CN117836971A - Carbon nanotube dispersion, conductive paste using same, electrode paste for secondary battery, electrode for secondary battery, and secondary battery - Google Patents

Abstract

Providing: the dispersion is suitable for manufacturing carbon nanotube dispersion liquid, conductive paste, electrode paste for secondary battery, electrode for secondary battery, and secondary battery of secondary battery such as lithium ion battery. The carbon nanotube dispersion liquid disclosed in item 1 is characterized by comprising at least: the Y of an XYZ chromaticity system of a dry coating film prepared by coating a dispersion liquid having a concentration of carbon nanotubes of 2 mass% with an applicator having a gap of 50 μm, the dry coating film comprising carbon nanotubes, a water-soluble polymer material and a dispersion medium is 6.0 or less, the carbon nanotube dispersion liquid disclosed in item 2 is characterized in that the dry coating film prepared by adjusting the concentration of the carbon nanotubes to 2 mass% of the dispersion liquid is coated with an applicator having a gap of 50 μm, and both of the color spaces of L, a and b are negative values.

Description

Carbon nanotube dispersion, conductive paste using same, electrode paste for secondary battery, electrode for secondary battery, and secondary battery

Technical Field

The present specification relates to: a carbon nanotube dispersion having excellent stability and conductivity, a conductive paste using the dispersion, an electrode paste for a secondary battery suitable for manufacturing a secondary battery such as a lithium ion battery, an electrode for a secondary battery, and a secondary battery.

Background

With the popularization of electric vehicles, the miniaturization and weight reduction and the high performance of portable devices such as mobile phones and notebook personal computers, secondary batteries having a high energy density and further the high capacity of the secondary batteries are demanded. In this context, lithium ion secondary batteries using nonaqueous electrolytes are used in many devices because of their characteristics of high energy density and high voltage.

The following studies were performed: by using a carbon nanotube dispersion or the like for the negative electrode material, the positive electrode material, and particularly the positive electrode material used in these lithium ion secondary batteries, it is possible to realize good conductivity, reduce electrode resistance, and effectively form a conductive network in a small amount.

For example, patent document 1 discloses a carbon nanotube dispersion liquid which contains a dispersant having a number average molecular weight of 1 to 15 ten thousand and a solvent, and contains the dispersant in a proportion of 250 to 2000 parts by weight based on 100 parts by weight of carbon nanotubes, and has a pH of 8 to 12.

Patent document 2 discloses that a dispersion liquid of carbon nanotubes includes: a dispersion medium, carbon nanotubes having an average length of 8 [ mu ] m or more and 10mm or less, and two or more surfactants each having a hydrophilic structure and a hydrophobic structure in the molecule.

Patent document 3 discloses a carbon nanotube dispersion liquid which maintains high dispersibility of carbon nanotubes even when the amount of a conventional dispersant is smaller than the amount of the conventional dispersant, and which comprises: a composition containing carbon nanotubes, a dispersant having a weight average molecular weight of 0.1 to 40 tens of thousands inclusive, a volatile salt and an aqueous solvent.

Patent document 4 discloses a carbon nanotube dispersion liquid that exhibits excellent dispersibility in an organic solvent and thus exhibits high conductivity on a substrate, and a method for producing the same, the carbon nanotube dispersion liquid comprising: the composition containing carbon nanotubes, a cellulose derivative of a specific structure, and an organic solvent, wherein the organic solvent contains 1 or more selected from aprotic polar solvents and terpenes, the concentration of the composition containing carbon nanotubes contained in the carbon nanotube dispersion is 1 mass% or less, and when the dispersion is centrifuged at 1 ten thousand G for 10 minutes and 90vol% is recovered as a supernatant, the concentration of the carbon nanotube dispersion in the supernatant is 80% or more of the concentration of the carbon nanotube dispersion before the centrifugation.

Patent document 5 discloses a dispersion containing Carbon Nanotubes (CNT) and having an aspect ratio of CNT of 1300 or more and a viscosity of 2.0mpa·s or more at a shear rate of 1000/s, and further discloses a dispersion containing CNT comprising 50 to 500 parts by mass of a dispersant having a weight average molecular weight of 1 to 40 ten thousand as measured by gel permeation chromatography and an aqueous solvent, based on 100 parts by mass of CNT, and further discloses a dispersion containing CNT, wherein the dispersant is preferably an anionic dispersant, particularly preferably carboxymethyl cellulose or a salt thereof (Na salt, NH ₄ Salts, etc.) as a main component.

Patent document 6 discloses a carbon nanotube dispersion liquid comprising: carbon nanotube (A), dispersant (B), and solvent (C) containing water and/or water-soluble organic solvent, the specific surface area of carbon nanotube (A) being 500-800 m ² And/g, the cumulative particle diameter D50 measured by the dynamic light scattering method is 200 to 1000nm.

However, in the carbon nanotube dispersions and the like of patent documents 1 to 6, it is currently difficult to achieve both stability and conductivity with high degree of dispersion with time, and there is a strong demand for carbon nanotube dispersions, conductive pastes, electrode pastes for secondary batteries, electrodes for secondary batteries, and secondary batteries such as lithium ion batteries using the same, which can achieve both high stability and conductivity.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2013-199419 (claims, examples, etc.)

