Aqueous dispersion for forming an electrode layer

Abstract

To provide a novel electrode layer formation water dispersed body with an excellent resistance to corrosion, the water dispersed body being capable of forming an electrode layer with a more excellent conductivity.SOLUTION: The electrode layer formation water dispersed body of the present invention contains water, polyvinyl pyrrolidone, and alcohol, and more specifically contains 0.5-45 pts.mass of the alcohol to 1 pt.mass of the polyvinyl pyrrolidone.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

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

[0004] In the case of such an aqueous slurry, there are problems in long-term storage, such as corrosion and mold generation depending on the passage of time and the storage environment.

[0005] Therefore, proposals have been made to use acids, salts, isothiazoline-based preservatives, alcohols, etc. as preservatives and fungicides for aqueous slurries (see Patent Document 2), and 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

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] When alcohols are used as preservatives or bactericides for the dispersion for forming an electrode layer, it is necessary to add high-concentration alcohols in order to exhibit sufficient effects.

[0008] However, adding high-concentration alcohol causes problems such as reducing the dispersibility of conductive materials and deteriorating the conductivity of the formed electrode layer. Therefore, there is a demand for a new aqueous dispersion for forming an electrode layer that achieves both anti-corrosion properties and conductivity.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a new aqueous dispersion for forming an electrode layer that can form an electrode layer having good conductivity and has good anti-corrosion properties.

Means for Solving the Problems

[0010] As a result of intensive studies, 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, containing at least water, polyvinylpyrrolidone, and alcohol, and the content of the alcohol is 0.5 to 45 parts by mass with respect to 1 part by mass of the polyvinylpyrrolidone, an aqueous dispersion for forming an electrode layer. <Aspect 2> The aqueous dispersion for forming an electrode layer according to Aspect 1, wherein the average molecular weight of the polyvinylpyrrolidone is 5,000 to 3,000,000. <Aspect 3> The aqueous dispersion for forming an electrode layer according to Aspect 1 or 2, wherein the alcohol is ethanol or isopropyl alcohol. <Aspect 4> The aqueous dispersion for forming an electrode layer according to any one of Aspects 1 to 3, further containing carboxymethyl cellulose. <Aspect 5> The aqueous dispersion for forming an electrode layer according to any one of Aspects 1 to 4, further containing a conductive material. <Aspect 6> The aqueous dispersion for forming an electrode layer according to any one of Aspects 1 to 5, further containing an active material. <Aspect 7> The aqueous dispersion for forming an electrode layer according to Aspect 6, wherein the active material is metal oxide-based active material particles.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a novel aqueous dispersion for forming an electrode layer that can provide an electrode layer having good conductivity and good corrosion resistance.

Modes for Carrying Out the Invention

[0012] 《Aqueous Dispersion for Forming an Electrode Layer》 The aqueous dispersion for forming an electrode layer of the present invention contains at least water, a conductive material, polyvinylpyrrolidone, and alcohol, and the content of the alcohol is 0.5 to 45 parts by mass with respect to 1 part by mass of the polyvinylpyrrolidone.

[0013] Conventionally, in order to suppress the deterioration of the aqueous dispersion for forming an electrode layer and thereby enable long-term storage in the form of a dispersion, a preservative may be used. However, when a commonly used preservative is contained in the aqueous dispersion for forming an electrode layer and an electrode layer is formed using this, the preservative remains in the electrode layer. As a result, compared with the case where no preservative is present, the conductivity may deteriorate.

[0014] In contrast, it was considered to use a substance that volatilizes during the film formation process of the electrode layer, such as alcohol, as a preservative. However, even when alcohol is used in an amount generally used as a preservative, for example, 0.0001 to 1 part by mass with respect to 100 parts by mass of a binder (binder), that is, 0.000001 to 0.01 part by mass with respect to 1 part by mass of the binder, sufficient anti-corrosion performance cannot be obtained. Conversely, when the amount of alcohol is increased, the action of the dispersant may be inhibited, and an electrode layer having sufficient conductivity may not be obtained.

