Aqueous dispersion for forming an electrode layer

Abstract

To provide a novel water dispersion for electrode layer formation, which enables formation of an electrode layer having favorable conductivity, has favorable antiseptic property, and has favorable dispersion stability.SOLUTION: The water dispersion for electrode layer formation contains at least water, a conductive material, ethanol and a second alcohol, wherein the contained amount of ethanol is 0.005 to 0.15 pts.mass for 1.0 pts.mass of the water and the water dispersion has favorable antiseptic property and also has favorable dispersibility.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous dispersion for forming an electrode layer. [Background technology]

[0002] In recent years, secondary batteries have been widely used in various fields such as electric vehicles, power storage, and information devices. Electrodes of these secondary batteries are produced by coating a current collector with a dispersion for forming an electrode layer, which contains a conductive material, an active material, a binder, and the like.

[0003] For example, Patent Document 1 discloses a negative electrode mixture slurry for a non-aqueous electrolyte secondary battery, in which surface-modified natural graphite as an active material, a carbon nanotube dispersion, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) as a binder are dispersed in water.

[0004] Such aqueous slurries have problems with long-term storage, such as corrosion and mold growth depending on the time and storage environment.

[0005] For this reason, there have been proposals to use acids, salts, isothiazolinone-based preservatives, alcohols, etc. as preservatives or disinfectants for aqueous slurries (see Patent Document 2), as well as proposals to use alcohols, chlorines, acids, alkalis, nitrogen-containing organic sulfur compounds, etc. (see Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-195143 A [Patent Document 2] International Publication No. 2015 / 016283 [Patent Document 3] JP 2011-181195 A Summary of the Invention [Problem to be solved by the invention]

[0007] When alcohols are used as a preservative or disinfectant in the electrode layer-forming dispersion, it is necessary to add the alcohols at a high concentration in order to achieve a sufficient effect.

[0008] However, the addition of a high concentration of alcohol reduces the dispersibility of conductive materials and the like, resulting in problems such as a deterioration in the conductivity of the formed electrode layer. Therefore, a new aqueous dispersion for forming an electrode layer that combines antiseptic properties and conductivity is required.

[0009] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a novel aqueous dispersion for forming an electrode layer, which is capable of forming an electrode layer having good electrical conductivity, has good antiseptic properties, and has good dispersion stability. [Means for solving the problem]

[0010] As a result of intensive research, the present inventors have found that the above problems can be solved by the following means, and have completed the present invention. That is, the present invention is as follows: <Aspect 1> An aqueous dispersion for forming an electrode layer, The method includes the steps of: The total content of the ethanol and the second alcohol is 0.005 to 0.15 parts by mass relative to 1.0 part by mass of the water. Aqueous dispersion for electrode layer formation. <Aspect 2> The aqueous dispersion for forming an electrode layer according to aspect 1, wherein the content of the second alcohol is 0.03 to 1.5 parts by mass per part by mass of the ethanol. <Aspect 3> The aqueous dispersion for forming an electrode layer according to Aspect 1 or 2, wherein the second alcohol has a boiling point of more than 78.4°C and not more than 150°C. <Aspect 4> The aqueous dispersion for forming an electrode layer according to aspect 3, wherein the second alcohol is selected from the group consisting of isopropyl alcohol, propyl alcohol, sec-butanol, and t-butanol. <Aspect 5> The aqueous dispersion for forming an electrode layer according to any one of Aspects 1 to 4, further comprising polyvinylpyrrolidone. <Aspect 6> The aqueous dispersion for forming an electrode layer according to aspect 5, wherein the polyvinylpyrrolidone has a viscosity average molecular weight of 5,000 to 3,000,000. <Embodiment 7> Further containing carboxymethyl cellulose, and The total content of the ethanol and the second alcohol is 1.0 part by mass or more relative to 1.0 part by mass of the carboxymethyl cellulose. The electrode layer-forming water dispersion according to any one of the first to sixth aspects. <Aspect 8> The aqueous dispersion for forming an electrode layer according to any one of Aspects 1 to 7, further comprising an active material. Aspect 9: The aqueous dispersion for forming an electrode layer according to Aspect 8, wherein the active material is metal oxide-based active material particles. Effect of the Invention

[0011] According to the present invention, it is possible to provide a novel aqueous dispersion for forming an electrode layer, which is capable of forming an electrode layer having good electrical conductivity, has good antiseptic properties, and has good dispersion stability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 《Aqueous dispersion for electrode layer formation》 The aqueous dispersion for forming an electrode layer of the present invention comprises The method includes the steps of: The content of the ethanol is 0.005 to 0.15 part by mass with respect to 1.0 part by mass of the water.