Patent document 2: japanese patent laid-open publication No. 2013-100206 (claims, examples, etc.)

Patent document 3: international publication WO2016/136428 (claims, examples, etc.)

Patent document 4: international publication WO2017/188175 (claims, examples, etc.)

Patent document 5: japanese patent laid-open No. 2017-65964 (claims, examples, etc.)

Patent document 6: japanese patent laid-open No. 2020-105316 (claims, examples, etc.)

Disclosure of Invention

Problems to be solved by the invention

The present disclosure has been made in view of the above-described conventional problems and the like, and an object thereof is to provide: carbon nanotube dispersion liquid capable of achieving both high stability and conductivity, conductive paste using the same, electrode paste for secondary battery and electrode for secondary battery, and secondary battery such as lithium ion battery using the electrode.

Solution for solving the problem

The present inventors have conducted intensive studies with respect to the above-described conventional problems, and as a result, found that: the present disclosure has been completed by the following disclosure 1 and 2, in which the disclosure 1 includes at least: a dry coating film prepared by coating a dispersion liquid having a concentration of carbon nanotubes of 2 mass% with an applicator having a gap of 50 μm, wherein Y in an XYZ chromaticity system of the dry coating film is set to a predetermined value or less; the 2 nd publication at least comprises: the dry coating film prepared by coating a dispersion liquid having a concentration of carbon nanotubes of 2 mass% with an applicator having a gap of 50 μm, the color spaces of L, a, b being defined as predetermined values.

Specifically, the carbon nanotube dispersion liquid disclosed in item 1 is characterized by comprising at least: the carbon nanotube dispersion liquid disclosed in item 2 is characterized by comprising at least: carbon nanotubes, water-soluble polymer materials and dispersion media, the dry coating film prepared by coating the dispersion liquid having a concentration of carbon nanotubes adjusted to 2 mass% with an applicator having a gap of 50 μm had negative values of both a and b in the color space.

The water-soluble polymer material is preferably 1 or more selected from nonionic water-soluble polymers and anionic water-soluble polymers.

In the present disclosure, the conductive paste is characterized by containing at least the carbon nanotube dispersion liquid having the above-described respective constitution, and the electrode paste for a secondary battery is characterized by containing at least the carbon nanotube dispersion liquid having the above-described respective constitution and the active material for a secondary battery.

The electrode for a secondary battery of the present disclosure is characterized by using the electrode paste for a secondary battery having the above-described configuration, and the secondary battery is characterized by using the electrode for a secondary battery having the above-described configuration.

In the present specification, the term "the present disclosure" means that the 1 st disclosure and the 2 nd disclosure are included.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, there may be provided: carbon nanotube dispersion liquid capable of achieving both high stability and conductivity, conductive paste using the same, electrode paste for secondary battery and electrode for secondary battery, and secondary battery suitable for lithium ion battery using the electrode.

The objects and effects of the present disclosure are particularly identified and attained by the use of the elements and combinations pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the disclosure, as set forth in the claims.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described in detail. However, it should be noted that the scope of protection of the present disclosure is not limited to the embodiments described in detail below, but relates to the aspects of the invention described in the claims and their equivalents. In addition, the present disclosure may be implemented based on the disclosure in the present specification and technical common knowledge in the field (including conventional technical choices, obvious features).

Carbon nanotube dispersion

The carbon nanotube dispersion liquid disclosed in the present 1 is characterized by comprising at least: the dry coating film prepared by coating a dispersion having a concentration of carbon nanotubes of 2 mass% with an applicator having a gap of 50 μm, wherein the carbon nanotube dispersion disclosed in item 2 has a Y of 6.0 or less in an XYZ chromaticity system, and is characterized by comprising at least: carbon nanotubes, water-soluble polymer materials and dispersion media, the dry coating film prepared by coating the dispersion liquid having a concentration of carbon nanotubes adjusted to 2 mass% with an applicator having a gap of 50 μm had negative values of both a and b in the color space.

Carbon Nanotube (CNT)

The Carbon Nanotubes (CNT) used in the present disclosure (the 1 st and 2 nd disclosures, and the same applies hereinafter) are not particularly limited as long as they have a shape substantially formed by winding 1 sheet of graphite into a tube shape, and single-layer CNTs obtained by winding 1 sheet of graphite into 1 layer, or multi-layer CNTs wound into two or more layers may be used.

Examples of the form of the carbon nanotube include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers, but the form is not limited to these, and two or more types (hereinafter, simply referred to as "at least 1") may be used alone or in combination.

Further, the average outer diameter of the carbon nanotubes is preferably 1nm to 90nm, more preferably 3nm to 30nm, still more preferably 3nm to 15nm, from the viewpoints of viscosity, conductivity and stability of the dispersion.

