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 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), R1 represents a hydrogen atom, a methyl group, or an ethyl group. R2 represents a hydrogen atom, a methyl group or a hydrocarbon group forming a five-membered heterocyclic ring or a six-membered heterocyclic ring together with-N-C (= O)-N-R3-. And R3 represents a hydrogen atom, a methyl group or a hydrocarbon group forming a five-membered heterocyclic ring or a six-membered heterocyclic ring together with-N-C (= O)-N-R2-. And R4 represents a methyl group or an ethyl group. R1 and R2 are not both hydrogen atoms. The compound has 4 or more carbon atoms. # imgabs0 #

Description

Technical Field

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

[0002] Carbon nanotubes have excellent electrical conductivity and are therefore used as a conductive agent constituting electrodes in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. However, carbon nanotubes are difficult to disperse uniformly in water because of their strong Van der Waals force.

[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 containing 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, carboxymethyl cellulose sodium salt as a dispersant, water as a dispersion medium, and monoethanolamine as a basic compound are mixed.

[0004] Prior art literature

[0005] Patent Literature

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

[0007] Technical problem that the invention aims to solve

[0008] As mentioned above, carbon nanotubes usually form high-density bundles due to van der Waals forces, and the bundles need to be dissociated in order to be uniformly dispersed in water. 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 an embodiment of the present invention is to provide a carbon nanotube dispersion liquid capable of improving the dispersibility and dispersion stability of carbon nanotubes.

[0010] Technical solutions to the problem

[0011] The present invention includes the following embodiments.

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

[0013] [Chemistry 1]

[0014]

[0015] In formula (1), R 1 represents a hydrogen atom, a methyl group or an ethyl group, R 2 represents a hydrogen atom, a methyl group or -NC(=O)-NR 3 - hydrocarbon groups that together form a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 3 represents a hydrogen atom, a methyl group or -NC(=O)-NR 2 - hydrocarbon groups that together form a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 4 represents a methyl group or an ethyl group, wherein R 1 and R 2 Not all of them are hydrogen atoms, and the number of carbon atoms in the compound is 4 or more.

[0016] [2] The carbon nanotube dispersion according to [1], wherein the compound represented by the formula (1) has 4 or 5 carbon atoms.

[0017] [3] The carbon nanotube dispersion according to [1] or [2], wherein R in the formula (1) 2 represents a hydrogen atom, a methyl group or -NC(=O)-NR 3 - a saturated hydrocarbon group that together forms a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 3 represents a hydrogen atom, a methyl group or -NC(=O)-NR 2 - saturated hydrocarbon groups which together form a five-membered heterocyclic ring or a six-membered heterocyclic ring.

[0018] [4] The carbon nanotube dispersion according to any one of [1] to [3], wherein the carboxymethyl cellulose and / or its salt has a degree of etherification of 0.60 to 0.85 and a viscosity of a 2 mass % aqueous solution at 25° C. of 1 to 300 mPa·s.

[0019] [5] The carbon nanotube dispersion according to any one of [1] to [4], wherein the content of the compound is 1 to 30 mol per 100 g of the carbon nanotubes.

[0020] [6] The carbon nanotube dispersion according to any one of [1] to [5], 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 in terms of mass ratio.

[0021] [7] The carbon nanotube dispersion according to any one of [1] to [6], wherein the amount of the compound relative to the total amount of the compound and water is 0.005 to 0.1 in terms of mass ratio.

[0022] [8] A composition for a battery electrode, comprising the carbon nanotube dispersion according to any one of [1] to [7].

[0023] [9] A battery electrode produced using the battery electrode composition described in [8].

[0024]

[10] A battery comprising an electrode produced using the carbon nanotube dispersion according to any one of [1] to [7].

[0025] Effects of the Invention

[0026] According to the embodiment of the present invention, the dispersibility and dispersion stability of carbon nanotubes can be improved. DETAILED DESCRIPTION

[0027] The carbon nanotube dispersion of the present embodiment contains (A) carbon nanotubes, (B) carboxymethyl cellulose and / or a salt thereof, (C) water, and (D) a compound represented by the general formula (1).

[0028] [(A) Carbon nanotubes]

[0029] Carbon nanotubes are substances in which a six-membered ring network (graphene sheet) composed of carbon becomes a single-layer or multi-layer coaxial tube. As carbon nanotubes, single-layer carbon nanotubes (SMCNT: single-walled carbon nanotubes) with a single-layer structure and multi-layer carbon nanotubes (MWCNT: multi-walled carbon nanotubes) with a multi-layer structure can be cited. In particular, carbon nanotubes with two layers in the multilayer are called double-layer carbon nanotubes (DWCNT: double-walled carbon nanotubes). Any one of them or any two or more of them can be used in combination. From the aspect of excellent cycle characteristics of the battery, it is preferred to use single-layer carbon nanotubes.

