Slurry composition for electrode film, method for manufacturing electrode film, method for manufacturing battery electrode, and method for manufacturing non-aqueous electrolyte secondary battery

Abstract

To provide a slurry composition for an electrode film, having good dispersibility and good stability.SOLUTION: A method for producing a slurry composition for an electrode film includes: preparing a carbon nanotube dispersion which contains carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, and an amide-based organic solvent (C), and a slurry precursor for an electrode film which contains an active material (D), a low-molecular-weight acidic compound (E) having a molecular weight of less than 10,000, a fluorine-based polymer (F), and an amide-based organic solvent (C'); and mixing the carbon nanotube dispersion and the slurry precursor for an electrode film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for producing a slurry composition for an electrode film, a method for producing an electrode film, a method for producing a battery electrode, and a method for producing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Lithium ion secondary batteries, which are typical non-aqueous electrolyte secondary batteries, are widely used as batteries for electric vehicles, portable devices, etc. As the performance of electric vehicles and portable devices improves, demands for lithium ion secondary batteries with high capacity, high output, and small size and light weight are increasing year by year.

[0003] Because the capacity of nonaqueous electrolyte secondary batteries is highly dependent on the cathode and anode active materials, various materials for these electrode active materials have been actively researched. However, the charge capacity of commercially available electrode active materials is close to the theoretical value, and improvement is near its limit. Therefore, since the charge capacity can be simply increased by increasing the amount of electrode active material filled in the electrode film, attempts have been made to reduce the amount of conductive material and binder resin added, which do not directly contribute to the charge capacity.

[0004] Conductive materials play a role in forming conductive paths within the electrode film and connecting particles of the electrode active material, and these conductive paths and connections must be resistant to breakage due to the expansion and contraction of the electrode film. To maintain the conductive paths and connections with a small amount of additive, it is effective to use nanocarbons with a large specific surface area, particularly carbon nanotubes (CNTs), as the conductive material to form an efficient conductive network. However, carbon nanotubes with a large specific surface area have strong cohesion, making it difficult to disperse them well in the electrode film slurry and / or the electrode film.

[0005] In light of this background, many methods have been proposed in which a conductive material dispersion is prepared using various dispersants, and a slurry composition for an electrode film is produced via the conductive material dispersion (see, for example, Patent Documents 1 to 5). Patent Document 6 also proposes that a slurry for a secondary battery positive electrode is produced by a specific production process using a specific binder, thereby enabling the formation of a good conductive network between conductive materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-162877 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-193986 [Patent Document 3] Special Publication No. 2018-522803 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-128012 [Patent Document 5] Korean Patent Registration No. 10-1831562 [Patent Document 6] Patent No. 6413242 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Documents 1 and 2 propose improving the initial characteristics and cycle life of a battery by dispersing carbon nanotubes in a solvent in advance using a polymer such as polyvinylpyrrolidone or polyvinyl alcohol as a dispersant. However, although polyvinylpyrrolidone or polyvinyl alcohol can produce a carbon nanotube dispersion liquid in a well-dispersed state, the dispersion state may become poor during the process of forming an electrode film, resulting in a decrease in conductivity.

[0008] Patent Documents 3 and 4 propose conductive material dispersions using hydrogenated nitrile rubber as a dispersant. However, these hydrogenated nitrile rubbers have poor dispersibility, and therefore may not be able to form a satisfactory conductive network. Furthermore, because hydrogenated nitrile rubber solutions have high viscosity, it may take a long time to produce a conductive material dispersion, or the conductive material dispersion may have poor fluidity and be difficult to handle, making it difficult to put into practical use on an industrial scale.

[0009] Patent Document 5 proposes a carbon nanotube dispersion in which dispersibility is improved by adding aminoethanol or the like to hydrogenated nitrile rubber. In this CNT dispersion, it is believed that the effect of the dispersant is improved by changing the polarity of the solvent. However, the resulting dispersion has high viscosity and is still insufficient to form a good conductive network. Patent documents 1 to 5 discuss improving the initial dispersibility of conductive material dispersions by specifying the type of dispersant, but do not fully consider the phenomenon in which the dispersibility and stability of carbon nanotubes decrease during the stage of preparing a composite slurry by adding an active material and a binder resin to the conductive material dispersion.

[0010] In a specific example of Patent Document 6, polyvinylidene fluoride is added to a conductive paste 1 containing a hydrogenated product of a polymer containing conjugated diene monomer units, (meth)acrylic acid ester monomer units, and nitrile group-containing monomer units, acetylene black, and N-methyl-2-pyrrolidone to obtain a conductive paste 2, and a positive electrode active material is further added to produce a positive electrode slurry. In contrast to the acetylene black used in this specific example, high-aspect ratio carbon nanotubes exhibit excellent conductivity when finely dispersed in an electrode film, but carbon nanotubes tend to aggregate, which presents a problem of reduced dispersibility in the positive electrode slurry.

[0011] An object of one embodiment of the present invention is to provide a slurry composition for an electrode film having good dispersibility and good stability. Another object of one embodiment of the present invention is to provide an electrode film and a battery electrode that can improve the output and cycle life of a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery that has high output and good cycle life. [Means for solving the problem]

[0012] As a result of extensive investigations, the present inventors have found that when a slurry composition for an electrode membrane contains carbon nanotubes (A) and an active material (C) in the presence of a polymer (B) containing a nitrile group-containing structural unit and a fluoropolymer (F), the temporal stability of the slurry composition for an electrode membrane decreases, resulting in an increase in electrode resistance. One of the factors behind this decrease in temporal stability is that the fluoropolymer (F) contained in the slurry composition for an electrode membrane gels due to its basicity. One method for suppressing this gelation of the fluoropolymer (F) is to add a low-molecular-weight acidic compound to the slurry composition for an electrode membrane. The inventors have noticed that the timing of adding a low molecular weight acidic compound in a manufacturing method of a slurry composition for an electrode membrane affects the dispersibility and stability of carbon nanotubes in the slurry composition for an electrode membrane, and have prepared a carbon nanotube dispersion containing carbon nanotubes (A) and a polymer (B) containing a nitrile group-containing structural unit, and a slurry precursor for an electrode membrane containing an active material (D), a low molecular weight acidic compound (E) and a fluoropolymer (F), and by mixing the carbon nanotube dispersion with the slurry precursor for an electrode membrane, it has become possible to suppress gelation of the fluoropolymer (F) in the slurry composition for an electrode membrane and to obtain good dispersibility and stability of carbon nanotubes. In a method for producing a slurry composition for an electrode film, when the timing of adding the low-molecular-weight acidic compound is determined by continuously mixing carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, an active material (D), a low-molecular-weight acidic compound (E), and a fluoropolymer (F) into a solvent, the viscosity of the mixed composition may increase when the carbon nanotubes (A) and the low-molecular-weight acidic compound (E) are mixed, and the carbon nanotubes (A) may aggregate. This is thought to be because, when the low-molecular-weight acidic compound (E) is directly added to a composition containing the carbon nanotubes (A) and the polymer (B) containing a nitrile group-containing structural unit, the polymer (B) containing the nitrile group-containing structural unit aggregates, causing a decrease in the dispersibility and stability of the carbon nanotubes (A).Furthermore, the electrode film and the battery electrode obtained using the electrode film slurry composition obtained according to the production method of this embodiment have good conductivity and low electrode resistance, and the nonaqueous electrolyte secondary battery obtained using this electrode film and battery electrode can improve the rate characteristics and cycle characteristics of the battery.

[0013] Some aspects of the invention are as follows. <1> A method for producing a slurry composition for an electrode film, comprising: preparing a carbon nanotube dispersion liquid containing carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, and an amide-based organic solvent (C); and preparing a slurry precursor for an electrode film containing an active material (D), a low-molecular-weight acidic compound (E) having a molecular weight of less than 10,000, a fluorine-based polymer (F), and an amide-based organic solvent (C'), and mixing the carbon nanotube dispersion liquid and the slurry precursor for an electrode film.

[0014] <2> In the polymer (B) containing the nitrile group-containing structural unit, 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 (B). <1> 2. A method for producing a slurry composition for an electrode film according to claim 1. <3> The polymer (B) containing a nitrile group-containing structural unit has a weight average molecular weight of 5,000 or more and 500,000 or less. <1> or <2> 2. A method for producing a slurry composition for an electrode film according to claim 1. <4> In the carbon nanotube dispersion, the carbon nanotube concentration x (mass %) and the complex modulus y (Pa) of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz as determined by dynamic viscoelasticity measurement satisfy the relationships of the following formulas (1), (2), and (3): <1> from <3> 10. A method for producing a slurry composition for an electrode membrane according to claim 9. y<17x (1) y<120 (2) 0.1≦x≦10 (3)

[0015] <5> the above <1> from <4> 10. A method for producing an electrode film, comprising: preparing a slurry composition for an electrode film by the production method according to any one of claims 1 to 9; and producing an electrode film using the slurry composition for an electrode film. <6> the above <1> from <4> 10. A method for producing an electrode for a battery, the method comprising: preparing a slurry composition for an electrode film by the production method according to any one of claims 1 to 9; and producing an electrode film on a current collector using the slurry composition for an electrode film. <7> A method for manufacturing a non-aqueous electrolyte secondary battery including a negative electrode, a positive electrode, and an electrolyte, wherein the step of preparing either the negative electrode or the positive electrode comprises the steps of: <1> from <4> 1. A method for producing a non-aqueous electrolyte secondary battery, the method comprising: preparing a slurry composition for an electrode film by the production method according to any one of claims 1 to 9; and forming an electrode film on a current collector using the slurry composition for an electrode film. [Effects of the Invention]

[0016] According to one embodiment of the present invention, it is possible to provide a slurry composition for an electrode film having good dispersibility and good stability. Furthermore, according to one embodiment of the present invention, it is possible to provide an electrode film and a battery electrode that can improve the output and cycle life of a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery having high output and good cycle life. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a graph showing the relationship between the CNT concentration (mass %) of a CNT dispersion and the complex modulus of elasticity [G*] (Pa) determined by dynamic viscoelasticity measurement. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a slurry composition for an electrode film, an electrode film, a battery electrode, a nonaqueous electrolyte secondary battery, etc., which are one embodiment of the present invention, will be described in detail. The present invention is not limited to the following embodiment, and the present invention also includes embodiments that are implemented within the scope of the present invention.

[0019] <Method for producing a slurry composition for an electrode film> The method for producing a slurry composition for an electrode film of this embodiment is characterized by comprising preparing a carbon nanotube dispersion liquid containing carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, and an amide-based organic solvent (C), and a slurry precursor for an electrode film containing an electrode active material (D), a low-molecular-weight acidic compound (E) having a molecular weight of less than 10,000, a fluoropolymer (F), and an amide-based organic solvent (C'), and mixing the carbon nanotube dispersion liquid and the slurry precursor for an electrode film.

[0020] In this specification, carbon nanotubes may be referred to as "CNT." In addition, in this specification, carbon nanotube dispersion may be simply referred to as "dispersion." In addition, N-methyl-2-pyrrolidone may be referred to as "NMP." In this specification, polymer (B) containing a nitrile group-containing structural unit may be simply referred to as "polymer (B)."

[0021] <Carbon nanotube dispersion> The carbon nanotube dispersion contains carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, and an amide organic solvent (C).

[0022] The carbon nanotubes (A) are contained in the carbon nanotube dispersion as a conductive material. The carbon nanotube dispersion may optionally contain other conductive materials in addition to the carbon nanotubes. Examples of other conductive materials include metal powders such as gold, silver, copper, silver-plated copper powder, silver-copper composite powder, silver-copper alloy, amorphous copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, malbutene, and platinum; inorganic powders coated with these metals; powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide; inorganic powders coated with these metal oxides; and carbon materials such as carbon black and graphite. These other conductive materials may be used alone or in combination. When using other conductive materials, carbon black is preferred from the viewpoint of the adsorption performance of the dispersant.

[0023] Carbon nanotubes have a cylindrical shape formed by rolling up planar graphite, and may be either single-walled carbon nanotubes or multi-walled carbon nanotubes, or a combination thereof. Single-walled carbon nanotubes have a structure in which one layer of graphite is rolled up. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are rolled up. The sidewalls of carbon nanotubes do not have to have a graphite structure. For example, carbon nanotubes having sidewalls with an amorphous structure are also defined as carbon nanotubes in this specification. Carbon nanotubes may also be surface-treated carbon nanotubes. Carbon nanotubes may also be carbon nanotube derivatives to which functional groups, such as carboxyl groups, have been added.

