Carbon nanotube dispersion compositions, composite slurry materials, electrode films, secondary batteries, and vehicles

Abstract

To provide a CNT dispersion composition and composite slurry that have good dispersibility, and can be suitably used to form an electrode film that has improved safety and good conductivity. [Solution] The problem is solved by a carbon nanotube dispersion composition comprising carbon nanotubes satisfying (i), (ii), and (iii) below, a dispersant, and an organic solvent, and satisfying (1) below. (i) The total content of iron and cobalt is less than 1,000 ppm. (ii) The aluminum content is 3,000 ppm or less. (iii) Raman spectrum 1560-1600 cm -1 Within the range of G, the maximum peak intensity is 1310-1350 cm. -1 When the maximum peak intensity within the specified range is denoted as D, the G / D ratio is between 0.5 and 50. (1) The moisture content is 1,500 ppm or less.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to carbon nanotube dispersion compositions, composite slurry, electrode films, secondary batteries, and vehicles. [Background technology]

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

[0003] Non-aqueous electrolyte secondary batteries use carbon black, Ketjenblack, graphene, and fine carbon materials as conductive additives. Among these, carbon nanotubes (hereinafter also referred to as "CNTs"), a type of fibrous fine carbon material, are widely used. For example, by adding CNTs to the electrode active material, electrode resistance can be reduced, the load resistance of the battery can be improved, the material strength of the electrodes can be increased, and the resistance to expansion and contraction of the electrodes can be improved, thereby improving the rate characteristics and cycle life of the secondary battery.

[0004] Carbon nanotubes (CNTs) can generally be manufactured by methods such as arc discharge, laser evaporation, and chemical vapor deposition. Of these, chemical vapor deposition is the most suitable for mass production from the standpoint of productivity and economic efficiency, and is widely used. In chemical vapor deposition, a catalyst containing metals such as iron, cobalt, and nickel is used to react with a gas that serves as a carbon source to produce CNTs. Therefore, CNTs obtained by chemical vapor deposition contain catalysts containing metals such as iron, cobalt, and nickel, or particles such as carbides or oxides derived from the catalyst. Catalysts containing metals (hereinafter also referred to as catalyst metals) are indispensable in several methods of CNT production. However, metals derived from the catalyst metal remaining in the CNTs after production can become impurities. In addition, regardless of the CNT manufacturing method, metals may be introduced into the CNTs due to wear of metals used in synthesis equipment, filling equipment, or piping during production. These introduced metals can become impurities. From the viewpoint of obtaining desired properties from CNTs, it is desirable to have a low metal content in the CNTs.

[0005] For example, if carbon nanotubes (CNTs) containing large amounts of metals derived from catalyst metals are used in secondary batteries, it can accelerate the decomposition of the electrolyte, causing the internal pressure of the secondary battery to rise due to the decomposition gases, and potentially degrading the battery's performance. In particular, with high-capacity secondary batteries, the amount of heat generated increases, and the electrode temperature rises, which can lead to increased gas generation. Therefore, several methods have been proposed to purify CNTs and remove metals derived from catalyst metals and other sources in order to suppress problems caused by metals contained in CNTs and to further enhance safety.

[0006] Patent Document 1 describes that by performing liquid-phase oxidation with nitric acid on CNTs with a G-band to D-band intensity ratio (G / D ratio) of 50 or more in Raman spectroscopy, higher quality CNTs can be obtained that are free of catalyst metal residue, have high heat resistance, and produce fewer carbon by-products.

[0007] Patent Document 2 describes how to produce high-purity CNTs by purification treatment using halogen gas and then perform oxidation treatment to achieve a BET specific surface area of ​​100 m². 2 / g over 500m2 It is described that hydrophilic CNTs can be obtained with a specific surface area of less than / g, a dibutyl phthalate (DBP) absorption of 150 ml / 100 g or more and 400 ml / 100 g or less, and a water vapor adsorption of 0.5 mg / g or more at a relative pressure P / P0 = 0.3.

[0008] Patent Document 3 describes a method for removing metal foreign particles by passing through a magnetic filter and a filtration membrane made of polypropylene after obtaining a CNT dispersion composition.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, performing liquid-phase oxidation of CNTs with nitric acid can reduce the residue of catalytic metal. However, due to the strong oxidizing power of nitric acid, the surface of CNTs may be oxidized, which may lead to a decrease in the conductivity of the electrode film using CNTs.

[0011] Also, when hydrophilicity is imparted to CNTs, water is likely to adsorb to CNTs. When preparing a CNT dispersion composition, a composite slurry, an electrode, or a secondary battery, moisture is likely to be mixed in. As a result, when the secondary battery is overcharged, it may react with the solvent or solute of the electrolyte, generating gas, which may cause an increase in the internal pressure and resistance of the secondary battery.

[0012] Therefore, the problem that the present invention aims to solve is to provide a CNT dispersion composition and composite slurry that can be suitably used to form an electrode film having good dispersibility, improved safety, and good conductivity. Another embodiment is to provide a secondary battery that suppresses gas generation and has excellent rate characteristics and high-temperature cycle characteristics, and a vehicle that has high safety and improved fuel efficiency by having said secondary battery. [Means for solving the problem]

[0013] In other words, the present invention includes the following embodiments. Embodiments of the present invention are not limited to the following: [1] A carbon nanotube dispersion composition comprising carbon nanotubes satisfying (i), (ii), and (iii) below, a dispersant, and an organic solvent, wherein (1) below is satisfied. (i) The total content of iron and cobalt is less than 1,000 ppm. (ii) The aluminum content is 3,000 ppm or less. (iii) 1,560–1,600 cm⁻¹ in Raman spectrum -1 G represents the maximum peak intensity within the range of 1,310-1,350 cm. -1 When the maximum peak intensity within the specified range is denoted as D, the G / D ratio is between 0.5 and 50. (1) The moisture content is 1,500 ppm or less. [2] The carbon nanotube dispersion composition according to [1], wherein the carbon nanotubes further satisfy (iv) below. (iv) The surface oxygen content is less than 1.0 atm%. [3] The carbon nanotube dispersion composition according to [1] or [2], wherein the carbon nanotubes further satisfy (v) below. (v) The amount of water vapor adsorbed at a relative humidity of 90% is 50 mg / g or less. [4] A carbon nanotube dispersion composition according to any of [1] to [3], further satisfying (2) below. (2) When dynamic viscoelasticity measurements are performed using a rheometer with a 25 mm diameter, 2° cone at 25°C, a frequency of 1 Hz, and a strain of 0.01% to 5%, the phase angle exceeds 60°. [5] Furthermore, the carbon nanotube dispersion composition described in any of [1] to [4] satisfies (3) below. (3) The amount of metal foreign matter particles determined by the following condition 1 is 1.0 mg or less. <Condition 1> Metallic particles from 20 kg of carbon nanotube dispersion composition are collected using an electromagnet (with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm). After washing with an organic solvent, the resulting metallic particles are deposited onto a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic particles on the filter is measured. [6] A composite slurry containing a carbon nanotube dispersion composition described in any of [1] to [5] and an active material. [7]; An electrode film formed from the composite slurry described in [6]. [8] 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 described in [7]. A vehicle equipped with the secondary battery described in [9]; [8]. [Effects of the Invention]

[0014] According to the present invention, a CNT dispersion composition having good dispersibility can be provided. Furthermore, using this CNT dispersion composition, a composite slurry and an electrode film having good conductivity can be provided. In addition, a secondary battery having suppressed gas generation and excellent rate characteristics and high-temperature cycle characteristics, and a vehicle having this secondary battery that is highly safe and has improved fuel efficiency can be provided. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view showing a homogenization valve in a valve-type homogenizer, which is an example of a dispersion device. [Modes for carrying out the invention]

[0016] The carbon nanotube dispersion composition, composite slurry, electrode film, and secondary battery according to embodiments of the present invention will be described in detail below, but are not limited thereto. The numerical values ​​specified herein are those obtained by the methods disclosed in the embodiments or examples.

[0017] Furthermore, in this specification, numerical ranges specified using "~" include the numbers written before and after "~" as the lower and upper limits. In this specification, carbon nanotubes may be referred to as "CNTs" and N-methyl-2-pyrrolidone as "NMPs". In this specification, carbon nanotube dispersion compositions may be referred to as "CNT dispersion compositions" or simply as "dispersion compositions". In this invention, metallic foreign particles are not limited to those of any particular size or shape, and include fine metal powders, but do not include those that exist in a dissolved state as metal ions. Unless otherwise noted, the various components mentioned herein may be used individually or in combination of two or more.

[0018] Furthermore, the term "CNT dispersion composition" refers to the state before the addition of the active material. In this respect, the CNT dispersion composition is distinguished from the asphalt slurry containing the active material. That is, the CNT dispersion composition substantially does not contain the active material. This concept excludes the state in which the active material has been intentionally added to the CNT dispersion composition, and the amount of the active material relative to the total mass of the CNT dispersion composition may be 1% by mass or less, 0.5% by mass or less, 0.1% by mass or less, or even 0% by mass. The active material will be described later.

[0019] ≪CNT dispersion composition≫ The CNT dispersion composition of this embodiment comprises carbon nanotubes satisfying the following (i), (ii), and (iii), a dispersant, and an organic solvent, and satisfies the following (1). (i) The total content of iron and cobalt is less than 1,000 ppm. (ii) The aluminum content is 3,000 ppm or less. (iii) 1560–1600 cm⁻¹ in Raman spectrum -1 Within the range of G, the maximum peak intensity is 1310-1350 cmcm. -1 When the maximum peak intensity within the specified range is denoted as D, the G / D ratio is between 0.5 and 50. (1) The moisture content is 1,500 ppm or less.

[0020] In other words, by using a CNT dispersion composition with limited iron and cobalt content, limited aluminum content, a specific G / D ratio, and limited water content, gas generation in secondary batteries due to metal impurities can be suppressed, thereby enhancing safety. Furthermore, an electrode film with excellent conductivity can be formed. Secondary batteries made using such a CNT dispersion composition can exhibit good performance.

[0021] The CNT dispersion composition preferably further satisfies at least one of the following (2) and (3). (2) When dynamic viscoelasticity measurements are performed using a rheometer with a 25 mm diameter, 2° cone at 25°C and a frequency of 1 Hz, the phase angle exceeds 60°. (3) The content of metallic foreign particles determined by condition 1 below is 1.0 mg or less. <Condition 1> Metal foreign particles in 20 kg of CNT dispersion composition are collected using an electromagnet (an electromagnet with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm), washed with a solvent, and the resulting metal foreign particles are deposited onto a filter with a disk diameter of 47 mm and a mesh size of 5 μm. The weight of the metal foreign particles on the filter is then measured.

[0022] By satisfying (2), the dispersion particle size and dispersion state of the CNTs are improved, resulting in a CNT dispersion composition with excellent aging stability. Furthermore, a secondary battery with superior rate characteristics and high-temperature cycle characteristics can be obtained. By satisfying (3), a CNT dispersion composition with better dispersibility and lower initial viscosity can be obtained. Furthermore, using a CNT dispersion composition that satisfies (3) is preferable because it can yield a secondary battery with excellent rate characteristics, high-temperature cycling characteristics, and gas generation suppression. From the viewpoint of excellent safety and high-temperature storage characteristics of the secondary battery, it is particularly preferable to satisfy all of (1), (2), and (3).

[0023] The CNT dispersion composition, by containing CNTs that satisfy (i), (ii), and (iii), enables the formation of conductive paths even in small amounts when used as a conductive additive for secondary battery electrodes, resulting in excellent rate characteristics and high-temperature cycle characteristics.

[0024] The CNT content is preferably 0.4% by mass or more and 10% by mass or less, based on the mass of the CNT dispersion composition (with the mass of the CNT dispersion composition being 100% by mass), more preferably 0.6% by mass or more and 8% by mass or less, and even more preferably 1% by mass or more and 6% by mass or less.

[0025] The dispersant content is preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of CNT. When the dispersant content is within the above range, the dispersion stability of carbon nanotubes in the CNT dispersion composition tends to be good. In addition, the peel strength of electrodes for secondary batteries tends to be good.

[0026] The organic solvent content is preferably 90% to 99.6% by mass, more preferably 92% to 99.4% by mass, and even more preferably 94% to 99% by mass, based on the CNT dispersion composition as a reference (100% by mass). When the organic solvent content is within the above range, a CNT dispersion composition with excellent fluidity and dispersion stability is easily obtained. By using a CNT dispersion composition with excellent fluidity and dispersion stability, metal foreign particles can be easily removed, and a secondary battery with stable quality can be obtained.

[0027] [Moisture content] The moisture content of the CNT dispersion composition in this embodiment is 1,500 ppm or less. Preferably, it is 1,000 ppm or less, more preferably 750 ppm or less, even more preferably 600 ppm or less, and particularly preferably 500 ppm or less. When the moisture content of the CNT dispersion composition is within the above range, the moisture content of the secondary battery electrodes is reduced, which can suppress electrolyte decomposition reactions on the electrode surface and increases in the internal pressure of the secondary battery. The moisture content of the CNT dispersion composition may be 1 ppm or more, or it may be 0 ppm. The moisture content of the CNT dispersion composition can be measured using a trace moisture measuring device, with the moisture vaporization device attached to the device set to a temperature of 230°C.

[0028] The water content of CNT dispersion compositions can be reduced by various methods. For example, [1] drying and dehydrating the raw materials such as CNTs, dispersants, and organic solvents used in the CNT dispersion composition, [2] hydrophobizing the raw materials, and [3] controlling the manufacturing environment (temperature and humidity) for producing the CNT dispersion composition.