[0015] In contrast, the present inventors have found that the above configuration, particularly the combination of polyvinylpyrrolidone as a dispersant and the above amount of alcohol, can provide an electrode layer having good conductivity and good corrosion resistance, that is, a water-dispersible composition for forming an electrode layer. That is, when these are combined, good corrosion resistance can be obtained and conductivity when producing the electrode layer can be inhibited.

[0016] The water-dispersible composition for forming an electrode layer of the present invention may further contain any other components. Examples of other components include active materials, binders, thickeners, dispersion aids, pH adjusters, and the like.

[0017] In particular, when the water-dispersible composition for forming an electrode layer contains an active material, the solid content in the water-dispersible composition for forming an electrode layer is 40% by mass or more, 43% by mass or more, 45% by mass or more, 48% by mass or more, or 50% by mass or more based on the total mass of the water-dispersible composition for forming an electrode layer, and 60% by mass or less, 58% by mass or less, 55% by mass or less, or 53% by mass or less, which is preferable from the viewpoint of dispersion stability.

[0018] The pH of the water-dispersible composition 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. This pH 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, for example, aluminum, when coating the material.

[0019] Hereinafter, each component of the present invention will be described.

[0020] 〈Water〉 The water can be ion-exchanged water, distilled water, or the like.

[0021] 〈Conductive material〉 As the conductive material, for example, a carbon-based conductive material can be used. The carbon-based conductive material may be carbon fiber and / or carbon particles.

[0022] Examples of carbon fibers include, but are not limited to, mild fibers and chopped fibers. These may be used alone or in combination.

[0023] The average length of the carbon fiber 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 also be 100 μm or less, 70 μm or less, 50 μm or less, or 30 μm or less.

[0024] Examples of carbon particles include graphene, carbon nanotubes, graphite, and carbon blacks such as acetylene black and ketjen black. These may be used alone or in combination.

[0025] The shape of the carbon particles is not particularly limited and may be, for example, flat, array-like, spherical, or the like.

[0026] The average particle diameter 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 also be 20 μm or less, 15 μm or less, 10 μm or less, or 7 μm or less. Here, the average particle diameter adopted in this specification is appropriately selected according to the size of the target carbon particles. In the case of particles with a size of less than 1 μm, it is the value of the histogram average particle diameter (D50) based on the scattering intensity distribution measured by the dynamic light scattering method. In the case of particles with a size of 1 μm or more, it is the value of the median diameter (D50) calculated based on volume by the laser diffraction method. The measurement by the dynamic light scattering method can be performed, for example, using DelsaMax CORE (Beckman Coulter). The measurement by the laser diffraction method can be performed, for example, using a particle size distribution measuring device MT3300II (Microtrac Bell Co., Ltd.).

[0027] The content rate of the carbonaceous conductive material in the aqueous dispersion for forming the electrode layer may be 1.0 mass% or more, 1.5 mass% or more, 2.0 mass% or more, or 2.5 mass% or more based on the total mass of the aqueous dispersion for forming the electrode layer, and may also 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.

[0028] 〈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.

[0029] The content rate of the polyvinylpyrrolidone in the aqueous dispersion for forming the 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 based on the total mass of the aqueous dispersion for forming the electrode layer, and may also 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.

[0030] The viscosity average molecular weight of polyvinylpyrrolidone may be 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 also 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.

[0031] This viscosity average molecular weight can be measured, for example, by the method of measuring molecular weight described in Polymer Journal vol.38, No.7, pp.457 - 463 (July, 1981), that is, by the following procedure: (1) Add the sample to excess acetone for precipitation purification. After repeating this operation twice, dry it under reduced pressure until the acetone odor disappears. (2) Prepare an aqueous solution of the purified sample, and use an Ubbelohde viscometer (water, 120 seconds) to obtain the viscosity average molecular weight using the following formula.