[0013] In the past, a preservative was sometimes used to suppress deterioration of the aqueous dispersion for forming an electrode layer, thereby enabling the dispersion to be stored for a long period of time. However, when a commonly used preservative was contained in the aqueous dispersion for forming an electrode layer and the aqueous dispersion was used to form an electrode layer, the preservative remained in the electrode layer, and as a result, the electrical conductivity was sometimes deteriorated compared to when the preservative was not present.

[0014] In response to this, the use of a substance that volatilizes during the film formation process of the electrode layer, such as alcohol, as a preservative was investigated. However, even when alcohol is used in an amount generally used as a preservative, for example, 0.0001 to 1 part by mass per 100 parts by mass of the binder, that is, 0.000001 to 0.01 part by mass per 1 part by mass of the binder, as mentioned in Patent Document 2, sufficient preservative performance cannot be obtained, and conversely, when the amount of alcohol is increased, the action of the dispersant is inhibited, and an electrode layer having sufficient conductivity cannot be obtained.

[0015] In response to this, the present inventors have found that the above-mentioned composition, particularly the combination of the above-mentioned amount of ethanol and the second alcohol, can provide an electrode layer having good electrical conductivity, and can provide an aqueous dispersion for forming an electrode layer having good antiseptic properties and good dispersion stability. That is, when these are combined, good antiseptic properties and dispersion stability can be obtained, and electrical conductivity when the electrode layer is produced can be prevented from being hindered.

[0016] The total content of ethanol and the second alcohol may be 0.005 parts by mass or more, 0.007 parts by mass or more, 0.009 parts by mass or more, 0.010 parts by mass or more, 0.015 parts by mass or more, 0.020 parts by mass or more, 0.025 parts by mass or more, 0.030 parts by mass or more, 0.035 parts by mass or more, 0.040 parts by mass or more, 0.045 parts by mass or more, 0.050 parts by mass or more, or 0.055 parts by mass or more, and may be 0.15 parts by mass or less, 0.12 parts by mass or less, 0.10 parts by mass or less, or 0.08 parts by mass or less, relative to 1.0 parts by mass of water. By having the total content of ethanol and the second alcohol in the above range, an electrode layer having good electrical conductivity and good antiseptic properties can be obtained, and an aqueous dispersion for forming an electrode layer can be obtained.

[0017] When the aqueous dispersion for forming an electrode layer contains carboxymethylcellulose, the total content of ethanol and the second alcohol is preferably 1.0 parts by mass or more relative to 1.0 parts by mass of carboxymethylcellulose from the viewpoint of antiseptic performance. This content may be 1.5 parts by mass or more, 1.8 parts by mass or more, 2.0 parts by mass or more, 2.2 parts by mass or more, 2.5 parts by mass or more, 2.8 parts by mass or more, 3.0 parts by mass or more, or 3.2 parts by mass or more, and may be 10.0 parts by mass or less, 9.0 parts by mass or less, 8.0 parts by mass or less, 7.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, or 4.5 parts by mass or less.

[0018] In addition, when the aqueous dispersion for forming an electrode layer contains a binder, the total content of ethanol and the second alcohol is preferably 1.0 parts by mass or more relative to 1.0 parts by mass of the binder from the viewpoint of antiseptic performance. This content may be 1.5 parts by mass or more, 1.8 parts by mass or more, 2.0 parts by mass or more, 2.2 parts by mass or more, 2.5 parts by mass or more, 2.8 parts by mass or more, 3.0 parts by mass or more, or 3.2 parts by mass or more, and may be 10.0 parts by mass or less, 9.0 parts by mass or less, 8.0 parts by mass or less, 7.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, 4.5 parts by mass or less, or 4.0 parts by mass or less.