[0029] [1] Methods for drying and dehydrating raw materials include using heat drying of the raw materials, heating and drying under vacuum conditions, introducing an inert gas such as nitrogen, and storing in a drying chamber (dry booth). In particular, from the viewpoint of the efficiency of removing moisture from the raw materials, heat drying of the raw materials under vacuum conditions is preferred. [2] Methods for hydrophobizing the raw materials include, for CNTs, removing functional groups from the CNT surface by heat treatment, and reducing CNT defects by promoting the graphitization of CNTs. In particular, a method of removing functional groups from the CNT surface by heat treatment at a temperature of 2000°C or lower is preferred. For dispersants, methods include adjusting the amount of functional groups in the dispersant and selecting a dispersant type suitable for the surface condition of the CNTs. [3] Methods for controlling the manufacturing environment (temperature and humidity) for manufacturing CNT dispersion compositions include manufacturing the CNT dispersion composition in a low-humidity environment, and manufacturing the CNT dispersion composition in a sealed or positive-pressure environment while sealing an inert gas such as nitrogen inside the manufacturing equipment.

[0030] Since CNTs have a structure in which planar graphite is wound into a cylindrical shape, and due to this structure they can absorb moisture from the environment, and moisture may be present in all manufacturing processes of CNT dispersion compositions, such as preparation, dispersion, filtration, and filling, it is preferable to manufacture the CNT dispersion composition taking all of the above [1] to [3] into consideration.

[0031] [Phase angle] The CNT dispersion composition of this embodiment preferably has a phase angle of 51° or greater, more preferably 56° or greater, and even more preferably 61° or greater, when dynamic viscoelasticity measurement is performed using a rheometer with a 25 mm diameter, 2° cone at 25°C, a frequency of 1 Hz, and a strain of 0.01% to 5%. Furthermore, it is preferably 81° or less, more preferably 76° or less, and even more preferably 71° or less. When the phase angle of the CNT dispersion composition is within the above range, the CNTs are homogeneously dispersed in the dispersion medium, and the CNT dispersion composition tends to have good temporal stability. The phase angle of the CNT dispersion composition of this embodiment can be evaluated by dynamic viscoelasticity measurement.

[0032] In addition to good long-term stability of the CNT dispersion composition, it is preferable that the phase angle of the CNT dispersion composition exceeds 60°, as this also ensures good efficiency in removing metallic foreign matter during the manufacturing process. By using such a CNT dispersion composition, electrolyte decomposition reactions at the electrode surface and increases in internal pressure of the secondary battery can be suppressed, resulting in a secondary battery with excellent rate characteristics and high-temperature cycle characteristics.

[0033] [Content of metallic foreign particles] The CNT dispersion composition preferably contains 1.0 mg or less of metal foreign particles, as determined by the following condition 1. <Condition 1> Metallic particles from 20 kg of carbon nanotube dispersion composition are collected using an electromagnet (with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm). After washing with an organic solvent, the resulting metallic particles are deposited onto a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic particles on the filter is measured.

[0034] The content of metallic foreign particles is more preferably 0.4 mg or less, and even more preferably 0.1 mg or less. When the content of metallic foreign particles contained in the CNT dispersion composition, as determined by Condition 1, is within the above range, a CNT dispersion composition with good dispersibility and low initial viscosity can be obtained. Furthermore, by using this CNT dispersion composition, electrolyte decomposition reactions at the electrode surface and increases in internal pressure of the secondary battery can be suppressed. In addition, a secondary battery with excellent rate characteristics and high-temperature cycle characteristics can be obtained. Specifically, the content of metallic foreign particles can be determined, for example, by the method described in the examples.

[0035] The amount of metallic foreign particles required by Condition 1 can be controlled, for example, by minimizing the introduction of metallic foreign matter from the raw materials, removing metallic foreign matter from the dispersion equipment and dispersion process during the process, and filtering the dispersed CNT dispersion composition. Furthermore, the amount of metallic foreign particles can be further reduced by magnetic separation using magnets with narrow pole spacing, such as electromagnets. Since metallic foreign particles often have orientation, it is preferable to pass them through magnets and filters multiple times. By controlling the content of metallic foreign particles in the CNT dispersion composition using these methods, it becomes possible to achieve both dispersion stability, which cannot be achieved simply by reducing the metallic element content in the CNT dispersion composition, and excellent battery characteristics.

[0036] Furthermore, the organic solvent used to wash the recovered metal foreign matter particles in <Condition 1> is the same organic solvent contained in the CNT dispersion composition. For example, if the CNT dispersion composition contains CNTs, a dispersant, and, for example, CNTs, a dispersant, and an "organic solvent containing an amide-based polar solvent," the metal foreign matter particles can be washed with the same "solvent containing an amide-based polar solvent." If the organic solvent consists only of an "amide-based polar organic solvent," the particles can be washed with the same "amide-based polar organic solvent."

[0037] Metal foreign particles deposited on the filter may be washed using an organic solvent. As the organic solvent, for example, a water-soluble organic solvent such as alcohol (e.g., ethanol) can be used.

[0038] The CNT dispersion composition preferably contains 1.0 mg or less of metallic foreign particles collected by a magnet and recovered by a 5 μm mesh filter under condition 1. If the content of metallic foreign particles larger than 5 μm collected by the magnet is high, the metallic foreign particles may be exposed from the electrode surface, potentially leading to increased internal pressure or short circuits in the secondary battery due to gas generation from the decomposition of the electrolyte or dissolution and leaching of metallic foreign particles.

[0039] As described later, the metal content in the CNT dispersion composition other than iron, cobalt, aluminum, and magnesium is preferably as low as possible, preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less. Examples of metals other than iron, cobalt, aluminum, and magnesium include nickel, chromium, molybdenum, and copper. Nickel, chromium, and molybdenum may be introduced from wear particles in tanks and agitators used to prepare the CNT dispersion composition, while copper may be introduced from motors in the dispersion equipment. Of these, copper has a low oxidation-reduction potential, can dissolve into the electrolyte, and can precipitate as dendrites on the negative electrode surface, potentially leading to voltage problems in secondary batteries; therefore, its reduction is particularly desirable. The amounts of these metal elements can be measured, for example, by ICP emission spectrometry.

[0040] [Initial Viscosity] The CNT dispersion composition preferably has an initial viscosity, measured at 25°C and 100 rpm using a B-type viscometer, of less than 1,500 mPa·s. More preferably, it is less than 500 mPa·s, and even more preferably, it is less than 200 mPa·s. Note that it may be 50 mPa·s or more. When the initial viscosity is within the above range, the dispersion state of CNTs contained in the CNT dispersion composition is appropriate, and it is easy to remove metal foreign substances using a filter or an electromagnet. The CNT dispersion composition with an initial viscosity within the above range is considered to have an appropriate composition ratio and dispersion process of CNTs, a dispersant, and a solvent, and good dispersion stability. Specifically, for example, it can be measured by the method described in the examples. The initial viscosity may be the viscosity measured within 12 hours after producing the carbon nanotube dispersion composition.

[0041] [Cumulative Particle Size D 90 The CNT dispersion composition preferably has a cumulative particle size D 90 measured by the laser diffraction method of 10 μm or less, more preferably 6.0 μm or less, and even more preferably 4.0 μm or less. Also, it is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. When the cumulative particle size D 90 is within the above range, it is easy to form a good conductive network by CNTs in the electrode. Also, the CNT dispersion composition has good filterability, and metal foreign particles can be removed using a filter with high filtration accuracy, so that the mixing of metal foreign particles inside the secondary battery can be suppressed, the increase in the internal pressure of the secondary battery due to the decomposition of the electrolytic solution can be suppressed, and the high-temperature storage characteristics tend to be good. Also, the rate characteristics and cycle characteristics of the secondary battery are further improved.

[0042] <cnt> CNTs have a structure in which planar graphite is wound into a cylindrical shape. Examples of CNTs include single-walled CNTs and multi-walled CNTs. CNTs include single-walled CNTs and multi-walled CNTs, and these may be mixed. For example, CNTs include multi-walled CNTs. Multi-walled CNTs have a structure in which two or more layers of graphite are wound, while single-walled CNTs have a structure in which one layer of graphite is wound. The side walls of CNTs do not have to be of a graphite structure. For example, CNTs with side walls having an amorphous structure can also be used.

[0043] The CNTs used in the CNT dispersion composition of this embodiment satisfy the following conditions (i), (ii), and (iii). (i) The total content of iron and cobalt is less than 1,000 ppm. (ii) The aluminum content is 3,000 ppm or less. (iii) Raman spectrum 1560-1600 cm -1 When the maximum peak intensity within the specified range is denoted as G, and the maximum peak intensity within the range of 1310-1350 cm-1 is denoted as D, the G / D ratio is between 0.5 and 50.

[0044] Furthermore, it is preferable that at least one of (iv) and (v) is satisfied. (iv) The surface oxygen content is less than 1.0 atm%. (v) The amount of water vapor adsorbed at a relative humidity of 90% is 50 mg / g or less.

[0045] (iv) is preferable because it provides better conductivity as an electrode film, suppresses thickening due to gelation of the composite slurry, and prevents performance degradation of the secondary battery due to electrolyte decomposition within the secondary battery. (v) is preferable because it further suppresses problems such as electrolyte decomposition within the secondary battery and allows for the acquisition of a secondary battery of stable quality. From the viewpoint of obtaining a superior secondary battery, it is more preferable to satisfy (i) to (iii) and (v), and it is particularly preferable to satisfy all of (i) to (v).

[0046] [Iron and cobalt content] The CNTs used in the CNT dispersion composition of this embodiment have a total iron and cobalt content of less than 1,000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm, and even more preferably less than 50 ppm. The total iron and cobalt content in the CNTs can be calculated, for example, by acid-decomposing the CNTs, extracting the metals contained in the CNTs, and analyzing the extract using inductively coupled plasma (ICP).

[0047] Iron and cobalt are sometimes used as catalyst raw materials during CNT (carbon nanotube) production. Iron and cobalt may also be introduced as wear particles from tanks and agitators used in CNT production. Because iron and cobalt have low oxidation-reduction potentials, they can leach into the electrolyte or accelerate its decomposition, potentially leading to voltage failure, increased internal pressure, and reduced capacity in secondary batteries. On the other hand, since CNTs are manufactured under a reducing atmosphere, some iron and cobalt are embedded in the CNTs in the form of pure metals. In this case, they cannot be completely removed by calcination or acid washing and remain. However, in this invention, we have found that even if embedded metals remain, if the total content of iron and cobalt in the CNTs used is within the above range, dissolution into the electrolyte and electrolyte decomposition reactions can be suppressed, resulting in a secondary battery of stable quality.

[0048] [Iron content] The CNTs used in the CNT dispersion composition of this embodiment preferably have an iron content of less than 1,000 ppm, more preferably less than 600 ppm, even more preferably less than 300 ppm, particularly preferably less than 100 ppm, and may be less than 10 ppm. When manufacturing secondary batteries using CNTs with an iron content exceeding the above range, the standard electrode potential E° (25°C) of iron in an aqueous solution is -0.44V. During charging of the secondary battery, iron may dissolve into the electrolyte and precipitate at the negative electrode, potentially piercing the separator of the secondary battery and causing contact between the positive and negative electrodes, leading to an internal short circuit in the battery. In particular, since iron has a lower standard electrode potential compared to cobalt, iron tends to precipitate in a dendrite-like manner during charging of the secondary battery. Therefore, a lower iron content is preferable than that of cobalt.

[0049] [Cobalt content] The CNTs used in the CNT dispersion composition of this embodiment preferably have a cobalt content of less than 1,000 ppm, more preferably less than 800 ppm, even more preferably less than 500 ppm, particularly preferably less than 300 ppm, and may be less than 100 ppm. When manufacturing secondary batteries using carbon nanotubes (CNTs) with a cobalt content exceeding the above range, the standard electrode potential E° (25°C) in an aqueous cobalt solution is -0.277V. During charging of the secondary battery, cobalt may dissolve into the electrolyte and precipitate at the negative electrode, potentially piercing the battery's separator and causing contact between the positive and negative electrodes, leading to an internal short circuit in the battery.

[0050] [Aluminum content] The carbon nanotubes (CNTs) used in the CNT dispersion composition of this embodiment have an aluminum content of 3,000 ppm or less. The aluminum content in the CNTs is preferably 2,000 ppm or less, more preferably 1,100 ppm or less, may be 500 ppm or less, or may be 0 ppm. When aluminum oxide is included as a catalyst support during the synthesis of carbon nanotubes (CNTs), insulating aluminum oxide nanoparticles may remain in the CNTs, potentially impairing conductivity. When the aluminum content in the CNTs is within the above range, a CNT dispersion composition can be prepared that produces a good conductive electrode film with fewer insulating aluminum oxide nanoparticles.

[0051] [Magnesium content] The CNTs used in the CNT dispersion composition of this embodiment preferably have a magnesium content of 3,000 ppm or less. More preferably, it is 2,000 ppm or less, even more preferably 1,100 ppm or less, may be 500 ppm or less, or even 0 ppm. When magnesium oxide is included as a catalyst support during the synthesis of CNTs, magnesium ions may be released during charging and discharging, potentially leading to magnesium deposition at the negative electrode. A CNT dispersion composition with a magnesium content within the above range is preferable because it allows for the creation of a CNT dispersion composition with low magnesium oxide content and the formation of an electrode film with good rate characteristics.

[0052] [G / D ratio] The G / D ratio (peak ratio of G-band to D-band) of the CNTs used in the CNT dispersion composition of this embodiment is determined by Raman spectroscopy. While various laser wavelengths can be used in Raman spectroscopy, 532 nm is used in this embodiment. In the Raman spectrum, 1,580 cm⁻¹ -1 The Raman shift observed in the vicinity is called the graphite-derived G-band, and is 1,330 cm. -1 The Raman shift observed in this area is called the D band, originating from defects in amorphous carbon and graphite. Since the wavenumber of Raman spectroscopy can vary depending on the measurement conditions, the wavenumber specified here is ±20 cm. -1 This shall be defined as follows: CNTs with a high G / D ratio have higher crystallinity. Furthermore, firing CNTs at high temperatures tends to increase the G / D ratio, and the longer the firing time, the higher the G / D ratio tends to be.

