon nanotubes) × 100

[0385] <Content of metallic foreign particles in carbon nanotube dispersion composition>

[0386] Pass 20 kg of the carbon nanotube dispersion composition through an electromagnet (manufactured by Daebo Magnetic, EMF - 100S, including 31 grid meshes with a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm) 5 times via a hose pump at a flow rate of 30 L / min. Then, pass the solvent used in preparing the carbon nanotube dispersion composition and contained in the carbon nanotube dispersion composition through the electromagnet (manufactured by Daebo Magnetic, EMF - 100S, including 31 grid meshes with a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), and squeeze out and clean the carbon nanotube dispersion composition in the hose pump and the electromagnet until there is substantially no solid component. Furthermore, then, turn off the power of the electromagnet, and after confirming that there is no magnetic force of the filter, pass 10 kg of the solvent used in preparing the carbon nanotube dispersion composition and contained in the carbon nanotube dispersion composition through the electromagnet at a flow rate of 30 L / min to obtain 10 kg of the solvent containing metallic foreign particles. Then, for the 10 kg of the solvent containing metallic foreign particles, use an ultrasonic processor (manufactured by Aiwa Medical Industry, ultrasonic cleaner), perform ultrasonic treatment and dispersion for 2 minutes under the conditions of an output power of 300 W and a frequency of 28 kHz, and then pass all of it through a filter (weight (W1), material: polyester, disc diameter: 47 mm, mesh size: 5 μm). Then, wash the metallic foreign particles accumulated on the filter with 100 g of ethanol. Furthermore, then, remove the filter on which the metallic foreign particles are accumulated, and use a hot air oven to dry the filter at 60 °C for 10 minutes, and measure the weight (W2). Subtract the weight of the filter (W1) from the weight of the dried filter (W2) on which the metallic foreign particles are accumulated to calculate the content (weight of metallic foreign particles) of the metallic foreign particles in the carbon nanotube dispersion composition.

[0387] The evaluation criteria for the weight of metallic foreign particles are set as follows: A: less than or equal to 0.1 mg; B: more than 0.1 mg and less than or equal to 0.4 mg; C: more than 0.4 mg and less than or equal to 1.0 mg; D: more than 1.0 mg.

[0388] <Amount of metal elements in carbon nanotube dispersion composition>

[0389] For the carbon nanotube dispersion composition, after drying with a hot air oven, acid decomposition is carried out using a microwave sample pretreatment device (manufactured by Milestone-general, ETHOS 1) to extract the metals contained in the carbon nanotubes. Then, analysis is performed using a multi-type ICP emission spectroscopic analysis device (manufactured by Agilent, 720-ES) to calculate the amount of metal elements (total content of iron, cobalt, nickel, chromium, molybdenum, and copper) contained in the extract.

[0390] The less the amount of metal elements, the more the voltage defects of the secondary battery can be suppressed.

[0391] The evaluation criteria for the amount of metal elements are set as follows: ◎ (excellent) for 30 ppm or less, 〇 (good) for more than 30 ppm and 50 ppm or less, △ (acceptable) for more than 50 ppm and 100 ppm or less, and × (unacceptable) for more than 100 ppm.

[0392] <Particle size of carbon nanotube dispersion composition>

[0393] The cumulative particle size D based on the particle size distribution 90 is measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.; Partical LA-960V2). The laser light wavelength of the measuring device is 650 nm, and as the detector, it includes a 1-point ring-shaped 64-segment silicon photodiode, a 5-point 4-channel array detector, and a 3-point silicon photodetector. In addition, a flow cell (sample cell) based on synthetic quartz is used for the measuring section.

[0394] First, the same solvent as the solvent contained in the carbon nanotube dispersion composition is put into the sample bath containing the sample cell, and circulation / ultrasonic cleaning is carried out. As the operation mode, the circulation speed is set to 3, the ultrasonic intensity is set to 7, the ultrasonic time is 1 minute, the stirring speed is set to 7, and the stirring mode is set to continuous. Subsequently, for degassing, after ultrasonic operation with an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds, blank (background) measurement is carried out. The particle size standard is set to volume, the particle refractive index is set to 1.920 - 0.522i (carbon nanotube), and the solvent refractive index is set to the refractive index of the solvent used when preparing the carbon nanotube dispersion composition (1.468 (NMP) or 1.333 (water)). The carbon nanotube dispersion composition is dropped so that the laser light transmittance during measurement becomes 60% ± 1%, and sample adjustment is carried out. The operation mode during measurement is set to a circulation speed of 3, a stirring speed of 7, and a stirring mode of continuous to carry out the measurement.

[0395] Cumulative particle size D 90The evaluation criteria are set as follows: less than 4.0 μm: A, more than 4.0 μm and less than or equal to 6.0 μm: B, more than 6.0 μm and less than or equal to 10 μm: C, more than 10 μm: D.

