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

Abstract

[Problem] The present invention provides a carbon nanotube dispersion liquid which can be easily produced. The present invention also provides 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] Provided is a carbon nanotube dispersion liquid for electrode production, which contains multilayer carbon nanotubes, a polyallylamine derivative that is composed of a constitutional unit represented by formula (1), and an organic solvent. The content of the polyallylamine derivative is 0.2 part by mass to 1.5 parts by mass inclusive relative to 1 part by mass of the multilayer carbon nanotubes.

Description

Carbon nanotube dispersion for electrode fabrication and slurry for electrode fabrication

[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.

[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, with the polyallylamine derivative being present in an amount of 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 per 100 parts by mass of the single-walled carbon nanotubes. The carbon nanotube dispersion of Patent Document 1 requires the polyallylamine derivative to be blended in a relatively large amount. Furthermore, paragraph

[0017] describes that the dispersibility of single-walled carbon nanotubes differs 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.

[0007] JP 2021-187701 A (claims, description, etc.) JP 2017-203143 A (claims, description, etc.) JP 2020-11873 A (claims, description, etc.)

[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.

[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 relates to a carbon nanotube dispersion for electrode fabrication, comprising multi-walled carbon nanotubes, a polyallylamine derivative having a constitutional unit represented by formula (1), and an organic solvent, wherein the content of the polyallylamine derivative is 0.15 parts by mass or more and less than 4 parts by mass per part by mass of the multi-walled carbon nanotubes.

[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).

[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. 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.)

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

[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 a result, the carbon nanotube dispersion of the present invention has a lower viscosity than a carbon nanotube dispersion using single-walled carbon nanotubes, making it easier to produce and handle, and reducing the cost required for producing electrodes.

[0019] <Multi-walled carbon nanotubes> The multi-walled carbon nanotubes used in the present invention are layered carbon nanotubes having a structure in which two or more cylindrical carbon nanotubes with different nanometer-sized diameters are stacked on top of each other. Multi-walled carbon nanotubes have different dispersion characteristics from single-walled carbon nanotubes.

[0020] In X-ray diffraction measurement, single-walled carbon nanotubes exhibit a peak at a diffraction angle 2θ of approximately 6° to 10°. In contrast, in X-ray diffraction measurement, multi-walled carbon nanotubes exhibit a peak at a diffraction angle 2θ of approximately 23° to 27°. By performing X-ray diffraction measurement, 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 mass % or more and 10.0 mass % or less, more preferably 0.2 mass % or more and 6.0 mass % or less, and even more preferably 0.5 mass % or more and 4.0 mass % or less, 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 favorably obtained.

[0022] The multi-walled carbon nanotubes used in the present invention are preferably 70 mm ２ / g to 500m ２ / g, more preferably 100m ２ / g~400m ２ / g, more preferably 140m ２ / g to 300m ２ The BET specific surface area of ​​the multi-walled carbon nanotube 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 or more and 2.0 or less, more preferably 0.8 or more and 1.6 or less, in Raman spectroscopy. Here, the peak intensity ratio G / D is the peak intensity ratio at 1570 cm －１ ~1620cm －１ The maximum intensity of the G-band scattered light peak in the range of G, 1320 cm －１ ~1370cm －１ The maximum value of the D-band scattered light peak intensity within the range is defined as D, and the G / D ratio is expressed as D. The Raman scattered light peak intensity can be measured using a Raman spectrometer.

[0024] The peak intensity ratio G / D in the Raman spectrum is related to the crystallinity of the carbon nanotube. If the crystallinity of the carbon nanotube is too high, the carbon edges will decrease due to the development of the graphite structure, resulting in fewer coordination sites for the electrolyte, leading to problems such as reduced characteristics at low temperatures and increased resistance. Furthermore, if the crystallinity of the carbon nanotube is too low, the amorphous content will increase, increasing electrical resistance and reducing the utilization efficiency of the electric double layer at the interface between the electrolyte and the electrode material. The use of carbon nanotubes with a G / D ratio within the above range has the advantage that, when an electrode is fabricated, it will have fewer defects, be highly resistant to high-voltage operation, and maintain high conductivity over a long period of time.

