Carbon nanotube dispersion liquid and its use

Abstract

To provide a CNT dispersion and a resin composition for improving the storage stability of a composite slurry and for obtaining an electrode film with high conductivity, more specifically provide a CNT dispersion, a resin composition, and a composite slurry having high dispersibility and allowing the composite slurry to have excellent storage stability, and provide a non-aqueous electrolyte secondary battery with excellent rate characteristics and high productivity.SOLUTION: The above problem can be solved by using a carbon nanotube dispersion comprising a carbon nanotube (A), a solvent (B), a dispersant (C), and an acidic compound (D) with a molecular weight of 350 or less, in which 1 to 25 parts by mass of the acidic compound (D) is added to 100 parts by mass of the carbon nanotube (A).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a dispersion of carbon nanotubes containing an acidic compound. More specifically, it relates to a carbon nanotube dispersion containing an acidic compound, a resin composition containing a carbon nanotube dispersion containing an acidic compound and a resin, a composite slurry containing a carbon nanotube dispersion containing an acidic compound, a resin and an active material, an electrode film coated with the same, and a non-aqueous electrolyte secondary battery comprising the electrode film and an electrolyte containing lithium.

Background Art

[0002] In recent years, with the popularization of mobile phones, notebook personal computers, etc., non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have attracted attention. A lithium-ion secondary battery usually includes a negative electrode made of a carbon-based material, a positive electrode containing an active material that reversibly allows lithium ions to enter and exit, and a non-aqueous electrolyte that immerses them. The positive electrode is manufactured by coating a composite slurry composed of an active material, a conductive material, and a binder on a current collector plate.

[0003] As the conductive material, carbon black, ketjen black, fullerene, graphene, fine carbon materials, etc. are used. In particular, carbon nanotubes (hereinafter also referred to as CNTs), which are a type of fine carbon fiber, are tube-shaped carbons with a thickness of 1 μm or less, and their use as a conductive material for lithium-ion secondary batteries has been studied due to their high conductivity based on their unique structure. (For example, Patent Documents 1 and 2) Among them, multi-walled CNTs with an outer diameter of several nm to several tens of nm are relatively inexpensive and are expected to be put into practical use. Multi-walled CNTs with an average outer diameter are relatively inexpensive and are expected to be put into practical use.

[0004] When CNTs with a small average outer diameter are used, a conductive network can be efficiently formed with a small amount, and the amount of the conductive material contained in the positive and negative electrodes for lithium-ion secondary batteries can be reduced. However, since CNTs with a small average outer diameter have a strong cohesive force and are difficult to disperse, it is difficult to obtain a CNT dispersion having sufficient dispersibility.

[0005] In addition, there is a demand for increasing the capacity of lithium-ion secondary batteries, and the use of electrode active materials containing a large amount of Al, Ni, Mn, etc. with strong basicity is being considered for increasing the capacity. However, when these active materials are used, bases elute into the composite material slurry, resulting in low storage stability of the composite material slurry, and concerns arise regarding the difficulty of the coating film, the production process, and the uniformity of the coating film.

[0006] There have also been reports on investigations to reduce the reaction with alkalis and enhance the storage stability of the composite material slurry by carrying out the production environment and coating environment of the composite material slurry in a low-temperature and low-humidity atmosphere (Patent Documents 3 and 4), but there are issues that require a large initial investment.

[0007] Improving the storage stability of the composite material slurry has been investigated by using additives or the like when the conductive aid is carbon black (Patent Document 5). However, when the conductive aid is CNT, thickening of the composite material slurry is observed, and concerns arise regarding the production process and the uniformity of the coating film. In addition, there is a problem that CNT, which is a conductive aid with strong cohesive force, re-aggregates in the composite material slurry from the dispersed state, resulting in the inability to form a conductive network and a decrease in the performance of the electrode.

[0008] For the CNT dispersion liquid, by sufficiently dispersing CNTs with high cohesive force, in addition to efficiently forming a conductive network in the electrode film with a lower addition amount than conventional carbon black or the like, it is required to have good storage stability in the composite material slurry in order to maintain the dispersed state of the CNTs.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0010] The problem to be solved by the present invention is to solve the above-mentioned conventional problems, and to provide a CNT dispersion liquid and a resin composition for enhancing the storage stability of the composite material slurry and obtaining an electrode film with high conductivity. More specifically, it is to provide a CNT dispersion liquid, a resin composition, and a composite material slurry having high dispersibility and excellent storage stability of the composite material slurry. More specifically, it is to provide a non-aqueous electrolyte secondary battery having excellent rate characteristics and excellent productivity. [Means for Solving the Problems]

[0011] The inventors of the present invention have intensively studied to solve the above problems. The inventors have found that by using a CNT dispersion liquid containing an acidic compound, an electrode film with high conductivity can be obtained, and a CNT dispersion liquid with excellent storage stability of the composite material slurry can be obtained. Based on such an invention, the present invention has been completed.

[0012] That is, the present invention relates to a carbon nanotube dispersion liquid containing carbon nanotubes (A), a solvent (B), a dispersant (C), and an acidic compound (D) having a molecular weight of 350 or less, wherein the acidic compound (D) is 1 to 25 parts by mass with respect to 100 parts by mass of the carbon nanotubes (A).

[0013] Further, the present invention relates to the above-mentioned carbon nanotube dispersion liquid, wherein the acidic compound (D) is an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a thiol group.

[0014] In addition, the present invention relates to the above CNT dispersion characterized in that, in the Raman spectrum of the carbon nanotube (A), when the maximum peak intensity in the range of 1560 to 1600 cm -1 is G and the maximum peak intensity in the range of 1310 to 1350 cm -1 is D, the G / D ratio is 0.5 to 5.0.

[0015] In addition, the present invention relates to the above carbon nanotube dispersion characterized in that the BET specific surface area of the carbon nanotube (A) is 180 to 850 m 2 / g.

[0016] In addition, the present invention relates to the above carbon nanotube dispersion characterized in that, in the powder X-ray diffraction analysis of the carbon nanotube (A), a peak exists at a diffraction angle 2θ = 25° ± 2°, and the half-value width of the peak is 2° to 6°.

[0017] In addition, the present invention relates to the above carbon nanotube dispersion characterized in that the outer diameter of the carbon nanotube (A) is 3 to 25 nm.

[0018] In addition, the present invention relates to the above carbon nanotube dispersion characterized in that, in the Raman spectrum of the carbon nanotube (A), when the maximum peak intensity in the range of 1560 to 1600 cm -1 is G and the maximum peak intensity in the range of 1310 to 1350 cm -1 is D, the G / D ratio is 1.8 to 4.5.

