Monolayer carbon nanotube dispersion liquid for electrode manufacturing

Abstract

To provide a carbon nano tube dispersion liquid easy to be handled or a slurry for electrode manufacturing appropriate for manufacturing an electrode of a lithium ion secondary battery, etc.SOLUTION: A dispersion liquid contains at least monolayer carbon nanotubes, carboxymethyl cellulose and / or salt thereof, and an aqueous solvent. In the carbon nanotube dispersion liquid for electrode manufacturing, the content of the monolayer carbon nanotubes is 0.1 mass% or more to 1.5 mass% or less with respect to the entire dispersion liquid. A weight average molecular weight of the carboxymethyl cellulose and / or salt thereof is 300,000 or more to 2,000,000 or less. A loss tangent under a shear stress of 1.0 Pa and an angular frequency of 100 rad / s in an aqueous solution of a concentration of 3 mass% is 0.45 or more. The content of the carbon nanotube dispersion liquid for electrode manufacturing is 0.7 times or more of the mass to 1.2 times of the mass of the monolayer carbon nanotubes.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] Carbon electrodes are commonly used for electrodes in non-aqueous secondary batteries, including lithium-ion batteries. Carbon electrodes are fabricated by applying a dispersion of a carbon material to an electrode substrate and drying it. Carbon materials include carbon black and carbon nanotubes. Carbon nanotubes are classified into single-walled carbon nanotubes and multi-walled carbon nanotubes based on their higher-order structure, and both are commercially available.

[0004] Patent Document 1 discloses a carbon nanotube dispersion containing single-walled carbon nanotubes, carboxymethyl cellulose and / or a salt thereof, and water, wherein the content of the single-walled carbon nanotubes is 0.47 to 1.00 mass %, the carboxymethyl cellulose and / or salt thereof includes at least one type having an etherification degree of 0.65 to 0.85 and a weight-average molecular weight of 120,000 to 250,000, and the content of the carboxymethyl cellulose and / or salt thereof is 120 to 220 parts by mass per 100 parts by mass of the single-walled carbon nanotubes.

[0005] Patent Document 2 discloses a carbon nanotube dispersion containing carbon nanotubes, carboxymethyl cellulose or a salt thereof, and water, wherein the carboxymethyl cellulose or the salt thereof has a weight average molecular weight of 10,000 to 100,000 and a degree of etherification of 0.5 to 0.9, and the product (X×Y) of the complex modulus X (Pa) and the phase angle Y (°) of the carbon nanotube dispersion is 100 or more and 1,500 or less.

[0006] Patent Document 3 discloses a carbon nanotube dispersion for use in a lithium ion battery electrode, which contains a dispersion resin (A), carbon nanotubes (B), and water, and is characterized in that the dispersion resin (A) contains a polar functional group-containing resin (a), and a carbon nanotube dispersion for use in a lithium ion battery electrode, which is characterized in that the polar functional group-containing resin (a) is a carboxymethylcellulose. However, none of Patent Documents 1 to 3 describes the viscoelastic properties of carboxymethyl cellulose. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7194860 [Patent Document 2] Japanese Patent Publication No. 2023-24526 [Patent Document 3] International Publication No. 2023 / 286793 Summary of the Invention [Problem to be solved by the invention]

[0008] When preparing a carbon nanotube dispersion, powdered carbon nanotubes are generally mixed into a solvent and dispersed using a disperser. This process often results in high viscosity, making it difficult to prepare a uniform carbon nanotube dispersion. Furthermore, when the carbon nanotube dispersion is stored for a long period of time, the carbon nanotubes separate and the viscosity of the dispersion increases, making it difficult to handle.

[0009] Furthermore, the carbon nanotube dispersion is generally applied uniformly to a current collector such as aluminum foil and then dried to produce an electrode for a lithium ion secondary battery, etc. In this case, depending on the state of the carbon nanotube dispersion, it may be difficult to apply it to the current collector, or the surface resistivity of the produced electrode may become high, making it difficult to produce a suitable electrode.

[0010] An object of the present invention is to provide a carbon nanotube dispersion liquid that is easy to handle, and to provide a slurry for producing electrodes that is suitable for producing carbon electrodes for lithium ion secondary batteries and the like. [Means for solving the problem]

[0011] The inventors investigated the above-mentioned problems by focusing on the viscoelastic properties of carboxymethyl cellulose, and discovered that a suitable carbon nanotube dispersion can be obtained by combining single-walled carbon nanotubes with a specific carboxymethyl cellulose dispersant.Based on this finding, they completed the present invention.