[0019] The total content of ethanol and the second alcohol may be 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, or 2.5% by mass or more, and may be 10.0% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, or 3.5% by mass or less, based on the total mass of the aqueous dispersion for forming an electrode layer. By having the alcohol content in the above range, an aqueous dispersion for forming an electrode layer having good electrical conductivity and good antiseptic properties can be obtained.

[0020] The aqueous dispersion for forming an electrode layer of the present invention may further contain other optional components, such as an active material, a polymer, a dispersant, a pH adjuster, and the like.

[0021] In particular, when the water dispersion for forming an electrode layer contains an active material, the solids content in the water dispersion for forming an electrode layer may be 40 mass % or more, 43 mass % or more, 45 mass % or more, 48 mass % or more, or 50 mass % or more, based on the total mass of the water dispersion for forming an electrode layer, and is preferably 60 mass % or less, 58 mass % or less, 55 mass % or less, or 53 mass % or less, from the viewpoint of dispersion stability.

[0022] The pH of the aqueous dispersion for forming an electrode layer is preferably 5.0 or more, 5.5 or more, 6.0 or more, or 6.5 or more from the viewpoint of dispersion stability, and is preferably 9.0 or less, 8.5 or less, 8.0 or less, or 7.5 or less from the viewpoint of suppressing corrosion of the material constituting the current collector, such as aluminum, when the aqueous dispersion is applied to the current collector.

[0023] Each component of the present invention will now be described.

[0024] <water> The water can be ion-exchanged water, distilled water, or the like.

[0025] <Conductive material> The conductive material may be, for example, a carbon-based conductive material, which may be carbon fibers and / or carbon particles.

[0026] Carbon fibers include, but are not limited to, milled fibers, chopped fibers, etc. These may be used alone or in combination.

[0027] The average length of the carbon fibers can be 1 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more, and can be 100 μm or less, 70 μm or less, 50 μm or less, or 30 μm or less.

[0028] Examples of carbon particles include graphene, carbon nanotubes, graphite, and carbon black such as acetylene black and ketjen black, etc. These may be used alone or in combination.

[0029] The shape of the carbon particles is not particularly limited, and may be, for example, flat, array-like, spherical, or the like.

[0030] The average particle size of the carbon particles can be 100 nm or more, 200 nm or more, 300 nm or more, 500 nm or more, 700 nm or more, 1 μm or more, 2 μm or more, or 3 μm or more, and can be 20 μm or less, 15 μm or less, 10 μm or less, or 7 μm or less. Here, the average particle size adopted in this specification is appropriately selected depending on the size of the target carbon particles, and in the case of particles less than about 1 μm, it is the value of the histogram average particle size (D50) based on the scattering intensity distribution measured by the dynamic light scattering method, and in the case of particles of 1 μm or more, it is the value of the median size (D50) calculated on a volume basis in the laser diffraction method. Measurement by the dynamic light scattering method can be performed using, for example, DelsaMax CORE (Beckman Coulter, Inc.). Measurement by the laser diffraction method can be performed using, for example, a particle size distribution measuring device MT3300II (Microtrack Bell, Inc.).

[0031] The content of the carbonaceous conductive material in the electrode layer-forming water dispersion may be 1.0 mass % or more, 1.5 mass % or more, 2.0 mass % or more, or 2.5 mass % or more, and may be 15.0 mass % or less, 12.0 mass % or less, 10.0 mass % or less, 8.0 mass % or less, 6.0 mass % or less, 5.0 mass %, 4.5 mass % or less, 4.0 mass % or less, 3.5 mass % or less, or 3.0 mass % or less, based on the total mass of the electrode layer-forming water dispersion.

[0032] <Polyvinylpyrrolidone> The aqueous dispersion for forming an electrode layer of the present invention may contain polyvinylpyrrolidone. As the polyvinylpyrrolidone, commercially available polyvinylpyrrolidone can be used. Polyvinylpyrrolidone can act as a dispersant for the active material and the conductive material without being inhibited by alcohol.