In the present disclosure, the average outer diameter of the carbon nanotubes means an arithmetic average of the shape of a sufficient number n measured using an image of a magnification of 10 ten thousand times or more of a transmission electron microscope.

The purity of the carbon nanotubes used in the present disclosure is preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass%. The purity of the carbon nanotubes was calculated as follows: the ash content measured in accordance with JIS K1469 and JIS K6218 was calculated based on the amount of the impurity.

As concrete examples of the Carbon Nanotubes (CNTs), at least 1 of FloTube9000 (average outer diameter 11 nm) manufactured by Cnano corporation, MWNT-7 (average outer diameter 70 nm) manufactured by Baohu chemical Co., ltd.), VGCF-S (average outer diameter 80 nm) manufactured by Showa electric Co., ltd., VGCF-X (average outer diameter 15 nm) and the like can be used.

The content of these Carbon Nanotubes (CNT) is not particularly limited, and may be set as appropriate according to the application.

For example, when the composition is used for a conductive paste, an electrode paste for a secondary battery, an electrode for a secondary battery, or the like, the content thereof is preferably 0.1 to 15.0% by mass, more preferably 0.1 to 10.0% by mass, even more preferably 0.5 to 8.0% by mass, 1.0 to 6.0% by mass, and particularly 2.0 to 5.0% by mass, relative to the total amount of the dispersion, from the viewpoint of both high stability and conductivity and viscosity at the time of producing the dispersion.

The Carbon Nanotubes (CNT) content of 0.1 mass% or more can ensure sufficient conductivity, while the Carbon Nanotubes (CNT) content of 15.0 mass% or less can ensure stability of the dispersion and good conductivity.

Water-soluble polymer material

The water-soluble polymer material used in the present disclosure may be used without any particular limitation as long as it is soluble in water or in a dispersion medium (a solvent other than water) used.

Examples of the water-soluble polymer materials include natural polymer materials such as protein and starch, and synthetic polymer materials such as polyacrylic acid, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl amide and polyamine. These water-soluble polymer materials function as dispersants and binders for Carbon Nanotubes (CNT).

The water-soluble polymer material dissolved in a solvent other than water may be partially dissolved, as well as completely dissolved. By using these water-soluble polymers, dispersion can be stably performed without impairing the conductivity of Carbon Nanotubes (CNT).

As the water-soluble polymer material, at least 1 or more selected from nonionic water-soluble polymers and anionic water-soluble polymers is particularly preferably used, and is particularly suitable for stable dispersion without impairing the conductivity of Carbon Nanotubes (CNTs).

Examples of nonionic water-soluble polymers that can be used include at least 1 of polyoxyethylene alkyl ether, polyoxyalkylene derivative, polyoxyethylene phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester and alkyl allyl ether, glycerol borate fatty acid ester and polyoxyethylene glycerol fatty acid ester, xanthan gum, welan gum, succinoglycan, polyvinyl alcohol (PVAL or PVOH), polyvinylpyrrolidone, polyvinyl acetal, and the like.

Examples of the anionic water-soluble polymer that can be used include at least 1 of an acrylic polymer such as a fatty acid and a salt thereof, a polysulfonic acid and a salt thereof, a polycarboxylic acid and a salt thereof, an alkyl sulfate and a salt thereof, an alkylaryl sulfonic acid and a salt thereof, an alkyl naphthalene sulfonic acid and a salt thereof, a dialkyl sulfosuccinic acid and a salt thereof, an alkyl phosphoric acid and a salt thereof, a polyoxyethylene alkyl ether sulfuric acid and a salt thereof, a polyoxyethylene alkylaryl ether sulfuric acid and a salt thereof, a naphthalene sulfonic acid formaldehyde condensate and a salt thereof, a polyoxyethylene alkylphosphorsulfonic acid and a salt thereof, a styrene acrylic resin and a cellulose polymer such as carboxymethyl cellulose or sodium (Na) salt thereof.

From the viewpoint of not interfering with conductivity, it is preferable to use polyvinyl pyrrolidone as the nonionic water-soluble polymer, and among the anionic water-soluble polymers, it is preferable to use an acrylic polymer or a cellulose polymer.

The (total) content of these water-soluble polymer materials is not particularly limited, and may be set as appropriate according to the application.

For example, when the composition is used for a conductive paste, an electrode paste for a secondary battery, an electrode for a secondary battery, or the like, the content thereof is preferably 0.005 to 20% by mass, particularly preferably 0.025 to 16% by mass, relative to the total amount of the dispersion, in order to achieve both high stability and conductive performance.

When the content of these polymer materials is 0.005 mass% or more, the dispersion stability of the Carbon Nanotubes (CNT) is improved, while when the content is 20 mass% or less, the stability of the dispersion and the good conductivity can be ensured.

Dispersion medium

The dispersion medium used in the present disclosure may be one which can partially dissolve a water-soluble polymer material such as a nonionic water-soluble polymer or an anionic water-soluble polymer, and water (purified water, distilled water, pure water, ultrapure water, or the like), an organic solvent, or the like may be used without particular limitation.