[0032] [η]=0.393M 0.59

[0033] The above formula is 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 journal, and is a relational formula between the intrinsic viscosity [η] and the viscosity average molecular weight.

[0034] As long as it is a measurement method that can obtain equivalent results, other methods may be used to measure the viscosity average molecular weight.

[0035] 〈Alcohol〉 As the alcohol, any arbitrary alcohol may be used. It is preferable that the boiling point of this alcohol is 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 95°C or lower, 90°C or lower, 88°C or lower, 85°C or lower, or 83°C or lower in order to be volatilized and removed together with water. Further, the boiling point of this alcohol may be 60°C or higher, 70°C or higher, or 75°C or higher.

[0036] As such alcohol, methanol (boiling point 64.7°C), ethanol (boiling point 78.4°C), isopropyl alcohol (boiling point 82.5°C), propyl alcohol (boiling point 97 - 98°C), sec-butanol (boiling point 99°C), t-butanol (boiling point 82.4°C), etc. can be used. Among them, it is preferable to use ethanol or isopropyl alcohol from the viewpoint of improving the antiseptic performance.

[0037] The alcohol content is 0.5 part by mass or more, 0.7 part by mass or more, 0.9 part by mass or more, 1.0 part by mass or more, 1.5 part by mass or more, 2.0 part by mass or more, 2.5 part by mass or more, 3.0 part by mass or more, 3.5 part by mass or more, or 4.0 part by mass or more with respect to 1.0 part by mass of polyvinylpyrrolidone, and is 45 part by mass or less, 40 part by mass or less, 35 part by mass or less, 30 part by mass or less, 25 part by mass or less, 20 part by mass or less, 15 part by mass or less, 13 part by mass or less, 10 part by mass or less, or 8 part by mass or less. When the alcohol content is within the above range, an electrode layer having good conductivity can be obtained, and a water-dispersion for forming an electrode layer having good antiseptic properties can be obtained.

[0038] The alcohol content is 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 with respect to 1.0 part by mass of water, and is 0.25 parts by mass or less, 0.22 parts by mass or less, 0.20 parts by mass or less, 0.18 parts by mass or less, 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. When the alcohol content is within the above range, an electrode layer having good conductivity can be obtained, and a water-dispersion for forming an electrode layer having good antiseptic properties can be obtained.

[0039] When the water-dispersion for forming an electrode layer contains carboxymethyl cellulose, from the viewpoint of antiseptic performance, it is preferable that the alcohol content is 1.0 part by mass or more with respect to 1.0 part by mass of carboxymethyl cellulose. 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 also 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.

[0040] Also, when the water-dispersion for forming an electrode layer contains a binder, from the viewpoint of antiseptic performance, it is preferable that the alcohol content is 1.0 part by mass or more with respect to 1.0 part by mass of the binder. 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 also 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, 5.5 parts by mass or less, 5.0 parts by mass or less, or 4.0 parts by mass or less.

[0041] The alcohol content is 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 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, 5.5% 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 the electrode layer. By the alcohol content being within the above range, an electrode layer having good conductivity can be obtained, and an aqueous dispersion for forming an electrode layer having good antiseptic properties can be obtained.

[0042] 〈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-based emulsion-type polymers.

[0043] Among such polymers, it is preferable from the viewpoint of conductivity to use an elastomer-based emulsion-type polymer, particularly a styrene-based elastomer-based emulsion-type polymer, and particularly styrene-butadiene rubber.

[0044] In addition, as the polymer, for example, natural polymers such as polysaccharides and synthetic polymers can be used. Such polymers may be used as thickeners.

[0045] Examples of the polysaccharides include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starch glycolic acid, and salts thereof. Among these, use of carboxymethyl cellulose is preferred from the viewpoint of dispersion stability.

[0046] Examples of the synthetic polymers include water-soluble resins such as polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylic acid and salts thereof, polyethylene oxide, vinyl acetate-polyvinyl pyrrolidone copolymer, styrene-acrylic acid copolymer and salts thereof, isobutylene maleic anhydride copolymer and salts thereof.