[0030] The method for producing carbon nanotubes is not particularly limited, and the carbon nanotubes can be obtained by various known production methods such as a thermal decomposition method using a catalyst, an arc discharge method, a laser evaporation method, and a CVD method such as a HiPco method and a CoMoCAT method.

[0031] The average diameter (fiber diameter) of the carbon nanotubes is not particularly limited, and may be, for example, 0.4 to 100 nm, 0.5 to 50 nm, or 1 to 20 nm. The average length of the carbon nanotubes is not particularly limited, and may be, for example, 50 nm to 10 mm, 500 nm to 100 μm, or 1 to 50 μm. The aspect ratio (i.e., the ratio of the average length to the average diameter) of the carbon nanotubes is not particularly limited, and may be, for example, greater than 10, or greater than 100.

[0032] The average diameter and average length of carbon nanotubes can be obtained by measuring the dimensions of 50 randomly selected carbon nanotubes in the atomic force microscope image and taking the arithmetic mean. For the mm-level length that cannot be measured by atomic force microscope, it can be measured using the microscope image.

[0033] In a preferred embodiment, the carbon nanotubes include single-walled carbon nanotubes. In this case, the carbon nanotubes may consist of only single-walled carbon nanotubes, but may also include multi-walled carbon nanotubes while including single-walled carbon nanotubes. Specifically, the ratio of the single-walled carbon nanotubes to the entire carbon nanotubes may be 80% by mass or more, preferably 95% by mass or more, and more preferably 98% by mass or more.

[0034] [(B) carboxymethyl cellulose and / or its salt]

[0035] Carboxymethylcellulose 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 with carboxymethyl ether groups. CMC may have a carboxyl group (-COOH) or may have a carboxylate salt form, or both may be used in combination.

[0036] As the salt of carboxymethyl cellulose, there can be mentioned alkali metal salts such as sodium salt, lithium salt, potassium salt, alkaline earth metal salts such as calcium salt, magnesium salt, ammonium salt, alkylamine salt, alkanolamine salt and other organic salts. These salts may contain only one kind or two or more kinds of salts. Among them, alkali metal salts are preferred, and sodium salts are more preferred.

[0037] In this embodiment, CMC having an etherification degree of 0.60 to 0.85 and a 2 mass % aqueous solution viscosity of 1 to 300 mPa·s at 25° C. is preferably used. By using CMC having such an etherification degree and 2 mass % aqueous solution viscosity, the dispersion stability of carbon nanotubes can be enhanced.

[0038] The degree of etherification of CMC is more preferably 0.65 to 0.85, and still more preferably 0.70 to 0.80. In the present specification, the degree of etherification of CMC is measured by the following method.

[0039] (Degree of etherification)

[0040] 0.6 g of CMC was dried at 105 ° C for 4 hours. After accurately weighing the mass of the dried product, it was wrapped with filter paper and ashed in a magnetic crucible. The ash was transferred to a 500 mL beaker, 250 mL of water and 35 mL of 0.05 mol / L sulfuric acid aqueous solution were added, and boiled for 30 minutes. After cooling, the excess acid was back-titrated with 0.1 mol / L potassium hydroxide aqueous solution (using phenolphthalein as an indicator). The degree of etherification was calculated by the following formula.

[0041] Formula: (etherification degree) = 162 × A / (10000-80A)

[0042] A = (af-bf1) / mass of dried product (g)

[0043] A: The amount of 0.05 mol / L sulfuric acid aqueous solution consumed by the binding base in 1 g of sample (mL)

[0044] a: Amount of 0.05 mol / L sulfuric acid aqueous solution used (mL)

[0045] f: Titer of 0.05 mol / L sulfuric acid aqueous solution

[0046] b: Titration of 0.1 mol / L potassium hydroxide aqueous solution (mL)

[0047] f1: Titer of 0.1 mol / L potassium hydroxide aqueous solution

[0048] The viscosity of a 2 mass % aqueous solution of CMC at 25° C. is more preferably 1 to 150 mPa·s, and even more preferably 1 to 30 mPa·s. In the present specification, the viscosity of a 2 mass % aqueous solution of CMC is measured by the following method.

[0049] (2 mass % aqueous solution viscosity)

[0050] Add CMC to a conical flask, add water to a concentration of 2% by mass, and shake for 30 seconds. After standing for 12 hours, mix for 5 minutes to prepare a 2% by mass aqueous solution. Transfer the resulting aqueous solution to a tall beaker and adjust to 25°C. Measure the viscosity using a B-type viscometer (single cylinder type rotational viscometer) in accordance with JIS Z8803:2011. At this time, set the rotor speed to 60 rpm for measurement. When the upper limit of the measurement is reached, change to 30 rpm and 12 rpm in sequence for measurement.

