Carbon nanotube dispersion liquid, and composition for battery electrode and battery using same

Abstract

The dispersity and the dispersion stability of the carbon nano tube are improved. A carbon nanotube dispersion liquid according to an embodiment includes carbon nanotubes, carboxymethyl cellulose and / or a salt thereof, water, and a compound represented by general formula (1). In formula (1), R represents a hydrogen atom or a methyl group. # imgabs0 #

Description

Technical Field

[0001] Embodiments of the present invention relate to a carbon nanotube dispersion, a battery electrode composition using the carbon nanotube dispersion, and a battery. Background Art

[0002] Since carbon nanotubes have excellent electrical conductivity, they are used, for example, as a conductive agent for forming electrodes in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. However, carbon nanotubes have strong aggregation due to van der Waals forces and are difficult to uniformly disperse in water.

[0003] In order to improve the dispersibility of carbon nanotubes in water, it is known to use carboxymethyl cellulose and / or its salt as a dispersant. For example, Patent Document 1 describes a fine carbon fiber dispersion liquid composed of fine carbon fibers, a dispersion medium, a polymer-based dispersant, and a basic compound having a pKa of 7.5 or more. Specifically, a carbon nanotube dispersion liquid is described in which carbon nanotubes as fine carbon fibers, sodium carboxymethyl cellulose as a dispersant, water as a dispersion medium, and monoethanolamine as a basic compound are mixed.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-181140 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] As described above, generally, carbon nanotubes form high-density bundles due to van der Waals forces, and in order to uniformly disperse in water, it is necessary to dissociate the bundles. However, it is difficult to dissociate the bundles and uniformly disperse them in water, and it is necessary to improve the dispersibility. In addition, it is necessary to maintain the dispersed state, that is, the dispersion stability.

[0009] An object of embodiments of the present invention is to provide a carbon nanotube dispersion liquid capable of improving the dispersibility and dispersion stability of carbon nanotubes.

[0010] Means for Solving the Problems

[0011] The present invention includes the following embodiments.

[0012] [1] A carbon nanotube dispersion liquid containing carbon nanotubes, carboxymethyl cellulose and / or its salt, water, and a compound represented by the following general formula (1),

[0013] [Chemical Formula 1]

[0014]

[0015] In formula (1), R represents a hydrogen atom or a methyl group.

[0016] [2] The carbon nanotube dispersion according to [1], wherein the degree of etherification of the carboxymethyl cellulose and / or its salt is 0.60 to 0.85, and the viscosity of a 2% by mass aqueous solution at 25°C is 1 to 300 mPa·s.

[0017] [3] The carbon nanotube dispersion according to [1] or [2], wherein the content of the compound is 1 to 30 moles per 100 g of the carbon nanotubes.

[0018] [4] The carbon nanotube dispersion according to any one of [1] to [3], wherein the ratio of the amount of the carboxymethyl cellulose and / or its salt to the amount of the carbon nanotubes is 0.3 to 3.0 by mass ratio.

[0019] [5] The carbon nanotube dispersion according to any one of [1] to [4], wherein the ratio of the amount of the compound to the total amount of the compound and water is 0.005 to 0.1 by mass ratio.

[0020] [6] A composition for a battery electrode, which comprises the carbon nanotube dispersion according to any one of [1] to [5].

[0021] [7] A battery electrode, which is produced by using the composition for a battery electrode according to [6].

[0022] [8] A battery, which includes an electrode made of the carbon nanotube dispersion according to any one of [1] to [5].

[0023] Advantages of the Invention

[0024] According to the embodiments of the present invention, the dispersibility and dispersion stability of carbon nanotubes can be improved. Detailed Embodiments

[0025] The carbon nanotube dispersion of the present embodiment includes: (A) carbon nanotubes, (B) carboxymethyl cellulose and / or its salt, (C) water, and (D) a compound represented by the general formula (1).

[0026] [(A) Carbon Nanotubes]

[0027] A carbon nanotube is a substance in which a six-membered ring network composed of carbon (graphene sheet) forms a single-layer or multi-layer coaxial tubular structure. Examples of carbon nanotubes include: single-walled carbon nanotubes (SMCNT) with a single-layer structure, multi-walled carbon nanotubes (MWCNT) with a multi-layer structure. In particular, a carbon nanotube with two layers in the multi-layers is called a double-walled carbon nanotube (DWCNT). Any one of them or a combination of two or more can be used. Due to its excellent battery cycling characteristics, single-walled carbon nanotubes are preferably used.