[0012] The present invention provides a dispersion containing at least single-walled carbon nanotubes, carboxymethyl cellulose and / or a salt thereof, and an aqueous solvent, The content of the single-walled carbon nanotubes is 0.1% by mass or more and 1.5% by mass or less with respect to the entire dispersion liquid, The carboxymethyl cellulose and / or salt thereof has a weight average molecular weight of 300,000 or more and 2,000,000 or less, a loss tangent of 0.45 or more at a shear stress of 1.0 Pa and an angular frequency of 100 rad / s when the carboxymethyl cellulose and / or salt thereof is a 3% by mass aqueous solution, and the content thereof is 0.7 times to 1.2 times by mass of the single-walled carbon nanotubes. The present invention relates to a carbon nanotube dispersion liquid for producing an electrode.

[0013] The present invention also relates to a slurry for producing an electrode, which contains the carbon nanotube dispersion for producing an electrode and at least a positive electrode active material or a negative electrode active material.

[0014] The carbon nanotube dispersion liquid for producing an electrode or the slurry for producing an electrode of the present invention may contain auxiliary agents such as conductive particles and binders as components other than those mentioned above. [Effects of the Invention]

[0015] The carbon nanotube dispersion for electrode production of the present invention is a slurry that is highly stable during storage and exhibits little increase in viscosity even after long-term storage, making the carbon nanotube dispersion of the present invention highly convenient for industrial use.

[0016] Furthermore, the slurry prepared using the carbon nanotube dispersion for electrode fabrication of the present invention was easy to knead. Furthermore, the carbon electrode fabricated from the slurry prepared using the carbon nanotube dispersion of the present invention had extremely low surface resistivity. Therefore, this slurry is useful as a raw material for fabricating electrodes for secondary batteries such as lithium-ion batteries. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Carbon nanotubes> The carbon nanotubes used in the present invention are single-walled carbon nanotubes, which are cylindrical carbon nanotubes with nanometer-sized diameters. Single-walled carbon nanotubes have different dispersion characteristics than multi-walled carbon nanotubes. Single-walled carbon nanotubes are more flexible than multi-walled carbon nanotubes, and when used as a conductive agent for electrodes, they provide excellent battery performance (cycle characteristics).

[0018] The single-walled carbon nanotubes used in the present invention are preferably 300 mm 2 / g~2000m 2 / g, more preferably 500m 2 / g~1500m 2 / g, more preferably 800m 2 / g~1300m 2 The BET specific surface area of ​​the single-walled carbon nanotube can be measured using a specific surface area measuring device.

[0019] In the carbon nanotube dispersion of the present invention, the content of single-walled carbon nanotubes to be blended is 0.1 to 1.5% by mass, more preferably 0.2 to 1.0% by 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.

[0020] The single-walled carbon nanotubes used in the present invention have a peak intensity ratio G / D in Raman spectroscopy of preferably 10 or more and 200 or less, more preferably 30 or more and 150 or less. 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.

[0021] The single-walled carbon nanotubes used in the present invention preferably have an average fiber width of 0.5 nm to 10 nm, more preferably 1.0 nm to 5.0 nm. The average fiber width of carbon nanotubes refers to the average value of the outer diameter of a sufficient number (n) of fibers measured using an electron microscope. Carbon nanotubes can generally be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, or a combustion method.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The 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. These treatments allow the properties of the carbon nanotubes to be adjusted.

[0027] 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.

[0028] The classification operation is an operation for aligning the size of carbon nanotubes. Applicable classification operations include devices that utilize gravity, inertial force, or centrifugal force, or devices that utilize filters, and can be used in dry or wet methods. The demetallization operation is an operation for removing metal components contained in carbon nanotubes. Because carbon nanotubes contain metal components contained in the catalyst used in their production, it is preferable to remove the metal components from the carbon nanotubes.

[0029] <Carboxymethyl cellulose> In the present invention, carboxymethyl cellulose and / or a salt thereof is used as a dispersant. Carboxymethyl cellulose and / or its salts (hereinafter sometimes referred to as CMC) are polymers with a cellulose structure in which carboxymethyl groups are bonded to some of the hydroxy groups of the glucose units that make up the CMC. CMC may contain residues of carboxyl groups or their salts in its structure.

