Carbon nanotube dispersion liquid for electrode production and slurry for electrode production

Abstract

To provide a carbon nanotube dispersion liquid which can be easily produced. and to provide a carbon nanotube dispersion liquid which is suitable for the production of an electrode for a high-performance lithium-ion secondary battery or the like.SOLUTION: There is provided a carbon nanotube dispersion liquid for electrode production, which includes: multilayer carbon nanotubes; a polyallylamine derivative that is composed of a constitutional unit represented by formula (1); and an organic solvent. A content of the polyallylamine derivative is 0.2 pts.mass or more and 1.5 pts.mass or less with respect to 1 pts.mass of the multilayer carbon nanotube.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode-producing slurry suitable for producing electrodes for secondary batteries such as lithium-ion secondary batteries, and to a dispersion of carbon nanotubes (sometimes abbreviated as CNT) used in the production of the electrode-producing slurry. [Background technology]

[0002] With the widespread use of electric vehicles and the trend toward smaller, lighter, and more powerful portable devices such as mobile phones and laptop computers, secondary batteries with high energy density, as well as higher output and longer life, are being demanded. Against this background, non-aqueous secondary batteries, including lithium-ion batteries using non-aqueous electrolytes, have come to be used in many devices due to their high energy density and high voltage, and their development is being actively pursued.

[0003] Electrodes for non-aqueous secondary batteries, including lithium-ion batteries, are fabricated by applying a dispersion of a carbon material onto an electrode substrate and drying it. Carbon materials such as carbon black and carbon nanotubes are sometimes used. Carbon nanotubes are classified into single-walled carbon nanotubes and multi-walled carbon nanotubes based on their higher-order structure. Both single-walled and multi-walled carbon nanotubes are commercially available.

[0004] Patent Document 1 discloses a carbon nanotube dispersion containing single-walled carbon nanotubes, a polyallylamine derivative, and an organic solvent, and containing 400 to 40,000 parts by mass, preferably 500 to 30,000 parts by mass, and more preferably 1,000 to 20,000 parts by mass of the polyallylamine derivative per 100 parts by mass of the single-walled carbon nanotubes. In the carbon nanotube dispersion of Patent Document 1, the polyallylamine derivative needs to be blended in a relatively large amount. Furthermore, paragraph

[0017] states that the dispersibility of single-walled carbon nanotubes is different from that of carbon black and multi-walled carbon nanotubes. Patent Document 1 does not describe the use of a dispersion containing carbon nanotubes in an electrode.

[0005] Patent Document 2 discloses a polyallylamine derivative having 10 to 450 polymer structural units represented by a specific chemical formula, and gives examples of applications such as a liquid developer containing carbon black, but does not describe the use of a dispersion containing carbon nanotubes in an electrode.

[0006] Patent Document 3 discloses a carbon nanotube dispersion and various vinyl alcohol skeleton-containing resins as dispersants, but does not disclose a carbon nanotube dispersion containing an amino group-containing resin as a dispersant. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2021-187701 A (claims, specification, etc.) [Patent Document 2] JP 2017-203143 A (claims, description, etc.) [Patent Document 3] JP 2020-11873 A (claims, specification, etc.) Summary of the Invention [Problem to be solved by the invention]

[0008] When a carbon nanotube dispersion is used to prepare an electrode for a lithium-ion secondary battery or the like, it is generally applied to a current collector such as aluminum foil and then dried. In this case, it is desirable to reduce the amount of solvent contained in the dispersion, but reducing the amount of solvent usually increases the viscosity of the dispersion containing carbon nanotubes, making it difficult to prepare the carbon nanotube dispersion and to apply it uniformly.

[0009] Furthermore, when dispersing carbon nanotubes in a solvent, it is common to mix powdered carbon nanotubes into the solvent and disperse them using a disperser. In this case, depending on the properties of the carbon nanotubes used, the viscosity of the carbon nanotube dispersion may become very high, which may hinder the dispersion operation and make the dispersion process difficult.

[0010] An object of the present invention is to provide a carbon nanotube dispersion liquid that can be easily produced as a dispersion liquid for producing electrodes, and to provide a carbon nanotube dispersion liquid that is suitable for producing electrodes for high-performance lithium-ion secondary batteries and the like. [Means for solving the problem]

[0011] As a result of extensive research into the conventional problems, the inventors discovered that a carbon nanotube dispersion for electrode production can be suitably obtained by using a combination of multi-walled carbon nanotubes and a specific dispersant, and based on this finding, they have completed the present invention.

[0012] The present invention provides a method for producing a polyallylamine derivative comprising a multi-walled carbon nanotube, a polyallylamine derivative having a constitutional unit represented by formula (1), and an organic solvent, The carbon nanotube dispersion for electrode production has a content of the polyallylamine derivative of 0.15 parts by mass or more and less than 4 parts by mass per part by mass of the multi-walled carbon nanotubes. [ka]

[0013] (In formula (1), A 1 represents a group represented by general formula (2), general formula (3), general formula (4), or general formula (5), and a plurality of A 1 may be the same or different from each other. 1 At least one of the groups is a group represented by general formula (4) or general formula (5). [ka]

[0014] (In formula (2) and formula (3), R 1 represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group having an ether bond which may have a substituent. In formula (4) and formula (5), R 1 represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group which has an ether bond which may have a substituent, R 2 represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkyl group having an ether bond which may have a substituent, or a phenyl group which may have a substituent. In the formulas (2) to (5), a represents an integer of 0 to 100. 1 , R 2 may be the same or different.)