[0033] The content of polyvinylpyrrolidone in the water dispersion for forming an electrode layer may be 0.05 mass % or more, 0.12 mass % or more, 0.15 mass % or more, 0.18 mass % or more, or 0.20 mass % or more, and may be 1.00 mass % or less, 0.90 mass % or less, 0.80 mass % or less, 0.70 mass % or less, 0.60 mass % or less, 0.50 mass % or less, 0.40 mass % or less, or 0.30 mass % or less, based on the total mass of the water dispersion for forming an electrode layer.

[0034] The viscosity average molecular weight of polyvinylpyrrolidone is 5,000 or more, 6,000 or more, 7,000 or more, 8,000 or more, 10,000 or more, 20,000 or more, 30,000 or more, 40,000 or more, 50,000 or more, 80,000 or more, 100,000 or more, 150,000 or more, 200,000 or more, 250,000 or more, 300,000 or more, 350,000 or more, 400,000 or more, 500,000 or more , or 600,000 or more, and may be 3,000,000 or less, 2,500,000 or less, 2,300,000 or less, 2,000,000 or less, 1,800,000 or less, 1,500,000 or less, 1,200,000 or less, 1,000,000 or less, 900,000 or less, 850,000 or less, 800,000 or less, 750,000 or less, 700,000 or less, or 650,000 or less.

[0035] The viscosity average molecular weight can be measured, for example, by the method for measuring molecular weight described in Polymer Review, vol. 38, No. 7, pp. 457-463 (July, 1981), that is, by the following procedure: (1) The sample is added to an excess of acetone for precipitation purification. This procedure is repeated twice, and then the sample is dried under reduced pressure until the odor of acetone disappears. (2) Prepare an aqueous solution of the purified sample, and use an Ubbelohde viscometer (water, 120 seconds) to calculate the viscosity average molecular weight using the following formula.

[0036] [η]=0.393M 0.59

[0037] The above formula is the relational expression between the intrinsic viscosity [η] and the viscosity average molecular weight obtained by substituting the constants K and a in the following Mark-Kuhn-Houwink formula (Mark-Houwink-Sakurada formula) with reference to the above-mentioned collection of papers.

[0038] It should be noted that other methods may be used to measure the viscosity average molecular weight as long as the measurement method can give equivalent results.

[0039] <ethanol> The content of ethanol may be 0.005 parts by mass or more, 0.007 parts by mass or more, 0.009 parts by mass or more, 0.010 parts by mass or more, 0.015 parts by mass or more, 0.020 parts by mass or more, 0.025 parts by mass or more, 0.030 parts by mass or more, 0.035 parts by mass or more, 0.040 parts by mass or more, 0.045 parts by mass or more, 0.050 parts by mass or more, or 0.055 parts by mass or more, and may be 0.15 parts by mass or less, 0.12 parts by mass or less, 0.10 parts by mass or less, or 0.08 parts by mass or less, relative to 1.0 parts by mass of water. By the content of ethanol being in the above range, an electrode layer having good electrical conductivity and good antiseptic properties can be obtained.

[0040] When the aqueous dispersion for forming an electrode layer contains carboxymethylcellulose, the content of ethanol is preferably 1.0 parts by mass or more relative to 1.0 parts by mass of carboxymethylcellulose from the viewpoint of antiseptic performance. This content may be 1.5 parts by mass or more, 1.8 parts by mass or more, 2.0 parts by mass or more, 2.2 parts by mass or more, 2.5 parts by mass or more, 2.8 parts by mass or more, 3.0 parts by mass or more, or 3.2 parts by mass or more, and may be 10.0 parts by mass or less, 9.0 parts by mass or less, 8.0 parts by mass or less, 7.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, or 4.0 parts by mass or less.