[0051] [(D) Compound represented by general formula (1)]

[0052] In this embodiment, a compound represented by the following general formula (1) (hereinafter sometimes referred to as "compound (1)") may be used as component (D) while using CMC as component (B). Compound (1) is a compound containing a urea bond represented by -NC(=O)-N- in the molecule. By using compound (1) together with CMC, the dispersibility and dispersion stability of carbon nanotubes in water can be improved, and the cycle characteristics when the battery is made can be improved. The reason is believed to be as follows, but is not limited to this. That is, compound (1) enters between carbon nanotubes that are attracted to each other due to van der Waals force, dissociates the bundle of carbon nanotubes, and disperses the carbon nanotubes in water. It is believed that compound (1) has a methyl group or ethyl group as an electron-donating group bonded to the nitrogen atom, so that the electrons flow in C=O and are localized, thereby easily entering between carbon nanotubes, which helps to improve the dispersibility of carbon nanotubes. In addition, it is believed that by adsorbing CMC on the dissociated carbon nanotubes, the dispersed state of the carbon nanotubes can be maintained.

[0053] [Chemistry 2]

[0054]

[0055] In formula (1), R 1 represents a hydrogen atom, a methyl group or an ethyl group. 2 represents a hydrogen atom, a methyl group or -NC(=O)-NR 3 - hydrocarbon groups that together form a five-membered heterocyclic ring or a six-membered heterocyclic ring. 1 and R 2 The five-membered heterocyclic ring or the six-membered heterocyclic ring may be saturated or unsaturated, but is preferably saturated from the viewpoint of improving the dispersibility of the carbon nanotubes. Therefore, the hydrocarbon group is preferably a saturated hydrocarbon group.

[0056] R 3 represents a hydrogen atom, a methyl group or -NC(=O)-NR 2 - hydrocarbon groups that together form a five-membered heterocyclic ring or a six-membered heterocyclic ring. 2 As described in, the five-membered heterocyclic ring or the six-membered heterocyclic ring may be saturated or unsaturated, and is preferably saturated from the viewpoint of improving the dispersibility of the carbon nanotubes. Therefore, the hydrocarbon group is preferably a saturated hydrocarbon group. 4 It represents a methyl or ethyl group.

[0057] In R 2 and R 3 When a five-membered heterocyclic ring or a six-membered heterocyclic ring is formed, -R 2 -R 3 -, can be used as an example -CH 2 -CH 2 -、-CH=CH-、-CH 2 -CH 2 -CH 2 -、-CH=CH-CH 2 -、-CH 2 -CH=CH-, etc.

[0058] The number of carbon atoms in the compound (1) is 4 or more. When the number of carbon atoms in the compound (1) is 4 or more, the dispersibility and dispersion stability of the carbon nanotubes can be improved, and the cycle characteristics of the battery can be improved. The number of carbon atoms in the compound (1) is more preferably 4 or 5.

[0059] As described above, compound (1) may be a compound having a five-membered heterocyclic ring or a compound having a six-membered heterocyclic ring. However, from the viewpoint of further improving the effect of entering between carbon nanotubes and dissociating the bundles thereof, a smaller five-membered heterocyclic ring is preferred.

[0060] The compound (1) may be solid or liquid at room temperature (25° C.), but is water-soluble. In the carbon nanotube dispersion, the compound (1) dissolves in water as the component (C).

[0061] Specific examples of compound (1) include 1,3-dimethyl-2-imidazolidinone, 1-methyl-2-imidazolidinone, 1-methyl-2,3-dihydro-1H-imidazol-2-one, 1-methyltetrahydropyrimidin-2(1H)-one, 1,1,3-trimethylurea, 1,1,3,3-tetramethylurea, 1,3-diethylurea, 1-ethyl-1,3-dimethylurea, etc. Any one of these may be used, or two or more of them may be used in combination.

[0062] [Carbon Nanotube Dispersion]

[0063] The carbon nanotube dispersion of the present embodiment is a dispersion containing the above-mentioned components (A), (B) and (D), and water as the component (C), wherein the carbon nanotubes are dispersed in the water. More specifically, since the CMC of the component (B) and the compound (1) of the component (D) are water-soluble, the carbon nanotubes of the component (A) are dispersed in an aqueous solution in which the CMC and the compound (1) are dissolved.

[0064] In the carbon nanotube dispersion, the content of compound (1) is preferably 1 to 30 mol, more preferably 1.5 to 20 mol, further preferably 2 to 15 mol, further preferably 5 to 12 mol, based on 100 g of carbon nanotubes, from the viewpoint of enhancing the effect of the present embodiment.