[0030] Examples of carboxymethylcellulose salts containing the above residues include alkali metal salts such as sodium salt, lithium salt, and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, and organic salts such as ammonium salt, alkylamine salt, and alkanolamine salt. Only one of these salts may be contained, or two or more salts may be contained. Among these, alkali metal salts are preferred, and sodium salt is more preferred.

[0031] The carboxymethyl cellulose and / or its salt (CMC) used in the present invention has a weight average molecular weight (Mw) of 300,000 to 2,000,000, preferably 500,000 to 1,000,000. The weight average molecular weight of CMC can be measured using GPC (Gel Permeation Chromatography).

[0032] In addition to having the weight-average molecular weight described above, the CMC used in the present invention has a loss tangent (tanδ) of 0.45 or greater, preferably 0.50 or greater, when used as a 3% by mass aqueous solution at a shear stress of 1.0 Pa and an angular frequency of 100 rad / s. The loss tangent is measured using a dynamic viscoelasticity measuring device by applying a sinusoidal force and shear force of a predetermined frequency as stress to a 3% by mass aqueous CMC solution sample, detecting the resulting deformation (strain) of the sample, and calculating the loss tangent from the strain. Using a CMC with such characteristics efficiently applies dispersing force to the carbon nanotubes during the dispersion process, resulting in a good slurry.

[0033] The carbon nanotube dispersion of the present invention has excellent stability when stored for a long period of time by using a CMC that has a weight average molecular weight within the above range and gives a loss tangent (tan δ) equal to or greater than the above lower limit.

[0034] The degree of etherification of the CMC is preferably 0.5 to 0.9, more preferably 0.6 to 0.8. By using a CMC with such a degree of etherification, the storage stability of the carbon nanotube dispersion can be further improved, and the battery performance can be improved when the CMC is used as an electrode coating material.

[0035] The amount of CMC blended is 0.7 to 1.2 times, more preferably 0.8 to 1.1 times, by mass, the mass of the single-walled carbon nanotubes. When the amount of CMC blended is within this range, the dispersibility of the single-walled carbon nanotubes in the carbon nanotube dispersion can be exhibited, while the performance of the electrode fabricated from the carbon nanotube dispersion can be ensured. <Solvent>

[0036] An aqueous solvent is used for the carbon nanotube dispersion of the present invention. For example, distilled water, ion-exchanged water, tap water, industrial water, etc. can be used as the solvent. Among these, distilled water and ion-exchanged water are preferred. Also, an aqueous solution obtained by mixing water with a highly hydrophilic organic solvent such as alcohol, ether, ester, or amide can be used.

[0037] <Preparation of carbon nanotube dispersion> The carbon nanotube dispersion of the present invention can be produced through a dispersion step in which at least single-walled carbon nanotubes, the specific CMC, and a solvent are mixed and homogenized. When dispersing carbon nanotubes in a solvent, it is preferable to carry out premixing (hereinafter referred to as "premixing") by mixing powdered carbon nanotubes into a solvent, and then dispersing the premixed mixture with a disperser.

[0038] 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.

[0039] The amount of single-walled carbon nanotubes to be blended in the carbon nanotube dispersion of the present invention is preferably 0.1% by mass or more and 1.5% by mass or less, more preferably 0.2% by mass or more and 1.3% by mass or less, based on the total amount of the dispersion. When the blending amount of single-walled carbon nanotubes in the dispersion is within this range, a carbon nanotube dispersion that can be used for electrode slurries can be obtained.

[0040] Carbon nanotube dispersions often have the property that, when stored for a long period of time, their viscosity increases significantly, making them difficult to handle. In contrast, the carbon nanotube dispersion of the present invention does not exhibit a significant increase in viscosity even when stored for a long period of time, and is highly stable during storage. For this reason, the carbon nanotube dispersion of the present invention is suitable for industrial use as a slurry for producing electrodes.

[0041] <Slurry for electrode production> A preferred form of use of the carbon nanotube dispersion for electrode production of the present invention is a slurry for electrode production, 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 at least a positive electrode active material or a negative electrode active material.

[0042] 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. Hereinafter, an embodiment of producing a negative electrode using the electrode-fabricating slurry of the present invention will be described.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] 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).

[0047] 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.

[0048] 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.

[0049] The content of single-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 negative 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 carbon electrode to be produced.

[0050] 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.