[0024] The shape of the carbon nanotubes is not limited. Examples of the shape of the carbon nanotubes include various shapes, including needle-like, cylindrical, fishbone-like (fishbone or cup-stacked), trump-like (platelet), and coil-like. Among these, the shape of the carbon nanotubes is preferably needle-like or cylindrical. The carbon nanotubes may have a single shape or a combination of two or more shapes.

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

[0026] The BET specific surface area of ​​carbon nanotubes is 20 to 1,000 m 2 / g, and 30 to 800m 2 / g is more preferred.

[0027] The fiber length of the carbon nanotubes is preferably 50 nm or more and 5,000 nm or less, but may also be 80 nm or more and 2,000 nm or less, or 100 nm or more and 1,000 nm or less. Carbon nanotubes with a fiber length of 100 nm or more can further improve conductivity and toughness. Furthermore, carbon nanotubes with a fiber length of 1,000 nm or less can suppress the occurrence of aggregation even when defibration progresses during dispersion treatment, thereby further preventing an increase in the viscosity of the dispersion.

[0028] Carbon nanotubes are evaluated by the G / D ratio (peak ratio between the G-band and D-band). The G / D ratio of carbon nanotubes is determined by Raman spectroscopy. Carbon nanotubes have a peak between 1560 and 1600 cm in the Raman spectrum. -1 The maximum peak intensity in the range of 1310 to 1350 cm is G. -1When the maximum peak intensity within this range is defined as D, the G / D ratio is preferably 0.5 to 10, more preferably 0.5 to 4.5, and even more preferably 0.5 to 2.0.

[0029] The carbon nanotubes preferably have an average outer diameter of 2 to 25 nm, more preferably 5 to 20 nm, and even more preferably 5 to 15 nm. Within the above range, the electrical conductivity and toughness of the carbon nanotubes can be further improved.

[0030] The outer diameter and average outer diameter of carbon nanotubes can be determined as follows: First, carbon nanotubes are observed and photographed using a transmission electron microscope. Next, 300 carbon nanotubes are randomly selected from the photograph and their outer diameters are measured. Next, the average outer diameter (nm) of the carbon nanotubes is calculated as the number average of the outer diameters.

[0031] The volume resistivity of carbon nanotubes is 1.0×10 -2 ~3.0×10 -2 Ω·cm is preferred, and 1.0×10 -2 ~2.0×10 -2 It is more preferable that the volume resistivity is Ω·cm. The volume resistivity of carbon nanotubes can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Nitto Seiko Analytech Co., Ltd.).

[0032] The carbon purity of carbon nanotubes can be determined by standard CHN elemental analysis and is expressed as the carbon atom content (mass%) in the carbon nanotubes. The carbon purity is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 98 mass% or more, based on the mass of the carbon nanotubes (the mass of the carbon nanotubes being 100 mass%). By keeping the carbon purity within the above range, problems such as short circuits caused by the formation of dendrites by impurities when used in secondary batteries can be prevented.

[0033] The amount of metal contained in carbon nanotubes is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 2% by mass, based on 100% by mass of the carbon nanotubes. Examples of metals contained in carbon nanotubes include metals and metal oxides used as catalysts when synthesizing carbon nanotubes. Specific examples include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, as well as metal oxides and composite oxides thereof.

[0034] The polymer (B) containing a nitrile group-containing structural unit is contained in the carbon nanotube dispersion as a dispersant. The dispersant preferably contains the polymer (B) containing a nitrile group-containing structural unit as a main component. For example, the polymer (B) containing a nitrile group-containing structural unit may account for 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more of the total amount of the dispersant. The dispersant may entirely be the polymer (B) containing a nitrile group-containing structural unit. The polymer (B) contains a nitrile group-containing structural unit, which allows it to exhibit excellent flexibility and stability due to its binding strength, and therefore maintains a good conductive network even in an electrode film formed by mixing a carbon nanotube dispersion with a slurry precursor for an electrode film and using the resulting slurry composition for an electrode film.

[0035] In the polymer (B), 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, more preferably a structural unit consisting of only 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 a structural unit containing (or consisting of) an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one.

[0036] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (1A).

[0037] General formula (1A) [ka]

[0038] In general formula (1A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2. In this specification, "*" represents a bond to another structure.

[0039] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (1B).

[0040] General formula (1B) [ka]

[0041] In general formula (2B), R represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom.

[0042] The method for introducing the nitrile group-containing structural unit into the polymer (B) is not particularly limited, but a method of preparing a polymer by polymerization using a monomer composition containing a nitrile group-containing monomer is preferred. The finally obtained polymer (B) contains the nitrile group-containing monomer unit as the nitrile group-containing structural unit. Examples of the nitrile group-containing monomer capable of forming the nitrile group-containing structural unit include a monomer containing a polymerizable carbon-carbon double bond and a nitrile group. Examples include α,β-ethylenically unsaturated group-containing compounds having a nitrile group, such as acrylonitrile and methacrylonitrile. In particular, from the viewpoint of increasing the intermolecular forces between the polymers (B) and / or between the polymer (B) and the dispersed substance (adsorbate), the nitrile group-containing monomer preferably contains acrylonitrile. The nitrile group-containing monomer may be used alone or in combination of two or more.

[0043] The content of the nitrile group-containing structural unit is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the mass of the polymer (B) (i.e., when the mass of the polymer (B) is 100% by mass). The content of the nitrile group-containing structural unit is preferably 50% by mass or less, more preferably 46% by mass or less, and even more preferably 40% by mass or less, based on the mass of the polymer (B) (i.e., when the mass of the polymer (B) is 100% by mass). By setting the content of the nitrile group-containing structural unit within the above range, it is possible to control the adsorption to the dispersed substance and the affinity to the dispersion medium, and to ensure that the dispersed substance is present stably in the dispersion medium. In addition, it is possible to control the affinity of the polymer (B) to the electrolyte solution, and it is possible to prevent problems such as the polymer (B) dissolving in the electrolyte solution in the battery and increasing the resistance of the electrolyte solution.

[0044] Furthermore, the polymer (B) preferably contains an aliphatic hydrocarbon structural unit. The aliphatic hydrocarbon structural unit is a structural unit containing an aliphatic hydrocarbon structure, and preferably a structural unit consisting solely of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure and may further contain an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably contains at least a linear aliphatic hydrocarbon structure and may further contain a branched aliphatic hydrocarbon structure.

[0045] Examples of the aliphatic hydrocarbon structural unit include an alkylene structural unit, an alkenylene structural unit, an alkyl structural unit, an alkanetriyl structural unit, an alkanetetrayl structural unit, etc. The aliphatic hydrocarbon structural unit preferably contains at least an alkylene structural unit.

[0046] The alkylene structural unit is a structural unit containing an alkylene structure, and is preferably a structural unit consisting of only an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0047] The alkylene structural unit preferably contains a structural unit represented by the following general formula (2A).

[0048] General formula (2A) [ka]

[0049] In general formula (2A), n represents an integer of 1 or greater. n is preferably an integer of 2 or greater, more preferably an integer of 3 or greater, and particularly preferably an integer of 4 or greater. n is preferably an integer of 6 or less, and more preferably an integer of 5 or less. In particular, n is preferably 4.

[0050] The alkylene structural unit preferably contains a structural unit represented by the following general formula (2B).

[0051] General formula (2B) [ka]

[0052] In general formula (2B), n represents an integer of 1 or greater. n is preferably an integer of 2 or greater, and more preferably an integer of 3 or greater. n is preferably an integer of 5 or less, and more preferably an integer of 4 or less. In particular, n is preferably 3.

[0053] The alkylene structural unit preferably contains a structural unit represented by the following general formula (2C).

[0054] General formula (2C) [ka]

[0055] In general formula (2C), n represents an integer of 1 or greater. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, and even more preferably an integer of 2 or less. In particular, n is preferably 2.

[0056] The method for introducing the aliphatic hydrocarbon structural unit into the polymer (B) is not particularly limited, but examples thereof include the following method (2a) or (2b).

[0057] In method (2a), a polymer is prepared by polymerization using a monomer composition containing a conjugated diene monomer. The prepared polymer contains monomer units derived from the conjugated diene monomer. In the present invention, "monomer units derived from a conjugated diene monomer" may be referred to as "conjugated diene monomer units," and the same may be abbreviated for monomer units derived from other monomers. Next, the conjugated diene monomer units are hydrogenated to convert at least a portion of the conjugated diene monomer units into alkylene structural units. Hereinafter, "hydrogenation" may be referred to as "hydrogenation." The finally obtained polymer (B) contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0058] The conjugated diene monomer unit contains at least a monomer unit having one carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, contains at least one monomer unit selected from the group consisting of a monomer unit having a cis-1,4 structure, a monomer unit having a trans-1,4 structure, and a monomer unit having a 1,2 structure, and may contain two or more monomer units. The conjugated diene monomer unit may further contain a monomer unit having no carbon-carbon double bond and including a branch point. In this specification, the term "branch point" refers to a branch point in a branched polymer. When the conjugated diene monomer unit contains a monomer unit having a branch point, the polymer prepared above and polymer (B) are branched polymers.

[0059] In the method (2b), a polymer is prepared by polymerization using a monomer composition containing an α-olefin monomer. The prepared polymer contains α-olefin monomer units. The finally obtained polymer (B) contains the α-olefin monomer units as alkylene structural units.

[0060] Among these, method (2a) is preferred because it allows for easy production of the polymer. The conjugated diene monomer has 4 or more carbon atoms, preferably 4 to 6. Examples of the conjugated diene monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Of these, 1,3-butadiene is preferred. The alkylene structural unit preferably contains a structural unit (hydrogenated conjugated diene monomer unit) obtained by hydrogenating a conjugated diene monomer unit, and more preferably contains a structural unit (hydrogenated 1,3-butadiene monomer unit) obtained by hydrogenating a 1,3-butadiene monomer unit. The conjugated diene monomer may be used alone or in combination of two or more.

[0061] The hydrogenation is preferably carried out by a method capable of selectively hydrogenating the conjugated diene monomer units. Examples of the hydrogenation method include known methods such as oil phase hydrogenation and aqueous phase hydrogenation.

[0062] The hydrogenation can be carried out by a conventional method. For example, the hydrogenation can be carried out by treating a polymer having conjugated diene monomer units dissolved in a suitable solvent with hydrogen gas in the presence of a hydrogenation catalyst. Examples of the hydrogenation catalyst include iron, nickel, palladium, platinum, and copper.

[0063] In the method (2b), the carbon number of the α-olefin monomer is 2 or more, preferably 3 or more, and more preferably 4 or more. The carbon number of the α-olefin monomer is preferably 6 or less, and more preferably 5 or less. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomers can be used alone or in combination of two or more.

[0064] The alkylene structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkylene structure and structural units containing a branched alkylene structure, 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 further preferably includes at least one selected from the group consisting of structural units represented by the above formula (2B) and structural units represented by the above formula (2C).

[0065] The alkylene structural unit may include a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure. When the alkylene structural unit includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, 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 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 (B) includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, the content of the branched alkylene structure is, for example, 1% by mass or more, optionally 5% by mass or more, or even 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 100% by mass).

[0066] In the 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 the aliphatic hydrocarbon structural units (i.e., when the mass of the aliphatic hydrocarbon structural units is 100% by mass). The content of alkylene structural units is, based on the total mass of the aliphatic hydrocarbon structural units (i.e., when the mass of the aliphatic hydrocarbon structural units is 100% by mass), 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. The content of alkylene structural units may be 100% by mass.

[0067] The content of the aliphatic hydrocarbon structural unit is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on the mass of polymer (B) (i.e., when the mass of polymer (B) is 100% by mass). The content of the aliphatic hydrocarbon structural unit is preferably less than 85% by mass, more preferably 75% by mass or less, and even more preferably 70% by mass or less, based on the mass of polymer (B) (i.e., when the mass of polymer (B) is 100% by mass).

[0068] Furthermore, the polymer (B) may contain any structural unit. Examples of the structural unit include an amide group-containing structural unit, a carboxyl group-containing structural unit, an alkenylene structural unit, an alkyl structural unit, and structural units containing a branch point such as an alkanetriyl structural unit or an alkanetetrayl structural unit. A structural unit containing a branch point is a structural unit different from a structural unit containing a branched alkylene structure and a structural unit containing a branched alkyl structure.

[0069] 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, more preferably a structural unit consisting of only 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 a structural unit containing (or consisting 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.