[0065] In the carbon nanotube dispersion, from the viewpoint of improving the effect of the present embodiment, the ratio of the amount of CMC (B) to the amount of carbon nanotubes (A) is preferably B / A = 0.3 to 3.0, more preferably 0.5 to 2.5, further preferably 1.0 to 2.0, and further preferably 1.1 to 1.8 in terms of mass ratio.

[0066] In the carbon nanotube dispersion, the ratio of the amount (D) of the compound (1) to the total amount (C+D) of the compound (1) and water is preferably D / (C+D)=0.005 to 0.1, more preferably 0.01 to 0.08, and even more preferably 0.02 to 0.07 in terms of mass ratio. By setting the mass ratio D / (C+D) to 0.005 or more, the effect of adding the compound (1) can be enhanced, and by setting the mass ratio D / (C+D) to 0.1 or less, a decrease in the solubility of CMC in water can be prevented.

[0067] In the carbon nanotube dispersion, the ratio of the amount (D) of the compound (1) to the amount (B) of CMC is preferably D / B=1 to 20, more preferably 1.5 to 15 in terms of mass ratio.

[0068] 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, more preferably 0.70 to 0.97, and even more preferably 0.80 to 0.96 in terms of mass ratio.

[0069] The content of each component is not particularly limited relative to 100 mass % of the carbon nanotube dispersion. For example, the content of carbon nanotubes can be 0.01 mass % to 5 mass %, 0.1 mass % to 3 mass %, or 0.2 mass % to 2 mass %. The content of CMC can be 0.01 mass % to 5 mass %, 0.1 mass % to 3 mass %, or 0.2 mass % to 2 mass %. The content of compound (1) can be 0.5 mass % to 12 mass %, 1 mass % to 10 mass %, or 2 mass % to 8 mass %. The content of water can be 70 mass % to 99 mass %, 80 mass % to 98 mass %, or 90 mass % to 97 mass %.

[0070] The carbon nanotube dispersion may contain other components as needed in addition to the above-mentioned components (A) to (D). For example, as a dispersion medium, a water-soluble organic solvent 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. may be used together with the water of component (C). In addition, other additives include, for example, conductive agents other than carbon nanotubes, water-soluble polymers other than CMC, dispersants, surfactants, wetting agents, defoaming agents, pH adjusters, etc.

[0071] The method for preparing the carbon nanotube dispersion is not particularly limited. For example, the above-mentioned components (A), (B) and (D) are mixed with water of component (C), and a dispersion device such as a homogenizer, a high-pressure homogenizer, and an ultrasonic homogenizer is used to perform a dispersion treatment, thereby preparing the carbon nanotube dispersion. In one embodiment, a dispersion device having a circulation unit can be used to circulate the mixed solution containing components (A) to (D) while performing a dispersion treatment using a dispersion device such as a homogenizer.

[0072] [Battery electrode composition]

[0073] The carbon nanotube dispersion can be used as a coating (electrode coating) for producing an electrode of a battery such as a non-aqueous electrolyte secondary battery. That is, the battery electrode composition of the embodiment includes the carbon nanotube dispersion.

[0074] In one embodiment, the battery electrode composition is used to form the above-mentioned active material layer in an electrode having a current collector and an active material layer formed on the current collector. That is, by applying the battery electrode composition to the current collector and drying it, the electrode can be made. In this case, the battery electrode composition includes the above-mentioned carbon nanotube dispersion and the electrode active material. In the active material layer, the carbon nanotube has the function of ensuring a conductive path connecting the active material between the active material particles whose contacts are lost due to the expansion and contraction of the electrode active material. The battery electrode composition 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.

[0075] As the electrode active material for the battery electrode composition, known positive electrode active materials and negative electrode active materials can be used, preferably negative electrode active materials. As negative electrode active materials, for example, silicon-based negative electrode active materials and carbon-based active materials can be cited, and metal materials such as metal lithium / alloys and tin compounds, 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 can be used in combination.

[0076] Examples of the silicon-based negative electrode active material include SiO x Silicon oxide (hereinafter referred to as SiO) represented by (0.5≦x≦1.6), Li 2y SiO (2+y) The silicon-containing compound represented by (0<y<2) is a compound in which Si fine particles are dispersed in a lithium silicate phase. Examples of the carbon-based active material include graphites such as natural graphite, artificial graphite, non-graphitizable carbon, and easily graphitizable carbon.

[0077] The amount of the carbon nanotube dispersion in the battery electrode composition is not particularly limited, and the content of the carbon nanotubes can be 0.05% to 1.0% by mass, or 0.07% to 0.5% by mass, relative to 100% by mass of the solid content of the battery electrode composition. The content of the electrode active material (preferably the negative electrode active material) is also not particularly limited, and can be 80% to 98% by mass, or 90% to 97% by mass, relative to 100% by mass of the solid content of the battery electrode composition. The content of the silicon-based active material is also not particularly limited, and can be 10% to 90% by mass, or 15% to 35% by mass, relative to 100% by mass of the solid content of the battery electrode composition.