[0041] In addition, when the aqueous dispersion for forming an electrode layer contains a binder, the content of ethanol is preferably 1.0 parts by mass or more relative to 1.0 parts by mass of the binder from the viewpoint of antiseptic performance. This content may be 1.5 parts by mass or more, 1.8 parts by mass or more, 2.0 parts by mass or more, 2.2 parts by mass or more, 2.5 parts by mass or more, 2.8 parts by mass or more, 3.0 parts by mass or more, or 3.2 parts by mass or more, and may be 10.0 parts by mass or less, 9.0 parts by mass or less, 8.0 parts by mass or less, 7.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, or 4.0 parts by mass or less.

[0042] The content of ethanol may be 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, or 2.5% by mass or more, and may be 10.0% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, or 3.5% by mass or less, based on the total mass of the aqueous dispersion for forming an electrode layer. By having the alcohol content in the above range, an aqueous dispersion for forming an electrode layer having good electrical conductivity and good antiseptic properties can be obtained.

[0043] <Second Alcohol> The second alcohol is an alcohol other than ethanol. The boiling point of the second alcohol is preferably 150° C. or less, 140° C. or less, 130° C. or less, 120° C. or less, 110° C. or less, 100° C. or less, 95° C. or less, 90° C. or less, 88° C. or less, 85° C. or less, or 83° C. or less in order to volatilize and remove the alcohol together with water. The boiling point of the alcohol may be 60° C. or more, 70° C. or more, 75° C. or more, more than 78.4° C., 80° C. or more, or 82° C. or more.

[0044] Examples of such alcohols that can be used include methanol (boiling point 64.7°C), isopropyl alcohol (boiling point 82.5°C), 1-propyl alcohol (boiling point 97 to 98°C), sec-butanol (boiling point 99°C), and t-butanol (boiling point 82.4°C). Of these, isopropyl alcohol is preferred from the viewpoint of improving preservative performance.

[0045] The content of the second alcohol is preferably 0.03 to 1.5 parts by mass relative to 1.0 part by mass of ethanol from the viewpoint of dispersion stability. This content may be 0.03 parts by mass or more, 0.05 parts by mass or more, 0.07 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, 0.4 parts by mass or more, or 0.5 parts by mass or more, and may be 1.5 parts by mass or less, 1.3 parts by mass or less, 1.1 parts by mass or less, 1.0 parts by mass or less, less than 1.0 parts by mass, 0.9 parts by mass or less, 0.8 parts by mass or less, 0.7 parts by mass or less, or 0.6 parts by mass or less.

[0046] <polymer> As the polymer, for example, a polymer that can be used as a binder can be used. As such a polymer, for example, various emulsion type polymers can be used, such as fluorine-based emulsion type polymers such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), elastomer-based emulsion type polymers such as ethylene-propylene-diene copolymer (EPDM), nitrile-butadiene rubber (NBR), and styrene-butadiene rubber (SBR), and acrylic emulsion type polymers can be used.

[0047] As such a polymer, it is preferable to use an elastomer-based emulsion type polymer, particularly a styrene-based elastomer-based emulsion type polymer, in particular a styrene-butadiene rubber, from the viewpoint of electrical conductivity.

[0048] As the polymer, for example, natural polymers such as polysaccharides or synthetic polymers can be used. Such polymers are sometimes used as thickeners.

[0049] Examples of polysaccharides that can be used include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid, and salts thereof. Among these, carboxymethylcellulose is preferred from the viewpoint of dispersion stability.

[0050] Examples of synthetic polymers that can be used include water-soluble resins such as polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, vinyl acetate-polyvinylpyrrolidone copolymers, styrene-acrylic acid copolymers and their salts, and isobutylene-maleic anhydride copolymers and their salts.

[0051] As the polymer, for example, non-ionic dispersants such as polyalkylene oxides, polyvinyl acetals, polyvinyl ethers, chitins, chitosans, starch, etc. can be used. These polymers are sometimes used as dispersion assistants.

[0052] <Active material> The active material can be any active material particle without any particular limitation. For example, metal oxide-based active material particles, particularly metal oxide-based negative electrode active material particles, can be used.