[0396] <Initial Viscosity of Carbon Nanotube Dispersion Composition>

[0397] After allowing the carbon nanotube dispersion composition to stand in a constant temperature bath at 25 °C for 1 hour or more, immediately measure the viscosity of the carbon nanotube dispersion composition at a rotational speed of 100 rpm using a B-type viscometer rotor. Use rotor No. 4 during the measurement.

[0398] The evaluation criteria for the initial viscosity are set as follows: less than 500 mPa·s: ◎ (excellent), 500 mPa·s or more and less than 1000 mPa·s: 〇 (good), 1000 mPa·s or more and less than 2000 mPa·s: △ (acceptable), 2000 mPa·s or more: × (poor).

[0399] <Conductivity>

[0400] The conductivity is evaluated by the volume resistivity of the electrode film.

[0401] Using a coater, apply the composite material slurry to the aluminum foil so that the unit area weight per unit of the electrode becomes 20 mg / cm 2 Then, dry the coating film in an electric oven at 120 °C ± 5 °C for 25 minutes. Then, measure the surface resistivity (Ω / Υ) of the dried coating film using a resistivity meter (manufactured by Nittoseiko Analytech Co., Ltd.: Loresta GP (MCP-T610), probe: AP2 probe (RMH333)). After the measurement, multiply by the thickness of the electrode composite material layer formed on the aluminum foil to obtain the volume resistivity (Ω·cm) of the electrode film. The thickness of the electrode composite material layer is obtained by subtracting the film thickness of the aluminum foil from the average value measured at three points in the electrode film using a film thickness meter (manufactured by NIKON Corporation, digital micrometer (DIGIMICRO) MH-15M) as the volume resistivity (Ω·cm) of the electrode film.

[0402] The evaluation criteria for the volume resistivity are set as follows: less than 8 Ω·cm: ◎ (excellent), 8 Ω·cm or more and less than 12 Ω·cm: 〇 (good), 12 Ω·cm or more and less than 15 Ω·cm: △ (acceptable), 15 Ω·cm or more (poor).

[0403] <Peel Strength (Electrode Film for Positive Electrode)>

[0404] The adhesion is evaluated by the peel strength of the electrode film.

[0405] Using an applicator, coat the composite material slurry onto the aluminum foil such that the weight per unit area of the electrode becomes 20 mg / cm 2 After that, dry the coating film in an electric oven at 120 °C ± 5 °C for 25 minutes. Then, with the coating direction as the major axis, cut it into two rectangles of 90 mm × 20 mm. In the measurement of the peel strength, use a bench-top tensile testing machine (manufactured by Toyo Seiki Seisakusho Co., Ltd., Strograph E3), and evaluate it using the 180-degree peel test method. Specifically, attach a double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) with a size of 100 mm × 30 mm to a stainless steel plate, make the fabricated electrode composite material layer in close contact with the other side of the double-sided tape, and peel it while stretching from the bottom to the top at a constant speed (50 mm / minute). Take the average value of the stress at this time as the peel strength.

[0406] The evaluation criteria for the peel strength are set as follows: 0.7 N / cm or more: ◎ (excellent), 0.5 N / cm or more and less than 0.7 N / cm: 〇 (good), 0.3 N / cm or more and less than 0.5 N / cm: △ (acceptable), less than 0.3 N / cm: × (poor).

[0407] <Peel Strength (Negative Electrode Membrane)>

[0408] The adhesion is evaluated by the peel strength of the electrode membrane.

[0409] Using an applicator, coat the composite material slurry onto the aluminum foil such that the weight per unit area of the electrode becomes 8 mg / cm 2 After that, dry the coating film in an electric oven at 120 °C ± 5 °C for 25 minutes. Then, with the coating direction as the major axis, cut it into two rectangles of 90 mm × 20 mm. In the measurement of the peel strength, use a bench-top tensile testing machine (manufactured by Toyo Seiki Seisakusho Co., Ltd., Strograph E3), and evaluate it using the 180-degree peel test method. Specifically, attach a double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) with a size of 100 mm × 30 mm to a stainless steel plate, make the fabricated negative electrode membrane in close contact with the other side of the double-sided tape, and peel it while stretching from the bottom to the top at a constant speed (50 mm / minute). Take the average value of the stress at this time as the peel strength.

[0410] The evaluation criteria for the peel strength are set as follows: 0.5 N / cm or more: ◎ (excellent), 0.3 N / cm or more and less than 0.5 N / cm: 〇 (good), 0.1 N / cm or more and less than 0.3 N / cm: △ (acceptable), less than 0.1 N / cm: × (unacceptable).