[0015] The present invention also relates to a slurry for producing an electrode, which contains the carbon nanotube dispersion liquid for producing an electrode and a positive electrode active material or a negative electrode active material. The slurry for producing an electrode of the present invention may contain, as other components, conductive particles, auxiliary agents such as a binder, a solvent, and the like. [Effects of the Invention]

[0016] In the carbon nanotube dispersion of the present invention, multi-walled carbon nanotubes are uniformly dispersed and have a relatively low viscosity. In particular, the dispersion treatment operation when dispersing carbon nanotubes in a solvent to prepare a dispersion is easy and can be performed without imposing a burden. In other words, the carbon nanotube dispersion of the present invention is easy to produce and handle.

[0017] The carbon nanotube dispersion of the present invention can be used to prepare a slurry for electrode fabrication. An electrode fabricated from a slurry for electrode fabrication prepared using the carbon nanotube dispersion of the present invention has low resistance and good conductivity, making it suitable for use as an electrode for a lithium-ion secondary battery. In particular, the carbon nanotube dispersion of the present invention requires only a small amount of dispersant, allowing for a higher active material content. This ensures that the performance of the active material in the fabricated electrode is not compromised, resulting in low electrode resistance. Furthermore, side reactions of the dispersant due to electrical reactions can be suppressed. As a result, the carbon nanotube dispersion of the present invention is advantageous for fabricating high-performance electrodes without impairing the properties of the carbon nanotubes.

[0018] Furthermore, the multi-walled carbon nanotubes used in the carbon nanotube dispersion of the present invention are generally cheaper than single-walled carbon nanotubes.Furthermore, in the present invention, only a small amount of dispersant is required. As described above, the carbon nanotube dispersion liquid of the present invention has a lower viscosity than a carbon nanotube dispersion liquid using single-walled carbon nanotubes, making it easier to manufacture and handle, and also reducing the cost required for manufacturing electrodes. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Multi-walled carbon nanotubes> The multi-walled carbon nanotubes used in the present invention are layered carbon nanotubes consisting of two or more cylindrical carbon nanotubes with different nanometer-sized diameters stacked together. Multi-walled carbon nanotubes have different dispersion characteristics than single-walled carbon nanotubes.

[0020] In X-ray diffraction measurements, single-walled carbon nanotubes exhibit a peak at a diffraction angle 2θ of approximately 6° to 10°. In contrast, multi-walled carbon nanotubes exhibit a peak at a diffraction angle 2θ of approximately 23° to 27°. By performing X-ray diffraction measurements, multi-walled carbon nanotubes can be distinguished from single-walled carbon nanotubes.

[0021] In the carbon nanotube dispersion of the present invention, the content of multi-walled carbon nanotubes to be blended is preferably 0.1 to 10.0 mass %, more preferably 0.2 to 6.0 mass %, and even more preferably 0.5 to 4.0 mass %, based on the total amount of the carbon nanotube dispersion. When the carbon nanotube content is within this range, the flowability of the carbon nanotube dispersion is good, the dispersion can be uniformly applied to a current collector, and the performance of a secondary battery electrode made from the carbon nanotube dispersion can be improved.

[0022] The multi-walled carbon nanotubes used in the present invention are preferably 70 mm 2 / g~500m 2 / g, more preferably 100m 2 / g~400m 2 / g, more preferably 140m 2 / g~300m 2 The BET specific surface area of ​​the multi-walled carbon nanotubes can be measured using a specific surface area measuring device.

[0023] The multi-walled carbon nanotubes used in the present invention preferably have a peak intensity ratio G / D of 0.5 to 2.0, more preferably 0.8 to 1.6, in Raman spectroscopy. Here, the peak intensity ratio G / D is the ratio of the peak intensity at 1570 cm to the peak intensity at 1570 cm in Raman spectroscopy. -1 ~1620cm -1 The maximum intensity of the G-band scattered light peak is within the range of G, 1320 cm -1 ~1370cm -1 The G / D ratio is expressed by taking D as the maximum value of the D-band scattered light peak intensity within the range. The Raman scattered light peak intensity can be measured using a Raman spectrometer.

[0024] The peak intensity ratio G / D in a Raman spectrum is related to the crystallinity of carbon nanotubes. If the crystallinity of carbon nanotubes is too high, the carbon edges decrease due to the development of a graphite structure, reducing the number of electrolyte coordination sites, resulting in problems such as reduced low-temperature properties and increased resistance. Furthermore, if the crystallinity of carbon nanotubes is too low, the amount of amorphous material increases, increasing electrical resistance and reducing the utilization efficiency of the electric double layer at the interface between the electrolyte and the electrode material. Using carbon nanotubes with a G / D ratio within the above range has the advantage of producing electrodes with fewer defects, high resistance to high-voltage operation, and high long-term conductivity.