[0028] The manufacturing method of carbon nanotubes is not particularly limited. For example, it can be obtained by various known manufacturing methods such as thermal decomposition method using a catalyst, arc discharge method, laser evaporation method, and CVD methods such as HiPco method and CoMoCAT method.

[0029] The average diameter (fiber diameter) of carbon nanotubes is not particularly limited. For example, it can be 0.4 - 100 nm, 0.5 - 50 nm, or 1 - 20 nm. The average length of carbon nanotubes is not particularly limited. For example, it can be 50 nm - 10 mm, 500 nm - 100 μm, or 1 - 50 μm. The aspect ratio of carbon nanotubes (i.e., the ratio of the average length to the average diameter) is not particularly limited. For example, it can be 10 or more, or 100 or more.

[0030] The average diameter and average length of carbon nanotubes can be obtained by measuring the sizes of 50 randomly selected carbon nanotubes in an atomic force microscope image and taking their arithmetic mean. For lengths in the mm range that cannot be measured by atomic force microscopy, measurement using a microscope-based image is sufficient.

[0031] In a preferred embodiment, the carbon nanotubes contain single-walled carbon nanotubes. In this case, the carbon nanotubes can be composed only of single-walled carbon nanotubes, or can contain both single-walled carbon nanotubes and multi-walled carbon nanotubes at the same time. Specifically, the ratio of single-walled carbon nanotubes in the overall carbon nanotubes can be 80% by mass or more, preferably 95% by mass or more, and more preferably 98% by mass or more.

[0032] [(B) Carboxymethyl cellulose and / or its salt]

[0033] Carboxymethyl cellulose and / or its salt (hereinafter sometimes referred to as CMC) has a structure in which the hydroxyl groups in the glucose residues constituting cellulose are substituted by carboxymethyl ether groups. CMC can have a carboxyl group (-COOH), can be in the form of a carboxylate salt, or can use both.

[0034] As salts of carboxymethyl cellulose, examples include: alkali metal salts such as sodium salt, lithium salt, potassium salt, etc., alkaline earth metal salts such as calcium salt, magnesium salt, ammonium salt, organic salts such as alkylamine salt, alkanolamine salt, etc. These salts may contain only any one kind, or may contain two or more kinds of salts. Among them, alkali metal salts are preferred, and sodium salt is more preferred.

[0035] In the present embodiment, as CMC, it is preferable to use CMC having an etherification degree of 0.60 to 0.85 and a viscosity of 2 mass% aqueous solution at 25°C of 1 to 300 mPa·s. By using CMC having such an etherification degree and a viscosity of 2 mass% aqueous solution, the effect of enhancing the dispersion stability of carbon nanotubes can be improved.

[0036] The etherification degree of CMC is more preferably 0.65 to 0.85, and further preferably 0.70 to 0.80. In this specification, the etherification degree of CMC is measured by the following method.

[0037] (Degree of etherification)

[0038] 0.6 g of CMC is dried at 105°C for 4 hours. After accurately weighing the mass of the dried product, it is wrapped with filter paper and ashed in a magnetic crucible. The ashed product is transferred to a 500 mL beaker, 250 mL of water and 35 mL of 0.05 mol / L sulfuric acid aqueous solution are added, and it is boiled for 30 minutes. After cooling, the excess acid is back-titrated with 0.1 mol / L potassium hydroxide aqueous solution (using phenolphthalein as an indicator). The degree of etherification is calculated by the following formula.

[0039] Formula: (Degree of etherification) = 162 × A / (10000 - 80A)

[0040] A = (af - bf1) / mass of dried product (g)

[0041] A: Amount of 0.05 mol / L sulfuric acid aqueous solution consumed by combined alkali in 1 g of sample (mL)

[0042] a: Amount of 0.05 mol / L sulfuric acid aqueous solution used (mL)

[0043] f: Titration factor of 0.05 mol / L sulfuric acid aqueous solution

[0044] b: Titration amount of 0.1 mol / L potassium hydroxide aqueous solution (mL)

[0045] f1: Titration factor of 0.1 mol / L potassium hydroxide aqueous solution

[0046] The viscosity of 2 mass% aqueous solution of CMC at 25°C is more preferably 1 to 150 mPa·s, and further preferably 1 to 30 mPa·s. In this specification, the viscosity of 2 mass% aqueous solution of CMC is measured by the following method.