[0078] The battery electrode composition may contain various components other than carbon nanotubes, such as a conductive agent, a binder, a thickener, a dispersant, a defoaming agent, a leveling agent, a solvent (such as water), etc., in addition to the carbon nanotube dispersion and the electrode active material as required.

[0079] The conductive agent other than the carbon nanotubes is not particularly limited, and examples thereof include carbon blacks such as acetylene black and Ketjen black. The amount of the conductive agent in the battery electrode composition is not particularly limited, and may be 0.1% to 5.0% by mass, or 0.2% to 2.5% by mass, based on the total amount of the conductive agent and the carbon nanotubes, relative to 100% by mass of the solid content of the battery electrode composition.

[0080] The binder (binder resin) is not particularly limited, and examples thereof include 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, and may be 1.5% to 9.5% by mass, or 2% to 4% by mass, relative to 100% by mass of the solid content of the battery electrode composition.

[0081] The thickener is not particularly limited, and for example, the same carboxymethyl cellulose and / or its salt as the above-mentioned component (B) may be added, and CMC different from component (B) may be added. The amount of the thickener in the battery electrode composition is not particularly limited, and may be 0.05% to 3% by mass, or 0.1% to 2% by mass, relative to 100% by mass of the solid content of the battery electrode composition.

[0082] As a current collector, there is no particular limitation as long as it is an electronic conductor that does not have adverse effects in the constructed battery. For example, in addition to copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., in order to improve adhesion, conductivity, and oxidation resistance, materials in which the surface of copper, etc. is treated with carbon, nickel, titanium, silver, etc. can also be used. These current collectors can be current collectors after the surface has been oxidized. Regarding the shape of the current collector, in addition to foil, a film-like, sheet-like, mesh-like, an object that has been punched or stretched, a lath body, a porous body, a foamed body, etc. can also be used.

[0083] [Battery]

[0084] The battery of one embodiment has an electrode made using the above-mentioned carbon nanotube dispersion. The electrode may be a positive electrode or a negative electrode, preferably a negative electrode. The battery is preferably a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

[0085] In one embodiment, the nonaqueous electrolyte secondary battery has a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte, and the negative electrode and / or the positive electrode (preferably the negative electrode) use an electrode made using the above-mentioned battery electrode composition. As one embodiment, the nonaqueous electrolyte secondary battery can have a laminate formed by alternately stacking the negative electrode and the positive electrode across a separator, a container for accommodating the laminate, and an electrolyte such as a nonaqueous electrolyte injected into the container. As a nonaqueous electrolyte, for example, a nonaqueous electrolyte formed by dissolving a lithium salt as a supporting electrolyte in an organic solvent can be used to form a lithium ion secondary battery.

[0086] Example

[0087] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited thereto.

[0088] The details of each component used in Examples and Comparative Examples are shown below.

[0089] [(A) ingredient]

[0090] · 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

[0091] · CNT-2: Multi-walled carbon nanotube (MWCNT). Purity = 98 mass %, average diameter = 10 nm, average fiber length = 10 μm. “FT9000” manufactured by Cnano Corporation

[0092] [(B) ingredient]

[0093] · CMC-1: sodium carboxymethylcellulose. Etherification degree = 0.75, 2 mass % aqueous solution viscosity (25°C) = 18 mPa·s. "Selogen 7A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0094] · CMC-2: sodium carboxymethylcellulose. Etherification degree = 0.68, 2 mass % aqueous solution viscosity (25°C) = 79 mPa·s. "Selogen PR" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0095] · CMC-3: sodium carboxymethylcellulose. Etherification degree = 0.73, 2 mass % aqueous solution viscosity (25°C) = 3 mPa·s. "Serogen 5A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0096] [(D) ingredient]

[0097] Compound D-1: 1,3-dimethyl-2-imidazolidinone (Formula (D-1))

[0098] Compound D-2: 1,1,3-trimethylurea (Formula (D-2))

[0099] Compound D-3: 1,1,3,3-tetramethylurea (Formula (D-3))

[0100] Compound D-4: 1-methyl-2-imidazolidinone (Formula (D-4))

[0101] Compound D-5: 1-methyl-2,3-dihydro-1H-imidazol-2-one (Formula (D-5))

[0102] Compound D-6: 1,3-diethylurea (Formula (D-6))

[0103] Compound D-7: 1-methyltetrahydropyrimidin-2(1H)-one (Formula (D-7))

[0104] [other]

[0105] Compound D-8: Urea (Formula (D-8))

[0106] Compound D-9: 1,3-dimethylurea (Formula (D-9))