[0025] The carbon nanotubes used in the present invention preferably have an average fiber length of 1 μm to 1000 μm, more preferably 3 μm to 500 μm, and an average fiber width of 1 nm to 50 nm, more preferably 5 nm to 20 nm. The average fiber length and average fiber width of carbon nanotubes refer to the average outer diameter of a sufficient number (n) of fibers measured using an electron microscope. A short average fiber length of multi-walled carbon nanotubes tends to decrease the viscosity of the carbon nanotube dispersion, while a long average fiber length of multi-walled carbon nanotubes tends to increase the viscosity. Using carbon nanotubes with a fiber length and fiber width within the above ranges has the advantage of improving entanglement with the active material and resulting in a low-resistance electrode.

[0026] Multi-walled carbon nanotubes can generally be produced by laser ablation, arc discharge, thermal CVD, plasma CVD, and combustion methods. Preferably, the multi-walled carbon nanotubes can be produced by a thermal CVD method in which a raw material gas serving as a carbon source is introduced into a low-oxygen atmosphere at 500 to 1000°C in the presence of a powdered catalyst, and the raw material gas is brought into contact with the catalyst in a fluidized state or in a stationary state with a substrate to which the catalyst is attached.

[0027] The low-oxygen atmosphere is preferably an atmosphere of an inert gas such as a rare gas typified by argon gas or nitrogen gas, and the oxygen concentration in the atmosphere is preferably 1% by volume or less. In the contact reaction, a reducing gas may be added to the atmosphere to activate the catalyst. The reducing gas may be, for example, hydrogen or ammonia, preferably hydrogen.

[0028] A carbon-containing gas is used as a carbon source. Examples include hydrocarbons, carbon monoxide, and alcohols, which can be used alone or in combination of two or more. Among these, one or more selected from saturated or unsaturated hydrocarbons and alcohols are preferred. Examples of hydrocarbons include methane, propane, butane, ethylene, and acetylene, with ethylene being preferred. When ethylene is used as a raw material gas serving as a carbon source, it is preferable to bring ethylene into contact with a catalyst and react it at 600 to 800°C, particularly 650 to 750°C, in an atmosphere with an oxygen concentration of 1% by volume or less.

[0029] The catalyst for the catalytic reaction is preferably a mixture of an active component such as cobalt, nickel, or iron and a catalyst support such as magnesium, aluminum, or silicon, which is then molded and pulverized. Particularly preferred is a powdery catalyst obtained by mixing and molding a metal oxide containing cobalt as the active component and magnesium as the catalyst support, and then pulverizing the mixture.

[0030] When a hydrocarbon is used as the raw material gas, the reaction operating conditions may vary depending on the size of the reaction vessel and the amount of catalyst in the reaction vessel. However, when the amount of carbon nanotubes produced per gram of catalyst is Y (g) and the contact reaction time between the catalyst and the hydrocarbon is Z (minutes), it is preferable to adjust the amount of catalyst and / or the flow rate of the hydrocarbon to be supplied so that Y / Z (g / minute) satisfies 1.5≦Y / Z≦2.7.

[0031] The multi-walled carbon nanotubes used in the present invention are preferably those that have been subjected to one or a combination of the following treatments after production: pulverization, classification, and demetallization. The properties of the multi-walled carbon nanotubes can be adjusted by the treatments.

[0032] The pulverization operation is an operation for pulverizing carbon nanotubes to an appropriate size. Applicable pulverization operations include dry pulverization using a pin mill, pulverizer, hammer mill, jet mill, ball mill, Henschel mixer, or attritor, and wet pulverization using an ultrasonic disperser, disperser, homomixer, planetary mixer, high-pressure homogenizer, paint conditioner, colloid mill, bead mill, cone mill, wet jet mill, or thin film rotary high-speed mixer.

[0033] The classification operation is an operation for making the size of the multi-walled carbon nanotubes uniform. Applicable classification operations include a device using gravity, inertial force, or centrifugal force, or a device using a filter, which can be used in a dry method or a wet method. The demetallization operation is an operation for removing metal components contained in multi-walled carbon nanotubes. Since multi-walled carbon nanotubes contain metal components contained in the catalyst used in their production, it is preferable to remove the metal components from the multi-walled carbon nanotubes.

[0034] <Dispersant> The dispersant used in the present invention is a polyallylamine derivative having a constituent unit represented by the following formula (1). [ka] (In formula (1), A 1 represents a group represented by general formula (2), general formula (3), general formula (4), or general formula (5), and a plurality of A 1 may be the same or different from each other. 1 At least one of the groups is a group represented by general formula (4) or general formula (5).

[0035] [ka] (In formula (2) and formula (3), R 1 represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group having an ether bond which may have a substituent.

[0036] In formula (4) and formula (5), R 1 represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group which has an ether bond which may have a substituent, R 2 represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkyl group having an ether bond which may have a substituent, or a phenyl group which may have a substituent. In the formulas (2) to (5), a represents an integer of 0 to 100. 1 , R 2 may be the same or different.)