[0019] In addition, the present invention relates to the above carbon nanotube dispersion characterized in that, in the powder X-ray diffraction analysis of the carbon nanotube (A), a peak exists at a diffraction angle 2θ = 25° ± 2°, and the half-value width of the peak is 2° to 3°.

[0020] In addition, the present invention relates to a resin composition characterized by containing the above carbon nanotube dispersion and a binder (E).

[0021] The present invention also relates to a composite material slurry characterized by containing the above resin composition and the active material (F).

[0022] The present invention also relates to an electrode film (G) coated with the above composite material slurry.

[0023] The present invention also relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode contains the above electrode film (G).

Advantages of the Invention

[0024] By using the CNT dispersion of the present invention, a CNT dispersion, a resin composition, a composite material slurry, and an electrode film excellent in conductivity and storage stability of the composite material slurry can be obtained. Further, a non-aqueous electrolyte secondary battery having excellent rate characteristics can be obtained. Therefore, it is possible to use the CNT dispersion of the present invention in various application fields where high conductivity is required.

Modes for Carrying Out the Invention

[0025] Hereinafter, the CNT dispersion, acidic compound, resin composition, composite material slurry, and electrode film coated therewith, and non-aqueous electrolyte secondary battery of the present invention will be described in detail.

[0026] (1) Carbon nanotube (A) The carbon nanotube (A) (CNT (A)) of the present embodiment has a shape in which planar graphite is wound into a cylindrical shape. CNT (A) may contain mixed single-walled CNTs. A single-walled CNT has a structure in which one layer of graphite is wound. A multi-walled CNT has a structure in which two or more layers of graphite are wound. Further, the side wall of CNT (A) does not have to be a graphite structure. For example, a CNT having a side wall with an amorphous structure can also be used as CNT (A).

[0027] The shape of CNT(A) in this embodiment is not limited. Such shapes include various shapes such as needle-like, cylindrical tube-like, fishbone-like (fishbone or cup stacking type), trump-like (platelet), and coil-like. In this embodiment, the shape of CNT(A) is preferably needle-like or cylindrical tube-like among others. CNT(A) may be in a single shape or a combination of two or more shapes.

[0028] Examples of the form of CNT(A) in this embodiment include, but are not limited to, graphite whiskers, filamentous carbon, graphite fibers, ultra-thin carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. CNT(A) may have these single forms or a combined form of two or more of them.

[0029] CNT(A) in this embodiment usually exists as secondary particles. The shape of these secondary particles may be, for example, a state in which CNT(A), which is a general primary particle, is intricately intertwined. It may also be an aggregate of linear CNT(A). Secondary particles that are an aggregate of linear CNT(A) are more likely to be loosened compared to those that are intertwined. Also, linear ones have good dispersibility compared to those that are intertwined, so they can be suitably used as CNT(A).

[0030] CNT(A) in this embodiment may be CNT that has been surface-treated. Also, CNT(A) may be a CNT derivative to which a functional group represented by a carboxyl group is imparted. Further, carbon nanotube (A) encapsulating a substance represented by an organic compound, a metal atom, or fullerene can also be used.

[0031] The manufacturing method of CNT(A) in this embodiment is not particularly limited, and CNT manufactured by any method may be used.

[0032] The G / D ratio of the CNT(A) of this embodiment is determined by Raman spectroscopy. The CNT(A) of this embodiment has a maximum peak intensity within the range of 1560 to 1600 cm -1 in the Raman spectrum defined as G, and a maximum peak intensity within the range of 1310 to 1350 cm -1 defined as D. When the G / D ratio is preferably 0.5 to 5.0, more preferably 1.0 to 4.5, still more preferably 1.8 to 4.5, and even more preferably 1.8 to 3.0.

[0033] There are various laser wavelengths used in Raman spectroscopy. Here, 532 nm and 632 nm are utilized. The Raman shift observed around 1590 cm -1 in the Raman spectrum is called the G band derived from graphite, and the Raman shift observed around 1350 cm -1 is called the D band derived from defects in amorphous carbon or graphite. The higher the G / D ratio of the CNT, the higher the degree of graphitization.

[0034] The BET specific surface area of the CNT(A) of this embodiment is preferably 180 to 850 m 2 / g, and more preferably 200 to 550 m 2 / g.

[0035] The layer structure of CNT(A) can be analyzed by powder X-ray diffraction analysis using the following method.

[0036] First, fill CNT(A) into a predetermined sample holder so that its surface becomes flat, set it on a powder X-ray diffractometer, and measure by changing the irradiation angle of the X-ray source from 15° to 35°. For example, CuKα rays are used as the X-ray source. By reading the diffraction angle 2θ at which a peak appears at that time, CNT(A) can be evaluated. In graphite, a peak is usually detected at around 2θ = 26°, and this is known to be a peak due to interlayer diffraction. Since CNT(A) also has a graphite structure, a peak due to graphite interlayer diffraction is detected in this vicinity. However, because CNT has a cylindrical structure, its value is different from that of graphite. When a peak appears at a position where the value 2θ is 25° ± 2°, it can be determined that the composition contains a multi-layer structure rather than a single layer. Since the peak appearing at this position is a peak due to interlayer diffraction of the multi-layer structure, it becomes possible to determine the number of layers of CNT(A). Since single-layer CNT has only one layer, a peak does not appear at the position of 25° ± 2° with only single-layer CNT. However, even for single-layer CNT, it is not 100% single-layer CNT, and when multi-layer CNT or the like is mixed in, a peak may appear at the position of 2θ = 25° ± 2°.

[0037] That is, it is considered that the smaller the half-width of this peak, the larger the number of layers of multi-layer CNT(A). Conversely, the larger the half-width of this peak, the smaller the number of layers of CNT.

[0038] When powder X-ray diffraction analysis is performed on CNT(A) of this embodiment, a peak exists at the diffraction angle 2θ = 25° ± 2 °, and the half-width of the peak is preferably 2° to 6°, more preferably 2° to 5°, and even more preferably 2° to 3°.

[0039] The outer diameter of CNT(A) of this embodiment is preferably 3 nm to 25 nm, more preferably 3 nm to 20 nm, and even more preferably 3 nm to 16 nm.

