Conductive material dispersion, composite material composition for secondary battery electrodes using the same, electrode film, secondary battery

Abstract

To provide a conductive material dispersion having high flowability and a mixture composition for a secondary battery electrode by finely controlling a dispersion state of a conductive material, and further to provide a secondary battery with high output, high capacity and long life.SOLUTION: The problem is solved by using a conductive material dispersion containing a single-layer carbon nanotube and a multi-layer carbon nanotube, a polymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit, and a dispersion medium. Mooney viscosity (ML1+4, 100°C) of the polymer is 20-80. The aliphatic hydrocarbon structural unit includes an alkylene structural unit. A content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass%, and a content of a nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less based on the mass of the polymer. A product (X×Y) of a complex elastic modulus X (Pa) and a phase angle Y(°) by dynamic viscoelasticity measurement of the conductive material dispersion is 30 or more and 3,000 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a conductive material dispersion, a composite material composition for secondary battery electrodes using the same, an electrode film, and a secondary battery. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, possess characteristics such as being small, lightweight, having high energy density, and being able to be repeatedly charged and discharged. Due to these characteristics, secondary batteries are used in a wide range of applications. In the field of secondary batteries, in particular, studies are being conducted to improve the characteristics of secondary batteries by dispersing conductive materials using polymers with good dispersibility, such as fine carbon nanotubes with excellent conductivity or acetylene black with a well-developed structure, as conductive materials for the cathode, which has poor conductivity.

[0003] For example, Patent Document 1 describes a Mooney viscosity (ML) having alkylene structural units and nitrile group-containing monomer units. 1+4 An invention has been reported that uses a copolymer (e.g., hydrogenated nitrile rubber) with a temperature of 40 or less (at 100°C) as a binder composition for secondary battery electrodes. Furthermore, Patent Document 2 describes a carbon nanotube dispersion containing bundled carbon nanotubes and hydrogenated nitrile rubber, and improves the characteristics of secondary batteries by setting the particle size of the dispersed carbon nanotubes in the dispersion or the viscosity of the dispersion to a preferred range.

[0004] Furthermore, Patent Document 3 describes a conductive material dispersion containing bundled carbon nanotubes and hydrogenated nitrile rubber, in which the phase angle at a frequency of 1 Hz during rheometer measurement is 3° to 18°. Since a conductive material dispersion with a phase angle of 3° to 18° has properties closer to solid-like characteristics compared to a low-viscosity conductive material dispersion, it can improve the coating properties and coating stability during electrode manufacturing. In Patent Document 4, a conductive material containing bundled carbon nanotubes and a conductive material dispersion liquid containing hydrogenated nitrile rubber, with a complex elastic modulus (G*|@1Hz) of 20 Pa to 500 Pa at a frequency of 1 Hz during rheometer measurement, has been studied, and an invention has been reported in which the dispersibility of the conductive material dispersion liquid is improved by controlling the complex elastic modulus.

[0005] Also, the finer the conductive material, ideally, an efficient conductive network can be formed. However, the finer the conductive material, the larger the specific surface area and the higher the cohesive force, making it difficult to obtain a highly concentrated and well-dispersed conductive material dispersion liquid. If the concentration of the conductive material is forcibly increased, the dispersion liquid becomes highly viscous and its fluidity deteriorates. In a conductive material dispersion liquid with poor fluidity, when transporting the conductive material dispersion liquid in a tank or the like, or storing and using it for a long time, there may be a problem that it becomes difficult to take it out from the tank or the like. On the other hand, in a dispersion liquid with a low concentration of the conductive material, there are problems such as a lower degree of freedom in design when blending materials such as the active material and the binder, and an increase in the transportation cost per solid content of the conductive material. Therefore, it has been an urgent task to obtain a conductive material dispersion liquid in which fine conductive materials are well dispersed at a high concentration and in a highly fluid state.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] The conductive material dispersions described in Patent Documents 1 to 4 enable the provision of superior secondary batteries by using polymers such as hydrogenated nitrile rubber, which have excellent dispersibility and binding properties. However, further improvements were needed to meet the ever-increasing demand for high output, high capacity, long lifespan, and low cost. Patent Document 1 specifically examines acetylene black as a conductive material, but carbon nanotubes are not sufficiently considered. When fibrous carbon materials such as carbon nanotubes are broken by dispersion or stirring during the manufacturing process of the composite slurry, the conductive network between conductive materials in the electrode film may decrease. Furthermore, when carbon nanotubes with long fiber lengths are included in the composite slurry, the fibers and resin components tend to entangle and aggregate. If the electrode film is manufactured with the fibers not untangled, the conductive network between conductive materials in the electrode film may decrease.

[0008] The conductive material dispersion disclosed in Patent Document 3 has relatively strong solid-like properties, and the conductive material dispersion disclosed in Patent Document 4 has relatively strong elastic behavior. As a result, both have poor fluidity and are unsuitable for transport in tanks or long-term storage. In Patent Document 3, a conductive material dispersion with high solid-like properties is obtained by controlling the phase angle, and then an active material and binder are added to prepare a composition. However, conductive material dispersions with high solid-like properties tend to have high viscosity, which can reduce miscibility with the binder added thereafter. In Patent Document 4, a conductive material dispersion is obtained in which dispersibility and viscosity properties are controlled by the complex modulus, and then an active material and binder are added to prepare a composition. However, controlling the conductive material dispersion only by the complex modulus may not result in sufficient miscibility with the binder added thereafter. For example, when a binder resin is added to a carbon nanotube dispersion in which carbon nanotubes are finely dispersed while maintaining their fiber length, the carbon nanotubes may aggregate or the binder resin may gel, reducing the dispersibility and fluidity of the resin composition.

[0009] Furthermore, because the carbon nanotube fibers are broken during dispersion or stirring, the dispersions obtained in Patent Documents 2-4 have short carbon nanotube fiber lengths, and there is still room for improvement in fully extracting the potential conductivity of the carbon nanotubes. Moreover, the difficulty of using carbon nanotubes with different outer diameters, such as single-walled carbon nanotubes and multi-walled carbon nanotubes, is even higher, and the structural viscosity between the carbon nanotubes is even greater. As a result, the methods for preparing conductive material dispersions disclosed in Patent Documents 2-4 may result in increased viscosity or gelation over time.

[0010] The inventors conducted a detailed comparative study of subtle differences in the dispersion state of conductive materials and found that when fibrous carbon nanotubes are used as conductive materials, it is difficult to control the dispersion state using conventional dispersion indexes. Specifically, while particle size distribution or viscosity have traditionally been used as indicators of dispersion, it was found that even with the same measurement value, the characteristics when used in secondary batteries can differ, and these do not accurately capture the dispersion state of the conductive material. For example, in the case of particle size distribution, non-spherical particles with a high aspect ratio are calculated assuming they are spherical, which easily leads to discrepancies with reality. Furthermore, even if particles larger or smaller than the detectable range are included, the measured value cannot be distinguished from a state that does not contain these particles.

[0011] In the case of viscosity, it is generally said that the better the dispersion state of the conductive material, the lower the viscosity. However, when the aspect ratio of the conductive material is high (especially when it is long and fibrous and easily entangled), even if the conductive material is uniformly and stably dispersed in the dispersion medium, the structural viscosity of the conductive material itself increases its elasticity. Furthermore, when the fibers are broken, the viscosity changes due to two factors: deaggregation and breakage, making it difficult to accurately represent the state of the conductive material based on viscosity alone. When carbon material fibers are broken, the increased contact resistance between carbon materials makes it difficult to form a well-developed conductive network in the electrode, so it is effective to disperse the fibers uniformly while minimizing breakage.

[0012] In other words, the problem that the present invention aims to solve is to provide a conductive material dispersion liquid and a composite material composition for secondary battery electrodes that have high fluidity by precisely controlling the dispersion state of the conductive material. More specifically, it aims to provide a secondary battery with high output, high capacity, and long lifespan. [Means for solving the problem]

[0013] According to the inventors' diligent research, a specific structure and Mooney viscosity (ML) are found to be important. 1+4 We discovered that by dispersing and preparing a polymer having a temperature of 0.5 to 100°C, a dispersion medium, single-walled carbon nanotubes, and multi-walled carbon nanotubes such that the product of the complex modulus X (Pa) and phase angle Y (°) (X × Y), as measured by dynamic viscoelasticity, is between 30 and 3,000, it is possible to disperse the long fibers of carbon nanotubes while maintaining them appropriately without breaking them, thereby forming a well-developed conductive network in the electrode. This makes it possible to provide a secondary battery with high output, high capacity, and long lifespan even with a small amount of conductive material in the electrode.

[0014] In other words, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. [1] A conductive material dispersion comprising a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, and a dispersion medium, The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. The Mooney viscosity (ML1+4, 100℃) of the polymer is between 20 and 80. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 3,000. Conductive material dispersion. [2] The conductive material dispersion according to [1], further containing carbon black. [3] A conductive material dispersion according to [1] or [2], further comprising a fluororesin. [4] A conductive material dispersion according to any of [1] to [3], wherein the complex modulus of elasticity determined by dynamic viscoelastic measurement is 0.1 Pa or more and 200 Pa or less. [5] A conductive material dispersion according to any of [1] to [4], wherein the phase angle determined by dynamic viscoelasticity measurement is 1° or more and 60° or less. [6] The conductive material dispersion according to any one of [1] to [5], wherein the gloss of the film obtained by coating and drying the conductive material dispersion onto a substrate is 5 to 120 as measured at 60°. A composite material composition for secondary battery electrodes, comprising a conductive material dispersion liquid as described in any of [7], [1], to [6]. An electrode film obtained by coating with the composite material composition for secondary battery electrodes described in [8] and [7]. A secondary battery having the electrode film described in [9] and [8].

[0015]

[10] A method for producing a conductive material dispersion, comprising the following step (I-1): The conductive material dispersion comprises a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, a fluororesin, and a dispersion medium. The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. The Mooney viscosity (ML1+4, 100℃) of the polymer is between 20 and 80. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 3,000. A method for producing a conductive material dispersion. (I-1) A step of dispersing a mixed solution containing single-walled carbon nanotubes and multi-walled carbon nanotubes, a polymer, a fluororesin, and a dispersion medium.

[0016]

[11] A method for producing a conductive material dispersion, comprising the steps (II-1) to (II-3) below, The conductive material dispersion comprises a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, a fluororesin, and a dispersion medium. The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. The Mooney viscosity (ML1+4, 100℃) of the polymer is between 20 and 80. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 3,000. A method for producing a conductive material dispersion. (II-1) A step to produce a first conductive material dispersion by dispersing a mixed solution containing single-walled carbon nanotubes, fluororesin, and a dispersion medium. (II-2) A step to produce a second conductive material dispersion by dispersing a mixed solution containing multi-walled carbon nanotubes, a polymer, and a dispersion medium. (II-3) A step of mixing the first conductive material dispersion and the second conductive material dispersion. [Effects of the Invention]

[0017] According to embodiments of the present invention, it is possible to provide a resin composition for secondary battery electrodes having high fluidity and dispersibility. According to another embodiment of the present invention, it is possible to provide a composite slurry for secondary battery electrodes with good dispersibility of carbon nanotubes. According to yet another embodiment of the present invention, it is possible to provide a secondary battery with high output, high capacity, and long lifespan, and an electrode film used therein. [Modes for carrying out the invention]

[0018] The following describes in detail embodiments of the present invention, including conductive materials, polymers, conductive material dispersions, composite compositions for secondary battery electrodes, electrode films, and secondary batteries. The present invention is not limited to the following embodiments, and includes embodiments that are implemented without changing the essence of the invention. The numerical values ​​specified herein are values ​​obtained by the methods disclosed in the embodiments or examples.

[0019] In this specification, carbon nanotubes may be referred to as "CNT". Hydrogenated nitrile rubber may be referred to as "H-NBR" or "dispersant", and N-methyl-2-pyrrolidone may be referred to as "NMP". In this specification, conductive material dispersions may be simply referred to as "dispersion". Also, "electrode composite composition" may be referred to as "composite slurry", and the fiber diameter of carbon nanotubes may be referred to as "outer diameter". In this specification, "Mw" is the weight-average molecular weight in polystyrene terms, determined by gel permeation chromatography (GPC), and "Mn" is the number-average molecular weight in polystyrene terms, determined by GPC. These can be measured by the method described in the [Examples] section.

[0020] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. Unless otherwise noted, the various components mentioned herein may be used individually or in combination of two or more.

[0021] <Conductive material dispersion> The conductive material dispersion of the embodiment of the present invention contains a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, and a dispersion medium. Furthermore, the conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. The Mooney viscosity (ML1+4, 100℃) of the polymer is between 20 and 80. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 3,000.

[0022] <Conductive material> In one embodiment of the present invention, the conductive material includes single-walled carbon nanotubes (single-walled CNTs) and multi-walled carbon nanotubes (multi-walled CNTs). The conductive material dispersion may also contain conductive materials other than single-walled carbon nanotubes and multi-walled carbon nanotubes. Examples of other conductive materials include carbon materials such as carbon black, fullerene, graphene, multi-walled graphene, and graphite. When using conductive materials other than CNTs, carbon black is preferred from the viewpoint of dispersant adsorption performance, and examples of carbon blacks include acetylene black, furnace black, hollow carbon black, and Ketjen black. These carbon blacks may be neutral, acidic, or basic, and oxidized carbon black or graphitized carbon black may be used. Other conductive materials may be used individually or in combination of two or more.

[0023] A carbon nanotube (CNT) has a cylindrical shape formed by winding planar graphite. A single-walled CNT has a structure in which one layer of graphite is wound. A multi-walled CNT has a structure in which two or more layers of graphite are wound. The sidewalls of a CNT do not have to be of a graphite structure. For example, a CNT having sidewalls with an amorphous structure is also considered a CNT in this specification.

[0024] The shape of the CNT is not limited. Examples of such shapes include needle-shaped, cylindrical tubular, fishbone-shaped (fishbone or cup-stacked), playing card-shaped (platelet), and coil-shaped. In this embodiment, the shape of the CNT is preferably needle-shaped or cylindrical tubular. The CNT may be a single shape or a combination of two or more shapes.