[0411] <Rate Characteristics Evaluation of Lithium-Ion Secondary Battery>

[0412] The laminated lithium-ion secondary battery is placed in a constant temperature chamber at 25°C, and charge and discharge measurements are performed using a charge and discharge device (manufactured by Hokuto Denko Corporation, SM-8). After constant current and constant voltage charging at a charging current of 10 mA (0.2C) with a charging cut-off voltage of 4.2V (cut-off current 1.0 mA (0.02C)), constant current discharge is performed at a discharge current of 10 mA (0.2C) with a discharge cut-off voltage of 2.5V. After repeating the above operation three times, constant current and constant voltage charging is performed at a charging current of 10 mA (0.2C) with a charging cut-off voltage of 4.2V (cut-off current (1.0 mA and 0.02C)), and constant current discharge is performed at a discharge current of 0.2C and a discharge current of 3C until the discharge cut-off voltage of 2.5V is reached, and the discharge capacities are calculated respectively. The rate characteristic is the ratio of the 0.2C discharge capacity to the 3C discharge capacity, and can be expressed by the following formula 1.

[0413] (Formula 1)

[0414] Rate characteristic = 3C discharge capacity / 0.2C discharge capacity of the third time × 100 (%)

[0415] The evaluation criteria for the rate characteristic are as follows: a rate characteristic of 80% or more is rated as ◎ (excellent), 70% or more and less than 80% is rated as 〇 (good), 60% or more and less than 70% is rated as △ (acceptable), and less than 60% is rated as × (poor).

[0416] <High Temperature Cycle Characteristics Evaluation of Lithium-Ion Secondary Battery>

[0417] The laminated lithium-ion secondary battery is placed in a constant temperature chamber at 45°C, and charge and discharge measurements are performed using a charge and discharge device (manufactured by Hokuto Denko Corporation, SM-8). At a charging current of 50 mA (1C), constant current and constant voltage charging is performed with a charging cut-off voltage of 4.2V (cut-off current 1.25 mA (0.025C)), and constant current discharge is performed at a discharge current of 50 mA (1C) with a discharge cut-off voltage of 2.5V. The above operation is repeated 100 times. 1C is defined as the current value for discharging the theoretical capacity of the positive electrode in 1 hour. The high temperature cycle characteristic is the ratio of the 1C discharge capacity of the third time at 45°C to the 1C discharge capacity of the one-hundredth time, and can be expressed by the following formula 2.

[0418] (Formula 2)

[0419] High temperature cycle characteristic = 1C discharge capacity of the one-hundredth time / 1C discharge capacity of the third time × 100 (%)

[0420] The evaluation criteria for the high-temperature cycle characteristics are as follows: a high-temperature cycle characteristic of 90% or more is rated as ◎ (excellent), 85% or more and less than 90% is rated as 〇 (good), 80% or more and less than 85% is rated as △ (acceptable), and less than 80% is rated as × (poor).

[0421] [Example A]

[0422] (Example 1-1)

[0423] 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. After the dispersant (A) was completely dissolved, it was passed through a nylon mesh with a mesh size of 48 μm, and then through a high magnetic amplification filter (magFilter) (manufactured by Eishin, surface magnetic flux density 17000 gauss) to prepare an 8% solution of dispersant (A).

[0424] Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 7.5 parts of an 8% solution of dispersant (A) were added to a stainless-steel container and stirred using a disperser until homogeneous. Then, 3 parts of carbon nanotubes (C1) were taken and added while stirring using a disperser. A fine emulsion screen was assembled on a high-shear mixer (L5M-A, manufactured by SILVERSON), and the whole was made uniform at a speed of 9000 rpm. Batch dispersion was carried out using a grindgauge until the dispersion particle size became 200 μm or less, and then a carbon nanotube preliminary dispersion liquid (C1) was prepared via a high-magnetic amplification filter (magFilter, manufactured by Eishin, surface magnetic flux density 17000 gauss). Further, then, the carbon nanotube preliminary dispersion liquid was transported and passed through a bead mill (manufactured by Ashizawa Finetech, Mugen Flow (registered trademark)) filled with zirconia beads having a diameter of 1.0 mmφ for a circulation-type dispersion treatment with a residence time of 15 minutes (bead filling rate 80%, circumferential speed 12 m / s). Dispersion was carried out while adjusting the ejection amount so that the number of passes per 1 minute of residence time became 4 passes, and the total number of passes for a residence time of 15 minutes was 60 passes. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (manufactured by SUGINO MACHINE Co., Star Burst Labo) for 15 channel-type dispersion treatments. The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 Mpa. Then, the dispersion liquid was supplied to an electromagnet (manufactured by Daebo Magnetic, EMF-100S, including a grid screen with 31 magnetic flux density of 16000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm) for 3 channel-type treatments and then passed through two series-connected depth filters (manufactured by 3M, PP non-woven fabric depth cartridge NT-T series, filtration accuracy 20 μm) to prepare a carbon nanotube dispersion composition 1.