[0040] The outer diameter and average outer diameter of CNT(A) in this embodiment are obtained as follows. First, CNT(A) is observed and imaged with a transmission electron microscope. Next, in the observation photograph, any 300 CNT(A) are selected and the outer diameter of each is measured. Next, the average outer diameter (nm) of CNT(A) is calculated as the number average of the outer diameters.

[0041] (2) Solvent (B) The solvent (B) in this embodiment is not particularly limited as long as CNT(A) can be dispersed therein, but is preferably any one or a mixed solvent composed of two or more of water and / or a water-soluble organic solvent.

[0042] Examples of water-soluble organic solvents include alcohol-based solvents (such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.), polyhydric alcohol-based solvents (such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ether-based solvents (such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine-based solvents (such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amide-based solvents (such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic-based solvents (such as cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide-based (dimethyl sulfoxide, etc.), sulfone-based (hexamethylphosphoramide, sulfolane, etc.), lower ketone-based (acetone, methyl ethyl ketone, etc.), and others such as tetrahydrofuran, urea, and acetonitrile can be used. Among these, water or an amide-based organic solvent is more preferable, and among the amide-based organic solvents, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone are particularly preferable.,

[0043] When only an amide-based organic solvent is used as the solvent (B) of this embodiment, the water content in the solvent (B) is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0044] (3) Dispersant (C) The dispersant (C) of this embodiment is not particularly limited as long as it can disperse and stabilize CNT (A), and triazine derivatives, resin-type dispersants, surfactants, etc. can be used. Appropriate types of dispersants can be used in appropriate blending amounts according to the characteristics required for the dispersion of CNT (A). However, the dispersant (C) does not include those that satisfy the conditions of the following acidic compound (D).

[0045] As the triazine derivative, the triazine derivative represented by the following general formula (1) is preferable.

Chemical formula

[0046] In the general formula (1), R 1 represents a group represented by -X 1 -Y 1 X 1 represents an arylene group which may have a substituent, and Y 1 represents a sulfo group, a carboxyl group, or a phosphoric acid group.

[0047] X 1The "substituent" of the arylene group which may have a substituent may be the same or different. Specific examples thereof include a hydroxyl group, a halogen group such as fluorine, chlorine, bromine, a nitro group, an alkyl group, an aryl group, a cycloalkyl group, an alkoxyl group, an aryloxy group, an alkylthio group, an arylthio group and the like. Further, a plurality of these substituents may be present.

[0048] Examples of the "arylene group" of the arylene group which may have a substituent include a phenylene group, a naphthylene group and the like.

[0049] Q 1 represents -OH or -NH-R. 2 Q 2 represents -OH or -NH-R. 3 R 2 and R 3 each independently represents an aryl group which may have a substituent, a heterocyclic group which may have a substituent or a group represented by -X -Y 1 -Y. However, 1 R 2 and 3 R 1 will not simultaneously become -X 1 -Y.

[0050] R 2 and 3 The "substituent" of the aryl group which may have a substituent and the heterocyclic group which may have a substituent of R is synonymous with the substituent of X. 1

[0051] R 2 and 3 Examples of the "aryl group" of the aryl group which may have a substituent of R include a phenyl group, a naphthyl group and the like.

[0052] R 2 and 3The "heterocyclic group" of the heterocyclic group which may have a substituent includes, for example, aromatic or aliphatic heterocycles containing a nitrogen atom, an oxygen atom, a sulfur atom, or a phosphorus atom. Specifically, thienyl group, benzo[b]thienyl group, naphtho[2,3-b]thienyl group, pyrrolyl group, thianthrenyl group, furyl group, pyranyl group, isobenzofuranyl group, chromenyl group, xanthenyl group, phenoxathiinyl group, 2H-pyrrolyl group, imidazolyl group, pyr azolyl group, pyridyl group, pyrazinyl group, pyrimidinyl group, pyridazinyl group, indolizinyl group, isoindolyl group, 3H-indolyl group, indolyl group, 1H-indazolyl group, purinyl group, 4H-quinolizinyl group, isoquinolyl group, quinolyl group, phthalazinyl group, naphthyridinyl group, quinoxalinyl group, quinazolinyl group, cinnolinyl group, pteridinyl group, 4aH-carbazolyl group, carbazolyl group, β-carbolinyl group, phenanthridinyl group, acridinyl group, perimidinyl group, phenanthrolinyl group, phenazinyl group, phenarsazinyl group, isothiazolyl group, phenothiazinyl group, isoxazolyl group, furazanyl group, phenoxazinyl group, isochromanyl group, chromanyl group, pyrrolidinyl group, pyrrolinyl group, imidazolidinyl group, imidazolinyl group, pyrazolidinyl group, pyrazolinyl group, piperidyl group, piperazinyl group, indolinyl group, isoindolinyl group, quinuclidinyl group, morpholinyl group, thioxanthryl group, benzofuryl group, benzothiazolyl group, benzoxazolyl group, benzimidazolyl group, benzotriazolyl group, etc. can be mentioned. Among them, a heterocyclic group containing at least one of a nitrogen atom and an oxygen atom is preferable because of excellent dispersibility, and among them, a carbazolyl group and a benzimidazolyl group are more preferable.

[0053] The structure of the triazine derivative is exemplified below. The production method of the triazine derivative is not particularly limited, and a well-known method can be applied. For example, the method described in JP-A-2004-217842 etc. can be applied. By referring to the disclosure of the above publication, it is incorporated into a part of this specification.

[0054]

Chem.

[0055]

Chem.

[0056] Specific examples of the resin-type dispersant include cellulose derivatives (such as cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, etc.), vinyl alcohol-based resins such as polyvinyl alcohol and polyvinyl butyral, and polyvinyl pyrrolidone. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinyl pyrrolidone are preferred.

[0057] Examples of the surfactant include anionic, cationic, nonionic, and amphoteric surfactants. The selected surfactant is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. The blending amount at that time is preferably a suitable blending amount for each surfactant component.

[0058] Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples include stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercapto pyridine, poly(vinyl pyridine)-dodecyl bromide, and dodecyl benzyl triethyl ammonium chloride, but are not limited thereto. Examples of amphoteric surfactants include aminocarboxylates, but are not limited thereto.

[0059] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers, but are not limited thereto. Specific examples include polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octyl phenyl ether, but are not limited thereto.

[0060] (4) Acidic compound (D) The acidic compound (D) of this embodiment is a compound having a molecular weight of 350 or less, and represents a compound that behaves as an acid relative to the electrode active material used. Regardless of whether it is a commercially available product or a synthetic product, it can be used alone or in combination of two or more.