[0047] (Viscosity of 2 mass% aqueous solution)

[0048] Add CMC to an Erlenmeyer flask, add water to make the concentration reach 2 mass%, and shake for 30 seconds. After standing for 12 hours, mix for 5 minutes to prepare a 2 mass% aqueous solution. Transfer the obtained aqueous solution to a tall beaker, adjust to 25 °C, and measure the viscosity in accordance with JIS Z8803:2011 using a B-type viscometer (single cylinder type rotational viscometer). At this time, set the rotor speed to 60 rpm for measurement, and in the case of reaching the measurement upper limit, sequentially change to 30 rpm and 12 rpm for measurement.

[0049] [(D) Compound represented by general formula (1)]

[0050] In the present embodiment, while using CMC as the above-mentioned component (B), a compound represented by the following general formula (1) (hereinafter sometimes referred to as "compound (1)") is used as the component (D). By using compound (1) together with CMC, the dispersibility and dispersion stability of carbon nanotubes in water can be improved, and the cycle characteristics during battery production can be improved. The reason is considered as follows, but is not limited thereto. That is, compound (1) enters between carbon nanotubes that are attracted to each other by van der Waals forces, dissociates the bundles of carbon nanotubes, and disperses the carbon nanotubes in water. Moreover, it is considered that by adsorbing CMC to the dissociated carbon nanotubes, the dispersed state of the carbon nanotubes can be maintained.

[0051] [Chemical formula 2]

[0052]

[0053] In formula (1), R represents a hydrogen atom or a methyl group.

[0054] Compound (1) is specifically N,N-dimethylacetamide (the above R = hydrogen atom) and N,N-dimethylpropanamide (the above R = methyl group). As compound (1), any one of them can be used, or both can be used in combination.

[0055] [Carbon nanotube dispersion]

[0056] The carbon nanotube dispersion of the present embodiment contains the above-mentioned components (A), (B), and (D), and contains water as the component (C), and is a dispersion in which carbon nanotubes are dispersed in water. More specifically, since CMC as the component (B) and compound (1) as the component (D) are water-soluble, it is a dispersion obtained by dispersing the carbon nanotubes of the component (A) in an aqueous solution in which CMC and compound (1) are dissolved.

[0057] In the carbon nanotube dispersion, regarding the content of compound (1), from the viewpoint of enhancing the effects of the present embodiment, it is preferable that 1 to 30 moles of compound (1) are contained per 100 g of carbon nanotubes, more preferably 1.5 to 20 moles, still more preferably 2 to 15 moles, and yet more preferably 5 to 12 moles.

[0058] In the carbon nanotube dispersion, from the viewpoint of enhancing the effects of the present embodiment, the ratio of the amount (B) of CMC to the amount (A) of carbon nanotubes is preferably B / A = 0.3 to 3.0 in terms of mass ratio, more preferably 0.5 to 2.5, still more preferably 1.0 to 2.0, and yet more preferably 1.1 to 1.8.

[0059] In the carbon nanotube dispersion, the ratio of the amount (D) of compound (1) to the total amount (C + D) of compound (1) and water is preferably D / (C + D) = 0.005 to 0.1 in terms of mass ratio, more preferably 0.01 to 0.08, still more preferably 0.02 to 0.07. By making the mass ratio D / (C + D) 0.005 or more, the addition effect of compound (1) can be enhanced. In addition, by making the mass ratio D / (C + D) 0.1 or less, the solubility of CMC in water can be prevented from decreasing.

[0060] In the carbon nanotube dispersion, the ratio of the amount (D) of compound (1) to the amount (B) of CMC is preferably D / B = 1 to 20 in terms of mass ratio, more preferably 1.3 to 15.

[0061] In the carbon nanotube dispersion, the ratio of the total amount (B + D) of CMC and compound (1) to the total amount (A + B + D) of carbon nanotubes, CMC, and compound (1) is preferably (B + D) / (A + B + D) = 0.60 to 0.98 in terms of mass ratio, more preferably 0.67 to 0.97, still more preferably 0.77 to 0.96.

[0062] The content of each component is not particularly limited with respect to 100% by mass of the carbon nanotube dispersion. For example, the content of carbon nanotubes can be 0.01% by mass to 5% by mass, can be 0.1% by mass to 3% by mass, or can be 0.2% by mass to 2% by mass. The content of CMC can be 0.01% by mass to 5% by mass, can be 0.1% by mass to 3% by mass, or can be 0.2% by mass to 2% by mass. The content of compound (1) can be 0.5% by mass to 12% by mass, can be 1% by mass to 10% by mass, or can be 1.5% by mass to 7% by mass. The content of water can be 70% by mass to 99% by mass, can be 80% by mass to 98% by mass, or can be 90% by mass to 97% by mass.