[0025] Examples of CNT forms include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes may have these forms individually or in combination of two or more of them.

[0026] The average outer diameter of the CNTs is preferably 1 nm or more, more preferably 3 nm or more. It is also preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. The average outer diameter of the CNTs can be calculated by first observing and imaging the CNTs using a transmission electron microscope, then selecting 300 arbitrary CNTs from the observation images and measuring the outer diameter of each.

[0027] Here, the average outer diameter of single-walled carbon nanotubes may be 0.1 nm to 3 nm, 0.5 nm to 3.0 nm, 0.7 nm to 3.0 nm, or 1.0 nm to 3.0 nm. The average outer diameter of multi-walled carbon nanotubes may be greater than 3 nm and less than or equal to 30 nm, greater than 3 nm and less than or equal to 20 nm, or greater than or equal to 5 nm and less than or equal to 10 nm. The resin composition may include a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes as carbon nanotubes. In this case, the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is preferably 10:1 to 1:10, more preferably 2:1 to 1:10, even more preferably 2:1 to 1:8, and even more preferably 1:1 to 1:6. Since single-walled carbon nanotubes and multi-walled carbon nanotubes have different outer diameters and fiber lengths, the state of good conductive network formation and dispersion stabilization differs. By setting the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes within the above range, entanglement between carbon nanotubes is suppressed, resulting in a dispersion with excellent fluidity.

[0028] The average fiber length of the CNTs is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. It is also preferably 200 μm or less, and more preferably 100 μm or less. The average fiber length of the CNTs can be calculated by first observing and imaging the CNTs using a scanning electron microscope, then selecting 300 arbitrary CNTs from the observation images and measuring the fiber length of each.

[0029] The aspect ratio of a carbon nanotube (CNT) is obtained by dividing its fiber length by its outer diameter. A typical aspect ratio can be determined using the average fiber length and average outer diameter. Conductive materials with higher aspect ratios can achieve higher conductivity when electrodes are formed from them. The aspect ratio of a CNT is preferably 30 or higher, more preferably 50 or higher, and even more preferably 80 or higher. It is also preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

[0030] The specific surface area of ​​CNT is 100m². 2 It is preferable that it be 150m or more / g. 2 It is more preferable that it be 200m or more per gram. 2 It is even more preferable that it be 1200m or more. 2 It is preferable that it be less than or equal to / g, and 1000m 2 It is more preferable that the value be less than or equal to / g. The specific surface area of ​​CNTs is calculated by the BET method using nitrogen adsorption measurement.

[0031] The carbon purity of CNTs is expressed as the carbon atom content (mass%) within the CNT. The carbon purity is preferably 80% by mass, more preferably 90% or higher, even more preferably 95% or higher, and particularly preferably 98% or higher, based on 100% mass of CNT. By setting the carbon purity within the above range, problems such as dendrite formation due to impurities causing short circuits can be prevented.

[0032] To remove or reduce impurities such as metal catalysts and increase carbon purity, high-purity treated CNTs may be used. The method of high-purity treatment is not particularly limited, and known methods can be used. For example, a method may be used in which impurities are evaporated by treating at a high temperature (e.g., 3000°C) under an inert atmosphere. This method is preferable because it can be performed under conditions with relatively little risk of explosion. Alternatively, a method may be used in which a halogen-containing gas (chlorine gas, fluorine gas, carbon tetrachloride gas, carbon tetrafluoride gas, etc.) is mixed with an inert gas and heat-treated to evaporate the halogenated impurities. Since halogenation lowers the boiling point of the impurities, they can be removed at a lower temperature (e.g., 1600°C) compared to when halogenation is not performed, and this method is preferable because it can increase carbon purity without changing the physical properties of the CNTs, such as crystallinity, density, and conductivity. Furthermore, if the CNTs are densified before heat treatment, the amount of processing can be increased while suppressing the scattering of CNTs, and purification can be performed efficiently. Alternatively, a method may be used in which CNTs are impregnated in an acidic or basic solution to dissolve and remove impurities. Treatment with acidic or basic solutions may introduce functional groups to the surface or ends of carbon nanotubes (CNTs). If the amount of functional groups is small, it may improve dispersibility. However, if the amount of functional groups is large, it may decrease conductivity.

[0033] When the CNT is dispersed by a disperser through collision with media such as a bead mill, or when a process of repeatedly passing the disperser over a long period of time is performed, the CNT may be damaged to produce short carbonaceous substances. When short carbonaceous substances are produced, the viscosity of the resin composition decreases, and the gloss of the coating film obtained by coating and drying the resin composition increases. Therefore, judging only from these evaluation results, the dispersion state seems to be good. However, short carbonaceous substances have a high contact resistance and it is difficult to form a conductive network. Therefore, the resin composition produced through such a dispersion treatment may deteriorate the resistance of the electrode. The degree of generation of short carbonaceous substances can be confirmed by methods such as diluting the dispersion liquid, dropping it onto a substrate with a smooth surface and good affinity for the dispersion medium, drying the sample, and observing it with a scanning electron microscope. By adjusting the dispersion conditions or the formulation of the dispersion liquid so that carbonaceous substances of 0.1 μm or less do not occur, an electrode with high conductivity can be obtained.

[0034] The content of CNT is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 1% by mass or more in the non-volatile content of the carbon nanotube dispersion liquid. Also, it is preferably 20% by mass or less, more preferably 10% by mass or less. By setting it within the above range, the CNT can be made to exist well and stably without causing sedimentation or gelation. Also, the content of CNT is appropriately adjusted so that a carbon nanotube dispersion liquid with appropriate fluidity or viscosity can be obtained depending on the specific surface area of the CNT, the mass ratio of single-walled CNTs to multi-walled CNTs, the affinity for the dispersion medium, the dispersibility of the dispersant, and the like.

[0035] When the amount of acidic groups of the CNT is within the following preferred range, the affinity balance among the CNT, the polymer, and the dispersion medium becomes good, and a better conductive material dispersion liquid can be obtained. The amount of acidic groups of the conductive material can be determined by back-titration from the adsorption amount of hexylamine. The conductive material has an amount of acidic groups determined from the adsorption amount of hexylamine of 0.1 μmol / m 2 or more, preferably 0.2 μmol / m 2It is more preferable that the above is true. Also, 0.8 μmol / m³ 2 Preferably, it is 0.7 μmol / m². 2 The following is more preferable: Furthermore, the conductive material preferably has an acidic group content determined from the amount of hexylamine adsorbed, which is 40 μmol / g or more, more preferably 50 μmol / g or more, and even more preferably 120 μmol / g or more, based on the mass of the conductive material. It is also preferably 250 μmol / g or less, and more preferably 220 μmol / g or less.

[0036] <polymer> In one embodiment of the present invention, the polymer is a polymer comprising at least aliphatic hydrocarbon structural units and nitrile group-containing structural units. The aliphatic hydrocarbon structural units of the polymer include alkylene structural units. This polymer may be hydrogenated. Also, the Mooney viscosity of the polymer (ML) 1+4 The temperature (at 100°C) is between 20 and 80, the content of the aliphatic hydrocarbon structural units is between 40% by mass and less than 85% by mass based on the mass of the polymer, and the content of the nitrile group-containing structural units is between 15% by mass and 50% by mass based on the mass of the polymer.

[0037] An aliphatic hydrocarbon structural unit is a structural unit that includes an aliphatic hydrocarbon structure, and preferably a structural unit consisting only of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure includes at least a saturated aliphatic hydrocarbon structure and may further include an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably includes at least a linear aliphatic hydrocarbon structure and may further include a branched aliphatic hydrocarbon structure.

[0038] Examples of aliphatic hydrocarbon structural units include alkylene structural units, alkenylene structural units, alkyl structural units, alkanetriyl structural units, and alkanetetrayl structural units. It is preferable that the aliphatic hydrocarbon structural units include at least alkylene structural units.

[0039] An alkylene structural unit is a structural unit that contains an alkylene structure, and preferably a structural unit consisting only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0040] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1A).

[0041] General formula (1A) [ka]

[0042] In general formula (1A), n represents an integer greater than or equal to 1. n is preferably an integer greater than or equal to 2, more preferably an integer greater than or equal to 3, and particularly preferably an integer greater than or equal to 4. n is preferably an integer less than or equal to 6, and more preferably an integer less than or equal to 5. In particular, n is preferably 4. In this specification, "*" indicates a connection to another structure.

[0043] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1B).

[0044] General formula (1B) [ka]

[0045] In general formula (1B), n represents an integer greater than or equal to 1. It is preferable that n is an integer greater than or equal to 2, and more preferably an integer greater than or equal to 3. It is preferable that n is an integer less than or equal to 5, and more preferably an integer less than or equal to 4. In particular, it is preferable that n is 3.

[0046] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1C).

[0047] General formula (1C) [ka]

[0048] In the general formula (1C), n represents an integer greater than or equal to 1. It is preferable that n is an integer less than or equal to 4, more preferably less than or equal to 3, and even more preferably less than or equal to 2. In particular, it is preferable that n is 2.

[0049] The method for introducing alkylene structural units into a polymer is not particularly limited, but examples include the following methods (1a) or (1b).

[0050] In method (1a), a polymer is produced by a polymerization reaction using a monomer composition containing a conjugated diene monomer. The polymer produced contains monomer units derived from the conjugated diene monomer. In this specification, "monomer units derived from a conjugated diene monomer" may be referred to as "conjugated diene monomer units," and similarly, monomer units derived from other monomers may be omitted. Next, at least a portion of the conjugated diene monomer units are converted into alkylene structural units by hydrogenation. In this specification, "hydrogenation" may be referred to as "hydrogenation." The polymer finally obtained contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0051] Furthermore, each conjugated diene monomer unit includes at least one monomer unit having one carbon-carbon double bond. For example, a 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, includes at least one monomer unit selected from the group consisting of monomer units having a cis-1,4 structure, monomer units having a trans-1,4 structure, and monomer units having a 1,2 structure, and may include two or more monomer units. In addition, each conjugated diene monomer unit may further include monomer units that do not have a carbon-carbon double bond and contain a branch point. In this specification, "branch point" refers to a branch point in a branched polymer, and if a conjugated diene monomer unit includes a monomer unit containing a branch point, the polymer prepared above is a branched polymer.

[0052] In method (1b), a polymer is produced by a polymerization reaction using a monomer composition containing α-olefin monomers. The polymer produced contains α-olefin monomer units. The final polymer obtained contains α-olefin monomer units as alkylene structural units.

[0053] Among these, method (1a) is preferred because it facilitates the production of polymers. The number of carbon atoms in the conjugated diene monomer is 4 or more, preferably 4 to 6. Examples of conjugated diene monomers include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. The alkylene structural unit preferably includes structural units obtained by hydrogenating the conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably includes structural units obtained by hydrogenating the 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer can be used individually or in combination of two or more types.

[0054] Hydrogenation is preferably a method that can selectively hydrogenate conjugated diene monomer units. Examples of known hydrogenation methods include the oil layer hydrogenation method or the aqueous layer hydrogenation method.

[0055] Hydrogenation can be carried out by conventional methods. For example, hydrogenation can be performed by treating a polymer having conjugated diene monomer units with hydrogen gas in the presence of a hydrogenation catalyst while the polymer is dissolved in a suitable solvent. Examples of hydrogenation catalysts include iron, nickel, palladium, platinum, and copper.

[0056] In method (1b), the number of carbon atoms in the α-olefin monomer is 2 or more, preferably 3 or more, and more preferably 4 or more. The number of carbon atoms in the α-olefin monomer is preferably 6 or less, and more preferably 5 or less. Examples of α-olefin monomers include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomer can be used alone or in combination of two or more.

[0057] The alkylene structural unit preferably includes at least one selected from the group consisting of structural units including linear alkylene structures and structural units including branched alkylene structures; more preferably includes at least one selected from the group consisting of structural units consisting only of linear alkylene structures and structural units consisting only of branched alkylene structures; and even more preferably includes at least one selected from the group consisting of structural units represented by formula (1B) and structural units represented by formula (1C).

[0058] The alkylene structural unit may include structural units containing linear alkylene structures and structural units containing branched alkylene structures. When the alkylene structural unit includes structural units containing linear alkylene structures and structural units containing branched alkylene structures, the content of the branched alkylene structure is preferably 70% by mass or less, more preferably 65% ​​by mass or less, based on the mass of the alkylene structural unit (i.e., when the mass of the alkylene structural unit is set to 100% by mass). In particular, it is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. When the polymer includes structural units containing linear alkylene structures and structural units containing branched alkylene structures, the content of the branched alkylene structure is, for example, 1% by mass or more, may be 5% by mass or more, and may be 10% by mass or more, based on the mass of the alkylene structural unit (i.e., when the mass of the alkylene structural unit is set to 100% by mass).

[0059] In aliphatic hydrocarbon structural units, the content of alkylene structural units is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total mass of aliphatic hydrocarbon structural units (i.e., when the mass of aliphatic hydrocarbon structural units is set to 100% by mass). The content of alkylene structural units is, for example, less than 100% by mass, and may be 99.5% by mass or less, 99% by mass or less, or 98% by mass or less, based on the total mass of aliphatic hydrocarbon structural units (i.e., when the mass of aliphatic hydrocarbon structural units is set to 100% by mass). The content of alkylene structural units may be 100% by mass.

[0060] The content of aliphatic hydrocarbon structural units is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass). The content of aliphatic hydrocarbon structural units is less than 85% by mass, preferably 75% by mass or less, and more preferably 70% by mass or less, based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass).

[0061] The nitrile group-containing structural unit is a structural unit containing a nitrile group, preferably a structural unit containing an alkylene structure substituted with a nitrile group, and more preferably a structural unit consisting solely of an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further contain (or consist solely of) an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one.

[0062] The nitrile group-containing structural unit preferably includes a structural unit represented by the following general formula (2A).

[0063] General formula (2A) [ka]

[0064] In general formula (2A), n represents an integer greater than or equal to 2. It is preferable that n is an integer less than or equal to 6, more preferably less than or equal to 4, and even more preferably less than or equal to 3. In particular, it is preferable that n is 2.