[0051] <Conductive particles> The slurry for producing a carbon electrode of the present invention may 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 from the single-walled carbon nanotubes contained in the carbon nanotube dispersion liquid. 3 A slurry 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 producing carbon electrodes.

[0052] 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 100 parts by mass of the negative electrode active material.

[0053] <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, styrene-butadiene rubber (SBR), and carboxymethyl cellulose. Two or more binders may be used in combination.

[0054] 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.

[0055] 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.

[0056] <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.

[0057] More specifically, a carbon 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 slurry for preparing a carbon electrode 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 materials 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.

[0058] 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.

[0059] 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.

[0060] 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 5.0 kΩ / □, more preferably less than 1.0 kΩ / □. The surface resistivity can be measured using a resistivity meter.

[0061] An electrode produced from a slurry for producing an electrode obtained by using the carbon nanotube dispersion liquid for producing an electrode 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]

[0062] Example 1 <Preparation of carbon nanotube dispersion> Sodium carboxymethylcellulose (Daicel Millize Co., Ltd., tanδ: 3.72; CMC-1) was added as a dispersant to ion-exchanged water as a solvent, and single-walled carbon nanotubes (Meijo Nanocarbon Co., Ltd., EC2.0P; Carbon Nanotube A) were then added. Zirconia beads with a diameter of 0.5 mm were used in a disperser (Shinmaru Enterprises Co., Ltd., DYNO-MILL) to disperse the mixture, preparing a carbon nanotube dispersion for electrode fabrication. The blending ratios of the components contained in the carbon nanotube dispersion are shown in Table 1. The loss tangent of the CMC was evaluated by dynamic viscoelasticity measurement, and the storage stability of the prepared CNT dispersion was evaluated as follows.

[0063] [Loss tangent of CMC] The loss tangent of the sodium carboxymethyl cellulose used was evaluated by the following method. A 3% by mass aqueous solution of carboxymethylcellulose sodium was prepared and allowed to stand without applying any load. The loss tangent (tanδ) was then measured using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, product name: MCR) at a measurement temperature of 25°C, a shear stress of 1.0 Pa, and an angular frequency of 100 rad / s. The loss tangent of each CMC is shown in Table 1.

[0064] [Storage stability of CNT dispersion liquid] The storage stability of the carbon nanotube dispersion liquid for electrode production was evaluated by the following method. The obtained carbon nanotube dispersion electrode for electrode preparation was filled into a container, and immediately measured using an E-type viscometer (Toki Sangyo Co., Ltd., TV-22 model) at a sample temperature of 40°C, a 1°34' cone, and a shear rate of 38.3 s -1 The viscosity was measured under the conditions above and recorded as the initial viscosity (mPa·s). Next, the container was left to stand at 40°C for one week without applying any load, and the viscosity was then measured using the method described above, and the storage viscosity (mPa·s) was calculated.

[0065] The value (percentage) obtained by dividing the storage viscosity by the initial viscosity was taken as the viscosity increase rate over time. If the viscosity increase rate over time was less than 140%, i.e., the increase in viscosity value was less than 40% of the viscosity before storage, the dispersion viscosity increase was considered small and rated as good; if the viscosity increase rate over time was 140% or more, i.e., the increase in viscosity value was 40% or more of the viscosity before storage, the dispersion viscosity increase was considered large and rated as bad. The evaluation results of the storage stability of the CNT dispersion are shown in Table 1.

[0066] <Preparation of slurry for electrode fabrication> A negative electrode active material (LTO-2S, manufactured by Beiterui Advanced Energy Materials Co., Ltd.), the carbon nanotube dispersion obtained above, and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC1380, manufactured by Daicel Corporation) as binders were blended in amounts such that, per 100 parts by mass of the negative electrode active material, the carboxymethyl cellulose was 1.5 parts by mass, the carbon nanotubes were 0.3 parts by mass, and the styrene butadiene rubber was 1.25 parts by mass. The mixture was then kneaded until completely homogeneous using a mixer (Thinky Corporation, Awatori Rentaro ARE-310) to prepare a slurry for electrode (negative electrode). The kneadability of the electrode slurry was evaluated as follows.

[0067] <Preparation of electrodes> The resulting electrode slurry was applied to a soda glass test piece using a 50 μm thick applicator. The coated glass piece was then dried under reduced pressure at 90°C for 10 minutes using a hot plate to prepare a lithium battery positive electrode. The surface resistivity of the electrode was evaluated as follows.