[0070] The amide group-containing structural unit preferably contains a structural unit represented by the following general formula (3A).

[0071] General formula (3A) [ka]

[0072] In general formula (3A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2. R' each independently represents a hydrogen atom or a substituent. The substituent is preferably an alkyl group or a hydroxyalkyl group. It is preferable that at least one R' is a hydrogen atom, and more preferably two R' are hydrogen atoms.

[0073] The amide group-containing structural unit preferably contains a structural unit represented by the following general formula (3B).

[0074] General formula (3B) [ka]

[0075] In general formula (3B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom. R' each independently represents a hydrogen atom or a substituent. The substituent is preferably an alkyl group or a hydroxyalkyl group. It is preferable that at least one R' is a hydrogen atom, and more preferably two R's are hydrogen atoms.

[0076] The method for introducing the amide group-containing structural unit into the polymer (B) is not particularly limited, but for example, a polymer can be prepared by polymerization using a monomer composition containing an amide group-containing monomer. The prepared polymer contains the amide group-containing monomer unit. The finally obtained polymer (B) contains the amide group-containing monomer unit as the amide group-containing structural unit.

[0077] Examples of amide group-containing monomers include monoalkyl(meth)acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, and N-isopropyl(meth)acrylamide; dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; N-(hydroxyalkyl)(meth)acrylamides such as N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, and N-(2-hydroxybutyl)(meth)acrylamide; diacetone(meth)acrylamide; and acryloylmorpholine. In this specification, "(meth)acryl" refers to acrylic or methacrylic. In particular, the amide group-containing monomer preferably includes at least one selected from the group consisting of acrylamide, methacrylamide, and N,N-dimethylacrylamide. The amide group-containing monomers may be used singly or in combination of two or more.

[0078] The content of the amide group-containing structural unit is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less, based on the mass of the polymer (B) (i.e., when the mass of the polymer (B) is 100% by mass). When the content of the amide group-containing structural unit is within the above range, it is possible to prevent the problem of gelation of the conductive material dispersion during storage, which may occur when the hydrogen bonds between the polymers (B) become too strong.

[0079] The carboxyl group-containing structural unit is a structural unit containing a carboxyl group, preferably a structural unit containing an alkylene structure substituted with a carboxyl group, and more preferably a structural unit consisting solely of an alkylene structure substituted with a carboxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The carboxyl group-containing structural unit may further contain a structural unit containing (or consisting solely of) an alkyl structure substituted with a carboxyl group. The number of carboxyl groups contained in the carboxyl group-containing structural unit is preferably one or two. By including a carboxyl group-containing structural unit in the polymer (B), it is possible to improve the adsorptivity to the dispersed material, reduce the viscosity of the conductive material dispersion, and improve dispersion efficiency.

[0080] The carboxyl group-containing structural unit preferably contains a structural unit represented by the following general formula (4A).

[0081] General formula (4A) [ka]

[0082] In general formula (4A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2.

[0083] The carboxyl group-containing structural unit preferably contains a structural unit represented by the following general formula (4B).

[0084] General formula (4B) [ka]

[0085] In general formula (4B), R represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom.

[0086] The method for introducing the carboxyl group-containing structural unit is not particularly limited, but examples thereof include the following method (4a) or (4b).

[0087] In the method (4a), a polymer is prepared by polymerization using a composition containing a carboxyl group-containing monomer. The prepared polymer contains carboxyl group-containing monomer units. The final polymer (B) contains the carboxyl group-containing monomer units as carboxyl group-containing structural units.

[0088] In method (4b), a polymer containing an amide group-containing structural unit is first prepared by method (3a) or the like. Next, the amide group contained in the amide group-containing structural unit is hydrolyzed in an acidic atmosphere to convert the amide group-containing structural unit into a carboxyl group-containing structural unit. The finally obtained polymer (B) contains, as a carboxyl group-containing structural unit, a unit obtained by modifying the amide group contained in the amide group-containing structural unit by hydrolysis.

[0089] In the method (4a), examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and isocrotonic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, and itaconic acid. It is particularly preferable that the carboxyl group-containing monomer contains at least one selected from the group consisting of acrylic acid and maleic acid. The carboxyl group-containing monomer may be used singly or in combination of two or more.

[0090] In the method (4b), at least one acid selected from the group consisting of inorganic acids and organic acids can be used to create an acidic atmosphere.

[0091] In the method (4b), examples of inorganic acids include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, and hydrofluoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, oxalic acid, succinic acid, malic acid, benzoic acid, and benzenesulfonic acid. Among these, succinic acid and citric acid are preferred.

[0092] In the method (4b), the amount of acid used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the mass of polymer (B). The amount of acid used is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the mass of polymer (B). If the amount used is too small, modification of amide groups by hydrolysis tends to be difficult. If the amount used is too large, it may cause corrosion of the dispersion device and / or the inside of the battery.

[0093] The content of the carboxyl group-containing structural unit is preferably less than 1 mass %, more preferably 0.5 mass % or less, and even more preferably 0.3 mass % or less, based on the mass of the polymer (B) (i.e., when the mass of the polymer (B) is 100 mass %). If the content of the carboxyl group-containing structural unit is less than (or less than) the above range, it is possible to prevent the problem of gelation of the conductive material dispersion during storage, which will be described later, that can occur when hydrogen bonds between polymers (B) become too strong.

[0094] The alkenylene structural unit is a structural unit containing an alkenylene structure, and is preferably a structural unit consisting of only an alkenylene structure. The alkenylene structure is preferably a linear alkenylene structure or a branched alkenylene structure.

[0095] The alkenylene structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkenylene structure and structural units containing a branched alkenylene structure, and more preferably includes at least one selected from the group consisting of structural units consisting only of a linear alkenylene structure and structural units consisting only of a branched alkenylene structure.

[0096] For example, when polymer (B) is obtained via the above method (2a), conjugated diene monomer units having a carbon-carbon double bond within the unit may remain in the molecule of polymer (B) without being hydrogenated. The finally obtained polymer (B) may contain conjugated diene monomer units having a carbon-carbon double bond within the unit as alkenylene structural units.

[0097] The alkyl structural unit is a structural unit containing an alkyl structure (however, it is a structural unit that does 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 is preferably a structural unit consisting only of an alkyl structure. The alkyl structure is preferably a linear alkyl structure or a branched alkyl structure.

[0098] The alkyl structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkyl structure and structural units containing a branched alkyl structure, and more preferably includes at least one selected from the group consisting of structural units consisting only of a linear alkyl structure and structural units consisting only of a branched alkyl structure.

[0099] For example, when the polymer (B) is obtained via the above method (2a) or (2b), it is preferable that at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit is introduced as a terminal group of the polymer (B). The finally obtained polymer (B) may contain these monomer units as alkyl structural units.

[0100] The alkanetriyl structural unit is a structural unit containing an alkanetriyl structure, preferably a structural unit consisting solely of an alkanetriyl structure. The alkanetetrayl structural unit is a structural unit containing an alkanetetrayl structure, preferably a structural unit consisting solely of an alkanetetrayl structure.

[0101] For example, when polymer (B) is obtained via the above method (2a), conjugated diene monomer units may be introduced into the molecule of polymer (B) as monomer units that do not contain a carbon-carbon double bond and contain a branch point. In this case, the finally obtained polymer (B) is a branched polymer and may contain the conjugated diene monomer units as aliphatic hydrocarbon structural units containing a branch point, such as alkanetriyl structural units or alkanetetrayl structural units. When the aliphatic hydrocarbon structural units contain structural units containing a branch point, polymer (B) is a branched polymer. The branched polymer may be a network polymer. Polymer (B) containing structural units containing a branch point can be three-dimensionally adsorbed to the dispersed material, thereby further improving dispersibility and stability.

[0102] Preferred embodiments of the polymer (B) include the following. A polymer (B) in which the total content of aliphatic hydrocarbon structural units and nitrile group-containing structural units contained in the polymer (B) is 80% by mass or more and 100% by mass or less, based on the mass of the polymer (B). 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. A polymer (B) in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, and amide group-containing structural units contained in the polymer (B) is 80% by mass or more and 100% by mass or less, based on the mass of the polymer (B). 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. A polymer (B) in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, amide group-containing structural units, and carboxyl group-containing structural units contained in the polymer (B) is 80% by mass or more and 100% by mass or less, based on the mass of the polymer (B). 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.

[0103] In this specification, the content of the structural unit can be determined by utilizing the amount of the monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurement.

[0104] The polymerization reaction used to prepare the polymer (B) is preferably an emulsion polymerization reaction, and a conventional emulsion polymerization method can be used. The polymerization agents used in the emulsion polymerization, such as emulsifiers (surfactants), polymerization initiators, chelating agents, oxygen scavengers, and molecular weight modifiers, can be any conventionally known agent and are not particularly limited. For example, anionic emulsifiers or anionic and nonionic emulsifiers are usually used.

[0105] Examples of anionic emulsifiers include fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, potassium oleate, and sodium oleate; resin acid salts such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate. Examples of nonionic emulsifiers include emulsifiers of the polyethylene glycol ester type, polypropylene glycol ester type, and Pluronic (registered trademark) type such as a block copolymer of ethylene oxide and propylene oxide.

[0106] Examples of polymerization initiators include thermal decomposition initiators such as persulfates, e.g., potassium persulfate and ammonium persulfate; organic peroxides, e.g., t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, octanoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide; azo compounds, e.g., azobisisobutyronitrile; and redox initiators formed from these and a reducing agent, e.g., divalent iron ions. Among these, redox initiators are preferred. The amount of initiator used is, for example, in the range of 0.01 to 10% by mass based on the total amount of monomers.

[0107] Examples of the molecular weight modifier include alkyl mercaptans such as octyl mercaptan, nonyl mercaptan, decyl mercaptan, t-dodecyl mercaptan, and 3-mercapto-1,2-propanediol; thioglycolic acid esters such as octyl thioglycolate, nonyl thioglycolate, and 2-ethylhexyl thioglycolate; 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, and β-pinene.

[0108] The emulsion polymerization reaction may be either continuous or batchwise. The polymerization temperature may be either low-temperature or high-temperature polymerization, but is preferably 0 to 60°C, and more preferably 20 to 50°C. There are no particular limitations on the method of adding the monomers (such as all-at-once addition or divided addition), the polymerization time, or the polymerization conversion rate. The conversion rate is preferably 85% by mass or higher, and more preferably 90% by mass or higher.

[0109] The weight-average molecular weight of polymer (B) is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 50,000 or more. The weight-average molecular weight of polymer (B) is preferably 500,000 or less, more preferably 400,000 or less, and even more preferably 300,000 or less. When the weight-average molecular weight of polymer (B) is 5,000 or more and 500,000 or less, the adsorption to the dispersed substance and the affinity to the dispersion medium are improved, and the stability of the dispersion tends to be improved. In this specification, the weight-average molecular weight is the weight-average molecular weight in terms of polystyrene and can be measured by gel permeation chromatography (GPC). Specifically, it may be measured by the method described in the examples.

[0110] Polymer (B) has a Mooney viscosity (ML 1+4 , 100℃) is preferably 100 or less. 1+4 The polymer (B) having a Mooney viscosity (ML , 100°C) of 100 or less can further improve the dispersibility, stability, and handleability of the carbon nanotube dispersion. 1+4 The "temperature (100°C)" can be measured at a temperature of 100°C in accordance with JIS K6300-1. Specifically, it may be measured by the method described in the examples.

[0111] The Mooney viscosity of polymer (B) is preferably 100 or less, more preferably 70 or less, even more preferably 65 or less, even more preferably 60 or less, and even more preferably 50 or less. If the Mooney viscosity of polymer (B) is too high, the adsorption force of polymer (B) to the carbon fiber surface is low, making it impossible to disperse carbon fibers with strong cohesive force, and it may be difficult to prepare a uniform conductive material dispersion. In addition, since the obtained conductive material dispersion has a high viscosity, metal foreign matter contained in the raw materials cannot be efficiently removed by methods such as iron removal with a magnet, filtration, and centrifugation, and battery performance may be reduced due to the remaining metal foreign matter.

[0112] The Mooney viscosity of polymer (B) can be adjusted by the following method, but is not particularly limited thereto. For example, the Mooney viscosity can be adjusted by changing the composition (e.g., structural unit type and content, hydrogenation rate), structure (e.g., linearity), molecular weight, preparation conditions (e.g., polymerization temperature, amount of molecular weight modifier) ​​of polymer (B).