[0065] The nitrile group-containing structural unit preferably includes a structural unit represented by the following general formula (2B).

[0066] General formula (2B) [ka]

[0067] In general formula (2B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

[0068] The method for introducing nitrile group-containing structural units into a polymer is not particularly limited, but a method of producing a polymer by polymerization reaction using a monomer composition containing a nitrile group-containing monomer (method (2a)) can be preferably used. The polymer ultimately obtained contains nitrile group-containing monomer units as nitrile group-containing structural units. Examples of nitrile group-containing monomers that can form nitrile group-containing structural units include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. For example, α,β-ethylenically unsaturated group-containing compounds having a nitrile group can be used, specifically acrylonitrile and methacrylonitrile. In particular, from the viewpoint of increasing intermolecular forces between polymers and / or between polymers and dispersed materials (adsorbed materials), it is preferable that the nitrile group-containing monomer contains acrylonitrile. Nitrile group-containing monomers can be used individually or in combination of two or more types.

[0069] The content of nitrile group-containing structural units is 15% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more, based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass). The content of nitrile group-containing structural units is 50% by mass or less, preferably 46% by mass or less, and more preferably 40% by mass or less, based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass). By setting the content of nitrile group-containing structural units within the above range, the adsorption to the dispersed material and affinity to the dispersion medium can be controlled, and the dispersed material can be stably contained in the dispersion medium. Furthermore, the affinity of the polymer to the electrolyte can also be controlled, preventing problems such as the polymer dissolving in the electrolyte within the battery and increasing the resistance of the electrolyte.

[0070] The polymer may contain any structural units. Examples of arbitrary structural units include amide group-containing structural units; carboxyl group-containing structural units; alkenylene structural units; alkyl structural units; and structural units containing branching points, such as alkanetriyl structural units and alkanetetrayl structural units. Structural units containing branching points are different from structural units containing branched alkylene structures and structural units containing branched alkyl structures.

[0071] The amide group-containing structural unit is a structural unit containing an amide group, preferably a structural unit containing an alkylene structure substituted with an amide group, and more preferably a structural unit consisting solely of an alkylene structure substituted with an amide group. The alkylene structure is preferably a linear or branched alkylene structure. The amide group-containing structural unit may further contain (or consist solely of) an alkyl structure substituted with an amide group. The number of amide groups contained in the amide group-containing structural unit is preferably one.

[0072] An alkenylene structural unit is a structural unit that contains an alkenylene structure, and preferably a structural unit consisting only of alkenylene structures. The alkenylene structure is preferably a linear alkenylene structure or a branched alkenylene structure.

[0073] The alkenylene structural unit preferably includes at least one selected from the group consisting of structural units including linear alkenylene structures and structural units including branched alkenylene structures, and more preferably includes at least one selected from the group consisting of structural units consisting only of linear alkenylene structures and structural units consisting only of branched alkenylene structures.

[0074] For example, when a polymer is obtained by the method described in (1a) above, the polymer may contain conjugated diene monomer units having a carbon-carbon double bond within the unit, which may remain in the molecule without being hydrogenated. The polymer ultimately obtained may contain conjugated diene monomer units having a carbon-carbon double bond within the unit as alkenylene structural units.

[0075] Alkyl structural units are structural units that contain an alkyl structure (however, they do not fall under other aliphatic hydrocarbon structural units such as branched alkylene structural units, nitrile group-containing structural units, amide group-containing structural units, or carboxyl group-containing structural units), and are preferably structural units consisting only of alkyl structures. The alkyl structure is preferably a linear alkyl structure or a branched alkyl structure.

[0076] The alkyl structural unit preferably includes at least one selected from the group consisting of a linear alkyl structure and a branched alkyl structure, and more preferably includes at least one selected from the group consisting of a linear alkyl structure only and a branched alkyl structure only.

[0077] For example, when obtaining a polymer by the method described in (1a) or (1b) above, it is preferable that the polymer has at least hydrogenated conjugated diene monomer units or α-olefin monomer units introduced as terminal groups of the polymer. The final polymer may also contain these monomer units as alkyl structural units.

[0078] An alkantriyl structural unit is a structural unit that includes an alkantriyl structure, and preferably a structural unit consisting only of an alkantriyl structure. An alkanetetrayl structural unit is a structural unit that includes an alkanetetrayl structure, and preferably a structural unit consisting only of an alkanetetrayl structure.

[0079] For example, when obtaining a polymer via the method described in (1a) above, the polymer may contain conjugated diene monomer units, which are monomer units that do not have carbon-carbon double bonds within the unit and include branching points. In this case, the final polymer obtained is a branched polymer, and may contain conjugated diene monomer units as aliphatic hydrocarbon structural units including branching points, such as alkanetriyl structural units and alkanetetrayl structural units. When the aliphatic hydrocarbon structural units include structural units including branching points, the polymer is a branched polymer. The branched polymer may also be a network polymer. A polymer containing structural units including branching points can be adsorbed three-dimensionally onto the dispersed material, thereby improving dispersibility and stability.

[0080] A preferred embodiment of the polymer is one in which the total content of aliphatic hydrocarbon structural units and nitrile group-containing structural units contained in the polymer is 80% by mass or more and 100% by mass or less, based on the mass of the polymer. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0081] In this specification, the content of structural units can be determined by the amount of monomer used, NMR (nuclear magnetic resonance), and / or IR (infrared spectroscopy) measurements.

[0082] The polymer in the embodiments of the present invention has a Mooney viscosity (ML). 1+4 The present invention is characterized by having a Mooney viscosity (at 100°C) of 20 or more and 80 or less. The Mooney viscosity of the polymer in this invention is 20 or more, preferably 30 or more, and more preferably 40 or more. It is also 80 or less, preferably 70 or less, and more preferably 65 or less. The above polymer has a "Mooney viscosity (ML)" 1+4The viscosity can be measured at 100°C in accordance with JIS K6300-1. By setting the Mooney viscosity within the above range, it is thought that an appropriate repulsive force can be provided when the conductive material is adsorbed, thereby improving dispersion stability. If the Mooney viscosity falls below the above range, there is a concern that the solubility in the solvent will increase, leading to an imbalance between the conductive material and the dispersion medium. Furthermore, if the Mooney viscosity exceeds the above range, the viscosity of the conductive material dispersion may become too high, reducing the energy transfer efficiency of the disperser, or metal foreign matter from the raw materials may not be efficiently removed by methods such as magnetic removal, filtration, or centrifugation, potentially leading to a decrease in battery performance due to residual metal foreign matter.

[0083] There are no particular limitations on the method for adjusting the Mooney viscosity of a polymer, but for example, the Mooney viscosity can be adjusted by changing the composition of the polymer (structural unit types and content, hydrogenation rate, etc.), structure (linearity, etc.), molecular weight, and manufacturing conditions (polymerization temperature, amount of molecular weight adjusting agent, etc.). Specifically, the Mooney viscosity of a polymer can be adjusted by the following methods. In method (2a), the Mooney viscosity is reduced by increasing the amount of molecular weight modifier used in the production of the polymer. In method (2b), the Mooney viscosity of the polymer is reduced by modifying it, for example, by adding a base to hydrolyze the nitrile groups contained in the nitrile group-containing structural units of the polymer. In method (2c), the Mooney viscosity is reduced by applying a mechanical shear force to the polymer.

[0084] The method described in (2b) above may also be adjusted by adding a base when preparing a polymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units. Alternatively, a polymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units that has already been prepared may be dissolved in a solvent in which it can be dissolved, and then adjusted by adding a base. The base to be added can be at least one selected from the group consisting of inorganic bases and organic hydroxides (organic bases). When adjusting by adding a base, applying heat that does not cause the solvent to ignite or boil can reduce the Mooney viscosity in a shorter time.

[0085] Examples of inorganic bases include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates, or alkoxides of alkali metals or alkaline earth metals; and ammonium hydroxide. Among these, hydroxides or alkoxides of alkali metals or alkaline earth metals are preferred from the viewpoint of easily supplying cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkali metal alkoxides include lithium methoxide, lithium ethoxide, lithium propoxide, lithium t-butoxide, lithium n-butoxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium t-butoxide, sodium n-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium t-butoxide, and potassium n-butoxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, and sodium t-butoxide. The metal contained in the inorganic base may be a transition metal.

[0086] Organic hydroxides are salts containing an organic cation and a hydroxide ion. Examples of organic hydroxides include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, and benzyltrimethylammonium hydroxide. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide.

[0087] The amount of base used is preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of polymer. The amount of base used is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, based on the mass of polymer. If the amount used is too small, a decrease in Mooney viscosity tends not to occur. If the amount used is too large, it may cause corrosion inside the dispersion device and / or battery.

[0088] In method (2b), the reduction of Mooney viscosity can be achieved by mixing a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing monomer units with a base and a solvent. Any additional components may be mixed. There are no restrictions on the order in which the polymer, base and solvent are added to the container or the method of mixing them. They may be added to the container simultaneously; the polymer, base and solvent may be added to the container separately; or either the polymer or the base, or both, may be mixed with the solvent to prepare a polymer-containing solution and / or a base-containing solution, and then the polymer-containing solution and / or the base-containing solution may be added to the container. In particular, a method of adding a base dispersion, in which the base is dispersed in the solvent, to a polymer solution, in which the polymer is dissolved in the solvent, while stirring is preferred, as this allows for efficient modification of the nitrile groups. A disperser or homogenizer can be used for stirring. The solvents described later can be used.

[0089] There are no restrictions on the temperature during mixing, but heating to 30°C or higher can accelerate the denaturation process. Additionally, small amounts of water and / or alcohol may be added to the container to promote polymer denaturation. Water and / or alcohol may be added to the container while mixing the polymer and base, before adding the polymer and base, or simultaneously with or immediately after the polymer and base. Furthermore, if the polymer, base, or any optional components used are highly hygroscopic, water may be included as absorbed water. The amount of water and / or alcohol is preferably 0.05 to 20% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.05 to 1% by mass, based on the mass of the polymer.

[0090] Examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, and thiodiglycol. Alcohols can be used individually or in combination of two or more. Hydrolysis is preferably carried out in the presence of at least one substance selected from the group consisting of methanol, ethanol, butanol, hexanol, and water, and is particularly preferably carried out in the presence of water.

[0091] The method described in (2c) above may be adjusted by applying mechanical shear force when preparing a polymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units, or by dissolving a polymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units that has already been prepared in a solvent in which it can be dissolved, and then applying mechanical shear force. The Mooney viscosity can also be reduced by applying mechanical shear force to the polymer before dissolution using a roll or kneader, but it is more preferable to apply shear force to the polymer solution because it is more efficient to use the polymer as a dispersant when it is dissolved in a solvent in which it can be dissolved.

[0092] Methods for applying shear force to a polymer solution include using dispersion means such as homogenizers and Silverson mixers. While shear force can also be applied using dispersers, it is preferable to use dispersion means that can apply higher shear force, such as homogenizers and Silverson mixers. Methods for applying mechanical shear force to a polymer before dissolution include using dispersion means such as kneaders and two-roll mills.

[0093] <Dispersion medium> In one embodiment of the present invention, the dispersion medium is not particularly limited as long as it is miscible with the polymer of the above embodiment. In this specification, "miscible with polymer" means that when 0.5 g of polymer is dissolved in 100 g of dispersion medium at 25°C, the insoluble matter is 10% by mass or less. The insoluble matter can be calculated by filtering the undissolved polymer from the solution to recover the undissolved polymer, then drying the recovered polymer with hot air and measuring its mass. The dispersion medium is preferably capable of dissolving the polymer, and more preferably a high dielectric constant solvent capable of dissolving the polymer. In this specification, "capable of dissolving the polymer" means that when 0.5 g of the polymer is dissolved in 100 g of the dispersion medium at 25°C, no insoluble matter can be visually detected, and the solution is clear and transparent. When a dispersion medium capable of dissolving the polymer is used, a good dispersion state can be easily obtained.

[0094] In one embodiment, the dispersion medium 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" preferably has a relative permittivity value of 25 or higher at 20°C, as described in a solvent handbook or the like. When a conductive material dispersion is prepared using a high dielectric constant solvent as the dispersion medium, the interaction between the nitrile groups contained in the polymer of the above embodiment, the conductive material, and the dispersion medium can be enhanced. From the viewpoint of polymer solubility, the relative permittivity of the high dielectric constant solvent is preferably 60 or less, and more preferably 50 or less, at 20°C. In one embodiment, the relative permittivity of the high dielectric constant solvent may preferably be 30 to 50.

[0095] In one embodiment, the dispersion medium is preferably a non-aqueous dispersion medium. The polymers in the above embodiment tend to have low solubility in water. Therefore, if water is present in the conductive material dispersion, it tends to be difficult to obtain the desired good dispersion state. Accordingly, it is preferable that the dispersion medium is 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 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. Even when a conductive material dispersion is prepared without the addition of water, the conductive material dispersion may contain about 0.1% by mass of water due to moisture absorption, etc. From the above viewpoint, the dispersion medium is preferably an organic solvent, and more preferably a polar organic solvent that does not donate protons. As a high dielectric constant solvent capable of dissolving polymers, non-proton-donating polar organic solvents can be used. Examples of non-proton-donating polar organic solvents 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. In one embodiment, the dispersion medium preferably contains an amide-based organic solvent, and more preferably contains 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 conductive material dispersion, thus easily improving the storage stability of the conductive material dispersion.

[0096] <Other optional ingredients> A conductive material dispersion, which is one embodiment of the present invention, may optionally contain other additives such as dispersants, wetting agents, surfactants, pH adjusters, wetting and penetrating agents, leveling agents, other conductive materials, and polymer components other than the polymer of the present invention, as long as they do not hinder the objectives of the present invention. These additives can be added at any time, such as before, during, or after the preparation of the dispersion, or during the preparation of the electrode-forming composition.