[0061] The acid dissociation constant (pKa) of the acidic compound is preferably -5 or more and 10 or less, more preferably -3 or more and 9 or less, even more preferably -3 or more and 7 or less, even more preferably -3 or more and 5 or less, even more preferably -3 or more and 3 or less, and particularly preferably 1 or more and 3 or less. The value of the acid dissociation constant is obtained from a chemical handbook or the like as the value in an aqueous solution at 25°C. If the value of the acid dissociation constant is too large, the expected effect may not be obtained. On the other hand, if it is too small, corrosion of the production line or handling precautions may be required.

[0062] Specific examples of the acidic compound used in the present invention 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; hydroxy acids such as tartaric acid, citric acid, and glyceric 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 acid anhydrides such as acetic anhydride, benzoic anhydride, phthalic anhydride, and maleic anhydride; sulfonic acids such as benzenesulfonic acid and toluenesulfonic acid; 1,3-diketones such as acetylacetone; inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; other oxo acid compounds; compounds having a thiol group; compounds having a phosphate group; phenols; enols; and derivatives of these compounds, polymers, etc. However, the present invention is not limited thereto.

[0063] The acidic compound used in the present invention is preferably an organic acid or 1,3-diketone having a molecular weight of 350 or less, more preferably an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphate group, and a thiol group, even more preferably an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group and a sulfonic acid group, even more preferably an organic acid having a carboxyl group or a sulfonic acid group, and particularly preferably an organic acid having a carboxylic acid group. Further, it preferably has an aromatic ring.

[0064] The molecular weight of the acidic compound is 350 or less. Among them, those with a molecular weight of 30 to 350 are preferred, those with a molecular weight of 100 to 350 are more preferred, and those with a molecular weight of 100 to 200 are particularly preferred.

[0065] The number of acidic groups in one molecule of the acidic compound is preferably 1 to 3, and more preferably 1 to 2.

[0066] The acidic compound is preferably soluble in the CNT dispersion liquid, and more preferably dissolves 0.1 part by mass or more with respect to 100 parts by mass of N-methyl-2-pyrrolidone at 0 ° C to 40 ° C under atmospheric pressure.

[0067] (5) Carbon nanotube dispersion liquid The CNT dispersion liquid of the present embodiment contains CNT (A), a solvent (B), a dispersant (C), and an acidic compound (D).

[0068] In order to obtain the CNT dispersion liquid of the present embodiment, it is preferable to perform a process of dispersing CNT (A) in a solvent (B). The dispersion device used for performing such a process is not particularly limited.

[0069] As the dispersion device, a disperser usually used for pigment dispersion or the like can be used. For example, mixers such as a disper, a homomixer, and a planetary mixer, a homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON), "Creamix" manufactured by M-Technique, PRIMI Media-type dispersers such as "Filmix" of Company X, etc., "Abramix" of Silver Son Co., etc., paint conditioner (manufactured by Red Devil Co.), colloid mills (such as "PUC Colloid Mill" of PUC Co., "Colloid Mill MK" of IKA Co.), corn mills (such as "Corn Mill MKO" of IKA Co.), ball mills, sand mills (such as "Dynomill" of Simar Enterprises Co., etc.), attritors, pearl mills (such as "DCP Mill" of Ehrlich Co., etc.), coball mills, etc., media-less dispersers such as wet jet mills (such as "Genus PY" of Genus Co., "Starburst" of Sugino Machine Co., "Nanomizer" of Nanomizer Co., etc.), "Clear SS-5" of M Tech Co., "MICROS" of Nara Machinery Co., etc., and other roll mills, etc. may be mentioned, but are not limited thereto.

[0070] The amount of the solid content of the CNT dispersion of this embodiment is preferably 0.1 to 30% by mass, more preferably 0.5 to 25% by mass, still more preferably 1 to 10% by mass, and particularly preferably 2 to 10% by mass with respect to 100% by mass of the CNT dispersion.

[0071] The amount of the dispersant (C) in the CNT dispersion of this embodiment is preferably 3 to 300% by mass, more preferably 5 to 100% by mass, and particularly preferably 10 to 50% by mass with respect to 100% by mass of the CNT (A).

[0072] The amount of the acidic compound (D) in the CNT dispersion of this embodiment is preferably 1 to 25% by mass, and particularly preferably 5 to 20% by mass with respect to 100% by mass of the CNT in the CNT dispersion.

[0073] (6) Binder (E) The binder (E) means a resin that binds substances.

[0074] Examples of the binder (E) of the present embodiment include polymers or copolymers containing, as constituent units, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters, methacrylic acid, methacrylic esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluorine resins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Further, modified products, mixtures, and copolymers of these resins may also be used. In particular, from the viewpoint of resistance, it is preferable to use a polymer compound having a fluorine atom in the molecule, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc.

[0075] The weight average molecular weight of these resins as the binder (E) of the present embodiment is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,000,000, and particularly preferably from 200,000 to 1,000,000. If the molecular weight is small, the resistance and adhesion of the binder may decrease. Although the resistance and adhesion of the binder improve as the molecular weight increases, the viscosity of the binder itself increases, the workability decreases, and it may act as a flocculant, causing the dispersed particles to aggregate significantly.

[0076] From the assumed industrial applicability of the present invention, the binder (E) preferably contains a polymer compound having a fluorine atom, is preferably a polymer compound having a fluorine atom, more preferably a vinylidene fluoride-based copolymer, and particularly preferably polyvinylidene fluoride.

[0077] (7) Resin composition The resin composition of the present embodiment contains CNT (A), solvent (B), dispersant (C), acidic compound (D), and binder (E).

[0078] To obtain the resin composition of the present embodiment, it is preferable to mix and homogenize the CNT dispersion and the binder (E). As the mixing method, various conventionally known methods can be used. The resin composition can be produced using the dispersion device described for the CNT dispersion.

[0079] (8) Active material (F) The active material (F) of the present embodiment refers to 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.

[0080] The positive electrode active material is not particularly limited, and metal oxides, metal compounds such as metal sulfides, and conductive polymers that can be doped or intercalated with lithium ions can be used. For example, oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. can be mentioned. Specifically, transition metal oxide powders such as MnO, V2O5, V6O 13 , TiO2, etc., composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2 and FeS, etc. can be mentioned. Also, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0081] The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloy systems such as its alloys tin alloy, silicon alloy, lead alloy, etc., Li X Fe2O3, Li X Fe3O4, Li X WO2 (x is 0 < It is a number less than 1.). Examples include metal oxide-based materials such as lithium titanate, lithium vanadate, and lithium silicate; conductive polymer-based materials such as polyacetylene and poly-p-phenylene; amorphous carbonaceous materials such as soft carbon and hard carbon; artificial graphite such as highly graphitized carbon materials; carbonaceous powders such as natural graphite; carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, and carbon fibers. These negative electrode active materials can be used alone or in combination of two or more.