[0425] (Examples 1-2 to 1-20), (Comparative Examples 1-1 to 1-13)

[0426] Except for changing the dispersion conditions, carbon nanotubes, and dispersants described in Table 2, dispersion compositions 1-1 to 1-20 and comparative dispersion compositions 1-1 to 1-13 were obtained by the same method as in Example 1-1. The depth filters in the examples and comparative examples used 3M-manufactured PP nonwoven fabric depth cartridges NT-T series, and the surface filters used nylon nets. When using nylon nets, instead of passing through two serially arranged depth filters (3M-manufactured PP nonwoven fabric depth cartridges NT-T series, filtration accuracy 20 μm), the filtration bell was used to pass through the nylon net to obtain the carbon nanotube dispersion compositions of the examples and comparative examples. The dispersion compositions of Comparative Example 1-4 and Comparative Example 1-11 could not be filtered through filters with a filtration accuracy of 3 μm or 20 μm and could not be produced.

[0427] [Table 2]

[0428]

[0429] The evaluation results of the dispersion compositions prepared in (Examples 1-1 to 1-20) and (Comparative Examples 1-1 to 1-13) are shown in Table 3.

[0430] [Table 3]

[0431] Table 3

[0432]

[0433] (Example 2-1)

[0434] Weighed and dissolved 18.8 parts by mass of an NMP solution containing 8% by mass of PVDF (polyvinylidene fluoride, manufactured by Solvay, Solef #5130) and 5.8 parts by mass of NMP into a plastic container with a capacity of 150 cm 3 . Then, 13.3 parts by mass of a carbon nanotube dispersion composition (dispersion composition 1) was added, and using a rotation / revolution mixer (Nuken Ryoritaro, ARE-310), it was stirred at 2000 rpm for 30 seconds. Furthermore, then, 98.1 parts by mass of a positive electrode active material (manufactured by BASF TODA Battery Materials Co., Ltd., HED (registered trademark) NCM-1111100) was added, and using a rotation / revolution mixer (Nuken Ryoritaro, ARE-310), it was stirred at 2000 rpm for 2.5 minutes to obtain a composite material slurry (composite material slurry 1).

[0435] Subsequently, using a coater, the unit area weight per unit of the electrode was made 20 mg / cm2 After applying the composite material slurry (composite material slurry 1) to the aluminum foil in the described manner, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain the electrode film (electrode film 1). Then, the electrode film (electrode film 1) was subjected to a rolling process using a rolling press (manufactured by Thank-Metal, 3t hydraulic rolling press) to obtain the positive electrode (positive electrode 1). In addition, the unit area weight per unit area of the composite material layer became 20 mg / cm 2 The density of the composite material layer after the rolling process was set to 3.1 g / cc.

[0436] (Examples 2-2 to 2-20), (Comparative Examples 2-1 to 2-13)

[0437] Except for using Dispersion Composition 2 to Comparative Dispersion Composition 13 instead of Dispersion Composition 1 as described in Table 4, composite material slurries 2 to Comparative Composite Material Slurries 13, electrode films 2 to Comparative Electrode Films 13, and positive electrodes 2 to Comparative Positive Electrodes 13 were obtained by the same method as in Example 2-1.

[0438] The evaluation results of the electrode films produced in (Examples 2-1 to 2-20), (Comparative Examples 2-1 to 2-13) are shown in Table 4.

[0439] [Table 4]

[0440] Table 4

[0441]

[0442] (Example 3-1)

[0443] The positive electrode (positive electrode 1) and the standard negative electrode were respectively punched into 45 mm × 40 mm and 50 mm × 45 mm, and together with the separator (porous polypropylene film) inserted therebetween, they were inserted into an aluminum laminated bag and dried in an electric oven at 60 °C for 1 hour. Then, 2 mL of the electrolyte solution was injected inside a glove box filled with argon (a non-aqueous electrolyte solution was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 1:1:1 (volume ratio), and further, as an additive, 2 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M). After that, the aluminum laminated bag was sealed to fabricate a laminated lithium ion secondary battery (secondary battery 1).

[0444] (Examples 3-2 to 3-20), (Comparative Examples 3-1 to 3-13)

[0445] Except for changing to the positive electrode described in Table 5, laminate-type lithium ion secondary batteries (Secondary Battery 2) to (Comparative Secondary Battery 13) were fabricated by the same method as that for fabricating the laminate-type lithium ion secondary battery (Secondary Battery 1).

[0446] Table 5 shows the evaluation results of the secondary batteries fabricated in (Examples 3-1 to 3-20) and (Comparative Examples 3-1 to 3-13).

[0447] [Table 5]

[0448] Table 5

[0449]

[0450] (Example 1-21)

[0451] 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. After the dispersant (F) was completely dissolved, it was passed through a nylon mesh with a mesh size of 48 μm and then through a high magnetic amplification filter (magFilter) (manufactured by Eishin, surface magnetic flux density: 17000 Gauss) to prepare an 8% solution of the dispersant (F).