[0025] The carbon nanotubes used in the present invention preferably have an average fiber length of 1 μm or more and 1000 μm or less, more preferably 3 μm or more and 500 μm or less, and also preferably have an average fiber width of 1 nm or more and 50 nm or less, more preferably 5 nm or more and 20 nm or less. The average fiber length and average fiber width of carbon nanotubes refer to the average values ​​of the outer diameters of a sufficient number (n) of fibers measured using an electron microscope. If the average fiber length of multi-walled carbon nanotubes is short, the viscosity of the carbon nanotube dispersion tends to decrease, while if the average fiber length of multi-walled carbon nanotubes is long, the viscosity tends to increase. 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, multi-walled carbon nanotubes can be produced by thermal CVD, which involves introducing a raw material gas serving as a carbon source into a low-oxygen atmosphere at 500 to 1000°C in the presence of a powdery catalyst, and causing a contact reaction with the catalyst in a fluidized state or with a substrate with a catalyst attached in a stationary state.

[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 raw material. 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 preferred to bring the 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 multi-walled carbon nanotubes uniform. Applicable classification operations include devices that utilize gravity, inertial force, or centrifugal force, or devices that utilize filters, and can be used in either 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). (In formula (1), A １represents 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] (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 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 includes 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 of Ajinomoto Fine-Techno Co., Inc.

[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 part 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 the cost required for production and can also ensure that the performance of the carbon nanotubes is excellent 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 water content that can be tolerated in 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 in 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 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 hydrocarbon solvents include hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, heptane, octane, benzene, toluene, xylene, cymene, mesitylene, styrene, ethylbenzene, diethylbenzene, isopropylbenzene, pentylbenzene, etc. 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, type 1 or type 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 comprising constitutional units represented by formula (1), and an organic solvent are mixed and homogenized. When dispersing carbon nanotubes in a solvent, premixing (hereinafter referred to as "premixing") is performed in which powdered carbon nanotubes are mixed into the solvent, and then the premixed mixture is dispersed using a disperser.

[0050] Dispersion can be carried out using an ultrasonic disperser, mixers such as a Disper, a Homomixer, a rotation-revolution mixer, a Henschel mixer, or a planetary mixer, a (high-pressure) homogenizer, a paint conditioner, colloid mills, media-type dispersers such as a bead mill, a cone mill, a ball mill, a sand mill, an attritor, a pearl mill, or a Coball mill, media-less dispersers such as a wet jet mill or a thin film rotary high-speed mixer, or other dispersing devices such as a roll mill. From the viewpoints of the stability of the dispersing action and dispersion efficiency, preferred dispersing devices are a bead mill-type disperser and an ultra-high-pressure wet 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 the 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 Fabrication> A preferred use form of the carbon nanotube dispersion of the present invention is a slurry for electrode fabrication obtained by adding at least a positive electrode active material or a negative electrode active material to the carbon nanotube dispersion and mixing it. That is, the present invention relates to a slurry for electrode fabrication containing the carbon nanotube dispersion for electrode fabrication 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] 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. The positive electrode active material can be a material that helps lithium ions 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; TiS ２ , FeS, MoS ２ transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２ 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 O ２ (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 singly 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 %, 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] The slurry for producing a negative electrode of the present invention includes the carbon nanotube dispersion liquid having the above-described configuration and at least a negative electrode active material. Examples of the negative electrode active material include metal oxide-based active material particles, silicon-based active material particles, and spherical graphite. In particular, metal oxide-based negative electrode active material particles are preferably used.

[0065] As the metal oxide-based negative electrode active material particles, for example, titanium oxide can be used. The titanium oxide is not particularly limited as long as it can absorb and release lithium, but preferred are spinel-type lithium titanate, ramsdellite-type lithium titanate, titanium-containing metal composite oxide, and titanium dioxide (TiO) having a monoclinic crystal structure. ２ (B)) and anatase type titanium dioxide can be used.

[0066] The spinel-type lithium titanate includes Li ４＋ｘ Ti ５ O １２ (x varies in the range of -1≦x≦3 depending on the charge / discharge reaction). Ramsdellite-type lithium titanate includes Li ２＋ｙ Ti ３ O ７ (y varies in the range of -1≦y≦3 depending on the charge / discharge reaction). ２ (B) and anatase type titanium dioxide include Li １＋ｚ TiO ２ (z varies 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 TiO ２ -P ２ O ５ , TiO ２ -V ２ O ５ , TiO ２ -P ２ O ５-SnO ２ , TiO ２ -P ２ O ５ -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 %, more preferably 35 to 55 mass %, based on the total amount 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 the 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-fabricating slurry of the present invention can further contain conductive particles. By adding conductive particles, the conductivity of the secondary battery electrode produced from the dispersion can be increased. The conductive particles have a specific gravity difference of ±0.2 g / cm between the conductive particles and the multi-walled carbon nanotubes contained in the carbon nanotube dispersion. ３A 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, ketjen black, etc. The amount of the conductive particles to be blended 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] <Binder> The electrode preparation 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 slurry for producing an electrode can also appropriately contain a leveling agent, a solid electrolyte, a preservative, and the like.