The dispersion medium may be used not only singly but also by mixing 2 or more kinds, and may be used by being suitably adjusted in a mixing range even if water and an organic solvent are combined.

Examples of the organic solvent include aromatic solvents, alcohols, polyols, glycol ethers, and esters. These solvents may be used alone or in combination.

Examples of the aromatic compound include benzyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, phenyl alkylsulfonate, butyl phthalate, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, and dipropylene glycol dibenzoate.

Examples of the alcohols include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, 1-pentanol, isopentanol, sec-pentanol, 3-pentanol, t-pentanol, n-hexanol, methylpentanol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-ethylhexanol, 3, 5-trimethylhexanol, nonanol, n-decanol, undecanol, n-dodecanol, trimethylnonanol, tetradecanol, heptadecanol, cyclohexanol, and 2-methylcyclohexanol.

Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexylene glycol, pentylene glycol, glycerol, hexanetriol, thiodiglycol, 3-methyl-1, 3-butylene glycol, triethylene glycol, dipropylene glycol, 1, 3-propylene glycol, 1, 3-butylene glycol, 1, 5-pentylene glycol, hexylene glycol, and octylene glycol.

Examples of glycol ethers include methyl isopropyl ether, diethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethyl butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methyl-3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol t-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isopentyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isopentyl propionate, methyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl pivalate, ethyl trimethyl acetate, propyl trimethyl acetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl oleate, triglycerate, tributyl acetate citrate, octyl hydroxystearate, methyl propanediol, 2-hydroxy isobutyrate, and 3-methoxybutyl acetate.

Further, at least one of amine systems such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, amide systems such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N-dimethylformamide, N-dimethylacetamide, N-diethylacetamide, N-methylcaprolactam, heterocyclic systems such as cyclohexylpyrrolidone, 2-oxazolidone, 1, 3-dimethyl-2-imidazolidone, and γ -butyrolactone, sulfoxide systems such as dimethyl sulfoxide, sulfone systems such as hexamethylphosphoric triamide, sulfolane, urea, acetonitrile, and the like may be used.

Additives consistent with the use of the carbon nanotube dispersion of the present disclosure may also be added to the dispersion. Examples of the thickener include sodium carboxymethylcellulose, an anti-settling agent, a wetting agent, an emulsifier, an anti-sagging agent, an antifoaming agent, a leveling agent, a plasticizer, an antifungal/algicidal agent, and an antibacterial agent.

The carbon nanotube dispersion liquid disclosed in item 1 is characterized by comprising at least: the carbon nanotube, the water-soluble polymer material and the dispersion medium are coated with an applicator having a gap of 50 μm, and the Y of an XYZ chromaticity system of a dried coating film prepared by adjusting the concentration of the carbon nanotube to 2% by mass is 6.0 or less, and the carbon nanotube dispersion liquid disclosed in the 2 nd publication is characterized by comprising at least: the above-mentioned carbon nanotubes, water-soluble polymer material and dispersion medium were coated with a dispersion liquid having a gap of 50 μm and having a concentration of carbon nanotubes adjusted to 2 mass%, and the dry coating film produced by coating the dispersion liquid was negative in both of the color spaces of L x a and b.

In the carbon nanotube dispersion having the above-mentioned compounding property disclosed in the item 1, many experimental evaluations were performed on the correlation between the dried coating film and X, Y, Z in the XYZ chromaticity system, and as a result, it was determined that: the XYZ chromaticity system of the dried coating film of the carbon nanotube dispersion, particularly, Y is at most a predetermined value or less, and is highest in terms of both conductivity and stability.

In the publication 1, Y of the XYZ chromaticity system of the dried coating film of the carbon nanotube dispersion liquid, which is the highest in both conductivity and stability, is preferably 6.0 or less, more preferably 0 or more and 5.0 or less, still more preferably 0 or more and 4.5 or less, and particularly preferably 0 or more and 4.0 or less.

In the carbon nanotube dispersion disclosed in the item 1, the dispersion in which Y of the XYZ chromaticity system of the dried coating film exceeds 6.0 is not preferable because the conductivity is deteriorated.

In the publication 1, the reason why the color tone is evaluated under the same conditions is specified in the above-mentioned "dry coating film prepared by coating a dispersion in which the concentration of carbon nanotubes is adjusted to 2 mass% with an applicator having a gap of 50 μm".

In the present disclosure 1 (including examples described below), the XYZ chromaticity system-based measurement of the dried coating film is based on a spectrocolorimeter, and can be measured using, for example, SC-T (P) (manufactured by Suga Test instruments co., ltd.).

In addition, in the carbon nanotube dispersion having the above-mentioned compounding property in the publication 2, from a view point different from that in the publication 1, both of conductivity and stability were studied, and as a result, many experimental evaluations were performed on the correlation between the dry coating film and the a and b in the color space of l×a×b, and as a result, it was determined that: the dry coating film of the carbon nanotube dispersion has a highest electrical conductivity and stability at the same time, that is, a predetermined value of L, a, b, and particularly a and b in the color space.