[0063] In the carbon nanotube dispersion, other components may be contained as needed in addition to the above components (A) to (D). For example, as the dispersion medium, water-soluble organic solvents mixed with water such as methanol, ethanol, propanol, butanol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, acetone, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), etc. can be used together with the water of component (C). In addition, as other additives, for example, conductive agents other than carbon nanotubes, water-soluble polymers other than CMC, dispersants, surfactants, wetting agents, defoamers, pH adjusters, etc. can be cited.

[0064] The method for preparing the carbon nanotube dispersion is not particularly limited. For example, the above components (A), (B), and (D) can be mixed with the water of component (C), and a dispersion treatment can be performed using a dispersion device such as a homogenizer, a high-pressure homogenizer, an ultrasonic homogenizer, etc., thereby preparing the carbon nanotube dispersion. In one embodiment, a dispersion device equipped with a circulation unit can be used, and while circulating the mixed solution containing components (A) to (D), a dispersion treatment can be performed using a dispersion device such as a homogenizer.

[0065] [Composition for battery electrode]

[0066] The above carbon nanotube dispersion can be used, for example, as a coating material (coating material for electrode) for making electrodes of batteries such as non-aqueous electrolyte secondary batteries. That is, the composition for battery electrode in the embodiment contains the above carbon nanotube dispersion.

[0067] In one embodiment, the composition for battery electrode is used to form the above active material layer in an electrode having a current collector and an active material layer formed on the current collector. That is, by coating the composition for battery electrode on the current collector and drying it, an electrode can be fabricated. In this case, in the composition for battery electrode, an electrode active material is contained together with the above carbon nanotube dispersion. In the active material layer, the carbon nanotubes have the function of ensuring a conductive path between the active materials that connects the active material particles that lose contact points due to the expansion and contraction of the electrode active material. The composition for battery electrode can be used for the positive electrode of a non-aqueous electrolyte secondary battery, but is preferably used for the negative electrode to form the active material layer of the negative electrode.

[0068] As the electrode active material for the composition for battery electrode, known positive electrode active materials and negative electrode active materials can be used, and negative electrode active materials are preferably used. As the negative electrode active material, for example, silicon-based negative electrode active materials, carbon-based active materials can be cited, and metal materials such as metallic lithium, alloys, tin compounds, etc., lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, conductive polymers, etc. can also be cited. Any one of these can be used, or two or more of them can be used in combination.

[0069] As the above-mentioned silicon-based negative electrode active material, for example, there can be cited: silicon oxides represented by SiO x (0.5 ≦ x ≦ 1.6) (hereinafter referred to as SiO), and silicon-containing compounds in which Si fine particles are dispersed in a lithium silicate phase represented by Li 2y SiO (2+y) (0 < y < 2). As the above-mentioned carbon-based active material, for example, there can be cited: natural graphite, artificial graphite, non-graphitizable carbon, graphitizable carbon, and other graphites.

[0070] The blending amount of the carbon nanotube dispersion liquid in the battery electrode composition is not particularly limited. With respect to 100% by mass of the solid content of the battery electrode composition, the content of carbon nanotubes can be 0.05% by mass to 1.0% by mass, or can also be 0.07% by mass to 0.5% by mass. The content of the electrode active material (preferably the negative electrode active material) is also not particularly limited. With respect to 100% by mass of the solid content of the battery electrode composition, it can be 80% by mass to 98% by mass, or can also be 90% by mass to 97% by mass. The content of the silicon-based active material is also not particularly limited. With respect to 100% by mass of the solid content of the battery electrode composition, it can be 10% by mass to 90% by mass, or can also be 15% by mass to 35% by mass.

[0071] The battery electrode composition can contain, as needed, together with the above-mentioned carbon nanotube dispersion liquid and the electrode active material, various components such as a conductive agent other than carbon nanotubes, a binder, a thickener, a dispersant, an antifoaming agent, a leveling agent, a solvent (such as water), and the like.

[0072] As the conductive agent other than carbon nanotubes, there is no particular limitation. For example, there can be cited carbon blacks such as acetylene black and Ketjen black. The amount of the conductive agent in the battery electrode composition is not particularly limited. Based on the total amount with carbon nanotubes, with respect to 100% by mass of the solid content of the battery electrode composition, it can be 0.1% by mass to 5.0% by mass, or can also be 0.2% by mass to 2.5% by mass.

[0073] As the binder (adhesive resin), there is no particular limitation. For example, there can be cited various resin emulsions such as styrene-butadiene rubber (SBR) emulsion, polyurethane emulsion, polyvinyl acetate emulsion, and acrylic resin emulsion. The amount of the binder in the battery electrode composition is not particularly limited. With respect to 100% by mass of the solid content of the battery electrode composition, it can be 1.5% by mass to 9.5% by mass, or can also be 2% by mass to 4% by mass.