[0097] (Other dispersants) Other dispersants besides the polymers in the above embodiments can be known dispersants suitable for secondary batteries. In particular, it is preferable that at least one is selected from polyvinylpyrrolidone, polyvinyl alcohol, and polyvinyl acetal. The other dispersants may have other substituents introduced into them or may be modified. When using a dispersant other than the polymer of the above embodiment, the weight-average molecular weight is preferably 30,000 or less, more preferably 20,000 or less, and preferably 3,000 or more. If it falls outside this range, there is a concern that it may hinder the adsorption between the polymer of the above embodiment and the conductive material.

[0098] One embodiment of the conductive material dispersion may further contain a fluororesin in addition to the polymer. The fluororesin is a fluorine-containing resin that has excellent heat resistance, chemical resistance, and tackiness, and functions as a binder resin. The fluororesin may have a structure in which the hydrogen atoms of polyethylene are replaced with fluorine or trifluoromethyl. Examples of fluororesins include homopolymers such as polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), and polychlorotrifluoroethylene (PCTFE); and copolymers such as perfluoroalkoxyalkanes (PFA), perfluoroethylenepropene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and tetrafluoroethylene-perfluorodioxysol copolymer (TPE / PDD). These may be used individually or in combination of two or more. Among fluororesins, polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), resins having these structural units, modified versions thereof, or combinations thereof are preferred in terms of resistance. Among these, polyvinylidene fluoride-based resins are particularly preferred, such as homopolymers of polyvinylidene fluoride; copolymers of polyvinylidene fluoride with hexafluoropropylene, tetrafluoroethylene, etc. Polyvinylidene fluoride-based resins may be modified, for example, by introducing acidic groups such as carboxyl groups. Fluororesins may be used individually or in combination of two or more types.

[0099] The weight-average molecular weight (Mw) of the fluororesin is preferably 1,000,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 500,000 to 1,500,000, in order to maintain a good balance between resistance, adhesion, and resin viscosity. The glass transition temperature of the fluororesin is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 0°C or lower, from the viewpoint of electrode film formation.

[0100] Examples of commercially available polyvinylidene fluoride and its modified forms include the KF Polymer series from Kureha Corporation, such as "W#7300, W#7200, W#1700, W#1300, W#1100, W#9700, W#9300, W#9100, L#7305, L#7208, L#1710, L#1320, L#1120," and the solvay Solf series from Solvay, such as "6008, 6010, 6012, 1015, 6020, 5130, 9007, 460, 41308, 11010, 21510, 31508, 60512" (all are product names).

[0101] <Method for manufacturing conductive material dispersion> The conductive material dispersion in the embodiment of the present invention is not particularly limited, but it is preferable to manufacture it by mixing CNTs, a polymer, and a dispersion medium and performing a dispersion treatment using a dispersion apparatus to finely disperse them. The dispersion treatment can be performed in two or more stages by arbitrarily adjusting the timing of adding the materials used.

[0102] The conductive material dispersion of this embodiment can be prepared by various conventionally known methods. A carbon nanotube dispersion may be prepared and used by dispersing a mixture containing single-walled carbon nanotubes, multi-walled carbon nanotubes, a polymer, a dispersion medium, and optionally other components, or a dispersion of single-walled carbon nanotubes and a dispersion of multi-walled carbon nanotubes may be prepared separately and then used. The order in which single-walled carbon nanotubes, multi-walled carbon nanotubes, polymers, and dispersion media are mixed is not particularly limited; they may be added sequentially, or two or more may be added simultaneously. For example, polymers may be added to single-walled carbon nanotubes and multi-walled carbon nanotubes, or polymers may be added to multi-walled carbon nanotubes and dispersed, and then single-walled carbon nanotubes may be added and dispersed further. Alternatively, a dispersion of multi-walled carbon nanotubes may be prepared, and then a dispersion of single-walled carbon nanotubes may be added simultaneously or sequentially to prepare a conductive material dispersion. In particular, the method of preparing dispersions of single-walled carbon nanotubes and multi-walled carbon nanotubes separately and then mixing the obtained dispersions is preferred from the viewpoint of obtaining a uniformly dispersed dispersion without the formation of entangled aggregates of carbon nanotubes.

[0103] The conductive material dispersion of this embodiment may contain a fluororesin in addition to the polymer and solvent mentioned above. The order in which the single-walled carbon nanotubes, multi-walled carbon nanotubes, polymer, dispersion medium, and fluororesin are mixed is not particularly limited; they may be added sequentially, or two or more of them may be added simultaneously. For example, a polymer may be added to single-walled carbon nanotubes and multi-walled carbon nanotubes at the same time as a fluororesin is added. Alternatively, a polymer and a fluororesin may be added to multi-walled carbon nanotubes simultaneously or sequentially and dispersed, and then single-walled carbon nanotubes may be further added and dispersed. Another method is to prepare a dispersion by adding a polymer to multi-walled carbon nanotubes, and then prepare a dispersion by adding a polymer to single-walled carbon nanotubes, and then simultaneously or sequentially add the fluororesin to this dispersion to prepare a conductive material dispersion. Furthermore, a dispersion may be prepared by adding a polymer to multi-walled carbon nanotubes, and separately, a single-walled carbon nanotube solution containing a fluororesin may be prepared by adding a fluororesin to single-walled carbon nanotubes, and then simultaneously or sequentially add these to the dispersion to prepare a conductive material dispersion.

[0104] In particular, manufacturing method (I): a method including the steps of (I-1) below, or manufacturing method (II): a method including the steps of (II-1) to (II-3) below, is preferred from the viewpoint of suppressing the aggregation of carbon nanotubes and the gelation of fluororesin, and (II) a method including the steps of (2-1) to (2-3) below is more preferred. ·Manufacturing method (I) (I-1) A step of dispersing a mixed solution containing single-walled carbon nanotubes and multi-walled carbon nanotubes, a polymer, a fluororesin, and a dispersion medium. ·Manufacturing method (II) (II-1) A step to produce a first conductive material dispersion by dispersing a mixed solution containing single-walled carbon nanotubes, fluororesin, and a dispersion medium. (II-2) A step to produce a second conductive material dispersion by dispersing a mixed solution containing multi-walled carbon nanotubes, a polymer, and a dispersion medium. (II-3) A step of mixing the first conductive material dispersion and the second conductive material dispersion.

[0105] Examples of dispersion devices include kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, annular bead mills, attritors, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers. In particular, from the viewpoint of promoting wetting of the conductive material and dissolving coarse particles, it is most preferable to use a high-shear mixer in the initial dispersion step, followed by a high-pressure homogenizer from the viewpoint of dispersing while maintaining the aspect ratio of the conductive material. Furthermore, by dispersing with a bead mill after dispersion with a high-pressure homogenizer, the dispersion state can be made uniform while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 40 to 150 MPa, and more preferably 60 to 120 MPa.

[0106] Dispersion methods using a dispersion device include batch dispersion, pass-through dispersion, and circulating dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method of dispersion using only the dispersion device itself, without the use of piping. Because it is easy to handle, it is preferable for small-scale production. Pass-through dispersion is a dispersion method in which the dispersion device is equipped with a tank to supply the liquid to be dispersed via piping and a tank to receive the liquid to be dispersed, and the liquid is dispersed by passing it through the dispersion device. Circulating dispersion is a method in which the liquid to be dispersed, after passing through the dispersion device, is returned to the tank to supply the liquid and dispersed while being circulated. In all cases, dispersion progresses as the processing time increases, so it is sufficient to repeat the pass-through or circulation until the desired dispersion state is achieved, and the processing volume can be increased by changing the size of the tanks or the processing time. Pass-through dispersion is preferable to circulating dispersion because it is easier to achieve a uniform dispersion state. Circulating dispersion is preferable to pass-through dispersion because the work and manufacturing equipment are simpler. In the dispersion process, the disintegration of aggregated particles, the loosening of conductive materials, wetting, stabilization, etc., proceed sequentially or simultaneously. Since the final dispersion state differs depending on how these processes proceed, it is preferable to control the dispersion state in each dispersion process by using various evaluation methods. For example, this can be controlled by the method described in the examples.

[0107] [Complex modulus of elasticity and phase angle] The dispersibility of a conductive material in a conductive material dispersion can be evaluated by its complex modulus and phase angle, measured by dynamic viscoelasticity. In this specification, the complex modulus and phase angle of the resin composition are measured at 25°C and a frequency of 1 Hz. For details, these can be measured by the method described in the examples. The complex modulus of a conductive material dispersion indicates its hardness. When the conductive material is nearly spherical, or when the fiber length of the carbon nanotubes is broken and shortened, the complex modulus tends to be smaller as the dispersibility of the conductive material improves and as the viscosity of the conductive material dispersion decreases. However, when the fiber length of the carbon nanotubes is large, especially when carbon nanotubes of different fiber lengths are used in combination as in the present invention, even if the conductive material is uniformly and stably unraveled in the medium, the complex modulus may be high due to the structural viscosity of the conductive material itself. Furthermore, the complex modulus changes not only due to the dispersion state of the conductive material, but also due to the entanglement of the conductive material, polymer, and other resin components, or the intermolecular forces between them.

[0108] In one embodiment, the complex modulus of elasticity of the conductive material dispersion, as measured by dynamic viscoelasticity measurement, is preferably 0.1 Pa or higher, more preferably 0.3 Pa or higher, and even more preferably 0.5 Pa or higher. It is also preferably 300 Pa or lower, more preferably 200 Pa or lower, and even more preferably 100 Pa or lower. More preferably, it may be between 0.1 Pa and 100 Pa. When the complex modulus of elasticity is within the above range, it becomes easy to obtain (X × Y) values ​​within a predetermined range described later, and a uniform and well-dispersed state can be obtained while maintaining the length of the CNTs.

[0109] The phase angle refers to the phase shift of the stress wave when the strain applied to the conductive material dispersion is considered as a sine wave. For a purely elastic material, the stress wave is in phase with the applied strain, resulting in a phase angle of 0°. On the other hand, for a purely viscous material, the stress wave is 90° ahead. For typical viscoelasticity measurement samples, the phase angle is greater than 0° and less than 90°, resulting in a sine wave. If the conductive material is nearly spherical, or if the carbon nanotube fiber length is broken and shortened, the phase angle approaches 90°, which is the case for a purely viscous material, if the dispersion of the conductive material in the dispersion is good. However, similar to the complex modulus, if the CNTs themselves have structural viscosity in the conductive material dispersion, the phase angle may be low even if the CNTs are uniformly and stably dissolved in the dispersion medium. Also, similar to the complex modulus, it changes not only due to the dispersion state of the CNTs, but also due to the entanglement of the CNTs, dispersant, and other resin components, or the influence of their intermolecular forces.

[0110] In one embodiment, the phase angle measured by dynamic viscoelasticity measurement of the conductive material dispersion is preferably 1° or more, more preferably 3° or more, even more preferably 5° or more, and particularly preferably 10° or more. It may also be 90° or less, preferably 85° or less, more preferably 80° or less, and even more preferably 60° or less. When the phase angle is within the above range, it becomes easy to obtain (X×Y) values ​​within the desired range described later, and a uniform and well-dispersed state can be obtained while maintaining the length of the CNTs.

[0111] In one embodiment, the average fiber length of the CNTs in the dispersion (after dispersion treatment) may preferably be in the range of 0.1 to 50 μm, and more preferably in the range of 0.3 to 40 μm. In another embodiment, the average fiber length of the CNTs may be in the range of 0.5 μm to 40 μm, and more preferably in the range of 0.5 to 30 μm. A well-developed conductive network is formed by uniformly and effectively dispersing CNTs with large fiber lengths while maintaining their length above a certain level. In particular, an efficient conductive network is formed by dispersing single-walled CNTs and multi-walled CNTs with different outer diameters and fiber lengths, i.e., different dispersibility properties, at an optimal degree of dispersion while maintaining their respective fibers appropriately without breaking them, and then stably unraveling them. Therefore, it is not sufficient for the conductive material dispersion to simply have low viscosity and good (apparent) dispersibility; as seen in the embodiments of the present invention, it is particularly effective to determine the dispersion state by combining the complex modulus and phase angle with conventional indicators such as viscosity. From this viewpoint, the embodiments of the present invention are characterized by adjusting the product (X×Y) of the complex modulus X (Pa) and the phase angle Y (°) to a specific range, as will be described later. With this feature, when the complex modulus and phase angle are set to the above range as described above, the adjustment of the (X×Y) value becomes easy, and a conductive material dispersion with good conductivity and electrode strength (adhesion) can be easily obtained.

[0112] In one embodiment, the conductive material dispersion has a product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) that is between 30 and 3,000. When the above product falls within the above specific range in the conductive material dispersion, an electrode film can be obtained that has high concentration and high fluidity, and has very good conductivity. The product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) is 30 or more, preferably 40 or more, more preferably 50 or more, and even more preferably 100 or more. It is also 3,000 or less, preferably 2,500 or less, more preferably 1,700 or less, even more preferably 1,500 or less, and even more preferably 1,400 or less. Furthermore, it is preferable that the resin composition satisfies the above-mentioned preferred range for the product of the complex modulus X (Pa) and the phase angle Y (°), and that the complex modulus and phase angle measured by dynamic viscoelasticity measurement each satisfy the above-mentioned preferred range.

[0113] [Glossy] The dispersibility of a conductive material in a conductive material dispersion can also be evaluated by measuring the gloss at 60° (i.e., the intensity of reflected light at 60° of the incident angle) of a coating obtained by coating a smooth glass substrate and baking it dry. When light is incident on the coating, the better the dispersion, the smoother the surface of the coating becomes, resulting in higher gloss. Conversely, if the dispersion is poor, light scattering occurs due to the irregularities on the surface of the coating, resulting in lower gloss. The gloss at 60° can be measured by the method described in the examples. The glossiness at 60° is preferably 5 or higher, more preferably 10 or higher, even more preferably 30 or higher, particularly preferably 50 or higher, and most preferably 70 or higher. It is also preferably 120 or lower, and even more preferably 110 or lower. By setting it within the above range, a conductive material dispersion with an appropriate dispersion state can be obtained. If it is below the above range, aggregated conductive material will be present, and if it is above the above range, many finely cut conductive material fragments will be generated, which may make it difficult to form an efficient conductive network.