[0113] Preferred embodiments of the polymer (B) include the following. 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 (B), and the weight average molecular weight of the polymer is 5,000 or more and 500,000 or less, more preferably 10,000 or more and 400,000 or less. 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 (B), the weight average molecular weight of the polymer is 5,000 or more and 500,000 or less, more preferably 10,000 or more and 400,000 or less, and the Mooney viscosity (ML 1+4 ,100℃) is 70 or less.

[0114] The polymer (B) may be either a synthetic product or a commercially available product as long as it contains a nitrile group-containing structural unit. Commercially available polymer (B) includes, for example, Therban (registered trademark) 4307 (manufactured by ARLANXEO Co., Ltd.), Mooney viscosity (ML 1+4 , 100℃) 70, acrylonitrile content 43.0%), Zetpol (registered trademark) 2000L (manufactured by Zeon Corporation, Mooney viscosity (ML 1+4 , 100°C) 65, acrylonitrile content less than 36.2%.

[0115] The carbon nanotube dispersion may contain other dispersants in addition to the polymer (B). The other dispersants are not particularly limited as long as they can stably disperse the carbon nanotubes, and surfactants, resin-type dispersants, etc. can be used, with resin-type dispersants being preferred.

[0116] Specific examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose, etc., or salts thereof), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, poly(meth)acrylic acid or salts thereof, poly(meth)acrylate, etc. Polymers in which other substituents have been introduced into a portion of these polymers, modified polymers, etc. may also be used. Resin-type dispersants may be used alone or in combination of two or more. The molecular weight of the resin-type dispersant is preferably 10,000 to 150,000, more preferably 10,000 to 100,000.

[0117] The solvent for the carbon nanotube dispersion is preferably an amide organic solvent. The solvent preferably contains an amide organic solvent as a main component. For example, the amide organic solvent may be 50 mass %, 80 mass % or more, 90 mass % or more, or 95 mass % or more of the total amount of the dispersion medium solvent, and the entire solvent may be an amide organic solvent. The amide organic solvent is preferably a solvent that can dissolve the polymer (B) containing a nitrile group-containing structural unit, and is preferably a solvent that can dissolve the polymer (B) containing a nitrile group-containing structural unit when each component is contained in a predetermined amount in the carbon nanotube dispersion.

[0118] Examples of amide-based organic solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. The amide-based organic solvents may be used alone or in combination of two or more. In particular, the amide-based organic solvent preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and more preferably contains N-methyl-2-pyrrolidone.

[0119] It is preferable that the carbon nanotube dispersion is substantially free of water. In this specification, "substantially free of water" means that water is not intentionally added. In the carbon nanotube dispersion, the water content is preferably less than 5% by mass, more preferably less than 1% by mass, based on the mass of the polymer (B) containing a nitrile group-containing structural unit. Water in excess of the allowable amount may cause a decrease in the adsorption of the polymer (B) to the dispersed material, and may prevent the dispersed material from being stably present in the dispersion solvent. By setting the water content within the above range, it is possible to more effectively prevent the carbon nanotube dispersion from gelling during storage.

[0120] The solvent for the carbon nanotube dispersion is preferably an amide-based organic solvent, which is substantially free of water. The "pH" of a carbon nanotube dispersion that is substantially free of water refers to the value measured using a general pH meter after adding water to the carbon nanotube dispersion so that the solid concentration after adding water is 50% by mass, assuming that the solid concentration before adding water is 100% by mass, and can be measured, for example, by the following method.

[0121] While stirring a carbon nanotube dispersion with a solids concentration of 5% by mass using a disperser or similar, water is added so that the solids concentration of the carbon nanotube dispersion becomes 2.5% by mass. After stirring uniformly, the pH of the carbon nanotube dispersion can be measured at 25°C using a benchtop pH meter (Seven Compact S220 Expert Pro, manufactured by Mettler Toledo). The carbon nanotube dispersion preferably has a pH of 9.0 or higher. The pH of the carbon nanotube dispersion is preferably 9.0 or higher and 14.0 or lower, and more preferably 9.0 or higher and 13.0 or lower. If the pH exceeds the above range, corrosion of various raw materials and exterior materials in the battery, or gelation of the binder, is likely to occur.

[0122] The pH of the carbon nanotube dispersion can be adjusted by adding a base or by using basic carbon nanotubes. When adjusting the pH by adding a base, the base to be added can be at least one base selected from the group consisting of inorganic bases and organic bases.

[0123] Examples of inorganic bases include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, or borates of alkali metals or alkaline earth metals; and ammonium hydroxide. Among these, alkali metal or alkaline earth metal hydroxides are preferred from the viewpoint of easy supply of cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. The metal contained in the inorganic base may be a transition metal.

[0124] Examples of organic bases include amine compounds such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, dioctylamine, trioctylamine, aminoethanol, aminopropanol, aminobutanol, and 2-methoxyethylamine. Other examples include organic hydroxides such as trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, and benzyltrimethylammonium hydroxide. Organic hydroxides are salts containing an organic cation and a hydroxide ion. Among these, it is particularly preferred to use at least one selected from the group consisting of aminoethanol, aminopropanol, trimethyl-2-hydroxyethylammonium hydroxide, and tetramethylammonium hydroxide.

[0125] The content of the base is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the mass of the polymer (B). The content of the base is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the mass of the copolymer. If the amount used is too small, the resulting carbon nanotube dispersion tends to have high viscosity. If the amount used is too large, the stability of the resulting carbon nanotube dispersion may be poor, and further, corrosion of the dispersion device and / or the inside of the battery may occur.

[0126] In the carbon nanotube dispersion, the content of carbon nanotubes (A) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and may be 1% by mass or more, based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion is 100% by mass). The content of carbon nanotubes (A) is preferably 30% by mass or less, more preferably 20% by mass or less, and may be 15% by mass or less or 10% by mass or less, based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion is 100% by mass). By setting the content of carbon nanotubes in the carbon nanotube dispersion within the above range, the carbon nanotubes can be present in a good and stable state without sedimentation or gelation. Furthermore, it is preferable to appropriately adjust the content of carbon nanotubes so as to obtain a carbon nanotube dispersion exhibiting an appropriate viscosity, taking into account the specific surface area of ​​the carbon nanotubes, their affinity for the dispersion medium, and the like.

[0127] For example, from the viewpoint of achieving both good dispersibility and stability, the carbon nanotube content may be 10% by mass or less, and preferably 8% by mass or less, based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion being 100% by mass). On the other hand, since copolymer (B) can further improve both the dispersibility and stability of carbon nanotubes, the carbon nanotube content may be 2% by mass or more, or 5% by mass or more, based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion being 100% by mass).

[0128] In the carbon nanotube dispersion, the content of the polymer (B) is preferably 0.1 to 200 parts by mass, more preferably 0.5 to 100 parts by mass, and even more preferably 1.0 to 80 parts by mass, per 100 parts by mass of the carbon nanotubes (A). From the viewpoint of good dispersibility and stability, the content of the polymer (B) is preferably 2 parts by mass or more per 100 parts by mass of the carbon nanotubes (A). Furthermore, from the viewpoint of the conductivity of the dispersion, the content of the polymer (B) is preferably 50 parts by mass or less per 100 parts by mass of the carbon nanotubes (A). In the carbon nanotube dispersion, the content of polymer (B) is not particularly limited based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion being 100 mass%), but is preferably 0.01 to 20 mass%, more preferably 0.05 to 10 mass%, and even more preferably 0.1 to 8 mass%. When the carbon nanotube dispersion liquid contains other dispersants in addition to the polymer (B), the total content of the polymer (B) and other dispersants in the carbon nanotube dispersion liquid is preferably 0.1 to 200 parts by mass, more preferably 0.5 to 100 parts by mass, and even more preferably 1.0 to 80 parts by mass, per 100 parts by mass of the carbon nanotubes (A). When the carbon nanotube dispersion contains other dispersants and other polymer compounds in addition to the polymer (B), the total content of the polymer compounds in the carbon nanotube dispersion is preferably 30 mass % or less, more preferably 20 mass % or less, and even more preferably 15 mass % or less, based on the mass of the carbon nanotube dispersion (the mass of the carbon nanotube dispersion being 100 mass %). Furthermore, the carbon nanotube dispersion may be substantially free of other polymer compounds than the polymer (B) and other dispersants. The solid content of the carbon nanotube dispersion liquid is preferably 0.5 to 30 mass %, more preferably 1.0 to 25 mass %, and even more preferably 2.0 to 20 mass %.

[0129] The method for producing a carbon nanotube dispersion is not particularly limited. The carbon nanotube dispersion can be obtained, for example, by mixing a dispersant, a solvent, and carbon nanotubes and dispersing the carbon nanotubes in the solvent. In addition to the dispersant, solvent, and carbon nanotubes, any other component may be mixed. Alternatively, the carbon nanotube dispersion can be obtained, for example, by dissolving a dispersant in a solvent, mixing the carbon nanotubes, and dispersing the carbon nanotubes in the solvent. In addition to the dispersant, solvent, and carbon nanotubes, any other component, such as an additional solvent, may be mixed. When a solvent is mixed, it is preferable that the solvent used is the same as the solvent used to dissolve the dispersant. The order in which the dispersant and carbon nanotubes are added to the container is not particularly limited. It is preferable that the dispersant be present together with the carbon nanotubes at some point during the process of dispersing the carbon nanotubes.

[0130] As the dispersing device, a dispersing machine that is commonly used for dispersing pigments, etc., can be used. For example, mixers such as a Disper, a Homomixer, and a Planetary Mixer, a homogenizer (Advanced Digital Sonifer (registered trademark), Model 1 manufactured by Branson), Examples of suitable dispersers include, but are not limited to, media-type dispersers such as 450DA, M. Technique's "Clearmix," PRIMIX's "Filmix," and Silverson's "Abramix," paint conditioners (manufactured by Red Devil), colloid mills (PUC's "PUC Colloid Mill," IKA's "Colloid Mill MK"), cone mills (IKA's "Cone Mill MKO," etc.), ball mills, sand mills (Shinmaru Enterprises' "Dynomill," etc.), attritors, pearl mills (Eirich's "DCP Mill," etc.), and Coball mills; high-pressure homogenizers (Genus' "Genus PY," Sugino Machine's "Starburst," Nanomizer's "Nanomizer," etc.); media-less dispersers such as M. Technique's "Clear SS-5" and Nara Kikai's "MICROS," and other roll mills.

[0131] For example, a high shear mixer is preferably used in the initial dispersion step to promote wetting of the carbon nanotubes and to disintegrate coarse particles, followed by a high-pressure homogenizer to disperse the carbon nanotubes while maintaining their fiber length. Furthermore, after dispersion with the high-pressure homogenizer, further dispersion with a bead mill can be performed to achieve a uniform dispersion state while maintaining the fiber length. The pressure when using the high-pressure homogenizer is preferably 60 to 150 MPa, more preferably 60 to 120 MPa.

[0132] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, and circulation dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device itself, without using piping or the like. Because it is easy to handle, it is preferred for small-scale production. Pass dispersion is a dispersion method in which the dispersing device itself is equipped with a tank that supplies the dispersion liquid via piping and a tank that receives the dispersion liquid, and the dispersion passes through the dispersing device itself. Furthermore, circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device itself is returned to the tank that supplies the dispersion liquid and dispersed while circulating. In both methods, the longer the processing time, the more the dispersion progresses; therefore, the pass or circulation can be repeated until the desired dispersion state is achieved, and the processing volume can be increased by changing the tank size or processing time. Pass dispersion is preferred over circulation dispersion because it is easier to achieve a uniform dispersion state. Circulation dispersion is preferred over pass dispersion because the operation and production equipment are simpler. In the dispersion step, the disintegration of aggregated particles, the loosening, wetting, stabilization, etc. of carbon nanotubes proceed sequentially or simultaneously, and the final dispersion state differs depending on how the steps proceed, so it is preferable to control the dispersion state in each dispersion step by using various evaluation methods. For example, it can be controlled by the methods described in the examples.

[0133] The dispersibility of carbon nanotubes in a carbon nanotube dispersion can be measured by the phase angle and complex modulus obtained by dynamic viscoelasticity measurements. The phase angle represents the phase shift of the stress wave when the strain applied to the carbon nanotube dispersion is a sine wave. A purely elastic material will produce a sine wave in phase with the applied strain, resulting in a phase angle of 0°. On the other hand, a purely viscous material will produce a stress wave that is 90° ahead. A typical viscoelasticity measurement sample will produce a sine wave with a phase angle greater than 0° and less than 90°. If the carbon nanotubes in the carbon nanotube dispersion are well dispersed, the phase angle will approach 90°, which is the case for a purely viscous material. Furthermore, the complex modulus of a carbon nanotube dispersion decreases as the carbon nanotubes become more dispersible and the viscosity of the carbon nanotube dispersion decreases.