[0068] [Coating properties of electrode-making slurry] The obtained electrode-forming slurry was applied to a soda glass test piece using an applicator with a thickness of 50 μm. The obtained coating film was visually observed, and the coatability was evaluated according to the following criteria. ◯: No pinholes or uneven coating on the film surface, good. △: Pinholes and uneven coating occurred on the film surface. Table 1 shows the evaluation results of the coating properties of the electrode-forming slurry.

[0069] [Electrode surface resistivity] The surface resistivity (Ω / □) of the prepared electrodes was measured using a resistivity meter (Mitsubishi Chemical Analytech Co., Ltd., Loresta GP, MCP-T610, four-point probe, ASP pin spacing 5 mm). The measurement results of the surface resistivity of the electrodes prepared from the electrode preparation slurry are shown in Table 1.

[0070] Examples 2 to 4, Comparative Examples 1 to 5 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the type and amount of the CMC dispersant were changed as shown in Table 2. In particular, as the CMC, the same carboxymethylcellulose sodium as in Example 1 (manufactured by Daicel Millize Co., Ltd., tanδ: 3.72; CMC-1) was used, as well as carboxymethylcellulose sodium having a loss tangent tanδ within the range of the present invention (manufactured by Daicel Millize Co., Ltd., tanδ: 0.53; CMC-2) or carboxymethylcellulose sodium having a loss tangent tanδ outside the range of the present invention (manufactured by Daicel Millize Co., Ltd., tanδ: 0.43; CMC-3).

[0071] Furthermore, using the obtained carbon nanotube dispersion liquid, a slurry for electrode production was prepared and an electrode (negative electrode) was produced by the same method as in Example 1. The surface resistivity (Ω / □) of the produced electrode was measured by the same method as in Example 1. Table 1 shows the compositions (mass %) of the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 5 and the evaluation results.

[0072] [Table 1]

[0073] The carbon nanotube dispersions of Examples 1 to 4, which are embodiments of the present invention, had excellent storage stability, as shown in Table 1. Furthermore, the electrode fabrication slurries prepared using the carbon nanotube dispersions of Examples 1 to 4 had excellent kneadability, and the electrodes fabricated from the electrode fabrication slurries exhibited low surface resistivity.

[0074] On the other hand, the carbon nanotube dispersions of Comparative Examples 1 to 4, which are not embodiments of the present invention, sometimes exhibited poor storage stability or unevenness on the coated surface of the electrode slurry, as shown in Table 1. The electrodes fabricated from the electrode-fabrication slurries prepared using the carbon nanotube dispersions of Comparative Examples 1 to 5 sometimes exhibited low surface resistivity. [Industrial Applicability]

[0075] The electrode-fabricating slurry of the present invention can be suitably used for producing electrodes such as electrodes for lithium secondary batteries. The carbon nanotube dispersion of the present invention can be suitably used for preparing a slurry for producing an electrode.

Claims

1. A dispersion containing at least single-walled carbon nanotubes, carboxymethyl cellulose and / or a salt thereof, and an aqueous solvent, The content of the single-walled carbon nanotubes is 0.1% by mass or more and 1.5% by mass or less with respect to the entire dispersion liquid, The carboxymethyl cellulose and / or salt thereof has a weight average molecular weight of 300,000 or more and 2,000,000 or less, a loss tangent of 0.45 or more at a shear stress of 1.0 Pa and an angular frequency of 100 rad / s when the carboxymethyl cellulose and / or salt thereof is a 3% by mass aqueous solution, and the content thereof is 0.7 times by mass to 1.2 times by mass of the single-walled carbon nanotubes. Carbon nanotube dispersion for electrode fabrication.

2. 2. The carbon nanotube dispersion for electrode fabrication according to claim 1, wherein the single-walled carbon nanotube slurry has a peak intensity ratio G / D of 30 or more and 150 or less in Raman spectroscopy. (However, the intensity ratio G / D is determined by the Raman spectrum at 1570 cm －１ ~1620cm －１ The maximum intensity of the G-band scattered light peak in the range of 1320 cm －１ ~1370cm －１ The maximum intensity of the D-band scattered light peak in the range is defined as D, and this represents the ratio.)

3. 3. A slurry for producing an electrode, comprising the carbon nanotube dispersion for producing an electrode according to claim 1 or 2, and at least a positive electrode active material or a negative electrode active material.

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