[0074] As the thickener, there is no particular limitation. For example, carboxymethyl cellulose and / or its salt which is the same as the above component (B) can be additionally added, and CMC different from the component (B) can also be added separately. The amount of the thickener in the battery electrode composition is not particularly limited, and can be 0.05% by mass to 3% by mass, or can also be 0.1% by mass to 2% by mass, based on 100% by mass of the solid content of the battery electrode composition.

[0075] As the current collector, as long as it is an electron conductor that does not cause adverse effects in the battery constituted, there is no particular limitation. For example, in addition to copper, stainless steel, nickel, aluminum, titanium, fired carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., for the purpose of improving adhesiveness, conductivity, and oxidation resistance, materials obtained by treating the surface of copper, etc. with carbon, nickel, titanium, silver, etc. can be used. These current collectors can also be current collectors with an oxidized surface. Regarding the shape of the current collector, in addition to foil-like, molded bodies such as film-like, sheet-like, net-like, objects subjected to stamping or stretching treatment, slat bodies, porous bodies, and foamed bodies can also be used.

[0076] [Battery]

[0077] A battery of one embodiment includes an electrode made using the above carbon nanotube dispersion. As the electrode, it can be a positive electrode or a negative electrode, and preferably a negative electrode. As the battery, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is preferred.

[0078] In one embodiment, the non-aqueous electrolyte secondary battery includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte. In the negative electrode and / or the positive electrode (preferably the negative electrode), an electrode made using the above battery electrode composition is used. As one embodiment, the non-aqueous electrolyte secondary battery can include: a laminate in which the negative electrode and the positive electrode are alternately laminated with a separator therebetween, a container housing the laminate, and an electrolyte such as a non-aqueous electrolyte solution injected into the container. As the non-aqueous electrolyte, for example, a substance obtained by dissolving a lithium salt as a supporting electrolyte in an organic solvent can be used, and a lithium ion secondary battery can be constituted.

[0079] Examples

[0080] Hereinafter, it will be described in more detail based on examples and comparative examples, but the present invention is not limited thereto.

[0081] The details of each component used in the examples and comparative examples are shown below.

[0082] [Component (A)]

[0083] · CNT-1: Single-walled carbon nanotube (SWCNT). Purity = 96.5 mass%, average diameter = 1.6 nm, average fiber length = 5 μm. "TUBALL BATT" manufactured by OCSiAl

[0084] · CNT-2: Multi-walled carbon nanotube (MWCNT). Purity = 98 mass%, average diameter = 10 nm, average fiber length = 10 μm. "FT9000" manufactured by Cnano

[0085] [(B) component]

[0086] · CMC-1: Sodium carboxymethyl cellulose. Degree of etherification = 0.75, viscosity of 2 mass% aqueous solution (25 °C) = 18 mPa·s. "Cellogen 7A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0087] · CMC-2: Sodium carboxymethyl cellulose. Degree of etherification = 0.68, viscosity of 2 mass% aqueous solution (25 °C) = 79 mPa·s. "Cellogen PR" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0088] · CMC-3: Sodium carboxymethyl cellulose. Degree of etherification = 0.73, viscosity of 2 mass% aqueous solution (25 °C) = 3 mPa·s. "Cellogen 5A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0089] [(D) component]

[0090] · Compound D-1: N,N-dimethylacetamide (Formula (D-1))

[0091] · Compound D-2: N,N-dimethylpropanamide (Formula (D-2))

[0092] [Others]

[0093] · Compound D-3: N,N-dimethylformamide (Formula (D-3))

[0094] · Compound D-4: N-methylacetamide (Formula (D-4))

[0095] · Compound D-5: 3-methyl-2-butanone (Formula (D-5))

[0096] · Compound D-6: N,N-dimethylethylamine (Formula (D-6))

[0097] [Chemical formula 3]

[0098]

[0099] [Examples 1 to 10 and Comparative Examples 1 to 6]

[0100] In Example 1, 0.40 g of CNT-1, 0.60 g of CMC-1, 3.13 g of Compound D-1, and 95.87 g of water were added to a 200 mL beaker and stirred and mixed for 12 hours with a stirrer (1000 rpm). Then, using a device in which a tube pump was connected to an ultrasonic homogenizer (“US-600T” manufactured by Nippon Seiki Co., Ltd., equipped with a circulation unit), the mixture was dispersed at an output power of 70 μA for 60 minutes while circulating the mixed solution to obtain a carbon nanotube dispersion.