[0134] The phase angle and complex modulus measured by dynamic viscoelasticity measurement generally depend on the concentration of carbon nanotubes in the dispersion. Because carbon nanotubes have a high specific surface area, the lower the carbon nanotube content, the closer the resulting dispersion becomes to a pure viscous liquid, and the closer the phase angle becomes to 90°. Conversely, it is difficult to uniformly disperse carbon nanotubes in a dispersion containing a high concentration of carbon nanotubes, and the phase angle of the resulting dispersion may be less than 2°. In the present invention, since copolymer (B) can achieve both good dispersibility and stability, it is possible to obtain a carbon nanotube dispersion having a phase angle of 2° or more at 25°C and a frequency of 1 Hz, even when the carbon nanotube concentration is high.

[0135] The complex modulus of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz, as measured by dynamic viscoelasticity measurement, may be less than 120 Pa, more preferably 60 Pa or less, and even more preferably 20 Pa or less. The complex modulus of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is preferably 0.01 Pa or more, more preferably 0.05 Pa or more, and even more preferably 0.1 Pa or more. The phase angle of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz may be 2° or more, more preferably 5° or more, even more preferably 10° or more, and even more preferably 45° or more. The phase angle at 25°C and a frequency of 1 Hz is preferably 90° or less, more preferably 85° or less, and even more preferably 80° or less. The complex modulus and phase angle of the carbon nanotubes can be evaluated by dynamic viscoelasticity measurement. Specifically, the complex modulus and phase angle can be measured by the methods described in the Examples.

[0136] The carbon nanotube dispersion has a small complex modulus because the aggregation of carbon nanotubes is broken down by the effect of the dispersant containing polymer (B). In the carbon nanotube dispersion, it is preferable that the carbon nanotube concentration x (mass%) in the carbon nanotube dispersion and the complex modulus y (Pa) of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz as determined by dynamic viscoelasticity measurement satisfy the relationships of the following formulas (1), (2), and (3): y<17x (1) y<120 (2) 0.1≦x≦10 (3)

[0137] That is, from the above formulas (1) and (2), it is preferable that the complex modulus y of the carbon nanotube dispersion liquid measured by dynamic viscoelasticity measurement is less than 120 Pa, and that y<17x is satisfied. Furthermore, from the above formula (3), it is preferable that the carbon nanotube concentration x (mass%) is in the range of 0.1≦x≦10. In formula (2), the complex modulus y may be less than 120 Pa, but is preferably 100 Pa or less, or 50 Pa or less. The complex modulus y is not particularly limited, but may be 0.1 Pa, 0.5 Pa, 1 Pa or more. In formula (3), the carbon nanotube concentration x may be 0.1 mass% or more, but is preferably 0.5 mass% or more, or 1 mass% or more. The carbon nanotube concentration x may be 10 mass% or less, but is preferably 8 mass% or less, or 5 mass% or less.

[0138] The carbon nanotube dispersion preferably exhibits no sedimentation or separation of carbon nanotubes immediately after the dispersion treatment. The carbon nanotube dispersion preferably maintains a dispersed state for a long period of time after the dispersion treatment. Furthermore, since gelation during storage makes redispersion difficult, it is preferable that the carbon nanotube dispersion does not undergo gelation for a long period of time. The dispersibility of the carbon nanotube dispersion can also be evaluated by its viscosity; the lower the viscosity, the better the dispersibility. From this perspective, the viscosity of the carbon nanotube dispersion, measured at 25°C at 60 rpm using a Brookfield viscometer, is preferably less than 10,000 mPa·s, more preferably less than 5,000 mPa·s, even more preferably less than 2,000 mPa·s, and even more preferably less than 500 mPa·s. The initial viscosity may be 1 mPa·s or more, 10 mPa·s or more, or 100 mPa·s or more. Specific viscosity measurement methods are described in the Examples.

[0139] <Slurry precursor for electrode membrane> The electrode membrane slurry precursor contains an electrode active material (D), a low-molecular-weight acidic compound (E), a fluorine-based polymer (F), and an amide-based organic solvent (C').

[0140] The active material (D) is a material that serves as the basis for the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force.

[0141] The positive electrode active material is not particularly limited, but a material capable of reversibly doping or intercalating lithium ions can be used. For example, metal compounds such as metal oxides and metal sulfides can be mentioned. Specifically, metal oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. can be mentioned. Specifically, transition metal oxide powders such as MnO, V2O5, V6O 13 , TiO2, etc.; composite oxide powders of lithium and transition metals such as lithium nickelate, lithium cobaltate, lithium manganate with a layered structure, and lithium manganate with a spinel structure; lithium iron phosphate-based materials that are phosphate compounds with an olivine structure; transition metal sulfide powders such as TiS2 and FeS, etc. The positive electrode active material is preferably a substance containing at least Ni. The positive electrode active material can also be used by combining one or more of them.

[0142] As the negative electrode active material, a material capable of reversibly doping or intercalating lithium ions can be used. For example, alloy systems such as metallic Li, its alloys such as tin alloys, silicon alloys, and lead alloys; Li X Fe2O3, Li X Fe3O4, Li X WO2 (x is a number where 0 < x < 1.), metal oxide systems such as lithium titanate, lithium vanadate, and lithium silicate; conductive polymer systems such as polyacetylene and poly-p-phenylene; carbonaceous powders such as artificial graphite and natural graphite of highly graphitized carbon materials; carbon-based materials such as resin-fired carbon materials. The negative electrode active material can also be used by combining one or more of them.

[0143] The low-molecular-weight acidic compound (E) is preferably a low-molecular-weight compound that behaves as an acid relative to the active material used. The low-molecular-weight compound is a compound having a molecular weight of less than 10,000, preferably a compound having a molecular weight of 5,000 or less, 1,000 or less, 500 or less, or 350 or less. More specifically, the molecular weight of the low-molecular-weight acidic compound (E) is preferably 10 to 1,000, more preferably 30 to 350, even more preferably 40 to 250, and even more preferably 50 to 200. The low-molecular-weight acidic compound (E) may be either a synthetic product or a commercially available product, and may be used alone or in combination of two or more types.

[0144] When an electrode membrane slurry precursor contains an active material (D) and a fluoropolymer (F), basic impurities from the active material (D) may react with the fluoropolymer (F), causing gelation of the fluoropolymer (F). Examples of basic impurities include lithium hydroxide, which remains during the synthesis of the active material (D). Adding a low-molecular-weight acidic compound (E) to the electrode membrane slurry precursor neutralizes the basic impurities and inhibits gelation of the fluoropolymer (F). Direct addition of the low-molecular-weight acidic compound (E) to a composition containing carbon black can reduce the dispersibility of the carbon black. However, mixing the low-molecular-weight acidic compound (E) with the active material (D) and the fluoropolymer (F) before adding it to the carbon black dispersion and then mixing it with the carbon black dispersion to form an electrode membrane slurry precursor can prevent the reduction in dispersibility of the carbon black.

[0145] The acid dissociation constant (pKa) of the low-molecular-weight acidic compound (E) is preferably -5 to 10, more preferably -3 to 9, even more preferably -1 to 7, and particularly preferably 1 to 6. The acid dissociation constant value can be obtained from a chemical handbook or the like as a value in an aqueous solution at 25°C. If the acid dissociation constant value is too large, the expected effect may not be obtained, whereas if it is too small, corrosion of the production line or caution in handling may be required.

[0146] The low molecular weight acidic compound (E) may be either an inorganic acid or an organic acid, or a combination thereof. Examples of the low molecular weight acidic compound (E) include carboxylic acid compounds, oxo acid compounds, hydroxy acid compounds, and compounds having a carboxy group, a sulfo group, or a phosphate group. The low molecular weight acidic compound (E) preferably has 1 to 3 acidic groups, more preferably 1 to 2, per molecule. Specific examples of the low-molecular-weight acidic compound (E) include saturated fatty acids such as acetic acid, propionic acid, caprylic acid, and stearic acid; unsaturated carboxylic acids such as oleic acid and sorbic acid; aromatic carboxylic acids such as benzoic acid, salicylic acid, and phthalic acid; dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, and maleic acid; carboxylic anhydrides such as acetic anhydride, benzoic anhydride, phthalic anhydride, and maleic anhydride; hydroxy acids such as tartaric acid, citric acid, and glyceric acid; aromatic sulfonic acids such as benzenesulfonic acid and toluenesulfonic acid; and inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. These inorganic and organic acids may have counterions.

[0147] The low-molecular-weight acidic compound (E) is preferably an organic acid, more preferably a carboxylic acid, an oxo acid, or a hydroxy acid, more specifically, a saturated or unsaturated monocarboxylic acid, a saturated or unsaturated dicarboxylic acid, an aromatic carboxylic acid, a hydroxy acid, or an aromatic sulfonic acid. The low-molecular-weight acidic compound (E) preferably has a carboxy group, more preferably a saturated or unsaturated monocarboxylic acid or a saturated or unsaturated dicarboxylic acid, and even more preferably a saturated monocarboxylic acid or a saturated dicarboxylic acid.

[0148] The low molecular weight acidic compound (E) is preferably soluble in the electrode membrane slurry precursor, and more preferably dissolves in an amount of 0.1 part by mass or more per 100 parts by mass of N-methyl-2-pyrrolidone at atmospheric pressure and at 0 to 40°C.

[0149] The fluoropolymer (F) is contained in the electrode film slurry precursor as a binder resin. The binder resin is a resin used to bond materials such as active materials and carbon nanotubes together. In this specification, the binder resin is different from the polymer (B). That is, the binder resin is selected from resins other than the polymer (B). The binder resin preferably contains the fluoropolymer (F) as a main component. For example, the fluoropolymer (F) may account for 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more of the total amount of the binder resin, and the binder resin may be entirely the fluoropolymer (F).

[0150] The fluoropolymer (F) is a polymer compound having fluorine atoms, and is preferably a polymer of a fluorohydrocarbon. Examples of the fluoropolymer (F) include polyvinylidene fluoride, polyvinyl fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, and ethylene fluoride-propylene copolymer, and may also be modified products or copolymers thereof. The fluoropolymer (F) may be used alone or in combination of two or more. Preferably, the fluoropolymer (F) contains polyvinylidene fluoride.

[0151] The weight average molecular weight (Mw) of the fluorine-based polymer (F) is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,000,000, and even more preferably from 200,000 to 1,000,000.

[0152] The binder resin may contain other binder resins in addition to the fluorine-based polymer (F). Examples of other binder resins include homopolymers 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, vinyl pyrrolidone, or the like as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, and silicone resins; cellulose resins such as carboxymethyl cellulose or salts thereof; rubbers such as hydrogenated or unhydrogenated styrene-butadiene rubber and fluororubbers; and conductive resins such as polyaniline and polyacetylene. Modified versions or copolymers of these may also be used. These may be used alone or in combination of two or more. When used as a binder resin for a slurry composition for a positive electrode membrane, it is preferable to use the fluoropolymer (F) alone from the viewpoint of durability, and it is preferable to use polyvinylidene fluoride as the fluoropolymer (F).When used as a binder resin for a slurry composition for a negative electrode membrane, it is preferable to use, in addition to the fluoropolymer (F), carboxymethyl cellulose or a salt thereof, styrene-butadiene rubber or a hydrogenated product thereof, polyacrylic acid, etc., which have good adhesiveness.

[0153] The weight average molecular weight of the binder resin is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and even more preferably 200,000 to 1,000,000.

[0154] The solvent for the electrode membrane slurry precursor is preferably an amide organic solvent. The solvent preferably contains an amide organic solvent as a main component. For example, the amide organic solvent may be 50 mass %, 80 mass % or more, 90 mass % or more, or 95 mass % or more of the total amount of solvent, or the entire solvent may be an amide organic solvent. Details of the amide organic solvent are as described above. The electrode membrane slurry precursor preferably does not substantially contain water. The amide organic solvent (C) contained in the carbon nanotube dispersion and the amide organic solvent (C') contained in the electrode membrane slurry precursor may be the same or different. When multiple types are contained, all components may be the same, or some or all components may be different. Preferably, the amide organic solvent (C) contained in the carbon nanotube dispersion and the amide organic solvent (C') contained in the electrode membrane slurry precursor contain the same solvent, and when multiple types are contained, all components may be the same and in the same proportions.