[0452] Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 15 parts of an 8% solution of a dispersant (F) were added to a stainless-steel container, and stirred with a disperser until homogeneous. Then, 3 parts of carbon nanotubes (H1) were taken and added while stirring with a disperser. A fine emulsion screen was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and the whole was made uniform at a speed of 9000 rpm. After batchwise dispersion with a grindometer until the dispersion particle size became 200 μm or less, a carbon nanotube preliminary dispersion was prepared via a high-magnetic amplification filter (magFilter, manufactured by Eishin, surface magnetic flux density 17000 gauss). Furthermore, then, the carbon nanotube preliminary dispersion was transported and subjected to a circulating dispersion treatment (bead filling rate 80%, circumferential speed 12 m / s) with a retention time of 15 minutes in a bead mill (manufactured by Ashizawa Finetech, Mugen Flow (registered trademark)) filled with zirconia beads having a diameter of 1.0 mmφ. Dispersion was carried out while adjusting the ejection amount so that the number of passes per 1 minute of retention time became 4 passes, and the total number of passes for a retention time of 15 minutes was 60 passes. Subsequently, the dispersion was supplied to a valve-type high-pressure homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd., HC3-5 (trade name)) for a circulating dispersion treatment. During the dispersion treatment, the pressure was set to 80 Mpa, the treatment flow rate was 2000 L / H, and the total number of passes was 15 times. After the dispersion treatment, the dispersion was supplied to an electromagnet (manufactured by Daebo Magnetic, EMF-100S, including 31 grid screens with a magnetic flux density of 16000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), passed through three channel-type treatments, and then passed through two serially arranged depth filters (manufactured by 3M, PP non-woven fabric depth cartridge NT-T series, filtration accuracy 20 μm) to prepare a carbon nanotube dispersion composition 21.

[0453] (Example 1-22)

[0454] A carbon nanotube dispersion composition 22 was prepared in the same manner as in Example 1-21, except that the total number of passes of the valve-type homogenizer was set to 10 passes.

[0455] (Example 1-23)

[0456] A carbon nanotube dispersion composition 23 was prepared in the same manner as in Example 1-21, except that the total number of passes of the valve-type homogenizer was set to 5 passes.

[0457] (Examples 2-21 to 2-23)

[0458] Except for using (carbon nanotube dispersion composition 21) to (carbon nanotube dispersion composition 23) in place of the carbon nanotube dispersion composition 1, (composite material slurry 21) to (composite material slurry 23), (electrode film 21) to (electrode 23), and (positive electrode 21) to (positive electrode 23) were produced by the same method as in Example 2-1.

[0459] (Examples 3-21 to 3-23)

[0460] Except for using (positive electrode 21) to (positive electrode 23) in place of the positive electrode 1, (secondary batteries 21) to (secondary batteries 23) were produced by the same method as in Example 3-1.

[0461] The evaluation results of the carbon nanotube dispersion compositions produced in (Examples 1-21 to 1-23), the electrode films produced using them, and the secondary batteries are shown in Table 6.

[0462] [Table 6]

[0463] Table 6

[0464]

[0465] In the above examples, the following carbon nanotube dispersion compositions were used: containing carbon nanotubes, copolymer N, and an amide-based polar solvent, the content of metal foreign particles determined under Condition 1 was 1.0 mg or less, and the copolymer N had an alkylene structural unit with a content of 50% by mass or more and 75% by mass or less, and a nitrile group-containing structural unit with a content of 25% by mass or more and 50% by mass or less. In the examples, compared with the comparative examples, the carbon nanotube dispersion composition had a low initial viscosity, and a lithium-ion secondary battery with excellent secondary battery characteristics, especially high-temperature cycle characteristics, could be obtained. Thus, it was clarified that the present invention could provide a lithium-ion secondary battery with high capacity, high output power, and high durability that was difficult to achieve with existing carbon nanotube dispersion liquid compositions.

[0466] The vehicle equipped with the lithium-ion secondary battery of the present invention has high charge and discharge performance and excellent high-temperature cycle characteristics, so a vehicle with high safety and improved fuel consumption rate can be obtained.

[0467] [Example B]

[0468] (Example 1-W1)

[0469] Add 98 parts of ion-exchanged water and 2 parts of dispersant (J) to a stainless-steel container, stir using a disperser until the dispersant (J) is completely dissolved, pass through a nylon mesh with a mesh size of 48 μm, and then pass through a high-magnetic amplification filter (magFilter) (manufactured by Eishin, surface magnetic flux density 17,000 gauss) to prepare a 2% solution of dispersant (J).