[0107] Compound D-10: Thiourea (Formula (D-10))

[0108] Compound D-11: Phenylurea (Formula (D-11))

[0109] Compound D-12: N-methylsuccinimide

[0110] [Chemistry 3]

[0111]

[0112] [Examples 1 to 15, Comparative Examples 1 to 6 and Reference Example 1]

[0113] In Example 1, 0.40 g of CNT-1, 0.60 g of CMC-1, 4.16 g of compound D-1, and 94.84 g of water were added to a 200 mL beaker, and the mixture was stirred and mixed for 12 hours with a stirrer (1000 rpm). Then, a device with a tube pump connected to an ultrasonic homogenizer ("US-600T" manufactured by Nippon Seiki Co., Ltd., with a circulation unit) was used to circulate the mixed solution while dispersing it at an output power of 70 μA for 60 minutes to obtain a carbon nanotube dispersion.

[0114] In Examples 2 to 15, Comparative Examples 1 to 6, and Reference Example 1, except that the types and usage amounts of the components were changed as shown in Tables 1 to 3, a carbon nanotube dispersion was obtained in the same manner as in Example 1.

[0115] In Tables 1 to 3, "Compound D amount (mol / CNT100g)" is the content (mole) of Compound D-1 to Compound D-12 per 100g 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 Compound D-1 to Compound D-12 (D) to the total amount of Compound D-1 to Compound D-12 and water (C+D). "Mass ratio D / B" is the ratio (mass ratio) of the amount of Compound D-1 to Compound D-12 (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 (B+D) of carboxymethyl cellulose and / or its salt and compounds D-1 to D-12 to the total amount (A+B+D) of carbon nanotubes, carboxymethyl cellulose and / or its salt and compounds D-1 to D-12.

[0116] The carbon nanotube dispersions of Examples 1 to 15, Comparative Examples 1 to 6, and Reference Example 1 were evaluated for dispersibility, dispersion stability, viscosity, electrode coating properties, and battery performance (cycle characteristics). The evaluation methods are as follows.

[0117] [Dispersibility]

[0118] The carbon nanotube dispersion was diluted with water to a carbon nanotube content of 0.1 mass %, and a microscope specimen was prepared. The remaining coarse particles were observed using an optical microscope (magnification 35 times). 2 The size of the aggregates in the carbon nanotubes was evaluated according to the following 5-level dispersibility, and 3 or more was considered acceptable.

[0119] 5: There are 2 or less agglomerates smaller than 0.6 mm, 1 or less agglomerates larger than 0.6 mm and smaller than 1 mm, and no agglomerates larger than 1 mm.

[0120] 4: There are 3 or more agglomerates smaller than 0.6 mm, 1 or less agglomerates larger than 0.6 mm and smaller than 1 mm, and no agglomerates larger than 1 mm.

[0121] 3: There are two or more agglomerates that are larger than 0.6 mm and smaller than 1 mm, and there are no agglomerates larger than 1 mm.

[0122] 2: Agglomerates of 1 mm or more and less than 2 mm are present, and there are no agglomerates of 2 mm or more.

[0123] 1: Agglomerates of 2 mm or more are present.

[0124] [Dispersion stability]

[0125] The carbon nanotube dispersion was allowed to stand for 1 month, and water was added to dilute the carbon nanotube content to 0.001% by mass. The absorbance (A1) at a wavelength specific to carbon nanotubes was then measured using an ultraviolet-visible spectrophotometer (manufactured by Hitachi, Ltd., model: U-3900H). Thereafter, a centrifugal separation treatment was performed at 5000×g (500×g in Example 4) and 25°C for 80 minutes using a centrifuge (manufactured by himac, model: CF16RN), and the absorbance (A2) of the supernatant after the centrifugal separation treatment was similarly measured. The absorbance change rate before and after centrifugation was calculated by the following formula. As a wavelength specific to carbon nanotubes, 503nm specific to metallic carbon nanotubes was used. The larger the value of the absorbance change rate, the less sedimentation caused by centrifugal separation of the carbon nanotubes after agglomeration over time, and the better the dispersion stability. The dispersion stability was evaluated according to the following 5 levels, and 3 or more was considered qualified.

[0126] Absorbance change rate before and after centrifugation (%) = (A2 / A1) × 100

[0127] 5: The value of the absorbance change rate is 82% or more.

[0128] 4: The value of the absorbance change rate is 78% or more and less than 82%.

[0129] 3: The value of the absorbance change rate is 74% or more and less than 78%.

[0130] 2: The value of the absorbance change rate is 70% or more and less than 74%.

[0131] 1: The value of the absorbance change rate is less than 70%.