Therefore, in the disclosure 2, it is determined that, for a carbon nanotube dispersion liquid having the highest degree of both conductivity and stability, both of the a and b of the color spaces of the dry coating film prepared by coating a solution having a concentration of carbon nanotubes adjusted to 2 mass% with an applicator having a gap of 50 μm must be negative.

Preferably, when a and B are both negative values and the maximum value of the absolute value of a is A, B, and B is the maximum value of the absolute value of a, it is desirable that 0.1A or more and 1.0A or less and/or 0.1B or more and 1.0B or less be satisfied, and it is particularly desirable that a be 0.5A or more and 1.0A or less and B be 0.5B or more and 1.0B or less.

In the dispersion in which at least 1 of the L x a x b x color space and the L x b x of the dry coating film of the carbon nanotube dispersion is positive, the conductivity is deteriorated, which is not preferable.

In addition, in the publication 2, the reason why the color tone is evaluated under the same conditions as in the publication 1 is specified in the "dry coating film prepared by coating a dispersion in which the concentration of carbon nanotubes is adjusted to 2 mass% with an applicator having a gap of 50 μm".

In this disclosure 2 (including examples described below), the XYZ chromaticity system-based measurement of the dried coating film is based on a spectrocolorimeter, and can be measured using, for example, SC-T (P) (manufactured by Suga Test instruments co., ltd.).

In the present disclosure, in order to obtain the carbon nanotube dispersion liquid having the above-described characteristics, the components having the above-described compounding characteristics may be dispersed under appropriate conditions by using a dispersing apparatus shown below.

For example, as the dispersing device, a dispersing machine commonly used for dispersing pigment and the like can be used, and examples thereof include a dispersing machine, a homomixer, a rotation-revolution mixer, a henschel mixer, a mixer such as a planetary mixer, a (high pressure) homogenizer, a paint shaker, a colloid mill, a bead mill, a cone mill, a ball mill, a sand mill, a abrader, a bead mill, a medium-free dispersing machine such as a CoBall mill, a wet jet mill, a film rotation-type high-speed mixer, and other roll mills, but are not limited thereto.

The preferable dispersing device is preferably a film rotary high-speed mixer, a bead mill, or the like in terms of stability and dispersing efficiency.

In addition, the viscosity (25 ℃) of the carbon nanotube dispersion of the present disclosure was measured by a cone-plate viscometer and a rotor rotating speed of 10rpm (shear speed 38.3 s) from the aspects of stability and handling ^-1 ) Hereinafter, it is preferably 1 to 10000 mPas, more preferably 1 to 5000 mPas.

The carbon nanotube dispersion of the present disclosure thus constituted becomes capable of achieving both high stability and conductivity. The carbon nanotube dispersion has excellent properties that have not been conventionally used, and therefore, it has become useful for a conductive paste, an electrode paste for a secondary battery, an electrode for a secondary battery, a secondary battery suitable for a lithium ion battery using the electrode, and the like.

Conductive paste

The conductive paste of the present disclosure is characterized by containing at least the carbon nanotube dispersion liquid disclosed in the above 1 or 2, and can be used for conductive resin products, conductive adhesives, printed circuit applications, and the like.

The conductive paste may be formed by adding at least a resin component to the carbon nanotube dispersion liquid disclosed in the above 1 or 2, which is capable of achieving both high stability and conductivity. As the resin component, for example, a thermosetting resin, an ultraviolet curable resin, or the like can be used.

Electrode paste for secondary battery and electrode for secondary battery

The electrode paste for a secondary battery of the present disclosure is characterized by comprising at least the carbon nanotube dispersion liquid disclosed in the above 1 st publication or the carbon nanotube dispersion liquid disclosed in the above 2 nd publication and an active material for a secondary battery, and the electrode paste for a secondary battery of the present disclosure is characterized by using the electrode paste for a secondary battery of the above constitution.

The carbon nanotube dispersion disclosed in the above 1 or 2 may be used as it is, diluted or concentrated.

The electrode paste for secondary batteries and the carbon nanotubes contained in the secondary battery electrode can be suitably adjusted according to the electrode characteristics, the battery capacity after unitization, the charge/discharge characteristics, and the like, and when the content is set to an optimum level, it is desirable to contain the carbon nanotubes in an amount of 1 to 15 parts by mass.

As the active material used in the electrode paste for a secondary battery, either a positive electrode active material or a negative electrode active material may be used.

The positive electrode active material for a secondary battery is not particularly limited as long as it is a normal positive electrode active material (active material capable of reversibly intercalating/deintercalating lithium ions) that can be used in a positive electrode of a lithium ion battery.