[0470] Then, add 67 parts of ion-exchanged water and 30 parts of the 2% solution of dispersant (J) to a stainless-steel container and stir using a disperser until homogeneous. Then, take 3 parts of carbon nanotubes (C1) and add them while stirring using a disperser. Assemble a fine emulsion screen on a high-shear mixer (L5M-A, manufactured by SILVERSON), homogenize the whole at a speed of 9000 rpm, and perform batchwise dispersion using a fineness gauge until the dispersion particle size becomes 200 μm or less. Then, pass through a high-magnetic amplification filter (magFilter) (manufactured by Eishin, surface magnetic flux density 17,000 gauss) to prepare a preliminary dispersion of carbon nanotubes. Furthermore, then, transfer the preliminary dispersion of carbon nanotubes and perform a circulating dispersion treatment with a residence time of 15 minutes (bead filling rate 80%, circumferential speed 12 m / s) using a bead mill (manufactured by Ashizawa Finetech, Mugen Flow (registered trademark)) filled with zirconia beads with a diameter of 1.0 mmφ. Disperse while adjusting the ejection volume so that the number of passes per 1-minute residence time is 4 passes, and the total number of passes for a residence time of 15 minutes is 60 passes. Subsequently, supply the dispersed liquid to a high-pressure homogenizer (manufactured by SUGINOMACHINE Co., Star Burst Labo) and perform 15 channel-type dispersion treatments. The dispersion treatment is performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 Mpa. Then, supply the dispersed liquid to an electromagnet (manufactured by Daebo Magnetic, EMF-100S, an electromagnet including 31 grid screens with a magnetic flux density of 16,000 gauss, a space volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm), perform 3 channel-type treatments, and then pass through two serially arranged depth filters (manufactured by 3M, PP (polypropylene) non-woven fabric depth cartridges NT-T series, filtration accuracy 20 μm) to prepare a carbon nanotube dispersion composition (dispersion composition W1).

[0471] (Example 1-W2 to 1-W19), (Comparative Example 1-W1 to 1-W11)

[0472] Except for changing the dispersion conditions, carbon nanotubes, dispersants, and water described in Table 2-2, dispersion compositions W2 to W19 and comparative dispersion compositions W1 to W11 were obtained by the same method as in Example 1-W1.

[0473] For the depth filters in the examples and comparative examples, a PP non-woven fabric depth cartridge NT-T series manufactured by 3M was used, and for the surface filter, a nylon mesh was used. When using the nylon mesh, instead of passing through two series-connected depth filters (manufactured by 3M, PP non-woven fabric depth cartridge NT-T series, filtration accuracy 20 μm), a filter bell was used to pass through the nylon mesh to obtain the carbon nanotube dispersion compositions of the examples and comparative examples. The dispersion compositions of Comparative Example 1-W4 and Comparative Example 1-W9 could not be filtered through the filter and could not be prepared.

[0474] (Example 1-N20)

[0475] Except for using dispersant (H) instead of dispersant (J) and using NMP instead of ion-exchanged water, a carbon nanotube dispersion composition (dispersion composition N20) was prepared by the same method as in Example 1-W19.

[0476] [Table B2]

[0477]

[0478] The evaluation results of the dispersion compositions prepared in (Examples 1-W1 to 1-N20) and (Comparative Examples 1-W1 to 1-W11) are shown in Table B3.

[0479] [Table B3]

[0480] Table B3

[0481]

[0482] (Example 2-W1)

[0483] To a volume of 150 cm 3In a plastic container, 2.5 parts by mass of a carbon nanotube dispersion composition (dispersion composition W1), 12.5 parts by mass of an aqueous solution in which 2% by mass of CMC (manufactured by Daicel Finechem Co., Ltd., #1190) is dissolved, and 12.0 parts by mass of ion-exchanged water were measured. Then, using a rotation / revolution mixer (Defoaming Ryorotaro, ARE-310 manufactured by Thinky Corporation), it was stirred at 2000 rpm for 30 seconds to obtain a carbon nanotube dispersion composition (carbon nanotube dispersion composition W1). Then, 2.4 parts by mass of silicon monoxide (manufactured by OSAKA Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5μm) was added, and using the rotation / revolution mixer, it was stirred at 2000 rpm for 30 seconds. Furthermore, 21.9 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) was added, and using the rotation / revolution mixer, it was stirred at 2000 rpm for 30 seconds. Furthermore, then, 0.78 parts by mass of styrene-butadiene latex (manufactured by JSR Corporation, TRD2001) was added, and using the rotation / revolution mixer, it was stirred at 2000 rpm for 30 seconds to obtain a composite material slurry (composite material slurry W1).

[0484] Subsequently, using a coater, the composite material slurry (composite material slurry W1) was applied to a copper foil such that the unit area weight per unit area of the electrode became 8 mg / cm 2 . After that, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain an electrode film (electrode film W1). Then, the electrode film (electrode film W1) was subjected to a rolling treatment using a rolling press to produce a negative electrode (negative electrode W1) having a unit area weight per unit area of the electrode of 8 mg / cm 2 and a density of the rolled composite material layer of 1.6 g / cm 3 .

[0485] (Example 2-W2 to 2-W17), (Comparative Example 2-W1 to 2-W11)

[0486] Except as described in Table B4, by using dispersion compositions W2 to comparative dispersion compositions W11 in place of dispersion composition W1, composite material slurries W2 to comparative composite material slurries W11, electrode films W2 to comparative electrode films W11, and negative electrodes W2 to comparative negative electrodes W11 were obtained by the same method as in Example 2-W1.