[0155] In the electrode membrane slurry precursor, the active material (D) is preferably 40 to 90 mass %, more preferably 50 to 85 mass %, and even more preferably 60 to 80 mass %, based on the mass of the electrode membrane slurry precursor (the mass of the electrode membrane slurry precursor being 100 mass %). In the electrode membrane slurry precursor, the low molecular weight acidic compound (E) is preferably 0.005 to 2.0 mass%, more preferably 0.01 to 1.0 mass%, and even more preferably 0.02 to 0.5 mass%, based on the mass of the electrode membrane slurry precursor (the mass of the electrode membrane slurry precursor being 100 mass%). In the slurry precursor for an electrode membrane, the fluoropolymer (F) is preferably 0.1 to 10 mass %, more preferably 0.3 to 8 mass %, and even more preferably 0.5 to 5 mass %, based on the mass of the slurry precursor for an electrode membrane (the mass of the slurry precursor for an electrode membrane being 100 mass %). From the viewpoint of neutralizing basic impurities derived from the active material (D), the amount of the low-molecular-weight acidic compound (E) is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, even more preferably 0.03 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the active material (D). Furthermore, within these ranges, a decrease in dispersibility of carbon nanotubes due to the action of the low-molecular-weight acidic compound (E) can be prevented when the electrode membrane slurry precursor is mixed with the carbon nanotube dispersion. The amount of the low molecular weight acidic compound (E) is preferably 1.0 to 30 parts by mass, more preferably 2.0 to 20 parts by mass, and even more preferably 3.0 to 10 parts by mass, per 100 parts by mass of the fluoropolymer (F). The amount of the fluorine-based polymer (F) may be adjusted depending on the composition of the slurry composition for an electrode film, but is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the active material (D). The solid content of the electrode membrane slurry precursor is preferably 60 to 95 mass %, more preferably 65 to 93 mass %, and even more preferably 70 to 90 mass %. The content and solid content of each component of the electrode membrane slurry precursor may be adjusted appropriately according to the content of each component of the desired electrode membrane slurry composition.

[0156] The method for producing the electrode membrane slurry precursor is not particularly limited. The electrode membrane slurry precursor can be obtained, for example, by mixing an active material, a binder resin, a low-molecular-weight acidic compound, and a solvent, and then homogenizing the mixture appropriately. In addition to the active material, binder resin, low-molecular-weight acidic compound, and solvent, any other component may be mixed. The order in which the active material, binder resin, and low-molecular-weight acidic compound are added to a container is not particularly limited. As a mixing method, various conventionally known methods can be used. When mixing the electrode membrane slurry precursor, for example, a planetary mixer, a rotation-revolution mixer, or the like can be used to uniformly mix the solid components of the active material (D) and the fluoropolymer (F). A planetary mixer can enhance mixing efficiency by stirring the raw materials with blades that revolve while rotating, thereby applying a large shear force. A rotation-revolution mixer can enhance mixing efficiency by rotating and revolving a container into which the raw materials are charged, thereby applying shear force and centrifugal force to the raw materials. Examples of rotation-revolution mixers include the "Awatori Rentaro" (product name) series manufactured by Thinky Corporation. The electrode membrane slurry precursor may also be mixed using the dispersing device described above for the carbon nanotube dispersion.

[0157] <Slurry Composition> The electrode membrane slurry composition is obtained by mixing a carbon nanotube dispersion liquid with an electrode membrane slurry precursor. Specifically, the electrode membrane slurry composition can contain carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, and an amide-based organic solvent (C), as well as an active material (D), a low-molecular-weight acidic compound (E), a fluorine-based polymer (F), and an amide-based organic solvent (C'). If a low-molecular-weight acidic compound is added later to a slurry composition for an electrode membrane, the stability of the dispersion system is lost, which may result in thickening of the composition or aggregation of the carbon nanotubes. By preparing a carbon nanotube dispersion and a slurry precursor for an electrode membrane in advance, the dispersibility of the carbon nanotubes is maintained by the polymer (B) in the carbon nanotube dispersion, and by mixing a low-molecular-weight acidic compound, a fluoropolymer, and an active material in the slurry precursor for an electrode membrane, in particular by allowing the low-molecular-weight acidic compound and the active material to interact with each other, it is possible to maintain good dispersibility and stability of the carbon nanotubes even after mixing the carbon nanotube dispersion and the slurry precursor for an electrode membrane.

[0158] In the slurry composition for an electrode film, the content of the carbon nanotubes (A) is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, and even more preferably 0.03 to 3 parts by mass, relative to 100 parts by mass of the active material. In the slurry composition for an electrode film, the content of the fluorine-based polymer (F) is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the active material.

[0159] In the slurry composition for an electrode film, the content of the polymer (B) may be adjusted appropriately depending on the content of the carbon nanotubes (A), but is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the active material. In the slurry composition for an electrode film, the content of the low-molecular-weight acidic compound (E) may be adjusted appropriately depending on the content of the active material, but is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, even more preferably 0.03 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the active material. The solid content of the slurry composition for an electrode membrane is preferably 30 to 90 mass %, more preferably 30 to 80 mass %, and even more preferably 40 to 75 mass %, based on the mass of the slurry composition for an electrode membrane (the mass of the slurry composition for an electrode membrane being 100 mass %).

[0160] In the method for producing a slurry composition for an electrode membrane, the mixing ratio of the carbon nanotube dispersion liquid and the slurry precursor for an electrode membrane is not particularly limited, and may be appropriately adjusted so that the respective components and solid contents in the slurry composition for an electrode membrane are in the above-mentioned content ratios. In addition, a solvent such as an amide-based organic solvent may be further added to adjust the solid content. The electrode membrane slurry composition may further contain other optional components, such as wetting agents, antifoaming agents, surfactants, pH adjusters, wetting and penetrating agents, antioxidants, preservatives, antifungal agents, and leveling agents, as long as the components do not impair the objectives of the present invention. Furthermore, the electrode membrane slurry composition may further contain a conductive material other than carbon nanotubes and a polymer compound other than the polymer (B) and the fluoropolymer (F), as long as the components do not impair the objectives of the present invention. These optional components may be added to each composition before mixing the carbon nanotube dispersion and the electrode membrane slurry precursor, or may be added at any time, such as during or after the mixing process. It is preferable that the active material (D), the low-molecular-weight acidic compound (E), and the fluoropolymer (F) are not added to the carbon nanotube dispersion before mixing with the electrode membrane slurry precursor. It is also preferable that the carbon nanotubes (A) and the polymer (B) containing a nitrile group-containing structural unit are not added to the electrode membrane slurry precursor before mixing with the carbon nanotube dispersion.

[0161] The electrode membrane slurry can be prepared by mixing a carbon nanotube dispersion and a slurry precursor for the electrode membrane. A variety of conventionally known methods can be used as the mixing method. For mixing the electrode membrane slurry, a planetary mixer, a rotation-revolution mixer, or the like can be used to apply shear force to the slurry and mix the components more uniformly. Examples of the rotation-revolution mixer include the "Awatori Rentaro" (product name) series manufactured by Thinky Corporation. The electrode membrane slurry may also be mixed using the dispersing device described above for the carbon nanotube dispersion. The electrode membrane slurry precursor may be added to the carbon nanotube dispersion all at once or in portions, or the carbon nanotube dispersion may be added to the electrode membrane slurry precursor all at once or in portions.

[0162] <Electrode film manufacturing method> The method for producing an electrode film can include, for example, preparing a slurry composition for an electrode film and preparing an electrode film using the slurry composition for an electrode film. The method for preparing the slurry composition for an electrode film is as described above.

[0163] The electrode film can be obtained by applying a slurry composition for an electrode film to a substrate and drying it. A current collector can be used as the substrate. The material and shape of the current collector are not particularly limited, and can be appropriately selected to suit various batteries. For example, the material of the current collector can be metal or alloy such as aluminum, copper, nickel, titanium, or stainless steel. Furthermore, while a flat foil is generally used as the shape, a current collector with a roughened surface, a perforated foil current collector, or a mesh current collector can also be used.

[0164] The method for applying the electrode film slurry composition to the current collector is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Drying methods include, but are not limited to, leaving the composition to dry, or drying using a blower dryer, a warm air dryer, an infrared heater, or a far-infrared heater.

[0165] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the formed electrode film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0166] <Method of manufacturing battery electrodes> The method for producing a battery electrode may include, for example, preparing a slurry composition for an electrode film and preparing an electrode film on a current collector using the slurry composition for an electrode film. The method for preparing the slurry composition for an electrode film is as described above. Details of the current collector and the electrode film are as described above.

[0167] <Method of manufacturing non-aqueous electrolyte secondary battery> The method for producing a nonaqueous electrolyte secondary battery is, for example, a method for producing a nonaqueous electrolyte secondary battery including a negative electrode, a positive electrode, and an electrolyte, and the step of producing one of the negative electrode and the positive electrode can include preparing a slurry composition for an electrode film and producing an electrode film on an electrode substrate using the slurry composition for an electrode film. The method for preparing the slurry composition for an electrode film is as described above. The details of the current collector and the electrode film are as described above.

[0168] The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode includes an electrode film formed using the electrode film slurry composition obtained by the manufacturing method of one embodiment.

[0169] As the positive electrode, for example, an electrode film can be used which is prepared by applying a slurry composition for an electrode film containing a positive electrode active material onto a current collector and drying it. As the negative electrode, for example, an electrode film can be used which is prepared by applying a slurry composition for an electrode film containing a negative electrode active material onto a current collector and drying the composition.

[0170] Various conventionally known electrolytes capable of ion mobility can be used. Examples include, but are not limited to, lithium salts such as LiBF, LiClO, LiPF, LiAsF, LiSbF, LiCFSO, Li(CFSO)N, LiCFSO, Li(CFSO)C, LiI, LiBr, LiCl, LiAlCl, LiHF, LiSCN, or LiBPh (where Ph is a phenyl group). The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0171] The non-aqueous solvent is not particularly limited, but examples thereof 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; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination.

[0172] The non-aqueous electrolyte secondary battery may include a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, porous polyethylene, porous polypropylene, porous polyamide, and any of these that have been subjected to a hydrophilic treatment.

[0173] The structure of the nonaqueous electrolyte secondary battery is not particularly limited, but typically includes a positive electrode, a negative electrode, and a separator that is provided as needed, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type. [Example]

[0174] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Furthermore, in the examples, "polymer (B)" may be referred to as "copolymer" or "dispersant," "carbon nanotubes" may be referred to as "CNT," and "N-methyl-2-pyrrolidone" may be referred to as "NMP."

[0175] Table 1 shows the synthesis recipe for polymer (B), Table 2 shows the recipe for the CNT dispersion and the evaluation results thereof, Table 3 shows the relationship between the CNT concentration of the CNT dispersion and the complex modulus of elasticity, Table 4 shows the recipe for the slurry precursor for the electrode film, Tables 5 and 6 show the recipes for the slurries for the electrode film, and Table 7 shows the evaluation results of the positive electrode and the battery.

[0176] <Measurement of weight average molecular weight (Mw) of copolymer> The weight-average molecular weight (Mw) of the copolymer was measured by gel permeation chromatography (GPC) equipped with an RI detector. The instrument used was an HLC-8320GPC (manufactured by Tosoh Corporation). Three separation columns were connected in series, and the packing materials were Tosoh Corporation's "TSK-GEL SUPER AW-4000," "AW-3000," and "AW-2500." The oven temperature was 40°C, and the eluent was a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide. The measurement was performed at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a 1% concentration using a solvent consisting of the eluent, and 20 μL was injected. The weight-average molecular weight is a polystyrene equivalent value.

[0177] <Mooney viscosity of copolymer (ML 1+4 , 100℃) The Mooney viscosity of a copolymer is measured by preparing a measurement sample from a copolymer solution containing a solvent capable of dissolving it. When the copolymer is dissolved in NMP, the NMP solution of the copolymer is coagulated with water, washed with methanol, and vacuum dried at 60°C for 12 hours to prepare a measurement sample. The Mooney viscosity (ML) of 40 g of the measurement sample is measured using an L-type rotor at 100°C in accordance with Japanese Industrial Standard JIS K6300-1. 1+4 , 100℃) were measured.