[0037] The polyallylamine derivative is a polymer containing preferably 10 to 450, more preferably 50 to 300, structural units represented by formula (1) in one molecule, and functions as a dispersant for multi-walled carbon nanotubes. 1 The polyallylamine derivative contains a group represented by general formula (4) or general formula (5). 1Preferably, the polyallylamine derivative contains a group represented by general formula (4) or (5) and at the same time contains a group represented by general formula (2) or (3). The polyallylamine derivative preferably has an acid value of 1 to 50 mgKOH / g, more preferably 5 to 20 mgKOH / g. A preferred example of the polyallylamine derivative is Ajisper, a product name manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0038] The amount of the polyallylamine derivative dispersant in the carbon nanotube dispersion of the present invention is 0.2 to 1.5 parts by mass, preferably 0.3 to 1.0 parts by mass, and more preferably 0.4 to 0.8 parts by mass, per part by mass of multi-walled carbon nanotubes. When the amount of the polyallylamine derivative dispersant is within this range, the dispersibility of multi-walled carbon nanotubes in the carbon nanotube dispersion can be exhibited, while the performance of an electrode produced from the carbon nanotube dispersion can be ensured.

[0039] For comparison, in a carbon nanotube dispersion containing single-walled carbon nanotubes, the dispersant must be blended in an amount that is about 4 to 400 times the mass of the carbon nanotubes. For example, in Patent Document 1, 400 to 40,000 parts by mass of dispersant is blended per 100 parts by mass of single-walled carbon nanotubes.

[0040] In contrast, the carbon nanotube dispersion of the present invention requires a much smaller amount of dispersant than a carbon nanotube dispersion using single-walled carbon nanotubes. As a result, the present invention can reduce manufacturing costs and can effectively utilize the performance of carbon nanotubes in the produced electrode without impairing the properties of the carbon nanotubes. <Solvent>

[0041] The carbon nanotube dispersion of the present invention is blended with an organic solvent that is substantially free of water. The acceptable water content of the organic solvent is preferably less than 1000 ppm, more preferably less than 500 ppm, and even more preferably less than 280 ppm. ppm is the same as mg / L. When the water content of the organic solvent is within this range, the fluidity of the carbon nanotube dispersion and the characteristics of the electrode to be produced are ensured. The amount of water contained in the organic solvent can be measured using a Karl Fischer moisture meter (coulometric titration method).

[0042] Examples of the organic solvent to be blended in the carbon nanotube dispersion of the present invention include alcohol solvents such as methanol, ethanol, isopropanol, butanol, ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol;

[0043] ether solvents such as diethylene glycol diethyl ether, propylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl-n-propyl ether, methyl monoglycidyl ether, ethyl monoglycidyl ether, butyl monoglycidyl ether, phenyl monoglycidyl ether, methyl diglycidyl ether, ethyl diglycidyl ether, butyl diglycidyl ether, phenyl diglycidyl ether, tetrahydrofuran, dioxane, dioxolane, anisole, phenetole, butyl phenyl ether, ethyl benzyl ether, cresyl methyl ether, diphenyl ether, and dibenzyl ether;

[0044] Methyl acetate, ethyl acetate, propyl acetate, butyl acetate, cyclohexyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, hexyl butyrate, methyl lactate, ethyl lactate, γ-butyrolactone, ethylene glycol monoacetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoacetate, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl carboxylic acid ester solvents such as methyl ether acetate, dipropylene glycol monoacetate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, 1,4-butanediol diacetate, 1,6-hexanediol diacetate, methyl methacrylate, 2-hydroxyethyl acrylate, tetrahydrofurfuryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, neopentyl glycol diacrylate, hexanediol diacrylate, and trimethylolpropane triacrylate;

[0045] carbonate ester solvents such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate; ketone solvents such as acetone, methyl ethyl ketone, methyl-n-pentyl ketone, methyl isobutyl ketone, methyl isopentyl ketone, 2-heptanone, cycloheptanone, and cyclohexanone;

[0046] Amine solvents such as ethylenediamine, aniline, and 4-vinylpyridine, nitrile solvents such as acetonitrile and benzonitrile, Amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone, sulfur-containing solvents such as dimethyl sulfoxide,

[0047] Examples of the hydrocarbon solvent include hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, heptane, octane, benzene, toluene, xylene, cymene, mesitylene, styrene, ethylbenzene, diethylbenzene, isopropylbenzene, and pentylbenzene. One solvent selected from the above group of organic solvents may be used, or a mixed solvent consisting of two or more solvents may be used.

[0048] When the carbon nanotube dispersion of the present invention is used as a slurry for producing an electrode, a process for removing the solvent by evaporation is carried out, so the organic solvent to be blended into the carbon nanotube dispersion is preferably highly volatile. As a measure of high volatility, an organic solvent having a flash point of less than 150°C is preferred. Alternatively, an organic solvent classified as a hazardous petroleum, Class 1 or Class 2, is preferred.

[0049] <Preparation of carbon nanotube dispersion> The carbon nanotube dispersion of the present invention can be produced through a dispersion step in which at least multi-walled carbon nanotubes, a polyallylamine derivative consisting of a structural unit represented by formula (1), and an organic solvent are mixed and homogenized. When dispersing carbon nanotubes in a solvent, powdered carbon nanotubes are mixed into a solvent to form a premix (hereinafter referred to as "premixing"), and then the premix is ​​dispersed in a disperser.