[0487] (Example 2-W18 to 2-W19)

[0488] Except for changing the addition amounts of the CNT dispersion composition and ion-exchanged water, composite material slurries W18 to W19 were obtained in the same manner as in Example 2-W1. The addition amount of the CNT dispersion composition was set to 16.7 parts by mass, and the addition amount of ion-exchanged water was set to 10.3 parts by mass.

[0489] (Example 2-N20)

[0490] Weighed and dissolved 18.8 parts by mass of an NMP solution containing 8 mass% of PVDF (polyvinylidene fluoride, manufactured by Solvay, Solef #5130) and 9.0 parts by mass of NMP into a plastic container with a volume of 150 cm 3 . Then, 16.7 parts by mass of a carbon nanotube dispersion composition (dispersion composition N20) was added, and using a rotation / revolution mixer (Neri Tarō, ARE-310), it was stirred at 2000 rpm for 30 seconds. Furthermore, then, 98.4 parts by mass of a positive electrode active material (manufactured by BASF TODA Battery Materials Co., Ltd., HED (registered trademark) NCM-1111100) was added, and using a rotation / revolution mixer (Neri Tarō, ARE-310), it was stirred at 2000 rpm for 2.5 minutes to obtain a composite material slurry (composite material slurry N20).

[0491] Subsequently, using a coater, the composite material slurry (composite material slurry N20) was coated onto an aluminum foil such that the areal weight per unit area of the electrode became 20 mg / cm 2 . Then, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain an electrode film (electrode film N20). Then, the electrode film (electrode film N20) was subjected to a rolling process using a rolling press (manufactured by Thank-Metal, 3t hydraulic rolling press) to obtain a positive electrode (positive electrode N20). In addition, the areal weight per unit area of the composite material layer was 20 mg / cm 2 , and the density of the composite material layer after the rolling process was set to 3.1 g / cc.

[0492] The evaluation results of the electrode films produced in (Examples 2-W1 to 2-N20) and (Comparative Examples 2-W1 to 2-W11) are shown in Table B4.

[0493] [Table B4]

[0494] Table B4

[0495]

[0496] (Example 3-W1)

[0497] The negative electrode W1 and the standard positive electrode were respectively punched into sizes of 50 mm × 45 mm and 45 mm × 40 mm, and together with the separator (porous polypropylene film) inserted therebetween, were inserted into an aluminum laminated bag and dried in an electric oven at 60 °C for 1 hour. Then, 2 mL of an electrolyte solution was injected into a glove box filled with argon (a mixed solvent was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 3:5:2 (by volume), and further, as additives, 1 part by mass of vinylene carbonate (VC) and 1 part by mass of fluoroethylene carbonate (FEC) were respectively added per 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M to form a non-aqueous electrolyte solution), and then the aluminum laminate was sealed to fabricate a laminated lithium ion secondary battery (secondary battery W1).

[0498] (Examples 3-W2 to 3-W19), (Comparative Examples 3-W2 to 3-W11)

[0499] Except for changing to the negative electrodes described in Table B5, laminated lithium ion secondary batteries (secondary batteries W2) to (comparative secondary batteries W11) were fabricated by the same method as the fabrication of the laminated lithium ion secondary battery (secondary battery W1).

[0500] (Example 3-N20)

[0501] The standard negative electrode and the positive electrode N20 were punched into sizes of 50 mm × 45 mm and 45 mm × 40 mm, and together with the separator (porous polypropylene film) inserted therebetween, were inserted into an aluminum laminated bag and dried in an electric oven at 60 °C for 1 hour. Then, 2 mL of an electrolyte solution was injected into a glove box filled with argon (a mixed solvent was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 3:5:2 (by volume), and further, as additives, 1 part by mass of vinylene carbonate (VC) and 1 part by mass of fluoroethylene carbonate (FEC) were respectively added per 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M to form a non-aqueous electrolyte solution), and then the aluminum laminate was sealed to fabricate a laminated lithium ion secondary battery (secondary battery N20).

[0502] The evaluation results of the laminated lithium ion secondary batteries fabricated in (Examples 3-W1 to 3-N20), (Comparative Examples 3-W1 to 3-W11) are shown in Table B5.

[0503] [Table B5]

[0504] Table B5

[0505]

[0506] In the above-described embodiment, the following carbon nanotube dispersion composition is used: comprising carbon nanotubes, a dispersant, and a solvent, and the content of metallic foreign matter particles determined under Condition 1 is 1.0 mg or less. In the embodiment, compared with the comparative example, the carbon nanotube dispersion composition has a low initial viscosity, and a lithium ion secondary battery excellent in secondary battery characteristics, particularly high-temperature cycle characteristics, can be obtained. Thus, it is clarified that the present invention can provide a lithium ion secondary battery having high capacity, high output power, and high durability, which are difficult to achieve with existing carbon nanotube dispersion compositions.

[0507] The vehicle having the lithium ion secondary battery of the present invention has high charge and discharge performance and excellent high-temperature cycle characteristics, and thus a vehicle with high safety and improved fuel consumption rate can be obtained.