[0101] In Examples 2 to 10 and Comparative Examples 1 to 6, the types and amounts of use of the respective components were changed as shown in Table 1, and a carbon nanotube dispersion was obtained in the same manner as in Example 1.

[0102] In Table 1, “amount of Compound D (mol / CNT 100 g)” is the content (moles) of Compounds D-1 to D-6 relative to 100 g of carbon nanotubes. “mass ratio B / A” is the ratio (mass ratio) of the amount of CMC (B) to the amount of carbon nanotubes (A). “mass ratio D / (C + D)” is the ratio (mass ratio) of the amount of Compounds D-1 to D-6 (D) to the total amount of Compounds D-1 to D-6 and water (C + D). “mass ratio D / B” is the ratio (mass ratio) of the amount of Compounds D-1 to D-6 (D) to the amount of carboxymethyl cellulose and / or its salt (B). “mass ratio (B + D) / (A + B + D)” is the ratio (mass ratio) of the total amount of carboxymethyl cellulose and / or its salt and Compounds D-1 to D-6 (B + D) to the total amount of carbon nanotubes, carboxymethyl cellulose and / or its salt, and Compounds D-1 to D-6 (A + B + D).

[0103] For the carbon nanotube dispersions of Examples 1 to 10 and Comparative Examples 1 to 6, the dispersibility, dispersion stability, viscosity, electrode coating property, and battery performance (cycle characteristics) were evaluated. The respective evaluation methods are as described below.

[0104] [Dispersibility]

[0105] The carbon nanotube dispersion was diluted with water so that the content of carbon nanotubes was 0.1 mass%, a specimen for microscopy was prepared, and residual coarse particles were observed with an optical microscope (magnification 35 times). The size of the aggregates present in the observation area of 5 mm 2 was measured, and the dispersibility of the carbon nanotubes was evaluated according to the following 5 grades, with 3 or more being considered qualified.

[0106] 5: There are 2 or fewer aggregates smaller than 0.6 mm, 1 or fewer aggregates of 0.6 mm or more and smaller than 1 mm, and no aggregates of 1 mm or more.

[0107] 4: There are 3 or more aggregates smaller than 0.6 mm, 1 or fewer aggregates of 0.6 mm or more and smaller than 1 mm, and no aggregates of 1 mm or more.

[0108] 3: There are 2 or more aggregates of 0.6 mm or more and smaller than 1 mm, and no aggregates of 1 mm or more.

[0109] 2: There are aggregates of 1 mm or more and smaller than 2 mm, and no aggregates of 2 mm or more.

[0110] 1: There are aggregates of 2 mm or more.

[0111] [Dispersion stability]

[0112] The carbon nanotube dispersion was allowed to stand for 1 month, water was added for dilution to make the content of carbon nanotubes reach 0.001% by mass, and then the absorbance (A1) at the wavelength unique to carbon nanotubes was measured using an ultraviolet-visible spectrophotometer (manufactured by Hitachi, Ltd., model: U-3900H). Then, a centrifugal separator (manufactured by himac, model: CF16RN) was used to perform a centrifugation treatment at 5000×g (wherein, in Example 4, it was 500×g) and 25°C for 80 minutes. Similarly, the absorbance (A2) of the supernatant after the centrifugation treatment was measured. The change rate of absorbance before and after centrifugation was calculated by the following formula. As the wavelength unique to carbon nanotubes, 503 nm unique to metallic carbon nanotubes was set. The larger the value of the absorbance change rate, the less sedimentation of carbon nanotubes caused by centrifugation after coagulation over time, and the more excellent the dispersion stability. The dispersion stability was evaluated according to the following 5 grades, and a value of 3 or more was regarded as qualified.

[0113] Change rate of absorbance before and after centrifugation (%) = (A2 / A1) × 100

[0114] 5: The value of the absorbance change rate is 82% or more.

[0115] 4: The value of the absorbance change rate is 78% or more and less than 82%.

[0116] 3: The value of the absorbance change rate is 74% or more and less than 78%.

[0117] 2: The value of the absorbance change rate is 70% or more and less than 74%.

[0118] 1: The value of the absorbance change rate is less than 70%.

[0119] [Viscosity]

[0120] For the carbon nanotube dispersion, the viscosity was measured using a B-type viscometer ("TVB-10" manufactured by Toki Sangyo Co., Ltd.). The conditions during measurement were 60 rpm and 25 °C (3 minutes). The results of each viscosity evaluation were expressed according to the following five grades.