[0050] Examples of dispersing machines that can be used include ultrasonic dispersers, mixers such as Disper, Homomixer, rotation-revolution mixer, Henschel mixer, and planetary mixer, (high-pressure) homogenizers, paint conditioners, colloid mills, media-type dispersers such as bead mills, cone mills, ball mills, sand mills, attritors, pearl mills, and Co-ball mills, media-less dispersers such as wet jet mills and thin-film rotary high-speed mixers, and other dispersing devices such as roll mills. From the viewpoint of the stability of the dispersing action and the dispersing efficiency, the preferred dispersing apparatuses are a bead mill type disperser and an ultra-high pressure wet type atomizer.

[0051] The amount of multi-walled carbon nanotubes to be blended in the carbon nanotube dispersion of the present invention is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 10% by mass or less, based on the total amount of the dispersion. When the blending amount of multi-walled carbon nanotubes in the dispersion is within this range, the dispersion is suitable for use as a slurry for electrode fabrication while ensuring fluidity.

[0052] The viscosity of the carbon nanotube dispersion is preferably low. A high viscosity of the carbon nanotube dispersion means that it is difficult to prepare and handle the dispersion industrially. The viscosity of the carbon nanotube dispersion is greatly influenced by the properties of the carbon nanotubes contained in the dispersion, so the selection of the carbon nanotubes is important. The carbon nanotube dispersion of the present invention is a low-viscosity dispersion for electrode production in which multi-walled carbon nanotubes are uniformly dispersed and which has excellent fluidity.

[0053] Carbon nanotube dispersions have thixotropy, meaning that their viscosity changes with shear rate. Therefore, the viscosity suited to the handling conditions of a carbon nanotube dispersion can be determined by changing the rotation speed of the rotor when measuring the viscosity using a rotational viscometer.

[0054] The rotational viscometer may be an E-type rotational viscometer. The viscosity of the carbon nanotube dispersion measured using an E-type rotational viscometer is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, when the rotational speed of the rotor of the rotational viscometer is 1 rpm, preferably 3,000 mPa·s or less, more preferably 2,000 mPa·s or less, when the rotational speed is 10 rpm, and preferably 1,000 mPa·s or less, more preferably 800 mPa·s or less, when the rotational speed is 100 rpm.

[0055] <Slurry for electrode production> A preferred form of use of the carbon nanotube dispersion of the present invention is a slurry for producing an electrode, which is obtained by adding at least a positive electrode active material or a negative electrode active material to the dispersion and mixing it. That is, the present invention relates to a slurry for producing an electrode, which contains the carbon nanotube dispersion liquid for producing an electrode and a positive electrode active material or a negative electrode active material.

[0056] The electrode-fabricating slurry of the present invention may further contain conductive particles and a binder. The electrode-fabricating slurry of the present invention is used as a raw material for producing a positive electrode or a negative electrode of a secondary battery such as a lithium ion battery.

[0057] <Slurry for producing positive electrodes> The slurry for producing a positive electrode of the present invention includes the carbon nanotube dispersion liquid having the above-described configuration and at least a positive electrode active material, which can be a material that helps lithium ions to reversibly enter and exit the positive electrode of a lithium ion secondary battery.

[0058] Positive electrode active materials include composite oxides of lithium and transition metals such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt composite oxide, lithium-nickel-aluminum composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-manganese-cobalt composite oxide, lithium-nickel-manganese-aluminum composite oxide, and lithium-nickel-cobalt-manganese-aluminum composite oxide; transition metal sulfides such as TiS2, FeS, and MoS2; MnO, VO5, and VO 13 transition metal oxides such as TiO2, and olivine-type lithium phosphate.

[0059] The olivine-type lithium phosphate is a compound containing lithium, phosphorus, and oxygen, as well as at least one element selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, Nb, and Fe. The olivine-type lithium phosphate may be a compound in which some of the elements are substituted with other elements in order to improve its properties.

[0060] A preferred positive electrode active material is a lithium-nickel composite oxide, more preferably a lithium-nickel composite oxide represented by the formula: LiNi X M1 Y M2 Z The compound is a lithium-nickel composite oxide represented by the formula: O2 (M1 and M2 are at least one metal element selected from the group consisting of Al, B, alkali metals, alkaline earth metals, and transition metals; 0.8≦X≦1.0, 0≦Y≦0.2, 0≦Z≦0.2), or lithium phosphate. The positive electrode active material may be used alone or in combination of two or more.

[0061] In the positive electrode slurry of the present invention, the content of the positive electrode active material is preferably 50 to 70 mass % and more preferably 50 to 63 mass % based on the total amount of the positive electrode slurry. When the content of the positive electrode active material in the positive electrode slurry is within this range, the fluidity of the dispersion can be maintained while ensuring the performance of the produced electrode.

[0062] The content of the multi-walled carbon nanotubes in the positive electrode slurry is preferably 0.05 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.05 to 1 part by mass, per 100 parts by mass of the positive electrode active material.

[0063] The slurry for producing a positive electrode of the present invention contains the carbon nanotube dispersion liquid and the positive electrode active material having the above-described configuration, and may also contain a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte, as necessary.