[0114] [Viscosity and TI value] The viscosity of the conductive material dispersion is preferably 10 mPa·s or more and less than 10,000 mPa·s when measured using a B-type viscometer at 25°C and 60 rpm, more preferably 10 mPa·s or more and less than 3,000 mPa·s, and even more preferably 10 mPa·s or more and less than 2,000 mPa·s.

[0115] The TI value of a conductive material dispersion can be calculated by dividing the viscosity (mPa·s) at 60 rpm, measured with a B-type viscometer, by the viscosity (mPa·s) at 6 rpm. A TI value of less than 7.0 is preferable, more preferably between 1.0 and 6.0, even more preferably between 1.5 and 6.0, and even more preferably between 1.5 and 4.0. A higher TI value indicates greater structural viscosity due to entanglement of conductive materials, polymers, and other resin components, or their intermolecular forces. A lower TI value indicates lower structural viscosity. By setting the TI value within the above range, it is possible to suppress entanglement of conductive materials, polymers, and other resin components while allowing these intermolecular forces to act appropriately.

[0116] The dispersion state of the conductive material in a conductive material dispersion is determined by the cumulative particle size D in the volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution analysis. 50 However, it can be evaluated. A size of 4 μm or larger is preferable. The cumulative particle size D was determined using a laser diffraction / scattering particle size analyzer. 50 Therefore, the particle size of aggregated conductive material particles can be estimated from the scattered light intensity distribution by the particles. Cumulative particle size D 50 The cumulative particle size D is preferably 4 μm or larger, more preferably 8 μm or larger, and even more preferably 10 μm or larger. It is also preferably 100 μm or smaller, more preferably 50 μm or smaller, and even more preferably 30 μm or smaller. 50 By adjusting the above range, carbon nanotubes can be unraveled in the dispersion without rupturing, and a carbon nanotube dispersion with long conductive paths can be obtained. In addition, the viscosity increase due to the structural viscosity between carbon nanotubes can be suppressed, achieving both conductivity and stability.

[0117] The average fiber length of the CNTs in the conductive material dispersion is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. It is also preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The larger the fiber length of the CNTs in the conductive material dispersion, the more efficiently a conductive network can be formed with a small amount, and the amount of conductive material required in the battery electrode can be reduced. However, CNTs with long fiber lengths have strong cohesive forces and are difficult to disperse, and furthermore, carbon nanotubes are prone to breaking during the dispersion process, making it difficult to control the fiber length of the carbon nanotubes. When the average fiber length of the CNTs in the conductive material dispersion containing single-walled carbon nanotubes is within the above range, a good conductive network can be formed, and the amount of conductive material required in the battery electrode can be reduced. In addition, both dispersibility and stability can be achieved, and good dispersion can be maintained in the electrode film slurry and / or in the electrode film. The average fiber length of CNTs in a conductive material dispersion can be calculated by observing a sample prepared by dropping a resin composition diluted 50 times with a non-aqueous solvent such as NMP onto a substrate and drying it, then selecting 300 random CNTs from the observation image and measuring the fiber length of each.

[0118] [pH] The conductive material dispersion in the embodiments of the present invention is preferably substantially water-free. The "pH" of the conductive material dispersion in the embodiments of the present invention refers to the value measured using a general pH meter after adjusting the conductive material dispersion by adding water so that the solid content concentration after adding water becomes 50%, compared to 100% when the solid content concentration before adding water is 100%. For example, it can be measured by the following method. A conductive material dispersion with a solid content of 5% is stirred with a disperser or similar device, and water is added until the solid content of the conductive material dispersion becomes 2.5%. After uniform stirring, the pH of the conductive material dispersion can be measured at 25°C using a benchtop pH meter (Seven Compact S220 Expert Pro, manufactured by Mettler Toledo). The pH of the conductive material dispersion is preferably 8.0 or higher. It is also preferably 12.0 or lower, and more preferably 11.0 or lower. Adjusting the pH within this range improves the wettability of the CNTs and enhances the polymer's dispersant properties. If the pH exceeds this range, problems such as corrosion of various raw materials and casing materials within the battery, or gelation of the binder, are more likely to occur.

[0119] The pH of the conductive material dispersion in the embodiments of the present invention can be adjusted by (1) the amount of metal hydroxide contained in the CNTs, (2) the type and amount of functional groups on the CNT surface, and (3) the type and amount of bases added. By adjusting the pH by considering all of the above factors (1) to (3), it is possible not only to improve the wettability of the CNTs, but also to stabilize single-walled CNTs and multi-walled CNTs with different dispersibility properties without them competing for the dispersants that contribute to the dispersion of each, thereby obtaining a conductive material dispersion that is excellent not only in dispersibility but also in stability. Furthermore, it is preferable to adjust the pH of the conductive material dispersion to an appropriate range in order to obtain a buffering effect that responds to pH changes when mixing with active materials and binder resins added when manufacturing the composite composition.

[0120] As described above, CNTs contain residual metals, metal oxides, and metal hydroxides used as catalysts during their manufacturing process. The pH can be adjusted by controlling the amount of metal hydroxides, in particular, as described in (1) above, among the residual metals in the CNTs. Furthermore, the residual metals and carbon purity of CNTs can be adjusted by conventionally known purification methods.

[0121] The functional groups on the CNT surface as described in (2) above are not particularly limited, but examples include carboxyl groups, sulfo groups, and hydroxyl groups. The method for introducing functional groups to CNTs is not particularly limited. For example, to introduce carboxyl groups to CNTs, heating with an oxidizing acid is sufficient. This operation is relatively easy and is preferable because it allows for the addition of highly reactive carboxyl groups. Examples of oxidizing acids include concentrated nitric acid, hydrogen peroxide, a mixture of sulfuric acid and nitric acid, and aqua regia. When using concentrated nitric acid in particular, its concentration is preferably 5% by mass or more, and more preferably 60% by mass or more. Heating can be carried out by conventional methods, but the temperature is preferably below the boiling point of the acid used. For example, with concentrated nitric acid, a range of 50 to 130°C is preferred. The heating time is preferably in the range of 30 minutes to 20 hours, and more preferably in the range of 1 hour to 8 hours. In the embodiments of the present invention, in terms of using single-walled CNTs and multi-walled CNTs with different dispersibility in combination, it is preferable that the carbon nanotubes do not have acidic functional groups such as carboxyl groups and sulfo groups. If the carbon nanotube dispersion contains a large number of acidic functional groups, there is a risk that it may gel during storage.

[0122] The base added for pH adjustment as described in (3) above is not particularly limited, and specifically, at least one of the base species mentioned above can be used.

[0123] The following factors are considered to be the reasons why adjusting the pH to a predetermined value improves dispersibility. However, the reasons for improved dispersibility are not limited to the factors listed in (1) to (4) below. (1) To improve the dispersibility of polymers By adjusting the pH to a predetermined value, the nitrile groups contained in the nitrile group-containing structural units of the polymer are hydrolyzed, forming amide groups. By incorporating amide group-containing structural units into the polymer, the adsorption capacity to the dispersed material can be increased. Furthermore, since amide groups can form strong hydrogen bonds, incorporating amide group-containing structural units into the polymer introduces a cross-linked structure through hydrogen bonding within the polymer molecule, allowing for three-dimensional adsorption to CNTs. This is expected to result in a dispersion with excellent not only dispersibility but also stability. (2) Reduce the viscosity of the polymer solution When using polymers dissolved in a solvent, a low viscosity polymer solution allows the dispersant to penetrate more easily into the interior of carbon nanotubes (CNTs), which have strong cohesive forces, thus enabling the creation of a uniform dispersion. (3) Improve the wettability of CNTs When dispersing carbon nanotubes (CNTs), the cohesive force between CNTs is reduced by wetting them with a solvent, and then they are crushed and stabilized to exist as a dispersion. Since CNTs have significantly lower wettability compared to other conductive materials such as carbon black, pretreatment such as chemical treatment or mechanical crushing is necessary to improve their wettability, but these treatments may reduce their conductivity. It is believed that by adjusting the pH to a predetermined value, the wettability can be dramatically improved without impairing the conductivity of the CNTs. (4) Mitigating mixed shock when using single-walled carbon nanotubes / multi-walled carbon nanotubes in combination. Single-walled carbon nanotubes (WYSTs) and multi-walled carbon nanotubes (WYSTs) differ in fiber diameter and outer diameter, resulting in different levels of difficulty in disintegrating and dispersing them to form a good conductive network, and in stabilizing that dispersion. Therefore, even if WYSTs and WYSTs can be dispersed well individually, mixing can disrupt the dispersion state of one of them, leading to aggregation—a mixing shock. Adjusting the pH to a predetermined value is thought to mitigate this mixing shock and improve stability.

[0124] ≪Mixture composition for secondary battery electrodes≫ The composite material composition for secondary battery electrodes comprises a conductive material dispersion and a positive electrode active material or a negative electrode active material. It may further contain a binder resin or other conductive materials, a solvent, and any other components.

[0125] In this specification, positive electrode active material and negative electrode active material may be simply referred to as "active material." Active material refers to the material that forms the basis of the 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, composite compositions for secondary battery electrodes containing positive electrode active material or negative electrode active material may be referred to as "positive electrode composite composition," "negative electrode composite composition," or simply "composite composition," respectively. The composite composition is preferably in slurry form to improve uniformity and processability.

[0126] In other words, the conductive material dispersion in the embodiments of the present invention refers to the state before the active material is added. In this respect, the conductive material dispersion is distinguished from a composite material composition for secondary battery electrodes that contains an active material. That is, the conductive material dispersion substantially does not contain an active material. This is a concept that excludes the state in which an active material is intentionally added to the conductive material dispersion, and the amount of active material relative to the total mass of the conductive material dispersion may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, or even 0% by mass. The active material will be described later.

[0127] <Cathode active material> The positive electrode active material is not particularly limited, but for example, in secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, lithium manganese composite oxide (e.g., Li x Mn2O4 or LixMnO2), lithium nickel composite oxide (e.g., Li x Lithium cobalt composite oxide (Li O2), Li O2 x CoO2), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2), lithium manganese cobalt composite oxide (e.g., Li xMn y Co 1-y (O2), lithium nickel manganese cobalt composite oxide (e.g., Li x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-y Ni y O4), etc., composite oxide powders of lithium and transition metals, lithium phosphate oxide powders having an olivine structure (e.g., Li x FePO4, Li x Fe 1-y Mn y PO4, Li x CoPO4, etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V2O5, V6O 13 ), etc., transition metal oxide powders, iron sulfate (Fe2(SO4)3), TiS2, and FeS, etc., transition metal sulfide powders. However, x, y, and z are numbers, 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. These cathode active materials can also be used alone or in combination of two or more. Among these active materials, in particular, active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metal is 50 mol% or more) tend to become highly basic due to components derived from raw materials or elution of metal ions, and due to this influence, gelation of the binder and deterioration of the dispersion state are likely to occur, so the problems of the present invention may become prominent. Therefore, in the case of a battery containing an active material containing Ni and / or Mn, the present invention is particularly effective.

[0128] <Negative electrode active material> The negative electrode active material is not particularly limited. For example, metal Li capable of reversibly doping or intercalating lithium ions, or an alloy thereof, a tin alloy, a silicon alloy negative electrode, Li X TiO2, Li X Fe2O3, Li X Fe3O4, Li XMetal oxide systems such as WO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number and 0 < x < 1. These negative electrode active materials can be used alone or in combination of two or more. In particular, when using a silicon alloy negative electrode, although the theoretical capacity is large, the volume expansion is extremely large, so it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, resin-fired carbon materials, etc.

[0129] The content of CNT in the composite material composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. Further, when further containing carbon black as a conductive material, the content of carbon black is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 20% by mass or less, more preferably 10% by mass or less. When using CNT and carbon black in combination as a conductive material, the total addition amount of each is preferably within the above range. If it exceeds the above range, the filling amount of the active material in the electrode decreases, leading to a reduction in the battery's low-dose performance. Also, if it is below the above range, the conductivity of the electrode and the battery may be insufficient.

[0130] The content of the dispersant in the composite material composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0131] If the composite composition contains a binder resin, the binder resin content in the composite composition is preferably 0.5% by mass or more, more preferably 0.5% by mass or more, based on the mass of the active material (with the mass of the active material being 100% by mass). Furthermore, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0132] The solid content in the asphalt mixture composition is preferably 30% by mass or more, and more preferably 40% by mass or more, based on the mass of the asphalt mixture composition (with the mass of the asphalt mixture composition being 100% by mass). Furthermore, it is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0133] The composite composition can be prepared by various conventionally known methods. For example, methods include adding an active material to a conductive material dispersion; adding an active material to a conductive material dispersion and then adding a binder resin; and adding a binder resin to a conductive material dispersion and then adding an active material. As a method for preparing the composite composition, a method is preferred in which a binder resin is added to a conductive material dispersion, and then an active material is further added and dispersed. The dispersion apparatus used for dispersion is not particularly limited. The composite composition can be obtained using the dispersion means mentioned in the description of the conductive material dispersion. Therefore, as a method for preparing the composite composition, an electrode active material may be added and dispersed without adding a binder resin to the conductive material dispersion.

[0134] <Binder resin> If the composite material composition for secondary battery electrodes further contains a binder resin, there are no particular restrictions as long as it is a binder resin commonly used in paints, and it can be appropriately selected according to the purpose. Furthermore, the binder resin used in the composite material composition for secondary battery electrodes is a resin that can bond between substances such as active material and conductive material. Examples of binder resins used in composite compositions for secondary battery electrodes include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, etc. as constituent units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; cellulose resins; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms, mixtures, and copolymers of these resins are also acceptable. Among these, when used as a binder resin for the positive electrode, the aforementioned fluororesins, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene, are preferred from a structural standpoint. When used as a binder resin for the negative electrode, CMC, styrene-butadiene rubber, and polyacrylic acid, which have good adhesion properties, are preferred.