[0053] The CNTs used in the CNT dispersion composition of this embodiment have a Raman spectrum of 1,560 to 1,600 cm⁻¹. -1 G represents the maximum peak intensity within the range of 1,310-1,350 cm. -1 When the maximum peak intensity within the range is denoted as D, the G / D ratio is preferably 0.5 to 50, more preferably 1.0 to 30, and even more preferably 1.2 to 10. When the G / D ratio of the CNTs is within the above range, electrolyte decomposition reactions at the electrode surface and increases in the internal pressure of the secondary battery can be suppressed. When the G / D ratio is 0.5 or higher, the amount of amorphous carbon is small, the conductivity of the CNTs becomes higher, and pathways at the electrodes are more easily formed.

[0054] [Surface oxygen content] The CNTs used in the CNT dispersion composition of this embodiment preferably have a surface oxygen content of less than 1.0 atm%. The surface oxygen content is preferably 0.9 atm% or less, more preferably 0.8 atm% or less, even more preferably 0.7 atm% or less, and particularly preferably 0.6 atm% or less. It may also be 0.1 atm% or more, or 0.2 atm% or more. By using CNTs with a surface oxygen content within the above range, excellent conductivity as an electrode film can be obtained more easily. In particular, a surface oxygen content of less than 1.0 atm% reduces the amount of water adsorbed by the CNTs, thereby reducing the amount of water mixed into the CNT dispersion composition, and thus suppressing thickening due to gelation of the composite slurry and the deterioration of secondary battery performance due to electrolyte decomposition in the secondary battery. The surface oxygen content of CNTs can be controlled, for example, by suppressing oxidation of the CNT surface during the manufacturing conditions of CNT synthesis or during the process of removing catalyst metals from the CNTs. Specifically, the amount of functional groups on the CNT surface can be reduced by heat treatment at temperatures above 300°C or by firing at temperatures below 300°C with controlled pressure. In this specification, "surface oxygen content" is a value expressed as the ratio (atm%) of oxygen atoms to carbon atoms on the surface of a CNT, determined by X-ray photoelectron spectroscopy.

[0055] [Water vapor adsorption capacity] The CNTs used in the CNT dispersion composition of this embodiment preferably have a water vapor adsorption amount of 50 mg / g or less, more preferably 40 mg / g or less, and even more preferably 30 mg / g or less, when the relative water vapor pressure P / P0 at 25°C is 0.90 (meaning a relative humidity of 90%; hereinafter sometimes referred to as RH90). When the water vapor adsorption amount is within the above range, the CNTs do not easily absorb moisture, thus reducing the moisture content of the CNT dispersion composition. Furthermore, even after electrode fabrication, they do not easily adsorb moisture, suppressing problems such as electrolyte decomposition in the secondary battery, and enabling the acquisition of a secondary battery of stable quality. The water vapor adsorption amount may be 1 mg / g or more, or 2 mg / g or more. The water vapor adsorption of CNTs can be measured using the BELSORP-18 automatic gas / vapor adsorption amount measuring device manufactured by Nippon Bell Co., Ltd., in the manner described in the examples.

[0056] [Average outer diameter] The CNTs used in the CNT dispersion composition of this embodiment preferably have an average outer diameter of 1 nm to 25 nm, more preferably 1 nm to 9 nm, and even more preferably 1 nm to 5 nm. When the average outer diameter is within the above range, a good conductive network is easily formed within the electrode, the active material particles can contribute to discharge without becoming isolated inside the secondary battery, degradation of the active material is suppressed, and the cycle characteristics of the secondary battery are further improved. The average outer diameter of the CNTs can be obtained by observing the CNTs using a transmission electron microscope, measuring the outer diameter of 300 CNTs arbitrarily extracted, and taking the arithmetic mean of the measured values.

[0057] [BET specific surface area] The CNTs used in the CNT dispersion composition of this embodiment have a BET specific surface area of ​​100 m². 2 / g or more 1,000m 2 It is preferable that it be less than / g, and 200m 2 / g or more 800m 2 It is more preferable that it be less than or equal to / g, and 200m 2 / g or more 500m 2 It is even more preferable that the BET specific surface area is less than or equal to / g. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount, and the amount of conductive material in the electrode can be reduced. This increases the degree of freedom in battery design, such as increasing the amount of active material or binder resin. Furthermore, when preparing the composite slurry, the compounding of the active material and CNTs is promoted, so an electrode film with a homogeneous conductive network in which the surface of the active material is coated with CNTs can be obtained, suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material, and improving the battery's cycle characteristics. The BET specific surface area can be measured by the BET method described in JIS Z 8830:2013.

[0058] [Volume resistivity] The CNTs used in the CNT dispersion composition of this embodiment are 1.0 × 10⁻⁶. -3 Ω·cm~3.0×10 -2 It is preferable that the ratio is Ω·cm, and 1.0 × 10 -3 Ω·cm~2.0×10 -2 It is more preferable that it be Ω·cm, 5.0 × 10 -3 Ω·cm ~ 1.4 × 10 -2 It is even more preferable that the volume resistivity is within the above range. When the volume resistivity is within the above range, the conductivity of the electrode film is good, and a secondary battery with excellent rate characteristics and cycle characteristics can be obtained. The volume resistivity of CNTs can be determined by measuring the volume resistivity of CNTs at a density of 1 g / cc using a powder resistivity measuring device (Rolestar GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Nitto Seikou Analytech Co., Ltd.).

[0059] [Moisture content of CNTs] The water content of the CNTs used in the CNT dispersion composition of this embodiment is preferably as low as possible, more preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 500 ppm or less, and particularly preferably 160 ppm or less. By keeping the water content of the CNTs within the above range, even if a certain amount of water is mixed in during the production of the CNT dispersion composition, the water content of the secondary battery electrodes can be reduced, thereby suppressing electrolyte decomposition reactions on the electrode surface and an increase in the internal pressure of the secondary battery. The moisture content of CNTs can be measured using a trace moisture measuring device, with the moisture vaporization device attached to the device set to a temperature of 230°C.

[0060] The water content of CNTs used in CNT dispersion compositions can be reduced by various methods. For example, these include (a) drying and dehydrating the CNTs, (b) hydrophobizing the CNTs, and (c) controlling the environment (temperature and humidity) in which the CNTs are synthesized and manufactured. [i] Methods for drying and dehydrating CNTs include using heat-dried raw materials, heating and drying under vacuum conditions, introducing inert gases such as nitrogen, and storing them in a drying chamber (dry booth). In particular, from the viewpoint of the efficiency of removing moisture from the raw materials, the method of heat-drying the raw materials under vacuum conditions is preferred. [b] Methods for hydrophobizing CNTs include removing functional groups from the CNT surface by heat treatment and reducing CNT defects by promoting the graphitization of CNTs. In particular, a method of removing functional groups from the CNT surface by heat treatment at a temperature of 2000°C or lower is preferred. [H] Methods for controlling the environment (temperature and humidity) for synthesizing and manufacturing CNTs include manufacturing the CNT dispersion composition in a low-humidity environment, and manufacturing the CNT dispersion composition in a sealed or positive-pressure environment while sealing an inert gas such as nitrogen inside the manufacturing apparatus.

[0061] Since CNTs have a structure in which planar graphite is wound into a cylindrical shape, and due to this structure they can absorb moisture from the environment, and moisture may be present in all manufacturing processes of CNT dispersion compositions, such as preparation, dispersion, filtration, and filling, it is preferable to manufacture the CNT dispersion composition taking all of the above [a] to [c] into consideration.

[0062] [Water content of CNTs over time] In the CNT dispersion composition of this embodiment, it is preferable that the moisture content of the CNTs used is adjusted to an appropriate range not only in addition to the moisture content described above, but also after storage for a certain period of time. In the present invention, the moisture content over time of the CNTs used in the CNT dispersion composition refers to the moisture content of the CNTs after being stored for one month in an environment of 23°C ± 2°C and 50°C ± 10% humidity, based on the initial moisture content of the CNTs. Specifically, the amount of moisture after storing CNTs whose moisture content has been measured in an environment of 23°C ± 2°C and 50% ± 10% humidity for one month can be measured using a trace moisture measuring device, with the moisture vaporization device attached to the device set to 230°C.

[0063] The initial moisture content, which serves as the basis for the moisture content over time, is the moisture content of the CNTs when the CNT dispersion composition is prepared. For example, in the case of commercially available products, this is the measurement taken when a product that has been stored unopened under normal conditions is opened.

[0064] The moisture content of CNTs over time should be as low as possible, preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 500 ppm or less, and particularly preferably 200 ppm or less. By keeping the moisture content of CNTs over time within the above range, it is possible to suppress moisture contamination during the production of the CNT dispersion composition. Furthermore, even if a certain amount of moisture is mixed in during the production of the CNT dispersion composition, the moisture content of the secondary battery electrodes can be reduced, thereby suppressing electrolyte decomposition reactions on the electrode surface and the rise in internal pressure of the secondary battery. As a method for reducing the moisture content of CNTs over time, among the methods described in [b] above, it is preferable to hydrophobize the raw material CNTs, specifically by removing functional groups from the CNT surface by heat treatment and / or by promoting the graphitization of CNTs to reduce CNT defects. In particular, a method of heat treatment at a temperature of 2000°C or lower to remove functional groups from the CNT surface is preferred. This method makes it possible to produce CNTs that are less susceptible to moisture absorption and to reduce the moisture content of the CNT dispersion composition. Furthermore, even after electrode fabrication, moisture is less likely to be adsorbed, suppressing problems such as electrolyte decomposition in secondary batteries and enabling the production of secondary batteries of stable quality.

[0065] [Percentage change in the water content of CNTs over time] The rate of change in the moisture content of CNTs over time, which is determined by dividing the moisture content of CNTs over time by the moisture content of CNTs at the start of the process, is preferably 180% or less, more preferably 150% or less, even more preferably 130% or less, and particularly preferably 110% or less, with the moisture content of CNTs at the start of the process set at 100%. The rate of change in the moisture content of CNTs over time may also be 100%. By keeping the rate of change in the moisture content of CNTs over time within the above range, it is possible to reduce moisture contamination due to hygroscopic absorption by CNTs and lower the moisture content of the CNT dispersion composition. Furthermore, even after electrode fabrication, moisture is less likely to be adsorbed, suppressing problems such as electrolyte decomposition in the secondary battery and enabling the production of a secondary battery of stable quality.

[0066] [Manufacturing method for CNTs] The carbon nanotubes (CNTs) used in the CNT dispersion composition of this embodiment can be produced by, for example, laser ablation, arc discharge, thermal CVD, plasma CVD, and combustion. However, they are not limited to these methods. For example, CNTs can be produced by contacting a carbon source with a catalyst metal at 500 to 1000°C in an atmosphere with an oxygen concentration of 1 volume% or less. The carbon source may be at least one of hydrocarbons and alcohols. Alternatively, they may be prepared by a method that does not use a metal catalyst as a nucleus. When CNTs are manufactured by chemical vapor deposition (thermal CVD), catalyst metals are used in which active components such as iron, cobalt, and nickel are immobilized on supporting components such as aluminum and magnesium. Therefore, CNTs obtained by the above manufacturing process tend to retain metals such as iron, cobalt, aluminum, magnesium, and nickel, derived from the catalyst metal. For this reason, it is preferable to reduce the amount of metal elements in the CNTs through purification.

[0067] • Method for purifying carbon nanotubes (CNTs) The CNTs used in the CNT dispersion composition of this embodiment are not limited to those produced through a purification method, but it is preferable that the amount of metal elements in the CNTs is reduced by a purification method such as (a) acid treatment or (b) heat treatment.

[0068] (a) In the purification of CNTs by acid treatment, metals such as iron, cobalt, and nickel can be easily removed, but metals such as aluminum and magnesium are difficult to remove. Therefore, it is preferable to select a purification method that matches the catalyst used in CNT production. Also, when using nitric acid or other highly oxidizing agents for CNT purification, there is a risk that the conductivity will be impaired due to oxidation of the CNT surface. Furthermore, there is a risk that the water content of the CNTs will increase due to hydrophilization of the CNT surface. (b) In the purification of CNTs by heat treatment (calcination), the amount of metallic elements in the CNTs, including aluminum and magnesium, can be reduced. On the other hand, if the CNTs are calcined for a long time at a temperature above the boiling point of the metals contained in the CNTs (for example, above 2,000°C and below 3,000°C) in order to remove metals such as aluminum and magnesium, the crystallinity of the CNTs will increase. Highly crystallinic CNTs become hard and are prone to breaking when preparing CNT dispersion compositions. From this perspective, it is preferable to remove the metal contained in the CNTs at a temperature of 2,000°C or lower, and preferably include a step of heat treatment in an inert atmosphere under reduced pressure and vacuum. Heat treatment of the CNTs in an inert atmosphere can suppress oxidation of the CNT surface and shorten the heat treatment time, thereby suppressing the high crystallinity of the CNTs.

[0069] (Purification of CNTs by reduced-pressure calcination) The following provides a detailed explanation of a method for purifying carbon nanotubes (CNTs) that includes a step of heat treatment in an inert atmosphere under reduced pressure and vacuum (hereinafter referred to as reduced pressure calcination). Examples of inert atmospheres include nitrogen, argon, vacuum, and combinations thereof. For example, an inert atmosphere can be obtained by introducing an inert gas such as nitrogen gas into the equipment used during heat treatment and replacing the contents of the equipment with the inert gas. Subsequently, the heat treatment is carried out while maintaining a vacuum state (hereinafter referred to as reduced vacuum) by reducing the pressure inside the equipment.