[0178] <Measurement of initial viscosity of carbon nanotube dispersion> The viscosity value was measured using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) at 25°C. After thoroughly stirring the carbon nanotube dispersion with a spatula, the viscosity was measured immediately at a rotor speed of 60 rpm. The rotors used for the measurements were No. 1 for viscosity values ​​less than 100 mPa·s, No. 2 for viscosity values ​​between 100 and 500 mPa·s, No. 3 for viscosity values ​​between 500 and 2,000 mPa·s, and No. 4 for viscosity values ​​between 2,000 and 10,000 mPa·s. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the worse the dispersibility. Obtained carbon nanotube dispersions that clearly separated or settled were judged to have poor dispersibility. Judgment criteria ◎: Less than 500 mPa·s (excellent) ○: 500 mPa·s or more and less than 2,000 mPa·s (good) △: 2,000 mPa·s or more and less than 10,000 mPa·s (acceptable) ×: 10,000 mPa·s or more, sedimentation or separation (failure)

[0179] <Measurement of the complex modulus and phase angle of carbon nanotube dispersion> The complex modulus and phase angle of the carbon nanotube dispersion were evaluated by dynamic viscoelasticity measurements using a rheometer (RheoStress1 rotational rheometer manufactured by Thermo Fisher Scientific) with a 60 mm diameter, 2° cone angle, at 25°C, a frequency of 1 Hz, and a strain rate range of 0.01% to 5%. The smaller the complex modulus obtained, the better the dispersibility, and the larger the phase angle obtained, the worse the dispersibility. Furthermore, the larger the phase angle obtained, the better the dispersibility, and the smaller the phase angle obtained, the worse the dispersibility. Complex modulus of elasticity criteria ◎: Less than 20Pa (excellent) ○: 20 Pa or more and less than 60 Pa (good) △: 60 Pa or more but less than 120 Pa (acceptable) ×: 120Pa or more (defective) Phase angle judgment criteria ◎: 45° or more (excellent) ○: 10° or more and less than 45° (good) △: 2° or more and less than 5° (acceptable) ×: Less than 2° (poor)

[0180] <Evaluation of positive electrode resistance> The positive electrode composite slurry was applied to a PET film (100 μm thick) using an applicator with a 175 μm gap, and then dried in a hot air oven at 70 °C for 10 minutes and then at 120 °C for 15 minutes to obtain a positive electrode film for conductivity evaluation. The surface resistivity (Ω / □) of the positive electrode composite layer was measured using a Loresta GP MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd. After measurement, the volume resistivity (Ω·cm) was calculated by multiplying it by the thickness of the positive electrode composite layer formed on the PET film. The thickness of the positive electrode composite layer was measured at three points using a film thickness meter (NIKON Corporation, DIGIMICRO MH-15M) to determine the average value of the positive electrode film, and then calculated as the difference between the average value of the positive electrode film and the thickness of the PET film. Judgment criteria ◎: The volume resistivity (Ω·cm) of the positive electrode composite layer is less than 10 (excellent) 〇: The volume resistivity (Ω·cm) of the positive electrode mixture layer is 10 or more and less than 20 (good) ×: The volume resistivity (Ω·cm) of the positive electrode mixture layer is 20 or more (poor)

[0181] <Evaluation of rate characteristics of non-aqueous electrolyte secondary batteries> The nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to charge / discharge measurements using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). The battery was charged at a constant current / constant voltage of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA (0.02 C)), followed by a constant current discharge at a discharge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA (0.02 C)). This procedure was repeated three times, followed by a constant current / constant voltage charge at a charge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA (0.02 C)). The battery was then discharged at constant currents of 0.2 C and 3 C until the discharge cutoff voltage reached 3.0 V, and the discharge capacity was calculated for each battery. The rate characteristic can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, using the following equation: (Formula 1) Rate characteristics = 3C discharge capacity / 3rd 0.2C discharge capacity × 100 (%) Judgment criteria ◎: Rate characteristics are 80% or more (excellent) 〇: Rate characteristics are 60% or more and less than 80% (good) ×: Rate characteristics are less than 60% (bad)

[0182] <Method for evaluating cycle characteristics of non-aqueous electrolyte secondary batteries> The nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to charge / discharge measurements using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). A constant-current / constant-voltage charge (cutoff current 2.5 mA (0.05 C)) was performed at a charge current of 25 mA (0.5 C) with a charge cutoff voltage of 4.3 V, followed by a constant-current discharge at a discharge current of 25 mA (0.5 C) with a discharge cutoff voltage of 3 V. This procedure was repeated 200 times. The cycle performance can be expressed as the ratio of the 3rd 0.5 C discharge capacity to the 200th 0.5 C discharge capacity at 25°C, as shown in Equation 2 below. (Formula 2) Cycle characteristics = 3rd 0.5C discharge capacity / 200th 0.5C discharge capacity × 100 (%) Judgment criteria ◎: Cycle characteristics are 85% or more (excellent) 〇: Cycle characteristics are 80% or more and less than 85% (good) ×: Cycle characteristics are less than 80% (bad)

[0183] <Preparation of Polymer (B)> (Preparation of Polymer 1) According to the composition shown in Table 1, 30 parts of acrylonitrile (AN), 70 parts of 1,3-butadiene (BD), 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.55 parts of t-dodecyl mercaptan (TDM), and 200 parts of ion-exchanged water were added to a stainless steel polymerization reactor. Under a nitrogen atmosphere, polymerization was carried out at 45°C for 20 hours with stirring, and terminated at a conversion of 90%. Unreacted monomer was removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%. The mixture was then placed in a 1-L autoclave equipped with a stirrer, and dissolved oxygen in the contents was removed by flowing nitrogen gas for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The autoclave was purged twice with hydrogen gas, and then the contents were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to recover Polymer 1. The hydrogenation rate of Polymer 1 was 99.6%, and the weight-average molecular weight (Mw) was 150,000. In the acrylonitrile-conjugated diene rubber, the content of conjugated diene monomer units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of the acrylonitrile-conjugated diene rubber. Furthermore, in Polymer 1, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of Polymer 1. The contents of these monomer units and structural units are mass proportions calculated from the amounts of monomers used (the same applies hereinafter). The Mooney viscosity (ML 1+4 , 100℃) was measured and found to be 50.

[0184] (Preparation of Polymers 2 to 5) The monomer composition used was changed according to Table 1, and the content of t-dodecyl mercaptan, which is the molecular weight regulator used, was appropriately changed so that the Mooney viscosity of the target polymer was obtained, and Polymers 2 to 5 were prepared. Polymer 5 further contains acrylamide (AAm) in the monomer composition. The other procedures were the same as those for the preparation of Polymer 1 above. The measurement results of the weight average molecular weight and Mooney viscosity of the obtained Polymers 2 to 5 were as shown in Table 1.

[0185] <Preparation of CNT Dispersion Liquid> (CNT Dispersion Liquid 1) According to the composition shown in Table 2, 94 parts of NMP as an amide-based organic solvent (C) and 1 part of Polymer 1 as a polymer (B) containing a nitrile group-containing structural unit were added to a stainless steel container, and the stainless steel container was uniformly stirred with a disper while heating at 40 °C to dissolve Polymer 1. Subsequently, the heating of the stainless steel container was stopped, and while cooling at 25 °C, 100T5 parts of carbon nanotubes (A) were slowly added to the solution while stirring with a disper, and then batch dispersion treatment was performed with a high-shear mixer (manufactured by SILVERSON) equipped with a square-hole high-shear screen until the particle size at the grind gauge became 250 μm or less. Next, the dispersion liquid was supplied from the stainless steel tank to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) via a pipe for additional dispersion treatment. The additional dispersion treatment was performed using a single nozzle chamber, and a 25-pass dispersion treatment was performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain CNT Dispersion Liquid 1.

[0186] (CNT Dispersion Liquids 2 to 5 and CNT Dispersion Liquids 10 to 15) According to the composition shown in Table 2, CNT Dispersion Liquids 2 to 5 and 10 to 15 were obtained in the same manner as CNT Dispersion Liquid 1, except that the types and amounts of carbon nanotubes (A), polymers (B) containing nitrile group-containing structural units, and amide-based organic solvents (C) were changed.

[0187] (CNT Dispersion Liquid 6) According to the composition shown in Table 2, 93.8 parts of NMP as the amide organic solvent (C) and 1 part of polymer 1 as the polymer (B) containing a nitrile group-containing structural unit were added to a stainless steel container. The stainless steel container was heated to 40°C while stirring uniformly with a disperser to dissolve polymer 1. Next, heating of the stainless steel container was stopped, and while cooling to 25°C, 0.2 parts of ethanolamine as another additive was added to the solution. 5 parts of 100T carbon nanotubes (A) were slowly added with stirring with a disperser. The mixture was subjected to batch dispersion treatment using a high-shear mixer (manufactured by Silverson) equipped with a square-hole high-shear screen until the particle size measured on a grind gauge reached 250 μm or less. Next, the dispersion liquid was fed from the stainless steel tank via piping to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) for additional dispersion treatment. The additional dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, performing 25 passes to obtain CNT dispersion liquid 6.

[0188] (CNT dispersions 7 and 9) CNT Dispersions 7 and 9 were obtained in the same manner as CNT Dispersion 6, except that the types and amounts of carbon nanotubes (A), polymer containing a nitrile group-containing structural unit (B), other additives, and amide organic solvent (C) were changed according to the composition shown in Table 2.

[0189] (CNT dispersion liquid 8) According to the composition shown in Table 2, 94 parts of NMP as the amide organic solvent (C), 0.6 parts of polymer 1 as the polymer (B) containing a nitrile group-containing structural unit, and 0.4 parts of PVP as other additives were added to a stainless steel container. The stainless steel container was heated to 40°C and stirred uniformly with a disperser to dissolve polymer 1. Next, heating of the stainless steel container was stopped, and while cooling to 25°C, the solution was added. 5 parts of 100T carbon nanotubes (A) were slowly added while stirring with a disperser. A batch dispersion treatment was carried out using a high-shear mixer (manufactured by Silverson) equipped with a square-hole high-shear screen until the particle size measured on a grind gauge reached 250 μm or less. Next, the dispersion liquid was fed from the stainless steel tank via piping to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) for additional dispersion treatment. The additional dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, performing 25 passes to obtain CNT dispersion liquid 8.

[0190] (Comparison CNT dispersion 1) According to the composition shown in Table 2, 94 parts of NMP as the amide organic solvent (C) and 1 part of PVP as an additive were added to a stainless steel container. The stainless steel container was heated to 40°C and stirred uniformly with a disperser to dissolve the PVP. Next, the heating of the stainless steel container was stopped, and the solution was added while cooling to 25°C. 5 parts of 100T carbon nanotubes (A) were slowly added while stirring with a disperser. A batch dispersion process was carried out using a high-shear mixer (manufactured by Silverson) equipped with a square-hole high-shear screen until the particle size measured on a grind gauge reached 250 μm or less. Next, the dispersion liquid was fed from the stainless steel tank via piping to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) for additional dispersion. The additional dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, performing 25 passes to obtain comparative CNT dispersion liquid 1.

[0191] (Comparative CNT dispersion liquid 2) Comparative CNT dispersion liquid 2 was obtained in the same manner as comparative CNT dispersion liquid 1, except that the type and amount of carbon nanotubes (A) and the amount of amide organic solvent (C) added were changed according to the composition shown in Table 2.

[0192] The other ingredients used are as follows: Carbon nanotubes "100T": K-Nanos 100T (Kumho Petrochemical Co., Ltd., multi-walled CNT, outer diameter 10-15 nm) Carbon nanotubes "Flotube9110": Cnano FT9110CNT (manufactured by Cnano Technology Ltd., multi-walled CNT, average outer diameter 11 nm) Carbon nanotubes "BT1003M": LUCAN BT1003M (LG Chem Ltd., multi-walled CNT, average outer diameter 13 nm) Carbon nanotube "8A": JENOTUBE8A (manufactured by JEIO Corporation, multi-walled CNT, outer diameter 6-9 nm) Dispersant "HNBR": Zetpol (registered trademark) 2000L (manufactured by Zeon Corporation, Mooney viscosity (ML 1+4 , 100℃) 65, acrylonitrile content 36.2%) Ethanolamine: 2-aminoethanol (Fujifilm Wako Pure Chemical Industries, Ltd.) NaOH: Sodium hydroxide, granular (Fujifilm Wako Pure Chemical Industries, Ltd.) PVP: Polyvinylpyrrolidone ("Polyvinylpyrrolidone K-30" manufactured by Nippon Shokubai Co., Ltd.)