[0132] [Viscosity]

[0133] The viscosity of the carbon nanotube dispersion was measured using a B-type viscometer ("TVB-10" manufactured by Toki Sangyo Co., Ltd.) under conditions of 60 rpm and 25° C. (3 minutes). The viscosity evaluation results were expressed in the following five levels.

[0134] 5: Less than 3Pa·s

[0135] 4: 3Pa·s or more and less than 4Pa·s

[0136] 3: 4Pa·s or more and less than 6Pa·s

[0137] 2: 6Pa·s or more and less than 8Pa·s

[0138] 1: 8Pa·s or more

[0139] [Electrode coating properties]

[0140] 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 (containing ratio 20 / 80), carbon nanotube dispersion (Examples 1 to 15, Comparative Examples 1 to 6, Reference Example 1) as a conductive agent in terms of carbon nanotube amount 0.2 parts by mass and acetylene black 11.0 parts by mass, carboxymethyl cellulose sodium salt ("Selogen BSH-6" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1.5% by mass aqueous solution in terms of solid content 0.65 parts by mass, polyurethane sodium salt aqueous dispersion obtained by the following synthesis example P1 as a binder in terms of solid content 3.5 parts by mass, and ion exchange water, were mixed with a planetary mixer to prepare a negative electrode slurry (battery electrode composition) having a solid content of 49% by mass. Electrolytic copper foil having a thickness of 10 μm was used as a current collector, and a negative electrode active material layer containing the above-mentioned negative electrode slurry was formed on the electrolytic copper foil. Specifically, the negative electrode slurry was coated on an electrolytic copper foil using a coating machine, roll-pressed, and then dried under reduced pressure at 130° C., thereby obtaining a negative electrode active material with a concentration of 7 to 8 mg / cm 2 The surface condition at this time was observed and evaluated according to the following 5 levels, and 3 or more was regarded as passing.

[0141] 5: The color tone of the electrode surface is uniform, and no bumps caused by condensation or scratches on the electrode are observed.

[0142] 4: A ripple pattern caused by the physical properties of the coating was observed on the electrode surface, but no unevenness caused by aggregates or streaks caused by scratches on the electrode were observed.

[0143] 3: Concavities and convexities caused by condensation were observed on the electrode surface, but no scratches were observed on the electrode.

[0144] 2: Depressions caused by condensation were observed on the electrode surface, and scratches on the electrode were also observed.

[0145] 1: Difficulty in coating

[0146] Synthesis example P1:

[0147] In a four-necked flask equipped with a stirrer, a reflux cooling tube, a thermometer, and a nitrogen blowing tube, 77.2 parts by mass of polybutadiene polyol ("PolyVestHT" manufactured by Evonic Corporation, average hydroxyl value 46.5 mgKOH / g, number of active hydrogen groups 2.32), 3.0 parts by mass of dimethylol propionic acid (number of active hydrogen groups 2), 19.8 parts by mass of dicyclohexylmethane diisocyanate, and 150 parts by mass of methyl ethyl ketone were added, and reacted 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 relative to non-volatile components. The solution was cooled to 45° C., and a sodium hydroxide aqueous solution (0.89 parts by mass of sodium hydroxide, 300 parts by mass of water) was slowly added, and the solution was emulsified and dispersed using a homogenizer. Next, an aqueous solution prepared by diluting 1.6 parts by mass of diethylenetriamine (3 active hydrogen groups) with 100 parts by mass of water was added to carry out a chain extension reaction for 1 hour. The solvent was removed under reduced pressure and heating at 50° C. to obtain a polyurethane aqueous dispersion having a nonvolatile content of about 32% by mass.

[0148] [Battery performance (cycle characteristics)]

[0149] Preparation of positive electrode for evaluation:

[0150] LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 100 parts by mass of (NCM), 7.8 parts by mass of acetylene black ("Li-400" manufactured by Denka Co., Ltd.) as a conductive aid, 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 with a planetary mixer to prepare a positive electrode slurry in a manner such that the solid content was 65% by mass. The positive electrode slurry was coated on an aluminum foil with a thickness of 15 μm with a coater, dried at 130°C, and then roll-pressed to obtain a positive electrode active material of 22 mg / cm 2 The positive electrode.

[0151] Production of lithium-ion secondary batteries:

[0152] The positive electrode obtained above was combined with the negative electrode prepared in the electrode coating evaluation, and a polyolefin-based (PE / PP / PE) separator was sandwiched between the electrodes for stacking. The positive terminal and the negative terminal were ultrasonically welded on each positive and negative electrode. The stack was placed in an aluminum laminate packaging material, leaving an opening for liquid injection and heat-sealed. The positive electrode area was 18 cm 2 , the negative electrode area is 19.8cm 2 Next, LiPF was dissolved in a solvent containing ethylene carbonate and diethyl carbonate (30 / 70 vol. ratio) and injected into the battery. 6(1.0 mol / L) of electrolyte solution was added, and the opening was heat-sealed to obtain a battery for evaluation.