[0070] Vacuum reduction means that a state of reduced pressure (vacuum state) is maintained below atmospheric pressure by a vacuum pump. Specifically, vacuum pumps such as oil rotary pumps, booster pumps, Roots pumps, and oil diffusion pumps are used to reduce the pressure inside the device and maintain a vacuum state. Vacuum pumps may be used individually or in combination. By reducing the pressure inside the device, it is possible to counteract pressure increase factors such as leaks from the device or gas expansion due to heating, and to control the internal pressure of the device to below the target pressure. The internal pressure in a reduced vacuum is preferably 10 Pa or less, more preferably 0.1 Pa or less, and even more preferably 0.05 Pa or less. The internal pressure may be 0.03 Pa or less. To obtain the internal pressure within the above range, it is preferable to reduce the pressure in stages. In one embodiment, it is preferable to reduce the pressure in two stages. For example, in the first stage, the internal pressure is preferably adjusted to 10 Pa or less, more preferably 9.8 Pa or less, and even more preferably 9.6 Pa or less. In the first stage, the internal pressure may be in the range of 9.5 to 9.8 Pa. After adjusting the internal pressure within the above range and maintaining it for a certain period of time, in the second stage, the internal pressure can be adjusted to preferably 1 Pa or less, more preferably 0.1 Pa or less, and even more preferably 0.05 Pa or less. In some embodiments, the internal pressure in the second stage may be 0.03 Pa or less. In some cases, the pressure increase due to the pyrolysis gas of CNTs and sublimated metals may be large compared to the pump's pressure reduction capacity, making staged pressure reduction difficult. In such cases, only the first stage of depressurization may be performed, or a third stage may be added following the second stage. In the third stage, the internal pressure is preferably adjusted to 10 Pa or less, more preferably 9.8 Pa or less, and even more preferably 9.6 Pa or less. There may be any number of such internal pressure stages. In some embodiments, there may be six or more stages, or even seven or more stages.

[0071] The heat treatment conditions, such as the heat treatment temperature and heat treatment time, can be appropriately determined depending on the type of CNT and the type of metal derived from the catalyst metal contained in the CNT. The heat treatment temperature is preferably the temperature at which all metals—aluminum, magnesium, cobalt, iron, copper, zinc, nickel, chromium, manganese, and molybdenum—begin to melt. Furthermore, since the catalyst metal used in the production of CNTs is nanoscale and melts at a lower temperature than bulk metals due to the nanoscale effect, a heat treatment temperature lower than that of bulk metals is also acceptable. From this viewpoint, a heat treatment temperature of 1,000°C to 2,000°C is preferred. From the viewpoint of suppressing high crystallinity of CNTs, it may be 1,800°C or lower, 1,700°C or lower, or 1,600°C or lower. In some examples, the heat treatment temperature may be 1,600°C or lower, or 1,500°C or lower. Note that the heat treatment temperature refers to the temperature inside the apparatus (internal temperature).

[0072] Furthermore, the heat treatment time can be set appropriately according to the firing apparatus and firing scale. However, firing CNTs at high temperatures for a long time increases the crystallinity of the CNTs. Highly crystallinic CNTs become hard and more prone to breakage when preparing the CNT dispersion composition. From this viewpoint, in some embodiments, the heat treatment time may be, for example, 10 hours or less, 8 hours or less, or 6 hours or less. In some embodiments, the heat treatment time may be 1 to 3 hours.

[0073] In some embodiments, heat treatment under reduced pressure and vacuum is preferably carried out by adjusting the temperature inside the apparatus (internal temperature) to a range of 500 to 2000°C and maintaining that temperature for 1 to 100 hours. In the above heat treatment, the internal temperature may more preferably be 900 to 1800°C, and even more preferably 1200 to 1500°C. The holding time may more preferably be 1 to 50 hours, and even more preferably 2 to 10 hours.

[0074] From the viewpoint of further reducing the amount of metal elements in the CNTs, the purification method of this embodiment may be performed two or more times as needed. In addition, other processing steps may be added as needed, provided that they do not degrade the properties of the CNTs.

[0075] <Dispersant> The dispersant is not particularly limited as long as it can disperse and stabilize the CNTs, and surfactants, resin-type dispersants, etc., can be used. Depending on the properties required for the dispersion of the CNTs, a suitable type of dispersant can be used in a suitable amount. For example, surfactants are preferred as dispersants from the viewpoint of improving the wettability of CNTs in organic solvents and obtaining a homogeneous CNT dispersion composition. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric. For example, resin-type dispersants are preferred in terms of electrochemical resistance, solubility in electrolyte solvents, and viscosity stability of the mixture slurry. Preferred resin-type dispersants include cellulose derivatives, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, or polyacrylonitrile polymers. In particular, cellulose derivatives, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers are preferred. Among cellulose derivatives, methylcellulose and ethylcellulose are preferred. For resin-type dispersants, polyvinylpyrrolidone and polyacrylonitrile polymers are preferred, with polyacrylonitrile polymers being particularly preferred.

[0076] When selecting an anionic surfactant, the type is not particularly limited. Specifically, examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfons, alkylnaphthalene sulfons, dialkyl sulfons, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfons, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. Furthermore, specifically, examples include, but are not limited to, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salts of β-naphthalene sulfonic acid formalin condensates. The anionic surfactant is preferably a polycarboxylate or naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0077] Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specifically, these include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyl dioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride. Examples of amphoteric surfactants include, but are not limited to, aminocarboxylate salts.

[0078] Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

[0079] The selected surfactant is not limited to a single surfactant. Therefore, it is possible to use two or more surfactants in combination. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. In this case, the amount blended should preferably be an amount suitable for each surfactant component. A combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate salt or a naphthalene sulfonic acid formalin condensate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0080] Specific examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers. Cellulose derivatives, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers are particularly preferred. Among cellulose derivatives, methylcellulose and ethylcellulose are preferred. For resin-type dispersants, polyvinylpyrrolidone and polyacrylonitrile polymers are preferred.

[0081] Polyacrylonitrile polymers are polymers having nitrile group-containing structural units, and may be copolymers having nitrile group-containing structural units and structural units other than nitrile group-containing structural units. When the polyacrylonitrile polymer is a copolymer, the content of nitrile group-containing structural units is preferably 15% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and even more preferably 25% by mass or more and 50% by mass or less. Examples of structural units other than nitrile group-containing structural units, based on the total structural units contained in the copolymer, include alkylene structural units, amide group-containing structural units, and carboxyl group-containing structural units. The polyacrylonitrile polymer preferably includes a copolymer having alkylene structural units in a content of 50% by mass or more and 75% by mass or less, and nitrile group-containing structural units in a content of 25% by mass or more and 50% by mass or less.

[0082] The weight-average molecular weight of the resin-type dispersant is preferably 5,000 to 500,000, preferably 10,000 to 300,000, and more preferably 10,000 to 100,000. Using a dispersant with an appropriate weight-average molecular weight improves adsorption to CNTs and further improves the stability of the CNT dispersion composition. Furthermore, if a dispersant exceeding the above range is used, the viscosity of the CNT dispersion composition will increase, and the dispersion efficiency may decrease when using a disperser through which the dispersion liquid passes through narrow channels, such as a nozzle-type or valve-type high-pressure homogenizer. Here, the weight-average molecular weight (Mw) of the resin-type dispersant can be measured using gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector.

[0083] <organic solvents> The organic solvent used as the dispersion medium is not particularly limited as long as it is miscible with the dispersant. In this specification, "miscible with the dispersant" means that when 0.5 g of the dispersant is dissolved in 100 g of the organic solvent at 25°C, the insoluble matter is 10% by mass or less. The insoluble matter can be calculated by filtering the undissolved dispersant from the solution, recovering the undissolved dispersant, then drying the recovered polymer with hot air and measuring its mass.

[0084] The organic solvent is preferably capable of dissolving the dispersant, and more preferably a high dielectric constant solvent capable of dissolving the dispersant. In this specification, "capable of dissolving the dispersant" means that when 0.5 g of the dispersant is dissolved in 100 g of the organic solvent serving as the dispersion medium at 25°C, no insoluble matter can be visually detected, and the solution is clear and transparent. When an organic solvent capable of dissolving the dispersant is used, a good dispersion state can be easily obtained.

[0085] The organic solvent is preferably a polar organic solvent that does not donate protons, and preferably contains a solvent consisting of one of the high dielectric constant solvents, or a mixed solvent consisting of two or more. Alternatively, one or more other solvents may be mixed with the high dielectric constant solvent. In this specification, "high dielectric constant solvent" refers to a solvent whose relative permittivity value, as described in a solvent handbook, is preferably 2.5 or higher at 20°C, and more preferably 25 or higher. When a CNT dispersion composition is prepared using a high dielectric constant solvent as the dispersion medium, the interaction between the CNTs and the dispersion medium can be enhanced. From the viewpoint of dispersant solubility, the relative permittivity of the high dielectric constant solvent is preferably 60 or lower at 20°C, and more preferably 50 or lower. In one embodiment, the relative permittivity of the high dielectric constant solvent may preferably be 30 to 50.

[0086] The organic solvent is preferably substantially water-free. "Substantially water-free" means that water is not intentionally added in an amount exceeding the amount that would be present due to moisture absorption, etc. The water content based on the total mass of the dispersion medium is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.02% by mass or less. Even when a CNT dispersion composition is prepared without the addition of water, the CNT dispersion composition may contain about 0.1% by mass of water due to moisture absorption, etc.

[0087] Examples of polar organic solvents that do not donate protons include amide, heterocyclic, sulfoxide, sulfone, lower ketone, and carbonate solvents. More specifically, the following are examples: Amides: N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc. Heterocyclic systems: cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc. Sulfoxide derivatives: such as dimethyl sulfoxide, Sulfone compounds: Hexamethylphosphotriamide, sulfolane, etc. Lower ketones: such as acetone and methyl ethyl ketone. Carbonate-based compounds: diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate) Others: Tetrahydrofuran, acetonitrile, etc.

[0088] The organic solvent preferably includes an amide-based organic solvent, and more preferably includes at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. If the dispersion medium is a polar organic solvent that does not donate protons, protons are less likely to be generated in the CNT dispersion composition, thus easily improving the storage stability of the CNT dispersion composition.

[0089] <Optional ingredients> The CNT dispersion composition may optionally contain other additives such as inorganic bases, inorganic metal salts, acids, amine compounds, defoamers, wetting agents, pH adjusters, wetting and penetrating agents, and leveling agents, as well as other conductive materials and resins other than CNTs, as long as they do not hinder the objectives of the present invention. Optional components can be added at any time, such as before the preparation of the CNT dispersion composition, during mixing, after mixing, or in combination thereof.

[0090] The inorganic base and inorganic metal salt are preferably compounds having at least one of an alkali metal and an alkaline earth metal. More specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Among these, alkali metal and alkaline earth metal chlorides, hydroxides, and carbonates are preferred because they can easily supply cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

[0091] The CNT dispersion composition may contain an inorganic base and / or an inorganic metal salt in addition to the dispersant. The inorganic base and inorganic metal salt are preferably compounds having at least one of an alkali metal and an alkaline earth metal, and more specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Among these, alkali metal and alkaline earth metal chlorides, hydroxides, and carbonates are preferred because they can easily supply cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

[0092] The CNT dispersion composition may contain an acid. Adding an acid can change the charge state and the balance between hydrophilic and hydrophobic parts in the dispersion, which may improve dispersibility. The type of acid is not particularly limited; one type or a combination of several may be used. The acid may be, for example, an organic or inorganic acid with 6 or fewer carbon atoms. Examples include oxalic acid, lactic acid, citric acid, acetic acid, malonic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, and phosphoric acid. If the active material contained in the composite slurry described later is, for example, a lithium-containing negative electrode active material and is basic, the dispersibility of the CNT dispersion composition may break down and it may thicken. However, if an acid is included in addition to the dispersant, the pH change of the slurry can be mitigated, and the rapid thickening of the composite slurry can be suppressed. Therefore, the storage stability of the composite slurry is excellent, coating unevenness of electrodes using the composite slurry can be suppressed, and the quality of the battery can be stabilized.

[0093] The CNT dispersion composition may contain an antifoaming agent. The antifoaming agent can be arbitrarily used as long as it has an antifoaming effect, such as a commercially available antifoaming agent or a wetting agent, and may be used alone or in combination of a plurality of kinds.

[0094] The CNT dispersion composition may contain an amine compound. As the amine compound, primary amine (1° amine), secondary amine (2° amine), and tertiary amine (3° amine) are used, and ammonia and quaternary ammonium compounds are not included. In addition to monoamines, amine compounds having a plurality of amino groups in the molecule, such as diamines, triamines, and tetraamines, can be used as the amine-based compound. Specifically, for example, aliphatic primary amines such as methylamine, ethylamine, butylamine, and octylamine, aliphatic secondary amines such as dimethylamine, diethylamine, and dibutylamine, aliphatic tertiary amines such as trimethylamine, triethylamine, and dimethyloctylamine, amino acids such as alanine, methionine, proline, serine, asparagine, glutamine, lysine, arginine, histidine, aspartic acid, glutamic acid, and cysteine, alkanolamines such as dimethylaminoethanol, monoethanolamine, diethanolamine, methylethanolamine, and triethanolamine, and alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine can be mentioned, but are not limited thereto.

[0095] <Method for producing CNT dispersion composition> The CNT dispersion composition of the present embodiment is obtained by dispersing a mixture containing CNT, a dispersant, and an organic solvent with a disperser. Moreover, although the production method is not particularly limited, it is preferable to include a step of applying a shear stress to the CNT to crush the CNT, a magnetic separation step for removing magnetic foreign substances, a filtering step using a filter, and a metal foreign substance removal step such as a centrifugation step. From the viewpoint of the metal foreign substance removal efficiency, the metal foreign substance removal step is preferably a magnetic separation step and / or a filtering step. The metal foreign matter removal step may be performed at any time, such as before, during, or after the dispersion of the CNT dispersion composition. However, it is preferable to remove the metal foreign matter before the dispersion process refines the particles, and it is preferable to include the metal foreign matter removal step before and / or during the dispersion of the CNT dispersion composition.

[0096] • Process of crushing carbon nanotubes (CNTs) In the process of crushing CNTs by applying shear stress, the CNTs can be crushed using a dispersion device or the like, either dry or wet.