[0508] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited thereto. Various modifications that can be understood by those skilled in the art can be made to the structure or details of the present invention within the scope of the invention.

Claims

1. A carbon nanotube dispersion composition comprising: carbon nanotubes, a dispersant, and a solvent, wherein the carbon nanotube dispersion composition: The content of metallic foreign matter particles determined according to the following condition 1 is 1.0 mg or less. <Condition 1> After recovering the metal foreign matter particles in 20 kg of the carbon nanotube dispersed composition using an electromagnet (including 31 electromagnets with a magnetic flux density of 16,000 Gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and a grid screen with a thickness of 1.3 cm), the metal foreign matter particles were washed with a solvent, and the obtained metal foreign matter particles were deposited on a filter with a disk diameter of 47 mm and a mesh of 5 μm, and the weight of the metal foreign matter particles on the filter was measured.

2. The carbon nanotube dispersion composition according to claim 1, wherein The dispersant includes at least one selected from the group consisting of carboxymethyl cellulose, polyacrylic acid, polyvinyl pyrrolidone, and acrylonitrile polymers.

3. The carbon nanotube dispersion composition according to claim 1 or 2, wherein The dispersant comprises a copolymer, 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.

4. The carbon nanotube dispersion composition according to any one of claims 1 to 3, wherein The vehicle comprises water.

5. The carbon nanotube dispersion composition according to any one of claims 1 to 4, wherein The solvent includes an amide-based polar solvent.

6. The carbon nanotube dispersion composition according to any one of claims 1 to 5, wherein The cumulative particle size D measured by laser diffraction 90 Less than 10 μm.

7. The carbon nanotube dispersion composition according to any one of claims 1 to 5, wherein The cumulative particle size D measured by laser diffraction 90 It is less than 6.0μm.

8. A carbon nanotube dispersion composition comprising: carbon nanotubes, a dispersant, and water, wherein: The content of metallic foreign matter particles determined according to the following condition 1 is 1.0 mg or less. The cumulative particle size D measured by laser diffraction 90 Less than 6.0μm; <Condition 1> After recovering the metal foreign matter particles in 20 kg of the carbon nanotube dispersed composition using an electromagnet (including 31 electromagnets with a magnetic flux density of 16,000 Gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and a grid screen with a thickness of 1.3 cm), the metal foreign matter particles were washed with water, and the obtained metal foreign matter particles were deposited on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metal foreign matter particles on the filter was measured.

9. A carbon nanotube dispersion composition comprising: carbon nanotubes, a copolymer, and an amide-based polar solvent, wherein: The content of metallic foreign matter 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. The cumulative particle size D measured by laser diffraction 90 Less than 6.0μm; <Condition 1> After recovering the metal foreign matter particles in 20 kg of the carbon nanotube dispersed composition using an electromagnet (including 31 electromagnets with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, a diameter of 10 cm, and a grid screen with a thickness of 1.3 cm), the metal foreign matter particles were washed with an amide-based polar solvent, and the obtained metal foreign matter particles were deposited on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metal foreign matter particles on the filter was measured.

10. The carbon nanotube dispersion composition according to any one of claims 1 to 9, wherein The total content of iron, cobalt, nickel, chromium, molybdenum and copper is less than 100 ppm.

11. The carbon nanotube dispersion composition according to any one of claims 1 to 10, wherein The carbon nanotubes have a repose angle of 40° or more.

12. The carbon nanotube dispersion composition according to any one of claims 1 to 11, wherein The viscosity at 25° C. measured by a B-type viscometer is less than 2,000 mPa·s.

13. The carbon nanotube dispersion composition according to any one of claims 1 to 12, wherein The Buerter specific surface area of ​​the carbon nanotubes is 500 m 2 / g~1000m 2 / g.

14. The carbon nanotube dispersion composition according to any one of claims 1 to 13, wherein The Raman spectrum of the carbon nanotubes is 1560 cm -1 ~1600cm -1 The maximum peak intensity in the range of 1310 cm is set as G, and the peak intensity at 1310 cm is set as -1 ~1350cm -1 The G / D ratio when the maximum peak intensity in the range of is set to D is 5 to 100. 15 . A composite material slurry comprising the carbon nanotube dispersion composition according to claim 1 and an active substance.

16. An electrode membrane formed from the composite material slurry according to claim 15.

17. A secondary battery comprising a positive electrode and a negative electrode, wherein: At least one of the positive electrode and the negative electrode has the electrode film according to claim 16.

18. A vehicle comprising the secondary battery according to claim 17.

19. A production method, which is a production method of a carbon nanotube dispersion composition according to any one of claims 1 to 14, comprising all of the following steps (1) to (3); [Step (1): Crushing step] Process of applying shear stress to carbon nanotubes to break them apart [Step (2): Magnetic separation step] The process of 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 Separation Step] A step of performing filtration separation using a depth filter having a filtration accuracy of 5 μm or more and 50 μm or less.

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