[0064] <Slurry for making negative electrodes> The negative electrode slurry of the present invention includes the carbon nanotube dispersion liquid having the above-described structure and at least a negative electrode active material, such as metal oxide-based active material particles, silicon-based active material particles, and spherical graphite, and is particularly preferably a metal oxide-based negative electrode active material particle.

[0065] The metal oxide-based negative electrode active material particles may be, for example, titanium oxide. The titanium oxide is not particularly limited as long as it can absorb and release lithium, but preferred examples include spinel-type lithium titanate, ramsdellite-type lithium titanate, titanium-containing metal composite oxides, titanium dioxide (TiO(B)) having a monoclinic crystal structure, and anatase-type titanium dioxide.

[0066] Spinel-type lithium titanate includes Li 4+x Ti5O 12 (x varies in the range of -1≦x≦3 depending on the charge / discharge reaction). Ramsdellite-type lithium titanate includes Li 2+y Ti3O7 (where y varies in the range of -1≦y≦3 depending on the charge / discharge reaction). TiO2(B) and anatase titanium dioxide include Li 1+z Examples include TiO2 (where z changes in the range of -1≦z≦0 depending on the charge / discharge reaction).

[0067] Examples of titanium-containing metal composite oxides include metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. Examples of metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe include TiO2-P2O5, TiO2-V2O5, TiO2-P2O5-SnO2, and TiO2-P2O5-MeO (Me is at least one element selected from the group consisting of Cu, Ni, and Fe).

[0068] Such a metal composite oxide preferably has a microstructure with low crystallinity, in which a crystalline phase and an amorphous phase coexist, or in which an amorphous phase exists alone, which can further improve cycle performance.

[0069] In the negative electrode slurry of the present invention, the content of the negative electrode active material is preferably 30 to 60 mass % and more preferably 35 to 55 mass % based on the total mass of the negative electrode slurry. When the content of the negative electrode active material in the negative electrode slurry is within this range, the fluidity of the dispersion can be maintained while ensuring the performance of the produced electrode.

[0070] The content of multi-walled carbon nanotubes in the negative electrode slurry is preferably 0.05 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.05 to 1 part by mass, relative to 100 parts by mass of the positive electrode active material. When the content of the negative electrode active material in the negative electrode slurry is within this range, the fluidity of the dispersion can be maintained while ensuring the performance of the produced electrode.

[0071] The slurry for producing a negative electrode of the present invention contains the carbon nanotube dispersion liquid and the negative electrode active material having the above-described configuration, and may also contain a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte, as necessary.

[0072] <Conductive particles> The electrode-forming slurry of the present invention may further contain conductive particles, which can enhance the conductivity of the secondary battery electrode produced from the dispersion. The conductive particles have a specific gravity difference of ±0.2 g / cm from the multi-walled carbon nanotubes contained in the carbon nanotube dispersion liquid. 3 A material having a specific gravity within this range is particularly preferred because it is less likely to separate due to differences in specific gravity when stored as a slurry for electrode production.

[0073] The conductive particles that can be used are preferably conductive carbon particles made of graphite-type carbonaceous material, and preferably include carbon black such as acetylene black and ketjen black. The amount of conductive particles to be mixed is preferably 0.5 to 10 mass %, more preferably 0.5 to 7 mass %, and even more preferably 0.5 to 5 mass %, relative to the multi-walled carbon nanotubes.

[0074] <Binding material> The above-mentioned electrode-forming slurry preferably further contains a binder. Examples of binders that can be used include fluororesins such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers, polyolefin resins such as polyethylene and polypropylene, polyimide resins, polyvinylpyrrolidone, polyvinyl alcohol resins, acrylic resins, and styrene-butadiene rubber (SBR). Two or more binders may be used in combination.

[0075] The amount of binder used is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 4.5 parts by mass, and even more preferably 0.5 to 4.5 parts by mass, per 100 parts by mass of the active material in the slurry for producing each electrode for a secondary battery. When the amount of binder added is within this range, an electrode with high adhesion to the current collector can be obtained without adversely affecting the battery capacity or charge / discharge characteristics. In addition to the above components, the electrode-forming slurry may further contain a leveling agent, a solid electrolyte, an antiseptic, and the like, as appropriate.

[0076] The electrode-forming slurry can be prepared by mixing a carbon nanotube dispersion, an active material for a positive electrode or a negative electrode of a secondary battery, and optionally conductive particles, a binder, a solvent, and / or other components. For example, a twin-screw kneader can be used for the mixing operation.

[0077] <Preparation of electrodes> The electrode-fabrication slurry of the present invention is applied to a current collector, which is a conductive member of a secondary battery such as a lithium-ion secondary battery, and then dried to produce a positive or negative electrode. The electrode-fabrication slurry of the present invention is a low-viscosity dispersion liquid even at high concentrations, allowing it to be uniformly applied to the current collector. The resulting positive or negative electrode achieves high output and battery performance that can withstand repeated charge and discharge over a long period of time as an electrode for a secondary battery.