[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 preparation 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 prepare a positive or negative electrode. The electrode preparation slurry of the present invention is a dispersion liquid with low viscosity even at high concentrations, so it can 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 electrode production slurry for a positive electrode or a negative electrode of the present invention as follows. First, the electrode production 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 from those suitable for the secondary battery to be used. Examples of materials for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, as the shape of the current collector, a flat metal foil is generally used, but a foil with a roughened surface, a perforated foil, or 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 surface resistivity of the formed electrode is preferably 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.

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

[0084]

[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. Then, the BET specific surface area was measured by the single-point BET method using a fully automatic specific surface area measuring device (Macsorb model HM-1208, manufactured by Mountec Co., Ltd.).

[0086] [Raman Spectral 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 (DXR2xi, manufactured by Thermo Fisher Scientific). －１ The 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 G / D of the two was calculated.

[0087] [Fiber Length and Fiber Width] Each carbon nanotube was observed using a scanning electron microscope (Hitachi High-Tech Corporation, S-3400N; SEM), and the arithmetic mean value of the fiber lengths of 10 carbon nanotubes measured using images at a magnification of 1000 times was calculated. In addition, each carbon nanotube was observed using a transmission electron microscope (Hitachi High-Tech Corporation, H-7650; TEM), and the arithmetic mean value of the fiber widths of 10 carbon nanotubes measured using images at a magnification of 50,000 times was calculated.

[0088] [Peak Half Width] Each carbon nanotube was observed using a powder X-ray diffraction analyzer (Miniflex 600, manufactured by Rigaku Corporation), and the average value of the 2θ peak half width of 10 carbon nanotubes was determined.

[0089] Example 1 <Preparation of Carbon Nanotube Dispersion> A polyallylamine derivative having a structural unit of formula (1) (Ajinomoto Fine-Techno Co., Ltd., 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 further 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 ratios of carbon nanotubes, dispersant, and organic solvent in the carbon nanotube dispersion are shown in Table 2. The viscosity properties of the carbon nanotube dispersion prepared in this manner were evaluated by the following method.

[0090] [Viscosity of Carbon Nanotube Dispersion] The viscosity of the obtained 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 by changing the rotor rotation speed to 1 rpm, 10 rpm, and 1000 rpm.

[0091] <Preparation of Slurry for Electrode Production> The carbon nanotube dispersion obtained by the method described above, a dimethyl carbonate dispersion of carbon black, and polyvinylidene fluoride (PVdF) as a binder (GE51308, 8% NMP solution, manufactured by Kishida Chemical Co., Ltd.) were blended into 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, and the mixture was kneaded until uniform using a mixer (THINKY MIXER ARE-310, manufactured by THINKY Corporation) to prepare a slurry for electrode (positive electrode).

[0092] <Preparation of Electrode> The obtained electrode preparation 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 film thickness of the prepared electrode was 50 μm.

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

[0094] Examples 2 to 9 and Comparative Examples 1 to 7 Carbon nanotube dispersions were prepared in the same manner as in Example 1, except that the types and amounts of carbon nanotubes, dispersants, and solvents 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 dispersions 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 indicates the mass % of the components contained, and the evaluation results indicate 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]

[0098]

[0099] The carbon nanotube dispersions of Examples 1 to 9 exhibited relatively low viscosity and a uniform flow state. Furthermore, when electrodes were produced from the electrode dispersions prepared using the carbon nanotube dispersions of Examples 1 to 9, the coating operation was easy. 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 resistivity.

[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. Also, in Comparative Examples 3 and 4, in which the blending amount of the polyallylamine derivative was outside the range specified in the present invention, the viscosity of the carbon nanotube dispersion increased, making it difficult to prepare the dispersion, or the surface resistivity of the produced electrode increased.

[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.

[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 carbon nanotube dispersion for electrode fabrication, comprising multi-walled carbon nanotubes, a polyallylamine derivative having a structural unit represented by formula (1), and an organic solvent, wherein the content of the polyallylamine derivative is 0.2 parts by mass or more and 1.5 parts by mass or less per 1 part by mass of the multi-walled carbon nanotubes. (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). (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. 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. The carbon nanotube dispersion for electrode fabrication 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. The carbon nanotube dispersion liquid for electrode fabrication according to claim 1, containing 0.3 to 1.0 part by mass of the polyallylamine derivative per 1 part by mass of the multi-walled carbon nanotubes.

4. 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. A slurry for producing an electrode, comprising the carbon nanotube dispersion for producing an electrode according to any one of claims 1 to 4, and at least a positive electrode active material or a negative electrode active material.

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