[0135] The binder resin content used in the composite material composition for secondary battery electrodes is preferably 0.1 to 30% by mass, and more preferably 0.5 to 20% by mass, of the nonvolatile content of the composite material composition for secondary battery electrodes.

[0136] ≪Electrode film≫ An electrode film according to one embodiment of the present invention includes at least one selected from the group consisting of a film formed using the conductive material dispersion of the above embodiment and a film formed using the secondary battery electrode composite composition of the above embodiment. The electrode film may further include a current collector. The electrode film can be obtained, for example, by coating the secondary battery electrode composite composition onto a current collector and drying it, and includes a current collector and a film. An electrode film formed using the positive electrode composite composition can be used as a positive electrode. An electrode film formed using the negative electrode composite composition can be used as a negative electrode. In this specification, a film formed using a secondary battery electrode composite composition containing an active material may be referred to as an "electrode composite layer".

[0137] The material and shape of the current collector used to form the electrode film are not particularly limited, and can be appropriately selected to suit various types of secondary batteries. Examples of current collector materials include conductive metals or alloys 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 foil-shaped current collectors, and mesh-shaped current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0138] There are no particular limitations on the method for coating the current collector with a conductive material dispersion or a composite material composition for secondary battery electrodes; known methods can be used. Specifically, examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, or electrostatic coating. Drying methods include, but are not limited to, drying by standing or drying using a forced-air dryer, hot-air dryer, infrared heater, far-infrared heater, etc.

[0139] After coating, rolling may be performed using a flatbed press, calender roll, or the like. The thickness of the formed film is, for example, 1 μm to 500 μm, preferably 10 μm to 300 μm.

[0140] A film formed using a conductive material dispersion or a composite material composition for secondary battery electrodes can also be used as an underlayer for the electrode composite material layer to improve adhesion between the electrode composite material layer and the current collector, or to improve the conductivity of the electrode film.

[0141] ≪Secondary battery≫ A secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte, wherein at least one selected from the group consisting of the positive electrode and the negative electrode includes the electrode film of the above embodiment.

[0142] Various conventionally known electrolytes that allow ion movement can be used. For example, the electrolyte may include, but is not limited to, 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). It is preferable to dissolve the electrolyte in a non-aqueous solvent and use it as an electrolyte solution.

[0143] Non-aqueous solvents are not particularly limited, but examples include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glycines such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used individually or in combination of two or more.

[0144] The secondary battery preferably includes a separator. Examples of separators include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics thereof that have been treated to be hydrophilic.

[0145] The structure of the secondary battery in this embodiment is not particularly limited, but it typically comprises a positive electrode, a negative electrode, and a separator provided as needed, and can be in various shapes depending on the intended use, such as paper type, cylindrical type, button type, or laminated type. [Examples]

[0146] 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 "mass percent". In addition, the amounts in the table are in parts by mass, and except for the solvent, the values ​​are calculated on a non-volatile content basis. Blank spaces in the table indicate that an ingredient is not included.

[0147] ≪Methods for measuring and analyzing the physical properties of polymers≫ (Mooney viscosity of polymer (ML) 1+4 ,100℃)) After dissolving the polymer in NMP, purified water was added dropwise to the polymer / NMP solution to solidify the polymer. The solidified material was collected, washed with methanol, transferred to a petri dish, and vacuum-dried at 60°C for 12 hours to obtain a 40 g plate-shaped sample for measurement. The Mooney viscosity (ML) was measured at 100°C using an L-type rotor in accordance with Japanese Industrial Standard JIS K6300-1. 1+4 The temperature (100℃) was measured.

[0148] (Hydrogenation rate of polymers) The hydrogenation rate was determined by IR measurement using total internal reflection spectroscopy. Specifically, the double bond originating from the conjugated diene monomer unit was 970 cm⁻¹. -1 A peak appears, and the hydrogenated single bond is 723 cm⁻¹. -1 Since a peak appears at this point, the hydrogenation rate was calculated from the ratio of the heights of these two peaks.

[0149] (Structural analysis of polymers) The content of polymer structural units was determined using a nuclear magnetic resonance spectrometer (ADVANCE400 Nanobay: Bruker Japan) with the measurement solvent (D3C) 2S=O and a 1mm NMR tube. 1 Quantitative NMR spectra were obtained using the measurement solvent (D3C) 2S=O and a 10 mm NMR tube. 13The concentrations were determined from 1C-NMR quantitative spectra. However, if peaks originating from structures where polymerization initiators or chain transfer agents were bonded to the polymer were detected, these were excluded from the calculation of the content of each structural unit in the polymer.

[0150] <Polymer manufacturing> (Manufacturing Example 1: Preparation of Polymer Solution 1) In a stainless steel polymerization reactor, 31 parts acrylonitrile, 69 parts 1,3-butadiene, 3 parts potassium soap oleate, 0.3 parts azobisisobutyronitrile, 0.48 parts t-dodecyl mercaptan, and 200 parts deionized water were added. Polymerization was carried out at 45°C for 20 hours under a nitrogen atmosphere with stirring, and the polymerization was terminated when the conversion rate reached 90%. Unreacted monomers were removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solid content of approximately 30%. Subsequently, deionized water was added to the latex to adjust the total solid content to 12%, and the mixture was placed in a 1 L autoclave with a stirrer. Dissolved oxygen in the contents was removed by flowing nitrogen gas through the mixture for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of deionized water with 4 molar amounts of nitric acid relative to the palladium was added to the autoclave. After purging the autoclave twice with hydrogen gas, the contents of the autoclave were heated to 50°C under a hydrogen gas pressure of 3 MPa and the hydrogenation reaction was carried out for 6 hours. After that, the contents were allowed to return to room temperature, the autoclave was subjected to a nitrogen atmosphere, and the solids were dried to recover the polymer product. The obtained polymer product was dissolved in NMP to make a 9% solution, and a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and a shear force was applied at a speed of 8,600 rpm for 1 hour to obtain a 9% polymer solution 1.

[0151] (Manufacturing Example 2: Preparation of Polymer 2-Solution) A 9% polymer solution 2 was obtained in the same manner as in Production Example 1, except that the content of t-dodecyl mercaptan, the molecular weight adjusting agent used, was changed to 0.55 parts.

[0152] (Manufacturing Example 3: Preparation of Polymer Solution 3) A 9% polymer solution 3 was obtained in the same manner as in Production Example 1, except that the content of t-dodecyl mercaptan, a molecular weight modifier used, was changed to 0.6 parts, and the high-shear mixer treatment was changed to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine). The high-pressure homogenizer treatment was performed using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 85 MPa.

[0153] (Manufacturing Example 4: Preparation of Polymer Solution 4) Hydrogenated nitrile rubber (Hydrogenated acrylonitrile-butadiene rubber, Therban(R)3406, manufactured by ARLANXEO) was dissolved in NMP to prepare a 7% container. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and a shear force was applied at a speed of 8,600 rpm for 1 hour to obtain a 9% polymer solution.

[0154] (Manufacturing Example 5: Preparation of Polymer Solution 5) A 9% polymer solution 5 was obtained in the same manner as in Production Example 4, except that hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Therban(R)AT 3404, manufactured by ARLANXEO) was used.

[0155] (Manufacturing Example 6: Preparation of Polymer 6 Solution) A 9% polymer solution 6 was obtained in the same manner as in Production Example 4, except that hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Zetpol(R) 2000L, manufactured by Nippon Zeon Co., Ltd.) was used.

[0156] (Manufacturing Example 7: Preparation of Polymer Solution 7) In a stainless steel polymerization reactor, 31 parts acrylonitrile, 69 parts 1,3-butadiene, 3 parts potassium soap oleate, 0.3 parts azobisisobutyronitrile, 0.6 parts t-dodecyl mercaptan, and 200 parts deionized water were added. Polymerization was carried out at 45°C for 20 hours under a nitrogen atmosphere with stirring, and the polymerization was terminated when the conversion rate reached 90%. Unreacted monomers were removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solid content of approximately 30%. Subsequently, deionized water was added to the latex to adjust the total solid content to 12%, and the mixture was placed in a 1 L autoclave with a stirrer. Dissolved oxygen in the contents was removed by flowing nitrogen gas through the mixture for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of deionized water with 4 molar amounts of nitric acid relative to the palladium was added to the autoclave. After purging the autoclave twice with hydrogen gas, the contents of the autoclave were heated to 50°C under a hydrogen gas pressure of 3 MPa and the hydrogenation reaction was carried out for 6 hours. Afterward, the contents were allowed to return to room temperature, the autoclave was subjected to a nitrogen atmosphere, and the solids were dried to recover the polymer product. The obtained polymer product was dissolved in NMP to obtain a 9% polymer solution.

[0157] (Production Example 8: Preparation of Polymer Solution 8) Hydrogenated nitrile rubber (Hydrogenated acrylonitrile-butadiene rubber manufactured by ARLANXEO, Thermon(R)3407) was dissolved in NMP to obtain a 9% polymer solution.

[0158] (Manufacturing Example 9: Preparation of Polymer Solution 9) Hydrogenated nitrile rubber (Hydrogenated acrylonitrile-butadiene rubber manufactured by ARLANXEO, Thermon(R)3629) was dissolved in NMP to obtain a 9% polymer solution.

[0159] Table 1 shows the Mooney viscosity, hydrogenation rate, and ratios of aliphatic hydrocarbon structural units and nitrile group-containing structural units in polymers 1-9.

[0160] [Table 1]

[0161] ≪Method for measuring the physical properties of conductive materials≫ (Method for measuring the average outer diameter of carbon nanotubes) The average outer diameter of carbon nanotubes was calculated by forming a film using a diluted conductive material, observing it at 50,000x magnification using a direct transmission electron microscope (H-7650, Hitachi, Ltd.), measuring the outer diameter of 300 randomly selected carbon nanotubes, and then using the average value.

[0162] (Method for measuring the amount of acidic groups in conductive materials) The amount of acidic groups in the conductive material was calculated by back titration, determining the amount of hexylamine adsorbed as follows: 0.2 g of the conductive material was placed in a glass bottle (M-70, manufactured by Kashiwayo Glass Co., Ltd.), and 30 ml of hexylamine / NMP solution (0.02 mol / l) was added. The glass bottle was irradiated with ultrasound (frequency 28 Hz) for 1 hour, and coarse particles were removed using a nylon mesh with a mesh size of 25 μm. Further centrifugation was performed at 10,000 rpm for 10 minutes using a mini centrifuge (MCF-1350 (manufactured by LMS)), the supernatant was collected, filtered through a membrane filter (filter pore size 0.22 μm), and the filtrate was recovered. 10 ml of the obtained filtrate was taken and diluted with 40 ml of deionized water to be used as the titrant. In addition, 10 ml of hexylamine / NMP solution (0.02 mol / l) that had not been ultrasonically treated with the conductive material was diluted with 40 ml of deionized water to be used as the standard titrant. The titrant and standard titrant were separately titrated with a 0.1 mol / l HCl / ethanol solution using a potentiometric automatic titrator (AT-710S, Kyoto Electronics Manufacturing Co., Ltd.), and the amount of hexylamine adsorbed onto the conductive material ([hexylamine adsorbed amount] (μmol)) was calculated from the difference in titration volume at the isoelectric point. The titration solution used was 10 ml of 30 ml of hexylamine / NMP solution, and the mass of the CNT was 0.2 g. Therefore, the value obtained by multiplying the [hexylamine adsorption amount] by 3 and dividing by 0.2 is the [hexylamine adsorption amount] (μmol / g) per unit weight of the conductive material, and further dividing by the specific surface area of ​​the conductive material gives the [hexylamine adsorption amount] (μmol / m²) per CNT surface area. 2 )

[0163] (Method for measuring the specific surface area of ​​conductive materials) The conductive material was weighed to 0.03 g using an electronic balance (Sartorius, MSA225S100DI), and then dried at 110°C for 15 minutes while degassing. After that, the specific surface area (m²) of the conductive material was measured using a fully automatic specific surface area analyzer (MOUNTECH, HM-model1208). 2 The measurement ( / g) was taken.

[0164] The following conductive materials were used in the examples. • TUBALL: Single-walled carbon nanotube (OCSiAl, average outer diameter 1.6nm, purity 93%, specific surface area 975m²) 2 / g, acidic group amount 0.21μmol / m 2 (205 μmol / g) ·BT1003M: LUCAN BT1003M (manufactured by LG chem Ltd, multilayer CNT, average outer diameter 13 nm, specific surface area 201 m 2 / g, acidic group amount 0.25μmol / m 2 (50 μmol / g) ·6A:JENOTUBE6A (manufactured by JEIO, multilayer CNT, average outer diameter 6nm, specific surface area 700m 2 / g, acidic group amount 0.27μmol / m 2 (190 μmol / g) ·10B: JENOTUBE10B (manufactured by JEIO, multilayer CNT, average outer diameter 10 nm, specific surface area 230 m 2 / g, acidic group amount 0.67μmol / m 2 (154 μmol / g) • Super-P (manufactured by IMERYS Graphite & Carbon, conductive carbon black, BET specific surface area 62 m²) 2 / g)

[0165] ≪Methods for measuring and evaluating the physical properties of conductive material dispersions≫ (Method for measuring dispersed particle size) The particle size of the conductive material dispersion was determined using a grind gauge with a maximum groove depth of 300 μm, according to the determination method conforming to JIS K5600-2-5.