[0078] More specifically, an electrode can be produced from the slurry for producing a positive electrode or a negative electrode of the present invention as follows. First, the electrode preparation slurry is applied to a current collector. The current collector is a component that serves as an electrode substrate for a secondary battery such as a lithium-ion secondary battery. The material and shape of the current collector used as the electrode substrate can be appropriately selected based on the secondary battery to be used. Examples of the material for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while a flat metal foil is generally used as the shape of the current collector, a foil with a roughened surface, a perforated foil, and a mesh-like foil can also be used.

[0079] Examples of methods for applying the electrode-preparing slurry to a current collector include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic coating. After coating, the surface may be smoothed using a lithographic press, a calendar roll, or the like.

[0080] Next, the current collector coated with the electrode-preparing slurry is dried. Drying methods that can be used include natural drying and forced drying using a blower dryer, a hot air dryer, an infrared heater, or a far-infrared heater. This produces an electrode in which an electrode film is formed on the current collector.

[0081] The thickness of the electrode formed on the current collector is preferably 1 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less. The electrode formed preferably has a surface resistivity of less than 500,000 Ω / □, more preferably less than 300,000 Ω / □. The surface resistivity can be measured using a resistivity meter.

[0082] An electrode produced from a slurry for producing an electrode obtained by using the carbon nanotube dispersion liquid of the present invention has a low electrical resistance value and is suitable for use as a positive electrode or a negative electrode of a secondary battery such as a lithium ion battery. [Example]

[0083] Examples of embodiments of the present invention will be described below. The properties of various commercially available multi-walled carbon nanotubes (MWCNT) A to D and single-walled carbon nanotubes (CWCNT) A to C used in the examples and comparative examples are shown in Table 1. The carbon nanotube properties were measured by the following methods.

[0084] [Table 1]

[0085] [BET specific surface area] Each carbon nanotube was precisely weighed using an electronic balance and dried at 110°C for 30 minutes while degassing. The BET specific surface area was then measured using a fully automatic specific surface area measuring device (Mountec Co., Ltd., Macsorb model HM-1208) using the BET single-point method.

[0086] [Raman spectrum G / D ratio] Each carbon nanotube was dispersed in water, applied to a test piece with an applicator, and dried at 80 °C. After that, a Raman spectrum was measured by mapping in a 100 μm square section using a Raman spectrometer (Thermo Fisher Scientific, DXR2xi). -1The absorbance G at the peak top position within the range of 1310 to 1350 cm -1 The absorbance D at the peak top position within the range was measured, and the ratio of the two, G / D, was calculated.

[0087] [Fiber length / fiber width] Each carbon nanotube was observed using a scanning electron microscope (Hitachi High-Tech Corporation, S-3400N; SEM), and the arithmetic mean fiber length of 10 carbon nanotubes was calculated using images at 1000x magnification. The carbon nanotubes were also observed using a transmission electron microscope (Hitachi High-Tech Corporation, H-7650; TEM), and the arithmetic mean fiber width of 10 carbon nanotubes was calculated using images at 50,000x magnification.

[0088] [Peak half width] Each carbon nanotube was observed using a powder X-ray diffraction analyzer (Rigaku Corporation, miniflex600), and the average value of the 2θ peak half width of 10 carbon nanotubes was calculated.

[0089] Example 1 <Preparation of carbon nanotube dispersion> A polyallylamine derivative having the structural unit of formula (1) (Ajinomoto Fine-Techno Co., Inc., AJISPER PB881; acid value 17 mgKOH / g) was added as a dispersant to dimethyl carbonate as an organic solvent, and multi-walled carbon nanotubes (MWCNT A) were then added as carbon nanotubes. A carbon nanotube dispersion was prepared by bead dispersion using zirconia beads with a diameter of 0.5 mm in a disperser (Ashizawa Fine Tech Co., Ltd., LMZ015). The blending ratio of carbon nanotubes, dispersant, and organic solvent in the carbon nanotube dispersion is shown in Table 2. The viscosity properties of the carbon nanotube dispersion liquid thus prepared were evaluated by the following method.

[0090] [Viscosity of Carbon Nanotube Dispersion Liquid] The viscosity of the resulting carbon nanotube dispersion was measured using an E-type viscometer (TV-22 model, manufactured by Toki Sangyo Co., Ltd.) at a sample temperature of 25°C, with a 1°34' cone and rotor rotation speeds of 1 rpm, 10 rpm, and 1000 rpm.

[0091] <Preparation of slurry for electrode fabrication> The carbon nanotube dispersion obtained by the above-described method, a carbon black dimethyl carbonate dispersion, and polyvinylidene fluoride (PVdF) as a binder (GE51308, 8% NMP solution, manufactured by Kishida Chemical Co., Ltd.) were mixed with a dimethyl carbonate dispersion containing a positive electrode active material (5E-12D, manufactured by Beijing Dangsheng Materials Technology Co., Ltd.) in amounts such that the carbon nanotubes were 0.3 parts by mass, the carbon black was 0.7 parts by mass, and the polyvinylidene fluoride was 0.6 parts by mass, relative to 100 parts by mass of the positive electrode active material. The mixture was then kneaded until homogeneous using a mixer (Thinky Corporation, Awatori Rentaro ARE-310) to prepare a slurry for producing an electrode (positive electrode).