[0153] Evaluation of battery performance:

[0154] The prepared lithium-ion secondary battery was subjected to a performance test of the charge and discharge cycle characteristics at 20°C. The charge and 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 charging for 1.5 hours, CC discharge was performed at a current density equivalent to 0.5C until 2.7V. The cycle was repeated for 300 cycles at 20°C, and the ratio of the 1C discharge capacity after 300 cycles to the initial 1C discharge capacity was taken as the 1C charge and discharge cycle retention rate. The cycle retention rate at this time was evaluated according to the following 5 levels, and 3 or more were considered qualified.

[0155] 5: 1C charge and discharge cycle retention rate is above 95%

[0156] 4: 1C charge and discharge cycle retention rate is above 90% and less than 95%

[0157] 3: 1C charge and discharge cycle retention rate is more than 80% and less than 90%

[0158] 2: 1C charge and discharge cycle retention rate is above 70% and less than 80%

[0159] 1: 1C charge and discharge cycle retention rate is less than 70%

[0160] [Table 1]

[0161]

[0162] [Table 2]

[0163]

[0164] [Table 3]

[0165]

[0166] The results are shown in Tables 1 to 3. In Comparative Example 6, since the compound represented by the above formula (1) was not used, the dispersibility of the carbon nanotubes was poor. In Comparative Example 5, although the compound represented by the formula (1) was used, CMC was not added, so the dispersion stability was poor. In Comparative Examples 1 to 4, compounds D-8 to D-11 containing urea bonds or thiourea bonds were added together with CMC, but compounds D-8 to D-11 were not compounds represented by formula (1), so the dispersion stability was poor.

[0167] In contrast, in Examples 1 to 15, since the compounds represented by formula (1), namely Compounds D-1 to D-7, are blended together with CMC, they have excellent dispersibility and dispersion stability, low viscosity, and excellent electrode coating properties and battery performance.

[0168] Reference Example 1 is an example in which Compound D-12 is blended with CMC. Although Compound D-12 (methylsuccinimide) is not a compound represented by Formula (1), the results are generally good compared to Comparative Examples 1 to 6.

[0169] It should be noted that, for various numerical ranges described in the specification, their upper limits and lower limits can be arbitrarily combined, and all of their combinations are described in this specification as preferred numerical ranges. In addition, the description of the numerical range of "X to Y" means more than X and less than Y.

[0170] Several embodiments of the present invention are described above, but these embodiments are given as examples only 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 scope of the subject matter of the invention. These embodiments or their omissions, substitutions, changes, etc. are included in the scope or subject matter of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A carbon nanotube dispersion, It is characterized in that Include: Carbon nanotubes, Carboxymethyl cellulose and / or its salts, Water, and A compound represented by the following general formula (1), [Chemistry 1] In formula (1), R 1 represents a hydrogen atom, a methyl group or an ethyl group, R 2 represents a hydrogen atom, a methyl group or -NC(=O)-NR 3 - hydrocarbon groups which together form a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 3 represents a hydrogen atom, a methyl group or -NC(=O)-NR 2 - hydrocarbon groups which together form a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 4 represents a methyl or ethyl group, Among them, R 1 and R 2 Not all of them are hydrogen atoms, and the number of carbon atoms in the compound is 4 or more.

2. The carbon nanotube dispersion according to claim 1, in, The compound represented by the formula (1) has 4 or 5 carbon atoms.

3. The carbon nanotube dispersion according to claim 1, in, In the formula (1), R 2 represents a hydrogen atom, a methyl group or -NC(=O)-NR 3 - a saturated hydrocarbon group that together forms a five-membered heterocyclic ring or a six-membered heterocyclic ring, R 3 represents a hydrogen atom, a methyl group or -NC(=O)-NR 2 - saturated hydrocarbon groups which together form a five-membered heterocyclic ring or a six-membered heterocyclic ring.

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

5. The carbon nanotube dispersion according to claim 1, in, The content of the compound is 1 to 30 mol per 100 g of the carbon nanotubes.

6. The carbon nanotube dispersion according to claim 1, in, 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 in terms of mass ratio.

7. The carbon nanotube dispersion according to claim 1, in, The ratio of the amount of the compound to the total amount of the compound and water is 0.005 to 0.1 in terms of mass ratio.

8. A composition for battery electrodes, It is characterized in that A carbon nanotube dispersion comprising the carbon nanotube dispersion according to any one of claims 1 to 7.

9. A battery electrode, It is characterized in that The method is prepared by using the battery electrode composition according to claim 8.

10. A battery, It is characterized in that An electrode produced using the carbon nanotube dispersion according to any one of claims 1 to 7 is provided.

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