[0166] (Laser diffraction / scattering particle size distribution measurement of conductive material dispersions) Particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Partical LA-960V2, manufactured by Horiba, Ltd.). The laser wavelength of this analyzer is 650 nm, and it is equipped with one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. The measurement unit uses a flow cell (sample cell) made of synthetic quartz. First, the dispersion and the solvent NMP were added to the sample bath containing the sample cell, and circulation / ultrasonic cleaning was performed. The operating mode was set to circulation speed: 3, ultrasonic intensity: 7, ultrasonic duration: 1 minute, stirring speed: 7, and stirring mode: continuous. Next, to remove air, ultrasonic operation was performed at ultrasonic intensity: 7 and ultrasonic duration: 5 seconds, and then a blank (background) measurement was performed. The particle size standard was volume, the particle refractive index was set to 1.920-0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The dispersion was added dropwise so that the laser light transmittance during measurement was 60% ± 1%, and the sample was prepared. During the measurement, the operating mode was set to circulation speed: 3, stirring speed: 7, and stirring mode: continuous. For example, Figure 1 is a graph showing the frequency distribution of particle sizes in conductive material dispersion 1, where the left vertical axis represents the frequency relative to the total (%), and the right vertical axis represents the cumulative frequency. Cumulative frequency D 50 A: 10 μm or more and less than 30 μm (Excellent) B: 4 μm or more and less than 10 μm, 30 μm or more and less than 50 μm (Good) C: 50 μm or more and less than 100 μm (defective) D: Less than 4 μm, 100 μm or more (not acceptable)

[0167] (Method for measuring the viscosity of conductive material dispersions) The viscosity of the conductive material dispersion was measured using a B-type viscometer (BL, manufactured by Toki Sangyo Co., Ltd.) at a dispersion temperature of 25°C. After thoroughly stirring the dispersion with a spatula, the viscosity was measured immediately at a B-type viscometer rotor speed of 6 rpm, followed by measurement at 60 rpm. Lower viscosity indicates better dispersibility, while higher viscosity indicates poorer dispersibility. Dispersions that clearly separated or settled were considered to have poor dispersibility. The TI value was calculated by dividing the viscosity at 60 rpm (mPa·s) by the viscosity at 6 rpm (mPa·s). Initial viscosity judgment criteria ◎: Less than 2,000 mPa·s (Excellent) ○: 2,000 mPa·s or more and less than 3,000 mPa·s (Good) △: 3,000 mPa·s or more and less than 10,000 mPa·s (acceptable) ×: Above 10,000 mPa·s, sedimentation or separation (not permitted) TI value judgment criteria ◎: Less than 4.0 (Excellent) ○: 4.0 or higher and less than 6.0 (Good) △: 6.0 or higher and less than 7.0 (Poor) ×: 7.0 or higher, sedimentation or separation (not allowed)

[0168] (Method for measuring gloss) For gloss measurement, a sample was prepared by dropping 1 mL of conductive material dispersion onto a smooth glass substrate, coating it with a No. 7 bar coater at 2 cm / second, baking it in a 140°C hot air oven for 10 minutes, and then allowing it to cool. The coated area was approximately 10 cm × 10 cm. Using a gloss meter (BYK Gardner micro-gross60° gloss meter), three locations were randomly selected within the coated film surface, excluding the edges, and each location was measured once. The average value was then used to determine the gloss at 60°. Glossiness evaluation criteria ◎: 30 or more (Excellent) ○: 20 or more but less than 30 (Good) △: 10 or more but less than 20 (Poor) ×: Less than 10 (Not allowed)

[0169] (Measurement of complex modulus and phase angle of conductive material dispersion) The complex modulus X and phase angle Y of the conductive material dispersion were measured using a rheometer (RheoStress1 rotational rheometer, Thermo Fisher Scientific Co., Ltd.) with a 60 mm diameter, 2° cone, by performing dynamic viscoelastic measurements at 25°C and a frequency of 1 Hz, within a strain range of 0.01% to 5%. The product (X × Y) of the obtained complex modulus X (Pa) and phase angle Y (°) was calculated.

[0170] (Method for evaluating the storage stability of conductive material dispersions) Storage stability was evaluated by measuring the viscosity of the dispersion after it was left to stand at 50°C for 7 days. The measurement method was the same as that used for the initial viscosity. Storage stability assessment criteria ◎: Same as initial (excellent) ○: Viscosity changed slightly (good) △: Viscosity has increased, but gelation has not occurred (defective) ×: Gelated (extremely poor quality)

[0171] (pH of conductive material dispersion) After allowing the conductive material dispersion to stand in a 25°C constant temperature bath for at least one hour, the conductive material dispersion was thoroughly stirred to bring the solid content concentration of the conductive material dispersion to 100%, and then water was added to the carbon nanotube dispersion while stirring with a disperser until the solid content concentration of the conductive material dispersion was reduced to 50%. After uniform stirring, the pH was measured at 25°C using a benchtop pH meter (Seven Compact S220 Expert Pro, Mettler Toledo).

[0172] <Manufacturing of single-walled carbon nanotube resin composition> (Manufacturing Example 10: Manufacturing of TUBALL-F) 97.6 parts of NMP were added to a stainless steel container, and while stirring with a disperser, 2.0 parts of polyvinylidene fluoride resin (solef5130, manufactured by solvay) were added and stirred with the disperser until the polyvinylidene fluoride resin dissolved. Then, 0.4 parts of single-walled carbon nanotubes (TUBALL: manufactured by OCSiAl, carbon purity 93%) were weighed and added while stirring with a disperser, and a square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and the pass-type dispersion treatment was performed 5 times to obtain the single-walled carbon nanotube resin composition (TUBALL-F). The dispersion treatment was performed using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 60 MPa.

[0173] <Preparation of conductive material dispersion> (Example 1-1) A 9% polymer solution and NMP were added to a stainless steel container so that the polymer amounted to 0.4 parts by mass and the total amount of NMP was 92.58 parts by mass. Then, 1.0 part by mass of 6A(CNT) was added and stirred with a disperser. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 180 μm. Next, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion treatment was performed. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After dispersion until the viscosity of the dispersion liquid at 60 rpm, measured with a Type B viscometer (manufactured by Toki Sangyo, VISCOMETER, MODEL: BL), was 3,000 mPa·s or less, 0.5 parts by mass of 6A and 0.2 parts by mass of polymer 1 solution were added to the stainless steel container while stirring with a disperser, and the circulating dispersion treatment was performed again with the high-pressure homogenizer. The process of circulating dispersion with the high-pressure homogenizer until the viscosity was 3,000 mPa·s or less, followed by adding 6A and polymer 1 solution to the stainless steel container while stirring with a disperser, was repeated (the total amount of 6A added was 2.0 parts by mass). Subsequently, a 25-pass dispersion treatment was performed using a high-pressure homogenizer to prepare a multilayer CNT dispersion containing 2.0 parts by mass of multilayer CNTs. Subsequently, the multilayer CNT dispersion was placed in another stainless steel container, and the single-walled CNT resin composition (TUBALL-F) prepared in Production Example 10 was added in a mass ratio of 5:1 between multilayer CNTs and single-walled CNTs. The mixture was then stirred with a disperser until homogeneous to obtain conductive material dispersion 1. The pH of conductive material dispersion 1 was measured using the method described above and was found to be 8.3.

[0174] (Examples 1-2 to 1-7) Conductive material dispersions (dispersions 2-7) were obtained in the same manner as in Example 1-1, except that polymer solution 1 was replaced with the polymer solutions shown in Table 2.

[0175] (Examples 1-8 to 1-9) Conductive material dispersions (dispersions 8-9) were obtained in the same manner as in Example 1-1, except that the type of multilayer CNT and the polymer solution were changed as shown in Table 2.

[0176] (Examples 1-10) A 9% polymer 2 solution and NMP were added to a stainless steel container, with 0.4 parts by mass of polymer 2 and a total of 94.32 parts by mass of NMP. Two parts by mass of 6A (multilayer CNT) were then added and stirred with a disperser. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 240 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion treatment was performed. The dispersion treatment was performed using a single-nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After dispersing the dispersion until its viscosity at 60 rpm, measured with a Type B viscometer (TOKI SANGYO, VISCOMETER, MODEL: BL), was 3,000 mPa·s or less, 0.2 parts by mass of TUBALL (single-walled carbon nanotubes) and 0.22 parts by mass of polymer 2 solution were added to the stainless steel container while stirring with a disperser, and the mixture was again dispersed using a high-pressure homogenizer in a circulating manner. The process of circulating dispersion using a high-pressure homogenizer until the viscosity was 3,000 mPa·s or less, followed by adding 6A and polymer 2 solution to the stainless steel container while stirring with a disperser, was repeated. Subsequently, the mixture was dispersed 25 times using a high-pressure homogenizer to obtain a conductive material dispersion (dispersion 10) containing 0.4 parts by mass of single-walled carbon nanotubes and 2.0 parts by mass of multi-walled carbon nanotubes. The pH of dispersion 10 was measured using the method described above and was found to be 8.4.

[0177] (Examples 1-11 to 1-12) Conductive material dispersions (dispersions 11-12) were obtained in the same manner as in Examples 1-10, except that the content of single-walled carbon nanotubes (WNTs) and polymers was changed as shown in Table 2.

[0178] (Examples 1-13) In a stainless steel container, a 9% polymer solution and NMP were added, with the polymer amounting to 0.4 parts by mass and the total amount of NMP to 90.98 parts by mass. Then, 2 parts by mass of 6A (multilayer CNT) and 5 parts by mass of Super-P (carbon black) were added and stirred with a disperser. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 180 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. After dispersing the dispersion until its viscosity at 60 rpm, measured with a Type B viscometer (TOKI SANGYO, VISCOMETER, MODEL: BL), was 3,000 mPa·s or less, 0.2 parts by mass of TUBALL (single-walled carbon nanotubes) and 0.22 parts by mass of polymer 2 solution were added to the stainless steel container while stirring with a disperser, and the mixture was again dispersed using a high-pressure homogenizer in a circulating manner. The process of circulating dispersion using a high-pressure homogenizer until the viscosity was 3,000 mPa·s or less, followed by adding 6A and polymer 2 solution to the stainless steel container while stirring with a disperser, was repeated. Subsequently, the mixture was dispersed 25 times using a high-pressure homogenizer to obtain a conductive material dispersion (dispersion 13) containing 0.4 parts by mass of single-walled carbon nanotubes, 2.0 parts by mass of multi-walled carbon nanotubes, and 5.0 parts by mass of carbon black. The pH of dispersion 13 was measured using the method described above and was found to be 8.3.

[0179] (Examples 1-14) In a stainless steel container, a 9% polymer solution and NMP were added so that the polymer amounted to 0.84 parts by mass and the total amount of NMP to 96.76 parts by mass. While stirring with a disperser, 2 parts by mass of 6A (multilayer CNT) and 0.4 parts by mass of TUBALL were added while stirring with the disperser. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 240 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulating dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersion was dispersed until its viscosity at 60 rpm, measured using a Type B viscometer (TOKI SANGYO, VISCOMETER, MODEL: BL), was 3,000 mPa·s or less. Subsequently, a high-pressure homogenizer was used to perform a 25-pass dispersion treatment to obtain a conductive material dispersion (dispersion 14) containing 0.4 parts by mass of single-walled carbon nanotubes and 2.0 parts by mass of multi-walled carbon nanotubes. The pH of dispersion 14 was measured using the method described above and was found to be 8.3.

[0180] (Examples 1-15 to 1-17) Conductive material dispersions (dispersions 15-17) were obtained in the same manner as in Example 1-2, except that a portion of the NMP initially added to the stainless steel container was replaced with the additives listed in Table 2. When the pH of the conductive material dispersions was measured using the method described above, dispersion 15 was 9.0, dispersion 16 was 9.3, and dispersion 17 was 9.1.

[0181] (Examples 1-18) A conductive material dispersion (dispersion 18) was obtained in the same manner as in Example 1-2, except that a 9% PVP / NMP solution was prepared and 40% of the polymer solution 2 used in Example 1-2 was replaced with the 9% PVP / NMP solution. The pH of dispersion 14 was measured using the method described above and was found to be 8.4.

[0182] (Comparative Example 1-1) A 9% PVP / NMP solution was prepared. The 9% PVP / NMP solution and NMP were added to a stainless steel container, with 0.4 parts by mass of PVP and a total of 94.58 parts by mass of NMP. 1.0 part by mass of 6A (multilayer CNT) was added and stirred with a disperser. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 180 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a bead mill (Picomill, manufactured by Asada Iron Works) via piping, and a circulating dispersion treatment was performed. Zirconia beads with a diameter of 0.5 mm were used at a packing rate of 80%. After circulating dispersion until the viscosity of the dispersion was 3,000 mPa·s or less, 0.5 parts by mass of 6A and 0.2 parts by mass of PVP / NMP solution were added to the stainless steel container while stirring with a disperser, and the circulating dispersion treatment was performed again with a bead mill. After circulating dispersion with a bead mill until the viscosity was 3,000 mPa·s or less, the process of adding 10B and PVP / NMP solution to the stainless steel container while stirring with a disperser was repeated (the total amount of 6A added was 2.0 parts by mass). Subsequently, the dispersion treatment was performed 30 times using a bead mill to obtain a multilayer CNT dispersion containing 2.0 parts by mass of CNTs. Then, the multilayer CNT dispersion was placed in another stainless steel container, and the single-walled CNT resin composition (TUBALL-F) prepared in Production Example 4 was added so that the mass ratio of multilayer CNTs to single-walled CNTs was 5:1, and the mixture was stirred with a disperser until homogeneous to obtain comparative dispersion 1.

[0183] (Comparative Example 1-2) A conductive material dispersion (comparative dispersion 2) containing 0.4 parts by mass of single-walled carbon nanotubes and 2.0 parts by mass of multi-walled carbon nanotubes was obtained in the same manner as in Example 1-2, except that the pass-type dispersion treatment in the high-pressure homogenizer was performed 10 times instead of 25 times.

[0184] (Comparative Examples 1-3) In a stainless steel container, a 9% polymer solution and NMP were added so that the polymer amounted to 0.4 parts by mass and the total amount of NMP to 92.76 parts by mass. Then, 2 parts by mass of 6A(CNT) were added and stirred with a disperser. A square-hole high-sear screen was attached to a high-sear mixer (L5M-A, manufactured by Silverson), and batch dispersion was performed at a speed of 8,600 rpm until the mixture was uniform and the dispersed particle size was 250 μm or less as measured by a grind gauge. At this time, the dispersed particle size confirmed by the grind gauge was 240 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a bead mill (Picomill, manufactured by Asada Iron Works) via piping, and a circulating dispersion treatment was performed. Zirconia beads with a diameter of 0.5 mm were used at a packing rate of 80%. After circulating dispersion until the viscosity of the dispersion was 3,000 mPa·s or less, 0.2 parts by mass of TUBALL and 0.22 parts by mass of polymer 2 solution were added to the stainless steel container while stirring with a disperser, and the circulating dispersion treatment was performed again with a bead mill. The process of circulating dispersion with a bead mill until the viscosity was 3,000 mPa·s or less, and then adding TUBALL and polymer 2 solution to the stainless steel container while stirring with a disperser was repeated again. Subsequently, the dispersion treatment was performed 25 times with a bead mill to obtain a conductive material dispersion (comparative dispersion 3) containing 0.4 parts by mass of single-walled carbon nanotubes and 2.0 parts by mass of multi-walled carbon nanotubes.