[0097] The dispersion apparatus used to crush the carbon nanotubes (CNTs) is not particularly limited. Dispersers commonly used for pigment dispersion and the like can be used. For example, the dispersion may be carried out using one or more dispersion apparatuses selected from the group consisting of mixers, homogenizers, paint shakers, media-type dispersers, and media-less dispersers. The homogenizers are classified into ultrasonic, agitation, and high-pressure types depending on the crushing method, and any of these may be used. In some embodiments, it is preferable to perform the dispersion using a dispersion apparatus classified as at least a high-pressure homogenizer. Dispersions classified as high-pressure homogenizers (hereinafter also referred to as high-pressure homogenizers) include nozzle-type and valve-type homogenizers, and either may be used. Valve-type high-pressure homogenizers (hereinafter also referred to as valve-type homogenizers) are more preferably used.

[0098] While not strictly limited, the following are examples of distributed devices. Mixers: Dispersers, homomixers, planetary mixers, high-shear mixers, etc. Ultrasonic homogenizers: such as BRANSON's "Advanced Digital Sonifer (registered trademark), MODEL 450DA". Stirring homogenizers: such as M-Technic's "Clearmix," PRIMIX's "Filmix," and Silverson's "Abramix," etc. High-pressure homogenizers: Genus PY from Genus Corporation, Starburst from Sugino Machine Co., Ltd., Nanomizer from Nanomizer Co., Ltd., HC3 series from Sanmaru Machinery Industry Co., Ltd., HV-H series from Izumi Food Machinery Co., Ltd. Paint shakers: Fast & Fluid's "SO400" paint mixer, Red Devil's "Paint Conditioner", etc. Media-type dispersers: Colloid mills (PUC's "PUC Colloid Mill," IKA's "Colloid Mill MK"); cone mills (IKA's "Corn Mill MKO," etc.); ball mills; sand mills (Shinmaru Enterprises' "Dyno Mill," Ashizawa Finetech's "Star Mill (registered trademark) LMZ," etc.), Longly's "Nanobeads Mill"; attritors; pearl mills (Eirich's "DCP Mill," etc.); ball mills, etc. Media-less distribution machines: SPXflow's "R-Model," M-Technique's "CREA SS-5," Nara Machinery's "MICROS," etc. Other options: 2-roll mills, 3-roll mills, etc.

[0099] In some embodiments, the dispersion device (disperser) may be selected from the group consisting of a disperser, homogenizer, high-shear mixer, kneader, two-roll mill, three-roll mill, ball mill, horizontal sand mill, vertical sand mill, annular bead mill, paint shaker, attritor, planetary mixer, and high-pressure homogenizer. The stator / screen of the high-shear mixer can be a round-hole stator, a square-hole high-shear screen, a slotted stator, an emulser screen, etc., and these may be used in combination. In some embodiments, the high-shear mixer may be in the form of a double stator, for example, having a square-hole high-shear screen on the inside and a fine emulser screen on the outside. The above-mentioned dispersion devices (dispersers) may be used individually or in combination of two or more types. It is preferable to use two or more dispersion devices in combination because it tends to make it easier to adjust the dispersion state of the CNTs.

[0100] While wear particles may be generated during the crushing of CNTs, it is desirable to minimize the inclusion of friction particles in the production of CNT dispersion compositions. From this viewpoint, a media-less disperser is preferably used in the dispersion process. The rotor and stator of the disperser are preferably made of ceramics. Furthermore, when using a bead mill in wet dispersion, it is preferable to use a ceramic dispersion media. When using a bead mill as a wet disperser, it is preferable to perform a CNT crushing process before the dispersion process by the bead mill. Specifically, it is preferable to crush the CNTs by applying shear stress to them using a media-less disperser, and then disperse the crushed CNTs using a bead mill. By applying such a method, it is possible to improve the problem of beads becoming prone to wear when the bead mill is operated at high peripheral speed on a low-viscosity material to be dispersed where the CNTs have not been sufficiently crushed. In addition, when a high-pressure homogenizer is used in combination as a disperser, the presence of wear particles from the beads during the dispersion process may cause problems such as nozzle clogging and valve damage in the high-pressure homogenizer. In contrast, by applying the above method, the occurrence of the above-mentioned problem can be easily suppressed.

[0101] When using a high-pressure homogenizer as a disperser, for example, a nozzle-type high-pressure homogenizer that discharges the processing liquid from a nozzle, or a valve-type high-pressure homogenizer that discharges the processing liquid from a homogenization valve can be used. Examples of nozzle-type high-pressure homogenizers include "Genus PY" from Genus Corporation, "Starburst" from Sugino Machinery Co., Ltd., and "Nanomizer" from Nanomizer Corporation. Examples of valve-type high-pressure homogenizers include "HC3 series" from Sanmaru Machinery Co., Ltd., "HV-H series" from Izumi Food Machinery Co., Ltd., and "R-Model" from SPX Flow Corporation, but are not limited to these. In particular, valve-type high-pressure homogenizers can increase the flow rate of the processing liquid, and when producing CNT dispersion compositions by circulating dispersion, homogenization is improved, and the cumulative particle size D of the CNT dispersion composition is increased. 90 The particles become smaller, improving filterability, allowing the use of filters with superior filtration accuracy in the filtration process, and making it easier to obtain CNT dispersion compositions with a lower content of metallic foreign particles.

[0102] When using a valve-type high-pressure homogenizer, the flow rate of the processing liquid is preferably 1,000 L / h to 15,000 L / h, and more preferably 2,000 L / h to 12,000 L / h. When the flow rate of the processing liquid is within the above range, shear stress suitable for CNT dispersion is applied, making it easier to obtain a CNT dispersion composition with excellent conductivity.

[0103] Furthermore, the pressure when using a valve-type high-pressure homogenizer is not particularly limited. For example, when dispersing CNTs using a high-pressure homogenizer, the pressure is preferably 40 to 150 MPa, more preferably 40 to 120 MPa, and even more preferably 60 to 120 MPa. When the pressure is within the above range, homogeneity can be efficiently improved, and the cumulative particle size D of the CNT dispersion composition can be improved. 90 This reduces the size of the material, improving filtration efficiency.

[0104] Figure 1 is a schematic cross-sectional view of a homogenization valve in a valve-type high-pressure homogenizer, an example of a dispersion device. In Figure 1, the homogenization valve comprises a valve seat 31, an impact ring 32, and a homovalve 33. The CNT dispersion composition supplied from the pump is supplied to the homogenization valve at high pressure in the direction of the arrow in the figure and subjected to fine dispersion treatment. After that, it is discharged from the outlet (not shown). Increasing the pressure and flow rate during dispersion increases the impact force when the material collides with the valve seat, impact ring, and homovalve, and the dispersibility of the CNTs can also be improved. To withstand this impact force, it is necessary to increase the hardness of the materials of the valve seat, impact ring, and homovalve. Materials with high hardness include ceramics and steel, such as zirconia, titanium nitride, tungsten carbide, alumina, silicon carbide, silicon nitride, diamond, tool steel, high-speed steel, and superhard steel. In particular, the Vickers hardness of the material is preferably 1,000 or higher, and more preferably 1,400 or higher. If the material has a Vickers hardness of 1,000 or higher, it can withstand the impact force during CNT dispersion.

[0105] In some embodiments, a method for producing a CNT dispersion composition comprises a step of crushing CNTs in a valve-type high-pressure homogenizer having a homogenization valve, wherein the homogenization valve comprises a valve seat, an impact ring, and a homovalve, and at least one of the materials of the valve seat, impact ring, and homovalve may have a Vickers hardness of 1,000 or higher. Alternatively, at least one of the valve seat, impact ring, and homovalve may be a ceramic or steel material having a Vickers hardness of 1,000 or higher.

[0106] The wetted material of the pump used during dispersion is preferably a non-metallic material such as ceramic or resin. For example, zirconia, alumina, polytetrafluoroethylene (PTFE), vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), tetrafluoroethylene-purple orovinyl ether rubber (FFKM), carbon fiber reinforced plastic. Examples include carbon fiber reinforced polymer (CFRP) and polyether ether ketone (PEEK). If the pump is made of metal, wear particles from the pump may be mixed in during dispersion, potentially increasing the amount of metal.

[0107] In this embodiment, the CNT dispersion composition is preferably dispersed by circulating dispersion or pass dispersion until the undisintegrated CNTs are substantially eliminated. In the case of circulating dispersion, if the holding tank is uniformly agitated, the probability of the presence of undisintegrated CNTs in the CNT dispersion composition can be reduced to 1% by mass or less, so it is preferable to use 5 passes or more, more preferably 10 passes or more, and even more preferably 15 passes or more. In the case of pass dispersion, it is preferable to disperse using 3 passes or more, more preferably 5 passes or more, and even more preferably 10 passes or more. If undisintegrated CNTs are present, the cumulative particle size D 90 This can easily lead to increased size, potentially reducing the filterability of the CNT dispersion composition.

[0108] ·Metal foreign particle removal process Methods for reducing the content of metallic foreign particles in the CNT dispersion composition are not particularly limited, but include a filtration process using a filter and a magnetic separation process such as magnetic separation using an electromagnet. It is preferable to include a filtration step and a magnetic separation step, because the magnetic separation step can remove metal foreign particles derived from CNTs grown around a metal catalyst, and the filtration step can recover metal foreign particles that cannot be removed by magnets. Furthermore, it is more preferable to perform a magnetic separation process after the filtration process. By making the filtration process the final step in the production of the CNT dispersion composition, the amount of metallic foreign particles that may be mixed in from piping during transport can be reduced, and the characteristics of the resulting battery can be improved.

[0109] (Magnetic selection process) Various conventionally known methods can be used to reduce the content of metallic foreign particles in a CNT dispersion composition using magnetic force through a magnetic separation process. For example, a preferred method involves setting up an electromagnet during the manufacturing process of the CNT dispersion composition and passing the composition through it to remove metallic foreign particles.

[0110] The magnetic flux density of the electromagnet is preferably between 5,000 gauss and 20,000 gauss, and more preferably between 10,000 gauss and 20,000 gauss. By using an electromagnet within the above range, not only metallic foreign particles contained in the CNTs but also metallic foreign particles mixed in during the manufacturing process of the CNT dispersion composition can be removed.

[0111] Specifically, for example, you can use CS-150HHH, CS-250HHH, CS-300HHH from Nippon Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 from Nippon Elise Magnetics Co., Ltd., and EMF-100S, EMF-150S, EMF-250S, EMF-300S from Taiho Magnetic Co., Ltd.

[0112] The flow velocity of the CNT dispersion composition when it comes into contact with the electromagnet is preferably 1 L / min or more and 200 L / min or less, and more preferably 30 L / min or more and 100 L / min or less. If the flow velocity when it comes into contact with the electromagnet is high, there is a possibility that metal foreign particles with low magnetic force that have been collected by the electromagnet may flow back into the CNT dispersion composition.

[0113] It is preferable that the CNT dispersion composition passes through the electromagnet three or more times. If the number of passes is insufficient, metallic foreign particles may not be removed. When passing through the electromagnet in a circulating manner, it is preferable to pass the composition through more times, taking into account the uniformity within the tank used in the manufacturing process.

[0114] (filtration process) The filter used to separate metallic foreign particles can be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferred. Since metallic foreign particles are not spherical and are often oriented, using a depth filter can efficiently reduce the amount of metallic foreign particles in the CNT dispersion composition.

[0115] Unlike surface filters (filters that primarily capture particulate matter in a fluid on their surface), depth filters primarily capture particulate matter in a fluid within the filter medium, and are characterized by high particle retention performance and resistance to clogging. By using depth filters, the content of metallic foreign particles in the CNT dispersion composition can be further reduced.

[0116] For depth filters, for example, 3M™ PP nonwoven depth cartridges NT-T series, Profile II from Nippon Pall Co., Ltd., and Rokitechno PP depth filter cartridges Celia Clean can be used.

[0117] The filtration accuracy of the filter is preferably 3 μm to 50 μm, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 40 μm. If a filter with a small pore size is used to increase the efficiency of removing metal foreign particles from the CNT dispersion composition, the efficiency of removing metal foreign particles may decrease due to clogging of the CNTs. By using a filter with a filtration accuracy within the above range, the content of metal foreign particles in the CNT dispersion composition can be efficiently reduced.

[0118] Even if filtration is performed using filters with a filtration accuracy of 3 μm or 5 μm, metal foreign particles may have orientation due to their needle-like shape, and it may not be possible to completely remove them, resulting in some remaining in the CNT dispersion composition. Therefore, it is preferable to appropriately control the composition and viscosity of the CNT dispersion composition, the dispersion process, or the method of the metal foreign matter removal process to reduce the amount of metal foreign particles in the CNT dispersion composition required under condition 1.

[0119] ≪Asphalt mixture slurry≫ The asphalt slurry of this embodiment comprises at least a CNT dispersion composition and an active material. That is, the asphalt slurry comprises at least CNTs, a dispersant, an organic solvent, and an active material. Preferably, the asphalt slurry further comprises a binder resin. In this case, it is preferable that the asphalt slurry comprises a CNT dispersion composition, a binder resin, and an active material, that is, it is preferable that it comprises CNTs, a dispersant, an organic solvent, a binder resin, and an active material.

[0120] A binder resin is a resin used to bond substances together. While there are no particular restrictions on the type of binder resin, examples include polymers or copolymers containing fluororesins, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, etc., as constituent units; Polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; Cellulose resins such as carboxymethylcellulose; Rubbers such as styrene-butadiene rubber; Examples include conductive resins such as polyaniline and polyacetylene. Among these, the use of fluororesin as a binder resin is preferable from the viewpoint of electrochemical oxidation-reduction resistance. The asphalt slurry may also contain a resin-type dispersant that functions as a binder resin.

[0121] As fluororesins, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferred, for example.

[0122] The weight-average molecular weight of the fluororesin is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,500,000, and particularly preferably 200,000 to 1,500,000. The weight-average molecular weight is the weight-average molecular weight on a polystyrene basis and can be measured by gel permeation chromatography (GPC).

[0123] Active material refers to the material that forms the basis of a battery reaction. Active material can be divided into positive electrode active material and negative electrode active material based on its electromotive force. In this specification, positive electrode active material and negative electrode active material may sometimes be simply referred to as "active material." Active material refers to the material that forms the basis of a battery reaction. Active material can be divided into positive electrode active material and negative electrode active material based on its electromotive force.