Examples thereof include lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-cobalt composite oxides, lithium-nickel-aluminum composite oxides, lithium-nickel-cobalt-aluminum composite oxides, lithium-nickel-manganese-cobalt composite oxides, lithium-nickel-manganese-aluminum composite oxides, lithium-nickel-cobalt-manganese-aluminum composite oxides, lithium-nickel-manganese-aluminum composite oxides, and the like, and composite oxides of lithium and transition metals, tiS ₂ 、FeS、MoS ₂ Equal transition metal sulfide, mnO, V ₂ O ₅ 、V ₆ O ₁₃ 、TiO ₂ And transition metal oxides, olivine-type lithium phosphorus oxides, and the like. Olivine-type lithium phosphorus oxides include, for example: at least 1 element of the group consisting of Mn, cr, co, cu, ni, V, mo, ti, zn, al, ga, mg, B, nb, and Fe, lithium, phosphorus, and oxygen. These compounds may be obtained by partially replacing a part of the elements with other elements to improve the characteristics thereof.

As a preferable positive electrode active material for secondary batteries, a lithium-nickel composite oxide is used, and it is further preferable that the lithium-nickel composite oxide is desirably of the formula: liNi _X M1 _Y M2 _Z O ₂ (M1 and M2 are at least 1 metal element among Al, B, alkali metal, alkaline earth metal and transition metal elements, X is more than or equal to 0.8 and less than or equal to 1.0, Y is more than or equal to 0 and less than or equal to 0.2, and Z is more than or equal to 0 and less than or equal to 0.2).

The active material of the positive electrode for a secondary battery may be used alone or in combination of two or more.

As the negative electrode for a secondary battery, a normal negative electrode active material that can be used in a negative electrode of a lithium ion battery may be used without particular limitation.

As the negative electrode active material for the secondary battery, a normal negative electrode active material that can be used in a negative electrode of a lithium ion battery may be used without particular limitation.

Examples of the negative electrode active material for secondary batteries that can be used include inorganic compounds such as lithium metal, lithium alloy, and tin compound, carbonaceous materials capable of absorbing and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbonaceous material include cokes, glassy carbons, graphites, hardly graphitizable carbons, thermally cracked carbons, and carbon fibers. Among them, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, and are preferable because they can charge and discharge at a high operating voltage, inhibit self-discharge when a lithium salt is used as a supporting salt, and reduce irreversible capacity at the time of charging. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. Among them, a metal oxide material and a carbonaceous material are preferable from the viewpoint of safety.

The electrode paste for a secondary battery preferably contains the carbon nanotube dispersion liquid disclosed in the above 1 or 2, an active material for a positive electrode or a negative electrode for a secondary battery, and a further binder (binder).

Examples of the usable adhesive material (adhesive) include polyimide-based resins, polyvinylidene fluoride (PVdF), polytetrafluoroethylene, ethylene tetrafluoride/propylene hexafluoride/vinylidene fluoride-based copolymers, fluororesins such as propylene hexafluoride/vinylidene fluoride-based copolymers, ethylene tetrafluoride/perfluorovinyl ether-based copolymers, polyolefin resins such as polyethylene and polypropylene, polyvinylpyrrolidone, polyvinyl alcohol, styrene Butadiene Rubber (SBR), and acrylic resins. These binder materials may be used by mixing 2 or more kinds.

In terms of adhesion to a collector foil, battery capacity after unitization, and charge/discharge characteristics, it is desirable that the amount of these binder materials is preferably 0.2 to 3.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, relative to the total amount of the electrode paste for a secondary battery.

Further, various solvents can be used for the electrode paste for a secondary battery. Examples of the solvent include water (purified water, ion-exchanged water, distilled water, ultrapure water, etc.), an aromatic solvent, alcohols, polyols, ether solvents, glycol ether solvents, ester solvents, amine solvents, amide solvents, heterocyclic solvents, sulfoxide solvents, sulfone solvents, and the like. These solvents may be used alone or in combination of 2 or more kinds.

The amount of these solvents is preferably 0.5 to 80 parts by mass, more preferably 1 to 70 parts by mass, relative to the total amount of the electrode paste for a secondary battery, from the viewpoint of necessity of forming an appropriate viscosity when coating the electrode dispersion.

Further, in addition to the above-described carbon nanotube dispersion liquid, active material, binder, a leveling agent, solid electrolyte material, and the like may be suitably blended within a range that does not impair the effects of the present disclosure.

The electrode paste for a secondary battery thus constituted can be prepared as follows: the carbon nanotube dispersion liquid disclosed in the above 1 or 2, the active material of the positive electrode or negative electrode for a secondary battery, the binder (binder), the solvent, and the like are prepared by using, for example, a twin-screw kneader or the like.

The obtained electrode paste for secondary batteries is applied to a current collector which is a conductive member of a lithium ion secondary battery and dried to obtain a positive electrode and a negative electrode for a predetermined lithium ion secondary battery.

The material and shape of the current collector used in the electrode are not particularly limited, and may be appropriately selected so as to be compatible with various secondary batteries. Examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. In addition, although a foil on a flat plate is generally used as the shape, a surface roughened, a foil-shaped perforated, and a net-shaped current collector may be used.

The method of applying the electrode paste to the current collector is not particularly limited, and a known method may be used. Specifically, a die coating method, a dip coating method, a roll coating method, a doctor blade coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, an electrostatic coating method, or the like may be mentioned, and as a drying method, a stand drying, a blow dryer, a hot air dryer, an infrared heater, a far infrared heater, or the like may be used, but is not particularly limited thereto.