[0121] 5: Less than 3 Pa·s

[0122] 4: 3 Pa·s or more and less than 4 Pa·s

[0123] 3: 4 Pa·s or more and less than 6 Pa·s

[0124] 2: 6 Pa·s or more and less than 8 Pa·s

[0125] 1: 8 Pa·s or more

[0126] [Electrode coating property]

[0127] SiO (average particle size 4.5 μm, specific surface area 5.5 m 2 / g) and graphite (average particle size 18 μm, specific surface area 3.2 m 2 / g), 100 parts by mass (content ratio 20 / 80), a carbon nanotube dispersion as a conductive agent (Examples 1 to 10, Comparative Examples 1 to 6), 0.2 parts by mass based on the amount of carbon nanotubes, 1.0 part by mass of acetylene black, a 1.5 mass% aqueous solution of sodium carboxymethyl cellulose ("Cellogen BSH-6" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.65 parts by mass based on the solid content, an aqueous dispersion of the sodium salt of polyurethane obtained from the following Synthesis Example P1 as a binder, 3.5 parts by mass based on the solid content, and ion-exchanged water were mixed using a planetary mixer to prepare a negative electrode paste (battery electrode composition) with a solid content of 49 mass%. An electrolytic copper foil with a thickness of 10 μm was used as the current collector, and a negative electrode active material layer containing the above negative electrode paste was formed on the electrolytic copper foil. Specifically, the above negative electrode paste was coated on the electrolytic copper foil using a coater, and after roll pressing, it was dried under reduced pressure at 130 °C to obtain a negative electrode with a negative electrode active material of 7 to 8 mg / cm 2 . The surface state at this time was observed and evaluated according to the following five grades, and a rating of 3 or more was considered qualified.

[0128] 5: The color tone of the electrode surface is uniform, and no unevenness caused by aggregates or scratched stripes on the electrode are observed.

[0129] 4: Wave stripe patterns originating from the physical properties of the coating are observed on the electrode surface, but no unevenness caused by aggregates or scratched stripes on the electrode are observed.

[0130] 3: Unevenness caused by aggregates is observed on the electrode surface, but no scratched stripes on the electrode are observed.

[0131] 2: Concavities caused by condensates were observed on the electrode surface, and streaks where the electrode was scratched were also observed.

[0132] 1: Difficult to coat

[0133] Synthesis Example P1:

[0134] In a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube, 77.2 parts by mass of polybutadiene polyol (manufactured by Evonik Industries AG, "PolyVest HT", average hydroxyl value 46.5 mg KOH / g, number of active hydrogens 2.32), 3.0 parts by mass of dimethylolpropionic acid (number of active hydrogens 2), 19.8 parts by mass of dicyclohexylmethane diisocyanate, and 150 parts by mass of methyl ethyl ketone were added. The reaction was carried out at 75 °C for 4 hours to obtain a methyl ethyl ketone solution of a urethane prepolymer having a free isocyanate group content of 2.15% by mass based on the non-volatile components. The solution was cooled to 45 °C, and an aqueous sodium hydroxide solution (0.89 parts by mass of sodium hydroxide and 300 parts by mass of water) was slowly added, and emulsification and dispersion were carried out using a homogenizer. Then, an aqueous solution prepared by diluting 1.6 parts by mass of diethylenetriamine (number of active hydrogens 3) with 100 parts by mass of water was added, and a chain extension reaction was carried out for 1 hour. It was desolvated under reduced pressure and heating at 50 °C to obtain a polyurethane aqueous dispersion having a non-volatile component of about 32% by mass.

[0135] [Battery Performance (Cycling Characteristics)]

[0136] Fabrication of the positive electrode for evaluation:

[0137] 100 parts by mass of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM), 7.8 parts by mass of acetylene black (manufactured by Denka Co., Ltd., "Li-400") as a conductive additive, 6 parts by mass of polyvinylidene fluoride as a binder, and 61.3 parts by mass of N-methyl-2-pyrrolidone as a dispersion medium were mixed using a planetary mixer to prepare a positive electrode paste so that the solid content reached 65%. The positive electrode paste was coated on an aluminum foil with a thickness of 15 μm using a coater, dried at 130 °C, and then roll-pressed to obtain a positive electrode having a positive electrode active material of 22 mg / cm 2 .