[0053] For example, titanium oxide can be used as the metal oxide-based negative electrode active material particles. The titanium oxide is not particularly limited as long as it can absorb and release lithium, but for example, spinel-type lithium titanate, ramsdellite-type lithium titanate, titanium-containing metal composite oxide, titanium dioxide (TiO2(B)) having a monoclinic crystal structure, and anatase-type titanium dioxide can be used.

[0054] 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-type titanium dioxide include Li 1+z TiO2 (z changes in the range of -1≦z≦0 depending on the charge / discharge reaction).

[0055] 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).

[0056] 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.

[0057] The content of the metal oxide active material particles in the water dispersion for forming an electrode layer may be 20 mass % or more, 25 mass % or more, 30 mass % or more, 35 mass % or more, or 40 mass % or more, and may be 70 mass % or less, 65 mass % or less, 60 mass % or less, 55 mass % or less, or 50 mass % or less, based on the total mass of the water dispersion for forming an electrode layer.

[0058] <pH adjuster> As the optional pH adjuster, at least one of ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, sodium tripophosphate, alkali metal salts of carbonate or phosphoric acid such as sodium carbonate, and alkali metal hydroxides such as sodium hydroxide can be used.

[0059] <Dispersant> In addition to or instead of the polyvinylpyrrolidone, for example, an anionic dispersant can be used as the dispersant. Examples of the anionic dispersant that can be used include acrylic resins such as styrene acrylic resins, urethane resins, polyester resins, polyvinyl chloride resins, and epoxy resins.

[0060] <others> In terms of electrical conductivity, the aqueous dispersion for forming an electrode layer of the present invention preferably contains no more than 0.5% by mass, no more than 0.3% by mass, no more than 0.1% by mass, or no more than 0% by mass of preservatives that are solid or liquid at a temperature sufficient to evaporate the solvent, for example, 150° C., 140° C., 130° C., 120° C., 110° C., or 100° C. Examples of such preservatives include phenol (boiling point 181.7° C.), sodium omadine (boiling point 109° C.), sodium pentachlorophenol (boiling point 309° C.), 1,2-benzisothiazolin-3-one (melting point 154° C., boiling point 360° C.), 2,3,5,6-tetrachloro-4(methylphonyl)pyridine, alkali metal salts of benzoic acid, sorbic acid, or dehydroacetic acid, and benzimidazole-based compounds.

[0061] <<Method for producing aqueous dispersion for forming electrode layer>> The aqueous dispersion for forming an electrode layer of the present invention can be produced, for example, by dispersing the substances constituting the aqueous dispersion for forming an electrode layer by a dispersing means such as a bead mill or a mixer. EXAMPLES

[0062] The present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these. Example 1 2 parts by mass of carbon nanotubes (CNT, average length 2 μm) and 2 parts by mass of acetylene black (AB, primary particle diameter 35 nm) as carbon-based conductive materials, 0.4 parts by mass of polyvinylpyrrolidone B (PVP K-30, ISP, viscosity average molecular weight 40,000), 45 parts by mass of lithium titanate as active material particles, 0.6 parts by mass of styrene butadiene rubber (SBR), 0.6 parts by mass of carboxymethyl cellulose, 2.0 parts by mass of ethanol and 0.5 parts by mass of t-butanol as preservatives, and 46.9 parts by mass of water were mixed and stirred with a planetary mixer to prepare 100 parts by mass of the water dispersion of Example 1. The styrene butadiene rubber as a binder was in an emulsion state.

[0063] Examples 2 to 14 and Comparative Examples 1 to 6 Water dispersions for forming an electrode layer of Examples 2 to 14 and Comparative Examples 1 to 6 were prepared in the same manner as in Example 1, except that the content and type of polymer or dispersant were changed as shown in Table 1.

[0064] Details of each substance mentioned in Tables 1 and 3 are as follows: Polyvinylpyrrolidone B: PVP K-120, ISP, viscosity average molecular weight 320,000 Alkyl acrylate copolymer: Luvimer 100P, BASF BIT: 1,2-benzothiazolin-3-one

[0065] "evaluation" <Preservative performance> The preservative performance of each of the electrode layer forming aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 6 was evaluated by the preservative effectiveness test specified in the Japanese Pharmacopoeia. Specifically, the number of bacteria in each electrode layer forming aqueous dispersion was measured immediately after production and 14 days after production, and the change in the number of bacteria was confirmed. The evaluation criteria were as follows: S: The number of bacteria after 14 days has decreased to 1 / 100 of the initial number. A: The number of bacteria is decreasing, but more than 1 / 100 of the initial number remains. B: No change in the number of bacteria C: The number of bacteria is increasing

[0066] <Sheet resistance> Using each of the electrode layer-forming aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 6, an electrode layer was produced as follows.