In addition, a rolling treatment by a lithographic press machine, a rolling roller, or the like may be performed after the coating. The thickness of the electrode material layer is usually 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

Secondary battery and lithium ion secondary battery

The secondary battery of the present disclosure is characterized in that the secondary battery electrode is used, and the secondary battery electrode is preferably used for a positive electrode and a negative electrode of a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte. Hereinafter, a case of using the lithium ion secondary battery will be described.

As the positive electrode, an electrode can be produced by coating the current collector with the electrode paste containing a positive electrode active material and drying the paste.

As the negative electrode, an electrode paste containing a negative electrode active material is applied to a current collector, and dried to produce an electrode.

As the electrolyte, various conventionally known substances capable of moving ions can be used. Examples include LiBF ₄ 、LiClO ₄ 、LiPF ₆ 、LiAsF ₆ 、LiSbF ₆ 、LiCF ₃ SO ₃ 、Li(CF ₃ SO ₂ ) ₂ N、LiC ₄ F ₉ SO ₃ 、Li(CF ₃ SO ₂ ) ₃ C、LiI、LiBr、LiCl、LiAlCl、LiHF ₂ LiSCN, or LiBPh ₄ And lithium salts such as phenyl, but not limited thereto. The electrolyte is preferably dissolved in a nonaqueous solvent and used as the electrolyte solution.

Examples of the nonaqueous solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methylethyl carbonate, and diethyl carbonate; lactones such as gamma-butyrolactone, gamma-valerolactone, and gamma-octanolide; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 2-methoxyethane, 1, 2-ethoxyethane, and 1, 2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; nitriles such as acetonitrile. These solvents may be used alone or in combination of 2 or more.

In the present disclosure, a separator is preferably included in the lithium ion secondary battery. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and hydrophilic treated nonwoven fabric.

The structure of the lithium ion secondary battery is not particularly limited, and it is generally composed of a positive electrode, a negative electrode, and a separator provided as needed, and it is possible to form various shapes, such as paper type, cylindrical type, button type, and laminated type, which are suitable for the purpose of use.

The lithium ion secondary battery and the like that are secondary batteries of the present disclosure configured as described above are secondary batteries that achieve battery performance that can withstand repeated charge and discharge for a long period of time.

Examples

The present disclosure is described below with reference to examples, but the present disclosure is not limited to these examples.

[ 1 st publication: examples 1 to 11 and comparative examples 1 to 2: preparation of carbon nanotube Dispersion

Carbon nanotube dispersions were prepared by dispersing the carbon nanotubes, dispersant (polymer material) and dispersion medium in the following compounding compositions shown in table 1 under the following dispersing apparatus and dispersing conditions.

Dispersing device: horizontal bead mill

Dispersion conditions: phi 0.5mm zirconia beads

The concentration of carbon nanotubes in the obtained carbon nanotube dispersion was adjusted to 2 mass% with purified water or NMP used as a dispersion medium, the concentration-adjusted dispersion was applied to a PET film by an applicator (model YD-2/manufactured by Yoshimitsu SEIKI Co., ltd.) having a gap of 50 μm, and the values of XYZ chromaticity system of the dried coating film produced by drying at a temperature of 80℃were shown in Table 1 below, and stability and conductivity were evaluated according to the following evaluation criteria by the following methods. The evaluation results are shown in table 1 below.

[ 2 nd publication: examples 12 to 22 and comparative examples 3 to 6: preparation of carbon nanotube Dispersion

Carbon nanotube dispersions were prepared by dispersing the carbon nanotubes, dispersant (polymer material) and dispersion medium in the following compounding compositions shown in table 2 under the following dispersing apparatus and dispersing conditions.

Dispersing device: horizontal bead mill

Dispersion conditions: phi 0.5mm zirconia beads

The concentration of carbon nanotubes in the obtained carbon nanotube dispersion was adjusted to 2 mass% with purified water or NMP used as a dispersion medium, the concentration-adjusted dispersion was applied to a PET film by an applicator (model YD-2/yoshinitinsu SEIKI company) having a gap of 50 μm, and each value of a and b in the color space of the dried coating film produced by drying at a temperature of 80 ℃ was described in table 2 below, and stability and conductivity were evaluated according to the following evaluation criteria by the following method. The evaluation results are shown in table 2 below.

(method for measuring each value in XYZ chromaticity system or l×a×b×color space of a dried coating film)

Measurement device: spectrometer (SC-T (P), suga Test Instruments Co., ltd.)

Optical conditions: diffusion illumination 8 degree light receiving d8 mode (excluding specular reflection)

Light source: color measurement conditions for 12V50W halogen lamp: d65 light, 2 ° field of view

Measurement area:(average measured at 3)

(method for measuring viscosity of Dispersion)

With a cone-plate viscometer (cone 34' R24, manufactured by Tokyo Co., ltd.) at 25℃according to 10rpm (shear rate 38.3s ^-1 ) The viscosity was measured under the conditions of (2).