[0047] Examples of the polymers include nonionic dispersants such as polyalkylene oxide, polyvinyl acetal, polyvinyl ether, chitins, chitosans, and starch. These polymers may be used as dispersion aids.

[0048] 〈Active material〉 As the active material, any active material particles can be used without particular limitation. For example, metal oxide-based active material particles, particularly metal oxide-based negative electrode active material particles can be used.

[0049] Examples of the metal oxide-based negative electrode active material particles include titanium oxides. The titanium oxides are not particularly limited as long as they can occlude and release lithium. For example, spinel-type lithium titanate, lamellar-type lithium titanate, titanium-containing metal composite oxides, titanium dioxide (TiO 2 (B)) having a monoclinic crystal structure, and anatase-type titanium dioxide can be used.

[0050] Examples of the spinel-type lithium titanate include Li 4+x Ti 5O 12 (x varies in the range of -1 ≦ x ≦ 3 due to the charge-discharge reaction), etc. are exemplified. As the ramsdellite-type lithium titanate, Li 2+y Ti 3 O 7 (y varies in the range of -1 ≦ y ≦ 3 due to the charge-discharge reaction), etc. are exemplified. TiO 2 (B) and as anatase-type titanium dioxide, Li 1+z TiO 2 (z varies in the range of -1 ≦ z ≦ 0 due to the charge-discharge reaction), etc. are exemplified.

[0051] Examples of the titanium-containing metal composite oxide include a metal composite oxide containing at least one element selected from the group consisting of Ti and at least one element selected from P, V, Sn, Cu, Ni, and Fe. Examples of the metal composite oxide containing at least one element selected from the group consisting of Ti and at least one element selected from P, V, Sn, Cu, Ni, and Fe include, for example, TiO 2 -P 2 O 5 , TiO 2 -V 2 O 5 , TiO 2 -P 2 O 5 -SnO 2 , TiO 2 -P 2 O 5 -MeO (Me is at least one element selected from the group consisting of Cu, Ni, and Fe), etc. can be mentioned.

[0052] Such a metal composite oxide preferably has a microstructure in which the crystallinity is low and a crystalline phase and an amorphous phase coexist, or the amorphous phase exists alone. Due to the microstructure, the cycle performance can be further improved.

[0053] The content ratio of the metal oxide-based active material particles in the aqueous dispersion for forming the electrode layer may be 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, or 40% by mass or more, based on the mass of the entire aqueous dispersion for forming the electrode layer, and may also be 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less.

[0054] 〈pH adjuster〉 As an optional pH adjuster, for example, at least one of ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, hydroxides of alkali metals such as sodium hydroxide, etc. can be used.

[0055] 〈Dispersant〉 As the dispersant, in addition to polyvinylpyrrolidone, for example, an anionic dispersant can be used. As the anionic dispersant, acrylic resins such as styrene acrylic resins, urethane resins, polyester resins, polyvinyl chloride resins, and epoxy resins, etc. can be used.

[0056] 〈Others〉 In the aqueous dispersion for forming the electrode layer of the present invention, the content ratio of the preservative which is 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, is 0.5% by mass or less, 0.3% by mass or less, 0.1% by mass or less, or 0% by mass, that is, not containing this preservative is preferable from the viewpoint of conductivity. 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(methylsulfonyl)pyridine, alkali metal salts of benzoic acid, sorbic acid, and dehydroacetic acid, benzimidazole-based compounds, etc.

[0057] 《Manufacturing method of the aqueous dispersion for forming the 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 means of a dispersing means such as a bead mill or a mixer.

Examples

[0058] The present invention will be specifically described by way of Examples and Comparative Examples, but the present invention is not limited thereto. 〈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), 40 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, 3.0 parts by mass of ethanol as a preservative, and 51.4 parts by mass of water were mixed, and these were stirred by a planetary mixer to prepare 100 parts by mass of the aqueous dispersion of Example 1. The styrene-butadiene rubber as a binder was in an emulsion state.