[0092] <Preparation of electrodes> The obtained electrode-preparing slurry was applied to a piece of soda glass using an applicator. The coated glass piece was then heated and dried under reduced pressure on a hot plate at 90°C for 10 minutes to prepare an electrode (positive electrode) for a lithium battery. The thickness of the electrode was 50 μm.

[0093] [Measurement of resistivity] The surface resistivity (Ω / □) of the obtained electrode was measured using a resistivity meter (Mitsubishi Chemical Analytech Co., Ltd., Loresta GP, MCP-T610, four-point probe, ASP pin spacing 5 mm).

[0094] Examples 2 to 9, Comparative Examples 1 to 7 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the types and amounts of carbon nanotubes, dispersant, and solvent were changed as shown in Table 2. Commercially available multi-walled or single-walled carbon nanotubes listed in Table 1 were used as the carbon nanotubes. The viscosity of the obtained carbon nanotube dispersion was measured in the same manner as in Example 1, with the rotor rotation speed changed to 1 rpm, 10 rpm, and 1000 rpm. When the viscosity of the carbon nanotube dispersion exceeded 30,000 mPa s, viscosity measurement was not possible.

[0095] Furthermore, using the prepared carbon nanotube dispersion liquid, a slurry for preparing an electrode (positive electrode) was prepared by the same method as in Example 1, and an electrode (positive electrode) was prepared. The surface resistivity (Ω / □) of the prepared electrode was measured by the same method as in Example 1.

[0096] The carbon nanotube dispersion compositions and evaluation results for Examples 1 to 9 and Comparative Examples 1 to 7 are shown in Tables 2 and 3. In each table, the dispersion composition shows the mass % of the components contained, and the evaluation results show the viscosity of the carbon nanotube dispersion measured at different rotor rotation speeds. Furthermore, the surface resistivity (Ω / □) of the produced electrodes is shown.

[0097] [Table 2]

[0098] [Table 3]

[0099] The carbon nanotube dispersions of Examples 1 to 9 exhibited a relatively low viscosity and had a uniform flow state. Furthermore, the coating operation was easy when producing electrodes from the electrode dispersions prepared using the carbon nanotube dispersions of Examples 1 to 9. As is clear from Table 2, the electrodes of Examples 1 to 9 produced from the electrode production slurries using the carbon nanotube dispersions of the present invention exhibited low surface resistivities.

[0100] In contrast, in Comparative Examples 1 and 2, in which a polymeric dispersant other than a polyallylamine derivative was used as the dispersant, the viscosity of the carbon nanotube dispersion increased, making it difficult to prepare the dispersion, or the surface resistivity of the produced electrode increased. Furthermore, in Comparative Examples 3 and 4, in which the amount of polyallylamine derivative was not within the range specified in the present invention, the viscosity of the carbon nanotube dispersion liquid became high, making it difficult to prepare the dispersion liquid, or the surface resistivity of the produced electrode became high.

[0101] Furthermore, in Comparative Examples 5 to 7 in which single-walled carbon nanotubes were used instead of multi-walled carbon nanotubes, the viscosity of the carbon nanotube dispersion increased, making it difficult to prepare the dispersion. [Industrial Applicability]

[0102] The carbon nanotube dispersion of the present invention can be suitably used in the field of non-aqueous batteries or electronic materials, and in particular, can be suitably used as a slurry for producing electrodes for lithium secondary batteries.

Claims

1. A method for producing a polyallylamine polymer comprising: a multi-walled carbon nanotube; a polyallylamine derivative having a constitutional unit represented by formula (1); and an organic solvent; The carbon nanotube dispersion for electrode production has a content of the polyallylamine derivative of 0.2 parts by mass or more and 1.5 parts by mass or less per part by mass of the multi-walled carbon nanotubes. 【Chemical 1】 (In formula (1), A １ represents a group represented by general formula (2), general formula (3), general formula (4) or general formula (5), and a plurality of A １ may be the same or different from each other. １ At least one of the groups is a group represented by general formula (4) or general formula (5). 【Chemistry 2】 (In formula (2) and formula (3), R １ represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group having an ether bond which may have a substituent. In formula (4) and formula (5), R １ represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent, or an alkylene group which has an ether bond which may have a substituent, R ２ represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkyl group having an ether bond which may have a substituent, or a phenyl group which may have a substituent. In formulas (2) to (5), a represents an integer of 0 to 100. １ , R ２ may be the same or different.)

2. 2. The carbon nanotube dispersion for producing an electrode according to claim 1, wherein the content of the multi-walled carbon nanotubes is 0.1% by mass to 10.0% by mass based on the total amount of the carbon nanotube dispersion.

3. 2. The carbon nanotube dispersion liquid for producing an electrode according to claim 1, comprising 0.3 parts by mass or more and 1.0 parts by mass or less of the polyallylamine derivative per 1 part by mass of the multi-walled carbon nanotubes.

4. 2. The carbon nanotube dispersion liquid for electrode production according to claim 1, wherein the organic solvent is an organic solvent having a water content of less than 5000 ppm.

5. 5. A slurry for producing an electrode, comprising the carbon nanotube dispersion for producing an electrode according to claim 1, and at least a positive electrode active material or a negative electrode active material.

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