(evaluation method of stability)

The stability was evaluated based on the results (1) to (3) of the rate of change of viscosity with time, (2) the appearance of the liquid with time, and (3) the state of the liquid after time was formed into a film.

(1) Method for evaluating rate of change in viscosity with time

The change rate (after 1 week/initially) was determined from the change in the viscosity value obtained by the above-mentioned viscosity measurement method when the completed dispersion was left to stand for 1 week at 25 ℃, and the viscosity change rate with time was evaluated on the basis of the following evaluation.

Evaluation reference:

a: the change rate is lower than 200 percent

B: the change rate is more than 200% and less than 500%

C: the change rate is more than 500 percent

(2) Appearance of liquid over time

The appearance of the dispersion of the above (1) when left in an environment of 25 ℃ for 1 week was evaluated by the following evaluation criteria.

Evaluation reference:

a: no separation or concentration difference, is uniform

B: the separation and concentration difference are slightly visible, but homogenization can be simply carried out based on remixing

C: sedimentation of carbon nanotubes, and homogenization by re-stirring was not possible

(3) State when forming a film from a liquid after the lapse of time

The resulting dispersion was applied to one side of a PET film (Lumiror #100-T60, toli Co., ltd.) with a gap of 50 μm using an applicator, and then dried at a temperature of 80℃to give a film having a state of sensory evaluation based on the following evaluation criteria.

A: obtain a uniform and smooth coating film

B: multiple aggregate grains can be seen, or the concentration difference is slightly in the plane

C: rough surface, or uneven coating

Evaluation criteria for stability:

and (3) the following materials: the 3 items of the evaluation results of the above (1) to (3) were all A-evaluation

And (2) the following steps: 2 items in the evaluation results of the above (1) to (3) are an a evaluation and no C evaluation.

Delta: the A-evaluation in the evaluation results of the above (1) to (3) is 0 to 1 item, and no C-evaluation

X: the C-evaluation in the evaluation results of the above (1) to (3) is 1 item or more

(method for evaluating conductivity)

The resulting dispersion was applied to one side of a PET film (Lumiror #100-T60, toli Co., ltd.) with a gap of 50 μm using an applicator, and then dried at a temperature of 80℃to measure the resistance value of the film. The electrical conductivity was evaluated by a sheet resistance meter using a device comprising a 4-point probe and an mΩ HiTESTER 3227 (manufactured by Nippon Motor Co., ltd.) with a probe spacing of 10mm, and the following evaluation criteria.

Evaluation reference:

and (3) the following materials: sheet resistance is lower than 250Ω/≡

And (2) the following steps: the sheet resistance is 250Ω/≡or more and less than 400Ω/≡

Delta: the sheet resistance is 400Ω/≡or more and less than 800Ω/≡

X: the sheet resistance was 800 Ω/≡or more [ table 1]

The evaluation results of table 1 and the like show that the carbon nanotube dispersions of examples 1 to 11 within the range disclosed in table 1 are excellent in both stability and conductivity. In contrast, the carbon nanotube dispersions of comparative examples 1 and 2 cannot satisfy the above characteristics.

TABLE 2

The results of the evaluation and the like in table 2 show that the carbon nanotube dispersions of examples 12 to 22 in the range disclosed in table 2 are excellent in both stability and conductivity. In contrast, the carbon nanotube dispersions of comparative examples 3 to 6 cannot satisfy the above characteristics.

Industrial applicability

The carbon nanotube dispersion is excellent in stability and conductivity, and is useful as a material for fuel cells, various electrodes, electromagnetic wave shielding materials, conductive resins, field emission display members, and the like, and is particularly useful for the production of electrode pastes and electrodes suitable for the production of electrodes for lithium ion secondary batteries, and the like, and can realize excellent battery performance capable of withstanding repeated charge and discharge for a long period of time.

Claims (7)

1. A carbon nanotube dispersion comprising at least: the Y of an XYZ chromaticity system of a dry coating film prepared by coating a dispersion liquid having a concentration of carbon nanotubes of 2 mass% with an applicator having a gap of 50 μm, a water-soluble polymer material and a dispersion medium is 6.0 or less.

2. A carbon nanotube dispersion comprising at least: carbon nanotubes, water-soluble polymer materials and dispersion media, the dry coating film prepared by coating the dispersion liquid having a concentration of carbon nanotubes adjusted to 2 mass% with an applicator having a gap of 50 μm had negative values of both a and b in the color space.

3. The carbon nanotube dispersion according to claim 1 or 2, wherein the water-soluble polymer material is 1 or more polymer materials selected from nonionic water-soluble polymers and anionic water-soluble polymers.

4. A conductive paste comprising at least the carbon nanotube dispersion liquid according to any one of claims 1 to 3.

5. An electrode paste for a secondary battery, comprising at least an active material for a secondary battery and the carbon nanotube dispersion liquid according to any one of claims 1 to 3.

6. An electrode for a secondary battery, wherein the electrode paste for a secondary battery according to claim 5 is used.

7. A secondary battery using the electrode for a secondary battery according to claim 6.