[0193] The initial viscosity, complex modulus and phase angle of the obtained CNT dispersion were evaluated, and the evaluation results are shown in the table.

[0194] CNT dispersions 12 to 15 all use the same carbon nanotubes (8A) and are dispersions with CNT concentrations of 2.5, 2.0, 1.5, and 1.0 (mass%), respectively. For each dispersion, the complex modulus [G * ] (Pa) are shown in Table 3. The CNT concentration (mass%) in the dispersion is plotted on the x-axis, and the complex modulus [G* The relationship is shown in the graph in Figure 1, with ](Pa) on the y-axis.

[0195] 1, it can be confirmed that CNT dispersions 12 to 15 satisfy y<17x. That is, the CNT dispersions of the examples satisfy the relationships of the following formulas (1), (2), and (3). y<17x (1) y<120 (2) 0.1≦x≦10 (3)

[0196] <Preparation of Slurry Precursor for Electrode Membrane> (Slurry precursor 1) According to the composition shown in Table 4, 87.03 parts of NMC as the active material (D) and 12.43 parts of a 10% by mass NMP solution of PVDF-1 (containing 1.243 parts of PVDF-1 as solids) as the fluoropolymer (F) were added to a 150 mL plastic container, and the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Next, 0.533 parts of a 10% NMP solution of benzoic acid (containing 0.053 parts of benzoic acid as solids) was added as the low molecular weight acidic compound (E), and the mixture was stirred at 2,000 rpm for 20 minutes using a centrifugal mixer to obtain a slurry precursor 1. The solid content of the slurry precursor was 88.33% by mass, and the ratio of the active material (D) to the fluoropolymer (F) was adjusted based on the ratio of the electrode membrane slurry composition (active material (D):fluoropolymer (F):CNT (A) = 98:1.4:0.6). The low molecular weight acidic compound (E) was added so that the ratio of the active material (D):low molecular weight acidic compound (E) was 100:0.061.

[0197] (Slurry precursors 2 to 9) Slurry precursors 2 to 9 were obtained in the same manner as slurry precursor 1, except that the active material (D), fluoropolymer (F) and low-molecular-weight acidic compound (E) were changed according to the composition shown in Table 4.

[0198] (Comparative Slurry Precursor 1) According to the composition shown in Table 4, 87.03 parts of NMC as the active material (D) and 12.43 parts of a 10% by mass NMP solution of PVDF-1 (containing 1.243 parts of PVDF-1 as solids) as the fluoropolymer (F) were added to a 150 mL plastic container, and the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Next, 0.533 parts of a 10% NMP solution of ISOBAM-10 (containing 0.053 parts of ISOBAM-10 as solids) was added as another acidic compound, and the mixture was stirred at 2,000 rpm for 20 minutes using a centrifugal mixer to obtain Comparative Slurry Precursor 1.

[0199] (Comparative Slurry Precursor 2) Comparative slurry precursor 2 was obtained in the same manner as comparative slurry precursor 1, except that the types of other acidic compounds were changed according to the composition shown in Table 4.

[0200] The ingredients used are as follows: Active material "NMC": NCM811 (manufactured by Ningbo Ronbay New Energy Technology, composition: LiNi 0.8 Co 0.1 Mn 0.1 O2, 100% solids Active material "NCA": HED (registered trademark) NAT-7050 (manufactured by BASF Toda Battery Materials LLC, composition: LiNi 0.8 Co 0.15 Al 0.05 O2, 100% solids Comparative additive "ISOBAM-10": manufactured by Kuraray Co., Ltd., weight average molecular weight 160,000 to 170,000, volatile content ≦ 4% Comparative additive "Polyacrylic acid": Fujifilm Wako Pure Chemical Industries, Ltd., polyacrylic acid 25,000, molecular weight 25,000 Fluorine-based polymer "PVDF-1": Polyvinylidene fluoride Kureha KF Polymer W#7300 (manufactured by Kureha Corporation), 100% solids Fluoropolymer "PVDF-2": Polyvinylidene fluoride with polar functional groups, Solef #5130 (Solvey Co., Ltd.), 100% solids The low molecular weight acidic compounds used were benzoic acid, adipic acid, succinic acid, o-phthalic acid, benzenesulfonic acid, citric acid, and acetic acid, all of which are available from Fujifilm Wako Pure Chemical Industries, Ltd.

[0201] <Slurry composition for electrode film and preparation of electrode film> (Example 1-1) According to the formulation shown in Table 5, the CNT dispersion and the electrode membrane slurry precursor were weighed out so that the mass ratio of active material (D):fluoropolymer (F):CNT (A) was 98:1.4:0.6, and added to a 150 mL plastic container. The mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain an electrode membrane slurry composition. The solids content of the electrode membrane slurry composition was 72 mass%. The obtained electrode film slurry composition was applied to a 20 μm thick aluminum foil as a current collector using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​20 mg / cm. 2 Further, a rolling treatment was carried out using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to adjust the density of the electrode layer to 3.1 g / cm. 3 A positive electrode 1a having the following structure was fabricated.

[0202] (Examples 1-2 to 1-21, Comparative Examples 1-1 to 1-5) Positive electrodes 2a to 21a and comparative positive electrodes 1a to 5a were produced in the same manner as in Example 1-1, except that the types of CNT dispersion liquid and electrode membrane slurry precursor were changed.

[0203] <Production of Slurry Composition for Electrode Membrane and Electrode Membrane Not Containing Low-Molecular-Weight Acidic Compound (E)> (Comparative Examples 1-6) According to the formulation shown in Table 6, a slurry composition for electrode membranes was prepared with a mass ratio of 98:1.4:0.6 for the active material (D):fluoropolymer (F):CNT (A). First, CNT dispersion 1 and a 10% by mass NMP solution of PVDF-1 (as the fluoropolymer (F)) were added to a 150 mL plastic container, followed by the addition of NMP to adjust the solids content (the amount of NMP added was adjusted so that the final electrode membrane slurry composition would have a solids content of 72%). The mixture was then stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain a binder resin-containing CNT dispersion. Next, NMC was added as the active material (D), and the mixture was stirred at 2,000 rpm for 20 minutes using a centrifugal mixer to obtain a slurry composition for electrode membranes. This addition order is referred to as Comparative Procedure 1. The obtained electrode film slurry composition was applied to a 20 μm thick aluminum foil as a current collector using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​20 mg / cm. 2 Further, a rolling treatment was carried out using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to adjust the density of the electrode layer to 3.1 g / cm. 3 A comparative positive electrode 6a was fabricated.

[0204] <Preparation of electrode membrane slurry composition and electrode membrane with modified addition procedure> (Comparative Examples 1-7) A slurry composition for an electrode film was prepared according to the formulation shown in Table 6, with a mass ratio of active material (D):fluoropolymer (F):CNT (A) of 98:1.4:0.6. First, CNT dispersion 1 and a 10 mass% NMP solution of PVDF-1 (as the fluoropolymer (F)) were added to a 150 mL plastic container, followed by the addition of NMP to adjust the solids content (the amount added was adjusted so that the final electrode film slurry composition would have a solids content of 72%). The mixture was then stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain a binder resin-containing CNT dispersion. Next, NMC was added as the active material (D) and stirred at 2,000 rpm for 30 seconds using a centrifugal mixer. A 10% by mass solution of benzoic acid in NMP was then added as the low molecular weight acidic compound (E) and stirred at 2,000 rpm for 20 minutes using a centrifugal mixer to obtain a slurry composition for an electrode membrane. The low molecular weight acidic compound (E) was added so that the ratio of the active material (D) to the low molecular weight acidic compound (E) was 100:0.061. This addition order is referred to as Comparative Procedure 2. The obtained electrode film slurry composition was applied to a 20 μm thick aluminum foil as a current collector using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​20 mg / cm. 2 Further, a rolling treatment was carried out using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to adjust the density of the electrode layer to 3.1 g / cm. 3 A comparative positive electrode 7a was fabricated.

[0205] (Comparative Examples 1-8 to 1-13) Comparative positive electrodes 8a to 13a were produced in accordance with the formulations shown in Table 6 in the same manner as in Comparative Examples 1-7, except that the types of CNT dispersion liquid and electrode membrane slurry precursor were changed. The resistance of the obtained positive electrode was evaluated, and the results are shown in Table 7.

[0206] <Battery construction> (Examples 1-1 to 1-21, Comparative Examples 1-1 to 1-13) The standard negative electrode shown below and the positive electrode shown in Tables 5 and 6 were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively. The separator (porous polypropylene film) between them was inserted into an aluminum laminate bag and dried in an electric oven at 70 °C for 1 hour. Next, 2 mL of electrolyte was poured into a glove box filled with argon gas, and the aluminum laminate bag was sealed to produce batteries 1a to 21a and comparative batteries 1a to 13a. The electrolyte used was a nonaqueous electrolyte prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 1:1:1 (volume ratio) mixed solvent. One part of VC (vinylene carbonate) was added to 100 parts of the electrolyte solution, and LiPF6 was dissolved in the nonaqueous electrolyte to a concentration of 1 M.

[0207] (Preparation of standard negative electrode) Acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka Co., Ltd.), CMC, and water were added to a 150 mL plastic container and stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, ARE-310, Awatori Rentaro). Artificial graphite was then added as the negative electrode active material and stirred at 2,000 rpm for 150 seconds using a centrifugal mixer (Thinky Corporation, ARE-310, Awatori Rentaro). SBR was then added and stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, ARE-310, Awatori Rentaro). A standard negative electrode composite slurry was obtained. The solids content of the standard negative electrode composite slurry was 48% by mass. The solid content ratio of the negative electrode active material:conductive material:CMC:SBR in the standard negative electrode mixture slurry was 97:0.5:1:1.5. The abbreviations described above have the following meanings. HS-100: Denka Black HS-100 (manufactured by Denka Co., Ltd., acetylene black, average primary particle diameter 48 nm, specific surface area 39 m 2 / g) Artificial graphite: CGB-20 (manufactured by Nippon Graphite Industries Co., Ltd.), 100% solids CMC: #1190 (manufactured by Daicel FineChem Co., Ltd.), solid content 100% SBR: TRD2001 (JSR Corporation), solid content 48%

[0208] The obtained negative electrode composite slurry was applied to a 20 μm thick copper foil current collector using an applicator, and then dried in an electric oven at 80°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​10 mg / cm. 2 Further, a rolling treatment was carried out using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to adjust the density of the negative electrode composite layer to 1.6 g / cm. 3 A negative electrode having the following structure was fabricated.

[0209] The rate characteristics and cycle characteristics of the obtained battery were evaluated, and the results are shown in Table 7. As described above, by achieving both dispersibility and stability of carbon nanotubes in the electrode film slurry composition, a good dispersion state can be maintained in the electrode film, and an efficient conductive network can be formed, enabling the production of a battery with good rate characteristics and cycle characteristics.

[0210] [Table 1]

[0211] [Table 2]

[0212] [Table 3]

[0213] [Table 4]

[0214] [Table 5]

[0215] [Table 6]

[0216] [Table 7]

[0217] Although the present invention has been described with reference to the above-mentioned embodiment, the present invention is not limited to the above-mentioned embodiment. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims

1. The present invention comprises carbon nanotubes (A), a polymer (B) containing a nitrile group-containing structural unit, an amide organic solvent (C), an active material (D), a low-molecular-weight acidic compound (E) having a molecular weight of less than 10,000, and a fluorine-containing polymer (F), the fluorine-based polymer (F) is not gelled by the action of the active material (D); Slurry composition for electrode membrane.

2. 2. The slurry composition for an electrode membrane according to claim 1, wherein the content of the nitrile group-containing structural unit in the polymer (B) containing the nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less based on the mass of the polymer (B).

3. 3. The slurry composition for an electrode film according to claim 1, wherein the polymer (B) containing a nitrile group-containing structural unit has a weight average molecular weight of 5,000 or more and 500,000 or less.

4. A method for producing an electrode film, comprising producing an electrode film using the slurry composition for an electrode film according to claim 1 .

5. A method for producing a battery electrode, comprising forming an electrode film on a current collector using the slurry composition for an electrode film according to claim 1 .

6. 4. A method for manufacturing a nonaqueous electrolyte secondary battery including a negative electrode, a positive electrode, and an electrolyte, wherein a step of manufacturing one of the negative electrode and the positive electrode comprises manufacturing an electrode film on a current collector using the slurry composition for an electrode film according to claim 1.

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