[0124] The positive electrode active material is not particularly limited, but metal compounds such as metal oxides and metal sulfides that can be doped or intercalated with lithium ions, and conductive polymers can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, MnO, V2O5, V6O 13 Examples include transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobaltate, lithium manganate, and spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphoric acid compounds, and transition metal sulfide powders such as TiS2 and FeS. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the above inorganic and organic compounds may be mixed and used.

[0125] The positive electrode active material is preferably a composite oxide with lithium containing transition metals such as Al, Fe, Co, Ni, and Mn, more preferably a composite oxide with lithium containing any one of Al, Co, Ni, and Mn, and particularly preferably a composite oxide with lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained on the battery characteristics.

[0126] The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metallic Li, alloy systems such as its alloys tin alloy, silicon alloy, lead alloy, etc., Li X Fe2O3, Li X Fe3O4, Li X WO2 (x is a number where 0 < x < 1.), metal oxide systems such as lithium titanate, lithium vanadate, lithium silicate, conductive polymer systems such as polyacetylene, poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, vapor-grown carbon fibers, carbon fiber and other carbon-based materials can be mentioned. These negative electrode active materials can also be used alone or in combination of two or more.

[0127] 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 even more preferably 0.3 m 2 / g or more and 3 m 2 / g or less.

[0128] The average particle diameter of the active material is preferably within the range of 0.05 μm to 100 μm, and more preferably within the range of 0.1 μm to 50 μm. The average particle diameter of the active material as referred to in this specification is the average value of the particle diameters measured by an electron microscope for the active material.

[0129] To obtain the asphalt slurry, it is preferable to add an active material to the CNT dispersion composition and then perform a dispersion treatment. The dispersion apparatus used for this treatment is not particularly limited. The asphalt slurry can be obtained using the dispersion apparatus described in the CNT dispersion composition section.

[0130] The content of the active material in the asphalt slurry is preferably 20% to 85% by mass, and particularly preferably 40% to 85% by mass, based on 100% by mass of the asphalt slurry.

[0131] The CNT content in the asphalt slurry is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and most preferably 0.1 to 3 parts by mass, based on 100 parts by mass of active material.

[0132] The amount of dispersant in the asphalt slurry is preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 20 to 50 parts by mass, based on 100 parts by mass of CNT.

[0133] If the asphalt slurry contains a binder resin, the amount of binder resin in the asphalt slurry is preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the active material.

[0134] The solid content concentration of the asphalt slurry is preferably 30% to 90% by mass, and more preferably 40% to 85% by mass, based on 100% by mass of the asphalt slurry.

[0135] When the organic solvent used as the dispersion medium includes an amide-based organic solvent, the water content in the mixture slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less.

[0136] ≪Electrode, electrode film≫ The electrode of this embodiment comprises a current collector and an electrode film formed from the asphalt slurry of the above embodiment. The electrode film is a coating film of asphalt slurry. The electrode film is a coating film formed by coating and drying the asphalt slurry onto the current collector, for example, to form an electrode asphalt layer.

[0137] The material and shape of the current collector are not particularly limited, and can be appropriately selected to suit various types of secondary batteries. For example, the material of the current collector can be a metal or alloy such as aluminum, copper, nickel, titanium, or stainless steel. In terms of shape, a flat foil is generally used, but current collectors with roughened surfaces, perforated foils, and mesh-shaped current collectors can also be used.

[0138] There are no particular limitations on the method for applying the asphalt slurry onto the current collector to form an electrode film, and known methods can be used. Specifically, die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, or electrostatic coating methods can be used, and drying methods such as standing drying, forced-air drying, hot-air drying, infrared heating, and far-infrared heating can be used, but are not limited to these.

[0139] Furthermore, rolling treatment using a flatbed press or calender roll may be performed after coating. The thickness of the electrode film (electrode composite layer) is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0140] ≪Secondary battery≫ The secondary battery of this embodiment comprises an electrode having an electrode film and an electrolyte. The secondary battery comprises a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode may have the electrode film of the embodiment. The CNT dispersion composition of this embodiment has excellent rate characteristics because it forms a good conductive network within the electrodes of the secondary battery, and because the active material is utilized homogeneously during charging and discharging, degradation of the active material is less likely to occur. Furthermore, overcharging and over-discharging during charging and discharging are suppressed. In addition, because there are few metallic foreign substances derived from the CNT dispersion composition, degradation of battery characteristics due to electrolyte decomposition and metal deposition is less likely to occur, and it has excellent high-temperature cycle characteristics.

[0141] As the positive electrode, an electrode film can be prepared by coating a slurry containing the positive electrode active material onto a current collector and drying it.

[0142] As the negative electrode, an electrode film can be prepared by coating a slurry containing the negative electrode active material onto a current collector and drying it.

[0143] Various conventionally known electrolytes that allow ion movement can be used. Examples include 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), but are not limited to these, and sodium salts can also be used. It is preferable to dissolve the electrolyte in a non-aqueous solvent and use it as an electrolyte solution.

[0144] Non-aqueous solvents are not particularly limited, but examples include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glycyles such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used individually or in combination of two or more.

[0145] The secondary battery of this embodiment preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those treated to be hydrophilic, but are not limited to these.

[0146] The structure of the secondary battery in this embodiment is not particularly limited, but it typically consists of a positive electrode, a negative electrode, and a separator provided as needed, and can take on various shapes depending on the intended use, such as paper type, cylindrical type, button type, or laminated type.

[0147] The secondary battery of this embodiment is not particularly limited in its use, and can be used specifically as a power source for consumer electronics such as mobile phones, laptop computers, and digital cameras; as an emergency power source for hospitals, factories, and buildings; and for vehicles such as hybrid cars, plug-in hybrid cars, electric cars, electric assist bicycles, and railway vehicles. The secondary battery, for example, recovers regenerative energy from the power of a vehicle.

[0148] In particular, because it is a secondary battery with high charge / discharge performance and excellent cycle characteristics, it can be suitably used in vehicles, resulting in vehicles that are highly safe and can be expected to improve fuel efficiency. Furthermore, it can demonstrate excellent performance even in vehicle applications where high-current charging and discharging are desired.

[0149] The mounting location of the secondary battery in the vehicle of this embodiment is not particularly limited. For example, when the secondary battery is installed in an automobile, it can be installed in the engine compartment, at the rear of the vehicle, or under the seats. [Examples]

[0150] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples unless it exceeds the gist of the invention. Unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "percentage by mass". In addition, the blending amounts in the table are in parts by mass, and except for the dispersion medium, the values ​​are calculated on a non-volatile content basis. Blank spaces in the table indicate that an ingredient is not blended.

[0151] The materials used in the examples and comparative examples are shown below. <Dispersant> Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35056, Mooney viscosity 65, weight-average molecular weight 180,000, alkylene structural units 64% by mass, nitrile group-containing structural unit content 36% by mass) was used as a dispersant (B-1). Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35053, Mooney viscosity 35, weight-average molecular weight 130,000, alkylene structural units 64% by mass, nitrile group-containing structural unit content 36% by mass) was used as a dispersant (B-2). Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, weight-average molecular weight 110,000, alkylene structural units 66% by mass, nitrile group-containing structural unit content 34% by mass) or less was used as a dispersant (B-3). Polyvinylpyrrolidone (PVP) (manufactured by Nippon Shokubai Co., Ltd., K-30, weight-average molecular weight 40,000) or less was used as a dispersant (B-4). · A solution in which hydrogenated acrylonitrile-butadiene rubber was dispersed in NMP (manufactured by Zeon Corporation, trade name "BM-720H", solid content 8% by weight, weight average molecular weight 300,000) was used as the dispersant (B-5) hereinafter.

[0152] <Measurement of weight average molecular weight (Mw)> The weight average molecular weight (Mw) of the dispersant used was measured by gel permeation chromatography (GPC) equipped with a RI detector using a molecular weight measurement sample. As the apparatus, HLC-8320GPC (manufactured by Tosoh Corporation) was used. Three separation columns were connected in series, and as the packing materials, "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" manufactured by Tosoh Corporation were used in order. The oven temperature was 40 °C, and a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide was used as the eluent, and the measurement was carried out at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% using the solvent consisting of the eluent and 20 microliters were injected. The weight average molecular weight is a polystyrene conversion value.

[0153] <Additives> · NaOH; Sodium hydroxide (manufactured by Tosoh Corporation, granular caustic soda "Tosopearl") · Ethanolamine; 2-Aminoethanol (manufactured by Fujifilm Wako Pure Chemical Corporation, Wako special grade 1)

[0154] <Preparation of CNT (A-1)> 60 parts of CNT (JENOTUBE10B) were placed in a graphite crucible with a diameter of 10 cm and a height of 10 cm. The crucible containing the above CNT was placed in a multi-purpose high-temperature furnace (manufactured by Fuji Denpa Kogyo Co., Ltd., Himulti 5000), and heat treatment was carried out under reduced pressure vacuum as follows. First, nitrogen gas was introduced into the above multi-purpose high-temperature furnace, and the substitution operation with nitrogen gas was performed twice. Next, the pressure was reduced using an oil rotary pump, and after adjusting the furnace pressure to 9.8 - 9.5 Pa, subsequently, the pressure was further reduced using an oil diffusion pump, and the furnace pressure was adjusted to 0.03 Pa or less. Subsequently, while maintaining the pressure reduction by the oil diffusion pump, the temperature was raised to 1,500 °C at a heating rate of 20 °C / min and held at 1,500 °C for 10 hours. Thereafter, it was naturally cooled until the furnace temperature reached 50 °C or lower, and CNT (A-1) was obtained.

[0155] <Production of CNT (A-2) to (A-5)> CNT (A-2) to (A-5) were obtained by the same method as CNT (A-1), except that the holding temperature of CNT shown in Table 1 was changed.

[0156] <Production of CNT (A'-3)> Two parts of CNT (JENOTUBE10B) were weighed into a 1 L glass container, 98 parts of 5% hydrogen peroxide (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) were added, and then stirred for 4 hours using a stirrer. Thereafter, it was washed with 20% hydrochloric acid, diluted sufficiently with ion-exchanged water, and vacuum filtration was performed using a membrane filter. After repeating the dilution and filtration operations, the CNT was transferred to a PTFE bat and then dried at 140 °C using an oven to obtain CNT (A'-3).

[0157] <Metal content of CNT> A microwave sample pretreatment device (ETHOS, manufactured by Milestone General Co., Ltd.) was used to decompose CNT with acid and extract the metals contained in CNT. The analysis of the extracted metals was performed using a multi-type ICP emission spectroscopic analyzer (720-ES, manufactured by Agilent), and the content of the metals contained in CNT was calculated. In Table 1 described later, as the metal content, the mass ratio (ppm) of iron, cobalt, aluminum, magnesium, respectively, to the mass of CNT before metal extraction is shown. Also, from the calculated metal contents, the total content of iron, cobalt, aluminum, magnesium, copper, zinc, nickel, chromium, manganese, and molybdenum was determined. The total content of iron, cobalt, aluminum, magnesium, copper, zinc, nickel, chromium, manganese, and molybdenum in CNT is represented by the mass ratio (ppm) of the total mass content of the extracted iron, cobalt, aluminum, magnesium, copper, zinc, nickel, chromium, manganese, and molybdenum to the mass of CNT before metal extraction.

[0158] <G / D ratio of CNT> CNT was placed on a Raman microscope (Horiba, Ltd., XploRA), and measurements were performed using a laser wavelength of 532 nm. The measurement conditions were an acquisition time of 60 seconds, an integration number of 2 times, a dimming filter of 10%, an objective lens magnification of 20 times, a confocal hole of 500, a slit width of 100 μm, and a measurement wavelength of 100 - 3000 cm -1 The CNT for measurement was aliquoted onto a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity within the range of 1560 - 1600 cm -1 in the spectrum was defined as G, and the maximum peak intensity within the range of 1310 - 1350 cm -1 in the spectrum was defined as D. The ratio of G / D was calculated and used as the G / D ratio of CNT.

[0159] <Amount of surface oxygen of CNT> The amount of surface oxygen of CNT was measured using an X-ray photoelectron spectrometer (XPS, Thermo Fisher Scientific, K-Alpha). After pelletizing the CNT, this sample was fixed to the sample stage with double-sided tape for measurement. Carbon atoms and oxygen atoms on the surface of the CNT sample were detected by XPS. Here, the ratio (atm%) of oxygen atoms to carbon atoms was calculated as the amount of surface oxygen.

[0160] <BET specific surface area of CNT> CNT was weighed using an electronic balance (Sartorius, MSA225S100DI) to a measurement of 0.03 g, and then dried while degassing at 110 °C for 15 minutes. Subsequently, the BET specific surface area of the carbon nanotube was measured using a fully automatic specific surface area measuring device (MOUNTECH, HM-model1208).

[0161] <Volume resistivity of CNT> Using a powder resistivity measurement device (manufactured by Nitto Seiko Analytic Co., Ltd.: Loresta GP Powder Resistivity Measurement System MCP-PD-51), the volume resistivity of CNT at a density of 1 g / cc was measured.

[0162] <Water vapor adsorption amount of CNT> After weighing 0.03 g of CNT using an electronic balance (manufactured by Sartorius, MSA225S100DI), it was dried while degassing at 110°C for 15 minutes. Then, using an automatic gas / vapor adsorption amount measurement device BERSORP MAX (manufactured by Microtrac) The measurement was carried out. The measurement conditions were an adsorption temperature of 25°C and a relative pressure (P / P0) range of 0.00 to 0.99. Also, as the water serving as the adsorbate, distilled water purified by repeating the freezing and defoaming processes 5 times was used. The obtained adsorption isotherm was plotted with the horizontal axis being the water vapor relative pressure (P / P0) and the vertical axis being the amount of water vapor adsorbed per 1 g of the sample (mg / g), and the water vapor adsorption amount at P / P0 = 0.90 (relative humidity 90%) was calculated.