[0082] The positive electrode active material is preferably a composite oxide with lithium containing transition metals such as Al, Fe, Co, Ni, and Mn, more preferably a composite oxide with lithium containing any one of Al, Co, Ni, and Mn, and particularly preferably a composite oxide with lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained.

[0083] The BET specific surface area of the active material is preferably in the range of 0.1 to 10 m 2 / g, more preferably in the range of 0.2 to 5 m 2 / g, and even more preferably in the range of 0.3 to 3 m 2 / g.

[0084] The average particle diameter of the active material is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. The average particle diameter of the active material referred to in this specification is the average value of the particle diameters measured by an electron microscope for the active material.

[0085] (9) Composite material slurry The composite material slurry of this embodiment contains CNT (A), solvent (B), dispersant (C), acidic compound (D), binder (E), and active material (F).

[0086] To obtain the composite material slurry of this embodiment, after adding the active material to the CNT resin composition, it is dispersed It is preferable to perform the treatment. The dispersion device used for performing such treatment is not particularly limited. The composite material slurry can be obtained by using the dispersion device described for the CNT dispersion liquid.

[0087] The amount of the active material (F) in the composite material slurry is preferably 20 to 85% by mass, and particularly preferably 40 to 85% by mass with respect to 100% by mass of the composite material slurry.

[0088] The amount of CNT (A) in the composite material slurry is preferably 0.05 to 10% by mass, preferably 0.1 to 5% by mass, and preferably 0.1 to 3% by mass with respect to 100% by mass of the active material.

[0089] The amount of the binder (E) in the composite material slurry is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, and particularly preferably 1 to 5% by mass with respect to 100% by mass of the active material.

[0090] The amount of the solid content of the composite material slurry is preferably 30 to 90% by mass, and preferably 40 to 85% by mass with respect to 100% by mass of the composite material slurry.

[0091] The amount of moisture in the composite material slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0092] (10) Electrode film The electrode film of this embodiment is a coating film in which an electrode composite layer is formed by coating and drying a composite material slurry on a current collector.

[0093] The material and shape of the current collector used for the electrode film of the present embodiment are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, as the material of the current collector, metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel can be mentioned. Also, as the shape, generally, a foil on a flat plate is used, but those with a roughened surface, perforated foil-like ones, and mesh-shaped current collectors can also be used.

[0094] As a method for coating the composite slurry on the current collector, there is no particular limitation, and known methods can be used. Specifically, the die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method, electrostatic coating method, etc. can be mentioned. As the drying method, air drying, hot air drying, infrared heating, far-infrared heating, etc. can be used, but it is not particularly limited to these.

[0095] Also, after coating, rolling treatment may be performed using a flat plate press, calender roll, etc. The thickness of the electrode composite layer is generally 1 to 500 μm, preferably 10 to 300 μm.

[0096] (11) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte, and uses an electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent. The non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, and examples include lithium-ion secondary batteries, lead-acid batteries, nickel-metal hydride batteries, etc.

[0097] As the positive electrode, an electrode film prepared by coating and drying a composite slurry containing a positive electrode active material can be used.

[0098] As the negative electrode, an electrode film prepared by coating and drying a composite slurry containing a negative electrode active material can be used.

[0099] As the electrolyte, various conventionally known ones can be used. For example, LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is a phenyl group), etc. can be mentioned, but not limited thereto.

[0100] The non-aqueous solvent is not particularly limited. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-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, etc. can be mentioned. These solvents may be used alone or in combination of two or more.

[0101] The non-aqueous electrolyte secondary battery of this embodiment preferably includes a separator. Examples of the separator include, but are not particularly limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those obtained by subjecting these to hydrophilic treatment.

[0102] The structure of the non-aqueous electrolyte secondary battery of this embodiment is not particularly limited. Usually, it is composed of a positive electrode and a negative electrode, and a separator provided as necessary, and can have various shapes such as a paper type, a cylindrical type, a button type, a laminated type, etc., according to the purpose of use.

Examples

[0103] The following are examples for more specifically explaining the present invention. The present invention is not limited to the following examples as long as it does not exceed the gist thereof.

[0104] <Method for Measuring Physical Properties> The physical properties of CNTs used in each of the following examples and comparative examples were measured by the following methods.

[0105] <Raman Spectroscopic Analysis of CNT> CNTs were placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.), and measurements were performed using a laser wavelength of 532 nm. The measurement conditions were an acquisition time of 60 seconds, an integration number of 3 times, a neutral density filter of 10%, an objective lens magnification of 20 times, a confocal hole of 500, a slit width of 100 μm, and a measurement wavelength of 100 to 3000 cm -1 . The CNTs for measurement were separated on a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity within the range of 1560 - 1600 cm -1 in the spectrum was defined as G, and the maximum peak intensity within the range of 1310 - 1350 cm -1 was defined as D, and the ratio of G / D was defined as the G / D ratio of the CNT.

[0106] <Specific Surface Area of CNT> CNTs were weighed to 0.03 g using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried while degassing at 110°C for 20 minutes. Then, the specific surface area of the CNTs was measured using a fully automatic specific surface area measuring device (HM-model1208, manufactured by MOUNTECH).

[0107] <Powder X-ray Diffraction Analysis of CNT> CNT was placed in the central concave part of an aluminum sample plate (outer diameter φ46 mm, thickness 3 mm, sample part φ26.5 mm, thickness 2 mm), and was flattened using a slide glass. Then, a medicine wrapping paper was placed on the surface where the sample was placed, and a load of 1 ton was applied to the surface where an aluminum high sheet packing was placed to flatten it. Then, the medicine wrapping paper and the aluminum high sheet packing were removed to obtain a sample for powder X-ray diffraction analysis of CNT. Then, the sample for powder X-ray diffraction analysis of CNT was installed in an X-ray diffractometer (Ultima2100, manufactured by Rigaku Corporation), and the operation was performed from 15° to 35° for analysis. Sampling was performed every 0.02°, and the scan speed was 2° / min. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα ray. The plots that appeared at the diffraction angle 2θ = 25° ± 2° obtained at this time were each averaged by simple moving average of 11 points, and the half-width of the peak was taken as the half-width of CNT. The baseline was the line connecting the plots of 2θ = 15° and 2θ = 34°.