[0138] Fabrication of the lithium ion secondary battery:

[0139] The obtained positive electrode was combined with the negative electrode fabricated in the evaluation of electrode coating property, and a polyolefin-based (PE / PP / PE) separator as a separator was sandwiched between the electrodes and laminated. The positive and negative electrode terminals were ultrasonically welded to the positive and negative electrode ends respectively. The laminate was placed in an aluminum laminated packaging material, and the opening for injecting electrolyte was left and heat-sealed. A pre-injection battery with a positive electrode area of 18 cm 2 and a negative electrode area of 19.8 cm 2 was fabricated. Subsequently, an electrolyte solution in which LiPF 6 (1.0 mol / L) was dissolved in a solvent mixture of ethylene carbonate and diethyl carbonate (30 / 70 vol ratio) was injected, and the opening was heat-sealed to obtain an evaluation battery.

[0140] Evaluation of battery performance:

[0141] For the fabricated lithium ion secondary battery, a performance test of charge-discharge cycle characteristics at 20 °C was conducted. The charge-discharge cycle characteristics were measured under the following conditions. CC (constant current) charging was performed at a current density equivalent to 0.5C until 4.2V, and then switched to CV (constant voltage) charging at 4.2V. After 1.5 hours of charging, CC discharge was performed at a current density equivalent to 0.5C until 2.7V. This cycle was carried out 300 times at 20 °C, and the ratio of the 1C discharge capacity after 300 cycles to the initial 1C discharge capacity was defined as the 1C charge-discharge cycle retention rate. The cycle retention rate was evaluated according to the following 5 grades, and a value of 3 or more was regarded as qualified.

[0142] 5: The 1C charge-discharge cycle retention rate is 95% or more

[0143] 4: The 1C charge-discharge cycle retention rate is 90% or more and less than 95%

[0144] 3: The 1C charge-discharge cycle retention rate is 80% or more and less than 90%

[0145] 2: The 1C charge-discharge cycle retention rate is 70% or more and less than 80%

[0146] 1: The 1C charge-discharge cycle retention rate is less than 70%

[0147] [Table 1]

[0148]

[0149] The results are shown in Table 1. In Examples 1 to 10, Compound D-1 or D-2 represented by Formula (1) was used together with CMC. Therefore, compared with Comparative Example 6 using only CMC, the dispersion and dispersion stability of carbon nanotubes were excellent, and in addition, the viscosity was low, and the electrode coating property and battery performance were excellent.

[0150] In Comparative Example 5, although the compound represented by the formula (1) was used, the dispersibility and dispersion stability were poor because CMC was not incorporated. In Comparative Examples 1 to 4, amide, ketone or amine, namely compounds D-3 to D-6, were incorporated together with CMC. Compounds D-3 to D-6 are not compounds represented by the formula (1). Therefore, compared with Examples 1 to 10, the dispersibility and / or dispersion stability of Comparative Examples 1 to 4 are poor, and the battery performance is also insufficient.

[0151] It should be noted that the various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all of these combinations are described in this specification as preferred numerical ranges. In addition, the description of the numerical range of "X to Y" means X or more and Y or less.

[0152] As described above, several embodiments of the present invention have been described, but these embodiments are given only as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments, their omissions, substitutions, changes, etc. are included in the scope and gist of the invention, and similarly, are included in the invention described in the claims and its equivalent scope.

Claims

1. A carbon nanotube dispersion liquid, characterized in that, it contains carbon nanotubes, carboxymethyl cellulose and / or its salt, water, and a compound represented by the following general formula (1), [Chemical formula 1] In formula (1), R represents a hydrogen atom or a methyl group.

2. The carbon nanotube dispersion liquid according to claim 1, wherein, the degree of etherification of the carboxymethyl cellulose and / or its salt is 0.60 to 0.85, and the viscosity of a 2% by mass aqueous solution at 25 °C is 1 to 300 mPa·s.

3. The carbon nanotube dispersion liquid according to claim 1, wherein, the content of the compound is 1 to 30 moles relative to every 100 g of the carbon nanotubes.

4. The carbon nanotube dispersion liquid according to claim 1, wherein, the ratio of the amount of the carboxymethyl cellulose and / or its salt to the amount of the carbon nanotubes is 0.3 to 3.0 by mass ratio.

5. The carbon nanotube dispersion liquid according to claim 1, wherein, the ratio of the amount of the compound to the total amount of the compound and water is 0.005 to 0.1 by mass ratio.

6. A composition for a battery electrode, characterized in that, it contains the carbon nanotube dispersion liquid according to any one of claims 1 to 5.

7. A battery electrode, characterized in that, it is made using the composition for a battery electrode according to claim 6.

8. A battery, characterized in that, it includes an electrode made using the carbon nanotube dispersion liquid according to any one of claims 1 to 5.

Images