[0059] 〈Examples 2 to 11 and Comparative Examples 1 to 9〉 Except that the content and type of each component were changed as shown in Tables 1 and 3, the aqueous dispersions for forming an electrode layer of Examples 2 to 11 and Comparative Examples 1 to 9 were prepared in the same manner as in Example 1.

[0060] Details of each substance mentioned in Tables 1 and 3 are as follows: Polyvinylpyrrolidone A: PVP K-15, ISP, viscosity average molecular weight 10,000 Polyvinylpyrrolidone C: PVP K-120, ISP, viscosity average molecular weight 2,800,000 Styrene acrylic resin: HDP-96J, BASF Sodium lauryl sulfate: NIKKOL SLS, Nikko Chemicals Co., Ltd. BIT: 1,2-benzothiazolin-3-one

[0061] "Evaluation" 〈Anticorrosion performance〉 The anticorrosion performance of each aqueous dispersion for forming an electrode layer in Examples 1 to 11 and Comparative Examples 1 to 9 was evaluated by the storage efficacy test defined in the Japanese Pharmacopoeia. Specifically, the number of bacteria immediately after production and 14 days after production in each prepared aqueous dispersion for forming an electrode layer was measured, and the change in the number of bacteria was confirmed. The evaluation criteria are as follows: A: The number of bacteria shows a decreasing trend B: There is no increase or decrease in the number of bacteria C: The number of bacteria shows an increasing trend

[0062] 〈Sheet resistance〉 Using each aqueous dispersion for forming an electrode layer in Examples 1 to 11 and Comparative Examples 1 to 9, an electrode layer was prepared as follows.

[0063] Using each aqueous dispersion for forming an electrode layer in Examples 1 to 11 and Comparative Examples 1 to 9, it was applied to one side of a PET film (Lumirror #100-T60, Toray Industries, Inc.) with an applicator so that the liquid film became 50 μm, and then dried at room temperature for 30 minutes. Further, it was dried at 80 °C for 5 minutes to obtain an electrode layer.

[0064] The sheet resistance of the electrode layer thus prepared was measured using an apparatus consisting of a four-probe with a probe interval of 10 mm and a milliohm high tester 3227 (Hioki Electric).

[0065] From the viewpoint of electrode layer formation, the lower the sheet resistance, the better the characteristics, and the sheet resistance was evaluated based on the following evaluation criteria: A: The sheet resistance was less than 5.0 kΩ / □ B: The sheet resistance was 5.0 kΩ / □ or more and less than 8.0 kΩ / □ C: The sheet resistance was 8.0 kΩ / □ or more

[0066] The configurations and evaluation results of the examples and comparative examples are shown in Tables 1 to 4.

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070]

Table 4

[0071] It can be understood from Tables 1 to 4 that the aqueous dispersions for forming the electrode layers of Examples 1 to 11 contain both polyvinylpyrrolidone and alcohol, and the alcohol content is 0.5 to 45 parts by mass with respect to 1.0 part by mass of polyvinylpyrrolidone, and both the anti-corrosion performance and the conductivity are good.

Claims

1. An aqueous dispersion for forming an electrode layer, Contains at least water, polyvinylpyrrolidone, and alcohol; and The content of the alcohol is 0.5 to 45 parts by mass relative to 1 part by mass of the polyvinylpyrrolidone. Aqueous dispersion for electrode layer formation.

2. 2. The aqueous dispersion for forming an electrode layer according to claim 1, wherein the polyvinylpyrrolidone has an average molecular weight of 5,000 to 3,000,000.

3. The aqueous dispersion for forming an electrode layer according to claim 1 or 2, wherein the alcohol is ethanol or isopropyl alcohol.

4. The aqueous dispersion for forming an electrode layer according to any one of claims 1 to 3, further comprising carboxymethyl cellulose.

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

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

7. The electrode layer forming aqueous dispersion according to claim 6 , wherein the active material is a metal oxide-based active material particle.

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