[0108] <Outer diameter of CNT> CNT was observed and imaged by a transmission electron microscope. Next, in the observation photograph, 300 arbitrary CNTs were selected, and the outer diameter of each was measured. Next, the average outer diameter (nm) of CNT was calculated as the number average of the outer diameters.

[0109] <Viscosity measurement of CNT dispersion> After the CNT dispersion was allowed to stand in a thermostatic bath at 25°C for 1 hour or more, the CNT dispersion was sufficiently stirred, and then the viscosity at a stirring speed of 60 rpm was measured using a viscometer (TOKISANGYO CO.LTD, VISCOMETER, MODEL BL).

[0110] <Storage stability of CNT dispersion> The storage stability of the CNT dispersion was evaluated from the change in viscosity after the CNT dispersion was allowed to stand and stored at 50°C for 7 days. For the viscosity measurement, after the CNT dispersion was allowed to stand in a thermostatic bath at 25°C for 1 hour or more, the CNT dispersion was sufficiently stirred, and then the viscosity at a stirring speed of 60 rpm was measured using a viscometer (TOKISANGYO CO.LTD, VISCOMETER, MODEL BL). Based on the degree of change in viscosity before subjecting to the storage stability test, it was rated as +++: ~120% (excellent), ++: ~150% (good), +: ~200% (acceptable), and ‐: 200% (unacceptable).

[0111] <Viscosity measurement and storage stability of CNT resin composition> For the CNT resin composition, it was measured in the same manner as the CNT dispersion liquid.

[0112] <Viscosity measurement and storage stability of composite material slurry> For the composite material slurry, it was measured in the same manner as the CNT dispersion liquid.

[0113] <Volume resistivity of electrode film> The composite material slurry was applied onto the aluminum foil using an applicator so that the weight per unit area of the electrode was 20 mg / cm 2 Then, the coating film was dried in an electric oven at 140 °C ± 5 °C for 25 minutes. Thereafter, the surface resistivity (Ω / □) of the dried coating film was measured using Loresta GP and MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd. After the measurement, it was multiplied by the thickness of the electrode composite layer formed on the aluminum foil to obtain the volume resistivity (Ω·cm) of the electrode film. The thickness of the electrode composite layer was obtained by subtracting the film thickness of the aluminum foil from the average value measured at three points in the electrode film using a film thickness gauge (DIGIMICRO MH-15M manufactured by NIKON Corporation), which was taken as the thickness of the electrode film.

[0114] <Rate characteristics of lithium-ion secondary battery> A laminated lithium secondary battery was installed in a thermostatic chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current-constant voltage charging (cutoff current: 0.6 mA) at a charging current of 12 mA (0.2C) and a charging termination voltage of 4.3 V, constant current discharge was performed at a discharge current of 12 mA and a discharge termination voltage of 3 V. After repeating this operation three times, constant current-constant voltage charging (cutoff current: 0.6 mA) was performed at a charging current of 12 mA (0.2C) and a charging termination voltage of 4.3 V, and constant current discharge was performed at discharge currents of 12 mA (0.2C) and 120 mA (2C) until the discharge termination voltage reached 3.0 V, and the discharge capacities were determined respectively. The rate performance can be expressed by the ratio of the 2C discharge capacity to the 0.2C discharge capacity, as shown in Equation 1 below. (Equation 2) Rate performance = 2C discharge capacity / 0.2C discharge capacity × 100 (%)

[0115] <Catalyst for CNT synthesis and production example of CNT> The CNTs used in each of the following examples were produced by the following method.

[0116] <Synthesis of CNT-A> 10 kg of multi-walled CNTs (manufactured by JEIO Co., Ltd., JENOTUBE 8S) were weighed into a 120 L heat-resistant container, and the heat-resistant container containing the CNTs was installed in the furnace. Then, nitrogen gas was introduced into the furnace, and while maintaining a positive pressure, the air in the furnace was discharged. After the oxygen concentration in the furnace reached 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the furnace temperature at 1600°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain CNT-A.

[0117] <Catalyst B for CNT synthesis> Weighed 60 parts by mass of cobalt hydroxide, 138 parts by mass of magnesium acetate tetrahydrate, and 16.2 parts by mass of manganese acetate into heat-resistant containers respectively. Using an electric oven, dried at a temperature of 170 ± 5 °C for 1 hour to evaporate the moisture. Then, using a crusher (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.), adjusted the SPEED dial to 3 and crushed for 1 minute. After that, using the crusher (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.), adjusted the SPPED dial to 2 for each of the crushed powders and mixed for 30 seconds to prepare the catalyst precursor B for CNT synthesis. Then, transferred the catalyst precursor B for CNT synthesis to a heat-resistant container, used a muffle furnace (FO510, manufactured by Yamato Scientific Co., Ltd.), calcined for 30 minutes under the conditions of an air atmosphere and 450 ± 5 °C, and then crushed in a mortar to obtain the catalyst B for CNT synthesis.

[0118] <Synthesis of CNT-B> Installed a heat-resistant dish made of quartz glass sprayed with 2 g of the catalyst B for CNT synthesis at the center of a horizontal reaction tube with an internal volume of 10 L that can be pressurized and heated by an external heater. Exhausted while injecting nitrogen gas to replace the air in the reaction tube with nitrogen gas, and made the atmosphere in the horizontal reaction tube have an oxygen concentration of 1% by volume or less. Then, heated with an external heater until the central temperature in the horizontal reaction tube reached 680 °C. After reaching 680 °C, introduced propane gas as a carbon source into the reaction tube at a flow rate of 2 L per minute and carried out a contact reaction for 1 hour. After the reaction ended, replaced the gas in the reaction tube with nitrogen gas, cooled the temperature of the reaction tube to 100 °C or less and took it out to obtain CNT-B.

[0119] <Catalyst C for CNT Synthesis> Weighed 40 parts by mass of cobalt hydroxide, 138 parts by mass of magnesium acetate tetrahydrate, and 26.2 parts by mass of manganese acetate into heat-resistant containers respectively. Using an electric oven, dried at a temperature of 170 ± 5 °C for 1 hour to evaporate the moisture. Then, using a crusher (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.), adjusted the SPEED dial to 3 and crushed for 5 minutes. After that, using the crusher (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.) Using a mixer (manufactured by Mikaru Co., Ltd.), the dial of the SPPED was adjusted to 3 and mixed for 5 minutes to prepare a catalyst precursor C for CNT synthesis. Then, the catalyst precursor C for CNT synthesis was transferred to a heat-resistant container and calcined for 30 minutes under the conditions of an air atmosphere and 800 ± 5 °C using a muffle furnace (FO510, manufactured by Yamato Scientific Co., Ltd.), and then pulverized in a mortar to obtain a catalyst C for CNT synthesis.