[0185] (Comparative Examples 1-4, 1-5) Conductive material dispersions (comparative dispersions 4 and 5) were obtained in the same manner as in Example 1-1, except that the polymer solution 1 in Example 1-1 was replaced with the polymer solutions shown in Table 2.

[0186] Table 2 shows the total amount (parts by mass) of each material contained in the conductive material dispersion. [Table 2]

[0187] The additives listed in Table 2 are as follows: • Aminoethanol: 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd., purity >99.0%) · NaOH: Sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity > 98.0%, granular) · BuONa: Sodium - t - butoxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity > 98.0%) · PVP: Polyvinylpyrrolidone K - 30 (manufactured by Nippon Shokubai Co., Ltd., non - volatile content 100%, acid value 0 mgKOH / g)

[0188] The characteristics and evaluation results of each conductive material dispersion are shown in Table 3.

[0189]

Table 3

[0190] <Preparation of Composite Composition for Cathode and Cathode> (Example 2 - 1a) A plastic container with a volume of 150 cm 3 was added with a conductive material dispersion (Dispersion 1) and PVdF (solef5130, manufactured by Solvay, non - volatile content 100%) previously dissolved in NMP to a concentration of 8%. Then, using a planetary mixer (manufactured by Shinki Co., Ltd., Awatori Rentaro, ARE - 310), it was stirred at 2,000 rpm for 30 seconds. After that, as a cathode active material, NMC1 (NCM523, LiNi 0.5 Co 0.2 Mn 0.3 O₂, manufactured by Nippon Chemical Industry Co., Ltd., non - volatile content 100%) was added, and using a planetary mixer (manufactured by Shinki Co., Ltd., Awatori Rentaro, ARE - 310), it was stirred at 2,000 rpm for 150 seconds to obtain a composite composition for the cathode. The non - volatile content of the composite composition for the cathode was 74.60 mass%. Among the non - volatile content of the composite composition for the cathode, the non - volatile content ratio of NMC1:TUBALL:6A:PVdF was 98.20:0.05:0.25:1.4.

[0191] The positive electrode composite composition was coated onto a 20 μm thick aluminum foil using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to produce an electrode film (composite layer). The electrode film was then rolled using a roll press (Sankmetal, 3t hydraulic roll press) to obtain a positive electrode (positive electrode 1a). The basis weight per unit area of ​​the composite layer was 20 mg / cm². 2 The density of the asphalt layer after rolling was 3.2 g / cc.

[0192] (Examples 2-2a to 2-18a, Comparative Examples 2-1a to 2-5a) Positive electrodes 2a to 18a and comparative positive electrodes 1a to 5a were obtained by the same method as in Example 2-1, except that the conductive material dispersions were changed to the solid content composition ratios shown in Table 4 (dispersions 2 to 18, comparative dispersions 1 to 5).

[0193] <Evaluation of the positive electrode> (Method for evaluating the conductivity of the positive electrode) The surface resistivity (Ω / □) of the composite layer of the obtained positive electrode was measured using a Mitsubishi Chemical Analytec Rolester GP, MCP-T610. After measurement, the volume resistivity (Ω·cm) of the positive electrode was obtained by multiplying by the thickness of the composite layer. The thickness of the composite layer was determined by subtracting the thickness of the aluminum foil from the average value of measurements taken at three points in the electrode using a film thickness gauge (NIKON, DIGIMICRO MH-15M) to obtain the volume resistivity (Ω·cm) of the positive electrode. Conductivity criteria ◎: Less than 4Ω·cm (Excellent) ○: 4Ω·cm or more and less than 10Ω·cm (Good) △: 10Ω·cm or more and less than 20Ω·cm (defective) ×: 20Ω cm or more (not possible)

[0194] (Method for evaluating the adhesion of the positive electrode) The obtained positive electrode was cut into two 90mm x 20mm rectangles with the coating direction as the long axis. A benchtop tensile testing machine (Strograph E3, manufactured by Toyo Seiki Seisakusho) was used to measure the peel strength, and it was evaluated using the 180-degree peel test method. Specifically, a 100mm x 30mm double-sided tape (No. 5000NS, manufactured by Nitoms) was attached to a stainless steel plate, and the composite layer side of the prepared positive electrode was pressed against the other side of the double-sided tape to create a test sample. Next, the test sample was fixed vertically with the shorter sides of the rectangle facing upwards and downwards, and the end of the aluminum foil was peeled off by pulling it from bottom to top at a constant speed (50mm / min). The average value of the stress at this time was taken as the peel strength. Adhesion Criteria ◎: 1N / cm or more (excellent) ○: 0.5 N / cm or more and less than 1 N / cm (Good) △: 0.3 N / cm or more and less than 0.5 N / cm (Poor) ×: Less than 0.3 N / cm (extremely poor)

[0195] [Table 4]

[0196] (Examples 2-2b to 2-18b, Comparative Examples 2-1b to 2-5b) The positive electrode active material is changed from NMC1 to NMC2 (S800, LiNi 0.8 Mn 0.1 Co 0.1 Positive electrodes 1b to 18b and comparative positive electrodes 1b to 5b were obtained in the same manner as in Example 2-1a, except that the material was changed to O2 (made from Kinwa, 100% non-volatile content). The conductivity and adhesion of the obtained positive electrodes showed similar trends to positive electrodes 1a to 18a and comparative positive electrodes 1a to 5a, respectively, which were obtained using the same conductive material dispersion.

[0197] <Fabrication and evaluation of secondary batteries> (Fabrication 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 MAC500L, manufactured by Nippon Paper Industries, 100% non-volatile content), and 98.4 parts by mass of water were added. The mixture was then stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Furthermore, 97 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industry) was added as an active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Next, 3.1 parts by mass of SBR (styrene-butadiene rubber, TRD2001, 48% non-volatile content, manufactured by JSR) were added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotational / revolving mixer (Sinky Awatori Rentaro, ARE-310) to obtain a standard anode composite composition. The non-volatile content of the standard anode composite composition was 50% by mass.

[0198] The above-mentioned standard negative electrode composite composition was applied to a 20 μm thick copper foil, which would serve as the current collector, using an applicator. After drying in an electric oven at 80°C ± 5°C for 25 minutes, the basis weight per unit area of ​​the electrode was reduced to 10 mg / cm². 2 The mixture was adjusted to achieve the following result. Furthermore, rolling was performed using a roll press (Sankmetal, 3t hydraulic roll press), resulting in a density of 1.6 g / cm³ in the asphalt layer. 3 A standard negative electrode was fabricated.

[0199] (Examples 3-1a to 3-18a, Comparative Examples 3-1a to 3-5a) (Manufacturing of secondary batteries) Using the positive electrode and the standard negative electrode described in Table 5, they were punched out into sizes of 50 mm × 45 mm and 45 mm × 40 mm respectively. The punched positive electrode, standard negative electrode, and the separator (porous polypropylene film) inserted between them were inserted into an aluminum laminate bag and dried in an electric oven at 70 °C for 1 hour. Then, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a volume ratio of 1:1:1, and further adding 1 part by mass of vinylene carbonate to 100 parts by mass, and then dissolving LiPF6 at a concentration of 1 M to obtain a non-aqueous electrolytic solution) was injected with 2 mL. After that, the aluminum laminate was sealed to fabricate secondary batteries respectively.

[0200] (Method for evaluating rate characteristics of secondary battery) The obtained secondary batteries were placed in a constant temperature chamber at 25 °C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Beidou Electric Works, SM-8). After performing constant current and constant voltage charging (cut-off current 1 mA (0.02C)) at a charging current of 10 mA (0.2C) and a charging termination voltage of 4.3V, constant current discharge was performed at a discharge current of 10 mA (0.2C) and a discharge termination voltage of 3V. After repeating this operation 3 times, constant current and constant voltage charging (cut-off current (1 mA 0.02C)) was performed at a charging current of 10 mA (0.2C) and a charging termination voltage of 4.3V, and constant current discharge was performed at discharge currents of 0.2C and 3C until the discharge termination voltage reached 3.0V to obtain the discharge capacity respectively. The rate characteristics can be represented by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in the following formula 1. (Formula 1) Rate characteristics = 3C discharge capacity / 0.2C discharge capacity of the third cycle × 100 (%) Rate characteristics judgment criteria ◎: 80% or more (excellent) ○: 60% or more and less than 80% (good) △: 40% or more and less than 60% (poor) ×: Less than 40% (extremely poor)

[0201] (Method for evaluating cycle characteristics of secondary battery) The obtained secondary batteries were placed in a constant temperature room at 25°C, and charge / discharge measurements were performed using a charge / discharge device (Hokuto Denko, SM-8). Constant current constant voltage charging (cutoff current 2.5mA (0.05C)) was performed with a charging current of 25mA (0.5C) and a charging termination voltage of 4.3V, followed by constant current discharge with a discharge current of 25mA (0.5C) and a discharge termination voltage of 3V. This operation was repeated 200 times. The cycle characteristics can be expressed by the ratio of the 0.5C discharge capacity at 25°C after the 3rd cycle to the 0.5C discharge capacity after the 200th cycle, as shown in Equation 2 below. (Formula 2) Cycle characteristics = 0.5C discharge capacity at 3rd cycle / 0.5C discharge capacity at 200th cycle × 100 (%) Cycle characteristics judgment criteria ◎: 85% or higher (Excellent) ○: 80% to less than 85% (Good) △: 50% to less than 80% (defective) ×: Less than 50% (extremely poor)

[0202] [Table 5]

[0203] (Examples 3-1b to 3-18b, Comparative Examples 3-1b to 3-5b) Batteries 1b to 18b and comparative batteries 1b to 5b were fabricated in the same manner as in Example 3-1a, except that positive electrode 1a was replaced with positive electrodes 1b to 18b and comparative positive electrodes 1b to 5b, respectively. The rate characteristics and cycle characteristics of the obtained batteries showed similar trends to batteries 1a to 18a and comparative batteries 1a to 5a, respectively, which used the same conductive material dispersion.

[0204] The positive electrodes using the conductive material dispersion, which is an embodiment of the present invention, all exhibited good conductivity and adhesion. Furthermore, the batteries using the said positive electrodes all exhibited good rate characteristics and cycle characteristics. It is believed that by satisfying the constituent requirements of the present invention, it was possible to disperse the fibers and structures more uniformly and without breaking them as much as possible compared to conventional methods for determining the dispersion state, resulting in the formation of a well-developed conductive network within the electrode. Therefore, it has become clear that the present invention can provide a non-aqueous electrolyte secondary battery with rate characteristics and cycle characteristics that are difficult to achieve with conventional conductive material dispersions.

Claims

1. A conductive material dispersion containing a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, and a dispersion medium, The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. Mooney viscosity (ML) of the polymer １＋４ The temperature (100°C) is between 20 and 80 degrees Celsius. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 1,700. Conductive material dispersion.

2. The conductive material dispersion according to claim 1, wherein the conductive material further contains carbon black.

3. The conductive material dispersion according to claim 1, further comprising a fluororesin.

4. The conductive material dispersion according to claim 1, wherein the complex modulus of elasticity determined by dynamic viscoelasticity measurement is 0.1 Pa or more and 200 Pa or less.

5. The conductive material dispersion according to claim 1, wherein the phase angle determined by dynamic viscoelasticity measurement is 1° or more and 60° or less.

6. The conductive material dispersion according to claim 1, wherein the gloss of the film obtained by coating and drying the conductive material dispersion onto a substrate is 5 to 120, as measured at 60°.

7. A composite material composition for secondary battery electrodes, comprising a conductive material dispersion according to any one of claims 1 to 6.

8. An electrode film coated with the composite composition for secondary battery electrodes described in claim 7.

9. A secondary battery comprising the electrode film described in claim 7.

10. A method for producing a conductive material dispersion, comprising the following step (I-1): The conductive material dispersion comprises a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, a fluororesin, and a dispersion medium. The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. Mooney viscosity (ML) of the polymer １＋４ The temperature (100°C) is between 20 and 80 degrees Celsius. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) obtained by dynamic viscoelasticity measurement of the conductive material dispersion is between 30 and 1,700. A method for producing a conductive material dispersion. (I-1) A step of dispersing a mixed solution containing single-walled carbon nanotubes, multi-walled carbon nanotubes, a polymer, a fluororesin, and a dispersion medium.

11. A method for producing a conductive material dispersion, comprising the steps (II-1) to (II-3) below, The conductive material dispersion comprises a conductive material, a polymer containing aliphatic hydrocarbon structural units and nitrile group-containing structural units, a fluororesin, and a dispersion medium. The conductive material contains single-walled carbon nanotubes and multi-walled carbon nanotubes. Mooney viscosity (ML) of the polymer １＋４ The temperature (100°C) is between 20 and 80 degrees Celsius. The aliphatic hydrocarbon structural unit includes alkylene structural units, The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the polymer. The content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, based on the mass of the polymer. The product of the complex modulus X (Pa) and phase angle Y (°) of the conductive material dispersion, as determined by dynamic viscoelasticity measurement, is (X × Y) between 30 and 3,000. A method for producing a conductive material dispersion. (II-1) A step to produce a first conductive material dispersion by dispersing a mixed solution containing single-walled carbon nanotubes, fluororesin, and a dispersion medium. (II-2) A step to produce a second conductive material dispersion by dispersing a mixed solution containing multi-walled carbon nanotubes, a polymer, and a dispersion medium. (II-3) A step of mixing the first conductive material dispersion and the second conductive material dispersion.

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