[0163] <Moisture content of CNT> The CNT was measured using a trace moisture measurement device (manufactured by Nitto Seiko Analytic Co., Ltd., CA200). For the measurement, the vaporization device (manufactured by Nitto Seiko Analytic Co., Ltd., VA200) was set to 230°C, and while flowing dry nitrogen gas, the glass sample boat was baked empty. Subsequently, 0.05 to 0.10 g of CNT was placed in the sample boat to measure the moisture content of CNT.

[0164] <Moisture content of CNT over time, Rate of change of moisture content of CNT over time> The CNT with the measured moisture was stored in an environment of temperature 23°C ± 2°C and humidity 50% ± 10% for 1 month. The value measured using a trace moisture measurement device (manufactured by Nitto Seiko Analytic Co., Ltd., CA200) for this CNT was taken as the moisture content over time. Also, the rate of change of the moisture content of CNT over time was determined by (moisture content of CNT over time / moisture content of CNT × 100 (%)). The moisture content of the CNT refers to the measured value when an unopened purchased product is opened under general environmental conditions. Since it is opened immediately before preparing the CNT dispersion composition, it is regarded as the measured value immediately before preparing the CNT dispersion composition.

[0165] Table 1 shows the physical properties of the CNTs used in the examples and comparative examples.

[0166]

Table 1-1

[0167]

Table 1-2

[0168] <Moisture content of the CNT dispersion composition> The moisture content of the CNT dispersion composition was measured using a trace moisture measuring device (manufactured by Nitto Seiko Analytic Co., Ltd., CA200). For the measurement, the vaporizer (manufactured by Nitto Seiko Analytic Co., Ltd., VA200) was set at 230°C, and while flowing dried nitrogen gas, the glass sample boat was baked empty. Subsequently, 0.5 to 1.0 g of the CNT dispersion composition was placed in the sample boat to measure the moisture content of the CNT dispersion composition.

[0169] <Measurement of the phase angle of the CNT dispersion composition> The phase angle of the CNT dispersion composition was evaluated by performing dynamic viscoelasticity measurement using a rheometer (MCR302e, manufactured by Anton Paar) with a 25-mm diameter and 2° cone at 25°C and a frequency of 1 Hz in the range of strain rate from 0.01% to 5%, and calculating the phase angle at a strain rate of 1%.

[0170] <Content of metallic foreign particles in the CNT dispersion composition> 20 kg of the CNT dispersion composition was passed through an electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, diameter: 10 cm, equipped with 31 grid screens with a thickness of 1.3 cm) via a hose pump at a flow rate of 30 L / min for 5 passes. Then, when preparing the CNT dispersion composition, the solvent contained in the CNT dispersion composition was passed through an electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, diameter: 10 cm, equipped with 31 grid screens with a thickness of 1.3 cm), and the CNT dispersion composition in the hose pump and the electromagnet was extruded and washed until the solid content was substantially eliminated. Further, after that, the power supply of the electromagnet was turned off, and after confirming that the magnetic force of the filter disappeared, 10 kg of the solvent used when preparing the CNT dispersion composition was passed through the electromagnet at a flow rate of 30 L / min to obtain 10 kg of a solvent containing metal foreign particles. Then, 10 kg of the solvent containing metal foreign particles was dispersed by ultrasonic treatment for 2 minutes under the conditions of an output of 300 W and a frequency of 28 kHz using an ultrasonic processor (manufactured by Iwa Medical Industry Co., Ltd., ultrasonic cleaner), and then the entire amount was passed through a filter (weight (W1), material: polyester, disk diameter: 47 mm, mesh opening: 5 μm) using a filtering bell, and then 100 g of ethanol was used to wash the metal foreign particles deposited on the filter. Further, after that, the filter on which the metal foreign particles were deposited was removed, and the filter was dried at 60°C for 10 minutes using a hot air oven, and the weight (W2) was measured. The filter weight (W1) was subtracted from the dried filter weight (W2) with metal foreign particles deposited to calculate the content (weight of metal foreign particles) of metal foreign particles in the CNT dispersion composition. The criteria for determining the content of metal foreign particles were set as follows: 0.1 mg or less: A, more than 0.1 mg and 0.4 mg or less: B, more than 0.4 mg and 1.0 mg or less: C, more than 1.0 mg: D.

[0171] <Amount of metal elements in the CNT dispersion composition> After drying the CNT dispersion composition using a hot air oven, acid decomposition was performed using a microwave sample pretreatment device (manufactured by Milestone General, ETHOS1) to extract the metals contained in the CNT. Subsequently, analysis was carried out using a multi-type ICP emission spectrometer (manufactured by Agilent, 720-ES), and the amount of metal elements (total content of iron, cobalt, nickel, chromium, molybdenum, aluminum, magnesium, and copper) contained in the extract was calculated. The smaller the amount of metal elements, the more effectively the voltage failure of the secondary battery can be suppressed. The evaluation criteria for the amount of metal elements were set as follows: 30 ppm or less: ◎ (excellent), more than 30 ppm and 50 ppm or less: ○ (good), more than 50 ppm and 100 ppm or less: △ (acceptable), more than 100 ppm: × (unacceptable).

[0172] <Particle size of CNT dispersion composition> Cumulative particle size D by particle size distribution 50 and D 90 The measurement of was carried out using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.; Partical LA-960V2). The laser light wavelength of this measuring device is 650 nm, and it has a ring-shaped 64-segment silicon photodiode at 1 point, a 4ch array detector at 5 points, and a silicon photodetector at 3 points as detectors. Also, the measurement unit uses a flow cell (sample cell) made of synthetic quartz. First, the same solvent as the organic solvent contained in the CNT dispersion composition was introduced into the sample bath containing the sample cell, and circulation / ultrasonic cleaning was performed. As the operation mode, the circulation speed was 3, the ultrasonic intensity was 7, the ultrasonic time was 1 minute, the stirring speed was 7, and the stirring mode was continuous. Subsequently, for air extraction, ultrasonic operation was performed at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds, and then blank (background) measurement was carried out. The particle size standard was volume, the particle refractive index was 1.920 - 0.522i (CNT), and the solvent refractive index was the refractive index of the solvent used when preparing the CNT dispersion composition (1.468 (NMP)). The CNT dispersion composition was dropped so that the laser light transmittance during measurement was 60% ± 1%, and sample adjustment was carried out. The operation mode during measurement was set as circulation speed: 3, stirring speed: 7, and stirring mode: continuous for measurement. Cumulative particle size D 90 The judgment criteria were as follows: 4.0 μm or less: A, more than 4.0 μm and 6.0 μm or less: B, more than 6.0 μm and 10 μm or less: C, more than 10 μm: D.

[0173] <Initial viscosity of CNT dispersion composition> After leaving the CNT dispersion composition standing in a constant temperature bath at 25°C for 1 hour or more, the viscosity of the CNT dispersion composition was immediately measured using a B-type viscometer with a rotor rotation speed of 100 rpm. A No. 4 rotor was used for the measurement. The evaluation criteria for the initial viscosity were as follows: less than 200 mPa·s: ◎ (excellent), 200 mPa·s or more and less than 500 mPa·s: ○ (good), 500 mPa·s or more and less than 1500 mPa·s: △ (fair), 1500 mPa·s or more: × (poor).

[0174] <Vickers hardness> The Vickers hardness was determined based on JIS Z2251:2009 using a Fisherscope H100C (manufactured by Fisher Instruments) microhardness tester. The measurement was performed on 10 disc-shaped measurement samples with a thickness of 3.0 ± 0.5 mm, and the average value was taken as the Vickers hardness.

[0175] <Preparation of standard negative electrode> In a 150ml plastic container, 0.5 parts by mass of acetylene black (Denka Black® HS-100, manufactured by Denka), 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt, Sunrose special type MAC500LC, manufactured by Nippon Paper Industries, 100% non-volatile content), and 98.4 parts by mass of water were added. The mixture was then stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Furthermore, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry, CGB-20) and 5 parts by mass of silicon (manufactured by Osaka Titanium Technology, SILICON MONOOXIDE SiO 1.3C 5μm, 100% non-volatile content) were added as active materials, and the mixture was stirred at 3,000 rpm for 10 minutes using a high-speed stirrer. Next, 3.1 parts by mass of SBR (styrene-butadiene rubber, TRD2001, manufactured by JSR Corporation) were added, and the mixture was stirred at 2,000 rpm for 30 seconds using the aforementioned rotation-revolution mixer to obtain a negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was measured using an applicator to obtain a basis weight of 8 mg / cm³ per unit area of ​​the electrode. 2 After coating the copper foil in this manner, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Furthermore, it was rolled using a roll press (manufactured by Sankumetal Co., Ltd., 3t hydraulic roll press) to obtain a density of 1.6 g / cm³ in the asphalt layer. 3 A standard negative electrode was fabricated.

[0176] <Rate characteristic evaluation of lithium-ion secondary batteries> A laminated lithium-ion secondary battery was placed in a constant temperature room at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). Constant current and constant voltage charging (cutoff current 1.0mA (0.02C)) was performed with a charging current of 10mA (0.2C) and a charging termination voltage of 4.2V, followed by constant current discharge at a discharge current of 10mA (0.2C) and a discharge termination voltage of 2.5V. This operation was repeated three times, and then constant current and constant voltage charging (cutoff current 1.0mA (0.02C)) was performed with a charging current of 10mA (0.2C) and a charging termination voltage of 4.2V, followed by constant current discharge at 0.2C and 3C until the discharge termination voltage reached 2.5V, and the discharge capacity was determined for each. The rate characteristic can be expressed as the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 1 below. (Formula 1) Rate characteristic = 3C discharge capacity / 3rd 0.2C discharge capacity × 100 (%) The evaluation criteria for rating characteristics were as follows: ◎ (Excellent) for rating characteristics of 80% or higher, ○ (Good) for those between 70% and 80%, △ (Acceptable) for those between 60% and 70%, and × (Poor) for those below 60%.

[0177] <Evaluation of High-Temperature Cycle Characteristics of Lithium-ion Secondary Batteries> A laminated lithium-ion secondary battery was placed in a constant temperature chamber at 45°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). Constant current constant voltage charging (cutoff current 1.25mA (0.025C)) was performed with a charging current of 50mA (1C) and a charging termination voltage of 4.2V, followed by constant current discharge with a discharge current of 50mA (1C) and a discharge termination voltage of 2.5V. This operation was repeated 100 times. 1C was defined as the current value required to discharge the theoretical capacity of the positive electrode in one hour. The high-temperature cycle characteristics can be expressed by the ratio of the 1C discharge capacity at the 3rd cycle to the 1C discharge capacity at the 100th cycle at 45°C, as shown in Equation 2 below. (Formula 2) High-temperature cycle characteristics = 1C discharge capacity at 100 cycles / 1C discharge capacity at 3 cycles × 100 (%) The evaluation criteria for high-temperature cycle characteristics were as follows: ◎ (Excellent) for high-temperature cycle characteristics of 90% or more, ○ (Good) for 85% or more but less than 90%, △ (Acceptable) for 80% or more but less than 85%, and × (Poor) for less than 80%.

[0178] <Evaluation of gas generation amount in lithium-ion secondary batteries> A laminated lithium-ion secondary battery was placed in a constant temperature room at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). Constant current and constant voltage charging (cutoff current 1.0mA (0.02C)) was performed with a charging current of 10mA (0.2C) and a charging termination voltage of 4.2V, followed by constant current discharge with a discharge current of 10mA (0.2C) and a discharge termination voltage of 2.5V. This operation was repeated three times. Next, ultrapure water at 25°C was placed in a graduated cylinder, and this volume was defined as V01. The laminated lithium-ion battery that had been repeatedly charged and discharged at 25°C was submerged in this graduated cylinder, and the water level in the graduated cylinder was visually read, and this volume was defined as V1. Next, a separately prepared laminated lithium-ion secondary battery was placed in a constant temperature chamber at 60°C and charged with a constant current at a charging current of 25mA (0.5C) and a charging termination voltage of 5.0V using a charge / discharge device (Hokuto Denko Co., Ltd., SM-8). After that, it was charged with a constant voltage of 5.0V for 100 hours. After that, the laminated lithium-ion secondary battery was cooled to 25°C. Subsequently, another graduated cylinder was prepared and filled with ultrapure water at 25°C, and this volume was defined as V02. The laminated lithium-ion battery that had been charged at 60°C was then submerged in this graduated cylinder, and this volume was defined as V2. The gas generation rate was calculated using the following equation 3 for V01, V02, V1, and V2. (Formula 3) Gas generation rate = (V2-V02) / (V1-V01)×100(%) The evaluation criteria for gas emission rates were as follows: a gas emission rate of 90% or more but less than 130% was marked ◎ (Excellent), 130% or more but less than 170% was marked ○ (Good), 170% or more but less than 250% was marked △ (Acceptable), and 250% or more was marked × (Poor).

[0179] (Preparation of CNT dispersion composition) [Example 1-1] 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (B-1) were added to a stainless steel container with a sealed inlet while blowing nitrogen gas into it, and the mixture was stirred with a disperser at 80°C to prepare an 8% solution of dispersant (B-1). Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 7.5 parts of the 8% solution of dispersant (B-1) were added to the stainless steel container with a sealed inlet while blowing nitrogen gas into it, and the mixture was stirred with a disperser until homogeneous. Next, 3 parts of CNT (A-1) were weighed out and added while stirring with a disperser, and batch dispersion was performed in a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsion screen at a speed of 9,000 rpm until the mixture was homogeneous and the dispersed particle size was 200 μm or less as measured by a grind gauge, to prepare a CNT pre-dispersion. Subsequently, the obtained CNT pre-dispersion was supplied and subjected to a circulating dispersion treatment (80% bead filling rate, 12 m / s peripheral speed) with a residence time of 15 minutes using a bead mill (Star Mill LMZ®, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. The pump used in the bead milling process was a rotary pump (with ceramic wetted parts), and the discharge rate was adjusted so that there were 4 passes per minute of residence time, resulting in a total of 60 passes during the 15-minute residence time. Next, the dispersion was supplied to a valve-type high-pressure homogenizer "HC3-5" (product name) manufactured by Maru Machinery Industry Co., Ltd., and subjected to a 15-pass dispersion treatment. The pump used in the homogenizer process was a rotary pump (with ceramic wetted parts). The dispersion treatment was performed at a pressure of 100 MPa, with a flat valve for the homogenizing section, zirconia for the valve material, and a flow rate of 2000 L / H for the CNT dispersion composition. Subsequently, the dispersion liquid was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, with a diameter of 10 cm and equipped with 31 grid screens of 1.3 cm thickness), and after three pass-throughs, the mixture was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series to produce CNT dispersion composition 1.