[0067] The aqueous dispersions for forming the electrode layer of each of the above-mentioned Examples 1 to 14 and Comparative Examples 1 to 6 were applied to one side of a PET film (Lumirror #100-T60, Toray Industries, Inc.) with an applicator so that the liquid film was 50 μm thick, and then dried at room temperature for 30 minutes and further dried at 80° C. for 5 minutes to obtain an electrode layer.

[0068] The sheet resistance of the electrode layer thus produced was measured using an apparatus consisting of a four-point probe with a probe spacing of 10 mm and a Milliohm HiTester 3227 (HIOKI ELECTRIC CO., LTD.).

[0069] From the viewpoint of electrode layer formation, the lower the sheet resistance, the better the characteristics. The sheet resistance was evaluated based on the following evaluation criteria: A: The sheet resistance was less than 5.0 kΩ / □. B: Sheet resistance was 5.0 kΩ / □ or more and less than 8.0 kΩ / □ C: Sheet resistance was 8.0 kΩ / □ or more.

[0070] <Dispersion stability> The electrode layer-forming aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 6 were each left to stand for 24 hours, and then the D90 value was measured on a volume basis using a laser diffraction method to evaluate the dispersion stability of the electrode layer-forming aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 6. The evaluation criteria were as follows: A: D90 value is 10μm or less B: D90 value is 10 to 50 μm C: D90 value is 50μm or more

[0071] The configurations and evaluation results of the Examples, Comparative Examples, and Reference Examples are shown in Tables 1 to 4.

[0072] [Table 1]

[0073] [Table 2]

[0074] [Table 3]

[0075] [Table 4]

[0076] It can be seen from Tables 1 and 2 that the aqueous dispersions for forming an electrode layer of Examples 1 to 14, which contained at least ethanol and a second alcohol and had an ethanol content of 0.005 to 0.15 parts by mass per 1.0 part by mass of water, had extremely good antiseptic performance and were both good in conductivity and dispersion stability.

Claims

1. An aqueous dispersion for forming an electrode layer, The method includes the steps of: The total content of the ethanol and the second alcohol is 0.005 to 0.15 parts by mass per 1.0 part by mass of the water. Aqueous dispersion for electrode layer formation.

2. 2. The aqueous dispersion for forming an electrode layer according to claim 1, wherein the content of the second alcohol is 0.1 to 1.5 parts by mass per 1 part by mass of the ethanol.

3. The aqueous dispersion for forming an electrode layer according to claim 1 or 2, wherein the second alcohol is an alcohol having a boiling point of more than 78.4°C and not more than 150°C.

4. 4. The aqueous dispersion for forming an electrode layer according to claim 3, wherein the second alcohol is selected from the group consisting of isopropyl alcohol, propyl alcohol, sec-butanol, and t-butanol.

5. The aqueous dispersion for forming an electrode layer according to any one of claims 1 to 4, further comprising polyvinylpyrrolidone.

6. 6. The aqueous dispersion for forming an electrode layer according to claim 5, wherein the polyvinylpyrrolidone has a viscosity average molecular weight of 5,000 to 3,000,000.

7. Further containing carboxymethylcellulose, and The total content of the ethanol and the second alcohol is 1.0 part by mass or more relative to 1.0 part by mass of the carboxymethyl cellulose. The aqueous dispersion for forming an electrode layer according to any one of claims 1 to 6.

8. The aqueous dispersion for forming an electrode layer according to any one of claims 1 to 7, further comprising an active material.

9. The electrode layer forming aqueous dispersion according to claim 8 , wherein the active material is a metal oxide-based active material particle.

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