[0120] <Synthesis of CNT-C> A heat-resistant dish made of quartz glass, on which 2 g of the catalyst C for CNT synthesis was sprayed, was installed at the center of a horizontal reaction tube with an internal volume of 10 L that could be pressurized and heated by an external heater. Exhaust was carried out while injecting nitrogen gas to replace the air in the reaction tube with nitrogen gas, and the atmosphere in the horizontal reaction tube was adjusted to an oxygen concentration of 0.5% by volume or less. Then, it was heated with an external heater until the central temperature in the horizontal reaction tube reached 800 °C. After reaching 800 °C, acetylene gas was introduced into the reaction tube at a flow rate of 3 L per minute as a carbon source and subjected to a contact reaction for 2 hours. After the reaction was completed, the gas in the reaction tube was replaced with nitrogen gas, and the gas in the reaction tube was replaced with nitrogen gas. The temperature of the reaction tube was cooled to 100 °C or less and taken out to obtain CNT-C.

[0121] <Synthesis of CNT-D> 10 kg of CNT (manufactured by KUMHO PETROCHEMICAL, 100T) was weighed into a 120 L heat-resistant container, and the heat-resistant container containing the CNT was installed in the furnace. Then, nitrogen gas was introduced into the furnace to discharge the air in the furnace while maintaining a positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, it was heated to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain CNT-D.

[0122] <Preparation of Composite Slurry for Standard Anode and Standard Anode> The composite slurry for the anode and the anode used in each of the following Examples and Comparative Examples were prepared by the following method.

[0123] <Preparation of Composite Slurry for Standard Anode> As the negative electrode active material, 49 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries, Ltd., CGB-20) and 25 parts by mass of an aqueous solution composition (0.5 part by mass as a solid content) in which 2% by mass of carboxymethyl cellulose (manufactured by Daicel Chemical Industries, Ltd., #1190) was dissolved were put into a planetary mixer and kneaded. Then, 22 parts by mass of ion-exchanged water and 1 part by mass (0.5 part by mass as a solid content) of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) were mixed to obtain a composite material slurry for the negative electrode. <Fabrication of Standard Negative Electrode> After applying the above-mentioned composite material slurry for the negative electrode onto a copper foil with a thickness of 20 μm serving as a current collector using an applicator, it was dried in an electric oven at 120 °C ± 5 °C for 25 minutes so that the weight per unit area of the electrode was 12 mg / cm 2 And adjusted. Further, rolling treatment was performed using a roll press (manufactured by Sanko Metal Co., Ltd., 3t hydraulic roll press) to fabricate a negative electrode with a density of the composite material layer of 1.5 g / cm 3

[0124] <Dispersant> The structures of triazine derivatives A, B, and C, which are dispersants A, E, and G used in each of the following examples, are shown in (Chemical Formula 4). The method for producing triazine derivative A is not particularly limited, and a well-known method can be applied. For example, the method described in JP-A-2004-217842 can be applied. By referring to the disclosure of the above publication, it is incorporated into a part of this specification.

[0125]

Chemical Formula

[0126] Table 1 shows the G / D ratio, specific surface area (m 2 / g), half-width (°), outer diameter (nm) of CNTs used in the examples and comparative examples, and the specific surface area of carbon black.

[0127]

Table 1

[0128] Table 2 shows the dispersants used in the examples and comparative examples.

[0129] [Table 2]

[0130] Table 3 shows the acidic compounds used in the examples and comparative examples.

[0131] [Table 3]

[0132] (Example 1) In a glass bottle (M-225, manufactured by Kashiwa Glass Co., Ltd.), 2.400 parts of CNT-D, 0.720 parts of dispersant A (triazine derivative A), 0.024 parts of acidic compound A (benzoic acid), 76.856 parts of NMP and 80.000 of zirconia beads (bead diameter 0.5 mmφ) were charged, and after performing a dispersion treatment for 8 hours using a paint conditioner manufactured by Red Devil Co., Ltd., the zirconia beads were separated to obtain a CNT dispersion (A1).

[0133] (Examples 2 to 32), (Comparative Examples 1 to 5) CNT dispersions were obtained in the same manner as in Example 1, except that the CNT, CNT concentration, dispersant type, acidic compound type, and amount of acidic compound listed in the table were changed. When using Denka black instead of CNT, a dispersion treatment was performed for 2 hours.

[0134] [Table 4]

[0135] Table 5 shows the evaluation results of the CNT dispersions prepared in Examples 1 to 32 and Comparative Examples 1 to 5.

[0136] [Table 5]

[0137] (Example 33) 10.6 parts by mass of NMP in which 8% by mass of PVDF (manufactured by Solvey, Solef#5130) was dissolved was measured into a plastic container with a capacity of 150 cm 3 . Subsequently, 0.5 part by mass of the CNT dispersion (A1) was added, and using a rotation / revolution mixer (Sumiki Awatori Rentaro, ARE-310 manufactured by Shinki Co., Ltd.), it was stirred at 2000 rpm for 30 seconds. Further, 6.5 parts by mass of the CNT dispersion (A1) was added, and using the said mixer, it was stirred at 2000 rpm for 30 seconds to obtain a CNT resin composition (A1). Furthermore, 55.1 parts by mass of a positive electrode active material (NAC7150 manufactured by Toda Kogyo) was added, and using the said mixer, it was stirred at 2000 rpm for 2.5 minutes. Finally, 2.3 parts by mass of NMP was added, and using the said mixer, it was stirred at 2000 rp m for 2.5 minutes to obtain a composite material slurry (A1).

[0138] (Examples 34 to 64), (Comparative Examples 6 to 10) A composite material slurry was obtained in the same manner as in Example 33 except that the CNT dispersion listed in Table 6 was changed.

[0139] Table 6 shows the evaluation results of the CNT resin compositions and composite material slurries prepared in Examples 34 to 64 and Comparative Examples 6 to 10.

[0140] [Table 6]

[0141] (Example 65) The composite material slurry (A1) was applied onto an aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg / cm 2 , and then the coating film was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (A1).