[0180] [Examples 1-9] 85 parts NMP and 15 parts NaOH (manufactured by Tosoh Corporation, Tosoh Pearl) were added to a plastic container. The mixture was then dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by Silverson) equipped with a fine emulsion screen until the mixture was uniform. Finally, the mixture was passed through a nylon filter with a mesh size of 150 μm using a filtration bell to prepare the NaOH dispersion. While blowing nitrogen gas into a stainless steel container with a sealed inlet, 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (B-1) were added and stirred with a disperser at 80°C to prepare an 8% solution of dispersant (B-1). Then, while blowing nitrogen gas into a stainless steel container with a sealed inlet, 89.34 parts of N-methyl-2-pyrrolidone (NMP), 7.5 parts of the 8% solution of dispersant (B-1), and 0.16 parts of NaOH dispersion were added and stirred with a disperser until homogeneous. Next, 3 parts of CNT (A-1) were weighed out and added while stirring with a disperser, and batch dispersion was performed in a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsion screen at a speed of 9,000 rpm until the entire mixture was homogeneous and the dispersed particle size was 200 μm or less as measured by a grind gauge to prepare a CNT pre-dispersion. Subsequently, the obtained CNT pre-dispersion was supplied and subjected to a circulating dispersion treatment (80% bead filling rate, 12 m / s peripheral speed) with a residence time of 15 minutes using a bead mill (Star Mill LMZ®, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. The pump used in the bead milling process was a rotary pump (with ceramic wetted parts), and the discharge rate was adjusted so that there were 4 passes per minute of residence time, resulting in a total of 60 passes during the 15-minute residence time. Next, the dispersion was supplied to a valve-type high-pressure homogenizer "HC3-5" (product name) manufactured by Maru Machinery Industry Co., Ltd., and subjected to a 15-pass dispersion treatment. The pump used in the homogenizer process was a rotary pump (with ceramic wetted parts). The dispersion treatment was performed at a pressure of 100 MPa, with a flat valve for the homogenizing section, zirconia for the valve material, and a flow rate of 2000 L / H for the CNT dispersion composition. Subsequently, the dispersion liquid was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, diameter: 10 cm, equipped with 31 grid screens with a thickness of 1.3 cm), and after three pass-through processing, the mixture was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series to produce CNT dispersion composition 9.

[0181] [Examples 1-19] While blowing nitrogen gas into a stainless steel container with a sealed inlet, 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (B-1) were added and stirred with a disperser at 80°C to prepare an 8% solution of dispersant (B-1). Then, while blowing nitrogen gas into a stainless steel container with a sealed inlet, 89.48 parts of N-methyl-2-pyrrolidone (NMP), 7.5 parts of the 8% solution of dispersant (B-1), and 0.024 parts of ethanolamine were added and stirred with a disperser until homogeneous. Next, 3 parts of CNT (A-1) were weighed out and added while stirring with a disperser, and batch dispersion was performed in a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsion screen at a speed of 9,000 rpm until the entire mixture was homogeneous and the dispersed particle size was 200 μm or less as measured by a grind gauge to prepare a CNT pre-dispersion. Subsequently, the obtained CNT pre-dispersion was supplied and subjected to a circulating dispersion treatment (80% bead filling rate, 12 m / s peripheral speed) with a residence time of 15 minutes using a bead mill (Star Mill LMZ®, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. The pump used in the bead milling process was a rotary pump (with ceramic wetted parts), and the discharge rate was adjusted so that there were 4 passes per minute of residence time, resulting in a total of 60 passes during the 15-minute residence time. Next, the dispersion was supplied to a valve-type high-pressure homogenizer "HC3-5" (product name) manufactured by Maru Machinery Industry Co., Ltd., and subjected to a 15-pass dispersion treatment. The pump used in the homogenizer process was a rotary pump (with ceramic wetted parts). The dispersion treatment was performed at a pressure of 100 MPa, with a flat valve for the homogenizing section, zirconia for the valve material, and a flow rate of 2000 L / H for the CNT dispersion composition. Subsequently, the dispersion liquid was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and equipped with 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm), and after three pass-through processing, the mixture was passed through two depth filters (NT-T series nonwoven PP depth cartridges, manufactured by 3M, with a filtration accuracy of 20 μm) installed in series to produce the CNT dispersion composition 19.

[0182] [Examples 1-2 to 1-8, 1-17, 1-18, Comparative Examples 1-1 to 1-3] Except for changing the dispersion conditions, CNTs, dispersant, organic solvent type, and amount (parts by mass) listed in Table 2, CNT dispersion compositions 2-8, 17, 18, and comparative CNT dispersion compositions 1-3 were obtained by the same method as in Example 1-1.

[0183] [Examples 1-10 to 1-16, 1-20 to 1-25] CNT dispersion compositions 10-16 and 20-25 were obtained by the same method as in Examples 1-9, except that the dispersion conditions, CNTs, dispersant, organic solvent type, and amount (parts by mass) were changed as shown in Table 2.

[0184] [Comparative Examples 1-4] In an open stainless steel container, 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (B-1) were added and stirred with a disperser at 80°C to prepare an 8% solution of dispersant (B-1). Then, 89.5 parts of N-methyl-2-pyrrolidone (NMP) with a water content of 1,500 ppm and 7.5 parts of the 8% solution of dispersant (B-1) were added to the open stainless steel container and stirred with a disperser until homogeneous. Next, 3 parts of CNT (A-1) were weighed out and added while stirring with a disperser. A fine emulsion screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON) and batch dispersion was performed at a speed of 9,000 rpm until the mixture was homogeneous and the dispersed particle size was 200 μm or less as measured by a grind gauge to prepare a CNT pre-dispersion. Subsequently, the obtained CNT pre-dispersion was supplied and subjected to a circulating dispersion treatment (80% bead filling rate, 12 m / s peripheral speed) with a residence time of 15 minutes using a bead mill (Star Mill LMZ®, manufactured by Ashizawa Finetech Co., Ltd.) filled with 1.0 mm diameter zirconia beads. The pump used in the bead milling process was a rotary pump (with ceramic wetted parts), and the discharge rate was adjusted so that there were 4 passes per minute of residence time, resulting in a total of 60 passes during the 15-minute residence time. Next, the dispersion was supplied to a valve-type high-pressure homogenizer "HC3-5" (product name) manufactured by Maru Machinery Industry Co., Ltd., and subjected to a 15-pass dispersion treatment. The pump used in the homogenizer process was a rotary pump (with ceramic wetted parts). The dispersion treatment was performed at a pressure of 100 MPa, with a flat valve for the homogenizing section, zirconia for the valve material, and a flow rate of 2000 L / H for the CNT dispersion composition. Subsequently, the dispersion liquid was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and equipped with 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm), and after three pass-through processing, the mixture was passed through two depth filters (NT-T series nonwoven PP depth cartridges, manufactured by 3M, with a filtration accuracy of 20 μm) installed in series to prepare CNT comparative dispersion composition 4.

[0185] [Table 2-1]

[0186] [Table 2-2]

[0187] Examples 1-1 to 1-25 and Comparative Examples 1-1 to 1-4 confirmed that a CNT dispersion composition with small particle size and low viscosity can be prepared by ensuring that the total content of iron and cobalt in the CNTs, the aluminum content, and the G / D ratio are within a predetermined range.

[0188] Furthermore, as shown in Table 2, the dispersibility of CNTs improved with increasing flow rate. We hypothesize that higher flow rates increased the impact force in the homogeneous section, allowing for finer dispersion of CNTs and lower viscosity. Additionally, the higher the Vickers hardness of the material in the homogeneous section of the disperser, the better the dispersion was achieved, possibly because it could withstand the impact during dispersion. Moreover, using ceramic or resin materials for the pump and disperser reduced the amount of metallic foreign particles.

[0189] (Example 2-1) <Fabrication of electrode films> Capacity 150cm 3 In a plastic container, 18.8 parts by mass of an NMP solution containing 8% by mass of PVDF (polyvinylidene fluoride, Solvay, Solef #5130) and 5.8 parts by mass of NMP were weighed out. Then, 13.3 parts by mass of CNT dispersion composition 1 were added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro, ARE-310). Subsequently, 98.1 parts by mass of positive electrode active material (BASF Toda Battery Materials LLC, HED® NCM-111 1100) was added, and the mixture was stirred at 2,000 rpm for 2.5 minutes using a rotation / revolution mixer (Awatori Rentaro, ARE-310) to obtain a composite slurry (composite slurry 1).

[0190] Next, the asphalt slurry (asphalt slurry 1) was applied using an applicator, with a basis weight of 20 mg / cm³ per unit area of ​​the electrode. 2 After coating the aluminum foil in this manner, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain the electrode film (electrode film 1). Subsequently, the electrode film (electrode film 1) was rolled using a roll press (Sankmetal, 3t hydraulic roll press) to obtain the positive electrode (positive electrode 1). The basis weight per unit area of ​​the composite layer was 20 mg / cm². 2 The density of the asphalt layer after rolling was set to 3.1 g / cc.

[0191] <Manufacturing of secondary batteries> The positive electrode (positive electrode 1) and the standard negative electrode were punched out to 45mm x 40mm and 50mm x 45mm respectively, and a separator (porous polypropylene film) to be inserted between them was placed in an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Then, in a glove box filled with argon gas, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 1:1:1 (volume ratio) mixture, and further adding 2 parts by mass of VC (vinylene carbonate) as an additive per 100 parts by mass of the mixed solvent, and then dissolving LiPF6 at a concentration of 1M) was injected, and the aluminum laminate bag was sealed to produce a laminate-type lithium-ion secondary battery (secondary battery 1).

[0192] (Examples 2-2 to 2-25, Comparative Examples 2-1 to 2-4) Electrodes 2-25, reference electrodes 1 and 2, secondary batteries 2-25, and reference secondary batteries 1-4 were fabricated using the same method as for the laminate-type lithium-ion secondary battery (secondary battery 1), except that the carbon nanotube dispersion composition was changed to the one shown in Table 3.

[0193] [Table 3]

[0194] As shown in Table 3, secondary batteries equipped with electrodes formed from a CNT dispersion composition using CNTs with a total iron and cobalt content of less than 1,000 ppm, an aluminum content of 3,000 ppm or less, and a G / D ratio of 0.5 to 50, and a water content of 1,500 ppm or less, showed good results in rate characteristics, high-temperature cycle characteristics, and gas generation evaluation.

[0195] On the other hand, secondary batteries using dispersions of Comparative Examples 1 and 2, in which the combined iron and cobalt content of CNTs was 1,000 ppm or more and the aluminum content exceeded 3,000 ppm, all showed poor high-temperature cycling characteristics and gas generation evaluation results. Furthermore, Comparative Example 3, which used CNTs with a G / D ratio of less than 0.5, had poor conductivity and poor rate characteristics, high-temperature cycling characteristics, and gas generation evaluation results. In addition, Comparative Example 4, which had a high water content, also showed poor high-temperature cycling characteristics and gas generation evaluation results.

[0196] As a result, secondary batteries equipped with electrode films manufactured using the CNT dispersion composition produced by the manufacturing method of this embodiment exhibit excellent cycle characteristics and can therefore be widely used as batteries for vehicles such as electric vehicles, stationary power supplies, large electronic devices such as large servers, personal computers, mobile phones, and tablet terminals. In particular, it is evident that by installing secondary batteries according to this embodiment in vehicles, vehicles with high safety and improved fuel efficiency can be obtained. [Explanation of Symbols]

[0197] 31 Valve Seat 32 Impact Rings 33 Homo Valve< / cnt> ​

Claims

1. A carbon nanotube dispersion composition comprising carbon nanotubes satisfying the following (i), (ii), and (iii), a dispersant, and an organic solvent, and satisfying the following (1). (i) The total content of iron and cobalt is less than 1,000 ppm. (ii) The aluminum content is 3,000 ppm or less. (iii) 1,560–1,600 cm⁻¹ in Raman spectrum －１ The maximum peak intensity within the range is G, 1,310–1,350 cm. －１ When the maximum peak intensity within the specified range is denoted as D, the G / D ratio is between 0.5 and 50. (1) The moisture content is 1,500 ppm or less.

2. The carbon nanotube dispersion composition according to claim 1, wherein the carbon nanotubes further satisfy (iv) below. (iv) The surface oxygen content is less than 1.0 atm%.

3. The carbon nanotube dispersion composition according to claim 1, wherein the carbon nanotubes further satisfy (v) below. (v) The amount of water vapor adsorbed at a relative humidity of 90% is 50 mg / g or less.

4. Furthermore, the carbon nanotube dispersion composition according to claim 1 satisfies (2) below. (2) When dynamic viscoelasticity measurements were performed using a rheometer with a 25 mm diameter, 2° cone at 25°C and a frequency of 1 Hz, with strains ranging from 0.01% to 5%, the phase angle exceeded 60°.

5. Furthermore, the carbon nanotube dispersion composition according to claim 1 satisfies (3) below. (3) The amount of metal foreign matter particles determined by the following condition 1 is 1.0 mg or less. <Condition 1> Metallic particles in 20 kg of carbon nanotube dispersion composition are collected using an electromagnet (an electromagnet with a magnetic flux density of 16,000 gauss, a spatial volume of 1.7 L, and 31 grid screens with a diameter of 10 cm and a thickness of 1.3 cm). After washing with an organic solvent, the resulting metallic particles are deposited onto a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic particles on the filter is measured.

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

7. An electrode film formed from the composite slurry described in claim 6.

8. 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 described in claim 7.

9. A vehicle equipped with the secondary battery described in claim 8.

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