[0142] (Examples 66 to 96), (Comparative Examples 11 to 15) An electrode film was obtained in the same manner as in Example 65, except that the composite slurry listed in Table 6 was used.

[0143] Table 7 shows the evaluation results of the fabricated electrode films. For the evaluation of conductivity, the volume resistivity (Ω·cm) of the electrode film was defined as follows: less than 5: ++++(excellent), 5 or more and less than 10: +++(good), 10 or more and less than 20: ++(fair), 20 or more and less than 100: +(passable), 100 or more: -(non - passable).

[0144]

Table 7

[0145] (Example 97) The electrode film (A1) was subjected to rolling treatment using a roll press (manufactured by Sanku Metal Co., Ltd., 3t hydraulic roll press) to produce a positive electrode with a density of the composite layer of 3.2 g / cm 3 ³.

[0146] (Examples 98 - 128), (Comparative Examples 16 - 20) Positive electrodes were fabricated in the same manner as in Example 97, except that the electrode films listed in Table 8 were used.

[0147]

Table 8

[0148] (Example 129) The positive electrode (A1) and the negative electrode were each punched out to be 45 mm × 40 mm and 50 mm × 45 mm, and a separator (porous polypropylene film) inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Then, in a glove box filled with argon gas, 2 mL of an electrolytic composition (a non - aqueous electrolytic composition in which LiPF6 was dissolved at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a ratio of 1:1:1 (volume ratio)) was injected, and then the aluminum laminate was sealed to fabricate a laminated lithium - ion secondary battery (A1).

[0149] (Examples 130 to 160), (Comparative Examples 21 to 25) A laminated lithium-ion secondary battery was fabricated in the same manner except that the positive electrode shown in Table 8 was changed.

[0150] Table 9 shows the evaluation results of the fabricated laminated lithium secondary battery. The rate characteristics were defined as follows: rate characteristics of 90% or more: ++++(excellent), 80% or more and less than 90%: +++(good), 70% or more and less than 80%: ++(fair), 60% or more and less than 70%: +(passable), less than 60%: -(non-passable).

[0151]

Table 9

[0152] In the above examples, a CNT dispersion containing CNT, a dispersant, and an acidic compound was used. In the examples, a lithium-ion secondary battery having excellent storage stability of the composite material and excellent rate characteristics was obtained as compared with the comparative examples. Therefore, it has become clear that the present invention can provide a lithium secondary battery having productivity and conductivity that are difficult to achieve with conventional CNT dispersions.

[0153] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited thereto. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

Claims

1. A resin composition comprising a carbon nanotube (A), a solvent (B), a dispersant (C), an acidic compound (D) having a molecular weight of 350 or less, and a binder (E), wherein the outer diameter of the carbon nanotube (A) is 3 to 25 nm, the solvent (B) contains N-methyl-2-pyrrolidone, the binder (E) contains polyvinylidene fluoride, the acidic compound (D) contains at least any one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone, A resin composition used for a composite material slurry for a positive electrode, wherein the acidic compound (D) is 1 to 25 parts by mass with respect to 100 parts by mass of the carbon nanotube (A).

2. In the Raman spectrum of the carbon nanotube (A), the maximum peak intensity within the range of 1560 to 1600 cm -1 is defined as G, and when the maximum peak intensity within the range of 1310 to 1350 cm -1 is defined as D, the resin composition used in the composite slurry for the positive electrode according to claim 1, characterized in that the G / D ratio is 0.5 to 5.

0.

3. The BET specific surface area of the carbon nanotube (A) is 180 to 850 m 2 / g, and the resin composition is used for the composite material slurry for the positive electrode according to claim 1 or 2.

4. The carbon nanotube (A) has a peak at a diffraction angle 2θ = 25° ± 2° in powder X-ray diffraction analysis, and the half-value width of the peak is 2° to 6°. The resin composition is used for the composite material slurry for a positive electrode according to any one of Claims 1 to 3.

5. A method for producing a resin composition comprising a carbon nanotube (A), a solvent (B), a dispersant (C), an acidic compound (D) having a molecular weight of 350 or less, and a binder resin (E), comprising a step of dispersing the carbon nanotube (A) in the solvent (B), the outer diameter of the carbon nanotube (A) is 3 to 25 nm, the solvent (B) contains N-methyl-2-pyrrolidone, the binder (E) contains polyvinylidene fluoride, the acidic compound (D) contains at least any one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone, and the acidic compound (D) is 1 to 25 parts by mass with respect to 100 parts by mass of the carbon nanotube (A). A method for producing a resin composition used for a composite material slurry for a positive electrode.

6. A method for manufacturing a positive electrode composite material slurry containing carbon nanotubes (A), a solvent (B), a dispersant (C), an acidic compound (D) with a molecular weight of 350 or less, a binder resin (E), and a positive electrode active material, comprising: a step of dispersing carbon nanotubes (A) in a solvent (B); the outer diameter of the carbon nanotubes (A) is 3 to 25 nm; the solvent (B) contains N-methyl-2-pyrrolidone; the binder (E) contains polyvinylidene fluoride; the acidic compound (D) contains at least any one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone; 1 to 25 parts by mass of the acidic compound (D) is used per 100 parts by mass of the carbon nanotubes (A); A method for manufacturing a positive electrode composite material slurry. **Claim 7**: A method for manufacturing a positive electrode composite material slurry containing carbon nanotubes (A), a solvent (B), a dispersant (C), an acidic compound (D) with a molecular weight of 350 or less, a binder resin (E), and a positive electrode active material, comprising: a step of manufacturing a carbon nanotube dispersion liquid containing carbon nanotubes (A), a solvent (B), a dispersant (C), and an acidic compound (D) with a molecular weight of 350 or less; the outer diameter of the carbon nanotubes (A) is 3 to 25 nm; the solvent (B) contains N-methyl-2-pyrrolidone; the binder (E) contains polyvinylidene fluoride; the acidic compound (D) contains at least any one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone; 1 to 25 parts by mass of the acidic compound (D) is used per 100 parts by mass of the carbon nanotubes (A); A method for manufacturing a positive electrode composite material slurry.

8. The method for manufacturing a composite material slurry for a positive electrode according to claim 7, wherein the positive electrode active material is a composite oxide with lithium containing one or more transition metals selected from Al, Fe, Co, Ni, and Mn.

9. A carbon nanotube dispersion used in the method for manufacturing a composite material slurry for a positive electrode according to claim 7 or 8.

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